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Sample records for se te compounds

  1. Superconducting and magnetic properties of Fe-Se-Te compounds

    NASA Astrophysics Data System (ADS)

    Tomy, C. V.; Balakrishnan, G.; Lees, M. R.

    2009-03-01

    The discovery of a new Fe based superconductor ?-FeSex with a Tc of 8 K, hot on the heels of the discovery of superconductivity in LaOFeP/As compounds, has triggered a fresh interest in the study of Fe based superconductors. Se can be replaced with Te in FeSe1-xTex and this results in an increase in Tc from 8 K for x = 0 to 15 K for x = 0.5 while compounds for x > 0.8 are no longer superconducting. We report the synthesis and characterization of the compounds FeSe1-xTex covering the entire solid solution range. The superconducting transition in resistivity measurements does not show any broadening in magnetic fields up to 9 T, but shifts to lower temperatures linearly with a value ˜ -0.22 K/T. This results in extremely high upper critical fields (Hc2) of the order of 70-80 T in these compounds. The superconducting properties are also sensitive to applied pressure and exhibit a positive dTc/dP of around 0.41 K/kbar for the x = 0.5 composition. We observe a jump in specific heat at Tc corresponding to a superconducting gap of 1.8 meV, indicating the bulk nature of superconductivity. Detailed investigations through magnetization, transport and specific heat measurements are presented. A study of the magnetic properties of the non superconducting end compound, FeTe is also presented to gain insight into the onset of superconductivity in the doped systems.

  2. Liquid-Phase Epitaxial Growth of ZnS, ZnSe and Their Mixed Compounds Using Te as Solvent

    NASA Astrophysics Data System (ADS)

    Nakamura, Hiroshi; Aoki, Masaharu

    1981-01-01

    Epitaxial layers of ZnS, ZnSe and their mixed compounds were grown on ZnS substrates by the liquid-phase epitaxial growth (LPE) method using Te as the solvent. The open-tube slide-boat technique was used, and a suitable starting temperature for growth was found to be 850°C for ZnS and 700-800°C for ZnSe. The ZnS epitaxial layers grown on {111}A and {111}B oriented ZnS substrates were thin (˜1 ?m) and smooth, had low, uniform Te concentrations (˜0.1 at.%) and were highly luminescent. The ZnSe epitaxial layers were relatively thick (10-30 ?m) and had fairly high Te concentrations (a few at.%). Various mixed compound ZnS1-xSex were also grown on ZnS substrates.

  3. Thermoelectric Properties of Ag-Doped Bi2(Se,Te)3 Compounds: Dual Electronic Nature of Ag-Related Lattice Defects.

    PubMed

    Lu, Meng-Pei; Liao, Chien-Neng; Huang, Jing-Yi; Hsu, Hung-Chang

    2015-08-01

    Effects of Ag doping and thermal annealing temperature on thermoelectric transport properties of Bi2(Se,Te)3 compounds are investigated. On the basis of the comprehensive analysis of carrier concentration, Hall mobility, and lattice parameter, we identified two Ag-related interstitial (Agi) and substitutional (AgBi) defects that modulate in different ways the thermoelectric properties of Ag-doped Bi2(Se,Te)3 compounds. When Ag content is less than 0.5 wt %, Agi plays an important role in stabilizing crystal structure and suppressing the formation of donor-like Te vacancy (VTe) defects, leading to the decrease in carrier concentration with increasing Ag content. For the heavily doped Bi2(Se,Te)3 compounds (>0.5 wt % Ag), the increasing concentration of AgBi is held responsible for the increase of electron concentration because formation of AgBi defects is accompanied by annihilation of hole carriers. The analysis of Seebeck coefficients and temperature-dependent electrical properties suggests that electrons in Ag-doped Bi2(Se,Te)3 compounds are subject to a mixed mode of impurity scattering and lattice scattering. A 10% enhancement of thermoelectric figure-of-merit at room temperature was achieved for 1 wt % Ag-doped Bi2(Se,Te)3 as compared to pristine Bi2(Se,Te)3. PMID:26200130

  4. The energy gap of the compound FeSe0.5Te0.5 determined by specific heat and Point Contact Spectroscopy

    NASA Astrophysics Data System (ADS)

    Escudero, Roberto; López-Romero, Rodolfo E.

    2015-10-01

    The superconductor FeSe0.5Te0.5 was studied with Point Contact spectroscopy and specific heat in polycrystalline samples. The transition temperature determined by magnetic measurement was TC=14.5 K. The size of the energy gap measured by junctions is ? = 1.9 meV, whereas the gap determined by the specific heat measurements was ? = 2.3 meV. The gap evolution with temperature follows BCS, the ratio 2?/KBTC has values between 2.88 ? 2 ? /KBTC ? 3.04. The compound was grown by solid state synthesis in quartz ampoules under vacuum at 950 °C. Crystal structure was characterized by X-ray diffraction. The superconducting properties were characterized by magnetization, resistivity and specific heat. This superconductor shows an isotropic energy gap as observed with the fitting of the specific heat at low temperature.

  5. Ab initio study of structural, electronic and optical properties of Be-doped CdS, CdSe and CdTe compounds

    NASA Astrophysics Data System (ADS)

    Noor, N. A.; Tahir, W.; Aslam, Fatima; Shaukat, A.

    2012-03-01

    Full-potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method within density functional theory (DFT) has been utilized to calculate structural, electronic and optical properties of Be-doped CdS, CdSe and CdTe compounds with the dopant concentration x in the range 0?x?1. For the contribution of exchange-correlation potential, we used Wu-Cohen generalized gradient approximation (GGA) to calculate structural parameters, whereas both Wu-Cohen and Engel-Vosko GGA have been applied to calculate electronic structure of the materials. Only a slight deviation from Vegard's law has been observed for the calculated lattice constants and bulk moduli of the alloys. Structural and chemical factors that affect the band-gap bowing of these semiconductor alloys have been estimated and discussed. Density of states curves and charge density maps have been calculated and analyzed. Lastly, optical properties of both binary and their related ternary alloys have been discussed in terms of the calculated dielectric function. The resultant optical parameters are compared with the available experimental data and other calculations.

  6. X-ray diffraction, Raman study and electrical properties of the new mixed compound Rb1.7K0.3(SO4)0.88(SeO4)0.12Te(OH)6

    NASA Astrophysics Data System (ADS)

    Djemel, M.; Abdelhedi, M.; Ktari, L.; Dammak, M.

    2013-09-01

    At room temperature, the new compound Rb1.7K0.3(SO4)0.88(SeO4)0.12Te(OH)6 crystallizes in the monoclinic system with space group C2. The unit cell parameters are: a = 11.4168 (4), b = 6.6321 (4), c = 13.6078 (6), ? = 106.975 (3), V = 985.46 (8), Z = 4 and ?cal = 3.25 g cm-1. The title compound undergoes a superionic phase transition at T = 479 K. This transition was confirmed by an abrupt increase of conductivity. Differential scanning calorimetry of Rb1.7K0.3(SO4)0.88(SeO4)0.12Te(OH)6 material showed three anomalies at 411, 461, and 479 K, respectively. Raman and IR spectra of Rb1.7K0.3(SO4)0.88(SeO4)0.12Te(OH)6, recorded at room temperature in the frequency 50-4000 cm-1 show that the SO42-, SeO42- and TeO66- groups coexist in the crystal independently.

  7. Heterojunctions of model CdTe/CdSe mixtures

    NASA Astrophysics Data System (ADS)

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-04-01

    We report on the strain behavior of compound mixtures of model group II-VI semiconductors. We use the Stillinger-Weber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group II-VI compounds such as CdTe and CdSe. We employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1° deflection between neighboring planes. To analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization to find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. From this we learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.

  8. Binding energies and heat-of-formation data for USb/sub x/Te/sub 1-x/ and UAs/sub x/Se/sub 1-x/ compounds as derived from photoelectron spectroscopy

    SciTech Connect

    Martensson, N.; Reihl, B.; Vogt, O.

    1982-01-15

    Using high-resolution photoelectronspectroscopy with synchrotron radiation we have accurately determined the core-level binding energies in the nonuranium atoms in USb/sub x/Te/sub 1-x/ and UAs/sub x/Se/sub 1-x/ as a function of the stoichiometric composition. With the use of a Born-Haber cycle a relation between the measured shifts and heat-of-formation data for these compounds is formulated. The analysis demonstrates that photoelectron spectroscopy can become a most valuable method for deriving new heat-of-formation data.

  9. Na2TeS3, Na2TeSe3-mP24, and Na2TeSe3-mC48: Crystal Structures and Optical and Electrical Properties of Sodium Chalcogenidotellurates(IV).

    PubMed

    Pompe, Constantin; Preitschaft, Christian; Weihrich, Richard; Pfitzner, Arno

    2015-12-01

    Pure samples of Na2TeS3 and Na2TeSe3 were synthesized by the reactions of stoichiometric amounts of the elements Na, Te, and Q (Q = S, Se) in the ratio 2:1:3. Both compounds are highly air- and moisture-sensitive. The crystal structures were determined by single-crystal X-ray diffraction. Yellow Na2TeS3 crystallizes in the space group P21/c. Na2TeSe3 exists in a low-temperature modification (Na2TeSe3-mP24, space group P21/c) and a high-temperature modification (Na2TeSe3-mC48, space group C2/c); both modifications are red. Density functional theory calculations confirmed the coexistence of both modifications of Na2TeSe3 because they are very close in energy (?E = 0.18 kJ mol(-1)). To the contrary, hypothetic Na2TeS3-mC48 is significantly less favored (?E = 1.8 kJ mol(-1)) than the primitive modification. Na2TeS3 and Na2TeSe3-mP24 are isotypic to Li2TeS3, whereas Na2TeSe3-mC48 crystallizes in its own structure type, which was first described by Eisenmann and Zagler. The title compounds have two common structure motifs. Trigonal TeQ3 pyramids form layers, and the Na atoms are surrounded by a distorted octahedral environment of chalcogen atoms. Raman spectra are dominated by the vibration modes of the TeQ3 units. The activation energies of the total conductivity of the title compounds range between 0.68 eV (Na2TeS3) and 1.1 eV (Na2TeSe3). Direct principal band gaps of 1.20 and 1.72 eV were calculated for Na2TeSe3 and Na2TeS3, respectively. The optical band gaps are in the range from 1.38 eV for Li2TeSe3 to 2.35 eV for Na2TeS3. PMID:26600068

  10. Superconductivity in strong spin orbital coupling compound Sb?Se?.

    PubMed

    Kong, P P; Sun, F; Xing, L Y; Zhu, J; Zhang, S J; Li, W M; Liu, Q Q; Wang, X C; Feng, S M; Yu, X H; Zhu, J L; Yu, R C; Yang, W G; Shen, G Y; Zhao, Y S; Ahuja, R; Mao, H K; Jin, C Q

    2014-01-01

    Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but further theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10?GPa proceeded by a pressure induced insulator to metal like transition at ~3?GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0?K with pressure up to 40?GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10?GPa and 20?GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures. PMID:25327696

  11. Optical Characterization of Bulk ZnSeTe Solid Solutions

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Feth, S.; Zhu, Shen; Lehoczky, S. L.; Wang, Ling Jun

    2000-01-01

    Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe, and ZnSe(1-x)Te(x)(0 less than x less than 0.4) grown by physical vapor transport. Energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. A best fit curve to the band gap versus composition x data gives a bowing parameter of 1.45. This number lies between the value of 1.23 determined previously on ZnSeTe bulk crystals and the value of 1.621 reported on ZnSeTe epilayers. Low-temperature photoluminescence (PL) spectra were measured on six samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe(1-x)Te(x) samples, 0.09 less than x less than 0.39. For x=0.09, this emission energy is about 0.2 eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x=0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted as being associated with the exciton bound to Te clusters because of the high Te content in these samples.

  12. Synthesis of near-infrared-emitting CdTe/CdSe/ZnSe/ZnS heterostructure.

    PubMed

    Yang, Ping

    2014-04-01

    Near-infrared-emitting quantum dots (QDs) were fabricated via organic synthesis strategies through constructing CdTe/CdSe/ZnSe/ZnS multishell heterostructure. An effective shell-coating route was developed for multishell growth on CdTe cores. Core/shell growth was monitored by absorption and photoluminescence (PL) spectroscopy and transmission electron microscopy observation. Yellow emitting CdTe cores were coated with a CdSe shell to generate type II structure. This yields core/shell QDs with red photoluminescence. The passivation by the ZnSe shell having a substantially wide bandgap confines the excitons within the CdTe/CdSe interface and isolates them from the solution environment and consequently improves the stability of the heterostructure. An additional ZnS shell was deposited around the outer layer of CdTe/CdSe/ZnSe QDs to form a heterostructure through the reaction between zinc oleate and trioctylphosphine sulfur in the crude CdTe/CdSe/ZnSe solution. By varying CdTe core size and each shell thickness, the PL wavelength of the obtained heterostructure can span from 580 to 770 nm. The PL efficiency is quenched in CdTe QDs in diluted solution but increases substantially up to 24% for CdTe/CdSe core/shell QDs. The PL efficiency of CdTe/CdSe/ZnSe/ZnS QDs with average diameter of 5.4 nm and a PL peak wavelength of 770 nm is 20%. PMID:24734747

  13. Investigation of correlation effects in FeSe and FeTe by LDA + U method

    NASA Astrophysics Data System (ADS)

    Lohani, H.; Mishra, P.; Sekhar, B. R.

    2015-05-01

    We present a comparative study of the influence of Coulomb interaction and Hund's coupling on the electronic structure of FeSe and FeTe. Our calculations are based on density functional theory (DFT) with local density approximation (LDA + U) framework employed in TB-LMTO ASA code. We found the correlation effects are orbital selective due to the strength of interorbital hybridization among the different Fe-3d orbitals mediated via the chalcogen (Se/Te-p) orbitals and are different in both the compounds. The Coulomb interaction is screened significantly by Te-p bands in FeTe. Similarly the orbital selection is different in both the compounds because of the difference in the chalcogen height.

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

    NASA Astrophysics Data System (ADS)

    Grivel, J.-C.; Andersen, N. H.; Pallewatta, P. G. A. P.; Zhao, Y.; von Zimmermann, M.

    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 to the presence of remaining Mg3Bi2 particles that formed as an intermediate compound during reaction. Likewise, in the Se-and Te-doped samples, MgSe and MgTe respectively form below 450 °C. Whereas jc is also depressed in the Se-doped sample, the MgTe particles do not appear to affect the performance of the Te-doped wire.

  15. Impact of Te on the structure and (77)Se NMR spectra of Se-rich Ge-Te-Se glasses: a combined experimental and computational investigation.

    PubMed

    Bouëssel du Bourg, Lila; Roiland, Claire; le Pollès, Laurent; Deschamps, Michaël; Boussard-Plédel, Catherine; Bureau, Bruno; Pickard, Chris J; Furet, Eric

    2015-10-28

    Selenium-rich Ge-Te-Se glasses have been synthesized along the GeSe4-GeTe4 pseudo-composition line and acquired by (77)Se Hahn echo magic-angle spinning NMR. The comparison with the GeSe4 spectrum shows a drastic modification of the typical double-resonance lineshape even at low Te concentrations (<10%). In order to rationalize this feature and to understand the effect of Te on the structure of our glasses, first-principles molecular dynamics simulations and gauge including projector augmented wave NMR parameter calculations have been performed. The distribution of the tellurium atoms in the selenium phase was shown to be mainly responsible for the (77)Se lineshape changes. Another possible factor related to the perturbation of the ?iso value due to Te proximity appears to be much more limited in the bulk, while the results obtained using molecular models suggest shifts of several hundreds of ppm. PMID:26456891

  16. Type-II CdSe/CdTe/ZnTe (core-shell-shell) quantum dots with cascade band edges: the separation of electron (at CdSe) and hole (at ZnTe) by the CdTe layer.

    PubMed

    Chen, Chun-Yen; Cheng, Chiu-Ting; Lai, Chih-Wei; Hu, Ya-Hui; Chou, Pi-Tai; Chou, Yi-Hsuan; Chiu, Hsin-Tien

    2005-12-01

    The rational design and synthesis of CdSe/CdTe/ZnTe (core-shell-shell) type-II quantum dots are reported. Their photophysical properties are investigated via the interband CdSe-->ZnTe emission and its associated relaxation dynamics. In comparison to the strong CdSe (core only) emission (lambda(max) approximately 550 nm, Phi(f) approximately 0.28), a moderate CdSe-->CdTe emission (lambda(max) approximately 1026 nm, Phi(f) approximately 1.2 x 10(-3)) and rather weak CdSe-->ZnTe interband emission (lambda(max) approximately 1415 nm, Phi(f) approximately 1.1 x 10(-5)) are resolved for the CdSe/CdTe/ZnTe structure (3.4/1.8/1.3 nm). Capping CdSe/CdTe with ZnTe results in a distant electron-hole separation between CdSe (electron) and ZnTe (hole) via an intermediate CdTe layer. In the case of the CdSe/CdTe/ZnTe structure, a lifetime as long as 150 ns is observed for the CdSe-->ZnTe (1415 nm) emission. This result further indicates an enormously long radiative lifetime of approximately 10 ms. Upon excitation of the CdSe/CdTe/ZnTe structure, the long-lived charge separation may further serve as an excellent hole carrier for catalyzing the redox oxidation reaction. PMID:17193422

  17. Optical Characterization of Bulk ZnSeTe Solid Solutions

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Feth, S.; Zhu, Shen; Lehoczky, S. L.; Wang, Ling Jun

    2000-01-01

    Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe and ZnSe (sub 1-x) Te (sub x) (0 less than x less than 0.4) grown by physical vapor transport technique. The energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. The best fit to the band gap vs. composition, x, data gives a bowing parameter of 1.336 which is between the value of 1.23 determined previously on ZnSeTe bulk crystals by reflectivity and the value of 1.621 reported on epilayers by photoconductivity. Low-temperature photoluminescence (PL) spectra were measured on 6 samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe (sub 1-x) Te (sub x) samples, 0.09 less than x less than 0.39. For x = 0.09, this emission energy is about 0.2eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x = 0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted to be associated with the exciton bound to Te clusters because of the high Te content in these samples.

  18. Reverse Monte Carlo simulation of Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} glasses

    SciTech Connect

    Abdel-Baset, A. M.; Rashad, M.; Moharram, A. H.

    2013-12-16

    Two-dimensional Monte Carlo of the total pair distribution functions g(r) is determined for Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} alloys, and then it used to assemble the three-dimensional atomic configurations using the reverse Monte Carlo simulation. The partial pair distribution functions g{sub ij}(r) indicate that the basic structure unit in the Se{sub 80}Te{sub 15}Sb{sub 5} glass is di-antimony tri-selenide units connected together through Se-Se and Se-Te chain. The structure of Se{sub 80}Te{sub 20} alloys is a chain of Se-Te and Se-Se in addition to some rings of Se atoms.

  19. Structural and electronic properties of -In2X3 (X=O, S, Se, Te) using ab initio calculations

    E-print Network

    Khare, Sanjay V.

    solids Several III-VI body-centered tetragonal layered compounds belonging to space group I41/amd have and environmentally friendly copper­indium­gallium­selenide solar cells and molecules. Here we have studied the structural, energetic, and electronic properties of four compounds -In2X3 (X=O, S, Se, Te), in this space

  20. Synthesis and characterization of Bi-Te-Se thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Tripathi, S. K.; Kumari, Ankita; Ridhi, R.; Kaur, Jagdish

    2015-08-01

    Bismuth Telluride (Bi2Te3) and its related alloys act as a promising thermoelectric material and preferred over other thermoelectric materials due to their high stability and efficiency under ambient conditions. In the present work, we have reported economical, environment friendly and low-temperature aqueous chemical method for the synthesis of Bi-Se-Te alloy. The prepared samples are characterized by X-Ray Diffraction to investigate the structural properties and UV-Visible spectroscopy for the spectroscopic analysis. The absorption spectrum reveals the sensitivity in the ultraviolet as well as in visible region.

  1. Electron microscopy of iron chalcogenide FeTe(Se) films

    NASA Astrophysics Data System (ADS)

    Shchichko, I. O.; Presnyakov, M. Yu.; Stepantsov, E. A.; Kazakov, S. M.; Antipov, E. V.; Makarova, I. P.; Vasil'ev, A. L.

    2015-05-01

    The structure of Fe1 + ?Te1 - x Se x films ( x = 0; 0.05) grown on single-crystal MgO and LaAlO3 substrates has been investigated by transmission and scanning transmission electron microscopy. The study of Fe1.11Te/MgO structures has revealed two crystallographic orientation relationships between the film and substrate. It is shown that the lattice mismatch between the film and substrate is compensated for by the formation of misfit dislocations. The Burgers vector projection is determined. The stresses in the film can partially be compensated for due to the formation of an intermediate disordered layer. It is shown that a FeTe0.5Se0.5 film grown on a LaAlO3 substrate is single-crystal and that the FeTe0.5Se0.5/LaAlO3 interface in a selected region is coherent. The orientation relationships between the film and substrate are also determined for this case.

  2. Conventional versus unconventional magnetic polarons: ZnMnTe/ZnSe and ZnTe/ZnMnSe quantum dots

    NASA Astrophysics Data System (ADS)

    Barman, B.; Tsai, Y.; Scrace, T.; Murphy, J. R.; Cartwright, A. N.; Pientka, J. M.; Zutic, I.; McCombe, B. D.; Petrou, A.; Sellers, I. R.; Oszwaldowski, R.; Petukhov, A.; Fan, W. C.; Chou, W. C.; Yang, C. S.

    2014-08-01

    We used time resolved photoluminescence (TRPL) spectroscopy to compare the properties of magnetic polarons in two related, spatially indirect, II-VI epitaxially grown quantum dot systems. In sample A (ZnMnTe/ZnSe), the photoexcited holes are confined in the magnetic ZnMnTe quantum dots (QDs), while the electrons remain in the surrounding non-magnetic ZnSe matrix. In sample B (ZnTe/ZnMnSe) on the other hand, the holes are confined in the non-magnetic ZnTe QDs and the electrons move in the magnetic ZnMnSe matrix. The magnetic polaron formation energies, EMP , in these samples were measured from the temporal red-shift of the excitonic emission peak. The magnetic polarons in the two samples exhibit distinct characteristics. In sample A, the magnetic polaron is strongly bound with EMP=35 meV. Furthermore, EMP has unconventionally weak dependence of on both temperature T and magnetic field Bappl . In contrast, magnetic polarons in sample B show conventional characteristics with EMP decreasing with increasing temperature and increasing external magnetic field. We attribute the difference in magnetic polaron properties between the two types of QDs to the difference in the location of the Mn ions in the respective structures.

  3. Design of half-metallic ferrimagnets: Doped MnX (X=Te, Se, S)

    NASA Astrophysics Data System (ADS)

    Long, Nguyen Hoang; Ogura, Masako; Akai, Hisazumi

    2009-12-01

    Half-metallic ferrimagnetism of transition-metal-doped MnX (transition-metal=V, Cr and X=Te, Se, S) is examined in the framework of first-principles Korringa-Kohn-Rostoker-coherent potential approximation calculation. Such unusual ferrimagnetism becomes possible due to the coexistence of ferromagnetic coupling among transition-metal impurities (here, Cr and V) and antiferro-magnetic coupling among Mn ions. In particular, NaCl-type MnSe and MnS compounds exhibit clear half-metallic ferrimagnetism even when the doping concentrations are as low as a few percents. On the other hand, NiAs-type MnTe compounds exhibit pseudo half-metallic ferrimagnetism. For a metastable zinc-blende structure, half-metallic ferrimagnetism is realized in all cases except in a low doping region.

  4. Fabrication of Bi2Te3/Sb2Te3 and Bi2Te3/Bi2Te2Se multilayered thin film-based integrated cooling devices

    SciTech Connect

    Xiao, Z.; DiMasi, E.; Hedgemen, K.; Harris, M.

    2010-06-29

    In this article, the authors report on the development of solid-state integrated cooling devices using Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 3}/Bi{sub 2}Te{sub 2}Se thermoelectric thin films fabricated using sputtering deposition. The multilayer thin films have a periodic structure consisting of alternating Bi{sub 2}Te{sub 3} and Sb{sub 2}Te{sub 3} layers or Bi{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 2}Se layers, where each layer is about 10 nm thick. The deposited Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} multilayer thin film has a p-type conductivity and the deposited Bi{sub 2}Te{sub 3}/Bi{sub 2}Te{sub 2}Se multilayer thin film has an n-type conductivity. The multilayer structure of films and the interface of layers were analyzed by x-ray diffraction and reflectivity. Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 3}/Bi{sub 2}Te{sub 2}Se multilayer thin film-based integrated cooling devices were fabricated using standard integrated circuit fabrication process. The temperature difference was measured from the fabricated cooling devices. The devices could be good candidates for the application of high-efficiency solid-state microcooling.

  5. Resonance photoelectron spectroscopy of TiX{sub 2} (X = S, Se, Te) titanium dichalcogenides

    SciTech Connect

    Shkvarin, A. S. Yarmoshenko, Yu. M.; Skorikov, N. A.; Yablonskikh, M. V.; Merentsov, A. I.; Shkvarina, E. G.; Titov, A. N.

    2012-11-15

    The photoelectron valence band spectra of TiS{sub 2}, TiSe{sub 2}, and TiTe{sub 2} dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS{sub 2} and TiTe{sub 2}. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS{sub 2}, TiSe{sub 2}, and TiTe{sub 2} compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS{sub 2} is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe{sub 2} is caused by occupation of the 3d band in Ti.

  6. Hydrogen passivation of Se and Te in AlSb

    SciTech Connect

    McCluskey, M.D.; Haller, E.E.; Walukiewicz, W.; Becla, P.

    1996-06-01

    Using infrared absorption spectroscopy we have observed local vibrational modes (LVM{close_quote}s) arising from {ital DX}-hydrogen complex in AlSb. Hydrogen was diffused into bulk AlSb:Se and AlSb:Te by annealing in sealed quartz ampoules with either hydrogen gas or methanol (CH{sub 3}OH). The persistent photoabsorption of the {ital DX}-like Se donor is significantly reduced after hydrogenation. In hydrogenated AlSb:Se, we attribute the LVM peaks at 1608.6 and 1615.7 cm{sup {minus}1} to hydrogen stretch modes. Deuterated AlSb:Se has only one stretch mode at 1173.4 cm{sup {minus}1}. The second, third, and fourth harmonics of the wag modes are observed and show splittings consistent with {ital C}{sub 3{ital v}} symmetry. In AlSb:Te, we find a hydrogen stretch mode at 1599.0 cm{sup {minus}1} and a deuterium mode at 1164.4 cm{sup {minus}1}. We propose a model in which the hydrogen attaches to an aluminum in a [111] antibonding orientation. {copyright} {ital 1996 The American Physical Society.}

  7. Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Brebrick, R. F.; Burger, A.; Dudley, M.; Ramachandran, N.

    2003-01-01

    The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyance-driven convection and growth interface fluctuations caused by irregular fluid-flows. ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, were grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals were characterized extensively to correlate the grown crystal properties with the growth conditions.

  8. Connecting Thermoelectric Performance and Topological-Insulator Behavior: Bi2Te3 and Bi2Te2Se from First Principles

    NASA Astrophysics Data System (ADS)

    Shi, Hongliang; Parker, David; Du, Mao-Hua; Singh, David J.

    2015-01-01

    Thermoelectric performance is of interest for numerous applications such as waste-heat recovery and solid-state energy conversion and will be seen to be closely connected to topological-insulator behavior. In this context, we here report first-principles transport and defect calculations for Bi2Te2Se in relation to Bi2Te3 . The two compounds are found to contain remarkably different electronic structures in spite of being isostructural and isoelectronic. We discuss these results in terms of the topological-insulator characteristics of these compounds.

  9. Resistance To Oxidation Of Te-Se Optical Recording Films

    NASA Astrophysics Data System (ADS)

    Terao, Motoyasu; Horigome, Shinkichi; Shigematsu, Kazuo; Miyauchi, Yasushi; Nakazawa, Masatoshi

    1983-01-01

    The resistance to oxidation and cracking of metal-Te-Se recording films and their mechanisms have been studied. The metals included In, Pb, Sn, Bi, and Sb. The films were deposited by multi-source, high-speed rotary evaporation on substrates with glass-U.V. light curing resin-cellulose nitrate or acetate structures. The role of Se is to inhibit the oxidation and the role of metallic elements are to inhibit cracking and to decrease noise in reproduced signals by making crystal grains smaller. Selection of substrate surface material, especially selection of U.V.light curing resin, is also important to avoid oxidation of the recording film. Depth profiles of the recording films have been analyzed by Auger electron spectroscopy and X-ray photoelectron spectroscopy to clarify the mechanisms of oxidation inhibition.

  10. Metalorganic vapor phase epitaxy growth of ternary tetradymite Bi2Te3-xSex compounds

    NASA Astrophysics Data System (ADS)

    Kuznetsov, P. I.; Yakushcheva, G. G.; Luzanov, V. A.; Temiryazev, A. G.; Shchamkhalova, B. S.; Jitov, V. A.; Sizov, V. E.

    2015-01-01

    We report on a metal organic vapor epitaxy (MOVPE) of Bi2Te3-xSex films over the entire range of compositions (0 ? x ? 3) for the first time. The films were grown on Al2O3(0001) substrates at 465 °C using trimethylbismuth (Bi2Me3), diethyltellurium (Et2Te) and diisopropylselenium (iPro2Se) as metalorganic sources. To realize the 2D growth mode and to grow films with flat surfaces and high crystalline quality, a thin ZnTe buffer layer was used. As-grown films were studied using optical and AFM microscopy techniques and X-ray diffraction. It was found that under steady growth conditions the composition of Bi2Te3-xSex films strongly depends on the film thickness. But a high rate of interdiffusion of chalcogens at the growth temperature rapidly leads to a homogeneous composition of the film in the growth direction. Dependence of the intensity of X-ray reflection (0012) on the composition of Bi2Te3-xSex films x has extremes near x=1 (Bi2Te2 Se) and x=2 (Bi2Se2 Te). The AFM micrographs and profiles show large (above 2 ?m) triangle-shaped atomically flat terraces with step height of a quintuple layer (0.90 nm) of the tetradymite-type compounds. The electronic properties of the grown films have been characterized via four probe magnetotransport measurements.

  11. High Critical Field Superconductivity in FeSe0.1 Te0.9 Coated Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Wang, Haiyan; Cornell, Nicholas; Huang, Jijie; Salamon, Myron; Zakhidov, Anvar; Anvar Zakhidov; Haiyan Wang Team; Utd; Tamu Afosr Team

    2015-03-01

    Thin films of FeSe0.1Te0.9, grown on SrTi03, have been shown to possess an increased critical temperature, field, and current relative to both bulk samples of FeSe0.1Te0.9 and thin films of the related compound FeSe0.5Te0.5. Empirical measurement of FeSe0.1Te0.9 thin films reveal a zero temperature Hc2(0) ~ 45T. Carbon nanotubes are a promising lightweight flexible material for superconducting applications and have proven a robust substrate when conformally coated by superconducting MgB2. Thin film coatings of FeSe0.1Te0.9 have been deposited via pulsed laser deposition on dry- drawn multiwall carbon nanotube sheets drawn from CVD grown forests. While true zero resistance isn't achieved due to inter-connectivity issues or junction effects in multiwall CNT case, clear superconducting transitions with R reaching zero can be seen on other single wall CNT, and non-oriented carbon nanotube substrates. Properties of these superconducting FeSe0.1Te0.9@SWCNT thin films are discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3

    DOE PAGESBeta

    Kong, P. P.; Sun, F.; Xing, L. Y.; Zhu, J.; Zhang, S. J.; Li, W. M.; Liu, Q. Q.; Wang, X. C.; Feng, S. M.; Yu, X. H.; et al

    2015-02-17

    Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. We report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related tomore »the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.« less

  14. Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3

    PubMed Central

    Kong, P. P.; Sun, F.; Xing, L. Y.; Zhu, J.; Zhang, S. J.; Li, W. M.; Liu, Q. Q.; Wang, X. C.; Feng, S. M.; Yu, X. H.; Zhu, J. L.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Ahuja, R.; Mao, H. K.; Jin, C. Q.

    2014-01-01

    Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but further theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10?GPa proceeded by a pressure induced insulator to metal like transition at ~3?GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0?K with pressure up to 40?GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10?GPa and 20?GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures. PMID:25327696

  15. Crystal growth of ZnSe and related ternary compound semiconductors by physical vapor transport

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    1993-01-01

    The materials to be investigated are ZnSe and related ternary semiconducting alloys (e.g., ZnS(x)Se(1-x), ZnTe(x)Se(1-x), and Zn(1-x)Cd(x)Se). These materials are useful for opto-electronic applications such as high efficient light emitting diodes and low power threshold and high temperature lasers in the blue-green region of the visible spectrum. The recent demonstration of its optical bistable properties also makes ZnSe a possible candidate material for digital optical computers. The investigation consists of an extensive ground-based study followed by flight experimentation, and involves both experimental and theoretical work. The objectives of the ground-based work are to establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low gravity environment and to obtain the experimental data and perform the analyses required to define the optimum parameters for the flight experiments. During the six months of the Preliminary Definition Phase, the research efforts were concentrated on the binary compound ZnSe - the purification of starting materials of Se by zone refining, the synthesis of ZnSe starting materials, the heat treatments of the starting materials, the vapor transport rate measurements, the vapor partial pressure measurements of ZnSe, the crystal growth of ZnSe by physical vapor transport, and various characterization on the grown ZnSe crystals.

  16. Electronic structure of titanium dichalcogenides TiX{sub 2} (X = S, Se, Te)

    SciTech Connect

    Shkvarin, A. S. Yarmoshenko, Yu. M.; Skorikov, N. A.; Yablonskikh, M. V.; Merentsov, A. I.; Shkvarina, E. G.; Titov, A. N.

    2012-01-15

    The electronic structure and the chemical bond in titanium dichalcogenides TiX{sub 2} (X = S, Se, Te), which are promising electrode materials for lithium batteries, are studied experimentally and theoretically. It is found that the X-ray photoelectron spectra of the valence bands and the core levels of titanium and its X-ray L{sub 2,3} absorption spectra demonstrate a change in the ionic and covalent components of the chemical bond in these compounds. The densities of states in these compounds are calculated by the full-potential augmented-plane-wave method, and multiplet calculations of the X-ray L{sub 2,3} absorption spectra of titanium are performed. It is shown that, in the row TiS{sub 2}-TiSe{sub 2}-TiTe{sub 2}, the covalence increases, the ionicity of the chemical bond decreases, and the effect of the crystal field of a ligand is weakened.

  17. Stillinger-Weber potential for the II-VI elements Zn-Cd-Hg-S-Se-Te

    NASA Astrophysics Data System (ADS)

    Zhou, X. W.; Ward, D. K.; Martin, J. E.; van Swol, F. B.; Cruz-Campa, J. L.; Zubia, D.

    2013-08-01

    Bulk and multilayered thin film crystals of II-VI semiconductor compounds are the leading materials for infrared sensing, ?-ray detection, photovoltaics, and quantum dot lighting applications. The key to achieving high performance for these applications is reducing crystallographic defects. Unfortunately, past efforts to improve these materials have been prolonged due to a lack of understanding with regards to defect formation and evolution mechanisms. To enable high-fidelity and high-efficiency atomistic simulations of defect mechanisms, this paper develops a Stillinger-Weber interatomic potential database for semiconductor compounds composed of the major II-VI elements Zn, Cd, Hg, S, Se, and Te. The potential's fidelity is achieved by optimizing all the pertinent model parameters, by imposing reasonable energy trends to correctly capture the transformation between elemental, solid solution, and compound phases, and by capturing exactly the experimental cohesive energies, lattice constants, and bulk moduli of all binary compounds. Verification tests indicate that our model correctly predicts crystalline growth of all binary compounds during molecular dynamics simulations of vapor deposition. Two stringent cases convincingly show that our potential is applicable for a variety of compound configurations involving all the six elements considered here. In the first case, we demonstrate a successful molecular dynamics simulation of crystalline growth of an alloyed (Cd0.28Zn0.68Hg0.04) (Te0.20Se0.18S0.62) compound on a ZnS substrate. In the second case, we demonstrate the predictive power of our model on defects, such as misfit dislocations, stacking faults, and subgrain nucleation, using a complex growth simulation of ZnS/CdSe/HgTe multilayers that also contain all the six elements considered here. Using CdTe as a case study, a comprehensive comparison of our potential with literature potentials is also made. Finally, we also propose unique insights for improving the Stillinger-Weber potential in future developments.

  18. On the thermodynamic behavior of cadmium in Te-saturated HgTe-CdTe and CdSe-CdTe solid alloys

    SciTech Connect

    Shamsuddin, M.; Nasar, A.

    1995-06-01

    In recent years, chalcogenides of group IIB elements have gained prominence for the applications in various electronic devices, such as infrared, X-ray and {gamma}-ray detectors, light-emitting diodes, photoresistors, thin-film transistors, and high-efficient solar cells. The activity of cadmium in Te-saturated HgTe-CdTe and CdSe-CdTe alloys in the temperature range of 720 to 840 K was measured by an electrochemical technique using LiCl-KCl + 5 wt pct CdCl{sub 2} as the molten salt electrolyte. From the electromotive force (emf), values measured at different temperatures, the partial and excess molar thermodynamic quantities, have been calculated. From the activity data, the equilibrium vapor pressure of cadmium over the alloys have been estimated. The thermodynamic data obtained in the presence investigation are consistent with the view that the HgTe-CdTe system consists of a single-phase field throughout the entire range of composition and with the structural changes in the CdSe-CdTe system. The results have been discussed in the light of Darken`s stability and excess stability parameters of the systems and physical properties, viz., energy gap and magnetic susceptibility.

  19. On the thermodynamic behavior of cadmium in Te-saturated HgTe-CdTe and CdSe-CdTe solid alloys

    NASA Astrophysics Data System (ADS)

    Shamsuddin, M.; Nasar, A.

    1995-05-01

    The activity of cadmium in Te-saturated HgTe-CdTe and CdSe-CdTe alloys in the temperature range of 720 to 840 K was measured by an electrochemical technique using LiCl-KCl + 5 wt pct CdCl2 as the molten salt electrolyte. From the electromotive force (emf), values measured at different temperaturesi the partial and excess molar thermodynamic quantities, viz., ? G{Cd/M}, ? G{Cd/XS}, ? H{Cd/M}, ? S{Cd/M} and ? S{XS/Cd}, have been calculated. From the activity data, the equilibrium vapor pressure of cadmium over the alloys have been estimated. The thermodynamic data obtained in the present investigation are consistent with the view that the HgTe-CdTe system consists of a single-phase field throughout the entire range of composition and with the structural changes in the CdSe-CdTe system. The results have been discussed in the light of Darken’s stability and excess stability parameters of the systems and physical properties, viz., energy gap and magnetic susceptibility.

  20. Electronic properties of GaSe, InSe, GaS and GaTe layered semiconductors: charge neutrality level and interface barrier heights

    NASA Astrophysics Data System (ADS)

    Brudnyi, V. N.; Sarkisov, S. Yu; Kosobutsky, A. V.

    2015-11-01

    Density functional theory calculations have been applied to study the structural and electronic properties of layered ?-GaSe, ?-InSe, ?-GaS and GaTe compounds. The optimized lattice parameters have been obtained using vdW-DF2-C09 exchange-correlation functional, which is able to describe dispersion forces and produces interlayer distances in close agreement with experiments. Based on the calculated electronic band structures, the energy position of the charge neutrality level (CNL) in the III–VI semiconductors has been estimated for the first time. The room-temperature values of CNL are found to be 0.80 eV, 1.02 eV, 0.72 eV and 0.77 eV for ?-GaSe, ?-GaS, GaTe and ?-InSe, respectively. The persistent p-type conductivity of the intentionally undoped ?-GaSe, ?-GaS and GaTe and n-type conductivity of ?-InSe crystals are discussed and explained using the concept of CNL. We also estimated the barrier heights for a number of metal/semiconductor and semiconductor/semiconductor interfaces assuming partial Fermi level pinning at the CNL. A reasonable agreement between our calculations and the available experimental data has been obtained.

  1. Crystallization behavior in Se{sub 90}Te{sub 10} and Se{sub 80}Te{sub 20} thin films

    SciTech Connect

    Barták, Jaroslav Málek, Jirí; Koštál, Petr; Segawa, Hiroyo; Yamabe-Mitarai, Yoko

    2014-03-28

    Isothermal crystal growth kinetics in Se{sub 90}Te{sub 10} and Se{sub 80}Te{sub 20} thin films was studied by microscopy and in situ X-ray diffraction (XRD) measurements. The spherulite-like crystals grew linearly with time. In a narrow temperature range of between 65 and 85?°C, crystal growth rates exhibit simple exponential behavior with activation energies E{sub G}?=?193?±?4?kJ mol{sup ?1} for Se{sub 90}Te{sub 10} and E{sub G}?=?195?±?4?kJ mol{sup ?1} for Se{sub 80}Te{sub 20}. The crystal growth in both compositions is controlled by liquid-crystal interface kinetics and can be described by a screw dislocation growth model. From the XRD data, the crystallization fraction was estimated. The crystallization data were described by Johnson-Mehl-Avrami (JMA) model with Avrami exponents m?=?1.4?±?0.3 for Se{sub 90}Te{sub 10} and m?=?1.6?±?0.4 for Se{sub 80}Te{sub 20}. Activation energies were estimated from the temperature dependence of rate constant evaluated from the JMA model. The activation energies of nucleation-growth process were found to be E{sub c}?=?184?±?21?kJ mol{sup ?1} for Se{sub 90}Te{sub 10} and E{sub c}?=?179?±?7?kJ mol{sup ?1} for Se{sub 80}Te{sub 20}, and are comparable with activation energies of crystal growth.

  2. Synthesis and Characterization of a Series of Quaternary Chalcogenides Ba LnMQ3 ( Ln=Rare Earth, M=Coinage Metal, Q=Se or Te)

    NASA Astrophysics Data System (ADS)

    Yang, Yuting; Ibers, James A.

    1999-10-01

    The compounds BaGdAuSe3, BaLaCuTe3, BaYCuTe3, BaYAgTe3, BaLaAgTe3, BaYbCuTe3, BaGdAgTe3, BaNdCuTe3, and BaPrCuTe3 were prepared by the reaction in a BaBr2/KBr flux at 850°C of a rare earth, a coinage-group metal, a chalcogen, and BaSe or BaTe. The unit cells of all of the compounds and the crystal structures of the first four compounds were determined by single-crystal X-ray diffraction methods. With the exception of BaLaCuTe3, which crystallizes with four formula units in the orthorhombic space group Pnma, all of these compounds crystallize with four formula units in the orthorhombic space group Cmcm. BaLaCuTe3, isostructural with ?-BaLaCuSe3 and Eu2CuS3 (i.e., Eu2+Eu3+Cu+(S2-)3), and BaGdAuSe3, BaYCuTe3, and BaYAgTe3, isostructural with KZrCuS3, crystallize in a layered structure in which there are 2?[LnMQ2-3] layers separated by Ba2+ ions. Ln atoms are coordinated by six Q atoms at the corners of a distorted octahedron, and M atoms are coordinated by four Q atoms at the corners of a tetrahedron. The layers are formed by the connection of edge-sharing octahedral chains and corner-sharing tetrahedral chains. Ba atoms are coordinated by seven Q atoms in BaLaCuTe3 and by eight Q atoms in BaGdAuSe3, BaYCuTe3, and BaYAgTe3. BaNdAgTe3 shows temperature-dependent paramagnetism. Its magnetic susceptibility follows the Curie-Weiss law. The effective magnetic moment of 3.4(3) ?B is in agreement with the theoretical value of 3.6 ?B for Nd3+.

  3. Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Brebrick, R. F.; Dudley, M.; Ramachandran, N.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyance-driven convection and growth interface fluctuations caused by irregular fluid-flows. ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, were grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals were characterized extensively to correlate the grown crystal properties with the growth conditions. The following are the research progress in the past two years. In-situ monitoring of partial pressure by optical absorption technique and visual observation of the growing crystal were performed during vapor growth of ZnSe. Low-temperature photoluminescence (PL) spectra and glow discharge mass spectroscopy (GDMS) were measured on ZnSe starting materials provided by various vendors and on bulk crystals grown from these starting materials by physical vapor transport (PVT) to study the effects of purification and contamination during crystal growth process. Optical characterization was performed on wafers sliced from the grown crystals of ZnSe, ZnTe and ZnSe(1-x),Te(x), (0Se and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for the ZnSe(1-x),Te(x), samples, 0.09Te clusters because of the high Te content in these samples. To validate numerical codes, in-situ monitoring during the PVT of HgI2 was designed. Optical absorption spectra of the vapor phase over HgI2 were measured for wavelengths between 200 and 600nm at sample temperatures between 349 and 610K. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were determined. From these constants the vapor pressure of HgI2 was established as a function of temperature for the liquid and the solid Beta-phases To characterize the growth conditions during the PVT growth of In-doped ZnSe the optical absorbance of the vapor phase over the In-Se system were measured and were used to obtain the partial pressures of Se2(g) and In2Se(g).

  4. Effect of Te-Se-S Triple Doping on the Thermoelectric Properties of CoSb3 Skutterudites

    NASA Astrophysics Data System (ADS)

    Ye, Xiangrong; Chen, Gang; Duan, Bo; Zhai, Pengcheng

    2015-06-01

    Te-Se or Te-S co-doping is an effective way of reducing the thermal conductivity and enhancing the thermoelectric performance of skutterudite compounds. In this work, to achieve higher ZT values, we used a new combination of doping, Te-Se-S doping. Dense samples of CoSb2.79Te0.16Se0.05- x S x ( x = 0.0, 0.01, 0.025, 0.04, 0.05) were prepared by traditional solid-state reaction then spark plasma sintering (SPS). X-ray diffraction patterns showed all the samples were single-phase CoSb3 skutterudites. The lattice thermal conductivity of all the samples decreased monotonically on addition of elemental S at each temperature, indicating that S is superior to Se at reducing lattice thermal conductivity when the Te-doping fraction is stable at 0.16. A maximum ZT of 1.25 at 800 K was obtained for the x = 0.05 sample, because of the low lattice thermal conductivity, which is approximately 12% higher than that of the x = 0.0 sample.

  5. Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyancy-driven convection and growth interface fluctuations caused by irregular fluid-flows. ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, were grown by vapor transport technique with real time in situ non-invasive monitoring techniques. The grown crystals were characterized extensively to correlate the grown crystal properties with the growth conditions. Significant effects of gravity vector orientation on the growth crystal morphology and point defect distribution were observed.

  6. Antisite defects in n-type Bi2(Te,Se)3: Experimental and theoretical studies

    NASA Astrophysics Data System (ADS)

    Oh, M. W.; Son, J. H.; Kim, B. S.; Park, S. D.; Min, B. K.; Lee, H. W.

    2014-04-01

    Intrinsic defects in Bi2Te3 were analyzed using first-principles density functional theory calculations. The results demonstrated that antisite defects were dominant in both p- and n-type Bi2Te3. To investigate the characteristics of these defects, n-type Bi2(Te,Se)3 compounds were fabricated using powder prepared by high-energy ball milling and their electrical properties were examined. Electrical resistivity and the Seebeck coefficient increased with ball milling time. These changes in both properties were attributed to a reduction in the carrier concentration, which was supported by the Hall coefficient measurement. The antisite defects were found to be responsible for the changes in carrier concentration. Lattice parameter analysis supported the postulate that variations in the concentration of antisite defects were responsible for the changes in carrier concentration. These findings suggest that optimization of carrier concentration should be considered in the high-energy ball milling process, in which reductions in grain size are expected to improve thermoelectric properties.

  7. Beneficial effect of Se substitution on thermoelectric properties of Co{sub 4}Sb{sub 11.9-x}Te{sub x}Se{sub 0.1} skutterudites

    SciTech Connect

    Duan, Bo; Zhai, Pengcheng; Liu, Lisheng; Zhang, Qingjie; Ruan, Xuefeng

    2012-09-15

    Skutterudite-based compounds, Co{sub 4}Sb{sub 12-x-y}Te{sub x}Se{sub y} (x=0.4, 0.5, 0.6 and y=0.0, 0.1), are synthesized by the solid state reaction and the spark plasma sintering methods, and their structure and the thermoelectric properties have been investigated systematically. It is found that Se doping results in decrease of the lattice parameter and refinement of the particle size compared with those of Se-free samples. The Se-doped samples do not yield a certain increase in the power factor, but show a significant depression in the lattice thermal conductivity. The highest dimensionless figure of merit ZT=1.09 is achieved at 800 K for the Co{sub 4}Sb{sub 11.3}Te{sub 0.6}Se{sub 0.1} compound, which is improved by 15% compared with that of Te alone doped Co{sub 4}Sb{sub 11.4}Te{sub 0.6} compound at the corresponding temperature. - Graphical abstract: The Te and Se co-doped Co{sub 4}Sb{sub 11.9-x}Te{sub x}Se{sub 0.1} skutterudites show amazingly lower thermal conductivity ({kappa}) and lattice thermal conductivity ({kappa}{sub L}) compared with those of Co{sub 4}Sb{sub 12-x}Te{sub x} skutterudites. Highlights: Black-Right-Pointing-Pointer Te and Se co-doped Co{sub 4}Sb{sub 12-x-y}Te{sub x}Se{sub y} compounds have been synthesized by the solid state reaction method. Black-Right-Pointing-Pointer Doping of Se resulted in decrease of the lattice parameter and refinement of the particle size. Black-Right-Pointing-Pointer The co-doped skutterudites show amazingly lower lattice thermal conductivity. Black-Right-Pointing-Pointer Co-doping with Te and Se is an attractive approach to enhance the TE performance of skutterudites.

  8. Cyclotron resonance in modulation-doped ZnSe/Zn1 xCdxSe and ZnTe/CdSe single quantum wells

    E-print Network

    Knobel, Robert

    Cyclotron resonance in modulation-doped ZnSe/Zn1 xCdxSe and ZnTe/CdSe single quantum wells H. K Received 6 July 1999; accepted for publication 13 October 1999 We report low-temperature 4.2 K cyclotron of conduction-band electrons m* whose direct determination by cyclotron reso- nance CR has been largely obviated

  9. Charge transport in mixed CdSe and CdTe colloidal nanocrystal films

    E-print Network

    Bawendi, Moungi G.

    We report the influence of trap states on charge transport through films of mixed CdTe and CdSe nanocrystals (NCs) between lateral electrodes, through layered films of CdTe and CdSe NCs in a layered geometry, and through ...

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

    SciTech Connect

    Shuaibu, Alhassan; Rahman, Md. Mahmudur; Zainuddin, Hishamuddin; Talib, Zainal Abidin; Muhida, Rifki

    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.

  11. Diverse lattice dynamics in ternary Cu-Sb-Se compounds.

    PubMed

    Qiu, Wujie; Wu, Lihua; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2015-01-01

    Searching and designing materials with extremely low lattice thermal conductivity (LTC) has attracted considerable attention in material sciences. Here we systematically demonstrate the diverse lattice dynamics of the ternary Cu-Sb-Se compounds due to the different chemical-bond environments. For Cu3SbSe4 and CuSbSe2, the chemical bond strength is nearly equally distributed in crystalline bulk, and all the atoms are constrained to be around their equilibrium positions. Their thermal transport behaviors are well interpreted by the perturbative phonon-phonon interactions. While for Cu3SbSe3 with obvious chemical-bond hierarchy, one type of atoms is weakly bonded with surrounding atoms, which leads the structure to the part-crystalline state. The part-crystalline state makes a great contribution to the reduction of thermal conductivity that can only be effectively described by including a rattling-like scattering process in addition to the perturbative method. Current results may inspire new approaches to designing materials with low lattice thermal conductivities for high-performance thermoelectric conversion and thermal barrier coatings. PMID:26328765

  12. Diverse lattice dynamics in ternary Cu-Sb-Se compounds

    NASA Astrophysics Data System (ADS)

    Qiu, Wujie; Wu, Lihua; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2015-09-01

    Searching and designing materials with extremely low lattice thermal conductivity (LTC) has attracted considerable attention in material sciences. Here we systematically demonstrate the diverse lattice dynamics of the ternary Cu-Sb-Se compounds due to the different chemical-bond environments. For Cu3SbSe4 and CuSbSe2, the chemical bond strength is nearly equally distributed in crystalline bulk, and all the atoms are constrained to be around their equilibrium positions. Their thermal transport behaviors are well interpreted by the perturbative phonon-phonon interactions. While for Cu3SbSe3 with obvious chemical-bond hierarchy, one type of atoms is weakly bonded with surrounding atoms, which leads the structure to the part-crystalline state. The part-crystalline state makes a great contribution to the reduction of thermal conductivity that can only be effectively described by including a rattling-like scattering process in addition to the perturbative method. Current results may inspire new approaches to designing materials with low lattice thermal conductivities for high-performance thermoelectric conversion and thermal barrier coatings.

  13. Diverse lattice dynamics in ternary Cu-Sb-Se compounds

    PubMed Central

    Qiu, Wujie; Wu, Lihua; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2015-01-01

    Searching and designing materials with extremely low lattice thermal conductivity (LTC) has attracted considerable attention in material sciences. Here we systematically demonstrate the diverse lattice dynamics of the ternary Cu-Sb-Se compounds due to the different chemical-bond environments. For Cu3SbSe4 and CuSbSe2, the chemical bond strength is nearly equally distributed in crystalline bulk, and all the atoms are constrained to be around their equilibrium positions. Their thermal transport behaviors are well interpreted by the perturbative phonon-phonon interactions. While for Cu3SbSe3 with obvious chemical-bond hierarchy, one type of atoms is weakly bonded with surrounding atoms, which leads the structure to the part-crystalline state. The part-crystalline state makes a great contribution to the reduction of thermal conductivity that can only be effectively described by including a rattling-like scattering process in addition to the perturbative method. Current results may inspire new approaches to designing materials with low lattice thermal conductivities for high-performance thermoelectric conversion and thermal barrier coatings. PMID:26328765

  14. Phonon conduction in PbSe, PbTe, and PbTe1?xSex from first-principles calculations

    E-print Network

    Tian, Zhiting

    We apply first-principles calculations to lead selenide (PbSe) and lead telluride (PbTe) and their alloys (PbTe[subscript 1?x]Se[subscript x]), which are potentially good thermoelectric materials, to investigate their ...

  15. Effects of Synthesis Temperature on the Microstructure and Thermoelectric Properties of Te-Se Codoped Skutterudites

    NASA Astrophysics Data System (ADS)

    Ding, Shijie; Duan, Bo; Xu, Chenglong; Li, Yao; Liu, Lisheng; Zhai, Pengcheng

    2014-06-01

    Skutterudite compounds Co4Sb11.3Te0.5Se0.2 were synthesized by solid-state reaction at different temperatures (853 K, 903 K, 953 K, and 1003 K) with subsequent spark plasma sintering. x-Ray diffraction, field-emission scanning electron microscopy, and electron probe microanalysis were utilized to analyze the phase structure, microstructure, and actual compositions of the samples. The results showed that the actual composition and the grain size vary with the synthesis temperature. The thermoelectric properties of all samples were measured in the temperature range of 300 K to 800 K. As the synthesis temperature increases, the electrical conductivity increases rapidly, the absolute Seebeck coefficient falls, and the thermal conductivity first decreases and then increases. The highest dimensionless figure of merit ZT was achieved for the sample synthesized at 953 K, exceeding 1.0 at high temperature.

  16. Preparation and thermoelectric properties of Bi2Te3-Bi2Se3 solid solutions

    NASA Astrophysics Data System (ADS)

    Lee, Go-Eun; Kim, Il-Ho; Lim, Young Soo; Seo, Won-Seon; Choi, Byeong-Jun; Hwang, Chang-Won

    2014-05-01

    Bi2Te3-ySey (y = 0.0 - 0.6) solid solutions were prepared by encapsulated melting and hot pressing. The lattice constants decreased linearly with increasing Se content, which confirmed the successful formation of the Bi2Te3-ySey solid solutions. All specimens exhibited n-type conduction in the measured temperature range (323-523 K) and slightly decreased electrical conductivities with increasing temperature. By substituting Se for Te, the Seebeck coefficients were increased, but the electrical and thermal conductivities were reduced: consequently, the dimensionless figures of merit were improved. The highest ZT was obtained as 0.56 at 323 K for Bi2Te2.85Se0.15 and as 0.60 at 423 K for Bi2Te2.4Se0.6.

  17. Electric current enhanced defect elimination in thermally annealed Bi-Sb-Te and Bi-Se-Te thermoelectric thin films

    NASA Astrophysics Data System (ADS)

    Liou, K. M.; Liao, C. N.

    2010-09-01

    An electric-current assisted thermal treatment is demonstrated to be an effective process for eliminating crystal lattice defects and improving thermoelectric properties of both Bi-Sb-Te and Bi-Se-Te nanocrystalline thin films. A model based on electromigration-induced preferential Sb and Te diffusion is proposed to explain the observed Sb-rich and Te precipitation as well as the enhancement of Seebeck coefficient and electrical conductivity of the electrically stressed thin films. Owing to anisotropic diffusion and electrical transport properties, charged lattice defects are preferentially eliminated in the direction parallel to the basal plane of bismuth telluride crystal under electric current stressing. The presented current assisted annealing approach can be an efficient postdeposition treatment that prevents from gross grain growth and evaporation of volatile constituents in Bi-Te based nanocrystalline thin films during high-temperature annealing process.

  18. Effects of Se substitution on the thermoelectric performance of n-type Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} skutterudites

    SciTech Connect

    Duan, Bo; Zhai, Pengcheng; Liu, Lisheng; Zhang, Qingjie

    2012-07-15

    Highlights: ? The simple solid state reaction technique was employed to prepare Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} skutterudites. ? The thermal conductivity decreases gradually with the increasing Se content. ? Doping with moderate Se is an effective way to enhance the thermoelectric performance of Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x}. ? The highest ZT of 1.11 at 800 K is obtained for the Co{sub 4}Sb{sub 11.3}Te{sub 0.58}Se{sub 0.12} sample. -- Abstract: A series of double-substituted Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} skutterudites have been fabricated by combining the solid state reaction and the spark plasma sintering method, and the effects of Se substitution on the thermoelectric properties are characterized by measurements of the electrical conductivity, the Seebeck coefficient and the thermal conductivity in the temperature range of 300–800 K. Doping Se into the Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x} matrix suppresses the carrier concentration, and the electrical conductivity actually decreases with the Se content. However, moderate Se doping is effective in enhancing the thermoelectric performance of the n-type Co{sub 4}Sb{sub 11.3}Te{sub 0.7?x}Se{sub x}, because of the resulted dramatically decreased thermal conductivity. Analyses indicate that the heightened point-defect scattering induced by Se doping together with the electron–phonon scattering induced by Te doping is responsible for the reduction of lattice thermal conductivity of these compounds.

  19. Three-dimensional topological insulators Bi{sub 2}Te{sub 3}, Bi{sub 2}Se{sub 3}, and Bi{sub 2}Te{sub 2}Se - a microwave spectroscopy study

    SciTech Connect

    Wolos, A.; Strzelecka, S. G.; Hruban, A.; Materna, A.; Piersa, M.

    2013-12-04

    We present results of investigations of three-dimensional topological insulators from a family of bismuth compounds performed in electron spin resonance spectrometer. Next to the standard spin resonance spectra in Bi{sub 2}Se{sub 3} originating from bulk conduction electrons (g{sub Verbar;} = 27.5 ± 0.1 and g{sub ?} = 19.5 ± 0.1), we observed also cyclotron resonance due to topological surface states in Bi{sub 2}Te{sub 3} and non-resonant signal related to weak anti-localization in Bi{sub 2}Te{sub 2}Se. The analysis of the cyclotron resonance signal yields low Fermi velocity equal to 3250 m/s in Bi{sub 2}Te{sub 3}. The phase coherence length determined from weak anti-localization signal equals to 550 nm at low temperatures in Bi{sub 2}Te{sub 2}Se. Relation of the signals to bulk, topological surface or two-dimensional quantum well states is discussed and where possible indicated.

  20. Electronic structure of the quantum spin Hall parent compound CdTe and related topological issues

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Bian, Guang; Fu, Li; Liu, Chang; Wang, Tao; Zha, Gangqiang; Jie, Wanqi; Neupane, Madhab; Miller, T.; Hasan, M. Z.; Chiang, T.-C.

    2014-11-01

    Cadmium telluride (CdTe), a compound widely used in devices, is a key base material for the experimental realization of the quantum spin Hall phase. We report herein a study of the electronic structure of CdTe by angle-resolved photoemission spectroscopy from well-ordered (110) surfaces. The results are compared with first-principles calculations to illustrate the topological distinction between CdTe and a closely related compound HgTe. Through a theoretical simulation a topological phase transition as well as the Dirac-Kane semimetal phase at the critical point was demonstrated in the mixed compound H gxC d1 -xTe .

  1. Observation of an electron band above the Fermi level in FeTe?.??Se?.?? from in-situ surface doping

    DOE PAGESBeta

    Zhang, P.; Richard, P.; Xu, N.; Xu, Y. -M.; Ma, J.; Qian, T.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.; Ding, H.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe?.??Se?.??. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe??xSe? compound.

  2. Nano-sized Minerals of Elemental Selenium and Tellurium Formed by Bacterial Dissimilatory Reduction of Se- and Te-Oxyanions.

    NASA Astrophysics Data System (ADS)

    Oremland, R. S.

    2007-12-01

    Selenium and tellurium are both Group 16 elements that have curious opto-electrical properties making them of potential interest for photovoltaic applications. The process of dissimilatory reduction of selenate and selenite by 3 diverse species of anaerobes, Bacillus selenitireducens, Sulfurospirillum barnesii, and Selenihalanaerobacter shriftii resulted in the accumulation of many uniformly-sized nanospheres (diameter = approx. 300 nm) that aggregated on the outside of their cell envelopes (Oremland et al., 2004). Despite their uniformity of shape, purified Se-nanospheres from the 3 different species displayed significantly different spectral properties (UV- visible light and Raman) indicating differing internal arrangements of their Se atoms. Se-nanospheres from all 3 species also had lower bandgap energies than that of elemental selenium formed by chemical means. We subsequently determined that S. barnesii and B. selenitireducens could grow by dissimilatory reduction of Te- oxyanions, although progress was hampered by the fact that Te concentrations above 0.6 mM proved toxic to cells (Baesman et al., 2007). Unlike the case for Se-nanospheres, the Te-nanoparticles formed by the two microbes were entirely different. S. barnesii formed small, irregularly shaped spheroids (smaller than 50 nm diameter) that coalesced into larger aggregates. In contrast, B. selenitreducens formed nano-rods (10 nm diameter x 200 nm length) that coalesced into larger shards which formed even larger rosette-shaped aggregates once they sloughed off the cells. Spectroscopy of purified Te-rosettes indicated an internal trigonally-shaped array of Te atoms. Future research on Te(0) nano-materials formed by anaerobic bacteria would be aided by isolation of novel species adapted to growth at high batch culture concentrations of Te-oxyanions (approx. 10 mM). Furthermore, the ability of microbes like B. selenitreducens to form selenide by reduction of Se(0) suggests an application in the biological formation of CdSe or perhaps CdTe type-nanomaterials that bypasses the need for highly reactive compounds required for chemical syntheses. Oremland, R.S. et al. (2004). Appl. Environ. Microbiol. 70: 52 - 60. Baesman, S.M., et al. (2007). Appl. Environ. Microbiol. 73: 2135 - 2143.

  3. Synthesis and structural characterization of ZnTe/ZnSe core/shell tunable quantum dots

    E-print Network

    Guan, Juan

    2008-01-01

    Colloidal semiconductor nanocrystals or quantum dots have attracted much attention recently with their unique optical properties. Here we present a novel approach to synthesize ZnTe/ZnSe core/shell tunable quantum dots. ...

  4. (77)Se and (125)Te NMR spectroscopy on a selectivity study of organochalcogenanes with L-amino acids.

    PubMed

    Silva, Marcio S; Andrade, Leandro H

    2015-06-01

    The hypervalent selenium- and tellurium-containing compounds (halo-organoselenuranes and halo-organotelluranes) were treated with amino acids to evaluate their reactivity and chemoselectivity by (1)H, (13)C, (77)Se and (125)Te NMR spectroscopy. The study of forced thermal stability was performed and analyzed by NMR. The organotelluranes remained stable at temperatures around 60 °C but in the case of organoselenuranes, there was formation of new products at 37 °C as a result of halogen loss. (77)Se and (125)Te NMR spectroscopy has proved to be a very efficient and fast technique to evidence the high selectivity of organochalcogenanes against l-amino acids, specific to l-cysteine. PMID:25923042

  5. Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure

    PubMed Central

    Zhao, Yanfei; Chang, Cui-Zu; Jiang, Ying; DaSilva, Ashley; Sun, Yi; Wang, Huichao; Xing, Ying; Wang, Yong; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Jian

    2013-01-01

    In spite of much work on topological insulators (TIs), systematic experiments for TI/TI heterostructures remain absent. We grow a high quality heterostructure containing single quintuple layer (QL) of Bi2Se3 on 19 QLs of Bi2Te3 and compare its transport properties with 20 QLs Bi2Se3 and 20 QLs Bi2Te3. All three films are grown on insulating sapphire (0001) substrates by molecular beam epitaxy (MBE). In situ angle-resolved photoemission spectroscopy (ARPES) provides direct evidence that the surface state of 1 QL Bi2Se3/19 QLs Bi2Te3 heterostructure is similar to the surface state of the 20 QLs Bi2Se3 and different with that of the 20 QLs Bi2Te3. In ex situ transport measurements, the observed linear magnetoresistance (MR) and weak antilocalization (WAL) of the hybrid heterostructure are similar to that of the pure Bi2Se3 film and not the Bi2Te3 film. This suggests that the single Bi2Se3 layer on top of 19 QLs Bi2Te3 dominates its transport properties. PMID:24162440

  6. Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure.

    PubMed

    Zhao, Yanfei; Chang, Cui-Zu; Jiang, Ying; DaSilva, Ashley; Sun, Yi; Wang, Huichao; Xing, Ying; Wang, Yong; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Jian

    2013-01-01

    In spite of much work on topological insulators (TIs), systematic experiments for TI/TI heterostructures remain absent. We grow a high quality heterostructure containing single quintuple layer (QL) of Bi2Se3 on 19 QLs of Bi2Te3 and compare its transport properties with 20 QLs Bi2Se3 and 20 QLs Bi2Te3. All three films are grown on insulating sapphire (0001) substrates by molecular beam epitaxy (MBE). In situ angle-resolved photoemission spectroscopy (ARPES) provides direct evidence that the surface state of 1 QL Bi2Se3/19 QLs Bi2Te3 heterostructure is similar to the surface state of the 20 QLs Bi2Se3 and different with that of the 20 QLs Bi2Te3. In ex situ transport measurements, the observed linear magnetoresistance (MR) and weak antilocalization (WAL) of the hybrid heterostructure are similar to that of the pure Bi2Se3 film and not the Bi2Te3 film. This suggests that the single Bi2Se3 layer on top of 19 QLs Bi2Te3 dominates its transport properties. PMID:24162440

  7. Spin-texture of three-dimensional topological insulators: Bi2 Te 3, Bi2 Se 3 and Sb2 Te 3

    NASA Astrophysics Data System (ADS)

    Basak, Susmita; Lin, Hsin; Wray, L. A.; Xu, S.-Y.; Hasan, M. Z.; Bansil, A.

    2011-03-01

    We have investigated the nature of surface states in the Bi 2 Te 3 , Bi 2 Se 3 and Sb 2 Te 3 family of 3D topological insulators using first-principles calculation as well as k . p scheme. Recent spin-resolved photoemission experiments suggest that electrons on the surface of a topological insulator behave as massless relativistic particles with an intrinsic angular momentum (spin) which is locked to their translational momentum [2,3]. We have computed the in-plane spin-textures of all three aforementioned compounds to demonstrate the `spin-helical' nature of the 2D fermions. In addition, the spin must acquire a finite out-of-the-plane component to preserve the bulk topological invariant. We study this quantity in particular since there are possibilities of observing new quantum effects. Work supported by the US DOE.

  8. High-pressure phase transitions in ordered and disordered Bi2Te2Se.

    PubMed

    Nielsen, M B; Parisiades, P; Madsen, S R; Bremholm, M

    2015-08-21

    We report studies of pressure-induced phase transitions of ordered and disordered ternary tetradymite-like Bi2Te2Se by synchrotron powder X-ray diffraction (PXRD) in diamond anvil cells (DACs) for pressures up to 59 and 49 GPa, respectively. The first sample (SB) was prepared from a single crystal with ordered Se/Te sites while the second sample (Q) was prepared from a quenched melt resulting in disordered Se/Te. This allows for an investigation of the effect of disorder on the phase transitions and the equation of states (EoS) of the tetradymite-like ? phase. Fitting of a third order Birch-Murnaghan EoS to the ? phases yielded bulk moduli K0 of 34.5(10) and 38.3(17) GPa and K' of 6.2(3) and 5.0(5) for the SB and Q samples, respectively. An electronic topological transition (ETT) was identified in both samples at pressures of 4.4 and 3.1 GPa, respectively. This was followed by a transition near 11 GPa to a phase that is isostructural with the ? phase of Bi2Te3. The Se/Te ordering only affects the transition pressure to a small extent. A cubic phase that resembles the ? phase observed in high-pressure studies of Bi2Te3 appears at 17-20 GPa, but the ternary composition leads to a more complex structure. The presence of a low angle diffraction peak in the ? phase demonstrates that the true structure is not simply body-centred cubic. In this way the samples resemble Bi2Se3 where Bi and Se show a high degree of ordering, but the proposed structure of ?-Bi2Se3 also does not fully describe the data for ?-Bi2Te2Se. PMID:26169469

  9. Interface vibrational modes and interface structure of CdSe/ZnTe superlattices Y. Jin, G. G. Siu, and M. J. Stokes

    E-print Network

    Chen, Haydn H.

    binary compounds without common anions or cations. Raman scat- tering studies on CdSe/ZnTe SL Ref. 1 show-D and C-B are distinct from the A-B and C-D bonds owing to the lack of common anions or cations

  10. Magnetic property of layered compound NbFeTe2 Jian H. Zhang

    E-print Network

    Li, Jing

    Magnetic property of layered compound NbFeTe2 Jian H. Zhang Department of Chemistry, XavierFeTe2 is a layered cluster compound in which intra Fe­Fe bond distance is 2.488 Å. The magnetic magnetic moment of 3.67 B per Fe at 300 K corresponding to three unpaired electrons may suggest

  11. Colloidal synthesis and optical properties of type-II CdSe-CdTe and inverted CdTe-CdSe core-wing heteronanoplatelets

    NASA Astrophysics Data System (ADS)

    Antanovich, A. V.; Prudnikau, A. V.; Melnikau, D.; Rakovich, Y. P.; Chuvilin, A.; Woggon, U.; Achtstein, A. W.; Artemyev, M. V.

    2015-04-01

    We developed colloidal synthesis to investigate the structural and electronic properties of CdSe-CdTe and inverted CdTe-CdSe heteronanoplatelets and experimentally demonstrate that the overgrowth of cadmium selenide or cadmium telluride core nanoplatelets with counterpartner chalcogenide wings leads to type-II heteronanoplatelets with emission energies defined by the bandgaps of the CdSe and CdTe platelets and the characteristic band offsets. The observed conduction and valence band offsets of 0.36 eV and 0.56 eV are in line with theoretical predictions. The presented type-II heteronanoplatelets exhibit efficient spatially indirect radiative exciton recombination with a quantum yield as high as 23%. While the exciton lifetime is strongly prolonged in the investigated type-II 2D systems with respect to 2D type-I systems, the occurring 2D giant oscillator strength (GOST) effect still leads to a fast and efficient exciton recombination. This makes type-II heteronanoplatelets interesting candidates for low threshold lasing applications and photovoltaics.We developed colloidal synthesis to investigate the structural and electronic properties of CdSe-CdTe and inverted CdTe-CdSe heteronanoplatelets and experimentally demonstrate that the overgrowth of cadmium selenide or cadmium telluride core nanoplatelets with counterpartner chalcogenide wings leads to type-II heteronanoplatelets with emission energies defined by the bandgaps of the CdSe and CdTe platelets and the characteristic band offsets. The observed conduction and valence band offsets of 0.36 eV and 0.56 eV are in line with theoretical predictions. The presented type-II heteronanoplatelets exhibit efficient spatially indirect radiative exciton recombination with a quantum yield as high as 23%. While the exciton lifetime is strongly prolonged in the investigated type-II 2D systems with respect to 2D type-I systems, the occurring 2D giant oscillator strength (GOST) effect still leads to a fast and efficient exciton recombination. This makes type-II heteronanoplatelets interesting candidates for low threshold lasing applications and photovoltaics. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07134d

  12. Sublattice effect on topological surface states in complex (SnTe )n>1(Bi2Te3)m=1 compounds

    NASA Astrophysics Data System (ADS)

    Eremeev, S. V.; Menshchikova, T. V.; Silkin, I. V.; Vergniory, M. G.; Echenique, P. M.; Chulkov, E. V.

    2015-06-01

    An exotic type of topological spin-helical surface state was found in layered van der Waals bonded (SnTe) n =2 ,3(Bi2Te3)m =1 compounds which comprise two covalently bonded band inverted sublattices, SnTe and Bi2Te3 , within a building block. This topological state demonstrates unusual dispersion within the band gap. The dispersion of the surface state has two linear sections of different slope with a shoulder feature between them. Such a dispersion of the topological surface state enables an effective switch of the velocity of topological carriers by means of applying an external electric field.

  13. Enhanced thermoelectric properties of solution grown Bi2Te(3-x)Se(x) nanoplatelet composites.

    PubMed

    Soni, Ajay; Yanyuan, Zhao; Ligen, Yu; Aik, Michael Khor Khiam; Dresselhaus, Mildred S; Xiong, Qihua

    2012-03-14

    We report on the enhanced thermoelectric properties of selenium (Se) doped bismuth telluride (Bi(2)Te(3-x)Se(x)) nanoplatelet (NP) composites synthesized by the polyol method. Variation of the Se composition within NPs is demonstrated by X-ray diffraction and Raman spectroscopy. While the calculated lattice parameters closely follow the Vegard's law, a discontinuity in the shifting of the high frequency (E(g)(2) and A(1g)(2)) phonon modes illustrates a two mode behavior for Bi(2)Te(3-x)Se(x) NPs. The electrical resistivity (?) of spark plasma sintered pellet composites shows metallic conduction for pure Bi(2)Te(3) NP composites and semiconducting behavior for intermediate Se compositions. The thermal conductivity (?) for all NP composites is much smaller than the bulk values and is dominated by microstructural grain boundary scattering. With temperature dependent electrical and thermal transport measurements, we show that both the thermoelectric power S (-259 ?V/K) and the figure of merit ZT (0.54) are enhanced by nearly a factor of 4 for SPS pellets of Bi(2)Te(2.7)Se(0.3) in comparison to Bi(2)Te(3) NP composites. Tentatively, such an enhancement of the thermoelectric performance in nanoplatelet composites is attributed to the energy filtering of low energy electrons by abundant grain boundaries in aligned nanocomposites. PMID:22295990

  14. Thermal behavior in Se-Te chalcogenide system: Interplay of thermodynamics and kinetics

    SciTech Connect

    Svoboda, Roman Málek, Ji?í

    2014-12-14

    Heat capacity measurements were performed for Se, Se{sub 90}Te{sub 10}, Se{sub 80}Te{sub 20}, and Se{sub 70}Te{sub 30} materials in the 230–630 K temperature range. Both glassy and crystalline C{sub p} dependences were found to be identical within the experimental error. The compositional dependence of the N-type undercooled liquid C{sub p} evolution was explained on the basis of free-volume theory; vibrational and chemical contributions to heat capacity were found to be roughly similar for all Se-Te compositions. The thermal behavior in the Se-Te chalcogenide system was thoroughly studied: glass transition, cold crystallization, and melting were investigated in dependence on composition and various experimental conditions (heating rate, particle size, and pre-nucleation period). The kinetics of the structural relaxation and crystallization processes are described in terms of the Tool-Narayanaswamy-Moynihan and Johnson-Mehl-Avrami models. The complexity of these processes is thoroughly discussed with regard to the compositionally determined changes of molecular structures. The discussion is conducted in terms of the mutual interplay between the thermodynamics and kinetics in this system.

  15. Atomic arrangement at ZnTe/CdSe interfaces determined by high resolution scanning transmission electron microscopy and atom probe tomography

    SciTech Connect

    Bonef, Bastien; Rouvière, Jean-Luc; Jouneau, Pierre-Henri; Bellet-Amalric, Edith; Gérard, Lionel; Mariette, Henri; André, Régis; Bougerol, Catherine; Grenier, Adeline

    2015-02-02

    High resolution scanning transmission electron microscopy and atom probe tomography experiments reveal the presence of an intermediate layer at the interface between two binary compounds with no common atom, namely, ZnTe and CdSe for samples grown by Molecular Beam Epitaxy under standard conditions. This thin transition layer, of the order of 1 to 3 atomic planes, contains typically one monolayer of ZnSe. Even if it occurs at each interface, the direct interface, i.e., ZnTe on CdSe, is sharper than the reverse one, where the ZnSe layer is likely surrounded by alloyed layers. On the other hand, a CdTe-like interface was never observed. This interface knowledge is crucial to properly design superlattices for optoelectronic applications and to master band-gap engineering.

  16. Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3

    SciTech Connect

    Kong, P. P.; Sun, F.; Xing, L. Y.; Zhu, J.; Zhang, S. J.; Li, W. M.; Liu, Q. Q.; Wang, X. C.; Feng, S. M.; Yu, X. H.; Zhu, J. L.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Ahuja, R.; Mao, H. K.; Jin, C. Q.

    2015-02-17

    Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. We report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.

  17. Electrodeposited CuGa(Se,Te)2 thin-film prepared from sulfate bath

    NASA Astrophysics Data System (ADS)

    Oda, Yusuke; Minemoto, Takashi; Takakura, Hideyuki; Hamakawa, Yoshihiro

    2006-09-01

    CuGa(Se,Te)2 (CGST) thin films were prepared on a soda-lime glass substrate sputter coated with molybdenum by electrodeposition. The aqueous solution which contained CuSO4-5H2O, Ga2(SO4)3-19.3H2O, H2SeO3, H6TeO6, Li2SO4 and gelatin was adjusted to pH 2.6 with dilute H2SO4 and NaOH. It has been observed that (i) a crack-less and smooth CGST film with a composition close to the stoichiometric ratio was deposited at -600 mV (vs. Ag/AgCl) when Te was hardly included in the film and (ii) cracks and products on the surface increased with increasing Te content in the film. Annealing at 600 °C for 10 min improved the crystallinity of the as-deposited films.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Colloidal synthesis and optical properties of type-II CdSe-CdTe and inverted CdTe-CdSe core-wing heteronanoplatelets.

    PubMed

    Antanovich, A V; Prudnikau, A V; Melnikau, D; Rakovich, Y P; Chuvilin, A; Woggon, U; Achtstein, A W; Artemyev, M V

    2015-05-01

    We developed colloidal synthesis to investigate the structural and electronic properties of CdSe-CdTe and inverted CdTe-CdSe heteronanoplatelets and experimentally demonstrate that the overgrowth of cadmium selenide or cadmium telluride core nanoplatelets with counterpartner chalcogenide wings leads to type-II heteronanoplatelets with emission energies defined by the bandgaps of the CdSe and CdTe platelets and the characteristic band offsets. The observed conduction and valence band offsets of 0.36 eV and 0.56 eV are in line with theoretical predictions. The presented type-II heteronanoplatelets exhibit efficient spatially indirect radiative exciton recombination with a quantum yield as high as 23%. While the exciton lifetime is strongly prolonged in the investigated type-II 2D systems with respect to 2D type-I systems, the occurring 2D giant oscillator strength (GOST) effect still leads to a fast and efficient exciton recombination. This makes type-II heteronanoplatelets interesting candidates for low threshold lasing applications and photovoltaics. PMID:25873332

  20. Thermoelectric properties of Nb3SbxTe7-x compounds

    NASA Technical Reports Server (NTRS)

    Snyder, J.; Wang, S.; Caillat, T.

    2002-01-01

    Niobium antimony telluride, Nb3Sbx,Te7-x, was synthesized and tested for thermoelectric properties in the Thermoelectrics group at the Jet Propulsion Laboratory. The forty atoms per unit cell of Nb3Sb2Te5 and its varied mixture of atoms yield acomplicated structure, suggesting that Nb3Sb2Te5 and related compounds may exhibit low thermal conductivity and hence a higher ZT value. Nb3SbxTe7-x, compounds were synthesized and subsequently analyzed for their Seebeck voltage, heat conduction, and electrical resistivity. Results indicate that Nb3Sb2Te5 is a heavily doped semiconductor whose thermoelectric properties are compromised by compensating n-type and p-type carriers. Attempts to dope in favor of either carrier by varying the Sb:Te ratio yielded samples containing secondary metallic phases that dominated the transport properties of the resulting compounds.

  1. Analysis of the Influence of Thermal Treatment on the Stability of Ag1-xSb1+xTe2+x and Se-Doped AgSbTe2

    NASA Astrophysics Data System (ADS)

    Wyzga, P. M.; Wojciechowski, K. T.

    2015-10-01

    In order to systematize the knowledge on thermodynamic stability and thermoelectric properties of AgSbTe2-based alloys, several experiments examining the influence of thermal treatment on their structural and thermoelectric properties were performed. Samples with a nominal composition of AgSbTe2 and AgSbTe1.98Se0.02 were prepared and then annealed in various temperature conditions. It was confirmed that Ag1-xSb1+xTe2+x (? phase) is the only thermodynamically stable ternary compound in the Ag2Te-Sb2Te3 pseudobinary system. It was also proved that thermal stability of ? phase is limited—it slowly decomposes below 633 K. In contrast to some reports, it was also indicated that a small amount of Se does not lead to stabilisation of AgSbTe2 crystal structure. Despite slow kinetics of the decomposition processes, thermoelectric properties of the material are notably affected by thermal treatment and amount of Ag2Te precipitations. Maximal ZT value of prepared materials varies from 0.65 at 575 K to 1.07 at 563 K.

  2. Ga-modified As2Se3-Te glasses for active applications in IR photonics

    NASA Astrophysics Data System (ADS)

    Shpotyuk, Ya.; Boussard-Pledel, C.; Nazabal, V.; Chahal, R.; Ari, J.; Pavlyk, B.; Cebulski, J.; Doualan, J. L.; Bureau, B.

    2015-08-01

    Effect of Ga addition on physical properties of glassy As2Se3 alloys within Gax(As0.4Se0.6)100-x system (x = 0-5) is studied for further improvement as rare earth ions matrix hosts. Following conventional synthesis conditions, it has been shown it is possible to introduce up to 3 at.% of Ga into As2Se3 matrix without any crystallization and up to 2 at.% of Ga without any changes in the properties of these alloys. The synthesized Gax(As0.4Se0.6)100-x alloys with 4 and 5 at.% of Ga are partly crystallized by cubic Ga2Se3 crystallites. Tellurium has been introduced in the selected Ga2(As0.4Se0.6)98 glass following the Ga2(As0.4Se0.6)98-yTey cut-section to lower phonon energy and enhance quantum efficiency of the incorporated rare earth ions. The Ga2(As0.4Se0.6)88Te10 glass composition is the richest in Ga and Te, keeping its vitreous state without any crystallization. It has been successfully doped with 500 and 1000 ppmw Pr3+ and drawn into optical fiber possessing low attenuation in mid-IR region. Emission in mid-IR was efficiently recorded by pumping Pr3+: Ga2(As0.4Se0.6)88Te10 glasses at 2 ?m.

  3. Fabrication of the Iron-Based Superconducting Wire Using Fe(Se,Te)

    NASA Astrophysics Data System (ADS)

    Mizuguchi, Yoshikazu; Deguchi, Keita; Tsuda, Shunsuke; Yamaguchi, Takahide; Takeya, Hiroyuki; Kumakura, Hiroaki; Takano, Yoshihiko

    2009-08-01

    We have fabricated the Fe(Se,Te) superconducting wire by a special process based on a powder-in-tube method. The pure Fe tube plays the role of not only the sheath but also the raw material for synthesizing the superconducting phases. We succeeded in observing zero resistivity current on the current-voltage measurements for the Fe(Se,Te) wire. Introduction of the pinning centers and fabricating a multi-core wire will enhance the critical current density for the next step.

  4. Electron beam crystallization of Te 1-xSe x films

    NASA Astrophysics Data System (ADS)

    Vermaak, J. S.; Raubenheimer, D.

    1987-11-01

    In situ transmission electron microscopy has been used to study the effect of high energy electrons on the amorphous-to-crystalline phase transformation, the isothermal growth rates, as well as the structure and orientation of the recrystallized Te 0.7Se 0.3 thin films. It is shown that the beam effect is not a pure thermal effect. It is proposed that the electron beam initiates nucleation and promotes growth by the interaction of the high energy electrons with the van der Waals type bonds between the short composite Te-Se chains.

  5. Synthesis, Calorimetric and X ray diffraction studies in the solid solution Tl2(SO4)1-X(SeO4)X.Te(OH)6 0?X?1

    NASA Astrophysics Data System (ADS)

    Ktari, L.; Dammak, M.; Mhiri, T.; Kolsi, A. W.

    2009-11-01

    The crystal structures of the thallium tellurate solid solutions Tl2(SO4)1-x(SeO4)x.Te(OH)6 were determined by X-ray diffraction method. The Tl2SeO4.Te(OH)6 (TlSeTe) and Tl2(SO4)0.6(SeO4)0.4.Te(OH)6 (TlSSeTe) compounds crystallize in the monoclinic system with P21/c space group. Whereas the Tl2SO4.Te(OH)6 (TlSTe) compound crystallizes in the P21/a one. The following parameters of TlSeTe structure are: a=12.358(3)Å; b=7.231(1)Å; c=11.986(2)Å; ?=111.092(2)?; Z=4. The TlSeTe structure can be regarded as being built of isolated TeO6 octahedra and SeO4 tetrahedra. The Tl+ cations are intercalated between these kinds of polyhedra. The main feature of this structure is the coexistence of two different and independent anions (SeO42- and TeO66-) in the same unit cell. The structure is stable thanks to O-H…O hydrogen bonds which link tetrahedral and octahedral groups. Crystals of Tl2SeO4.Te(OH)6 undergo two endothermal peaks at 373 K and 437 K. These transitions detected by DSC and analysed by dielectric measurements. However, the evolution of the conductivity versus temperature showed the presence of a protonic conduction phase transition at 437 K. The phase transition at 373 K can be related to structural phase transition.

  6. Magnetic properties of Ce3+ in PbCeA (A= Te, Se, S)

    NASA Astrophysics Data System (ADS)

    Isber, S.; Gratens, X.; Charar, S.; Golacki, Z.

    2013-01-01

    The magnetic susceptibility of Pb1-xCexA (A = S, Se and Te) crystals with 0.006 ? x ? 0.036 were studied in the temperature range from 20 mK up to room temperature. X-band (~9.5 GHz) Electron Paramagnetic Resonance (EPR) showed small shifts in the effective Landé factors that were attributed to crystal-field admixture. The EPR measurements were correlated with the magnetic susceptibility data and resulted in estimating the crystal-field splitting ? = E(?8) - E(?7) of the lowest 2F5/2 manifold for Ce3+ ions in PbA (A = S, Se and Te) of about 340 K, 440 K and 540 K for Pb1-xCexTe, Pb1-xCexSe, and Pb1-xCexS, respectively. The values for the crystal-field splitting deduced from the magnetic data were found to be in agreement with the calculated ones based on the point charge model. Moreover, the deHaas van-Alphen magnetic oscillations in the susceptibility measurements of Pb1-xCexTe (x~ 0.05 and 0.07) were observed at ultra-low temperature (20 mK); The oscillations were investigated and the values of the oscillatory period for Pb1-xCexTe (x = 0.0048 and 0.007) are reported.

  7. Thermoelectric properties of indium doped PbTe{sub 1-y}Se{sub y} alloys

    SciTech Connect

    Bali, Ashoka; Mallik, Ramesh Chandra; Wang, Heng; Snyder, G. Jeffrey

    2014-07-21

    Lead telluride and its alloys are well known for their thermoelectric applications. Here, a systematic study of PbTe{sub 1-y}Se{sub y} alloys doped with indium has been done. The powder X-Ray diffraction combined with Rietveld analysis confirmed the polycrystalline single phase nature of the samples, while microstructural analysis with scanning electron microscope results showed densification of samples and presence of micrometer sized particles. The temperature dependent transport properties showed that in these alloys, indium neither pinned the Fermi level as it does in PbTe, nor acted as a resonant dopant as in SnTe. At high temperatures, bipolar effect was observed which restricted the zT to 0.66 at 800?K for the sample with 30% Se content.

  8. Hydrothermally synthesized and hot-pressed Bi 2(Te,Se) 3 thermoelectric alloys

    NASA Astrophysics Data System (ADS)

    Ni, H. L.; Zhu, T. J.; Zhao, X. B.

    2005-07-01

    Bi 2(Te,Se) 3 nanopowders have been synthesized by an aqueous chemical route in an open beaker at 70 °C for 72 h. The powders were hot-pressed under a pressure of 50 MPa at 250 °C for 15 min. X-ray diffraction and energy-dispersive analysis of X-rays show that both the powders and the hot-pressed samples are mainly composed of Bi 2(Te,Se) 3 and Te. Scanning electron microscopy observation shows that the crystallite size is smaller than 100 nm in the powders and the width of the polygonal prismatic rods is about 100 nm in the hot-pressed sample. The alloys were doped with SbI 3 before hot pressing. The SbI 3-doped sample shows a higher electrical conductivity and a lower Seebeck coefficient, indicating that SbI 3 is electrically actively incorporated into the alloys.

  9. Topological nature of the FeSe0.5Te0.5 superconductor

    NASA Astrophysics Data System (ADS)

    Wang, Zhijun; Zhang, P.; Xu, Gang; Zeng, L. K.; Miao, H.; Xu, Xiaoyan; Qian, T.; Weng, Hongming; Richard, P.; Fedorov, A. V.; Ding, H.; Dai, Xi; Fang, Zhong

    2015-09-01

    We demonstrate, using first-principles calculations, that the electronic structure of FeSe1 -xTex(x =0.5 ) is topologically nontrivial and characterized by an odd Z2 invariant and Dirac cone type surface states, in sharp contrast to the end member FeSe (x =0 ) . This topological state is induced by the enhanced three-dimensionality and spin-orbit coupling due to Te substitution (compared to FeSe), and characterized by a band inversion at the Z point of the Brillouin zone, which is confirmed by our ARPES measurements. The results suggest that the surface of FeSe0.5Te0.5 may support a nontrivial superconducting channel in proximity to the bulk.

  10. Spray Deposition of High Quality CuInSe2 and CdTe Films: Preprint

    SciTech Connect

    Curtis, C. J.; van Hest, M.; Miedaner, A.; Leisch, J.; Hersh, P.; Nekuda, J.; Ginley, D. S.

    2008-05-01

    A number of different ink and deposition approaches have been used for the deposition of CuInSe2 (CIS), Cu(In,Ga)Se2 (CIGS), and CdTe films. For CIS and CIGS, soluble precursors containing Cu, In, and Ga have been developed and used in two ways to produce CIS films. In the first, In-containing precursor films were sprayed on Mo-coated glass substrates and converted by rapid thermal processing (RTP) to In2Se3. Then a Cu-containing film was sprayed down on top of the In2Se3 and the stacked films were again thermally processed to give CIS. In the second approach, the Cu-, In-, and Ga-containing inks were combined in the proper ratio to produce a mixed Cu-In-Ga ink that was sprayed on substrates and thermally processed to give CIGS films directly. For CdTe deposition, ink consisting of CdTe nanoparticles dispersed in methanol was prepared and used to spray precursor films. Annealing these precursor films in the presence of CdCl2 produced large-grained CdTe films. The films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Optimized spray and processing conditions are crucial to obtain dense, crystalline films.

  11. Ultrafast quasiparticle dynamics of FeTe0.75Se0.25 superconductor

    NASA Astrophysics Data System (ADS)

    Kabasawa, Y.; Eda, T.; Hu, J.; Katayama, I.; Takeda, J.; Kitajima, M.; Katagiri, T.; Sasagawa, T.; Nakamura, K. G.

    2013-03-01

    The electron-phonon coupling constant (??0.45) obtained from femtosecond pump-probe reflection measurements suggests that a phonon-mediated process cannot be the dominant mechanism for superconductivity of FeTe0.75Se0.25.

  12. Evolution of the surface state in Bi2Se2Te thin films during phase transition

    NASA Astrophysics Data System (ADS)

    Choi, Hyejin; Kim, Tae Hyeon; Chae, Jimin; Baeck, Juheyuck; Kee, Chul-Sik; Jeong, Kwang-Ho; Jeong, Hong-Sik; Kang, Chul; Cho, Mann-Ho

    2015-09-01

    Topological insulators, a new quantum state of matter, have created exciting opportunities for studies in topological quantum physics and for exploring spintronics applications due to their gapless helical metallic surface states. In this study, thin films composed of alternate layers of Bi and Se (Te) ({Bi(3 Å)Te(9 Å)}n/{Bi(3 Å)Se(9 Å)}n) were fabricated by controlling the layer thickness within the atomic scale using thermal evaporation techniques. The high-purity growth of uniform Bi2Se2Te1 thin films has not yet been achieved using a thermal evaporation method. However, as a result of a self-ordering process during annealing, an as-grown amorphous film with p-type polarity could transform into single crystalline Bi2Se2Te1 with n-type polarity. Using THz-time domain spectroscopy (THz-TDS) and ultraviolet photoemission spectroscopy (UPS), we concluded that the conductivity is dominated by the Drude contribution, suggesting the presence of a quantum well state and surface states. Moreover we demonstrated that the emission of terahertz waves from the (001) surface of the single crystalline Bi2Se2Te1 thin film would be possible under the excitation of 790 nm femtosecond optical pulses, indicating the presence of a Dirac-fermion, a photo-Dember effect at the surface state and the transient current within the surface depletion region. The results reported herein provide useful information regarding a valuable deposition method that can be useful in studies of the evolution of surface state electrons in topological insulators.Topological insulators, a new quantum state of matter, have created exciting opportunities for studies in topological quantum physics and for exploring spintronics applications due to their gapless helical metallic surface states. In this study, thin films composed of alternate layers of Bi and Se (Te) ({Bi(3 Å)Te(9 Å)}n/{Bi(3 Å)Se(9 Å)}n) were fabricated by controlling the layer thickness within the atomic scale using thermal evaporation techniques. The high-purity growth of uniform Bi2Se2Te1 thin films has not yet been achieved using a thermal evaporation method. However, as a result of a self-ordering process during annealing, an as-grown amorphous film with p-type polarity could transform into single crystalline Bi2Se2Te1 with n-type polarity. Using THz-time domain spectroscopy (THz-TDS) and ultraviolet photoemission spectroscopy (UPS), we concluded that the conductivity is dominated by the Drude contribution, suggesting the presence of a quantum well state and surface states. Moreover we demonstrated that the emission of terahertz waves from the (001) surface of the single crystalline Bi2Se2Te1 thin film would be possible under the excitation of 790 nm femtosecond optical pulses, indicating the presence of a Dirac-fermion, a photo-Dember effect at the surface state and the transient current within the surface depletion region. The results reported herein provide useful information regarding a valuable deposition method that can be useful in studies of the evolution of surface state electrons in topological insulators. Electronic supplementary information (ESI) available: RBS results as a function of annealing temperature of {(Bi(3 Å)Te(9 Å)}n/{(Bi(3 Å)Se(9 Å)}n layered film series. HR-TEM images and EDX results of the as-grown, 150 °C, 200 °C and 250 °C annealed thin films. XRD patterns of the {(Bi(3 Å)Te(9 Å)n/{(Bi(3 Å)Se(9 Å)n layered film and SEM images as a function of annealing temperature in {(Bi(3 Å)Te(9 Å)}n/{(Bi(3 Å)Se(9 Å)}n layered film series. Schematic of Bi2Te3 and Bi2Se2Te phonon mode. Vegard's law as a function of annealing temperature of {(Bi(3 Å)Te(9 Å)}n/{(Bi(3 Å)Se(9 Å)}n films in (006) and (0015) diffraction peaks of thin film series. Hall measurement results as a function of annealing temperature. XRR fitting data for each sample in the as-grown and crystal phases. See DOI: 10.1039/c5nr04354a

  13. Evolution of the surface state in Bi2Se2Te thin films during phase transition.

    PubMed

    Choi, Hyejin; Kim, Tae Hyeon; Chae, Jimin; Baeck, Juheyuck; Kee, Chul-Sik; Jeong, Kwang-Ho; Jeong, Hong-Sik; Kang, Chul; Cho, Mann-Ho

    2015-09-28

    Topological insulators, a new quantum state of matter, have created exciting opportunities for studies in topological quantum physics and for exploring spintronics applications due to their gapless helical metallic surface states. In this study, thin films composed of alternate layers of Bi and Se (Te) ({Bi(3 Å)Te(9 Å)}n/{Bi(3 Å)Se(9 Å)}n) were fabricated by controlling the layer thickness within the atomic scale using thermal evaporation techniques. The high-purity growth of uniform Bi2Se2Te1 thin films has not yet been achieved using a thermal evaporation method. However, as a result of a self-ordering process during annealing, an as-grown amorphous film with p-type polarity could transform into single crystalline Bi2Se2Te1 with n-type polarity. Using THz-time domain spectroscopy (THz-TDS) and ultraviolet photoemission spectroscopy (UPS), we concluded that the conductivity is dominated by the Drude contribution, suggesting the presence of a quantum well state and surface states. Moreover we demonstrated that the emission of terahertz waves from the (001) surface of the single crystalline Bi2Se2Te1 thin film would be possible under the excitation of 790 nm femtosecond optical pulses, indicating the presence of a Dirac-fermion, a photo-Dember effect at the surface state and the transient current within the surface depletion region. The results reported herein provide useful information regarding a valuable deposition method that can be useful in studies of the evolution of surface state electrons in topological insulators. PMID:26300223

  14. Heavy Doping and Band Engineering by Potassium to Improve the Thermoelectric Figure of Merit in p-Type PbTe, PbSe, and PbTe[subscript 1– y]Se[subscript y

    E-print Network

    Zhang, Qian

    We present detailed studies of potassium doping in PbTe[subscript 1– y]Se[subscript y] (y = 0, 0.15, 0.25, 0.75, 0.85, 0.95, and 1). It was found that Se increases the doping concentration of K in PbTe as a result of the ...

  15. Electrical characterization of vacuum-deposited p-CdTe/n-ZnSe heterojunctions

    NASA Astrophysics Data System (ADS)

    Acharya, Shashidhara; Bangera, Kasturi V.; Shivakumar, G. K.

    2015-11-01

    In this paper, we report a heterojunction of p-CdTe/n-ZnSe fabricated on a quartz substrate using thermal evaporation technique. The materials have a larger band gap difference in comparison to other II-VI heterojunctions-involving CdTe. The larger band gap difference is expected to increase diffusion potential and photovoltaic conversion efficiency. The electrical conduction mechanism involved, barrier height and band offset at the interface that are crucial to determine device performance are evaluated using electrical characterization of heterojunction. The junction exhibited excellent rectification behavior with an estimated barrier height of 0.9 eV.

  16. Magneto-optical studies of (Zn,Mn)Se/ZnTe quantum dots

    NASA Astrophysics Data System (ADS)

    Barman, B.; Tsai, Y.; Scrace, T.; Zutic, I.; McCombe, B. D.; Petrou, A.; Chou, W. C.; Tsou, M. H.; Yang, C. S.; Sellers, I. R.; Oszwaldowski, R.; Petukhov, A. G.

    2014-03-01

    We have recorded the circular polarization P of photoluminescence from (Zn,Mn)Se/ZnTe quantum dots (QDs) as function of magnetic field B. The polarization at a fixed temperature increases monotonically with B and saturates for B >3 tesla at Psat. The value of Psat depends strongly on the laser photon energy. When we excite above (below) the ZnMnSe gap with photons of energy of 3.81 eV (2.54 eV), we measure Psat = 55 %(Psat = 20 %) . We interpret these results as due to the difference in the Zeeman band splitting between the magnetic (Zn,Mn)Se matrix and the non-magnetic ZnTe QDs. For 3.81 eV excitation, electron-hole pairs are generated mainly in the (Zn,Mn)Se matrix. The majority of the holes relax to the +3/2 state before capture by the ZnTe QDs. With 2.54 eV excitation, all electron-hole pairs are excited in the QDs where the Zeeman splitting is negligible. Thus, Psat is determined in this case by the relatively small Zeeman splitting of ZnMnSe conduction band. We relate these findings to our previous results for magnetic type-II QDs, where Psat does not depend on the exciting photon energy. The work at SUNY Buffalo is supported by NSF, DOE-BES, and ONR.

  17. First-principles calculations of properties for chalcogen (S, Se, Te) doped silicon

    NASA Astrophysics Data System (ADS)

    Du, Lingyan; Wu, Zhiming; Li, Shibin; Hu, Zheng; Jiang, Yadong

    2016-01-01

    In this paper, density-functional theory based methods are utilized to systematically investigate the properties of chalcogens (S, Se, Te) doped silicon at different doping concentration. The calculated crystal structures indicate that Se-implanted Si at concentration of 1.56% show minimum lattice distortion and formation energy. Intermediate band caused by introduction of chalcogen impurities is beneficial to strong optical absorption in the infrared range. The calculations carried out demonstrate that energy band structure and optical absorption coefficient are all associated with the doping concentration. The bandwidth of intermediate band and forbidden energy gap are broadened due to the increase of impurities concentration. The dependence of optical absorption on doping concentration is confirmed by the calculations. The results reveal that S/Se/Te-doped silicon at concentration on the order of 1.04% is probably suitable candidate for intermediate band materials.

  18. Thermoelectric properties of Bi2Te3-Bi2Se3 solid solutions prepared by attrition milling and hot pressing

    NASA Astrophysics Data System (ADS)

    Lee, Go-Eun; Kim, Il-Ho; Choi, Soon-Mok; Lim, Young Soo; Seo, Won-Seon; Park, Jae-Soung; Yang, Seung-Ho

    2014-12-01

    Bi2Te3- y Se y ( y = 0.15-0.6) solid solutions were prepared by attrition milling and hot pressing. The lattice constants decreased with increasing Se content, indicating that the Se atoms were successfully substituted into the Te sites. All specimens exhibited n-type conduction, and their electrical resistivities increased slightly with increasing temperature. With increasing Se content, the Seebeck coefficients increased while the thermal conductivity decreased due to the increase in phonon scattering. The maximum figure of merit obtained was 0.63 at 440 K for the undoped Bi2Te2.4Se0.6 solid solution.

  19. Structural and conductivity studies of CsK(SO4)0.32(SeO4)0.68Te(OH)6

    NASA Astrophysics Data System (ADS)

    Djemel, M.; Abdelhedi, M.; Zouari, N.; Dammak, M.; Kolsi, A. W.

    2012-12-01

    The compound CsK(SO4)0.32(SeO4)0.68Te(OH)6 crystallizes in the monoclinic P21/n space group. It was analyzed, at room temperature, using X-ray diffractometer data. The main feature of these atomic arrangements is the coexistence of three and different anions (SO42-, SeO42- and TeO66-groups) in the unit cell, connected by hydrogen bonds which make the building of the crystal. The thermal analysis of the title compound shows three distinct endothermal peaks at 435, 460 and 475 K. Complex impedance measurements are performed on this material as a function of both temperature and frequency. The electric conduction has been studied. The temperature dependence on the conductivity indicates that the sample became an ionic conductor at high temperature.

  20. Hydrogen passivation of Se and Te in AlSb M. D. McCluskey and E. E. Haller

    E-print Network

    McCluskey, Matthew

    Hydrogen passivation of Se and Te in AlSb M. D. McCluskey and E. E. Haller Lawrence Berkeley observed local vibrational modes LVM's arising from DX-hydrogen complex in AlSb. Hydrogen was diffused into bulk AlSb:Se and AlSb:Te by annealing in sealed quartz ampoules with either hydrogen gas or methanol CH

  1. Thickness effects on optical and photoelectric properties of PbSeTeO quaternary thin films prepared by magnetron

    E-print Network

    Volinsky, Alex A.

    Thickness effects on optical and photoelectric properties of PbSeTeO quaternary thin films prepared, indicating that increasing the thickness is an effective method to expand the absorption range of the sputtered PbSeTeO quaternary thin films. The photoelectric sensi- tivity increased almost linearly

  2. New application of scintillator ZnSe(Te) in scintielectronic detectors for detection of neutrons, medical imaging, explosive detection, and NDT

    NASA Astrophysics Data System (ADS)

    Ryzhikov, Volodymyr D.; Opolonin, Oleksandr D.; Fedorov, Alexander G.; Lysetska, Olena K.; Kostioukevitch, Sergey A.

    2008-08-01

    Scintillators on the basis of AIIBVI compounds, such as ZnSe(Te), can be used for detection of secondary charged particles coming from nuclear reactions in which neutrons interact with target nuclei of atoms present in transparent materials of dispersion scintillation detectors matrices. Using unique properties of scintillator ZnSe(Te) we show possibility of increase detection efficiency for soft x-ray radiation (20 - 90 keV). The amorphous silicon flat panels and the photodiode arrays wide used for non-destructive testing and medical imaging (spatial resolution 20 - 400 mkm). By our estimations, using of such detectors in combination with thin film of ZnSe(Te) can increase efficiency of registration of x-ray radiation (for the source of 60-140kV) in 1,2 - 2 times. We obtained thin films (10-450mkm) of scintillator ZnSe(Te) on the different substrate materials and estimated the relative light yield of the layers deposited on the graphite and Al2O3 ceramic substrates and the bulk ZnSe(Te) crystal. Use of ZnSe(Te) in the low-energy "scintillator - photodiode" type detector allowed to increase accuracy of authentication of explosives (HEIMANN X-RAY INSPECTION SYSTEM EDtS10080). Using the dual energy digital radiography system prototype we obtained the x-ray images (60 projections of each object). These images are basic data for computer tomography and three-dimensional reconstruction of density and effective atomic number. The color identification palette provides clearly show variations of effective atomic number in biological and inorganic objects. So, for example, changes of calcium concentration in a bone. The research described in this publication was supported by STCU #4115 and NATO SfP-982823.

  3. Diffusion doping and Infrared Optical Properties of Transition Metal Ions in ZnSe windows and Cd0.55Mn0.45Te crystals

    NASA Astrophysics Data System (ADS)

    Nyein, Ei; Hommerich, Uwe; Jones, Ivy; Calhoun, Monique; Haynes, Erica; Trivedi, Sudhir

    2006-03-01

    Transition metal (TM) doped II-VI semiconductors are of current interest for tunable solid state lasers in the mid-infrared (IR) spectral region as well as passive optical Q-switches. Laser action has been demonstrated at ˜2.3 ?m from Cr: ZnSe, Cr: ZnS, Cr: CdSe, Cr: CdTe, Cr: Cr: CdMnTe, and at ˜4 ?m from Fe: ZnSe. In this work, we report on the material preparation and IR optical properties of diffusion-doped TM ions (Cr^2+, Fe^2+, Co^2+) in polycrystalline ZnSe windows and Cd0.55Mn0.45Te crystals. Different dopant sources were employed in thermal diffusion experiments including TM chloride compounds, TM selenides, and elemental TM powders. The characteristic IR absorption bands from Cr^2+, Co^2+, and Fe^2+ doped II-VI hosts were observed in all samples, independent of the dopant source. Details of the absorption and luminescence properties of these TM: ZnSe and TM: CdMnTe samples will be presented at the conference.

  4. The role of point defects in PbS, PbSe and PbTe: a first principles study.

    PubMed

    Li, Wun-Fan; Fang, Chang-Ming; Dijkstra, Marjolein; van Huis, Marijn A

    2015-09-01

    Intrinsic defects are of central importance to many physical and chemical processes taking place in compound nanomaterials, such as photoluminescence, accommodation of off-stoichiometry and cation exchange. Here, the role of intrinsic defects in the above mentioned processes inside rock salt (RS) lead chalcogenide systems PbS, PbSe and PbTe (PbX) was studied systematically using first principles density functional theory. Vacancy, interstitial, Schottky and Frenkel defects were considered. Rock salt PbO was included for comparison. The studied physical properties include defect formation energy, local geometry relaxation, Bader charge analysis, and electronic structure. The defect formation energies show that monovacancy defects and Schottky defects are favoured over interstitial and Frenkel defects. Schottky dimers, where the cation vacancy and anion vacancy are adjacent to each other, have the lowest defect formation energies at 1.27?eV, 1.29?eV and 1.21?eV for PbS, PbSe and PbTe, respectively. Our results predict that a Pb monovacancy gives rise to a shallow acceptor state, while an X vacancy generates a deep donor state, and Schottky defects create donor-acceptor pairs inside the band gap. The surprisingly low formation energy of Schottky dimers suggests that they may play an important role in cation exchange processes, in contrast to the current notion that only single point defects migrate during cation exchange. PMID:26290521

  5. The role of point defects in PbS, PbSe and PbTe: a first principles study

    NASA Astrophysics Data System (ADS)

    Li, Wun-Fan; Fang, Chang-Ming; Dijkstra, Marjolein; van Huis, Marijn A.

    2015-08-01

    Intrinsic defects are of central importance to many physical and chemical processes taking place in compound nanomaterials, such as photoluminescence, accommodation of off-stoichiometry and cation exchange. Here, the role of intrinsic defects in the above mentioned processes inside rock salt (RS) lead chalcogenide systems PbS, PbSe and PbTe (PbX) was studied systematically using first principles density functional theory. Vacancy, interstitial, Schottky and Frenkel defects were considered. Rock salt PbO was included for comparison. The studied physical properties include defect formation energy, local geometry relaxation, Bader charge analysis, and electronic structure. The defect formation energies show that monovacancy defects and Schottky defects are favoured over interstitial and Frenkel defects. Schottky dimers, where the cation vacancy and anion vacancy are adjacent to each other, have the lowest defect formation energies at 1.27?eV, 1.29?eV and 1.21?eV for PbS, PbSe and PbTe, respectively. Our results predict that a Pb monovacancy gives rise to a shallow acceptor state, while an X vacancy generates a deep donor state, and Schottky defects create donor-acceptor pairs inside the band gap. The surprisingly low formation energy of Schottky dimers suggests that they may play an important role in cation exchange processes, in contrast to the current notion that only single point defects migrate during cation exchange.

  6. Phonons in Bi2Te3 and Bi2Se3 Thin Films

    NASA Astrophysics Data System (ADS)

    Ren, Shang-Fen; Cheng, Wei

    2011-03-01

    Bi2Te3 and Bi2Se3 are topological insulators attracted great research attention in recent years. In this research, some of calculated results on phonons in Bi2Te3 and Bi2Se3 bulk and single quintuple thin films are presented. The effects of spin-orbit couplings on phonon properties in these materials are discussed. Some features of Raman observations of these materials are explained. Acknowledgement: (1) Subcontract of Dr. Y. Cui's KAUST Investigator Award (No. KUS-l1-001-12). (2) Prof. D. S. Wang at Institute of Physics (CAS), his grant (NSFC-10634070), and Supercomputing Center of CAS in Beijing. (3) WC's visit to LBNL.

  7. Modified magnetism within the coherence volume of superconducting FeSeTe

    SciTech Connect

    Leiner, Jonathan C; Thampy, Vivek; Christianson, Andrew D; Abernathy, D.; Stone, Matthew B; Lumsden, Mark D; Sales, Brian C; Safa-Sefat, Athena; Hu, Jin; Mao, Zhiqiang; Bao, Wei; Broholm, Collin L

    2014-01-01

    Neutron Scattering is used to probe magnetic interactions as superconductivity develops in opti- mally doped Fe_(1+ )Se_xTe_(1 x). Applying the first moment sum-rule to comprehensive neutron scatter- ing data, we extract the change in magnetic exchange energy [J_(R-R ) S_R S_R ] in the superconducting state referenced to the normal state. Oscillatory changes are observed for Fe-Fe displacements | R| < , where = 1.3(1) nm is the superconducting coherence length. Dominated by a large reduction in the second nearest neighbor exchange energy (-1.2(2) meV/Fe), the overall reduction in magnetic interaction energy is Hmag = 0.31(9) meV/Fe. Comparison to the superconducting condensation energy E_sc = 0.013(1) meV/Fe, which we extract from specific heat data, suggests the modified magnetism we probe drives superconductivity in Fe_(1+ )Se_xTe_(1 x)

  8. Competition between applied and exchange magnetic fields in (Zn,Mn)Se/ZnTe quantum dots

    NASA Astrophysics Data System (ADS)

    Barman, Biplob; Tsai, Y.; Scrace, T.; Zutic, I.; McCombe, B. D.; Petrou, A.; Chou, W.-C.; Tsou, M.-H.; Yang, C.-S.; Sellers, I. R.; Oszwaldowski, R.; SUNY Buffalo Collaboration; National Chiao Tung University, Taiwan Collaboration; Graduate Institute of Electro-Optical Engineering, Tatung University, Taiwan Collaboration; University of Oklahoma Collaboration; South Dakota School of Mines; Technology Collaboration

    2015-03-01

    We have measured the peak energy of the photoluminescence (PL) emission and its circular polarization from type II (Zn,Mn)Se/ZnTe Quantum Dot structures in the Faraday and Voigt geometries. In the Faraday geometry the PL energy shows a 6 meV red shift at B =6 tesla. This result verifies that the holes are confined in the non-magnetic ZnTe QDs, while the electrons move in the magnetic (Zn,Mn)Se matrix. The PL circular polarization saturates at 45%. In the Voigt geometry, the circular polarization is near-zero and the red shift is 2 meV. These results are discussed using a model that takes into account that electrons are influenced by the combination of the externally applied magnetic field and the exchange field due to the interaction between the Mn-spins and the carriers. This work is supported by DOE-BES and NSF-DMR.

  9. Photoluminescence waveguiding in CdSe and CdTe QDs-PMMA nanocomposite films.

    PubMed

    Suárez, I; Gordillo, H; Abargues, R; Albert, S; Martínez-Pastor, J

    2011-10-28

    In this paper, active planar waveguides based on the incorporation of CdSe and CdTe nanocrystal quantum dots in a polymer matrix are demonstrated. In the case of doping the polymer with both types of quantum dots, the nanocomposite film guides both emitted colors, green (550 nm, CdTe) and orange (600 nm, CdSe). The optical pumping laser can be coupled not only with a standard end-fire coupling system, but also directing the beam to the surface of the sample, indicating a good absorption cross-section and waveguide properties. To achieve these results, a study of the nanocomposite optical properties as a function of the nanocrystal concentration is presented and the optimum conditions are found for waveguiding. PMID:21955572

  10. Assessing the anticancer compounds Se-methylselenocysteine and glucosinolates in Se-biofortified broccoli (brassica oleracea L. var. italica) sprouts and florets

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Broccoli (Brassica oleracea L. var. italica) is a rich source of chemopreventive compounds. Here, we evaluated and compared the effect of selenium (Se) treatment on the accumulation of anticancer compound Se-methylselenocysteine (SeMSCys) and glucosinolates in broccoli sprouts and florets. Total Se ...

  11. ZnSe interlayer effects on properties of (CdS/ZnSe)/BeTe superlattices grown by molecular beam epitaxy

    SciTech Connect

    Li, B.S.; Akimoto, R.; Akita, K.; Hasama, T.

    2006-02-15

    We study the dependence of structural properties on the thickness of the ZnSe interlayer (IL) in (CdS/ZnSe)/BeTe superlattices (SLs); this is crucial for improving the growth mode in this heterostructure. The in situ reflection of high-energy electron diffraction oscillation and high-resolution x-ray diffraction spectra show a perfect structure that is obtained by introducing a ZnSe IL between CdS and BeTe. An intersubband transition (ISB-T) down to 1.57 {mu}m with a full width at half maximum of 90 meV has been observed in (CdS/ZnSe)/BeTe SLs. A strong ISB-T is observed when the ZnSe IL {>=}1 monolayer (ML); however, it completely disappears with the introduction of a 0.5 ML ZnSe IL in (CdS/ZnSe)/BeTe SLs. High-resolution transmission electron microscopy images reveal that a sharp interface is formed in the barrier and well transition region in the structure with ZnSe IL {>=}1 ML; however, the interfaces become rough and thick in those with a 0.5 ML ZnSe IL. This indicates that the properties of the interface in (CdS/ZnSe)/BeTe SLs play an important role in the performance of ISB absorption. A growth model is proposed to explain two-dimensional growth with the insertion of a ZnSe ML into the BeTe/CdS heterostructure. Based on this growth model, the properties of the interface in this structure are explained.

  12. Magnetic polarons in type-II (Zn,Mn)Se/ZnTe quantum dots

    NASA Astrophysics Data System (ADS)

    Murphy, J. R.; Barman, B.; Tsai, Y.; Scrace, T.; Pientka, J. M.; Zutic, I.; McCombe, B. D.; Petrou, A.; Cartwright, A. N.; Chou, W. C.; Tsou, M. H.; Yang, C. S.; Sellers, I. R.; Oszwaldowski, R.; Petukhov, A. G.

    2014-03-01

    We have studied magnetic polaron formation dynamics in (Zn,Mn)Se/ZnTe quantum dots2 (QDs) using time-resolved photoluminescence (TRPL) spectroscopy. The emitted light was spectrally and temporally analyzed; the emission spectra were recorded as function of time delay (?t) from the exciting laser pulse. The recombination time at T = 10 K in our samples is 2.3 ns. The peak energy of the emission red shifts with increasing ?t due to the lowering of the hole-Mn spin complex (magnetic polaron) energy. From this shift we determined the magnetic polaron formation energy (EMP) at T = 10 K to be 20 meV, which is half the value observed in the ZnSe/(Zn,Mn)Te system studied previously.3EMP decreases with increasing temperature, in contrast to the behavior of the ZnSe/(Zn,Mn)Te system3 in which EMP is temperature independent. These results are discussed in terms of a theoretical model. This work is supported by DOE-BES, ONR and NSF.

  13. A Unified Interpretation of Structures of Liquid Se and Te —Molecular Dynamics Study—

    NASA Astrophysics Data System (ADS)

    Aoyama, Takashi; Hiwatari, Yasuaki; Ueda, Akira

    1999-03-01

    A molecular dynamics simulation is carried out to studythe structures of liquid Se and liquid Te in the semiconducting andmetallic states from a unified point of view.A classical system is used which consists of an assembly of chainswith monodisperse length. We assume that the interaction potentialsof pairs of atoms of different chains aredescribed by an inverse power potential, i.e. soft-core potential?(?/r) n,and that the interactions are much softerin the metallic state than in the semiconducting state.The forces concerning the bonding, including geometricalconstraints between bonds are given by potentials of harmonic type.For semiconducting liquid Se the softness parameter n is set to be 24and for both metallic liquid Te and Se n to be 6 together withweak bond-stretching forces.Overall good agreements are obtained with the experimental results.The chain structure of our model realizes naturally shortand long bonds observed with EXAFS for liquid Te.Some information which may be useful for analyses of experimental datais also given.

  14. Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport in Low Gravity

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Ramachandran, N.

    2013-01-01

    Crystals of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, will be grown by physical vapor transport in the Material Science Research Rack (MSRR) on International Space Station (ISS). The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyance-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions.

  15. The variation of the equilibrium of chemical reactions in the process of (Bi 2Te 3)(Sb 2Te 3)(Sb 2Se 3) crystal growth

    NASA Astrophysics Data System (ADS)

    Sokolov, O. B.; Skipidarov, S. Ya; Duvankov, N. I.

    2002-03-01

    Methods of computation for thermodynamic and differential thermal analysis were used to study the effect of the variation of the chemical equilibrium in the synthesis of (Bi 2Te 3) x(Sb 2Te 3) y(Sb 2Se 3) z ( x+ y+ z=100%) in an ampoule on the characteristics of crystals grown by vertical zone-melting technique. Measurements of thermoelectric characteristics of reference samples were made. The case study of pseudo-binary systems (antimony telluride—antimony selenide, x=0; bismuth telluride—antimony selenide, y=0; bismuth telluride—antimony telluride, z=0) proves the following. As a result of some components turning into a gas-vapour phase, some unreacted original components may be found in a condensed phase. With a single-stage synthesis the products of side reactions of chemical interactions may be formed in the condensed phase. The case study of (Bi 2Te 3) 25(Sb 2Te 3) 72(Sb 2Se 3) 3; (Bi 2Te 3) 70(Sb 2Te 3) 25(Sb 2Se 3) 5; (Bi 2Te 3) 90(Sb 2Te 3) 5(Sb 2Se 3) 5 shows that both the synthesis temperature and the dopants greatly affect the thermodynamic equilibrium between the condensed and gas-vapour phases through the variation of the content of basic components in a condensed phase. On the basis of the performed research, recommendations on the synthesis conditions and crystal growth by zone-melting technique are given.

  16. Possible mixed coupling mechanism in FeTe(1-x)Se(x) within a multiband Eliashberg approach.

    PubMed

    Ummarino, G A; Daghero, D

    2015-11-01

    We show that the phenomenology of the iron chalcogenide superconductor FeTe(1-x)Se(x) can be explained within an effective three-band s±-wave Eliashberg model. In particular, various experimental data reported in literature-the critical temperature, the energy gaps, the upper critical field, the superfluid density-can be reproduced by this model in a moderate strong-coupling regime provided that both an intraband phononic term and an interband antiferromagnetic spin-fluctuations term are included in the coupling matrix. The intraband coupling is unusual in Fe-based compounds and is required to explain the somehow anomalous association between gap amplitudes and Fermi surfaces, already evidenced by ARPES. PMID:26445023

  17. Possible mixed coupling mechanism in FeTe1-x Se x within a multiband Eliashberg approach

    NASA Astrophysics Data System (ADS)

    Ummarino, G. A.; Daghero, D.

    2015-11-01

    We show that the phenomenology of the iron chalcogenide superconductor FeTe1-x Se x can be explained within an effective three-band s+/- -wave Eliashberg model. In particular, various experimental data reported in literature—the critical temperature, the energy gaps, the upper critical field, the superfluid density—can be reproduced by this model in a moderate strong-coupling regime provided that both an intraband phononic term and an interband antiferromagnetic spin-fluctuations term are included in the coupling matrix. The intraband coupling is unusual in Fe-based compounds and is required to explain the somehow anomalous association between gap amplitudes and Fermi surfaces, already evidenced by ARPES.

  18. Preparation and Thermoelectric Properties of n-Type Bi2Te2.7Se0.3:D m

    NASA Astrophysics Data System (ADS)

    Lee, Go-Eun; Eum, A.-Young; Song, Kwon-Min; Kim, Il-Ho; Lim, Young Soo; Seo, Won-Seon; Choi, Byeong-Jun; Hwang, Chang-Won

    2015-06-01

    Bismuth chalcogenides such as p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 are excellent thermoelectric materials near room temperature. They can form homogeneous solid solutions because Bi2Te3, Sb2Te3, and Bi2Se3 have the same class of crystal symmetry. The thermoelectric figure of merit can be improved by increasing the power factor through doping and/or by reducing the thermal conductivity by forming a solid solution. In this study, n-type Bi2Te2.7Se0.3:D m (D: dopant such as I, Cu, Ag) solid solutions were prepared by encapsulated melting and hot pressing. The undoped solid solution had a power factor (PF) of 1.71 mW m-1 K-1 at 323 K and a figure of merit ( ZT) of 0.55 at 423 K. The ZT value was improved due to the increased PF by I or Cu doping, and maximum ZT values were obtained as 1.13 for Bi2Te2.7Se0.3:I0.0075 and 0.74 for Bi2Te2.7Se0.3:Cu0.01 at 423 K. However, the thermoelectric properties of Ag-doped Bi2Te2.7Se0.3 solid solutions barely improved.

  19. Chalcogen (O2, S, Se, Te) atmosphere annealing induced bulk superconductivity in Fe1+yTe1-xSex single crystal

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Tsuchiya, Y.; Yamada, T.; Taen, T.; Pyon, S.; Shi, Z. X.; Tamegai, T.

    2014-09-01

    We reported a detailed study of Fe1+yTe0.6Se0.4 single crystals annealed in the atmosphere of chalcogens (O2, S, Se, Te). After annealing with appropriate amount of chalcogens, Fe1+yTe0.6Se0.4 single crystals show Tc higher than 14 K with a sharp transition width ?1 K. Critical current density Jc for the annealed crystals reach a very high value ?2-4 × 105 A/cm2 under zero field, and is also robust under applied field at low temperatures. Magneto-optical imaging reveal that the Jc is homogeneously distributed in the annealed crystals and isotropic in the ab-plane. Our results show that annealing in the atmosphere of chalcogens can successfully induce bulk superconductivity in Fe1+yTe0.6Se0.4.

  20. Antioxidant profile of ethoxyquin and some of its S, Se, and Te analogues.

    PubMed

    Kumar, Sangit; Engman, Lars; Valgimigli, Luca; Amorati, Riccardo; Fumo, Maria Grazia; Pedulli, Gian Franco

    2007-08-01

    6-(Ethylthio)-, 6-(ethylseleno)-, and 6-(ethyltelluro)-2,2,4-trimethyl-1,2-dihydroquinoline-three heavier chalcogen analogues of ethoxyquin-were prepared by dilithiation of the corresponding 6-bromodihydroquinoline followed either by treatment with the corresponding diethyl dichalcogenide (sulfur derivative) or by insertion of selenium/tellurium into the carbon-lithium bond, oxidation to a diaryl dichalcogenide, borohydride reduction, and finally alkylation of the resulting areneselenolate/arenetellurolate. Ethoxyquin, its heavier chalcogen analogues, and the corresponding 6-PhS, 6-PhSe, and 6-PhTe derivatives were assayed for both their chain-breaking antioxidative capacity and their ability to catalyze reduction of hydrogen peroxide in the presence of a stoichiometric amount of a thiol reducing agent (thiol peroxidase activity). Ethoxyquin itself turned out to be the best inhibitor of azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system. In the absence of N-acetylcysteine as a coantioxidant in the aqueous phase, it inhibited peroxidation as efficiently as alpha-tocopherol but with a more than 2-fold longer inhibition time. In the presence of 0.25 mM coantioxidant in the aqueous phase, the inhibition time was further increased by almost a factor of 2. This is probably due to thiol-mediated regeneration of the active antioxidant across the lipid-aqueous interphase. The ethyltelluro analogue 1d of ethoxyquin was a similarly efficient quencher of peroxyl radicals compared to the parent in the two-phase system, but less regenerable. Ethoxyquin was found to inhibit azo-initiated oxidation of styrene in the homogeneous phase (chlorobenzene) almost as efficiently (kinh = (2.0 +/- 0.2) x 106 M-1 s-1) as alpha-tocopherol with a stoichiometric factor n = 2.2 +/- 0.1. At the end of the inhibition period, autoxidation was additionally retarded, probably by ethoxyquin nitroxide formed during the course of peroxidation. The N-H bond dissociation enthalpy of ethoxyquin (81.3 +/- 0.3 kcal/mol) was determined by a radical equilibration method using 2,6-dimethoxyphenol and 2,6-di-tert-butyl-4-methylphenol as equilibration partners. Among the investigated compounds, only the tellurium analogues 1d and, less efficiently, 1g had a capacity to catalyze reduction of hydrogen peroxide in the presence of thiophenol. Therefore, analogue 1d is the only antioxidant which is multifunctional (chain-breaking and preventive) in character and which can act in a truly catalytic fashion to decompose both peroxyl radicals and organic hydroperoxides in the presence of suitable thiol reducing agents. PMID:17602530

  1. Evidence of a Positron bound state on the surface of Bi2Te2Se

    NASA Astrophysics Data System (ADS)

    Shastry, K.; Lim, Z. H.; Joglekar, P. V.; Chirayath, Varghese Anto; Badih, B. A.; Heiman, D.; Barbiellini, B.; Weiss, A. H.,

    2015-03-01

    We describe experiments aimed at probing the sticking of positrons to the surfaces of topological insulators performed at University of Texas at Arlington using the Positron Annihilation induced Auger electron Spectrometer. A magnetically guided beam was used to deposit positrons at the surface of Bi2Te2Se sample at energy of ~ 2 eV. Peaks observed in the energy spectra and intensities of electrons emitted as a result of positron annihilation showed peaks at energies corresponding to Auger peaks in Bi and Te providing clear evidence of Auger emission associated with the annihilation of positrons in a surface bound state. Theoretical estimates of the binding energy of this state are compared with estimates obtained by measuring the incident beam energy threshold for secondary electron emission and the temperature dependence positronium emission. The experiments provide strong evidence for the existence of a positron bound state at the surface of Bi2Te2Se and indicate the practicality of using positron annihilation to selectively probe the critically important top most layer of topological insulator system. Welch Grant 1100 NSF DMR 0907679.

  2. Observation of an electron band above the Fermi level in FeTe?.??Se?.?? from in-situ surface doping

    SciTech Connect

    Zhang, P.; Richard, P.; Xu, N.; Xu, Y. -M.; Ma, J.; Qian, T.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.; Ding, H.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe?.??Se?.??. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe??xSe? compound.

  3. Electronic Structure of Quantum Spin Hall Parent Compound CdTe

    NASA Astrophysics Data System (ADS)

    Bian, Guang

    2015-03-01

    Cadmium telluride, a compound widely used in devices, is a key base material for the experimental realization of the quantum spin Hall phase. The electronic structure of CdTe has been studied by various theoretical and experimental methods. However, high-resolution band mapping has been lacking to this date. The detailed low-energy electronic structure of CdTe is thus unavailable, but it is of fundamental importance for understanding the topological properties and trends of this type of materials. We report herein, for the first time, a systematic study of the electronic structure of CdTe by angle-resolved photoemission spectroscopy from well-ordered (110) surfaces. The results are compared with first-principles calculations to illustrate the topological distinction between CdTe and a closely related compound HgTe. In addition, topological phase transition from CdTe to HgTe upon alloying and the massless Dirac-Kane semimetal phase at the critical composition are illustrated by computations based on a mixed-pseudopotential simulation.

  4. Lattice dynamics of BaFe2X3(X=S,Se) compounds

    DOE PAGESBeta

    Popovi?, Z. V.; Š?epanovi?, M.; Lazarevi?, N.; Opa?i?, M.; Radonji?, M. M.; Tanaskovi?, D.; Lei, Hechang; Petrovic, C.

    2015-02-27

    We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe?X? (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe?S? (BaFe?Se?) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe?S(Se)? is supported by themore »lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe?Se? below TN=255K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy.« less

  5. Hybrid morphology dependence of CdTe:CdSe bulk-heterojunction solar cells

    PubMed Central

    2014-01-01

    A nanocrystal thin-film solar cell operating on an exciton splitting pattern requires a highly efficient separation of electron-hole pairs and transportation of separated charges. A hybrid bulk-heterojunction (HBH) nanostructure providing a large contact area and interpenetrated charge channels is favorable to an inorganic nanocrystal solar cell with high performance. For this freshly appeared structure, here in this work, we have firstly explored the influence of hybrid morphology on the photovoltaic performance of CdTe:CdSe bulk-heterojunction solar cells with variation in CdSe nanoparticle morphology. Quantum dot (QD) or nanotetrapod (NT)-shaped CdSe nanocrystals have been employed together with CdTe NTs to construct different hybrid structures. The solar cells with the two different hybrid active layers show obvious difference in photovoltaic performance. The hybrid structure with densely packed and continuously interpenetrated two phases generates superior morphological and electrical properties for more efficient inorganic bulk-heterojunction solar cells, which could be readily realized in the NTs:QDs hybrid. This proved strategy is applicable and promising in designing other highly efficient inorganic hybrid solar cells. PMID:25386107

  6. Exploring the feasibility of Fe(Se,Te) conductors by ex-situ powder-in-tube method

    NASA Astrophysics Data System (ADS)

    Palombo, M.; Malagoli, A.; Pani, M.; Bernini, C.; Manfrinetti, P.; Palenzona, A.; Putti, M.

    2015-06-01

    In this work, the feasibility condition of Powder-In-Tube (PIT) processed wires of Fe(Se,Te) superconductor has been investigated. We faced several technical issues that are extensively described and discussed. In particular, we tested different metals and alloys as external sheaths (Cu, Ag, Nb, Ta, Ni, Fe, cupronickel, brass) concluding that the only sheath that does not affect substantially the Fe(Se,Te) phase is Fe. On the other hand, Fe sheath introduces excess iron in the Fe(Se,Te) phase, which affects the superconducting properties; we investigated the effects of the thermal treatments and of the powder composition in order to avoid it. The maximum Jc value obtained in our samples is 4 × 102 A/cm2, comparable to other published values of PIT conductors of the 11 family. We conclude that the fabrication of Fe(Se,Te) wires by PIT method is quite challenging and other approaches should be developed.

  7. Disordered stoichiometric nanorods and ordered off-stoichiometric nanoparticles in n-type thermoelectric Bi?Te?.?Se?.?

    E-print Network

    Carlton, Christopher

    N-type Bi?Te?.?Se?.? bulk thermoelectric materials with peak ZT values up to ?1 were examined by transmission electron microscopy and electron diffraction. Two nanostructural features were found: (i) a structural modulation ...

  8. CdSe/CdTe type-II superlattices grown on GaSb (001) substrates by molecular beam epitaxy

    SciTech Connect

    Li Jingjing; Liu Shi; Wang Shumin; Ding Ding; Johnson, Shane R.; Zhang Yonghang; Liu Xinyu; Furdyna, Jacek K.; Smith, David J.

    2012-03-19

    CdSe/CdTe superlattices are grown on GaSb substrates using molecular beam epitaxy. X-ray diffraction measurements and cross-sectional transmission electron microscopy images indicate high crystalline quality. Photoluminescence (PL) measurements show the effective bandgap varies with the superlattice layer thicknesses and confirm the CdSe/CdTe heterostructure has a type-II band edge alignment. The valence band offset between unstrained CdTe and CdSe is determined as 0.63 {+-} 0.06 eV by fitting the measured PL peak positions using the envelope function approximation and the Kronig-Penney model. These results suggest that CdSe/CdTe superlattices are promising candidates for multi-junction solar cells and other optoelectronic devices based on GaSb substrates.

  9. Role of polycrystallinity in CdTe and CuInSe[sub 2] photovoltaic cells

    SciTech Connect

    Sites, J.R. )

    1992-11-01

    The limiting role of polycrystallinity in thin-film solar calls has been reduced somewhat during the past year, and efficiencies of both CdTe and CuInSe[sub 2] cells are approaching 15%. Quantitative separation of loss mechanisms shows that individual losses, with the exception of forward recombination current, can be made comparable to their single crystal counterparts. One general manifestation of the extraneous trapping states in that the voltage of all polycrystalline thin-film cells drifts upward by 10--50 mV following the onset of illumination.

  10. CdTe and CdSe quantum dots: synthesis, characterizations and applications in agriculture

    NASA Astrophysics Data System (ADS)

    Dieu Thuy Ung, Thi; Tran, Thi Kim Chi; Nga Pham, Thu; Nghia Nguyen, Duc; Khang Dinh, Duy; Liem Nguyen, Quang

    2012-12-01

    This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ˜500 and 700 nm with the luminescence quantum yield (LQY) of 30-85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml-1. For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3-50 ng ?l-1 with a detection limit of 3 ng ?L-1 has been performed based on the antibody-antigen recognition.

  11. Structural, elastic, electronic and optical properties of KAlQ2 (Q = Se, Te): A DFT study

    NASA Astrophysics Data System (ADS)

    Benmakhlouf, A.; Bentabet, A.; Bouhemadou, A.; Maabed, S.; Khenata, R.; Bin-Omran, S.

    2015-10-01

    First-principles calculations in the framework of density functional theory have been conducted to explore the structural, elastic, electronic and optical properties of two layered ternary compounds chalcogenides of aluminum KAlSe2 and KAlTe2. We have calculated all of the equilibrium structural parameters; the lattice parameters (a, b and c), angle ? and twenty three internal atomic coordinates. The obtained results are in excellent agreement with the available experimental data. We have predicted the single-crystal elastic constants Cij of the title materials using stress-strain approach and then derived the elastic moduli of the polycrystalline aggregates and related properties via the Voigt-Reuss-Hill approximations. The band structure and density of states diagrams have been calculated and analyzed. Both compounds demonstrate semiconducting behavior with direct band gap. The linear optical properties, namely the frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and energy-loss function, have been calculated and analyzed in a wide energy range up to 20 eV.

  12. Upper critical field and AC-Susceptibility studies on FeTe0.5Se0.5 superconductor

    NASA Astrophysics Data System (ADS)

    Zargar, Rayees A.; Pal, Anand; Hafiz, A. K.; Awana, V. P. S.

    2015-06-01

    In this study we present synthesis and characterization of FeTe0.5Se0.5 sample that has been prepared by solid state reaction route by encapsulation of stoichiometric high purity (5N) ingredients in an evacuated quartz tube at 750 °C. The resultant compound is crystallized in single phase tetragonal structure with space group P4/nmm, having lattice parameters a = 3.792(1) Å and c = 6.0081(3) Å. The studied compound is superconducting at below 13K in both magnetic and transport measurements. Further superconductivity is barely affected by external applied magnetic field, giving rise to upper critical field of above 180 Tesla at 0 K. The sample is studied extensively for AC susceptibility measurements in superconducting state. The AC drive field and frequency are varied from 1-13 Oe and 33-9999 Hz respectively. It is concluded that though the grain boundaries of this superconductor are mainly metallic the minor (undetectable in XRD) foreign phases and the role of porosity cannot be ruled out completely. This is because both frequency and amplitude affects slightly the superconductivity coupling temperature of the grains.

  13. Optimization of Thermoelectric Performance of Anisotropic Ag x Sn1-x Se Compounds

    NASA Astrophysics Data System (ADS)

    Leng, Huaqian; Zhou, Min; Zhao, Jie; Han, Yemao; Li, Laifeng

    2015-10-01

    SnSe is a promising thermoelectric material due to its ultralow thermal conductivity. However, stoichiometric SnSe compounds exhibit very low intrinsic defect concentration (3 × 1017 cm-3) and poor electrical transport properties, limiting the thermoelectric performance. In the present work, we investigated the effect of Ag dopant on the thermoelectric properties of SnSe. The results demonstrate that all the Ag x Sn1-x Se compounds exhibited anisotropic thermoelectric properties. The carrier concentration in the Ag x Sn1-x Se compounds greatly increased with increase of the Ag content, saturating at 1.9 × 1019 cm-3 for Ag0.01Sn0.99Se at room temperature. We found that a maximum zT value of 0.74 was obtained for Ag0.01Sn0.99Se perpendicular to the pressing direction at 823 K, being 23% higher than that of undoped SnSe (zT = 0.6).

  14. Signatures of charge inhomogeneities in the infrared spectra of topological insulators Bi2Se3, Bi2Te3 and Sb2Te3.

    PubMed

    Dordevic, S V; Wolf, M S; Stojilovic, N; Lei, Hechang; Petrovic, C

    2013-02-20

    We present the results of an infrared spectroscopy study of topological insulators Bi(2)Se(3), Bi(2)Te(3) and Sb(2)Te(3). Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi(2)Se(3), whereas in Bi(2)Te(3) and Sb(2)Te(3) it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature. PMID:23328626

  15. Structural inhomogeneities in FeTe0.6Se0.4: Relation to superconductivity

    NASA Astrophysics Data System (ADS)

    Prokeš, K.; Schulze, M.; Hartwig, S.; Schäfer, N.; Landsgesell, S.; Blum, C. G. F.; Abou-Ras, D.; Hacisalihoglu, M. Y.; Ressouche, E.; Ouladdiaf, B.; Büchner, B.; Wurmehl, S.

    2015-12-01

    Chemical and structural phase compositions of two single-crystalline samples prepared with different cooling rates from stoichiometric FeTe0.6Se0.4 melts were studied. Both types of samples were investigated in a very comprehensive way using magnetic and electrical transport measurements combined with X-ray, neutron and electron backscatter diffraction. We show that slowly cooled samples are homogeneous on a microscopic scale with only a small excess of iron. Those slowly cooled samples do not exhibit bulk superconductivity down to 1.8 K. In contrast, fast-cooled samples are superconducting below about 14 K but are composed of several chemical phases: they consist of a matrix preserving the crystal structure of slow-cooled samples, and of core-shell structured dendritic inclusions (about 20-30 vol%). These have different crystal structures and chemical compositions and order magnetically at temperatures far above the superconducting transition temperature of the inhomogeneous samples. These structural and chemical inhomogeneities seem to play a vital role in the superconducting properties of this and similar iron-based systems as they lead to internal stress and act in a similar way as the application of the external pressure that reportedly increase the superconducting transition temperature in many iron pnictides and chalcogenides. We argue that a phase pure, homogeneous and stress-free FeTe0.6Se0.4 is non-superconducting.

  16. Structural, Electronic and Optical Properties of MgSxSe1-x, MgSxTe1-x and MgSexTe1-x (0 ?x ?1) Alloys from First Principles

    NASA Astrophysics Data System (ADS)

    Sajid, A.; Alay-E-Abbas, S. M.; Afaq, A.; Shaukat, A.

    2012-07-01

    First principles total energy calculations have been performed using full potential linear augmented plane wave method (FP-LAPW) within density functional theory to study the structural, electronic and optical properties of MgSxSe1-x, MgSxTe1-x and MgSexTe1-x alloys in the rock salt crystallographic phase. The generalized gradient approximation parameterization scheme has been used for calculating the ground state structural parameters and their deviation from the Vegard's law has been discussed. Full relativistic electronic band structures and density of states have been calculated to study the electronic properties of the end binary compounds and ternary alloys MgSxSe1-x, MgSxTe1-x and MgSexTe1-x (0.25 < x < 0.75). Optical bowing for these semiconductor alloys has been discussed in term of volume deformation, electronegativity and structural relaxation. Optical properties of the binary and ternary magnesium chalcogenides have been calculated in terms of the complex dielectric function and the results are compared with available theoretical and experimental data.

  17. Reaction Routes for the Synthesis of CuInSe2 Using Bilayer Compound Precursors

    SciTech Connect

    Krishnan, Rangarajan; Wood, David; Chaudhari, Vaibhav U.; Payzant, E Andrew; Noufi, Rommel; Rozeveld, Steve; Kim, Woo Kyoung; Anderson, Timothy J

    2012-01-01

    The reaction pathways and phase evolution during synthesis of CuInSe{sub 2} (CIS) by a novel bilayer approach were investigated using in situ high-temperature X-ray diffraction. Two bilayer precursor structures, glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se and glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se, were examined in this study. Temperature ramp experiments revealed that the phase transformation sequence for each bilayer precursor qualitatively follows that predicted by the phase diagram and that the onset temperatures for decomposition of the sub-binary compounds depend on the Se partial pressure. Measurement of the isothermal rate of formation of CuInSe{sub 2} at six temperatures in the range 260 to 310 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se bilayer suggests relatively slow nucleation followed by diffusion-limited reaction with estimated activation energy of 162({+-}7) and 225 ({+-}16) kJ/mol from Avrami and parabolic models, respectively. Interestingly, the measured activation energy for the same precursor in a 4 mol % H{sub 2}/He ambient (108 ({+-}8) kJ/mol) was lower than that observed in pure N{sub 2} (158 ({+-}16) kJ/mol). The results of isothermal measurements in the temperature range 250 to 300 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se precursor film in an inert ambient are consistent with one-dimensional diffusion-limited growth with estimated activation energy from the Avrami and parabolic models of 194 ({+-}10) and 203 ({+-}12) kJ/mol, respectively.

  18. Preparation and thermoelectric properties of iodine-doped Bi2Te3-Bi2Se3 solid solutions

    NASA Astrophysics Data System (ADS)

    Lee, Go-Eun; Kim, Il-Ho; Lim, Young Soo; Seo, Won-Seon; Choi, Byeong-Jun; Hwang, Chang-Won

    2014-09-01

    Bismuth chalcogenides, such as p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3, are known to have excellent thermoelectric properties at temperatures near room temperature. Since Bi2Te3, Sb2Te3 and Bi2Se3 have the same class of crystal symmetry, they can form homogeneous solid solutions. The thermoelectric figure of merit can be improved by increasing the power factor through doping to optimize the carrier concentration and/or by reducing the thermal conductivity through the formation of solid solutions for phonon scattering. In this study, n-type Bi2Te2.7Se0.3:I m (m = 0.0 - 0.015) solid solutions were successfully prepared by using encapsulated melting and hot pressing. The increase in the carrier concentration induced by I doping led to an increase in both the electrical conductivity and the electronic thermal conductivity, with I atoms acting as phonon scattering centers reducing the lattice thermal conductivity. The undoped solid solution had a carrier concentration of 6.27 × 1019 cm-3, a power factor ( PF) of 1.71 mWm-1K-2, and a dimensionless figure of merit ( ZT) of 0.54 at 323 K. However, the ZT value was improved by I doping due to the increased PF, demonstrating a maximum of ZT = 1.13 at 423 K for Bi2Te2.7Se0.3:I0.0075.

  19. Transport properties of the system Bi2Te2.7Se0.3-xPbx fabricated by a conventional melting technique

    NASA Astrophysics Data System (ADS)

    Abdel Hakeem, A. M.

    2015-03-01

    N-type Bi2Te2.7Se0.3-xPbx (x = 0, 0.02, 0.04, 0.06 and 0.08) thermoelectric compounds have been prepared by a conventional melting technique. Microstructure analyses have been carried out for all samples using x-ray diffraction and a scanning electron microscope. The data reveal that the samples are crystallized in the polycrystalline rhombohedral Bi2Te3 phase and the grains have irregular shapes and sizes. The chemical stoichiometry has been examined by means of energy dispersive x-ray spectroscopy (EDAX). The stoichiometries match with the chemical formula (Bi)2(Te-Se-Pb)3. However, superstoichiometry of Pb at the expense of Se content has been observed. The thermoelectric measurements prove that the dominant charge carriers in all materials are electrons over the temperature range of measurements (200-400 K). The temperature dependence of the electrical conductivity shows metallic behavior for all the nominal compositions and over the whole range of temperature. The highest power factor value was recorded for the undoped sample at T = 330 K and was found to be 15.51 ?WK-2 cm-1.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    We investigated the effects of applied high pressure on thermoelectric, electric, structural, and optical properties of single-crystalline thermoelectrics, Bi2Te3, BixSb2-xTe3 (x = 0.4, 0.5, 0.6), and Bi2Te2.73Se0.27 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 Bi2Te3 and Bi0.5Sb1.5Te3 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.

  1. Observation of amorphous to crystalline phase transformation in Te substituted Sn-Sb-Se thin films

    SciTech Connect

    Chander, Ravi

    2015-05-15

    Thin films of Sn-Sb-Se-Te (8 ? x ? 14) chalcogenide system were prepared by thermal evaporation technique using melt quenched bulk samples. The as-prepared thin films were found amorphous as evidenced from X-ray diffraction studies. Resistivity measurement showed an exponential decrease with temperature upto critical temperature (transition temperature) beyond which a sharp decrease was observed and with further increase in temperature showed an exponential decrease in resistivity with different activation energy. The transition temperature showed a decreasing trend with tellurium content in the sample. The resistivity measurement during cooling run showed no abrupt change in resistivity. The resistivity measurements of annealed films did not show any abrupt change revealing the structural transformation occurring in the material. The transition width showed an increase with tellurium content in the sample. The resistivity ratio showed two order of magnitude improvements for sample with higher tellurium content. The observed transition temperature in this system was found quite less than already commercialized Ge-Sb-Te system for optical and electronic memories.

  2. Growth of Lattice-Matched ZnTeSe Alloys on (100) and (211)B GaSb

    NASA Astrophysics Data System (ADS)

    Chai, J.; Lee, K.-K.; Doyle, K.; Dinan, J. H.; Myers, T. H.

    2012-10-01

    A key issue with the current HgCdTe/Si system is the high dislocation density due to the large mismatch between HgCdTe and Si. An alternative system that has superior lattice matching is HgCdSe/GaSb. A buffer layer to mitigate issues with direct nucleation of HgCdSe on GaSb is ZnTe1- x Se x . We have performed preliminary studies into the growth of lattice-matched ZnTe1- x Se x on both (100) and (211)B GaSb. The effects of substrate orientation, substrate temperature, and growth conditions on the morphology and crystallography of ZnTe0.99Se0.01 alloys were investigated. The lattice-matching condition yielded minimum root-mean-square (rms) roughness of 1.1 nm, x-ray rocking curve full-width at half-maximum (FWHM) value of ~29 arcsec, and density of nonradiative defects of mid-105 cm-2 as measured by imaging photoluminescence.

  3. Investigation of basic thermal behavior of a-Te-Se-Ge-Sb glassy system

    NASA Astrophysics Data System (ADS)

    Nidhi, Anant Vidya; Modgil, Vivek; Chaudhary, Shobhna; Kumar, Prashant; Rangra, V. S.

    2015-05-01

    The bulk material Te9Se72Ge19-xSbx (8?x?12) has been prepared by melt quenching technique. The amorphous and glassy nature has been confirmed using XRD and DSC analysis respectively. The thermal kinetics of material is studied through differential scanning calorimetry under non-isothermal condition at constant heating rate. The thermal behavior, activation energy of glass transition and crystallization has been determined using appropriate models. The thermal parameter accounting for thermal stability and quality has been explored along with compositional dependence. A stable glass with high value of Tg and quality has been formed. The mild phase separation has been observed in the material at x=8, 9 and this phase separation dissolves when the Sb content further increases in glassy matrix.

  4. Te-As-Se glass microstructured optical fiber for the middle infrared

    SciTech Connect

    Desevedavy, Frederic; Renversez, Gilles; Troles, Johann; Brilland, Laurent; Houizot, Patrick; Coulombier, Quentin; Smektala, Frederic; Traynor, Nicholas; Adam, Jean-Luc

    2009-07-01

    We present the first fabrication, to the best of our knowledge, of chalcogenide microstructured optical fibers in Te-As-Se glass, their optical characterization, and numerical simulations in the middle infrared. In a first fiber, numerical simulations exhibit a single-mode behavior at 3.39 and 9.3 {mu}m, in good agreement with experimental near-field captures at 9.3 {mu}m. The second fiber is not monomode between 3.39 and 9.3 {mu}m, but the fundamental losses are 9 dB/m at 3.39 {mu}m and 6 dB/m at 9.3 {mu}m. The experimental mode field diameters are compared to the theoretical ones with a good accordance.

  5. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    PubMed Central

    Gomes, Suzete A.O.; Vieira, Cecilia Stahl; Almeida, Diogo B.; Santos-Mallet, Jacenir R.; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Feder, Denise

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

  6. N-type Doped PbTe and PbSe Alloys for Thermoelectric Applications

    NASA Technical Reports Server (NTRS)

    Snyder, G. Jeffrey (Inventor); LaLonde, Aaron (Inventor); Pei, Yanzhong (Inventor); Wang, Heng (Inventor)

    2014-01-01

    The present invention demonstrates that weak scattering of carriers leads to a high mobility and therefore helps achieve low electric resistivity with high Seebeck coefficient for a thermoelectric material. The inventors demonstrate this effect by obtaining a thermoelectric figure of merit, zT, higher than 1.3 at high temperatures in n-type PbSe, because of the weak scattering of carriers in the conduction band as compared with that in the valence band. The invention further demonstrates favorable thermoelectric transport properties of n-type PbTe.sub.1-xI.sub.x with carrier concentrations ranging from 5.8.times.10.sup.18-1.4.times.10.sup.20 cm.sup.-3.

  7. Photoluminescence of two-dimensional GaTe and GaSe films

    NASA Astrophysics Data System (ADS)

    Del Pozo-Zamudio, O.; Schwarz, S.; Sich, M.; Akimov, I. A.; Bayer, M.; Schofield, R. C.; Chekhovich, E. A.; Robinson, B. J.; Kay, N. D.; Kolosov, O. V.; Dmitriev, A. I.; Lashkarev, G. V.; Borisenko, D. N.; Kolesnikov, N. N.; Tartakovskii, A. I.

    2015-09-01

    Gallium chalcogenides are promising building blocks for novel van der Waals heterostructures. We report on the low-temperature micro-photoluminescence (PL) of GaTe and GaSe films with thicknesses ranging from 200 nm to a single unit cell. In both materials, PL shows a dramatic decrease by 104-105 when film thickness is reduced from 200 to 10 nm. Based on evidence from continuous-wave (cw) and time-resolved PL, we propose a model explaining the PL decrease as a result of non-radiative carrier escape via surface states. Our results emphasize the need for special passivation of two-dimensional films for optoelectronic applications.

  8. Impact of Pb content on the physical parameters of Se-Te-Pb system

    SciTech Connect

    Anjali,; Sharma, Raman; Thakur, Nagesh; Patial, Balbir Singh; Tripathi, S. K.

    2015-05-15

    In the present study, we have investigated the impact of Pb content on the physical parameters in Se-Te-Pb system via average coordination number, constraints, the fraction of floppy modes, cross-linking density, lone pairs electrons, heat of atomization, mean bond energy, cohesive energy and electronegativity. The bulk samples have been prepared by using melt quenching technique. X-ray diffraction pattern of various samples indicates the amorphous nature of investigated glassy alloys. It is observed that average coordination number, average number of constraints and cross-linking density increase with Pb content. However, lone-pair electrons, floppy modes, average heat of atomization, cohesive energy and mean bond energy are found to decrease with Pb atomic percentage.

  9. Properties of high-angle Fe(Se,Te) bicrystal grain boundary junctions

    NASA Astrophysics Data System (ADS)

    Sarnelli, E.; Adamo, M.; Nappi, C.; Braccini, V.; Kawale, S.; Bellingeri, E.; Ferdeghini, C.

    2014-04-01

    We report on the characterization of Fe(Se,Te) grain boundary junctions fabricated on a 45° tilt symmetric bicrystal substrate. The junctions show critical current densities of the order of 104 A/cm2, showing a decay of about one order of magnitude with respect to the critical current density of the film, which is very promising for applications. The current-voltage characteristics show resistively shunted junction-like behaviors, with very low normal-state resistance values, typical of superconducting/normal-metal/superconducting junctions. The magnetic field dependences of the critical currents show the typical behaviors of large Josephson junctions. Nevertheless, the critical current is uniformly distributed across the barrier. We present a simplified theoretical model accounting for this effect. The small influence of faceting along the grain boundary on the electrical parameters may be consistent with an s-wave symmetry of the order parameter.

  10. Assessment of the anticancer compounds Se-methylselenocysteine and glucosinolates in Se-biofortified broccoli (Brassica oleracea L. var. italica) sprouts and florets.

    PubMed

    Ávila, Fabricio William; Faquin, Valdemar; Yang, Yong; Ramos, Silvio Junio; Guilherme, Luiz Roberto G; Thannhauser, Theodore W; Li, Li

    2013-07-01

    Broccoli (Brassica oleracea L. var. italica) is a rich source of chemopreventive compounds. Here, we evaluated and compared the effect of selenium (Se) treatment on the accumulation of anticancer compounds Se-methylselenocysteine (SeMSCys) and glucosinolates in broccoli sprouts and florets. Total Se and SeMSCys content in sprouts increased concomitantly with increasing Se doses. Selenate was superior to selenite in inducing total Se accumulation, but selenite is equally effective as selenate in promoting SeMSCys synthesis in sprouts. Increasing sulfur doses reduced total Se and SeMSCys content in sprouts treated with selenate, but not in those with selenite. Examination of five broccoli cultivars reveals that sprouts generally have better fractional ability than florets to convert inorganic Se into SeMSCys. Distinctive glucosinolate profiles between sprouts and florets were observed, and sprouts contained approximately 6-fold more glucoraphanin than florets. In contrast to florets, glucosinolate content was not affected by Se treatment in sprouts. Thus, Se-enriched broccoli sprouts are excellent for simultaneous accumulation of chemopreventive compounds SeMSCys and glucoraphanin. PMID:23763668

  11. Pressure-induced superconductivity in topological parent compound Bi2Te3.

    PubMed

    Zhang, J L; Zhang, S J; Weng, H M; Zhang, W; Yang, L X; Liu, Q Q; Feng, S M; Wang, X C; Yu, R C; Cao, L Z; Wang, L; Yang, W G; Liu, H Z; Zhao, W Y; Zhang, S C; Dai, X; Fang, Z; Jin, C Q

    2011-01-01

    We report a successful observation of pressure-induced superconductivity in a topological compound Bi(2)Te(3) with T(c) of ?3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the hole-type carrier in the pressure-induced superconducting Bi(2)Te(3) single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi(2)Te(3) due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor. PMID:21173267

  12. Fabrication of CdS/CdTe solar cells with transparent p-type conductive BaCuSeF back contact

    NASA Astrophysics Data System (ADS)

    Yamamoto, Koichi; Sakakima, Hiroshi; Ogawa, Yohei; Hosono, Aikyo; Okamoto, Tamotsu; Wada, Takahiro

    2015-08-01

    BaCuSeF films were applied to CdS/CdTe solar cells as back electrodes. The interfaces between the CdTe and BaCuSeF layers in the CdS/CdTe solar cells with BaCuSeF back contact deposited at substrate temperatures (TS) of 200 and 300 °C were analyzed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). We clearly observed many dislocations in the CdTe layer in the CdS/CdTe solar cell with the BaCuSeF layer deposited at TS = 300 °C. We also observed a reaction layer of Cu2.72Te2 between the BaCuSeF and CdTe layers in both solar cells. We concluded that (1) the substrate temperature for the pulsed laser deposition of the BaCuSeF layer and (2) the interface between the CdTe and BaCuSeF layers are important factors for the performance of the CdTe solar cells. We obtained high conversion efficiency of 8.31% for a solar cell with a BaCuSeF layer deposited at TS = 200 °C on a CdTe surface etched in a NH3 aqueous solution. The highest conversion efficiency of 9.91% was obtained for a solar cell with a CdTe surface etched in a bromide-bromate solution.

  13. Effects of Composition and Compositional Distribution on the Electronic Structure of ZnSe(1-x)Te(x) Ternary Quantum Dots

    SciTech Connect

    Pandey, Sumeet C.; Maroudas, Dimitrios

    2011-01-01

    We report results of first-principles density functional theory(DFT) calculations for the electronic structure of ZnSe1- x Te x ternary quantum dots (TQDs) and the effects of composition and compositional distribution on the electron density distribution, electronic density of states, and band gap. We analyze the electronic structure of five types of nanocrystal configurations, namely, pristine ZnSe and ZnTe quantum dots, as well as ZnSe/ZnTe core/shell, ZnTe/ZnSe reverse core/shell, and randomly alloyed ZnSe1- x Te x TQDs. We find that the band gaps for ZnSe/ZnTe core/shell TQDs are nonlinearly dependent on the number of Te atoms in the shell, whereas presence of Te in the core of alloyed ZnSe1- x Te x TQDs modifies the electronic energy levels abruptly and significantly in the limits of x ? 0 and x ? 1. Our results imply that distribution of Te atoms in the TQD in the form of a ZnSe/ZnTe core/shell configuration allows for optimum tunability of the band gap and wave function confinement in TQDs.

  14. Composition Dependence of the Hydrostatic Pressure Coefficients of the Bandgap of ZnSe(1-x)Te(x) Alloys

    NASA Technical Reports Server (NTRS)

    Wu, J.; Yu, K. M.; Walukiewicz, W.; Shan, W.; Ager, J. W., III; Haller, E. E.; Miotkowski, I.; Ramdas, A. K.; Su, Ching-Hua

    2003-01-01

    Optical absorption experiments have been performed using diamond anvil cells to measure the hydrostatic pressure dependence of the fundamental bandgap of ZnSe(sub 1-xTe(sub x) alloys over the entire composition range. The first and second-order pressure coefficients are obtained as a function of composition. Starting from the ZnSe side, the magnitude of both coefficients increases slowly until x approx. 0.7, where the ambient-pressure bandgap reaches a minimum. For larger values of x the coefficients rapidly approach the values of ZnTe. The large deviations of the pressure coefficients from the linear interpolation between ZnSe and ZnTe are explained in terms of the band anticrossing model.

  15. Inelastic x-ray scattering measurements of phonon dispersion and lifetimes in PbTe1-x Se x alloys

    NASA Astrophysics Data System (ADS)

    Tian, Zhiting; Li, Mingda; Ren, Zhensong; Ma, Hao; Alatas, Ahmet; Wilson, Stephen D.; Li, Ju

    2015-09-01

    PbTe1-x Se x alloys are of special interest to thermoelectric applications. Inelastic x-ray scattering determination of phonon dispersion and lifetimes along the high symmetry directions for PbTe1-x Se x alloys are presented. By comparing with calculated results based on the virtual crystal model calculations combined with ab initio density functional theory, the validity of virtual crystal model is evaluated. The results indicate that the virtual crystal model is overall a good assumption for phonon frequencies and group velocities despite the softening of transverse acoustic phonon modes along [1?1?1] direction, while the treatment of lifetimes warrants caution. In addition, phonons remain a good description of vibrational modes in PbTe1-x Se x alloys.

  16. Water-Soluble Fluorescent CdTe/ZnSe Core/Shell Quantum Dot: Aqueous Phase Synthesis and Cytotoxicity Assays.

    PubMed

    Li, Yansheng; Wang, Wenqian; Zhao, Dan; Chen, Peng; Du, Hongwu; Wen, Yongqiang; Zhang, Xueji

    2015-06-01

    In this manuscript, we demonstrate a novel, facile and environmentally friendly method to directly obtain CdTe/ZnSe core/shell QDs in the aqueous phase based on the method of epitaxial growth of ZnSe shells on CdTe cores. The ZnSe shell and the capping reagent glutathione of the CdTe/ZnSe core/shell QDs greatly increased the biocompatibility and stability of the original CdTe cores. The optical property of the as-prepared CZ QDs could be controlled by precisely adjusting the size of CdTe cores, which showed broad emission spectra from 530 to 688 nm. The crystalline structure of the CZ QDs was extensively characterized by XRD, TEM and HRTEM, etc. Furthermore, since there were several functional groups on glutathione molecules, the QDs could be potentially used for connecting other functional small molecules, biomolecules or nanoparticles. Such QDs have bright future perspectives in the development biological and nanomedical fields. PMID:26369092

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

    NASA Astrophysics Data System (ADS)

    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 ? 2, and first- and third-order susceptibilities [ ? (1) and ? (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 ? 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 ? 2 with changing bandgap E g is also reported. The values of n 2 and ? (3) of the investigated chalcogenides are compared with those of pure silica, oxide, and other Se-based glasses.

  18. Trends in the band-gap pressure coefficients and bulk moduli in different structures of ZnGa2S4, ZnGa2Se4 and ZnGa2Te4

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao-Shu; Yan, Ying-Ce; Yuan, Shi-Min; Mi, Shu; Niu, Zhen-Guo; Liang, Jiu-Qing

    2010-10-01

    We have performed a first-principles investigation for the family of compounds ZnGa2X4 (X = S, Se, Te). The properties of two possible structures, defect chalcopyrite and defect famatinite are both calculated. We reveal that ZnGa2S4 and ZnGa2Se4 have direct band gaps, while ZnGa2Te4 has an indirect band gap. The local density approximation band gaps are found to be very different in two structures, while the lattice parameters and bulk moduli are similar. We extend Cohen's empirical formula for zinc-blende compounds to this family of compounds. The pressure coefficients are calculated and metallization pressures are discussed. We find that aig remains fairly constant when the group-VI element X is varied in ZnGa2X4(II-III2—VI4).

  19. Thermoelectric properties of Bi2Te3-In2Se3 composite thin films prepared by co-sputtering.

    PubMed

    Kim, Kwang-Chon; Choi, Won Chel; Kim, Hyun Jae; Lyeo, Ho-Ki; Kim, Jin-Sang; Park, Chan

    2012-04-01

    Bi2Te3-In2Se3 films were prepared by co-sputtering followed by annealing, and their structural and thermoelectric properties were investigated. The immiscible nature of the two alloys results in precipitation of the second phase, thus leading to structures with self-assembled dots that are a few nanometers in scale. HAADF-STEM and HRTEM were used to confirm that In2Se3 nanodots that were a few nanometers in size did indeed form in the Bi2Te3 thin film. It was found that the incorporation of these nanodots can reduce the thermal conductivity of the thin film. PMID:22849184

  20. Cs7Sm11[TeO3]12Cl16 and Rb7Nd11[TeO3]12Br16, the new tellurite halides of the tetragonal Rb6LiNd11[SeO3]12Cl16 structure type

    NASA Astrophysics Data System (ADS)

    Charkin, Dmitri O.; Black, Cameron; Downie, Lewis J.; Sklovsky, Dmitry E.; Berdonosov, Peter S.; Olenev, Andrei V.; Zhou, Wuzong; Lightfoot, Philip; Dolgikh, Valery A.

    2015-12-01

    Two new rare-earth - alkali - tellurium oxide halides were synthesized by a salt flux technique and characterized by single-crystal X-ray diffraction. The structures of the new compounds Cs7Sm11[TeO3]12Cl16 (I) and Rb7Nd11[TeO3]12Br16 (II) (both tetragonal, space group I4/mcm) correspond to the sequence of [MLn11(TeO3)12] and [M6X16] layers and bear very strong similarities to those of known selenite analogs. We discuss the trends in similarities and differences in compositions and structural details between the Se and Te compounds; more members of the family are predicted.

  1. Aqueous synthesis of glutathione-capped CdTe/CdS/ZnS and CdTe/CdSe/ZnS core/shell/shell nanocrystal heterostructures.

    PubMed

    Samanta, Anirban; Deng, Zhengtao; Liu, Yan

    2012-05-29

    Here we demonstrate the aqueous synthesis of colloidal nanocrystal heterostructures consisting of the CdTe core encapsulated by CdS/ZnS or CdSe/ZnS shells using glutathione (GSH), a tripeptide, as the capping ligand. The inner CdTe/CdS and CdTe/CdSe heterostructures have type-I, quasi-type-II, or type-II band offsets depending on the core size and shell thickness, and the outer CdS/ZnS and CdSe/ZnS structures have type-I band offsets. The emission maxima of the assembled heterostructures were found to be dependent on the CdTe core size, with a wider range of spectral tunability observed for the smaller cores. Because of encapsulation effects, the formation of successive shells resulted in a considerable increase in the photoluminescence quantum yield; however, identifying optimal shell thicknesses was required to achieve the maximum quantum yield. Photoluminescence lifetime measurements revealed that the decrease in the quantum yield of thick-shell nanocrystals was caused by a substantial decrease in the radiative rate constant. By tuning the diameter of the core and the thickness of each shell, a broad range of high quantum yield (up to 45%) nanocrystal heterostructures with emission ranging from visible to NIR wavelengths (500-730 nm) were obtained. This versatile route to engineering the optical properties of nanocrystal heterostructures will provide new opportunities for applications in bioimaging and biolabeling. PMID:22551311

  2. NaCu6Se4: a layered compound with mixed valency and metallic properties.

    PubMed

    Sturza, Mihai; Malliakas, Christos D; Bugaris, Daniel E; Han, Fei; Chung, Duck Young; Kanatzidis, Mercouri G

    2014-11-17

    A new ternary compound NaCu6Se4 was synthesized from the reaction of Cu in a molten sodium polyselenide flux. The compound crystallizes in trigonal space group R3?m with a = 4.0465(3) Å and c = 41.493(5) Å. The crystal structure contains flat two-dimensional slabs of (1)/?[Cu6Se4] with a unique structural arrangement, separated by Na cations. The compound contains mixed valency and has a high conductivity of ?3 × 10(3) S cm(-1) at room temperature, and exhibits increasing conductivity with decreasing temperature, indicating metallic behavior. A small positive thermopower (4-11 ?V K(-1) from 300 to 500 K) and Hall effect measurements indicate p-type transport with a carrier concentration of ?2.8(3) × 10(21) cm(-3) and a hole mobility of ?8.75 cm(2) V(-1) s(-1) at 300 K. NaCu6Se4 exhibits temperature-independent Pauli paramagnetism. PMID:25360672

  3. Enhancement of thermoelectric performance in n-type PbTe1-ySey by doping Cr and tuning Te:Se ratio

    SciTech Connect

    Chere, Eyob K.; Zhang, Qian; McEnaney, Kenneth; Yao, Mengliang; Cao, Feng; Sun, Jingying; Chen, Shuo; Opeil, Cyril; Chen, Gang; Ren, Zhifeng

    2015-04-01

    Lead telluride and its alloys have been extensively studied for medium temperature thermoelectric applications due to decent figure-of-merit (ZT) at temperature close to 900 K. However, little emphasis has been given to improve the ZT near room temperature. In this investigation, we report a systematic study of Cr doping in PbTe1-ySey with y=0, 0.25, 0.5, 0.75, 0.85, and 1. We found the peak ZT temperature increased with increasing concentration of Se. The highest ZT of ~0.6 at room temperature in Te-rich Cr0.015Pb0.985Te0.75Se0.25 was obtained due to a lowered thermal conductivity and enhanced power factor resulted from high Seebeck coefficient of about -220 µV K-1 and high Hall mobility ~1120 cm2 V-1 s-1 at room temperature. A room temperature ZT of ~0.5 and peak ZT of ~1 at about 573–673 K is shown by Se-rich sample Cr0.01Pb0.99Te0.25Se0.75. This improvement of the room temperature ZTimproved the average ZT over a wide temperature range and could potentially lead to a single leg efficiency of thermoelectric conversion for Te-rich Cr0.015Pb0.985Te0.75Se0.25 up to ~11% and Se-rich Cr0.01Pb0.99Te0.25Se0.75 up to ~13% with cold side and hot side temperature at 300 K and 873 K, respectively, if matched with appropriate p-type legs.

  4. Distinguishability of stacks in ZnTe/ZnSe quantum dots via spectral analysis of Aharonov-Bohm oscillations

    NASA Astrophysics Data System (ADS)

    Roy, Bidisha; Ji, Haojie; Dhomkar, Siddharth; Cadieu, Fred J.; Peng, Le; Moug, Richard; Tamargo, Maria C.; Kuskovsky, Igor L.

    2013-02-01

    A spectral analysis of the Aharonov-Bohm (AB) oscillations in photoluminescence intensity was performed for stacked type-II ZnTe/ZnSe quantum dots (QDs) fabricated within multilayered Zn-Se-Te system with sub-monolayer insertions of Te. Robust AB oscillations allowed for fine probing of distinguishable QDs stacks within the ensemble of QDs. The AB transition magnetic field, B AB , changed from the lower energy side to the higher energy side of the PL spectra revealing the presence of different sets of QDs stacks. The change occurs within the spectral range, where the contributing green and blue bands of the spectra overlapped. "Bundling" in lifetime measurements is seen at transition spectral regions confirming the results.

  5. Many-body effects on the width of the band gap in Bi2Te2X (X = Te, Se, S) topological insulators

    NASA Astrophysics Data System (ADS)

    Rusinov, I. P.; Nechaev, I. A.; Chulkov, E. V.

    2013-12-01

    The spectrum of quasiparticles of Bi2Te2X (X = Te, Se, S) three-dimensional topological insulators has been theoretically studied in the GW approximation with the inclusion of the spin-orbit interaction in the construction of the Green's function and self-energy. It has been shown that many-body corrections to the Kohn-Sham states in Bi2Te2X increase the fundamental band gap similar to conventional semiconductors. However, the band gap at the ? point decreases in this case. Gaps in the quasiparticle spectrum obtained in agreement with the experimental data correspond to the difference between the minimum of the conduction band, which is located on the ?-Z line, and the maximum of the valence band, which lies beyond the symmetric directions in the mirror plane.

  6. Thermoelectric properties of topological insulator Bi2Te3, Sb2Te3, and Bi2Se3 thin film quantum wells

    NASA Astrophysics Data System (ADS)

    Osterhage, Hermann; Gooth, Johannes; Hamdou, Bacel; Gwozdz, Paul; Zierold, Robert; Nielsch, Kornelius

    2014-09-01

    The thermoelectric (TE) figure of merit ZT of topological insulator Bi2Te3, Sb2Te3, and Bi2Se3 thin film quantum wells is calculated for thicknesses below 10 nm, for which hybridization of the surface states as well as quantum confinement in the bulk are individually predicted to enhance ZT. Here, the question is addressed what ZT can be expected from coexisting surface and bulk states in such quantum wells. It is demonstrated that the parallel contributing bulk and surface channels tend to cancel each other out. This is because the surface-to-volume ratios of the thin films prevent the domination of transport through a single channel and because the individual bulk and surface ZTs are optimized at different Fermi levels.

  7. DETERMINATION OF BACK CONTACT BARRIER HEIGHT IN Cu(In,Ga)(Se,S)2 AND CdTe SOLAR CELLS

    E-print Network

    Sites, James R.

    DETERMINATION OF BACK CONTACT BARRIER HEIGHT IN Cu(In,Ga)(Se,S)2 AND CdTe SOLAR CELLS Galymzhan T-contact metallization. The input data is the current- voltage (J-V) curves for the solar cell measured over a range point technique and apply it to specific solar-cell examples. The range of Jt that can be practically

  8. Continuous synthesis of CdSe(x)Te(1-x) nanocrystals: chemical composition gradient and single-step capping.

    PubMed

    Wan, Zhen; Luan, Weiling; Tu, Shan-tung

    2011-04-01

    A capillary microreactor was firstly utilized to continuously synthesize near-infrared emitting CdSe(x)Te(1-)(x) nanocrystals (NCs). By using trioctylphosphine oxide and trioctylphosphine as the solvents for anion precursor as well as oleic acid and oleylamine as the solvents for cation precursor, high quantum yield zinc-blend CdSe(x)Te(1-)(x) NCs with a chemical composition gradient internal structure and tunable emission from 634 to 783 nm were synthesized. Thus, the nonlinear relationship between the composition and the emission energies were verified. Moreover, a facile single-step capping approach was developed by using the dissolution of cadmium oxide and free element sulfur in oleic acid, and a very thin CdS shell was successfully epitaxial grown around the as-prepared CdSe(x)Te(1-)(x) NCs to enhance the photostability. After the capping process, the core/shell structured CdSe(x)Te(1-)(x)/CdS NCs remained 15-40% of their initial PL intensity after 3h of illumination. PMID:21288534

  9. Pulsed electrodeposition and characterization of Bi{sub 2}Te{sub 3?y}Se{sub y} films

    SciTech Connect

    Zou, Z.G.; Cai, K.F.; Chen, S.; Qin, Z.

    2012-11-15

    Highlights: ? Bi{sub 2}Te{sub 3?y}Se{sub y} films synthesized by pulsed electrodeposition. ? The thermoelectric properties of the film were measured at room temperature. ? The films show much better properties then galvanostatically deposited film. -- Abstract: Bi{sub 2}Te{sub 3?y}Se{sub y} films were synthesized by pulsed electrodeposition on indium tin oxide (ITO)-coated glass substrates from aqueous acidic solution at room temperature. The films were deposited at the same average current density but different cathodic current density. The crystal structure, surface morphology and elemental composition of the films were investigated. Smooth and compact Bi{sub 2}Te{sub 3?y}Se{sub y} films were obtained. As the cathodic current density increased, the grain size of the films decreased. The electrical resistivity and Seebeck coefficient of each Bi{sub 2}Te{sub 3?y}Se{sub y} film were measured after the film being transferred onto a non-conductive rubberized fabric support. The films showed n-type conduction, with Seebeck coefficient in the range of ??84 to ?92 ?V/K and electrical resistivity in the range of 102.9–109.4 ?? m. The films showed much better thermoelectric properties compared with the film galvanostatically deposited at the same average current density.

  10. Proximity Effect Induced Electronic Properties of Graphene on Bi2Te2Se.

    PubMed

    Lee, Paengro; Jin, Kyung-Hwan; Sung, Si Jin; Kim, Jin Gul; Ryu, Min-Tae; Park, Hee-Min; Jhi, Seung-Hoon; Kim, Namdong; Kim, Yongsam; Yu, Seong Uk; Kim, Kwang S; Noh, Do Young; Chung, Jinwook

    2015-11-24

    We report that the ?-electrons of graphene can be spin-polarized to create a phase with a significant spin-orbit gap at the Dirac point (DP) using a graphene-interfaced topological insulator hybrid material. We have grown epitaxial Bi2Te2Se (BTS) films on a chemical vapor deposition (CVD) graphene. We observe two linear surface bands from both the CVD graphene notably flattened and BTS coexisting with their DPs separated by 0.53 eV in the photoemission data measured with synchrotron photons. We further demonstrate that the separation between the two DPs, ?D-D, can be artificially fine-tuned by adjusting the amount of Cs atoms adsorbed on the graphene to a value as small as ?D-D = 0.12 eV to find any proximity effect induced by the DPs. Our density functional theory calculation shows the opening of a spin-orbit gap of ?20 meV in the ?-band, enhanced by 3 orders of magnitude from that of a pristine graphene, and a concomitant phase transition from a semimetallic to a quantum spin Hall phase when ?D-D ? 0.20 eV. We thus present a practical means of spin-polarizing the ?-band of graphene, which can be pivotal to advance graphene-based spintronics. PMID:26549323

  11. In vivo NIR imaging with CdTe/CdSe quantum dots entrapped in PLGA nanospheres.

    PubMed

    Kim, Jin Soo; Cho, Kwang Jae; Tran, Thanh Huyen; Nurunnabi, Md; Moon, Tae Hyun; Hong, Suk Min; Lee, Yong-kyu

    2011-01-15

    Luminescent near-infrared (NIR) CdTe/CdSe QDs were synthesized and encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanospheres to prepare stable and biocompatible QDs-loaded nanospheres for in vivo imaging. QDs were encapsulated with PLGA nanospheres by a solid dispersion method and optimized to have high fluorescence intensity for in vivo imaging detection. The resultant QDs-loaded PLGA nanospheres were characterized by various analytical techniques such as UV-Vis measurement, dynamic light scattering (DLS), fluorescence spectroscopy, and transmission electron microscopy (TEM). Finally, we evaluated toxicity and body distribution of QDs loaded in PLGA nanospheres in vitro and in vivo, respectively. From the results, the QDs loaded in PLGA nanospheres were spherical and showed a diameter range of 135.0-162.3 nm in size. The QD nanospheres increased their stability against photooxidation and photobleaching, which have the high potential for applications in biomedical imaging. We have also attained non-invasive in vivo imaging with light photons, representing an intriguing avenue for obtaining biological information by the use of NIR light. PMID:20961554

  12. Optical and structural properties of amorphous Se x Te100- x aligned nanorods

    NASA Astrophysics Data System (ADS)

    Al-Agel, Faisal A.

    2013-12-01

    In the present work, we report studies on optical and structural phenomenon in as-deposited thin films composed of aligned nanorods of amorphous Se x Te100- x ( x = 3, 6, 9, and 12). In structural studies, field emission scanning electron microscopic (FESEM) images suggest that these thin films contain high yield of aligned nanorods. These nanorods show a completely amorphous nature, which is verified by X-ray diffraction patterns of these thin films. Optical studies include the measurement of spectral dependence of absorption, reflection, and transmission of these thin films, respectively. On the basis of optical absorption data, a direct optical band gap is observed. This observation of a direct optical band gap in these nanorods is interesting as chalcogenides normally show an indirect band gap, and due to this reason, these materials could not become very popular for semiconducting devices. Therefore, this is an important report and will open up new directions for the application of these materials in semiconducting devices. The value of this optical band gap is found to decrease with the increase in selenium (Se) concentration. The reflection and absorption data are employed to estimate the values of optical constants (extinction coefficient ( k) and refractive index ( n)). From the spectral dependence of these optical constants, it is found that the values of refractive index ( n) increase, whereas the values of extinction coefficient ( k) decrease with the increase in photon energy. The real and imaginary parts of dielectric constants calculated with the values of extinction coefficient ( k) and refractive index ( n), are found to vary with photon energy and dopant concentration.

  13. Oxidation behavior of amorphous metallic Ni{sub 3}(SbTe{sub 3}){sub 2} compound

    SciTech Connect

    Jun, Jong-Ho; Jung, Jin-Seung . E-mail: jjscm@kangnung.ac.kr; Oh, Seung-Lim; Kim, Yong-Rok; Lee, Sung-Han; O'Connor, Charles J.

    2006-03-09

    Amorphous Ni{sub 3}(SbTe{sub 3}){sub 2} compound was prepared from a metathesis between Zintl phase K{sub 3}SbTe{sub 3} and NiBr{sub 2} in solution and its oxidation behavior was investigated in the temperature range of 200-700 deg. C in air. To characterize the sample, thermogravimetry (TG), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (EDAX) analyses were performed and electrical conductivity was measured as a function of temperature in the range of 25-800 deg. C in air. The specimen showed a metallic conducting-like behavior below 585 deg. C while a semiconducting-like behavior above 585 deg. C. At a first oxidation step of Ni{sub 3}(SbTe{sub 3}){sub 2} below 500 deg. C, TeO{sub 2} phase is formed. Above 500 deg. C, NiO phase is formed, then some NiO reacts with TeO{sub 2} to form NiTeO{sub 3} and NiSb{sub 2}O{sub 6} is simultaneously formed. Above 700 deg. C, NiTeO{sub 3} is further reacted with TeO{sub 2} to form NiTe{sub 2}O{sub 5}. Both NiTeO{sub 3} and NiTe{sub 2}O{sub 5} are decomposed above 774 deg. C.

  14. Synthesis and transport property of AgSbTe{sub 2} as a promising thermoelectric compound

    SciTech Connect

    Wang Heng; Li Jingfeng; Zou Minmin; Sui Tao

    2008-11-17

    Polycrystalline AgSbTe{sub 2} ternary compound materials with high phase purity were fabricated using a combined process of mechanical alloying and spark plasma sintering. It was found that stoichiometric AgSbTe{sub 2} is a promising composition for low-and-mediate temperature applications, whose ZT reaches 1.59 at 673 K, benefiting from its extremely low thermal conductivity (0.30 W/mK) in addition to its low electrical resistivity (<1.1x10{sup -4} {omega} m) and large positive Seebeck coefficient (260 {mu}V/K). On the other hand, deviating from this formula would lead to unstable phase structures and higher thermal conductivity, which make the samples less attractive as thermoelectric materials or components of thermoelectric systems.

  15. An investigation of new infrared nonlinear optical material: BaCdSnSe4, and three new related centrosymmetric compounds: Ba2SnSe4, Mg2GeSe4, and Ba2Ge2S6.

    PubMed

    Wu, Kui; Su, Xin; Yang, Zhihua; Pan, Shilie

    2015-11-18

    A series of new metal chalcongenides, BaCdSnSe4 (), Ba2SnSe4 (), Mg2GeSe4 (), and Ba2Ge2S6 (), were successfully synthesized for the first time. Among them, compounds and were prepared by a molten flux method with Zn as the flux. In their structures, all of them have MQ4 (M = Sn, Ge; Q = S, Se) units. For compound , the CdSe4 and SnSe4 groups are connected to form CdSnSe6 layers and these layers are linked together by the Ba atoms. Compounds and are composed of isolated MSe4 (M = Sn, Ge) units and charge-balanced by the Ba or Mg atoms, respectively, while compound has infinite ?(GeS3)n chains, which is different from the structures of the other three compounds that only have isolated MSe4 (M = Sn, Ge) units. The measured IR and Raman data of the title compounds show wide infrared transmission ranges. The experimental band gaps of compounds , , and were determined to be 1.79, 1.90, and 2.02 eV, respectively. Band structures were also calculated and indicate that their tetrahedral units, such as [SnSe4], [GeS4] and [GeSe4], determine the energy band gaps of the title compounds, respectively. As for compound , based on fundamental light at 2.09 ?m, the experimental second harmonic generation (SHG) response is about 1.6 times that of the benchmark AgGaS2, which is also consistent with the calculated value. Based on the above results, compound has promising applications in the IR field as a NLO material. PMID:26509847

  16. Structure, stability, and properties of the intergrowth compounds ([SnSe]1+?)m(NbSe2)n, where m = n = 1-20.

    PubMed

    Alemayehu, Matti B; Ta, Kim; Falmbigl, Matthias; Johnson, David C

    2015-04-15

    Intergrowth compounds of ([SnSe]1+?)m(NbSe2)n, where 1 ? m = n ? 20, with the same atomic composition but different c-axis lattice parameters and number of interfaces per volume were synthesized using the modulated elemental reactant technique. A c-axis lattice parameter change of 1.217(6) nm as a function of one unit of m = n was observed. In-plane X-ray diffraction shows an increase in distortion of the rock salt layer as a function of m and a broadening of the NbSe2 reflections as n increases, indicating the presence of different coordination environments for Nb (trigonal prismatic and octahedral) and smaller crystallite size, which were confirmed via scanning transmission electron microscopy investigations. The electrical resistivities of all 12 compounds exhibit metallic temperature dependence and are similar in magnitude as would be expected for isocompositional compounds. Carrier concentration and mobility of the compounds vary within a narrow range of 2-6 × 10(21) cm(-3) and 2-6 cm(2) V(-1) s(-1), respectively. Even at a thickness of 12 nm for the SnSe and NbSe2 blocks, the properties of the intergrowth compounds cannot be explained as composite behavior, due to significant charge transfer between them. Upon being annealed at 500 °C, the higher order m = n compounds were found to convert to the thermodynamically stable phase, the (1,1) compound. This suggests that the capacitive energy of the interfaces stabilizes these intergrowth compounds. PMID:25807217

  17. A non-primitive origin of near-chondritic S-Se-Te ratios in mantle peridotites; implications for the Earth?s late accretionary history

    NASA Astrophysics Data System (ADS)

    König, Stephan; Lorand, Jean-Pierre; Luguet, Ambre; Graham Pearson, D.

    2014-01-01

    The chalcophile and highly siderophile elements Se and Te, like the other Highly Siderophile Elements (HSE) in the terrestrial mantle, may constitute powerful key tracers for meteoritic materials that hit the Earth in its latest accretionary stages (“Late Veneer”). Here the Se and Te systematics of mantle-derived peridotites (orogenic peridotites, ophiolites, cratonic peridotite xenoliths) are assessed. Combined with published in-situ analyses of HSE host minerals, whole-rock data are modelled with respect to current petrogenetic models that affect mantle composition, for example partial melting and magmatic refertilisation. We demonstrate that the near-chondritic Se/Te signature (SeN/TeN?9±4; N = CI-chondrite normalised) of “fertile” ophiolitic and orogenic lherzolites cannot be a primitive signature of the Earth's mantle. This signature can however be explained by simple refertilisation models. The HSE-Se-Te budget of these fertile rocks can be modelled by mixing various proportions of a residual assemblage of Fe-Ni monosulphide solid solutions (Mss) and/or refractory platinum group minerals (PGMs - Ru-Os-Ir sulphides + Pt-Ir-Os alloys) with a metasomatic assemblage comprising low-temperature Pt-Pd-Te phases and Cu-Ni-rich sulphides. On the other hand, the reported Se and Te ratios in fertile peridotites are not consistent with melt depletion alone. Additions of late-stage metasomatic S-Se-Te-HSE-rich phases render Primitive Upper Mantle (PUM) estimates for Se and Te highly debatable, especially without appropriate consideration of refertilisation and metasomatism. Our results indicate that there is currently no firm evidence for chondritic S-Se-Te signatures in the Primitive Upper Mantle. This conclusion challenges the simplistic perception that near-chondritic Se/Te ratios may readily trace the Late Veneer composition.

  18. Ab initio study of the structural, electronic and optical properties of ZnTe compound

    SciTech Connect

    Bahloul, B.; Deghfel, B.; Amirouche, L.; Bounab, S.; Bentabet, A.; Bouhadda, Y.; Fenineche, N.

    2015-03-30

    Structural, electronic and optical properties of ZnTe compound were calculated using Density Functional Theory (DFT) based on the pseudopotentials and planewaves (PP-PW) method as implemented in the ABINIT computer code, where the exchange–correlation functional is approximated using the local density approximation (LDA) and the generalized gradient approximation (GGA). The obtained results from either LDA or GGa calculation for lattice parameter, energy band gap and optical parameters, such as the fundamental absorption edge, the peaks observed in the imaginary part of the dielectric function, the macroscopic dielectric constants and the optical dielectric constant, are compared with the available theoretical results and experimental data.

  19. Syntheses, crystal structures and optical properties of the first strontium selenium(IV) and tellurium(IV) oxychlorides: Sr{sub 3}(SeO{sub 3})(Se{sub 2}O{sub 5})Cl{sub 2} and Sr{sub 4}(Te{sub 3}O{sub 8})Cl{sub 4}

    SciTech Connect

    Jiang Hailong; Mao Jianggao

    2008-02-15

    Two new quaternary strontium selenium(IV) and tellurium(IV) oxychlorides, namely, Sr{sub 3}(SeO{sub 3})(Se{sub 2}O{sub 5})Cl{sub 2} and Sr{sub 4}(Te{sub 3}O{sub 8})Cl{sub 4}, have been prepared by solid-state reaction. Sr{sub 3}(SeO{sub 3})(Se{sub 2}O{sub 5})Cl{sub 2} features a three-dimensional (3D) network structure constructed from strontium(II) interconnected by Cl{sup -}, SeO{sub 3}{sup 2-} as well as Se{sub 2}O{sub 5}{sup 2-} anions. The structure of Sr{sub 4}(Te{sub 3}O{sub 8})Cl{sub 4} features a 3D network in which the strontium tellurium oxide slabs are interconnected by bridging Cl{sup -} anions. The diffuse reflectance spectrum measurements and results of the electronic band structure calculations indicate that both compounds are wide band-gap semiconductors. - Graphical abstract: Solid-state reactions of SrO, SrCl{sub 2}, and SeO{sub 2} or TeO{sub 2} in different molar ratios and under different temperatures lead to two new strontium selenium(IV) or tellurium(IV) oxychlorides with two different types of structures, namely, Sr{sub 3}(SeO{sub 3})(Se{sub 2}O{sub 5})Cl{sub 2} and Sr{sub 4}(Te{sub 3}O{sub 8})Cl{sub 4}. Both compounds are wide band-gap semiconductors based on the diffuse reflectance spectra and the electronic band structures.

  20. Density functional theory investigation of the electronic structure and thermoelectric properties of layered MoS{sub 2}, MoSe{sub 2} and their mixed-layer compound

    SciTech Connect

    Lee, Changhoon; Hong, Jisook; Lee, Wang Ro; Kim, Dae Yeon; Shim, Ji Hoon

    2014-03-15

    First principles density functional theory calculations were carried out for the 2H-MoQ{sub 2} (Q=S and Se) and their hypothetical mixed-layer compound. Due to the different electronegativities of S and Se atoms on MoQ{sub 2}, the band gap size could be adjusted in mixed-layer compound MoS{sub 2}/MoSe{sub 2}. Also, the indirect band gap in pure MoQ{sub 2} compounds is changed to the pseudo direct band gap in mixed-layer MoS{sub 2}/MoSe{sub 2} which is similar to the monolayer compound. The layer mixing enhances the thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Therefore, we suggest that this layer mixing approach should be regarded as a useful way to modulate their electronic structures and to improve their thermoelectric properties. -- Graphical abstract: On the basis of density functional calculations we predict that the mixed-layer compounds 2H-MoS{sub 2}/2H-MoSe{sub 2}, in which two different layers 2H-MoS{sub 2} and 2H-MoSe{sub 2}, have enhanced thermoelectric properties because of the increased density of states around the Fermi level and the decreased band gap size. Highlights: • We explored a way of improving TE properties of 2H-MoQ{sub 2} on DFT methods. • The mixed-layer compounds MoS{sub 2}/MoSe{sub 2} have enhanced thermoelectric properties. • This is caused by modulated electronic structure of mixed layer compound. • Layer mixing approach should be regarded as a useful way to improve TE properties.

  1. Infrared probe of the bulk insulating response in Bi 2 -xSb xTe 3 -ySe y topological insulator alloys

    NASA Astrophysics Data System (ADS)

    Post, K. W.; Lee, Y. S.; Chapler, B. C.; Schafgans, A. A.; Novak, Mario; Taskin, A. A.; Segawa, Kouji; Goldflam, M. D.; Stinson, H. T.; Ando, Yoichi; Basov, D. N.

    2015-04-01

    We have investigated the electronic structure and carrier dynamics of the topological insulator Bi 2 -xSb xTe 3 -ySe y, for x =0.5 ,y =1.3 and x =1 ,y =2 , using infrared spectroscopy. Our results show that both of these BSTS alloys are highly insulating in the bulk, with analysis of the infrared data indicating an upper limit to the carrier density of 4.4 ×1017 cm-3. Furthermore, analysis of the interband transitions of Bi 1.5Sb 0.5Te 1.7Se 1.3 revealed distinct band-structure critical points, which suggest high crystallographic order of our crystals. Motivated by the low carrier density and crystallographic order identified in these compounds, we searched for the Landau level transitions associated with the surface states through magneto-optical measurements in the far infrared range. We failed to observe any indications of the Landau level resonances at fields up to 8 T in sharp contrast with our earlier finding for a related Bi 1 -xSb x alloy. We discuss factors that may be responsible for suppressed magneto-optics response of these single crystals.

  2. Interplay between magnetic impurity and superconductivity in annealed Fe1.05Te0.75Se0.25

    NASA Astrophysics Data System (ADS)

    Lin, Wenzhi; Ganesh, Panchapakesan; Gianfrancesco, Anthony; Berlijn, Tom; Maier, Thomas; Kalilin, Sergei; Sales, Brian; Pan, Minghu

    2014-03-01

    By annealing Fe1.05Te0.75Se0.25 in Te vapor, we are able to recover the moment of the magnetic impurity in the bulk chalcogenide superconductor, and enhance the superconductivity in the material. Scanning tunneling microscopy/ spectroscopy studies across a local magnetic impurity reveal the modification of electronic structure around the impurity on the surface of Fe1.05Te0.75Se0.25 sample after being annealed in the Te-vapor. The superconducting gap feature, normally seen on a pristine area, is suppressed around the magnetic impurity. In addition, density-functional theory calculations are carried out to identify the atomic structure, chemical composition and magnetic moment of impurity. Research was supported (WL, BCS, SVK) by Materials Sciences and Engineering Division, Basic Energy Sciences, the U.S. Department of Energy. This research was conducted (WL, MP) at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Fellowship support (AG) from the UT/ORNL Bredesen Center for Interdisciplinary Research and Graduate Education.

  3. Printed Se-Doped MA n-Type Bi2Te3 Thick-Film Thermoelectric Generators

    NASA Astrophysics Data System (ADS)

    Madan, Deepa; Chen, Alic; Wright, Paul K.; Evans, James W.

    2012-06-01

    In this work, we highlight new materials processing developments and fabrication techniques for dispenser-printed thick-film single-element thermoelectric generators (TEG). Printed deposition techniques allow for low-cost and scalable manufacturing of microscale energy devices. This work focuses on synthesis of unique composite thermoelectric systems optimized for low-temperature applications. We also demonstrate device fabrication techniques for high-density arrays of high-aspect-ratio planar single-element TEGs. Mechanical alloyed (MA) n-type Bi2Te3 powders were prepared by taking pure elemental Bi and Te in 36:64 molar ratio and using Se as an additive. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the as-milled powders to confirm the Bi2Te3 phase formation and particle size below 50 ?m. Thermoelectric properties of the composites were measured from room temperature to 100°C. We achieved a dimensionless figure of merit ( ZT) of 0.17 at 300 K for MA n-type Bi2Te3-epoxy composites with 2 wt.% Se additive. A 20 single-leg TEG prototype with 5 mm × 400 ?m × 120 ?m printed element dimensions was fabricated on a polyimide substrate with evaporated gold contacts. The prototype device produced a power output of 1.6 ?W at 40 ?A and 40 mV voltage for a temperature difference of 20°C.

  4. Thermoelectric Properties of Nanocrystalline Bi2(Te1- x Se x )3 Prepared by High-Pressure Sintering

    NASA Astrophysics Data System (ADS)

    Zou, Ping; Xu, Guiying; Wang, Song

    2015-06-01

    Bi2(Te1- x Se x )3 ( x = 0, 0.03, 0.05, 0.07, 0.10) bulk materials were prepared by high-pressure (6.0 GPa) sintering (HPS) at 673 K. The samples were then annealed under vacuum, at 633 K, for 36 h. Phase composition, morphology, and thermoelectric (TE) properties were characterized. The alloys consisted of nanoparticles before and after annealing. Such nanostructures effectively reduce lattice thermal conductivity by enhancing phonon scattering. Substitution of tellurium by selenium had a substantial effect on the electron transport properties of the Bi2(Te1- x Se x )3 alloys. HPS with annealing can improve TE properties by improving the electron transport properties and simultaneously reducing the lattice thermal conductivity of nanostructured samples. A peak thermoelectric figure of merit ( ZT) of 0.81 at 373 K was achieved for the annealed sample with x = 0.10; this value ZT was approximately 8% higher than that of n-type zone-melted material, making these materials more attractive for commercial applications.

  5. Structural and conductivity studies of CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6}

    SciTech Connect

    Djemel, M.; Abdelhedi, M.; Dammak, M.; Kolsi, A.W.

    2012-12-15

    The compound CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6} crystallizes in the monoclinic P2{sub 1}/n space group. It was analyzed, at room temperature, using X-ray diffractometer data. The main feature of these atomic arrangements is the coexistence of three and different anions (SO{sub 4}{sup 2-}, SeO{sub 4}{sup 2-} and TeO{sub 6}{sup 6-}groups) in the unit cell, connected by hydrogen bonds which make the building of the crystal. The thermal analysis of the title compound shows three distinct endothermal peaks at 435, 460 and 475 K. Complex impedance measurements are performed on this material as a function of both temperature and frequency. The electric conduction has been studied. The temperature dependence on the conductivity indicates that the sample became an ionic conductor at high temperature. - Graphical abstract: Projection of crystal structure CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6} on the ab plane. Highlights: Black-Right-Pointing-Pointer We have studied the results of the crystal structure of the new mixed compound. Black-Right-Pointing-Pointer We have characterized the phase transition observed in DSC curve. Black-Right-Pointing-Pointer The protonic conduction in our material is probably due to a hopping mechanism.

  6. Study of Some Physical Properties of Se{sub 30}Te{sub 70-x}Sn{sub x} Glasses

    SciTech Connect

    Heera, Pawan; Sharma, Raman

    2011-12-12

    In the present work the effect of Sn doping on the physical properties of, tellurium rich, Se{sub 30}Te{sub 70-x}Sn{sub x} system is studied theoretically. The average coordination number, constraints, lone pair electrons and heat of atomization for Se{sub 30}Te{sub 70-x}Sn{sub x} system are calculated for x = 0,1.5,2.5,5.5 using the well defined relations. The present study shows that the values of lone pair electrons and average single bond energy goes on decreasing with increasing Sn content whereas the average coordination number, constraints and heat of atomization increases with increase in the Sn content.

  7. Magneto-optical characterizations of FeTe???Se??? thin films with critical current density over 1 MA/cm²

    DOE PAGESBeta

    Sun, Yue; Li, Qiang; Tsuchiya, Yuji; Pyon, Sunseng; Tamegai, Tsuyoshi; Zhang, Cheng; Ozaki, Toshinori

    2014-12-03

    We performed magneto-optical (MO) measurements on FeTe???Se??? thin films grown on LaAlO? (LAO) and Yttria-stabilized zirconia (YSZ) single-crystalline substrates. These thin films show superconducting transition temperature Tc ~19 K, 4 K higher than the bulk sample. Typical roof-top patterns can be observed in the MO images of thin films grown on LAO and YSZ, from which a large and homogeneous critical current density Jc ~ 3 - 4 x 10? A/cm² at 5 K was obtained. In this study, magnetic flux penetration measurement reveals that the current is almost isotropically distributed in the two thin films. Compared with bulk crystals,more »FeTe???Se??? thin film demonstrates not only higher Tc, but also much larger Jc, which is attractive for applications.« less

  8. Magneto-optical characterizations of FeTe???Se??? thin films with critical current density over 1 MA/cm²

    SciTech Connect

    Sun, Yue; Li, Qiang; Tsuchiya, Yuji; Pyon, Sunseng; Tamegai, Tsuyoshi; Zhang, Cheng; Ozaki, Toshinori

    2014-12-03

    We performed magneto-optical (MO) measurements on FeTe???Se??? thin films grown on LaAlO? (LAO) and Yttria-stabilized zirconia (YSZ) single-crystalline substrates. These thin films show superconducting transition temperature Tc ~19 K, 4 K higher than the bulk sample. Typical roof-top patterns can be observed in the MO images of thin films grown on LAO and YSZ, from which a large and homogeneous critical current density Jc ~ 3 - 4 x 10? A/cm² at 5 K was obtained. In this study, magnetic flux penetration measurement reveals that the current is almost isotropically distributed in the two thin films. Compared with bulk crystals, FeTe???Se??? thin film demonstrates not only higher Tc, but also much larger Jc, which is attractive for applications.

  9. Quantifying electron-phonon coupling in CdTe{sub 1?x}Se{sub x} nanocrystals via coherent phonon manipulation

    SciTech Connect

    Spann, B. T.; Xu, X.

    2014-08-25

    We employ ultrafast transient absorption spectroscopy with temporal pulse shaping to manipulate coherent phonon excitation and quantify the strength of electron-phonon coupling in CdTe{sub 1?x}Se{sub x} nanocrystals (NCs). Raman active CdSe and CdTe longitudinal optical phonon (LO) modes are excited and probed in the time domain. By temporally controlling pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe{sub 1?x}Se{sub x} NCs, we estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode.

  10. Magneto-optical imaging of polycrystalline FeTe 1-xSe x prepared at various conditions

    NASA Astrophysics Data System (ADS)

    Ding, Q.; Taen, T.; Mohan, S.; Nakajima, Y.; Tamegai, T.

    2011-11-01

    We have prepared high-quality polycrystalline FeTe 1-xSe x by sintering at different temperatures and characterized their structural and magnetic properties with X-ray diffraction, magnetization measurements, and magneto-optical imaging. The intragranular Jc was estimated to be 5 × 10 4 A/cm 2, which is smaller than the single crystal, but still in the range for practical applications.

  11. Surface Collective Modes in the Topological Insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}.

    PubMed

    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

    2015-12-18

    We used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}. 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 ?^{"}(q,?) 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. PMID:26722943

  12. Cadmium amido alkoxide and alkoxide precursors for the synthesis of nanocrystalline CdE (E=S,Se, Te).

    SciTech Connect

    Boyle, Timothy J.; Avilucea, Gabriel; Bunge, Scott D.; Alam, Todd Michael; Headley, Thomas Jeffrey; Holland, Gregory P.

    2004-12-01

    The synthesis and characterization of a family of alternative precursors for the production of CdE nanoparticles (E = S, Se, and Te) is reported. The reaction of Cd(NR{sub 2}){sub 2} where NR{sub 2} = N(SiMe{sub 3}){sub 2} with n HOR led to the isolation of the following: n = 1 [Cd({mu}-OCH{sub 2}CMe{sub 3})(NR{sub 2})(py)]{sub 2} (1, py = pyridine), Cd[({mu}-OC{sub 6}H{sub 3}(Me){sub 2}-2,6){sub 2}Cd(NR{sub 2})(py)]{sub 2} (2), [Cd({mu}-OC{sub 6}H{sub 3}(CHMe{sub 2}){sub 2}-2,6)(NR{sub 2})(py)]{sub 2} (3), [Cd({mu}-OC{sub 6}H{sub 3}(CMe{sub 3}){sub 2}-2,6)(NR{sub 2})(py)]{sub 2} (4), [Cd({mu}-OC{sub 6}H{sub 2}(NH{sub 2}){sub 3}-2,4,6)(NR{sub 2})(py)]{sub 2} (5), and n = 2 [Cd({mu}-OC{sub 6}H{sub 3}(Me){sub 2}-2,6)(OC{sub 6}H{sub 3}(Me){sub 2}-2,6)(py){sub 2}]{sub 2} (6), and [Cd({mu}-OC{sub 6}H{sub 3}(CMe{sub 3}){sub 2}-2,6)(OC{sub 6}H{sub 3}(CMe{sub 3}){sub 2}-2,6)(THF)]{sub 2} (7). For all but 2, the X-ray crystal structures were solved as discrete dinuclear units bridged by alkoxide ligands and either terminal -NR{sub 2} or -OR ligands depending on the stoichiometry of the initial reaction. For 2, a trinuclear species was isolated using four {mu}-OR and two terminal -NR{sub 2} ligands. The coordination of the Cd metal center varied from 3 to 5 where the higher coordination numbers were achieved by binding Lewis basic solvents for the less sterically demanding ligands. These complexes were further characterized in solution by {sup 1}H, {sup 13}C, and {sup 113}Cd NMR along with solid-state {sup 113}Cd NMR spectroscopy. The utility of these complexes as 'alternative precursors' for the controlled preparation of nanocrystalline CdS, CdSe, and CdTe was explored. To synthesize CdE nanocrystals, select species from this family of compounds were individually heated in a coordinating solvent (trioctylphosphine oxide) and then injected with the appropriate chalcogenide stock solution. Transmission electron spectroscopy and UV-vis spectroscopy were used to characterize the resultant particles.

  13. Two-dimensional topological insulators with tunable band gaps: Single-layer HgTe and HgSe

    PubMed Central

    Li, Jin; He, Chaoyu; Meng, Lijun; Xiao, Huaping; Tang, Chao; Wei, Xiaolin; Kim, Jinwoong; Kioussis, Nicholas; Malcolm Stocks, G.; Zhong, Jianxin

    2015-01-01

    Two-dimensional (2D) topological insulators (TIs) with large band gaps are of great importance for the future applications of quantum spin Hall (QSH) effect. Employing ab initio electronic calculations we propose a novel type of 2D topological insulators, the monolayer (ML) low-buckled (LB) mercury telluride (HgTe) and mercury selenide (HgSe), with tunable band gap. We demonstrate that LB HgTe (HgSe) monolayers undergo a trivial insulator to topological insulator transition under in-plane tensile strain of 2.6% (3.1%) due to the combination of the strain and the spin orbital coupling (SOC) effects. Furthermore, the band gaps can be tuned up to large values (0.2?eV for HgTe and 0.05?eV for HgSe) by tensile strain, which far exceed those of current experimentally realized 2D quantum spin Hall insulators. Our results suggest a new type of material suitable for practical applications of 2D TI at room-temperature. PMID:26365502

  14. Effects of annealing, acid and alcoholic beverages on Fe1+yTe0.6Se0.4

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Taen, T.; Tsuchiya, Y.; Shi, Z. X.; Tamegai, T.

    2013-01-01

    We have systematically investigated and compared different methods to induce superconductivity in the iron chalcogenide Fe1+yTe0.6Se0.4, including annealing in a vacuum, N2, O2 and I2 atmospheres and immersing samples into acid and alcoholic beverages. Vacuum and N2 annealing are proved to be ineffective in inducing superconductivity in a Fe1+yTe0.6Se0.4 single crystal. Annealing in O2 and I2 and immersion in acid and alcoholic beverages can induce superconductivity by oxidizing the excess Fe in the sample. Superconductivity in O2 annealed samples is of a bulk nature, while I2, acid and alcoholic beverages can only induce superconductivity near the surface. By comparing the different effects of O2, I2, acid and alcoholic beverages we propose a scenario to explain how the superconductivity is induced in the non-superconducting as-grown Fe1+yTe0.6Se0.4.

  15. Two-dimensional topological insulators with tunable band gaps: Single-layer HgTe and HgSe

    NASA Astrophysics Data System (ADS)

    Li, Jin; He, Chaoyu; Meng, Lijun; Xiao, Huaping; Tang, Chao; Wei, Xiaolin; Kim, Jinwoong; Kioussis, Nicholas; Malcolm Stocks, G.; Zhong, Jianxin

    2015-09-01

    Two-dimensional (2D) topological insulators (TIs) with large band gaps are of great importance for the future applications of quantum spin Hall (QSH) effect. Employing ab initio electronic calculations we propose a novel type of 2D topological insulators, the monolayer (ML) low-buckled (LB) mercury telluride (HgTe) and mercury selenide (HgSe), with tunable band gap. We demonstrate that LB HgTe (HgSe) monolayers undergo a trivial insulator to topological insulator transition under in-plane tensile strain of 2.6% (3.1%) due to the combination of the strain and the spin orbital coupling (SOC) effects. Furthermore, the band gaps can be tuned up to large values (0.2?eV for HgTe and 0.05?eV for HgSe) by tensile strain, which far exceed those of current experimentally realized 2D quantum spin Hall insulators. Our results suggest a new type of material suitable for practical applications of 2D TI at room-temperature.

  16. Synthesis of organic (trimethylsilyl)chalcogenolate salts Cat[TMS-E] (E = S, Se, Te): the methylcarbonate anion as a desilylating agent.

    PubMed

    Finger, Lars H; Scheibe, Benjamin; Sundermeyer, Jörg

    2015-10-01

    A high-yield synthesis of the class of (trimethylsilyl)chalcogenolate organic salts [Cat][TMS-E] (E = S, Se, Te; Cat = BMPyr, DMPyr, NMe4, nBu3MeP) is presented. The title compounds have been prepared by the strictly aprotic reaction between the respective bis(trimethylsilyl)chalcogenide (TMS2E) and methylcarbonate ionic liquids (ILs). This constitutes a novel reaction behavior of methylcarbonate ILs, acting as a nucleophilic desilylating agent and a Lewis base instead of as a Brønsted base. Thus prepared silylchalcogenolate salts represent an activated form of the multifunctional TMS2E reactant series. Pyrrolidinium TMS-S salts have proven to be excellent precursors for the synthesis of pyrrolidinium hexasulfides. The scope of the desilylation reaction can be extended to other silyl-bearing synthons such as (trimethylsilyl)azide and (trimethylsilyl)cyanide. PMID:26371537

  17. Graphene-like Dirac states and quantum spin Hall insulators in square-octagonal M X2 (M =Mo , W; X =S , Se, Te) isomers

    NASA Astrophysics Data System (ADS)

    Sun, Yan; Felser, Claudia; Yan, Binghai

    2015-10-01

    We studied the square-octagonal lattice of the transition metal dichalcogenide M X2 (with M =Mo , W; X =S , Se, and Te), as an isomer of the normal hexagonal compound of M X2 . By band-structure calculations, we observe the graphene-like Dirac band structure in a rectangular lattice of M X2 with nonsymmorphic space group symmetry. Two bands with van Hove singularity points cross each at the Fermi energy, leading to two Dirac cones that locate at opposite momenta. Spin-orbit coupling can open a gap at these Dirac points, inside which gapless topological edge states exists as the quantum spin Hall (QSH) effect, the 2D topological insulator.

  18. Synthesis and characterization of a new mid-infrared transparent compound: acentric Ba5In4Te4S7.

    PubMed

    Tan, De-Ming; Lin, Chen-Sheng; Luo, Zhong-Zhen; Zhang, Hao; Zhang, Wei-Long; He, Zhang-Zhen; Cheng, Wen-Dan

    2015-04-28

    A new noncentrosymmetric (NCS) sulfide, Ba5In4Te4S7, was synthesized by a conventional solid-state reaction in evacuated closed silica tubes. The compound crystallizes in the orthorhombic space group Imm2 (44), with unit cell parameters a = 39.110(3) Å, b = 4.3763(3) Å, c = 7.3452(6) Å, Z = 2, and V = 1257.18(17) Å(3). The 3D framework of Ba5In4Te4S7 is composed of infinite 1(?)[InS2Te2](5-) and 1(?)[In2S3Te2](4-) anionic chains. The optical band gap of Ba5In4Te4S7 is 2.13 eV and it shows the UV-visible cutoff at 0.57 ?m and the infrared transparency extends to 25 ?m. The compound exhibits a powder second harmonic generation (SHG) signal at 2.05 ?m with about half of the AgGaS2 at a particle size of 74-106 ?m. According to first-principles calculation, the calculated major SHG tensor element is d32 = 18.8 pm V(-1). The SHG process of nonlinear optical response of Ba5In4Te4S7 originates from the electronic transitions from occupied S-3p and Te-5p states to unoccupied In-5s and In-5p states. PMID:25813051

  19. Thermoelectric properties of n-Bi2Te3 - x - y Se x S y solid solutions under high pressure

    NASA Astrophysics Data System (ADS)

    Korobeinikov, I. V.; Luk'yanova, L. N.; Vorontsov, G. V.; Shchennikov, V. V.; Kutasov, V. A.

    2014-02-01

    The thermoelectric properties of n-Bi2Te3 - x - y Se x S y solid solutions with atomic substitutions in the tellurium sublattice ( x = 0.27, 0.3, y = 0, and x = y = 0.09) have been studied under a pressure to 8 GPa. It has been found that the Seebeck coefficient and the resistance decrease with increasing P, and power factor ? increases in all compositions and becomes maximal at pressures of 2-4 GPa. It has been shown that the power factor ?, which is proportional to the product of the effective mass of the density of states m/m m/m 0 and the charge carrier mobility ?0 in the form ( m/m 0)3/2?0, increases with increasing pressure mainly due to the increase in the mobility and also depends on the solid solution composition. In the composition with substitution Te ? Se + S ( x = y = 0.09), the peculiarity of the dependence of m/m 0 on P in the pressure range corresponding to maximal values of the power factor can be explained by the existence of an electronic topological transition. The increase in the power factor under pressure in n-type Bi2Te3 - x - y Se x S y solid solutions combined with similar data for p-type Bi2 - x Sb x Te3 solid solutions obtained earlier, including the estimations of possible changes in the thermal conductivity with increasing pressure, give grounds to design thermoelements with improved value of the thermoelectric figure-of-merit, which can be 50-70% at pressures of 2-4 GPa.

  20. Design and synthesis of highly luminescent near-infrared-emitting water-soluble CdTe/CdSe/ZnS core/shell/shell quantum dots.

    PubMed

    Zhang, Wenjin; Chen, Guanjiao; Wang, Jian; Ye, Bang-Ce; Zhong, Xinhua

    2009-10-19

    Applications of water-dispersible near-infrared (NIR)-emitting quantum dots (QDs) have been hampered by their instability and low photoluminescence (PL) efficiencies. In this paper, water-soluble highly luminescent NIR-emitting QDs were developed through constructing CdTe/CdSe/ZnS core/shell/shell nanostructure. The CdTe/CdSe type-II structure yields the QDs with NIR emission. By varying the size of CdTe cores and the thickness of the CdSe shell, the emission wavelength of the obtained nanostructure can span from 540 to 825 nm. In addition, the passivation of the ZnS shell with a substantially wide bandgap confines the excitons within the CdTe/CdSe interface and isolates them from the solution environment and consequently improves the stability of the nanostructure, especially in aqueous media. An effective shell-coating route was developed for the preparation of CdTe/CdSe core/shell nanostructures by selecting capping reagents with a strong coordinating capacity and adopting a low temperature for shell deposition. An additional ZnS shell was deposited around the outer layer of CdTe/CdSe QDs to form the core/shell/shell nanostructure through the decomposition of single molecular precursor zinc diethyldithiocarbamate in the crude CdTe/CdSe reaction solution. The water solubilization of the initially oil-soluble CdTe/CdSe/ZnS QDs was achieved through ligand replacement by 3-mercaptopropionic acid. The as-prepared water-soluble CdTe/CdSe/ZnS QDs possess PL quantum yields as high as 84% in aqueous media, which is one of the best results for the luminescent semiconductor nanocrystals. PMID:19772326

  1. Variable-Temperature In Situ X-ray Diffraction Study of the Thermodynamic Evolution of AgSbTe2 Thermoelectric Compound

    NASA Astrophysics Data System (ADS)

    Du, B.; Yan, Y.; Tang, X.

    2015-06-01

    Although AgSbTe2 compound has been intensively studied as a promising medium-temperature p-type thermoelectric (TE) material, its thermodynamic stability is still a controversial issue. We have prepared selenium-doped and pristine AgSbTe2 compounds from high-purity elements by a melt-quench-spark plasma sintering (Melt-SPS) or a melt spinning-SPS technique (MS-SPS). The influences of rapid solidification and selenium impurity on the thermodynamic evolution of AgSbTe2 TE compound have been studied by variable-temperature in situ x-ray diffraction over the temperature range from 25°C to 450°C. AgSbTe2 is a high-temperature metastable phase, and ultrahigh cooling rate in melt spinning is favorable to achieve phase-pure and homogeneous AgSbTe2 compound. The maximum possible short-time working temperature for AgSbTe2 TE compound is 250°C. Above 300°C, pristine AgSbTe2 is prone to slow decomposition to Sb2Te3, Ag5Te3, and ?-Ag2Te binary compounds, regardless of preparation route. The MS-SPS sample underwent a nearly reversible phase transition on cooling to room temperature, while the Melt-SPS sample decomposed irreversibly after measurement. Selenium-doped specimen showed robust thermodynamic stability below 300°C, and experienced distinct phase transition compared with pristine specimen above 330°C, evidencing a profound influence of selenium doping on the thermodynamic stability of AgSbTe2 thermoelectric compound.

  2. Controllable Growth of Vertical Heterostructure GaTe(x)Se(1-x)/Si by Molecular Beam Epitaxy.

    PubMed

    Liu, Shanshan; Yuan, Xiang; Wang, Peng; Chen, Zhi-Gang; Tang, Lei; Zhang, Enze; Zhang, Cheng; Liu, Yanwen; Wang, Weiyi; Liu, Cong; Chen, Chen; Zou, Jin; Hu, Weida; Xiu, Faxian

    2015-08-25

    Two dimensional (2D) alloys, especially transition metal dichalcogenides, have attracted intense attention owing to their band-gap tunability and potential optoelectrical applications. Here, we report the controllable synthesis of wafer-scale, few-layer GaTexSe1-x alloys (0 ? x ? 1) by molecular beam epitaxy (MBE). We achieve a layer-by-layer growth mode with uniform distribution of Ga, Te, and Se elements across 2 in. wafers. Raman spectroscopy was carried out to explore the composition-dependent vibration frequency of phonons, which matches well with the modified random-element-isodisplacement model. Highly efficient photodiode arrays were also built by depositing few-layer GaTe0.64Se0.36 on n-type Si substrates. These p-n junctions have steady rectification characteristics with a rectifying ratio exceeding 300 and a high external quantum efficiency around 50%. We further measured more devices on MBE-grown GaTexSe1-x/Si heterostructures across the full range to explore the composition-dependent external quantum efficiency. Our study opens a new avenue for the controllable growth of 2D alloys with wafer-scale homogeneity, which is a prominent challenge in 2D material research. PMID:26234804

  3. Observation of an electron band above the Fermi level in FeTe{sub 0.55}Se{sub 0.45} from in-situ surface doping

    SciTech Connect

    Zhang, P.; Ma, J.; Qian, T.; Richard, P. Ding, H.; Xu, N.; Xu, Y.-M.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe{sub 0.55}Se{sub 0.45}. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe{sub 2?x}Se{sub 2} compound.

  4. Optical and thermoelectric characterizations of electroplated n-Bi2(Te0.9Se0.1)3

    NASA Astrophysics Data System (ADS)

    Zimmer, Alexandre; Stein, Nicolas; Terryn, Herman; Boulanger, Clotilde

    2007-10-01

    Bismuth selenotelluride (Bi2(Te0.9Se0.1)3) films were electrodeposited at constant current density from acidic aqueous solutions with Arabic gum in order to produce thin films for miniaturized thermoelectric devices. X-ray fluorescence spectroscopy determined film compositions. X-ray diffraction pattern shows that the films as deposited are polycrystalline, isostructural to Bi2Te3 and covered by crystallites. Mueller-matrix analysis reveals that the electroplated layers are optically like an isotropic medium. Their pseudo-dielectric functions were determined using mid-infrared spectroscopic ellipsometry. Tauc Lorentz combined with Drude dispersion relations were successfully used. The energy band gap Eg was found to be about 0.15 eV. Moreover, the fundamental absorption edge was described by an indirect optical band-to-band transition. From Seebeck coefficient measurement, films exhibit n-type charge carrier and the value of thermoelectric power is about -40 ?V/K.

  5. Highly sensitive and selective detection of phosphate using novel highly photoluminescent water-soluble Mn-doped ZnTe/ZnSe quantum dots.

    PubMed

    Song, Yu; Li, Yang; Liu, Yunling; Su, Xingguang; Ma, Qiang

    2015-11-01

    Herein, the facile method with high selectivity for phosphate ion (Pi) sensing using novel Type-II core/shell Mn: ZnTe/ZnSe quantum dots (QDs) was reported. This was the first time that Mn: ZnTe/ZnSe QDs with highlighted optical properties were used for sensing. The water-soluble Mn: ZnTe/ZnSe QDs with a high quantum yield of 7% were synthesized by aqueous synthetic method. Compared with traditional ZnSe QDs or Mn: ZnSe QDs, the smaller effective band gap, longer wavelength and lower ionization potential (high valence band edge) for effective hole localization made Type-II core/shell Mn: ZnTe/ZnSe QDs to be stable and had high photoluminescence (PL). Only Mg(2+) was found to be able to enhance Mn: ZnTe/ZnSe QDs PL selectively. The mechanism of fluorescence enhancement was attributed to the passivated surface nonradiative relaxation centers of Mn: ZnTe/ZnSe QDs. In the presence of Pi anion, the PL intensity got quenched due to the aggregation species of QDs via electrostatic attraction between Pi and Mg(2+) on the surface of Mn: ZnTe/ZnSe QDs. Therefore, the quenching effect can be used to detect Pi selectively. The PL was observed to be linearly proportional to the Pi analyte concentration in the range from 0.67 to 50.0?mol/L, with a detection limit of 0.2?mol/L (S/N=3). The novel "on-off" fluorescence nanosensor for Pi detection was sensitive and convenient in the real analysis application. The reported analytical method of Mn: ZnTe/ZnSe QDs is highly sensitive and selective, which can corroborate the extension of its usages in chemo/ biosensing and bioimaging. PMID:26452877

  6. Disorder-induced structural transitions in topological insulating Ge-Sb-Te compounds

    SciTech Connect

    Kim, Jeongwoo; Jhi, Seung-Hoon

    2015-05-21

    The mechanism for the fast switching between amorphous, metastable, and crystalline structures in chalcogenide phase-change materials has been a long-standing puzzle. Based on first-principles calculations, we study the atomic and electronic properties of metastable Ge{sub 2}Sb{sub 2}Te{sub 5} and investigate the atomic disorder to understand the transition between crystalline hexagonal and cubic structures. In addition, we study the topological insulating property embedded in these compounds and its evolution upon structural changes and atomic disorder. We also discuss the role of the surface-like states arising from the topological insulating property in the metal-insulator transition observed in the hexagonal structure.

  7. Electronic structure and morphology of epitaxial Bi{sub 2}Te{sub 2}Se topological insulator films

    SciTech Connect

    Maaß, H. Schatz, S.; Fiedler, S.; Seibel, C.; Lutz, P.; Bentmann, H. Reinert, F.; Schreyeck, S.; Gould, C.; Brunner, K.; Molenkamp, L. W.; Karczewski, G.

    2014-11-21

    Epitaxial films of the ternary topological insulator Bi{sub 2}Te{sub 2}Se were grown on Si(111) substrates and investigated for their surface electronic properties and morphology. We employ a Se-capping procedure allowing for the preparation of clean films in the surface-analysis experimental setups. Using angle-resolved photoelectron spectroscopy, we determine the dispersion of the topological surface state. With time after surface preparation, the spectroscopic features in the surface electronic structure exhibit significant temperature-dependent shifts to higher binding energies. Scanning tunneling microscopy images show terraces with typical step edge separations of 50?nm–150?nm. X-ray photoelectron spectroscopy indicates an increased Se concentration at the surface.

  8. Direct hexagonal transition of amorphous (Ge2Sb2Te5)0.9Se0.1 thin films

    NASA Astrophysics Data System (ADS)

    Vinod, E. M.; Ramesh, K.; Ganesan, R.; Sangunni, K. S.

    2014-02-01

    Ge2Sb2Te5 (GST) is well known for its phase change properties and applications in memory and data storage. Efforts are being made to improve its thermal stability and transition between amorphous and crystalline phases. Various elements are doped to GST to improve these properties. In this work, Se has been doped to GST to study its effect on phase change properties. Amorphous GST film crystallized in to rock salt (NaCl) type structure at 150 °C and then transformed to hexagonal structure at 250 °C. Interestingly, Se doped GST ((GST)0.9Se0.1) film crystallized directly into hexagonal phase and the intermediate phase of NaCl is not observed. The crystallization temperature (Tc) of (GST)0.9Se0.1 is around 200 °C, which is 50 °C higher than the Tc of GST. For (GST)0.9Se0.1, the threshold switching occurs at about 4.5 V which is higher than GST (3 V). Band gap (Eopt) values of as deposited films are calculated from Tauc plot which are 0.63 eV for GST and 0.66 eV for (GST)0.9Se0.1. The Eopt decreases for the films annealed at higher temperatures. The increased Tc, Eopt, the contrast in resistance and the direct transition to hexagonal phase may improve the data readability and thermal stability in the Se doped GST film.

  9. Synthesis of Multishell Nanoplates by Consecutive Epitaxial Growth of Bi2Se3 and Bi2Te3 Nanoplates and Enhanced Thermoelectric Properties.

    PubMed

    Min, Yuho; Park, Gyeongbae; Kim, Bongsoo; Giri, Anupam; Zeng, Jie; Roh, Jong Wook; Kim, Sang Il; Lee, Kyu Hyoung; Jeong, Unyong

    2015-07-28

    We herein demonstrate the successive epitaxial growth of Bi2Te3 and Bi2Se3 on seed nanoplates for the scalable synthesis of heterostructured nanoplates (Bi2Se3@Bi2Te3) and multishell nanoplates (Bi2Se3@Bi2Te3@Bi2Se3, Bi2Se3@Bi2Te3@Bi2Se3@Bi2Te3). The relative dimensions of the constituting layers are controllable via the molar ratios of the precursors added to the seed nanoplate solution. Reduction of the precursors produces nanoparticles that attach preferentially to the sides of the seed nanoplates. Once attached, the nanoparticles reorganize epitaxially on the seed crystal lattices to form single-crystalline core-shell nanoplates. The nanoplates, initially 100 nm wide, grew laterally to 620 nm in the multishell structure, while their thickness increased more moderately, from 5 to 20 nm. The nanoplates were pelletized into bulk samples by spark plasma sintering and their thermoelectric properties are compared. A peak thermoelectric figure of merit (ZT) ?0.71 was obtained at 450 K for the bulk of Bi2Se3@Bi2Te3 nanoplates by simultaneous modulation of electronic and thermal transport in the presence of highly dense grain and phase boundaries. PMID:26134746

  10. Control of interstitial Fe and its impact on superconductivity of FeTe1/2Se1/2

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Kumar, Anuj; Pal, Anand

    2012-06-01

    The FeTe1/2Se1/2 samples are quenched during the vacuum sealed synthesis process to room temperature from 700°C, 500°C, 300°C and room temperature (RT); named as 700Q, 500Q, 300Q and RTQ respectively. Though all samples except 700Q are crystallized in single phase with space group P4/nmm, the presence of interstitial Fe (Feint) at 2c site is increased from 5% for RTQ to 8% for 500Q. The 700Q sample is crystallized in Fe7Se8 phase. Also though the RTQ and 300Q are superconducting at 10 K and 13 K respectively, the 500Q and 700Q are not. Magnetic ordering (Tmag) is observed at around 125 K for all the samples. The prominence of Tmag in terms of effective moment is sufficiently higher for 500Q and 700Q than RTQ and 300Q. Summarily, it is found that quenching induced disorder affects the occupancy of Feint in FeTe1/2Se1/2 and thus both its superconducting and magnetic properties.

  11. Polycrystalline CuInSe{sub 2} and CdTe PV solar cells. Annual subcontract report, 15 April 1993--14 April 1994

    SciTech Connect

    Dhere, N.G.

    1994-11-01

    This is an annual technical report on the Phase 2 of a three-year phased research program. The principal objective of the research project is to develop novel and low-cost processes for the fabrication of stable and efficient CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} and CdTe polycrystalline-thin-film solar cells using reliable techniques amenable to scale-up for economic, large-scale manufacture. The aims are to develop a process for the non-toxic selenization so as to avoid the use of extremely toxic H{sub 2}Se in the fabrication of CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} thin-film solar cells; to optimize selenization parameters; to develop a process for the fabrication of CdTe solar cells using Cd and Te layers sputtered from elemental targets; to develop an integrated process for promoting the interdiffusion between Cd/Te layers, CdTe phase formation, grain growth, type conversion, and junction formation; to improve adhesion; to minimize residual stresses; to improve the metallic back-contact; to improve the uniformity, stoichiometry, and morphology of CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} and CdTe thin films; and to improve the efficiency of CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} and CdTe solar cells.

  12. Physical reasons of emission transformation in infrared CdSeTe/ZnS quantum dots at bioconjugation

    NASA Astrophysics Data System (ADS)

    Torchynska, T. V.

    2015-04-01

    The core/shell CdSeTe/ZnS quantum dots (QDs) with emission at 780-800 nm (1.55-1.60 eV) have been studied by means of photoluminescence (PL) and Raman scattering methods in the nonconjugated state and after conjugation to different antibodies (Ab): (i) mouse monoclonal [8C9] human papilloma virus Ab, anti-HPV 16-E7 Ab, (ii) mouse monoclonal [C1P5] human papilloma virus HPV16 E6+HPV18 E6 Ab, and (iii) pseudo rabies virus (PRV) Ab. The transformations of PL and Raman scattering spectra of QDs, stimulated by conjugated antibodies, have been revealed and discussed. The energy band diagram of core/shell CdSeTe/ZnS QDs has been designed that helps to analyze the PL spectra and their transformations at the bioconjugation. It is shown that the core in CdSeTe/ZnS QDs is complex and including the type II quantum well. The last fact permits to explain the nature of infrared (IR) optical transitions (1.55-1.60 eV) and the high energy PL band (1.88-1.94 eV) in the nonconjugated and bioconjugated QDs. A set of physical reasons has been analyzed with the aim to explain the transformation of PL spectra in bioconjugated QDs. Finally it is shown that two factors are responsible for the PL spectrum transformation at bioconjugation to charged antibodies: (i) the change of energy band profile in QDs and (ii) the shift of QD energy levels in the strong quantum confinement case. The effect of PL spectrum transformation is useful for the study of QD bioconjugation to specific antibodies and can be a powerful technique for early medical diagnostics.

  13. X-ray diffraction study of (TlInSe{sub 2}){sub 1-x}(TlGaTe{sub 2}){sub x} crystal system

    SciTech Connect

    Sheleg, A. U. Zub, E. M.; Yachkovskii, A. Ya.; Mustafaeva, S. N.; Kerimova, E. M.

    2012-03-15

    The crystallographic and dynamic characteristics of TlInSe{sub 2} and TlGaTe{sub 2} crystals have been studied by X-ray diffraction in the temperature range of 85-320 K. The temperature dependences of the unit-cell parameters a of TlInSe{sub 2} and TlGaTe{sub 2} crystals, as well as their coefficients of thermal expansion along the [100] direction, are determined. The concentration dependences of the unit-cell parameters a and c for (TlInSe{sub 2}){sub 1-x}(TlGaTe{sub 2}){sub x} crystals are measured. Anomalies are found in the temperature dependences of the unit-cell parameters a and, correspondingly, the coefficient of thermal expansion, indicating the existence of phase transitions in TlInSe{sub 2} and TlGaTe{sub 2} crystals.

  14. Incoherent c-Axis Interplane Response of the Iron Chalcogenide FeTe0:55Se0:45 Superconductor from Infrared Spectroscopy

    SciTech Connect

    Gu, G.D.; Moon, S.J.; Homes, C.C.; Akrap, A.; Xu,, Z.J.; Wen, J.S.; Lin,, Z.W.; Li, Q.; Basov, D.N.

    2011-05-23

    We report on the interplane c-axis electronic response of FeTe{sub 0.55}Se{sub 0.45} investigated by infrared spectroscopy. We find that the normal-state c-axis electronic response of FeTe{sub 0.55}Se{sub 0.45} is incoherent and bears significant similarities to those of mildly underdoped cuprates. The c-axis optical conductivity {sigma}{sub c}({omega}) of FeTe{sub 0.55}Se{sub 0.45} does not display well-defined Drude response at all temperatures. As temperature decreases, {sigma}{sub c}({omega}) is continuously suppressed. The incoherent c-axis response is found to be related to the strong dissipation in the ab-plane transport: a pattern that holds true for various correlated materials as well as FeTe{sub 0.55}Se{sub 0.45}.

  15. 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}

    SciTech Connect

    Vats, Bal Govind; Phatak, Rohan; Krishnan, K.; Kannan, S.

    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) ? and c = 9.91861(17) ?. 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 site for bismuth (Bi) atom, one chromium rich (Cr/Te = 68/32), and one tellurium rich (Te/Cr = 68/32) sites, and one distinct site for oxygen (O) atom in the unit cell. All cations in this structure show an octahedral coordination with oxygen atoms at the corners. The thermogravimetric analysis (TGA) of the compound in air shows that it is stable up to 1103 K and decomposes thereafter. The thermal expansion behavior of Cr{sub 2}TeO{sub 6}, Bi{sub 2}TeO{sub 6} and BiCrTeO{sub 6} was studied using High Temperature X-ray diffraction (HTXRD) method from room temperature to 973, 873 and 923 K respectively under vacuum of 10{sup ?8} atmospheres. All the compounds showed positive thermal expansion with the average volume thermal expansion coefficients of 14.38 × 10{sup ?6}/K, 22.0 × 10{sup ?6}/K and 16.0 × 10{sup ?6}/K respectively.

  16. Competition and cooperativity between tetrel bond and chalcogen bond in complexes involving F2CX (X = Se and Te)

    NASA Astrophysics Data System (ADS)

    Guo, Xin; Liu, Yan-Wen; Li, Qing-Zhong; Li, Wen-Zuo; Cheng, Jian-Bo

    2015-01-01

    F2CX (X = Se and Te) have two Lewis acid sites of ?-hole and ?-hole located respectively in the vicinity of X and C ends, participating in the chalcogen and tetrel bonds with HCN and NH3, respectively. F2CSe forms a stronger tetrel bond, while F2CTe forms a stronger chalcogen bond. F2CX shows weaker tetrel and chalcogen bonds in the ternary system, exhibiting anticooperativity with some different features from positive one. The nature of two interactions and the origin of anticooperativity have been analyzed by means of energy decomposition, molecular electrostatic potential, and orbital interaction.

  17. Stable Four-Coordinate Guanidinatosilicon(IV) Complexes with SiN3 El Skeletons (El=S, Se, Te) and Si?El Double Bonds.

    PubMed

    Mück, Felix M; Kloß, Dorit; Baus, Johannes A; Burschka, Christian; Bertermann, Rüdiger; Poater, Jordi; Fonseca Guerra, Célia; Bickelhaupt, F Matthias; Tacke, Reinhold

    2015-09-28

    To get information about the reactivity profile of the donor-stabilized guanidinatosilicon(II) complexes 2 and 3, a series of oxidative addition reactions was studied. Treatment of 2 and 3 with S8 , Se, or Te afforded the respective four-coordinate silicon(IV) complexes 8-10 and 12-14, which contain an SiN3 El skeleton (El=S, Se, Te) with an Si?El double bond. Treatment of 2 with N2 O yielded the dinuclear four-coordinate silicon(IV) complex 11 with an SiN3 O skeleton and a central four-membered Si2 O2 ring. Compounds 8-14 exist both in the solid state and in solution. They were characterized by elemental analyses, NMR spectroscopic studies in the solid state and in solution, and crystal structure analyses. The reactivity profile of 2 was compared with that of the structurally related bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) (1), which is three-coordinate in the solid state and four-coordinate in solution (1'). In contrast, as shown by state-of-the-art relativistic DFT analyses and experimental studies, silylene 2 is three-coordinate both in the solid state and solution. The three-coordinate species 2 is 9.3?kcal?mol(-1) more stable in benzene than the four-coordinate isomer 2'. The reason for this was studied by bonding analyses of 2 and 2', which were compared with those of 1 and 1'. The gas-phase proton affinities of the relevant species in solution (1' and 2) amount to 288.8 and 273.8?kcal?mol(-1) , respectively. PMID:26284318

  18. Pseudo Jahn-Teller origin of puckering in cyclohexahomoatomic molecules E6 (E = S, Se, Te) and restoring S6 planar ring configuration

    NASA Astrophysics Data System (ADS)

    Ilkhani, Ali Reza

    2015-10-01

    The pseudo Jahn-Teller effect (PJTE) is employed to explore the origin of the puckering structure of cyclohexasulfur (S6), cyclohexaselenium (Se6) and cyclohexatellurium (Te6) and their nondegenerate and degenerate vibronic excited states and their planar structure instabilities have investigated. The ab initio geometry optimization and frequency calculations show that all these cyclohexahomoatomic molecules chose D6h symmetry in the planar con?guration, and according the S6 and Se6 experimental structure, the chair form of the molecules is stable structure. The vibronic coupling between the ground state 1A1g and excited state 1B2g is the cause of chair puckering in all these series compounds and the numerical solutions of the PJTE (1A1g+1B2g)?b2g problems describe their instability. The adiabatic potential energy surfaces (APES) cross sections of low-lying electronic states along the b2g puckering normal coordinates have calculated by the state-average complete active space self-consistent field (SA-CASSCF) method. The calculation results show that, the chair puckering instability in the S6 from unstable planar configuration with D6h symmetry to a stable D3d distorted geometry, is stronger than others, whereas it is weaker in Te6. Additionally, coordination two canions (X = H+, He2+) to the S6 chair structure restore the planarity of S6 puckered ring in the S6X2 systems, although the D6h symmetry in S6 planar ring configuration changes to the Cs symmetry in the systems.

  19. Development of a computer model for polycrystalline thin-film CuInSe sub 2 and CdTe solar cells

    SciTech Connect

    Gray, J.L.; Schwartz, R.J.; Lee, Y.J. )

    1992-04-01

    This report describes work to develop a highly accurate numerical model for CuInSe{sub 2} and CdTe solar cells. ADEPT (A Device Emulation Program and Toolbox), a one-dimensional semiconductor device simulation code developed at Purdue University, was used as the basis of this model. An additional objective was to use ADEPT to analyze the performance of existing and proposed CuInSe{sub 2} and CdTe solar cell structures. The work is being performed in two phases. The first phase involved collecting device performance parameters, cell structure information, and material parameters. This information was used to construct the basic models to simulate CuInSe{sub 2} and CdTe solar cells. This report is a tabulation of information gathered during the first phase of this project on the performance of existing CuInSe{sub 2} and CdTe solar cells, the material properties of CuInSr{sub 2}, CdTe, and CdS, and the optical absorption properties of CuInSe{sub 2}, CdTe, and CdS. The second phase will entail further development and the release of a version of ADEPT tailored to CuInSe{sub 2} and CdTe solar cells that can be run on a personal computer. In addition, ADEPT will be used to analyze the performance of existing and proposed CuInSe{sub 2} and CdTe solar cell structures. 110 refs.

  20. Thermoelectric Properties of Cu-Doped n-Type Bi2Te2.85Se0.15 Prepared by Liquid Phase Growth Using a Sliding Boat

    NASA Astrophysics Data System (ADS)

    Kitagawa, Hiroyuki; Matsuura, Tsukasa; Kato, Toshihito; Kamata, Kin-ya

    2015-06-01

    N-type Bi2Te2.85Se0.15 thermoelectric materials were prepared by liquid phase growth (LPG) using a sliding boat, a simple and short fabrication process for Bi2Te3-related materials. Cu was selected as a donor dopant, and its effect on thermoelectric properties was investigated. Thick sheets and bars of Cu x Bi2 Te2.85Se0.15 ( x=0-0.25) of 1-2mm in thickness were obtained using the process. X-ray diffraction patterns and scanning electron micrographs showed that the in-plane direction tended to correspond to the hexagonal c-plane, which is the preferred direction for thermoelectric conversion. Cu-doping was effective in controlling conduction type and carrier (electron) concentration. The conduction type was p-type for undoped Bi2Te2.85Se0.15 and became n-type after Cu-doping. The Hall carrier concentration was increased by Cu-doping. Small resistivity was achieved in Cu0.02Bi2Te2.85Se0.15 owing to an optimized amount of Cu-doping and high crystal orientation. As a result, the maximum power factor near 310K for Cu0.02Bi2Te2.85Se0.15 was approximately 4×10-3W/K2m and had good reproducibility. Furthermore, the thermal stability of Cu0.02Bi2Te2.85Se0.15 was also confirmed by thermal cycling measurements of electrical resistivity. Thus, n-type Bi2Te2.85Se0.15 with a large power factor was prepared using the present LPG process.

  1. Selenium and Tellurium concentrations of ultradepleted peridotites determined by isotope dilution ICPMS: implications for Se-Te systematics of the Earth's mantle

    NASA Astrophysics Data System (ADS)

    König, S.; Luguet, A.; Lorand, J.-P.; Wombacher, F.; Lissner, M.

    2012-04-01

    As for highly siderophile elements, selenium and tellurium may constitute key tracers for planetary processes such as formation of the Earth's core and the Late Veneer composition, provided that their geochemical behaviour and abundances in the primitive upper mantle (PUM) are constrained. Within this scope, we have developed a high precision analytical method for the simultaneous determination of selenium and tellurium concentrations from a single sample aliquot and various rock matrices, including ultradepleted peridotites. The technique employs isotope dilution, thiol cotton fiber (TCF) separation and hydride generation MC-ICP-MS. A selection of international mafic and ultramafic rock reference materials BIR-1, BE-N, TDB-1, UB-N, FON B 93, BIR-1 and BHVO-2 with a range of 30 to 350 ppb Se and 0.7 to 12 ppb Te show external reproducibilities of 3 to 8% for Se and 0.4 to 11% for Te (2 relative standard deviations (r.s.d.)). We have applied this method to a suite of refractory mantle peridotites (Al2O3 <1.5 wt. %) from Lherz, previously shown to be strongly and uniformly depleted in Se, Te and incompatible elements by high degree of partial melting (20 ± 5%). In contrast to fertile lherzolites which remain at broadly chondritic values (Se/Te = 9), the ultradepleted harzburgites show highly fractionated and up to suprachondritic Se/Te (< 35) that correlate with decreasing Te concentrations. The fractionation is displayed by the depleted peridotites as well as multiple analysis of a single Lherz harzburgite sample (64-3). This shows 1) a strong sample heterogeneity effect for Te and 2) a more incompatible behaviour of Te compared to Se on the whole rock scale, once base metal sulfides are highly depleted and in some cases entirely consumed by partial melting. The marked differences in Se-Te systematics observed between fertile lherzolites and depleted harzburgites can be explained by the combined effect of i) different abundances and proportions of residual and metasomatic base metal sulfides ii) discrete micrometric platinum-group minerals. In addition to re-fertilized lherzolites, harzburgites therefore offer new insights into the behaviour of Se and Te during mantle depletion which is a prerequisite to further constrain the Se and Te abundances of the primitive upper mantle.

  2. Towards a predictive route for selection of doping elements for the thermoelectric compound PbTe from first-principles

    SciTech Connect

    Joseph, Elad; Amouyal, Yaron

    2015-05-07

    Striving for improvements of the thermoelectric (TE) properties of the technologically important lead telluride (PbTe) compound, we investigate the influence of different doping elements on the thermal conductivity, Seebeck coefficient, and electrical conductivity applying density functional theory calculations. Our approach combines total-energy calculations yielding lattice vibrational properties with the Boltzmann transport theory to obtain electronic transport properties. We find that doping with elements from the 1st and 3rd columns of the periodic table reduces the sound velocity and, consequently, the lattice thermal conductivity, while 2nd column dopants have no such influence. Furthermore, 1.6 at.?% doping with 4th and 5th column elements provides the highest reduction of lattice thermal conductivity. Out of this group, Hf doping results in maximum reduction of the sound velocity from 2030?m s{sup ?1} for pure PbTe to 1370?m s{sup ?1}, which is equivalent to ca. 32% reduction of lattice thermal conductivity. The highest power factor values calculated for 1.6 at.?% doping range between 40 and 56??W cm{sup ?1} K{sup ?2}, and are obtained for substitution with dopants having the same valence as Pb or Te, such as those located at the 2nd, 14th, and 16th columns of the periodic table. We demonstrate how this method may be generalized for dopant-selection-oriented materials design aimed at improving TE performance of other compounds.

  3. Ab initio study of point defects in PbSe and PbTe: Bulk and nanowire

    SciTech Connect

    Wrasse, E. O.; Venezuela, P.; Baierle, R. J.

    2014-11-14

    First principles investigations, within the spin-polarized density functional theory, are performed to study energetic stability and electronic properties of point defects (vacancies and antisites) in PbSe and PbTe: bulk and nanowire (NW). Our results show that the energetic stability of these defects is ruled by relaxation process. These defects have lower formation energies in the nanowire structures as compared to the bulk, being more stable in the surface of the NWs. We also show that in the bulk system only one charge state is stable, otherwise, due to the larger band gaps, more than one charge state may be stable in the NWs. In addition, we have investigated how the presence of intrinsic defects affects the electronic properties of bulk and NW systems. Vacancies give rise to new electronic states near to the edges of the valence and conduction bands while the energetic position of the electronic states from antisites depends on the charge state, being localized inside the band gap or near the edges of the valence or conduction bands. We discuss how these changes in the electronic properties due to intrinsic defects may affect the thermoelectric properties of PbSe and PbTe NWs.

  4. Effect of Sn Doping on the Thermoelectric Properties of n-type Bi2(Te,Se)3 Alloys

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Uk; Lee, Deuk-Hee; Kwon, Beomjin; Hyun, Dow-Bin; Nahm, Sahn; Baek, Seung-Hyub; Kim, Jin-Sang

    2015-06-01

    In the present work, 0.01-0.05wt.% Sn-doped Bi2(Te0.9Se0.1)3 alloys were prepared by mechanical deformation followed by hot pressing, and their thermoelectric properties were studied. We observed that the Sn element is a very effective dopant as an acceptor to control the carrier concentration in the n-type Bi2(Te0.9Se0.1)3 alloys to optimize their thermoelectric property. The n-type carrier concentration can be controlled from 4.2 × 1019/cm3 to 2.4 × 1019/cm3 by 0.05wt.% Sn-doping. While the Seebeck coefficient and the electrical resistivity are both increased with doping, the power factor remains the same. Therefore, we found that the thermoelectric figure-of-merit becomes maximized at 0.75 when the thermal conductivity has a minimum value for the 0.03wt.% Sn-doped sample.

  5. Surface origin of quasi-2D Shubnikov-de Haas oscillations in Bi2Te2Se

    NASA Astrophysics Data System (ADS)

    Kapustin, A. A.; Stolyarov, V. S.; Bozhko, S. I.; Borisenko, D. N.; Kolesnikov, N. N.

    2015-08-01

    Transport measurements at liquid helium temperatures were done on a number of Bi2Te2Se samples with thicknesses ranging from 30 to 200 ?m 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 Bi2Te2Se 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.

  6. Application of CdTe/ZnSe quantum dots in in vitro imaging of chicken tissue and embryo.

    PubMed

    Moulick, Amitava; Blazkova, Iva; Milosavljevic, Vedran; Fohlerova, Zdenka; Hubalek, Jaromir; Kopel, Pavel; Vaculovicova, Marketa; Adam, Vojtech; Kizek, Rene

    2015-01-01

    The present work is aimed to synthesize CdTe/ZnSe core/shell quantum dots (QDs) in an easy way and to explore the possibilities of its application in in vitro imaging of chicken tissue and embryo. The QDs were prepared using microwave irradiation with different temperatures, which is a very easy and less time-consuming method. Subsequently, these QDs were characterized by spectrofluorimetry, Transmission Electron Microscopy, X-ray fluorescence analysis and Dynamic Light Scattering measurement. A blueshifting of the emission was found when ZnSe was deposited on CdTe QDs. The QDs showed its fluorescence emission quantum yields up to 25%. They were applied into chicken embryos and breast muscle tissues to study their efficiency in in vitro imaging. All the QDs of different color were able to visualize in in vitro imaging. The highest fluorescence intensity was detected in the case of red QDs prepared at 100°C. The green and red QDs were possible to detect up to the depth of 3 and 4 mm of the tissue, respectively. PMID:25476270

  7. New bi-epitaxial Grain boundary Josephson Junction of FeSe0.3Te0.7

    NASA Astrophysics Data System (ADS)

    Li, You-Sheng; Shen, Y. T.; Wang, M. J.; Wu, M. K.; Chi, C. C.

    2013-03-01

    We have successfully fabricated epitaxial FeSe0.3Te0.7films on MgO substrate with its in-plane crystalline axis either parallel to or rotated 45° with respect to the MgO lattice. We use this technique to fabricate the 45° grain-boundary Josephson junction. The IV-curve measured at 4.2 K can be fitted with the RSJ model, and the measured IcRnvalue is 9.24 ?V, which is in general agreement with the values obtained by previous results for Fe-based grainboundary junctions on bi-crystal substrates. We have also measured the dc Josephson current as a function of applied magnetic fields, which shows a clear Fraunhofer-like pattern. Hence we can rule out the possibility of d-wave symmetry in FeSe0.3Te0.7 superconductor. Upon applying 6 GHz microwave irradiation, the junction IV curve exhibits clear Shapiro steps. Thus we have demonstrated our ability to fabricate high quality grain-boundary Josephson junctions of this new class of material. Further physical properties, such as the noise power spectrum, are currently being investigated. We would like to acknowledge the support from grants of NSC 101-2112-M-007-013 and NSC 99-2112-M-001-028-MY3

  8. Compound

    NASA Astrophysics Data System (ADS)

    Suzumura, Akitoshi; Watanabe, Masaki; Nagasako, Naoyuki; Asahi, Ryoji

    2014-06-01

    Recently, Cu-based chalcogenides such as Cu3SbSe4, Cu2Se, and Cu2SnSe3 have attracted much attention because of their high thermoelectric performance and their common feature of very low thermal conductivity. However, for practical use, materials without toxic elements such as selenium are preferable. In this paper, we report Se-free Cu3SbS4 thermoelectric material and improvement of its figure of merit ( ZT) by chemical substitutions. Substitutions of 3 at.% Ag for Cu and 2 at.% Ge for Sb lead to significant reductions in the thermal conductivity by 37% and 22%, respectively. These substitutions do not sacrifice the power factor, thus resulting in enhancement of the ZT value. The sensitivity of the thermal conductivity to chemical substitutions in these compounds is discussed in terms of the calculated phonon dispersion and previously proposed models for Cu-based chalcogenides. To improve the power factor, we optimize the hole carrier concentration by substitution of Ge for Sb, achieving a power factor of 16 ?W/cm K2 at 573 K, which is better than the best reported for Se-based Cu3SbSe4 compounds.

  9. Se-Te fractionation by sulfide-silicate melt partitioning: Implications for the composition of mantle-derived magmas and their melting residues

    NASA Astrophysics Data System (ADS)

    Brenan, James M.

    2015-07-01

    Partitioning of Se and Te has been measured between coexisting sulfide liquid, monosulfide solid solution (MSS) and silicate melt at 0.9-1.5 GPa, 1200-1300 °C, fO2 controlled near the fayalite-magnetite-quartz buffer (FMQ-1.2 to -1.6) and 3-22 wt% FeO in the silicate melt. Both elements are highly compatible in the sulfide phase relative to silicate liquid (Dsulfide phase/silicate liquid > 600), with the identity of the sulfide dictating the sense of Se-Te fractionation. Whereas the measured DTe/DSe is ?5-9 for sulfide liquid/silicate liquid partitioning, MSS/silicate melt partitioning fractionates Te from Se in the opposite sense, with DTe/DSe of ?0.5-0.8. At fixed fO2, DSulLiq/SilLiq values for both Se and Te decrease ?8-fold over the range in silicate melt FeO content investigated. The relative values of DSulLiq/SilLiq for Cu to Se increase with increasing FeO in the silicate melt, such that DCu exceeds DSe only for melts with >11 wt% FeO. Hence the standard belief that DCu >DSe as indicative of sulfide removal should be carefully assessed in the context of the FeO content of the magmas involved. Assuming a chondritic mantle Se/Te, predicted MSS and sulfide liquid compositions are generally in accord with natural mantle sulfides, in terms of their designation as MSS or sulfide liquid, based on independent criteria. However, additional variability is likely due to Te redistribution in accessory platinum group minerals (PGM), or that some sulfides are metasomatic. Calculations show that the Se/Te ratio of silicate melt derived from a sulfide liquid-saturated mantle is significantly higher, and more variable, than for silicate melt in equilibrium with residual MSS; modest sulfide liquid removal at low pressure, however, likely obscures the Se/Te fractionation imposed by the source sulfide phase. Models indicate that the composition of MORB is consistent with melts produced from sulfide-bearing sources with chondritic Se/Te, and source sulfur contents higher than estimates for depleted mantle. The calculated composition of sulfide-saturated melting residues show relatively little deviation in Se/Te if MSS is residual, but a sharp drop in this ratio for sulfide liquid control. Although the data are scattered, a portion of the peridotite array near the primitive mantle composition is consistent with model trends, and suggests control by residual MSS.

  10. 187Re-187Os systematics, highly siderophile element, S-Se-Te abundances in the components of unequilibrated L chondrites

    NASA Astrophysics Data System (ADS)

    Kadlag, Yogita; Becker, Harry

    2016-01-01

    The 187Re-187Os systematics, abundances of highly siderophile elements (HSE: Re, platinum group elements and Au), Te, Se and S as well as major and minor elements were determined in separated components of two unequilibrated L chondrites QUE 97008 (L3.05) and Ceniceros (L3.7). The 187Re-187Os systematics are disturbed in the components of both meteorites, most likely due to open system behavior of Re during terrestrial weathering of QUE 97008 and alteration on the L chondrite parent body as indicated by an internal errorchron generated for components of Ceniceros. The HSE abundance patterns suggest that the bulk rock abundances were mainly controlled by two different end members. Non-magnetic fractions display lower Re/Os and HSE/Ir than CI chondrites. Chondrules, metal-troilite spherules and fine magnetic fractions, are depleted in refractory HSE and show higher Rh/Ir, Pd/Ir and Au/Ir than in CI chondrites. The different HSE compositions indicate the presence of unequilibrated alloys and loss of refractory HSE-rich carrier phases from the precursors of some L chondrite components. Gold is decoupled from other HSE in magnetic fractions and shows chalcophile affinities with a grain size dependent variation similar to S and Se, presumably inherited from preaccretionary processes. Tellurium is depleted in all components compared to other analysed siderophile elements, and its abundance was most likely controlled by fractional condensation and different geochemical affinities. The volatility dependent depletion of Te requires different physical and chemical conditions than typical for the canonical condensation sequence as represented by carbonaceous chondrites. Tellurium also shows variable geochemical behavior, siderophile in Ceniceros, predominantly chalcophile in QUE 97008. These differences may have been inherited from element partitioning during chondrule formation. Selenium and S on the other hand are almost unfractionated from each other and only show complementary S/Se in a few components, presumably due to the effects of volatility or metal-silicate partitioning during chondrule formation. Terrestrial weathering had negligible effects on the S, Se and Te systematics.

  11. Anisotropic thermoelectric properties of layered compounds in SnX2 (X = S, Se): a promising thermoelectric material.

    PubMed

    Sun, Bao-Zhen; Ma, Zuju; He, Chao; Wu, Kechen

    2015-11-28

    Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 ?W cm(-1) K(-2) along the a direction, while a relatively low value (11.72 ?W cm(-1) K(-2)) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (?min) along the a direction is estimated to be about 0.67 and 0.55 W m(-1) K(-1) for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m(-1) K(-1) at 300 K). The reasonable PF and ?min suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 10(19) (SnSe2) vs. 2.87 × 10(19) cm(-3) (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials. PMID:26486877

  12. First-principles calculation of the bulk photovoltaic effect in the polar compounds LiAsS2, LiAsSe2, and NaAsSe2

    E-print Network

    Rappe, Andrew M.

    First-principles calculation of the bulk photovoltaic effect in the polar compounds LiAsS2, LiAsSe2 (2014) First-principles calculation of the bulk photovoltaic effect in the polar compounds LiAsS2, Li mechanism for the bulk photovoltaic effect, for the polar compounds LiAsS2, LiAsSe2, and NaAsSe2. We find

  13. Cadmium telluride (CdTe) and cadmium selenide (CdSe) leaching behavior and surface chemistry in response to pH and O2.

    PubMed

    Zeng, Chao; Ramos-Ruiz, Adriana; Field, Jim A; Sierra-Alvarez, Reyes

    2015-05-01

    Cadmium telluride (CdTe) and cadmium selenide (CdSe) are increasingly being applied in photovoltaic solar cells and electronic components. A major concern is the public health and ecological risks associated with the potential release of toxic cadmium, tellurium, and/or selenium species. In this study, different tests were applied to investigate the leaching behavior of CdTe and CdSe in solutions simulating landfill leachate. CdTe showed a comparatively high leaching potential. In the Toxicity Characteristic Leaching Procedure (TCLP) and Waste Extraction Test (WET), the concentrations of cadmium released from CdTe were about 1500 and 260 times higher than the regulatory limit (1 mg/L). In contrast, CdSe was relatively stable and dissolved selenium in both leaching tests was below the regulatory limit (1 mg/L). Nonetheless, the regulatory limit for cadmium was exceeded by 5- to 6- fold in both tests. Experiments performed under different pH and redox conditions confirmed a marked enhancement in CdTe and CdSe dissolution both at acidic pH and under aerobic conditions. These findings are in agreement with thermodynamic predictions. Taken as a whole, the results indicate that recycling of decommissioned CdTe-containing devices is desirable to prevent the potential environmental release of toxic cadmium and tellurium in municipal landfills. PMID:25710599

  14. Syntheses, crystal structures and characterizations of BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}

    SciTech Connect

    Jiang Hailong; Feng Meiling; Mao Jianggao . E-mail: mjg@ms.fjirsm.ac.cn

    2006-06-15

    Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by the solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with three ZnO{sub 3}Cl tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements. -- Graphical abstract: Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features 1D double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The 1D double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with one ZnO{sub 3}Cl and two ZnO{sub 2}Cl{sub 2} tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements.

  15. Improved power conversion efficiency for bulk heterojunction solar cells incorporating CdTe-CdSe nanoheterostructure acceptors and a conjugated polymer donor

    NASA Astrophysics Data System (ADS)

    Dayal, Smita; Zhong, Haizheng; Kopidakis, Nikos; Scholes, Gregory D.; Rumbles, Garry

    2015-01-01

    We report photovoltaic devices based on composites of a branched nanoheterostructure containing a CdTe core and CdSe arms, CdTe(c)-CdSe(a), combined with either poly(3-hexylthiophene), P3HT, or poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b3,4-b?]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT, with solar power conversion efficiencies of 1.2% and 1.8%, respectively. A comparison with previously reported composite devices of a related branched nanoheterostructure: CdSe(c)-CdTe(a) reveals an improved device performance that is attributed to a better electron percolation pathway provided by the dominant, higher electron affinity CdSe arms of the nanoheterostructures.

  16. Synthesis and Optical Properties of CdTe(x)Se(1-x)-Based Red to Near-Infrared Emitting Quantum Dots.

    PubMed

    Ma, Qian; Yue, Hanxiao; Zhu, Yuanna; Wang, Junpeng; Che, Quande; Shi, Ruixia; Yang, Ping

    2015-06-01

    A series of red to near-infrared (NIR) emitting quantum dots (QDs) with spherical morphologies and tunable photoluminescence (PL) properties have been synthesized by a facile organic route using octadecene (ODE) as solvent and oleic acid (OA) as single capping agent. CdSe cores with the average size of 4.5 nm display the typical optical behaviors with the PL emission peak around 610 nm. The coating CdZnS shells are introduced on the surface of CdSe cores for improving the photostability and PL efficiency of the initial QDs. As the thickness of CdZnS shells increasing, the gradual red-shift of emission wavelength varying from 617 to 634 nm of the resulting QDs can be observed, along with the remarkable increase of PL quantum yield (QY). The composition-dependent CdTe(x)Se(1-x) (CdTeSe) cores with the emission in NIR region are easily carried out by adjusting the molar ratio of Se/Te. The abnormal variation of optical bowling effect is mainly ascribed to the composition effect of alloyed QDs. Compared with CdTe0.1Se0.9/CdZnS core/shell QDs, the introducing of CdZnS shells on CdTe0.05Se0.95 cores can exhibit better passivation effect on surface status, consequently leading to the red-shifted emission peaks in the range of 739-752 nm with the maximum PL QY reaching up to 45.09%. The unique PL properties of CdTeSe-based QDs in the red to NIR range make these core/shell QDs attractive for future biological sensing and labeling applications. PMID:26369063

  17. The influence of capping thioalkyl acid on the growth and photoluminescence efficiency of CdTe and CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Aldeek, Fadi; Balan, Lavinia; Lambert, Jacques; Schneider, Raphaël

    2008-11-01

    The influence of thioalkyl acid ligand was evaluated during aqueous synthesis at 100 °C and under hydrothermal conditions (150 °C) of CdTe and CdSe quantum dots (QDs). Experiments performed with 3-mercaptopropionic acid (MPA), 6-mercaptohexanoic acid (MHA) and 11-mercaptoundecanoic acid (MUA) demonstrated that the use of MHA and MUA allowed for the preparation of very small nanoparticles (0.6-2.5 nm) in carrying out the reaction under atmospheric pressure or in an autoclave and that the photophysical properties of QDs were dependent on the ligand and on the synthesis conditions. The influence of various experimental conditions, including the Te-to-Cd ratio, temperature, and precursor concentration, on the growth rate of CdTe or CdSe QDs has been systematically investigated. The fluorescence intensities of CdTe QDs capped with MPA, MHA, or MUA versus pH were also found to be related to the surface coverage of the nanoparticles.

  18. Effect of Se treatment on glucosinolate metabolism and health-promoting compounds in the broccoli sprouts of three cultivars.

    PubMed

    Tian, Ming; Xu, Xiaoyun; Liu, Yanlong; Xie, Lin; Pan, Siyi

    2016-01-01

    Broccoli sprouts are natural functional foods for cancer prevention because of their high glucosinolate (GSL) content and high selenium (Se) accumulation capacity. The regulation mechanism of Se on GSL metabolism in broccoli sprouts was explored. In particular, the effects of Se treatment (100 ?mol/L selenite and selenate) on the Se, sulfur (S), glucosinolate and sulforaphane contents; myrosinase activity and health-promoting compounds (ascorbic acid, anthocyanin, total phenolics and flavonoids) of three, 5 day old, cultivars were investigated. The treatment did not influence the total GSL and ascorbic acid contents; significantly increased the myrosinase activity and sulforaphane, anthocyanin and flavonoids contents; and decreased the total phenolics content. The increase in sulforaphane during early growth can be primarily attributed to the increased myrosinase activity caused by Se treatment. Broccoli sprouts with suitable selenite and selenate concentrations, in the early growth days, could be desirable for improved human health. PMID:26212985

  19. In-Situ Optical Determination of Thermomechanical Properties of ZnSe and ZnTe Crystals

    NASA Technical Reports Server (NTRS)

    Burger, A.; Ndap, J.-O.; Chattopadhyay, K.; Ma, X.; Silberman, E.; Feth, S.; Palosz, W.; Su, C.-H.

    1999-01-01

    At temperatures above 1/2 T(sub m), the generation and movement of dislocations may result due to the load created by the weight of the crystal itself The deformation may be expected to increase the line defect density and may result in generation of low angle grain boundaries, especially in the regions of the crystal attached to the ampule. It has often been suspected that elimination of this effect in space can improve crystallinity of crystals grown under microgravity conditions, however, a direct experimental proof of such relation is still missing. In this work we have designed and built a system of in-situ optical detection and measurement of the mechanical deformations of a crystal wafer under its own weight, and studied the deformation effects as a function of temperature. The results of the measurements for ZnSe and ZnTe crystal wafers will be presented.

  20. Laser operation by dissociation of metal complexes. II - New transitions in Cd, Fe, Ni, Se, Sn, Te, V, and Zn

    NASA Technical Reports Server (NTRS)

    Chou, M. S.; Cool, T. A.

    1977-01-01

    The reported investigation is a continuation of a study conducted by Chou and Cool (1976). The experimental results discussed are partly related to laser transitions in Cd(I), Cd(II), and Zn(II). Laser transitions in Fe(I), Ni(I), Sn(I), Te(I), and V(I) are also considered along with the observation of a laser pulse with two peaks in connection with the study of laser transitions in Se(I). Experiments related to prospective visible laser operation in thallium at 6550 and 6714 are also discussed, giving attention to spontaneous emission measurements at 6550 and 5350 A, the effects of additive molecules, and laser cavity experiments at 6550 and 6714 A.

  1. Evidence for orbital order and its relation to superconductivity in FeSe0.4Te0.6

    PubMed Central

    Singh, Udai R.; White, Seth C.; Schmaus, Stefan; Tsurkan, Vladimir; Loidl, Alois; Deisenhofer, Joachim; Wahl, Peter

    2015-01-01

    The emergence of nematic electronic states accompanied by a structural phase transition is a recurring theme in many correlated electron materials, including the high-temperature copper oxide– and iron-based superconductors. We provide evidence for nematic electronic states in the iron-chalcogenide superconductor FeSe0.4Te0.6 from quasi-particle scattering detected in spectroscopic maps. The symmetry-breaking states persist above Tc into the normal state. We interpret the scattering patterns by comparison with quasi-particle interference patterns obtained from a tight-binding model, accounting for orbital ordering. The relation to superconductivity and the influence on the coherence length are discussed. PMID:26601277

  2. Vertical/Planar Growth and Surface Orientation of Bi2Te3 and Bi2Se3 Topological Insulator Nanoplates.

    PubMed

    Jiang, Ying; Zhang, Xun; Wang, Yong; Wang, Na; West, Damien; Zhang, Shengbai; Zhang, Ze

    2015-05-13

    Nanostructures are not only attractive for fundamental research but also offer great promise for bottom-up nanofabrications. In the past, the growth of one-dimensional vertical/planar nanomaterials such as nanowires has made significant progresses. However, works on two-dimensional nanomaterials are still lacking, especially for those grown out of a substrate. We report here a vertical growth of topological insulator, Bi2Se3 and Bi2Te3, nanoplates on mica. In stark contrast to the general belief, these nanoplates are not prisms exposing (100) lateral surfaces, which are expected to minimize the surface area. Instead, they are frustums, enclosed by (01-4), (015), and (001) facets. First-principles calculations, combined with experiments, suggest the importance of surface oxidation in forming these unexpected surfaces. PMID:25919088

  3. Electronic and mechanical properties of ZnX (X = S, Se and Te)--An ab initio study

    SciTech Connect

    Verma, Ajay Singh; Sharma, Sheetal; Jindal, Vijay Kumar; Sarkar, Bimal Kumar

    2011-12-12

    Zinc chalcogenides (ZnX, X = S, Se and Te) have been increasing attention as wide and direct band gap semiconductor for blue and ultraviolet optical devices. This paper analyzes electronic and mechanical properties of these materials by ab initio pseudo-potential method that uses non conserving pseudopotentials in fully nonlocal form, as implemented in SIESTA code. In this approach the local density approximation (LDA) is used for the exchange-correlation (XC) potential. The calculations are given for band gap, elastic constants (C{sub 11}, C{sub 12} and C{sub 44}), shear modulus, and Young's modulus. The results are in very good agreement with previous theoretical calculations and available experimental data.

  4. Magnetotransport properties and Seebeck effect in the superconductor FeSe0.5Te0.5

    NASA Astrophysics Data System (ADS)

    Pimentel, J. L., Jr.; Pureur, P.; Avila, M. A.; Ribeiro, R. A.

    2014-04-01

    We carried out measurements of the electrical resistivity, magnetoresistance, Hall resistivity and Seebeck effect in a highly oriented sample of the Fe-based FeSe0.5Te0.5 superconductor. Complementary structural and magnetic characterizations were also performed. Our sample do not show long-range magnetic order down to 4.2 K. Superconductivity occurs with critical temperature Tc ? 15 K. In the normal phase, the resistivity versus temperature behavior mimics that of a Kondo-lattice system. The magnetoresistance, Hall coefficient and Seebeck coefficient show sign reversals. These results are discussed with basis on the combined effects from two-band conduction and weak magnetic fluctuations. Effects from superconducting fluctuations are also observed near Tc.

  5. Vapour phase growth and surface topography of ( ZnSe) x( CdTe) 1- x single crystals

    NASA Astrophysics Data System (ADS)

    Chandrasekharam, P.; Raja Reddy, D.; Reddy, B. K.

    1983-10-01

    Single crystals—a few centimetres in length and 5 mm in diameter—of the ( ZnSe) x( CdTe) 1- x system have been grown in the entire range of composition (0.00? x ? 1.00) using a self-sealing vapour phase growth technique. The optimum growth conditions for these crystals have been established. One hollow crystal with composition x=0.40 has been obtained. Growth spirals were observed on all the mixed crystals, suggesting a screw dislocation mechanism of crystal growth. The room temperature conductivity of these crystals decreased as the composition x is increased. The energy gap of these crystals varied nonlinearly with composition. All the crystals with x?0.60 were p-type and the remaining were n-type.

  6. Electrically tunable in-plane anisotropic magnetoresistance in topological insulator BiSbTeSe2 nanodevices.

    PubMed

    Sulaev, Azat; Zeng, Minggang; Shen, Shun-Qing; Cho, Soon Khuen; Zhu, Wei Guang; Feng, Yuan Ping; Eremeev, Sergey V; Kawazoe, Yoshiyuki; Shen, Lei; Wang, Lan

    2015-03-11

    We report tunable in-plane anisotropic magnetoresistance (AMR) in nanodevices based on topological insulator BiSbTeSe2 (BSTS) nanoflakes by electric gating. The AMR can be changed continuously from negative to positive when the Fermi level is manipulated to cross the Dirac point by an applied gate electric field. We also discuss effects of the gate electric field, current density, and magnetic field on the in-plane AMR with a simple physical model, which is based on the in-plane magnetic field induced shift of the spin-momentum locked topological two surface states that are coupled through side surfaces and bulk weak antilocalization (WAL). The large, tunable and bipolar in-plane AMR in BSTS devices provides the possibility of fabricating more sensitive logic and magnetic random access memory AMR devices. PMID:25665017

  7. A ZnSe/BeTe p-grading superlattice with a low voltage drop for efficient hole injection in green-yellow BeZnCdSe quantum well laser

    NASA Astrophysics Data System (ADS)

    Akimoto, R.

    2015-03-01

    A ZnSe/BeTe p-grading superlattice (p-GSL) with a low voltage drop is reported for BeZnCdSe quantum well laser diode (LD) in green-yellow visible range. A p-GSL is inserted between a p+-BeTe for ohmic contact layer and a ZnSe/BeMgZnSe p-cladding layer in a LD, for an efficient hole injection in spite of a large potential barrier height of ~0.8 eV between these layers. A GSL design has hence a great impact on a threshold voltage of lasing and thus reliability in LDs. Simple p-n junction devices with various GSL designs are fabricated, where a p-n junction is formed between p-ZnSe and a n-GaAs. In a p-GSL where a pair of ZnSe/BeTe is repeated, BeTe thickness increases with fixed monolayer (ML) step, while ZnSe thickness decreases with the same step when next pair of ZnSe/BeTe is grown. While a grading of 1 ML step is used in the previous LDs, the new GSL design with smaller grading step of 0.5 ML gives a 2 V lower voltage at 200 A/cm2 current injection. Then, LDs characteristics are compared with the GSL of new and old designs, while other layers in LDs are kept nearly identical, which is confirmed by a similar threshold current of ~80 mA and an emission wavelength at ~540 nm in these LDs. The LD with the new GSL design showed a lower threshold voltage for a lasing as well as a higher output power due to a lower device heating.

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

    NASA Astrophysics Data System (ADS)

    Güler-K?l?ç, Sümeyra; K?l?ç, ?etin

    2015-06-01

    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 of van der Waals dispersion. It is found for BiTeI and AuTeI that the energy versus volume curve is anomalously flat in the vicinity of equilibrium volume and the calculated equation of state has an excessively steep slope in the low-pressure region; these are also fixed in the dispersion-corrected calculations. Analysis based on the computation of the volume and axial compressibilities shows that predicting the anisotropy of BiTeI via the semilocal calculations yields an unrealistic result, whereas the results of dispersion-corrected calculations agree with the experimental compressibility data. Our calculations render that BiTeI (AuTeI) is a narrow band gap semiconductor with Rashba-type spin splitting at the band edges (with an indirect band gap) while PdTeI is a metal with relatively low density of states at the Fermi level. The band gaps of BiTeI and AuTeI obtained via semilocal (dispersion-corrected) calculations are found to be greater (smaller) than the respective experimental values, which is against (in line with) the expected trend. Similarly, the Rashba parameters of BiTeI are bracketed by the respective values obtained via semilocal and dispersion-corrected calculations, e.g., a larger value for the Rashba parameter ?R is obtained in association with the reduction of the band gap caused by modification of the crystal structure owing to van der Waals attraction. Excellent agreement with the experimental Rashba parameters is obtained via interpolation of the calculated (semilocal and dispersion-corrected) values.

  9. Fusarium oxysporum induces the production of proteins and volatile organic compounds by Trichoderma harzianum T-E5.

    PubMed

    Zhang, Fengge; Yang, Xingming; Ran, Wei; Shen, Qirong

    2014-10-01

    Trichoderma species have been used widely as biocontrol agents for the suppression of soil-borne pathogens. However, some antagonistic mechanisms of Trichoderma are not well characterized. In this study, a series of laboratory experiments were designed to characterize the importance of mycoparasitism, exoenzymes, and volatile organic compounds (VOCs) by Trichoderma harzianum T-E5 for the control of Fusarium oxysporum f. sp. cucumerinum (FOC). We further tested whether these mechanisms were inducible and upregulated in presence of FOC. The results were as follows: T-E5 heavily parasitized FOC by coiling and twisting the entire mycelium of the pathogen in dual cultures. T-E5 growing medium conditioned with deactivated FOC (T2) showed more proteins and higher cell wall-degrading enzyme activities than T1, suggesting that FOC could induce the upregulation of exoenzymes. The presence of deactivated FOC (T2') also resulted in the upregulation of VOCs that five and eight different types T-E5-derived VOCs were identified from T1' and T2', respectively. Further, the excreted VOCs in T2' showed significantly higher antifungal activities against FOC than T1'. In conclusion, mycoparasitism of T-E5 against FOC involved mycelium contact and the production of complex extracellular substances. Together, these data provide clues to help further clarify the interactions between these fungi. PMID:25135494

  10. Manipulation of structural and optical properties in charge-separating ZnTe/ZnSe chalcogenide core/shell semiconductor nanocrystals: Atomistic tight-binding theory

    NASA Astrophysics Data System (ADS)

    Sukkabot, Worasak

    2015-11-01

    The atomistic tight-binding theory (TB) is utilized to study the electronic structures and optical properties of type-II ZnTe/ZnSe chalcogenide core/shell nanocrystals. The purpose of the present study is to theoretically understand the atomistic impact of the ZnSe growth shell on the single-particle spectra, charge densities, optical band gaps, electron-hole overlaps and oscillation strengths. The sensitivity of ZnSe growth shell thickness in analyzing the electronic structures and optical properties of ZnTe/ZnSe core/shell nanocrystals reflects the charge separation of type-II band alignment. The comprehensive calculations of ZnTe/ZnSe core/shell nanocrystals are effectively manipulated by including and changing the ZnSe growth shell thickness. As a comparison, the atomistic tight-binding calculations demonstrate a reasonable agreement with effective mass approximation and experiment. Finally, the computations successfully discover the important factors of the growth shell on the natural behaviors of type-II ZnTe/ZnSe core/shell nanocrystals which affords a guideline to be implemented to the novel electronic cadmium-free nanodevices and the environmentally friendly applications.

  11. Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te).

    PubMed

    Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J C Séamus; Ghigo, Gianluca; Gu, Genda D; Kwok, Wai-Kwong

    2015-05-01

    Maximizing the sustainable supercurrent density, J C, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because J C amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSe x Te1-x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or "columnar defects," plus a higher density of single atomic site "point" defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields. PMID:26601180

  12. Significance of the whole rock Re-Os ages in cryptically and modally metasomatised cratonic peridotites: Constraints from HSE-Se-Te systematics

    NASA Astrophysics Data System (ADS)

    Luguet, Ambre; Behrens, Melanie; Pearson, D. Graham; König, Stephan; Herwartz, Daniel

    2015-09-01

    The Re-Os isotopic system is the geochronometer of choice to constrain the timing of lithospheric mantle root formation and reconstruct the evolution of Earth's dynamics from the "mantle" perspective. In order to constrain the effects of metasomatic processes on the Re-Os isotopic system, eleven peridotites from the Letlhakane kimberlite pipe were investigated for whole rock major and trace elements, highly siderophile elements (HSE), Se, Te and 187Os/188Os signatures. These spinel peridotites (SP), garnet peridotites (GP), garnet-phlogopite peridotites (GPP) and phlogopite peridotites (PP) experienced cryptic metasomatism and the GP-GPP-PP additionally constitute a sequence of increasing modal metasomatism. The cryptically metasomatised SP appear devoid of base metal sulphides (BMS) and show suprachondritic Se/Te ratios (15-40) and extremely Pd- and Pt-depleted HSE patterns. These features are characteristic of high-degree partial melting residues. Their 187Os/188Os signatures are thus considered to be inherited from the partial melting event. This implies a Neoarchean (2.5-2.8 Ga, TRD eruption) stabilisation of the Letlhakane mantle root and supports the Letlhakane mantle root being a westerly extension of the Zimbabwe cratonic root. The modally metasomatised peridotites contain BMS whose abundance significantly increases from the GPP to the GP and PP. The BMS-poor GPP are only slightly richer in Pt and Pd than the BMS-free SP but have similarly high Se/Te ratios. The BMS-rich GP and PP exhibit significant enrichments in Pt, Pd, Se, Te resulting in HSE-Se-Te signatures similar to that of the Primitive Upper Mantle (PUM). Addition of 0.001-0.05 wt.% metasomatic BMS ± PGM (platinum group minerals, i.e., Pt-tellurides) to highly refractory residues, such as the Letlhakane SP, reproduce well the HSE-Se-Te systematics observed in the BMS-poor and BMS-rich modally metasomatised peridotites. In the GPP, the negligible addition of metasomatic BMS ± PGM did not disturb the 187Os/188Os signatures, indicating TRD eruption ages identical with those of the SP. By contrast, the PP and GP, which suffered significant BMS ± PGM addition, have 187Os/188Os considerably shifted toward more radiogenic values. As a result, unrealistically young TRD eruption ages are obtained that cannot be used to constrain the time frame of the stabilisation of the cratonic roots and the mechanisms of craton formation. The Se-Te and incompatible HSE (i.e., Pt, Pd) are powerful geochemical tools to assess the robustness of the Re-Os isotopic system in mantle peridotites. Specifically, Se/Te and Pd/Ir ratios provide complementary insights into the complex metasomatic history of mantle peridotites. The Se/Te ratio is very sensitive to Os-free PGM metasomatism producing highly variable Se/Te >15 at low, relatively constant Pd/Ir< 0.4 but does not affect the 187Os/188Os systematics. This contrasts with BMS metasomatism, where Pd/Ir becomes more variable (>0.4), at constant but low Se/Te <10 and which is accompanied by modification of the Os isotopic composition of the host peridotite. As they are sensitive indicators of BMS ± PGM metasomatism, HSE, Se and Te should be systematically considered when investigating the timing of stabilisation of lithospheric mantle and its petrogenetic history. This would allow a more robust assessment of the Re-Os ages obtained and provide firmer constraints on the evolution and formation of Archean cratons and early Earth dynamics.

  13. The homogeneity of Czochralski-grown Bi{sub 2}Te{sub 2.85}Se{sub 0.15} single crystals

    SciTech Connect

    Svechnikova, T.E.; Maksimova, N.M.; Sussmann, G.

    1995-01-01

    The Bi{sub 2}Te{sub 2.85}Se{sub 0.15} solid solution is an optimal material for n-arms of thermoelectric coolers operating in the range of 250-400 K. The use of Bi{sub 2}Te{sub 2.85}Se{sub 0.15} single crystals in thermoelectric coolers substantially improves their power parameters and raises the maximum degree of cooling {Delta}T{sub max}, and extends the range of their application in cooling microdevices of various types. The objective of this work was to investigate the effect of growth conditions and the purity of starting materials on the axial and radial homogeneity of Bi{sub 2}Te{sub 2.85}Se{sub 0.15} single crystals.

  14. Microstructure and transport properties of FeTe 0.5Se 0.5 superconducting wires fabricated by ex-situ Powder-in-tube process

    NASA Astrophysics Data System (ADS)

    Ozaki, T.; Deguchi, K.; Mizuguchi, Y.; Kumakura, H.; Takano, Y.

    2011-11-01

    We fabricated FeTe 0.5Se 0.5 superconducting wires using ex-situ Powder-in-tube method with an Fe sheath. It was amazing that superconducting current was observed in the as-drawn wire without any heat treatments. By heat treatment at 200 °C for 2 hours, Tczero and Jc at 4.2 K were enhanced up to 9.1 K and 64.1 A/cm 2 ( Ic = 182.6 mA), respectively. Furthermore, the Jc of FeTe 0.5Se 0.5 wire heat treated at 200 °C for 2 h was not much sensitive to the applied magnetic fields. Therefore, FeTe 0.5Se 0.5 wires have a great potential for applications.

  15. Structure and properties of a non-traditional glass containing TeO2, SeO2 and MoO3

    NASA Astrophysics Data System (ADS)

    Bachvarova-Nedelcheva, A.; Iordanova, R.; Kostov, K. L.; Yordanov, St.; Ganev, V.

    2012-09-01

    A glass containing SeO2, TeO2, MoO3 and La2O3 was obtained at high oxygen pressure (P = 36 MPa) using pure oxides as precursors. The real bulk chemical composition of the glass according to LA-ICP-MS analysis is 17SeO2·50TeO2·32MoO3·1La2O3 (wt.%). The glass was characterized by X-ray diffraction, scanning electron microscopy (SEM), differential thermal analysis (DTA), UV-Vis, XPS, IR and EPR spectroscopy. According to DTA the glass transition temperature (Tg) is below 300 °C. By IR and X-ray photoelectron spectroscopy was determined the main building units (TeO3, TeO4, SeO3, Mo2O8) and the existing of mixed bridging bonds only, which build up the amorphous network. It was established by UV-Vis that the glass is transparent above 490 nm. As a result of a lengthy heat treatment, crystallization took place and crystals rich in SeO2 and TeO2 were found incorporated into the amorphous part containing all components.

  16. Y{sub 2}MoSe{sub 3}O{sub 12} and Y{sub 2}MoTe{sub 3}O{sub 12}: Solid-state synthesis, structure determination, and characterization of two new quaternary mixed metal oxides containing asymmetric coordination environment

    SciTech Connect

    Bang, Seong-eun; Pan, Zhi; Kim, Yeong Hun; Lee, Dong Woo; Ok, Kang Min

    2013-12-15

    Two new quaternary yttrium molybdenum selenium/tellurium oxides, Y{sub 2}MoSe{sub 3}O{sub 12} and Y{sub 2}MoTe{sub 3}O{sub 12} have been prepared by standard solid-state reactions using Y{sub 2}O{sub 3}, MoO{sub 3}, and SeO{sub 2} (or TeO{sub 2}) as reagents. Single-crystal X-ray diffraction was used to determine the crystal structures of the reported materials. Although both of the materials contain second-order Jahn–Teller (SOJT) distortive cations and are stoichiometrically similar, they reveal different structural features: while Y{sub 2}MoSe{sub 3}O{sub 12} shows a three-dimensional framework consisting of YO{sub 8}, MoO{sub 6}, and SeO{sub 3} groups, Y{sub 2}MoTe{sub 3}O{sub 12} exhibits a layered structure composed of YO{sub 8}, MoO{sub 4}, TeO{sub 3}, and TeO{sub 4} polyhedra. With the Mo{sup 6+} cations in Y{sub 2}MoSe{sub 3}O{sub 12}, a C{sub 3}-type intraoctahedral distortion toward a face is observed, in which the direction of the out-of-center distortion for Mo{sup 6+} is away from the oxide ligand linked to a Se{sup 4+} cation. The Se{sup 4+} and Te{sup 4+} cations in both materials are in asymmetric coordination environment attributed to the lone pairs. Elemental analyses, infrared spectroscopy, thermal analyses, intraoctahedral distortions, and dipole moment calculations for the compounds are also presented. - Graphical abstract: Y{sub 2}MoSe{sub 3}O{sub 12} reveals a three-dimensional framework consisting of YO{sub 8}, MoO{sub 6}, and SeO{sub 3} polyhedra, whereas Y{sub 2}MoTe{sub 3}O{sub 12} exhibits a layered structure composed of YO{sub 8}, MoO{sub 4}, TeO{sub 3}, and TeO{sub 4} groups. - Highlights: • Two new selenite and tellurite (Y{sub 2}MoQ{sub 3}O{sub 12}; Q=Se and Te) are synthesized. • Y{sub 2}MoQ{sub 3}O{sub 12} contain second-order Jahn–Teller distortive cations in asymmetric environments. • The intra-octahedral distortion of the Mo{sup 6+} is influenced by the Se{sup 4+}.

  17. Structural transition and enhanced phase transition properties of Se doped Ge2Sb2Te5 alloys

    NASA Astrophysics Data System (ADS)

    Vinod, E. M.; Ramesh, K.; Sangunni, K. S.

    2015-01-01

    Amorphous Ge2Sb2Te5 (GST) alloy, upon heating crystallize to a metastable NaCl structure around 150°C and then to a stable hexagonal structure at high temperatures (>=250°C). It has been generally understood that the phase change takes place between amorphous and the metastable NaCl structure and not between the amorphous and the stable hexagonal phase. In the present work, it is observed that the thermally evaporated (GST)1-xSex thin films (0 <= x <= 0.50) crystallize directly to the stable hexagonal structure for x >= 0.10, when annealed at temperatures >= 150°C. The intermediate NaCl structure has been observed only for x < 0.10. Chemically ordered network of GST is largely modified for x >= 0.10. Resistance, thermal stability and threshold voltage of the films are found to increase with the increase of Se. The contrast in electrical resistivity between the amorphous and crystalline phases is about 6 orders of magnitude. The increase in Se shifts the absorption edge to lower wavelength and the band gap widens from 0.63 to 1.05 eV. Higher resistance ratio, higher crystallization temperature, direct transition to the stable phase indicate that (GST)1-xSex films are better candidates for phase change memory applications.

  18. Polytypism, polymorphism, and superconductivity in TaSe2–xTex

    SciTech Connect

    Luo, Huixia; Xie, Weiwei; Tao, Jing; Inoue, Hiroyuki; Gyenis, András; Krizan, Jason W.; Yazdani, Ali; Zhu, Yimei; Cava, Robert Joseph

    2015-03-03

    Polymorphism in materials often leads to significantly different physical properties - the rutile and anatase polymorphs of TiO? are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivity of TaSe?, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access 2 stable polytypes and 2 stable polymorphs in the TaSe2-xTex solid solution, and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. Thus, the reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of Tc on subtle differences in the characteristics of the single layers present, or from a surprising effect of the layer stacking sequence on electronic properties that instead are expected to be dominated by the properties of a single layer in materials of this kind.

  19. Electrical injection and detection of spin-polarized currents in topological insulator Bi2Te2Se

    PubMed Central

    Tian, Jifa; Miotkowski, Ireneusz; Hong, Seokmin; Chen, Yong P.

    2015-01-01

    Topological insulators (TIs) are an unusual phase of quantum matter with nontrivial spin-momentum-locked topological surface states (TSS). The electrical detection of spin-momentum-locking of TSS has been lacking till very recently. Many of the results are from samples with significant bulk conduction, such as Bi2Se3, where it can be challenging to separate the surface and bulk contribution to the spin signal. Here, we report spin potentiometric measurements in flakes exfoliated from bulk insulating Bi2Te2Se crystals, using two outside nonmagnetic contacts for driving a DC spin helical current and a middle ferromagnetic (FM)-Al2O3 contact for detecting spin polarization. The voltage measured by the FM electrode exhibits a hysteretic step-like change when sweeping an in-plane magnetic field between opposite directions along the easy axis of the FM contact. Importantly, the direction of the voltage change can be reversed by reversing the direction of current, and the amplitude of the change as measured by the difference in the detector voltage between opposite FM magnetization increases linearly with increasing current, consistent with the current-induced spin polarization of spin-momentum-locked TSS. Our work directly demonstrates the electrical injection and detection of spin polarization in TI and may enable utilization of TSS for applications in nanoelectronics and spintronics. PMID:26391089

  20. Electrical injection and detection of spin-polarized currents in topological insulator Bi2Te2Se.

    PubMed

    Tian, Jifa; Miotkowski, Ireneusz; Hong, Seokmin; Chen, Yong P

    2015-01-01

    Topological insulators (TIs) are an unusual phase of quantum matter with nontrivial spin-momentum-locked topological surface states (TSS). The electrical detection of spin-momentum-locking of TSS has been lacking till very recently. Many of the results are from samples with significant bulk conduction, such as Bi2Se3, where it can be challenging to separate the surface and bulk contribution to the spin signal. Here, we report spin potentiometric measurements in flakes exfoliated from bulk insulating Bi2Te2Se crystals, using two outside nonmagnetic contacts for driving a DC spin helical current and a middle ferromagnetic (FM)-Al2O3 contact for detecting spin polarization. The voltage measured by the FM electrode exhibits a hysteretic step-like change when sweeping an in-plane magnetic field between opposite directions along the easy axis of the FM contact. Importantly, the direction of the voltage change can be reversed by reversing the direction of current, and the amplitude of the change as measured by the difference in the detector voltage between opposite FM magnetization increases linearly with increasing current, consistent with the current-induced spin polarization of spin-momentum-locked TSS. Our work directly demonstrates the electrical injection and detection of spin polarization in TI and may enable utilization of TSS for applications in nanoelectronics and spintronics. PMID:26391089

  1. Structural transition and enhanced phase transition properties of Se doped Ge2Sb2Te5 alloys

    PubMed Central

    Vinod, E. M.; Ramesh, K.; Sangunni, K. S.

    2015-01-01

    Amorphous Ge2Sb2Te5 (GST) alloy, upon heating crystallize to a metastable NaCl structure around 150°C and then to a stable hexagonal structure at high temperatures (?250°C). It has been generally understood that the phase change takes place between amorphous and the metastable NaCl structure and not between the amorphous and the stable hexagonal phase. In the present work, it is observed that the thermally evaporated (GST)1-xSex thin films (0 ? x ? 0.50) crystallize directly to the stable hexagonal structure for x ? 0.10, when annealed at temperatures ? 150°C. The intermediate NaCl structure has been observed only for x < 0.10. Chemically ordered network of GST is largely modified for x ? 0.10. Resistance, thermal stability and threshold voltage of the films are found to increase with the increase of Se. The contrast in electrical resistivity between the amorphous and crystalline phases is about 6 orders of magnitude. The increase in Se shifts the absorption edge to lower wavelength and the band gap widens from 0.63 to 1.05?eV. Higher resistance ratio, higher crystallization temperature, direct transition to the stable phase indicate that (GST)1-xSex films are better candidates for phase change memory applications. PMID:25634224

  2. Effect of thermal annealing on structure and optical band gap of Se{sub 66}Te{sub 25}In{sub 9} thin films

    SciTech Connect

    Dwivedi, D. K.; Pathak, H. P.; Shukla, Nitesh; Kumar, Vipin

    2015-05-15

    Thin films of a-Se{sub 66}Te{sub 25}In{sub 9} have been deposited onto a chemically cleaned glass substrate by thermal evaporation technique under vacuum. Glassy nature of the films has been ascertained by X-ray diffraction pattern. The analysis of absorption spectra, measured at normal incidence, in the spectral range 400-1100 nm has been used for the optical characterization of thin films under investigation. The effect of thermal annealing on structure and optical band gap (E{sub g}) of a-Se{sub 66}Te{sub 25}In{sub 9} have been studied.

  3. Fermi level tuning of topological insulator Bi{sub 2}(Se{sub x}Te{sub 1-x}){sub 3} nanoplates

    SciTech Connect

    Hao Guolin; Qi Xiang; Xue Lin; Cai Canying; Li Jun; Wei Xiaolin; Zhong Jianxin

    2013-01-14

    The crystal structures and morphologies of ternary Bi{sub 2}(Se{sub x}Te{sub 1-x}){sub 3} nanoplates have been systematically characterized by employing atomic force microscopy, scanning electron microscopy, high-resolution transmission electron microscopy equipped with the energy dispersive X-ray spectrometer, and the X-ray diffraction. We find that the Bi{sub 2}(Se{sub x}Te{sub 1-x}){sub 3} nanoplates exhibit uniform charge and surface potential distributions. And their Fermi levels can be effectively tuned up to 0.23 eV by varying the selenium/tellurium composition ratios.

  4. Superconductivity and disorder effect in TlNi2Se2-x S x compounds.

    PubMed

    Wang, Hangdong; Mao, Qianhui; Chen, Huimin; Su, Qiping; Dong, Chiheng; Khan, Rajwali; Yang, Jinhu; Chen, Bin; Fang, Minghu

    2015-10-01

    After our first discovery of multi-band superconductivity (SC) in the TlNi2Se2 crystal, we successfully grew a series of TlNi2Se2-x S x ([Formula: see text]) single crystals. Measurements of resistivity, specific heat, and susceptibility were carried out on these crystals. Superconductivity with [Formula: see text] K was first observed in the TlNi2S2 crystal, which also appears to involve heavy electrons with an effective mass [Formula: see text]-[Formula: see text], as inferred from the normal state electronic specific heat and the upper critical field, [Formula: see text]. It was found that bulk SC and heavy-electron behavior is preserved in all the studied TlNi2Se2-x S x samples. In the mixed state, a novel change of the field dependence of the residual specific heat coefficient, [Formula: see text], occurs in TlNi2Se2-x S x with increasing S content. We also found that the [Formula: see text] value changes with the disorder degree induced by the partial substitution of S for Se, characterized by the residual resistivity ratio (RRR). Thus, the TlNi2Se2-x S x system provides a platform to study the effect of disorder on the multi-band SC. PMID:26381523

  5. Superconductivity and disorder effect in TlNi2Se2-x S x compounds

    NASA Astrophysics Data System (ADS)

    Wang, Hangdong; Mao, Qianhui; Chen, Huimin; Su, Qiping; Dong, Chiheng; Khan, Rajwali; Yang, Jinhu; Chen, Bin; Fang, Minghu

    2015-10-01

    After our first discovery of multi-band superconductivity (SC) in the TlNi2Se2 crystal, we successfully grew a series of TlNi2Se2-x S x (0.0?slant x?slant 2.0 ) single crystals. Measurements of resistivity, specific heat, and susceptibility were carried out on these crystals. Superconductivity with {{T}\\text{C}}=2.3 K was first observed in the TlNi2S2 crystal, which also appears to involve heavy electrons with an effective mass m*=13 -25 {{m}\\text{b}} , as inferred from the normal state electronic specific heat and the upper critical field, {{H}\\text{C2}}(T) . It was found that bulk SC and heavy-electron behavior is preserved in all the studied TlNi2Se2-x S x samples. In the mixed state, a novel change of the field dependence of the residual specific heat coefficient, {?\\text{N}}(H) , occurs in TlNi2Se2-x S x with increasing S content. We also found that the {{T}\\text{C}} value changes with the disorder degree induced by the partial substitution of S for Se, characterized by the residual resistivity ratio (RRR). Thus, the TlNi2Se2-x S x system provides a platform to study the effect of disorder on the multi-band SC.

  6. Anomalous heat capacity and x-ray photoelectron spectroscopy of superconducting FeSe1/2Te1/2

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Govind, Pal, Anand; Gahtori, Bhasker; Kaushik, S. D.; Vajpayee, A.; Kumar, Jagdish; Kishan, H.

    2011-04-01

    The bulk polycrystalline sample FeSe1/2Te1/2 is synthesized via the solid state reaction route in an evacuated, sealed quartz tube at 750°C. The presence of superconductivity is confirmed through magnetization/thermoelectric/resistivity studies. It is found that the superconducting transition temperature (Tc) is around 12 K. The heat capacity (Cp) of superconducting FeSe1-xTex exhibits a hump near Tc, instead of a well-defined lambda transition. X-ray photoelectron spectroscopy studies reveal well-defined positions for divalent Fe, Se, and Te, but with sufficient hybridization of the Fe (2p) and Se/Te (3d) core levels. In particular, divalent Fe is shifted to a higher binding energy, and Se and Te to a lower one. The situation is similar to that observed previously for the famous Cu-based high Tc superconductors, where the Cu (3d) orbital hybridizes with O (2p). We also found the satellite peak of Fe at 712.00 eV, which is attributed to the charge-carrier localization induced by Fe at the 2c site.

  7. Characterization of Electronic Materials HgZnSe and HgZnTe Using Innovative and Conventional Techniques

    NASA Technical Reports Server (NTRS)

    Tanton, George; Kesmodel, Roy; Burden, Judy; Su, Ching-Hua; Cobb, Sharon D.; Lehoczky, S. L.

    2000-01-01

    HgZnSe and HgZnTe are electronic materials of interest for potential IR detector and focal plane array applications due to their improved strength and compositional stability over HgCdTe, but they are difficult to grow on Earth and to fully characterize. Conventional contact methods of characterization, such as Hall and van der Paw, although adequate for many situations are typically labor intensive and not entirely suitable where only very small samples are available. To adequately characterize and compare properties of electronic materials grown in low earth orbit with those grown on Earth, innovative techniques are needed that complement existing methods. This paper describes the implementation and test results of a unique non-contact method of characterizing uniformity, mobility, and carrier concentration together with results from conventional methods applied to HgZnSe and HgZnTe. The innovative method has advantages over conventional contact methods since it circumvents problems of possible contamination from alloying electrical contacts to a sample and also has the capability to map a sample. Non- destructive mapping, the determination of the carrier concentration and mobility at each place on a sample, provides a means to quantitatively compare, at high spatial resolution, effects of microgravity on electronic properties and uniformity of electronic materials grown in low-Earth orbit with Earth grown materials. The mapping technique described here uses a 1mm diameter polarized beam of radiation to probe the sample. Activation of a magnetic field, in which the sample is placed, causes the plane of polarization of the probe beam to rotate. This Faraday rotation is a function of the free carrier concentration and the band parameters of the material. Maps of carrier concentration, mobility, and transmission generated from measurements of the Faraday rotation angles over the temperature range from 300K to 77K will be presented. New information on band parameters, obtained by combining results from conventional Hall measurements of the free carrier concentration with Faraday rotation measurements, will also be presented. One example of how this type of information was derived is illustrated in the following figure which shows Faraday rotation vs wavelength modeled for Hg(l-x)ZnxSe at a temperature of 300K and x=0.07. The plasma contribution, total Faraday rotation, and interband contribution to the Faraday rotation, are designated in the Figure as del(p), FR tot, and del(i) respectively. Experimentally measured values of FR tot, each indicated by + , agree acceptably well with the model at the probe wavelength of 10.6 microns. The model shows that at the probe wavelength, practically all the rotation is due to the plasma component, which can be expressed as delta(sub p)= 2pi(e(sup 3))NBL/c(sup 2)nm*(sup 2) omega(sup 2). In this equation, delta(sub p) is the rotation angle due to the free carrier plasma, N is the free carrier concentration, B the magnetic field strength, L the thickness of the sample, n the index of refraction, omega the probe radiation frequency, c the speed of light, e the electron charge, and m* the effective mass. A measurement of N by conventional techniques, combined with a measurement of the Faraday rotation angle allows m* to be accurately determined since it is an inverse square function.

  8. Interface Driven Energy Filtering of Thermoelectric Power in Spark Plasma Sintered Bi2Te2.7Se0.3 Nanoplatelet Composites

    E-print Network

    Xiong, Qihua

    Interface Driven Energy Filtering of Thermoelectric Power in Spark Plasma Sintered Bi2Te2.7Se0 of Material Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore § Division of Manufacturing Engineering, School of Mechanical and Aerospace Engineering, Nanyang Technological University

  9. Enhanced thermoelectric properties of n-type Bi2Te2.7Se0.3 by indium and sodium co-doping

    NASA Astrophysics Data System (ADS)

    Duan, Xingkai; Hu, Konggang; Ding, Shifeng; Man, Dahu; Zhang, Wangnian; Ma, Mingliang

    2015-09-01

    Bi(1.98-x)In0.02NaxTe2.7Se0.3 (x = 0, 0.02, 0.04, 0.06) and Bi2Te2.7Se0.3 alloys were prepared by vacuum melting and hot pressing methods. The phase structure of the bulk samples were characterized by X-ray diffraction. Effects of indium and sodium co-substitutions for bismuth on the electrical and thermal transport properties were investigated in the temperature range of 298-473 K. Indium and sodium co-doping can enhance the carrier concentration, and accordingly the electrical conductivity can be improved effectively. The Seebeck coefficients of the co-doped samples have not been derogated strongly. The power factors are enhanced for the Bi(1.98-x)In0.02NaxTe2.7Se0.3 (x = 0.02) within the whole testing temperature range. The Bi(1.98-x)In0.02NaxTe2.7Se0.3 (x = 0.02) samples have the lower thermal conductivity due to reduction in lattice thermal conductivity, which leads to a great improvement in the thermoelectric figure of merit ZT. The highest ZT of the sample can reach 0.87 at 398 K.

  10. Thermoelectric properties of the quaternary chalcogenides BaCu5.9STe6 and BaCu5.9SeTe6.

    PubMed

    Oudah, Mohamed; Kleinke, Katja M; Kleinke, Holger

    2015-02-01

    These quaternary chalcogenides are isostructural, crystallizing in a unique structure type comprising localized Cu clusters and Te(2)(2-) dumbbells. With less than six Cu atoms per formula unit, these materials are p-type narrow-gap semiconductors, according to the balanced formula Ba(2+)(Cu(+))6Q(2-)(Te(2)(2-))3 with Q = S, Se. Encouraged by the outstanding thermoelectric performance of Cu(2-x)Se and the low thermal conductivity of cold-pressed BaCu(5.7)Se(0.6)Te(6.4), we determined the thermoelectric properties of hot-pressed pellets of BaCu(5.9)STe(6) and BaCu(5.9)SeTe(6). Both materials exhibit a high Seebeck coefficient and a low electrical conductivity, combined with very low thermal conductivity below 1 W m(-1) K(-1). Compared to the sulfide-telluride, the selenide-telluride exhibits higher electrical and thermal conductivity and comparable Seebeck coefficient, resulting in superior figure-of-merit values zT, exceeding 0.8 at relatively low temperatures, namely, around 600 K. PMID:25299429

  11. Reactive molten core fabrication of glass-clad Se0.8Te0.2 semiconductor core optical fibers.

    PubMed

    Tang, Guowu; Qian, Qi; Wen, Xin; Chen, Xiaodong; Liu, Wangwang; Sun, Min; Yang, Zhongmin

    2015-09-01

    Phosphate glass-clad optical fibers comprising amorphous Se0.8Te0.2 semiconductor core were fabricated by a reactive molten core approach. The Se0.8Te0.2 crystals were precipitated in core region by a postdrawing annealing process, which were confirmed by X-ray diffraction, micro-Raman spectra, electron probe X-ray micro-analyzer, and transmission electron microscope measurement results. A two-cm-long crystalline Se0.8Te0.2 semiconductor core optical fiber, electrically contacted to external circuitry through the fiber end facets, exhibits a two-orders-of-magnitude change in conductivity between dark and illuminated states. The great discrepancy in light and dark conductivity suggests that such crystalline Se0.8Te0.2 semiconductor core optical fibers have promising applications in optical switch and photoconductivity of optical fiber array. PMID:26368460

  12. Structural and dynamical properties of Bridgman-grown CdSe[subscript x]Te[subscript 1?x] (0

    E-print Network

    Talwar, Devki N.

    Measurements of the Raman scattering and extended x-ray-absorption fine-structure (EXAFS) spectroscopy are reported on a series of Bridgman-grown zinc-blende CdTe[subscript 1?x]Se[subscript x] (0.35 ? x > 0.05) ternary ...

  13. TE Scattering from Mushroom-type EBG Structures in Parallel Plate Sang-Ho Lim, Ho Lim, Se-Young Kim, Noh-Hoon Myung

    E-print Network

    Myung, Noh-Hoon

    TE Scattering from Mushroom-type EBG Structures in Parallel Plate Waveguide Sang-Ho Lim, Ho Lim, Se Mushroom-type Electromagnetic Band Gap (EBG) structures which have a high impedance characteristic are used and efficient for computation. Theory and Numerical Result Consider a TEs-mode incident on a mushroom-type EBG

  14. Suppression of phase separation and giant enhancement of superconducting transition temperature in FeSe(1-x)Te(x) thin films.

    PubMed

    Imai, Yoshinori; Sawada, Yuichi; Nabeshima, Fuyuki; Maeda, Atsutaka

    2015-02-17

    We demonstrate the successful fabrication on CaF2 substrates of FeSe(1-x)Tex films with 0 ? x ? 1, including the region of 0.1 ? x ? 0.4, which is well known to be the "phase-separation region," via pulsed laser deposition that is a thermodynamically nonequilibrium method. In the resulting films, we observe a giant enhancement of the superconducting transition temperature, Tc, in the region of 0.1 ? x ? 0.4: The maximum value reaches 23 K, which is ? 1.5 times as large as the values reported for bulk samples ofFeSe(1-x)Te(x). We present a complete phase diagram of FeSe(1-x)Te(x) films. Surprisingly, a sudden suppression of Tc is observed at 0:1 < x < 0.2, whereas Tc increases with decreasing x for 0.2 ? x < 1. Namely, there is a clear difference between superconductivity realized in x = 0-0.1 and in x ? 0.2. To obtain a film of FeSe(1-x)Te(x) with high Tc, the controls of the Te content x and the in-plane lattice strain are found to be key factors. PMID:25646450

  15. Molecular beam epitaxy growth and novel properties of topological insulator films of Bi2Te3 and Bi2Se3

    NASA Astrophysics Data System (ADS)

    Xue, Qi-Kun

    2010-03-01

    In this talk, we summarize our recent activity in state-of-art molecular beam epitaxy (MBE) growth and characterization of nontrivial surface states of topological insulator films of Bi2Te3 and Bi2Se3 on Si(111) and 6H-SiC(0001) substrates. We studied the growth dynamics and epitaxial relationship under different flux ratios and substrate temperatures, and identified the optimized conditions for stoichiometric and layer-by-layer MBE deposition of both Bi2Te3 and Bi2Se3 films by real time reflection high energy electron diffraction (RHEED). We demonstrate the atomically flat morphology and intrinsic topological property of the resulted films by angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS). By direct imaging standing waves associated with magnetic and nonmagnetic impurities and steps on Bi2Te3 and Bi2Se3 (111) surfaces, we show that the topological states have a surface nature and are protected by the time reversal symmetry. We also studied the growth of conventional superconductor and magnetic thin films on Bi2Te3 and Bi2Se3. Implication on probing Majorana states and topological magneto-electric effect will be discussed. Work done in collaboration with Xi Chen, Jinfeng Jia, Xucun Ma, Ke He, Lili Wang, Yayu Wang, Xi Dai, Zhong Fang, Xincheng Xie, Shunqing Shen, Qian Niu, Ying Liu, Xiao-Liang Qi, and Shou-Cheng Zhang.

  16. Catalyst-free vapour-solid technique for deposition of Bi2Te3 and Bi2Se3 nanowires/nanobelts with topological insulator properties.

    PubMed

    Andzane, J; Kunakova, G; Charpentier, S; Hrkac, V; Kienle, L; Baitimirova, M; Bauch, T; Lombardi, F; Erts, D

    2015-10-14

    We present a simple two-stage vapour-solid synthesis method for the growth of bismuth chalcogenide (Bi2Te3, Bi2Se3) topological insulator nanowires/nanobelts by using Bi2Se3 or Bi2Te3 powders as source materials. During the first stage of the synthesis process nanoplateteles, serving as "catalysts" for further nanowire/nanobelt growth, are formed. At a second stage of the synthesis, the introduction of a N2 flow at 35 Torr pressure in the chamber induces the formation of free standing nanowires/nanobelts. The synthesised nanostructures demonstrate a layered single-crystalline structure and Bi?:?Se and Bi?:?Te ratios 40?:?60 at% for both Bi2Se3 and Bi2Te3 nanowires/nanobelts. The presence of Shubnikov de Haas oscillations in the longitudinal magneto-resistance of the nanowires/nanobelts and their specific angular dependence confirms the existence of 2D topological surface states in the synthesised nanostructures. PMID:26365282

  17. Catalyst-free vapour-solid technique for deposition of Bi2Te3 and Bi2Se3 nanowires/nanobelts with topological insulator properties

    NASA Astrophysics Data System (ADS)

    Andzane, J.; Kunakova, G.; Charpentier, S.; Hrkac, V.; Kienle, L.; Baitimirova, M.; Bauch, T.; Lombardi, F.; Erts, D.

    2015-09-01

    We present a simple two-stage vapour-solid synthesis method for the growth of bismuth chalcogenide (Bi2Te3, Bi2Se3) topological insulator nanowires/nanobelts by using Bi2Se3 or Bi2Te3 powders as source materials. During the first stage of the synthesis process nanoplateteles, serving as ``catalysts'' for further nanowire/nanobelt growth, are formed. At a second stage of the synthesis, the introduction of a N2 flow at 35 Torr pressure in the chamber induces the formation of free standing nanowires/nanobelts. The synthesised nanostructures demonstrate a layered single-crystalline structure and Bi : Se and Bi : Te ratios 40 : 60 at% for both Bi2Se3 and Bi2Te3 nanowires/nanobelts. The presence of Shubnikov de Haas oscillations in the longitudinal magneto-resistance of the nanowires/nanobelts and their specific angular dependence confirms the existence of 2D topological surface states in the synthesised nanostructures.

  18. Enhanced thermoelectric performance in Cd doped CuInTe{sub 2} compounds

    SciTech Connect

    Cheng, N.; Liu, R.; Bai, S.; Shi, X. Chen, L.

    2014-04-28

    CuIn{sub 1?x}Cd{sub x}Te{sub 2} materials (x?=?0, 0.02, 0.05, and 0.1) are prepared using melting-annealing method and the highly densified bulk samples are obtained through Spark Plasma Sintering. The X-ray diffraction data confirm that nearly pure chalcopyrite structures are obtained in all the samples. Due to the substitution of Cd at In sites, the carrier concentration is greatly increased, leading to much enhanced electrical conductivity and power factor. The single parabolic band model is used to describe the electrical transport properties of CuInTe{sub 2} and the low temperature Hall mobility is also modeled. By combing theoretical model and experiment data, the optimum carrier concentration in CuInTe{sub 2} is proposed to explain the greatly enhanced power factors in the Cd doped CuInTe{sub 2}. In addition, the thermal conductivity is reduced by extra phonon scattering due to the atomic mass and radius fluctuations between Cd and In atoms. The maximum zTs are observed in CuIn{sub 0.98}Cd{sub 0.02}Te{sub 2} and CuIn{sub 0.9}Cd{sub 0.1}Te{sub 2} samples, which are improved by over 100% at room temperature and around 20% at 600?K.

  19. Optical properties of the charge-density-wave rare-earth tri-telluride compounds: A view on PrTe3

    E-print Network

    Fisher, Ian

    Optical properties of the charge-density-wave rare-earth tri-telluride compounds: A view on PrTe3 F in transition metal di- and trichalcogenides [4,5], in the ladder compounds Sr14ÀxCaxCu24 O41 [6] and in some copper oxide high temperature super- conductors [7] (where they are known as ``stripes'') as well

  20. Study on Corrosion Performance of Cu-Te-Se Alloys in a 3.5% Sodium Chloride Solution

    NASA Astrophysics Data System (ADS)

    Jiao, Lin; Li, Meng; Zeng, Tao; Zhu, Dachuan

    2015-11-01

    Samples of Cu-Te-Se alloys, previously aged or treated as a solid solution, were immersed in 3.5% (mass fraction) sodium chloride solution to investigate their corrosion resistance at room temperature by determining their corrosive weight loss. The morphologies of the precipitated phase and surface products following immersion were observed by scanning electron microscope. In addition, energy-dispersive spectroscopic analysis was used to determine the elemental constituents of precipitated phase and corroded surface of the alloy samples. The phase composition was measured by x-ray diffraction, and the electrochemical polarization behavior of the samples was determined using an electrochemical workstation. The experimental results revealed that the alloy samples appeared to corrode uniformly, which was accompanied by a small amount of localized corrosion. There was the possibility that localized corrosion could increase following aging treatment. The addition of a small amount of tellurium and selenium to the alloy appeared to retard oxygen adsorption on the copper in the alloy, which has ameliorated the alloy corrosion due to the similar physical and chemical properties of oxygen. In comparison to the solid solution state, the corrosion resistance of the alloy appeared to decline slightly following aging treatment.

  1. Evolution of the level anticrossing signal in magnetoluminescence of localized excitons in the GaSe-GaTe solid solution

    NASA Astrophysics Data System (ADS)

    Starukhin, A. N.; Nelson, D. K.; Razbirin, B. S.; Fedorov, D. L.; Syunyaev, D. K.

    2015-10-01

    The time dependence of the Zeeman-sublevel anticrossing signal in triplet localized exciton emission in the GaSe0.87Te0.13 semiconductor solid solution has been studied by the time-resolved spectroscopy method under conditions of unpolarized pumping. It has been shown that the anticrossing signal shape changes significantly for the lifetime t of localized excitons. At the time point t = 0, the anticrossing signal is not detected; as t increases, a maximum is formed in the dependence of the exciton emission intensity on the magnetic field (at this stage, the anticrossing signal shape is identical to that observed under conditions of steady-state excitation), which is split into a doublet as t further increases. A theoretical interpretation of the observed time dependence of the Zeeman-sublevel anticrossing signal in localized exciton emission has been proposed. The fine structure parameters and lifetimes of the triplet localized excitons have been determined in different spin states by comparing theory and experiment.

  2. Thermally activated flux flow in Fe1.06Te0.6Se0.4 single crystal

    NASA Astrophysics Data System (ADS)

    Shahbazi, M.; Wang, X. L.; Ghorbani, S. R.; Dou, S. X.; Lin, C. T.

    2015-12-01

    Resistivity of Fe1.06Te0.6Se0.4 single crystal is investigated around superconducting transition region in different magnetic fields. The thermally activated energy (TAE) is analysed using the Arrhenius relation and modified thermally activated flux flow (TAFF) model. The results indicate that the Arrhenius curve slopes are directly related to but not equal to TAE. Therefore, use of the modified TAFF model is suggested, ?(T,B) = ?0f exp(-U/T), where the temperature dependence of the pre-factor ?0f = 2?cU/T and the nonlinear relation of the TAE should be considered. The modified TAFF method results are in good agreement with the very high critical current density values from the experimental data. It was found that the vortex glass has a narrow region, and it depends weakly on magnetic field. The vortex phase diagram was determined based on the evolution of the vortex-glass transition temperature with magnetic field and the upper critical field.

  3. Optical Properties of the Charge-Density-Wave Polychalcogenide Compounds R2Te5 (R=Nd, Sm and Gd)

    SciTech Connect

    Pfuner, F.; Degiorgi, L.; Shin, K.Y.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2010-02-15

    We investigate the rare-earth polychalcogenide R{sub 2}Te{sub 5} (R = Nd, Sm and Gd) charge-density-wave (CDW) compounds by optical methods. From the absorption spectrum we extract the excitation energy of the CDW gap and estimate the fraction of the Fermi surface which is gapped by the formation of the CDW condensate. In analogy to previous findings on the related RTe{sub n} (n = 2 and 3) families, we establish the progressive closing of the CDW gap and the moderate enhancement of the metallic component upon chemically compressing the lattice.

  4. Infrared investigation of the phonon spectrum in the frustrated spin cluster compound FeTe(2)O(5)Cl.

    PubMed

    Pfuner, F; Degiorgi, L; Berger, H; Forró, L

    2009-09-16

    We present our optical investigations on the frustrated spin cluster compound FeTe(2)O(5)Cl, which develops a long-range antiferromagnetic order below 10 K. We measure the optical reflectivity from the far-infrared to the ultraviolet with polarized light. We focus our attention on the lattice dynamics by discussing the infrared-active modes. Our findings reveal a polarization dependence of the vibrational modes but which do not seem to be affected by structural anomalies linked to the magnetically ordered state at low temperatures. PMID:21832346

  5. Measurement and control of size and density of type-II ZnTe/ZnSe submonolayer quantum dots grown by migration enhanced epitaxy

    NASA Astrophysics Data System (ADS)

    Dhomkar, S.; Ji, H.; Roy, B.; Deligiannakis, V.; Wang, A.; Tamargo, M. C.; Kuskovsky, I. L.

    2015-07-01

    For practical applications of self-assembled semiconductor quantum dots (QDs), it is important to control their densities and sizes, however these parameters are difficult to quantify. This is particularly challenging in case of submonolayer QDs, in spite of their remarkable features including absence of wetting layers and significantly small dimensions that are advantageous for many device application. We report here the investigation of submonolayer type-II ZnTe/ZnSe QDs grown via migration enhanced epitaxy (MEE) with varying Te content. The employment of MEE assists in the formation of QDs and facilitates improvement in overall material quality. The structural and optical properties of these QD structures were investigated using a variety of characterization tools. Low temperature photoluminescence measurement allowed for a good estimate of QD thicknesses, while observation of robust Aharanov-Bohm-oscillations in magneto-PL spectra was used to precisely determine diameters of these disc-shaped QDs. These results, in conjunction with high resolution x-ray diffraction and secondary ion mass spectrometry data of the Te concentration, were then used to evaluate the QD density. It is evident from the results that the dot density increases much faster than the QD size with respect to the increase in overall Te content. Most importantly, this study provides the dependence of average QD size and density as a function of Te flux and Te MEE cycles, and shows that these are the key parameters to control the QD dimension and distribution.

  6. High Compositional Homogeneity of CdTexSe1-x Crystals Grown by the Bridgman Method

    SciTech Connect

    Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Lee, K.; Lee, W.; Tappero, R.; Yang, G.; Gul, R.; James, R. B.

    2015-02-03

    We obtained high-quality CdTexSe1-x (CdTeSe) crystals from ingots grown by the vertical Bridgman technique. The compositional uniformity of the ingots was evaluated by X-ray fluorescence at BNL’s National Synchrotron Light Source X27A beam line. The resulting compositional homogeneity was highly uniform throughout the ingot, and the effective segregation coefficient of Se was ~1.0. This uniformity offers potential opportunity to enhance the yield of the materials for both infrared substrate and radiation-detector applications, so greatly lowering the cost of production and also offering us the prospect to grow large-diameter ingots for use as large-area substrates and for producing higher efficiency gamma-ray detectors. The concentration of secondary phases was found to be much lower, by eight- to ten fold compared to that of conventional CdxZn1-xTe (CdZnTe or CZT).

  7. Magnetic properties of Mn-doped Bi2Se3 compound: temperature dependence and pressure effects

    NASA Astrophysics Data System (ADS)

    Panfilov, A. S.; Grechnev, G. E.; Fedorchenko, A. V.; Conder, K.; Pomjakushina, E. V.

    2015-11-01

    Magnetic susceptibility ? of Bi2?x Mn x Se3 (x??=??0.01–0.2) was measured in the temperature range 4.2–300 K. For all the samples, a Curie–Weiss behaviour of ? (T) was revealed with effective magnetic moments of Mn ions corresponding to the spin value S??=??5/2, which couple antiferromagnetically with the paramagnetic Curie temperature \\Theta? -50 K. In addition, for the samples of nominal composition x??=??0.1 and 0.2 the effect of a hydrostatic pressure P up to 2 kbar on ? has been measured at fixed temperatures 78 and 300 K that allowed to estimate the pressure derivative of \\Theta to be \\text{d} \\Theta/\\text{d}P? -0.8 K kbar?1. Based on the observed behaviour of \\Theta with varied Mn concentration and pressure, a possible mechanism of interaction between localized Mn moments is discussed.

  8. Magnetic properties of Mn-doped Bi2Se3 compound: temperature dependence and pressure effects.

    PubMed

    Panfilov, A S; Grechnev, G E; Fedorchenko, A V; Conder, K; Pomjakushina, E V

    2015-11-18

    Magnetic susceptibility ? of Bi2-x Mn x Se3 (x??=??0.01-0.2) was measured in the temperature range 4.2-300 K. For all the samples, a Curie-Weiss behaviour of [Formula: see text] was revealed with effective magnetic moments of Mn ions corresponding to the spin value S??=??5/2, which couple antiferromagnetically with the paramagnetic Curie temperature [Formula: see text] K. In addition, for the samples of nominal composition x??=??0.1 and 0.2 the effect of a hydrostatic pressure P up to 2 kbar on ? has been measured at fixed temperatures 78 and 300 K that allowed to estimate the pressure derivative of [Formula: see text] to be [Formula: see text] K kbar(-1). Based on the observed behaviour of [Formula: see text] with varied Mn concentration and pressure, a possible mechanism of interaction between localized Mn moments is discussed. PMID:26471893

  9. Comparative nm-Resolution Electrical Potential and Resistance Mapping of Cu(In,Ga)Se2, Cu2ZnSnSe4, and CdTe Thin Films

    NASA Astrophysics Data System (ADS)

    Jiang, Chunsheng; Repins, Ingrid; Mansfield, Lorelle; Contreras, Miguel; Moutinho, Helio; Ramanathan, Kannan; Al-Jassim, Mowafak; National Renewable Energy Laboratory Team

    2014-03-01

    We report on a comparative study of three leading thin-film PV materials of Cu(In,Ga)Se2 (CIGS), Cu2ZnSnSe4 (CZTS), and CdTe, by mapping the local electrical potential and resistance using atomic force microscopy (AFM)-based electrical techniques of scanning Kelvin probe force microscopy (SKPFM) and scanning spreading resistance microscopy (SSRM). The SKPFM potential mapping shows consistent results among the three films. The energy bands around the grain boundaries (GBs) bent downward and the GBs are positively charged. However, whether the carriers around the GBs are depleted or inverted could not be determined solely by the potential contrast between the GB and grain surface because surface band bending decreases this contrast. The SSRM resistance mapping shows different results between the films. A higher conduction channel was imaged along the GBs of CIGS and CZTS, indicating an inversion of carriers around the GBs. However, no characteristic resistance was imaged on the GBs of CdTe. This difference of local resistance on the GBs suggests a depletion of carriers in CdTe, in contrast to CIGS and CZTS. These nm-electrical mapping proposes an active GB of CdTe for minority carrier recombination, but inactive GBs of CIGS and CZTS.

  10. Thermal characterization of ZnBeMnSe mixed compounds by means of photopyroelectric and lock-in thermography methods

    NASA Astrophysics Data System (ADS)

    Strza?kowski, K.; Dadarlat, D.; Streza, M.; Zakrzewski, J.

    2015-06-01

    In this work, a thermal characterization (measurement of dynamic thermal parameters) of quaternary Zn1-x-yBexMnySe mixed crystals was carried out. The crystals under investigation were grown from the melt by the modified high-pressure Bridgman method with different Be and Mn contents. The effect of Be and Mn contents on thermal properties of Zn1-x-yBexMnySe compounds was analyzed, by using the photopyroelectric (PPE) method in the back configuration (BPPE) for thermal diffusivity measurements and the PPE technique in the front configuration for thermal effusivity investigations. Infrared lock-in thermography was used in order to validate the BPPE results. The measured thermal effusivity and diffusivity allowed the calculation of thermal conductivity of the investigated materials.

  11. Optical detection of organophosphorus compounds based on Mn-doped ZnSe d-dot enzymatic catalytic sensor.

    PubMed

    Gao, Xue; Tang, Guangchao; Su, Xingguang

    2012-01-01

    In this paper, we report a sensitive and selective method for detection of organophosphorus compounds (OPs) based on Mn:ZnSe d-dots-enzyme-hydrogen peroxide (H(2)O(2)) fluorescence quenching system. Acetylcholine esterase (AChE) can hydrolyze acetylcholine (ACh) to choline. Subsequently, choline oxidase (ChOx) oxidizes choline to generate H(2)O(2). The enzyme-generated H(2)O(2) can quench the fluorescence of Mn:ZnSe d-dots. When paraoxon are introduced in solution, it can interact with the active centers of AChE and decrease the enzyme activity. This leads to the decrease of the H(2)O(2) production and then the fluorescence quenching rate of Mn:ZnSe d-dots. Experimental results showed that the enzyme inhibition percentage of Mn:ZnSe d-dots-ChOx-AChE-ACh system was proportional to the logarithm of paraoxon in the range 4.84×10(-11) to 4.84×10(-6) mol/L with the detection limit (S/N=3) of 1.31×10(-11) mol/L. The proposed biosensor has been employed for quick determination of paraoxon in tap water and milk samples with satisfactory reproducibility and accuracy. This nano-biosensor was proved to be sensitive, rapid, simple and tolerance of most interfering substances. PMID:22534106

  12. Electrical and Switching Properties of TlBiSe2 Chalcogenide Compounds

    NASA Astrophysics Data System (ADS)

    Kalkan, N.; Bas, H.

    2015-11-01

    The electrical conductivity of TlBiSe2 narrow gap semiconductors prepared by the Bridgman-Stockbarger method was investigated. The temperature dependence of the electrical conductivity was measured to establish the dominant conductivity mechanism in a temperature range between 293 K and 373 K. The conduction activation energy has a single value indicating the existence of one type of conduction mechanism in the investigated temperature range. The electrical conductivity of the sample is controlled by a thermally activated mechanism. It was also found that these samples exhibit a current-controlled negative resistance and threshold switching. The value of the threshold voltage decreases exponentially with increasing temperature. The calculated ratio of the threshold energy to the activation energy is one half, and is derived from the electro-thermal model for the switching process. Therefore, the electrical switching in the investigated samples can be explained in terms of the electro-thermal model. A possible conduction mechanism in the pre-switching state of the sample associated with the space charge limited current is described.

  13. FeTe0.55Se0.45 : A multiband superconductor in the clean and dirty limit

    NASA Astrophysics Data System (ADS)

    Homes, C. C.; Dai, Y. M.; Wen, J. S.; Xu, Z. J.; Gu, G. D.

    2015-04-01

    The detailed optical properties of the multiband iron-chalcogenide superconductor FeTe0.55Se0.45 have been reexamined for a large number of temperatures above and below the critical temperature Tc=14 K for light polarized in the a -b planes. Instead of the simple Drude model that assumes a single band, above Tc the normal-state optical properties are best described by the two-Drude model that considers two separate electronic subsystems; we observe a weak response (?p ,D ;1?3000 cm-1) where the scattering rate has a strong temperature dependence (1 /?D ,1?32 cm-1 for T ?Tc ), and a strong response (?p ,D ;2?14 500 cm-1) with a large scattering rate (1 /?D ,2?1720 cm-1) that is essentially temperature independent. The multiband nature of this material precludes the use of the popular generalized-Drude approach commonly applied to single-band materials, implying that any structure observed in the frequency-dependent scattering rate 1 /? (? ) is spurious and it cannot be used as the foundation for optical inversion techniques to determine an electron-boson spectral function ?2F (? ) . Below Tc the optical conductivity is best described using two superconducting optical gaps of 2 ?1?45 and 2 ?2?90 cm-1 applied to the strong and weak responses, respectively. The scattering rates for these two bands are vastly different at low temperature, placing this material simultaneously in both clean and dirty limit. Interestingly, this material falls on the universal scaling line initially observed for the cuprate superconductors.

  14. Probing the local environment of two-dimensional ordered vacancy structures in Ga{sub 2}SeTe{sub 2} via aberration-corrected electron microscopy

    SciTech Connect

    Abdul-Jabbar, N. M.; Ercius, P.; Gronsky, R.; Bourret-Courchesne, E. D.; Wirth, B. D.

    2014-02-03

    There has been considerable interest in chalcogenide alloys with high concentrations of native vacancies that lead to properties desirable for thermoelectric and phase-change materials. Recently, vacancy ordering has been identified as the mechanism for metal-insulator transitions observed in GeSb{sub 2}Te{sub 4} and an unexpectedly low thermal conductivity in Ga{sub 2}Te{sub 3}. Here, we report the direct observation of vacancy ordering in Ga{sub 2}SeTe{sub 2} utilizing aberration-corrected electron microscopy. Images reveal a cation-anion dumbbell inversion associated with the accommodation of vacancy ordering across the entire crystal. The result is a striking example of the interplay between native defects and local structure.

  15. Formation Phases and Electrical Properties of Ge-Bi-Te Compounds with Homologous Structures

    NASA Astrophysics Data System (ADS)

    Omoto, Tatsuro; Kanaya, Hiroki; Ishibashi, Hiroki; Kubota, Yoshiki; Kifune, Kouichi; Kosuga, Atsuko

    2015-10-01

    We prepared polycrystalline samples of GeBi6-x In x Te10 (x = 0, 0.06, 0.18, 0.3, and 0.6) by melting a stoichiometric mixture of Ge, Bi, In, and Te, followed by quenching in water and annealing at 723 K for 1 week. Under these preparation conditions and irrespective of the degree of In-substitution, the samples contained two different periodic structures: GeBi6Te10 and GeBi4Te7 structures. The relationship between the Seebeck coefficient, electrical resistivity, and phase fraction of the two structures was investigated at room temperature. We concluded that changes in the transport properties for all samples may reflect a mixture effect of the phase fraction of the two structures and the amounts of In-substitution in the framework of the assumed structure model in this study. The thermoelectric properties of the samples with x = 0 and 0.18 were determined from 300 K to 723 K from the measured electrical properties and the reported lattice thermal conductivity. The sample with x = 0.18 had the highest dimensionless figure of merit: ZT max = 0.11 at 466 K, which was 1.8 times larger than that of the sample with x = 0.

  16. The new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} and the role of dimensionality in the Cu{sub x}(BiSe){sub 1+?}(TiSe{sub 2}){sub n} series

    SciTech Connect

    Trump, Benjamin A.; Livi, Kenneth J.T.; McQueen, Tyrel M.

    2014-01-15

    The synthesis and physical properties of the new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} are reported. Transmission electron microscopy and powder X-ray diffraction show that the structure consists of alternating rock-salt type BiSe layers and hexagonal (TiSe{sub 2}){sub 2} double layers. Resistivity, specific heat, and magnetization measurements show that it has metallic and diamagnetic behaviors. These results are interpreted and discussed in the context of the transition between single-layer (BiSe){sub 1.13}(TiSe{sub 2}), which shows no charge density wave, and infinite-layered (bulk) 1T-TiSe{sub 2}, which undergoes a charge density wave transition at T=202 K. Intercalation with copper, Cu{sub x}(BiSe){sub 1.15}(TiSe{sub 2}){sub 2}, (0?x?0.10) is also reported, but unlike Cu{sub x}TiSe{sub 2}, no superconductivity is observed down to T=0.05 K. Thus, the series Cu{sub x}(BiSe){sub 1+?}(TiSe{sub 2}){sub n} provides an effective approach to elucidate the impact of dimensionality on charge density wave formation and superconductivity. - Graphical abstract: The newly discovered misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} shown in the series (BiSe){sub 1+?}(TiSe{sub 2}){sub n}. Display Omitted - Highlights: • Reports the structure and properties of the new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2}. • The structure consists of a rock salt type BiSe layer and a double (TiSe{sub 2}){sub 2} layer. • The n=1, 2 misfits (BiSe){sub 1+?}(TiSe{sub 2}){sub n} are found not to exhibit CDW transitions. • Evidence is presented that there is likely a low-lying CDW excited state. • The series Cu{sub x}(BiSe){sub 1+?}(TiSe{sub 2}){sub 2} does not superconduct, unlike Cu{sub x}TiSe{sub 2}.

  17. First-principle investigation of half-metallic ferromagnetism in octahedrally bonded Cr-doped rock-salt SrS, SrSe, and SrTe

    NASA Astrophysics Data System (ADS)

    Doumi, Bendouma; Mokaddem, Allel; Temimi, Lahouari; Beldjoudi, Nadir; Elkeurti, Mohammed; Dahmane, Fethallah; Sayede, Adlane; Tadjer, Abdelkader; Ishak-Boushaki, Mustapha

    2015-04-01

    We have investigated the electronic structure and half-metallic ferromagnetism of Sr1- x Cr x Z (Z = S, Se, and Te) in rock-salt structure at concentrations x ( x = 0.125, 0.25, 0.5, 0.75 and 0.875) of Cr, using first-principles calculations of density functional theory. The electronic and magnetic properties show that Sr1- x Cr x Z (Z = S and Se) at x = 0.125, 0.25, 0.5, 0.75 and Sr1- x Cr x Te at all concentrations are half-metallic ferromagnets (HMF) with spin polarization of 100% and total magnetic moments of 4 ? B per Cr atom, whereas the HMF character destroyed for Sr1- x Cr x Z (Z = S and Se) at x = 0.875. The integrals Bohr magneton of total magnetic moments confirm the half-metallic ferromagnetic behavior of Sr1- x Cr x Z. We have found that the ferromagnetic state is stable by the 3 d- eg (Cr) partially filled states associated with the double-exchange mechanism. Therefore, the Sr1- x Cr x S, Sr1- x Cr x Se, and Sr1- x Cr x Te at low concentration are predicted to be new potential candidates for spintronic applications.

  18. Thermoelectric properties of topological insulator Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3}, and Bi{sub 2}Se{sub 3} thin film quantum wells

    SciTech Connect

    Osterhage, Hermann Gooth, Johannes; Hamdou, Bacel; Gwozdz, Paul; Zierold, Robert; Nielsch, Kornelius

    2014-09-22

    The thermoelectric (TE) figure of merit ZT of topological insulator Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3}, and Bi{sub 2}Se{sub 3} thin film quantum wells is calculated for thicknesses below 10?nm, for which hybridization of the surface states as well as quantum confinement in the bulk are individually predicted to enhance ZT. Here, the question is addressed what ZT can be expected from coexisting surface and bulk states in such quantum wells. It is demonstrated that the parallel contributing bulk and surface channels tend to cancel each other out. This is because the surface-to-volume ratios of the thin films prevent the domination of transport through a single channel and because the individual bulk and surface ZTs are optimized at different Fermi levels.

  19. Micro-Raman spectroscopy of mechanically exfoliated few-quintuple layers of Bi2Te3, Bi2Se3, and Sb2Te3 materials

    E-print Network

    Te3 materials K. M. F. Shahil,a) M. Z. Hossain,b) V. Goyal,c) and A. A. Balandind) Department of Electrical Engineering, Materials Science and Engineering Program, Bourns College of Engineering, University strong interest, owing to the discovery of the topological insulator properties in many members

  20. The influence of capping thioalkyl acid on the growth and photoluminescence efficiency of CdTe and CdSe quantum dots.

    PubMed

    Aldeek, Fadi; Balan, Lavinia; Lambert, Jacques; Schneider, Raphaël

    2008-11-26

    The influence of thioalkyl acid ligand was evaluated during aqueous synthesis at 100?°C and under hydrothermal conditions (150?°C) of CdTe and CdSe quantum dots (QDs). Experiments performed with 3-mercaptopropionic acid (MPA), 6-mercaptohexanoic acid (MHA) and 11-mercaptoundecanoic acid (MUA) demonstrated that the use of MHA and MUA allowed for the preparation of very small nanoparticles (0.6-2.5 nm) in carrying out the reaction under atmospheric pressure or in an autoclave and that the photophysical properties of QDs were dependent on the ligand and on the synthesis conditions. The influence of various experimental conditions, including the Te-to-Cd ratio, temperature, and precursor concentration, on the growth rate of CdTe or CdSe QDs has been systematically investigated. The fluorescence intensities of CdTe QDs capped with MPA, MHA, or MUA versus pH were also found to be related to the surface coverage of the nanoparticles. PMID:21836270

  1. Temperature and composition phase diagram in the iron-based ladder compounds Ba 1 - x Cs x Fe 2 Se 3

    DOE PAGESBeta

    Hawai, Takafumi; Nambu, Yusuke; Ohgushi, Kenya; Du, Fei; Hirata, Yasuyuki; Avdeev, Maxim; Uwatoko, Yoshiya; Sekine, Yurina; Fukazawa, Hiroshi; Ma, Jie; et al

    2015-05-28

    We investigated the iron-based ladder compounds (Ba,Cs)Fe?Se?. Their parent compounds BaFe?Se? and CsFe?Se? have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe?Se? is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe?Se? is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe?Se?, but interladder spin configuration is different. Intermediatemore »compounds show insulating behavior, nevertheless a finite T-linear contribution in specific heat was obtained at low temperatures.« less

  2. Thermal studies of Se{sub 85-x}Te{sub 15}In{sub x} (x = 3,6,9,12) glasses

    SciTech Connect

    Sushama, D.; George, Achamma; Asokan, S.

    2011-10-20

    Bulk glasses of compositions Se{sub 85-x}Te{sub 15}In{sub x} (x = 3,6,9,12) are prepared by melt quenching technique and Differential scanning calorimetry (DSC) is employed to study the thermal stability, crystallization mechanism as well as specific heat of these glasses. It is found that the addition of indium increases the glass transition temperature. From the heating rate dependence of the glass transition temperature the activation energy of glass transition is determined using Kissinger's equation for non-isothermal crystallization of materials. An attempt has been made to explain the variation in the value of T{sub c}, T{sub p} and {Delta}C{sub p} for the composition Se{sub 73}Te{sub 15}In{sub 12} using rigidity percolation threshold (RPT). From the values of (T{sub c}-T{sub g}) the stable glass system is determined.

  3. A DFT study of electron-phonon coupling in proxy rocksalt CuX (X = S, Se, Te) structures and its relationship to possible manifestation of superconductivity

    NASA Astrophysics Data System (ADS)

    Grant, Paul; Hammond, Robert

    2015-03-01

    We have previously reported our computational studies on idealized copper monochalcogenide rocksalt structures, both cubic and tetragonal, focusing on their possible antiferromagnetic properties as determined within a Van Vleck-Mott-Anderson-Hubbard framework. For all values of Hubbard U in the range 0-7 eV, only copper monoxide exhibits a Mott-Hubbard electronic structure, the remainder (S, Se, Te) yielding metallic states characterized by nesting Fermi surfaces arising from Jahn-Teller degenerate s-p overlap. These results suggest exploring possible manifestation of superconductivity via electron-phonon mediated Cooper pairing. We will disclose our results to date applying the Eliashberg-McMillan-Allen-Dynes strong coupling framework to the DFT -derived electronic and vibrational states of CuS, CuSe and CuTe.

  4. New Layered Structures of Cuprous Chalcogenides as Thin Film Solar Cell Materials: Cu2Te and Cu2Se

    SciTech Connect

    Nguyen, Manh; Choi, Jin-Ho; Zhao, Xin; Wang, Cai-Zhuang; Zhang, Zhenyu; Ho, Cai-Ming

    2013-10-01

    The stable crystal structures of two cuprous chalcogenides of Cu2X (X = Te or Se) are predicted using an adaptive genetic algorithm in combination with first-principles density functional theory calculations. Both systems are found to prefer a unique and previously unrecognized layered structure, with the total energies much lower than all structures proposed in the literature so far. The newly discovered structures are further shown to be dynamically and mechanically stable, and possess electronic properties consistent with existing experimental observations. In particular, their layered nature is expected to prevail over other structural forms at the interfaces of thin-film solar cells, and knowledge about the precise atomic structures of the interfaces is a prerequisite for achieving long-term stability and high efficiency of CdTe and Cu(In; Ga)Se2 solar cells.

  5. The role of stoichiometric vacancy periodicity in pressure-induced amorphization of the Ga{sub 2}SeTe{sub 2} semiconductor alloy

    SciTech Connect

    Abdul-Jabbar, N. M.; Kalkan, B.; MacDowell, A. A.; Huang, G.-Y.; Gronsky, R.; Bourret-Courchesne, E. D.; Wirth, B. D.

    2014-08-04

    We observe that pressure-induced amorphization of Ga{sub 2}SeTe{sub 2} (a III-VI semiconductor) is directly influenced by the periodicity of its intrinsic defect structures. Specimens with periodic and semi-periodic two-dimensional vacancy structures become amorphous around 10–11?GPa in contrast to those with aperiodic structures, which amorphize around 7–8?GPa. The result is an instance of altering material phase-change properties via rearrangement of stoichiometric vacancies as opposed to adjusting their concentrations. Based on our experimental findings, we posit that periodic two-dimensional vacancy structures in Ga{sub 2}SeTe{sub 2} provide an energetically preferred crystal lattice that is less prone to collapse under applied pressure. This is corroborated through first-principles electronic structure calculations, which demonstrate that the energy stability of III-VI structures under hydrostatic pressure is highly dependent on the configuration of intrinsic vacancies.

  6. Effect of thermal annealing on structure and optical band gap of amorphous Se{sub 72}Te{sub 25}Sb{sub 3} thin films

    SciTech Connect

    Dwivedi, D. K. Pathak, H. P. Shukla, Nitesh; Kumar, Vipin

    2014-04-24

    Thin films of a?Se{sub 72}Te{sub 25}Sb{sub 3} were prepared by vacuum evaporation technique in a base pressure of 10{sup ?6} Torr on to well cleaned glass substrate. a?Se{sub 72}Te{sub 25}Sb{sub 3} thin films were annealed at different temperatures below their crystallization temperatures for 2h. The structural analysis of the films has been investigated using X-ray diffraction technique. The optical band gap of as prepared and annealed films as a function of photon energy in the wavelength range 400–1100 nm has been studied. It has been found that the optical band gap decreases with increasing annealing temperatures in the present system.

  7. Orbital Processing of High-Quality Zn-Alloyed CdTe Compound Semiconductors

    NASA Technical Reports Server (NTRS)

    Larson, David J., Jr.; Dudley, M.; Raghothamachar, B.; Alexander, J. I. D.; Carlson, F. M.; Gillies, D.; Volz, M.; Ritter, T. M.; DiMarzio, D.

    1999-01-01

    The objective of this research is to investigate the influences of gravitationally-dependent phenomena (hydrostatic and buoyant) on the growth and quality of doped and alloyed Cadmium-Zinc-Telluride (CdZnTe) crystals grown by the modified seeded Bridgman-Stockbarger technique. It is hypothesized that the damping of the gravitationally-dependent buoyancy convection will substantially enhance chemical homogeneity and the near-elimination of hydrostatic pressure will enable significant reduction in defect (dislocations and twins) density.

  8. Effect of charge trapping on effective carrier lifetime in compound semiconductors: High resistivity CdZnTe

    SciTech Connect

    Kamieniecki, Emil

    2014-11-21

    The dominant problem limiting the energy resolution of compound semiconductor based radiation detectors is the trapping of charge carriers. The charge trapping affects energy resolution through the carrier lifetime more than through the mobility. Conventionally, the effective carrier lifetime is determined using a 2-step process based on measurement of the mobility-lifetime product (??) and determining drift mobility using time-of-flight measurements. This approach requires fabrication of contacts on the sample. A new RF-based pulse rise-time method, which replaces this 2-step process with a single non-contact direct measurement, is discussed. The application of the RF method is illustrated with high-resistivity detector-grade CdZnTe crystals. The carrier lifetime in the measured CdZnTe, depending on the quality of the crystals, was between about 5??s and 8??s. These values are in good agreement with the results obtained using conventional 2-step approach. While the effective carrier lifetime determined from the initial portion of the photoresponse transient combines both recombination and trapping in a manner similar to the conventional 2-step approach, both the conventional and the non-contact RF methods offer only indirect evaluation of the effect of charge trapping in the semiconductors used in radiation detectors. Since degradation of detector resolution is associated not with trapping but essentially with detrapping of carriers, and, in particular, detrapping of holes in n-type semiconductors, it is concluded that evaluation of recombination and detrapping during photoresponse decay is better suited for evaluation of compound semiconductors used in radiation detectors. Furthermore, based on previously reported data, it is concluded that photoresponse decay in high resistivity CdZnTe at room temperature is dominated by detrapping of carriers from the states associated with one type of point defect and by recombination of carriers at one type of extended defects. The recombination at the extended defects produces long, logarithmic decay limiting substantially performance of CdZnTe detectors. This decay is associated with the “electrostatic trapping” of excess holes by the Schottky-type depletion space-charge regions formed around the defects.

  9. Thermoelectric Properties of Heavily Doped n-type Pb1- x Y x Te Compounds

    NASA Astrophysics Data System (ADS)

    Ruan, Limin; Luo, Jun; Zhu, Hangtian; Zhao, Huaizhou; Liang, Jingkui

    2015-10-01

    Structure, transport and thermoelectric properties of Y-doped PbTe samples are reported. The combined analysis of powder x-ray diffraction patterns and scanning electron microscopy images indicates that the Pb1- x Y x Te samples with x = 0.015, 0.02, 0.04, and 0.06 are single phase with the NaCl-type structure. Hall effect measurements reveal that all the samples are heavily doped n-type thermoelectric materials. The substitution of trivalent Y for bivalent Pb provides additional electrons to the PbTe matrix, leading to an increase in carrier concentration at room temperature ranging from 4.36 × 1019 cm-3 for the sample with x = 0.015 to 2.50 × 1020 cm-3 for the sample with x = 0.06. Both electrical resistivity and the Seebeck coefficient decrease with the increase of Y content. Meanwhile, the total thermal conductivity presents a notable and unsurprising decline with the increase of Y content, which can be ascribed to the mass fluctuation effect. An optimized figure of merit, ZT, of 1.0 is achieved at 831 K for the sample with x = 0.02.

  10. Nearly lattice matched all wurtzite CdSe/ZnTe type II core-shell nanowires with epitaxial interfaces for photovoltaics.

    PubMed

    Wang, Kai; Rai, Satish C; Marmon, Jason; Chen, Jiajun; Yao, Kun; Wozny, Sarah; Cao, Baobao; Yan, Yanfa; Zhang, Yong; Zhou, Weilie

    2014-04-01

    Achieving a high-quality interface is of great importance in core-shell nanowire solar cells, as it significantly inhibits interfacial recombination and thus improves the photovoltaic performance. Combining thermal evaporation of CdSe and pulsed laser deposition of ZnTe, we successfully synthesized nearly lattice matched all wurtzite CdSe/ZnTe core-shell nanowires on silicon substrates. Comprehensive morphological and structural characterizations revealed that a wurtzite ZnTe shell layer epitaxially grows over a wurtzite CdSe core nanowire with an abrupt interface. Further optical studies confirmed a high-quality interface and demonstrated efficient charge separation induced by the type-II band alignment. A representative photovoltaic device has been demonstrated and yielded an energy-conversion efficiency of 1.7% which can be further improved by surface passivation. The all-wurtzite core-shell nanowire with an epitaxial interface offers an attractive platform to explore the piezo-phototronic effect and promises an efficient hybrid nano-sized, energy harvesting system. PMID:24567192

  11. Influence of Thallium on the Shubnikov - de Haas effect and Thermoelectric Properties of Sb2Te3 and Bi2Se3

    NASA Astrophysics Data System (ADS)

    Kulbachinskii, V. A.; Kudryashov, A. A.; Kytin, V. G.

    2014-12-01

    Influence of Tl-doping on the Shubnikov de Haas effect (SdH) at T=4.2 K in magnetic field up to 38 T of p-Sb2-xTlxTe3 (x=0; 0.005; 0.015; 0.05) and n-Bi2-xTlxSe3 (x=0, 0.01; 0.02; 0.04; 0.06) single crystals has been investigated. By increasing the Tl content, the frequency of the SdH effect and hence the extremal cross-sections of the Fermi-surface decreases in both materials. The hole concentration decreases in Sb2-xTlxTe3 due to a donor effect of Tl and the electron concentration decreases in n-Bi2-xTlxSe3 due to an acceptor effect of Tl. Temperature dependence of the Seebeck coefficient S, electrical conductivity ?, thermal conductivity k and the figure of merit ZT single crystals were measured in the temperature range 77 K - 300 K. The values of k and ? decrease due to Tl doping in Sb2-xTlxTe3 and n-Bi2-xTlxSe3 and the Seebeck coefficient S for all compositions increases in the whole temperature range. The figure of merit ZT increases in both materials. The preferential scattering mechanism in Tl-doped samples changes from the acoustic phonon scattering to the ionized impurity scattering.

  12. Influence of substrate type on transport properties of superconducting FeSe0.5Te0.5 thin films

    NASA Astrophysics Data System (ADS)

    Yuan, Feifei; Iida, Kazumasa; Langer, Marco; Hänisch, Jens; Ichinose, Ataru; Tsukada, Ichiro; Sala, Alberto; Putti, Marina; Hühne, Ruben; Schultz, Ludwig; Shi, Zhixiang

    2015-06-01

    FeSe0.5Te0.5 thin films were grown by pulsed laser deposition on CaF2, LaAlO3 and MgO substrates and structurally and electro-magnetically characterized in order to study the influence of the substrate on their transport properties. The in-plane lattice mismatch between FeSe0.5Te0.5 bulk and the substrate shows no influence on the lattice parameters of the films, whereas the type of substrate affects the crystalline quality of the films and, therefore, the superconducting properties. The film on MgO showed an extra peak in the angular dependence of critical current density Jc(?) at ? = 180° (H||c), which arises from c-axis defects as confirmed by transmission electron microscopy. In contrast, no Jc(?) peaks for H||c were observed in films on CaF2 and LaAlO3. Jc(?) can be scaled successfully for both films without c-axis correlated defects by the anisotropic Ginzburg-Landau approach with appropriate anisotropy ratio ?J. The scaling parameter ?J is decreasing with decreasing temperature, which is different from what we observed in FeSe0.5Te0.5 films on Fe-buffered MgO substrates.

  13. Preferential orientation and thermoelectric properties of n-type Bi2Te2.85Se0.15 alloys by mechanical alloying and equal channel angular extrusion

    NASA Astrophysics Data System (ADS)

    Fan, X. A.; Yang, J. Y.; Zhu, W.; Bao, S. Q.; Duan, X. K.; Xiao, C. J.; Li, K.

    2007-09-01

    Starting from elemental bismuth, tellurium and selenium powders, n-type Bi2Te2.85Se0.15 solid solution with a fine microstructure was prepared by mechanical alloying and equal channel angular extrusion (ECAE) in the present work. The effect of extrusion temperature on the microstructure and thermoelectric properties of the as-ECAEed samples was investigated. A preferentially oriented microstructure with the basal planes (0 0 l) in the parallel direction to extrusion was formed, and the orientation factors F of the (0 0 l) planes of the 703 K and 753 K ECAEed Bi2Te2.85Se0.15 alloys were 0.26 and 0.28, respectively. The electrical resistivity and the Seebeck coefficient decreased, and the thermal conductivity increased with increasing extrusion temperature. The electrical and thermal transmission performances were strongly affected by the preferentially oriented microstructure and the preferential orientation improved the thermoelectric properties of the ECAEed Bi2Te2.85Se0.15 alloys in the parallel direction to extrusion. The maximum dimensionless figure of merit was obtained when extruded at 753 K at a testing temperature of 343 K, ZT = 0.66.

  14. Solar-energy conversion by combined photovoltaic converters with CdTe and CuInSe{sub 2} base layers

    SciTech Connect

    Khrypunov, G. S. Sokol, E. I.; Yakimenko, Yu. I.; Meriuts, A. V.; Ivashuk, A. V.; Shelest, T. N.

    2014-12-15

    The possibility of the combined use of bifacial thin-film solar cells based on CdTe and frontal solar cells with a CuInSe{sub 2} base layer in tandem structures is experimentally confirmed. It is found that, for the use of bifacial solar cells based on cadmium telluride in a tandem structure, the optimal thickness of their base layer should be 1 ?m. The gain in the efficiency of the tandem structure, compared with an individual CuInSe{sub 2}-based solar cell, is 1.8% in the case of series-connected solar cells and 1.3%, for parallel-connected.

  15. Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Final subcontract report, 1 April 1990--30 November 1993

    SciTech Connect

    Sites, J.R.

    1994-07-01

    The report describes the exploration of several aspects of the role of polycrystallinity in the operation of CdTe, CuInSe{sub 2}, and Cu(In,Ga)Se{sub 2} solar cells. The work included the refinement of several analytical techniques, the documentation and understanding of time-dependent voltage effects, the analysis of a large number of individual cells, and significant progress toward developing a viable current-voltage model. This work was integral to the doctoral training of four students and was greatly assisted by several active collaborations within the polycrystalline thin-film solar cell community.

  16. Interface driven energy filtering of thermoelectric power in spark plasma sintered Bi(2)Te(2.7)Se(0.3) nanoplatelet composites.

    PubMed

    Soni, Ajay; Shen, Yiqiang; Yin, Ming; Zhao, Yanyuan; Yu, Ligen; Hu, Xiao; Dong, Zhili; Khor, Khiam Aik; Dresselhaus, Mildred S; Xiong, Qihua

    2012-08-01

    Control of competing parameters such as thermoelectric (TE) power and electrical and thermal conductivities is essential for the high performance of thermoelectric materials. Bulk-nanocomposite materials have shown a promising improvement in the TE performance due to poor thermal conductivity and charge carrier filtering by interfaces and grain boundaries. Consequently, it has become pressingly important to understand the formation mechanisms, stability of interfaces and grain boundaries along with subsequent effects on the physical properties. We report here the effects of the thermodynamic environment during spark plasma sintering (SPS) on the TE performance of bulk-nanocomposites of chemically synthesized Bi(2)Te(2.7)Se(0.3) nanoplatelets. Four pellets of nanoplatelets powder synthesized in the same batch have been made by SPS at different temperatures of 230, 250, 280, and 350 °C. The X-ray diffraction, transmission electron microscopy, thermoelectric, and thermal transport measurements illustrate that the pellet sintered at 250 °C shows a minimum grain growth and an optimal number of interfaces for efficient TE figure of merit, ZT?0.55. For the high temperature (350 °C) pelletized nanoplatelet composites, the concurrent rise in electrical and thermal conductivities with a deleterious decrease in thermoelectric power have been observed, which results because of the grain growth and rearrangements of the interfaces and grain boundaries. Cross section electron microscopy investigations indeed show significant grain growth. Our study highlights an optimized temperature range for the pelletization of the nanoplatelet composites for TE applications. The results provide a subtle understanding of the grain growth mechanism and the filtering of low energy electrons and phonons with thermoelectric interfaces. PMID:22823516

  17. Chemical and structural evolution in the Th-SeO3(2-)/SeO4(2-) system: from simple selenites to cluster-based selenate compounds.

    PubMed

    Xiao, Bin; Langer, Eike; Dellen, Jakob; Schlenz, Hartmut; Bosbach, Dirk; Suleimanov, Evgeny V; Alekseev, Evgeny V

    2015-03-16

    While extensive success has been gained in the structural chemistry of the U-Se system, the synthesis and characterization of Th-based Se structures are widely unexplored. Here, four new Th-Se compounds, ?-Th(SeO3)2, ?-Th(SeO3)2, Th(Se2O5)2, and Th3O2(OH)2(SeO4)3, have been obtained from mild hydrothermal or low-temperature (180-220 °C) flux conditions and were subsequently structurally and spectroscopically characterized. The crystal structures of ?-Th(SeO3)2 and ?-Th(SeO3)2 are based on ThO8 and SeO3 polyhedra, respectively, featuring a three-dimensional (3D) network with selenite anions filling in the Th channels along the a axis. Th(Se2O5)2 is a 3D framework composed of isolated ThO8 polyhedra interconnected by [Se2O5](2-) dimers. Th3O2(OH)2(SeO4)3 is also a 3D framework constructed by octahedral hexathorium clusters [Th6(?3-O)4(?3-OH)4](12+), which are interlinked by selenate groups SeO4(2-). The positions of the vibrational modes associated with both Se(IV)O3(2-) and Se(VI)O4(2-) units, respectively, were determined for four compounds, and the Raman spectra of ?- and ?-Th(SeO3)2 are compared and discussed in detail. PMID:25719971

  18. Liquid-phase syntheses and material properties of two-dimensional nanocrystals of rare earth-selenium compound containing planar Se layers: RESe2 nanosheets and RE4O4Se3 nanoplates.

    PubMed

    Gu, Jun; Zhao, Ze-Qiong; Ding, Yi; Chen, Hong-Liang; Zhang, Ya-Wen; Yan, Chun-Hua

    2013-06-01

    Synthesis of diverse two-dimensional nanostructures with unique material properties is of current interest and multidisciplinary importance but remains a challenge for trivalent rare earth (RE)-selenium (Se) compounds because of the weak affinity between hard rare earth cations and soft selenium anions. In this article, for the first time, we report a mild solution approach toward a series of two-dimensional trivalent RE-selenium compound nanocrystals, namely RESe2 nanosheets (RE = La to Nd, for EuSe2, nanobars were obtained) and RE4O4Se3 nanoplates (RE = Nd, Sm, Gd to Ho), under a high chemical potential of selenium obtained by activating SeO2 powder with oleylamine in high boiling point organic solvents. Both kinds of nanocrystals contain Se with -1 valence in planar Se layers, allowing for a great variability in their crystal structures. Satellite diffraction peaks were observed in the electron diffraction pattern of LaSe2 nanosheets, indicating the presence of Peierls distortion in the Se layers. In the RE4O4Se3 nanoplates, the interaction between Se(2-) ions and [Se-Se](2-) dumbbells in the Se layers increases when the radii of the RE(3+) ions decrease along the lanthanide series, resulting in a narrower optical band gap (from 1.96 to 1.73 eV). The LaSe2 nanosheet films fabricated by drop-casting exhibited good electrical conductivity at room temperature (about 1 ?·cm(-1)). Further, the RE4O4Se3 nanoplates showed very high light extinction capacity in the visible region (extinction coefficient ?i: 4.4 × 10(5) cm(-1) for Nd4O4Se3, and 3.1 × 10(5) cm(-1) for Gd4O4Se3), comparable to that (5 × 10(5) cm(-1)) of CuInS2 commonly used in solar cells. PMID:23672182

  19. Selenium bioaccessibility in stomach, small intestine and colon: Comparison between pure Se compounds, Se-enriched food crops and food supplements.

    PubMed

    Lavu, Rama V Srikanth; Van De Wiele, Tom; Pratti, Varalakshmi L; Tack, Filip; Du Laing, Gijs

    2016-04-15

    Selenium (Se) is an essential nutrient for humans as it plays an important role in glutathione peroxidase (GPx) activity. Moreover, it may reduce cancer risks. The objective of this work was to examine in vitro the bioaccessibility of Se in three different Se-enriched food supplements and two different Se-enriched food crops, with reference to two pure Se standards, and changes in its speciation during intestinal digestion. Selenate was found to be stable throughout the entire digestion, whereas incubation of selenomethionine resulted in the chemical and microbial production of minor metabolites. The bioaccessibility of Se in Se-enriched food supplements and food crops was found to be highest in the small intestine. Compared to SelenoPrecise and Se-ACE tablets, a yoghurt-based supplement exhibited a much lower Se bioaccessibility, possibly due to the presence of nano- or microparticles of elemental Se. Colon microbiota were found to primarily affect Se bioaccessibility in the colon environment, with the presence of inactivated microbiota resulting in a higher bioaccessibility. A higher potential of Se to reach the colon and become accessible in this phase may result in beneficial effects on the colon health. PMID:26616964

  20. Thermoelectric generation device based on p-type Bi0.4Sb1.6Te3 and n-type Bi2Se0.6Te2.4 bulk materials prepared by solid state microwave synthesis

    NASA Astrophysics Data System (ADS)

    Kadhim, A.; Hmood, A.; Abu Hassan, H.

    2013-07-01

    This study reports on the fabrication of a chalcogen-based thermoelectric power generation (TEG) device using p-type Bi0.4Sb1.6Te3 and n-type Bi2Se0.6Te2.4 bulk thermoelectric materials. The microstructure of the samples was characterized by scanning electron microscope (SEM). The phase composition of the powders was characterized by X-ray diffraction (XRD), revealing a rhombohedral structure. The thermoelectric (TE) properties such as the Seebeck coefficient (S) and the electrical conductivity (?) of the resulting alloys were studied in the temperature range of 300-523 K. The power factor (Pfactor) for a Bi0.4Sb1.6Te3 as p-type sample was found to be 4.96 mW/mK2 at 373 K, whereas 2.22 mW/mK2 was obtained at 383 K for a Bi2Se0.6Te2.4 as n-type sample. Electrical power generation characteristics such as high open circuit voltage (Voc) and maximum output power (Pmax) were monitored by changing the temperature conditions required to generate maximum power. The significance of the resistances including the internal resistance (Rin) and contact resistance (RC) between legs and electrodes, are discussed. The maximum output power obtained with the 9 p-n couples device was 39.4 mW under the thermal condition of TH=523 K hot side temperature and ?T=184 K temperature difference.

  1. Mechanical and Electrical Properties of p-type Bi0.4Sb1.6Te3 and n-type Bi2Se0.6Te2.4 Bulk Material for Thermoelectric Applications

    NASA Astrophysics Data System (ADS)

    Kadhim, A.; Hmood, A.; Hassan, H. A.

    2013-04-01

    This study reports on the fabrication of a chalcogen-based thermoelectric power generation (TEG) device using p-type Bi0.4Sb1.6Te3 and n-type Bi2Se0.6Te2.4 bulk thermoelectric materials. The microstructure of the samples was characterized by field emission scanning electron microscopy (FESEM). The phase composition of the powders was characterized by X-ray diffraction (XRD), revealing a rhombohedral structure. The thermoelectric (TE) properties such as Seebeck coefficient (S) and the electrical conductivity (?) of the resulting alloys were studied in the temperature range of 300 K to 523 K. The power factor (Pfactor) for a Bi0.4Sb1.6Te3 as p-type sample was found to be 4.96 mW/mK2 at 373 K, whereas 2.22 mW/mK2 was obtained at 383 K for a Bi2Se0.6Te2.4 as n-type sample. Electrical power generation characteristics such as high open circuit voltage (Voc) and maximum output power (Pmax) were monitored by changing the temperature conditions required to generate maximum power. The significance of the resistances including the internal resistance (Rin) and contact resistance (RC) between legs and electrodes, are discussed. The maximum output power obtained with the 9 p-n couples device was 39.4 mW under the thermal condition of TH = 523 K hot side temperature and ?T = 184 K temperature difference.

  2. Microscopic origin of resistance drift in the amorphous state of the phase-change compound GeTe

    NASA Astrophysics Data System (ADS)

    Gabardi, S.; Caravati, S.; Sosso, G. C.; Behler, J.; Bernasconi, M.

    2015-08-01

    Aging is a common feature of the glassy state. In the case of phase-change chalcogenide alloys the aging of the amorphous state is responsible for an increase of the electrical resistance with time. This phenomenon called drift is detrimental in the application of these materials in phase-change nonvolatile memories, which are emerging as promising candidates for storage class memories. By means of combined molecular dynamics and electronic structure calculations based on density functional theory, we have unraveled the atomistic origin of the resistance drift in the prototypical phase-change compound GeTe. The drift results from a widening of the band gap and a reduction of Urbach tails due to structural relaxations leading to the removal of chains of Ge-Ge homopolar bonds. The same structural features are actually responsible for the high mobility above the glass transition which boosts the crystallization speed exploited in the device.

  3. Crystal Structures and Magnetic Properties of Nickel Chain Compounds PbM2Ni6Te3O18 (M = Mn, Cd).

    PubMed

    Doi, Yoshihiro; Suzuki, Ryo; Hinatsu, Yukio; Kodama, Katsuaki; Igawa, Naoki

    2015-11-16

    The synthesis, crystal structures, and magnetic properties of the pentanary oxides PbM2Ni6Te3O18 (M = Mn and Cd) were investigated. These compounds crystallize in a hexagonal structure with space group P63/m, in which the Ni(2+) ions form a zigzag chain along the c axis. From the magnetic susceptibility and specific heat measurements, we found that the PbCd2Ni6Te3O18 behaves as a low-dimensional magnet due to the intrachain antiferromagnetic interaction between Ni(2+) ions. Both compounds show a long-range antiferromagnetic ordering at 25.7 K (M = Cd) and 86.0 K (Mn). The magnetic structure of PbMn2Ni6Te3O18 determined by neutron diffraction measurements is a collinear antiferromagnetic arrangement of Mn(2+) ions in the Mn2O9 dimeric unit and Ni(2+) ions in the zigzag chain. PMID:26496353

  4. Dynamics and mechanism of oxygen annealing in Fe1+yTe0.6Se0.4 single crystal

    NASA Astrophysics Data System (ADS)

    Sun, Yue; Tsuchiya, Yuji; Taen, Toshihiro; Yamada, Tatsuhiro; Pyon, Sunseng; Sugimoto, Akira; Ekino, Toshikazu; Shi, Zhixiang; Tamegai, Tsuyoshi

    2014-04-01

    Iron chalcogenide Fe(Te,Se) attracted much attention due to its simple structure, which is favorable for probing the superconducting mechanism. Its less toxic nature compared with iron arsenides is also advantageous for applications of iron-based superconductors. By intercalating spacer layers, superconducting transition temperature has been raised over 40 K. On the other hand, the presence of excess Fe is almost unavoidable in Fe(Te,Se) single crystals, which hinders the appearance of bulk superconductivity and causes strong controversies over its fundamental properties. Here we report a Systematical study of O2-annealing dynamics in Fe1+yTe1-xSex by controlling the amount of O2, annealing temperature, and time. Bulk superconductivity can be gradually induced by increasing the amount of O2 and annealing time at suitable temperatures. The optimally annealed crystals can be easily obtained by annealing with ~1.5% molar ratio of oxygen at 400°C for more than 1 hour. Superconductivity was witnessed to evolve mainly from the edge of the crystal to the central part. After the optimal annealing, the complete removal of excess Fe was demonstrated via STM measurements. Some fundamental properties were recharacterized and compared with those of as-grown crystals to discuss the influence of excess Fe.

  5. Dynamics and mechanism of oxygen annealing in Fe1+yTe0.6Se0.4 single crystal.

    PubMed

    Sun, Yue; Tsuchiya, Yuji; Taen, Toshihiro; Yamada, Tatsuhiro; Pyon, Sunseng; Sugimoto, Akira; Ekino, Toshikazu; Shi, Zhixiang; Tamegai, Tsuyoshi

    2014-01-01

    Iron chalcogenide Fe(Te,Se) attracted much attention due to its simple structure, which is favorable for probing the superconducting mechanism. Its less toxic nature compared with iron arsenides is also advantageous for applications of iron-based superconductors. By intercalating spacer layers, superconducting transition temperature has been raised over 40 K. On the other hand, the presence of excess Fe is almost unavoidable in Fe(Te,Se) single crystals, which hinders the appearance of bulk superconductivity and causes strong controversies over its fundamental properties. Here we report a Systematical study of O2-annealing dynamics in Fe(1+y)Te(1-x)Sex by controlling the amount of O2, annealing temperature, and time. Bulk superconductivity can be gradually induced by increasing the amount of O2 and annealing time at suitable temperatures. The optimally annealed crystals can be easily obtained by annealing with ~1.5% molar ratio of oxygen at 400 °C for more than 1 hour. Superconductivity was witnessed to evolve mainly from the edge of the crystal to the central part. After the optimal annealing, the complete removal of excess Fe was demonstrated via STM measurements. Some fundamental properties were recharacterized and compared with those of as-grown crystals to discuss the influence of excess Fe. PMID:24695095

  6. GLOBAL EMISSIONS INVENTORIES OF ACID-RELATED COMPOUNDS T.E. GRAEDEL t , C.M. BENKOVITZ 2, W.C. KEENE 3, D.S. LEE 4,

    E-print Network

    GLOBAL EMISSIONS INVENTORIES OF ACID-RELATED COMPOUNDS T.E. GRAEDEL t , C.M. BENKOVITZ 2, W, and future rely in part on inventories of emissions constructed on appropriate spatial and temporal scales and the regulatory and policy communities. The production of global emissions inventories is the task of the GlobalEmissions

  7. Sensitized chemiluminescence of Tween 20 on CdTe/H(2)O(2) and its analytical applications for determination of phenolic compounds.

    PubMed

    Kang, Jing; Li, Juan; Tang, Jieli; Li, Minjie; Li, Xiaozhou; Zhang, Yihua

    2010-03-01

    In this paper, we proposed a simple and sensitive assay of phenolic compounds (PCs) using 3-mercaptocarboxylic acid (MPA) modified CdTe nanocrystals (CdTe NCs), which contain abundant carboxylic groups (-COOH) and are water-soluble, stable and biocompatible. The effects of surfactants on the CdTe/H(2)O(2) chemiluminescence (CL) system were investigated. It is found that the addition of Tween 20 into the system could induce a significant enhancement on CL intensity. PCs were observed to inhibit the CL signal of the CdTe/H(2)O(2)/Tween 20 system and determined by the proposed method. The CL mechanism was also discussed briefly based on the photoluminescence (PL) and CL spectra. PMID:19954934

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

    SciTech Connect

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

    2014-06-07

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

  9. Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe2.7Se0.3 and p-type Bi0.5Sb1.5Te3

    NASA Astrophysics Data System (ADS)

    Bhame, Shekhar D.; Pravarthana, Dhanapal; Prellier, Wilfrid; Noudem, Jacques G.

    2013-05-01

    Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe2.7Se0.3 and p-type Bi0.5Sb1.5Te3 showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications.

  10. Orbital processing of high-quality CdTe compound semiconductors

    NASA Technical Reports Server (NTRS)

    Larson, David J., Jr.; Alexander, J. I. D.; Gillies, D.; Carlson, F. M.; Wu, J.; Black, D.

    1994-01-01

    CdZnTe crystals were grown in one-g and in micro-g for comparative analysis. The two micro-g crystals were grown in the Crystal Growth Furnace during the First United States Microgravity Laboratory mission (USML-1). The samples were analyzed for chemical homogeneity, structural perfection, and optoelectronic performance (infrared transmission). Fourier Transform Infrared (FTIR) transmission of both ground and flight materials showed that the infrared transmission was close to theoretical, 63% versus 66%, suggesting that the material was close to the stochiometric composition during both the ground and flight experiments. Infrared microscopy confirmed that the principal precipitates were Te and their size (1-10 microns) and density suggested that the primary flight and ground base samples experienced similar cooling rates. Macrosegregation was predicted, using scaling analysis, to be low even in one-g crystals and this was confirmed experimentally, with nearly diffusion controlled growth achieved even in the partial mixing regime on the ground. Radial segregation was monitored in the flight samples and was found to vary with fraction solidified, but was disturbed due to the asymmetric grvitational and thermal fields experienced by the flight samples. The flight samples, however, were found to be much higher in structural perfection than the ground samples produced in the same furnace under identical growth conditions except for the gravitational level. Rocking curve widths were found to be substantially reduced, from 20/35 (one-g) to 9/20 (micro-g) for the best regions of the crystals. The full width at half maximum (FWHM) of 9 arc seconds is as good as the best reported terrestrially for this material. The ground samples were found to have a fully developed mosaic structure consisting of subgrains, whereas the flight sample dislocations were discrete and no mosaic substructure was evident. The defect density was reduced from 50-100,000 (one-g) to 500-25000 EPD (micro-g). These results were confirmed using rocking curve analysis, synchrotron topography, and etch pit analysis. The low dislocation density is thought to have resulted from the near-absence of hydrostatic pressure which allowed the melt to solidify with minimum or no wall contact, resulting in very low stress being exerted on the crystal during growth or during post-solidification cooling.

  11. Resonant photoemission and absorption spectroscopy of the Cu{sub x}TiSe{sub 2} compound

    SciTech Connect

    Shkvarin, A. S. Yarmoshenko, Yu. M.; Skorikov, N. A.; Titov, A. A.; Titov, A. N.

    2012-02-15

    Single crystals of the Cu{sub x}TiSe{sub 2} compound with x = 0.05, 0.09, and 0.33 have been grown. Resonance photoelectron Cu 3p-3d and 2d-3d spectra of the valence bands, the spectra of the core levels, and the L absorption spectra for titanium and copper have been obtained. It is shown that the degree of oxidation of titanium atoms is +4 and the state of copper atoms is close to the state of free copper ions. It is found that the spectra of the valence bands obtained under the Cu 3p and 2p resonance conditions radically differ. For the spectra in the Cu 2p excitation regime, several bands corresponding to different decay channels of the excited state are observed. According to calculations of the density of states, the 3d states of copper are filled incompletely; the occupancy of the 3d band of copper is 9.5 electrons per atom.

  12. Reducing Lattice Thermal Conductivity of the Thermoelectric Compound AgSbTe2 (P4/mmm) by Lanthanum Substitution: Computational and Experimental Approaches

    NASA Astrophysics Data System (ADS)

    Amouyal, Yaron

    2014-10-01

    In this study we performed lattice dynamics first-principles calculations for the promising thermoelectric (TE) compound AgSbTe2, and estimated the stability of its three polymorphs over a wide temperature range from 0 to 600 K. We calculated the vibrational density of states of the AgSbTe2 (P4/mmm) phase. The results suggested that formation of substitutional defects at Ag-sublattice sites impedes lattice vibrations, thereby reducing lattice thermal conductivity. We focused on calculations based on the Debye approximation for the compound La0.125Ag0.875SbTe2, and predicted reduction of the average sound velocity from 1684 to 1563 m s-1 as a result of La doping. This is manifested as a ca. 14% reduction in thermal conductivity. To confirm the results from computation we produced two Ag-Sb-Te-based alloys, a ternary alloy without La addition and a quaternary alloy containing La. We measured the thermal conductivity of both alloys by use of the laser flash analysis method, and, as a result of La alloying, observed a reduction in thermal conductivity from 0.92 to 0.71 W m-1 K-1 at 573 K, as calculated from first principles.

  13. Structural properties of Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} topological insulators grown by molecular beam epitaxy on GaAs(001) substrates

    SciTech Connect

    Liu, X.; Leiner, J.; Dobrowolska, M.; Furdyna, J. K.; Smith, D. J.; Fan, J.; Zhang, Y.-H.; Cao, H.; Chen, Y. P.; Kirby, B. J.

    2011-10-24

    Thin films of Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} have been grown on deoxidized GaAs(001) substrates using molecular beam epitaxy. Cross-sectional transmission electron microscopy established the highly parallel nature of the Te(Se)-Bi-Te(Se)-Bi-Te(Se) quintuple layers deposited on the slightly wavy GaAs substrate surface and the different crystal symmetries of the two materials. Raman mapping confirmed the presence of the strong characteristic peaks reported previously for these materials in bulk form. The overall quality of these films reveals the potential of combining topological insulators with ferromagnetic semiconductors for future applications.

  14. Optical properties of (Se{sub 80}Te{sub 20}){sub 100?x}Ag{sub x} (0 ? x ? 4) thin films

    SciTech Connect

    Singh, D. Kumar, S. Sandhu, S. Thangaraj, R.

    2014-04-24

    Thin films of (Se{sub 80}Te{sub 20}){sub 100?x}Ag{sub x} (0 ? x ? 4) glasses were prepared by thermal evaporation of the bulk samples. The transmittance (T) and reflection (R) spectra of amorphous thin films were obtained in the spectral region in the range 400–2500 nm. The optical band gap (E{sub g}) has been determined by Tauc’s extrapolation method. The surface morphology has been determined by the Scanning Electron Microscopy (SEM)

  15. Determination of the London penetration depth of FeSe0.3Te0.7 thin films by scanning SQUID microscope

    NASA Astrophysics Data System (ADS)

    Lin, H. T.; Wu, S. L.; Wang, J. W.; Chen, T. J.; Wang, M. J.; Chen, J. C.; Wu, M. K.; Chi, C. C.

    2015-08-01

    We use the scanning SQUID microscope (SSM) to image the vortices in superconducting FeSe0.3Te0.7 (FST) thin films. The observed peak flux value of FST is nearly a quarter of that of an accompanying Nb film. We developed a method for quantitatively determining the London penetration depth of the FST film from the known value of Nb. The obtained value, 0.88 ?m, is significantly larger than those obtained from single crystals of similar compositions by using other methods. The methodology developed for this study is useful for measuring London penetration depths of thin-film superconductors in general.

  16. Probing the core-shell-shell structure of CdSe/CdTe/CdS type II quantum dots for solar cell applications

    NASA Astrophysics Data System (ADS)

    Lewis, E. A.; Page, R. C.; Binks, D. J.; Pennycook, T. J.; O'Brien, P.; Haigh, S. J.

    2014-06-01

    A greater understanding of multiple exciton generation in heterostructured colloidal quantum dots can be achieved through detailed modelling, and used to optimise their design for solar cell applications. However, such modelling requires an accurate knowledge of the physical structure of the quantum dots. Here we report the use of high angle annular dark field (HAADF) scanning transmission electron microscope (STEM) imaging to study the size and shape of CdSe/CdTe/CdS type II quantum dots at each of the three stages of their synthesis.

  17. Thermoelectric properties of thin-film Sb0.9Bi1.1Te2.9Se0.1-C composites

    NASA Astrophysics Data System (ADS)

    Kalinin, Yu. E.; Makagonov, V. A.; Sitnikov, A. V.

    2015-10-01

    Thin-film nanocomposites of a Sb0.9Bi1.1Te2.9Se0.1 semiconductor solid solution in the carbon matrix have been synthesized. The low-temperature dependences of the electrical resistivity and thermoelectric power have been investigated in the temperature range of 77-300 K. It has been shown that there is a successive change in the dominant mechanisms of electrical conduction: variable-range hopping conduction over localized states lying in a narrow energy band near the Fermi level, hopping conduction over the nearest neighbors, and hopping electron transfer associated with charge carriers excited into localized states near the band edges.

  18. Structural Characterization and Compositional Dependence of Optical Properties of Ge16Se52Te32- x Sb x ( x = 0, 2, 4, 6, 8) Glassy Alloys

    NASA Astrophysics Data System (ADS)

    Kaistha, Arpit; Modgil, Vivek; Rangra, V. S.

    2015-12-01

    Antimony-substituted Ge-Se-Te quaternary chalcogenide glasses have been synthesized using the melt quench technique. The bonding arrangements in the glassy matrices have been studied through infrared spectra in the spectral region from 50 cm-1 to 300 cm-1. The effect of Sb addition on the optical properties has also been studied using ultraviolet-visible-infrared (UV-Vis-IR) spectroscopy on thin films of uniform thickness. The materials possess high refractive index and tunable bandgap with low values of optical loss. They also possess good infrared transparency regions, high refractive index, and low optical bandgap, making them suitable for use in photonic applications.

  19. Photoinduced effects in thin films of Te{sub 20}As{sub 30}Se{sub 50} glass with nonlinear characterization

    SciTech Connect

    Fedus, K.; Boudebs, G.; Araujo, Cid B. de; Cathelinaud, M.; Charpentier, F.; Nazabal, V.

    2009-02-09

    We discuss the influence of photoinduced effects (PIEs) on the measurements of nonlinear refractive indices and nonlinear absorption coefficients. A chalcogenide glass film Te{sub 20}As{sub 30}Se{sub 50} was studied using picosecond laser pulses at 1064 nm. The nonlinear imaging technique with phase object (NIT-PO) and the Z-scan technique were applied and their results are compared. The NIT-PO technique reveals clearly the influence of PIE on the samples' response, while by using the Z-scan technique we measured the deepness of ablated regions (holes) produced during the measurements.

  20. Synthesis and multinuclear ( sup 13 C, sup 77 Se, sup 125 Te, sup 199 Hg) magnetic resonance spectra of adamantane-like anions of mercury(II), ((. mu. -ER) sub 6 (HgX) sub 4 ) sup 2 minus (E = S, Se, Te; X = Cl, Br, I)

    SciTech Connect

    Dean, P.A.W.; Manivannan, V. )

    1990-08-08

    Multinuclear magnetic resonance has been used to characterize the new adamantane-like anions (({mu}-ER){sub 6}(HgX){sub 4}){sup 2{minus}} (ER = SPr{sup n}, SPh, SePh, TePh; X = Cl, Br, I), which are formed in CH{sub 2}Cl{sub 2} and (or) DMF from Hg(ER){sub 2}, HgX{sub 2} and (R{sub 4}N)X in the correct stoichiometric ratio. The products (Et{sub 4}N){sub 2}(({mu}-EPh){sub 6}(HgCl){sub 4}) (E = Se, Te) have been isolated analytically pure. At ambient probe temperature, only the complexities (({mu}-TePh){sub 6}(HgX){sub 4}){sup 2{minus}} are stable to dissociation of the ({mu}-ER){sub 6}Hg{sub 4} core. However, at 213 K, only the core of (({mu}-SPh){sub 6}(HgCl){sub 4}){sup 2{minus}} is measurably dissociated. Overall, the stability of the complexes to dissociation varies with E in the order Te > Se > S. At reduced temperature inversion at Te is slow on the NMR time scale in (({mu}-TePh){sub 6}(HgX){sub 4}){sup 2{minus}}, and these complexes are shown to exist as on predominant configurational isomer or an equilibrium mixture of, probably, two such isomers. Similar behavior is found for (({mu}-SePh){sub 6}(HgX){sub 4}){sup 2{minus}} (X = Cl, Br), which are the first examples of SeR-bridged adamantanoid clusters to exhibit inversion at Se that is slow on the NMR time scale. Metal ({sup 113}Cd, {sup 199}Hg) NMR data for (({mu}-SPr{sup n}){sub 6}(MI){sub 4}){sup 2{minus}}/(({mu}-SPr{sup n}){sub 6}(M{prime}I){sub 4}){sup 2{minus}} (M = Hg, M{prime} = Cd, Zn; M = Zn, M{prime} = Cd) mixtures at 213 K show that an approximately statistical metal redistribution occurs to give (({mu}-SPr{sup n}){sub 6}(MI){sub 4{minus}n}(M{prime}I){sub n}){sup 2{minus}}. 37 refs., 1 fig., 4 tabs.

  1. Impact of In Situ Generated Ag2Te Nanoparticles on the Microstructure and Thermoelectric Properties of AgSbTe2 Compounds

    NASA Astrophysics Data System (ADS)

    Du, B.; Xu, J.; Zhang, W.; Tang, X.

    2011-05-01

    A series of ternary (Ag2Te) x (Sb2Te3)100- x ( x = 44 to 54) bulk materials with in situ generated Ag2Te nanoparticles were prepared from high-purity elements by combining the melt-quench technique with the spark plasma sintering technique. The influence of the Ag2Te nanoparticles on the thermoelectric transport properties, and the mechanism of nanoparticle formation were investigated. With increasing x, the concentration of the Ag2Te nanoparticles increased monotonically, but their diameter remained nearly unchanged. Due to the possible carrier energy filtering effect caused by the Ag2Te nanoparticle inclusions, the Seebeck coefficient of the sample with x = 50 was two times higher than that of the sample prepared by the melting method. Moreover, notable scattering of mid-to-long wavelength phonons arising from the evenly distributed Ag2Te nanoparticles led to a large reduction of the lattice thermal conductivity. All these effects led to the enhancement of the ZT value of the x = 50 sample (AgSbTe2) compared with the single-phase sample ( x = 44).

  2. Experiment 1: Orbital Processing of High-Quality Zn-Alloyed CdTe Compound Semiconductors

    NASA Technical Reports Server (NTRS)

    Larson, D. J., Jr.; Dudley, M.; Alexander, J. I. D.; Carlson, F. M.; Gillies, D.; DiMarzio, D.

    1998-01-01

    Zinc-alloyed cadmium telluride (Zn:CdTe) crystals were grown in unit gravity and in microgravity for comparative analysis. Two crystals were grown on USML-1/STS-50 in 1992, and two additional crystals were grown on USML-2/STS-73 in 1995. The Crystal Growth Furnace (CGF) in the seeded Bridgman-Stockbarger crystal growth geometry was utilized on both missions. Crystals grown on USML-1/STS-50 were found to have solidified with partial wall contact due to the near-absence of the hydrostatic pressure in microgravity, a residual g-vector that was not axial, and the nonwetting sample/ampoule wetting conditions. Crystals grown on USML-2/STS-73 included: a sample/ampoule identical to the USML-1/STS-73 sample/ampoule, with the addition of a restraining spring to simulate hydrostatic pressure internally, and a tapered ampoule which accomplished 2.2 cm of crystal growth without wall contact. Infrared transmission of all ground and flight samples was found to be 63-66 percent, very close to the theoretical 66 percent, suggesting good stoichiometric control. Infrared microscopy confirmed that the primary precipitates were Te and their size (1-10 microns) and density suggested that the flight- and ground-base samples experienced similar thermal histories. Longitudinal macrosegregation, calculated using scaling analysis, was predicted to be low. Nearly diffusion controlled growth was achieved even in unit gravity and macrosegregation data could be fit with a diffusion controlled model. Radial segregation was monitored and was found to vary with fraction solidified, particularly through the shoulder region, where the sample cross section was varying significantly. It was also disturbed in the flight samples in regions where asymmetric wall contact was noted. In regions where a steady state was established, the radial segregation was invariant within our experimental measurement error. Flight samples were found to be much higher in structural perfection than samples processed in unit gravity under identical growth conditions. In regions where solidification had occurred without wall contact, the free surfaces evidenced virtually no twinning, although twins appeared in the flight samples in regions of wall contact and were pervasive in the ground samples. These results were confirmed using optical microscopy and synchrotron x-ray white beam topography. Full-width half-maximum rocking curve widths (FWHM), recorded in arc-seconds, were significantly reduced from 20 a-s (1 g) to 9 a-s (micro-g) for the best regions of the crystals. The 9 a-s (FWHM) rocking curve value in the unconfined flight samples equals the best value reported terrestrially for this material. The ground samples exhibited a fully developed (111)[110] dislocation mosaic structure, whereas dislocations within the flight samples were discrete and no mosaic structure was evident. The defect density was quantitatively reduced from 75,000 (1 g) to 800 (micro-g) +/-50 percent. Dislocation etch pit density results were confirmed using transmission synchrotron white beam and monochromated beam topography. The low defect density is thought to have resulted from the near absence of hydrostatic pressure, which allowed the molten boule to solidify with little or no wall contact. This minimized the transfer of hoop stresses during solidification and post-solidification processing.

  3. Magnetic and magnetotransport studies of iron-chalcogenide superconductor Fe(Se0.4Te0.6)0.82: observation of thermally activated transport and flux jump

    NASA Astrophysics Data System (ADS)

    Dutta, P.; Chattopadhyay, S.; Das, D.; Majumdar, S.; Chatterjee, S.

    2015-11-01

    The magnetic and magneto-transport behavior of the Fe-based superconductor of nominal composition Fe(Se0.4Te0.6)0.82 has been investigated. Different superconducting parameters such as critical fields, coherence length, penetration depth and the Ginzburg-Landau parameter (?) have been estimated for the present compound. The large value of ? (˜253) is in line with the unconventional type-II nature of the studied superconductor. Thermally activated transport behavior in the presence of an external magnetic field across the superconducting transition region indicates a crossover from a single-vortex pinning regime to a collective flux creep regime at 50 kOe. The sample shows anomalous field dependence of flux flow resistance, which is presumably connected to the inherent superconducting state of the sample. The isothermal resistivity data as a function of external magnetic field show a signature of flux jump below the superconducting transition temperature (T c). The effect of hydrostatic pressure on the superconducting properties of the compound has also been investigated and about 3 K shift in T c has been observed with the application of 10 kbar of pressure.

  4. Development of a computer model for polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells. Annual subcontract report, 1 January 1990--31 December 1990

    SciTech Connect

    Gray, J.L.; Schwartz, R.J.; Lee, Y.J.

    1992-04-01

    This report describes work to develop a highly accurate numerical model for CuInSe{sub 2} and CdTe solar cells. ADEPT (A Device Emulation Program and Toolbox), a one-dimensional semiconductor device simulation code developed at Purdue University, was used as the basis of this model. An additional objective was to use ADEPT to analyze the performance of existing and proposed CuInSe{sub 2} and CdTe solar cell structures. The work is being performed in two phases. The first phase involved collecting device performance parameters, cell structure information, and material parameters. This information was used to construct the basic models to simulate CuInSe{sub 2} and CdTe solar cells. This report is a tabulation of information gathered during the first phase of this project on the performance of existing CuInSe{sub 2} and CdTe solar cells, the material properties of CuInSr{sub 2}, CdTe, and CdS, and the optical absorption properties of CuInSe{sub 2}, CdTe, and CdS. The second phase will entail further development and the release of a version of ADEPT tailored to CuInSe{sub 2} and CdTe solar cells that can be run on a personal computer. In addition, ADEPT will be used to analyze the performance of existing and proposed CuInSe{sub 2} and CdTe solar cell structures. 110 refs.

  5. Integration of CdSe/CdSexTe1?x Type-II Heterojunction Nanorods into Hierarchically Porous TiO2 Electrode for Efficient Solar Energy Conversion

    PubMed Central

    Lee, Sangheon; Flanagan, Joseph C.; Kang, Joonhyeon; Kim, Jinhyun; Shim, Moonsub; Park, Byungwoo

    2015-01-01

    Semiconductor sensitized solar cells, a promising candidate for next-generation photovoltaics, have seen notable progress using 0-D quantum dots as light harvesting materials. Integration of higher-dimensional nanostructures and their multi-composition variants into sensitized solar cells is, however, still not fully investigated despite their unique features potentially beneficial for improving performance. Herein, CdSe/CdSexTe1?x type-II heterojunction nanorods are utilized as novel light harvesters for sensitized solar cells for the first time. The CdSe/CdSexTe1?x heterojunction-nanorod sensitized solar cell exhibits ~33% improvement in the power conversion efficiency compared to its single-component counterpart, resulting from superior optoelectronic properties of the type-II heterostructure and 1-octanethiol ligands aiding facile electron extraction at the heterojunction nanorod-TiO2 interface. Additional ~32% enhancement in power conversion efficiency is achieved by introducing percolation channels of large pores in the mesoporous TiO2 electrode, which allow 1-D sensitizers to infiltrate the entire depth of electrode. These strategies combined together lead to 3.02% power conversion efficiency, which is one of the highest values among sensitized solar cells utilizing 1-D nanostructures as sensitizer materials. PMID:26638994

  6. Fermi-level stabilization in the topological insulators Bi2Se3 and Bi2Te3: Origin of the surface electron gas

    NASA Astrophysics Data System (ADS)

    Suh, Joonki; Fu, Deyi; Liu, Xinyu; Furdyna, Jacek K.; Yu, Kin Man; Walukiewicz, Wladyslaw; Wu, Junqiao

    2014-03-01

    Two-dimensional electron gas (2DEG) coexists with topological states on the surface of topological insulators (TIs), while the origin of the 2DEG remains elusive. In this work, electron density in TI thin films (Bi2Se3,Bi2Te3, and their alloys) were manipulated by controlling the density of electronically active native defects with particle irradiation. The measured electron concentration increases with irradiation dose but saturates at different levels for Bi2Se3 and Bi2Te3. The results are in quantitative agreement with the amphoteric defect model, which predicts that electronically active native defects shift the Fermi energy (EF) toward a Fermi stabilization level (EFS) located universally at ˜4.9 eV below the vacuum level. Combined with thickness-dependent data, it is demonstrated that regardless of the bulk doping, the surface EF is always pinned at EFS, producing a band bending and 2DEG on TI film surfaces. Our work elucidates native defect physics of TIs with a model universally applicable to other semiconductors and has critical implications for potential device applications of TIs.

  7. Thermoelectric Properties of Cu-doped Bi2Te2.85Se0.15 Prepared by Pulse-Current Sintering Under Cyclic Uniaxial Pressure

    NASA Astrophysics Data System (ADS)

    Kitagawa, Hiroyuki; Mimura, Naoki; Takimura, Kodai; Morito, Shigekazu; Kikuchi, Kotaro

    2015-10-01

    N-type Cu-doped Bi2Te2.85Se0.15 thermoelectric materials were prepared by pulse-current sintering under cyclic uniaxial pressure, and the effect of the cyclic uniaxial pressure on texture and thermoelectric properties was investigated. Cu x Bi2Te2.85Se0.15 (x = 0-0.03) powder prepared by mechanical alloying was sintered at 673 K using pulse-current heating under 100 MPa of cyclic uniaxial pressure. X-ray diffraction patterns and electron backscattered diffraction analyses showed that the cyclic uniaxial pressure was effective for texture control. The flattened crystal grains were stacked in the thickness direction of the sintered materials and the hexagonal c-plane strongly tended to align in the direction perpendicular to the uniaxial pressure. As a result of this crystal alignment, the electrical resistivity in the direction perpendicular to the uniaxial pressure became smaller than that of equivalent samples prepared with a constant uniaxial pressure. The smaller resistivity led to a larger power factor, and the figure of merit was improved by the application of cyclic uniaxial pressure.

  8. Transport and thermoelectric properties of Bi2Te2.7Se0.3 prepared by mechanical alloying and hot pressing

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    Bi2Te2.7Se0.3 was prepared by mechanical alloying (MA) and hot pressing (HP), after which the effects of HP temperature on the transport and the thermoelectric properties were evaluated. Bismuth chalcogenide phases were synthesized afterMA for 4 h, and no secondary phases were observed. The relative densities of all hot-pressed specimens were higher than 95%. The carrier concentration and the mobility increased with increasing HP temperature, possibly due to the grain growth and the reduced number of lattice defects. All specimens showed n-type conductions in the temperature range from 323 K to 523 K. The electrical conductivity slightly decreased with increasing temperature, exhibiting a degenerate semiconductor behavior. With increasing HP temperature, an increase in the electrical conductivity and a decrease in the Seebeck coefficient were observed. The maximum dimensionless figure of merit obtained was 0.72 at 473 K for the Bi2Te2.7Se0.3 hot-pressed at 673 K due to its low thermal conductivity and high electrical conductivity.

  9. Enhancement of transition temperature in Fe{sub x}Se{sub 0.5}Te{sub 0.5} film via iron vacancies

    SciTech Connect

    Zhuang, J. C.; Yeoh, W. K. E-mail: zxshi@seu.edu.cn; Cui, X. Y.; Ringer, S. P.; Kim, J. H.; Shi, D. Q.; Wang, X. L.; Dou, S. X.; Shi, Z. X. E-mail: zxshi@seu.edu.cn

    2014-06-30

    The effects of iron deficiency in Fe{sub x}Se{sub 0.5}Te{sub 0.5} thin films (0.8???x???1) on superconductivity and electronic properties have been studied. A significant enhancement of the superconducting transition temperature (T{sub C}) up to 21?K was observed in the most Fe deficient film (x?=?0.8). Based on the observed and simulated structural variation results, there is a high possibility that Fe vacancies can be formed in the Fe{sub x}Se{sub 0.5}Te{sub 0.5} films. The enhancement of T{sub C} shows a strong relationship with the lattice strain effect induced by Fe vacancies. Importantly, the presence of Fe vacancies alters the charge carrier population by introducing electron charge carriers, with the Fe deficient film showing more metallic behavior than the defect-free film. Our study provides a means to enhance the superconductivity and tune the charge carriers via Fe vacancy, with no reliance on chemical doping.

  10. Integration of CdSe/CdSexTe1-x Type-II Heterojunction Nanorods into Hierarchically Porous TiO2 Electrode for Efficient Solar Energy Conversion.

    PubMed

    Lee, Sangheon; Flanagan, Joseph C; Kang, Joonhyeon; Kim, Jinhyun; Shim, Moonsub; Park, Byungwoo

    2015-01-01

    Semiconductor sensitized solar cells, a promising candidate for next-generation photovoltaics, have seen notable progress using 0-D quantum dots as light harvesting materials. Integration of higher-dimensional nanostructures and their multi-composition variants into sensitized solar cells is, however, still not fully investigated despite their unique features potentially beneficial for improving performance. Herein, CdSe/CdSexTe1-x type-II heterojunction nanorods are utilized as novel light harvesters for sensitized solar cells for the first time. The CdSe/CdSexTe1-x heterojunction-nanorod sensitized solar cell exhibits ~33% improvement in the power conversion efficiency compared to its single-component counterpart, resulting from superior optoelectronic properties of the type-II heterostructure and 1-octanethiol ligands aiding facile electron extraction at the heterojunction nanorod-TiO2 interface. Additional ~32% enhancement in power conversion efficiency is achieved by introducing percolation channels of large pores in the mesoporous TiO2 electrode, which allow 1-D sensitizers to infiltrate the entire depth of electrode. These strategies combined together lead to 3.02% power conversion efficiency, which is one of the highest values among sensitized solar cells utilizing 1-D nanostructures as sensitizer materials. PMID:26638994

  11. Photoluminescence of double core/shell infrared (CdSeTe)/ZnS quantum dots conjugated to Pseudo rabies virus antibodies

    NASA Astrophysics Data System (ADS)

    Torchynska, T. V.; Casas Espinola, J. L.; Jaramillo Gómez, J. A.; Douda, J.; Gazarian, K.

    2013-06-01

    Double core CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm (1.60 eV) have been studied by photoluminescence (PL) and Raman scattering methods in the non-conjugated state and after the conjugation to the Pseudo rabies virus (PRV) antibodies. The transformation of PL spectra, stimulated by the electric charge of antibodies, has been detected for the bioconjugated QDs. Raman scattering spectra are investigated with the aim to reveal the CdSeTe core compositions. The double core QD energy diagrams were designed that help to analyze the PL spectra and their transformation at the bioconjugation. It is revealed that the interface in double core QDs has the type II quantum well character that permits to explain the near IR optical transition (1.60 eV) in the double core QDs. It is shown that the essential transformation of PL spectra is useful for the study of QD bioconjugation with specific antibodies and can be a powerful technique in early medical diagnostics.

  12. Improvement of thermoelectric properties induced by uniquely ordered lattice field in Bi{sub 2}Se{sub 0.5}Te{sub 2.5} pillar array

    SciTech Connect

    Tan, Ming Hao, Yanming; Wang, Gangzhi

    2014-07-01

    In this study, it was found that uniquely ordered lattice field favors transport of carriers but hinder that of phonons. The n-Bi{sub 2}Se{sub 0.5}Te{sub 2.5} pillar array film was successfully achieved by a simple ion beam assisted deposition technique. This oriented pillar array structure is clear with pillar diameter of about 30 nm, exhibiting a uniquely ordered lattice field. The properties of the ordered Bi{sub 2}Se{sub 0.5}Te{sub 2.5} pillar array were greatly enhanced in comparison with those of the ordinary film. The Bi{sub 2}Se{sub 0.5}Te{sub 2.5} pillar array with a thermoelectric dimensionless figure-of-merit ZT=1.28 was obtained at room temperature. The in-plane transport mechanisms of the ordered pillar array and the ordinary structures, lattice field model, are proposed and investigated. The specially ordered lattice field is the main reason for the properties enhancement observed in the Bi{sub 2}Se{sub 0.5}Te{sub 2.5} film. Introduction of such ordered lattice field into TE films is therefore a very promising approach. - Graphical abstract: In this study, it was found that uniquely ordered lattice field favors transport of carriers but hinder that of phonons. The Bi{sub 2}Se{sub 0.5}Te{sub 2.5} pillar array film with a thermoelectric dimensionless figure-of-merit ZT=1.28 was obtained at room temperature. The in-plane transport mechanisms of the ordered pillar array and the ordinary structures, the lattice field model, are proposed and investigated. The specially ordered lattice field is the main reason for the properties enhancement observed in the Bi{sub 2}Se{sub 0.5}Te{sub 2.5} pillar array. Introduction of such uniquely ordered lattice field into TE films is therefore a very promising approach. In (a) TEM and (b) HRTEM images of the ordered Bi{sub 2}Se{sub 0.5}Te{sub 2.5} column array. - Highlights: • Uniquely ordered Bi{sub 2}Se{sub 0.5}Te{sub 2.5} pillar array was achieved by an IBAD method. • The pillar array with an ordered lattice field exhibits attractive TE property. • The transport mechanism of such ordered pillar array is proposed and investigated. • Introduction of such ordered lattice field into film is a very promising approach.

  13. CsPb3Bi3Te8 and CsPb4Bi3Te9: low-dimensional compounds and the homologous series CsPbmBi3Te5 + m.

    PubMed

    Hsu, Kuei-Fang; Lal, Sangeeta; Hogan, Tim; Kanatzidis, Mercouri G

    2002-07-01

    Two new thermoelectric materials of quaternary bismuth telluride CsPb3Bi3Te8 and CsPb4Bi3Te9 are reported, which are members of a homologous series featuring anionic slabs [PbmBi3Te5 + m]- (m = 1-4) of monotonically increasing thickness. PMID:12125565

  14. Enhancement of thermoelectric properties by Na doping in Te-free p-type AgSbSe2.

    PubMed

    Cai, Songting; Liu, Zihang; Sun, Jianyong; Li, Rui; Fei, Weidong; Sui, Jiehe

    2015-01-21

    AgSbSe2 possesses extremely low thermal conductivity and high Seebeck coefficient, but the low electronic conductivity leads to a low ZT value. In this paper, Na is used to substitute Sb to improve the electronic conductivity. The results show that Na doping not only improves the power factor caused by the enhanced carrier concentration, but also decreases the thermal conductivity due to point defects, nanoscale stacking faults and Na-rich precipitate. Consequently, a high ZT value of 0.92 is achieved in the AgSb0.99Na0.01Se2 sample. PMID:25407495

  15. Hydrothermal synthesis and thermoelectric properties of nanostructured Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds

    SciTech Connect

    Zhang, Yanhua; Academy of Equipment Command and Technology, Beijing 102249 ; Xu, Guiying; Mi, Jianli; Han, Fei; Wang, Ze; Ge, Changchun

    2011-05-15

    Research highlights: {yields} Single-phase Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} powders have been synthesized by a hydrothermal route. {yields} Hexagonal Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} naosheets due to the anisotropic growth of the crystals. {yields} The temperature gradients lead to directional arrangement nanosheet-agglomerates. {yields} Nanosheet-agglomerates are beneficial for improving the TE property of products. {yields} A maximum figure of merit of 0.86 is achieved at about 100 {sup o}C. -- Abstract: Single-phase Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds have been prepared by hydrothermal synthesis at 150 {sup o}C for 24 h using SbCl{sub 3}, BiCl{sub 3} and tellurium powder as precursors. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) have been applied to analyze the phase distributions, microstructures and grain sizes of the as-grown Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} products. It is found that the hydrothermally synthesized Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} nanopowders have a morphology dominated by irregular hexagonal sheets due to the anisotropic growth of the crystals. The Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} nanosheets are parallelly stacked in certain direction to form sheet-agglomerates attribute to the temperature gradients in the solution.

  16. First-principles calculation of the bulk photovoltaic effect in the polar compounds LiAsS2, LiAsSe2, and NaAsSe2.

    PubMed

    Brehm, John A; Young, Steve M; Zheng, Fan; Rappe, Andrew M

    2014-11-28

    We calculate the shift current response, which has been identified as the dominant mechanism for the bulk photovoltaic effect, for the polar compounds LiAsS2, LiAsSe2, and NaAsSe2. We find that the magnitudes of the photovoltaic responses in the visible range for these compounds exceed the maximum response obtained for BiFeO3 by 10-20 times. We correlate the high shift current response with the existence of p states at both the valence and conduction band edges, as well as the dispersion of these bands, while also showing that high polarization is not a requirement. With low experimental band gaps of less than 2 eV and high shift current response, these materials have potential for use as bulk photovoltaics. PMID:25429954

  17. First-principles calculation of the bulk photovoltaic effect in the polar compounds LiAsS2, LiAsSe2, and NaAsSe2

    NASA Astrophysics Data System (ADS)

    Brehm, John A.; Young, Steve M.; Zheng, Fan; Rappe, Andrew M.

    2014-11-01

    We calculate the shift current response, which has been identified as the dominant mechanism for the bulk photovoltaic effect, for the polar compounds LiAsS2, LiAsSe2, and NaAsSe2. We find that the magnitudes of the photovoltaic responses in the visible range for these compounds exceed the maximum response obtained for BiFeO3 by 10-20 times. We correlate the high shift current response with the existence of p states at both the valence and conduction band edges, as well as the dispersion of these bands, while also showing that high polarization is not a requirement. With low experimental band gaps of less than 2 eV and high shift current response, these materials have potential for use as bulk photovoltaics.

  18. Dispersion of the linear and nonlinear optical susceptibilities of the CuAl(S{sub 1–x}Se{sub x})? mixed chaclcopyrite compounds

    SciTech Connect

    Reshak, A. H.; Brik, M. G.; Auluck, S.

    2014-09-14

    Based on the electronic band structure, we have calculated the dispersion of the linear and nonlinear optical susceptibilities for the mixed CuAl(S{sub 1–x}Se{sub x})? chaclcopyrite compounds with x=0.0, 0.25, 0.5, 0.75, and 1.0. Calculations are performed within the Perdew-Becke-Ernzerhof general gradient approximation. The investigated compounds possess a direct band gap of about 2.2 eV (CuAlS?), 1.9 eV (CuAl(S?.??Se?.??)?), 1.7 eV (CuAl(S?.?Se?.?)?), 1.5 eV (CuAl(S?.??Se?.??)?), and 1.4 eV (CuAlSe?) which tuned to make them optically active for the optoelectronics and photovoltaic applications. These results confirm that substituting S by Se causes significant band gaps' reduction. The optical function's dispersion ??{sup xx}(?) and ??{sup zz}(?)/??{sup xx}(?), ??{sup yy}(?), and ??{sup zz}(?) was calculated and discussed in detail. To demonstrate the effect of substituting S by Se on the complex second-order nonlinear optical susceptibility tensors, we performed detailed calculations for the complex second-order nonlinear optical susceptibility tensors, which show that the neat parents compounds CuAlS? and CuAlSe? exhibit | ????²}(-2?;?;?) | as the dominant component, while the mixed alloys exhibit | ????²(-2?;?;?) | as the dominant component. The features of | ????²}(-2?;?;?) | and | ?{sub 111}²}(-2?;?;?) | spectra were analyzed on the basis of the absorptive part of the corresponding dielectric function ??(?) as a function of both ?/2 and ?.

  19. Investigation of scanning tunneling spectra on iron-based superconductor FeSe0.5Te0.5(in Chinese)

    DOE PAGESBeta

    Du, Z. -Y.; Fang, D. -L.; Wang, Z. -Y.; Du, G.; Yang, X.; Yang, H.; Gu, G.; -H, Wen H.

    2015-05-05

    FeSe0.5Te0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73± 0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. Accordingmore »to the positions of coherence peaks, we determine the superconducting gap 2? = 5.5 meV, and the reduced gap 2?/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy ? of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature ?/kBTc ? 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.« less

  20. Microwave (MW), thermal, and ultraviolet (UV) annealing were used to explore the response of Ag structures on a Ge-Se chalcogenide glass (ChG) thin film as flexible radiation sensors, and Te-Ti

    E-print Network

    Microwave (MW), thermal, and ultraviolet (UV) annealing were used to explore the response of Ag structures on a Ge-Se chalcogenide glass (ChG) thin film as flexible radiation sensors, and Te of metallized Cu. Flexible resistive radiation sensors consisting of Ag electrodes on a Ge20Se80 ChG thin film

  1. Magnetic properties of Fe{sub 2}P-type R{sub 6}CoTe{sub 2} compounds (R=Gd-Er)

    SciTech Connect

    Morozkin, A.V.; Mozharivskyj, Yu; Svitlyk, V.; Nirmala, R.; Isnard, O.; Ritter, C.

    2010-06-15

    The magnetic structure of the Fe{sub 2}P-type R{sub 6}CoTe{sub 2} phases (R=Gd-Er, space group P6-bar 2m) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: T{sub C}=220 K and T{sub CN}=180 K for Gd{sub 6}CoTe{sub 2}, T{sub C}=174 K and T{sub CN}=52 K for Tb{sub 6}CoTe{sub 2}, T{sub C}=125 K and T{sub CN}=26 K for Dy{sub 6}CoTe{sub 2}, T{sub CN}=60 K and T{sub N}=22 K for Ho{sub 6}CoTe{sub 2} and T{sub CN{approx}}30 K and T{sub N{approx}}14 K for Er{sub 6}CoTe{sub 2}. Between 174 and 52 K Tb{sub 6}CoTe{sub 2} has a collinear magnetic structure with K{sub 0}=[0, 0, 0] and with magnetic moments along the c-axis, whereas below 52 K it adopts a non-collinear ferromagnetic one. Below 60 K the magnetic structure of Ho{sub 6}CoTe{sub 2} is that of a non-collinear ferromagnet. The holmium magnetic components with a K{sub 0}=[0, 0, 0] wave vector are aligned ferromagneticaly along the c-axis, whereas the magnetic component with a K{sub 1}=[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at {approx}22 K coincides with the reorientation of the Ho magnetic component with the K{sub 0} vector from the collinear to the non-collinear state. Below 30 K Er{sub 6}CoTe{sub 2} shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K{sub 0}=[0, 0, 0] and K{sub 1}=[1/2, 1/2, 0]. The low-temperature magnetic transition at {approx}14 K corresponds to the variation in the magnitudes of the M{sub Er}{sup K0} and M{sub Er}{sup K1} magnetic components. In these phases, no local moment was detected on the cobalt site. The magnetic entropy of Gd{sub 6}CoTe{sub 2} increases from {Delta}S{sub mag}=-4.5 J/kg K at 220 K up to {Delta}S{sub mag}=-6.5 J/kg K at 180 K for the field change {Delta}{mu}{sub 0}H=0-5 T. - Graphical abstract: The novel Fe{sub 2}P-type R{sub 6}CoTe{sub 2} phases (R=Gd-Er, space group P6-bar 2m) show ferromagnetic type ordering in the temperature range 14-220 K.All compounds demonstrate high-temperature ferromagnetic and low-temperature antiferromagnetic ordering.The magnetic entropy of Gd{sub 6}CoTe{sub 2} increases from {Delta}S{sub mag}=-4.5 J/kg K at 220 K up to {Delta}S{sub mag}=-6.5 J/kg K at 180 K for the field change {Delta}{mu}{sub 0}H=0-5 T.The R{sub 6}CoTe{sub 2} compounds exhibit the commensurate magnetic structures with wave vectors K{sub 0}=[0, 0, 0] and K{sub 1}=[1/2, 1/2, 1/2].

  2. Compound Radix Sophorae Flavescentis exerts antitumor effects by inhibiting the proliferation and inducing the apoptosis of esophageal carcinoma TE-8 cells

    PubMed Central

    YANG, XIAOYU; CAI, WEIMEI; YANG, QINGHUI; LU, ZHIHONG; LI, JINSONG; YU, JIAN

    2015-01-01

    The aim of this study was to examine the effects of compound Radix Sophorae Flavescentis on the proliferation of esophageal carcinoma TE-8 cells and to elucidate the mechanisms involved. For this purpose, we incubated TE-8 cells in medium containing various concentrations (0, 0.0125, 0.025, 0.05, 0.1, 0.2, 0.4 and 0.8 mg/ml) of the compound Radix Sophorae Flavescentis injection and its effects on the proliferation of TE-8 cells were examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In addition, we observed the morphological changes and measured the expression levels of apoptosis-related genes (caspase-3, Bcl-2 and Bax) in the cells treated with different doses of the compound (low-dose group, 0.05 mg/ml; medium-dose group, 0.2 mg/ml; and high-dose group, 0.8 ng/ml) by reverse transcription-quantitative PCR (RT-qPCR). The apoptotic index of the cancer cells treated with different doses of the compound was determined by TUNEL assay. Our results revealed that compared with the control group (untreated cells), the proliferation of the cancer cells treated with the compound was significantly inhibited (P?0.05); the inhibition of the proliferation of the cancer cells occured in a dose-dependent manner. Compared with the control group, the apoptotic rate of the cells in the low-dose, medium-dose and high-dose groups increased significantly (P<0.05) in a dose-dependent manner. In addition, compared with the control group, the mRNA expression of caspase-3 and Bax increased significantly in the cells treated with the compound. However, the mRNA expression of Bcl-2 markedly decreased (P<0.05). With the gradual increase in the drug concentration, the mRNA expression levels of caspase-3, Bcl-2 and Bax in the cancer cells were altered in a dose-dependent manner. In conclusion, our data demonstrate that compound Radix Sophorae Flavescentis injection significantly enhances the expression of pro-apoptotic genes in esophageal carcinoma TE-8 cells by increasing apoptosis and inhibiting cell proliferation. Thus, this study provides a theoretical basis for the clinical treatment of esophageal carcinoma. PMID:26622820

  3. Mechanical and thermal properties of h-MX{sub 2} (M?=?Cr, Mo, W; X?=?O, S, Se, Te) monolayers: A comparative study

    SciTech Connect

    Çak?r, Deniz Peeters, François M.; Sevik, Cem

    2014-05-19

    Using density functional theory, we obtain the mechanical and thermal properties of MX{sub 2} monolayers (where M?=?Cr, Mo, W and X?=?O, S, Se, Te). The ?-centered phonon frequencies (i.e., A{sub 1}, A{sub 2}{sup ?}, E?, and E?), relative frequency values of A{sub 1}, and E? modes, and mechanical properties (i.e., elastic constants, Young modulus, and Poisson's ratio) display a strong dependence on the type of metal and chalcogenide atoms. In each chalcogenide (metal) group, transition-metal dichalcogenides (TMDCs) with W (O) atom are found to be much stiffer. Consistent with their stability, the thermal expansion of lattice constants for TMDCs with O (Te) is much slower (faster). Furthermore, in a heterostructure of these materials, the difference of the thermal expansion of lattice constants between the individual components becomes quite tiny over the whole temperature range. The calculated mechanical and thermal properties show that TMDCs are promising materials for heterostructures.

  4. Experimental detection of a Majorana mode in the core of a magnetic vortex inside a topological insulator-superconductor Bi(2)Te(3)/NbSe(2) heterostructure.

    PubMed

    Xu, Jin-Peng; Wang, Mei-Xiao; Liu, Zhi Long; Ge, Jian-Feng; Yang, Xiaojun; Liu, Canhua; Xu, Zhu An; Guan, Dandan; Gao, Chun Lei; Qian, Dong; Liu, Ying; Wang, Qiang-Hua; Zhang, Fu-Chun; Xue, Qi-Kun; Jia, Jin-Feng

    2015-01-01

    Majorana fermions have been intensively studied in recent years for their importance to both fundamental science and potential applications in topological quantum computing. They are predicted to exist in a vortex core of superconducting topological insulators. However, it is extremely difficult to distinguish them experimentally from other quasiparticle states for the tiny energy difference between Majorana fermions and these states, which is beyond the energy resolution of most available techniques. Here, we circumvent the problem by systematically investigating the spatial profile of the Majorana mode and the bound quasiparticle states within a vortex in Bi(2)Te(3) films grown on a superconductor NbSe(2). While the zero bias peak in local conductance splits right off the vortex center in conventional superconductors, it splits off at a finite distance ?20??nm away from the vortex center in Bi(2)Te(3). This unusual splitting behavior has never been observed before and could be possibly due to the Majorana fermion zero mode. While the Majorana mode is destroyed by the interaction between vortices, the zero bias peak splits as a conventional superconductor again. This work provides self-consistent evidences of Majorana fermions and also suggests a possible route to manipulating them. PMID:25615497

  5. Nanojunction-mediated photocatalytic enhancement in heterostructured CdS/ZnO, CdSe/ZnO, and CdTe/ZnO nanocrystals.

    PubMed

    Eley, Clive; Li, Tong; Liao, Fenglin; Fairclough, Simon Michael; Smith, Jason M; Smith, George; Tsang, Shik Chi Edman

    2014-07-21

    A series of highly efficient semiconductor nanocrystal (NC) photocatalysts have been synthesized by growing wurtzite-ZnO tetrahedrons around pre-formed CdS, CdSe, and CdTe quantum dots (QDs). The resulting contact between two small but high-quality crystals creates novel CdX/ZnO heterostructured semiconductor nanocrystals (HSNCs) with extensive type-II nanojunctions that exhibit more efficient photocatalytic decomposition of aqueous organic molecules under UV irradiation. Catalytic testing and characterization indicate that catalytic activity increases as a result of a combination of both the intrinsic chemistry of the chalcogenide anions and the heterojunction structure. Atomic probe tomography (APT) is employed for the first time to probe the spatial characteristics of the nanojunction between cadmium chalcogenide and ZnO crystalline phases, which reveals various degrees of ion exchange between the two crystals to relax large lattice mismatches. In the most extreme case, total encapsulation of CdTe by ZnO as a result of interfacial alloying is observed, with the expected advantage of facilitating hole transport for enhanced exciton separation during catalysis. PMID:24962739

  6. Critical thickness and strain relaxation in high-misfit heteroepitaxial systems: PbTe1-xSex on PbSe (001)

    NASA Astrophysics Data System (ADS)

    Wiesauer, Karin; Springholz, G.

    2004-06-01

    Strain relaxation and misfit dislocation formation is investigated for the high-misfit PbTe1-xSex/PbSe (001) heteroepitaxial system in which the lattice mismatch varies from 0% to 5.5%. Because a two-dimensional (2D) layer growth prevails for all PbTe1-xSex ternary compositions, the lattice mismatch is relaxed purely by misfit dislocations. In addition, it is found that strain relaxation is not hindered by dislocation kinetics. Therefore, this material combination is an ideal model system for testing the equilibrium Frank van der Merwe and Matthews Blakeslee strain relaxation models. In our experiments, we find significantly lower values of the critical layer thickness as compared to the model predictions. This discrepancy is caused by the inappropriate description of the dislocation self-energies when the layer thickness becomes comparable to the dislocation core radius. To resolve this problem, a modified expression for the dislocation self-energy is proposed. The resulting theoretical critical thicknesses are in excellent agreement with the experimental data. In addition, a remarkable universal scaling behavior is found for the strain relaxation data. This underlines the breakdown of the current strain relaxation models.

  7. Nonlinear optical diagnostic of semimagnetic semiconductors Pb{sub 1-x}Yb {sub x}X (X = S, Se, Te)

    SciTech Connect

    Nouneh, K.; Kityk, I.V.; Benet, S.; Charar, S.; Plucinski, K.J.

    2007-02-15

    Nonlinear optical measurements were performed to elucidate the influence of magnetic ions on the behavior of charge carriers in magnetic semiconductors-Pb{sub 1-x}Yb {sub x}X (X = S, Se, Te at x = 1-3%). It was shown that nonlinear optical methods could be used as sensitive tools for investigations of electron-phonon anharmonicity near low-temperature semiconductor-insulator phase transitions. There exists a difference between surface and bulk-like contributions to the nonlinear optical effects. It was shown that only low-temperature Two Photon Absorption (TPA) oscillator may be related to the number of the electron-phonon anharmonic modes responsible for the observed phase transformation. The explanation of the anomalous temperature dependences is given in accordance with dipole momentum's behaviors determined by low-temperature spin-spin interactions and by electron-phonon anharmonic interactions. We have discovered that low-temperature dependence of specific heat of Pb{sub 1-x}R {sub x}Te (R = Yb, Pr with x = 3% and 1.6%, respectively) exhibits a non-magnetic order caused by large electron-phonon contributions and structural disorder effects.

  8. Theory of the evolution of magnetic order in Fe1+yTe compounds with increasing interstitial iron

    NASA Astrophysics Data System (ADS)

    Ducatman, Samuel; Fernandes, Rafael M.; Perkins, Natalia B.

    2014-10-01

    We examine the influence of the excess of interstitial Fe on the magnetic properties of Fe1+yTe compounds. Because in iron chalcogenides the correlations are stronger than in the iron arsenides, we assume in our model that some of the Fe orbitals give rise to localized magnetic moments. These moments interact with each other via exchange interactions as well as phonon-mediated biquadratic interactions that favor a collinear double-stripe state, corresponding to the ordering vectors (±?/2,±?/2). The remaining Fe orbitals are assumed to be itinerant, giving rise to the first-principles derived Fermi surface displaying nesting features at momenta (?,0)/(0,?). Increasing the amount of itinerant electrons due to excess Fe, y, leads to changes in the Fermi surface and to the suppression of its nesting properties. As a result, due to the Hund's coupling between the itinerant and localized moments, increasing y leads to modifications in the local moments' exchange interactions via the multiorbital generalization of the long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. By numerically computing the RKKY corrections and minimizing the resulting effective exchange Hamiltonian, we find, in general, that the excess electrons introduced in the system change the classical magnetic ground state from a double-stripe state to an incommensurate spiral, consistent with the experimental observations. We show that these results can be understood as a result of the suppression of magnetic spectral weight of the itinerant electrons at momenta (?,0)/(0,?), combined with the transfer of broad magnetic spectral weight from large to small momenta, promoted by the introduction of excess Fe.

  9. Suppressing a charge density wave by changing dimensionality in the ferecrystalline compounds ([SnSe]1.15)1(VSe2)n with n = 1, 2, 3, 4.

    PubMed

    Falmbigl, Matthias; Fiedler, Andreas; Atkins, Ryan E; Fischer, Saskia F; Johnson, David C

    2015-02-11

    The compounds, ([SnSe]1.15)1(VSe2)n with n = 1, 2, 3, and 4, were prepared using designed precursors in order to investigate the influence of the thickness of the VSe2 constituent on the charge density wave transition. The structure of each of the compounds was determined using X-ray diffraction and scanning transmission electron microscopy. The charge density wave transition observed in the resistivity of ([SnSe]1.15)1(VSe2)1 was confirmed. The electrical properties of the n = 2 and 3 compounds are distinctly different. The magnitude of the resistivity change at the transition temperature is dramatically lowered and the temperature of the resistivity minimum systematically increases from 118 K (n = 1) to 172 K (n = 3). For n = 1, this temperature correlates with the onset of the charge density wave transition. The Hall-coefficient changes sign when n is greater than 1, and the temperature dependence of the Hall coefficient of the n = 2 and 3 compounds is very similar to the bulk, slowly decreasing as the temperature is decreased, while for the n = 1 compound the Hall coefficient increases dramatically starting at the onset of the charge density wave. The transport properties suggest an abrupt change in electronic properties on increasing the thickness of the VSe2 layer beyond a single layer. PMID:25546501

  10. Point defects in CdTexSe1-x crystals grown from a Te-rich solution for applications in detecting radiation

    DOE PAGESBeta

    Gul, R.; Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Lee, W.; Yang, G.; Burger, A.; James, R. B.; et al

    2015-04-15

    We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from (1–30) V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material.

  11. Microwave-Assisted Synthesis of Glutathione-Capped CdTe/CdSe Near-Infrared Quantum Dots for Cell Imaging.

    PubMed

    Chen, Xiaogang; Li, Liang; Lai, Yongxian; Yan, Jianna; Tang, Yichen; Wang, Xiuli

    2015-01-01

    These glutathione (GSH)-conjugated CdTe/CdSe core/shell quantum dot (QD) nanoparticles in aqueous solution were synthesized using a microwave-assisted approach. The prepared type II core/shell QD nanoparticles were characterized by UV-Vis absorption, photoluminescence (PL) spectroscopy, X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). Results revealed that the QD nanoparticles exhibited good dispersity, a uniform size distribution and tunable fluorescence emission in the near-infrared (NIR) region. In addition, these nanoparticles exhibited good biocompatibility and photoluminescence in cell imaging. In particular, this type of core/shell NIR QDs may have potential applications in molecular imaging. PMID:25997004

  12. Robust protection from backscattering in the topological insulator Bi1.5Sb0.5Te1.7Se1.3.

    PubMed

    Kim, Sunghun; Yoshizawa, Shunsuke; Ishida, Yukiaki; Eto, Kazuma; Segawa, Kouji; Ando, Yoichi; Shin, Shik; Komori, Fumio

    2014-04-01

    Electron scattering in the topological surface state (TSS) of the topological insulator Bi1.5Sb0.5Te1.7Se1.3 was studied using quasiparticle interference observed by scanning tunneling microscopy. It was found that not only the 180° backscattering but also a wide range of backscattering angles of 100°-180° are effectively prohibited in the TSS. This conclusion was obtained by comparing the observed scattering vectors with the diameters of the constant-energy contours of the TSS, which were measured for both occupied and unoccupied states using time- and angle-resolved photoemission spectroscopy. The robust protection from backscattering in the TSS is good news for applications, but it poses a challenge to the theoretical understanding of the transport in the TSS. PMID:24745448

  13. In situ electron microscope study of the phase transformation, structure and growth of thin Te 1- xSe x films

    NASA Astrophysics Data System (ADS)

    Vermaak, J. S.; Raubenheimer, D.

    1990-01-01

    An in-situ electron microscope technique was utilized to observe directly the amorphous-to-crystalline phase transformation, the isothermal growth rates, as well as the orientation and structure of the recrystallized films for the Te 1-xSe x alloy system for x=0.2, 0.3 and 0.4. Activation energies of E=0.91, 0.93 and 0.96 eV and crystallization temperatures of Tc=-14, 81.5 and 85°C for the three alloys, respectively, were found. In all three cases the crystallization process originated from single crystalline nuclei with a hexagonal structure and with the c-axis in general parallel to the substrate surface.

  14. Ab initio studies of structural, electronic, optical, elastic and thermal properties of silver gallium dichalcogenides (AgGaX{sub 2}: X = S, Se, Te)

    SciTech Connect

    Sharma, Sheetal; Verma, A.S.; Jindal, V.K.

    2014-05-01

    Graphical abstract: - Highlights: • FP-LAPW method has been used to compute the solid state properties of AgGaX{sub 2} (X = S, Se, Te). • Electronic and optical properties reported with recently developed mBJ potential. • Thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter were evaluated. • Hardness was calculated for the first time at different temperature and pressure. - Abstract: We have performed ab initio calculations for the structural, electronic, optical, elastic and thermal properties of the silver gallium dichalcogenides (AgGaX{sub 2}: X = S, Se, Te). In this study, we have used the accurate full potential linearized augmented plane wave (FP-LAPW) method to find the equilibrium structural parameters and to compute the six elastic constants (C{sub 11}, C{sub 12}, C{sub 13}, C{sub 33}, C{sub 44} and C{sub 66}). We have reported electronic and optical properties with the recently developed density functional theory of Tran and Blaha, and this theory is used along with the Wu-Cohen generalized gradient approximation (WC-GGA) for the exchange-correlation potential. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 40 eV. The thermodynamical properties such as thermal expansion, heat capacity, debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures (0–900 K) and pressures (0–8 GPa) and the silent results were interpreted. Hardness of the materials was calculated for the first time at different temperatures and pressures.

  15. Anisotropy analysis of thermoelectric properties of Bi{sub 2}Te{sub 2.9}Se{sub 0.1} prepared by SPS method

    SciTech Connect

    Zybala, Rafal; Wojciechowski, Krzysztof T.

    2012-06-26

    The n-type Bi{sub 2}Te{sub 2.9}Se{sub 0.1} materials were synthesized by the direct fusion technique. The polycrystalline samples were fabricated by the uniaxial pressing of powders in spark plasma sintering (SPS) apparatus. The materials were subjected to the heat treatment in H{sub 2}-Ar atmosphere at 470 K for 24 h. The influence of preparation conditions on the anisotropy of electrical and thermal properties was thoroughly studied for the direction perpendicular and parallel to the pressing force. The microstructure and the chemical composition of both types of samples were examined using a scanning microscope (SEM) equipped with an X-ray energy dispersion detector (EDX). The XRD method was applied for the phase analysis of materials, as well as, for determination of preferred orientation of Bi{sub 2}Te{sub 2.9}Se{sub 0.1} grains. The Seebeck coefficient distribution was studied by the scanning thermoelectric microprobe (STM). Temperature dependences of thermoelectric properties (thermal and electrical conductivities, Seebeck coefficient) were measured in the temperature from 300 K to 550 K. The statistical analysis of results has shown strong influence of pressing force direction both on structural and transport properties. The applied heat treatment of materials significantly improves their thermoelectric figure of merit. Particularly, it was found that annealing in H2-Ar atmosphere leads to enhancement of the ZT three times up to {approx}0.7 at 370 K in perpendicular direction to the pressing force.

  16. Flux free growth of large FeSe1/2Te1/2 superconducting single crystals by an easy high temperature melt and slow cooling method

    NASA Astrophysics Data System (ADS)

    Maheshwari, P. K.; Jha, Rajveer; Gahtori, Bhasker; Awana, V. P. S.

    2015-09-01

    We report successful growth of flux free large single crystals of superconducting FeSe1/2Te1/2 with typical dimensions of up to few cm. The AC and DC magnetic measurements revealed the superconducting transition temperature (Tc) value of around 11.5K and the isothermal MH showed typical type-II superconducting behavior. The lower critical field (Hc1) being estimated by measuring the low field isothermal magnetization in superconducting regime is found to be above 200Oe at 0K. The temperature dependent electrical resistivity ?(T ) showed the Tc (onset) to be 14K and the Tc(? = 0) at 11.5K. The electrical resistivity under various magnetic fields i.e., ?(T)H for H//ab and H//c demonstrated the difference in the width of Tc with applied field of 14Tesla to be nearly 2K, confirming the anisotropic nature of superconductivity. The upper critical and irreversibility fields at absolute zero temperature i.e., Hc2(0) and Hirr(0) being determined by the conventional one-band Werthamer-Helfand-Hohenberg (WHH) equation for the criteria of normal state resistivity (?n) falling to 90% (onset), and 10% (offset) is 76.9Tesla, and 37.45Tesla respectively, for H//c and 135.4Tesla, and 71.41Tesla respectively, for H//ab. The coherence length at the zero temperature is estimated to be above 20Å ´ by using the Ginsburg-Landau theory. The activation energy for the FeSe1/2Te1/2 in both directions H//c and H//ab is determined by using Thermally Activation Flux Flow (TAFF) model.

  17. Cytotoxicity assessment of functionalized CdSe, CdTe and InP quantum dots in two human cancer cell models.

    PubMed

    Liu, Jing; Hu, Rui; Liu, Jianwei; Zhang, Butian; Wang, Yucheng; Liu, Xin; Law, Wing-Cheung; Liu, Liwei; Ye, Ling; Yong, Ken-Tye

    2015-12-01

    The toxicity of quantum dots (QDs) has been extensively studied over the past decade. Some common factors that originate the QD toxicity include releasing of heavy metal ions from degraded QDs and the generation of reactive oxygen species on the QD surface. In addition to these factors, we should also carefully examine other potential QD toxicity causes that will play crucial roles in impacting the overall biological system. In this contribution, we have performed cytotoxicity assessment of four types of QD formulations in two different human cancer cell models. The four types of QD formulations, namely, mercaptopropionic acid modified CdSe/CdS/ZnS QDs (CdSe-MPA), PEGylated phospholipid encapsulated CdSe/CdS/ZnS QDs (CdSe-Phos), PEGylated phospholipid encapsulated InP/ZnS QDs (InP-Phos) and Pluronic F127 encapsulated CdTe/ZnS QDs (CdTe-F127), are representatives for the commonly used QD formulations in biomedical applications. Both the core materials and the surface modifications have been taken into consideration as the key factors for the cytotoxicity assessment. Through side-by-side comparison and careful evaluations, we have found that the toxicity of QDs does not solely depend on a single factor in initiating the toxicity in biological system but rather it depends on a combination of elements from the particle formulations. More importantly, our toxicity assessment shows different cytotoxicity trend for all the prepared formulations tested on gastric adenocarcinoma (BGC-823) and neuroblastoma (SH-SY5Y) cell lines. We have further proposed that the cellular uptake of these nanocrystals plays an important role in determining the final faith of the toxicity impact of the formulation. The result here suggests that the toxicity of QDs is rather complex and it cannot be generalized under a few assumptions reported previously. We suggest that one have to evaluate the QD toxicity on a case to case basis and this indicates that standard procedures and comprehensive protocols are urgently needed to be developed and employed for fully assessing and understanding the origins of the toxicity arising from different QD formulations. PMID:26354258

  18. Thermoelectric properties and chlorine doping effect of In4Pb0.01Sn0.03Se2.9Clx polycrystalline compounds.

    PubMed

    Hee Kim, Jin; Jae Kim, Min; Oh, Suekyung; Rhyee, Jong-Soo; Park, Su-Dong; Ahn, Docheon

    2015-02-21

    We investigated the thermoelectric properties of Cl-doped polycrystalline compounds In4Pb0.01Sn0.03Se2.9Clx (x = 0.02, 0.04, and 0.06). X-ray diffraction measurement shows a gradual change in lattice volume for x ? 0.04 without any impurity phases indicating a systemic change in Cl doping. The Cl doping in the compounds has the effect of increasing carrier concentration and the effective mass of carriers, resulting in an increase in power factor at a high temperature (?700 K). Because of the increased electrical conductivity at a high temperature, the dimensionless thermoelectric figure of merit ZT reaches 1.25 at 723 K for the x = 0.04 Cl-doped compound, which is a relatively high value for n-type polycrystalline materials. PMID:25579326

  19. The effects of melt depletion and metasomatism on highly siderophile and strongly chalcophile elements: S-Se-Te-Re-PGE systematics of peridotite xenoliths from Kilbourne Hole, New Mexico

    NASA Astrophysics Data System (ADS)

    Harvey, Jason; König, Stephan; Luguet, Ambre

    2015-10-01

    The composition of the Earth's upper mantle is a function of melt depletion and subsequent metasomatism; the latter obscuring many of the key characteristics of the former, and potentially making predictions of Primitive Upper Mantle (PUM) composition problematic. To date, estimates of PUM abundances of highly siderophile element (HSE = platinum group elements (PGE) and Re) and the strongly chalcophile elements Se and Te, have been the subject of less scrutiny than the lithophile elements. Critically, estimates of HSE and strongly chalcophile element abundances in PUM may have been derived by including a large number of metasomatized and refertilized samples whose HSE and chalcophile element abundances may not be representative of melt depletion alone. Unravelling the effects of metasomatism on the S-Se-Te-HSE abundances in peridotite xenoliths from Kilbourne Hole, New Mexico, USA, potentially provides valuable insights into the abundances of HSE and strongly chalcophile element abundances in PUM. Superimposed upon the effects of melt depletion is the addition of metasomatic sulfide in approximately half of the xenoliths from this study, while the remaining half have lost sulfide to a late S-undersaturated melt. Despite these observations, the Kilbourne Hole peridotite xenoliths have HSE systematics that are, in general, indistinguishable from orogenic peridotites and peridotite xenoliths used for determination of PUM HSE abundances. This study represents the first instance where Se-Te-HSE systematics in peridotite xenoliths are scrutinized in detail in order to test their usefulness for PUM estimates. Despite earlier studies attesting to the relative immobility of Se during supergene weathering, low S, Se, Os and Se/Te in peridotite xenoliths suggests that Se may be more mobile than originally thought, and for this reason, peridotite xenoliths may not be suitable for making predictions of the abundance of these elements in PUM. Removal of Se, in turn, lowers the Se/Te in basalt-borne xenolithic peridotites to subchondritic values. This is in contrast to what has been recently reported in kimberlite-borne peridotite xenoliths. Moreover, Te added to melt depleted peridotite in metasomatic sulfide is more difficult to remove in a S-undersaturated melt than the HSE and Se due to the generation of micron-scale tellurides. The effects of these processes in orogenic peridotites and xenoliths, from which PUM abundances have been calculated, require further scrutiny before unequivocal Se-Te-Re-PGE values for PUM can be derived.

  20. Structural evolvement and thermoelectric properties of Cu(3-x)Sn(x)Se? compounds with diamond-like crystal structures.

    PubMed

    Fan, Jing; Schnelle, Walter; Antonyshyn, Iryna; Veremchuk, Igor; Carrillo-Cabrera, Wilder; Shi, Xun; Grin, Yuri; Chen, Lidong

    2014-11-28

    Polycrystalline samples of Cu(3-x)Sn(x)Se3 were synthesized in the composition range x = 0.87-1.05. A compositionally induced evolvement from tetragonal via cubic to monoclinic crystal structures is observed, when the composition changes from a Cu-rich to a Sn-rich one. The Cu(3-x)Sn(x)Se3 materials show a metal-to-semiconductor transition with increasing x. Electronic transport properties are governed by the charge-carrier concentration which is well described by a linear dispersion-band model. The lattice component of the thermal conductivity is practically independent of x which is attributed to the opposite influence of the atomic ordering and the inhomogeneous distribution of the Cu-Se or Sn-Se bonds with different polarities in the crystal structure. The highest thermoelectric figure of merit ZT of 0.34 is achieved for x = 1.025 at 700 K. PMID:25286143

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  2. Electronic structure of antifluorite Cu{sub 2}X (X = S, Se, Te) within the modified Becke-Johnson potential plus an on-site Coulomb U

    SciTech Connect

    Zhang, Yubo; Wang, Youwei; Xi, Lili; Qiu, Ruihao; Shi, Xun; Zhang, Peihong E-mail: pzhang3@buffalo.edu; Beijing Computational Science Research Center, Beijing 100084 ; Zhang, Wenqing E-mail: pzhang3@buffalo.edu; School of Chemistry and Chemical Engineering, and Sate Key Laboratory of Coordination Chemistry, Nanjing University, Jiangsu 210093

    2014-02-21

    The traditional photon absorbers Cu{sub 2?x}X (X = S, Se, and Te) have regained significant research attention in the search of earth-abundant photovoltaic materials. These moderate- and narrow-gap materials have also been shown to exhibit excellent thermoelectric properties recently. However, semimetallic band structures with inverted band orderings are predicted for antifluorite structure Cu{sub 2}X using density functional theory with the local density approximation or the generalized gradient approximation. We find that semiconducting band structures and normal band orderings can be obtained using the modified Becke-Johnson potential plus an on-site Coulomb U (the mBJ+U approach), which is consistent with our earlier finding for diamond-like Cu-based multinary semiconductors [Y. Zhang, J. Zhang, W. Gao, T. A. Abtew, Y. Wang, P. Zhang, and W. Zhang, J. Chem. Phys. 139, 184706 (2013)]. The trend of the chemical bonding of Cu{sub 2}X is analyzed, which shows that the positions of the valence band maximum and conduction band minimum are strongly affected by the inter-site pd and intra-site sp hybridizations, respectively. The calculated gaps of Cu{sub 2}S and Cu{sub 2}Se still seem to be underestimated compared with experimental results. We also discuss the effects of different structural phases and Cu disordering and deficiency on the bandgaps of these materials.

  3. First-principles studies of the structural, electronic, and optical properties of a novel thorium compound Rb{sub 2}Th{sub 7}Se{sub 15}

    SciTech Connect

    Brik, M.G.

    2014-04-01

    The structural, electronic, and optical properties of a recently synthesized thorium compound Rb{sub 2}Th{sub 7}Se{sub 15} have been calculated in the density functional theory framework for the first time. The calculated direct band gap was 1.471 eV (generalized gradient approximation) and 1.171 eV (local density approximation), with both results being close to the experimental result of 1.83 eV. High covalency/iconicity of the Th–Se/Rb–Se bonds was demonstrated by calculating effective Mulliken charges of all ions. The polarized calculations of the complex dielectric function are presented; dependence of the calculated index of refraction was fitted to the Sellmeyer equation in the wavelength range from 500 to 2500 nm. - Graphical abstract: Calculated band structure of Rb{sub 2}Th{sub 7}Se{sub 15}. - Highlights: • The first theoretical analysis of the Rb{sub 2}Th{sub 7}Se{sub 15} properties is reported. • Structural, electronic and optical properties of Rb{sub 2}Th{sub 7}Se{sub 15} were calculated. • An indirect character of Rb{sub 2}Th{sub 7}Se{sub 15} band gap was confirmed. • Dependence of the refractive index on the wavelength was calculated.

  4. Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te)

    PubMed Central

    Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J. C. Séamus; Ghigo, Gianluca; Gu, Genda D.; Kwok, Wai-Kwong

    2015-01-01

    Maximizing the sustainable supercurrent density, JC, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because JC amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSexTe1?x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or “columnar defects,” plus a higher density of single atomic site “point” defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields. PMID:26601180

  5. Effect of carrier density and valence states on superconductivity of oxygen annealed Fe{sub 1.06}Te{sub 0.6}Se{sub 0.4} single crystals

    SciTech Connect

    Su, T. S.; Yin, Y. W. E-mail: lixg@ustc.edu.cn; Teng, M. L.; Gong, Z. Z.; Zhang, M. J.; Li, X. G. E-mail: lixg@ustc.edu.cn

    2013-11-14

    The variations of carrier density and valence states in oxygen annealed Fe{sub 1.06}Te{sub 0.6}Se{sub 0.4} single crystals were studied systematically. It was found that the carrier density n{sub H} increases after oxygen annealing by Hall coefficient measurements. The X-ray photoelectron spectroscopy experiments reveal that the oxygen annealing changes Fe{sup 0} and Te{sup 0} states to Fe{sup 2+/3+} and Te{sup 4+}, respectively, while the valence variation of Se is negligible. Our results indicate that the improvement of superconductivity, such as the zero resistance transition temperature T{sub c}{sup zero}, shielding and Meissner fraction value 4?? and upper critical field H{sub c2}, could be closely related to the proper manipulation of n{sub H} and the valence states by oxygen annealing in the system.

  6. A strategy to boost the cell performance of CdSexTe1-x quantum dot sensitized solar cells over 8% by introducing Mn modified CdSe coating layer

    NASA Astrophysics Data System (ADS)

    Wang, Guoshuai; Wei, Huiyun; Luo, Yanhong; Wu, Huijue; Li, Dongmei; Zhong, Xinhua; Meng, Qingbo

    2016-01-01

    CdSexTe1-x alloyed colloidal quantum dots show great potential application on quantum dot-sensitized solar cells (QDSCs) due to its relatively wide light absorption range and high chemical stability. In this respect, a thin Mn modified CdSe layer is introduced into TiO2/CdSexTe1-x alloyed QDs surface via a simple chemical bath deposition method (CBD) in order to further improve the cell performance. The power conversion efficiency of CdSexTe1-x QDSCs has been improved to 8.14%. Detailed investigation on the influence of this modification toward the TiO2/CdSexTe1-x interface on the cell performance reveals that introduction of Mn into CdSe QDs is found to facilitate the Mn-doped CdSe deposition and improve the light absorption of the device. In the meantime, the existence of the (Mn-)CdSe layer can also work as a passivation layer to reduce charge recombination.

  7. Order-disorder phase transitions in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1?xWxX2 (X = S, Se, and Te)

    PubMed Central

    Gan, Li-Yong; Zhang, Qingyun; Zhao, Yu-Jun; Cheng, Yingchun; Schwingenschlögl, Udo

    2014-01-01

    A combination of density functional theory, an empirical model, and Monte Carlo simulations is used to shed light on the evolution of the atomic distribution in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1?xWxX2 (X = S, Se, and Te) as a function of the W concentration and temperature. Both random and ordered phases are discovered and the origin of the phase transitions is clarified. While the empirical model predicts at x = 1/3 and 2/3 ordered alloys, Monte Carlo simulations suggest that they only exist at low temperature due to a small energetic preference of Mo-X-W over Mo-X-Mo and W-X-W interactions, explaining the experimental observation of random alloy Mo1?xWxS2. Negative formation energies point to a high miscibility. Tunability of the band edges and band gaps by alteration of the W concentration gives rise to a broad range of applications. PMID:25331363

  8. Ab initio and relativistic DFT study of spin–rotation and NMR shielding constants in XF{sub 6} molecules, X = S, Se, Te, Mo, and W

    SciTech Connect

    Ruud, Kenneth; Demissie, Taye B.; Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warszawa, Kasprzaka 44 ; Jaszu?ski, Micha?

    2014-05-21

    We present an analysis of the spin–rotation and absolute shielding constants of XF{sub 6} molecules (X = S, Se, Te, Mo, W) based on ab initio coupled cluster and four-component relativistic density-functional theory (DFT) calculations. The results show that the relativistic contributions to the spin–rotation and shielding constants are large both for the heavy elements as well as for the fluorine nuclei. In most cases, incorporating the computed relativistic corrections significantly improves the agreement between our results and the well-established experimental values for the isotropic spin–rotation constants and their anisotropic components. This suggests that also for the other molecules, for which accurate and reliable experimental data are not available, reliable values of spin–rotation and absolute shielding constants were determined combining ab initio and relativistic DFT calculations. For the heavy nuclei, the breakdown of the relationship between the spin–rotation constant and the paramagnetic contribution to the shielding constant, due to relativistic effects, causes a significant error in the total absolute shielding constants.

  9. Characterization of surface conducting states in Bi1.5Sb0.5Te1.7Se1.3 topological insulator single crystals

    NASA Astrophysics Data System (ADS)

    Lee, Janghee; Park, Joonbum; Lee, Jae-Hyeong; Kim, Jun Sung; Lee, Hu-Jong

    2013-03-01

    Topologically protected surface state (TSS) of a topological insulator (TI) can be described in terms of a spin-resolved Dirac band with helical-spin texture. In general, however, as-grown TIs are doped so that the surface conduction can be dominated by the bulk conduction. In this study, we minimized the bulk conduction using high-quality Bi1.5Sb0.5Te1.7Se1.3 TI thin single crystals, with the Fermi level lying in the bulk gap without gating. We confirmed that the weak anti-localization (WAL) effect and universal conductance fluctuations in our samples arose from the top and bottom surfaces. By back-gate tuning the WAL characteristics, we identified the TSS conducting characteristics and the coupling between the TSS and the topologically trivial two-dimensional electron gas (2DEG) states that emerged due to the band bending near the surface. The ambipolar Hall resistivity of the bottom surface was consistent with the back-gate-voltage dependence of the longitudinal resistance of the TSS. This study provides a highly coherent picture of the surface transport properties of TIs by successfully differentiating the transport of the TSS from those of the bulk conducting state and the topologically trivial 2DEG states.

  10. Coherent A1g Phonon in thin Film Superconductor FeSe0.5Te0.5: ?/2 Phase Difference over Superconducting Phase Transition

    NASA Astrophysics Data System (ADS)

    Zhao, Jimin; Wu, Yanling; Hu, Minhui; Tian, Yichao; Cao, Lixin; Wang, Rui

    2014-03-01

    Coherent A1 g phonon mode in a thin film superconductor FeSe0.5Te0.5 was generated and detected using ultrafast laser pulses. At below and above the transition temperature Tc, the coherent lattice oscillation we observed exhibited a ?/2 phase difference, manifesting a ``displacive limit ~ impulsive limit'' transition upon crossing a phase transition within the same sample. We ascribe this ?/2 phase difference to the different lifetimes (?c) of excited charge density components that couples to the fully symmetric A1 g phonon mode, i.e. the different strength of electron-phonon couplings. In the superconducting and paramagnetic metallic states the lifetimes of such carrier excitations are largely different. Our investigation reveals possible correlation of superconducting electrons with zone-center optical phonons. Our 170nm thin film sample contains tension stress, which leads to enhanced Tc and thus facilitated our measurements. Financially supported by the National Basic Research Program of China (2012CB821402), the NSFC (11274372, 10974246) and the External Cooperation Program of Chinese Academy of Sciences (GJHZ1403).

  11. Shubnikov-de Haas Oscillations from topological surface states of metallic Bi2Se2.1Te0.9

    NASA Astrophysics Data System (ADS)

    Shrestha, Keshav; Marinova, Vera; Lorenz, Bernd; Chu, Paul C. W.

    2015-03-01

    We have studied the quantum oscillations in the conductivity of metallic, p-type Bi2Se2.1Te0.9. The dependence of the oscillations on the angle of the magnetic field with the surface as well as the Berry phase determined from the Landau level fan plot indicate that the observed oscillations arise from surface carriers with the characteristic Dirac dispersion. Several quantities characterizing the surface conduction are calculated employing on the Lifshitz-Kosevich theory. The low value of the Fermi energy with respect to the Dirac point is consistent with the metallic character of the bulk hole carriers. We conclude that, due to the peculiar shape of the valence band, the Shubnikov-de Haas oscillations of the bulk carriers are shifted to higher magnetic fields which allows for the detection of the quantum oscillations from the topological surface states at lower field. This work is supported in part by the US Air Force Office of Scientific Research, the Robert A. Welch Foundation (E-1297), the T.L.L. Temple Foundation, the J. J. and R. Moores Endowment, and the State of Texas through the TCSUH and at LBNL by the DoE.

  12. Conductance spectrum and superconducting gap structures observed in c-axis FeSe0.46Te0.54/Au junctions

    NASA Astrophysics Data System (ADS)

    Shen, Y. T.; Li, Y. S.; Lin, K. C.; Wu, M. K.; Chi, C. C.

    2013-09-01

    The electric transport properties of superconducting c-axis FeSe0.46Te0.54/Au (S/N) junctions, fabricated using pulsed laser deposition, have been investigated in the temperature range of 2 K to the superconducting transition temperature Tc (˜ 13.5 K) and in the presence of applied magnetic fields from 0 to 9 T. A large zero bias conductance peak has always been observed in every conductance spectrum of several batches of junctions. In addition, we have found several gap-like features. Using the extended BTK theory with the currently favored nodeless S±-wave symmetry, our conductance spectrum can be reproduced quite well in the low bias range with ?1 = 4 meV and ?2 = 6 meV at 2 K. However, the experimental conductance spectrum is substantially below the one calculated in the high bias range. Furthermore, there is a conductance minimum at approximately 20 meV, which may be the reason for the discrepancy.

  13. High-output-power densities from molecular beam epitaxy grown n- and p-type PbTeSe-based thermoelectrics via improved contact metallization

    SciTech Connect

    Goodhue, W. G.; Reeder, R. E.; Vineis, C. J.; Calawa, S. D.; Walsh, M. P.; Harman, T. C.; Dauplaise, H. M.; Vangala, S.

    2012-05-15

    Electrical power densities of up to 33 W/cm{sup 2} and up to 12 W/cm{sup 2} were obtained for n-type and p-type PbTeSe-based stand-alone thermoelectric devices, respectively, at modest temperature gradients of {approx}200 deg. C (T{sub cold}= 25 deg. C). These large power densities were enabled by greatly improving electrical contact resistivities in the thermoelectric devices. Electrical contacts with contact resistivities as low as 3.9 x 10{sup -6}{Omega} cm{sup 2} and 4.0 x 10{sup -6}{Omega} cm{sup 2} for n- and p-type telluride-based- materials, respectively, were developed by investigating several metallization schemes and contact layer doping/alloy combinations, in conjunction with a novel contact application process. This process exposes heated semiconductor surfaces to an atomic hydrogen flux under high vacuum for surface cleaning (oxide and carbon removal), followed immediately by an in-situ electron-beam evaporation of the metal layers.

  14. On the bad metallicity and phase diagrams of Fe1+?X (X =Te, Se, S, solid solutions): an electrical resistivity study

    NASA Astrophysics Data System (ADS)

    El Massalami, M.; Deguchi, K.; Machida, T.; Takeya, H.; Takano, Y.

    2014-12-01

    Based on a systematic analysis of the thermal evolution of the resistivities of Fe-based chalcogenides Fe1+?Te1-xXx (X = Se, S), it is inferred that their often observed nonmetallic resistivities are related to a presence of two resistive channels: one is a high- temperature thermally-activated process while the other is a low-temperature log-in-T process. On lowering temperature, there are often two metal-to-nonmetall crossover events: one from the high-T thermally-activated nonmetallic regime into a metal-like phase and the other from the log-in-T regime into a second metal-like phase. Based on these events, together with the magnetic and superconducting transitions, a phase diagram is constructed for each series. We discuss the origin of both processes as well as the associated crossover events. We also discuss how these resistive processes are being influenced by pressure, intercalation, disorder, doping, or sample condition and, in turn, how these modifications are shaping the associated phase diagrams.

  15. Quasi-two-dimensional superconductivity in FeSe0.3Te0.7 thin films and electric-field modulation of superconducting transition.

    PubMed

    Lin, Zhu; Mei, Chenguang; Wei, Linlin; Sun, Zhangao; Wu, Shilong; Huang, Haoliang; Zhang, Shu; Liu, Chang; Feng, Yang; Tian, Huanfang; Yang, Huaixin; Li, Jianqi; Wang, Yayu; Zhang, Guangming; Lu, Yalin; Zhao, Yonggang

    2015-01-01

    We report the structural and superconducting properties of FeSe0.3Te0.7 (FST) thin films with different thicknesses grown on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the FST films undergo biaxial tensile strains which are fully relaxed for films with thicknesses above 200?nm. Electrical transport measurements reveal that the ultrathin films exhibit an insulating behavior and superconductivity appears for thicker films with Tc saturated above 200?nm. The current-voltage curves around the superconducting transition follow the Berezinskii-Kosterlitz-Thouless (BKT) transition behavior and the resistance-temperature curves can be described by the Halperin-Nelson relation, revealing quasi-two-dimensional phase fluctuation in FST thin films. The Ginzburg number decreases with increasing film thickness indicating the decrease of the strength of thermal fluctuations. Upon applying electric field to the heterostructure, Tc of FST thin film increases due to the reduction of the tensile strain in FST. This work sheds light on the superconductivity, strain effect as well as electric-field modulation of superconductivity in FST films. PMID:26382136

  16. Influence of thickness and annealing on optical constants of Se82.5Te15Sb2.5 chalcogenide thin films

    NASA Astrophysics Data System (ADS)

    Abdel-Rahim, M. A.; Hafiz, M. M.; Mahmoud, A. Z.

    2015-10-01

    Chalcogenide thin films of Se82.5Te15Sb2.5 with different thickness (50-300 nm) are prepared by thermal evaporation technique. Crystalline phases of the deposited films are identified by x-ray diffraction (XRD). The influence of the film thickness and annealing temperature on the structure is studied by using XRD. The XRD studies show that the crystallinity improved by increasing film thickness and annealing temperature. Furthermore, the particle size and the crystallinity increase whereas dislocation density and strain decrease with increasing both the film thickness and annealing temperature. Transmittance and reflectance of the films are measured in wavelength range 300-2500 nm. It is found that, the optical energy gap, Eg, decreases and the localized state tails, Ee, increases by increasing film thickness and annealing temperature. Dispersion of the refractive index is described using Wemple-DiDomenico (WDD) single oscillator model. Dispersion parameters are calculated as a function of the film thickness and annealing temperature.

  17. Electronic structures and elastic properties of monolayer and bilayer transition metal dichalcogenides MX2 (M = Mo, W; X = O, S, Se, Te): A comparative first-principles study

    NASA Astrophysics Data System (ADS)

    Zeng, Fan; Zhang, Wei-Bing; Tang, Bi-Yu

    2015-09-01

    First-principle calculations with different exchange-correlation functionals, including LDA, PBE, and vdW-DF functional in the form of optB88-vdW, have been performed to investigate the electronic and elastic properties of two-dimensional transition metal dichalcogenides (TMDCs) with the formula of MX2(M = Mo, W; X = O, S, Se, Te) in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO2 and WO2. When the monolayers are stacked into a bilayer, the reduced indirect band gaps are found except for bilayer WTe2, in which the direct gap is still present at the K point. The calculated in-plane Young moduli are comparable to that of graphene, which promises possible application of TMDCs in future flexible and stretchable electronic devices. We also evaluated the performance of different functionals including LDA, PBE, and optB88-vdW in describing elastic moduli of TMDCs and found that LDA seems to be the most qualified method. Moreover, our calculations suggest that the Young moduli for bilayers are insensitive to stacking orders and the mechanical coupling between monolayers seems to be negligible. Project supported by the Construct Program of the Key Discipline in Hunan Province, China and Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province, China.

  18. Modeling of the band structure of Bi 2Se 2Te crystallites deposited on Si and SiO 2 substrates

    NASA Astrophysics Data System (ADS)

    Jankowska-Sahraoui, E.; Slezak, A.; Kimura, J.

    2004-06-01

    The band structure (BS) of crystalline Bi 2Se 2Te both pure as well as deposited on Si or SiO 2 (substrates) was calculated for the first time. The calculation approach consists of an orthogonalization of the plane wave basis set with respect to the core-like orbitals and the application of the Perdew-Alder exchange-correlation scheme. In addition, a virtual crystal approach was applied. Experimental ellipsometric spectra were used as a criterion of the advantages of the different calculation techniques. The results of traditional one-electron methods of BS calculations, using norm-conserving pseudo-potential (NCPP), and full linear augmented plane wave (FLAPW), were compared with the experimental data. Better agreement with experiment is achieved when the NCPP wave functions are orthogonalized to the 4dBi core-like states. Concerning the LMTO and the FLAPW all-electron methods, only appropriate application of the virtual crystal approximation to these approaches produces results that are in agreement with ellipsometric experimental data.

  19. Quasi-two-dimensional superconductivity in FeSe0.3Te0.7 thin films and electric-field modulation of superconducting transition

    PubMed Central

    Lin, Zhu; Mei, Chenguang; Wei, Linlin; Sun, Zhangao; Wu, Shilong; Huang, Haoliang; Zhang, Shu; Liu, Chang; Feng, Yang; Tian, Huanfang; Yang, Huaixin; Li, Jianqi; Wang, Yayu; Zhang, Guangming; Lu, Yalin; Zhao, Yonggang

    2015-01-01

    We report the structural and superconducting properties of FeSe0.3Te0.7 (FST) thin films with different thicknesses grown on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the FST films undergo biaxial tensile strains which are fully relaxed for films with thicknesses above 200?nm. Electrical transport measurements reveal that the ultrathin films exhibit an insulating behavior and superconductivity appears for thicker films with Tc saturated above 200?nm. The current-voltage curves around the superconducting transition follow the Berezinskii-Kosterlitz-Thouless (BKT) transition behavior and the resistance-temperature curves can be described by the Halperin–Nelson relation, revealing quasi-two-dimensional phase fluctuation in FST thin films. The Ginzburg number decreases with increasing film thickness indicating the decrease of the strength of thermal fluctuations. Upon applying electric field to the heterostructure, Tc of FST thin film increases due to the reduction of the tensile strain in FST. This work sheds light on the superconductivity, strain effect as well as electric-field modulation of superconductivity in FST films. PMID:26382136

  20. Grain boundary junctions of FeSe0.5Te0.5 thin films on SrTiO3 bi-crystal substrates

    NASA Astrophysics Data System (ADS)

    Si, Weidong; Zhang, Cheng; Shi, Xiaoya; Ozaki, Toshinori; Jaroszynski, Jan; Li, Qiang

    2015-01-01

    Grain boundary junctions were fabricated in the epitaxial FeSe0.5Te0.5 thin films on [001] tilt SrTiO3 bi-crystal substrates with a CeO2 buffer layer. Critical current densities across the junctions with different mis-orientation angles of 4°, 7°, 15°, and 24° were measured at magnetic fields up to 30 T. It was found that the 4° and 7° junctions carry critical current densities comparable to that of the intra-grain film while those of the 15° and 24° junctions were suppressed drastically. A critical mis-orientation angle of around 9° was identified that separates the strong coupling region from the weak link region. We found that the critical current densities across the grain boundary with a 24° mis-orientation angle are modulated by the magnetic field, indicating a Josephson Effect. This junction is estimated to be in the intermediate-size regime with an effective transverse junction width L ˜ 2.6-2.8 ?m and a Josephson penetration depth ?J ˜ 1.2 ?m.

  1. Synergetic catalytic effect of Cu2-xSe nanoparticles and reduced graphene oxide coembedded in electrospun nanofibers for the reduction of a typical refractory organic compound.

    PubMed

    Yang, Tong; Zou, Hong Yan; Huang, Cheng Zhi

    2015-07-22

    A new heterogeneous catalytic composite composed of nonstoichiometric Cu2-xSe nanoparticles (NPs) with high copper deficiency and graphene oxide (GO) is prepared by coembedding in electrospun nanofibers of a poly(vinylpyrrolidone) (PVP) support, wherein GO in the nanofibers is converted into reduced GO (rGO) via heat treatment. The as-prepared composite Cu2-xSe/rGO/PVP nanofibers have demonstrated superior catalytic activity toward the reduction of a refractory organic compound by taking 4-nitrophenol (4-NP) as an example. In the presence of NaBH4, the Cu2-xSe/rGO/PVP nanofibers display a synergetic effect between Cu2-xSe and rGO in PVP nanofibers compared to their independent components or corresponding nanofibers. Furthermore, the Cu2-xSe/rGO/PVP nanofibers exhibit a favorable water-stable property via heat treatment to solidify the hydrophilic PVP matrix, which makes the composite display good reusability, stability in aqueous solution, and separability from a water medium. This work not only presents a direct, convenient, and effective approach to doping semiconductor nanomaterials into polymer nanofibers but also provides fundamental routes for further investigations about the synergetic effect between different materials based on the platform of electrospun nanofibers. PMID:26114332

  2. Density functional theory calculations of the turbostratically disordered compound [(SnSe)1+y]m(VSe2)n

    DOE PAGESBeta

    Rudin, Sven P.; Johnson, David C.

    2015-04-30

    Among composite materials that layer constituent substances of nanoscale thicknesses, [(SnSe)1+y ]m(VSe2)n emerges as an example where the constituents retain incommensurate lattice structures. Perpendicular to the stacking direction, the system exhibits random translations and random rotations on average, i.e., turbostratic disorder, with local regions showing twelvefold diffraction patterns. Earlier theoretical work on these structures showed that combining density functional theory with an empirical treatment of the van der Waals interaction gave structural parameters in good agreement with experiment, but no attempt was made to examine the relative orientations. Here we approximate the extended system with one extended constituent and onemore »finite constituent, which allows the treatment of all relative orientations on equal footing. Furthermore, the calculations show how the twelvefold periodicity follows from how the ions of the SnSe layer lock in with favored positions relative to the VSe2 layer, and the associated energy scale supports arguments for the overall turbostratic disorder.« less

  3. Time-resolved photoluminescence spectroscopy of localized exciton magnetic polarons in Cd{sub 0.70}Mn{sub 0.30}Te spin glass compound

    SciTech Connect

    Gnatenko, Yu. P. Bukivskij, P. M.; Piryatinski, Yu. P.

    2014-04-07

    We have investigated dynamics of different localized exciton magnetic polarons (LEMPs) in Cd{sub 0.70}Mn{sub 0.30}Te spin glass (SG) compound below the freezing temperature T{sub f} in the crystal regions, where various microscopic magnetic spin states (MMSSs), namely, “loose” spins, finite, and infinite clusters, are formed. It was shown that there is a broad distribution of the LEMPs lifetimes. The presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states, i.e., the “brightening” of the dark LEMPs which exist along with the bright LEMPs. The lifetimes of the dark LEMPs correspond to hundreds of nanoseconds. It was found that the time decay of photoluminescence band intensity is approximated by the sum of two functions: a single exponential function and the Kohlrausch–Williams–Watts stretched exponential function. The stretched exponential function describes the recombination processes of the LEMPs formed in the crystal regions of the finite clusters as well as the infinite cluster. This reflects the appearance of spatially heterogeneous dynamics in Cd{sub 0.70}Mn{sub 0.30}Te SG compound below T{sub f} which is due to the disorder in the spin distribution caused by the formation of different MMSSs.

  4. Influence of impurities on the thermoelectric properties of layered anisotropic PbBi{sub 4}Te{sub 7} compound: Experiment and calculations

    SciTech Connect

    Zhitinskaya, M. K. Nemov, S. A.; Muhtarova, A. A.; Shelimova, L. E.; Svechnikova, T. E.; Konstantinov, P. P.

    2010-06-15

    The kinetic coefficients of high-quality single crystals of ternary layered n-PbBi{sub 4}Te{sub 7} compounds have been measured in the temperature range of 77-400 K. These crystals, doped with electroactive Cd and Ag impurities, were grown by Czochralski pulling with melt supply through a floating crucible. A significant anisotropy of the thermoelectric properties is found. The means of incorporation of electroactive impurities into the ternary compound lattice is established. The experimental values of the Nernst-Ettingshausen coefficient have been analyzed together with the Seebeck, Hall, and conductivity data. The features of transport phenomena in PbBi{sub 4}Te{sub 7} can be explained within the single-band model of nonparabolic energy spectrum and mixed mechanism of electron scattering from acoustic phonons and the Coulomb potential of impurities. It is suggested that acoustic phonon scattering is dominant along the cleavage plane, whereas the impurity scattering dominates along the trigonal axis.

  5. Shuttle Mission STS-50: Orbital Processing of High-Quality CdTe Compound Semiconductors Experiment: Final Flight Sample Characterization Report

    NASA Technical Reports Server (NTRS)

    Larson, David J.; Casagrande, Luis G.; DiMarzio, Don; Alexander, J. Iwan D.; Carlson, Fred; Lee, Taipo; Dudley, Michael; Raghathamachar, Balaji

    1998-01-01

    The Orbital Processing of High-Quality Doped and Alloyed CdTe Compound Semiconductors program was initiated to investigate, quantitatively, the influences of gravitationally dependent phenomena on the growth and quality of bulk compound semiconductors. The objective was to improve crystal quality (both structural and compositional) and to better understand and control the variables within the crystal growth production process. The empirical effort entailed the development of a terrestrial (one-g) experiment baseline for quantitative comparison with microgravity (mu-g) results. This effort was supported by the development of high-fidelity process models of heat transfer, fluid flow and solute redistribution, and thermo-mechanical stress occurring in the furnace, safety cartridge, ampoule, and crystal throughout the melting, seeding, crystal growth, and post-solidification processing. In addition, the sensitivity of the orbital experiments was analyzed with respect to the residual microgravity (mu-g) environment, both steady state and g-jitter. CdZnTe crystals were grown in one-g and in mu-g. Crystals processed terrestrially were grown at the NASA Ground Control Experiments Laboratory (GCEL) and at Grumman Aerospace Corporation (now Northrop Grumman Corporation). Two mu-g crystals were grown in the Crystal Growth Furnace (CGF) during the First United States Microgravity Laboratory Mission (USML-1), STS-50, June 24 - July 9, 1992.

  6. Near-infrared emitting CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots: synthesis and bright luminescence

    NASA Astrophysics Data System (ADS)

    Yang, Ping; Wang, Shiquan; Murase, Norio

    2012-11-01

    We present how CdTe0.5Se0.5 cores can be coated with Cd0.5Zn0.5S shells at relatively low temperature (around 200°C) via facile synthesis using organic ammine ligands. The cores were firstly fabricated via a less toxic procedure using CdO, trioctylphosphine (TOP), Se, Te, and trioctylamine. The cores with small sizes (3.2-3.5 nm) revealed green and yellow photoluminescence (PL) and spherical morphologies. Hydrophobic core/shell CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots (QDs) with tunable PL between green and near-infrared (a maximum PL peak wavelength of 735 nm) were then created through a facile shell coating procedure using trioctylphosphine selenium with cadmium and zinc acetate. The QDs exhibited high PL efficiencies up to 50% because of the formation of a protective Cd0.5Zn0.5S shell on the CdTe0.5Se0.5 core, even though the PL efficiency of the cores is low (?1%). Namely, the slow growth process of the shell plays an important role for getting high PL efficiencies. The properties of the QDs are largely determined by the properties of CdTe0.5Se0.5 cores and shells preparation conditions such as reaction temperature and time. The core/shell QDs exhibited a small size diameter. For example, the average diameter of the QDs with a PL peak wavelength of 735 nm is 6.1 nm. Small size and tunable bright PL makes the QDs utilizable as bioprobes because the size of QD-based bioprobes is considered as the major limitation for their broad applications in biological imaging.

  7. Near-infrared emitting CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots: synthesis and bright luminescence.

    PubMed

    Yang, Ping; Wang, Shiquan; Murase, Norio

    2012-01-01

    We present how CdTe0.5Se0.5 cores can be coated with Cd0.5Zn0.5S shells at relatively low temperature (around 200°C) via facile synthesis using organic ammine ligands. The cores were firstly fabricated via a less toxic procedure using CdO, trioctylphosphine (TOP), Se, Te, and trioctylamine. The cores with small sizes (3.2-3.5 nm) revealed green and yellow photoluminescence (PL) and spherical morphologies. Hydrophobic core/shell CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots (QDs) with tunable PL between green and near-infrared (a maximum PL peak wavelength of 735 nm) were then created through a facile shell coating procedure using trioctylphosphine selenium with cadmium and zinc acetate. The QDs exhibited high PL efficiencies up to 50% because of the formation of a protective Cd0.5Zn0.5S shell on the CdTe0.5Se0.5 core, even though the PL efficiency of the cores is low (?1%). Namely, the slow growth process of the shell plays an important role for getting high PL efficiencies. The properties of the QDs are largely determined by the properties of CdTe0.5Se0.5 cores and shells preparation conditions such as reaction temperature and time. The core/shell QDs exhibited a small size diameter. For example, the average diameter of the QDs with a PL peak wavelength of 735 nm is 6.1 nm. Small size and tunable bright PL makes the QDs utilizable as bioprobes because the size of QD-based bioprobes is considered as the major limitation for their broad applications in biological imaging. PMID:23130948

  8. Near-infrared emitting CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots: synthesis and bright luminescence

    PubMed Central

    2012-01-01

    We present how CdTe0.5Se0.5 cores can be coated with Cd0.5Zn0.5S shells at relatively low temperature (around 200°C) via facile synthesis using organic ammine ligands. The cores were firstly fabricated via a less toxic procedure using CdO, trioctylphosphine (TOP), Se, Te, and trioctylamine. The cores with small sizes (3.2-3.5 nm) revealed green and yellow photoluminescence (PL) and spherical morphologies. Hydrophobic core/shell CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots (QDs) with tunable PL between green and near-infrared (a maximum PL peak wavelength of 735 nm) were then created through a facile shell coating procedure using trioctylphosphine selenium with cadmium and zinc acetate. The QDs exhibited high PL efficiencies up to 50% because of the formation of a protective Cd0.5Zn0.5S shell on the CdTe0.5Se0.5 core, even though the PL efficiency of the cores is low (?1%). Namely, the slow growth process of the shell plays an important role for getting high PL efficiencies. The properties of the QDs are largely determined by the properties of CdTe0.5Se0.5 cores and shells preparation conditions such as reaction temperature and time. The core/shell QDs exhibited a small size diameter. For example, the average diameter of the QDs with a PL peak wavelength of 735 nm is 6.1 nm. Small size and tunable bright PL makes the QDs utilizable as bioprobes because the size of QD-based bioprobes is considered as the major limitation for their broad applications in biological imaging. PMID:23130948

  9. Enhancement of singlet oxygen production based on FRET between Coumarin tri-compound and CdSe/ZnS QDs

    NASA Astrophysics Data System (ADS)

    Duong, Hong Dinh; Lee, Jee Won; Rhee, Jong Il

    2014-08-01

    The compatibility between coumarin-derived dendrimer (CdD)-captured silica particles (SiCdDs) and watersoluble CdSe/ZnS quantum dots (QDs) in the FRET process improved the excited state of QDs in the reaction of singlet oxygen production under LED irradiation. Sol-gel GA was successfully used to improve the binding between SiCdDs and QDs. Singlet oxygen production using QDs coated with SiCdDs through sol-gel GA was enhanced by about 80 % compared to that achieved using QDs only. The single oxygen produced by the QDs, the QDs/GA-SiCdDs complexes and the SiCdDs/GA-QDs complexes in this study could be used in the treatment of HeLa cells.

  10. De Haas-van Alphen oscillations in the charge-density wave compound lanthanum tritelluride (LaTe3)

    SciTech Connect

    Ru, N.; Borzi, R.A.; Rost, A.; Mackenzie, A.P.; Laverock, J.; Dugdale, S.B.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2009-12-14

    De Haas-van Alphen oscillations were measured in lanthanum tritelluride (LaTe{sub 3}) to probe the partially gapped Fermi surface resulting from charge density wave (CDW) formation. Three distinct frequencies were observed, one of which can be correlated with a FS sheet that is unaltered by CDW formation. The other two frequencies arise from FS sheets that have been reconstructed in the CDW state.

  11. Comparison of Sn-doped and nonstoichiometric vertical-Bridgman-grown crystals of the topological insulator Bi{sub 2}Te{sub 2}Se

    SciTech Connect

    Kushwaha, S. K. Gibson, Q. D.; Cava, R. J.; Xiong, J.; Ong, N. P.; Pletikosic, I.; Weber, A. P.; Fedorov, A. V.; Valla, T.

    2014-04-14

    A comparative study of the properties of topological insulator Bi{sub 2}Te{sub 2}Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8?×?10{sup 14}?cm{sup ?3}. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (E{sub F}) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, which the Dirac point for the surface states lies approximately 60?meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near E{sub F}. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed.

  12. Zone leveling and solution growth of complex compound semiconductors in space

    NASA Technical Reports Server (NTRS)

    Bachmann, K. J.

    1986-01-01

    A research program on complex semiconducting compounds and alloys was completed that addressed the growth of single crystals of CdSe(y)Te(1-y), Zn(x)Cd(1-x)Te, Mn(x)Cd(1-x)Te, InP(y)As(1-y) and CuInSe2 and the measurement of fundamental physico-chemical properties characterizing the above materials. The purpose of this ground based research program was to lay the foundations for further research concerning the growth of complex ternary compound semiconductors in a microgravity environment.

  13. Electronic, optical properties and chemical bonding in six novel 1111-like chalcogenide fluorides AMChF (A=Sr, Ba; M=Cu, Ag; and Ch=S, Se, Te) from first principles calculations

    SciTech Connect

    Bannikov, V.V.; Shein, I.R.; Ivanovskii, A.L.

    2012-12-15

    Employing first-principles band structure calculations, we have examined the electronic, optical properties and the peculiarities of the chemical bonding for six newly synthesized layered quaternary 1111-like chalcogenide fluorides SrAgSF, SrAgSeF, SrAgTeF, BaAgSF, BaAgSeF, and SrCuTeF, which are discussed in comparison with some isostructural 1111-like chalcogenide oxides. We found that all of the studied phases AMChF (A=Sr, Ba; M=Cu, Ag; and Ch=S, Se, Te) are semiconductors for which the fitted 'experimental' gaps lie in the interval from 2.23 eV (for SrAgSeF) to 3.07 eV (for SrCuTeF). The near-Fermi states of AMChF are formed exclusively by the valence orbitals of the atoms from the blocks (MCh); thus, these phases belong to the layered materials with 'natural multiple quantum wells'. The bonding in these new AMChF phases is described as a high-anisotropic mixture of ionic and covalent contributions, where ionic M-Ch bonds together with covalent M-Ch and Ch-Ch bonds take place inside blocks (MCh), while inside blocks (AF) and between the adjacent blocks (MCh)/(AF) mainly ionic bonds emerge. - Graphical Abstract: Isoelectronic surface for SrAgSeF and atomic-resolved densities of states for SrAgTeF, and SrCuTeF. Highlights: Black-Right-Pointing-Pointer Very recently six new layered 1111-like chalcogenide fluorides AMChF were synthesized. Black-Right-Pointing-Pointer Electronic, optical properties for AMChF phases were examined from first principles. Black-Right-Pointing-Pointer All these materials are characterized as non-magnetic semiconductors. Black-Right-Pointing-Pointer Bonding is highly anisotropic and includes ionic and covalent contributions. Black-Right-Pointing-Pointer Introduction of magnetic ions in AMChF is proposed for search of novel magnetic materials.

  14. High Temperature Transport Properties of Tetrahedrite Cu12-x M x Sb4-y Te y S13 (M = Zn, Ni) Compounds

    NASA Astrophysics Data System (ADS)

    Bouyrie, Y.; Candolfi, C.; Vaney, J. B.; Dauscher, A.; Lenoir, B.

    2015-10-01

    Natural and synthetic tetrahedrites are currently the focus of attention in thermoelectricity due to their abundance, numerous possibilities of substitution, and their complex crystal structure ( Ibar{4}3m ) resulting in extremely low lattice thermal conductivity (below 1 W m-1 K-1 above 300 K). Here, we report on the synthesis, structural and chemical characterizations, and high-temperature thermoelectric properties of polycrystalline Cu12-x M x Sb4-y Te y S13 (M = Zn, Ni) tetrahedrites. Upon substituting on both the Cu and Sb sites, we successfully improved the thermoelectric properties with respect to the ternary compound Cu12Sb4S13 with peak ZT values of 0.7 at 700 K.

  15. Mo{sub 6}Se{sub 8}-cluster-based superconducting compounds Cs{sub 2}Mo{sub 12}Se{sub 14} and Rb{sub 4}Mo{sub 18}Se{sub 20}: Evidence for a strongly correlated and anisotropic electron system

    SciTech Connect

    Brusetti, R.; Laborde, O.; Sulpice, A.; Calemczuk, R.; Potel, M.; Gougeon, P.

    1995-08-01

    We studied the normal and superconducting states of the title compounds by measuring the conductivity and magnetization of single crystals and powder samples. From the upper and lower critical fields we deduced the characteristic lengths and thermodynamical fields. These results are borne out by our specific-heat measurements. We recognize in these compounds many features of the Chevrel-phase superconductors, including very small coherence lengths and strong-coupling-like effects. However, we show that the electron system is much more anisotropic and still less delocalized in these materials where the Mo{sub 6}Se{sub 8} clusters have condensed in Mo{sub 6{ital n}}Se{sub 6{ital n}+2} finite chains. This condensation is accompanied by an enhancement of the magnetic response whereas the lengthening of the chains leads to a counteracting reduction of the density of carriers. This indicates that superconductivity is built upon highly correlated molecular states. Reviewing the available data on the other Chevrel-cluster-based superconductors confirms this picture and suggests that the small coherence lengths reflect the local character of the electron pairing. This comparison also shows that forming finite chains of Mo{sub 6}Se{sub 8} clusters makes the electron correlations more repulsive and pushes the electron system near the borderline between superconductivity and magnetism. In this respect these compounds could provide valuable complementary information on issues which are at the center of the research upon high-{ital Y}{sub {ital c}} superconductivity.

  16. Improvement of superconductivity in Fe1+yTe0.6Se0.4 induced by annealing with CaF2 and SmF3

    NASA Astrophysics Data System (ADS)

    Li, Xiong; Sun, Yue; Zhang, Yufeng; Zhou, Wei; Yuan, Feifei; Shi, Zhixiang

    2015-10-01

    We report detailed studies of the CaF2 and SmF3 annealing effects in Fe1+yTe0.6Se0.4 single crystals. Superconductivity in Fe1+yTe0.6Se0.4 single crystals was improved after annealing, which strongly suggested the effectiveness of the CaF2 and SmF3 annealing. In detail, no matter which annealing material was employed, the largest values of superconducting transition temperature and critical current density reached about 14 K and 1.0 × 105 A/cm2 (5 K, in self-field), respectively. Furthermore, compared with the pervious annealing materials, CaF2 and SmF3 are safe and easy-handing.

  17. Preparation, crystal structure and infrared spectroscopy of the new compound Rb 4Be(SeO 4) 2(HSeO 4) 2·4H 2O

    NASA Astrophysics Data System (ADS)

    Georgiev, M.; Wildner, M.; Marinova, D.; Stoilova, D.

    2010-05-01

    A new compound, Rb 4Be(SeO 4) 2(HSeO 4) 2·4H 2O, crystallizes in a comparatively wide concentration range from mixed beryllium rubidium selenate solutions (from solutions containing 29.06 mass% beryllium selenate and 25.75 mass% rubidium selenate up to solutions containing 12.53 mass% beryllium selenate and 55.32 mass% rubidium selenate). Rb 4Be(SeO 4) 2(HSeO 4) 2·4H 2O crystallizes in the acentric orthorhombic space group Pmn2 1 ( a = 32.607(4), b = 10.676(2), c = 6.069(1) Å, V = 2112.8 Å 3, Z = 4, R1 = 0.047 for 4059 F o > 4?(F o) and 311 variables). The crystal structure is composed of Be(H 2O) 4 tetrahedra arranged in layers at x = 0 and x = ½, alternating with broad layers built up from SeO 4 and HSeO 4 selenate tetrahedra and Rb cations. The beryllium-water layers are linked to the rest of the structure via hydrogen bonds only. The H 2O molecules as well as the OH molecules of the acid HSeO 4 groups form strong to very strong hydrogen bonds with donor-acceptor distances between 2.58 and 2.74 Å. Vibrational spectra (infrared and Raman) of Rb 4Be(SeO 4) 2(HSeO 4) 2·4H 2O are presented and discussed in the region of the fundamentals of both the selenate and the beryllium tetrahedra (skeleton motions) as well as in the region of the OH vibrations at ambient and liquid nitrogen temperature (LNT). The appearance of four Raman bands corresponding to ? 1 of the selenate ions reflects the existence of four crystallographically different selenate tetrahedra in the structure. The spectroscopic experiments reveal that the ? 1 modes of the selenate ions appear at higher frequencies than some components of ? 3. Bands of an AB doublet structure (2950, 2390 cm -1) arising from the OH stretching modes of the HSeO 4- ions are recognized in the infrared spectra. The appearance of two infrared bands (1308, 1250 cm -1) corresponding to ?(OH) (in-plane bending modes of the OH groups) confirms the structural data regarding the existence of two crystallographically different OH groups. The water librations are also briefly commented. The appearance of a band at a comparatively large wavenumber (1013 cm -1) corresponding to rocking librations of the water molecules indicate that strong hydrogen bonds are formed in the title compound.

  18. Pressure dependence of the optical properties of the charge-density-wave compound LaTe2

    SciTech Connect

    Lavagnini, M.; Sacchetti, A.; Degiorgi, L.; Arcangeletti, E.; Baldassarre, L.; Postorino, P.; Lupi, S.; Perucchi, A.; Shin, K.Y.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2009-12-14

    We report the pressure dependence of the optical response of LaTe{sub 2}, which is deep in the charge-density-wave (CDW) ground state even at 300 K. The reflectivity spectrum is collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 7 GPa. We extract the energy scale due to the single particle excitation across the CDW gap and the Drude weight. We establish that the gap decreases upon compressing the lattice, while the Drude weight increases. This signals a reduction in the quality of nesting upon applying pressure, therefore inducing a lesser impact of the CDW condensate on the electronic properties of LaTe{sub 2}. The consequent suppression of the CDW gap leads to a release of additional charge carriers, manifested by the shift of weight from the gap feature into the metallic component of the optical response. On the contrary, the power-law behavior, seen in the optical conductivity at energies above the gap excitation and indicating a weakly interacting limit within the Tomonaga-Luttinger liquid scenario, seems to be only moderately dependent on pressure.

  19. Transport and optical properties of heavily hole-doped semiconductors BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2}

    SciTech Connect

    McGuire, Michael A.; May, Andrew F.; Singh, David J.; Du, Mao-Hua; Jellison, Gerald E.

    2011-10-15

    Experimental and theoretical studies of the electronic and optical properties of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2} are reported. Experimental data include the electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, and lattice constants for T{<=}300K, and optical transmission and diffuse reflectance data at room temperature. Nominally stoichiometric, polycrystalline samples form with hole concentrations inferred from Hall measurements of 2x10{sup 18} and 5x10{sup 19} cm{sup -3} near room temperature for the selenide and telluride, respectively. The corresponding mobilities are near 15 cm{sup 2} V{sup -1} s{sup -1} for both materials. Optical measurements reveal a transition near 1.8 eV in BaCu{sub 2}Se{sub 2}, while no similar feature was observed for BaCu{sub 2}Te{sub 2}. First principles calculations indicate both materials are direct or nearly direct gap semiconductors with calculated gaps near 1.0 eV and 1.3 eV for the telluride and selenide, respectively, and predict weak absorption below about 2 eV. Transport properties calculated from the electronic structure are also presented. - Graphical abstract: Combined experimental and theoretical study of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2} to assess potential for photovoltaic and thermoelectric applications. Highlights: > Comparative experimental and theoretical study of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2}. > Measured and calculated optical and transport properties. > Temperature dependence of lattice parameters and transport properties. > Hall and Seebeck coefficient measurements indicate heavy hole doping. > Good agreement between measured and modeled room temperature Seebeck coefficients.

  20. Synthesis and characterization of FeSe1-xTex (x=0, 0.5, 1) superconductors

    NASA Astrophysics Data System (ADS)

    Zargar, Rayees A.; Hafiz, A. K.; Awana, V. P. S.

    2015-08-01

    In this study, FeTe1-xSex (x=0,0.5,1) samples were prepared by conventional solid state reaction method and investigated by powder XRD, SEM, Raman and resistivity measurement techniques to reveal the effect of tellurium (Te) substitution in FeSe matrix. Rietveld analysis was performed on room temperature recorded, X-ray diffraction (XRD) patterns of pure FeSe, FeTe and FeSe0.5Te0.5 which shows that all the compounds are crystallized in a tetragonal structure. SEM images show the dense surface morphology. Raman spectra recorded in the range from 100 to 700 cm-1 at ambient temperature has been interpreted by P4/nmm space group of the lattice. The variation in intensity and shift in peak positions of some phonon modes has been discussed on the basis of variation in crystalline field effect by substituting Te in FeSe lattice. The resistivity versus temperature curves reveals that FeSe becomes superconductor at 7 K and FeSe0.5Te0.5 shows superconductivity below 14 K while FeTe is non-superconducting compound.

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

    SciTech Connect

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

    2009-02-01

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

  2. Thermodynamic Modeling of the Pt-Te and Pt-Sb-Te Systems

    NASA Astrophysics Data System (ADS)

    Guo, Cuiping; Huang, Liang; Li, Changrong; Shang, Shunli; Du, Zhenmin

    2015-08-01

    The Pt-Te and the Pt-Sb-Te systems are modeled using the calculation of phase diagram (CALPHAD) technique. In the Pt-Te system, the liquid phase is modeled as (Pt, PtTe2, Te) using the associate model, and four intermediates, PtTe2, Pt2Te3, Pt3Te4 and PtTe, are treated as stoichiometric compounds and their enthalpies of formation are obtained by means of first-principles calculations. The solution phases, fcc(Pt) and hex(Te), are described as substitutional solutions. Combined with the thermodynamic models of the liquid phase in the Pt-Sb and Sb-Te systems in the literature, the liquid phase of the Pt-Sb-Te ternary system is modeled as (Pt, Sb, Te, Sb2Te3, PtTe2) also using the associate model. The compounds, PtTe2, Pt2Te3, Pt3Te4 and PtTe in the Pt-Te system and PtSb2, PtSb, Pt3Sb2 and Pt7Sb in the Pt-Sb system are treated as line compounds Pt m (Sb,Te) n in the Pt-Sb-Te system, and the compound Pt5Sb is treated as (Pt,Sb)5(Pt,Sb,Te). A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Pt-Te phase diagram, the experimental heat capacities of PtTe and PtTe2, the enthalpies of formation from first-principles calculations for PtTe2, Pt2Te3, Pt3Te4, and PtTe, and the ternary isothermal sections at 873 K, 923 K, 1073 K and 1273 K are well reproduced.

  3. Single crystal growth of Ga[subscript 2](Se[subscript x]Te[subscript 1;#8722;x])[subscript 3] semiconductors and defect studies via positron annihilation spectroscopy

    SciTech Connect

    Abdul-Jabbar, N.M.; Bourret-Courchesne, E.D.; Wirth, B.D.

    2012-12-10

    Small single crystals of Ga{sub 2}(Se{sub x}Te{sub 1-x}){sub 3} semiconductors, for x = 0.1, 0.2, 0.3, were obtained via modified Bridgman growth techniques. High resolution powder x-ray diffractometry confirms a zincblende cubic structure, with additional satellite peaks observed near the (111) Bragg line. This suggests the presence of ordered vacancy planes along the [111] direction that have been previously observed in Ga{sub 2}Te{sub 3}. Defect studies via positron annihilation spectroscopy show an average positron lifetime of {approx} 400 ps in bulk as-grown specimens. Such a large lifetime suggests that the positron annihilation sites in these materials are dominated by defects. Moreover, analyzing the electron momenta via coincidence Doppler broadening measurements suggests a strong presence of large open-volume defects, likely to be vacancy clusters or voids.

  4. New adamantane-like mercury-chalcogen cages. 2. Synthetic and multinuclear ( sup 31 P, sup 77 Se, sup 125 Te, sup 199 Hg) magnetic resonance study of tellurolate-bridged mercury(III) clusters ((. mu. -TeR) sub 6 (HgPR prime sub 3 ) sub 4 ) sup 2+ and ((. mu. -TeR) sub 6 (Hg)(HgPR prime sub 3 ) sub 3 ) sup 2+ and related species with mixed-bridging chalcogenates

    SciTech Connect

    Dean, P.A.W.; Manivannan, V.; Vittal, J.J. )

    1989-06-14

    The salts (({mu}-TePh){sub 6}(HgPR{prime}{sub 3}){sub 3}(Hg))(ClO{sub 4}){sub 2} (R{prime} = Ph, 4-C{sub 6}H{sub 4}Me, 4-C{sub 6}H{sub 4}Cl) are preparable from Hg(TePh){sub 2}, Mg(PR{prime}{sub 3}){sub 2}(ClO{sub 4}){sub 2}, and PR{prime}P{sub 3} in a 3:1:1 ratio in CH{sub 2}Cl{sub 2} or CHCl{sub 3}. The new cations have been characterized in CH{sub 2}Cl{sub 2} and DMF by multinuclear ({sup 31}P, {sup 125}Te, {sup 199}Hg) magnetic resonance and shown to be of adamantanoid structure with novel tellurolate bridging. These spectra provide clear evidence for preferential formation of one (R{prime} = Ph) or a mixture of both (R{prime} = 4-C{sub 6}H{sub 4}Cl, in DMF solution) of the two C{sub 3} isomers that are possible for adamantane-like ({mu}-TeR){sub 6}M{sub 4} as a result of inversion at the pyramidal Te atoms. Such preferential isomer formation has not been demonstrated previously for any adamantanoid chalcogenate-bridge ({mu}-ER){sub 6}M{sub 4} in solution. Isomer formation at various temperatures is reported. For the cations with R = Ph, the rate of inversion at Te varies with R{prime} in the order alkyl > 4-C{sub 6}H{sub 4}Me > Ph > 4-C{sub 6}H{sub 4}Cl. When R = Ph, R{prime} = 4-C{sub 6}H{sub 4}Me, NMR spectra ({sup 31}P, {sup 77}Se, {sup 125}Te, {sup 199}Hg) of mixtures of ((TeR){sub 6}(HgPR{prime}{sub 3}){sub 4}){sup 2+} and (({mu}-ER){sub 6}(HgPR{prime}{sub 3}){sub 4}){sup 2+} (E = S, Se) provide evidence for the formation of the mixed-chalcogen cores ({mu}-Te){sub 6-m}({mu}-E){sub m}Hg{sub 4}. 35 refs., 8 figs., 3 tabs.

  5. Sb2Se3 under pressure

    PubMed Central

    Efthimiopoulos, Ilias; Zhang, Jiaming; Kucway, Melvin; Park, Changyong; Ewing, Rodney C.; Wang, Yuejian

    2013-01-01

    Selected members of the A2B3 (A = Sb, Bi; B = Se, Te) family are topological insulators. The Sb2Se3 compound does not exhibit any topological properties at ambient conditions; a recent high-pressure study, however, indicated that pressure transforms Sb2Se3 from a band insulator into a topological insulator above ~2?GPa; in addition, three structural transitions were proposed to occur up to 25?GPa. Partly motivated by these results, we have performed x-ray diffraction and Raman spectroscopy investigations on Sb2Se3 under pressure up to 65?GPa. We have identified only one reversible structural transition: the initial Pnma structure transforms into a disordered cubic bcc alloy above 51?GPa. On the other hand, our high-pressure Raman study did not reproduce the previous results; we attribute the discrepancies to the effects of the different pressure transmitting media used in the high-pressure experiments. We discuss the structural behavior of Sb2Se3 within the A2B3 (A = Sb, Bi; B = Se, Te) series. PMID:24045363

  6. Synthesis of CdIn2Se4 and Cu0.5Ag1.5InSe3 Compounds via Chemical and Solid-State Methods

    NASA Astrophysics Data System (ADS)

    Laokawee, Viratchara; Sarakonsri, Thapanee; Thanachayanont, Chanchana

    2014-04-01

    CdIn2Se4 and Cu0.5Ag1.5InSe3 are high-performance thermoelectric materials. In this study, both CdIn2Se4 and Cu0.5Ag1.5InSe3 powders were synthesized using a microwave and solution method followed by annealing in nitrogen atmosphere. CdIn2Se4 was synthesized by two routes. First, CdSe was prepared using a microwave method. Second, In metal was prepared using a solution method. The prepared metals were annealed in nitrogen atmosphere. From the x-ray diffraction (XRD) results, CdIn2Se4 was observed as the main phase with CdSe and In2O3 as contaminant phases. The synthesis of Cu0.5Ag1.5InSe3 was also divided into two steps. First, CuAg and Se were prepared using a microwave method. Second, In metal was prepared using a solution method. The prepared metals were annealed in nitrogen atmosphere. From the XRD results, Cu0.5Ag1.5InSe3 was observed as the main phase with Cu0.5- x Ag1.5- y In x+ y Se and Se as contaminant phases.

  7. Electron-phonon interaction and thermal boundary resistance at the crystal-amorphous interface of the phase change compound GeTe

    NASA Astrophysics Data System (ADS)

    Campi, Davide; Donadio, Davide; Sosso, Gabriele C.; Behler, Jörg; Bernasconi, Marco

    2015-01-01

    Phonon dispersion relations and electron-phonon coupling of hole-doped trigonal GeTe have been computed by density functional perturbation theory. This compound is a prototypical phase change material of interest for applications in phase change non-volatile memories. The calculations allowed us to estimate the electron-phonon contribution to the thermal boundary resistance at the interface between the crystalline and amorphous phases present in the device. The lattice contribution to the thermal boundary resistance has been computed by non-equilibrium molecular dynamics simulations with an interatomic potential based on a neural network scheme. We find that the electron-phonon term contributes to the thermal boundary resistance to an extent which is strongly dependent on the concentration and mobility of the holes. Further, for measured values of the holes concentration and electrical conductivity, the electron-phonon term is larger than the contribution from the lattice. It is also shown that the presence of Ge vacancies, responsible for the p-type degenerate character of the semiconductor, strongly affects the lattice thermal conductivity of the crystal.

  8. Lattice location and local magnetism of recoil implanted Fe impurities in wide and narrow band semiconductors CdTe, CdSe, and InSb: Experiment and theory

    SciTech Connect

    Mohanta, S. K.; Mishra, S. N.

    2014-05-07

    Employing the time differential perturbed angular distribution method, we have measured local susceptibility and spin relaxation rate of {sup 54}Fe nuclei implanted in III-V and II-VI semiconductors, CdTe, CdSe, and InSb. The magnetic response of Fe, identified to occupy the metal as well as the semi-metal atom sites, exhibit Curie-Weiss type susceptibility and Korringa like spin relaxation rate, revealing the existence of localized moments with small spin fluctuation temperature. The experimental results are supported by first principle electronic structure calculations performed within the frame work of density functional theory.

  9. Theoretical study of influencing factors on the dispersion of bulk band-gap edges and the surface states in topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3}

    SciTech Connect

    Rusinov, I. P. Nechaev, I. A.; Chulkov, E. V.

    2013-06-15

    The dispersion of the band-gap edge states in bulk topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} is considered within density functional theory. The dependences of this dispersion both on the approximation used for an exchange-correlation functional at fixed unit cell parameters and atomic positions and on these parameters and positions that are obtained upon structural relaxation performed using a certain approximated functional are analyzed. The relative position of the Dirac point of topologically protected surface states and the valence band maximum in the surface electronic structure of the topological insulators is discussed.

  10. Synthesis of U3Se5 and U3Te5 type polymorphs of Ta3N5 by combining high pressure-temperature pathways with a chemical precursor approach.

    PubMed

    Salamat, Ashkan; Woodhead, Katherine; Shah, S Imran U; Hector, Andrew L; McMillan, Paul F

    2014-09-11

    Combining metastable precursors with high pressure-temperature treatment is a powerful tool to make nitrogen-rich metal nitrides. Two new dense polymorphs of Ta3N5 have previously been theoretically predicted, with U3Se5 (Pnma) and U3Te5 (Pnma) structure types, and are now shown to exist. Amorphous Ta3N5 from thermal ammonolysis of an amorphous polymeric precursor was laser heated at 22 GPa and examined using synchrotron X-ray diffraction to reveal the emergence of these two novel polymorphs. PMID:25051155

  11. Courses: Modern Languages and Literatures (MLL) Page 345Sonoma State University 2015-2016 Catalog MLL 450 Foreign LAnguAge teACHing SeMinAr (2-4)

    E-print Network

    Ravikumar, B.

    MLL 450 Foreign LAnguAge teACHing SeMinAr (2-4) This course is designed as a seminar and Practicum for a total of 4 units. Modern Languages and Literatures (MLL) MLL 101 SpeCiAL topiCS in Foreign LAnguAge (1-4) MLL 102 SpeCiAL topiCS in Foreign LAnguAge (1-4) MLL 160A HuMAnitieS LeArning CoMMunity (4) MLL 160 A

  12. Uni ted St~te s Depar tment of the I n t e ri or Fi sh and Wi l dli fe Se r v i ce

    E-print Network

    E" quality or sul)sr, {'1 ncl~ w;,ich we c8.l1 ;:1, vit"l."'"!i n. R.lso is necessary in our diet . A deficie erC1.1 supuly of ':)ro te i ns for the bu i L' i ng of mus cles nncl other i)oclv t i ssues ; ;:1ncl n nations h,"lVe r e ~liz ocl for cen turie s th;lt f i s h A.ncl she ll fi r· r" 8.~d ) r o0.ucts i

  13. Magnetic properties of Fe{sub 2}P-type Tb{sub 6}FeTe{sub 2}, Tb{sub 6}CoTe{sub 2}, Tb{sub 6}NiTe{sub 2} and Er{sub 6}FeTe{sub 2} compounds

    SciTech Connect

    Morozkin, A.V.; Mozharivskyj, Yu.; SvitlyK, V.; Nirmala, R.; Nigam, A.K.

    2010-12-15

    The magnetic ordering of the Fe{sub 2}P-type Tb{sub 6}FeTe{sub 2}, Tb{sub 6}CoTe{sub 2} Tb{sub 6}NiTe{sub 2} and Er{sub 6}FeTe{sub 2} phases (space group P6-bar 2m) has been investigated through magnetization measurement and neutron powder diffraction. Tb{sub 6}FeTe{sub 2}, Tb{sub 6}CoTe{sub 2} and Tb{sub 6}NiTe{sub 2} demonstrate high-temperature ferromagnetic and low-temperature spin reorientation transitions, whereas Er{sub 6}FeTe{sub 2} shows antiferromagnetic transition, only. The Tb{sub 6}FeTe{sub 2} and Tb{sub 6}NiTe{sub 2} phases show same high-temperature collinear ferromagnetic structure, whereas Tb{sub 6}FeTe{sub 2} is the commensurate non-collinear ferromagnet and Tb{sub 6}NiTe{sub 2} is the canted ferromagnetic cone with K{sub 1}=[0, 0, {+-}3/10] and K{sub 2}=[{+-}2/9, {+-}2/9, 0] wave vectors at 2 K. The magnetic structure of Er{sub 6}FeTe{sub 2} is a flat spiral with K{sub 1}=[0, 0, {+-}1/10] at 2 K. The magnetic entropy change for Tb{sub 6}NiTe{sub 2} is {Delta}S{sub m}=-4.86 J/kg K at 229 K for the field change {Delta}{mu}{sub 0}H=0-5 T. In addition, novel Fe{sub 2}P-type Gd{sub 6}FeTe{sub 2}, Zr{sub 6}FeTe{sub 2}, Hf{sub 6}FeTe{sub 2}, Dy{sub 6}NiTe{sub 2}, Zr{sub 6}NiTe{sub 2} and Hf{sub 6}NiTe{sub 2} phases have been obtained. -- Graphical abstract: The novel Fe{sub 2}P-type Tb{sub 6{l_brace}}Fe, Co, Te{r_brace}Te{sub 2} and Er{sub 6}FeTe{sub 2} phases (space group P6-bar 2m) show the complex magnetic ordering below 18-228 K. The magnetocaloric effect for Tb{sub 6}NiTe{sub 2} in terms of the isothermal entropy change, -{Delta}S{sub m}, has the maximum value of 4.86 J/kg K at 229 K for the 0-5 T field change.

  14. Te nanowires

    NASA Astrophysics Data System (ADS)

    Schönherr, Piet; Collins-McIntyre, Liam J.; Zhang, ShiLei; Kusch, Patryk; Reich, Stephanie; Giles, Terence; Daisenberger, Dominik; Prabhakaran, Dharmalingam; Hesjedal, Thorsten

    2014-03-01

    High-density growth of single-crystalline Bi2Se2Te nanowires was achieved via the vapour-liquid-solid process. The stoichiometry of samples grown at various substrate temperatures is precisely determined based on energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy on individual nanowires. We discuss the growth mechanism and present insights into the catalyst-precursor interaction.

  15. Advanced processing of CdTe- and CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2}-based solar cells. Phase 1 annual subcontract report, 18 April 1995--17 April 1996

    SciTech Connect

    Morel, D.L.; Ferekides, C.S.

    1997-03-01

    The main objective of this project to develop high-efficiency CdTe solar cells based on processing conditions favorable for manufacturing processes. This report presents the results on work performed during the first phase of this project. One of the major issues addressed is the use of soda-lime glass substrates in place of the borosilicate glass often used for laboratory devices; another task is the preparation of Cu(In, Ga) Se{sub 2} solar cells by selenizing suitable precursor films. Emphasis is placed on processing and how different reaction schemes affect device performance. It was found that different reaction schemes not only change the bulk properties of Cu(In, Ga) Se{sub 2}, but also its surface properties, which critically affect device performance. Although the objective is to optimize processing to meet the manufacturing constraints, work has not been limited within these requirements.

  16. Electrical detection of the spin polarization due to charge flow in the surface state of the topological insulator Bi(1.5)Sb(0.5)Te(1.7)Se(1.3).

    PubMed

    Ando, Yuichiro; Hamasaki, Takahiro; Kurokawa, Takayuki; Ichiba, Kouki; Yang, Fan; Novak, Mario; Sasaki, Satoshi; Segawa, Kouji; Ando, Yoichi; Shiraishi, Masashi

    2014-11-12

    We detected the spin polarization due to charge flow in the spin nondegenerate surface state of a three-dimensional topological insulator by means of an all-electrical method. The charge current in the bulk-insulating topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was injected/extracted through a ferromagnetic electrode made of Ni80Fe20, and an unusual current-direction-dependent magnetoresistance gave evidence for the appearance of spin polarization, which leads to a spin-dependent resistance at the BSTS/Ni80Fe20 interface. In contrast, our control experiment on Bi2Se3 gave null result. These observations demonstrate the importance of the Fermi-level control for the electrical detection of the spin polarization in topological insulators. PMID:25330016

  17. Effects of partial anion substitution on the thermoelectric properties of silver(I) chalcogenide halides in the system Ag 5Q2X with Q=Te, Se and S and X=Br and Cl

    NASA Astrophysics Data System (ADS)

    Eckstein, Nadine; Nilges, Tom; Decourt, Rodolphe; Bobet, Jean-Louis; Chevalier, Bernard

    2011-04-01

    A selection of mixed conducting silver chalcogenide halides of the general formula Ag 5Q2X with Q=sulfur, selenium and tellurium and X=chlorine and bromine has been investigated due to their thermoelectric properties. Recently, the ternary counterpart Ag 5Te 2Cl showed a defined d10- d10 interaction in the disordered cation substructure at elevated temperatures where Ag 5Te 2Cl is present in its high temperature ?-phase. A significant drop of the thermal diffusivity has been observed during the ?-? phase transition reducing the values from 0.12 close to 0.08 mm 2 s -1. At the same transition the thermopower reacts on the increasing silver mobility and jumps towards less negative values. Thermal conductivities, thermopower and thermal diffusivity of selected compounds with various grades of anion substitution in Ag 5Q2X were determined around the silver-order/disorder ?-? phase transition. A formation of attractive interactions could be observed for selenium substituted phases while no effect was detected for bromide and sulfide samples. Depending on the grade and type of substitution the thermopower changes significantly at and after the ?-? phase transition. Thermal conductivities are low reaching values around 0.2-0.3 W m -1 K -1 at 299 K. Partial anion exchange can substantially tune the thermoelectric properties in Ag 5Q2X phases.

  18. Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3}

    SciTech Connect

    Bhame, Shekhar D.; Noudem, Jacques G.; LUSAC , Universite de Caen, Basse Normandie , BP 78, 50130 Cherbourg Octeville ; Pravarthana, Dhanapal; Prellier, Wilfrid

    2013-05-27

    Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications.

  19. Effects of partial anion substitution on the thermoelectric properties of silver(I) chalcogenide halides in the system Ag{sub 5}Q{sub 2}X with Q=Te, Se and S and X=Br and Cl

    SciTech Connect

    Eckstein, Nadine; Nilges, Tom; Decourt, Rodolphe; Bobet, Jean-Louis; Chevalier, Bernard

    2011-04-15

    A selection of mixed conducting silver chalcogenide halides of the general formula Ag{sub 5}Q{sub 2}X with Q=sulfur, selenium and tellurium and X=chlorine and bromine has been investigated due to their thermoelectric properties. Recently, the ternary counterpart Ag{sub 5}Te{sub 2}Cl showed a defined d{sup 10}-d{sup 10} interaction in the disordered cation substructure at elevated temperatures where Ag{sub 5}Te{sub 2}Cl is present in its high temperature {alpha}-phase. A significant drop of the thermal diffusivity has been observed during the {beta}-{alpha} phase transition reducing the values from 0.12 close to 0.08 mm{sup 2} s{sup -1}. At the same transition the thermopower reacts on the increasing silver mobility and jumps towards less negative values. Thermal conductivities, thermopower and thermal diffusivity of selected compounds with various grades of anion substitution in Ag{sub 5}Q{sub 2}X were determined around the silver-order/disorder {beta}-{alpha} phase transition. A formation of attractive interactions could be observed for selenium substituted phases while no effect was detected for bromide and sulfide samples. Depending on the grade and type of substitution the thermopower changes significantly at and after the {beta}-{alpha} phase transition. Thermal conductivities are low reaching values around 0.2-0.3 W m{sup -1} K{sup -1} at 299 K. Partial anion exchange can substantially tune the thermoelectric properties in Ag{sub 5}Q{sub 2}X phases. -- Graphical abstract: A structure section of the {alpha}-Ag{sub 5}Te{sub 2}Cl structure type and the thermopower evolution of Ag{sub 5}Te{sub 2}Cl{sub 0.4}Br{sub 0.6} undergoing a silver ion order/disorder phase transition. Display Omitted Research highlights: > We report on thermoelectric properties of silver(I) chalcogenide halides. > We examine thermopower, thermal diffusivity and thermal behavior. > Silver mobility, phase transitions and order/disorder phenomena are discussed. > Partial anion exchange can tune thermoelectric properties significantly.

  20. Measurement of the thermodynamic properties of saturated solid solutions of compounds in the Ag-Sn-Se system by the EMF method

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    The dependence of the EMF ( E) of galvanic cells Ag|AgI|Ag2GeS3 glass| D on temperature (where Ag, D denotes the electrodes of an electrochemical cell; D represents equilibrium two- and three-phase alloys of the Ag-Sn-Se system; and AgI|Ag2GeS3 glass is a bilayer membrane with purely ionic (Ag+) conductivity) is studied in the range of 480-580 K. Analytical equations of E( T) are used to calculate the values of the thermodynamic functions of saturated solid solutions of the SnSe, ?-Ag2Se, AgSnSe2, and Ag8SnSe6 phases of the Ag-Sn-Se system in the standard state.

  1. Te-Te and Te-C bond cleavage reactions using a monovalent gallanediyl.

    PubMed

    Ganesamoorthy, Chelladurai; Bendt, Georg; Bläser, Dieter; Wölper, Christoph; Schulz, Stephan

    2015-03-21

    LGa (L = [(2,6-i-Pr2-C6H3)NC(Me)]2CH) reacts with elemental tellurium with formation of the Te-bridged compound [LGa-?-Te]2 1, whereas the reactions with Ph2Te2 and i-Pr2Te occurred with cleavage of the Te-Te and Te-C bond, respectively, and subsequent formation of LGa(TePh)2 2 and LGa(i-Pr)Tei-Pr 3. 1-3 were characterized by heteronuclear NMR ((1)H, (13)C, (125)Te) and IR spectroscopy and their solid state structures were determined by single crystal X-ray analyses. PMID:25680084

  2. Sputtered n-type Bi2Te3 / (Bi,Sb)2Te3 superlattice systems

    NASA Astrophysics Data System (ADS)

    Winkler, M.; Liu, X.; Hansen, A.-L.; König, J. D.; Bensch, W.; Kienle, L.; Böttner, H.; Bartholomé, K.

    2013-10-01

    Bi2Te3, (Bi1-xSbx )2Te3 and layered Bi2Te3/(Bi1-xSbx)2Te3 superlattices fabricated by nanoalloying. Our approach is based on the sequential sputtering of nanoscale layers of the elements and subsequent annealing in order to induce a solid state reaction. While conventionally Bi2(SexTe1-x )3 compounds are used as n-type V2VI3 material system, the deposition of Se proves to be problematic especially for sputtering deposition and is therefore replaced by (Bi1-xSbx )2Te3. A superlattice consisting of 25 nm Bi2Te3/25 nm (Bi0:9Sb0:1)2Te3 - ML (periodicity of 50 nm) was synthesized and annealed at temperatures of 150, 200, 225, and 250°C. The layers are slightly rough and polycrystalline, and the grain sizes increase with increasing annealing temperature. The XRD analysis shows a pronounced (00l) texture of the sputtered layers. SIMS depth profiles reveal that the chemical separation into layers is present, yet smeared out to some degree after annealing at 200°C. High Seebeck coefficients of up to ~-190 ?V/K were achieved. A high maximum power factor of 22 ?W/cmK2 can be attained after annealing at 250 °C for 12 h. The superlattice system Bi2Te3 / (Bi1-xSbx )2Te3 can compete with Bi2Te3 / Bi2(SexTe1-x )3 in terms of electrical properties while representing a good practical alternative for the sputter deposition due to the substitution of problematic Se with Sb. Cross-plane thermal conductivities are in the range of 0.55 to 0.6 W/mK. The thermal conductivity is generally reduced due to the nanocrystallinity of the material, however, there seems to be no measurable reduction of the thermal conductivity by the superlattice-type 2D nanostructuring.

  3. A photoelectron spectroscopy study of the electronic structure evolution in CuInSe{sub 2}-related compounds at changing copper content

    SciTech Connect

    Kuznetsova, T. V.; Grebennikov, V. I.; Zhao, H.; Derks, C.; Taubitz, C.; Neumann, M.; Persson, C.; Kuznetsov, M. V.; Bodnar, I. V.; Martin, R. W.; Yakushev, M. V.

    2012-09-10

    Evolution of the valence-band structure at gradually increasing copper content has been analysed by x-ray photoelectron spectroscopy (XPS) in In{sub 2}Se{sub 3}, CuIn{sub 5}Se{sub 8}, CuIn{sub 3}Se{sub 5}, and CuInSe{sub 2} single crystals. A comparison of these spectra with calculated total and angular-momentum resolved density-of-states (DOS) revealed the main trends of this evolution. The formation of the theoretically predicted gap between the bonding and non-bonding states has been observed in both experimental XPS spectra and theoretical DOS.

  4. First detection of a selenenyl fluoride ArSe-F by NMR spectroscopy: the nature of Ar2Se2/XeF2 and ArSe-SiMe3/XeF2 reagents.

    PubMed

    Poleschner, Helmut; Seppelt, Konrad

    2004-12-01

    Arylselenenyl fluorides ArSeF are obtained from diselenides Ar2Se2 or arylselenotrimethylsilanes ArSe-SiMe3, and XeF2. They are detected by low-temperature 19F and 77Se NMR spectroscopy. Substitution in the ortho position of the aromatic ring to provide electronic or steric protection is a requirement for their formation. ArSe--F compounds decompose according to 3 ArSe-F-->[ArSe-SeF2Ar]+ArSe-F-->ArSeF3+Ar2Se2. Reaction energies for this disproportionation as well as that of the sulfur and tellurium homologues have been calculated with MP2, CCSD(T,) and B3 LYP methods. They were found to be increasingly exothermic in the sequence S<Se. For selected Se-C and Se-F compounds the 77Se and 19F chemical shifts have been calculated by GIAO-MP2 and GIAO-B3 LYP methods and are in good agreement with experimental values. PMID:15540265

  5. Determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer quantum dots via spectral analysis of optical signature of the Aharanov-Bohm excitons

    SciTech Connect

    Ji, Haojie; Dhomkar, Siddharth; Roy, Bidisha; Kuskovsky, Igor L.; Shuvayev, Vladimir; Deligiannakis, Vasilios; Tamargo, Maria C.; Ludwig, Jonathan; Smirnov, Dmitry; Wang, Alice

    2014-10-28

    For submonolayer quantum dot (QD) based photonic devices, size and density of QDs are critical parameters, the probing of which requires indirect methods. We report the determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer QDs, based on spectral analysis of the optical signature of Aharanov-Bohm (AB) excitons, complemented by photoluminescence studies, secondary-ion mass spectroscopy, and numerical calculations. Numerical calculations are employed to determine the AB transition magnetic field as a function of the type-II QD radius. The study of four samples grown with different tellurium fluxes shows that the lateral size of QDs increases by just 50%, even though tellurium concentration increases 25-fold. Detailed spectral analysis of the emission of the AB exciton shows that the QD radii take on only certain values due to vertical correlation and the stacked nature of the QDs.

  6. Surface-dominated transport and enhanced thermoelectric figure of merit in topological insulator Bi(1.5)Sb(0.5)Te(1.7)Se(1.3).

    PubMed

    Hsiung, Te-Chih; Mou, Chung-Yu; Lee, Ting-Kuo; Chen, Yang-Yuan

    2015-01-14

    We report the observation of an order of magnitude enhancement of the thermoelectric figure of merit (ZT = 0.36) in topological insulator Bi1.5Sb0.5Te1.7Se1.3 nanowires at 300 K as compared with the bulk specimen (ZT = 0.028). The enhancement was primarily due to an order of magnitude increase in the electrical conductivity of the surface-dominated transport and thermally activated charge carriers in the nanowires. Magnetoresistance analysis revealed the presence of Dirac electrons and determined that the Fermi level was near the conduction band edge. This may be the first thermoelectric measurement of samples with a chemical potential in the gap of a topological insulator without gate tuning, and provides an opportunity to study the contribution of surface states to the Seebeck coefficient and resistivity without concern for the complex effect of band bending. PMID:25409984

  7. Substitution of Ni for Fe in superconducting Fe0.98Te0.5Se0.5 depresses the normal-state conductivity but not the magnetic spectral weight

    DOE PAGESBeta

    Wang, Jinghui; Zhong, Ruidan; Li, Shichao; Gan, Yuan; Xu, Zhijun; Zhang, Cheng; Ozaki, T.; Matsuda, M.; Zhao, Yang; Li, Qiang; et al

    2015-01-05

    We have performed systematic resistivity and inelastic neutron scattering measurements on Fe?.???zNizTe?.?Se?.? samples to study the impact of Ni substitution on the transport properties and the low-energy (? 12 meV) magnetic excitations. It is found that, with increasing Ni doping, both the conductivity and superconductivity are gradually suppressed; in contrast, the low-energy magnetic spectral weight changes little. Comparing with the impact of Co and Cu substitution, we find that the effects on conductivity and superconductivity for the same degree of substitution grow systematically as the atomic number of the substituent deviates from that of Fe. The impact of the substituentsmore »as scattering centers appears to be greater than any contribution to carrier concentration. The fact that low-energy magnetic spectral weight is not reduced by increased electron scattering indicates that the existence of antiferromagnetic correlations does not depend on electronic states close to the Fermi energy.« less

  8. Advanced processing technology for high-efficiency, thin-film CuInSe{sub 2} and CdTe solar cells. Final subcontract report, March 1, 1992--April 30, 1995

    SciTech Connect

    Morel, D.L.; Ferekides, C.S.

    1996-01-01

    This report describes work performed by the University of South Florida to develop a manufacturing-friendly fabrication process for CuInSe{sub 2} (CIS) solar cells. The process developed under this project uses conventional deposition processes and equipment, does not require stringent process control, and uses elemental Se as the selenium source. The authors believe it can be readily scaled up using off-the-shelf processing equipment and that it will meet the low manufacturing-cost objectives. Another significant achievement under this project was the development of a reactive sputtering deposition technology for ZnO. ZnO is used in many solar cell devices, and sputtering is a desirable manufacturing technology. The application of sputtering has been limited because conventional deposition uses ceramic targets that result in low sputtering rates. The use of Zn metal as the target in reactive sputtering overcomes this limitation. The authors have demonstrated that ZnO deposited by reactive sputtering has state-of-the-art opto-electronic properties. These developments result in large-area uniformity and optimized performance and provide a significant opportunity for applying and commercializing the technology. The second objective of this project was to fabricate high-efficiency CdTe solar cells using manufacturing-friendly processes. Three deposition processes were used to deposit CdS films: chemical bath deposition, rf sputtering, and close-spaced sublimation (CSS). The CdTe films were deposited by CSS. A cell with a record efficiency of 15.8% was obtained.

  9. Surface-dominated transport and enhanced thermoelectric figure of merit in topological insulator Bi1.5Sb0.5Te1.7Se1.3

    NASA Astrophysics Data System (ADS)

    Hsiung, Te-Chih; Mou, Chung-Yu; Lee, Ting-Kuo; Chen, Yang-Yuan

    2014-12-01

    We report the observation of an order of magnitude enhancement of the thermoelectric figure of merit (ZT = 0.36) in topological insulator Bi1.5Sb0.5Te1.7Se1.3 nanowires at 300 K as compared with the bulk specimen (ZT = 0.028). The enhancement was primarily due to an order of magnitude increase in the electrical conductivity of the surface-dominated transport and thermally activated charge carriers in the nanowires. Magnetoresistance analysis revealed the presence of Dirac electrons and determined that the Fermi level was near the conduction band edge. This may be the first thermoelectric measurement of samples with a chemical potential in the gap of a topological insulator without gate tuning, and provides an opportunity to study the contribution of surface states to the Seebeck coefficient and resistivity without concern for the complex effect of band bending.We report the observation of an order of magnitude enhancement of the thermoelectric figure of merit (ZT = 0.36) in topological insulator Bi1.5Sb0.5Te1.7Se1.3 nanowires at 300 K as compared with the bulk specimen (ZT = 0.028). The enhancement was primarily due to an order of magnitude increase in the electrical conductivity of the surface-dominated transport and thermally activated charge carriers in the nanowires. Magnetoresistance analysis revealed the presence of Dirac electrons and determined that the Fermi level was near the conduction band edge. This may be the first thermoelectric measurement of samples with a chemical potential in the gap of a topological insulator without gate tuning, and provides an opportunity to study the contribution of surface states to the Seebeck coefficient and resistivity without concern for the complex effect of band bending. Electronic supplementary information (ESI) available: Magnetoresistance and thermal conductivity measurements of additional samples. See DOI: 10.1039/c4nr05376a

  10. The spatial distributions of large gap-like structure on Fe(Se,Te) single crystals observed by STM/STS

    NASA Astrophysics Data System (ADS)

    Sugimoto, Akira; Sakai, Yuta; Nagasaka, Kouhei; Ekino, Toshikazu

    2015-11-01

    The nanoscale spatial distributions of large gap-like structure on superconducting FeSe1-xTex were investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The STM topography shows regular atomic lattice arrangements with the lattice spacing ?0.38 nm, together with the randomly distributed large spots due to the excess Fe atoms. From the STS measurements, the small gap structures of ? ? 7 meV were partly observed. On the other hand, the high-bias dI/dV curves exhibit the broad peak structures at the negative biases of VPG = -200 to -400 mV in the measured whole surface area. The average of these large gaps is |VPGave| ? 305 mV with the standard deviation of ? ? 48 mV. The spatial distributions of the VPG exhibit the domain structures consisting of the relatively smaller gaps (<250 meV), which correspond to the excess Fe positions. The small gap ? ? 7 meV is also observed at those positions, suggesting that the excess Fe affects the electronic structures of FeSe1-xTex.

  11. DFT and modified Becke Johnson (mBJ) potential investigations of the optoelectronic properties of SnGa4Q7 (Q = S, Se) compounds: Transparent materials for large energy conversion

    NASA Astrophysics Data System (ADS)

    Khan, Wilayat; Azam, Sikander; Shah, Fahad Ali; Goumri-Said, Souraya

    2015-10-01

    Electronic structure and optical properties of SnGa4Q7 (Q = S, Se) compounds were investigated using a full potential linearized augmented plane wave method based on density functional formalism. Electronic band structures show an indirect semiconducting wide band gap two different approaches (EV-GGA and mBJ). The band gap values are estimated at 2.90 (2.25 eV) and 3.11 (2.49 eV) for EV-GGA and mBJ for SnGa4S7 (SnGa4Se7), respectively. Densities of states show that Sn-5s and S/Se-3p/4p states are dominating the region around Fermi level form valence band maximum and conduction band minimum. The computed electronic charge density contours demonstrate that SnGa4Q7 (Q = S, Se) show a mixture between ionic and covalent characters. Optical parameters including the dielectric constant, absorption coefficient, reflectivity, refractive index, energy loss function, and birefringence are also reported to investigate the potential role of SnGa4Q7 (Q = S, Se) compounds for solar energy conversion application.

  12. Crystal chemistry of selenates with mineral-like structures. IV. Crystal structure of Zn(SeO4)(H2O)2, a new compound with a mixed framework of the variscite type

    NASA Astrophysics Data System (ADS)

    Krivovichev, S. V.

    2007-12-01

    The crystal structure of a new compound Zn(SeO4)(H2O)2 (orthorhombic, Pbca, a = 9.0411(13), b = 10.246(2), c = 10.3318(15) Å, V = 957.1(3) Å3) has been solved by direct methods and refined to R 1 = 0.033 on the basis of 1076 observed reflections with | F hkl | ? 4?| F hkl |. The structure contains one independent Zn2+ cation coordinated by two water molecules and four oxygen atoms of selenate group. The only independent (SeO4)2- tetrahedral oxoanion is tetradentate, sharing its corners with four adjacent [Zn2+O2(H2O4)]2+ octahedrons. The structure can be described as consisting of heteropolyhedral sheets parallel to the (001) plane and linked together into a three-dimensional network. The compound belongs to the variscite structure type and is the first structurally characterized selenate of this group.

  13. Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Annual subcontract report, 1 April 1992--31 March 1993

    SciTech Connect

    Sites, J.R.

    1994-02-01

    This report describes work to conduct several investigations of thin-film polycrystalline solar cells. (1) An analysis of high-efficiency solar cells fabricated at the University of South Florida showed significant reduction in forward recombination current, and the cells were stable over a 3-month test period. (2) Transient voltage effects were documented in a large number of polycrystalline cells and were attributed to long-lived trapping states sensitive to voltage changes near one-half open-circuit voltage. (3) Collection efficiency and its voltage dependence were carefully calculated. The typical effect on photocurrent at operating voltages is about 2% for CuInSe{sub 2}, and less for other cells.

  14. Transannular E···E' Interactions in Neutral, Radical Cationic, and Dicationic Forms of cyclo-[E(CH2CH2CH2)2E'] (E, E' = S, Se, Te, and O) with Structural Feature: Dynamic and Static Behavior of E···E' Elucidated by QTAIM Dual Functional Analysis.

    PubMed

    Hayashi, Satoko; Matsuiwa, Kohei; Nishizawa, Nozomu; Nakanishi, Waro

    2015-12-18

    The nature of the transannular E-?-E' interactions in neutral, radical cationic, and dicationic forms of cyclo-E(CH2CH2CH2)2E' (1) (E, E' = S, Se, Te, and O) (1, 1(•+), and 1(2+), respectively) is elucidated by applying QTAIM dual functional analysis (QTAIM-DFA). Hb(rc) are plotted versus Hb(rc) - Vb(rc)/2 for the data of E-?-E' at BCPs in QTAIM-DFA, where ? emphasizes the existence of BCP. Plots for the fully optimized structures are analyzed by the polar coordinate (R, ?) representation. Those containing the perturbed structures are by (?p, ?p): ?p corresponds to the tangent line of the plot, and ?p is the curvature. While (R, ?) describes the static nature, (?p, ?p) represents the dynamic nature of interactions. The nature is well-specified by (R, ?) and (?p, ?p). E-?-E' becomes stronger in the order of 1 < 1(•+) < 1(2+), except for O-?-O. While E-?-E' (E, E' = S, Se, and Te) in 1(2+) are characterized as weak covalent bonds, except for S-?-Te (MC nature through CT) and Se-?-Te (TBP nature through CT), O-?-E' seems more complex. The behavior of E-?-E' in 1(2+) is very close to that of cyclo-E(CH2CH2CH2)E' (E, E' = S, Se, Te, and O), except for O-?-O. PMID:26554342

  15. Synthesis, crystal structure and magnetic properties of the open framework compound Co{sub 3}Te{sub 2}O{sub 2}(PO{sub 4}){sub 2}(OH){sub 4}

    SciTech Connect

    Zimmermann, Iwan; Kremer, Reinhard K.; Johnsson, Mats

    2011-11-15

    The new compound Co{sub 3}Te{sub 2}O{sub 2}(PO{sub 4}){sub 2}(OH){sub 4} was synthesized using hydrothermal techniques. It crystallizes in the monoclinic space group C2/m with the unit cell a=19.4317(10) A, b=6.0249(3) A, c=4.7788(2) A, {beta}=103.139(5){sup o}. The crystal structure is an open framework having chains of edge sharing [Co(1)O{sub 6}] octahedra. Other building blocks are [TeO{sub 3}(OH){sub 2}], [PO{sub 4}] and [Co({sub 2})O{sub 2}(OH){sub 4}] connected mainly via corner sharing. The -OH groups protrude into channels in the structure. The magnetic susceptibility measured from 2 to 300 K shows two broad anomalies at around 21 K and 4 K, respectively. The peak at {approx}20 K is ascribed to a two-dimensional antiferromagnetic ordering of linear [Co(1)O{sub 6}] chains coupled by interchain interaction via [PO{sub 4}] groups in the Co(1) sheets. The second transition at 4 K is ascribed to a second antiferromagnetic ordering of the moments of the Co(2) entities via super-super exchange involving [PO{sub 4}] and [TeO{sub 3}(OH){sub 2}] groups. This assignment is strongly supported by low-temperature heat capacity measurements indicating an entropy removal within the high-temperature transition of about twice the magnitude of the low-temperature transition. - Graphical Abstract: The new compound Co{sub 3}Te{sub 2}O{sub 2}(PO{sub 4}){sub 2}(OH){sub 4} has been synthesized using hydrothermal techniques. It crystallizes in the monoclinic space group C2/m. Building blocks are [Co(1)O{sub 6}], [TeO{sub 3}(OH){sub 2}], [PO{sub 4}] and [Co(2)O{sub 2}(OH){sub 4}]. The magnetic susceptibility shows two antiferromagnetic transitions at 21 K and 4 K, respectively. Highlights: > The first cobalt tellurium phosphate has been synthesized and structurally determined. > There are two antiferromagnetic orderings identified, one at 21 K and one at 4 K respectively. > A spin flop transition is observed at low temperatures.

  16. Rb2Hg3Te4: A New Layered Compound Synthesized from Solvothermal Reactions Jing Li,*, Zhen Chen, and Kin-Chung Lam

    E-print Network

    Li, Jing

    -liquid-solid (VLS) growth,3 flux growth,4 and solution alloy growth,5 have been used to grow crystals of many and Science of Growing Crystals; Gilman, J. J., Ed.; Wiley: New York, 1963. Krucheanu, E.; Nikulesku, D the boiling point of ethylenediamine. Crystals of Rb2Hg3Te4 were grown from solvothermal reactions using

  17. A first-principles examination of conducting monolayer 1T'-MX? (M = Mo, W; X = S, Se, Te): promising catalysts for hydrogen evolution reaction and its enhancement by strain.

    PubMed

    Putungan, Darwin Barayang; Lin, Shi-Hsin; Kuo, Jer-Lai

    2015-09-01

    We investigated the application of 1T'-MX2 (M = Mo, W; X = S, Se, Te) 2D materials as hydrogen evolution reaction (HER) catalysts using density functional theory. Our results show that 1T'-MX2 have lower energies and are dynamically more stable than their 1T counterparts, therefore likely more relevant to previous experimental findings and applications. We found that sulfides are better catalysts, followed by selenides and tellurides. Specifically, 1T'-MoS2 and WS2 are the best HER catalysts among MX2. We proposed a mechanism, rather than the metallicity surmised previously, based on the calculated density of states. On the other hand, the effectively stretched (compressed) X site on the 1T' 2 × 1 reconstruction from 1T is shown to be more (less) active for the HER. We further exploited the application of external strain to tune and boost the HER performance. Our findings are of significance in the elucidation of previous experimental studies and exploration of potential materials for clean energy applications. PMID:26234741

  18. Substitution of Ni for Fe in superconducting Fe0.98Te0.5Se0.5 depresses the normal-state conductivity but not the magnetic spectral weight

    NASA Astrophysics Data System (ADS)

    Wang, Jinghui; Zhong, Ruidan; Li, Shichao; Gan, Yuan; Xu, Zhijun; Zhang, Cheng; Ozaki, T.; Matsuda, M.; Zhao, Yang; Li, Qiang; Xu, Guangyong; Gu, Genda; Tranquada, J. M.; Birgeneau, R. J.; Wen, Jinsheng

    2015-01-01

    We have performed systematic resistivity and inelastic neutron scattering measurements on Fe0.98 -zNizTe0.5Se0.5 samples to study the impact of Ni substitution on the transport properties and the low-energy (?12 meV) magnetic excitations. It is found that, with increasing Ni doping, both the conductivity and superconductivity are gradually suppressed; in contrast, the low-energy magnetic spectral weight changes little. Comparing with the impact of Co and Cu substitution, we find that the effects on conductivity and superconductivity for the same degree of substitution grow systematically as the atomic number of the substituent deviates from that of Fe. The impact of the substituents as scattering centers appears to be greater than any contribution to carrier concentration. The fact that low-energy magnetic spectral weight is not reduced by increased electron scattering indicates that the existence of antiferromagnetic correlations does not depend on electronic states close to the Fermi energy.

  19. Magnetic (CoFe2O4)0.1(CeO2)0.9 nanocomposite as effective pinning centers in FeSe0.1Te0.9 thin films.

    PubMed

    Huang, Jijie; Chen, Li; Jian, Jie; Tyler, Kevin; Li, Leigang; Wang, Han; Wang, Haiyan

    2016-01-20

    Magnetic epitaxial (CoFe2O4)0.1(CeO2)0.9 nanocomposite layers were incorporated into superconducting FeSe0.1Te0.9 thin films as either a cap layer or a buffer layer. Both capped and buffered samples show an enhancement of the superconducting property compared to the reference sample without the incorporated layer, while the capped one shows the best pinning properties of all the samples. Specifically for the capped sample, the critical temperature [Formula: see text] is ~12.5?K, while the self-field critical current density [Formula: see text] increases to as high as 1.20 MA cm(-2) at 4?K. Its [Formula: see text] value shows a slower decrease with increasing applied magnetic field, with the lowest power-law exponent ? values (derived following [Formula: see text] by the [Formula: see text] plot) of 0.20, 0.23 and 0.33 at 2?K, 4?K and 8?K, respectively. This nanocomposite capped sample also exhibits a high upper critical field [Formula: see text] of 166 T, which indicates its potential in high field applications. This pinning method provides an effective way of enhancing the superconducting property of iron chalcogenide thin film. PMID:26654936

  20. Influence of the interaction between the inter- and intragranular magnetic responses in the analysis of the ac susceptibility of a granular FeSe0.5Te0.5 superconductor

    NASA Astrophysics Data System (ADS)

    Mancusi, D.; Polichetti, M.; Cimberle, M. R.; Pace, S.

    2015-09-01

    The temperature-dependent fundamental ac susceptibility of a granular superconductor in the absence of dc fields has been analyzed by developing a phenomenological model for effective magnetic fields, taking into account the influence of the magnetic interaction between the intergranular and the intragranular magnetizations due to demagnetizing effects. For this purpose a policrystal Fe-based superconductor FeSe0.5Te0.5 sample has been studied. By the frequency dependence of the peaks of the temperature-dependent imaginary part of the fundamental complex susceptibility, the dependence on temperature of the characteristic times both for intergranular and intragranular relaxations of magnetic flux are derived, and the corresponding relaxation processes due to combinations of the flux creep, the flux flow and the thermally activated flux flow regimes are identified on the basis of the effective magnetic fields both at the sample surface and at the grains’ surfaces. Such characteristic times, through the Havriliak-Negami function, determine the temperature and the frequency dependences of the complex susceptibility. The comparison of the numerically obtained curves with the experimental ones confirms the relevance, for identifying the intergranular and intragranular contributions to the ac magnetic response and the corresponding flux dynamical regimes, of the interaction between the intergranular and intragranular magnetizations due to demagnetizing effects.

  1. Electronic structure and ferromagnetism of Mn-substituted CuAlS2, CuGaS2, CuInS2, CuGaSe2, and CuGaTe2

    NASA Astrophysics Data System (ADS)

    Zhao, Yu-Jun; Zunger, Alex

    2004-03-01

    The electronic and magnetic properties of Mn doping at either cation sites in the class of I III VI2 chalcopyrites are studied by first-principles calculation. It is found that Mn doping at the III site provides holes and stabilizes the ferromagnetic interaction between neutral Mn defects; the neutral Mn0Cu also stabilizes the ferromagnetism, although it provides electrons to the conduction band, instead of holes. The ferromagnetic stability is generally weaker when the cation or the anion becomes heavier in these chalcopyrites, i.e., along the sequences CuAlS2?CuGaS2?CuInS2 and CuGaS2? CuGaSe2?CuGaTe2. Interestingly, CuAlO2 in the chalcopyrite structure is predicted to have lower FM energy than CuAlS2 despite its lighter anion and shorter bonds. In general, III site substitution gives stabler ferromagnetism than Cu substitution. Thus, the preferred growth conditions are Cu-rich and III-poor, which maximize MnIII replacement. In n-type samples, when MnIII is negatively charged, the antiferromagnetic coupling is preferred. In p-type samples, the ground state of positively charged Mn+Cu is also antiferromagnetism. The main feature of the calculated electronic properties of Mn defect at either Cu or III site is explained using a simple picture of dangling bond hybride and crystal-field resonance.

  2. Generation of continuously tunable 5?µm coherent radiation by second harmonic conversion of the emission of a multi-atmosphere TE CO2 laser in AgGaSe2

    NASA Astrophysics Data System (ADS)

    Padma Nilaya, J.; Saiprasad, M. B.; Biswas, D. J.

    2014-08-01

    Operation of a continuously tunable coherent source in the 5?micron region of the mid-infrared by frequency doubling of the continuously tunable emission of a multi-atmosphere TE CO2 laser in an AgGaSe2 crystal is reported. The performance has been characterized with regard to energy and power conversion efficiency as well as the threshold pump intensities at which the onset and termination of the second harmonic (S?H) conversion process occurs. The absence of a gain switched peak in the emission of the pump laser that stemmed from its operation with a lean CO2 gas mixture enabled error-free threshold measurement for the onset of the S?H generation process. Further, the excellent phase and amplitude synchronization of the SH emission with the pump pulse, that could be established by taking advantage of the rich modulation in the emission of the multimode pump laser in nanosecond time scale, bore experimental testimony to the instantaneous nature of the SH generation process.

  3. Synthesis of wurtzite-zincblende Cu2ZnSnS4 and Cu2ZnSnSe4 nanocrystals: insight into the structural selection of quaternary and ternary compounds influenced by binary nuclei.

    PubMed

    Li, Yingwei; Han, Qifeng; Kim, Tae Whan; Shi, Wangzhou

    2014-04-01

    Nearly monodispersed wurtzite-dominant Cu2ZnSnS4 and zincblende-dominant Cu2ZnSnSe4 nanocrystals were successfully synthesized by mixing metal salts with heated thiourea or selenourea in oleylamine. A perspective of the structural relationship between quaternary and ternary semiconductors was investigated through the application of different anion sources to prepare Cu2SnS3 and Cu2SnSe3 nanocrystals. Investigations on copper-based binary compounds found that CuSe (or CuS) and Cu2Se (or Cu1.96S, Cu9S5) nuclei were primarily responsible for the formation of zincblende or wurtzite structures, respectively. Further management over these binary intermediates corresponded to slight structural transformations of the quaternary nanocrystals which could be observed not only in XRD patterns, but from optical and electrical properties as well. According to these results, Cu2ZnGeS4 nanocrystals with wurtzite-dominant structures were first reported using SC(NH2)2, which also verified that the binary semiconductors are the determinative factors. PMID:24573321

  4. Thermoelectric properties of Cu-doped n-type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Cu{sub x}Se{sub 3}){sub 0.1}(x=0-0.2) alloys

    SciTech Connect

    Cui, J.L. Mao, L.D.; Yang, W.; Xu, X.B.; Chen, D.Y.; Xiu, W.J.

    2007-12-15

    n-Type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Cu{sub x}Se{sub 3}){sub 0.1} (x=0-0.2) alloys with Cu substitution for Bi were prepared by spark plasma-sintering technique and their structural and thermoelectric properties were evaluated. Rietveld analysis reveals that approximate 9.0% of Bi atomic sites are occupied by Cu atoms and less than 4.0 wt% second phase Cu{sub 2.86}Te{sub 2} precipitated in the Cu-doped parent alloys. Measurements show that an introduction of a small amount of Cu (x{<=}0.1) can reduce the lattice thermal conductivity ({kappa}{sub L}), and improve the electrical conductivity and Seebeck coefficient. An optimal dimensionless figure of merit (ZT) value of 0.98 is obtained for x=0.1 at 417 K, which is obviously higher than those of Cu-free Bi{sub 2}Se{sub 0.3}Te{sub 2.7} (ZT=0.66) and Ag-doped alloys (ZT=0.86) prepared by the same technologies. - Graphical abstract: After Cu-doping with x=0.1, the highest ZT value of 0.98 is obtained at 417 K, which is about 0.32 and 0.12 higher than those of Cu-free Bi{sub 2}Se{sub 0.3}Te{sub 2.7} and the Ag-doped alloys (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Ag{sub x}Se{sub 3}){sub 0.1} (x=0.4), respectively.

  5. Importance of cluster distortions in the tetrahedral cluster compounds GaM{sub 4}X{sub 8} (M=Mo,V,Nb,Ta; X=S,Se): Ab initio investigations

    SciTech Connect

    Sieberer, M.; Turnovszky, S.; Redinger, J.; Mohn, P.

    2007-12-01

    In this paper, we study the structural properties of selected representatives of the so-called molybdenum cluster compounds. Belonging to this family are the GaM{sub 4}X{sub 8} compounds with M=Mo as a group VIB element and V, Nb, or Ta as a group VB element. X denotes either S or Se. These compounds are known to exhibit semiconducting behavior in the electrical resistivity, caused by hopping of electrons between well-separated metal clusters. The large separation of the tetrahedral metal (M{sub 4}) clusters is believed to be the origin of strong correlations. We show that recent calculations neglected an important type of structural distortion, namely, those happening only within the M{sub 4} unit at a fixed angle {alpha}=60 deg. of the trigonal (fcc-like) cell. These internal distortions gain a significant amount of energy compared to the cubic cell and they are--to our knowledge--almost undetectable with powder x-ray diffraction experiments. However, they strongly influence the band-structure by opening up a gap at the Fermi-energy. This, however, puts into question whether all compounds of this family are really Mott insulators as stated elsewhere. In particular, ferromagnetic GaMo{sub 4}S{sub 8} and GaV{sub 4}S{sub 8} are well described within density functional theory. Only the Nb- and Ta-based representatives require a large effort due to the lack of magnetic long-range order caused by frustrated antiferromagnetic M-M interactions.

  6. Temperature and composition phase diagram in the iron-based ladder compounds Ba 1 - x Cs x Fe 2 Se 3

    SciTech Connect

    Hawai, Takafumi; Nambu, Yusuke; Ohgushi, Kenya; Du, Fei; Hirata, Yasuyuki; Avdeev, Maxim; Uwatoko, Yoshiya; Sekine, Yurina; Fukazawa, Hiroshi; Ma, Jie; Chi, Songxue; Ueda, Yutaka; Yoshizawa, Hideki; Sato, Taku J.

    2015-05-28

    We investigated the iron-based ladder compounds (Ba,Cs)Fe?Se?. Their parent compounds BaFe?Se? and CsFe?Se? have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe?Se? is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe?Se? is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe?Se?, but interladder spin configuration is different. Intermediate compounds show insulating behavior, nevertheless a finite T-linear contribution in specific heat was obtained at low temperatures.

  7. Nanostructures versus solid solutions: low lattice thermal conductivity and enhanced thermoelectric figure of merit in Pb9.6Sb0.2Te10-xSex bulk materials.

    PubMed

    Poudeu, Pierre F P; D'Angelo, Jonathan; Kong, Huijun; Downey, Adam; Short, Jarrod L; Pcionek, Robert; Hogan, Timothy P; Uher, Ctirad; Kanatzidis, Mercouri G

    2006-11-01

    The series of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compounds with different Se content (x) were prepared, and their structure was investigated at the atomic and nanosized regime level. Thermoelectric properties were measured in the temperature range from 300 to 700 K. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) series was designed after the refinement of the single-crystal structure of Pb(3.82)Sb(0.12)Te(4) (Pb(9.6)Sb(0.3)Te(10); S.G. Pmm) by substituting isoelectronically in anion positions Te by Se. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x)() compounds show significantly lower lattice thermal conductivity (kappa(L)) compared to the well-known PbTe(1)(-)(x)Se(x) solid solutions. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a kappa(L) value as low as 0.40 W/m.K was determined at 700 K. High-resolution transmission electron microscopy of several Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) samples showed widely distributed Sb-rich nanocrystals in the samples which is the key feature for the strong reduction of the lattice thermal conductivity. The reduction of kappa(L) results in a significantly enhanced thermoelectric figure of merit of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compared to the corresponding PbTe(1)(-)(x)Se(x) solid solution alloys. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a maximum figure of merit of ZT approximately 1.2 was obtained at approximately 650 K. This value is about 50% higher than that of the state-of-the-art n-type PbTe. The work provides experimental validation of the theoretical concept that embedded nanocrystals can promote strong scattering of acoustic phonons. PMID:17076508

  8. Partial Pressures of Te2 and Thermodynamic Properties of Ga-Te System

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

    2001-01-01

    The partial pressures of Te2 in equilibrium with Ga(1-x)Te(x) samples were measured by optical absorption technique from 450 to 1100 C for compositions, x, between 0.333 and 0.612. To establish the relationship between the partial pressure of Te, and the measured optical absorbance, the calibration runs of a pure Te sample were also conducted to determine the Beer's Law constants. The partial pressures of Te2 in equilibrium with the GaTe(s) and Ga2Te3(s)compounds, or the so-called three-phase curves, were established. These partial pressure data imply the existence of the Ga3Te4(s) compound. From the partial pressures of Te2 over the Ga-Te melts, partial molar enthalpy and entropy of mixing for Te were derived and they agree reasonable well with the published data. The activities of Te in the Ga-Te melts were also derived from the measured partial pressures of Te2. These data agree well with most of the previous results. The possible reason for the high activity of Te measured for x less than 0.60 is discussed.

  9. Partitioning of platinum-group elements (PGE) and chalcogens (Se, Te, As, Sb, Bi) between monosulfide-solid solution (MSS), intermediate solid solution (ISS) and sulfide liquid at controlled fO2-fS2 conditions

    NASA Astrophysics Data System (ADS)

    Liu, Yanan; Brenan, James

    2015-06-01

    In order to better understand the behavior of highly siderophile elements (HSEs: Os, Ir, Ru, Rh, Pt, Pd, Au, Re), Ag, Pb and chalcogens (As, Se, Sb, Te and Bi) during the solidification of sulfide magmas, we have conducted a series of experiments to measure partition coefficients (D values) between monosulfide solid solution (MSS) and sulfide melt, as well as MSS and intermediate solid solution (ISS), at 0.1 MPa and 860-926 °C, log fS2 -3.0 to -2.2 (similar to the Pt-PtS buffer), with fO2 controlled at the fayalite-magnetite-quartz (FMQ) buffer. The IPGEs (Os, Ir, Ru), Rh and Re are found to be compatible in MSS relative to sulfide melt with D values ranging from ?20 to ?5, and DRe/DOs of ?0.5. Pd, Pt, Au, Ag, Pb, as well as the chalcogens, are incompatible in MSS, with D values ranging from ?0.1 to ?1 × 10-3. For the same metal/sulfur ratio, D values for the IPGEs, Rh and Re are systematically larger than most past studies, correlating with higher oxygen content in the sulfide liquid, reflecting the significant effect of oxygen on increasing the activity coefficients for these elements in the melt phase. MSS/ISS partitioning experiments reveal that Ru, Os, Ir, Rh and Re are partitioned into MSS by a factor of >50, whereas Pd, Pt, Ag, Au and the chalcogens partition from weakly (Se, As) to strongly (Ag, Au) into ISS. Uniformly low MSS- and ISS- melt partition coefficients for the chalcogens, Pt, Pd, Ag and Au will lead to enrichment in the residual sulfide liquid, but D values are generally too large to reach early saturation in Pt-Pd-chalcogen-rich accessory minerals, based on current solubility estimates. Instead, these phases likely precipitate at the last dregs of crystallization. Modeled evolution curves for the PGEs and chalcogens are in reasonably good agreement with whole-rock sulfide compositions for the McCreedy East deposit (Sudbury, Ontario), consistent with an origin by crystallization of MSS, then MSS + ISS from sulfide magma.

  10. The mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds

    NASA Astrophysics Data System (ADS)

    Deguchi, Keita; Demura, Satoshi; Okazaki, Hiroyuki; Denholme, Saleem; Fujioka, Masaya; Ozaki, Toshinori; Yamaguchi, Takahide; Takeya, Hiroyuki; Takano, Yoshihiko

    2013-03-01

    We have clarified the mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds. Previously we reported that the bulk superconductivity in Fe-based compounds Fe(Te, Se) and Fe(Te, S) is achieved by heating in alcoholic beverages. However, the exact mechanism of how they act to enhance the superconductivity in the compounds remains unsolved. To understand the effect of alcoholic beverage treatment, we investigated the mechanism using a technology of metabolomic analysis. We found that weak acid in alcoholic beverages has the ability to deintercalate the excess Fe, which is not in favor of superconductivity. In this presentation, we will discuss the systematic mechanism to induce superconductivity in Fe-chalcogenide compounds.

  11. Emergence of a few distinct structures from a single formal structure type during high-throughput screening for stable compounds: The case of RbCuS and RbCuSe

    NASA Astrophysics Data System (ADS)

    Trimarchi, Giancarlo; Zhang, Xiuwen; DeVries Vermeer, Michael J.; Cantwell, Jacqueline; Poeppelmeier, Kenneth R.; Zunger, Alex

    2015-10-01

    Theoretical sorting of stable and synthesizable "missing compounds" from those that are unstable is a crucial step in the discovery of previously unknown functional materials. This active research area often involves high-throughput (HT) examination of the total energy of a given compound in a list of candidate formal structure types (FSTs), searching for those with the lowest energy within that list. While it is well appreciated that local relaxation methods based on a fixed list of structure types can lead to inaccurate geometries, this approach is widely used in HT studies because it produces answers faster than global optimization methods (that vary lattice vectors and atomic positions without local restrictions). We find, however, a different failure mode of the HT protocol: specific crystallographic classes of formal structure types each correspond to a series of chemically distinct "daughter structure types" (DSTs) that have the same space group but possess totally different local bonding configurations, including coordination types. Failure to include such DSTs in the fixed list of examined candidate structures used in contemporary high-throughput approaches can lead to qualitative misidentification of the stable bonding pattern, not just quantitative inaccuracies. In this work, we (i) clarify the understanding of the general DST-FST relationship, thus improving current discovery HT approaches, (ii) illustrate this failure mode for RbCuS and RbCuSe (the latter being a yet unreported compound and is predicted here) by developing a synthesis method and accelerated crystal-structure determination, and (iii) apply the genetic-algorithm-based global space-group optimization (GSGO) approach which is not vulnerable to the failure mode of HT searches of fixed lists, demonstrating a correct identification of the stable DST. The broad impact of items (i)-(iii) lies in the demonstrated predictive ability of a more comprehensive search strategy than what is currently used—use HT calculations as the preliminary broad screening followed by unbiased GSGO of the final candidates.

  12. Single Dirac Cone Topological Surface State and Unusual Thermoelectric Property of Compounds from a New Topological Insulator Family

    SciTech Connect

    Chen, Y

    2011-08-18

    Angle resolved photoemission spectroscopy (ARPES) study on TlBiTe2 and TlBiSe2 from a Thallium-based III-V-VI2 ternary chalcogenides family revealed a single surface Dirac cone at the center of the Brillouin zone for both compounds. For TlBiSe{sub 2}, the large bulk gap ({approx} 200meV) makes it a topological insulator with better mechanical properties than the previous binary 3D topological insualtor family. For TlBiTe{sub 2}, the observed negative bulk gap indicates it as a semi-metal, rather than a narrow gap semi-conductor as conventionally believed; this semi-metality naturally explains its mysteriously small thermoelectric figure of merit comparing to other compounds in the family. Finally, the unique band structures of TlBiTe{sub 2} also suggests it as a candidate for topological superconductors.

  13. Thermoelectric properties of Ag-doped n-type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-} {sub x} Ag {sub x} Se{sub 3}){sub 0.1} (x=0-0.4) alloys prepared by spark plasma sintering

    SciTech Connect

    Cui, J.L. Xiu, W.J.; Mao, L.D.; Ying, P.Z.; Jiang, L.; Qian, X.

    2007-03-15

    Ag-doped n-type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-} {sub x} Ag {sub x} Se{sub 3}){sub 0.1} (x=0-0.4) alloys were prepared by spark plasma sintering and their physical properties evaluated. When at low Ag content (x=0.05), the temperature dependence of the lattice thermal conductivity follows the trend of (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2}Se{sub 3}){sub 0.1}; while at higher Ag content, a relatively rapid reduction above 400 K can be observed due possibly to the enhancement of scattering of phonons by the increased defects. The Seebeck coefficient increases with Ag content, with some loss of electrical conductivity, but the maximum dimensionless figure of merit ZT can be obtained to be 0.86 for the alloy with x=0.4 at 505 K, about 0.2 higher than that of the alloy (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2}Se{sub 3}){sub 0.1} without Ag-doping. - Graphical abstract: The temperature dependence of dimensionless thermoelectric figure of merit ZT for different (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-} {sub x} Ag {sub x} Se{sub 3}){sub 0.1} (x=0-0.4) alloys prepared by spark plasma sintering.

  14. The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, and review of mixed-ligand CuOmCln coordination geometries in minerals and inorganic compounds

    NASA Astrophysics Data System (ADS)

    Krivovichev, Sergey V.; Filatov, Stanislav K.; Vergasova, Lidiya P.

    2013-04-01

    The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, a rare copper selenite chloride from volcanic fumaroles of the Great fissure Tolbachik eruption (Kamchatka peninsula, Russia), has been solved by direct methods and refined to R 1 = 0.044 on the basis of 2720 unique observed reflections. The mineral is orthorhombic, Pnma, a = 17.769(7), b = 6.448(3), c = 10.522(4) Å, V = 1205.6(8) Å3, Z = 4. The The CuOmCln coordination polyhedra share edges to form tetramers that have 'additional' O1 and O2 atoms as centers. The O1Cu4 and O2Cu4 tetrahedra share common Cu atoms to form [O2Cu5]6+ sheets. The SeO3 groups and Cl atoms are adjacent to the [O2Cu5]6+ sheets to form complex layers parallel to (100). The Na+ cations are located in between the layers. A review of mixed-ligand CuOmCln coordination polyhedra in minerals and inorganic compounds is given. There are in total 26 stereochemically different mixed-ligand Cu-O-Cl coordinations.

  15. Structural stability of ternary C22–Zr{sub 6}X{sub 2}Co (X=Al, Ga, Sn, As, Sb, Bi, Te) and C22–Zr{sub 6}Sn{sub 2}T? (T?=Fe, Co, Ni, Cu) compounds

    SciTech Connect

    Colinet, Catherine; Crivello, Jean-Claude; Tedenac, Jean-Claude

    2013-09-15

    The crystal and electronic structures, and the thermodynamic properties of Zr{sub 6}X{sub 2}Co (X=Al, Ga, Sn, As, Sb, Bi, Te) and Zr{sub 6}Sn{sub 2}T? (T?=Fe, Co, Ni, Cu) ternary compounds in the Fe{sub 2}P-type structure have been investigated by means of first principle calculations. The calculated structural parameters are in good agreement with the experimental data. The total electronic densities of states as well as the Bader charges of the atoms have been computed. Both electronic and size effects allow to explain the stability of the ternary Zr{sub 6}X{sub 2}Co (X=Al, Ga, Sn, As, Sb, Bi, Te) and Zr{sub 6}Sn{sub 2}T? (T?=Fe, Co, Ni, Cu) compounds. - Graphical abstract: Valence charge electronic localization function (ELF) calculated for Zr{sub 6}Sb{sub 2}Co compound. Display Omitted - Highlights: • Structural stability of Zr{sub 6}X{sub 2}T? compounds (X: p element, T?: late transition metal) in the Fe{sub 2}P-type structure. • First principles calculation of lattice parameters and enthalpies of formation. • Electronic densities of state in the series Zr{sub 6}Sn{sub 2}T? (T?=Fe, Co, Ni, Cu). • Electronic densities of state in the series Zr{sub 6}X{sub 2}Co (X=Al, Ga, Sn, As, Sb, Bi, Te)

  16. Superconducting properties of single crystalline FeTe1-xSex (x = 0, 0.15, 0.25, 0.35, 0.40 and 0.50)

    NASA Astrophysics Data System (ADS)

    Sudesh, Kumar, R.; Varma, G. D.

    2015-06-01

    In this paper we have grown single crystalline samples of Se-doped FeTe compound using self-flux technique and studied the structural and electrical transport properties of the as-grown crystals. The samples have been grown with compositions FeTe1-xSex (x = 0, 0.15, 0.25, 0.35, 0.40 and 0.50). The as-grown samples are then investigated for their structural and superconducting properties by means of X-ray diffraction and physical property measurements. The XRD results of powdered samples reveal a single (tetragonal) phase with space group symmetry P4/nmm for all the samples. The lattice parameters are observed to reduce with increase of Se-doping at Te-site. Highest Hc2(0) (˜180 T) value has been observed for FeTe0.5Se0.5 sample.

  17. Thermodynamic and Transport Properties of YTe3, LaTe3 and CeTe3

    SciTech Connect

    Ru, N.

    2011-08-19

    Measurements of heat capacity, susceptibility, and electrical resistivity are presented for single crystals of the charge density wave compounds YTe{sub 3}, LaTe{sub 3}, and CeTe{sub 3}. The materials are metallic to low temperatures, but have a small density of states due to the charge density wave gapping large portions of the Fermi surface. CeTe{sub 3} is found to be a weak Kondo lattice, with an antiferromagnetic ground state and T{sub N} = 2.8 K. The electrical resistivity of all three compounds is highly anisotropic, confirming the weak dispersion perpendicular to Te planes predicted by band structure calculations.

  18. Large magnetoresistance in non-magnetic silver chalcogenides and new class of magnetoresistive compounds

    DOEpatents

    Saboungi, Marie-Louis (Chicago, IL); Price, David C. L. (Chicago, IL); Rosenbaum, Thomas F. (Chicago, IL); Xu, Rong (Den Haag, NL); Husmann, Anke (Kiel, DE)

    2001-01-01

    The heavily-doped silver chalcogenides, Ag.sub.2+.delta. Se and Ag.sub.2+.delta. Te, show magnetoresistance effects on a scale comparable to the "colossal" magnetoresistance (CMR) compounds. Hall coefficient, magnetoconductivity, and hydrostatic pressure experiments establish that elements of narrow-gap semiconductor physics apply, but both the size of the effects at room temperature and the linear field dependence down to fields of a few Oersteds are surprising new features.

  19. Crystal Growth of CdTe by Gradient Freeze in Universal Multizone Crystallizator (UMC)

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Lehoczky, S. L.; Li, C.; Knuteson, D.; Raghothamachar, B.; Dudley, M.; Szoke, J.; Barczy, P.

    2004-01-01

    In the case of unsealed melt growth of an array of II-VI compounds, namely, CdTe, CdZnTe and ZnSe, there is a tremendous amount of experimental data describing the correlations between melt conditions and crystal quality. The results imply that the crystallinity quality can be improved if the melt was markedly superheated or long-time held before growth. It is speculated that after high superheating the associated complex dissociate and the spontaneous nucleation is retarded. In this study, crystals of CdTe were grown from melts which have undergone different thermal history by the unseeded gradient freeze method using the Universal Multizone Crystallizator (UMC). The effects of melt conditions on the quality of grown crystal were studied by various characterization techniques, including Synchrotron White Beam X-ray Topography (SWSXT), infrared microscopy, chemical analysis by glow discharge mass spectroscopy (GDMS), electrical conductivity and Hall measurements.

  20. Hierarchical stripe phases in IrTe2 driven by competition between Ir dimerization and Te bonding

    NASA Astrophysics Data System (ADS)

    Wu, Weida; Dai, Jixia; Haule, Kristjan; Yang, Junjie; Oh, Yoon Seok; Cheong, Sang Wook

    2015-03-01

    Iridium di-telluride (IrTe2) belongs to the family of transition metal dichalcogenides (TMD), but it distinguishes from the traditional TMDs due to the existence of multi-step single-q charge-density wave like phase transitions. Despite of intensive studies, there is still no consensus on the physical origin of the stripe phases or even the ground state modulation for this 5d material. In this study, we present atomic-resolving images and spectroscopic measurements from scanning tunneling microscopy and spectroscopy (STM/STS). We show that the ground state of IrTe2 is a q=1/6 stripe phase, identical to that of the Se-doped compound. Furthermore, our data suggest that the multi-step transitions and the stripe phases are driven by the intralayer Ir-Ir dimerization that competes against the interlayer Te-Te bonding. This competition results in a unified phase diagram with a series of hierarchical modulated stripe phases. This work is supported by NSF Grant # DMR-0844807.

  1. 263H. Li and Z.M. Wang (eds.), Bismuth-Containing Compounds, Springer Series in Materials Science 186, DOI 10.1007/978-1-4614-8121-8_11,

    E-print Network

    Chen, Yong P.

    of pseudo-hexagonal Bi2Te3, Bi2Se3, and their alloys were successfully grown by molecular beam epitaxy (MBE263H. Li and Z.M. Wang (eds.), Bismuth-Containing Compounds, Springer Series in Materials Science and mapping. The results indicate that the epitaxial films are highly uniform and of high crystalline quality

  2. Exploratory synthesis in molten salts: Characterization, nonlinear optical and phase-change properties of new chalcophosphate compounds

    NASA Astrophysics Data System (ADS)

    Chung, In

    The polychalcophosphate flux technique has played an important role in discovery of new chalcophosphate compounds via access to low and intermediate temperature of 160--600°C. Chalcophosphates are compounds that possess phosphorus and chalcogen atoms with P-Q bond, where Q = S, Se, or Te. The structural diversity within the class of metal chalcophosphates is extensive, and members of this family can exhibit technologically important ion-exchange, intercalation, magnetic, electrical, and optical properties. In the present work exploratory synthesis of chalcophosphate compounds using polychalcophosphate molten salt method and characterization of physicochemical properties that are mainly concentrate upon nonlinear optical properties and crystal-glass phase-change behavior are described. Chapters 2-6 focus on the effort of systematic study of alkali metal selenophosphate ternary compounds. The first family of this class is one-dimensional compounds, APSe6 (A = K, Rb, Cs) and A2P2Se6 (A = K, Rb). The compounds adopt noncentrosymmetric polar space group and exhibited remarkably strong second harmonic generation response in both crystalline and glassy phases. They also show a reversible crystal-glass phase-change behavior. By coupling noncentrosymmetry in crystal structure and phase-change behavior, we proposed general fabrication strategy for optical glassy fibers that yield strong, intrinsic, second-order nonlinear optical properties. The APSe 6 (A = K, Rb) glassy optical fiber exhibited waveguided second harmonic and difference frequency generation. The second family of this class is phosphorus-rich, novel molecular complex salts of Rb4P 6Se12, Cs4P6Se12, and Cs 5P5Se12. All compounds feature low valent P in two different formal oxidation states. We attempted rational synthetic conditions to stabilize less oxidized phosphorus compounds by utilizing excess P in the flux. The polychalcophosphate flux also produced rare phosphorus telluride compound. The new compound K4P8Te4 featuring P-Te bonding exhibited reversible crystal-glass phase-change behavior, dissolution process to photoluminescent solution with hydrazine, and evolution of nanosphere by precipitating the resulting solution with alcohol. Finally stabilizing Bi metal with selenophosphate flux at high temperature gave naturally growing flexible nanowires of Cs5BiP4Se12 that can be dispersed in alcohol. The compound that adopts the noncentrosymmetric polar space group exhibited strong near-IR second harmonic generation response.

  3. II-VI compounds 1985; Proceedings of the Second International Conference, Aussois, France, March 4-8, 1985

    NASA Astrophysics Data System (ADS)

    Marfaing, Y.; Triboulet, R.; Lunn, B.; Mullin, J. B.

    1985-08-01

    Among the topics considered concerning II-VI compounds are growth of low resistivity high-quality ZnSe, ZnS films by low-pressure metal-organic vapor phase epitaxy growth of Cd(x)Zn(1-x)S, growth of high-purity ZnSe by sublimation traveling-heater method (THM) and the characteristics of the Y and Z deep level emission line, properties of CdTe crystals grown by THM using Cd as the solvent, and liquid-phase epitaxy growth and characterization of 1.3-micron (Hg, Cd)Te layers. Also considered are the self-consistent electronic structure of vacancies in semiconductors, defects in cadmium selenide, luminescence characterization of residual impurities in CdTe grown by molecular beam epitaxy, and photoluminescence of Cd-rich Hg(1-x)Cd(x)Te alloys with x = 0.7-1.0. Additional topics discussed are optically detected magnetic resonance studies of recombination emission in II-VI compounds, X-ray photoemission spectroscopy and magnetotransport studies on the surface of CdHgTe, cadmium mercury telluride infrared detectors, and electron beam-pumped II-VI lasers.

  4. Crystal Growth of Ternary Compound Semiconductors in Low Gravity Environment

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    2014-01-01

    A low gravity material experiment will be performed in the Material Science Research Rack (MSRR) on International Space Station (ISS). There are two sections of the flight experiment: (I) crystal growth of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, by physical vapor transport (PVT) and (II) melt growth of CdZnTe by directional solidification. The main objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the grown crystals as results of buoyancy-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. This talk will focus on the ground-based studies on the PVT crystal growth of ZnSe and related ternary compounds. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions.

  5. Ground-based research of crystal growth of II-VI compound semiconductors by physical vapor transport

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Gillies, D. C.; Szofran, F. R.; Lehoczky, S. L.; Su, Ching-Hua; Sha, Yi-Gao; Zhou, W.; Dudley, M.; Liu, Hao-Chieh; Brebrick, R. F.; Wang, J. C.

    1994-01-01

    Ground-based investigation of the crystal growth of II-VI semiconductor compounds, including CdTe, CdS, ZnTe, and ZnSe, by physical vapor transport in closed ampoules was performed. The crystal growth experimental process and supporting activities--preparation and heat treatment of starting materials, vapor partial pressure measurements, and transport rate measurements are reported. The results of crystal characterization, including microscopy, microstructure, optical transmission photoluminescence, synchrotron radiation topography, and chemical analysis by spark source mass spectrography, are also discussed.

  6. First-principles study of the electronic and structural properties of (CdTe)n/(ZnTe)n superlattices

    NASA Astrophysics Data System (ADS)

    Boucharef, M.; Benalia, S.; Rached, D.; Merabet, M.; Djoudi, L.; Abidri, B.; Benkhettou, N.

    2014-11-01

    We present the results of a first-principles study of the electronic and structural properties of binary CdTe and ZnTe compounds and their (CdTe)n/(ZnTe)n superlattices (SLs). The computational method is based on the full-potential linear muffin tin orbitals method (FP-LMTO) augmented by a plane-wave basis (PLW). The exchange and correlation energy is described in the local density approximation (LDA) using the Perdew-Wang parameterization including a generalized gradient approximation (GGA). The calculated structural properties of CdTe and ZnTe compounds are in good agreement with available experimental and theoretical data. We have also carried out band-structure calculations for the binary CdTe and ZnTe compounds and their (CdTe)n/(ZnTe)n superlattices (SLs). From the results of the electronic properties, we find that the parent material CdTe and ZnTe and their superlattices have a direct band gaps. The fundamental band gap decreases with increasing the number of monolayer n.

  7. Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys

    NASA Technical Reports Server (NTRS)

    Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

    2001-01-01

    Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(sub x)V(sub 1-x) alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(sub x)V(sub 1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(sub x)Te(sub 1-x) and ZnSe(sub y)Te(sub 1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(sub y)Te(sub 1-y) alloys in the entire composition range, y between 0 and 1. The samples used in this study are bulk ZnSe(sub y)Te(sub 1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the interaction between localized Se states and the conduction band. On the other hand we show that the large band gap reduction observed on the Se-rich side of the alloy system is a result of an interaction between the localized Te level and the valence bands. This interaction leads to the formation of a Te-like valence band edge that strongly interacts with the light hole valence band. Calculations based on a modified k(sup dot)p model account for the reduction of the band gap and the large increase of the spin-orbit splitting observed in Se-rich ZnSe(sub y)Te(sub 1-y) alloys. We will also discuss the importance of these new results for understanding of the electronic structure and band offsets in other highly mismatched alloy systems.

  8. Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys

    NASA Technical Reports Server (NTRS)

    Yu, Kin Man; Wu, J.; Walukiewicz, W.; Ager, J. W.; Haller, E. E.; Miotkowski, I.; Ramdas, A.; Su, Ching-Hua; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(x)V(1-x), alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(x),V(1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(x)Te(l-x) and ZnSe(Y)Te(1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(y)Te(1-y) alloys in the entire composition range, 0 less than or equal to y less than or equal to 1. The samples used in this study are bulk ZnSe(y)Te(1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the interaction between localized Se states and the conduction band. On the other hand we show that the large band gap reduction observed on the Se-rich side of the alloy system is a result of an interaction between the localized Te level and the valence bands. This interaction leads to the formation of a Te-like valence band edge that strongly interacts with the light hole valence band. Calculations based on a modified k p model account for the reduction of the band gap and the large increase of the spin-orbit splitting observed in Se-rich ZnSe(y)Te(l-y) alloys. We will also discuss the importance of these new results for understanding of the electronic structure and band offsets in other highly mismatched alloy systems.

  9. IMPROVEMENT OF CdMnTe DETECTOR PERFORMANCE BY MnTe PURIFICATION

    SciTech Connect

    Kim, K.H.; Bolotnikov, A.E.; Camarda, G.S.; Tappero, R.; Hossain, A.; Cui, Y.; Yang, G.; Gul, R.; and James, R.B.

    2011-04-25

    Residual impurities in manganese (Mn) are a big obstacle to obtaining high-performance CdMnTe (CMT) X-ray and gamma-ray detectors. Generally, the zone-refining method is an effective way to improve the material's purity. In this work, we purified the MnTe compounds combining the zone-refining method with molten Te, which has a very high solubility for most impurities. We confirmed the improved purity of the material by glow-discharge mass spectrometry (GDMS). We also found that CMT crystals from a multiply-refined MnTe source, grown by the vertical Bridgman method, yielded better performing detectors.

  10. Lattice dynamics of BaFe2X3(X=S,Se) compounds

    SciTech Connect

    Popovi?, Z. V.; Š?epanovi?, M.; Lazarevi?, N.; Opa?i?, M.; Radonji?, M. M.; Tanaskovi?, D.; Lei, Hechang; Petrovic, C.

    2015-02-27

    We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe?X? (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe?S? (BaFe?Se?) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe?S(Se)? is supported by the lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe?Se? below TN=255K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy.

  11. Bismaleimide compounds

    DOEpatents

    Adams, Johnnie E. (Grandview, MO); Jamieson, Donald R. (Merriam, KS)

    1986-01-14

    Bismaleimides of the formula ##STR1## wherein R.sub.1 and R.sub.2 each independently is H, C.sub.1-4 -alkyl, C.sub.1-4 -alkoxy, C1 or Br, or R.sub.1 and R.sub.2 together form a fused 6-membered hydrocarbon aromatic ring, with the proviso that R.sub.1 and R.sub.2 are not t-butyl or t-butoxy; X is O, S or Se; n is 1-3; and the alkylene bridging group, optionally, is substituted by 1-3 methyl groups or by fluorine, form polybismaleimide resins which have valuable physical properties. Uniquely, these compounds permit extended cure times, i.e., they remain fluid for a time sufficient to permit the formation of a homogeneous melt prior to curing.

  12. Bismaleimide compounds

    DOEpatents

    Adams, J.E.; Jamieson, D.R.

    1986-01-14

    Bismaleimides of the formula shown in the diagram wherein R[sub 1] and R[sub 2] each independently is H, C[sub 1-4]-alkyl, C[sub 1-4]-alkoxy, Cl or Br, or R[sub 1] and R[sub 2] together form a fused 6-membered hydrocarbon aromatic ring, with the proviso that R[sub 1] and R[sub 2] are not t-butyl or t-butoxy; X is O, S or Se; n is 1--3; and the alkylene bridging group, optionally, is substituted by 1--3 methyl groups or by fluorine, form polybismaleimide resins which have valuable physical properties. Uniquely, these compounds permit extended cure times, i.e., they remain fluid for a time sufficient to permit the formation of a homogeneous melt prior to curing.

  13. Anomalous pressure dependence of thermal conductivities of large mass ratio compounds

    NASA Astrophysics Data System (ADS)

    Lindsay, L.; Broido, D. A.; Carrete, Jesús; Mingo, Natalio; Reinecke, T. L.

    2015-03-01

    The lattice thermal conductivities (?) of binary compound materials are examined as a function of hydrostatic pressure P using a first-principles approach. Compounds with relatively small mass ratios, such as MgO, show an increase in ? with P , consistent with measurements. Conversely, compounds with large mass ratios that create significant frequency gaps between acoustic and optic phonons (e.g., BSb, BAs, BeTe, BeSe) exhibit decreasing ? with increasing P , a behavior that cannot be understood using simple theories of ?. This anomalous P dependence of ? arises from the fundamentally different nature of the intrinsic scattering processes for heat-carrying acoustic phonons in large mass ratio compounds compared to those with small mass ratios. This work demonstrates the power of first-principles methods for thermal properties and advances a broad paradigm for understanding thermal transport in nonmetals.

  14. Anomalous pressure dependence of thermal conductivities of large mass ratio compounds

    SciTech Connect

    Lindsay, Lucas R; Broido, David; Carrete, Jesus; Mingo, Natalio; Reinecke, Tom

    2015-01-01

    The lattice thermal conductivities ( ) of binary compound materials are examined as a function of hydrostatic pressure, P, using a first-principles approach. Compound materials with relatively small mass ratios, such as MgO, show an increase in with P, consistent with measurements. Conversely, compounds with large mass ratios (e.g., BSb, BAs, BeTe, BeSe) exhibit decreasing with increasing P, a behavior that cannot be understood using simple theories of . This anomalous P dependence of arises from the fundamentally different nature of the intrinsic scattering processes for heat-carrying acoustic phonons in large mass ratio compounds compared to those with small mass ratios. This work demonstrates the power of first principles methods for thermal properties and advances the understanding of thermal transport in non-metals.

  15. A Simple Sb2Te3 Back-Contact Process for CdTe Solar Cells

    NASA Astrophysics Data System (ADS)

    Siepchen, B.; Späth, B.; Drost, C.; Krishnakumar, V.; Kraft, C.; Winkler, M.; König, J.; Bartholomé, K.; Peng, S.

    2015-10-01

    CdTe solar technology has proved to be a cost-efficient solution for energy production. Formation of the back contact is an important and critical step in preparing high-efficiency, stable CdTe solar cells. In this paper we report a simple CdTe solar cell (Sb2Te3) back contact-formation process. The CdS and CdTe layers were deposited by close-space sublimation. After CdCl2 annealing treatment, the CdTe surface was etched by use of a mixture of nitric and phosphoric acids to obtain a Te-rich surface. Elemental Sb was sputtered on the etched surface and successive post-annealing treatment induced Sb2Te3 alloy formation. Structural characterization by x-ray diffraction analysis confirmed formation of the Sb2Te3 phase. The performance of solar cells with nanoalloyed Sb2Te3 back contacts was comparable with that of reference solar cells prepared with sputtered Sb2Te3 back contact from a compound sputter target.

  16. Synthesis, calorimetric, structural and conductivity studies in a new thallium selenate tellurate adduct compound

    SciTech Connect

    Ktari, L.; Abdelhedi, M.; Bouhlel, N.; Dammak, M.; Cousson, A.

    2009-08-05

    The crystal structure of the thallium selenate tellurate Tl{sub 2}SeO{sub 4}.Te(OH){sub 6} (TlSeTe) was determined by X-ray diffraction method. The title compound crystallizes in the monoclinic system with P2{sub 1}/c space group. The following parameters are: a = 12.358(3) A; b = 7.231(1) A; c = 11.986(2) A; {beta} = 111.092(2){sup o}; Z = 4. The structure can be regarded as being built of isolated TeO{sub 6} octahedra and SeO{sub 4} tetrahedra. The Tl{sup +} cations are intercalated between these kinds of polyhedra. The main feature of this structure is the coexistence of two different and independent anions (SeO{sub 4}{sup 2-} and TeO{sub 6}{sup 6-}) in the same unit cell. The structure is stable due to O-H...O hydrogen bonds which link tetrahedral and octahedral groups. Crystals of Tl{sub 2}SeO{sub 4}.Te(OH){sub 6} undergo three endothermal transitions at 373, 395 and 437 K. These transitions are detected by DSC and analyzed by dielectric measurements with impedance spectroscopy. The evolution of conductivity versus temperature showed the presence of a protonic conduction phase transition at 437 K. The phase transition at 373 K can be related to a structural phase transition, whereas the one at 395 K is ascribed as likely due to a ferroelectric-paraelectric phase transition.

  17. Substitution of Ni for Fe in superconducting Fe0.98Te0.5Se0.5 depresses the normal-state conductivity but not the magnetic spectral weight

    SciTech Connect

    Wang, Jinghui; Zhong, Ruidan; Li, Shichao; Gan, Yuan; Xu, Zhijun; Zhang, Cheng; Ozaki, T.; Matsuda, M.; Zhao, Yang; Li, Qiang; Xu, Guangyong; Gu, Genda; Tranquada, J. M.; Birgeneau, R. J.; Wen, Jinsheng

    2015-01-05

    We have performed systematic resistivity and inelastic neutron scattering measurements on Fe?.???zNizTe?.?Se?.? samples to study the impact of Ni substitution on the transport properties and the low-energy (? 12 meV) magnetic excitations. It is found that, with increasing Ni doping, both the conductivity and superconductivity are gradually suppressed; in contrast, the low-energy magnetic spectral weight changes little. Comparing with the impact of Co and Cu substitution, we find that the effects on conductivity and superconductivity for the same degree of substitution grow systematically as the atomic number of the substituent deviates from that of Fe. The impact of the substituents as scattering centers appears to be greater than any contribution to carrier concentration. The fact that low-energy magnetic spectral weight is not reduced by increased electron scattering indicates that the existence of antiferromagnetic correlations does not depend on electronic states close to the Fermi energy.

  18. Resistive switching properties in CdZnTe films

    NASA Astrophysics Data System (ADS)

    Zha, Gangqiang; Lin, Yun; Zeng, Dongmei; Tan, Tingting; Jie, Wanqi

    2015-02-01

    The ternary II-VI compound semiconductor cadmium zinc telluride (CdZnTe) has bi-stable conduction characteristics. In this letter, CdZnTe films are grown on indium tin oxide (ITO) substrates by radio frequency magnetron sputtering. The current-voltage characteristics show that there is resistive switching in a structure consisting of an 800-nm-thick CdZnTe film, an Au Schottky contact, and an ITO bottom electrode. The electroresistance in Au/CdZnTe/ITO may be related to the polarization of the CdZnTe film and the Schottky contact.

  19. Condensed rare-earth metal-rich tellurides. Extension of layered Sc{sub 6}PdTe{sub 2}-type compounds to yttrium and lutetium analogues and to Y{sub 7}Te{sub 2}, the limiting binary member

    SciTech Connect

    Castro-Castro, Laura M.; Chen Ling; Corbett, John D.

    2007-11-15

    Six isotypic R{sub 6}ZTe{sub 2} phases have been synthesized in Ta at elevated temperatures and characterized by single crystal X-ray refinements for R=Y, Z=Rh, Pd, Ag, Y and for R=Lu, Z=Cu, Ag. All crystallize in the Sc{sub 6}PdTe{sub 2}-type structure, Pnma, Z=4, a{approx}21.5 A, b{approx}4.1 A, c{approx}11.4 A. The results can be viewed as the replacement of Te3 atoms in the parent isotypic Sc{sub 2}Te (or in the hypothetical Y{sub 2}Te or Lu{sub 2}Te analogues) by the above the Z, the Y example giving the new binary phase Y{sub 7}Te{sub 2}. The shorter (and stronger) metal-metal bonds concentrate in the region of metal (Z, Y) substitution, as revealed by larger integrated crystal orbital Hamilton population (ICOHP) values derived from linear muffin-tin-orbital (LMTO) calculations. Partial densities-of-states data for Y{sub 7}Te{sub 2} reflect a similar behavior. Individual R-R bond distances are seen to deviate appreciably from the more fundamental overlap population measures for each. - Graphical abstract: Substitutions at the same site in a common orthorhombic host structure convert the hypothetical Y{sub 2}Te (above) to eitherY{sub 6}ZTe{sub 2} or the new binary Y{sub 7}Te{sub 2}.

  20. Structure and thermoelectric properties of the new quaternary bismuth selenides A(1-x)M(4-x)Bi(11+x)Se21 (A = K and Rb and Cs; M = Sn and Pb)--members of the grand homologous series Km(M6Se8)m(M(5+n)Se(9+n)).

    PubMed

    Mrotzek, A; Chung, D Y; Ghelani, N; Hogan, T; Kanatzidis, M G

    2001-05-01

    Several members of the new family A(1-x)M(4-x)Bi(11+x)Se21 (A = K, Rb, Cs; M = Sn, Pb) were prepared by direct combination of A2Se, Bi2Se3, Sn (or Pb), and Se at 800 degrees C. The single-crystal structures of K(0.54)Sn(3.54)Bi(11.46)Se21, K(1.46)Pb(3.08)Bi(11.46)Se21, Rb(0.69)Pb(3.69)Bi(11.31)Se21, and Cs(0.65)Pb(3.65)Bi(11.35)Se21 were determined. The compounds A(1-x)M(4-x)Bi(11+x) Se21 crystallize in a new structure type with the monoclinic space group C2/m, in which building units of the Bi2Te3 and NaCl structure type join to give rise to a novel kind of three-dimensional anionic framework with alkali-ion-filled tunnels. The building units are assembled from distorted, edge-sharing (Bi,Sn)Se6 octahedra. Bi and Sn/Pb atoms are disordered over the metal sites of the chalcogenide network, while the alkali site is not fully occupied. A grand homologous series Km(M6Se8)m(M(5+n)Se(9+n)) has been identified of which the compounds A(1-x)M(4-x)Bi(11+x)Se21 are members. We discuss here the crystal structure, charge-transport properties, and very low thermal conductivity of A(1-x)M(4-x)Bi(11+x)Se21. PMID:11405470