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1

Superconducting and magnetic properties of Fe-Se-Te compounds  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

2

Magnetic and electrical transport properties of Cr 3(Se 1? x Te x ) 4 compounds  

Microsoft Academic Search

The magnetic and electrical transport behaviors of Cr3(Se1?xTex)4 compounds are investigated. A transition from antiferromagnetism to ferromagnetism occurs at x=0.2 in this system and abnormal changes of the lattice parameter a and angle ? take place around the magnetic transition point. When Se is partially substituted by Te, a minimum of resistivity (?min) is observed in the temperature dependence of

Y. B. Li; E. Brück; O. Tegus; Y. Q. Zhang; W. J. Feng; N. K. Sun; D. Li; J. Li; T. J. Gortenmulder; Y. K. Huang; Z. D. Zhang

2008-01-01

3

Chalcogen-Rich Lanthanide Clusters: Compounds with Te2-, (TeTe)2-, TePh, TeTePh, (TeTeTe(Ph)TeTe)5-, and [(TeTe)4TePh]9-Ligands; Single  

E-print Network

ion by pyridine, to give the pentaanion (µ-2 -2 -Te2Te(Ph)Te2).5- In the Tm compound, the displaced Te with PhTeTePh and elemental Te in pyridine to give (py)yLn4(Te)(TeTe)2(TeTeTe(Ph)- TeTe)(TexTePh) (Ln ) Sm

Lawson, Catherine L.

4

Effect of ball milling and post treatment on crystal defects and transport properties of Bi2(Se,Te)3 compounds  

NASA Astrophysics Data System (ADS)

Ionized point defects that act as electron donors or acceptors can strongly affect thermoelectric transport properties of bismuth telluride compounds. These crystal imperfections including antisite defects and vacancies can be generated or annihilated during material processing. Here, we reported the effect of ball milling, thermal annealing, and electrical stressing on defect population in the Bi2(Se,Te)3 prepared by powder metallurgy. The milling process can modulate the relative portion of antisite defects and vacancies in crystal, and the Bi2(Se,Te)3 made of the powders with extended milling time showed high electron concentration and poor carrier mobility. The crystal defects, Te vacancies in particular, were eliminated to some degree during subsequent thermal treatment. An electric-current assisted thermal treatment was found to be very efficient in eliminating crystal defects, which can improve transport properties of Bi2(Se,Te)3 without causing re-evaporation of volatile Te and Se elements during high-temperature annealing.

Lin, Sin-Shien; Liao, Chien-Neng

2011-11-01

5

ZnSe/ZnSeTe Superlattice Nanotips  

PubMed Central

The authors report the growth of ZnSe/ZnSeTe superlattice nanotips on oxidized Si(100) substrate. It was found the nanotips exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. It was also found that photoluminescence intensities observed from the ZnSe/ZnSeTe superlattice nanotips were much larger than that observed from the homogeneous ZnSeTe nanotips. Furthermore, it was found that activation energies for the ZnSe/ZnSeTe superlattice nanotips with well widths of 16, 20, and 24 nm were 76, 46, and 19 meV, respectively. PMID:20672085

2010-01-01

6

Fundamental and transport properties of ZnX, CdX and HgX (X = S, Se, Te) compounds  

NASA Astrophysics Data System (ADS)

We have performed ab initio self-consistent calculations based on full potential linear augmented plane-wave method (FP-LAPW) with the local density approximation (LDA) and generalised gradient approximation (GGA) to investigate the relativistic effects on the structural, electronic, transport and optical properties of II-VI compounds. We mainly show that the stabilisation (destabilisation) of s, p*(p) orbital energies reduces the lattice parameters of II-VI compounds, the band gaps and the effective masses. This, however, induces strong spin-orbit splitting of heavier II-VI compounds.

Boutaiba, F.; Zaoui, A.; Ferhat, M.

2009-12-01

7

Heteroleptic Lanthanide Compounds with Chalcogenolate Ligands: Reduction of PhNNPh/ PhEEPh (E ) Se or Te) Mixtures with Ln (Ln ) Ho, Er, Tm, Yb). Thermolysis Can Give  

E-print Network

reduce mixtures of azobenzene and PhEEPh (E ) Se or Te) in pyridine to give the bimetallic compounds [(py), Yb (8)). The structures of [(py)2Er(µ-2-2-PhNNPh)(SePh)]2,2py (2) and [(py)2Ho(µ-2-2-PhNNPh)- (TePh)]2,2py (5) have been determined by low-temperature single-crystal X-ray diffraction, and the nearly

Lawson, Catherine L.

8

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

9

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

Microsoft Academic Search

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

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

1987-01-01

10

Spin Excitations in Fe(Se,Te)  

NASA Astrophysics Data System (ADS)

The full spectrum of magnetic excitations in both superconducting FeTe0.51Se0.49 (x=0.49) and non- superconducting Fe1.04Te0.73Se0.27 (x=0.27) was studied using inelastic neutron scattering on single crystal samples. The magnetic excitations are two-dimensional in nature and are observed for energy transfers as high as 300 meV. The zero energy extrapolation of the measured dispersion shows incommensurate excitations emanating from a wavevector near (0.5,0.5), the location of the resonance in the superconducting material. For low energy transfers, the spectrum consists of a set of incommensurate spots, four-fold symmetric about the (1,0) (square lattice (?,?)) wavevector. At higher energies, these spots evolve into rings centered on Q=(1,0). These excitations are notably different than the cones of scattering expected from a long-range magnetically ordered material and likely reflect the itinerant nature of the magnetism. The qualitative evolution of the incommensurate excitation spectrum is similar that seen previously in the cuprates. Despite the incommensurate nature of the spectrum, the observed resonance in the x=0.49 sample remains peaked at the (0.5,0.5) wavevector as in other Fe-based superconductors. At low energies, the x=0.27 sample exhibits an additional feature in the excitation spectrum centered near Q=(0.5,0), the wavevector of magnetic order in Fe1+yTe. This scattering persists for all energies below about 10 meV and forms the short range order observed for this concentration. This scattering is completely absent in the x=0.49 sample which contains no excess Fe.

Lumsden, Mark

2011-03-01

11

Near-infrared emission spectra of TeS, TeSe and Te2  

NASA Astrophysics Data System (ADS)

Emission spectra of the radicals TeS, TeSe and Te2 in the near-infrared spectral region have been measured with a high-resolution Fourier-transform spectrometer. The molecules were generated in a fast-flow system by reacting microwave-discharged mixtures of Tex, Sx, and/or Sex vapour and Ar carrier gas and excited by energy transfer and energy pooling processes in collisions with metastable oxygen O2(a1?g). The b1?+(b0+) ? X3?-(X10+,X21) electric dipole transitions of TeS and TeSe and the b1?+g(b0+g) ? X3?-g(X21g) magnetic dipole transition of Te2 were measured at medium and high spectral resolution. A very weak emission at 3356 cm-1 observed in the spectrum of TeSe was identified to be the 0-0 band of the hitherto unknown a1?(a2) ? X3?-(X21) transition of the molecule. Analyses of the spectra have yielded a number of new or improved spectroscopic parameters of the molecules.

Setzer, K. D.; Fink, E. H.

2014-10-01

12

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

13

Sealed crucible technique for thermal analysis of volatile compounds up to 2500 °C: Melting points of EuO, EuS, EuSe and EuTe  

NASA Astrophysics Data System (ADS)

Thermal analysis and crystal growth are particularly difficult for compounds that have vapor pressures above a few Torr or melting points above 2000 °C. A technique utilizing welded refractory metal crucibles has been developed for performing these operations. The metals tungsten, molybdenum and rhenium are suitable for this technique, since they have melting points exceeding 2600 °C, do not react with compounds of the more active metals, can be obtained in crucible form, are easily welded and are relatively inexpensive. For thermal analysis, a crucible with a thermocouple well is mounted on a tungsten-tungsten (0.26 Re) thermocouple in a resistance-heated furnace, and the thermal arrest of the compound on melting or freezing is observed. The method was tested by measuring the melting point of Al 2O 3. The melting point, 2044 ± 5 °C, agrees well with 2045 ± 6 °C recently measured in a tungsten crucible. This method has been used to determine the previously unreported melting points of EuO, EuS, EuSe and EuTe (1976, 2558, 2215 and 2183 °C respectively), as well as those of several other compounds.

Reed, T. B.; Fahey, R. E.; Strauss, A. J.

1972-08-01

14

Mixed valent ternary iron chalcogenides: AFe 2X 3 (A = Rb, Cs; X = Se, Te)  

Microsoft Academic Search

The isostructural compounds RbFe2Se3, RbFe2Te3, CsFe2Se3 and CsFe2Te3 were obtained as coarse lustrous crystals by reacting Fe, Se or Te and the corresponding alkali monochalcogenide. They are orthorhombic, oC24, space group Cmcm, Z = 4, with a = 9.507(3)Å, b = 11.583(4) Å, c = 5.638(2) Å (RbFe2Se3); a = 10.126(9) Å, b = 12.486(7) Å, c = 5.921(1) Å

K. O. Klepp; W. Sparlinek; H. Boller

1996-01-01

15

The performance of thin film solar cells employing photovoltaic ZnSe\\/CdTe, CdS\\/CdTe and ZnTe\\/CdTe heterojunctions  

Microsoft Academic Search

This paper focuses on the photovoltaic parameters of ZnSe\\/CdTe, CdS\\/CdTe, and ZnTe\\/CdTe thin film heterojunction solar cells. ZnSe\\/CdTe, CdS\\/CdTe, and ZnTe\\/CdTe thin film heterojunction solar cells were fabricated by Close Space Sublimation (CSS) on TCO-coated glass substrates. All types of solar cells were fabricated in a superstrate configuration. The thickness of ZnSe and ZnTe layers was varied in order to

T. Potlog; N. Spalatu; V. Fedorov; N. Maticiuc; C. Antoniuc; V. Botnariuc; J. Hiie; T. Raadik; V. Valdna

2011-01-01

16

Optical Characterization of Bulk ZnSeTe Solid Solutions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

17

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

PubMed

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

Yang, Ping

2014-04-01

18

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

19

Optical Characterization of Bulk ZnSeTe Solid Solutions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

20

Calculation of the phase equilibria in the system Pb-PbTe-PbSe  

SciTech Connect

We present the results of calculations of the low-temperature part of the liquidus and solidus of Pb/sub 1-y/(Te/sub 1/x/Se/sub x/)/sub y/ with the chalcogen content y less than or equal to 0.10. The phase equilibria were described with the help of the model of simple regular solutions with renormalized entropies of melting of the binary compounds. The interaction parameters of the components in the solid phase /sup ..cap alpha../PbTe-PbSe/ was determined taking into account the ratio z/x = 1.30 of the Se concentrations in the solid and liquid phases at 773 K. The interaction parameter in the liquid phase ..cap alpha../sub Te-Se/ for small values of y does not significantly affect the computational results.

Dombrugov, M.R.; Zhovnir, G.I.

1988-07-01

21

X-Ray spectra and electronic correlations of FeSe(1-x)Te(x).  

PubMed

Critical issues concerning emerging Fe-based superconductors include the degree of electron correlation and the origin of the superconductivity. X-Ray absorption spectra (XAS) and resonant inelastic X-ray scattering spectra (RIXS) of FeSe(1-x)Te(x) (x = 0-1) single crystals were obtained to study their electronic properties that relate to electron correlation and superconductivity. The linewidth of Fe L(2,3)-edges XAS of FeSe(1-x)Te(x) is narrower than that of Fe-pnictides, revealing the difference between their hybridization effects and localization character and those of other Fe-pnictides. While no significant differences exist between the Fe L-edge XAS and RIXS of FeSe(1-x)Te(x) and those of Fe-pnictides, Se K-edge and Te K-edge XAS exhibit substantial edge shift, suggesting that the superconductivity in an Fe-Se superconductor is strongly associated with the ligand states. A comparison of the Se K-edge and Te K-edge spectra reveals that the charge transfer may occur between Se and Te. Given the Coulomb interaction and the bandwidth, the spectral results indicate that FeSe(1-x)Te(x) is unlikely to be a weakly correlated system unlike the Fe-pnictides of the "1111" and "122" families. The spectral results further demonstrate that superconductivity in this class of Fe-based compounds is strongly associated with the ligand 4p hole state. PMID:21804990

Chen, C L; Dong, C L; Chen, J L; Guo, J-H; Yang, W L; Hsu, C C; Yeh, K W; Huang, T W; Mok, B H; Chan, T S; Lee, J F; Chang, C L; Rao, S M; Wu, M K

2011-09-14

22

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

23

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

24

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

E-print Network

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

Osswald, Sebastian

25

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

PubMed Central

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

2014-01-01

26

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

27

Low Temperature Photoluminescence of PVT Grown ZnSe and ZnSeTe  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

28

Thermoelectric properties of polycrystalline In4Se3 and In4Te3  

SciTech Connect

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

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

2010-01-01

29

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

30

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

31

Transport studies in topological insulator Bi2Te2Se  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

32

Theoretical study of [XN 6] 2- (X = O, S, Se, Te) systems  

NASA Astrophysics Data System (ADS)

A series of [XN 6] 2- (X = O, S, Se, Te) compounds have been examined with ab initio and density functional theory (DFT) methods. The five-membered nitrogen ring series of structures are global minima for all singlet [XN 6] 2- systems. Kinetic analysis shows that the five-membered nitrogen ring [XN 6] 2- (X = S, Se, Te) species may exist or be characterized due to their significant dissociation barriers (22.2-30.4 kcal/mol). Nucleus-independent chemical shifts (NICS) criteria and the presence of (4 n + 2) number of ?-electrons confirmed that some five-, six- and seven-membered rings in their structures exhibit characteristics of aromaticity.

Cheng, Li Ping; Liu, Yan

2006-01-01

33

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

34

Photoluminescence properties of hybrid SiO2-coated CdTe/CdSe quantum dots.  

PubMed

Hybrid SiO2-coated CdTe/CdSe quantum dots (QDs) were prepared using CdTe/CdSe QDs prepared by hydrothermal synthesis. A CdSe interlayer made CdTe/CdSe cores with unique type II heterostructures. The hybrid SiO2-coated CdTe/CdSe QDs revealed excellent photoluminescence (PL) properties compared with hybrid SiO2-coated CdTe QDs. Because of the existence of spatial separations of carriers in the type II CdTe/CdSe core/shell QDs, the hybrid QDs had a relatively extended PL lifetime and high stability in phosphate-buffered saline buffer solutions. This is ascribed to the unique components and stable surface state of hybrid SiO2-coated CdTe/CdSe QDs. During the stabilization test in phosphate-buffered saline buffer solutions, both static and dynamic quenching occurred. The quenching mechanism of the hybrid QDs was not suited with the Stern–Volmer equation. However, the relative stable surface of CdTe/CdSe QDs resulted in lower degradation and relative high PL quantum yields compared with hybrid SiO2-coated CdTe QDs. As a result, hybrid SiO2-coated CdTe/CdSe QDs can be used in bioapplications. PMID:25337614

Liu, Ning; Yang, Ping

2014-09-01

35

A case study: Te in ZnSe and Mn-doped ZnSe quantum dots.  

PubMed

Photoluminescence (PL) behavior of ZnSe(1-y)Te(y) quantum dots is investigated by varying Te concentration as well as size. The striking effect of quantum confinement is the observation of isoelectronic center-related emission at room temperature in lieu of near-band-edge emission that dominates the optical scenario. ZnSe(0.99)Te(0.01) quantum dots were also doped by Mn(2+) ions. The Mn(2+) ion-related d-d transition is drastically suppressed by Te isoelectronic centers. Incorporation of Mn(2+) at substitutional sites in ZnSe(0.99)Te(0.01) quantum dots is also confirmed by the electron paramagnetic resonance measurements. Effect of Te isoelectronic impurity on the emission behavior is more pronounced than that of Mn(2+) ions. A subtle blueshift in the orange d-d transition is a sign of a decrease in crystal field strength. PL and photoluminescence excitation measurements on Zn(1-x)Se(0.99)Te(0.01)Mn(x) quantum dots indicate that the transition probability from the lowest unoccupied molecular orbital to Te levels is substantially larger than that to Mn(2+) d-d levels. PMID:21705825

Sonawane, Kiran G; Rajesh, Ch; Temgire, Mayur; Mahamuni, Shailaja

2011-07-29

36

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

37

Theoretical study of pressure-driven phase transitions in HgSe and HgTe  

NASA Astrophysics Data System (ADS)

We present the results of a density-functional-theory study of the stability of high-pressure phases of HgSe and HgTe up to the so-called Cmcm phase, which is the highest-pressure phase that has been fully characterized in experiments in these compounds. We compare the results obtained using different exchange-correlation functionals for the energetics, stability, and structure of the high-pressure phases, finding that the qualitative picture is very similar and essentially in agreement with the experimental observations. We study the cinnabar?NaCl and the NaCl?Cmcm transitions in detail and provide the structural evolution under pressure of the cinnabar and Cmcm phases. We find that the mechanism for the NaCl?Cmcm transition is somewhat different from other related compounds exhibiting this transition, with cell deformation playing an important role in the stabilization of the Cmcm state in HgSe and HgTe. Our results support the view of a NaCl?Cmcm transition that is distinctly first order, in good agreement with the experimental observations and contrary to other materials where this transition is of second order.

Radescu, S.; Mujica, A.; López-Solano, J.; Needs, R. J.

2011-03-01

38

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

39

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

40

Galvanomagnetic and thermomagnetic properties of thallium doped PbSnTe and PbSeTe  

Microsoft Academic Search

Thallium acts as a resonant level in PbTe, so that PbTe:Tl shows a significant improvement of thermoelectric properties due to an increase in thermopower as compared to that of similarly Na-doped PbTe [2]. Further improvements in zT are expected from a reduction of the thermal conductivity by alloy scattering in Pb1-x-y TlySnxTe and Pb1-yTlyTe1-xSex alloys. However, the band structure of

Vladimir Jovovic; Joseph Heremans

2009-01-01

41

Charge transport in mixed CdSe and CdTe colloidal nanocrystal films  

E-print Network

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

Bawendi, Moungi G.

42

In Situ X-ray Diffraction Study of the Formation of Fe(Se,Te) from Various Precursors  

NASA Astrophysics Data System (ADS)

The formation of the FeSe0.5Te0.5 phase was studied by means of high energy synchrotron x-ray diffraction. The precursors consisted of Fe, Se and Te or Se0.5Te0.5 powder mixtures and were encased in a metal (Cu/Nb) composite sheath to prevent evaporation of Se and Te during high temperature processing. In all cases (Fe - Se - Te ternary mixture; Fe - Se0.5Te0.5 binary mixtures with two different Fe particle sizes) the ternary alloy forms via Fe(Se,Te)2 and Fe3(Se,Te)4 intermediate phases. When unreacted Se and Te powders are used in the precursor, partial Se1-xTex alloying takes place during heating prior and during the formation of the intermediate phases. As the alloying is incomplete, the resulting Fe(Se,Te) phase is not homogeneous. Using pre-alloyed Se0.5Te0.5 allows a better control of the reaction although homogeneisation also occurs in the Fe(Se,Te) phase as a consequence of the phase equilibria of the Se - Te system. The grain size of the starting Fe powder has no influence on the reaction path for the grain sizes used in the present study. However, the reaction rate for Fe(Se,Te) formation is clearly sensitive to this parameter.

Grivel, J.-C.; Zhao, Y.; Wulff, A. C.; Pallewatta, P. G. A. P.; Bednar?'k, J.; Zimmermann, M. v.

43

Prismatic punching defects in CdTe compounds  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

44

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

E-print Network

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

Tian, Zhiting

45

Electronic properties of BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF/ZnPc interfaces  

NASA Astrophysics Data System (ADS)

BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF interfaces with zinc phthalocyanine (ZnPc) were studied by photoelectron spectroscopy. BaCuChF compounds oxidize when exposed to ambient atmosphere. Se capping layers were studied as a means to produce representative surfaces for photoelectron spectroscopic measurements. Decapped BaCuSeF surfaces remain O-free and C-free when the Se layer is evaporated but they become F-deficient. The resulting surfaces have work functions of 4.85 eV and Fermi levels located 0.25 eV above the valence band maximum. In situ stepwise deposition of ZnPc on a BaCuSeF film surface produced a chemically inert interface with a hole-injection barrier of 0.11 eV.

Zakutayev, Andriy; Tate, Janet; Platt, Heather A. S.; Keszler, Douglas A.; Hein, Corinna; Mayer, Thomas; Klein, Andreas; Jaegermann, Wolfram

2010-05-01

46

Effects on superconductivity of transition-metal doping in FeSe0.5Te0.5  

NASA Astrophysics Data System (ADS)

We investigate superconductivity in the compound FeSe0.5Te0.5 and in its transition-metal-substituted derivatives Fe1 - xTMxSe0.5Te0.5, where x = 5% and the substituent ions studied were Mn, Co, Ni, Cu and Zn. Electronic and magnetic measurements indicate that doping with Mn or by Co acts respectively to cause a slight enhancement or suppression of the transition temperature. However, doping with this concentration of Ni or Cu destroys the superconductivity completely, and leads to semiconducting behaviour. Zn ions cannot be incorporated properly into the parent compound. The reasons for these contrasting effects are associated with the differing magnetic properties of the substituent ions, which determine their local impurity moments and the net carrier concentrations in the doped 11 system. The effects of magnetic ion substitution on superconductivity suggest that the pairing symmetry may not be either pure s wave or pure d wave.

Zhang, A. M.; Xia, T. L.; Kong, L. R.; Xiao, J. H.; Zhang, Q. M.

2010-06-01

47

Emission variation in infrared (CdSeTe)/ZnS quantum dots conjugated to antibodies  

NASA Astrophysics Data System (ADS)

The paper presents the photoluminescence (PL) and Raman scattering investigations of infrared CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm (1.60 eV) in nonconjugated states and after the conjugation to the anti-papilloma virus antibodies (Ab). The Raman scattering study has shown that the CdSeTe core includes two layers with different material compositions such as: CdSe0.5Te0.5 and CdSe0.7Te0.3. PL spectra of nonconjugated CdSeTe/ZnS QDs are characterized by two Gaussian shape PL bands related to exciton emission in the CdSeTe core and in intermediate layer at the core/shell interface. PL spectra of bioconjugated QDs have changed essentially: the main PL band related to the core emission shifts into high energy and become asymmetric. The energy diagram of double core/shell CdSeTe/ZnS QDs has been analyzed to explain the PL spectrum of nonconjugated QDs and its transformation at the bioconjugation to the papiloma virus antibodies. It is shown that the PL spectrum transformation in bioconjugated QDs can be a powerful technique for biology and medicine.

Jaramillo Gómez, J. A.; Casas Espinola, J. L.; Douda, J.

2014-11-01

48

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

49

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

SciTech Connect

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

Wolos, A. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland and Faculty of Physics, University of Warsaw, ul Hoza 69, 00-681 Warsaw (Poland); Drabinska, A.; Szyszko, S.; Kaminska, M. [Faculty of Physics, University of Warsaw, ul Hoza 69, 00-681 Warsaw (Poland); Strzelecka, S. G.; Hruban, A.; Materna, A.; Piersa, M. [Institute of Electronic Materials Technology, ul. Wolczynska 133, 01-919 Warsaw (Poland)

2013-12-04

50

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

51

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3  

PubMed Central

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

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

2014-01-01

52

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3.  

PubMed

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

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

2014-01-01

53

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

E-print Network

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

Guan, Juan

2008-01-01

54

Band alignment and interdiffusion at the BaCuSeF/ZnTe interface  

NASA Astrophysics Data System (ADS)

In-situ ultraviolet- and x-ray photoemission spectroscopy experiments (XPS/UPS) on the wide-bandgap p-type semiconductor BaCuSeF indicate that it forms an ideal p-type contact to ZnTe. The interface is interdiffused, and there is no valence band offset. The transitivity rule for the valence band offsets and the similar chemistry of ZnTe and CdTe suggest that BaCuSeF is a promising p-type window layer for CdTe p-i-n double-heterojunction solar cells. BaCuSeF anode may also improve collection of charge carriers in thin film inorganic photovoltaic devices based on Cu(InGa)Se2 (CIGS) and Cu2ZnSnS4 (CZTS) absorbers.

Zakutayev, Andriy; Tate, Janet; Platt, Heather; Keszler, Douglas; Barati, Alireza; Jaegermann, Wolfram; Klein, Andreas

2010-03-01

55

Au-Ag-Te-Se minerals in the Elatsite porphyry-copper deposit, Bulgaria  

Microsoft Academic Search

Elatsite is one of the largest operating porphyry-copper deposits in Eastern Europe, and is also enriched in Au-Ag-Te-Se and PGE. The magnetite-bornite-chalcopyrite ore assemblage, preserved mainly in the central K-alteration core, has been examined by means of electron microprobe and SEM. Au-Ag-Te- Se minerals are abundant, and include macroscopic gold with high fineness. The ores are also enriched in hessite,

Kamen Bogdanov; Alexander Filipov; Radoslav Kehayov

56

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

57

High efficiency nCd(Se,Te)\\/S = photoelectrochemical cell resulting from solution chemistry control  

Microsoft Academic Search

High efficiency (12.7%) CdSe0.68Te0.32\\/cesium polysulfide photoelectrochemical cells are demonstrated in this work. Crystals of the ternary alloy Cd(Se, Te) of type n type were synthesized by the traveling heater method. The nature of the polysulfide electrolyte, based on Cs polysulfide without excess hydroxide and containing small amounts of copper ions, is shown to be of particular importance in determining the

Stuart Licht; Reshef Tenne; Geulah Dagan; Gary Hodes; Joost Manassen; David Cahen; Robert Triboulet; Jacques Rioux; Claude Levy-Clement

1985-01-01

58

Structure stability and carrier localization in CdX (X=S, Se, Te) semiconductors  

Microsoft Academic Search

We studied systematically the structural and electronic properties of binary CdX (X=S, Se, and Te) semiconductors in both zinc-blende (ZB) and wurtzite (WZ) structures, the band alignment on the ZB\\/WZ interfaces, and carrier localization induced by the band offsets. We show, by first-principles band-structure calculation that at low temperature, CdS is stable in the wurtzite structure, while CdSe and CdTe

Su-Huai Wei; S. B. Zhang

2000-01-01

59

Ab-initio calculation of stability and structural properties of cadmium chalcogenides CdS, CdSe, and CdTe under high pressure  

NASA Astrophysics Data System (ADS)

The structural phase transformations of Cd chalcogenide compounds (CdS, CdSe, and CdTe) under high pressure are studied using the local approximation to the density functional theory, and the one-electron equations are solved by means of the full potential linear muffin-tin-orbital method. CdS, CdSe, and CdTe are found to have nearly similar behaviour of the structural properties under high pressure. In the CdS compound, the Pmmn phase is predicted to be thermodynamically stable after the rock-salt structure, and the Cmcm structure is found to be thermodynamically stable before the rock-salt structure in both CdSe and CdTe. The resulting structural properties of the zinc-blende, wurtzite, cinnabar, rock-salt, Pmmn, CsCl, Cmcm, and ?-Sn phases for these considered compounds are found to be in agreement with the existing experimental data.

Benkhettou, N.; Rached, D.; Rabah, M.

2006-04-01

60

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

61

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

62

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

63

Quantum size effect on cubic PbTe nanocrystals embedded in amorphous InSe thin film matrix  

NASA Astrophysics Data System (ADS)

PbTe nanocrystals (NCs) embedded in a multilayered structure with amorphous InSe has been prepared and investigated. PbTe/InSe multilayered structures composed of alternating InSe and PbTe layers were prepared with different numbers of PbTe NCs layers by thermal evaporation technique. The presence of cubic PbTe NCs was confirmed from transmission electron microscopy images of the film cross section. High resolution X-ray diffraction characterization demonstrated face centered cubic rock salt structure of PbTe and the average size of PbTe NCs are varied by the number of PbTe NCs layers. Quantum size effect was revealed by the blue shift in the absorption edges of the multiple PbTe NCs layers structure with respect to the reference PbTe films. The experimentally observed absorption edge shift is compared with the theoretical values predicted based on the effective mass approximation model.

Manonmani Parvathi, M.; Arivazhagan, V.; Rajesh, S.

2014-11-01

64

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

SciTech Connect

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

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

2012-07-15

65

Ab initio study of Sb 2Se xTe 3- x ( x=0, 1, 2) phase change materials  

NASA Astrophysics Data System (ADS)

By means of ab initio total energy calculations, we have investigated the structure and properties of Sb 2Se xTe 3- x ( x = 0, 1, 2) alloys, a family of phase change materials for data storage. On the basis of analyzing the chemical bonding and electronic properties of Sb 2Se xTe 3- x ( x = 1, 2) and Sb 2Te 3 alloys, we have shown that the crystalline-to-amorphous transition of Sb 2Se 2Te may be faster than that of Sb 2Te 3. Furthermore, the substitution of Te by Se in Sb 2Te 3 can increases the electric resistance of Sb 2Se xTe 3- x ( x = 1, 2) alloys and hence may lower the reset power consumption.

Xuelai, Li; Zhimei, Sun; Zhitang, Song; Feng, Rao; Liangcai, Wu; Weili, Liu

2011-01-01

66

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

67

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

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

2014-07-23

68

Incommensurate lattice modulation in CDW compound TbTe3  

NASA Astrophysics Data System (ADS)

The layered materials RTe3 (R= rare earth) are simple charge-density wave (CDW) compounds, for which large regions of the original quasi-2D Fermi surface are nested by a single incommensurate wavevector. We use high resolution x-ray diffraction and scanning tunneling microscopy (STM) to study how the lattice responds to the incommensurate ordering. The superlattice of TbTe3 reveals a unidirectional lattice modulation characterized by qCDW = 0.296 c*. Higher harmonics are several orders of magnitude lower in intensity, implying an almost sinusoidal lattice modulation. The CDW is well correlated within and between planes, with correlation lengths in excess of 1000 å. STM measurements reveal the CDW gap and real-space lattice modulation.

Ru, N.; Fang, A.; Kapitulnik, A.; Fisher, I. R.; Toney, M. F.

2006-03-01

69

High efficiency n-Cd(Se,Te)/S/sup photoelectrochemical cell resulting from solution chemistry control  

SciTech Connect

High efficiency (12.7%) CdSe/sub 0.68/Te/sub 0.32//cesium polysulfide photoelectrochemical cells are demonstrated in this work. Crystals of the ternary alloy Cd(Se, Te) of type n type were synthesized by the traveling heater method. The nature of the polysulfide electrolyte, based on Cs polysulfide without excess hydroxide and containing small amounts of copper ions, is shown to be of particular importance in determining the cell efficiency. Reasonable output stability of the cell was obtained under accelerated tests.

Licht, S.; Tenne, R.; Dagan, G.; Hodes, G.; Manassen, J.; Cahen, D.; Triboulet, R.; Rioux, J.; Levy-Clement, C.

1985-03-15

70

Liquid phase diffusion bonding and thermoelectric properties of Pb 1-xSnxTe compounds  

Microsoft Academic Search

The solidified Pb1-xSnxTe compounds with different x were joined by liquid phase diffusion bonding technique in order to prepare the segmented thermoelectric materials which had a fundamental FGM (functionally graded materials) structure. The Pb1-xSnxTe compound is a p-type semiconductor whose carrier concentration increases with increasing x. Therefore the maximum thermoelectric figure of merit of Pb1-xSnxTe shifted to a higher temperature

M. Hashimoto; I. Shiota; O. Ohashi; Y. Isoda; Y. Imai; Y. Shinohara; I. A. Nishida

1998-01-01

71

Pressure-induced superconductivity in topological parent compound Bi2Te3  

E-print Network

Pressure-induced superconductivity in topological parent compound Bi2Te3 J. L. Zhanga,b , S. J November 19, 2010 (received for review September 21, 2010) We report a successful observation of pressure-induced supercon- ductivity in a topological compound Bi2Te3 with Tc of 3 K between 3 to 6 GPa. The combined high-pressure

Wang, Wei Hua

72

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

73

Structure stability and carrier localization in CdX (X=S, Se, Te) semiconductors  

SciTech Connect

We studied systematically the structural and electronic properties of binary CdX (X=S, Se, and Te) semiconductors in both zinc-blende (ZB) and wurtzite (WZ) structures, the band alignment on the ZB/WZ interfaces, and carrier localization induced by the band offsets. We show, by first-principles band-structure calculation that at low temperature, CdS is stable in the wurtzite structure, while CdSe and CdTe are stable in the zinc-blende structure. However, coherent substrate strain can change CdTe to be more stable in the wurtzite form. We find that CdX in the wurtzite structure has a larger band gap than the one in the zinc-blende structure. The band alignment on the ZB/WZ interface is found to be type II with holes localized on the wurtzite side and electrons on the zinc-blende side. (c) 2000 The American Physical Society.

Wei, Su-Huai [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Zhang, S. B. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

2000-09-15

74

High Electric Field Transport in Degenerate n-Type PbTe And PbSe.  

National Technical Information Service (NTIS)

Nanosecond pulse techniques are used to determine velocity-field characteristics of bulk samples of n-type PbTe and n-type PbSe at 77K and 4.2K for carrier concentrations ranging from 1 x 10 to the 17the power/cc to 5 x 10 to the 17the power/cc. At fields...

H. St-Onge, J. N. Walpole, R. H. Rediker

1970-01-01

75

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

76

Microstructural magnetic phases in superconducting FeTe0.65Se0.35  

NASA Astrophysics Data System (ADS)

In this paper, we address a number of outstanding issues concerning the nature and the role of magnetic inhomogeneities in the iron chalcogenide system FeTe1-xSex and their correlation with superconductivity in this system. We report morphology of superconducting single crystals of FeTe0.65Se0.35 studied with transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy and their magnetic and superconducting properties characterized with magnetization, specific heat and magnetic resonance spectroscopy. Our data demonstrate the presence of nanoscale hexagonal regions coexisting with a tetragonal host lattice, a chemical disorder demonstrating a nonhomogeneous distribution of host atoms in the crystal lattice, as well as iron-deficient bands hundreds of nanometres in length. From the magnetic data and ferromagnetic resonance temperature dependence, we attribute magnetic phases in Fe-Te-Se to Fe3O4 inclusions and to hexagonal symmetry nanoscale regions with a structure of the Fe7Se8 type. Our results suggest that a nonhomogeneous distribution of host atoms might be an intrinsic feature of superconducting Fe-Te-Se chalcogenides and we find a surprising correlation indicating that a faster grown crystal of inferior crystallographic properties is a better superconductor.

Wittlin, A.; Aleshkevych, P.; Przybyli?ska, H.; Gawryluk, D. J.; D?u?ewski, P.; Berkowski, M.; Pu?niak, R.; Gutowska, M. U.; Wi?niewski, A.

2012-06-01

77

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

78

Surface-state-mediated charge-transfer dynamics in CdTe/CdSe core-shell quantum dots.  

PubMed

Herein, we report the synthesis of aqueous CdTe/CdSe type-II core-shell quantum dots (QDs) in which 3-mercaptopropionic acid is used as the capping agent. The CdTe QDs and CdTe/CdSe core-shell QDs are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), steady-state absorption, and emission spectroscopy. A red shift in the steady-state absorption and emission bands is observed with increasing CdSe shell thickness over CdTe QDs. The XRD pattern indicates that the peaks are shifted to higher angles after growth of the CdSe shell on the CdTe QDs. HR-TEM images of both CdTe and CdTe/CdSe QDs indicate that the particles are spherical, with a good shape homogeneity, and that the particle size increases by about 2 nm after shell formation. In the time-resolved emission studies, we observe that the average emission lifetime (?(av)) increases to 23.5 ns for CdTe/CdSe (for the thickest shell) as compared to CdTe QDs (?(av) =12 ns). The twofold increment in the average emission lifetime indicates an efficient charge separation in type-II CdTe/CdSe core-shell QDs. Transient absorption studies suggest that both the carrier cooling and the charge-transfer dynamics are affected by the presence of traps in the CdTe QDs and CdTe/CdSe core-shell QDs. Carrier quenching experiments indicate that hole traps strongly affect the carrier cooling dynamics in CdTe/CdSe core-shell QDs. PMID:21567706

Rawalekar, Sachin; Kaniyankandy, Sreejith; Verma, Sandeep; Ghosh, Hirendra N

2011-06-20

79

Effects on superconductivity of transition-metal doping in FeSe(0.5)Te(0.5).  

PubMed

We investigate superconductivity in the compound FeSe(0.5)Te(0.5) and in its transition-metal-substituted derivatives Fe(1-x)TM(x)Se(0.5)Te(0.5), where x = 5% and the substituent ions studied were Mn, Co, Ni, Cu and Zn. Electronic and magnetic measurements indicate that doping with Mn or by Co acts respectively to cause a slight enhancement or suppression of the transition temperature. However, doping with this concentration of Ni or Cu destroys the superconductivity completely, and leads to semiconducting behaviour. Zn ions cannot be incorporated properly into the parent compound. The reasons for these contrasting effects are associated with the differing magnetic properties of the substituent ions, which determine their local impurity moments and the net carrier concentrations in the doped 11 system. The effects of magnetic ion substitution on superconductivity suggest that the pairing symmetry may not be either pure s wave or pure d wave. PMID:21393789

Zhang, A M; Xia, T L; Kong, L R; Xiao, J H; Zhang, Q M

2010-06-23

80

Transport Properties of SbTeSe Phase-Change Media  

NASA Astrophysics Data System (ADS)

The low-temperature electrical resistivities ?, magneticsusceptibility ? and structure of Sb2Te3-xSex compounds (x=0, 0.6, 0.9, 1.2, 3) have been investigated. In all the samples, the ?behavior with temperature T is metallic except in the case of the samplewith x = 3. We extract the electron-phonon coupling constant ? bycomparing our experimental results with the Boltzmann transport theory. Thehigh residual electrical resistivity is explained as being due to thelow-conduction electron density. All the compounds exhibit diamagneticbehavior, however, the magnetic susceptibility ?(T) exhibitsparamagnetic behavior with T.

Wu, Chih; Yao, Yeong; Huang, Der

1998-04-01

81

Effect of In Additive in the Density of Defect States in a-Se{sub 85}Te{sub 15} and a-Se{sub 75}Te{sub 25} Thin Films  

SciTech Connect

In this paper we report the effect of In incorporation in the density of defect states of two binary Se-Te glassy systems. For this purpose, we have chosen here two well known and well studied a-Se{sub 85}Te{sub 15} and a-Se{sub 75}Te{sub 25} glassy alloys. The d. c. conductivity measurements at high electric fields in vacuum evaporated amorphous thin films of Se{sub 85}Te{sub 15}, Se{sub 75}Te{sub 15}In{sub 10} and Se{sub 75}Te{sub 25}, glassy alloys have been made. Current-Voltage (I-V) Characteristics have been measured at various fixed temperatures. In these samples, at low electric fields, ohmic behavior is observed. However, at high electric fields (E{approx}10{sup 4} V/cm), non-ohmic behavior is observed. An analysis of the experimental data confirms the presence of space charge limited conduction (SCLC) in the glassy materials studied in the present case. From the fitting of the data to the theory of SCLC, the density of defect states (DOS) near Fermi level is calculated. The peculiar role of third element In as an impurity in the pure binary Se{sub 75}Te{sub 25} and Se{sub 85}Te{sub 15} glassy alloys is also discussed in terms of electronegativity difference.

Sharma, N.; Shukla, S.; Singh, S. P.; Kumar, S. [Department of Physics, Christ Church College, Kanpur-208001 (India)

2011-07-15

82

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

E-print Network

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

Zhang, Qian

83

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

84

Low Field Microwave Absorption in thin films of FeSe and FeTeSe deposited by PLD  

NASA Astrophysics Data System (ADS)

Our motivation is to study the 2D superconductivity of Fe-based materials deposited on different substrates - glass, STO and CNT. Pulsed laser deposition of FeSe and FeSe0.5Te0.5 films was performed. Deposition conditions including laser fluences, frequency, temperature and back pressure were optimized for different substrates. When anisotropic superconductors are confined to lower dimensions, interesting effects have been observed. Enhanced superconductivity might occur from interfacial effects, and it has been claimed that an atomic layer of FeSe may exhibit higher Tc at STO interface. LFMA (microwave absorption at low magnetic fields) is a highly sensitive tool for searching for possible higher Tc phases in FeSe based films, especially when combined with ESR, SQUID magnetometry and resistivity measurements. LFMA uses an external magnetic field to create Josephson Junction vortices, which are non-resonantly excited by MW radiation. Such vortices have strong angle dependence in 2D systems and can be used to carefully probe and understand confinement effects. The LFMA spectrum exhibits two distinct features in different temperatures: a hysteretic LFMA below 8K and non-hysteretic narrow LFMA at higher T. Angle dependences of the LFMA signals are analyzed and the origin of the higher Tc LFMA signals will be discussed.

Yuen, Jonathan; Howard, Austin; Chen, Li; Wang, Haiyan; Salamon, Myron; Zakhidov, Anvar

2013-03-01

85

Accuracy of existing atomic potentials for the CdTe semiconductor compound  

Microsoft Academic Search

CdTe and CdTe-based Cd1–xZnxTe (CZT) alloys are important semiconductor compounds that are used in a variety of technologies including solar cells, radiation detectors, and medical imaging devices. Performance of such systems, however, is limited due to the propensity of nano- and micro-scale defects that form during crystal growth and manufacturing processes. Molecular dynamics simulations offer an effective approach to study

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

2011-01-01

86

Photoluminescence studies of type-II CdSe/CdTe superlattices  

SciTech Connect

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

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

2012-08-06

87

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

88

X-ray absorption spectroscopy of doped Bi2Se3 and Bi2Te3  

NASA Astrophysics Data System (ADS)

Topological insulators are a prototypical system to investigate correlated electron physics. Analogous to quantum hall states, these remarkable materials have conducting surface/edge states surrounding an insulating in the bulk state. Unlike quantum hall systems the conducting states of topological insulators do no arise from an applied magnetic field but instead emerge as a result of spin-orbit interactions. Furthermore, doping with different 3d-metals can significantly alter the electronic structure, inducing superconductivity in the case of CuxBi2-xSe3, and ferromagnetism in Bi2-xMnxTe3. In an effort to elucidate the role of the local bonding environment on the electronic structure in the chalchogenide topological insulators, Bi2Te3 and Bi2Se3 with various transition metal as dopants, we have preformed a series of soft x-ray absorption spectroscopy measurements.

McChesney, Jessica; Rosenberg, Richard; Chung, Duck Young; Kanatzidis, Mercouri

2013-03-01

89

Modified magnetism within the coherence volume of superconducting FeSeTe  

SciTech Connect

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

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

2014-01-01

90

Photoluminescence waveguiding in CdSe and CdTe QDs-PMMA nanocomposite films  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

91

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

92

Template assisted growth of microporous structures of CdSe x Te1 - x and thin film photocurrent studies  

NASA Astrophysics Data System (ADS)

Ternary alloyed II-VI group semiconducting CdSe x Te1 - x thin films (x = 0.1 to 1) have been fabricated using electrodeposition technique for detailed photoelectrochemical study and to eventually grow their two-dimensional microporous photonic structures using self-assembled template for optoelectronic devices. Band gap tuning is achieved by controlling Se:Te ratio and the ratio of Se:Te has been controlled using appropriate precursors ratios and their respective concentrations, electrolyte pH etc. Extensive structural and photonic studies have been explored for alloyed CdSe x Te1 - x thin films (x = 0.1 to 1) to establish correlation between structural and optical properties for the series of x. The photoelectrochemical studies have shown a stable photocurrent response and confirmed the n-type semiconducting behaviour of CdSe x Te1 - x thin films with photocurrent densities up to 0.6 mA cm-2.

Shakya, Suman; Vijaya Prakash, G.

2014-09-01

93

Magneto-photoluminescence studies of CdTe\\/CdSe\\/ZnS nanoparticles  

Microsoft Academic Search

Recently, the effect of the magnetic flux on the excitonic energy has received much attention. Optical Aharonov-Bohm was observed on negatively charged exciton in InGaAs\\/GaAs quantum ring as well as neutral exciton in type-II InP-GaAs heterostrcture. In this talk we'll present our magneto-photoluminescence studies on the optical properties of CdTe\\/CdSe\\/ZnS system. The nanoparticles that were grown by chemical method have

Y. H. Chang; C. C. Huang; L. W. Chang; C. H. Hsu; Chih-Wei Lai; Chien-Liang Liu; Pi-Tai Chou; Y. W. Suen

2008-01-01

94

Sonochemical synthesis of nanocrystalline lead chalcogenides: PbE (E = S, Se, Te)  

Microsoft Academic Search

Nanocrystalline lead chalcogenides PbE (E=S, Se, Te) were synthesized conveniently by the reaction of Pb(CH3COO)2·3H2O and elemental chalcogens in ethylenediamine (en) under ultrasonic irradiation. XRD and TEM techniques were employed to characterize the products. The solubility of chalcogen in en was found to be the key factor of the reaction. A three-step mechanism was proposed to account for the formation

Qing Li; Yi Ding; Mingwang Shao; Ji Wu; Guihua Yu; Yitai Qian

2003-01-01

95

Combined solution effects yield stable thin-film Cd(Se,Te)\\/polysulfide photoelectrochemical solar cells  

Microsoft Academic Search

Photocurrent-voltage and long-term stability (greater than a year) results of thin-film Cd(Se,Te)\\/aqueous polysulfide photoelectrochemical solar cells (PEC) are presented. In outdoor experiments, it is demonstrated that small modifications of polysulfide electrolyte composition can increase cadmium chalcogenide\\/polysulfide PEC solar cell lifetimes from months to years. After an initial small rise and fall in solar to electrical conversion efficiency, a photoelectrochemical solar

Licht

1986-01-01

96

Combined solution effects yield stable thin-film Cd(Se,Te)/polysulfide photoelectrochemical solar cells  

SciTech Connect

Photocurrent-voltage and long-term stability (greater than a year) results of thin-film Cd(Se,Te)/aqueous polysulfide photoelectrochemical solar cells (PEC) are presented. In outdoor experiments, it is demonstrated that small modifications of polysulfide electrolyte composition can increase cadmium chalcogenide/polysulfide PEC solar cell lifetimes from months to years. After an initial small rise and fall in solar to electrical conversion efficiency, a photoelectrochemical solar cell, containing a pasted thin-film Cd(Se,Te) photoelectrode immersed in an electrolyte of 1.8 M Cs/sub 2/S and 3 M S, exhibited complete stability (for an 8-month outdoors operation) at 4.1% conversion efficiency. Optimization of (i) nominal sulfide concentration, (ii) the ratio of dissolved sulfur to sulfide, (iii) removal of hydroxide, and (iv) correct choice of cation (cesium) in polysulfide electrolyte, in addition to increasing solution or cell stability, improves thin-film and single-crystal Cd(Se,Te) solar to electrical relative efficiencies by 24% and 65%, respectively, when compared to those in commonly used polysulfide electrolytes. 26 references, 3 figures, 1 table.

Licht, S.

1986-03-13

97

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

98

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

99

Thermal annealing effects on the properties of intersubband absorption in CdS/ZnSe and (CdS/ZnSe)/BeTe II-VI quantum wells  

NASA Astrophysics Data System (ADS)

The authors report the study of thermal annealing (TA) effects on the intersubband transitions (ISB-T) properties in (CdS/ZnSe)/BeTe and CdS/ZnSe multiple quantum wells (MQWs). The samples were grown on (001)-GaAs substrates by molecular beam epitaxy. With the increase of annealing temperature, the ISB-T shifts to longer wavelength in (CdS/ZnSe)/BeTe MQWs, but to short wavelength in CdS/ZnSe MQWs. The ISB absorption vanishes at the annealing temperature of 270 °C for CdS/ZnSe QWs while survives to up to 440 °C for (CdS/ZnSe)/BeTe QWs. For (CdS/ZnSe)/BeTe MQWs after 20 minutes of TA, absorption wavelength and intensity become stable. For CdS/ZnSe MQWs, however we observed a blue shift in wavelength accompanied by a decrease of intensity after 45 minutes of TA. Photo-induced ISB-T measurements indicate that the disappearance of ISB absorption results from the loss of free-carriers in the well layers. ?/2? scan and two-dimensional reciprocal space mapping (2DRSM)) measurements of X-ray diffraction (XRD) indicate that a built-up of tensile strain and interdiffusion at interfacial region in the annealed (CdS/ZnSe)/BeTe heterostructrues. 2DRSM also shows the enhanced structural relaxation in CdS/ZnSe MQWs. Based on the XRD analysis, the effects of TA on the ISB-T in (CdS/ZnSe)/BeTe and CdS/ZnSe MQWs are explained.

Li, Bing-Sheng; Akimoto, Ryoichi; Shen, Aidong

2013-09-01

100

Effect of surrounding medium on light absorption characteristics of CdSe, CdS & CdTe nanospheres and their comparison  

NASA Astrophysics Data System (ADS)

The absorption efficiency of cadmium compounds, prospective nanosolar cell materials, as spherical nanoparticles of radius less than 100 nm and effect of surrounding medium refractive index on them have been studied by Mie Plot. It is found that the absorption efficiency of CdSe, CdS, and CdTe increases with radius of the nanoparticle and also the UV-Visible absorption spectra shifts towards red. The maximum of absorption efficiency is observed at 80 nm radius and is in visible region for all the selected materials. Also with increase in surrounding refractive index, the absorption efficiency is found to be decreasing and absorption spectra is blue-shifted. For all these presently selected cadmium compounds, CdTe possess highest efficiency as compared to both CdS and CdSe.

Bansal, Amit; Sekhon, Jagmeet Singh; Verma, S. S.

2013-06-01

101

E2(CN)2 (E = S, Se) and related compounds.  

PubMed

A synthetic, spectroscopic, and theoretical study of Ex(CN)2 (E = S, Se; x = 1-3) is described. The X-ray structures of Se2(CN)2 and Se3(CN)2 have been determined. Se2(CN)2 crystallizes in a chiral space group with the CN groups approximately gauche. PMID:16411706

Burchell, Colin J; Kilian, Petr; Slawin, Alexandra M Z; Woollins, J Derek; Tersago, Karla; Van Alsenoy, Christian; Blockhuys, Frank

2006-01-23

102

Long life operations over 5000 hours of BeZnSeTe/MgZnCdSe visible light emitting diodes on InP substrates  

NASA Astrophysics Data System (ADS)

Aging characteristics of BeZnSeTe yellow light emitting diodes (LEDs) fabricated on InP substrates by molecular beam epitaxy were investigated under direct current injections at room temperature. It was shown that the decay speed of the light output during the aging was slower than that of conventional ZnCdSe/MgZnSSe LEDs. A long lifetime more than 5000 h and a half lifetime of 5180 h were obtained at a current density of 130 A/cm2. The half lifetimes of the BeZnSeTe LEDs were about three orders of magnitude greater than that of the ZnCdSe/MgZnSSe LEDs. These results proved high reliability of the BeZnSeTe LED. Investigating the aging characteristics of the applied voltage, the injection current, and the emission spectra showed that the output decay was caused by degradation of the active layer of the LEDs.

Nomura, Ichirou; Nakai, Yuki; Hayami, Koichi; Saitoh, Takumi; Kishino, Katsumi

103

High-pressure phase diagram of ZnSe{sub x}Te{sub 1-x} alloys  

SciTech Connect

We have performed high-pressure energy dispersive x-ray diffraction experiments in ZnSe{sub x}Te{sub 1-x} alloys (x=0, 0.1, 0.2, 0.55, 0.81, 0.93, 0.99, and 1.0) in order to establish their pressure-composition phase diagram, and characterize the equation of state of all the involved phases. We conclude that the electronic energy-volume dependence is similar in all compounds. The differences observed in the stability range of the cinnabar and Cmcm phases should then be discussed in terms of other factors, as the presence of energy barriers (cinnabar) or dynamical instabilities (Cmcm). We also argue that the cinnabar phase found is similar for all compositions. Finally we discuss the different compressibility observed in the Cmcm and rocksalt phases.

Pellicer-Porres, J.; Martinez-Garcia, D.; Ferrer-Roca, Ch.; Segura, A.; Munoz-Sanjose, V.; Itie, J.P.; Polian, A.; Munsch, P. [ICMUV, Universitat de Valencia, c/Dr. Moliner 50, 46100 Burjassot, Valencia (Spain); Physique des Milieux Condenses, CNRS-UMR 7602, Universite Pierre et Marie Curie, B77, 4, Place Jussieu, 75252 Paris CEDEX 05 (France); Laboratoire pour l'Utilisation du Rayonnement Electromagnetique, Centre Universitaire Paris-Sud, Batiment 209 A, Boite Postale 34, 91898 Orsay Cedex (France)

2005-01-15

104

Ge2Sb2Te5/SnSe2 nanocomposite multilayer thin films for phase change memory application  

NASA Astrophysics Data System (ADS)

By nanocompositing Ge2Sb2Te5 and SnSe2, the electrical and thermal proprieties of Ge2Sb2Te5/SnSe2 multilayer films for phase change random access memory (PCRAM) are better than those of Ge2Sb2Te5 films. The crystallization temperature rises and can be controlled. The resistance gap can reach approximately five orders of magnitude to ensure high data reliability. The activity energy (Ea) is more than 2.60 eV and the temperature for 10 year data retention reach 110 °C. The analysis of both XRD patterns and TEM images confirmed the reversible phase change transition between amorphous and crystalline state in Ge2Sb2Te5/SnSe2 nanocomposite multilayer films. According to transient photoreflectance traces, the speed of crystallization process was about 33 ns. Among different Ge2Sb2Te5/SnSe2 multilayer films, the film constitute of [Ge2Sb2Te5 (4 nm)/SnSe2(10 nm)]7 showed better properties and was manufactured by CMOS technology to phase change memory (PCM) cells. This result revealed that the Ge2Sb2Te5/SnSe2 nanocomposite multilayer film is a promising phase change material.

Feng, Xiaoyi; Wen, Ting; Zhai, Jiwei; Lai, Tianshu; Wang, Changzhou; Song, Sannian; Song, Zhitang

2014-10-01

105

Effect of iodine on morphology changes of spray deposited nanocrystalline CdSe:I, CdTe:I and HgTe:I thin films  

NASA Astrophysics Data System (ADS)

The low-temperature preparation of nanofibres and nanotubes in iodine-doped CdX (X = Se, Te) and HgTe thin films is reported. Iodine was used as an n-type dopant in CdX and HgTe. The films were deposited on glass substrates at 200 °C by spray deposition of iodine-doped nanoparticles prepared using a solvothermal method. The surface morphology of iodine-doped CdX films shows the formation of nanofibers and that of iodine-doped HgTe films shows the formation of nanotubes 4 ?m long with an average diameter of 45 nm. Selected-area diffraction patterns show the formation of cubic HgTe nanotubes with lattice parameter a = 0.6467 nm.

Rangarao, A.; Dutta, V.

2006-04-01

106

Energy band-gap calculations of short-period (ZnTe)m(ZnSe)n and (ZnS)m(ZnSe)n strained-layer superlattices  

Microsoft Academic Search

We report on the calculations of energy band gaps based on the semiempirical tight-binding model for short-period (ZnTe)m(ZnSe)n and (ZnS)m(ZnSe)n strained-layer superlattices (SLSs). During the calculation, much attention has been paid to the modeling of strain effect. It is found that (ZnTe)m(ZnSe)n superlattices grown on InAs, InP, and GaAs substrates show very different electronic properties from each other, which is

Yi-Hong Wu; Shizuo Fujita; Shigeo Fujita

1990-01-01

107

Magneto-photoluminescence studies of CdTe/CdSe/ZnS nanoparticles  

NASA Astrophysics Data System (ADS)

Recently, the effect of the magnetic flux on the excitonic energy has received much attention. Optical Aharonov-Bohm was observed on negatively charged exciton in InGaAs/GaAs quantum ring as well as neutral exciton in type-II InP-GaAs heterostrcture. In this talk we'll present our magneto-photoluminescence studies on the optical properties of CdTe/CdSe/ZnS system. The nanoparticles that were grown by chemical method have size of about 6 nm and the band alignment between the core (CdTe) and the shell (CdSe) is a type--II band alignment. The addition of ZnS layer is to passivate the surface of CdSe and to enhance the light emitting efficiency. Magneto-photoluminescence experiment was performed at T=1.4 K with a 14 T superconducting magnet in conjunction with a green diode laser and a monochromator. Oscillation on the peak energy of the photoluminescence spectra as well as oscillation in the integrated intensity as a function of magnetic field were observed and are attributed to the optical Aharonov-Bohm-like effect.

Chang, Y. H.; Huang, C. C.; Chang, L. W.; Hsu, C. H.; Lai, Chih-Wei; Liu, Chien-Liang; Chou, Pi-Tai; Suen, Y. W.

2008-03-01

108

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

PubMed Central

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

2014-01-01

109

Frequency dependence of dielectric constants of Ag doped Se-Bi-Te system  

NASA Astrophysics Data System (ADS)

The effect of Ag addition on dielectric properties of Se80.5Bi1.5Te18-yAgy (y= 0, 1.0 and 1.5) glassy system. Dielectric relaxation studies are important to understand the nature and origin of dielectric losses, which in turn may be useful in the determination of structure and defects in solids. dielectric parameters (dielectric constant ?'(?) and dielectric loss ??(?)) are studied in the frequency range 1 kHz-50 kHz over the temperature range 300K - 365K, using parallel impedance measurements.

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

2013-06-01

110

Effect of substitutional doping on temperature dependent electrical parameters of amorphous Se-Te semiconductors  

NASA Astrophysics Data System (ADS)

Steady state current-voltage characteristics of the amorphous (Se80Te20)98Y2 (Y = Ag, Bi, Ge, Cd) semiconductors at different temperatures are reported. The measurements were performed using direct-current voltage bias to understand the basic conductivity mechanism and to evaluate the impact of each substituent on electrical response. The space charge limited conduction mechanism, and the density of states near Fermi level have been calculated. The difference in electrical response due to different substitutions in the glassy matrix is analyzed.

Sharma, Neha; Sharda, Sunanda; Sharma, Dheeraj; Sharma, Vineet; Barman, P. B.; Katyal, S. C.; Sharma, Pankaj; Hazra, S. K.

2013-09-01

111

Sonochemical synthesis of nanocrystalline lead chalcogenides: PbE (E = S, Se, Te)  

SciTech Connect

Nanocrystalline lead chalcogenides PbE (E=S, Se, Te) were synthesized conveniently by the reaction of Pb(CH{sub 3}COO){sub 2}{center_dot}3H{sub 2}O and elemental chalcogens in ethylenediamine (en) under ultrasonic irradiation. XRD and TEM techniques were employed to characterize the products. The solubility of chalcogen in en was found to be the key factor of the reaction. A three-step mechanism was proposed to account for the formation of the products.

Li Qing; Ding Yi; Shao Mingwang; Wu Ji; Yu Guihua; Qian Yitai

2003-02-20

112

Electrodeposited heterojunctions based on cadmium chalcogenide, CdX (X = S, Se, Te) and polyaniline  

Microsoft Academic Search

We have fabricated heterojunctions based on all-electrodeposited cadmium chalcogenides CdX (X = S, Se, Te) and polyaniline\\u000a thin film. Cadmium chalcogenide films were deposited onto low cost stainless steel substrate using potentiostatic mode. Over\\u000a Cd chalcogenide film, polyaniline was deposited potentiodynamically. The junctions were heated at 353 K for 20 min and junction\\u000a current–voltge (I–V) and capacitance–voltage (C–V) plots were studied. From I–V plots,

S. S. Joshi; C. D. Lokhande

2007-01-01

113

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

114

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

115

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

SciTech Connect

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

Li Jingjing; Liu Shi; Wang Shumin; Ding Ding; Johnson, Shane R.; Zhang Yonghang [Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287 (United States); School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Liu Xinyu; Furdyna, Jacek K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Smith, David J. [Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287 (United States); Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)

2012-03-19

116

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

E-print Network

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

Carlton, Chris E.

117

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

Microsoft Academic Search

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

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

1992-01-01

118

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

SciTech Connect

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

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

1998-12-31

119

Temperature-dependent xerographic depletion discharge studies of a-Se:Te alloys  

NASA Astrophysics Data System (ADS)

The time evolution of the surface potential of xerographic photoreceptors charged in the dark can yield valuable information conerning, the underlying thermal generation processes and the energetic distribution of emission centres. Xerographic dark discharge of a-Se :Te films proceeds according to the xerographic depletion discharge (XDD) model. According to this model the depletion time td should be singly activated. We find that for a-Se :Te alloys in the alloying regime 5-1 2wt% Arrhenius plots of td are non-linear and yield characteristic attempt-to-escape frequencies typically 1 8 times greater than phonon frequencies in these materials. This result can be only partially accounted for by the recent fourth-order approximation of the demarcation energy concept. The presence of exponential distributions of emission centres in this material system is shown by the application of the field-enhanced XDD model at constant temperture. A theoretical fit of temperature-dependent data is then achieved by consideration of the occupation function of emission centres close to EF and the temperature dependence of the mobility gap. For the materials studied, the best fit to the experimental data was achieved with EF located at an energy corresponding to half the optical gap from the mobility edges. The thermal generation mechanism is identified as the process C3 -* C30+h followed by C3° C1 + h.

Baxendale, M.; Juhasz, C.

1990-07-01

120

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. PMID:24218617

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

2013-01-01

121

GaSe and GaTe anisotropic layered semiconductors for radiation detectors  

NASA Astrophysics Data System (ADS)

High quality detector grade GaSe and GaTe single crystals have been grown by a modified vertical Bridgman technique using high purity Ga (7N) and in-house zone refined (ZR) precursor materials (Se and Te). A state-of-the-art computer model, MASTRAPP, is used to model heat and mass transfer in the Bridgman growth system and to predict the stress distribution in the as-grown crystals. The model accounts for heat transfer in the multiphase system, convection in the melt, and interface dynamics. The crystals harvested from ingots of 8-10 cm length and 2.5 cm diameter, have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, low temperature photoluminescence (PL), atomic force microscopy (AFM), and optical absorption/transmission measurements. Single element devices up to 1 cm2 in area have been fabricated from the crystals and tested as radiation detectors by measuring current-voltage (I-V) characteristics and pulse height spectra using 241Am source. The crystals have shown high promise as nuclear detectors with their high dark resistivity (>=10 9 ? .cm), good charge transport properties (?? e ~ 1.4x10 -5 cm2/V and ?? h ~ 1.5x10 -5 cm2/V), and relatively good energy resolution (~4% energy resolution at 60 keV). Details of numerical modeling and simulation, detector fabrication, and testing using a 241Am energy source (60 keV) is presented in this paper.

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

2007-09-01

122

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

123

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

NASA Astrophysics Data System (ADS)

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

Joseph, Elad; Amouyal, Yaron

2014-10-01

124

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

125

Properties of lattice matched ZnMgSeTe quaternary alloys grown on ZnTe substrates  

Microsoft Academic Search

Lattice-matched high crystal quality Zn1?xMgxSeyTe1?y quaternary alloys are grown on ZnTe substrates. For high crystalline and homogeneous alloy growth, the molecular beam pressure ratio is controlled as PSeTe substrates is obtained as y=0.63 x by both the correlated-function-expansion method and experiment. The growth temperature is optimized in terms of the X-ray rocking curve

J. H Chang; M. W Cho; H Makino; K Shim; H Rabitz; T Yao

2000-01-01

126

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

127

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 ). 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.

2014-10-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

129

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

E-print Network

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

130

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

131

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

PubMed Central

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

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

2011-01-01

132

Role of oxidation on surface conductance of the topological insulator Bi2Te2Se  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

133

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

134

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

SciTech Connect

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

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

2009-07-01

135

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

NASA Astrophysics Data System (ADS)

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

Sharma, Ambika; Yadav, Preeti; Kumari, Anshu

2014-04-01

136

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

137

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

Microsoft Academic Search

Research on electrochemical photovoltaic incorporating thin film n-CdSe and n-CdSe sub 1-x\\/Te sub x photoanodes 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

W. L. Wallace

1984-01-01

138

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

139

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

140

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

141

Three-dimensional structure of CdX (X =Se,Te) nanocrystals by total x-ray diffraction  

NASA Astrophysics Data System (ADS)

The three-dimensional structure of oleic acid-capped CdSe and thiol-capped CdTe nanocrystals used as quantum dots has been determined by total synchrotron radiation x-ray diffraction and atomic pair distribution function analysis. Both CdSe and CdTe are found to exhibit the zinc-blende-type atomic ordering. It is only slightly distorted in CdSe implying the presence of nanosize domains and very heavily distorted in CdTe due to the presence of distinct core-shell regions. The results well demonstrate the great potential of the experimental approach and thus encourage its wider application in quantum dot research.

Pradhan, S. K.; Deng, Z. T.; Tang, F.; Wang, C.; Ren, Y.; Moeck, P.; Petkov, V.

2007-08-01

142

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

143

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

145

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

NASA Technical Reports Server (NTRS)

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

Su, Ching-Hua; Ramachandran, N.

2013-01-01

146

Review: three synthesis methods of CdX (X = Se, S or Te) quantum dots.  

PubMed

Quantum dots (QDs) are one of the first nanotechnologies to be integrated with the biological sciences that used for imaging or tracking macromolecules/cells in cell/tissue. Because of QDs are important in biomedical and biological applications, identify a variety of synthesis methods to produce QDs with different characteristics also is particularly important. Hence, in this review the authors discussed three methods for synthesis of heavy metal chalcogenide-based QDs for use in biomedical field: (i) Organometallic method for synthesis of QDs consists of three components: precursors, organic surfactants and solvents. The authors also discussed water-solubilisation strategies of synthesised QDs including encapsulation and ligand exchange. (ii) Aqueous synthesis technique using short-chain thiols as stabilising agents is a useful alternative to organometallic synthesis of CdSe, CdS and CdTe QDs. (iii) The third method discussed in this article for QDs synthesis involves the utilise of microorganisms to prepare QDs with controlled size, shape, chemical composition and functionality. The authors also discussed recently new methods for the synthesis of the appropriate QDs for use in biology. In addition, attachment of biomolecules such as antibodies, oligonucleotides on the surface of QDs for specific targeting and different opinions about toxicity of QD have been studied. PMID:25014077

Mussa Farkhani, Samad; Valizadeh, Alireza

2014-06-01

147

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

SciTech Connect

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

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

2010-02-24

148

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

E-print Network

for spectroscopic studies. Hydrogen can be introduced into a sample by boiling in water, electrolysis, implantationHydrogen passivation of Se and Te in AlSb M. D. McCluskey and E. E. Haller Lawrence Berkeley observed local vibrational modes LVM's arising from DX-hydrogen complex in AlSb. Hydrogen was diffused

McCluskey, Matthew

149

Bi-nanoparticle (CdTe and CdSe) mixed polyaniline hybrid thin films prepared using spin coating technique  

NASA Astrophysics Data System (ADS)

Polyaniline (Pani) films containing CdTe, CdSe, and both nanoparticles were deposited using spin coating technique. Pani was chemically synthesized by oxidation method, whereas surfactant free CdTe and CdSe nanoparticles were prepared using solvothermal method. Binanoparticle films showed an increase in the absorption from 350 nm to the near IR region. Absorption spectra also showed charge transfer complex formation for the binanoparticle hybrid thin films prepared with weight ratio of [Pani (camphor sulfonic acid, CSA):CdTe:CdSe] 200:100:75. Photoluminescence measurement for the bi-nanoparticle hybrid thin films confirmed that the required dissociation of excitons was taking place at the interface. Scanning electron microscopy images showed homogeneity and an interconnected network on the surface of the films prepared with Pani (CSA):CdTe:CdSe weight ratios of 200:100:50 and 200:100:75, respectively. Cyclic voltammetry confirmed better stability for the bi-nanoparticle hybrid films in comparison to Pani film. It also established the process of electrochemical charge transfer between the nanoparticles and the polymer matrix.

Verma, Deepak; Dutta, V.

2009-02-01

150

Evolution of superconductivity in isovalent Te-substituted KxFe2-ySe2 crystals  

NASA Astrophysics Data System (ADS)

We report the evolution of superconductivity and the phase diagram of the KxFe2-ySe2-zTez (z = 0-0.6) crystals grown by a one-step synthesis. The one-step synthesis is much simpler than a conventional process to grow the KxFe2-ySe2 system. No structural transition is observed in any crystals, while lattice parameters exhibit a systematic expansion with increasing Te content. The Tc exhibits a gradual decrease with increasing Te content from {T}_{{c}}^{{onset}}=3 2.9 K at z = 0 to {T}_{{c}}^{{zero}}=2 7.9 K at z = 0.5, followed by a sudden suppression of superconductivity at z = 0.6. Upon approaching a Te concentration of 0.6, the shielding volume fraction decreases and eventually drops to zero. Simultaneously, hump positions in the ?-T curve shift to lower temperatures. These results suggest that isovalent substitution of Te for Se in KxFe2-ySe2 crystals suppresses the superconductivity in this system.

Ozaki, Toshinori; Takeya, Hiroyuki; Deguchi, Keita; Demura, Satoshi; Hara, Hiroshi; Watanabe, Tohru; Denholme, Saleem James; Okazaki, Hiroyuki; Fujioka, Masaya; Yokota, Yoshiko; Yamaguchi, Takahide; Takano, Yoshihiko

2013-05-01

151

Synthesis, characterization and performance of Cd1xInxTe compound for solar cell applications  

E-print Network

. There are contin- ued interests in CdTe thin films due to interests in their photovol- taic properties, optical parameters can be varied by changing the cation composition. CuInGaSe2 (CIGS) chalcopyrite thin film absorber material is one of the most promising candidates for its high efficiency and low cost thin film solar cell

Chow, Lee

152

Crystal Structures and Thermoelectric Properties of Layered Compounds in the ATe–Bi2Te3(A = Ge, Sn, Pb) Systems  

Microsoft Academic Search

Single-crystal and powder x-ray diffraction studies of compounds in the nATe · mBi2Te3 (A = Ge, Sn, Pb) homologous series in the pseudobinary systems ATe–Bi2Te3 reveal a marked dissimilarity of the GeTe–Bi2Te3 system from SnTe–Bi2Te3 and PbTe–Bi2Te3. The GeTe–Bi2Te3 system contains, along with GeBi2Te4 (n\\/m = 1), GeTe-rich (n\\/m > 1) and Bi2Te3-rich (n\\/m < 1) members of the nGeTe

L. E. Shelimova; O. G. Karpinskii; P. P. Konstantinov; E. S. Avilov; M. A. Kretova; V. S. Zemskov

2004-01-01

153

Enhanced thermoelectric performance in Bi-doped p-type AgSbTe2 compounds  

NASA Astrophysics Data System (ADS)

The influence of bismuth (Bi) substitution on the thermoelectric properties of AgSbTe2 compounds was investigated and compared with the undoped AgSbTe2. The addition of Bi dopants not only resulted in a reduction in thermal conductivity but also markedly increased the thermopower in the Ag(Sb1-xBix)Te2 series. Additional phonon scatterings were created by Bi doping and led to a reduction of thermal conductivity. The lattice thermal conductivity is significantly reduced which could be ascribed to enhancement of phonon scattering by dopants with greater atomic weight. In addition, the thermopower was enhanced, which was attributed to the electron-filtering effects caused by the nanoscaled microstructures. Because of the extremely low thermal conductivity (0.48 Wm-1K-1) and moderate power factor of AgBi0.05Sb0.95Te2, a maximum ZT value of (1.04 ± 0.08) was reached at 570 K; yielding an enhancement of greater than 10% compared with an undoped AgSbTe2. this result shows promising thermoelectric properties in the medium temperature range.

Mohanraman, Rajeshkumar; Sankar, Raman; Chou, F. C.; Lee, C. H.; Chen, Yang-Yuan

2013-10-01

154

Luminescence of ZnSe(Te) crystals melt-grown from the charge and enriched in selenium  

NASA Astrophysics Data System (ADS)

The evolution of the radioluminescence (RL) spectra and spectral-kinetic characteristics of ZnSe100-xTex (0.01 Se added to the initial charge. The crystals were grown from the melt under argon pressure. The elemental composition of the samples was checked by x-ray luminescence and chemical analysis. It is shown that, depending upon the degree of doping with Te, different RL bands compete with each other. Thus, at 0.01 Te clusters, while the formation of the `green' RL band is presumably due to Zn vacancies. The presence of the intense `red' band in ZnSe100-xTex samples, corresponding to the whole range of x, is considered as an indication of the fact that the luminescence center {V Zn- + Te0 + Zn+} comprises the isovalent dopant Te and the excess Zn.

Ryzhikov, Vladimir D.; Gal'chinetsky, Leonid P.; Galkin, S. N.; Katrunov, Konstantin A.; Lisetskaya, Elena K.

1998-04-01

155

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

156

Aqueous synthesis of type-II CdTe/CdSe core-shell quantum dots for fluorescent probe labeling tumor cells.  

PubMed

In this paper, we report a two-step aqueous synthesis of highly luminescent CdTe/CdSe core/shell quantum dots (QDs) via a simple method. The emission range of the CdTe/CdSe QDs can be tuned from 510 to 640 nm by controlling the thickness of the CdSe shell. Accordingly, the photoluminescence quantum yield (PL QY) of CdTe/CdSe QDs with an optimized thickness of the CdSe shell can reach up to 40%. The structures and compositions of the core/shell QDs were characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy experiments, and their formation mechanism is discussed. Furthermore, folate conjugated CdTe/CdSe QDs in Hela cells were assessed with a fluorescence microscope. The results show that folate conjugated CdTe/CdSe QDs could enter tumor cells efficiently. PMID:19417477

Zeng, Ruosheng; Zhang, Tingting; Liu, Jincheng; Hu, Song; Wan, Qiang; Liu, Xuanming; Peng, Zhiwei; Zou, Bingsuo

2009-03-01

157

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

158

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

SciTech Connect

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

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

2011-09-15

159

Super Sensitization: Grand Charge (Hole/Electron) Separation in ATC Dye Sensitized CdSe, CdSe/ZnS Type-I, and CdSe/CdTe Type-II Core-Shell Quantum Dots.  

PubMed

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

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

2014-10-01

160

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

161

Modulation of the Aharonov Bohm effect in type-II II V ZnSe:Te quantum dots by a far-infrared laser  

Microsoft Academic Search

We present magneto-photoluminescence of a ZnTe\\/ZnSe multilayer structure in which the clustering of Te atoms results in the formation of columns of type-II ZnSe:Te quantum dots. This unique geometry permits the observation of strong Aharonov Bohm oscillations in both the emission energy and peak intensity with increasing magnetic field. Furthermore, far-infrared optically detected resonance techniques exhibit resonances that are ascribed

Ian R. Sellers; Vincent R. Whiteside; Igor L. Kuskovsky; Alexander O. Govorov; Bruce D. McCombe

2008-01-01

162

Modulation of the Aharonov–Bohm effect in type-II II–V ZnSe:Te quantum dots by a far-infrared laser  

Microsoft Academic Search

We present magneto-photoluminescence of a ZnTe\\/ZnSe multilayer structure in which the clustering of Te atoms results in the formation of columns of type-II ZnSe:Te quantum dots. This unique geometry permits the observation of strong Aharonov–Bohm oscillations in both the emission energy and peak intensity with increasing magnetic field. Furthermore, far-infrared optically detected resonance techniques exhibit resonances that are ascribed to

Ian R. Sellers; Vincent R. Whiteside; Igor L. Kuskovsky; Alexander O. Govorov; Bruce D. McCombe

2008-01-01

163

Experimental evaluation of aSe and CdTe flat-panel x-ray detectors for digital radiography and fluoroscopy  

Microsoft Academic Search

Described are two types of direct-detection flat-panel X-ray detectors utilizing amorphous selenium (a-Se) and cadmium telluride (CdTe). The a-Se detector is fabricated using direct deposition onto a thin film transistor (TFT) substrate, whereas the CdTe detector is fabricated using a novel hybrid method, in which CdTe is pre-deposited onto a glass substrate and then connected to a TFT substrate. The

Susumu Adachi; Naoyuki Hori; Kenji Sato; Satoshi Tokuda; Toshiyuki Sato; Kazuhiro Uehara; Yoshihiro Izumi; Hisashi Nagata; Youji Yoshimura; Satoshi Yamada

2000-01-01

164

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

165

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

NASA Astrophysics Data System (ADS)

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

Zou, Ping; Xu, Guiying; Wang, Song

2014-11-01

166

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

167

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

SciTech Connect

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

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

2013-01-15

168

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

PubMed

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

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

2014-08-01

169

Effect of photo-crystallization on the photoconductivity of a-Se85Te15 (*) A. Kumar, R. Misra, S. Goel and S. K. Tripathi  

E-print Network

265 Effect of photo-crystallization on the photoconductivity of a-Se85Te15 (*) A. Kumar, R. Misra de films minces de l'alliage amorphe Se85Te15 avant et apr�s photocristallisation. Celle-ci est showed that photo-crystallization effects result from the production of hole-electron pairs

Boyer, Edmond

170

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

PubMed

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

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

2010-12-20

171

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

172

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

PubMed

The stable crystal structures of two cuprous chalcogenides of Cu2X (X=Te or Se) are predicted using an adaptive genetic algorithm in combination with first-principles density functional theory calculations. Both systems are found to prefer a unique and previously unrecognized layered structure, with the total energies much lower than all structures proposed in the literature so far. The newly discovered structures are further shown to be dynamically and mechanically stable, and possess electronic properties consistent with existing experimental observations. In particular, their layered nature is expected to prevail over other structural forms at the interfaces of thin-film solar cells, and knowledge about the precise atomic structures of the interfaces is a prerequisite for achieving long-term stability and high efficiency of CdTe and Cu(In,Ga)Se2 solar cells. PMID:24182279

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

2013-10-18

173

New Layered Structures of Cuprous Chalcogenides as Thin Film Solar Cell Materials: Cu2Te and Cu2Se  

NASA Astrophysics Data System (ADS)

The stable crystal structures of two cuprous chalcogenides of Cu2X (X=Te or Se) are predicted using an adaptive genetic algorithm in combination with first-principles density functional theory calculations. Both systems are found to prefer a unique and previously unrecognized layered structure, with the total energies much lower than all structures proposed in the literature so far. The newly discovered structures are further shown to be dynamically and mechanically stable, and possess electronic properties consistent with existing experimental observations. In particular, their layered nature is expected to prevail over other structural forms at the interfaces of thin-film solar cells, and knowledge about the precise atomic structures of the interfaces is a prerequisite for achieving long-term stability and high efficiency of CdTe and Cu(In,Ga)Se2 solar cells.

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

2013-10-01

174

Nanostructured pinning centers in FeSe0.1Te0.9 thin films for enhanced superconducting properties  

NASA Astrophysics Data System (ADS)

FeSe0.1Te0.9 thin films were deposited on single crystal SrTiO3 (STO) (100) substrates by a pulse laser deposition (PLD) technique. CeO2 nanolayer was introduced as either cap layer or buffer layer to investigate its pinning effects in FeSe0.1Te0.9 thin films. The results show improved film quality after doping with CeO2 nanolayers, and no impurity phase was identified. All the samples achieve T c of 12.5 K, and in-field J c was greatly enhanced after doping with either cap or buffer CeO2 nanolayer for the field range up to 7 T. The buffered one shows the best self-field J c of 0.89 MA cm−2 at 4 K and a high upper critical field H c 2 of 186 T.

Huang, Jijie; Chen, Li; Jian, Jie; Khatkhatay, Fauzia; Wang, Haiyan

2014-10-01

175

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

Microsoft Academic Search

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

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

2008-01-01

176

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

Microsoft Academic Search

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

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

2009-01-01

177

Structural and elastic properties of barium chalcogenides (BaX, X=O, Se, Te) under high pressure  

Microsoft Academic Search

In the present paper we have investigated the high-pressure, structural phase transition of Barium chalcogenides (BaO, BaSe\\u000a and BaTe) using a three-body interaction potential (MTBIP) approach, modified by incorporating covalency effects. Phase transition\\u000a pressures are associated with a sudden collapse in volume. The phase transition pressures and associated volume collapses\\u000a obtained from TBIP show a reasonably good agreement with experimental

Purvee Bhardwaj; Sadhna Singh; Neeraj Kumar Gaur

2008-01-01

178

Synthesis and characterization of lead chalcogenide nanoparticles (PbE, E = Se, Te) semiconductor nanocomposite materials in silica matrices  

Microsoft Academic Search

The semiconductors such as PbE (E = Se, Te) are known for their large band gaps. These band gaps provide unique properties to PbE. At the nanoscale the properties are enhanced due to increase in the surface area to volume ratio and the emergence of new properties such as photoluminescence and multiple electron generation. The sol-gel method has been used

Prashant Bajaj

2009-01-01

179

Synthesis of nanocrystalline lead chalcogenides PbE (E = S, Se, or Te) from alkaline aqueous solutions  

Microsoft Academic Search

Reaction of a sulfur, selenium, or tellurium alkaline aqueous solution and Pb(CH3COO)2·3H2O aqueous solution produces nanocrystalline lead chalcogenides PbE (E = S, Se, or Te) with a cubic phase at low temperature under atmospheric pressure. The products are characterized through X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analysis. The average particle size is in the

Weixin Zhang; Lei Zhang; Youwei Cheng; Zehua Hui; Xiaoming Zhang; Yi Xie; Yitai Qian

2000-01-01

180

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

181

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

182

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

183

Charge density wave formation and physical properties of R2Te5 (R=Nd, Gd) compounds  

NASA Astrophysics Data System (ADS)

R2Te5 (R=Nd, Gd) has a layered tetragonal structure based on alternating single and double square planar Te sheets separated by corrugated RTe layers, and has a quasi-two dimensional electronic structure. The material shares important physical properties with other two single and double Te layer variants, RTe2 and RTe3 (R=La Yb), including a charge density wave (CDW) instability. Using a binary self-flux method, we have grown high-quality single crystals of Gd2Te5 and Nd2Te5 compounds and have characterized their structural, thermodynamic and transport properties. Our measurements reveal, for the first time, the charge density wave in this material. We will discuss the properties and origin of the CDW, and the relation to the better known RTe2 and RTe3 compounds.

Shin, K. Y.; Ru., N.; Toney, M. F.; Fisher, I. R.

2007-03-01

184

Photoluminescence and magneto-optical properties of multilayered type-II ZnTe/ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

Multilayered Zn-Se-Te structures grown by migration enhanced epitaxy are studied by temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL. The PL consists of two bands: a blue band, overlaid with band edge sharp lines, dominant at low temperatures and high excitation, and a green band, which appears at elevated temperature and low excitation. Upon varying excitation intensity by four orders of magnitude, the green band peak energy shifts by ˜60 meV, indicating recombination of excitons in type-II quantum dots (QDs); no significant shift is observed for the blue band. Therefore, the green emission is attributed to ZnTe/ZnSe type-II QDs, which co-exist with isoelectronic centers, responsible for the blue and band edge emissions. The existence of type-II ZnTe/ZnSe QDs is further confirmed by magneto-PL, for which the observed oscillations in the PL intensity as a function of magnetic field is explained in terms of the optical Aharonov-Bohm effect.

Kuskovsky, Igor L.; Gong, Y.; Neumark, G. F.; Tamargo, M. C.

2010-01-01

185

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. PMID:23061009

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

186

Windowless CdSe/CdTe Solar Cells with Differentiated Back Contacts: J-V, EQE, and Photocurrent Mapping.  

PubMed

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

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

2014-09-24

187

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

188

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

189

Influence of Mn on crystal structure and thermoelectric properties of GeTe compounds  

NASA Astrophysics Data System (ADS)

The thermoelectric properties of the Ge1- x Mn x Te compounds were investigated in the temperature range from 300 K to 773 K. The crystal structure of the compound was gradually changed with Mn, changing from a rhombohedral to a cubic-like cell. The Seebeck coefficient and the electrical resistivity were increased with Mn. From the Hall coefficient measurement, the reduction of the carrier concentration was confirmed and was responsible for the change of the electrical properties. The thermal conductivity was also reduced with Mn. The maximum dimensionless figure of merit, ZT, was obtained for x = 0.05 composition, where the value was ZT = 1.3 at 773 K. The evolution of the crystal structure with Mn attributed to the change of the thermoelectric properties. The Mn-doped compound which has a more cubic phase than a rhombohedral exhibited superior thermoelectric properties to the pure rhombohedral phase. [Figure not available: see fulltext.

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

2014-07-01

190

Magnetic and Superconducting Properties of Single Crystals of Fe$_{1+\\\\delta}$Te$_{1-x}$Se$_x$ System  

Microsoft Academic Search

The spin-fluctuation effect in the Se-substituted system Fe$_{1+\\\\delta}$Te$_{1-x}$Se$_x$ ($x$ = 0, 0.05, 0.12, 0.20, 0.28, 0.33, 0.45, 0.48 and 1.00; $0<\\\\delta < 0.12$) has been studied by the measurements of the X-ray diffraction, the magnetic susceptibility under high magnetic fields and the electrical resistivity under magnetic fields up to 14 T. The samples with $x$ = 0.05, 0.12, 0.20, 0.28,

Jinhu Yang; Mami Matsui; Masatomo Kawa; Hiroto Ohta; Chishiro Michioka; Chiheng Dong; Hangdong Wang; Huiqiu Yuan; Minghu Fang; Kazuyoshi Yoshimura

2009-01-01

191

Stabilization of charge-density waves in 1T-TaX2(X=S,Se,Te): First-principles total energy calculations  

NASA Astrophysics Data System (ADS)

The quasi-two-dimensional transition-metal dichalcogenide compounds 1T-TaX2(X=S,Se,Te) at low temperature form charge-density waves (CDW), manifested in periodic lattice distortions. In order to investigate the effect of the CDW on the Fermi surface (FS) of these compounds, the FS cross sections in various planes are calculated and the nesting vectors are determined. The CDW is treated as single q commensurate frozen phonons of wave vectors around the candidate FS nesting vectors. The lattice distortions caused by the CDW are then reproduced using the total energy and force calculations performed within these supercells using the full potential linearized augumented plane-wave method. It was found that these compounds are unstable towards the CDW state. Our FS calculations for the CDW distorted state confirm the presence of gaping in the FS indicating that electron-phonon coupling plays an important role in the stabilization of the CDW in the compounds under investigation.

Sharma, S.; Nordström, L.; Johansson, B.

2002-11-01

192

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. 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

193

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

194

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

195

Reactions of Ph4Se4Br4 with tertiary phosphines. Structural isomerism within a series of R3PSe(Ph)Br compounds.  

PubMed

The synthesis and characterisation of Ph(4)Se(4)Br(4) (1) directly from the reaction of Ph(2)Se(2) with dibromine is reported. The solid-state structure of 1 consists of four PhSeBr units linked by weak selenium-selenium bonds [3.004(2)-3.051(2) A] into a Se(4) square, and is structurally analogous to the previously reported Ph(4)Te(4)I(4). The reactions of Ph(4)Se(4)Br(4) with a variety of tertiary phosphines have been undertaken, resulting in the formation of compounds of formula R(3)PSe(Ph)Br. X-Ray crystallographic analysis of three of the compounds reveals different structural isomers. Ph(3)PSe(Ph)Br (2) is a charge-transfer (CT) compound [Se-Br 3.0020(8) A], with an essentially linear P-Se-Br bond angle, 172.15(4) degrees and T-shaped geometry at selenium. Me(3)PSe(Ph)Br (5) also contains the selenium atom in a T-shaped geometry, consistent with a CT formulation, although the Se-Br distance of 3.327(3) A is considerably longer than observed for 2. In contrast, Cy(3)PSe(Ph)Br (6) is an ionic phosphonium salt, [Cy(3)PSePh]Br with no short Se-Br interactions. Geometry at selenium is bent, as expected for an ionic compound. These results are discussed with reference to the previously reported iodo-compounds Ph(3)PSe(Ph)I and [(Me(2)N)(3)PSe(Ph)]I. PMID:16538270

Barnes, Nicholas A; Godfrey, Stephen M; Halton, Ruth T A; Mushtaq, Imrana; Pritchard, Robin G; Sarwar, Shamsa

2006-03-28

196

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

197

Effect of Fe Substitution on Thermoelectric Properties of Fe x In4- x Se3 Compounds  

NASA Astrophysics Data System (ADS)

Starting from elemental powder mixtures of Fe x In4- x Se3 ( x = 0, 0.05, 0.1, 0.15), polycrystalline In4Se3-based compounds with homogeneous microstructures were prepared by mechanical alloying (MA) and hot pressing (HP). With the increase of x from 0 to 0.15, the electrical resistivity and the absolute value of the Seebeck coefficient increased, while the thermal conductivity first decreased and then increased. The maximal dimensionless figure of merit ZT of 0.44 was obtained for the Fe x In4- x Se3 ( x = 0.05) sample at 723 K.

Li, Gen; Yang, Junyou; Xiao, Ye; Fu, Liangwei; Peng, Jiangying; Deng, Yuan; Zhu, Pinwen; Yan, Haixue

2013-04-01

198

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

SciTech Connect

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

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

2011-01-01

199

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

PubMed

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

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

2013-07-01

200

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

201

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

202

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

203

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

Microsoft Academic Search

Optical emission from type-II ZnTe\\/ZnSe quantum dots demonstrates large and\\u000apersistent oscillations in both the peak energy and intensity indicating the\\u000aformation of coherently rotating states. Furthermore, the Aharanov-Bohm (AB)\\u000aeffect is shown to be remarkably robust and persists until 180K. This is at\\u000aleast one order of magnitude greater than the typical temperatures in\\u000alithographically defined rings. To our

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

2008-01-01

204

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

205

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

206

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

207

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

208

Microwave assisted aqueous synthesis of core-shell CdSe(x)Te(1-x)-CdS quantum dots for high performance sensitized solar cells.  

PubMed

A facile microwave assisted aqueous method has been developed to rapidly prepare stable CdSe(x)Te(1-x)-CdS quantum dots. Based on this material, core-shell type II CdSe(x)Te(1-x)-CdS quantum dot sensitized solar cells have been assembled and a power conversion efficiency as high as 5.04% has been obtained. PMID:24554167

Luo, Jianheng; Wei, Huiyun; Li, Fan; Huang, Qingli; Li, Dongmei; Luo, Yanhong; Meng, Qingbo

2014-04-01

209

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

210

Structural investigations on an amorphous Se90Te10 alloy produced by mechanical alloying using EXAFS, cumulant expansion and RMC simulations.  

PubMed

We investigated an amorphous Se(90)Te(10) alloy produced by mechanical alloying using two different approaches. First, we used extended x-ray absorption fine structure (EXAFS) spectroscopy and the cumulant expansion method using the Einstein model for the temperature dependence of the cumulants to obtain the cumulants C(*)(1), C(*)(2), and C(*)(3). From these, we found information about the structure of the alloy as well as the thermal and structural disorder, anharmonicity of the effective interatomic pair potentials, thermal expansion of the Se-Se and Se-Te bonds and asymmetry of the partial distribution functions g(Se-Se)(r) and g(Se-Te)(r). The cumulants C(*)(1), C(*)(2), and C(*)(3) also allowed us to reconstruct the g(EXAFS)(ij)(r,T) functions from EXAFS. Then, we made reverse Monte Carlo (RMC) simulations using the total structure factor S(K) obtained from synchrotron x-ray diffraction and the EXAFS oscillations ?(k) on the Se K edge as input data to obtain the g(RMC)(ij)(r) functions. Both methods furnished very similar g(ij)(r) functions, and the structural data obtained from them were also very similar. The results obtained from both methods showed the presence of Se-Te pairs indicating that there is alloying at the atomic level. In addition, we could not find any evidence of the presence of Te clusters in the alloy. PMID:22371432

Kostrzepa, I M; Siqueira, M C; Machado, K D; Maciel, G A; Sanchez, D F; Brunatto, S F

2012-03-28

211

Modulation of the Aharonov Bohm effect in type-II II V ZnSe:Te quantum dots by a far-infrared laser  

NASA Astrophysics Data System (ADS)

We present magneto-photoluminescence of a ZnTe/ZnSe multilayer structure in which the clustering of Te atoms results in the formation of columns of type-II ZnSe:Te quantum dots. This unique geometry permits the observation of strong Aharonov-Bohm oscillations in both the emission energy and peak intensity with increasing magnetic field. Furthermore, far-infrared optically detected resonance techniques exhibit resonances that are ascribed to the activation and recapture of electrons by different subsets of quantum dots.

Sellers, Ian R.; Whiteside, Vincent R.; Kuskovsky, Igor L.; Govorov, Alexander O.; McCombe, Bruce D.

2008-04-01

212

NaCu6Se4: A Layered Compound with Mixed Valency and Metallic Properties.  

PubMed

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

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

2014-11-17

213

Evidence of surface transport and weak antilocalization in a single crystal of the Bi2Te2Se topological insulator  

NASA Astrophysics Data System (ADS)

Topological insulators are known for their metallic surface states, a result of strong spin-orbit coupling, that exhibit unique surface transport phenomenon. However, these surface transport phenomena are buried in the presence of metallic bulk conduction. We synthesized very high quality Bi2Te2Se single crystals by using a modified Bridgman method that possess high bulk resistivity of >20 ? cm below 20 K, whereas the bulk is mostly inactive and surface transport dominates. The temperature dependence of resistivity follows an activation law like a gap semiconductor in temperature range 20-300 K. To extract the surface transport from that of the bulk, we designed a special measurement geometry to measure the resistance and found that single-crystal Bi2Te2Se exhibits a crossover from bulk to surface conduction at 20 K. Simultaneously, the material also shows strong evidence of weak antilocalization in magnetotransport owing to the protection against scattering by conducting surface states. This simple geometry facilitates finding evidence of surface transport in topological insulators, which are promising materials for future spintronic applications.

Shekhar, Chandra; Viol Barbosa, C. E.; Yan, Binghai; Ouardi, Siham; Schnelle, W.; Fecher, Gerhard H.; Felser, Claudia

2014-10-01

214

Structural and optical investigations of Fe1.03Se0.5Te0.5 under high pressure.  

PubMed

Optimally doped iron-chalcogenide superconductor Fe1.03Se0.5Te0.5 has been investigated under high pressures using synchrotron-based x-ray diffraction and mid-infrared reflectance measurements at room temperature. The superconducting transition temperature (Tc) of the same sample has been determined by temperature-dependent resistance measurements up to 10 GPa. The tetragonal phase (P4/nmm) is found to exist in phase-separated states where both the phases have remarkably high compressibility. A first-order structural transition to the orthorhombic phase (Pbnm) is reported above 10 GPa. For the tetragonal phase, a strong correlation is observed between the Fe(Se,Te)4 tetrahedral deformation and the sharp rise of Tc up to ? 4 GPa, above which Tc shows marginal pressure dependence at least up to 10 GPa. The evolution with pressure of the optical conductivity shows that with increasing pressure the tetragonal phase approaches towards a conventional metallic state. Above ? 6 GPa, the Drude term reduces drastically, indicating poor metallic character of the high-pressure orthorhombic phase. PMID:24594794

Malavi, Pallavi S; Karmakar, S; Patel, N N; Bhatt, H; Sharma, Surinder M

2014-03-26

215

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

216

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

217

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

218

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

SciTech Connect

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

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

2011-07-01

219

Calorimetric study of thermal crystallization kinetics in Se78-xTe20Sn2Pbx (0 ? x ? 6) alloys  

NASA Astrophysics Data System (ADS)

Glassy samples of Se78-xTe20Sn2Pbx (0 ? x ? 6) system are prepared by melt quenching method. For non-isothermal study of crystallization kinetics, DSC scans have been taken at the heating rates 5, 10, 15 and 20 K/min in non-isothermal mode. Activation energy of crystallization (Ec) has been calculated using Kissinger method, Matusita-Sakka method and Augis-Bennett method. Various kinetic parameters of crystallization kinetics like peak crystallization temperature (Tc), Rate constants (K) and order parameter (n) are determined using these DSC scans. Thermodynamic parameters such as crystallization enthalpy (?Hc) and entropy change during the crystallization (?S) are also evaluated. Results are discussed using chemical bond approach.

Kumar, H.; Mehta, N.

2013-05-01

220

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

221

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

SciTech Connect

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

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

2012-08-10

222

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

223

Iron-chalcogenide FeSe0.5Te0.5 coated superconducting tapes for high field applications  

NASA Astrophysics Data System (ADS)

The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe0.5Te0.5 layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1 × 104 A/cm2) at about 4.2 K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.

Si, Weidong; Zhou, Juan; Jie, Qing; Dimitrov, Ivo; Solovyov, V.; Johnson, P. D.; Jaroszynski, J.; Matias, V.; Sheehan, C.; Li, Qiang

2011-06-01

224

Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates  

NASA Astrophysics Data System (ADS)

We report on the isotropic pinning obtained in epitaxial Fe(Se,Te) thin films grown on CaF2(001) substrate. High critical current density values - larger than 1 MA/cm2 in self field and liquid helium - are reached together with a very weak dependence on the magnetic field and a complete isotropy. Analysis through transmission electron microscopy evidences the presence of defects looking like lattice disorder at a very small scale, between 5 and 20 nm, which are thought to be responsible for such isotropic behavior in contrast to what was observed on SrTiO3, where defects parallel to the c-axis enhance pinning in that direction.

Braccini, V.; Kawale, S.; Reich, E.; Bellingeri, E.; Pellegrino, L.; Sala, A.; Putti, M.; Higashikawa, K.; Kiss, T.; Holzapfel, B.; Ferdeghini, C.

2013-10-01

225

First principles study on the elastic and electronic properties of CdX (X = S, Se and Te)  

NASA Astrophysics Data System (ADS)

Wide band gap semiconductors are emerging as a potential candidate for optically active materials in blue green spectral region and operating at high power level and high temperature. CdX, X = S, Se and Te are wide band gap semiconductors having applications in optoelectronics devices. In this paper we investigated the elastic and electronic properties of Cadmium chalcogenide (cubic zinc-blende (ZB) structure) using standard Kohn-Sham self consistent density functional theory method (DFT) that uses non conserving pseudopotentials in fully nonlocal form within the generalized gradient approximation (GGA) for the exchange-correlation potential. The independent elastic constants, C11, C12 and C44, are calculated from direct computation of stresses generated by small strains. The shear modulus and Young's modulus are estimated for CdX. Using the GGA for the exchange correlation potential, the calculated direct fundamental band gap value is in very good agreement with the measured one.

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

2011-12-01

226

Synthesizing new [(SnSe)1.15]m(TSe2)n, [(SnSe)1.16]m(VSe2)n[(SnSe)1.16]p(TaSe2)q, and (SnSe)1.16(V.51Ta.49Se2) intergrowth compounds (T = V and Ta)  

NASA Astrophysics Data System (ADS)

A modification of the modulated elemental reactants synthetic technique was developed and used to synthesize several new layered compounds. Several TSe2, [(SnSe)1+y] m(TSe2)n, [(SnSe) 1+y] m(TSe2) n[(SnSe)1+y]p(T'Se 2)q, and (SnSe)1+y(V 1-xTaxSe2) layered compounds were synthesized by the new modulated elemental reactant (MER) technique with T = V, Ta, and Ti. The MER approach is a low-temperature synthesis that allows the kinetic trapping of metastable compounds, allowing a designed synthesis with control over the value of m, n, p, and q. These layered compounds were structurally characterized by X-ray diffraction and transmission electron microscopy studies. Each integer increase of m, n, p, and q resulted in a linear increase in thickness, representing the single structural units of SnSe (a Sn/Se atomic bilayer) and TSe2 (an X-T-X trilayer sandwich). All of the compounds contained preferentially oriented layering, with the layer's (00l ) plane parallel to the substrate surface. From Bragg-Brentano and in-plane X-ray diffraction studies, the layers are found to be regularly spaced along c with abrupt interfaces and contain crystallinity in their ab-plane. Many of these layered compounds were found to exhibit turbostratic disorder, a random rotational disorder that is usually present in materials made by the MER technique. The presence of turbostratic disorder was found to be dependent on the polytypes that exist in the bulk form of the TSe2 constituent. The electrical properties of the layered compounds were studied by means of temperature-dependent resistivity and Hall measurements. Interesting electrical properties were found as a result of the turbostratic disorder, including a charge density wave transition found in the [(SnSe)1.15]m(VSe2) ferecrystal. The onset temperature of the CDW transition was found to be a sensitive function of the layering sequence, increasing with higher m values. The CDW transition was attributed to the VSe2 constituent and was found in all the composite crystals that contained VSe2. It was found that the [(SnSe)1+y]m(VSe 2)n and [(SnSe)1+y] m(TaSe2)n intergrowths could be combined into an ABCB layered [(SnSe)1+y] m(VSe2)n[(SnSe) 1+y]p(TaSe2) q intergrowth, with chemical separation of the VSe2 and TaSe2 constituents. This dissertation includes previously published and unpublished co-authored material.

Atkins, Ryan Elliot

227

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

228

Investigation of Zn m Cd n X y (y = m + n; X = Te, Se and S) Clusters with TDDFT Method  

Microsoft Academic Search

Based on zinc blende and wurtzite structures of experimental ZnTe and CdTe nanocrystals, ZnmCdnXy (X = Te, Se and S) clusters were investigated using DFT\\/B3LYP\\/LANL2DZ. From analyses of their characters of conformations,\\u000a HOMO–LUMO gaps, Raman and absorption spectra, Mulliken charges and WBI (Wiberg Bond Index) values, we have discovered that\\u000a ZnmCdnTey, ZnmCdnSey and ZnmCdnSy molecules had similar characters. In this paper, characters

Chunlei Wang; Shuhong Xu; Lihua Ye; Wei Lei; Yiping Cui

2011-01-01

229

Reversible amorphous-crystalline phase changes in a wide range of Se(1-x)Te(x) alloys studied using ultrafast differential scanning calorimetry.  

PubMed

The reversible amorphous-crystalline phase change in a chalcogenide material, specifically the Se1-xTex alloy, has been investigated for the first time using ultrafast differential scanning calorimetry. Heating rates and cooling rates up to 5000 K/s were used. Repeated reversible amorphous-crystalline phase switching was achieved by consecutively melting, melt-quenching, and recrystallizing upon heating. Using a well-conditioned method, the composition of a single sample was allowed to shift slowly from 15 at. %Te to 60 at. %Te, eliminating sample-to-sample variability from the measurements. Using Energy Dispersive X-ray Spectroscopy composition analysis, the onset of melting for different Te-concentrations was confirmed to coincide with the literature solidus line, validating the use of the onset of melting Tm as a composition indicator. The glass transition Tg and crystallization temperature Tc could be determined accurately, allowing the construction of extended phase diagrams. It was found that Tm and Tg increase (but Tg/Tm decrease slightly) with increasing Te-concentration. Contrarily, the Tc decreases substantially, indicating that the amorphous phase becomes progressively unfavorable. This coincides well with the observation that the critical quench rate to prevent crystallization increases about three orders of magnitude with increasing Te concentration. Due to the employment of a large range of heating rates, non-Arrhenius behavior was detected, indicating that the undercooled liquid SeTe is a fragile liquid. The activation energy of crystallization was found to increase 0.5-0.6 eV when the Te concentration increases from 15 to 30 at. % Te, but it ceases to increase when approaching 50 at. % Te. PMID:25028022

Vermeulen, Paul A; Momand, Jamo; Kooi, Bart J

2014-07-14

230

Constrained Optimization Applied to Graded Compound Semiconductor Structures: Graded Contacts to p-type ZnSe  

NASA Astrophysics Data System (ADS)

A variational technique is described which applies the methods of constrained optimization to the achievement of specified energy band profiles in graded semiconductor structures. This design tool, more fully developed, will eliminate the uncertainty and grueling process of trial and error, especially as more complicated structures are entertained and material dependencies on composition become known. As an example, the technique is applied to the optimization of the graded contacting to p-type ZnSe via the structure ZnSe-ZnSe(1-x)BeTe(x)-BeTe. In this case, once a maximum grading length has been specified, a best possible grade x(z) is sought by attempting to minimize the "length" of the valence band between bulk regions, subject to the constraint imposed by electrostatics, namely the Poisson equation.

Richards, Douglas L.; Boone, Jack L.; Parks, William F.

1996-03-01

231

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

PubMed

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

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

2013-06-25

232

Thermoelectric Properties of Ag-Doped n-Type (Bi2- x Ag x Te3)0.96-(Bi2Se3)0.04 Pseudobinary Alloys  

NASA Astrophysics Data System (ADS)

n-Type thermoelectric powders of (Bi2- x Ag x Te3)0.96-(Bi2Se3)0.04 (0 ? x ? 0.05) have been synthesized by mechanical alloying and then consolidated by spark plasma sintering. The analysis results show that the grain size of pure Bi, Te, Ag, and Se powders is decreased to about 1 ?m to 0.5 ?m after they are mechanically alloyed for 2 h. The power factor of bulk material increases with increasing Ag-doping content, while the trend for the lattice thermal conductivity is the opposite. Bulk (Bi0.99Ag0.04)2(Te0.96Se0.04)3 after milling for 12 h exhibits a higher power factor, lower thermal conductivity, and thus a higher ZT of 0.74 at 373 K.

Zhang, Xin; Ma, Xu-Yi; Lu, Qing-Mei; Zhang, Fei-Peng; Liu, Yan-Qin; Zhang, Jiu-Xing; Wang, Lei

2011-05-01

233

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

234

Two isostructural layered oxohalide compounds containing Mn2+, Te4+ and Si4+; crystal structure and magnetic susceptibility  

NASA Astrophysics Data System (ADS)

The new compounds Mn4(TeO3)(SiO4)X2 (X=Br, Cl) were synthesized by solid state reactions in sealed evacuated silica tubes. The compounds crystallize in the monoclinic space group P21/m with the unit cell parameters a=5.5463(3) Å (5.49434(7) Å), b=6.4893(4) Å (6.44184(9) Å), c=12.8709(7) Å (12.60451(18) Å), ?=93.559(5)° (94.1590(12)°) and Z=2 for the respective Br and Cl analogues. Manganese adopts various distorted coordination polyhedra; [MnO6] octahedra, [MnO5] tetragonal pyramids and [MnO2X2] tetrahedra. Other building blocks are [SiO4] tetrahedra and [TeO3] trigonal pyramids. The structure is made up from layers having no net charge that are connected via weak Van der Waal interactions. The layers that are parallel to (1 1 0) consist of two manganese oxide sheets which are separated by [SiO4] tetrahedra. On the outer sides of the sheets are the [MnO2X2] tetrahedra and the [TeO3] trigonal pyramids connected so that the halide ions and the stereochemically active lone pairs on the tellurium atoms protrude from the layers. Magnetic susceptibility measurements reveal a Curie law with a Weiss temperature of ?=-153(3) K for temperatures ?100 K and indicate antiferromagnetic ordering at TN ~4 K. Possible structural origins of the large frustration parameter of f=38 are discussed. The new compounds Mn4(TeO3)(SiO4)X2 (X=Br, Cl) are layered with weak Van der Waal interactions in between the layers. Manganese adopts various distorted coordination polyhedral, other building blocks are [SiO4] tetrahedra and [TeO3] trigonal pyramids. Magnetic susceptibility measurements indicate antiferromagnetic ordering at low temperatures and a large frustration parameter.

Zimmermann, Iwan; Kremer, Reinhard K.; Johnsson, Mats

2014-10-01

235

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

PubMed

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

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

2014-10-01

236

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

237

?SR studies of the low?temperature magnetism in a valence?fluctuation compound Sm 3 Se 4  

Microsoft Academic Search

?+SR measurements have been performed on a semiconducting valence?fluctuation compound Sm3Se4 and its reference system Sm2Se3. The ?+SR data indicate the development of spin?glass?like magnetic order in Sm3Se4 at low temperatures, while no evidence for the onset of static or quasi?static magnetism has been detected in Sm2Se3 down to \\\\cong0.1 K. The results are discussed in connection with the previous

S. Takagi; T. Suzuki; A. Amato; F. N. Gygax; A. Schenck; A. Ochiai

1997-01-01

238

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

239

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

240

CuSe-based layered compound Bi2YO4Cu2Se2 as a quasi-two-dimensional metal  

NASA Astrophysics Data System (ADS)

We have investigated the physical properties of a new layered oxyselenide Bi2YO4Cu2Se2, which crystallizes in an unusual intergrowth structure with Cu2Se2 and Bi2YO4 layers. Electric transport measurement indicates that Bi2YO4Cu2Se2 behaves metallic. Thermal transport and Hall measurements show that the type of the carriers is holelike and it may be a potential thermoelectric material at high temperatures. First-principles calculations are in agreement with experimental results and show that Bi2YO4Cu2Se2 is a quasi-two-dimensional metal. Further theoretical investigation suggests the ground states of the Bi2YO4Cu2Se2 type can be tuned by designing the blocking layers, which will enrich the physical properties of these compounds.

Tan, S. G.; Shao, D. F.; Lu, W. J.; Yuan, B.; Liu, Y.; Yang, J.; Song, W. H.; Lei, Hechang; Sun, Y. P.

2014-08-01

241

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

E-print Network

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

Myung, Noh-Hoon

242

Synthesis of terminal monochalcogenide and dichalcogenide complexes of uranium using polychalcogenides, [en](2-) (e = te, N = 2; e = se, N = 4), as chalcogen atom transfer reagents.  

PubMed

Reaction of KH with elemental tellurium, in the presence of 18-crown-6, results in the formation of the ditelluride, [K(18-crown-6)]2[Te2] (1), in good yield. Similarly, reaction of KH with elemental selenium, in the presence of 18-crown-6, results in the formation of [K(18-crown-6)]2[Se4] (4). Both 1 and 4 are capable of chalcogen atom transfer to U(III). For example, addition of 0.5 equiv or 1 equiv of [K(18-crown-6)]2[Te2] (1) to [U(NR2)3] (R = SiMe3) or [U(I)(NR2)3], respectively, results in the formation of the new U(IV) tellurides, [K(18-crown-6)][U(Te)(NR2)3] (2), and [K(18-crown-6)][U(?(2)-Te2)(NR2)3] (3), in moderate yields, while addition of 0.5 equiv of [K(18-crown-6)]2[Se4] (4) to [U(NR2)3] results in the formation of the U(IV) diselenide, [K(18-crown-6)][U(?(2)-Se2)(NR2)3] (5). Interestingly, 5 can be converted into the monoselenide [K(18-crown-6)][U(Se)(NR2)3] (6) via reaction with Ph3P. PMID:25203671

Smiles, Danil E; Wu, Guang; Hayton, Trevor W

2014-10-01

243

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

E-print Network

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

Talwar, Devki N.

244

Spin dynamics and magnetoelectric properties of the coupled-spin tetrahedral compound Cu2Te2O5Cl2  

NASA Astrophysics Data System (ADS)

We report on the spin dynamics and discovery of magnetoelectricity in the coupled-spin tetrahedral compound Cu2Te2O5Cl2. Te125 NMR measurements show an anomalous resonance frequency shift and a signal wipe-out phenomenon around the Néel temperature TN = 18.2 K, which could be attributed to the anomalous critical slowing down of the Cu spin fluctuations on the NMR time scale (˜10-100 MHz). The critical exponent of (T1T)-1?(T-TN)-? is 0.40 ± 0.03, as compared to 0.5 for a three-dimensional mean-field model. This is in contrast to the Br compound [S.-H. Baek et al., Phys. Rev. B 86, 180405 (2012), 10.1103/PhysRevB.86.180405], which exhibits pronounced singlet dynamics with a large spin gap. Electric polarization (Pc) is observed along the c axis for temperatures below TN under finite magnetic field but not sensitive to the electric poling. Pc increases sharply over zero to 2 T and then reaches saturation. Below TN, Pc changes its sign depending on the applied magnetic field direction, positive for the H?c axis and negative for H ? c axis. We discuss possible explanations for the observed magnetoelectric (ME) behavior in terms of linear ME effect, spin-driven multiferroicity, and an exchange striction of intertetrahedral exchange paths involving the Te4+ lone-pair ions. Our results suggest that Cu2Te2O5Cl2 is a type of ME material whose properties are tuned by intertetrahedral exchange interactions involving polarizable Te4+ ions.

Besara, T.; Choi, E. S.; Choi, K.-Y.; Kuhns, P. L.; Reyes, A. P.; Lemmens, P.; Berger, H.; Dalal, N. S.

2014-08-01

245

Thermoelectric properties of n-type Bi 2Te 2.7Se 0.3 and p-type Bi 0.5Sb 1.5Te 3 thin films deposited by direct current magnetron sputtering  

Microsoft Academic Search

n-type and p-type thermoelectric thin films have been deposited by direct current magnetron sputtering from n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3 targets on glass and Al2O3 substrates. X-ray diffraction and energy dispersive spectrometry combined with electrical measurements such as Seebeck coefficient and electrical resistivity were used for the thermoelectric thin films characterization. It was found that the composition of the sputtered

D. Bourgault; C. Giroud Garampon; N. Caillault; L. Carbone; J. A. Aymami

2008-01-01

246

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

247

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 25GPa. 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

248

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

NASA Astrophysics Data System (ADS)

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

Bagheri, Mehran

2010-07-01

249

Interfacial processes induced by dissolved oxidising species at p-ZnTe and n-ZnSe electrodes  

Microsoft Academic Search

The reduction processes of oxygen at p-ZnTe electrodes lead the authors to suppose that decomposition of the semiconductor takes place by means of chemical species produced during the electrochemical reduction of oxygen. At pH 0, hydrogen peroxide in its form H2O2 reacts chemically with ZnTe, whereas at pH 14, the chemical reaction is induced by OH radicals. On the other

B. L. Wu; J. Gautron; A. Forveille-Boutry; P. Lemasson

1983-01-01

250

Crystal structure, electronic and physical properties of monoclinic RECuTe2 in contrast to RECuSe2 (RE = Pr, Sm, Gd, Dy and Er)  

NASA Astrophysics Data System (ADS)

The ternary tellurides RECuTe2 (RE = Gd, Dy and Er) have been synthesized, their crystal structure and charge transport properties have been investigated. The tellurides adopt a monoclinicly distorted variant (C2/m, z = 2) of the trigonal structure (P3barm1, Z = 1) observed for RECuSe2 with RE = Dy, Er. The charge transport properties of RECuSe2 with RE = Pr and Sm have been also explored. While RECuTe2 display a metallic type resistivity, RECuSe2 show semiconducting properties. The room-temperature resistivities are between 0.22 and 10.5 ? cm, with larger values observed for the selenides. Electronic structure calculations support metallic and semiconducting conductivities for the tellurides and selenides, respectively. The Seebeck coefficient indicates that the dominant charge carries are holes for all phases.

Esmaeili, Mehdi; Forbes, Scott; Tseng, Yu-Chih; Mozharivskyj, Yurij

2014-10-01

251

Fabrication of transparent p-type conductive BaCuSeF films by pulsed laser deposition and their application to CdS/CdTe solar cells  

NASA Astrophysics Data System (ADS)

Transparent p-type conductive BaCuSeF films prepared by pulsed laser deposition (PLD) were studied for application to tandem configuration solar cells. The BaCuSeF films were deposited at low substrate temperatures (TS) of 150, 200, 250, and 300 °C. The films prepared at TS ? 200 °C showed considerably high transmittance in the visible light region. The highest transmittance of 63% was obtained for the film deposited at TS = 300 °C. All of the films showed p-type conductivities of more than 1 S/cm. These BaCuSeF films were deposited on the CdTe surface of CdS/CdTe solar cells. A high conversion efficiency of 2.82% was obtained for the solar cell with the transparent p-type conductive BaCuSeF film deposited at TS = 200 °C. The higher efficiency of 3.12% was obtained by inserting a thin Ni0.97Li0.03O buffer layer between the BaCuSeF and CdTe layers.

Yamamoto, Koichi; Okamoto, Hirokazu; Sakakima, Hiroshi; Hayashi, Ryoji; Ogawa, Yohei; Okamoto, Tamotsu; Wada, Takahiro

2014-01-01

252

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

SciTech Connect

This report describes work to develop an accurate numerical model for CuInSe{sub 2} (CIS) and CdTe-based solar cells capable of running on a personal computer. Such a model will aid researchers in designing and analyzing CIS- and CdTe-based solar cells. ADEPT (A Device Emulation Pregrain and Tool) was used as the basis for this model. An additional objective of this research was to use the models developed to analyze the performance of existing and proposed CIS- and CdTe-based solar cells. The development of accurate numerical models for CIS- and CdTe-based solar cells required the compilation of cell performance data (for use in model verification) and the compilation of measurements of material parameters. The development of the numerical models involved implementing the various physical models appropriate to CIS and CdTe, as well as some common window. A version of the model capable of running on an IBM-comparable personal computer was developed (primary code development is on a SUN workstation). A user-friendly interface with pop-up menus is continuing to be developed for release with the IBM-compatible model.

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

1992-09-01

253

Minority-carrier lifetime of compound semiconductors: Polycrystalline CdTe  

NASA Astrophysics Data System (ADS)

The minority-carrier lifetime of polycrystalline CdTe has been measured for a variety of samples produced by two different growth techniques. The CdS/CdTe solar cell structures were either grown by a proprietary spray technique at Photon Energy, Inc. or by close-spaced sublimation at the University of South Florida. The photoluminescence decay lifetime is investigated as a function of grain size, excess carrier density, and temperature. Results are consistent with carrier recombination at grain boundaries, indicate some defects act as traps, and show relatively high efficiency solar cells can be made from material exhibiting sub-nanosecond lifetimes.

Keyes, B. M.; Emery, K. A.; Ahrenkiel, R. K.

1992-12-01

254

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

SciTech Connect

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

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

2010-02-15

255

Superconducting FeSe0.5Te0.5 thin films: a morphological and structural investigation with scanning tunnelling microscopy and x-ray diffraction  

NASA Astrophysics Data System (ADS)

We used scanning tunnelling microscopy to study the morphology of superconducting FeSe0.5Te0.5 thin films epitaxially grown by pulsed laser deposition. Samples with critical temperature Tc above the bulk value (>16 K) show large atomic terraces, and a square lattice of periodicity 3.8 Å associated with the Se/Te surface termination. Differences in the height coordinate of the chalcogenide atoms are clearly visible at the atomic level. On the contrary, samples with lower Tc (11 K) show hillocks generated by a spiral surface growth driven by threading dislocations of screw character. A comparative x-ray diffraction analysis reveals differences of compressive strain for the two classes of specimens. Variations in the deposition rate are found to affect film growth and inner strain, which ultimately tune Tc.

Gerbi, A.; Buzio, R.; Bellingeri, E.; Kawale, S.; Marrè, D.; Siri, A. S.; Palenzona, A.; Ferdeghini, C.

2012-01-01

256

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

257

Raman and interband optical spectra of epitaxial layers of the topological insulators Bi2Te3 and Bi2Se3 on BaF2 substrates  

NASA Astrophysics Data System (ADS)

We report results of Raman and ellipsometric spectroscopy of the topological insulators Bi2Te3 and Bi2Se3 grown by molecular beam epitaxy on BaF2 (111) substrates. Surfaces and interfaces of the films are probed by Raman scattering from the front and back sides of the samples, which is possible owing to the transparent substrate. Surface modifications induced by intense illumination with exciting laser light have been detected, with excess tellurium at the surface during and after exposure. We also report data for thin epilayers containing a fractional number of unit cells and/or incomplete Bi2Te3 and Bi2Se3 quintuples. We have used spectroellipsometric measurements to obtain response functions and have derived the penetration depth of light in the 1.0–6.5 eV range.

Humlí?ek, J.; Hemzal, D.; Dubroka, A.; Caha, O.; Steiner, H.; Bauer, G.; Springholz, G.

2014-09-01

258

Synthesis and Investigation of the Linear and Nonlinear Optical Properties of Alloyed CdSe0.3Te0.7Nanocrystals  

NASA Astrophysics Data System (ADS)

Alloyed CdSe0.3Te0.7nanocrystals (NCs) were prepared by a thermochemical method using Thioglycolic acid (TGA) as a capping agent molecule. X-ray diffraction (XRD) and Transmission electron microscopy (TEM) analysis demonstrated hexagonal phase NCs with an average size of around 2.5 nm. Synthesized NCs indicated a narrow band emission with a peak located at 561 nm. Nonlinear optical (NLO) properties of the CdSe0.3Te0.7NCs have been investigated by z-scan technique using Continuum Wave He-Ne laser. The nonlinear absorption coefficient and nonlinear refraction index were obtained in the order of 10-2 and 10-8, respectively. The results revealed that these NCs exhibit strong NLO properties effects such as self-defocusing and two photons absorption.

Bahari, H. S.; Dehghani, Z.; Saievar-Iranizad, E.; Molaei, M.; Ara, M. H. Majles

2014-04-01

259

Development of a computer model for polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells; Annual subcontract report, 1 March 1992--28 February 1993  

SciTech Connect

Solar cells operate by converting the radiation power from sun light into electrical power through photon absorption by semiconductor materials. The elemental and compound material systems widely used in photovoltaic applications can be produced in a variety of crystalline and non-crystalline forms. Although the crystalline group of materials have exhibited high conversion efficiencies, their production cost are substantially high. Several candidates in the poly- and micro-crystalline family of materials have recently gained much attention due to their potential for low cost manufacturability, stability, reliability and good performance. Among those materials, CuInSe{sub 2} and CdTe are considered to be the best choices for production of thin film solar cells because of the good optical properties and almost ideal band gap energies. Considerable progress was made with respect to cell performance and low cost manufacturing processes. Recently conversion efficiencies of 14.1 and 14.6% have been reported for CuInSe{sub 2} and CdTe based solar cells respectively. Even though the efficiencies of these cells continue to improve, they are not fully understood materials and there lies an uncertainty in their electrical properties and possible attainable performances. The best way to understand the details of current transport mechanisms and recombinations is to model the solar cells numerically. By numerical modeling, the processes which limit the cell performance can be sought and therefore, the most desirable designs for solar cells utilizing these materials as absorbers can be predicted. The problems with numerically modeling CuInSe{sub 2} and CdTe solar cells are that reported values of the pertinent material parameters vary over a wide range, and some quantities such as carrier concentration are not explicitly controlled.

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

1994-03-01

260

Magnesium-induced copper-catalyzed synthesis of unsymmetrical diaryl chalcogenide compounds from aryl iodide via cleavage of the Se-Se or S-S bond.  

PubMed

The methodology for a copper-catalyzed preparation of diaryl chalcogenide compounds from aryl iodides and diphenyl dichalcogenide molecules is reported. Unsymmetrical diaryl sulfide or diaryl selenide can be synthesized from aryl iodide and PhYYPh (Y = S, Se) with a copper catalyst (CuI or Cu(2)O) and magnesium metal in one pot. This reaction can be carried out under neutral conditions according to an addition of magnesium metal as the reductive reagent. Furthermore, it is efficiently available for two monophenylchalcogenide groups generated from diphenyl dichalcogenide. PMID:14750822

Taniguchi, Nobukazu; Onami, Tetsuo

2004-02-01

261

Highly efficient near-infrared light-emitting diodes by using type-II CdTe/CdSe core/shell quantum dots as a phosphor  

NASA Astrophysics Data System (ADS)

In this paper, we present an innovative method for the synthesis of CdTe/CdSe type-II core/shell structure quantum dots (QDs) using ‘greener’ chemicals. The PL of CdTe/CdSe type-II core/shell structure QDs ranges from 600 to 820 nm, and the as-synthesized core/shell structures show narrow size distributions and stable and high quantum yields (50-75%). Highly efficient near-infrared light-emitting diodes (LEDs) have been demonstrated by employing the CdTe/CdSe type-II core/shell QDs as emitters. The devices fabricated based on these type-II core/shell QDs show color-saturated near-infrared emission from the QD layers, a low turn-on voltage of 1.55 V, an external quantum efficiency (EQE) of 1.59%, and a current density and maximum radiant emittance of 2.1 × 103 mA cm-2 and 17.7 mW cm-2 at 8 V it is the first report to use type-II core/shell QDs as near-infrared emitters and these results may offer a practicable platform for the realization of near-infrared QD-based light-emitting diodes, night-vision-readable displays, and friend/foe identification system.

Shen, Huaibin; Zheng, Ying; Wang, Hongzhe; Xu, Weiwei; Qian, Lei; Yang, Yixing; Titov, Alexandre; Hyvonen, Jake; Li, Lin Song

2013-11-01

262

Highly efficient near-infrared light-emitting diodes by using type-II CdTe/CdSe core/shell quantum dots as a phosphor.  

PubMed

In this paper, we present an innovative method for the synthesis of CdTe/CdSe type-II core/shell structure quantum dots (QDs) using 'greener' chemicals. The PL of CdTe/CdSe type-II core/shell structure QDs ranges from 600 to 820 nm, and the as-synthesized core/shell structures show narrow size distributions and stable and high quantum yields (50–75%). Highly efficient near-infrared light-emitting diodes (LEDs) have been demonstrated by employing the CdTe/CdSe type-II core/shell QDs as emitters. The devices fabricated based on these type-II core/shell QDs show color-saturated near-infrared emission from the QD layers, a low turn-on voltage of 1.55 V, an external quantum efficiency (EQE) of 1.59%, and a current density and maximum radiant emittance of 2.1 × 10(3) mA cm?2 and 17.7 mW cm?2 at 8 V; it is the first report to use type-II core/shell QDs as near-infrared emitters and these results may offer a practicable platform for the realization of near-infrared QD-based light-emitting diodes, night-vision-readable displays, and friend/foe identification system. PMID:24192490

Shen, Huaibin; Zheng, Ying; Wang, Hongzhe; Xu, Weiwei; Qian, Lei; Yang, Yixing; Titov, Alexandre; Hyvonen, Jake; Li, Lin Song

2013-11-29

263

FeSe0.5Te0.5 thin films with critical current density above 1MA/cm^2  

NASA Astrophysics Data System (ADS)

High quality FeSe0.5Te0.5 thin films have been prepared on various substrates, such as SrTiO3, LaAlO3 and YSZ, some with buffer layers. Tc's as high as 20K with superconducting transition widths of about 1K were obtained. These Tc's are much higher than those of bulk FeSe0.5Te0.5 (˜15K). Our films carry high critical current densities Jc's (above 1MA/cm^2) at liquid helium temperature. These films hold Jc's above 1x10^5A/cm^2 and very low Jc anisotropies (< 3) under magnetic fields as high as 30T at 4.2K. We have also prepared textured FeSe0.5Te0.5 thin films on a buffered metal template with results similar to the ones mentioned above. This shows that iron chalcogenides have a very promising future for high-field applications at liquid helium temperatures. Pinning force analysis indicates the presence of a point defect flux-pinning mechanism, suggesting a straightforward approach to conductor optimization.

Si, Weidong; Han, Su Jung; Dimitrov, Ivo; Li, Qiang

2012-02-01

264

Studies on the Bi[subscript 2]Te[subscript 3]–Bi[subscript 2]Se[subscript 3]–Bi[subscript 2]S[subscript 3] system for mid-temperature thermoelectric energy conversion  

E-print Network

Bismuth telluride (Bi[subscript 2]Te[subscript 3]) and its alloys have been widely investigated as thermoelectric materials for cooling applications at around room temperature. We report a systematic study on many compounds ...

Liu, Weishu

265

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. With an energy gap of 2.7 eV at room temperature, and an efficient band- to-band transition, ZnSe has been studied extensively as the primary candidate for a blue light emitting diode for optical displays, high density recording, and military communications. By employing a ternary or quaternary system, the energy band gap of II-VI materials can be tuned to a specific range. While issues related to the compositional inhomogeneity and defect incorporation are still to be fully resolved, ZnSe bulk crystals and ZnSe-based heterostructures such as ZnSe/ZnSeS, ZnSe/ZnCdSe and ZnCdSe/ZnSeS have showed photopumped lasing capability in the blue-green region at a low threshold power and high temperatures. 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 H-VI semiconductor materials has not advanced far enough to provide the low price, high quality substrates needed for the thin film growth technology.

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

2000-01-01

266

Coherent Aharonov-Bohm oscillations in type-II (Zn,Mn)Te\\/ZnSe quantum dots  

Microsoft Academic Search

The magneto-photoluminescence of type-II (Zn,Mn)Te quantum dots is presented. As a result of the type-II band alignment, Aharonov-Bohm (AB) oscillations in the photoluminescence intensity are evident. In addition, an interesting interplay between the AB effect and the spin polarization in these diluted magnetic semiconductor quantum dots is observed. The intensity of the AB oscillations increases with both magnetic field and

I. R. Sellers; V. R. Whiteside; A. O. Govorov; W. C. Fan; W.-C. Chou; I. Khan; A. Petrou; B. D. McCombe

2008-01-01

267

High performance n-type (Bi,Sb)2(Te,Se)3 for low temperature thermoelectric generator  

Microsoft Academic Search

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

Shanyu Wang; Wenjie Xie; Han Li; Xinfeng Tang

2010-01-01

268

Orbital Processing of High-Quality Zn-Alloyed CdTe Compound Semiconductors  

NASA Technical Reports Server (NTRS)

The objective of this research is to investigate the influences of gravitationally-dependent phenomena (hydrostatic and buoyant) on the growth and quality of doped and alloyed Cadmium-Zinc-Telluride (CdZnTe) crystals grown by the modified seeded Bridgman-Stockbarger technique. It is hypothesized that the damping of the gravitationally-dependent buoyancy convection will substantially enhance chemical homogeneity and the near-elimination of hydrostatic pressure will enable significant reduction in defect (dislocations and twins) density.

Larson, David J., Jr.; Dudley, M.; Raghothamachar, B.; Alexander, J. I. D.; Carlson, F. M.; Gillies, D.; Volz, M.; Ritter, T. M.; DiMarzio, D.

1999-01-01

269

CdTe detector efficiency calibration using thick targets of pure and stable compounds  

Microsoft Academic Search

Quantitative PIXE measurements require perfectly calibrated set-ups. Cooled CdTe detectors have good efficiency for energies above those covered by Si(Li) detectors and turn on the possibility of studying K X-rays lines instead of L X-rays lines for medium and eventually heavy elements, which is an important advantage in various cases, if only limited resolution systems are available in the low

P. C. Chaves; A. Taborda; M. A. Reis

270

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

NASA Astrophysics Data System (ADS)

Nanostructuring of thermoelectric material can lead to improved performance through suppression of the lattice contribution to thermal conductivity and enhancement of the power factor by quantum confinement or thermionic energy filtering. To take advantage of these effects in a Peltier microcooler or Seebeck generator, it is necessary to prepare nanostructure materials with leg lengths ranging from tens of microns to millimeters. We have developed a process for fabrication of thick, self-supporting (Bi0.11,Sb0.29)(Te0.25,Se0.41) nanowire arrays using a novel branched porous anodic alumina template that can be removed completely by selective etching following electrodeposition of the thermoelectric material, resulting in 100-micron-thick nanostructured thermoelectric material without the parasitic thermal shunt that is associated with the template. The electrodeposition process allows composition modulation and grading, effects that are difficult to achieve by bulk synthesis. Bandgaps of the electrodeposited material range from 0.13 eV for Bi2Te3 to an optical gap of 0.52 eV measured for a (Bi,Sb)2(Te,Se)3 alloy, suggesting an operating tempurature range from below room temperature to ˜300 C.

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

2009-03-01

271

Effect of impurity (Sb and Ag) incorporation on the a.c. conductivity and dielectric properties of a-Se 70Te 30 glassy alloy  

NASA Astrophysics Data System (ADS)

The effect of additives (Sb and Ag) on a.c. conductivity and dielectric properties of Se 70Te 30 glassy alloy at temperature range 300-350 K and frequency range 1 kHz-5 MHz has been studied. Experimental results indicate that a.c. conductivity and dielectric parameters depend on temperature, frequency and the impurity incorporated in Se-Te glassy system. The a.c. conductivity in the aforesaid frequency range is found to obey the ?s law. A strong dependence of a.c. conductivity and exponent s in the entire temperature and frequency range contradicts quantum-mechanical tunneling (QMT) model and can be interpreted in terms of the correlated barrier hopping (CBH) model. The temperature and frequency dependence of the dielectric parameters are also studied and it is found that the results agrees by the theory of hopping of charge carriers over potential barrier as suggested by Elliott in chalcogenide glasses. The change in the dielectric parameters with the opposite influence of the replacement of Te by Sb on the one hand, and by Ag, on the other hand is being correlated by the nature of covalent character of the studied composition and with the change in density of defect states.

Sharma, J.; Kumar, S.

2012-02-01

272

Specific features of the structure, magnetic properties, and heat capacity of intercalated compounds Cr x TiSe2  

NASA Astrophysics Data System (ADS)

Structural features, magnetic properties, and heat capacity of Cr x TiSe2 intercalated compounds with a layered structure have been studied experimentally for 0 ? x ? 0.5. It is shown that, at high chromium concentrations ( x > 0.25), the magnetic properties of the compounds are strongly affected by the degree of ordering and distribution pattern of the intercalated atoms. Depending on the cooling rate of samples of the same composition ( x = 0.5), an antiferromagnetic or a cluster-glass-type state can be obtained. Heat capacity measurements have revealed a nonmonotonic variation in the lattice rigidity with increasing concentration of intercalated atoms.

Pleshchev, V. G.; Selezneva, N. V.; Maksimov, V. I.; Korolev, A. V.; Podlesnyak, A. V.; Baranov, N. V.

2009-05-01

273

Coherent Aharonov-Bohm oscillations in type-II (Zn,Mn)Te\\/ZnSe quantum dots  

Microsoft Academic Search

The magneto-photoluminescence of type-II (ZnMn)Te quantum dots is presented.\\u000aAs a result of the type-II band alignment Aharonov-Bohm (AB) oscillations in\\u000athe photoluminescence intensity are evident, confirming previous predictions\\u000afor the suitability of this geometry to control the optical Aharonov-Bohm\\u000aeffect in semiconductor systems. Moreover, the system demonstrates an\\u000ainteresting interplay between the AB effect and the spin polarization in

I. R. Sellers; V. R. Whiteside; A. O. Govorov; W. C. Fan; I. Khan; A. Petrou; B. D. McCombe

2008-01-01

274

Coherent Aharonov-Bohm oscillations in type-II (Zn,Mn)Te/ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

The magneto-photoluminescence of type-II (Zn,Mn)Te quantum dots is presented. As a result of the type-II band alignment, Aharonov-Bohm (AB) oscillations in the photoluminescence intensity are evident. In addition, an interesting interplay between the AB effect and the spin polarization in these diluted magnetic semiconductor quantum dots is observed. The intensity of the AB oscillations increases with both magnetic field and the degree of optical polarization, indicating that the suppression of spin fluctuations improves the coherence of the system.

Sellers, I. R.; Whiteside, V. R.; Govorov, A. O.; Fan, W. C.; Chou, W.-C.; Khan, I.; Petrou, A.; McCombe, B. D.

2008-06-01

275

Surface and substrate induced effects on thin films of the topological insulators Bi2Se3 and Bi2Te3  

SciTech Connect

Based on van der Waals density functional calculations, we have studied few-quintuple-layer (QL) films of Bi2Se3 and Bi2Te3. The separation between the QLs near the surface is found to have a large increase after relaxation, whereas, the separation between the inner QLs is smaller and approaches the bulk value as the thickness grows, showing a two-dimensional to three-dimensional structural crossover. Accordingly, the surface Dirac cone of the Bi2Se3 film is evidently gapped for small thicknesses (two to four QLs), and the gap is reduced and, finally, is closed with the increasing thickness, agreeing well with the experiments. We further studied the substrate effect by investigating the Bi2Se3/graphene system. It is found that the underlying graphene induces a giant thickness-dependent Rashba splitting and Dirac point shift. Because Bi2Te3 films have smaller relative inter-QL expansion and stronger spin-orbit coupling, the topological features start to appear in the film as thin as two QLs in good accord with the experiments.

Liu, Wenliang [Xiangtan University, Xiangtan Hunan, China; Peng, Xiangyang [Xiangtan University, Xiangtan Hunan, China; Wei, Xiaolin [Xiangtan University, Xiangtan Hunan, China; Yang, Hong [Xiangtan University, Xiangtan Hunan, China; Stocks, George Malcolm [ORNL; Zhong, Jianxin [Xiangtan University, Xiangtan Hunan, China

2013-01-01

276

Probing the core-shell-shell structure of CdSe/CdTe/CdS type II quantum dots for solar cell applications  

NASA Astrophysics Data System (ADS)

A greater understanding of multiple exciton generation in heterostructured colloidal quantum dots can be achieved through detailed modelling, and used to optimise their design for solar cell applications. However, such modelling requires an accurate knowledge of the physical structure of the quantum dots. Here we report the use of high angle annular dark field (HAADF) scanning transmission electron microscope (STEM) imaging to study the size and shape of CdSe/CdTe/CdS type II quantum dots at each of the three stages of their synthesis.

Lewis, E. A.; Page, R. C.; Binks, D. J.; Pennycook, T. J.; O'Brien, P.; Haigh, S. J.

2014-06-01

277

Photoinduced effects in thin films of Te{sub 20}As{sub 30}Se{sub 50} glass with nonlinear characterization  

SciTech Connect

We discuss the influence of photoinduced effects (PIEs) on the measurements of nonlinear refractive indices and nonlinear absorption coefficients. A chalcogenide glass film Te{sub 20}As{sub 30}Se{sub 50} was studied using picosecond laser pulses at 1064 nm. The nonlinear imaging technique with phase object (NIT-PO) and the Z-scan technique were applied and their results are compared. The NIT-PO technique reveals clearly the influence of PIE on the samples' response, while by using the Z-scan technique we measured the deepness of ablated regions (holes) produced during the measurements.

Fedus, K.; Boudebs, G. [Laboratoire des Proprietes Optiques des Materiaux et Applications, FRE CNRS 2988, Universite d'Angers, 2 Boulevard Lavoisier, 49045 Angers (France); Araujo, Cid B. de [Departamento de Fisica, Universidade Federal de Pernambuco, 50670-901 Recife (Brazil); Cathelinaud, M. [Institut FRESNEL, UMR CNRS 6133, Universite Paul Cezanne, Ecole Centrale Marseille, Universite de Provence, 13397 Marseille (France); Missions des Ressources et Competences Technologiques, UPS CNRS 2274, 92135 Meudon (France); Charpentier, F.; Nazabal, V. [Sciences Chimiques de Rennes, UMR6226, Universite Rennes 1, 35042 Rennes (France)

2009-02-09

278

Preparation and bioapplication of high-quality, water-soluble, biocompatible, and near-infrared-emitting CdSeTe alloyed quantum dots.  

PubMed

A facile method is developed for the preparation of high-quality, water-soluble, and near-infrared (NIR)-emitting CdSeTe alloyed quantum dots (AQdots) with L-cysteine as the capping agent. By changing the size and the composition of AQdots the photoluminescent quantum yield (QY) can reach as high as 53% and the emission color can be tuned between visible and NIR regions (580-814 nm). Furthermore, the prepared NIR-emitting AQdots have been successfully applied for HL-60 cell imaging and glucose and cholesterol assay, which demonstrates the great potential of the AQdots for biological applications. PMID:19762946

Liang, Guo-Xi; Gu, Miao-Miao; Zhang, Jian-Rong; Zhu, Jun-Jie

2009-10-14

279

Wannier function study of the relative stability of zinc-blende and wurtzite structures in the CdX (X = S, Se, Te) series  

NASA Astrophysics Data System (ADS)

Tetrahedrally coordinated binary II-VI semiconductors are reported to crystallize both in cubic zinc-blende and hexagonal wurtzite structures. The relative stability of these structures and its origin have caught the attention of several researchers in the past. In this work, we revisit this issue for the CdX (X = S, Se, Te) series employing the Nth-order muffin-tin orbital technique. Our study correctly brings out the trend in this series, providing useful insight in terms of constructed Wannier functions.

Datta, Soumendu; Saha-Dasgupta, Tanusri; Sarma, D. D.

2008-11-01

280

Effect of heating rate on the glass transition temperature in Se79Te15In6-xPbx bulk alloys using power-law behaviour  

NASA Astrophysics Data System (ADS)

In the present study, the effect of heating rate on the glass transition temperature (Tg) in quaternary Se79Te15In6-xPbx (x = 0.5, 1, 2 and 4) chalcogenide bulk alloys using differential scanning calorimetry (DSC) experiment under non-isothermal conditions has been reported and discussed. The heating rate dependence of Tg has been investigated theoretically using power-law behaviour. An excellent agreement of Tg has been observed between experimental values obtained from DSC scans and theoretical values using power-law behaviour.

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

2014-04-01

281

First quaternary A-Pb-Bi-Q (A = K, Rb, Cs; Q = S, Se) compounds: Synthesis, structure, and properties of {alpha}- and {beta}-CsPbBi{sub 3}Se{sub 6}, APbBi{sub 3}Se{sub 6}, (A = K, Rb), and APbBi{sub 3}S{sub 6} (A = Rb, Cs)  

SciTech Connect

{alpha}-CsPbBi{sub 3}Se{sub 6} (I), {beta}-CsPbBi{sub 3}Se{sub 6} (II), RbPbBi{sub 3}Se{sub 6} (III), KPbBi{sub 3}Se{sub 6} (IV), CsPbBi{sub 3}S{sub 6} (V), and RbPbBi{sub 3}S{sub 6} (VI) were synthesized by the polychalcogenide flux method. {alpha}-CsPbBi{sub 3}Se{sub 6} was obtained at 720 C and crystallizes in the space group Pnma (No. 62) with a = 23.564(6) {angstrom}, b = 4.210(2) {angstrom}, c = 13.798(3) {angstrom} at room temperature. Final R/R{sub w} = 3.0/3.6%. In this compound, parallel NaCl-type Pb/Bi/Se columns with rectangularly shaped cross-sections are interconnected by edge sharing to build a 3-D tunnel framework with Cs atoms located inside the tunnels. The hexagonal plates of {beta}-CsPbBi{sub 3}Se{sub 6} were obtained at 400 C and crystallize in the space group P6{sub 3}/mmc (No. 194) with a = 4.213(2) {angstrom}, c = 25.22(1) {angstrom}, {gamma} = 120 at {minus}100 C. Final R/R{sub w} = 4.2/4.7%. APbBi{sub 3}Se{sub 6} (A = Rb, K) and APbBi{sub 3}S{sub 6} (A = Cs, Rb) are isostructural with {beta}-CsPbBi{sub 3}Se{sub 6} and their hexagonal cell parameters were obtained at room temperature. The structure is composed of negatively charged Bi{sub 2}Te{sub 3}-type bilayers separated by alkali metals, which are distributed over two different crystallographic sites. The alkali metal ions are loosely packed in the interlayer space making them mobile. Topotactic ion-exchange reactions of two compounds, {beta}-CsPbBi{sub 3}Se{sub 6} and RbPbBi{sub 3}Se{sub 6}, were examined with LiI and NaI in the solid state and in aqueous solution. Prolonged water contact of the hexagonal compounds leads to decomposition and leaching of alkali metal and Pb{sup 2+} ions. Electrical conductivity and thermopower measurements for single crystals of I, II, and III show n-type semiconductor behavior with 0.6, 0.3, and 0.3 S/cm and {minus}730, {minus}550, and {minus}560 {micro}V/K at room temperature, respectively. The optical band gaps of all compounds range from 0.27 to 0.89 eV. Thermal properties of the compounds are reported.

Chung, D.Y.; Iordanidis, L.; Rangan, K.K.; Kanatzidis, M.G. [Michigan State Univ., East Lansing, MI (United States)] [Michigan State Univ., East Lansing, MI (United States); Brazis, P.W.; Kannewurf, C.R. [Northwestern Univ., Evanston, IL (United States). Dept. of Electrical and Computer Engineering] [Northwestern Univ., Evanston, IL (United States). Dept. of Electrical and Computer Engineering

1999-05-01

282

Experimental determination of the absorption cross-section and molar extinction coefficient of CdSe and CdTe nanowires.  

PubMed

Absorption cross-sections and corresponding molar extinction coefficients of solution-based CdSe and CdTe nanowires (NWs) are determined. Chemically grown semiconductor NWs are made via a recently developed solution-liquid-solid (SLS) synthesis, employing low melting Au/Bi bimetallic nanoparticle "catalysts" to induce one-dimensional (1D) growth. Resulting wires are highly crystalline and have diameters between 5 and 12 nm as well as lengths exceeding 10 microm. Narrow diameters, below twice the corresponding bulk exciton Bohr radius of each material, place CdSe and CdTe NWs within their respective intermediate to weak confinement regimes. Supporting this are solution linear absorption spectra of NW ensembles showing blue shifts relative to the bulk band gap as well as structure at higher energies. In the case of CdSe, the wires exhibit band edge emission as well as strong absorption/emission polarization anisotropies at the ensemble and single-wire levels. Analogous photocurrent polarization anisotropies have been measured in recently developed CdSe NW photodetectors. To further support fundamental NW optical/electrical studies as well as to promote their use in device applications, experimental absorption cross-sections are determined using correlated transmission electron microscopy, UV/visible extinction spectroscopy, and inductively coupled plasma atomic emission spectroscopy. Measured CdSe NW cross-sections for 1 microm long wires (diameters, 6-42 nm) range from 6.93 x 10(-13) to 3.91 x 10(-11) cm2 at the band edge (692-715 nm, 1.73-1.79 eV) and between 3.38 x 10(-12) and 5.50 x 10(-11) cm2 at 488 nm (2.54 eV). Similar values are obtained for 1 microm long CdTe NWs (diameters, 7.5-11.5 nm) ranging from 4.32 x 10(-13) to 5.10 x 10(-12) cm2 at the band edge (689-752 nm, 1.65-1.80 eV) and between 1.80 x 10(-12) and 1.99 x 10(-11) cm2 at 2.54 eV. These numbers compare well with previous theoretical estimates of CdSe/CdTe NW cross-sections far to the blue of the band edge, having order of magnitude values of 1.0 x 10(-11) cm2 at 488 nm. In all cases, experimental NW absorption cross-sections are 4-5 orders of magnitude larger than those for corresponding colloidal CdSe and CdTe quantum dots. Even when volume differences are accounted for, band edge NW cross-sections are larger by up to a factor of 8. When considered along with their intrinsic polarization sensitivity, obtained NW cross-sections illustrate fundamental and potentially exploitable differences between 0D and 1D materials. PMID:17165978

Protasenko, Vladimir; Bacinello, Daniel; Kuno, Masaru

2006-12-21

283

Synthesis and superconducting properties of FeTe1-xSe Single Crystals under high magnetic fields  

NASA Astrophysics Data System (ADS)

Single crystals of superconductor FeTe1-xSex (0.1 <= x <= 0.5) were synthesized using optical floating zone, Bridgeman technique, and solid stat reaction. The samples were synthesized under various temperature gradients and cooling rates. Crystals were characterized via EDX, X-ray scattering, magnetization and transport measurements. Upper critical fields Hc2 as estimated through the Werthamer-Hohenberg-Helfand (WHH) formalism indicate that these materials strongly surpass the weak coupling Pauli limiting field indicating that the shape of their phase diagram under field is essentially controlled by the Pauli effect. Annealing, leads to a metallic temperature dependence of the resistivity, and to sharper superconducting transitions. Despite the relatively small increase in single crystallinity, as quantified by single crystal x-ray diffraction measurements, we observe a different phase diagram under high magnetic fields when compared to non-annealed samples.

Gebre, Tesfaye; Li, G.; Whalen, J.; Conner, B.; Kostov, M.; Siegrist, T.; Balicas, L.

2011-03-01

284

Structural properties of Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} topological insulators grown by molecular beam epitaxy on GaAs(001) substrates  

SciTech Connect

Thin films of Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} have been grown on deoxidized GaAs(001) substrates using molecular beam epitaxy. Cross-sectional transmission electron microscopy established the highly parallel nature of the Te(Se)-Bi-Te(Se)-Bi-Te(Se) quintuple layers deposited on the slightly wavy GaAs substrate surface and the different crystal symmetries of the two materials. Raman mapping confirmed the presence of the strong characteristic peaks reported previously for these materials in bulk form. The overall quality of these films reveals the potential of combining topological insulators with ferromagnetic semiconductors for future applications.

Liu, X.; Leiner, J.; Dobrowolska, M.; Furdyna, J. K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Smith, D. J. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Fan, J. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287 (United States); Zhang, Y.-H. [Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287 (United States); School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Cao, H.; Chen, Y. P. [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Kirby, B. J. [Center for Neutron Research, NIST, Gaithersburg, Maryland 20899 (United States)

2011-10-24

285

Fermi-level stabilization in the topological insulators Bi2Se3 and Bi2Te3: Origin of the surface electron gas  

NASA Astrophysics Data System (ADS)

Two-dimensional electron gas (2DEG) coexists with topological states on the surface of topological insulators (TIs), while the origin of the 2DEG remains elusive. In this work, electron density in TI thin films (Bi2Se3,Bi2Te3, and their alloys) were manipulated by controlling the density of electronically active native defects with particle irradiation. The measured electron concentration increases with irradiation dose but saturates at different levels for Bi2Se3 and Bi2Te3. The results are in quantitative agreement with the amphoteric defect model, which predicts that electronically active native defects shift the Fermi energy (EF) toward a Fermi stabilization level (EFS) located universally at ˜4.9 eV below the vacuum level. Combined with thickness-dependent data, it is demonstrated that regardless of the bulk doping, the surface EF is always pinned at EFS, producing a band bending and 2DEG on TI film surfaces. Our work elucidates native defect physics of TIs with a model universally applicable to other semiconductors and has critical implications for potential device applications of TIs.

Suh, Joonki; Fu, Deyi; Liu, Xinyu; Furdyna, Jacek K.; Yu, Kin Man; Walukiewicz, Wladyslaw; Wu, Junqiao

2014-03-01

286

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

287

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

PubMed

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

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

2014-01-01

288

London penetration depth measurements of Fe1+y(Te1-xSe x) single-crystals at ultra-low temperatures  

NASA Astrophysics Data System (ADS)

The evolution of the superconducting properties as derived from the in-plane penetration depth measurements as a function of temperature in single crystals of Fe1.02(Te1-xSe x), with Se concentration spanning from 25% to 45%, was studied using a tunnel diode oscillator technique in a dilution refrigerator down to a temperature of 30mK. By using a set of two mutually coupled planar inductors parallel to the ab plane of the samples, the probing ac field is uniform across the sample along the c axis making the variation in susceptibility solely due to in-plane currents while significantly increasing the signal to noise ratio compared to usual inductors used in similar experiments The evolution of the topology of the superconducting gap from underdoped to optimally doped samples, as derived from exponential and power law behavior of ?ab at low temperatures, is presented.

Diaconu, Andrei; Hu, Jin; Liu, Tijiang; Qian, Bin; Mao, Zhiqiang; Spinu, Leonard

2012-02-01

289

Orbital processing of high-quality CdTe compound semiconductors  

NASA Technical Reports Server (NTRS)

CdZnTe crystals were grown in one-g and in micro-g for comparative analysis. The two micro-g crystals were grown in the Crystal Growth Furnace during the First United States Microgravity Laboratory mission (USML-1). The samples were analyzed for chemical homogeneity, structural perfection, and optoelectronic performance (infrared transmission). Fourier Transform Infrared (FTIR) transmission of both ground and flight materials showed that the infrared transmission was close to theoretical, 63% versus 66%, suggesting that the material was close to the stochiometric composition during both the ground and flight experiments. Infrared microscopy confirmed that the principal precipitates were Te and their size (1-10 microns) and density suggested that the primary flight and ground base samples experienced similar cooling rates. Macrosegregation was predicted, using scaling analysis, to be low even in one-g crystals and this was confirmed experimentally, with nearly diffusion controlled growth achieved even in the partial mixing regime on the ground. Radial segregation was monitored in the flight samples and was found to vary with fraction solidified, but was disturbed due to the asymmetric grvitational and thermal fields experienced by the flight samples. The flight samples, however, were found to be much higher in structural perfection than the ground samples produced in the same furnace under identical growth conditions except for the gravitational level. Rocking curve widths were found to be substantially reduced, from 20/35 (one-g) to 9/20 (micro-g) for the best regions of the crystals. The full width at half maximum (FWHM) of 9 arc seconds is as good as the best reported terrestrially for this material. The ground samples were found to have a fully developed mosaic structure consisting of subgrains, whereas the flight sample dislocations were discrete and no mosaic substructure was evident. The defect density was reduced from 50-100,000 (one-g) to 500-25000 EPD (micro-g). These results were confirmed using rocking curve analysis, synchrotron topography, and etch pit analysis. The low dislocation density is thought to have resulted from the near-absence of hydrostatic pressure which allowed the melt to solidify with minimum or no wall contact, resulting in very low stress being exerted on the crystal during growth or during post-solidification cooling.

Larson, David J., Jr.; Alexander, J. I. D.; Gillies, D.; Carlson, F. M.; Wu, J.; Black, D.

1994-01-01

290

Reducing Lattice Thermal Conductivity of the Thermoelectric Compound AgSbTe2 (P4/mmm) by Lanthanum Substitution: Computational and Experimental Approaches  

NASA Astrophysics Data System (ADS)

In this study we performed lattice dynamics first-principles calculations for the promising thermoelectric (TE) compound AgSbTe2, and estimated the stability of its three polymorphs over a wide temperature range from 0 to 600 K. We calculated the vibrational density of states of the AgSbTe2 (P4/mmm) phase. The results suggested that formation of substitutional defects at Ag-sublattice sites impedes lattice vibrations, thereby reducing lattice thermal conductivity. We focused on calculations based on the Debye approximation for the compound La0.125Ag0.875SbTe2, and predicted reduction of the average sound velocity from 1684 to 1563 m s-1 as a result of La doping. This is manifested as a ca. 14% reduction in thermal conductivity. To confirm the results from computation we produced two Ag-Sb-Te-based alloys, a ternary alloy without La addition and a quaternary alloy containing La. We measured the thermal conductivity of both alloys by use of the laser flash analysis method, and, as a result of La alloying, observed a reduction in thermal conductivity from 0.92 to 0.71 W m-1 K-1 at 573 K, as calculated from first principles.

Amouyal, Yaron

2014-10-01

291

Experiment 1: Orbital Processing of High-Quality Zn-Alloyed CdTe Compound Semiconductors  

NASA Technical Reports Server (NTRS)

Zinc-alloyed cadmium telluride (Zn:CdTe) crystals were grown in unit gravity and in microgravity for comparative analysis. Two crystals were grown on USML-1/STS-50 in 1992, and two additional crystals were grown on USML-2/STS-73 in 1995. The Crystal Growth Furnace (CGF) in the seeded Bridgman-Stockbarger crystal growth geometry was utilized on both missions. Crystals grown on USML-1/STS-50 were found to have solidified with partial wall contact due to the near-absence of the hydrostatic pressure in microgravity, a residual g-vector that was not axial, and the nonwetting sample/ampoule wetting conditions. Crystals grown on USML-2/STS-73 included: a sample/ampoule identical to the USML-1/STS-73 sample/ampoule, with the addition of a restraining spring to simulate hydrostatic pressure internally, and a tapered ampoule which accomplished 2.2 cm of crystal growth without wall contact. Infrared transmission of all ground and flight samples was found to be 63-66 percent, very close to the theoretical 66 percent, suggesting good stoichiometric control. Infrared microscopy confirmed that the primary precipitates were Te and their size (1-10 microns) and density suggested that the flight- and ground-base samples experienced similar thermal histories. Longitudinal macrosegregation, calculated using scaling analysis, was predicted to be low. Nearly diffusion controlled growth was achieved even in unit gravity and macrosegregation data could be fit with a diffusion controlled model. Radial segregation was monitored and was found to vary with fraction solidified, particularly through the shoulder region, where the sample cross section was varying significantly. It was also disturbed in the flight samples in regions where asymmetric wall contact was noted. In regions where a steady state was established, the radial segregation was invariant within our experimental measurement error. Flight samples were found to be much higher in structural perfection than samples processed in unit gravity under identical growth conditions. In regions where solidification had occurred without wall contact, the free surfaces evidenced virtually no twinning, although twins appeared in the flight samples in regions of wall contact and were pervasive in the ground samples. These results were confirmed using optical microscopy and synchrotron x-ray white beam topography. Full-width half-maximum rocking curve widths (FWHM), recorded in arc-seconds, were significantly reduced from 20 a-s (1 g) to 9 a-s (micro-g) for the best regions of the crystals. The 9 a-s (FWHM) rocking curve value in the unconfined flight samples equals the best value reported terrestrially for this material. The ground samples exhibited a fully developed (111)[110] dislocation mosaic structure, whereas dislocations within the flight samples were discrete and no mosaic structure was evident. The defect density was quantitatively reduced from 75,000 (1 g) to 800 (micro-g) +/-50 percent. Dislocation etch pit density results were confirmed using transmission synchrotron white beam and monochromated beam topography. The low defect density is thought to have resulted from the near absence of hydrostatic pressure, which allowed the molten boule to solidify with little or no wall contact. This minimized the transfer of hoop stresses during solidification and post-solidification processing.

Larson, D. J., Jr.; Dudley, M.; Alexander, J. I. D.; Carlson, F. M.; Gillies, D.; DiMarzio, D.

1998-01-01

292

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

PubMed Central

Bi2?xSbxTe3?ySey has been argued to exhibit both topological surface states and insulating bulk states, but has not yet been studied with local probes on the atomic scale. Here we report on the atomic and electronic structures of Bi1.5Sb0.5Te1.7Se1.3 studied using scanning tunnelling microscopy (STM) and spectroscopy (STS). Although there is significant surface disorder due to alloying of constituent atoms, cleaved surfaces of the crystals present a well-ordered hexagonal lattice with 10 Å high quintuple layer steps. STS results reflect the band structure and indicate that the surface state and Fermi energy are both located inside the energy gap. In particular, quasi-particle interference patterns from electron scattering demonstrate that the surface states possess linear dispersion and chirality from spin texture, thus verifying its topological nature. This finding demonstrates that alloying is a promising route to achieve full suppression of bulk conduction in topological insulators whilst keeping the topological surface state intact. PMID:24030733

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

2013-01-01

293

Heat Capacity And Structural Relaxation In Se{sub 80-x}Te{sub 20}Ag{sub x}(x = 3 and 9) Glassy Alloys  

SciTech Connect

This paper reports the effects of annealing time and temperature on the thermodynamics of enthalpy relaxation of Se{sub 80-x}Te{sub 20}Ag{sub x} (x = 3,9) glasses. Differential Scanning Calorimetry (DSC) method is optimized for the measurement of enthalpy relaxation in the vicinity of glass transition. The recovery of excess enthalpy ({Delta}H{sub excess}) has been calculated from the knowledge of excess specific heat ({Delta}C{sub p}). It is found that excess enthalpy released ({Delta}H{sub excess}) increase with increase in annealing time (t{sub a}). From the knowledge of excess specific heat ({Delta}C{sub p}) and {Delta}H{sub excess}, it has been found that sub-T{sub g} annealing of glass leads to decrease in enthalpy of the system and thereby taking it to the more equilibrium state.

Naqvi, S. Faheem; Saxena, N. S. [Semi-conductor and Polymer Science Laboratory, 5-6, Vigyan Bhawan, Department of Physics, University of Rajasthan, Jaipur-302004 (India)

2011-10-20

294

Aqueous synthesis of CdTe/CdSe core/shell quantum dots as pH-sensitive fluorescence probe for the determination of ascorbic acid.  

PubMed

By controlling the reflux time and the quantity of the shell materials, different sizes of thioglycollic acid (TGA) modified CdTe/CdSe core/shell quantum dots were synthesized in aqueous solution. This type of QDs was used for sensitive and selective determination of ascorbic acid in commercial tablets. Under optimal conditions, a good linearity was observed between the relative fluorescence (FL) intensity and the concentration of ascorbic acid in the range of 4.0 to 64.0 ?g/mL with a correlation coefficient of 0.9968. The limit of detection was 2.4 ?g/mL. This method was applied to the determination of the ascorbic acid in Vitamin C tablets and Vitamin C Yinqiao pills, and satisfactory results were obtained. PMID:21161344

Yang, Shan-Shan; Ren, Cui-Ling; Zhang, Zhen-Yang; Hao, Jun-Jie; Hu, Qin; Chen, Xing-Guo

2011-05-01

295

Theoretical estimates of the anapole magnetizabilities of C4H4X2 cyclic molecules for X=O, S, Se, and Te  

NASA Astrophysics Data System (ADS)

Calculations have been carried out for C4H4X2 cyclic molecules, with X=O, S, Se, and Te, characterized by the presence of magnetic-field induced toroidal electron currents and associated orbital anapole moments. The orbital anapole induced by a static nonuniform magnetic field B, with uniform curl {{C}}=nabla × {{B}}, is rationalized via a second-rank anapole magnetizability tensor a??, defined as minus the second derivative of the second-order interaction energy with respect to the components C? and B?. The average anapole magnetizability overline{a} equals -overline{? }, the pseudoscalar obtained by spatial averaging of the dipole-quadrupole magnetizability ??,??. It has different sign for D and L enantiomeric systems and can therefore be used for chiral discrimination. Therefore, in an isotropic chiral medium, a homogeneous magnetic field induces an electronic anapole A_{? }, having the same magnitude, but opposite sign, for two enantiomorphs.

Pagola, G. I.; Ferraro, M. B.; Provasi, P. F.; Pelloni, S.; Lazzeretti, P.

2014-09-01

296

Nucleus-independent chemical shifts and aromaticity in hexanuclear cluster complexes [Mo6X8]n- (X = S, Se, and Te; n = 0 and 4) of Chevrel phases.  

PubMed

Molecular diamagnetism and multicentered X-Mo-Mo and Mo-Mo-Mo interactions in hexanuclear cluster complexes [Mo(6)X(8)](n-) (X = S, Se, and Te; n = 0 and 4) are studied using calculations of nuclear independent chemical shifts (NICS) and the methods "atoms in molecules" and electron localization function. It is shown that [Mo(6)X(8)](4-) complexes are characterized by large negative NICSs related to the aromaticity of Mo-Mo bondings and to diatropic currents in Mo(6) metallic core of the cuboctahedral clusters. The calculated currents can participate in the mechanism of nucleation of the vortex lattice of macroscopic Abrikosov's electronic whirls responsible for the magnetic high-?eld stability of the superconducting currents in type II superconductors. PMID:23116293

Kozlova, Svetlana G; Ryzhikov, Maxim R; Gabuda, Svyatoslav P; Fedorov, Vladimir E

2012-11-29

297

Measurement of the {sup 77}Se, {sup 99}Ru, {sup 101}Ru and {sup 123}Te(n,{alpha}) Cross Sections with Thermal Neutrons  

SciTech Connect

Results of (n,{alpha}) cross section measurements performed at the high flux reactor of the Institute Laue-Langevin in Grenoble (France) are reported. Cross section values are given for the {alpha}{sub 0}, {alpha}{sub 1} and {alpha}{sub 2} transitions in {sup 77}Se(n,{alpha}){sup 74}Ge, the {alpha}{sub 0} and {alpha}{sub 1} transitions in {sup 99}Ru(n,{alpha}){sup 96}Mo, the {alpha}{sub 0} and {alpha}{sub 1} transitions in {sup 101}Ru(n,{alpha}){sup 98}Mo and the {alpha}{sub 0}, {alpha}{sub 1} and {gamma}{alpha} transitions in {sup 123}Te(n,{alpha}){sup 120}Sn. Corresponding resonance data reported in the literature are confronted with these results.

Wagemans, Cyriel [Department of Subatomic and Radiation Physics, University of Gent, B-9000 Gent (Belgium); Wagemans, Jan [Nuclear Research Centre SCKCEN, B-2400 Mol (Belgium); Geltenbort, Peter [Institute Laue-Langevin, BP 156, F-38042 Grenoble (France)

2009-01-28

298

Combining ligand-induced quantum-confined stark effect with type II heterojunction bilayer structure in CdTe and CdSe nanocrystal-based solar cells.  

PubMed

We show that it is possible to combine several charge generation strategies in a single device structure, the performance of which benefits from all methods used. Exploiting the inherent type II heterojunction between layered structures of CdSe and CdTe colloidal quantum dots, we systematically study different ways of combining such nanocrystals of different size and surface chemistry and with different linking agents in a bilayer solar cell configuration. We demonstrate the beneficial use of two distinctly different sizes of NCs not only to improve the solar spectrum matching but also to reduce exciton binding energy, allowing their efficient dissociation at the interface. We further make use of the ligand-induced quantum-confined Stark effect in order to enhance charge generation and, hence, overall efficiency of nanocrystal-based solar cells. PMID:22390408

Yaacobi-Gross, Nir; Garphunkin, Natalia; Solomeshch, Olga; Vaneski, Aleksandar; Susha, Andrei S; Rogach, Andrey L; Tessler, Nir

2012-04-24

299

Specific heat of Pb/sub 0. 93/Sn/sub 0. 07/Se and Hg/sub 0. 80/Cd/sub 0. 20/Te solid solutions  

SciTech Connect

In this work, the temperature dependence of the specific heat is determined for Pb/sub 0.93/Sn/sub 0.07/Se and Hg/sub 0.80/Cd/sub 0.20/Te single crystals in the temperature ranges 298-973/sup 0/K and 298-958/sup 0/K respectively. Single crystals were used, which were grown from the melt by the Czochralski method and by zone recrystallization. The concentrations of the components contained in the single crystals and the homogeneity along the length and cross section were checked by local x-ray spectral analysis and chemical analysis. Unit-cell parameter, thermal linear-expansion coefficient, isothermal isostatic compressibility, and elastic constants of the solid solutions are given, as are the calculated values of the Gruneisen constant and Debye temperature.

Mendibaev, K.R.; Vigdorovich, V.N.; Sokolov, A.M.; Sadykov, E.

1987-07-01

300

The structure of the oxygen-annealed Fe1.08Te0.55Se0.45Ox superconductor  

NASA Astrophysics Data System (ADS)

Effect of oxygen annealing on the iron chalcogenide superconductor with excess Fe is studied and structure change is investigated by using electron microscopy. The as-grown single crystal Fe1.08Te0.55Se0.45 with the tetragonal PbO-type structure is non-superconducting owing to the excess Fe. Superconductivity is induced after oxygen annealing with an onset and zero resistance transition temperature around 14.5 K and 11.5 K, respectively. The oxygen doping is evidenced by electron energy loss spectroscopy, and accompanied by improved homogeneity in the remaining PbO-type phase as well as an increase in the L3/L2 intensity ratio of the Fe-L2,3 edge, indicating an increase in Fe valence. Local phase transformation from the tetragonal PbO-type phase to the hexagonal NiAs-type phase is also observed after oxygen annealing.

Hu, Hefei; Zuo, Jian-Min; Zheng, Mao; Eckstein, James N.; Park, Wan Kyu; Greene, Laura H.; Wen, Jinsheng; Xu, Zhijun; Lin, Zhiwei; Li, Qiang; Gu, Genda

2012-02-01

301

Structure of the oxygen-annealed chalcogenide superconductor Fe1.08Te0.55Se0.45Ox  

NASA Astrophysics Data System (ADS)

The as-grown single crystal Fe1.08Te0.55Se0.45 with the tetragonal PbO-type structure is nonsuperconducting owing to the excess Fe. Superconductivity is induced after oxygen annealing with an onset and zero resistance transition temperature around 14.5 K and 11.5 K, respectively. The oxygen doping is evidenced by electron energy loss spectroscopy and accompanied by improved homogeneity in the remaining PbO-type phase, as well as an increase in the L3/L2 intensity ratio of the Fe-L2,3 edge, indicating an increase in Fe valence. Local phase transformation from the tetragonal PbO-type phase to the hexagonal NiAs-type phase is also observed after oxygen annealing.

Hu, Hefei; Zuo, Jian-Min; Zheng, Mao; Eckstein, James N.; Park, Wan Kyu; Greene, Laura H.; Wen, Jinsheng; Xu, Zhijun; Lin, Zhiwei; Li, Qiang; Gu, Genda

2012-02-01

302

Anisotropy analysis of thermoelectric properties of Bi{sub 2}Te{sub 2.9}Se{sub 0.1} prepared by SPS method  

SciTech Connect

The n-type Bi{sub 2}Te{sub 2.9}Se{sub 0.1} materials were synthesized by the direct fusion technique. The polycrystalline samples were fabricated by the uniaxial pressing of powders in spark plasma sintering (SPS) apparatus. The materials were subjected to the heat treatment in H{sub 2}-Ar atmosphere at 470 K for 24 h. The influence of preparation conditions on the anisotropy of electrical and thermal properties was thoroughly studied for the direction perpendicular and parallel to the pressing force. The microstructure and the chemical composition of both types of samples were examined using a scanning microscope (SEM) equipped with an X-ray energy dispersion detector (EDX). The XRD method was applied for the phase analysis of materials, as well as, for determination of preferred orientation of Bi{sub 2}Te{sub 2.9}Se{sub 0.1} grains. The Seebeck coefficient distribution was studied by the scanning thermoelectric microprobe (STM). Temperature dependences of thermoelectric properties (thermal and electrical conductivities, Seebeck coefficient) were measured in the temperature from 300 K to 550 K. The statistical analysis of results has shown strong influence of pressing force direction both on structural and transport properties. The applied heat treatment of materials significantly improves their thermoelectric figure of merit. Particularly, it was found that annealing in H2-Ar atmosphere leads to enhancement of the ZT three times up to {approx}0.7 at 370 K in perpendicular direction to the pressing force.

Zybala, Rafal; Wojciechowski, Krzysztof T. [Thermoelectric Research Laboratory, Department of Inorganic Chemistry, Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Av. Mickiewicza 30, 30-059, Cracow (Poland)

2012-06-26

303

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

SciTech Connect

Research highlights: {yields} Single-phase Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} powders have been synthesized by a hydrothermal route. {yields} Hexagonal Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} naosheets due to the anisotropic growth of the crystals. {yields} The temperature gradients lead to directional arrangement nanosheet-agglomerates. {yields} Nanosheet-agglomerates are beneficial for improving the TE property of products. {yields} A maximum figure of merit of 0.86 is achieved at about 100 {sup o}C. -- Abstract: Single-phase Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds have been prepared by hydrothermal synthesis at 150 {sup o}C for 24 h using SbCl{sub 3}, BiCl{sub 3} and tellurium powder as precursors. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) have been applied to analyze the phase distributions, microstructures and grain sizes of the as-grown Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} products. It is found that the hydrothermally synthesized Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} nanopowders have a morphology dominated by irregular hexagonal sheets due to the anisotropic growth of the crystals. The Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} nanosheets are parallelly stacked in certain direction to form sheet-agglomerates attribute to the temperature gradients in the solution.

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

2011-05-15

304

Comparison of the pinning energy in Fe(Se1-xTex) compound between single crystals and thin films  

NASA Astrophysics Data System (ADS)

Among the families of iron-based superconductors, we investigate flux pinning mechanisms in the Fe(Se1-xTex) compound. We perform magneto-resistance and current-voltage measurements on single-crystals, as well as on several epitaxial thin films grown on different substrates (CaF2, LaAlO3). The activation energy is derived as a function of magnetic field, U(H). The influence of magnetic field orientation on the pinning energy activation mechanism is also studied, leading to the anisotropy analysis which reveals low anisotropy in thin films grown on CaF2 substrate with respect to single crystals and films grown on LaAlO3. Concerning the dominant pinning regime, the exponents of the power law dependence U0(H) ~ H-? have been evaluated, confirm that weak pinning is a general characteristic of this compound. The single exponent feature, generally noticed on thin films grown on SrTiO3 substrate and associated to a strong single vortex regime, has been observed in thin films grown on LaAlO3, only in the parallel configuration. At the end, this overall comparison can be useful to develop a technological material able to compete with high temperature superconductors.

Leo, A.; Guarino, A.; Grimaldi, G.; Nigro, A.; Pace, S.; Bellingeri, E.; Kawale, S.; Ferdeghini, C.; Giannini, E.

2014-05-01

305

The comprehensive phase evolution for Bi[subscript 2]Te[subscript 3] topological compound as function of pressure  

SciTech Connect

The recently discovered three-dimensional topological insulator Bi{sub 2}Te{sub 3} is studied as function of pressure in terms of crystal structures, resistance, and Hall coefficient. The superconductivity is found in phase I (ambient phase) Bi{sub 2}Te{sub 3} with T{sub c}-3 K, which is related to the topological features. The evolution of crystal structure with pressure is investigated by high pressure synchrotron radiation experiments that reveal structural transitions occurring at about 8 GPa, 13 GPa, and 16 GPa, respectively. Furthermore, the high pressure phases of Bi{sub 2}Te{sub 3} are also superconducting but with much higher T{sub c}-8 K. The superconducting transitions are compared with those for Bi, Te elements. A global phase diagram of Bi{sub 2}Te{sub 3} as function of pressure up to 30 GPa is obtained.

Zhang, S.J.; Zhang, J.L.; Yu, X.H.; Zhu, J.; Kong, P.P.; Feng, S.M.; Liu, Q.Q.; Yang, L.X.; Wang, X.C.; Cao, L.Z.; Yang, W.G.; Wang, L.; Mao, H.K.; Zhao, Y.S.; Liu, H.Z.; Dai, X.; Fang, Z.; Zhang, S.C.; Jin, C.Q. (Stanford); (Harbin); (UST - China); (CIW); (Chinese Aca. Sci.); (LANL)

2012-06-26

306

Theory of the evolution of magnetic order in Fe1+yTe compounds with increasing interstitial iron  

NASA Astrophysics Data System (ADS)

We examine the influence of the excess of interstitial Fe on the magnetic properties of Fe1+yTe compounds. Because in iron chalcogenides the correlations are stronger than in the iron arsenides, we assume in our model that some of the Fe orbitals give rise to localized magnetic moments. These moments interact with each other via exchange interactions as well as phonon-mediated biquadratic interactions that favor a collinear double-stripe state, corresponding to the ordering vectors (±?/2,±?/2). The remaining Fe orbitals are assumed to be itinerant, giving rise to the first-principles derived Fermi surface displaying nesting features at momenta (?,0)/(0,?). Increasing the amount of itinerant electrons due to excess Fe, y, leads to changes in the Fermi surface and to the suppression of its nesting properties. As a result, due to the Hund's coupling between the itinerant and localized moments, increasing y leads to modifications in the local moments' exchange interactions via the multiorbital generalization of the long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. By numerically computing the RKKY corrections and minimizing the resulting effective exchange Hamiltonian, we find, in general, that the excess electrons introduced in the system change the classical magnetic ground state from a double-stripe state to an incommensurate spiral, consistent with the experimental observations. We show that these results can be understood as a result of the suppression of magnetic spectral weight of the itinerant electrons at momenta (?,0)/(0,?), combined with the transfer of broad magnetic spectral weight from large to small momenta, promoted by the introduction of excess Fe.

Ducatman, Samuel; Fernandes, Rafael M.; Perkins, Natalia B.

2014-10-01

307

Order-disorder phase transitions in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1-xWxX2 (X = S, Se, and Te).  

PubMed

A combination of density functional theory, an empirical model, and Monte Carlo simulations is used to shed light on the evolution of the atomic distribution in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1-xWxX2 (X = S, Se, and Te) as a function of the W concentration and temperature. Both random and ordered phases are discovered and the origin of the phase transitions is clarified. While the empirical model predicts at x = 1/3 and 2/3 ordered alloys, Monte Carlo simulations suggest that they only exist at low temperature due to a small energetic preference of Mo-X-W over Mo-X-Mo and W-X-W interactions, explaining the experimental observation of random alloy Mo1-xWxS2. Negative formation energies point to a high miscibility. Tunability of the band edges and band gaps by alteration of the W concentration gives rise to a broad range of applications. PMID:25331363

Gan, Li-Yong; Zhang, Qingyun; Zhao, Yu-Jun; Cheng, Yingchun; Schwingenschlögl, Udo

2014-01-01

308

High-output-power densities from molecular beam epitaxy grown n- and p-type PbTeSe-based thermoelectrics via improved contact metallization  

SciTech Connect

Electrical power densities of up to 33 W/cm{sup 2} and up to 12 W/cm{sup 2} were obtained for n-type and p-type PbTeSe-based stand-alone thermoelectric devices, respectively, at modest temperature gradients of {approx}200 deg. C (T{sub cold}= 25 deg. C). These large power densities were enabled by greatly improving electrical contact resistivities in the thermoelectric devices. Electrical contacts with contact resistivities as low as 3.9 x 10{sup -6}{Omega} cm{sup 2} and 4.0 x 10{sup -6}{Omega} cm{sup 2} for n- and p-type telluride-based- materials, respectively, were developed by investigating several metallization schemes and contact layer doping/alloy combinations, in conjunction with a novel contact application process. This process exposes heated semiconductor surfaces to an atomic hydrogen flux under high vacuum for surface cleaning (oxide and carbon removal), followed immediately by an in-situ electron-beam evaporation of the metal layers.

Goodhue, W. G. [Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420 (United States); Photonics Center, University of Massachusetts Lowell, Lowell, Massachusetts 01854 (United States); Reeder, R. E.; Vineis, C. J.; Calawa, S. D.; Walsh, M. P.; Harman, T. C. [Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420 (United States); Dauplaise, H. M. [Air Force Research Laboratory, Sensors Directorate, Hanscom AFB, MA 01731 (United States); Vangala, S. [Photonics Center, University of Massachusetts Lowell, Lowell, Massachusetts 01854 (United States)

2012-05-15

309

Characterization of surface conducting states in Bi1.5Sb0.5Te1.7Se1.3 topological insulator single crystals  

NASA Astrophysics Data System (ADS)

Topologically protected surface state (TSS) of a topological insulator (TI) can be described in terms of a spin-resolved Dirac band with helical-spin texture. In general, however, as-grown TIs are doped so that the surface conduction can be dominated by the bulk conduction. In this study, we minimized the bulk conduction using high-quality Bi1.5Sb0.5Te1.7Se1.3 TI thin single crystals, with the Fermi level lying in the bulk gap without gating. We confirmed that the weak anti-localization (WAL) effect and universal conductance fluctuations in our samples arose from the top and bottom surfaces. By back-gate tuning the WAL characteristics, we identified the TSS conducting characteristics and the coupling between the TSS and the topologically trivial two-dimensional electron gas (2DEG) states that emerged due to the band bending near the surface. The ambipolar Hall resistivity of the bottom surface was consistent with the back-gate-voltage dependence of the longitudinal resistance of the TSS. This study provides a highly coherent picture of the surface transport properties of TIs by successfully differentiating the transport of the TSS from those of the bulk conducting state and the topologically trivial 2DEG states.

Lee, Janghee; Park, Joonbum; Lee, Jae-Hyeong; Kim, Jun Sung; Lee, Hu-Jong

2013-03-01

310

Order-disorder phase transitions in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1?xWxX2 (X = S, Se, and Te)  

PubMed Central

A combination of density functional theory, an empirical model, and Monte Carlo simulations is used to shed light on the evolution of the atomic distribution in the two-dimensional semiconducting transition metal dichalcogenide alloys Mo1?xWxX2 (X = S, Se, and Te) as a function of the W concentration and temperature. Both random and ordered phases are discovered and the origin of the phase transitions is clarified. While the empirical model predicts at x = 1/3 and 2/3 ordered alloys, Monte Carlo simulations suggest that they only exist at low temperature due to a small energetic preference of Mo-X-W over Mo-X-Mo and W-X-W interactions, explaining the experimental observation of random alloy Mo1?xWxS2. Negative formation energies point to a high miscibility. Tunability of the band edges and band gaps by alteration of the W concentration gives rise to a broad range of applications. PMID:25331363

Gan, Li-Yong; Zhang, Qingyun; Zhao, Yu-Jun; Cheng, Yingchun; Schwingenschlogl, Udo

2014-01-01

311

FTIR Spectroscopic Study of Mn(II) Oxidizing Pseudomonas putida GB1 Biofilms on ZnSe, Ge, and CdTe Crystal Surfaces  

NASA Astrophysics Data System (ADS)

Pseudomonas putida strain GB1 is an aerobic, gram-negative bacterium capable of gaining energy from the biological oxidation of Mn(II). The increased kinetics of Mn(II) oxidation resulting from this microbial catalysis is known to contribute to the formation of Mn(IV) oxides in natural waters. Environmental conditions, including aqueous and surface chemistry, greatly affect the macromolecular composition and surface adhesion behavior of bacteria. For example, the chemistry of GB1 biofilms forming on crystal surfaces is expected to vary with Mn(II) concentration in solution. We used Fourier transform infrared (FTIR) spectroscopy to probe the formation of GB1 biofilms on the surfaces of negatively-charged IR transparent ZnSe, Ge, and CdTe crystal windows. Bacterial adhesion experiments were carried out both in the presence and absence of Mn(II)(aq) with FTIR windows suspended in a bioreactor comprising GB1 cells in a mineral growth medium at pH 7.6 and 30° C. After 85 h, windows were removed from the reactor and IR spectra were collected. Oxidation of Mn(II) was confirmed via leucoberbelin blue (LBB) indicator and the appearance of Mn-O stretches in biofilm IR spectra. Transmission FTIR spectra do not reveal detectable effects of crystal type on biofilm composition, but do indicate changes in chemistry resulting from introduction of Mn(II). In the presence of Mn(II), spectra of biofilms show higher relative intensity in the carbohydrate region (specifically 1160, 1052 cm-1). A down frequency shift in the P=O absorbance was also observed (1240 to 1222 cm-1). These results indicate a modification of bacterial cell/biofilm composition resulting during biological oxidation of Mn(II). The CdTe transmission window permits measurements to low wavenumbers (<600 cm-1) and a peak at 588 cm-1 was observed when bacteria were surface-adhered in the presence of Mn(II). This peak, which has been attributed to Mn-O stretching vibrations, may provide an index of Mn oxide crystal growth. Scanning electron microscopy (SEM) images of the transmission crystal surfaces show similar bacterial coverage for each treatment. Transmission electron microscopy (TEM) of the bioreactor suspension revealed needle-like clusters of Mn oxide crystals in association with GB1 biomass and extracellular materials.

Parikh, S. J.; Gilbert, H. L.; Conklin, M. H.; Chorover, J.

2003-12-01

312

Energy band gap of the alloy Zn 1? x Mg x Se y Te 1? y lattice matched to ZnTe, InAs and InP  

Microsoft Academic Search

The correlated function expansion (CFE) methodology has been used to estimate the energy band gap and the alloy bond length of Zn1?xMgxSeyTe1?y over the entire composition space (x,y). The lattice matching condition was obtained by optimizing the alloy bond length to the bond length of the substrates (ZnTe, InAs and InP), and the corresponding band gap and its bowing effect

Kyurhee Shim; Herschel Rabitz; Ji-Ho Chang; Takafumi Yao

2000-01-01

313

Comparison of Sn-doped and nonstoichiometric vertical-Bridgman-grown crystals of the topological insulator Bi2Te2Se  

NASA Astrophysics Data System (ADS)

A comparative study of the properties of topological insulator Bi2Te2Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8 × 1014 cm-3. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (EF) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, which the Dirac point for the surface states lies approximately 60 meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near EF. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed.

Kushwaha, S. K.; Gibson, Q. D.; Xiong, J.; Pletikosic, I.; Weber, A. P.; Fedorov, A. V.; Ong, N. P.; Valla, T.; Cava, R. J.

2014-04-01

314

Identification of the major selenium compound, Se-Methionine, in three yeast (Saccharomyces cerevisiae) dietary supplements by on-line narrowbore liquid chromatography-electrospray tandem mass spectrometry.  

PubMed

On-line monitoring of six Se-compounds was accomplished by using an XTerra MS C18 column coupled to electrospray tandem mass spectrometry (ES-MS-MS). In view of the nature of the compounds, the positively charged ion pairing agent tetraethylammoniumchloride (TEACl) was added to the mobile phase. The HPLC-ES-MS-MS method was optimized with six commercially available Se-compounds. Substitution of the analytical column by the narrowbore type significantly enhanced the sensitivity of the method. We were able to detect the m/z of these six molecules on-line. Furthermore, all product ions could be monitored. The method was applied to three different yeast-based supplements. They were submitted to proteolytic digestion and screened for their Se-content by HPLC-HG-AFS (hydride generation-atomic fluorescence spectrometry). By application of on-line narrowbore HPLC-electrospray tandem mass spectrometry, the main compound present in these three supplements, Se-Methionine, could be measured on its m/z and its product ions. The method can be further extended for on-line measurement of different Se-species in complex matrices PMID:15865193

Dumont, Emmie; De Cremer, Koen; Van Hulle, Marijn; Chéry, Cyrille C; Vanhaecke, Frank; Cornelis, Rita

2005-04-15

315

Ag1.75InSb5.75Se11: A new noncentrosymmetric compound with congruent-melting behavior  

NASA Astrophysics Data System (ADS)

A new type of quaternary selenide Ag1.75InSb5.75Se11 has been synthesized. It crystallizes in the non-centrosymmetric space group Cm of monoclinic system, with a=13.419 (1) Å, b=4.084 (1) Å, and c=19.165 (2) Å, Z=2. The compound has a new three-dimensional layer structure which consists of infinite [AgSb2Se4]?2 layers and [Ag1(Sb6)Ag3InSb3Se8]?2 layers. The band gap of Ag1.75InSb5.75Se11 is 0.94(2) eV, which agrees with its dark gray color. Moreover, the compound exhibits congruent-melting behavior.

Hao, Wenyu; Han, Yemao; Huang, Rongjin; Feng, Kai; Yin, Wenlong; Yao, Jiyong; Wu, Yicheng

2014-10-01

316

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

PubMed

We calculate the shift current response, which has been identified as the dominant mechanism for the bulk photovoltaic effect, for the polar compounds LiAsS2, LiAsSe2, and NaAsSe2. We find that the magnitudes of the photovoltaic responses in the visible range for these compounds exceed the maximum response obtained for BiFeO3 by 10-20 times. We correlate the high shift current response with the existence of p states at both the valence and conduction band edges, as well as the dispersion of these bands, while also showing that high polarization is not a requirement. With low experimental band gaps of less than 2 eV and high shift current response, these materials have potential for use as bulk photovoltaics. PMID:25429954

Brehm, John A; Young, Steve M; Zheng, Fan; Rappe, Andrew M

2014-11-28

317

Influence of impurities on the thermoelectric properties of layered anisotropic PbBi{sub 4}Te{sub 7} compound: Experiment and calculations  

SciTech Connect

The kinetic coefficients of high-quality single crystals of ternary layered n-PbBi{sub 4}Te{sub 7} compounds have been measured in the temperature range of 77-400 K. These crystals, doped with electroactive Cd and Ag impurities, were grown by Czochralski pulling with melt supply through a floating crucible. A significant anisotropy of the thermoelectric properties is found. The means of incorporation of electroactive impurities into the ternary compound lattice is established. The experimental values of the Nernst-Ettingshausen coefficient have been analyzed together with the Seebeck, Hall, and conductivity data. The features of transport phenomena in PbBi{sub 4}Te{sub 7} can be explained within the single-band model of nonparabolic energy spectrum and mixed mechanism of electron scattering from acoustic phonons and the Coulomb potential of impurities. It is suggested that acoustic phonon scattering is dominant along the cleavage plane, whereas the impurity scattering dominates along the trigonal axis.

Zhitinskaya, M. K., E-mail: m_zhitinskaya@mail.ru; Nemov, S. A.; Muhtarova, A. A. [St. Petersburg State Politechnical University (Russian Federation); Shelimova, L. E.; Svechnikova, T. E. [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation); Konstantinov, P. P. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2010-06-15

318

Electronic, optical properties and chemical bonding in six novel 1111-like chalcogenide fluorides AMChF (A=Sr, Ba; M=Cu, Ag; and Ch=S, Se, Te) from first principles calculations  

SciTech Connect

Employing first-principles band structure calculations, we have examined the electronic, optical properties and the peculiarities of the chemical bonding for six newly synthesized layered quaternary 1111-like chalcogenide fluorides SrAgSF, SrAgSeF, SrAgTeF, BaAgSF, BaAgSeF, and SrCuTeF, which are discussed in comparison with some isostructural 1111-like chalcogenide oxides. We found that all of the studied phases AMChF (A=Sr, Ba; M=Cu, Ag; and Ch=S, Se, Te) are semiconductors for which the fitted 'experimental' gaps lie in the interval from 2.23 eV (for SrAgSeF) to 3.07 eV (for SrCuTeF). The near-Fermi states of AMChF are formed exclusively by the valence orbitals of the atoms from the blocks (MCh); thus, these phases belong to the layered materials with 'natural multiple quantum wells'. The bonding in these new AMChF phases is described as a high-anisotropic mixture of ionic and covalent contributions, where ionic M-Ch bonds together with covalent M-Ch and Ch-Ch bonds take place inside blocks (MCh), while inside blocks (AF) and between the adjacent blocks (MCh)/(AF) mainly ionic bonds emerge. - Graphical Abstract: Isoelectronic surface for SrAgSeF and atomic-resolved densities of states for SrAgTeF, and SrCuTeF. Highlights: Black-Right-Pointing-Pointer Very recently six new layered 1111-like chalcogenide fluorides AMChF were synthesized. Black-Right-Pointing-Pointer Electronic, optical properties for AMChF phases were examined from first principles. Black-Right-Pointing-Pointer All these materials are characterized as non-magnetic semiconductors. Black-Right-Pointing-Pointer Bonding is highly anisotropic and includes ionic and covalent contributions. Black-Right-Pointing-Pointer Introduction of magnetic ions in AMChF is proposed for search of novel magnetic materials.

Bannikov, V.V.; Shein, I.R. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation)] [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation); Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation)

2012-12-15

319

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

NASA Astrophysics Data System (ADS)

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

Kashi, Siamak

320

De Haas-van Alphen oscillations in the charge-density wave compound lanthanum tritelluride (LaTe3)  

SciTech Connect

De Haas-van Alphen oscillations were measured in lanthanum tritelluride (LaTe{sub 3}) to probe the partially gapped Fermi surface resulting from charge density wave (CDW) formation. Three distinct frequencies were observed, one of which can be correlated with a FS sheet that is unaltered by CDW formation. The other two frequencies arise from FS sheets that have been reconstructed in the CDW state.

Ru, N.; /Stanford U., Geballe Lab.; Borzi, R.A.; Rost, A.; Mackenzie, A.P.; /St. Andrews U., Phys. Astron.; Laverock, J.; Dugdale, S.B.; /Bristol U.; Fisher, I.R.; /Stanford U., Geballe Lab.

2009-12-14

321

Optical and structural properties of nanostructured CuIn0.7Ga0.3(Se(1-x)Te(x))2 chalcopyrite thin films--effect of stoichiometry and annealing.  

PubMed

The aim of this work was to study the dependence of the optical, structural and morphological properties of CuIn0.7Ga0.3(Se(1-x)Te(x))2 (briefly CIGSeTe) thin films for two different stoichiometries (for x = 0.2 and 0.8). The films have been deposited onto soda lime glass (SLG) substrates by the e-beam evaporation technique. The films showed high absorption and revealed optical band gaps ranging from 1.17 eV to 1.06 eV for x = 0 with highest annealing temperatute at 525 degrees C and 1.12 eV to 1.02 eV for x = 0.8 and with highest annealed temperature at 600 degrees C. These results were correlated with the microstructural analysis by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray diffractometry (XRD). The linear dependence of the lattice parameters as a function of Se and Te contents was examined. X-ray diffraction analyses showed that the films had the single phase chalcopyrite structure. The lattice parameters (a and c) varied linearly with the increase in Te content x from x = 0.2 to x = 0.8. The peak correspondng to the (1 1 2) plane orientation of the films increased with annealing process. Also, SEM images showed that both the grains size and the RMS (root mean square) values increased with annealing and higher Te amount that caused grains aggregation. The relative 600 degrees C elemental composition present in the deposited CIGS films have been measured by using energy dispersive X-ray analysis (EDX). PMID:24757973

Fiat, Songül; Polat, Ismail; Bacaksiz, Emin; Cankaya, Güven; Koralli, Panagiota; Manolakos, Demitrios E; Kompitsas, Michael

2014-07-01

322

The effect of lithium intercalation on the electronic structure of the ternary compound semiconductors ZrSe2-xSx  

NASA Astrophysics Data System (ADS)

The electronic properties of the lithium intercalated layered transition metal dichalcogenide semiconductors ZrSxSe2-x for x = 0-2 have been calculated by density functional theory (DFT) using the WIEN2k code. The calculations have been carried out by the PBE functional and the TB-MBJ potential as proposed by Tran and Blaha. The calculations have been performed with and without spin-orbit coupling and reveal that the intercalation of lithium causes the conduction bands of LiZrSxSe2-x to shift by about 2 eV towards lower binding energy. From this, a Fermi level crossing and metallic behavior in the three intercalated compounds result. Moreover, a number of trends can be observed. Due to the contributions of the dichalcogenide p-states in the valence band the inclusion of SO coupling in the calculations lifts the degeneracy at the points ? and A of the Brillouin zone in the same way as in the parent compounds. With regard to crystal field effects for each compound the splitting is larger at the A point than at the ? point and the absolute value of the splitting increases with the atomic number of the chalcogenide. In particular, the simple Fermi surface consisting solely of barrels centered along the LML line makes LiZrSxSe2-x a promising Fermi liquid reference compound.

Ghafari, A.; Janowitz, C.; Manzke, R.

2013-08-01

323

Structural evolvement and thermoelectric properties of Cu3-xSnxSe3 compounds with diamond-like crystal structures.  

PubMed

Polycrystalline samples of Cu3-xSnxSe3 were synthesized in the composition range x = 0.87-1.05. A compositionally induced evolvement from tetragonal via cubic to monoclinic crystal structures is observed, when the composition changes from a Cu-rich to a Sn-rich one. The Cu3-xSnxSe3 materials show a metal-to-semiconductor transition with increasing x. Electronic transport properties are governed by the charge-carrier concentration which is well described by a linear dispersion-band model. The lattice component of the thermal conductivity is practically independent of x which is attributed to the opposite influence of the atomic ordering and the inhomogeneous distribution of the Cu-Se or Sn-Se bonds with different polarities in the crystal structure. The highest thermoelectric figure of merit ZT of 0.34 is achieved for x = 1.025 at 700 K. PMID:25286143

Fan, Jing; Schnelle, Walter; Antonyshyn, Iryna; Veremchuk, Igor; Carrillo-Cabrera, Wilder; Shi, Xun; Grin, Yuri; Chen, Lidong

2014-10-22

324

Structural Changes in Pulsed Laser Ablated CuInSe2 Compound STRUKTUR?L?S IZMAI?AS Impulsa L?ZERA ABL?TAJ? CuInSe2 SAVIENOJUM?  

NASA Astrophysics Data System (ADS)

CuInSe2 (CISe) compound was produced by high-temperature synthesis. After mechanical milling, the average CISe particle size decreased to 10?m. The authors study structural changes of the compound after ablation in liquid by a 1064 nm pulsed laser. The SEM examination indicated the presence of spherical particles with the average size of ~ 450 nm. A nonlinear relationship was established between the laser radiation dose and the quantity of spherical particles. The XRD analysis has shown an improvement in the CISe crystalline structure and the absence of significant changes in its stoichiometry. The 3 ?m thick experimental CISe samples were screen-printed on planar Ni electrodes, and improvement also was revealed in their photosensitivity. The conclusion is that the pulsed-laser ablation can be applied to chalcopyrite structures like CISe without destruction of their initial properties. Darba autori apskata impulsa l?zera abl?cijas pielietojuma iesp?ju CuInSe2 savienojumam. Eksperimentu gait? tika konstat?ts, ka abl?cijas proces? CuInSe2 vid? veidojas sf?riskas formas da?i?as, kuru izm?ri ir atkar?gi no l?zera starojuma parametriem un no vides ?paš?b?m. Apstarot? materi?la anal?ze uzr?d?ja CuInSe2 strukt?ras kvalit?tes uzlabojumus, k? ar? gaismj?t?bas palielin?šanos par 8%, sal?dzin?jum? ar neapstarotu materi?lu. Darba rezult?ti liecina par to, ka, mainot l?zera starojuma parametrus, ir iesp?jams uzlabot CuInSe2 savienojumu, nesagraujot t? darba ?paš?bas. Aprakst?t?s eksperiment?l?s metodes un tehnolo?ijas sniedz plašu darb?bas lauku t?l?kiem p?t?jumiem šaj? jom?.

Ogurcovs, A.; Gerbreders, V.; Tamanis, E.; Sledevskis, E.; Gerbreders, A.

2013-12-01

325

Magnetic, structural, and electronic properties of the multiferroic compound FeTe?O?Br with geometrical frustration.  

PubMed

We report electron spin resonance (ESR), Raman scattering, and interband absorption measurements of the multiferroic FeTe?O?Br with two successive magnetic transitions at T(N1) = 11.0 K and T(N2) = 10.5 K. ESR measurements show all characteristics of a low-dimensional frustrated magnet: (i) the appearance of an antiferromagnetic resonance (AFMR) mode at 40 K, a much higher temperature than T(N1), and (ii) a weaker temperature dependence of the AFMR linewidth than in classical magnets, ?H(pp)(T) ? T(n) with n = 2.2-2.3. Raman spectra at ambient pressure show a large variation of phonon intensities with temperature while there are no appreciable changes in phonon numbers and frequencies. This demonstrates the significant role of the polarizable Te?? lone pairs in inducing multiferroicity. Under pressure at P = 2.12-3.04 GPa Raman spectra undergo drastic changes and absorption spectra exhibit an abrupt drop of a band gap. This evidences a pressure-induced structural transition related to changes of the electronic states at high pressures. PMID:24501196

Choi, K-Y; Choi, I H; Lemmens, P; van Tol, J; Berger, H

2014-02-26

326

Pressure dependence of the optical properties of the charge-density-wave compound LaTe2  

SciTech Connect

We report the pressure dependence of the optical response of LaTe{sub 2}, which is deep in the charge-density-wave (CDW) ground state even at 300 K. The reflectivity spectrum is collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 7 GPa. We extract the energy scale due to the single particle excitation across the CDW gap and the Drude weight. We establish that the gap decreases upon compressing the lattice, while the Drude weight increases. This signals a reduction in the quality of nesting upon applying pressure, therefore inducing a lesser impact of the CDW condensate on the electronic properties of LaTe{sub 2}. The consequent suppression of the CDW gap leads to a release of additional charge carriers, manifested by the shift of weight from the gap feature into the metallic component of the optical response. On the contrary, the power-law behavior, seen in the optical conductivity at energies above the gap excitation and indicating a weakly interacting limit within the Tomonaga-Luttinger liquid scenario, seems to be only moderately dependent on pressure.

Lavagnini, M.; Sacchetti, A.; Degiorgi, L.; /Zurich, ETH; Arcangeletti, E.; Baldassarre, L.; Postorino, P.; Lupi, S.; /Rome U.; Perucchi, A.; /INFM, Trieste; Shin, K.Y.; Fisher, I.R.; /Stanford U., Geballe Lab.

2009-12-14

327

Reactivities of the chalcogen-capped triiron clusters [EFe 3(CO) 9] 2– (E = Te, Se, S): cluster growth and transformations  

Microsoft Academic Search

Transition-metal carbonyl clusters incorporated with chalcogen elements are of particular interests due to their structural and chemical diversity. Up to now, quite a large number of chalcogen-containing iron carbonyl clusters have been synthesized and structurally characterized. In this short review, we will describe our recent developments on the interesting cluster expansions and transformations of the chalcogen-capped triiron clusters [EFe3(CO)9]2– (E=Te,

Minghuey Shieh; Chia-Hua Ho

2005-01-01

328

Isotropic superconducting gaps with enhanced pairing on electron Fermi surfaces in FeTe0.55Se0.45  

NASA Astrophysics Data System (ADS)

We used angle-resolved photoemission spectroscopy to reveal directly the momentum distribution of the superconducting gap in FeTe1-xSex, which has the simplest structure of all Fe-based superconductors. We found isotropic superconducting gaps on all Fermi surfaces whose sizes can be fitted by a single gap function derived from a strong coupling approach, promoting local antiferromagnetic exchange interactions as a serious candidate for the pairing origin.

Miao, H.; Richard, P.; Tanaka, Y.; Nakayama, K.; Qian, T.; Umezawa, K.; Sato, T.; Xu, Y.-M.; Shi, Y. B.; Xu, N.; Wang, X.-P.; Zhang, P.; Yang, H.-B.; Xu, Z.-J.; Wen, J. S.; Gu, G.-D.; Dai, X.; Hu, J.-P.; Takahashi, T.; Ding, H.

2012-03-01

329

Influence of the chalcogen substitution on the character of magnetic ordering in Fe0.5TiS2 - x Se x intercalated compounds  

NASA Astrophysics Data System (ADS)

The crystal structure and magnetic properties of layered Fe0.5TiS2 - x Se x (0 ? x ? 2) compounds intercalated by iron atoms have been investigated. It has been shown that the substitution of selenium for sulfur is accompanied by an increase in the unit cell volume, a transition from the ferromagnetic to antiferromagnetic behavior, and a nonmonotonic variation in the paramagnetic Curie temperature. The intercalated iron atoms are characterized by lower values of the effective moment (3.4-4.0?B) as compared to the predicted value (4.89?B) for the Fe2+ ion at g = 2. The results obtained have been discussed under the assumption that there are the hybridization of 3 d electronic states of intercalated Fe atoms with the electronic states of the TiS2 - x Se x host compounds and the competition of exchange interactions of different types.

Baranov, N. V.; Pleshchev, V. G.; Sherokalova, E. M.; Selezneva, N. V.; Volegov, A. S.

2011-04-01

330

Room temperature synthesis of nanostructured mixed-ordered-vacancy compounds (OVCs) and chalcopyrite CuInSe2 (CIS) thin films in alkaline chemical bath  

Microsoft Academic Search

Room temperature synthesis of ordered-vacancy-compounds (OVCs) and copper indium diselenide (CuInSe2, CIS) by cation and anion exchange reactions of solid CdS thin films with CIS ionic solution in an alkaline chemical bath is reported. The growth parameters such as pH, deposition time and concentration of the solutions were optimized to achieve uniform thin films. Nanostructured CdS thin films (150 nm

Ramphal Sharma; Rajaram S Mane; Gangri Cai Anil Ghule; Duk-Ho Ham; Sun-Ki Min; Seung-Eon Lee; Sung-Hwan Han

2009-01-01

331

First principles determination of vibrational and elastic properties of quaternary compounds Cu2ZnSnS4 and Cu2ZnSnSe4  

Microsoft Academic Search

Recently, the quaternary compounds, Cu2ZnSnS4 and Cu2ZnSnSe4, have been attracted pretty much attention because of their potential use in the field of energy harvesting applications. Several theoretical calculations have been reported about their first principles electronic, optic and transport properties. However, no lattice dynamic calculations have been published yet despite the discussions about their possible ground state crystal structures and

Tanju Gurel; Cem Sevik; Tahir Cagin

2011-01-01

332

Single crystal growth of Ga[subscript 2](Se[subscript x]Te[subscript 1;#8722;x])[subscript 3] semiconductors and defect studies via positron annihilation spectroscopy  

SciTech Connect

Small single crystals of Ga{sub 2}(Se{sub x}Te{sub 1-x}){sub 3} semiconductors, for x = 0.1, 0.2, 0.3, were obtained via modified Bridgman growth techniques. High resolution powder x-ray diffractometry confirms a zincblende cubic structure, with additional satellite peaks observed near the (111) Bragg line. This suggests the presence of ordered vacancy planes along the [111] direction that have been previously observed in Ga{sub 2}Te{sub 3}. Defect studies via positron annihilation spectroscopy show an average positron lifetime of {approx} 400 ps in bulk as-grown specimens. Such a large lifetime suggests that the positron annihilation sites in these materials are dominated by defects. Moreover, analyzing the electron momenta via coincidence Doppler broadening measurements suggests a strong presence of large open-volume defects, likely to be vacancy clusters or voids.

Abdul-Jabbar, N.M.; Bourret-Courchesne, E.D.; Wirth, B.D. (UCB); (Tennessee-K); (LBNL)

2012-12-10

333

Magnetothermoelectric effects in Fe1+dTe1-xSex  

NASA Astrophysics Data System (ADS)

We report data on resistivity as well as Hall, Seebeck and Nernst coefficients for the Fe1+dTe1-xSex single crystals with x = 0, 0.39, and 0.40. The parent compound Fe1.04Te exhibits a Fermi surface reconstruction at T = 61 K, which is ascribed to the onset of the antiferromagnetic order. Two very closely doped samples: Fe1.01Se0.39Te0.61 (Se39) and Fe1.01Se0.4Te0.6 (Se40) are superconductors with Tc = 13.4 K and 13.9 K, respectively. Properties of these two single crystals are almost identical at high temperatures, but start to diverge below T 80 K. Despite there is no magnetic transition in neither Se39 nor Se40, the observed differences seem to be a consequence of varying with selenium content spin correlations.

Matusiak, Marcin; Conder, Kazimierz

2012-02-01

334

Computational Nano-materials Design of Self-Organized Cd(Te,S) and Cd(Te,Se)Type II Nanowire (Konbu-Phase) by Spinodal Nano-Decomposition for High-Efficiency Photovoltaic Solar-Cells  

NASA Astrophysics Data System (ADS)

Based on multi-scale simulations combined ab initio electronic structure calculation (KKR-CPA) and Monte Carlo simulation (MCS) of the two-dimensional layer-by-layer crystal growth, we have designed the self-organized quasi-one-dimensional nano-structures (Konbu-Phase) fabricated by two-dimensional spinodal nano-decomposition for high-efficiency photovoltaic solar cells (PVSCs) in Cd(Te1-xSx), and Cd(Te1-xSex). The Konbu-Phase enhances the nano-scale electron-hole separation in PVSCs due to their Type II band alignment. The Konbu-Phase also increases the efficiency of PVSCs by multi-exciton formation using the inverse Auger effect in the self-organized quasi-one-dimensional nanostructures. We also discuss how to fabricate Konbu-Phase starting from the uniform nano-particles made by the photo-chemical reactions. Reference: M. Oshitani, K. Sato, H. Katayama-Yoshida, Applied Physics Express 4 (2011) 022302.

Katayama-Yoshida, Hiroshi; Oshitani, Masamune; Sato, Kazunori

2012-02-01

335

Enhancement of singlet oxygen production based on FRET between Coumarin tri-compound and CdSe/ZnS QDs  

NASA Astrophysics Data System (ADS)

The compatibility between coumarin-derived dendrimer (CdD)-captured silica particles (SiCdDs) and watersoluble CdSe/ZnS quantum dots (QDs) in the FRET process improved the excited state of QDs in the reaction of singlet oxygen production under LED irradiation. Sol-gel GA was successfully used to improve the binding between SiCdDs and QDs. Singlet oxygen production using QDs coated with SiCdDs through sol-gel GA was enhanced by about 80 % compared to that achieved using QDs only. The single oxygen produced by the QDs, the QDs/GA-SiCdDs complexes and the SiCdDs/GA-QDs complexes in this study could be used in the treatment of HeLa cells.

Duong, Hong Dinh; Lee, Jee Won; Rhee, Jong Il

2014-08-01

336

Analysis of the electrodeposition and surface chemistry of CdTe, CdSe, and CdS thin films through substrate-overlayer surface-enhanced Raman spectroscopy.  

PubMed

The substrate-overlayer approach has been used to acquire surface enhanced Raman spectra (SERS) during and after electrochemical atomic layer deposition (ECALD) of CdSe, CdTe, and CdS thin films. The collected data suggest that SERS measurements performed with off-resonance (i.e. far from the surface plasmonic wavelength of the underlying SERS substrate) laser excitation do not introduce perturbations to the ECALD processes. Spectra acquired in this way afford rapid insight on the quality of the semiconductor film during the course of an ECALD process. For example, SERS data are used to highlight ECALD conditions that yield crystalline CdSe and CdS films. In contrast, SERS measurements with short wavelength laser excitation show evidence of photoelectrochemical effects that were not germane to the intended ECALD process. Using the semiconductor films prepared by ECALD, the substrate-overlayer SERS approach also affords analysis of semiconductor surface adsorbates. Specifically, Raman spectra of benzenethiol adsorbed onto CdSe, CdTe, and CdS films are detailed. Spectral shifts in the vibronic features of adsorbate bonding suggest subtle differences in substrate-adsorbate interactions, highlighting the sensitivity of this methodology. PMID:25105710

Gu, Junsi; Fahrenkrug, Eli; Maldonado, Stephen

2014-09-01

337

Lattice location and local magnetism of recoil implanted Fe impurities in wide and narrow band semiconductors CdTe, CdSe, and InSb: Experiment and theory  

NASA Astrophysics Data System (ADS)

Employing the time differential perturbed angular distribution method, we have measured local susceptibility and spin relaxation rate of 54Fe nuclei implanted in III-V and II-VI semiconductors, CdTe, CdSe, and InSb. The magnetic response of Fe, identified to occupy the metal as well as the semi-metal atom sites, exhibit Curie-Weiss type susceptibility and Korringa like spin relaxation rate, revealing the existence of localized moments with small spin fluctuation temperature. The experimental results are supported by first principle electronic structure calculations performed within the frame work of density functional theory.

Mohanta, S. K.; Mishra, S. N.

2014-05-01

338

Synthesis of U3Se5 and U3Te5 type polymorphs of Ta3N5 by combining high pressure-temperature pathways with a chemical precursor approach.  

PubMed

Combining metastable precursors with high pressure-temperature treatment is a powerful tool to make nitrogen-rich metal nitrides. Two new dense polymorphs of Ta3N5 have previously been theoretically predicted, with U3Se5 (Pnma) and U3Te5 (Pnma) structure types, and are now shown to exist. Amorphous Ta3N5 from thermal ammonolysis of an amorphous polymeric precursor was laser heated at 22 GPa and examined using synchrotron X-ray diffraction to reveal the emergence of these two novel polymorphs. PMID:25051155

Salamat, Ashkan; Woodhead, Katherine; Shah, S Imran U; Hector, Andrew L; McMillan, Paul F

2014-09-11

339

Electron and Hole Injection via Charge Transfer at the Topological-Insulator $Bi_{2-x}Sb_xTe_{3-y}Se_y$/Organic-Molecule Interface  

E-print Network

As a methodology for controlling the carrier transport of topological insulators (TI's), a flexible tuning in carrier number on the surface states (SS's) of three dimensional TI's by surface modifications using organic molecules is described. The principle of the carrier tuning and its type conversion of TI's presented in this research are based on the charge transfer of holes or electrons at the TI/organic molecule interface. By employing 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) as an electron acceptor or tetracyanoquinodimethane (TCNQ) as a donor for n- and p- Bi2-xSbxTe3-ySey (BSTS) single crystals, successful carrier conversion from n to p and its reverse mode is demonstrated depending on the electron affinities of the molecules. The present method provides a nondestructive and efficient method for local tuning in carrier density of TI's, and is useful for future applications.

Tanabe, Yoichi; Nouchi, Ryo; Heguri, Satoshi; Mu, Gang; Xu, Jingtao; Shimotani, Hidekazu; Tanigaki, Katsumi

2014-01-01

340

compounds  

NASA Astrophysics Data System (ADS)

Size is the key factor of nanostructured materials, since all the structural, transport, electrical, magnetic and other physical properties can be tuned by this factor of materials. Only the condition is to choose appropriate inexpensive scale-processing method for material synthesis which offers good control over the stoichiometry, morphology and particle size distribution. Present communication deals with the studies on the sol-gel grown Y0.95Ca0.05MnO3 (YCMO) nanostructured compounds for their size-induced tuning of dielectric behavior. Structural studies reveal the single phasic nature with improved crystallite size with sintering temperature. Dielectric constant (real and imaginary) is found to increase with temperature and crystallite size/sintering temperature. High dielectric loss has been observed in the present system. Size dependent activation energy ( E a), obtained from modulus measurement, showing the increase in E a with crystallite size. The variation in various dielectric parameters and E a has been discussed in the light of crystallite size, crystallite boundaries, oxygen vacancies and charge carrier hopping.

Shah, N. A.

2014-10-01

341

The antitumor effects of selenium compound Na5SeV5O18.3H20 in K562 cell.  

PubMed

With an approach to study the anti-tumor effects and mechanism of selenium compound, we investigated the anti-tumor activity and mechanism of Na5SeV5O18.H20 (NaSeVO) in K562 cells. The results showed that 0.625-20 mg/L NaSeVO could significantly inhibit the proliferation of K562 cells in vitro in a time- and concentration-dependent manner as determined by microculture tetrazolium (MTT) assay, the IC50 values were 14.41 (4.45-46.60) and 3.45 (2.29-5.22) mg/L after 48 h and 72 h treatment with NaSeVO respectively. In vivo experiments demonstrated that i.p. administration of 5, 10 mg/kg NaSeVO exhibited an significant inhibitory effect on the growth of transplantation tumor sarcoma 180 (S180) and hepatoma 22 (H22) in mice, with inhibition rate 26.8% and 58.4% on S180 and 31.3% and 47.4% on H22, respectively. Cell cycle studies indicated that the proportion of G0/G1 phase was increased at 2.5 mg/ L while decreased at 10 mg/L after treatment for 24, 48 h. Whereas S phase was decreased at 2.5-5 mg/L and markedly increased at 10 mg/L after treatment for 48 h. After treatment for 24 h, 10 mg/L NaSeVO also markedly increased S and G2/M phases. Take together, the result clearly showed that NaSeVO markedly increased S and G2/M phases at 10 mg/L. The study of immunocytochemistry showed that the expression bcl-2 is significantly inhibited by 10 mg/L NaSeVO, and bax increased. Morphology observation also revealed typical apoptotic features. NaSeVO also significantly caused the accumulation of Ca2+ and Mg2+, reactive oxygen species (ROS) and the reduction of pH value and mitochondrial membrane potential in K562 cells as compared with control by confocal laser scanning microscope. These results suggest that NaSeVO has anti-tumor effects and its mechanism is attributed partially to apoptosis induced by the elevation of intracellular Ca2+, Mg2+ and ROS concentration, and a reduction of pH value and mitochondria membrane potential (MMP). PMID:17121180

Yang, Jun-Ying; Wang, Zi-Ren

2006-10-01

342

Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3}  

SciTech Connect

Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe{sub 2.7}Se{sub 0.3} and p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications.

Bhame, Shekhar D.; Noudem, Jacques G. [Laboratoire CRISMAT, CNRS UMR 65086, ENSICAEN, 6 Bld., Marechal Juin, 14050 Caen (France) [Laboratoire CRISMAT, CNRS UMR 65086, ENSICAEN, 6 Bld., Marechal Juin, 14050 Caen (France); LUSAC (EA 2607), Universite de Caen, Basse Normandie (UCBN), BP 78, 50130 Cherbourg Octeville (France); Pravarthana, Dhanapal; Prellier, Wilfrid [Laboratoire CRISMAT, CNRS UMR 65086, ENSICAEN, 6 Bld., Marechal Juin, 14050 Caen (France)] [Laboratoire CRISMAT, CNRS UMR 65086, ENSICAEN, 6 Bld., Marechal Juin, 14050 Caen (France)

2013-05-27

343

Electrical Detection of the Spin Polarization Due to Charge Flow in the Surface State of the Topological Insulator Bi1.5Sb0.5Te1.7Se1.3.  

PubMed

We detected the spin polarization due to charge flow in the spin nondegenerate surface state of a three-dimensional topological insulator by means of an all-electrical method. The charge current in the bulk-insulating topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was injected/extracted through a ferromagnetic electrode made of Ni80Fe20, and an unusual current-direction-dependent magnetoresistance gave evidence for the appearance of spin polarization, which leads to a spin-dependent resistance at the BSTS/Ni80Fe20 interface. In contrast, our control experiment on Bi2Se3 gave null result. These observations demonstrate the importance of the Fermi-level control for the electrical detection of the spin polarization in topological insulators. PMID:25330016

Ando, Yuichiro; Hamasaki, Takahiro; Kurokawa, Takayuki; Ichiba, Kouki; Yang, Fan; Novak, Mario; Sasaki, Satoshi; Segawa, Kouji; Ando, Yoichi; Shiraishi, Masashi

2014-11-12

344

Advanced processing of CdTe- and CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2}-based solar cells. Phase 1 annual subcontract report, 18 April 1995--17 April 1996  

SciTech Connect

The main objective of this project to develop high-efficiency CdTe solar cells based on processing conditions favorable for manufacturing processes. This report presents the results on work performed during the first phase of this project. One of the major issues addressed is the use of soda-lime glass substrates in place of the borosilicate glass often used for laboratory devices; another task is the preparation of Cu(In, Ga) Se{sub 2} solar cells by selenizing suitable precursor films. Emphasis is placed on processing and how different reaction schemes affect device performance. It was found that different reaction schemes not only change the bulk properties of Cu(In, Ga) Se{sub 2}, but also its surface properties, which critically affect device performance. Although the objective is to optimize processing to meet the manufacturing constraints, work has not been limited within these requirements.

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

1997-03-01

345

First-Principles Studies on Cd Doping in CuInSe2 and Related Compounds during Chemical Bath Deposition of CdS Buffer Layer  

NASA Astrophysics Data System (ADS)

First-principles calculations using plane-wave basis functions were performed to quantitatively evaluate the substitution energies of Cd atom for Cu atom and for In atoms in chalcopyrite-type CuInSe2 (CIS) and related compounds, CuGaSe2 (CGS) and CuAlSe2 (CAS). The substitution energies of Cd atoms in CIS and the related compounds were calculated in considering of the atomic chemical potentials of the constituent elements of Cu and In, and doping Cd atoms. During the chemical bath deposition (CBD) of the CdS layer on the CIGS layer, Cu and Cd atoms dissolved in the ammonia aqueous solution and formed [Cu(NH3)2]+ and [Cd(NH3)4]2+ complex ions. Therefore, the chemical potentials of Cu and Cd atoms in [Cu(NH3)2]+ and [Cd(NH3)4]2+ complex ions were calculated. We found that the substitution energy of n-type CdCu is smaller than that of p-type CdIn. The substitution energy of CdCu in CIS is smaller than those in CGS and CAS. However, the substitution energies of CdCu and CdIn in CIS are positive values. The formation energy of charge-neutral Cd doping with the Cu vacancy (CdCu+VCu) pair is a negative value and greatly smaller than those of n-type CdCu in CIS, CGS, and CAS. These results indicate that the charge-neutral (CdCu+VCu) vacancy pair is easily formed during the CBD of the CdS layer on the CIS layer and a small amount of n-type CdCu would also be formed.

Maeda, Tsuyoshi; Wada, Takahiro

2013-06-01

346

Oswald ripening and shape transitions of self-assembled PbSe quantum dots on PbTe (111) during annealing  

Microsoft Academic Search

The thermal stability of faceted self-assembled PbSe quantum dots during annealing is investigated. With increasing annealing time, the dot density is found to decrease rapidly with a simultaneous increase of the average island volumes. In addition, a shape transition from pyramidal islands to truncated pyramids is observed for islands exceeding a critical height of 160 Å. The evolution of island

A. Raab; G. Springholz

2000-01-01

347

Periodic hexagonal mesostructured chalcogenides based on platinum and [SnSe4]4- and [SnTe4]4- precursors. Solvent dependence of nanopore and wall organization.  

PubMed

Mesostructured chalcogenide-based materials with long-range order and semiconducting properties can be prepared using suitable molecular building blocks, linkage metal ions and surfactant molecules. In this paper we present surfactant templated, open framework platinum tin selenide and telluride materials assembled using K4SnQ4 (Q = Se, Te) salts and K2PtCl4 as precursors and a study of pore and wall organization. We find that materials prepared in water exhibit disordered pore organization, whereas those prepared in formamide are long-range ordered with hexagonal symmetry. In formamide the [SnQ4]4- anions undergo condensation-oligomerization reactions that produce different chalcogenido molecular species, whereas in water the anions remain intact. In addition to solvent, the pore organization and overall quality of the mesostructured materials strongly depend on the surfactant molecules, i.e., chain length and headgroup size. For example, highly ordered mesostructured platinum tin selenides with hexagonal symmetry were obtained using the hydroxyl-functionalized surfactants CnH2n+1N(CH3)(CH2CH2OH)2Br (n = 16, 18, and 20), but when the headgroup was triethylammonium, hexagonal pore order was achieved only for n = 20 and not for n = 16 and 18. The experimental results imply that in order to achieve highly ordered chalcogenide frameworks a single building anionic block might be insufficient. Finally, we also report the first examples of hexagonal mesostructured Pt/Sn/Te materials based on K4SnTe4 as the precursor. The tellurides behave differently for their selenium analogues and have very low energy band gaps, in the range 0.5-0.7 eV. PMID:15771527

Trikalitis, Pantelis N; Bakas, Thomas; Kanatzidis, Mercouri G

2005-03-23

348

Effect of disorder in the charge-density-wave compounds LaTe1.95 and CeTe1.95-xSex (x=0 and 0.16) as revealed by optical spectroscopy  

NASA Astrophysics Data System (ADS)

We present optical spectroscopy measurements on rare-earth ditelluride single crystals of LaTe1.95 and CeTe1.95-xSex (x=0 and 0.16). The measurements reveal formation of charge-density-wave energy gaps at rather high-energy levels, for example, 2?˜8500 cm-1 for LaTe1.95 and 6800 cm-1 for CeTe1.95. More strikingly, the study reveals that, different from the rare-earth tritellurides, the Te vacancies and disorder effect play a key role in the low-energy charge excitations of ditelluride systems. Although an eminent peak is observed between 800 and 1500 cm-1 in conductivity spectra for LaTe1.95, and CeTe1.95-xSex (x=0 and 0.16), our analysis indicates that it could not be attributed to the formation of a small energy gap, instead it could be well accounted for by the localization modified Drude model. Our study also indicates that the low-temperature optical spectroscopic features are distinctly different from a semiconducting charge-density-wave (CDW) state with entirely gapped Fermi surfaces.

Huang, Y.; Hu, B. F.; Dong, T.; Fang, A. F.; Zheng, P.; Wang, N. L.

2012-11-01

349

Crystallographic site swapping of La3+ ion in BaA'LaTeO6 (A' = Na, K, Rb) double perovskite type compounds: diffraction and photoluminescence evidence for the site swapping.  

PubMed

Double perovskite type compounds of the formula BaA'LaTeO6 (A' = Na, K, Rb) were synthesized by solid state route and their crystal structures were determined by Rietveld analysis using powder X-ray diffraction and neutron diffraction data. Na compound crystallizes in the monoclinic system with P2?/n space group whereas, K and Rb compounds crystallize in Fm3m space group. All the three compounds show rock salt type ordering at B site. Crystal structure analysis shows that La ion occupies A site in Na compound whereas, it occupies B site in K and Rb compounds according to the general formula of AA'BB'O6 for a double perovskite type compound. Effect of this crystallographic site swapping of the La ion was also observed in the photoluminescence study by doping Eu(3+) in La(3+) site. The large decrease in the intensity of the electric dipole ((5)D0-(7)F2) transition in the Rb compound compared to the Na compound indicates that Eu(3+) ion resides in the centrosymmetric octahedral environment in the Rb compound. PMID:24363108

Phatak, R; Gupta, S K; Krishnan, K; Sali, S K; Godbole, S V; Das, A

2014-02-28

350

High-pressure optical and vibrational properties of CdGa2Se4: Order-disorder processes in adamantine compounds  

NASA Astrophysics Data System (ADS)

High-pressure optical absorption and Raman scattering measurements have been performed in defect chalcopyrite (DC) CdGa2Se4 up to 22 GPa during two pressure cycles to investigate the pressure-induced order-disorder phase transitions taking place in this ordered-vacancy compound. Our measurements reveal that on decreasing pressure from 22 GPa, the sample does not revert to the initial phase but likely to a disordered zinc blende (DZ) structure the direct bandgap and Raman-active modes of which have been measured during a second upstroke. Our measurements have been complemented with electronic structure and lattice dynamical ab initio calculations. Lattice dynamical calculations have helped us to discuss and assign the symmetries of the Raman modes of the DC phase. Additionally, our electronic band structure calculations have helped us in discussing the order-disorder effects taking place above 6-8 GPa during the first upstroke.

Gomis, O.; Vilaplana, R.; Manjón, F. J.; Pérez-González, E.; López-Solano, J.; Rodríguez-Hernández, P.; Muñoz, A.; Errandonea, D.; Ruiz-Fuertes, J.; Segura, A.; Santamaría-Pérez, D.; Tiginyanu, I. M.; Ursaki, V. V.

2012-01-01

351

X-ray Characterization, Electronic Band Structure, and Thermoelectric Properties of the Cluster Compound Ag2Tl2Mo9Se11.  

PubMed

We report on a detailed investigation of the crystal and electronic band structures and of the transport and thermodynamic properties of the Mo-based cluster compound Ag2Tl2Mo9Se11. This novel structure type crystallizes in the trigonal space group R3?c and is built of a three-dimensional network of interconnected Mo9Se11 units. Single-crystal X-ray diffraction indicates that the Ag and Tl atoms are distributed in the voids of the cluster framework, both of which show unusually large anisotropic thermal ellipsoids indicative of strong local disorder. First-principles calculations show a weakly dispersive band structure around the Fermi level as well as a semiconducting ground state. The former feature naturally explains the presence of both hole-like and electron-like signals observed in Hall effect. Of particular interest is the very low thermal conductivity that remains quasi-constant between 150 and 800 K at a value of approximately 0.6 W·m(-1)·K(-1). The lattice thermal conductivity is close to its minimum possible value, that is, in a regime where the phonon mean free path nears the mean interatomic distance. Such extremely low values likely originate from the disorder induced by the Ag and Tl atoms giving rise to strong anharmonicity of the lattice vibrations. The strongly limited ability of this compound to transport heat is the key feature that leads to a dimensionless thermoelectric figure of merit ZT of 0.6 at 800 K. PMID:25338311

Al Rahal Al Orabi, Rabih; Gougeon, Patrick; Gall, Philippe; Fontaine, Bruno; Gautier, Régis; Colin, Malika; Candolfi, Christophe; Dauscher, Anne; Hejtmanek, Jiri; Malaman, Bernard; Lenoir, Bertrand

2014-11-01

352

Synthesis and multinuclear NMR study ( 1H, 11B, 13C, 14N, 15N, 31P, 77Se) of N-azolyl-phosphorus compounds  

NASA Astrophysics Data System (ADS)

The synthesis of N-azolyl (pyrrole, pyrazole, 1,2,4-triazole) phosphorus compounds containing P III or P V is described. The title compounds were studied by multinuclear NMR ( 1H, 11B, 13C, 14N, 15N, 31P, 77Se) with particular emphasis on [ 15N]NMR parameters. Experimental details are given for the natural abundance [ 15N]NMR spectra and the advantage of the various techniques is discussed. The comparison between values 1J( 31P 15N azole) and 1J( 31P 15N alkyl) shows that the nature of the lone electron pair of the trigonal nitrogen atoms is of minor importance as far as the changes in the magnitude of the coupling constants are concerned. Sterical interactions and inductive effects are reflected by the [ 15N]NMR parameters. Both P III and P V appear to be very weak ?-acceptors as is evident from ? 15N and ? 13C values. P?N( dp)? interactions are hardly reflected by [ 15N]NMR parameters.

Wrackmeyer, Bernd

353

Oswald ripening and shape transitions of self-assembled PbSe quantum dots on PbTe (111) during annealing  

NASA Astrophysics Data System (ADS)

The thermal stability of faceted self-assembled PbSe quantum dots during annealing is investigated. With increasing annealing time, the dot density is found to decrease rapidly with a simultaneous increase of the average island volumes. In addition, a shape transition from pyramidal islands to truncated pyramids is observed for islands exceeding a critical height of 160 Å. The evolution of island volumes and densities is consistent with Oswald ripening by interface-reaction-limited mass transfer. This is a clear indication that the as-grown islands do not represent an equilibrium structure and that their narrow size dispersion is a purely kinetic effect.

Raab, A.; Springholz, G.

2000-11-01

354

A comparative density functional study of the high-pressure phases of solid ZnX, CdX, and HgX (X = S, Se, and Te): Trends and relativistic effects  

NASA Astrophysics Data System (ADS)

The pressure dependence of bulk properties for the group 12 chalcogenides MX (M = Zn, Cd, Hg; X = S, Se, Te) from density functional theory are presented. Energy-volume and corresponding enthalpy-pressure relationships are determined to obtain the transition paths and properties of various high-pressure phases. The influence of relativistic effects is discussed with the aim to explain the unique behavior of the mercury chalcogenides as compared to the lighter zinc and cadmium homologs at high pressures. The neglect of relativistic effects leads to a more CdX like behavior of the mercury chalcogenides, and the pronounced change in coordination of the cinnabar phase at high pressures is due to relativistic effects.

Biering, S.; Schwerdtfeger, P.

2012-07-01

355

A comparative density functional study of the high-pressure phases of solid ZnX, CdX, and HgX (X = S, Se, and Te): trends and relativistic effects.  

PubMed

The pressure dependence of bulk properties for the group 12 chalcogenides MX (M = Zn, Cd, Hg; X = S, Se, Te) from density functional theory are presented. Energy-volume and corresponding enthalpy-pressure relationships are determined to obtain the transition paths and properties of various high-pressure phases. The influence of relativistic effects is discussed with the aim to explain the unique behavior of the mercury chalcogenides as compared to the lighter zinc and cadmium homologs at high pressures. The neglect of relativistic effects leads to a more CdX like behavior of the mercury chalcogenides, and the pronounced change in coordination of the cinnabar phase at high pressures is due to relativistic effects. PMID:22830722

Biering, S; Schwerdtfeger, P

2012-07-21

356

Determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer quantum dots via spectral analysis of optical signature of the Aharanov-Bohm excitons  

NASA Astrophysics Data System (ADS)

For submonolayer quantum dot (QD) based photonic devices, size and density of QDs are critical parameters, the probing of which requires indirect methods. We report the determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer QDs, based on spectral analysis of the optical signature of Aharanov-Bohm (AB) excitons, complemented by photoluminescence studies, secondary-ion mass spectroscopy, and numerical calculations. Numerical calculations are employed to determine the AB transition magnetic field as a function of the type-II QD radius. The study of four samples grown with different tellurium fluxes shows that the lateral size of QDs increases by just 50%, even though tellurium concentration increases 25-fold. Detailed spectral analysis of the emission of the AB exciton shows that the QD radii take on only certain values due to vertical correlation and the stacked nature of the QDs.

Ji, Haojie; Dhomkar, Siddharth; Roy, Bidisha; Shuvayev, Vladimir; Deligiannakis, Vasilios; Tamargo, Maria C.; Ludwig, Jonathan; Smirnov, Dmitry; Wang, Alice; Kuskovsky, Igor L.

2014-10-01

357

Can aromaticity coexist with diradical character? An ab initio valence bond study of S2N2 and related 6?-electron four-membered rings E2N2 and E4(2+) (E=S, Se, Te).  

PubMed

A series of 6?-electron 4-center species, E(2)N(2) and E(4)(2+) (E=S, Se, Te) is studied by means of ab initio valence bond methods with the aims of settling some controversies on 1) the diradical character of these molecules and 2) the radical sites, E or N, of the preferred diradical structure. It was found that for all molecules, the cumulated weights of the two possible diradical structures are always important and close to 50 %, making these molecules comparable to ozone in terms of diradical character. While the two diradical structures are degenerate in the E(4)(2+) dications, they have on the contrary strongly unequal weights in the E(2)N(2) neutral molecules. In these three molecules, the electronic structure is dominated by one diradical structure, in which the radical sites are the two nitrogen atoms, while the other diradical structure is much less important. The ordering of the various VB structures in terms of their calculated weights is confirmed by the relative energies of individual VB structures. In all cases, the major diradical structure (or both diradical structures when they are degenerate) is (are) the lowest one(s), while the covalent VB structures lie higher in energy. The vertical resonance energies are considerable in S(2)N(2) and S(4)(2+), about 80 % of the estimated value for benzene, and diminish as one goes down the periodic table (S?Se?Te). This confirms the aromatic character of these species, as already demonstrated for S(2)N(2) on the basis of magnetic criteria. This and the high weights and stabilities of one or both diradical structures in all systems indicates that aromaticity and diradical character do not exclude each other, contrary to what is usually claimed. Furthermore, it is shown that the diradical structures find their place in a collective electron flow responsible for the ring currents in the ? system of these species. PMID:22275164

Braïda, Benoît; Lo, Aurélien; Hiberty, Philippe C

2012-02-01

358

Sb2Se3 under pressure  

PubMed Central

Selected members of the A2B3 (A = Sb, Bi; B = Se, Te) family are topological insulators. The Sb2Se3 compound does not exhibit any topological properties at ambient conditions; a recent high-pressure study, however, indicated that pressure transforms Sb2Se3 from a band insulator into a topological insulator above ~2?GPa; in addition, three structural transitions were proposed to occur up to 25?GPa. Partly motivated by these results, we have performed x-ray diffraction and Raman spectroscopy investigations on Sb2Se3 under pressure up to 65?GPa. We have identified only one reversible structural transition: the initial Pnma structure transforms into a disordered cubic bcc alloy above 51?GPa. On the other hand, our high-pressure Raman study did not reproduce the previous results; we attribute the discrepancies to the effects of the different pressure transmitting media used in the high-pressure experiments. We discuss the structural behavior of Sb2Se3 within the A2B3 (A = Sb, Bi; B = Se, Te) series. PMID:24045363

Efthimiopoulos, Ilias; Zhang, Jiaming; Kucway, Melvin; Park, Changyong; Ewing, Rodney C.; Wang, Yuejian

2013-01-01

359

Induced lattice strain in epitaxial Fe-based superconducting films on CaF2 substrates: A comparative study of the microstructures of SmFeAs(O,F), Ba(Fe,Co)2As2, and FeTe0.5Se0.5  

NASA Astrophysics Data System (ADS)

The microstructures of SmFeAs(O,F), Ba(Fe,Co)2As2, and FeTe0.5Se0.5 prepared on CaF2 substrates were investigated using transmission electron microscopy. The SmFeAs(O,F)/CaF2 interface is steep, without a disordered layer. By contrast, a chemical reaction occurs at the interface in the cases of Ba(Fe,Co)2As2 and FeTe0.5Se0.5. The reaction layers are located on opposite sides of the interface for Ba(Fe,Co)2As2 and FeTe0.5Se0.5. We found that the lattice distortion of the three superconducting films on the CaF2 substrates enhances the TC values compared with films prepared on oxide substrates. The origin of this lattice deformation varies depending on the superconducting material.

Ichinose, Ataru; Tsukada, Ichiro; Nabeshima, Fuyuki; Imai, Yoshinori; Maeda, Atsutaka; Kurth, Fritz; Holzapfel, Bernhard; Iida, Kazumasa; Ueda, Shinya; Naito, Michio

2014-03-01

360

Order/disorder phenomena in Zn1-xMnxGa2Se4 ordered vacancy compounds: high temperature neutron powder diffraction experiments  

NASA Astrophysics Data System (ADS)

We present a study of order-disorder phenomena in the series of tetrahedral ordered vacancy compounds Zn1-xMnxGa2Se4 by means of time-of-flight neutron diffraction at high temperature together with dc magnetic susceptibility, Raman spectroscopy, differential thermal analysis and optical absorption experiments. Samples of nominal composition x = 0, 0.24, 0.5, 0.77 and 1 have been studied. An order-disorder phase transition has been detected, with Tc ranging from 472 to 610?° C, which involves a structural change from a defect chalcopyrite phase, with I\\bar {4} space group (s.g.) and three different cation sites, to a partially disordered defect stannite, in which Zn, Mn and half of the Ga ions share the 4d site in I\\bar {4}2 m s.g. Neither the vacancies nor the Ga ions occupying site 2a are involved in the phase transition. An additional ordering process is observed on approaching the phase transition from below, which is attributed to several factors: the activation of cation diffusion at ˜300?° C, the partially disordered cation distribution exhibited by the as-grown single crystals and the preference of Mn atoms for the 2d crystallographic site in the I\\bar {4} structure. The reversibility of the phase transition is analysed with the aid of magnetic, optical and Raman experiments.

Alonso-Gutiérrez, P.; Morón, M. C.; Hull, S.; Sanjuán, M. L.

2013-12-01

361

Order/disorder phenomena in Zn1-xMnxGa2Se4 ordered vacancy compounds: high temperature neutron powder diffraction experiments.  

PubMed

We present a study of order-disorder phenomena in the series of tetrahedral ordered vacancy compounds Zn1-xMnxGa2Se4 by means of time-of-flight neutron diffraction at high temperature together with dc magnetic susceptibility, Raman spectroscopy, differential thermal analysis and optical absorption experiments. Samples of nominal composition x = 0, 0.24, 0.5, 0.77 and 1 have been studied. An order-disorder phase transition has been detected, with Tc ranging from 472 to 610?° C, which involves a structural change from a defect chalcopyrite phase, with I4 space group (s.g.) and three different cation sites, to a partially disordered defect stannite, in which Zn, Mn and half of the Ga ions share the 4d site in I42m s.g. Neither the vacancies nor the Ga ions occupying site 2a are involved in the phase transition. An additional ordering process is observed on approaching the phase transition from below, which is attributed to several factors: the activation of cation diffusion at ?300?° C, the partially disordered cation distribution exhibited by the as-grown single crystals and the preference of Mn atoms for the 2d crystallographic site in the I4 structure. The reversibility of the phase transition is analysed with the aid of magnetic, optical and Raman experiments. PMID:24177226

Alonso-Gutiérrez, P; Morón, M C; Hull, S; Sanjuán, M L

2013-12-01

362

Gate-tuned differentiation of surface-conducting states in Bi1.5Sb0.5Te1.7Se1.3 topological-insulator thin crystals  

NASA Astrophysics Data System (ADS)

Using field-angle, temperature, and back-gate-voltage dependence of the weak antilocalization (WAL) and universal conductance fluctuations of thin Bi1.5Sb0.5Te1.7Se1.3 topological-insulator single crystals, in combination with gate-tuned Hall resistivity measurements, we reliably separated the surface conduction of the topological nature from both the bulk conduction and topologically trivial surface conduction. We minimized the bulk conduction in the crystals and back-gate tuned the Fermi level to the topological bottom-surface band while keeping the top surface insensitive to back-gating with the optimal crystal thickness of ˜100 nm. We argue that the WAL effect occurring by the coherent diffusive motion of carriers in relatively low magnetic fields is more essential than other transport tools such as the Shubnikov-de Hass oscillations for confirming the conduction by the topologically protected surface state. Our approach provides a highly coherent picture of the surface transport properties of topological insulators and a reliable means of investigating the fundamental topological nature of surface conduction and possible quantum-device applications related to momentum-locked spin polarization in surface states.

Lee, Janghee; Park, Joonbum; Lee, Jae-Hyeong; Kim, Jun Sung; Lee, Hu-Jong

2012-12-01

363

Determination of traces of As, B, Bi, Ga, Ge, P, Pb, Sb, Se, Si and Te in high-purity nickel using inductively coupled plasma-optical emission spectrometry (ICP-OES).  

PubMed

A method has been developed for the determination of traces of arsenic, boron, bismuth, gallium, germanium, phosphorus, lead, antimony, selenium, silicon and tellurium in nickel matrix. The sample was dissolved in HClO4 (~150°C) and nickel was settled as crystalline nickelperchlorate [Ni(ClO4)2] on cooling. The mixture was ultrasonicated and after the separation of Ni(ClO4)2, analytes of interest were determined in the supernatant using ICP-OES. Similarly, it was also found that, after the dissolution of nickel in perchloric acid, when the solution temperature was maintained at ~100°C, long needle like crystals of nickel perchlorate were formed. The crystals were separated from the mixture and trace elements in the supernatant were determined using ICP-OES. In both methods the matrix removal was >99% and the recoveries of analytes were in the range 92-97%. The limits of detection for As, B, Bi, Ga, Ge, P, Pb, Sb, Se, Si and Te were found to be 0.18, 0.21, 0.07, 0.06, 0.25, 0.11, 0.09, 0.10, 0.17, 0.20 and 0.07?gg(-1) respectively. The procedure was applied for the analysis of a standard reference material nickel oxide (SRM 761, Nickel Oxide No.1, NBS, USA) and the values obtained are in close agreement with the certified values. PMID:25281133

Thangavel, S; Dash, K; Dhavile, S M; Sahayam, A C

2015-01-01

364

Electronic structure and ferromagnetism of Mn-substituted CuAlS2, CuGaS2, CuInS2, CuGaSe2, and CuGaTe2  

NASA Astrophysics Data System (ADS)

The electronic and magnetic properties of Mn doping at either cation sites in the class of I III VI2 chalcopyrites are studied by first-principles calculation. It is found that Mn doping at the III site provides holes and stabilizes the ferromagnetic interaction between neutral Mn defects; the neutral Mn0Cu also stabilizes the ferromagnetism, although it provides electrons to the conduction band, instead of holes. The ferromagnetic stability is generally weaker when the cation or the anion becomes heavier in these chalcopyrites, i.e., along the sequences CuAlS2?CuGaS2?CuInS2 and CuGaS2? CuGaSe2?CuGaTe2. Interestingly, CuAlO2 in the chalcopyrite structure is predicted to have lower FM energy than CuAlS2 despite its lighter anion and shorter bonds. In general, III site substitution gives stabler ferromagnetism than Cu substitution. Thus, the preferred growth conditions are Cu-rich and III-poor, which maximize MnIII replacement. In n-type samples, when MnIII is negatively charged, the antiferromagnetic coupling is preferred. In p-type samples, the ground state of positively charged Mn+Cu is also antiferromagnetism. The main feature of the calculated electronic properties of Mn defect at either Cu or III site is explained using a simple picture of dangling bond hybride and crystal-field resonance.

Zhao, Yu-Jun; Zunger, Alex

2004-03-01

365

Electronic structures of HgTe and CdTe surfaces and HgTe/CdTe interfaces  

NASA Technical Reports Server (NTRS)

A Green's-function method has been used to study the surface and interface electronic structures of the II-VI compounds HgTe and CdTe. Localized surface and resonance states near the cation-terminated (100) surface of CdTe and the anion-terminated surface of HgTe have been found for the ideal surfaces. The energies and strengths of these surface states are altered by surface perturbations. The bulk states near the surface are drastically modified by the creation of the surface, but the band gaps remain unchanged. Numerical evaluation of the local densities of states at the Gamma and J points shows that, at the (100) interface of HgTe/CdTe, the previously observed surface states are no longer present. However, in the interface region, bulk states of one material penetrate some distance into the other material.

Schick, J. T.; Bose, S. M.; Chen, A.-B.

1989-01-01

366

Partial Pressures of Te2 and Thermodynamic Properties of Ga-Te System  

NASA Technical Reports Server (NTRS)

The partial pressures of Te2 in equilibrium with Ga(1-x)Te(x) samples were measured by optical absorption technique from 450 to 1100 C for compositions, x, between 0.333 and 0.612. To establish the relationship between the partial pressure of Te, and the measured optical absorbance, the calibration runs of a pure Te sample were also conducted to determine the Beer's Law constants. The partial pressures of Te2 in equilibrium with the GaTe(s) and Ga2Te3(s)compounds, or the so-called three-phase curves, were established. These partial pressure data imply the existence of the Ga3Te4(s) compound. From the partial pressures of Te2 over the Ga-Te melts, partial molar enthalpy and entropy of mixing for Te were derived and they agree reasonable well with the published data. The activities of Te in the Ga-Te melts were also derived from the measured partial pressures of Te2. These data agree well with most of the previous results. The possible reason for the high activity of Te measured for x less than 0.60 is discussed.

Su, Ching-Hua; Curreri, Peter A. (Technical Monitor)

2001-01-01

367

Synthesis, crystal structure and magnetic properties of the open framework compound Co{sub 3}Te{sub 2}O{sub 2}(PO{sub 4}){sub 2}(OH){sub 4}  

SciTech Connect

The new compound Co{sub 3}Te{sub 2}O{sub 2}(PO{sub 4}){sub 2}(OH){sub 4} was synthesized using hydrothermal techniques. It crystallizes in the monoclinic space group C2/m with the unit cell a=19.4317(10) A, b=6.0249(3) A, c=4.7788(2) A, {beta}=103.139(5){sup o}. The crystal structure is an open framework having chains of edge sharing [Co(1)O{sub 6}] octahedra. Other building blocks are [TeO{sub 3}(OH){sub 2}], [PO{sub 4}] and [Co({sub 2})O{sub 2}(OH){sub 4}] connected mainly via corner sharing. The -OH groups protrude into channels in the structure. The magnetic susceptibility measured from 2 to 300 K shows two broad anomalies at around 21 K and 4 K, respectively. The peak at {approx}20 K is ascribed to a two-dimensional antiferromagnetic ordering of linear [Co(1)O{sub 6}] chains coupled by interchain interaction via [PO{sub 4}] groups in the Co(1) sheets. The second transition at 4 K is ascribed to a second antiferromagnetic ordering of the moments of the Co(2) entities via super-super exchange involving [PO{sub 4}] and [TeO{sub 3}(OH){sub 2}] groups. This assignment is strongly supported by low-temperature heat capacity measurements indicating an entropy removal within the high-temperature transition of about twice the magnitude of the low-temperature transition. - Graphical Abstract: The new compound Co{sub 3}Te{sub 2}O{sub 2}(PO{sub 4}){sub 2}(OH){sub 4} has been synthesized using hydrothermal techniques. It crystallizes in the monoclinic space group C2/m. Building blocks are [Co(1)O{sub 6}], [TeO{sub 3}(OH){sub 2}], [PO{sub 4}] and [Co(2)O{sub 2}(OH){sub 4}]. The magnetic susceptibility shows two antiferromagnetic transitions at 21 K and 4 K, respectively. Highlights: > The first cobalt tellurium phosphate has been synthesized and structurally determined. > There are two antiferromagnetic orderings identified, one at 21 K and one at 4 K respectively. > A spin flop transition is observed at low temperatures.

Zimmermann, Iwan, E-mail: iwan.zimmermann@mmk.su.se [Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm (Sweden); Kremer, Reinhard K., E-mail: rekre@fkf.mpg.de [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Johnsson, Mats, E-mail: mats.johnsson@mmk.su.se [Department of Materials and Environmental Chemistry, Stockholm University, SE-106 91 Stockholm (Sweden)

2011-11-15

368

Understanding of the contact of nanostructured thermoelectric n-type Bi[subscript 2]Te[subscript 2.7]Se[subscript 0.3] legs for power generation applications  

E-print Network

Traditional processes of making contacts (metallization layer) onto bulk crystalline Bi2Te3-based materials do not work for nanostructured thermoelectric materials either because of weak bonding strength or an unstable ...

Liu, Weishu

369

Experimental and theoretical comparison of actinide and lanthanide bonding in M[N(EPR(2))(2)](3) complexes (M = U, Pu, La, Ce; E = S, Se, Te; R = Ph, iPr, H).  

PubMed

Treatment of M[N(SiMe3)2]3 (M = U, Pu (An); La, Ce (Ln)) with NH(EPPh2)2 and NH(EPiPr2)2 (E = S, Se), afforded the neutral complexes M[N(EPR2)2]3 (R = Ph, iPr). Tellurium donor complexes were synthesized by treatment of MI3(sol)4 (M = U, Pu; sol = py and M = La, Ce; sol = thf) with Na(tmeda)[N(TePiPr2)2]. The complexes have been structurally and spectroscopically characterized with concomitant computational modeling through density functional theory (DFT) calculations. The An-E bond lengths are shorter than the Ln-E bond lengths for metal ions of similar ionic radii, consistent with an increase in covalent interactions in the actinide bonding relative to the lanthanide bonding. In addition, the magnitude of the differences in the bonding is slightly greater with increasing softness of the chalcogen donor atom. The DFT calculations for the model systems correlate well with experimentally determined metrical parameters. They indicate that the enhanced covalency in the M-E bond as group 16 is descended arises mostly from increased metal d-orbital participation. Conversely, an increase in f-orbital participation is responsible for the enhancement of covalency in An-E bonds compared to Ln-E bonds. The fundamental and practical importance of such studies of the role of the valence d and f orbitals in the bonding of the f elements is emphasized. PMID:18020446

Gaunt, Andrew J; Reilly, Sean D; Enriquez, Alejandro E; Scott, Brian L; Ibers, James A; Sekar, Perumal; Ingram, Kieran I M; Kaltsoyannis, Nikolas; Neu, Mary P

2008-01-01

370

A photoelectron spectroscopy study of the electronic structure evolution in CuInSe{sub 2}-related compounds at changing copper content  

SciTech Connect

Evolution of the valence-band structure at gradually increasing copper content has been analysed by x-ray photoelectron spectroscopy (XPS) in In{sub 2}Se{sub 3}, CuIn{sub 5}Se{sub 8}, CuIn{sub 3}Se{sub 5}, and CuInSe{sub 2} single crystals. A comparison of these spectra with calculated total and angular-momentum resolved density-of-states (DOS) revealed the main trends of this evolution. The formation of the theoretically predicted gap between the bonding and non-bonding states has been observed in both experimental XPS spectra and theoretical DOS.

Kuznetsova, T. V.; Grebennikov, V. I. [Institute of Metal Physics, UB RAS, 620041 Ekaterinburg (Russian Federation); Zhao, H. [Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Derks, C.; Taubitz, C.; Neumann, M. [University of Osnabrueck, D-49069 Osnabrueck (Germany); Persson, C. [Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm (Sweden); Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo (Norway); Kuznetsov, M. V. [Institute of Solid State Chemistry, UB RAS, 620990 Ekaterinburg (Russian Federation); Urals Federal University, 19 Mira Str., Ekaterinburg 620002 (Russian Federation); Bodnar, I. V. [Department of Chemistry, Belarusian State University of Informatics and Radioelectronics, P. Brovka 6, 220027 Minsk (Belarus); Martin, R. W.; Yakushev, M. V. [Department of Physics, SUPA, Strathclyde University, G4 0NG Glasgow (United Kingdom)

2012-09-10

371

Thermoelectric properties of Cu-doped n-type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Cu{sub x}Se{sub 3}){sub 0.1}(x=0-0.2) alloys  

SciTech Connect

n-Type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Cu{sub x}Se{sub 3}){sub 0.1} (x=0-0.2) alloys with Cu substitution for Bi were prepared by spark plasma-sintering technique and their structural and thermoelectric properties were evaluated. Rietveld analysis reveals that approximate 9.0% of Bi atomic sites are occupied by Cu atoms and less than 4.0 wt% second phase Cu{sub 2.86}Te{sub 2} precipitated in the Cu-doped parent alloys. Measurements show that an introduction of a small amount of Cu (x{<=}0.1) can reduce the lattice thermal conductivity ({kappa}{sub L}), and improve the electrical conductivity and Seebeck coefficient. An optimal dimensionless figure of merit (ZT) value of 0.98 is obtained for x=0.1 at 417 K, which is obviously higher than those of Cu-free Bi{sub 2}Se{sub 0.3}Te{sub 2.7} (ZT=0.66) and Ag-doped alloys (ZT=0.86) prepared by the same technologies. - Graphical abstract: After Cu-doping with x=0.1, the highest ZT value of 0.98 is obtained at 417 K, which is about 0.32 and 0.12 higher than those of Cu-free Bi{sub 2}Se{sub 0.3}Te{sub 2.7} and the Ag-doped alloys (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-x}Ag{sub x}Se{sub 3}){sub 0.1} (x=0.4), respectively.

Cui, J.L. [School of Mechanical Engineering, Ningbo University of Technology, Ningbo 315016 (China)], E-mail: cuijl@nbip.net; Mao, L.D. [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China); School of Mechanical Engineering, Ningbo University of Technology, Ningbo 315016 (China); Yang, W.; Xu, X.B. [School of Mechanical Engineering, Ningbo University of Technology, Ningbo 315016 (China); Chen, D.Y.; Xiu, W.J. [School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221008 (China); School of Mechanical Engineering, Ningbo University of Technology, Ningbo 315016 (China)

2007-12-15

372

Phase Equilibria of the Sn-Bi-Te Ternary System  

NASA Astrophysics Data System (ADS)

Bi2Te3 is one of the most promising thermoelectric materials, and Sn is the primary constituent of most electronic solders. Knowledge of phase equilibria of the Sn-Bi-Te ternary system is important for thermoelectric applications. Twenty-seven Sn-Bi-Te alloys were prepared and equilibrated at 160°C and 500°C. The equilibrium phases were determined, and the isothermal sections were constructed based on three binary constituent phase diagrams and ternary phase equilibria results. No ternary compounds were observed in the Sn-SnTe-Bi region. The SnTe phase is very stable and has tie-lines with the Sn, liquid, and Bi phases at 160°C. At 500°C, in addition to the already known SnBi2Te4 and SnBi4Te7 ternary phases, two new ternary compounds (Sn2Bi2Te5 and SnBiTe2 phases) were found. SnTe and Bi2Te3 have significant mutual solubilities, and the ternary compounds SnBi2Te4, SnBi4Te7, and Sn2Bi2Te5 are all in the SnTe-Bi2Te3 pseudobinary section.

Chiu, Chen-Nan; Hsu, Chia-Ming; Chen, Sinn-Wen; Wu, Hsin-Jay

2012-01-01

373

Charge carrier localization induced by excess Fe in the Fe1+y(Te1-xSex) superconductor system  

NASA Astrophysics Data System (ADS)

Iron chalcogenide Fe1+y(Te1-xSex) is the simplified version of Fe-based superconductors. Its non-superconducting parent compound Fe1+yTe exhibits an AFM structure distinct from those seen in undoped FeAs compounds. Understanding of the superconducting properties of this system has been considered critical. We have investigated the effect of Fe nonstoichiometry on properties of the Fe1+y(Te1-xSex) superconductor system by means of resistivity, Hall coefficient, magnetic susceptibility, and specific heat measurements. We find that the excess Fe at interstitial sites of the (Te, Se) layers not only suppresses superconductivity, but also results in a weakly localized electronic state. Together with neutron scattering studies and recent DFT calculations, our results suggest that such weak charge carrier localization originates from the magnetic coupling between the excess Fe and the adjacent Fe square planar sheets.

Hu, Jin; Liu, Tijiang; Ke, Xianglin; Bin, Qian; Fobes, David; Vehstedt, Erin; Pham, Huy; Yang, Jinhu; Fang, Minghu; Spinu, Leonard; Schiffer, Peter; Liu, Ying; Mao, Zhiqiang

2010-03-01

374

Synthesis, structure, and optical properties of the quaternary diamond-like compounds I{sub 2}–II–IV–VI{sub 4} (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se)  

SciTech Connect

Three new diamond-like compounds with the formula of I{sub 2}?II?IV?VI{sub 4} (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se) have been synthesized via traditional high-temperature solid-state reactions and structurally characterized by single crystal X-ray diffraction analysis. All the three compounds crystallize in the space group Pmn2{sub 1} in the wurtzite-type superstructure with a=7.563(4), b=6.448(3), c=6.179(3) Å, Z=2 for Cu{sub 2}MgSiS{sub 4} (1); a=7.953(5), b=6.797(4), c=6.507(4) Å, Z=2 for Cu{sub 2}MgGeS{sub 4} (2); a=7.638(4), b=6.515(4), c=6.225(3) Å, Z=2 for Cu{sub 2}MgSiSe{sub 4} (3). All atoms in these compounds are tetrahedrally coordinated. Optical diffuse reflectance UV/Vis/NIR spectra indicate that compounds 1 and 2 have the band gaps of 3.20 and 2.36 eV, respectively. Electronic structure calculations using the CASTEP code indicate that they are all direct band gap compounds. - Graphical abstract: Three new diamond-like compounds, Cu{sub 2}MgSiS{sub 4}, Cu{sub 2}MgGeS{sub 4}, and Cu{sub 2}MgSiSe{sub 4}, have been synthesized. All the three compounds crystallize in the space group Pmn2{sub 1} and all atoms are tetrahedrally coordinated. Highlights: • Three new diamond-like compounds Cu{sub 2}MgSiS{sub 4}, Cu{sub 2}MgGeS{sub 4} and Cu{sub 2}MgSiSe{sub 4} have been synthesized. • All ions are tetrahedrally coordinated. • Electronic structure calculations indicate that they are all direct band gap compounds.

Liu, Bin-Wen; Zhang, Ming-Jian; Zhao, Zhong-Yan; Zeng, Hui-Yi, E-mail: zhy@fjirsm.ac.cn; Zheng, Fa-Kun; Guo, Guo-Cong, E-mail: gcguo@fjirsm.ac.cn; Huang, Jin-Shun

2013-08-15

375

Analysis of the solidus lines for PbTe and SnTe  

Microsoft Academic Search

Experimental valúes of p-n, PTe\\u000a 2, and T along the solidus lines of PbTe and SnTe, and for compositions within the homogeneity range of SnTe are fit using\\u000a the simple model of a nondegenerate semiconductor compound containing fully-ionized native defects. As a result values for\\u000a the intrinsic material parameters of these compounds at high temperature are obtained as well as

R. F. Brebrick

1977-01-01

376

First detection of a selenenyl fluoride ArSe-F by NMR spectroscopy: the nature of Ar2Se2/XeF2 and ArSe-SiMe3/XeF2 reagents.  

PubMed

Arylselenenyl fluorides ArSeF are obtained from diselenides Ar2Se2 or arylselenotrimethylsilanes ArSe-SiMe3, and XeF2. They are detected by low-temperature 19F and 77Se NMR spectroscopy. Substitution in the ortho position of the aromatic ring to provide electronic or steric protection is a requirement for their formation. ArSe--F compounds decompose according to 3 ArSe-F-->[ArSe-SeF2Ar]+ArSe-F-->ArSeF3+Ar2Se2. Reaction energies for this disproportionation as well as that of the sulfur and tellurium homologues have been calculated with MP2, CCSD(T,) and B3 LYP methods. They were found to be increasingly exothermic in the sequence S<Se. For selected Se-C and Se-F compounds the 77Se and 19F chemical shifts have been calculated by GIAO-MP2 and GIAO-B3 LYP methods and are in good agreement with experimental values. PMID:15540265

Poleschner, Helmut; Seppelt, Konrad

2004-12-01

377

Magnetic Properties of Some Divalent Europium Compounds  

Microsoft Academic Search

The compounds of divalent europium form an attractive series for magnetic investigations because the magnetic ions are in S states and the crystal structures are generally simple. Moreover, true ferromagnetism, which is quite unusual in compounds, has been observed in EuO by Matthias, Bozorth, and Van Vleck.We have prepared samples of EuS, EuSe, EuTe, EuCO3, EuTiO3, EuZrO3, EuSO4, and EuCl2,

T. R. McGuire; B. E. Argyle; M. W. Shafer; J. S. Smart

1963-01-01

378

Phonon, two-magnon, and electronic Raman scattering of Fe1+yTe1-xSex  

NASA Astrophysics Data System (ADS)

We have measured Raman-scattering spectra of single-crystalline FeTe0.6Se0.4 (Tc~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In the parent compound Fe1.074Te, A1g and B1g modes have been observed at 158 and 202 cm-1, respectively, at 5 K. These frequencies agree qualitatively with the calculated results. Two-magnon excitation has been observed around 2300 cm-1 for both compounds. A temperature dependence between the electronic Raman spectra below and above Tc has been observed, and 2? and 2?/kBTC have been estimated as 5.0 meV and 4.0, respectively.

Okazaki, K.; Sugai, S.; Niitaka, S.; Takagi, H.

2011-01-01

379

Thermoelectric properties of Ag-doped n-type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-} {sub x} Ag {sub x} Se{sub 3}){sub 0.1} (x=0-0.4) alloys prepared by spark plasma sintering  

SciTech Connect

Ag-doped n-type (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-} {sub x} Ag {sub x} Se{sub 3}){sub 0.1} (x=0-0.4) alloys were prepared by spark plasma sintering and their physical properties evaluated. When at low Ag content (x=0.05), the temperature dependence of the lattice thermal conductivity follows the trend of (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2}Se{sub 3}){sub 0.1}; while at higher Ag content, a relatively rapid reduction above 400 K can be observed due possibly to the enhancement of scattering of phonons by the increased defects. The Seebeck coefficient increases with Ag content, with some loss of electrical conductivity, but the maximum dimensionless figure of merit ZT can be obtained to be 0.86 for the alloy with x=0.4 at 505 K, about 0.2 higher than that of the alloy (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2}Se{sub 3}){sub 0.1} without Ag-doping. - Graphical abstract: The temperature dependence of dimensionless thermoelectric figure of merit ZT for different (Bi{sub 2}Te{sub 3}){sub 0.9}-(Bi{sub 2-} {sub x} Ag {sub x} Se{sub 3}){sub 0.1} (x=0-0.4) alloys prepared by spark plasma sintering.

Cui, J.L. [School of Mechanical Engineering, Ningbo University of Technology, Ningbo 315016 (China)], E-mail: cuijl@nbip.net; Xiu, W.J. [School of Mechanical Engineering, Ningbo University of Technology, Ningbo 315016 (China); School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221008 (China); Mao, L.D. [School of Mechanical Engineering, Ningbo University of Technology, Ningbo 315016 (China); College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China); Ying, P.Z. [School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221008 (China); Jiang, L. [School of Materials Science and Engineering, China University of Mining and Technology, Xuzhou 221008 (China); Qian, X. [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China)

2007-03-15

380

Electronic structure and phase stability of MgTe, ZnTe, CdTe, and their alloys in the B3, B4, and B8 structures  

E-print Network

efficiency multi- junction solar cell materials to complement existing CdTe and Cu In,Ga Se2 technologies.10Electronic structure and phase stability of MgTe, ZnTe, CdTe, and their alloys in the B3, B4, and BTe, and CdTe were examined in the zinc-blende B3 , wurtzite B4 , and NiAs-type B8 crystal structures using

Gong, Xingao

381

Magnetic behavior of the metamagnetic compounds Co(S 1- xSe x) 2 under high pressure and high magnetic field  

NASA Astrophysics Data System (ADS)

The magnetization of the metamagnetic Co(Si 1- xSe x) 2 system with 0 ? x ? 0.2 has been measured under high pressure and high magnetic field. The magnetic phase diagram is determined in the T- x plane. The metamagnetic behavior under high pressure and high magnetic field and the magnetic phase diagram can be elucidated well with a theory of itinerant electron metamagnetism at finite temperatures.

Goto, T.; Shindo, Y.; Ogawa, S.; Harada, T.

1997-07-01

382

Topological electronic structure and Weyl semimetal in the TlBiSe2 class of semiconductors  

NASA Astrophysics Data System (ADS)

We present an analysis of bulk and surface electronic structures of thallium-based ternary III-V-VI2 series of compounds TlMQ2, where M=Bi or Sb and Q=S, Se, or Te, using the ab initio density functional theory framework. Based on parity analysis and (111) surface electronic structure, we predict TlSbSe2, TlSbTe2, TlBiSe2, and TlBiTe2 to be nontrivial topological insulators with a single Dirac cone at the ? point and TlSbS2 and TlBiS2 to be trivial band insulators. Our predicted topological phases agree well with available angle-resolved photoemission spectroscopy measurements, in particular, the topological phase changes between TlBiSe2 and TlBiS2. Moreover, we propose that Weyl semimetal can be realized at the topological critical point in TlBi(S1-xSex)2 and TlBi(S1-xTex)2 alloys by breaking the inversion symmetry in the layer-by-layer growth in the order Tl-Se(Te)-Bi-S, yielding six Dirac cones centered along the ?-L directions in the bulk band structure.

Singh, Bahadur; Sharma, Ashutosh; Lin, H.; Hasan, M. Z.; Prasad, R.; Bansil, A.

2012-09-01

383

Magnetothermoelectric effects in Fe1+dTe1-xSex  

NASA Astrophysics Data System (ADS)

We report resistivity as well as the Hall, Seebeck and Nernst coefficients data for Fe1+dTe1-xSex single crystals with x = 0, 0.38, and 0.40. In the parent compound Fe1.04Te we observe at TN = 61 K a sudden change of all quantities studied, which can be described to the Fermi surface reconstruction due to onset of the antiferromagnetic order. Two very closely doped samples: Fe1.01Te0.62Se0.38 (Se38) and Fe1.01Te0.60Se0.40 (Se40) are superconductors with Tc = 13.4 K and 13.9 K, respectively. There are no evident magnetic transitions in either Se38 or Se40. Properties of these two single crystals are almost identical at high temperatures, but start to diverge below T ? 80 K. Perhaps we see the onset of scattering that might be a related to changes in short range magnetic correlations caused by selenium doping.

Matusiak, Marcin; Pomjakushina, Ekaterina; Conder, Kazimierz

2012-12-01

384

CdTe: effective Landé g factors  

Microsoft Academic Search

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

J. Gutowski; K. Sebald; T. Voss

2009-01-01

385

Thermodynamic and Transport Properties of YTe3, LaTe3 and CeTe3  

SciTech Connect

Measurements of heat capacity, susceptibility, and electrical resistivity are presented for single crystals of the charge density wave compounds YTe{sub 3}, LaTe{sub 3}, and CeTe{sub 3}. The materials are metallic to low temperatures, but have a small density of states due to the charge density wave gapping large portions of the Fermi surface. CeTe{sub 3} is found to be a weak Kondo lattice, with an antiferromagnetic ground state and T{sub N} = 2.8 K. The electrical resistivity of all three compounds is highly anisotropic, confirming the weak dispersion perpendicular to Te planes predicted by band structure calculations.

Ru, N.

2011-08-19

386

Vacancy-associated Te sites in GaAs  

NASA Astrophysics Data System (ADS)

Defect structures, observed by 129I Mössbauer spectroscopy in high-dose Te-doped GaAs, are identified by a reference study of the semiconducting compound Ga2Te3. The formation of TeAs-VGa complexes (tellurium atoms quasisubstitutional on an As site with a gallium vacancy in the first-neighbor shell) is proposed, in agreement with theoretical predictions. The relevance of this assignment in relation to the earlier proposed Te DX configuration is also discussed.

Wuyts, K.; Langouche, G.; van Rossum, M.; Silverans, R. E.

1992-03-01

387

Crystallographic properties of some ternary and multinary Te-based semiconductors  

NASA Astrophysics Data System (ADS)

Crystallographic properties of several single crystals of ternary ABC 2 ( A = Cu, Ag; B = In, Ga; C = Te, Se) compounds, of Cd 1- xMn xTe (0.5 ? x ? 0.66), of quaternary and pentenary (CuIn 1- xGa xSe 2(1- yTe 2 y with x = 0, 0.7, 1 and y = 0.135, 0.65, 0.4) solid solutions have been determined by single crystal X-ray diffraction. Many chalcopyrite compounds and alloys show thermal polymorphism involving order-disorder phase transitions, and the structure changes are characterized by a first order transition from ordered tetragonal chalcopyrite to the completely disordered zinc-blende and/or wurtzite structures. All the single crystals were grown by chemical vapour phase transport in a close tube using iodine as the transport agent. The phases observed in growing ternary compounds depend on the temperature used during the growth process. For the multinary solid solutions the situation appears to be more complex: in fact, together with the expected phases some altogether unexpected ones were detected, confirming the idea that the growth process of these compounds is dependent not only on temperature but also on parameters involving the composition and growth kinetics.

Bocelli, G.; Calestani, G.; de Melo, O.; Leccabue, F.; Pelosi, C.; Watts, B. E.

1991-09-01

388

Synthesis of wurtzite-zincblende Cu2ZnSnS4 and Cu2ZnSnSe4 nanocrystals: insight into the structural selection of quaternary and ternary compounds influenced by binary nuclei.  

PubMed

Nearly monodispersed wurtzite-dominant Cu2ZnSnS4 and zincblende-dominant Cu2ZnSnSe4 nanocrystals were successfully synthesized by mixing metal salts with heated thiourea or selenourea in oleylamine. A perspective of the structural relationship between quaternary and ternary semiconductors was investigated through the application of different anion sources to prepare Cu2SnS3 and Cu2SnSe3 nanocrystals. Investigations on copper-based binary compounds found that CuSe (or CuS) and Cu2Se (or Cu1.96S, Cu9S5) nuclei were primarily responsible for the formation of zincblende or wurtzite structures, respectively. Further management over these binary intermediates corresponded to slight structural transformations of the quaternary nanocrystals which could be observed not only in XRD patterns, but from optical and electrical properties as well. According to these results, Cu2ZnGeS4 nanocrystals with wurtzite-dominant structures were first reported using SC(NH2)2, which also verified that the binary semiconductors are the determinative factors. PMID:24573321

Li, Yingwei; Han, Qifeng; Kim, Tae Whan; Shi, Wangzhou

2014-04-01

389

Sodium selenite penta­hydrate, Na2SeO3·5H2O  

PubMed Central

In the crystal structure of Na2SeO3·5H2O [disodium selen­ate(IV) penta­hydrate], two Se, two selenite O atoms and one water O atom are located on a mirror plane, and one water O atom is located on a twofold rotation axis. The coordination of one Na+ cation is distorted trigonal bipyramidal, formed by three equatorial H2O ligands and two axial selenite O atoms. The other Na+ cation has an octa­hedral coordination by six water mol­ecules. The two independent SeO3 groups form almost undistorted trigonal pyramids, with Se—O bond lengths in the range 1.6856?(7)–1.7202?(10)?Å and O—Se—O angles in the range 101.98?(3)–103.11?(5)°, and both are ?2-O:O-bonded to a pair of Na+ cations. Hydrogen bonds involving all water molecules and selenite O atoms consolidate the crystal packing. Although anhydrous Na2SeO3 and Na2TeO3 are isotypic, the title compound is surprisingly not isotypic with Na2TeO3·5H2O. In the tellurite hydrate, all Na+ cations have an octa­hedral coordination and the TeO3 groups are bonded to Na+ only via one of their three O atoms. PMID:24454013

Mereiter, Kurt

2013-01-01

390

Sodium selenite penta-hydrate, Na2SeO3·5H2O.  

PubMed

In the crystal structure of Na2SeO3·5H2O [disodium selen-ate(IV) penta-hydrate], two Se, two selenite O atoms and one water O atom are located on a mirror plane, and one water O atom is located on a twofold rotation axis. The coordination of one Na(+) cation is distorted trigonal bipyramidal, formed by three equatorial H2O ligands and two axial selenite O atoms. The other Na(+) cation has an octa-hedral coordination by six water mol-ecules. The two independent SeO3 groups form almost undistorted trigonal pyramids, with Se-O bond lengths in the range 1.6856?(7)-1.7202?(10)?Å and O-Se-O angles in the range 101.98?(3)-103.11?(5)°, and both are ?2-O:O-bonded to a pair of Na(+) cations. Hydrogen bonds involving all water molecules and selenite O atoms consolidate the crystal packing. Although anhydrous Na2SeO3 and Na2TeO3 are isotypic, the title compound is surprisingly not isotypic with Na2TeO3·5H2O. In the tellurite hydrate, all Na(+) cations have an octa-hedral coordination and the TeO3 groups are bonded to Na(+) only via one of their three O atoms. PMID:24454013

Mereiter, Kurt

2013-10-23

391

Crystal chemistry of selenates with mineral-like structures: V. Crystal structures of (H 3 O) 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)](H 2 O) 2 and (H 3 O) 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)](H 2 O), new compounds with rhomboclase and goldichite topology  

Microsoft Academic Search

The crystal structures of two new compounds (H3O)2[(UO2)(SeO4)2(H2O)](H2O)2 (1, orthorhombic, Pnma, a = 14.0328(18), b = 11.6412(13), c = 8.2146(13) Å, V = 134.9(3) Å3) and (H3O)2[(UO2)(SeO4)2(H2O)](H2O) (2, monoclinic, P21\\/c, a = 7.8670(12), b = 7.5357(7), c = 21.386(3) Å, ? = 101.484(12)°, V = 1242.5(3) Å3) have been solved by direct methods and refined to R\\u000a 1 = 0.076

S. V. Krivovichev

2008-01-01

392

Advanced Processing of CdTe- and CuIn1-xGaxSe2-Based Solar Cells: Final Technical Report, 26 May 1998--22 December 2001  

SciTech Connect

This project addresses most of the key CdTe technology areas, with focus on improving the manufacturability and long-term stability of this technology. The activities over this 3-year period include developing simplified processing, studying novel front and back contacts, and improving long-term stability. This report describes work carried out during the last year of the project. The solar cells discussed below are fabricated by various deposition technologies that include chemical vapor deposition, chemical-bath deposition, close-spaced sublimation, and rf-sputtering. The devices are routinely evaluated using standard solar cell analytical techniques such as dark and light current-voltage, spectral response, and capacitance-voltage measurements.

Morel, D. L.; Ferekides, C. S.

2003-10-01

393

First-principles study of the electronic and structural properties of (CdTe)n/(ZnTe)n superlattices  

NASA Astrophysics Data System (ADS)

We present the results of a first-principles study of the electronic and structural properties of binary CdTe and ZnTe compounds and their (CdTe)n/(ZnTe)n superlattices (SLs). The computational method is based on the full-potential linear muffin tin orbitals method (FP-LMTO) augmented by a plane-wave basis (PLW). The exchange and correlation energy is described in the local density approximation (LDA) using the Perdew-Wang parameterization including a generalized gradient approximation (GGA). The calculated structural properties of CdTe and ZnTe compounds are in good agreement with available experimental and theoretical data. We have also carried out band-structure calculations for the binary CdTe and ZnTe compounds and their (CdTe)n/(ZnTe)n superlattices (SLs). From the results of the electronic properties, we find that the parent material CdTe and ZnTe and their superlattices have a direct band gaps. The fundamental band gap decreases with increasing the number of monolayer n.

Boucharef, M.; Benalia, S.; Rached, D.; Merabet, M.; Djoudi, L.; Abidri, B.; Benkhettou, N.

2014-11-01

394

Crystal Growth of CdTe by Gradient Freeze in Universal Multizone Crystallizator (UMC)  

NASA Technical Reports Server (NTRS)

In the case of unsealed melt growth of an array of II-VI compounds, namely, CdTe, CdZnTe and ZnSe, there is a tremendous amount of experimental data describing the correlations between melt conditions and crystal quality. The results imply that the crystallinity quality can be improved if the melt was markedly superheated or long-time held before growth. It is speculated that after high superheating the associated complex dissociate and the spontaneous nucleation is retarded. In this study, crystals of CdTe were grown from melts which have undergone different thermal history by the unseeded gradient freeze method using the Universal Multizone Crystallizator (UMC). The effects of melt conditions on the quality of grown crystal were studied by various characterization techniques, including Synchrotron White Beam X-ray Topography (SWSXT), infrared microscopy, chemical analysis by glow discharge mass spectroscopy (GDMS), electrical conductivity and Hall measurements.

Su, Ching-Hua; Lehoczky, S. L.; Li, C.; Knuteson, D.; Raghothamachar, B.; Dudley, M.; Szoke, J.; Barczy, P.

2004-01-01

395

Optical conductivity of FeTe1-xSex  

NASA Astrophysics Data System (ADS)

The ab-plane optical conductivity of two single crystals belonging to the chalcogenide family, FeTe0.91 and FeTe0.7Se0.3, has been studied in the normal phase between 16 and 450 K. Several differences with respect to both conventional metals and other exotic superconductors, like the cuprates, have been found both in the undoped and in the doped material. In the former compound, the transition to an antiferromagnetic (AF) state at 67 K causes the opening of a pseudogap at ?0 = 270 ± 25 cm-1 and a decrease by 70% in the free carrier density, accompanied by a strong reduction in the carrier scattering rate. The multiband analysis of the low-energy optical conductivity requires at least two Drude components, in addition to a mid-infrared band. Above 350 K, a transfer of spectral weight between those terms produces a cusp anomaly in the spectral weight. This indicates a well-defined transition, rather than a crossover, to a less-metallic regime. Finally, in FeTe0.7Se0.3 the far-infrared conductivity decreases with T, in agreement with the semiconducting behavior of the resistivity, and precursor phenomena of superconductivity appear above Tc.

Mirri, C.; Calvani, P.; Vitucci, F. M.; Perucchi, A.; Yeh, K. W.; Wu, M. K.; Lupi, S.

2012-04-01

396

Ab initio study of deep defect states in narrow band-gap semiconductors: group III impurities in PbTe.  

PubMed

The nature of deep defect states, in general, and those associated with group III elements (Ga, In, Tl) in narrow band-gap IV-VI semiconductors (PbTe and PbSe), in particular, have been of great interest over the past three decades. We present ab initio electronic structure calculations that give a new picture of these states compared to the currently accepted model in terms of a negative-U Hubbard model. The Fermi surface pinning and why In-doped PbTe and related compounds show excellent high temperature thermoelectric behavior can be understood within the new picture. PMID:16486963

Ahmad, Salameh; Hoang, Khang; Mahanti, S D

2006-02-10

397

Ab Initio Study of Deep Defect States in Narrow Band-Gap Semiconductors: Group III Impurities in PbTe  

NASA Astrophysics Data System (ADS)

The nature of deep defect states, in general, and those associated with group III elements (Ga, In, Tl) in narrow band-gap IV-VI semiconductors (PbTe and PbSe), in particular, have been of great interest over the past three decades. We present ab initio electronic structure calculations that give a new picture of these states compared to the currently accepted model in terms of a negative-U Hubbard model. The Fermi surface pinning and why In-doped PbTe and related compounds show excellent high temperature thermoelectric behavior can be understood within the new picture.

Ahmad, Salameh; Hoang, Khang; Mahanti, S. D.

2006-02-01

398

Ab initio calculations of the pressure-induced structural phasetransitions for four II-VI compounds  

SciTech Connect

We report on pseudopotential calculations of the structural properties and pressure-induced solid-solid phase transitions for four II-VI compounds: ZnSe, ZnTe, CdSe, and CdTe. for each of these compounds,we fix the zinc-blende structure as the ambient pressure phase and consider the rocksalt, cinnabar, and Cmcm structures as candidates for the high-pressure phases. We calculate the transition pressures and the changes in specific volume for each compound. The pressure dependences of the structural parameters of the cinnabar and the Cmcm phases are determined. The Cmcm structure appears to be a common high-pressure phase for the II-VI and III-V semiconductors.

Cote, Michel; Zakharov, Oleg; Rubio, Angel; Cohen, Marvin L.

1996-11-15

399

Characterization of PbTe/p-Si and SnTe/p-Si heterostructures  

NASA Astrophysics Data System (ADS)

Heterostructures which utilize a thin film of narrow-gap semiconductor deposited on a p-Si substrate have the potential to function as high-efficiency, easily fabricated infrared detectors. We have characterized two such systems, namely PbTe and SnTe. The structures were prepared by congruently evaporating films of PbTe and SnTe from single sources of the compounds onto <100> p-Si wafers which were chemically cleaned prior to deposition. We have analyzed the composition and electrical properties of the deposited films, as well as the electrical and photoresponse properties of the heterostructures. Current-voltage measurements indicated rectifying behavior with good ideality factor and low leakage down to 77 K for the case of SnTe/Si. High series resistance of the PbTe/Si structures made electrical characterization difficult, though they also showed rectifying behavior and low reverse leakage. Photoresponse measurements indicate a threshold of 0.36-0.4 eV for SnTe/p-Si and 0.3 eV for PbTe/p-Si. These results indicate that the PbSnTe alloy on p-Si will have a lower energy threshold than either of the binary compounds.

Scott, G.; Helms, C. R.

1991-10-01

400

Evolution of Superconductivity in Fe1+yTe1-xSex Annealed in Te Vapor  

NASA Astrophysics Data System (ADS)

We report a detailed study of the Te vapor annealing effect in Fe1+yTe0.6Se0.4 single crystals. Bulk superconductivity can be gradually induced by annealing with increasing amount of Te, until the molar ratio of Te to the sample reaches 1 : 10. By further increasing Te molar ratio, superconducting volume is gradually reduced. Resistivity and Hall effect measurements manifest that annealing in Te vapor delocalizes the charge carriers by removing excess Fe. The optimally Te annealed crystal shows homogeneous critical current densities with a large value of ˜4.3 × 105 A/cm2, which proves that the Te annealing is effective to induce bulk superconductivity in Fe1+yTe1-xSex.

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

2013-09-01

401

Galvanomagnetic and thermoelectric properties of BiTeBr and BiTeI single crystals and their electronic structure  

SciTech Connect

BiTeI and BiTeBr single crystals are synthesized by the Bridgman method, and their galvanomagnetic and thermoelectrical properties are investigated. Both semiconductors have n-type conductivity. The thermoelectric efficiency of BiTeBr is much higher than that of BiTeI, which is related mainly to a larger See-beck coefficient for the former compound. For both crystals, the band structure is calculated from the density-functional theory. It is shown that both compounds are semiconductors with an indirect energy band gap.

Kulbachinskii, V. A., E-mail: kulb@mig.phys.msu.ru; Kytin, V. G.; Lavrukhina, Z. V.; Kuznetsov, A. N.; Shevelkov, A. V. [Moscow State University (Russian Federation)

2010-12-15

402

Revised phase diagram for the FeTe1-xSex system with fewer excess Fe atoms  

NASA Astrophysics Data System (ADS)

We observed bulk superconductivity in the FeTe1-xSex crystals with lower Se concentrations after annealed in air. A revised magnetism and superconductivity phase diagram is obtained via resistance and magnetic-susceptibility measurements for the FeTe1-xSex system. It is found that bulk superconductivity coexists with antiferromagnetic order in the crystals with 0.05 ? x ? 0.18. The phase diagram is very similar to the case of the K-doping or Co-doping BaFe2As2 as well as that of the SmFeAsO1-xFx system, perhaps indicating that all the iron-based systems have a generic phase diagram, although the antiferromagnetic wave vectors in the parent compounds of both iron pnictides and FeTe1-xSex systems are remarkably different.

Dong, Chiheng; Wang, Hangdong; Li, Zujuan; Chen, Jian; Yuan, H. Q.; Fang, Minghu

2011-12-01

403

Single Dirac cone on the Cs-covered topological insulator surface Sb2Te3(0001)  

NASA Astrophysics Data System (ADS)

Using angle-resolved photoelectron spectroscopy we investigate the surface electronic structure of the three-dimensional topological insulator (TI) Sb2Te3(0001). Our data show the presence of a topological surface state in the bulk energy gap with the Dirac point located above the Fermi level. The adsorption of Cs atoms on Sb2Te3(0001) gives rise to a downward energy shift of the electronic valence band states which saturates at a value of ˜200 meV. For the saturation coverage the Dirac point of the linearly dispersive surface state resides in close proximity to the Fermi level. The electronic structure of the Cs/Sb2Te3 interface therefore considerably deviates from previously studied metal-TI interfaces based on the isostructural compound Bi2Se3 which points to the importance of atomic composition in these hetero systems.

Seibel, Christoph; Maaß, Henriette; Ohtaka, Minoru; Fiedler, Sebastian; Jünger, Christian; Min, Chul-Hee; Bentmann, Hendrik; Sakamoto, Kazuyuki; Reinert, Friedrich

2012-10-01

404

{bold {ital Ab initio}} calculations of the pressure-induced structural phase transitions for four II-VI compounds  

SciTech Connect

We report on pseudopotential calculations of the structural properties and pressure-induced solid-solid phase transitions for four II-VI compounds: ZnSe, ZnTe, CdSe, and CdTe. For each of these compounds, we fix the zinc-blende structure as the ambient pressure phase and consider the rocksalt, cinnabar, and Cmcm structures as candidates for the high-pressure phases. We calculate the transition pressures and the changes in specific volume for each compound. The pressure dependences of the structural parameters of the cinnabar and the Cmcm phases are determined. The Cmcm structure appears to be a common high-pressure phase for the II-VI and III-V semiconductors. {copyright} {ital 1997} {ital The American Physical Society}

Cote, M.; Zakharov, O.; Rubio, A.; Cohen, M.L. [Department of Physics, University of California at Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

1997-05-01

405

Ann bay lodyans 6 / se Bryant Freeman ("Tonton Liben") ki pare ti liv sa a  

E-print Network

("Tonton Liben") ki pare ti liv sa a. AYITI SE PEP AYISYEN PM 7 8 5 4 .H39 A 5 6 2 0 0 0 V . 6 Enstiti Etid Ayisyen - Inivesite Kannzas Bon Nouvel Fondasyon Alfa Lwes 1997 PINGALOT AK ELIFET Vwala te gen yon wa ki rele Pingalot. Men wa sa a... te yon neg sitelman rayisab tout peyi a t ap soufri. Nan peyi sa a te gen yon msye ki rele Elifet. Se te yon bon moun ki te konn travay di, e ki te fe ekonomi jous li rive monte yon gwo kay menm pi bel pase kay wa a. Konsa, Pingalot moveanpil...

Freeman, Bryant C., ed.

2000-01-01

406

125Te NMR chemical-shift trends in PbTe–GeTe and PbTe–SnTe alloys  

SciTech Connect

Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in 125Te NMR chemical shift due to bonding to dopant or “solute” atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the 125Te NMR chemical shifts in PbTe-based alloys, Pb1?xGexTe and Pb1?xSnxTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS 125Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the 125Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.

Njegic, Bosiljka [Ames Laboratory; Levin, Evgenii M. [Ames Laboratory; Schmidt-Rohr, Klaus [Ames Laboratory

2013-10-08

407

On the Chalcogenophilicity of Mercury: Evidence for a Strong Hg-Se Bond in [TmBut]HgSePh and its Relevance to the Toxicity of Mercury  

PubMed Central

One of the reasons for the toxic effects of mercury has been attributed to its influence on the biochemical roles of selenium. For this reason, it is important to understand details pertaining to the nature of Hg–Se interactions and this has been achieved by comparison of a series of mercury chalcogenolate complexes that are supported by tris(2-mercapto-1-t-butyl-imidazolyl)hydroborato ligation, namely [TmBut]HgEPh (E = S, Se, Te). In particular, X–ray diffraction studies on [TmBut]HgEPh demonstrate that although the Hg–S bonds involving the [TmBut] ligand are longer than the corresponding Cd–S bonds of [TmBut]CdEPh, the Hg–EPh bonds are actually shorter than the corresponding Cd–EPh bonds, an observation which indicates that the apparent covalent radii of the metals in these compounds are dependent on the nature of the bonds. Furthermore, the difference in Hg–EPh and Cd–EPh bond lengths is a function of the chalcogen and increases in the sequence S (0.010 Å) < Se (0.035 Å) < Te (0.057 Å). This trend indicates that the chalcogenophilicity of mercury increases in the sequence S < Se < Te. Thus, while mercury is often described as being thiophilic, it is evident that it actually has a greater selenophilicity, a notion that is supported by the observation of facile selenolate transfer from zinc to mercury upon treatment of [TmBut]HgSCH2C(O)N(H)Ph with [TmBut]ZnSePh. The significant selenophilicity of mercury is in accord with the aforementioned proposal that one reason for the toxicity of mercury is associated with it reducing the bioavailability of selenium. PMID:20020759

Melnick, Jonathan G.; Yurkerwich, Kevin

2009-01-01

408

Sta te a n d E v e n ts fo r W e b Se r v ic e s: A C o m p a r iso n o f F iv e W S-R e so u r c e F r a m e w o r k a n d W S-N o tific a tio n  

E-print Network

Sta te a n d E v e n ts fo r W e b Se r v ic e s: A C o m p a r iso n o f F iv e W S-R e so u r c e n n W a sso n D e p a rtm e n t o f C o m p u te r S c ie n c e , U n iv e rsity o f V irg in ia , C h a rlo tte sv ille , V A U S A K e ith Ja c k so n , Jo sh u a B o v e rh o f, M a tt R o d rig u e

Humphrey, Marty

409

Investigation of structural phase transition behavior by thermal analysis, high temperature X-ray single crystal and vibrational study of Rb2HAsO4?Te(OH)6 compound  

NASA Astrophysics Data System (ADS)

The differential scanning calorimetry (DSC) analysis of Rb2HAsO4?Te(OH)6 (RbAsTe) material shows three phase transitions at 332 K, 464 K and 476 K. In order to identify the first phase transition, we have conducted the X-ray single crystal analysis at high temperature (363 K). X-ray powder diffraction and Raman studies at different temperatures confirmed the presence of the phase transitions in this material as well as the presence of reconstructive phase transition, with such considerable changes of structural parameters. In fact, at T = 363 K, the crystal structure of (RbAsTe) is found to crystallize in the monoclinic system I2/a with the following cell parameters: a = 16.7279(11) Å, b = 7.1339(6) Å, c = 12.4841(10) Å, ? = 90.295(6)°, Z = 8, V = 1489.5(2) Å3. At this temperature, the structure is made up of planes of TeO6 groups alternating with those of AsO4 polyhedra. The Rb+ cations are intercalated between these pure planes. The increase in temperature affected the structural arrangement in which the coordinated polyhedra are distorted and the “a” lattice cell dimension increases with a slight variation of the other parameters. The planes of octahedra and tetrahedra were parallel to the c direction like those in the structure at room temperature but the planes formed by the cations atoms changed their direction.

Bechibani, I.; Litaiem, H.; Ktari, L.; Garcia-Granda, S.; Dammak, M.

2014-10-01

410

New ?-SnTe4 and ?-Sn2Te6 ligands to transition metal: Solvothermal syntheses and characterizations of zinc tellurostannates containing polyamine ligands  

NASA Astrophysics Data System (ADS)

Zinc tellurostannates [{Zn(teta)}2(?-1?:2?-SnTe4)] (1), [{Zn(teta)}3(?3-1?:2?:3?-SnTe4)]I2 (2), [{Zn(tren)}2(?-1?:2?-Sn2Te6)] (3), and [Zn(dien)2]4(Sn2Te6)1.75(Sn2Te8)0.25·dien (4) were prepared by the reactions of Zn, Sn, and Te with iodine ion assistant in teta and dien. The tetrahedral [SnTe4]4- anion coordinates to two [Zn(teta)]2+ units as a bidentate ?-1?:2?-SnTe4 ligand to form the neutral complex 1. It coordinates to three [Zn(teta)]2+ units with a tridentate ?3-1?:2?:3? coordination modes, generating a complex cation [{Zn(teta)}3(?3-1?:2?:3?- SnTe4)]2+ in 2. In 3, the [Sn2Te6]4- anion joins two [Zn(tren)]2+cations with the trans terminal Te atoms, forming neutral complex 3. The ?-1?:2?-SnTe4, ?3-1?:2?:3?-SnTe4, and ?-1?:2?-Sn2Te6 ligands to TM centers in 1-3 have not been observed before. Compound 4 contains a normal [Sn2Te6]4- and an abnormal [(Sn2Te6)0.75(Sn2Te8)0.25]4- anions. Compounds 1-4 exhibit narrow band gaps in the range of 1.47-1.98 eV, and a distinct red-shift of the band gaps is observed from 4 to 1-3.

Lu, Jialin; Wang, Fang; Shen, Yali; Tang, Chunying; Zhang, Yong; Jia, Dingxian

2014-08-01

411

A refined parameterization of the analytical Cd-Zn-Te bond-order potential.  

PubMed

This paper reports an updated parameterization for a CdTe bond order potential. The original potential is a rigorously parameterized analytical bond order potential for ternary the Cd-Zn-Te systems. This potential effectively captures property trends of multiple Cd, Zn, Te, CdZn, CdTe, ZnTe, and Cd(1-x)Zn(x)Te phases including clusters, lattices, defects, and surfaces. It also enables crystalline growth simulations of stoichiometric compounds/alloys from non-stoichiometric vapors. However, the potential over predicts the zinc-blende CdTe lattice constant compared to experimental data. Here, we report a refined analytical Cd-Zn-Te bond order potential parameterization that predicts a better CdTe lattice constant. Characteristics of the second potential are given based on comparisons with both literature potentials and the quantum mechanical calculations. PMID:24220925

Ward, Donald K; Zhou, Xiaowang; Wong, Bryan M; Doty, F Patrick

2013-12-01

412

Band Anticrossing in Highly Mismatched Compound Semiconductor Alloys  

NASA Technical Reports Server (NTRS)

Compound semiconductor alloys in which metallic anions are partially replaced with more electronegative isoelectronic atoms have recently attracted significant attention. Group IIIN(x)V(1-x), alloys with a small amount of the electronegative N substituting more metallic column V elements has been the most extensively studied class of such Highly Mismatched Alloys (HMAs). We have shown that many of the unusual properties of the IIIN(x),V(1-x) alloys can be well explained by the Band Anticrossing (BAC) model that describes the electronic structure in terms of an interaction between highly localized levels of substitutional N and the extended states of the host semiconductor matrix. Most recently the BAC model has been also used to explain similar modifications of the electronic band structure observed in Te-rich ZnS(x)Te(l-x) and ZnSe(Y)Te(1-y) alloys. To date studies of HMAs have been limited to materials with relatively small concentrations of highly electronegative atoms. Here we report investigations of the electronic structure of ZnSe(y)Te(1-y) alloys in the entire composition range, 0 less than or equal to y less than or equal to 1. The samples used in this study are bulk ZnSe(y)Te(1-y) crystals grown by either a modified Bridgman method or by physical vapor transport. Photomodulated reflection (PR) spectroscopy was used to measure the composition dependence of optical transitions from the valence band edge and from the spin-orbit split off band to the conduction band. The pressure dependence of the band gap was measured using optical absorption in a diamond anvil cell. We find that the energy of the spin-orbit split off valence band edge does not depend on composition and is located at about 3 eV below the conduction band edge of ZnSe. On the Te-rich side the pressure and the composition dependence of the optical transitions are well explained by the BAC model which describes the downward shift of the conduction band edge in terms of the interaction between localized Se states and the conduction band. On the other hand we show that the large band gap reduction observed on the Se-rich side of the alloy system is a result of an interaction between the localized Te level and the valence bands. This interaction leads to the formation of a Te-like valence band edge that strongly interacts with the light hole valence band. Calculations based on a modified k p model account for the reduction of the band gap and the large increase of the spin-orbit splitting observed in Se-rich ZnSe(y)Te(l-y) alloys. We will also discuss the importance of these new results for understanding of the electronic structure and band offsets in other high