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1

Impressive structural diversity and polymorphism in the modular compounds ABi3Q5 (A = Rb, Cs; Q = S, Se, Te).  

PubMed

An outstanding example of structural diversity and complexity is found in the compounds with the general formula ABi(3)Q(5) (A = alkali metal; Q = chalcogen). gamma-RbBi(3)S(5) (I), alpha-RbBi(3)Se(5) (II), beta-RbBi(3)Se(5) (III), gamma-RbBi(3)Se(5) (IV), CsBi(3)Se(5) (V), RbBi(3)Se(4)Te (VI), and RbBi(3)Se(3)Te(2) (VII) were synthesized from A(2)Q (A = Rb, Cs; Q = S, Se) and Bi(2)Q(3) (Q = S, Se or Te) at temperatures above 650 degrees C using appropriate reaction protocols. gamma-RbBi(3)S(5) and alpha-RbBi(3)Se(5) have three-dimensional tunnel structures while the rest of the compounds have lamellar structures. gamma-RbBi(3)S(5), gamma-RbBi(3)Se(5), and its isostructural analogues RbBi(3)Se(4)Te and RbBi(3)Se(3)Te(2) crystallize in the orthorhombic space group Pnma with a = 11.744(2) A, b = 4.0519(5) A, c = 21.081(3) A, R1 = 2.9%, wR2 = 6.3% for (I), a = 21.956(7) A, b = 4.136(2) A, c = 12.357(4) A, R1 = 6.2%, wR2 = 13.5% for (IV), and a = 22.018(3) A, b = 4.2217(6) A, c = 12.614(2) A, R1 = 6.2%, wR2 = 10.3% for (VI). gamma-RbBi(3)S(5) has a three-dimensional tunnel structure that differs from the Se analogues. alpha-RbBi(3)Se(5) crystallizes in the monoclinic space group C2/m with a = 36.779(4) A, b = 4.1480(5) A, c = 25.363(3) A, beta = 120.403(2) degrees, R1 = 4.9%, wR2 = 9.9%. beta-RbBi(3)Se(5) and isostructural CsBi(3)Se(5) adopt the space group P2(1)/m with a = 13.537(2) A, b = 4.1431(6) A, c = 21.545(3) A, beta = 91.297(3) degrees, R1 = 4.9%, wR2 = 11.0% for (III) and a = 13.603(3) A, b = 4.1502(8) A, c = 21.639(4) A, beta = 91.435(3) degrees, R1 = 6.1%, wR2 = 13.4% for (V). alpha-RbBi(3)Se(5) is also three-dimensional, whereas beta-RbBi(3)Se(5) and CsBi(3)Se(5) have stepped layers with alkali metal ions found disordered in several trigonal prismatic sites between the layers. In gamma-RbBi(3)Se(5) and RbBi(3)Se(4)Te, the layers consist of Bi(2)Te(3)-type fragments, which are connected in a stepwise manner. In the mixed Se/Te analogue, the Te occupies the chalcogen sites that are on the "surface" of the layers. All compounds are narrow band-gap semiconductors with optical band gaps ranging 0.4-1.0 eV. The thermal stability of all phases was studied, and it was determined that gamma-RbBi(3)Se(5) is more stable than the and alpha- and beta-forms. Electronic band calculations at the density functional theory (DFT) level performed on alpha-, beta-, and gamma-RbBi(3)Se(5) support the presence of indirect band gaps and were used to assess their relative thermodynamic stability. PMID:14599213

Iordanidis, Lykourgos; Bilc, Daniel; Mahanti, Subhendra D; Kanatzidis, Mercouri G

2003-11-12

2

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

Microsoft Academic Search

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

Pramod Kumar Yadawa

2011-01-01

3

Synthesis, structural characterization and optical properties of new compounds: Centrosymmetric Ba2GaMQ5 (M=Sb,Bi; Q=Se,Te), Ba2InSbTe5 and noncentrosymmetric Ba2InSbSe5  

NASA Astrophysics Data System (ADS)

The six compounds Ba2GaMQ5 (M=Sb,Bi; Q=Se,Te) and Ba2InSbQ5 (Q=Se,Te) have been synthesized for the first time. Ba2GaMQ5 (M=Sb,Bi; Q=Se,Te) and Ba2InSbTe5 crystallize in the centrosymmetric space group Pnma, while Ba2InSbSe5 belongs to the noncentrosymmetric polar space group Cmc21. The structures of the six new compounds contain infinite [MM]4-?1 anionic chains built by MQ4 (M'=Ga,In) tetrahedra and heavily distorted M'Q6 (M'=Sb,Bi) octahedra. Ba2InSbSe5 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.

Hao, Wenyu; Mei, Dajiang; Yin, Wenlong; Feng, Kai; Yao, Jiyong; Wu, Yicheng

2013-02-01

4

Pressure-induced reversible amorphization in superconducting compound FeSe0.5Te0.5  

Microsoft Academic Search

We report pressure-induced amorphization phenomenon in a superconducting compound FeSe0.5Te0.5 to a pressure of 27 GPa in a diamond anvil cell. The synchrotron x-ray diffraction studies reveal that the ambient pressure tetragonal phase (space group P4\\/nmm) transforms to an amorphous phase at 11.5 GPa during compression and reverts back to the tetragonal phase during decompression at 2.8 GPa. The measured

Andrew K. Stemshorn; Yogesh K. Vohra; Phillip M. Wu; F. C. Hsu; Y. L. Huang; M. K. Wu; K. W. Yeh

2009-01-01

5

Optimum dopant content of n-type 95% Bi 2Te 3 + 5% Bi 2Se 3 compounds fabricated by gas atomization and extrusion process  

Microsoft Academic Search

The n-type (Bi2Te3–Bi2Se3) compound was newly fabricated by gas atomization and hot extrusion, which is considered to be a mass production technique of this alloy. The aim of this research is to analyze the effect of the amount of dopant on the thermoelectric properties for n-type 95% Bi2Te3+5% Bi2Se3 compounds. The microstructure of extruded bar shows homogeneous and fine distribution

Soon-Jik Hong; Yun-Seock Lee; Jai-Won Byeon; Byong-Sun Chun

2006-01-01

6

Determination of the thermodynamic properties of compounds in the Ag-Au-Se and Ag-Au-Te systems by the EMF method  

NASA Astrophysics Data System (ADS)

The standard thermodynamic properties (?f G°, S°, ?f H°) of the following synthetic minerals and compounds in the Ag-Au-Se and Ag-Au-Te systems were determined by the EMF method: ?-Ag2Se (low-temperature naumannite), ?-Ag2Se (high-temperature naumannite), Ag3AuSe2 (fischesserite), AuSe, Ag5Te3 (stützite), Ag2 Te (hessite), and Ag3AuTe2 (petzite). All minerals and compounds were produced by solid-phase synthesis from elements or electrum of the given composition in evacuated ampoules made of quartz glass. The phases were verified by X-ray diffraction analysis, microscopically in reflected light, and with an electron microprobe. The absence of the ternary compound AgAuSe in the Ag-Au-Se system was confirmed by solid-phase annealing. On the basis of experimental data on the electromotive force E versus temperature, the equations E( T) were calculated, from which the temperature-dependent relationships of the Gibbs energy in the relevant reactions and the standard thermodynamic functions of compounds within the range 300-502 K were obtained.

Echmaeva, E. A.; Osadchii, E. G.

2009-06-01

7

The system SnTe-InSe  

SciTech Connect

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.

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

1986-03-01

8

Structural and optical properties of electron-beam-evaporated ZnSe 1- x Te x Ternary compounds with various Te contents  

NASA Astrophysics Data System (ADS)

ZnSe1- x Te x films with different tellurium (Te) contents were deposited by using an electron beam (EB) evaporation technique onto glass substrates for applications to optoelectronic devices. The structural and the optical properties of the ZnSe1- x Te x films were studied in the present work. The host material ZnSe1- x Te x , were prepared by using the physical vapor deposition method of the electron beam evaporation technique (PVD: EBE) under a pressure of 1 × 10-5 mbar. The X-ray diffractogram indicated that these alloy films had cubic structure with a strong preferential orientation of the crystallites along the (1 1 1) direction. The optical properties showed that the band gap (E g ) values varied from 2.73 to 2.41 eV as the tellurium content varied from 0.2 to 0.8. Thus the material properties can be altered and excellently controlled by controlling the system composition x.

Suthagar, J.; Suthan Kissinger, N. J.; Sharli Nath, G. M.; Perumal, K.

2014-01-01

9

Pressure-induced reversible amorphization in superconducting compound FeSe[subscript 0.5]Te[subscript 0.5  

Microsoft Academic Search

We report pressure-induced amorphization phenomenon in a superconducting compound FeSe0.5Te0.5 toa pressure of 27 GPa in a diamond anvil cell. The synchrotron x-ray diffraction studies reveal that the ambient pressure tetragonal phase (space group P4\\/nmm) transforms to an amorphous phase at 11.5 GPa during compression and reverts back to the tetragonal phase during decompression at 2.8 GPa. The measured equation

Andrew K. Stemshorn; Yogesh K. Vohra; Phillip M. Wu; F. C. Hsu; Y. L. Huang; M. K. Wu; K. W. Yeh

2009-01-01

10

Pressure-induced reversible amorphization in superconducting compound FeSe[subscript 0.5]Te[subscript 0.5  

SciTech Connect

We report pressure-induced amorphization phenomenon in a superconducting compound FeSe0.5Te0.5 toa pressure of 27 GPa in a diamond anvil cell. The synchrotron x-ray diffraction studies reveal that the ambient pressure tetragonal phase (space group P4/nmm) transforms to an amorphous phase at 11.5 GPa during compression and reverts back to the tetragonal phase during decompression at 2.8 GPa. The measured equation of state for the tetragonal phase and the amorphous phase is presented. The disordering of Fe(SeTe)4 tetrahedra under compression is attributed to a kinetic hindrance to a stable phase and is likely to impact its superconducting properties under high pressures.

Stemshorn, Andrew K.; Vohra, Yogesh K.; Wu, Phillip M.; Hsu, F.C.; Huang, Y.L.; Wu, M.K.; Yeh, K.W.; (IP-Taiwan); (UAB); (Duke)

2009-06-01

11

Itinerant electron magnetism in the Mo4 tetrahedral cluster compounds GaMo4S8, GaMo4Se8, and GaMo4Se4Te4  

NASA Astrophysics Data System (ADS)

The specific heat and magnetic properties of GaMo4X8 (X=S, Se, SeTe) between 1.4 and 290 K are reported. Our measurements tend to demonstrate that these compounds have a very high density of states, leading to a Stoner magnetic instability of conduction electrons at low temperatures. The linear temperature-dependent term in the specific heat is enhanced by electron-phonon coupling and spin fluctuation effects. These compounds could indicate an electron-phonon contribution to the Stoner enhancement factor.

Rastogi, A. K.; Berton, A.; Chaussy, J.; Tournier, R.; Potel, M.; Chevrel, R.; Sergent, M.

1983-09-01

12

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)

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.

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

2013-04-01

13

Reverse Monte Carlo simulation of SeTe and SeTeSb glasses  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

14

The Atomic Order of the Pnictogen and Chalcogen Atoms in Equiatomic Ternary Compounds TPnCh ( T=Ni, Pd; Pn=P, As, Sb; Ch= S, Se, Te)  

NASA Astrophysics Data System (ADS)

The crystal structures of the compounds NiAsS, NiSbS, PdAsS, PdAsSe, PdSbSe, and PdSbTe were refined from single-crystal X-ray diffractometer data. In these cubic compounds the pnictogen and chalcogen atoms show an ordered distribution corresponding to the ullmannite (NiSbS) type structure (space group P2 13, Z=4). By analogy this can be assumed for NiPS and NiAsSe, although for these compounds the structure refinements did not make it possible to distinguish between a disordered distribution of the pnictogen and chalcogen atoms (corresponding to the pyrite structure) or an ordered distribution (corresponding to ullmannite or cobaltite). All atomic positions are fully occupied within the error limits of ±2%. A refinement from X-ray powder data established the ullmannite structure also for NiSbSe. The PdPS type structure of PdPSe was refined from single-crystal data. No equiatomic ternary compounds were observed in the ternary systems Ni-P-Se, Ni-P-Te, Ni-As-Te, Ni-Sb-Te, Pd-P-Te, and Pd-As-Te. A refinement from single-crystal data showed Ni 0.766(5)Sb 0.50(3)Te 0.50(3) to crystallize with a defect-NiAs type structure. Extended solid solutions were observed for the pseudobinary system NiP 2-NiSe 2, where a slowly cooled equiatomic sample contained NiP 1.86(4)Se 0.14(4) and NiP 0.24(4)Se 1.76(4) as limiting compositions, as shown by structure refinements from X-ray powder data. Chemical bonding in these compounds is briefly discussed.

Foecker, Aloys J.; Jeitschko, Wolfgang

2001-11-01

15

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

NASA Astrophysics Data System (ADS)

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.

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

2012-03-01

16

Three-dimensional topological insulators BiTe, BiSe, and BiTeSe - a microwave spectroscopy study  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

17

Crystallization behavior in Se90Te10 and Se80Te20 thin films  

NASA Astrophysics Data System (ADS)

Isothermal crystal growth kinetics in Se90Te10 and Se80Te20 thin films was studied by microscopy and in situ X-ray diffraction (XRD) measurements. The spherulite-like crystals grew linearly with time. In a narrow temperature range of between 65 and 85 °C, crystal growth rates exhibit simple exponential behavior with activation energies EG = 193 ± 4 kJ mol-1 for Se90Te10 and EG = 195 ± 4 kJ mol-1 for Se80Te20. The crystal growth in both compositions is controlled by liquid-crystal interface kinetics and can be described by a screw dislocation growth model. From the XRD data, the crystallization fraction was estimated. The crystallization data were described by Johnson-Mehl-Avrami (JMA) model with Avrami exponents m = 1.4 ± 0.3 for Se90Te10 and m = 1.6 ± 0.4 for Se80Te20. Activation energies were estimated from the temperature dependence of rate constant evaluated from the JMA model. The activation energies of nucleation-growth process were found to be Ec = 184 ± 21 kJ mol-1 for Se90Te10 and Ec = 179 ± 7 kJ mol-1 for Se80Te20, and are comparable with activation energies of crystal growth.

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

2014-03-01

18

Dynamic structure of liquid Se, Te and Se-Te mixtures by neutron scattering measurements  

SciTech Connect

Inelastic neutron scattering measurements are performed to investigate the dynamic structure of liquid Se, Te, and Te50Se50. The bond-stretching modes for liquid Se and Te50Se50 (both are in the semiconducting phase) are clearly observed at higher-energy regions than that for their trigonal phase. This shift is a reflection of their pronounced molecular-like properties without prominent inter-molecular interactions, whereas the vibrational modes for liquid Te (in the metallic phase) show its metallic-like bonding character with remarkable inter-molecular interactions. We thus observed a change in dynamic structure that accompanies the semiconductor-to-metal transition; the change that would be related to the slow dynamics induced by the transition.

Chiba, Ayano; Yao, Makoto; Ohmasa, Yoshinori [Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan); Taylor, Jon; Bennington, Stephen M. [Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX (United Kingdom)

2004-04-30

19

Photoluminescence of Zn(SeTe) annealed phosphors  

NASA Astrophysics Data System (ADS)

The quenching mechanism of the self-activated (SA) and Cu-Cl photoluminescence (PL) bands and 1.05 eV PL band in Zn(SeTe) solid solutions are investigated. It is supposed that SA and Cu-Cl PL bands in ZnTe-rich Zn(SeTe) solid solutions are quenched due to the complex defects TeiClTe and Tei2ClTe, which formation decrease the VZnClTe and single ClTe concentration. This assumption is confirmed experimentally. By annealing under Zn vapour pressure the intensity of SA and Cu-Cl PL bands in ZnTe-rich Zn(SeTe) solid solutions are restored. It is supposed that 1.05 eV PL band in ZnTe is formed due to a Te excess in ZnTe and the VTe-Tei pair is proposed for this band.

Valdna, V.; Mellikov, E.; Mere, A.

1997-01-01

20

The insertion of chalcogen atoms into the In?In bond of tetrakis[bis(trimethylsilyl)methyl]diindane(4): monomeric compounds with In?S?In, In?Se?In, and In?Te?In groups  

Microsoft Academic Search

The insertion of chalcogen atoms into the indium-indium bond of tetrakis[bis(trimethylsilyl)methyl]diindane(4)(1) by the reaction of 1 with the chalcogen atom donors propylene sulphide, triethyl phosphonium selenide or telluride yields homoleptic compounds with up to now unknown R2In?S?InR2 (2), R2In?Se?InR2 (3), and R2In?Te?InR2 (4) groups. All products are monomeric, both in solution and in the solid state, as shown by the

Werner Uhl; Rene Graupner; Hans Reuter

1996-01-01

21

Fabrication and thermoelectric properties on n-type SbI{sub 3}-doped Bi{sub 2}Te{sub 2.85}Se{sub 0.15} compounds by hot extrusion  

SciTech Connect

The n-type 0.1 wt% SbI{sub 3}-doped bi{sub 2}Te{sub 2.85}Se{sub 0.15} compounds were fabricated by hot extrusion in the temperature range 300--510 C under an extrusion ratio of 20:1. The extruded compounds were highly dense. The grains were small, equiaxed ({approximately} 1.0 {micro}m), and contained many dislocations due to the dynamic recrystallization during the extrusion. The grains were also preferentially oriented through the extrusion. The bending strength and the figure of merit of the compounds, hot-extruded at 440 C, were 97 MPa and 2.62 {times} 10{sup {minus}3}/K, respectively.

Seo, J.; Lee, C. [Inha Univ., Inchon (Korea, Republic of). Dept. of Metallurgical Engineering] [Inha Univ., Inchon (Korea, Republic of). Dept. of Metallurgical Engineering; Park, K. [Chung-ju National Univ., Chungbuk (Korea, Republic of). Dept. of Materials Engineering] [Chung-ju National Univ., Chungbuk (Korea, Republic of). Dept. of Materials Engineering

1998-04-01

22

PbTe/PbSeTe Quantum dot superlattices with high thermoelectric figures of merit  

NASA Astrophysics Data System (ADS)

High-quality PbTe/PbSeTe quantum-dot superlattice (QDSL) structures have been grown by molecular beam epitaxy and investigated for high thermoelectric figures of merit ZT. Background information on the band structure and properties of PbSeTe alloyed with other binary compounds (in which the 300 K energy gap can approach zero) are presented. Various physical properties of PbTe/PbSeTe QDSL structures on film thicknesses up to approximately 100 µm have been measured. Hall coefficient, electrical resistivity, Seebeck coefficient, and x-ray data will be displayed. The measurement of the thermal conductivity on thick QDSL structures using the Peltier heat method will be discussed. This work was sponsored by the Department of the Navy, the Army Research Office, and the Defense Advanced Research Projects Agency (DARPA) under AF Contract No. F19628-95-0002. The opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the United States Air Force.

Harman, Theodore C.

2000-03-01

23

Phase equilibria and liquid phase epitaxy growth of PbSnSeTe lattice matched to PbSe  

NASA Technical Reports Server (NTRS)

The necessary phase diagram data for growing lattice-matched layers of PbSnSeTe on PbSe are presented. Solid compounds of Pb(1-x)Sn(x)Se(1-y)Te(y) lattice-matched to PbSe were grown from liquid melts consisting of (Pb/1-x/Sn/x/)(1-z)(Se/1-y/Te/y/)(z); phase equilibria data were determined together with liquidus data for values of x(liquid) from 0 to 40 percent and y(liquid) from 0 to 40 percent for temperatures between 450 and 540 C. It was found that relatively large amounts of Te must be added to the melt to achieve lattice matching because of its low segregation coefficient relative to Se. A significant lattice-pulling effect was discovered for the 5-percent Sn case, and a similar effect is expected for the 10- and 20-percent Sn cases.

Mccann, Patrick J.; Fonstad, Clifton G.; Fuchs, Jacob; Feit, Ze'ev

1987-01-01

24

Electrochemical Atomic Layer Epitaxy: Deposition of PbSe, PbTe, and PbSe/PbTe-superlattice thin films.  

NASA Astrophysics Data System (ADS)

We report the growth of PbSe, PbTe, and PbSe/PbTe-superlattice thin films using Electrochemical Atomic Layer Epitaxy. This method allows the compounds to be deposited one monolayer at a time. An advantage of this method is deposition control with atomic precision. Also, the method allows for the growth of template-based nanostructures are possible. The films were characterized via AFM, electron microprobe, x-ray scattering, and infrared absorption.

Compton, S. P.; Cox, S. M.; Happek, U.; Vaidyanathan, R.; Stickney, J. L.

2002-10-01

25

(ZnCd)S, (ZnCd)Se and Zn(SeTe) downconverting phosphors  

NASA Astrophysics Data System (ADS)

The efficiency of (ZnCd)S, (ZnCd)Se and Zn(SeTe) solid solutions, doped with copper and chlorine, as x-ray downconverting phosphors for photodetectors is investigated. It is found, that the phosphors based on the solid solutions of the group II-VI wide-bandgap compounds and prepared in oxygen-free medium, can increase the photodetectors sensitivity to x-ray radiation more than one order of magnitude and enhance the detectors photocurrent versus radiant flux characteristics linearity.

Valdna, V.; Hiie, J.; Mellikov, E.; Mere, A.

1997-01-01

26

Photoelectric properties of ZnTe-CdSe and CdSe-ZnTe thin film heterojunctions  

Microsoft Academic Search

For the first time heterojunctions (HJs) of ZnTe-CdSe were grown by deposition of ZnTe layer on glass substrate by the discrete evaporation method and CdSe layer by the quasiclosed volume method. Also for the first time the CdSe-ZnTe HJ was grown by quasiclosed volume method. Results of investigation of the photoelectric properties of these heterojunctions are presented

Lidia Ghimpu

1999-01-01

27

The local atomic structure of superconducting Fe-Se-Te  

Microsoft Academic Search

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

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

28

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

NASA Astrophysics Data System (ADS)

The isovalent substitution of Te for Se in the superconductor FeSe1-xTex increases Tc in comparison to ?-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 types of bond angles and bond lengths with Fe. Simultaneously, ab-initio calculations based on spin density function theory yielded an optimized structure with distinct z -coordinates for Se and Te, in agreement with the experiment.

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

2010-03-01

29

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

Microsoft Academic Search

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

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

2010-01-01

30

Role of Cu additive on the dielectric relaxation of Se75Te25 and Se85Te15 glassy alloys  

NASA Astrophysics Data System (ADS)

The effect of Cu additive on the dielectric relaxation of two binary Se-Te glassy systems, comparing the properties of a-Se75Te25, a-Se85Te15 and a-Se75Te15Cu10 alloys has been reported. The temperature and frequency dependence of dielectric parameters in Glassy Se75Te25, Se85Te15 and Se75Te15Cu10 alloys are studied by measuring capacitance and dissipation factor in the frequency range (1 kHz-5 MHz) and temperature range (300-350 K). A Debye like relaxation of dielectric behavior has been observed. A comprehensive study on the relaxation mechanism revealed that the presence of grains and grain boundaries across the pallet thickness is the basic relaxation process. A detailed analysis shows that the observed dielectric loss is in agreement with the Guintini's theory of dielectric dispersion based on two electron hopping over a potential barrier and is applicable in the present case. Dielectric constant (?’), dielectric loss (?”), loss tangent (?) and capacitive reactance (Xc) are found highly frequency and temperature dependent. Dependence of these dielectric parameters over the metallic impurity Cu, has also been found in the present glassy system and has been discussed in terms of electronegativity difference between the elements used in making the aforesaid glassy system.

Sharma, J.; Kumar, S.

2010-07-01

31

Resonance photoelectron spectroscopy of TiX2 (X = S, Se, Te) titanium dichalcogenides  

NASA Astrophysics Data System (ADS)

The photoelectron valence band spectra of TiS2, TiSe2, and TiTe2 dichalcogenides are investigated in the Ti 2 p-3 d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS2 and TiTe2. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS2, TiSe2, and TiTe2 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 TiS2 is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe2 is caused by occupation of the 3 d band in Ti.

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

2012-11-01

32

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

NASA Astrophysics Data System (ADS)

The formation of the MgB2 superconducting compound from a mixture of Mg and amorphous B powders with various low melting point metals (Bi, Se and Te) was studied in situ by means of high-energy (synchrotron) x-ray diffraction in wires with a composite Cu/Nb sheath. In comparison with an undoped sample, it was found that the addition of Bi results in a clear lowering of the formation temperature of MgB2, whereas Se and Te have no significant influence. Tc is slightly higher in the Bi-doped sample than in the others but the jc in this case is lower than in the pure MgB2 sample, probably due to the presence of remaining Mg3Bi2 particles that formed as an intermediate compound during reaction. Likewise, in the Se-and Te-doped samples, MgSe and MgTe respectively form below 450 °C. Whereas jc is also depressed in the Se-doped sample, the MgTe particles do not appear to affect the performance of the Te-doped wire.

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

2012-01-01

33

Improving Hardness and Thermoelectric Performance in Pseudo-ternary Thermoelectric Alloys (Bi2Te3)(Bi2Se3)(Nd2Te3)  

NASA Astrophysics Data System (ADS)

The solid solution of three elements Bi, Te and Se is known to be an appropriate n-type thermoelectric (TE) module. Although it shows high TE performance, it suffers from low hardness. Neodymium (Nd) is an appropriate element that can be introduced into the solid solution to overcome this problem. The TE and microstructural properties dependence on the amount of Nd addition in different into Bi2(Te1-xSex)3 are studied. The mechanical durability of the (Bi2Te3)(Bi2Se3)(Nd2Te3) compounds had been evaluated as a function of Nd2Te3 content (0.0-0.4% mole), the solubility limit of 0.12% mole Nd2Te3 in Bi2Te2.88Se0.12 is obtained. The samples are characterized by phase formation and hardness measurements. The optimum figure of merit of 3.06 × 10-3 K-1 at 300 K is obtained using 0.12% mole Nd2Te3, with the corresponding 2.5 kg\\cdotmm-2 of hardness. Finally, vast studies of the TE parameters of defined compound in the temperature range of 300-500 K are performed.

Kavei, G.

2006-07-01

34

Anisotropic Scattering in the (Bi, Sb)2 (Te, Se, S)3 Solid Solutions  

Microsoft Academic Search

Analysis of thermoelectric and galvanomagnetic properties is carried out for solid solutions (Bi, Sb)2(Te, Se, S)3 with various substitutions of atoms in sublattices of basic Bi 2Te3 compound. The increase in thermoelectric figure of merit Z is observed in the compositions with a weak anisotropy of charge carriers in mirror plane. In addition, relaxation time tensor component along trigonal direction

L. N. Lukyanova; V. A. Kutasov; V. V. Popov; P. P. Konstantinov; M. I. Fedorov

2006-01-01

35

Thermoelectric Properties of TlGdQ2 (Q = Se, Te) and Tl9GdTe6  

NASA Astrophysics Data System (ADS)

The ternary thallium chalcogenides TlGdQ2 (Q = Se, Te), and Tl9GdTe6 were synthesized, and their thermoelectric properties were evaluated. The chalcogenides TlGdQ2 are isostructural with TlSbQ2 (space group Rbar{3}m ), adopting the ?-NaFeO2 structure type, and Tl9GdTe6 is isostructural with Tl9BiTe6 (space group I4/ mcm). TlGdSe2 was found to be a wide-bandgap semiconductor with rather high Seebeck coefficient and low electrical conductivity. The corresponding telluride TlGdTe2 behaves like a doped semiconductor, and possesses very low thermal conductivity at room temperature on the order of 0.5 W m-1 K-1, a property advantageous for thermoelectric applications. Tl9GdTe6 exhibits relatively high room-temperature electrical conductivity of around 850 ?-1 cm-1 and a low Seebeck coefficient of 27 ?V K-1, yielding a low power factor. Of these three compounds, TlGdTe2 exhibits the best thermoelectric properties, with maximum dimensionless figure of merit in the measured temperature regime of 0.5 at 550 K.

Sankar, Cheriyedath Raj; Bangarigadu-Sanasy, Savitree; Kleinke, Holger

2012-06-01

36

Raman and infrared study of amorphous SeTe/CdSe superlattices  

NASA Astrophysics Data System (ADS)

Structural modifications induced by the interfaces in the amorphous sublayers of SeTe/CdSe superlattices are studied by means of Raman and infrared spectroscopy. The prevalence of polymer chain molecules in the SeTe sublayers is explained in terms of the intermolecular interactions. The relation between the root mean square bond angle deviations induced by the interfaces, spectral band width of LO phonons in CdSe, and amorphization of CdSe sublayers is studied. The increase of the distortion energy on CdSe sublayers amorphization is evaluated.

Ionov, R.; Dudev, T.

1992-08-01

37

High-pressure thermopower of PbTe-based compounds  

Microsoft Academic Search

In the present paper the thermoelectric properties of p-type PbTe-based compounds (Pb1-xGaxTe, Pb1-xSnxTe, Pb1-xSixTe, Pb1-xMnxTe, PbTe1-y, Pb1-yTe) have been investigated at high pressure up to 12 GPa. Structural phase transitions from cubic NaCl into orthorhombic GeS structure have been observed with thermoelectric measurements. A low sensitivity of thermoelectric properties to high-pressure treatment has been found for PbSnTe compounds (x 0.29).

Sergey V. Ovsyannikov; Vladimir V. Shchennikov

2004-01-01

38

The crystal structure of FeSeTe  

NASA Astrophysics Data System (ADS)

The crystal structure of the superconductor FeSeTe was redetermined by high-resolution X-ray single crystal diffraction at 173 K (anti-PbO-type, P4/nmm, a=3.7996(2), c=5.9895(6) Å, R1=0.022, wR2=0.041, 173 F2). Significantly different z-coordinates of tellurium and selenium at the 2c site are clearly discernible and were refined to z=0.2868(3) and z=0.2468(7). Thus the chalcogen heights differ by 0.24 Å and the Fe-Se bonds are by 0.154 Å shorter than the Fe-Te bonds, while three independent (Te, Se)-Fe-(Te, Se) bond angles occur. An elevated U33 displacement parameter of the iron atom is suggestive of a slightly puckered Fe layer resulting from different combinations of Se or Te neighbors. Such strong disorder underlines the robustness of superconductivity against structural randomness and has not yet been considered in theoretical studies of this system.

Tegel, M.; Löhnert, C.; Johrendt, D.

2010-03-01

39

A Quaternary ZnCdSeTe Nanotip Photodetector  

PubMed Central

The authors report the growth of needle-like high density quaternary Zn0.87Cd0.13Se0.98Te0.02nanotips on oxidized Si(100) substrate. It was found that average length and average diameter of the nanotips were 1.3 ?m and 91 nm, respectively. It was also found that the as-grown ZnCdSeTe nanotips exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. Furthermore, it was found that the operation speeds of the fabricated ZnCdSeTe nanotip photodetector were fast with turn-on and turn-off time constants both less than 2 s.

2009-01-01

40

Structural Transformation in Some Chevrel Phase Compounds: ZnMo5S6, ZnMo5Se6 and CuO.7Mo3Se4.  

National Technical Information Service (NTIS)

Low temperature x-ray powder diffraction and electrical resistivity experiments show that the Chevrel phase compounds ZnMo5S6, ZnMo5Se6 and CuO.7Mo3Se4 are structurally unstable near or below room temperature. The binary compounds Mo3S4, Mo3Se4 and Mo3Te4...

A. C. Lawson R. N. Shelton

1977-01-01

41

Electrochemical Deposition and Characterization of Thermoelectric Ternary (Bi x Sb1- x )2Te3 and Bi2(Te1- y Se y )3 Thin Films  

NASA Astrophysics Data System (ADS)

Thermoelectric thin films of the ternary compounds (Bi x Sb1- x )2Te3 and Bi2(Te1- y Se y )3 were synthesized using potentiostatic electrochemical deposition on gold-coated silicon substrates from aqueous acidic solutions at room temperature. The surface morphology, elemental composition, and crystal structure of the deposited films were studied and correlated with preparation conditions. The thermoelectric properties of (Bi x Sb1- x )2Te3 and Bi2(Te1- y Se y )3 films, i.e., Seebeck coefficient and electrical resistivity, were measured after transferring the films to a nonconductive epoxy support. (Bi x Sb1- x )2Te3 thin films showed p-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively large negative potential with composition close to Bi0.5Sb1.5Te3. In addition, Bi2(Te1- y Se y )3 thin films showed n-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively small negative potential, having composition close to Bi2Te2.7Se0.3. In contrast to Bi2Te2.7Se0.3 thin films, an annealing treatment was required for Bi0.5Sb1.5Te3 thin films to achieve the same magnitude of power factor as Bi2Te2.7Se0.3. Therefore, Bi2Te2.7Se0.3 thin films appear to be good candidates for multilayer preparation using electrochemical deposition, but the morphology of the films must be further improved.

Ma, Yi; Wijesekara, Waruna; Palmqvist, Anders E. C.

2012-06-01

42

Structural and Vibrational Study of K 2SeO 4·Te(OH) 6 Material  

NASA Astrophysics Data System (ADS)

At room temperature, the new compound K 2SeO 4·Te(OH) 6 was synthesized from water solutions of H 6TeO 6/K 2SeO 4. The potassium selenate tellurate (KTSe), Mm=480.81 g, possesses a monoclinic structure with Cc space group. The crystal and refinement cell parameters are: a=11.552(2) Å, b=6.432(1) Å, c=13.919(2) Å, ?=105.92(1), V=994.5(3) Å 3, Z=4, Dx= 3.011 g/cm 3, and F(000)=840. The residuals are R1=0.023 and W R2=0.069 for 1139 observed reflections (1108 with I>2? ( I)) refined with 152 parameters. The main interest of this structure is the presence of two different and independent anionic groups (TeO 6-6 and SeO 2-4) in the same crystal. Raman and IR spectra of K 2SeO 4·Te(OH) 6, recorded at room temperature in the frequency range 200-4000 cm -1, show that both SeO 2-4 and TeO 6-6 groups coexist in the crystal independently.

Dammak, M.; Khemakhem, H.; Mhiri, T.; Kolsi, A. W.; Daoud, A.

1999-07-01

43

Chemical reactions on the Bi 2Te 3-Bi 2Se 3 section in the process of crystal growth  

NASA Astrophysics Data System (ADS)

By methods of differential-thermal analysis and X-ray-phase analysis it is proved that the Bi 2Te 3-Bi 2Se 3 section is a system with a continuous series of solid solutions, with the formation of Bi 2Te 2Se compound below the solidus line. The formation of this compound has been confirmed both in experiment and by thermodynamic analysis (TDA). It has been found that after zone melting the temperature values of the liquidus and solidus lines correlate with those obtained for equilibrium systems and mentioned in the literature. The boundary has been identified for the existence of Bi 2Te 3- xSe x solid solutions, which lies at ˜14 mol% Bi 2Se 3 (Bi 2Te 2.58Se 0.42). TDA shows chemical interactions (reactions) resulting in the formation of Bi 2Te 2Se. It has been found that in the two-phase zone, the Seebeck coefficient values dramatically change in a jumping manner, with the points of extremum located on the boundaries of the two-phase zone. In the zone of Bi 2Te 2Se compound occurrence (33.3 mol% Bi 2Se 3), the values of the Seebeck coefficient and power factor are minimal.

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

2004-02-01

44

Electrical Conductivity of Liquid In2Te3, Tl2Te, Tl2Se and Ag2Te at High Temperatures and Pressures  

Microsoft Academic Search

Electrical conductivity sigma of liquid semiconductors In2Te3, Tl2Te, Tl2Se and Ag2Te is measured up to 1500°C and up to 1000 bar. With increasing temperature, sigma for liquid In2Te3 rapidly increases near the melting point and its temperature derivative becomes extremely small above 1100°C, while the temperature derivatives for liquid Tl2Te, Tl2Se and Ag2Te are weakly temperature dependent. This difference is

Kazuhiko Tsuji; Makoto Yao; Katsuhiko Ishida; Hirohisa Endo

1978-01-01

45

Differential genotoxicity of diphenyl diselenide (PhSe)2 and diphenyl ditelluride (PhTe)2.  

PubMed

Organoselenium compounds have been pointed out as therapeutic agents. In contrast, the potential therapeutic aspects of tellurides have not yet been demonstrated. The present study evaluated the comparative toxicological effects of diphenyl diselenide (PhSe)2 and diphenyl ditelluride (PhTe)2 in mice after in vivo administration. Genotoxicity (as determined by comet assay) and mutagenicicity were used as end-points of toxicity. Subcutaneous administration of high doses of (PhSe)2 or (PhTe)2 (500 µmol/kg) caused distinct genotoxicity in mice. (PhSe)2 significantly decreased the DNA damage index after 48 and 96 h of its injection (p < 0.05). In contrast, (PhTe) caused a significant increase in DNA damage (p < 0.05) after 48 and 96 h of intoxication. (PhSe)2 did not cause mutagenicity but (PhTe)2 increased the micronuclei frequency, indicating its mutagenic potential. The present study demonstrated that acute in vivo exposure to ditelluride caused genotoxicity in mice, which may be associated with pro-oxidant effects of diphenyl ditelluride. In addition, the use of this compound and possibly other related tellurides must be carefully controlled. PMID:24711962

Meinerz, Daiane Francine; Allebrandt, Josiane; Mariano, Douglas O C; Waczuk, Emily P; Soares, Felix Antunes; Hassan, Waseem; Rocha, João Batista T

2014-01-01

46

Raman spectra of ZnSe-ZnTe strained-layer superlattice  

NASA Astrophysics Data System (ADS)

Various experimental and theoretical studies have been carried out on the phonon modes of III-V compounds semiconductor superlattices and II-VI SLS. Olego et al. have reported the confined LO modes in the ZnSe layer of the Zn-SeSxSe1-x SLS with resonant Raman scattering at low temperatures. Menendez et al. obtained the confined LOm modes in the CdTe-ZnTe SLS with the near resonance Raman scattering at 10 K. We report, for the first time, the confined LOm modes of the ZnSe-ZnTe SLS. The measurements were performed at room temperatures and under off-resonance conditions. There are a lot of studies on the strain in the SLS. Raman scattering provides a powerful techniques for the study of crystalline quality and especially strain fields of SLSs. By measuring phonon frequencies and their shifts, we can determine the strength of the strains in superlattice layers. In this paper, we report the strain effect on the phonon modes and the critical thickness of individual layers in ZnSe-ZnTe SLSs.

Cui, Jie; Wang, Hai L.; Gan, Fuxi

1991-11-01

47

Stepwise optical absorption in amorphous SeTe/CdSe superlattices  

NASA Astrophysics Data System (ADS)

Optical absorption and photoconductivity of new chalcogenide amorphous SeTe/CdSe superlattices of pnpn type are investigated. The optical absorption coefficient ? changes stepwise with the variation of the intensity and duration of the illumination. The analysis of the experimental results indicates the formation of subbands in the conduction and valence band. The essential role of the indirect transitions at sublayer thickness below 100 Å is discussed.

Ionov, Radoslav; Nesheva, Diana

48

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

49

Electronic structure of titanium dichalcogenides TiX2 (X = S, Se, Te)  

NASA Astrophysics Data System (ADS)

The electronic structure and the chemical bond in titanium dichalcogenides TiX2 (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 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 2, 3 absorption spectra of titanium are performed. It is shown that, in the row TiS2-TiSe2-TiTe2, the covalence increases, the ionicity of the chemical bond decreases, and the effect of the crystal field of a ligand is weakened.

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

2012-01-01

50

Synthesis of near-infrared-emitting CdTeSe and CdZnTeSe quantum dots.  

PubMed

We exploited the synthesis of near-infrared (NIR) emitting ternary-alloyed CdTeSe and quaternary-alloyed CdZnTeSe quantum dots (QDs) with rod and tetrapod morphologies, which have tunable emission in the NIR electromagnetic spectrum. The morphologies of the QDs depended strongly on their growth kinetics, probably due to the coordinating ligands used in the preparation. Using oleic acid, stearic acid and hexadecylamine as ligands and keeping the same reaction parameters, QDs with tetrapod and rod morphologies were created. Not only had the capping ligands influenced the morphologies of QDs, but also they influenced the optical properties of QDs. The molar ratios of Cd/Zn and Te/Se upon preparation were adjusted for investigating the effect of composition on the properties of resulting QDs. By varying the composition of QDs, the photoluminescence (PL) wavelength of QDs was tuned from 650 nm to 800 nm. To enhance PL efficiency and stability, QDs were coated with a CdZnS shell. As NIR PL has numerous advantages in biological imaging detection, these QDs hold great potential for application. PMID:23060275

Yang, Fanghong; Yang, Ping; Zhang, Lipeng

2013-01-01

51

Semiconductive devices utilizing MgTe, MgSe, ZnSe, ZnTe and alloys thereof  

US Patent & Trademark Office Database

An injection laser for operation in the yellow to violet portion of optical spectrum utilizes an indium phosphide substrate on which are lattice matched three successive layers each of the form (MgSe).sub.x (ZnSeTe).sub.1-x, where x has a positive value for each layer up to 1 in the first and third layers but in the second layer has a value less than that of either the first or third layer and the first and third layers are doped to be of opposite conductivity type.

1995-01-03

52

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

SciTech Connect

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.

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

53

Metastable photoenhanced thermal generation in a-SeTe alloys  

NASA Astrophysics Data System (ADS)

The mechanism of isothermal bulk carrier generation in the dark and the sensitizing effects of prior penetrating illumination and thermal history have been investigated in a composition series of a-Se:Te alloy films using xerographic techniques. In all cases, thermal generation is characterized by the simultaneous production of free holes and deeply trapped negative space charge. Results suggest that dark carrier generation is controlled by deep native (thermodynamic) defect centers whose population at a given temperature below Tg can be temporarily altered by photo and/or thermal excitation.

Abkowitz, M.; Foley, G. M. T.; Markovics, J. M.; Palumbo, A. C.

1984-10-01

54

Progress Towards a Micromachined Thermoelectric Generator using PbTe and PbSnSeTe Thin Films.  

National Technical Information Service (NTIS)

This paper presents etching techniques and metal contact resistance studies for vapor-deposited PbTe and PbSnSeTe films to enable micromachining of thermoelectric (TE) generators within integrated MEMS devices (e.g. micro heat engines, microcombustors). F...

C. D. Meyer D. P. Arnold I. Boniche N. K. Dhar P. J. Taylor

2006-01-01

55

Strength and fractographic analysis of chalcogenide As–S–Se and Ge–As–Se–Te glass fibers  

Microsoft Academic Search

The strengths and Weibull parameters of chalcogenide As–S–Se and Ge–As–Se–Te glass fibers were measured, and the fiber fracture surfaces examined. The sulfide (As–S–Se) fibers have a mean strength of 545 MPa, characteristic strength of 567 MPa, and Weibull slope, m, of 8.5. The weaker telluride (Ge–As–Se–Te) fibers have a mean strength of 427 MPa, characteristic strength of 441 MPa, and

J. B Quinn; V. Q Nguyen; J. S Sanghera; I. K Lloyd; P. C Pureza; R. E Miklos; I. D Aggarwal

2003-01-01

56

Electrochemical synthesis of photosensitive nano-nest like CdSe0.6Te0.4 thin films  

NASA Astrophysics Data System (ADS)

Polycrystalline CdSe0.6Te0.4 thin films were deposited on stainless steel and ITO coated glass (ITO) substrates by using simple and inexpensive electrodeposition method. CdSe0.6 Te0.4 films are characterized by different characterization techniques such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR) and contact angle measurement. The X-ray diffraction analysis shows that the films are polycrystalline with hexagonal crystal structure. FE-SEM studies reveal that the entire substrate surface is covered with CdSe0.6 Te0.4 nano-nest. Formation of CdSe0.6Te0.4 compound was confirmed from the FTIR studies. Optical absorption study shows the presence of direct transition and a considerable band gap, Eg = 1.7 eV. Surface wettability with solid-liquid interface showed hydrophilic nature with water contact angle 57° (<90°). Further photovoltaic activity of CdSe0.6Te0.4 films were studied by forming the photoelectrochemical cell having CdSe0.6Te0.4/1 M (Na2S + S + NaOH)/C cell configuration. The efficiency and fill factor of these PEC cells are found to be 0.64% and 0.49 respectively.

Shinde, Surendra K.; Thombare, Jagannath V.; Dubal, Deepak P.; Fulari, Vijay J.

2013-10-01

57

Electronic band structures and physical properties of ALnTe 4 and ALn3Te 8 compounds ( A=alkali metal; Ln=lanthanoid)  

NASA Astrophysics Data System (ADS)

We report about the LMTO-ASA band structure, ELF and COHP calculations for a number of alkali metal rare earth tellurides of the formulas ALnTe 4 ( A=K, Rb, Cs and Ln=Pr, Nd, Gd) and K Ln3Te 8 ( Ln=Pr, Nd) to point out structure-properties relations. The ALnTe 4 compounds crystallize in the KCeSe 4 structure type with Te ions arranged in the form of 4.3 2.4.3 nets, in which interatomic homonuclear distances indicate an arrangement of isolated dumbbells. This could be verified by the COHP and ELF calculations, both of which revealed isolated [Te 2] units. But in contrast to the ionic formulation as A+Ln3+ ([Te 2] 2-) 2, which can be deduced from this observation, the band structure calculations for KPrTe 4, KNdTe 4, RbNdTe 4 and CsNdTe 4 reveal metallic conductivity. This behavior was verified for KNdTe 4 by resistivity measurements performed by a standard four-probe technique. We explain these results by an incomplete carryover of electrons from the rare earth cation onto tellurium due to covalent bonding leaving parts of the Te-Te pp?* antibonding states unoccupied. On the other hand the calculations suggest insulating behavior for KGdTe 4 resulting from a complete filling of the Te-Te pp?* antibonding states due to the increased stability of the half filled 4 f shell. The ALn3Te 8 compounds crystallize in the KNd 3Te 8 structure type, a distorted addition-defect variant of the NdTe 3 type with 4 4 Te nets. As polyanionic fragments L-shaped [Te 3] 2- and infinite zig-zag chains ?1[Te 4] 4- are observed (with interatomic homonuclear distances in the range 2.82-3.00 Å), which are separated from each other by distances in the range 3.27-3.49 Å. Again COHP calculations made evident that these latter interactions are secondary. Within the infinite zig-zag chains ?1[Te 4] 4- the Te ions at the corners of the chain have a higher negative charge than the linear coordinated ones in the middle. KPr 3Te 8 and KNd 3Te 8 are semiconductors, verified for the latter by resistivity measurements.

Stöwe, Klaus

2003-12-01

58

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

SciTech Connect

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

Shamsuddin, M.; Nasar, A. [Banaras Hindu Univ., Varanasi (India)

1995-06-01

59

Morphological defects of molecular beam epitaxy-grown CdTe and CdSeTe on Si  

Microsoft Academic Search

For the first time, focused ion beam milling, secondary electron microscopy, and transmission electron microscopy were used\\u000a to examine in depth morphological defects during epitaxial growth of CdTe and CdSeTe on Si. Contrary to the literature regarding\\u000a the formation of morphological defects at the epi\\/substrate interface, the present defects appear to originate from either\\u000a the CdTe\\/CdSeTe interface or 3–4 m

Eva M. Campo; Thomas Hierl; James C. M. Hwang; Yuanping Chen; Gregory Brill

2005-01-01

60

ZnCdTe/ZnTe/ZnMgSeTe quantum-well structures for the application to pure-green light-emitting devices  

NASA Astrophysics Data System (ADS)

A ZnCdTe/ZnTe/ZnMgSeTe quantum-well (QW) structure lattice matched to ZnTe is proposed for the light-emitting devices in the pure-green wavelength region. Thin ZnTe layers are inserted in between the ZnCdTe QW layer and ZnMgSeTe cladding layers, which improve the quality of the QW structure as demonstrated by its narrow photoluminescence line width (6.5 meV at 10 K). Optically pumped lasing at 552 nm at room temperature with a threshold optical power of 215 kW cm-2 is achieved. The present results clearly show the feasibility of ZnTe-based QW structures for the application to light-emitting devices in the pure-green wavelength region.

Chang, J. H.; Song, J. S.; Godo, K.; Yao, T.; Shen, M. Y.; Goto, T.

2001-01-01

61

Thermoelectric properties and crystal structure of ternary compounds in the Ge(Sn,Pb)Te–Bi 2Te 3 systems  

Microsoft Academic Search

Polycrystalline samples of stoichiometric ternary compounds in the quasi-binary systems GeTe–Bi2Te3, SnTe–Bi2Te3 and PbTe–Bi2Te3 have been prepared and characterised by X-ray powder diffraction analysis. Lattice parameters have been determined and compared with literature data. At room temperature all the samples exhibit a high carrier concentration in the range 3.4×1019–2.6×1020cm?3. All AIVBi4Te7 and PbBi2Te4 compounds possess negative type of conductivity, while

L. A. Kuznetsova; V. L. Kuznetsov; D. M. Rowe

2000-01-01

62

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

PubMed

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

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

2011-12-14

63

Preliminary studies in the electrodeposition of PbSe/PbTe superlattice thin films via electrochemical atomic layer deposition (ALD).  

PubMed

This paper concerns the electrochemical growth of compound semiconductor thin film superlattice structures using electrochemical atomic layer deposition (ALD). Electrochemical ALD is the electrochemical analogue of atomic layer epitaxy (ALE) and ALD, methods based on nanofilm formation an atomic layer at a time, using surface-limited reactions. Underpotential deposition (UPD) is a type of electrochemical surfaced-limited reaction used in the present studies for the formation of PbSe/PbTe superlattices via electrochemical ALD. PbSe/PbTe thin-film superlattices with modulation wavelengths (periods) of 4.2 and 7.0 nm are reported here. These films were characterized using electron probe microanalysis, X- ray diffraction, atomic force microscopy (AFM), and infrared reflection absorption measurements. The 4.2 nm period superlattice was grown after deposition of 10 PbSe cycles, as a prelayer, resulting in an overall composition of PbSe0.52Te0.48. The 7.0 nm period superlattice was grown after deposition of 100 PbTe cycle prelayer, resulting for an overall composition of PbSe0.44Te0.56. The primary Bragg diffraction peak position, 2theta, for the 4.2 superlattice was consistent with the average (111) angles for PbSe and PbTe. First-order satellite peaks, as well as a second, were observed, indicating a high-quality superlattice film. For the 7.0 nm superlattice, Bragg peaks for both the (200) and (111) planes of the PbSe/PbTe superlattice were observed, with satellite peaks shifted 1 degrees closer to the (111), consistent with the larger period of the superlattice. AFM suggested conformal superlattice growth on the Au on glass substrate. Band gaps for the 4.2 and 7.0 nm period superlattices were measured as 0.48 and 0.38 eV, respectively. PMID:17129034

Vaidyanathan, Raman; Cox, Steven M; Happek, Uwe; Banga, Dhego; Mathe, Mkhulu K; Stickney, John L

2006-12-01

64

Structure of Melt Quenched Chalcogen rich CuInSeTe  

NASA Astrophysics Data System (ADS)

Melt quenched CuIn(SexTe1-x)2, where x = 0.1 and 0.9, have been analyzed using X-ray diffraction (XRD) and Raman spectroscopy. Rietveld refinements of XRD data revealed that CuIn(Se0.1Te0.9)2 has formed as a single phase whereas CuIn(Se0.9Te0.1)2 has exhibited two phases, CuIn(Se0.87Te0.13)2 and CuIn(Se0.95Te0.05)2, with phase fraction of 67 and 33% respectively. Raman spectra of CuIn(Se0.1Te0.9)2 showed a well defined high intensity peak at 130 cm-1 while CuIn(Se0.9Te0.1)2 exhibited a high intensity peak at 165.6 cm-1 and an adjacent peak at 174.2 cm-1. The peaks observed at 130, 165.5 and 174.2 cm-1 were attributed to the characteristic A1 mode of the phases with Se percentage 10, 87 and 95 respectively. The XRD and Raman results showed that substitution of 10% of selenium in CuInTe2 yields single phase while 10% substitution of Te in CuInSe2 yields two phases.

Rangasami, C.; Jain, Mahaveer K.; Kasiviswanathan, S.

2011-07-01

65

Neutron diffraction study of liquid (Tl1/(2)Pb1/(2)-X (X: Te, Se) systems  

NASA Astrophysics Data System (ADS)

Neutron diffraction measurements have been carried out on liquid (Tl 1/2 Pb 1/2) 1- y X y (X:Te,Se) systems which exhibit a typical compound-forming behaviour at y=3/7. Radial distribution analysis at y=3/7 has indicated that the bonding nature of Tl sbnd X and Pb sbnd X is more or less ionic, as expected from the previous result of electronic properties. In order to investigate the difference in electronic behaviour between these two liquid systems in the chalcogen rich region, we derive the X-X partial distribution function gX-X( r, assuming that each partial function at y>3/7 is independent of the alloy composition. gSe-Se( r) has a well-resolved first peak at r ? 0.230 nm, suggesting that covalent Se sbnd Se bonds appear in the Se rich region. On the other hand, gTe-Te( r) is somewhat structureless, although the first peak is included in the covalent region. The whole functional form of both gX-X( r) is roughly similar to that of g ( r) in pure liquid Te or Se.

Usuki, T.; Uemura, O.; Itoh, K.; Kameda, Y.

1995-02-01

66

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

SciTech Connect

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.

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

67

Electrical Anisotropy of Layered Compound ZrSe2 and HfSe2  

NASA Astrophysics Data System (ADS)

The electrical resistivity and the Hall coefficient of the layered compound ZrSe2 and HfSe2 grown by iodine vapour transport method have been measured. High anisotropy in electrical resistivities has been found for these compounds. The Hall mobility exhibits a temperature dependence of the form ?{\\propto}T-1.6 in ZrSe2 as well as in HfSe2. It is well explained in terms of homo-polar-mode optical scattering.

Zheng, Xu-guang; Kuriyaki, Hisao; Hirakawa, Kazuyoshi

1989-02-01

68

Effect of photoelectrode crystal structure on output stability of Cd(Se,Te)\\/polysulfide photoelectrochemical cells  

Microsoft Academic Search

Thin-film polycrystalline Cd(Se,Te) alloy photoelectrodes, which show output stability comparable to CdSe photoelectrodes when possessing the hexagonal (wurtzite) structure and which have optical band gaps similar to that of pure CdTe, are discussed.

Gary Hodes; Joost Manassen; David Cahen

1980-01-01

69

Modeling study for developing CdZnTe(CdSe)/CIGS tandem solar cells  

NASA Astrophysics Data System (ADS)

Based on Crosslight APSYS, single junction ZnTe/CdSe, CdZnTe/CdSe and CIGS/CdS solar cells as well as CdZnTe(CdSe)/CIGS tandem cells are modeled. Basic physical quantities like band diagrams, optical absorption and generation are obtained. Quantum efficiency and I-V curves are presented. The results are discussed with respect to the interface recombination velocity and the related material defect trap states for ZnTe/CdSe single junction solar cells and the top TCO layer affinity for tandem cells. The projected efficiency obtained is 28% for one of the modeled twoterminal tandem cells. The modeling results give possible clues for developing CdZnTe(CdSe)/CIGS tandem solar cells with increased efficiency.

Xiao, Y. G.; Li, Z. Q.; Lestrade, M.; Li, Z. M. S.

2010-08-01

70

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

71

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

72

MBE growth of ZnTe and HgCdSe on Si: a new IR material  

NASA Astrophysics Data System (ADS)

Growth of ZnTe and HgCdSe on Si has been pursued using molecular beam epitaxy (MBE) as a new class of IR materials. Besides, ZnTe/Si can also be used as a lattice-matching, large area and low cost alternate substrate for other III-V and II-VI compound semiconductors, such as GaSb based type-II superlattice materials around 6.1A. We report in this paper our systematic studies on MBE growth conditions for ZnTe(211) on Si and highlights of MBE growth of HgCdSe on ZnTe/Si. A close to optimal growth window has been established for MBE growth of ZnTe(211)/Si(211) to achieve high crystalline quality, low defect and dislocation densities as well as excellent surface morphology. Using this baseline MBE growth process, we are able to obtain ZnTe(211)/Si wafers with X-ray full-width at half-maximum (FWHM) as low as 70 arcsec, low dislocation density (~105 cm-2) and defect density (1000 cm-2).

Chen, Yuanping; Brill, Gregory; Benson, David; Wijewarnasuriya, Priyalal; Dhar, Nibir

2011-09-01

73

First-principles study of layered antiferromagnetic CuCrX2 (X = S, Se and Te)  

NASA Astrophysics Data System (ADS)

We present detailed electronic band-structure calculations for antiferromagnetic chromium compounds, CuCrX2 (X = S, Se or Te), carried out using spin-polarized density functional theory within the generalized-gradient approximation (GGA). A narrow-band semiconductor-to-metal transition is observed upon replacement of S or Se by Te. The indirect bandgap is found at 0.58 eV and 0.157 eV for CuCrS2 and CuCrSe2, respectively. The results for our theoretical calculations are well in line with the electronic transport properties experimentally observed for CuCrS2 and CuCrSe2.

Srivastava, Divya; Tewari, Girish C.; Karppinen, Maarit; Nieminen, R. M.

2013-03-01

74

Solution-liquid-solid (SLS) growth of ZnSe-ZnTe quantum wires having axial heterojunctions.  

PubMed

Heterostructured ZnSe-ZnTe quantum wires are grown by the solution-liquid-solid (SLS) mechanism. The nature of the axial or radial heterostructure obtained is strongly influenced by the growth sequence and related synthetic conditions. Compositionally graded ZnSe(x)Te(1-x) wires, ZnSe-ZnTe axial heterostructures containing a ZnSe(x)Te(1-x) transitional segment, ZnSe-ZnTe wires with sharp axial heterojunctions, and radial core-shell ZnSe-ZnTe quantum wires have been selectively prepared. The axial and radial quantum-wire heterostructures are characterized microscopically and spectroscopically. PMID:17388642

Dong, Angang; Wang, Fudong; Daulton, Tyrone L; Buhro, William E

2007-05-01

75

Preparation and thermoelectric properties of Bi2Te3-Bi2Se3 solid solutions  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

76

Transmission Electron Microscopy Study on the Crystallization of Sb-Se-Te Ternary Alloys  

NASA Astrophysics Data System (ADS)

The microstructure of Sb-Se-Te ternary alloy thin films annealed at 220, 230, and 300 °C by rapid thermal annealing (RTA) was investigated using high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) analysis. Compared to the Tm of Ge2Sb2Te5 (˜616 °C), the lower Tm of the Sb-Se-Te (417 °C) thin film can contribute toward reducing power consumption for the reset process of phase change materials. The horizontal long grains — grown along the interface in a fully crystallized Sb-Se-Te thin film sample and annealed at 300 °C for 10 min — were hexagonal structured Sb2SeTe2 with 15 layers; the c-axis was perpendicular to the substrate.

Yoon, Jong Moon; Kim, Eun Tae; Lee, Jeong Yong; Kim, Yong Tae

2009-10-01

77

Electronic structures and local atomic configurations in amorphous GeSe and GeTe  

NASA Astrophysics Data System (ADS)

The valence- and conduction-band electronic densities of states (DOSs) in amorphous (a-) GeSe and GeTe were investigated by means of ultraviolet photoemission and inverse-photoemission spectroscopy (UPS and IPES), respectively. The UPS spectra for both a-GeSe and a-GeTe are very similar to those obtained in previous experiments; a distinct peak appears near the top of the valence band. The IPES spectra for both a-GeSe and a-GeTe corrected by subtracting the background exclude the possibility of a structure with 3(Ge):3(chalcogen) coordination if one compares them with the theoretical DOS calculated by O'Reilly, Robertson and Kelly. The corrected IPES spectrum for a-GeSe resembles the broadened theoretical DOS for chemically ordered 4(Ge):2(Se) structure, whereas that for a-GeTe resembles the theoretical DOS for randomly bonded 4(Ge):2(Te) structure. The characters of the conduction-band DOSs for a-GeSe and a-GeTe were also examined by means of soft-x-ray core absorption spectroscopy. The Ge and Se 0953-8984/10/8/024/img12 core absorption spectra of a-GeSe are very similar to those of a-0953-8984/10/8/024/img13, and were discussed using a simple bonding model with a 4(Ge):2(Se) local configuration. The Ge 0953-8984/10/8/024/img12 and Te 0953-8984/10/8/024/img15 core absorption spectra of a-GeTe were also discussed using a simple local bonding model. All of the present measurements indicate that both a-GeSe and a-GeTe have structures with 4(Ge):2(chalcogen) coordination.

Hosokawa, S.; Hari, Y.; Kouchi, T.; Ono, I.; Sato, H.; Taniguchi, M.; Hiraya, A.; Takata, Y.; Kosugi, N.; Watanabe, M.

1998-03-01

78

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

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.

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

79

CdTe thin film solar cells with ZnSe buffer layer  

Microsoft Academic Search

We investigate CdTe based solar cells fabricated with an unconventional structure which includes a Mo thin film deposited by sputtering as back contact and a ZnSe film deposited by evaporation as buffer layer. The use of window materials like the ZnSe which present wider band gap than CdS, could lead to enhancement in the photocurrent. Solar cells with structure Mo\\/CdTe\\/ZnSe\\/ZnO

G. Gordillo; C. Calderon; H. Infante

2002-01-01

80

Formation of PbTe-PbSe Superlattices Using Electrochemical - Atomic Layer Epitaxy  

NASA Astrophysics Data System (ADS)

EC-ALE is a room-temperature deposition technique in which the elments of a compound semiconductor are electrochemically deposited onto a substrate one atomic layer at a time. This atomic layer control is achieved by depositing each elemental layer at a potential less than that required to deposit the element onto itself. An advantage over other deposition methods such as molecular beam epitaxy is the low temperature at which the epitaxial growth occurs. This advantage is most useful in the synthesis of superlattices, where the low deposition temperature greatly suppresses interlayer diffusion. Because EC-ALE provides also deposition control at the atomic level, superlattices with sharp interfaces can be deposited.// Here we apply EC-ALE to grow PbTe-PbSe thin film semiconductor superlattices on a gold substrate. The PbSe-PbTe superlattice thin films were characterized via electron microprobe, X-ray diffraction, and infrared absorption. We will demonstrate that EC-ALE is an attractive design alternative for semiconductor engineering.

Cox, S. M.; Compton, S. P.; Happek, U.; Vaidyanathan, R.; Stickney, J. L..

2003-03-01

81

Charge separation in CdSe/CdTe hetero-nanowires measured by electrostatic force microscopy  

NASA Astrophysics Data System (ADS)

The charge state of free standing axial type-II CdSe/CdTe hetero-nanowires is monitored via electrostatic force microscopy. The CdSe and the CdTe segment which are identified by Raman spectroscopy are found to be negatively and positively charged, respectively. The charge state is monitored without and with local illumination. We found that the magnitude of opposite charging in the respective nanowire segment is increasing with illumination power, which is attributed to a charge separation of the photogenerated electron-hole pairs across the CdSe/CdTe interface.

Schäfer, Sebastian; Reich, Aina; Wang, Zhe; Kipp, Tobias; Mews, Alf

2012-01-01

82

Observation of interface carrier states in no-common-atom heterostructures ZnSe/BeTe.  

PubMed

The existence of intrinsic carrier interface states in heterostructures with no common atom at the interface (such as ZnSe/BeTe) is shown experimentally by ellipsometry and photoluminescence spectroscopy. These states are located on interfaces and lie inside the effective bandgap of the structure; they are characterized by a high density and a long lifetime. A tight binding model confirms theoretically the existence of these states in ZnSe/BeTe heterostructures for a ZnTe-type interface, in contrast to the case of the BeSe-type interface for which they do not exist. PMID:21844640

Gurevich, A S; Kochereshko, V P; Bleuse, J; Mariette, H; Waag, A; Akimoto, R

2011-09-01

83

Optimal Te-doping in GaSe for non-linear applications.  

PubMed

Centimeter-sized Te-doped GaSe ingots were grown from the charge compositions of GaSe with nominals 0.05, 0.1, 0.5, 1, and 3 mass% Te, which were identified as ?-GaSe:Te (0.01, 0.07, 0.38, 0.67, and 2.07 mass%) single crystals. The evolution of the absorption peaks of the phonon modes E'(2) (? 0.584 THz) and E"(2) (1.77 THz) on Te-doping in GaSe:Te crystals was studied by THz time-domain spectroscopy. This study proposes that the evolution of both E'(2) and E''(2) absorption peaks correlates well with the optical quality of Te-doped GaSe crystals, which was confirmed by experimental results on the efficiency of THz generation by optical rectification. Maximal intensity of the absorption peak of the rigid layer mode E'(2) is proposed as a criterion for identification of optimal Te-doping in GaSe crystals. PMID:22418307

Ku, Shin An; Chu, Wei-Chen; Luo, Chih Wei; Andreev, Yu M; Lanskii, Grigory; Shaidukoi, Anna; Izaak, Tatyana; Svetlichnyi, Valery; Wu, Kaung Hsiung; Kobayashi, T

2012-02-27

84

Indium donor complexes with cation vacancies in CdTe and ZnSe.  

National Technical Information Service (NTIS)

Very dilute (10(sub 12) cm(sup (minus)3)) indium donors in CdTe and ZnSe powders and in CdTe single crystals were investigated using (sup 111)In Perturbed angular correlation spectroscopy. Most indium atoms are in uncomplexed sites but can form weakly-bou...

J. W. Griffith R. Lundquist R. Platzer J. A. Gardner G. Karczewski

1993-01-01

85

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

86

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

87

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

Microsoft Academic Search

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 20GPa. 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 3GPa, the maxima of both Nernst–Ettingshausen

Sergey V. Ovsyannikov; Vladimir V. Shchennikov

2004-01-01

88

A simple route to Bi2Se3 and Bi2Te3 nanocrystals  

NASA Astrophysics Data System (ADS)

Monodisperse nanocrystals of Bi2Se3 and Bi2Te3 capped with alkylamines have been synthesized via facile solution based method. The method involves reduction of selenium or tellurium using sodium borohydride, followed by thermolysis in an alkylamine at high temperature. Spherical shaped Bi2Se3 nanocrystals were obtained at 190 °C, whereas the reaction at 270 °C, yielded faceted nanocrystals. Similarly, spherical Bi2Te3 nanocrystals were obtained at all temperatures with hexadecylamine and oleylamine capping agents.

Mntungwa, Nhlakanipho; Rajasekhar, Pullabhotla V. S. R.; Ramasamy, Karthik; Revaprasadu, Neerish

2014-05-01

89

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

NASA Astrophysics Data System (ADS)

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

Oremland, R. S.

2007-12-01

90

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

NASA Technical Reports Server (NTRS)

Complete and systematic ground-based experimental and theoretical analyses on the Physical Vapor Transport (PVT) of ZnSe and related ternary compound semiconductors have been performed. The analyses included thermodynamics, mass flux, heat treatment of starting material, crystal growth, partial pressure measurements, optical interferometry, chemical analyses, photoluminescence, microscopy, x-ray diffraction and topography as well as theoretical, analytical and numerical analyses. The experimental results showed the influence of gravity orientation on the characteristics of: (1) the morphology of the as-grown crystals as well as the as-grown surface morphology of ZnSe and Cr doped ZnSe crystals; (2) the distribution of impurities and defects in ZnSe grown crystals; and (3) the axial segregation in ZnSeTe grown crystals.

Su, Ching-Hua; Brebrick, R. F.; Burger, A.; Dudley, M.; Matyi, R.; Ramachandran, N.; Sha, Yi-Gao; Volz, M.; Shih, Hung-Dah

1999-01-01

91

Electrical Conductivity and Thermoelectromotive Force of Solid Solutions of the Systems: BI2SE3 -- SB2 TE3 and BI2TE3 -- SB2SE3.  

National Technical Information Service (NTIS)

On the basis of measurements of electrical conductivity and thermal E M F of solid solutions with laminar structure of the tetradymite type, it was established that in the system Bi2Se3 -- Sb2Te3 at room temperature, electrical conductivity changes on a c...

V. G. Kuznetsov K. K. Palkina A. V. Dmitriev

1964-01-01

92

Photoacoustic measurement of the thermal diffusivity of Bi added Ge–Se and Ge–Se–Te glasses  

Microsoft Academic Search

The photoacoustic (PA) technique has been employed to measure the thermal diffusivity of Ge20BixSe80?x (xat.%=2 to 11) and Ge20BixSe70?xTe10 (xat.%=2.5 to 12) glasses. The PA cell developed for these studies is also described briefly. The thermal diffusivity measurements show an anomaly near the p to n transition. Possible explanations have been given in the light of percolation threshold and chemically

B. Thangaraju; R. Ganesan; K. S. Sangunni; E. S. R. Gopal

1998-01-01

93

Photoelectrochemical Characterization of Polycrystalline CdSe, CdTe and CuInSe2 Semiconductor Films  

NASA Astrophysics Data System (ADS)

Useful optical parameters of thin semiconducting films can be determined by electrochemical and electrical techniques. This work is an attempt to characterize cathodically electrodeposited binary cadmium chalcogenide (CdSe, CdTe) and ternary Cu-chalcopyrite (CuInSe2) films by photoelectrochemical techniques. Namely, photovoltammetry, photocurrent spectroscopy and onset potential method. Some fundamentals, regarding the estimation of band gap energy and flat band potential values of these semiconductors, are briefly discussed.

Koutsikou, R.; Bouroushian, M.

2010-01-01

94

Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

95

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

PubMed

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

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

96

Composition-Dependent Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 Doped with In4Se3  

NASA Astrophysics Data System (ADS)

We present the effects of In4Se3 addition on thermoelectric properties of n-type Bi2Te2.7Se0.3. In this study, polycrystalline (In4Se3) x -(Bi2Te2.7Se0.3)1- x pellets were prepared by mechanical alloying followed by spark plasma sintering (SPS). The thermoelectric properties such as Seebeck coefficient and electrical and thermal conductivities were measured in the temperature range of 300 K to 500 K. Addition of In4Se3 into Bi2Te2.7Se0.3 resulted in segregation of In4Se3 phase within Bi2Te2.7Se0.3 matrix. The Seebeck coefficient of the (In4Se3) x -(Bi2Te2.7Se0.3)1- x samples exhibited lower values compared with that of pure Bi2Te2.7Se0.3 phase. This reduction of Seebeck coefficient in n-type (In4Se3) x -(Bi2Te2.7Se0.3)1- x is attributed to the formation of unwanted p-type phases by interdiffusion through the interface between (In4Se3) x and (Bi2Te2.7Se0.3)1- x as well as consequently formed Te-deficient matrix. However, the decrease in electrical resistivity and thermal conductivity with addition of In4Se3 leads to an enhanced thermoelectric figure of merit ( ZT) at a temperature range over 450 K: a maximum ZT of 1.0 is achieved for the n-type (In4Se3)0.03-(Bi2Te2.7Se0.3)0.97 sample at 500 K.

Yim, Ju-Hyuk; Baek, Seung-Hyub; Shin, Hyun-Yong; Hyun, Dow Bin; Kim, Jin-Sang

2013-07-01

97

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

PubMed

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

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

2012-11-21

98

Anistropy of the Constant-Energy Surfaces in n-Type Bi2Te3 and Bi2Se3 from Galvanomagnetic Coefficients  

Microsoft Academic Search

Low-field galvanomagnetic coefficients have been measured on single crystals of Bi2Te3 and Bi2Se3 at 76 °K in fields to 9 kG. Using a six-valley ellipsoid model in the isotropic relaxation-time approximation, the mass parameters of the ellipsoids are calculated for both compounds. The discrepancy between previously reported galvanomagnetic data and de Haas-van Alphen data for Bi2Te3 can be minimized by

L. P. Caywood; G. R. Miller

1970-01-01

99

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

NASA Technical Reports Server (NTRS)

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

Su, Ching-Hua

1993-01-01

100

Development of ion-implantation confined, shallow mesa stripe (Pn,Sn)Te/Pb(Te,Se) DH laser diodes  

NASA Technical Reports Server (NTRS)

Preliminary results of a program to develop ion implantation confined, shallow mesa stripe (Pb,Sn)Te laser diodes are presented. The practicality of using a shallow mesa stripe to produce single mode laser output and to increase the single mode tuning range are demonstrated. The first results of p-type ion implantation in the lead-tin salts are also reported. It is shown that sodium and lithium both can be used to convert n-type Pb(Te,Se) to p-type. The implant and anneal procedures are described, and electrical characteristics of Li-implanted layers are presented.

Fonstad, C. G.; Harton, A.; Jiang, Y.-N.; Appelman, H.

1983-01-01

101

Low pressure MOVPE growth of ZnSe, ZnTe, and ZnSe/ZnTe strained-layer superlattices  

NASA Astrophysics Data System (ADS)

ZnSe and ZnTe single-crystal layers have been grown onto (100) GaAs substrates by low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) using the triethylamine-dimethylzinc adduct [DMZn(NEt3)] as the zinc precursor. The selenium and tellurium precursors were H2Se (5% in H2) and di-isopropyltellurium (DiPTe), respectively. These two semiconductors have been grown with different VI/II molar ratios, at different growth temperatures, and with an overall growth pressure ranging from 40 to 400 Torr. Optimal growth parameters have been determined by optical means for the two materials. This information was then used to grow ZnTe/ZnSe strained-layer superlattices. We have studied structures grown on both ZnSe and ZnTe relaxed buffer layers which display a drastic dependence of the Stokes shift between photoluminescence and the optical bandgap on the nature of the buffer layer. Growth interruptions have been used to optimize the optical properties of the superlattices. Theoretical modeling of superlattice band structures has been performed using results of optical and structural characterizations. Observations of zone center transitions as well as excitons associated with the miniband dispersion of the superlattices are reported, in agreement with the theoretical calculation.

Briot, N.; Cloitre, T.; Briot, O.; Gil, B.; Bertho, D.; Jouanin, C.; Aulombard, R. L.; Hirtz, J. P.; Huber, A.

1993-05-01

102

Highly luminescent (Zn,Cd)Te/CdSe colloidal heteronanowires with tunable electron-hole overlap.  

PubMed

We report the synthesis of ultranarrow (Zn,Cd)Te/CdSe colloidal heteronanowires, using ZnTe magic size clusters as seeds. The wire formation starts with a partial Zn for Cd cation exchange, followed by self-organization into segmented heteronanowires. Further growth occurs by inclusion of CdSe. The heteronanowires emit in the 530 to 760 nm range with high quantum yields. The electron-hole overlap decreases with increasing CdSe volume fraction, allowing the optical properties to be controlled by adjusting the heteronanowire composition. PMID:22214477

Groeneveld, Esther; van Berkum, Susanne; van Schooneveld, Matti M; Gloter, Alexandre; Meeldijk, Johannes D; van den Heuvel, Dave J; Gerritsen, Hans C; de Mello Donega, Celso

2012-02-01

103

Photoelectrochemical storage cell with n-CdSe and p-CdTe electrodes  

SciTech Connect

Charge and energy storage is presented for a photoelectrochemical cell, in which in a CdSO4 electrolyte one electrode, n-CdSe, is photodecomposed under illumination, and the other electrode, p-CdTe, is photoelectroplated by Cd. These processes lead to a galvanic cell with Se on CdSe as one electrode, and Cd on CdTe as the other electrode. The discharge products, when the cell is discharged in the dark, are the original photosensitive semiconductors. Each of these photosensitive electrodes, as well as their combined performance, is discussed, together with the source of irreversibilities for this method of photoelectrochemical energy conversion. 15 references.

Gerritsen, H.J.; Ruppel, W.

1984-09-01

104

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

PubMed

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

Reyes, J C Salcedo

2008-12-01

105

Electrical transport characterizations of nitrogen doped ZnSe and ZnTe films  

SciTech Connect

Temperature-dependent Hall effect measurements are reported on a series of nitrogen doped ZnSe and ZnTe epilayers using a van der Pauw configuration. A Zn(Se,Te) pseudo-graded band gap layer was used to form ohmic contacts to p-type ZnSe. The activation energy of nitrogen in ZnSe at the infinite dilution limit was extrapolated to be 114 meV. For a ZnTe film having a room temperature free hole concentration of p = 4.1 x 10{sup 16} cm{sup -3}, the activation energy of the nitrogen acceptors was found to be 46 meV. 21 refs., 4 figs.

Fan, Y.; Han, J.; He, L. [Purdue Univ., West Lafayette, IN (United States)] [and others

1994-03-01

106

Thermoelectric Performance of n-Type (PbTe)0.75(PbS)0.15(PbSe)0.1 Composites.  

PubMed

Lead chalcogenides (PbQ, Q = Te, Se, S) have proved to possess high thermoelectric efficiency for both n-type and p-type compounds. Recent success in tuning of electronic band structure, including manipulating the band gap, multiple bands, or introducing resonant states, has led to a significant improvement in the thermoelectric performance of p-type lead chalcogenides compared to the n-type ones. Here, the n-type quaternary composites of (PbTe)0.75(PbS)0.15(PbSe)0.1 are studied to evaluate the effects of nanostructuring on lattice thermal conductivity, carrier mobility, and effective mass variation. The results are compared with the similar ternary systems of (PbTe)1-x(PbSe)x, (PbSe)1-x(PbS)x, and (PbS)1-x(PbTe)x. The reduction in the lattice thermal conductivity owing to phonon scattering at the defects and interfaces was found to be compensated by reduced carrier mobility. This results in a maximum figure of merit, zT, of ?1.1 at 800 K similar to the performance of the single phase alloys of PbTe, PbSe, and (PbTe)1-x(PbSe)x. PMID:24960418

Aminorroaya Yamini, Sima; Wang, Heng; Ginting, Dianta; Mitchell, David R G; Dou, Shi Xue; Snyder, G Jeffrey

2014-07-23

107

Synthesis and characterization of CdTe/CdS and CdTe/CdSe core/shell type-II quantum dots in a noncoordinating solvent  

NASA Astrophysics Data System (ADS)

A synthetic route to CdTe/CdS and CdTe/CdSe core/shell type-II quantum dots in noncoordinating solvents (1-octadecene) was obtained. The results showed redshift in the emission spectra of CdTe/CdS and CdTe/CdSe compared with the CdTe core nanocrystals. This phenomenon is believed to indicate the formation of core/shell nanostructures. Transmission electron microscopy and powder x-ray diffraction were also consistent with nanocrystals containing a core of nearly monodisperse CdTe with CdS or CdSe capping. The photoluminescence quantum yield was enhanced by epitaxial growth of CdS or CdSe shells. Stepwise increasing concentration of sulfur or selenium monomers into the CdTe core solution allowed the examination of monomer activities, which are very relevant for synthesizing core/shell quantum dots.

Chang, Jia-Yaw; Wang, Shiuann-Ren; Yang, Cheng-Hsien

2007-08-01

108

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

NASA Technical Reports Server (NTRS)

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).

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

2002-01-01

109

Structure and Electronic Properties of Te Se Mixtures under High Pressure  

Microsoft Academic Search

X-ray diffraction and electrical resistance have been measured for amorphous and crystalline Te1-xSex mixtures (0<=x<=1) under high pressure up to 30 GPa, and four high pressure phases of Te-Se mixtures have been observed: a monoclinic phase with 6 atoms per unit cell (M-I phase); a monoclinic phase with 4 atoms per unit cell (M-II phase); an orthorhombic phase; a beta-Po-type

Yoshinori Ohmasa; Itsuro Yamamoto; Makoto Yao; Hirohisa Endo

1995-01-01

110

Indium donor complexes with cation vacancies in CdTe and ZnSe  

SciTech Connect

Very dilute (10{sub 12} cm{sup {minus}3}) indium donors in CdTe and ZnSe powders and in CdTe single crystals were investigated using {sup 111}In Perturbed angular correlation spectroscopy. Most indium atoms are in uncomplexed sites but can form weakly-bound complexes with native defects in very defective material. The only complex observed in CdTe is an indium-Cd vacancy pair. The CdTe in which these pairs occur is apparently n-type, most Cd vacancies are free and doubly-charged, and the binding energy with indium is 0.15 eV. In ZnSe, indium can pair with a Zn vacancy or with some other presently unidentified defect. These complexes form in ZnSe containing large concentrations of both free Zn vacancies and complexes of Zn vacancies with other defects. In CdTe, the pair formation equilibration time constant is two days at 15C,an implication that Cd vacancies are mobile at room temperature. Lattice relaxation around a Cd vacancy in CdTe was probed by single crystal PAC experiments.

Griffith, J.W.; Lundquist, R.; Platzer, R.; Gardner, J.A. [Oregon State Univ., Corvallis, OR (United States). Dept. of Physics; Karczewski, G.; Furdyna, J.K. [Notre Dame Univ., IN (United States). Dept. of Physics

1993-11-01

111

Thermoelectric Properties of n-Type Bi2Te3/PbSe0.5Te0.5 Segmented Thermoelectric Material  

NASA Astrophysics Data System (ADS)

To investigate the effects of segmentation of thermoelectric materials on performance levels, n-type segmented Bi2Te3/PbSe0.5Te0.5 thermoelectric material was fabricated, and its output power was measured and compared with those of Bi2Te3 and PbSe0.5Te0.5. The two materials were bonded by diffusion bonding with a diffusion layer that was ˜18 ?m thick. The electrical conductivity, Seebeck coefficient, and power factor of the segmented Bi2Te3/PbSe0.5Te0.5 sample were close to the average of the values for Bi2Te3 and PbSe0.5Te0.5. The output power of Bi2Te3 was higher than those of PbSe0.5Te0.5 and the segmented sample for small ? T (300 K to 400 K and 300 K to 500 K), but that of the segmented sample was higher than those of Bi2Te3 and PbSe0.5Te0.5 when ? T exceeded 300 K (300 K to 600 K and 300 K to 700 K). The output power of the segmented sample was about 15% and 73% higher than those of the Bi2Te3 and PbSe0.5Te0.5 samples, respectively, when ? T was 400 K (300 K to 700 K). The efficiency of thermoelectric materials for large temperature differences can be enhanced by segmenting materials with high performance in different temperature ranges.

Yoon, Sejin; Cho, Jun-Young; Koo, Hyun; Bae, Sung-Hwan; Ahn, Seunghyun; Kim, Gwi Rang; Kim, Jin-Sang; Park, Chan

2014-02-01

112

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

NASA Astrophysics Data System (ADS)

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.

Ovsyannikov, Sergey V.; Shchennikov, Vladimir V.

2004-02-01

113

Role of polycrystallinity in CdTe and CuInSe sub 2 photovoltaic cells  

SciTech Connect

The polycrystalline nature of thin-film CdTe and CuInSe{sub 2} solar cells continues to be a major factor in several individual losses that limit overall cell efficiency. This report describes progress in the quantitative separation of these losses, including both measurement and analysis procedures. It also applies these techniques to several individual cells to help document the overall progress with CdTe and CuInSe{sub 2} cells. Notably, CdTe cells from Photon Energy have reduced window photocurrent losses to 1 mA/Cm{sup 2}; those from the University of South Florida have achieved a maximum power voltage of 693 mV; and CuInSe{sub 2} cells from International Solar Electric Technology have shown a hole density as high as 7 {times} 10{sup 16} cm{sup {minus}3}, implying a significant reduction in compensation. 9 refs.

Sites, J.R. (Colorado State Univ., Fort Collins, CO (United States))

1991-01-01

114

Proposal of BeZnTe/ZnSeTe superlattice quasi-quaternaries on InP substrates for yellow/green light emitting devices  

NASA Astrophysics Data System (ADS)

We proposed BeZnTe/ZnSeTe superlattice quasi-quaternaries (SLQQs) as an active layer material replaced with BeZnSeTe quaternaries for yellow/green light emitting devices. BeZnTe/ZnSeTe SLQQs with various layer thickness combinations of BeZnTe and ZnSeTe were grown on InP substrates by a molecular beam epitaxy (MBE). In photoluminescence (PL) measurements at room temperature, high PL intensities were obtained for the SLQQs compared with BeZnSeTe. The peak wavelength was controlled from 589 to 480 nm by changing the layer thickness combination (BeZnTe/ZnSeTe) from 1 monolayer (ML)/20 ML to 4 ML/2 ML. Applying the SLQQ for the active layer, LEDs were fabricated on n-type InP substrates. Single-peak yellow electroluminescence at 584 nm was observed with the full wave half maximum (FWHM) of 105 meV.

Kobayashi, Toshiki; Nomura, Ichirou; Murakami, Keisuke; Kishino, Katsumi

2013-09-01

115

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

116

Influence of Sn Migration on Phase Transition in GeTe and Ge2Se3 Thin Films  

SciTech Connect

Phase transitions in GeTe/SnSe and Ge{sub 2}Se{sub 3}/SnTe are investigated using time resolved x-ray diffraction. GeTe exhibits a structural transition from rhombohedral to the cubic phase at 300 C, which is - 100 C lower than that of pure GeTe. This is facilitated by incorporation of Sn from SnSe. Sn migration is observed explicitly in Ge{sub 2}Se{sub 3}/SnTe by separation of SnSe phase. Amorphous Ge{sub 2}Se{sub 3} is also found to crystallize at a lower temperature of 300 C resulting in orthorhombic GeSe and monoclinic GeSe{sub 2}. Thus, inclusion of a Sn containing layer may offer a means to tailor phase transition in Ge-chalcogenide thin films for phase change memory applications.

Devasia, A.; Kurinec, S; Campbell, K; Raoux, S

2010-01-01

117

Crystalline intermetallic compounds in the K-Te system: The Zintl-Klemm principle revisited  

NASA Astrophysics Data System (ADS)

We have investigated the crystal structure, chemical bonding, and electronic properties of all known intermetallic compounds in the K-Te system, employing a first-principles local-density-functional approach including generalized gradient corrections. The structural parameters, such as equilibrium volume, lattice constants, and internal parameters are in very good agreement with experiment. The evaluation of the total and angular-momentum decomposed densities of states (DOS) and the partial charge densities gives further insight into the bonding properties of these solids. Our results confirm the validity of the Zintl-Klemm principle for the saltlike compound K2Te and for the two equiatomic phases ?-K2Te2 and ?-K2Te2 consisting of isolated K ions and covalently bounded Te2 dimers. In the compound K5Te3 ionic regions consisting of K+ and Te2- ions with closed octet shells and polyanionic regions with an atomic arrangement dominated by Te2-2 dianions coexist in the crystal lattice. In the electron-deficient-compound K2Te3, larger polyanions-Te2-3 trimers-have to be formed to achieve saturated covalent bonds. Our results illustrate the validity and astonishing flexibility of the Zintl-Klemm principle, which allows us to interpret all crystal structures in the K-Te system, from the saltlike octet compound to the Te-rich phases with extended polyanionic superstructures, on a common footing.

Seifert-Lorenz, Karin; Hafner, Jürgen

2002-09-01

118

Facile synthesis and photoluminescence of near-infrared-emitting CdTe(x)Se(1-x) and CdTe(x)Se(1-x)/Cd(y)Zn(-1-y)S quantum dots.  

PubMed

High-quality colloidal photoluminescent (PL) CdTe(x)Se(1-x) quantum dots (QDs) with gradient distribution of components, consisting of Te-rich inner cores and Se-rich outer shells, were synthesized via a facile organic method using stearic acid as a capping agent. The transmission electron microscopy observation and X-ray diffraction analysis indicated that the CdTe(x)Se(1-x) QDs revealed a "dot" shaped morphology and exhibited a zinc-blende structure which located between those of bulk CdTe and CdSe (with the lattice parameters between those of bulk CdTe and CdSe). The ternary CdTe(x)Se(1-x) QDs were emitting in the red to near-infrared (NIR) range. In order to enhance the PL properties and reduce the sensitivity to oxidation of CdTe-based QDs, the CdTe(x)Se(1-x) QDs were coated with Cd(y)Zn(1-y)S multishells by using different growth kinetics of CdS and ZnS. The coated QDs exhibited a controlled red shift of PL compared with the initial CdTe(x)Se(1-x) cores and revealed much improved PL intensity. Because of thier tunable emission from red to NIR, these composite QDs open new possibilities in band gap engineering and in developing NIR fluorescent probes for biological imaging and detection. PMID:24745260

Zhang, Ruili; Wang, Jianrong; Yang, Ping

2014-03-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2005-07-01

120

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

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

121

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

PubMed

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

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

2013-09-25

122

Electronic and optical properties of the 1T phases of TiS2, TiSe2, and TiTe2  

Microsoft Academic Search

The electronic properties of the 1T phase of TiX2 (X=S, Se, and Te) compounds are calculated using the full potential linear augmented plane wave method as embodied in the WIEN97 code. Our calculations show that all the compounds are semimetallic. The density of states at the Fermi energy N(EF), controlled by the overlap between the Ti d and X p

Ali Hussain Reshak; S. Auluck

2003-01-01

123

Electrodeposition of CdSe xTe 1 - x by periodic pulse technique  

NASA Astrophysics Data System (ADS)

Cadmium chalcogenides have been electrodeposited from an aqueous solution on titanium and graphite substrates by potentiostatic and periodic pulse techniques. Deposits have been characterized with X-ray diffractograms, surface micrographs, X-ray microprobe analysis and voltammetry. The mechanism and deposition kinetics of CdSe xTe 1 - x have been determined. The results are discussed.

Babu, S. Moorthy; Rajalakshmi, T.; Dhanasekaran, R.; Ramasamy, P.

1991-03-01

124

Effect of Deformation on the Thermoelectric Properties of Bi2Te3 - Bi2Se3.  

National Technical Information Service (NTIS)

The effect of an external unilateral pressure up to 250 kgf/sq cm on electrical conductivity, thermal emf and thermal conductivity of n-type Bi2Te3 - Bi2Se3 was investigated over the 300-550K temperature range. Electrical conductivity at 300K increases li...

A. Z. Kuliev A. S. Okhotin D. A. Asadov K. S. Kakhramanov

1974-01-01

125

Preparation and Thermoelectric Properties of Doped Bi2Te3-Bi2Se3 Solid Solutions  

NASA Astrophysics Data System (ADS)

Since Bi2Te3 and Bi2Se3 have the same crystal structure, they form a homogeneous solid solution. Therefore, the thermal conductivity of the solid solution can be reduced by phonon scattering. The thermoelectric figure of merit can be improved by controlling the carrier concentration through doping. In this study, Bi2Te2.85Se0.15:D m (D: dopants such as I, Cu, Ag, Ni, Zn) solid solutions were prepared by encapsulated melting and hot pressing. All specimens exhibited n-type conduction in the measured temperature range (323 K to 523 K), and their electrical conductivities decreased slightly with increasing temperature. The undoped solid solution showed a carrier concentration of 7.37 × 1019 cm-3, power factor of 2.1 mW m-1 K-1, and figure of merit of 0.56 at 323 K. The figure of merit (ZT) was improved due to the increased power factor by I, Cu, and Ag dopings, and maximum ZT values were obtained as 0.76 at 323 K for Bi2Te2.85Se0.15:Cu0.01 and 0.90 at 423 K for Bi2Te2.85Se0.15:I0.005. However, the thermoelectric properties of Ni- and Zn-doped solid solutions were not enhanced.

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

2013-10-01

126

Performance of Bi–Te–Sb–Se Thermoelectric Material at Low Temperature  

Microsoft Academic Search

Thermoelectric materials are of interest for applications as heat pump and power generators. The performance of a thermoelectric material, the figure of merit, ZT, is measured. The figure of merit is interrelated to the thermal conductivity, electrical conductivity, and Seebeck coefficient. All of these parameters are functions of temperature. The performance of a Bi–Te–Sb–Se thermoelectric material at low temperature was

Lei Jia; Peng Hu; Zeshao Chen; Wei Sun

2006-01-01

127

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

PubMed

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

Boyer-Richard, Soline; Robert, Cédric; Gérard, Lionel; Richters, Jan-Peter; André, Régis; Bleuse, Joël; Mariette, Henri; Even, Jacky; Jancu, Jean-Marc

2012-01-01

128

Spray Deposition of High Quality CuInSe2 and CdTe Films: Preprint  

SciTech Connect

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

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

2008-05-01

129

Effect of extrusion temperature and dopant on thermoelectric properties for hot-extruded p-type Te-doped Bi 0.5Sb 1.5Te 3 and n-type SbI 3-doped Bi 2Te 2.85Se 0.15  

Microsoft Academic Search

The p-type Te-doped Bi0.5Sb1.5Te3 and n-type SbI3-doped Bi2Te2.85Se0.15 compounds were fabricated by hot extrusion in the temperature range of 300–440°C under an extrusion ratio of 20:1. The grains of the two compounds contained many dislocations and were fine equiaxed (?1.0 ?m) owing to the dynamic recrystallization during the extrusion. The hot extrusion gave rise to a slightly preferred orientation of

J. Seo; C. Lee

1998-01-01

130

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

PubMed Central

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.

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

2007-01-01

131

The role of Fe deficiency in FeySe0.5Te0.5 samples prepared by a melting process  

NASA Astrophysics Data System (ADS)

Fe content plays a primary role in the structural, magnetic and transport properties of Fe(Se,Te) compounds. In this work we investigate some of these properties in ipo-stoichiometric FeySe0.5Te0.5 samples (y ? 1.00) prepared by a novel synthesis technique, involving a melting process. These samples are characterized by a pore-free microstructure with large and well interconnected grains. The composition Fe0.99Se0.5Te0.5 exhibits the best properties with an optimal critical temperature, sharp resistive and magnetic transitions, large hysteresis loops and high value of critical current density at zero field and 5 K.

Sala, A.; Palenzona, A.; Bernini, C.; Caglieris, F.; Cimberle, M. R.; Ferdeghini, C.; Lamura, G.; Martinelli, A.; Pani, M.; Putti, M.

2013-11-01

132

197Au and125Te Mössbauer spectroscopic study on the low temperature phases of Ag3AuX2 (X=S, Se, and Te)  

NASA Astrophysics Data System (ADS)

197Au and125Te Mössbauer spectroscopy has been applied for the low-temperature ?-phases of Ag3AuX2 (X=S, Se, and Te). The values of I. S. and Q. S. for197Au suggest that the gold atoms, linearly coordinated by two chalcogen atoms in these phases, exist as monovalent cations. The125Te Mössbauer spectra suggest that the tellurium atoms are substantially ionic for both Ag2Te and Ag3AuTe2. The nature of X-Au-X bonds is discussed on the basis of the Mössbauer data and the bond distances.

Sakai, Hiroshi; Ando, Manabu; Maeda, Yutaka

1992-04-01

133

The superconducting transition temperatures of Fe(1+x)Se(1-y), Fe(1+x)Se(1-y)Te(y) and (K/Rb/Cs)(z)Fe(2-x)Se2.  

PubMed

In a recent contribution to this journal, it was shown that the transition temperatures of optimal high-T(C) compounds obey the algebraic relation T(C0) = k(-1)(B)/??, where ? is related to the mean spacing between interacting charges in the layers, ? is the distance between interacting electronic layers, ? is a universal constant and k(B) is Boltzmann's constant. The equation was derived assuming pairing based on interlayer Coulomb interactions between physically separated charges. This theory was initially validated for 31 compounds from five different high-T(C) families (within an accuracy of ±1.37 K). Herein we report the addition of Fe(1+x)Se(1-y) and Fe(1+x)Se(1-y)Te(y) (both optimized under pressure) and A(z)Fe(2-x)Se(2) (for A = K, Rb or Cs) to the growing list of Coulomb-mediated superconducting compounds in which T(C0) is determined by the above equation. Doping in these materials is accomplished through the introduction of excess Fe and/or Se deficiency, or a combination of alkali metal and Fe vacancies. Consequently, a very small number of vacancies or interstitials can induce a superconducting state with a substantial transition temperature. The confirmation of the above equation for these Se-based Fe chalcogenides increases to six the number of superconducting families for which the transition temperature can be accurately predicted. PMID:22370161

Harshman, Dale R; Fiory, Anthony T

2012-04-01

134

Transport properties of amorphous Se80-xTE20Pbx (0  

NASA Astrophysics Data System (ADS)

Thin films of Se80-xTe20Pbx (0 < x < 2) glassy semiconductors have been prepared by thermal evaporation of bulk material of the above composition prepared by melt quenching technique. The glass transition temperature ‘Tg’, the peak crystallization temperature ‘'Tp’ and the melting temperature ‘Tm’ of the bulk samples have been estimated from the Differential Scanning Calorimetry (DSC) data. The DSC studies were performed at a heating rate of 10 deg/min. It has been found that ‘Tg’ initially decreases with small addition of Pb (x = 0.6), however its value increases with further addition of Pb (x > 0.6). This indicates that the addition of Pb (x >0.6) cross-links the already existing Se-Te chains, which in turn increases the chain length and results in the increase of Tg. The dc conductivity of the films has been measured as a function of temperature and is found to be activated in the entire temperature range. Its value increases from 10-9 to 10-5 (Ohm-m)-l with the addition of Pb to Se-Te system. The dc activation energy has been found to decrease from 0.67-0.23 eV with increase in Pb content. The optical energy gap determined at room temperature is found to decrease from 1.67-1.34eV with the addition of lead to the Se-Te matrix. The results are explained on the basis of enhanced valence band tailing when Pb is incorporated into the Se- Te system.

Kamboj, Maninder S.; Thangaraj, R.

2002-12-01

135

Time-resolved temperature measurements during laser-induced synthesis of Cu-Te compounds  

NASA Astrophysics Data System (ADS)

Synthesis of thin films of Cu xTe y compounds on glass is performed under CW Ar + laser irradiation. The variation of temperature with time is measured by an interferometric method. Experiments tell us that: (1) reactions start at the centrum of the laser spot on the sample; (2) at fixed position, the composition of the compounds begins with CuTe, followed by Cu 7Te 5 and Cu 2Te; (3) the different compounds begin to form at a fixed threshold temperature, independent of the laser beam power (CuTe: 115°C, Cu 7Te 5: 250°C; Cu 2Te: 275°C); (4) in this regime, reactions take place in the solid phase.

Hanus, F.; Wautelet, M.

1989-12-01

136

Anisotropic strain-induced curvature in type-II CdSe/CdTe nanorod heterostructures.  

PubMed

Type-II band-offset CdSe/CdTe nanorod heterostructures with curved and linear shapes have been synthesized and examined with atomic-resolution transmission electron microscopy techniques. Strain from growth of larger-lattice CdTe partly on the sides of CdSe nanorod seeds is shown to lead to an overall curvature in the rods. Lattice expansion from the inner to the outer portion of the curved region exceeds the expected lattice mismatch between the two materials because of the buildup of an unusual compressive strain in the CdSe. In contrast, exclusive tip growth results in linear barbell-shaped heterostructures that do not exhibit strain-induced curvature. The ability to vary the anisotropic lattice strain should allow control over the underlying electronic structure, providing new approaches to directing photogenerated carriers that may facilitate incorporation of nanorod heterostructures in various energy applications. PMID:20163144

McDaniel, Hunter; Zuo, Jian-Min; Shim, Moonsub

2010-03-17

137

Carrier multiplication yields of CdSe and CdTe nanocrystals by transient photoluminescence spectroscopy  

NASA Astrophysics Data System (ADS)

Engineering semiconductors to enhance carrier multiplication (CM) could lead to increased photovoltaic cell performance and a significant widening of the materials range suitable for future solar technologies. Semiconductor nanocrystals (NCs) have been proposed as a favorable structure for CM enhancement, and recent measurements by transient absorption have shown evidence for highly efficient CM in lead chalcogenide and CdSe NCs. We report here an assessment of CM yields in CdSe and CdTe NCs by a quantitative analysis of biexciton and exciton signatures in transient photoluminescence decays. Although the technique is particularly sensitive due to enhanced biexciton radiative rates relative to the exciton, kBXrad>2kXrad , we find no evidence for CM in CdSe and CdTe NCs up to photon energies ??>3Eg , well above previously reported relative energy thresholds.

Nair, Gautham; Bawendi, Moungi G.

2007-08-01

138

Thermoelectric properties of the hot-pressed (Bi,Sb){sub 2}(Te,Se){sub 3} alloys  

SciTech Connect

Thermoelectric properties of the (Bi,Sb){sub 2}Te{sub 3} and Bi{sub 2}(Te,Se){sub 3} single crystals were well characterized for the whole composition range of the Bi{sub 2}Te{sub 3}-Sb{sub 2}Te{sub 3} and Bi{sub 2}Te{sub 3}-Bi{sub 2}Se{sub 3} systems. However, the same work has been seldom conducted for the hot-pressed alloys. Thermoelectric properties of the hot-pressed (Bi,Sb){sub 2}Te{sub 3} and Bi{sub 2}(Te,Se){sub 3} alloys have been investigated mainly at the compositions of (Bi{sub 0.25}Sb{sub 0.75}){sub 2}Te{sub 3} and Bi{sub 2}(Te{sub 0.95}Se{sub 0.05}){sub 3} where the maximum figure-of-merits of p-type and n-type, respectively, were obtained for the single crystals with doping. In this study, thermoelectric properties of the hot-pressed (Bi,Sb){sub 2}(Te,Se){sub 3} alloys, prepared by powder metallurgy such as melting/grinding and mechanical alloying, were measured at room temperature and compared with the characteristics of the single crystals grown by the Bridgman technique for a wide range of compositions of the alloys.

Oh, T.S.; Hyun, D.B.; Kolomoets, N.V.

2000-04-01

139

Electronic and optical properties of the 1T phases of TiS2, TiSe2, and TiTe2  

NASA Astrophysics Data System (ADS)

The electronic properties of the 1T phase of TiX2 (X=S, Se, and Te) compounds are calculated using the full potential linear augmented plane wave method as embodied in the WIEN97 code. Our calculations show that all the compounds are semimetallic. The density of states at the Fermi energy N(EF), controlled by the overlap between the Ti d and X p states, increases from 0.35 to 0.9 to 1.6 states/eV unit cell as we go from S to Se to Te. We report calculations of the anisotropic frequency-dependent optical properties of these compounds and find excellent agreement with the available experimental data. The optical properties show three main structures that can be attributed to transitions between the X p states and the Ti d states.

Reshak, Ali Hussain; Auluck, S.

2003-12-01

140

Infrared Spectroscopy of the Stretching Modes of SeH- and TeH- in KCl and KBr.  

National Technical Information Service (NTIS)

The fundamental stretching modes near 4.5 micrometers of SeH(-) and TeH(-) doped in KCl and KBr are measured at high resolution at 1.7 K. For the KCl-doped samples, prepared by adding elemental Se(Te) to the melt and growing under H2, the concentrations o...

C. E. Mungan U. Happek T. Z. Hossain A. J. Sievers

1995-01-01

141

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

SciTech Connect

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.

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

2010-01-01

142

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

SciTech Connect

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.

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

2012-10-23

143

Dielectric studies of Se85-xTe15Inx glasses  

NASA Astrophysics Data System (ADS)

In this paper we report the frequency and temperature dependence of ac conductivity and dielectric studies of Se85-xTe15Inx glasses. The measurements have been made on Se85-xTe15Inx (x = 2, 6, 10, 15) in the frequency range 2 kHz to 50 kHz and temperature range 203 K and 313 K. Results indicate that dielectric dispersion occurs in this frequency and temperature range. The results have been explained on the basis of correlated Barrier Hopping (CBH) model. The dc conductivity increases with increase in temperature for all composition. The Log ?dc versus 1000/T plots are almost straight lines in whole studied temperature range indicative of singly activated phenomena having single activation energy.

Kumar, Anil; Singh, Gurpreet; Lal, Manohar; Tripathi, S. K.; Goyal, Navdeep

2011-12-01

144

Bandgap bowing and spontaneous ordering in ZnSe xTe 1- x  

NASA Astrophysics Data System (ADS)

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.

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

1995-04-01

145

Thermoelectric properties of Nb3SbxTe7-x compounds  

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

146

Methyl and arylchalcogenolate complexes of cadmium in a sulfur rich coordination environment: syntheses and structural characterization of the tris(2-mercapto-1-tert-butylimidazolyl)hydroborato cadmium complexes [Tm(Bu(t))]CdMe, and [Tm(Bu(t))]CdEAr (E = O, S, Se, Te) and analysis of the bonding in chalcogenolate compounds.  

PubMed

A series of arylchalcogenolate complexes of cadmium supported by tris(2-mercapto-1-tert-butylimidazolyl)hydroborato ligation, namely [Tm(Bu(t))]CdEAr (EAr = OC(6)H(3)Ph(2), SPh, SePh, TePh), has been synthesized from [Tm(Bu(t))]CdMe; structural characterization by X-ray diffraction indicates that the variation in Cd-EAr bond lengths is similar to that of Zn-EAr and correlates closely with the covalent radius of the chalcogen, in marked contrast to the large variation in M-OAr and M-SAr bond lengths observed for other metals (Zr and Sm). PMID:16932812

Melnick, Jonathan G; Parkin, Gerard

2006-09-21

147

Fe–Te–Se epitaxial thin films with enhanced superconducting properties  

Microsoft Academic Search

Epitaxial Fe–Te–Se thin films were deposited by pulsed laser deposition at 250–600 °C on SrTiO3 (100), MgO (100), LaAlO3 (100) and CaF2 (100) single crystal substrates. The best superconducting film was grown on CaF2: K and K with Tdep = 300 °C and 3 Hz. Critical current density Jc (T = 4.2 K) was 0.41 × 106 A cm?2 at

Paolo Mele; Kaname Matsumoto; Kouhei Fujita; Yutaka Yoshida; Takanobu Kiss; Ataru Ichinose; Masashi Mukaida

2012-01-01

148

Vapour-liquid-solid growth of ternary Bi2Se2Te nanowires  

PubMed Central

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.

2014-01-01

149

Doping effects in Bi2Se3 and Bi2Te3 topological insulators  

Microsoft Academic Search

Topological insulators are found to have a bulk electronic gap and a gapless surface state. The surface state has been observed in Bi2Se3 and Bi2Te3 by ARPES and STM, but is still considered a challenging problem for transport measurements due to the dominant bulk conductance. By chemical doping, the Fermi level can be tuned to fall inside the band gapfootnotetextHor

Y. S. Hor; A. J. Williams; J. G. Checkelsky; P. Roushan; J. Seo; A. Richardella; Y. Xia; Q. Xu; H. W. Zandbergen; M. Z. Hasan; A. Yazdani; N. P. Ong; R. J. Cava

2010-01-01

150

Thermoelectric and galvanomagnetic properties of chalcogens (Te, Se) at high pressures up to 30 GPa  

Microsoft Academic Search

The longitudinal and transverse Nernst-Ettingshausen effects have been measured at high pressures up to 30 GPa. The results\\u000a of studying Te and Se in the region of metal-semiconductor phase transformations are presented as a demonstration of the possibilities\\u000a of the given technique. In agreement with magnetoresistance data, it was found that the hole mobility grows with increasing\\u000a pressure as a

V. V. Shchennikov; S. V. Ovsyannikov

2001-01-01

151

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

Microsoft Academic Search

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

Il-Ho Kim

2000-01-01

152

Optical bistability in GaSe single crystals and ZnTe thin films  

Microsoft Academic Search

By means of two-beam experiments, the transmission properties of highly excited GaSe crystal of different thicknesses (2 micrometers to 1.5 mm) have been investigated in the fundamental absorption and free exciton region. Induced transmission was observed in the whole considered region for lower pump intensities. Results of bistability in an entire ZnTe thin films are present for the first time.

V. Mushinschi; M. Caraman; V. Lichman; C. Ghizdeanu; G. Rusu; Marius Stamate

1995-01-01

153

Electronic Structures and Chemical Bonding of TiX2 (X=S, Se, and Te)  

Microsoft Academic Search

A systematic study of the electronic structures and chemical bonding of the titanium dichalcogenide TiX2 (X=S, Se, and Te) layered structures is performed by a first-principles molecular orbital calculation using the discrete-variational (DV)-Xalpha cluster method. The intra- and interlayer chemical bonding properties are also investigated using the bond overlap population. Valence band structures obtained by the calculation are in good

Yang-Soo Kim; Masataka Mizuno; Isao Tanaka; Hirohiko Adachi

1998-01-01

154

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

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

155

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

NASA Astrophysics Data System (ADS)

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.

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

2011-11-01

156

N-heterocyclic carbene (NHC)-stabilized silanechalcogenones: NHC-->Si(R2)=E (E=O, S, Se, Te).  

PubMed

A series of N-heterocyclic carbene-stabilized silanechalcogenones 2 a,b (Si=O), 3 a,b (Si=S), 4 a,b (Si=Se), and 5 a,b (Si=Te) are described. The silanone complexes 2 a,b were prepared by facile oxygenation of the carbene-silylene adducts 1 a,b with N(2)O, whereas their heavier congeners were synthesized by gentle chalcogenation of 1 a,b with equimolar amounts of elemental sulfur, selenium, and tellurium, respectively. These novel compounds have been isolated in a crystalline form in high yields and have been fully characterized by a variety of techniques including IR spectroscopy, ESIMS, and multinuclear NMR spectroscopy. The structures of 2 b, 3 a, 4 a, 4 b, and 5 b have been confirmed by single-crystal X-ray crystallography. Due to the NHC-->Si donor-acceptor electronic interaction, the Si=E (E=O, S, Se, Te) moieties within these compounds are well stabilized and thus the compounds possess several ylide-like resonance structures. Nevertheless, these species also exhibit considerable Si=E double-bond character, presumably through a nonclassical Si=E pi-bonding interaction between the chalcogen lone-pair electrons and two antibonding Si-N sigma* orbitals, as evidenced by their high stretching vibration modes and the shortening of the Si-E distances (between 5.4 and 6.3%) compared with the corresponding Si-E single-bond lengths. PMID:20013763

Yao, Shenglai; Xiong, Yun; Driess, Matthias

2010-01-25

157

NMR spectroscopic studies on chalcogen compounds. 4. Carbon-13 isotope effect on selenium-77 and tellurium-125 nuclear shielding and its correlation with C-Se bond distances. Tellurium-123 isotope effect on tellurium-125 nuclear shielding  

SciTech Connect

A one-bond isotope effect of /sup 13/C on the nuclear shielding of /sup 77/Se and /sup 125/Te was observed for the first time. Thirty values for Se(II) and Se(IV) compounds containing sp/sup 3/-, sp/sup 2/-, and sp-hybridized carbon were measured, and a wide range of low frequency shifts was found between -0.012 and -1.099 ppM. A correlation was established between the isotope shift and the C-Se bond distance for CF/sub 3/- and CH/sub 3/-substituted selenium compounds. The isotope shift of the linear molecules SeCO, SeCS, and SeCSe is inversely dependent on the force constant of the C=Se bond. This is attributed to different vibrational amplitudes. The CSe bond order plays an important role for the isotope shift and appreciable substituent effects were observed. Five Te(II) and Te(IV) compounds were studied. The isotope shifts are larger than for the corresponding Se compounds, and the results can be qualitatively interpreted in analogy to those found for the selenium compounds. The isotope shift can be temperature dependent; this was shown, for example, on liquid samples of CF/sub 3/SeCN and SeCO. This behavior is explained by a substantial contribution of vibrationally excited states. Furthermore, an isotope effect of /sup 123/Te on the screening of /sup 125/Te (and vice versa) in CF/sub 3/TeTeCF/sub 3/ was detected, and the coupling constant /sup 1/J(/sup 125/Te-/sup 123/Te) was determined.

Gombler, W.

1982-12-01

158

Doping effects in Bi2Se3 and Bi2Te3 topological insulators  

NASA Astrophysics Data System (ADS)

Topological insulators are found to have a bulk electronic gap and a gapless surface state. The surface state has been observed in Bi2Se3 and Bi2Te3 by ARPES and STM, but is still considered a challenging problem for transport measurements due to the dominant bulk conductance. By chemical doping, the Fermi level can be tuned to fall inside the band gapfootnotetextHor et al. PRB 79 195208 (09) and therefore suppress the bulk conductivity. Non-metallic conducting Bi2Se3 crystals are obtained. Previously unobserved p-type behavior has been inducedfootnotetextIbid. and a novel magnetofingerprint signalfootnotetextCheckelsky et al. arXiv:0909.1840 is seen through low level Ca-doping in Bi2Se3. Bi2Se3 can also be tuned to a bulk superconductor, with Tc˜3.8 K, by Cu-intercalation in the van der Waals gaps.footnotetextHor et al. arXiv:0909.2890. This shows that Cooper pairing is possible in Bi2Se3 with implications for Majorana fermion physics study and potential quantum computing devices. Mn-doped Bi2Te3 has ferromagnetic transition at ˜15 K, suggesting a possible magnetic topological insulator.

Hor, Y. S.; Williams, A. J.; Checkelsky, J. G.; Roushan, P.; Seo, J.; Richardella, A.; Xia, Y.; Xu, Q.; Zandbergen, H. W.; Hasan, M. Z.; Yazdani, A.; Ong, N. P.; Cava, R. J.

2010-03-01

159

The gas phase structures of XF 5NCO (X = S, Se, Te): an electron diffraction study  

NASA Astrophysics Data System (ADS)

The geometric structures of the three title compounds have been studied in the gas phase by electron diffraction. The possibility of the cyanate structure for the selenium compound (i.e., SeF 5?O?C?N) has to be rejected on the basis of this study. The N?C and C?O bond lengths in all three compounds are longer than in other isocyanates. For the X?N bond lengths in the sulphur, selenium and tellurium compounds values of 1.668(6), 1.789(6) and 1.859( Å, respectively, were determined. The nitrogen bond angle is the same for the sulphur and tellurium compounds (124.9(1.2)° and 126.5(2.4)°), while this angle is smaller in SeF 5NCO (116.9(0.8)°). The isocyanate groups are slightly tilted in the trans direction for all three compounds.

Oberhammer, Heinz; Seppelt, Konrad; Mews, Rüdiger

1983-09-01

160

Vapor Growth and Characterization of ZnSeTe Solid Solutions  

NASA Technical Reports Server (NTRS)

Six ZnSe(1-x)Te(x) crystals were grown by the physical vapor transport technique. For each of the source material compositions, x = 0.10, 0.20 and 0.30, two crystals were grown - one under the horizontal and the other under the vertical stabilized configurations. The axial and radial compositional uniformity were measured by precision density measurements, wavelength dispersive X-ray spectroscopy (WDS) and optical transmission mappings. The measured radial ZnTe content was quite uniform for all the grown crystals except the horizontally grown crystal for x = 0.30. The WDS results on this crystal indicated a core with uniform ZnTe content, about 0.38, surrounded by a thin region of high ZnTe content with x = 0.8. This feature was confirmed by the SEM back scattering electron images. For the three source compositions the axial compositional variations for the vertically grown crystals were more uniform than that for the horizontally grown crystals. The measured compositions in the crystals grown from source composition of x = 0.10 suggest that the transport mechanism in the system can not be interpreted by a simple one-dimensional diffusion limited model.

Su, Ching-Hua; Sha, Yi-Gao; Volz, M. P.; Carpenter, P.; Lehoczky, S. L.

2000-01-01

161

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

162

Widely linear and non-phase-matched optical-to-terahertz conversion on GaSe:Te crystals.  

PubMed

We demonstrate the widely linear and broadband terahertz (THz) generation on GaSe:Te crystals by femtosecond laser pulses. It was found that the dopant, Te atoms, in GaSe crystals significantly enhances the efficiency of THz generation, and its central frequency can be tuned by varying the crystal thickness through non-phase-matched optical rectification. Moreover, the wide-ranging linearity for the optical-to-THz conversion and central-frequency-tunable THz generation promise for GaSe:Te crystals to be potential materials for high-power (>1.36 ?W) THz applications. PMID:22378447

Chu, Wei-Chen; Ku, Shin An; Wang, Harn Jiunn; Luo, Chih Wei; Andreev, Yu M; Lanskii, Grigory; Kobayashi, T

2012-03-01

163

Theoretical Characters of MgX (x = Te, Se, S and o) Clusters  

NASA Astrophysics Data System (ADS)

At DFT/B3LYP/LANL2DZ theoretical level, a series of MgX clusters with Mg3X3 hexagon, Mg4X4-t tetrahedron and Mg4X4-o octagon conformations are investigated. Their wavelengths of absorption spectra are calculated with time-dependent Density Functional Theory (TDDFT) using water as solvent. Firstly, the lowest vibrational frequencies, bond lengths, Dipole Moment and Raman spectra of them present regular change. Dipole Moment result shows that different clusters have different charges. From Raman spectra, we have discovered that they correlate with the conformation and variety of clusters. Conformations of MgO clusters have different optimizing characters with MgS, MgSe and MgTe molecules. Secondly, through Molecular Orbital and Nature Bond Orbital (NBO) analysis, we have found that all these clusters are materials with wider gaps. MgTe structures have stronger bonding. Besides, MgO have different transition from the other clusters. The order of wavelengths of absorption spectra is MgTe > MgSe > MgS. In a word, except MgO molecules, these clusters have similar or regular characters. These results are significant for experimental study of MgX nanocrystals.

Xu, Shuhong; Wang, Chunlei; Cui, Yiping

164

Electronic structure of ZnS, ZnSe, ZnTe, and their pseudobinary alloys  

NASA Astrophysics Data System (ADS)

Using the all-electron mixed-basis approach to the density-functional formalism for crystals, we calculate from first principles the electronic structure of zinc-blende ZnS, ZnSe, and ZnTe as well as that of their ordered pseudobinary alloys Zn2SSe, Zn2SeTe, and Zn2STe. For the latter we use as a model a CuAu I-like structure (space group P4¯m2), and analyze the observed optical bowing in terms of three contributions: (i) a volume deformation of the band structure due to the replacement of the lattice constants of the binary constituents by that of the alloy, (ii) a chemical-electronegativity contribution due to charge exchange in the alloy relative to its constituent binary subsystems, and (iii) a structural contribution due to the relaxation of the anion-cation bond lengths in the alloy. The total bowing effect [the sum of (i)-(iii) above] agrees well with observations, yet the present analysis suggests a physical mechanism for optical bowing which differs profoundly from that offered by the popular virtual-crystal approach. The maximum contribution of disorder to the optical bowing is calculated for ZnSxTe1-x using a cluster-averaging method, resulting in a reduction in the bowing of the fundamental gap. We further discuss the band structures, x-ray scattering factors, charge distribution, and deformation potentials of the binary zinc chalcogenides and their ordered alloys.

Bernard, James E.; Zunger, Alex

1987-08-01

165

Colloidal synthesis and characterization of CdSe/CdTe core/shell nanowire heterostructures  

NASA Astrophysics Data System (ADS)

CdSe/CdTe core/shell nanowire heterostructures were synthesized not only in a noncoordinating octadecene (ODE) solvent but also in a coordinating tri- n-octylphosphine oxide (TOPO) solvent, using a relatively safe CdO as the Cd precursor instead of the highly toxic Cd(Me) 2 by a colloidal approach. The polycrystalline CdTe shell was formed in the Volmer-Weber island mode, and its morphology was controlled by delicately adjusting the reaction parameters. The as-prepared core/shell nanowires were characterized by various electron microscopic techniques, energy-dispersive X-ray spectroscopy (EDX) and corresponding elemental mapping, X-ray diffraction (XRD), UV-vis spectroscopy and transient absorption spectroscopy.

Liu, Sheng; Zhang, Wen-Hua; Li, Can

2011-12-01

166

Quantum Oscillations in a topological insulator Bi2SeTe2 with large bulk resistivity  

NASA Astrophysics Data System (ADS)

To date, transport experiments on Topological Insulators are seriously hampered by bulk conductance Gb arising from impurity bands or band bending. Because of the large Gb, the surface currents carried by the massless Dirac surface states have been very difficult to resolve. We report measurements on the new topological insulator Bi2SeTe2 which has an unusually highly bulk resistivity ? (6 ?cm at 4 K, or 1,000 times higher than in Bi2Te3). Despite the large ?, Shubnikov-de Haas (SdH) oscillations are clearly resolved in the Hall conductance up to 38 K, which implies a very high surface mobility. In a field B of 14 T, Landau Levels (LLs) n = 4-9 are well resolved. We will describe the value of the Onsager phase ? fixed by the index plot of the LLs.

Xiong, Jun; Qu, Dongxia; Cava, Robert; Phuan Ong, N.

2011-03-01

167

The metal-rich palladium chalcogenides Pd2MCh2 (M=Fe, Co, Ni; Ch=Se, Te): Crystal structure and topology of the electron density  

Microsoft Academic Search

Crystals of Pd2MCh2 (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 K2ZnO2 type (Ibam, Z=4, Pd2CoSe2: a=5.993(1), b=10.493(2), c=5.003(1) Å; Pd2FeSe2: a=5.960(1), b=10.576(2), c=5.078(1) Å; Pd2CoTe2: a=6.305(1),

Regina Pocha; Catrin Löhnert; Dirk Johrendt

2007-01-01

168

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

Microsoft Academic Search

Crystals of Pd2MCh2 (M=Fe, Co, Ni; Ch=Se, Te) were synthesized by heating the elements at 823–1323K 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 K2ZnO2 type (Ibam, Z=4, Pd2CoSe2: a=5.993(1), b=10.493(2), c=5.003(1) Å; Pd2FeSe2: a=5.960(1), b=10.576(2), c=5.078(1) Å; Pd2CoTe2: a=6.305(1), b=11.100(2), c=5.234(1)

Regina Pocha; Catrin Loehnert; Dirk Johrendt

2007-01-01

169

Fabrication of CuInTe2 and CuInTe(2-x)Se(x) ternary gradient quantum dots and their application to solar cells.  

PubMed

We report the first synthesis of colloidal CuInTe2, CuInTe2-xSex gradient alloyed quantum dots (QDs) through a simple hot injection method. We confirmed the composition of synthesized QDs to cationic rich phase of CuIn1.5Te2.5 and Cu0.23In0.36Te0.19Se0.22 with XPS and ICP analysis, and we have also found that the gradient alloyed Cu0.23In0.36Te0.19Se0.22 QDs exhibit greatly improved stability over the CuIn1.5Te2.5 QDs. The solution-processed solar cell based on the gradient alloyed Cu0.23In0.36Te0.19Se0.22 QDs exhibited 17.4 mA/cm(2) of short circuit current density (Jsc), 0.40 V of open circuit voltage (Voc), 44.1% of fill factor (FF), and 3.1% of overall power conversion efficiency at 100 mW/cm(2) AM 1.5G illumination. PMID:23656273

Kim, Sungwoo; Kang, Meejae; Kim, Seajin; Heo, Jin-Hyuk; Noh, Jun Hong; Im, Sang Hyuk; Seok, Sang Il; Kim, Sang-Wook

2013-06-25

170

Raman spectra of CuInTe2, CuIn3Te5, and CuIn5Te8 ternary compounds  

NASA Astrophysics Data System (ADS)

From the analysis of Raman spectra, a comparative study of the lattice vibrational modes in CuInTe2, and of the ordered defect compounds (ODC) CuIn3Te5 and CuIn5Te8 of the Cu-In-Te system is reported. It is found that Raman lines in the ODCs appear at very nearly the same frequency as in CuInTe2. This is explained on the basis that the cation vacancy should not be considered merely as an empty site in the lattice but a localized region of positive Coulomb potential that attracts the valence electrons of the surrounding anions. It is proposed that the vacancy-Te force constant caused by the positive potential is of the same magnitude as in the Cu-Te stretching bond. The symmetry assignment of the observed lines is tentatively made by a comparative study of the vibrational modes of its binary analog Zn0.5Cd0.5Te, with phonon modes observed in CuInTe2 from polarized infrared optical measurements, and by estimating the modes frequency using several models reported in the literature for the chalcopyrite compounds. These are A1 mode at 127 cm-1 B1 at 58, 114, and 146 cm-1, E modes at around 48, 72, 137, 160, 192, and 218 cm-1 B2 at 64 and 104 cm-1 and E and/or B2 at 170 and 184 cm-1. The highest phonon frequencies observed at 237 and 270 cm-1 are attributed to the combination of E and B2 modes.

Rincón, C.; Wasim, S. M.; Marín, G.; Hernández, E.; Delgado, J. M.; Galibert, J.

2000-09-01

171

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

PubMed

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

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

2007-08-01

172

Proximity-effect-induced superconductivity in Bi2Se3 and Bi2Te3  

NASA Astrophysics Data System (ADS)

In this talk I will present our experimental investigations on the proximity effect between conventional superconductors such as Sn, Pb and the strong spin-orbit coupling materials Bi2Se3 or Bi2Te3 [1-3]. Several types of hybrid devices were fabricated, and their electron transport properties were measured down to ˜10 milli-Kelvin temperatures. The results show that a superconducting phase can be easily induced in Bi2Se3 and Bi2Te3 single crystals by superconducting Pb electrodes that are deposited on the surface of the former. The induced superconducting phase can be regarded as a true superconducting phase, i.e., it has an energy gap of the order 0.1 meV, and carries a Josephson supercurrent over a distance as far as several microns. The conductance spectrum of the interface between the induced superconducting phase and the normal phase of Bi2Se3 or Bi2Te3 exhibits a zero-bias peak. Based on the induced superconducting phase, single Josephson junction devices and superconducting quantum interference devices (SQUIDs) were constructied, and their critical supercurrent were investigated as a function of applied magnetic flux. We will discuss the implication of the results in terms of the pairing symmetry of the induced superconducting phase.[4pt] [1] F. Yang, et al., Phys. Rev. B 85, 104508 (2012).[0pt] [2] F. M. Qu, et al., Scientific Reports 2, 339 (2012). [0pt] [3] F. Yang, et al., Phys. Rev. B 86, 134504 (2012).

Lu, Li; Shen, Jie; Ding, Yue; Qu, Fanming; Yang, Fan; Chen, Jun; Ji, Zhongqing; Liu, Guangtong; Fan, Jie; Jing, Xiunian; Yang, Changli

2013-03-01

173

Structural and physical–chemical properties of the CuGa 5Se 8, CuGa 3Se 5 and CuIn 3Se 5 compounds  

Microsoft Academic Search

Large-block (8×4×3 mm3) CuGa5Se8 crystals were obtained by the horizontal Bridgman method. Homogeneous CuGa3Se5 and CuIn3Se5 single crystals 12 mm in diameter and up to 40 mm in length were grown by directed crystallization of the melt. All three compounds were found to have the chalcopyrite-related structure. The melting points of these compounds were defined by means of the differential

N. S. Orlova; I. V. Bodnar; T. L. Kushner

2003-01-01

174

Numerical analysis of crystallization in amorphous Bi-Se-Te thin films  

NASA Astrophysics Data System (ADS)

The results obtained for the isothermal crystallization for Bi3Te17Se80 thin films have been used to determine the expressions for phase transformation rate for a non-isothermal regime. This formalism enables one to determine the apparent energies of the growth rate and nucleation rate. The results show that a temperature range exists where the heterogeneous crystallization is preponderant and, for higher temperatures, the crystallization becomes homogenous with crystallites of size greater than the film thickness. The apparent activation energy for nucleation EN is about 1.09eV while for growth E? is 0.55eV.

Kalla, Jaya; Suthar, B.; Bhargava, A.

2013-06-01

175

Band-overlap metallization of BaS, BaSe and BaTe  

NASA Technical Reports Server (NTRS)

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%.

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

1983-01-01

176

Relativistic calculation of the SeH 2 and TeH 2 photoelectron spectra  

NASA Astrophysics Data System (ADS)

Photoelectron (PE) spectra provide detailed insight into the electronic structure of atoms, molecules and solids. Hereby electron correlation and relativistic effects influence the structure of the PE spectrum in a complicated way necessitating a consistent theoretical treatment. By embedding the one-particle propagator technique in a four-component framework the interplay between relativistic and correlation effects can be described correctly. In this article the Dirac-Hartree-Fock algebraic diagrammatic construction scheme (DHF-ADC) together with recent applications is reviewed and fully relativistic PE spectra of SeH 2 and TeH 2 in combination with basis set studies are presented.

Pernpointner, Markus

2006-10-01

177

Size-dependent absorption properties of CdX (X = S, Se, Te) quantum dots  

NASA Astrophysics Data System (ADS)

A unified nanothermodynamic model was developed to study the size effects on first absorption peak energy and molar extinction coefficient of semiconductor quantum dots (QDs) based on size-dependent cohesive energy and quantum confinement effect. It is found that: (1) the first absorption peak energy increases as QD size decreases; (2) the molar extinction coefficient decreases with decreasing QD size in strong confinement regime and (3) tunable absorption properties of semiconductor QDs are caused by size-induced cohesive energy variation owing to severe bond dangling. The accuracy of the developed model was verified with experimental data of CdS, CdSe and CdTe QDs.

Yang, C. C.; Mai, Y.-W.

2012-05-01

178

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

PubMed

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

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

2013-02-20

179

Thermal physics of the lead chalcogenides PbS, PbSe, and PbTe from first principles  

NASA Astrophysics Data System (ADS)

The lead chalcogenides represent an important family of functional materials, in particular due to the benchmark high-temperature thermoelectric performance of PbTe. A number of recent investigations, experimental and theoretical, have aimed to gather insight into their unique lattice dynamics and electronic structure. However, the majority of first-principles modeling has been performed at fixed temperatures, and there has been no comprehensive and systematic computational study of the effect of temperature on the material properties. We report a comparative lattice-dynamics study of the temperature dependence of the properties of PbS, PbSe, and PbTe, focusing particularly on those relevant to thermoelectric performance, viz. phonon frequencies, lattice thermal conductivity, and electronic band structure. Calculations are performed within the quasiharmonic approximation, with the inclusion of phonon-phonon interactions from many-body perturbation theory, which are used to compute phonon lifetimes and predict the lattice thermal conductivity. The results are critically compared against experimental data and other calculations, and add insight to ongoing research on the PbX compounds in relation to the off-centering of Pb at high temperatures, which is shown to be related to phonon softening. The agreement with experiment suggests that this method could serve as a straightforward, powerful, and generally applicable means of investigating the temperature dependence of material properties from first principles.

Skelton, Jonathan M.; Parker, Stephen C.; Togo, Atsushi; Tanaka, Isao; Walsh, Aron

2014-05-01

180

Preparation of Uncapped CdSe x Te1- x Nanocrystals with Strong Near-IR Tunable Absorption  

NASA Astrophysics Data System (ADS)

Semiconducting nanocrystals with near-infrared (NIR) photosensitivity are appealing materials for application as photodetectors and in medical diagnostics. Herein, we report the preparation of composition-tunable, uncapped CdSe x Te1- x ( x = 0 to 1) nanocrystals by simple mechanical alloying. The resulting ternary CdSe x Te1- x ( x = 0.25, 0.5, 0.75) nanocrystals with average sizes smaller than 10 nm have zincblende crystal structure, instead of the wurtzite structure commonly obtained by wet chemical routes, and show strong NIR absorption even beyond 1400 nm. While a linear relationship between the lattice parameter and the chemical composition (Se/Te ratio) is observed, indicating the formation of homogeneous alloys, the bandgap energy of the three ternary samples is found to be substantially lower than that of binary CdSe or CdTe nanocrystals, and lower than any ternary CdSeTe reported so far. Existence of a small number of tellurium metal defects in the CdSe x Te1- x ( x = 0.25, 0.5, 0.75) nanocrystals is confirmed by x-ray diffraction and Raman spectroscopy. Both the optical bowing effect and tellurium metal-induced defects of the mechanically alloyed samples are believed to cause the strong NIR photosensitivity.

Li, Shaohua; Tan, Guolong; Murowchick, James B.; Wisner, Clarissa; Leventis, Nickolas; Xia, Ting; Chen, Xiaobo; Peng, Zhonghua

2013-12-01

181

Stability, electronic, and magnetic properties of the magnetically doped topological insulators Bi2Se3,Bi2Te3, and Sb2Te3  

NASA Astrophysics Data System (ADS)

Magnetic interaction with the gapless surface states in a topological insulator (TI) has been predicted to give rise to a few exotic quantum phenomena. However, the effective magnetic doping of TI is still challenging in the experiment. Using first-principles calculations, the magnetic doping properties (V, Cr, Mn, and Fe) in three strong TIs (Bi2Se3,Bi2Te3, and Sb2Te3) are investigated. We find that for all three TIs the cation-site substitutional doping is most energetically favorable with the anion-rich environment as the optimal growth condition. Further, our results show that under the nominal doping concentration of 4%, Cr- and Fe-doped Bi2Se3,Bi2Te3, and Cr-doped Sb2Te3 remain as insulators, while all the V- and Mn-doped TIs, and Fe-doped Sb2Te3 become metal. We also show that the magnetic interaction of Cr-doped Bi2Se3 tends to be ferromagnetic, while Fe-doped Bi2Se3 is likely to be antiferromagnetic. Finally, we estimate the magnetic coupling and the Curie temperature for the promising ferromagnetic insulator (Cr-doped Bi2Se3) by Monte Carlo simulation. These findings may provide important guidance for the magnetism incorporation in TIs experimentally.

Zhang, Jian-Min; Ming, Wenmei; Huang, Zhigao; Liu, Gui-Bin; Kou, Xufeng; Fan, Yabin; Wang, Kang L.; Yao, Yugui

2013-12-01

182

MBE grown BeTe and ZnBeTe films as a new p-contact layer of ZnSe-based II VI lasers  

NASA Astrophysics Data System (ADS)

Non-alloyed Au/p-ZnSe/p-BeTe ohmic contact layers for ZnSe-based blue-green laser diodes with contact resistivity as low as 4.2×10 -4 ? cm 2 are reported. This contact layer is basically dislocation free due to small lattice misfit as long as the thickness is thinner than 500 Å, as confirmed by transmission electron microscopy (TEM) observation. The ZnSe layer serves as a contact layer for BeTe and protecting layer against oxidation as well. The electrical properties of the contact layers are strongly dependent on the ZnSe layer thickness. Au diffusion through the ZnSe layer down to the BeTe layer at room temperature is found to be responsible for ohmic properties. A series of ZnBeTe epilayers with different x values have been grown on GaAs by molecular beam epitaxy (MBE). We can easily control the composition by changing the Zn or Be cell temperatures. Hall effect measurement was performed on as-grown Zn 0.05Be 0.95Te epilayer doped with nitrogen. Hole concentration as high as 2×10 19 cm -3 has been achieved.

Cho, M. W.; Hong, S. K.; Chang, J. H.; Saeki, S.; Nakajima, M.; Yao, T.

2000-06-01

183

Thickness dependence study of inorganic CdTe/CdSe solar cells fabricated from colloidal nanoparticle solutions  

NASA Astrophysics Data System (ADS)

The thickness dependence of cadmium telluride/cadmium selenide (CdTe/CdSe) heterojunctions is studied in order to maximize the performance of solar cells. The best overall performance of 3.02% efficiency at air mass 1.5 was achieved from a device with 300 nanometers (nm) of sintered CdTe and 100 nm CdSe, using indium tin oxide and evaporated aluminum as the electrodes. In contrast to thin film CdTe solar cells, the power efficiency was strongly dependent on the thickness of the nanoparticle layer, indicating that the device efficiency is limited by charge transport.

Ju, Tong; Yang, Lily; Carter, Sue

2010-05-01

184

Electronic structure and magnetic properties of transition-metal doped Bi2Te3, Bi2Se3, and Sb2Te3 for diluted magnetic semiconductors  

Microsoft Academic Search

The semiconducting tetradymite-structure materials Bi2Te3, Bi2Se3, and Sb2Te3 serve as the basis for high-performance room-temperature thermoelectric devices. Recently, it was found that these materials act as diluted magnetic semiconductors (DMS) with Tc˜ 10 K using a few percent doping of transition metal atoms (T = Ti, V, Cr, Mn, Fe). Electronic structure calculations have been performed using the full-potential linear

Paul Larson

2005-01-01

185

Thermoelectric properties of Bi 2 Te 3 Sb 2 Te 3 Sb 2 Se 3 pseudo-ternary alloys in the temperature range 77 to 300° K  

Microsoft Academic Search

The electrical resistivity, thermoelectric power and thermal conductivity of pseudo-ternary Bi2Te3-Sb2Te3-Sb2Se3 alloys were measured in the temperature range 77 to 300° K. From these measurements, figures of merit at various temperatures were calculated and compared with effective figures of merit obtained from the results of Peltier cooling. Best n-type figure of merit, 3.2×10-3 deg at 300° K, was found at

W. M. Yim; E. V. Fitzke; F. D. Rosi

1966-01-01

186

Thermoelectric and Galvanomagnetic Measurements on (Bi2Te3)5(Bi2Se3)1 (Sb2Te3)18  

Microsoft Academic Search

The galvanomagnetic parameters &rgr;123, &rgr;1111, &rgr;1133, &rgr;1131, and &rgr;1122 have been measured at 77°K for two samples of p-type (Bi2Te3)5(Bi2Se3)1 (Sb2Te3)18 and the results fitted to a six-ellipsoid model similar to that proposed for Bi2Te3. An anomalous rise in the Hall coefficient with temperature and an apparent change in the effective mass ratios are explained by assuming the existence of

Richard J. Schwartz

1967-01-01

187

Crystallization of the chalcogenide compound Sb8Te3.  

PubMed

The crystallization of a sputtered Sb(8)Te(3) film was examined in an X-ray powder diffraction experiment. An as-sputtered, amorphous Sb(8)Te(3) film crystallized during heating into a structure of Sb-Te homologous series modulated along the stacking direction. During heating the lattice parameters and the modulation period ? were found to change significantly and continuously; this observation suggests a continuous change in the stacking sequence. A superspace analysis revealed that with heating the modulation period ? increased to a value that seemed to be determined by the atomic composition. Once ? reached this value it remained unchanged with cooling. A three-dimensional projection of the converged four-dimensional superspace structure corresponded to the homologous Sb(8)Te(3) structure. PMID:21931207

Kifune, Kouichi; Fujita, Tomoko; Kubota, Yoshiki; Yamada, Noboru; Matsunaga, Toshiyuki

2011-10-01

188

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

SciTech Connect

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.

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

1990-04-01

189

Phototropic growth control of nanoscale pattern formation in photoelectrodeposited Se-Te films  

PubMed Central

Photoresponsive materials that adapt their morphologies, growth directions, and growth rates dynamically in response to the local incident electromagnetic field would provide a remarkable route to the synthesis of complex 3D mesostructures via feedback between illumination and the structure that develops under optical excitation. We report the spontaneous development of ordered, nanoscale lamellar patterns in electrodeposited selenium–tellurium (Se–Te) alloy films grown under noncoherent, uniform illumination on unpatterned substrates in an isotropic electrolyte solution. These inorganic nanostructures exhibited phototropic growth in which lamellar stripes grew toward the incident light source, adopted an orientation parallel to the light polarization direction with a period controlled by the illumination wavelength, and showed an increased growth rate with increasing light intensity. Furthermore, the patterns responded dynamically to changes during growth in the polarization, wavelength, and angle of the incident light, enabling the template-free and pattern-free synthesis, on a variety of substrates, of woodpile, spiral, branched, or zigzag structures, along with dynamically directed growth toward a noncoherent, uniform intensity light source. Full-wave electromagnetic simulations in combination with Monte Carlo growth simulations were used to model light–matter interactions in the Se–Te films and produced a model for the morphological evolution of the lamellar structures under phototropic growth conditions. The experiments and simulations are consistent with a phototropic growth mechanism in which the optical near-field intensity profile selects and reinforces the dominant morphological mode in the emergent nanoscale patterns.

Sadtler, Bryce; Burgos, Stanley P.; Batara, Nicolas A.; Beardslee, Joseph A.; Atwater, Harry A.; Lewis, Nathan S.

2013-01-01

190

Electronic Structures and Chemical Bonding of TiX2 (X=S, Se, and Te)  

NASA Astrophysics Data System (ADS)

A systematic study of the electronic structures and chemical bonding of the titanium dichalcogenide TiX2 (X=S, Se, and Te) layered structures is performed by a first-principles molecular orbital calculation using the discrete-variational (DV)-X? cluster method. The intra- and interlayer chemical bonding properties are also investigated using the bond overlap population. Valence band structures obtained by the calculation are in good agreement with experimental results obtained by X-ray photoemission spectroscopy. Each peak in the density of states (DOS) is identified from the viewpoint of chemical bonding. There is a considerably strong covalent bonding between Ti and chalcogen atoms in TiX2. The covalency of chemical bonding is shown to increase and the ionicity to decrease in the series of TiS2 TiSe2 TiTe2. Both in intra- and interlayer chalcogen-chalcogen bonding and intralayer Ti Ti bonding are much weaker than Ti-chalcogen intralayer bonding. However, interlayer interaction is found to be not purely of the van der Waals type.

Kim, Yang-Soo; Mizuno, Masataka; Tanaka, Isao; Adachi, Hirohiko

1998-09-01

191

Synthesis, structure, and optical properties of BiCuOCh (Ch=S, Se, and Te)  

SciTech Connect

Crystals of BiCuOSe were grown from a salt flux, and the crystal structure was determined by single-crystal X-ray diffraction. BiCuOSe adopts the tetragonal layered structure of LnCuOCh (Ln=lanthanide; Ch=S, Se, and Te) with bond lengths and bond angles in good agreement with those published for powders. Powders comprising mixed chalcogenides across the series BiCuOCh (Ch=S, Se, and Te) were made by reacting Bi{sub 2}O{sub 2}Ch and Cu{sub 2}Ch. Band gaps determined via infrared diffuse reflectance from powders are E{sub g}=0.82 eV for BiCuOSe, 0.89 eV for BiCuOS{sub 0.5}Se{sub 0.5}, and 1.07 eV for BiCuOS. The band gap of BiCuOSe inferred from infrared transmission measurements on single crystals is in good agreement with the value obtained from diffuse reflectance from the powder. - Graphical abstract: IR absorption of BiCuOCh powders from diffuse reflection (left scale) and polished BiCuOSe single crystal from transmission (right scale). Spectra are normalized to the maximum absorption. Inset: band gap as a function of composition. Highlights: Black-Right-Pointing-Pointer BiCuOSe single crystals are synthesized, and the band gap is measured by direct transmission. Black-Right-Pointing-Pointer A new powder synthesis of BiCuOCh{sub 1-x}Ch Prime {sub x} is demonstrated. Black-Right-Pointing-Pointer Band gaps of BiCuO(S{sub 1-x}Se{sub x}) are determined from diffuse reflection from powders.

Richard, A.P. [Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, OR 97331-4003 (United States); Russell, J.A.; Zakutayev, A. [Department of Physics, Oregon State University, 301 Weniger Hall, Corvallis, OR 97331-6507 (United States); Zakharov, L.N.; Keszler, D.A. [Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, OR 97331-4003 (United States); Tate, J., E-mail: tate@physics.oregonstate.edu [Department of Physics, Oregon State University, 301 Weniger Hall, Corvallis, OR 97331-6507 (United States)

2012-03-15

192

Enhanced thermoelectric properties of N-type polycrystalline In4Se3-x compounds via thermally induced Se deficiency  

NASA Astrophysics Data System (ADS)

In4Se3-x compound is considered as a potential thermoelectric material due to its comparably low thermal conductivity among all existing ones. While most studies investigated In4Se3-x thermoelectric properties by controlling selennium or other dopants concentrations, in the current study, it was found that even for a fixed initial In/Se ratio, the resulting In/Se ratio varied significantly with different thermal processing histories (i.e., melting and annealing), which also resulted in varied thermoelectric properties as well as fracture surface morphologies of In4Se3-x polycrystalline specimens. Single phase polycrystalline In4Se3-x compounds were synthesized by combining a sequence of melting, annealing, pulverizing, and spark plasma sintering. The extension of previous thermal history was observed to significantly improve the electrical conductivity (about 121%) and figure of merit (about 53%) of In4Se3-x polycrystalline compounds. The extended thermal history resulted in the increase of Se deficiency (x) from 0.39 to 0.53. This thermally induced Se deficiency was observed to associate with increasing carrier mobility but decreasing concentration, which differs from the general trend observed for the initially adjusted Se deficiency at room temperature. Unusually large dispersed grains with nanosize layers were observed in specimens with the longest thermal history. The mechanism(s) by which previous thermal processing enhances carrier mobility and affect microstructural evolution are briefly discussed.

Zhao, Ran; Shu, Yu-Tian; Guo, Fu

2014-03-01

193

Y2MoSe3O12 and Y2MoTe3O12: Solid-state synthesis, structure determination, and characterization of two new quaternary mixed metal oxides containing asymmetric coordination environment  

NASA Astrophysics Data System (ADS)

Two new quaternary yttrium molybdenum selenium/tellurium oxides, Y2MoSe3O12 and Y2MoTe3O12 have been prepared by standard solid-state reactions using Y2O3, MoO3, and SeO2 (or TeO2) as reagents. Single-crystal X-ray diffraction was used to determine the crystal structures of the reported materials. Although both of the materials contain second-order Jahn-Teller (SOJT) distortive cations and are stoichiometrically similar, they reveal different structural features: while Y2MoSe3O12 shows a three-dimensional framework consisting of YO8, MoO6, and SeO3 groups, Y2MoTe3O12 exhibits a layered structure composed of YO8, MoO4, TeO3, and TeO4 polyhedra. With the Mo6+ cations in Y2MoSe3O12, a C3-type intraoctahedral distortion toward a face is observed, in which the direction of the out-of-center distortion for Mo6+ is away from the oxide ligand linked to a Se4+ cation. The Se4+ and Te4+ cations in both materials are in asymmetric coordination environment attributed to the lone pairs. Elemental analyses, infrared spectroscopy, thermal analyses, intraoctahedral distortions, and dipole moment calculations for the compounds are also presented.

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

2013-12-01

194

Material engineering of GexTe100-x compounds to improve phase-change memory performances  

NASA Astrophysics Data System (ADS)

In this paper we provide a detailed physical and electrical characterization of Germanium Telluride compounds (GexTe100-x) targeting phase-change memory applications. Thin films of Germanium-rich as well as Tellurium-rich phase-change materials are deposited for material analysis (XRD, resistivity and optical characterization). GexTe100-x compounds are then integrated in lance-type analytical phase-change memory devices allowing for a thorough analysis of the switching characteristics, data retention and endurance performances. Tellurium-rich GeTe alloys exhibit stable programming characteristics and can sustain endurance up to 107 cycles, while Germanium-rich compounds show an unstable RESET state during repeated write/erase cycles, probably affected by Ge segregation. Finally we demonstrate that data retention is strongly improved departing from Ge50Te50 stoichiometric composition.

Navarro, G.; Sousa, V.; Persico, A.; Pashkov, N.; Toffoli, A.; Bastien, J.-C.; Perniola, L.; Maitrejean, S.; Roule, A.; Zuliani, P.; Annunziata, R.; De Salvo, B.

2013-11-01

195

Rich Structural Chemistry in Scandium Selenium/Tellurium Oxides: Mixed-Valent Selenite-Selenates, Sc2(SeO3)2(SeO4) and Sc2(TeO3)(SeO3)(SeO4), and Ternary Tellurite, Sc2(TeO3)3.  

PubMed

Both single crystals and pure bulk phases of three new scandium selenium/tellurium oxides, Sc2(SeO3)2(SeO4), Sc2(TeO3)(SeO3)(SeO4), and Sc2(TeO3)3, have been synthesized through hydrothermal and solid-state reactions. X-ray diffractions were used to determine the structures and confirm the phase purities of the reported materials. Isostructural Sc2(SeO3)2(SeO4) and Sc2(TeO3)(SeO3)(SeO4) reveal three-dimensional frameworks with ScO7 pentagonal bipyramids, SeO3 (and TeO3) trigonal pyramids, and SeO4 tetrahedra. A novel ternary scandium tellurite, Sc2(TeO3)3, also shows a three-dimensional framework that is composed of ScO6 octahedra, ScO7-capped octahedra, and TeO3 trigonal pyramids. All three materials accommodate local asymmetric coordination moieties owing to the lone pairs on Se(4+) and Te(4+) cations. The effect of coordination environments of constituent cations on the frameworks, dimensionalities, and centricities of products is discussed. Thorough characterizations including elemental analyses, infrared and UV-vis diffuse reflectance spectroscopies, thermal analyses, and dipole moment calculations for the reported materials are reported. Crystal data: Sc2(SeO3)2(SeO4), monoclinic, space group P21/c (No. 14), a = 6.5294(2) Å, b = 10.8557(4) Å, c = 12.6281(6) Å, ? = 103.543(3)°, V = 870.21(6) Å(3), and Z = 4; Sc2(TeO3)(SeO3)(SeO4), monoclinic, space group P21/c (No. 14), a = 6.5345(12) Å, b = 10.970(2) Å, c = 12.559(2) Å, ? = 102.699(10)°, V = 878.3(6) Å(3), and Z = 4; Sc2(TeO3)3, monoclinic, space group P21/n (No. 14), a = 5.2345(3) Å, b = 24.3958(15) Å, c = 6.8636(4) Å, ? = 106.948(2)°, V = 838.42(9) Å(3), and Z = 4. PMID:24918773

Song, Seung Yoon; Lee, Dong Woo; Ok, Kang Min

2014-07-01

196

Low-Cost Lattice Matching Zn(Se)Te/Si Composite Substrates for HgCdSe and Type-2 Superlattices.  

National Technical Information Service (NTIS)

Growth of ZnTe on Si using molecular beam epitaxy (MBE) has been pursued as a new approach for a lattice-matched, large-area, low-cost alternate substrate for both II-VI and III-V compound semiconductors with lattice constants very near 6.1 , such as HgCd...

Y. Chen

2013-01-01

197

Thermoelectric Properties of Cu2HgSnSe4-Cu2HgSnTe4 Solid Solution  

NASA Astrophysics Data System (ADS)

Copper-based semiconductors from the family Cu2-II-IV-VI4 have recently attracted a great deal of attention because of their promising thermoelectric (TE) properties. Polycrystalline samples from the Cu2HgSnSe x Te4âˆ'x (x = 0, 0.8, 2, 3.2, 4) solid solution were prepared and structurally characterized by powder x-ray diffraction. The samples from this solid solution crystallize in the stannite structure (space group Ibar{4}2m ). Transport, TE, and thermal properties of hot-pressed samples are reported. About a 20 % reduction in calculated lattice thermal conductivities, compared to the lattice thermal conductivities of pure components of the alloys (i.e. Cu2HgSnSe4 and Cu2HgSnTe4), was observed for Cu2HgSnSe2Te2 alloy. The maximum ZT of the Cu2HgSnSe2Te2 sample reaches 0.6 at 575 K.

Navrátil, J.; Kucek, V.; Plechá?ek, T.; ?ernošková, E.; Laufek, F.; Drašar, ?.; Knotek, P.

2014-03-01

198

Nitrogen doping of Te-based II-VI compounds during growth by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

We present a detailed study of p-type doping of Te-based compounds (CdTe, ZnTe) and alloys (CdMgTe, ZnMgTe, and CdZnTe) during molecular beam epitaxy, using nitrogen atoms produced by a direct current glow plasma source. Characterization includes capacitance-voltage, Hall effect, low temperature reflectivity and luminescence, double crystal x-ray diffraction (XRD), nuclear reaction analysis and secondary ion mass spectroscopy. Doping introduces shallow hydrogenic acceptors NTe, whose ionization energy was determined. For ZnTe, doping as high as p~1020 cm-3 can be obtained when ~1.5×1020 cm-3 nitrogen atoms are incorporated in the layer. This doping level decreases considerably for CdZnTe and ZnMgTe alloys as the Zn content decreases. The highest concentration obtained for CdTe is p~1018 cm-3. For a CdTe layer with a doping level p~1017 cm-3 the hole mobility is ?p=235 cm2/V s at 65 K. In ZnTe, incorporation of nitrogen atoms in NTe configurations induces a noticeable change of the lattice parameter, a change which was not observed in CdTe:N layers. The XRD pattern of ZnTe:N/ZnTe pseudosuperlattices allows measurement of the Zn-N bond distance dZn-N=2.16+/-0.05 Å. Study of the doping efficiency as a function of the growth conditions indicates that the compensation mechanism is related to the formation of nitrogen interstitial defects or complex defects involving metal vacancies, but no deep center has been detected in luminescence. A comparative study of various doped telluride materials indicates that presence of Zn atoms strongly enhances the solubility limit of NTe, hence the key role of Zn in the doping efficiency. Results are discussed on the basis of geometric and thermodynamic considerations. The first argument is that the Zn-Te distance is the closest fit to the metal-N bond distance, and this minimizes the elastic contribution to the energy of formation of the NTe acceptor. As a corollary, the doping efficiency decreases when the alloy lattice parameter increases. The second argument compares the formation enthalpies ?HF of II3N2 nitride (II being Zn, Cd, or Mg) to that of the IITe compound.

Baron, T.; Saminadayar, K.; Magnea, N.

1998-02-01

199

Intermolecular weak interactions in HTeXH dimers (X=O, S, Se, Te): hydrogen bonds, chalcogen-chalcogen contacts and chiral discrimination.  

PubMed

A theoretical study of the HTeXH (X=O, S, Se and Te) monomers and homodimers was carried out by means of second-order Møller-Plesset perturbation theory (MP2) computational methods. In the case of monomers, the isomerization energy from HTeXH to H(2) Te=X and H(2) X=Te (X=O, S, Se, and Te) and the rotational transition-state barriers were obtained. Due to the chiral nature of these compounds, homo and heterochiral dimers were found. The electron density of the complexes was characterized with the atoms-in-molecules (AIM) methodology, finding a large variety of interactions. The charge transfer within the dimers was analyzed by means of natural bond orbitals (NBO). The density functional theory-symmetry adapted perturbation theory (DFT-SAPT) method was used to compute the components of the interaction energies. Hydrogen bonds and chalcogen-chalcogen interactions were characterized and their influence analyzed concerning the stability and chiral discrimination of the dimers. PMID:22253208

Sánchez-Sanz, Goar; Trujillo, Cristina; Alkorta, Ibon; Elguero, José

2012-02-01

200

Enhanced performances of melt spun Bi 2(Te,Se) 3 for n-type thermoelectric legs  

Microsoft Academic Search

In this article, a rapid and cost-effective melt spinning (MS) subsequently combined with a spark plasma sintering (SPS) process was utilized to prepared n-type Bi2(Te1?xSex)3 (x = 0.0–1.0) solid solutions from high purity single elemental chunks. The substitution of tellurium by selenium has significant impacts on the electrical and thermal transport properties of the Bi2(SexTe1?x)3 compounds in a manner which can be

Shanyu Wang; Wenjie Xie; Han Li; Xinfeng Tang

2011-01-01

201

Electrical conductivity, photoconductivity and gas sensitivity of Ge-Se-Te thin films  

NASA Astrophysics Data System (ADS)

Films of GexSeyTez (x?33) with a thickness of 0.8 ?m and four different compositions were prepared by thermal evaporation of preliminary synthesized glasses. The glass and film compositions were determined by Energy-Dispersive X-ray Spectroscopy. X-ray diffraction measurements have confirmed the amorphous structure of both bulk and thin film samples. The temperature dependence of the dark conductivity has been measured in the range 20 - 110 °C. No significant change of the room temperature conductivity (around 5x10-7 S/cm) and the dark current activation energy (around 0.7 eV) have been observed with increasing z. Spectral photocurrent measurements have revealed that the increase of Te content results in: (i) a photoconductivity decrease and (ii) a red shift of the low-energy side of the spectrum which indicates an optical band gap decrease. Resistive chemical sensing tests carried out at room temperature with ammonia, acetone, ethanol or water vapours in air as carrying gas have shown that the Ge32Se55Te13 films are sensitive to ammonia but not to water vapour and hence they are suitable for selective ammonia sensors operating at room temperature. The observed sensitivity is related to the specific lattice structure of the region nearest to the film surface.

Nesheva, D.; Levi, Z.; Raptis, Y. S.; Raptis, C.; Petkov, K.; Vassilev, V.

2012-12-01

202

Structural and Electronic Properties in multilayer (BiSe)n(TiSe2)m Misfit compounds  

NASA Astrophysics Data System (ADS)

The nature of the charge density wave (CDW) transition in 1T-TiSe2 has been hotly debated, and variously described as a simple CDW to the formation of an excitonic insulator. Here we report the synthesis and basic physical properties of the incommensurate layered chalcogenides (BiSe)n(TiSe2)m. Their structure consists of a rock-salt type BiSe layer separated by one or more edge-sharing TiSe2 octahedral layer. These octahedral layers are isomorphic to the layers found in 1T-TiSe2, and thus provide a mechanism to study the electronically driven structural transition in TiSe2 as a function of the number of layers. Structural determinations from electron and x-ray diffraction, using 4/5-D superspace approach, will be presented, and the implications of our results on the understanding of CDW formation in TiSe2 will be discussed. The effects of doping with Cu to observe possible superconducting behavior is also explored.

Trump, Benjamin; Siegler, Maxime; Livi, Ken; McQueen, Tyrel

2013-03-01

203

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

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

204

Weak anti-localization behavior in Bi2(SeTe)3 grown on GaAs (001) substrate  

NASA Astrophysics Data System (ADS)

A series of Bi2(SeTe)3 thin films were grown by molecular beam epitaxy on GaAs(001) substrates in order to obtain ternary Te-Bi-Se-Bi-Te alloys with large bulk resistivities. X-Ray diffraction data reveals many reflections from only the 003-type lattice planes, indicative of highly directed c-axis growth of these films despite the very different crystal symmetries of the film and the substrate along the film growth direction. The X-ray data reveal that a wide spectrum of mixed Bi2(SeTe)3 alloys can be obtained by this method [1]. Our studies show that the alloy films are highly uniform, and the crystallinity is comparable to that of films grown on substrates with hexagonal surface structure. In this work, we have carried out comprehensive magneto-transport measurements on a series of Bi2(SeTe)3 thin films. We find that the conductivities of the films are strongly affected by alloy composition, and that insulating samples can be obtained at Se concentrations of ˜30%. Moreover, we observe weak anti-localization behavior in all samples, which is also composition-dependent. In order to understand diffusive transport in these topological insulator alloys, both disorder and electron-electron interaction effects are considered in our analysis. [1] X. Liu et al, J. Vac. Sci. Tech. B (submitted).

Hagmann, Joseph; Furdyna, Jacek; Dobrowolska, Malgorzata; Liu, Xinyu

2012-02-01

205

Modifications of the electronic structure of GaSb surface by chalcogen atoms: S, Se, and Te  

NASA Astrophysics Data System (ADS)

Modifications to the electronic properties and chemical structures of the GaSb surface using the chalcogen atoms S, Se, and Te were investigated theoretically and experimentally. A self-consistent density-functional theory study indicates that an adsorption of a full monolayer coverage of chalcogen atoms on a Ga-terminated surface reduces the density of gap region states significantly. A greater photoluminescence enhancement was observed from GaSb samples treated by chalcogenide (Na2S, Na2Se, or Na2Te) in a nonaqueous than in an aqueous passivation medium. X-ray photoelectron spectroscopy reveals a Ga-rich surface after a nonaqueous passivation, with sulfidization providing a higher concentration of Ga(Sb)-chalcogen bonds than does a passivation with Na2Se or Na2Te. The uptake of chalcogen during the passivation is accompanied by the loss of surface antimony. The formation of Sb-X(X=S, Se, or Te) bonds competes with X displacing surface Sb, which dominates Se or Te incorporation in the GaSb surface lattice. The passivation kinetics was analyzed on basis of a single precursor-mediated coverage-dependent chemisorption proces.

Liu, Z. Y.; Gokhale, A. A.; Mavrikakis, M.; Saulys, D. A.; Kuech, T. F.

2004-10-01

206

Fe-Te-Se epitaxial thin films with enhanced superconducting properties  

NASA Astrophysics Data System (ADS)

Epitaxial Fe-Te-Se thin films were deposited by pulsed laser deposition at 250-600?°C on SrTiO3 (100), MgO (100), LaAlO3 (100) and CaF2 (100) single crystal substrates. The best superconducting film was grown on CaF2: {T}_{{c}}^{{onset}}=2 0.0 K and {T}_{{c}}^{0}=1 6.1 8 K with Tdep = 300?°C and 3 Hz. Critical current density Jc (T = 4.2 K) was 0.41 × 106 A cm-2 at 0 T and 0.23 × 106 A cm-2 at 9 T. The angular dependence of Jc shows a broad c-axis correlated peak when B ? 3 T.

Mele, Paolo; Matsumoto, Kaname; Fujita, Kouhei; Yoshida, Yutaka; Kiss, Takanobu; Ichinose, Ataru; Mukaida, Masashi

2012-08-01

207

Terahertz conductivity in FeSe0.5Te0.5 superconducting films  

NASA Astrophysics Data System (ADS)

Complex conductivity of FeSe0.5Te0.5 superconducting films has been investigated using backward-wave-oscillator spectroscopy in the terahertz frequency range. The normal state conductivity corresponds well to the low-frequency limit of a Drude metal. In the superconducting state, the real part of the complex conductivity is not completely suppressed, indicating the existence of a strongly anisotropic gap. Weak features in the conductivity are consistent with the superconducting gap value close to 12 cm-1(1.5 meV). The experimental results are discussed within the framework of a two-gap model based on the s± symmetry of the order parameter.

Pimenov, A.; Engelbrecht, S.; Shuvaev, A. M.; Jin, B. B.; Wu, P. H.; Xu, B.; Cao, L. X.; Schachinger, E.

2013-01-01

208

Chalcogenide coatings of Ge15Sb20S65 and Te20As30Se50.  

PubMed

Chalcogenide coatings are investigated to obtain either optical components for spectral applications or optochemical sensors in the mid-infrared. The deposition of Ge(15)Sb(20)S(65) and Te(20)As(30)Se(50) chalcogenide glasses is performed by two physical techniques: electron-beam and pulsed-laser deposition. The quality of the film is analyzed by scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy to characterize the morphology, topography, and chemical composition. The optical properties and optical constants are also determined. A CF(4) dry etching is performed on these films to obtain a channeled optical waveguide. For a passband filter made by electron-beam deposition, cryolite as a low-refractive-index material and chalcogenide glasses as high-refractive-index materials are used to favor a large refractive-index contrast. A shift of a centered wavelength of a photosensitive passband filter is controlled by illumination time. PMID:18449231

Nazabal, Virginie; Cathelinaud, Michel; Shen, Weidong; Nemec, Petr; Charpentier, Frédéric; Lhermite, Hervé; Anne, Marie-Laure; Capoulade, Jérémie; Grasset, Fabien; Moreac, Alain; Inoue, Satoru; Frumar, Miloslav; Adam, Jean-Luc; Lequime, Michel; Amra, Claude

2008-05-01

209

Photosensitive post tuning of chalcogenide Te 20As 30Se 50 narrow bandpass filters  

NASA Astrophysics Data System (ADS)

We present an experimental study on the photosensitive properties of narrow bandpass filters based on a chalcogenide Te 20As 30Se 50 (TAS) spacer. The transmittance curve of single TAS layer was shifted towards long wavelength direction after 2 h exposure by Xenon arc lamp. The refractive index and extinction coefficient were both increased together with a red shift of optical gap. A maximum 1.7% photo-induced effect was observed. Narrow band filters constituted by TAS and cryolite were manufactured by electron beam deposition. The transmittance spectrum of the filter during the exposure by a wide band source was in situ measured and the resonant wavelength was observed to turn longer gradually till saturation. A spatially localized central wavelength change up to 5.7 nm was finally obtained. The stability of the photo-induced effect was studied and some comments were given at the end of this paper.

Shen, Weidong; Cathelinaud, Michel; Lequime, Michel; Nazabal, Virginie; Liu, Xu

2008-07-01

210

Photoconductivity of Se85-xTe15Hgx thin films  

NASA Astrophysics Data System (ADS)

The photoconductive properties such as dark conductivity, steady state and transient characteristics of a-Se85-xTe15Hgx thin films, prepared by thermal vacuum evaporation technique have been studied in the temperature range 312-380 K. Analysis of data shows that the activation energy of dark current is greater as compared to the activation energy of photocurrent. The activation energy increases at higher concentration of Hg which shows that the defect density of states decreases. Analysis of intensity dependent photoconductivity shows that the bimolecular recombination is predominant. The transient photoconductivity shows that the carrier lifetime decreases with the increase in Hg concentration and increases at higher concentration of Hg. This decrease is due to the transition trapping process. Further the photosensitivity and carrier lifetime increases at higher concentration of Hg which also confirms that the density of defect states decreases.

Chaudhary, Neetu; Bahishti, Adam A.; Zulfequar, M.

2012-06-01

211

Photoinduced fluorescence enhancement in colloidal CdSeTe/ZnS core/shell quantum dots  

NASA Astrophysics Data System (ADS)

Photoinduced fluorescence enhancement (PFE) in colloidal CdSeTe/ZnS core/shell quantum dots (QDs) was investigated by monitoring ensemble fluorescence and single-QD fluorescence blinking behavior upon illumination. Ensemble fluorescence was increased in air and in vacuum with different enhanced factors. At the single-QD levels, fluorescence was also enhanced for some individual QDs. Relatively long on times, high quantum yields within the on times, and multilevel on states were found in fluorescence time traces. We suggest that the PFE origin from single-QD viewpoint is attributed to the contributions of surface passivation by photoinduced charged carriers and the formation of neutral core/charged shell QD states.

Yuan, C. T.; Chou, W. C.; Chuu, D. S.; Chen, Y. N.; Lin, C. A.; Chang, W. H.

2008-05-01

212

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

213

Engineering topological surface states: HgS, HgSe, and HgTe.  

PubMed

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. PMID:24138263

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

2013-10-01

214

Morphological properties of Ag?SeTe nano thin films prepared by thermal evaporation.  

PubMed

Semiconducting silver selenide telluride (Ag?SeTe) thin films were prepared with different thicknesses onto glass substrates at room temperature using thermal evaporation technique. The structural properties were determined as a function of thickness by X-ray diffraction exhibiting no preferential orientation along any plane; however, the films are found to have peaks corresponding to mixed phase. The morphology of these films was studied using scanning electron microscope and atomic force microscopy respectively, and is reported. The morphological properties are found to be very sensitive to the thin film thickness. The composition of the films is also estimated using energy dispersive analysis using X-rays and are also reported. PMID:21756251

Vijayan, C; Soundararajan, N; Chandramohan, R; Dhanasekaran, V; Sundaram, K; Neyvasagam, K; Mahalingam, T

2011-09-01

215

Ultrafast exciton dynamics in Type II ZnTe-ZnSe colloidal quantum dots.  

PubMed

Ultrafast transient absorption spectroscopy is used to investigate the exciton dynamics of Type II ZnTe-ZnSe core-shell colloidal quantum dots. Surface-trapping is shown to occur within a few picosecond for hot electrons and with a few 10s of picoseconds for electrons cooled to the band-edge, and is the dominant process in the decay of the band-edge bleach for well-stirred samples pumped at moderate powers. The surface-trapped electrons produce a broad photo-induced absorption that spectrally overlaps with the band-edge, distorting and partially cancelling out the bleach feature. At high pump powers and for unstirred samples, these surface-trapped electrons can survive sufficiently long within the pumped volume to accumulate under repeated excitation of the sample, resulting in the formation of an additional exciton decay channel. PMID:22964845

Cadirci, M; Stubbs, S K; Fairclough, S M; Tyrrell, E J; Watt, A A R; Smith, J M; Binks, D J

2012-10-21

216

CuInSe sub 2 and CdTe: Scale-up for manufacturing  

SciTech Connect

The information in this report was originally compiled to serve as a chapter in a photovoltaic reference book. The particular focus of this chapter was on the development of low-cost photovoltaic materials, namely CuInSe{sub 2} and CdTe{endash}two leading polycrystalline thin film materials exhibiting high efficiencies and low production costs. Both materials demonstrate significant potential as usable technologies in the commercial market. While the primary focus of this review is on the characteristics of these materials, the authors also provide a look at key methods for making these materials as well as for making added layers that are required for completing a device. In addition, the authors discuss related issues to specific materials (e.g., availability, stability, toxicity) and to each approach (e.g., advantages and drawbacks).

Zweibel, K.; Mitchell, R.

1989-12-01

217

CuInSe2 and CdTe: Scale-up for manufacturing  

NASA Astrophysics Data System (ADS)

The information in this report was originally compiled to serve as a chapter in a photovoltaic reference book. The particular focus of this chapter was on the development of low-cost photovoltaic materials, namely CuInSe2 and CdTe, two leading polycrystalline thin film materials exhibiting high efficiencies and low production costs. Both materials demonstrate significant potential as usable technologies in the commercial market. While the primary focus of this review is on the characteristics of these materials, the authors also provide a look at key methods for making these materials as well as for making added layers that are required for completing a device. In addition, the authors discuss related issues to specific materials (e.g., availability, stability, toxicity) and to each approach (e.g., advantages and drawbacks).

Zweibel, Ken; Mitchell, Richard

1989-12-01

218

Engineering Topological Surface States: HgS, HgSe, and HgTe  

NASA Astrophysics Data System (ADS)

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.

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

2013-10-01

219

Oscillatory surface dichroism of the insulating topological insulator Bi2Te2Se  

NASA Astrophysics Data System (ADS)

Using circular dichroism-angle resolved photoemission spectroscopy, we report a study of the effect of angular momentum transfer between polarized photons and topological surface states on the surface of the insulating topological insulator Bi2Te2Se. The photoelectron dichroism is found to be strongly modulated by the frequency of the helical photons including a dramatic sign flip. Our results suggest that the observed dichroism and its sign flip are consequences of strong coupling between the photon field and the spin-orbit nature of the Dirac modes on the surface. Our studies reveal the intrinsic dichroic behavior of topological surface states and point toward the potential utility of bulk insulating topological insulators in opto-spintronics device applications.

Neupane, M.; Basak, S.; Alidoust, N.; Xu, S.-Y.; Liu, Chang; Belopolski, I.; Bian, G.; Xiong, J.; Ji, H.; Jia, S.; Mo, S.-K.; Bissen, M.; Severson, M.; Lin, H.; Ong, N. P.; Durakiewicz, T.; Cava, R. J.; Bansil, A.; Hasan, M. Z.

2013-10-01

220

A magnetic glassy phase in Fe(1+y)Se(x)Te(1-x) single crystals.  

PubMed

The evolution of magnetic order in Fe1+ySexTe1-x crystals as a function of Se content was investigated by means of ac/dc magnetometry and muon-spin spectroscopy. Experimental results and self-consistent density functional theory calculations both indicate that muons are implanted in vacant iron-excess sites, where they probe a local field mainly of dipolar origin, resulting from an antiferromagnetic (AFM) bicollinear arrangement of iron spins. This long-range AFM phase becomes progressively disordered with increasing Se content. At the same time all the tested samples manifest a marked glassy character that vanishes for high Se contents. The presence of local electronic/compositional inhomogeneities most likely favours the growth of clusters whose magnetic moment 'freezes' at low temperature. This glassy magnetic phase justifies both the coherent muon precession seen at short times in the asymmetry data, as well as the glassy behaviour evidenced by both dc and ac magnetometry. PMID:23515268

Lamura, G; Shiroka, T; Bonfà, P; Sanna, S; Bernardini, F; De Renzi, R; Viennois, R; Giannini, E; Piriou, A; Emery, N; Cimberle, M R; Putti, M

2013-04-17

221

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

NASA Astrophysics Data System (ADS)

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.

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

2013-06-01

222

Anomalous dependence of c-axis polarized Fe B1g phonon mode with Fe and Se concentrations in Fe1+yTe1-xSex  

NASA Astrophysics Data System (ADS)

We report on an investigation of the lattice dynamical properties in a range of Fe1+yTe1-xSex compounds, with special emphasis on the c-axis polarized vibration of Fe with B1g symmetry, a Raman active mode common to all families of Fe-based superconductors. We have carried out a systematic study of the temperature dependence of this phonon mode as a function of Se x and excess Fe y concentrations. In parent compound Fe1+yTe, we observe an unconventional broadening of the phonon between room temperature and magnetic ordering temperature TN. The situation smoothly evolves toward a regular anharmonic behavior as Te is substituted for Se and long-range magnetic order is replaced by superconductivity. Irrespective to Se contents, excess Fe is shown to provide an additional damping channel for the B1g phonon at low temperatures. We performed density functional theory ab initio calculations within the local density approximation to calculate the phonon frequencies, including magnetic polarization and Fe nonstoichiometry in the virtual crystal approximation. We obtained a good agreement with the measured phonon frequencies in the Fe-deficient samples, while the effects of Fe excess are poorly reproduced. This may be due to excess Fe-induced local magnetism and low-energy magnetic fluctuations that cannot be treated accurately within these approaches. As recently revealed by neutron scattering and muon spin rotation studies, these phenomena occur in the temperature range where anomalous decay of the B1g phonon is observed and suggests a peculiar coupling of this mode with local moments and spin fluctuations in Fe1+yTe1-xSex.

Um, Y. J.; Subedi, A.; Toulemonde, P.; Ganin, A. Y.; Boeri, L.; Rahlenbeck, M.; Liu, Y.; Lin, C. T.; Carlsson, S. J. E.; Sulpice, A.; Rosseinsky, M. J.; Keimer, B.; Le Tacon, M.

2012-02-01

223

Ternary compound CuInTe2: a promising thermoelectric material with diamond-like structure.  

PubMed

We report a ternary compound CuInTe(2) with diamond-like structure as a promising thermoelectric material in moderate temperature range. Due to the good electrical properties and low thermal conductivity, the zT value of CuInTe(2) reaches 1.18 at 850 K, better than any other un-doped diamond-like material. PMID:22414929

Liu, Ruiheng; Xi, Lili; Liu, Huili; Shi, Xun; Zhang, Wenqing; Chen, Lidong

2012-04-21

224

Study of thermally activated a.c. conduction in a-Se 80Te 20 and a-Se 80Te 19.5M 0.5 (M = Cd, In, Sb) alloys  

NASA Astrophysics Data System (ADS)

The temperature and frequency dependence of a.c. conductivity in a-Se 80Te 20 and a-Se 80Te 19.5M 0.5 (M = Cd, In, Sb) alloys have been investigated. Measurements have been carried out for the frequency range 0.5 kHz-10 kHz in the temperature range from room temperature to glass transition temperature. The a.c. conductivity ? ac is found to be proportional to ? s where s < 1. The temperature dependence of both ? ac and the parameter s is reasonably well interpreted by the correlated barrier hopping (CBH) model.

Chandel, N.; Mehta, N.; Kumar, A.

2011-01-01

225

Thermoelectric transport properties of nickel-doped Co4-xNixSb11.6Te0.2Se0.2 skutterudites  

NASA Astrophysics Data System (ADS)

In this paper, skutterudite compounds Co4-xNixSb11.6Te0.2Se0.2 (x=0, 0.05, 0.1 and 0.2) were successfully prepared by the solid state reaction and spark plasma sintering methods. The component phases and the chemical composition of all samples were characterized by the X-ray diffraction and the electron microprobe analysis, respectively. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured in the 300-800 K temperature range. It is found that suitable amount of Ni dopant in the Co4-xNixSb11.6Te0.2Se0.2 system not only resulted in an improvement of the electrical conductivity but also a drop of the lattice thermal conductivity. The maximum dimensionless figure of merit of 0.83 was obtained at 800 K for sample Co3.8Ni0.2Sb11.6Te0.2Se0.2, representing a 23% improvement compared with that of the Ni-free sample.

Xu, Chenglong; Duan, Bo; Ding, Shijie; Zhai, Pengcheng; Li, Peng

2013-09-01

226

Coupling of chalcocarbonyl ligands (CE: E = S, Se, Te) on an iron carbonyl site: effect of the chalcogen.  

PubMed

B3LYP/DZP(Lanl2dz) study of Fe(CO)n(CE)2 (E = S, Se, Te; n = 4, 3) suggests that the Fe(?(2)-E-C) structures are energetically preferred for singlet Fe(CO)4(C2E2) and triplet Fe(CO)3(C2E2). The tendency for coupling reactions of CE ligands to form C2E2 ligands by carbon-carbon bond formation increases in the sequence S < Se < Te. PMID:23612351

Zhang, Zhong; Pu, Liang; King, R Bruce

2013-06-01

227

Phase diagram of the Cu 2GeSe 3–ZnSe system and crystal structure of the Cu 2ZnGeSe 4 compound  

Microsoft Academic Search

The phase diagram of the Cu2GeSe3–ZnSe system was investigated by differential thermal analysis, X-ray powder diffraction and metallography. The eutectic type of the diagram was established. The formation of the Cu2ZnGeSe4 phase which melts incongruently at 1163 K was confirmed. The crystal structure of this quaternary phase was determined by X-ray powder diffraction. The investigated Cu2ZnGeSe4 compounds crystallize in the

O. V. Parasyuk; L. D. Gulay; Ya. E. Romanyuk; L. V. Piskach

2001-01-01

228

Exploring the doping effects of Ag in p-type PbSe compounds with enhanced thermoelectric performance  

NASA Astrophysics Data System (ADS)

In this study, we prepared a series of Ag-doped PbSe bulk materials by a melting-quenching process combined with a subsequent spark plasma sintering process, and systematically investigated the doping effects of Ag on the thermoelectric properties. Ag substitution in the Pb site does not introduce resonant levels near the valence band edge or detectable change in the density of state in the vicinity of the Fermi level, but moves the Fermi level down and increases the carrier concentration to a maximum value of ~4.7 × 1019 cm-3 which is still insufficient for heavily doped PbSe compounds. Nonetheless, the non-monotonic variation in carrier concentration with increasing Ag content indicates that Ag doping reaches the solution limit at ~1.0% and the excessive Ag presumably acts as donors in the materials. Moreover, the large energy gap of the PbSe-based material wipes off significant 'roll-over' in the Seebeck coefficient at elevated temperatures which gives rise to high power factors, being comparable to p-type Te analogues. Consequently, the maximum ZT reaches ~1.0 for the 1.5% Ag-doped samples with optimized carrier density, which is ~70% improvement in comparison with an undoped sample and also superior to the commercialized p-type PbTe materials.

Wang, Shanyu; Zheng, Gang; Luo, Tingting; She, Xiaoyu; Li, Han; Tang, Xinfeng

2011-11-01

229

Préparation et étude de couches minces de CuXY2 (X = Ga, In ; Y = Se, Te) pour applications en cellules solaires  

NASA Astrophysics Data System (ADS)

This paper concerns the study of thin films of CuXY2 (X = Ga, In; Y = Se, Te) photovoltaic materials. The thin films were grown from a close-spaced vapour transport technique in closed tube, with iodine as reagent. After a review of the method and the published results concerning the thermodynamical aspect, we give some results of characterization of the thin films grown with this method. The conditions of quasi-stoichiometric deposition were determined. Phase transitions were observed: for example, for CuInSe2 and at source temperatures above 580°C, the films are formed of (In, Se) compounds, mainly In2Se3 and InSe. These films have a n-type conductivity, while the CuInSe2 films, obtained at T < 580 ^circC, have a p-type conductivity. Hence, either p-type or n-type films can be grown, simply by varying the source temperature. These results were complemented by a study of the films grown by close-spaced sublimation (CSS) at moderate temperature, using the same apparatus. The films are also formed of (In, Se) compounds. Cet article concerne l'étude de couches minces de matériaux photovoltaïques CuXY2 (X = Ga, In ; Y = Se, Te) obtenues par une méthode de transport chimique à courte distance (CSVT) en tube fermé, en présence d'iode. Après un rappel de la méthode, et une synthèse des résultats déjà publiés sur l'aspect thermodynamique, nous donnons des résultats de caractérisation des couches minces obtenues. Les conditions de dépôt quasi-stœchiométriques ont été déterminées. Des transitions de phase ont été trouvées : par exemple, pour CuInSe2 et pour des températures de source >580 ^circC, les couches sont formées de composés (In, Se), en particulier In2Se3 et InSe. Ces couches sont de type n, alors que les couches de CuInSe2, obtenues pour T < 580 ^circC, sont de type p. On peut donc déposer successivement des couches p et n simplement en variant la température. Ces résultats ont été complétés par une étude des couches obtenues par sublimation à courte distance (CSS) à température modérée, en utilisant le même appareillage. On retrouve des couches formées de composés (In, Se).

Massé, G.; Yarzhou, L.; Djessas, K.

1993-11-01

230

Synthesis and Structures of Ternary Chalcogenides of Aluminum and Gallium with Stacking Faults: K MQ2 ( M=Al, Ga; Q=Se, Te)  

NASA Astrophysics Data System (ADS)

The synthesis and crystal structures of new ternary chalcogenides of aluminum and gallium, K MQ2 ( M=Al, Ga; Q=Se, Te) are reported. These compounds were synthesized by solid-state reaction at 800°C in Nb containers. The single-crystal structures of K MTe 2 ( M=Al, Ga) have been determined; KAlTe 2, a=11.808(2) Å, b=11.812(2) Å, c=16.456(3) Å, ?=100.32(3)°, C2/ c (No. 15, Z=16); KGaTe 2, a=11.768(3) Å, b=11.775(3) Å, c=16.503(4) Å, ?=100.36(2)°, C2/ c (No. 15, Z=16). The fundamental building blocks of the title compounds are adamantane-like M4Q10 ( M4Q10= M4Q4Q12/2) supertetrahedra consisting of four MQ4 ( M=Al, Ga; Q=Se, Te) tetrahedra. These supertetrahedra form two-dimensional 2?[ M4Q6Q4/2= MQ2] - layers by sharing terminal chalcogen atoms with adjacent supertetrahedra. These layers form a stack up to the c axis with each layer rotated by 90° relative to its neighbors. Potassium cations are located inside trigonal prisms formed by six chalcogen atoms. Stacking faults up the c* axis are evidenced by streaks in oscillation photographs. Only half of the data set is affected by this type of faulting. We demonstrate both analytically and by use of the DIFFaX program that our structural model for the faulting is consistent with the observed streaking patterns.

Kim, Joonyeong; Hughbanks, Timothy

2000-02-01

231

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

232

Growth of Compound Semiconductors in a Low Gravity Environment: Microgravity Growth of PbSnTe  

NASA Technical Reports Server (NTRS)

The growth of the alloy compound semiconductor lead tin telluride (PbSnTe) was chosen for a microgravity flight experiment in the Advanced Automated Directional Solidification Furnace (AADSF), on the United States Microgravity Payload-3 (USMP-3) and on USMP-4 Space Shuttle flights in February, 1996, and November, 1997. The objective of these experiments was to determine the effect of the reduction in convection, during the growth process, brought about by the microgravity environment. The properties of devices made from PbSnTe are dependent on the ratio of the elemental components in the starting crystal. Compositional uniformity in the crystal is only obtained if there is no significant mixing in the liquid during growth. Lead tin telluride is an alloy of PbTe and SnTe. The technological importance of PbSnTe lies in its band gap versus composition diagram which has a zero energy crossing at approximately 40% SnTe. This facilitates the construction of long wavelength (>6 micron) infrared detectors and lasers. Observations and experimental methods of crystal growth of PbSnTe on both Space Shuttle Flights are presented.

Fripp, Archibald L.; Debnam, William J.; Rosch, William R.; Baker, N. R.; Narayanan, R.

1999-01-01

233

Determination of a pseudo-binary SrSe–Ga 2Se 3 phase diagram and single crystal growth of SrGa 2Se 4 compounds  

Microsoft Academic Search

We have investigated chemical reaction processes and thermal characteristics of IIa–III2–VI4 compounds in order to grow their single bulk crystals. Up to now, single crystals of Ca and Sr thiogallates have been successfully grown by the melt growth method based on their pseudo-binary phase diagrams. Here, a similar diagram of the SrSe–Ga2Se3 system has been constructed for the first time,

Chiharu Hidaka; Nobuyasu Makabe; Takeo Takizawa

2003-01-01

234

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)

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.

Pocha, Regina; Löhnert, Catrin; Johrendt, Dirk

2007-01-01

235

Electron diffraction studies of supersonic jets. 8. Nucleation of various phases of SF/sub 6/, SeF/sub 6/, and TeF/sub 6/  

SciTech Connect

Old microcrystals of SF/sub 6/, SeF/sub 6/, and TeF/sup 6/ are condensed when the gaseous hexafluorides in monatomic carriers flow supersonically through aminiature Laval nozzle. Electron diffraction records of the condensates display strong Debye-Scherrer rings. The diffraction patterns depend markedly upon the carrier gas and expansion conditions. For the hexafluorides of sulfur and selenium the well-known body-centered plastic cubic phase forms if the molecular weight of the carrier gas is low and the subject mole fraction exceeds several percent. A phase II of low symmetry begins to appear only at low mole fractions of SF/sub 6/ and requires a carrier at least has heavy as argon. Phase II appears for SeF/sub 6/ with argon carrier under all conditions examined and with neon under extreme conditions. It appears readily even with helium in the case of TeF/sub 6/, provided the subject mole fraction is comparatively high. At lower mole fractions and total pressures another, as yet unidentified, phase III of TeF/sub 6/ is produced. Patterns of phase II are well accounted for by the triclinic lattice P1, Z = 3. Refinements based on this space group, for the two compounds yielding nearly pure phase II, led to the following cell constants (3sigma): SeF/sub 6/ (T < 140 K), a = 14.51 (8) A, b = 8.22 (3) A, c = 4.92 (3) A, ..cap alpha.. = 85.6 (3)/sup 0/; ..beta.. = 93.7 (4)/sup 0/, ..gamma.. = 88.14 (4)/sup 0/; TeF/sub 6/ (T < 160 K.), a = 14.99 (7) A, b = 8.53 (3) A, c = 5.06 (3) A, ..cap alpha.. = 85.6 (3)/sup 0/, ..beta.. = 93.5 (3)/sup 0/ = 88.9 (3)/sup 0/.

Bartell, L.S.; Valente, E.J.; Caillat, J.C.

1987-05-07

236

Refractive Index of ZnS, ZnSe, and ZnTe and Its Wavelength and Temperature Derivatives.  

National Technical Information Service (NTIS)

Refractive index data of ZnS, ZnSe, and ZnTe were searched, compiled, and analyzed. Recommended values of refractive index for the transparent spectral region were generated in the ranges 0.5-14 micrometers and 93-1000 K for ZnS, 0.55-18 micrometers and 9...

H. H. Li

1984-01-01

237

Thermal kinetics and short range order parameters of Se80X20 (X = Te, Sb) binary glasses  

NASA Astrophysics Data System (ADS)

Bulk Se80Te20 and Se80Sb20 glasses were prepared using the melt-quench technique. Differential scanning calorimetry (DSC) curves measured at different heating rates (5 K/min? ??50 K/min) and X-ray diffraction (XRD) are used to characterize the as-quenched specimens. Based on the obtained results, the activation energy of glass transition and the activation energy of crystallization ( E g, E c) of the Se80Te20 glass are (137.5, 105.1 kJ/mol) higher than the corresponding values of the Se80Sb20 glass (106.8, 71.2 kJ/mol). An integer n value ( n=2) of the Se80Te20 glass indicates that only one crystallization mechanism is occurring while a non-integer exponent ( n=1.79) in the Se80Sb20 glass means that two mechanisms are working simultaneously during the amorphous-crystalline transformations. The total structure factor, S( K), indicates the presence of the short-range order (SRO) and the absence of the medium-range order (MRO) inside the as-quenched alloys. In an opposite way to the activation energies, the values of the first peak position and the total coordination number ( r 1, ? 1), obtained from a Gaussian fit of the radial distribution function, of the Se80Te20 glass are (2.42 nm, 1.99 atom) lower than the corresponding values (2.55 nm, 2.36 atom) of the Se80Sb20 specimens.

Moharram, A. H.; Abu El-Oyoun, M.; Abdel-Baset, A. M.

2014-06-01

238

Theoretical investigation on the electronic and thermoelectric properties of RuSb2Te compound  

NASA Astrophysics Data System (ADS)

The skutterudites are an excellent candidate for thermoelectric materials used in mechanic free heat pump and electric generator. Using the ab initio density functional theory we have calculated the electronic band structure and thermoelectric properties of skutterudite RuSb2Te. RuSb2Te compound belongs to an indirect band gap semiconductor. The density of states has a sharp upturn at the conduction band edge and is very low at the valence band top. This feature suggests that Seebeck coefficient is larger for n doped than for p doped RuSb2Te compound. The calculated Seebeck coefficient confirms this trend. It is in a qualitative agreement with the experiments if the temperature is not too high.

Kong, Shi; Zhang, Weiyi; Shi, Daning

2013-11-01

239

Temperature and solvent dependence of CdSe/CdTe heterostructure nanorod spectra.  

PubMed

Charge separation is known to occur in heterostructure nanocrystals with type II alignment. Transfer rates have been inferred from ultrafast measurements, but other elements relevant to this process, such as the role of the solvent and the internal degrees of freedom, are still poorly understood. The present study investigates temperature and solvent effects on the optical properties of the charge-separated state in CdSe/CdTe collinear nanorods. The importance of the surrounding medium in the steady state photoluminescence is suggested both in the solvent and temperature studies. The latter also provides evidence that a charge-separated bound state is formed at the interface of the two materials, while states where electron and hole behave as free carriers are only accessible through an activated process in which the interfacial exciton is dissociated. Finally, using a dipole-dielectric continuum model, we found that the optical properties of the charge-separated state in these nanocrystals change as a function of solvent polarity. PMID:19725628

Lo, Shun S; Khan, Yaser; Jones, Marcus; Scholes, Gregory D

2009-08-28

240

Effect of Cd Addition in Band Gap and Volume Conductivity of SeTe Based Glasses  

NASA Astrophysics Data System (ADS)

Presented paper discusses the variation in optical band gap and volume dc conductivity of Se-Te-Cd ternary Chalcogenide glasses as a function of concentration of Cd i.e. the composition of the glasses. Also, the temperature dependence of volume conductivity has been studied. The amorphous nature of these glasses has been confirmed by XRD patterns. Keithley Electrometer/High resistance meter 6517A was used in its FVMI mode to record I_V characteristics at different temperatures. Variation in conductivity, derived from I_V curves, as a function of composition of sample could be accounted for the bonds formed in the system. Additionally, the Poole-Frenkel conduction mechanism has also been verified in order to investigate the good agreement with the established fact that most of Chalcogenide glasses obey the Poole-Frenkel conduction mechanism. Absorption spectra were recorded using Ocean Optics USB2000 spectrophotometer in visible region. Band gap calculation using Tauc relation reveals that the system under test is semi-conducting in nature. The observed results are found to be in good agreement with each other.

Saraswat, Vibhav K.; Kishore, V.; Saraswat, Y. K.; Saxena, N. S.

2011-10-01

241

CdSe and CdTe Nanostructure Deposition by Electrochemical Atomic Layer Epitaxy  

NASA Astrophysics Data System (ADS)

Electrochemical Atomic Layer Epitaxy (EC-ALE), in conjunction with templated substrates, is applied for the deposition of nanostructured II-VI semiconductors. In EC-ALE, deposits are formed with atomic layer control on a metal electrode (gold) in a wet electrochemical process. To obtain nanostructured deposits, we take advantage of the fact that electrodeposition takes place only on metal surfaces in direct contact with the electrolyte. To produce a nanotemplate, the metal electrode is first spin-coated with PMMA and the desired structure is then imprinted into the coating via e-beam lithography. In the subsequent electrochemical process, deposition will take place in those areas where the PMMA film has been removed in the lithography process. Thus, nanostructured semiconductor deposits are formed. This technique is demonstrated for the deposition of CdSe and CdTe. The obtained nanostructures are imaged with AFM and SEM, and a Dimension 3000 scanning microscope is used in scanning tunneling spectroscopy (STS) mode to determine the bandgap of the individual deposits. This work is supported in part by an Engineering Grant from the Office of the Vice President of Research at The University of Georgia. D. J. P. was supported in part by a National Foundation Research Experience for Undergraduates grant (PHY 00-97457) to the University of Georgia.

Poxson, David J.; Cox, Stephen M.; Happek, Uwe; Mathe, Mahlanyane K.; Stickney, John L.

2004-03-01

242

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

NASA Astrophysics Data System (ADS)

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.

Al-Agel, Faisal A.

2013-12-01

243

Ab initio study of topological insulating property in the heterojunction of Bi (111) bilayer and Bi2Te2Se  

NASA Astrophysics Data System (ADS)

Study of topological insulator (TI) is showing rapid progress in both theory and experiment, particularly on three dimensional materials. Examples of two dimensional TI (quantum spin Hall) materials are, on the other hand, comparatively less common. As such, theoretical predictions of single Bi (111) bilayers as TI draw great attention from experiment. A recent report of ARPES measurements claims verification of the 2D TI property of Bi bilayer, but analysis leaves much room for further clarification. Because Bi (111) bilayers grown on 3D TI substrates such as Bi2Te3 and Bi2Te2Se; understanding the details of the interface between the Bi bilayer and 3D TI substrates is essentially required. We study the electronic structures of Bi bilayer-Bi2Te2Se heterojunction from first-principles calculations. We find a substantial shift of Dirac cone from the TI substrates into Bi bilayer that thus becomes metallic on TI substrates. It is shown that the origin of this change is the inversion-symmetry breaking in Bi bilayer due to TI substrate. By comparing our calculations of Bi bilayer nanoribbons on Bi2Te2Se with STM/STS measurements, we successfully resolve and locate the edge states of a single Bi bilayer and confirm its 2D TI character.

Jin, Kyung-Hwan; Jhi, Seung-Hoon

2013-03-01

244

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)

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.

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

2014-01-01

245

Anomalous Transport Properties in Fe Intercalation Compound Fe x TiSe2 Single Crystals  

NASA Astrophysics Data System (ADS)

The transport and magnetic properties of single-crystalline Fe-intercalation-compound Fe x TiSe2 have been compared with the transport properties of single-crystalline Ti-self-intercalation-compound Ti x TiSe2. At low concentration of intercalated guest atoms, Fe x TiSe2 exhibits carrier localization behavior without magnetic ordering, while Ti x TiSe2 shows an itinerant behavior. The superstructure and the carrier localization observed in Fe x TiSe2 single crystals simultaneously disappear at the critical concentration x c˜0.07, which agrees well with theoretical value based on a percolation theory. Fe intercalation compounds show paramagnetism and nonexistence of magnetism is attributed to the large distance between guest Fe atoms. We discuss the effect of guest intercalation on the stability of superstructure formed in the host.

Sasaki, M.; Ohnishi, A.; Kikuchi, T.; Kitaura, M.; Shimada, K.; Kim, H.-J.

2010-11-01

246

A modified two-stage process for the preparation of Zn(Te{sub x}Se{sub 1{minus}x}) films  

SciTech Connect

A modified low-pressure vapor-phase selenization process that enables controlled incorporation of multiple chalcogens in ZnSe semiconductor thin films has been demonstrated. Growth of polycrystalline ZnTe{sub x}Se{sub 1{minus}x} films and modification of the Te/Se ratio by varying the reactor pressure have been observed. Te incorporation results in the lowering of the band gap to 2.45 eV from 2.65 eV for pure ZnSe and reduction resistivity by a factor of 3. The increased Te incorporation in the film correlates with the value estimated from modeling of the gas dynamics of the system and is independently confirmed by XRD. These results indicate that the Te{sub 2}-Zn reaction is competitive with the Se{sub 5-7}-Zn reaction under the experimental conditions investigated.

Jeyakumar, R.; Lakshmikumar, S.T.; Rastogi, A.C. [National Physical Lab., New Delhi (India). Materials Div.] [National Physical Lab., New Delhi (India). Materials Div.; Chadda, G.K. [Univ. of Delhi (India). Dept. of Physics and Astrophysics] [Univ. of Delhi (India). Dept. of Physics and Astrophysics

1999-01-01

247

First-Principles Study of Electronic Structure and Ground-State Properties of Alkali-Metal Selenides and Tellurides (M2A) [M: Li, Na, k; a: Se, Te  

NASA Astrophysics Data System (ADS)

First-principles calculations have been performed to investigate the electronic structure and ground-state properties of alkali-metal Selenides (M2Se) and Tellurides (M2Te) [M: Li, Na, K] using the Tight-Binding Linear Muffin-Tin Orbital (TB-LMTO) method. The exchange correlation energy is described within the local density approximation (LDA) using the von Barth and Hedin parameterization scheme. At ambient conditions, these compounds are found to crystallize in the face center cubic antifluorite (anti-CaF2-type) structure. Ground-state properties such as total energy, equilibrium lattice parameter, and bulk modulus are calculated for these compounds. The calculated equilibrium lattice parameter is in agreement with experimental result. From the electronic structure calculations, we find that Li2Se, Li2Te, K2Se, and K2Te are indirect bandgap semiconductors, whereas Na2Se and Na2Te are direct bandgap semiconductors. The present results are compared with the earlier results of series of alkali-metal sulfides (M2S) and alkali-metal oxides (M2O), allowing us to make predictions about the total energy, bulk modulus, valence-band width, and bandgap behavior of the rest of the alkali-chalcogenide crystals.

Eithiraj, R. D.; Jaiganesh, G.; Kalpana, G.

248

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

PubMed

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

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

249

Electrochemical Control over Photoinduced Electron Transfer and Trapping in CdSe-CdTe Quantum-Dot Solids.  

PubMed

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

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

2014-07-22

250

Pressure-induced superconductivity in topological parent compound Bi2Te3  

PubMed Central

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.

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

251

Pressure-induced superconductivity in topological parent compound Bi2Te3.  

PubMed

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

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

252

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

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

253

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

254

Surface Stabilities of Various Crystal Faces of CuInSe2 and Related Compounds by First-Principles Calculation  

NASA Astrophysics Data System (ADS)

The typical crystal surfaces of CuInSe2 (CISe) and related compounds were studied using density functional theory (DFT) methods. We evaluated energies and surface structures of (112), (\\bar{1}\\bar{1}\\bar{2}), (110), (102), (100), (\\bar{1}00), (001), and (00\\bar{1}) surfaces on CISe. For CISe, the (112) surface had the lowest energy among these surfaces, and the (110) and (102) surfaces had slightly higher energies than the (112) surface. These surface atoms coordinate with the three surrounding atoms. We found that the (112) surface is most stable for CISe, and this result is consistent with the experimental results showing that the (112) surface is most frequently observed in polycrystalline CISe thin films. We also evaluated the surface energies of CuGaSe2 (CGSe), CuAlSe2 (CASe), CuInS2 (CIS), CuInTe2 (CIT), and AgInSe2 (AISe). For CGSe, CIS, and CIT, the (112) surface had the lowest energy as in the case of CISe. However, for CASe and AISe, the (110) surface had the lowest energy.

Shigemi, Akio; Wada, Takahiro

2012-10-01

255

High storage density optical disks using pit-edge recording on PbTeSe thin film.  

PubMed

Pit-edge recording, where, the leading and trailing edges of the pit correspond to code-data 1, can achieve about one and a half times more bit density than that of pit-position recording. Using pit-edge recording with an effective write-read compensation scheme, we have achieved high linear density of 0.63 microm/bit on a PbTeSe ablative type optical disk. The write compensation is able to cancel pit expansion caused by thermal diffusion and surface tension of the recording film. We also confirmed the possibility of 0.50-microm/bit recording with an advanced compensation scheme on a PbTeSe optical disk. The corresponding user data capacity is ~1 Gbyte/side on a 130-mm diam optical disk. PMID:20539556

Saito, A; Maeda, T; Sugiyama, H; Tsunoda, Y

1988-10-15

256

Effect of thermal annealing on structure and optical band gap of amorphous Se72Te25Sb3 thin films  

NASA Astrophysics Data System (ADS)

Thin films of a-Se72Te25Sb3 were prepared by vacuum evaporation technique in a base pressure of 10-6 Torr on to well cleaned glass substrate. a-Se72Te25Sb3 thin films were annealed at different temperatures below their crystallization temperatures for 2h. The structural analysis of the films has been investigated using X-ray diffraction technique. The optical band gap of as prepared and annealed films as a function of photon energy in the wavelength range 400-1100 nm has been studied. It has been found that the optical band gap decreases with increasing annealing temperatures in the present system.

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

2014-04-01

257

Effect of Zn incorporation on the optical properties of thin films of Se85Te15 glassy alloy  

NASA Astrophysics Data System (ADS)

Amorphous thin films of Se85-xTe15Znx (x = 4, 6 and 10) have been prepared by vacuum evaporation technique. The transmittance of as-deposited thin films was measured in the wavelength region 400-1800 nm. The optical band gap and optical constants of amorphous thin films have been studied as a function of wavelength. It has been found that the value of refractive index (n) decreases while the value of the extinction coefficient (k) increases with increasing wavelength. Also the value of optical band gap increases on incorporation of Zn in Se85-xTe15Znx system. The results are interpreted in terms of electronegativity difference of the elements involved.

Shukla, S.; Kumar, S.

2013-02-01

258

Phase diagram of thermoelectric Bi2S3-Bi2Se3-Bi2Te3 system  

NASA Astrophysics Data System (ADS)

It is well known that the highest ZT value, at an optimized carrier concentration, is mainly determined by a material parameter ?=?(m*/m0)3/2/?lat, where ?(m*/m0)3/2 and ?lat are the weighted carrier mobility and lattice thermal conductivity, respectively. In order to explore some new compositions in Bi2S3-Bi2Se3-Bi2Te3 system, we propose a compositional thermoelectric phase diagram (TPD), including weighted carrier mobility, lattice thermal conductivity, and material parameter, for the 1% copper doped Bi2S3-Bi2Se3-Bi2Te3 solid solution fabricated by MA-HP method. Here, the ?(m*/m0)3/2 and ?lat values could be deduced from the measured electrical resistivity, Seebeck coefficient, and thermal conductivity. The alloying effect on the thermoelectric phase diagram will be discussed from varying atomic size, chemical bond, lattice structure, etc.

Liu, Weishu; Zhang, Qinyong; Zhang, Qian; Yu, Bo; Chen, Gang; Ren, Zhifeng

2011-03-01

259

Magnetic relaxation and collective vortex creep in FeTe0.6Se0.4 single crystal  

NASA Astrophysics Data System (ADS)

We study the vortex dynamics in a high-quality FeTe0.6Se0.4 single crystal by performing magnetization measurements of the screening current density Js and flux creep rate S. The temperature dependence of S shows a plateau in the intermediate-temperature region with a high creep rate ? 0.03, which is interpreted in the framework of the collective creep theory. A crossover from elastic to plastic creep is observed. The glassy exponent and barrier height for the flux creep are directly determined by the extended Maley's method. Js with flux creep, obtained from magnetic hysteresis loops, is successfully reproduced based on the collective creep analysis. We also approach the critical current density without flux creep by means of the generalized inversion scheme, which proves that the \\delta l and \\delta T_c pinning coexist in the FeTe0.6Se0.4 single crystal.

Sun, Yue; Taen, Toshihiro; Tsuchiya, Yuji; Pyon, Sunseng; Shi, Zhixiang; Tamegai, Tsuyoshi

2013-09-01

260

Study of phase change technology for computer memory using Se70Te30-xAgx system  

NASA Astrophysics Data System (ADS)

The phase change memory is the revolutionary technology for computer world today. Phase change memory alloy is composed of chalcogenide glasses. In the present work Ag is doped in binary Se70Te30 system and activation energy of crystallization is calculated. These ternary alloys are explored in various fields like photo doping, optical imaging, and phase change optical recording. The crystallization kinetics of various ternary Se70Te30-xAgx(x = 0,2,4,6) alloys are studied by using Non-isothermal Iso-Conversional methods. The dependence of activation energy Ec is discussed by various methods. The result shows that the activation energy Ec plays a vital role in proving these materials as best applicable materials in optical phase change recording devices.

Kumar, A.; Agarwal, Pragya; Saxena, Abhay

2013-06-01

261

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

SciTech Connect

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

Heera, Pawan; Sharma, Raman [Department of Physics, Himachal Pradesh University, Shimla-171005 (India)

2011-12-12

262

Thermoelectric properties of I-doped Bi2Te2.85Se0.15 solid solutions  

NASA Astrophysics Data System (ADS)

I-doped Bi2Te2.85Se0.15 solid solutions were prepared by encapsulated melting and hot pressing. The electrical conductivity and the electronic thermal conductivity were increased due to an increase in the carrier concentration with increasing I content, but the lattice thermal conductivity was reduced because I atoms affected the lattice disorder, with I atoms acting as phonon scattering centers. The undoped solid solution showed a carrier concentration of 7.37 × 1019 cm-3, a power factor of 2.1 mWm-1K-2 and a dimensionless figure of merit (ZT) of 0.56 at 323 K. The ZT value was improved due to an increase in the power factor by I doping, and the maximum ZT was obtained as 0.90 at 423 K for Bi2Te2.85Se0.15:I0.005.

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

2014-06-01

263

Theoretical studies of g factors for V³+ in ZnS, ZnSe and ZnTe crystals.  

PubMed

In this paper, complete high-order perturbation formulas are established based not only on the contributions of the spin-orbit coupling effect of the central ion and the ligands, but also on that of the charge-transfer levels. The electron paramagnetic resonance g-factors of ZnS:V(3+), ZnSe:V(3+), and ZnTe:V(3+) crystals are calculated from the formulas. The calculations of the EPR g-factors agree well with the experimental values. The contribution rate of the charge-transfer levels (|?g(T)/?g(F)|) are 20.16%, 24.86%, and 24.87% for ZnS:V(3+), ZnSe:V(3+), and ZnTe:V(3+) crystals, respectively. PMID:22609567

Zhu, Lianxuan; Zhao, Anqing; Wang, Minjie

2012-09-01

264

Electronic, vibrational, and thermodynamic properties of metacinnabar ?-HgS , HgSe, and HgTe  

NASA Astrophysics Data System (ADS)

We report ab initio calculations of the electronic band structure and the phonon dispersion relations of the zincblende-type mercury chalcogenides ( ?-HgS , HgSe, and HgTe). The latter have been used to evaluate the temperature dependence of the specific heat, which has been compared with experimental data. The electronic band structure of these materials has been confirmed to have an inverted direct gap of the ? -tin type, which makes HgSe and HgTe semimetallic. For ?-HgS , however, our calculations predict a negative spin-orbit splitting that restores semiconducting properties to the material in spite of the inverted gap. We have calculated the spin-orbit induced linear terms in k , which appear at the ?8 valence bands. We have also investigated the pressure dependence of the crystal structure and the phonons.

Cardona, M.; Kremer, R. K.; Lauck, R.; Siegle, G.; Muñoz, A.; Romero, A. H.

2009-11-01

265

A study of Sn addition on bonding arrangement of Se-Te alloys using far infrared transmission spectroscopy  

NASA Astrophysics Data System (ADS)

Far infrared transmission spectra of Se92Te8-xSnx (x = 0, 1, 2, 3, 4, 5) glassy alloys are obtained in the spectral range 50-600 cm-1 at room temperature. The results are interpreted in terms of the vibrations of the isolated molecular units in such a way so as to preserve fourfold and twofold coordination for Sn and chalcogen atoms (Se,Te), respectively. With the addition of Sn, Far-IR spectra shift toward high frequency side and some new bands start appearing. Sn atoms appear to substitute for the selenium atoms in the outrigger sites due to large bond formation probability. Theoretical calculations of bond energy, relative probability of bond formation, force constant, and wave number were also made to justify the result.

Kumar, Rajneesh; Sharma, Parikshit; Katyal, S. C.; Sharma, Pankaj; Rangra, V. S.

2011-07-01

266

A study of Sn addition on bonding arrangement of Se-Te alloys using far infrared transmission spectroscopy  

SciTech Connect

Far infrared transmission spectra of Se{sub 92}Te{sub 8-x}Sn{sub x} (x = 0, 1, 2, 3, 4, 5) glassy alloys are obtained in the spectral range 50-600 cm{sup -1} at room temperature. The results are interpreted in terms of the vibrations of the isolated molecular units in such a way so as to preserve fourfold and twofold coordination for Sn and chalcogen atoms (Se,Te), respectively. With the addition of Sn, Far-IR spectra shift toward high frequency side and some new bands start appearing. Sn atoms appear to substitute for the selenium atoms in the outrigger sites due to large bond formation probability. Theoretical calculations of bond energy, relative probability of bond formation, force constant, and wave number were also made to justify the result.

Kumar, Rajneesh; Rangra, V. S. [Department of Physics, Himachal Pradesh University, Summer-Hill, Shimla, H.P. - 171005 (India); Sharma, Parikshit [Department of Physics, Sri Sai University, Palampur, HP (India); Katyal, S. C. [Department of Physics, Jaypee Institute of Information Technology, Noida, U.P. (India); Sharma, Pankaj [Department of Physics, Jaypee University of Information Technology, Waknghat, Solan, H.P. 173215 (India)

2011-07-01

267

Structure and optical properties of films of the ternary compound CuGa5Se8  

NASA Astrophysics Data System (ADS)

We have used a laser deposition method to obtain films of the ternary compound CuGa5Se8. We have studied their composition and structure. We have established that both the crystals and the films of the indicated compound crystallize in a defect-containing chalcopyrite structure. We have determined the energy and nature of the optical transitions from the transmission spectra in the region of the intrinsic absorption edge. We have calculated the valence-band crystal-field (?CF) and spin-orbit (?SO) splitting energies according to Hopfield's quasicubic model for the ternary compound CuGa5Se8.

Bodnar, I. V.

2011-03-01

268

The gigantic Rashba effect of surface states energetically buried in the topological insulator Bi2Te2Se  

NASA Astrophysics Data System (ADS)

We have clarified that a topological insulator, Bi2Te2Se, shows two surface states with gigantic Rashba-type spin-splitting located at a binding energy deeper than the topological surface state. The magnitude of the Rashba parameter, as well as the momentum splitting, is found to be large enough to realize a number of nanometer-sized spintronic devices. This novel finding paves the way to studies of gigantic Rashba systems that are suitable for future spintronic applications.

Miyamoto, K.; Okuda, T.; Nurmamat, M.; Nakatake, M.; Namatame, H.; Taniguchi, M.; Chulkov, E. V.; Kokh, K. A.; Tereshchenko, O. E.; Kimura, A.

2014-06-01

269

Optical properties of (Se80Te20)100-xAgx (0 ? x ? 4) thin films  

NASA Astrophysics Data System (ADS)

Thin films of (Se80Te20)100-xAgx (0 ? x ? 4) glasses were prepared by thermal evaporation of the bulk samples. The transmittance (T) and reflection (R) spectra of amorphous thin films were obtained in the spectral region in the range 400-2500 nm. The optical band gap (Eg) has been determined by Tauc's extrapolation method. The surface morphology has been determined by the Scanning Electron Microscopy (SEM).

Singh, D.; Kumar, S.; Sandhu, S.; Thangaraj, R.

2014-04-01

270

Fabrication and thermoelectric performance of textured n-type Bi 2(Te,Se) 3 by spark plasma sintering  

Microsoft Academic Search

The n-type Bi2(Te,Se)3 thermoelectric materials with preferred grain orientation have been fabricated through the spark plasma sintering (SPS) technique. The c-axis of the grains in the sintered samples were preferentially oriented parallel to the pressing direction, the orientation factor of the (00l) planes changed from 0.4 to 0.85 with the sintering conditions. The anisotropy was investigated by measuring the electrical

Jun Jiang; Lidong Chen; Shengqiang Bai; Qin Yao; Qun Wang

2005-01-01

271

Thermoelectric and galvanomagnetic investigations of VI group semiconductors Se and Te at high pressure up to 30 GPa  

Microsoft Academic Search

At ultrahigh pressures up to 30GPa the thermomagnetic Nernst–Ettingshausen effect was measured for Te and Se samples in the vicinity of semiconductor–metal phase boundary. The significant longitudinal and transverse Nernst–Ettingshausen effects observed for both semiconductors allowed one to estimate the scattering parameter for charge carriers. The increase in hole mobility obtained from longitudinal and transverse Nernst–Ettingshausen effects being consistent with

V. V Shchennikov; S. V Ovsyannikov

2002-01-01

272

Thermal expansion coefficients of Bi2Se3 and Sb2Te3 crystals from 10 K to 270 K  

NASA Astrophysics Data System (ADS)

Lattice constant of Bi2Se3 and Sb2Te3 crystals is determined by x-ray powder diffraction measurement in a wide temperature range. Linear thermal expansion coefficients (?) of the crystals are extracted, and considerable anisotropy between ?|| and ?? is observed. The low temperature values of ? can be fit well by the Debye model, while an anomalous behavior at above 150 K is evidenced and explained. Grüneisen parameters of the materials are also estimated at room temperature.

Chen, X.; Zhou, H. D.; Kiswandhi, A.; Miotkowski, I.; Chen, Y. P.; Sharma, P. A.; Lima Sharma, A. L.; Hekmaty, M. A.; Smirnov, D.; Jiang, Z.

2011-12-01

273

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

Microsoft Academic Search

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

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

1998-01-01

274

Fabrication of fluorescence-based biosensors from functionalized CdSe and CdTe quantum dots for pesticide detection  

Microsoft Academic Search

This paper presents the results on the fabrication of highly sensitive fluorescence biosensors for pesticide detection. The biosensors are actually constructed from the complex of quantum dots (QDs), acetylcholinesterase (AChE) and acetylthiocholine (ATCh). The biosensor activity is based on the change of luminescence from CdSe and CdTe QDs with pH, while the pH is changed with the hydrolysis rate of

Thi Kim Chi Tran; Duc Chinh Vu; Thi Dieu Thuy Ung; Hai Yen Nguyen; Ngoc Hai Nguyen; Tran Cao Dao; Thu Nga Pham; Quang Liem Nguyen

2012-01-01

275

Twoband model of the electron spectrum in n-Bi2Te2.7Se0.3  

Microsoft Academic Search

The Hall factor and thermoelectric properties of n-Bi2Te2.7Se0.3 solid solution with the room-temperature Seebeck coefficient S = 212 ?V\\/K have been studied in the temperature range 77-350 K. The observed temperature dependences demonstrate some specific features, which were found earlier in samples with lower electron density N. The effect of these specific features on the thermoelectric figure of merit Z

P. P. Konstantinov; L. V. Prokofieva; M. I. Fedorov; D. A. Pshenay-Severin; Yu. I. Ravich; V. V. Kompaniets; V. A. Chistyakov

2005-01-01

276

Modifications of the electronic structure of GaSb surface by chalcogen atoms: S, Se, and Te  

Microsoft Academic Search

Modifications to the electronic properties and chemical structures of the GaSb surface using the chalcogen atoms S, Se, and Te were investigated theoretically and experimentally. A self-consistent density-functional theory study indicates that an adsorption of a full monolayer coverage of chalcogen atoms on a Ga-terminated surface reduces the density of gap region states significantly. A greater photoluminescence enhancement was observed

Z. Y. Liu; A. A. Gokhale; M. Mavrikakis; D. A. Saulys; T. F. Kuech

2004-01-01

277

The influence of Se doping upon the phase change characteristics of GeSb 2Te 4  

Microsoft Academic Search

Se substituted GeSb2Te4 films have been investigated for property contrast using electrical four-point-probe measurements, in-situ X-ray diffraction (XRD), a static tester probing the optical changes and atomic force microscopy (AFM). The temperature dependent sheet resistance measurements show two transitions at 125 and 262°C. The first transition at 125°C is accompanied by a large resistance change of three orders of magnitude.

Jan Tomforde; Saskia Buller; Marscha Ried; Wolfgang Bensch; Daniel Wamwangi; Markus Heidelmann; Matthias Wuttig

2009-01-01

278

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

279

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

PubMed Central

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.

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

280

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

PubMed

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

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

281

Magneto-Optical Faraday and Kerr Effects in Topological Insulators Bi2Te3 and Bi2Se3  

NASA Astrophysics Data System (ADS)

Three-dimensional topological insulator is a new quantum material which is insulating in the bulk but has current-carrying massless Dirac surface states. In this article, we investigate the magneto-optical properties of Bi2Te3 and Bi2Se3. Our analysis shows that the Faraday rotation can be affected by the magnetic coupling strength. The peak position shows a hypochromic shift with increasing magnetic coupling strength. There are two giant Kerr rotations with one (-?/2) in the low-frequency area and the other one in the non-low-frequency area. The spectral range of Kerr rotation reduces with increasing film thickness, magnetic coupling strength and incident angle. For the Bi2Se3 film, the giant Kerr rotation in the non-low-frequency area shows an obvious red shift. In addition, it is observed that the Faraday rotation peak position of Bi2Se3 is the same as that of Bi2Te3, so the Faraday rotation can be only determined by magnetic coupling strength. The giant Kerr rotation spectral range in the non-low-frequency area is larger than that of Bi2Te3.

Wang, Xiao; Lian, Jie; Huang, Yue; Sun, Zhaozong; Liu, Junliang; Zhang, Fujun; Gao, Shang; Yu, Xiaohong; Li, Ping; Zhao, Minglin

2013-10-01

282

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

NASA Astrophysics Data System (ADS)

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.

Bao, Lihong; 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

2012-10-01

283

Edge and interfacial states in a two-dimensional topological insulator: Bi(111) bilayer on Bi2Te2Se  

NASA Astrophysics Data System (ADS)

The electronic states of a single Bi(111) bilayer and its edges, suggested as a two-dimensional topological insulator, are investigated by scanning tunneling spectroscopy (STS) and first-principles calculations. Well-ordered bilayer films and islands with zigzag edges are grown epitaxially on a cleaved Bi2Te2Se crystal. The calculation shows that the band gap of the Bi bilayer closes with a formation of a new but small hybridization gap due to the strong interaction between Bi and Bi2Te2Se. Nevertheless, the topological nature of the Bi bilayer and the topological edge state are preserved only with an energy shift. The edge-enhanced local density of states are identified and visualized unambiguously by STS in good agreement with the calculation. This is a clear sign of the topological edge state, which corresponds to the quantum spin Hall state. The interfacial state between Bi and Bi2Te2Se is also identified inside the band gap region. This state exhibits a subtle edge modulation, which was previously interpreted as the evidence of the topological edge state [Yang et al., Phys. Rev. Lett. 109, 016801 (2012), 10.1103/PhysRevLett.109.016801].

Kim, Sung Hwan; Jin, Kyung-Hwan; Park, Joonbum; Kim, Jun Sung; Jhi, Seung-Hoon; Kim, Tae-Hwan; Yeom, Han Woong

2014-04-01

284

Multiband effects and possible Dirac fermions in Fe1+yTe0.6Se0.4  

NASA Astrophysics Data System (ADS)

We investigated the transport properties of Fe1+yTe0.6Se0.4 single crystals with different amounts of excess Fe prepared by O2 annealing. The O2 annealing remarkably improved transport properties. In particular, a strongly nonlinear Hall resistivity was observed only in the fully annealed crystal, and the magnetoresistance (MR) was drastically enhanced after annealing, reaching a value larger than 17% at 16 K and 14 T. The obvious change of transport properties after the annealing indicates that the band structure of Fe1+yTe0.6Se0.4 is affected by the excess Fe. The nonlinear Hall resistivity and violation of (modified) Kohler's scaling of the large MR prove the multiband effects in the Fe1+yTe0.6Se0.4 single crystal. The MR for the fully annealed crystal develops linearly against the magnetic field from the intermediate field (e.g., 2 T at 16 K) to the measurement limit of 14 T. This phenomenon is interpreted by the existence of the Dirac cone state, in which all the Dirac fermions occupy only the lowest Landau level in the quantum limit.

Sun, Yue; Taen, Toshihiro; Yamada, Tatsuhiro; Pyon, Sunseng; Nishizaki, Terukazu; Shi, Zhixiang; Tamegai, Tsuyoshi

2014-04-01

285

Synthesis and crystal structure of Zr{sub 2}Te. Distinctions in bonding to isotypic Sc{sub 2}Te and the relationship to the structures of congeneric Hf{sub 2}Te and Zr{sub 2}Se  

SciTech Connect

Zr{sub 2}Te is accessible by high-temperature synthesis. The structure of the zirconium-rich telluride was determined by means of powder X-ray diffraction to be orthorhombic, Pnma (No. 61), Z = 12, Pearson symbol oP36, a = 1995.0(2) pm, b = 382.36(2) pm, c = 1065.63(9) pm. Pairwise interpenetrating columns of trans-face-shared, centered Zr{sub 9} cuboids, reminiscent of the bcc high-temperature form of zirconium can be recognized as the topologically characteristic structural feature. Tellurium atoms capping the remaining square faces complete the motif of a {sub {infinity}}{sup 1}[Zr{sub 8}Te{sub 4}] double string running parallel [010]. The tellurium atoms are 7-, 8- and 9-fold coordinated by zirconium. The coordination figures represent mono-, bi- and tricapped distorted trigonal prisms, with zirconium atoms capping the square faces of the prisms. Extended Hueckel calculations revealed distinctions in bonding in Zr{sub 2}Te and the isotypic Sc{sub 2}Te. According to Mulliken overlap populations, the heteronuclear interactions are similar in both tellurides. However, the lower valence electron concentration available for M-M bonding in Sc{sub 2}Te is reflected in a considerable restriction of the attractive homonuclear interactions to one-dimensional metal cores, whereas in Zr{sub 2}Te M-M bonding regions extend in space. The structure of Zr{sub 2}Te is contrasted with two other types of bcc fragment structures adopted by the congeneric Hf{sub 2}Te and Zr{sub 2}Se. The authors show that the structural diversity observed for various dimetal chalcogenides is controlled by an intimate interplay of electronic and geometric factors.

Oerlygsson, G.; Harbrecht, B. [Philipps Univ., Marburg (Germany)] [Philipps Univ., Marburg (Germany)

1999-07-12

286

Half-metallicity of the FeCrTe half-Heusler compound: Ab initio study  

NASA Astrophysics Data System (ADS)

The ab initio density functional theory (DFT) calculations have been performed to investigate the electronic structure and magnetic properties of the FeCrTe half-Heusler compound. Both generalized gradient approximation (GGA) and local density approximation (LDA) calculations show that the FeCrTe half-Heusler compound is half-metallic ferrimagnetic. The total spin moment is 2 ?B at the equilibrium lattice constant a0=5.87 Å, which agrees with the Slater-Pauling rule. The spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.97 eV, and the spin-flip gap is of 0.40 eV.

Kervan, Selçuk

2013-02-01

287

2D metal slabs in new nickel-tin chalcogenides Ni 7- ?Sn Q2 ( Q?Se, Te): average crystal and electronic structures, chemical bonding and physical properties  

NASA Astrophysics Data System (ADS)

A systematic search for mixed low-valence, nickel-tin chalcogenides performed by establishing phase relations in the parts of Ni-Sn-Se and Ni-Sn-Te ternary systems resulted in the discovery of two new compounds, Ni 5.62SnSe 2 and Ni 5.78SnTe 2. Single crystals of both compounds were prepared by chemical transport with iodine and crystal structures were determined by single crystal X-ray investigation. The ED patterns for Ni 5.78SnTe 2 showed the presence of satellite reflections, which indicate a modulated structure with q?0.4 a*. Average crystal structures of both compounds were determined to be of tetragonal symmetry (Sp.gr. I4/ mmm, Z=2) with a=3.6890(8) Å, c=18.648(3) Å, Rw=0.0716 and a=3.7680(5) Å, c=19.419(4) Å, Rw=0.0832, correspondingly, and are isostructural to known Ni 5.72SbSe 2 and Ni 5.66SbTe 2. Measurements were carried out for both compounds with respect to thermal, electrical and magnetic properties. Ab initio band structure calculations were also performed to take a first glance into the electronic structure of such type compounds. The anisotropy of their band structure was found. Physical property measurements showed both compounds to be the anisotropic metallic conductors and paramagnetics. Calculated difference charge density maps revealed pairwise covalent and multicenter metallic nature of the d-metal—chalcogen and d-metal— p-metal interactions, respectively.

Baranov, A. I.; Isaeva, A. A.; Kloo, L.; Kulbachinskii, V. A.; Lunin, R. A.; Nikiforov, V. N.; Popovkin, B. A.

2004-10-01

288

Radical cations of aromatic selenium compounds: role of Se···X nonbonding interactions.  

PubMed

Selenium centered radical cations in aliphatic selenium compounds are stabilized by formation of two-center-three electron (2c-3e) hemi bonds either with nearby heteroatoms forming monomer radicals or with selenium atoms of the parent molecules forming dimer radicals. Such radicals in aromatic selenium compounds would generally be stabilized as monomers by the delocalization of the spin density along the aromatic ring. To test the assumption if aromatic selenides having Se···X nonbonding interactions can show different types of radical cations, we have performed pulse radiolysis studies of three structurally related aromatic selenium compounds and the results have been substantiated with cyclic voltammetry and quantum chemical calculations. The three aromatic selenium compounds have functional groups like -CH2N(CH3)2 (1), -CH2OH (2), and -CH3 (3) at ortho position to the -SeCH3 moiety. The energy of Se···X nonbonding interactions (E(nb)) for these compounds is in the order 1 (Se···N) > 2 (Se···O) > 3 (Se···H). Radical cations, 1(•+), 2(•+) and 3(•+) were produced by the one-electron oxidation of 1, 2 and 3 by radiolytically generated (•)OH and Br2(•-) radicals. Results on transient spectra, lifetime, and secondary reactions of 1(•+), 2(•+), and 3(•+) indicated that 1(•+) shows a significantly different absorption spectrum, longer lifetime, and less oxidizing power compared to those of 2(•+) or 3(•+). Quantum chemical calculations suggested that 1(•+) is stabilized by the formation of a 2c-3e bond between Se and N atoms, whereas 2(•+) and 3(•+) acquire stability through the delocalization of the spin density on the aromatic ring. These results provide evidence for the first time that stronger nonbonding interactions between Se···N in the ground state, facilitate the formation of stabilized radical cations, which can significantly influence the redox chemistry and the biological activity of aromatic selenium compounds. PMID:23977839

Singh, Beena G; Thomas, Elizabeth; Sawant, Shilpa N; Takahashi, Kohei; Dedachi, Kenchi; Iwaoka, Michio; Priyadarsini, K Indira

2013-09-26

289

From (pi,0) magnetic order to superconductivity with (pi,pi) magnetic resonance in Fe(1.02)Te(1-x)Se(x).  

PubMed

The iron chalcogenide Fe(1+y)(Te(1-x)Se(x)) is structurally the simplest of the Fe-based superconductors. Although the Fermi surface is similar to iron pnictides, the parent compound Fe(1+y)Te exhibits antiferromagnetic order with an in-plane magnetic wave vector (pi,0) (ref. 6). This contrasts the pnictide parent compounds where the magnetic order has an in-plane magnetic wave vector (pi,pi) that connects hole and electron parts of the Fermi surface. Despite these differences, both the pnictide and chalcogenide Fe superconductors exhibit a superconducting spin resonance around (pi,pi) (refs 9, 10, 11). A central question in this burgeoning field is therefore how (pi,pi) superconductivity can emerge from a (pi,0) magnetic instability. Here, we report that the magnetic soft mode evolving from the (pi,0)-type magnetic long-range order is associated with weak charge carrier localization. Bulk superconductivity occurs as magnetic correlations at (pi,0) are suppressed and the mode at (pi, pi) becomes dominant for x>0.29. Our results suggest a common magnetic origin for superconductivity in iron chalcogenide and pnictide superconductors. PMID:20639892

Liu, T J; Hu, J; Qian, B; Fobes, D; Mao, Z Q; Bao, W; Reehuis, M; Kimber, S A J; Prokes, K; Matas, S; Argyriou, D N; Hiess, A; Rotaru, A; Pham, H; Spinu, L; Qiu, Y; Thampy, V; Savici, A T; Rodriguez, J A; Broholm, C

2010-09-01

290

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

Microsoft Academic Search

Transition metal (TM) doped II-VI semiconductors are of current interest for tunable solid state lasers in the mid-infrared (IR) spectral region as well as passive optical Q-switches. Laser action has been demonstrated at ˜2.3 mum from Cr: ZnSe, Cr: ZnS, Cr: CdSe, Cr: CdTe, Cr: Cr: CdMnTe, and at ˜4 mum from Fe: ZnSe. In this work, we report on

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

2006-01-01

291

Electron microscopy study of thermoelectric n-type Bi2(Te0.9Se0.1)3 film deposited by dc sputtering  

NASA Astrophysics Data System (ADS)

Thermoelectric +90 film of the ternary compound was deposited by dc. sputtering from n-type Bi2Te2.7Se0.3 target on polyimide foil substrate at 200 °C. The surface morphology and elemental composition of the deposited film was characterised by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). SEM images and EDX spectra showed that the surface morphology of thermoelectric film exists in the form of big grains with small grains, rough surface and expected structure. The percentage of deviation from stoichiometry was calculated as ±3.599% for Bi2(Te0.9Se0.1)3. Therefore, it was found that the composition of the film stoichiometry was close to the sputtering target stoichiometry. It was seen from transmission electron microscopy (TEM) images and selected area diffraction (SAD) patterns that the thermoelectric film has poly crystalline structures with nano-sized and different orientations. It was also observed that the film have no second phase, precipitate and separation between the layers. Study of lattice images for the sample was done by high-resolution TEM. dhkl values of grains with different orientations were measured and some deformed areas were observed. In addition to, a structural modulation structure was monitorized in the sample. These modulations have a periodicity of approximate 1 nm.

Yildiz, Koksal; Akgul, Unal; Leipner, Hartmut S.; Atici, Yusuf

2013-06-01

292

Growth of Compound Semiconductors in a Low Gravity Environment: Microgravity Growth of PbSnTe  

NASA Technical Reports Server (NTRS)

The growth of the alloy compound semiconductor lead tin telluride (PbSnTe) was chosen for a microgravity flight experiment in the Advanced Automated Directional Solidification Furnace (AADSF), on the United States Microgravity Payload-3 (USNP-3) in February, 1996 and on USNW- 4 in November, 1997. The objective of these experiments was to determine the effect of the reduction in convection, during the growth process, brought about by the microgravity environment. The properties of devices made from PbSnTe, an alloy of PbTe and SnTe, are dependent on the ratio of the elemental components in the starting crystal. Compositional uniformity in the crystal is only obtained if there is no significant mixing in the liquid during growth. The technological importance of PbSnTe lies in its band gap versus composition diagram which has a zero energy crossing at approximately 40% SnTe. This facilitates the construction of long wavelength (greater than 6 gm) infrared detectors and lasers. The properties and utilization of PbSnTe are the subject of other papers. 1,2 PbSnTe is also interesting from a purely scientific point of view. It is, potentially, both solutally and thermally unstable due to the temperature and density gradients present during growth. Density gradients, through thermal expansion, are imposed in directional solidification because temperature gradients are required to extract heat. Solutal gradients occur in directional solidification of alloys due to segregation at the interface. Usually the gradients vary with both experiment design and inherent materials properties. In a simplified one dimensional analysis with the growth axis parallel to the gravity vector, only one of the two instabilities work at a time. During growth, the temperature in the liquid increases ahead of the interface. Therefore the density, due to thermal expansion, is decreasing in that direction. However, the phase diagram shows that the lighter SnTe is preferentially rejected at the interface. This causes the liquid density to increase with distance away from the interface.

Fripp, A. L.; Debnam, W. J.; Rosch, W. R.; Baker, N. R.; Narayanan, R.

1999-01-01

293

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

SciTech Connect

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.

Wallace, W.L.

1984-05-01

294

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

295

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

SciTech Connect

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

Jiang Hailong [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Mao Jianggao [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002 (China)], E-mail: mjg@fjirsm.ac.cn

2008-02-15

296

Reaction Routes for the Synthesis of CuInSe2 Using Bilayer Compound Precursors  

SciTech Connect

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.

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

297

Thin-film CdTe and CuInSe(sub 2) photovoltaic technologies.  

National Technical Information Service (NTIS)

Total-area conversion efficiency of 15%--15.8% have been achieved for thin-film CdTe and CIS solar cells. Modules with power output of 5--53 W have been demonstrated by several groups world-wide. Critical processes and reaction pathways for achieving exce...

H. S. Ullal K. Zweibel B. G. von Roedern

1993-01-01

298

A.C. conduction in glassy Se{70}Te{30-x}Sb{x} alloys: observation of Meyer-Neldel rule  

NASA Astrophysics Data System (ADS)

Temperature and frequency dependence of a.c. conductivity have been studied in glassy Se{70}Te{30-x}Sb{x} (2 ? x ? 10). An agreement between experimental and theoretical results suggests that the a.c. conductivity behaviour of Se-Te-Sb system can be successfully explained by correlated barrier hopping (CBH) model. The observation of Meyer-Neldel rule in case of a.c. conductivity at high temperatures is also reported for glassy Se{70}Te{30-x}Sb{x} (2 ? x ? 10) alloys.

Mehta, N.; Kumar, S.; Kumar, A.

2007-02-01

299

Few-layer nanoplates of Bi 2 Se 3 and Bi 2 Te 3 with highly tunable chemical potential.  

PubMed

A topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk band gap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that group V-VI materials Bi(2)Se(3), Bi(2)Te(3), and Sb(2)Te(3) are TIs with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi(2)Te(3) and Bi(2)Se(3) nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor-solid (VS) growth mechanism. Optical images reveal thickness-dependent color and contrast for nanoplates grown on oxidized silicon (300 nm SiO(2)/Si). As a new member of TI nanomaterials, ultrathin TI nanoplates have an extremely large surface-to-volume ratio and can be electrically gated more effectively than the bulk form, potentially enhancing surface state effects in transport measurements. Low-temperature transport measurements of a single nanoplate device, with a high-k dielectric top gate, show decrease in carrier concentration by several times and large tuning of chemical potential. PMID:20486680

Kong, Desheng; Dang, Wenhui; Cha, Judy J; Li, Hui; Meister, Stefan; Peng, Hailin; Liu, Zhongfan; Cui, Yi

2010-06-01

300

Partitioning of Se, As, Sb, Te and Bi between monosulfide solid solution and sulfide melt - Application to magmatic sulfide deposits  

NASA Astrophysics Data System (ADS)

The chalcogenes (S, Se, Te), semimetals (As, Sb) and the metal Bi are important ligands for noble metals and form a wide range of compositionally diverse minerals with the platinum-group elements (PGE). With the exception of S, few experimental data exist to quantify the behavior of these elements in magmatic sulfide systems. Here we report experimental partition coefficients for Se, Te, As, Sb, and Bi between monosulfide solid solution (mss) and sulfide melt, determined at 950 °C at a range of sulfur fugacities ( fS2) bracketed by the Fe-FeS (metal-troilite) and the Fe 1-×S-S x (mss-sulfur) equilibria. Selenium is shown to partition in mss-saturated sulfide melt as an anion replacing S 2-. Arsenic changes its oxidation state with fS 2 from predominantly anionic speciation at low fS 2, to cationic speciation at high fS 2. The elements Sb, Te, and Bi are so highly incompatible with mss that they can only be present in sulfide melt as cations and/or as neutral metallic species. The partition coefficients derived fall with increasing atomic radius of the element. They also reflect the positions of the respective elements in the Periodic Table: within a group (e.g., As, Sb, Bi) the partition coefficients fall with increasing atomic radius, and within a period the elements of the 15th group are more incompatible with mss than the neighboring elements of the 16th group.

Helmy, Hassan M.; Ballhaus, Chris; Wohlgemuth-Ueberwasser, Cora; Fonseca, Raúl O. C.; Laurenz, Vera

2010-11-01

301

Superconductivity at 2.3 K in the misfit compound (PbSe)1.16(TiSe2)2  

Microsoft Academic Search

The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent compound, TiSe2 , which shows a charge-density wave transition and no superconductivity. The crystal structure, characterized by high-resolution electron microscopy and powder x-ray diffraction, consists of two layers of 1T- TiSe2 alternating with a double layer of (100)

N. Giang; Q. Xu; Y. S. Hor; A. J. Williams; S. E. Dutton; H. W. Zandbergen; R. J. Cava

2010-01-01

302

Defects and high bulk resistivities in the Bi-rich tetradymite topological insulator Bi2+xTe2-xSe  

NASA Astrophysics Data System (ADS)

Defects in the topological insulator Bi2Te2Se are studied by scanning tunneling microscopy. Small numbers of TeBi antisite defects are found and are postulated to be the origin of n-type carriers in this tetradymite composition near the n-to-p crossover. Based on this defect chemistry, we design an alternative method for obtaining resistive Bi2+xTe2-xSe samples, by the introduction of compensating p-type carriers through BiTe antisite defects induced by making the material slightly Bi rich. Our resistivity and Hall coefficient measurements of Bi2+xTe2-xSe crystals grown by the Bridgeman-Stockbarger method show that the carrier concentration at base temperature is significantly reduced from that of stoichiometric samples. Analysis of the measurements reveals the possible underlying chemical distribution along the boules during growth.

Jia, Shuang; Beidenkopf, Haim; Drozdov, Ilya; Fuccillo, M. K.; Seo, Jungpil; Xiong, Jun; Ong, N. P.; Yazdani, Ali; Cava, R. J.

2012-10-01

303

Electrical Switching Studies of Amorphous Ge1Se1Te2 Thin Film for a High-Performance Nonvolatile Phase-Change Memory  

NASA Astrophysics Data System (ADS)

In the present work, we studied the changes in the electrical conductivity occurring in a new composition of amorphous Ge1Se1Te thin film for a high-performance nonvolatile phase-change memory. A phase-change random access memory (PRAM) device without an access transistor is successfully fabricated with the Ge1Se1Te2 phase-change resistor, which has a much higher electrical resistivity than that of conventional Ge2Sb2Te5, and its electric resistivity can be varied by the factor of 105, related to the degree of crystallization. Chalcogenide Ge1Se1Te2 thin film of 100 nm thickness was formed by vacuum deposition at 1.5× 10-5 Torr. The static mode switching characteristics are tested for the 100 ?m-sized Ge1Se1Te2 PRAM device. In the first sweep, the amorphous Ge1Se1Te2 thin film showed a high resistance state in the low voltage region. However, when it reached the threshold voltage, Vth, the electrical resistance of the device was drastically reduced through the formation of an electrically conducting path. The results of pulsed mode switching of the 20 ?m-sized Ge1Se1Te2 PRAM devices show that the reset process of the device was accomplished with an 80 ns-8.6 V pulse and the set process of the device was accomplished with a 200 ns-4.3 V pulse.

Lee, Jae?Min; Shin, Kyung; Yeo, Cheol?Ho; Chung, Hong?Bay

2006-06-01

304

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

NASA Astrophysics Data System (ADS)

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

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

2007-10-01

305

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

SciTech Connect

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

Djemel, M., E-mail: jmal_manel@yahoo.fr [Laboratoire de Chimie Inorganique, Universite de Sfax, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia); Abdelhedi, M., E-mail: m_abdelhedi2002@yahoo.fr [Laboratoire de Chimie Inorganique, Universite de Sfax, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia); Laboratoire Leon Brouillon, CE/Saclay, 91191 Gif-Sur-Yvette Cedex (France); Zouari, N., E-mail: bizrirl@yahoo.fr [Laboratoire de l'Etat solide, Universite de Sfax, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia); Dammak, M., E-mail: meddammak@yahoo.fr [Laboratoire de Chimie Inorganique, Universite de Sfax, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia); Kolsi, A.W., E-mail: kolsi_abdelhwaheb@yahoo.fr [Laboratoire de Chimie Inorganique, Universite de Sfax, Faculte des Sciences de Sfax, BP 1171, 3000 Sfax (Tunisia)

2012-12-15

306

Thermodynamic, kinetic, and computational study of heavier chalcogen (S, Se, and Te) terminal multiple bonds to molybdenum, carbon, and phosphorus.  

PubMed

Enthalpies of chalcogen atom transfer to Mo(N[t-Bu]Ar)3, where Ar = 3,5-C6H3Me2, and to IPr (defined as bis-(2,6-isopropylphenyl)imidazol-2-ylidene) have been measured by solution calorimetry leading to bond energy estimates (kcal/mol) for EMo(N[t-Bu]Ar)3 (E = S, 115; Se, 87; Te, 64) and EIPr (E = S, 102; Se, 77; Te, 53). The enthalpy of S-atom transfer to PMo(N[ t-Bu]Ar) 3 generating SPMo(N[t-Bu]Ar)3 has been measured, yielding a value of only 78 kcal/mol. The kinetics of combination of Mo(N[t-Bu]Ar)3 with SMo(N[t-Bu]Ar)3 yielding (mu-S)[Mo(N[t-Bu]Ar)3]2 have been studied, and yield activation parameters Delta H (double dagger) = 4.7 +/- 1 kcal/mol and Delta S (double dagger) = -33 +/- 5 eu. Equilibrium studies for the same reaction yielded thermochemical parameters Delta H degrees = -18.6 +/- 3.2 kcal/mol and Delta S degrees = -56.2 +/- 10.5 eu. The large negative entropy of formation of (mu-S)[Mo(N[t-Bu]Ar)3]2 is interpreted in terms of the crowded molecular structure of this complex as revealed by X-ray crystallography. The crystal structure of Te-atom transfer agent TePCy3 is also reported. Quantum chemical calculations were used to make bond energy predictions as well as to probe terminal chalcogen bonding in terms of an energy partitioning analysis. PMID:18260626

McDonough, James E; Mendiratta, Arjun; Curley, John J; Fortman, George C; Fantasia, Serena; Cummins, Christopher C; Rybak-Akimova, Elena V; Nolan, Steven P; Hoff, Carl D

2008-03-17

307

Charge transport mechanism in intercalated Cu x HfSe2 compounds  

NASA Astrophysics Data System (ADS)

Alternating current resistivity measurements have been performed for the first time on intercalated Cu x HfSe2 (0 ? x ? 0.18) samples using the impedance spectroscopy technique together with direct current measurements. The results obtained indicate the hopping mechanism of charge transport in Cu x HfSe2 compounds. It has been found that an increase in the copper content in samples enhances relaxation processes. The ac conductivity exhibits frequency dispersion described by the universal dynamic response.

Pleshchev, V. G.; Baranov, N. V.; Melnikova, N. V.; Selezneva, N. V.

2012-07-01

308

Improved thermoelectric properties of AgSbTe 2 based compounds with nanoscale Ag 2Te in situ precipitates  

Microsoft Academic Search

Ternary AgxSb2?xTe3?x thermoelectric materials have been prepared with x value varying from 0.78 to 0.93. By adjusting the Ag2Te ratio, double-phased in situ nanocomposites were obtained with the nanostructured Ag2Te embedded in the AgSbTe2 matrix when x>0.81. The high-resolution transmission electron microscopy observation showed that the Ag2Te precipitates were in situ formed as nanodots and nanoscale lamellar structures. Compared with

S. N. Zhang; T. J. Zhu; S. H. Yang; C. Yu; X. B. Zhao

2010-01-01

309

Magnetic state and properties of the Fe0.5TiSe2 intercalation compound  

NASA Astrophysics Data System (ADS)

The Fe0.5TiSe2 compound with a monoclinic crystal structure has been prepared by intercalation of Fe atoms between Se-Ti-Se sandwiches in the layered structure of TiSe2. The crystal and magnetic structures, electrical resistivity, and magnetization of the Fe0.5TiSe2 compound have been investigated. According to the neutron diffraction data, the Fe0.5TiSe2 compound has a tilted antiferromagnetic structure at temperatures below the Néel temperature of 135 K, in which the magnetic moments of Fe atoms are antiferromagnetically ordered inside layers and located at an angle of approximately 74.4° with respect to the layer plane. The magnetic moment of Fe atoms is equal to (2.98 ± 0.05)?B. The antiferromagnetic ordering is accompanied by anisotropic spontaneous magnetostrictive distortions of the crystal lattice, which is associated with the spin-orbit interaction and the effect of the crystal field.

Selezneva, N. V.; Baranov, N. V.; Pleshchev, V. G.; Mushnikov, N. V.; Maksimov, V. I.

2011-02-01

310

Pressure-induced semiconductor-metal transition in Te-Se mixtures  

Microsoft Academic Search

X-ray diffraction patterns, electrical resistance and optical reflectivity for amorphous and crystalline Te1 ? xSex have been measured under high pressure. It is found that the high pressure monoclinic phase with x ~ 0.6, which has a puckered layer structure containing planar zigzag chains with period 3, can be quenched to atmospheric pressure. The correlation between the chain structure and

Yoshinori Ohmasa; Itsuro Yamamoto; Hirohisa Endo

1996-01-01

311

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

SciTech Connect

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.

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

312

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

SciTech Connect

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.

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

1994-08-01

313

The new misfit compound (BiSe)1.15(TiSe2)2 and the role of dimensionality in the Cux(BiSe)1+?(TiSe2)n series  

NASA Astrophysics Data System (ADS)

The synthesis and physical properties of the new misfit compound (BiSe)1.15(TiSe2)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 (TiSe2)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)1.13(TiSe2), which shows no charge density wave, and infinite-layered (bulk) 1T-TiSe2, which undergoes a charge density wave transition at T=202 K. Intercalation with copper, Cux(BiSe)1.15(TiSe2)2, (0?x?0.10) is also reported, but unlike CuxTiSe2, no superconductivity is observed down to T=0.05 K. Thus, the series Cux(BiSe)1+?(TiSe2)n provides an effective approach to elucidate the impact of dimensionality on charge density wave formation and superconductivity.

Trump, Benjamin A.; Livi, Kenneth J. T.; McQueen, Tyrel M.

2014-01-01

314

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

SciTech Connect

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.

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

315

CuIn1?xGaxSe2 and CdTe PV solar cells  

Microsoft Academic Search

Higher indium proportion in the first precursor was employed to eliminate pits in CuIn1?xGaxSe2 films prepared by two Se-vapor selenizations of metallic precursors. CuIn1?xGaxSe2 films had large, faceted grains, and a near-optimum composition Cu:In:Ga:Se 24.25:22.21:4.40:49.14. Ga incorporated using a Cu-Ga(22 at. %) alloy target was enhanced by optimizing the time-temperature profiles of selenizations. CuIn1?xGaxSe2 solar cells gave Voc of 451.8

Neelkanth G. Dhere

1996-01-01

316

CuIn1-xGaxSe2 and CdTe PV solar cells  

Microsoft Academic Search

Higher indium proportion in the first precursor was employed to eliminate pits in CuIn1-xGaxSe2 films prepared by two Se-vapor selenizations of metallic precursors. CuIn1-xGaxSe2 films had large, faceted grains, and a near-optimum composition Cu:In:Ga:Se 24.25:22.21:4.40:49.14. Ga incorporated using a Cu-Ga(22 at. %) alloy target was enhanced by optimizing the time-temperature profiles of selenizations. CuIn1-xGaxSe2 solar cells gave Voc of 451.8

Neelkanth G. Dhere

1996-01-01

317

Superconductivity at 2.3 K in the misfit compound (PbSe)1.16(TiSe2)2  

NASA Astrophysics Data System (ADS)

The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent compound, TiSe2 , which shows a charge-density wave transition and no superconductivity. The crystal structure, characterized by high-resolution electron microscopy and powder x-ray diffraction, consists of two layers of 1T- TiSe2 alternating with a double layer of (100) PbSe. Transport measurements suggest that the superconductivity is induced by charge transfer from the PbSe layers to the TiSe2 layers.

Giang, N.; Xu, Q.; Hor, Y. S.; Williams, A. J.; Dutton, S. E.; Zandbergen, H. W.; Cava, R. J.

2010-07-01

318

Experimental verification of theoretically calculated parameters of Te15(Se100-xBix)85(x = 0,2,4at.%) amorphous semiconductors  

NASA Astrophysics Data System (ADS)

The Se-Te-Bi amorphous semiconductors have been prepared by melt quenching technique. In the present study, we have theoretically calculated the optical energy band gap, glass transition temperature and density of Se-Te-Bi amorphous semiconductors. Experimentally the optical energy band gap has been found from transmission spectra of thin films using Tauc's method, glass transition temperature from Differential Thermal Analysis data and density using Archimedes method.

Kumar, Kameshwar; Thakur, Nagesh

2013-06-01

319

Mutual influence of sublattices in the Cu y Fe x TiSe2 cointercalate compound  

NASA Astrophysics Data System (ADS)

The concentration dependence of parameters of the Cu y Fe x TiSe2 cointercalate compound has been interpreted based on the statistical approach relating the structural characteristics of the material to the probability of implementation of various configurations of defects. The Vegard's law approximation assuming the absence of interactions between the defects has been used.

Balakirev, V. F.; Titov, A. A.

2013-03-01

320

Aharonov-Bohm Excitons at Elevated Temperatures in Type-II ZnTe/ZnSe Quantum Dots  

NASA Astrophysics Data System (ADS)

Optical emission from type-II ZnTe/ZnSe quantum dots demonstrates large and persistent oscillations in both the peak energy and intensity indicating the formation of coherently rotating states. Furthermore, these Aharonov-Bohm oscillations are shown to be remarkably robust and persist until 180 K. This is at least one order of magnitude greater than the typical temperatures in lithographically defined rings. To our knowledge, this is the highest temperature at which the AB effect has been observed in solid-state and molecular nanostructures.

Sellers, I. R.; Whiteside, V. R.; Kuskovsky, I. L.; Govorov, A. O.; McCombe, B. D.

2008-04-01

321

Aharonov-Bohm excitons at elevated temperatures in type-II ZnTe/ZnSe quantum dots.  

PubMed

Optical emission from type-II ZnTe/ZnSe quantum dots demonstrates large and persistent oscillations in both the peak energy and intensity indicating the formation of coherently rotating states. Furthermore, these Aharonov-Bohm oscillations are shown to be remarkably robust and persist until 180 K. This is at least one order of magnitude greater than the typical temperatures in lithographically defined rings. To our knowledge, this is the highest temperature at which the AB effect has been observed in solid-state and molecular nanostructures. PMID:18517978

Sellers, I R; Whiteside, V R; Kuskovsky, I L; Govorov, A O; McCombe, B D

2008-04-01

322

X-ray near-edge structure of the II-VI group ternary compounds: Experimental and theoretical studies of CdxHg1-xTe and CdxZn1-xTe  

NASA Astrophysics Data System (ADS)

Measurements of the x-ray-absorption edges for ternary II-VI group semiconducting compounds CdxHg1-xTe and CdxZn1-xTe have been made for the Cd and Te L edges and the K edge of Zn. These data are compared with calculations based on electron densities of states for the conduction-band states in CdxHg1-xTe and CdxZn1-xTe for x=0.0,0.5,1.0. The calculations, based on linear-muffin-tin-orbital results, cover energies up to about 17 eV above the conduction-band edge. Both the experimental data and calculated density of states are used to analyze results for the ternary compounds in terms of a virtual-crystal model based on CdTe, HgTe, and ZnTe. Using a virtual-crystal model based on the Te L1 and L3 x-ray edges for CdTe, HgTe, and ZnTe, predicted edges for the ternary compounds Cd-Hg-Te and Cd-Zn-Te are compared with the direct experimental data and theoretical calculations. Results obtained in these two ways are found to be in good agreement with each other.

Kisiel, A.; Dahr, A.-I. Ali; Lee, P. M.; Dalba, G.; Fornasini, P.; Burattini, E.

1990-12-01

323

Fabrication of Cu3Zn3Se ternary compounds by AP-MOCVD  

NASA Astrophysics Data System (ADS)

I-II-VI Ternary chalcopyrite semiconductors of Cu1-xZn1-ySe2-? (Cu3Zn3Se) were successfully fabricated by the atmospheric pressure metal-organic chemical vapor deposition method for the first time. Four major peaks of (112), (220)/(204), (312)/(116), and (400), accompanied by three minor peaks of (103), (211) and (301) were observable in the X-ray diffraction spectra. In particular, the presence of those latter low-intensity peaks featured the formation of the chalcopyrite type Cu3Zn3Se compound. Typical absorption coefficients of the films produced were found to vary from 2.75×10cm-1 to 5.75×10cm-1 over all visible light range and from the same optical absorption spectra the energy gap of the material was extracted to be about 2.02 eV. Moreover, the photoluminescence measurement conducted at room temperature also exhibited a strong orange-colored emission line at 1.94 eV, which further confirmed that the Cu3Zn3Se ternary compound has been prepared. In addition, the cross-sectional and top-view scanning electron microscopy images characterized the fabricated Cu3Zn3Se compound as a polycrystalline film of thickness about 1-1.3 ?m and consisting of 1-2.5 ?m sized grains.

Chen, Tsung-Ming; Lan, Shan-Ming; Uen, Wu-Yih; Yang, Tsun-Neng; Chang, Kuo-Jen; Shen, Chin-Chang; Hsu, Cheng-Fang; Jhao, Jian-Chang

2013-10-01

324

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

NASA Astrophysics Data System (ADS)

Atomically resolved structural and electronic properties of FeTe1-xSex (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 FeTe0.55Se0.45. 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.

He, Xiaobo; Li, Guorong; Zhang, Jiandi; Karki, A. B.; Jin, Rongying; Sales, B. C.; Sefat, A. S.; McGuire, M. A.; Mandrus, D.; Plummer, E. W.

2011-06-01

325

Band structure of MoS2, MoSe2, and ?-MoTe2: Angle-resolved photoelectron spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

In this work the complete valence-band structure of the molybdenum dichalcogenides MoS2, MoSe2, and ?-MoTe2 is presented and discussed in comparison. The valence bands have been studied using both angle-resolved photoelectron spectroscopy (ARPES) with synchrotron radiation, as well as ab initio band-structure calculations. The ARPES measurements have been carried out in the constant-final-state (CFS) mode. The results of the calculations show in general very good agreement with the experimentally determined valence-band structures allowing for a clear identification of the observed features. The dispersion of the valence bands as a function of the perpendicular component k? of the wave vector reveals a decreasing three-dimensional character from MoS2 to ?-MoTe2 which is attributed to an increasing interlayer distance in the three compounds. The effect of this k? dispersion on the determination of the exact dispersion of the individual states as a function of k|| is discussed. By performing ARPES in the CFS mode the k|| component for off-normal emission spectra can be determined. The corresponding k? value is obtained from the symmetry of the spectra along the ?A, KH, and ML lines, respectively.

Böker, Th.; Severin, R.; Müller, A.; Janowitz, C.; Manzke, R.; Voß, D.; Krüger, P.; Mazur, A.; Pollmann, J.

2001-12-01

326

GW study of topological insulators Bi2Se3, Bi2Te3, and Sb2Te3: Beyond the perturbative one-shot approach  

NASA Astrophysics Data System (ADS)

We present GW calculations of the topological insulators Bi2Se3, Bi2Te3, and Sb2Te3 within the all-electron full-potential linearized augmented-plane-wave formalism. Quasiparticle effects produce significant qualitative changes in the band structures of these materials when compared to density functional theory (DFT), especially at the ? point, where band inversion takes place. There, the widely used perturbative one-shot GW approach can produce unphysical band dispersions, as the quasiparticle wave functions are forced to be identical to the noninteracting single-particle states. We show that a treatment beyond the perturbative approach, which incorporates the off-diagonal GW matrix elements and thus enables many-body hybridization to be effective in the quasiparticle wave functions, is crucial in these cases to describe the characteristics of the band inversion around the ? point in an appropriate way. In addition, this beyond one-shot GW approach allows us to calculate the values of the Z2 topological invariants and compare them with those previously obtained within DFT.

Aguilera, Irene; Friedrich, Christoph; Bihlmayer, Gustav; Blügel, Stefan

2013-07-01

327

Electronic structure and magnetic properties of transition-metal doped Bi2Te3, Bi2Se3, and Sb2Te3 for diluted magnetic semiconductors  

NASA Astrophysics Data System (ADS)

The semiconducting tetradymite-structure materials Bi2Te3, Bi2Se3, and Sb2Te3 serve as the basis for high-performance room-temperature thermoelectric devices. Recently, it was found that these materials act as diluted magnetic semiconductors (DMS) with Tc˜ 10 K using a few percent doping of transition metal atoms (T = Ti, V, Cr, Mn, Fe). Electronic structure calculations have been performed using the full-potential linear muffin-tin orbital (FP-LMTO) method to understand these materials magnetic properties. The T atoms substitute at the much larger Bi/Sb sites which leads to isolated atomic-like states with very little crystal-field splitting and approximately 3+ valence. This leads to a high spin state with the magnetic moments essentially following Hund's rule. The position of the T 3d states in the band gap will be investigated by analysis of the density of states (DOS). The effects of lattice relaxation and the magnetic interaction of T atoms in the unit cell will also be investigated.

Larson, Paul

2005-03-01

328

New bismuth selenium oxides: syntheses, structures, and characterizations of centrosymmetric Bi2(SeO3)2(SeO4) and Bi2(TeO3)2(SeO4) and noncentrosymmetric Bi(SeO3)(HSeO3).  

PubMed

Three new mixed metal selenium oxides materials, Bi2(SeO3)2(SeO4), Bi2(TeO3)2(SeO4), and Bi(SeO3)(HSeO3), have been synthesized by hydrothermal and solid-state reactions using Bi(NO3)3·5H2O, SeO2 (or TeO2), H2SeO4, and Bi2O3 as reagents. The reported materials have been structurally characterized by single crystal X-ray diffraction. While Bi2(SeO3)2(SeO4) and Bi2(TeO3)2(SeO4) are crystallographically centrosymmetric (CS), Bi(SeO3)(HSeO3) crystallizes in a noncentrosymmetric (NCS) space group. The isostructural Bi2(SeO3)2(SeO4) and Bi2(TeO3)2(SeO4) exhibit three-dimensional framework structures that are composed of BiO6, Se(4+)O3 (or Te(4+)O3), and Se(6+)O4 polyhedra. However, Bi(SeO3)(HSeO3) exhibits corrugated layers that are composed of BiO5, Se(4+)O3, and Se(4+)O2(OH) polyhedra. All three materials contain local asymmetric coordination environments attributable to the lone pairs on the Bi(3+), Se(4+), and/or Te(4+) cations. Powder second-harmonic generation (SHG) measurements on NCS Bi(SeO3)(HSeO3) using 1064 nm radiation indicate that the material has a SHG efficiency of approximately 20 times that of ?-SiO2 and is not phase-matchable (type 1). The origin and magnitude of the SHG efficiency of Bi(SeO3)(HSeO3) is explained by determining the net direction of the polarizations arising from individual asymmetric polyhedra. Infrared spectroscopy, thermal analysis, elemental analysis, and dipole moment calculations for the reported materials are also presented. PMID:23506341

Lee, Eun Pyo; Song, Seung Yoon; Lee, Dong Woo; Ok, Kang Min

2013-04-01

329

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

SciTech Connect

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

Gray, J.L.; Schwartz, R.J.; Lee, Y.J. (Purdue Univ., Lafayette, IN (United States))

1992-04-01

330

Improvement in Thermoelectric Properties of Se-Free Cu3SbS4 Compound  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

331

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

332

Figure of Merit of (Sb0.75Bi0.25)2- x In x Te2.8Se0.2 Single Crystals  

NASA Astrophysics Data System (ADS)

We have shown previously that indium doping is beneficial for thermoelectric properties of (Sb0.75Bi0.25)2Te3. This effect was ascribed to a change in the magnitude and mechanism of hole scattering and a decrease in thermal conductivity. Since the state-of-the-art material for p-type legs in low-temperature applications is the quaternary Bi0.5Sb1.5Te3- y Se y , we have attempted to dope this material with In, hoping to improve its properties further. Indeed, the doping enhances the figure of merit of (Sb0.75Bi0.25)2- x In x Te2.8Se0.2 by more than 15% compared with the values measured on undoped (Sb0.75Bi0.25)2Te2.8Se0.2 below room temperature.

Drasar, C.; Hovorkova, A.; Lostak, P.; Ballikaya, S.; Li, C.-P.; Uher, C.

2010-09-01

333

Nuclear magnetic resonance data of C14H10O2SeTe2  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

334

Nuclear magnetic resonance data of C18H18O4SeTe2  

NASA Astrophysics Data System (ADS)

This document is part of Part 6 `Organic Metalloid Compounds' of Subvolume D 'Chemical Shifts and Coupling Constants for Carbon-13' of Landolt-Börnstein III/35 'Nuclear Magnetic Resonance Data', Group III 'Condensed Matter'.

Mikhova, B. M.

335

Spatial inhomogeneity of the superconducting gap and order parameter in FeSe0.4Te0.6  

NASA Astrophysics Data System (ADS)

We have performed a low-temperature scanning tunneling microscopy and spectroscopy study of the iron chalcogenide superconductor FeSe0.4Te0.6 with TC?14 K. Spatially resolved measurements of the superconducting gap reveal substantial inhomogeneity on a nanometer length scale. Analysis of the structure of the gap seen in tunneling spectra by comparison with calculated spectra for different superconducting order parameters (s-wave, d-wave, and anisotropic s-wave) yields the best agreement for an order parameter with anisotropic s-wave symmetry with an anisotropy of ˜40%. The temperature dependence of the superconducting gap observed in places with large and small gap size indicates that it is indeed the superconducting transition temperature which is inhomogeneous. The temperature dependence of the gap size has been found to differ from the one predicted by BCS theory. An analysis of the local gap size in relation to the local chemical composition shows almost no correlation with the local concentration of Se/Te atoms at the surface.

Singh, U. R.; White, S. C.; Schmaus, S.; Tsurkan, V.; Loidl, A.; Deisenhofer, J.; Wahl, P.

2013-10-01

336

Raman spectroscopy determination of the Debye temperature and atomic cohesive energy of CdS, CdSe, Bi2Se3, and Sb2Te3 nanostructures  

NASA Astrophysics Data System (ADS)

We have formulated the size and temperature dependence of the phonon relaxation dynamics for CdS, CdSe, Bi2Se3, and Sb2Te3 nanostructures based on the framework of bond order-length-strength correlation, core-shell configuration, and local bond averaging approach. The Raman shifts are correlated directly to the identities (nature, order, length, and energy) of the representative bond of the specimen without needing involvement of the Grüneisen mode parameters or considering the processes of phonon decay or multi-phonon resonant scattering. Quantitative information of the Debye temperature, the atomic cohesive energy, the reference frequencies from which the Raman shifts proceed, and the effective coordination numbers of the randomly sized particles, as well as the length and energy of the representative bond, has been obtained. It is clarified that the size-induced phonon softening arises intrinsically from the cohesive weakening of the undercoordinated atoms in the skin up to three atomic layers and the thermally derived phonon softening results from the thermally lengthening and weakening of bonds. Developed approach empowers the Raman technique in deriving quantitative and direct information regarding bond stiffness relaxation with applied stimuli such as coordination, mechanical, thermal, and chemical environment, which are crucial to practical applications.

Yang, X. X.; Zhou, Z. F.; Wang, Y.; Jiang, R.; Zheng, W. T.; Sun, Chang Q.

2012-10-01

337

Superconductivity at 2.3 K in the misfit compound (PbSe)_{1.16}(TiSe_{2})_{2}  

Microsoft Academic Search

The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a\\u000asuperconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent\\u000acompound, TiSe2, which shows a charge density wave transition and no\\u000asuperconductivity. The crystal structure, characterized by high resolution\\u000aelectron microscopy and powder x-ray diffraction, consists of two layers of\\u000a1T-TiSe2 alternating with a double layer of (100)

N. Giang; Q. Xu; Y. S. Hor; A. J. Williams; S. E. Dutton; H. W. Zandbergen; R. J. Cava

2010-01-01

338

Enhancement of carrier transport properties of BixSb2-xTe3 compounds by electrical sintering process  

NASA Astrophysics Data System (ADS)

BixSb2-xTe3 (x=0.4 and 0.5) powders were pressed and sintered by passing a high-density electric current under nitrogen ambient. The electrically sintered BixSb2-xTe3 was found to have a marked increase in Hall mobility but a moderate reduction in carrier density. We propose that electric-current induced atomic diffusion plays an important role in modulating crystal defects in BixSb2-xTe3 compounds. The hot-pressed Bi0.4Sb1.6Te3 shows a threefold increase in ZT after electrical sintering process. With the electrical sintering approach we can preserve fine-grain microstructure, and hence low thermal conductivity of BixSb2-xTe3 with reasonable electrical resistivity and Seebeck coefficient.

Liao, Chien-Neng; Wu, Li-Chieh

2009-08-01

339

Magnetic Order and Transitions in the Spin-web Compound Cu3TeO6  

NASA Astrophysics Data System (ADS)

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.

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

340

Growth of Single Crystals of ZnTe and ZnTe(1-X) Se(X) BY Temperature Gradient Solution Zoning.  

National Technical Information Service (NTIS)

Single crystals of ZnTe and ZnTe1-xSex with x up to 0.13 have been grown from the elements by temperature gradient solution zoning using excess tellurium as a solvent. Best results have been obtained with charges with the compositions 45/55 at. pct Zn, Te...

J. Steininger R. E. England

1967-01-01

341

Effect of Substrate on the Structure and Thermoelectric Properties of n-Type Bi2Te3- y Se y Thin Films Prepared by Electrodeposition  

NASA Astrophysics Data System (ADS)

n-Type Bi2Te3- y Se y thin films were prepared by potentiodynamic electrodeposition onto Au, Bi, and Bi2Te3- y Se y substrates at room temperature. The electrochemical behaviors of Bi3+, HTeO2 +, and H2SeO3 on different substrates were investigated by cyclic voltammetry. The morphology, composition, and structure of the films were studied by using environmental scanning electron microscopy (ESEM), energy-dispersive spectroscopy (EDS), and x-ray diffraction (XRD), respectively. The thermoelectric properties of n-type Bi2Te3- y Se y films were determined by measuring the Seebeck coefficient ( ?) and electrical resistivity ( ?). The results showed that the composition and morphology of the films were sensitive to the substrate material. X-ray diffraction (XRD) analysis indicated that the preferred orientation of annealed films was affected by the substrate and that the film prepared on the Bi2Te3- y Se y substrate exhibited the strongest (015) orientation, with rhombohedral structure. It was proved that the properties of the annealed films could be affected by the substrate and that the film with the highest power factor ( P = ? 2/ ?) was obtained on the Bi2Te3- y Se y substrate.

Jin, Yiteng; Wang, Wei

2010-09-01

342

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

SciTech Connect

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

Jiang Hailong [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, and the Graduate School of the Chinese Academy of Sciences, Fuzhou 350002 (China); Feng Meiling [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, and the Graduate School of the Chinese Academy of Sciences, Fuzhou 350002 (China); Mao Jianggao [State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, and the Graduate School of the Chinese Academy of Sciences, Fuzhou 350002 (China)]. E-mail: mjg@ms.fjirsm.ac.cn

2006-06-15

343

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

PubMed

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

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

344

Thermoelectric efficiency of the extruded samples of Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 solid solutions with different grain size  

NASA Astrophysics Data System (ADS)

The effect of grain size of a starting powder and heat treatment on thermoelectric efficiency (Z) of extruded samples of Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 solid solutions in temperature range from 77 up to 350 K. It is clarified, that in case of Bi0.5Sb1.5Te3 solid solution maximal Z is observed in samples with of grains 630 microns and passed heat treatment in vacuum at 690K within 5 hours. In a case of Bi2Te2.7Se0.3 solid solutions in samples with dimension of grains 630 microns, non-passed heat treatment. It is shown, that the obtained results are satisfactorily explained by effect of texture and structural imperfection son density and mobility of charge carriers, and also on the scattering mechanism of photons in extruded samples of the investigated solid solutions.

Djafarov, E. G.; Aliyeva, T. D.; Abdinov, D. S.

2000-11-01

345

First-Principles Study of Structural and Electronic Properties of Alkali Metal Chalcogenides: M2CH [M: li, NA, K, Rb; Ch: O, S, se, TE  

NASA Astrophysics Data System (ADS)

Ground-state structural properties of alkali metal selenides and tellurides (M2X) [M: Li, Na, K, Rb; X: Se, Te] have been studied in the framework of density functional theory for the first time using local density approximation, Perdew-Burke-Ernzerhof generalized gradient approximation (GGA) and Wu-Cohen (WC) GGA parameterization schemes. Also structural properties of alkali metal oxides and sulfides (M2X) [M: Li, Na, K, Rb; X: O, S] have been reinvestigated using WC GGA. Electronic band structures of alkali metal chalcogenide compounds have been calculated using the aforementioned schemes as well as the modified GGA proposed by Engel and Vosko. The calculated structural parameters for all 16 materials have been compared with earlier theoretical and experimental results, and certain trends are discussed. Furthermore, electronic density of states for these compounds has also been presented herein and behavior in electronic properties analyzed. Li, K and Rb chalcogenides have been found to have indirect bandgap, whereas Na chalcogenides appear to have direct bandgap.

Alay-E-Abbas, S. M.; Sabir, N.; Saeed, Y.; Shaukat, A.

346

High performance n-type (Bi,Sb)2(Te,Se)3 for low temperature thermoelectric generator  

NASA Astrophysics Data System (ADS)

Starting with elemental chunks of bismuth, antimony, tellurium and selenium, densified bulk materials (Bi0.95Sb0.05)2(Te1-xSex)3 (x = 0.10, 0.13, 0.15 and 0.17) were prepared by melt spinning subsequently combined with a spark plasma sintering process. The prepared bulk materials display fine grain size and numerous layered structures with a size of 10-100 nm; moreover, details of the composition difference and phase difference cannot be observed. Measurements of electrical conductivity, Seebeck coefficient and thermal conductivity have been performed in the temperature range 300-500 K, and it is found that the thermoelectric properties are significantly affected by the content of selenium. All the prepared samples show higher ratios of electrical conductivity and total thermal conductivity compared with state-of-the-art commercial zone melted materials, mainly a large reduction in lattice thermal conductivity, which is more beneficial to the concept of 'electron crystal phonon glass'. Subsequently, the resulting thermoelectric figure of merit ZT value reaches a maximum of 1.0 at 460 K for the n-type (Bi0.95Sb0.05)2(Te0.85Se0.15)3 bulk material. Compared with traditional zone melted materials, the peak ZTs move towards a higher temperature and this study demonstrates the possibility of preparing materials with high performance, which can be applied for low temperature power generation or multi-stage devices.

Wang, Shanyu; Xie, Wenjie; Li, Han; Tang, Xinfeng

2010-08-01

347

Electrical properties of the 85% Bi 2Te 3-15% Bi 2Se 3 thermoelectric material doped with SbI 3 and CuBr  

Microsoft Academic Search

The temperature dependences of the Seebeck coefficient, resistivity, Hall coefficient, and carrier mobility of SbI3- and CuBr-doped 85% Bi2Te3-15% Bi2Se3 single crystals have been characterized at temperatures ranging from 77 to 600 K, and the degenerate temperature, scattering parameter, bandgap energy, and the effective masses of the electron and hole have been determined. The degenerate temperature of the 85% Bi2Te3-15%

D. B. Hyun; J. S. Hwang; T. S. Oh; J. D. Shim; N. V. Kolomoets

1998-01-01

348

Optical Properties and Growth Mechanism of Multiple Type-II ZnTe/ZnSe Quantum Dots Grown by Migration-Enhanced Epitaxy  

SciTech Connect

The properties of multiple type-II ZnTe/ZnSe quantum dots (QDs), which are coexistent with isoelectronic centers formed by Te, grown by migration-enhanced epitaxy, are studied. The samples with a single deposition cycle of Zn-Te-Zn sandwiched between ZnSe barriers are investigated via temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL measurements. It is found that the PL consists of two broad bands: a 'blue' band, which is dominant at low temperatures, and a 'green' band, which is observed at T=60 K. Upon increasing the excitation intensity by about 4 orders of magnitude, the peak energy position of the blue band remains nearly the same, whereas the green band exhibits a large blueshift of {approx}50 meV, which suggests that the green band is due to, at least partially, the recombination of excitons bound to type-II QDs. The existence of type-II ZnTe/ZnSe QDs is further supported by the results of magneto-PL, for which the oscillation in the PL intensity as a function of magnetic field is observed. The properties of ZnTe/ZnSe QDs grown under the same Zn/Te flux ratio but with one and three contiguous deposition cycles of Zn-Te-Zn are compared. It is concluded that type-II QDs are formed in both types of samples; however, the density, size, and chemical composition of QDs strongly depend on the deposition of the submonolayer quantities of ZnTe.

Gong,Y.; MacDonald, W.; Neumark, G.; Tamargo, M.; Kuskovsky, I.

2008-01-01

349

Specific features in the behavior of the effective mass and mobility in n -(Bi, Sb) 2 (Te, Se, S) 3 solid solutions  

Microsoft Academic Search

The thermoelectric properties of the multicomponent solid solutions Bi2?x\\u000a SbxTe3?y?z\\u000a SeySz with substitutions of atoms in both sublattices of Bi2Te3 were studied. The data obtained in studies of the galvanomagnetic effects in weak magnetic fields were used to properly take\\u000a into account the change in the carrier scattering mechanisms due to the substitutions Sb ? Bi, Se, and S ?

L. N. Luk’yanova; V. A. Kutasov; P. P. Konstantinov; V. V. Popov

2006-01-01

350

Size- effect induced high thermoelectric figure of merit in PbSe and PbTe nanowires.  

PubMed

The fundamental properties that compose the thermoelectric figure of merit are investigated in the confined systems of PbSe and PbTe nanowires, with the goal to improve the thermoelectric efficiency. Using the Landauer electronic transport theory, we verify that the figure of merit can be several times larger than the bulk value for nanowires with diameters down to the one nanometer scale. This enhancement in the thermoelectric efficiency is primarily due to the reduction of the thermal conductivity and an increase in the power factor. The origin of these desireable properties, that enable the transformation of heat into electricity, comes from the confinement effect which increases the density of states around the Fermi level, either for an n- or p-type system. PMID:24654001

Wrasse, Ernesto O; Torres, Alberto; Baierle, Rogério J; Fazzio, Adalberto; Schmidt, Tome M

2014-05-01

351

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

352

First indications of spontaneous ordering in ZnSe[sub 0. 50]Te[sub 0. 50] alloy  

SciTech Connect

We describe our study of II--VI alloy ZnSe[sub 0.5]Te[sub 0.5] in search of spontaneous ordering. Samples were prepared by molecular beam epitaxy in a variety of structure configurations and growth temperatures, in order to scan a wide range of parameters and identify a favorable condition for ordering. Transmission electron microscopy was carried out on these samples and revealed indications of spontaneous ordering in several samples, where regions with stacking of atoms that appear to be different from the zinc-blende structure were observed. Preliminary study shows that such regions have the CuAu [i.e., the (100) superlattice] structure.

Luo, H.; Samarth, N.; Short, S.W.; Xin, S.H.; Furdyna, J.K. (Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)); Ahrenkiel, P.; Bode, M.H.; Al-Jassim, M.M. (National Renewable Energy Laboratory, Golden, Colorado 80401 (United States))

1994-03-01

353

Enhanced Superconducting Transition Temperature in FeSe0.5Te0.5 Thin Films  

SciTech Connect

We report magnetoresistive and structural measurements of superconducting FeSe0.5Te0.5 epitaxial thin films grown by pulsed laser deposition. Enhanced onset superconducting transition temperature ({approx} 17 K) is observed in some of these films. Structural analysis by x-ray diffraction and high resolution transmission electron microscopy reveal that these films generally have significantly shorter out-of-plane lattice constant c than the bulk value, suggesting that the out-of-plane changes have a dominating impact on the superconducting transition in iron-based superconductors. Our data also indicate that the upper critical field Hc2(0) of those films may reach as high as 50 T.

Si, W.; Lin, Z.-W.; Jie, Q.; Yin, W.-G.; Zhou, J.; Gu, G.; Johnson, P.D.; Li, Q.

2009-08-03

354

Chemical Bondings around Intercalated Li Atoms in LiTiX2 (X=S, Se, and Te)  

NASA Astrophysics Data System (ADS)

A systematic study of the electronic structure and chemical bonding of the Li-intercalated titanium dichalcogenides, LiTiX2 (X=S, Se, and Te), is performed by a first-principles molecular-orbital method using a model cluster composed of 75 atoms. The discrete-variational (DV)-X? method was employed and Mulliken's population analyses were thoroughly conducted. The net charge of Li is found to be approximately 0.1 independently of X-species. Net charges of Ti and X are not significantly affected by the Li intercalation. Strong covalent bonding is formed between Li and X with a bond-overlap population (BOP) of 0.173 0.176. The BOP of Ti X bonding decreases by about 10% due to the presence of Li. These results should be important for determining battery properties when the dichalcogenide are used for positive electrodes.

Kim, Yang-Soo; Koyama, Yukinori; Tanaka, Isao; Adachi, Hirohiko

1998-12-01

355

Effect of Zn incorporation on the a.c. conductivity of glassy Se{70}Te{30} alloy  

NASA Astrophysics Data System (ADS)

The present work reports the temperature and frequency dependence of a.c. conductivity in glassy Se{70}Te{30-x}Zn{x} (x = 0, 2, 4 and 6) alloys in the temperature range 300-500 K and frequency range 1 kHz. An agreement between experimental and theoretical results suggests that the a.c. conductivity behaviour of the present samples can be successfully explained by correlated barrier hopping (CBH) model. The density of defect states has been determined using this model for all the glassy alloys. The results show that bipolaron hopping dominates over single-polaron hopping in this glassy system. This is explained in terms of lower values of the maximum barrier height for single-polaron hopping.

Srivastava, S.; Mehta, N.; Shukla, R. K.; Kumar, A.

2008-12-01

356

Anisotropic spin-singlet pairings in CuxBi2Se3 and Bi2Te3  

NASA Astrophysics Data System (ADS)

Possible anisotropic spin-singlet pairings in Bi2X3 (X is Se or Te) are studied. Among six pairings compatible with the crystal symmetry, two novel pairings show nontrivial surface Andreev bound states, which form flat bands and could produce zero-bias conductance peak in measurements such as point-contact spectroscopy. By considering purely repulsive short-range Coulomb interaction as the pairing mechanism, the dominant superexchange terms are all antiferromagnetic, which would usually favor spin-singlet pairing in Bi2X3. Mean field analyses show that the interorbital pairing interaction favors a mixed spatial-parity anisotropic pairing state, and one pairing channel with zero-energy surface states has a sizable component. The results provide important information for future experiments.

Hao, Lei; Wang, Gui-Ling; Lee, Ting-Kuo; Wang, Jun; Tsai, Wei-Feng; Yang, Yong-Hong

2014-06-01

357

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

358

First-principles study of electronic and optical properties of BaS, BaSe and BaTe  

NASA Astrophysics Data System (ADS)

The optimized crystal structure, energy band structures, density of states (DOS) and optical properties of BaX (X=S, Se and Te) were investigated by the full potential linearized augmented plane wave plus local orbitals method (FP-LAPW+lo). The exchange-correlation potential was treated using the generalized gradient approximation (GGA). We have used also Engel and Vosko GGA (EV-GGA) formalism to improve the band gap results. The calculated results such as band gaps, dielectric constants and reflectivity spectra showed good agreement with the experimental data. The effect of the spin-orbit coupling (SOC) on the optical properties was also studied and found to be very small, especially in the low-energy region.

Feng, Zhenbao; Hu, Haiquan; Lv, Zengtao; Cui, Shouxin

2010-10-01

359

Structural and elastic properties of barium chalcogenides (BaX, X=O, Se, Te) under high pressure  

NASA Astrophysics Data System (ADS)

In the present paper we have investigated the high-pressure, structural phase transition of Barium chalcogenides (BaO, BaSe and BaTe) using a three-body interaction potential (MTBIP) approach, modified by incorporating covalency effects. Phase transition pressures are associated with a sudden collapse in volume. The phase transition pressures and associated volume collapses obtained from TBIP show a reasonably good agreement with experimental data. Here, the transition pressure, NaCl-CsCl structure increases with decreasing cation-to-anion radii ratio. In addition, the elastic constants and their combinations with pressure are also reported. It is found that TBP incorporating a covalency effect may predict the phase transition pressure, the elastic constants and the pressure derivatives of other chalcogenides as well.

Bhardwaj, Purvee; Singh, Sadhna; Gaur, Neeraj Kumar

2008-06-01

360

Model for the magnetoresistance of the silver-rich Ag2+? Se and Ag2+?Te thin films  

NASA Astrophysics Data System (ADS)

This work proposes a model for linear magnetoresistance (MR) by considering Ag2+?Se and Ag2+? Te thin films as two-dimensional two-component (silver metal component and semiconductor component) compositions. The model addresses the dependence of the MR on the magnetic field, temperature and the conductivities of the two components without the magnetic field. The model predictions agree well with the available experimental data. It is found that there is a critical volume fraction of the silver component at which the MR reaches a maximum value. We interpret the occurrence of the critical volume fraction as a consequence of the percolation between silver particles and the variation of the disorder of the microstructure in the material.

Xu, Jie; Zhang, Duanming; Yang, Fengxia; Li, Zhihua; Deng, Zongwei; Pan, Yuan

2008-06-01

361

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

SciTech Connect

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

Verma, Ajay Singh; Sharma, Sheetal; Jindal, Vijay Kumar [Department of Physics, Panjab University, Chandigarh, 160014 (India); Sarkar, Bimal Kumar [Department of Physics, VIT University, Vellore, TN, 632014 (India)

2011-12-12

362

High ZT in p-type (PbTe)1-2x(PbSe)x(PbS)x thermoelectric materials.  

PubMed

Lead chalcogenide thermoelectric systems have been shown to reach record high figure of merit values via modification of the band structure to increase the power factor or via nanostructuring to reduce the thermal conductivity. Recently, (PbTe)1-x(PbSe)x was reported to reach high power factors via a delayed onset of interband crossing. Conversely, the (PbTe)1-x(PbS)x was reported to achieve low thermal conductivities arising from extensive nanostructuring. Here we report the thermoelectric properties of the pseudoternary 2% Na-doped (PbTe)1-2x(PbSe)x(PbS)x system. The (PbTe)1-2x(PbSe)x(PbS)x system is an excellent platform to study phase competition between entropically driven atomic mixing (solid solution behavior) and enthalpy-driven phase separation. We observe that the thermoelectric properties of the PbTe-PbSe-PbS 2% Na doped are superior to those of 2% Na-doped PbTe-PbSe and PbTe-PbS, respectively, achieving a ZT ?2.0 at 800 K. The material exhibits an increased the power factor by virtue of valence band modification combined with a very reduced lattice thermal conductivity deriving from alloy scattering and point defects. The presence of sulfide ions in the rock-salt structure alters the band structure and creates a plateau in the electrical conductivity and thermopower from 600 to 800 K giving a power factor of 27 ?W/cmK(2). The very low total thermal conductivity values of 1.1 W/m·K of the x = 0.07 composition is accounted for essentially by phonon scattering from solid solution defects rather than the assistance of endotaxial nanostructures. PMID:24533466

Korkosz, Rachel J; Chasapis, Thomas C; Lo, Shih-han; Doak, Jeff W; Kim, Yoon Jun; Wu, Chun-I; Hatzikraniotis, Euripidis; Hogan, Timothy P; Seidman, David N; Wolverton, Chris; Dravid, Vinayak P; Kanatzidis, Mercouri G

2014-02-26

363

Designed synthesis, structure, and properties of a family of ferecrystalline compounds [(PbSe)(1.00)](m)(MoSe2)(n).  

PubMed

The targeted synthesis of multiple compounds with specific controlled nanostructures and identical composition is a grand challenge in materials chemistry. We report the synthesis of the new metastable compounds [(PbSe)1.00]m(MoSe2)n using precursors each designed to self-assemble into a specific compound. To form a compound with specific values for m and n, the number of atoms within each deposited elemental layer was carefully controlled to provide the correct absolute number of atoms to form complete layers of each component structural unit. On low-temperature annealing, these structures self-assemble with a specific crystallographic orientation between the component structural units with atomically abrupt interfaces. There is rotational disorder between the component structural units and between MoSe2 basal plane units within the MoSe2 layers themselves. The lead selenide constituent has a distorted rock salt structure exactly m bilayers thick leading to peaks in the off-axis diffraction pattern as a result of the finite size of and rotational disorder between the crystallites. The in-plane lattice parameters of the PbSe and MoSe2 components are independent of the value of m and n, suggesting little or no strain caused by the interface between them. These compounds are small band gap semiconductors with carrier properties dominated by defects and exhibit extremely low thermal conductivity as a result of the rotational disorder. The thermal conductivity can be tuned by varying the ratio of the number of ordered PbSe rock salt layers relative to the number of rotationally disordered MoSe2 layers. This approach, based on controlling the local composition of the precursor and low temperature to limit diffusion rates, provides a general route to the synthesis of new compounds containing alternating layers of constituents with designed nanoarchitecture. PMID:23819532

Heideman, Colby L; Tepfer, Sara; Lin, Qiyin; Rostek, Raimar; Zschack, Paul; Anderson, Michael D; Anderson, Ian M; Johnson, David C

2013-07-31

364

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

365

Crystal structure of the R 7Cu 3Te 12 (R = Tb, Dy, Ho, Er and Tm) compounds  

Microsoft Academic Search

The crystal structures of the R7Cu3Te12 (R=Tb, Dy, Ho, Er and Tm) compounds (space group R3¯m, Pearson symbol hR27-5) were determined by means of X-ray single crystal diffraction: a=0.43020(6)nm, c=4.1720(8)nm, RI=0.0498 (Ho7Cu3Te12) and X-ray powder diffraction: a=0.43279(3)nm, c=4.1896(3)nm, RI=0.0932 (Tb7Cu3Te12); a=0.43114(5)nm, c=4.1779(8)nm, RI=0.0891 (Dy7Cu3Te12); a=0.42802(2)nm, c=4.1575(2)nm, RI=0.0849 (Er7Cu3Te12); a=0.42709(3)nm, c=4.1540(3)nm, RI=0.0858 (Tm7Cu3Te12). The close packed Te layers in …hhcc… stacking

L. D. Gulay; I. D. Olekseyuk; A. Pietraszko

2005-01-01

366

Spin-phonon coupling in the superconductor FeTe0.5Se0.5 from first-principles calculations  

NASA Astrophysics Data System (ADS)

We present a first-principles pseudopotential study on the phonon structure and the electron-phonon (EP) interaction of superconductor FeTe0.5Se0.5 in both the nonmagnetic (NM) and striped antiferromagnetic (SAF) phases with the ordered and disordered structural models. The calculations give similar results for the two different structural models, implying that the superconductivity in FeTe0.5Se0.5 may be insensitive to the local atomic structure. Comparing the phonon behavior in the SAF phase with that in the NM phase, we find that the spin-lattice interaction can lead to the phonon softening and increase EP coupling constant ? by about 50%. This enhancement EP coupling may play an important role in the superconducting pairing, but this mechanism alone cannot explain the high Tc in superconductor FeTe0.5Se0.5.

Li, Jian; Huang, GuiQin

2013-04-01

367

Magnetization hysteresis and time decay measurements in FeSe0.50Te0.50: Evidence for fluctuation in mean free path induced pinning  

NASA Astrophysics Data System (ADS)

We present results of magnetic measurements relating to vortex phase diagram in a single crystal of FeSe0.5Te0.5 which displays a second magnetization peak anomaly for H?c. The possible role of the crystalline anisotropy on vortex pinning is explored via magnetic torque magnetometry. We present evidence in favor of pinning related to spatial variations of the charge carrier mean free path leading to small bundle vortex pinning by randomly distributed (weak) pinning centers for both H?c and H?c. This is further corroborated using magnetization data for H?c in a single crystal of FeSe0.35Te0.65. Dynamical response across the second magnetization peak (SMP) anomaly in FeSe0.5Te0.5 has been compared with that across the well-researched phenomenon of peak effect (PE) in a single crystal of CeRu2.

Das, P.; Thakur, Ajay D.; Yadav, Anil K.; Tomy, C. V.; Lees, M. R.; Balakrishnan, G.; Ramakrishnan, S.; Grover, A. K.

2011-12-01

368

Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Annual subcontract report, 1 April 1990--31 March 1991  

SciTech Connect

The polycrystalline nature of thin-film CdTe and CuInSe{sub 2} solar cells continues to be a major factor in several individual losses that limit overall cell efficiency. This report describes progress in the quantitative separation of these losses, including both measurement and analysis procedures. It also applies these techniques to several individual cells to help document the overall progress with CdTe and CuInSe{sub 2} cells. Notably, CdTe cells from Photon Energy have reduced window photocurrent losses to 1 mA/Cm{sup 2}; those from the University of South Florida have achieved a maximum power voltage of 693 mV; and CuInSe{sub 2} cells from International Solar Electric Technology have shown a hole density as high as 7 {times} 10{sup 16} cm{sup {minus}3}, implying a significant reduction in compensation. 9 refs.

Sites, J.R. [Colorado State Univ., Fort Collins, CO (United States)

1991-12-31

369

Experimental and theoretical investigations of the contact ion pairs formed by reactions of the anions [(EPR2)2N]- (R = (i)Pr, (t)Bu; E = S, Se) with the cations [(TePR2)2N]+ (R = (i)Pr, (t)Bu).  

PubMed

Reactions of the sodium salts [(EPR(2))(2)N]Na(TMEDA) (R = (i)Pr, (t)Bu; E = S, Se) with the iodide salts [(TePR(2))(2)N]I (R = (i)Pr, (t)Bu) in toluene produce the mixed-chalcogen systems [(EPR(2))(2)N][(TePR(2))(2)N] (6b, E = Se, R = (t)Bu; 6c, E = S, R = (t)Bu; 7b, E = Se, R = (i)Pr; 7c, E = S, R = (i)Pr). Compounds 6b, 6c, 7b, and 7c have been characterized in solution by variable-temperature multinuclear ((31)P, (77)Se, and (125)Te) NMR spectroscopy and in the solid state by single-crystal X-ray crystallography. The structures are comprised of contact ion pairs linked by bonds between Te and S or Se atoms. For the tert-butyl derivatives 6b and 6c, the anionic half of the molecule is coordinated in a bidentate (E,E') fashion to one Te atom of the cationic half to give a spirocycle, whereas in the isopropyl derivatives 7b and 7c, the anion acts as a monodentate ligand with only one E-Te bond and the second S or Se atom pointing away from the cation. A comparison of the chalcogen-chalcogen bond orders in 6b, 6c, and the all-tellurium system 6a (E = Te), as determined from the experimental bond lengths, shows that the Te-Te bond order in the cations decreases as the strength of the E-Te interaction increases. This trend is attributed to increased electron donation from the anion into the lowest unoccupied molecular orbital [sigma*(Te-Te)] of the cation along the series S < Se < Te. A similar trend is observed for the monodentate contact ion pairs 7b and 7c. Density functional theory calculations provided information about the relative energies of bidentate and monodentate contact ion pair structures and the extent of intramolecular electron transfer in these systems. PMID:20507112

Robertson, Stuart D; Chivers, Tristram; Tuononen, Heikki M

2009-07-20

370

Improvement of thermoelectric properties induced by uniquely ordered lattice field in Bi2Se0.5Te2.5 pillar array  

NASA Astrophysics Data System (ADS)

In this study, it was found that uniquely ordered lattice field favors transport of carriers but hinder that of phonons. The n-Bi2Se0.5Te2.5 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 Bi2Se0.5Te2.5 pillar array were greatly enhanced in comparison with those of the ordinary film. The Bi2Se0.5Te2.5 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 Bi2Se0.5Te2.5 film. Introduction of such ordered lattice field into TE films is therefore a very promising approach.

Tan, Ming; Hao, Yanming; Wang, Gangzhi

2014-07-01

371

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

372

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

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.

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

1983-01-01

373

Effect of Ce Substitution for Sb on the Thermoelectric Properties of AgSbTe2 Compound  

NASA Astrophysics Data System (ADS)

We have prepared Ce-doped polycrystalline AgSbTe2.01 compounds from high-purity elements by a melt-quench technique followed by spark plasma sintering, and their thermoelectric transport properties have been investigated in the temperature range of 300 K to 625 K. The actual concentration of Ce was much less than the initial composition, but roughly proportional to it. Small additions of Ce shifted the composition of the homogeneity range from the nearly ideal atomic ratio Ag:Sb:Te = 0.98:1.02:2.01 toward Sb rich (Ag poor), and led to the reemergence of Ag2Te impurity in AgSbTe2 compound. The Ce-doped samples possessed lower electrical conductivity compared with the undoped AgSbTe2.01 compound at room temperature, but the carrier mobility and effective mass were essentially constant, indicating intact band structure near the covalent band maximum upon Ce substitution for Sb. Due to the decrease of lattice vibration anharmonicity resulting from Ce substitution for Sb, the lattice conductivity of the Ce-doped samples was about 0.1 W m-1 K-1 higher than that of the AgSbTe2.01 sample, and the magnitude spanned the range from 0.30 W m-1 K-1 to 0.55 W m-1 K-1. A ZT of 1.20 was achieved at about 615 K for the AgSb0.99Ce0.01Te2.01 sample.

Du, B.; Li, H.; Tang, X.

2014-04-01

374

Transport properties and polarization phenomena in intercalated Ag x HfSe2 compounds  

NASA Astrophysics Data System (ADS)

The electrical properties of intercalated Ag x HfSe2 compounds ( x = 0.1, 0.2) have been investigated for the first time. Investigations have been performed using various current electrodes, which make it possible to pass either the electron current or the ion current across the sample. Polarization effects, which indicate the self-consistent migration of charge carriers in the samples, have been found for the samples at room temperature. Based on the characteristic features of polarization decay, coefficients of conjugated chemical diffusion have been evaluated.

Pleshchev, V. G.; Selezneva, N. V.; Baranov, N. V.

2013-01-01

375

Structure and properties of the intercalation compound Cu x TiSe2  

NASA Astrophysics Data System (ADS)

Compounds in the pseudobinary Cu-TiSe2 intercalation system are directly synthesized from elements. The phase diagram of the system is investigated, the solubility limit of copper is measured, and the structure of the material is determined. In the copper concentration range up to 60 mol %, single crystals are grown and the temperature dependence of the electrical resistance is measured. It is demonstrated that, in the concentration range under investigation, the intercalation of the system with copper gives rise to a set of phenomena observed upon intercalation of alkali metals.

Titov, A. A.; Merentsov, A. I.; Kar'kin, A. E.; Titov, A. N.; Fedorenko, V. V.

2009-02-01

376

Resistive switching at the nanoscale in the Mott insulator compound GaTa4Se8.  

PubMed

We study the Mott insulator compound GaTa4Se8 in which we previously discovered an electric-field-induced resistive transition. We show that the resistive switching is associated to the appearance of metallic and super-insulating nanodomains by means of scanning tunneling microscopy/spectroscopy (STM/STS). Moreover, we show that local electronic transitions can be controlled at the nanoscale at room temperature using the electric field of the STM tip. This opens the way for possible applications in resistive random access memories (RRAM) devices. PMID:23826620

Dubost, Vincent; Cren, Tristan; Vaju, Cristian; Cario, Laurent; Corraze, Benoît; Janod, Etienne; Debontridder, François; Roditchev, Dimitri

2013-08-14

377

Compound  

NASA Astrophysics Data System (ADS)

We have prepared Ce-doped polycrystalline AgSbTe2.01 compounds from high-purity elements by a melt-quench technique followed by spark plasma sintering, and their thermoelectric transport properties have been investigated in the temperature range of 300 K to 625 K. The actual concentration of Ce was much less than the initial composition, but roughly proportional to it. Small additions of Ce shifted the composition of the homogeneity range from the nearly ideal atomic ratio Ag:Sb:Te = 0.98:1.02:2.01 toward Sb rich (Ag poor), and led to the reemergence of Ag2Te impurity in AgSbTe2 compound. The Ce-doped samples possessed lower electrical conductivity compared with the undoped AgSbTe2.01 compound at room temperature, but the carrier mobility and effective mass were essentially constant, indicating intact band structure near the covalent band maximum upon Ce substitution for Sb. Due to the decrease of lattice vibration anharmonicity resulting from Ce substitution for Sb, the lattice conductivity of the Ce-doped samples was about 0.1 W m-1 K-1 higher than that of the AgSbTe2.01 sample, and the magnitude spanned the range from 0.30 W m-1 K-1 to 0.55 W m-1 K-1. A ZT of 1.20 was achieved at about 615 K for the AgSb0.99Ce0.01Te2.01 sample.

Du, B.; Li, H.; Tang, X.

2014-06-01

378

Laser-induced crystallization in amorphous films of ? (C = S, Se, Te), potential optical storage media  

NASA Astrophysics Data System (ADS)

The amorphous-to-crystalline phase change induced by a continuous-wave 0022-3727/32/3/001/img7 laser was investigated systematically in the case of as-grown amorphous films of 0022-3727/32/3/001/img8, 0022-3727/32/3/001/img9 and 0022-3727/32/3/001/img10 and results were compared. The photo-thermal process is found to be responsible for the phase change in all three compounds. The minimum threshold laser power required to induce optical contrast at an irradiated site was found to depend on the film thickness; however, the required power density was found to be of the order of 0022-3727/32/3/001/img11 for all three films. All three films exhibited good potential for use as the WORM kind of storage devices, 0022-3727/32/3/001/img9 films having the minimum threshold power. 0022-3727/32/3/001/img9 and 0022-3727/32/3/001/img10 films in the non-stoichiometric phase exhibited potential for reversible storage.

Arun, P.; Vedeshwar, A. G.; Mehra, N. C.

1999-02-01

379

Vortex creep down to 0.3 K in superconducting Fe(Te,Se) single crystals  

NASA Astrophysics Data System (ADS)

We report on a study of the vortex creep in Fe1+?(TexSe1-x) single crystals (x =0.5 and 0.4) down to 0.28 K (˜Tc/50) and up to ?0Ha=2T. The relaxation of the current density [J (t)] has been measured during 20 hours and the decay of J (t) can be well described by a J(t )?[ln(t/t0)]-1/? law. We show that the relaxation exponent ? tends towards 0 for T <2K and ?0Ha<0.1T [i.e. J(t )?(t0/t)?] and increases for increasing T and/or Ha. Our measurements strongly suggest that the logarithmic creep rate R =-d ln(J)/dln(t) remains finite at zero temperature (R|T?0 ?2%) and hence that quantum creep plays a dominant role in the relaxation process at low temperature. A maximum is observed in both the temperature and field dependence of R (t=100s,T,Ha), which can be associated to a crossover from a single vortex (one-dimensional) to a bundle (three-dimensional) creep regime.

Klein, T.; Grasland, H.; Cercellier, H.; Toulemonde, P.; Marcenat, C.

2014-01-01

380

Preparation and electrical transport properties of n-type GaxPb1-xTe compounds  

Microsoft Academic Search

N-type GaxPb1-xTe(x = 0.01~0.05) compounds were prepared by melting reaction method, and the influence of Ga content on the electric properties of this compounds were investigated. The results showed that the carrier concentration increased while the Hall mobility decreased with increasing Ga content. The electrical conductivity also increased significantly with increasing Ga content.

Lingling Yin; Yonggao Yan; Xinfeng Tang; Haijun Liu; Qingjie Zhang

2007-01-01

381

High Thermopower and Low Thermal Conductivity in Semiconducting Ternary K?Bi?Se Compounds. Synthesis and Properties of ?-K 2 Bi 8 Se 13 and K 2.5 Bi 8.5 Se 14 and Their Sb Analogues  

Microsoft Academic Search

‚-K2Bi8Se13 (I), K2Sb8Se13 (II), K2.5Bi8.5Se14 (III), and K2.5Sb8.5Se14 (IV) were synthesized by a molten flux method. The black needles of compound I were formed at 600 °C and crystallized in the monoclinicP21\\/m space group (No. 11) witha ) 17.492(3) Å, b ) 4.205(1) Å, c ) 18.461(4) Å, ‚ ) 90.49(2)°. The final R\\/Rw ) 6.7\\/5.7%. Compound II is isostructural

Duck-Young Chung; Kyoung-Shin Choi; Lykourgos Iordanidis; Jon L. Schindler; Paul W. Brazis; Carl R. Kannewurf; Baoxing Chen; Siqing Hu; Ctirad Uher; Mercouri G. Kanatzidis

1997-01-01

382

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

383

Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe{sub 0.92}-FeSe{sub 0.5}Te{sub 0.5} system  

SciTech Connect

Thin films of FeSe{sub 0.92} and FeSe{sub 0.5}Te{sub 0.5} iron chalcogenide superconductors and solid solutions containing these components in different ratios have been grown on the surface of LaAlO{sub 3} (10 1-bar 2) crystals by pulsed laser deposition. Films of solid solutions have been deposited by simultaneous laser ablation from two targets of the FeSe{sub 0.92} and FeSe{sub 0.5}Te{sub 0.5} stoichiometric compositions onto one substrate. An X-ray diffraction study of the film structure shows that the films grown are epitaxial and their lattice parameters regularly vary with the ratio of the deposited components, which was controllably varied by changing the ablation intensities from the targets.

Stepantsov, E. A., E-mail: stepantsov@ns.cryst.ras.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Kazakov, S. M.; Belikov, V. V. [Moscow State University (Russian Federation)] [Moscow State University (Russian Federation); Makarova, I. P. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)] [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Arpaia, R.; Gunnarsson, R.; Lombardi, F. [Chalmers University of Technology, Department of Microtechnology and Nanoscience (Sweden)] [Chalmers University of Technology, Department of Microtechnology and Nanoscience (Sweden)

2013-09-15

384

Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe0.92-FeSe0.5Te0.5 system  

NASA Astrophysics Data System (ADS)

Thin films of FeSe0.92 and FeSe0.5Te0.5 iron chalcogenide superconductors and solid solutions containing these components in different ratios have been grown on the surface of LaAlO3 (102) crystals by pulsed laser deposition. Films of solid solutions have been deposited by simultaneous laser ablation from two targets of the FeSe0.92 and FeSe0.5Te0.5 stoichiometric compositions onto one substrate. An X-ray diffraction study of the film structure shows that the films grown are epitaxial and their lattice parameters regularly vary with the ratio of the deposited components, which was controllably varied by changing the ablation intensities from the targets.

Stepantsov, E. A.; Kazakov, S. M.; Belikov, V. V.; Makarova, I. P.; Arpaia, R.; Gunnarsson, R.; Lombardi, F.

2013-09-01

385

Effect of the substrate on the electrodeposition of Bi{sub 2}Te{sub 3-y}Se{sub y} thin films  

SciTech Connect

The potentiostatic electrodeposition of n-type Bi{sub 2}Te{sub 3-y}Se{sub y} thermoelectric films onto stainless steel and gold substrates from nitric acid aqueous solutions has been carried out at room temperature. The cathodic process during the electrodeposition of Bi{sub 2}Te{sub 3-y}Se{sub y} films was investigated by cyclic voltammetric experiments. The structure and surface morphology of Bi{sub 2}Te{sub 3-y}Se{sub y} films deposited on both substrates were characterized by X-ray diffraction (XRD) and environment scanning electron microscopy (ESEM) coupled with energy dispersive spectroscopy (EDS). Electrical and thermoelectric properties of as-deposited films were also measured at room temperature. The results show that the reduction process under the same depositing conditions on gold and stainless steel substrates is very different. On gold substrates, H{sub 2}SeO{sub 3} in the electrolyte is firstly reduced to elemental Se, and then the deposited Se reacts with HTeO{sub 2}{sup +} and Bi{sup 3+} to form Bi{sub 2}Te{sub 3-y}Se{sub y} alloy. On stainless steel substrates, HTeO{sub 2}{sup +} in the electrolyte is firstly replaced by elemental Fe to produce elemental Te, and subsequently the generated Te reacts with H{sub 2}SeO{sub 3} and Bi{sup 3+} to form Bi{sub 2}Te{sub 3-y}Se{sub y} alloy. Analysis of ESEM show that the surface morphology of the films electrodeposited on gold substrates is more compact than that on stainless steel substrates. The XRD patterns indicate that the films electrodeposited on both substrates exhibit preferential orientation along (1 1 0) plane, but the relative peak intensity of (0 1 5) and (2 0 5) planes on stainless steel substrates is stronger than that on gold substrates. The Seebeck coefficient and electrical resistivity of the films deposited on stainless steel substrates are higher than that on gold substrates.

Bu Luxia [Department of Applied Chemistry, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Wang Wei [Department of Applied Chemistry, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)], E-mail: wwangg@vip.sina.com; Wang Hui [Analytical Center, Tianjin University, Tianjin 300072 (China)

2008-07-01

386

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

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

387

Half-metallic properties of the (001) surfaces of vanadium-substituted Rock-salt GeTe-based compounds  

NASA Astrophysics Data System (ADS)

We study the properties of the (001) surfaces of ternary vanadium compounds based on the rocksalt semiconductor GeTe. In one of the compounds 25% of Ge atoms are replaced by V atoms, and in another, the substitution is as large as 50%. Using a first-principles method, we calculate the electronic structure of the two systems for two different surface terminations. The studied systems are found to be half-metallic ferromagnets. The half-metallic gap in every system is found to be larger than it is in the bulk. However, in Ge-terminated surfaces, the bottom of the conduction band is very near the Fermi level, and this may cause an instability of the half-metallicity in the systems. VGe-terminated surfaces are characterized by a more stable half-metallic ferromagnetic order. The larger amount of replacement of Ge atoms by V atoms also supresses the magnetic properties of the system. The largest calculated magnetic moment on the V atom at the topmost layer of the (001) surface is 2.602 µ B . The presence of a magnetic center causes polarization of the metalloids: in the 50%-substituted GeTe, Te atoms are negatively polarized, and Ge atoms are slightly positively polarized. The largest magnetic moment on Te is calculated for Te atom at the topmost layer and is -0.107 µ B .

Cho, Lee-Hyun; Bialek, Beata; Lee, Jae Il

2012-11-01

388

Thermal Expansion of n-Type Doped Bi2Te2.88Se0.12 and p-Type Doped Bi0.52Sb1.48Te3 Solid Solutions from -60°C to +60°C  

NASA Astrophysics Data System (ADS)

An automated dilatometric system was developed to measure the thermal expansion of solid materials from -60°C to +400°C. This system was then applied to measure the linear thermal expansions of n-type doped Bi2Te2.88Se0.12 and p-type doped Bi0.52Sb1.48Te3 solid solutions along the a-axis from -60°C to +60°C. The experiments were performed using a vertical “tube/push rod” dilatometer under constant-temperature conditions. The initial alloys were synthesized from Bi, Te, and Se or Sb (each at 99.999 mass% purity) in stoichiometric ratios. The method based on the correlation between the thermal expansion and the heat capacity was proposed to calculate the axial expansion coefficients along the c-axis.

Stern, Yu.; Pavlova, L.; Mironov, R.

2010-09-01

389

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)

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.

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

2010-06-01

390

First-principles calculations of the structural, phonon and thermal properties of ZnX (X = S, Se,Te) chalcogenides  

NASA Astrophysics Data System (ADS)

Zinc chalcogenides, ZnX (X = S, Se and Te), are investigated with the full-potential linear-augmented plane wave method within the framework of the density functional theory for their structural, phonon and thermal properties. We consider the generalized gradient approximation for the purpose of exchange-correlation energy determination. Murnaghan’s equation of state is used for volume optimization by minimizing the total energy with respect to the unit cell volume. The elastic constants are calculated to examine the crystal structure stability, binding properties and bond character of zinc chalcogenides. By means of frozen-phonon method within the harmonic approximation, we work out phonon dispersion, lattice dynamics and thermal properties of ZnX compounds. The phonon frequencies in the first Brillouin zone, at the zone centre (?) and at the zone boundary (X or L) are estimated. The calculated lattice parameters and thermal parameters are in good agreement with other theoretical calculations as well as with the available experimental data.

Sarkar, B. K.; Verma, A. S.; Sharma, S.; Kundu, S. K.

2014-07-01

391

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

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.

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

392

Density functional theory analysis of the local chemical bonds in the periodic tantalum dichalcogenides TaX2 (X=S, Se, Te)  

NASA Astrophysics Data System (ADS)

The electronic structure of layered tantalum dichalcogenides 1T-TaX2 (X=S, Se, Te) have been studied both with the linear muffin tin orbitals-atomic sphere approximation (LMTO-ASA) and the Amsterdam density functional for band (ADF-band) programs. The first code (LMTO) provides band structures, density of states (DOS), and crystal orbitals Hamiltonian populations (COHP) while the second one allows accurate atomic charge calculations by means of a powerful electron density numerical integration. All those analyses were used to rationalize the electronic structures of the three 1T-TaX2 phases, in particular to enlighten the 13×13 structural modulations observed in TaS2 and TaSe2, and to put forward the influence of the local chemical Ta-Te bonds on the relative stability of the 1T-TaTe2 phase vs the distorted monoclinical one. The indirect overlap between the two bands responsible for the metallic properties of TaS2 and TaSe2 has been shown to significantly increase the tantalum d electron count compared to its formal value (d1) leading to a more realistic occupation of the threefolded t2g-like bands involved in the 13×13 instability. Owing to the low electronegative character of Te compared to S and Se, the direct overlap occurring at the Fermi level results in an electron transfer from local Ta-Te bonding states to local Ta-Te antibonding ones yielding a destabilization of the metal-chalcogen bonds.

Doublet, M.-L.; Remy, S.; Lemoigno, F.

2000-10-01

393

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

SciTech Connect

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.

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

394

Kinetics of Crystal Growth in Amorphous Solid and Supercooled Liquid TeSe sub 20 Using DTA and D.C. Conductivity Measurements.  

National Technical Information Service (NTIS)

Curves of reaction rate versus temperature for constant heating rates (phi=1-10 exp 0 C/min) constructed by analytical methods have been used to demonstrate the crystallization kinetics of amorphous solid TeSe sub 20 . The devitrification process takes pl...

M. F. Kotkata E. A. Mahmoud M. K. El-Mously

1979-01-01

395

Ab initio study of the BiSe and BiTe electronic spectra: What happens with X2-X1 emission in the heavier Bi chalcogenides?  

NASA Astrophysics Data System (ADS)

A series of spin-orbit configuration interaction calculations has been carried out for the BiSe and BiTe molecules and analyzed in comparison with data obtained earlier for the isovalent BiO and BiS systems. An avoided crossing caused by the spin-orbit interaction between the X 2? and A 4? electronic states is shown to have a decisive effect on the lower-energy spectrum in each case. Irregularities in the X2 3/2 state vibrational manifold occur as a consequence of this nonadiabatic interaction, and the v vibrational number for the onset of these perturbations is found to gradually decrease in going from BiO to BiSe, in agreement with experiment. In BiTe the shape of the X2 potential curve is so altered by the avoided crossing that its minimum becomes shifted to a significantly larger distance than for the X1 state, unlike the case for BiSe or the lighter Bi chalcogenides. This characteristic appears to be the root cause for the fact that the X2 state has not yet been found experimentally in the BiTe spectrum, despite careful searches in the expected energy range. Radiative lifetimes have also been calculated for the low-lying states of both the BiSe and BiTe molecules, and these results are found to be consistent with experimental observations.

Lingott, Rainer M.; Liebermann, Heinz-Peter; Alekseyev, Aleksey B.; Buenker, Robert J.

2004-04-01

396

Structural influence on transport properties in [(PbSe)1.00]m(MoSe2)n misfit layered compounds  

NASA Astrophysics Data System (ADS)

The dependence of the electrical properties on the structural variation and annealing conditions are explored for the turbostratically disordered misfit layered compounds [(PbSe)1.00]m(MoSe2)n where m and n range between 1 and 5 layers. The thickness of the PbSe and MoSe2 layers both appear to have a significant impact on the transport properties of these materials, although variations in defect levels also make a significant contribution. When the thickness of the MoSe2 unit is thick relative to the PbSe unit, typically both a low resistivity (?0.05 ?m) as well as a low Seebeck coefficient (?50 µV K?1) are observed, compared to when m and n are both small, which tends to result in a relatively high resistivity and moderate Seebeck coefficient. When the m is large (corresponding to a thick PbSe unit), a large, negative Seebeck coefficient (??400 µV K?1) is observed simultaneous with a relatively low resistivity (0.01 ?m). Considering the exceptionally low thermal conductivity values that have been reported for these compounds, this could be a promising regime for optimizing doping levels for thermoelectric applications, where a low electrical resistivity and high Seebeck coefficient result in high efficiencies.

Heideman, Colby L.; Johnson, David C.

2014-06-01

397

Kinetics and mechanisms of ligand substitution reactions of the vanadium triad metals. Syntheses and reactivities of (. eta. sup 5 -C sub 5 H sub 5 )M(CO) sub 3 (C sub 4 H sub 8 E) (M = Nb, E = S, Se, Te; M = Ta, E = S)  

SciTech Connect

Kinetic studies were performed for CO substitution reactions of CpM(CO){sub 4} (M = Nb, Ta) and for dialkylchalcogenide substitution reactions of CpM(CO){sub 3}(C{sub 4}H{sub 8}E) (M = V, E = S; M = Nb, E = O, S, Se, Te; M = Ta, E = O, S) with phosphines. The syntheses and characterization of the new compounds CpM(CO){sub 3}(C{sub 4}H{sub 8}E) (M = Nb, E = S, Se, Te; M = Ta, E = S) are reported. Both CpM(CO){sub 4} and CpM(CO){sub 3}(C{sub 4}H{sub 8}E) were found to react by the same mechanism. For M = V, a dissociative mechanism was observed, while for M = Nb, Ta both dissociative and associative mechanisms were observed. This change in mechanism is attributed to the larger size of the Nb and Ta centers. The reactivity of the compounds was found to increase in the order V > Nb > Ta. The higher reactivity of the V compounds compared to the Nb compounds is unusual when compared to other triads, where the second-row metal usually forms the most reactive compound. The reactivity of the CpM(CO){sub 3}(C{sub 4}H{sub 8}E) compounds was found to increase in the order Te < Se < S < O, indicating that the heavier chalcogenides form more stable complexes than the higher chalcogenides.

Freeman, J.W.; Basolo, F. (Northwestern Univ., Evanston, IL (United States))

1991-01-01

398

ICP emission spectrometer relative response by the branching-ratio method: branching ratios for Fe, Se, Te, Ge and Pd  

NASA Astrophysics Data System (ADS)

The relative spectral response of a commercially available inductively coupled argon plasma (ICP) emission spectrometer has been determined over a wide spectral range (approx. 190 to >900 nm) using overlapping sets of radiative branching ratios of several atomic and ionic species. Response curves were determined in two ways. In the first, calibrations were based on Ar II and Ar I lines emitted by Ar-filled hollow-cathode lamps used as line sources instead of the plasma torch. In the second, the ICP emission of selected lines of Ni and Fe was used. Branching ratios determined from the ICP emission of lines of Fe I, Se I, and Te I, using Ar lines for the intensity calibrations, were compared with previously published branching ratios or f-values for these atoms, and good agreement was found. The calibrations based on Ar II and Ni I were used to measure further branching ratios, and application to the measurement of branching ratios from selected levels of Ge I and Pd I is shown.

Doidge, P. S.

1999-12-01

399

High current superconductivity in FeSe0.5Te0.5-coated conductors at 30 tesla.  

PubMed

Although high-temperature superconductor cuprates have been discovered for more than 25 years, superconductors for high-field application are still based on low-temperature superconductors, such as Nb(3)Sn. The high anisotropies, brittle textures and high manufacturing costs limit the applicability of the cuprates. Here we demonstrate that the iron superconductors, without most of the drawbacks of the cuprates, have a superior high-field performance over low-temperature superconductors at 4.2?K. With a CeO(2) buffer, critical current densities >10(6) ?A?cm(-2) were observed in iron-chalcogenide FeSe(0.5)Te(0.5) films grown on single-crystalline and coated conductor substrates. These films are capable of carrying critical current densities exceeding 10(5)?A?cm(-2) under 30 tesla magnetic fields, which are much higher than those of low-temperature superconductors. High critical current densities, low magnetic field anisotropies and relatively strong grain coupling make iron-chalcogenide-coated conductors particularly attractive for high-field applications at liquid helium temperatures. PMID:23299897

Si, Weidong; Han, Su Jung; Shi, Xiaoya; Ehrlich, Steven N; Jaroszynski, J; Goyal, Amit; Li, Qiang

2013-01-01

400

Avalanche breakdown in GaTa4Se(8-x)Te(x) narrow-gap Mott insulators.  

PubMed

Mott transitions induced by strong electric fields are receiving growing interest. Recent theoretical proposals have focused on the Zener dielectric breakdown in Mott insulators. However, experimental studies are still too scarce to conclude about the mechanism. Here we report a study of the dielectric breakdown in the narrow-gap Mott insulators GaTa4Se(8-x)Te(x). We find that the I-V characteristics and the magnitude of the threshold electric field (Eth) do not correspond to a Zener breakdown, but rather to an avalanche breakdown. Eth increases as a power law of the Mott-Hubbard gap (Eg), in surprising agreement with the universal law Eth is proportional to Eg(2.5) reported for avalanche breakdown in semiconductors. However, the delay time for the avalanche that we observe in Mott insulators is over three orders of magnitude greater than in conventional semiconductors. Our results suggest that the electric field induces local insulator-to-metal Mott transitions that create conductive domains that grow to form filamentary paths across the sample. PMID:23591889

Guiot, V; Cario, L; Janod, E; Corraze, B; Phuoc, V Ta; Rozenberg, M; Stoliar, P; Cren, T; Roditchev, D

2013-01-01

401

Direct Probe of Interplay between Local Structure and Superconductivity in FeTe0.55Se0.45  

NASA Astrophysics Data System (ADS)

We explore the interplay between local crystallographic structure, composition and local electronic and superconductive properties. Direct structural analysis of scanning tunneling microscopy (STM) data allows local lattice distortions and structural defects across a FeTe0.55Se0.45 surface to be explored on a single unit-cell level. Concurrent superconducting gap (SG) mapping reveals suppression of the SG at well-defined structural defects, identified as a local structural distortion (Guinier-Preston zone). The strong structural distortion is related to the vanishing of the superconducting state. This study provides insight into the origins of superconductivity in iron chalcogenides by providing an example of atomic-level studies of the structure-property relationship. Research was supported (WL, BCS, AS, SVK) by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. This research was conducted (MP, QL) at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. (Wenzhi Lin and Qing Li, these authors contributed equally to this work)

Lin, Wenzhi; Li, Qing; Sales, Brian; Jesse, Stephen; Safa-Sefat, Athena; Kalinin, Sergei; Pan, Minghu

2013-03-01

402

Synthesis of a potential semiconductor neutron detector crystal LiGa(Se/Te)2: materials purity and compatibility effects  

NASA Astrophysics Data System (ADS)

Lithium containing AIBIIICVI semiconductors are being considered as alternative materials for room temperature neutron detection. One of the primary challenges in growing a high quality crystal of such a material is the reactivity of lithium metal. The presence of nitrides, oxides, and a variety of alkali and alkaline earth metal impurities prevent pure synthesis and truncate crystal growth by introducing multiple nucleation centers during growth. Multiple lithium metal purification methods have been investigated which ultimately raised the metal purity to 99.996%. Multi-cycle vacuum distillation removed all but 40 ppm of metal impurities in lithium metal. LiGa(Se/Te)2 was then synthesized with the high purity lithium metal by a variety of conditions. Lithium metal reacts violently with many standard crucible materials, and thermodynamic studies were undertaken to insure that an appropriate crucible choice was made, with high purity iron and boron nitride crucibles being the least reactive practical materials. Once conditions were optimized for synthesis of the chalcopyrite, vertical Bridgman crystal growth resulted in red crystals. The optical, electronic, and thermodynamic properties were collected.

Stowe, Ashley C.; Morrell, J.; Battacharya, Pijush; Tupitsyn, Eugene; Burger, Arnold

2011-09-01

403

Isomeric metamorphosis: Si3E (E = S, Se, and Te) bicyclo[1.1.0]butane and cyclobutene.  

PubMed

Group 14 and 16 hybrid heavy bicyclo[1.1.0]butanes (tBu2MeSi)4Si3E (E = S, Se, and Te) 2a-c have been prepared by the [1 + 2] cycloaddition reaction of trisilirene 1 and the corresponding chalcogen. Bicyclo[1.1.0]butanes 2 have exceedingly short bridging Si-Si bonds (2.2616(19) A for 2b and 2.2771(13) A for 2c), a phenomenon explained by the important contribution of the trisilirene-chalcogen pi-complex character to the overall bonding of 2. Photolysis of 2a and 2b produced their valence isomers, the heavy cyclobutenes 3a and 3b, featuring flat four-membered Si3E rings and a planar geometry of the Si=Si double bond. The mechanism of such isomerization was studied using deuterium-labeled 2a-d6 to ascertain the preference of the pathway, involving the direct concerted symmetry-allowed transformation of bicyclo[1.1.0]butane 2 to cyclobutene 3. PMID:18260666

Lee, Vladimir Ya; Miyazaki, Shogo; Yasuda, Hiroyuki; Sekiguchi, Akira

2008-03-01

404

Microwave-assisted aqueous synthesis of new quaternary-alloyed CdSeTeS quantum dots; and their bioapplications in targeted imaging of cancer cells.  

PubMed

In this study, we report for the first time a one-pot approach for the synthesis of new CdSeTeS quaternary-alloyed quantum dots (QDs) in aqueous phase by microwave irradiation. CdCl2 was used as a Cd precursor during synthesis, NaHTe and NaHSe were used as Te and Se precursors and mercaptopropionic acid (MPA) was used as a stabilizer and source of sulfur. A series of quaternary-alloyed QDs of different sizes were prepared. CdSeTeS QDs exhibited a wide emission range from 549 to 709 nm and high quantum yield (QY) up to 57.7 %. Most importantly, the quaternary-alloyed QDs possessed significantly long fluorescence lifetimes > 100 ns as well as excellent photostability. Results of high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX) and powder X-ray diffraction (XRD) spectroscopy showed that the nanocrystals possessed a quaternary alloy structure with good crystallinity. Fluorescence correlation spectroscopy (FCS) showed that QDs possessed good water solubility and monodispersity in aqueous solution. Furthermore, CdSeTeS QDs were modified with alpha-thio-omega-carboxy poly(ethylene glycol) (HS-PEG-COOH) and the modified QDs were linked to anti-epidermal growth factor receptor (EGFR) antibodies. QDs with the EGFR antibodies as labeling probes were successfully applied to targeted imaging for EGFR on the surface of SiHa cervical cancer cells. We believe that CdSeTeS QDs can become useful probes for in vivo targeted imaging and clinical diagnosis. PMID:22696455

Yang, Fengzhao; Xu, Zhancheng; Wang, Jinjie; Zan, Feng; Dong, Chaoqing; Ren, Jicun

2013-01-01

405

Fluorescence quenching of CdSe quantum dots by nitroaromatic explosives and their relative compounds  

NASA Astrophysics Data System (ADS)

CdSe quantum dots (QDs) were synthesized in oleic acid and octadecene medium under high-temperature and dispersed in chloroform. Nitroaromatic explosives and their relative compounds, 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), nitrobenzene (NB), 2,4-dinitrochlorobenzene (DNBCl) and p-nitrotoluene (NT) can obviously cause the fluorescence quenching of the synthesized QDs. Under the optimum conditions, a nonlinear response was observed over the concentration range of 10 -8 to 10 -5 M for them all. The modified Stern-Volmer quenching equations of ln I0/ I versus C show a good linear relation in 10 -5 M order of magnitude, and the detection limits approach 10 -6 to 10 -7 M.

Shi, Guo Hua; Shang, Zhuo Bin; Wang, Yu; Jin, Wei Jun; Zhang, Tian Cai

2008-07-01

406

Fluorescence quenching of CdSe quantum dots by nitroaromatic explosives and their relative compounds.  

PubMed

CdSe quantum dots (QDs) were synthesized in oleic acid and octadecene medium under high-temperature and dispersed in chloroform. Nitroaromatic explosives and their relative compounds, 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), nitrobenzene (NB), 2,4-dinitrochlorobenzene (DNBCl) and p-nitrotoluene (NT) can obviously cause the fluorescence quenching of the synthesized QDs. Under the optimum conditions, a nonlinear response was observed over the concentration range of 10(-8) to 10(-5) M for them all. The modified Stern-Volmer quenching equations of ln I(0)/I versus C show a good linear relation in 10(-5) M order of magnitude, and the detection limits approach 10(-6) to 10(-7) M. PMID:17870656

Shi, Guo Hua; Shang, Zhuo Bin; Wang, Yu; Jin, Wei Jun; Zhang, Tian Cai

2008-07-01

407

Surface conductivity and bulk thermoelectric properties of thermoelements on the basis of extruded samples of Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 solid solutions  

NASA Astrophysics Data System (ADS)

Surface conductivity of the thermoelements on a basis of the extruded samples of Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 solid solutions and influence of the distorted surface layer, arising at manufacturing thermoelements on their bulk thermoelectric properties have been investigated over 77-470 K temperature range. It is found that thermoelectrical efficiency of thermoelements after treatment of a surface increases by 10-20%. The obtained results are explained by creating of the distorted layer of approximately 20 micrometers thickness on a surface of thermoelements in the course of their manufacturing.

Bagiyeva, G. Z.; Mustafayev, N. B.; Abdinov, D. S.

2000-11-01

408

Transport properties of Ni, Co, Fe, Mn doped Cu0.01Bi2Te2.7Se0.3 for thermoelectric device applications  

NASA Astrophysics Data System (ADS)

Bi2Te3 based thermoelectric devices typically use a nickel layer as a diffusion barrier to block the diffusion of solder or copper atoms from the electrode into the thermoelectric material. Previous studies have shown degradation in the efficiency of these thermoelectric devices may be due to the diffusion of the barrier layer into the thermoelectric material. In this work, Ni, Co, Fe, and Mn are intentionally doped into Cu0.01Bi2Te2.7Se0.3 in order to understand their effects on the thermoelectric material. Thermoelectric transport properties including the Seebeck coefficient, thermal conductivity, electrical resistivity, carrier concentration, and carrier mobility of Cu0.01Bi2Te2.7Se0.3 doped with 2 atomic percent M (M = Ni, Co, Fe, Mn) as Cu0.01Bi2Te2.7Se0.3M0.02 are studied in a temperature range of 5-525 K. It is seen that the introduction of Ni, Co, Fe, or Mn does not affect the overall figure of merit, and therefore demonstrates that the diffusion barrier is not leading to device degradation as previously hypothesized. Any of these elements may be used as a diffusion barrier with Co being the best candidate based on both its electrical and mechanical properties.

Lukas, K. C.; Liu, W. S.; Ren, Z. F.; Opeil, C. P.

2012-09-01

409

Microstructural Characterization of HgCdSe Grown by Molecular Beam Epitaxy on ZnTe/Si(112) and GaSb(112) Substrates  

NASA Astrophysics Data System (ADS)

Transmission electron microscopy and small-probe microanalysis have been used to investigate the microstructure of HgCdSe thin films grown by molecular beam epitaxy on ZnTe/Si(112) and GaSb(112) substrates. The quality of the HgCdSe material was dependent on the growth temperature and materials flux, independent of the substrate. Samples grown at 100°C were generally of high quality, while those grown at 140°C had {111}-type stacking defects and increased dislocation densities. Improved preparation of the GaSb buffer layer should be developed for future HgCdSe growth on GaSb(112) substrates.

Zhao, W. F.; Brill, G.; Chen, Y.; Smith, David J.

2012-10-01

410

CdS enhances Voc and fill factor in CdS/CdTe and CdS/CuInSe2 solar cells  

NASA Astrophysics Data System (ADS)

A cover layer of CdS enhances the efficiency of CdTe and CuInSe2 based solar cells. The experimental results are summarized, giving the reasons why a CdS layer causes Voc and the fill factor to increase. Field quenching by Frenkel-Poole excitation in copper doped CdS leads to a negative differential conductivity and a high-field domain with a field of 50 kV/cm, limiting the maximum field in the CdS/CdTe junction. This prevents tunneling through the junction and reducing electron leakage. Other evidence indicates an adjustment of the electron affinity, hence in a shift of the band connection at different bias conditions. A band model of the CdS/CdTe cell is proposed.

Böer, Karl W.

2010-01-01

411

Synthesis and Electronic Properties of the Misfit Layer Compound [(PbSe)1.00]1[MoSe2]1  

NASA Astrophysics Data System (ADS)

An ultralow-thermal-conductivity compound with the ideal formula [(PbSe)1.00]1[MoSe2]1 has been successfully crystallized across a range of compositions. The lattice parameters varied from 1.246 nm to 1.275 nm, and the quality of the observed 00 ? diffraction patterns varied through the composition region where the structure crystallized. Measured resistivity values ranged over an order of magnitude, from 0.03 ? m to 0.65 ? m, and Seebeck coefficients ranged from -181 ?V K-1 to 91 ?V K-1 in the samples after the initial annealing to form the basic structure. Annealing of samples under a controlled atmosphere of selenium resulted in low conductivities and large negative Seebeck coefficients, suggesting an n-doped semiconductor. Scanning transmission electron microscopy cross-sections confirmed the interleaving of bilayers of PbSe with Se-Mo-Se trilayers. High-angle annular dark-field images revealed an interesting volume defect, where PbSe grew through a region where a layer of MoSe2 would be expected in the perfect structure. Further studies are required to correlate the density of these defects with the observed electrical properties.

Heideman, Colby L.; Rostek, Raimar; Anderson, Michael D.; Herzing, Andrew A.; Anderson, Ian M.; Johnson, David C.

2010-09-01

412

Nearly lattice matched all wurtzite CdSe/ZnTe type II core-shell nanowires with epitaxial interfaces for photovoltaics  

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06137j

Wang, Kai; Rai, Satish C.; Marmon, Jason; Chen, Jiajun; Yao, Kun; Wozny, Sarah; Cao, Baobao; Yan, Yanfa; Zhang, Yong; Zhou, Weilie

2014-03-01

413

Formation of an intermetallic compound Pd 3 Te with deactivation of Te\\/Pd\\/C catalysts for selective oxidation of sodium lactate to pyruvate in aqueous phase  

Microsoft Academic Search

The addition of a trace amount of Te promoted the activity of Pd\\/C in the liquid-phase oxidation of lactic acid, but the Te\\/Pd\\/C catalyst, for which Pd3Te crystalline phase extended over the bulk at a higher Te-doping above Te\\/Pd = 0.3 (atom), was again inactive. A powder XRD evidence for Pd3Te is given.

H. Hayashi; S. Sugiyama; N. Shigemoto; K. Miyaura; S. Tsujino; K. Kawashiro; S. Uemura

1993-01-01

414

Crystallographic properties of the MnGa2Se4 compound under high pressure  

NASA Astrophysics Data System (ADS)

X-ray diffraction measurements on MnGa2Se4, a II-III2-VI4 magnetic semiconductor compound, are made as a function of pressure up to 25 GPa. It is found that in the range of 0

Marquina, J.; Power, Ch.; Grima, P.; Morocoima, M.; Quintero, M.; Couzinet, B.; Chervin, J. C.; Munsch, P.; González, J.

2006-11-01

415

Resonant photoemission and absorption spectroscopy of the Cu x TiSe2 compound  

NASA Astrophysics Data System (ADS)

Single crystals of the Cu x TiSe2 compound with x = 0.05, 0.09, and 0.33 have been grown. Resonance photoelectron Cu 3 p-3 d and 2 d-3 d spectra of the valence bands, the spectra of the core levels, and the L absorption spectra for titanium and copper have been obtained. It is shown that the degree of oxidation of titanium atoms is +4 and the state of copper atoms is close to the state of free copper ions. It is found that the spectra of the valence bands obtained under the Cu 3 p and 2 p resonance conditions radically differ. For the spectra in the Cu 2 p excitation regime, several bands corresponding to different decay channels of the excited state are observed. According to calculations of the density of states, the 3 d states of copper are filled incompletely; the occupancy of the 3 d band of copper is 9.5 electrons per atom.

Shkvarin, A. S.; Yarmoshenko, Yu. M.; Skorikov, N. A.; Titov, A. A.; Titov, A. N.

2012-02-01

416

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

SciTech Connect

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.

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

417

Top-down fabrication of nano-scaled Bi2Se(0.3)Te(2.7) associated by electrochemical Li intercalation.  

PubMed

A convenient top-down method for preparation of Bi(2)Se(0.3)Te(2.7) crystalline nano-particles has been demonstrated. It contains two steps: (1) lithium was intercalated between the van der Waals bonded quintuple-layers by electrochemical process inside lithium ion batteries with precisely controlled speed and amount; (2) subsequent alcohol exposure of Li(x)Bi(2)Se(0.3)Te(2.7) to make the intercalated Li atoms explode like atom-scaled bombs and exfoliate the original micro/macro scaled materials into nano-scaled single crystalline particles with sizes around 10 nm. The intercalation process does not cost external energy, and can be scaled up by amplification of the intercalation devices. PMID:21082143

Chen, Jikun; Sun, Zhengliang; Zhu, Yingjie; Chen, Nuofu; Zhou, Yanfei; Ding, Juan; Chen, Xihong; Chen, Lidong

2011-01-14