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1

Ultra-stable nanoparticles in A(II)B(VI), (A(II) = Cd, Zn; BVI, = S, Se, Te) compounds.  

PubMed

Laser ablation on binary A(II)B(VI) compounds exhibits in time-of-flight mass spectra abundant peaks at stoichiometric (A(II)B(VI)),n with n = 13, 19, 33 and 34 measured on bulk powders of CdSe, CdS, CdTe, ZnS and ZnSe. Investigation on solution grown nanometer size particles of CdSe shown an existence of ultra-stable stoichiometric clusters (CdSe)13, (CdSe)19, (CdSe)33, (CdSe)34 and (CdSe)48. This set of n has not been predicted as particularly stable particles in previous bulk fragment models based on either zinc-blende or wurtzite, and a different type of structures is required to explain our experimental results. Present investigation shows that nanoparticles formed in vacuum as magic numbers above are found in solution as preferentially grown species in CdSe, and possibly in other A(II)B(VI). It is suggested that the high stability of the observed magic clusters originates from their specific structure as endohedral binary fullerenes, supposedly. These molecular-like particles composed of few tens of atoms lie between atom and solid, and exhibit novel materials functions not realizable in the bulk. PMID:19435089

Romanyuk, V R; Dmitruk, I M; Barnakov, Yu A; Belosludov, R V; Kasuya, A

2009-03-01

2

Comparative study of E?N (E=Se/Te) intramolecular interactions in organochalcogen compounds using density functional theory.  

PubMed

The intramolecular E?N (E=Se, Te) interactions between the selenium (and tellurium) and the nitrogen atom in four series of o-substituted organochalcogen compounds have been analyzed using density functional theory. The nature and the strength of this interactions and their dependence on substituents and the rigidity are predicted using B3LYP/6-31G(d)/LanL2DZ method. The strength of these E?N interactions are found to be dependent on the nature of EX (X=Cl, Br, I, SPh, CH2Ph; Ph: Phenyl) acceptor orbitals and follows the order I>Br>Cl>SPh>CH2Ph. The Natural Bond Orbital (NBO) analysis using DFT methods points to nN??E-X electron delocalization as the key contributing factor toward E?N nonbonding interactions. Both NBO and AIM methods suggest that the intramolecular interaction in these compounds is dominantly covalent in nature. Studies on the effect of solvent on the E?N interactions show that polar solvent stabilizes these interactions by shortening the E?N distances. PMID:24412286

Panda, Arunashree; Behera, Raghu Nath

2014-03-30

3

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

4

Fermi level tuning and weak localization/weak antilocalization competition of bulk single crystalline Bi2?xSbxSe2Te compounds  

NASA Astrophysics Data System (ADS)

From the investigation of the electrical transport properties of single crystalline Bi2?xSbxSe2Te (x = 0.0, 0.6, 0.8, 1.0, 1.2 and 1.4) compounds, we observed a systematic change of the Fermi level from n-type metallic (x = 0.0 and 0.6) or small-gap semiconducting (x = 0.8) to p-type semiconducting (x = 1.0) and metallic (x = 1.2 and 1.4), respectively, with increasing Sb-substitution concentration based on temperature-dependent electrical resistivity ?(T) and Hall resistivity ?xy(H) measurements, respectively. The parent compound Bi2Se2Te exhibits linear negative magnetoresistance at low magnetic fields (H ? 1 T) by weak localization. The intermediate doped compounds of x = 0.8 and 1.0 showed weak antilocalization (WAL) and weak localization (WL) crossover behavior from the field-dependent magnetoresistance measurements at low temperatures. From the HikamiLarkinNagaoka analysis of the compounds (x = 0.8 and 1.0), we found that there is a competing behavior between WL and WAL in terms of Sb-doping and magnetic field strength.

Shon, Won Hyuk; Rhyee, Jong-Soo

2015-01-01

5

Fermi level tuning and weak localization/weak antilocalization competition of bulk single crystalline Bi2-xSbxSe2Te compounds.  

PubMed

From the investigation of the electrical transport properties of single crystalline Bi2-xSbxSe2Te (x=0.0, 0.6, 0.8, 1.0, 1.2 and 1.4) compounds, we observed a systematic change of the Fermi level from n-type metallic (x=0.0 and 0.6) or small-gap semiconducting (x=0.8) to p-type semiconducting (x=1.0) and metallic (x=1.2 and 1.4), respectively, with increasing Sb-substitution concentration based on temperature-dependent electrical resistivity ?(T) and Hall resistivity ?xy(H) measurements, respectively. The parent compound Bi2Se2Te exhibits linear negative magnetoresistance at low magnetic fields (H?1T) by weak localization. The intermediate doped compounds of x=0.8 and 1.0 showed weak antilocalization (WAL) and weak localization (WL) crossover behavior from the field-dependent magnetoresistance measurements at low temperatures. From the Hikami-Larkin-Nagaoka analysis of the compounds (x=0.8 and 1.0), we found that there is a competing behavior between WL and WAL in terms of Sb-doping and magnetic field strength. PMID:25524919

Shon, Won Hyuk; Rhyee, Jong-Soo

2015-01-21

6

Temperature-dependent nuclear magnetic resonance in CuInX2 (X=S,Se,Te) chalcopyrite-structure compounds  

Microsoft Academic Search

The NMR spectra of 63Cu and 115In in CuInS2, CuInSe2, and CuInTe2 have been measured between room temperature and 550C. The effects of motional narrowing and of phase transitions on the shape and width of the absorption spectra were evaluated. In all three compounds, the absorption signal of 63Cu shows motional narrowing. For Cu1.00In1.00S2.00 the mean jump frequency of the

K. D. Becker; Sigurd Wagner

1983-01-01

7

Matrix and impurity element distributions in CdHgTe (CMT) and (Cd,Zn)(Te,Se) compounds by chemical analysis  

Microsoft Academic Search

This review describes several of the main techniques used to determine matrix element distributions and those which can provide a survey of impurity levels and assess deliberate doping concentrations in CdxHg1 ? xTe and CdTe-based substrate materials. The most widely used method to non-destructively determine x is that of Fourier transform infrared (FTIR) spectrometry and lateral x variations in current

P. Capper; E. S. O'Keefe; C. Maxey; D. Dutton; P. Mackett; C. Butler; I. Gale

1996-01-01

8

Temperature-dependent nuclear magnetic resonance in CuInX2 (X=S,Se,Te) chalcopyrite-structure compounds  

NASA Astrophysics Data System (ADS)

The NMR spectra of 63Cu and 115In in CuInS2, CuInSe2, and CuInTe2 have been measured between room temperature and 550C. The effects of motional narrowing and of phase transitions on the shape and width of the absorption spectra were evaluated. In all three compounds, the absorption signal of 63Cu shows motional narrowing. For Cu1.00In1.00S2.00 the mean jump frequency of the Cu+ ions, ?(Cu+), is 21013exp[-(1.25+/-0.10 eV)kT] s-1. For both CuInSe2 and CuInTe2, ?(Cu+) is about 3103 s-1 at 350C. In copper-deficient Cu0.96In1.02S2.00 no motional narrowing of the 63Cu absorption was observed up to 550C. However, the 63Cu line shape in CuInS2 depends on the copper-to-indium ratio. A line-shape analysis as a function of composition shows that, at 450C, CuInS2 exists in the composition range between Cu1.00In1.00S2 and Cu0.85In1.05S2. For specimens with [Cu]/[In]>1, Cu2S contributes to the absorption signal. In a separate study of the 63Cu absorption in Cu2S, the hexagonal-to-cubic transformation was observed at 440C. The activation energy for ?(Cu+) in cubic Cu2S is 0.15 eV. The phase-transformation temperatures for the three CuInX2 compounds (where X is a group-VI element) were determined by differential thermal analysis. A previously unnoticed transformation was found in CuInSe2 at 665C. Finally, the quadrupole coupling constant ?q (63Cu) of a number of CuZX2 compounds (where Z is a group-III element) is shown to be a linear function of the tetragonal distortion parameter ?=2-ca with |?q|=1.50+90? MHz. The value for ?=0 is of the same order of magnitude as the result of a simple model of a point charge on a cubic lattice.

Becker, K. D.; Wagner, Sigurd

1983-05-01

9

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

10

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

11

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

NASA Astrophysics Data System (ADS)

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

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

1987-10-01

12

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

13

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

NASA Astrophysics Data System (ADS)

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

Harman, Theodore C.

2000-03-01

14

The influence of the substitution of Te for Se on the photoconductive properties of In2Se3-xTe3x thin films  

Microsoft Academic Search

Thin films of In2Se3-3xTe3x compounds have been synthesized by annealing, in constant argon flow, a multilayer structure of indium, selenium and tellurium, sequentially deposited. The films have been characterized by x-ray diffraction (XRD), electron microprobe analysis and x-ray photoelectron spectroscopy (XPS) measurements. These studies have shown that the thin films after annealing are stoichiometric with In at.%\\/(Se + Te) at.%

H. El Maliki; S. Marsillac; J. C. Bernde; E. Faulques; J. Wery

2001-01-01

15

Dynamics of exciton recombination in low-dimensional heterostructures of IIVI semiconductors ( CdTe CdMnTe , ZnCdSe ZnSe )  

Microsoft Academic Search

The present knowledge of exciton dynamics in quantum-well structures of IIVI semiconductors is still rather limited. Exciton properties related to an increased density of interface defects in the heterostructures of IIVI compounds are discussed. The influence of an interface morphology on defect-related recombination processes in quantum-well structures of CdTeCdMnTe and ZnCdSeZnSe is analyzed. We show that the formation scenario of

M. Godlewski

1998-01-01

16

Near-infrared emission spectra of TeS, TeSe and Te2  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

17

Photoluminescence from Cd(Se,Te) quantum dots in a ZnSe matrix  

NASA Astrophysics Data System (ADS)

We report on the photoluminescence (PL) and PL excitation studies of CdSe/ZnSe quantum dots (QDs) grown by molecular beam epitaxy using super-strained CdTe fractional monolayer deposition prior to the CdSe growth. We have shown that introduction of CdTe stressor initiates the formation of a dense array of Cd(Se,Te) QDs and demonstrated the co-existence of type-I and type-II structures within the dot sheet.

Lyublinskaya, O. G.; Sedova, I. V.; Sorokin, S. V.; Nekrutkina, O. V.; Toropov, A. A.; Ivanov, S. V.

2006-03-01

18

Electric Properties of the ITO-ZnSe-CdTe-ZnTe Photo Sensor Cell  

NASA Astrophysics Data System (ADS)

In this report, the ITO-ZnSe-CdTe-ZnTe cell was used for a photo sensor. ITO(Indium Tin Oxide) was used on the glass substrates as the transparent electrode, and ZnSe and CdTe layer were prepared by the vacuum deposition on this ITO, and were treated with heat at 560C. The ZnSe-CdTe sample that CdTe layer was prepared on ITO-ZnSe(0.1?m) substrate has not high-density level at the junction surface, and the CdTe layer with little lattice imperfection can be prepared. In spite of improvement in the crystalline form, this ZnSe-CdTe sample cell has not sufficient electric current response for the light absorption of CdTe layer. In order to increase the electric current response for the light, ZnTe layer was prepared by the vacuum deposition on the ZnSe-CdTe layer, and were treated with heat at 560C. This ITO-ZnSe-CdTe-ZnTe photo sensor cell has sufficient electric current response for the visible light and near infrared light. It is presumed that the electric filed in the CdTe layer is enough to drive the cell.

Ichibakase, Tsuyoshi

19

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

PubMed

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

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

2014-01-01

20

Optical Characterization of Bulk ZnSeTe Solid Solutions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

21

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

PubMed

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

Yang, Ping

2014-04-01

22

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-Brnstein, 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.

23

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

PubMed

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

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

2005-12-01

24

Optical Characterization of Bulk ZnSeTe Solid Solutions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

25

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

PubMed

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

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

2011-09-14

26

Amorphous-Te-mediated self-organization of CdSe/ZnSe nanostructures  

NASA Astrophysics Data System (ADS)

Deposition of amorphous Te on a strained epitaxial CdSe layer at room temperature, and its subsequent desorption in the temperature range of 200-310 C results in novel morphological reorganization of the CdSe surface. Dashes, long chains of quantum dots (QDs), and lateral QD molecules have been observed in atomic force microscopy images of CdSe surfaces, after such a treatment. Te admixture of the QD-layer may not be ruled out. The morphology of the CdSe (Te) surface is strongly governed by the thickness of the deposited amorphous Te layer, but shows almost no dependence on the temperature at which this layer is desorbed. The observed self-ordering of nanostructures over length scales of 600 nm by this process strongly suggests that Te leads to an enormous enhancement of adatom migration. While at low temperature, photoluminescence (PL) consists of emissions from localized excitons in both the observed large QD-based nanostructures and a residual inhomogeneous CdSe(Te) layer, at room temperature the entire contribution is apparently from the former. This leads to a redshift of the spectra, with increase in temperature from 7 to 300 K, by as much as 600 meV.

Mahapatra, S.; Margapoti, E.; Worschech, L.; Forchel, A.; Brunner, K.

2007-04-01

27

Optical Properties of PbTe and PbSe  

SciTech Connect

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

Ekuma, Chinedu E [Louisiana State University; Singh, David J [ORNL; Moreno, Juana [University of North Dakota, Grand Forks; Jarrell, Mark [Louisiana State University

2012-01-01

28

Electric Field Analysis of the ITO-ZnSe-CdTe Photo Sensor Cell  

NASA Astrophysics Data System (ADS)

In this report, the ITO-ZnSe-CdTe cell and the ITO-ZnSe-CdTe-ZnTe cell as a photo sensor were analyzed comparatively with the use of the electric field analysis from spectral sensitivity data. From analysis, it is presumed that there is the depletion layer from the junction surface to 0.194?m in zone of CdTe layer at the ITO-ZnSe-CdTe cell. On the other hand, the ITO-ZnSe-CdTe-ZnTe cell has the depletion layer in whole region of CdTe layer. It is presumed that both ZnSe layer and ZnTe layer form the depletion layer of CdTe layer in the ITO-ZnSe-CdTe-ZnTe cell. The CdTe layer, which has 0.8?m in thickness, absorbs all of visible wavelengths, and both of two cells have CdTe layer 0.8?m in thickness. Luminous sensitivity of the ITO-ZnSe-CdTe cell is much less than luminous sensitivity of the ITO-ZnSe-CdTe-ZnTe cell. It is presumed that differences of the luminous sensitivity between those two cells arise from differences of the electric field distribution. From this analysis, it is presumed that the structure of ZnSe-CdTe-ZnTe makes depletion layer in whole region of CdTe layer.

Ichibakase, Tsuyoshi

29

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

SciTech Connect

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

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

2013-12-16

30

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

PubMed Central

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

Meinerz, Daiane Francine; Allebrandt, Josiane; Mariano, Douglas O.C.; Waczuk, Emily P.; Soares, Felix Antunes

2014-01-01

31

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

E-print Network

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

Osswald, Sebastian

32

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

33

Xerographic properties of a Se:Te photoconductors  

SciTech Connect

In this paper due to their desirable spectral response, amorphous Se:Te alloys are widely used as commercial xerographic photoreceptor materials. It is shown that the dark decay of the electrostatic surface potential on a corona-charged a-Se:Te alloy photoreceptor occurs via electric field-enhanced xerographic depletion discharge (FEXDD) in which Polle-Frenkel-assisted thermal emission of holes from deep mobility-gap states and their subsequent sweep out generates a negative bulk space charge. A theoretical expression is derived for the dependence of the xerographic depletion time t{sub d} and the time required for the surface potential to decay to half its value t{sub 1/2} on the initial charging voltage V{sub 0}. Experimental data show good agreement with the theory and enable the Poole-Frenkel coefficient for a-Se:Te to be evaluated. Furthermore, it is shown that at the highest charging voltages, t{sub 1/2} actually decreases with V{sub 0}, which is directly attributable to the FEXDD process.

Kasap, S.O. (Dept. of Electrical Engineering, Univ. of Saskatchewan, Saskatoon S7N 0W0 (CA))

1991-07-01

34

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

SciTech Connect

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

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

2012-11-15

35

Time-resolved photoluminescence measurements of CdSe\\/ZnSe and CdTe\\/ZnTe self-assembled quantum dots  

Microsoft Academic Search

We use time-resolved photoluminescence to probe the dynamics of excitons confined to CdTe\\/ZnTe and CdSe\\/ZnSe self-assembled quantum dots (SAQD) at 6K. When QDs are excited non-resonantly just below the barriers, we directly measure the radiative lifetime of the excitons, which can be as long as 4 ns (<1.5ns) for CdSe (CdTe) QDs. A tunable 2 ps laser pulse with a

N. Mukolobwiez; L. M. Robinson; H. E. Jackson; L. M. Smith; S. Lee; M. Dobrowolska; J. Furdyna; S. Mackowski; G. Karczewski

2002-01-01

36

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

37

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

38

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

39

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

40

Optical properties of highly resistive Bi2Te2Se  

NASA Astrophysics Data System (ADS)

Topological insulators are characterized by strong spin-orbit coupling, producing metallic surface states while the bulk remains insulating. Experimental observations of surface states in transport and optical measurements have been obstructed by bulk contributions due to sample defects, placing the Fermi level in the bulk energy gap. Bi2Te2Se (BTS), a three-dimensional topological insulator, has recently been shown to exhibit a bulk resistivity larger than any other topological insulator measured to date. However, quantum oscillations are still observed, and attributed to the surface states. In this talk I will present the optical properties of BTS, obtained by broadband FTIR spectroscopy combined with ellipsometry, over a range of 20 - 45,000 cm-1, as well as the Raman spectrum of BTS.

Reijnders, Anjan; Zhao, S. Y. F.; Niemeyer, Louise; Bouskila, Raphael; Cho, H. J.; Mohajerani, Seyedyara; Sandilands, Luke J.; Cava, Robert J.; Burch, Kenneth S.

2012-02-01

41

Magnetic susceptibility study of Ce3+ in PbCeA (A=Te, Se, S)  

NASA Astrophysics Data System (ADS)

The magnetic susceptibility of Pb1-xCexA (A=S, Se and Te) crystals with Ce3+ concentrations 0.006?x?0.036 was investigated in the temperature range from 2 K to 300 K. The magnetic susceptibility data was found to be consistent with a 2F5/2 lowest manifold for Ce3+ ions with a crystal-field splitting ?=E(?8)-E(?7) of about 340 K, 440 K and 540 K for Pb1-xCexTe, Pb1-xCexSe, and Pb1-xCexS, respectively. For all the three compounds the doublet ?7 lies below the ?8 quadruplet which confirms the substitution of Pb2+ by Ce3+ ions in the host crystals. The observed values for the crystal-field splitting are in good agreement with the calculated ones based on the point-charge model. Moreover, the effective Land factors were determined by X-band (?9.5 GHz), electron paramagnetic measurements (EPR) to be g=1.333, 1.364, and 1.402 for Ce ions in PbA, A = S, Se and Te, respectively. The small difference with the predicted Land factor g of 10/7 for the ?7 (J=5/2) ground state was attributed to crystal-field admixture.

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

2012-09-01

42

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

43

Peculiarities of defect formation processes in ZnSe crystals with isovalent Te impurity  

Microsoft Academic Search

Using quasi-chemical reaction methods, we calculated concentrations of equilibrium defects for zinc selenide crystals doped with ZnSeTe during the growth process and with ZnSe:Te from the vapour phase. It was found that the main irradiation peak at m 1.7 eV for ZnSeTe samples is defined with the associates formed by single-charge intrinsic defects - positive interstitial zinc atoms and its

Victor P. Makhniy; Irina V. Tkachenko; Petro M. Gorley; Paul P. Horley; Vitalii K. Dugaev; Joseph Barna; Maria Manuela Vieira; Witold Dobrowolski

2006-01-01

44

Interrelation of superconductivity and magnetism in FeSe1-xTex compounds. Pressure effects  

NASA Astrophysics Data System (ADS)

The effect of isotropic pressures P up to 5 kbar on the superconducting transition temperature Tc of the FeSe1-xTex system (x = 0, 0.85, 0.88, 0.90) is studied. For the first time, a change in the sign of the effect of pressure on Tc on going from FeSe to the tellurium-rich alloys is observed. This makes it possible to specify more precisely the form of the dependence of the pressure derivative dTc/dP on composition in this system. This dependence is compared with first principles calculations of the electron structure and magnetism of FeSe, FeTe, and FeSe0.5Te0.5 as functions of pressure, as well as with our earlier experimental data on the effect of pressure on the magnetic susceptibility of the normal state in FeSe and FeTe. This comparison is indicative of a competitive interrelationship between superconductivity and magnetism in tellurium rich FeSe1-xTex compounds.

Panfilov, A. S.; Pashchenko, V. A.; Grechnev, G. E.; Desnenko, V. A.; Fedorchenko, A. V.; Bludov, A. N.; Gnatchenko, S. L.; Chareev, D. A.; Mitrofanovа, E. S.; Vasiliev, A. N.

2014-07-01

45

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

46

Resonant and non-resonant PL and PLE spectra of CdSe\\/ZnSe and CdTe\\/ZnTe self-assembled quantum dots  

Microsoft Academic Search

Using micro- and nano-scale resonantly excited PL and PLE, we study the excitonic structure of CdSe\\/ZnSe and CdTe\\/ZnTe self assembled quantum dots (SAQD). Strong resonantly enhanced PL is seen at one to four optic phonon energies below the laser excitation energy. The maximum enhancement is not just one phonon energy above the peak energy distribution of QDs, but rather is

T. A. Nguyen; S. Mackowski; L. M. Robinson; H. Rho; H. E. Jackson; L. M. Smith; M. Dobrowolska; J. K. Furdyna; G. Karczewski

2003-01-01

47

Magneto-Photoluminescence Imaging of CdSe\\/ZnSe and CdTe\\/ZnTe self-assembled quantum dots  

Microsoft Academic Search

Using polarized Magneto-Photoluminescence (PL) spectroscopy, we study the excitonic structure of CdSe\\/ZnSe and CdTe\\/ZnTe self-assembled quantum dots. With a solid immersion lens, we are able to directly image single quantum dots (QD) at 5K with 250 nm resolution. Polarized magneto-PL measurements for magnetic fields from 0 to 4T are used to determine the shape and size distribution of the quantum

Kapila P. Hewaparakrama; Sebastian Mackowski; Firoze H. Haque; Howard E. Jackson; Leigh M. Smith; Malgorzata Dobrowolska; Jacek K. Furdyna; Grzegorz Karczewski

2004-01-01

48

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

49

Indium donor complexes with cation vacancies in CdTe and ZnSe  

Microsoft Academic Search

Very dilute (10(exp 12) cm(exp -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

J. W. Griffith; R. Lundquist; R. Platzer; J. A. Gardner; G. Karczewski; J. K. Furdyna

1993-01-01

50

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

51

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

52

Charge transport in mixed CdSe and CdTe colloidal nanocrystal films  

E-print Network

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

Bawendi, Moungi G.

53

High-resolution angle-resolved photoemission study of layered transition-metal dichalcogenides Nb 1?xTi xXc 2 (Xc = S, Se, Te)  

Microsoft Academic Search

High-resolution angle-resolved photoemission spectroscopy (ARPES) has been performed on Nb1?xTixXc2 (Xc = S, Se, Te) to elucidate the change in the band structure as a function of x and Xc. We found that spectral intensity near EF of S- and Se-based compounds is remarkably suppressed, suggesting the strong scattering of electrons by the substitution of transition metals. In contrast, Te-based

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

2005-01-01

54

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

NASA Technical Reports Server (NTRS)

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

Su, Ching-Hua

1993-01-01

55

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

E-print Network

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

Tian, Zhiting

56

Se (IV) triggers faster Te (IV) reduction by soil isolates of heterotrophic aerobic bacteria: formation of extracellular SeTe nanospheres.  

PubMed

BackgroundSelenium and Tellurium have many common chemical properties as both belong to group 16 of the periodic table. High toxicities of Se and Te oxyanions cause environmental problems in contaminated soils and waters. Three strains (C4, C6 and C7) of selenite reducing and nanoparticle forming aerobic bacteria which were isolated from agricultural soils of India containing high concentrations of Se were investigated after 3.5months of freeze-storage for their resistance against the toxic oxyanion tellurite and its reduction to non toxic elemental form Te0 as well as nanoparticles formation.ResultsStrains C4, C6 and C7 reduced tellurite at maximum reduction rates of 2.3, 1.5 and 2.1mg Te (IV)/L/d, respectively and produced extracellular Te0 nanospheres as revealed from SEM-EDX analysis. Production of extracellular Te nanospheres has been described seldom. Further, concurrent reduction of both selenite and tellurite by bacteria was examined as these toxic oxyanions are often present together in natural environments, mine tailings or wastewater from copper refining. Interestingly, bioreduction of 100mg/L selenite in shake flasks was not much affected by the presence of 10mg/L tellurite but tellurite reduction rate increased 13 fold with selenite in the medium. The concurrent reduction of these oxyanions resulted in rarely described bioformation of extracellular nanoparticles composed of both Se and Te, reported first time for aerobically growing heterotrophic non-halophilic bacterial cultures. Duganella violacienigra, the closely related strain to C4 was also found to be resistant to oxyanions of Se and Te.ConclusionsSelenite reducing heterotrophic non-halophilic aerobic bacteria revived from 3.5months freeze storage could successfully reduce toxic tellurite to non toxic elemental form and produced extracellular nanospheres during detoxification. Presence of relatively less toxic selenite in the medium triggers bioreduction of more toxic tellurite leading to formation of extracellular SeTe nanospheres which are sought by solar and optical recording media industry because of their excellent photovoltaic and optical properties. The bacterial cultures investigated in this study could be exploited commercially to remediate not only selenite and tellurite-contaminated soil and water but also for green synthesis of extracellular Se, Te and Se+Te nanospheres. PMID:25425453

Bajaj, Mini; Winter, Josef

2014-11-26

57

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

58

Nano Cd(Se,Te) Thin Films Prepared by Pulse Plating Technique  

Microsoft Academic Search

In this paper, pulse plating technique has been employed for the preparation of nano crystalline CdSexTe1-x (x = 0 to 1) films coated on gold susbtrate. CdSexTe1-x nanofilms, the as-deposit exhibited hexagonal structure for all compositions. Better crystallinity was observed for the CdSe0.90Te0.10 nanofilms. The crystallite size was calculated from the Scherrer's equation, as the duty cycle decreases the size

V. Saaminathan; K. R. Murali

2002-01-01

59

Anisotropic strain in SmSe and SmTe: Implications for electronic transport  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

60

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

SciTech Connect

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

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

2013-12-04

61

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

62

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

63

Hybrid InAsSb/CdSeTe heterostructures lattice-matched to GaSb  

NASA Astrophysics Data System (ADS)

We have studied molecular beam epitaxial growth of CdSeTe alloys on InAs1-xSbx layers (x0.06-0.1) nearly lattice-matched to GaSb(001) substrate. The preferential Se incorporation in the CdSeTe layers has been found. Sulfide passivation technique has been applied to the uncapped InAsSb surface to form the flat coherent InAsSb/CdSeTe heterovalent interface mediated by a ZnTe interface layer. The strong etching mode has been observed during the initial stage of InAsSb surface treatment in a 1M Na2S-water solution.

Sedova, I. V.; Sorokin, S. V.; Semenov, A. N.; L'vova, T. V.; Lyublinskaya, O. G.; Solov'ev, V. A.; Usikova, A. A.; Ivanov, S. V.

2007-04-01

64

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

NASA Astrophysics Data System (ADS)

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 (?-) 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 ``?-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 ``?-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.

2006-03-01

65

Photoconductivity in amorphous thin films of Se70Te30-xCdx  

Microsoft Academic Search

Steady-state and transient photoconductivity is studied in amorphous thin films of Se70Te30-xCdx (0⪕x⪕8) with the purpose to see the effect of Cd incorporation in binary Se70Te30 glassy alloys. The results indicate that photoconductivity is highly composition dependent in this system. A discontinuity in various electrical parameters is observed at 4 at% Cd. This is explained in terms of an ordered

P. K. Dwivedi; S. K. Srivastava; R. K. Shukla; A. Kumar

1994-01-01

66

Study of phase separation in amorphous Se-Te-Bi material  

NASA Astrophysics Data System (ADS)

We have prepared ternary Se80Te17Bi3 and Se80Te14Bi6 glasses using melt-quench technique and performed the non-isothermal kinetics by differential scanning calorimetry (DSC) at various heating rates (?). X-ray diffraction and FESEM have been used to identify the transformed phases. The change in glass transition temperature (Tg) and crystallization temperature (Tc) with heating rates have been used to calculate different crystallization parameters in Se80Te20-xBix chalcogenide glasses. We found that both Tg and Tc becomes larger with increasing ?. Activation energies of glass transition (Eg) and crystallization (Ec), the crystallization enthalpy (Hc), thermal stability and glass forming ability (GFA) were determined from the dependency of Tg and Tc on heating rates. From our experimental data, the temperature difference (Tc - Tg) and Hc are largest and lowest, respectively, for Se80Te17Bi3 glass, which shows that Se80Te17Bi3 glass is more stable than Se80Te14Bi6 glass.

Alvi, M. A.

2014-09-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

68

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

NASA Astrophysics Data System (ADS)

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

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

2005-07-01

69

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

70

Thermoelectric performance of n-type (PbTe)0.75(PbS)0.15(PbSe)0.1 composites.  

PubMed

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

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

2014-07-23

71

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

NASA Astrophysics Data System (ADS)

Heat capacity measurements were performed for Se, Se90Te10, Se80Te20, and Se70Te30 materials in the 230-630 K temperature range. Both glassy and crystalline Cp dependences were found to be identical within the experimental error. The compositional dependence of the N-type undercooled liquid Cp evolution was explained on the basis of free-volume theory; vibrational and chemical contributions to heat capacity were found to be roughly similar for all Se-Te compositions. The thermal behavior in the Se-Te chalcogenide system was thoroughly studied: glass transition, cold crystallization, and melting were investigated in dependence on composition and various experimental conditions (heating rate, particle size, and pre-nucleation period). The kinetics of the structural relaxation and crystallization processes are described in terms of the Tool-Narayanaswamy-Moynihan and Johnson-Mehl-Avrami models. The complexity of these processes is thoroughly discussed with regard to the compositionally determined changes of molecular structures. The discussion is conducted in terms of the mutual interplay between the thermodynamics and kinetics in this system.

Svoboda, Roman; Mlek, Ji?

2014-12-01

72

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

PubMed

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

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

2012-03-14

73

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

PubMed

Heat capacity measurements were performed for Se, Se90Te10, Se80Te20, and Se70Te30 materials in the 230-630 K temperature range. Both glassy and crystalline Cp dependences were found to be identical within the experimental error. The compositional dependence of the N-type undercooled liquid Cp evolution was explained on the basis of free-volume theory; vibrational and chemical contributions to heat capacity were found to be roughly similar for all Se-Te compositions. The thermal behavior in the Se-Te chalcogenide system was thoroughly studied: glass transition, cold crystallization, and melting were investigated in dependence on composition and various experimental conditions (heating rate, particle size, and pre-nucleation period). The kinetics of the structural relaxation and crystallization processes are described in terms of the Tool-Narayanaswamy-Moynihan and Johnson-Mehl-Avrami models. The complexity of these processes is thoroughly discussed with regard to the compositionally determined changes of molecular structures. The discussion is conducted in terms of the mutual interplay between the thermodynamics and kinetics in this system. PMID:25494760

Svoboda, Roman; Mlek, Ji?

2014-12-14

74

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

NASA Astrophysics Data System (ADS)

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

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

2006-09-01

75

Magneto-Photoluminescence Imaging of CdSe/ZnSe and CdTe/ZnTe self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

Using polarized Magneto-Photoluminescence (PL) spectroscopy, we study the excitonic structure of CdSe/ZnSe and CdTe/ZnTe self-assembled quantum dots. With a solid immersion lens, we are able to directly image single quantum dots (QD) at 5K with 250 nm resolution. Polarized magneto-PL measurements for magnetic fields from 0 to 4T are used to determine the shape and size distribution of the quantum dots. In particular, we show the range and variation of the exchange splitting and in particular we find that the large fraction of the dots is completely symmetric. For these completely symmetric dots we determine their size through measurement of the diamagnetic shift, and therefore show that the g-factor decreases with increasing size of the QDs. We acknowledge the support of NSF through Grants DMR 0071797, 0216374 and project SPINOSA (Poland).

Hewaparakrama, Kapila P.; Mackowski, Sebastian; Haque, Firoze H.; Jackson, Howard E.; Smith, Leigh M.; Dobrowolska, Malgorzata; Furdyna, Jacek K.; Karczewski, Grzegorz

2004-03-01

76

Distribution of tellurium in melt-grown ZnSe(Te) crystals  

Microsoft Academic Search

The properties of semiconductor scintillation crystals are largely determined by the presence and distribution of the activator dopant. Influence of growth technological parameters (overheating ?T, inert gas pressure P, crystallization rate Vk) upon distribution of tellurium dopant was studied for ZnSe(Te) crystals grown by Bridgman technique in compression furnaces. Values of the apparent distribution coefficient of tellurium (kTe) over crystal

L. V Atroshchenko; L. P Gal'chinetskii; S. N Galkin; V. D Ryzhikov; V. I Silin; N. I Shevtsov

1999-01-01

77

Role of polycrystallinity in CdTe and CuInSe sub 2 photovoltaic cells  

SciTech Connect

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

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

1991-01-01

78

Growth and properties of LiGaX2 (X = S, Se, Te) single crystals for nonlinear optical applications in the mid-IR  

Microsoft Academic Search

compounds. PACS 42.70.Mp, 78.20.Ci Single crystals LiGaX2 (X = S, Se, Te) of optical quality were grown, with transparency ranges at 5 cm-1 absorption level of 0.32 -11.6 m, 0.37-13.2 m and 0.54-14.2 m, respectively. The first two, LiGaS2 and LiGaSe2, have a wurtzite -type structure whereas LiGaTe2 is tetragonal (chalcopyrite lattice). The three refractive indices were measured in the

L. Isaenko; A. Yelisseyev; S. Lobanov; A. Titov; V. Petrov; J.-J. Zondy; P. Krinitsin; A. Merkulov; V. Vedenyapin; J. Smirnova

2003-01-01

79

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

80

Far-infrared spectroscopy of HgMnTe-MnSe mixture  

Microsoft Academic Search

Far-infrared reflectivity spectrum of Hg0.91Mn0.09Te-MnSe mixture, grown by Bridgman method, was measured in the 80-500 cm-1 range at room temperature. The investigated mixture consists of MnSe clusters randomly distributed in Hg0.91Mn0.09Te matrix. The analysis of the far-infrared spectrum was made by a fitting procedure. The Maxwell-Garnett effective medium theory is used for modeling the effective dielectric function, and by that

N. Rom?evi?; M. Rom?evi?; A. Milutinovi; R. Kosti

2006-01-01

81

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

82

Thermoelectric properties of Nb3SbxTe7-x compounds  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

83

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

PubMed

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

Zhang, Ruili; Wang, Jianrong; Yang, Ping

2014-03-01

84

Unabridged phase diagram for single-phased FeSe(x)Te(1-x) thin films.  

PubMed

A complete phase diagram and its corresponding physical properties are essential prerequisites to understand the underlying mechanism of iron-based superconductivity. For the structurally simplest 11 (FeSeTe) system, earlier attempts using bulk samples have not been able to do so due to the fabrication difficulties. Here, thin FeSe(x)Te(1-x) films with the Se content covering the full range (0 ? x ? 1) were fabricated by using pulsed laser deposition method. Crystal structure analysis shows that all films retain the tetragonal structure in room temperature. Significantly, the highest superconducting transition temperature (T(C) = 20 K) occurs in the newly discovered domain, i.e., 0.6 ? x ? 0.8. The single-phased superconducting dome for the full Se doping range is the first of its kind in iron chalcogenide superconductors. Our results present a new avenue to explore novel physics as well as to optimize superconductors. PMID:25449669

Zhuang, Jincheng; Yeoh, Wai Kong; Cui, Xiangyuan; Xu, Xun; Du, Yi; Shi, Zhixiang; Ringer, Simon P; Wang, Xiaolin; Dou, Shi Xue

2014-01-01

85

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

86

Trivalent uranium phenylchalcogenide complexes: exploring the bonding and reactivity with CS2 in the Tp*2UEPh series (E = O, S, Se, Te).  

PubMed

The trivalent uranium phenylchalcogenide series, Tp*2UEPh (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, E = O (1), S (2), Se (3), Te (4)), has been synthesized to investigate the nature of the U-E bond. All compounds have been characterized by (1)H NMR, infrared and electronic absorption spectroscopies, and in the case of 4, X-ray crystallography. Compound 4 was also studied by SQUID magnetometry. Computational studies establish Mulliken spin densities for the uranium centers ranging from 3.005 to 3.027 (B3LYP), consistent for uranium-chalcogenide bonds that are primarily ionic in nature, with a small covalent contribution. The reactivity of 2-4 toward carbon disulfide was also investigated and showed reversible CS2 insertion into the U(III)-E bond, forming Tp*2U(?(2)-S2CEPh) (E = S (5), Se (6), Te (7)). Compound 5 was characterized crystallographically. PMID:25415677

Matson, Ellen M; Breshears, Andrew T; Kiernicki, John J; Newell, Brian S; Fanwick, Phillip E; Shores, Matthew P; Walensky, Justin R; Bart, Suzanne C

2014-12-15

87

Ab initio calculations of half-metallic ferromagnetism in Cr-doped MgSe and MgTe semiconductors  

NASA Astrophysics Data System (ADS)

The full-potential linear-augmented-plane-waves plus local-orbitals (FP-LAPW+lo) method has been employed for investigation of half-metallic ferromagnetism in Cr-doped ordered zinc-blende MgSe and MgTe semiconductors. Calculations of exchange and correlation (XC) effects have been carried out using generalized gradient approximation (GGA) and orbital independent modified Becke-Johnson potential coupled with local (spin) density approximation (mBJLDA). The thermodynamic stability of the compounds and their preferred magnetic orders have been analyzed in terms of the heat of formation and minimum total energy difference in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering, respectively. Calculated electronic properties reveal that the Cr-doping induces ferromagnetism in MgSe and MgTe which gives rise to a half-metallic (HM) gap at Fermi level (EF). Further, the electronic band structure is discussed in terms of s (p)-d exchange constants that are consistent with typical magneto-optical experiment and the behavior of charge spin densities is presented for understanding the bonding nature. Our results demonstrate that the higher effective potential for the spin-down case is responsible for p-d exchange splitting. Total magnetic moment (mainly due to Cr-d states) of these compounds is 4?B. Importantly, the electronic properties and HM gap obtained using mBJLDA show remarkable improvement as compared to the results obtained using standard GGA functional.

Noor, N. A.; Alay-e-Abbas, S. M.; Sohaib, M. U.; Ghulam Abbas, S. M.; Shaukat, A.

2015-01-01

88

Ab initio study of ZnSe and CdTe semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

We apply first principles density functional and time dependent density functional computational methods to study the structures, densities of states, absorption spectra, and optical gaps of spherical ZnSe and CdTe semiconductor quantum dots in the size range 0.3-2.2 nm. Our calculations are performed in real space without an explicit basis. The surfaces of the quantum dots are passivated with partially charged hydrogen atoms. We find that this passivation technique effectively removes the electronic states associated with the surface atoms from the gaps of ZnSe and CdTe nanocrystals, but does not affect the energies of the quantum-confined electronic states. Our study shows that the absorption gaps of ZnSe and CdTe quantum dots decrease with increasing dot diameter. The size-dependent variations of the computed optical gaps in surface-passivated ZnSe and CdTe quantum dots are found to be consistent with the effects of quantum confinement observed in group IV and group III-V semiconductor nanocrystals.

Alnemrat, Sufian; Ho Park, Young; Vasiliev, Igor

2014-03-01

89

Influence of CdTe sub-monolayer stressor on CdSe quantum dot self-assembling in ZnSe  

NASA Astrophysics Data System (ADS)

This paper reports on the attempt to apply the stressor-controlled quantum dot (QD) fabrication technique to the conventional CdSe/ZnSe nanostructures. Super-strained CdTe fractional monolayer (a/a 14% for CdTe/ZnSe) grown on top of the Te-stabilized ZnSe surface prior to deposition of the QD material (CdSe) has been used as a stressor which is expected to affect size, composition and density of CdSe QDs. The grown structures are studied by X-ray diffraction, transmission-electron microscopy, photoluminescence (PL) and PL excitation in comparison with conventional CdSe/ZnSe QDs obtained by a modified migration enhanced epitaxy technique.

Sedova, I. V.; Lyublinskaya, O. G.; Sorokin, S. V.; Sitnikova, A. A.; Solnyshkov, D. D.; Rykhova, O. V.; Toropov, A. A.; Ivanov, S. V.

2006-03-01

90

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

NASA Astrophysics Data System (ADS)

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

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

91

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

E-print Network

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

Zhang, Qian

92

Bi-Se-Te mineralization from horn (Spisko Gemersk Rudohorie Mts., S?ovakia): A preliminary report  

NASA Astrophysics Data System (ADS)

An unusual association of Se minerals was studied. Se enters into the structures of sulphosalts - into bournonite, jamesonite and tintinaite at concentrations up to 0.10, 0.38 and 1.11 apfu, respectively. However, Se and Te, together with Bi, also form discrete minerals such as tetradymite, laitakarite, ikunolite and hedleyite. Members of the laitakarite-ikunolite solid solution display a wide range of anion substitution from the nearly Se-free (0.10 apfu) end member to the S-poor (0.42 apfu) end member. Their contents of Te are low. Accompanying tetrahedrite does not contain Se or Te.

Prek, Jaroslav; Peterec, Duan

2008-01-01

93

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

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

2005-05-16

94

Composition and type of conductivity of Pb(1-x)Sn(x)Se(1-y)Te(y) epitaxial layers  

NASA Astrophysics Data System (ADS)

Isoperiodic heterostructures for injection lasers are analyzed, and phase equilibria in the case of liquid-phase epitaxy are investigated. Attention is given to a method for fabricating quaternary solid solutions of Pb(1-x)Sn(x)Se(1-y)Te(y) by liquid-phase epitaxy on PbSe, PbTe, and Pb(1-x)Sn(x)Te substrates.

Davarashvili, O. I.; Zlomanov, V. P.; Krialashvili, I. V.; Saginuri, M. I.; Chikovani, R. I.; Shotov, A. P.

95

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

E-print Network

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

McCluskey, Matthew

96

Is a 'Late Veneer' Necessary? Answers From Metal-Silicate Partitioning of Te, Se, and S  

NASA Astrophysics Data System (ADS)

Chondrite-normalized mantle abundances of Te, Se, and S show depletions from the Planetary Volatility Trend (McDonough and Sun, 1995). This is likely due to their siderophile behavior under reducing conditions (Kilburn and Wood, 1997), resulting in strong partitioning into the core-forming Fe-Ni liquid. A mass balance calculation using Te, Se, and S concentrations in C1-chondrites and a modeled primitive mantle shows similar depletions for each element, with core/mantle "partitioning" of about 100 (McDonough and Sun, 1995). Values for Se and Te relative to S used in this estimate are consistent with those measured in sulfide globules from the upper mantle (Hattori et al., 2001). Experiments have been done to investigate whether this depletion could be achieved solely by equilibrium metal-silicate partitioning at the P-T-fO2 conditions relevant to core formation. If experimental results match the estimated Dcore-mantle, this could reflect either a single P-T condition at the base of a magma ocean where metallic liquid ponded, or an average P-T condition covering a depth range within which metallic liquid droplets rained through semi-crystalline silicate. If the results are discrepant, the abundance of Te, Se, and S were disrupted after initial equilibrium partitioning. Higher experimental DTe,Se,S necessitates the addition of chalcophile-rich material to the mantle after core formation (i.e. a 'late veneer') and lower experimental DTe,Se,S requires removal of chalcophiles from the mantle, perhaps in a late 'Hadean sulfide matte' (Wood and Halliday, 2003). Liquid metal-liquid silicate partitioning experiments were performed using both piston-cylinder and multi-anvil presses over a range of pressure (1-12 GPa) and temperature (1835-2135C). Powdered oxide and metal added in 50:50 proportion was contained within MgO crucibles. Oxygen fugacity was varied by adding different amounts of Si to the starting material. Experiments ranged from -7 to -0.5 log units below the iron-wstite buffer (IW). Major elements in both quenched metal and silicate were determined by EMPA while Te and Se abundance in the quenched silicate portion was measured using LA-ICP-MS at the University of Toronto. At constant P and T, all three metal-silicate partition coefficients increase with increasing fO2. Te and S are the most siderophile, followed by Se. The presence of 5-10 wt% S increased both DTe and DSe by a factor of three. At 2.9 GPa, 1960C and log fO2 between IW-4 and IW-1.5, metal- silicate partitioning of the three elements converge to 100, matching the observed core-mantle partitioning. Previously, it was shown that both DS and DSe are positively correlated with P while increased T lowers DS (Li and Agee, 1996; Li, 2000). After applying these corrections and extrapolating our data to the estimated conditions of core formation (P=25-40 GPa; T=2000-3500C; e.g. Li and Agee, 1996; Righter et al., 1997), the point of equal metal- silicate partitioning of Te, Se, and S is only raised by a factor of 3. Consequently, the observed core-mantle partitioning of Te, Se, and S is consistent with high temperature equilibrium within a magma ocean, obviating the need for a 'late veneer'. Chalcophile element (including Pb) loss to the core with the separation of a Hadean sulfide 'matte' would have further depleted the mantle. It would be quite fortuitous if a 'late veneer' refertilized the mantle to match the expected equilibrium abundances prescribed by metal-silicate partitioning. This result is consistent with conclusions based on the metal-silicate partitioning behavior of other elements, for instance Ni, Co, and Pt.

Rose, L. A.; Brenan, J. M.

2006-05-01

97

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

98

Coexistence of type-I and type-II band lineups in Cd(Te ,Se)/ZnSe quantum-dot structures  

NASA Astrophysics Data System (ADS)

The authors report on transmission electron microscopy, cathodoluminescence, and time resolved photoluminescence studies of thin Cd(Te,Se) layers in a ZnSe matrix, grown by molecular beam epitaxy. All observations confirm strain-induced self-assembly of quantum dots (QD's), induced primarily by the 14% lattice mismatch between CdTe and ZnSe. The emission spectrum of the structure is the superposition of a relatively narrow luminescence line originating from CdSe-enriched type-I QD's and a broad band attributed to the emission of an ultrathin ZnTeSe /ZnSe layer with type-II band lineup, formed in between the QD's.

Toropov, A. A.; Sedova, I. V.; Lyublinskaya, O. G.; Sorokin, S. V.; Sitnikova, A. A.; Ivanov, S. V.; Bergman, J. P.; Monemar, B.; Donatini, F.; Si Dang, Le

2006-09-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

100

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

101

Modified magnetism within the coherence volume of superconducting FeSeTe  

SciTech Connect

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

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

2014-01-01

102

High field vortex phase diagram of Fe(Se, Te) thin films  

NASA Astrophysics Data System (ADS)

We report on the (H, T) vortex phase diagram up to 35 T of Fe(Se, Te) thin films deposited on CaF2 substrates as determined by resistivity, Nernst effect and critical current measurements. We found the presence of a large region where the vortex is firmly pinned, allowing the adoption of chalcogenides for low temperature but extremely high magnetic field applications. The fact that high critical current density valueslarger than 1 MA cm-2 in self-field and liquid heliumare reached together with a very weak dependence on the magnetic field and a complete isotropy, joined with the very high rigidity of the vortex lattice at very high field, makes the Fe(Se, Te) phase very promising for low temperature (?4.2 K) and high field (?25 T) applications.

Bellingeri, E.; Kawale, S.; Caglieris, F.; Braccini, V.; Lamura, G.; Pellegrino, L.; Sala, A.; Putti, M.; Ferdeghini, C.; Jost, A.; Zeitler, U.; Tarantini, C.; Jaroszynski, J.

2014-04-01

103

Preparation and thermoelectric properties of Bi2Te2.7Se0.3 nanocomposites  

NASA Astrophysics Data System (ADS)

Cu- or Ag-dispersed Bi2Te2.7Se0.3 nanocomposites were prepared by using metal-acetate decomposition and hot pressing. Cu or Ag nanoparticles were well-dispersed in the Bi2Te2.7Se0.3 matrix, and thereby the power factor was greatly increased due to the increase in the effective mass of a carrier. However, Cu or Ag dispersion did not affect the carrier concentration and could not reduce the lattice thermal conductivity because Cu or Ag nanoparticles did not act as phonon scattering centers effectively. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K due to the high power factor. Compared to Ag dispersion, Cu dispersion was much more effective in enhancing the thermoelectric performance.

Kim, Il-Ho; Choi, Soon-Mok; Seo, Won-Seon; Cheong, Dong-Ik

2012-11-01

104

Transient photoconductivity in amorphous thin films of Se 75 Te 20 Ag 5  

Microsoft Academic Search

The present paper reports the transient photoconductivity measurements in vacuum evaporated thin films of Se75Te20Ag5. It has been observed that under certain experimental conditions, the rise and decay of photoconductivity shows the anomalous behaviour. The photoconductivity increases initially, attains a maximum, and then decreases with time. Under the same experimental conditions, the decay of photocurrent shows a negative photoconductivity during

D. Sharma; R. K. Shukla; A. Kumar

1999-01-01

105

Photoconductivity in Thin Films of aIn40Se30Te30  

Microsoft Academic Search

Photoconductivity in thin film of a-In40Se30Te30, obtained by vacuum evaporation, was studied at different temperatures and illumination intensities. Photoconductivity increases exponentially with T in the range 310-370 K. Intensity dependence of photocurrent at various temperatures reveals power dependence of incident radiation. Transient photoconductivity observations made at different temperatures and intensities show that rise and decay of photocurrent are quite slow

A. S. Maan; D. R. Goyal; A. Kumar

1988-01-01

106

Composition Dependence of Photoconductivity in Amorphous Thin Films of Se.80-xTe.20Gex  

Microsoft Academic Search

The present paper reports the dependence on composition of photoconductivity in vacuum evaporated thin films of amorphous Se.80-xTe.20Gex (x = .05, .10, .15 and .20). Temperature dependence of conductivity in dark as well as in presence of light show that conduction is through a thermally activated process in both cases. The activation energy is found to decrease with increase in

Deepak Kumar; Santosh Kumar

2005-01-01

107

Composition dependence of photoconductivity in amorphous thin films of Se 70 Te 30?x Sb x  

Microsoft Academic Search

SummaryThe present paper reports the composition dependence of steady-state and transient photoconductivity in amorphous thin films\\u000a of Se70Te30-xSbx, wherex is varied from 0 to 10. The results indicate that photoconductivity is highly composition dependent in this system and a\\u000a discontinuity in various electrical parameters is observed at 4 at. % of Sb. This is explained in terms of increased disorder

P. K. Dwivedi; S. K. Srivastava; A. Kumar

1993-01-01

108

The chromium impurity photogeneration transitions in ZnS, ZnSe and ZnTe  

Microsoft Academic Search

The results of photo-EPR and optical absorption measurements are presented for chromium doped ZnS, ZnSe and ZnTe. An analysis of these experiments enables the authors to determine the character of the absorption bands observed beneath the 'band-band' transitions as being due to the Cr2+ to Cr+ photogeneration processes. The experimental results are interpreted within the framework of the theory for

M. Godlewski; M. Kaminska

1980-01-01

109

Thermoelectric properties and electronic structure of CoSb 3 doped with Se and Te  

Microsoft Academic Search

This work presents structural and electron transport properties of Se- and Te-doped CoSb3 skutterudites in relation to results of electronic structure calculations performed for this system. The physical quantities were determined from crystal structure studies and measurements of transport coefficients: electrical conductivity, thermal conductivity and Seebeck coefficient as a function of composition and temperature. The electronic structure of CoSb3 was

K. T Wojciechowski; J Tobo?a; J Leszczy?ski

2003-01-01

110

Vapour-liquid-solid growth of ternary Bi2Se2Te nanowires  

PubMed Central

High-density growth of single-crystalline Bi2Se2Te nanowires was achieved via the vapour-liquid-solid process. The stoichiometry of samples grown at various substrate temperatures is precisely determined based on energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy on individual nanowires. We discuss the growth mechanism and present insights into the catalyst-precursor interaction. PMID:24641967

2014-01-01

111

Half-metallic ferromagnetism in hypothetical semi-Heusler alloys NiVM (M=P, As, Sb, S, Se, and Te)  

Microsoft Academic Search

A theoretical study based on first-principle band-structure calculations is carried out for the hypothetical semi-Heusler alloys NiVM (M=P, As, Sb, S, Se, and Te). For all compounds it is found that the ferromagnetic state is more favorable than the paramagnetic state. NiVAs is predicted to be a half-metallic ferromagnet with a small half-metallic gap of 0.07 eV and an integer

Ming Zhang; Zhu-Hong Liu; Hai-Ning Hu; Guo-Dong Liu; Yu-Ting Cui; Guang-Heng Wu; Ekkes Brck; Frank R. de Boer; Yang-Xian Li

2004-01-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

113

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

114

Tunable (, )-Type Antiferromagnetic Order in -Fe(Te,Se) Superconductors Wei Bao,1,2,* Y. Qiu,3,4  

E-print Network

Mexico 87545, USA 3 NIST Center for Neutron Research, National Institute of Standards and Technology (, ) was determined for the parent compound Fe1þyTe in this powder and single-crystal neutron diffraction study

Spinu, Leonard

115

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

Microsoft Academic Search

Crystals of Pd2MCh2 (M=Fe, Co, Ni; Ch=Se, Te) were synthesized by heating the elements at 8231323K in silica ampoules under argon atmosphere. Their structures were determined by single-crystal X-ray diffraction at room temperature. The metallic compounds crystallize in a variant of the K2ZnO2 type (Ibam, Z=4, Pd2CoSe2: a=5.993(1), b=10.493(2), c=5.003(1) ; Pd2FeSe2: a=5.960(1), b=10.576(2), c=5.078(1) ; Pd2CoTe2: a=6.305(1), b=11.100(2), c=5.234(1)

Regina Pocha; Catrin Loehnert; Dirk Johrendt

2007-01-01

116

Vapor Growth and Characterization of ZnSeTe Solid Solutions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

117

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

118

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

120

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

SciTech Connect

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

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

2005-08-11

121

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

122

Observation of an electron band above the Fermi level in FeTe0.55Se0.45 from in-situ surface doping  

NASA Astrophysics Data System (ADS)

We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe0.55Se0.45. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe2-xSe2 compound.

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

2014-10-01

123

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

PubMed

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

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

2014-01-01

124

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

125

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

NASA Astrophysics Data System (ADS)

This paper highlights the results of the whole work including the synthesis of highly luminescent quantum dots (QDs), characterizations and testing applications of them in different kinds of sensors. Concretely, it presents: (i) the successful synthesis of colloidal CdTe and CdSe QDs, their core/shell structures with single- and/or double-shell made by CdS, ZnS or ZnSe/ZnS; (ii) morphology, structural and optical characterizations of the synthesized QDs; and (iii) testing examples of QDs as the fluorescence labels for agricultural-bio-medical objects (for tracing residual pesticide in agricultural products, residual clenbuterol in meat/milk and for detection of H5N1 avian influenza virus in breeding farms). Overall, the results show that the synthesized QDs have very good crystallinity, spherical shape and strongly emit at the desired wavelengths between ?500 and 700 nm with the luminescence quantum yield (LQY) of 3085%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml?1. For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 350 ng ?l?1 with a detection limit of 3 ng ?L?1 has been performed based on the antibody-antigen recognition.

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

2012-12-01

126

Temperature Dependence Of The Exciton Homogeneous Linewidth In CdTe and CdSe Self-assembled Quantum Dots: Limit Of Single Photon Source Operation  

NASA Astrophysics Data System (ADS)

Excitonic emission in single CdTe/ Zn0.7Mg0.3Te and CdSe/ZnSe quantum dots has been obtained up to 160 K and 220 K respectively. The study of the linewidth thermal broadening allows us to estimate the temperature limit of single photon emission in CdTe and CdSe QDs.

Kheng, Kuntheak; Moehl, Sebatian; Robin, Ivan-Christophe; Maingault, Laurent; Andr, Rgis; Mariette, Henri

2007-04-01

127

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

128

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

NASA Astrophysics Data System (ADS)

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

Joseph, Elad; Amouyal, Yaron

2014-10-01

129

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

Microsoft Academic Search

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

Paul Larson

2005-01-01

130

Effect of TeI 4 content on the thermoelectric properties of n-type BiTeSe crystals prepared by zone melting  

Microsoft Academic Search

n-Type (Bi2Te3)0.93(Bi2Se3)0.07 thermoelectric materials doped with various content of TeI4 (0, 0.05, 0.10, 0.13, and 0.15wt.%) have been fabricated through the zone melting method. Electrical conductivity (?), Seebeck coefficient (?) and thermal conductivity (?) were measured along the crystal growth direction in the temperature range of 300500K. The influence of the variations of TeI4 content on thermoelectric properties was studied.

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

2005-01-01

131

Phototropic growth control of nanoscale pattern formation in photoelectrodeposited SeTe films  

PubMed Central

Photoresponsive materials that adapt their morphologies, growth directions, and growth rates dynamically in response to the local incident electromagnetic field would provide a remarkable route to the synthesis of complex 3D mesostructures via feedback between illumination and the structure that develops under optical excitation. We report the spontaneous development of ordered, nanoscale lamellar patterns in electrodeposited seleniumtellurium (SeTe) alloy films grown under noncoherent, uniform illumination on unpatterned substrates in an isotropic electrolyte solution. These inorganic nanostructures exhibited phototropic growth in which lamellar stripes grew toward the incident light source, adopted an orientation parallel to the light polarization direction with a period controlled by the illumination wavelength, and showed an increased growth rate with increasing light intensity. Furthermore, the patterns responded dynamically to changes during growth in the polarization, wavelength, and angle of the incident light, enabling the template-free and pattern-free synthesis, on a variety of substrates, of woodpile, spiral, branched, or zigzag structures, along with dynamically directed growth toward a noncoherent, uniform intensity light source. Full-wave electromagnetic simulations in combination with Monte Carlo growth simulations were used to model lightmatter interactions in the SeTe films and produced a model for the morphological evolution of the lamellar structures under phototropic growth conditions. The experiments and simulations are consistent with a phototropic growth mechanism in which the optical near-field intensity profile selects and reinforces the dominant morphological mode in the emergent nanoscale patterns. PMID:24218617

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

2013-01-01

132

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

NASA Astrophysics Data System (ADS)

This work studied the structural and optical properties of ZnTe epilayers grown on GaAs substrates with ZnSe/ZnTe strained superlattices buffer layers. Material properties were characterized using cross-sectional transmission electron microscopy, photoluminescence (PL), contactless electroreflectance (CER), and piezoreflectance (PzR). PL spectra clearly distinguished the strong free exciton peaks, weak donor-acceptor pair, Y lines, and oxygen-bound exciton peaks, indicating the high quality of the films. In addition, the CER and PzR spectra were compared to ascertain that ZnTe epilayers of 1.5 ?m in thickness grown on GaAs substrates are under a biaxial tensile strain. An attempt was also made to identify the origins of the near-band-edge transitions of ZnTe epilayer in the CER and PzR spectra by comparing these spectra with PL spectra and the second harmonic frequency CER. By doing so, the interference below the band gap of ZnTe could be effectively eliminated. Moreover, the energy splitting between heavy- and light-hole valence bands at 15 K was calculated by utilizing the temperature-dependent elastic constants for ZnTe and the thermal-expansion coefficients for ZnTe and GaAs. The discrepancy between experiment and calculation indicates that the residual mismatch-induced strain and the thermally induced strain in ZnTe epilayers grown on GaAs during cooling must be simultaneously considered.

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

1998-09-01

133

Self-surface passivation of CdX (X = Se, Te) quantum dots.  

PubMed

A small portion of a reaction mixture including unpurified CdX (X = Se or Te) quantum dots (QDs), in which unreacted Cd and Se ions were left together with coordinating solvents, was dropped into an organic solvent. The CdX QDs in this organic solution showed enhancement of photoluminescence (PL) efficiency, growth of particles, and focusing of size distribution for more than 10 h at room temperature (RT, -23 degrees C). These effects were attributed to passivation of QDs' surface by Cd and X ions present in the solution. No external energy source was used for these achievements; therefore, the process is termed as self-surface passivation. The self-surface passivation was reproduced using purified CdX QDs with additional Cd and X ions in an organic solvent. The self-surface passivation method was applied to RT-synthesized CdSe QDs, which is characterized by a broad PL spectrum (fwhm - 150 nm) for monodispersed QDs, to modify their emission characteristics. On self-surface passivation, the broad PL spectrum was narrowed (fwhm - 35 nm) and the QDs were grown. The X-ray diffraction measurements of RT-synthesized CdSe QDs and that subsequently aged in 1-butanol showed that crystallinity of the samples was improved on aging. PMID:16573112

Jose, Rajan; Zhelev, Zhivko; Nagase, Toshimi; Bakalova, Rumiana; Baba, Yoshinobu; Ishikawa, Mitsuru

2006-03-01

134

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 Cr 2+-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 Cr 2+ 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 Cr 2+ ions decreased by a factor of two for Cr concentrations of 2.610 19 cm -3 for Cr:ZnSe and 0.710 19 cm -3 for Cr:CdTe.

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

2006-01-01

135

Ferrocenyl-functionalized Sn/Se and Sn/Te complexes: synthesis, reactivity, optical, and electronic properties.  

PubMed

An adamantane-shaped, ferrocenyl-substituted tin selenide complex, [(FcSn)4Se6] (1; Fc = ferrocenyl), and a ferrocenyl-substituted tin telluride five-membered ring, [(Fc2Sn)3Te2] (2), were obtained upon treatment of FcSnCl3 with K2E (E = Se, Te). Complex 1 further reacts with Na2S9H2O and [Cu(PPh3)3Cl] to form a ternary complex, [(CuPPh3)6(S/Se)6(SnFc)2] (3). We discuss structures, optical and electrochemical properties as well as Mssbauer spectra. PMID:25396280

You, Zhiliang; Bergunde, Jakob; Gerke, Birgit; Pttgen, Rainer; Dehnen, Stefanie

2014-12-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

137

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

E-print Network

Te15 thin films before and after photo-crystallization which is induced by shining white light (3 000 of amorphous Se85Te15 thin films prepared by vacuum evaporation technique described earlier [9265 Effect of photo-crystallization on the photoconductivity of a-Se85Te15 (*) A. Kumar, R. Misra

Boyer, Edmond

138

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

NASA Astrophysics Data System (ADS)

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

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

2004-10-01

139

Memory effect in a topological surface state of Bi2Te2Se.  

PubMed

We demonstrate the controllable local manipulation of the Dirac surface state in a topological insulator, Bi2Te2Se, which has suppressed bulk carrier density. Using scanning tunneling microscopy/spectroscopy under magnetic fields, we observe Landau levels of the Dirac surface state in the conductance spectra. The Landau levels start to shift in their energy once the bias voltage between the tip and the sample exceeds a threshold value. The amount of shift depends on the history of bias ramping. As a result, conductance spectra show noticeable hysteresis, giving rise to a memory effect. The conductance images exhibit spatially inhomogeneous patterns which can also be controlled by the bias voltage in a reproducible way. On the basis of these observations, we argue that the memory effect is associated with the tip-induced local charging effect which is pinned by the defect-generated random potential. Our study opens up a new avenue to controlling the topological surface state. PMID:23560470

Fu, Ying-Shuang; Hanaguri, Tetsuo; Yamamoto, Shuhei; Igarashi, Kyushiro; Takagi, Hidenori; Sasagawa, Takao

2013-05-28

140

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 IIVI or IIIV of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

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

2011-01-01

141

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

NASA Astrophysics Data System (ADS)

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

Sharma, Ambika; Yadav, Preeti; Kumari, Anshu

2014-04-01

142

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

143

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3  

E-print Network

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3 P. P. Kong1 , F. Sun1,3 , L. Y induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition

Shen, Guoyin

144

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

145

Specific features of linear and nonlinear optical responses of chalcogenide glasses in the As-S-Se and As-Se-Te systems  

NASA Astrophysics Data System (ADS)

Transmission and reflection spectra of samples of chalcogenide glasses in the As-S-Se and As-Se-Te systems have been measured in the wavelength range of 0.4-2.5 ?m. Spectral dependences of the single-photon absorption coefficient and refractive index are obtained, the parameters characterizing the fundamental absorption edge are determined, and the Kerr constant in the low-frequency limit is calculated. Based on the obtained results and the data in the literature, dispersion curves are plotted for the Kerr constants of As2S3 and As2Se3 glasses near the absorption edge.

Kuzyutkina, Yu. S.; Romanova, E. A.; Kochubei, V. I.; Shiryaev, V. S.

2014-07-01

146

Radical cations of aromatic selenium compounds: role of SeX 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 SeX 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 SeX nonbonding interactions (E(nb)) for these compounds is in the order 1 (SeN) > 2 (SeO) > 3 (SeH). 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 SeN in the ground state, facilitate the formation of stabilized radical cations, which can significantly influence the redox chemistry and the biological activity of aromatic selenium compounds. PMID:23977839

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

2013-09-26

147

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

NASA Astrophysics Data System (ADS)

The present paper reports the nonlinear optical properties of chalcogenide Se85-x Te15Bi x (0 ? x ? 5) thin films. The formulation proposed by Boling, Fournier, and Snitzer and Tichy and Ticha has been used to compute the nonlinear refractive index n 2. The two-photon absorption coefficient ? 2, and first- and third-order susceptibilities [? (1) and ? (3)] are also reported. The nonlinear refractive index n 2 is well correlated with the linear refractive index n and Wemple-DiDomenico (WDD) parameters, in turn depending on the density ? and molar volume V m of the system. The density of the system is calculated experimentally by using Archimedes' principle. The linear optical parameters, viz. n, WDD parameters, and optical bandgap E g, are measured experimentally using ellipsometric curves obtained by spectrophotometry. The composition-dependent behavior of n 2 is analyzed on the basis of various parameters, viz. density, bond distribution, cohesive energy (CE), and optical bandgap E g, of the system. The variation of n 2 and ? 2 with changing bandgap E g is also reported. The values of n 2 and ? (3) of the investigated chalcogenides are compared with those of pure silica, oxide, and other Se-based glasses.

Yadav, Preeti; Sharma, Ambika

2015-01-01

148

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

PubMed

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

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

2012-04-01

149

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

NASA Astrophysics Data System (ADS)

We apply first-principles calculations to lead selenide (PbSe) and lead telluride (PbTe) and their alloys (PbTe1-xSex), which are potentially good thermoelectric materials, to investigate their phonon transport properties. By accurately reproducing the lattice thermal conductivity, we validate the approaches adopted in this work. We, then, compare and contrast PbSe and PbTe, evaluate the importance of the optical phonons to lattice thermal conductivity, and estimate the impacts of nanostructuring and alloying on further reducing the lattice thermal conductivity. The results indicate that (1) the optical phonons are important not only because they directly comprise over 20% of the lattice thermal conductivity but also because they provide strong scattering channels for acoustic phonons, which is crucial for the low thermal conductivity; (2) nanostructures of less than 10 nm are needed to reduce the lattice thermal conductivity for pure PbSe and PbTe; and (3) alloying should be a relatively effective way to reduce the lattice thermal conductivity.

Tian, Zhiting; Garg, Jivtesh; Esfarjani, Keivan; Shiga, Takuma; Shiomi, Junichiro; Chen, Gang

2012-05-01

150

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 ?3K between 3 to 6GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the hole-type carrier in the pressure-induced superconducting Bi2Te3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor. PMID:21173267

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

151

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

152

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

PubMed

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

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

2006-03-28

153

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. PMID:21711922

2011-01-01

154

Surface processing of CdTe compound semiconductor by excimer laser doping  

NASA Astrophysics Data System (ADS)

Laser processing technique has been developed to achieve heavy impurity doping in II-VI compound semiconductor such as CdTe which is excellent material for application in high energy flux detector because of its high absorption coefficient and energy resolution due to large atomic number and high carrier mobility. At first, transient temperature increment in CdTe due to excimer laser radiation will be discussed using computer simulation data. Using KrF excimer laser with a pulse width of 20 ns and a wavelength of 248 nm, one shot of laser of energy 80 mJ/cm 2 increases the surface temperature of CdTe more than 1000C, the melting point of CdTe. As the laser pulse is very short and the penetration depth of UV laser light is very short, the depth of processed and modified layer is limited to few hundred angstroms. Secondly, we have experimentally studied the laser doping process for the application to detectors of high energy flux. Resistivities of CdTe surface processed by laser doping drastically decreased from 10 5 to 10 -1 ? cm. p-i-n diode was thus fabricated on a high resistivity single crystal CdTe using excimer laser doping on one side for p-layer and n-type CdTe grown epitaxially on the other side. The p-i-n diodes resulted showed promising characteristics and high energy sensitivity. This technique is also promising to form ohmic contacts in other II-VI semiconductor devices. Because we can adapt this process at the final stages during device fabrication and also the laser effect is limited to a very thin layer, hence there will be no influence in the bulk characteristics of the device.

Hatanaka, Y.; Niraula, M.; Aoki, Y.; Aoki, T.; Nakanishi, Y.

1999-04-01

155

Adsorption and dissociation of O2 on MoSe2 and MoTe2 monolayers: ab initio study  

NASA Astrophysics Data System (ADS)

Adsorption and dissociation of O2 molecule on the MoSe2 and MoTe2 monolayers are studied by using density functional theory (DFT) within the generalized gradient approximation (GGA) and a supercell approach. The physisorbed O2 molecule on MoSe2 and MoTe2 with a magnetic moment (MM) close to that for an isolated O2 molecule has small adsorption energy and long distance from the surface. The dissociative adsorption of configuration R5(R6) is the most stable adsorption site, whereas the chemisorption of O2 is unfavorable at all adsorption sites. The dissociative adsorption of configuration R4 induces dramatic changes of electronic structures and localized spin polarization both for monolayer MoSe2 and MoTe2. The analysis of electronic density of states (DOSs) shows that the contribution of spin polarization is mainly from the hybridization between O-p, Se(Te)-p and Mo-d orbitals.

Zhu, X. F.; Wang, L.; Chen, L. F.

2014-07-01

156

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

E-print Network

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

Sites, James R.

157

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

SciTech Connect

Highlights: ? Bi{sub 2}Te{sub 3?y}Se{sub y} films synthesized by pulsed electrodeposition. ? The thermoelectric properties of the film were measured at room temperature. ? The films show much better properties then galvanostatically deposited film. -- Abstract: Bi{sub 2}Te{sub 3?y}Se{sub y} films were synthesized by pulsed electrodeposition on indium tin oxide (ITO)-coated glass substrates from aqueous acidic solution at room temperature. The films were deposited at the same average current density but different cathodic current density. The crystal structure, surface morphology and elemental composition of the films were investigated. Smooth and compact Bi{sub 2}Te{sub 3?y}Se{sub y} films were obtained. As the cathodic current density increased, the grain size of the films decreased. The electrical resistivity and Seebeck coefficient of each Bi{sub 2}Te{sub 3?y}Se{sub y} film were measured after the film being transferred onto a non-conductive rubberized fabric support. The films showed n-type conduction, with Seebeck coefficient in the range of ??84 to ?92 ?V/K and electrical resistivity in the range of 102.9109.4 ?? m. The films showed much better thermoelectric properties compared with the film galvanostatically deposited at the same average current density.

Zou, Z.G. [Functional Materials Research Laboratory, Tongji University, 1239 Siping Road, Shanghai 200092 (China)] [Functional Materials Research Laboratory, Tongji University, 1239 Siping Road, Shanghai 200092 (China); Cai, K.F., E-mail: kfcai@tongji.edu.cn [Functional Materials Research Laboratory, Tongji University, 1239 Siping Road, Shanghai 200092 (China); State Key Lab of Silicon Materials, Zhejiang University, Hangzhou 310027 (China); Chen, S.; Qin, Z. [Functional Materials Research Laboratory, Tongji University, 1239 Siping Road, Shanghai 200092 (China)] [Functional Materials Research Laboratory, Tongji University, 1239 Siping Road, Shanghai 200092 (China)

2012-11-15

158

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

NASA Astrophysics Data System (ADS)

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

Verma, Deepak; Dutta, V.

2009-02-01

159

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

160

Proximity-induced superconductivity in topological Bi2Te2Se and Bi2Se3 films: Robust zero-energy bound state possibly due to Majorana fermions  

NASA Astrophysics Data System (ADS)

Point contact conductance measurements on topological Bi2Te2Se and Bi2Se3 films reveal a signature of superconductivity below 2-3 K. In particular, critical current dips and a robust zero-bias conductance peak are observed. The latter suggests the presence of zero-energy bound states that could be assigned to Majorana fermions in an unconventional topological superconductor. We attribute these observations to proximity-induced local superconductivity in the films by small amounts of superconducting Bi inclusions or segregation to the surface, and provide supportive evidence for these effects.

Koren, G.; Kirzhner, T.; Lahoud, E.; Chashka, K. B.; Kanigel, A.

2011-12-01

161

Theoretical studies on the spin Hamiltonian parameters for monovalent chromium in ZnX (X=S, Se, Te) and CdTe  

NASA Astrophysics Data System (ADS)

The spin Hamiltonian parameters (g factor and hyperfine structure constants) of Cr+ in ZnX (X = S, Se, Te) and CdTe are theoretically investigated, using the perturbation formulas of these parameters for a tetrahedral 3d5 cluster. Both the contributions from the crystal-field (CF) and charge transfer (CT) mechanisms are considered from the cluster approach. The calculated results show good agreement with the experimental data. The CT contribution to g-shift ?g (=g - g s, where g s =2.0023 is the spin only value) is opposite (positive) in sign related to the CF one, and its importance (characterized by the relative ratio (|?g CT/?g CF|) is 11%, 66% and 104% (71%) for ZnS, ZnSe and ZnTe (CdTe), respectively. ACT from the CT contribution to hyperfine structure constant is the same (positive) in sign and about 50-53% in magnitude as compared with ACF from the CF one.

Hu, Xian-Fen; Wu, Shao-Yi; Kuang, Min-Quan; Li, Guo-Liang

2014-03-01

162

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.

2014-02-01

163

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

PubMed

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

Mussa Farkhani, Samad; Valizadeh, Alireza

2014-06-01

164

Analysis of size distributions of type II ZnTe/ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

The photoluminescence (PL) spectrum of the ZnTe/ZnSe quantum dot (QD) structure which has a type II band alignment was investigated. A broader structure peaking at 2.180 eV together with the features of the ZnSe buffer layer located at 2.820 eV in the PL spectrum at 10 K were observed. The broadness of the PL attributes to the spatial inhomogeneity of the QD sizes. The PL spectrum was a normal distribution with a variance of 0.002 eV2. However, the dot size distribution was a deformed Gaussian. Using only one set of data of dot size distribution measured by the Atomic Force Microscopy (AFM), the statistical estimates with standard errors were evaluated using the bootstrap methodology. The probability distribution was inferred by calculating the means, percentiles and correlation coefficients of the base diameter and the height of the QDs. We concluded that the dot distributions were indeed a deformed Gaussian and the correlation coefficient of the diameter and the height of the QDs was 0.49 +/- 0.01. The uniformity of the dot size distribution was poor. To infer the dot size distribution from the PL spectrum, we numerically solved the Schrdinger equation by elaborating on the orthogonal periodic functions (OPF) approximation for the type II lens shaped QDs. The convergence of the probability density was discussed in a great detail. We found that the band edge discontinuities inside the dot acts as a barrier with Ec = 315 meV for the conduction band and as a well with Ev = 735 meV for the valence band. In the AFM measurement, the offset in dot height is 14 and the aspect ratio is 0.04. We employed the Schrdinger equation to correlated the PL spectrum (intensity versus optical energy) to the AFM data (number of QDs versus dot size) and the agreement was excellent.

Lee, Johnson; Yang, Chu Shou; Chang, Chun Tai; Liu, Jerron; Chou, Wu Ching; Lai, Chih Ming; Jan, Gwo Jen; Huang, Yin Sheng

2004-12-01

165

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

PubMed

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

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

2014-10-01

166

Electrical transport properties of thin film of aSe87Te13nanorods  

Microsoft Academic Search

We have studied the electrical transport properties of thin film of a-S87Te13 nanorods. Initially, the glassy alloy of S87Te13 is prepared by melt-quenching technique. The amorphous nature of this alloy is verified by using X-ray diffraction technique. The nanorods of a-S87Te13 are synthesised on a glass substrate under an ambient gas (Ar) atmosphere using physical vapour condensation system. The morphology

Zishan Husain Khan; Shamshad A. Khan; Numan Salah; Sami S. Habib; A. A. Al-Ghamdi

2011-01-01

167

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

E-print Network

of the resulting compounds. Introduction The search for more efficient thermoelectric materials has largely as a possible thermoelectric material by Jensen and Kjekshus, who predicted Nb3Sb2Te5 to be a semiconductor. In this study, the potential of Nb3Sb2Te5 as a thermoelectric material was examined via tests on Seebeck

168

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 2.7510 cm-1 to 5.7510 cm-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

169

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 4 T and the formation of magnetic polarons with a formation time of 7.4 ns were demonstrated.

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

2013-09-01

170

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

SciTech Connect

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

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

2013-01-15

171

Growth of CdTexSe1-x from a Te-rich solution for applications in radiation detection  

NASA Astrophysics Data System (ADS)

We grew CdTexSe1-x (CTS) crystals from a Te-rich solution by using the traveling heater method (THM). The average size distribution and concentration of Te inclusions/precipitates in these as-grown samples were measured to be ~7104 cm-3, which is much lower than values typical for the present state-of-the-art commercial CdZnTe (CZT) material. Their low-temperature photoluminescence measurement indicates high quality of the material; however the resistivity obtained via I-V curve measurements was ~5108 ?-cm, which is low in comparison to that required for gamma detectors. A well-resolved alpha response peak can be detected for both planar- and hemispherical detector geometry. The (??)e value for our as-grown sample at room temperature was found to be ~410-3 cm2/V.

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

2014-01-01

172

Synthesis, structure, optical, and electric properties of Ce-doped CuInTe2 compound  

NASA Astrophysics Data System (ADS)

Ce-doped CuInTe2 (CICT) semiconducting compounds are successfully synthesized. The phase structures, optical, and electric properties are investigated using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectrometer (XPS), Raman spectrometer, ultraviolet and visible spectrophotometer (UV-Vis), and a standard four-probe method. CuIn1?xCexTe2 crystallizes into a tetragonal structure with predominant orientation along the [112] direction. The lattice parameters are a = 6.190(6) Ŗ6.193(0) and c = 12.406(5) Ŗ12.409(5) . Ce prefers to occupy the 4b crystal position. According to the analysis of XPS spectra, Ce shows the mixture of valences 4+ and 3+. Raman spectra reveal that the photon vibrating model in the CICT follows A1 mode in a wavenumber range of 123 cm?1128 cm?1. UV-Vis spectra show that the band gap Eg values before and after 0.1 mole Ce doped into CuInTe2 are 1.28 eV and 1.16 eV, respectively. It might be due to the mixture of valences for Ce. Ce doped into CuInTe2 still shows the semiconductor characteristics.

Fu, Li; Guo, Yong-Quan

2014-12-01

173

Template Synthesis of Hierarchical Bi2E3 (E ) S, Se, Te) Core-Shell Microspheres and Their Electrochemical and Photoresponsive Properties  

E-print Network

Template Synthesis of Hierarchical Bi2E3 (E ) S, Se, Te) Core-Shell Microspheres-shell structured microspheres of bismuth chalcogenides (Bi2E3, E ) S, Se, Te) have been synthesized by chemical and their subsequent hydrothermal transformation into Bi2E3 core-shell microspheres. The uniform precursor microspheres

Qi, Limin

174

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

PubMed

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

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

2014-07-22

175

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

SciTech Connect

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

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

2008-11-17

176

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

NASA Astrophysics Data System (ADS)

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

Zou, Ping; Xu, Guiying; Wang, Song

2014-11-01

177

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

178

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

179

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

180

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

SciTech Connect

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

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

2011-12-12

181

Scotch tape induced strains for enhancing superconductivity of FeSe0.5Te0.5 single crystals  

NASA Astrophysics Data System (ADS)

We investigated the superconducting transition temperature Tc of FeSe0.5Te0.5 single crystals, which can be enhanced up to 14% by attaching onto a commercial Scotch tape. The Scotch tape exhibits a large cooling shrinkage at low temperatures, which is considerably more pronounced than that of the metallic FeSe0.5Te0.5 single crystal, thus providing a compressive strain of 2.4 10-3 at 15 K. For such strain, we calculated that the lattice parameter of c/a can be increased to 0.31%, which corresponds to the enhancement of the superconductivity. The present finding provides a rapid and simple method to examine the microstructure sensitive physical properties of the layered-structure materials by using the Scotch tape as strain generator.

Wang, Weike; Li, Jun; Yang, Jiyong; Gu, Chuanchuan; Chen, Xuliang; Zhang, Zhitao; Zhu, Xuebin; Lu, Wenjian; Wang, Hua-Bing; Wu, Pei-Heng; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng; Moshchalkov, Victor V.

2014-12-01

182

Substrate Dependence of Structural and Transport Properties in FeSe0.5Te0.5 Thin Films  

Microsoft Academic Search

In order to clarify the best condition for the growth of iron chalcogenide superconductor thin films, we investigated the effect of the substrate on the transport and structural properties of films. Thin films of FeSe0.5Te0.5 grown by pulsed laser deposition were characterized by DC electrical resistivity, Hall effect, X-ray diffraction measurements, and transmission electron microscopy (TEM) observation. The c-axis length

Masafumi Hanawa; Ataru Ichinose; Seiki Komiya; Ichiro Tsukada; Takanori Akiike; Yoshinori Imai; Tatsuo Hikage; Takahiko Kawaguchi; Hiroshi Ikuta; Atsutaka Maeda

2011-01-01

183

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

Microsoft Academic Search

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

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

2009-01-01

184

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

185

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

PubMed

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

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

2014-09-24

186

Weak anti-localization and quantum oscillations of surface states in topological insulator Bi?Se?Te.  

PubMed

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

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

2012-01-01

187

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

PubMed Central

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

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

2012-01-01

188

The low-frequency Raman spectra and nanostructure of As-Se-S and As-Se-Te chalcogenide semiconductors doped by samarium  

NASA Astrophysics Data System (ADS)

It has been established that the Raman scattering (RS) of chalcogenide glass-like semiconductors (CGS) materials As-Se-S and As-Se-Te at frequencies below 100 cm-1 consists of two parts: first - which the intensity with increasing frequency up to 30 40 cm-1 decreases (quasi-elastic scattering); second - which have been observed a broad band with a maximum at frequencies of ~ 63 67 cm-1 (boson peak - BP). Such a case is absent in the respective crystals. The observed features are associated with relaxation and excess density of states of acoustic vibrations in irregularities is localized with nanometer-size of material. It is shown that the contribution of the different types of scattering in a low-frequency range depends on the degree of disorder in the material, which varies with the change of chemical composition and by doping.

Isayeva, G. A.; Alekberov, R. I.; Mekhtiyeva, S. I.; Isayev, A. I.

2014-09-01

189

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

190

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

SciTech Connect

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

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

2012-12-15

191

Spectral dependence of the Aharonov Bohm effect in the magneto-photoluminescence of layered ZnTe-ZnSe structures  

NASA Astrophysics Data System (ADS)

Aharonov-Bohm (AB) oscillations in the mangeto-photoluminescence (PL) intensity of multilayered ZnTe/ZnSe structures grown via migration enhanced epitaxy (MEE) using three submonolayer deposition cycles of Zn-Te-Zn sandwiched between ZnSe barriers confirmed the presence of type-II ZnTe-based QDs. These co-exist with isoelectronic centers (ICs) as evident from the PL spectra. The spectral dependence of the transition magnetic field and the magnitude of the AB oscillation in intensity are investigated. A qualitative probing of distribution in the ensemble of QDs and ICs was done. The transition magnetic field changed from a lower value at the lower energy side of the PL emission to a higher value at the higher energy side which confirmed the lateral QD size distribution. AB oscillations at spectral positions dominated by emission from ICs were also observed suggesting that the presence of QDs also affects the ICs although the magnitude of the oscillation in the AB peak decreases at such spectral positions.

Roy, Bidisha; Ji, Haojie; Dhomkar, Siddharth; Peng, Le; Moug, Richard; Manna, Uttam; Tamargo, Maria; Cadieu, Fred; Kuskovsky, Igor

2012-02-01

192

Formation of a precursor layer in self-assembled CdTe quantum dots grown on ZnSe by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

The growth mode of CdTe quantum dots (QDs) grown on highly lattice-mismatched ZnSe buffer was investigated. CdTe QDs (0.6 to 5.0 mono-layers (MLs)) were deposited on the Se-stabilized ZnSe buffer layers using an alternating supply of Cd and Te atomic sources. Cross-sectional transmission electron microscopy and photoluminescence (PL) measurements revealed the existence of a CdSe-like two-dimensional precursor layer (PCL). The prominent difference in the temperature-dependent PL peak shift was associated with the emissions from the respective CdSe PCL and CdTe QDs. In addition, the PL excitation measurement demonstrated the existence of the first QD excited excitonic state.

Yang, C. S.; Wang, J. S.; Lai, Y. J.; Luo, C. W.; Chen, D. S.; Shih, Y. T.; Jian, S. R.; Chou, W. C.

2007-09-01

193

Aqueous synthesis and fluorescence-imaging application of CdTe/ZnSe core/shell quantum dots with high stability and low cytotoxicity.  

PubMed

CdTe/ZnSe core/shell quantum dots were directly synthesized in an aqueous condition by heating a mixed solution of ZnCI2, NaHSe and CdTe QDs in the presence of mercaptosuccinic acid as a stabilizer. By controlling the size and composition, the CdTe/ZnSe QDs with emission wavelength ranging from 540 to 630 nm, high quantum yield (44%) and narrow full width at half maximum (FWHM) could be obtained. Characterization results with HRTEM, XRD and EDX have shown that the synthesized CdTe/ZnSe QDs have good monodispersity and a nice crystal structure, and exhibited better stability and less cytotoxicity as compared with CdTe QDs. Furthermore, luminescent QD-IgG bioprobes were produced to detect the breast cancer marker Her2 on the surface of fixed MCF-7 cancer cells for their optical imaging. PMID:20355568

Fu, Tao; Qin, Hai-Yan; Hu, Hua-Jun; Hong, Zhi; He, Sailing

2010-03-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

195

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

NASA Astrophysics Data System (ADS)

This paper presents the results on the fabrication of highly sensitive fluorescence biosensors for pesticide detection. The biosensors are actually constructed from the complex of quantum dots (QDs), acetylcholinesterase (AChE) and acetylthiocholine (ATCh). The biosensor activity is based on the change of luminescence from CdSe and CdTe QDs with pH, while the pH is changed with the hydrolysis rate of ATCh catalyzed by the enzyme AChE, whose activity is specifically inhibited by pesticides. Two kinds of QDs were used to fabricate our biosensors: (i) CdSe QDs synthesized in high-boiling non-polar organic solvent and then functionalized by shelling with two monolayers (2-ML) of ZnSe and eight monolayers (8-ML) of ZnS and finally capped with 3-mercaptopropionic acid (MPA) to become water soluble; and (ii) CdTe QDs synthesized in aqueous phase then shelled with CdS. For normal checks the fabricated biosensors could detect parathion methyl (PM) pesticide at very low contents of ppm with the threshold as low as 0.05 ppm. The dynamic range from 0.05 ppm to 1 ppm for the pesticide detection could be expandable by increasing the AChE amount in the biosensor.

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

2012-09-01

196

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

SciTech Connect

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

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

1994-11-01

197

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

SciTech Connect

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

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

1994-08-01

198

Crystal orientation control of CdTe epitaxial layers grown on (100) GaAs with ZnSe buffer layer by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

Based on our previous experience with the growth of ZnSe on GaAs, we have improved the substrate, on which we deposit CdTe by first depositing a ZnSe buffer on the bulk GaAs crystals. This allows us to control the II-VI/III-V heterovalent epitaxy prior to the CdTe deposition. Depending on the control of the interface between ZnSe and CdTe, it was possible to stabilize the growth of either (100) or (111) CdTe epitaxial layers on the (100) ZnSe/GaAs substrate. Reflection high-energy electron diffraction was used to observe the nucleation of the epitaxial layers in situ during the growth, while x-ray diffraction and photoluminescence measurements indicate that the CdTe is of high structural quality despite the large lattice constant mismatch of 14.3% between CdTe and ZnSe. To explore the full impact of controllable-orientation growth technique, optical pumping and time-resolved Faraday rotation experiments were performed on CdTe films grown in different crystal orientation.

Zhang, Qiang; Charles, William; Li, Bingsheng; Shen, Aidong; Meriles, Carlos; Tamargo, Maria

2009-03-01

199

Control of crystal orientation of CdTe epitaxial layers grown on (0 0 1) GaAs with ZnSe buffer layer by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

CdTe layers were grown on (0 0 1) GaAs substrates with a ZnSe buffer layer by molecular beam epitaxy. The high-quality ZnSe (0 0 1) epitaxy on GaAs allows us to control the II-VI/III-V heterovalent interface prior to the CdTe deposition. By subsequently adjusting the interface between ZnSe and CdTe, it was possible to selectively obtain the growth of either (0 0 1) or (1 1 1) CdTe epitaxial layers on the (0 0 1) ZnSe/GaAs substrate. Reflection high energy electron diffraction indicates that the nucleation of the CdTe epitaxial layers turns two-dimensional within a few seconds of initiating the growth. X-ray diffraction and photoluminescence measurements indicate that both the (1 1 1) and the (0 0 1) CdTe films are of high structural quality despite the large lattice constant mismatch of 14.6% between CdTe and the (0 0 1) ZnSe/GaAs substrate.

Zhang, Qiang; Charles, William; Li, Bingsheng; Shen, Aidong; Meriles, Carlos A.; Tamargo, Maria C.

2009-04-01

200

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

201

Synthesis of cRGD-peptide conjugated near-infrared CdTe/ZnSe core-shell quantum dots for in vivo cancer targeting and imaging.  

PubMed

Cyclic RGD-peptide functionalized phospholipids micelle-encapsulated near-infrared CdTe/ZnSe quantum dots were synthesized as multifunctional probes for targeting and imaging tumors in live animals. PMID:20820500

Yong, Ken-Tye; Roy, Indrajit; Law, Wing-Cheung; Hu, Rui

2010-10-14

202

Steady state and transient photoconductivity in amorphous thin films of Se 0.8 Te 0.2  

Microsoft Academic Search

The present paper reports on steady state and transient photoconductivity measurements in amorphous thin films of Se0.8Te0.2. The paper also reports the effect of crystallization on the photoconductive behaviour. The photosensitivity(I\\u000a \\u000a ph\\u000a \\/I\\u000a d\\u000a ) reduces by a factor of 5 and the decay of photocurrent becomes much slower in the films annealed above the crystallization\\u000a temperature (state B) as

S. K. Tripathi; A. Kumar

1988-01-01

203

Hf(Se/sub x/Te/sub 1-x//sub 2/: deviation from Vegard's law in mixed systems  

SciTech Connect

Polycrystalline Hf(Se/sub x/Te/sub 1-x/)/sub 2/ has been prepared by iodine mineralization from the elements at 800/sup 0/C. Homogeneous solid solutions result over the range 0 < x < 1. Hexagonal a and c parameters, determined by using the Debye-Scherrer method, were found to vary linearly and parabolically, respectively, with composition. The non-Vegard behavior is ascribed to packing mismatches in the layers and is compared to behavior in other mixed transition-metal dichalcogenides. A brief comparison to pyrite systems is presented, and some general aspects of mixed materials are discussed.

Hodul, D.T. (Argonne National Lab., IL); Sienko, M.J.

1981-11-01

204

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

205

Experimental evidence and control of the bulk-mediated intersurface coupling in topological insulator Bi2Te2Se nanoribbons  

NASA Astrophysics Data System (ADS)

We present evidence for the existence and control of bulk-surface coupling in Bi2Te2Se nanoribbons. Our magnetoresistance measurements reveal that the number of coherent channels contributing to quantum interference in the nanoribbons changes abruptly when the film thickness exceeds the bulk phase relaxation length. We interpret this observation as an evidence for bulk-mediated coupling between metallic states located on opposite surfaces. This hypothesis is supported by additional magnetoresistance measurements conducted under a set of gate voltages and in a parallel magnetic field, the latter of which alters the intersurface coupling in a controllable way.

Li, Zhaoguo; Garate, Ion; Pan, Jian; Wan, Xiangang; Chen, Taishi; Ning, Wei; Zhang, Xiaoou; Song, Fengqi; Meng, Yuze; Hong, Xiaochen; Wang, Xuefeng; Pi, Li; Wang, Xinran; Wang, Baigeng; Li, Shiyan; Reed, Mark A.; Glazman, Leonid; Wang, Guanghou

2015-01-01

206

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

207

Temperature dependent band gap in PbX (X = S, Se, Te)  

NASA Astrophysics Data System (ADS)

PbTe is an important thermoelectric material for power generation applications due its high conversion efficiency and reliability. Its extraordinary thermoelectric performance is attributed to band convergence of the light L and heavy ? bands. However, the temperature at which these bands converge is disputed. In this letter, we provide direct experimental evidence combined with ab initio calculations that confirm an increasing optical gap up to 673 K and predict a band convergence temperature of 700 K, much higher than previous measurements showing saturation and band convergence at 450 K.

Gibbs, Zachary M.; Kim, Hyoungchul; Wang, Heng; White, Robert L.; Drymiotis, Fivos; Kaviany, Massoud; Jeffrey Snyder, G.

2013-12-01

208

Magnetic-crystallographic phase diagram of the superconducting parent compound Fe1+xTe  

NASA Astrophysics Data System (ADS)

Through neutron diffraction experiments, including spin-polarized measurements, we find a collinear incommensurate spin-density wave with propagation vector k= [0.4481(4)0(1)/(2)] at base temperature in the superconducting parent compound Fe1+xTe. This critical concentration of interstitial iron corresponds to x?12% and leads to crystallographic phase separation at base temperature. The spin-density wave is short-range ordered with a correlation length of 22(3) , and as the ordering temperature is approached its propagation vector decreases linearly in the H direction and becomes long-range ordered. Upon further populating the interstitial iron site, the spin-density wave gives way to an incommensurate helical ordering with propagation vector k= [0.3855(2)0(1)/(2)] at base temperature. For a sample with x?9(1)%, we also find an incommensurate spin-density wave that competes with the bicollinear commensurate ordering close to the Nel point. The shifting of spectral weight between competing magnetic orderings observed in several samples is supporting evidence for the phase separation being electronic in nature, and hence leads to crystallographic phase separation around the critical interstitial iron concentration of 12%. With results from both powder and single crystal samples, we construct a magnetic-crystallographic phase diagram of Fe1+xTe for 5%

Rodriguez, E. E.; Stock, C.; Zajdel, P.; Krycka, K. L.; Majkrzak, C. F.; Zavalij, P.; Green, M. A.

2011-08-01

209

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

PubMed

Here we report for the first time on a complete simulation assisted "material to module" development of a high performance thermoelectric generator (TEG) based on the combination of a phase change material and established thermoelectrics yielding the compositions (1 - x)(GeTe) x(Bi2Se0.2Te2.8). For the generator design our approach for benchmarking thermoelectric materials is demonstrated which is not restricted to the determination of the intrinsically imprecise ZT value but includes the implementation of the material into a TEG. This approach is enabling a much more reliable benchmarking of thermoelectric materials for TEG application. Furthermore we analyzed the microstructure and performance close to in-operandi conditions for two different compositions in order to demonstrate the sensitivity of the material against processing and thermal cycling. For x = 0.038 the microstructure of the as-prepared material remains unchanged, consequently, excellent and stable thermoelectric performance as prerequisites for TEG production was obtained. For x = 0.063 we observed strain phenomena for the pristine state which are released by the formation of planar defects after thermal cycling. Consequently the thermoelectric performance degrades significantly. These findings highlight a complication for deriving the correlation of microstructure and properties of thermoelectric materials in general. PMID:25559337

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

2015-01-28

210

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

211

Band Engineering in Core/Shell ZnTe/CdSe for Photovoltage and Efficiency Enhancement in Exciplex Quantum Dot Sensitized Solar Cells.  

PubMed

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

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

2015-01-27

212

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

213

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

214

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

215

Anisotropy analysis of thermoelectric properties of Bi2Te2.9Se0.1 prepared by SPS method  

NASA Astrophysics Data System (ADS)

The n-type Bi2Te2.9Se0.1 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 H2-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 Bi2Te2.9Se0.1 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 0.7 at 370 K in perpendicular direction to the pressing force.

Zybala, Rafal; Wojciechowski, Krzysztof T.

2012-06-01

216

JOURNAL DE PHYSIQUE Colloque C 4, supplbment au no 11-12, Tome 29, Novembre-Dkembre 1968,page C 4 -62 RELATIVISTIC BAND STRUCTURE OF GeTe, SnTe, PbTe, PbSe, AND PbS (*)  

E-print Network

- 62 RELATIVISTIC BAND STRUCTURE OF GeTe, SnTe, PbTe, PbSe, AND PbS (*) Frank HERMAN,Richard L. KORTUM understanding of the princi- pal band edges stems from the analyses of Dimmock and Wright [3] Cuff et al., [4], and Mitchell and Wallis [5]. Further insight into the nature of the band edges and information concerning

Boyer, Edmond

217

Quasi-Stranski Krastanow growth mode of self-assembled CdTe quantum dots grown on ZnSe by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

This study investigates the growth mode of highly lattice-mismatch ( 14%) CdTe self-assembled quantum dots grown on a ZnSe buffer-layer by molecular beam epitaxy. Two growth processes were used to prepare the samples. For the group-I samples, Te and Cd sources were alternately used to deposit a CdTe coverage layer of 0.6 to 8.0 mono-layers on a Zn-stabilized ZnSe buffer layer. The growth process of group-II samples was reversed; that is, the Cd beam was supplied first on a Se-stabilized ZnSe buffer layer. The optical spectra, including the power-dependent, time-resolved photoluminescence (PL) and PL excitation measurement, demonstrate a ZnTe-like and a CdSe-like two-dimensional precursor layer (wetting layer) in the group-I and group-II samples, respectively. Following the formation of the precursor layer, three-dimensional highly strained CdTe quantum dots were formed. Accordingly, the growth of CdTe self-assembled quantum-dot structures was attributed to the quasi-Stranski-Krastanow mode.

Yang, C. S.; Lai, Y. J.; Chou, W. C.; Chen, D. S.; Wang, J. S.; Chien, K. F.; Shih, Y. T.

2007-04-01

218

Fluorescence quenching of CdSe quantum dots by nitroaromatic explosives and their relative compounds  

NASA Astrophysics Data System (ADS)

CdSe quantum dots (QDs) were synthesized in oleic acid and octadecene medium under high-temperature and dispersed in chloroform. Nitroaromatic explosives and their relative compounds, 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), nitrobenzene (NB), 2,4-dinitrochlorobenzene (DNBCl) and p-nitrotoluene (NT) can obviously cause the fluorescence quenching of the synthesized QDs. Under the optimum conditions, a nonlinear response was observed over the concentration range of 10 -8 to 10 -5 M for them all. The modified Stern-Volmer quenching equations of ln I0/ I versus C show a good linear relation in 10 -5 M order of magnitude, and the detection limits approach 10 -6 to 10 -7 M.

Shi, Guo Hua; Shang, Zhuo Bin; Wang, Yu; Jin, Wei Jun; Zhang, Tian Cai

2008-07-01

219

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

SciTech Connect

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

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

2014-02-21

220

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

2012-09-25

221

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

SciTech Connect

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

Verma, Ajay Singh; Sharma, Sheetal; Jindal, Vijay Kumar [Department of Physics, Panjab University, Chandigarh, 160014 (India); Sarkar, Bimal Kumar [Department of Physics, VIT University, Vellore, TN, 632014 (India)

2011-12-12

222

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

223

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

SciTech Connect

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

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

2012-09-15

224

High ZT in p-type (PbTe)1-2x(PbSe)x(PbS)x thermoelectric materials.  

PubMed

Lead chalcogenide thermoelectric systems have been shown to reach record high figure of merit values via modification of the band structure to increase the power factor or via nanostructuring to reduce the thermal conductivity. Recently, (PbTe)1-x(PbSe)x was reported to reach high power factors via a delayed onset of interband crossing. Conversely, the (PbTe)1-x(PbS)x was reported to achieve low thermal conductivities arising from extensive nanostructuring. Here we report the thermoelectric properties of the pseudoternary 2% Na-doped (PbTe)1-2x(PbSe)x(PbS)x system. The (PbTe)1-2x(PbSe)x(PbS)x system is an excellent platform to study phase competition between entropically driven atomic mixing (solid solution behavior) and enthalpy-driven phase separation. We observe that the thermoelectric properties of the PbTe-PbSe-PbS 2% Na doped are superior to those of 2% Na-doped PbTe-PbSe and PbTe-PbS, respectively, achieving a ZT ?2.0 at 800 K. The material exhibits an increased the power factor by virtue of valence band modification combined with a very reduced lattice thermal conductivity deriving from alloy scattering and point defects. The presence of sulfide ions in the rock-salt structure alters the band structure and creates a plateau in the electrical conductivity and thermopower from 600 to 800 K giving a power factor of 27 ?W/cmK(2). The very low total thermal conductivity values of 1.1 W/mK of the x = 0.07 composition is accounted for essentially by phonon scattering from solid solution defects rather than the assistance of endotaxial nanostructures. PMID:24533466

Korkosz, Rachel J; Chasapis, Thomas C; Lo, Shih-han; Doak, Jeff W; Kim, Yoon Jun; Wu, Chun-I; Hatzikraniotis, Euripidis; Hogan, Timothy P; Seidman, David N; Wolverton, Chris; Dravid, Vinayak P; Kanatzidis, Mercouri G

2014-02-26

225

PUBLISHED ONLINE: 10 MAY 2009 | DOI: 10.1038/NPHYS1270 Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3  

E-print Network

of the 2D HgTe quantum wells are well described by a 2+1-dimensional Dirac equation where the mass term, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface Haijun Zhang1 , Chao-Xing Liu2 , Xiao insulators by inverting the bulk Dirac gap spectrum can also be generalized to other 2D and 3D sys- tems

Loss, Daniel

226

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

227

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

PubMed

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

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

2014-07-14

228

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

229

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

PubMed

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

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

2015-01-01

230

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

PubMed Central

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

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

2015-01-01

231

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

232

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

SciTech Connect

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

Hao Guolin; Qi Xiang; Xue Lin; Cai Canying; Li Jun; Wei Xiaolin; Zhong Jianxin [Hunan Key Laboratory for Micro-Nano Energy Materials and Devices, Xiangtan University, Hunan 411105 (China); Laboratory for Quantum Engineering and Micro-Nano Energy Technology and Faculty of Materials and Optoelectronic Physics, Xiangtan University, Hunan 411105 (China)

2013-01-14

233

Thermoelectric properties of n-type Bi2Te2.7Se0.3 with addition of nano-ZnO:Al particles  

NASA Astrophysics Data System (ADS)

Nano Al-doped ZnO (AZO) particles were added into n-type Bi2Te2.7Se0.3 alloys by ball milling and hot pressing method. The power factor was improved by ?22% with addition of nano-AZO particles, accompanied with a ?40% decrease of lattice thermal conductivity, leading to peak ZT of ?0.85 at 323 K for Bi2Te2.7Se0.3(AZO)0.005 sample. The effects of the addition of AZO nanoparticles on the microstructure and thermoelectric transport properties are discussed.

Song, Shaowei; Wang, Jueling; Xu, Bo; Lei, Xiaobo; Jiang, Hongchuan; Jin, Yingrong; Zhang, Qinyong; Ren, Zhifeng

2014-09-01

234

First-principles calculations of the structural, phonon and thermal properties of ZnX (X = S, Se,Te) chalcogenides  

NASA Astrophysics Data System (ADS)

Zinc chalcogenides, ZnX (X = S, Se and Te), are investigated with the full-potential linear-augmented plane wave method within the framework of the density functional theory for their structural, phonon and thermal properties. We consider the generalized gradient approximation for the purpose of exchange-correlation energy determination. Murnaghans equation of state is used for volume optimization by minimizing the total energy with respect to the unit cell volume. The elastic constants are calculated to examine the crystal structure stability, binding properties and bond character of zinc chalcogenides. By means of frozen-phonon method within the harmonic approximation, we work out phonon dispersion, lattice dynamics and thermal properties of ZnX compounds. The phonon frequencies in the first Brillouin zone, at the zone centre (?) and at the zone boundary (X or L) are estimated. The calculated lattice parameters and thermal parameters are in good agreement with other theoretical calculations as well as with the available experimental data.

Sarkar, B. K.; Verma, A. S.; Sharma, S.; Kundu, S. K.

2014-07-01

235

Formation of a reliable intermediate band in Si heavily coimplanted with chalcogens (S, Se, Te) and group III elements (B, Al)  

NASA Astrophysics Data System (ADS)

This first-principles study describes the properties of Si implanted with several chalcogen species (S, Se, Te) at doses considerably above the equilibrium solubility limit, especially when coimplanted with the group III atoms B and Al. The measurements of chalcogen-implanted Si show strong optical absorption in the infrared range. The calculations carried out show that substitution of Si by chalcogen atoms requires lower formation energy than the interstitial implantation. In the resulting electronic structure, at concentrations close to 0.5%, an impurity band determined by the properties of the chalcogens introduced is observed in the forbidden energy gap of Si. Although this band is a few tenths of an electron volt wide, it remains energetically isolated from both the valence and the conduction bands. Appropriate coimplantation with group III elements allows control over the occupation of the intermediate band while modifying its energies only slightly. A moderate energy gain (especially small for B) seems to be obtained when p -doping atoms occupy the sites next to those of the chalcogens. Therefore, the apparent electrostatic attraction between species that in isolation would act as acceptors and double donors is smaller than expected. The intermediate-band properties have been preserved for all of the coimplanted compounds analyzed here, regardless of the species involved or the distance between them, which constitutes an appreciable advantage for the design of new experimental materials.

Snchez, K.; Aguilera, I.; Palacios, P.; Wahnn, P.

2010-10-01

236

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

PubMed

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

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

2014-10-01

237

Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe{sub 0.92}-FeSe{sub 0.5}Te{sub 0.5} system  

SciTech Connect

Thin films of FeSe{sub 0.92} and FeSe{sub 0.5}Te{sub 0.5} iron chalcogenide superconductors and solid solutions containing these components in different ratios have been grown on the surface of LaAlO{sub 3} (10 1-bar 2) crystals by pulsed laser deposition. Films of solid solutions have been deposited by simultaneous laser ablation from two targets of the FeSe{sub 0.92} and FeSe{sub 0.5}Te{sub 0.5} stoichiometric compositions onto one substrate. An X-ray diffraction study of the film structure shows that the films grown are epitaxial and their lattice parameters regularly vary with the ratio of the deposited components, which was controllably varied by changing the ablation intensities from the targets.

Stepantsov, E. A., E-mail: stepantsov@ns.cryst.ras.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Kazakov, S. M.; Belikov, V. V. [Moscow State University (Russian Federation)] [Moscow State University (Russian Federation); Makarova, I. P. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)] [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Arpaia, R.; Gunnarsson, R.; Lombardi, F. [Chalmers University of Technology, Department of Microtechnology and Nanoscience (Sweden)] [Chalmers University of Technology, Department of Microtechnology and Nanoscience (Sweden)

2013-09-15

238

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

239

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

240

Determination of selenium and tellurium concentrations in Pyrenean peridotites (Ariege, France): New insight into S/Se/Te systematics of the upper in  

E-print Network

Determination of selenium and tellurium concentrations in Pyrenean peridotites (Ariege, France.L. Rudnick Keywords: Selenium Tellurium Upper mantle Peridotites Chondrites Refertilization Whole-rock concentrations of Se and Te were determined in 53 peridotite samples collected in orogenic bodies from

Demouchy, Sylvie

241

Thermoelectric Properties of the Quaternary Chalcogenides BaCu5.9STe6 and BaCu5.9SeTe6.  

PubMed

These quaternary chalcogenides are isostructural, crystallizing in a unique structure type comprising localized Cu clusters and Te2(2-) dumbbells. With less than six Cu atoms per formula unit, these materials are p-type narrow-gap semiconductors, according to the balanced formula Ba(2+)(Cu(+))6Q(2-)(Te2(2-))3 with Q = S, Se. Encouraged by the outstanding thermoelectric performance of Cu2-xSe and the low thermal conductivity of cold-pressed BaCu5.7Se0.6Te6.4, we determined the thermoelectric properties of hot-pressed pellets of BaCu5.9STe6 and BaCu5.9SeTe6. Both materials exhibit a high Seebeck coefficient and a low electrical conductivity, combined with very low thermal conductivity below 1 W m(-1) K(-1). Compared to the sulfide-telluride, the selenide-telluride exhibits higher electrical and thermal conductivity and comparable Seebeck coefficient, resulting in superior figure-of-merit values zT, exceeding 0.8 at relatively low temperatures, namely, around 600 K. PMID:25299429

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

2015-02-01

242

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

243

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

244

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

SciTech Connect

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

Cheng, N. [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China); CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China); University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049 (China); Liu, R. [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China); Bai, S. [CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China); Shi, X., E-mail: xshi@mail.sic.ac.cn; Chen, L. [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China); CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)

2014-04-28

245

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

246

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

Microsoft Academic Search

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

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

2008-01-01

247

A Review of the Characterization Techniques for the Analysis of Etch Processed Surfaces of HgCdTe and Related Compounds  

NASA Astrophysics Data System (ADS)

HgCdTe is the material system of choice for many infrared sensing applications. Growth of this material can often be challenging. However, processing of this material system can be equally as challenging. Incorrect processing can cause shunting, surface inversion, or high surface recombination velocities that can be detrimental. In order to produce an effective device in HgCdTe, one needs to understand what happens to the HgCdTe surface. Factors like the chemical termination of the HgCdTe surface, surface roughness, and surface reconstruction after a process is performed can dramatically affect the performance of devices made with HgCdTe. We will review different surface characterization techniques and how these techniques can be used conventionally and unconventionally, and how different processes can affect the surfaces of HgCdTe and related compounds.

Stoltz, A. J.; Benson, J. D.; Jaime-Vasquez, M.; Smith, P. J.; Almeida, L. A.; Jacobs, R.; Markunas, J.; Brogden, K.; Brown, A.; Lennon, C.; Maloney, P.; Supola, N.

2014-09-01

248

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

SciTech Connect

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

Abdul-Jabbar, N. M. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Ercius, P. [National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Gronsky, R. [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Bourret-Courchesne, E. D. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Wirth, B. D. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States); Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States)

2014-02-03

249

Nearly lattice matched all wurtzite CdSe/ZnTe type II core-shell nanowires with epitaxial interfaces for photovoltaics  

NASA Astrophysics Data System (ADS)

Achieving a high-quality interface is of great importance in core-shell nanowire solar cells, as it significantly inhibits interfacial recombination and thus improves the photovoltaic performance. Combining thermal evaporation of CdSe and pulsed laser deposition of ZnTe, we successfully synthesized nearly lattice matched all wurtzite CdSe/ZnTe core-shell nanowires on silicon substrates. Comprehensive morphological and structural characterizations revealed that a wurtzite ZnTe shell layer epitaxially grows over a wurtzite CdSe core nanowire with an abrupt interface. Further optical studies confirmed a high-quality interface and demonstrated efficient charge separation induced by the type-II band alignment. A representative photovoltaic device has been demonstrated and yielded an energy-conversion efficiency of 1.7% which can be further improved by surface passivation. The all-wurtzite core-shell nanowire with an epitaxial interface offers an attractive platform to explore the piezo-phototronic effect and promises an efficient hybrid nano-sized, energy harvesting system.Achieving a high-quality interface is of great importance in core-shell nanowire solar cells, as it significantly inhibits interfacial recombination and thus improves the photovoltaic performance. Combining thermal evaporation of CdSe and pulsed laser deposition of ZnTe, we successfully synthesized nearly lattice matched all wurtzite CdSe/ZnTe core-shell nanowires on silicon substrates. Comprehensive morphological and structural characterizations revealed that a wurtzite ZnTe shell layer epitaxially grows over a wurtzite CdSe core nanowire with an abrupt interface. Further optical studies confirmed a high-quality interface and demonstrated efficient charge separation induced by the type-II band alignment. A representative photovoltaic device has been demonstrated and yielded an energy-conversion efficiency of 1.7% which can be further improved by surface passivation. The all-wurtzite core-shell nanowire with an epitaxial interface offers an attractive platform to explore the piezo-phototronic effect and promises an efficient hybrid nano-sized, energy harvesting system. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06137j

Wang, Kai; Rai, Satish C.; Marmon, Jason; Chen, Jiajun; Yao, Kun; Wozny, Sarah; Cao, Baobao; Yan, Yanfa; Zhang, Yong; Zhou, Weilie

2014-03-01

250

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

251

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

SciTech Connect

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

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

1992-09-01

252

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

SciTech Connect

Bulk glasses of compositions Se{sub 85-x}Te{sub 15}In{sub x} (x = 3,6,9,12) are prepared by melt quenching technique and Differential scanning calorimetry (DSC) is employed to study the thermal stability, crystallization mechanism as well as specific heat of these glasses. It is found that the addition of indium increases the glass transition temperature. From the heating rate dependence of the glass transition temperature the activation energy of glass transition is determined using Kissinger's equation for non-isothermal crystallization of materials. An attempt has been made to explain the variation in the value of T{sub c}, T{sub p} and {Delta}C{sub p} for the composition Se{sub 73}Te{sub 15}In{sub 12} using rigidity percolation threshold (RPT). From the values of (T{sub c}-T{sub g}) the stable glass system is determined.

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

2011-10-20

253

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

254

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

NASA Astrophysics Data System (ADS)

We performed magneto-optical (MO) measurements on FeTe0.5Se0.5 thin films grown on LaAlO3 (LAO) and Yttria-stabilized zirconia (YSZ) single-crystalline substrates. These thin films show superconducting transition temperature Tc ?19 K, 4 K higher than the bulk sample. Typical roof-top patterns can be observed in the MO images of thin films grown on LAO and YSZ, from which a large and homogeneous critical current density Jc over 1 {{10}6} A c{{m}-2} at 5 K was obtained. Magnetic flux penetration measurement reveals that the current is almost isotropically distributed in the two thin films. Compared with bulk crystals, FeTe0.5Se0.5 thin film demonstrates not only higher Tc, but also much larger Jc, which is attractive for applications.

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

2015-01-01

255

Electrochemical studies of the effects of the size, ligand and composition on the band structures of CdSe, CdTe and their alloy nanocrystals.  

PubMed

In this paper, we have elucidated the fundamental principle of employing CV to investigate the band structures of semiconductor nanocrystals (SNCs), and have also built up an optimal protocol for performing such investigation. By utilizing this protocol, we are able to obtain well-defined and characteristic electrochemical redox signals of SNCs, which allows us to intensively explore the influences of the particle size, the surface ligand and particle composition on the band structures of CdSe, CdTe and their alloy nanocrystals. The size-, ligand- and composition-dependent band structures of CdSe and CdTe nanocrystals (NCs) have therefore been mapped out, respectively, which are generally consistent with the previous theoretical and experimental reports. We believe that the optimal protocol and the original results regarding electrochemical characterization of SNCs demonstrated in this paper will definitely benefit the better understanding, modulation and application of the unique electronic and optical properties of SNCs. PMID:24468655

Liu, Jinjin; Yang, Wanting; Li, Yunchao; Fan, Louzhen; Li, Yongfang

2014-03-14

256

Effect of thermal annealing on structure and optical band gap of amorphous Se{sub 72}Te{sub 25}Sb{sub 3} thin films  

SciTech Connect

Thin films of a?Se{sub 72}Te{sub 25}Sb{sub 3} were prepared by vacuum evaporation technique in a base pressure of 10{sup ?6} Torr on to well cleaned glass substrate. a?Se{sub 72}Te{sub 25}Sb{sub 3} thin films were annealed at different temperatures below their crystallization temperatures for 2h. The structural analysis of the films has been investigated using X-ray diffraction technique. The optical band gap of as prepared and annealed films as a function of photon energy in the wavelength range 4001100 nm has been studied. It has been found that the optical band gap decreases with increasing annealing temperatures in the present system.

Dwivedi, D. K., E-mail: dwivedidkphys@rediffmail.com; Pathak, H. P., E-mail: dwivedidkphys@rediffmail.com; Shukla, Nitesh [Amorphous Semiconductor Research Lab, Department of Physics, M.M.M. E.C., Gorakhpur-273010 (India); Kumar, Vipin [Department of Physics, K.I.E.T., Ghaziabad-201206 (India)

2014-04-24

257

The role of stoichiometric vacancy periodicity in pressure-induced amorphization of the Ga2SeTe2 semiconductor alloy  

NASA Astrophysics Data System (ADS)

We observe that pressure-induced amorphization of Ga2SeTe2 (a III-VI semiconductor) is directly influenced by the periodicity of its intrinsic defect structures. Specimens with periodic and semi-periodic two-dimensional vacancy structures become amorphous around 10-11 GPa in contrast to those with aperiodic structures, which amorphize around 7-8 GPa. The result is an instance of altering material phase-change properties via rearrangement of stoichiometric vacancies as opposed to adjusting their concentrations. Based on our experimental findings, we posit that periodic two-dimensional vacancy structures in Ga2SeTe2 provide an energetically preferred crystal lattice that is less prone to collapse under applied pressure. This is corroborated through first-principles electronic structure calculations, which demonstrate that the energy stability of III-VI structures under hydrostatic pressure is highly dependent on the configuration of intrinsic vacancies.

Abdul-Jabbar, N. M.; Kalkan, B.; Huang, G.-Y.; MacDowell, A. A.; Gronsky, R.; Bourret-Courchesne, E. D.; Wirth, B. D.

2014-08-01

258

BaCu2Se2 based compounds as promising thermoelectric materials.  

PubMed

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

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

2015-01-20

259

Comparative study of performance of CdTe, CdSe and CdS thin films-based photoelectrochemical solar cells  

Microsoft Academic Search

Polycrystalline films of CdTe and CdSe were electrodeposited onto titanium substrates from acidic baths, and, polycrystalline CdS thin films were prepared by chemical bath deposition method. Due to surface treatment these films show good photoelectrochemical behaviour in a polysulphide electrolyte with high conversion efficiency and stability. The solid-state parameters of annealed films are calculated and compared with those of unannealed

R. K. Pandey; Shikha Mishra; Sanjay Tiwari; P. Sahu; B. P. Chandra

2000-01-01

260

IU dependence of TlInX2 (X=Se,Te) single crystals: The Ohmic and S-type regions  

Microsoft Academic Search

Electrical conductivity measurements were performed on TlInSe2 and TlInTe2 single crystals. The corresponding current-voltage (I-U) characteristics consist of two parts: An Ohmic part, at low current densities, and a nonlinear one of the S type, at moderate and higher current densities. In the latter part a well-formed negative-differential-resistance (NDR) region appears. Acceptor levels and their concentrations were determined from lnp

M. Hanias; A. N. Anagnostopoulos; K. Kambas; J. Spyridelis

1991-01-01

261

Upper critical fields in a FeSe0.5Te0.5 superconducting single crystal  

NASA Astrophysics Data System (ADS)

A single crystal with a nominal composition FeSe0.5Te0.5 was obtained by the Bridgman method. A quartz ampulla with the sample inside was vacuum-sealed and maintained at 1050 C for 37 h to homogenize the sample. Subsequently, the quartz ampulla with the sample was moved with a speed of 2.2 mm/h to a furnace which was at 450 C. X-ray diffraction confirmed the tetragonal structure of the grown single crystal with the cleavage plane corresponding to the ab plane. Resistance measurements were carried out with magnetic fields from 0 to 9 T, applied parallel to the c axis and ab plane, respectively. A zero-field critical temperature Tc = 14 K was determined. The upper critical field vs. temperature phase diagram was built for temperatures where the resistance drops to 90%, 50%, and 10% of the normal state resistance. The linear extrapolation to T = 0 K gave upper critical fields of 57.2, 51.8, and 46.0 T for H?c axis and 109.6, 95.5, and 80.9 T for H?ab. Applying the Werthamer-Helfand-Hohenberg (WHH) theory, upper critical fields of 39.6, 35.9, and 31.8 T and coherence lengths of 28.8, 30.3, and 32.1 were obtained for H?c; while for H?ab, upper critical fields of 51.3, 40.7, and 37.5 T and coherence lengths of 22.3, 26.7, and 31.5 were obtained. The value of ?0Hc2/kBTc calculated by the WHH theory exceeds the Pauli limit (1.84 T/K) indicating the unconventional nature of superconductivity. The activation energy U0 has two different rates of change with the applied magnetic field probably due to two different thermal activation mechanisms; the origin of which requires further investigation. A similar behavior is observed in the irreversibility lines.

Velasco-Soto, D.; Rivera-Gmez, F. J.; Santilln-Rodrguez, C. R.; Senz-Hernndez, R. J.; Botello-Zubiate, M. E.; Matutes Aquino, J. A.

2013-05-01

262

Nearly lattice matched all wurtzite CdSe/ZnTe type II core-shell nanowires with epitaxial interfaces for photovoltaics.  

PubMed

Achieving a high-quality interface is of great importance in core-shell nanowire solar cells, as it significantly inhibits interfacial recombination and thus improves the photovoltaic performance. Combining thermal evaporation of CdSe and pulsed laser deposition of ZnTe, we successfully synthesized nearly lattice matched all wurtzite CdSe/ZnTe core-shell nanowires on silicon substrates. Comprehensive morphological and structural characterizations revealed that a wurtzite ZnTe shell layer epitaxially grows over a wurtzite CdSe core nanowire with an abrupt interface. Further optical studies confirmed a high-quality interface and demonstrated efficient charge separation induced by the type-II band alignment. A representative photovoltaic device has been demonstrated and yielded an energy-conversion efficiency of 1.7% which can be further improved by surface passivation. The all-wurtzite core-shell nanowire with an epitaxial interface offers an attractive platform to explore the piezo-phototronic effect and promises an efficient hybrid nano-sized, energy harvesting system. PMID:24567192

Wang, Kai; Rai, Satish C; Marmon, Jason; Chen, Jiajun; Yao, Kun; Wozny, Sarah; Cao, Baobao; Yan, Yanfa; Zhang, Yong; Zhou, Weilie

2014-04-01

263

Preferential orientation and thermoelectric properties of n-type Bi2Te2.85Se0.15 alloys by mechanical alloying and equal channel angular extrusion  

NASA Astrophysics Data System (ADS)

Starting from elemental bismuth, tellurium and selenium powders, n-type Bi2Te2.85Se0.15 solid solution with a fine microstructure was prepared by mechanical alloying and equal channel angular extrusion (ECAE) in the present work. The effect of extrusion temperature on the microstructure and thermoelectric properties of the as-ECAEed samples was investigated. A preferentially oriented microstructure with the basal planes (0 0 l) in the parallel direction to extrusion was formed, and the orientation factors F of the (0 0 l) planes of the 703 K and 753 K ECAEed Bi2Te2.85Se0.15 alloys were 0.26 and 0.28, respectively. The electrical resistivity and the Seebeck coefficient decreased, and the thermal conductivity increased with increasing extrusion temperature. The electrical and thermal transmission performances were strongly affected by the preferentially oriented microstructure and the preferential orientation improved the thermoelectric properties of the ECAEed Bi2Te2.85Se0.15 alloys in the parallel direction to extrusion. The maximum dimensionless figure of merit was obtained when extruded at 753 K at a testing temperature of 343 K, ZT = 0.66.

Fan, X. A.; Yang, J. Y.; Zhu, W.; Bao, S. Q.; Duan, X. K.; Xiao, C. J.; Li, K.

2007-09-01

264

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

PubMed

In this paper, we present an innovative method for the synthesis of CdTe/CdSe type-II core/shell structure quantum dots (QDs) using 'greener' chemicals. The PL of CdTe/CdSe type-II core/shell structure QDs ranges from 600 to 820 nm, and the as-synthesized core/shell structures show narrow size distributions and stable and high quantum yields (5075%). Highly efficient near-infrared light-emitting diodes (LEDs) have been demonstrated by employing the CdTe/CdSe type-II core/shell QDs as emitters. The devices fabricated based on these type-II core/shell QDs show color-saturated near-infrared emission from the QD layers, a low turn-on voltage of 1.55 V, an external quantum efficiency (EQE) of 1.59%, and a current density and maximum radiant emittance of 2.1 10(3) mA cm?2 and 17.7 mW cm?2 at 8 V; it is the first report to use type-II core/shell QDs as near-infrared emitters and these results may offer a practicable platform for the realization of near-infrared QD-based light-emitting diodes, night-vision-readable displays, and friend/foe identification system. PMID:24192490

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

2013-11-29

265

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

PubMed Central

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

266

Influence of Thallium on the Shubnikov - de Haas effect and Thermoelectric Properties of Sb2Te3 and Bi2Se3  

NASA Astrophysics Data System (ADS)

Influence of Tl-doping on the Shubnikov de Haas effect (SdH) at T=4.2 K in magnetic field up to 38 T of p-Sb2-xTlxTe3 (x=0; 0.005; 0.015; 0.05) and n-Bi2-xTlxSe3 (x=0, 0.01; 0.02; 0.04; 0.06) single crystals has been investigated. By increasing the Tl content, the frequency of the SdH effect and hence the extremal cross-sections of the Fermi-surface decreases in both materials. The hole concentration decreases in Sb2-xTlxTe3 due to a donor effect of Tl and the electron concentration decreases in n-Bi2-xTlxSe3 due to an acceptor effect of Tl. Temperature dependence of the Seebeck coefficient S, electrical conductivity ?, thermal conductivity k and the figure of merit ZT single crystals were measured in the temperature range 77 K - 300 K. The values of k and ? decrease due to Tl doping in Sb2-xTlxTe3 and n-Bi2-xTlxSe3 and the Seebeck coefficient S for all compositions increases in the whole temperature range. The figure of merit ZT increases in both materials. The preferential scattering mechanism in Tl-doped samples changes from the acoustic phonon scattering to the ionized impurity scattering.

Kulbachinskii, V. A.; Kudryashov, A. A.; Kytin, V. G.

2014-12-01

267

Diffusion coefficients of two mobile ions in three AB3In7VI12 single crystals (AB=Cu and Ag VI=Se or Te). Proposition of an equivalent electrical circuit  

NASA Astrophysics Data System (ADS)

Diffusion coefficients of two mobile ions are computed from the conductivity variation with time of three In-rich chalcopyrite single crystals of the ABn-3Inn+1VI2n system (AB=Cu and Ag and VI=Se or Te). The coefficients have similar values in the three compounds, higher than in chalcopyrite compounds (ABInSe2) due to a higher number of (2VCu+InCu) defect pairs in the lattice. In each compound, the potential across the sample or the current intensity, Vm and I, can increase or decrease within time due to a change in the interface potential by the ion arrival, where the decrease could be explained by a charge decrease. Mobile ions arrive while others, with higher charge, should leave related to the formation or disappearance of (2VCu+InCu) defect pairs. Compositional measurements confirm the motion of Cu ions and In antisites, InCu, in the Cu sublattice. Therefore, these compounds are mixed ionic and electronic conductors, MIECs, with two mobile ions, where the electronic and ionic conductions are non-blocked and blocked in the metal/semiconductor interface respectively. An equivalent electrical circuit is proposed, extensible at MIECs with j mobile ions, where the interface potential is similar to the potential drop in the charge or discharge in the capacitor. The analysis of the total flux of ions due to diffusion, jdiff, and to the action of electrical field, jdrift, permits compute the number of ions, their diffusion coefficients and the change of the potential drop within time in the interface in compounds with several mobile ions. This electrical model is checked using the experimental data in the three single crystals in a computer program. To know different mobile ions in In-rich chalcopyrites and their diffusion coefficients will permit to understand and have mechanisms of control in solar cell fabrication based in chalcopyrite thin films.

Daz, R.

2012-06-01

268

Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Final subcontract report, 1 April 1990--30 November 1993  

SciTech Connect

The report describes the exploration of several aspects of the role of polycrystallinity in the operation of CdTe, CuInSe{sub 2}, and Cu(In,Ga)Se{sub 2} solar cells. The work included the refinement of several analytical techniques, the documentation and understanding of time-dependent voltage effects, the analysis of a large number of individual cells, and significant progress toward developing a viable current-voltage model. This work was integral to the doctoral training of four students and was greatly assisted by several active collaborations within the polycrystalline thin-film solar cell community.

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

1994-07-01

269

Solar-energy conversion by combined photovoltaic converters with CdTe and CuInSe{sub 2} base layers  

SciTech Connect

The possibility of the combined use of bifacial thin-film solar cells based on CdTe and frontal solar cells with a CuInSe{sub 2} base layer in tandem structures is experimentally confirmed. It is found that, for the use of bifacial solar cells based on cadmium telluride in a tandem structure, the optimal thickness of their base layer should be 1 ?m. The gain in the efficiency of the tandem structure, compared with an individual CuInSe{sub 2}-based solar cell, is 1.8% in the case of series-connected solar cells and 1.3%, for parallel-connected.

Khrypunov, G. S., E-mail: khrip@ukr.net; Sokol, E. I. [National Technical University Kharkiv Polytechnic Institute (Ukraine); Yakimenko, Yu. I. [National Technical University Kyiv Polytechnic Institute, Research Institute of Applied Electronics (Ukraine); Meriuts, A. V. [National Technical University Kharkiv Polytechnic Institute (Ukraine); Ivashuk, A. V. [National Technical University Kyiv Polytechnic Institute, Research Institute of Applied Electronics (Ukraine); Shelest, T. N. [National Technical University Kharkiv Polytechnic Institute (Ukraine)

2014-12-15

270

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

NASA Astrophysics Data System (ADS)

Quantitative PIXE measurements require perfectly calibrated set-ups. Cooled CdTe detectors have good efficiency for energies above those covered by Si(Li) detectors and turn on the possibility of studying K X-rays lines instead of L X-rays lines for medium and eventually heavy elements, which is an important advantage in various cases, if only limited resolution systems are available in the low energy range. In this work we present and discuss spectra from a CdTe semiconductor detector covering the energy region from Cu (K ?1 = 8.047 keV) to U (K ?1 = 98.439 keV). Pure thick samples were irradiated with proton beams at the ITN 3.0 MV Tandetron accelerator in the High Resolution High Energy PIXE set-up. Results and the application to the study of a Portuguese Ossa Morena region Dark Stone sample are presented in this work.

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

2012-02-01

271

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

E-print Network

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

Liu, Weishu

272

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

Microsoft Academic Search

On-line monitoring of six Se-compounds was accomplished by using an XTerra MS C18 column coupled to electrospray tandem mass spectrometry (ESMSMS). In view of the nature of the compounds, the positively charged ion pairing agent tetraethylammoniumchloride (TEACl) was added to the mobile phase. The HPLCESMSMS method was optimized with six commercially available Se-compounds. Substitution of the analytical column by the

Emmie Dumont; Koen De Cremer; Marijn Van Hulle; Cyrille C. Chry; Frank Vanhaecke; Rita Cornelis

2005-01-01

273

Single crystal growth of SrIn 2VI 4 (VI=S,Se) compounds solidifying through supercooling  

NASA Astrophysics Data System (ADS)

The IIa-III 2-VI 4 (IIa=Ca,Sr, III=Ga,In, VI=S,Se) compounds generally have high melting points more than 1100 C, and some of them, e.g., SrIn 2VI 4 (VI=S,Se) prefer freezing with supercooling, which makes their crystal growth very difficult. Here, we have adopted a carbon crucible sealed in a quartz ampoule to escape from both the supercooling and the reactivity near the melting point. We have devised the shape of a crucible by preparing a small capillary followed by a bigger hollow pipe for obtaining a large single crystal. A compound is filled in the hole of a crucible by setting the thin part down. It is first heated above the meting point to melt and then cooled down below the supercooling point, where it is solidified. It is again heated to melt but this time keeping the temperature of the small bottom part of a capillary a little below the melting point. Then the melt is slowly cooled down. The nucleation is started from the polycrystalline remainder near the bottom, resulting in a seed crystal in the rest of the thin part as temperature lowers. With the help of the seed, a single crystal continues to grow in a bigger hollow-pipe part of a crucible. Single crystals of SrIn 2S 4 and SrIn 2Se 4 are grown by this method, and their optical absorption is measured.

Takizawa, T.; Kubo, M.; Hidaka, C.

2005-02-01

274

The new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} and the role of dimensionality in the Cu{sub x}(BiSe){sub 1+?}(TiSe{sub 2}){sub n} series  

SciTech Connect

The synthesis and physical properties of the new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} are reported. Transmission electron microscopy and powder X-ray diffraction show that the structure consists of alternating rock-salt type BiSe layers and hexagonal (TiSe{sub 2}){sub 2} double layers. Resistivity, specific heat, and magnetization measurements show that it has metallic and diamagnetic behaviors. These results are interpreted and discussed in the context of the transition between single-layer (BiSe){sub 1.13}(TiSe{sub 2}), which shows no charge density wave, and infinite-layered (bulk) 1T-TiSe{sub 2}, which undergoes a charge density wave transition at T=202 K. Intercalation with copper, Cu{sub x}(BiSe){sub 1.15}(TiSe{sub 2}){sub 2}, (0?x?0.10) is also reported, but unlike Cu{sub x}TiSe{sub 2}, no superconductivity is observed down to T=0.05 K. Thus, the series Cu{sub x}(BiSe){sub 1+?}(TiSe{sub 2}){sub n} provides an effective approach to elucidate the impact of dimensionality on charge density wave formation and superconductivity. - Graphical abstract: The newly discovered misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2} shown in the series (BiSe){sub 1+?}(TiSe{sub 2}){sub n}. Display Omitted - Highlights: Reports the structure and properties of the new misfit compound (BiSe){sub 1.15}(TiSe{sub 2}){sub 2}. The structure consists of a rock salt type BiSe layer and a double (TiSe{sub 2}){sub 2} layer. The n=1, 2 misfits (BiSe){sub 1+?}(TiSe{sub 2}){sub n} are found not to exhibit CDW transitions. Evidence is presented that there is likely a low-lying CDW excited state. The series Cu{sub x}(BiSe){sub 1+?}(TiSe{sub 2}){sub 2} does not superconduct, unlike Cu{sub x}TiSe{sub 2}.

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

2014-01-15

275

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

PubMed Central

Iron chalcogenide Fe(Te,Se) attracted much attention due to its simple structure, which is favorable for probing the superconducting mechanism. Its less toxic nature compared with iron arsenides is also advantageous for applications of iron-based superconductors. By intercalating spacer layers, superconducting transition temperature has been raised over 40?K. On the other hand, the presence of excess Fe is almost unavoidable in Fe(Te,Se) single crystals, which hinders the appearance of bulk superconductivity and causes strong controversies over its fundamental properties. Here we report a Systematical study of O2-annealing dynamics in Fe1+yTe1?xSex by controlling the amount of O2, annealing temperature, and time. Bulk superconductivity can be gradually induced by increasing the amount of O2 and annealing time at suitable temperatures. The optimally annealed crystals can be easily obtained by annealing with ~1.5% molar ratio of oxygen at 400C for more than 1?hour. Superconductivity was witnessed to evolve mainly from the edge of the crystal to the central part. After the optimal annealing, the complete removal of excess Fe was demonstrated via STM measurements. Some fundamental properties were recharacterized and compared with those of as-grown crystals to discuss the influence of excess Fe. PMID:24695095

Sun, Yue; Tsuchiya, Yuji; Taen, Toshihiro; Yamada, Tatsuhiro; Pyon, Sunseng; Sugimoto, Akira; Ekino, Toshikazu; Shi, Zhixiang; Tamegai, Tsuyoshi

2014-01-01

276

Comparison of crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te nanocrystalline thin films: Effects of homogeneous irradiation with an electron beam  

SciTech Connect

The effects of homogenous electron beam (EB) irradiation on the crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te thin films were investigated. Both types of thin films were prepared by flash evaporation, after which homogeneous EB irradiation was performed at an acceleration voltage of 0.17?MeV. For the n-type thin films, nanodots with a diameter of less than 10?nm were observed on the surface of rice-like nanostructures, and crystallization and crystal orientation were improved by EB irradiation. The resulting enhancement of mobility led to increased electrical conductivity and thermoelectric power factor for the n-type thin films. In contrast, the crystallization and crystal orientation of the p-type thin films were not influenced by EB irradiation. The carrier concentration increased and mobility decreased with increased EB irradiation dose, possibly because of the generation of defects. As a result, the thermoelectric power factor of p-type thin films was not improved by EB irradiation. The different crystallization behavior of the n-type and p-type thin films is attributed to atomic rearrangement during EB irradiation. Selenium in the n-type thin films is more likely to undergo atomic rearrangement than the other atoms present, so only the crystallinity of the n-type Bi-Se-Te thin films was enhanced.

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

2014-06-07

277

Magnetic properties of the magnetoelectric compound Cu2OSeO3: Magnetization and 77Se NMR study  

NASA Astrophysics Data System (ADS)

We present magnetization and 77Se Nuclear Magnetic Resonance (NMR) measurements in single crystals of the magneteoelectric compound Cu2OSeO3. The temperature and field dependence of the magnetization suggest a ferrimagnetic ordering at Tc ? 60 K in a 3up-1down configuration. The easy axis of the magnetization is along the [100] crystallographic direction. The 77Se NMR line shape data collected at 14.09 T are consistent with the symmetries imposed by the cubic P213 space group in the temperature range 20-290 K and confirm that the magnetic transition is not accompanied by any lowering of the crystal symmetry as has recently been proposed by Bos et al. [Phys. Rev. B 78 094416 (2008)].

Belesi, M.; Philippe, T.; Rousochatzakis, I.; Wu, H. C.; Berger, H.; Granville, S.; Shvets, I. V.; Ansermet, J.-Ph

2011-07-01

278

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

SciTech Connect

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

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

2006-06-01

279

Transport Properties of ZnSe- ITO Hetero Junction  

NASA Astrophysics Data System (ADS)

In this report, ITO(Indium Tin Oxide) was used on the glass substrates as the transparent electrode, and ZnSe layer was prepared by the vacuum deposition on this ITO. Then, the electrical characteristics of this sample were investigated by mans of the electric current transport analysis. The sample that ZnSe was prepared as 3.4 ?m in case of ITO-ZnSe sample, has high density level at the junction surface. The ITO-ZnSe junction has two type of diffusion current. However, the ITO-ZnSe sample that ZnSe layer was prepared as 0.1 ?m can be assumed as the ohmic contact, and ITO-ZnSe(0.1?m) -CdTe sample shows the avalanche breakdown, and it is considered that the avalanche breakdown occurs in CdTe layer. It is difficult to occur the avalanche breakdown, if ZnSe-CdTe junction has high-density level and CdTe layer has high-density defect. Hence, the ZnSe-CdTe sample that CdTe layer was prepared on ITO-ZnSe(0.1?m) substrate has not high-density level at the junction surface, and the CdTe layer with little lattice imperfection can be prepared. It found that ITO-ZnSe(0.1?m) substrate is available for the II-VI compounds semiconductor device through above analysis result.

Ichibakase, Tsuyoshi

280

Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe2.7Se0.3 and p-type Bi0.5Sb1.5Te3  

NASA Astrophysics Data System (ADS)

Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe2.7Se0.3 and p-type Bi0.5Sb1.5Te3 showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications.

Bhame, Shekhar D.; Pravarthana, Dhanapal; Prellier, Wilfrid; Noudem, Jacques G.

2013-05-01

281

Characterization of defects in (ZnMg)Se compounds by positron annihilation and photoluminescence  

NASA Astrophysics Data System (ADS)

Defect characterization of as-grown Zn1-xMgxSe mixed crystals (0?x<0.6) and the effect of Zn vapor annealing has been studied by positron lifetime and photoluminescence measurements. We obtain both experimental and theoretical evidence that the bulk lifetime of free positrons increases linearly with Mg alloying. The average positron lifetime increases with temperature indicating that both vacancies and negative ions trap positrons. The decompositions of the lifetime spectra show that the vacancy has the characteristic positron lifetime of 325 ps. The comparison with theoretical calculations indicate that the lifetime 325 ps corresponds either to divacancies relaxed inwards or to monovacancies strongly relaxed outwards. We consider the latter identification more likely and attribute the positron lifetime 325 ps to Zn vacancy or a complex involving VZn. The vacancy concentration is almost independent of Mg content above x=0.2 but decreases strongly at x=0.56. The Zn vapor annealing decreases the concentration of Zn vacancies. The intensity of the green photoluminescence correlates with the concentration of VZn both as a function of Mg alloying and Zn vapor annealing. We thus conclude that the electron levels of the Zn vacancy are involved in the optical transition leading to the green photoluminescence.

Plazaola, F.; Saarinen, K.; Dobrzynski, L.; Reniewicz, H.; Firszt, F.; Szatkowski, J.; Meczynska, H.; Legowski, S.; Chabik, S.

2000-08-01

282

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

SciTech Connect

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

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

2010-10-15

283

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

284

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

285

In- and out-of-plane London penetration depths in single crystals of FeSe0.4Te0.6 superconductor  

NASA Astrophysics Data System (ADS)

In- and out-of-plane London penetration depths ?(T) were measured in single crystals of FeSe0.4Te0.6 superconductor by means of the tunnel diode resonator technique. The penetration depth does not show BCS-like exponential saturation at low temperature. Instead, we found that both ??ab(T) and ??c(T) has nearly quadratic behavior, similar to that observed in the FeAs-based superconductors. We also calculated the in-plane superfluid density ?(T)=2?(0)/2?(T), and fitted with various possible models.

Kim, Hyunsoo; Tanatar, Makariy; Gordon, Ryan; Martin, Catalin; Mao, Zhiqiang; Prozorov, Ruslan

2009-11-01

286

Optical properties of (Se{sub 80}Te{sub 20}){sub 100?x}Ag{sub x} (0 ? x ? 4) thin films  

SciTech Connect

Thin films of (Se{sub 80}Te{sub 20}){sub 100?x}Ag{sub x} (0 ? x ? 4) glasses were prepared by thermal evaporation of the bulk samples. The transmittance (T) and reflection (R) spectra of amorphous thin films were obtained in the spectral region in the range 4002500 nm. The optical band gap (E{sub g}) has been determined by Taucs extrapolation method. The surface morphology has been determined by the Scanning Electron Microscopy (SEM)

Singh, D., E-mail: rthangaraj@rediffmail.com; Kumar, S., E-mail: rthangaraj@rediffmail.com; Sandhu, S., E-mail: rthangaraj@rediffmail.com; Thangaraj, R., E-mail: rthangaraj@rediffmail.com [Semiconductors Laboratory, Department of Physics, Guru Nanak Dev University, Amritsar-143005, Punjab (India)

2014-04-24

287

Ballistic performance comparison of monolayer transition metal dichalcogenide MX{sub 2} (M = Mo, W; X = S, Se, Te) metal-oxide-semiconductor field effect transistors  

SciTech Connect

We study the transport properties of monolayer MX{sub 2} (M?=?Mo, W; X?=?S, Se, Te) n- and p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using full-band ballistic non-equilibrium Green's function simulations with an atomistic tight-binding Hamiltonian with hopping potentials obtained from density functional theory. We discuss the subthreshold slope, drain-induced barrier lowering (DIBL), as well as gate-induced drain leakage (GIDL) for different monolayer MX{sub 2} MOSFETs. We also report the possibility of negative differential resistance behavior in the output characteristics of nanoscale monolayer MX{sub 2} MOSFETs.

Chang, Jiwon; Register, Leonard F.; Banerjee, Sanjay K. [Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758 (United States)

2014-02-28

288

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

289

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

2013-06-01

290

Orbital processing of high-quality CdTe compound semiconductors  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

291

Ab initio calculations of the electronic structure of the wurtzite compounds CdS and CdSe  

NASA Astrophysics Data System (ADS)

We report ab initio calculations of the lattice constants and the electronic structure of the hexagonal wurtzite semiconductors CdS and CdSe. The calculations have been carried out self-consistently in the local-density approximation employing nonlocal, separable, and norm-conserving pseudopotentials. We use Cd12+ ionic pseudopotentials so that the Cd 4d electrons are explicitly taken into account as valence electrons. The calculated electronic structure is compared with photoemission data. Calculated and measured bands show good agreement in the energy region of the mostly anion-derived s-p valence bands. The calculated Cd 4d bands result for both compounds roughly 3 eV too high in energy as compared to the measured data. This rigid shift of the narrow 4d bands is related to correlation effects which are not fully taken into account in the local-density approximation.

Schrer, Peter; Krger, Peter; Pollmann, Johannes

1993-12-01

292

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

293

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

294

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

295

Ab initio calculation of the CdSe/CdTe heterojunction band offset using the local-density approximation-1/2 technique with spin-orbit corrections  

NASA Astrophysics Data System (ADS)

We performed ab initio calculations of the electronic structures of bulk CdSe and CdTe and of their interface. We employed the local-density approximation-1/2 self-energy correction scheme [L. G. Ferreira, M. Marques, and L. K. Teles, Phys. Rev. B 78, 125116 (2008)] to obtain improved band gaps and band offsets, as well as spin-orbit coupling to further correct the valence band edges. Our results are in good agreement with experimental values for bulk band gaps and reproduce the staggered band alignment characteristic of this system. We found that the spin-orbit effect is of considerable importance for the bulk band gaps, but has little impact on the band offset of this particular system. Moreover, the electronic structure calculated along the 61.4 transition region across the CdSe/CdTe interface shows a non-monotonic variation of the bandgap in the range 0.8-1.8 eV. This finding may have important implications to the absorption of light along the interface between these two materials in photovoltaic applications.

Ribeiro, M.; Fonseca, L. R. C.; Sadowski, T.; Ramprasad, R.

2012-04-01

296

Enhancement of transition temperature in Fe{sub x}Se{sub 0.5}Te{sub 0.5} film via iron vacancies  

SciTech Connect

The effects of iron deficiency in Fe{sub x}Se{sub 0.5}Te{sub 0.5} thin films (0.8???x???1) on superconductivity and electronic properties have been studied. A significant enhancement of the superconducting transition temperature (T{sub C}) up to 21?K was observed in the most Fe deficient film (x?=?0.8). Based on the observed and simulated structural variation results, there is a high possibility that Fe vacancies can be formed in the Fe{sub x}Se{sub 0.5}Te{sub 0.5} films. The enhancement of T{sub C} shows a strong relationship with the lattice strain effect induced by Fe vacancies. Importantly, the presence of Fe vacancies alters the charge carrier population by introducing electron charge carriers, with the Fe deficient film showing more metallic behavior than the defect-free film. Our study provides a means to enhance the superconductivity and tune the charge carriers via Fe vacancy, with no reliance on chemical doping.

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

2014-06-30

297

Effect of p-d hybridization and structural distortion on the electronic properties of AgAlM 2(M=S,Se,Te) chalcopyrite semiconductors  

NASA Astrophysics Data System (ADS)

We report an ab initio calculation and study of the structural and electronic properties of AgAlM 2(M=S,Se,Te) chalcopyrite semiconductors using the density functional theory (DFT)-based self-consistent tight-binding linear muffin tin orbital (TB-LMTO) method. The calculated equilibrium values of the lattice constants, anion displacement parameter (u), tetragonal distortion (?=c/2a) and bond lengths are in good agreement with experimental values. Our study suggests these semiconductors to be direct band gap semiconductors with band gaps 1.98 eV, 1.59 eV and 1.36 eV, respectively. These values are in good agreement with experimental values, within the limitation of the local density approximation (LDA). Our explicit study of the effects of anion displacement and p-d hybridization show that the band gap increases by 9.8%, 8.2% and 5.1%, respectively, for AgAlM 2(M=S,Se,Te) due to former effect and decreases by 51%, 47% and 42%, respectively, due to latter effect.

Mishra, S.; Ganguli, B.

2011-04-01

298

Disordered stoichiometric nanorods and ordered off-stoichiometric nanoparticles in n-type thermoelectric Bi2Te2.7Se0.3  

NASA Astrophysics Data System (ADS)

N-type Bi2Te2.7Se0.3 bulk thermoelectric materials with peak ZT values up to 1 were examined by transmission electron microscopy and electron diffraction. Two nanostructural features were found: (i) a structural modulation of 10 nm, which consisted of nanorods with crystalline and nearly amorphous regions, having the rod axes normal to (0,1,5)-type planes, and wave vector normal to (1,0,10)-type planes and (ii) non-stoichiometric ordered Bi-rich nanoparticles. The presence of the structural modulation was not influenced by the ion milling energy or temperature in this study while the non-stoichiometric ordered nanoparticles were only observed when ion milling at low temperatures and low energy was used. It is proposed that both the structural modulation of 10 nm and the presence of non-stoichiometric nanoparticles are responsible for the low lattice thermal conductivity (0.6 W/mK) of the Bi2Te2.7Se0.3 bulk thermoelectric materials studied.

Carlton, Chris E.; Kuryak, Chris A.; Liu, Wei-shu; Ren, Zhifeng; Chen, Gang; Shao-Horn, Yang

2012-11-01

299

Photoluminescence of double core/shell infrared (CdSeTe)/ZnS quantum dots conjugated to Pseudo rabies virus antibodies  

NASA Astrophysics Data System (ADS)

Double core CdSeTe/ZnS quantum dots (QDs) with emission at 800 nm (1.60 eV) have been studied by photoluminescence (PL) and Raman scattering methods in the non-conjugated state and after the conjugation to the Pseudo rabies virus (PRV) antibodies. The transformation of PL spectra, stimulated by the electric charge of antibodies, has been detected for the bioconjugated QDs. Raman scattering spectra are investigated with the aim to reveal the CdSeTe core compositions. The double core QD energy diagrams were designed that help to analyze the PL spectra and their transformation at the bioconjugation. It is revealed that the interface in double core QDs has the type II quantum well character that permits to explain the near IR optical transition (1.60 eV) in the double core QDs. It is shown that the essential transformation of PL spectra is useful for the study of QD bioconjugation with specific antibodies and can be a powerful technique in early medical diagnostics.

Torchynska, T. V.; Casas Espinola, J. L.; Jaramillo Gmez, J. A.; Douda, J.; Gazarian, K.

2013-06-01

300

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

PubMed

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

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

2014-01-01

301

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

2012-01-01

302

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

NASA Astrophysics Data System (ADS)

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

Amouyal, Yaron

2014-10-01

303

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

304

Enhancement of thermoelectric properties by Na doping in Te-free p-type AgSbSe2.  

PubMed

AgSbSe2 possesses extremely low thermal conductivity and high Seebeck coefficient, but the low electronic conductivity leads to a low ZT value. In this paper, Na is used to substitute Sb to improve the electronic conductivity. The results show that Na doping not only improves the power factor caused by the enhanced carrier concentration, but also decreases the thermal conductivity due to point defects, nanoscale stacking faults and Na-rich precipitate. Consequently, a high ZT value of 0.92 is achieved in the AgSb0.99Na0.01Se2 sample. PMID:25407495

Cai, Songting; Liu, Zihang; Sun, Jianyong; Li, Rui; Fei, Weidong; Sui, Jiehe

2015-01-21

305

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

PubMed

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

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

2011-03-01

306

Investigations of the half-metallic behavior and the magnetic and thermodynamic properties of half-Heusler CoMnTe and RuMnTe compounds: A first-principles study  

NASA Astrophysics Data System (ADS)

First-principles spin-polarized density functional theory (DFT) investigations of the structural, electronic, magnetic, and thermodynamics characteristics of the half-Heusler, CoMnTe and RuMnTe compounds are carried out. Calculations are accomplished within a state of the art full-potential (FP) linearized (L) augmented plane wave plus a local orbital (APW + lo) computational approach framed within DFT. The generalized gradient approximation (GGA) parameterized by Perdew, Burke, and Ernzerhof (PBE) is implemented as an exchange correlation functional as a part of the total energy calculation. From the analysis of the calculated electronic band structure as well as the density of states for both compounds, a strong hybridization between d states of the higher valent transition metal (TM) atoms (Co, Ru) and lower valent TM atoms of (Mn) is observed. Furthermore, total and partial density of states (PDOS) of the ground state and the results of spin magnetic moments reveal that these compounds are both stable and ideal half-metallic ferromagnetic. The effects of the unit cell volume on the magnetic properties and half-metallicity are crucial. It is worth noting that our computed results of the total spin magnetic moments, for CoMnTe equal to 4 ?B and 3 ?B per unit cell for RuMnTe, nicely follow the rule ?tot = Zt - 18. Using the quasi-harmonic Debye model, which considers the phononic effects, the effecs of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and heat capacity for these compounds are investigated for the first time.

Djaafri, T.; Djaafri, A.; Elias, A.; Murtaza, G.; Khenata, R.; R., Ahmed; Bin Omran, S.; Rached, D.

2014-08-01

307

Structural perfection and mechanical properties of ZnSe 1? x Te x crystals grown by the Bridgman technique  

Microsoft Academic Search

Preparation conditions of ZnSe1?xTex crystals should guarantee stability of their scintillation parameters (light output, after glow, luminescence maximum wavelength), optical uniformity, high mechanical strength and resistance to cracking. These crystals were grown by the Bridgman technique under different degrees of melt overheating and related evaporation of the more volatile components. Annealing was carried out at 11701270K under zinc vapor and

L. W Atroshchenko; L. P Gal'chinetskii; S. N Galkin; V. D Ryzhikov; N. I Shevtsov; V. I Silin

1999-01-01

308

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

PubMed

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 high quintuple layer steps. STS results reflect the band structure and indicate that the surface state and Fermi energy are both located inside the energy gap. In particular, quasi-particle interference patterns from electron scattering demonstrate that the surface states possess linear dispersion and chirality from spin texture, thus verifying its topological nature. This finding demonstrates that alloying is a promising route to achieve full suppression of bulk conduction in topological insulators whilst keeping the topological surface state intact. PMID:24030733

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

2013-01-01

309

Nanojunction-mediated photocatalytic enhancement in heterostructured CdS/ZnO, CdSe/ZnO, and CdTe/ZnO nanocrystals.  

PubMed

A series of highly efficient semiconductor nanocrystal (NC) photocatalysts have been synthesized by growing wurtzite-ZnO tetrahedrons around pre-formed CdS, CdSe, and CdTe quantum dots (QDs). The resulting contact between two small but high-quality crystals creates novel CdX/ZnO heterostructured semiconductor nanocrystals (HSNCs) with extensive type-II nanojunctions that exhibit more efficient photocatalytic decomposition of aqueous organic molecules under UV irradiation. Catalytic testing and characterization indicate that catalytic activity increases as a result of a combination of both the intrinsic chemistry of the chalcogenide anions and the heterojunction structure. Atomic probe tomography (APT) is employed for the first time to probe the spatial characteristics of the nanojunction between cadmium chalcogenide and ZnO crystalline phases, which reveals various degrees of ion exchange between the two crystals to relax large lattice mismatches. In the most extreme case, total encapsulation of CdTe by ZnO as a result of interfacial alloying is observed, with the expected advantage of facilitating hole transport for enhanced exciton separation during catalysis. PMID:24962739

Eley, Clive; Li, Tong; Liao, Fenglin; Fairclough, Simon Michael; Smith, Jason M; Smith, George; Tsang, Shik Chi Edman

2014-07-21

310

Mechanical and thermal properties of h-MX{sub 2} (M?=?Cr, Mo, W; X?=?O, S, Se, Te) monolayers: A comparative study  

SciTech Connect

Using density functional theory, we obtain the mechanical and thermal properties of MX{sub 2} monolayers (where M?=?Cr, Mo, W and X?=?O, S, Se, Te). The ?-centered phonon frequencies (i.e., A{sub 1}, A{sub 2}{sup ?}, E?, and E?), relative frequency values of A{sub 1}, and E? modes, and mechanical properties (i.e., elastic constants, Young modulus, and Poisson's ratio) display a strong dependence on the type of metal and chalcogenide atoms. In each chalcogenide (metal) group, transition-metal dichalcogenides (TMDCs) with W (O) atom are found to be much stiffer. Consistent with their stability, the thermal expansion of lattice constants for TMDCs with O (Te) is much slower (faster). Furthermore, in a heterostructure of these materials, the difference of the thermal expansion of lattice constants between the individual components becomes quite tiny over the whole temperature range. The calculated mechanical and thermal properties show that TMDCs are promising materials for heterostructures.

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

2014-05-19

311

Experimental Detection of a Majorana Mode in the core of a Magnetic Vortex inside a Topological Insulator-Superconductor Bi2Te3/NbSe2 Heterostructure  

NASA Astrophysics Data System (ADS)

Majorana fermions have been intensively studied in recent years for their importance to both fundamental science and potential applications in topological quantum computing. They are predicted to exist in a vortex core of superconducting topological insulators. However, it is extremely difficult to distinguish them experimentally from other quasiparticle states for the tiny energy difference between Majorana fermions and these states, which is beyond the energy resolution of most available techniques. Here, we circumvent the problem by systematically investigating the spatial profile of the Majorana mode and the bound quasiparticle states within a vortex in Bi2Te3 films grown on a superconductor NbSe2 . While the zero bias peak in local conductance splits right off the vortex center in conventional superconductors, it splits off at a finite distance 20 nm away from the vortex center in Bi2Te3 . This unusual splitting behavior has never been observed before and could be possibly due to the Majorana fermion zero mode. While the Majorana mode is destroyed by the interaction between vortices, the zero bias peak splits as a conventional superconductor again. This work provides self-consistent evidences of Majorana fermions and also suggests a possible route to manipulating them.

Xu, Jin-Peng; Wang, Mei-Xiao; Liu, Zhi Long; Ge, Jian-Feng; Yang, Xiaojun; Liu, Canhua; Xu, Zhu An; Guan, Dandan; Gao, Chun Lei; Qian, Dong; Liu, Ying; Wang, Qiang-Hua; Zhang, Fu-Chun; Xue, Qi-Kun; Jia, Jin-Feng

2015-01-01

312

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

313

Nonlinear optical properties of quaternary amorphous Se80.5Bi1.5Te18-yAy (A = Sb, Ag) thin films  

NASA Astrophysics Data System (ADS)

Effect of Sb and Ag addition on the optical constants of Se80.5Bi1.5Te18-yAy (A = Sb, Ag and y = 2.0 at. %) thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index increases with an increase in Sb or Ag content and the absorption coefficient is also found to increases with increase in optical energy. Whereas the optical band gap decreases with an increase in Sb content and increases with an increase in Ag content. Hence, the present results reveals that the addition of Sb and Ag produce remarkable change on the nonlinear optical properties of the thin film.

Kumar, Anup; Heera, Pawan; Sharma, Raman

2014-04-01

314

Two-band conductivity of a FeSe_{0.5}Te_{0.5} film by reflectance measurements in the terahertz and infrared range  

NASA Astrophysics Data System (ADS)

We report an infrared spectroscopy study of a 200 nm thick FeSe0.5Te0.5 film grown on LaAlO3 with Tc = 13.7 K. We analyze the 20 K normal state absolute reflectance RN measured over a broad infrared range and the reflectance ratio RS/RN, RS being the superconducting state reflectance, measured at 6 K in the terahertz range down to 12 cm?1. We show that the normal state model conductivity is given by two Drude components, one of which much broader and intense than the other. In the superconducting state, we find that a gap ? = 37 3 cm?1 opens up in the narrow Drude band only, while the broad Drude band results to be ungapped, at least in the explored spectral range. Our results show that only a two-band model can coherently describe both normal and superconducting state data.

Perucchi, A.; Joseph, B.; Caramazza, S.; Autore, M.; Bellingeri, E.; Kawale, S.; Ferdeghini, C.; Putti, M.; Lupi, S.; Dore, P.

2014-12-01

315

In-Plane Transport and Enhanced Thermoelectric Performance in Thin Films of the Topological Insulators Bi2Te3 and Bi2Se3  

NASA Astrophysics Data System (ADS)

Several small-band-gap semiconductors are now known to protect metallic surface states as a consequence of the topology of the bulk electron wave functions. The known topological insulators with this behavior include the important thermoelectric materials Bi2Te3 and Bi2Se3, whose surfaces are observed in photoemission experiments to have an unusual electronic structure with a single Dirac cone. We study in-plane (i.e., horizontal) transport in thin films made of these materials. The surface states from top and bottom surfaces hybridize, and conventional diffusive transport predicts that the tunable hybridization-induced band gap leads to increased thermoelectric performance at low temperatures. Beyond simple diffusive transport, the conductivity shows a crossover from the spin-orbit-induced antilocalization at a single surface to ordinary localization.

Ghaemi, Pouyan; Mong, Roger S. K.; Moore, J. E.

2010-10-01

316

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

317

Structural phase transition associated with van Hove singularity in 5d transition metal compound IrTe2  

NASA Astrophysics Data System (ADS)

We have investigated the electronic states of IrTe2 by using angle-resolved photoemission spectroscopy to elucidate the origin of the structural phase transition. Both the Ir 4f and Te 4d core level spectra exhibit dramatic splitting below the phase transition temperature Ts, suggesting that there exist two inequivalent Ir and Te sites with distinctly different electronic states in the distorted phase. The band related to the saddle points at the Fermi level (EF) is strongly reconstructed, which removes the van Hove singularity from EF below Ts. The wavevector connecting the adjacent saddle points is consistent with the in-plane superstructure modulation wavevector. These results indicate that the phase transition in IrTe2 is intimately associated with the saddle points. As the van Hove singularity mainly originates from the Te px+py orbitals, the Te 5p electronic states play a dominant role in the structural phase transition.

Qian, T.; Miao, H.; Wang, Z. J.; Shi, X.; Huang, Y. B.; Zhang, P.; Xu, N.; Zeng, L. K.; Ma, J. Z.; Richard, P.; Shi, M.; Xu, G.; Dai, X.; Fang, Z.; Fang, A. F.; Wang, N. L.; Ding, H.

2014-12-01

318

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

SciTech Connect

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

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

2011-05-15

319

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

PubMed

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

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

2005-04-15

320

Electronic structure of antifluorite Cu2X (X = S, Se, Te) within the modified Becke-Johnson potential plus an on-site Coulomb U  

NASA Astrophysics Data System (ADS)

The traditional photon absorbers Cu2-xX (X = S, Se, and Te) have regained significant research attention in the search of earth-abundant photovoltaic materials. These moderate- and narrow-gap materials have also been shown to exhibit excellent thermoelectric properties recently. However, semimetallic band structures with inverted band orderings are predicted for antifluorite structure Cu2X using density functional theory with the local density approximation or the generalized gradient approximation. We find that semiconducting band structures and normal band orderings can be obtained using the modified Becke-Johnson potential plus an on-site Coulomb U (the mBJ+U approach), which is consistent with our earlier finding for diamond-like Cu-based multinary semiconductors [Y. Zhang, J. Zhang, W. Gao, T. A. Abtew, Y. Wang, P. Zhang, and W. Zhang, J. Chem. Phys. 139, 184706 (2013)]. The trend of the chemical bonding of Cu2X is analyzed, which shows that the positions of the valence band maximum and conduction band minimum are strongly affected by the inter-site pd and intra-site sp hybridizations, respectively. The calculated gaps of Cu2S and Cu2Se still seem to be underestimated compared with experimental results. We also discuss the effects of different structural phases and Cu disordering and deficiency on the bandgaps of these materials.

Zhang, Yubo; Wang, Youwei; Xi, Lili; Qiu, Ruihao; Shi, Xun; Zhang, Peihong; Zhang, Wenqing

2014-02-01

321

Electronic structure of antifluorite Cu{sub 2}X (X = S, Se, Te) within the modified Becke-Johnson potential plus an on-site Coulomb U  

SciTech Connect

The traditional photon absorbers Cu{sub 2?x}X (X = S, Se, and Te) have regained significant research attention in the search of earth-abundant photovoltaic materials. These moderate- and narrow-gap materials have also been shown to exhibit excellent thermoelectric properties recently. However, semimetallic band structures with inverted band orderings are predicted for antifluorite structure Cu{sub 2}X using density functional theory with the local density approximation or the generalized gradient approximation. We find that semiconducting band structures and normal band orderings can be obtained using the modified Becke-Johnson potential plus an on-site Coulomb U (the mBJ+U approach), which is consistent with our earlier finding for diamond-like Cu-based multinary semiconductors [Y. Zhang, J. Zhang, W. Gao, T. A. Abtew, Y. Wang, P. Zhang, and W. Zhang, J. Chem. Phys. 139, 184706 (2013)]. The trend of the chemical bonding of Cu{sub 2}X is analyzed, which shows that the positions of the valence band maximum and conduction band minimum are strongly affected by the inter-site pd and intra-site sp hybridizations, respectively. The calculated gaps of Cu{sub 2}S and Cu{sub 2}Se still seem to be underestimated compared with experimental results. We also discuss the effects of different structural phases and Cu disordering and deficiency on the bandgaps of these materials.

Zhang, Yubo; Wang, Youwei; Xi, Lili; Qiu, Ruihao; Shi, Xun [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China)] [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Zhang, Peihong, E-mail: wqzhang@mail.sic.ac.cn, E-mail: pzhang3@buffalo.edu [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States) [Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260 (United States); Beijing Computational Science Research Center, Beijing 100084 (China); Zhang, Wenqing, E-mail: wqzhang@mail.sic.ac.cn, E-mail: pzhang3@buffalo.edu [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China) [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); School of Chemistry and Chemical Engineering, and Sate Key Laboratory of Coordination Chemistry, Nanjing University, Jiangsu 210093 (China)

2014-02-21

322

Terahertz conductivity of topological surface states in Bi1.5Sb0.5Te1.8Se1.2  

PubMed Central

Topological insulators are electronic materials with an insulating bulk and conducting surface. However, due to free carriers in the bulk, the properties of the metallic surface are difficult to detect and characterize in most topological insulator materials. Recently, a new topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was found, showing high bulk resistivities of 110??.cm and greater contrast between the bulk and surface resistivities compared to other Bi-based topological insulators. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we present complex conductivity of BSTS single crystals, disentangling the surface and bulk contributions. We find that the Drude spectral weight is 12 orders of magnitude smaller than in other Bi-based topological insulators, and similar to that of Bi2Se3 thin films, suggesting a significant contribution of the topological surface states to the conductivity of the BSTS sample. Moreover, an impurity band is present about 30?meV below the Fermi level, and the surface and bulk carrier densities agree with those obtained from transport data. Furthermore, from the surface Drude contribution, we obtain a ~98% transmission through one surface layer this is consistent with the transmission through single-layer or bilayer graphene, which shares a common Dirac-cone feature in the band structure. PMID:24343202

Tang, Chi Sin; Xia, Bin; Zou, Xingquan; Chen, Shi; Ou, Hong-Wei; Wang, Lan; Rusydi, A.; Zhu, Jian-Xin; Chia, Elbert E. M.

2013-01-01

323

Stripelike magnetism in a mixed-valence insulating state of the Fe-based ladder compound CsFe2Se3  

NASA Astrophysics Data System (ADS)

Structural and electronic properties of the Fe-based spin-ladder compound CsFe2Se3 was investigated by means of resistivity, susceptibility, specific heat, Mssbauer, and neutron diffraction measurements. Despite the single-site nature in a mixed-valence state, the ground state is a magnetic insulator characterized by a charge gap 0.34 eV and an antiferromagnetic transition temperature 175 K. The magnetic structure was stripelike, with magnetic moments of 1.77(6)?B coupled ferromagnetically (antiferromagnetically) along the rung (leg) direction. Both the insulating behavior and stripelike ordering can be understood by assuming extra carriers delocalized on the rung. Our findings reveal that CsFe2Se3 is an appealing compound with the stripelike magnetic structure in an insulating state among Fe-based compounds, and provide significant supplemental insight into the magnetism of Fe-based superconductors.

Du, Fei; Ohgushi, Kenya; Nambu, Yusuke; Kawakami, Takateru; Avdeev, Maxim; Hirata, Yasuyuki; Watanabe, Yoshitaka; Sato, Taku J.; Ueda, Yutaka

2012-06-01

324

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

PubMed

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

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

2014-11-28

325

Intercalation and thermal instability of intercalation compounds Zn/sub x/Nb/sub 1+y/Se/sub 2/ in air  

SciTech Connect

During the intercalation of niobium diselenide with zinc from the vapor-gas phase the implantation of zinc is accompanied by the release of selenium into the vapor-phase and self-intercalation takes place in addition to the intercalation with zinc. The intercalation process occurs in two stages: the formation of intercalation compounds with a zinc content x = 0.27-0.33 in the surface region and subsequent movement of the intercalation-compound front deeper into the microcrystal until a homogeneous intercalation compound has been formed. Using Zn/sub x/Nb/sub 1+y/Se/sub 2/ as an example, for the first time we have determined for intercalation compounds of transition-metal dichalcogenides that the limit of their thermal stability in air increases linearly with the amount of zinc implanted.

Kulikov, L.M.; Semenov-Kobzar', A.A.; Yanaki, A.A.; Zaletilo, L.S.; Aksel'rud, L.G.; Koshel', O.S.

1988-05-01

326

Transparent Conductive Cu-doped ZnSe Film Deposited at Room Temperature Using Compound Sources Followed by Laser Annealing  

NASA Astrophysics Data System (ADS)

The evaporation of ZnSe and Cu2Se powders was used to deposit a Cu-doped ZnSe film on a glass substrate at room temperature; this was followed by laser beam (? = 355 nm) annealing. The film consisted of a zinc blende, ZnSe, crystalline single phase with the chemical composition (Zn0.9Cu0.1)Se. Over 70% optical transmittance was obtained in the green-red region. The film had a p-type polarity with a conductivity of 0.45 S cm-1 and a workfunction of 4.7 eV. P-n diodes fabricated with the film on an n-type ZnSe:Cl layer showed rectangular behavior with a small turn-on voltage of 1.5 V, which is plausibly explained by development of an impurity band.

Orita, Masahiro; Narushima, Takashi; Yanagita, Hiroaki

2007-10-01

327

Grain boundary junctions of FeSe0.5Te0.5 thin films on SrTiO3 bi-crystal substrates  

NASA Astrophysics Data System (ADS)

Grain boundary junctions were fabricated in the epitaxial FeSe0.5Te0.5 thin films on [001] tilt SrTiO3 bi-crystal substrates with a CeO2 buffer layer. Critical current densities across the junctions with different mis-orientation angles of 4, 7, 15, and 24 were measured at magnetic fields up to 30 T. It was found that the 4 and 7 junctions carry critical current densities comparable to that of the intra-grain film while those of the 15 and 24 junctions were suppressed drastically. A critical mis-orientation angle of around 9 was identified that separates the strong coupling region from the weak link region. We found that the critical current densities across the grain boundary with a 24 mis-orientation angle are modulated by the magnetic field, indicating a Josephson Effect. This junction is estimated to be in the intermediate-size regime with an effective transverse junction width L 2.6-2.8 ?m and a Josephson penetration depth ?J 1.2 ?m.

Si, Weidong; Zhang, Cheng; Shi, Xiaoya; Ozaki, Toshinori; Jaroszynski, Jan; Li, Qiang

2015-01-01

328

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

329

Ab initio and relativistic DFT study of spinrotation and NMR shielding constants in XF{sub 6} molecules, X = S, Se, Te, Mo, and W  

SciTech Connect

We present an analysis of the spinrotation and absolute shielding constants of XF{sub 6} molecules (X = S, Se, Te, Mo, W) based on ab initio coupled cluster and four-component relativistic density-functional theory (DFT) calculations. The results show that the relativistic contributions to the spinrotation and shielding constants are large both for the heavy elements as well as for the fluorine nuclei. In most cases, incorporating the computed relativistic corrections significantly improves the agreement between our results and the well-established experimental values for the isotropic spinrotation constants and their anisotropic components. This suggests that also for the other molecules, for which accurate and reliable experimental data are not available, reliable values of spinrotation and absolute shielding constants were determined combining ab initio and relativistic DFT calculations. For the heavy nuclei, the breakdown of the relationship between the spinrotation constant and the paramagnetic contribution to the shielding constant, due to relativistic effects, causes a significant error in the total absolute shielding constants.

Ruud, Kenneth [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of TromsThe Arctic University of Norway, N-9037 Troms (Norway)] [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of TromsThe Arctic University of Norway, N-9037 Troms (Norway); Demissie, Taye B. [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of TromsThe Arctic University of Norway, N-9037 Troms (Norway) [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of TromsThe Arctic University of Norway, N-9037 Troms (Norway); Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warszawa, Kasprzaka 44 (Poland); Jaszu?ski, Micha?, E-mail: michal.jaszunski@icho.edu.pl [Institute of Organic Chemistry, Polish Academy of Sciences, 01-224 Warszawa, Kasprzaka 44 (Poland)] [Institute of Organic Chemistry, Polish Academy of Sciences, 01-224 Warszawa, Kasprzaka 44 (Poland)

2014-05-21

330

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

331

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

332

Importance of structural distortions in enhancement of transition temperature in FeSe1 ? xTex superconductors  

NASA Astrophysics Data System (ADS)

Temperature (12 K ?slant T ?slant 300 K) dependent extended x-ray absorption fine structure (EXAFS) studies at the Fe K edge in FeSe1-xTex (x = 0, 0.5 and 1.0) compounds have been carried out to understand the reasons for the increase in TC upon Te doping in FeSe. While local distortions are present near superconducting onset in FeSe and FeSe0.5Te0.5, they seem to be absent in non superconducting FeTe. Of crucial importance is the variation of anion height. In FeSe0.5Te0.5, near the superconducting onset, the two heights, {{h}Fe-Se} and {{h}Fe-Te} show a nearly opposite behaviour. These changes indicate a possible correlation between Fe-chalcogen hybridization and the superconducting transition temperature in these Fe-chalcogenides.

Ingle, Kapil E.; Priolkar, K. R.; Pal, Anand; Zargar, Rayees A.; Awana, V. P. S.; Emura, S.

2015-01-01

333

Suppressing a Charge Density Wave by Changing Dimensionality in the Ferecrystalline Compounds ([SnSe]1.15)1(VSe2)n with n = 1, 2, 3, 4.  

PubMed

The compounds, ([SnSe]1.15)1(VSe2)n with n = 1, 2, 3, and 4, were prepared using designed precursors in order to investigate the influence of the thickness of the VSe2 constituent on the charge density wave transition. The structure of each of the compounds was determined using X-ray diffraction and scanning transmission electron microscopy. The charge density wave transition observed in the resistivity of ([SnSe]1.15)1(VSe2)1 was confirmed. The electrical properties of the n = 2 and 3 compounds are distinctly different. The magnitude of the resistivity change at the transition temperature is dramatically lowered and the temperature of the resistivity minimum systematically increases from 118 K (n = 1) to 172 K (n = 3). For n = 1, this temperature correlates with the onset of the charge density wave transition. The Hall-coefficient changes sign when n is greater than 1, and the temperature dependence of the Hall coefficient of the n = 2 and 3 compounds is very similar to the bulk, slowly decreasing as the temperature is decreased, while for the n = 1 compound the Hall coefficient increases dramatically starting at the onset of the charge density wave. The transport properties suggest an abrupt change in electronic properties on increasing the thickness of the VSe2 layer beyond a single layer. PMID:25546501

Falmbigl, Matthias; Fiedler, Andreas; Atkins, Ryan E; Fischer, Saskia F; Johnson, David C

2015-02-11

334

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 200C) via facile synthesis using organic ammine ligands. The cores were firstly fabricated via a less toxic procedure using CdO, trioctylphosphine (TOP), Se, Te, and trioctylamine. The cores with small sizes (3.2-3.5 nm) revealed green and yellow photoluminescence (PL) and spherical morphologies. Hydrophobic core/shell CdTe0.5Se0.5/Cd0.5Zn0.5S quantum dots (QDs) with tunable PL between green and near-infrared (a maximum PL peak wavelength of 735 nm) were then created through a facile shell coating procedure using trioctylphosphine selenium with cadmium and zinc acetate. The QDs exhibited high PL efficiencies up to 50% because of the formation of a protective Cd0.5Zn0.5S shell on the CdTe0.5Se0.5 core, even though the PL efficiency of the cores is low (?1%). Namely, the slow growth process of the shell plays an important role for getting high PL efficiencies. The properties of the QDs are largely determined by the properties of CdTe0.5Se0.5 cores and shells preparation conditions such as reaction temperature and time. The core/shell QDs exhibited a small size diameter. For example, the average diameter of the QDs with a PL peak wavelength of 735 nm is 6.1 nm. Small size and tunable bright PL makes the QDs utilizable as bioprobes because the size of QD-based bioprobes is considered as the major limitation for their broad applications in biological imaging. PMID:23130948

2012-01-01

335

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

336

Structural evolvement and thermoelectric properties of Cu(3-x)Sn(x)Se? compounds with diamond-like crystal structures.  

PubMed

Polycrystalline samples of Cu(3-x)Sn(x)Se3 were synthesized in the composition range x = 0.87-1.05. A compositionally induced evolvement from tetragonal via cubic to monoclinic crystal structures is observed, when the composition changes from a Cu-rich to a Sn-rich one. The Cu(3-x)Sn(x)Se3 materials show a metal-to-semiconductor transition with increasing x. Electronic transport properties are governed by the charge-carrier concentration which is well described by a linear dispersion-band model. The lattice component of the thermal conductivity is practically independent of x which is attributed to the opposite influence of the atomic ordering and the inhomogeneous distribution of the Cu-Se or Sn-Se bonds with different polarities in the crystal structure. The highest thermoelectric figure of merit ZT of 0.34 is achieved for x = 1.025 at 700 K. PMID:25286143

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

2014-11-28

337

Growth and characterization of the ternary ZnSe-based compounds obtained by low temperature vapour transport  

Microsoft Academic Search

We employed the low temperature physical vapour transport (PVT) method to grow ZnSe and ZnSe1 ? xSx (x ? 0.15), high quality, large (25 mm in diameter) bulk crystals. Characterization of the obtained crystals was performed by means of X-ray diffraction, X-ray full width half maximum (FWHM) rocking curves and the energy dispersive X-ray fluorescence (EDXRF) spectrometry. Optical properties were

A. Mycielski; L. Kowalczyk; B. Witkowska

1996-01-01

338

Trigonal-bipyramidal and square-pyramidal chromium-manganese chalcogenide clusters, [E2CrMn2(CO)n](2-) (E=S, Se, Te; n=9, 10): synthesis, electrochemistry, UV/Vis absorption, and computational studies.  

PubMed

The reactions of E powder (E=S, Se) with a mixture of Cr(CO)6 and Mn2(CO)10 in concentrated solutions of KOH/MeOH produced two new mixed Cr-Mn-carbonyl clusters, [E2CrMn2(CO)9](2-) (E=S, 1; Se, 2). Clusters 1 and 2 were isostructural with one another and each displayed a trigonal-bipyramidal structure, with the CrMn2 triangle axially capped by two ?3-E atoms. The analogous telluride cluster, [Te2CrMn2(CO)9](2-) (3), was obtained from the ring-closure of Te2Mn2 ring complex [Te2Mn2Cr2(CO)18](2-) (4). Upon bubbling with CO, clusters 2 and 3 were readily converted into square-pyramidal clusters, [E2CrMn2(CO)10](2-) (E=Se, 5; Te, 6), accompanied with the cleavage of one Cr-Mn bond. According to SQUID analysis, cluster 6 was paramagnetic, with S=1 at room temperature; however, the Se analogue (5) was spectroscopically proposed to be diamagnetic, as verified by TD-DFT calculations. Cluster 6 could be further carbonylated, with cleavage of the Mn-Mn bond to produce a new arachno-cluster, [Te2CrMn2(CO)11](2-) (7). The formation and structural isomers, as well as electrochemistry and UV/Vis absorption, of these clusters were also elucidated by DFT calculations. PMID:23610078

Shieh, Minghuey; Yu, Chun-Hsien; Chu, Yen-Yi; Guo, Yu-Wen; Huang, Chung-Yi; Hsing, Kai-Jieah; Chen, Pei-Chi; Lee, Chung-Feng

2013-05-01

339

Thermoelectric properties and chlorine doping effect of In4Pb0.01Sn0.03Se2.9Clx polycrystalline compounds.  

PubMed

We investigated the thermoelectric properties of Cl-doped polycrystalline compounds In4Pb0.01Sn0.03Se2.9Clx (x = 0.02, 0.04, and 0.06). X-ray diffraction measurement shows a gradual change in lattice volume for x ? 0.04 without any impurity phases indicating a systemic change in Cl doping. The Cl doping in the compounds has the effect of increasing carrier concentration and the effective mass of carriers, resulting in an increase in power factor at a high temperature (?700 K). Because of the increased electrical conductivity at a high temperature, the dimensionless thermoelectric figure of merit ZT reaches 1.25 at 723 K for the x = 0.04 Cl-doped compound, which is a relatively high value for n-type polycrystalline materials. PMID:25579326

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

2015-02-01

340

Discovery of a single topological Dirac fermion in the strong inversion asymmetric compound BiTeCl  

NASA Astrophysics Data System (ADS)

In the past few years, a new state of quantum matter known as the time-reversal-invariant topological insulator has been predicted theoretically and realized experimentally. All of the topological insulators discovered so far in experiment are inversion symmetric--except for strained HgTe, which has weak inversion asymmetry, a small bulk gap but no bulk charge polarization. Strong inversion asymmetry in topological insulators would not only lead to many interesting phenomena, such as crystalline-surface-dependent topological electronic states, pyroelectricity and intrinsic topological p-n junctions, but would also serve as an ideal platform for the realization of topological magneto-electric effects, which result from the modification of Maxwell equations in topological insulators. Here we report the discovery of a strong inversion asymmetric topological insulator phase in BiTeCl by angle-resolved photoemission spectroscopy, which reveals Dirac surface states and crystalline-surface-dependent electronic structures. Moreover, we observe a tenfold increase of the bulk energy gap in BiTeCl over the weak inversion asymmetric topological insulator HgTe, making it a promising platform for topological phenomena and possible applications at high temperature.

Chen, Y. L.; Kanou, M.; Liu, Z. K.; Zhang, H. J.; Sobota, J. A.; Leuenberger, D.; Mo, S. K.; Zhou, B.; Yang, S.-L.; Kirchmann, P. S.; Lu, D. H.; Moore, R. G.; Hussain, Z.; Shen, Z. X.; Qi, X. L.; Sasagawa, T.

2013-11-01

341

Comparison of Sn-doped and nonstoichiometric vertical-Bridgman-grown crystals of the topological insulator Bi{sub 2}Te{sub 2}Se  

SciTech Connect

A comparative study of the properties of topological insulator Bi{sub 2}Te{sub 2}Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8??10{sup 14}?cm{sup ?3}. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (E{sub F}) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, which the Dirac point for the surface states lies approximately 60?meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near E{sub F}. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed.

Kushwaha, S. K., E-mail: kushwaha@princeton.edu; Gibson, Q. D.; Cava, R. J. [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Xiong, J.; Ong, N. P. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Pletikosic, I. [Department of Physics, Princeton University, Princeton, New Jersey 08544 (United States); Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973 (United States); Weber, A. P. [National Synchrotron Light Source, Brookhaven National Lab, Upton, New York 11973 (United States); Fedorov, A. V. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Valla, T. [Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973 (United States)

2014-04-14

342

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

343

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

SciTech Connect

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

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

2010-06-15

344

Time-resolved photoluminescence spectroscopy of localized exciton magnetic polarons in Cd{sub 0.70}Mn{sub 0.30}Te spin glass compound  

SciTech Connect

We have investigated dynamics of different localized exciton magnetic polarons (LEMPs) in Cd{sub 0.70}Mn{sub 0.30}Te spin glass (SG) compound below the freezing temperature T{sub f} in the crystal regions, where various microscopic magnetic spin states (MMSSs), namely, loose spins, finite, and infinite clusters, are formed. It was shown that there is a broad distribution of the LEMPs lifetimes. The presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states, i.e., the brightening of the dark LEMPs which exist along with the bright LEMPs. The lifetimes of the dark LEMPs correspond to hundreds of nanoseconds. It was found that the time decay of photoluminescence band intensity is approximated by the sum of two functions: a single exponential function and the KohlrauschWilliamsWatts stretched exponential function. The stretched exponential function describes the recombination processes of the LEMPs formed in the crystal regions of the finite clusters as well as the infinite cluster. This reflects the appearance of spatially heterogeneous dynamics in Cd{sub 0.70}Mn{sub 0.30}Te SG compound below T{sub f} which is due to the disorder in the spin distribution caused by the formation of different MMSSs.

Gnatenko, Yu. P., E-mail: yuriygnatenko@ukr.net; Bukivskij, P. M.; Piryatinski, Yu. P. [Institute of Physics of NASU, Prospect Nauky 46, Kyiv 03028 (Ukraine)

2014-04-07

345

Development of a computer model for polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells. Final subcontract report, 1 January 1991--31 December 1991  

SciTech Connect

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

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

1992-09-01

346

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

SciTech Connect

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

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

2009-12-14

347

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 experimental and theoretical study of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2} to assess potential for photovoltaic and thermoelectric applications. Highlights: > Comparative experimental and theoretical study of orthorhombic BaCu{sub 2}Se{sub 2} and BaCu{sub 2}Te{sub 2}. > Measured and calculated optical and transport properties. > Temperature dependence of lattice parameters and transport properties. > Hall and Seebeck coefficient measurements indicate heavy hole doping. > Good agreement between measured and modeled room temperature Seebeck coefficients.

McGuire, Michael A., E-mail: McGuireMA@ornl.gov [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); May, Andrew F.; Singh, David J.; Du, Mao-Hua; Jellison, Gerald E. [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States)

2011-10-15

348

compounds  

NASA Astrophysics Data System (ADS)

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

Shah, N. A.

2014-10-01

349

Two new binary lanthanide polytellurides: Syntheses and crystal structures of CeTe{sub 1.90} and SmTe{sub 1.80}  

SciTech Connect

Single crystals of the new binaries CeTe{sub 1.90} and SmTe{sub 1.80} have been obtained. CeTe{sub 1.90} was synthesized at 1023K from the reaction of Ce, TeO{sub 2}, and Te with the use of a CsCl flux. It crystallizes in the tetragonal space group P4{sub 2}/n with 20 formula units in a cell of dimensions at 153K of a=10.0261(5), c=18.1336(12)A, V=1822.84(18)A{sup 3}. It is isostructural with the LnSe{sub 1.9} polyselenides (Ln=La, Ce, Pr) and with SmS{sub 1.90}. SmTe{sub 1.80} was synthesized at 1223K from the reaction of Sm and Te in a KBr flux. SmTe{sub 1.80} crystallizes in a new structural type in the tetragonal space group P4/n with 20 formula units in a cell of dimensions at 153K of a=9.7026(4), c=18.0072(14)A, V=1695.21(14)A{sup 3}. Both of these layered structures, which may be derived from the ZrSiS structure type, consist of double layers of [LnTe] polyhedra separated by planar Te nets that contain vacancies. In these nets the shortest Te-Te distances are 2.9194(5), 3.1204(5), and 3.3324(6)A in CeTe{sub 1.90} and 2.878(1), 2.9932(3), and 3.2114(7)A in SmTe{sub 1.80}. Neither a simple delineation of the Te-Te bonding nor an assignment of individual formal oxidation states is possible in either of these compounds if one takes strict account of the Te-Te distances.

Ijjaali, Ismail [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113 (United States); Ibers, James A. [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113 (United States)]. E-mail: ibers@chem.northwestern.edu

2006-11-15

350

Two new binary lanthanide polytellurides: Syntheses and crystal structures of CeTe 1.90 and SmTe 1.80  

NASA Astrophysics Data System (ADS)

Single crystals of the new binaries CeTe 1.90 and SmTe 1.80 have been obtained. CeTe 1.90 was synthesized at 1023 K from the reaction of Ce, TeO 2, and Te with the use of a CsCl flux. It crystallizes in the tetragonal space group P4 2/n with 20 formula units in a cell of dimensions at 153 K of a=10.0261(5), c=18.1336(12) , V=1822.84(18) 3. It is isostructural with the LnSe 1.9 polyselenides ( Ln=La, Ce, Pr) and with SmS 1.90. SmTe 1.80 was synthesized at 1223 K from the reaction of Sm and Te in a KBr flux. SmTe 1.80 crystallizes in a new structural type in the tetragonal space group P4 /n with 20 formula units in a cell of dimensions at 153 K of a=9.7026(4), c=18.0072(14) , V=1695.21(14) 3. Both of these layered structures, which may be derived from the ZrSiS structure type, consist of double layers of [ LnTe] polyhedra separated by planar Te nets that contain vacancies. In these nets the shortest Te-Te distances are 2.9194(5), 3.1204(5), and 3.3324(6) in CeTe 1.90 and 2.878(1), 2.9932(3), and 3.2114(7) in SmTe 1.80. Neither a simple delineation of the Te-Te bonding nor an assignment of individual formal oxidation states is possible in either of these compounds if one takes strict account of the Te-Te distances.

Ijjaali, Ismail; Ibers, James A.

2006-11-01

351

Order-disorder structural phase transition in the system of intercalated Ni atoms in the Ni0.5TiSe2 compound  

NASA Astrophysics Data System (ADS)

Changes in the crystal structure of the Ni0.5TiSe2 intercalated compound have been thoroughly investigated using powder X-ray diffractometry in the temperature range from 93 to 700 K. It has been shown that upon heating to the temperature of about 400 K, this compound undergoes a phase transition from the monoclinic structure described by space group I12/ m1 to the trigonal structure , which is associated with the disorder in the subsystem of intercalated Ni atoms. The supercooling effect with the formation of the metastable state, which is characteristic of first-order phase transitions such as melting and crystallization, has been revealed in the region of the order-disorder phase transition, and the anomalous behavior of the resistivity has been observed.

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

2014-12-01

352

Synthesis and X-ray structural characterization of a series of dimeric [Hg2(SePh)2X2(PR2R?)2] compounds (R = tert-butyl; R? = 4-N,N-dimethylaniline and X = Cl, Br, I, SCN, SePh)  

NASA Astrophysics Data System (ADS)

This article presents the syntheses and characterization of five new compounds with the general formula [Hg2(SePh)2X2(PR2R?)2] (R = tert-butyl; R? = 4-N,N-dimethylaniline), where X = Cl (1a), Br (1b), I (1c), SCN (2), SePh (3). The compounds crystallized as dimeric {HgSe} units, although most of these chalcogenolate compounds appeared to be polymeric adamantanoid or fused adamantanoid species. The ligand structures of these compounds limited the growth of the molecular structures and promoted the formation of the dimeric form alone. The mercury centers were connected to one another through one ?-Cl and one ?-SePh bridge in 1a, and through two ?-SePh bridges in 1b, 1c, 2, and 3. The compounds were characterized by single crystal X-ray diffractometry, TGA, elemental analysis, and infrared spectroscopy.

Stieler, Rafael; Faoro, Eliandro; Cechin, Camila Nunes; Floriano, Luana; Lang, Ernesto Schulz

2015-01-01

353

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

SciTech Connect

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

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

2009-12-14

354

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

PubMed

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

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

2014-02-26

355

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

NASA Astrophysics Data System (ADS)

Using polarized and unpolarized neutron scattering we show that interstitial Fe in superconducting Fe1+yTe1-xSex induces a magnetic Friedel-like oscillation that diffracts at Q=(120) and involves >50 neighboring Fe sites. The interstitial >2 ?B moment is surrounded by compensating ferromagnetic four spin clusters that may seed double stripe ordering in Fe1+yTe. A semi-metallic 5-band model with (1212) 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; Kang, J.; Rodriguez-Rivera, J. A.; Bao, W.; Savici, A. T.; Hu, J.; Liu, T. J.; Qian, B.; Fobes, D.; Mao, Z. Q.; Fu, C. B.; Chen, W. C.; Ye, Q.; Erwin, R. W.; Gentile, T. R.; Tesanovic, Z.; Broholm, C.

2012-02-01

356

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

NASA Astrophysics Data System (ADS)

Using polarized and unpolarized neutron scattering, we show that interstitial Fe in superconducting Fe1+yTe1-xSex induces a magnetic Friedel-like oscillation that diffracts at Q?=((1)/(2)0) and involves >50 neighboring Fe sites. The interstitial >2?B moment is surrounded by compensating ferromagnetic four-spin clusters that may seed double stripe ordering in Fe1+yTe. A semimetallic five-band model with ((1)/(2)(1)/(2)) Fermi surface nesting and fourfold symmetric superexchange between interstitial Fe and two in-plane nearest neighbors largely accounts for the observed diffraction.

Thampy, V.; Kang, J.; Rodriguez-Rivera, J. A.; Bao, W.; Savici, A. T.; Hu, J.; Liu, T. J.; Qian, B.; Fobes, D.; Mao, Z. Q.; Fu, C. B.; Chen, W. C.; Ye, Q.; Erwin, R. W.; Gentile, T. R.; Tesanovic, Z.; Broholm, C.

2012-03-01

357

Study of the electronic surface states of III-V compounds and silicon. Final technical progress report 1 Oct 78-30 Sep 82. [HgCdTe  

SciTech Connect

The work performed over the four year span of this contract comprises a large body of research. Its results are summarized in this document. The technical problem was to study the electronic and atomic structure of the surfaces of several semiconductors. The III-V compound semiconductors, especially GaAs, InP, and GaSb, and the column IV semiconductor Si were emphasized, but some work on Ge and HgCdTe was also performed. The predominant methodology used was laboratory experimentation: photoemission spectroscopy excited by synchrotron radiation was utilized heavily, along with angle-resolved photoemission, photoemission excited by conventional ultraviolet and x-ray illumination, low energy electron diffraction, Auger electron spectroscopy, contact potential difference (Kelvin probe) measurements, as well as other techniques which are detailed in the publications.

Spicer, W.E.; Lindau, I.

1982-09-30

358

Zone leveling and solution growth of complex compound semiconductors in space  

NASA Technical Reports Server (NTRS)

A research program on complex semiconducting compounds and alloys was completed that addressed the growth of single crystals of CdSe(y)Te(1-y), Zn(x)Cd(1-x)Te, Mn(x)Cd(1-x)Te, InP(y)As(1-y) and CuInSe2 and the measurement of fundamental physico-chemical properties characterizing the above materials. The purpose of this ground based research program was to lay the foundations for further research concerning the growth of complex ternary compound semiconductors in a microgravity environment.

Bachmann, K. J.

1986-01-01

359

Quasiparticle self-consistent GW calculations for PbS, PbSe, and PbTe: Band structure and pressure coefficients  

E-print Network

and in solar-energy panels.8 With Tl doping PbTe may even exhibit superconductivity.9,10 The lead chalcogenides by small direct semiconduct- ing gaps, which occur at the L point of the Brillouin zone BZ . The gaps reveals that the LDA, in fact, leads to the valence-band maximum VBM and conduction-band mini- mum CBM

Svane, Axel Torstein

360

The effect of the Wyckoff position of the K atom on the crystal structure and electronic properties of the compound KFe?Se?.  

PubMed

By means of first-principles electronic structure calculations, we study the effect of the Wyckoff position of the K atom on the crystal and electronic structures of the compound KFe(2)Se(2). When the K atoms take up the Wyckoff positions 2a, 2b and 4c (the related structures of KFe(2)Se(2) are referred to as Struc-2a, Struc-2b and Struc-4c), the calculated lattice constants c lie in the ranges 13.5-14.5, 15.5-16.7 or 18.6-19.1 ? respectively. Three concentric cylinder-like Fermi surfaces emerge around ?-Z in the Brillouin zone for Struc-2b in the nonmagnetic state, unlike the cases for Struc-2a and Struc-4c. The Fe-Se-Fe angles are 107.8, 108.8 and 110.7 respectively in the collinear antiferromagnetic state, and the superexchange interactions J(2) between two next neighbor Fe moments are 13.08 meV S(-2), 20.75 meV S(-2) and 11.86 meV S(-2) for the Struc-2a, Struc-2b and Struc-4c structures respectively. Struc-2b and Struc-4c have good correspondence with the newly discovered superconducting phases with T(c) = 40 and 30 K in KFe(2)Se(2). Our findings suggest a reasonable approach for achieving an understanding of the existence of multiple superconducting phases in alkali metal intercalated FeSe superconductor. PMID:23086104

Yan, Xun-Wang; Gao, Miao

2012-11-14

361

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

NASA Astrophysics Data System (ADS)

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

Maeda, Tsuyoshi; Wada, Takahiro

2013-06-01

362

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

SciTech Connect

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

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

2012-12-10

363

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

Microsoft Academic Search

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

Minghuey Shieh; Chia-Hua Ho

2005-01-01

364

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

Microsoft Academic Search

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 ((1+x)=1.25, 1.28, 1.34, 1.37, 1.41, 1.43) and a low-temperature (LT) modification with trigonal

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

2008-01-01

365

Mo{sub 6}Se{sub 8}-cluster-based superconducting compounds Cs{sub 2}Mo{sub 12}Se{sub 14} and Rb{sub 4}Mo{sub 18}Se{sub 20}: Evidence for a strongly correlated and anisotropic electron system  

SciTech Connect

We studied the normal and superconducting states of the title compounds by measuring the conductivity and magnetization of single crystals and powder samples. From the upper and lower critical fields we deduced the characteristic lengths and thermodynamical fields. These results are borne out by our specific-heat measurements. We recognize in these compounds many features of the Chevrel-phase superconductors, including very small coherence lengths and strong-coupling-like effects. However, we show that the electron system is much more anisotropic and still less delocalized in these materials where the Mo{sub 6}Se{sub 8} clusters have condensed in Mo{sub 6{ital n}}Se{sub 6{ital n}+2} finite chains. This condensation is accompanied by an enhancement of the magnetic response whereas the lengthening of the chains leads to a counteracting reduction of the density of carriers. This indicates that superconductivity is built upon highly correlated molecular states. Reviewing the available data on the other Chevrel-cluster-based superconductors confirms this picture and suggests that the small coherence lengths reflect the local character of the electron pairing. This comparison also shows that forming finite chains of Mo{sub 6}Se{sub 8} clusters makes the electron correlations more repulsive and pushes the electron system near the borderline between superconductivity and magnetism. In this respect these compounds could provide valuable complementary information on issues which are at the center of the research upon high-{ital Y}{sub {ital c}} superconductivity.

Brusetti, R.; Laborde, O.; Sulpice, A. [Centre de Recherches sur les Tres Basses Temperatures, Laboratoire associe a l`Universite Joseph Fourier, CNRS, Boite Postale 166, 38042 Grenoble-Cedex 9 (France)] [Centre de Recherches sur les Tres Basses Temperatures, Laboratoire associe a l`Universite Joseph Fourier, CNRS, Boite Postale 166, 38042 Grenoble-Cedex 9 (France); Calemczuk, R. [Laboratoire de Cryophysique, Centre d`Etudes Nucleaires de Grenoble, Boite Postale 85 X, 38042 Grenoble-Cedex (France)] [Laboratoire de Cryophysique, Centre d`Etudes Nucleaires de Grenoble, Boite Postale 85 X, 38042 Grenoble-Cedex (France); Potel, M.; Gougeon, P. [Laboratoire de Chimie Minerale B, Universite de Rennes, Avenue du General Leclerc, 35042 Rennes-Cedex (France)] [Laboratoire de Chimie Minerale B, Universite de Rennes, Avenue du General Leclerc, 35042 Rennes-Cedex (France)

1995-08-01

366

Structure and basic magnetic properties of the honeycomb lattice compounds Na{sub 2}Co{sub 2}TeO{sub 6} and Na{sub 3}Co{sub 2}SbO{sub 6}  

SciTech Connect

The synthesis, structure, and basic magnetic properties of Na{sub 2}Co{sub 2}TeO{sub 6} and Na{sub 3}Co{sub 2}SbO{sub 6} are reported. The crystal structures were determined by neutron powder diffraction. Na{sub 2}Co{sub 2}TeO{sub 6} has a two-layer hexagonal structure (space group P6{sub 3}22) while Na{sub 3}Co{sub 2}SbO{sub 6} has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co{sup 2+} and Te{sup 6+}/Sb{sup 5+} ions in the ab plane such that the Co{sup 2+} ions form a honeycomb array. The stacking of the honeycomb arrays differ in the two compounds. Both Na{sub 2}Co{sub 2}TeO{sub 6} and Na{sub 3}Co{sub 2}SbO{sub 6} display magnetic ordering at low temperatures, with what appears to be a spin-flop transition found in Na{sub 3}Co{sub 2}SbO{sub 6}. - Graphical abstract: The layer of edge-shared MO{sub 6} octahedra, showing the honeycomb Co array.

Viciu, L. [Department of Chemistry, Princeton University, Princeton NJ 08544 (United States)], E-mail: mviciu@Princeton.edu; Huang, Q. [NIST Center for Neutron Research, NIST, Gaithersburg, MD 20899 (United States); Morosan, E. [Department of Chemistry, Princeton University, Princeton NJ 08544 (United States); Zandbergen, H.W. [National Centre for HREM, Department of Nanoscience, Delft Institute of Technology, Al Delft (Netherlands); Greenbaum, N.I. [Department of Chemistry, Princeton University, Princeton NJ 08544 (United States); McQueen, T. [Department of Chemistry, Princeton University, Princeton NJ 08544 (United States); Cava, R.J. [Department of Chemistry, Princeton University, Princeton NJ 08544 (United States)

2007-03-15

367

X-ray characterization, electronic band structure, and thermoelectric properties of the cluster compound Ag2Tl2Mo9Se11.  

PubMed

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

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

2014-11-01

368

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

SciTech Connect

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

Mohanta, S. K.; Mishra, S. N. [Tata Institute of Fundamental Research (TIFR), Homi Bhabha Road, Mumbai 400005 (India)

2014-05-07

369

Theoretical study of influencing factors on the dispersion of bulk band-gap edges and the surface states in topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3}  

SciTech Connect

The dispersion of the band-gap edge states in bulk topological insulators Bi{sub 2}Te{sub 3} and Bi{sub 2}Se{sub 3} is considered within density functional theory. The dependences of this dispersion both on the approximation used for an exchange-correlation functional at fixed unit cell parameters and atomic positions and on these parameters and positions that are obtained upon structural relaxation performed using a certain approximated functional are analyzed. The relative position of the Dirac point of topologically protected surface states and the valence band maximum in the surface electronic structure of the topological insulators is discussed.

Rusinov, I. P., E-mail: rusinovip@gmail.com; Nechaev, I. A. [Tomsk State University (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC) (Spain)

2013-06-15

370

Biomonitoring of arsenic through mangrove oyster (Crassostrea corteziensis Hertlein, 1951) from coastal lagoons (SE Gulf of California): occurrence of arsenobetaine and other arseno-compounds.  

PubMed

In this study, we examined the bioavailability of arsenic through the mangrove oyster Crassostrea corteziensis sampled from seven coastal lagoons in SE Gulf of California during the rainy and dry seasons. As concentrations in soft tissue of oysters C. corteziensis fluctuated between 5.2 and 11.6 ?g/g on dry weight; organisms from the control site presented the lowest As concentrations in the two sampling seasons. As speciation was evaluated in selected samples and indicated that arsenobetaine was the major arseno-compound accounting for 53.5-74.7 % of total As. Lower percentage contributions were obtained for nonextractable As (9.7-25.5 %) and other molecules such as arsenocholine and methyl-arsonate (<5 %). Inorganic As was detectable in only two samples, at concentrations lower than 0.1 ?g/g. These As data are the first generated in NW Mexico and indicate that C. corteziensis is safe for human consumption in terms of arseno-compounds. It is evident that As bioavailability in these lagoons is low. PMID:23412954

Bergs-Tiznado, Magdalena E; Pez-Osuna, Federico; Notti, Alessandra; Regoli, Francesco

2013-09-01

371

Point defects and self-diffusion of tellurium in the solid solution Pb/sub 1-y/(Te/sub 0. 92/Se/sub 0. 08/)y  

SciTech Connect

The self-diffusion parameters of tellurium were determined by the method of radioactive markers using the isotope /sup 125m/Te without the appreciable quantity of radioactive impurities of other elements. The equations of the isothermal dependences of the coefficient of self-diffusion of tellurium on the vapor pressure of lead in equilibrium with the title solid solutions of different composition were obtained for 600, 650, and 700/sup 0/C. The interrelationship of the coefficients of diffusion of tellurium, the concentration of point defects, and the lead vapor pressure were established.

Firsova, L.P.; Simirskaya, G.P.

1987-05-01

372

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

373

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

SciTech Connect

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

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

1997-03-01

374

Electrical detection of the spin polarization due to charge flow in the surface state of the topological insulator Bi(1.5)Sb(0.5)Te(1.7)Se(1.3).  

PubMed

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

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

2014-11-12

375

Sb2Se3 under pressure  

PubMed Central

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

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

2013-01-01

376

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

PubMed

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

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

2014-02-28

377

Electron-phonon interaction and thermal boundary resistance at the crystal-amorphous interface of the phase change compound GeTe  

NASA Astrophysics Data System (ADS)

Phonon dispersion relations and electron-phonon coupling of hole-doped trigonal GeTe have been computed by density functional perturbation theory. This compound is a prototypical phase change material of interest for applications in phase change non-volatile memories. The calculations allowed us to estimate the electron-phonon contribution to the thermal boundary resistance at the interface between the crystalline and amorphous phases present in the device. The lattice contribution to the thermal boundary resistance has been computed by non-equilibrium molecular dynamics simulations with an interatomic potential based on a neural network scheme. We find that the electron-phonon term contributes to the thermal boundary resistance to an extent which is strongly dependent on the concentration and mobility of the holes. Further, for measured values of the holes concentration and electrical conductivity, the electron-phonon term is larger than the contribution from the lattice. It is also shown that the presence of Ge vacancies, responsible for the p-type degenerate character of the semiconductor, strongly affects the lattice thermal conductivity of the crystal.

Campi, Davide; Donadio, Davide; Sosso, Gabriele C.; Behler, Jrg; Bernasconi, Marco

2015-01-01

378

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

SciTech Connect

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

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

2013-05-27

379

Experimental Studies on Anisotropic Thermoelectric Properties and Structures of n-type Bi{sub 2}Te{sub 2.7}Se{sub 0.3}  

SciTech Connect

The peak dimensionless thermoelectric figure-of-merit (ZT) of Bi{sub 2}Te{sub 3}-based n-type single crystals is about 0.85 in the ab plane at room temperature, which has not been improved over the last 50 years due to the high thermal conductivity of 1.65 W m{sup ?1} K{sup ?1} even though the power factor is 47 10{sup ?4} W m{sup ?1} K{sup ?2}. In samples with random grain orientations, we found that the thermal conductivity can be decreased by making grain size smaller through ball milling and hot pressing, but the power factor decreased with a similar percentage, resulting in no gain in ZT. Reorienting the ab planes of the small crystals by repressing the as-pressed samples enhanced the peak ZT from 0.85 to 1.04 at about 125 C, a 22% improvement, mainly due to the more increase on power factor than on thermal conductivity. Further improvement is expected when the ab plane of most of the small crystals is reoriented to the direction perpendicular to the press direction and grains are made even smaller.

Yan, X.; Poudel, Bed; Ma, Yi; Liu, W. S.; Joshi, G.; Wang, H.; Lan, Y. C.; Wang, D Z; Chen, Gang; Ren, Zhifeng

2010-01-01

380

Effects of partial anion substitution on the thermoelectric properties of silver(I) chalcogenide halides in the system Ag{sub 5}Q{sub 2}X with Q=Te, Se and S and X=Br and Cl  

SciTech Connect

A selection of mixed conducting silver chalcogenide halides of the general formula Ag{sub 5}Q{sub 2}X with Q=sulfur, selenium and tellurium and X=chlorine and bromine has been investigated due to their thermoelectric properties. Recently, the ternary counterpart Ag{sub 5}Te{sub 2}Cl showed a defined d{sup 10}-d{sup 10} interaction in the disordered cation substructure at elevated temperatures where Ag{sub 5}Te{sub 2}Cl is present in its high temperature {alpha}-phase. A significant drop of the thermal diffusivity has been observed during the {beta}-{alpha} phase transition reducing the values from 0.12 close to 0.08 mm{sup 2} s{sup -1}. At the same transition the thermopower reacts on the increasing silver mobility and jumps towards less negative values. Thermal conductivities, thermopower and thermal diffusivity of selected compounds with various grades of anion substitution in Ag{sub 5}Q{sub 2}X were determined around the silver-order/disorder {beta}-{alpha} phase transition. A formation of attractive interactions could be observed for selenium substituted phases while no effect was detected for bromide and sulfide samples. Depending on the grade and type of substitution the thermopower changes significantly at and after the {beta}-{alpha} phase transition. Thermal conductivities are low reaching values around 0.2-0.3 W m{sup -1} K{sup -1} at 299 K. Partial anion exchange can substantially tune the thermoelectric properties in Ag{sub 5}Q{sub 2}X phases. -- Graphical abstract: A structure section of the {alpha}-Ag{sub 5}Te{sub 2}Cl structure type and the thermopower evolution of Ag{sub 5}Te{sub 2}Cl{sub 0.4}Br{sub 0.6} undergoing a silver ion order/disorder phase transition. Display Omitted Research highlights: > We report on thermoelectric properties of silver(I) chalcogenide halides. > We examine thermopower, thermal diffusivity and thermal behavior. > Silver mobility, phase transitions and order/disorder phenomena are discussed. > Partial anion exchange can tune thermoelectric properties significantly.

Eckstein, Nadine [TU Muenchen, Lichtenbergstrasse 4, Garching (Germany); Nilges, Tom, E-mail: tom.nilges@lrz.tum.d [TU Muenchen, Lichtenbergstrasse 4, Garching (Germany); Decourt, Rodolphe; Bobet, Jean-Louis; Chevalier, Bernard [CNRS, Universite de Bordeaux, ICMCB, Avenue du Docteur Schweitzer 87, 33608 PESSAC cedex (France)

2011-04-15

381

Surface-dominated transport and enhanced thermoelectric figure of merit in topological insulator Bi1.5Sb0.5Te1.7Se1.3.  

PubMed

We report the observation of an order of magnitude enhancement of the thermoelectric figure of merit (ZT = 0.36) in topological insulator Bi1.5Sb0.5Te1.7Se1.3 nanowires at 300 K as compared with the bulk specimen (ZT = 0.028). The enhancement was primarily due to an order of magnitude increase in the electrical conductivity of the surface-dominated transport and thermally activated charge carriers in the nanowires. Magnetoresistance analysis revealed the presence of Dirac electrons and determined that the Fermi level was near the conduction band edge. This may be the first thermoelectric measurement of samples with a chemical potential in the gap of a topological insulator without gate tuning, and provides an opportunity to study the contribution of surface states to the Seebeck coefficient and resistivity without concern for the complex effect of band bending. PMID:25409984

Hsiung, Te-Chih; Mou, Chung-Yu; Lee, Ting-Kuo; Chen, Yang-Yuan

2014-12-11

382

Evidence for a cos(4?) modulation of the superconducting energy gap of optimally doped FeTe(0.6)Se(0.4) single crystals using laser angle-resolved photoemission spectroscopy.  

PubMed

We study the superconducting-gap anisotropy of the ?-centered hole Fermi surface in optimally doped FeTe(0.6)Se(0.4) (T(c)=14.5 K), using laser-excited angle-resolved photoemission spectroscopy. We observe sharp superconducting (SC) coherence peaks at T=2.5 K. In contrast to earlier angle-resolved photoemission spectroscopy studies but consistent with thermodynamic results, the momentum dependence shows a cos(4?) modulation of the SC-gap anisotropy. The observed SC-gap anisotropy strongly indicates that the pairing interaction is not a conventional phonon-mediated isotropic one. Instead, the results suggest the importance of second-nearest-neighbor electronic interactions between the iron sites in the framework of s()-wave superconductivity. PMID:23368253

Okazaki, K; Ito, Y; Ota, Y; Kotani, Y; Shimojima, T; Kiss, T; Watanabe, S; Chen, C -T; Niitaka, S; Hanaguri, T; Takagi, H; Chainani, A; Shin, S

2012-12-01

383

First principle investigations of the optical properties of Zn1-xMgxS, Zn1-xMgxSe and Zn1-xMgxTe ternary alloys  

NASA Astrophysics Data System (ADS)

Optical properties of Zn1-xMgxS, Zn1-xMgxSe and Zn1-xMgx Te(0 ? x ? 1) ternary semiconductor alloys are calculated using the full potential linearized augmented plane wave within the density functional theory. The exchange correlation potential is treated by the generalized gradient approximation (GGA) within Perdew et al. scheme. The real and imaginary parts of the dielectric function ?(?), the refractive index n(?), the extinction coefficient k(?), the optical absorption coefficient ?(?), the reflectivity R(?) and the electron energy loss function (EELS) are calculated within random phase approximation (RPA). Our results are compared with the previous theoretical calculations and available experimental data. Moreover, the interband transitions responsible for the structures seen in the spectra are specified. It is shown that, the chalcogen p states as initial and Zn4s, Mg3s, chalcogen d states as final states perform the major role in optical transitions.

Dadsetani, M.; Zeinivand, A.

2014-08-01

384

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

PubMed

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

Biering, S; Schwerdtfeger, P

2012-07-21

385

Surface-dominated transport and enhanced thermoelectric figure of merit in topological insulator Bi1.5Sb0.5Te1.7Se1.3  

NASA Astrophysics Data System (ADS)

We report the observation of an order of magnitude enhancement of the thermoelectric figure of merit (ZT = 0.36) in topological insulator Bi1.5Sb0.5Te1.7Se1.3 nanowires at 300 K as compared with the bulk specimen (ZT = 0.028). The enhancement was primarily due to an order of magnitude increase in the electrical conductivity of the surface-dominated transport and thermally activated charge carriers in the nanowires. Magnetoresistance analysis revealed the presence of Dirac electrons and determined that the Fermi level was near the conduction band edge. This may be the first thermoelectric measurement of samples with a chemical potential in the gap of a topological insulator without gate tuning, and provides an opportunity to study the contribution of surface states to the Seebeck coefficient and resistivity without concern for the complex effect of band bending.We report the observation of an order of magnitude enhancement of the thermoelectric figure of merit (ZT = 0.36) in topological insulator Bi1.5Sb0.5Te1.7Se1.3 nanowires at 300 K as compared with the bulk specimen (ZT = 0.028). The enhancement was primarily due to an order of magnitude increase in the electrical conductivity of the surface-dominated transport and thermally activated charge carriers in the nanowires. Magnetoresistance analysis revealed the presence of Dirac electrons and determined that the Fermi level was near the conduction band edge. This may be the first thermoelectric measurement of samples with a chemical potential in the gap of a topological insulator without gate tuning, and provides an opportunity to study the contribution of surface states to the Seebeck coefficient and resistivity without concern for the complex effect of band bending. Electronic supplementary information (ESI) available: Magnetoresistance and thermal conductivity measurements of additional samples. See DOI: 10.1039/c4nr05376a

Hsiung, Te-Chih; Mou, Chung-Yu; Lee, Ting-Kuo; Chen, Yang-Yuan

2014-12-01

386

Unusual microwave response and bulk conductivity of very thin FeSe0.3Te0.7 films as a function of temperature  

NASA Astrophysics Data System (ADS)

Results of X-band microwave surface impedance measurements of FeSe1-xTex very thin film are reported. The effective surface resistance shows appearance of peak at T ? Tc when plotted as a function of temperature. The authors suggests that the most well-reasoned explanation can be based on the idea of the changing orientation of the microwave magnetic field at a S-N phase transition near the surface of a very thin film. The magnetic penetration depth exhibits a power-law behavior of ??L(T) ? CTn, with an exponent n ? 2.4 at low temperatures, which is noticeably higher than in the published results on FeSe1-xTex single crystal. However the temperature dependence of the superfluid conductivity remains very different from the behavior described by the BCS theory. Experimental results are fitted very well by a two-gap model with ?1/kTc = 0.43 and ?2/kTc = 1.22, thus supporting s-wave symmetry. The rapid increase of the quasiparticle scattering time is obtained from the microwave impedance measurements.

Barannik, A. A.; Cherpak, N. T.; Kharchenko, M. S.; Wu, Yun; Luo, Sheng; He, Yusheng; Porch, A.

2014-06-01

387

Synthesis, structure, and optical properties of the quaternary diamond-like compounds I{sub 2}IIIVVI{sub 4} (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se)  

SciTech Connect

Three new diamond-like compounds with the formula of I{sub 2}?II?IV?VI{sub 4} (I=Cu; II=Mg; IV=Si, Ge; VI=S, Se) have been synthesized via traditional high-temperature solid-state reactions and structurally characterized by single crystal X-ray diffraction analysis. All the three compounds crystallize in the space group Pmn2{sub 1} in the wurtzite-type superstructure with a=7.563(4), b=6.448(3), c=6.179(3) , Z=2 for Cu{sub 2}MgSiS{sub 4} (1); a=7.953(5), b=6.797(4), c=6.507(4) , Z=2 for Cu{sub 2}MgGeS{sub 4} (2); a=7.638(4), b=6.515(4), c=6.225(3) , Z=2 for Cu{sub 2}MgSiSe{sub 4} (3). All atoms in these compounds are tetrahedrally coordinated. Optical diffuse reflectance UV/Vis/NIR spectra indicate that compounds 1 and 2 have the band gaps of 3.20 and 2.36 eV, respectively. Electronic structure calculations using the CASTEP code indicate that they are all direct band gap compounds. - Graphical abstract: Three new diamond-like compounds, Cu{sub 2}MgSiS{sub 4}, Cu{sub 2}MgGeS{sub 4}, and Cu{sub 2}MgSiSe{sub 4}, have been synthesized. All the three compounds crystallize in the space group Pmn2{sub 1} and all atoms are tetrahedrally coordinated. Highlights: Three new diamond-like compounds Cu{sub 2}MgSiS{sub 4}, Cu{sub 2}MgGeS{sub 4} and Cu{sub 2}MgSiSe{sub 4} have been synthesized. All ions are tetrahedrally coordinated. Electronic structure calculations indicate that they are all direct band gap compounds.

Liu, Bin-Wen; Zhang, Ming-Jian; Zhao, Zhong-Yan; Zeng, Hui-Yi, E-mail: zhy@fjirsm.ac.cn; Zheng, Fa-Kun; Guo, Guo-Cong, E-mail: gcguo@fjirsm.ac.cn; Huang, Jin-Shun

2013-08-15

388

Substitution of Ni for Fe in superconducting Fe0.98Te0.5Se0.5 depresses the normal-state conductivity but not the magnetic spectral weight  

NASA Astrophysics Data System (ADS)

We have performed systematic resistivity and inelastic neutron scattering measurements on Fe0.98 -zNizTe0.5Se0.5 samples to study the impact of Ni substitution on the transport properties and the low-energy (?12 meV) magnetic excitations. It is found that, with increasing Ni doping, both the conductivity and superconductivity are gradually suppressed; in contrast, the low-energy magnetic spectral weight changes little. Comparing with the impact of Co and Cu substitution, we find that the effects on conductivity and superconductivity for the same degree of substitution grow systematically as the atomic number of the substituent deviates from that of Fe. The impact of the substituents as scattering centers appears to be greater than any contribution to carrier concentration. The fact that low-energy magnetic spectral weight is not reduced by increased electron scattering indicates that the existence of antiferromagnetic correlations does not depend on electronic states close to the Fermi energy.

Wang, Jinghui; Zhong, Ruidan; Li, Shichao; Gan, Yuan; Xu, Zhijun; Zhang, Cheng; Ozaki, T.; Matsuda, M.; Zhao, Yang; Li, Qiang; Xu, Guangyong; Gu, Genda; Tranquada, J. M.; Birgeneau, R. J.; Wen, Jinsheng

2015-01-01

389

Excess vibrational modes and high thermoelectric performance of the quenched and slow-cooled two-phase alloy Cu0.2Ag2.8SbSeTe2.  

PubMed

In this article we examine the low-temperature specific heat of slow-cooled Cu(0.2)Ag(2.8)SbSeTe(2) and the thermoelectric performance of quenched samples. We find that the low-temperature specific heat is dominated by two Einstein terms of approximate energies of 2.5 and 5 meV. The specific-heat behavior is consistent with the amorphous low-temperature thermal conductivity behavior and validates the glassy nature of the structure. We performed the synthesis of quenched samples in an attempt to eliminate the presence of micro-cracks, whose existence presumably enhances electronic scattering. We find that quenching eliminates the presence of micro-cracks but does not result in an improvement of the figure of merit. Specifically, the highest ZT obtained in the quenched samples (ZT = 1.5), though very competitive, is still significantly less that the ZT obtained in the slow-cooled samples (ZT = 1.75). PMID:21415478

Drymiotis, F R; Lindsey, S; Capps, J; Lashley, J C; Rhodes, D; Zhang, Q R; Nucklos, C; Drye, T B

2011-04-01

390

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

SciTech Connect

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

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

2011-11-15

391

Iodine as an oxidant in the topotactic deintercalation of interstitial iron in Fe(1+x)Te.  

PubMed

The layered telluride, Fe(1+x)Te, is a parent compound of the isostructural and superconducting phases, Fe(1+x)(Te, Se, S). Here we show that, through a simple reaction of I(2) vapor with both powder and single crystal samples, the interstitial iron can be removed from the FeTe framework topotactically. Neutron powder diffraction and X-ray single crystal diffraction confirm that the iron being extracted is the partially occupied site that lies between the 2-D blocks of edge-sharing FeTe(4) tetrahedra. The deintercalation process has consequences for both magnetic and crystallographic phase transitions in the compound at low temperatures. This technique could be of use for the tuning of stoichiometry of the superconducting phases and therefore enable more careful studies on how chemical composition affects magnetic and superconducting properties. PMID:20608638

Rodriguez, Efrain E; Zavalij, Peter; Hsieh, Ping-Yen; Green, Mark A

2010-07-28

392

Infrared thermooptic coefficient measurement of polycrystalline ZnSe, ZnS, CdTe, CaF(2), and BaF(2), single crystal KCI, and TI-20 glass.  

PubMed

An interferometric technique has been used to determine the thermooptic coefficient (dn/dT) of polycrystalline ZnSe and ZnS at 0.6328 microm, 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CdTe and TI-20 glass at 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CaF(2) and BaF(2) at 0.6328 microm, 1.15 microm, and 3.39 microm, and pure and europium-doped single crystal KCl at 0.6328 microm, 1.15microm, 3.39 microm, and 10.6 microm. The values were obtained over the temperature range of 25-65 degrees C and were calculated using the observed change in optical path of the samples as they were heated. Some difficulties in thermometry were encountered in the standard configuration of sample and thermocouple probe, so measurements were made in an oil bath at the shortest wavelength at which the sample was transparent to provide temperature correction factors for each sample. An empirical dispersion relation for dn/dT has also been found for the semiconductor materials. This dispersion relation is of the form dn/dT = aR(b), where R is defined as lambda(2)/(lambda(2) - lambda(g)(2)), lambda(g) is the short wavelength cutoff associated with the energy gap, and a and b are constants which are different for each material. PMID:20168506

Harris, R J; Johnston, G T; Kepple, G A; Krok, P C; Mukai, H

1977-02-01

393

Heterometallic cuboidal clusters M(3)M'Q(4) (M = Mo, W; M'= Sn, Pb, As, Sb; Q = S, Se): from coordination compounds to supramolecular adducts.  

PubMed

Reactions of the incomplete cuboidal clusters [M3Q4(acac)3(py)3]+ (M = Mo, W; Q = S, Se) with group 14 and 15 metal complexes with the s2p0 electronic configuration (AsPh3, SbPh3, SbCl3, SbI3, PbI3-, SnCl3-) led to heterometal incorporation with the formation of cuboidal clusters of the type [M3(EX3)Q4(acac)3(py)3]n+ (n = 0 for Sn, Pb; n = 1 for As, Sb), whose structures were determined by X-ray diffraction. The cuboidal clusters can be described as complexes of the cluster tridentate ligand [M3Q4(acac)3(py)3]+ (mu2-chalcogen atoms as donors) with the EX3, where the E atom attains a distorted octahedral coordination. Analysis based on the bond distances E-Q gives the following sequence of affinity: As < Sb; Pb < Sn approximately Sb; SbPh3 < SbI3 approximately SbCl3; W3S4 < W3Se4. Interaction energies at the gas phase between [W3Q4(acac)3(py)3]+ (Q = S, Se) and SbX3 (X = I, Ph) were computed at the DFT level (BP86/TZP). The magnitude of the interaction depends strongly on the substituents at Sb, and the replacement of iodine by the phenyl group decreases the interaction energy from -9.21 to -2.70 kcal/mol and from -12.73 to -3.85 kcal/mol for the W3SbS4 and W3SbSe4 cores, respectively. PMID:18069825

Hernandez-Molina, Rita; Kalinina, Irina V; Abramov, Pavel A; Sokolov, Maxim N; Virovets, Alexandr V; Platas, Javier G; Llusar, Rosa; Polo, Victor; Vicent, Cristian; Fedin, Vladimir P

2008-01-01

394

Thermoelectric properties of Cu and Cr disordered CuCrX2(X=S, Se): a first principles study.  

PubMed

The layered antiferromagnetic ACrX(2) -type compounds are currently highlighted as prominent material candidates for low- and intermediate-temperature thermoelectric (TE) applications. A key to attain the enhanced TE characteristics is to apply high-temperature sintering which presumably introduces some cation disorder. Here we present spin unrestricted density functional theory analysis of electronic band structures and TE properties of Cu and Cr disordered CuCrX(2)(X = S, Se) phases. A narrow band gap semiconductor to metal transition is observed on 8.3% Cr-site disorder for both the compounds, X = S and Se. The large p-type Seebeck coefficient realized in the metallic state for the Cr-disordered phases is the factor that makes these phases promising TE materials. These theoretical findings for the Cr-disordered phases are well in line with reported experimental data for electronic transport properties. Contrarily, the results revealed for the Cu-disordered phases do not agree with the experimental data. Hence the results of our theoretical analysis strongly point towards the Cr rather than the Cu disorder picture to explain the TE electronic transport characteristics of the high-temperature sintered phases of CuCrX(2)(X = S, Se). PMID:25406713

Srivastava, Divya; Tewari, Girish C; Karppinen, Maarit

2014-12-17

395

Study of Te aggregation at the initial growth stage of CdZnTe films deposited by CSS  

NASA Astrophysics Data System (ADS)

Te aggregation at the initial growth stage of CdZnTe films deposited by close-spaced sublimation (CSS) is studied with the combination of energy dispersive spectroscopy (EDS) and high resolution transmission electron microscopy (TEM). Te atoms aggregate in the form of Te-rich amorphous layers, and then these layers grow into stoichiometric and crystalline compounds through interdiffusion as the films thickened. Te aggregation is led by the high dissociation energy of Te-Te bond and the less volatile nature of Te2 molecules than Cd and Zn molecules absorbed on the substrate.

Gao, Junning; Jie, Wanqi; He, Yihui; Sun, Jie; Zhou, Hao; Zha, Gangqiang; Yuan, Yanyan; Tong, Junli; Yu, Hui; Wang, Tao

2012-08-01

396

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

E-print Network

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

Liu, Weishu

397

Resistance and Susceptibility Anomalies in IrTe 2 and CuIr 2 Te 4  

Microsoft Academic Search

IrTe2has the CdI2structure and CuIr2Te4has a defect-NiAs structure at room temperature. Both compounds show basically metallic behavior. Magnetic and resistance anomalies, showing a hysteresis in temperature, have been found in IrTe2and CuIr2Te4. On heating, the resistivity ? exhibits a hump-shaped maximum around 270 and 250 K for IrTe2and CuIr2Te4, respectively. The magnetic susceptibility ? reveals a step-like anomaly which gives

Nobuhiro Matsumoto; Kouji Taniguchi; Ryo Endoh; Hideaki Takano; Shoichi Nagata

1999-01-01

398

Induced lattice strain in epitaxial Fe-based superconducting films on CaF{sub 2} substrates: A comparative study of the microstructures of SmFeAs(O,F), Ba(Fe,Co){sub 2}As{sub 2}, and FeTe{sub 0.5}Se{sub 0.5}  

SciTech Connect

The microstructures of SmFeAs(O,F), Ba(Fe,Co){sub 2}As{sub 2}, and FeTe{sub 0.5}Se{sub 0.5} prepared on CaF{sub 2} substrates were investigated using transmission electron microscopy. The SmFeAs(O,F)/CaF{sub 2} interface is steep, without a disordered layer. By contrast, a chemical reaction occurs at the interface in the cases of Ba(Fe,Co){sub 2}As{sub 2} and FeTe{sub 0.5}Se{sub 0.5}. The reaction layers are located on opposite sides of the interface for Ba(Fe,Co){sub 2}As{sub 2} and FeTe{sub 0.5}Se{sub 0.5}. We found that the lattice distortion of the three superconducting films on the CaF{sub 2} substrates enhances the T{sub C} values compared with films prepared on oxide substrates. The origin of this lattice deformation varies depending on the superconducting material.

Ichinose, Ataru, E-mail: ai@criepi.denken.or.jp; Tsukada, Ichiro [Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka 240-0195 (Japan); Nabeshima, Fuyuki; Imai, Yoshinori; Maeda, Atsutaka [Department of Basic Science, The University of Tokyo, Meguro, Tokyo 153-8902 (Japan); Kurth, Fritz; Holzapfel, Bernhard; Iida, Kazumasa [Institute for Metallic Materials, IFW Dresden, 01171 Dresden (Germany); Ueda, Shinya; Naito, Michio [Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan)

2014-03-24

399

Syntheses and Structures of the New Quaternary Compounds Ba 4Nd 2Cd 3Se 10 and Ba 4Ln2Cd 3S 10 ( Ln=Sm, Gd, Tb)  

NASA Astrophysics Data System (ADS)

The compounds Ba4Nd2Cd3Se10 and Ba4Ln2Cd3S10 (Ln=Sm, Gd, Tb) have been synthesized at 1173 K with the use of a BaBr2/KBr eutectic flux. These isostructural compounds crystallize as racemic twins in space group Cmc21 of the orthorhombic system in cells of (Ln, Q, a, b, c (), T (K)): Nd, Se, 4.3340(9), 18.667(4), 27.376(6), 115; Sm, S, 4.1907(8), 17.931(4), 26.594(5), 153; Gd, S, 4.1726(4), 17.928(2), 26.638(3), 153; Tb, S, 4.1643(8), 17.916(4), 26.581(5), 153. The corresponding R1 indices for the refined structures are 0.053, 0.029, 0.032, and 0.030. The structure comprises [Ln2Cd3Q10]4- layers interconnected by Ba atoms. There are LnQ6 octahedra and severely distorted CdQ4 tetrahedra in the structure. Ba4Tb2Cd3S10, which is paramagnetic, obeys the Curie-Weiss law and has an effective magnetic moment of 9.94(3) ?B. A band gap of 3.0 eV for this material was deduced from its diffuse reflectance spectrum.

Yang, Yuting; Ibers, James A.

2000-02-01

400

Single Dirac cone topological surface state and unusual thermoelectric property of compounds from a new topological insulator family.  

PubMed

Angle resolved photoemission spectroscopy study on TlBiTe2 and TlBiSe2 from a thallium-based ternary chalcogenides family revealed a single surface Dirac cone at the center of the Brillouin zone for both compounds. For TlBiSe2, the large bulk gap (?200 meV) makes it a topological insulator with better mechanical properties than the previous binary 3D topological insualtor family. For TlBiTe2, the observed negative bulk gap indicates it as a semimetal, instead of a narrow-gap semiconductor as conventionally believed; this semimetality naturally explains its mysteriously small thermoelectric figure of merit comparing to other compounds in the family. Finally, the unique band structures of TlBiTe2 also suggest it as a candidate for topological superconductors. PMID:21231687

Chen, Y L; Liu, Z K; Analytis, J G; Chu, J-H; Zhang, H J; Yan, B H; Mo, S-K; Moore, R G; Lu, D H; Fisher, I R; Zhang, S C; Hussain, Z; Shen, Z-X

2010-12-31

401

The mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds  

NASA Astrophysics Data System (ADS)

We have clarified the mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds. Previously we reported that the bulk superconductivity in Fe-based compounds Fe(Te, Se) and Fe(Te, S) is achieved by heating in alcoholic beverages [1,2]. However, the exact mechanism of how they act to enhance the superconductivity in the compounds remains unsolved. To understand the effect of alcoholic beverage treatment, we investigated the mechanism using a technology of metabolomic analysis [3]. We found that weak acid in alcoholic beverages has the ability to deintercalate the excess Fe, which is not in favor of superconductivity. In this presentation, we will discuss the systematic mechanism to induce superconductivity in Fe-chalcogenide compounds. [1] K. Deguchi et al., Supercond. Sci. Technol. 24 (2011) 055008. [2] K. Deguchi et al., arXiv: 1210.5889. [3] K. Deguchi et al., Supercond. Sci. Technol. 25 (2012) 084025.

Deguchi, Keita; Demura, Satoshi; Okazaki, Hiroyuki; Denholme, Saleem; Fujioka, Masaya; Ozaki, Toshinori; Yamaguchi, Takahide; Takeya, Hiroyuki; Takano, Yoshihiko

2013-03-01

402

Thermodynamic and Transport Properties of YTe3, LaTe3 and CeTe3  

SciTech Connect

Measurements of heat capacity, susceptibility, and electrical resistivity are presented for single crystals of the charge density wave compounds YTe{sub 3}, LaTe{sub 3}, and CeTe{sub 3}. The materials are metallic to low temperatures, but have a small density of states due to the charge density wave gapping large portions of the Fermi surface. CeTe{sub 3} is found to be a weak Kondo lattice, with an antiferromagnetic ground state and T{sub N} = 2.8 K. The electrical resistivity of all three compounds is highly anisotropic, confirming the weak dispersion perpendicular to Te planes predicted by band structure calculations.

Ru, N.

2011-08-19

403

Be1-x Mn x Te: hysteresis  

Microsoft Academic Search

This document is part of Volume 44 `Semiconductors', Subvolume B `New Data and Updates for II-VI Compounds' of Landolt-Brnstein Group III `Condensed Matter'. It contains data on Be1-xMnxTe (beryllium manganese telluride), Element System Be-Mn-Te.

Tomasz Dietl; Witold Dobrowolski; Tomasz Story

2009-01-01

404

New adamantane-like mercury-chalcogen cages. 2. Synthetic and multinuclear ( sup 31 P, sup 77 Se, sup 125 Te, sup 199 Hg) magnetic resonance study of tellurolate-bridged mercury(III) clusters ((. mu. TeR) sub 6 (HgPR prime sub 3 ) sub 4 ) sup 2+ and ((. mu. TeR) sub 6 (Hg)(HgPR prime sub 3 ) sub 3 ) sup 2+ and related species with mixed-bridging chalcogenates  

Microsoft Academic Search

The salts ((μ-TePh)(HgPR)(Hg))(ClO) (R = Ph, 4-CHMe, 4-CHCl) are preparable from Hg(TePh), Mg(PR)(ClO), and PRP in a 3:1:1 ratio in CHCl or CHCl. The new cations have been characterized in CHCl and DMF by multinuclear (³¹P, ¹²⁵Te, ¹⁹⁹Hg) magnetic resonance and shown to be of adamantanoid structure with novel tellurolate bridging. These spectra provide clear evidence for preferential formation of

P. A. W. Dean; V. Manivannan; J. J. Vittal

1989-01-01

405

The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, and review of mixed-ligand CuOmCln coordination geometries in minerals and inorganic compounds  

NASA Astrophysics Data System (ADS)

The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, a rare copper selenite chloride from volcanic fumaroles of the Great fissure Tolbachik eruption (Kamchatka peninsula, Russia), has been solved by direct methods and refined to R 1 = 0.044 on the basis of 2720 unique observed reflections. The mineral is orthorhombic, Pnma, a = 17.769(7), b = 6.448(3), c = 10.522(4) , V = 1205.6(8) 3, Z = 4. The The CuOmCln coordination polyhedra share edges to form tetramers that have 'additional' O1 and O2 atoms as centers. The O1Cu4 and O2Cu4 tetrahedra share common Cu atoms to form [O2Cu5]6+ sheets. The SeO3 groups and Cl atoms are adjacent to the [O2Cu5]6+ sheets to form complex layers parallel to (100). The Na+ cations are located in between the layers. A review of mixed-ligand CuOmCln coordination polyhedra in minerals and inorganic compounds is given. There are in total 26 stereochemically different mixed-ligand Cu-O-Cl coordinations.

Krivovichev, Sergey V.; Filatov, Stanislav K.; Vergasova, Lidiya P.

2013-04-01

406

Crystal structure, physical properties, and electronic and magnetic structure of the spin S = 5/2 zigzag chain compound Bi2Fe(SeO3)2OCl3.  

PubMed

We report the synthesis and characterization of the new bismuth iron selenite oxochloride Bi2Fe(SeO3)2OCl3. The main feature of its crystal structure is the presence of a reasonably isolated set of spin S = 5/2 zigzag chains of corner-sharing FeO6 octahedra decorated with BiO4Cl3, BiO3Cl3, and SeO3 groups. When the temperature is lowered, the magnetization passes through a broad maximum at Tmax ? 130 K, which indicates the formation of a magnetic short-range correlation regime. The same behavior is demonstrated by the integral electron spin resonance intensity. The absorption is characterized by the isotropic effective factor g ? 2 typical for high-spin Fe(3+) ions. The broadening of ESR absorption lines at low temperatures with the critical exponent ? = 7/4 is consistent with the divergence of the temperature-dependent correlation length expected for the quasi-one-dimensional antiferromagnetic spin chain upon approaching the long-range ordering transition from above. At TN = 13 K, Bi2Fe(SeO3)2OCl3 exhibits a transition into an antiferromagnetically ordered state, evidenced in the magnetization, specific heat, and Mssbauer spectra. At T < TN, the (57)Fe Mssbauer spectra reveal a low saturated value of the hyperfine field Hhf ? 44 T, which indicates a quantum spin reduction of spin-only magnetic moment ?S/S ? 20%. The determination of exchange interaction parameters using first-principles calculations validates the quasi-one-dimensional nature of magnetism in this compound. PMID:24823990

Berdonosov, Peter S; Kuznetsova, Elena S; Dolgikh, Valery A; Sobolev, Alexei V; Presniakov, Igor A; Olenev, Andrei V; Rahaman, Badiur; Saha-Dasgupta, Tanusri; Zakharov, Konstantin V; Zvereva, Elena A; Volkova, Olga S; Vasiliev, Alexander N

2014-06-01

407

Crystal Growth of CdTe by Gradient Freeze in Universal Multizone Crystallizator (UMC)  

NASA Technical Reports Server (NTRS)

In the case of unsealed melt growth of an array of II-VI compounds, namely, CdTe, CdZnTe and ZnSe, there is a tremendous amount of experimental data describing the correlations between melt conditions and crystal quality. The results imply that the crystallinity quality can be improved if the melt was markedly superheated or long-time held before growth. It is speculated that after high superheating the associated complex dissociate and the spontaneous nucleation is retarded. In this study, crystals of CdTe were grown from melts which have undergone different thermal history by the unseeded gradient freeze method using the Universal Multizone Crystallizator (UMC). The effects of melt conditions on the quality of grown crystal were studied by various characterization techniques, including Synchrotron White Beam X-ray Topography (SWSXT), infrared microscopy, chemical analysis by glow discharge mass spectroscopy (GDMS), electrical conductivity and Hall measurements.

Su, Ching-Hua; Lehoczky, S. L.; Li, C.; Knuteson, D.; Raghothamachar, B.; Dudley, M.; Szoke, J.; Barczy, P.

2004-01-01

408

About the preferential sputtering of chalcogen from transition metal dichalcogenide compounds and the determination of compound stoichiometry from XPS peak positions  

Microsoft Academic Search

We use the fact that for 2keV Ar+ ion bombardment the sputtering yield of the chalcogen X is higher than that of the transition metal M in transition metal dichalcogenide compounds MX2 (M=W, Mo; X=Te, Se, S) to obtain variations of stoichiometry in these materials. While the binding energy of the chalcogen is independent of the MXx stoichiometry (2?x?0.7), we

J. C Bernde

2001-01-01

409

Tunable multifunctional topological insulators in ternary Heusler and related compounds  

NASA Astrophysics Data System (ADS)

Recently the quantum spin Hall effect was theoretically predicted and experimentally realized in quantum wells based on the binary semiconductor HgTe. The quantum spin Hall state and topological insulators are new states of quantum matter interesting for both fundamental condensed-matter physics and material science. Many Heusler compounds with C1b structure are ternary semiconductors that are structurally and electronically related to the binary semiconductors. The diversity of Heusler materials opens wide possibilities for tuning the bandgap and setting the desired band inversion by choosing compounds with appropriate hybridization strength (by the lattice parameter) and magnitude of spin--orbit coupling (by the atomic charge). Based on first-principle calculations we demonstrate that around 50 Heusler compounds show band inversion similar to that of HgTe. The topological state in these zero-gap semiconductors can be created by applying strain or by designing an appropriate quantumwell structure, similar to the case of HgTe. Many of these ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the rare-earth element Ln, which can realize additional properties ranging from superconductivity (for example LaPtBi) to magnetism (for example GdPtBi) and heavy fermion behaviour (for example YbPtBi). These properties can open new research directions in realizing the quantized anomalous Hall effect and topological superconductors. Heusler compounds are similar to a stuffed diamond, correspondingly, it should be possible to find the "high Z" equivalent of graphene in a graphite-like structure with 18 valence electrons and with inverted bands. Indeed the ternary compounds, such as LiAuSe and KHgSb with a honeycomb structure of their Au-Se and Hg-Sb layers feature band inversion very similar to HgTe which is a strong precondition for existence of the topological surface states. These materials have a gap at the Fermi energy and are therefore candidates for 3D-topological insulators. Additionally they are centro-symmetric, therefore, it is possible to determine the parity of their wave functions, and hence, their topological character. Surprisingly, the compound KHgSb with the strong SOC is topologically trivial, whereas LiAuSe is found to be a topological non-trivial insulator.

Felser, Claudia

2011-03-01

410

The Growth of P-type TlGaSe2(1-x) S2x Single Crystals  

NASA Astrophysics Data System (ADS)

TlGaSe2(1-x) S2x single crystals were grown by the modified Bridgman-Stockbarger method in our crystal growth laboratory. AIIIBIII C2 VI compounds are formed of elements from vertical groups of the periodic table (group III: Tl, Ga, In; group VI: Se, S, Te) and are classified into two types. The first type has a layer structure: TlGaSe2, TlGaS2 and TlInS2. The second type has a chained structure: TlInSe2, TlInTe2 and TlGaTe2. None of the grown crystals had cracks and voids on the surface. The freshly cleaved crystals had a mirror-like surface and there was no need for mechanical or chemical polishing treatments. By the hot probe technique, we have found that the crystals were of p-type. The ingots produced were single crystalline and the useful region of single crystal was 90% with steps of 10 K if changes were small, and with steps of 3 and 5 K if changes were large in the direct and indirect band gaps energies. The direct and indirect band gaps for TlGaSe2(1-x)S2x samples were calculated as a function of temperature.

Grbulak, B.; Duman, S.; Ate?, A.

2004-08-01

411

IMPROVEMENT OF CdMnTe DETECTOR PERFORMANCE BY MnTe PURIFICATION  

SciTech Connect

Residual impurities in manganese (Mn) are a big obstacle to obtaining high-performance CdMnTe (CMT) X-ray and gamma-ray detectors. Generally, the zone-refining method is an effective way to improve the material's purity. In this work, we purified the MnTe compounds combining the zone-refining method with molten Te, which has a very high solubility for most impurities. We confirmed the improved purity of the material by glow-discharge mass spectrometry (GDMS). We also found that CMT crystals from a multiply-refined MnTe source, grown by the vertical Bridgman method, yielded better performing detectors.

Kim, K.H.; Bolotnikov, A.E.; Camarda, G.S.; Tappero, R.; Hossain, A.; Cui, Y.; Yang, G.; Gul, R.; and James, R.B.

2011-04-25

412

Evolution of Superconductivity in Fe1+yTe1-xSex Annealed in Te Vapor  

NASA Astrophysics Data System (ADS)

We report a detailed study of the Te vapor annealing effect in Fe1+yTe0.6Se0.4 single crystals. Bulk superconductivity can be gradually induced by annealing with increasing amount of Te, until the molar ratio of Te to the sample reaches 1 : 10. By further increasing Te molar ratio, superconducting volume is gradually reduced. Resistivity and Hall effect measurements manifest that annealing in Te vapor delocalizes the charge carriers by removing excess Fe. The optimally Te annealed crystal shows homogeneous critical current densities with a large value of 4.3 105 A/cm2, which proves that the Te annealing is effective to induce bulk superconductivity in Fe1+yTe1-xSex.

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