Sample records for se te compounds

  1. Electronic properties of HffXY intermetallic compounds (X =Si, Ge; Y =S, Se, Te)

    Microsoft Academic Search

    I. Yaar; I. Halevy; S. Kahane; A. Beck; Z. Berant

    2008-01-01

    The electric field gradient (efg) parameters were calculated for the ternary system HfXY (X =Si, Ge; Y =S, Se, Te), using the full-potential linear augmented plane wave (LAPW) method applying the generalized gradient approximation (GGA). The major contribution to the efg value in these compounds comes from the p-p contribution next to the probe nucleus. The intermetallic compounds HfXY (X

  2. Electronic properties of Hf XY intermetallic compounds ( X = Si, Ge; Y = S, Se, Te)

    Microsoft Academic Search

    I. Yaar; I. Halevy; S. Kahane; A. Beck; Z. Berant

    2007-01-01

    The electric field gradient (efg) parameters were calculated for the ternary system HfXY (X = Si, Ge; Y = S, Se, Te), using the full-potential linear augmented plane wave (LAPW) method applying the generalized gradient approximation\\u000a (GGA). The major contribution to the efg value in these compounds comes from the p-p contribution next to the probe nucleus.\\u000a The intermetallic compounds

  3. 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.

  4. Ultrasonic wave propagation in cadmium chalcogenides (CdS, CdSe and CdTe) compounds

    Microsoft Academic Search

    Pramod Kumar Yadawa

    2011-01-01

    Purpose – The purpose of this paper is to evaluate the second- and third-order elastic constants (SOEC and TOEC) and then velocities and attenuation of ultrasonic waves along unique direction in hexagonal II-VI group semiconductors, cadmium chalcogenides (CdS, CdSe and CdTe) compounds at room temperature and obtained the ultrasonic behaviour and mechanical properties of these compounds. Design\\/methodology\\/approach – Lennard-Jones potential

  5. Crystal chemistry of AB2X4 (X = S, Se, Te) compounds

    Microsoft Academic Search

    J. E. Iglesias; H. Steinfink

    1973-01-01

    An attempt is made to correlate the crystal structures of ternary chalcogenides of composition AB2X4 with the cationic radius ratio and a pseudo force-constant involving their electronegativities. The resultant diagram adequately resolves structures based on the types K2SO4, monoclinic, olivine, MnY2S4, Th3P4, and CaFe2O4 but structure types based on spinel, Cr3Se4, and Ag2HgI4 are not resolved. Crystal chemical arguments are

  6. The system SnTe-InSe

    SciTech Connect

    Gurshumov, A.P.; Alidzhanov, M.A.; Aliev, A.S.; Gadzhiev, T.G.; Mamedov, N.A.

    1986-03-01

    This paper discusses the nature of the interaction and physicochemical properties of the alloys of the system SnTe-InSe. The DTA was performed on an NTR-74 pyrometer, XPA on a Dron-2.0 diffractometer and MSA on an MIM-7 metallographic microscope. The microhardness of the samples was determined on a PMT-3 microhardness tester. The congruently melting compound SnInTeSe and solid solutions based on the starting components are formed in the system.

  7. A Mössbauer effect study of single crystals of the non-superconducting parent compound Fe1.09Te and the superconductor FeSe0.4Te0.6.

    PubMed

    Stadnik, Zbigniew M; Wang, Pu; Zukrowski, Jan; Noji, Takashi; Koike, Yoji

    2013-10-16

    The results of a (57)Fe Mössbauer spectroscopy study between 2.0 and 297 K of the parent compound Fe1.09Te and the superconductor FeSe0.4Te0.6 are reported. It is shown that in both compounds the magnitude of the quadrupole splitting increases with decreasing temperature and is well described by a T(3/2) power-law relation. The presence of incommensurate spin-density-wave antiferromagnetism in Fe1.09Te is demonstrated, with the Néel temperature T(N) = 71.1(6) K. A theoretical prediction (Zhang et al 2009 Phys. Rev. B 79 012506) of the Fe magnetic moment at the 2c sites being significantly larger than that at the 2a sites in the parent compound is confirmed experimentally by showing that these moments at 4.4 K are, respectively, 3.20(4) and 1.78(3) ?(B). The absence of magnetic order in FeSe0.4Te0.6 down to 2.0 K is confirmed. The Debye temperatures of Fe1.09Te and FeSe0.4Te0.6 are found to be 290(1) and 233(1) K, respectively. PMID:24061219

  8. Observation of Single Dirac Cone Topological Surface State in Compounds TlBiTe2 and TlBiSe2 from a New Topological Insulator Family

    Microsoft Academic Search

    Yulin Chen; Zhongkai Liu; James G. Analytis; Jiun-Haw Chu; Haijun Zhang; Sung-Kwan Mo; Robert G. Moore; Donghui Lu; Ian Fisher; Shoucheng Zhang; Zahid Hussain; Z.-X. Shen

    2010-01-01

    Angle resolved photoemission spectroscopy (ARPES) studies were performed on two compounds (TlBiTe$_2$ and TlBiSe$_2$) from a recently proposed three dimensional topological insulator family in Thallium-based III-V-VI$_2$ ternary chalcogenides. For both materials, we show that the electronic band structures are in broad agreement with the $ab$ $initio$ calculations; by surveying over the entire surface Brillouin zone (BZ), we demonstrate that there

  9. Thermal conductivity of TmSeTe

    NASA Astrophysics Data System (ADS)

    Bucher, Benno; Malar, Jan; Wachter, Peter

    2000-03-01

    The rare earth compound TmSeTe is a mixed valent semiconductor at ambient pressure. On increasing pressure the substance reveals a phase transition into an excitonic insulator phase(B. Bucher et al., PRL 66, (1991) 2717). The transition into the coherent excitonic groundstate might be interpreted as a Bose condensation. Different methodes have been applied on TmSeTe in order to search for features which are typical for a Bose condensate. The thermal conductivity of TmSeTe has been measured for pressures up to 20 kbar and temperatures down to 2 K. The thermal conductivity is enhanced within the excitonic phase. Furthermore the elastic properties of TmSeTe revealed an extremely small compressibility which must be attributed to the formation of the coherent ground state.

  10. Variation of half metallicity and magnetism of Cd1-xCrxZ (Z=S, Se and Te) DMS compounds on reducing dilute limit

    NASA Astrophysics Data System (ADS)

    Saini, Hardev S.; Singh, Mukhtiyar; Reshak, Ali H.; Kashyap, Manish K.

    2013-04-01

    The electronic and magnetic properties of Cr-doped Cd-Chalcogenides, Cd1-xCrxZ (Z=S, Se and Te) for dopant concentration, x=0.25 and 0.125 are presented in order to search new Dilute Magnetic Semiconductor (DMS) compounds suitable for spintronic applications. The calculations have been performed using full potential Linear Augmented Plane Wave (FPLAPW) method within generalized gradient approximation (GGA) as exchange-correlation (XC) potential. The calculated results show that the doping of Cr atom induces ferromagnetism in these compounds. Moreover, all DMS compounds retain half metallicity at both dopant concentrations with 100% spin polarization at Fermi level (EF). The total magnetic moments of these compounds are mainly due to Cr-d states present at EF where as there exist small induced magnetic moments on other non-magnetic atoms as well.

  11. A density functional (PBE, PBEsol, HSE06) study of the structural, electronic and optical properties of the ternary compounds AgAlX2 (X = S, Se, Te)

    NASA Astrophysics Data System (ADS)

    Dongho Nguimdo, G. M.; Joubert, Daniel P.

    2015-05-01

    First principles density functional theory (DFT) calculations for bulk structural, electronic and optical properties of ternary compounds AgAlX2 (X = S, Se, Te) were performed with two flavours of generalised gradient approximations (PBE and PBEsol) and the hybrid functional HSE06. Using cohesive energy as a stability criterion, we found that the chalcopyrite structure is the favoured phase for these materials. PBEsol gives structural properties closer to the experimental values when compared to the results of PBE. Tetragonal distortion and anion displacement were calculated and we found them to be the cause of the crystal field splitting. Reduction of the bandgap and band splitting around the ? in the Brillouin zone was noted when spin-orbit coupling was included in our study especially in the case of AgAlTe2. The HSE06 bandgap and frequency dependent dielectric function were in very good agreement with experimental results. We have also shown that the maximum absorption peak lies in the ultraviolet range irrespective of the functional used. The refractive index is also discussed.

  12. 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.

  13. Synthesis, structural characterization and optical properties of new compounds: Centrosymmetric Ba{sub 2}GaMQ{sub 5} (M=Sb,Bi; Q=Se,Te), Ba{sub 2}InSbTe{sub 5} and noncentrosymmetric Ba{sub 2}InSbSe{sub 5}

    SciTech Connect

    Hao, Wenyu; Mei, Dajiang; Yin, Wenlong; Feng, Kai [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China) [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Graduate University of Chinese Academy of Sciences, Beijing 100049 (China); Yao, Jiyong, E-mail: jyao@mail.ipc.ac.cn [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China) [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Wu, Yicheng [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China) [Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

    2013-02-15

    The six compounds Ba{sub 2}GaMQ{sub 5} (M=Sb,Bi; Q=Se,Te) and Ba{sub 2}InSbQ{sub 5} (Q=Se,Te) have been synthesized for the first time. Ba{sub 2}GaMQ{sub 5} (M=Sb,Bi; Q=Se,Te) and Ba{sub 2}InSbTe{sub 5} crystallize in the centrosymmetric space group Pnma, while Ba{sub 2}InSbSe{sub 5} belongs to the noncentrosymmetric polar space group Cmc2{sub 1}. The structures of the six new compounds contain infinite {sup 1}{sub {infinity}}[MM'Q{sub 5}]{sub 4-} anionic chains built by MQ{sub 4} (M Prime =Ga,In) tetrahedra and heavily distorted M Prime Q{sub 6} (M Prime =Sb,Bi) octahedra. Ba{sub 2}InSbSe{sub 5} possesses a band gap of 1.92(5) eV and exhibits a weak powder second harmonic generation signal using the 2090 nm laser as fundamental wavelength. - Graphical abstract: Ba{sub 2}InSbSe{sub 5} contains infinite {sup 1}{sub {infinity}}[InSbSe{sub 5}]{sub 4-} chains which are built by corner-shared InSe{sub 4} tetrahedra chains and edge-shared SbSe{sub 6} octahedra chains connected through edge sharing . Highlights: Black-Right-Pointing-Pointer Ba{sub 2}GaMQ{sub 5} (M=Sb,Bi; Q=Se,Te) and Ba{sub 2}InSbQ{sub 5} (Q=Se,Te) have been synthesized. Black-Right-Pointing-Pointer The structures contain infinite {sup 1}{sub {infinity}}[MM'Q{sub 5}]{sub 4-} (M Prime =Ga,In) anionic chains. Black-Right-Pointing-Pointer The chains are built by distorted MQ{sub 6} (M=Sb,Bi) octahedra and M Prime Q{sub 4} (M Prime =Ga,In) tetrahedra. Black-Right-Pointing-Pointer Ba{sub 2}InSbSe{sub 5} exhibits a weak powder second harmonic generation signal.

  14. Photopumped Lasing Characteristics in Green-to-Yellow Range for BeZnSeTe II-VI Compound Quaternary Double Heterostructures Grown on InP Substrates

    NASA Astrophysics Data System (ADS)

    Nomura, Ichirou; Sawafuji, Yutaka; Kishino, Katsumi

    2011-03-01

    The photopumped lasing characteristics of double heterostructures with a BeZnSeTe active layer grown on InP substrates were systematically investigated. Green-to-yellow lasing emissions from 538 to 570 nm were observed at room temperature (RT). The threshold excitation power density (Pth) was approximately 30 kW/cm2. From the temperature dependence of Pth, stable lasing emissions were obtained up to 353 K. The characteristic temperatures of Pth were 106 to 140 K above RT. The relationship between the threshold gain (Gth) and the threshold carrier density (Nth) was estimated from the cavity length dependence of Pth and by waveguide analysis. Using the relationship between Gth and Nth, the threshold current densities (Jth) of electrically pumped BeZnSeTe laser diode structures were calculated to be less than 1.3 kA/cm2. Jth decreases as the lasing wavelength increases from 538 to 570 nm. The above results demonstrate that BeZnSeTe is a promising active-layer material for high-performance green-to-yellow LDs.

  15. Tunable (??, ??)-Type Antiferromagnetic Order in ?-Fe(Te,Se) Superconductors

    NASA Astrophysics Data System (ADS)

    Bao, Wei; Qiu, Y.; Huang, Q.; Green, M. A.; Zajdel, P.; Fitzsimmons, M. R.; Zhernenkov, M.; Chang, S.; Fang, Minghu; Qian, B.; Vehstedt, E. K.; Yang, Jinhu; Pham, H. M.; Spinu, L.; Mao, Z. Q.

    2009-06-01

    The new ?-Fe(Te,Se) superconductors share the common iron building block and ferminology with the LaFeAsO and BaFe2As2 families of superconductors. In contrast with the predicted commensurate spin-density-wave order at the nesting wave vector (?, 0), a completely different magnetic order with a composition tunable propagation vector (??, ??) was determined for the parent compound Fe1+yTe in this powder and single-crystal neutron diffraction study. The new antiferromagnetic order survives as a short-range one even in the highest TC sample. An alternative to the prevailing nesting Fermi surface mechanism is required to understand the latest family of ferrous superconductors.

  16. ZnSe1-x Te x : band gaps, bowing parameter

    NASA Astrophysics Data System (ADS)

    Gutowski, J.; Sebald, K.; Voss, T.

    This document is part of Volume 44 `Semiconductors', Subvolume B `New Data and Updates for II-VI Compounds' of Landolt-Börnstein Group III `Condensed Matter'. It contains data on ZnSexTe1-x (zinc selenide telluride), Element System Se-Te-Zn.

  17. CdSe x Te1-x : energy gaps, bowing parameter, band offsets

    NASA Astrophysics Data System (ADS)

    Gutowski, J.; Sebald, K.; Voss, T.

    This document is part of Volume 44 `Semiconductors', Subvolume B `New Data and Updates for II-VI Compounds' of Landolt-Börnstein Group III `Condensed Matter'. It contains data on CdSexTe1-x (cadmium selenide telluride), Element System Cd-Se-Te.

  18. 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

  19. The local atomic structure of superconducting Fe-Se-Te

    Microsoft Academic Search

    Martin C. Lehman; Despina Louca; Kazumasa Horigane; Anna Llobet; Ryotaro Arita; Sungdae Ji; Naoyuki Katayama; Shun Konbu; Kazuma Nakamura; Peng Tong; Tae-Yeong Koo; Kazuyoshi Yamada

    2009-01-01

    We report on the first local atomic structure study via the pair density function (PDF) analysis of neutron diffraction data and show a direct correlation of local coordinates to TC in the newly discovered superconducting FeSe1-xTex. The isovalent substitution of Te for Se such as in FeSe0.5Te0.5 increases Tc by twofold in comparison to a-FeSe without changing the carrier concentration

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  1. Dielectric properties of glassy Se80Te20 and Se80Te10M10 Cd, In and Sb) (*)

    E-print Network

    Boyer, Edmond

    169 Dielectric properties of glassy Se80Te20 and Se80Te10M10 (M = Cd, In and Sb) (*) R. Arora and A dipolaire qui considère le saut des porteurs de charge à travers la barrière de potentiel entre niveaux de défauts chargés. Abstract. 2014 The temperature and frequency dependence of dielectric constant and loss

  2. Local distortions with the substitution of Se for Te in FeSe0.5Te0.5

    Microsoft Academic Search

    Despina Louca; K. Horigane; A. Llobet; R. Arita

    2010-01-01

    The isovalent substitution of Te for Se in the superconductor FeSe1-xTex increases Tc in comparison to alpha-FeSe but, on average, decreases the chalcogen-Fe bond angle. However, we find that the local symmetry is lower than the one presumed on average, P4\\/nmm, because the Se and Te ions do not share the same site, and have two distinct textitz-coordinates exhibiting two

  3. 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.

  4. Synthesis and characterization of KTh 2SeE 6, KTh 2 Te 6 and CsTh 2Se 6

    Microsoft Academic Search

    Eric J. Wu; Michael A. Pell; James A. Ibers

    1997-01-01

    The compounds KTh2Se6, KTh2Te6 and CsTh2Se6 have been synthesized in the temperature range 873 to 923 K. These compounds are isostructural with the previously synthesized compound CsTh2Te6. They crystallize in the space group D2h17-Cmcm of the orthorhombic system with two formula units in cells: a=4.14(2) A?, b=21.88(4) A?, c=5.64(1) A?, V=511(4) A?3 (T=298 K) for KTh2Se6; a=4.356(1) A?, b=23.702(7) A?,

  5. 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.

  6. Hydrogen passivation of Se and Te in AlSb

    Microsoft Academic Search

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

    1996-01-01

    Using infrared absorption spectroscopy we have 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 (CH3OH). The persistent photoabsorption of the DX-like Se donor is significantly reduced after hydrogenation. In hydrogenated AlSb:Se, we attribute the LVM peaks at

  7. Recycling ZnTe, CdTe, and Other Compound Semiconductors by Ambipolar Electrolysis

    E-print Network

    Osswald, Sebastian

    The electrochemical behavior of ZnTe and CdTe compound semiconductors dissolved in molten ZnCl[subscript 2] and equimolar CdCl[subscript 2]–KCl, respectively, was examined. In these melts dissolved Te is present as the ...

  8. Optical properties of PbTe and PbSe

    NASA Astrophysics Data System (ADS)

    Ekuma, Chinedu E.; Singh, David J.; Moreno, J.; Jarrell, M.

    2012-02-01

    We report optical properties of PbTe and PbSe as obtained from first-principles calculations with the Tran-Blaha modified Becke-Johnson potential. The results are discussed in relation to existing experimental data, particularly in relation to the temperature dependence of the band gap.

  9. Optical Properties of PbTe and PbSe

    NASA Astrophysics Data System (ADS)

    Ekuma, Chinedu; Singh, David; Moreno, Juana; Jarrell, Mark

    2012-02-01

    We report optical properties of PbTe and PbSe as obtained from first principles calculations with the Tran-Blaha modified Becke-Johnson potential. The results are discussed in relation to existing experimental data, particularly in relation to the temperature dependence of the band gap.

  10. 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. [Physics Department, Faculty of Science , Assiut University, Assiut, P.O. Box 71516 (Egypt); Moharram, A. H. [Faculty of Science, King Abdul Aziz Univ., Rabigh Branch, P.O. Box 433 (Saudi Arabia)

    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.

  11. 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.

  12. 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.

  13. Thermoelectric properties of polycrystalline In4Se3 and In4Te3

    SciTech Connect

    Shi, Xun [Optimal Inc., Plymouth, Michigan 48170, USA; Cho, Jung Y [GM R& D and Planning, Warren, Michigan; Salvador, James R. [GM R& D and Planning, Warren, Michigan; Yang, Jihui [General Motors Corporation-R& D; Wang, Hsin [Oak Ridge National Laboratory (ORNL)

    2010-01-01

    High thermoelectric performance of a single crystal layered compound In{sub 4}Se{sub 3} was reported recently. We present here an electrical and thermal transport property study over a wide temperature range for polycrystalline samples of In{sub 4}Se{sub 3} and In{sub 4}Te{sub 3}. Our data demonstrate that these materials are lightly doped semiconductors, leading to large thermopower and resistivity. Very low thermal conductivity, below 1 W/m K, is observed. The power factors for In{sub 4}Se{sub 3} and In{sub 4}Te{sub 3} are much smaller when compared with state-of-the-art thermoelectric materials. This combined with the very low thermal conductivity results in the maximum ZT value of less than 0.6 at 700 K for In{sub 4}Se{sub 3}.

  14. Carrier transport mechanisms and photoelectrical properties of PbSnTe\\/PbTeSe heterojunctions

    Microsoft Academic Search

    V. V. Teterkin; V. B. Alenberg; F. F. Sizov; E. V. Susov; Iu. G. Troian

    1990-01-01

    I-V, C-V characteristics, R(0)A product, and spectral photoresponse are analyzed in lattice-matched PbSnTe\\/PbTeSe heterojunctions grown by the molecular epitaxy method. Bulk generation-recombination and diffusion current is shown to be dominant at T higher than 30 K. The leakage current is presumably dominated by surface tunneling or by bulk defects at the depletion at T = 30 K or lower. Values

  15. Low Temperature Photoluminescence of PVT Grown ZnSe and ZnSeTe

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    ZnSe and ZnSeTe single crystals were grown by physical vapor transport (PVT) technique horizontally and vertically. The grown ZnSe and ZnSeTe single crystals were characterized by low temperature photoluminescence at 5 to 10 K using the 3.4 eV emission of an argon laser. The intensity of the sharp near band edge defect lines at 2.799, 2.783 eV and the intrinsic free exciton line at 2.802 eV were mapped on various crystal surfaces with different orientations to the gravitational field. The results show the effects of gravity vector orientation on the defect segregation. Comparison of the photoluminescence spectra of the ZeSe crystal before and after annealing in the Zn vapor shows that the 2.783 eV line of ZnSe crystal is related to the zinc vacancy. The photoluminescence spectra of the ternary ZnSeTe crystal were characterized by a single broad band from 2.2 to 2.4 eV, with a Full Width at Half Maximum (FWHM) of about 100 meV. The temperature dependence of the peak position and intensity were determined from 7 to 150 K.

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

    SciTech Connect

    Shkvarin, A. S., E-mail: shkvarin@ifmlrs.uran.ru; Yarmoshenko, Yu. M.; Skorikov, N. A. [Russian Academy of Sciences, Institute of Metal Physics, Ural Division (Russian Federation); Yablonskikh, M. V. [Sincrotrone Trieste SCp A (Italy); Merentsov, A. I.; Shkvarina, E. G.; Titov, A. N. [Russian Academy of Sciences, Institute of Metal Physics, Ural Division (Russian Federation)

    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.

  17. Transport studies in topological insulator Bi2Te2Se

    NASA Astrophysics Data System (ADS)

    Cao, Helin; Miotkowski, Ireneusz; Tian, Jifa; Chen, Yong

    2013-03-01

    Recently, 3D topological insulators, featuring spin helical topological surface states (SS), have attracted strong attention in condensed matter physics. Although the SS have been directly revealed and intensively studied by surface sensitive measurements, such as ARPES and STM, transport measurements remain challenging due to coexistence of the surface and bulk conduction channels and the sensitivity of sample surfaces to ambient exposure. We have grown high quality Bi2Te2Se crystals by the Bridgeman method. Resistance showed an insulating behavior followed by saturation at low temperature, indicating surface conduction. Through magnetotransport measurements, we demonstrated high mobility SS on freshly cleaved crystals. The transport signatures of surface Dirac fermions were uncovered from 2D SdH oscillations and non-linear Hall effect. We have also compared transport properties of the samples before and after exposure to air. A giant cusp in magnetoresistance at zero B field was observed after exposure. Our studies may help understand the interplay between the surface and the bulk conduction channels and the degradation of SS due to environmental exposure. We will also present some experimental results of gate tuning and thermoelectric measurements on Bi2Te2Se. Recently, 3D topological insulators, featuring spin helical topological surface states (SS), have attracted strong attention in condensed matter physics. Although the SS have been directly revealed and intensively studied by surface sensitive measurements, such as ARPES and STM, transport measurements remain challenging due to coexistence of the surface and bulk conduction channels and the sensitivity of sample surfaces to ambient exposure. We have grown high quality Bi2Te2Se crystals by the Bridgeman method. Resistance showed an insulating behavior followed by saturation at low temperature, indicating surface conduction. Through magnetotransport measurements, we demonstrated high mobility SS on freshly cleaved crystals. The transport signatures of surface Dirac fermions were uncovered from 2D SdH oscillations and non-linear Hall effect. We have also compared transport properties of the samples before and after exposure to air. A giant cusp in magnetoresistance at zero B field was observed after exposure. Our studies may help understand the interplay between the surface and the bulk conduction channels and the degradation of SS due to environmental exposure. We will also present some experimental results of gate tuning and thermoelectric measurements on Bi2Te2Se. We acknowledge support from DARPA MESO program (Grant N66001-11-1-4107).

  18. 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.

  19. Recycling ZnTe, CdTe, and other compound semiconductors by ambipolar electrolysis.

    PubMed

    Bradwell, David J; Osswald, Sebastian; Wei, Weifeng; Barriga, Salvador A; Ceder, Gerbrand; Sadoway, Donald R

    2011-12-14

    The electrochemical behavior of ZnTe and CdTe compound semiconductors dissolved in molten ZnCl(2) and equimolar CdCl(2)-KCl, respectively, was examined. In these melts dissolved Te is present as the divalent telluride anion, Te(2-), which was found able to be converted to elemental metal by electrochemical oxidation at the anode. ZnTe-ZnCl(2) melts were studied at 500 °C by standard electrochemical techniques. On the basis of these results, electrolysis was performed, resulting in the simultaneous extraction of phase-pure liquid Zn at the cathode and phase-pure liquid Te at the anode. This new process, involving the simultaneous deposition of liquid metals at electrodes of opposite polarity, is termed herein as ambipolar electrolysis. A melt consisting of CdTe dissolved in equimolar CdCl(2)-KCl was processed by ambipolar electrolysis, resulting in the production of liquid Cd at the cathode and liquid Te at the anode. Ambipolar electrolysis could enable new approaches to recycling compound semiconductors and semiconductor devices, such as CdTe solar cells. PMID:22035469

  20. 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.

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

    Microsoft Academic Search

    S. V. Khare; S. Marsillac; N. S. Mangale; V. Gade

    2011-01-01

    Several III-VI body-centered tetragonal layered compounds belonging to space group I41\\/amd have been a subject of interest recently because of their potential applications in high efficiency and environmentally friendly copper-indium-gallium-selenide (CIGS) solar cells and molecules. Here we have studied the structural, energetic, and electronic properties of four compounds beta-In2X3 (X = O, S, Se, Te), in this space group. Using

  2. Structural and electronic properties of ?-In 2X 3 (X = O, S, Se, Te) using ab initio calculations

    Microsoft Academic Search

    S. Marsillac; N. S. Mangale; V. Gade; S. V. Khare

    2011-01-01

    Several III-VI body-centered tetragonal layered compounds belonging to space group I41\\/amd have been a subject of interest recently because of their potential applications in high efficiency and environmentally friendly copper–indium–gallium–selenide 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 group. Using first principles computations,

  3. Advancements in cost effective processing for CdTe and CuInSe{sub 2} solar cells

    SciTech Connect

    Ferekides, C.S.; Morel, D.L. [Univ. of South Florida, Tampa, FL (United States). Dept. of Electrical Engineering

    1995-12-31

    The compound semiconductor technologies based upon CdTe and CuInSe{sub 2} have achieved remarkable efficiencies, in the 16% range, over the past two years. This level of performance in laboratory devices is sufficient to warrant commercialization efforts which are underway in the US and abroad. A number of important issues still remain in order to successfully transfer the current laboratory processes to a manufacturing environment. The highest efficiency CdTe devices were prepared at high temperatures (600 C) and required the use of expensive borosilicate glass. The record efficiency CuInSe{sub 2} Cells were fabricated using processes that involve significant and delicate control, or utilize H{sub 2}Se. This paper reports on recent progress in advancing the efficiencies of CdTe and CuInSe{sub 2} solar cells prepared by manufacturing friendly processes.

  4. 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.

  5. 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

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

    SciTech Connect

    Shkvarin, A. S., E-mail: shkvarin@ifmlrs.uran.ru; Yarmoshenko, Yu. M.; Skorikov, N. A. [Russian Academy of Sciences, Ural Branch, Institute of Metal Physics (Russian Federation); Yablonskikh, M. V. [Sincritrone Trieste SCp A (Italy); Merentsov, A. I.; Shkvarina, E. G.; Titov, A. N. [Russian Academy of Sciences, Ural Branch, Institute of Metal Physics (Russian Federation)

    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.

  7. Compositional Dependence of the Optical Properties of Vacuum Evaporated Thin GeSe2-GeTe-PbTe Films

    NASA Astrophysics Data System (ADS)

    Petkov, Kiril; Tasseva, Jordanka; Vassilev, Venceslav; Aljihmani, Lilia

    Chalcogenide glasses from the GeSe2-GeTe-PbTe system were synthesized by taking preliminary prepared GeSe2, GeTe and PbTe in their molecular percentages and melting them in an evacuated quartz ampoule. Thin films were deposited on optical glass substrates BK-7 and Si-wafer substrates by thermal evaporation. Using X-ray microanalysis it was found that the film composition differs to a certain degree from the bulk composition. The changes in the optical properties of thin GeSe2-GeTe-PbTe films were studied as a function of their composition, exposure to light and annealing. It is shown by XRD analysis that the thin films are amorphous up to layers with composition of Ge27Se51Te14Pb8. The optical constants (refractive index, n and absorption coefficient, ?), the thickness, d as well as the optical band gap, Eg, depending on the film composition were determined by spectrophotometric measurements in the region 450-2500 nm applying the Swanepoel's envelop method and Tauc's procedure. With the increase of the Te content in the layers, the absorption edge is shifted to the higher wavelengths, the refractive index increases from 2.54 for Ge31Se66Te3 up to 3.37 for Ge32Se55Te13 while the optical band gap decreases from 1.86 eV for to 1.30 eV for the same compositions. Similar dependence was observed with the increase of the PbTe content in the layers. After annealing of thin films, the values of n decrease, the optical band gap increases and a shift of the absorption edge to the shorter wavelengths is observed.

  8. Prismatic punching defects in CdTe compounds

    NASA Astrophysics Data System (ADS)

    Kim, K. H.; Bolotnikov, A. E.; Camarda, G. S.; Franc, J.; Fochuk, P.; James, R. B.

    2014-03-01

    The origin and nature of star-shaped prismatic punching defects (PPDs) were analyzed by white-beam X-ray diffraction topography (WBXDT) and photoluminescence (PL) measurements. PPDs were observed in CdTe-based compounds that had Te-rich secondary phase defects and were annealed only under Cd overpressure. The evolutional features of the PPDs during annealing were similar to those of a diffusion process, that is, the in-diffusion of Cd vapor via Cd vacancies. PL mapping around the PPDs reveals that the stoichiometry of PPDs is the same as that of a normal matrix, and that PPDs are just structural defects with non-radiative emission induced by the exothermic reaction between Cd and Te. We find that Te-rich secondary phase defects can be removed without the generation of star-shaped PPDs, if the exothermic reaction rate can be slowed down to reduce the thermal gradient between the Te-rich region and the surrounding matrix.

  9. 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.

  10. 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).

  11. 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 [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China)] [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China); Zhai, Pengcheng, E-mail: pczhai@126.com [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China)] [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China); Liu, Lisheng; Zhang, Qingjie [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China)] [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China); Ruan, Xuefeng [Nanoscience and Technology Center, Wuhan University, No. 138, Bayi Road, Wuhan 430072 (China)] [Nanoscience and Technology Center, Wuhan University, No. 138, Bayi Road, Wuhan 430072 (China)

    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.

  12. 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 ...

  13. Carrier generation and recombination dynamics in type-II ZnSeTe/ZnMnSe quantum structures.

    PubMed

    Lin, Yan-Cheng; Chou, Wu-Ching

    2015-07-31

    Type-II band alignment structure is coveted in the design of photovoltaic devices, since it is beneficial for the transport of photogenerated carriers. Here we study the generation and recombination dynamics of carriers in a type-II quantum structure composed of ZnSe0.92Te0.08 highly mismatched alloys (HMAs) and Zn0.97Mn0.03Se. The photoinduced holes at the ZnSe0.92Te0.08 HMAs firstly undergo rapid relaxation to the isoelectronic centers above the valence band edge and subsequently recombine with the free electrons in the Zn0.97Mn0.03Se. The long carrier lifetimes over 120 ns induced by spatially indirect excitons that are bound to isoelectronic Te trapping states further increase with increasing temperature. PMID:26152911

  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. Synthesis, morphology, and optical properties of colloidal CdTe\\/CdSe and CdTe\\/CdS nanoheterostructures based on CdTe tetrapods

    Microsoft Academic Search

    D. N. Dirin; R. B. Vasiliev; M. S. Sokolikova; A. M. Gaskov

    2011-01-01

    We report the synthesis of colloidal CdTe\\/CdSe and CdTe\\/CdS nanoheterostructures based on CdTe tetrapods with a CdSe or CdS\\u000a shell. The shell growth takes place on the lateral faces of the tetrapod legs, whereas the leg length remains essentially\\u000a unchanged. Both the CdSe and CdS shell growth shifts the luminescence of the nanoheterostructures to the near-IR range, up\\u000a to 850

  16. Observation of phase separation in some Se–Te–Sn chalcogenide glasses

    Microsoft Academic Search

    Fouad Abdel-Wahab

    2011-01-01

    Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) techniques were employed here to investigate the glass transition behavior and crystallization kinetics of Se80?x Te20Snx (x=0.0, 2.5 and 5) alloys, which were prepared by the conventional melt quenching method. Two exothermic peaks have been observed in the DSC scans for the samples that contain Sn. Three crystalline phases (Se7.68Te0.32, SnSe and

  17. Anisotropic strain in SmSe and SmTe: Implications for electronic transport

    NASA Astrophysics Data System (ADS)

    Kuroda, Marcelo A.; Jiang, Zhengping; Povolotskyi, Michael; Klimeck, Gerhard; Newns, Dennis M.; Martyna, Glenn J.

    2014-12-01

    Mixed valence rare-earth samarium compounds Sm X (X =Se,Te ) have been recently proposed as candidate materials for use in high-speed, low-power digital switches driven by stress induced changes of resistivity. At room temperature these materials exhibit a pressure driven insulator-to-metal transition with resistivity decreasing by up to seven orders of magnitude over a small pressure range. Thus, the application of only a few GPa's to the piezoresistor (Sm X ) allows the switching device to perform complex logic. Here we study from first principles the electronic properties of these compounds under uniaxial strain and discuss the implications for carrier transport. Based on changes in the band structure and a model we show that the piezoresistive response is mostly governed by the reduction of band gap with strain. Furthermore, the piezoresistive reponse becomes optimal when the Fermi level is pinned near the localized valence band. The piezoresistive effect under uniaxial strain, which must be taken into account in thin films and other systems with reduced dimensionality, is also studied. Under uniaxial strain we find that the piezoresistive response can be substantially larger than in the isotropic case. Analysis of the complex band structure of SmSe yields a tunneling length of the order of 1 nm. This suggest that the conduction mechanism governing the piezoresistive effect in bulk, i.e., thermal promotion of electrons, should still be dominant in few-nanometer-thick films.

  18. 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.

  19. 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 [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China)] [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China); Zhai, Pengcheng, E-mail: pczhai@126.com [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China)] [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China); Liu, Lisheng; Zhang, Qingjie [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China)] [State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, No. 122, Luoshi Road, Wuhan 430070 (China)

    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.

  20. Thermoelectric Investigation of the Pseudo Binary System PbTe-CoSe2

    NASA Astrophysics Data System (ADS)

    Ponnambalam, V.; Morelli, Donald T.

    2015-06-01

    Composites of nominal composition (Pb0.98Na0.02Te)1- y (CoSe2) y and (Pb0.95Na0.05Te)1- y (CoSe2) y with y = 0.05-0.15 have been synthesized to study their thermoelectric properties. In these composites CoTe2 is the secondary phase. The room temperature carrier concentration covers a wide range, 0.5-3.3 × 1020/cm3 depending on the composition. The high-temperature thermoelectric properties are similar to those of Na-doped Pb(Te,Se) alloys. The Seebeck coefficient can be as high as ~250 ?V/K when the electrical resistivity is approximately 3.5 m? cm. The thermal conductivity of all the composites are very low. The CoTe2 seems to have little effect on the transport properties. The highest ZT achieved is ~1.2.

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

    DOE PAGESBeta

    Zhang, P. [Chinese Academy of Sciences (CAS), Beijing (China); Gu, G. D. [Brookhaven National Lab. (BNL), Upton, NY (United States); Richard, P. [Chinese Academy of Sciences (CAS), Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Xu, N. [Chinese Academy of Sciences (CAS), Beijing (China); Paul Scherrer Inst. (PSI), Villigen (Switzerland); Xu, Y. -M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ma, J. [Chinese Academy of Sciences (CAS), Beijing (China); Qian, T. [Chinese Academy of Sciences (CAS), Beijing (China); Fedorov, A. V. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Denlinger, J. D. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ding, H. [Chinese Academy of Sciences (CAS), Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)

    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. Superconductivity in defective pyrite-type iridium chalcogenides Ir(x)Ch2 Ch = Se and Te.

    PubMed

    Qi, Yanpeng; Matsuishi, Satoru; Guo, Jiangang; Mizoguchi, Hiroshi; Hosono, Hideo

    2012-11-21

    We report superconductivity in defective pyrite-type iridium chalcogenides Ir(x)Ch2 (Ch = Se and Te). Maximum values of T(c) of 6.4 K for Ir(0.91)Se(2) and 4.7 K for Ir(0.93)Te(2) were observed. It was found that Ir(0.75)Ch(2) (Ir(3)Ch(8)) is close to the boundary between metallic and insulating states and Ir(x)Ch(2) systems undergo nonmetal to metal transitions as x increases. On the basis of density functional theory calculations and the observed large variation in the Ch-Ch distance with x, we suggest that Ir(0.75)Ch(2) (Ir(3)Ch(8)) is the parent compound for the present superconductors. PMID:23215608

  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. Effect of Tin Incorporation on Thermo-Mechanical Properties of Glassy Se80Te20 Alloy

    NASA Astrophysics Data System (ADS)

    H., Kumar; Sharma, A.; N., Mehta

    2014-03-01

    We report an analysis on the hardness behavior of glassy Se80-xTe20Snx alloy. The crucial thermo-mechanical parameters (micro-hardness, volume and formation energy of micro-voids and the modulus of elasticity) are examined. The results indicate that the thermo-mechanical parameters are changed significantly after incorporation of Sn in glassy Se80Te20 alloy.

  5. GaSe and GaTe anisotropic layered semiconductors for radiation detectors

    Microsoft Academic Search

    Krishna C. Mandal; Michael Choi; Sung Hoon Kang; R. David Rauh; Jiuan Wei; Hui Zhang; Lili Zheng; Y. Cui; M. Groza; A. Burger

    2007-01-01

    High quality detector grade GaSe and GaTe single crystals have been grown by a modified vertical Bridgman technique using high purity Ga (7N) and in-house zone refined (ZR) precursor materials (Se and Te). A state-of-the-art computer model, MASTRAPP, is used to model heat and mass transfer in the Bridgman growth system and to predict the stress distribution in the as-grown

  6. Surfactant?Assisted Synthesis of Cube?Shaped PbTe and PbSe Nanocrystals

    Microsoft Academic Search

    Debao Wang; Caixia Song; Xun Fu; Zhengshui Hu

    2007-01-01

    Uniform cubic?shaped PbTe and PbSe nanocrystals have been synthesized through the surfactant?assisted hydrothermal reaction between Pb(NO3)2 and Te or Se powders with hydrazine hydrate as reducing reagent. The products were characterized by powder x?ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the shapes of nanocubes are well controlled by using ethylenediaminetetraacetic acid as chelating reagent and

  7. Frequency-Dependent Spontaneous Emission Rate from CdSe and CdTe Nanocrystals: Influence of Dark States

    E-print Network

    Vos, Willem L.

    Frequency-Dependent Spontaneous Emission Rate from CdSe and CdTe Nanocrystals: Influence of Dark studied the rate of spontaneous emission from colloidal CdSe and CdTe nanocrystals at room temperature, in practice CdTe and CdSe. Because of quantum confinement, nanocrystals pos- sess discrete electron and hole

  8. CdTe/CdSe quantum dots improve the binding affinities between ?-amylase and polyphenols.

    PubMed

    Ni, Xiaoling

    2012-03-01

    People exposed to engineered nanomaterials have potential health risks associated. Human ?-amylase is one of the key enzymes in the digestive system. There are few reports about the influence of quantum dots (QDs) on the digestive enzymes and their inhibition system. This work focused on the toxic effect of CdTe/CdSe QDs on the interactions between ?-amylase and its natural inhibitors. Thirty-six dietary polyphenols, natural ?-amylase inhibitors from food, were studied for their affinities for ?-amylase in the absence and presence of CdTe/CdSe QDs by a fluorescence quenching method. The magnitudes of apparent binding constants of polyphenols for ?-amylase were almost in the range of 10(5)-10(7) L mol(-1) in the presence of CdTe/CdSe QDs, which were higher than the magnitudes of apparent binding constants in the absence of CdTe/CdSe QDs (10(4)-10(6) L mol(-1)). CdTe/CdSe QDs obviously improved the affinities of dietary polyphenols for ?-amylase up to 389.04 times. It is possible that the binding interaction between polyphenols and ?-amylase in the presence of CdTe/CdSe QDs was mainly caused by electrostatic interactions. QDs significantly influence the digestive enzymes and their inhibition system. PMID:22286694

  9. 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

  10. 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

  11. Molecular beam epitaxy (MBE) growth of ZnMgSeTe light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Faschinger, Wolfgang; Ferreira, S.; Krump, R.; Brunthaler, G.; Sitter, Helmut

    1994-12-01

    One of the main problems for the fabrication of optoelectronic devices in the blue spectral range is the limited p-dopability and the resulting high contact resistivity of p-ZnSe. We show that the admixture of even small Te fractions to ZnSe has a strong beneficial effect on doping levels and contacts of MBE grown material doped with DC nitrogen plasma. Since the energy gap decreases through the admixture of Te, we additionally introduced Mg in order to remain in the blue range of the spectrum. P-doping levels above 1018 cm-3 and Ohmic contacts to ZnMgSeTe could be obtained for Te contents of more than 20%, the highest levels being 1020 cm-3 for Zn(1-x)MgxSe(1-y)Tey with x < 0.2 and y > 0.4. On the other hand, the admixture of Te to ZnSe strongly reduced the obtained n-doping levels. As a viable alternative we used n-type layers of Chlorine doped ZnMgSe. This allowed the growth of pn-junctions of n-ZnMgSe and p- ZnMgSeTe. The Mg content in the n- and p-layer was adjusted in a way that both layers had the same lattice constant and the same doping level of 1018 cm-3. The diodes emit light in the blue-green spectral range at 77 K. Although the optical properties have to be improved for device applications, ZnMgSeTe could be an interesting alternative for blue light emitters since high doping levels, ohmic p- contacts and low operation voltages are obtainable in a relatively easy way.

  12. Molecular beam epitaxy (MBE) growth of ZnMgSeTe light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Faschinger, Wolfgang; Ferreira, S.; Krump, R.; Brunthaler, G.; Sitter, Helmut

    1995-12-01

    One of the main problems for the fabrication of optoelectronic devices in the blue spectral range is the limited p-dopability and the resulting high contact resistivity of p-ZnSe. We show that the admixture of even small Te fractions to ZnSe has a strong beneficial effect on doping levels and contacts of MBE grown material doped with DC nitrogen plasma. Since the energy gap decreases through the admixture of Te, we additionally introduced Mg in order to remain in the blue range of the spectrum. P-doping levels above 1018 cm-3 and Ohmic contacts to ZnMgSeTe could be obtained for Te contents of more than 20%, the highest levels being 1020 cm-3 for Zn(1-x)MgxSe(1-y)Tey with x < 0.2 and y > 0.4. On the other hand, the admixture of Te to ZnSe strongly reduced the obtained n-doping levels. As a viable alternative we used n-type layers of Chlorine doped ZnMgSe. This allowed the growth of pn-junctions of n-ZnMgSe and p- ZnMgSeTe. The Mg content in the n- and p-layer was adjusted in a way that both layers had the same lattice constant and the same doping level of 1018 cm-3. The diodes emit light in the blue-green spectral range at 77 K. Although the optical properties have to be improved for device applications, ZnMgSeTe could be an interesting alternative for blue light emitters since high doping levels, ohmic p- contacts and low operation voltages are obtainable in a relatively easy way.

  13. Radiation effects on the optical properties of Se85-xTe15Sbx thin films

    NASA Astrophysics Data System (ADS)

    Bakry, A.; Soltan, A. S.; El-Korashy, A.

    2005-07-01

    The optical absorption of the as-deposited and gamma-irradiated (doses of 3, 10, 12, 15 Mrad) thermally evaporated Se85-xTe15Sbx (x =0, 6, 9) films was measured. The refractive index n and the extinction coefficient k of the films were calculated using an analytical method developed by Zheng et al . The Urbach relation was used in the fundamental edge region to calculate the width of the band tail states. The behavior of the composition with high concentration of antimony ( x =9) was attributed to the produced Se-Sb bonds and an excess of Te-Te bonds, which break the chain structure of the Se-Te system and generate defects in the film. The related optical parameters were also calculated and discussed.

  14. 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.

  15. Photo-rechargeable battery using new layer compound CuFeTe 2

    Microsoft Academic Search

    T. Nomiyama; H. Kuriyaki; K. Hirakawa

    1995-01-01

    Photo-rechargeable battery is a device that converts photo-energy to electrochemical energy and stores it. Many electrode materials have been studied for this device. These materials are mainly layered semiconducting compounds. We synthesized a new layered compound CuFeTe2. In this study, CuFeTe2 was tested for photo-rechargeable battery electrode. As a result, we revealed that CuFeTe2 was charged by a Xe lamp

  16. Stable five-coordinate silicon(IV) complexes with SiN4 X skeletons (X = S, Se, Te) and Si=X double bonds.

    PubMed

    Junold, Konstantin; Baus, Johannes A; Burschka, Christian; Auerhammer, Dominic; Tacke, Reinhold

    2012-12-14

    Silylenes: Reaction of the donor-stabilized silylene 1 with elemental sulfur, selenium, or tellurium led to the formation of 2?a-c [SiN(4)X skeletons (X = S, Se, Te)], the first stable five-coordinate silicon(IV) compounds with silicon-chalcogen double bonds (see figure). PMID:23172801

  17. 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

  18. Thermal behavior in Se-Te chalcogenide system: interplay of thermodynamics and kinetics.

    PubMed

    Svoboda, Roman; Málek, Ji?í

    2014-12-14

    Heat capacity measurements were performed for Se, Se90Te10, Se80Te20, and Se70Te30 materials in the 230-630 K temperature range. Both glassy and crystalline Cp dependences were found to be identical within the experimental error. The compositional dependence of the N-type undercooled liquid Cp 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. PMID:25494760

  19. Kinematic study of refraction properties of a ZnSe-ZnTe dielectric grating.

    PubMed

    Reyes, J C Salcedo

    2008-12-01

    The plane wave expansion method is applied to determine the thickness of the ZnSe-ZnTe slabs in a semi-infinite dielectric grating in such a way that the maximum reflectivity of the system is obtained. In this way the potential of the ZnSe-ZnTe system for applications in CdSe ultra thin quantum well based monolithic II-VI Vertical Cavity Surface Emitting Laser for the green spectral region is demonstrated. A kinematic analysis of the thickness-dependent refraction at the boundary between a ZnSe-ZnTe semi-infinite one dimensional photonic crystal and a homogeneous material in transverse magnetic polarization and oblique incidence case is presented. PMID:19205245

  20. Pressure dependence of the bowing parameter of direct band gap of CdSe xTe 1-x

    NASA Astrophysics Data System (ADS)

    Lemos, V.; Moro, J. R.; de Souza, Q. A. G.; Motisuke, P.

    1986-12-01

    The variation of the lowest direct band gap of compounds CdSe xTe 1-x with hydrostatic pressure has been measured by photoluminescence at room temperature. This allowed determination of pressure dependence of the bowing parameter. Our data compared to theoretical calculations based on the dielectric model indicates that the average ionic potential is constant with pressure. This result has been previously assumed in the calculation of energy-band pressure coefficients and proved fundamental for the agreement with experimental values for a wide variety of semiconductors.

  1. 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.

  2. Te4Se2O6 macrocycle stabilizing triangular planar and tetrahedral anions.

    PubMed

    Srungavruksham, Nagarjuna Kumar; Baskar, Viswanathan

    2015-03-14

    The anion exchange reactions of Cl-macrocycle 1a [(p-MeO-C6H4)2Te)2(?-O)(?-PhSeO2)(?4-Cl)]2 with AgNO3, AgClO4 and AgBF4 yielded colourless solids whose single crystal X-ray diffraction studies revealed the formation of 12-membered macrocycles [(p-MeO-C6H4)2Te)2(?-O)(?-PhSeO2)(?-X)]2 [X = NO3 (2), ClO4 (3), BF4 (4)]. ESI-MS studies revealed that macrocycles 2–4 retain their integrity in solution. The solution (125)Te NMR spectrum of 4 shows the appearance of a triplet ((1)JTe···F = 568 Hz) that can be assigned to coupling between (125)Te nuclei and two fluorine atoms in BF4(?) ions. PMID:25652207

  3. 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

  4. First principles studies of the structural, electronic and optical properties of LiInSe2 and LiInTe2 chalcopyrite crystals

    NASA Astrophysics Data System (ADS)

    Ma, C.-G.; Brik, M. G.

    2015-02-01

    Detailed first principles calculations of the structural, electronic and optical properties of two representatives of the chalcopyrite group of compounds (LiInSe2 and LiInTe2) are reported in the present paper. Both materials are shown to be the direct band gap semiconductors. Analysis of the electronic properties showed that the degree of covalency increases if Se is substituted by Te. Calculations of the optical properties of both crystals allowed to get reliable approximation of the refractive index as a function of the wavelength. All calculated results were compared with the available experimental data; good agreement was demonstrated.

  5. Regioselective synthesis of bis(2-halo-3-pyridyl) dichalcogenides (E = S, Se and Te): directed ortho-lithiation of 2-halopyridines.

    PubMed

    Bhasin, K K; Singh, Neelam; Doomra, Shivani; Arora, Ekta; Ram, Ganga; Singh, Sukhjinder; Nagpal, Yogesh; Mehta, S K; Klapotke, T M

    2007-01-01

    A novel method for the preparation of hitherto unknown symmetrical bis(2-halo-3-pyridyl) dichalcogenides (E = S, Se and Te) by the oxidation of intermediate 2-halo-3-pyridyl chalcogenolate, prepared by lithiation of 2-halo pyridines using lithium diisopropylamine is being reported. All the newly synthesized compounds have been characterized through elemental analysis employing various spectroscopic techniques, namely, NMR ((1)H, (13)C, (77)Se), infrared, mass spectrometry, and X-ray crystal structures in representative cases. PMID:17611613

  6. Regioselective Synthesis of Bis(2-halo-3-pyridyl) Dichalcogenides (E = S, Se and Te): Directed Ortho-Lithiation of 2-halopyridines

    PubMed Central

    Bhasin, K. K.; Singh, Neelam; Doomra, Shivani; Arora, Ekta; Ram, Ganga; Singh, Sukhjinder; Nagpal, Yogesh; Mehta, S. K.; Klapotke, T. M.

    2007-01-01

    A novel method for the preparation of hitherto unknown symmetrical bis(2-halo-3-pyridyl) dichalcogenides (E = S, Se and Te) by the oxidation of intermediate 2-halo-3-pyridyl chalcogenolate, prepared by lithiation of 2-halo pyridines using lithium diisopropylamine is being reported. All the newly synthesized compounds have been characterized through elemental analysis employing various spectroscopic techniques, namely, NMR (1H, 13C, 77Se), infrared, mass spectrometry, and X-ray crystal structures in representative cases. PMID:17611613

  7. Second Cyclotron Resonance in ZnSe\\/Zn_1-x-yCd_xMn_ySe and ZnTe\\/CdSe Heterostructures

    Microsoft Academic Search

    Y. A. Leem; K. Storr; H. K. Ng

    2000-01-01

    We have made detailed cyclotron resonance studies of the two-dimensional electron gas (2DEG) structures based on modulation doped ZnSe\\/Zn_1-x-yCd_xMn_ySe and ZnTe\\/CdSe single quantum wells. The samples have, typically, carrier densities from 1 to 4 × 10^11 cm-2 and mobilities around 5000 cm^2\\/V\\\\cdots. The measurements were taken at a nominal temperature of 4.2 K and in magnetic fields up to 31

  8. Thermomagnetic and thermoelectric properties of semiconductors (PbTe, PbSe) at ultrahigh pressures

    NASA Astrophysics Data System (ADS)

    Ovsyannikov, Sergey V.; Shchennikov, Vladimir V.

    2004-02-01

    The longitudinal and transverse thermomagnetic Nernst-Ettingshausen (LNE, TNE) effects and the Maggi-Reghi-Leduc (MRL) effect were measured on PbTe and PbSe micro-samples at ultrahigh pressures upto 20 GPa. Values of the mobility of charge carriers as well as the scattering parameter were estimated both for the low- and high-pressure phase of PbTe and PbSe. At about 3 GPa, the maxima of both Nernst-Ettingshausen effects and magnetoresistance (MR) (and hence of the mobility of charge carriers ?), attributed to the gapless state of PbTe and PbSe were established. The TNE effect was found to be the largest among the effects measured, while the MRL was hardly visible even at the highest mobility values of the charge carriers. The possibilities for using thermomagnetic effects in micro-device technologies are discussed.

  9. Growth and Characterization of Bi2Te3/Bi2Se3 Bilayers

    NASA Astrophysics Data System (ADS)

    Henderson, Rachel; Babakiray, Sercan; Johnson, Trent; Borisov, Pavel; Lederman, David; West Virginia University Team

    2014-03-01

    Bi2Te3/Bi2Se3 bilayers were grown on Al2O3 (0001) substrates using molecular beam epitaxy. Bi2Te3 was grown at a stoichiometric ratio (Te/Bi) of 3:2 and Bi2Se3 was grown at stoichiometric ratio (Se/Bi) of 15:1. Reflection high energy electron diffraction and x-ray diffraction were used to confirm the epitaxial growth of these films. X-ray reflectivity was used to determine the thickness and roughness of these bilayers. The magnetotransport of these heterostructures was used to determine whether charge compensation can be achieved within the bulk of the material in order to enhance the properties of surface topological states. This work was supported by a Research Challenge Grant from the West Virginia Higher Education Policy Commission (HEPC.dsr.12.29) and the West Virginia University Shared Research Facilities.

  10. 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.

  11. Raman spectroscopy of highly oriented FeSe0.5Te0.5 superconductor

    NASA Astrophysics Data System (ADS)

    Santos Lopes, Cristiano; Eugênio Foerster, Carlos; Serbena, Francisco Carlos; Rodrigues Júnior, Pedro; Jurelo, Alcione Roberto; Pimentel Júnior, Jorge Luiz; Pureur, Paulo; Chinelatto, Adilson Luiz

    2012-02-01

    Melt-textured superconducting samples of FeSe0.5Te0.5 were successfully prepared. The measured critical temperature was TC = 14.5 K. The Fe-Se-Te samples were composition and magnetically inhomogeneous, consisting of magnetic grains with diameters in the range 10-100 nm. Raman spectra were obtained at room temperature and 77 K on ab and a(b)c planes. All phonon modes allowed by symmetry were identified. Some additional lines were observed that could be associated with inhomogeneities.

  12. Phonons in Bi2Te3 and Bi2Se3 Thin Films

    NASA Astrophysics Data System (ADS)

    Ren, Shang-Fen; Cheng, Wei

    2010-03-01

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

  13. Structural and Electronic properties of ?- In2 X 3 (X = O, S, Se, Te) using ab initio calculations

    NASA Astrophysics Data System (ADS)

    Khare, S. V.; Marsillac, S.; Mangale, N. S.; Gade, V.

    2011-03-01

    Several III-VI body-centered tetragonal layered compounds belonging to space group I 4 1 /amd have been a subject of interest recently because of their potential applications in high efficiency and environmentally friendly copper-indium-gallium-selenide (CIGS) solar cells and molecules. Here we have studied the structural, energetic, and electronic properties of four compounds ? - In 2 X3 (X = O, S, Se, Te), in this space group. Using first principles computations, we have fully determined the lattice constants a and c, as well as 10 internal parameters that define this unique structure of primitive unit cells of 40 atoms. For ? - In 2 S3 our computed values are found to be consistent with experimental measurements. The bulk modulus B, local electronic density of states (LDOS), total density of states (DOS), and band gap Ef of these phases have been investigated. Supported by Ohio Supercomputing Center, National Center for Supercomputing Applications, Wright Center for PVIC, National Science Foundation, DARPA.

  14. Photocurrent mapping of 3D CdSe/CdTe windowless solar cells.

    PubMed

    Hangarter, Carlos M; Debnath, Ratan; Ha, Jong Y; Sahiner, Mehmet A; Reehil, Christopher J; Manners, William A; Josell, Daniel

    2013-09-25

    This paper details the use of scanning photocurrent microscopy to examine localized current collection efficiency of thin-film photovoltaic devices with in-plane patterning at a submicrometer length scale. The devices are based upon two interdigitated comb electrodes at the micrometer length scale prepatterned on a substrate, with CdSe electrodeposited on one electrode and CdTe deposited over the entire surface of the resulting structure by pulsed laser deposition. Photocurrent maps provide information on what limits the performance of the windowless CdSe/CdTe thin-film photovoltaic devices, revealing "dead zones" particularly above the electrodes contacting the CdTe which is interpreted as recombination over the back contact. Additionally, the impact of ammonium sulfide passivation is examined, which enables device efficiency to reach 4.3% under simulated air mass 1.5 illumination. PMID:23968397

  15. Quasiparticle band structures of ?-HgS, HgSe, and HgTe

    NASA Astrophysics Data System (ADS)

    Christensen, Niels E.; Svane, Axel; Cardona, Manuel; Chantis, Athanasios; van Schilfgaarde, Mark; Kotani, Takao

    2012-02-01

    The electronic structures of mercury chalcogenides in the zinc-blende strucrure have been calculated by the LDA, GW (one-shot, G0W0) and quasi-particle self-consistent GW (QSGW) approximations including spin-orbit coupling (SO). The slight tendency to overestimation of the band gaps by QSGW is avoided by using a hybrid scheme (20% LDA and 80 % QSGW. The results of G0W0 depend strongly starting wave functions and are thus quite different from those from QSGW. Within QSGW HgS is found to be a semiconductor, with a ?6 s-like conduction-band minimum state above the valence-band top ?7 and ?8 (``negative'' SO splitting). HgSe and HgTe have ``negative'' gaps (inverted band structure). In HgTe the ?7 state is below ?6 due to the large Te SO splitting, in contrast HgSe where ?6 is below ?7.

  16. Direct bandgap materials based on the thin films of Se x Te100 - x nanoparticles

    NASA Astrophysics Data System (ADS)

    Salah, Numan; Habib, Sami S.; Khan, Zishan H.

    2012-09-01

    In this study, we fabricated thin films of Se x Te100 - x ( x = 0, 3, 6, 9, 12, and 24) nanoparticles using thermal evaporation technique. The results obtained by X-ray diffraction show that the as-synthesized nanoparticles have polycrystalline structure, but their crystallinity decreases by increasing the concentration of Se. They were found to have direct bandgap ( E g), whose value increases by increasing the Se content. These results are completely different than those obtained in the films of Se x Te100 - x microstructure counterparts. Photoluminescence and Raman spectra for these films were also demonstrated. The remarkable results obtained in these nanoparticles specially their controlled direct bandgap might be useful for the development of optical disks and other semiconductor devices.

  17. TOTAL EFFECTIVE NEUTRON CROSS SECTIONS OF As, Se, Sb, AND Te

    Microsoft Academic Search

    D. Balli; Z. Georgiu; T. Stadnikova

    1962-01-01

    The total cross sections of As, Se, Sb, and Te are at present known only ; in the energy range higher than 0.01 ev; knowledge of this value at lower ; energies would allow to estimate the influence of the crystalline structure. A ; neutron spectrometer provided with a flat, monocrystalline mica was used for the ; measurements which were

  18. Atomistic simulations of the optical absorption of type-II CdSe/ZnTe superlattices

    PubMed Central

    2012-01-01

    We perform accurate tight binding simulations to design type-II short-period CdSe/ZnTe superlattices suited for photovoltaic applications. Absorption calculations demonstrate a very good agreement with optical results with threshold strongly depending on the chemical species near interfaces. PMID:23031315

  19. Static and dynamical inhomogeneity at liquid - liquid phase transition of Se-Te mixtures

    NASA Astrophysics Data System (ADS)

    Kajihara, Y.; Inui, M.; Matsuda, K.; Ishikawa, D.; Tsutsui, S.; Baron, A. Q. R.

    2011-05-01

    We have carried out x-ray transmission and small-angle x-ray scattering (SAXS) measurements of liquid Se70-Te30 mixture up to 1000 °C and 100MPa and inelastic x-ray scattering (IXS) measurement of liquid Se50-Te50 mixture at SPring-8 in Japan. In this paper, we report the preliminary results. In liquid Se70Te30 at 6MPa, with increasing temperature from 400 °C, the density first normaly decreases but anomalously increases from 650 °C. This anomalous density behaviour can be interpreted that the sample exhibits continuous transition from low-density phase to high-density one in this temperature region. As a proof of that, the zero-wavenumber-limit of SAXS intensity I(0) increases and shows maximum in this region, which means that the static density inhomogeneity arises due to phase transition. When the pressure is elevated, the density and I(0) curves shift to lower temperature side. The velocity of acoustic mode in Se50-Te50 estimated by IXS data is much higher than the ultrasonic sound velocity (so-called "fast sound" state) and the temperature dependences of the two velocities are totally different. But the ratio of the two velocities, the strength of "fast sound", seems to increase with approaching to the transition region and thus it seems to be a good sign of dynamical inhomogeneity.

  20. IV MEASUREMENTS OF Se-Te-Sb GLASSY BULK AND THIN FILM SAMPLES

    Microsoft Academic Search

    Vibhav K. Saraswata; V. Kishorea; T. P. Sharmaa; P. K. Saraswatd; Vigyan Bhawan

    I-V characteristic curves of Se85-xTe15Sbx (x = 2, 4, 6, 8 & 10) glassy system prepared by melt quenching have been studied at different temperatures in bulk and at room temperature in thin film form. Experimental results indicate that the conduction mechanism in these systems is of Poole-Frenkel type. The change in dc electrical conductivity is attributed to the Se-Sb

  1. Physical properties, crystal and magnetic structure of layered Fe[subscript 1.11]Te[subscript 1;#8722;x]Se[subscript x] superconductors

    SciTech Connect

    Xiao, Y.; Su, Y.; Kumar, C.M.N.; Ritter, C.; Mittal, R.; Price, S.; Perßon, J.; Brückel, Th. (BARC); (Julich); (ILL)

    2012-10-23

    The physical and structural properties of Fe1.11Te and Fe1.11Te0.5Se0.5 have been investigated by means of X-ray and neutron diffraction as well as physical property measurements. For the Fe1.11Te compound, the structure distortion from a tetragonal to monoclinic phase takes place at 64 K accompanied with the onset of antiferromagnetic order upon cooling. The magnetic structure of the monoclinic phase was confirmed to be of antiferromagnetic configuration with a propagation vector k = (1/2, 0, 1/2) based on Rietveld refinement of neutron powder diffraction data. The structural/magnetic transitions are also clearly visible in magnetic, electronic and thermodynamic measurements. For superconducting Fe1.11Te0.5Se0.5 compound, the superconducting transition with T c = 13.4 K is observed in the resistivity and ac susceptibility measurements. The upper critical field H c2 is obtained by measuring the resistivity under different magnetic fields. The Kim's critical state model is adopted to analyze the temperature dependence of the ac susceptibility and the intergranular critical current density is calculated as a function of both field amplitude and temperature. Neutron diffraction results show that Fe1.11Te0.5Se0.5 crystalizes in tetragonal structure at 300 K as in the parent compound Fe1.11Te and no structural distortion is detected upon cooling to 2 K. However an anisotropic thermal expansion anomaly is observed around 100 K.

  2. Te concentration dependent photoemission and inverse-photoemission study of FeSe1-xTex

    NASA Astrophysics Data System (ADS)

    Yokoya, Takayoshi; Yoshida, Rikiya; Utsumi, Yuki; Tsubota, Koji; Okazaki, Hiroyuki; Wakita, Takanori; Mizuguchi, Yoshikazu; Takano, Yoshihiko; Muro, Takayuki; Kato, Yukako; Kumigashira, Hiroshi; Oshima, Masaharu; Harima, Hisatomo; Aiura, Yoshihiro; Sato, Hitoshi; Ino, Akihiro; Namatame, Hirofumi; Taniguchi, Masaki; Hirai, Masaaki; Muraoka, Yuji

    2012-10-01

    We have characterized the electronic structure of FeSe1-xTex for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe.

  3. Photo- and Thermo-Induced Changes in Optical Constants and Structure of Thin Films from GeSe2-GeTe-ZnTe System

    NASA Astrophysics Data System (ADS)

    Petkov, Kiril; Todorov, Rossen; Vassilev, Venceslav; Aljihmani, Lilia

    We examined the condition of preparation of thin films from GeSe2-GeTe-ZnTe system by thermal evaporation and changes in their optical properties after exposure to light and thermal annealing. The results for composition analysis of thin films showed absence of Zn independently of the composition of the bulk glass. By X-ray diffraction (XRD) analysis it was found that a reduction of ZnTe in ZnSe in bulk materials takes of place during the film deposition. A residual from ZnSe was observed in the boat after thin film deposition. Optical constants (refractive index, n and absorption coefficient, ?) and thickness, d as well as the optical band gap, Eg, depending of the content of Te in ternary Ge-Se-Te system are determined from specrophotometric measurements in the spectral range 400-2500 nm applying the Swanepoel's envelope method and Tauc's procedure. With the increase of Te content in the layers the absorption edge is shifted to the longer wavelengths, refractive index increases while the optical band gap decreases from 2.02 eV for GeSe2 to 1.26 eV for Ge34Se42Te24. The values of the refractive index decrease after annealing of all composition and Eg increase, respectively. Thin films with composition of Ge27Se47Te9Zn17 and Ge28Se49Te10Zn13 were prepared by co-evaporation of (GeSe2)78(GeTe)22 and Zn from a boat and a crucible and their optical properties, surface morphology and structure were investigated. The existence of a correlation between the optical band gap and the copostion of thin films from the system studied was demonstrated.

  4. Cd and Te-based ohmic contact materials to p-Type ZnSe

    Microsoft Academic Search

    K. Hashimoto; Y. Koide; O. Tadanaga; T. Oku; N. Teraguchi; Y. Tomomuea; A. Suzuki; Masanori Murakami

    1996-01-01

    In order to explore a possibility of forming an intermediate semiconductor layer with low Schottky barrier by the conventional\\u000a deposition and annealing technique, the electrical properties of Cd and Te-based contacts on the nitrogendoped ZnSe substrates\\u000a have been investigated. Cd in the Cd\\/W contact reacted with the ZnSe substrate after annealing at temperatures above 250?C\\u000a and formed epitaxial Ccx}Zn1?xSe layers,

  5. 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.

  6. A voltammetric study of compound formation in the Hg-Cd-Te system

    SciTech Connect

    Mori, E.; Mishra, K.K.; Rajeshwar, K. (Texas Univ., Arlington, TX (USA). Dept. of Chemistry)

    1990-04-01

    The cathodic electrodeposition chemistry in the ternary Hg-Cd-Te system has been studied using hydrodynamic voltammetry in conjunction with cyclic photovoltammetry, x-ray diffraction (XRD) analyses, and optical measurements. The binary Hg-Te system was studied first, as a prelude to the more complex ternary case. An H{sub 2}SO{sub 4} electrolyte matrix was used in these studies. The Hg stripping waves observed on the return scan at the disk were altered in shape when the disk was scanned into the Te{sup 4 +} {r arrow} Te{degrees} and Te{sup 4 +} {r arrow} Te{sup 2 {minus}} regimes on the forward sweep. Monitoring of the ring response both at 1.40 V and 0 V permitted selective detection of Hg and Te species generated at the disk. Evidence for the kinetic sluggishness of HgTe compound formation is presented and contrasted with the CdTe case. In both the Hg-Te and Hg-Cd-Te cases,the broad anodic dissolution envelope at potentials positive of {approximately} 0.70 V (contrasting the clean stripping behavior of the individual components in isolation) was taken to be diagnostic of compound formation. The ring response at 1.40 V, which is tuned to Hg{sub 2}{sup 2 +} collection, is shown to be an effective indicator of the presence of free Hg in the electrodeposits. The presence of Cd{sup 2 +} ions and also a sequential deposition mode (Hg first followed by Te and Cd) appeared to facilitate quantitative conversion of elemental Hg. XRD data also show that Te formation (as a separate phase) is less of a problem with the Hg-Cd-Te system, again contrasting the situation with the Cd-Te case. Optical response and Auger electron spectroscopy measurements of the Hg-Cd-Te thin films indicate incomplete alloying of the HgTe and CdTe phases at room temperature.

  7. Synthesis and properties of In2(Se1-xTex)3 thin films: a new semiconductor compound

    NASA Astrophysics Data System (ADS)

    Emziane, M.; Le Ny, R.

    2001-03-01

    In2(Se1-xTex)3 polycrystalline films were prepared by a dual-source thermal evaporation technique. The depositions onto glass and SnO2-coated glass substrates were carried out in a vacuum chamber and followed by an annealing in neutral ambient (Ar or N2). The structural, morphological and compositional studies of the films were made by X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, Raman scattering and optical transmission. Optimum conditions are investigated for the formation of the ternary compound In2(Se1-xTex)3 in order to tune the band gap by changing the Te concentration. The film properties as a function of Te amount are discussed. It is shown that single-phase, textured and homogeneous layers of In2(Se1-xTex)3 can be grown with x<=0.2 at optimal deposition and heat treatment conditions. For x?0.17 these films showed an energy band gap of about 1.45 eV and an electrical conductivity at room temperature six orders of magnitude higher than that of the binary ?-In2Se3 thin films.

  8. Effect of CdSe Nanoparticles on the Growth of Te Nanowires: Greater Length and Tortuosity and Nonmonotonic Concentration Effect

    SciTech Connect

    Lilly, G. Daniel; Chen, Yanbin; Pan, Xiaoqing; Kotov, Nicholas A.

    2010-01-01

    Improved control over nanowire (NW) geometry and composition offers multiple benefits for design material and devices, including uses in complex nanoelectronic circuits, facilitating their organization on substrates, providing more efficient charge transport over large distances, and greater mechanical strength. Te NWs have many interesting thermoelectric, piezoelectric, conducting, and photoconducting properties and are highly reactive with numerous chemicals, allowing Te NWs to be used as templates for NWs of other compositions. Te NWs are made in this work from CdTe nanoparticles (NPs) by slow oxidation. Te NWs with average lengths of 6.63 ± 1.07 ?m and aspect ratios of 50 were initially formed. Unexpectedly, the presence of CdSe NPs results in a drastic increase in the length, aspect ratio, and tortuosity of the Te NWs. We believe that Se{sup 2?} is being incorporated into the Te seeds as elemental Se, fouling them and reducing the number of viable Te seeds, which allows longer Te NWs to form. Excessive amount of CdTe NPs stops the growth of Te NWs completely making the concentration dependence strongly nonmonotonic. The longest tortuous NWs grown in this fashion have lengths of 15.56 ± 4.16 ?m and aspect ratios 103. This work reveals a novel process taking place between growing NW and NPs. These finding indicate advantages of using NPs for reaction control for preparation of NW with high practical relevance.

  9. Interface formation between polycrystalline Cu(In,Ga)Se\\/sub 2\\/ and II-VI-compounds

    Microsoft Academic Search

    T. Schulmeyer; R. Hunger; W. Jaegermann; A. Klein; R. Kniese; M. Powalla

    2003-01-01

    The interface between Cu(In,Ga)Se\\/sub 2\\/ (absorber) and CdS (buffer) is crucial for the performance of CIGS thin film solar cells. We have performed systematic studies of interface formation between Cu(In,Ga)Se\\/sub 2\\/ and II-Vl semiconductors CdX and ZnX (X= S, Se, Te) using in-situ photoelectron spectroscopy. Clean Cu(In,Ga)Se\\/sub 2\\/ surfaces with Cu deficient surface composition were prepared by heating-off of Se

  10. Bandgap bowing and spontaneous ordering in ZnSe xTe 1- x

    NASA Astrophysics Data System (ADS)

    Freytag, B.; Pavone, P.; Rössler, U.; Wolf, K.; Lankes, S.; Schötz, G.; Naumov, A.; Jilka, S.; Stanzl, H.; Gebhardt, W.

    1995-04-01

    We present the results of experimental investigations on bandgap bowing and spontaneous ordering in MOVPE grown ZnSe xTe 1- x. The bowing parameter of b = 1.40 ± 0.05eV found from different optical measurements on our epilayers is slightly larger than values found earlier from bulk material, indicating the possibility of spontaneous ordering in our samples. Ab-initio calculations for Zn 2SeTe in the ordered CuAu- and CuPt-structures lean support to this possibility. In fact X-ray measurements performed on our samples with x = 0.39 and x = 0.54 show peaks, forbidden in the zincblende structure, which give evidence for spontaneous ordering in the CuPt structure.

  11. 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.

  12. 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.

  13. Photoluminescence studies of type-II CdSe/CdTe superlattices

    SciTech Connect

    Li Jingjing; Johnson, Shane R.; Wang Shumin; Ding Ding; Ning Cunzheng; Zhang Yonghang [Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287-5706 (United States); School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287-5706 (United States); Yin Leijun [Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287-5706 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States); Skromme, B. J. [School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287-5706 (United States); Liu Xinyu; Furdyna, Jacek K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

    2012-08-06

    CdSe/CdTe type-II superlattices grown on GaSb substrates by molecular beam epitaxy are studied using time-resolved and steady-state photoluminescence (PL) spectroscopy at 10 K. The relatively long carrier lifetime of 188 ns observed in time-resolved PL measurements shows good material quality. The steady-state PL peak position exhibits a blue shift with increasing excess carrier concentration. Self-consistent solutions of the Schroedinger and Poisson equations show that this effect can be explained by band bending as a result of the spatial separation of electrons and holes, which is critical confirmation of a strong type-II band edge alignment between CdSe and CdTe.

  14. Modified magnetism within the coherence volume of superconducting FeSeTe

    SciTech Connect

    Leiner, Jonathan C [ORNL; Thampy, Vivek [ORNL; Christianson, Andrew D [ORNL; Abernathy, D. [Oak Ridge National Laboratory (ORNL); Stone, Matthew B [ORNL; Lumsden, Mark D [ORNL; Sales, Brian C [ORNL; Safa-Sefat, Athena [ORNL; Hu, Jin [Tulane University; Mao, Zhiqiang [Tulane University; Bao, Wei [Renmin University of China; Broholm, Collin L [ORNL

    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)

  15. Ternary phase relations of the chalcopyrite compound CuGaSe2

    Microsoft Academic Search

    J. C. Mikkelsen

    1981-01-01

    The ternary Cu-Ga-Se phase diagram has been determined by DTA and x-ray analysis. In addition to two ternary solid solutions based on the binary compounds Cu2.xSe and Ga2Se3, only one ternary phase, the chalcopyrite CuGaSe2 (peritectic m.p. 1030°C), was encountered. The liquidus contains two regions of liquid immiscibility, one which extends from the Cu-rich (Cu, Se) binary liquid immiscibility to

  16. CdSe\\/ZzTe heterojunction solar cells grown on GaSb

    Microsoft Academic Search

    S. Wang; D. Ding; R. Scott; J. Chen; M. DiNezza; X. Liu; J. Furdyna; Y.-H. Zhang

    2009-01-01

    This paper reports recent experimental work on single junction II-VI semiconductor heterostructure solar cells consisting of n-type CdSe and p-type ZnTe grown by molecular beam epitaxy on GaSb substrates. The structural and crystalline properties are characterized using high-resolution X-ray diffraction measurements. The current-voltage measurements reveal expected diode-like rectifying characteristics with considerable photo current and strong photovoltaic effects under light illumination.

  17. Time dependent voltage in CuInSe2 and CdTe solar cells

    Microsoft Academic Search

    R. A. Sasala; J. R. Sites

    1993-01-01

    The open circuit voltage of CuInSe2 and CdTe solar cells continues to increase during the time range of 10-3 to 104 s after the cell is illuminated or otherwise placed in forward bias. The effect is qualitatively similar in all samples measured to date, however, the magnitude of the voltage shift varies from 3 to 40 mV. The shift increases

  18. ZnSe\\/ZnTe(shell\\/shell) radial quantum-wire heterostructures: the excitonic properties

    Microsoft Academic Search

    Mehran Bagheri

    2010-01-01

    The ground-state characteristics of spatially indirect excitons trapped in radially heteronanostructured type-II band alignment ZnSe\\/ZnTe nanotubes as functions of the magnetic field for nanotubes with a radial size both smaller and larger than the effective Bohr radius are theoretically investigated. In the former case, dominated by the net kinetic energy of the electron and hole, the magnetic field modifies the

  19. Write-erase characteristics of phase change optical recording in Ga-Se-Te systems

    Microsoft Academic Search

    Jung Chul Rhee; Masahiro Okuda; Tatsushiko Matsushita

    1987-01-01

    Reversible optical changes in the thin-film system parylene\\/Te-Ga-Se film\\/parylene have been studied by measuring the time required to crystallize from the amorphous state (the erasing time) and the number of reversible reflectance changes occurring between amorphous (written) and crystalline (erased) states. For a specimen with a Ga content of 0.15, the erasing time is about 1 microsecond. From a discussion

  20. (Bi,Sb) 2(Te,Se) 3-based thin film thermoelectric generators

    Microsoft Academic Search

    Il-Ho Kim

    2000-01-01

    Microwatt power at relatively high voltage (order of volt) was produced by (Bi,Sb)2(Te,Se)3-based thin film thermoelectric generators (TFTEGs). The generators were composed of several layers of plate-modules. Each plate-module contained 15 p\\/n couples and was connected electrically in series or in parallel. Maximum output power varied with the square of the temperature difference. Output voltage and current were controlled by

  1. Large bulk resistivity and surface quantum oscillations in the topological insulator Bi2Te2Se

    Microsoft Academic Search

    Zhi Ren; A. A. Taskin; Satoshi Sasaki; Kouji Segawa; Yoichi Ando

    2010-01-01

    Topological insulators are predicted to present interesting surface transport phenomena but their experimental studies have been hindered by a metallic bulk conduction that overwhelms the surface transport. We show that the topological insulator Bi2Te2Se presents a high resistivity exceeding 1Omegacm and a variable-range hopping behavior, and yet presents Shubnikov-de Haas oscillations coming from the topological surface state. Furthermore, we have

  2. Vapour-liquid-solid growth of ternary Bi2Se2Te nanowires

    PubMed Central

    2014-01-01

    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. PMID:24641967

  3. Luminescent CdTe and CdSe semiconductor nanocrystals: preparation, optical properties and applications.

    PubMed

    Wang, Ying

    2008-03-01

    The novel optical and electrical properties of luminescent semiconductor nanocrystals are appealing for ultrasensitive multiplexing and multicolor applications in a variety of fields, such as biotechnology, nanoscale electronics, and opto-electronics. Luminescent CdSe and CdTe nanocrystals are archetypes for this dynamic research area and have gained interest from diverse research communities. In this review, we first describe the advances in preparation of size- and shape-controlled CdSe and CdTe semiconductor nanocrystals with the organometallic approach. This article gives particular focus to water soluble nanocrystals due to the increasing interest of using semiconductor nanocrystals for biological applications. Post-synthetic methods to obtain water solubility, the direct synthesis routes in aqueous medium, and the strategies to improve the photoluminescence efficiency in both organic and aqueous phase are discussed. The shape evolution in aqueous medium via self-organization of preformed nanoparticles is a versatile and powerful method for production of nanocrystals with different geometries, and some recent advances in this field are presented with a qualitative discussion on the mechanism. Some examples of CdSe and CdTe nanocrystals that have been applied successfully to problems in biosensing and bioimaging are introduced, which may profoundly impact biological and biomedical research. Finally we present the research on the use of luminescent semiconductor nanocrystals for construction of light emitting diodes, solar cells, and chemical sensors, which demonstrate that they are promising building blocks for next generation electronics. PMID:18468108

  4. Quasiparticle band structures of ?-HgS, HgSe, and HgTe

    NASA Astrophysics Data System (ADS)

    Svane, A.; Christensen, N. E.; Cardona, M.; Chantis, A. N.; van Schilfgaarde, M.; Kotani, T.

    2011-11-01

    The electronic structures of mercury chalcogenides in the zinc-blende structure have been calculated within the LDA, GW (G0W0, “one-shot”) and quasi-particle self-consistent GW (QSGW) approximations, including spin-orbit (SO) coupling. The slight tendency to overestimation of band gaps by QSGW is avoided by using a hybridscheme (20% LDA and 80% QSGW). The details of the GW bands near the top of the valence bands differ significantly from the predictions obtained by calculations within the LDA. The results obtained by G0W0 depend strongly on the starting wave functions and are thus quite different from those obtained from QSGW. Within QSGW, HgS is found to be a semiconductor, with a ?6 s-like conduction-band minimum state above the valence top ?7 and ?8 (“negative” SO splitting). HgSe and HgTe have negative gaps (inverted band structures), but for HgTe the ?7 state is below ?6 due to the large Te SO splitting, in contrast to HgSe where ?6 is below ?7. There appears to be significant differences, in particular for HgSe and HgS, between the ordering of the band-edge states as obtained from experiments and theory.

  5. 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.

  6. Tunable Intrinsic Spin Hall Conductivities in Bi2(Se,Te)3 Topological Insulators

    NASA Astrophysics Data System (ADS)

    ?ahin, Cüneyt; Flatté, Michael E.

    2015-03-01

    It has been recently shown by spin-transfer torque measurements that Bi2Se3 exhibits a very large spin Hall conductivity (SHC). It is expected that Bi2Te3, a topological insulator with similar crystal and band structures as well as large spin-orbit coupling, would also exhibit a giant SHC. In this study we have calculated intrinsic spin Hall conductivities of Bi2Se3andBi2Te3 topological insulators from a tight-binding Hamiltonian including two nearest-neighbor interactions. We have calculated the Berry curvature, used the Kubo formula in the static, clean limit and shown that both materials exhibit giant spin Hall conductivities, consistent with the results of Ref. 1 and larger than previously reported Bi1-xSbx alloys. The density of Berry curvature has also been computed from the full Brillouin zone in order to compute the dependence of the SHC in these materials on the Fermi energy. Finally we report the intrinsic SHC for Bi2(Se,Te)3 topological insulators, which changes dramatically with doping or gate voltage. This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  7. 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.

  8. Role of polycrystallinity in CdTe and CuInSe2 photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Sites, J. R.

    1994-07-01

    The report describes the exploration of several aspects of the role of polycrystallinity in the operation of CdTe, CuInSe2, and Cu(In,Ga)Se2 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.

  9. Superconductivity in NiTe2 compounds interspersed with layers of Ti and Cu

    NASA Astrophysics Data System (ADS)

    Santos, Frederico Benedetto; Correa, Lucas Eduardo; Renosto, Sergio Tuan; de Lima, Bruno Sanches; Jardim, Renato De Figueiredo; Torikachvili, Milton; Machado, Antonio Jefferson Da Silva

    2014-03-01

    NiTe2 compound crystallizes in an hexagonal layer structure, CdI2 prototype, where the layers of tellurium are between the layers of nickel and display some anomalies at the resistivity measurements but principally a metal-insulator like transition close to 25 K. In this work we will show that the intercalation of Copper, between Te-Te van der Waals gap displacement the metal-insulator like transition until reach an unusual metal like behavior from 2.0 K to 300 K temperature range. Another hand, Titanium intercalation between Te-Te van der Waals gap is able to induce superconductivity behavior with superconducting critical temperature close to 4.1 K, sustained by resistivity and magnetization measurements.

  10. 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.

  11. 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 ...

  12. Alternative back contacts for CdTe solar cells: a photoemission study of the VSe 2\\/CdTe and TiSe 2\\/CdTe interface formation

    Microsoft Academic Search

    D. Kraft; U. Weiler; Y. Tomm; A. Thissen; A. Klein; W. Jaegermann

    2003-01-01

    Low resistance ohmic and stable back contacts are still one of the major issues in improving CdTe based solar cells. According to band alignment arguments chemically inactive and conductive materials of high work functions are most promising for CdTe back contacts. In this study VSe2\\/CdTe and TiSe2\\/CdTe interfaces have been prepared by PVD under vacuum conditions and subsequently characterized by

  13. Pulsed Laser Deposition of Epitaxial Topological Insulator Thin Films: Bi2Te3 and Bi2Te2Se

    NASA Astrophysics Data System (ADS)

    Zhang, Shixiong; Yan, Li; Qi, Jingbo; Zhuo, Mujin; Wang, Yongqiang; Prasankumar, Rohit P.; Jia, Quanxi; Picraux, S. Tom

    2012-02-01

    While high quality epitaxial thin films of topological insulators have been achieved by molecular beam epitaxy, there has been little progress using other thin film growth techniques. Here, we report the growth of high quality epitaxial Bi2Te3 and Bi2Te2Se thin films on silicon (111) and YSZ (111) substrates by pulsed laser deposition (PLD). Systematic structural characterization of the films using x-ray diffraction and transmission electron microscopy has demonstrated that a low laser pulse rate is the key to achieving high quality epitaxial films. Rutherford backscattering spectrometry measurements suggest that the film composition is strongly influenced by the growth temperature and background gas pressure. The electrical transport properties of the films grown at the optimal conditions will also be discussed. Since PLD is an excellent tool to grow a variety of functional oxides, including multiferroics, magnetic semiconductors and high temperature superconductors, the growth of epitaxial topological insulator thin films by the same technique paves the way to synthesize multi-layered heterostructures of the above materials and search for novel physics arising from the resulting interfacial couplings.

  14. Enhancing Thermoelectric Performance of PbTe-Based Compounds by Substituting Elements: A First Principles Study

    NASA Astrophysics Data System (ADS)

    Joseph, Elad; Amouyal, Yaron

    2015-06-01

    We investigate the influence of doping on the thermoelectric (TE) properties of PbTe-based compounds applying first principles calculations. Our approach combines a solution of the Boltzmann transport equation to obtain electronic properties with total energy calculations yielding lattice vibrational properties. We show that electrical conductivity increases from 2.71 × 104 S m-1 to 3 × 105 S m-1 at 700 K due to 6.3 at.% lanthanum doping, whereas the Seebeck coefficient decreases from 341.5 ?V K-1 to -52.9 ?V K-1, since La atoms act as electron donors. This trend is accompanied by monotonous reduction of thermal conductivity due to La doping at different levels, e.g., 6.3 at.% La doping significantly affects the elastic bulk properties, resulting in reduction of the average sound velocity from 1980 m s-1 for the pure PbTe-lattice to 1347 m s-1 for the La-doped PbTe lattice, thereby reducing lattice thermal conductivity by ca. 32% at 700 K. We compare the TE performance of different PbTe compounds doped with either La, Y, or Sc, indicating that La doping yields the highest power factor. We demonstrate how this method could be utilized for dopant selection oriented toward improving TE performance.

  15. Structural, electrical and optical properties of Bi{sub 2}Se{sub 3} and Bi{sub 2}Se{sub (3-x)}Te {sub x} thin films

    SciTech Connect

    Augustine, Saji [Crystal Growth Laboratory, Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala, (India) and Materials and Process Simulation Laboratory, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305701 (Korea, Republic of)]. E-mail: sajia@kaist.ac.kr; Ampili, S. [Crystal Growth Laboratory, Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala (India); Kang, Jeung Ku [Materials and Process Simulation Laboratory, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305701 (Korea, Republic of); Mathai, Elizabeth [Crystal Growth Laboratory, Department of Physics, Cochin University of Science and Technology, Cochin 682022, Kerala (India)

    2005-08-11

    Thin films of Bi{sub 2}Se{sub 3}, Bi{sub 2}Se{sub 2.9}Te{sub 0.1}, Bi{sub 2}Se{sub 2.7}Te{sub 0.3} and Bi{sub 2}Se{sub 2.6}Te{sub 0.4} are prepared by compound evaporation. Micro structural, optical and electrical measurements are carried out on these films. X-ray diffraction pattern indicates that the as-prepared films are polycrystalline in nature with exact matching of standard pattern. The composition and morphology are determined using energy dispersive X-ray analysis and scanning electron microscopy (SEM). The optical band gap, which is direct allowed, is 0.67 eV for Bi{sub 2}Se{sub 3} thin films and the activation energy is 53 meV. Tellurium doped thin films also show strong optical absorption corresponding to a band gap of 0.70-0.78 eV. Absolute value of electrical conductivity in the case of tellurium doped thin film shows a decreasing trend with respect to parent structure.

  16. London penetration depth and superfluid density in single crystals of Fe(Te,Se) and

    SciTech Connect

    Kim, H.; Martin, C.; Gordon, R.T.; Tanatar, M.A.; Hu, J.; Qian, B.; Mao, Z.Q.; Hu, Rongwei; Petrovic, Cedomir; Salovich, N.; Giannetta, R.; Prozorov, R.

    2010-01-01

    The in-plane London penetration depth, ?(T) , was measured in single crystals of the iron-chalcogenide superconductors Fe{sub 1.03} (Te{sub 0.63} Se{sub 0.37} ) and Fe{sub 1.06} (Te{sub 0.88} S{sub 0.14} ) by using a radio-frequency tunnel diode resonator. Similar to the iron-arsenides and in stark contrast to the iron-phosphides, iron-chalcogenides exhibit a nearly quadratic temperature variation of ?(T) at low temperatures. The absolute value of the penetration depth in the T?0 limit was determined for Fe{sub 1.03} (Te{sub 0.63} Se{sub 0.37} ) by using an Al coating technique, giving ?(0)?560±20?nm . The superfluid density ?{sub s} (T)=?{sup 2} (0)/?{sup 2} (T) was fitted with a self-consistent two-gap ? model. While two different gaps are needed to describe the full-range temperature variation in ?{sub s} (T) , a nonexponential low-temperature behavior requires pair-breaking scattering, and therefore an unconventional (e.g., s{sub ±} or nodal) order parameter.

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

    SciTech Connect

    Zhang, P. [Chinese Academy of Sciences (CAS), Beijing (China); Gu, G. D. [Brookhaven National Lab. (BNL), Upton, NY (United States); Richard, P. [Chinese Academy of Sciences (CAS), Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Xu, N. [Chinese Academy of Sciences (CAS), Beijing (China); Paul Scherrer Inst. (PSI), Villigen (Switzerland); Xu, Y. -M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ma, J. [Chinese Academy of Sciences (CAS), Beijing (China); Qian, T. [Chinese Academy of Sciences (CAS), Beijing (China); Fedorov, A. V. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Denlinger, J. D. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Ding, H. [Chinese Academy of Sciences (CAS), Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)

    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.

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

    PubMed

    Tan, Furui; Qu, Shengchun; Zhang, Weifeng; Wang, Zhanguo

    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

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

    NASA Astrophysics Data System (ADS)

    Tan, Furui; Qu, Shengchun; Zhang, Weifeng; Wang, Zhanguo

    2014-10-01

    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.

  20. Quantum dot sensitized solar cells. A tale of two semiconductor nanocrystals: CdSe and CdTe.

    PubMed

    Bang, Jin Ho; Kamat, Prashant V

    2009-06-23

    CdSe and CdTe nanocrystals are linked to nanostructured TiO2 films using 3-mercaptopropionic acid as a linker molecule for establishing the mechanistic aspects of interfacial charge transfer processes. Both these quantum dots are energetically capable of sensitizing TiO2 films and generating photocurrents in quantum dot solar cells. These two semiconductor nanocrystals exhibit markedly different external quantum efficiencies ( approximately 70% for CdSe and approximately 0.1% for CdTe at 555 nm). Although CdTe with a more favorable conduction band energy (E(CB) = -1.0 V vs NHE) is capable of injecting electrons into TiO2 faster than CdSe (E(CB) = -0.6 V vs NHE), hole scavenging by a sulfide redox couple remains a major bottleneck. The sulfide ions dissolved in aqueous solutions are capable of scavenging photogenerated holes in photoirradiated CdSe system but not in CdTe. The anodic corrosion and exchange of Te with S dominate the charge transfer at the CdTe interface. Factors that dictate the efficiency and photostability of CdSe and CdTe quantum dots are discussed. PMID:19435373

  1. 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 [Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287 (United States); School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Liu Xinyu; Furdyna, Jacek K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Smith, David J. [Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)

    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.

  2. 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.

  3. Intrinsic topological insulator Bi(1.5)Sb(0.5)Te(3-x)Se(x) thin crystals.

    PubMed

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

    2015-01-01

    The quaternary topological insulator (Bi,Sb)2(Te,Se)3 has demonstrated topological surface states with an insulating bulk. Scientists have identified an optimized composition of Bi(1.5)Sb(0.5)Te(1.7)Se(1.3) with the highest resistivity reported. But the physics that drive to this composition remains unclear. Here we report the crystal structure and the magneto-transport properties of Bi(1.5)Sb(0.5)Te(3-x)Se(x) (BSTS) series. A correlation between the structure and the physical properties has been revealed. We found out that within the rhombohedral structure, the composition with most Te substituting Se has the highest resistivity. On the other hand, segregation of other composition phases will introduce much higher bulk concentration. PMID:25604579

  4. ARPES studies on FeTe1-x Se x iron chalcogenides epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Innocenti, Davide; Moreschini, Luca; Chang, Young Jun; Walter, Andrew; Bostwick, Aaron; di Castro, Daniele; Tebano, Antonello; Medaglia, Pier Gianni; Bellingeri, Emilio; Pallecchi, Ilaria; Ferdeghini, Carlo; Balestrino, Giuseppe; Rotenberg, Eli

    2011-03-01

    The physics of iron-based chalcogenides raises fundamental questions on the interplay of magnetic order and electron pairing at the origin of the superconducting state. We have performed angle-resolved photemission spectroscopy (ARPES) studies on high-quality epitaxial thin films of FeTe 1-x Se x , grown by in situ pulsed laser deposition (PLD) on beamline 7.0.1 at the ALS. Specifically, we are able to show the evolution of the band structure as a function of x. We discuss our experimental results in comparison to the available theoretical band calculations.

  5. 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.

  6. Temperature-dependent photovoltaic characterization of a CdTe/CdSe nanocrystal's solar cell

    NASA Astrophysics Data System (ADS)

    Zhang, Huichao; Li, Zhengyang; Qian, Jun; Guan, Qiumei; Du, Xiaowei; Cui, Yiping; Zhang, Jiayu

    2014-03-01

    An all-inorganic thin film solar cell was fabricated with colloidal CdTe and CdSe nanocrystals. Its temperaturedependent photovoltaic characterization was measured, and an open circuit voltage decay technique was used to determine the electron lifetime. The photovoltaic parameters, such as the exact carrier lifetime, were remarkably different between under low-temperature region and under temperature above 267 K. It is suggested that the temperature-dependent carrier conductivity results from a thermally-activated hopping process and this nanocrystals device is a kind of donor-acceptor solar cell.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  8. Electronic properties of intersubband transition in (CdS\\/ZnSe)\\/BeTe quantum wells

    Microsoft Academic Search

    S. Abdi-Ben Nasrallah; N. Sfina; M. Said

    2005-01-01

    In view of the fact that the bandwidth required in optical fiber \\u000acommunication systems will exceed 100 Gb?s-1, ultrafast optical \\u000aswitching and modulation devices with high efficiency must be developed. \\u000aGiven that intersubband transitions (ISBT) in quantum wells (QWs) are one of \\u000athe important ultrafast phenomena, a numerical study of intersubband \\u000atransition (ISBT) properties in (CdS\\/ZnSe)\\/BeTe QWs is considered. The \\u000astructure

  9. Band-overlap metallization of BaS, BaSe and BaTe

    NASA Technical Reports Server (NTRS)

    Carlsson, A. E.; Wilkins, J. W.

    1983-01-01

    The insulator-metal transition volumes for BaS, BaSe, and BaTe are calculated for the first time, using the self-consistent augmented spherical wave technique. The metallized transition volumes are smaller than those corresponding to the NaCl yields CsCl structural transitions, but, 10 to 15% larger than those obtained by the Herzfeld dielectric theory. The calculated equilibrium energy gaps in the NaCl structure underestimate the measured ones by 50 to 60%.

  10. Hydrogenation of undoped and nitrogen doped CdTe and ZnSe grown by molecular beam epitaxy

    SciTech Connect

    Hirsch, L.S.; Setzler, S.D.; Ptak, A.J.; Giles, N.C.; Myers, T.H. [West Virginia Univ., Morgantown, WV (United States). Physics Dept.

    1998-12-31

    Hydrogen incorporation in both undoped and nitrogen-doped CdTe and ZnSe is investigated. Evidence for a strong nitrogen-hydrogen interaction is presented. Preliminary data indicate that the growth of CdTe and ZnSe under an atomic hydrogen flux results in a significant concentration of paramagnetic defects possibly accompanied by enhanced auto-doping from residual impurities.

  11. Phonon properties of BaFe?X? (X=S, Se) spin ladder compounds

    DOE PAGESBeta

    Popovicq, Z. V.; Petrovic, C.; Scepanovic, M.; Lazarevic, N.; Opacic, M.; Radonjic, M. M.; Tanaskovic, D.; Lei, Hechang

    2015-02-01

    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

  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. Hydrothermal synthesis of high-quality thiol-stabilized CdTe(x)Se(1-x) alloyed quantum dots.

    PubMed

    Yang, Fanghong; Yang, Ping; Cao, Yongqiang

    2013-11-01

    Alloyed semiconductor quantum dots (QDs) enriched the synthetic routes for engineering materials with unique structural and optical properties. High-quality thiol-stabilized CdTe(x)Se(1-x) alloyed QDs were synthesized through a facile and economic hydrothermal method at 120 °C, a relatively low temperature. These water-soluble QDs were prepared using different capping agents including 3-mercaptopropionic acid (MPA) and L-cysteine (L-Cys). The photoluminescence (PL) intensity and stability of L-Cys-capped CdTe(x)Se(1-x) QDs were found to be higher than that of MPA-stabilized ones. The molar ratios of Se-to-Te upon preparation were adjusted for investigating the effect of composition on the properties of the resulting QDs. We also investigated the effect of the pH value of the reaction solution on the growth kinetics of the alloyed CdTe(x)Se(1-x) QDs. The resulting CdTe(x)Se(1-x) QDs were characterized by UV-vis absorbance and PL spectroscopy, powder X-ray diffraction, and transmission electron microscopy. Being coated with a CdS inorganic shell, the PL intensity and stability of the CdTe(x)Se(1-x)/CdS core-shell QDs were drastically enhanced, accompanied by the red-shift of the PL peak wavelength. Owing to the unique optical properties, the QDs hold great potential for application and have to be further exploited. PMID:23873206

  14. Ternary phase relations of the chalcopyrite compound CuGaSe 2

    Microsoft Academic Search

    J. C. Mikkelsen

    1981-01-01

    The ternary Cu-Ga-Se phase diagram has been determined by DTA and x-ray analysis. In addition to two ternary solid solutions\\u000a based on the binary compounds Cu2.xSe and Ga2Se3, only one ternary phase, the chalcopyrite CuGaSe2 (peritectic m.p. 1030°C), was encountered. The liquidus contains two regions of liquid immiscibility, one which extends from\\u000a the Cu-rich (Cu, Se) binary liquid immiscibility to

  15. Ternary phase relations of the chalcopyrite compound CuGaSe2

    NASA Astrophysics Data System (ADS)

    Mikkelsen, J. C.

    1981-05-01

    The ternary Cu-Ga-Se phase diagram has been determined by DTA and x-ray analysis. In addition to two ternary solid solutions based on the binary compounds Cu2.xSe and Ga2Se3, only one ternary phase, the chalcopyrite CuGaSe2 (peritectic m.p. 1030°C), was encountered. The liquidus contains two regions of liquid immiscibility, one which extends from the Cu-rich (Cu, Se) binary liquid immiscibility to the Ga-rich (Ga, Se) binary immiscibility, and the other which is a minor extension of the Se-rich (Cu, Se) binary liquid immiscibility. The liquidus maxima include those at the binary boundaries: Cu (1087°C), Cu67Se33 (1148°C), GaSe (960°C); and a ternary liquidus maximum at Cu19Ga28.5Se52.5 (1112°C), the maximum melting point of a solid solution based on the defect-zincblende phase of Ga2Se3. The primary phase fields are identified and the crystal growth of CuGaSe2 solid solutions from nonstoichiometric melts is discussed, especially the most satisfactory Bridgman growth from the Cu2Se-CuGaSe2 join. Subsolidus phase relations are also proposed for the Cu-Ga-Se system, and probable similaritics in all I-III-VI ternary diagrams are suggested.

  16. 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

  17. Determination of bound-electronic and free-carrier nonlinearities in ZnSe, GaAs, CdTe, and ZnTe

    Microsoft Academic Search

    A. A. Said; Mansoor Sheik-Bahae; David J. Hagan; T. H. Wei; J. Wang; James Young; Eric W. van Stryland

    1992-01-01

    Received May 30, 1991; revised manuscript received August 30, 1991 We extend the application of the Z-scan experimental technique to determine free-carrier nonlinearities in the presence of bound electronic refraction and two-photon absorption. We employ this method, using picosecond pulses in CdTe, GaAs, and ZnTe at 1.06 m and in ZnSe at 1.06 and 0.53 Am, to measure the refractive-index

  18. The structural and optical properties of high quality ZnTe grown on GaAs using ZnSe\\/ZnTe strained superlattices buffer layer

    Microsoft Academic Search

    R. C. Tu; Y. K. Su; H. J. Chen; Y. S. Huang; S. T. Chou; W. H. Lan; S. L. Tu

    1998-01-01

    This work studied the structural and optical properties of ZnTe epilayers grown on GaAs substrates with ZnSe\\/ZnTe strained superlattices buffer layers. Material properties were characterized using cross-sectional transmission electron microscopy, photoluminescence (PL), contactless electroreflectance (CER), and piezoreflectance (PzR). PL spectra clearly distinguished the strong free exciton peaks, weak donor-acceptor pair, Y lines, and oxygen-bound exciton peaks, indicating the high quality

  19. Effect of Sb additive on structural and optical properties of Se-Te-Sb thin films

    NASA Astrophysics Data System (ADS)

    Abdel-Rahim, M. A.; Hafiz, M. M.; Mahmoud, A. Z.

    2015-03-01

    Amorphous Se85- x Te15Sb x ( x = 2.5, 5 and 7.5 at.%) thin films were deposited on glass substrates by thermal evaporation. The absorption coefficient was determined from the transmittance, and reflectance spectra in the wavelength range 400-2500 nm. Various optical constants have been calculated for the studied compositions. The mechanism of the optical absorption follows the rule of non-direct transition. It was found that the optical energy gap, E g, decreases from 1.42 to 1.36 eV with increasing Sb content from 2.5 to 7.5 at.%. These results can be interpreted on the basis of the chemical bond approach proposed by Bicermo and Ovshinsky. On the other hand, the optical constants such as refractive index, n, and extinction coefficient, K ex, of the films were studied. The dispersion of the refractive index was discussed in terms of single-oscillator Wemple-DiDomenico model. The influence of Sb content on the structure for the annealed films was investigated using X-ray diffraction (XRD) and scanning electron microscopy. The average particle size of the crystalline size for Te0.04Se0.96 phase deduced from XRD pattern. This average decreases with increasing Sb content.

  20. 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.

  1. PHYSICAL REVIEW B 84, 205205 (2011) Quasiparticle band structures of -HgS, HgSe, and HgTe

    E-print Network

    Svane, Axel Torstein

    2011-01-01

    PHYSICAL REVIEW B 84, 205205 (2011) Quasiparticle band structures of -HgS, HgSe, and HgTe A. Svane functions and are thus quite different from those obtained from QSGW. Within QSGW, HgS is found to be significant differences, in particular for HgSe and HgS, between the ordering of the band-edge states

  2. The electronic structure of quasi-free-standing germanene on monolayer MX (M = Ga, In; X = S, Se, Te).

    PubMed

    Ni, Zeyuan; Minamitani, Emi; Ando, Yasunobu; Watanabe, Satoshi

    2015-07-15

    For the first time by using the ab initio density functional theory, the stability and electronic structures of germanene on monolayer GaS, GaSe, GaTe and InSe have been investigated. Germanene preserves its buckled-honeycomb structure on all the studied substrates similar to the free-standing case. Moreover, germanene stays neutral and preserves its Dirac-cone-like band structure on monolayer GaTe and InSe. In these two cases, a bandgap of 0.14-0.16 eV opens at the Dirac point of germanene, while the effective masses remain as small as 0.05-0.06 times the free-electron mass. The estimated carrier mobility is up to 2.2 × 10(5) cm(2) V(-1) s(-1). These features show that monolayer GaTe and InSe are promising as substrates for germanene devices. PMID:26130303

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

    NASA Astrophysics Data System (ADS)

    Chander, Ravi

    2015-05-01

    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.

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

    SciTech Connect

    Krishnan, Rangarajan [University of Florida; Wood, David [University of Florida; Chaudhari, Vaibhav U. [University of Florida; Payzant, E Andrew [ORNL; Noufi, Rommel [National Renewable Energy Laboratory (NREL); Rozeveld, Steve [Dow Chemical Company, The; Kim, Woo Kyoung [Yeungnam University, Korea; Anderson, Timothy J [University of Florida

    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.

  5. Emission of CdSe/ZnS and CdSeTe/ZnS quantum dots conjugated to IgG antibodies

    NASA Astrophysics Data System (ADS)

    Torchynska, T. V.; Casas Espinola, J. L.; Díaz Cano, A.; Douda, J.; Gazarian, K.

    2013-06-01

    Commercially available CdSe/ZnS QDs with emission at 605 nm (2.04 eV) and 655 nm (1.90 eV), as well as CdSeTe/ZnS QDs with emission at 705 nm (1.78 eV), have been studied by photoluminescence (PL) and Raman scattering methods in nonconjugated states and after the conjugation to immunoglobulin G (rabbit IgG) antibodies. PL spectra of nonconjugated QDs are characterized by one Gaussian shape PL band related to exciton emission in CdSe or CdSeTe cores. In PL spectra of bioconjugated QDs the PL bands shift into the high energy and become asymmetric. The PL spectrum transformation in bioconjugated QDs has been assigned to the QD interaction with the antibody electric charges (dipoles). Raman scattering spectra have been studied with the aim to reveal the CdSeTe core compositions, as well as to analyze the elastic strains in bioconjugated QDs. Optical band gaps in CdSe and CdSeTe cores of nonconjugated QDs is calculated numerically versus core radius using the effective mass approximation model with the aim to estimate the average core sizes in studied QD ensembles. It is shown that the PL energy shift increases versus QD core radius. The mechanism of PL energy shift has been discussed. The PL energy shift in bioconjugated QDs is promising for the study of bioconjugation with specific antibodies and can be a powerful technique in biology and medicine.

  6. Pressure-induced superconductivity in topological parent compound Bi2Te3

    PubMed Central

    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 Bi2Te3 with Tc 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 Bi2Te3 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 Bi2Te3 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

  7. Magnetoresistance and nonlinear Hall effect in quaternary topological insulator Bi1.5Sb0.5Te1.8Se1.2

    NASA Astrophysics Data System (ADS)

    Wang, W.; Zou, W. Q.; He, L.; Peng, J.; Zhang, R.; Wu, X. S.; Zhang, F. M.

    2015-05-01

    The quaternary topological insulator Bi2?xSbxTe3?ySey has exhibited pronounced topological surface states with an insulating bulk. While most transport studies of these compounds are focused on thin flakes peeled from bulk crystals, we carefully analyzed the magneto transport properties of bulk Bi1.5Sb0.5Te1.8Se1.2. We have observed weak anti-localization (WAL) and nonlinear Hall effects at low temperatures. Using a multi-channel model, we decomposed the total conductance into three conducting channels of the bulk, impurity band and surface states at various temperatures. The conductance of the surface states is almost constant in the whole temperature range, and contributes about 19.1% in the total conductance at 1.9?K.

  8. 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

  9. Surface optical and bulk acoustic phonons in the topological insulator, Bi2Se2Te

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Uditendu; Chaudhuri, Dipanjan; Sarkar, Jit; Singh, Sourabh; Gopal, Radha Krishna; Tammu, Sandeep; Upadhya, Prashanth C.; Mitra, Chiranjib

    2015-06-01

    We explore the phonon dynamics in thin films of the topological insulator material Bi2Se2Te using ultrafast pump-probe spectroscopy. The time resolved differential reflectivity in these films exhibit fast and slow oscillations. We have given a careful analysis of variation of phonon frequency as a function of film thickness, which we attribute to the existence of standing acoustic modes. However, no variation in the frequency of the optical phonon modes was found with film thickness. This indicates that the optical phonons intrinsically belong to the surface of topological insulators. The controllability of acoustic phonons by way of varying the film thickness will have tremendous implications in the application of these materials in low power spintronic device operating at room temperature.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  12. Engineering Topological Surface States: HgS, HgSe, and HgTe

    NASA Astrophysics Data System (ADS)

    Virot, François; Hayn, Roland; Richter, Manuel; van den Brink, Jeroen

    2013-10-01

    Using density functional electronic structure calculations, we establish the consequences of surface termination and modification on protected surface states of metacinnabar (?-HgS). Whereas we find that the Dirac cone is isotropic and well separated from the valence band for the (110) surface, it is highly anisotropic at the pure (001) surface. We demonstrate that the anisotropy is modified by surface passivation because the topological surface states include contributions from dangling bonds. Such dangling bonds exist on all pure surfaces within the whole class HgX with X=S, Se, or Te and directly affect the properties of the Dirac cone. Surface modifications also alter the spatial location (depth and decay length) of the topologically protected edge states, which renders them essential for the interpretation of photoemission data.

  13. 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.

  14. Weak-antilocalization and surface dominated transport in topological insulator Bi2Se2Te

    NASA Astrophysics Data System (ADS)

    Gopal, Radha Krishna; Singh, Sourabh; Chandra, Ramesh; Mitra, Chiranjib

    2015-04-01

    We explore the phase coherence of thin films of the topological insulator material Bi2Se2Te grown through pulsed laser deposition (PLD) technique. The films were characterised using various techniques for phase and composition. The films were found to be of good quality. We carried out extensive magneto-transport studies of these films and found that they exhibit two dimensional weak antilocalization behaviour. A careful analysis revealed a relatively high phase coherence length (58nm at 1.78K) for a PLD grown film. Since PLD is an inexpensive technique, with the possibility to integrate with other materials, one can make devices which can be extremely useful for low power spintronics and topological quantum computation.

  15. 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.

  16. Structural and optical properties of ZnSe x Te1- -x solid solutions in thin-film form

    NASA Astrophysics Data System (ADS)

    El-Nahass, M. M.; Khalifa, B. A.; El-Rahman, A. M. Abd; El-Ariny, R.

    1996-06-01

    Solid solutions of ZnSe x Te 1-x (0.1? x?1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc blende structure. The calculated unit cell lattice constant ( a) for the different compositions in powder form vary linearly, with molecular fraction x following Vegard’s law: a( x)=6.165-0.485 x. Thin films of ZnSe x Te 1-x (0.1? x?1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10-4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe x Te 1-x polycrystalline films of different compositions have two direct transitions with corresponding energy gaps E g and E g+?SO The variations in both E g and E g+?SO with x indicate that ZnSe x Te 1-x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.

  17. Accuracy of existing atomic potentials for the CdTe semiconductor compound.

    PubMed

    Ward, D K; Zhou, X W; Wong, B M; Doty, F P; Zimmerman, J A

    2011-06-28

    CdTe and CdTe-based Cd(1-x)Zn(x)Te (CZT) alloys are important semiconductor compounds that are used in a variety of technologies including solar cells, radiation detectors, and medical imaging devices. Performance of such systems, however, is limited due to the propensity of nano- and micro-scale defects that form during crystal growth and manufacturing processes. Molecular dynamics simulations offer an effective approach to study the formation and interaction of atomic scale defects in these crystals, and provide insight on how to minimize their concentrations. The success of such a modeling effort relies on the accuracy and transferability of the underlying interatomic potential used in simulations. Such a potential must not only predict a correct trend of structures and energies of a variety of elemental and compound lattices, defects, and surfaces but also capture correct melting behavior and should be capable of simulating crystalline growth during vapor deposition as these processes sample a variety of local configurations. In this paper, we perform a detailed evaluation of the performance of two literature potentials for CdTe, one having the Stillinger-Weber form and the other possessing the Tersoff form. We examine simulations of structures and the corresponding energies of a variety of elemental and compound lattices, defects, and surfaces compared to those obtained from ab initio calculations and experiments. We also perform melting temperature calculations and vapor deposition simulations. Our calculations show that the Stillinger-Weber parameterization produces the correct lowest energy structure. This potential, however, is not sufficiently transferrable for defect studies. Origins of the problems of these potentials are discussed and insights leading to the development of a more transferrable potential suitable for molecular dynamics simulations of defects in CdTe crystals are provided. PMID:21721653

  18. Logical se ttings for conce pt le arning from incomple te e xample s in First Orde r D. Bouthinon

    E-print Network

    Paris-Sud XI, Université de

    d he re by ide as pre se nte d by H. Hirsh in a work e xte nding the Ve rsion space inductive que nce s. In this proble m the data pre se nte d an e xtre me form of incomple te ne ss be the re al one . A frame work addre ssing such a situation has be e n pre se nte d in [Bouthinon

  19. The metal-rich palladium chalcogenides Pd 2MCh2 ( M=Fe, Co, Ni; Ch=Se, Te): Crystal structure and topology of the electron density

    NASA Astrophysics Data System (ADS)

    Pocha, Regina; Löhnert, Catrin; Johrendt, Dirk

    2007-01-01

    Crystals of Pd 2MCh2 ( M=Fe, Co, Ni; Ch=Se, Te) were synthesized by heating the elements at 823-1323 K in silica ampoules under argon atmosphere. Their structures were determined by single-crystal X-ray diffraction at room temperature. The metallic compounds crystallize in a variant of the K 2ZnO 2 type ( Ibam, Z=4, Pd 2CoSe 2: a=5.993(1), b=10.493(2), c=5.003(1) Å; Pd 2FeSe 2: a=5.960(1), b=10.576(2), c=5.078(1) Å; Pd 2CoTe 2: a=6.305(1), b=11.100(2), c=5.234(1) Å; Pd 2NiTe 2: a=6.286(1), b=11.194(2), c=5.157(1) Å). One-dimensional ?1[MCh] tetrahedra chains with remarkably short M— M bonds run along [001], separated by [Pd 2] dumbbells with palladium in fivefold coordination of selenium or tellurium atoms. The structure may also be described as a filled variant of the SiS 2 type. M atoms occupy {1}/{4} of the tetrahedral voids and the Pd atoms fill all octahedral voids in a distorted ccp motif of chalcogen atoms. Even though the Pd 2MCh2 compounds are isotypic to K 2ZnO 2 from the crystallographic viewpoint, we find a different bonding situation with additional homo- and heteronuclear metal-metal bonds between the Pd and Co atoms. The electronic structures and topologies of the electron densities of Pd 2CoSe 2 and isotypic Na 2CoSe 2 are analyzed and compared by using Bader's AIM theory. Different values of topological charge transfer and electron density flatness indices uncover striking quantitative differences in the nature of chemical bonding between the metallic compound Pd 2CoSe 2 and nonmetallic Na 2CoSe 2.

  20. Thermal annealing dependence of the optical and electrical properties of amorphous Se79Te15Sb6 thin films

    NASA Astrophysics Data System (ADS)

    Soltan, A. S.

    2005-01-01

    Glassy substrates Se79Te15Sb6 thin films are thermally evaporated onto chemically cleaned glass. Optical absorption measurements are carried out on as-deposited and thermal annealed Se79Te15Sb6 films. It is found that the mechanism of the optical absorption follows the rule of non-direct transition. The annealed Se79Te15Sb6 films show an increase in the optical energy gap with increasing temperature of annealing higher than the glass transition temperature (363 K). The electrical conductivity of the as-deposited and annealed films is found to be of Arrhenius type with temperature in the range 300 360 K. The effect of thermal annealing on the activation energy for conduction is also studied. The results are discussed on the basis of amorphous crystalline transformations.

  1. Influence of thickness on optical properties of a-(Se80Te20)96Ag4 thin films

    NASA Astrophysics Data System (ADS)

    Singh, D.; Kumar, S.; Thangaraj, R.; Sathiaraj, T. S.

    2013-01-01

    Bulk sample of (Se80Te20)96Ag4 was prepared by quenching technique. Thin films of (Se80Te20)96Ag4 glasses of different thickness (500-950 nm) were deposited on dry clean glass substrates by thermal evaporation technique. Energy dispersive X-ray spectroscopy (EDX) indicates that samples are nearly stoichiometric. X-ray diffraction patterns indicate that they are in the amorphous state. The optical constants, refractive index, absorption index, and optical band gap have been calculated from transmittance and reflectance data in spectral range of 400-2500 nm. It has been found that the optical band gap decreases, but the refractive index, extinction coefficient, optical conductivity, real and imaginary dielectric constant increase with increase in thickness of (Se80Te20)96Ag4 thin films. The results are discussed on the basis of rearrangements of defects and disorders in the chalcogenide systems.

  2. Ultrafast saturable absorption in topological insulator Bi2SeTe2 nanosheets.

    PubMed

    Zhang, Hang; He, Xin; Lin, Wei; Wei, Rongfei; Zhang, Fangteng; Du, Xi; Dong, Guoping; Qiu, Jianrong

    2015-05-18

    Topological insulator (TI) Bi2SeTe2 nanosheets with very regular hexagonal morphology were synthesized by a hydrothermal route. Open aperture (OA) z-scan method was performed to measure the saturable absorption (SA) characteristics of the as-prepared TI Bi2SeTe2 nanosheets. The measured modulation depth, saturation intensity and nonsaturable loss of the sample were 61.9%, 4.46 GW/cm2 and 4.5% respectively. An ultrafast intraband scattering time of ~50 fs was obtained through simulating the SA curve, which indicates the TI Bi2SeTe2 nanosheets may be a good candidate for mode-locking material. PMID:26074587

  3. 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.

  4. Layer-by-layer assembly of sintered CdSe(x)Te1-x nanocrystal solar cells.

    PubMed

    MacDonald, Brandon I; Martucci, Alessandro; Rubanov, Sergey; Watkins, Scott E; Mulvaney, Paul; Jasieniak, Jacek J

    2012-07-24

    Alloying is a versatile tool for engineering the optical and electronic properties of materials. Here, we explore the use of CdTe and CdSe nanocrystals in developing sintered CdSe(x)Te(1-x) alloys as bandgap tunable, light-absorbing layers for solution-processed solar cells. Using a layer-by-layer approach, we incorporate such alloyed materials into single- and graded-composition device architectures. Nanostructured solar cells employing CdSe(x)Te(1-x) layers are found to exhibit a spectral response deeper into the IR region than bulk CdTe devices as a result of optical bowing and achieve power conversion efficiencies as high as 7.1%. The versatility of the layer-by-layer approach is highlighted through the fabrication of compositionally graded solar cells in which the [Se]:[Te] ratio is varied across the device. Each of the individual layers can be clearly resolved through cross-sectional imaging and show limited interdiffusion. Such devices demonstrate the importance of band-alignment in the development of highly efficient, nanostructured solar cells. PMID:22690798

  5. A new n-type and improved p-type pseudo-ternary (Bi2Te 3)(Sb2Te3)(Sb2Se3 ) alloy for Peltier cooling

    Microsoft Academic Search

    M. H. Ettenberg; W. A. Jesser; F. D. Rosi

    1996-01-01

    The pseudo-ternary alloy of (Bi2Te3)(Sb2Te3)(Sb2 Se3) has been explored for over twenty-five years with little progress in the figure of merit, p-type 3.4×10-3\\/K and n-type 3.2×10-3\\/K. Using multiple dopants, Te and SbI3, higher figure of merit material can be achieved without creating more of the deleterious pure Te commonly found as a second phase in the p-type alloy, (Bi2Te3)25(Sb2Te3 )72(Sb2Se3)3.

  6. Effects of annealing on crystallization process in amorphous Ge 5Se 95- xTe x thin films

    NASA Astrophysics Data System (ADS)

    Khan, Shamshad A.; Zulfequar, M.; Husain, M.

    2002-11-01

    Amorphous Ge 5Se 95- xTe x (where x=0, 2, 5 and 10) thin films deposited by thermal evaporation were annealed at different temperatures below their crystallization temperatures for 2 h. The optical band gap has been studied of as-deposited and annealed films as a function of photon energy in the wave length range (400-900 nm). It has been found that the optical band gap increases with increasing annealing temperatures and on Te concentration in the present system. For as-deposited films: it has been found that refractive index ( n) and the extinction coefficient ( k) increases on incorporation of tellurium in Ge-Se system.

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

    NASA Astrophysics Data System (ADS)

    Cheng, Wei; Ren, Shang-Fen

    2011-03-01

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

  8. 2D Lowest Landau Level Scaling in FeTe0.5Se0.5

    NASA Astrophysics Data System (ADS)

    Pandya, Swati; Chandra, L. S. Sharath; Sherif, Siya; Ganesan, V.

    2011-07-01

    Magneto resistivity of FeSe0.5Te0.5 is investigated. Zero field resistivity shows onset of superconductivity at ˜14 K. Zero field and magnetic field induced fluctuation conductivity has been analyzed in light of Aslamozov-Larkin (AL) and Lowest Landau Level (LLL) theories. Zero field fluctuation conductivity shows 2D nature in a narrow temperature range just above the mean field TC, which is further supported by 2D LLL scaling observed for applied fields larger than ˜8 T for FeTe0.5Se0.5.

  9. Effect of thermal annealing on structure and optical band gap of Se66Te25In9 thin films

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    Thin films of a-Se66Te25In9 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 (Eg) of a-Se66Te25In9 have been studied.

  10. A comparison of the superconducting states of Ta4 Pd3 Te16 and Nb3 PdxSe7

    NASA Astrophysics Data System (ADS)

    Zhang, Qiu Run; Zeng, Bin; Rhodes, Daniel; Balicas, Luis

    2015-03-01

    We have measured the superconducting upper critical fields of a Ta4Pd3Te16 sample and a Nb3PdxSe7 sample with very close values of Tc. The Maki parameter of Ta4Pd3Te16(Hc2 (T --> 0 K) ~ 5 . 5 T) is small and hence it is an orbital limited system. However, Hc 2 shows an unconventional linear T dependence in the whole temperature range. Even though they have similar crystalline structures, the upper critical fields of Nb3PdxSe7 are extremely high (Hc 2 (T --> 0 K) ~ 25 T) and much more anisotropic.

  11. Effect of branching of tetrapod-shaped CdTe/CdSe nanocrystal heterostructures on their luminescence

    NASA Astrophysics Data System (ADS)

    Vitukhnovsky, A. G.; Shul'ga, A. S.; Ambrozevich, S. A.; Khokhlov, E. M.; Vasiliev, R. B.; Dirin, D. N.; Yudson, V. I.

    2009-06-01

    We have studied the CdTe/CdSe tetrapod-shaped nanocrystal heterostructures with the use of photoluminescence spectra measurements and time-correlated single photon counting technique. The tetrapods were grown to have CdTe arms with different thickness of the CdSe shell. We have observed non-exponential photoluminescence decay of excited tetrapod-nanocrystals and proposed kinetic theory based on the branched crystal morphology and on the assumption about a potential barrier in the junction point of tetrapod. Analysis of studied nanocrystal behavior gives an evidence for tetrapods to behave as four weakly connected quantum wells. This interesting effect might find applications in nanoelectronics.

  12. Structure and Chemistry of SeFx(CN)4-x Compounds.

    PubMed

    Fritz, Stefanie; Ehm, Christian; Lentz, Dieter

    2015-06-01

    Several new SeF2(CN)2-donor complexes with N or O based donor molecules are reported. Due to orbital overlap effects 12-crown-4 (1,4,7,10-tetraoxacyclododecane) shows unsymmetric ether oxygen coordination. Solvent coordination (secondary bonding interactions, SBI) in SeFx(CN)4-x compounds is weak and does not influence decomposition pathways (neutral and anionic). Barriers for decomposition are relatively high in SeF2(CN)2 but decrease significantly in compounds with higher cyanide content. In the presence of fluoride ions, facile substitution pathways exist; however, reductive elimination is also favored. In the absence of fluoride ions decomposition barriers are higher, but so are substitution barriers (?-metathesis). Therefore, successful isolation of Se(CN)4 appears to be significantly hampered. In addition, previously unknown trifluoromethyliminoseleniumdifluoride was cleanly synthesized utilizing the instability of SeF(CN)3 toward reductive FCN elimination (preferred over the thermodynamically favored NCCN elimination) and subsequent FCN incorporation to SeF4 through double F-migration. PMID:25964983

  13. Single crystals of ZnSe(1-x)Te(x), Zn(1-x)Cd(x)Se, Zn(x)Cd(1-x)S solid solutions for lasers with electron-beam pumping

    NASA Astrophysics Data System (ADS)

    Akhekyan, A. M.; Kozlovskiy, V. I.; Korostelin, Yu. V.; Nasibov, A. S.; Popov, Yu. M.; Shapkin, P. V.

    1986-05-01

    Blue lasers are now produced with ZnSe single crystals (450 nm wavelength) grown from the vapor phase, or epitaxially from organo-element compounds, or from the melt after additional high-temperature annealing in liquid zinc. Increasing the laser power above 3 W, with liquid-nitrogen cooling, to match the eye sensitivity at this wavelength requires larger single crystals and better electron-beam scanning. As a practical alternative, shifting the radiation wavelength into the 470-480 nm band, where the eye sensitivity is much better, has been considered. Raising the temperature of a ZnSe single crystal to room level will, however, either lower its emission power or shorten its life. Another solution to the problem is sought in replacement of ZnSe with ternary compounds ZnSe(1-x)Te(x), Zn(1-x)Cd(x)Se, Zn(x)Cd(1-x)S or certain quaternary ones. Single crystals of those ternary compounds were successfully grown from the gaseous phase on seeding substrates in a sealed crucible inside an electric resistance furnace, ingots 30-50 mm in diameter and up to 50 mm high after 80 hours of pulling. Their cathodoluminescence spectra were measured and compared with those of ZnSe single crystals, all specimens being cooled with liquid nitrogen while pumped with 50 keV electrons electrons at current densities from 10(-5) to 200 A/cm(2). Specimens of each kind were used as active laser medium, with a resonator formed by a 40 micron thick semiconductor wafer with an opaque coating (92% reflection) facing the electron beam for longitudinal pumping on one side and an semitransparent 6-layer interference coating (93% reflection) on the opposite side. A comparative evaluation of their performance characteristics indicates that the ZnSe(1-x)Te(x) group is unsuitable, because the emission line shifts fast toward shorter wavelengths while the longer-wave radiation saturates fast, hypothetically owing to formation of a deep level above the valence band. It also indicates that the performance of the Zn(1-x)Cd(x)Se group will not be significantly improved by increasing x, but hopefully by high-temperature annealing.

  14. First-principle study of structural, electronic and elastic properties of SrS, SrSe and SrTe under pressure

    NASA Astrophysics Data System (ADS)

    Khenata, R.; Baltache, H.; Rérat, M.; Driz, M.; Sahnoun, M.; Bouhafs, B.; Abbar, B.

    2003-12-01

    The full-potential linearized augmented plane wave method (FP-LAPW) within the generalized gradient approximation (GGA) is used to calculate the electronic band structures and the total energies of SrS, SrSe and SrTe in NaCl- and CsCl-type structures. The latter provide us with the ground state properties such as lattice parameter, bulk modulus and its pressure derivative, elastic constants and the structural phase stability of these compounds. The transition pressures at which these compounds undergo structural phase transition from NaCl to CsCl phase are calculated. The energy band gaps at room conditions in NaCl structure and volume dependence of the band gaps in the CsCl structure are presented. The pressure and volume at which band overlap metallization occurs are also determined. The ground state properties, the transition and metallization pressures (volumes) are found to agree with the experimental and other theoretical results. The elastic constants at room conditions in both NaCl and CsCl structures are calculated and compared with the available theoretical results for SrSe while, for SrS and SrTe, the elastic constants are not available.

  15. Secondary overprinting of S-Se-Te signatures in the Earth's mantle: Implications for the Late Veneer

    NASA Astrophysics Data System (ADS)

    Koenig, S.; Luguet, A.; Lorand, J.; Pearson, D.

    2013-12-01

    Sulphur, Selenium and Tellurium are both chalcophile and highly siderophile elements (HSE) with near-chondritic ratios and absolute abundances in the terrestrial mantle that exceed those predicted by core-mantle differentiation[1]. These 'excess' HSE abundances have been attributed to addition of ca. 0.5% of chondrite-like material that hit the Earth in its accretionary stage between 4 to 3.8 billion years ago after core-mantle differentiation (Late Veneer[2]). Therefore, like other HSE, S, Se and Te are considered potential tracers for the composition of the Late Veneer, provided that their bulk silicate Earth abundances are properly constrained. In contrast to ca. 250 ppm S, Se and Te are ultra-trace elements in the terrestrial mantle. Like all HSE, they are furthermore controlled by base metal sulphides (BMS) and micrometric platinum group minerals (PGMs)[3]. This strong control exerted by the host mineralogy and petrology on the S-Se-Te systematics at both the micro-scale and the whole-rock scale makes detailed mineralogical and petrological studies of BMS and PGM a pre-requisite to fully understand and accurately interpret the whole-rock signatures. Here we combine in-situ sulphide data and detailed mineralogical observations with whole-rock S-Se-Te-HSE signatures of both lherzolites and harburgites from different geodynamic settings. We demonstrate that the near-chondritic Se and Te signature of 'fertile' mantle rocks (Se/Te ?9×5) is not a primitive signature of the Earth's mantle, but rather reflects strong enrichment in metasomatic HSE host phases, which erased previous pristine signatures. Consequently, current attempts to identify a potential Late Veneer composition are seriously flawed because, neither refertilisation/metasomatism nor true melt depletion (e.g. harzburgitic residues) have been taken into account for the Primitive Upper Mantle composition estimate[4]. Our combined whole rock and in-situ sulphide data indicate a refertilisation trend towards sub-chondritic Se/Te ratios (i.e. Se/Te < 2). On the other hand, harzburgites that preserve depletion signatures show suprachondritic Se/Te ratios (< 31). Altogether this shows that metasomatic enrichment of mantle rocks may lead to a systematic bias and hence underestimation of the current Se/Te estimate of the primitive mantle. The metasomatic origin of the reported S, Se and Te ratios in peridotites that reflect the control of metasomatic BMS and PGMs[5;6] furthermore show that not all whole rock signatures in the Earth's mantle that scatter around near-chondritic values are primary and hence challenge the simple conception that these features may readily solve the long-standing conundrum of the Late Veneer composition. Refs: [1] Rose-Weston et al. (2009) GCA 73, 4598-4615; [2] Kimura et al. (1974) GCA 38, 683-701; [3] Lorand and Alard (2010) 67, 4137-4151; [4] Wang and Becker (2013) Nature 499, 328-331; [5] König et al. (2012) GCA 86, 354-366; [6] König et al. (2013, in press), EPSL.

  16. Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots

    PubMed Central

    2011-01-01

    A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported. The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity. The core/shell quantum dots exhibit tunable fluorescence emissions by controlling the thickness of the CdSe shell. The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell. PMID:21711922

  17. Structural properties of Bi2Te3 and Bi2Se3 topological insulators grown by molecular beam epitaxy on GaAs(001) substrates

    NASA Astrophysics Data System (ADS)

    Liu, X.; Smith, D. J.; Fan, J.; Zhang, Y.-H.; Cao, H.; Chen, Y. P.; Leiner, J.; Kirby, B. J.; Dobrowolska, M.; Furdyna, J. K.

    2011-10-01

    Thin films of Bi2Te3 and Bi2Se3 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.

  18. 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

  19. DIAGRAMME DES PHASES ET DOMAINE DE FORMATION DE VERRES DANS LE SYSTME PSEUDO-BINAIRE GeSe2-Te

    E-print Network

    Paris-Sud XI, Université de

    677 DIAGRAMME DES PHASES ET DOMAINE DE FORMATION DE VERRES DANS LE SYSTÈME PSEUDO-BINAIRE GeSe2-Te de phases et le domaine de formation de verres par trempe à l'air dans ce système par ATD en verres observées par ATD, et, d'autre part, le diagramme de phases, non seulement en ce qui concerne le

  20. CARACTRISATION PAR A. T. D. DE VERRES DU SYSTME Se-Te-Ge0,5Sb0,5

    E-print Network

    Paris-Sud XI, Université de

    681 CARACTÉRISATION PAR A. T. D. DE VERRES DU SYSTÈME Se-Te-Ge0,5Sb0,5 S. BORDAS, M. D. BARÓ, J on essaye d'étudier les propriétés des verres semiconducteurs est due à leur caractère métastable. Ainsi la verres obtenus par refroidissement du mélange liquide pour différentes conditions (vitesses comprises

  1. The rotational spectra, potential function, Born-Oppenheimer breakdown, and magnetic shielding of SnSe and SnTe.

    PubMed

    Bizzocchi, Luca; Giuliano, Barbara M; Hess, Mareike; Grabow, Jens-Uwe

    2007-03-21

    The pure rotational spectra of 27 isotopic species of SnSe and SnTe have been measured in the frequency range of 5-24 GHz using a Fabry-Perot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by laser ablation of suitable target rods and were stabilized in supersonic jets of Ar. Global multi-isotopolog analyses of all available high-resolution data produced spectroscopic Dunham parameters Y01, Y11, Y21, Y31, Y02, and Y12 for both species, as well as Born-Oppenheimer breakdown (BOB) coefficients delta01 for Sn, Se, and Te. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the X 1Sigma+ electronic state of both SnSe and SnTe. Additionally, the magnetic hyperfine interaction produced by the dipolar nuclei 119Sn, 117Sn, 77Se, and 125Te was observed, yielding first determinations of the corresponding spin-rotation coupling constants. PMID:17381204

  2. The rotational spectra, potential function, Born-Oppenheimer breakdown, and hyperfine structure of GeSe and GeTe.

    PubMed

    Giuliano, Barbara M; Bizzocchi, Luca; Sanchez, Raquel; Villanueva, Pablo; Cortijo, Vanessa; Sanz, M Eugenia; Grabow, Jens-Uwe

    2011-08-28

    The pure rotational spectra of 18 and 21 isotopic species of GeSe and GeTe have been measured in the frequency range 5-24 GHz using a Fabry-Pe?rot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by a combined dc discharge/laser ablation technique and stabilized in supersonic jets of Ne. Global multi-isotopologue analyses of the derived rotational data, together with literature high-resolution infrared data, produced very precise Dunham parameters, as well as rotational constant Born-Oppenheimer breakdown (BOB) coefficients (?(01)) for Ge, Se, and Te. A direct fit of the same datasets to an appropriate radial Hamiltonian yielded analytic potential-energy functions and BOB radial functions for the X(1)?(+) electronic state of both GeSe and GeTe. Additionally, the electric quadrupole and magnetic hyperfine interactions produced by the nuclei (73)Ge, (77)Se, and (125)Te were observed, yielding much improved quadrupole coupling constants and first determinations of the spin-rotation parameters. PMID:21895181

  3. A series of new ternary and quaternary compounds in the Li(I)-Ga(III)-Te(IV)-O system.

    PubMed

    Kong, Fang; Xu, Xiang; Mao, Jiang-Gao

    2010-12-20

    Systematic explorations of new compounds in the Li(I)-Ga(III)-Te(IV)-O system led to two new isomeric ternary gallium tellurites, namely, ?-Ga(2)(TeO(3))(3) and ?-Ga(2)(TeO(3))(3), and two new quaternary lithium gallium tellurites, namely, HLi(2)Ga(3)(TeO(3))(6)(H(2)O)(6) and Li(9)Ga(13)Te(21)O(66). ?-Ga(2)(TeO(3))(3) is a noncentrosymmetric structure (I4?3d) and displays a moderately strong second-harmonic-generation response that is comparable with that of KDP (KH(2)PO(4)). Its structure features a condensed three-dimensional (3D) network alternatively connected by GaO(4) tetrahedra and TeO(3) trigonal pyramids via corner sharing. ?-Ga(2)(TeO(3))(3) is centrosymmetric (P6(3)/m) and features a 3D open framework composed of Ga(2)O(9) dimers bridged by TeO(3) groups with one-dimensional (1D) 12-MR channels along the c axis. Although both HLi(2)Ga(3)(TeO(3))(6)(H(2)O)(6) and Li(9)Ga(13)Te(21)O(66) crystallized in the same space group R3?, they belong to different structure types. The structure of HLi(2)Ga(3)(TeO(3))(6)(H(2)O)(6) can be viewed as the 1D tunnels of the 3D gallium tellurite being occupied by Li(+) and H(+) ions whereas the structure of Li(9)Ga(13)Te(21)O(66) is a complicated 3D framework composed of alternating gallium tellurite layers and GaO(6) octahedral layers with Li(+) cations being located at the cavities of the structure. Optical diffuse-reflectance spectrum measurements indicate that all four compounds are insulators and transparent in the range of 300-2500 nm. PMID:21077650

  4. Magnetic field induced Raman excitations in Zn1-xCrxTe, Cd1-xCrxTe and Cd1-xCrxSe

    NASA Astrophysics Data System (ADS)

    Lu, X.; Tsoi, S.; Miotkowski, I.; Rodriguez, S.; Ramdas, A. K.; Alawadhi, H.; Pekarek, T. M.

    2007-03-01

    Raman electron paramagnetic resonance(Raman-EPR) of the transitions due to the ?ms=±1 spin-flip of the 3d electrons of Cr^+ in Zn1-xCrxTe and Cd1-xCrxTe are observed at ?PM=g(Cr^+)?BB, g(Cr^+)=2.0041± 0.0095 and 2.0039 ± 0.0093, respectively. Raman lines appear at ?LO± n?PM, n=1,2 and 3, resulting from the strong Fr"Ohlich interaction with LO phonon. The intensity of ?PM can be enhanced through the photo-generation process Cr^2+-> Cr^+; photoluminescence spectra reveal signatures of excitons bound to Cr^+ acceptors in Zn1-xCrxTe. The resonance profile of ?PM shows that the strong resonant enhancement is mediated via an exciton bound to a neutral acceptor. Spin flip Raman scattering (SFRS) at ?SFR from donor-bound electrons in Cd1-xCrxSe, as well as in pure CdSe, are observed, in turn yielding the s-d exchange energy. The magnetization of Cd1-xCrxSe is intermediate between van Vleck and a B2 Brillouin paramagnetism. The linear dependence of the s-d exchange energy as a function of magnetization yields the s-d exchange constant in Cd1-xCrxSe, ?N0=(213.7 ±13) meV.

  5. Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface

    SciTech Connect

    Zhang, Haijun; /Beijing, Inst. Phys.; Liu, Chao-Xing; /Tsinghua U., Beijing; Qi, Xiao-Liang; /Stanford U., Phys. Dept.; Dai, Xi; Fang, Zhong; /Beijing, Inst. Phys.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-02-24

    Topological insulators are new states of quantum matter in which surface states residing in the bulk insulating gap of such systems are protected by time-reversal symmetry. The study of such states was originally inspired by the robustness to scattering of conducting edge states in quantum Hall systems. Recently, such analogies have resulted in the discovery of topologically protected states in two-dimensional and three-dimensional band insulators with large spin-orbit coupling. So far, the only known three-dimensional topological insulator is Bi{sub x}Sb{sub 1-x}, which is an alloy with complex surface states. Here, we present the results of first-principles electronic structure calculations of the layered, stoichiometric crystals Sb{sub 2}Te{sub 3}, Sb{sub 2}Se{sub 3}, Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3}. Our calculations predict that Sb{sub 2}Te{sub 3}, Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} are topological insulators, whereas Sb{sub 2}Se{sub 3} is not. These topological insulators have robust and simple surface states consisting of a single Dirac cone at the point. In addition, we predict that Bi{sub 2}Se{sub 3} has a topologically non-trivial energy gap of 0.3 eV, which is larger than the energy scale of room temperature. We further present a simple and unified continuum model that captures the salient topological features of this class of materials.

  6. PHONONS OPTIQUES PAR RFLEXION INFRAROUGE DES COMPOSS TERNAIRES AgGaSe2 ET AgGaTe2

    E-print Network

    Paris-Sud XI, Université de

    -VI. Ils se cristallisent dans la structure de la chalcopyrite (Fig. 1) qui appartient au groupe d'espace IGaSe2 et AgGaTe2. La maille primitive de la chalcopyrite contient huit atomes au total. Les propri6t6strie B2 et les six modes optiques de sym6trie E. Les cristaux de la structure chalcopyrite sont uniaxes

  7. The effect of Ag addition on the optical properties of Se 90Te 10 films

    NASA Astrophysics Data System (ADS)

    Bekheet, A. E.; Hegab, N. A.; Afifi, M. A.; Atyia, H. E.; Sharaf, E. R.

    2009-02-01

    Se 90Te 10- xAg x (0 ? x ? 6) compositions were prepared by quenching technique. Thin films with different thicknesses of the obtained compositions were deposited on dry clean glass substrates by thermal evaporation technique. Energy dispersive X-ray spectroscopy (EDX) indicates that samples are nearly stoichiometric. X-ray diffraction patterns indicate that they are in the amorphous state. The optical constants, the refractive index n and the absorption index k, have been calculated from transmittance T and reflectance R through the spectral range of 400-2500 nm for the studied films with different thicknesses (165-711 nm). From the analysis of refractive index n data, high frequency dielectric constant ?? was determined. Both ?? and n are found to decrease with the increase of Ag content. The optical band gap Egopt is calculated for all compositions from the absorption coefficient analysis. The effect of the Ag addition on the obtained optical parameters has been discussed. The analysis of absorption index k data, revealed the existence of allowed indirect transitions for all compositions. It is indicated also that Egopt increase with increasing Ag content.

  8. Photoconductivity studies of Te-substituted Sn-Sb-Se semiconducting films

    NASA Astrophysics Data System (ADS)

    Chander, Ravi; Thangaraj, R.

    2014-02-01

    Amorphous thin films of chalcogenide Sn10Sb20Se70- X Te X (0? X?8) composition were deposited using the thermal evaporation technique. The dark conductivity measurement showed a thermally activated conduction process with single activation energy in a studied temperature regime. Photoconductivity showed no maxima in the measured temperature regime revealing that the material belongs to the type II photoconductor. The observed small difference between activation energy for photoconduction ? E ph and dark conduction ?E accounts for low photosensitivity of the material. The intensity variation of the photocurrent obeys the power law with the exponent ?˜0.56-0.64 revealing the dominant bimolecular recombination mechanism in the studied compositions. Transient photoconductivity revealed that initial rise of the photocurrent becomes slow with tellurium content in the sample. The change in the shape of the transient photocurrent with composition is qualitatively explained based upon change in defect statistics introduced by the tellurium content in the sample. The decay process after the initial decay was found to be nonexponential and is described with a differential life time of charge carrier that showed a decreasing trend with the tellurium content in the sample.

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

    NASA Astrophysics Data System (ADS)

    Kumar, Anup; Heera, Pawan; Sharma, Raman

    2015-05-01

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

  10. Super sensitization: grand charge (hole/electron) separation in ATC dye sensitized CdSe, CdSe/ZnS type-I, and CdSe/CdTe type-II core-shell quantum dots.

    PubMed

    Debnath, Tushar; Maity, Partha; Ghosh, Hirendra N

    2014-10-01

    Ultrafast charge-transfer dynamics has been demonstrated in CdSe quantum dots (QD), CdSe/ZnS type-I core-shell, and CdSe/CdTe type-II core-shell nanocrystals after sensitizing the QD materials by aurin tricarboxylic acid (ATC), in which CdSe QD and ATC form a charge-transfer complex. Energy level diagrams suggest that the conduction and valence band of CdSe lies below the LUMO and the HOMO level of ATC, respectively, thus signifying that the photoexcited hole in CdSe can be transferred to ATC and that photoexcited ATC can inject electrons into CdSe QD, which has been confirmed by steady state and time-resolved luminescence studies and also by femtosecond time-resolved absorption measurements. The effect of shell materials (for both type-I and type-II) on charge-transfer processes has been demonstrated. Electron injection in all the systems were measured to be <150?fs. However, the hole transfer time varied from 900?fs to 6?ps depending on the type of materials. The hole-transfer process was found to be most efficient in CdSe QD. On the other hand, it has been found to be facilitated in CdSe/CdTe type-II and retarded in CdSe/ZnS type-I core-shell materials. Interestingly, electron injection from photoexcited ATC to both CdSe/CdTe type-II and CdSe/ZnS type-I core-shell has been found to be more efficient as compared to pure CdSe QD. Our observation suggests the potential of quantum dot core-shell super sensitizers for developing more efficient quantum dot solar cells. PMID:25179856

  11. Large Structural Modulations in Incommensurate Te-III and Se-IV

    Microsoft Academic Search

    C. Hejny; M. I. McMahon

    2003-01-01

    The high-pressure phase of tellurium, Te-III, is found to have an incommensurate monoclinic structure, superspace group I'2\\/m(0q0)s0, of a type previously unknown in the elements. Te-III is stable from 4.5(2) to 29.2(7)GPa; the previously reported transition to a distinct Te-IV phase at 10.6GPa is not observed. The incommensurate wave vector of Te-III is strongly pressure dependent and varies in a

  12. Critical magnetic fields of the misfit layer compounds (LaSe)1.14 (NbSe2) m down to 50 mK

    NASA Astrophysics Data System (ADS)

    Nader, A.; Briggs, A.; Monceau, P.; Meerschaut, A.; Lafond, A.

    1996-02-01

    Upper critical magnetic field measurements of the misfit layer compounds (LaSe)1.14 (NbSe2) m ( m=1,2) perpendicular to the layer structure have been extended down to 50 mK by means of magnetoresistance measurements. For both compounds H c2? ( T) does not show any sign of saturation down to the lowest temperature and has an upward curvature which varies with temperature as ( T c - T)1.5.

  13. 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.

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

    SciTech Connect

    Wang Heng; Li Jingfeng; Zou Minmin; Sui Tao [State Key Laboratory of New Ceramics and Fine Processing, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China)

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

    NASA Astrophysics Data System (ADS)

    Kim, Jeongwoo; Jhi, Seung-Hoon

    2015-05-01

    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 Ge2Sb2Te5 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  17. Hybrid nanocrystal/polymer solar cells based on tetrapod-shaped CdSe(x)Te(1-x) nanocrystals.

    PubMed

    Zhou, Yi; Li, Yunchao; Zhong, Haizheng; Hou, Jianhui; Ding, Yuqin; Yang, Chunhe; Li, Yongfang

    2006-08-28

    A series of ternary tetrapodal nanocrystals of CdSe(x)Te(1-x) with x = 0 (CdTe), 0.23, 0.53, 0.78, 1 (CdSe) were synthesized and used to fabricate hybrid nanocrystal/polymer solar cells. Herein, the nanocrystals acted as electron acceptors, and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was used as an electron donor. It was found that the open circuit voltage (V(oc)), short-circuit current (J(sc)) and power conversion efficiency (?) of the devices all increased with increasing Se content in the CdSe(x)Te(1-x) nanocrystals under identical experimental conditions. The solar cell based on the blend of tetrapodal CdSe nanocrystals and MEH-PPV (9:1 w/w) showed the highest power conversion efficiency of 1.13% under AM 1.5, 80 mW cm(-2), and the maximum incident photon to converted current efficiency (IPCE) of the device reached 47% at 510 nm. The influence of nanocrystal composition on the photovoltaic properties of the hybrid solar cells was explained by the difference of the band level positions between MEH-PPV and the nanocrystals. PMID:21727535

  18. Molecular beam epitaxy growth of PbSe on Si (211) using a ZnTe buffer layer

    SciTech Connect

    Wang, X. J.; Chang, Y.; Hou, Y. B.; Becker, C. R.; Kodama, R.; Aqariden, F.; Sivananthan, S. [Microphysics Laboratory, Physics Department, University of Illinois at Chicago, Illinois 60607 (United States); Microphysics Laboratory, Physics Department, University of Illinois at Chicago, Illinois 60607 and Physics Department and Quantum Functional Semiconductor Research Center, Dongguk University 3-26, Seoul 100-715 (Korea, Republic of); Microphysics Laboratory, Physics Department, University of Illinois at Chicago, Illinois 60607 (United States); EPIR Technologies, Bolingbrook, Illinois 60440 (United States); Microphysics Laboratory, Physics Department, University of Illinois at Chicago, Illinois 60607 and EPIR Technologies, Bolingbrook, Illinois 60440 (United States)

    2011-09-15

    The authors report the results of successful growth of single crystalline PbSe on Si (211) substrates with ZnTe as a buffer layer by molecular beam epitaxy. Single crystalline PbSe with (511) orientation was achieved on ZnTe/Si (211), as evidenced by RHEED patterns indicative of 2 dimensional (2D) growth, x ray diffraction rocking curves with a full width at half maximum as low as 153 arc sec and mobility as large as 1.1x10{sup 4}cm{sup 2}V{sup -1}s{sup -1} at 77 K. Cross hatch patterns were found on the PbSe(511) surface in Nomarski filtered microscope images suggesting the presence of a surface thermal strain relaxation mechanism, which was confirmed by Fourier transformed high resolution transmission electron microscope images.

  19. Ce{sub 2}AgYb{sub 5/3}Se{sub 6}, La{sub 2}CuErTe{sub 5}, and Ce{sub 2}CuTmTe{sub 5}: Three new quaternary interlanthanide chalcogenides

    SciTech Connect

    Babo, Jean-Marie [Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556 (United States); Albrecht-Schmitt, Thomas E., E-mail: talbrec1@nd.edu [Department of Chemistry and Biochemistry, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States)

    2013-01-15

    Three new ordered quaternary interlanthanide chalcogenides, Ce{sub 2}AgYb{sub 5/3}Se{sub 6}, La{sub 2}CuErTe{sub 5}, and Ce{sub 2}CuTmTe{sub 5}, have been prepared by direct reaction of the elements in molten NaBr at 900 Degree-Sign C. Each compound forms a new structure-type. The Ce{sub 2}AgYb{sub 5/3}Se{sub 6} structure consists of {infinity}{sup 2}{l_brace} [AgYb{sub 5/6}Se{sub 6}]{sup 6-}{r_brace} layers intercalated by Ce{sup 3+} cations. These layers are composed of {infinity}{sup 1}{l_brace} [Yb{sub 5/3}Se{sub 6}]{sup 7-}{r_brace} quadruplet ribbons of [YbSe{sub 6}]{sup 9-} octahedra and infinite {infinity}{sup 1}{l_brace} [AgSe{sub 6}]{sup 11-}{r_brace} double chains of [AgSe{sub 5}]{sup 9-}. The La{sub 2}CuErTe{sub 5} structure is made of one-dimensional {infinity}{sup 1}{l_brace} [CuErTe{sub 5}]{sup 6-}{r_brace} ribbons separated by La{sup 3+} cations. These ribbons are formed by cis-edge sharing {infinity}{sup 1}{l_brace} [CuTe{sub 2}]{sup 3-}{r_brace} tetrahedral chains and trans-edge sharing {infinity}{sup 1}{l_brace} [ErTe{sub 4}]{sup 5-}{r_brace} chains. While La{sub 2}CuErTe{sub 5} crystallizes in the orthorhombic space group Pnma, Ce{sub 2}CuTmTe{sub 5} crystallizes in the monoclinic space group C2/m. The latter crystal structure is assembled from {infinity}{sup 2}{l_brace} [CuTmTe{sub 5}]{sup 6-}{r_brace} layers intercalated by Ce{sup 3+} cations. These layers consist of single {infinity}{sup 1}{l_brace} [TmTe{sub 4}]{sup 5-}{r_brace} chains connected to each other through dimers or pseudo-double chains. - Graphical abstract: [CuTe{sub 4}]{sup 7-} tetrahedra sharing cis-edges to yield chains in the La{sub 2}CuErTe{sub 5}. Highlights: Black-Right-Pointing-Pointer New ordered interlanthanide tellurides. Black-Right-Pointing-Pointer New quaternary chalcogenides. Black-Right-Pointing-Pointer Low-dimensional lanthanide chalcogenide substructures. Black-Right-Pointing-Pointer Flux synthesis of new chalcogenides.

  20. Superconductivity in the misfit layer compounds (BiSe) 1.10(NbSe 2) and (BiS) 1.11(NbS 2)

    NASA Astrophysics Data System (ADS)

    Nader, A.; Briggs, A.; Gotoh, Y.

    1997-01-01

    We report on the temperature dependence of the critical magnetic fields of the misfit layer compounds (BiSe) 1.10(NbSe 2) and (BiS) 1.11(NbS 2) in the directions parallel and perpendicular to the layer structure. They both behave as anisotropic 3D superconductors.

  1. Hydrothermal synthesis of high-quality type-II CdTe\\/CdSe quantum dots with near-infrared fluorescence

    Microsoft Academic Search

    Jing Wang; Heyou Han

    2010-01-01

    A simple hydrothermal method is developed for the synthesis of high-quality, water-soluble, and near-infrared (NIR)-emitting type-II core\\/shell CdTe\\/CdSe quantum dots (QDs) by employing thiol-capped CdTe QDs as core templates and CdCl2 and Na2SeO3 as shell precursors. Compared with the original CdTe core QDs, the core\\/shell CdTe\\/CdSe QDs exhibit an obvious red-shifted emission, whose color can be tuned between visible and

  2. 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.

  3. Magnetic Order and Transitions in the Spin-web Compound Cu3TeO6

    NASA Astrophysics Data System (ADS)

    Månsson, Martin; Prša, Krunoslav; Sugiyama, Jun; Andreica, Daniel; Luetkens, Hubertus; Berger, Helmuth

    The spin-web compound Cu3TeO6, belongs to an intriguing group of materials where magnetism is governed by3d9 copper Cu2+ ions. This compound has been sparsely experimentally studied and we here present the first investigation of its local magnetic properties using muon-spin relaxation/rotation(?+SR). Our results show a clear long-range 3D magnetic order below TN as indicated by clear zero-field (ZF) muon-precessions. At TN = 61.7K a very sharp transition is observed in the weak transverse-field (wTF) as well as ZF data. Contrary to suggestions by susceptibility measurements and inelastic neutron scattering, we find no evidence for either static or dynamic (on the time-scale of ?+SR) spin-correlations above TN.

  4. Investigation of the Effect of MoSe2 on the Thermoelectric Properties of n-Type Bi2Te2.4Se0.6

    NASA Astrophysics Data System (ADS)

    Shalev, Tom; Meroz, Omer; Beeri, Ofer; Gelbstein, Yaniv

    2015-06-01

    Thermoelectric materials as a means of direct conversion of heat into electricity are attracting increasing attention. The most efficient n-type thermoelectric materials for temperatures up to 300°C are currently Bi2Te x Se3- x -based. To compete with other methods of energy conversion, the efficiency of such materials should be further increased. The possibility of thermoelectric enhancement of such alloys by introduction of the layered structured MoSe2 phase has been investigated. On introduction of large amounts (up to 15 wt.%) of this phase, no effects of doping were observed, emphasizing the potential of sub-micron homogeneously distributed MoSe2 in such composites to effectively scatter phonons without any adverse contribution to the optimized electronic properties.

  5. Anomalous dressing of Dirac fermions in the topological surface state of Bi2Se3, Bi2Te3, and Cu-doped Bi2Se3.

    PubMed

    Kondo, Takeshi; Nakashima, Y; Ota, Y; Ishida, Y; Malaeb, W; Okazaki, K; Shin, S; Kriener, M; Sasaki, Satoshi; Segawa, Kouji; Ando, Yoichi

    2013-05-24

    Quasiparticle dynamics on the topological surface state of Bi(2(3), Bi(2)Te(3), and superconducting Cu(x)Bi(2)Se(3) are studied by 7 eV laser-based angle resolved photoemission spectroscopy. We find strong mode couplings in the Dirac-cone surface states at energies of ~3 and ~15-20 meV associated with an exceptionally large coupling constant ? of ~3, which is one of the strongest ever reported for any material. This result is compatible with the recent observation of a strong Kohn anomaly in the surface phonon dispersion of Bi(2)Se(3), but it appears that the theoretically proposed "spin-plasmon" excitations realized in helical metals are also playing an important role. Intriguingly, the ~3 meV mode coupling is found to be enhanced in the superconducting state of Cu(x)Bi(2)Se(3). PMID:23745936

  6. Tunnel diode oscillator measurements of the upper critical magnetic field of FeTe0.5Se0.5

    E-print Network

    Paris-Sud XI, Université de

    Tunnel diode oscillator measurements of the upper critical magnetic field of FeTe0.5Se0.5 Alain magnetic field (Hc2) of single crystalline FeTe0.5Se0.5 (Tc = 14.5 K) have been determined by tunnel diode

  7. CdTe(1-x)Se(x)/Cd0.5Zn0.5S core/shell quantum dots: core composition and property.

    PubMed

    Yang, Ping; Cao, Yongqiang; Li, Xiaoyu; Zhang, Ruili; Liu, Ning; Zhang, Yulan

    2014-08-01

    Alloy CdTe(1-x)Se(x) quantum dots (QDs) have been fabricated by an organic route using Cd, Te and Se precursors in a mixture of trioctylamine and octadecylphosphonic acid at 280?°C. The variation of photoluminescence (PL) peak wavelength of the CdTe(1-x)Se(x) QDs compared with CdTe QDs confirmed the formation of an alloy structure. The Se component drastically affected the stability of CdTe(1-x)Se(x) QDs. A Cd0.5Zn0.5S shell coating on CdTe(1-x)Se(x) cores was carried out using oleic acid as a capping agent. CdTe(1-x)Se(x)/Cd0.5Zn0.5S core/shell QDs revealed dark red PL while a yellow PL peak was observed for the CdTe(1-x)Se(x) cores. The PL efficiency of the core/shell QDs was drastically increased (less than 1% for the cores and up to 65% for the core/shell QDs). The stability of QDs in various buffer solutions was investigated. Core/shell QDs can be used for biological applications because of their high stability, tunable PL and high PL efficiency. PMID:23946281

  8. CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds.

    PubMed

    Algarra, M; Campos, B B; Miranda, M S; da Silva, Joaquim C G Esteves

    2011-02-15

    The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G(4) dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent water solubility of these compounds ?-cyclodextrin (?-CD) was used to promote the formation of inclusion complexes. The studied nitroaromatic compounds (plus ?-CD) significantly quenched the fluorescence intensity of the nanocomposite with linear Stern-Volmer plots. The Stern-Volmer constants (standard deviation in parenthesis) were: MNB, K(SV)=65(5)×10(4) M(-1); ACNB, K(SV)=19(2)×10(4) M(-1); and, MNP, K(SV)=33(1)×10(2) M(-1). These constants suggest the formation of a ground state complex between the nitroaromatric compounds and the sensor which confers a relatively high analytical sensitivity. The detection sensibilities are about 0.01 mg L(-1) for MNB and ACNB and about 0.1 mg L(-1) for MNP. No interferences or small interferences are observed for trinitrotoluene [K(SV)=10(2)×10(2)×M(-1)], 2,4-dinitrotoluene [K(SV)=20(3)×10 M(-1)], 2,6-dinitrotoluene [K(SV)=11(4)×10 M(-1)] and nitrobenzene [K(SV)=2(1)×10(3)×M(-1)]. PMID:21238718

  9. Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

    PubMed

    Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

    2014-07-22

    Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films. PMID:24883930

  10. 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.

  11. 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.

  12. Hc2(0) and the Kondo Effect in FeSe0.1Te0.9 Epitaxial Films

    NASA Astrophysics Data System (ADS)

    Cornell, Nicholas; Zakhidov, Anvar; Jaime, Marcelo; Huang, Jijie; Wang, Hayan; Salamon, Myron

    2015-03-01

    High-quality, [001]-oriented epitaxial films of FeSe0.1Te0.9 have been grown on SrTiO3. They are found to have increased critical temperatures and critical fields relative to both bulk samples and thin films of the sister compound, FeSe0.5Te0.5. Critical field values in excess of 114 T have been reported based on WHH theory. In addition to these improved properties, most samples show resistance minima above Tc, reminiscent of the Kondo effect, presumably from excess Fe. We report results of a high field investigation of these thin films that reveals an empirical zero-temperature value of Hc2(0) ~ 46 T along [001], significantly less than the WHH estimate, but still exceeding the maximum strong coupling correction to the Pauli limit. Large negative magnetoresistance above the critical field confirms the presence of Kondo behavior in the normal state and persists without saturation up to 60 T. Why the measured critical field exceeds the paramagnetic limit remains a question. However, a Kondo temperature that exceeds the superconducting Tc can lead to overestimated WHH upper critical fields and could explain the wide variation in Tc and Hc2 among the ``11'' iron chalcogenides.

  13. Ab initio study of the fundamental properties of HgSe, HgTe and their HgSexTe1-x alloys

    NASA Astrophysics Data System (ADS)

    El Haj Hassan, F.; Shafaay, B. Al; Meradji, H.; Ghemid, S.; Belkhir, H.; Korek, M.

    2011-12-01

    First-principles calculations were performed to study the structural, electronic and thermodynamic properties of HgSe, HgTe and HgSexTe1-x ternary alloys using the full potential-linearized augmented plane wave plus local orbitals method within the density functional theory. We use both the Wu-Cohen and Engel-Vosko generalized gradient approximations of the exchange-correlation energy that are based on the optimization of total energy and corresponding potential, respectively. Our investigation of the effect of composition on the lattice constant, bulk modulus and iconicity for ternary alloys shows almost nonlinear dependence on the composition. Besides, a regular-solution model is used to investigate the thermodynamic stability of the alloys, which mainly indicates a phase miscibility gap. In addition, the quasi-harmonic Debye model is used to determine the thermal properties of alloys up to 700 K.

  14. New layered structures of cuprous chalcogenides as thin film solar cell materials: Cu2Te and Cu2Se.

    PubMed

    Nguyen, Manh Cuong; Choi, Jin-Ho; Zhao, Xin; Wang, Cai-Zhuang; Zhang, Zhenyu; Ho, Kai-Ming

    2013-10-18

    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. PMID:24182279

  15. Thermal studies of Se85-xTe15Inx (x = 3,6,9,12) glasses

    NASA Astrophysics Data System (ADS)

    Sushama, D.; George, Achamma; Asokan, S.

    2011-10-01

    Bulk glasses of compositions Se85-xTe15Inx (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 Tc, Tp and ?Cp for the composition Se73Te15In12 using rigidity percolation threshold (RPT). From the values of (Tc-Tg) the stable glass system is determined.

  16. 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 [Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Lee, Wang Ro [Faculty of Liberal Education, Chonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of); Kim, Dae Yeon [Agency for Defense Development (ADD), Chinhae, Kyungnam 645-600 (Korea, Republic of); Shim, Ji Hoon, E-mail: jhshim@postech.ac.kr [Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Divisions of Advanced Nuclear Engineering, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)

    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.

  17. Moessbauer and magnetic studies of the ternary compound FeIn{sub 2}Se{sub 4}

    SciTech Connect

    Bodnar, I. V., E-mail: chemzav@bsuir.by; Pauliukavets, S. A. [Belarussian State University of Informatics and Radioelectronics (Belarus); Trukhanov, S. V. [National Academy of Sciences of Belarus, Scientific-Practical Materials Research Center (Belarus); Fedotova, Yu. A. [Belarus State University (Belarus)

    2012-05-15

    Single crystals of the ternary compound FeIn{sub 2}Se{sub 4} are grown by directional crystallization of the melt. The composition and structure of the single crystals are determined. The local states of iron ions in this compound are studied by nuclear {gamma}-resonance spectroscopy in transmission configuration. The temperature and field dependences of a specific magnetic moment for the ternary compound FeIn{sub 2}Se{sub 4} are measured in the temperature range 4-310 K in magnetic fields of 0-140 kOe. The reasons and mechanisms for magnetic state formation in single crystals of the obtained compound are discussed.

  18. Intensification of electroluminescence of ZnSe:(Te, O) crystals as a result of irradiation with ?-ray photons

    Microsoft Academic Search

    D. B. Él’murotova; É. M. Ibragimova

    2007-01-01

    The effects of irradiation with ?-ray photons of the 60Co isotope and of treatment in zinc vapors on the electroluminescence of ZnSe:(Te, O) crystals were studied with the aim of\\u000a revealing the potential for fabrication of light-emitting structures. The broadband electroluminescence with a peak at 600\\u000a nm is excited in the initial samples at voltages higher than 70 V. The

  19. Intensification of electroluminescence of ZnSe:(Te, O) crystals as a result of irradiation with -ray photons

    Microsoft Academic Search

    D. B. Elmurotova; E. M. Ibragimova

    2007-01-01

    The effects of irradiation with -ray photons of the °Co isotope and of treatment in zinc vapors on the electroluminescence of ZnSe:(Te, O) crystals were studied with the aim of revealing the potential for fabrication of light-emitting structures. The broadband electroluminescence with a peak at 600 nm is excited in the initial samples at voltages higher than 70 V. The

  20. T(z) phase diagram and optical energy gaps in CuGa(Se z Te1- z )2 alloys

    Microsoft Academic Search

    Miguel Quintero; Tibaire Tinoco; Carlos Rincón

    1991-01-01

    The T(z) phase diagram of the system CuGa(Se z Te1- z )2 was obtained from x-ray diffraction and differencial thermal analysis (DTA) measurements. DTA measurements were carried out on each sample and the transition temperatures were plotted as a function of alloy composition. Values of lattice parameter were determined in all cases. Values of the optical energy gap at 300

  1. Dispersion of the second-order nonlinear susceptibility in ZnTe, ZnSe, and ZnS

    Microsoft Academic Search

    H. P. Wagner; M. Kühnelt; W. Langbein; J. M. Hvam

    1998-01-01

    We have measured the absolute values of the second-harmonic generation (SHG) coefficient \\\\|d\\\\| for the zinc-blende II-VI semiconductors ZnTe, ZnSe, and ZnS at room temperature. The investigated spectral region of the fundamental radiation lambdaF ranges from 520 to 1321 nm using various pulsed laser sources. In the transparent region of the II-VI semiconductors, the SHG coefficient exceeds the values of

  2. The chemical fate of the Cd\\/Se\\/Te-based quantum dot 705 in the biological system: toxicity implications

    Microsoft Academic Search

    Chia-Hua Lin; Louis W. Chang; Han Chang; Mo-Hsiung Yang; Chung-Shi Yang; Wan-Hau Lai; Wan-Hsuan Chang; Pinpin Lin

    2009-01-01

    QD705 is a cadmium\\/selenium\\/tellurium (Cd\\/Se\\/Te)-based quantum dot with good potential for biomedical applications. Although the biological fate of QD705 is established, its chemical fate in the biological system is still unknown. Since the chemical nature of Cd in QD705 (either stays as bounded Cd or becomes free Cd) is closely related to the toxicity of this nanocrystal, information on its

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

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Burger, Arnold; Dudley, Michael; Matyi, Richard J.; Ramachandran, Narayanan; Sha, Yi-Gao; Volz, Martin; Shih, Hung-Dah

    1998-01-01

    Interest in optical devices which can operate in the visible spectrum has motivated research interest in the II-VI wide band gap semiconductor materials. The recent challenge for semiconductor opto-electronics is the development of a laser which can operate at short visible wavelengths, In the past several years, major advances in thin film technology such as molecular beam epitaxy and metal organic chemical vapor deposition have demonstrated the applicability of II-VI materials to important devices such as light-emitting diodes, lasers, and ultraviolet detectors.The demonstration of its optical bistable properties in bulk and thin film forms also make ZnSe a possible candidate material for the building blocks of a digital optical computer. Despite this, developments in the crystal growth of bulk II-VI semiconductor materials has not advanced far enough to provide the low price, high quality substrates needed for the thin film growth technology. The electrical and optical properties of semiconductor materials depend on the native point defects, (the deviation from stoichiometry), and the impurity or dopant distribution. To date, the bulk growth of ZnSe substrates has been plagued with problems related to defects such as non-uniform distributions of native defects, impurities and dopants, lattice strain, dislocations, grain boundaries, and second phase inclusions which greatly effect the device performance. In the bulk crystal growth of some technologically important semiconductors, such as ZnTe, CdS, ZnSe and ZnS, vapor growth techniques have significant advantages over melt growth techniques due to the high melting points of these materials.

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

    SciTech Connect

    Spann, B. T.; Xu, X., E-mail: xxu@purdue.edu [School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)

    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.

  5. 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

  6. The new nickel tellurite chloride compound Ni15Te12O34Cl10--synthesis, crystal structure and magnetic properties.

    PubMed

    Zhang, Dong; Johnsson, Mats; Lidin, Sven; Kremer, Reinhard K

    2013-02-01

    A new nickel tellurite oxohalide, Ni(15)Te(12)O(34)Cl(10), has been prepared by chemical vapour transport reactions and the crystal structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the triclinic space group P1[combining macron] with the pseudomonoclinic cell parameters a = 10.3248(6) Å, b = 10.3249(6) Å, c = 11.6460(8) Å, ? = 73.782(6)°, ? = 73.782(6)°, ? = 63.51(2)°, Z = 1, R(1) = 0.0264. The Ni(2+) ions have octahedral [NiO(6)] and [NiO(4)Cl(2)] coordinations, the Te(4+) ions have one-sided [TeO(3)] and [TeO(4)] coordinations. The crystal structure can be described as consisting of nickel oxide ribbons extending along (001) that are connected by corner sharing [TeO(3)] and [TeO(4)] groups to build the open framework structure. The chlorine atoms and the Te-lone pairs are facing voids in the oxide framework. The new compound undergoes two successive antiferromagnetic ordering transitions at ?50 K and ?10 K. The Curie-Weiss temperature obtained from detailed evaluation of the high-temperature magnetic susceptibilities is positive indicating predominant ferromagnetic superexchange interactions between the Ni magnetic moments. PMID:23135641

  7. Windowless CdSe/CdTe solar cells with differentiated back contacts: J-V, EQE, and photocurrent mapping.

    PubMed

    Josell, Daniel; Debnath, Ratan; Ha, Jong Y; Guyer, Jonathan; Sahiner, Mehmet A; Reehil, Christopher J; Manners, William A; Nguyen, Nhan V

    2014-09-24

    This study presents windowless CdSe/CdTe thin film photovoltaic devices with in-plane patterning at a submicrometer length scale. The photovoltaic cells are fabricated upon two interdigitated comb electrodes prepatterned at micrometer length scale on an insulating substrate. CdSe is electrodeposited on one electrode, and CdTe is deposited by pulsed laser deposition over the entire surface of the resulting structure. Previous studies of symmetric devices are extended in this study. Specifically, device performance is explored with asymmetric devices having fixed CdTe contact width and a range of CdSe contact widths, and the devices are fabricated with improved dimensional tolerance. Scanning photocurrent microscopy (also known as laser beam induced current mapping) is used to examine local current collection efficiency, providing information on the spatial variation of performance that complements current-voltage and external quantum efficiency measurements of overall device performance. Modeling of carrier transport and recombination indicates consistency of experimental results for local and blanket illumination. Performance under simulated air mass 1.5 illumination exceeds 5% for all dimensions examined, and the best-performing device achieved 5.9% efficiency. PMID:25157419

  8. Weak Anti-localization and Quantum Oscillations of Surface States in Topological Insulator Bi2Se2Te

    PubMed Central

    He, Liang; Meyer, Nicholas; Kou, Xufeng; Zhang, Peng; Chen, Zhi-gang; Fedorov, Alexei V.; Zou, Jin; Riedemann, Trevor M.; Lograsso, Thomas A.; Wang, Kang L.; Tuttle, Gary; Xiu, Faxian

    2012-01-01

    Topological insulators, a new quantum state of matter, create exciting opportunities for studying topological quantum physics and for exploring spintronic applications due to their gapless helical metallic surface states. Here, we report the observation of weak anti-localization and quantum oscillations originated from surface states in Bi2Se2Te crystals. Angle-resolved photoemission spectroscopy measurements on cleaved Bi2Se2Te crystals show a well-defined linear dispersion without intersection of the conduction band. The measured weak anti-localization effect agrees well with the Hikami-Larkin-Nagaoka model and the extracted phase coherent length shows a power-law dependence with temperature (?T?0.44), indicating the presence of the surface states. More importantly, the analysis of a Landau-level fan diagram of Shubnikov-de Hass oscillations yields a finite Berry phase of ?0.42?, suggesting the Dirac nature of the surface states. Our results demonstrate that Bi2Se2Te can serve as a suitable topological insulator candidate for achieving intrinsic quantum transport of surface Dirac fermions. PMID:23061009

  9. Negligible surface reactivity of topological insulators Bi2Se3 and Bi2Te3 towards oxygen and water.

    PubMed

    Yashina, Lada V; Sánchez-Barriga, Jaime; Scholz, Markus R; Volykhov, Andrey A; Sirotina, Anna P; Neudachina, Vera S; Tamm, Marina E; Varykhalov, Andrei; Marchenko, Dmitry; Springholz, Gunther; Bauer, Günther; Knop-Gericke, Axel; Rader, Oliver

    2013-06-25

    The long-term stability of functional properties of topological insulator materials is crucial for the operation of future topological insulator based devices. Water and oxygen have been reported to be the main sources of surface deterioration by chemical reactions. In the present work, we investigate the behavior of the topological surface states on Bi2X3 (X = Se, Te) by valence-band and core level photoemission in a wide range of water and oxygen pressures both in situ (from 10(-8) to 0.1 mbar) and ex situ (at 1 bar). We find that no chemical reactions occur in pure oxygen and in pure water. Water itself does not chemically react with both Bi2Se3 and Bi2Te3 surfaces and only leads to slight p-doping. In dry air, the oxidation of the Bi2Te3 surface occurs on the time scale of months, in the case of Bi2Se3 surface of cleaved crystal, not even on the time scale of years. The presence of water, however, promotes the oxidation in air, and we suggest the underlying reactions supported by density functional calculations. All in all, the surface reactivity is found to be negligible, which allows expanding the acceptable ranges of conditions for preparation, handling and operation of future Bi2X3-based devices. PMID:23679000

  10. Research on photoelectrochemical cells based on CdSe, CdSe/sub 1-x/Te/sub x/ and other photoelectrode materials

    SciTech Connect

    Wallace, W.L.

    1984-05-01

    Research on electrochemical photovoltaic cells incorporating thin film n-CdSe and n-CdSe/sub 1-x/Te/sub x/ photoanodes has resulted in efficiencies up to 7.5% using small area electrodes in polysulfide electrolytes. Efficiencies close to 10% can be achieved using alternate electrolytes in significantly less stable systems. The major limitations on the efficiency of II-VI photoelectrochemical cells are associated with the open circuit voltage and the fill factor. Research on CuInSe/sub 2/ electrochemical photovoltaic cells has resulted in efficiencies up to 11.7% using single crystal n-CuInSe/sub 2/ photoanodes in aqueous electrolytes. The n-CuInSe/sub 2/ surface and the electrolyte have been optimized to produce a highly stable semiconductor/electrolyte junction. A review will also be given on the status of photoelectrochemical storage cell research. In situ photoelectrochemical measurement techniques have been used to probe the semiconductor/electrolyte interface and have been used to support the characterization of semiconductor materials for solid state photovoltaic applications.

  11. The chemical fate of the Cd/Se/Te-based quantum dot 705 in the biological system: toxicity implications

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Hua; Chang, Louis W.; Chang, Han; Yang, Mo-Hsiung; Yang, Chung-Shi; Lai, Wan-Hau; Chang, Wan-Hsuan; Lin, Pinpin

    2009-05-01

    QD705 is a cadmium/selenium/tellurium (Cd/Se/Te)-based quantum dot with good potential for biomedical applications. Although the biological fate of QD705 is established, its chemical fate in the biological system is still unknown. Since the chemical nature of Cd in QD705 (either stays as bounded Cd or becomes free Cd) is closely related to the toxicity of this nanocrystal, information on its chemical fate is critically needed. In this study we investigated the chemical fate of QD705 in the kidneys of mice. We used the molar ratio of Cd and Te (increased Cd/Te ratio signifies increased Cd release from QD705) and the induction of tissue metallothionein (MT) as markers for elevated free Cd in tissues. Our study indicated that 100% of QD705 (measured as Cd) was still retained in the body 16 weeks after exposure, with significant time redistribution to the kidneys. Furthermore, there were an elevation in both the molar Cd/Te ratio and MT-1 expression in the kidneys, suggesting that free Cd was released from QD705. Thus QD705 is not as stable or biologically inert as many may have once believed. Our study demonstrated that free Cd indeed can be released from QD705 in the kidneys and increases the risk of renal toxicity.

  12. 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.

  13. Mössbauer study of the ‘11’ iron-based superconductors parent compound Fe1+xTe

    NASA Astrophysics Data System (ADS)

    B?achowski, A.; Ruebenbauer, K.; Zajdel, P.; Rodriguez, E. E.; Green, M. A.

    2012-09-01

    57Fe Mössbauer spectroscopy was applied to investigate the superconductor parent compound Fe1+xTe for x = 0.06, 0.10, 0.14, 0.18 within the temperature range 4.2-300 K. A spin density wave (SDW) within the iron atoms occupying regular tetrahedral sites was observed, with the square root of the mean square amplitude at 4.2 K varying between 9.7 and 15.7 T with increasing x. Three additional magnetic spectral components appeared due to the interstitial iron distributed over available sites between the Fe-Te layers. The excess iron showed hyperfine fields at approximately 16, 21 and 49 T for three respective components at 4.2 K. The component with a large field of 49 T indicated the presence of isolated iron atoms with large localized magnetic moments in interstitial positions. Magnetic ordering of the interstitial iron disappeared in accordance with the fallout of the SDW with increasing temperature.

  14. Ordered defect compounds in CuInSe{sub 2} for photovoltaic solar cell application

    SciTech Connect

    Sato, K. [Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University and PRESTO, Japan Science and Technology Agency (JST) (Japan); Katayama-Yoshida, H. [Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University (Japan)

    2014-02-21

    Due to the complete compensation, defect complex (2V{sub Cu}+In{sub Cu}), namely two Cu vacancies and In located at Cu site, is stable in CuInSe{sub 2} (CIS). It is known that the series of ordered defect compounds (ODC) are constracted by ordering the defect complex. Based on the total energy calcalation by using the Korringa-Kohn-Rostoker coherent potential approxiamtion (KKR-CPA) method, we discuss phase separation of the CIS with the defect complexes into ODC and CIS. Since the band alignment between ODC and CIS is calculated to be type 2, effective electron-hole separation at the interface between ODC and CIS can be expected. This causes the enhancement of conversion efficiency of CIS-based solar cell materials.

  15. Magneto-optical studies of magnetic polarons in type-II (Zn,Mn)Te/ZnSe quantum dots

    NASA Astrophysics Data System (ADS)

    Barman, Biplob; Russ, Andreas; Schweidenback, Lars; Murphy, Joseph; Oszwaldowski, Rafal; Sellers, Ian; Petrou, Athos; Zutic, Igor; McCombe, Bruce; Cartwright, Alexander; Petukhov, Andre; Chou, Wu-Ching; Fan, Wen Chung

    2011-03-01

    We have recorded time-resolved emission spectra from a series of MBE grown (Zn,Mn)Te/ZnSe quantum dots (QDs) at 7 K in the 0 - 4 tesla magnetic field range. The photoluminescence (PL) spectra were analyzed into their ? + and ? - circularly-polarized components. The holes in this type-II system are confined in the (Zn,Mn)Te QDs, while the electrons reside in the surrounding ZnSe matrix. The PL intensity, peak energy, and circular polarization were recorded as a function of time and magnetic field. These studies show evidence of exchange coupling between the holes and Mn spins in the (Zn,Mn)Te QDs, which leads to the formation of magnetic polarons. The time scale of polaron formation is shorter than the recombination time in this type-II system. We discuss our results within the framework of a model that describes the magnetic polaron formation in this system. This work is supported by NSF, ONR, DOE-BES, AFOSR, and the Rustgi professorship.

  16. The thermoelectric properties and crystallography of Bi-Sb-Te-Se thin films grown by ion beam sputtering

    NASA Astrophysics Data System (ADS)

    Noro, H.; Sato, K.; Kagechika, H.

    1993-02-01

    The effects of the substrate temperature on the composition and microstructure of Bi-Sb-Te-Se thin films are discussed and related to the Seebeck coefficient and resistivity. The films were prepared on silica substrates by argon ion beam sputtering. The effect of subsequent heat treatment is also discussed. The composition becomes stoichiometric at the substrate temperature around 500 K at which the Seebeck coefficient has a maximum and the resistivity has a minimum. The Seebeck coefficient changes its sign at the substrate temperature around 340 K. The crystal structure of the films deposited at room temperature is identified as the rock-salt type, and the change of the thermoelectric properties as a function of the substrate temperature can be mainly attributed to the volume fraction of the Bi2Te3 and rock-salt structures. The subsequent heat treatment is effective in improving the power factor of the stoichiometric thin films.

  17. Nanoscale chemical phase separation in FeTe0.55Se0.45 as seen via scanning tunneling spectroscopy

    SciTech Connect

    He, Xiaobo [Louisiana State University; Li, Guorong [Louisiana State University; Zhang, Jiandi [Louisiana State University; Karki, A B [Louisiana State University; Jin, Rongying [Louisiana State University; Sales, Brian C [ORNL; Safa-Sefat, Athena [ORNL; McGuire, Michael A [ORNL; Mandrus, David [ORNL; Plummer, E. W. [Louisiana State University

    2011-01-01

    Atomically resolved structural and electronic properties of FeTe{sub 1-x}Se{sub x} (x = 0 and 0.45) have been studied with scanning tunneling microscopy/spectroscopy (STM/STS). In contrast to the extreme flatness of the Te-terminated FeTe surface, nanoscale chemical phase separation between Te and Se atoms is unambiguously revealed on the surface of FeTe{sub 0.55}Se{sub 0.45}. A statistical counting of the two kinds of atoms has the same ratio as that in the bulk. Remarkably, there is no electronic phase separation seen in the tunneling spectroscopy. This indicates that the optimally doped superconductor is chemically inhomogeneous but electronically homogeneous, in contrast to many correlated electron materials.

  18. Thermal stability and thermoelectric properties of Cu{sub x}As{sub 40?x}Te{sub 60?y}Se{sub y} semiconducting glasses

    SciTech Connect

    Vaney, J.B., E-mail: Jean-baptiste.vaney@ijl.nancy-universite.fr [Université de Lorraine, CNRS, Institut Jean Lamour, Parc de Saurupt, F-54042 NANCY Cedex (France); Institut Charles Gerhardt, UMR 5253 CNRS, Université de. Montpellier 2, 34095 Montpellier (France); Piarristeguy, A.; Pradel, A. [Institut Charles Gerhardt, UMR 5253 CNRS, Université de. Montpellier 2, 34095 Montpellier (France); Alleno, E. [Institut de Chimie et des Matériaux Paris-Est, UMR 7182 CNRS UPEC 94320 Thiais (France); Lenoir, B.; Candolfi, C.; Dauscher, A. [Université de Lorraine, CNRS, Institut Jean Lamour, Parc de Saurupt, F-54042 NANCY Cedex (France); Gonçalves, A.P.; Lopes, E.B. [IST/ITN, Instituto Superior Técnico, Universidade Técnica de Lisboa/CFMCUL, Estrada Nacianal 10, P-2686-953 Sacavém (Portugal); Delaizir, G. [SPCTS, UMR CNRS 73125, Centre Européen de la Céramique, 87068 Limoges (France); Monnier, J. [Institut de Chimie et des Matériaux Paris-Est, UMR 7182 CNRS UPEC 94320 Thiais (France); Ribes, M. [Institut Charles Gerhardt, UMR 5253 CNRS, Université de. Montpellier 2, 34095 Montpellier (France); Godart, C. [Institut de Chimie et des Matériaux Paris-Est, UMR 7182 CNRS UPEC 94320 Thiais (France)

    2013-07-15

    We report on the thermal behavior and thermoelectric properties of bulk chalcogenide glasses in the systems Cu{sub x}As{sub 40?x}Te{sub 60} (20?x?32.5) and Cu{sub x}As{sub 40?x}Te{sub 60?y}Se{sub y}, (0?y?9) synthesized by conventional melt-quenching techniques. The thermal stability of these glasses was probed by differential scanning calorimetry to determine the characteristic T{sub g} and ?T temperatures, both of which increasing noticeably with y. Thermoelectric properties were found to be mainly influenced by the Cu concentration with respect to the Se content. The thermal conductivity is practically composition-independent throughout the compositional range covered. A maximum ZT value of 0.02 at 300 K increasing to 0.06 at 375 K was achieved for the composition Cu{sub 30}As{sub 10}Te{sub 54}Se{sub 6}. - Graphical abstract: Effect of substitution of Te by Se and As by Cu on thermal stability and thermoelectric properties of Cu{sub x}As{sub 40?x}Te{sub 60?y}Se{sub y} semiconducting glasses. - Highlights: • We studied substitution of Te by Se in Cu–As–Te thermoelectric chalcogenide glasses. • Cu–As–Te–Se glasses were prepared by conventional melt-quenching method. • Se inclusion increases thermal stability in Cu–As–Te glasses. • Increasing copper concentration enhances thermoelectric properties. • ZT of 0.02 was achieved at 300 K and 0.06 at 375 K.

  19. Redistribution and activation of implanted S, Se, Te, Be, Mg, and C in GaN

    Microsoft Academic Search

    R. G. Wilson; J. M. Zavada; X. A. Cao; R. K. Singh; S. J. Pearton; H. J. Guo; S. J. Pennycook; M. Fu; J. A. Sekhar; V. Scarvepalli; R. J. Shu; J. Han; D. J. Rieger; J. C. Zolper; C. R. Abernathy

    1999-01-01

    A variety of different possible donor and acceptor impurities have been implanted into GaN and annealed up to 1450thinsp°C. S{sup +} and Te{sup +} produce peak electron concentrations â¤5Ã10¹⁸ cm⁻³, well below that achievable with Si{sup +}. Mg produces {ital p}-type conductivity, but Be{sup +}- and C{sup +}- implanted samples remained {ital n} type. No redistribution was observed for any

  20. 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., E-mail: skannan@barc.gov.in

    2013-09-01

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

  1. 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.

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

    SciTech Connect

    Dhere, N.G. [Florida Solar Energy Center, Cape Canaveral, FL (United States)

    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.

  3. Polycrystalline CuInSe{sub 2} and CdTe solar cells. Annual subcontract report, April 15, 1992--April 14, 1993

    SciTech Connect

    Dhere, N.G. [Florida Solar Energy Center, Cape Canaveral, FL (United States)

    1994-08-01

    The principal objective of the research project is to develop processes for the fabrication of cadmium-telluride, CdTe, and copper-indium-gallium-diselenide, Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2}, polycrystalline-thin-film solar cells using techniques that can be scaled-up for economic manufacture on a large scale. The aims are to fabricate CdTe solar cells using Cd and Te layers sputtered from elemental targets; to promote the interdiffusion between Cd/Te layers, CdTe phase formation, and grain growth; to utilize non-toxic selenization so as to avoid the use of extremely toxic H{sub 2}Se in the fabrication of Cu(In{sub l{minus}x}Ga{sub x})Se{sub 2} thin-film solar cells; to optimize selenization parameters; to improve adhesion; to minimize residual stresses; to improve the uniformity, stoichiometry, and morphology of CdTe and Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2} thin films, and the efficiency of CdTe and Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2} solar cells.

  4. 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.

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

    SciTech Connect

    Sheleg, A. U., E-mail: sheleg@ifttp.bas-net.by; Zub, E. M.; Yachkovskii, A. Ya. [National Academy of Sciences of Belarus, State Scientific and Production Association, Scientific and Practical Materials Research Center (Belarus); Mustafaeva, S. N.; Kerimova, E. M. [Azerbaijan National Academy of Sciences, Institute of Physics (Azerbaijan)

    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.

  6. Characterization of CdS/CdTe and CdS/CuInSe2 thin film solar cells

    NASA Technical Reports Server (NTRS)

    Cheng, L. J.; Nguyen, T. T.; Shyu, C. M.; Basol, B. M.; Yoo, H. I.

    1984-01-01

    A study on low cost polycrystalline thin film CdS/CdTe and CdS/CuInSe2 solar cells using measurements of spectral response and capacitance-voltage-frequency relationships was performed. Because of high concentrations of localized levels in the energy gap existing in materials and at interfaces, the redistribution of charge among the levels due to illumination plays an important role in the collection of light-generated current in these cells. The results illustrate some related phenomena observed in these cells.

  7. Separating Lattice and Electronic Thermal Conductivity Contributions in Bi2Se3andBi2Te3 Single Crystals

    NASA Astrophysics Data System (ADS)

    Opeil, Cyril; Yao, Mengliang; Wilson, Stephen; Zebarjadi, Mona

    2015-03-01

    Nanostructured materials are an effective approach in reducing lattice thermal conductivity and improving overall thermoelectric efficiency. A challenge for experimental measurements of thermal conductivity is separating the contributions from both carriers and phonons. Building on the work of K. Lukas et al., Phys. Rev. B 85, 205410 (2012),we report measurements of thermal and electrical conductivity of single crystal thermoelectrics: Bi2Se3andBi2Te3 in a transverse magnetic field up to 9 Tesla. Our experiments provide a separation of the lattice/electronic components and make possible a better theoretical model of the lattice portion of the thermal conductivity in materials.

  8. Spin-Induced Optical Second Harmonic Generation in the Centrosymmetric Magnetic Semiconductors EuTe and EuSe

    NASA Astrophysics Data System (ADS)

    Kaminski, B.; Lafrentz, M.; Pisarev, R. V.; Yakovlev, D. R.; Pavlov, V. V.; Lukoshkin, V. A.; Henriques, A. B.; Springholz, G.; Bauer, G.; Abramof, E.; Rappl, P. H. O.; Bayer, M.

    2009-07-01

    Spectroscopy of the centrosymmetric magnetic semiconductors EuTe and EuSe reveals spin-induced optical second harmonic generation (SHG) in the band gap vicinity at 2.1-2.4 eV. The magnetic field and temperature dependence demonstrates that the SHG arises from the bulk of the materials due to a novel type of nonlinear optical susceptibility caused by the magnetic dipole contribution combined with spontaneous or induced magnetization. This spin-induced susceptibility opens access to a wide class of centrosymmetric systems by harmonics generation spectroscopy.

  9. Atomic structure of Bi2Se3 and Bi2Te3 (111) surfaces probed by photoelectron diffraction and holography

    NASA Astrophysics Data System (ADS)

    Kuznetsov, Mikhail V.; Yashina, Lada V.; Sánchez-Barriga, Jaime; Ogorodnikov, Ilya I.; Vorokh, Andrey S.; Volykhov, Andrey A.; Koch, Roland J.; Neudachina, Vera S.; Tamm, Marina E.; Sirotina, Anna P.; Varykhalov, Andrei Yu.; Springholz, Gunther; Bauer, Günther; Riley, John D.; Rader, Oliver

    2015-02-01

    Understanding how topologically protected surface states behave at surfaces and interfaces requires knowledge of the atomic structure. Whether the (111) surfaces of the prototypical topological insulators Bi2Se3 and Bi2Te3 are Bi or chalcogen terminated is the subject of current controversies. We employ photoelectron diffraction and holography, combining the advantages and avoiding the disadvantages of the contesting techniques previously used. We find bulklike chalcogen termination with a very small surface relaxation (<1 % ) in agreement with density functional theory simulations. We prove the chalcogen termination for cleaved crystals and epitaxial films which shows the robustness of our conclusions.

  10. Inelastic x-ray scattering from valence electrons near absorption edges of FeTe and TiSe2

    NASA Astrophysics Data System (ADS)

    Barbiellini, B.; Hancock, J. N.; Monney, C.; Joly, Y.; Ghiringhelli, G.; Braicovich, L.; Schmitt, T.

    2014-06-01

    We study resonant inelastic x-ray scattering (RIXS) peaks corresponding to low-energy particle-hole excited states of metallic FeTe and semimetallic TiSe2 for photon incident energy tuned near the L3 absorption edge of Fe and Ti, respectively. We show that the cross-section amplitudes are well described within a renormalization-group theory where the effect of the core electrons is captured by effective dielectric functions expressed in terms of the the atomic scattering parameters f1 of Fe and Ti. This method can be used to extract the dynamical structure factor from experimental RIXS spectra in metallic systems.

  11. Development of a computer model for polycrystalline thin-film CuInSe2 and CdTe solar cells

    Microsoft Academic Search

    JEFFERY L. GRAY; RICHARD J. SCHWARTZ; YOUN JUNG LEE

    1992-01-01

    This report describes work to develop a highly accurate numerical model for CuInSe2 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 CuInSe2 and CdTe

  12. NONLINEAR OPTICAL EFFECTS IN ROTATIONALLY-TWINNED CRYSTALS: AN EVALUATION OF CdTe, ZnTe AND ZnSe

    E-print Network

    Boyer, Edmond

    405 NONLINEAR OPTICAL EFFECTS IN ROTATIONALLY-TWINNED CRYSTALS: AN EVALUATION OF CdTe, ZnTe AND Zn une loi en N2. On discutera les avantages potentiels en optique non linéaire des cristaux de CdTe, Zn-spaced twin planes the enhancement is proportional to N2. A comparison is made between CdTe, ZnTe, and Zn

  13. Thermoelectric efficiency of (1 - x)(GeTe) x(Bi2Se0.2Te2.8) and implementation into highly performing thermoelectric power generators.

    PubMed

    Koenig, J; Winkler, M; Dankwort, T; Hansen, A-L; Pernau, H-F; Duppel, V; Jaegle, M; Bartholomé, K; Kienle, L; Bensch, W

    2015-02-14

    Here we report for the first time on a complete simulation assisted "material to module" development of a high performance thermoelectric generator (TEG) based on the combination of a phase change material and established thermoelectrics yielding the compositions (1 - x)(GeTe) x(Bi(2)Se(0.2)Te(2.8)). For the generator design our approach for benchmarking thermoelectric materials is demonstrated which is not restricted to the determination of the intrinsically imprecise ZT value but includes the implementation of the material into a TEG. This approach is enabling a much more reliable benchmarking of thermoelectric materials for TEG application. Furthermore we analyzed the microstructure and performance close to in-operandi conditions for two different compositions in order to demonstrate the sensitivity of the material against processing and thermal cycling. For x = 0.038 the microstructure of the as-prepared material remains unchanged, consequently, excellent and stable thermoelectric performance as prerequisites for TEG production was obtained. For x = 0.063 we observed strain phenomena for the pristine state which are released by the formation of planar defects after thermal cycling. Consequently the thermoelectric performance degrades significantly. These findings highlight a complication for deriving the correlation of microstructure and properties of thermoelectric materials in general. PMID:25559337

  14. 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.

  15. Effect of ordered defects on the crystal structure of In-rich ternary compounds of the Cu In Se system

    NASA Astrophysics Data System (ADS)

    Wasim, S. M.; Rincón, C.; Marín, G.; Delgado, J. M.; Contreras, J.

    2004-02-01

    A comparative study of the unit cell parameters and volume of the chalcopyrite-related ordered defect compounds and other In-rich phases of the Cu-In-Se ternary system is made. These compounds fall on the tie-line of (Cu2Se)1 - x(In2Se3)x. It is found that the unit cell parameters and volume of the compounds that can be derived from the formula Cun - 3Inn + 1Se2n, where n = 4,5,6,7,8 and 9, decrease with an increase in the fraction of cation vacancies to the total number of cation positions, m, or interacting donor-acceptor defect pairs (In_Cu^{ 2+},\\ 2V_Cu^{-1}) per unit l in the chemical formula. The reduction in the unit cell dimensions is explained as due to the decrease in the effective cation radius caused by the increase in m or l. This behaviour is consistent with Vegard's law. However, the unit cell parameters of other In-rich phases such as CuIn4Se6 and CuIn4Se7 reported in the literature do not follow this trend. It must be noted that with indium having a 3+ oxidation state, the formation of these materials can only be explained if the valence of Cu atoms is 0 and 2+, respectively, different from the 1+ expected for the members of the Cu2Se-In2Se3 system.

  16. Band engineering in core/shell ZnTe/CdSe for photovoltage and efficiency enhancement in exciplex quantum dot sensitized solar cells.

    PubMed

    Jiao, Shuang; Shen, Qing; Mora-Seró, Iván; Wang, Jin; Pan, Zhenxiao; Zhao, Ke; Kuga, Yuki; Zhong, Xinhua; Bisquert, Juan

    2015-01-27

    Even though previously reported CdTe/CdSe type-II core/shell QD sensitizers possess intrinsic superior optoelectronic properties (such as wide absorption range, fast charge separation, and slow charge recombination) in serving as light absorbers, the efficiency of the resultant solar cell is still limited by the relatively low photovoltage. To further enhance photovoltage and cell efficiency accordingly, ZnTe/CdSe type-II core/shell QDs with much larger conduction band (CB) offset in comparison with that of CdTe/CdSe (1.22 eV vs 0.27 eV) are adopted as sensitizers in the construction of quantum dot sensitized solar cells (QDSCs). The augment of band offset produces an increase of the charge accumulation across the QD/TiO2 interface under illumination and induces stronger dipole effects, therefore bringing forward an upward shift of the TiO2 CB edge after sensitization and resulting in enhancement of the photovoltage of the resultant cell devices. The variation of relative chemical capacitance, C?, between ZnTe/CdSe and reference CdTe/CdSe cells extracted from impedance spectroscopy (IS) characterization under dark and illumination conditions clearly demonstrates that, under light irradiation conditions, the sensitization of ZnTe/CdSe QDs upshifts the CB edge of TiO2 by the level of ? 50 mV related to that in the reference cell and results in the enhancement of V(oc) of the corresponding cell devices. In addition, charge extraction measurements have also confirmed the photovoltage enhancement in the ZnTe/CdSe cell related to reference CdTe/CdSe cell. Furthermore, transient grating (TG) measurements have revealed a faster electron injection rate for the ZnTe/CdSe-based QDSCs in comparison with the CdSe cells. The resultant ZnTe/CdSe QD-based QDSCs exhibit a champion power conversion efficiency of 7.17% and a certified efficiency of 6.82% under AM 1.5 G full one sun illumination, which is, as far as we know, one of the highest efficiencies for liquid-junction QDSCs. PMID:25562411

  17. Thermodynamic properties of PbTe, PbSe, and PbS: a ?rst-principles study

    SciTech Connect

    Zhang, Yi [University of Nevada, Las Vegas; Ke, Xuezhi [University of Nevada, Las Vegas; Chen, Changfeng [University of Nevada, Las Vegas; Yang, Jihui [General Motors Corporation-R& D; Kent, Paul R [ORNL

    2009-01-01

    The recent discovery of novel lead chalcogenide-based thermoelectric materials has attracted great interest. These materials exhibit low thermal conductivity which is closely related to their lattice dynamics and thermodynamic properties. In this paper, we report a systematic study of electronic structures and lattice dynamics of the lead chalcogenides PbX (X=Te, Se, S) using ?rst-principles density functional theory calculations and a direct force-constant method. We calculate the struc- tural parameters, elastic moduli, electronic band structures, dielectric constants, and Born e?ective charges. Moreover, we determine phonon dispersions, phonon density of states, and phonon softening modes in these materials. Based on the results of these calculations, we further employ quasihar- monic approximation to calculate the heat capacity, internal energy, and vibrational entropy. The obtained results are in good agreement with experimental data. Lattice thermal conductivities are evaluated in terms of the Gruneisen parameters. The mode Gruneisen parameters are calculated to explain the anharmonicity in these materials. The e?ect of the spin-orbit interaction is found to be negligible in determining the thermodynamic properties of PbTe, PbSe, and PbS.

  18. 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

  19. 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.

  20. Site Occupation Preferences in CdMnTeSe Quaternary Alloys. EXAFS Data Analysis

    Microsoft Academic Search

    A. Kisiel; J. Lazewski; M. Zimnal-Stamawska; E. Burathi; A. Mycielski

    1997-01-01

    Site occupation preferences in zinc-blende Cdl-,Mn,Tel-,Se, (0.0 5 z 5 0.15; 0.0 5 y 5 0.20) quaternary alloys have been determined by the Extended X-ray Absorption Fine Structure (EXAFS) analysis. The experimental data have been collected with the use of synchrotron radiation for Se- and Mn-K edges. For both K edges, the references of manganese distribution around selenium have been

  1. 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.

  2. First-principles investigations of the atomic, electronic, and thermoelectric properties of equilibrium and strained Bi2Se3 and Bi2Te3 including van der Waals interactions

    NASA Astrophysics Data System (ADS)

    Luo, Xin; Sullivan, Michael B.; Quek, Su Ying

    2012-11-01

    Bi2Se3 and Bi2Te3 are layered compounds of technological importance, being excellent thermoelectric materials as well as topological insulators. We report density functional theory calculations of the atomic, electronic, and thermoelectric properties of strained bulk and thin-film Bi2Se3 and Bi2Te3, focusing on an appropriate description of van der Waals (vdW) interactions. The calculations show that the van der Waals density functional (vdW-DF) with Cooper's exchange (vdW-DFC09x) can reproduce closely the experimental interlayer distances in unstrained Bi2Se3 and Bi2Te3. Interestingly, we predict atomic structures that are in much better agreement with the experimentally determined structure from Nakajima than that obtained from Wyckoff, especially for Bi2Se3, where the difference in atomic structures qualitatively changes the electronic band structure. The band structure obtained using the Nakajima structure and the vdW-DFC09x optimized structure are in much better agreement with previous reports of photoemission measurements, than that obtained using the Wyckoff structure. Using vdW-DFC09x to fully optimize atomic structures of bulk and thin-film Bi2Se3 and Bi2Te3 under different in-plane and uniaxial strains, we predict that the electronic bandgap of both the bulk materials and thin films decreases with tensile in-plane strain and increases with compressive in-plane strain. We also predict, using the semiclassical Boltzmann approach, that the magnitude of the n-type Seebeck coefficient of Bi2Te3 can be increased by the compressive in-plane strain while that of Bi2Se3 can be increased with tensile in-plane strain. Further, the in-plane power factor of n-doped Bi2Se3 can be increased with compressive uniaxial strain while that of n-doped Bi2Te3 can be increased by compressive in-plane strain. Strain engineering thus provides a direct method to control the electronic and thermoelectric properties in these thermoelectric topological insulator materials.

  3. Zintl anions from the extraction of zintl phases with non-amine solvents: isolation of (Me/sub 4/N)/sub 4/Sn/sub 9/, (K(HMPA)/sub 2/)/sub 4/Sn/sub 9/, and K/sub 4/SnTe/sub 4/ and structural characterization of (Bu/sub 4/N)/sub 2/M/sub x/ (M = Te, x = 5; M = Se, x = 6; M = S, x = 6)

    SciTech Connect

    Teller, R.G.; Krause, L.J.; Haushalter, R.C.

    1983-01-01

    Polyatomic main-group anions like Sn/sub 9//sup 4 -/, Te/sub 5//sup 2 -/, Se/sub 6//sup 2 -/, S/sub 6//sup 2 -/, and SnTe/sub 4//sup 4 -/ have been isolated without the use of cryptate ligands. The polychalcogenides (Bu/sub 4/N)/sub 2/M/sub x/ (where M = Te, x = 5; M = Se, x = 6; M = S, x = 6; Bu = n-C/sub 4/H/sub 9/) are obtained by the aqueous extraction of binary alkali-metal/main-group alloys in the presence of Bu/sub 4/NBr. These polychalcogenides are isomorphous and have been structurally characterized by x-ray crystallography. The nonastannide(4-) anion has been isolated both as the tetrakis(tetramethylammonium) compound, ((CH/sub 3/)N)3$Sn/sub 9/, and as the HMPA (hexamethylphosphoric triamide) solvate, (K(HMPA)/sup 2/)/sub 4/Sn/sub 9/. Both compounds are somewhat thermally unstable at 25/sup 0/C. The compound K/sub 4/SnTe/sub 4/ has been isolated by the aqueous extraction of ternary K/Sn/Te alloys. 44 references, 2 figures, 1 table.

  4. Impact of Ge-Sb-Te compound engineering on the set operation performance in phase-change memories

    NASA Astrophysics Data System (ADS)

    Boniardi, Mattia; Ielmini, Daniele; Tortorelli, Innocenzo; Redaelli, Andrea; Pirovano, Agostino; Allegra, Mario; Magistretti, Michele; Bresolin, Camillo; Erbetta, Davide; Modelli, Alberto; Varesi, Enrico; Pellizzer, Fabio; Lacaita, Andrea L.; Bez, Roberto

    2011-04-01

    The phase-change memory (PCM) technology is considered as one of the most attractive non-volatile memory concepts for next generation data storage. It relies on the ability of a chalcogenide material belonging to the Ge-Sb-Te compound system to reversibly change its phase between two stable states, namely the poly-crystalline low-resistive state and the amorphous high-resistive state, allowing the storage of the logical bit. A careful study of the phase-change material properties in terms of the set operation performance, the program window and the electrical switching parameters as a function of composition is very attractive in order to enlarge the possible PCM application spectrum. Concerning the set performance, a crystallization kinetics based interpretation of the observed behavior measured on different Ge-Sb-Te compounds is provided, allowing a physics-based comprehension of the reset-to-set transition.

  5. 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

  6. One-pot synthesis of oleic acid-capped cadmium chalcogenides (CdE: E = Se, Te) nano-crystals

    Microsoft Academic Search

    P. K. Khanna; K. Srinivasa Rao; K. R. Patil; V. N. Singh; B. R. Mehta

    2010-01-01

    Surface-capped CdSe and CdTe nano-crystals (NCs) have been synthesized using cadmium acetate, oleic acid and respective tri-octylphosphine\\u000a chalcogenide (TOPE; E = Se\\/Te) in diphenyl ether (DPE). Well-dispersed CdSe particles showed two absorption bands at the region\\u000a of 431–34 and 458–60 nm in optical absorption study. A band-edge emission resulted at 515 nm with an excitation energy of\\u000a 400 nm, in its photoluminescence (PL) spectrum. Similarly,

  7. Study of B1 (NaCl-type) to B2 (CsCl-type) pressure-induced structural phase transition in BaS, BaSe and BaTe using ab initio computations

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Roehl, J. L.; Lind, C.; Khare, S. V.

    2013-02-01

    We have studied the pressure-induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in BaS, BaSe and BaTe by using ab initio density functional theory computations in the local density approximation. The Buerger and WTM mechanisms were explored by mapping the enthalpy contours in two- and four-dimensional configuration space for the two mechanisms, respectively. Transition pressures for BaS, BaSe and BaTe were determined to be 5.5 GPa, 4.9 GPa and 3.4 GPa, respectively. From these configuration space landscapes, a low enthalpy barrier path was constructed for the transitions to proceed at three different pressures. We obtained barriers of 0.18, 0.16 and 0.15 eV/pair (17.4, 15.4 and 14.5 kJ mol-1) for the Buerger mechanism and 0.13, 0.13 and 0.12 eV/pair (12.5, 12.5 and 11.6 kJ mol-1) for the WTM mechanism at the transition pressures for BaS, BaSe and BaTe, respectively, indicating that the WTM mechanism is slightly more favorable in these compounds. We describe the difference between the two mechanisms by differences in their symmetry and atomic coordination.

  8. Surfactant-free scalable synthesis of Bi2 Te3 and Bi2Se3 nanoflakes and enhanced thermoelectric properties of their nanocomposites.

    PubMed

    Min, Yuho; Roh, Jong Wook; Yang, Heeseung; Park, Minwoo; Kim, Sang Il; Hwang, Sungwoo; Lee, Sang Mock; Lee, Kyu Hyoung; Jeong, Unyong

    2013-03-13

    Surfactant-free nanoflakes of n-type Bi2 Te3 and Bi2 Se3 are synthesized in high yields. Their suspensions are mixed to create nanocomposites with heterostructured nanograins. A maximum ZT (0.7 at 400 K) is achieved with a broad content of 10-15% Bi2 Se3 in the nanocomposites. PMID:23161759

  9. 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.

  10. 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

  11. Optical study of ZnSe{sub x}Te{sub 1-x} alloys using spectroscopic ellipsometry

    SciTech Connect

    Lee, Hosun; Kim, S. M.; Seo, B. Y.; Seong, E. Z.; Choi, S. H.; Lee, S.; Furdyna, J. K.

    2000-11-06

    We report pseudodielectric function data <{epsilon}>=<{epsilon}{sub 1}>+i<{epsilon}{sub 2}> of ZnSe{sub x}Te{sub 1-x} samples grown on GaAs substrates. The data were obtained from 1.5 to 6.5 eV using spectroscopic ellipsometry. Critical-point parameters were obtained by fitting model line shapes to numerically calculated second-energy derivatives of <{epsilon}>. The bowing parameters of E{sub 0}, E{sub 1}, and E{sub 1}+{Delta}{sub 1} were determined and were comparable to that of E{sub 0} quoted from the literature. We observed a monotonic increase of the linewidth of the E{sub 1} gap up to x=0.85, whereas that of E{sub 1}+{Delta}{sub 1} showed a maximum value near x=0.5. We attribute this anomalous broadening of the E{sub 1} gap to sample microstructures developed in the low-Te composition alloys.

  12. 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.

  13. Influence of Group IV-Te Alloying on Nanocomposite Structure and Thermoelectric Properties of Bi 2 Te 3 Compounds

    Microsoft Academic Search

    D. G. Ebling; A. Jacquot; H. Böttner; L. Kirste; J. Schmidt; M. Aguirre

    2009-01-01

    Thermoelectric compounds based on doped bismuth telluride and its alloys have recently attracted increasing interest. Due\\u000a to their structural features they show increased values of the thermoelectric figure of merit (ZT). A promising approach to improve the thermoelectric properties is to manufacture nanocomposite materials exhibiting lower\\u000a thermal conductivities and higher ZT. The ZT value of compounds can be shifted reasonably

  14. Iron-chalcogenide FeSe(0.5)Te(0.5) Coated Superconducting Tapes for High Field Applications

    SciTech Connect

    Si, W.; Johnson, P.; Zhou, J.; Jie, Q.; Dimitrov, I.; Solovyov, V.; Jaroszynski, J.; Matias, V.; Sheehan, C.; Li, Q.

    2011-07-01

    The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe{sub 0.5}Te{sub 0.5} layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (> 1 x 10{sup 4} A/cm{sup 2}) at about 4.2 K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.

  15. Single crystal growth and characterization of Na3Bi and Bi2Te2Se topological materials

    NASA Astrophysics Data System (ADS)

    Kushwaha, Satya K.; Krizan, Jason W.; Cava, R. J.

    2015-03-01

    In recent years, the discoveries of topological insulators (TI) and three-dimensional (3D) Dirac semimetals (TDS) have been of significant interest in condensed matter science. To study these materials experimentally, it is of great importance to grow them in the form of high quality single crystals. Na3Bi is recently discovered TDS and Bi2Te2Se3 (BTS) is one of the interesting TI materials. Na3Bi is extremely air sensitive and shows nontrivial crystallization behavior. BTS crystals usually grow with various point defects and typically exhibit metallic behavior. Here we will report the crystal growth of high quality Na3Bi and insulating BTS single crystals. The characterization of their electronic properties by our collaborators in physics at Princeton and Brookhaven National Laboratory will be briefly described. The growth of single crystals of TIs and TDS is supported at Princeton by grants from the ARO MURI and DARPA.

  16. 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

  17. Size dependent acoustic phonon dynamics of CdTe0.68Se0.32 nanoparticles in borosilicate glass

    NASA Astrophysics Data System (ADS)

    Gupta, Sanjeev K.; Jha, Prafulla K.; Arora, A. K.

    2008-06-01

    Low frequency acoustic vibration and phonon linewidth for CdTe0.68Se0.32 nanoparticle embedded in borosilicate glass are calculated using two different approaches by considering the elastic continuum model and fixed boundary condition. The presence of medium significantly affects the phonon peaks and results into the broadening of the modes. The linewidth is found to depend inversely on the size, similar to that reported experimentally. The damping time and quality factor have also been calculated. The damping time that is of the order of picoseconds decreases with the decrease in size. High value of quality factor for l =2 normal mode suggests the less loss of energy for this mode.

  18. Reversible tuning of the surface state in a pseudobinary Bi2(Te-Se)3 topological insulator

    SciTech Connect

    Jiang, Rui; Wang, Lin-Lin; Huang, Mianliang; Dhaka, Rajendra S.; Johnson, Duane D.; Lograsso, Thomas A.; Kaminski, Adam

    2012-08-10

    We use angle-resolved photoemission spectroscopy to study a nontrivial surface state in a pseudobinary Bi2Te2.8Se0.2 topological insulator. We show that, unlike previously studied binaries, this is an intrinsic topological insulator with the conduction bulk band residing well above the chemical potential. Our data indicate that under a good vacuum condition there are no significant aging effects for more than two weeks after cleaving. We also demonstrate that the shift of the Kramers point at low temperature is caused by UV-assisted absorption of molecular hydrogen. Our findings pave the way for applications of these materials in devices and present an easy scheme to tune their properties.

  19. 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

  20. Synthesis and characterization of CdTe/CdSe core/shell nanoparticles with high emission from 570 to 610 nm

    NASA Astrophysics Data System (ADS)

    Rojas Valencia, O. G.; Casas Espinola, J. L.; Corea Tellez, M.

    2015-06-01

    The paper presents the advance process of synthesis of CdTe/CdSe core/shell Quantum Dots (QDs) with emission wavelength from 570 to 610 nm. This synthesis was performed using modified Hot-Injection method. The CdTe/CdSe core-shell QDs have been characterized by the transmission electron microscopy (TEM) with the aim to control the QDs shape and the average size. The optical absorption and photoluminescence (PL) spectra are investigated in four samples obtained at different reaction times (5, 10, 15 and 20 s) of core growth after the CdSe passivation of the CdTe cores. Obtained results have shown that synthesized QDs have a good crystallinity, spherical shape and bright emission at 610 nm. The reaction time enlargement permits increasing the average size of CdTe/CdSe core-shell QDs, together with “red” shifting the PL wavelength and increasing the PL intensity. The advantages of synthesized CdTe/CdSe core/shell QDs are discussed.

  1. 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.

  2. Structural investigation of the CuSe-InSe-GaSe phase diagram, X-ray photoemission and optical properties of the Cu{sub 1-z}(In{sub 0.5}Ga{sub 0.5}){sub 1+z\\/3}Se compounds

    Microsoft Academic Search

    M. Souilah; A. Lafond; C. Guillot-Deudon; S. Harel; M. Evain

    2010-01-01

    Structures of compounds in the CuSe-InSe-GaSe system have been investigated through X-ray diffraction. Single crystal structure studies for the so-called stoichiometric compounds Cu(In,Ga)Se (CIGSe) confirm that the chalcopyrite structure (space group I4-bar 2d) is very flexible and can adapt itself to the substitution of Ga for In. On the other hand a structure modification is evidenced in the Cu{sub 1-z}(In{sub

  3. Transmittance spectra of the CuGa{sub 3}Se{sub 5} ternary compound near the fundamental absorption edge

    SciTech Connect

    Bodnar, I. V., E-mail: chemzav@bsuir.by [Belarusian State University of Information and Radio Electronics (Belarus)

    2011-04-15

    The CuGa{sub 3}Se{sub 5} ternary compound films are produced by laser deposition at the substrate temperatures 480 and 580 K. The composition and structure of the films are studied. It is shown that, similarly to the corresponding crystals, the CuGa{sub 3}Se{sub 5} films crystallize into the imperfect chalcopyrite structure. The transmittance spectra near the fundamental absorption edge are used to establish the energies and nature of optical transitions. The energies of crystal-field splitting ({Delta}{sub cr}) and spin-orbit splitting ({Delta}{sub SO} of the valence band of the CuGa{sub 3}Se{sub 5} ternary compound are calculated in the context of the Hopfield quasi-cubic model.

  4. Thermoelectric properties of Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} single crystals with magnetic impurities

    SciTech Connect

    Kulbachinskii, V.A., E-mail: kulb@mig.phys.msu.ru [M.V. Lomonosov Moscow State University, Low Temperature Physics and Superconductivity, Faculty of Physics, Leninskie Gory, 1-3, 119991 GSP-1 Moscow (Russian Federation); Kytin, V.G.; Kudryashov, A.A.; Tarasov, P.M. [M.V. Lomonosov Moscow State University, Low Temperature Physics and Superconductivity, Faculty of Physics, Leninskie Gory, 1-3, 119991 GSP-1 Moscow (Russian Federation)] [M.V. Lomonosov Moscow State University, Low Temperature Physics and Superconductivity, Faculty of Physics, Leninskie Gory, 1-3, 119991 GSP-1 Moscow (Russian Federation)

    2012-09-15

    Temparature dependence of Seebeck coefficients S, electrical conductivity, heat conductivity k and dimensionless thermoelectric figure of merit ZT of p-Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and n-Bi{sub 2}Se{sub 3}-doped by Fe or Cr were carried out in the temperature interval 7Te{sub 3}, while the electron concentration increases in n-Bi{sub 2-x}Fe{sub x}Se{sub 3}. The decrease of the hole concentration was observed in p-Sb{sub 2-x}Cr{sub x}Te{sub 3} single crystals with Cr-doping. This demonstrates that Fe or Cr act as donors. The Seebeck coefficient increases in p-Bi{sub 2-x}Fe{sub x}Te{sub 3} and Sb{sub 2-x}Cr{sub x}Te{sub 3} with increasing Fe or Cr content, while it decreases in n-Bi{sub 2-x}Fe{sub x}Se{sub 3}. Cr-doping increases dimensionless thermoelectric figure of merit ZT in Sb{sub 2}Te{sub 3} at T>150 K. - Graphical abstract: Temparature dependence of Seebeck coefficients S, electrical conductivity {sigma}, heat conductivity k and dimensionless thermoelectric figure of merit ZT of p-Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and n-Bi{sub 2}Se{sub 3} doped by Fe or Cr were measured in the temperature interval 7Te{sub 3} and Sb{sub 2-x}Cr{sub x}Te{sub 3} with increasing Fe or Cr content, while it decreases in n-Bi{sub 2-x}Fe{sub x}Se{sub 3}. Cr-doping increases thermoelectric figure of merit in Sb{sub 2}Te{sub 3} at T>150 K up to ZT=0.4 as shown in figure. Highlights: Black-Right-Pointing-Pointer Fe and Cr act as donors in Bi{sub 2}Te{sub 3}, Sb{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3.} Black-Right-Pointing-Pointer The Seebeck coefficient increases in p-Bi{sub 2-x}Fe{sub x}Te{sub 3} and Sb{sub 2-x}Cr{sub x}Te{sub 3}. Black-Right-Pointing-Pointer Dimensionless figure of merit ZT increased up to 0.4 in Cr-doped Sb{sub 2}Te{sub 3} at T=300 K.

  5. Ordered vacancy compound CuIn3Se5 on GaAs (100): Epitaxial growth and characterization

    NASA Astrophysics Data System (ADS)

    Nelson, A. J.; Horner, G. S.; Sinha, K.; Bode, M. H.

    1994-06-01

    Epitaxial growth of the ordered vacancy compound CuIn3Se5 has been achieved on GaAs (100) by molecular beam epitaxy from Cu2Se and In2Se3 sources. Electron probe microanalysis and x-ray diffraction have confirmed the composition for the 1-3-5 phase and that the films are single-crystal CuIn3Se5 (100). Transmission electron microscopy characterization of the material also showed it to be single crystalline. Structural defects in the layer consisted mainly of stacking faults. Photoluminescence measurements performed at 7.5 K indicate that the band gap is 1.28 eV. Raman spectra reveal a strong polarized peak at 152 cm-1, which is believed to arise from the totally symmetric vibration of the Se atoms in the lattice.

  6. CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES: Phase Transition and Phonon Spectrum of Zinc-Blende Structure ZnX (X = S, Se, Te)

    NASA Astrophysics Data System (ADS)

    Tan, Jia-Jin; Ji, Guang-Fu; Chen, Xiang-Rong; Gou, Qing-Quan

    2010-06-01

    Calculations have been performed to investigate the pressure-induced solid-solid phase transitions and the mechanical stability for three zinc-blende II-VI semiconductor compounds: ZnS, ZnSe, ZnTe by ab initio plane-wave pseudopotential density functional theory (DFT). Using the generalized gradient approximation (GGA) for exchange and correlation in the scheme of Perdew-Wang 1991 (PW91), the ground state properties and equation of state are obtained, which are well consistent with the experimental data available and other calculations. On the basis of the forth-order Birch-Murnaghan equation of states, the transition pressures Pt are determined through the analysis of enthalpy variation with pressure. A linear-response approach is used to calculate the frequencies of the phonon dispersion. Finally, by the calculations of phonon frequencies, some thermodynamic properties such as the vibrational contribution to the Helmholtz free energy (F), enthalpy (H), entropy (S), and the heat capacity (CV) are also successfully obtained.

  7. Synthesis and superconductivity in spark plasma sintered pristine and graphene-doped FeSe0.5Te0.5

    NASA Astrophysics Data System (ADS)

    Puneet, Pooja; Podila, Ramakrishna; He, Jian; Rao, Apparao; Howard, Austin; Cornell, Nicholas; Zakhidov, Anvar A.; Department of Physics; Astronomy, Clemson Nanomaterials Center, Clemson University Team; Nanotech Institute, University of Texas at Dallas Team

    2015-03-01

    Replace this text with your abstract body. Here, we present a new ball-milling and spark plasma sintering based technique for the facile synthesis FeSe0.5Te0.5 superconductors (SC) without the need for pre-alloying. This method is advantageous since it is quick and flexible for incorporating other dopants such as graphene for vortex pinning. We observed that FeSe0.5Te0.5 exhibits a coexistence of ferromagnetic (FM) and SC signature plausibly arising from a FM core-SC shell structure. More importantly, the Hc2 values observed from resistivity data are higher than 7 T indicating that SPS process synthesized FeSe0.5Te0.5 samples could lead to nextgeneration superconducting wires and cables.

  8. Ambipolar charge injection and transport of few-layer topological insulator Bi2Te3 and Bi2Se3 nanoplates

    NASA Astrophysics Data System (ADS)

    Hao, Guolin; Qi, Xiang; Liu, Yundan; Huang, Zongyu; Li, Hongxing; Huang, Kai; Li, Jun; Yang, Liwen; Zhong, Jianxin

    2012-06-01

    We report the electrostatic properties of few-layer Bi2Te3 and Bi2Se3 nanoplates (NPs) grown on 300 nm SiO2/Si substrate. Electrons and holes are locally injected in Bi2Te3 and Bi2Se3 nanoplates by the apex of an atomic force microscope tip. Both carriers are delocalized uniformly over the whole nanoplate. The electrostatic property of topological insulator Bi2Te3 and Bi2Se3 nanoplates after charge injection is characterized by Kelvin probe force microscopy under ambient environment and exhibits an ambipolar surface potential behavior. These results provide insight into the electronic properties of topological insulators at the nanometer scale.

  9. Near infrared absorption of CdSe(x)Te(1-x) alloyed quantum dot sensitized solar cells with more than 6% efficiency and high stability.

    PubMed

    Pan, Zhenxiao; Zhao, Ke; Wang, Jin; Zhang, Hua; Feng, Yaoyu; Zhong, Xinhua

    2013-06-25

    CdSe0.45Te0.55 alloyed quantum dots (QDs) with excitonic absorption onset at 800 nm and particle size of 5.2 nm were prepared via a noninjection high-temperature pyrolysis route and used as a sensitizer in solar cells. A postsynthesis assembly approach with use of bifunctional linker molecule mercaptopropionic acid (MPA) capped water-soluble QDs, obtained via ex situ ligand exchange from the initial oil-dispersible QDs, was adopted for tethering QDs onto mesoporous TiO2 film. With the combination of high loading of the QD sensitizer and intrinsic superior optoelectronic properties (wide absorption range, high conduction band edge, high chemical stability, etc., relative to their constituents CdSe and CdTe) of the adopted CdSe0.45Te0.55 QD sensitizer, the resulting CdSexTe1-x alloyed QD-based solar cells exhibit a record conversion efficiency of 6.36% (Jsc = 19.35 mA/cm(2), Voc = 0.571 V, FF = 0.575) under full 1 sun illumination, which is remarkably better than that of the reference CdSe and CdTe QD based ones. Furthermore, the solar cells with Cu2S counter electrodes based on eletrodeposition of Cu on conductive glass show long-term (more than 500 h) stability. PMID:23705771

  10. Pure rotational spectra of PbSe and PbTe: potential function, Born-Oppenheimer breakdown, field shift effect and magnetic shielding.

    PubMed

    Giuliano, Barbara M; Bizzocchi, Luca; Cooke, Stephen; Banser, Deike; Hess, Mareike; Fritzsche, Juliane; Grabow, Jens-Uwe

    2008-04-21

    The pure rotational spectra of 41 isotopic species of PbSe and PbTe have been measured in their X 1Sigma+ electronic state with a resonator pulsed-jet Fourier transform microwave spectrometer. The molecules were prepared by laser ablation of suitable target rods and stabilised in supersonic jets of noble gas. Global multi-isotopologue analyses yielded spectroscopic Dunham parameters Y01, Y11, Y21, Y31, Y02, and Y12 for both species, as well as effective Born-Oppenheimer breakdown (BOB) coefficients delta01 for Pb, Se and Te. Unusual large values of the BOB parameters for Pb have been rationalized in terms of finite nuclear size (field shift) effect. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the X 1Sigma+ electronic state of both PbSe and PbTe. Additionally, the magnetic hyperfine interactions produced by the uneven mass number A nuclei 207Pb, 77Se, 123Te, and 125Te were observed, yielding first determinations of the corresponding nuclear spin-rotation coupling constants. PMID:18688362

  11. Photoelectrical properties of Te-substituted Sn-Sb-Se Semiconducting thin films

    NASA Astrophysics Data System (ADS)

    Chander, Ravi; Thangaraj, R.

    2011-12-01

    Thin films of Sn10Sb20Se70-XTeX (0?X?8) composition were deposited using thermal evaporation technique. The prepared films were found amorphous by X-ray diffraction studies. Surface roughness was found to be ˜2 nm and grain size ˜30 nm from SPM studies. The dark conductivity measurements showed thermally activated conduction. Photoconductivity measurements showed no maxima in the measured temperature regime and thus materials belong to type II photoconductor. The dc-activation energy for photoconductivity ?Eph has values smaller than dc-activation energy for dark conductivity ?E. Intensity variation of photocurrent obeys power law with exponent ?˜0.56-0.64 revealing the dominant bimolecular recombination mechanism. Transient photoconductivity measurement showed that the initial rise and decay of photocurrent becomes slow with tellurium content in the sample. The decay process after initial decay was found to be non-exponential and described as differential life time of charge carrier which decreases with tellurium content in the sample.

  12. Anion substitution effects on the structure and magnetism of the chromium chalcogenide Cr{sub 5}Te{sub 8}-Part III: Structures and magnetism of the high-temperature modification Cr{sub (1+x)}Q{sub 2} and the low-temperature modification Cr{sub (5+x)}Q{sub 8} (Q=Te, Se; Te:Se=5:3)

    SciTech Connect

    Wontcheu, Joseph [Institute of Inorganic Chemistry, Christian-Albrechts-University Kiel, Olshausenstr. 40, D-24098 Kiel (Germany); Bensch, Wolfgang [Institute of Inorganic Chemistry, Christian-Albrechts-University Kiel, Olshausenstr. 40, D-24098 Kiel (Germany)], E-mail: wbensch@ac.uni-kiel.de; Mankovsky, Sergiy; Polesya, Svitlana; Ebert, Hubert [Department of Chemistry, LMU Munich, Butenandstr. 3-13, D-81377 Munich (Germany); Kremer, Reinhard K.; Bruecher, Eva [Max-Planck Institut fuer Festkoerperforschung, Heisenbergstr. 1, D-70506 Stuttgart (Germany)

    2008-06-15

    The title compounds were synthesized via the high-temperature (HT) route. The materials are characterized by Rietveld analysis, magnetic measurements, and electronic band-structure calculations. Two different structural modifications depending on the synthesis conditions are observed: a HT modification with trigonal basic cells (space group: P-3m1) for Cr{sub (1+x)}Q{sub 2} ((1+x)=1.25, 1.28, 1.34, 1.37, 1.41, 1.43) and a low-temperature (LT) modification with trigonal super-cell (space group: P-3m1) for Cr{sub (5+x)}Q{sub 8} ((5+x)=5.00, 5.12, 5.36, 5.48, 5.64, 5.72). The crystal structures are closely related to the NiAs-type structure with metal vacancies in every second metal layer. The substitution of Te by Se and the change of the Cr concentration induce significant alterations of the magnetic properties. With increasing Cr content the Weiss constant {theta} changes drastically from negative to strong positive values, i.e., with increasing Cr concentration a shift from predominant antiferromagnetic exchange to ferromagnetic exchange occurs. At LTs a complex magnetic behavior is observed. For some members a spin-glass (SG) behavior is found with the freezing temperature T{sub f} following the Vogel-Fulcher law. At the highest Cr concentrations ferromagnetic characteristics dominate with spontaneous magnetizations below the Curie temperatures. The differences of the magnetic properties of the LT and HT phases can be explained on the basis of interatomic distances and angles. For a deeper understanding of the experimental results, they have been compared with the results of spin polarized relativistic Korringa-Kohn-Rostoker electronic band-structure calculations and both results are consistent. To explain the features of temperature-dependent magnetization of the compounds, Monte Carlo (MC) simulations based on the Heisenberg model have been performed with the exchange coupling parameters obtained within the ab-initio calculations of the electronic structure. The possible reasons for a modification of the exchange coupling parameters responsible for the temperature-dependent features are also analyzed. - Graphical abstract: The magnetic properties of Cr{sub 1+x}Q{sub 2} and Cr{sub 5+x}Te{sub 5}Se{sub 3} (Q=Te, Se; ratio=5:3) are strongly influenced by the Cr content and the crystal structure with the Weiss constant and Curie temperature covering a large range.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Ambika; Barman, P. B.

    2010-02-01

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

  15. 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

  16. Kinetics of amorphous-crystallization transformation of Se85-xTe15Snx (x = 2, 4 and 6) alloys under non-isothermal conditions using Matusita's approach

    NASA Astrophysics Data System (ADS)

    Patial, Balbir Singh; Thakur, Nagesh; Tripathi, S. K.

    2013-02-01

    The present study reports the assessment of activation energy for crystallization and crystallization reaction order (Avrami exponent n) for the crystallization process of Se85-xTe15Snx (x = 2, 4 and 6) amorphous alloys by means of differential scanning calorimetry (DSC) technique under non-isothermal conditions at four different heating rates (5, 10, 15 and 20°Cmin-1) using Matusita's approach. It is remarkable to note that double crystallization behaviour has been observed for Sn additive Se-Te investigated samples. In the present paper, the kinetic analysis of amorphous-crystallization transformation for the first peak has been reported and discussed.

  17. 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.

  18. Photoinduced Dynamics in the Charge Density Wave Compound 4HB-TaSe2

    NASA Astrophysics Data System (ADS)

    Erasmus, N.; Eichberger, M.; Haupt, K.; Boshoff, I.; Kassier, G.; Bimurske, R.; Berger, H.; Demsar, J.; Schwoerer, H.

    2013-03-01

    We report on ultrafast photoindued charge density wave (CDW) dynamics in the transition-metal dichalcogenide 4Hb-TaSe2, studied with ultrafast electron diffraction. Fluence dependence of the lattice superstructure suppression show a phase transition from the commensurate to the incommensurate phase of 4Hb-TaSe2. Unusually long recovery times of perturbed charge density waves indicate th importance of a coupling between the two dimensional CDWs.

  19. Enhanced thermoelectric performance in Cd doped CuInTe2 compounds

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    CuIn1-xCdxTe2 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 CuInTe2 and the low temperature Hall mobility is also modeled. By combing theoretical model and experiment data, the optimum carrier concentration in CuInTe2 is proposed to explain the greatly enhanced power factors in the Cd doped CuInTe2. 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 CuIn0.98Cd0.02Te2 and CuIn0.9Cd0.1Te2 samples, which are improved by over 100% at room temperature and around 20% at 600 K.

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

    SciTech Connect

    Pfuner, F.; Degiorgi, L.; /Zurich, ETH; 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.

  1. 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 ...

  2. PHYSICAL REVIEW B 86, 066501 (2012) Comment on "Precision global measurements of London penetration depth in FeTe0.58Se0.42"

    E-print Network

    Paris-Sud XI, Université de

    2012-01-01

    PHYSICAL REVIEW B 86, 066501 (2012) Comment on "Precision global measurements of London penetration penetration depth deduced from tunnel diode oscillator (TDO) measurements in optimally doped Fe(Se,Te) single penetration depth below Tc/3. Moreover, they claim that their results are also ruling out the suggestion

  3. 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

  4. Integrated-optics elements based on CdS(x)Se(1-x) semiconducting compounds

    NASA Astrophysics Data System (ADS)

    Buachidze, Z. E.; Goldobin, I. S.; Morozov, V. N.; Pletnev, V. A.; Semenov, A. S.

    Recent developments in integrated optics based on CdS(x)Se(1-x) semiconductors are reviewed. These include the fabrication of planar and stripline waveguides with losses of 3-5 dB/cm, various forbidden zone widths, and light conversion efficiencies at waveguide interfaces greater than of 90 percent. Analytical and experimental data are presented on the acoustic and electrooptical interaction in a thin CdS(x)Se(1-x) layer on a Bragg-type transducer with a pin electrode system period of 8 mm. Attention is also given to the performance of a Mach-Zehnder interferometer controlled by 0.44-micron emission.

  5. Comment on 'Precision global measurements of London penetration depth in FeTe0.58Se0.42'

    SciTech Connect

    Cho, Kyuil; Kim, Hyunsoo; Tanatar, Makariy A.; Prozorov, Ruslan

    2012-08-21

    We reply to the Comment by Klein, Rodière, and Marcenat [ Phys. Rev. B 86 066501 (2012)] on our paper [ Phys. Rev. B 84 174502 (2011)]. Our work was motivated by Klein et al. [ Phys. Rev. B 82 184506 (2010)]. In their paper, Klein et al. have attributed a factor of 5 difference in the value of the London penetration depth obtained from their tunnel diode resonator (TDR) measurements and calculated from the “field of first penetration”to the surface roughness, although they have not verified it experimentally. In our paper, we have studied the effects of deliberately introduced surface roughness and found that its effects are minor and cannot be responsible for the difference of such magnitude. Instead, we suggest that the value of the field of first penetration measured with Hall arrays cannot be used to extract a true lower critical field due to several reasons outlined in our Reply. We emphasize that the accuracy of the calibration procedure of the TDR technique has been carefully verified in several prior studies and our work on FeTe0.58Se0.42 further confirms it. We show that in their Comment, Klein et al. use wrong arguments of the universal behavior of the superfluid density in the gapless limit, because it is inapplicable for the multiband superconductors. We also discuss the applicability of the clean-limit ? model and the influence of the disorder on the obtained results.

  6. Optical parameters of ternary Te15(Se100-xBix)85 thin films deposited by thermal evaporation

    NASA Astrophysics Data System (ADS)

    Kumar, Kameshwar; Sharma, Pankaj; Katyal, S. C.; Thakur, Nagesh

    2011-10-01

    Thin films of Te15(Se100-xBix)85 (x=0, 1, 2, 3, 4 and 5 at.%) glassy alloys were deposited by thermal evaporation (at 10-4 Pa) from bulk samples. Optical characterization of the films was done by analysing their transmission spectra taken in the spectral range 400-2300 nm. Swanepoel's method was used to calculate the refractive index (n) and extinction coefficient (k). It was found that the refractive index increases with an increase in Bi content. The Wemple-DiDomenico single-oscillator approach was used to calculate the average band gap energy (Eo), dispersion energy (Ed) and static refractive index (no). The absorption coefficient (?) and film thickness were calculated from the transmission spectra of the films. The optical band gap (Eg) was estimated using Tauc's extrapolation and was found to decrease from 1.37 to 1.21 eV with Bi addition from 0 to 5 at.% in glassy alloys. The decrease in optical band gap is explained on the basis of the decrease in cohesive energy of the samples and the difference of electronegativity of the atoms involved. The real (?r) and imaginary parts (?i) of the dielectric constant for the films were also calculated and reported.

  7. BaCu2Se2 based compounds as promising thermoelectric materials.

    PubMed

    Li, Jing; Zhao, Li-Dong; Sui, Jiehe; Berardan, David; Cai, Wei; Dragoe, Nita

    2015-02-01

    In the past few years, many studies have been devoted to the thermoelectric properties of copper selenides and sulfides, and several families of materials have been developed with promising performances. In this paper, we report on the synthesis and thermoelectric properties of Na-doped BaCu2Se2 from 20 K to 773 K. By Na doping at the Ba site, the electrical conductivity can be increased by 2 orders of magnitude, and the power factor can reach 8.2 ?W cm(-1) K(-2) at 773 K. Combined with a low thermal conductivity of 0.65 W m(-1) K(-1), a ZT of 1.0 has been obtained for Ba0.925Na0.075Cu2Se2 at 773 K, which is the highest value reported in this family to date. However, BaCu2Se2 volatilizes at 473 K, so a protective coating is necessary for its application. Besides, we studied the thermal expansion coefficient of BaCu2Se2 in this paper. PMID:25531095

  8. 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.

  9. Study of B1 (NaCl-type) to B2 (CsCl-type) pressure-induced structural phase transition in BaS, BaSe and BaTe using first-principles computations

    NASA Astrophysics Data System (ADS)

    Khare, Sanjay; Zhou, Xiuquan; Roehl, Jason L.; Lind, Cora

    2013-03-01

    We have studied the pressure-induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in BaS, BaSe and BaTe by using ab initio density functional theory computations in the local density approximation. The Buerger and WTM[2] mechanisms were explored by mapping the enthalpy contours in two and four dimensional configuration space for the two mechanisms, respectively. Transition pressures for BaS, BaSe and BaTe were determined to be 5.5 GPa, 4.9 GPa and 3.4 GPa, respectively. From these configuration space landscapes, a low enthalpy barrier path was constructed for the transitions to proceed at three different pressures. We obtained barriers of 0.18, 0.16 and 0.15 eV/pair (17.4, 15.4 and 14.5 kJ/mol) for the Buerger mechanism and 0.13, 0.13 and 0.12 eV/pair (12.5, 12.5 and 11.6 kJ/mol) for the WTM mechanism at the transition pressures for BaS, BaSe and BaTe, respectively, indicating that the WTM mechanism is slightly more favorable in these compounds. We describe the difference of the two mechanisms by differences in their symmetry and atomic coordination. We have studied the pressure-induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in BaS, BaSe and BaTe by using ab initio density functional theory computations in the local density approximation. The Buerger and WTM[2] mechanisms were explored by mapping the enthalpy contours in two and four dimensional configuration space for the two mechanisms, respectively. Transition pressures for BaS, BaSe and BaTe were determined to be 5.5 GPa, 4.9 GPa and 3.4 GPa, respectively. From these configuration space landscapes, a low enthalpy barrier path was constructed for the transitions to proceed at three different pressures. We obtained barriers of 0.18, 0.16 and 0.15 eV/pair (17.4, 15.4 and 14.5 kJ/mol) for the Buerger mechanism and 0.13, 0.13 and 0.12 eV/pair (12.5, 12.5 and 11.6 kJ/mol) for the WTM mechanism at the transition pressures for BaS, BaSe and BaTe, respectively, indicating that the WTM mechanism is slightly more favorable in these compounds. We describe the difference of the two mechanisms by differences in their symmetry and atomic coordination. National Science Foundation (#DMR 1005911, #DMR 0705464, #CMMI 1234777 and CNS 0855134), Ohio Supercomputer Center (OSC).

  10. Topological insulators with unexpectedly HgTe-like band inversion in hexagonal wurtzite-type binary compounds

    NASA Astrophysics Data System (ADS)

    Zhang, X. M.; Ma, R. S.; Liu, X. C.; Xu, G. Z.; Liu, E. K.; Liu, G. D.; Liu, Z. Y.; Wang, W. H.; Wu, G. H.

    2013-09-01

    By using first-principles calculations, we propose a new topological insulator family in hexagonal wurtzite-type binary compounds. As a result, we found that two compounds AuI and strained-AgI are three-dimensional topological insulators with a naturally opened band gap at the Fermi level. By considering the band inversion mechanism, this new family of topological insulators shows an unexpectedly HgTe-like, i.e., s(\\Gamma_{6})\\text{-} p(\\Gamma_{8}) band inversion. These findings suggest that, in these wurtzite-type compounds, the spin-orbit coupling may not play a crucial role in the band inversion mechanism; on the contrary, it is mainly responsible for the formation of the global band gaps. We further theoretically explore the feasibility of tuning the topological order of the wurtzite compounds AuI and AgI with two types of strains (hydrostatic and uniaxial). The results indicate that the uniaxial strain can significantly influence the band inversion behavior and the underlying physical mechanism is discussed.

  11. FAST TRACK COMMUNICATION: ZnSe/ZnTe(shell/shell) radial quantum-wire heterostructures: the excitonic properties

    NASA Astrophysics Data System (ADS)

    Bagheri, Mehran

    2010-07-01

    The ground-state characteristics of spatially indirect excitons trapped in radially heteronanostructured type-II band alignment ZnSe/ZnTe nanotubes as functions of the magnetic field for nanotubes with a radial size both smaller and larger than the effective Bohr radius are theoretically investigated. In the former case, dominated by the net kinetic energy of the electron and hole, the magnetic field modifies the exciton spectrum through the well-known Zeeman splitting, intra-orbital-state Aharonov-Bohm oscillations and inter-orbital-state crossovers occurring in very strong magnetic field strengths. However, in the latter case, dominated by the electron-hole Coulomb attraction, the magnetic field adjusts the exciton lines only by means of the Zeeman splitting and inter-orbital-state transitions happening in typical magnetic fields. As a result, the angular momentum transitions occurr at lower magnetic fields when the radial size of the nanotube is increased. Most importantly, another consequence is the substantially unusual exciton oscillator strength in such heteronanostructures. It is shown that when the exciton is optically active, due to the full cylindrical symmetry of the problem, the exciton oscillator strength shows undamped oscillations. This effect is associated with the periodic redistribution of the exciton density as the magnetic field is varied. Also, the magnitude of the magnetically induced excitonic persistent current is decreased with increasing radial size of the nanotube. This study may provide a platform to investigate new photonic quantum interference as well as polarization-sensitive photodetector and photovoltaic devices based on the Aharonov-Bohm effect.

  12. 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.

  13. 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.

  14. Structures, phase transitions and electrical properties of Ag 5Te 2? y Se y Cl ( y = 0 –0.7)

    Microsoft Academic Search

    Tom Nilges; Cornelia Dreher; Anna Hezinger

    2005-01-01

    Herein we report the structural, thermal and physical properties of Ag5Te2?ySeyCl (y=0–0.7). Polymorphic Ag5Te2Cl (y=0) is an ion conductor with two reversible phase transitions at 241 and 334 K. While the monoclinic room temperature ?- and the low temperature ?-phase show conductivities below ?=10?3??1cm?1, the tetragonal high temperature ?-phase is a promising conductor for electronic devices with conductivities up to

  15. 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

  16. Excitation spectra and ground-state properties from density functional theory for the inverted band-structure systems $\\beta$-HgS, HgSe, and HgTe

    E-print Network

    Delin, A

    2002-01-01

    We have performed a systematic density-functional study of the mercury chalcogenide compounds $\\beta$-HgS, HgSe, and HgTe using an all-electron full-potential linear muffin-tin orbital (FP-LMTO) method. We find that, in the zinc-blende structure, both HgSe and HgTe are semimetals whereas $\\beta$-HgS has a small spin-orbit induced band gap. Our calculated relativistic photoemission and inverse photoemission spectra (PES and IPES, respectively) reproduce very well the most recently measured spectra, as do also our theoretical optical spectra. In contrast to the normal situation, we find that the local density approximation (LDA) to the density functional gives calculated equilibrium volumes in much better agreement with experiment than does the generalized gradient corrected functional (GGA). We also address the problem of treating relativistic $p$ electrons with methods based on a scalar-relativistic basis set, and show that the effect is rather small for the present systems.

  17. Crystal structure and properties of a new mixed-valence compound LiMn 2TeO 6 and the survey of the LiMM'XO 6 family (X = Sb or Te)

    NASA Astrophysics Data System (ADS)

    Pospelov, A. A.; Nalbandyan, V. B.; Serikova, E. I.; Medvedev, B. S.; Evstigneeva, M. A.; Ni, E. V.; Lukov, V. V.

    2011-11-01

    A new compound, LiMn 2+Mn 3+TeO 6, was prepared by solid-state reactions and characterized by powder X-ray diffraction, redox titration, conductivity, magnetic measurements and cycling behaviour in an electrochemical cell with Li counter electrode. It is triclinic, P1, a = 5.1077(1), b = 8.5707(1), c = 5.0589(1), ? = 92.515(1)°, ? = 92.092(2)°, ? = 89.818(2)°, Z = 2. The structure is based on strongly distorted hexagonal close packing of oxygen anions with cations occupying octahedral voids and represents the ordered variant of orthorhombic Li 2TiTeO 6 structure, derived from LiSbO 3. TeO 6 octahedra are almost regular but all four independent MnO 6 octahedra display severe distortions. Room-temperature conductivity is unexpectedly low for a mixed-valence compound, 2 × 10 -7 S/cm. Together with the observed antiferromagnetic exchange interaction, this is a prerequisite for the colossal magnetoresistance effect. The unit cell volumes of LiMn 2TeO 6, LiSbO 3, Li 2M 4+TeO 6 and LiMM'XO 6 series (a total of 21 compounds) correlate well with average cationic radii, but LiMn 2SbO 6 deviates considerably, and its preparation could not be reproduced.

  18. 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., E-mail: btrump1@jhu.edu [Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218 (United States); Department of Physics and Astronomy, Institute for Quantum Matter, Johns Hopkins University, Baltimore, MD 21218 (United States); Livi, Kenneth J.T. [HRAEM Facility, Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD 21218 (United States); McQueen, Tyrel M., E-mail: mcqueen@jhu.edu [Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218 (United States); Department of Physics and Astronomy, Institute for Quantum Matter, Johns Hopkins University, Baltimore, MD 21218 (United States)

    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}.

  19. Magneto-optical characterizations of FeTe0.5Se0.5 thin films with critical current density over 1 MA cm?2

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    We performed magneto-optical (MO) measurements on FeTe0.5Se0.5 thin films grown on LaAlO3 (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 over 1× {{10}6} A c{{m}-2} at 5 K was obtained. Magnetic flux penetration measurement reveals that the current is almost isotropically distributed in the two thin films. Compared with bulk crystals, FeTe0.5Se0.5 thin film demonstrates not only higher Tc, but also much larger Jc, which is attractive for applications.

  20. 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.

  1. Thermal studies of Se{sub 85-x}Te{sub 15}In{sub x} (x = 3,6,9,12) glasses

    SciTech Connect

    Sushama, D. [Dept. of Physics, MSM College, Kayamkulam, Kerala (India); George, Achamma [Dept. of Physics, St. Stephans' College, Pathanapuram, Kerala (India); Asokan, S. [Dept. of Instrumentation, Indian Institute of Science, Bangalore (India)

    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.

  2. Structural investigation of the Cu{sub 2}Se-In{sub 2}Se{sub 3}-Ga{sub 2}Se{sub 3} phase diagram, X-ray photoemission and optical properties of the Cu{sub 1-z}(In{sub 0.5}Ga{sub 0.5}){sub 1+z/3}Se{sub 2} compounds

    SciTech Connect

    Souilah, M. [Institut des Materiaux Jean Rouxel (IMN), Universite de Nantes, CNRS 2, rue de la Houssiniere, BP 32229, 44322 Nantes Cedex 03 (France); Lafond, A., E-mail: Alain.Lafond@cnrs-imn.f [Institut des Materiaux Jean Rouxel (IMN), Universite de Nantes, CNRS 2, rue de la Houssiniere, BP 32229, 44322 Nantes Cedex 03 (France); Guillot-Deudon, C.; Harel, S.; Evain, M. [Institut des Materiaux Jean Rouxel (IMN), Universite de Nantes, CNRS 2, rue de la Houssiniere, BP 32229, 44322 Nantes Cedex 03 (France)

    2010-10-15

    Structures of compounds in the Cu{sub 2}Se-In{sub 2}Se{sub 3}-Ga{sub 2}Se{sub 3} system have been investigated through X-ray diffraction. Single crystal structure studies for the so-called stoichiometric compounds Cu(In,Ga)Se{sub 2} (CIGSe) confirm that the chalcopyrite structure (space group I4-bar 2d) is very flexible and can adapt itself to the substitution of Ga for In. On the other hand a structure modification is evidenced in the Cu{sub 1-z}(In{sub 0.5}Ga{sub 0.5}){sub 1+z/3}Se{sub 2} series when the copper vacancy ratio (z) increases; the chalcopyrite structure turns to a modified-stannite structure (I4-bar 2m) when z{>=}0.26. There is a continuous evolution of the structure from Cu{sub 0.74}(In{sub 0.5}Ga{sub 0.5}){sub 1.09}Se{sub 2} to Cu{sub 0.25}(In{sub 0.5}Ga{sub 0.5}){sub 1.25}Se{sub 2} ((i.e. Cu(In{sub 0.5}Ga{sub 0.5}){sub 5}Se{sub 8}), including Cu{sub 0.4}(In{sub 0.5}Ga{sub 0.5}){sub 1.2}Se{sub 2} (i.e. Cu(In{sub 0.5}Ga{sub 0.5}){sub 3}Se{sub 5}). From this single crystal structural investigation, it is definitively clear that no ordered vacancy compound exists in that series. X-ray photoemission spectroscopy study shows for the first time that the surface of powdered Cu{sub 1-z}(In{sub 0.5}Ga{sub 0.5}){sub 1+z/3}Se{sub 2} compounds (z{ne}0) is more copper-poor than the bulk. The same result has often been observed on CIGSe thin films material for photovoltaic applications. In addition, optical band gaps of these non-stoichiometric compounds increase from 1.2 to 1.4 eV when z varies from 0 to 0.75. - Abstract: Pseudo-ternary diagram in the Cu{sub 2}Se-In{sub 2}Se{sub 3}-Ga{sub 2}Se{sub 3} system showing the composition of all the synthesized compounds. The crystal structure of the compounds corresponding to red circles are presented in this study.

  3. Role of phonon subsystems in second order optical effects in semiconductor semimagnetic Pb1-xRxX (R=Pr, Yb and X=S, Se, Te)

    Microsoft Academic Search

    K. Nouneh; I. Kityk; S. Benet; R. Viennois; S. Charar; Z. Golacki

    2005-01-01

    Measurements of transport and non-linear optical properties in magnetic semiconductors Pb1-xRxX (R=Pr, Yb and X=S, Se, Te at x≈1-3%) were performed to elucidate an influence of magnetic ions on behavior of the charge carriers. It was shown that nonlinear optical methods may be used as a sensitive tool for investigation of electron-phonon an harmonicity near the low temperature semiconductor isolator

  4. Effect of temperature and pumping power on the photoluminescence properties of type-II CdTe/CdSe core-shell QDs

    NASA Astrophysics Data System (ADS)

    Saad, A. M.; Bakr, M. M.; Azzouz, I. M.; Abou Kana, Maram T. H.

    2011-08-01

    CdTe/CdSe core-shell QDs type II was prepared by two steps synthetic process and embedded in polymer host. Emission in the NIR region was recorded. The effect of Ar laser excitation at different powers on the optical properties of the prepared QDs is studied at different temperatures (300-10 K). Amplified spontaneous emission is observed at room temperature and at 10 K. Also, lifetime measurement of prepared QDs was documented using N 2-laser.

  5. A study of band-bending and barrier height variation in thin film n-CdSe 0.5Te 0.5 photoanode\\/polysulphide junctions

    Microsoft Academic Search

    V. Damodara Das; Laxmikant Damodare

    1996-01-01

    Polycrystalline thin films of n-CdSe0.5Te0.5 were deposited in a vacuum of 5 × 10?5torr by thermal flash evaporation with a deposition rate of 20 ± 1 A?s?1 on indium oxide coated glass plates [? = 1.25 × 104 (?cm)?1] held at a temperature of 473 K. The change in the pH value of the polysulphide electrolyte from 12.5 to 8.0

  6. Tight-binding study of ZnSe\\/ZnTe strained superlattices: Determination of the band offset from the optical properties

    Microsoft Academic Search

    F. Malonga; D. Bertho; C. Jouanin; J.-M. Jancu

    1995-01-01

    We have theoretically studied large-, short-, and very-short-period ZnSe\\/ZnTe strained superlattices. We use an sp3s* tight-binding model with spin-orbit coupling in order to calculate energies of superlattice electronic states and optical transition probabilities. This enables us to estimate the valence-band offset considering many experimental studies on a large range of samples with various thicknesses and strain states. For large-period superlattices,

  7. ATOMIC AND MOLECULAR PHYSICS: Calculated cross sections for the single ionization of atoms (N, Cu, As, Se, Sn, Sb, Te, I, Pb) by electron impact

    NASA Astrophysics Data System (ADS)

    Hou, Yu-Jun; Cheng, Xin-Lu; Chen, Heng-Jie

    2009-02-01

    By correcting some primary parameters in the semi-classical Deutsch-Märk (DM) formula, this paper calculates the absolute single electron-impact ionization cross sections of atoms N, Cu, As, Se, Sn, Sb, Te, I and Pb from threshold to 10000 eV. The calculated cross sections are compared with available experimental data and other theoretical results. An excellent agreement was achieved between the calculated and measured cross sections for these atoms over a wide range of impact energies.

  8. 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

    2015-05-01

    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

  9. Temperature and composition phase diagram in the iron-based ladder compounds Ba1-xCsxFe2Se3

    NASA Astrophysics Data System (ADS)

    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.

    2015-05-01

    We investigated the iron-based ladder compounds (Ba,Cs ) Fe2Se3 . Their parent compounds BaFe2Se3 and CsFe2Se3 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 BaFe2Se3 is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe2Se3 is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe2Se3 , 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.

  10. 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; Chi, Songxue; Ueda, Yutaka; Yoshizawa, Hideki; Sato, Taku J.

    2015-05-01

    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.

  11. 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

  12. Electrochemiluminescence energy transfer-promoted ultrasensitive immunoassay using near-infrared-emitting CdSeTe/CdS/ZnS quantum dots and gold nanorods

    PubMed Central

    Li, Lingling; Chen, Ying; Lu, Qian; Ji, Jing; Shen, Yuanyuan; Xu, Mi; Fei, Rong; Yang, Guohai; Zhang, Kui; Zhang, Jian-Rong; Zhu, Jun-Jie

    2013-01-01

    The marriage of energy transfer with electrochemiluminescence has produced a new technology named electrochemiluminescence energy transfer (ECL-ET), which can realize effective and sensitive detection of biomolecules. To obtain optimal ECL-ET efficiency, perfect energy overlapped donor/acceptor pair is of great importance. Herein, we present a sensitive ECL-ET based immunosensor for the detection of tumor markers, using energy tunable CdSeTe/CdS/ZnS double shell quantum dots (QDs) and gold nanorods (GNRs) as the donor and acceptor, respectively. Firstly a facile microwave-assisted strategy for the synthesis of green- to near-infrared-emitting CdSeTe/CdS/ZnS QDs with time- and component-tunable photoluminescence was proposed. And, on the basis of the adjustable optical properties of both CdSeTe/CdS/ZnS QDs and GNRs, excellent overlap between donor emission and acceptor absorption can be obtained to ensure effective ECL-ET quenching, thus improving the sensing sensitivity. This method represents a novel approach for versatile detection of biomolecules at low concentrations. PMID:23524874

  13. 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.

  14. 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.

  15. Electrochemiluminescence energy transfer-promoted ultrasensitive immunoassay using near-infrared-emitting CdSeTe/CdS/ZnS quantum dots and gold nanorods.

    PubMed

    Li, Lingling; Chen, Ying; Lu, Qian; Ji, Jing; Shen, Yuanyuan; Xu, Mi; Fei, Rong; Yang, Guohai; Zhang, Kui; Zhang, Jian-Rong; Zhu, Jun-Jie

    2013-01-01

    The marriage of energy transfer with electrochemiluminescence has produced a new technology named electrochemiluminescence energy transfer (ECL-ET), which can realize effective and sensitive detection of biomolecules. To obtain optimal ECL-ET efficiency, perfect energy overlapped donor/acceptor pair is of great importance. Herein, we present a sensitive ECL-ET based immunosensor for the detection of tumor markers, using energy tunable CdSeTe/CdS/ZnS double shell quantum dots (QDs) and gold nanorods (GNRs) as the donor and acceptor, respectively. Firstly a facile microwave-assisted strategy for the synthesis of green- to near-infrared-emitting CdSeTe/CdS/ZnS QDs with time- and component-tunable photoluminescence was proposed. And, on the basis of the adjustable optical properties of both CdSeTe/CdS/ZnS QDs and GNRs, excellent overlap between donor emission and acceptor absorption can be obtained to ensure effective ECL-ET quenching, thus improving the sensing sensitivity. This method represents a novel approach for versatile detection of biomolecules at low concentrations. PMID:23524874

  16. Variation of Nd and Vfb for different compositions of CdSe xTe 1-x thin films by pulse plating technique

    NASA Astrophysics Data System (ADS)

    Saaminathan, V.; Murali, K. R.

    2006-03-01

    CdSe xTe 1-x thin films with 0SeO 2, TeO 2 and H 2SO 4 as precursors. As-deposited and annealed films coated on Ti, Ni and SS were characterized by X-ray diffraction technique and SEM, and their electrical properties were studied. The as-deposited films exhibited a cubic structure; those after heat treatment at 500 °C in air exhibited a hexagonal structure. Variation of donor concentration and the flat band potential for different values of ‘ x’ and duty cycles were studied for CdSe xTe 1-x thin films. The semiconductor parameters for all compositions coated on Ti, Ni and SS were estimated. It showed good agreement with the earlier reports.

  17. Dynamics and mechanism of oxygen annealing in Fe1+yTe0.6Se0.4 single crystal

    PubMed Central

    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 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. PMID:24695095

  18. 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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    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.

  19. 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, E-mail: takashiri@tokai-u.jp; Imai, Kazuo; Uyama, Masato; Nishi, Yoshitake [Department of Materials Science, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292 (Japan); Hagino, Harutoshi; Miyazaki, Koji [Department of Mechanical and Control Engineering, Kyushu Institute of Technology, 1-1 Sensui, Tobata-ku, Kitakyushu 804-8550 (Japan); Tanaka, Saburo [Department of Mechanical Engineering, College of Engineering, Nihon University, Nakagawara, Tokusada, Tamuramachi, Koriyama, Fukushima 963-8642 (Japan)

    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.

  20. Compositional dependence of the local structure of Se{sub x}Te{sub 1-x} alloys: Electron energy-loss spectra, real-space multiple-scattering calculations, and first-principles molecular dynamics

    SciTech Connect

    Katcho, N. A. [Departamento de Quimica Inorganica I, Facultad CC. Quimicas, UCM, E-28040 Madrid (Spain); Instituto de Quimica Fisica Rocasolano, CSIC, Serrano 119, E-28006, Madrid (Spain); Lomba, E. [Instituto de Quimica Fisica Rocasolano, CSIC, Serrano 119, E-28006, Madrid (Spain); Urones-Garrote, E.; Otero-Diaz, L. C. [Departamento de Quimica Inorganica I, Facultad CC. Quimicas, UCM, E-28040 Madrid (Spain); Landa-Canovas, A. R. [Instituto Ciencia de Materiales, CSIC, 28049 Cantoblanco, Madrid (Spain)

    2006-06-01

    In this work we present an investigation on the composition dependence of the local structure in Se{sub x}Te{sub 1-x} crystalline alloys analyzing their experimental energy-loss spectra with the aid of a real-space multiple-scattering modeling approach and first-principles molecular dynamics. The concourse of this latter technique is essential for a proper modeling of the alloy spectra. From our results, it can be inferred that Se{sub x}Te{sub 1-x} alloys exhibit a high degree of substitutional disorder ruling out the existence of fully ordered alternating copolymer chains of Se and Te atoms.

  1. 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.

  2. New barium copper chalcogenides synthesized using two different chalcogen atoms: Ba2Cu(6-x)STe4 and Ba2Cu(6-x)Se(y)Te(5-y).

    PubMed

    Mayasree, Oottil; Sankar, Cheriyedath Raj; Assoud, Abdeljalil; Kleinke, Holger

    2011-05-16

    Ba(2)Cu(6-x)STe(4) and Ba(2)Cu(6-x)Se(y)Te(5-y) were prepared from the elements in stoichiometric ratios at 1123 K, followed by slow cooling. These chalcogenides are isostructural, adopting the space group Pbam (Z = 2), with lattice dimensions of a = 9.6560(6) Å, b = 14.0533(9) Å, c = 4.3524(3) Å, and V = 590.61(7) Å(3) in the case of Ba(2)Cu(5.53(3))STe(4). A significant phase width was observed in the case of Ba(2)Cu(6-x)Se(y)Te(5-y) with at least 0.17(3) ? x ? 0.57(4) and 0.48(1) ? y ? 1.92(4). The presence of either S or Se in addition to Te appears to be required for the formation of these materials. In the structure of Ba(2)Cu(6-x)STe(4), Cu-Te chains running along the c axis are interconnected via bridging S atoms to infinite layers parallel to the a,c plane. These layers alternate with the Ba atoms along the b axis. All Cu sites exhibit deficiencies of up to 26%. Depending on y in Ba(2)Cu(6-x)Se(y)Te(5-y), the bridging atom is either a Se atom or a Se/Te mixture when y ? 1, and the Te atoms of the Cu-Te chains are partially replaced by Se when y > 1. All atoms are in their most common oxidation states: Ba(2+), Cu(+), S(2-), Se(2-), and Te(2-). Without Cu deficiencies, these chalcogenides were computed to be small gap semiconductors; the Cu deficiencies lead to p-doped semiconducting properties, as experimentally observed on selected samples. PMID:21510642

  3. 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.

  4. Ferromagnetism of Narrow-Gap Ge1-x-ySnxMnyTe and Layered In1-xMnxSe Semiconductors

    NASA Astrophysics Data System (ADS)

    Lashkarev, G. V.; Sichkovskyi, V. I.; Radchenko, M. V.; Dmitriev, A. I.; Slyn'ko, V. E.; Slyn'ko, E. I.; Kovalyuk, Z. D.; Butorin, P. E.; Knoff, W.; Story, T.; Szymczak, R.; Jakie?a, R.; Aleshkevych, P.; Dobrowolski, W.

    2008-11-01

    Magnetic susceptibility, Hall effect and resistivity of narrow-gap Ge1-x-ySnxMnyTe single crystals (x=0.083÷0.115; y=0.025÷0.124) were investigated in the temperature range 4.2-300 K revealing a ferromagnetic ordering at TC?50 K. Temperature dependence of magnetization indicates a superparamagnetic phase with magnetic clusters arranging in a spin glass state below the freezing temperature Tf . Magnetic structure of InSe 2D-ferromagnetic single crystals was studied by SQUID magnetometry, neutron diffraction, secondary ion mass spectroscopy, and wave dispersive spectra. Hysteresis loops of magnetization were observed at least up to 350 K. The cluster model of ferromagnetism is considered. The formation of self-assembled superlattice ferromagnetic InSe:Mn/antiferromagnetic MnSe during growth process and further annealing was established.

  5. Resistivity anisotropy of the Bi-based misfit layer compounds (BiS)1.11(NbS2) and (BiSe)1.10(NbSe2) down to the liquid nitrogen temperature

    NASA Astrophysics Data System (ADS)

    Nader, A.

    2006-09-01

    The resistivity in the transverse and parallel directions of the superconducting misfit layer compounds (BiS)1.11(NbS2) and (BiSe)1.10(NbSe2) has been measured down to the liquid nitrogen temperature. The resistivity anisotropy for these two compounds was found to increase when the temperature is lowered and its value in the temperature range of our measurement is two orders of magnitude greater than the value expected by Lawrence and Doniach model.

  6. 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.

  7. 15% Efficiency CdS\\/CdTe thin film solar cells using CdS layers doped with metal organic compounds

    Microsoft Academic Search

    Kengo Matsune; Hiroyuki Oda; Toshihiko Toyama; Hiroaki Okamoto; Yuriy Kudriavysevand; René Asomoza

    2006-01-01

    For improving the photovoltaic performance of CdS\\/CdTe thin film solar cells, the CdS window layer is one of the most crucial factors. Here we demonstrate the photovoltaic performances of the low-environmental-load CdS\\/CdTe solar cell employing the CdS layer doped with various metal organic (MO) compounds, i.e., (CH3)2SnCl2, (C6H5)3GeCl, (CH3CO2)3In, [(C2H5)2NCS2]2Zn. Due to the MO doping, the degree of (111) preferential

  8. Raman scattering from vibrational and electronic excitations in a II-VI quaternary compound: Cd1-x-yZnxMnyTe

    Microsoft Academic Search

    Eunsoon Oh; R. G. Alonso; I. Miotkowski; A. K. Ramdas

    1992-01-01

    The Raman scattering in a II-VI quaternary compound (Cd1-x-yZnxMnyTe) exhibits zone-center optical phonons whose frequencies vary with composition in a manner amenable to an extension of the modified random-element isodisplacement model. As a member of diluted magnetic semiconductors, Cd1-x-yZnxMnyTe exhibits the characteristic large magnetic-field-dependent redshift of the excitonic photoluminescence, the Raman-electron paramagnetic resonance of Mn2+, and an evidence of the

  9. Thermoelectric Properties of Nb3SbxTe7-x Compounds Sidney Wang, G. Jeff Snyder, and Thierry Caillat

    E-print Network

    and subsequently analyzed for their Seebeck voltage, heat conduction, and electrical resistivity. Results indicate. Experimental Samples of Nb3SbxTe7-x were made from powders of 99.95% (Nb3SbTe6, Nb3Sb2Te5, Nb3Sb3Te4) or 99 environments, heated to 973 K, and hot pressed 20,000 psi for two hours. Compositions tested included

  10. Quantum anomalous Hall effect in doped ternary chalcogenide topological insulators TlBiTe2 and TlBiSe2

    NASA Astrophysics Data System (ADS)

    Niu, Chengwang; Dai, Ying; Yu, Lin; Guo, Meng; Ma, Yandong; Huang, Baibiao

    2011-10-01

    Ternary Chalcogenide TlBiTe2 and TlBiSe2 have been proved to be promising topological insulators. In the present work, the occurrence of quantum anomalous Hall effect for a model Hamiltonian with ferromagnetic order is predicted. The first-principle calculations reveal that Cr is the best candidate to induce the ferromagnetic order in the insulating phase among X (X = Ti, Cr, Fe, and Au). The magnetic order in insulating phase arises from the spin polarization of substitutional Cr atoms and the free carriers are not needed for the formation of the substantial ferromagnetic coupling. These are very significant for the dissipationless devices in spintronics.

  11. 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.

  12. Simulation of channel orientation dependent transport in ultra-scaled monolayer MoX2 (X = S, Se, Te) n-MOSFETs

    NASA Astrophysics Data System (ADS)

    Chang, Jiwon

    2015-04-01

    Transport properties of about 3?nm channel length monolayer MoX2 (X = S, Se, Te) n-channel metal-oxide-semiconductor field effect transistors (MOSFETs) are examined through ballistic full-band quantum transport simulations with atomistic tight-binding Hamiltonians. Our simulations reveal that single gate (SG) monolayer MoX2 MOSFETs with an approximately 2?nm gate underlap exhibit reasonable subthreshold characteristics. From these full-band simulations, we observe channel orientation dependent negative differential resistance (NDR) in the out characteristics in the ballistic transport regime. We discuss and compare NDR properties of monolayer MoX2 n-channel MOSFETs in different transport directions.

  13. Spin Polarization and Transport of Surface States in the Topological Insulators Bi2Se3 and Bi2Te3 from First Principles

    Microsoft Academic Search

    Oleg V. Yazyev; Joel E. Moore; Steven G. Louie

    2010-01-01

    We investigate the band dispersion and the spin texture of topologically\\u000aprotected surface states in the bulk topological insulators Bi2Se3 and Bi2Te3\\u000aby first-principles methods. Strong spin-orbit entanglement in these materials\\u000areduces the spin-polarization of the surface states to ~50% in both cases; this\\u000areduction is absent in simple models but of important implications to\\u000aessentially any spintronic application. We

  14. First-principles study on electronic and optical properties of Cu2ZnSiV I4 (VI=S, Se, and Te) quaternary semiconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Xuebiao; Rao, Dewei; Lu, Ruifeng; Deng, Kaiming; Chen, Dongguo

    2015-05-01

    The electronic and optical properties of Cu2ZnSiS4, Cu2ZnSiSe4 and Cu2ZnSiTe4 in kesterite and stannite structures are systematically studied using first-principles calculations. Crystal field splitting, optical transitions, p-d bonding, and anti-bonding overlapping are analyzed. The physical and chemical trends in these properties are investigated with respect to the crystal structure and anion atomic number. The optical spectra, such as dielectric function, refractive index, reflectivity and absorption coefficient are explored in a broad range of energy. A good agreement between the calculated results and experimental data is obtained.

  15. Estimation of the Activation Energy for the Non-isothermal Crystallization in Amorphous Se70Te15In15 Alloy Using Iso-conversional Methods

    NASA Astrophysics Data System (ADS)

    Patial, Balbir Singh; Thakur, Nagesh; Tripathi, S. K.

    2011-07-01

    Differential scanning calorimetry (DSC) has been used to study the kinetics of amorphous to crystalline transformation in Se70Te15In15 glass under non-isothermal conditions at four different heating rates of 5, 10, 15 and 20 °C/min. The activation energy of crystallization has been determined by analyzing the data using the iso-conversional methods of Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW) and Friedman. The present work shows that the activation energy of crystallization is not constant but varies with degree of conversion and hence with temperature.

  16. Ballistic performance comparison of monolayer transition metal dichalcogenide MX2 (M = Mo, W; X = S, Se, Te) metal-oxide-semiconductor field effect transistors

    NASA Astrophysics Data System (ADS)

    Chang, Jiwon; Register, Leonard F.; Banerjee, Sanjay K.

    2014-02-01

    We study the transport properties of monolayer MX2 (M = Mo, W; X = S, Se, Te) n- and p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using full-band ballistic non-equilibrium Green's function simulations with an atomistic tight-binding Hamiltonian with hopping potentials obtained from density functional theory. We discuss the subthreshold slope, drain-induced barrier lowering (DIBL), as well as gate-induced drain leakage (GIDL) for different monolayer MX2 MOSFETs. We also report the possibility of negative differential resistance behavior in the output characteristics of nanoscale monolayer MX2 MOSFETs.

  17. Single-crystal structures, optical absorptions, and electronic distributions of thorium oxychalcogenides ThOQ (Q = S, Se, Te).

    PubMed

    Koscielski, Lukasz A; Ringe, Emilie; Van Duyne, Richard P; Ellis, Donald E; Ibers, James A

    2012-08-01

    The compounds ThOS, ThOSe, and ThOTe have been synthesized, and their structures have been determined by means of single-crystal X-ray diffraction methods. All three compounds adopt the PbFCl structure type in the tetragonal space group D(4h)(7) - P4/nmm. More precise crystallographic data have been obtained for ThOS and ThOSe, which had previously only been known from X-ray powder diffraction data. ThOS, ThOSe, and ThOTe are yellow-, orange-, and black-colored, respectively. From single-crystal optical absorption measurements the band gaps are 2.22, 1.65, and 1.45 eV, respectively. Optical band gaps, ionic charges, and densities of states were calculated for the three compounds with the use of Density Functional methods. PMID:22799890

  18. Dynamics of bright and dark localized excitonic magnetic polarons in CdMnTe spin glass compound

    NASA Astrophysics Data System (ADS)

    Gnatenko, Yuriy; Bukivskij, Petro; Piryatinski, Yuriy

    2015-03-01

    The measurements of the magnetic properties of spin glass (SG) system indicate that the magnetic relaxation is characterized by a broad range of times below Tf. Here, for the first time, we have investigated time-resolved photoluminescence spectra of Cd0.70Mn0.30Te SG compound at the temperature below the freezing temperature Tf. This enables us to study the dynamics of different localized excitonic magnetic polarons (LEMPs) at T = 0.7Tfexcited in the crystal regions where various microscopic magnetic spin states (MMSSs) are formed. It was found that there is a broad distribution of the lifetimes of the LEMPs which have different lifetimes but same energies. It was shown that the presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states as a result of the local magnetic fields formation. The lifetimes of these dark LEMPs correspond to hundreds of nanoseconds. It was also found that the decay process of the PL exciton band intensity is described by the Kohlrausch-Williams-Watts stretched exponential function which describes the recombination processes which correspond to the emission of the LEMPs formed in the crystal region of the finite clusters as well as the infinite cluster. These complex dynamical phenomena, observed for Cd1-XMnXTe at low temperatures, reflect the spatially heterogeneous dynamics in the SG system which is due to the presence of different MMSSs below Tf.

  19. New Layered Compounds with the General Composition (MO) (CuSe), Where M = Bi, Nd, Gd, Dy, and BiOCuS: Syntheses and Crystal Structure

    NASA Astrophysics Data System (ADS)

    Kusainova, A. M.; Berdonosov, P. S.; Akselrud, L. G.; Kholodkovskaya, L. N.; Dolgikh, V. A.; Popovkin, B. A.

    1994-09-01

    The syntheses of four new copper oxyselenides with the general formula (MO)(CuSe) ( M = Bi, Nd, Gd, Dy) and one copper oxysulfide, BiOCuS, are reported. The tetragonal unit cell dimensions of all compounds are given. A new bismuth-copper oxyselenide, BiOCuSe, has been structurally characterized from powder X-ray diffraction data and finally solved by the Rietveld profile method with RI = 0.069. The BiCuSeO crystal structure is formed by alternating [Bi 2O 2] and [Cu 2Se 2] layers.

  20. Interlayer vibrational modes in few-quintuple-layer Bi2Te3 and Bi2Se3 two-dimensional crystals: Raman spectroscopy and first-principles studies

    NASA Astrophysics Data System (ADS)

    Zhao, Yanyuan; Luo, Xin; Zhang, Jun; Wu, Junxiong; Bai, Xuxu; Wang, Meixiao; Jia, Jinfeng; Peng, Hailin; Liu, Zhongfan; Quek, Su Ying; Xiong, Qihua

    2014-12-01

    Layered materials, such as graphite/graphene, boron nitride, transition metal dichalcogenides, represent materials in which reduced size, dimensionality, and symmetry play critical roles in their physical properties. Here, we report on a comprehensive investigation of the phonon properties in the topological insulator Bi2Te3 and Bi2Se3 two-dimensional (2D) crystals, with the combination of Raman spectroscopy, first-principles calculations, and group theory analysis. Low frequency (<30 c m-1) interlayer vibrational modes are revealed in few-quintuple-layer (QL) B i2T e3/B i2S e3 2D crystals, which are absent in the bulk crystal as a result of different symmetries. The experimentally observed interlayer shear and breathing mode frequencies both show blueshifts, with decreasing thickness in few-QL Bi2Te3 (down to 2QL) and Bi2Se3 (down to 1QL), in agreement with first-principles calculations and a linear chain model, from which the interlayer coupling force constants can be estimated. Besides, an intense ultralow (<12 c m-1) frequency peak is observed in 2-4QL Bi2Te3 , which is tentatively attributed to a substrate-induced interface mode supported by a linear chain model analysis. The high frequency Raman peaks exhibit frequency shifts and broadening from 3D to 2D as a result of the phonon confinement effect. Our studies shed light on a general understanding of the influence of dimensionality and crystal symmetry on the phonon properties in layered materials.

  1. Structural and optical absorption studies on polycrystalline PbxSn1-xTe0.5Se0.5 thin films

    NASA Astrophysics Data System (ADS)

    El-Sayad, E. A.; Farag, B. S.; Farag, I. S.; Amin, A. T.

    2007-09-01

    Polycrystalline ingots of PbxSn1-xTe0.5Se0.5 (x = 0.4, 0.6, 0.8 and 1.0) were synthesized. Thin films of PbxSn1-xTe0.5Se0.5 were prepared by conventional thermal evaporation of the prereacted materials. The chemical composition of the starting materials as well as thin films revealed that they are nearly stoichiomeric. The crystal structure and the unit cell lattice parameters of the starting materials were determined from x-ray diffraction studies. It was revealed that the as-deposited and annealed films are polycrystalline with the single phase of the rock salt (NaCl) structure as that of the bulk material with a (2 0 0) predominant reflecting plane. The optical absorption of the annealed films at 473 K was determined from the optical transmittance data in the spectral range 2.5-10 µm. The analysis of the optical absorption spectra of the investigated films revealed direct energy gaps. However, the band gaps showed linear variation with the value of x.

  2. Optical band gap and refractive index dispersion parameters of As x Se70Te30- x (0? x?30 at.%) amorphous films

    NASA Astrophysics Data System (ADS)

    Aly, Kamal A.

    2010-06-01

    Amorphous As x Se70Te30- x thin films with (0? x?30 at.%) were deposited onto glass substrates by using thermal evaporation method. The transmission spectra T( ?) of the films at normal incidence were measured in the wavelength range 400-2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model (WDD). Increasing As content is found to affect the refractive index and the extinction coefficient of the As x Se70Te30- x films. With increasing As content the optical band gap increases while the refractive index decreases. The optical absorption is due to allowed indirect transition. The chemical bond approach has been applied successfully to interpret the increase of the optical gap with increasing As content.

  3. Crystal structure and cation distribution in the solid solution series 2(ZnX) CuInX2 (X=S, Se, Te)

    NASA Astrophysics Data System (ADS)

    Schorr, S.; Tovar, M.; Sheptyakov, D.; Keller, L.; Geandier, G.

    2005-11-01

    The solid solution series (2ZnX)x (CuInX2)1-x (X=S, Se, Te) were studied by the combination of laboratory and synchrotron X-ray and by neutron powder diffraction. Within the homologous series the tetragonal distortion ¼-u increases in the sequence S?Se?Te whereas the tetragonal deformation ?=c/2a decreases. Besides that, with increasing 2ZnX content in CuInX2 the anion position parameter u increases as expected. The cation site occupancy in the chalcopyrite type phase of single phase tetragonal samples was obtained by Rietveld analysis of the neutron diffraction data. A non-statistic Zn distribution could be deduced for all three systems. The high temperature in situ diffraction experiments with synchrotron radiation on CuInX2 powder samples revealed the Cu In anti-site occupation as the driving force of the temperature dependent phase transition from the chalcopyrite to the zinc-blende type structure.

  4. 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. [Department of Physics and Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing 211189 (China); Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500 (Australia); Yeoh, W. K., E-mail: waikong.yeoh@sydney.edu.au, E-mail: zxshi@seu.edu.cn [Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500 (Australia); Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales 2006 (Australia); School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006 (Australia); Cui, X. Y.; Ringer, S. P. [Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, New South Wales 2006 (Australia); School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, Sydney, New South Wales 2006 (Australia); Kim, J. H.; Shi, D. Q.; Wang, X. L.; Dou, S. X. [Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500 (Australia); Shi, Z. X., E-mail: waikong.yeoh@sydney.edu.au, E-mail: zxshi@seu.edu.cn [Department of Physics and Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing 211189 (China)

    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.

  5. Transport and optical properties of heavily hole doped semiconductors BaCu2Se2 and BaCu2Te2

    SciTech Connect

    McGuire, Michael A [ORNL; May, Andrew F [ORNL; Singh, David J [ORNL; Du, Mao-Hua [ORNL; Jellison Jr, Gerald Earle [ORNL

    2011-01-01

    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 {le} 300 K, and optical transmission and diffuse reflectance data at room temperature. Nominally stoichiometric, polycrystalline samples form with hole concentrations inferred from Hall measurements of 2 x 10{sup 18} and 5 x 10{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.

  6. Electronic and Optical Properties of Core/Shell Pb16X16/Cd52X52 (X =S, Se, Te) Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tamukong, Patrick; Mayo, Michael; Kilina, Svetlana

    2015-03-01

    The electronic and optoelectronic properties of semiconductor quantum dots (QDs) are mediated by surface defects due to the presence of dangling bonds producing trap states within the HOMO-LUMO energy gap, and contributing to fluorescence quenching. Surface capping ligands are generally used to alleviate this problem and increase the quantum yields of QDs. An alternative way is to synthesize core-shell QD structures; i.e., a QD core with a shell of another semiconductor material. We have investigated the effects of Cd52X52 shells on the photoexcited dynamics of Pb16X16 (X =S, Se, Te) QDs. The thin (~ 0.50 nm) shells were found to result largely in type I core/shell structures and a blue shift of the absorption spectra. Our studies revealed fairly strong core-shell hybridization in the electronic states close to the conduction band (CB) edge for Pb16S16andPb16Se16 cores, whereas for the Pb16Te16 core, such CB states were largely shell-like in nature. Nonadiabatic DFT-based dynamics, coupled with the surface hopping method, was used to study the effects of the core and shell compositions on energy relaxation rates in these systems.

  7. 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.

  8. Ultraviolet and visible range plasmonics in the topological insulator Bi1.5Sb0.5Te1.8Se1.2.

    PubMed

    Ou, Jun-Yu; So, Jin-Kyu; Adamo, Giorgio; Sulaev, Azat; Wang, Lan; Zheludev, Nikolay I

    2014-01-01

    The development of metamaterials, data processing circuits and sensors for the visible and ultraviolet parts of the spectrum is hampered by the lack of low-loss media supporting plasmonic excitations. This has driven the intense search for plasmonic materials beyond noble metals. Here we show that the semiconductor Bi1.5Sb0.5Te1.8Se1.2, also known as a topological insulator, is also a good plasmonic material in the blue-ultraviolet range, in addition to the already-investigated terahertz frequency range. Metamaterials fabricated from Bi1.5Sb0.5Te1.8Se1.2 show plasmonic resonances from 350 to 550?nm, while surface gratings exhibit cathodoluminescent peaks from 230 to 1,050?nm. The observed plasmonic response is attributed to the combination of bulk charge carriers from interband transitions and surface charge carriers of the topological insulator. The importance of our result is in the identification of new mechanisms of negative permittivity in semiconductors where visible range plasmonics can be directly integrated with electronics. PMID:25295413

  9. 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, E-mail: tanming912@163.com; 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.

  10. Hydrothermal synthesis and thermoelectric properties of nanostructured Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds

    SciTech Connect

    Zhang, Yanhua [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China) [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China); Academy of Equipment Command and Technology, Beijing 102249 (China); Xu, Guiying [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China)] [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China); Mi, Jianli [Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, DK-8000 Aarhus (Denmark)] [Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, DK-8000 Aarhus (Denmark); Han, Fei; Wang, Ze [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China)] [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China); Ge, Changchun, E-mail: ccge@mater.ustb.edu.cn [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China)] [Institute of Special Ceramics and Powder Metallurgy, University of Science and Technology Beijing, No. 30, Xueyuan Road, Beijing 100083 (China)

    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.

  11. 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

  12. Dimerization of pentanuclear clusters [Fe3Q(AsMe)(CO)9] (Q = Se, Te) as a conversion pathway to novel cubane-like aggregates.

    PubMed

    Pushkarevsky, Nikolay A; Konchenko, Sergey N; Zabel, Manfred; Bodensteiner, Michael; Scheer, Manfred

    2011-03-01

    The first examples of carbonyl heterocubane-type clusters, [Fe(4)(?(3)-Q)(2)(?(3)-AsMe)(2)(CO)(12)] (2, Q = Se (a), Te (b)), which simultaneously contain elements of group 15 and 16, were obtained by thermolysis of [Fe(3)(?(3)-Q)(?(3)-AsMe)(CO)(9)] (1) in acetonitrile. The clusters 2 possess a cubic Fe(4)Q(2)As(2) core with alternating Fe and Q/As atoms. The coordination environment of the Fe atoms is close to octahedral, and those of Q or As atoms are tetrahedral, which determines the distorted cubic cluster core geometry. The second main products of thermolysis are the clusters [Fe(6)(?(3)-Q)(?(4)-Q)(?(4)-AsMe)(2)(CO)(12)] (3a,b), whose core contains double the elemental composition of the initial cluster 1. In the case of the Se-containing cluster two other minor products [Fe(4)(?(4)-Se)(?(4)-SeAsMe)(CO)(12)] (4) and [Fe(3)(?(3)-AsMe)(2)(CO)(9)] (5) are formed. Based on the structures and properties of the products, a reaction route for the conversion of 1 into 2 is proposed, which includes the associative formation of the clusters 3 as intermediates, unlike the dissociative pathways previously known for the transformations of similar clusters of the type [Fe(3)Q(2)(CO)(9)]. PMID:21258730

  13. Magnetic properties of Fe{sub 2}P-type R{sub 6}CoTe{sub 2} compounds (R=Gd-Er)

    SciTech Connect

    Morozkin, A.V., E-mail: morozkin@general.chem.msu.r [Department of Chemistry, Moscow State University, Leninskie Gory, House 1, Building 3, Gsp-2, Moscow 119992 (Russian Federation); Mozharivskyj, Yu; Svitlyk, V. [Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4M1 (Canada); Nirmala, R. [Indian Institute of Technology Madras, Chennai 600 036 (India); Isnard, O. [Institute Laue-Langevin, 6 Rue J. Horowitz, 38042 Grenoble (France); Institut Neel du CNRS/Universite J.Fourier, BP166X, 38042 Grenoble (France); Manfrinetti, P.; Provino, A. [Dipartimento di Chimica, Universita di Genova, Via Dodecaneso 31, 16146 Genova (Italy); LAMIA Laboratory-CNR-INFM, Corso Perrone 24, 16152 Genova (Italy); Ritter, C. [Institute Laue-Langevin, 6 Rue J. Horowitz, 38042 Grenoble (France)

    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].

  14. On the lamellar compounds CuBiP(2)Se(6), AgBiP(2)Se(6) and AgBiP(2)S(6). Antiferroelectric phase transitions due to cooperative Cu(+) and Bi(3+) ion motion.

    PubMed

    Gave, Matthew A; Bilc, Daniel; Mahanti, S D; Breshears, Jean D; Kanatzidis, Mercouri G

    2005-07-25

    CuBiP(2)Se(6), AgBiP(2)Se(6), and AgBiP(2)S(6) were prepared from the corresponding elements. CuBiP(2)Se(6) and AgBiP(2)Se(6) crystallize in the space group R with a = 6.5532(16) A and c = 39.762(13) A for CuBiP(2)Se(6) and a = 6.6524(13) A and c = 39.615(15) A for AgBiP(2)Se(6). AgBiP(2)S(6) crystallizes in the triclinic space group P with a = 6.3833(13) A, b = 7.1439(14) A, c = 9.5366(19) A, alpha = 91.89(3) degrees , beta = 91.45(3) degrees , gamma = 94.05(3) degrees . CuBiP(2)Se(6) was found to exhibit a temperature-dependent antiferroelectric ordering of the Cu(+) and Bi(3+) ions in the lattice. An intermediate and a fully ordered structure were refined at 173 and 97 K, respectively. Electronic band and total energy calculations at the DFT level clearly suggest that the antiferroelectric model is energetically favored over the paraelectric and hypothetical ferrielectric models. This phase transition can be classified as a second-order Jahn-Teller distortion. The antiferroelectric state of CuBiP(2)Se(6) is an indirect gap semiconductor. The compounds were characterized with differential thermal analysis and solid-state UV/vis diffuse reflectance spectroscopy. Generalized implications regarding the expected ferroelectric behavior of compounds in the CuMP(2)Se(6) system (M = trivalent metal) are discussed. PMID:16022528

  15. Thermoelectric properties of Cl-doped In4Pb0.01Sn0.03Se2.9Clx polycrystalline compounds

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Hee; Kim, Min Jae; Oh, Suekyung; Rhyee, Jong-Soo; Park, Su-Dong

    2015-03-01

    We investigated thermoelectric properties of Cl-doped polycrystalline compounds of In4Pb0.01Sn0.03Se2.9Clx (x = 0.02, 0.04 and 0.06). The x-ray diffraction measurement shows gradual change of lattice volume for x <= 0.04 without any impurity phases indicating systemic change of Cl-doping. The Cl-doping in the compounds has an effect of increasing carrier concentration and effective mass of carrier resulting in the increase of power factor near 700 K than In4Pb0.01Sn0.03Se2.9. Because of the increased electrical conductivity neat 700 K, the thermoelectric figure-of-merit ZT is 1.25 at 723 K for x = 0.04 Cl-doped compound which is relatively high value as n-type polycrystalline materials. Cl-doping.

  16. 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.

  17. 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, E-mail: deniz.cakir@uantwerpen.be; Peeters, François M., E-mail: francois.peeters@uantwerpen.be [Department of Physics, University of Antwerp, 2610 Antwerpen (Belgium); Sevik, Cem, E-mail: csevik@anadolu.edu.tr [Department of Mechanical Engineering, Faculty of Engineering, Anadolu University, Eskisehir TR 26555 (Turkey)

    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.

  18. Atomic and electronic structure of an alloyed topological insulator, Bi1.5Sb0.5Te1.7Se1.3

    PubMed Central

    Ko, Wonhee; Jeon, Insu; Kim, Hyo Won; Kwon, Hyeokshin; Kahng, Se-Jong; Park, Joonbum; Kim, Jun Sung; Hwang, Sung Woo; Suh, Hwansoo

    2013-01-01

    Bi2?xSbxTe3?ySey has been argued to exhibit both topological surface states and insulating bulk states, but has not yet been studied with local probes on the atomic scale. Here we report on the atomic and electronic structures of Bi1.5Sb0.5Te1.7Se1.3 studied using scanning tunnelling microscopy (STM) and spectroscopy (STS). Although there is significant surface disorder due to alloying of constituent atoms, cleaved surfaces of the crystals present a well-ordered hexagonal lattice with 10 Å high quintuple layer steps. STS results reflect the band structure and indicate that the surface state and Fermi energy are both located inside the energy gap. In particular, quasi-particle interference patterns from electron scattering demonstrate that the surface states possess linear dispersion and chirality from spin texture, thus verifying its topological nature. This finding demonstrates that alloying is a promising route to achieve full suppression of bulk conduction in topological insulators whilst keeping the topological surface state intact. PMID:24030733

  19. The comprehensive phase evolution for Bi[subscript 2]Te[subscript 3] topological compound as function of pressure

    SciTech Connect

    Zhang, S.J.; Zhang, J.L.; Yu, X.H.; Zhu, J.; Kong, P.P.; Feng, S.M.; Liu, Q.Q.; Yang, L.X.; Wang, X.C.; Cao, L.Z.; Yang, W.G.; Wang, L.; Mao, H.K.; Zhao, Y.S.; Liu, H.Z.; Dai, X.; Fang, Z.; Zhang, S.C.; Jin, C.Q. (Stanford); (Harbin); (UST - China); (CIW); (Chinese Aca. Sci.); (LANL)

    2012-06-26

    The recently discovered three-dimensional topological insulator Bi{sub 2}Te{sub 3} is studied as function of pressure in terms of crystal structures, resistance, and Hall coefficient. The superconductivity is found in phase I (ambient phase) Bi{sub 2}Te{sub 3} with T{sub c}-3 K, which is related to the topological features. The evolution of crystal structure with pressure is investigated by high pressure synchrotron radiation experiments that reveal structural transitions occurring at about 8 GPa, 13 GPa, and 16 GPa, respectively. Furthermore, the high pressure phases of Bi{sub 2}Te{sub 3} are also superconducting but with much higher T{sub c}-8 K. The superconducting transitions are compared with those for Bi, Te elements. A global phase diagram of Bi{sub 2}Te{sub 3} as function of pressure up to 30 GPa is obtained.

  20. 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.

  1. Transmission measurement at 10.6 ?m of Te2As3Se5 rib waveguides on As2S3 substrate

    NASA Astrophysics Data System (ADS)

    Vigreux-Bercovici, C.; Bonhomme, E.; Pradel, A.; Broquin, J.-E.; Labadie, L.; Kern, P.

    2007-01-01

    The feasibility of chalcogenide rib waveguides working at ? =10.6?m has been demonstrated. The waveguides comprised a several micron thick Te2As3Se5 film deposited by thermal evaporation on a polished As2S3 glass substrate and further etched by physical etching in Ar or CF4/O2 atmosphere. Output images at 10.6?m and some propagation losses roughly estimated at 10dB /cm proved that the obtained structures behaved as channel waveguides with a good lateral confinement of the light. The work opens the doors to the realization of components able to work in the mid- and thermal infrared up to 20?m and even more.

  2. Structure of the Oxygen-annealed Chalcogenide Superconductor Fe1.08Te0.55Se0.45Ox

    SciTech Connect

    Hu H.; Xu Z.; Zuo, J.-M.; Zheng, M.; Eckstein, J.N.; Park, W.K.; Greene, L.H.: Wen, J.; Lin, Z.; Li, Q.; Gu, G

    2012-02-01

    The as-grown single crystal Fe{sub 1.08}Te{sub 0.55}Se{sub 0.45} with the tetragonal PbO-type structure is nonsuperconducting owing to the excess Fe. Superconductivity is induced after oxygen annealing with an onset and zero resistance transition temperature around 14.5 K and 11.5 K, respectively. The oxygen doping is evidenced by electron energy loss spectroscopy and accompanied by improved homogeneity in the remaining PbO-type phase, as well as an increase in the L{sub 3}/L{sub 2} intensity ratio of the Fe-L{sub 2,3} edge, indicating an increase in Fe valence. Local phase transformation from the tetragonal PbO-type phase to the hexagonal NiAs-type phase is also observed after oxygen annealing.

  3. Substitution of Ni for Fe in superconducting Fe?.??Te?.?Se?.? depresses the normal-state conductivity but not the magnetic spectral weight

    DOE PAGESBeta

    Wang, Jinghui [Nanjing Univ., Nanjing (China); Tranquada, J. M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Zhong, Ruidan [Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., Stony Brook, NY (United States); Li, Shichao [Nanjing Univ., Nanjing (China); Gan, Yuan [Nanjing Univ., Nanjing (China); Xu, Zhijun [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Zhang, Cheng [Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., Stony Brook, NY (United States); Ozaki, T. [Brookhaven National Lab. (BNL), Upton, NY (United States); Matsuda, M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Zhao, Yang [National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States); Li, Qiang [Brookhaven National Lab. (BNL), Upton, NY (United States); Xu, G. [Brookhaven National Lab. (BNL), Upton, NY (United States); Gu, Genda [Brookhaven National Lab. (BNL), Upton, NY (United States); Birgeneau, R. J. [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Wen, Jinsheng [Nanjing Univ., Nanjing (China)

    2015-01-01

    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.

  4. Tunnel diode oscillator measurements of the upper critical magnetic field of FeTe(0.5)Se(0.5).

    PubMed

    Audouard, A; Drigo, L; Duc, F; Fabrèges, X; Bosseaux, L; Toulemonde, P

    2014-05-01

    Temperature dependence of the upper critical magnetic field (Hc2) of single crystalline FeTe0.5Se0.5(Tc = 14.5 K) have been determined by tunnel diode oscillator-based measurements in magnetic fields of up to 55 T and temperatures down to 1.6 K. The Werthamer-Helfand-Hohenberg model accounts for the data for magnetic field applied both parallel (H ? ab) and perpendicular (H ? c) to the iron conducting plane, in line with a single band superconductivity. Whereas Pauli pair breaking is negligible for H ? c, Pauli contribution is evidenced for H ? ab with Maki parameter ? = 1.4, corresponding to Pauli field HP = 79 T. As a result, the Hc2 anisotropy [Formula: see text] which is already rather small at Tc (? = 1.6) further decreases as the temperature decreases and becomes smaller than 1 at liquid helium temperatures. PMID:24727285

  5. Combining ligand-induced quantum-confined stark effect with type II heterojunction bilayer structure in CdTe and CdSe nanocrystal-based solar cells.

    PubMed

    Yaacobi-Gross, Nir; Garphunkin, Natalia; Solomeshch, Olga; Vaneski, Aleksandar; Susha, Andrei S; Rogach, Andrey L; Tessler, Nir

    2012-04-24

    We show that it is possible to combine several charge generation strategies in a single device structure, the performance of which benefits from all methods used. Exploiting the inherent type II heterojunction between layered structures of CdSe and CdTe colloidal quantum dots, we systematically study different ways of combining such nanocrystals of different size and surface chemistry and with different linking agents in a bilayer solar cell configuration. We demonstrate the beneficial use of two distinctly different sizes of NCs not only to improve the solar spectrum matching but also to reduce exciton binding energy, allowing their efficient dissociation at the interface. We further make use of the ligand-induced quantum-confined Stark effect in order to enhance charge generation and, hence, overall efficiency of nanocrystal-based solar cells. PMID:22390408

  6. Nonlinear optical properties of quaternary amorphous Se80.5Bi1.5Te18-yAy (A = Sb, Ag) thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Anup; Heera, Pawan; Sharma, Raman

    2014-04-01

    Effect of Sb and Ag addition on the optical constants of Se80.5Bi1.5Te18-yAy (A = Sb, Ag and y = 2.0 at. %) thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index increases with an increase in Sb or Ag content and the absorption coefficient is also found to increases with increase in optical energy. Whereas the optical band gap decreases with an increase in Sb content and increases with an increase in Ag content. Hence, the present results reveals that the addition of Sb and Ag produce remarkable change on the nonlinear optical properties of the thin film.

  7. Heat Capacity And Structural Relaxation In Se{sub 80-x}Te{sub 20}Ag{sub x}(x = 3 and 9) Glassy Alloys

    SciTech Connect

    Naqvi, S. Faheem; Saxena, N. S. [Semi-conductor and Polymer Science Laboratory, 5-6, Vigyan Bhawan, Department of Physics, University of Rajasthan, Jaipur-302004 (India)

    2011-10-20

    This paper reports the effects of annealing time and temperature on the thermodynamics of enthalpy relaxation of Se{sub 80-x}Te{sub 20}Ag{sub x} (x = 3,9) glasses. Differential Scanning Calorimetry (DSC) method is optimized for the measurement of enthalpy relaxation in the vicinity of glass transition. The recovery of excess enthalpy ({Delta}H{sub excess}) has been calculated from the knowledge of excess specific heat ({Delta}C{sub p}). It is found that excess enthalpy released ({Delta}H{sub excess}) increase with increase in annealing time (t{sub a}). From the knowledge of excess specific heat ({Delta}C{sub p}) and {Delta}H{sub excess}, it has been found that sub-T{sub g} annealing of glass leads to decrease in enthalpy of the system and thereby taking it to the more equilibrium state.

  8. Research Update: Point defects in CdTexSe1-x crystals grown from a Te-rich solution for applications in detecting radiation

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Current 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 to 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.

  9. 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

  10. Microwave-Assisted Synthesis of Glutathione-Capped CdTe/CdSe Near-Infrared Quantum Dots for Cell Imaging

    PubMed Central

    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

  11. Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe0.98-zCuzTe0.5Se0.5

    NASA Astrophysics Data System (ADS)

    Wen, Jinsheng; Li, Shichao; Xu, Zhijun; Zhang, Cheng; Matsuda, M.; Sobolev, O.; Park, J. T.; Christianson, A. D.; Bourret-Courchesne, E.; Li, Qiang; Gu, Genda; Lee, Dung-Hai; Tranquada, J. M.; Xu, Guangyong; Birgeneau, R. J.

    2013-10-01

    We have performed resistivity and inelastic neutron scattering measurements on three samples of Fe0.98-zCuzTe0.5Se0.5 with z=0, 0.02, and 0.1. It is found that with increasing Cu doping the sample's resistivity deviates progressively from that of a metal. However, in contrast to expectations that replacing Fe with Cu would suppress the magnetic correlations, the low-energy (?12 meV) magnetic scattering is enhanced in strength, with greater spectral weight and longer dynamical spin-spin correlation lengths. Such enhancements can be a consequence of either enlarged local moments or a slowing down of the spin fluctuations. In either case, the localization of the conduction states induced by the Cu doping should play a critical role. Our results are not applicable to models that treat 3d transition metal dopants simply as effective electron donors.

  12. High pressure phase transition in samarium monochalcogenides SmX (X = S, Se, Te) and their alloy SmS1-xSex

    NASA Astrophysics Data System (ADS)

    Dubey, Ritu; Singh, Sadhna

    2013-11-01

    Phase transition pressures, relative volume changes, elastic and thermophysical properties of Samarium monochalcogenides SmX (X = S, Se, Te) have been studied. An improved interaction potential model has been developed which includes Coulomb, three-body interaction, polarizability effect and overlap repulsive interaction operative up to second neighbor ions. In addition, we have investigated the phase transition pressure and associated volume collapse in SmS1-xSex alloy (0 ? x ? 1) which shows transition from discontinuous to continuous as x is reduces. The present results are in general in good agreement with experimental data available for the end point members (x = 0 and x = 1). The results for the alloy counter parts are also in fair agreement with experimental data generated from the vegard's law.

  13. Pressure induced evolution of superconductivity and magnetic hourglass dispersion in Fe1.02Te0.7Se0.3

    NASA Astrophysics Data System (ADS)

    Lançon, D.; Tsyrulin, N.; Böhm, M.; Viennois, R.; Zabihzadeh, S.; Kusmartseva, A.; Giannini, E.; Rønnow, H. M.

    2015-04-01

    Iron based high temperature superconductors have several common features with superconducting cuprates, including the square lattice and the proximity to an antiferromagnetic phase. The magnetic excitation spectrum below Tc of Fe1.02Te0.7Se0.3 shows an hourglass-shaped dispersion with a resonance around the commensurate point . In a previous inelastic neutron scattering study, we showed that the hourglass-shaped dispersion is most likely a prerequisite for superconductivity, while the consequences are the opening of a gap and a shift of spectral weight. In this paper we follow the evolution of the hourglass shaped dispersion under applied pressure up to 12 kbar. Our results show that that the pressure-induced 37% increase of Tc is concomitant with a change in the magnetic excitation spectrum, with an increase of the hourglass energy by 38%.

  14. Substitution of Ni for Fe in superconducting Fe?.??Te?.?Se?.? depresses the normal-state conductivity but not the magnetic spectral weight

    SciTech Connect

    Wang, Jinghui [Nanjing Univ., Nanjing (China); Tranquada, J. M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Zhong, Ruidan [Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., Stony Brook, NY (United States); Li, Shichao [Nanjing Univ., Nanjing (China); Gan, Yuan [Nanjing Univ., Nanjing (China); Xu, Zhijun [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Zhang, Cheng [Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., Stony Brook, NY (United States); Ozaki, T. [Brookhaven National Lab. (BNL), Upton, NY (United States); Matsuda, M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Zhao, Yang [National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States); Li, Qiang [Brookhaven National Lab. (BNL), Upton, NY (United States); Xu, G. [Brookhaven National Lab. (BNL), Upton, NY (United States); Gu, Genda [Brookhaven National Lab. (BNL), Upton, NY (United States); Birgeneau, R. J. [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Wen, Jinsheng [Nanjing Univ., Nanjing (China)

    2015-01-01

    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.

  15. Substitution of Ni for Fe in superconducting Fe?.??Te?.?Se?.? depresses the normal-state conductivity but not the magnetic spectral weight

    DOE PAGESBeta

    Wang, Jinghui; Tranquada, J. M.; Zhong, Ruidan; Li, Shichao; Gan, Yuan; Xu, Zhijun; Zhang, Cheng; Ozaki, T.; Matsuda, M.; Zhao, Yang; et al

    2015-01-01

    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

  16. 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. [Thermoelectric Research Laboratory, Department of Inorganic Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Av. Mickiewicza 30, 30-059, Cracow (Poland)

    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.

  17. Electrical and thermoelectric properties of 90% Bi{sub 2}Te{sub 3}-5% Sb{sub 2}Te{sub 3}-5% Sb{sub 2}Se{sub 3} single crystals doped with SbI{sub 3}

    SciTech Connect

    Hyun, D.B.; Hwang, J.S.; Shim, J.D.; Kolomoets, N.V. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Div. of Metals] [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Div. of Metals; Oh, T.S. [Hong Ik Univ., Seoul (Korea, Republic of). Dept. of Metallurgy and Materials Science] [Hong Ik Univ., Seoul (Korea, Republic of). Dept. of Metallurgy and Materials Science

    1998-12-04

    Bi{sub 2}Te{sub 3}-Sb{sub 2}Te{sub 3}-Sb{sub 2}Se{sub 3} alloys with Sb{sub 2}Te{sub 3} and Sb{sub 2}Se{sub 3} contents up to 10 mol%, e.g., the 90% Bi{sub 2}Te{sub 3}-5% Sb{sub 2}Te{sub 3}-5% Sb{sub 2}Se{sub 3} alloy, are among the best n-type thermoelectric materials for Peltier coolers used near room temperature. In this work, the electrical and thermoelectric properties of Sbl{sub 3}doped 90% Bi{sub 2}Te{sub 3}-5% Sb{sub 2}Te{sub 3}-5% Sb{sub 2}Se{sub 3} alloys were characterized at temperatures ranging from 80K to 600K. The temperature dependencies of the Hall coefficient, carrier mobility, Seebeck coefficient and thermal conductivity were measured, and the scattering parameter and bandgap energy were determined.

  18. The effect of lithium intercalation on the electronic structure of the ternary compound semiconductors ZrSe2-xSx

    NASA Astrophysics Data System (ADS)

    Ghafari, A.; Janowitz, C.; Manzke, R.

    2013-08-01

    The electronic properties of the lithium intercalated layered transition metal dichalcogenide semiconductors ZrSxSe2-x for x = 0-2 have been calculated by density functional theory (DFT) using the WIEN2k code. The calculations have been carried out by the PBE functional and the TB-MBJ potential as proposed by Tran and Blaha. The calculations have been performed with and without spin-orbit coupling and reveal that the intercalation of lithium causes the conduction bands of LiZrSxSe2-x to shift by about 2 eV towards lower binding energy. From this, a Fermi level crossing and metallic behavior in the three intercalated compounds result. Moreover, a number of trends can be observed. Due to the contributions of the dichalcogenide p-states in the valence band the inclusion of SO coupling in the calculations lifts the degeneracy at the points ? and A of the Brillouin zone in the same way as in the parent compounds. With regard to crystal field effects for each compound the splitting is larger at the A point than at the ? point and the absolute value of the splitting increases with the atomic number of the chalcogenide. In particular, the simple Fermi surface consisting solely of barrels centered along the LML line makes LiZrSxSe2-x a promising Fermi liquid reference compound.

  19. 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

  20. Transparent Conductive Cu-doped ZnSe Film Deposited at Room Temperature Using Compound Sources Followed by Laser Annealing

    NASA Astrophysics Data System (ADS)

    Orita, Masahiro; Narushima, Takashi; Yanagita, Hiroaki

    2007-10-01

    The evaporation of ZnSe and Cu2Se powders was used to deposit a Cu-doped ZnSe film on a glass substrate at room temperature; this was followed by laser beam (? = 355 nm) annealing. The film consisted of a zinc blende, ZnSe, crystalline single phase with the chemical composition (Zn0.9Cu0.1)Se. Over 70% optical transmittance was obtained in the green-red region. The film had a p-type polarity with a conductivity of 0.45 S cm-1 and a workfunction of 4.7 eV. P-n diodes fabricated with the film on an n-type ZnSe:Cl layer showed rectangular behavior with a small turn-on voltage of ˜1.5 V, which is plausibly explained by development of an impurity band.

  1. Effect of selenium deficiency on the thermoelectric properties of n-type In{sub 4}Se{sub 3?x} compounds

    SciTech Connect

    Zhu, G. H.; Lan, Y. C.; Wang, H.; Joshi, G.; Hao, Q.; Chen, Gang; Ren, Zhifeng

    2011-01-01

    Thermoelectric properties of dense bulk polycrystalline In{sub 4}Se{sub 3?x} (x = 0, 0.25, 0.5, 0.65, and 0.8) compounds are investigated. A peak dimensionless thermoelectric figure of merit (ZT) of about 1 is achieved for x = 0.65 and 0.8. The peak ZT is about 50% higher than the previously reported highest value for polycrystalline In{sub 4}Se{sub 3?x} compounds. Our In{sub 4}Se{sub 3?x} samples were prepared by ball milling and hot pressing. We show that it is possible to effectively control the electrical conductivity and thermal conductivity by controlling selenium (Se) deficiency x. The ZT enhancement is mainly attributed to the thermal conductivity reduction due to the increased phonon scattering by Se deficiency, defects, and nanoscale inclusions in the ball-milled and hot-pressed dense bulk In{sub 4}Se{sub 3?x} samples.

  2. Systematic study of the contamination of wastewater treatment plant effluents by organic priority compounds in Almeria province (SE Spain).

    PubMed

    Barco-Bonilla, Nieves; Romero-González, Roberto; Plaza-Bolaños, Patricia; Martínez Vidal, José L; Garrido Frenich, Antonia

    2013-03-01

    The occurrence of priority organic pollutants in wastewater (WW) effluents was evaluated in a semi-arid area, characterized by a high agricultural and tourism activity, as Almeria province (Southeastern Spain). Twelve wastewater treatment plants (WWTPs) were sampled in three campaigns during 2011, obtaining a total of 33 WW samples, monitoring 226 compounds, including pesticides, polycyclic aromatic hydrocarbons (PAHs), phenolic compounds and volatile organic compounds (VOCs). Certain banned organochlorine pesticides such as aldrin, pentachlorobenzene, o,p'-DDD and endosulfan lactone were found, and the most frequently detected pesticides were herbicides (diuron, triazines). PAHs and VOCs were also detected, noting that some of these pollutants were ubiquitous. Regarding phenolic compounds, 4-tertoctylphenol was found in all the WW samples at high concentration levels (up to 89.7 ?g/L). Furthermore, it was observed that WW effluent samples were less contaminated in the second and third sampling periods, which corresponded to dry season. This evaluation revealed that despite the WW was treated in the WWTP, organic contaminants are still being detected in WW effluents and therefore they are released into the environment. Finally the risk of environmental threat due to the presence of some compounds in WWTP effluents, especially concerning 4-tertoctylphenol must be indicated. PMID:23410859

  3. 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 [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China)] [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Zhang, Peihong, E-mail: wqzhang@mail.sic.ac.cn, E-mail: pzhang3@buffalo.edu [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States) [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States); Beijing Computational Science Research Center, Beijing 100084 (China); Zhang, Wenqing, E-mail: wqzhang@mail.sic.ac.cn, E-mail: pzhang3@buffalo.edu [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China) [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); School of Chemistry and Chemical Engineering, and Sate Key Laboratory of Coordination Chemistry, Nanjing University, Jiangsu 210093 (China)

    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.

  4. Terahertz conductivity of topological surface states in Bi1.5Sb0.5Te1.8Se1.2

    PubMed Central

    Tang, Chi Sin; Xia, Bin; Zou, Xingquan; Chen, Shi; Ou, Hong-Wei; Wang, Lan; Rusydi, A.; Zhu, Jian-Xin; Chia, Elbert E. M.

    2013-01-01

    Topological insulators are electronic materials with an insulating bulk and conducting surface. However, due to free carriers in the bulk, the properties of the metallic surface are difficult to detect and characterize in most topological insulator materials. Recently, a new topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was found, showing high bulk resistivities of 1–10??.cm and greater contrast between the bulk and surface resistivities compared to other Bi-based topological insulators. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we present complex conductivity of BSTS single crystals, disentangling the surface and bulk contributions. We find that the Drude spectral weight is 1–2 orders of magnitude smaller than in other Bi-based topological insulators, and similar to that of Bi2Se3 thin films, suggesting a significant contribution of the topological surface states to the conductivity of the BSTS sample. Moreover, an impurity band is present about 30?meV below the Fermi level, and the surface and bulk carrier densities agree with those obtained from transport data. Furthermore, from the surface Drude contribution, we obtain a ~98% transmission through one surface layer — this is consistent with the transmission through single-layer or bilayer graphene, which shares a common Dirac-cone feature in the band structure. PMID:24343202

  5. 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.

  6. 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

  7. Effect of nonstoichiometry on the electrophysical properties of the layered compounds Ge{sub 3}Bi{sub 2}Te{sub 6} and GeBi{sub 2}Te{sub 4}

    SciTech Connect

    Shelimova, L.E.; Karpinskii, O.G.; Avilov, E.S.; Kretova, M.A.; Lubman, C.U. [Baikov Institute of Metallurgy, Moscow (Russian Federation)

    1994-12-01

    The objective of this work was to investigate the effect of deviation from stoichiometry on the electrophysical properties (electrical and thermal conductivity, thermoelectric power, and carrier concentration) of the ternary layered semiconducting compounds Ge{sub 3{plus_minus}{delta}1}Bi{sub 2+{delta}2}Te{sub 6+{delta}3} and Ge{sub 1{plus_minus}{delta}3}, which are promising for use in thermoelectric converters.The electrophysical properties were measured at 300 K. The Ge{sub 1-{delta}1}Bi{sub 2+{delta}3} alloys were studied by powder X-ray diffraction analysis on a DRON UM-1 diffractometer (CoK{sub {alpha}} radiation). It was found that Ge{sub 3{plus_minus}{delta}1} Bi{sub 2+{delta}2}Te{sub 6{plus_minus}{delta}3} is a nonstoichiometric phase with p-type conductivity throughout the {delta}{sub 1}, {delta}{sub 2}, and {delta}{sub 3} ranges examined. Our results suggest that cation vacancies are likely to be the dominant nonstoichiometric defects responsible for the high concentration of holes. The conductivity of Ge{sub 1{plus_minus}{delta}1}Bi{sub 2}Te{sub 4} changes from the p-type in the Ge-deficient alloys to the n-type in the Gerich alloys.

  8. 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

  9. Cs{sub 4}P{sub 2}Se{sub 10}: A new compound discovered with the application of solid-state and high temperature NMR

    SciTech Connect

    Gave, Matthew A.; Canlas, Christian G. [Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States); Chung, In [Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States); Department of Chemistry, Northwestern University, Evanston, IL 60208 (United States); Iyer, Ratnasabapathy G. [Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States); Kanatzidis, Mercouri G. [Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States); Department of Chemistry, Northwestern University, Evanston, IL 60208 (United States)], E-mail: m-kanatzidis@northwestern.edu; Weliky, David P. [Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States)], E-mail: weliky@chemistry.msu.edu

    2007-10-15

    The new compound Cs{sub 4}P{sub 2}Se{sub 10} was serendipitously produced in high purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. {sup 31}P magic angle spinning (MAS) NMR of the products of the synthesis revealed that the dominant phosphorus-containing product had a chemical shift of -52.8 ppm that could not be assigned to any known compound. Deep reddish brown well-formed plate-like crystals were isolated from the NMR reaction ampoule and the structure was solved with X-ray diffraction. Cs{sub 4}P{sub 2}Se{sub 10} has the triclinic space group P-1 with a=7.3587(11) A, b=7.4546(11) A, c=10.1420(15) A, {alpha}=85.938(2){sup o}, {beta}=88.055(2){sup o}, and {gamma}=85.609(2){sup o} and contains the [P{sub 2}Se{sub 10}]{sup 4-} anion. To our knowledge, this is the first compound containing this anion that is composed of two tetrahedral (PSe{sub 4}) units connected by a diselenide linkage. It was also possible to form a glass by quenching the melt in ice water, and Cs{sub 4}P{sub 2}Se{sub 10} was recovered upon annealing. The static {sup 31}P NMR spectrum at 350 deg. C contained a single peak with a -35 ppm chemical shift and a {approx}7 ppm peak width. This study highlights the potential of solid-state and high-temperature NMR for aiding discovery of new compounds and for probing the species that exist at high temperature. - Graphical abstract: The new compound Cs{sub 4}P{sub 2}Se{sub 10} was discovered following a high-temperature in situ synthesis in the NMR spectrometer and the structure was determined by single-crystal X-ray diffraction. It contains the new [P{sub 2}Se{sub 10}]{sup 4-} anion.

  10. Importance of structural distortions in enhancement of transition temperature in FeSe1 ? xTex superconductors

    NASA Astrophysics Data System (ADS)

    Ingle, Kapil E.; Priolkar, K. R.; Pal, Anand; Zargar, Rayees A.; Awana, V. P. S.; Emura, S.

    2015-01-01

    Temperature (12 K ?slant T ?slant 300 K) dependent extended x-ray absorption fine structure (EXAFS) studies at the Fe K edge in FeSe1-xTex (x = 0, 0.5 and 1.0) compounds have been carried out to understand the reasons for the increase in TC upon Te doping in FeSe. While local distortions are present near superconducting onset in FeSe and FeSe0.5Te0.5, they seem to be absent in non superconducting FeTe. Of crucial importance is the variation of anion height. In FeSe0.5Te0.5, near the superconducting onset, the two heights, {{h}Fe-Se} and {{h}Fe-Te} show a nearly opposite behaviour. These changes indicate a possible correlation between Fe-chalcogen hybridization and the superconducting transition temperature in these Fe-chalcogenides.

  11. 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.

  12. 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., E-mail: yuriygnatenko@ukr.net; Bukivskij, P. M.; Piryatinski, Yu. P. [Institute of Physics of NASU, Prospect Nauky 46, Kyiv 03028 (Ukraine)

    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.

  13. Optical Properties and Determination of Thermal Transformation Parameters for Se0.65Te0.35 High Reflectance Thin Films

    NASA Astrophysics Data System (ADS)

    El-Amin, Ayman Ahmed; Badr, Aly Mohammed; Abdel-Wahaab, Foaud

    2007-11-01

    Chalcogenide glasses Se-Te have been prepared from the high purity constituent elements. Thin films of these materials have been deposited by vacuum evaporation. The thickness effects on the optical properties have been performed for the as-deposited films. The impact of varying thickness on the value of the optical gap is also reported and discussed. The resultant films were in amorphous nature. The reflectance and transmittance spectra were measured for the mentioned films and analyzed in the incident photon energy range from 1.16 to 2.47 eV. The refractive indices were determined as a function of wavelength via the transmittance analysis in the incident photon energy range from 1.16 to 1.38 eV. Also, the dispersion energy, oscillator energy, static refractive index and static dielectric constant were calculated for the thicknesses under investigation. The results of differential scanning calorimetry (DSC) at different heating rates are reported and analyzed. The activation energies for the glass transition and crystallization were calculated.

  14. Effect of surface treatment on an n-CdSe0.6Te0.4 thin-film photoanode/polysulphide electrolyte solar cell

    NASA Astrophysics Data System (ADS)

    Das, V. Damodara; Damodare, Laxmikant

    1997-02-01

    Polycrystalline thin films of n-CdSe0.6Te0.4 were deposited in a vacuum of 5×10-5 Torr by thermal flash evaporation with a deposition rate of 20±1 Å/s on indium oxide coated glass plates [?=1.25×104(? cm)-1] held at 200 °C. Application of surface treatment techniques such as annealing and photoelectrochemical etching on the films revealed that the films exhibit photoelectrochemical behavior with increased conversion efficiency and stability after treatment. Gärtner's model [Phys. Rev. 116, 84 (1954)] was used in the calculation of the solid state parameters of the films like the carrier concentration ND and minority carrier diffusion length Lp for different surface treatments. Chemical etching improves the efficiency and fill factor from 1.53% and 40% to 2.72% and 50% respectively, whereas photoelectrochemical etching improves further the efficiency to 3.83% and fill factor to 59% and the stability of the photoelectrode in the polysulphide electrolyte.

  15. Conduction mechanism and the dielectric relaxation process of a-Se75Te25-xGax (x=0, 5, 10 and 15 at wt%) chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Yahia, I. S.; Hegab, N. A.; Shakra, A. M.; AL-Ribaty, A. M.

    2012-07-01

    Se75Te25-xGax (x=0, 5, 10 and 15 at wt%) chalcogenide compositions were prepared by the well known melt quenching technique. Thin films with different thicknesses in the range (185-630 nm) of the obtained compositions were deposited by thermal evaporation technique. X-ray diffraction patterns indicate that the amorphous nature of the obtained films. The ac conductivity and the dielectric properties of the studied films have been investigated in the frequency range (102-105 Hz) and in the temperature range (293-333 K). The ac conductivity was found to obey the power low ?s where s?1 independent of film thickness. The temperature dependence of both ac conductivity and the exponent s can be well interpreted by the correlated barrier hopping (CBH) model. The experimental results of the dielectric constant ?1 and dielectric loss ?2 are frequency and temperature dependent. The maximum barrier height Wm calculated from the results of the dielectric loss according to the Guintini equation, and agrees with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The density of localized state was estimated for the studied film compositions. The variation of the studied properties with Ga content was also investigated. The correlation between the ac conduction and the dielectric properties were verified.

  16. A study of band-bending and barrier height variation in thin film n-CdSe 0.5Te 0.5 photoanode/polysulphide junctions

    NASA Astrophysics Data System (ADS)

    Damodara Das, V.; Damodare, Laxmikant

    1996-09-01

    Polycrystalline thin films of n-CdSe 0.5Te 0.5 were deposited in a vacuum of 5 × 10 -5torr by thermal flash evaporation with a deposition rate of 20 ± 1 Ås -1 on indium oxide coated glass plates [ ? = 1.25 × 10 4 (? cm) -1] held at a temperature of 473 K. The change in the pH value of the polysulphide electrolyte from 12.5 to 8.0 leads to a fall in the extent of band bending from 680 meV to 420 meV and decrease in the barrier height from 690 meV to 430 meV. The barrier heights as calculated from Mott-Schottky plots and current-voltage plots are compared. From the reverse saturation current ( I0) variation with temperature, it is found that the barrier height decreases from 690 meV to 430 meV with decrease in pH of the electrolyte from 12.5 to 8.0. The variation of diode ideality factor n, with temperature was also studied. It was found that the diode ideality factor n, decreases with increase of temperature, viz. from 3.00 to 2.00 with rise in temperature from 300 K to 333 K. This is due to the additional injection of electrons from the bulk into the junction region because of increase in temperature.

  17. External temperature and pressure effects on thermodynamic properties and mechanical stability of yttrium chalcogenides YX (X=S, Se and Te)

    NASA Astrophysics Data System (ADS)

    Seddik, T.; Khenata, R.; Bouhemadou, A.; Guechi, N.; Sayede, A.; Varshney, D.; Al-Douri, Y.; Reshak, A. H.; Bin-Omran, S.

    2013-11-01

    The full potential linearized augmented plane wave method within the framework of density functional theory is employed to investigate the structural, thermodynamic and elastic properties of the yttrium chalcogenides (YX: X=S, Se, and Te) in their low-pressure phase (Fm3barm) and high-pressure phase (Pm3barm). The exchange-correlation potential is treated with the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE). Temperature dependence of the volume and both adiabatic and isothermal bulk moduli is predicted for a temperature range from 0 to 1200 K for the both phases of the herein considered materials. Furthermore, we have analyzed the thermodynamic properties such as the heat capacities, CV and CP, thermal expansion, ?, and Debye temperature, ?D, under variable pressure and temperature. We have calculated the isothermal elastic constants CijT of the YX monochalcogenides in both NaCl-B1 and CsCl-B2 phases at zero pressure and a temperature range 0-1200 K. The results show that rare earth yttrium monochalcogenides are mechanically stable at high temperature. The elastic anisotropy of all studied materials in the two phases has been studied using three different methods.

  18. 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.

  19. 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

  20. High performance FeSe0.5Te0.5 thin films grown at low temperature by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Yuan, Pusheng; Xu, Zhongtang; Zhang, Haitao; Wang, Dongliang; Ma, Yanwei; Zhang, Ming; Li, Jianqi

    2015-06-01

    We report on fully epitaxial FeSe0.5Te0.5 (FST) thin films of high quality grown on CaF2 (00l) substrate at a low temperature of 300 °C by pulsed laser deposition. The transport Jc of thin films is up to 1.36 MA cm?2 in self-field and 0.97 MA cm?2 in 9 T at 4.2 K, indicating very weak field dependence. A near isotropy of Jc (? = JcH//ab/JcH//c) as low as 1.09 at 9 T is achieved in the FST thin films. Moreover, there is no clear amorphous interfacial layer between the film and the substrate, probably due to low temperature and low laser repetition rate, while the thickness of the reaction layer is approximate 5 nm in many other works. The transmission electron microscopy evidence shows that some lattices with lateral size <5 nm × 20 nm seem to be disturbed. These location defects are thought to be responsible for the nearly isotropic behavior of the superconductivity.

  1. 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. [Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420 (United States); Photonics Center, University of Massachusetts Lowell, Lowell, Massachusetts 01854 (United States); Reeder, R. E.; Vineis, C. J.; Calawa, S. D.; Walsh, M. P.; Harman, T. C. [Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420 (United States); Dauplaise, H. M. [Air Force Research Laboratory, Sensors Directorate, Hanscom AFB, MA 01731 (United States); Vangala, S. [Photonics Center, University of Massachusetts Lowell, Lowell, Massachusetts 01854 (United States)

    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.

  2. Density functional theory calculations of the turbostratically disordered compound [(SnSe )1 +y]m (VSe2)n

    NASA Astrophysics Data System (ADS)

    Rudin, Sven P.; Johnson, David C.

    2015-04-01

    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 one finite constituent, which allows the treatment of all relative orientations on equal footing. 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. The success of this approximation in describing the structural parameters of the extended [(SnSe) 1 +y]m(VSe2)n system encourages its use for other properties and for other similar systems with other chemistries.

  3. Anion substitution effects on structure and magnetism of the chromium chalcogenide Cr{sub 5}Te{sub 8}-Part II: Cluster-glass and spin-glass behavior in trigonal Cr{sub (1+x)}Q{sub 2} with basic cells and trigonal Cr{sub (5+x)}Q{sub 8} with superstructures (Q=Te, Se; Te:Se=6:2)

    SciTech Connect

    Huang Zhongle [Institute of Inorganic Chemistry, Christian-Albrechts-University Kiel, Olshausenstr.40, D-24098 Kiel (Germany)]. E-mail: zlhuang@ac.uni-kiel.de; Bensch, Wolfgang [Institute of Inorganic Chemistry, Christian-Albrechts-University Kiel, Olshausenstr.40, D-24098 Kiel (Germany); Mankovsky, Sergiy [Department of Chemistry, LMU-Munich, Butenandstr. 5-13, D-81377 Munich (Germany); Polesya, Svitlana [Department of Chemistry, LMU-Munich, Butenandstr. 5-13, D-81377 Munich (Germany); Ebert, Hubert [Department of Chemistry, LMU-Munich, Butenandstr. 5-13, D-81377 Munich (Germany); Kremer, Reinhard K. [Max-Planck Institut fuer Festkoerperforschung, Heisenbergstr. 1, D-70506 Stuttgart (Germany)

    2006-07-15

    The effect of substitution of up to two Te atoms by Se atoms on the crystal structure, the magnetic and electronic properties has been studied in the system Cr{sub (5+x)}Te{sub 8-y}Se{sub y}. Trigonal basic cells with space group P-3m1 for Cr{sub (1+x)}Q{sub 2} and trigonal supercells (doubling of the unit cell in all directions) with space group P-3m1 for Cr{sub (5+x)}Q{sub 8} ((1+x)=1.27, 1.32, 1.36; (5+x)=5.08, 5.28, 5.44; Q=Te, Se; Te:Se=6:2) have been identified in X-ray powder diffraction patterns and Rietveld refinements as high-temperature and low-temperature phases, respectively. The crystal structures are related to the hexagonal NiAs-type structure with metal vacancies in every second metal layer. The magnetic properties are closely related to the Cr content and the structure type. Cluster-glass and spin-glass behavior at low temperatures are observed for high and low Cr contents, respectively. For the same Cr content, the phases with trigonal basic cells have higher values for the Curie temperature T{sub c} and the freezing temperature T{sub f}, and larger magnetization than those for the phases with trigonal supercells. For the same structure type, the values for T{sub c}/T{sub f} do not show a linear relationship with the change of Cr content but exhibit a V-shape fashion. Our experimental investigations were accompanied by spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) electronic structure calculations. Cr deficiencies as well as atomic disorder on the chalcogen sites was accounted for using the coherent potential approximation (CPA) alloy theory. Calculation of the exchange coupling parameters J{sub ij} provided the basis for subsequent Monte Carlo simulations of the magnetic properties at finite temperatures.

  4. 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

  5. First principles determination of vibrational and elastic properties of quaternary compounds Cu2 ZnSnS 4 and Cu2 ZnSnSe 4

    NASA Astrophysics Data System (ADS)

    Gurel, Tanju; Sevik, Cem; Cagin, Tahir

    2011-03-01

    Recently, the quaternary compounds, Cu 2 ZnSn S4 and Cu 2 ZnSnSe 4 , have been attracted pretty much attention because of their potential use in the field of energy harvesting applications. Several theoretical calculations have been reported about their first principles electronic, optic and transport properties. However, no lattice dynamic calculations have been published yet despite the discussions about their possible ground state crystal structures and measured low thermal conductivity values. In this systematical study, we examined the vibrational and elastic properties of the two different crystal phases, kesterite (KS) with space group I 4 ? and stannite (ST) with space group I 4 ? 2 m , of this quaternary compounds by using density functional perturbation theory. In addition, we predicted the relaxation time dependent lattice thermal conductivity within the solution of phonon Boltzmann transport equation by making use of the acquired vibrational frequency data.

  6. Crystal structures of the R 3.33CuPb 1.5Se 7 (R = Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds

    Microsoft Academic Search

    L. D. Gulay; I. D. Olekseyuk

    2005-01-01

    The crystal structures of the R3.33CuPb1.5Se7 (R=Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds (space group Cm, Pearson symbol mC25.67) were determined by means of X-ray powder diffraction: a=1.3624(3)nm, b=0.41144(8)nm, c=1.2645(3)nm, ?=104.68(1)° (for Tb3.33CuPb1.5Se7); a=1.3557(5)nm, b=0.4091(1)nm, c=1.2574(4)nm, ?=104.59(2)° (for Dy3.33CuPb1.5Se7); a=1.35314(8)nm, b=0.40819(2)nm, c=1.25609(7)nm, ?=104.577(3)°, RI=0.0797 (for Ho3.33CuPb1.5Se7); a=1.35018(7)nm, b=0.40693(2)nm, c=1.25433(6)nm, ?=104.492(2)°, RI=0.0845 (for Er3.33CuPb1.5Se7); a=1.34584(7)nm, b=0.40560(2)nm, c=1.25083(6)nm, ?=104.342(3)°, RI=0.0866

  7. 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

  8. 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.

  9. Synthesis and X-ray structural characterization of a series of dimeric [Hg2(SePh)2X2(PR2R?)2] compounds (R = tert-butyl; R? = 4-N,N-dimethylaniline and X = Cl, Br, I, SCN, SePh)

    NASA Astrophysics Data System (ADS)

    Stieler, Rafael; Faoro, Eliandro; Cechin, Camila Nunes; Floriano, Luana; Lang, Ernesto Schulz

    2015-01-01

    This article presents the syntheses and characterization of five new compounds with the general formula [Hg2(SePh)2X2(PR2R?)2] (R = tert-butyl; R? = 4-N,N-dimethylaniline), where X = Cl (1a), Br (1b), I (1c), SCN (2), SePh (3). The compounds crystallized as dimeric {HgSe} units, although most of these chalcogenolate compounds appeared to be polymeric adamantanoid or fused adamantanoid species. The ligand structures of these compounds limited the growth of the molecular structures and promoted the formation of the dimeric form alone. The mercury centers were connected to one another through one ?-Cl and one ?-SePh bridge in 1a, and through two ?-SePh bridges in 1b, 1c, 2, and 3. The compounds were characterized by single crystal X-ray diffractometry, TGA, elemental analysis, and infrared spectroscopy.

  10. Reactions of Diphenyl(phenylethynyl)selenonium Salts with Active Methylene Compounds and Amides: First Isolation of Oxyselenuranes [10-Se-4(C3O)] as a Reaction Intermediate.

    PubMed

    Kataoka, Tadashi; Watanabe Si, Shin-ichi; Yamamoto, Keiichirou; Yoshimatsu, Mitsuhiro; Tanabe, Genzoh; Muraoka, Osamu

    1998-09-01

    The reaction of the diphenyl(phenylethynyl)selenonium triflate 1a with active methylene compounds 5 and t-BuOK in THF gave furan derivatives 6. The [10-Se-4(C3O)] selenuranes 8a and 8b could be isolated from the reactions with benzoylacetonitrile 5f and with 1,3-indandione 5g, respectively, as reaction intermediates. The structures of the selenuranes 8 were elucidated by X-ray crystallography and (77)Se high-resolution solid-state NMR spectroscopy. The selenuranes 8 underwent ligand coupling on standing at room temperature or refluxing in chloroform and gave the furan derivatives 6 and the ring-opened product 9. Similarly, the reaction of 1a with benzamide 13a and pivalamide 13d in the presence of NaH in THF afforded oxazole derivatives 14. PMID:11672273

  11. Electrical Conductivity and Dielectric Properties of Se85Te15- x Sb x ( x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) Thin Films

    NASA Astrophysics Data System (ADS)

    Hegab, N. A.; Fadel, M.; Yahia, I. S.; Salem, A. M.; Farid, A. S.

    2013-12-01

    The alternating-current (ac) conductivity and dielectric properties of Se85Te15- x Sb x ( x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) films are reported in this work. Thin films were deposited by thermal evaporation under base pressure of 10-5 Torr. The films were well characterized by x-ray diffraction, differential scanning calorimetry, and energy-dispersive x-ray spectroscopy. The ac conductivity and dielectric properties have been investigated for the studied films in the temperature range from 297 K to 333 K and over the frequency range from 102 Hz to 105 Hz. The experimental results indicate that the ac conductivity and the dielectric constant depend on temperature, frequency, and Sb content. The frequency dependence of was found to be linear with a slope lying very close to unity and is independent of temperature. This behavior can be explained in terms of correlated barrier hopping between centers forming intimate valence-alternation pairs. The density of localized states N( E F) at the Fermi level is estimated. The activation energy was found to decrease with increasing frequency. The dielectric constant ? 1 and dielectric loss ? 2 were found to decrease with increasing frequency and increased with increasing temperature over the ranges studied. The maximum barrier height W m for the studied films was calculated from an analysis of the dielectric loss ? 2 according to the Guintini equation. The values agree with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The variation of the studied properties with Sb content was also investigated.

  12. 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., E-mail: kushwaha@princeton.edu; Gibson, Q. D.; Cava, R. J. [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Xiong, J.; Ong, N. P. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Pletikosic, I. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973 (United States); Weber, A. P. [National Synchrotron Light Source, Brookhaven National Lab, Upton, New York 11973 (United States); Fedorov, A. V. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Valla, T. [Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973 (United States)

    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.

  13. Thoery of Charge Order and Heavy-Electron Formation in the Mixed-Valence Compound KNi2Se2

    NASA Astrophysics Data System (ADS)

    Murray, James; Tesanovic, Zlatko

    2013-03-01

    The material KNi2Se2 has recently been shown to posses a number of striking physical properties, many of which are apparently related to the mixed valency of this system, in which there is on average one quasi-localized electron per every two Ni sites. The material exhibits a charge density wave (CDW) phase that disappears upon cooling, giving way to a low-temperature coherent phase characterized by an enhanced electron mass, reduced resistivity, and an enlarged unit cell free of structural distortion. Starting from an extended periodic Anderson model and using the slave-boson formulation, we develop a model for this system and study its properties within mean-field theory. We find a reentrant first-order transition from a CDW phase, in which the localized moments form singlet dimers, to a heavy Fermi liquid phase as temperature is lowered. The magnetic susceptibility is Pauli-like in both the high- and low-temperature regions, indicating the absence of free local moments, which are typically present in heavy-fermion materials at temperatures above the coherence temperature. The material KNi2Se2 has recently been shown to posses a number of striking physical properties, many of which are apparently related to the mixed valency of this system, in which there is on average one quasi-localized electron per every two Ni sites. The material exhibits a charge density wave (CDW) phase that disappears upon cooling, giving way to a low-temperature coherent phase characterized by an enhanced electron mass, reduced resistivity, and an enlarged unit cell free of structural distortion. Starting from an extended periodic Anderson model and using the slave-boson formulation, we develop a model for this system and study its properties within mean-field theory. We find a reentrant first-order transition from a CDW phase, in which the localized moments form singlet dimers, to a heavy Fermi liquid phase as temperature is lowered. The magnetic susceptibility is Pauli-like in both the high- and low-temperature regions, indicating the absence of free local moments, which are typically present in heavy-fermion materials at temperatures above the coherence temperature. Supported by the Johns Hopkins Institute for Quantum Matter, under Grant No. DE-FG02-08ER46544 from the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

  14. 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.

  15. First-Principles Studies on Cd Doping in CuInSe2 and Related Compounds during Chemical Bath Deposition of CdS Buffer Layer

    NASA Astrophysics Data System (ADS)

    Maeda, Tsuyoshi; Wada, Takahiro

    2013-06-01

    First-principles calculations using plane-wave basis functions were performed to quantitatively evaluate the substitution energies of Cd atom for Cu atom and for In atoms in chalcopyrite-type CuInSe2 (CIS) and related compounds, CuGaSe2 (CGS) and CuAlSe2 (CAS). The substitution energies of Cd atoms in CIS and the related compounds were calculated in considering of the atomic chemical potentials of the constituent elements of Cu and In, and doping Cd atoms. During the chemical bath deposition (CBD) of the CdS layer on the CIGS layer, Cu and Cd atoms dissolved in the ammonia aqueous solution and formed [Cu(NH3)2]+ and [Cd(NH3)4]2+ complex ions. Therefore, the chemical potentials of Cu and Cd atoms in [Cu(NH3)2]+ and [Cd(NH3)4]2+ complex ions were calculated. We found that the substitution energy of n-type CdCu is smaller than that of p-type CdIn. The substitution energy of CdCu in CIS is smaller than those in CGS and CAS. However, the substitution energies of CdCu and CdIn in CIS are positive values. The formation energy of charge-neutral Cd doping with the Cu vacancy (CdCu+VCu) pair is a negative value and greatly smaller than those of n-type CdCu in CIS, CGS, and CAS. These results indicate that the charge-neutral (CdCu+VCu) vacancy pair is easily formed during the CBD of the CdS layer on the CIS layer and a small amount of n-type CdCu would also be formed.

  16. Hydrogen in compound semiconductors

    SciTech Connect

    Haller, E.E.

    1993-05-01

    Progress in the understanding of hydrogen and its interactions in III/V and II/VI compound semiconductors is reviewed. Donor, acceptor and deep level passivation is well established in III/V compounds based on electrical measurements and on spectroscopic studies. The hydrogen donor levels in GaAs and GaP are estimated to lie near E{sub v}+0.5 eV and E{sub v}+0.3 eV, respectively. Arsenic acceptors have been passivated by hydrogen in CdTe and the very first nitrogen-hydrogen local vibrational model spectra in ZnSe have been reported. This long awaited result may lead to an explanation for the poor activation of nitrogen acceptors in ZnSe grown by techniques which involve high concentrations of hydrogen.

  17. First-principles studies of ground-state and dynamical properties of MgS, MgSe, and MgTe in the rocksalt, zinc blende, wurtzite, and nickel arsenide phases

    NASA Astrophysics Data System (ADS)

    Duman, S.; Ba?c?, S.; Tütüncü, H. M.; Srivastava, G. P.

    2006-05-01

    An ab initio pseudopotential method is used to investigate the structural and electronic properties of MgS, MgSe, and MgTe in the rocksalt, zinc blende, wurtzite, and nickel arsenide phases. It is found that rocksalt is the most stable phase for MgS and MgSe, while nickel arsenide is the most stable phase for MgTe. Differences in the density of states for the upper valence bands and lower conduction bands between these competing phases are pointed out. The lattice dynamics of these semiconductors has been studied by employing a linear response approach based on the density functional theory. Differences in the phonon spectra and density of states both in the acoustic and optical ranges between the competing phases are investigated. The calculated zone-center phonon modes for the rocksalt and zinc blende phases of MgS are in good agreement with experimental observations.

  18. Synthesis and characterization of mid-infrared transparency compounds: acentric BaHgS2 and centric Ba8Hg4S5Se7.

    PubMed

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

    2015-03-16

    Two mid-IR transparency compounds, namely, acentric BaHgS2 (BHS) and centric Ba8Hg4S5Se7 (BHSSe), were successfully synthesized by a conventional solid-state reaction method. The space group of BHS is orthorhombic Pmc21 with [HgS4] tetrahedra and isolated dumbbell-shaped [HgS2] units, while BHSSe belongs to the orthorhombic space group Pnma with infinite isolated ?[HgSe2(S/Se)2](4-) chains. Raman spectra and thermal analysis of the titled materials were measured. In addition, their band gaps are found to be 1.93 (BHS) and 1.98 eV (BHSSe) from the measured diffuse reflectance spectra. Significantly, the powder BHS sample exhibits a good second harmonic generation (SHG) response of ?6.5 times compared with that of reference AgGaS2 at a fundamental wavelength (2.09 ?m). The calculated SHG coefficients of BHS are also reported, and the maximum result agrees well with the test observation. PMID:25742293

  19. Derivation of static low-energy effective models by an ab initio downfolding method without double counting of Coulomb correlations: Application to SrVO3, FeSe, and FeTe

    NASA Astrophysics Data System (ADS)

    Hirayama, Motoaki; Miyake, Takashi; Imada, Masatoshi

    2013-05-01

    Derivation of low-energy effective models by a partial trace summation of the electronic degrees of freedom far away from the Fermi level, called downfolding, is reexamined. We propose an improved formalism free from the double counting of electron correlation in the low-energy degrees of freedom. In this approach, the exchange-correlation energy in the local-density approximation (LDA) is replaced with the GW self-energy; herewith its low-energy part associated with the double counting is subtracted. Moreover, in our formalism, the frequency dependence of the effective parameter is renormalized into the static one. We apply the formalism to SrVO3 as well as to two iron-based superconductors, FeSe and FeTe. The resultant bandwidths of the effective models are nearly the same as those of the previous downfolding formalism because of striking cancellations between an increase arising from the exclusion of the low-energy correlation and a shrinking arising from the renormalization of the frequency dependence. In the nondegenerate multiband materials such as FeSe and FeTe, the momentum dependent self-energy effects yield substantial modifications of the band structures and relative shifts of orbital-energy levels of the effective models, which may explain the stability of the bicollinear antiferromagnetic phase in FeTe as well as the experimental absence of the antiferromagnetic phase in FeSe.

  20. X-ray characterization, electronic band structure, and thermoelectric properties of the cluster compound Ag2Tl2Mo9Se11.

    PubMed

    Al Rahal Al Orabi, Rabih; Gougeon, Patrick; Gall, Philippe; Fontaine, Bruno; Gautier, Régis; Colin, Malika; Candolfi, Christophe; Dauscher, Anne; Hejtmanek, Jiri; Malaman, Bernard; Lenoir, Bertrand

    2014-11-01

    We report on a detailed investigation of the crystal and electronic band structures and of the transport and thermodynamic properties of the Mo-based cluster compound Ag2Tl2Mo9Se11. This novel structure type crystallizes in the trigonal space group R3?c and is built of a three-dimensional network of interconnected Mo9Se11 units. Single-crystal X-ray diffraction indicates that the Ag and Tl atoms are distributed in the voids of the cluster framework, both of which show unusually large anisotropic thermal ellipsoids indicative of strong local disorder. First-principles calculations show a weakly dispersive band structure around the Fermi level as well as a semiconducting ground state. The former feature naturally explains the presence of both hole-like and electron-like signals observed in Hall effect. Of particular interest is the very low thermal conductivity that remains quasi-constant between 150 and 800 K at a value of approximately 0.6 W·m(-1)·K(-1). The lattice thermal conductivity is close to its minimum possible value, that is, in a regime where the phonon mean free path nears the mean interatomic distance. Such extremely low values likely originate from the disorder induced by the Ag and Tl atoms giving rise to strong anharmonicity of the lattice vibrations. The strongly limited ability of this compound to transport heat is the key feature that leads to a dimensionless thermoelectric figure of merit ZT of 0.6 at 800 K. PMID:25338311

  1. Synthesis, characterization, and structure-property relationships in two new polar oxides: Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3).

    PubMed

    Nguyen, Sau Doan; Kim, Sang-Hwan; Halasyamani, P Shiv

    2011-06-01

    Two new noncentrosymmetric (NCS) polar oxide materials, Zn(2)(MoO(4))(AO(3)) (A = Se(4+) or Te(4+)), have been synthesized by hydrothermal and solid-state techniques. Their crystal structures have been determined, and characterization of their functional properties (second-harmonic generation, piezoelectricity, and polarization) has been performed. The isostructural materials exhibit a three-dimensional network consisting of ZnO(4), ZnO(6), MoO(4), and AO(3) polyhedra that share edges and corners. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicate the materials exhibit moderate SHG efficiencies of 100 × and 80 × ?-SiO(2) for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively. Particle size vs SHG efficiency measurements indicate the materials are type 1 non-phase-matchable. Converse piezoelectric measurements resulted in d(33) values of ?14 and ?30 pm/V for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively, whereas pyroelectric measurements revealed coefficients of -0.31 and -0.64 ?C/m(2) K at 55 °C for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively. Frequency-dependent polarization measurements confirmed that all of the materials are nonferroelectric; that is, the macroscopic polarization is not reversible, or "switchable". Infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements were also performed. First-principles density functional theory (DFT) electronic structure calculations were also done. Crystal data: Zn(2)(MoO(4))(SeO(3)), monoclinic, space group P2(1) (No. 4), a = 5.1809(4) Å, b = 8.3238(7) Å, c = 7.1541(6) Å, ? = 99.413(1)°, V = 305.2(1) Å(3), Z = 2; Zn(2)(MoO(4))(TeO(3)), monoclinic, space group P2(1) (No. 4), a = 5.178(4) Å, b = 8.409(6) Å, c = 7.241(5) Å, ? = 99.351(8)°, V = 311.1(4) Å(3), Z = 2. PMID:21557565

  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

    2015-02-01

    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. Crystallographic site swapping of La3+ ion in BaA'LaTeO6 (A' = Na, K, Rb) double perovskite type compounds: diffraction and photoluminescence evidence for the site swapping.

    PubMed

    Phatak, R; Gupta, S K; Krishnan, K; Sali, S K; Godbole, S V; Das, A

    2014-02-28

    Double perovskite type compounds of the formula BaA'LaTeO6 (A' = Na, K, Rb) were synthesized by solid state route and their crystal structures were determined by Rietveld analysis using powder X-ray diffraction and neutron diffraction data. Na compound crystallizes in the monoclinic system with P2?/n space group whereas, K and Rb compounds crystallize in Fm3m space group. All the three compounds show rock salt type ordering at B site. Crystal structure analysis shows that La ion occupies A site in Na compound whereas, it occupies B site in K and Rb compounds according to the general formula of AA'BB'O6 for a double perovskite type compound. Effect of this crystallographic site swapping of the La ion was also observed in the photoluminescence study by doping Eu(3+) in La(3+) site. The large decrease in the intensity of the electric dipole ((5)D0-(7)F2) transition in the Rb compound compared to the Na compound indicates that Eu(3+) ion resides in the centrosymmetric octahedral environment in the Rb compound. PMID:24363108

  4. Electronic structure of Fe1.04Te0.66Se0.34 Fei Chen,1 Bo Zhou,1 Yan Zhang,1 Jia Wei,1 Hong-Wei Ou,1 Jia-Feng Zhao,1 Cheng He,1 Qing-Qin Ge,1 Masashi Arita,2

    E-print Network

    Hu, Jiangping

    temperature Tc up to 55 K in iron pnictides1­3 has generated great interests. The FeAs layer is considered pnictides and iron chalcogenides have many things in common. The FeSe Te layer in Fe1+yTe1-xSex is isostructural to the FeAs or FeP layer in iron pnictides. Moreover, the phase diagram of Fe1+yTe1-xSex resembles

  5. Magnetoreflectivity of Pb1 xEuxTe epilayers and PbTe/Pb1 xEuxTe multiple quantum wells Shu Yuan,* Heinz Krenn, Gunther Springholz, Yukio Ueta, and Gunther Bauer

    E-print Network

    McCann, Patrick

    screening of the polar interaction are considered as well, but are ruled out as an explanation are determined for Pb1 xEuxTe as a function of the composition up to x 0.034. It is found that the transverse, and quaternary compounds based on PbSe and PbTe.1 Multiple-element infrared focal-plane photodetector arrays have

  6. 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. (UCB); (Tennessee-K); (LBNL)

    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.

  7. Advanced Processing of CdTe- and CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2}-Based Solar Cells; Phase I Report

    SciTech Connect

    Morel, D.L.; Ferekides, C.S.

    2000-09-05

    The main tasks of the cadmium telluride portion of this project include the development of simplified processing for fabricating high-efficiency CdTe solar cells, studies on the long-term stability of CdTe devices, and the development of alternative transparent conducting oxides, window layers, and back contacts. The second portion of this project focused on CIGS solar cells. The main tasks include the development of a manufacturable process for CIGS devices and the development of high-band-gap alloys for use in tandem cell structures. Additional objectives include development of improved junction formation processing and contributing to the overall understanding of these materials and devices. Because the processing is manufacturing-driven, the authors use an all solid-state, simplified two-step process that relaxes the level of deposition control required.

  8. Reactivities of the chalcogen-capped triiron clusters [EFe 3(CO) 9] 2– (E = Te, Se, S): cluster growth and transformations

    Microsoft Academic Search

    Minghuey Shieh; Chia-Hua Ho

    2005-01-01

    Transition-metal carbonyl clusters incorporated with chalcogen elements are of particular interests due to their structural and chemical diversity. Up to now, quite a large number of chalcogen-containing iron carbonyl clusters have been synthesized and structurally characterized. In this short review, we will describe our recent developments on the interesting cluster expansions and transformations of the chalcogen-capped triiron clusters [EFe3(CO)9]2– (E=Te,

  9. Electrical properties and phase transitions in superconducting quasi-one-dimensional chalcogenides In[sub x]Nb[sub 3]X[sub 4] (X = S, Se, and Te)

    SciTech Connect

    Ohtani, T.; Sano, Y.; Yokota, Y. (Okayama Univ. of Science (Japan))

    1993-04-01

    Electrical properties and phase transitions were investigated in the quasi-one-dimensional ternary chalcogenides In[sub x]Nb[sub 3]X[sub 4] (X = S, Se, and Te; x = 0.5 for X = S, and 1.0 for X = Se and Te), with results indicating that the In[sub x]Nb[sub 3]Te[sub 4] system has two new kinds of phase transitions. Based on the values of the transition temperatures T[sub t], this system is classified into two groups, i.e., Group 1 samples with 0 [le] x < 0.55 having T[sub t] = [approx]40 and [approx]80 K, and Group 2 samples with 0.55 < x [le] 1.0 having T[sub t] = [approx]50 and [approx]140 K. Electron diffraction measurements showed the 140-K transition to be associated with a charge-density-wave (CDW) formation accompanied by the appearance of a superstructure that can be explained by the commensurate wave vectors q = ([+-]1/3a* + 1/3b*) + 4/9c*, which are slightly larger in the c* component as compared with those previously observed in Nb[sub 3]Te[sub 4] of q = [+-](1/3a* + 1/3b*) + 3/7c*. The increase in the c* component was interpreted as being caused by the increase in Fermi energy due to In insertion. Thermopower measurements on In[sub x]Nb[sub 3]Te[sub 4] showed the dominant carriers to be holes. In addition, the In[sub x]Nb[sub 3]Se[sub 3.84] system (0.40 [le] x [le] 1.0) showed a new CDW-like transition at [approx] 30 K. The superconducting critical temperature [Tc] of In[sub x]Nb[sub 3]X[sub 4] was increased by several degrees when the In content x was increased above 0.5. 27 refs., 10 figs., 1 tab.

  10. Weak antilocalization and disorder-enhanced electron interactions in annealed films of the phase-change compound GeSb2Te4

    NASA Astrophysics Data System (ADS)

    Breznay, Nicholas P.; Volker, Hanno; Palevski, Alexander; Mazzarello, Riccardo; Kapitulnik, Aharon; Wuttig, Matthias

    2012-11-01

    Phase-change materials can be reversibly switched between amorphous and crystalline states and often show strong contrast in the optical and electrical properties of these two phases. They are now in widespread use for optical data storage, and their fast switching and a pronounced change of resistivity upon crystallization are also very attractive for nonvolatile electronic data storage. Nevertheless, several open questions remain regarding the electronic states and charge transport in these compounds. In this work, we study electrical transport in thin metallic films of the disordered, crystalline phase-change material GeSb2Te4. We observe weak antilocalization and disorder-enhanced Coulomb interaction effects at low temperatures, and separate the contributions of these two phenomena to the temperature dependence of the resistivity, Hall effect, and magnetoresistance. Strong spin-orbit scattering causes positive magnetoresistance at all temperatures, and a careful analysis of the low-field magnetoresistance allows us to extract the temperature-dependent electron dephasing rate and study other scattering phenomena. We find electron dephasing due to inelastic electron-phonon scattering at higher temperatures, electron-electron scattering dephasing at intermediate temperatures, and a crossover to weak temperature dependence below 1 K.

  11. Surface state of Bi1.5Sb0.5Te1.7Se1.3 investigated by terahertz emission and visible second-harmonic generation techniques

    NASA Astrophysics Data System (ADS)

    Park, Soon-Hee; Hamh, S. Y.; Lee, J. S.; Park, Joonbum; Kim, Jun Sung

    2015-03-01

    One of the key issues in three-dimensional topological insulators is to separate a response of the surface from the bulk to exploit novel spin-momentum-locked Dirac fermionic surface state, and Bi1.5Sb0.5Te1.7Se1.3 is one of such materials having a negligible contribution of the bulk conduction. We investigate the surface state of Bi1.5Sb0.5Te1.7Se1.3 single crystals by using terahertz emission spectroscopy and second harmonic generation techniques. We observed a clear distinction in the phases of emitted terahertz electric field and azimuth-dependent second harmonic intensity in different pieces of the sample, and found their clear correlation with carrier types which can be attributed to upward or downward band bending. We examined variations of such optical responses after the cleavage of the samples under different atmospheric environments, and discussed the time-evolution of the surface state particularly in comparison with previous results on n-type Bi2Se3.

  12. Order/disorder phenomena in Zn1-xMnxGa2Se4 ordered vacancy compounds: high temperature neutron powder diffraction experiments.

    PubMed

    Alonso-Gutiérrez, P; Morón, M C; Hull, S; Sanjuán, M L

    2013-12-01

    We present a study of order-disorder phenomena in the series of tetrahedral ordered vacancy compounds Zn1-xMnxGa2Se4 by means of time-of-flight neutron diffraction at high temperature together with dc magnetic susceptibility, Raman spectroscopy, differential thermal analysis and optical absorption experiments. Samples of nominal composition x = 0, 0.24, 0.5, 0.77 and 1 have been studied. An order-disorder phase transition has been detected, with Tc ranging from 472 to 610?° C, which involves a structural change from a defect chalcopyrite phase, with I4 space group (s.g.) and three different cation sites, to a partially disordered defect stannite, in which Zn, Mn and half of the Ga ions share the 4d site in I42m s.g. Neither the vacancies nor the Ga ions occupying site 2a are involved in the phase transition. An additional ordering process is observed on approaching the phase transition from below, which is attributed to several factors: the activation of cation diffusion at ?300?° C, the partially disordered cation distribution exhibited by the as-grown single crystals and the preference of Mn atoms for the 2d crystallographic site in the I4 structure. The reversibility of the phase transition is analysed with the aid of magnetic, optical and Raman experiments. PMID:24177226

  13. Six-year efficiency gains for CdTe and CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} solar cells: What has changed?

    SciTech Connect

    Sites, J.R.; Liu, X. [Colorado State Univ., Fort Collins, CO (United States). Physics Dept.

    1994-12-31

    During a period of 6 years from roughly 1987 to 1993, a number of laboratories have contributed to truly remarkable efficiency gains for thin-film cells with polycrystalline CdTe and CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} (CIGS) absorbers. Total-area efficiencies have increased from just above 10% to over 16%, and these cells can now be sensibly compared with single-crystal cells of comparable bandgap. A number of factors have contributed to these gains, but the most significant has been the reduction of recombination states in the depletion region and the resulting drop in forward-current density.

  14. 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. [Tata Institute of Fundamental Research (TIFR), Homi Bhabha Road, Mumbai 400005 (India)

    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.

  15. 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., E-mail: rusinovip@gmail.com; Nechaev, I. A. [Tomsk State University (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC) (Spain)

    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.

  16. Effect of first-stage temperature on Cu(In,Ga)Se 2 solar cells using the evaporation of binary selenide compounds

    Microsoft Academic Search

    Doo Youl Lee; Byung Tae Ahn; Kyung Hoon Yoon; Jin Soo Song

    2003-01-01

    Cu(In,Ga)Se2 films were prepared by a three-stage process using the evaporation of In2Se3, Ga2Se3, Cu2Se, and Se. In the first stage, the (In,Ga)2Se3 layer was deposited at the substrate temperatures of 150°C and 325°C by the evaporation of In2Se3, Ga2Se3, and Se. The CIGS film had small grains with a bi-layer morphology at 150°C, while the film had large grains

  17. 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

  18. Single Dirac Cone Topological Surface State and Unusual Thermoelectric Property of Compounds from a New Topological Insulator Family

    Microsoft Academic Search

    Y. L. Chen; Z. K. Liu; J. G. Analytis; J.-H. Chu; H. J. Zhang; B. H. Yan; S.-K. Mo; R. G. Moore; D. H. Lu; I. R. Fisher; S. C. Zhang; Z. Hussain; Z.-X. Shen

    2010-01-01

    Angle resolved photoemission spectroscopy study on TlBiTe2 and TlBiSe2 from a thallium-based ternary chalcogenides family revealed a single surface Dirac cone at the center of the Brillouin zone for both compounds. For TlBiSe2, the large bulk gap (˜200meV) makes it a topological insulator with better mechanical properties than the previous binary 3D topological insualtor family. For TlBiTe2, the observed negative

  19. 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. [Univ. of South Florida, Tampa, FL (United States)] [Univ. of South Florida, Tampa, FL (United States)

    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.

  20. 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

  1. Recent developments in the MOVPE of II-VI compounds

    NASA Astrophysics Data System (ADS)

    Mullin, J. B.; Irvine, S. J. C.; Giess, J.; Royle, A.

    1985-08-01

    This review is concerned with developments that have taken place over the last year or so in the field of metal-organic vapor phase epitaxy of II-VI compounds. In this rapidly developing field the compounds attracting most study are CdTe, Cd(x)Hg(1-x)Te, HgTe, ZnSe, ZnS(x)Se(1-x), ZnS, CdS and ZnO. These developments, which are considered within the framework of existing knowledge, cover organic reagents or precursors, alternative substrates, reaction mechanisms and developments in growth technique. Prominence is given to Photo-MOVPE and low temperature growth. Improvements in material quality and recent device advances using MOVPE are also reported.

  2. Effect of fluctuations on electron and phonon processes and thermodynamic parameters of Ag{sub 2}Te and Ag{sub 2}Se in the region of phase transition

    SciTech Connect

    Aliev, S. A.; Aliev, F. F. [National Academy of Sciences of Azerbaijan, Institute of Physics (Azerbaijan)], E-mail: farzali@physics.ab.az

    2008-04-15

    Temperature dependences of electrical conductivity {sigma}, thermoelectric power {alpha}, results of differential thermal analysis {delta}T{sub y}, thermal conductivity {chi}, temperature conductivity {kappa}, and heat capacity C{sub p} were studied in Ag{sub 2}Te and Ag{sub 2}Se semiconductors in the region of the phase transition. Two extrema are observed in the temperature dependence {chi}(T): a maximum in the region of the {alpha}' {sup {yields}} {beta}' transition and a minimum in the region of the {beta}' {sup {yields}} {beta} transition; these extrema are caused by the similar dependence C{sub p}(T). It is shown that the {alpha} {sup {yields}} {alpha}' and {beta}' {sup {yields}} {beta} transitions are displacement transitions, while the {alpha}' {sup {yields}} {beta}' transition is of reconstruction type. It is established that the disorder parameter {eta} in silver chalcogenides is highly smeared in the region of the phase transition; therefore, disordering of phases at the point of the phase transition is incomplete: 73, 62, and 48% in Ag{sub 2}Te, Ag{sub 2}Se, and Ag{sub 2}S, respectively. The minimum volumes V{sub ph} for new phases are calculated; it is shown that the value of V{sub ph} in displacement transitions is larger than in the reconstruction-type transitions.

  3. Effect of disorder in the charge-density-wave compounds LaTe1.95 and CeTe1.95-xSex (x=0 and 0.16) as revealed by optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Hu, B. F.; Dong, T.; Fang, A. F.; Zheng, P.; Wang, N. L.

    2012-11-01

    We present optical spectroscopy measurements on rare-earth ditelluride single crystals of LaTe1.95 and CeTe1.95-xSex (x=0 and 0.16). The measurements reveal formation of charge-density-wave energy gaps at rather high-energy levels, for example, 2?˜8500 cm-1 for LaTe1.95 and 6800 cm-1 for CeTe1.95. More strikingly, the study reveals that, different from the rare-earth tritellurides, the Te vacancies and disorder effect play a key role in the low-energy charge excitations of ditelluride systems. Although an eminent peak is observed between 800 and 1500 cm-1 in conductivity spectra for LaTe1.95, and CeTe1.95-xSex (x=0 and 0.16), our analysis indicates that it could not be attributed to the formation of a small energy gap, instead it could be well accounted for by the localization modified Drude model. Our study also indicates that the low-temperature optical spectroscopic features are distinctly different from a semiconducting charge-density-wave (CDW) state with entirely gapped Fermi surfaces.

  4. 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 [TU Muenchen, Lichtenbergstrasse 4, Garching (Germany); Nilges, Tom, E-mail: tom.nilges@lrz.tum.d [TU Muenchen, Lichtenbergstrasse 4, Garching (Germany); Decourt, Rodolphe; Bobet, Jean-Louis; Chevalier, Bernard [CNRS, Universite de Bordeaux, ICMCB, Avenue du Docteur Schweitzer 87, 33608 PESSAC cedex (France)

    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.

  5. Experimental studies on anisotropic thermoelectric properties and structures of n-type Bi2Te2.7Se0.3.

    PubMed

    Yan, Xiao; Poudel, Bed; Ma, Yi; Liu, W S; Joshi, G; Wang, Hui; Lan, Yucheng; Wang, Dezhi; Chen, Gang; Ren, Z F

    2010-09-01

    The peak dimensionless thermoelectric figure-of-merit (ZT) of Bi(2)Te(3)-based n-type single crystals is about 0.85 in the ab plane at room temperature, which has not been improved over the last 50 years due to the high thermal conductivity of 1.65 W m(-1) K(-1) even though the power factor is 47 x 10(-4) W m(-1) K(-2). In samples with random grain orientations, we found that the thermal conductivity can be decreased by making grain size smaller through ball milling and hot pressing, but the power factor decreased with a similar percentage, resulting in no gain in ZT. Reorienting the ab planes of the small crystals by repressing the as-pressed samples enhanced the peak ZT from 0.85 to 1.04 at about 125 degrees C, a 22% improvement, mainly due to the more increase on power factor than on thermal conductivity. Further improvement is expected when the ab plane of most of the small crystals is reoriented to the direction perpendicular to the press direction and grains are made even smaller. PMID:20672824

  6. Synthesis, structure, and optical properties of the quaternary diamond-like compounds I{sub 2}–II–IV–VI{sub 4} (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se)

    SciTech Connect

    Liu, Bin-Wen; Zhang, Ming-Jian; Zhao, Zhong-Yan; Zeng, Hui-Yi, E-mail: zhy@fjirsm.ac.cn; Zheng, Fa-Kun; Guo, Guo-Cong, E-mail: gcguo@fjirsm.ac.cn; Huang, Jin-Shun

    2013-08-15

    Three new diamond-like compounds with the formula of I{sub 2}?II?IV?VI{sub 4} (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se) have been synthesized via traditional high-temperature solid-state reactions and structurally characterized by single crystal X-ray diffraction analysis. All the three compounds crystallize in the space group Pmn2{sub 1} in the wurtzite-type superstructure with a=7.563(4), b=6.448(3), c=6.179(3) Å, Z=2 for Cu{sub 2}MgSiS{sub 4} (1); a=7.953(5), b=6.797(4), c=6.507(4) Å, Z=2 for Cu{sub 2}MgGeS{sub 4} (2); a=7.638(4), b=6.515(4), c=6.225(3) Å, Z=2 for Cu{sub 2}MgSiSe{sub 4} (3). All atoms in these compounds are tetrahedrally coordinated. Optical diffuse reflectance UV/Vis/NIR spectra indicate that compounds 1 and 2 have the band gaps of 3.20 and 2.36 eV, respectively. Electronic structure calculations using the CASTEP code indicate that they are all direct band gap compounds. - Graphical abstract: Three new diamond-like compounds, Cu{sub 2}MgSiS{sub 4}, Cu{sub 2}MgGeS{sub 4}, and Cu{sub 2}MgSiSe{sub 4}, have been synthesized. All the three compounds crystallize in the space group Pmn2{sub 1} and all atoms are tetrahedrally coordinated. Highlights: • Three new diamond-like compounds Cu{sub 2}MgSiS{sub 4}, Cu{sub 2}MgGeS{sub 4} and Cu{sub 2}MgSiSe{sub 4} have been synthesized. • All ions are tetrahedrally coordinated. • Electronic structure calculations indicate that they are all direct band gap compounds.

  7. 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. [Department of Physics, Queens College of CUNY, Queens, New York 11367 (United States); The Graduate Center of CUNY, New York, New York 10016 (United States); Shuvayev, Vladimir [Department of Physics, Queens College of CUNY, Queens, New York 11367 (United States); Deligiannakis, Vasilios; Tamargo, Maria C. [The Graduate Center of CUNY, New York, New York 10016 (United States); Department of Chemistry, City College of CUNY, New York, New York 10031 (United States); Ludwig, Jonathan [National High Magnetic Field Laboratory, Tallahassee, Florida 32310 (United States); Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Smirnov, Dmitry [National High Magnetic Field Laboratory, Tallahassee, Florida 32310 (United States); Wang, Alice [Evans Analytical Group, Sunnyvale, California 94086 (United States)

    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.

  8. Temperature-dependent transformation of the magnetic excitation spectrum on approaching superconductivity in Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5).

    PubMed

    Xu, Zhijun; Wen, Jinsheng; Zhao, Yang; Matsuda, Masaaki; Ku, Wei; Liu, Xuerong; Gu, Genda; Lee, D-H; Birgeneau, R J; Tranquada, J M; Xu, Guangyong

    2012-11-30

    Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, T(c), for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5) that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T?T(c) to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperatures up to ~3T(c). If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to T(c) demonstrates that strong interactions are involved. PMID:23368150

  9. 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. [Institute of Metal Physics, UB RAS, 620041 Ekaterinburg (Russian Federation); Zhao, H. [Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Derks, C.; Taubitz, C.; Neumann, M. [University of Osnabrueck, D-49069 Osnabrueck (Germany); Persson, C. [Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo (Norway); Kuznetsov, M. V. [Institute of Solid State Chemistry, UB RAS, 620990 Ekaterinburg (Russian Federation); Urals Federal University, 19 Mira Str., Ekaterinburg 620002 (Russian Federation); Bodnar, I. V. [Department of Chemistry, Belarusian State University of Informatics and Radioelectronics, P. Brovka 6, 220027 Minsk (Belarus); Martin, R. W.; Yakushev, M. V. [Department of Physics, SUPA, Strathclyde University, G4 0NG Glasgow (United Kingdom)

    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.

  10. 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. [University of South Florida, Tampa, FL (United States)] [University of South Florida, Tampa, FL (United States)

    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.

  11. 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

  12. Synthesis of wurtzite-zincblende Cu2ZnSnS4 and Cu2ZnSnSe4 nanocrystals: insight into the structural selection of quaternary and ternary compounds influenced by binary nuclei

    NASA Astrophysics Data System (ADS)

    Li, Yingwei; Han, Qifeng; Kim, Tae Whan; Shi, Wangzhou

    2014-03-01

    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.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. Electronic supplementary information (ESI) available: Detailed information about the mole ratios used for reactions, EDS and XPS spectra of the synthesized nanocrystals, a table for structural comparison between quaternary and ternary compounds, Raman scattering spectra of the ternary compounds CTS and CTSe, and XRD patterns of the binary ZnS and ZnSe. See DOI: 10.1039/c3nr05358j

  13. Structural modulations in Bi2Te3

    NASA Astrophysics Data System (ADS)

    Peranio, N.; Eibl, O.

    2008-01-01

    Bi2Te3 is known for its large thermopower, a low thermal conductivity, and thereby a large thermoelectric figure of merit ZT at room temperature. Particularly, the low thermal conductivity is attributed to a high structural disorder. Electron probe microanalysis, transmission electron microscopy (TEM), and energy dispersive x-ray spectrometry in the TEM were applied on n-type Bi2(Te,Se)3 and p-type (Bi,Sb)2Te3 bulk materials for structural and chemical analysis. Significant variations in stoichiometry were found on the micrometer scale. Bulk materials showed a texture, grain sizes of 1-10 ?m, and dislocations in the basal plane with a density of 109 cm-2 having a high mobility at room temperature. A structural modulation [natural nanostructure (nns)] was found on the nanometer scale. This nns was also observed in Bi2Te3 thin films and Bi2Te3/Bi2(Te,Se)3 superlattices and turned out to be of general character for Bi2Te3 materials. The nns was analyzed in detail by stereomicroscopy in the TEM and by image simulation. The nns was found to be a pure sinusoidal displacement field with (i) a displacement vector parallel to ?5,-5,1? and an amplitude of about 10 pm and (ii) a wave vector parallel to {1,0,10} and a wavelength of 10 nm. Bi2Te3 samples from different batches produced under similar conditions showed different characteristics with respect to the nns: none, one, or two superimposed nns were observed. The nns is present in all parts of the sample with the same orientation. The formation of the nns is either bound to a certain stoichiometry range or to the thermal history of a sample and is related to the tendency of Te compounds to form amorphous phases. An ordered network of dislocations a few nanometers apart and chemical fluctuations on the nanometer scale as origins of the nns were ruled out. The displacement field of the nns is superimposed to the average structure and should significantly affect the thermoelectric properties. Particularly, the lattice thermal conductivity should be decreased due to phonon scattering on the sinusoidal strain field of the nns. Also, the nns should yield a one-dimensional or zero-dimensional behavior of the phonons and anisotropic transport coefficients in the basal plane.

  14. Systems based on A 2 TeC 6 (A = K, Rb, Cs, and Tl(I); C = Br and I) compounds with peritectic interactions

    Microsoft Academic Search

    E. Yu. Peresh; V. I. Sidei; O. V. Zubaka

    2009-01-01

    This work presents six peritectic quasi-binary systems based on A2TeC6 (A = K, Rb, Cs, and Tl(I); C = Br and I) ternary halides. We consider factors influencing physicochemical interactions between\\u000a components in these systems.

  15. Ternary chalcogenide compounds AB2X4: The crystal structures of SiPb2S4 and SiPb2Se4

    Microsoft Academic Search

    J. E. Iglesias; H. Steinfink

    1973-01-01

    The crystal structures of SiPb2S4 and SiPb2Se4 were determined from three dimensional X-ray diffraction data collected with Mo radiation. Both structures are monoclinic with space group P21\\/c and 4 formula units per unit cell. Lattice dimensions for SiPb2S4 are a = 6.4721(5) Å, b = 6.6344(9) Å, c = 16.832(1) Å, and beta = 108.805(7)°. For SiPb2Se4, a = 8.5670(2)

  16. Journal of Solid State Chemistry 180 (2007) 28772884 Cs4P2Se10: A new compound discovered with the application of

    E-print Network

    Weliky, David

    2007-01-01

    purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. 31 P by quenching the melt in ice water, and Cs4P2Se10 was recovered upon annealing. The static 31 P NMR spectrum: NMR; Solid state; High temperature; Chalcogenides; Metal selenophosphates; Phosphorus; 31 P 1

  17. Magnetic susceptibility and EPR of europium compounds: EuGa2S4, EuGa2Se4 and EuAl2S4

    Microsoft Academic Search

    R. Rimet; R. Buder; C. Schlenker; J. V. Zanchetta

    1980-01-01

    The magnetic susceptibility of EuGa2S4, EuGa2Se4 and EuAl2S4, measured between 4.2 and 300 K, is found to obey Curie-Weiss laws. EPR spectra show a single broad line at g = 2.00, characteristic of Eu2+; the linewidth (in the range 900-1500 G at 200 K) is found to increase steeply below ∽ 50 K.

  18. Direct Observation of Complete Fermi Surface, Imperfect Nesting, and Gap Anisotropy in the High-Temperature Incommensurate Charge-Density-Wave Compound SmTe{sub 3}

    SciTech Connect

    Gweon, G.; Denlinger, J.D.; Clack, J.A.; Allen, J.W.; DiMasi, E.; Aronson, M.C. [Randall Laboratory of Physics, University of Michigan, Ann Arbor, Michigan 48109-1120 (United States)] [Randall Laboratory of Physics, University of Michigan, Ann Arbor, Michigan 48109-1120 (United States); Olson, C.G. [Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States); Foran, B.; Lee, S. [Dow Laboratory of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055 (United States)] [Dow Laboratory of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055 (United States)

    1998-07-01

    We have carried out angle resolved photoemission spectroscopy of SmTe{sub 3} , a quasi-two-dimensional material with an incommensurate high-temperature charge density wave (CDW). This is the first direct experimental view of the full detail of an imperfectly nested Fermi surface, and the momentum space gap anisotropy, for an incommensurate CDW. {copyright} {ital 1998} {ital The American Physical Society}

  19. Power conversion efficiency studies of vacuum evaporated n-CdSe 0.6Te 0.4 semiconducting thin film/(aq) ferro-ferricyanide electrolyte photoelectrochemical solar cells

    NASA Astrophysics Data System (ADS)

    Damodara Das, V.; Damodare, Laxmikant

    1997-07-01

    Photoelectrochemical (PEC) solar cells made using as-grown polycrystalline thin films of n-CdSe 0.6Te 0.4 (thickness ? 5000 Å) (prepared by vacuum thermal flash evaporation with a deposition rate of 20 ± 1 Å s -1 in a vacuum better than 5 × 10 -5 torr on indium oxide coated microslide glass plates [ ? = 1.25 × 10 4 (?- cm) -1] held at 200°C) dipped in aqueous ferro-ferricyanide electrolyte have been studied to evaluate the conversion efficiency under white light illumination intensity of 100 mW cm -2 (AM1). Mott-Shottky plots have been drawn (in the dark condition) to evaluate the semiconductor parameters. The reasons for the observed high power conversion efficiency and high quantum efficiency in relation to the semiconductor parameters are explained. The films have been characterized by X-ray diffraction for structural studies, Energy Despersive Analysis of X-rays (EDAX) for compositional analysis, Scanning Electron Microscopy (SEM) technique for surface morphology studies and optical absorption for band gap determination.

  20. Excess vibrational modes and high thermoelectric performance of the quenched and slow-cooled two-phase alloy Cu0.2Ag2.8SbSeTe2.

    PubMed

    Drymiotis, F R; Lindsey, S; Capps, J; Lashley, J C; Rhodes, D; Zhang, Q R; Nucklos, C; Drye, T B

    2011-04-01

    In this article we examine the low-temperature specific heat of slow-cooled Cu(0.2)Ag(2.8)SbSeTe(2) and the thermoelectric performance of quenched samples. We find that the low-temperature specific heat is dominated by two Einstein terms of approximate energies of 2.5 and 5 meV. The specific-heat behavior is consistent with the amorphous low-temperature thermal conductivity behavior and validates the glassy nature of the structure. We performed the synthesis of quenched samples in an attempt to eliminate the presence of micro-cracks, whose existence presumably enhances electronic scattering. We find that quenching eliminates the presence of micro-cracks but does not result in an improvement of the figure of merit. Specifically, the highest ZT obtained in the quenched samples (ZT = 1.5), though very competitive, is still significantly less that the ZT obtained in the slow-cooled samples (ZT = 1.75). PMID:21415478