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1

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

NASA Astrophysics Data System (ADS)

The electric field gradient (efg) parameters were calculated for the ternary system Hf XY ( X = Si, Ge; Y = S, Se, Te), using the full-potential linear augmented plane wave (LAPW) method applying the generalized gradient approximation (GGA). The major contribution to the efg value in these compounds comes from the p-p contribution next to the probe nucleus. The intermetallic compounds Hf XY ( X = Si, Ge; Y = S, Se, Te) show similar electronic properties. This similarity can be attributed to the resemblance of the crystallographic structure and the alike electronic structure of the X and Y ligand atoms, having two and four p-electrons in the external orbital, respectively.

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

2007-04-01

2

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

NASA Astrophysics Data System (ADS)

The electric field gradient (efg) parameters were calculated for the ternary system HfXY (X =Si, Ge; Y =S, Se, Te), using the full-potential linear augmented plane wave (LAPW) method applying the generalized gradient approximation (GGA). The major contribution to the efg value in these compounds comes from the p-p contribution next to the probe nucleus. The intermetallic compounds HfXY (X =Si, Ge; Y =S, Se, Te) show similar electronic properties. This similarity can be attributed to the resemblance of the crystallographic structure and the alike electronic structure of the X and Y ligand atoms, having two and four p-electrons in the external orbital, respectively.

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

3

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

NASA Astrophysics Data System (ADS)

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

Nakamura, Hiroshi; Aoki, Masaharu

1981-01-01

4

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

Microsoft Academic Search

Epitaxial layers of ZnS, ZnSe and their mixed compounds were grown on ZnS substrates by the liquid-phase epitaxial growth (LPE) method using Te as the solvent. The open-tube slide-boat technique was used, and a suitable starting temperature for growth was found to be 850°C for ZnS and 700-800°C for ZnSe. The ZnS epitaxial layers grown on {111}A and {111}B oriented

Hiroshi Nakamura; Masaharu Aoki

1981-01-01

5

Optical properties of glasses activated by the compounds CuInSe 2 and CuInTe 2 and by the solid solutions CuInSe 2 x Te (1? x )  

Microsoft Academic Search

The spectral properties of amorphous media synthesized on the basis of glasses of the system SiO2-CaO-R2O (R=Na, K, Li), the ternary compounds CuInSe2, and CuInTe2, and solid solutions based on them have been investigated. It is shown that the absorption limit of the media investigated\\u000a lies within 1.4–1.6 ?m. It is noted that the three alkali ions constituting the system

I. V. Bodnar’; A. P. Molochko; N. P. Solovei

2000-01-01

6

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

PubMed

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

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

2013-09-24

7

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

NASA Astrophysics Data System (ADS)

The results of a 57Fe Mössbauer spectroscopy study between 2.0 and 297 K of the parent compound Fe1.09Te and the superconductor FeSe0.4Te0.6 are reported. It is shown that in both compounds the magnitude of the quadrupole splitting increases with decreasing temperature and is well described by a T3/2 power-law relation. The presence of incommensurate spin-density-wave antiferromagnetism in Fe1.09Te is demonstrated, with the Néel temperature TN = 71.1(6) K. A theoretical prediction (Zhang et al 2009 Phys. Rev. B 79 012506) of the Fe magnetic moment at the 2c sites being significantly larger than that at the 2a sites in the parent compound is confirmed experimentally by showing that these moments at 4.4 K are, respectively, 3.20(4) and 1.78(3) ?B. The absence of magnetic order in FeSe0.4Te0.6 down to 2.0 K is confirmed. The Debye temperatures of Fe1.09Te and FeSe0.4Te0.6 are found to be 290(1) and 233(1) K, respectively.

Stadnik, Zbigniew M.; Wang, Pu; ?ukrowski, Jan; Noji, Takashi; Koike, Yoji

2013-10-01

8

Binding energies and heat-of-formation data for USbxTe1-x and UAsxSe1-x compounds as derived from photoelectron spectroscopy  

Microsoft Academic Search

Using high-resolution photoelectron spectroscopy with synchrotron radiation we have accurately determined the core-level binding energies in the nonuranium atoms in USbxTe1-x and UAsxSe1-x as a function of the stoichiometric composition. With the use of a Born-Haber cycle a relation between the measured shifts and heat-of-formation data for these compounds is formulated. The analysis demonstrates that photoelectron spectroscopy can become a

N. Mårtensson; B. Reihl; O. Vogt

1982-01-01

9

Zinc-blende compounds of transition elements with N, P, As, Sb, S, Se, and Te as half-metallic systems  

Microsoft Academic Search

We report systematic first-principles calculations for ordered zinc-blende compounds of the transition metal elements V, Cr, and Mn with the sp elements N, P, As, Sb, S, Se, and Te, motivated by a recent fabrication of zinc-blende CrAs, CrSb, and MnAs. They show a ferromagnetic half-metallic behavior for a wide range of lattice constants. We discuss the origin and trends

Iosif Galanakis; Phivos Mavropoulos

2003-01-01

10

Temperature dependence of the band structure of ZnS, ZnSe, ZnTe, and CdTe wurtzite-type semiconductor compounds  

SciTech Connect

The temperature dependence of the energies of some characteristic energy extrema at the {gamma}, L, K, M, A, and H high-symmetry points of the Brillouin zone and the energies of the main interband transitions in hexagonal modifications of ZnS, ZnSe, ZnTe, and CdTe are calculated using the empirical pseudopotential method. The effect of the temperature dependence of electron-phonon interaction on the energy-band structure is taken into account using the Debye-Waller factors, and the effect of lattice linear expansion is described using the temperature dependence of the linear expansion coefficient. The features of the temperature dependence of electron levels, interband transitions, and temperature coefficients are discussed in detail. Possible applications of the obtained results are considered.

Gorkavenko, T. V. [Shevchenko National University (Ukraine)], E-mail: gorka@univ.kiev.ua; Zubkova, S. M. [National Academy of Sciences of Ukraine, Frantsevich Institute for Problems of Material Science (Ukraine)], E-mail: svzubkova@yahoo.com; Makara, V. A. [Shevchenko National University (Ukraine); Rusina, L. N. [National Academy of Sciences of Ukraine, Frantsevich Institute for Problems of Material Science (Ukraine)

2007-08-15

11

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.

2010-01-01

12

ZnSe/ZnSeTe Superlattice Nanotips  

NASA Astrophysics Data System (ADS)

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.

Hsiao, C. H.; Hung, S. C.; Chih, S. H.; Wang, S. B.; Cheng, Y. C.; Huang, B. R.; Young, S. J.; Chang, S. J.

2010-06-01

13

Zinc-blende compounds of transition elements with N, P, As, Sb, S, Se, and Te as half-metallic systems  

NASA Astrophysics Data System (ADS)

We report systematic first-principles calculations for ordered zinc-blende compounds of the transition metal elements V, Cr, and Mn with the sp elements N, P, As, Sb, S, Se, and Te, motivated by a recent fabrication of zinc-blende CrAs, CrSb, and MnAs. They show a ferromagnetic half-metallic behavior for a wide range of lattice constants. We discuss the origin and trends of half-metallicity, present the calculated equilibrium lattice constants, and examine the half-metallic behavior of their transition element terminated (001) surfaces.

Galanakis, Iosif; Mavropoulos, Phivos

2003-03-01

14

A comparative crystallochemical analysis of binary compounds and simple anhydrous salts containing pyramidal anions LO3 (L = S, Se, Te, Cl, Br, I).  

PubMed

A comparative analysis of binary compounds and 61 simple anhydrous salts M(y)(LO(3))(z) (L = S, Se, Te, Cl, Br, I) was performed using the crystallochemical program package TOPOS. A topological similarity was found between the salts and six types of binary compounds (NaCl, NiAs, PoCl(2), Tl(2)S(2), ZnTe, rutile). It is notable that these structure relationships are typical for other groups of inorganic salts: borates, carbonates, nitrates, orthophosphates, orthoarsenates, sulfates, selenates, perchlorates, molybdates and halogenides of d-metals. For all the M(y)(LO(3))(z) compounds the topology and uniformity of the ion arrays were investigated. It has been established that in 36 out of the 61 salts at least one ion array has the topology of close packing or the body-centred cubic lattice. The results obtained have allowed us to come to conclusions about the structure-forming role of the arrays of various chemical composition. PMID:16710065

Blatov, V A; Peskov, M V

2006-05-15

15

Thin film solar cells based on CdTe and Cu(In,Ga)Se2 (CIGS) compounds  

NASA Astrophysics Data System (ADS)

We are publishing recent results in chalcogenide photoelectric convertors fabrication, which are efforts of many scientific teams from Russia, Belarus, Ukraine, and Kazakhstan. Competitively high efficiency of photoelectric convertors (11.4% for CdTe and 11% for CIGS) was achieved in the process of our work. Furthermore, luminescent filters for improvement of spectral response of such chalcogenide solar cells in a short wavelengths region were also developed and investigated here.

Gladyshev, P. P.; Filin, S. V.; Puzynin, A. I.; Tanachev, I. A.; Rybakova, A. V.; Tuzova, V. V.; Kozlovskiy, S. A.; Gremenok, V. F.; Mudryi, A. V.; Zaretskaya, E. P.; Zalesskiy, V. B.; Kravchenko, V. M.; Leonova, U. R.; Khodin, A. A.; Pilipovich, V. A.; Polikanin, A. M.; Khrypunov, G. S.; Chernyh, E. P.; Kovtun, N. A.; Belonogov, E. K.; Ievlev, V. M.; Dergacheva, M. B.; Stacuk, V. N.; Fogel, L. A.

2011-04-01

16

Electrical properties of light-emitting devices based on the II–VI compounds BeTe and BeMgZnSe  

Microsoft Academic Search

Light-emitting diodes with BeMgZnSe cladding layers and an active region formed by a ZnSe, BeZnSe or BeZnSeTe single quantum well are characterized by means of current-voltage measurements and electroluminescence at room temperature. A longterm stability exceeding 4000 h has been estimated in first experiments at low current densities (15 A cm?2). The emission wavelength was tuned between 452 and 518

F. Fischer; J. Laubender; H. J. Lugauer; T. Litz; A. Weingärtner; U. Zehnder; T. Gerhard; W. Ossau; K. Schüll; A. Waag; G. Landwehr

1997-01-01

17

The Bacterial Response to the Chalcogen Metalloids Se and Te  

Microsoft Academic Search

Microbial metabolism of inorganics has been the subject of interest since the 1970s when it was recognized that bacteria are involved in the transformation of metal compounds in the environment. This area of research is generally referred to as bioinorganic chemistry or microbial biogeochemistry. Here, we overview the way the chalcogen metalloids Se and Te interact with bacteria. As a

Davide Zannoni; Francesca Borsetti; Joe J. Harrison; Raymond J. Turner

2007-01-01

18

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

Microsoft Academic Search

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

N. Martensson; B. Reihl; O. Vogt

1982-01-01

19

Scanning tunneling spectroscopy studies of Bi2Te2Se  

NASA Astrophysics Data System (ADS)

Topological insulators are a class of semiconductors characterized by the presence of current-carrying helical surface states lying within the bulk gap. The surface states of these materials possess massless Dirac-like dispersion. Helical spin texture of the surface states leads to suppression of backscattering in these materials. Results of scanning tunneling spectroscopy study of Bi2Te2Se (BTS) topological insulator will be presented. Similar to previously studied Bi2Te3 and Bi2Se3 the new material shows a relatively large band gap and a simple surface band structure. High bulk resistivity and high surface electron mobility make it a compound of interest for potential applications. Differential conductance mapping with scanning tunneling microscope is used to visualize surface states of this novel highest-bulk-resistivity topological insulator. These experiments enable us to assess the variation of local density of states in this compound under different growth conditions and to correlate the findings with transport properties

Drozdov, Ilya; Baidenkopf, Haim; Seo, Jungpil; Jia, Shuang; Cava, Robert; Yazdani, Ali

2012-02-01

20

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

NASA Astrophysics Data System (ADS)

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

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

2002-10-01

21

Mg y Zn1-y Te1-x Se x : energy gaps  

NASA Astrophysics Data System (ADS)

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 MgyZn1-yTe1-xSex (magnesium zinc telluride selenide), Element System Mg-Se-Te-Zn.

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

22

Structural changes in Se-Te bilayers by laser writing  

Microsoft Academic Search

Transmission electron microscopy is used to characterize the hole-formation process due to laser writing in evaporated and sputtered Te thin films and in a Se-Te bilayer. Bilayers, with Se as the top layer, combine the effect of an antireflective coating with protection against oxidation and provide the advantage of alloy formation during spot writing. Solidification of the melt in the

S. R. Herd; K. Y. Ahn; R. J. von Gutfeld; D. R. Vigliotti

1982-01-01

23

Topological surface states with persistent high spin polarization across the Dirac point in Bi2Te2Se and Bi2Se2Te.  

PubMed

Helical spin textures with marked spin polarizations of topological surface states have been unveiled for the first time by state-of-the-art spin- and angle-resolved photoemission spectroscopy for two promising topological insulators, Bi(2)Te(2)Se and Bi(2)Se(2)Te. Their highly spin-polarized natures are found to be persistent across the Dirac point in both compounds. This novel finding paves a pathway to extending the utilization of topological surface states of these compounds for future spintronic applications. PMID:23215110

Miyamoto, K; Kimura, A; Okuda, T; Miyahara, H; Kuroda, K; Namatame, H; Taniguchi, M; Eremeev, S V; Menshchikova, T V; Chulkov, E V; Kokh, K A; Tereshchenko, O E

2012-10-17

24

Photoluminescence (PL) of ?-doped ZnSe:Te,N  

NASA Astrophysics Data System (ADS)

It is well known that reliable p-type contact layers for ZnSe based light emitting devices are still a problem. Recently [1] it has been shown that the use of ?-doping of ZnSe with both Te and N increases doping levels to the upper 10^18 cm-3 range. A better understanding of N/Te/Se interactions appears of interest here. With this aim, we studied low temperature PL of ?-doped ZnSe:Te and ZnSe:Te,N layers grown by MBE. We show that PL from ?-doped ZnSe:Te is similar to that observed from undoped ZnSe_1-xTex alloys, where it was attributed to excitons localized at Te related defects. Our data suggest that these defects are Te clusters rather than single Te atoms. We also show that the presence of N reduces overall PL efficiency and modifies the PL from excitonic to a DAP like type. We shall propose possible microscopic models to explain the experimental observations. We acknowledge support from DOE under grants DE-FG02-98ER45694 and DE-FG02-98ER45695. [1] H.D. Jung, et. al., Appl. Phys. Lett., V.70, 1143 (1997).

Neumark, G. F.; Kuskovsky, I.; Tian, C.; Sudbrack, C.; Lin, W.; Guo, S. P.; Tamargo, M. C.

2000-03-01

25

Growth and characterization of CdTeSe for room-temperature radiation detector applications  

NASA Astrophysics Data System (ADS)

The near-unity segregation coefficient of Se in a CdTe matrix ensures the compositional homogeneity, both axial- and radial, of the CdTeSe ternary compound, so making it a material of choice for room- temperature radiation detectors. In this study, we grew CdTeSe crystals by the Traveling Heater Method (THM), using Te as the solvent, and characterized the crystals by IR transmission microscopy, white-beam X-ray diffraction topography, and low-temperature photoluminescence. The total average concentration of the secondary phases obtained for the CdTeSe sample was about 7x104 cm-3 for crystals grown at two different laboratories. The best resistivity registered was 5x109 ohm-cm, and the estimated ?? product for the electrons was 3-4x10-3 cm2/V.

Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Yang, G.; James, R. B.; Fauler, A.; Fiederle, M.; Sowinska, M.; Hennard, G.; Siffert, P.

2013-09-01

26

ZnO/ZnSe/ZnTe Heterojunctions for ZnTe-Based Solar Cells  

NASA Astrophysics Data System (ADS)

ZnO and ZnSe are proposed as n-type layers in ZnTe heterojunction diodes to overcome problems associated with the n-type doping of ZnTe. The structural properties and electrical characteristics of ZnO/ZnTe and ZnO/ZnSe/ZnTe heterojunctions grown by molecular beam epitaxy on (001) GaAs substrates are presented. ZnO shows a strong preference for c-plane (0001) orientation resulting in a nonepitaxial relationship and high density of rotational domains for growth on ZnTe (001). ZnSe/ZnTe structures demonstrate a (001) epitaxial relationship with high density of {111} stacking faults originating at the heterojunction interface. ZnO/ZnSe/ZnTe heterojunction diodes show excellent diode rectification and clear photovoltaic response with open-circuit voltage of V OC = 0.8 V.

Wang, W.; Phillips, J. D.; Kim, S. J.; Pan, X.

2011-08-01

27

Promising topological surface states with persistent high spin polarization across Dirac point in Bi2Te2Se and Bi2TeSe2  

NASA Astrophysics Data System (ADS)

Topological insulators (TIs) have attracted a great deal of atteion as key materials for spintronics technology. Among the established TIs, Bi2X3 (X=Se, Te) has been mostly studied because of their relatively large energy gap and the simplest topological surface state (TSS) with helical spin texture. However, an absence of the topological natures of TSS below Dirac point (ED) has been shown by spin- and angle-resolved photoemission spectroscopy (SARPES) and scanning tunneling spectroscopy under perpendicular magnetic field. It could be a disadvantage for extending its spintronic applications. Recently, one of the ternary tetradymite compounds, Bi2Te2Se was shown to be a TI by the ARPES measurement. Importantly, a highly bulk resistive feature in this compound has successfully led to the observation of its surface-derived quantum oscillations in the magnetotransport experiment. We have unambiguously clarified the spin feature of TSS in Bi2Te2Se and Bi2Se2Te for the first time by our novel SARPES. The markedly high spin polarization of topological surface states has been found to be 77% and is persistent in the wide energy range across ED in those compounds. The finding promises to extend the variety of spintoronic applications.

Miyamoto, Koji; Kimura, Akio; Okuda, Taichi; Miyahara, Hirokazu; Namatame, Hirofumi; Taniguchi, Masaki; Eremeev, Sergey; Chulkov, Evgueni; Tereshchenko, Oleg

2013-03-01

28

ZnO\\/ZnSe\\/ZnTe Heterojunctions for ZnTe-Based Solar Cells  

Microsoft Academic Search

ZnO and ZnSe are proposed as n-type layers in ZnTe heterojunction diodes to overcome problems associated with the n-type doping of ZnTe. The structural properties and electrical characteristics of ZnO\\/ZnTe and ZnO\\/ZnSe\\/ZnTe heterojunctions grown by molecular beam epitaxy on (001) GaAs substrates are presented. ZnO shows a strong preference for c-plane (0001) orientation resulting in a nonepitaxial relationship and high

W. Wang; J. D. Phillips; S. J. Kim; X. Pan

2011-01-01

29

ZnO\\/ZnSe\\/ZnTe Heterojunctions for ZnTe-Based Solar Cells  

Microsoft Academic Search

ZnO and ZnSe are proposed as n-type layers in ZnTe heterojunction diodes to overcome problems associated with the n-type doping of ZnTe. The structural properties and electrical characteristics of ZnO\\/ZnTe and ZnO\\/ZnSe\\/ZnTe heterojunctions\\u000a grown by molecular beam epitaxy on (001) GaAs substrates are presented. ZnO shows a strong preference for c-plane (0001) orientation resulting in a nonepitaxial relationship and high

W. Wang; J. D. Phillips; S. J. Kim; X. Pan

2011-01-01

30

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

31

HgTe, CdTe, (Cd,Mn)Te, (Cd,Mg)Te, ZnTe, HgSe, CdSe, ZnCdSe, (Cd,Mn)Se, ZnSe, HgS, CdS, ZnS, CdO, ZnO quantum dots -self-organized, epitaxially grown nanostructures  

NASA Astrophysics Data System (ADS)

This document is part of subvolume C2 'Optical Properties', of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter. Data for HgTe, CdTe, (Cd,Mn)Te, (Cd,Mg)Te, ZnTe, HgSe, CdSe, ZnCdSe, (Cd,Mn)Se, ZnSe, HgS, CdS, ZnS, CdO, ZnO quantum dots (self-organized, epitaxially grown nanostructures) are provided.

Woggon, U.

32

HgTe, CdTe, (Cd,Mn)Te, (Cd,Mg)Te, ZnTe, HgSe, CdSe, ZnCdSe, (Cd,Mn)Se, ZnSe, HgS, CdS, ZnS, CdO, ZnO quantum dots -self-organized, epitaxially grown nanostructures  

Microsoft Academic Search

This document is part of subvolume C2 'Optical Properties', of volume 34 'Semiconductor quantum structures' of Landolt-Börnstein, Group III, Condensed Matter. Data for HgTe, CdTe, (Cd,Mn)Te, (Cd,Mg)Te, ZnTe, HgSe, CdSe, ZnCdSe, (Cd,Mn)Se, ZnSe, HgS, CdS, ZnS, CdO, ZnO quantum dots (self-organized, epitaxially grown nanostructures) are provided.

U. Woggon

2004-01-01

33

A Quaternary ZnCdSeTe Nanotip Photodetector  

PubMed Central

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

2009-01-01

34

Growth and optical parameters of GaSe:Te crystals  

NASA Astrophysics Data System (ADS)

A series of technological experiments on the growth of GaSe:Te single crystals by the Bridgman-Stockbarger method is performed. Surface micromorphology and mechanical properties of crystals with different doping levels are studied. Spectral dependences of the complex refractive index are obtained using ellipsometry. The experimental data are approximated within the Lorentz-Drude model.

Sarkisov, S. Yu.; Atuchin, V. V.; Gavrilova, T. A.; Kruchinin, V. N.; Bereznaya, S. A.; Korotchenko, Z. V.; Tolbanov, O. P.; Chernyshev, A. I.

2010-09-01

35

Physical ageing in Se-Te-Sb glasses  

NASA Astrophysics Data System (ADS)

Bulk Se60-xTe40Sbx glasses in the composition range 0?x?14 were prepared by the melt quenching method. Differential Scanning Calorimetric (DSC) and thermal crystallization studies were performed to understand the thermodynamic property like glass transition and structural transformations. These glasses exhibit sharp endothermic peak at the glass transition (Tg). Disappearance of the endothermic peak at Tg in the rejuvenated samples clearly indicates the ageing effect in these glasses. Addition of Sb to Se-Te increases the connectivity of the structural network which is evidenced from the increase in Tg. A distinct change in the slope of the Tg at x=6, indicates a major change in the way the network is connected. The glass forming ability and the thermal stability also exhibit a maximum at x=6. Tg increases with the ageing time and the corresponding fictive temperature (Tf) calculated from the specific heat curves shows a decreasing trend. The molecular movements along the polymeric Se chains might cause the structural relaxation and the physical ageing. The physical ageing effect has been understood on the basis of the Bond Free Solid Angle (BFSA) model proposed by Kastner. Thermally crystallized samples show the formation of rhombohedral Sb2Te3, rhombohedral Sb2Se3 and hexagonal Te phases.

Vanitha, M. K.; Hanumantha Rao, M. V.; Asokan, S.; Ramesh, K.

2013-06-01

36

Electro-optical characterization of Ge–Se–Te glasses  

Microsoft Academic Search

Chalcogenide bulk glasses Ge20Se80?xTex for x?(0,15) have been prepared by systematic replacement of Se by Te. Selected glasses have been doped with Ho, Er and Pr, and samples have been characterized by transmission spectroscopy, measurements of dc electrical conductivity and low-temperature photoluminescence. Absorption coefficients have been derived from measured transmittance and estimated reflectance. Arrhenius plots of dc electrical conductivity, in

J. Zavadil; P. Kostka; J. Pedlikova; K. Zdansky; M. Kubliha; V. Labas; J. Kaluzny

2009-01-01

37

Luminescence decay studies on ?-doped ZnSe:Te  

NASA Astrophysics Data System (ADS)

The performance of II-VI wide-bandgap semiconductor based light emitting devices crucially depends on good bipolar conductivity of the constituting materials. For this reason, ZnSeTe has received much attention, as it is relatively easy to obtain n-type ZnSe and p-type ZnTe. Its optical properties have been extensively studied. We examined novel, single and triple ?-doped, ZnSe:Te systems. We previously studied the CW photoluminescence (PL) of these samples, and attributed the dominant PL to the radiative recombination of excitons bound to Te clusters of various sizes [1]. To further investigate the properties of the centers we performed time-resolved photoluminescence experiments, results of which will be presented. Specifically, we determined the decay times of different PL bands for both types of samples, and studied their temperature- and excitation power dependencies. We acknowledge support from DOE under grants #DE-FG02-98ER45694 and #DE-FG02-98ER45695. [1] I.L. Kuskovsky et al., abstract T17 6, APS March Meeting, 2000; I.L. Kuskovsky et al., submitted to Physical Review B.

van der Voort, Marjolein; Kuskovsky, Igor L.; Gu, Y.; Neumark, G. F.; Lin, W.; Guo, S. P.; Tamargo, M. C.

2001-03-01

38

Galvanomagnetic and thermomagnetic properties of thallium doped PbSnTe and PbSeTe  

NASA Astrophysics Data System (ADS)

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 PbTe is sensitive to alloying with Sn and Se, and thus the location of the Tl level with respect to the valence band can change with x. In this study, we investigate the effects that band structure modifications have on the enhancement of thermopower. Thermoelectric properties of Pb1-x-y TlySnxTe and Pb1-yTlyTe1-xSex alloys with y=0.01-0.04 and x=0-0.3 are measured in directions longitudinal and transverse to magnetic fields in the range of -1.5 to 1.5T. We report zero field values of electrical resistivity, thermopower, Hall coefficient and adiabatic Nernst-Ettinghausen coefficient as measured in temperature range 80-420K. From these we calculate carrier density and mobility and the density of states effective masses and Fermi energies. [2] J.P. Heremans et al., Science 321, 554 (2008)

Jovovic, Vladimir; Heremans, Joseph

2009-03-01

39

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

PubMed

We exploited the synthesis of near-infrared (NIR) emitting ternary-alloyed CdTeSe and quaternary-alloyed CdZnTeSe quantum dots (QDs) with rod and tetrapod morphologies, which have tunable emission in the NIR electromagnetic spectrum. The morphologies of the QDs depended strongly on their growth kinetics, probably due to the coordinating ligands used in the preparation. Using oleic acid, stearic acid and hexadecylamine as ligands and keeping the same reaction parameters, QDs with tetrapod and rod morphologies were created. Not only had the capping ligands influenced the morphologies of QDs, but also they influenced the optical properties of QDs. The molar ratios of Cd/Zn and Te/Se upon preparation were adjusted for investigating the effect of composition on the properties of resulting QDs. By varying the composition of QDs, the photoluminescence (PL) wavelength of QDs was tuned from 650?nm to 800?nm. To enhance PL efficiency and stability, QDs were coated with a CdZnS shell. As NIR PL has numerous advantages in biological imaging detection, these QDs hold great potential for application. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23060275

Yang, Fanghong; Yang, Ping; Zhang, Lipeng

2012-10-11

40

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

41

Detection of CdS(Te) and ZnSe(Te) scintillation light with silicon photodiodes  

SciTech Connect

In this paper, some scintillation characteristics of CdS(Te) are investigated. The scintillation emission spectrum of CdS(Te) single crystals is situated in a band between 560 and 800 nm with maximum at 640 nm. The light yield of this red emitting crystal on a [mu]s time scale is rather large approximately 1.7 [center dot] 10[sup 4] photons per MeV of absorbed [gamma]-ray energy. The scintillation light can be efficiently detected with silicon photodiodes; results are presented. Main decay time components of 270 ns and 3.0 [mu]s were measured. The scintillation mechanism and the application of the material is discussed. Also some data regarding a similar system, ZnSe(Te), are presented.

Schotanus, P. (Radiation Detectors and Crystals, Quartz and Silice Holland B.V., P.O. Box 168, 3454 ZK, DeMeern (Netherlands)); Dorenbos, P. (Radiation Technology Group, Dept. of Applied Physics, Delft Univ. of Technology, Mekelweg 15, 2629 JB, Delft (Netherlands)); Ryzhikov, V.D. (Inst. for Single Crystals, Lenin Av. 60, Kharkov, 310141 (USSR))

1992-08-01

42

The X-ray photoelectron spectra of MnS, MnSe, and MnTe  

Microsoft Academic Search

The core level binding energies and valence band spectra of MnS, MnSe, and MnTe have been examined by X-ray photoelectron spectroscopy. The results demonstrate that the compounds are substantially more ionic in character than related transition metal compounds, and that the compounds lack significant metalmetal interactions, accounting for the nontypical nature of the compounds as transition metal chalcides. Summer Faculty

Hugo Franzen; Carl Sterner

1978-01-01

43

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

44

Sputter deposited ZnTe\\/ZnSe\\/ZnO heterojunctions for photovoltaic applications  

Microsoft Academic Search

Films of ZnTe, ZnSe, and ZnO were deposited on (100) Si by RF magnetron sputtering from stoichiometric ZnTe, ZnSe, and ZnO targets for the purpose of fabricating a ZnTe\\/ZnSe heterojunction. Rutherford back scattering (RBS) analysis yielded a composition of Zn1.0Te1.0 for ZnTe, Zn1.1Se1.2 for ZnSe, and Zn1.0O0.8 for ZnO which indicates that near-stoichiometric films were obtained. Transmission electron microscopy (TEM)

O. Akpa; S. Shaik; T. Thompson; T. Isaacs-Smith; P. Anderson; S. Seraphin; K. Das

2010-01-01

45

High-purity As-S-Se and As-Se-Te glasses and optical fibers  

Microsoft Academic Search

We describe a procedure for the preparation of As-S-Se and As-Se-Te glasses with low contents of gas-forming impurities (hydrogen,\\u000a oxygen, and carbon) via melting of extrapure-grade elements in an evacuated silica ampule and purification of the melt by\\u000a chemical distillation. The impurity concentrations in the glasses thus prepared have been reduced to the following levels:\\u000a hydrogen, <0.02; oxygen, 0.2; carbon,

M. F. Churbanov; V. S. Shiryaev; A. I. Suchkov; A. A. Pushkin; V. V. Gerasimenko; R. M. Shaposhnikov; E. M. Dianov; V. G. Plotnichenko; V. V. Koltashev; Yu. N. Pyrkov; J. Lucas; J.-L. Adam

2007-01-01

46

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

47

Magnetic behavior of Fe(Se,Te) systems: First-principles calculations  

Microsoft Academic Search

The magnetic behaviors in Fe(Se,Te) systems have been investigated systematically using density functional calculations. At the experimental lattice parameters, the ground state is found to be in the double stripe magnetic phase for FeTe but in the single stripe magnetic phase for FeSe and FeSe0.5Te0.5, and there is no preference in the different easy axes of magnetization. Substitution of Se

Hongliang Shi; Zhong-Bing Huang; John S. Tse; Hai-Qing Lin

2011-01-01

48

Electronic structure of layered transition-metal dichalcogenides Nb1-xTixXc2 (Xc = S, Se, Te) studied by angle-resolved photoemission spectroscopy  

Microsoft Academic Search

We have performed systematic high-resolution angle-resolved photoemission spectroscopy (ARPES) on layered transition-metal dichalcogenides Nb1-xTixXc2 (Xc = S, Se, Te) to study the mechanism of metal semiconductor transition as a function of x and Xc. We found a pseudogap near EF in the S- and Se-based compounds while a clear Fermi edge is observed in the Te-based compound. The existence of

T. Sato; H. Komatsu; K. Terashima; T. Takahashi; M. Shimakawa; K. Hayashi

2004-01-01

49

Luminescence decay studies on delta-doped ZnSe:Te  

Microsoft Academic Search

The performance of II-VI wide-bandgap semiconductor based light emitting devices crucially depends on good bipolar conductivity of the constituting materials. For this reason, ZnSeTe has received much attention, as it is relatively easy to obtain n-type ZnSe and p-type ZnTe. Its optical properties have been extensively studied. We examined novel, single and triple delta-doped, ZnSe:Te systems. We previously studied the

Marjolein van der Voort; Igor L. Kuskovsky; Y. Gu; G. F. Neumark; W. Lin; S. P. Guo; M. C. Tamargo

2001-01-01

50

Magnetic behavior of Fe(Se,Te) systems: First-principles calculations  

NASA Astrophysics Data System (ADS)

The magnetic behaviors in Fe(Se,Te) systems have been investigated systematically using density functional calculations. At the experimental lattice parameters, the ground state is found to be in the double stripe magnetic phase for FeTe but in the single stripe magnetic phase for FeSe and FeSe0.5Te0.5, and there is no preference in the different easy axes of magnetization. Substitution of Se by Te enlarges the size of the Fermi surface in FeSe0.5Te0.5, resulting in a stronger nesting effect and thus enhancing the superconductivity. It is found that the double stripe order in FeTe1-xSex changes to the single stripe order when x> 0.18. Spiral calculations on FeSe0.5Te0.5 show that the lowest energy is at the commensurate point Qvec = (0.5,0.5), accompanied by additional local minima at two incommensurate points near Qvec = (0.5,0.5). This observation is consistent with the experimentally observed positions of low energy magnetic excitations. Geometry optimization calculations show that the tetragonal cell relaxes to orthorhombic and monoclinic cells for FeSe and FeTe, respectively, but remains unchanged for FeSe0.5Te0.5.

Shi, Hongliang; Huang, Zhong-Bing; Tse, John S.; Lin, Hai-Qing

2011-08-01

51

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

PubMed

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

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

2011-11-17

52

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

53

Syntheses, Crystal Structures, and Physical Properties of the New Thorium Chalcogenides CuTh(2)Te(6) and SrTh(2)Se(5).  

PubMed

Single crystals of CuTh(2)Te(6) form by a stoichiometric reaction of the elements at 1000 degrees C. The compound crystallizes in the space group -P2(1)/m with unit cell parameters a = 6.170(2) Å, b = 4.332(1) Å, c = 10.424(3) Å, beta = 98.85(1) degrees, and Z = 1 at 113 K. The structure was solved from single-crystal X-ray data. It consists of layers of [Th(2)Te(6)(-)] double chains joined by Cu(+) cations. Each Th atom is coordinated to eight Te atoms in a bicapped trigonal prismatic arrangement. There are three crystallographically unique Te atoms. Each ThTe(8) unit is bridged through one distinct Te atom, such that the capping Te atom of one unit forms the vertex of its neighbor. The two nonbridging Te atoms form infinite Te-Te chains along the exterior of the [Th(2)Te(6)(-)] layer. Copper atoms are coordinated to these Te atoms in a tetrahedral arrangement. Owing to the existence of Te-Te bonds of intermediate length, the assignment of formal oxidation states in this compound is not possible. Four-probe dc electrical conductivity measurements of a single crystal of CuTh(2)Te(6) indicate the compound is a semiconductor along [010]. Magnetic susceptibility measurements in the range 2-300 K show CuTh(2)Te(6) to be paramagnetic with &mgr;(eff) = 2.06 &mgr;(B) at 300 K. Single crystals of SrTh(2)Se(5) form from the reaction SrSe + Th + 3Sn + 3Se at 1000 degrees C. EDAX experiments show no tin present in several crystals analyzed. Transparent red blocks of SrTh(2)Se(5) crystallize in the space group -P2(1)/c with unit cell parameters a = 8.704(2) Å, b = 7.861(2) Å, c = 12.458(4) Å, beta = 90.00(2) degrees, and Z = 4 at 113 K. The structure, which is related to that of U(3)S(5), is a three-dimensional framework with Sr cations located in one-dimensional channels. There are two distinct Th environments, bicapped trigonal prismatic and distorted monocapped octahedral. There are no Se-Se bonds and so formal oxidation states of Sr(2+), Th(4+), and Se(2)(-) may be assigned. PMID:11670482

Narducci, Amy A.; Ibers, James A.

1998-07-27

54

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

55

Effect of Te on the self-activated emission of ZnSe  

SciTech Connect

An interpretation of the optical properties of ZnSe is suggested. The interpretation is based on the anticrossing band theory, which specifies the oxygen-induced splitting of the conduction band. It is shown that the new approach provides a means for understanding the specific features of the self-activated luminescence in ZnSe:O and (ZnSe:O):Te. The effect of small (<1%) Te additives on the luminescence of ZnSe:Te in the edge spectral region is interpreted. The model of electronic transitions is presented.

Morozova, N. K., E-mail: MorozovaNK@mail.ru; Mideros, D. A. [Moscow Power Engineering Institute (Technical University) (Russian Federation)

2008-12-15

56

Photoluminescence (PL) of delta-doped ZnSe:Te,N  

Microsoft Academic Search

It is well known that reliable p-type contact layers for ZnSe based light emitting devices are still a problem. Recently [1] it has been shown that the use of delta-doping of ZnSe with both Te and N increases doping levels to the upper 10^18 cm-3 range. A better understanding of N\\/Te\\/Se interactions appears of interest here. With this aim, we

G. F. Neumark; I. Kuskovsky; C. Tian; C. Sudbrack; W. Lin; S. P. Guo; M. C. Tamargo

2000-01-01

57

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

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

58

Doping Studies of BI2(TE,Se)3 Alloys.  

National Technical Information Service (NTIS)

Alloys of Bi2Te(3-x)Sex (0< or = X< or = 1) doped with controlled amounts of Cu, CuBr and BiI3 have been prepared according to the Bridgeman technique. The number, epsilon, of charge carriers per doping molecule as obtained from thermoelectric and galvano...

O. Beckman P. Bergvall K. Tripathi

1964-01-01

59

In and InSe doping influence on CdTe postmelting effect  

NASA Astrophysics Data System (ADS)

The influence of small In or InSe (up to 10 mol. %) additions to the CdTe melt on additional endothermic effects (AEE) positions in DTA thermograms was studied. It was observed, that both AEEs at 1392 K, typical for pure CdTe melt, and “own" at Tm+(9-10) K appear in CdTe+In melt heating curves during thermocycling. The melting of CdTe-InSe alloys occurs step-by-step without “own" postmelting effects. The solid CdTe dissociation enthalpy near Tm (? Hdiss=287± 22 kJ/mol) and the CdTe fusion enthalpy (? H_f=43.85± 1.15 kJ/mol) were estimated on the base of the obtained DTA data. L'influence de petites additions d'In ou d'InSe (jusqu'à 10 mol%) à du CdTe fondu sur les positions des effets endothermiques additionels (AEE) des thermogrammes d'analyse thermique différentielle (ATD) ont été étudiés. Nous avons observé, à la fois, que l'effet AEE à 1392± 1 K, typique du CdTe pure fondu et qu'un “novel" effet à la temperature de liquidus d'alliage CdTe+In ±(9-10) K sont reproduits dans les courbes de chauffage. La fusion des alliages CdTe-InSe s'effectue pas à pas sans effets de post-fusion particuliers. L'enthalpie de dissociation de CdTe solide près de Tm (? Hdiss=287± 22 kJ/mol) et l'enthalpie de fusion de CdTe (? H_f=43,85± 1,15 kJ/mol) ont été estimées à partir des donnes obtenues par ATD.

Shcherbak, L.; Feychuk, P.; Kopach, O.; Falenchuk, O.; Panchuk, O.

1998-07-01

60

Polycrystalline CdTe on CuInSe2 cascaded solar cells  

NASA Astrophysics Data System (ADS)

Experimental results obtained using a CdS/CdTe/ZnTe top cell on a CdS/CuInSe2 bottom cell are presented. Single cells of each type exhibit an 11 percent efficiency. The fabrication of a mechanically stacked CdTe-CuInSe2 tandem cell that shows an efficiency of 9.9 percent is discussed . The current of the CuInSe2 cell is limited by the transmission through the CdTe cell. Semiquantitative analysis of the optical losses in the structure indicates that substantial improvements in tandem device performance can be achieved by: 1) reducing free carrier absorption in the transparent (SnOx) top contact, e.g., by using an alternative transparent contact such as ITO or ZnO which has better near-IR transmission, and 2) reducing the absorption in the Cu-doped ZnTe layer-perhaps by reducing the Cu doping level.

Meyers, P. V.; Liu, C. H.; Russell, L.; Ramanathan, V.; Birkmire, R. W.

61

CdSe/ZnSe quantum dot structures grown by molecular beam epitaxy with a CdTe submonolayer stressor  

SciTech Connect

A procedure for formation of CdSe quantum dots (QDs) in a ZnSe matrix is suggested. The procedure is based on the introduction of a CdTe submonolayer stressor deposited on the matrix surface just before deposition of the material of the QDs. (For CdTe/ZnSe structure, the relative lattice mismatch is {delta}a/a {approx} 14%.) The stressor forms small strained islands at the ZnSe surface, thus producing local fields of high elastic stresses controlling the process of the self-assembling of the QDs. According to the data of transmission electron microscopy, this procedure allows a considerable increase in the surface density of QDs, with a certain decrease in their lateral dimensions (down to 4.5 {+-} 1.5 nm). In the photoluminescence spectra, a noticeable ({approx}150 meV) shift of the peak to longer wavelengths from the position of the reference CdSe/ZnSe QD structure is observed. The shift is due to some transformation of the morphology of the QDs and an increase in the Cd content in the QDs. Comprehensive studies of the nanostructures by recording and analyzing the excitation spectra of photoluminescence, the time-resolved photoluminescence spectra, and the cathodoluminescence spectra show that the emission spectra involve two types of optical transitions, namely, the type-I transitions in the CdSeTe/ZnSe QDs and the type-II transitions caused mainly by the low cadmium content (Zn,Cd)(Se,Te)/ZnSe layer formed between the QDs.

Sedova, I. V., E-mail: irina@beam.ioffe.ru; Lyublinskaya, O. G.; Sorokin, S. V.; Sitnikova, A. A.; Toropov, A. A. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Donatini, F.; Dang, Si Le [Universite J. Fourier-Grenoble, CEA-CNRS-UJF Group 'Nanophysique et Semiconducteurs', Laboratoire de Spectrometrie Physique (CNRS UMR5588) (France); Ivanov, S. V. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2007-11-15

62

Structure of Zn-Se-Te system with submonolayer insertion of ZnTe grown by migration enhanced epitaxy  

SciTech Connect

We here report results of high resolution x-ray diffraction, x-ray reflectivity (XRR), as well as optical absorption and reflection measurements on ZnSe samples grown by molecular beam epitaxy, with insertion of planar ({delta}-) regions of both N as an acceptor dopant and Te as a 'co-dopant' to facilitate a p-type doping. We note that to enhance the surface diffusion of Te, migration enhanced epitaxy was adopted in the growth of the '{delta}-layers';' i.e., Te is deposited in the absence of Zn flux. Structural parameters were extracted by simulating the experimental x-ray diffraction curves using a dynamical model. The results show that only the '{delta}-layers' (with submonolayer thickness) are rich in ZnTe, while the nominally undoped 'spacers' have only a low Te concentration. Moreover, the morphology of the surface and interfaces are studied by XRR. Furthermore, the optical absorption and reflection results show that our samples largely preserve the optical properties of the host material (ZnSe). We note that our results, in particular those on the Te concentration, explain the observed good p-type doping of such samples.

Gong, Y.; Yan, Hanfei F.; Kuskovsky, I.L.; Gu, Y.; Noyan, I.C.; Neumark, G.F.; Tamargo, M.C. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States); Queens College of CUNY, Flushing, New York 11367 (United States); Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States); Department of Chemistry, City College of CUNY, New York, New York 10031 (United States)

2006-03-15

63

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

National Technical Information Service (NTIS)

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

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

1964-01-01

64

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

65

Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure  

PubMed Central

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

2013-01-01

66

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

2013-10-28

67

Detection of CdS(Te) and ZnSe(Te) scintillation light with silicon photodiodes  

Microsoft Academic Search

Some scintillation characteristics of CdS(Te) have been investigated. The scintillation emission spectrum of CdS(Te) single crystals is situated in a band between 560 and 800 nm with, maximum at 640 nm. The light yield of this red emitting crystal on a microsecond time scale is rather large: approximately 1.7×104 photons per MeV of absorbed ?-ray energy. The scintillation light can

P. Schotanus; P. Dorenbos; V. D. Ryzhikov

1992-01-01

68

Growth, morphology, and microindentation analysis of Bi 2Se 3, Bi 1.8In 0.2Se 3, and Bi 2Se 2.8Te 0.2 single crystals  

Microsoft Academic Search

Bismuth Selenide single crystals have been grown by the vertical normal freezing technique. Confirmation of the compound formation and the lattice parameters are calculated from the X-ray diffractogram. SEM studies show the parallel cleavage lines in Te-doped samples. Triangular etch pits are obtained on the (111) planes of Bi2Se3. Microindentation studies are carried out on the same plane to understand

Saji Augustine; Elizabeth Mathai

2001-01-01

69

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

NASA Astrophysics Data System (ADS)

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

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

1995-12-01

70

Hall effect of FeTe and Fe(Se1-xTex) thin films  

NASA Astrophysics Data System (ADS)

The Hall effect is investigated in thin-film samples of iron-chalcogenide superconductors in detail. The Hall coefficient (RH) of FeTe and Fe(Se1-xTex) exhibits a similar positive value around 300 K, indicating that the high-temperature normal state is dominated by hole-channel transport. FeTe exhibits a sign reversal from positive to negative across the transition to the low-temperature antiferromagnetic state, indicating the occurrence of drastic reconstruction in the band structure. The mobility analysis using the carrier density theoretically calculated reveals that the mobility of holes is strongly suppressed to zero, and hence the electric transport looks to be dominated by electrons. The Se substitution to Te suppresses the antiferromagnetic long-range order and induces superconductivity instead. The similar mobility analysis for Fe(Se0.4Te0.6) and Fe(Se0.5Te0.5) thin films shows that the mobility of electrons increases with decreasing temperature even in the paramagnetic state, and keeps sufficiently high values down to the superconducting transition temperature. From the comparison between FeTe and Fe(Se1-xTex), it is suggested that the coexistence of 'itinerant' carriers both in electron and hole channels is indispensable for the occurrence of superconductivity.

Tsukada, I.; Hanawa, M.; Komiya, Seiki; Ichinose, A.; Akiike, T.; Imai, Y.; Maeda, A.

2011-11-01

71

Charge injection barriers and chemical interaction at the CdTe/NbSe2 interface  

NASA Astrophysics Data System (ADS)

The band line-up and the chemical interaction at the CdTe/NbSe2 interface were investigated with photoemission spectroscopy. NbSe2 is a layered metal dichalcogenide with metallic properties and a large work function. This makes it a potential candidate as back contact material for CdTe thin film solar cells. The interface was investigated by stepwise in situ deposition of NbSe2 and subsequent characterization with x-ray and ultraviolet photoemission spectroscopy. The experiments showed that Te and Se interdiffuse at the interface, causing the formation of a graded diffusion layer. The resulting band alignment indicates the formation of an interface dipole leading to a midband gap alignment of the NbSe2 Fermi level.

Wolak, Matthäus A.; Gutmann, Sebastian; Conrad, Matthew; Beerbom, Martin M.; Ferekides, Chris; Schlaf, Rudy

2011-01-01

72

Optical parameters of In Se and In Se Te thin amorphous films prepared by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

The thin films of materials based on In Se are under study for their applicability in photovoltaic devices, solid-state batteries and phase-change memories. The amorphous thin films of In2Se3-xTex (x=0 1.5) and InSe were prepared by pulsed laser deposition method (PLD) using a KrF excimer laser beam (?=248 nm, 0.5 J cm-2) from polycrystalline bulk targets. The compositions of films verified by energy-dispersive X-ray analysis (EDX) were close to the compositions of targets. The surfaces of PLD films containing small amount of droplets were viewed by optical and scanning electron microscopy (SEM). The optical properties (transmittance and reflectance spectra, spectral dependence of index of refraction, optical gap, single-oscillator energy, dispersion energy, dielectric constant) of the films were determined. The values of index of refraction increased with increasing substitution of Te for Se in In2Se3 films, the values of the optical gap decreased with increasing substitution of Te for Se in In2Se3 films.

Hrdlicka, M.; Prikryl, J.; Pavlista, M.; Benes, L.; Vlcek, M.; Frumar, M.

2007-05-01

73

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

SciTech Connect

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

Gerritsen, H.J.; Ruppel, W.

1984-09-01

74

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

PubMed

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

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

2012-01-05

75

Compounds in the system Cu2Se-As2Se3  

NASA Astrophysics Data System (ADS)

The phase diagram Cu2Se-As2Se3 was investigated by thermal and X-ray methods. Cu2Se has a limited solubility for As2Se3 (5 mole% at 769 K). The stoichiometric compound Cu3AsSe3 exists between 696 and 769 K. Cu4As2Se5, a phase at 66.6 mole% Cu2Se, decomposes peritectically at 746 K. The narrow homogeneity range (4 mole% at 683 K) extends far into the ternary space. CuAsSe2 also decomposes peritectically at 683 K. A degenerated eutectic between CuAsSe2 and As2Se3 was found at 641 K. Single crystals of Cu4As2Se5 were grown in a salt melt. A metastable modification of the high-temperature phase Cu3AsSe3 can be obtained by quenching. Cu4As2Se5 (space group R3, lattice constants a = 1404.0(1) pm, c = 960.2(1) pm), Cu6As4Se9, obtained by Cambi and Elli, and Cu7As6Se13 of Takeuchi and Horiuchi are different versions of a sphalerite-type compound with a broad homogeneity range in the system Cu-As-Se. CuAsSe2 is possibly monoclinic with lattice parameters of a = 946.5(1) pm, b = 1229.3(1) pm, c = 511.7(1) pm, and ? = 98.546(4)°. The enthalpy of mixing of Cu2Se and As2Se3 in the liquid state is endothermic.

Blachnik, R.; Kurz, G.

1984-11-01

76

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

National Technical Information Service (NTIS)

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...

A. Miedaner C. J. Curtis D. S. Ginley M. van Hest P. Hersh

2008-01-01

77

Assessment of thermoelectric performance of Cu2ZnSnX4, X=S, Se, and Te  

NASA Astrophysics Data System (ADS)

A recent experiment on In-doped Cu2ZnSnSe4 [X. Y. Shi et al., Appl. Phys. Lett. 94, 122103 (2009)] has shown promising thermoelectric performance characteristics. In this letter, we analyze relevant electronic and transport properties of Cu2ZnSnSe4 and similar compounds, Cu2ZnSnS4 and Cu2ZnSnTe4, to assess their potential as thermoelectric materials. Using density functional theory and Boltzmann transport equations, we determine Seebeck coefficients, conductivities, and power factors of closely related polymorphs with space groups, I4, I42m, and P42m for each compound. Based on their electronic structure and transport properties, we conclude that other two compounds could have similar potential as thermoelectric materials.

Sevik, C.; Ça??n, T.

2009-09-01

78

Carrier Mobility and Shallow Impurity States in ZnSe and ZnTe  

Microsoft Academic Search

Electrical transport measurements have been made on p-type ZnTe and n-type ZnSe. In ZnTe crystals, doping with Cu, Ag, and Au produces acceptor levels at 0.15, 0.11, and 0.22 eV, respectively. An acceptor with an ionization energy of 0.048 eV was found in the undoped crystals and is identified as the first charge state of the Zn vacancy. A shallow

M. Aven; B. Segall

1963-01-01

79

Indium donor complexes with cation vacancies in CdTe and ZnSe  

SciTech Connect

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

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

1993-11-01

80

Anisotropic optical and thermoelectric properties of In4Se3 and In4Te3  

NASA Astrophysics Data System (ADS)

The anisotropic optical and thermoelectric properties of In4Se3 and In4Te3 are studied by the first-principles calculation using the full-potential linearized augmented plane-wave method and the semiclassical Boltzmann theory. The optical properties show highly anisotropic in the energy range between 0.0 and 12.0 eV for In4Se3 and between 0.0 and 10.0 eV for In4Te3 while it is isotropic in the higher energy range for In4Se3. In contrast to S, the anisotropies of the electrical conductivities and power factors are great affected by the change of the temperature. Their anisotropies become larger along three directions with the growth of the temperature. S2?/? along the y direction is much higher than that along the x and z directions for In4Se3, which shows that the thermoelectric thin films with excellent performance can be obtained along the (010) surface. By studying the anisotropy of transport properties, we find that the transport properties of In4Se3 are better than that of In4Te3, which mainly comes from the small band gap of In4Se3. The anisotropy of S2?/? for In4Se3 is larger than that for In4Te3, and the anisotropy of S2?/? is mainly due to the anisotropy of ?/?.

Li, Xingfu; Xu, Bin; Yu, Gongqi; Xue, Li; Yi, Lin

2013-05-01

81

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

NASA Astrophysics Data System (ADS)

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

Ovsyannikov, Sergey V.; Shchennikov, Vladimir V.

2004-02-01

82

Effects of Oxygen Annealing in Fe(Te,Se) Single Crystals  

NASA Astrophysics Data System (ADS)

Iron-chalcogenide superconductor Fe(Te,Se) has the simplest structure among all iron-based superconductors. Yet, its superconducting properties except for Tc are not very much reproducible. This is partly due to the fact that the as-grown crystals of Fe(Te,Se) is not superconducting, and post-annealing is important to induce superconductivity. We found that the annealing in a controlled oxygen atmosphere is very important to induce superconductivity in this system. Upon annealing in oxygen atmosphere, the content of excess iron in the crystal decreases. We will demonstrate the dynamics of the oxygen annealing process by changing the annealing time and temperature. We also compare the effect of different annealing conditions, such as vacuum annealing, with that of oxygen annealing. Finally, physical properties of well-characterized Fe(Te,Se) crystals are discussed together with the vortex physics in this system.

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

2013-03-01

83

Phonons in Bi2Te3 and Bi2Se3 Thin Films  

NASA Astrophysics Data System (ADS)

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

Ren, Shang-Fen; Cheng, Wei

2010-03-01

84

Behavior of new ZnSe(Te,O) semiconductor scintillators under high doses of ionizing radiation  

Microsoft Academic Search

Changes in scintillation and optical properties of scintillators based on ZnSe(Te,O) crystals were studied under influence of ionizing radiations: gamma (~1.3 MeV, up to 500 Mrad), protons (~18 MeV, fluence up to 1016 per cm-2), electrons (0.54-2.26 MeV, up to 50 Mrad), and neutrons (source-thermal reactor channel, fluence up to 1016 per cm2), Light output of gamma-irradiated scintillator crystals ZnSe(Te,O)

Vladimir D. Ryzhikov; Nikolai G. Starzhinskiy; L. P. Gal'chinetskii; Magne Guttormsen; Alexander A. Kist; Wlodzimierz Klamra

2001-01-01

85

Resonance tunneling of charge carriers in photoexcited type-II ZnSe/BeTe heterostructures  

SciTech Connect

In is shown that, at high densities of spatially separated electrons and holes in type-II ZnSe/BeTe heterostructures, the conditions for resonance tunneling of photoexcited holes from the ZnSe layer to the BeTe layer are attainable. Nonlinear behavior of the intensity of the photoluminescence band corresponding to spatially direct optical transitions with photoexcitation intensity is observed. Numerical calculations are carried out, and the results are in good agreement with the experimental data in a wide region of variation of the optical pumping intensity.

Zaitsev, S. V., E-mail: zaitsev@issp.ac.ru; Maksimov, A. A.; Tartakovskii, I. I. [Institute of Solid State Physics (Russian Federation); Yakovlev, D. R. [University of Dortmund, Experimentelle Physik II (Germany); Waag, A. [Braunschweig Technical University, Institute of Semiconductor Technology (Germany)

2008-05-15

86

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

Microsoft Academic Search

Using the all-electron mixed-basis approach to the density-functional formalism for crystals, we calculate from first principles the electronic structure of zinc-blende ZnS, ZnSe, and ZnTe as well as that of their ordered pseudobinary alloys Zn2SSe, Zn2SeTe, and Zn2STe. For the latter we use as a model a CuAu I-like structure (space group P4¯m2), and analyze the observed optical bowing in

James E. Bernard; Alex Zunger

1987-01-01

87

Electrical conductivity and thermo-emf of melts of the system Tl-Te-Se  

SciTech Connect

A study was made of the temperature dependences of the electrical conductivity and thermo-emf of melts of ternary system Tl-Te-Se from the melting point to 1000 K. Concentration dependences of these parameters were also established. The data obtained were used with data for binary systems to construct isothermal surfaces of electrical conductivity and thermo-emf for the system Tl-Te-Se at T = 750 K. The results show that it is possible to control the electronic properties of melts of complex semiconductor systems having lamination regions.

Kazandzhan, B.I.; Matveev, V.M.; Umarov, A.M.

1988-07-01

88

Pinning mechanism in iron chalcogenide superconductor FeSe0.5Te0.5  

NASA Astrophysics Data System (ADS)

We explore the physics of vortex pinning mechanism in Iron chalcogenide superconductor FeSe0.5Te0.5., via magnetization based studies. In particular we try to: (i) understand the salient features of the pinning force density (Fp) within the Dew-Hughes scenario, and (ii) compare the experimental results with the theoretical pictures of fluctuation in mean free path induced (?l) pinning and the fluctuation in superconducting order parameter induced (?Tc) pinning. The results points to a ?l pinning scenario in FeSe0.5Te0.5.

Thakur, Ajay D.; Yadav, Anil K.; Das, P.; Tomy, C. V.; Lees, M. R.; Balakrishnan, G.; Ramakrishnan, S.; Grover, A. K.

2012-06-01

89

Neutron Scattering Study of the Dependence of Magnetic Correlations on Se and Fe Content in the Fe(Te,Se) System  

Microsoft Academic Search

We have performed a series of neutron scattering and magnetization measurements on Fe1+yTe1-xSex with different Fe and Se compositions to study the interplay between magnetism and superconductivity.[1] FeTeSe is rather unique for possessing two different types of spin configurations: one is a \\

Zhijun Xu; Jinsheng Wen; Guangyong Xu; Genda Gu; John Tranquada

2011-01-01

90

Role of Sn in the Density of Defect States in aSe0.75Te0.25 and aSe0.85Te0.15Thin Films  

Microsoft Academic Search

In this paper we report the effect of Sn incorporation in the density of defect states of two binary Se-Te glassy systems, comparing the properties of a-Se0.75Te0.25, a-Se0.85Te0.15 and a-Se0.75Te0.15Sn0.10 glassy alloys. Properties of d.c. conductivity at high electric fields in vacuum were examined; and current-voltage (I-V) characteristics have been measured at various fixed temperatures. Ohmic behavior is observed at

N. Sharma; S. Kumar

2007-01-01

91

Crystal structures and variable magnetism of PbCu2(XO3)2Cl2 with X = Se, Te.  

PubMed

Novel Cu(2+)-based compounds PbCu2(SeO3)2Cl2 (space group C2/c; a = 13.056(1) Å; b = 9.5567(9) Å; c = 6.9006(6) Å; ? = 90.529(7)°; RI = 0.0371) and PbCu2(TeO3)2Cl2 (space group P2(1); a = 7.2401(2) Å; b = 7.2688(2) Å; c = 8.2846(2) Å; ? = 96.416(2)°; R(I) = 0.0570) have been obtained by solid-state synthesis. Their crystal structures are remarkably dissimilar and underlie a very different magnetic behavior. While PbCu2(SeO3)2Cl2 can be well described by a spin-chain model with an exchange coupling of J1 ? 160 K, PbCu2(TeO3)2Cl2 is a spin-dimer system that, however, features a comparable magnetic nearest-neighbor coupling of J ? 213 K. PbCu2(SeO3)2Cl2 orders antiferromagnetically below 12 K, whereas PbCu2(TeO3)2Cl2 lacks long-range magnetic order down to at least 2 K, owing to the strong dimerization of the Cu(2+) spins. Crystal structures of both compounds are rationalized in terms of relevant magnetic exchange pathways, and the implications for a broader range of Cu(2+) compounds are discussed. PMID:23674051

Berdonosov, Peter S; Janson, Oleg; Olenev, Andrei V; Krivovichev, Sergey V; Rosner, Helge; Dolgikh, Valery A; Tsirlin, Alexander A

2013-05-14

92

Influence of Sn Migration on phase transition in GeTe and Ge2Se3 thin films  

NASA Astrophysics Data System (ADS)

Phase transitions in GeTe/SnSe and Ge2Se3/SnTe are investigated using time resolved x-ray diffraction. GeTe exhibits a structural transition from rhombohedral to the cubic phase at 300 °C, which is ~100 °C lower than that of pure GeTe. This is facilitated by incorporation of Sn from SnSe. Sn migration is observed explicitly in Ge2Se3/SnTe by separation of SnSe phase. Amorphous Ge2Se3 is also found to crystallize at a lower temperature of 300 °C resulting in orthorhombic GeSe and monoclinic GeSe2. Thus, inclusion of a Sn containing layer may offer a means to tailor phase transition in Ge-chalcogenide thin films for phase change memory applications.

Devasia, Archana; Kurinec, Santosh; Campbell, Kristy A.; Raoux, Simone

2010-04-01

93

Electrical properties of p-type and n-type ZnSe-ZnTe strained-layer  

Microsoft Academic Search

ZnSe and ZnTe semiconducting materials are highly promising candidates for the fabrication of short-wavelength light-emitting devices. We have grown ZnSe-ZnTe strained-layer superlattices (SLSs) on InP substrates by molecular beam epitaxy. In addition to undoped SLSs, two kinds of modulation doped SLS samples were prepared in this study, the first with Ga-doped ZnSe layers and undoped ZnTe layers, and the second

Masakazu Kobayashi; Shiro Dosho; Akira Imai; Ryuhei Kimura; Makoto Konagai; Kiyoshi Takahashi

1988-01-01

94

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

2013-09-10

95

Hydrothermally synthesized and hot-pressed Bi2(Te,Se)3 thermoelectric alloys  

NASA Astrophysics Data System (ADS)

Bi2(Te,Se)3 nanopowders have been synthesized by an aqueous chemical route in an open beaker at 70 °C for 72 h. The powders were hot-pressed under a pressure of 50 MPa at 250 °C for 15 min. X-ray diffraction and energy-dispersive analysis of X-rays show that both the powders and the hot-pressed samples are mainly composed of Bi2(Te,Se)3 and Te. Scanning electron microscopy observation shows that the crystallite size is smaller than 100 nm in the powders and the width of the polygonal prismatic rods is about 100 nm in the hot-pressed sample. The alloys were doped with SbI3 before hot pressing. The SbI3-doped sample shows a higher electrical conductivity and a lower Seebeck coefficient, indicating that SbI3 is electrically actively incorporated into the alloys.

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

2005-07-01

96

Growth of CdTe(1-x)Se(x) by the LEC and Bridgman Techniques.  

National Technical Information Service (NTIS)

Large-grain CdTe(1-x)Se(x) boules with X (nominal) = 0.05, 0.10 and 0.15 have been grown by the liquid-encapsulated Czochralski technique, using B(2)O(3) as the encapsulant, and also by a modified Bridgman technique. An argon pressure of 20 atm was used i...

N. Klausutis M. Hunt J. A. Adamski H. Lipson C. V. Collins

1974-01-01

97

Exciton self-trapping in ZnSe-ZnTe alloys  

Microsoft Academic Search

The low-intensity luminescence of ZnSe1-xTex with x=1% exhibits several unusual features which are attributed to the occurrence of efficient exciton self-trapping induced by Te atoms. This type of exciton localization is strikingly different from that observed in other II-VI or III-V mixed crystals.

D. Lee; A. Mysyrowicz; A. V. Nurmikko; B. J. Fitzpatrick

1987-01-01

98

Variation of Optical Constants of Se85-x Te15 Inx (0, 12) Glass System  

NASA Astrophysics Data System (ADS)

Chalcogenide glass system Se85-x Te15 Inx ( 0, 12 )glasses are prepared by melt quenching technique and thin films of glassy alloys are prepared by flash evaporation technique. Optical constants are calculated using a transmission spectrum in the wavelength range 375-1200 nm.

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

2011-10-01

99

Magnetic studies on UXY (X = P, Sb; Y = Se, Te) single crystals  

NASA Astrophysics Data System (ADS)

Magnetization and magnetic susceptibility measurements have been performed on single crystals of UPSe, UPTe, USbSe and USbTe. All these ternaries are uniaxial ferromagnets with TC of 55, 85, 128 and 127 K, respectively. Their magnetization behavior was found to exhibit a strongly anisotropic character in both the magnetically ordered and the paramagnetic region.

Kaczorowski, D.; Zygmunt, A.; Noël, H.

1995-02-01

100

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

101

Micro-Raman spectroscopy of mechanically exfoliated few-quintuple layers of Bi2Te3, Bi2Se3, and Sb2Te3 materials  

NASA Astrophysics Data System (ADS)

Bismuth telluride (Bi2Te3) and related compounds have recently attracted strong interest, owing to the discovery of the topological insulator properties in many members of this family of materials. The few-quintuple films of these materials are particularly interesting from the physics point of view. We report results of the micro-Raman spectroscopy study of the ``graphene-like'' exfoliated few-quintuple layers of Bi2Te3, Bi2Se3, and Sb2Te3. It is found that crystal symmetry breaking in few-quintuple films results in appearance of A1u-symmetry Raman peaks, which are not active in the bulk crystals. The scattering spectra measured under the 633-nm wavelength excitation reveals a number of resonant features, which could be used for analysis of the electronic and phonon processes in these materials. In order to elucidate the influence of substrates on the few-quintuple-thick topological insulators, we examined the Raman spectra of these films placed on mica, sapphire, and hafnium-oxide substrates. The obtained results help to understand the physical mechanisms of Raman scattering in the few-quintuple-thick films and can be used for nanometrology of topological insulator films on various substrates.

Shahil, K. M. F.; Hossain, M. Z.; Goyal, V.; Balandin, A. A.

2012-03-01

102

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

Microsoft Academic Search

One of the main problems for the fabrication of optoelectronic devices in the blue spectral range is the limited p-dopability and the resulting high contact resistivity of p-ZnSe. We show that the admixture of even small Te fractions to ZnSe has a strong beneficial effect on doping levels and contacts of MBE grown material doped with DC nitrogen plasma. Since

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

1995-01-01

103

Emission of quantum dots (QDs) and isoelectronic bound excitons (IBEs) from submonolayer ZnTe on ZnSe and dependence on thickness of ZnTe  

NASA Astrophysics Data System (ADS)

Zn-Se-Te systems have been of great interest for both lighting applications and their unique optical properties. It is known that the PL of the dilute alloys [1] or quantum wells [2] is usually due to IBEs. ZnTe/ZnSe QDs have been grwon with full monolayer coverage of ZnTe on ZnSe using Volmer-Weber growth [3]. We have shown [4] the existence of type-II QDs in ZnSeTe multilayers grown by migration enhanced epitaxy with sub-monolayer quantities of ZnTe. The multilayers were grown using three Zn-Te deposition cycles sandwiched between nominally pure ZnSe barriers. Here, we report ZnTe/ZnSe QDs grown by a similar method, but with only one ZnTe deposition cycle. It is interesting that at T = 10K the PL emission related to these QDs does not shift upon varying the excitation intensity, and attributed to IBEs; however, a large energy shift is observed at T = 80K, suggesting formation of type-II QDs. The presence of type-II QDs is also supported by magneto-PL measurements. [1] Permogorov and Reznitsky, J. Lumin. 52, 201 (1992). [2] Suzuki et al., J. Crystal Growth 184/185, 882 (1998). [3] Yang et al., JAP 97, 033514 (2005). [4] Kuskovsky, et al., Phys. Stat. Sol. (b) 241, 527 (2004); Gu et al., Phys. Rev. B 71, 045340 (2005).

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

2007-03-01

104

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

105

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

PubMed Central

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

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

2007-01-01

106

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

107

Photoluminescence of {delta}-doped ZnSe:(Te,N) grown by molecular beam epitaxy  

SciTech Connect

We have studied the low temperature photoluminescence (PL) of a {delta}-doped ZnSe:(Te,N) system using two different types of samples, one with single {delta} layers separated by undoped spacers and the other with three adjacent {delta} layers in each doping cycle. We have concluded that both Te and N participate in radiative recombination. We observe a relatively low PL efficiency (compared to samples without N) for these samples, and we suggest that Auger recombination is a likely mechanism, although a role of slow donor--acceptor pair PL and consequent nonradiative processes cannot be ruled out.

Kuskovsky, Igor L.; Tian, C.; Sudbrack, C.; Neumark, G. F.; Lin, W.-C.; Guo, S. P.; Tamargo, M. C.

2001-09-01

108

Time-resolved photoluminescence spectroscopy of individual Te impurity centers in ZnSe  

NASA Astrophysics Data System (ADS)

Tellurium impurity centers in ZnSe were individually probed with time-resolved photoluminescence (PL) spectroscopy. Resolution-limited peaks with an ultralow spatial density originate in the recombination of excitons deeply bound to isolated nearest-neighbor isoelectronic Te pairs (Te2) . This interpretation is supported by ab initio calculations. The peaks reveal antibunched photon emission and a doublet structure polarized along [110] and [1¯10] . The temperature dependence of the time-resolved PL decay exposes the dark excitonic states which indirectly affect the radiative recombination of single fine-structure split excitons.

Muller, A.; Bianucci, P.; Piermarocchi, C.; Fornari, M.; Robin, I. C.; André, R.; Shih, C. K.

2006-02-01

109

Photoemission investigation of the ZnSe/CdTe heterojunction band discontinuity  

SciTech Connect

Synchrotron radiation soft x-ray photoemission spectroscopy and reflection high-energy electron diffraction were used to investigate the structural and electronic properties at the ZnSe/CdTe(100) heterojunction interface. ZnSe overlayers were sequentially grown in steps on {ital p}-type CdTe(100) single crystals at 200 {degree}C. {ital In} {ital situ} photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Cd 4{ital d}, Zn 3{ital d}, and Te 4{ital d} core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the ZnSe/CdTe heterojunction valence band discontinuity and the consequent heterojunction band diagram. Results of these measurements reveal that the valence band offset is {Delta}{ital E}{sub {ital v}}=0.20 eV. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Nelson, A.J. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

1995-08-15

110

Formation of CdSe/CdTe quantum dots in multilayer thin films using PVD method  

NASA Astrophysics Data System (ADS)

Nanocrystals of CdSe have been produced in CdTe hetrostructure layer by thermal evaporation method. Structural studies were done by X-ray diffractometer. Quantum confinement effect of CdSe/CdTe nanocrystals was analysed from optical studies. Bulk CdSe has a bandgap energy of 1.756eV that can be shifted to larger values by reducing the crystal size to dimensions smaller than the Bohr radius of the exciton. Experimentally measured band gap shifts with respect to the bulk value for quantum dot thin films are compared with the predictions of the effective mass approximation model (i.e., Brus model) and Quantum mechanical model. Size of the crystallites calculated from both the models was found to agree with each other.

Kumar, M. Melvin David; Devadason, Suganthi; Rajesh, S.

2012-06-01

111

Photoluminescence of ZnSe{sub x}Te{sub 1-x}/ZnTe multiple-quantum-well structures grown by molecular-beam epitaxy  

SciTech Connect

This work investigates photoluminescence (PL) spectra from ZnSe{sub x}Te{sub 1-x}/ZnTe multiple-quantum-well structures grown on GaAs(001) substrates by molecular-beam epitaxy. The PL data reveal that the band alignment of the ZnSe{sub x}Te{sub 1-x}/ZnTe system is type II. The thermal activation energy for quenching the PL intensity was determined from the temperature-dependent PL spectra. The activation energy was found to increase initially and then decrease as the thickness of the ZnSe{sub x}Te{sub 1-x} layers decreases from 7 to 3 nm. The temperature-dependent broadening of the PL linewidth was also investigated. The LO-phonon scattering was found to be the dominant broadening mechanism.

Shih, Y.T.; Tsai, Y.L.; Yuan, C.T.; Chen, C.Y.; Yang, C.S.; Chou, W.C. [Institute of Photonics, National Changhua University of Education, Changhua, Taiwan 50007 (China); Institute of Applied Physics, Chung Yuan Christian University, Chungli, Taiwan 32023 (China); Institute of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 30050 (China)

2004-12-15

112

Composition dependence of optical band gap of the Se-Ge-Te far infrared transmitting glasses  

NASA Astrophysics Data System (ADS)

A systematic series of SexGe25-xTe75 (x=0, 5, 10, 15, 20 at%) far infrared transmitting glasses were prepared by traditional melt-quenching method. Physical, thermal and optical properties of the glass system were analyzed. The allowed indirect transition of samples was calculated according to the classical Tauc equation. The results show the density increases with the substitution of Ge by Se and a maximum ?g value of 175 °C was obtained for the Se15Ge10Te75 glass. The energy band gap of Se15Ge10Te75 glass is 1.25 eV, possessing the largest metallization criterion value (0.25) and the lowest refractive index (3.16). When the dissolved amount of Se increased from 0 to 15 at%, the values of indirect optical band gap were in the range from 0.573 to 0.679 eV. A wide optical transparent window with a cut-off wavelength beyond 18 ?m was shown.

Wang, Guoxiang; Nie, Qiuhua; Wang, Xunsi; Dai, Shixun; Xu, Tiefeng; Shen, Xiang; Zhang, Xianghua

2010-11-01

113

Silylchalcogenolates MESiR(t)Bu(2) (M = Na, Cu, Zn, Fe; E = S, Se, Te; R = tBu, Ph) and disilyldichalcogenides tBu2RSiE-ESiRtBu2 (E = S, Se, Te; R = tBu, Ph): synthesis, properties, and structures.  

PubMed

The sodium silyl chalcogenolates NaESiR(t)Bu(2) (R = Ph, (t)Bu; E = S, Se, Te), accessible by the nucleophilic degradation of S, Se, or Te by the sodium silanides NaSiR(t)Bu(2) (R = Ph, (t)Bu), have been characterized by X-ray structure analysis. Protonolysis of the sodium silyl chalcogenolates yields the corresponding chalcogenols. The Cu and Zn chalcogenolates, [Cu(SSiPh(t)Bu(2))](4) and [ZnCl(SSi(t)Bu(3))(THF)](2), have been synthesized by metathesis reactions of CuCl with NaSSiPh(t)Bu(2) and of ZnCl(2) with NaSSi(t)Bu(3), respectively. The solid-state structures of the transition metal thiolates have been determined. The compounds (t)Bu(2)RSiE-ESiR(t)Bu(2) (R = Ph, (t)Bu; E = S, Se, Te) are accessible via air oxidation. With the exception of (t)Bu(3)SiS-SSi(t)Bu(3), these compounds were analyzed using X-ray crystallography and represent the first structurally characterized silylated heavy dichalcogenides. Oxidative addition of (t)Bu(3)SiTe-TeSi(t)Bu(3) to Fe(CO)(5) yields [Fe(TeSi(t)Bu(3))(CO)(3)](2), which has also been structurally characterized. PMID:15877425

Kückmann, Theresa I; Hermsen, Melina; Bolte, Michael; Wagner, Matthias; Lerner, Hans-Wolfram

2005-05-16

114

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

115

Finite-temperature magnetism of CrTe and CrSe.  

PubMed

An investigation on the electronic and magnetic properties of NiAs-type CrTe and CrSe has been performed for ferromagnetic, antiferromagnetic and non-collinear spin configurations, using the spin-polarized relativistic KKR (Korringa-Kohn-Rostoker) band structure method. Calculated exchange coupling parameters, as well as the total energy calculated as a function of the tilt angle of magnetic moments, indicate the presence of a non-collinear spin structure in CrTe and CrSe. The existence of a non-collinear spin structure is also shown by Monte Carlo (MC) simulations used for studies on the temperature dependent magnetization. The results are compared with available results in the literature and are in satisfactory agreement with the experimental results. PMID:21389560

Polesya, S; Mankovsky, S; Benea, D; Ebert, H; Bensch, W

2010-03-29

116

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

117

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

PubMed

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

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

2011-09-29

118

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

119

Switching phenomenon in a Se{70}Te{30-x}Cd{x} films  

Microsoft Academic Search

Amorphous Se{70}Te{30-x}Cd{x} (x = 0, 10) are obtained by thermal evaporation under vacuum of bulk materials on pyrographite and glass substrates. The I-V characteristic curves for the two film compositions are typical for a memory switch. They exhibited a transition from an ohmic region in the lower field followed by non-ohmic region in the high field region in the preswitching

M. A. Afifi; A. E. Bekheet; N. A. Hegab; L. A. Wahab; H. A. Shehata

2007-01-01

120

Characterization of ZnSe(Te) scintillators by frequency domain luminescence lifetime measurements  

NASA Astrophysics Data System (ADS)

Dynamics of photoluminescence (PL) decay in Te-doped ZnSe scintillator crystal is studied using frequency domain luminescence lifetime measurement technique, which enables simultaneous characterization of components in multicomponent PL decay in a wide time window ranging from millisecond to nanosecond domain. Evolution of decay times and relative contributions of the decay components corresponding to different PL decay mechanisms was revealed as a function of temperature.

Mickevi?ius, J.; Tamulaitis, G.; Vitta, P.; Žukauskas, A.; Starzhinskiy, N.; Ryzhikov, V.

2009-10-01

121

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

Microsoft Academic Search

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

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

1998-01-01

122

Structural and optical characterization of hot wall deposited CdSe x Te 1? x films  

Microsoft Academic Search

CdSe0.3Te0.7 alloy was prepared from the individual components and its composition and structural analysis were done. Films were prepared by hot wall deposition technique using 0.15m length tube under a vacuum of 5×10?5Torr on well cleaned glass substrates. The composition, structural, morphological, and optical properties of hot wall deposited films were investigated. The XRD analysis revealed that the films are

S Velumani; Xavier Mathew; P. J Sebastian

2003-01-01

123

Magneto-optical properties of ZnMnTe\\/ZnSe quantum dots  

Microsoft Academic Search

The ?+ and ?? circularly polarized time-integrated and time-resolved Photoluminescence (PL) measurements were employed to investigate the carrier spin dynamics of ZnMnTe\\/ZnSe Quantum Dots (QDs) grown on GaAs substrates by molecular beam epitaxy. The Kohlrausch’s stretching exponential function well correlates both the ?+ and ?? decay profiles. The measured spin relaxation time is about 23ns.

W. C. Fan; J. T. Ku; W. C. Chou; W. K. Chen; W. H. Chang; C. S. Yang; C. H. Chia

2011-01-01

124

Properties of photoluminescence in type-II ZnTe\\/ZnSe quantum dots  

Microsoft Academic Search

Temperature and time evolution of the photoluminescence (PL) intensity of bimodal ZnTe\\/ZnSe type-II quantum dots (QDs) were investigated. A particular temperature dependence of PL was observed in large QDs. PL decay of small QDs is composed of a faster initial component and a slower tail component whereas PL decay of large QDs simply comprises a fast component. All phenomena could

T. Y. Lin; D. Y. Lyu; J. Chang; J. L. Shen; W. C. Chou

2006-01-01

125

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

126

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

127

Intrinsic pinning and the critical current scaling of clean epitaxial Fe(Se,Te) thin films  

NASA Astrophysics Data System (ADS)

We report on the transport properties of clean, epitaxial Fe(Se,Te) thin films prepared on Fe-buffered MgO (001) single crystalline substrates by pulsed laser deposition. Near Tc a steep slope of the upper critical field for H||ab was observed (74.1 T/K), leading to a very short out-of-plane coherence length, ?c(0), of 0.2 nm, yielding 2?c(0)?0.4nm. This value is shorter than the interlayer distance (0.605 nm) between the Fe-Se(Te) planes, indicative of modulation of the superconducting order parameter along the c axis. An inverse correlation between the power law exponent N of the electric field-current density(E-J) curve and the critical current density Jc has been observed at 4 K, when the orientation of H was close to the ab plane. These results prove the presence of intrinsic pinning in Fe(Se,Te). A successful scaling of the angular dependent Jc and the corresponding exponent N can be realized by the anisotropic Ginzburg Landau approach with appropriate ? values 2˜3.5. The temperature dependence of ? behaves almost identically to that of the penetration depth anisotropy.

Iida, Kazumasa; Hänisch, Jens; Reich, Elke; Kurth, Fritz; Hühne, Ruben; Schultz, Ludwig; Holzapfel, Bernhard; Ichinose, Ataru; Hanawa, Masafumi; Tsukada, Ichiro; Schulze, Michael; Aswartham, Saicharan; Wurmehl, Sabine; Büchner, Bernd

2013-03-01

128

The synthesis and characterization of new [(BiSe) 1.10] m [NbSe 2] n , [(PbSe) 1.10] m [NbSe 2] n , [(CeSe) 1.14] m [NbSe 2] n and [(PbSe) 1.12] m [TaSe 2] n misfit layered compounds  

Microsoft Academic Search

Fifty-three new misfit layered compounds within the [(BiSe)1.10]m[NbSe2]n, [(PbSe)1.10]m[NbSe2]n, [(CeSe)1.14]m[NbSe2]n, and [(PbSe)1.12]m[TaSe2]n families of compounds were successfully synthesized. This is the first report of compounds with n and m larger than 3, as self-assembly from designed precursors allows compounds with particular n and m values to be selectively prepared. The compounds form as crystallographically aligned films, with the c-axis perpendicular

Colby Heideman; Ngoc Nyugen; Jonathan Hanni; Qiyin Lin; Scott Duncombe; David C. Johnson; Paul Zschack

2008-01-01

129

The synthesis and characterization of new [(BiSe)1.10]m[NbSe2]n, [(PbSe)1.10]m[NbSe2]n, [(CeSe)1.14]m[NbSe2]n and [(PbSe)1.12]m[TaSe2]n misfit layered compounds  

Microsoft Academic Search

Fifty-three new misfit layered compounds within the [(BiSe)1.10]m[NbSe2]n, [(PbSe)1.10]m[NbSe2]n, [(CeSe)1.14]m[NbSe2]n, and [(PbSe)1.12]m[TaSe2]n families of compounds were successfully synthesized. This is the first report of compounds with n and m larger than 3, as self-assembly from designed precursors allows compounds with particular n and m values to be selectively prepared. The compounds form as crystallographically aligned films, with the c-axis perpendicular

Colby Heideman; Ngoc Nyugen; Jonathan Hanni; Qiyin Lin; Scott Duncombe; David C. Johnson; Paul Zschack

2008-01-01

130

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

NASA Astrophysics Data System (ADS)

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

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

2008-08-01

131

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

132

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

133

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

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

134

Comparison of the optical properties of diffusion-doped polycrystalline Cr:ZnSe and Cr:CdTe windows  

Microsoft Academic Search

Results of the material preparation and infrared (IR) optical properties of polycrystalline Cr:ZnSe and Cr:CdTe windows are reported. Cr doping of commercial ZnSe and CdTe windows was achieved through a thermal diffusion process employing CrSe powder as the dopant source. All samples exhibited the characteristic spectral features of Cr2+-doped II–VI materials with strong IR absorption bands between 1700 and 1900nm

U. Hömmerich; I. K. Jones; Ei Ei Nyein; S. B. Trivedi

2006-01-01

135

Comparison of the optical properties of diffusion-doped polycrystalline Cr:ZnSe and Cr:CdTe windows  

Microsoft Academic Search

Results of the material preparation and infrared (IR) optical properties of polycrystalline Cr:ZnSe and Cr:CdTe windows are reported. Cr doping of commercial ZnSe and CdTe windows was achieved through a thermal diffusion process employing CrSe powder as the dopant source. All samples exhibited the characteristic spectral features of Cr2+-doped II VI materials with strong IR absorption bands between 1700 and

U. Hömmerich; I. K. Jones; Ei Ei Nyein; S. B. Trivedi

2006-01-01

136

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

SciTech Connect

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

Li, B.S.; Akimoto, R.; Akita, K.; Hasama, T. [Ultrafast Photonic Devices Laboratory, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

2006-02-15

137

Structural and optical properties of CdTe/CdSe heterostructure multilayer thin films prepared by physical vapor deposition technique  

NASA Astrophysics Data System (ADS)

CdTe/CdSe heterostructure multilayer thin films and single layers of CdSe and CdTe thin films were prepared. Sequential thermal evaporation technique is made possible to adjust the layer thickness precisely. XRD studies were used to calculate average size of the crystallites and confirmed the (111) and (100) planes of CdTe and CdSe, respectively. Bulk CdTe has band gap energy of 1.54 eV that can be shifted to larger values by reducing the crystallite size to dimensions smaller than the Bohr radius of the exciton. Experimentally measured energy levels show the spin-orbit split of valance band of CdTe. Crystallite sizes (7-12 nm) were calculated with the predictions of effective mass approximation model (i.e., Brus model) which shows that the diameter of crystallites were much smaller than the Bohr exciton diameter (14 nm) of CdTe. It is found that the emission peaks of the prepared CdTe/CdSe ML samples were shifted from the peaks of CdSe and CdTe single layers toward red region as a characteristic of type II band alignment.

David Kumar, M. Melvin; Devadason, Suganthi

2013-10-01

138

Effect of Te doping on structural and superconducting properties of FeSe superconductor  

NASA Astrophysics Data System (ADS)

In the present work, we have studied the effect of doping Te at the Se-site on the superconducting properties, such as transition temperature (Tc), upper critical field (Hc2) and irreversibility field (Hirr) of FeSe. The polycrystalline samples have been prepared via solid state reaction route with nominal compositions FeSe1-xTex (x = 0.0, 0.25, 0.50 and 0.75). The X-ray diffraction results show the tetragonal ?-FeSe phase with the p4/nmm space group symmetry in all the samples. The values of Hc2(0) estimated from Werthamer-Helfand-Hohenberg (WHH) and Ginzburg-Landau (GL) theories are found to follow the same trends and maximum Hc2(0) is found for the composition x = 0.50. The irreversibility field, Hirr and activation energy, U0 were also calculated to see the vortex motion behavior in the samples.

Sudesh, Stuti; Varma, G. D.

2013-06-01

139

Specific heats of EuTe and EuSe near their magnetic transitions  

NASA Astrophysics Data System (ADS)

Specific-heat measurements near the magnetic phase transitions of single-crystal EuTe and EuSe are reported. EuTe data were analyzed following the method of Kornblit, Ahlers, and Buehler which assumes C=(A?)|t|-?+Et+B with and without the constraints E'=E. B'=B, and ?'=?. The data were analyzed over four reduced temperature ranges, and the parameters for the range 0.005<|t|<0.06 were chosen as representing data as close to the peak as possible without the inclusion of rounding error. We have obtained ?'=?=0.08+/-0.06, AA'=0.75+/-0.15, and TN=9.81+/-0.01 K.

Johanson, W. R.; McCollum, D. C.

1980-09-01

140

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

141

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

142

Electronic structure of quasi-one-dimensional conductors Nb3X4 (X=S,Se,Te) studied by angle-resolved photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

High-resolution angle-resolved photoemission spectroscopy (ARPES) has been performed on quasi-one-dimensional (1D) compounds Nb3X4 (X=S,Se,Te) . We have experimentally determined the band structure of these compounds and compared with several different band calculations. We found a fairly straight 1D Fermi surface in Nb3Te4 (charge density wave transition temperature TCDW=110K , superconducting transition temperature Tc=1.9K ), while the Fermi surface of Nb3Se4 (Tc=2.4K) and Nb3S4 (Tc=3.8K) shows a remarkable wiggling, indicative of the more two-dimensional-like (three-dimensional-like) character. We also found a sharp quasiparticle peak near the Fermi level (EF) at low temperatures for Nb3S4 and Nb3Se4 , while the spectral weight near EF of Nb3Te4 is considerably suppressed. These experimental results indicate that the anisotropy of the electronic structure remarkably changes with varying the chalcogen atom in the compounds.

Dobashi, T.; Sato, T.; Souma, S.; Takahashi, T.; Kaneko, H.; Ishihara, Y.; Okamoto, H.

2007-07-01

143

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

144

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

PubMed

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

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

2007-06-29

145

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

NASA Astrophysics Data System (ADS)

We present the results of an infrared spectroscopy study of topological insulators Bi2Se3, Bi2Te3 and Sb2Te3. Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi2Se3, whereas in Bi2Te3 and Sb2Te3 it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature.

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

2013-02-01

146

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

SciTech Connect

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

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

1992-11-01

147

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

148

Infrared transmission of chalcohalide glasses in the Ge-Se-Te-I system  

NASA Astrophysics Data System (ADS)

Infrared (IR) transmission spectra in the range from 4000 to 400 cm-1 have been measured at ambient temperature for the prepared, (Ge22Se14Te64)100-xIx, glasses where x = 0, 4, 6, 8 and 10 at.%. The effects of both iodine content and the annealing of glasses at different temperatures on the transmittance and observed absorption peaks have been evaluated. Scanning electron microscope (SEM) micrographs were performed to insure the effect of annealing on the obtained IR transmission spectra.

El-Hawary, M. M.; El-Mallawany, R.; Abousehly, A. M.; Hegazy, H. H.

2012-07-01

149

Electronic structures of of PuX (X=S, Se, Te)  

NASA Astrophysics Data System (ADS)

We have calculated the energy band structures and the Fermi surfaces of PuS, PuSe, and PuTe by using a self-consistent relativistic linear augmented-plane-wave method with the exchange and correlation potential in the local density approximation. In general, the energy bands near the Fermi level are mainly caused by the hybridization between the Pu 5 f and the monochalcogenide p electrons. The obtained main Fermi surfaces consisted of two hole sheets and one electron sheet, which were constructed from the band having both the Pu 5 f state and the monochalcogenide p state.

Maehira, Takahiro; Sakai, Eijiro; Tatetsu, Yasutomi

2013-08-01

150

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

151

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

152

Raman spectra of CuInTe2, CuIn3Te5, and CuIn5Te8 ternary compounds  

NASA Astrophysics Data System (ADS)

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

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

2000-09-01

153

Electrochemical properties of CdSe and CdTe quantum dots.  

PubMed

Semiconductor nanocrystal quantum dots (QDs), owing to their unique opto-electronic properties determined by quantum confinement effects, have been the subject of extensive investigations in different areas of science and technology in the past two decades. The electrochemical behaviour of QDs, particularly for CdSe and CdTe nanocrystals, has also been explored, although to a lesser extent compared to the optical properties. Voltammetric measurements can be used to probe the redox levels available for the nanocrystals, which is an invaluable piece of information if these systems are involved in electron transfer processes. Electrochemical data can also foster the interpretation of the spectroscopic properties of QDs, and give insightful information on their chemical composition, dimension, and surface properties. Hence, electrochemical methods constitute in principle an effective tool to probe the quality of QD samples in terms of purity, size dispersion, and surface defects. The scope of this critical review is to discuss the results of electrochemical studies carried out on CdSe and CdTe core and core-shell semiconductor nanocrystals of spherical shape. Examples of emerging or potential applications that exploit electroactive quantum dot-based systems will also be illustrated. PMID:22763461

Amelia, Matteo; Lincheneau, Christophe; Silvi, Serena; Credi, Alberto

2012-07-04

154

Electronographic Investigation of the Nature of Crystal Orientation and Formation of Phases in SB SB2TE4 and Pbbi4te7 Compounds.  

National Technical Information Service (NTIS)

The nature of crystal orientation in SnSb2Te4 and PbBi4Te7 compounds was investigated. It was established that in the case of sublimation of SnSb2Te4 alloy on a celluloid film and rock salt without subsequent annealing thin ploycrystalline films are obtai...

A. G. Talybov

1966-01-01

155

Superconductivity in copper intercalated topological compound CuxBi2Te3 induced via high pressure  

NASA Astrophysics Data System (ADS)

Copper intercalated Bi2Te3 topological single crystal Cu0.14Bi2Te3 was grown using Bridgman method. The transport properties were studied by temperature dependent resistance measurements at various pressures. Pressure induced superconductivity was found with Tc for ambient phase ˜6 K. The evolutions of crystal structure with pressure were investigated by high pressure synchrotron radiation experiments that reveal structural transitions occurring above 9.8 GPa. The superconducting properties of Cu0.14Bi2Te3 are compared with that of undoped topological compound Bi2Te3.

Zhang, J. L.; Zhang, S. J.; Kong, P. P.; Zhu, J.; Li, X. D.; Liu, J.; Cao, L. Z.; Jin, C. Q.

2013-10-01

156

Comparison of the optical properties of diffusion-doped polycrystalline Cr:ZnSe and Cr:CdTe windows  

NASA Astrophysics Data System (ADS)

Results of the material preparation and infrared (IR) optical properties of polycrystalline Cr:ZnSe and Cr:CdTe windows are reported. Cr doping of commercial ZnSe and CdTe windows was achieved through a thermal diffusion process employing CrSe powder as the dopant source. All samples exhibited the characteristic spectral features of Cr2+-doped II VI materials with strong IR absorption bands between 1700 and 1900 nm and broad emission spectra from 2000 to 3400 nm. The IR optical properties of Cr:CdTe were shifted by ˜150 200 nm to longer wavelengths compared to Cr:ZnSe due to the difference in crystal-field strength experienced by Cr2+ ions. The room-temperature decay times were measured to be 5 6 ?s for Cr:ZnSe and 3 4 ?s for Cr:CdTe. The emission lifetime of Cr2+ ions decreased by a factor of two for Cr concentrations of ˜2.6×1019 cm-3 for Cr:ZnSe and ˜0.7×1019 cm-3 for Cr:CdTe.

Hömmerich, U.; Jones, I. K.; Ei Nyein, Ei; Trivedi, S. B.

2006-01-01

157

Thermoelectric properties and electronic structure of Te-doped CoSb 3 compounds  

NASA Astrophysics Data System (ADS)

Co 4 Sb 12- x Te x compounds were prepared by mechanical alloying combined with cold isostatic pressing, and the effects of Te doping on the thermoelectric properties were studied. The electronic structure of Te-doped and undoped CoSb 3 compounds has been calculated using the first-principles plane-wave pseudo-potential based on density functional theory. The experimental and calculated results show that the value of the solution limit x of Te in Co 4 Sb 12- x Te x compounds is between 0.5 and 0.7. The Fermi surface of CoSb 3 is located between the conduction band and the valence band, and its electrical resistivity decreases with increasing temperature. The density of states is mainly composed of Co 3d and Sb 5p electrons for intrinsic CoSb 3 .The Fermi surface of Te-doped compounds moves to the conduction band and its electrical resistivity increases with increasing temperature, exhibiting n-type degenerated semiconductor character. Under the conditions of the experiment, the maximum value 2.67 mW/m K 2 of the power factor for Co 4 Sb 11.7 Te 0.3 is obtained at 600 K; this is about 14 times higher than that of CoSb 3 .

Zhu, Yunguang; Shen, Honglie; Zuo, Lianyong; Guan, Hao

2011-10-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

159

Microscopic analysis of the chemical reaction between Fe(Te, Se) thin films and underlying CaF2  

NASA Astrophysics Data System (ADS)

To understand the chemical reaction at the interface of Fe(Te, Se) and CaF2 materials, we used transmission electron microscopy to analyze five types of Fe(Te, Se) superconducting thin films prepared on different types of substrate: two on a CaF2 substrate, one on a CaF2 substrate with a CaF2 buffer layer, one on a CaF2 substrate with an FeSe buffer layer, and one on a LaAlO3 substrate with a CaF2 buffer layer. Energy-dispersive x-ray spectroscopy analysis revealed a potential interdiffusion between fluorine and selenium that plays a significant role in the variation of the lattice parameters. We conclude that the lattice parameters of the Fe(Te, Se) thin films are primarily determined by the chemical substitution of anions, while the lattice mismatch plays a secondary role.

Ichinose, A.; Nabeshima, F.; Tsukada, I.; Hanawa, M.; Komiya, Seiki; Akiike, T.; Imai, Y.; Maeda, A.

2013-07-01

160

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

161

Effect of Vacancy Distribution on the Thermal Conductivity of Ga2Te3 and Ga2Se3  

NASA Astrophysics Data System (ADS)

Our group has focused attention on Ga2Te3 as a natural nanostructured thermoelectric material. Ga2Te3 has basically a zincblende structure, but one-third of the Ga sites are structural vacancies due to the valence mismatch between Ga and Te. It has been confirmed that (1) vacancies in Ga2Te3 exist as two-dimensional (2D) vacancy planes, and (2) Ga2Te3 exhibits an unexpectedly low thermal conductivity ( ?), most likely due to highly effective phonon scattering by the 2D vacancy planes. However, the effect of the size and periodicity of the 2D vacancy planes on ? has been unclear. In addition, it has also been unclear whether only the 2D vacancy planes reduce ? or if point-type vacancies can also reduce ?. In the present study, we tried to prepare Ga2Te3 and Ga2Se3 with various vacancy distributions by controlling annealing conditions. The atomic structures of the samples were characterized by means of transmission electron microscopy, and ? was evaluated from the thermal diffusivity measured by the laser flash method. The effects of vacancy distributions on ? of Ga2Te3 and Ga2Se3 are discussed.

Kim, Chang-Eun; Kurosaki, Ken; Ishimaru, Manabu; Muta, Hiroaki; Yamanaka, Shinsuke

2011-05-01

162

Magnetic ordering of rare earth monochalcogenides. I. Neutron diffraction investigation of CeS, NdS, NdSe, NdTe and TbSe  

Microsoft Academic Search

The magnetic structures and ordered moments have been determined at 4.2K for the metallic antiferromagnets CeS, NdS, NdSe, NdTe, and TbSe with NaCl structure by means of neutron diffraction. In contrast to the monopnictides, the monochalcogenides of both light and heavy rare earths have FCC type II antiferromagnetic ordering at low temperatures similar to FeO and MnO. Except NdS, where

P. Schobinger-Papamantellos; A. Niggli; P. Fischer; E. Kaldis; V. Hildebrandt

1974-01-01

163

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

164

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

165

CdTe and CdSe quantum dots cytotoxicity: a comparative study on microorganisms.  

PubMed

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

2011-12-15

166

Optical second harmonic generation in the centrosymmetric magnetic semiconductors EuTe and EuSe  

NASA Astrophysics Data System (ADS)

The magnetic europium chalcogenide semiconductors EuTe and EuSe are investigated by the spectroscopy of second harmonic generation (SHG) in the vicinity of the optical band gap formed by transitions involving the 4f and 5d electronic orbitals of the magnetic Eu2+ ions. In these materials with centrosymmetric crystal lattice the electric-dipole SHG process is symmetry forbidden so that no signal is observed in zero magnetic field. Signal appears, however, in applied magnetic field with the SHG intensity being proportional to the square of magnetization. The magnetic field and temperature dependencies of the induced SHG allow us to introduce a type of nonlinear optical susceptibility determined by the magnetic-dipole contribution in combination with a spontaneous or induced magnetization. The experimental results can be described qualitatively by a phenomenological model based on a symmetry analysis and are in good quantitative agreement with microscopic model calculations accounting for details of the electronic energy and spin structure.

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

2010-04-01

167

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.

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

168

Terahertz conductivity in FeSe0.5Te0.5 superconducting films  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

169

Properties of photoluminescence in type-II ZnTe/ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

Temperature and time evolution of the photoluminescence (PL) intensity of bimodal ZnTe/ZnSe type-II quantum dots (QDs) were investigated. A particular temperature dependence of PL was observed in large QDs. PL decay of small QDs is composed of a faster initial component and a slower tail component whereas PL decay of large QDs simply comprises a fast component. All phenomena could be understood consistently by considering charge carrier transfer mechanism, band-bending effect, and the existence of nonradiative centers in the bimodal type-II QD array. We show that excitons play an important role in the emission properties of a self-assembled type-II QD system.

Lin, T. Y.; Lyu, D. Y.; Chang, J.; Shen, J. L.; Chou, W. C.

2006-03-01

170

Engineering Topological Surface States: HgS, HgSe, and HgTe  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

171

Thermal and electronic transport properties of CeTe2-xSnx compounds  

NASA Astrophysics Data System (ADS)

The thermal and electronic transport properties on rare-earth dichalcogenide compounds of CeTe2-xSnx (x<=0.1) were investigated by measuring electrical resistivity ?, thermal conductivity ?, and Seebeck coefficient S. Compound of CeTe2 exhibited very low ? (1.25 W m-1 K-1) at 300 K, which was understood by the charge density wave lattice distortion. From the ?(T) measurements, the metallic property of CeTe2 was significantly enhanced by Sn substitution. The temperature-dependent behavior of S(T) for CeTe2-xSnx (x=0.05 and 0.1) was well described by the inelastic Umklapp process and the phonon drag. The low Seebeck coefficient of CeTe2 (S~2.5 ?V/K at T~300 K) was increased by Sn doping. From the band structure calculation, the semimetallic band character of CeTe2 was revealed with symmetric electron-hole band dispersion near the Fermi level. The symmetric electron-hole band dispersion of CeTe2 is responsible for the low Seebeck coefficient. The enhancement of the metallic property and Seebeck coefficient because of Sn substitution could be understood by the charge imbalance between electrons and holes caused by hole doping in the Te monolayer.

Rhyee, Jong-Soo; Cho, Eunseog; Lee, Kyu Hyoung; Kim, Sang Il; Lee, Eun Sung; Lee, Sang Mock; Kwon, Yong Seung

2009-03-01

172

Material preparation and infrared spectroscopy of diffusion doped Cr: ZnSe and Cr: CdTe  

NASA Astrophysics Data System (ADS)

The preparation and infrared spectroscopy of diffusion doped Cr:ZnSe and Cr:CdTe windows will be reported. Cr^2+ doped II-VI semiconductors are of significant current interest as gain media in mid-infrared (2-3 ?m) solid-state lasers. Compared to Cr:ZnSe, Cr:CdTe exhibits an extended infrared emission, which is of interest for laser applications beyond 3?m. Cr doping in ZnSe and CdTe was achieved through a thermal diffusion process controlled by temperature and time. Commercial CrSe powder was used as the dopant source in the diffusion experiments. Various samples of Cr:ZnSe and Cr:CdTe were prepared with Cr^2+ peak absorption coefficients ranging from ˜0.8 cm-1 to 28.7 cm-1. The corresponding Cr^2+ concentrations ranged from ˜1x10^17cm-3 to ˜3x10^19cm-3 assuming absorption-cross sections of 1.1x10-18cm^2 for Cr:ZnSe and 2.2x10-18cm^2 for Cr:CdTe. For low Cr^2+ concentrations (˜1x10^18cm-3) the room-temperature decay time varied between 5-6 ?s for Cr:ZnSe and 2-3?s for Cr:CdTe. The effect of Cr concentration quenching on the mid-infrared emission was observed for doping concentrations above ˜1x10^19cm^3.

Krystal Jones, Ivy

2005-05-01

173

Sinusoidally modulated ZnSe{sub x}Te{sub 1-x} superlattices: Fabrication and structural studies  

SciTech Connect

Semiconductor ''sinusoidal superlattices'' of ZnSe{sub x}Te{sub 1-x}--that is, periodic structures in which the chemical composition parametrized by x varies sinusoidally along one direction--were fabricated by rotating a substrate through an inhomogeneous distribution of constituent fluxes within a molecular beam epitaxy growth chamber. The modulation of chemical composition x is accompanied by modulation of strain, owing to the difference in Zn-Se and Zn-Te bond lengths. By fitting x-ray diffraction scans around the (002), (004), and (006) Bragg reflections for (001)-oriented ZnSe{sub x}Te{sub 1-x} sinusoidal superlattices to a simple scattering theory, we have determined both the strain and the chemical modulation amplitudes in these structures. (c) 2000 The American Physical Society.

Reimer, P. M. [Turner Precision X-ray Laboratory, Goshen College, Goshen, Indiana 46526 (United States); Buschert, John R. [Turner Precision X-ray Laboratory, Goshen College, Goshen, Indiana 46526 (United States); Lee, S. [Physics Department, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Furdyna, J. K. [Physics Department, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2000-03-15

174

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

PubMed

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

Samanta, Anirban; Deng, Zhengtao; Liu, Yan

2012-05-14

175

Study of As2Se3 and As2Se2Te glass structure by neutron- and X-ray diffraction methods  

NASA Astrophysics Data System (ADS)

Neutron and high-energy X-ray diffraction measurements have been performed on As40Se60 and As40Se50Te10 glasses. Both the traditional Fourier transformation technique and the reverse Monte Carlo (RMC) simulation of the experimental data have been applied to model the 3-dimensional atomic configurations. From the analysis of the partial atomic correlation functions and structure factors the first and second neighbour distances, coordination numbers and bond-angle distributions were calculated. It is established that substitution of Se by Te does not change the basic glassy network structure. For the As-Se bonding is revealed that the first neighbour distance is at 2.42 Å, the average coordination numbers are CNAsSe=2.6±0.1 and CNSeAs=1.8±0.1 atoms and the three-atom-bond angle for <Se-As-Se>, Se-As> configurations is 95°, the same value within limit of error, as obtained from RMC calculations.

Fábián, M.; Sváb, E.; Pamukchieva, V.; Szekeres, A.; Vogel, S.; Ruett, U.

2010-11-01

176

Phonons of single quintuple Bi2Te3 and Bi2Se3 films and bulk materials  

NASA Astrophysics Data System (ADS)

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

Cheng, Wei; Ren, Shang-Fen

2011-03-01

177

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

Microsoft Academic Search

Refractive index data of ZnS, ZnSe, and ZnTe were searched, compiled, and analyzed. Recommended values of refractive index for the transparent spectral region were generated in the ranges 0.5–14 ?m and 93–1000 K for ZnS, 0.55–18 ?m and 93–618 K for ZnSe, and 0.55–30 ?m at room temperature for ZnTe. Generation of these values was based on a dispersion equation

H. H. Li

1984-01-01

178

An optical study of vacuum evaporated Se85-xTe15Bix chalcogenide thin films  

NASA Astrophysics Data System (ADS)

Thin films of Se85-xTe15Bix (x=0, 1, 2, 3, 4, 5) glassy alloys prepared by melt quenching technique, are deposited on glass substrate using thermal evaporation technique under vacuum. The analysis of transmission spectra, measured at normal incidence, in the spectral range 400-1500 nm helphelps us in the optical characterization of thin films under study. Well -known Swanepoel's method is employed to determine the refractive index (n) and film thickness (d). The increase in n with increasing Bi content over the entire spectral range is related to the increased polarizability of the larger Bi atom (atomic radius 1.46 Å) compared with the Se atom (atomic radius 1.16 Å). Dispersion energy (Ed), average energy gap (E0) and static refractive index (n0) isare calculated using Wemple-DiDomenico model (WDD). The value of absorption coefficient (?) and hence extinction coefficient (k) hashave been determined from transmission spectra. Optical band gap (Eg) is estimated using Tauc's extrapolation and is found to decrease from 1.46 to 1.24 eV with the Bi addition. This behavior of optical band gap is interpreted in terms of electronegativity difference of the atoms involved and cohesive energy of the system.

Ambika; Barman, P. B.

2010-02-01

179

Structural properties of Sb- and Te-based binary compounds: Spin-orbit effect  

NASA Astrophysics Data System (ADS)

The band structure of AlSb, GaSb, ZnTe and CdTe is calculated using the empirical pseudopotential method (EPM) coupled with spin-orbit (SO) splitting. We applied our empirical model of bulk modulus with SO effect. It has been noticed that SO has a crucial effect on the band structure of these compounds but does not influence the structural phase transition. The calculated results are in good agreement with the experimental data.

Al-Douri, Y.

2013-01-01

180

Intramolecular Nonbonded Interactions Between Oxygen and Group VIA Elements: An Ab Initio Molecular Orbital and Density Functional Theory Investigation of the Structures of HX—CH 2 —COOH (X=S, Se, and Te)  

Microsoft Academic Search

Ab initio molecular orbital and density functional methods have been used to study the potential energy surfaces of the substituted acetic acids HX—CH2—COOH, where X is one of the Group VIA Chalcophiles S, Se, or Te. The various conformers adopted by these compounds provide information regarding the energetic importance of nonbonded \\u000a

George D. Markham; Cindy L. Bock; Mendel Trachtman; Charles W. Bock

1999-01-01

181

Material characteristics of HgCdSe grown on GaSb and ZnTe/Si substrates by MBE  

NASA Astrophysics Data System (ADS)

Much progress has been made in developing high quality HgCdTe/Si for large area focal plane array (FPA) applications. However, even with all the material advances made to date, there is no guarantee that this technology will be mature enough to meet the stringent FPA specifications required for long wavelength infrared (LWIR) systems. With this in mind, the Army Research Laboratory (ARL) has begun investigating HgCdSe material for infrared (IR) applications. Analogous to HgCdTe, HgCdSe is a tunable semiconductor that can detect any wavelength of IR radiation through control of the alloy composition. In addition, several mature, large area bulk III-V substrates are nearly latticematched to HgCdSe giving this system a possible advantage over HgCdTe in which no scalable, bulk substrate technology exists. We have initiated a study of the growth of HgCdSe using molecular beam epitaxy (MBE). Growth temperature and material flux ratios were varied to ascertain the best growth conditions and study defect formation. Smooth surface morphology has been achieved using a growth temperature much lower than HgCdTe. Preliminary data suggest a linear relationship between the Se/Cd flux ratio used during growth and the cut-off wavelength as measured by FTIR.

Brill, G.; Chen, Y.; Wijewarnasuriya, P.

2011-09-01

182

Distribution patterns of chalcogens (S, Se, Te, and 210Po) in various tissues of a squid, Todarodes pacificus.  

PubMed

In order to elucidate the relationship between the chemically similar chalcogen elements S, Se, Te, and 210Po in marine invertebrates, we conducted a comparative study of the distribution patterns of these elements in a squid, Todarodes pacificus. Elemental concentrations of the four chalcogens were determined in (mantle) muscle, gill, stomach, and hepatopancreas tissues. No relationship between chalcogen concentrations and morphological parameters (mantle length, body weight, and sex) was evident. Gills showed slightly elevated levels of Se and 210Po, which may indicate absorption and uptake of these elements over the gill surface. All four chalcogens have their highest concentrations in the hepatopancreas and the lowest concentrations in the muscle tissue. However, concentration differences between tissues, revealed by (1) bioaccumulation values based on reference seawater values and (2) internal relative enrichment factors (IREF) based on enrichment of hepatopancreas compared to muscle tissue, were least pronounced for S, most distinct for 210Po, and moderate for Se and Te. Furthermore, no significant correlation for Se, Te, and 210Po with S within tissue concentrations, and only a slightly negative correlation between S and 210Po in the squid muscle and hepatopancreas tissues were found, which indicates either an antagonistic effect between, or a disconnection of the two elements through metabolic processing. Overall, the distribution patterns of Se and Te resemble those of essential trace elements, such as Zn and Cu, whereas 210Po is partitioned in a manner similar to toxic heavy metals, such as Cd and Ag. PMID:18191182

Waska, Hannelore; Kim, Seolwon; Kim, Guebuem; Kang, Mi Ran; Kim, Gi Beum

2008-01-11

183

Enhancement of p-type doping of ZnSe using a modified (N+Te){delta} -doping technique  

SciTech Connect

Delta doping techniques have been investigated to enhance the p-type doping of ZnSe. Tellurium was used as a codopant for improving the nitrogen doping efficiency. The net acceptor concentration (N{sub A}-N{sub D}) increased to 1.5x10{sup 18} cm{sup -3} using single {delta} doping of N and Te (N+Te), while it was limited to 8x10{sup 17} cm{sup -3} by {delta} doping of N alone. A promising approach was developed in which three consecutive {delta}-doped layers of N+Te were deposited for each {delta}-doping cycle. An enhancement in the (N{sub A}-N{sub D}) level to 6x10{sup 18} cm{sup -3} has been achieved in ZnSe using this technique. The resultant layer has an average ZnTe content of only about 3%. This doping method shows potential for obtaining highly p-type doped ohmic contact layers without introducing significant lattice mismatch to ZnSe. Low-temperature photoluminescence spectra reveal some Te-related emissions. (c) 2000 American Institute of Physics.

Lin, W. [Chemistry Department of City College and Graduate Center of CUNY, New York, New York 10031 (United States); Guo, S. P. [Chemistry Department of City College and Graduate Center of CUNY, New York, New York 10031 (United States); Tamargo, M. C. [Chemistry Department of City College and Graduate Center of CUNY, New York, New York 10031 (United States); Kuskovsky, I. [School of Mines and Department of Applied Physics, Columbia University, New York, New York 10027 (United States); Tian, C. [School of Mines and Department of Applied Physics, Columbia University, New York, New York 10027 (United States); Neumark, G. F. [School of Mines and Department of Applied Physics, Columbia University, New York, New York 10027 (United States)

2000-04-17

184

The Effect of Grain Size and Density on the Thermoelectric Properties of Bi2Te3-PbTe Compounds  

NASA Astrophysics Data System (ADS)

The effects of microstructure on thermoelectric properties were investigated in Bi2Te3-PbTe compounds of different grain size and density. Powders of two different sizes [0.1 ?m to 1 ?m (micropowder) and <50 nm (nanopowder)] were prepared from Bi2Te3-PbTe ingots by ball milling and high-energy ball milling. Three different samples were spark plasma sintered from each powder and the mixture of the two powders. The grain size and relative density of the sintered samples varied from 100 nm to a few micrometers and 89.7% to 97.3%, respectively. The dimensionless figure of merit zT of the sample sintered from nanopowder was about 0.50 at 500 K, being about 3.3 times larger than that of the sample sintered from micropowder (˜0.15 at 500 K), when the relative density of the former and the latter were 89.7% and 97.3%, respectively. The improved thermoelectric performance of the samples may originate from the decrease of the thermal conductivity, which was caused by the decrease of the grain size and the increase of the amount of pores.

Yoon, Sejin; Kwon, O.-Jong; Ahn, Seunghyun; Kim, Jae-Yeol; Koo, Hyun; Bae, Sung-Hwan; Cho, Jun-Young; Kim, Jin-Sang; Park, Chan

2013-10-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

186

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

187

Experimental and theoretical investigations of the redox behavior of the heterodichalcogenido ligands [(EP(i)Pr2)(TeP(i)Pr2)N](-) (E = S, Se): cyclic cations and acyclic dichalcogenide dimers.  

PubMed

The two-electron oxidation of the lithium salts of the heterodichalcogenidoimidodiphosphinate anions [(EP (i)Pr 2)(TeP (i)Pr 2)N] (-) ( 1a, E = S; 1b, E = Se) with iodine yields cyclic cations [(EP (i)Pr 2)(TeP (i)Pr 2)N] (+) as their iodide salts [(SP (i)Pr 2)(TeP (i)Pr 2)N]I ( 2a) and [(SeP (i)Pr 2)(TeP (i)Pr 2)N]I ( 2b). The five-membered rings in 2a and 2b both display an elongated E-Te bond as a consequence of an interaction between tellurium and the iodide anion. One-electron reduction of 2a and 2b with cobaltocene produces the neutral dimers (EP (i)Pr 2NP (i)Pr 2Te-) 2 ( 3a, E = S; 3b, E = Se), which are connected exclusively through a Te-Te bond. Two-electron reduction of 2a and 2b with 2 equiv of cobaltocene regenerates the corresponding dichalcogenidoimidodiphosphinate anions as ion-separated cobaltocenium salts Cp 2Co[(EP (i)Pr 2)(TeP (i)Pr 2)N] ( 4a, E = S; 4b, E = Se). The ditellurido analogue Cp 2Co[(TeP (i)Pr 2) 2N] ( 4c) has been prepared in the same manner for comparison. Density functional theory calculations reveal that the preferential interaction of the iodide anion with tellurium is determined by the polarization of the lowest unoccupied molecular orbital [sigma*(E-Te)] of the cations in 2a and 2b toward tellurium and that the formation of the dimers 3a and 3b with a central Te-Te linkage is energetically more favorable than the structural isomers with either E-Te or E-E bonds. Compounds 2a, 2b, 3a, 3b, 4a, 4b, and 4c have been characterized in solution by multinuclear NMR spectroscopy and in the solid state by X-ray crystallography. PMID:18844341

Robertson, Stuart D; Chivers, Tristram; Tuononen, Heikki M

2008-10-10

188

Preparation and thermoelectric properties of quaternary bismuth telluride–indium selenide compound  

Microsoft Academic Search

Quaternary In–Se–Bi–Te compounds (7.5Bi2Te3–In2Se3 and 7.5Bi2Te3–In4Se3) were prepared by water quenching and annealing, and the microstructures and thermoelectric properties were investigated. These materials were solidified to near-eutectic compositions in order to obtain micro-scale heterointerfaces. The formation of sub-micrometer-scale lamellae layers of Bi2Te3 and In–Se–Te compounds was observed. Through quenching, the 7.5Bi2Te3–In2Se3 consisted of a Bi2Te3 and In–Se–Te compound, while the

Ju-Hyuk Yim; Kyooho Jung; Myong-Jae Yoo; Hyung-Ho Park; Jin-Sang Kim; Chan Park

2011-01-01

189

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

PubMed Central

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

2011-01-01

190

Composite detector for mixed radiations based on CsI(Tl) and dispersions of small ZnSe(Te) crystals  

NASA Astrophysics Data System (ADS)

A new large area detector of high-energy X-ray and ?-radiation has been designed and studied. A composite material based on small-crystalline ZnSe(Te) was applied onto the wide surface of a light guide. An experimental specimen has been prepared, which showed ?-sensitivity C=5.5cm. The spectrograms of a 90Sr+90Y ?-source obtained with the specimen under study make it possible to evaluate the age of the source by the ratio of low- and high-energy regions of the spectrum. The combined detector (CD) comprises a single crystalline plate of ZnSe(Te) placed onto the output window of a scintillating transparent light guide made of CsI(Tl) in the shape of a truncated pyramid. The CsI(Tl) light guide is used to create an additional channel for detection of ?-radiation, as well as for protecting the photodiode from the penetrating radiation. It is shown that introduction of the light guide does not worsen the energy resolution characteristics of ZnSe(Te). Separate detection of ?- and ?-radiation has been achieved under simultaneous excitation by 239Pu (ZnSe(Te), R=6%) and 241Am (CsI(Tl), R=20%). The use of selective optical filters allows separation of the peaks of total absorption (p.t.a.) in the case of their superposition.

Ryzhikov, V.; Gal'Chinetskii, L.; Katrunov, K.; Lisetskaya, E.; Gavriluk, V.; Zelenskaya, O.; Starzhynskiy, N.; Chernikov, V.

2005-03-01

191

Absorption coefficient of intersubband transition at 1.55 µm in (CdS\\/ZnSe)\\/BeTe quantum wells  

Microsoft Academic Search

In this paper, the intersubband optical absorption coefficient is calculated in a ZnSe\\/CdS\\/ZnSe quantum well (QW) surrounded by BeTe barriers. First, the one-dimensional Poisson and Schrödinger equations have been solved self-consistently, and then the intersubband optical absorption between the lowest two levels has been theoretically studied under an external electric field. Simulated results including eigenvalues, absorption coefficient and electroabsorption properties

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

2009-01-01

192

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

Microsoft Academic Search

Preliminary results of a program to develop ion implantation confined, shallow mesa stripe (Pb,Sn)Te laser diodes are presented. The practicality of using a shallow mesa stripe to produce single mode laser output and to increase the single mode tuning range are demonstrated. The first results of p-type ion implantation in the lead-tin salts are also reported. It is shown that

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

1983-01-01

193

Simple silanization routes of CdSe and CdTe nanocrystals for biological applications  

NASA Astrophysics Data System (ADS)

Semiconductor colloidal quantum dots have been, for the past two decades, incorporated in a wide range of applications from catalysis and optical sensors to biolabels. For this reason, simple, cheap and reproducible routes of synthesis are the main goal of many research groups around the world. They seek the production of a very stable and extremely quantum efficient nanocrystal that can afford rough changes in the external environment. Silica capping is becoming a very common tool in the quest for a stable quantum dot, because of its strong and stable structure, this material provides a great insulator to the nanocrystal from the outside. The nanocrystal surface is not chemically favorable to the deposition of the bare silica shell, what demands a bifunctional molecule that provides the linkage between the core and the shell. In this work we present a comparison between several silanization methods of thiol capped CdSe and CdTe quantum dots, showing some simplifications of the routes and an application of the quantum dots produced as fluorescent cell markers in acquisition of confocal microscopy images.

Almeida, Diogo B.; Faustino, Wagner M.; Jacob, Gilberto J.; de Thomaz, André A.; Barbosa, Luiz C.; Alves, Oswaldo L.; Farias, Patricia M. A.; Santos, Beate S.; Fontes, Adriana; Gomes, Suzete A. O.; Feder, Denise; Mazali, Italo O.; Cesar, Carlos L.

2008-08-01

194

Anisotropic fluctuations and quasiparticle excitations in FeSe0.5Te0.5  

NASA Astrophysics Data System (ADS)

We present data for the temperature dependence of the magnetic penetration depth ?(T) , heat capacity C(T) , resistivity ?(T) , and magnetic torque ? for highly homogeneous single-crystal samples of Fe1.0Se0.44(4)Te0.56(4) . ?(T) was measured down to 200 mK in zero field. We find ?(T) follows a power law ??˜Tn with n=2.2±0.1 . This is similar to some 122 iron arsenides and likely results from a sign-changing pairing state combined with strong scattering. Magnetic fields of up to B=55 or 14 T were used for the ?(B) and C(T)/?(T) measurements, respectively. The specific heat, resistivity, and torque measurements were used to map out the (H,T) phase diagram in this material. All three measurements were conducted on exactly the same single-crystal sample so that the different information revealed by these probes is clearly distinguished. Heat-capacity data strongly resemble those found for the high- Tc cuprates, where strong fluctuation effects wipe out the phase transition at Hc2 . Unusually, here we find the fluctuation effects appear to be strongly anisotropic.

Serafin, A.; Coldea, A. I.; Ganin, A. Y.; Rosseinsky, M. J.; Prassides, K.; Vignolles, D.; Carrington, A.

2010-09-01

195

CdSe and CdTe Nanostructure Deposition by Electrochemical Atomic Layer Epitaxy  

NASA Astrophysics Data System (ADS)

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

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

2004-03-01

196

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

NASA Astrophysics Data System (ADS)

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

Chander, Ravi; Thangaraj, R.

2013-02-01

197

Two Dimensional universal conductance fluctuations in topological insulator Bi2Te2Se microribbons  

NASA Astrophysics Data System (ADS)

The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs) to date. Even if one delicately suppresses the bulk conductance of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of the surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se nanoribbons. The solely-B-dependent UCF is achieved and its temperature dependence is investigated. The surface transport is further revealed by weak antilocalizations. Such quantum interference unexpectedly survives through the limited dephasing length of the bulk carriers in the ternary TI crystals. Based on the temperature-dependent scaling behavior, the electron-phonon interaction is addressed as a secondary source of the surface state dephasing. (Scientific Reports, 2, 595 (2012))

Song, Fengqi; Li, Zhaoguo; Wang, Baigeng; Wang, Guanghou

2013-03-01

198

Indices of refraction of ZnS, ZnSe, ZnTe, CdS, and CdTe in the far infrared  

Microsoft Academic Search

The indices of refraction of pure ZnS, ZnSe and ZnTe at 2, 80, and 300°K have been measured in the spectral region from 10 to 100 cm-1. The indices of refraction can be described by the simple dispersion formula for an undamped harmonic oscillator. The static dielectric constants of these materials are obtained from the best fit parameters using a

T. Hattori; Y. Homma; A. Mitsuishi; M. Tacke

1973-01-01

199

First-principles investigation of 67Zn isomer shifts in ZnF2 and the chalcogenides ZnO, ZnS, ZnSe, and ZnTe  

Microsoft Academic Search

All-electron, self-consistent, Hartree-Fock cluster calculations have been carried out to derive electron densities at the zinc nucleus in the series of compounds ZnF2 (rutile-type structure), ZnO (rocksalt structure), ZnO (wurtzite structure), and the compounds ZnS, ZnSe, and ZnTe (all with the sphalerite structure). The derived density differences show a very good linear correlation with the experimental isomer shifts. The isomer

D. W. Mitchell; T. P. Das; W. Potzel; G. M. Kalvius; H. Karzel; W. Schiessl; M. Steiner; M. Köfferlein

1993-01-01

200

Growth evolution and magneto-optical characteristics of self-assembled ZnTe/ZnMnSe quantum dots  

NASA Astrophysics Data System (ADS)

The growth evolution and the magneto-optical characteristics of the self-assembled single-layer ZnTe/ZnMnSe quantum dots grown by molecular beam epitaxy were investigated. As the ZnTe coverage is above 2.0 monolayers, a Stranski–Krastanov growth process is observed with a significantly increased dot density on top of two-dimensional plateaus. As the coverage exceeds 2.7 monolayers, ripened dots dominate instead. Furthermore, a saturated degree of circular polarization of 76% at applied magnetic field of 4T and the formation of magnetic polarons with a formation time of 7.4ns were demonstrated.

Lee, Ling; Fan, Wen-Chung; Chien, Kun-Feng; Tzou, An-Jye; Chou, Wu-Ching

2013-09-01

201

Evolution of self-assembled type-II ZnTe/ZnSe nanostructures: Structural and electronic properties  

NASA Astrophysics Data System (ADS)

The strain-mediated evolution of epitaxial ZnTe/ZnSe quantum structures is studied at the atomic scale using spherical aberration-corrected scanning transmission electron microscopy, coupled with electronic properties characterized by photoluminescence spectroscopy. The growth development of these buried quantum dots clearly demonstrates a homogeneous profile with similar pyramidal geometry rather than bi-modal distribution; contradicting prior reports on ZnTe/ZnSe quantum dots. The result is consistent with atomistic theoretical calculations on strain distribution and electronic structure of a modeled quantum dot of similar geometry using a valence force field model. It is also found that the transition from 2-D islands to 3-D quantum dots involves thermally activated carrier transfer process and follows up with formation of extended defects at the quantum dot surface, acting as an effective source for remnant misfit strain relaxation. The new physical understanding concerning the growth of self-assembled ZnTe/ZnSe quantum dots embedded in the active regions provides important information for the measures to control the properties of buried ZnTe quantum dots, setting up a key footstep in developing novel materials of energy conversion.

Kim, S. J.; Juang, B.-C.; Wang, W.; Jokisaari, J. R.; Chen, C.-Y.; Phillips, J. D.; Pan, X. Q.

2012-05-01

202

Anomalous Dressing of Dirac Fermions in the Topological Surface State of Bi2Se3, Bi2Te3, and Cu-Doped Bi2Se3  

NASA Astrophysics Data System (ADS)

Quasiparticle dynamics on the topological surface state of Bi2Se3, Bi2Te3, and superconducting CuxBi2Se3 are studied by 7 eV laser-based angle resolved photoemission spectroscopy. We find strong mode couplings in the Dirac-cone surface states at energies of ˜3 and ˜15-20meV associated with an exceptionally large coupling constant ? of ˜3, which is one of the strongest ever reported for any material. This result is compatible with the recent observation of a strong Kohn anomaly in the surface phonon dispersion of Bi2Se3, but it appears that the theoretically proposed “spin-plasmon” excitations realized in helical metals are also playing an important role. Intriguingly, the ˜3meV mode coupling is found to be enhanced in the superconducting state of CuxBi2Se3.

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

2013-05-01

203

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

204

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

205

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

206

Optical Properties and Growth Mechanism of Multiple Type-II ZnTe\\/ZnSe Quantum Dots Grown by Migration-Enhanced Epitaxy  

Microsoft Academic Search

The properties of multiple type-II ZnTe\\/ZnSe quantum dots (QDs), which are coexistent with isoelectronic centers formed by Te, grown by migration-enhanced epitaxy, are studied. The samples with a single deposition cycle of Zn-Te-Zn sandwiched between ZnSe barriers are investigated via temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL measurements. It is found that the PL consists of two broad

Y. Gong; W. MacDonald; G. Neumark; M. Tamargo; Igor Kuskovsky

2008-01-01

207

Optical properties and growth mechanism of multiple type-II ZnTe\\/ZnSe quantum dots grown by migration-enhanced epitaxy  

Microsoft Academic Search

The properties of multiple type-II ZnTe\\/ZnSe quantum dots (QDs), which are coexistent with isoelectronic centers formed by Te, grown by migration-enhanced epitaxy, are studied. The samples with a single deposition cycle of Zn-Te-Zn sandwiched between ZnSe barriers are investigated via temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL measurements. It is found that the PL consists of two broad

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

2008-01-01

208

Robust Coherent Magneto-optical Properties of Columnar Type-II Quantum Dots in ZnTe/ZnSe and ZnMnTe/ZnSe Systems  

NASA Astrophysics Data System (ADS)

We present recent experimental results that show strong optical AB effects in the magneto-photoluminescence of columnar II-VI quantum dots (QDs). The AB effects manifest themselves as oscillations in the photoluminescence energy and intensity with magnetic field. It will be shown that this coherent behavior is remarkably robust, persisting at 180 K. We, also, present results for a magnetic system, ZnMnTe QDs. These magnetic type-II systems also display evidence of robust magnetic ordering. This behavior is attributed to the formation of magnetic polarons caused by the exchange interaction between strongly localized holes and Mn ions within the QDs. Time-resolved PL measurements display evidence of magnetic polarons up to 200 K with a binding energy of approximately 40 meV.

Whiteside, V. R.; Sellers, I. R.; Eginligil, M.; Oszwaldowski, R.; Petrou, A.; Zutic, I.; Chou, W.-C.; Kuskovsky, I. L.; Petukhov, A. G.; Govorov, A. O.; McCombe, B. D.

2011-12-01

209

Thin-film CdTe and CuInSe{sub 2} photovoltaic technologies  

SciTech Connect

Total-area conversion efficiency of 15%--15.8% have been achieved for thin-film CdTe and CIS solar cells. Modules with power output of 5--53 W have been demonstrated by several groups world-wide. Critical processes and reaction pathways for achieving excellent PV devices have been eluciated. Research, development and technical issues have been identified, which could result in potential improvements in device and module performance. A 1-kW thin-film CdTe array has been installed and is being tested. Multimegawatt thin-film CdTe manufacturing plants are expected to be completed in 1-2 years.

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

1993-08-01

210

Effects of Bi2Se3 Nanoparticle Inclusions on the Microstructure and Thermoelectric Properties of Bi2Te3-Based Nanocomposites  

NASA Astrophysics Data System (ADS)

A series of thermoelectric nanocomposite samples were prepared by integrating Bi2Se3 nanoparticles into a bulk Bi2Te3 matrix. Primarily, spherical Bi2Se3 nanoparticles with diameter of ˜30 nm were synthesized by combining bismuth acetate with elemental Te in oleic acid solution. Bi2Te3-based nanocomposite samples were prepared by consolidating the appropriate quantity of Bi2Se3 nanoparticles with the starting elements (Bi and Te) using typical solid-state synthetic reactions. The microstructure and composition of the Bi2Te3-based nanocomposites, as well as the effects of the Bi2Se3 nanoparticles on their thermoelectric properties, are investigated. Transmission electron microscopy observation of the Bi2Te3-based nanocomposites reveals two types of interface between the constituent materials, i.e., coherent and incoherent, depending on the Bi2Se3 concentration. The Bi2Se3 nanoparticles in the Bi2Te3 matrix act as scattering centers for a wider range of phonon frequencies, thereby reducing the thermal conductivity. As a result, the maximum ZT value of 0.75 is obtained for the Bi2Te3 nanocomposite with 10 wt.% Bi2Se3 nanoparticles at room temperature. It is clear that the reduction in the thermal conductivity plays a central role in the enhancement of the ZT value.

Kim, HeeJin; Han, Mi-Kyung; Yo, Chul-Hyun; Lee, Wooyoung; Kim, Sung-Jin

2012-12-01

211

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

NASA Astrophysics Data System (ADS)

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

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

212

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

213

SPECTROSCOPIC INVESTIGATION OF (NH4)2S TREATED GaSeTe FOR RADIATION DETECTOR APPLICATIONS  

SciTech Connect

The surface of the layered III-VI chalcogenide semiconductor GaSeTe was treated with (NH{sub 4}){sub 2}S at 60 C to modify the surface chemistry and determine the effect on transport properties. Room temperature photoluminescence (PL) measurements were used to assess the effect of the (NH{sub 4}){sub 2}S treatment on surface defect states. Evaluation of the subsequent surface chemistry was performed with high-resolution core-level photoemission measurements. Metal overlayers were deposited on the (NH{sub 4}){sub 2}S treated surfaces and the I-V characteristics were measured. The measurements were correlated to understand the effect of (NH{sub 4}){sub 2}S modification of the interfacial electronic structure with the goal of optimizing the metal/GaSeTe interface for radiation detector devices.

Nelson, A; Laurence, T; Conway, A; Behymer, E; Sturm, B; Voss, L; Nikolic, R; Payne, S; Mertiri, A; Pabst, G; Mandal, K; Burger, A

2009-08-04

214

Quantum confinement and spin-orbit interactions in PbSe and PbTe nanowires: First-principles calculation  

NASA Astrophysics Data System (ADS)

First-principles calculations have been used to investigate the energetic stability and electronic properties of PbSe and PbTe nanowires (NW). The stability of the NWs depends on the NW diameter, while the electronic properties are ruled by three effects: in-plane stoichiometry, quantum confinement, and spin-orbit (SO) interactions. The PbTe NWs present direct band gaps, as it is in the bulk. However the PbSe NWs present indirect or direct band gaps depending on the in-plane stoichiometry. Our results for NWs out of in-plane stoichiometry show that there is an electronic compensation mechanism between quantum confinement effects and SO interactions, resulting in an almost diameter-independent band gap.

Wrasse, E. O.; Baierle, R. J.; Schmidt, T. M.; Fazzio, A.

2011-12-01

215

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

PubMed

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

Zhu, Lianxuan; Zhao, Anqing; Wang, Minjie

2012-04-26

216

Characterization of n-CdSe0.7Te0.3/(aq) Polyiodide Energetic Interface and Photoelectrochemical Studies  

NASA Astrophysics Data System (ADS)

The vacuum deposited thin films of n-CdSe0.7Te0.3 of 5000 Å thickness have been characterized by X-ray diffraction (XRD) for structural analysis, by energy despersive analysis of X-rays (EDAX) for compositional analysis and the scanning electron microscopy (SEM) for surface studies. Similar films have been deposited on Indium Oxide precoated microslide glass plates and the photoelectrochemical properties of n-CdSe0.7Te0.3/polyiodide junction are investigated for suitability for solar energy conversion by I V measurements in the dark. Also, the carrier concentration and flat band potential have been calculated from the space charge capacitance vs voltage measurements. The minority carrier diffusion length, Lp has been determined using Gärtner's model. Using the Mott-Schottky plots, the energy band diagram at flat band condition has been constructed. The occurrence of high quantum efficiency and high power conversion efficiency have been explained.

Das, V.; Damodare, Laxmikant

1998-04-01

217

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

218

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

SciTech Connect

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

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

2011-07-01

219

The structure of a new one-dimensional compound: (TaTe 4) 4T 2(TaI 6)  

Microsoft Academic Search

The title compound consists of[TaTe4]n chains, TaI6? complex anions and isolated I? anions. In the[TaTe4]n chain, every tantalum atom is coordinated by four pairs of Te2 group and these Ta(Te2)2 polyhedra are joined with (Te2)2 planes. The tantalum atom in TaI6? complex anion is octahedrally coordinated by iodine atoms. The chains are held by inserting complex TaI6? anions and isolated

Shi-Xiong Liu; Da-Ping Huang; Chang-Cang Huang; Jin-Ling Huang

1996-01-01

220

Excitation intensity dependence of up-converted emission in ZnSe–ZnTe superlattice grown by MBE  

Microsoft Academic Search

The photoluminescence (PL) spectra of the type II ZnSe–ZnTe superlattices with dual-subband structures have two emission peaks. The PL peak at the higher energy side appears by the excitation even with the light, with the middle energy between the PL peaks. The emission energy of the up-converted light shows dependence similar to the case of direct excitation (high-energy excitation) on

M. Ohashi; Y. Ichinohe; G. Shigaura; Y. Sasaki; Y. Chikarayumi; Na. Kimura; No. Kimura; T. Sawada; K. Suzuki; K. Imai; H. Saito; P. A. Trubenko; Yu. V. Korostelin

2005-01-01

221

Electrical and switching properties of the Se 90Te 10? x Ag x (0? x?6) films  

Microsoft Academic Search

Amorphous Se90Te10?xAgx (0?x?6) films are obtained by thermal evaporation technique under vacuum from the synthesized bulk materials on pyrographite and glass substrates. X-ray analysis shows the amorphous nature of the obtained films. The dc electrical conductivity was studied for different thicknesses (165–711nm) as a function of temperature in the range (298–323K) below the corresponding Tg for the studied films. The

M. A. Afifi; N. A. Hegab; A. E. Bekheet; E. R. Sharaf

2009-01-01

222

Electrical and switching properties of the Se90Te10-xAgx (0<=x<=6) films  

Microsoft Academic Search

Amorphous Se90Te10-xAgx (0<=x<=6) films are obtained by thermal evaporation technique under vacuum from the synthesized bulk materials on pyrographite and glass substrates. X-ray analysis shows the amorphous nature of the obtained films. The dc electrical conductivity was studied for different thicknesses (165-711 nm) as a function of temperature in the range (298-323 K) below the corresponding Tg for the studied

M. A. Afifi; N. A. Hegab; A. E. Bekheet; E. R. Sharaf

2009-01-01

223

Polarized optical properties in type-II ZnTe\\/CdSe multiple quantum wells induced by interface chemical bonds  

Microsoft Academic Search

Photoluminescence (PL) and photoconductivity (PC) spectra were studied in type-II ZnTe\\/CdSe multiple quantum wells. It was found that the PL spectrum exhibits a strong in-plane polarization with respect to axis with a polarization degree up to 30%. The degree of polarization does not depend on the excitation intensity and temperature, which excludes extrinsic mechanisms related to the observed in-plane anisotropy.

W. S. Su; M. H. Ya; Y. S. Chiu; Y. F. Chen

2002-01-01

224

A Comparative Study of the Nonlinear Optical Properties of Cd n X n (X: S, Se and Te) Clusters  

Microsoft Academic Search

We report results of hyperpolarizability calculations on CdnXn (X: S, Se and Te; n = 1–10) clusters. Our results show that the geometric configurations of different types of clusters under\\u000a investigation are quite similar at specific values of n. Both static and frequency dependent components of first and second\\u000a order hyperpolarizability tensors of CdnSn, CdnSen and CdnTen are compared. It is observed

Sabyasachi Sen; Prasenjit Seal; Swapan Chakrabarti

2010-01-01

225

Electrical properties of p-type and n-type ZnSe-ZnTe strained-layer superlattices  

Microsoft Academic Search

ZnSe and ZnTe are semiconducting materials ideally suited for the fabrication of short wavelength light emitting devices. The realization of this potential hinges on obtaining low-resistivity material of controlled conduction type, carrier density, and carrier mobility. Superlattice structures using these materials, and introduction of modulation doping technique may prove to be a good technique to fabricate p-n junctions from wide-gap

Masakazu Kobayashi; Shiro Dosho; Akira Imai; Ryuhei Kimura; Makoto Konagai; Kiyoshi Takahashi

1987-01-01

226

Magnetic order and structural transition in BaFe2As2 and alpha-Fe(Se,Te)  

Microsoft Academic Search

We report neutron diffraction determination of magnetic structure in BaFe2As2 [1] and alpha-Fe(Se,Te) [2], the first in both the 122 and 11-type of the Fe-based materials. The former has the (,) and the later delta(,), delta= 0.346-0.5, kind of in-plane propagation vector. In both systems, the magnetic transition is accompanied by a first-order structural transition which breaks the tetragonal symmetry

Wei Bao; Yiming Qiu; Qingzheng Huang; Mark Green; P. Zajdel; Mike Fitzsimmons; M. Zhernenkov; Minhu Fang; B. Qian; E. K. Vehstedt; Jinhu Yang; Zhiqiang Mao; Jeff Lynn; Ying Chen; T. Wu; G. Wu; Xianhui Chen

2009-01-01

227

Radiative transitions in stacked type-II ZnMgTe quantum dots embedded in ZnSe  

NASA Astrophysics Data System (ADS)

Sub-monolayer quantities of Mg are introduced in multilayer stacked ZnMgTe quantum dots (QDs) embedded in ZnSe barriers in order to reduce the hole confinement energy by controlling the bandgaps and band-offsets of ZnTe/ZnSe system having type-II band alignment. The photoluminescence (PL) emission from such ZnMgTe/ZnSe QD structure is found to be a broad band centered at 2.35 eV. The higher energy side of the PL band shows a larger blue-shift with increasing excitation intensity and a faster life-time decay due to a greater contribution of the emission from the smaller size dots and the isoelectronic bound excitons. It is found that the characteristic decay time of the PL evolves along the band with a value of 129 ns at 2.18 eV to 19 ns at 2.53 eV. The temperature dependent PL emission is controlled by two thermally activated processes: ionization of electrons away from QD state to the barrier (EA1 ~ 3 meV) by breaking the type-II excitons and thermal escape of the holes from the ground state to the barrier (EA2 ~ 114-116 meV). We propose a modified band diagram and energy levels for this ZnMgTe/ZnSe multilayer QD system by determining the composition of Mg inside the QDs and solving the 1-D Schrodinger's equation and show that Mg incorporation lowers the hole activation energy via modification of the valence band offset without changing the barrier significantly.

Manna, U.; Zhang, Q.; Dhomkar, S.; Salakhutdinov, I. F.; Tamargo, M. C.; Noyan, I. C.; Neumark, G. F.; Kuskovsky, I. L.

2012-09-01

228

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

Microsoft Academic Search

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

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

2010-01-01

229

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

Microsoft Academic Search

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

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

2010-01-01

230

Millimeter wave absorption by confined acoustic modes in CdSe\\/CdTe core-shell quantum dots  

Microsoft Academic Search

Taking advantage of the specific core-shell charge separation structure in the CdSe\\/CdTe core-shell Type-II quantum dots (QDs), we experimentally observed the resonant-enhanced dipolar interaction between millimeter-wave (MMW) photons and their corresponding (l = 1) confined acoustic phonons. With proper choice of size, the absorption band can be tuned to desired frequency of MMW imaging. Exploiting this characteristic absorption, in a

T.-M. Liu; J.-Y. Lu; C.-C. Kuo; Y.-C. Wen; C.-W. Lai; M.-J. Yang; P.-T. Chou; D. B. Murray; L. Saviot; C.-Kuang Sun

2007-01-01

231

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

232

The effect of compaction and heat treatment on phase Transitions of ZnSe(Te) bulk material made of nanopowder  

NASA Astrophysics Data System (ADS)

ZnSe ceramic material doped with Te was produced at room temperature via compaction of nanocrystalline powders. Phase composition and microstructure were investigated and the effect of compression and heat treatment on phase transformations and grain growth was studied. Two ways of transition from metastable hexagonal to stable cubic phase were found. Two-staged annealing at ?=700 °?, 2 h followed by annealing at ?=800 °?, 2 h brings to complete transformation from wutzite to sphalerite phase. However, under these conditions some additive is lost during the heat treatment. Annealing of the compacted material at ?=800 °?, 2 h, its slow cooling to room temperature causes transformation into two sphalerite lattices with the unit cell parameters a1=5.660 Å and a2=5.686 Å, which transform during holding at room temperature into one sphalerite lattice with aZnSe(Te)=5.681±0.003 Å. This heat treatment provides formation of the stable cubic state of the solid solution containing 2.5 wt% Te in ZnSe(1-x)Tex.

Kolesnikov, N. N.; Borisenko, E. B.; Borisenko, D. N.; Zverkova, I. I.; Timonina, A. V.

2012-05-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

234

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

235

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

PubMed

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

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

2013-05-30

236

The influence of Te on thermal properties of Er-doped (Ge 30(Se 1? x Te x ) 70) 94Ga 6 chalcogenide glasses  

Microsoft Academic Search

We have studied the thermal properties of Er2S3 doped (Ge0.30(Se1?xTex)0.70)94Ga6 chalcogenide glasses alloyed with different amounts of Te (x=0.005–0.4). All the samples were doped with 1at.% of initial amount of Er3+ ions. The glass composition was chosen with respect to the possible use of this material system in optical amplifier applications operating in the 1550nm telecommunications window. We have prepared

K. Maeda; T. Sakai; D. Tonchev; M. Munzar; T. Ikari; S. O. Kasap

2005-01-01

237

The synthesis and characterization of new [(BiSe){sub 1.10}]{sub m}[NbSe]{sub n}, [(PbSe){sub 1.10}]{sub m}[NbSe]{sub n}, [(CeSe){sub 1.14}]{sub m}[NbSe]{sub n} and [(PbSe){sub 1.12}]{sub m}[TaSe]{sub n} misfit layered compounds  

Microsoft Academic Search

Fifty-three new misfit layered compounds within the [(BiSe){sub 1.10}]{sub m}[NbSe]{sub n,} [(PbSe){sub 1.10}]{sub m}[NbSe]{sub n}, [(CeSe){sub 1.14}]{sub m}[NbSe]{sub n}, and [(PbSe){sub 1.12}]{sub m}[TaSe]{sub n} families of compounds were successfully synthesized. This is the first report of compounds with n and m larger than 3, as self-assembly from designed precursors allows compounds with particular n and m values to be selectively

Colby Heideman; Ngoc Nyugen; Jonathan Hanni; Qiyin Lin; Scott Duncombe; David C. Johnson; Paul Zschack

2008-01-01

238

Pressure-induced superconductivity in topological parent compound Bi2Te3  

PubMed Central

We report a successful observation of pressure-induced superconductivity in a topological compound Bi2Te3 with Tc of ?3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the hole-type carrier in the pressure-induced superconducting Bi2Te3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor.

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

2011-01-01

239

Pressure-induced superconductivity in topological parent compound Bi2Te3.  

PubMed

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

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

2010-12-20

240

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

Microsoft Academic Search

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

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

2006-01-01

241

Synthesis and thermoelectric properties of Mn-doped AgSbTe2 compounds  

NASA Astrophysics Data System (ADS)

Polycrystalline p-type Ag0.9Sb1.1-xMnxTe2.05 (x = 0.05, 0.10, and 0.20) compounds have been prepared by a combined process of melt-quenching and spark plasma sintering. The sample composition of Ag0.9Sb1.1-xMnxTe2.05 has been specially designed in order to achieve the doping effect by replacing part of Sb with Mn and to present the uniformly dispersed Ag2Te phase in the matrix by adding insufficient Te, which is beneficial for optimizing the electrical transport properties and enhancing the phonon scattering effect. All the samples have the NaCl-type structure according to our X-ray powder diffraction analysis. After the treatment of spark plasma sintering, only the sample with x = 0.20 has a small amount of MnTe2 impurities. The thermal analysis indicates that a tiny amount of Ag2Te phase exists in all these samples. The presence of the MnTe2 impurity with high resistance and high thermal conductivity leads to the deteriorative thermoelectric performance of the sample with x = 0.20 due to the decreased electrical transport properties and the increased thermal conductivity. In contrast, the sample with x = 0.10 exhibits enhanced thermoeletric properties due to the Mn-doping effect. A dimensionless thermoelectric figure of merit of 1.2 is attained for the sample with x = 0.10 at 573 K, showing promising thermoelectric properties in the medium temperature range.

Zhang, He; Luo, Jun; Zhu, Hang-Tian; Liu, Quan-Lin; Liang, Jing-Kui; Li, Jing-Bo; Liu, Guang-Yao

2012-10-01

242

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

243

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

PubMed

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

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

2009-10-19

244

Accuracy of existing atomic potentials for the CdTe semiconductor compound  

NASA Astrophysics Data System (ADS)

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 the formation and interaction of atomic scale defects in these crystals, and provide insight on how to minimize their concentrations. The success of such a modeling effort relies on the accuracy and transferability of the underlying interatomic potential used in simulations. Such a potential must not only predict a correct trend of structures and energies of a variety of elemental and compound lattices, defects, and surfaces but also capture correct melting behavior and should be capable of simulating crystalline growth during vapor deposition as these processes sample a variety of local configurations. In this paper, we perform a detailed evaluation of the performance of two literature potentials for CdTe, one having the Stillinger-Weber form and the other possessing the Tersoff form. We examine simulations of structures and the corresponding energies of a variety of elemental and compound lattices, defects, and surfaces compared to those obtained from ab initio calculations and experiments. We also perform melting temperature calculations and vapor deposition simulations. Our calculations show that the Stillinger-Weber parameterization produces the correct lowest energy structure. This potential, however, is not sufficiently transferrable for defect studies. Origins of the problems of these potentials are discussed and insights leading to the development of a more transferrable potential suitable for molecular dynamics simulations of defects in CdTe crystals are provided.

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

2011-06-01

245

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

246

The therapeutic efficacy of CdTe and CdSe quantum dots for photothermal cancer therapy.  

PubMed

Fluorescent quantum dots (QDs) used for biomedical imaging and diagnostics have attracted considerable attention over the past decade. Here, we report our finding regarding the therapeutic efficacy of the popularly used red/brown, brown or close to black CdTe and CdSe QDs. Upon 671-nm laser irradiation, these QDs can rapidly convert light energy into heat, both in vitro and in vivo. In the present study, the growth of mouse melanoma tumors injected with CdTe(710) QDs coated with a silica shell (SiO(2)) was significantly inhibited after laser irradiation, with eventual disappearance of the tumor. In contrast, tumors injected with the silica-coated QDs without subsequent irradiation continued to grow over time. They had a growth rate close to that of tumors injected with SiO(2) or phosphate-buffered saline, with or without laser irradiation. In conclusion, our data suggest that the popularly used CdTe and CdSe QDs have great potential in the treatment of cancer using photothermal therapy. PMID:22818982

Chu, Maoquan; Pan, Xiaojing; Zhang, Ding; Wu, Qiang; Peng, Jinliang; Hai, Wangxi

2012-07-18

247

Semiconducting [(Bi4Te4Br2)(Al2Cl(6-x)Br(x))]Cl2 and [Bi2Se2Br](AlCl4): cationic chalcogenide frameworks from Lewis acidic ionic liquids.  

PubMed

Lewis acidic organic ionic liquids provide a novel synthetic medium to prepare new semiconducting chalcogenides, [(Bi4Te4Br2)(Al2Cl5.46Br0.54)]Cl2 (1) and [Bi2Se2Br](AlCl4) (2). Compound 1 features a cationic [(Bi4Te4Br2)(Al2Cl5.46Br0.54)](2+) three-dimensional framework, while compound 2 consists of cationic layers of [Bi2Se2Br](2+). Spectroscopically measured band gaps of 1 and 2 are ?0.6 and ?1.2 eV, respectively. Thermoelectric power measurements of single crystals of 1 indicate an n-type semiconductor. PMID:23627985

Biswas, Kanishka; Chung, In; Song, Jung-Hwan; Malliakas, Christos D; Freeman, Arthur J; Kanatzidis, Mercouri G

2013-04-29

248

The synthesis and characterization of new [(BiSe){sub 1.10}]{sub m}[NbSe{sub 2}]{sub n}, [(PbSe){sub 1.10}]{sub m}[NbSe{sub 2}]{sub n}, [(CeSe){sub 1.14}]{sub m}[NbSe{sub 2}]{sub n} and [(PbSe){sub 1.12}]{sub m}[TaSe{sub 2}]{sub n} misfit layered compounds  

SciTech Connect

Fifty-three new misfit layered compounds within the [(BiSe){sub 1.10}]{sub m}[NbSe{sub 2}]{sub n,} [(PbSe){sub 1.10}]{sub m}[NbSe{sub 2}]{sub n}, [(CeSe){sub 1.14}]{sub m}[NbSe{sub 2}]{sub n}, and [(PbSe){sub 1.12}]{sub m}[TaSe{sub 2}]{sub n} families of compounds were successfully synthesized. This is the first report of compounds with n and m larger than 3, as self-assembly from designed precursors allows compounds with particular n and m values to be selectively prepared. The compounds form as crystallographically aligned films, with the c-axis perpendicular to the substrate. The compounds are well ordered along the c-axis and in the ab plane, with shorter coherence lengths between the constituent layers. All 18 compounds that were measured were found to be metallic. - Graphical abstract: The synthesis and characterization of new [(BiSe){sub 1.10}]{sub m}[NbSe{sub 2}]{sub n}, [(PbSe){sub 1.10}]{sub m}[NbSe{sub 2}]{sub n}, [(CeSe){sub 1.14}]{sub m}[NbSe{sub 2}]{sub n}, and [(PbSe){sub 1.12}]{sub m}[TaSe{sub 2}]{sub n} misfit layered compounds.

Heideman, Colby; Nyugen, Ngoc; Hanni, Jonathan; Lin, Qiyin; Duncombe, Scott [Department of Chemistry, University of Oregon, 373 Klamath Hall, Eugene, OR 97403 (United States); Johnson, David C. [Department of Chemistry, University of Oregon, 373 Klamath Hall, Eugene, OR 97403 (United States)], E-mail: davej@uoregon.edu; Zschack, Paul [Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 (United States)

2008-07-15

249

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

SciTech Connect

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

Jun, Jong-Ho [Department of Applied Chemistry, Konkuk University, Choongju 380-701 (Korea, Republic of); Jung, Jin-Seung [Department of Chemistry, Kangnung National University, Kangnung 210-702 (Korea, Republic of)]. E-mail: jjscm@kangnung.ac.kr; Oh, Seung-Lim [Department of Chemistry, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Yong-Rok [Department of Chemistry, Yonsei University, Seoul 120-749 (Korea, Republic of); Lee, Sung-Han [Department of Chemistry, Yonsei University, Seoul 120-749 (Korea, Republic of); O'Connor, Charles J. [Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148 (United States)

2006-03-09

250

Thermoelectric properties of tetrahedrally bonded wide-gap stannite compounds Cu2ZnSn1-xInxSe4  

NASA Astrophysics Data System (ADS)

It is usually accepted that good thermoelectric (TE) materials should be narrow-gap semiconductors. Here we show an example that the tetrahedrally bonded stannite compound Cu2ZnSnSe4 with a band gap of 1.44 eV can also exhibit a high figure of merit at intermediate temperature. The highly distorted structure strives for the relatively low thermal conductivity, and the tunability of the electrical properties were demonstrated through doping. The maximum ZT of Cu2ZnSn0.90In0.10Se4 reaches 0.95 at 850 K. This work may open a way for exploring high-performance TE materials with the family of widely existing tetrahedrally bonded semiconductors.

Shi, X. Y.; Huang, F. Q.; Liu, M. L.; Chen, L. D.

2009-03-01

251

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

2010-11-15

252

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

SciTech Connect

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

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

2012-03-15

253

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

SciTech Connect

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

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

2011-05-23

254

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

255

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

NASA Astrophysics Data System (ADS)

We investigated an amorphous Se90Te10 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}^{\\ast }, {C}_{2}^{\\ast } and {C}_{3}^{\\ast }. 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 gSe-Se(r) and gSe-Te(r). The cumulants {C}_{1}^{\\ast }, {C}_{2}^{\\ast } and {C}_{3}^{\\ast } also allowed us to reconstruct the {g}_{i j}^{{EXAFS}}(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}_{i j}^{{RMC}}(r) functions. Both methods furnished very similar gij(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.

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

2012-03-01

256

Enhanced thermoelectric performance in the very low thermal conductivity Ag2Se0.5Te0.5  

NASA Astrophysics Data System (ADS)

In this letter, we report the high-temperature thermoelectric properties of Ag2Se0.5Te0.5. We find that this particular composition displays very low thermal conductivity and competitive thermoelectric performance. Specifically, in the temperature region 520 K <= T <= 620 K, we observe non-hysteretic behavior between the heating and cooling curves and zT values ranging from 1.2 to 0.8. Higher zT values are observed at lower temperatures on cooling. Our results suggest that this alloy is conducive to high thermoelectric performance in the intermediate temperature range, and thus deserves further investigation.

Drymiotis, Fivos; Day, Tristan W.; Brown, David R.; Heinz, Nicholas A.; Jeffrey Snyder, G.

2013-09-01

257

Carrier concentration modulation by hot pressing pressure in n-type nanostructured Bi(Se)Te alloy  

NASA Astrophysics Data System (ADS)

We demonstrate experimentally that an optimal hot pressing pressure is required for high thermoelectric power factor in different n-type Bi(Se)Te alloys for a given processing temperature. This phenomenon is attributed to the variations in carrier concentration, which changes the Seebeck coefficient and therefore the power factor. The variations could arise from the difference in the concentration of charged antisite defects as their formation energy changes with pressures. Furthermore, modifications of the energy gap resulting from the lattice distortions at high pressure also likely play a role.

Chan, Tsung-ta E.; LeBeau, James M.; Venkatasubramanian, Rama; Thomas, Peter; Stuart, Judy; Koch, Carl C.

2013-09-01

258

Electrophysical properties of doped (GeTe){sub 1-x}(PbSe){sub x} solid-solution alloys  

SciTech Connect

Solid-solution alloys based on germanium telluride are promising thermoelectric materials for use in the temperature range 600-900 K. At T{sub c}=700 K, Ge{sub 1-{delta}}Te ({delta}<0.02) undergoes an {alpha}{r_reversible}{beta} phase transition of the first kind from a rhombohedral (sp.gr.R3M, structure type {alpha}-As) to a cubic (sp.gr. Fm3m, NaCl-type structure) form. Anomalies in the electrophysical properties as well as volume changes in the vicinity of the {alpha}{r_reversible}{beta} phase transition have an unfavorable effect on the stability of the thermoelectric and mechanical characteristics of the alloys. Given this, it is necessary to dope Ge{sub 1-{delta}}Te with both electroinactive and electroactive species in order to bring T{sub c} beyond the working temperature range of the material and to reduce volume changes at the phase transition. In this work , the electrophysical properties of (GeTe){sub 1-x}(PbSe){sub x} solid solutions.

Shelimova, L.E.; Avilov, E.S.; Kretova, M.A. [Baikov Institute of Metallurgy, Moscow (Russian Federation)

1994-10-01

259

Structural properties and spatial ordering in multilayered ZnMgTe/ZnSe type-II quantum dot structures  

SciTech Connect

We report the structural properties and spatial ordering of multilayer ZnMgTe quantum dots (QDs) embedded in ZnSe, where sub-monolayer quantities of Mg were introduced periodically during growth in order to reduce the valence band offset of ZnTe QDs. The periodicity, period dispersion, individual layer thickness, and the composition of the multilayer structures were determined by comparing the experimental high resolution x-ray diffraction (HRXRD) spectra to simulated ones for the allowed (004) and quasi-forbidden (002) reflections in combination with transmission electron microscopy (TEM) results. Secondary ion mass spectroscopy (SIMS) profiles confirmed the incorporation of Mg inside the QD layers, and the HRXRD analysis revealed that there is approximately 32% Mg in the ZnMgTe QDs. The presence of Mg contributes to higher scattering intensity of the HRXRD, leading to the observation of higher order superlattice peaks in both the (004) and (002) reflections. The distribution of scattered intensity in the reciprocal space map (RSM) shows that the diffuse scattered intensity is elongated along the q{sub x} axis, indicating a vertical correlation of the dots, which is found to be less defined for the sample with larger periodicity. The diffuse scattered intensity is also found to be weakly correlated along the q{sub z} direction indicating a weak lateral correlation of the dots.

Manna, U.; Noyan, I. C.; Neumark, G. F. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States); Zhang, Q.; Moug, R. [Department of Chemistry, City College of CUNY, New York, New York 10031 (United States); Salakhutdinov, I. F. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States); Department of Physics, Queens College of CUNY, Flushing, New York 11367 (United States); Dunn, K. A.; Novak, S. W. [College of Nanoscale Science and Engineering, University at Albany-SUNY, Albany, New York 12203 (United States); Tamargo, M. C. [Department of Chemistry, City College of CUNY, New York, New York 10031 (United States); Graduate Center of CUNY, New York, New York 10016 (United States); Kuskovsky, I. L. [Department of Physics, Queens College of CUNY, Flushing, New York 11367 (United States); Graduate Center of CUNY, New York, New York 10016 (United States)

2012-02-01

260

Structural properties and spatial ordering in multilayered ZnMgTe/ZnSe type-II quantum dot structures  

NASA Astrophysics Data System (ADS)

We report the structural properties and spatial ordering of multilayer ZnMgTe quantum dots (QDs) embedded in ZnSe, where sub-monolayer quantities of Mg were introduced periodically during growth in order to reduce the valence band offset of ZnTe QDs. The periodicity, period dispersion, individual layer thickness, and the composition of the multilayer structures were determined by comparing the experimental high resolution x-ray diffraction (HRXRD) spectra to simulated ones for the allowed (004) and quasi-forbidden (002) reflections in combination with transmission electron microscopy (TEM) results. Secondary ion mass spectroscopy (SIMS) profiles confirmed the incorporation of Mg inside the QD layers, and the HRXRD analysis revealed that there is approximately 32% Mg in the ZnMgTe QDs. The presence of Mg contributes to higher scattering intensity of the HRXRD, leading to the observation of higher order superlattice peaks in both the (004) and (002) reflections. The distribution of scattered intensity in the reciprocal space map (RSM) shows that the diffuse scattered intensity is elongated along the qx axis, indicating a vertical correlation of the dots, which is found to be less defined for the sample with larger periodicity. The diffuse scattered intensity is also found to be weakly correlated along the qz direction indicating a weak lateral correlation of the dots.

Manna, U.; Noyan, I. C.; Zhang, Q.; Salakhutdinov, I. F.; Dunn, K. A.; Novak, S. W.; Moug, R.; Tamargo, M. C.; Neumark, G. F.; Kuskovsky, I. L.

2012-02-01

261

Radical cations of aromatic selenium compounds: role of se···x nonbonding interactions.  

PubMed

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

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

2013-09-13

262

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

SciTech Connect

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

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

1992-04-01

263

Improvement of superconducting properties of FeSe0.5Te0.5 single crystals by Mn substitution  

NASA Astrophysics Data System (ADS)

We report on structural, susceptibility, conductivity and heat-capacity studies of FeSe0.5Te0.5 single crystals with 2% substitution of Mn for Fe. Mn-doped samples show a higher onset temperature, a narrower width of the superconducting transition and a higher magnitude of the jump in the specific heat at Tc in comparison to undoped samples. The normal-state susceptibility exhibits a quasi-linear increase up to about 130 K. From the resistivity data in magnetic fields parallel to the c axis we derived an upper critical field Hc2 of ~ 420 kOe for doped samples compared to 370 kOe for pure samples. Using a single-band BCS model we can describe the electronic specific heat in the superconducting state with a gap ?(T = 0) = 31 K for the Mn-doped sample in comparison to 26 K for pure FeSe0.5Te0.5.

Günther, A.; Deisenhofer, J.; Kant, Ch; Krug von Nidda, H.-A.; Tsurkan, V.; Loidl, A.

2011-04-01

264

Intensification of electroluminescence of ZnSe:(Te, O) crystals as a result of irradiation with {gamma}-ray photons  

SciTech Connect

The effects of irradiation with {gamma}-ray photons of the {sup 60}Co isotope and of treatment in zinc vapors on the electroluminescence of ZnSe:(Te, O) crystals were studied with the aim of revealing the potential for fabrication of light-emitting structures. The broadband electroluminescence with a peak at 600 nm is excited in the initial samples at voltages higher than 70 V. The threshold voltage is decreased to several volts irrespective of polarity after treatment of the crystals in zinc vapors. A similar effect is observed after irradiation. The position of the peak in the electroluminescence band does not depend on the magnitude of voltage or on irradiation. This position is related to the recombination of charge carriers at the centers of interstitial zinc according to the mechanism of excitation of the prebreakdown type. Treatment in zinc vapors and irradiation with {gamma}-ray photons of ZnSe:(Te, O) bring about an increase in the electroluminescence intensity at both polarities of applied voltage.

El'murotova, D. B.; Ibragimova, E. M. [Academy of Sciences of Uzbekistan, Institute of Nuclear Physics (Uzbekistan)], E-mail: ibragimova@inp.uz

2007-10-15

265

Band structure and optical properties of sinusoidal superlattices: ZnSe{sub 1-x}Te{sub x}  

SciTech Connect

This paper examines the band structure and optical selection rules in superlattices with a sinusoidal potential profile. The analysis is motivated by the recent successful fabrication of high quality ZnSe{sub 1-x}Te{sub x} superlattices in which the composition x varies sinusoidally along the growth direction. Although the band alignment in the ZnSe{sub 1-x}Te{sub x} sinusoidal superlattices is staggered (type II), they exhibit unexpectedly strong photoluminescence, thus suggesting interesting optical behavior. The band structure of such sinusoidal superlattices is formulated in terms of the nearly-free-electron (NFE) approximation, in which the superlattice potential is treated as a perturbation. The resulting band structure is unique, characterized by a single minigap separating two wide, free-electron-like subbands for both electrons and holes. Interband selection rules are derived for optical transitions involving conduction and valence-band states at the superlattice Brillouin-zone center, and at the zone edge. A number of transitions are predicted due to wave-function mixing of different subband states. It should be noted that the zone-center and zone-edge transitions are especially easy to distinguish in these superlattices because of the large width of the respective subbands. The results of the NFE approximation are shown to hold surprisingly well over a wide range of parameters, particularly when the period of the superlattice is short. (c) 2000 The American Physical Society.

Yang, G. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Lee, S. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Furdyna, J. K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

2000-04-15

266

Site Occupation Preferences in CdMnTeSe Quaternary Alloys. EXAFS Data Analysis  

Microsoft Academic Search

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

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

1997-01-01

267

CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds  

Microsoft Academic Search

The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G4 dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent

M. Algarra; B. B. Campos; M. S. Miranda

2011-01-01

268

Electronic structure of ZrTe5  

NASA Astrophysics Data System (ADS)

Band-structure calculations were performed on ZrTe5 to probe the puzzling behavior of the resistive anomaly observed in ZrTe5 and HfTe5. This calculation shows that ZrTe5 is a semimetal and that the carriers originate primarily from the tellurium p orbitals. The nature of the bands is quite different from those in the structurally similar compound NbSe3, where the carriers are based on niobium d orbitals.

Whangbo, M.-H.; Disalvo, F. J.; Fleming, R. M.

1982-07-01

269

Magnetic properties for the Mn2GeTe4 compound  

NASA Astrophysics Data System (ADS)

Measurements of magnetic susceptibility ?, in the temperature range from 2 to 300 K, and of magnetization M vs. applied magnetic field B, up to 5 T, at various temperatures were made on polycrystalline samples of the Mn2GeTe4 compound. It was found that Mn2GeTe4 has a Néel temperature TN of about 135 K, shows mainly antiferromagnetic behavior with a very weak superimposed ferromagnetic component that is attributed to spin canting. Also, the magnetic results suggest that a possible spin-glass transition takes place at Tf?45 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory. The M vs. B results indicated that bound magnetic polarons (BMPs) occur in the compound, and that the effects from BMPs disappear at approximately 80 K. The M vs. B curves were well fitted by a Langevin type of equation, and the variation of the fitting parameters determined as a function of temperature. Using a simple spherical model, the radius of the BMP in the material was found to be about 27 Å; this value is similar to the effective Bohr radius for an acceptor in the II IV V2 and I III VI2 ternary semiconductor compounds.

Quintero, M.; Quintero, E.; Caldera, D.; Moreno, E.; Morocoima, M.; Grima, P.; Ferrer, D.; Marchan, N.; Bocaranda, P.; Delgado, G. E.; Henao, J. A.; Macías, M. A.; Pinto, J. L.; Ponce, C. A.

2009-02-01

270

Electronic specific heat of the iron chalcogenide superconductor Fe(Te0.55Se0.45)  

NASA Astrophysics Data System (ADS)

We report specific heat studies of superconducting Fe(Te0.55Se0.45)[1]. We have obtained the electronic specific heat by subtracting the phonon contribution evaluated from the normalization of the phonon specific heat of a non-superconducting reference sample (Fe0.9Cu0.1)(Te0.55Se0.45). Our results show that the superconducting ground state is accompanied by unpaired quasiparticles, as in FeAs superconductors, with ?0 ˜2.3 mJ/mol K^2. The temperature dependence of the electronic specific heat Ces(T)/T can be well fitted using either a single s-wave gap model with 2?= 5.2 kBTc or a two-gap model with 2?1/kBTc = 5.8 and 2?2/kBTc = 4.0; the two-gap model fitting is slightly better than the single gap fitting. Such large gaps, together with a large specific heat jump ?C(Tc)/Tc˜57.3 mJ/mol K^2, suggest a strong-coupling superconducting state. While Ces(T)/T exhibits isotropic s-wave gap behavior, the magnetic field-induced change in the electronic specific heat ??(H) exhibits sublinear field dependence, implying the superconducting pairing in iron chalcogenide superconductors also involves a multiple band effect, as seen in pnictide superconductors. [1] M. H. Fang, H. M. Pham, B. Qian, T. J. Liu, E. K. Vehstedt, Y. Liu, L. Spinu, and Z. Q. Mao, Superconductivity close to magnetic instability in Fe(Se1-xTex)0.82, Phys. Rev. B 78, 224503 (2008).

Hu, Jin; Liu, Tijiang; Qian, Bin; Mao, Zhiqiang

2011-03-01

271

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

2013-06-24

272

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

273

The birth of a type-II nanostructure: carrier localization and optical properties of isoelectronically doped CdSe:Te nanocrystals.  

PubMed

CdTe/CdSe core/shell nanocrystals are the prototypical example of type-II nanoheterostructures, in which the electron and the hole wave functions are localized in different parts of the nanostructure. As the thickness of the CdSe shell increases above a few monolayers, the spectroscopic properties of such nanocrystals change dramatically, reflecting the underlying type-I ? type-II transition. For example, the exciton Stokes shift and radiative lifetime increase, while the decreasing biexciton binding energy changes sign from positive to negative. Recent experimental results for CdSe nanocrystals isoelectronically doped with a few Te substitutional impurities, however, have revealed a very different dependence of the optical and electronic properties on the nanocrystal size. Here we use atomistic calculations based on the pseudopotential method for single-particle excitations and the configuration-interaction approach for many-particle excitations to investigate carrier localization and electronic properties of CdTe/CdSe nanocrystals as the size of the CdTe core decreases from a few nm (characteristic of core/shell CdTe/CdSe nanocrystals) to the single impurity limit. We find that the unusual spectroscopic properties of isoelectronically doped CdSe:Te nanocrystals can be rationalized in terms of the change in the localization volume of the electron and hole wave functions as the size of the nanocrystal increases. The size dependence of the exciton Stokes shift, exciton radiative lifetime, and biexciton binding energy reflects the extent of carrier localization around the Te impurities. PMID:22900638

Zhang, Lijun; Lin, Zhibin; Luo, Jun-Wei; Franceschetti, Alberto

2012-09-04

274

Electronic and magnetic properties of perfect, vacancy-doped, and nonmetal adsorbed MoSe2, MoTe2 and WS2 monolayers.  

PubMed

Very recently, two-dimensional nanosheets of MoSe(2), MoTe(2) and WS(2) were successfully synthesized experimentally [Science, 2011, 331, 568]. In the present work, the electronic and magnetic properties of perfect, vacancy-doped, and nonmetal element (H, B, C, N, O, and F) adsorbed MoSe(2), MoTe(2) and WS(2) monolayers are systematically investigated by means of first-principles calculations to give a detailed understanding of these materials. It is found that: (1) MoSe(2), MoTe(2) and WS(2) exhibit surprising confinement-induced indirect-direct-gap crossover; (2) among all the neutral native vacancies of MoSe(2), MoTe(2) and WS(2) monolayers, only the Mo vacancy in MoSe(2) can induce spin-polarization and long-range antiferromagnetic coupling; (3) adsorption of nonmetal elements on the surface of MoSe(2), MoTe(2) and WS(2) nanosheets can induce a local magnetic moment; H-absorbed WS(2), MoSe(2), and MoTe(2) monolayers and F-adsorbed WS(2) and MoSe(2) monolayers show long-range antiferromagnetic coupling between local moments even when their distance is as long as ?12 Å. These findings are a useful addition to the experimental studies of these new synthesized two-dimensional nanosheets, and suggest a new route to facilitate the design of spintronic devices for complementing graphene. Further experimental studies are expected to confirm the attractive predictions. PMID:21808797

Ma, Yandong; Dai, Ying; Guo, Meng; Niu, Chengwang; Lu, Jibao; Huang, Baibiao

2011-08-02

275

Optical properties and growth mechanism of multiple type-II ZnTe/ZnSe quantum dots grown by migration-enhanced epitaxy  

NASA Astrophysics Data System (ADS)

The properties of multiple type-II ZnTe/ZnSe quantum dots (QDs), which are coexistent with isoelectronic centers formed by Te, grown by migration-enhanced epitaxy, are studied. The samples with a single deposition cycle of Zn-Te-Zn sandwiched between ZnSe barriers are investigated via temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL measurements. It is found that the PL consists of two broad bands: a “blue” band, which is dominant at low temperatures, and a “green” band, which is observed at T?60K . Upon increasing the excitation intensity by about 4 orders of magnitude, the peak energy position of the blue band remains nearly the same, whereas the green band exhibits a large blueshift of ˜50meV , which suggests that the green band is due to, at least partially, the recombination of excitons bound to type-II QDs. The existence of type-II ZnTe/ZnSe QDs is further supported by the results of magneto-PL, for which the oscillation in the PL intensity as a function of magnetic field is observed. The properties of ZnTe/ZnSe QDs grown under the same Zn/Te flux ratio but with one and three contiguous deposition cycles of Zn-Te-Zn are compared. It is concluded that type-II QDs are formed in both types of samples; however, the density, size, and chemical composition of QDs strongly depend on the deposition of the submonolayer quantities of ZnTe.

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

2008-04-01

276

Optical Properties and Growth Mechanism of Multiple Type-II ZnTe/ZnSe Quantum Dots Grown by Migration-Enhanced Epitaxy  

SciTech Connect

The properties of multiple type-II ZnTe/ZnSe quantum dots (QDs), which are coexistent with isoelectronic centers formed by Te, grown by migration-enhanced epitaxy, are studied. The samples with a single deposition cycle of Zn-Te-Zn sandwiched between ZnSe barriers are investigated via temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL measurements. It is found that the PL consists of two broad bands: a 'blue' band, which is dominant at low temperatures, and a 'green' band, which is observed at T=60 K. Upon increasing the excitation intensity by about 4 orders of magnitude, the peak energy position of the blue band remains nearly the same, whereas the green band exhibits a large blueshift of {approx}50 meV, which suggests that the green band is due to, at least partially, the recombination of excitons bound to type-II QDs. The existence of type-II ZnTe/ZnSe QDs is further supported by the results of magneto-PL, for which the oscillation in the PL intensity as a function of magnetic field is observed. The properties of ZnTe/ZnSe QDs grown under the same Zn/Te flux ratio but with one and three contiguous deposition cycles of Zn-Te-Zn are compared. It is concluded that type-II QDs are formed in both types of samples; however, the density, size, and chemical composition of QDs strongly depend on the deposition of the submonolayer quantities of ZnTe.

Gong,Y.; MacDonald, W.; Neumark, G.; Tamargo, M.; Kuskovsky, I.

2008-01-01

277

Fabrication of Cu3Zn3Se ternary compounds by AP-MOCVD  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

278

(Co, Zn)O compound obtained from ZnTe vapor deposition on Co\\/Si substrates  

Microsoft Academic Search

(Co, Zn)O compound has been obtained by a non-expensive synthesis route. ZnTe thin films were obtained by isothermal close\\u000a space sublimation on the Co thin layer previously sputtered on silicon substrates. After the annealing process in humid ambient\\u000a cobalt atoms diffusion and Zn oxidation were obtained besides partial Te evaporation. The detailed characterization of the\\u000a samples by using XRD, RBS,

O. de Melo; S. Larramendi; L. Martínez; R. Sanz; A. Asenjo; M. Jaafar; M. Vázquez; M. Hernández-Vélez

2010-01-01

279

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

NASA Astrophysics Data System (ADS)

Cho [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.174502 84, 174502 (2011)] have reported on the temperature dependence of the London penetration depth deduced from tunnel diode oscillator (TDO) measurements in optimally doped Fe(Se,Te) single crystals. According to their analysis, these measurements could suggest a nodeless two-gap pairing symmetry with strong pair-breaking effects. However, to reach this conclusion, the authors fit the temperature dependence of the superfluid density with a two band clean limit model, which is incompatible with the presence of strong pair-breaking effects, deduced from the Tn temperature dependence of the London penetration depth below Tc/3. Moreover, they claim that their results are also ruling out the suggestion that surface conditions can significantly affect the TDO data, but this conclusion is based on one very specific damaging process and completely ignores the large dispersion in the previously published TDO data.

Klein, T.; Rodière, P.; Marcenat, C.

2012-08-01

280

Iso-conversional Analysis of Amorphous-Crystalline Transformation of Se75Te15Sn10 Glassy Alloy  

NASA Astrophysics Data System (ADS)

Differential scanning calorimetry (DSC) has been performed under non-isothermal conditions at four different heating rates (5, 10, 15 and 20 °C min-1) to study the activation energy for crystallization of Se75Te15Sn10 glassy alloy. The activation energy of crystallization has been determined by analyzing the data using three iso-conversional methods of Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW) and Friedman for different degrees of conversion (?). The variation of activation energy for crystallization with degree of conversion (?) and hence with temperature has been reported and discussed. The temperature dependence of activation energy is explained in the light of the nucleation theory of Turnbull and Fisher.

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

2011-12-01

281

Spinodal decomposition ranges of wurtzite and zinc blende ZnBVIxO1?x (BVI=S, Se, Te) alloys  

NASA Astrophysics Data System (ADS)

Spinodal decomposition ranges of wurtzite and zinc blende ZnBVIxO1?x (BVI=S, Se, Te) alloys from 0 °C to 1000 °C are represented. The strain energy was estimated in the framework of the valence force field model. All considered alloys have the very extensive decomposition zones in spite of the coherency strain energy. Spinodal decomposition in wurtzite alloys should occur in planes with an orientation that depends on the lattice parameters, stiffness coefficients and composition. Zinc blende alloys posses the larger zones and decomposition should take place only in the {100} oriented planes. Spinodal decomposition ranges are 0.02

Elyukhin, V. A.

2013-10-01

282

Tuning Quantum Oscillations of Dirac Surface States on the Topological Insulator Bi2Te2Se by Ionic Liquid Gating  

NASA Astrophysics Data System (ADS)

An in-situ method to tune the chemical potential near the Dirac Point (DP) of a topological insulator (TI) would greatly facilitate several key experiments. However, in as-grown crystals of Bi-based TIs, the chemical potential ? lies high above the DP. Using liquid gating on 50-?m thick crystals of Bi2Te2Se, we demonstrate that ? can be tuned by a factor of 6 by observing changes to the Shubnikov-de Haas (SdH) period. A surprise is that the SdH amplitudes increase sharply with gating. Liquid gating allows the n=1 Landau level to be accessed, and the ?-Berry phase to be determined with improved accuracy. We will discuss reversibility of liquid gating, and how we may distinguish the purely gating action from chemical reaction.

Xiong, Jun; Khoo, Yuehaw; Jia, Shuang; Cava, Robert J.; Phuan Ong, Nai

2013-03-01

283

Enhanced Superconducting Transition Temperature in FeSe0.5Te0.5 Thin Films  

SciTech Connect

We report magnetoresistive and structural measurements of superconducting FeSe0.5Te0.5 epitaxial thin films grown by pulsed laser deposition. Enhanced onset superconducting transition temperature ({approx} 17 K) is observed in some of these films. Structural analysis by x-ray diffraction and high resolution transmission electron microscopy reveal that these films generally have significantly shorter out-of-plane lattice constant c than the bulk value, suggesting that the out-of-plane changes have a dominating impact on the superconducting transition in iron-based superconductors. Our data also indicate that the upper critical field Hc2(0) of those films may reach as high as 50 T.

Si, W.; Lin, Z.-W.; Jie, Q.; Yin, W.-G.; Zhou, J.; Gu, G.; Johnson, P.D.; Li, Q.

2009-08-03

284

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

285

Renormalization of the band gap in highly photoexcited type-II ZnSe/BeTe structures  

SciTech Connect

For the type-II ZnSe/BeTe heterostructures, a large ({approx}0.1 eV) red shift of the edge of interband recombination in the ZnSe layers is observed at high densities of spatially separated photoexcited electrons and holes ({approx}10{sup 13} cm{sup -2}). The observed magnitude of renormalization of the band gap exceeds the magnitudes predicted by the multiparticle theory for dense type-I electron-hole systems at the same concentrations of two-dimensional charge carriers. Numerical calculations show that macroscopic electric fields induced by separated charges have a profound effect on the energy of direct transitions in type-II structures, resulting in an additional decrease in the energy of the transitions. In wide structures, where the ZnSe layer thickness is {>=} 15 nm, the renormalization effect is less pronounced. This is attributed to incomplete spatial separation of photoexcited charge carriers in the case of profound band bending and, thus, to the less-pronounced effect of electric fields.

Zaitsev, S. V. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation)], E-mail: szaitsev@issp.ac.ru; Yakovlev, D. R. [University of Dortmund, Experimentelle Physik II (Germany); Waag, A. [Braunschweig Technical University, Institute of Semiconductor Technology (Germany)

2009-02-15

286

Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Annual subcontract report, 1 April 1990--31 March 1991  

SciTech Connect

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

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

1991-12-31

287

Thermal Conductivity of Polycrystalline PbTe with PbSe Nanoparticle Additives  

NASA Astrophysics Data System (ADS)

Thermoelectric materials (TEMs) are semiconductor materials that use the Seebeck and Peltier effects to convert a temperature difference into an electric potential and vice versa. All thermoelectric materials are characterized by a figure of merit, ZT, which is directly correlated to the thermoelectric energy conversion efficiency. One option to obtain improved ZT values is to lower the thermal conductivity of the TEM. Nanostructuring of traditional TEMs is one avenue toward lowering thermal conductivity, hopefully without significantly diminishing the electrical properties. Pellets of bulk, polycrystalline lead telluride with varying concentrations of PbSe nanoparticle additives were prepared by pressing mixed powders. Measurements of thermal conductivity were performed in the temperature range 6 K -- 300 K. The data were compared to a theoretical model in an attempt to link the temperature dependent behavior of the thermal conductivity to the synthesis parameters, nanoparticle concentration, and sample morphology as revealed through Scanning Electron Microscope images.

Steward, Ian M.; Dyck, Jeffrey S.; Zhao, Yixin; Burda, Clemens

2008-03-01

288

Luminescent lanthanide selenites and tellurites decorated by MoO4 tetrahedra or MoO6 octahedra: Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12.  

PubMed

Solid state reactions of lanthanide oxide, MoO3 and SeO2 (or TeO2) at high temperature in an evacuated quartz tube lead to four new Ln-Mo-Se(Te)-O quaternary phases with four different types of structures, namely, Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12. The structure of Nd2MoSe2O10 features a 3D architecture built by the intergrowth of the Nd-Se-O layers with the Nd-Mo-O layers. The structure of Gd2MoSe3O12 contains a 3D network of gadolinium selenite with the MoO6 octahedra occupying the cavities of the structure. The structure of La2MoTe3O12 features a 3D network of La2(Te3O8)2+ with the tunnels along the a axis occupied by the MoO4 tetrahedra. Nd2MoTe3O12 features a 2D layer built by the lanthanide ions interconnected by tellurite groups and ditellurite groups, with the MoO4 tetrahedra as the interlayer pendant groups. Room temperature and low temperature luminescent studies indicate that Nd2MoSe2O10 and Nd2MoTe3O12 exhibit strong luminescence in the near-IR region. PMID:16323915

Shen, Yue-Ling; Jiang, Hai-Long; Xu, Jian; Mao, Jiang-Gao; Cheah, Kok Wai

2005-12-12

289

Influence of technological conditions upon the luminescence properties of ZnTe-ZnSe heterostructures grown by liquid-phase epitaxy  

SciTech Connect

This paper studies the luminescence characteristics of the components of ZnTe-ZnSe hetero-structures obtained by liquid-phase epitaxy of ZnTe and SnSe substrates oriented in the (III) plane; the epitaxy was based on a solution-melt in metal (Sn, Bi). The influence of the metal melt and the technological conditions of crystal growing upon the luminescence properties of the ZnSe substrate is studied. The authors followed the changes in the ZnSe luminescence spectrum in each stage of the study. Typical photoluminescence spectra is shown of ZnSe single crystals which had been grown recently and annealed in liquid Zn. When ZnTe-ZnSe heterostructures are produced by liquid phase epitaxy from solution melts in Bi and Sn, the radiative properties of ZnSe substrates do not change because disturbances of stoichiometry are prevented. The luminescence properties of ZnSe substrates which were subjected to annealing can be described by the concepts of annealing ZnSe with copper.

Skobeeva, V.M.; Semenyuk, L.N.; Serdyuk V.V.

1986-08-01

290

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

PubMed

We have studied the pressure-induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in BaS, BaSe and BaTe by using ab initio density functional theory computations in the local density approximation. The Buerger and WTM mechanisms were explored by mapping the enthalpy contours in two- and four-dimensional configuration space for the two mechanisms, respectively. Transition pressures for BaS, BaSe and BaTe were determined to be 5.5 GPa, 4.9 GPa and 3.4 GPa, respectively. From these configuration space landscapes, a low enthalpy barrier path was constructed for the transitions to proceed at three different pressures. We obtained barriers of 0.18, 0.16 and 0.15 eV/pair (17.4, 15.4 and 14.5 kJ mol(-1)) for the Buerger mechanism and 0.13, 0.13 and 0.12 eV/pair (12.5, 12.5 and 11.6 kJ mol(-1)) for the WTM mechanism at the transition pressures for BaS, BaSe and BaTe, respectively, indicating that the WTM mechanism is slightly more favorable in these compounds. We describe the difference between the two mechanisms by differences in their symmetry and atomic coordination. PMID:23341436

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

2013-01-22

291

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

NASA Astrophysics Data System (ADS)

We have studied the pressure-induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in BaS, BaSe and BaTe by using ab initio density functional theory computations in the local density approximation. The Buerger and WTMfootnotetextM. Watanabe et. al, Acta Crystallogr., Sect. A 33, 294 (1977). mechanisms were explored by mapping the enthalpy contours in two and four dimensional configuration space for the two mechanisms, respectively. Transition pressures for BaS, BaSe and BaTe were determined to be 5.5 GPa, 4.9 GPa and 3.4 GPa, respectively. From these configuration space landscapes, a low enthalpy barrier path was constructed for the transitions to proceed at three different pressures. We obtained barriers of 0.18, 0.16 and 0.15 eV/pair (17.4, 15.4 and 14.5 kJ/mol) for the Buerger mechanism and 0.13, 0.13 and 0.12 eV/pair (12.5, 12.5 and 11.6 kJ/mol) for the WTM mechanism at the transition pressures for BaS, BaSe and BaTe, respectively, indicating that the WTM mechanism is slightly more favorable in these compounds. We describe the difference of the two mechanisms by differences in their symmetry and atomic coordination.

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

2013-03-01

292

Effect of built-in electric field in stacked type-II ZnTe/ZnSe submonolayer quantum dots: enhancement and narrowing of Aharonov-Bohm oscillations  

NASA Astrophysics Data System (ADS)

Robust and narrow Aharonov-Bohm (AB) oscillations were observed in both intensity and energy of the mangeto-photoluminescence (PL) from stacked type-II ZnTe/ZnSe submonolayer quantum dots (QDs) grown via migration enhanced epitaxy. The narrowness and enhancement in the AB oscillations is a consequence of the built-in electric field in the system. Spectral analysis of cw magneto-PL and time-resolved PL suggest that the QD stacks size distribution is not large and thus broadening of the PL is possibly due to strong electron-phonon interaction as generally seen in bulk Zn-Se-Te systems.

Roy, Bidisha; Dhomkar, Siddharth; Ji, Haojie; Tamargo, Maria; Kuskovsky, Igor

2013-03-01

293

Locally deformed states of the crystal structure of double semiconductors ZnSe and ZnTe doped with vanadium ions  

SciTech Connect

Specific features of the crystal structure of a lightly doped Zn{sub 1-x}V{sub x}Te crystal (x = 0.0002) were investigated for the first time by thermal neutron diffraction. The experimental results are discussed together with the data of neutron diffraction measurements that were performed previously on Zn{sub 1-x}V{sub x}Se single crystals (x = 0.0018). An enhanced response of the ZnTe lattice (in comparison with ZnSe) to a perturbation introduced by an incorporated 3d ion is found.

Maksimov, V. I., E-mail: kokailo@rambler.ru; Dubinin, S. F.; Parkhomenko, V. D. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)

2011-12-15

294

Absorption coefficient of intersubband transition at 1.55 µm in (CdS/ZnSe)/BeTe quantum wells  

NASA Astrophysics Data System (ADS)

In this paper, the intersubband optical absorption coefficient is calculated in a ZnSe/CdS/ZnSe quantum well (QW) surrounded by BeTe barriers. First, the one-dimensional Poisson and Schrödinger equations have been solved self-consistently, and then the intersubband optical absorption between the lowest two levels has been theoretically studied under an external electric field. Simulated results including eigenvalues, absorption coefficient and electroabsorption properties have been discussed. The structure under investigation covers a large range of the electromagnetic spectra including the visible and near infrared (IR). For the 1.55 µm wavelength (0.8 eV), dependences of the intersubband optical absorption coefficient on the applied electric field, thickness of the barrier and concentration of doping are investigated. Our calculation shows that for an applied electric field lower than a critical value of around 100 kV cm-1, the ITSB optical absorption peak undergoes a red shift with the increase in the electric field. However, for an applied electric field above the critical value, the electrons move to the same side of the well for all states. The energy difference E2 - E1 increases leading to a blue shift of the absorption peak. As a result, the optical intersubband transition enhances its intensity. Taking into account the present results, we hope that important IR photodetectors and near-IR laser amplifiers can be constructed based on the group II-VI QWs.

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

2009-02-01

295

Subpicosecond saturation of intersubband absorption in (CdS/ZnSe)/BeTe quantum-well waveguides at telecommunication wavelength  

NASA Astrophysics Data System (ADS)

Ultrafast all-optical switching at an optical communication wavelength has been investigated by utilizing an intersubband transition (ISBT) of II-VI-based multiple quantum wells (MQWs) fabricated in high-mesa waveguide devices. The waveguide structure consists of a CdS/ZnSe/BeTe MQW core layer and two top and bottom ZnMgBeSe quaternary cladding layers grown by molecular beam epitaxy on a (001) GaAs substrate. A marked increase in waveguide transmittance was observed only for transverse-magnetic-polarized subpicosecond pulse with increasing incident pulse energy at ?=1.57 ?m, indicative of the ISBT absorption saturation. The pulse energy necessary for a 10 dB transmittance increase is as low as 13.3 pJ for a waveguide device with 2.7 ?m mesa, and the saturation pulse energy can be even further reduced by employing a narrower mesa structure. Ultrafast gate switching within a time window of 0.56 ps was also demonstrated with pump pulse at ?=1.57 ?m and probe pulse at ?=1.63 ?m in this waveguide device.

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

2005-10-01

296

Thermal Expansion of n-Type Doped Bi2Te2.88Se0.12 and p-Type Doped Bi0.52Sb1.48Te3 Solid Solutions from -60°C to +60°C  

NASA Astrophysics Data System (ADS)

An automated dilatometric system was developed to measure the thermal expansion of solid materials from -60°C to +400°C. This system was then applied to measure the linear thermal expansions of n-type doped Bi2Te2.88Se0.12 and p-type doped Bi0.52Sb1.48Te3 solid solutions along the a-axis from -60°C to +60°C. The experiments were performed using a vertical “tube/push rod” dilatometer under constant-temperature conditions. The initial alloys were synthesized from Bi, Te, and Se or Sb (each at 99.999 mass% purity) in stoichiometric ratios. The method based on the correlation between the thermal expansion and the heat capacity was proposed to calculate the axial expansion coefficients along the c-axis.

Stern, Yu.; Pavlova, L.; Mironov, R.

2010-09-01

297

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

298

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

NASA Astrophysics Data System (ADS)

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

Xue, Qi-Kun

2010-03-01

299

Nonlinear optical properties and blue-light-emitting diode of ZnSe/ZnS and ZnTe/ZnS strained-layer superlattices  

NASA Astrophysics Data System (ADS)

This paper reviews recent work on the nonlinear optics of ZnSe/ZnS and ZnTe/ZnS strained-layer superlattices (SLSs), with emphasis on their use in novel devices. The transmission spectra of ZnSe/ZnS SLS grown on CaF2 reveal the importance of excitonic processes, showing large energy shifts due to quantum confinement and strain. Refractive index modification and layer disordering of such superlattices results from implanation of N+ and Li+ ions. A transverse electric field spatially separates charge carriers. This leads to changes in the photoluminescence and optical transmission of ZnSe/ZnS SLS. Optical switching devices and optical frequency doublers are demontrated. By analysing the excitation power dependence of PL from ZnTe/ZnS doping superlattices, it is confirmed that the dominant emission process involves recombination across the indirect gap in real space between conduction band electrons and impurity band holes. Blue-light-emitting diodes at room temperature were fabricated using p-ZnTe/ZnS doping SLS. It clear that the optical properties of the ZnSe/ZnS and ZnTe/ZnS SLS are very useful for novel opto-electronic devices in the visible spectral region. Present address: Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA.

Yokogawa, Toshiya

1993-09-01

300

Designed synthesis, structure, and properties of a family of ferecrystalline compounds [(PbSe)(1.00)](m)(MoSe2)(n).  

PubMed

The targeted synthesis of multiple compounds with specific controlled nanostructures and identical composition is a grand challenge in materials chemistry. We report the synthesis of the new metastable compounds [(PbSe)1.00]m(MoSe2)n using precursors each designed to self-assemble into a specific compound. To form a compound with specific values for m and n, the number of atoms within each deposited elemental layer was carefully controlled to provide the correct absolute number of atoms to form complete layers of each component structural unit. On low-temperature annealing, these structures self-assemble with a specific crystallographic orientation between the component structural units with atomically abrupt interfaces. There is rotational disorder between the component structural units and between MoSe2 basal plane units within the MoSe2 layers themselves. The lead selenide constituent has a distorted rock salt structure exactly m bilayers thick leading to peaks in the off-axis diffraction pattern as a result of the finite size of and rotational disorder between the crystallites. The in-plane lattice parameters of the PbSe and MoSe2 components are independent of the value of m and n, suggesting little or no strain caused by the interface between them. These compounds are small band gap semiconductors with carrier properties dominated by defects and exhibit extremely low thermal conductivity as a result of the rotational disorder. The thermal conductivity can be tuned by varying the ratio of the number of ordered PbSe rock salt layers relative to the number of rotationally disordered MoSe2 layers. This approach, based on controlling the local composition of the precursor and low temperature to limit diffusion rates, provides a general route to the synthesis of new compounds containing alternating layers of constituents with designed nanoarchitecture. PMID:23819532

Heideman, Colby L; Tepfer, Sara; Lin, Qiyin; Rostek, Raimar; Zschack, Paul; Anderson, Michael D; Anderson, Ian M; Johnson, David C

2013-07-18

301

Nonlinear optical properties and blue-light-emitting diode of ZnSe\\/ZnS and ZnTe\\/ZnS strained-layer superlattices  

Microsoft Academic Search

This paper reviews recent work on the nonlinear optics of ZnSe\\/ZnS and ZnTe\\/ZnS strained-layer superlattices (SLSs), with emphasis on their use in novel devices. The transmission spectra of ZnSe\\/ZnS SLS grown on CaF2 reveal the importance of excitonic processes, showing large energy shifts due to quantum confinement and strain. Refractive index modification and layer disordering of such superlattices results from

Toshiya Yokogawa

1993-01-01

302

Radiative recombination in type-II ZnSe/BeTe heterostructures at high densities of free carriers  

SciTech Connect

We have studied in detail the photoluminescence in type-II ZnSe/BeTe structures with large band offsets at high optical excitation levels. Our goal is a qualitative and quantitative description of the effect of a high carrier density on the spectral and kinetic properties of the photoluminescence in such structures. We have established that a high photoexcitation density leads to a significant spectral rearrangement of the spatially indirect radiative recombination, which also depends on the thickness of the structure layers. The spectral and kinetic characteristics of the indirect optical transitions in narrow and wide structures have been found to differ qualitatively. Our numerical calculations of the effect of macroscopic electric fields on the energy spectrum of free carriers at high densities of spatially separated charges, n > 10{sup 13} cm{sup -2}, give a qualitative and quantitative description of the experimentally observed photoluminescence properties. The calculations also show that the degree of localization of the above-barrier hole states grows significantly with n under conditions of increasing band bending, which should cause a weakening of the charge separation, especially in wide structures. In an experiment, the effect manifests itself in an enhancement of the spatially direct transition at a simultaneous weakening of the indirect transition both with increasing structure width and with increasing n.

Zaitsev, S. V. [Russian Academy of Sciences, Institute of Solid-State Physics (Russian Federation)], E-mail: szaitsev@issp.ac.ru

2009-04-15

303

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

304

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

SciTech Connect

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

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

2012-08-21

305

Isomeric metamorphosis: Si3E (E = S, Se, and Te) bicyclo[1.1.0]butane and cyclobutene.  

PubMed

Group 14 and 16 hybrid heavy bicyclo[1.1.0]butanes (tBu2MeSi)4Si3E (E = S, Se, and Te) 2a-c have been prepared by the [1 + 2] cycloaddition reaction of trisilirene 1 and the corresponding chalcogen. Bicyclo[1.1.0]butanes 2 have exceedingly short bridging Si-Si bonds (2.2616(19) A for 2b and 2.2771(13) A for 2c), a phenomenon explained by the important contribution of the trisilirene-chalcogen pi-complex character to the overall bonding of 2. Photolysis of 2a and 2b produced their valence isomers, the heavy cyclobutenes 3a and 3b, featuring flat four-membered Si3E rings and a planar geometry of the Si=Si double bond. The mechanism of such isomerization was studied using deuterium-labeled 2a-d6 to ascertain the preference of the pathway, involving the direct concerted symmetry-allowed transformation of bicyclo[1.1.0]butane 2 to cyclobutene 3. PMID:18260666

Lee, Vladimir Ya; Miyazaki, Shogo; Yasuda, Hiroyuki; Sekiguchi, Akira

2008-02-09

306

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

SciTech Connect

Crystals of Pd{sub 2}MCh{sub 2} (M=Fe, Co, Ni; Ch=Se, Te) were synthesized by heating the elements at 823-1323K in silica ampoules under argon atmosphere. Their structures were determined by single-crystal X-ray diffraction at room temperature. The metallic compounds crystallize in a variant of the K{sub 2}ZnO{sub 2} type (Ibam, Z=4, Pd{sub 2}CoSe{sub 2}: a=5.993(1), b=10.493(2), c=5.003(1) A; Pd{sub 2}FeSe{sub 2}: a=5.960(1), b=10.576(2), c=5.078(1) A; Pd{sub 2}CoTe{sub 2}: a=6.305(1), b=11.100(2), c=5.234(1) A; Pd{sub 2}NiTe{sub 2}: a=6.286(1), b=11.194(2), c=5.157(1) A). One-dimensional {sub {approx}}{sup 1}[MCh{sub 4/2}] tetrahedra chains with remarkably short M-M bonds run along [001], separated by [Pd{sub 2}] dumbbells with palladium in fivefold coordination of selenium or tellurium atoms. The structure may also be described as a filled variant of the SiS{sub 2} type. M atoms occupy 14 of the tetrahedral voids and the Pd atoms fill all octahedral voids in a distorted ccp motif of chalcogen atoms. Even though the Pd{sub 2}MCh{sub 2} compounds are isotypic to K{sub 2}ZnO{sub 2} from the crystallographic viewpoint, we find a different bonding situation with additional homo- and heteronuclear metal-metal bonds between the Pd and Co atoms. The electronic structures and topologies of the electron densities of Pd{sub 2}CoSe{sub 2} and isotypic Na{sub 2}CoSe{sub 2} are analyzed and compared by using Bader's AIM theory. Different values of topological charge transfer and electron density flatness indices uncover striking quantitative differences in the nature of chemical bonding between the metallic compound Pd{sub 2}CoSe{sub 2} and nonmetallic Na{sub 2}CoSe{sub 2}.

Pocha, Regina [Department Chemie und Biochemie der Ludwig-Maximilians-Universitaet Muenchen, Butenandtstr. 5-13 (Haus D), D-81377 Munich (Germany); Department of Chemistry, Michigan State University, East Lansing, MI 48824 (United States); Loehnert, Catrin [Department Chemie und Biochemie der Ludwig-Maximilians-Universitaet Muenchen, Butenandtstr. 5-13 (Haus D), D-81377 Munich (Germany); Johrendt, Dirk [Department Chemie und Biochemie der Ludwig-Maximilians-Universitaet Muenchen, Butenandtstr. 5-13 (Haus D), D-81377 Munich (Germany)], E-mail: johrendt@lmu.de

2007-01-15

307

Half-metallic properties of the (001) surfaces of vanadium-substituted Rock-salt GeTe-based compounds  

NASA Astrophysics Data System (ADS)

We study the properties of the (001) surfaces of ternary vanadium compounds based on the rocksalt semiconductor GeTe. In one of the compounds 25% of Ge atoms are replaced by V atoms, and in another, the substitution is as large as 50%. Using a first-principles method, we calculate the electronic structure of the two systems for two different surface terminations. The studied systems are found to be half-metallic ferromagnets. The half-metallic gap in every system is found to be larger than it is in the bulk. However, in Ge-terminated surfaces, the bottom of the conduction band is very near the Fermi level, and this may cause an instability of the half-metallicity in the systems. VGe-terminated surfaces are characterized by a more stable half-metallic ferromagnetic order. The larger amount of replacement of Ge atoms by V atoms also supresses the magnetic properties of the system. The largest calculated magnetic moment on the V atom at the topmost layer of the (001) surface is 2.602 µ B . The presence of a magnetic center causes polarization of the metalloids: in the 50%-substituted GeTe, Te atoms are negatively polarized, and Ge atoms are slightly positively polarized. The largest magnetic moment on Te is calculated for Te atom at the topmost layer and is -0.107 µ B .

Cho, Lee-Hyun; Bialek, Beata; Lee, Jae Il

2012-11-01

308

Anion substitution effects on the structure and magnetism of the chromium chalcogenide Cr5Te8—Part III: Structures and magnetism of the high-temperature modification Cr(1+x)Q2 and the low-temperature modification Cr(5+x)Q8 (Q=Te, Se; Te:Se=5:3)  

NASA Astrophysics Data System (ADS)

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(1+x)Q2 ((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(5+x)Q8 ((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 ? 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 Tf 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.

Wontcheu, Joseph; Bensch, Wolfgang; Mankovsky, Sergiy; Polesya, Svitlana; Ebert, Hubert; Kremer, Reinhard K.; Brücher, Eva

2008-06-01

309

The Influence of Sintering Temperature on the Microstructure and Thermoelectric Properties of n-Type Bi2Te3-x Se x Nanomaterials  

NASA Astrophysics Data System (ADS)

Pure Bi2Te3 and Bi2Se3 nanopowders were hydrothermally synthesized, and n-type Bi2Te3-x Se x bulk samples were prepared by hot pressing a mixture of Bi2Te3 and Bi2Se3 nanopowders at 623 K, 648 K or 673 K and 80 MPa in vacuum. The phase composition of the powders and bulk samples were characterized by x-ray diffraction. The morphology of the powders was examined by transmission electron microscopy. The microstructure and composition of the bulk samples were characterized by field-emission scanning electron microscopy and energy-dispersive x-ray spectroscopy, respectively. The density of the samples increased with sintering temperature. The samples were somewhat oxidized, and the amount of oxide (Bi2TeO5) present increased with sintering temperature. The samples consisted of sheet-like grains with a thickness less than 100 nm. Seebeck coefficient, electrical conductivity, and thermal conductivity of the samples were measured from room temperature up to 573 K. Throughout the temperature range investigated, the sample sintered at 623 K had a higher power factor than the samples sintered at 648 K or 673 K.

Du, Y.; Cai, K. F.; Li, H.; An, B. J.

2010-12-01

310

The Influence of Sintering Temperature on the Microstructure and Thermoelectric Properties of n-Type Bi2Te3- x Se x Nanomaterials  

NASA Astrophysics Data System (ADS)

Pure Bi2Te3 and Bi2Se3 nanopowders were hydrothermally synthesized, and n-type Bi2Te3- x Se x bulk samples were prepared by hot pressing a mixture of Bi2Te3 and Bi2Se3 nanopowders at 623 K, 648 K or 673 K and 80 MPa in vacuum. The phase composition of the powders and bulk samples were characterized by x-ray diffraction. The morphology of the powders was examined by transmission electron microscopy. The microstructure and composition of the bulk samples were characterized by field-emission scanning electron microscopy and energy-dispersive x-ray spectroscopy, respectively. The density of the samples increased with sintering temperature. The samples were somewhat oxidized, and the amount of oxide (Bi2TeO5) present increased with sintering temperature. The samples consisted of sheet-like grains with a thickness less than 100 nm. Seebeck coefficient, electrical conductivity, and thermal conductivity of the samples were measured from room temperature up to 573 K. Throughout the temperature range investigated, the sample sintered at 623 K had a higher power factor than the samples sintered at 648 K or 673 K.

Du, Y.; Cai, K. F.; Li, H.; An, B. J.

2011-05-01

311

Synthesis of selenium compounds by free radical addition based on visible-light-activated se-se bond cleavage.  

PubMed

Upon irradiation with near-UV or visible light, organic diselenides undergo homolytic cleavage of their selenium-selenium linkage to generate the corresponding seleno radicals, which can add to alkynes, allenes, and related unsaturated compounds. In the case of alkynes, vicinally diselenated alkenes are synthesized successfully. Photoinduced bisselenation of allenes takes place selectively at the terminal double bond of allenes. In sharp contrast, photoinduced addition of organic diselenides to alkenes is an inefficient process. However, combination of diselenides and disulfides under photoirradiation conditions results in highly regioselective thioselenation of alkenes based on the higher reactivity of thio radicals toward alkenes and the higher carbon radical capturing ability of diselenides. Similar conditions can be employed with a variety of unsaturated compounds such as alkynes, allenes, conjugated dienes, vinylcyclopropanes, and isocyanides. This protocol can also be applied to selenotelluration, selenophosphination, and perfluoroalkylselenation of unsaturated compounds. The excellent carbon radical capturing ability of diselenides makes it possible to attain sequential addition of diselenides to several unsaturated compounds by suppression of polymerization of unsaturated compounds. When the sequential addition takes place intramolecularly under photoirradiation conditions, cyclic products are obtained successfully via a radical cyclization process. In addition, novel photoinduced electrocyclic reaction of o-alkynylaryl isocyanides with diselenides efficiently affords diselenated quinoline derivatives. PMID:23544462

Nomoto, Akihiro; Higuchi, Yoshihiro; Kobiki, Yohsuke; Ogawa, Akiya

2013-05-01

312

(Co, Zn)O compound obtained from ZnTe vapor deposition on Co/Si substrates  

NASA Astrophysics Data System (ADS)

(Co, Zn)O compound has been obtained by a non-expensive synthesis route. ZnTe thin films were obtained by isothermal close space sublimation on the Co thin layer previously sputtered on silicon substrates. After the annealing process in humid ambient cobalt atoms diffusion and Zn oxidation were obtained besides partial Te evaporation. The detailed characterization of the samples by using XRD, RBS, AFM, XPS, VSM and MFM techniques point to the formation of room temperature ferromagnetic Co x Zn(1- x)O phase ( x<0.15). This ferromagnetic behavior is mainly attributed to Co atoms substituting Zn atoms in the ZnO network.

de Melo, O.; Larramendi, S.; Martínez, L.; Climent Font, A.; Sanz, R.; Mínguez Bacho, I.; Asenjo, A.; Jaafar, M.; Vázquez, M.; Hernández-Vélez, M.

2010-06-01

313

Electronic properties of the III–VI layer compounds GaS, GaSe and InSe. I: Band structure  

Microsoft Academic Search

Summary  The electronic properties of the semiconducting layer compounds GaS, GaSe and InSe are considered comparatively in a series\\u000a of papers. In this first paper the band structures of the three compounds are computed by using the same method and the same\\u000a approximations for all of them. The overlap-reduced semi-empirical tight-binding method (ORSTB) is outlined by first. The\\u000a method consists in

E. Doni; R. Girlanda; V. Grasso; A. Balzarotti; M. Piacentini

1979-01-01

314

Effect of doping and heat treatment on the mechanical parameters of ZnSe{sub (1-x)}Te{sub x} crystals grown from the melt  

SciTech Connect

The mechanical properties of crystals of ZnSe{sub (1-x)}Te{sub x} (0 < x < 1.3 wt %) solid solutions are investigated using the indentation method. The breaking points of doped and undoped crystals are measured by the uniaxial compression method. It is revealed that the microhardness anisotropy coefficient for crystals with a tellurium dopant content of {approx}0.3 wt % is equal to unity. A change in the tellurium content in the solid solutions from 0.2 to 1.3 wt % leads to a linear increase in the microhardness by 23%. The brittle strength of the ZnSe and ZnSe{sub (1-x)}Te{sub x} crystals varies in a similar manner. It is demonstrated that heat treatment and the presence of interblock boundaries affect the ultimate strength and the cracking resistance of the ZnSe{sub (1-x)}Te{sub x} crystals. This is an important factor which should be taken into account in mechanical treatment of the materials under investigation.

Rybalka, I. A.; Galkin, S. N.; Voronkin, E. F.; Ryzhikov, V. D. [National Academy of Sciences of Ukraine, Institute for Scintillation Materials, Scientific and Technological Corporation 'Institute for Single Crystals,' (Ukraine)

2008-12-15

315

Synthesis of Cd-free water-soluble ZnSe(1-x)Te(x) nanocrystals with high luminescence in the blue region.  

PubMed

Cd-free core-shell nanocrystals (ZnSe(1-x)Te(x)/ZnS, 0Se(1-x)Te(x) and ZnS, post-preparative irradiation at high temperature resulted in the formation of a thick ZnS shell (ca. 1.6 nm) around the core (ca. 2.2 nm in diameter) without deterioration of PL efficiency. Surface substitution of Te by S and size-selective precipitation of nanocrystals before ultraviolet irradiation resulted in intense PL. Quantum mechanical calculations show that the wave function of the electron of the exciton in the Te-containing core extends well into the ZnS shell. The calculations also reveal that a thick shell can confine the electrons inside the particles and thereby improve the PL efficiency and stability against the pH of the solution. Nanocrystals that had been post-preparatively irradiated showed good stability in solution and in a glass matrix even after months of storage in air. PMID:18329662

Li, Chunliang; Nishikawa, Kazuhiro; Ando, Masanori; Enomoto, Hiroyuki; Murase, Norio

2008-02-14

316

Magnetic property of layered compound NbFeTe{sub 2}  

SciTech Connect

NbFeTe{sub 2} is a layered cluster compound in which intra Fe{endash}Fe bond distance is 2.488 {Angstrom}. The magnetic susceptibilities between 100 and 300 K are fit to Curie{endash}Weiss law with C=1.29 emuK/mol, and {theta}=+69.2 K. The effective magnetic moment of 3.67 {mu}{sub B} per Fe at 300 K corresponding to three unpaired electrons may suggest the formation of Fe{endash}Fe single bond. M{umlt o}ssbauer spectrum at 77 K shows a paramagnetic doublet with {delta}=0.36 mm/s and {Delta}E=0.62 mm/s. The {chi}{sub ac} measurement reveals the occurrence of a spin glass transition at T{sub f}=44.0 K. The irreversibility of magnetic properties below T{sub f} has been studied with the measurements of the dc susceptibility, remanent magnetization, and hysteresis loop for both zero field cooled and field cooled samples. The competition between antiferromagnetic and ferromagnetic interactions probably cause the spin glass behavior. {copyright} {ital 1997 American Institute of Physics.}

Zhang, J.H. [Department of Chemistry, Xavier University of Louisiana, New Orleans, Louisiana 70125 (United States); Chen, F. [Department of Chemistry, Rider University, Lawrenceville, New Jersey 08648 (United States); Li, J. [Department of Chemistry, Rutgers University, Camden, New Jersey 08102 (United States); OConnor, C.J. [Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 (United States)

1997-04-01

317

Determination of the Spin–Orbit and Trigonal-Field Splittings of the 5E State of Fe2+ in ZnO, ZnS, CdS, ZnSe, CdSe, ZnTe, and CdTe Crystals by Magnetic Susceptibilities  

Microsoft Academic Search

The magnetic susceptibilities of the Fe2+:ZnSe, Fe2+:CdSe, Fe2+:ZnTe, Fe2+:CdTe, Fe2+:ZnS, Fe2+:CdS, and Fe2+:ZnO crystals have been measured over the temperature range of 2–300°K in order to determine the spin–orbit and trigonal-field (for CdS and ZnO) splittings of the ground orbital state 5E of Fe2+ in the crystal lattice. The first five crystals are magnetically isotropic with no detectable trigonal-field effects,

J. Patrick Mahoney; Chun C. Lin; William H. Brumage; Franklin Dorman

1970-01-01

318

Evidence for dominant Pauli paramagnetic effect in the upper critical field of single-crystalline FeTe0.6Se0.4  

NASA Astrophysics Data System (ADS)

We investigated the temperature dependence of the upper critical fields Hc2(T) of a superconducting FeTe0.6Se0.4 single crystal by measuring its resistivity in static magnetic fields up to 45 T. Our observations of strong bending in the Hc2ab(T) curves and a nearly isotropic Hc2ab(0)?Hc2c(0)?48T support the presence of a strong Pauli paramagnetic effect. We show that the Werthamer-Helfand-Hohenberg formula that includes both the Pauli limiting and the spin-orbit scattering can effectively describe both the Hc2ab(T) and Hc2c(T) curves. An enhancement in the quasiparticle density of states or the increased scattering resulting from Te(Se) vacancies or excess Fe is discussed as a possible origin for the manifesting Pauli paramagnetic effect.

Khim, Seunghyun; Kim, Jae Wook; Choi, Eun Sang; Bang, Yunkyu; Nohara, Minoru; Takagi, Hidenori; Kim, Kee Hoon

2010-05-01

319

Local atomic strain in ZnSe{sub 1-x}Te{sub x} from high real-space resolution neutron pair distribution function measurements  

SciTech Connect

High real-space resolution atomic pair distribution functions (PDF's) have been obtained from ZnSe{sub 1-x}Te{sub x} using neutron powder diffraction. Distinct Zn-Se and Zn-Te nearest-neighbor (nn) bonds, differing in length by {Delta}r=0.14 Aa, are resolved in the measured PDF's, allowing the evolution with composition of the individual bond lengths to be studied. The local bond lengths change much more slowly with doping than the average bond length obtained crystallographically. The nn bond-length distributions are constant with doping, but higher-neighbor pair distributions broaden significantly, indicating that most of the strain from the alloying is accommodated by bond-bending forces in the alloy. PDF's of alloys across the whole doping range are well fit using a model based on the Kirkwood potential. The resulting PDF's give excellent agreement with the measured PDF's over the entire alloy range with no adjustable parameters.

Peterson, P. F.; Proffen, Th.; Jeong, I.-K.; Billinge, S. J. L.; Choi, K.-S.; Kanatzidis, M. G.; Radaelli, P. G.

2001-04-15

320

Intersubband resonant enhancement of the nonlinear optical properties in asymmetric (CdS/ZnSe)/X-BeTe based quantum wells  

NASA Astrophysics Data System (ADS)

The linear and nonlinear optical properties in asymmetric quantum wells, especially the second-harmonic generation susceptibility, the optical absorption and the refractive index change are investigated numerically for (CdS/ZnSe)/BeTe materials. The energy eigenvalues and their corresponding eigenfunctions are obtained numerically by solving the Schrodinger equation. The optical properties are calculated within the framework of the density matrix formalism. Various values of the doping density and the optical intensity on the nonlinear optical properties are considered in the calculations. Numerical results on typical CdS/ZnSe materials reveal a resonant enhancement of the second harmonic generation and the third-order optical nonlinearities. Our calculations show that results done for band alignment relative to X-BeTe conduction band minimum are extremely improved in comparison with those done for ?-minimum.

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

2013-03-01

321

A complete family of terminal uranium chalcogenides, [U(E)(N{SiMe3}2)3]- (E = O, S, Se, Te).  

PubMed

Addition of 1 equiv of E (E = 0.125 S(8), Se, Te) to U(H(2)C?PPh(3))(NR(2))(3) (R = SiMe(3)) (1) in Et(2)O results in generation of the terminal chalcogenide complexes, [Ph(3)PCH(3)][U(E)(NR(2))(3)] (E = S, 2; Se, 3; Te, 4; R = SiMe(3)), in modest yield. Complexes 2-4 represent extremely rare examples of terminal uranium monochalcogenides. Synthesis of the oxo analogue, [Cp*(2)Co][U(O)(NR(2))(3)] (5), was achieved by reduction of [U(O)(NR(2))(3)] with Cp*(2)Co. All complexes were fully characterized, including analysis by X-ray crystallography. In the solid state, complexes 2-5 feature short U-E bond lengths, suggestive of actinide-ligand multiple bonding. PMID:22920602

Brown, Jessie L; Fortier, Skye; Lewis, Richard A; Wu, Guang; Hayton, Trevor W

2012-09-06

322

Reverse Monte Carlo modeling of the neutron and X-ray diffraction data for new chalcogenide Ge–Sb–S(Se)–Te glasses  

NASA Astrophysics Data System (ADS)

New quaternary chalcogenide GexSb40?xS50Te10 and GexSb40?xSe50Te10 (x=20 and 27 at%) glasses have been synthesized and studied by neutron and high-energy X-ray diffraction. Both the traditional Fourier transformation technique and the Reverse Monte Carlo (RMC) modeling of the experimental data have been applied to model the 3-dimensional atomic configurations. From the analysis of the partial atomic correlation functions and structure factors the first and second neighbor distances, coordination numbers and bond-angle distributions are calculated. The influence of S(Se) content on the atomic environment in the glassy structure is considered and discussed in a function of glass composition. In addition, the packing density, average atomic volume and compactness for each composition are determined.

Fabian, M.; Svab, E.; Pamukchieva, V.; Szekeres, A.; Todorova, K.; Vogel, S.; Ruett, U.

2013-10-01

323

Theoretical investigations of the EPR parameters of cubic Yb3+ center in PbS, PbSe and PbTe semiconductors  

NASA Astrophysics Data System (ADS)

The important diluted magnetic semiconductors PbS, PbSe and PbTe have been studied by the electron paramagnetic resonance (EPR) technique. But there are not reasonable explanation reported. In this work, based on the crystal-field theory, the EPR parameters g factors of Yb3+ and hyperfine structure constants of 171Yb3+ and 173Yb3+ isotopes in PbS, PbSe and PbTe crystals are calculated by the aid of diagonalizing the full energy matrix. In the calculations, the contributions of various admixtures and interactions such as the J-mixing and the covalence are considered. The crystal field parameters are obtained from the superposition model. The calculated results are in reasonable agreement with the observed values. The results are discussed.

Xie, Guo-Ya; Liu, Xian-Rong

2013-10-01

324

Ab initio study of structural, dielectric, and dynamical properties of zinc-blende ZnX (X = O, S, Se, Te)  

Microsoft Academic Search

We have performed ab initio calculations of the structural, dielectric, and lattice-dynamical properties of the zinc-blende ZnX (X=O, S, Se, Te) using a plane-wave pseudopotential method within the density-functional theory. A linear-response approach to the density-functional theory as implemented in the code ABINIT is used to calculate the Born effective charges, electronic dielectric tensors, phonon frequencies and LO–TO splitting. Compared

You Yu; Jingjing Zhou; Huilei Han; Chuanyu Zhang; Tuo Cai; Chengqun Song; Tao Gao

2009-01-01

325

Anisotropic exciton and charged exciton dichroic photoluminescence in undoped ZnSe/BeTe type-II quantum wells in magnetic fields  

NASA Astrophysics Data System (ADS)

The in-plane anisotropy of the spatially indirect (SID) photoluminescence (PL) in an undoped ZnSe/BeTe type-II quantum structure has been systematically investigated and analyzed. With a new method we have succeeded in extracting intrinsic circular polarization degree of this SID PL by a special combination of a 14 wave-plate and a linear polarizer with respect to the in-plane crystal axis, without the influence of the in-plane anisotropy.

Shen, R.; Kojima, E.; Akimoto, R.; Takeyama, S.

2010-02-01

326

Isotropic Superconducting Gaps with Enhanced Pairing on Electron Fermi Surfaces in FeTe0.55Se0.45  

SciTech Connect

We used angle-resolved photoemission spectroscopy to reveal directly the momentum distribution of the superconducting gap in FeTe{sub 1-x}Se{sub x}, 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.

Yang H.; 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.

2012-03-06

327

Effect of Te doping and electron irradiation on thermal diffusivity of Bi2Se3 thin films by photo-thermal technique  

Microsoft Academic Search

Photo-thermal beam deflection technique has been employed for the measurement of thermal diffusivity of undoped, Te doped and electron irradiated Bi2Se3 thin films. Slope from the tangential component of deflection signal with the pump-probe offset is used to evaluate the numerical value of thermal diffusivity (alpha). Doped and electron irradiated samples show a substantial reduction in the value of alpha

Saji Augustine; Jyotsna Ravi; Ampili S; T. M. A. Rasheed; K. P. R. Nair; Tamio Endo; Elizabeth Mathai

2003-01-01

328

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

329

Trends in the structure and bonding in the layered platinum dioxide and dichalcogenides Pt Q 2 ( Q=O, S, Se, Te)  

Microsoft Academic Search

The structure and bonding of the layered platinum dioxide and dichalcogenides PtQ2 (Q=O, S, Se, Te) were analyzed on the basis of electronic band structure calculations using the full potential linearized augmented plane wave method. We examined why the c\\/a ratio in PtQ2 is considerably small compared with the value expected from the consideration of closely packed Q atoms (i.e.,

D. Dai; H.-J. Koo; M.-H. Whangbo; C. Soulard; X. Rocquefelte; S. Jobic

2003-01-01

330

Optical spectroscopy studies on FeTe1-xSex and AxFe2-ySe2 (A = K, Rb, Cs): A brief overview  

NASA Astrophysics Data System (ADS)

In this short overview, we summarize the optical spectroscopy studies on iron selenide superconducting systems FeTe1-xSex and A-xFe2-ySe2. We elaborate that optical spectroscopy measurements yield fruitful information about the band structure evolution across the AFM phase transition temperature, the electronic correlation effect, the superconducting pairing energy gap, the condensed carrier density or penetration depth, the inhomogeneity and the nanoscale phase separation between superconductivity and antiferromagnetism in those systems.

Yuan, Rui-Hua; Wang, Nan-Lin

2013-08-01

331

Femtosecond three-pulse photon echo and population grating studies of the optical properties of CdTe\\/ZnSe quantum dots  

Microsoft Academic Search

Femtosecond three-pulse two-color photon echo and population grating (PG) techniques have been used to characterize CdTe quantum dots (QDs) grown on ZnSe by molecular beam epitaxy. The time evolution of the PG signal exhibits a fast decay (2.5-3 ps), which is attributed to migration and tunneling of photoexcited carriers to neighboring QDs, followed by a slow decay (approx20 ps for

Lap Van Dao; Martin Lowe; Peter Hannaford; Hisao Makino; Toshiaki Takai; Takafumi Yao

2002-01-01

332

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

PubMed

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

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

2013-01-01

333

Utility of organosamarium(II) reagents in the formation of polyatomic group 16 element anions: Synthesis and structure of [(C{sub 5}Me{sub 5}){sub 2}Sm]{sub 2}(E{sub 3})(THF), [(C{sub 5}Me{sub 5}){sub 2}Sm(THF)]{sub 2}(E), and related species (E = S, Se, Te)  

SciTech Connect

Te and Se react with (C{sub 5}Me{sub 5}){sub 2}Sm(THF){sub 2} to form [(C{sub 5}Me{sub 5}){sub 2}Sm(THF)]{sub 2}({mu}-Te), 1, and [(C{sub 5}Me{sub 5}){sub 2}Sm(THF)]{sub 2}({mu}-Se), 2, respectively. (C{sub 5}Me{sub 5}){sub 2}Sm(THF){sub 2} reacts with Ph{sub 3}P{double_bond}Se and Ph{sub 2}{double_bond}S to form 2 and [(C{sub 5}Me{sub 5}){sub 2}Sm(THF)]{sub 2}({mu}-S), 3, respectively. Larger ratios of Te, Se, and S reacting with (C{sub 5}Me{sub 5}){sub 2}Sm(THF){sub 2} form [(C{sub 5}Me{sub 5}){sub 2}Sm]{sub 2}(Te{sub 3})(THF), 4, and [(C{sub 5}Me{sub 5}){sub 2}Sm]{sub 2}({mu}-{eta}{sup 2}:{eta}{sup 3}Se{sub 3})(THF), 5, and [(C{sub 5}Me{sub 5}){sub 2}Sm]{sub 2}(S{sub 3})(THF), 6. Reactions and X-ray crystal structures of these compounds are discussed.

Evans, W.J.; Rabe, G.W.; Ziller, J.W.; Doedens, R.J. [Univ. of California, Irvine, CA (United States)

1994-06-22

334

Structural and Thermal Diffusivity Studies of Polycrystalline (CuSe)1-XSeX Metal Chalcogenide Compound  

SciTech Connect

This paper reports the preparation and the characterization of the (CuSe)1-xSex metal chalcogenide semiconductor compounds with different stoichiometric compositions of Se (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) in bulk form. The (CuSe)1-xSex compounds were prepared using the solid state reaction by varying the ratio of CuSe:Se in the reaction mixture. X-ray powder diffraction analysis is used to identify and measure the mass absorption coefficient of the (CuSe)1-xSex compounds to support the thermal diffusivity behaviour. The thermal diffusivity of the polycrystalline (CuSe)1-xSex compounds were measured and analyzed for the first time, using the photoflash technique. The thermal diffusivity values were determined to be in the range of 2.524 x 10-3 cm2/s to 1.125 x 10-2 cm2/s. It was found that the thermal diffusivity value tends to decrease as the parameter x increases. The relationship between the thermal diffusivity, mass absorption coefficient and density of the (CuSe)1-xSex are discussed in detail.

Josephine, L. Y. C. [Malaysian Military Academy, Kem Sungai Besi, 57000 Kuala Lumpur (Malaysia); Talib, Z. A.; Yunus, W. M. M.; Moksin, M. M.; Lim, K. P.; Yusoff, W. D. W. [Department of Physics, Universiti Putra Malaysia, 43400 UPM, Serdang (Malaysia); Zainal, Z. [Department of Chemistry, Universiti Putra Malaysia, 43400 UPM, Serdang (Malaysia)

2007-05-09

335

Mineralogy and geochemical environment of formation of the Perama Hill high-sulfidation epithermal Au-Ag-Te-Se deposit, Petrota Graben, NE Greece  

NASA Astrophysics Data System (ADS)

The Perama Hill deposit is a high-sulfidation Au-Ag-Te-Se epithermal system hosted in silicic- and argillic altered andesitic rocks and overlying sandstones, which were emplaced on the eastern margin of the Petrota graben, northeastern Greece. The deposit evolved from an early stage silica-pyrite rock and argillic alteration followed by the deposition of sulfide-, sulfosalt- and telluride-bearing quartz-barite veins and stockworks. Early ore formation is characterized by a high-sulfidation-type enargite-galena-bearing ore assemblage (consisting of enargite, watanabeite, Fe-free sphalerite, covellite, kesterite, bismuthinite, selenian bismuthinite, lillianite homologues, kawazulite-tetradymite, goldfieldite, and native gold), followed by the formation of an intermediate-sulfidation-type tennantite-bearing assemblage characterized by ferrian/zincian tennantite, tellurobismuthite, tetradymite, melonite, native tellurium, Au-Ag-tellurides (calaverite, krennerite, sylvanite, hessite, petzite, stützite), altaite and electrum. Quartz, barite, kaolinite, sericite and minor aluminum-phosphate-sulfate minerals are gangue minerals. Fluid inclusion data demonstrate that the ore system evolved from an initial high temperature (up to 330°C) and low salinity (up to 4.9 wt.% NaCl equiv.) fluid towards a cooler (200°C) and very low salinity (0.7 wt.% NaCl equiv.) hydrothermal fluid suggesting progressive cooling and dilution of the ore fluid. The ore minerals at Perama Hill reflect variable fS2 and fTe2 conditions during base and precious metal deposition. Early ore deposition took place at ~300°C, at log fS2 values between ?-8.2 and -5.5, and log fTe2 from -11.8 and -7.8. Late ore deposition occurred at log fS2 = -11.8 to -9.8 and log fTe2 of ?-9.2 and -7.8. These data and paragenetic studies indicate a shift towards higher log fTe2 and lower log fS2 and log fSe2 values for the mineralizing fluids with time. The kawazulite/tetradymitess-gold association at Perama Hill suggests that it formed from a sulfide melt in the Bi-Au-Se-Te system as Au was scavenged from the hydrothermal ore-forming fluid at elevated temperatures. The presence of tellurides, and Bi- and Sn-bearing minerals in the ore system is compatible with direct deposition of metals from the vapor phase of a degassing magmatic (porphyry) body.

Voudouris, Panagiotis Christos; Melfos, Vasilios; Spry, Paul G.; Moritz, Robert; Papavassiliou, Constantinos; Falalakis, George

2011-11-01

336

Synthesis and Electronic Properties of the Misfit Layer Compound [(PbSe)1.00]1[MoSe2]1  

NASA Astrophysics Data System (ADS)

An ultralow-thermal-conductivity compound with the ideal formula [(PbSe)1.00]1[MoSe2]1 has been successfully crystallized across a range of compositions. The lattice parameters varied from 1.246 nm to 1.275 nm, and the quality of the observed 00 ? diffraction patterns varied through the composition region where the structure crystallized. Measured resistivity values ranged over an order of magnitude, from 0.03 ? m to 0.65 ? m, and Seebeck coefficients ranged from -181 ?V K-1 to 91 ?V K-1 in the samples after the initial annealing to form the basic structure. Annealing of samples under a controlled atmosphere of selenium resulted in low conductivities and large negative Seebeck coefficients, suggesting an n-doped semiconductor. Scanning transmission electron microscopy cross-sections confirmed the interleaving of bilayers of PbSe with Se-Mo-Se trilayers. High-angle annular dark-field images revealed an interesting volume defect, where PbSe grew through a region where a layer of MoSe2 would be expected in the perfect structure. Further studies are required to correlate the density of these defects with the observed electrical properties.

Heideman, Colby L.; Rostek, Raimar; Anderson, Michael D.; Herzing, Andrew A.; Anderson, Ian M.; Johnson, David C.

2010-09-01

337

A Structural Study of the Compound AgSbTe2  

Microsoft Academic Search

X-ray, optical and electron microscope, and chemical etching techniques have been used to investigate a striated microstructure observed in zone refined single crystals of the AgSbTe2 structure. This microstructure, originally thought to be fine twin lamellas, has been identified as a Widmanstatten precipitate of Sb2Te3 upon the {111} planes of the matrix face-centered cubic material. In addition, the evidence obtained

R. W. Armstrong; J. W. Faust; W. A. Tiller

1960-01-01

338

Tuning between Quantum-Dot and Quantum-Well-Like Behaviors in Type-II Zn-Se-Te Multilayers by Controlling Tellurium Flux during MBE Growth  

NASA Astrophysics Data System (ADS)

Type-II semiconductor quantum dots (QDs) characterized by spatial separation of charge carriers are good candidates for such applications as intermediate-band solar cells and IR photodetectors. Type-II QDs differ from type-I counterparts because one type of the carriers locates within the barrier material, so that their wavefunctions become to overlap early with increasing QD density. Thus, it is expected that type-II QDs coalescence into a - quantum well (QW) - like layer at much lower densities than similar type-I QDs with obvious consequences for device performance. We report here tuning between QD- and QW-like behaviors in the Zn-Se-Te multilayers with ZnTe sub-monolayer QDs. A set of samples, grown with increasing Tellurium flux, have been investigated. The critical density of QDs and the overlap of electron wavefunctions are estimated from secondary ion mass spectrometry, temperature dependent photoluminescence (PL), and magneto-PL measurements.

Ji, Haojie; Roy, Bidisha; Dhomkar, Siddharth; Moug, Richard; Tamargo, Maria; Wang, Alice; Kuskovsky, Igor

2013-03-01

339

Friedel-Like Oscillations from Interstitial Iron in Superconducting Fe1+yTe0.62Se0.38  

SciTech Connect

Using polarized and unpolarized neutron scattering we show that interstitial Fe in superconducting Fe$_{1+y}$Te$_{1-x}$Se$_x$ induces a magnetic Friedel-like oscillation that diffracts at ${\\bf Q}_{\\perp}=(\\frac{1}{2}0)$ and involves $>$50 neighboring Fe sites. The interstitial $>2$~$\\mu_B$ moment is surrounded by compensating ferromagnetic four spin clusters that may seed double stripe ordering in Fe$_{1+y}$Te. A semi-metallic 5-band model with $(\\frac{1}{2}\\frac{1}{2})$ Fermi surface nesting and four fold symmetric super-exchange between interstitial Fe and two in-plane nearest neighbors largely accounts for the observed diffraction.

Thampy, Vivek [ORNL; Kang, Jian [Johns Hopkins University; Rodriguez-Rivera, J A [NCNR and University of Maryland; Bao, Wei [Renmin University of China; Savici, Andrei T [ORNL; Hu, Jin [Tulane University; Liu, Tijiang [Tulane University; Qian, Bin [Tulane University; Fobes, David [Tulane University; Mao, Z Q [Tulane University; Fu, Changbo [ORNL; Chen, W. C. [National Institute of Standards and Technology (NIST); Ye, Qiang [ORNL; Erwin, R [National Institute of Standards and Technology (NIST); Gentile, T. R. [National Institute of Standards and Technology (NIST); Tesanovic, Zlatko [ORNL; Broholm, Collin L [ORNL

2012-01-01

340

The study of magnon-drag effects in the thermopower of CuCr2X4 (X = S, Se and Te)  

NASA Astrophysics Data System (ADS)

The electrical resistivity ? and thermopower S of metallic ferromagnets CuCr2X4 (X=S,Se or Te) are measured at low temperatures and in an external magnetic field of 1.5 Tesla. These properties are dominated by strong scattering effects in their ferromagnetic phase, resulting in (a) ?(T) ~A T2dependence with very large value of coefficient A approx 1 - 3×10-8 ?-cm/K2 in resistivity and (b) a peak in the thermopower around TC/3 . Thermopower is further increased by crystalline order and by the alignment of magnetic domains in an external magnetic field as has been found for Cu1+x Cr2Te4. We have interpreted these effects as due to strongly coherent momentum conserving electron-magnon scattering giving a large T2 - contribution in resistivity and a large drag effect in thermopower.

Tripathi, T. S.; Tewari, G. C.; Rastogi, A. K.

2010-01-01

341

Unusual Anomalous Hall Resistivities of CuCr2S4, Cu0.5Zn0.5Cr2Se4 and Cr3Te4  

NASA Astrophysics Data System (ADS)

Hall resistivities ?H, the magnetizations M and the magnetoresistances ?? have been measured as functions of the applied magnetic field H in the wide temperature range for ferromagnetic systems of CuCr2S4, Cu0.5Zn0.5Cr2Se4 and Cr3Te4, which are considered to have non-trivial spin structures below the temperature Tm. For CuCr2S4 and Cr3Te4, the Hall resistivities have been found to deviate from the ordinary expression ?H=R0H+4?RsM below Tm, where R0 and Rs are the ordinary and anomalous Hall coefficients, respectively. The sign change of Rs with T has also been observed for all the systems. These behaviors are discussed in relation to their possibly non-trivial magnetic structures.

Oda, Keisuke; Yoshii, Shunsuke; Yasui, Yukio; Ito, Masafumi; Ido, Takahiko; Ohno, Youhei; Kobayashi, Yoshiaki; Sato, Masatoshi

2001-10-01

342

Subchronic oral toxicity studies of Se-methylselenocysteine, an organoselenium compound for breast cancer prevention  

PubMed Central

Se-methylselenocysteine (MSC) is an organoselenium compound being developed for breast cancer chemoprevention. To characterize MSC toxicity, CD rats received daily gavage doses of 0, 0.5, 1.0, or 2.0 mg/kg/day (0, 3, 6, or 12 mg/m2/day), and beagle dogs received daily gavage doses of 0, 0.15, 0.3, or 0.6 mg/kg/day (0, 3, 6, or 12 mg/m2/day) for 28 days. In rats, MSC induced dose-related hepatomegaly in both sexes; mild anemia, thrombocytopenia, and elevated liver enzymes were observed in high dose females only. Microscopic pathology included hepatocellular degeneration (high dose males, all doses in females); arrested spermatogenesis (high dose males); and atrophy of corpora lutea (middle and high dose females). In dogs, MSC induced mild anemia in middle and high dose males, and in high dose females. Toxicologically significant microscopic lesions in dogs were seen only in the liver (peliosis and vacuolar degeneration in high dose males, midzonal necrosis in males in all dose groups). Based on liver pathology seen in female rats in all dose groups, the No Observed Adverse Effect Level [NOAEL] for MSC in rats is < 0.5 mg/kg/day. Based on alterations in hematology parameters and liver morphology in male dogs in all dose groups, the NOAEL for MSC in dogs is <0.15 mg/kg/day.

Johnson, W.D.; Morrissey, R.L.; Kapetanovic, I.; Crowell, J.A.; McCormick, D.L.

2008-01-01

343

Analysis of heavily tailed size distributions of ZnTe/ZnSe quantum dot structures by using the bootstrap methodology  

NASA Astrophysics Data System (ADS)

We have used the bootstrap methodology to analyze dot size distributions of ZnTe quantum dot (QD) structures. The photoluminescence (PL) spectrum indicates that the ZnTe QD structure belongs to a type-II band alignment. The broadness with small fluctuations in the PL represents the spatial inhomogeneity of the QD sizes. The Schrodinger equation together with the first-order perturbation correction was numerically solved to correlate the dot size and the photon energy. Using the bootstrap "loess" curve fitting method, the PL spectrum was determined to be a normal distribution with a high significance level of 46% tested by a null hypothesis H0. By examining the slope of the complementary cumulative distribution function, we found that the size distribution is heavy tailed.

Lee, Johnson; Chou, W. C.; Jan, G. J.

2002-09-01

344

Thermoelectric Generators Using p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 Thin Films Prepared by the Thermal Evaporation Method  

NASA Astrophysics Data System (ADS)

In this study, p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 ingots were used in a standard solid-state microwave synthesis route for fabricating thermally evaporated thin films. The nanostructure and composition of the films were studied through x-ray diffraction, field-emission scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Measurements of the Seebeck coefficient and electrical conductivity were performed at 298 K to 523 K. The microthermoelectric devices were composed of 20 pairs and 10 pairs of p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 thin films on glass substrates, respectively. The 20-pair p- n thermocouples in series generated a maximum output open-circuit voltage of 275.3 mV and a maximum output power of 54.37 nW at a temperature difference ? T = 162 K, and 109.4 mV and 16.68 nW at ? T = 162 K for 10 pairs, respectively.

Hmood, A.; Kadhim, A.; Hassan, J. J.; Abu Hassan, H.

2013-06-01

345

Phase transitions and vibrational study of (Cs3.5Rb0.5)[(Se0.85S0.15)O3]2[Te(OH)6]3 material  

NASA Astrophysics Data System (ADS)

The ionic-protonic conductor (Cs3.5Rb0.5)[(Se0.85S0.15)O3]2[Te(OH)6]3 crystallizes in the orthorhombic system. The space group is Pccn. Three endothermic peaks in thermal behavior were detected for this compound at T1 = 400 K, T2 = 435 K and T3 = 480 K, by DSC experiment. These transitions analyzed by dielectric measurements using the impedance and modulus spectroscopy techniques. Raman spectra of the material recorded at various temperatures (300-600 K) in the frequency range 100-1100 cm-1 and IR spectra achieved at room temperature between 400 and 4000 cm-1, confirm the presence of all the phase transitions detected in the material and show that anionic groups coexist independently in the same crystal.

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

2013-02-01

346

The microstructures and superconducting properties of FeSe0.5Te0.5 bulks with original milled powders  

NASA Astrophysics Data System (ADS)

A combination of mechanical alloying (MA) and solid-state reaction was applied to synthesize bulk FeSe0.5Te0.5 superconductor. The influence of milling time on microstructures and superconducting properties were investigated in detail. The results showed that both the grain size and the amount of ?-FeSe in the final sintered samples decreased as the milling time increased. In addition, lattice parameters a and c of ?-FeSe also decreased with the milling time increasing, implying the introduction of a positive chemical pressure, which was not favorable for superconductivity of Fe chalcogenides. According to the measured results of resistivity, only the 20 h-milled sintered sample exhibited superconductivity, with Tconset and Tc0 of values 14 K and 10 K, respectively. As the milling time increased, the superconductivity was depressed or even damaged completely.

Li, Xiaoting; Gao, Zhiming; Liu, Yongchang; Ma, Zongqing; Yu, Liming; Li, Huijun; Yang, Hanzhang

2013-10-01

347

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

348

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

349

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

NASA Astrophysics Data System (ADS)

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; Peng, Xiangyang; Wei, Xiaolin; Yang, Hong; Stocks, G. Malcolm; Zhong, Jianxin

2013-05-01

350

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

351

Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Annual subcontract report, 1 April 1991--31 March 1992  

SciTech Connect

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

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

1992-11-01

352

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

353

Photoluminescence properties of ZnSe 1? x Te x thin films on GaAs\\/ITO substrates by electron beam evaporation technique  

Microsoft Academic Search

Zinc chalcogenide which includes zinc selenide, zinc sulphide, zinc telluride and mixed crystals of these shows a great potential\\u000a as an optoelectronic device material. Zinc selenotelluride is a suitable material for visible light emitting devices which\\u000a are expected to cover the spectral range from yellow to blue. In our present study the composition controlled ZnSe1?x\\u000a Te\\u000a x\\u000a films with different

J. Suthagar; N. J. Suthan Kissinger; M. Balasubramaniam; K. Perumal

2011-01-01

354

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

355

The flux pinning mechanism, and electrical and magnetic anisotropy in Fe1.04Te0.6Se0.4 superconducting single crystal  

NASA Astrophysics Data System (ADS)

The temperature and magnetic field dependences of the magnetization and critical current density of Fe1.04Te0.6Se0.4 single crystals have been investigated, and the flux pinning mechanism has been analysed. The normalized pinning force (fp = Fp/Fp,max) vs. h(H/Hirr) curves, are scaled using the Dew-Hughes' theory, f(h) ~ hp(1 - h)q with p = 1.35 and q = 3.06. The angular dependence of the resistivity under different magnetic fields shows a dip-like structure, below the superconducting transition temperature. The anisotropic value of 2 was obtained using Ginzburg-Landau theory.

Shahbazi, M.; Wang, X. L.; Dou, S. X.; Fang, H.; Lin, C. T.

2013-05-01

356

Te and Se mineralogy of the high-sulfidation Kochbulak and Kairagach epithermal gold telluride deposits (Kurama Ridge, Middle Tien Shan, Uzbekistan)  

NASA Astrophysics Data System (ADS)

The Late Paleozoic Kochbulak and Kairagach deposits are located on the northern slope of the Kurama Ridge, Middle Tien Shan, in the same volcanic structure and the same ore-forming system. Au-Ag-Cu-Bi-Te-Se mineralization is confined to veins and dissemination zones accompanied by quartz-sericite wall-rock alteration. The tellurides, calaverite, altaite, hessite, and tetradymite are widespread at both deposits; at Kairagach selenides and sulfoselenides of Bi and Pb are common, while at Kochbulak Bi and Pb telluroselenides and sulfotelluroselenides are typical. The paragenetic sequence of telluride assemblages are similar for both deposits and change from calaverite + altaite + native Au to sylvanite + Bi tellurides + native Te, Bi tellurides + native Au, and, finally, to Au + Ag tellurides with time. These mineralogical changes are accompanied by an increase in the Ag content of native gold that correlates with a decrease in temperature, fTe2 and fO2 and an increase in pH.

Plotinskaya, O. Yu.; Kovalenker, V. A.; Seltmann, R.; Stanley, C. J.

2006-07-01

357

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

358

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

359

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

360

Development of a computer model for polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells. Annual subcontract report, 1 January 1990--31 December 1990  

SciTech Connect

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

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

1992-04-01

361

MOVPE of narrow and wide gap II-VI compounds  

NASA Astrophysics Data System (ADS)

The development of high quality II-VI compounds is dependent on advances made in certain key research activities. This review is concerned with these activities, which include precursors such as Pr2Te, t-Bu2Te, Me(allyl)Te, and (allyl)2Te for low temperature growth; substrates including CdZnTe, CdTe, CdTeSe, GaAs on Si for epitaxy; doping for p-n junction formation and photoassisted growth processes for low temperature growth; and photopatterning and selected-area deposition.

Mullin, J. B.; Irvine, S. J. C.; Hails, J. E.; Giess, J.; Cole-Hamilton, D. J.

1990-04-01

362

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

363

Superexchange interaction revisited: the role of the A-site cations in A CuO3 (A=Se, Te)  

NASA Astrophysics Data System (ADS)

To investigate the effects of A-site cations on the magnetic interaction in highly distorted perovskite ACuO3 (A=Se, Te), we have set the microscopic Hamiltonian for the Cu-O-Cu-A cluster, taking into account the \\tilde{{s}}{p} or \\tilde{{p}}{p} hybridization between A-\\tilde{{s}} or A-\\tilde{{p}} and O-2p orbitals. We have found that (i) the superexchange interaction of the simple Cu-O-Cu triad without considering the A-site effect is inadequate to explain the ferromagnetism of SeCuO3, (ii) the \\tilde{{p}}{p} hybridization weakens the superexchange interactions and (iii) the \\tilde{{s}}{p} hybridization induces the ferromagnetic superexchange interaction along the c-axis. We have also verified that the \\tilde{{s}}{p} hybridization affects the magnetic interaction through anisotropic charge transfer energy shift in the Cu-O-Cu interaction path.

Kim, Beom Hyun; Choi, Hongchul; Min, B. I.

2010-07-01

364

Doping effects of Co and Cu on superconductivity and magnetism in Fe1+yTe0.6Se0.4 single crystals  

NASA Astrophysics Data System (ADS)

We report on the investigation of Co and Cu substitution effects on superconductivity and magnetism in Fe1+yTe0.6Se0.4 single crystals. The parent Fe1.01Te0.59Se0.41 shows a nodeless bulk superconductivity as revealed in heat capacity measurement, which is gradually suppressed by either Co or Cu doping. It is found that the Co or Cu doping mainly serves as scatterers rather than charge carrier doping, which is in agreement with the DFT calculation (2010 Phys. Rev. Lett. 105 157004) reported by Wadati et al. In comparison with Cu doping, Co doping shows a stronger influence on magnetism while a less evident suppression effect on superconductivity. Upon substitution of Co for Fe, a Schottky heat capacity anomaly develops gradually at low temperatures, implying the existence of a paramagnetic moment in the Co-doped samples. In contrast, Cu doping may mainly serve as non-magnetic scatterers, where no Schottky anomaly is observed.

Zhang, Z. T.; Yang, Z. R.; Li, L.; Ling, L. S.; Zhang, C. J.; Pi, L.; Zhang, Y. H.

2013-01-01

365

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

SciTech Connect

Experimental and theoretical studies of the electronic and optical properties of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2} are reported. Experimental data include the electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, and lattice constants for T {le} 300 K, and optical transmission and diffuse reflectance data at room temperature. Nominally stoichiometric, polycrystalline samples form with hole concentrations inferred from Hall measurements of 2 x 10{sup 18} and 5 x 10{sup 19} cm{sup -3} near room temperature for the selenide and telluride, respectively. The corresponding mobilities are near 15 cm{sup 2} V{sup -1} s{sup -1} for both materials. Optical measurements reveal a transition near 1.8 eV in BaCu{sub 2}Se{sub 2}, while no similar feature was observed for BaCu{sub 2}Te{sub 2}. First principles calculations indicate both materials are direct or nearly direct gap semiconductors with calculated gaps near 1.0 eV and 1.3 eV for the telluride and selenide, respectively, and predict weak absorption below about 2 eV. Transport properties calculated from the electronic structure are also presented.

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

2011-01-01

366

Flow injection analysis of volatile phenols in environmental water samples using CdTe/ZnSe nanocrystals as a fluorescent probe.  

PubMed

On the basis of flow injection analysis technology, a simple, accurate, and sensitive method has been developed for the determination of volatile phenols in environmental water samples by using CdTe/ZnSe nanocrystals as a fluorescent probe. The influences of coexisting metal ions and volatile phenol substitutes were also investigated. The method developed for analysis of volatile phenols displayed very good linearity in the range from 1.0 × 10(-8) to 4.0 × 10(-7) g L(-1), with a correlation coefficient greater than 0.995 and a detection limit down to 2.7 × 10(-9) g L(-1) (signal-to-noise ratio 3). The proposed method was successfully applied to determine the content of volatile phenols in environmental water samples, and the quantitative recoveries were 93.4-106.1%. A possible reaction mechanism for the quenching of fluorescence is discussed using UV-vis absorption spectra, fluorescence spectra, and time-resolved luminescence spectra of volatile phenols obtained by titrating a CdTe/ZnSe nanocrystal aqueous solution and zeta potential data. PMID:22038584

Zhang, Wen-Hao; Zhang, Ding; Zhang, Rong-Jie; Xia, Fang; Liu, Ying-Fan

2011-10-26

367

Doping effects of Co and Cu on superconductivity and magnetism in Fe1+yTe0.6Se0.4 single crystals.  

PubMed

We report on the investigation of Co and Cu substitution effects on superconductivity and magnetism in Fe(1+y)Te(0.6)Se(0.4) single crystals. The parent Fe(1.01)Te(0.59)Se(0.41) shows a nodeless bulk superconductivity as revealed in heat capacity measurement, which is gradually suppressed by either Co or Cu doping. It is found that the Co or Cu doping mainly serves as scatterers rather than charge carrier doping, which is in agreement with the DFT calculation (2010 Phys. Rev. Lett. 105 157004) reported by Wadati et al. In comparison with Cu doping, Co doping shows a stronger influence on magnetism while a less evident suppression effect on superconductivity. Upon substitution of Co for Fe, a Schottky heat capacity anomaly develops gradually at low temperatures, implying the existence of a paramagnetic moment in the Co-doped samples. In contrast, Cu doping may mainly serve as non-magnetic scatterers, where no Schottky anomaly is observed. PMID:23238220

Zhang, Z T; Yang, Z R; Li, L; Ling, L S; Zhang, C J; Pi, L; Zhang, Y H

2012-12-13

368

Bis(sulfinylamino)selane, Se(NSO) 2: between S(NSO) 2 and Te(NSO) 2 in theoretical and spectroscopical considerations  

Microsoft Academic Search

Vibrational spectra of bis(sulfinylamino)selane, Se(NSO)2, together with the evaluation of its pre-resonance Raman effect, demonstrate that the C2v point group does not change upon electronic excitation. Computational chemistry results agree with the Z configuration of the molecule reported by X-ray analysis and that of R–N?S?O compounds investigated so far. Treatments using relativistic effects at the Se atom give comparable results

R. M Romano; C. O Della Védova

1999-01-01

369

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

SciTech Connect

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

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

2011-04-15

370

Photocurrent and Surface Photovoltage Spectroscopy Investigations of CdTe-based Compounds  

Microsoft Academic Search

The potentiality of photocurrent (PC) and surface photovoltage spectrosocopy (SPS) analyses in the determination of the band gap of CdTe-based ternary alloys was investigated. Both methods can detect band-to-band and defect state-to-band transitions. The role played by the surface states in both experimental methods has been studied since it may significantly alter the results. The below-band gap energy levels have

Anna Cavallini; Daniela Cavalcoli; Antonio Castaldini; Beatrice Fraboni

2006-01-01

371

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

PubMed

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

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

2012-07-16

372

Microstructure and thermoelectric properties of p-type Bi{sub 0.5}Sb{sub 0.5}Te{sub 0.5} compounds fabricated by hot pressing and hot extrusion  

SciTech Connect

Bismuth telluride (Bi{sub 2}Te{sub 0.5}) compounds have been used as thermoelectric cooling and power conversion materials, since they have a high figure of merit at room temperature and can be fabricated easily and cost effectively. The crystal structure of Bi{sub 2}Te{sub 0.5} at room temperature is rhombohedral (a = 0.438 nm and c = 3.049 nm). This crystal structure is composed of atomic layers in the order of Te/Bi/Te/Te/Bi/Te/Bi/Te/Te/... along the c-axis. The Te/Te layers are considered to be weakly bound with van der Waals-like forces. The electrical and mechanical properties along the directions parallel to the cleavage planes are better than those along the c-axis. The distinct cleavage planes are perpendicular t the c-axis. Owing to the cleavage features, the crystal has poor mechanical properties and fabricating of miniature thermoelectric modules is difficult. Many attempts were made by sintering to fabricate miniature modules without cleavage. However, the sintering technique is not effective because the figure of merit of sintered compounds is lower than that of single crystals. In this work, the authors fabricated the p-type Te-doped Bi{sub 0.5}Sb{sub 0.5}Te{sub 0.5} compounds by both hot pressing and hot extrusion and then investigated the microstructure and thermoelectric properties of the compounds.

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

1998-01-06

373

Effect of heat treatment on the heterojunction resistance at the interface between single crystals of solid solutions of the Bi/sub 2/Te/sub 3/-Be/sub 2/Se/sub 3/ and Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ systems and alloys of Bi with Sn and Bi with Sb  

SciTech Connect

The authors investigate the effect of heat treatment on the interface of single crystals of solid solutions of the systems Bi/sub 2/Te/sub 3/-Bi/sub 2/Se/sub 3/ and Bi/sub 2/Te/sub 3/-Sb/sub 2/Te/sub 3/ and the alloys Bi-Sn and Bi-Sb. Two methods were considered. In the first method, the surfaces of the samples were mechanically ground with an abrasive paste before treatment, and in the second method they were not ground. Methods of treatment were chemical etching, electrochemical etching, rubbing of the surfaces with cotton balls, and wetting with electrochemical-etching solutions. Dependences of the junction-contact resistance of surfaces of crystals of solid solutions of the systems investigated here on the heat treatment time and also on the method of preliminary treatment before soldering with alloy and on the soldering method after electrochemical etching are shown.

Alieva, T.D.; Barkhalov, B.Sh.; Akhundova, N.M.; Abdinov, D.Sh.

1987-07-01

374

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

375

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

376

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.

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

377

Impact of In Situ Generated Ag2Te Nanoparticles on the Microstructure and Thermoelectric Properties of AgSbTe2 Compounds  

NASA Astrophysics Data System (ADS)

A series of ternary (Ag2Te) x (Sb2Te3)100- x ( x = 44 to 54) bulk materials with in situ generated Ag2Te nanoparticles were prepared from high-purity elements by combining the melt-quench technique with the spark plasma sintering technique. The influence of the Ag2Te nanoparticles on the thermoelectric transport properties, and the mechanism of nanoparticle formation were investigated. With increasing x, the concentration of the Ag2Te nanoparticles increased monotonically, but their diameter remained nearly unchanged. Due to the possible carrier energy filtering effect caused by the Ag2Te nanoparticle inclusions, the Seebeck coefficient of the sample with x = 50 was two times higher than that of the sample prepared by the melting method. Moreover, notable scattering of mid-to-long wavelength phonons arising from the evenly distributed Ag2Te nanoparticles led to a large reduction of the lattice thermal conductivity. All these effects led to the enhancement of the ZT value of the x = 50 sample (AgSbTe2) compared with the single-phase sample ( x = 44).

Du, B.; Xu, J.; Zhang, W.; Tang, X.

2011-05-01

378

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

NASA Astrophysics Data System (ADS)

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

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

379

First-principles investigation of 67Zn isomer shifts in ZnF2 and the chalcogenides ZnO, ZnS, ZnSe, and ZnTe  

NASA Astrophysics Data System (ADS)

All-electron, self-consistent, Hartree-Fock cluster calculations have been carried out to derive electron densities at the zinc nucleus in the series of compounds ZnF2 (rutile-type structure), ZnO (rocksalt structure), ZnO (wurtzite structure), and the compounds ZnS, ZnSe, and ZnTe (all with the sphalerite structure). The derived density differences show a very good linear correlation with the experimental isomer shifts. The isomer shifts and results for the densities at the zinc nucleus have been combined to calculate a value for the change of the mean-square nuclear charge radius for the Mössbauer transition in 67Zn of ?=+(13.9+/-1.4)×10-3 fm2. Our calculations clearly show the importance of the covalency of the Zn-ligand bond for the origin of the isomer shift and fully corroborate the experimental linear correlation between decreasing isomer shift values and increasing electronegativity of the ligands. The most important contribution to the electron-density differences at the zinc nucleus comes from the Zn(4s) electrons with a smaller but significant contribution from the Zn(3s) electrons appearing to arise primarily from the repulsive influence of the ligand-ion orbitals.

Mitchell, D. W.; Das, T. P.; Potzel, W.; Kalvius, G. M.; Karzel, H.; Schiessl, W.; Steiner, M.; Köfferlein, M.

1993-12-01

380

High pressure phase transition in samarium monochalcogenides SmX (X = S, Se, Te) and their alloy SmS1?xSex  

NASA Astrophysics Data System (ADS)

Phase transition pressures, relative volume changes, elastic and thermophysical properties of Samarium monochalcogenides SmX (X = S, Se, Te) have been studied. An improved interaction potential model has been developed which includes Coulomb, three-body interaction, polarizability effect and overlap repulsive interaction operative up to second neighbor ions. In addition, we have investigated the phase transition pressure and associated volume collapse in SmS1?xSex alloy (0 ? x ? 1) which shows transition from discontinuous to continuous as x is reduces. The present results are in general in good agreement with experimental data available for the end point members (x = 0 and x = 1). The results for the alloy counter parts are also in fair agreement with experimental data generated from the vegard's law.

Dubey, Ritu; Singh, Sadhna

2013-11-01

381

A new approach for improving global critical current density in Fe(Se0.5Te0.5) polycrystalline materials  

NASA Astrophysics Data System (ADS)

A novel method to prepare bulk Fe(Se0.5Te0.5) samples is presented, based on a melting process and a subsequent annealing treatment. With respect to the standard sintering technique, it produces much more homogeneous and denser samples, characterized by large and well interconnected grains. The resulting samples exhibit optimal critical temperature values, sharp resistive and magnetic transitions, large magnetic hysteresis loops and high upper critical fields. Interestingly, the global critical current density is much enhanced as compared to the values reported in the literature for bulk samples of the same 11 family, reaching about 103 A cm-2 at zero field at 4.2 K, as assessed by magnetic, transport and magneto-optical techniques. Even more importantly, its field dependence turns out to be very weak, such that at ?0H = 7 T it is suppressed only by a factor ˜2.

Palenzona, A.; Sala, A.; Bernini, C.; Braccini, V.; Cimberle, M. R.; Ferdeghini, C.; Lamura, G.; Martinelli, A.; Pallecchi, I.; Romano, G.; Tropeano, M.; Fittipaldi, R.; Vecchione, A.; Polyanskii, A.; Kametani, F.; Putti, M.

2012-11-01

382

Structure of the Oxygen-annealed Chalcogenide Superconductor Fe1.08Te0.55Se0.45Ox  

SciTech Connect

The as-grown single crystal Fe{sub 1.08}Te{sub 0.55}Se{sub 0.45} with the tetragonal PbO-type structure is nonsuperconducting owing to the excess Fe. Superconductivity is induced after oxygen annealing with an onset and zero resistance transition temperature around 14.5 K and 11.5 K, respectively. The oxygen doping is evidenced by electron energy loss spectroscopy and accompanied by improved homogeneity in the remaining PbO-type phase, as well as an increase in the L{sub 3}/L{sub 2} intensity ratio of the Fe-L{sub 2,3} edge, indicating an increase in Fe valence. Local phase transformation from the tetragonal PbO-type phase to the hexagonal NiAs-type phase is also observed after oxygen annealing.

Hu H.; Xu Z.; Zuo, J.-M.; Zheng, M.; Eckstein, J.N.; Park, W.K.; Greene, L.H.: Wen, J.; Lin, Z.; Li, Q.; Gu, G

2012-02-01

383

Contribution to the study of electronic structure of crystalline semiconductors (Si, Ge, GaAs, Gap, ZnTe, ZnSe)  

NASA Astrophysics Data System (ADS)

The band structure of semiconductors was described by several theorists since the Fifties. The main objective of the present paper is to do a comparative study between various families of semi-conductors IV (Si,Ge), III-V (GaAs, GaP) and II-VI (ZnSe, ZnTe) with both methods; tight Binding1 method and pseudo potential method2. This work enables us to understand as well as the mechanism of conduction process in these semiconductors and powers and limits of the above methods. The obtained results allow to conclude that both methods are in a good agreement to describe the morphology of band structures of the cited semiconductors. This encourages us to study in the future the electronic behaviour through the structure of bands for more complex systems such as the heterostructures.

Mahi, N.; Bouhafs, B.

2012-06-01

384

Enhanced surface mobility and quantum oscillations in topological insulator Bi1.5Sb0.5Te1.7Se1.3 nanoflakes  

NASA Astrophysics Data System (ADS)

In this study, a series of Bi1.5Sb0.5Te1.7Se1.3 (BSTS) flakes 80-nm to 140-?m in thickness was fabricated to investigate their metallic surface states. We report the observation of surface-dominated transport in these topological insulator BSTS nanoflakes. The achievement of surface-dominated transport can be attributed to high surface mobility (~3000 cm2/V s) and low bulk mobility (12 cm2/V s). Up to 90% of the total conductance, the surface channel was estimated based on the thickness dependence of electrical conductance and the result of the Shubnikov-de Hass oscillations in a 200-nm BSTS. The nature of nontrivial Dirac surface states was also confirmed by the weak anti-localization effect.

Hsiung, Te-Chih; Chen, Ding-Yuan; Zhao, Li; Lin, Yi-Hsin; Mou, Chung-Yu; Lee, Ting-Kuo; Wu, Maw-Kuen; Chen, Yang-Yuan

2013-10-01

385

Effect of Te doping and electron irradiation on thermal diffusivity of Bi2Se3 thin films by photo-thermal technique  

NASA Astrophysics Data System (ADS)

Photo-thermal beam deflection technique has been employed for the measurement of thermal diffusivity of undoped, Te doped and electron irradiated Bi2Se3 thin films. Slope from the tangential component of deflection signal with the pump-probe offset is used to evaluate the numerical value of thermal diffusivity (alpha). Doped and electron irradiated samples show a substantial reduction in the value of alpha compared to undoped sample. The variations in the thermal diffusivity of doped and electron irradiated samples are explained in terms of phonon assisted heat transfer mechanism. It is seen that alpha is very sensitive to structural variations arising from doping and electron irradiation. The experimentally observed results are correlated with x-ray diffraction studies.

Augustine, Saji; Ravi, Jyotsna; S, Ampili; Rasheed, T. M. A.; Nair, K. P. R.; Endo, Tamio; Mathai, Elizabeth

2003-04-01

386

Effect of pressure on the neutron spin resonance in the unconventional superconductor FeTe0.6Se0.4  

SciTech Connect

We have carried out a pressure study of the unconventional superconductor FeTe0.6Se0.4 up to 1.5 GPa by neutron scattering, resistivity, and magnetic susceptibility measurements. The neutron spin resonance energy and the superconducting transition temperature have been extracted as a function of applied pressure in samples obtained from the same crystal. Both increase with pressure up to amaximum at approximate to 1.3 GPa, directly demonstrating a correlation between these two fundamental parameters of unconventional superconductivity. A comparison between the quantitative evolution of T-c and the resonance energy as a function of applied pressure is also discussed. These measurements serve to demonstrate the feasibility of using pressure dependent inelastic neutron scattering to explore the relationship between the resonance energy and T-c in unconventional superconductors

Marty, Karol J [ORNL; Christianson, Andrew D [ORNL; Moreira Dos Santos, Antonio F [ORNL; Sipos, Balazs [ORNL; Matsubayashi, Kazuyuki [University of Tokyo, Tokyo, Japan; Uwatoko, Yoshiya [University of Tokyo, Tokyo, Japan; Fernandez-Baca, Jaime A [ORNL; Tulk, Christopher A [ORNL; Maier, Thomas A [ORNL; Sales, Brian C [ORNL; Lumsden, Mark D [ORNL

2012-01-01

387

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

388

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

389

Tuning of the superconducting properties of FeSe0.5Te0.5 thin films through the substrate effect  

NASA Astrophysics Data System (ADS)

From recent literature, it became clear that the crystallographic lattice parameters and the superconducting properties of FeSe0.5Te0.5 thin films exhibit a non-trivial dependence on the in-plane lattice constant of the substrates on which they are grown. The strain, which depends on the type of growth, can play an important role both in enhancing the critical temperature Tc and in determining the pinning mechanisms. Here, we present the effects of the substrate on the superconducting properties of FeSe0.5Te0.5 thin films. After a comprehensive overview of the different substrates used, i.e. oxides and fluorides, we compare the superconducting properties of films grown on LaAlO3(001) and SrTiO3(001). We show that the pinning properties of the two types of film are completely different: the angular dependences of the critical current density are opposite due to the presence of extrinsic pinning along the c-axis on films grown on SrTiO3. The presence of strong correlated pinning for a field perpendicular to the surface in films grown on SrTiO3 is confirmed by the analysis of the activation energy for vortex motion U0 and supported by the observation through scanning tunnelling microscopy of nanoscale threading dislocations possibly induced by the lattice mismatch with the substrate, which are not seen on the films deposited on LaAlO3.

Bellingeri, E.; Kawale, S.; Braccini, V.; Buzio, R.; Gerbi, A.; Martinelli, A.; Putti, M.; Pallecchi, I.; Balestrino, G.; Tebano, A.; Ferdeghini, C.

2012-08-01

390

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

391

STRUCTURAL, ELECTRONIC, MAGNETIC AND OPTICAL PROPERTIES OF FERROMAGNETIC Pb1-xEuxSe AND Pb1-xEuxTe ALLOYS (x = 0, 0.25, 0.50, 0.75 AND 1)  

NASA Astrophysics Data System (ADS)

First-principles total energy calculations have been performed using full potential linear-augmented-plane-wave method within the framework of density functional theory to study the structural, electronic, magnetic and optical properties of the Pb1-xEux Se and Pb1-xEuxTe(0 ? x ?1) alloys in the ferromagnetic (FM) ordering. The calculations have been extended to treat the strongly localized f electrons of Eu atom by the self-interaction correction (SIC) approach. For structural optimization, the Wu and Cohen generalized gradient approximation (GGA) functional has been used, whereas for calculating electronic properties, the GGA parameterization scheme formulated by Engel and Vosko (EV) has also been utilized. It has been observed that the use of experimental value of Coulomb parameter (Uf-expt.) within the SIC does not yield an accurate EuSe and EuTe energy band structure. The improvement in the electronic band structures of nonmagnetic PbSe/PbTe and ferromagnetic EuSe/EuTe have been achieved by considering the effects of spin-orbit coupling for Pb atoms, by a suitable choice of U and by treating the U values for Eu atom's f and d electrons as parameters. The electronic and optical properties of FM Pb1-xEuxSe in agreement with experiments can be achieved by combining EV GGA with a Hubbard U < Uf-expt., however, a stronger and stable AFM coupling in EuTe leaves the above scheme unable to provide good electronic structure of FM Pb1-xEuxTe. In case of Pb1-xEuxSe the nonlinear behaviour of electronic structure is reflected in the optical properties of Eu-doped PbSe that have been studied in terms of incident photons' energy dependent complex dielectric function.

Alay-E-Abbas, S. M.; Younas, S.; Hanif, S.; Sharif, M.; Hussain, Iqbal; Ghulam Abbas, S. M.; Shaukat, A.

2013-07-01

392

CsPb3Bi3Te8 and CsPb4Bi3Te9: low-dimensional compounds and the homologous series CsPbmBi3Te5 + m.  

PubMed

Two new thermoelectric materials of quaternary bismuth telluride CsPb3Bi3Te8 and CsPb4Bi3Te9 are reported, which are members of a homologous series featuring anionic slabs [PbmBi3Te5 + m]- (m = 1-4) of monotonically increasing thickness. PMID:12125565

Hsu, Kuei-Fang; Lal, Sangeeta; Hogan, Tim; Kanatzidis, Mercouri G

2002-07-01

393

Magnetic properties of the dense Kondo compound CeSe studied by neutron scattering  

Microsoft Academic Search

Magnetic properties of the FCC type II antiferromagnetic CeSe have been studied by elastic, diffuse critical and inelastic neutron scattering experiments. The diffuse critical scattering above the Neel temperature corresponds to highly anisotropic longitudinal spin fluctuations with a lenslike intensity distribution. The magnetic phase diagram for fields along the (110) direction contains a first-order magnetic phase transition at H=Hcrit(T)

A. Donni; A. Furrer; P. Fischer; S. M. Hayden; F. Hulliger; T. Suzuki

1993-01-01

394

Linear Compressibilities of Ii-Vi Compound Single Crystals.  

National Technical Information Service (NTIS)

The isothermal linear compressibilities of the II-VI compound single crystals, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, and ZnTe were measured by an optical interferometer. The change in length of the crystals was obtained relative to iron under hydrostatic press...

D. W. Langer R. A. Montalvo

1970-01-01

395

SDW in the 2D Compound CuFeTe2  

NASA Astrophysics Data System (ADS)

In a previous work (ICAME'97) we presented the Mössbauer results for a non-stoichiometric sample of the quasi-two-dimensional (2D) dichalcogenide CuFeTe2, where a Spin Density Wave (SDW) ground state with T SDW=256±15 K was proposed. Here we report the study of the magnetic and electric properties determined by magnetic susceptibility, Mössbauer spectroscopy and resistance measurements, of an almost stoichiometric sample prepared by the vertical Bridgman growth technique. The SDW behavior is supported by the results obtained by the following different techniques: Magnetic susceptibility: A magnetic transition is observed at T SDW=308 K with a Pauli paramagnetic behavior above this temperature. Mössbauer effect: The shape of the spectra and the thermal evolution of the hyperfine field are characteristic of the SDW's in quasi-2D systems. Electrical resistance: There is a metal semiconductor transition along the layers as the temperature decreases indicating the opening of a gap at the Fermi level.

Rivas, A.; Gonzalez-Jimenez, F.; D'Onofrio, L.; Jaimes, E.; Quintero, M.; Gonzalez, J.

2001-05-01

396

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

Microsoft Academic Search

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

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

1992-01-01

397

Effect of Pressure on the Curie Temperature of CrTe and MnSb Compounds of the Nickel Arsenide Type  

Microsoft Academic Search

The effect of the pressure on the Curie temperature of CrTe and MnSb compounds of the nickel arsenide were studied up to a pressure of 4,000 kg\\/cm2. The rate of change of the Curie temperature was -5.5× 10-3°C kg-1cm2 for CrTe and (-3.2± 0.5)×10-3°C kg-1cm2 for MnSb. From the result of the present experiment, the critical pressure and temperature to

Hideaki Ido; Takejiro Kaneko; Kazuo Kamigaki

1967-01-01

398

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

PubMed

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

Gao, Xue; Tang, Guangchao; Su, Xingguang

2012-04-13

399

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  

NASA Astrophysics Data System (ADS)

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.

Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.

2012-12-01

400

Crystal structure of {approx}RCu{sub 3}S{sub 3} and {approx}RCuTe{sub 2} (R=Gd-Lu) compounds  

SciTech Connect

The crystal structures of ternary compounds TbCu{sub 3}S{sub 3}, Dy{sub 1.06}Cu{sub 2.84}S{sub 3} (space group R3-bar), Ho{sub 0.67}Cu{sub 2}S{sub 2} (space group P3-bar m1), ErCu{sub 3}S{sub 3} (space group P3-bar 1c), Yb{sub 0.80}Cu{sub 1.60}S{sub 2}, Lu{sub 0.67}Cu{sub 2}S{sub 2}, TbCuTe{sub 2}, DyCuTe{sub 2}, Tm{sub 1.07}Cu{sub 0.78}Te{sub 2}, LuCuTe{sub 2} (space group P3-bar m1), Gd{sub 0.75}Cu{sub 1.74}Te{sub 2} (space group P3-bar 1m) were determined by means of X-ray single crystal diffraction. The S(Te) atoms are stacked in a close packed arrangement with the layers in the sequence AB. The R atoms are distributed over octahedral interstices whereas Cu atoms are located in tetrahedral interstices. Disorder of R and Cu atoms in studied chalcogenides is found. Crystal structure comparison showed that TbCuTe{sub 2} and DyCuTe{sub 2} crystallize as superstructure 2a Multiplication-Sign 2a Multiplication-Sign {sub 2}c to CaAl{sub 2}Si{sub 2} structure type, whereas Gd{sub 0.75}Cu{sub 1.74}Te{sub 2}, ErCu{sub 3}S{sub 3} and TbCu{sub 3}S{sub 3} (Dy{sub 1.06}Cu{sub 2.84}S{sub 3}) have superstructure {radical}3a Multiplication-Sign {radical}3a Multiplication-Sign nc with n=1, 2, 3. - Graphical abstract: In the series of the {approx}RCu{sub 3}S{sub 3} and {approx}RCuTe{sub 2} compounds the R and Cu atoms occupy disordered positions. The S(Te) atoms are stacked in a close packed arrangement with the layers in the sequence AB. Highlights: Black-Right-Pointing-Pointer The {approx}RCu{sub 3}S{sub 3} and {approx}RCuTe{sub 2} (R=Gd-Lu) crystallize with layered structure. Black-Right-Pointing-Pointer Superstructure {radical}3a Multiplication-Sign {radical}3a Multiplication-Sign nc (n=1, 2, 3) to CaAl{sub 2}Si{sub 2} structure type is found. Black-Right-Pointing-Pointer TbCuTe{sub 2} and DyCuTe{sub 2} crystallize as superstructure 2a Multiplication-Sign 2a Multiplication-Sign 2c. Black-Right-Pointing-Pointer Disorder of R and Cu atoms in studied chalcogenides is found.

Gulay, L.D. [Department of Ecology and Protection of Environment, Volyn National University, Voli Ave 13, 43009 Lutsk (Ukraine); Daszkiewicz, M., E-mail: m.daszkiewicz@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P. O. Box 1410, 50-950 WrocLaw (Poland); Shemet, V.Ya. [Department of Chemistry, Lutsk National Technical University, L'vivska str. 75, 43018 Lutsk (Ukraine)

2012-02-15

401

Beryllium chalcogenides for ZnSe-based light emitting devices  

Microsoft Academic Search

Beryllium-containing ZnSe-based compound semiconductors introduce substantial additional degrees of freedom for the design of wide gap II–VI heterostructures. An overview of the advantages of beryllium chalcogenides is given here. A variety of BeTe-ZnSe and BeMgZnSe-ZnSe structures has been fabricated by molecular beam epitaxy, and their structural, optical and electrical properties have been investigated. The main aspects are the lattice matching

A. Waag; F. Fischer; H.-J. Lugauer; Th. Litz; T. Gerhard; J. Nürnberger; U. Lunz; U. Zehnder; W. Ossau; G. Landwehr; B. Roos; H. Richter

1997-01-01

402

Effect of Surface Preparation on Mechanical Properties of Ni Contacts on Polycrystalline (Bi1- x Sb x )2(Te1- y Se y )3 Alloys  

NASA Astrophysics Data System (ADS)

We present a comparison of different surface preparation techniques for hot-extruded (Bi1- x Sb x )2(Te1- y Se y )3 alloys prior to Ni plating and their consequences on adhesion. The surface preparation is carried out by a relatively fast and well-controlled electrochemical etching procedure that provides morphologies with homogeneous flat surfaces on a scale of tens of micrometers. This procedure is not optimal for Ni metallization since it does not ensure enough roughness on the surface. Applying wet chemical etching with hypochlorite and nitric acid after the electrochemical etching changes the morphology, and the surface roughness increases, as evidenced by scanning electron microscopy and atomic force microscopy. Tensile tests carried out on n-type and p-type 1-mm-thick specimens, covered with a 12- ?m Ni layer followed by Sn-Pb soldered joints, confirm a significant improvement in the ultimate adhesion strength, with fracture occurring within the thermoelectric material. Use of this two-step surface treatment, after slicing and prior to metallization, leads to maximum adhesion strength of around 38 MPa for either type of thermoelectric material. These results are consistent with the morphological changes observed by scanning electron microscopy on the surface after chemical etching.

Kashi, S.; Keshavarz, M. K.; Vasilevskiy, D.; Masut, R. A.; Turenne, S.

2012-06-01

403

Modeling of the band structure of Bi2Se2Te crystallites deposited on Si and SiO2 substrates  

NASA Astrophysics Data System (ADS)

The band structure (BS) of crystalline Bi2Se2Te both pure as well as deposited on Si or SiO2 (substrates) was calculated for the first time. The calculation approach consists of an orthogonalization of the plane wave basis set with respect to the core-like orbitals and the application of the Perdew-Alder exchange-correlation scheme. In addition, a virtual crystal approach was applied. Experimental ellipsometric spectra were used as a criterion of the advantages of the different calculation techniques. The results of traditional one-electron methods of BS calculations, using norm-conserving pseudo-potential (NCPP), and full linear augmented plane wave (FLAPW), were compared with the experimental data. Better agreement with experiment is achieved when the NCPP wave functions are orthogonalized to the 4dBi core-like states. Concerning the LMTO and the FLAPW all-electron methods, only appropriate application of the virtual crystal approximation to these approaches produces results that are in agreement with ellipsometric experimental data.

Jankowska-Sahraoui, E.; Slezak, A.; Kimura, J.

2004-06-01

404

Magnetic hourglass dispersion and its relation to high-temperature superconductivity in iron-tuned Fe1+yTe0.7Se0.3  

NASA Astrophysics Data System (ADS)

High-temperature superconductivity remains arguably the greatest enigma of condensed matter physics. The discovery of iron-based high-temperature superconductors [1, 2] has renewed the importance of understanding superconductivity in materials susceptible to magnetic order and fluctuations. Intriguingly, they show magnetic fluctuations reminiscent of superconducting (SC) cuprates [3], including a ‘resonance’ and an ‘hourglass’-shaped dispersion [4], which provides an opportunity to gain new insights into the coupling between spin fluctuations and superconductivity. In this paper, we report inelastic neutron scattering data on Fe1+yTe0.7Se0.3 using excess iron concentration to tune between an SC (y = 0.02) and a non-SC (y = 0.05) ground state. We find incommensurate spectra in both the samples but discover that in the one that becomes SC, a constriction toward a commensurate hourglass-shape develops well above Tc. Conversely, a spin gap and a concomitant spectral weight shift happen below Tc. Our results imply that the hourglass-shaped dispersion is most likely a prerequisite for superconductivity, whereas the spin gap and shift of spectral weight are the consequences of superconductivity. We explain this observation by pointing out that an inward dispersion toward the commensurate wave vector is needed for the opening of a spin gap to lower the magnetic exchange energy and hence provide the necessary condensation energy for the SC state to emerge.

Tsyrulin, N.; Viennois, R.; Giannini, E.; Boehm, M.; Jimenez-Ruiz, M.; Omrani, A. A.; Dalla Piazza, B.; Rønnow, H. M.

2012-07-01

405

Tunable dielectric response of transition metals dichalcogenides MX2 (M=Mo, W; X=S, Se, Te): Effect of quantum confinement  

NASA Astrophysics Data System (ADS)

The first principle calculations have been performed to study the influence of number of layers on the dielectric properties of dichalcogenides of Mo and W for in-plan (E?c) as well as out-of-plan polarization (E?c). We have taken bulk, mono, bi, four and 6-layer setup for this study. The EELS shows significant red shift in the energies of ? plasmons, while prominent red shift has been found for the energies of (?+?) plasmons of all the studied materials by reducing the number of layers from bulk to monolayer limit. The ?s has been found to red shifted by 62.5% (66.3%), 48.5% (62.1%), 52.7% (66.2%), 61.7% (64.6%), 61.5% (66.7%) and 62.5% (70.5%) from bulk values of MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2 respectively for E?c(E?c) as one goes from bulk to monolayer of these materials. The interband transitions are found to remain independent of the number of layers, however their intensity decreases with decrease in the number of layers. The dielectric functions are highly anisotropic in low energy range and becomes isotropic in high energy range.

Kumar, Ashok; Ahluwalia, P. K.

2012-12-01

406

AB INITIO STUDY OF STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF MgxCd1-xX (X = S, Se, Te) ALLOYS  

NASA Astrophysics Data System (ADS)

This study describes structural, electronic and optical properties of MgxCd1-xX (X = S, Se, Te) alloys in the complete range 0?x ?1 of composition x in the zinc-blende (ZB) phase with the help of full-potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method within density functional theory (DFT). In order to calculate total energy, generalized gradient approximation (Wu-Cohen GGA) has been applied, which is based on optimization energy. For electronic structure calculations, the corresponding potential is being optimized by Engel-Vosko GGA formalism. Our calculations reveal the nonlinear variation of lattice constant and bulk modulus with different concentration for the end binary and their ternary alloys, which slightly deviates from Vegard's law. The calculated band structures show a direct band gap for all three alloys with increasing order in the complete range of the compositional parameter x. In addition, we have discussed the disorder parameter (gap bowing) and concluded that the total band gap bowing is substantially influenced by the chemical (electronegativity) contribution. The calculated density of states (DOS) of these alloys is discussed in terms of contribution from various s-, p- and d-states of the constituent atoms and charge density distributions plots are analyzed. Optical properties have been presented in the form of the complex dielectric function ?(?), refractive index n(?) and extinction coefficient k(?) as function of the incident photon energy, and the results have been compared with existing experimental data and other theoretical calculations.

Noor, N. A.; Shaukat, A.

2012-12-01

407

Conductance spectrum and superconducting gap structures observed in c-axis FeSe0.46Te0.54/Au junctions  

NASA Astrophysics Data System (ADS)

The electric transport properties of superconducting c-axis FeSe0.46Te0.54/Au (S/N) junctions, fabricated using pulsed laser deposition, have been investigated in the temperature range of 2 K to the superconducting transition temperature Tc (~ 13.5 K) and in the presence of applied magnetic fields from 0 to 9 T. A large zero bias conductance peak has always been observed in every conductance spectrum of several batches of junctions. In addition, we have found several gap-like features. Using the extended BTK theory with the currently favored nodeless S+/--wave symmetry, our conductance spectrum can be reproduced quite well in the low bias range with ?1 = 4 meV and ?2 = 6 meV at 2 K. However, the experimental conductance spectrum is substantially below the one calculated in the high bias range. Furthermore, there is a conductance minimum at approximately 20 meV, which may be the reason for the discrepancy.

Shen, Y. T.; Li, Y. S.; Lin, K. C.; Wu, M. K.; Chi, C. C.

2013-09-01

408

External temperature and pressure effects on thermodynamic properties and mechanical stability of yttrium chalcogenides YX (X=S, Se and Te)  

NASA Astrophysics Data System (ADS)

The full potential linearized augmented plane wave method within the framework of density functional theory is employed to investigate the structural, thermodynamic and elastic properties of the yttrium chalcogenides (YX: X=S, Se, and Te) in their low-pressure phase (Fm3¯m) and high-pressure phase (Pm3¯m). The exchange-correlation potential is treated with the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE). Temperature dependence of the volume and both adiabatic and isothermal bulk moduli is predicted for a temperature range from 0to1200K for the both phases of the herein considered materials. Furthermore, we have analyzed the thermodynamic properties such as the heat capacities, CV and CP, thermal expansion, ?, and Debye temperature, ?D, under variable pressure and temperature. We have calculated the isothermal elastic constants CijT of the YX monochalcogenides in both NaCl-B1 and CsCl-B2 phases at zero pressure and a temperature range 0-1200K. The results show that rare earth yttrium monochalcogenides are mechanically stable at high temperature. The elastic anisotropy of all studied materials in the two phases has been studied using three different methods.

Seddik, T.; Khenata, R.; Bouhemadou, A.; Guechi, N.; Sayede, A.; Varshney, D.; Al-Douri, Y.; Reshak, A. H.; Bin-Omran, S.

2013-11-01

409

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

410

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

411

Liquid-Phase Syntheses and Material Properties of Two-Dimensional Nanocrystals of Rare Earth-Selenium Compound Containing Planar Se Layers: RESe2 Nanosheets and RE4O4Se3 Nanoplates.  

PubMed

Synthesis of diverse two-dimensional nanostructures with unique material properties is of current interest and multidisciplinary importance but remains a challenge for trivalent rare earth (RE)-selenium (Se) compounds because of the weak affinity between hard rare earth cations and soft selenium anions. In this article, for the first time, we report a mild solution approach toward a series of two-dimensional trivalent RE-selenium compound nanocrystals, namely RESe2 nanosheets (RE = La to Nd, for EuSe2, nanobars were obtained) and RE4O4Se3 nanoplates (RE = Nd, Sm, Gd to Ho), under a high chemical potential of selenium obtained by activating SeO2 powder with oleylamine in high boiling point organic solvents. Both kinds of nanocrystals contain Se with -1 valence in planar Se layers, allowing for a great variability in their crystal structures. Satellite diffraction peaks were observed in the electron diffraction pattern of LaSe2 nanosheets, indicating the presence of Peierls distortion in the Se layers. In the RE4O4Se3 nanoplates, the interaction between Se(2-) ions and [Se-Se](2-) dumbbells in the Se layers increases when the radii of the RE(3+) ions decrease along the lanthanide series, resulting in a narrower optical band gap (from 1.96 to 1.73 eV). The LaSe2 nanosheet films fabricated by drop-casting exhibited good electrical conductivity at room temperature (about 1 ?·cm(-1)). Further, the RE4O4Se3 nanoplates showed very high light extinction capacity in the visible region (extinction coefficient ?i: 4.4 × 10(5) cm(-1) for Nd4O4Se3, and 3.1 × 10(5) cm(-1) for Gd4O4Se3), comparable to that (5 × 10(5) cm(-1)) of CuInS2 commonly used in solar cells. PMID:23672182

Gu, Jun; Zhao, Ze-Qiong; Ding, Yi; Chen, Hong-Liang; Zhang, Ya-Wen; Yan, Chun-Hua

2013-05-22

412

Electronic structure of lanthanum copper oxychalcogenides LaCuOCh (Ch=S, Se, Te) by X-ray photoelectron and absorption spectroscopy  

SciTech Connect

X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) have been applied to examine the electronic structures of lanthanum copper oxychalcogenides LaCuOCh (Ch=S, Se, Te), whose structure has been conventionally viewed as consisting of nominally isolated [LaO] and [CuCh] layers. However, there is evidence for weak La-Ch interactions between these layers, as seen in small changes in the satellite intensity of the La 3d XPS spectra as the chalcogen is changed and as supported by band structure calculations. The O 1s and Cu 2p XPS spectra are insensitive to chalcogen substitution. Lineshapes in the Cu 2p XPS spectra and fine-structure in the Cu L- and M-edge XANES spectra support the presence of Cu{sup +} species. The Ch XPS spectra show negative BE shifts relative to the elemental chalcogen, indicative of anionic species; these shifts correlate well with greater difference in electronegativity between the Cu and Ch atoms, provided that an intermediate electronegativity is chosen for Se. - Graphical abstract: The presence of anionic chalcogen atoms in LaCuOCh is supported by the Ch binding energies, which undergo negative shifts proportional to the polarity of the Cu-Ch bonds. Highlights: > La 3d XPS confirms La-Ch interlayer interactions between [LaO] and [CuCh] layers. > O 1s and Cu 2p XPS are insensitive to chalcogen substitution. > Cu XANES spectra support the presence of Cu{sup +} species. > Negative shifts in Ch binding energies imply anionic chalcogen atoms.

Rudyk, Brent W.; Blanchard, Peter E.R.; Cavell, Ronald G. [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Mar, Arthur, E-mail: arthur.mar@ualberta.ca [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada)

2011-07-15

413

Near-infrared emitting CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots: synthesis and bright luminescence  

PubMed Central

We present how CdTe0.5Se0.5 cores can be coated with Cd0.5Zn0.5S shells at relatively low temperature (around 200°C) via facile synthesis using organic ammine ligands. The cores were firstly fabricated via a less toxic procedure using CdO, trioctylphosphine (TOP), Se, Te, and trioctylamine. The cores with small sizes (3.2-3.5 nm) revealed green and yellow photoluminescence (PL) and spherical morphologies. Hydrophobic core/shell CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots (QDs) with tunable PL between green and near-infrared (a maximum PL peak wavelength of 735 nm) were then created through a facile shell coating procedure using trioctylphosphine selenium with cadmium and zinc acetate. The QDs exhibited high PL efficiencies up to 50% because of the formation of a protective Cd0.5Zn0.5S shell on the CdTe0.5Se0.5 core, even though the PL efficiency of the cores is low (?1%). Namely, the slow growth process of the shell plays an important role for getting high PL efficiencies. The properties of the QDs are largely determined by the properties of CdTe0.5Se0.5 cores and shells preparation conditions such as reaction temperature and time. The core/shell QDs exhibited a small size diameter. For example, the average diameter of the QDs with a PL peak wavelength of 735 nm is 6.1 nm. Small size and tunable bright PL makes the QDs utilizable as bioprobes because the size of QD-based bioprobes is considered as the major limitation for their broad applications in biological imaging.

2012-01-01

414

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

415

Role of van der Waals corrections for the PtX2 (X=O, S, Se) compounds  

NASA Astrophysics Data System (ADS)

Dispersion (van der Waals) forces play an important role in determining the structural properties of the systems where dispersion is crucial, for example, layerlike crystals (CdI2 type). Thus, to contribute to the understanding of the role of van der Waals (vdW) corrections for the PtX2 (X=O, S, Se) compounds, we report a density functional theory (DFT) investigation within nonlocal vdW corrections for the atomic structure and electronic properties of bulk PtX2. From our calculations, we identified the lowest energy structures, CaCl2 type for PtO2 and CdI2 type for both PtS2 and PtSe2, i.e., CdI2 type is not the lowest energy structure for PtO2. We reported the structural changes for higher energy PtX2 systems and the changes in the stability order compared with plain DFT-PBE calculations. The structural changes induced by vdW corrections affects the electronic structure of the layered CdI2-type structures (PtS2 and PtSe2), where a metallic behavior is obtained in contrast to PBE calculations, which yields an energy separation between the unoccupied and occupied states.

Piotrowski, Maurício J.; Nomiyama, Ricardo K.; Da Silva, Juarez L. F.

2013-08-01

416

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

417

Superconductivity in the misfit compound of (LaSe)1.14(NbSe2): STM/S, calorimetric and magnetization studies  

NASA Astrophysics Data System (ADS)

(LaSe)1.14(NbSe2) is a low temperature superconductor with Tc around 1.2 K belonging to the family of the lamellar chalcogenides. Electron transfer from the LaSe to the NbSe2 slab results in a natural layered system of the insulating LaSe and (super) conducting NbSe2 sheets. In our previous investigations of the anisotropic transport [P. Szabó et al., Phys. Rev. Lett. 86, 5990 (2001)] indications have been found that this system behaves as a stack of Josephson-coupled superconducting NbSe2 sheets separated by insulating LaSe layers. We test this hypothesis by STM/S measurements at subkelvin temperatures and in magnetic fields. Superconducting energy gap obtained by STM opens at the same temperature and field where the interlayer resistivity starts to increase before drop to zero value. Before any conclusions are made homogeneity of the superconducting parameters is to be tested. STM indicates large areas without any gap but calorimetric measurements have shown the bulk superconductivity and magnetization revealed extremely low pinning.

Samuely, P.; Szabo, P.; Kacmarcik, J.; Pribulova, Z.; Samuely, T.; Rodrigo, J. G.; Marcenat, C.; Klein, T.; Cario, L.

2013-03-01

418

Effect of the framework flexibility on the centricities in centrosymmetric In2Zn(SeO3)4 and noncentrosymmetric Ga2Zn(TeO3)4.  

PubMed

The solid-state syntheses, crystal structures, and characterization of two stoichiometrically similar quaternary mixed metal selenite and tellurite, In(2)Zn(SeO(3))(4) and Ga(2)Zn(TeO(3))(4), respectively, are reported. While In(2)Zn(SeO(3))(4) crystallizes in the centrosymmetric monoclinic space group P2(1)/n (No. 14) with a = 8.4331(7) Å, b = 4.7819(4) Å, c = 14.6583(13) Å, and ? = 101.684(6)°, Ga(2)Zn(TeO(3))(4) crystallizes in the non-centrosymmetric space group I-43d (No. 220) with a = b = c = 10.5794(8) Å. In(2)Zn(SeO(3))(4) exhibits a two-dimensional crystal structure consisting of distorted InO(6) octahedra, ZnO(6) octahedra, and SeO(3) polyhedra. Ga(2)Zn(TeO(3))(4) shows a three-dimensional framework structure that is composed of GaO(4) or ZnO(4) and TeO(3) polyhedra. An effect of the framework flexibility on the space group centricity is discussed. The SHG (second harmonic generation) efficiency of noncentrosymmetric Ga(2)Zn(TeO(3))(4), using 1064 nm radiation, is similar to that of KH(2)PO(4) (KDP) and is not phase-matchable (Type 1). Complete characterizations including infrared spectroscopy and thermal analyses for the reported materials are also presented, as are dipole moment calculations. PMID:22793171

Lee, Dong Woo; Bak, Dan-bee; Kim, Saet Byeol; Kim, Jiwon; Ok, Kang Min

2012-07-02

419

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

420

Electrical Conductivity and Dielectric Properties of Se85Te15-x Sb x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) Thin Films  

NASA Astrophysics Data System (ADS)

The alternating-current (ac) conductivity and dielectric properties of Se85Te15-x Sb x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) films are reported in this work. Thin films were deposited by thermal evaporation under base pressure of 10-5 Torr. The films were well characterized by x-ray diffraction, differential scanning calorimetry, and energy-dispersive x-ray spectroscopy. The ac conductivity and dielectric properties have been investigated for the studied films in the temperature range from 297 K to 333 K and over the frequency range from 102 Hz to 105 Hz. The experimental results indicate that the ac conductivity ?_{{ac}} (? ) and the dielectric constant depend on temperature, frequency, and Sb content. The frequency dependence of ?_{{ac}} (? ) was found to be linear with a slope lying very close to unity and is independent of temperature. This behavior can be explained in terms of correlated barrier hopping between centers forming intimate valence-alternation pairs. The density of localized states N(E F) at the Fermi level is estimated. The activation energy Updelta E(? ) was found to decrease with increasing frequency. The dielectric constant ? 1 and dielectric loss ? 2 were found to decrease with increasing frequency and increased with increasing temperature over the ranges studied. The maximum barrier height W m for the studied films was calculated from an analysis of the dielectric loss ? 2 according to the Guintini equation. The values agree with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The variation of the studied properties with Sb content was also investigated.

Hegab, N. A.; Fadel, M.; Yahia, I. S.; Salem, A. M.; Farid, A. S.

2013-10-01

421

Surface Properties of II-VI Compounds  

Microsoft Academic Search

Single crystals of ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe have been cleaved in ultrahigh vacuum (p<=2×10-11 Torr) and measurements have been made of photoemission, contact potential, and surface photovoltage. In some cases, metal contacts were deposited onto the clean surfaces and the Schottky barrier heights determined. Photoelectric thresholds were similar for compounds having the same chalcogen, being higher

Robert K. Swank

1967-01-01

422

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

423

?-phonons in ZnSe(C2H8N2)1/2 and ZnTe(C2H8N2)1/2 hybrid materials  

NASA Astrophysics Data System (ADS)

Artificially synthesized organic/inorganic hybrid materials with semiconductor component are of growing interest due to potential applications in flexible microelectronics. Among them, hybrid ZnSe(C2H8N2)1/2 and ZnTe(C2H8N2)1/2 are two examples capable of tuning electronic and optical properties on a wide range. Engineering of these materials is difficult without deeper understanding of their fundamental physical characteristics, including electronic band structure and phonon spectra. Recent experimental investigations [1] performed on ?--ZnTe(C2H8N2)1/2 samples and showed multiple sharp phonon modes in frequencies very different from the LO(?) phonon of the binary semiconductor ZnTe. Motivated by these results, we have performed density-functional calculations of the ? phonon modes for both ?-- and ?--phases of ZnSe(C2H8N2)1/2 and ZnTe(C2H8N2)1/2. We found, in particular, that light hydrogen atoms not only define the high frequency motion (1500--3000 cm-1), but also dominate in some low frequency modes in the region of 100--150 cm-1 where they move mostly perpendicular to the superlattice stacking direction. Based on symmetry of the materials, the Raman modes at the ? point are identified. [1] X. Huang, J. Li, Y. Zhang, and A. Mascarenhas, J. Am. Chem. Soc. 125, 7049 (2003).

Naumov, Ivan; Fu, Huaxiang

2007-03-01

424

Transport and optical properties of heavily hole-doped semiconductors BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2}  

SciTech Connect

Experimental and theoretical studies of the electronic and optical properties of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2} are reported. Experimental data include the electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, and lattice constants for T{<=}300K, and optical transmission and diffuse reflectance data at room temperature. Nominally stoichiometric, polycrystalline samples form with hole concentrations inferred from Hall measurements of 2x10{sup 18} and 5x10{sup 19} cm{sup -3} near room temperature for the selenide and telluride, respectively. The corresponding mobilities are near 15 cm{sup 2} V{sup -1} s{sup -1} for both materials. Optical measurements reveal a transition near 1.8 eV in BaCu{sub 2}Se{sub 2}, while no similar feature was observed for BaCu{sub 2}Te{sub 2}. First principles calculations indicate both materials are direct or nearly direct gap semiconductors with calculated gaps near 1.0 eV and 1.3 eV for the telluride and selenide, respectively, and predict weak absorption below about 2 eV. Transport properties calculated from the electronic structure are also presented. - Graphical abstract: Combined