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1

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

NASA Astrophysics Data System (ADS)

The six compounds Ba2GaMQ5 (M=Sb,Bi; Q=Se,Te) and Ba2InSbQ5 (Q=Se,Te) have been synthesized for the first time. Ba2GaMQ5 (M=Sb,Bi; Q=Se,Te) and Ba2InSbTe5 crystallize in the centrosymmetric space group Pnma, while Ba2InSbSe5 belongs to the noncentrosymmetric polar space group Cmc21. The structures of the six new compounds contain infinite [MM]4-?1 anionic chains built by MQ4 (M'=Ga,In) tetrahedra and heavily distorted M'Q6 (M'=Sb,Bi) octahedra. Ba2InSbSe5 possesses a band gap of 1.92(5) eV and exhibits a weak powder second harmonic generation signal using the 2090 nm laser as fundamental wavelength.

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

2013-02-01

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

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

4

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

E-print Network

, yielding a variety of chalcogenido cluster compounds with unconventional physical properties. SinceHeteroleptic Lanthanide Compounds with Chalcogenolate Ligands: Reduction of PhNNPh/ PhEEPh (E ) Se reduce mixtures of azobenzene and PhEEPh (E ) Se or Te) in pyridine to give the bimetallic compounds [(py

Lawson, Catherine L.

5

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

SciTech Connect

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

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

2009-06-01

6

The related compounds MThTe3 (M = Mn, Mg) and ACuThSe3 (A = K, Cs): syntheses and characterization.  

PubMed

Single crystals of MnThTe3 (1) and MgThTe3 (2) grow as small black plates from the stoichiometric reaction of the elements, the former at 1,000 degrees C and the latter at 900 degrees C with the aid of a Sn flux. Both compounds crystallize in the space group Cmcm of the orthorhombic system with four formula units in cells of dimensions a = 4.2783(6) A, b = 13.8618(11) A, and c = 9.9568(15) A for 1 and a = 4.2854(6) A, b = 14.042(2) A, and c = 9.9450(14) A for 2 at T = 153(2) K. KCuThSe3 (3) forms as red blocks from a stoichiometric mixture of K2Se, Cu, Th, and Se at 800 degrees C, and CsCuThSe3 (4) forms as yellow blocks from a stoichiometric mixture of Cs2Se3, Cu, Th, and Se at 850 degrees C. Compounds 3 and 4 also crystallize in the space group Cmcm of the orthorhombic system with four formula units in cells of dimensions a = 4.1832(8) A, b = 14.335(3) A, and c = 10.859(2) A for 3 and a = 4.2105(7) A, b = 15.715(3) A, and c = 10.897(2) A for 4 at 153(2) K. Compounds 1 and 2 are isostructural with each other as well as with several uranium analogues and comprise pseudolayered structures with slabs of corner-shared MTe6 octahedra alternating with slabs of cap- and edge-shared ThTe8 bicapped trigonal prisms. The slabs are bonded together through the sharing of edges and vertices of the various polyhedra to form three-dimensional structures. Compounds 3 and 4 are two-dimensional layered structures that are closely related to 1 and 2. In 3 and 4, ThSe6 octahedra form the same slabs as MTe6 in 1 and 2 and Cu atoms occupy the tetrahedral holes in the layers. Alkali metal cations occupy bicapped trigonal prismatic sites between the layers. Neither structure type has short Q-Q interactions, and therefore the oxidation states of all atoms are straightforwardly assigned on the assumption of Th4+. Magnetic susceptibility measurements on compound 1 show a ferromagnetic transition at 70 K and a magnetic moment of 5.9(2) muB per Mn ion, indicating low-spin Mn2+. PMID:11272562

Narducci, A A; Ibers, J A

2000-02-21

7

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

NASA Astrophysics Data System (ADS)

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 Cd xHg 1 - 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 bulk, LPE and MOVPE material measured by this technique will be presented. Auger electron spectrometry (AES) has been used on bevelled samples to assess variations in x with depth and interface widths in LPE, MOVPE and MBE layers and examples will be given. Near IR spectrometry is also now being used to monitor the variations in Zn and Se content, in CdZnTe and CdTeSe respectively, and results in this area will be described along with measurements of Zn on the micro-scale using AES. All of these techniques need to be calibrated against an absolute chemical analysis technique and we have used atomic absorption spectrometry (AAS). The latter technique also provides the accurate measure of dopant and impurity elements to standardise other techniques. Secondary ion mass spectrometry (SIMS) is mainly used for the determination of dopant depth distributions while laser scan mass spectrometry (LSMS) has the unique capability of providing a survey of low levels of impurities in thin epitaxial layers. Depth profiles of arsenic and iodine in MOVPE heterostructures, using SIMS, will be given. Impurity surveys, using LSMS, in bulk CMT and substrate materials and in CMT epitaxial layers grown by LPE, MOVPE and MBE will be described. Reported glow discharge mass spectrometry (GDMS) results on substrate materials will be compared to the present results.

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

1996-04-01

8

ZnSe/ZnSeTe Superlattice Nanotips  

PubMed Central

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

2010-01-01

9

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

E-print Network

- terials with highly unusual or useful physical properties (i.e., CdHgTe semiconductors,1 Bi2Te3 potential energy surfaces, and the combination of ionic Ln metal and covalent Te ligands yields compounds examples of structurally characterized compounds containing Ln-S bonds, more than 35 examples of compounds

Lawson, Catherine L.

10

Heterojunctions of model CdTe/CdSe mixtures  

NASA Astrophysics Data System (ADS)

We report on the strain behavior of compound mixtures of model group II–VI semiconductors. We use the Stillinger–Weber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group II–VI compounds such as CdTe and CdSe. We employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1° deflection between neighboring planes. To analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization to find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. From this we learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.

van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

2015-04-01

11

Pressure effect on the Néel temperature of Cr 2Te 3- xSe x  

NASA Astrophysics Data System (ADS)

The Néel temperature ( TN) of ferrimagnetic pseudobinary compounds Cr 2Te 3- xSe x is examined as a function of Se concentration ( x) and pressure ( p). It is found that TN decreases with increase of x or p, respectively. The results are discussed in relation with the lattice parameters a and c dependence of magnetic properties of Cr 2Te 3.

Yuzuri, M.; Adachi, Y.; Kaneko, T.; Yoshida, H.; Abe, S.

1995-02-01

12

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

NASA Astrophysics Data System (ADS)

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

Harman, Theodore C.

2000-03-01

13

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

14

Electrical conductivity and the nature of charge carriers in ternary glassy and crystalline compounds AgAsXâ (X = S, Se, Te)  

Microsoft Academic Search

The authors' evaluation of the electronic component of conductivity (using Wagner's polarization method) confirms this that in crystalline and glassy AgAsSâ the electronic component of conductivity is 10⁻²%. Ionic conductivity has been established for the ternary AgAsSOâ compound in the single-crystal, polycrystalline, and glassy states. It is shown that it is possible to use glassy AgAsSâ as a solid electrolyte.

Z. V. Borisova; A. V. Bogdanova; E. A. Kazakova; I. A. Sokolov

1985-01-01

15

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

16

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

17

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

18

Low temperature activation of S8, Se(red) and ?-Te with [Cp(BIG)Fe(CO)2] radicals.  

PubMed

The bulky dimeric iron complex, [Cp(BIG)Fe(CO)2]2, readily activates elemental chalcogens (S8, Se(red) and ?-Te) under mild conditions at room temperature. Six compounds containing Q2(2-) ligands (Q = S, Se) and a Te(2-) ligand, respectively, were isolated and completely characterized, including by X-ray diffraction techniques. PMID:25078667

Heinl, S; Scheer, M

2014-11-21

19

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

Microsoft Academic Search

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

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

2006-01-01

20

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

NASA Astrophysics Data System (ADS)

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

Kavei, G.

2006-07-01

21

Novel inorganic ionic compounds based on Re 6 chalcocyanide cluster complexes: synthesis and crystal structures of [CuNH 3(trien)] 2[Re 6S 8(CN) 6] · 7H 2O, [CuNH 3(trien)] 2[Re 6Se 8(CN) 6] and [CuNH 3(trien)] 2[Re 6Te 8(CN) 6] · H 2O  

Microsoft Academic Search

Three new octahedral rhenium chalcocyanide cluster compounds [CuNH3(trien)]2[Re6S8(CN)6]·7H2O (1), [CuNH3(trien)]2[Re6Se8(CN)6] (2) and [CuNH3(trien)]2[Re6Te8(CN)6]·H2O (3) exhibiting ionic structures have been obtained by the diffusion of an ammonia solution of KCs3[Re6S8(CN)6] (for 1), K4[Re6Se8(CN)6]·3.5H2O (for 2) or Cs4[Re6Te8(CN)6]·2H2O (for 3) into a glycerol solution of CuCl2·2H2O in the presence of trien (trien=triethylenetetramine). The compounds have been characterized by single-crystal X-ray diffraction. All

Konstantin A Brylev; Nikolai G Naumov; Gabriel Peris; Rosa Llusar; Vladimir E Fedorov

2003-01-01

22

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

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

23

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

24

The Predicted fcc Superconducting Phase for Compressed Se and Te  

NASA Astrophysics Data System (ADS)

In the framework of the ab initio random structure search method, we show that elemental Se and Te undergo pressure-induced structural transition from the bcc to fcc phase, in agreement with the theoretical results previously reported. By means of the pseudopotential plane-wave method based on density functional perturbation theory, the fcc structure for both elements is found to be another phonon-mediated superconducting phase of these materials. With a reasonable value for the Coulomb pseudopotential ?* = 0.12, the maximum superconducting transition temperature Tc in the fcc phase of Se and Te is estimated to be about 5.7 K and 4.6 K, respectively. Furthermore, we show that in the entire fcc phase for Se and Te, the superconducting transition temperature decreases together with the increase in pressure, leading to the final suppression of the superconductivity. It is suggested that such behavior is mainly caused by the rapid increase in the mean-square phonon frequency with pressure. Finally, a very strong electron-phonon coupling value, for both Se and Te in the fcc phase, is found along the G—K high symmetry lines.

Zhou, Da-Wei; Pu, Chun-Ying; Szcz?ániak, Dominik; Zhang, Guo-Fang; Lu, Cheng; Li, Gen-Quan; Song, Jin-Fan

2013-02-01

25

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

26

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

27

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

PubMed Central

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

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

2014-01-01

28

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

29

Estimation of Density of Localized States in Amorphous Se80Te20 and Se80Te10M10 (M = Cd, In, Sb) Alloys Using AC Conductivity Measurements  

NASA Astrophysics Data System (ADS)

The ac conductivity of amorphous Se80Te20 (a-Se80Te20) and amorphous Se80Te10M10 (a-Se80Te10M10) alloys has been measured as a function of temperature and frequency in a low-temperature regime. An analysis of the experimental data confirms that ac conductivity is reasonably well interpreted by the Austin-Mott model. The density of localized states was determined in the low-temperature region from 201 K to 280 K. Possible explanations of "metal-induced effects" on the conduction mechanism of a-Se80Te20 alloy are discussed.

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

2015-03-01

30

Thermoelectric properties of polycrystalline In4Se3 and In4Te3  

SciTech Connect

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

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

2010-01-01

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

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

33

Unoccupied topological surface state in Bi2Te2Se  

NASA Astrophysics Data System (ADS)

Bias voltage dependent scattering of the topological surface state is studied by scanning tunneling microscopy/spectroscopy for a clean surface of the topological insulator Bi2Te2Se. A strong warping of constant energy contours in the unoccupied part of the spectrum is found to lead to a spin-selective scattering. The topological surface state persists to higher energies in the unoccupied range far beyond the Dirac point, where it coexists with the bulk conduction band. This finding sheds light on the spin and charge dynamics over a wide energy range and opens a way to designing optospintronic devices.

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

2013-08-01

34

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

35

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

NASA Astrophysics Data System (ADS)

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

Stöwe, Klaus

2003-12-01

36

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

37

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

38

Electronic band structures and physical properties of ALnTe 4 and ALn 3Te 8 compounds ( A=alkali metal; Ln=lanthanoid)  

Microsoft Academic Search

We report about the LMTO-ASA band structure, ELF and COHP calculations for a number of alkali metal rare earth tellurides of the formulas ALnTe4 (A=K, Rb, Cs and Ln=Pr, Nd, Gd) and KLn3Te8 (Ln=Pr, Nd) to point out structure-properties relations. The ALnTe4 compounds crystallize in the KCeSe4 structure type with Te ions arranged in the form of 4.32.4.3 nets, in

Klaus Stöwe

2003-01-01

39

Evidence of Ga2Se3-Related Compounds on Se-Stabilized GaAs Surfaces  

NASA Astrophysics Data System (ADS)

A Se-stabilized GaAs(001) surface is examined by extended X-ray absorption fine structure (EXAFS) analysis. The Se K-edge EXAFS shows components due not only to the first but also the second nearest neighbors, indicating that the Se atoms are incorporated into ordered atomic arrangements. Comparing the interatomic distances to those measured for Ga2Se3 and GaSe, it is concluded that the nature of the surface compound on the Se-stabilized GaAs surface is close to that of Ga2Se3.

Takatani, Shinichiro; Nakano, Asao; Ogata, Kiyoshi; Kikawa, Takeshi

1992-04-01

40

Excitons bound to Te isoelectronic dyads in ZnSe  

NASA Astrophysics Data System (ADS)

We report on the excitonic photoluminescence from individual Te dyads in ZnSe. Based on the emission characteristics of these pairs of pseudodonor impurities, we identify dyads of C2v symmetry and determine their orientation with respect to the host lattice. The diamagnetic shift of the exciton indicates that the hole bound to the dyad is extremely localized. Measurements of large number of individual dyads reveal that (1) light-hole transitions located at higher energy are strongly suppressed, (2) the line shape of the observed phonon replica allows probing the phonon density of states, (3) dyads of various interatomic separations are observed, (4) the emission energy is extremely sensitive to the local environment of the dyad, and (5) dynamic variations in this local environment results in the intensity fluctuations and spectral diffusion.

Marcet, S.; André, R.; Francoeur, S.

2010-12-01

41

Weak antilocalization in Bi2(Se(x)Te(1-x))3 nanoribbons and nanoplates.  

PubMed

Studying the surface states of Bi(2)Se(3) and Bi(2)Te(3) topological insulators has proven challenging due to the high bulk carrier density that masks the surface states. Ternary compound Bi(2)(Se(x)Te(1-x))(3) may present a solution to the current materials challenge by lowering the bulk carrier mobility significantly. Here, we synthesized Bi(2)(Se(x)Te(1-x))(3) nanoribbons and nanoplates via vapor-liquid-solid and vapor-solid growth methods where the atomic ratio x was controlled by the molecular ratio of Bi(2)Se(3) to Bi(2)Te(3) in the source mixture and ranged between 0 and 1. For the whole range of x, the ternary nanostructures are single crystalline without phase segregation, and their carrier densities decrease with x. However, the lowest electron density is still high (~10(19) cm(-3)) and the mobility low, suggesting that the majority of these carriers may come from impurity states. Despite the high carrier density, weak antilocalization (WAL) is clearly observed. Angle-dependent magnetoconductance study shows that an appropriate magnetic field range is critical to capture a true, two-dimensional (2D) WAL effect, and a fit to the 2D localization theory gives ? of -0.97, suggesting its origin may be the topological surface states. The power law dependence of the dephasing length on temperature is ~T(-0.49) within the appropriate field range (~0.3 T), again reflecting the 2D nature of the WAL. Careful analysis on WAL shows how the surface states and the bulk/impurity states may interact with each other. PMID:22263839

Cha, Judy J; Kong, Desheng; Hong, Seung-Sae; Analytis, James G; Lai, Keji; Cui, Yi

2012-02-01

42

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

NASA Astrophysics Data System (ADS)

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

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

43

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

44

Superconductivity in Strong Spin Orbital Coupling Compound Sb2Se3  

PubMed Central

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

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

2014-01-01

45

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

46

Crystallization behavior in Se{sub 90}Te{sub 10} and Se{sub 80}Te{sub 20} thin films  

SciTech Connect

Isothermal crystal growth kinetics in Se{sub 90}Te{sub 10} and Se{sub 80}Te{sub 20} thin films was studied by microscopy and in situ X-ray diffraction (XRD) measurements. The spherulite-like crystals grew linearly with time. In a narrow temperature range of between 65 and 85?°C, crystal growth rates exhibit simple exponential behavior with activation energies E{sub G}?=?193?±?4?kJ mol{sup ?1} for Se{sub 90}Te{sub 10} and E{sub G}?=?195?±?4?kJ mol{sup ?1} for Se{sub 80}Te{sub 20}. The crystal growth in both compositions is controlled by liquid-crystal interface kinetics and can be described by a screw dislocation growth model. From the XRD data, the crystallization fraction was estimated. The crystallization data were described by Johnson-Mehl-Avrami (JMA) model with Avrami exponents m?=?1.4?±?0.3 for Se{sub 90}Te{sub 10} and m?=?1.6?±?0.4 for Se{sub 80}Te{sub 20}. Activation energies were estimated from the temperature dependence of rate constant evaluated from the JMA model. The activation energies of nucleation-growth process were found to be E{sub c}?=?184?±?21?kJ mol{sup ?1} for Se{sub 90}Te{sub 10} and E{sub c}?=?179?±?7?kJ mol{sup ?1} for Se{sub 80}Te{sub 20}, and are comparable with activation energies of crystal growth.

Barták, Jaroslav, E-mail: j-bartak@seznam.cz; Málek, Jirí [Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, 532 10 Pardubice (Czech Republic); Koštál, Petr [Department of Inorganic Technology, Faculty of Chemical Technology, University of Pardubice, Doubravice 41, 532 10 Pardubice (Czech Republic); Segawa, Hiroyo; Yamabe-Mitarai, Yoko [National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

2014-03-28

47

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

NASA Astrophysics Data System (ADS)

Photoluminescence (PL) behavior of ZnSe1 - yTey quantum dots is investigated by varying Te concentration as well as size. The striking effect of quantum confinement is the observation of isoelectronic center-related emission at room temperature in lieu of near-band-edge emission that dominates the optical scenario. ZnSe0.99Te0.01 quantum dots were also doped by Mn2 + ions. The Mn2 + ion-related d-d transition is drastically suppressed by Te isoelectronic centers. Incorporation of Mn2 + at substitutional sites in ZnSe0.99Te0.01 quantum dots is also confirmed by the electron paramagnetic resonance measurements. Effect of Te isoelectronic impurity on the emission behavior is more pronounced than that of Mn2 + ions. A subtle blueshift in the orange d-d transition is a sign of a decrease in crystal field strength. PL and photoluminescence excitation measurements on Zn1 - xSe0.99Te0.01Mnx quantum dots indicate that the transition probability from the lowest unoccupied molecular orbital to Te levels is substantially larger than that to Mn2 + d-d levels.

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

2011-07-01

48

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

49

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.

50

Photoluminescence of -doped ZnSe:,,Te,N... grown by molecular beam epitaxy  

E-print Network

Photoluminescence of -doped ZnSe:,,Te,N... grown by molecular beam epitaxy Igor L. Kuskovsky,a) C for publication 4 June 2001 We have studied the low temperature photoluminescence PL of a -doped ZnSe: Te,N system

Mandelis, Andreas

51

Beneficial effect of Se substitution on thermoelectric properties of Co{sub 4}Sb{sub 11.9-x}Te{sub x}Se{sub 0.1} skutterudites  

SciTech Connect

Skutterudite-based compounds, Co{sub 4}Sb{sub 12-x-y}Te{sub x}Se{sub y} (x=0.4, 0.5, 0.6 and y=0.0, 0.1), are synthesized by the solid state reaction and the spark plasma sintering methods, and their structure and the thermoelectric properties have been investigated systematically. It is found that Se doping results in decrease of the lattice parameter and refinement of the particle size compared with those of Se-free samples. The Se-doped samples do not yield a certain increase in the power factor, but show a significant depression in the lattice thermal conductivity. The highest dimensionless figure of merit ZT=1.09 is achieved at 800 K for the Co{sub 4}Sb{sub 11.3}Te{sub 0.6}Se{sub 0.1} compound, which is improved by 15% compared with that of Te alone doped Co{sub 4}Sb{sub 11.4}Te{sub 0.6} compound at the corresponding temperature. - Graphical abstract: The Te and Se co-doped Co{sub 4}Sb{sub 11.9-x}Te{sub x}Se{sub 0.1} skutterudites show amazingly lower thermal conductivity ({kappa}) and lattice thermal conductivity ({kappa}{sub L}) compared with those of Co{sub 4}Sb{sub 12-x}Te{sub x} skutterudites. Highlights: Black-Right-Pointing-Pointer Te and Se co-doped Co{sub 4}Sb{sub 12-x-y}Te{sub x}Se{sub y} compounds have been synthesized by the solid state reaction method. Black-Right-Pointing-Pointer Doping of Se resulted in decrease of the lattice parameter and refinement of the particle size. Black-Right-Pointing-Pointer The co-doped skutterudites show amazingly lower lattice thermal conductivity. Black-Right-Pointing-Pointer Co-doping with Te and Se is an attractive approach to enhance the TE performance of skutterudites.

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

2012-09-15

52

The development of the superconducting PbO-type ?-FeSe and related compounds  

NASA Astrophysics Data System (ADS)

An overview of the recent development of the superconducting FeSe 1-x and related compounds is presented. Methods to synthesize high purity polycrystalline samples, single crystals and thin films with preferred orientation are described. In addition to the synthesis of FeSe and FeSeTe, the effects of various partial chemical substitutions on Fe and Se/Te site are described. It was found that the effects of chemical doping to the Se-site or Fe-site are rather different. Ionic size of the dopant is found to play a critical role on the occurrence of superconductivity. We also review the physical properties, including transport, magnetic, and thermal properties. There exist interesting transport anomalies in the resistivity at low temperature, and it was found that a structural distortion at low temperature is critical to the occurrence of superconductivity in these materials. However, the exact origin of these observed anomalies is not clear, and the exact pairing symmetry in FeSe-based superconductors is also still in question.

Wu, M. K.; Hsu, F. C.; Yeh, K. W.; Huang, T. W.; Luo, J. Y.; Wang, M. J.; Chang, H. H.; Chen, T. K.; Rao, S. M.; Mok, B. H.; Chen, C. L.; Huang, Y. L.; Ke, C. T.; Wu, P. M.; Chang, A. M.; Wu, C. T.; Perng, T. P.

2009-05-01

53

Cyclotron resonance in modulation-doped ZnSe/Zn1 xCdxSe and ZnTe/CdSe single quantum wells  

E-print Network

Cyclotron resonance in modulation-doped ZnSe/Zn1 xCdxSe and ZnTe/CdSe single quantum wells H. K Received 6 July 1999; accepted for publication 13 October 1999 We report low-temperature 4.2 K cyclotron of conduction-band electrons m* whose direct determination by cyclotron reso- nance CR has been largely obviated

Sirenko, Andrei

54

A general route for the rapid synthesis of one-dimensional nanostructured single-crystal Te, Se and Se Te alloys directly from Te or/and Se powders  

NASA Astrophysics Data System (ADS)

A general and template-free 'disproportionation and reversal' route was developed to synthesize one-dimensional (1D) nanostructures of Te, Se and Se-Te alloys directly from Te or/and Se powders. The products were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning electron microscopy (SEM). Te nanorods and nanowires with a width varying from about 40 nm to about 300 nm, Se nanowires with a width of 60-100 nm and a length of 4-6 µm, and SexTe100-x alloy nanorods with x in a wide range, and with a width of 30-70 nm and an aspect ratio of three to five, were prepared. The mechanism of formation of the nanorods and nanowires and the effects of the experimental conditions, such as solution concentration, cooling rate, solvent nature and heating process, on the morphology and size of the products have been discussed. We believe that this general route and some other proper reversible processes between solid state and solution state can be extended to the transformations from various bulk materials into nanosized materials with various morphologies.

Zhou, Bo; Zhu, Jun-Jie

2006-03-01

55

New ferroelectric compound SrTeO3  

Microsoft Academic Search

A synthetic compound SrTeO3 was discovered to exhibit ferroelectricity in the temperature range between 312 and 485°C. Small single crystals could be grown by the Kyropoulos method. The crystal belongs to the monoclinic system and its space group is C2? c ? C2 h6 at room temperature. A pronounced dielectric anomaly was observed along the b axis at 485°C. The

Tomoaki Yamada; Hiroshi Iwasaki

1972-01-01

56

Mechanical properties of highly oriented FeSe0.5Te0.5 superconductor  

NASA Astrophysics Data System (ADS)

We have synthesized highly oriented samples of the superconducting compound FeSe0.5Te0.5 and investigated its mechanical properties. These samples were characterized by scanning electron microscopy (SEM) with energy-dispersive analysis, x-ray diffraction, and electrical resistivity. The measured critical temperature is TC~ 14.5 K. Hardness and elastic modulus on the ab- and a(b)c-plane were obtained by instrumented indentation. The samples' morphology consists of plate-like crystals with a lamellar structure. Two phases were observed with a typically eutectic microstructure composed by white and gray lamellas when observed with SEM using backscattered electrons. The white phase is richer in Te and poorer in Se than the gray phase. No significant differences in hardness and elastic modulus were observed between ab- and a(b)c-planes. Hardness profiles indicated values in the range 0.6-0.8 GPa at deep tip penetration depths, while the elastic modulus showed values in between 20-25 GPa. Cracking was occasionally observed in the ab-plane and at low loads.

Luiz Pimentel Júnior, Jorge; Pureur, Paulo; Santos Lopes, Cristiano; Carlos Serbena, Francisco; Eugênio Foerster, Carlos; Aparecida da Silva, Simone; Roberto Jurelo, Alcione; Luiz Chinelatto, Adilson

2012-02-01

57

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 3.5 months 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 2.1 mg 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 100 mg/L selenite in shake flasks was not much affected by the presence of 10 mg/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 3.5 months 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

58

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

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

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

61

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

62

Thermoelectric Investigation of the Pseudo Binary System PbTe-CoSe2  

NASA Astrophysics Data System (ADS)

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

Ponnambalam, V.; Morelli, Donald T.

2015-02-01

63

Polycrystalline CdTe on CuInSe2 cascaded solar cells  

NASA Astrophysics Data System (ADS)

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

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

64

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

E-print Network

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

Guan, Juan

2008-01-01

65

Improved thermoelectric properties of PbTe0.5Se0.5  

NASA Astrophysics Data System (ADS)

We have synthesized PbTe and PbTe0.5Se0.5 alloys and investigated their thermoelectric properties. On Se doping, the thermopower (?) at an operating temperature of 650 K has been found to increase from 250 to 403 ?V/K. In addition, the room temperature thermal conductivity (?) value reduced from 4 to 1.28 Wm-1K-1, which is an important result from the viewpoint of application.

Basu, Ranita; Bhattacharya, S.; Bhatt, R.; Singh, A.; Aswal, D. K.; Gupta, S. K.

2012-06-01

66

A simple route to Bi2Se3 and Bi2Te3 nanocrystals  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

67

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

68

Demonstration of surface transport in a hybrid Bi2Se3/Bi2Te3 heterostructure  

PubMed Central

In spite of much work on topological insulators (TIs), systematic experiments for TI/TI heterostructures remain absent. We grow a high quality heterostructure containing single quintuple layer (QL) of Bi2Se3 on 19 QLs of Bi2Te3 and compare its transport properties with 20 QLs Bi2Se3 and 20 QLs Bi2Te3. All three films are grown on insulating sapphire (0001) substrates by molecular beam epitaxy (MBE). In situ angle-resolved photoemission spectroscopy (ARPES) provides direct evidence that the surface state of 1 QL Bi2Se3/19 QLs Bi2Te3 heterostructure is similar to the surface state of the 20 QLs Bi2Se3 and different with that of the 20 QLs Bi2Te3. In ex situ transport measurements, the observed linear magnetoresistance (MR) and weak antilocalization (WAL) of the hybrid heterostructure are similar to that of the pure Bi2Se3 film and not the Bi2Te3 film. This suggests that the single Bi2Se3 layer on top of 19 QLs Bi2Te3 dominates its transport properties. PMID:24162440

Zhao, Yanfei; Chang, Cui-Zu; Jiang, Ying; DaSilva, Ashley; Sun, Yi; Wang, Huichao; Xing, Ying; Wang, Yong; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Jian

2013-01-01

69

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

PubMed

In spite of much work on topological insulators (TIs), systematic experiments for TI/TI heterostructures remain absent. We grow a high quality heterostructure containing single quintuple layer (QL) of Bi2Se3 on 19 QLs of Bi2Te3 and compare its transport properties with 20 QLs Bi2Se3 and 20 QLs Bi2Te3. All three films are grown on insulating sapphire (0001) substrates by molecular beam epitaxy (MBE). In situ angle-resolved photoemission spectroscopy (ARPES) provides direct evidence that the surface state of 1 QL Bi2Se3/19 QLs Bi2Te3 heterostructure is similar to the surface state of the 20 QLs Bi2Se3 and different with that of the 20 QLs Bi2Te3. In ex situ transport measurements, the observed linear magnetoresistance (MR) and weak antilocalization (WAL) of the hybrid heterostructure are similar to that of the pure Bi2Se3 film and not the Bi2Te3 film. This suggests that the single Bi2Se3 layer on top of 19 QLs Bi2Te3 dominates its transport properties. PMID:24162440

Zhao, Yanfei; Chang, Cui-Zu; Jiang, Ying; DaSilva, Ashley; Sun, Yi; Wang, Huichao; Xing, Ying; Wang, Yong; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Jian

2013-01-01

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; Málek, Ji?í

2014-12-01

72

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; Málek, Ji?í

2014-12-14

73

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

74

Crystal structure of CuIn3Se5 and CuIn5Se8 ternary compounds  

NASA Astrophysics Data System (ADS)

The structures of single crystals of CuIn3Se5 and CuIn5Se8 ternary compounds have been studied by X-ray diffraction for the first time. The unit cell parameters of CuIn3Se5 and CuIn5Se8 crystals are determined. It is established that CuIn3Se5 has a thiogallate lattice with c = 2a, which leads to the domain structure formation. CuIn5Se8 has a hexagonal lattice and exhibits cleavage along the (001) plane. Relationships between the atomic composition and crystal structure of these new ternary semiconductor compounds are discussed.

Bodnar, I. V.; Va?polin, A. A.; Rud, V. Yu.; Rud, Yu. V.

2006-12-01

75

Excitons bound to isoelectronic Te traps in ZnSe quantum wells: A theoretical study  

Microsoft Academic Search

A theoretical study is made of excitons and holes bound to a single tellurium (Te) impurity in bulk ZnSe and centered in ZnSe-Zn1-xMnxSe strained quantum wells. We use an effective-bond-orbital model for the holes in order to account for the complicated valence-band structure, and the spherical effective-mass approximation to describe the electron. The mutual Coulomb interaction is included, and solutions

G. T. Einevoll; D. S. Citrin; Yia-Chung Chang

1991-01-01

76

Colloidal synthesis and optical properties of type-II CdSe-CdTe and inverted CdTe-CdSe core-wing heteronanoplatelets.  

PubMed

We developed colloidal synthesis to investigate the structural and electronic properties of CdSe-CdTe and inverted CdTe-CdSe heteronanoplatelets and experimentally demonstrate that the overgrowth of cadmium selenide or cadmium telluride core nanoplatelets with counterpartner chalcogenide wings leads to type-II heteronanoplatelets with emission energies defined by the bandgaps of the CdSe and CdTe platelets and the characteristic band offsets. The observed conduction and valence band offsets of 0.36 eV and 0.56 eV are in line with theoretical predictions. The presented type-II heteronanoplatelets exhibit efficient spatially indirect radiative exciton recombination with a quantum yield as high as 23%. While the exciton lifetime is strongly prolonged in the investigated type-II 2D systems with respect to 2D type-I systems, the occurring 2D giant oscillator strength (GOST) effect still leads to a fast and efficient exciton recombination. This makes type-II heteronanoplatelets interesting candidates for low threshold lasing applications and photovoltaics. PMID:25873332

Antanovich, A V; Prudnikau, A V; Melnikau, D; Rakovich, Y P; Chuvilin, A; Woggon, U; Achtstein, A W; Artemyev, M V

2015-04-24

77

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

78

Structural refinement of the ternary chalcogenide compound Cu2GeTe3 by X-ray powder diffraction  

NASA Astrophysics Data System (ADS)

The Cu2GeTe3 compound crystallizes in the Imm2 (N° 44) space group, Z = 2, with a = 12.641(1) Å, b = 4.2115(2) Å, c = 5.9261(2) Å, V = 315.49(3) Å3. Its structure was refined from X-ray powder diffraction data using the Rietveld method. The refinement of 23 instrumental and structural variables led to Rp = 8.2%, Rwp = 11.6%, Rexp = 6.8%, RB = 11.2 % and S = 1.7, for 5501 step intensities and 253 independent reflections. This compound is isostructural with Cu2GeSe3, and consists of a three-dimensional arrangement of slightly distorted CuTe4 and GeTe4 tetrahedra connected by common corners.

Delgado, Gerzon E.; Mora, Asiloé J.; Pirela, María; Velásquez-Velásquez, Ana; Villarreal, Manuel; Fernández, Braulio J.

2004-10-01

79

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

PubMed Central

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

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

2007-01-01

80

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

81

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

82

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

83

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

84

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

85

Thermoelectric properties of indium doped PbTe{sub 1-y}Se{sub y} alloys  

SciTech Connect

Lead telluride and its alloys are well known for their thermoelectric applications. Here, a systematic study of PbTe{sub 1-y}Se{sub y} alloys doped with indium has been done. The powder X-Ray diffraction combined with Rietveld analysis confirmed the polycrystalline single phase nature of the samples, while microstructural analysis with scanning electron microscope results showed densification of samples and presence of micrometer sized particles. The temperature dependent transport properties showed that in these alloys, indium neither pinned the Fermi level as it does in PbTe, nor acted as a resonant dopant as in SnTe. At high temperatures, bipolar effect was observed which restricted the zT to 0.66 at 800?K for the sample with 30% Se content.

Bali, Ashoka; Mallik, Ramesh Chandra, E-mail: rcmallik@physics.iisc.ernet.in [Thermoelectric Materials and Devices Laboratory, Department of Physics, Indian Institute of Science, Bangalore 560012, Karnataka (India); Wang, Heng; Snyder, G. Jeffrey [Department of Materials Science, California Institute of Technology, Pasadena, California 91125 (United States)

2014-07-21

86

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

87

Observation of phase separation in some Se-Te-Sn chalcogenide glasses  

NASA Astrophysics Data System (ADS)

Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) techniques were employed here to investigate the glass transition behavior and crystallization kinetics of Se 80- x Te 20Sn x ( x=0.0, 2.5 and 5) alloys, which were prepared by the conventional melt quenching method. Two exothermic peaks have been observed in the DSC scans for the samples that contain Sn. Three crystalline phases (Se 7.68Te 0.32, SnSe and SnTe) were classified after heat treating the Se 77.5 Te 20Sn 2.5 glass at temperature corresponding to the second crystallization peaks for 3 h. All the characteristic temperatures such as glass transition temperature ( Tg), crystallization temperature ( Tc) and crystallization peak temperatures ( Tp) were found to depend on both the heating rate and the composition. This dependence has been used to deduce the activation energy of the glass transition ( Eg), the activation energy of crystallization ( Ec), the Avrami exponent ( n), thermal stability and the fragility index ( Fi).

Abdel-Wahab, Fouad

2011-03-01

88

Magneto-optical properties of ZnMnTe/ZnSe quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

89

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

PubMed Central

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

2012-01-01

90

Photo induced cyclotron resonance in ZnSe/BeTe type-II quantum wells  

NASA Astrophysics Data System (ADS)

We have detected a cyclotron resonance signal of the electrons induced by an external photoexcitation in an undoped ZnSe/BeTe type-II quantum well. The experimental spectra have also been well reproduced by the dielectric function (Drude) model. The photo-induced electron density is estimated at 1 × 1012 cm-2.

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

2011-12-01

91

Single Crystal Growth of Se-Te Alloys onto Tellurium from the Melts  

Microsoft Academic Search

The method to obtain single crystals of Se-Te alloys is developed. In this method, it is possible to grow a single crystal of an alloy from the melt, using a single crystal of tellurium as a seed for a Bridgmanlike method. The crystal is grown epitaxially onto tellurium. The obtained crystals is homogeneous except the layer of a few mm

Tadashi Shiosaki; Akira Kawabata

1971-01-01

92

Spray Deposition of High Quality CuInSe2 and CdTe Films: Preprint  

SciTech Connect

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

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

2008-05-01

93

Heavy doping and band engineering by potassium to improve the thermoelectric figure of merit in p-type PbTe, PbSe, and PbTe(1-y)Se(y).  

PubMed

We present detailed studies of potassium doping in PbTe(1-y)Se(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 balance of electronegativity and also lowers the lattice thermal conductivity because of the increased number of point defects. Tuning the composition and carrier concentration to increase the density of states around the Fermi level results in higher Seebeck coefficients for the two valence bands of PbTe(1-y)Se(y). Peak thermoelectric figure of merit (ZT) values of ~1.6 and ~1.7 were obtained for Te-rich K(0.02)Pb(0.98)Te(0.75)Se(0.25) at 773 K and Se-rich K(0.02)Pb(0.98)Te(0.15)Se(0.85) at 873 K, respectively. However, the average ZT was higher in Te-rich compositions than in Se-rich compositions, with the best found in K(0.02)Pb(0.98)Te(0.75)Se(0.25). Such a result is due to the improved electron transport afforded by heavy K doping with the assistance of Se. PMID:22676702

Zhang, Qian; Cao, Feng; Liu, Weishu; Lukas, Kevin; Yu, Bo; Chen, Shuo; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

2012-06-20

94

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

95

Thermoelectric properties of Bi2Te3-Bi2Se3 solid solutions prepared by attrition milling and hot pressing  

NASA Astrophysics Data System (ADS)

Bi2Te3- y Se y ( y = 0.15-0.6) solid solutions were prepared by attrition milling and hot pressing. The lattice constants decreased with increasing Se content, indicating that the Se atoms were successfully substituted into the Te sites. All specimens exhibited n-type conduction, and their electrical resistivities increased slightly with increasing temperature. With increasing Se content, the Seebeck coefficients increased while the thermal conductivity decreased due to the increase in phonon scattering. The maximum figure of merit obtained was 0.63 at 440 K for the undoped Bi2Te2.4Se0.6 solid solution.

Lee, Go-Eun; Kim, Il-Ho; Choi, Soon-Mok; Lim, Young Soo; Seo, Won-Seon; Park, Jae-Soung; Yang, Seung-Ho

2014-12-01

96

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

97

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

SciTech Connect

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

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

2012-10-23

98

Raman spectra of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5  

NASA Astrophysics Data System (ADS)

The optical vibrational modes of the ordered vacancy compounds CuIn3Se5 and CuGa3Se5 have been obtained by Raman spectra at various temperatures. The totally symmetric A1 mode appears around 155 and 167 cm-1 in CuIn3Se5 and CuGa3Se5, respectively. All the lines observed, except the B1 modes, present a reduction in their frequencies by about 10% as compared to the corresponding values in the CuInSe2 and CuGaSe2 chalcopyrites. This is due to the presence in these compounds of an array of vacancies occupying particular sites in the cation sublattice. These tend to relax the stretching forces thus reducing the vibrational frequencies.

Rincón, C.; Wasim, S. M.; Marín, G.; Delgado, J. M.; Huntzinger, J. R.; Zwick, A.; Galibert, J.

1998-07-01

99

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

100

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

101

Thermoelectric Properties of Bi2Te2Se Compensated by Native Defects and Sn Doping  

NASA Astrophysics Data System (ADS)

In Bi2Te2Se the defect chemistry involves native defects that compete such that they can either exchange dominance or else significantly compensate each other. Here we show how the net carrier concentration, n - p, which depends on the relative amounts of these defects and is readily obtained from Hall data, can be used as a fundamental materials parameter to describe the varied behavior of the thermoelectric properties as a function of compensation. We report the effects of tuning this parameter over multiple orders of magnitude by hole-doping the n-type material Bi2Te2Se0.995, which is already significantly compensated because of its Se deficiency. Crystals with different levels of hole doping were achieved by two separate approaches, namely by selecting pieces from different locations in an undoped crystal in which a systematic carrier concentration gradient had been induced by its growth conditions, and alternatively by doping with Sn for Bi. The thermoelectric power factors for Bi2- x Sn x Te2Se0.995 for x = 0, 0.002, 0.005, 0.010, and 0.040 are reported, and the dependence of the transport properties on the extent of compensation is discussed.

Fuccillo, M. K.; Jia, Shuang; Charles, M. E.; Cava, R. J.

2013-06-01

102

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

SciTech Connect

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

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

2004-12-15

103

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

104

An infrared fibre evanescent wave spectroscopic (FEWS) sensor using purified GeTeSe chalcogenide fibres  

NASA Astrophysics Data System (ADS)

In this study, we report the fabrication and engineering of an infrared fibre evanescent wave spectroscopic (FEWS) sensor using GeTeSe chalcogenide fibres, which manifests high temperature durability (glass transformation temperature at 260°C) and extended infrared transmission from 1.5 to 18 ?m. We also report the methodologies adopted for the fabrication of fibres, including the purification of starting chemicals for high spectral purity, glass melting, quenching and annealing, fabrication of fibre performs. The designed FEWS sensor consists of a 40 cm unstructured GeTeSe fibre coupled with a Fourier transform infrared (FTIR) spectrometer and a Mercury-Cadmium-Tellurium (MCT) infrared detector, and the active sensing length of the fibre is 3 cm. In this paper, we demonstrate the sensing results with various analytes and investigate the sensitivity of this sensor.

Jiang, Xin; Jha, Animesh

2009-10-01

105

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

106

Transport properties in FeSe0.5Te0.5 nanobridges  

NASA Astrophysics Data System (ADS)

FeSeTe nanobridges of different widths have been fabricated on MgO substrates using focused ion beams. These nanobridges exhibit the Josephson effects. The current-voltage curves of junctions with 248-564 nm wide follow the resistively and capacitatively shunted junction model. Shapiro steps under microwave radiation were clearly observed in these nanobridges. The products of the critical current and normal state resistance (IcRn) are remarkably high. The temperature dependence of IcRn product followed the Ambegaokar-Baratoff (A-B) relation. The value of energy gap of FeSeTe calculated from the A-B relation is 3.5kBTc. The nanobridge junctions have a strong potential for high frequency applications.

Wu, C. H.; Chang, W. C.; Jeng, J. T.; Wang, M. J.; Li, Y. S.; Chang, H. H.; Wu, M. K.

2013-06-01

107

Magnetic properties of the Cr 2S 3- xSe x and Cr 2Te 3- ySe y systems  

NASA Astrophysics Data System (ADS)

Magnetic and crystallographic properties of the Cr 2S 3- xSe x and Cr 2Te 3- ySe y systems were investigated. An obvious transition point from ferrimagnetism or ferromagnetism to antiferromagnetism cannot be observed in both systems. But at low temperature, mictomagnetism was found in the range of x = 0.9-2.7 of the Cr 2S 3- xSe x system and y = 0.7-2.1 of the Cr 2Te 3- ySe y system. An interesting result was found in a relation between the paramagnetic Curie temperature ? p and the lattice parameter ratio c / a.

Adachi, Y.; Yuzuri, M.; Kaneko, T.; Abe, S.

1992-02-01

108

Two-dimensional magnetotransport in Bi2Te2Se nanoplatelets  

NASA Astrophysics Data System (ADS)

Single-crystalline Bi2Te2Se nanoplates with thicknesses between 8 and 30 nm and lateral sizes of several micrometers were synthesized by a vapour-solid growth method. Angle-dependent magnetoconductance measurements on individual nanoplates revealed the presence of a two-dimensional weak anti-localization effect. In conjunction with gate-dependent charge transport studies performed at different temperatures, evidence was gained that this effect originates from the topologically protected surface states of the nanoplates.

Gehring, Pascal; Gao, Bo; Burghard, Marko; Kern, Klaus

2012-07-01

109

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

110

Electronic structure and optical properties of CdSe xTe 1- x mixed crystals  

NASA Astrophysics Data System (ADS)

The band structure and optical properties of the CdSe xTe 1- x ternary mixed crystals have been studied using the pseudopotential formalism under an improved virtual crystal approximation approach. Quantities such as, energy gaps, band-gap bowing parameters, electron effective mass and dielectric constants are calculated. Our results agree well with the available data in the literature. The composition dependence of all studied quantities has been expressed by quadratic polynomial forms.

Hannachi, L.; Bouarissa, N.

2008-12-01

111

Magnetostriction-induced in situ strain control of superconductivity in FeSe0.5Te0.5  

NASA Astrophysics Data System (ADS)

In the superconductor of FeSe0.5Te0.5, the superconductivity is highly sensitive to variations of microstructure. Therefore, a fine manipulation of the microstructures will be crucial not only for a better understanding of the superconductivity but also for potential applications. Here, we demonstrate an approach to control the superconductivity in-situ by using a magnetostrictive substrate ZnCr2Se4 as the strain generator. By mounting an FeSe0.5Te0.5 single crystal onto a magnetostrictive substrate, we show that the magnetoresistance of FeSe0.5Te0.5 is directly coupled to the magnetostriction of ZnCr2Se4. The strain is fine-tuned in-situ by an external magnetic field, leading to the superconductivity of FeSe0.5Te0.5 correspondingly favored by compressive strain while suppressed by tensile strain.

Wang, Weike; Yang, Jiyong; Li, Jun; Gu, Chuanchuan; Chen, Xuliang; Zhang, Zhitao; Zhu, Xuebin; Wang, Huabing; Yang, Zhaorong; Tian, Mingliang; Zhang, Yuheng; Moshchalkov, Victor V.

2015-02-01

112

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

SciTech Connect

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

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

2006-02-15

113

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

114

Study of Extended Rigidity Percolation in Se-Te-Sn Glasses Using Dsc  

NASA Astrophysics Data System (ADS)

The effect of addition of Sn on amorphous Se80 Te20 system has been studied using UV VIS NIR Spectrum. The samples are prepared by conventional melt quenching method. It has been found that the addition of Sn reduces the crystalline nature of Se80 Te20 chalcogenide alloy and amorphous samples are obtained for Se80-xTe20Snx(x = 0,2,4,6,8,10,15). The metal influences both the disordered network structure of the glass matrix and the transport properties in accordance with its chemical properties. The glass transition temperature and the crystallization temperatures show detectable changes at composition x = 4, 6 and 10. From the observed DSC results, it is seen that the compositions x = 4 and x = 6 denote the onset and completion of rigidity percolation and x = 10 corresponds to the chemical threshold of the system. The mean bond energy calculated using the covalent bond approach of Tichy and Ticha shows the same anomalies at x = 4, 6 and 10.

Sushama, D.; George, Achamma; Predeep, P.

2008-04-01

115

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

116

(BiSe)1.23CrSe2 and (BiSe)1.22(Cr1.2Se2)2: Magnetic Anisotropy in the First Structurally Characterized Bi-Se-Cr Ternary Compounds.  

PubMed

Compounds containing both heavy main group elements and paramagnetic transition metals form a fertile area for the study of magnetic anisotropy. We pursued the synthesis, characterization, and magnetic measurements of Bi-Se-Cr compounds: a ternary system with no structurally characterized materials. Those efforts led to the isolation of two novel misfit layer compounds, namely, (BiSe)1.23CrSe2 (1) and (BiSe)1.22(Cr1.2Se2)2 (2). The crystal structure of 1 consists of alternating BiSe and CrSe2 layers along the c-axis, and 2 is composed of alternating BiSe and (Cr1.2Se2)2 layers along the c-axis. Lattice mismatch occurs in both compounds along the b-axis and leads to positional modulation of the atoms. Field- and temperature-dependent measurements were performed to assess the degree of magnetic anisotropy. Temperature-dependent susceptibility measurements on aligned crystals of 1 display increased bifurcation of zero-field cooled and field cooled data when crystals are oriented with H perpendicular to c than when the crystals are oriented with H parallel to c. Magnetic anisotropy is less pronounced in 2 where both crystallographic orientations exhibit bifurcation at 26 K. The complexity of the magnetic behavior in both compounds likely signifies a competition between CrSe2 intralayer ferromagnetic coupling and interlayer antiferromagnetic coupling. These results highlight the exciting magnetic properties that can arise from the exploration of new ternary phases. PMID:25706606

Clarke, Samantha M; Freedman, Danna E

2015-03-16

117

Specific heat and related thermodynamic properties of (Se80Te20)100-xAgx (1 < x < 4) glasses  

NASA Astrophysics Data System (ADS)

This paper presents the result of thermodynamic studies on (Se80Te20)100-xAgx ( 1< x < 4) glasses under non isothermal conditions using differential scanning calorimetric technique. The crystallization kinetics has also been discussed. Thermodynamic parameters like entropy difference between glassy and the crystalline phase, difference of Gibbs free energy, specific heat, and the enthalpy released during phase transformation have been evaluated. The heat capacity jump and fragility of these alloys are also calculated. The results show that the stability of sample is minimum for (Se80Te20)99Ag1 and maximum for (Se80Te20)97Ag3 among all the samples.

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

2011-02-01

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

Self-organization of PbTe and SnTe nanostructures on the van der Walls GaSe(0001) surface  

NASA Astrophysics Data System (ADS)

The formation of nanodimensional defects on the van der Waals (0001) surface of a gallium selenide (GaSe) layered crystal and the growth of lead telluride (PbTe) and tin telluride (SnTe) nanostructures by deposition on this surface from the vapor phase has been studied. It is established that linear defects of various shapes and nanodimensional cavities (nanocavities) are formed on the van der Waals surface of a GaSe crystal as a result of plastic deformation. The nucleation and growth of PbTe and SnTe nanostructures on the flat van der Waals surface and in the nanocavities proceeds according to different mechanisms. It is demonstrated that selective growth of lead and tin chalcogenide nanostructures is possible on the van der Waals surfaces with nanocavities formed as a result of self-organization in the uppermost (less than 1 nm thick) layer of a GaSe crystal.

Bakhtinov, A. P.; Vodop'yanov, V. N.; Slyn'ko, E. I.; Kovalyuk, Z. D.; Lytvyn, O. S.

2007-01-01

120

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

121

Facile preparation and control of Cu-Se compounds with various preparation conditions  

NASA Astrophysics Data System (ADS)

Preparation of Cu-Se compounds, chalcogenide-based materials, is studied in this paper. The Cu-Se compounds were synthesized by using a hydrothermal method. This method possesses the advantages of simple preparation, facile manipulation, and the use of nontoxic supercritical water as a solvent. The chemical composition of the Cu-Se compounds was controlled by varying the copper source, reaction time, temperature, and surfactant. When CuCl2 was used as a copper source, the Cu-Se compound tended to form a CuSe2 phase. This phase was also formed at short reaction times and low reaction temperatures. Additionally, we investigated the change in the chemical composition of various Cu-Se compounds by using an acid treatment. The CuSe phase easily decomposed in acidic media while the CuSe2 phase showed a high resistance to acidic media. This synthesized CuSe2 can be used as a Cu(In,Ga)Se2 (CIGS) precursor in a nonselenization method. This preparation method is expected to have potential applications in energy-related devices.

Jang, Seongwan; Yu, Chanyong; Park, Kang Hyun; Lee, Dooyong; Park, Sungkyun

2015-01-01

122

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

PubMed Central

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

2014-01-01

123

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

NASA Technical Reports Server (NTRS)

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

Su, Ching-Hua; Ramachandran, N.

2013-01-01

124

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

125

Pressure effects on strained FeSe0.5Te0.5 thin films  

NASA Astrophysics Data System (ADS)

The pressure effect on the resistivity and superconducting Tc of prestrained thin films of the iron chalcogenide superconductor FeSe0.5Te0.5 is studied. Films with different anion heights above the Fe layer showing different values of ambient pressure Tc's are compressed up to a pressure of 1.7 GPa. All films exhibit a significant increase of Tc with pressure. The results cannot solely be explained by a pressure-induced decrease of the anion height but other parameters have to be considered to explain the data for all films.

Gooch, M.; Lorenz, B.; Huang, S. X.; Chien, C. L.; Chu, C. W.

2012-06-01

126

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 30–85%. These synthesized QDs were used in fabrication of the three testing fluorescence QD-based sensors for the detection of residual pesticides, clenbuterol and H5N1 avian influenza virus. The specific detection of parathion methyl (PM) pesticide at a content as low as 0.05 ppm has been realized with the biosensors made from CdTe/CdS and CdSe/ZnSe/ZnS QDs and the acetylcholinesterase (AChE) enzymes. Fluorescence resonance energy transfer (FRET)-based nanosensors using CdTe/CdS QDs conjugated with 2-amino-8-naphthol-6-sulfonic acid were fabricated that enable detection of diazotized clenbuterol at a content as low as 10 pg ml?1. For detection of H5N1 avian influenza virus, fluorescence biosensors using CdTe/CdS QDs bound on the surface of chromatophores extracted and purified from bacteria Rhodospirillum rubrum were prepared and characterized. The specific detection of H5N1 avian influenza virus in the range of 3–50 ng ?l?1 with a detection limit of 3 ng ?L?1 has been performed based on the antibody-antigen recognition.

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

2012-12-01

127

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

SciTech Connect

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

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

1992-11-01

128

Pressure-driven semiconductor-metal transition in intermediate-valence TmSe sub 1 minus x Te sub x and the concept of an excitonic insulator  

SciTech Connect

This work studies the pressure-induced semiconductor-to-metal transition (SMT) in the TmSe-TmTe alloy system. This SMT is accompanied by a valence instability of the Tm ions. Single-crystalline semiconducting TmSe{sub 1{minus}{ital x}}Te{sub {ital x}} alloys are investigated under high pressure at low temperatures. Measurements of electrical resistivity, magnetic susceptibility, neutron diffraction, and optical properties are presented and discussed. A very unusual peak structure in the resistivity-pressure relation is observed at low temperatures. A discussion of the novel feature involves the concept of an excitonic insulator and {ital f}-{ital d} hybridization. The magnetic behavior of the compounds is significantly influenced by the SMT. This is thought to be mainly due to the additional coupling between the magnetic moments of Tm via free carriers which are present in the metallic state.

Neuenschwander, J.; Wachter, P. (Laboratorium fuer Festkoerperphysik, Eidgenoessische Technische Hochschule Zuerich, CH-8093 Zuerich (Switzerland))

1990-06-15

129

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

PubMed

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

Yang, Fanghong; Yang, Ping; Cao, Yongqiang

2013-11-01

130

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

131

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

NASA Astrophysics Data System (ADS)

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

Ju, Tong; Yang, Lily; Carter, Sue

2010-05-01

132

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

PubMed

We present the results of an infrared spectroscopy study of topological insulators Bi(2)Se(3), Bi(2)Te(3) and Sb(2)Te(3). Reflectance spectra of all three materials look similar, with a well defined plasma edge. However, there are some important differences. Most notably, as temperature decreases the plasma edge shifts to lower frequencies in Bi(2)Se(3), whereas in Bi(2)Te(3) and Sb(2)Te(3) it shifts to higher frequencies. In the loss function spectra we identify asymmetric broadening of the plasmon, and assign it to the presence of charge inhomogeneities. It remains to be seen if charge inhomogeneities are characteristic of all topological insulators, and whether they are of intrinsic or extrinsic nature. PMID:23328626

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

2013-02-20

133

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

Microsoft Academic Search

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

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

1992-01-01

134

Photoinduced effect in Te-As-Se thin films for photonic applications  

NASA Astrophysics Data System (ADS)

Amorphous TexAs40Se60-x (x = 0, 10) thin films were prepared using thermal evaporation technique onto cleaned glass substrate at room temperature, and then exposed to UV-VIS light (having accordance with ASTM standards CIE 85 Table 4) using a Xenon lamp for two hours duration. Thicknesses of the films were measured using a stylus based surface profilometer. Structural analysis of the films was done using XRD measurements. Optical changes under UVVIS exposure were investigated by UV/VIS spectroscopy in wavelength range 300~900 nm. Changes in optical parameters are proposed for environmental monitoring applications. These results are compared with other range of photoexposures for some different Te-As-Se compositions in order to analyze their usability for various photonic applications.

Chauhan, R.; Srivastava, A. K.; Tripathi, A.; Mishra, M.; Srivastava, K. K.

2010-12-01

135

Photoinduced effect in Te-As-Se thin films for photonic applications  

NASA Astrophysics Data System (ADS)

Amorphous TexAs40Se60-x (x = 0, 10) thin films were prepared using thermal evaporation technique onto cleaned glass substrate at room temperature, and then exposed to UV-VIS light (having accordance with ASTM standards CIE 85 Table 4) using a Xenon lamp for two hours duration. Thicknesses of the films were measured using a stylus based surface profilometer. Structural analysis of the films was done using XRD measurements. Optical changes under UVVIS exposure were investigated by UV/VIS spectroscopy in wavelength range 300~900 nm. Changes in optical parameters are proposed for environmental monitoring applications. These results are compared with other range of photoexposures for some different Te-As-Se compositions in order to analyze their usability for various photonic applications.

Chauhan, R.; Srivastava, A. K.; Tripathi, A.; Mishra, M.; Srivastava, K. K.

2011-08-01

136

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

PubMed Central

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

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

2013-01-01

137

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

138

Ga?Se bond lengths and EXAFS phase-shifts in tetrahedrally coordinated compounds  

NASA Astrophysics Data System (ADS)

We report on a study by the EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy of the Ga?Se bond lengths in different tetrahedrally coordinated compounds having different degree of internal distortions: the chalcopyrite CuGaSe 2, the defect chalcopyrites CdGa 2Se 4 and ZnGa 2Se 4 and the defective cubic compound Ga 2Se 3. The NN distances have been calculated from EXAFS data on Ga K-edge, using CuGaSe 2 as reference system for the EXAFS phase shifts. A comparison with theoretical phase shifts is presented. We have found essentially the same Ga?Se distance in all crystals: the result supports the validity of the CTB (conservation of tetrahedral bond) model.

Antonioli, G.; Lottici, P. P.

1990-04-01

139

Anisotropy in the upper critical field of FeSe and FeSe0.33Te0.67 single crystals  

NASA Astrophysics Data System (ADS)

The electric resistivity of single crystalline Fe-based superconductors FeSe and FeSe0.33Te0.67 was measured in pulsed magnetic fields up to 55 T. Te-doped iron selenide, FeSe0.33Te0.67, shows rather isotropic behavior in both magnetoresistance (MR) and upper critical fields (Hc2\\bot (0)/Hc2\\parallel (0) = 48 T/ 42 T ? 1.14), when an external magnetic field is applied parallel and perpendicular to the crystallographic c-axis. These isotropic behaviors are frequently observed in an iron-based superconductor, and the isotropy in Hc2 can likely be described by the Pauli effect. In contrast, our measurements elucidate that the undoped iron selenide, FeSe, exhibits a clear anisotropy in both MR and Hc2 (Hc2\\bot (0)/Hc2\\parallel (0) = 27 T/ 15 T ? 1.8). This behavior occurs because the clean in-plane conduction (RRR = 35) allows to form a closed electron orbit within the two-dimensional Fermi sheets only for the magnetic field parallel to the c-axis, which results in an appearance of an intrinsic (orbital-effect limited) upper critical field for the undoped FeSe. Doping of Te breaks the clean in-plane conduction and leads to a crossover from an orbital limit dominating behavior to a Pauli limit dominating one.

Her, J. L.; Kohama, Y.; Matsuda, Y. H.; Kindo, K.; Yang, W.-H.; Chareev, D. A.; Mitrofanova, E. S.; Volkova, O. S.; Vasiliev, A. N.; Lin, J.-Y.

2015-04-01

140

Rich structural chemistry in scandium selenium/tellurium oxides: mixed-valent selenite-selenates, Sc2(SeO3)2(SeO4) and Sc2(TeO3)(SeO3)(SeO4), and ternary tellurite, Sc2(TeO3)3.  

PubMed

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

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

2014-07-01

141

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

142

Synthesis and properties of a new superconducting compound (ZrCuxSe2)  

NASA Astrophysics Data System (ADS)

Since the discovery of superconductivity in chalcogenides in Fe-Se system and in iron pnictides much attention have been give for synthesis of new materials which can exhibit superconductivity. Within this context in this work we show results which suggest the existence of a new selenite intercalate with copper atoms in the ZrCuxSe2 nominal composition, where x is 0.1 <= x <= 0.4 interval. A superconductor behavior begins in the ZrCu0.3Se2 with superconducting critical temperature close to 9.0 K. ZrSe2 is a compound which crystallize in the hexagonal symmetry with CdI2 prototype structure belongs to the space group P-32/m1. Indeed, copper is intercalating between Se-Se which have van der Walls interaction in the ZrSe2 compound. This intercalation with copper atoms, produce superconductivity in the matrix compound (ZrSe2) which is not superconductor. The copper intercalation in the matrix compound crystallizes in a LiCrS2 prototype structure.

Generoso, Ana Carolina; Baptista, Naiara; Renosto, Sergio; Jefferson Machado, Antonio

2012-02-01

143

Optical properties of films of the ternary compound CuIn3Se5  

NASA Astrophysics Data System (ADS)

We have used the laser vaporization method to obtain films of the ternary compound CuIn3Se5 and have studied the composition and structure of the films obtained. We have determined the energy and nature of the optical transitions for the indicated compound from the transmission spectra in the region of the intrinsic absorption edge. We have calculated the valence-band crystal-field (?CF) and spin-orbit (?SO) splitting energies according to Hopfield’s quasicubic model for the ternary compound CuIn3Se5.

Bodnar', I. V.; Gremenok, V. F.

2007-01-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

145

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 Na2S·9H2O 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 Mössbauer spectra. PMID:25396280

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

2014-12-01

146

Transport properties of the system Bi2Te2.7Se0.3?xPbx fabricated by a conventional melting technique  

NASA Astrophysics Data System (ADS)

N-type Bi2Te2.7Se0.3?xPbx (x = 0, 0.02, 0.04, 0.06 and 0.08) thermoelectric compounds have been prepared by a conventional melting technique. Microstructure analyses have been carried out for all samples using x-ray diffraction and a scanning electron microscope. The data reveal that the samples are crystallized in the polycrystalline rhombohedral Bi2Te3 phase and the grains have irregular shapes and sizes. The chemical stoichiometry has been examined by means of energy dispersive x-ray spectroscopy (EDAX). The stoichiometries match with the chemical formula (Bi)2(Te-Se-Pb)3. However, superstoichiometry of Pb at the expense of Se content has been observed. The thermoelectric measurements prove that the dominant charge carriers in all materials are electrons over the temperature range of measurements (200–400 K). The temperature dependence of the electrical conductivity shows metallic behavior for all the nominal compositions and over the whole range of temperature. The highest power factor value was recorded for the undoped sample at T = 330 K and was found to be 15.51 ?WK?2 cm?1.

Abdel Hakeem, A. M.

2015-03-01

147

Theoretical understanding on band engineering of Mn-doped lead chalcogenides PbX (X = Te, Se, S)  

NASA Astrophysics Data System (ADS)

Electronic structures of Mn-doped PbX (X = Te, Se, S) are investigated by first-principles calculations. It is found that the Mn-doping in PbTe enlarges the band gap and increases the valence bands degeneracy, showing good agreement with experimental measurements. This band adjustment is demonstrated to be from the anti-bonding of Te-p and Mn-d orbitals. Along the series of PbTe-PbSe-PbS, the band modification of Mn-doping undergoes a gradual transition from multiple valence bands type to resonant states type, owing to the downwards shifted anion-p orbitals. This work provides essential understandings on the band engineering of Mn-doped lead chalcogenides thermoelectric materials.

Tan, Xiaojian; Shao, Hezhu; Hu, Tianqi; Liu, Guo-Qiang; Ren, Shang-Fen

2015-03-01

148

Chalcogenide coatings of Ge15Sb20S65 and Te20As30Se50.  

PubMed

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

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

2008-05-01

149

N-type Doped PbTe and PbSe Alloys for Thermoelectric Applications  

NASA Technical Reports Server (NTRS)

The present invention demonstrates that weak scattering of carriers leads to a high mobility and therefore helps achieve low electric resistivity with high Seebeck coefficient for a thermoelectric material. The inventors demonstrate this effect by obtaining a thermoelectric figure of merit, zT, higher than 1.3 at high temperatures in n-type PbSe, because of the weak scattering of carriers in the conduction band as compared with that in the valence band. The invention further demonstrates favorable thermoelectric transport properties of n-type PbTe.sub.1-xI.sub.x with carrier concentrations ranging from 5.8.times.10.sup.18-1.4.times.10.sup.20 cm.sup.-3.

Snyder, G. Jeffrey (Inventor); LaLonde, Aaron (Inventor); Pei, Yanzhong (Inventor); Wang, Heng (Inventor)

2014-01-01

150

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

PubMed Central

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

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

2011-01-01

151

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

152

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

SciTech Connect

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

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

2008-07-15

153

Thermodynamics of copper matte converting: Part III. Steady-state volatilization of Au, Ag, Pb, Zn, Ni, Se, Te, Bi, Sb, and As from slag, matte, and metallic copper  

Microsoft Academic Search

A comprehensive compilation of various thermodynamic data required for a complete analysis of copper matte converting reactions\\u000a is presented. The data comprise estimated free energies of formation for such gases as SeO, SeS, TeO, TeS, BiO, BiS, SbO,\\u000a SbS, AsO, and AsS, as well as activity coefficients in dilute copper alloys and vapor pressures of various elements and compounds.\\u000a The

M. Nagamori; P. C. Chaubal

1982-01-01

154

Metal-free inorganic ligands for colloidal nanocrystals: S2-, HS-, Se2-, HSe-, Te2-, HTe-, TeS3(2-), OH-, and NH2- as surface ligands.  

PubMed

All-inorganic colloidal nanocrystals were synthesized by replacing organic capping ligands on chemically synthesized nanocrystals with metal-free inorganic ions such as S(2-), HS(-), Se(2-), HSe(-), Te(2-), HTe(-), TeS(3)(2-), OH(-) and NH(2)(-). These simple ligands adhered to the NC surface and provided colloidal stability in polar solvents. The versatility of such ligand exchange has been demonstrated for various semiconductor and metal nanocrystals of different size and shape. We showed that the key aspects of Pearson's hard and soft acids and bases (HSAB) principle, originally developed for metal coordination compounds, can be applied to the bonding of molecular species to the nanocrystal surface. The use of small inorganic ligands instead of traditional ligands with long hydrocarbon tails facilitated the charge transport between individual nanocrystals and opened up interesting opportunities for device integration of colloidal nanostructures. PMID:21682249

Nag, Angshuman; Kovalenko, Maksym V; Lee, Jong-Soo; Liu, Wenyong; Spokoyny, Boris; Talapin, Dmitri V

2011-07-13

155

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

156

Composition Dependence of the Hydrostatic Pressure Coefficients of the Bandgap of ZnSe(1-x)Te(x) Alloys  

NASA Technical Reports Server (NTRS)

Optical absorption experiments have been performed using diamond anvil cells to measure the hydrostatic pressure dependence of the fundamental bandgap of ZnSe(sub 1-xTe(sub x) alloys over the entire composition range. The first and second-order pressure coefficients are obtained as a function of composition. Starting from the ZnSe side, the magnitude of both coefficients increases slowly until x approx. 0.7, where the ambient-pressure bandgap reaches a minimum. For larger values of x the coefficients rapidly approach the values of ZnTe. The large deviations of the pressure coefficients from the linear interpolation between ZnSe and ZnTe are explained in terms of the band anticrossing model.

Wu, J.; Yu, K. M.; Walukiewicz, W.; Shan, W.; Ager, J. W., III; Haller, E. E.; Miotkowski, I.; Ramdas, A. K.; Su, Ching-Hua

2003-01-01

157

Lattice dynamics of layered-structure compounds: PdTe2  

NASA Astrophysics Data System (ADS)

A complete data set for the phonon dispersion curves of PdTe2 along the [?00], [??0], and [00?] symmetry directions has been measured. A lattice-dynamical model consisting of axially symmetric Born-von Kármán interactions to seventh-nearest neighbors together with shell-model contributions, introduced specifically to model dips in the low-energy optic branches in the vicinity of the ? point, provides a reasonable fit to the measured dispersion curves. The results are discussed in relation to the known properties of PdTe2 and the dispersion data already available for related layered-structure compounds.

Finlayson, T. R.; Reichardt, W.; Smith, H. G.

1986-02-01

158

Lattice dynamics of layered-structure compounds: PdTe/sub 2/  

SciTech Connect

A complete data set for the phonon dispersion curves of PdTe/sub 2/ along the (zeta00), (zetazeta0), and (00zeta) symmetry directions has been measured. A lattice-dynamical model consisting of axially symmetric Born--von Karman interactions to seventh-nearest neighbors together with shell-model contributions, introduced specifically to model dips in the low-energy optic branches in the vicinity of the GAMMA point, provides a reasonable fit to the measured dispersion curves. The results are discussed in relation to the known properties of PdTe/sub 2/ and the dispersion data already available for related layered-structure compounds.

Finlayson, T.R.; Reichardt, W.; Smith, H.G.

1986-02-15

159

Terahertz conductivity of topological surface states in Bi?.?Sb?.?Te?.?Se?.?.  

PubMed

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 Bi?.?Sb?.?Te?.?Se?.? (BSTS) was found, showing high bulk resistivities of 1-10??.cm and greater contrast between the bulk and surface resistivities compared to other Bi-based topological insulators. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we present complex conductivity of BSTS single crystals, disentangling the surface and bulk contributions. We find that the Drude spectral weight is 1-2 orders of magnitude smaller than in other Bi-based topological insulators, and similar to that of Bi?Se? 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

160

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

2015-03-01

161

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

PubMed

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

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

2008-03-25

162

Band alignments and strain effects in PbTe/Pb1 -xSrxTe and PbSe/Pb1 -xSrxSe quantum-well heterostructures  

NASA Astrophysics Data System (ADS)

The optical transitions and band alignments of PbTe/Pb1 -xSrx Te and PbSe/Pb1 -xSrx Se multi-quantum-well heterostructures were studied using temperature-modulated absorption spectroscopy and envelope function calculations. By taking advantage of the strain-induced splitting of conduction- and valence-band states at the different L points of the Brillouin zone, a reliable determination of the band offsets is obtained, taking into account the biaxial strain of the quantum wells derived by x-ray diffraction. Through this analysis, the normalized conduction-band offsets are determined as ? Ec/? Eg=0.45 ±0.05 for the PbTe/Pb1 -xSrx Te system and 0.6 ±0.1 for the PbSe/Pb1 -xSrx Se system for Sr contents up to 13%. Within the experimental precision, the band offsets are independent of temperatures from 20-300 K. With these parameters, precise modeling of the energy levels and optical transitions is achieved as required for optoelectronic device applications.

Simma, M.; Bauer, G.; Springholz, G.

2014-11-01

163

Pressure-induced superconductivity in topological parent compound Bi2Te3  

PubMed Central

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

164

Magnetic properties of IV-VI compound GeTe based diluted magnetic semiconductors  

NASA Astrophysics Data System (ADS)

Magnetic properties of IV-VI compound GeTe based diluted magnetic semiconductors with 3d transition metals from Ti to Ni have been investigated. Ferromagnetic order is observed for the Cr, Mn, and Fe doped GeTe films, whereas the Ti, V, Co, and Ni doped films are paramagnetic. The ferromagnetic order could give rise to p-d exchange interaction because amplitudes of negative magnetoresistance and the anomalous Hall effect are proportional to that of spontaneous magnetization. The Curie temperatures determined by extrapolating the steep linear part of the temperature dependence of the squared residual magnetization for the Cr, Mn, and Fe doped GeTe films are 12, 47, and 100 K, respectively.

Fukuma, Y.; Asada, H.; Miyashita, J.; Nishimura, N.; Koyanagi, T.

2003-05-01

165

Non-abruptness of heterointerfaces during LPE growth of (Hg,Cd)Te on (Cd,Zn)Te and Cd(Te,Se) substrates  

Microsoft Academic Search

Interdiffusion of isoelectronic constituents across heterointerfaces during LPE growth of Hg1?xCdxTe on Cd1?yZnyTe and CdTe1?ySey substrates (x = 0.2 and 0.5; y = 0, ? 0.04, and ? 0.07) has been measured by means of EDXS and SIMS. The interdiffusion coefficients of the constituent cation components Cd and Hg have been found to be dependent on the concentration x as

I. Utke; W. Frentrup; I. Hähnert; H. Kirmse; O. Müller; M. Schenk; M. Winkler

1996-01-01

166

Accuracy of existing atomic potentials for the CdTe semiconductor compound.  

PubMed

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

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

2011-06-28

167

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

168

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

169

Thermoelectric properties of topological insulator Bi2Te3, Sb2Te3, and Bi2Se3 thin film quantum wells  

NASA Astrophysics Data System (ADS)

The thermoelectric (TE) figure of merit ZT of topological insulator Bi2Te3, Sb2Te3, and Bi2Se3 thin film quantum wells is calculated for thicknesses below 10 nm, for which hybridization of the surface states as well as quantum confinement in the bulk are individually predicted to enhance ZT. Here, the question is addressed what ZT can be expected from coexisting surface and bulk states in such quantum wells. It is demonstrated that the parallel contributing bulk and surface channels tend to cancel each other out. This is because the surface-to-volume ratios of the thin films prevent the domination of transport through a single channel and because the individual bulk and surface ZTs are optimized at different Fermi levels.

Osterhage, Hermann; Gooth, Johannes; Hamdou, Bacel; Gwozdz, Paul; Zierold, Robert; Nielsch, Kornelius

2014-09-01

170

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

171

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

PubMed

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

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

2011-08-28

172

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.

173

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 102.9–109.4 ?? 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

174

Fabrication of Cu3Zn3Se ternary compounds by AP-MOCVD  

NASA Astrophysics Data System (ADS)

I-II-VI Ternary chalcopyrite semiconductors of Cu1-xZn1-ySe2-? (Cu3Zn3Se) were successfully fabricated by the atmospheric pressure metal-organic chemical vapor deposition method for the first time. Four major peaks of (112), (220)/(204), (312)/(116), and (400), accompanied by three minor peaks of (103), (211) and (301) were observable in the X-ray diffraction spectra. In particular, the presence of those latter low-intensity peaks featured the formation of the chalcopyrite type Cu3Zn3Se compound. Typical absorption coefficients of the films produced were found to vary from 2.75×10 cm-1 to 5.75×10 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

175

MBE growth of topological insulator Bi2Se3 and Bi2Te3 films  

NASA Astrophysics Data System (ADS)

Three-dimensional (3D) topological insulators are a new state of quantum matter with a band gap in bulk but gapless states on the surface. The surface states with spin helicity can be the host of many striking quantum phenomena. In this work, we use ultrahigh vacuum molecular beam epitaxy to grow atomically flat topological insulator (TI) Bi2Se3 and Bi2Te3 films. High quality TI films were obtained using epitaxial graphene on SiC as a substrate for TI growth. The growth dynamics was characterized by real time reflection high-energy electron diffraction (RHEED). The growth condition was optimized by adjusting for proper flux rate and substrate temperature while monitoring the RHEED patterns. In situ Auger spectroscopy and scanning tunneling microscopy (STM) measurements at 5K are used to study the as-grown films for their stoichiometry and defect density. We expect these MBE grown samples will provide a good candidate for studying the topological surface states and related phenomena, which will be studied using scanning tunneling spectroscopy at millikelvin temperatures [1]. 1. Y. J. Song et al., Nature 467, 185 [2010].

Zhang, Tong; Levy, Niv; Song, Young Jae; Chae, Jungseok; Stroscio, Joseph A.

2011-03-01

176

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

NASA Astrophysics Data System (ADS)

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

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

177

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

E-print Network

antimony telluride, Nb3SbxTe7-x, was synthesized and tested for thermoelectric properties elements of Nb3Sb2Te5 also made the compound an attractive target for thermoelectric studies, as antimony which altered the antimony and tellurium ratios were investigated similarly for thermoelectric potential

178

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

179

Investigation of spatial correlation of type-II ZnTe quantum dots embedded in ZnCdSe barriers  

NASA Astrophysics Data System (ADS)

Doped and undoped multilayered structures of ZnTe type-II quantum dots (QDs) embedded in a ZnCdSe matrix have been grown in order to investigate the formation of an intermediate band, lying within the ZnCdSe band gap, with the aim of absorbing photons with energies below ZnCdSe bandgap. These materials may be useful for intermediate bandgap solar cells. The reciprocal space map (RSM) of the ZnTe/ZnCdSe multilayer QD structure consisting of periodic superlattice peaks in the qx direction have been studied for two different ZnCdSe spacer thicknesses (dA 3.5, dB 1.5 nm). The ZnTe QDs give rise to diffuse scattering in RSM, which is found to be elongated in the qx direction for both samples indicating a vertical correlation of the QDs. From the widths of the diffuse maxima in the qz direction, we found that 16% and 40% of QDs are correlated vertically for dA 3.5 nm and dB 1.5 nm, respectively. With increasing correlation, the pairing probability of the dots increases, leading to a larger average QD size. This conclusion is supported by a smaller blue-shift (26 vs 36 meV) of the photoluminescence peak position with increasing excitation intensity, over five orders of magnitude, for the structure with narrower spacers.

Manna, Uttam; Noyan, Ismail; Neumark, Gertrude; Dhomkar, Siddharth; Roy, Bidisha; Kuskovsky, Igor; Moug, Richard; Peng, Le; Tamargo, Maria

2012-02-01

180

Crossover from hole- to electron-dominant regions in iron-chalcogenide superconductors induced by Te/Se substitution  

NASA Astrophysics Data System (ADS)

We have investigated a Te/Se substitution effect on the field dependence of Hall resistivity in FeSe1?xTex (x = 0.5–0.7) thin films grown on LaAlO3 and CaF2 substrates. By observing the magnetic field dependence of Hall resistivity, the crossover from hole- to electron-dominant regions is observed to occur between x = 0.5 and 0.6 in the films on LaAlO3, while no such crossover is observed in those on CaF2. The results indicate that the substitution of Te for Se effectively acts as electron doping, while the lattice strain also has an additional effect on the balance of hole and electron densities. These two factors can be independently used to optimize superconducting transition temperature so as to tune the doping level near the boundary where the hole density becomes equal to the electron density.

Tsukada, Ichiro; Nabeshima, Fuyuki; Ichinose, Ataru; Komiya, Seiki; Hanawa, Masafumi; Imai, Yoshinori; Maeda, Atsutaka

2015-04-01

181

Lattice dynamics of BaFe2X3(X =S ,Se ) compounds  

NASA Astrophysics Data System (ADS)

We present the Raman scattering spectra of the BaFe2X3(X =S ,Se ) compounds in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe2S3( BaFe2Se3 ) is base-centered C m c m (primitive P n m a ), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe2S(Se ) 3 is supported by the lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe2Se3 below TN=255 K leaves a fingerprint both in the A1 g and B3 g phonon mode linewidth and energy.

Popovi?, Z. V.; Š?epanovi?, M.; Lazarevi?, N.; Opa?i?, M.; Radonji?, M. M.; Tanaskovi?, D.; Lei, Hechang; Petrovic, C.

2015-02-01

182

Mo (W,V)?Cu (Ag)?S(Se) cluster compounds  

Microsoft Academic Search

This review summarizes the preparation, skeletal structure, reactions, spectroscopic properties and non-linear optical properties of Mo(W,V)?Cu(Ag)?S(Se) cluster compounds; 190 such compounds belong to 23 structural types; 25 reactions are classified into ligand substitution, addition and decomposition reactions. Recently, some Mo(W)?Cu(Ag)?S clusters were found to exhibit strong non-linear optical properties; the optical limiting threshold measured for [(PPh3)4Ag4Mo2S8] is one order of

Hong-Wei Hou; Xin-Quan Xin; Shu Shi

1996-01-01

183

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

184

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

PubMed

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

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

2014-08-01

185

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

PubMed

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

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

2013-05-24

186

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

PubMed

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

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

2014-07-22

187

NaCu6Se4: a layered compound with mixed valency and metallic properties.  

PubMed

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

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

2014-11-17

188

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

189

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

SciTech Connect

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

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

2008-02-15

190

Synthesis and structural study of the AgIn5Te8 compound by X-ray powder diffraction  

NASA Astrophysics Data System (ADS)

The AgIn5Te8 compound was synthesized by the melt and annealing technique and its structure was refined from X-ray powder diffraction pattern using the Rietveld method. AgIn5Te8 crystallizes in the tetragonal space group P2m (No 111), Z = 1, with a = 6.1952(2) Å, c = 12.419(4) Å, V = 476.7(2) Å3. The refinement of 23 instrumental and structural parameters led to Rp = 8.2%, Rwp = 11.6%, Rexp = 6.8 % and S = 1.7; RB = 11.2 % for 5501 step intensities and 253 independent reflections. The structure is characterized by a double alternation of selenide-metal planes according to the In2-Te1-In1-Te2-Ag-Te2-In1-Te1-In2 sequence.

Mora, Asiloé J.; Delgado, Gerzon E.; Pineda, Carlos; Tinoco, Tibaire

2004-05-01

191

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

SciTech Connect

We employ ultrafast transient absorption spectroscopy with temporal pulse shaping to manipulate coherent phonon excitation and quantify the strength of electron-phonon coupling in CdTe{sub 1?x}Se{sub x} nanocrystals (NCs). Raman active CdSe and CdTe longitudinal optical phonon (LO) modes are excited and probed in the time domain. By temporally controlling pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe{sub 1?x}Se{sub x} NCs, we estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode.

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

2014-08-25

192

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

193

Systematic studies on adsorption of trace elements Pt, Pd, Au, Se, Te, As, Hg, Sb on thiol cotton fiber  

Microsoft Academic Search

The modified thiol cotton fiber (TCF) can quantitatively adsorb Pt(II), Pd(II), Au(III), Se(IV), Te(IV), As(III), Hg(II) and Sb(III) strongly in addition to its adsorption of Bi(III), Sn(II), Ag(I), Cu(II), In(III), Pb(II), Cd(II), Zn(II), Co(II), Ni(II), and Tl(I). In a HCl solution, the adsorption order for the eight elements is Pt(II)?Pd(II)>Au(III)?Se(IV)>Te(IV)>As(III)>Hg(II)>Sb(III). The adsorption capability of TCF for these eight ions depends

Muqing Yu; Daowei Sun; Wei Tian; Guoping Wang; Wanbin Shen; Ning Xu

2002-01-01

194

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

195

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

196

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

PubMed

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

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

2013-06-25

197

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

198

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

199

Element substitution from substrates in Bi2Se3, Bi2Te3 and Sb2Te3 overlayers deposited by hot wall epitaxy  

NASA Astrophysics Data System (ADS)

In depositing Bi2Se3, Bi2Te3 or Sb2Te3 layers on certain substrates by hot wall epitaxy, the Bi and Sb atoms in the layers are replaced by the atoms supplied from the substrates. We extend our exploration on this substitution phenomenon for a number of combinations of the layer and the substrate to infer the factors that determine the occurrence of the substitution. Using a series of Ga- and In-based III-V substrates, it is evidenced that the group III atoms substitute the group V overlayer atoms when the bonds in the substrates are weak. We demonstrate that Ag triggers the substitution more effectively than Cu as a catalyst. The competition between the catalyst-induced substitutions on ternary alloy substrates shows that the dependence on the bond strength is not as strong as to be exclusive. Additionally, defectiveness around the interface between a semicoherently grown ?-In2Se3 layer produced by the substitution and the InAs substrate is demonstrated. The cathodeluminescence properties are also provided focusing on the dependence on the phase of In2Se3.

Takagaki, Y.; Jahn, U.; Jenichen, B.; Berlin, K.; Kong, X.; Biermann, K.

2014-09-01

200

Magnetic Order and Transitions in the Spin-web Compound Cu3TeO6  

NASA Astrophysics Data System (ADS)

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

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

201

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

202

Coexistence of electron-glass phase and persistent photoconductivity in GeSbTe compounds  

NASA Astrophysics Data System (ADS)

It is demonstrated that persistent photoconductivity (PPC), well studied in lightly-doped semiconductors, is observable in GeSbTe compounds using infrared excitation at cryogenic temperatures. The low levels of energy flux necessary to induce an appreciable effect seems surprising given the high carrier concentration n of these ternary alloys (n >1020cm-3 ). On the other hand, their high density of carriers makes GeSbTe films favorable candidates for exhibiting intrinsic electron-glass effects with long relaxation times. These are indeed observed in GeSbTe thin films that are Anderson-localized. In particular, a memory dip is observed in samples with sheet resistances larger than ?105? at T ?4 K with similar characteristics as in other systems that exhibit intrinsic electron-glass effects. Persistent photoconductivity, however, is observable in GeSbTe films even for sheet resistances of the order of 103? , well below the range of disorder required for observing electron-glass effects. These two nonequilibrium phenomena, PPC and electron glass, are shown to be of different nature in terms of other aspects as well. In particular, their relaxation dynamics is qualitatively different; the excess conductance ? G associated with PPC decays with time as a stretched exponential whereas a logarithmic relaxation law characterizes ? G (t ) of all electron glasses studied to date. Surprisingly, the magnitude of the memory dip is enhanced when the system is in the PPC state. This counter-intuitive result may be related to the compositional disorder in these materials extending over mesoscopic scales. Evidence in support of this scenario is presented and discussed.

Ovadyahu, Z.

2015-03-01

203

Structure, Stability, and Properties of the Intergrowth Compounds ([SnSe]1+?)m(NbSe2)n, where m = n = 1-20.  

PubMed

Intergrowth compounds of ([SnSe]1+?)m(NbSe2)n, where 1 ? m = n ? 20, with the same atomic composition but different c-axis lattice parameters and number of interfaces per volume were synthesized using the modulated elemental reactant technique. A c-axis lattice parameter change of 1.217(6) nm as a function of one unit of m = n was observed. In-plane X-ray diffraction shows an increase in distortion of the rock salt layer as a function of m and a broadening of the NbSe2 reflections as n increases, indicating the presence of different coordination environments for Nb (trigonal prismatic and octahedral) and smaller crystallite size, which were confirmed via scanning transmission electron microscopy investigations. The electrical resistivities of all 12 compounds exhibit metallic temperature dependence and are similar in magnitude as would be expected for isocompositional compounds. Carrier concentration and mobility of the compounds vary within a narrow range of 2-6 × 10(21) cm(-3) and 2-6 cm(2) V(-1) s(-1), respectively. Even at a thickness of 12 nm for the SnSe and NbSe2 blocks, the properties of the intergrowth compounds cannot be explained as composite behavior, due to significant charge transfer between them. Upon being annealed at 500 °C, the higher order m = n compounds were found to convert to the thermodynamically stable phase, the (1,1) compound. This suggests that the capacitive energy of the interfaces stabilizes these intergrowth compounds. PMID:25807217

Alemayehu, Matti B; Ta, Kim; Falmbigl, Matthias; Johnson, David C

2015-04-15

204

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

SciTech Connect

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

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

2011-01-01

205

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

PubMed

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

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

2013-02-01

206

Observation of an electron band above the Fermi level in FeTe{sub 0.55}Se{sub 0.45} from in-situ surface doping  

SciTech Connect

We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe{sub 0.55}Se{sub 0.45}. 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 KFe{sub 2?x}Se{sub 2} compound.

Zhang, P.; Ma, J.; Qian, T. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Richard, P., E-mail: p.richard@iphy.ac.cn; Ding, H., E-mail: dingh@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Xu, N. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Paul Scherrer Institut, Swiss Light Source, CH-5232 Villigen PSI (Switzerland); Xu, Y.-M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Fedorov, A. V.; Denlinger, J. D. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Gu, G. D. [Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)

2014-10-27

207

Exceptional suppression of flux-flow resistivity in FeSe0.4Te0.6 by back-flow from excess Fe atoms and Se /Te substitutions  

NASA Astrophysics Data System (ADS)

We measured the microwave surface impedance of FeSe0.4Te0.6 single crystals with and without external magnetic fields. The superfluid density exhibited a quadratic temperature dependence, indicating a strong pair-breaking effect. The flux-flow resistivity behaved as ?f(B ?Bc 2) /?n=? B /Bc 2 . The observed ? value of ?0.66 was considerably smaller than that of other Fe-based materials (? ?1 ) and was attributed to a back-flow of superfluids remarkable in disordered superconductors. This is an observation of the back-flow phenomenon caused by an origin other than the vortex pinning in multiple-band systems.

Okada, Tatsunori; Nabeshima, Fuyuki; Takahashi, Hideyuki; Imai, Yoshinori; Maeda, Atsutaka

2015-02-01

208

The CuInSe2-CuIn3Se5 defect compound interface: Electronic structure and band alignment  

NASA Astrophysics Data System (ADS)

The interface formation between stoichiometric chalcopyrite CuInSe2 and the copper-deficient defect phase CuIn3Se5 is investigated by in situ photoelectron spectroscopy. The use of epitaxial samples allows for the preparation of highly defined surfaces and accurate analysis of the electronic structure. Valence band structures measured with synchrotron-based photoelectron spectroscopy are in agreement with density functional theory. We observe a lowering of the top valence band of CuIn3Se5 of 0.29 eV with respect to CuInSe2. The increased optical gap for copper-deficient material leads to aligned conduction bands.

Hofmann, A.; Pettenkofer, C.

2012-08-01

209

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

210

Enhanced photoelectrochemical aptasensing platform based on exciton energy transfer between CdSeTe alloyed quantum dots and SiO2@Au nanocomposites.  

PubMed

High-efficient exciton energy transfer between CdSeTe alloyed quantum dots and SiO2@Au nanocomposites was applied to develop an enhanced photoelectrochemical aptasensing platform with ultrahigh sensitivity, good selectivity, reproducibility and stability. PMID:25804131

Fan, Gao-Chao; Zhu, Hua; Shen, Qingming; Han, Li; Zhao, Ming; Zhang, Jian-Rong; Zhu, Jun-Jie

2015-04-25

211

Magnetoconductance crossover and non-linear Hall effect in MBE-grown Cr-doped Bi2Te2Se  

NASA Astrophysics Data System (ADS)

Recent predictions have shown that the magnetoconductance (MC) of a topological insulator should show a crossover from negative MC to positive MC when time-reversal symmetry is broken [1]. Observations of this crossover have been reported in 3 QL thick Cr-Bi2Se3 [2] in the quasi-2D regime where surface hybridization is not negligible. We report magneto-transport results on 15 QL thick Cr-doped and undoped Bi2Te2Se films grown on Si (111) substrates by MBE. The undoped film exhibits weak anti-localization at low temperatures. In the Cr-doped film, a crossover from negative to positive MC is observed versus temperature at T=12 K. SQUID measurements show that the sample is ferromagnetic in this temperature range. In addition, a non-linear Hall voltage is observed despite the large bulk carrier concentration. This paves the way for further experiments on (Bi,Cr)2Te2Se in our search for the quantum anomalous Hall effect. [1] H.Z. Lu et al. Phys. Rev. Lett. 107, 076801(2011). [2] M.Liu et al. arXiv 1103.3353(2011).

Assaf, Badih A.; Wei, Peng; Katmis, Ferhat; Moodera, Jagadeesh S.; Heiman, Don

2012-02-01

212

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

PubMed

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

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

2014-04-01

213

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

214

Dresselhaus field-induced anisotropic spin propagation in ZnSe/BeTe type-II quantum wells  

NASA Astrophysics Data System (ADS)

The dynamics of photo-injected electrons and the propagation of photo-created spins in nondoped ZnSe/BeTe type-II quantum wells were investigated by time-resolved photo-induced circular dichroism microscopy at room temperature. Spin propagation from the pump spot presents a directionally dependent spin precession frequency in a magnetic field in Voigt configuration. This anisotropic spin propagation is ascribed to the Dresselhaus effect (G. Dresselhaus, Phys. Rev. 100, 580, 1955) on the radially diffusing photo-injected electrons, since the anisotropy depends on both the directions of crystallographic axis and magnetic field.

Mino, H.; Yonaiyama, S.; Ohto, K.; Akimoto, R.

2011-10-01

215

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

216

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

217

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

218

Thermoelectric Properties of Cu-Doped n-Type Bi2Te2.85Se0.15 Prepared by Liquid Phase Growth Using a Sliding Boat  

NASA Astrophysics Data System (ADS)

N-type Bi2Te2.85Se0.15 thermoelectric materials were prepared by liquid phase growth (LPG) using a sliding boat, a simple and short fabrication process for Bi2Te3-related materials. Cu was selected as a donor dopant, and its effect on thermoelectric properties was investigated. Thick sheets and bars of Cu x Bi2 Te2.85Se0.15 (x=0-0.25) of 1-2mm in thickness were obtained using the process. X-ray diffraction patterns and scanning electron micrographs showed that the in-plane direction tended to correspond to the hexagonal c-plane, which is the preferred direction for thermoelectric conversion. Cu-doping was effective in controlling conduction type and carrier (electron) concentration. The conduction type was p-type for undoped Bi2Te2.85Se0.15 and became n-type after Cu-doping. The Hall carrier concentration was increased by Cu-doping. Small resistivity was achieved in Cu0.02Bi2Te2.85Se0.15 owing to an optimized amount of Cu-doping and high crystal orientation. As a result, the maximum power factor near 310K for Cu0.02Bi2Te2.85Se0.15 was approximately 4×10-3W/K2m and had good reproducibility. Furthermore, the thermal stability of Cu0.02Bi2Te2.85Se0.15 was also confirmed by thermal cycling measurements of electrical resistivity. Thus, n-type Bi2Te2.85Se0.15 with a large power factor was prepared using the present LPG process.

Kitagawa, Hiroyuki; Matsuura, Tsukasa; Kato, Toshihito; Kamata, Kin-ya

2014-12-01

219

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

220

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 V(oc) of the corresponding cell devices. In addition, charge extraction measurements have also confirmed the photovoltage enhancement in the ZnTe/CdSe cell related to reference CdTe/CdSe cell. Furthermore, transient grating (TG) measurements have revealed a faster electron injection rate for the ZnTe/CdSe-based QDSCs in comparison with the CdSe cells. The resultant ZnTe/CdSe QD-based QDSCs exhibit a champion power conversion efficiency of 7.17% and a certified efficiency of 6.82% under AM 1.5 G full one sun illumination, which is, as far as we know, one of the highest efficiencies for liquid-junction QDSCs. PMID:25562411

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

2015-01-27

221

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

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

2015-02-14

222

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

223

Two new compounds, ?-ScTe and Y3Au2, and a reassessment of Y2Au.  

PubMed

Two new compounds, ?-ScTe (scandium telluride) and Y(3)Au(2) (triyttrium digold), have been synthesized by high-temperature solid-state techniques and their crystal structures, along with that of Y(2)Au (diyttrium gold), have been refined by single-crystal X-ray diffraction methods. ?-ScTe is a superstructure of ScTe (NiAs-type), featuring double hexagonal close-packed layers of Te atoms with the octahedral cavities filled by Sc atoms. Y(3)Au(2) displays a U(3)Si(2)-type structure and is built from Au(2)-centered bitrigonal prisms and centered cubes of Y atoms. The structure of Y(2)Au is better described as an inverse PbCl(2)-type structure rather than a Co(2)Si-type. PMID:22051945

Chai, Ping; Corbett, John D

2011-11-01

224

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

225

Application of CdTe/ZnSe Quantum Dots in In Vitro Imaging of Chicken Tissue and Embryo.  

PubMed

The present work is aimed to synthesize CdTe/ZnSe core/shell quantum dots (QDs) in an easy way and to explore the possibilities of its application in in vitro imaging of chicken tissue and embryo. The QDs were prepared using microwave irradiation with different temperatures, which is a very easy and less time-consuming method. Subsequently, these QDs were characterized by spectrofluorimetry, Transmission Electron Microscopy, X-ray fluorescence analysis and Dynamic Light Scattering measurement. A blueshifting of the emission was found when ZnSe was deposited on CdTe QDs. The QDs showed its fluorescence emission quantum yields up to 25%. They were applied into chicken embryos and breast muscle tissues to study their efficiency in in vitro imaging. All the QDs of different color were able to visualize in in vitro imaging. The highest fluorescence intensity was detected in the case of red QDs prepared at 100°C. The green and red QDs were possible to detect up to the depth of 3 and 4 mm of the tissue, respectively. PMID:25476270

Moulick, Amitava; Blazkova, Iva; Milosavljevic, Vedran; Fohlerova, Zdenka; Hubalek, Jaromir; Kopel, Pavel; Vaculovicova, Marketa; Adam, Vojtech; Kizek, Rene

2015-03-01

226

Engineering the electronic properties of silicene by tuning the composition of MoX2 and GaX (X = S,Se,Te) chalchogenide templates  

NASA Astrophysics Data System (ADS)

By using first-principles simulations, we investigate the interaction of a 2D silicon layer with two classes of chalcogenide-layered compounds, namely MoX2 and GaX (X = S, Se, Te). A rather weak (van der Waals) interaction between the silicene layers and the chalcogenide layers is predicted. We found that the buckling of the silicene layer is correlated to the lattice mismatch between the silicene layer and the MoX2 or GaX template. The electronic properties of silicene on these different templates largely depend on the buckling of the silicene layer: highly buckled silicene on MoS2 is predicted to be metallic, while low buckled silicene on GaS and GaSe is predicted to be semi-metallic, with preserved Dirac cones at the K points. These results indicate new routes for artificially engineering silicene nanosheets, providing tailored electronic properties of this 2D layer on non-metallic substrates. These non-metallic templates also open the way to the possible integration of silicene in future nanoelectronic devices.

Scalise, E.; Houssa, M.; Cinquanta, E.; Grazianetti, C.; van den Broek, B.; Pourtois, G.; Stesmans, A.; Fanciulli, M.; Molle, A.

2014-06-01

227

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

SciTech Connect

A variety of different possible donor and acceptor impurities have been implanted into GaN and annealed up to 1450thinsp{degree}C. S{sup +} and Te{sup +} produce peak electron concentrations {le}5{times}10{sup 18} cm{sup {minus}3}, well below that achievable with Si{sup +}. Mg produces {ital p}-type conductivity, but Be{sup +}- and C{sup +}- implanted samples remained {ital n} type. No redistribution was observed for any of the implanted species for 1450thinsp{degree}C annealing. Much more effective damage removal was achieved for 1400thinsp{degree}C annealing of high-dose (5{times}10{sup 15} cm{sup {minus}2}) Si{sup +} implanted GaN, compared to the more commonly used 1100thinsp{degree}C annealing. {copyright} {ital 1999 American Vacuum Society.}

Wilson, R.G. [Consultant, Stevenson Ranch, California 91381 (United States)] [Consultant, Stevenson Ranch, California 91381 (United States); Zavada, J.M. [U.S. Army, Research Office, Research Triangle Park, North Carolina 27709 (United States)] [U.S. Army, Research Office, Research Triangle Park, North Carolina 27709 (United States); Cao, X.A.; Singh, R.K.; Pearton, S.J. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)] [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Guo, H.J.; Pennycook, S.J. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)] [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Fu, M.; Sekhar, J.A.; Scarvepalli, V. [Micropyretics Heaters International, Inc., Cincinnati, Ohio 45215 (United States)] [Micropyretics Heaters International, Inc., Cincinnati, Ohio 45215 (United States); Shu, R.J.; Han, J.; Rieger, D.J. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)] [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States); Zolper, J.C. [Office of Naval Research, Arlington, Virginia 22217 (United States)] [Office of Naval Research, Arlington, Virginia 22217 (United States); Abernathy, C.R. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)] [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)

1999-07-01

228

Robust magnetic polarons in type-II (Zn,Mn)Te/ZnSe magnetic quantum dots  

NASA Astrophysics Data System (ADS)

We present a magneto-optical study of magnetic polarons in type-II (Zn,Mn) Te quantum dots. The polarons are formed due to the exchange coupling between the spins of the holes and those of the Mn ions, both of which are localized in the dots. In our photoluminescence studies, the magnetic polarons are detected at temperatures up to ˜150K , with a formation energy of ˜40meV . The emission from these dots exhibits an unusually small Zeeman shift with applied magnetic field ( ˜2meV at 8 T) and at the same time a very large circular polarization. We attribute this apparently contradictory behavior by a low and weakly temperature-dependent magnetic susceptibility due to antiferromagnetic coupling of the Mn spins.

Sellers, I. R.; Oszwa?dowski, R.; Whiteside, V. R.; Eginligil, M.; Petrou, A.; Zutic, I.; Chou, W.-C.; Fan, W. C.; Petukhov, A. G.; Kim, S. J.; Cartwright, A. N.; McCombe, B. D.

2010-11-01

229

Cadmium telluride (CdTe) and cadmium selenide (CdSe) leaching behavior and surface chemistry in response to pH and O2.  

PubMed

Cadmium telluride (CdTe) and cadmium selenide (CdSe) are increasingly being applied in photovoltaic solar cells and electronic components. A major concern is the public health and ecological risks associated with the potential release of toxic cadmium, tellurium, and/or selenium species. In this study, different tests were applied to investigate the leaching behavior of CdTe and CdSe in solutions simulating landfill leachate. CdTe showed a comparatively high leaching potential. In the Toxicity Characteristic Leaching Procedure (TCLP) and Waste Extraction Test (WET), the concentrations of cadmium released from CdTe were about 1500 and 260 times higher than the regulatory limit (1 mg/L). In contrast, CdSe was relatively stable and dissolved selenium in both leaching tests was below the regulatory limit (1 mg/L). Nonetheless, the regulatory limit for cadmium was exceeded by 5- to 6- fold in both tests. Experiments performed under different pH and redox conditions confirmed a marked enhancement in CdTe and CdSe dissolution both at acidic pH and under aerobic conditions. These findings are in agreement with thermodynamic predictions. Taken as a whole, the results indicate that recycling of decommissioned CdTe-containing devices is desirable to prevent the potential environmental release of toxic cadmium and tellurium in municipal landfills. PMID:25710599

Zeng, Chao; Ramos-Ruiz, Adriana; Field, Jim A; Sierra-Alvarez, Reyes

2015-05-01

230

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

PubMed

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

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

2013-03-13

231

Syntheses, crystal structures and characterizations of BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}  

SciTech Connect

Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by the solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with three ZnO{sub 3}Cl tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements. -- Graphical abstract: Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features 1D double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The 1D double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with one ZnO{sub 3}Cl and two ZnO{sub 2}Cl{sub 2} tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements.

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

2006-06-15

232

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

SciTech Connect

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

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

2012-08-10

233

Electrically Tunable In-Plane Anisotropic Magnetoresistance in Topological Insulator BiSbTeSe2 Nanodevices.  

PubMed

We report tunable in-plane anisotropic magnetoresistance (AMR) in nanodevices based on topological insulator BiSbTeSe2 (BSTS) nanoflakes by electric gating. The AMR can be changed continuously from negative to positive when the Fermi level is manipulated to cross the Dirac point by an applied gate electric field. We also discuss effects of the gate electric field, current density, and magnetic field on the in-plane AMR with a simple physical model, which is based on the in-plane magnetic field induced shift of the spin-momentum locked topological two surface states that are coupled through side surfaces and bulk weak antilocalization (WAL). The large, tunable and bipolar in-plane AMR in BSTS devices provides the possibility of fabricating more sensitive logic and magnetic random access memory AMR devices. PMID:25665017

Sulaev, Azat; Zeng, Minggang; Shen, Shun-Qing; Cho, Soon Khuen; Zhu, Wei Guang; Feng, Yuan Ping; Eremeev, Sergey V; Kawazoe, Yoshiyuki; Shen, Lei; Wang, Lan

2015-03-11

234

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

235

Size- effect induced high thermoelectric figure of merit in PbSe and PbTe nanowires.  

PubMed

The fundamental properties that compose the thermoelectric figure of merit are investigated in the confined systems of PbSe and PbTe nanowires, with the goal to improve the thermoelectric efficiency. Using the Landauer electronic transport theory, we verify that the figure of merit can be several times larger than the bulk value for nanowires with diameters down to the one nanometer scale. This enhancement in the thermoelectric efficiency is primarily due to the reduction of the thermal conductivity and an increase in the power factor. The origin of these desireable properties, that enable the transformation of heat into electricity, comes from the confinement effect which increases the density of states around the Fermi level, either for an n- or p-type system. PMID:24654001

Wrasse, Ernesto O; Torres, Alberto; Baierle, Rogério J; Fazzio, Adalberto; Schmidt, Tome M

2014-05-01

236

In-Situ Optical Determination of Thermomechanical Properties of ZnSe and ZnTe Crystals  

NASA Technical Reports Server (NTRS)

At temperatures above 1/2 T(sub m), the generation and movement of dislocations may result due to the load created by the weight of the crystal itself The deformation may be expected to increase the line defect density and may result in generation of low angle grain boundaries, especially in the regions of the crystal attached to the ampule. It has often been suspected that elimination of this effect in space can improve crystallinity of crystals grown under microgravity conditions, however, a direct experimental proof of such relation is still missing. In this work we have designed and built a system of in-situ optical detection and measurement of the mechanical deformations of a crystal wafer under its own weight, and studied the deformation effects as a function of temperature. The results of the measurements for ZnSe and ZnTe crystal wafers will be presented.

Burger, A.; Ndap, J.-O.; Chattopadhyay, K.; Ma, X.; Silberman, E.; Feth, S.; Palosz, W.; Su, C.-H.

1999-01-01

237

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

NASA Astrophysics Data System (ADS)

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

Elyukhin, V. A.

2013-10-01

238

Laser operation by dissociation of metal complexes. II - New transitions in Cd, Fe, Ni, Se, Sn, Te, V, and Zn  

NASA Technical Reports Server (NTRS)

The reported investigation is a continuation of a study conducted by Chou and Cool (1976). The experimental results discussed are partly related to laser transitions in Cd(I), Cd(II), and Zn(II). Laser transitions in Fe(I), Ni(I), Sn(I), Te(I), and V(I) are also considered along with the observation of a laser pulse with two peaks in connection with the study of laser transitions in Se(I). Experiments related to prospective visible laser operation in thallium at 6550 and 6714 are also discussed, giving attention to spontaneous emission measurements at 6550 and 5350 A, the effects of additive molecules, and laser cavity experiments at 6550 and 6714 A.

Chou, M. S.; Cool, T. A.

1977-01-01

239

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

PubMed

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

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

2014-02-26

240

Hidden in-plane anisotropy of interfaces in Zn(Mn)Se /BeTe quantum wells with a type-II band alignment.  

PubMed

Circularly and linearly polarized radiation due to spatially indirect optical transitions is studied in semimagnetic (Zn,Mn)Se/BeTe and nonmagnetic ZnSe/BeTe quantum-well structures with a type-II band alignment. Because of the giant in-plane anisotropy of the optical matrix elements related to a particular interface, complete spin orientation of photocarriers induced by magnetic fields leads not to purely circular but instead to elliptical polarization of the luminescence. From comparison between theory and experiment the parameter of optical anisotropy of a ZnSe/BeTe interface is evaluated. The developed theoretical approach can be applied for the large class of nanostructures revealing optical anisotropy. PMID:12097127

Yakovlev, D R; Platonov, A V; Ivchenko, E L; Kochereshko, V P; Sas, C; Ossau, W; Hansen, L; Waag, A; Landwehr, G; Molenkamp, L W

2002-06-24

241

First-Principles Study of Topological Insulators A2B3 (A = Bi and Sb, and B = O, S, Se, and Te)  

NASA Astrophysics Data System (ADS)

We investigate the electronic states of rhombohedral A2B3 using first-principles calculations, where A = Bi and Sb, and B = O, S, Se, and Te. The topological states of insulators are predicted from Z2 topological invariants. We reveal topological phase diagrams of Bi2Te3 and Bi2Se3 in the space of the internal parameters. We find topological phase transitions in Bi2Te3 and Bi2Se3. The isostructural hypothetical materials A2B3 (where A = Bi and Sb and B = S and O) are also investigated. We find that non-trivial topological phases are realized in Bi2S3 due to the lattice strain.

Kato, Takehiro; Kotaka, Hiroki; Ishii, Fumiyuki

242

Y{sub 2}MoSe{sub 3}O{sub 12} and Y{sub 2}MoTe{sub 3}O{sub 12}: Solid-state synthesis, structure determination, and characterization of two new quaternary mixed metal oxides containing asymmetric coordination environment  

SciTech Connect

Two new quaternary yttrium molybdenum selenium/tellurium oxides, Y{sub 2}MoSe{sub 3}O{sub 12} and Y{sub 2}MoTe{sub 3}O{sub 12} have been prepared by standard solid-state reactions using Y{sub 2}O{sub 3}, MoO{sub 3}, and SeO{sub 2} (or TeO{sub 2}) as reagents. Single-crystal X-ray diffraction was used to determine the crystal structures of the reported materials. Although both of the materials contain second-order Jahn–Teller (SOJT) distortive cations and are stoichiometrically similar, they reveal different structural features: while Y{sub 2}MoSe{sub 3}O{sub 12} shows a three-dimensional framework consisting of YO{sub 8}, MoO{sub 6}, and SeO{sub 3} groups, Y{sub 2}MoTe{sub 3}O{sub 12} exhibits a layered structure composed of YO{sub 8}, MoO{sub 4}, TeO{sub 3}, and TeO{sub 4} polyhedra. With the Mo{sup 6+} cations in Y{sub 2}MoSe{sub 3}O{sub 12}, a C{sub 3}-type intraoctahedral distortion toward a face is observed, in which the direction of the out-of-center distortion for Mo{sup 6+} is away from the oxide ligand linked to a Se{sup 4+} cation. The Se{sup 4+} and Te{sup 4+} cations in both materials are in asymmetric coordination environment attributed to the lone pairs. Elemental analyses, infrared spectroscopy, thermal analyses, intraoctahedral distortions, and dipole moment calculations for the compounds are also presented. - Graphical abstract: Y{sub 2}MoSe{sub 3}O{sub 12} reveals a three-dimensional framework consisting of YO{sub 8}, MoO{sub 6}, and SeO{sub 3} polyhedra, whereas Y{sub 2}MoTe{sub 3}O{sub 12} exhibits a layered structure composed of YO{sub 8}, MoO{sub 4}, TeO{sub 3}, and TeO{sub 4} groups. - Highlights: • Two new selenite and tellurite (Y{sub 2}MoQ{sub 3}O{sub 12}; Q=Se and Te) are synthesized. • Y{sub 2}MoQ{sub 3}O{sub 12} contain second-order Jahn–Teller distortive cations in asymmetric environments. • The intra-octahedral distortion of the Mo{sup 6+} is influenced by the Se{sup 4+}.

Bang, Seong-eun; Pan, Zhi; Kim, Yeong Hun; Lee, Dong Woo; Ok, Kang Min, E-mail: kmok@cau.ac.kr

2013-12-15

243

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

244

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

245

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

246

Pressure effect on the superconductivity and the charge-density waves in Nb 3X 4 with X?S, Se, and Te  

NASA Astrophysics Data System (ADS)

The pressure effect on the superconductivity and the CDW formation in Nb 3X 4 has been studied up to 1.1 GPa by a resistive measurement. In both Nb 3S 4 and Nb 3Se 4, the superconducting-transition temperature TC decreases with increasing pressure. Pressure-induced-lattice stiffening mainly causes the decrease of TC in these compounds. The TC of Nb 3Te 4 increases with pressure. The pressure enhancement of TC is mainly due to the increase of N(0) by the recovery of the density of states N(0) associated with the depression of the CDWs. The magnitude of the resistivity anomalies at 90 and 30 K at atmospheric pressure is suppressed under pressure. The CDW-transition temperature TCDW at 90 K hardly changes with pressure. The TCDW at 30 K decreases with increasing pressure. The pressure effect on both CDW-transition temperatures is discussed in terms of both lattice stiffening and collapse of the nesting of the Fermi surfaces.

Taniguti, Hiromi; Kuga, Masanori; Okamoto, Hiroyuki; Kaneko, Hiroshi; Ishihara, Yutaka

2000-08-01

247

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

248

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

250

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

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

2015-01-01

251

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

252

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

253

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

SciTech Connect

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

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

2008-06-15

254

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

255

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

NASA Astrophysics Data System (ADS)

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

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

1994-06-01

256

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

E-print Network

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

Talwar, Devki N.

257

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

258

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

259

Synthesis of terminal monochalcogenide and dichalcogenide complexes of uranium using polychalcogenides, [E(n)]²? (E = Te, n = 2; E = Se, n = 4), as chalcogen atom transfer reagents.  

PubMed

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

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

2014-10-01

260

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

261

X-ray absorption spectroscopy study of diluted magnetic semiconductors: Zn1xMxSe ,,MMn, Fe, Co... and Zn1xMnxY ,,YSe, Te...  

E-print Network

hybridization between the transition metal 3d and the ligand p orbitals. In the study of Zn1 xMnxY (Y Se,Te , we of late 3d magnetic transition-metal TM at- oms such as Mn, Fe, and Co ions into cation sites in the II

Oh, Se-Jung

262

Tuning the quantum oscillations of surface Dirac electrons in the topological insulator Bi2Te2Se by liquid gating  

NASA Astrophysics Data System (ADS)

In Bi2Te2Se, the period of quantum oscillations arising from surface Dirac fermions can be increased sixfold using ionic liquid gating. At high gate voltages, the Fermi energy reaches the N=1 Landau level in a 14-T field. This enables the (1)/(2) shift predicted for the Dirac spectrum to be measured accurately. A surprising result is that liquid gating strongly enhances the surface mobility. By analyzing the Hall conductivity, we show that the enhancement occurs on only one surface. We present evidence that the gating process is fully reversible (hence consistent with band bending by the E field from the anion layer accumulated). In addition to the surface carriers, the experiment yields the mobility and density of the bulk carriers in the impurity band. By analyzing the charge accumulation vs gate voltage, we also obtain estimates of the depletion width and the areal depletion capacitance Cd/A. The value of Cd/A implies an enhanced electronic polarizability in the depletion region.

Xiong, Jun; Khoo, Yuehaw; Jia, Shuang; Cava, R. J.; Ong, N. P.

2013-07-01

263

Investigations of the electrical properties in CuInSe2 and the related ordered vacancy compounds  

NASA Astrophysics Data System (ADS)

The conductivity mechanisms in polycrystalline CuInSe2 and the ordered vacancy compounds CuIn3Se5, CuIn5Se8 and CuIn7Se12 were studied by low temperature conductivity measurements and room temperature Hall and photoconductivity measurements. The polycrystalline films were structurally, morphologically and compositionally characterized using x-ray diffraction, atomic force microscopy and energy dispersive analysis by x-rays, respectively. In general, the films showed Mott's variable range hopping conduction in the temperature range below 200 K while above 200 K thermally activated conductivity due to grain boundary effects and defect levels was observed. To investigate the reason for the metallic behaviour shown by Cu-rich films, the films were etched and the change in behaviour was studied.

Reena Philip, Rachel; Pradeep, B.; Okram, G. S.; Ganesan, V.

2004-07-01

264

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

NASA Technical Reports Server (NTRS)

Interest in optical devices which can operate in the visible spectrum has motivated research interest in the II-VI wide band gap semiconductor materials. The recent challenge for semiconductor opto-electronics is the development of a laser which can operate at short visible wavelengths. In the past several years, major advances in thin film technology such as molecular beam epitaxy and metal organic chemical vapor deposition have demonstrated the applicability of II-VI materials to important devices such as light-emitting diodes, lasers, and ultraviolet detectors. With an energy gap of 2.7 eV at room temperature, and an efficient band- to-band transition, ZnSe has been studied extensively as the primary candidate for a blue light emitting diode for optical displays, high density recording, and military communications. By employing a ternary or quaternary system, the energy band gap of II-VI materials can be tuned to a specific range. While issues related to the compositional inhomogeneity and defect incorporation are still to be fully resolved, ZnSe bulk crystals and ZnSe-based heterostructures such as ZnSe/ZnSeS, ZnSe/ZnCdSe and ZnCdSe/ZnSeS have showed photopumped lasing capability in the blue-green region at a low threshold power and high temperatures. The demonstration of its optical bistable properties in bulk and thin film forms also make ZnSe a possible candidate material for the building blocks of a digital optical computer. Despite this, developments in the crystal growth of bulk H-VI semiconductor materials has not advanced far enough to provide the low price, high quality substrates needed for the thin film growth technology.

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

2000-01-01

265

Synthesis and characterization of eight compounds of the MU8Q17 family: ScU8S17, CoU8S17, NiU8S17, TiU8Se17, VU8Se17, CrU8Se17, CoU8Se17, and NiU8Se17.  

PubMed

The solid-state MU8Q17 compounds ScU8S17, CoU8S17, NiU8S17, TiU8Se17, VU8Se17, CrU8Se17, CoU8Se17, and NiU8Se17 were synthesized from the reactions of the elements at 1173 or 1123 K. These isostructural compounds crystallize in space group C2h3 - C2/m of the monoclinic system in the CrU8S17 structure type. X-ray absorption near-edge structure spectroscopic studies of ScU8S17 indicate that it contains Sc3+, and hence charge balance is achieved with a composition that includes U3+ as well as U4+. The other compounds charge balance with M2+ and U4+. Magnetic susceptibility measurements on ScU8S17 indicate antiferromagnetic couplings and a highly reduced effective magnetic moment. Ab Initio calculations find the compound to be metallic. Surprisingly, the Sc–S distances are actually longer than all the other M–S interactions, even though the ionic radii of Sc3+, low-spin Cr2+, and Ni2+ are similar. PMID:24932673

Ward, Matthew D; Mesbah, Adel; Minasian, Stefan G; Shuh, David K; Tyliszczak, Tolek; Lee, Minseong; Choi, Eun Sang; Lebègue, Sébastien; Ibers, James A

2014-07-01

266

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

267

Electron tunneling effects on radiative recombination in modulation n-doped ZnSe/BeTe type-II quantum wells  

NASA Astrophysics Data System (ADS)

We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells. It is shown that only the doped sample shows electron cyclotron-resonance absorption. Also, the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra, and the doped one shows only one peak. The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other. The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field, and can cancel out a built-in electric field as observed in the undoped structures.

Ji, Zi-Wu; Zheng, Yu-Jun; Xu, Xian-Gang

2010-11-01

268

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 (P 3 bar m1, 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

269

Low Pressure Chemical Vapour Deposition of Crystalline Ga2Te3 and Ga2Se3 Thin Films from Single Source Precursors Using Telluroether and Selenoether Complexes  

NASA Astrophysics Data System (ADS)

Neutral telluro- and seleno-ether complexes of the form [GaCl3(nBu2E)] (E = Se, Te) and [(GaCl3)2{nBuE(CH2)nEnBu}] (E = Se, n = 2; E = Te, n = 3) have been synthesised via a facile, high yielding reaction. These complexes have been shown to be suitable precursors for the low pressure chemical vapour deposition of Ga2Te3 and Ga2Se3, the first reported example of a telluroether complex being used for the deposition of a metal telluride. The thin films have been characterised by X- ray diffraction, SEM, EDX, Raman and Hall measurements. The films are crystalline, have good, uniform coverage and Raman spectra match literature values. Hall measurements show that the thin films are p-type semiconductors. Competitive deposition of Ga2Te3 onto photolithographically patterned SiO2/TiN substrates shows a preference for deposition onto TiN.

George, Kathryn; Groot, C. H. (Kees) de; Gurnani, Chitra; Hector, Andrew L.; Huang, Ruomeng; Jura, Marek; Levason, William; Reid, Gillian

270

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

Microsoft Academic Search

The IIa–III2–VI4 (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., SrIn2VI4 (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

T. Takizawa; M. Kubo; C. Hidaka

2005-01-01

271

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

272

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

273

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

SciTech Connect

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

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

1994-03-01

274

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

275

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

NASA Astrophysics Data System (ADS)

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

Bagheri, Mehran

2010-07-01

276

Ordered Vacancy Compounds and Nanotube Formation in CuInSe2-CdS  

E-print Network

with chemical bath deposition (CBD) even at 60 °C. For the first time, an OVC was directly observed at the CIS-CdS be epitaxially deposited onto the CuInSe2 nanowire with chemical bath deposition even at 60 °C. For the first be transformed into nanotubes with chemical bath deposition progression through a nanoscale Kirkendall effect

Cui, Yi

277

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

SciTech Connect

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

Nguyen, Manh; Zhao, Xin; Wang, Cai-Zhuang; Ho, Cai-Ming

2013-10-18

278

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

279

The role of stoichiometric vacancy periodicity in pressure-induced amorphization of the Ga{sub 2}SeTe{sub 2} semiconductor alloy  

SciTech Connect

We observe that pressure-induced amorphization of Ga{sub 2}SeTe{sub 2} (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 Ga{sub 2}SeTe{sub 2} 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. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Kalkan, B.; MacDowell, A. A. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Huang, G.-Y. [Department of Nuclear Engineering, University of Tennessee, Knoxville, Tennessee 37996 (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)

2014-08-04

280

Interface excitons in a type-II ZnSe/ZnTe heterojunction under hydrostatic pressure: the triangle potential well approximation  

NASA Astrophysics Data System (ADS)

Taking into consideration the band bending near the interface and the electron LO phonon interaction, the ground-state binding energies of interface heavy-hole excitons in ZnSe/ZnTe type-II heterojunctions under the influence of hydrostatic pressure are calculated using a variational method. The heterojunction is approximated as a quantum well with finite triangle confining potentials for both electrons and holes. The subband energies and wavefunctions of the electrons and heavy holes are obtained with the help of the asymptotic transfer method. The results show that the effect of the electron (hole) LO phonon interaction on the exciton binding energy is not neglected for the ZnSe/ZnTe type-II heterojunctions. The pressure-induced increase of the exciton binding energy is obvious and the increase is mainly through the pressure influence on the electron effective masses.

Guo, Z. Z.; Liang, X. X.; Ban, S. L.

2006-02-01

281

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

282

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

283

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

NASA Astrophysics Data System (ADS)

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

Xie, Guo-Ya; Liu, Xian-Rong

2013-10-01

284

Theoretical Investigations of the EPR Parameters of Cubic Yb3+ Center in PbS, PbSe and PbTe Semiconductors  

NASA Astrophysics Data System (ADS)

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

Xie, Guo-Ya; Liu, Xian-Rong

2013-06-01

285

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

286

1.9- m and 2.0- m laser diode pumping of Cr(2+) :ZnSe and Cr(2+) :CdMnTe.  

PubMed

Efficient diode pumping at wavelengths of 1.9 and 2.0microm of a Cr(2+): ZnSe laser with an output power of 105 mW and a slope efficiency of 35% with respect to the absorbed pump power is presented. In addition, Cr(2+): CdMnTe has been laser diode pumped as well as operated in the continuous-wave regime, to the best of our knowledge for the first time. PMID:18026356

Mond, M; Albrecht, D; Heumann, E; Huber, G; Kück, S; Levchenko, V I; Yakimovich, V N; Shcherbitsky, V G; Kisel, V E; Kuleshov, N V; Rattunde, M; Schmitz, J; Kiefer, R; Wagner, J

2002-06-15

287

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

288

Ab initio study of electronic structure and magnetic properties in ferromagnetic Be1-xMnxSe and Be1-xMnxTe alloys  

NASA Astrophysics Data System (ADS)

Structural, electronic and magnetic properties of Mn-doped BeSe and BeTe have been studied by employing the full-potential linear augmented plane waves plus local orbitals (FP-LAPW+lo) method within the spin-polarized density functional theory (DFT). The investigations are carried out by varying the Mn concentration, "x", in BeSe and BeTe host matrices for x=0.25, 0.5 and 0.75. The results of spin-polarized calculations manifest the presence of ferromagnetic band structures with both spin-up and spin-down alignments. Our calculated results of band structures reveal that for x=0.25, 0.5 and 0.75, Be1-xMnxSe has a half-metallic (HM) band structure profile showing 100% spin polarization at the Fermi level. On the other hand, the Be1-xMnxTe band structure shows complete 100% spin polarization at the Fermi level only for x=0.25 and 0.5. Spin-dependent charge densities have been calculated to study the bonding nature, and the values of the exchange constants, N0? and N0?, are also determined which are consistent with the values from the typical magneto-optical experiment. In addition, the calculations of spin exchange splitting, ?X(d), exhibit important indication regarding the attractive effective potential for minority spin rather than majority spin. For each concentration x, the value of total magnetic moment has been estimated to be 5?B, which reveals that addition of Mn impurity does not affect the hole concentration of a perfect BeSe (Te) crystal.

Noor, N. A.; Alay-e-Abbas, S. M.; Saeed, Y.; Ghulam Abbas, S. M.; Shaukat, A.

2013-08-01

289

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.

Díaz, R.

2012-06-01

290

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

291

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

292

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

293

Interface driven energy filtering of thermoelectric power in spark plasma sintered Bi(2)Te(2.7)Se(0.3) nanoplatelet composites.  

PubMed

Control of competing parameters such as thermoelectric (TE) power and electrical and thermal conductivities is essential for the high performance of thermoelectric materials. Bulk-nanocomposite materials have shown a promising improvement in the TE performance due to poor thermal conductivity and charge carrier filtering by interfaces and grain boundaries. Consequently, it has become pressingly important to understand the formation mechanisms, stability of interfaces and grain boundaries along with subsequent effects on the physical properties. We report here the effects of the thermodynamic environment during spark plasma sintering (SPS) on the TE performance of bulk-nanocomposites of chemically synthesized Bi(2)Te(2.7)Se(0.3) nanoplatelets. Four pellets of nanoplatelets powder synthesized in the same batch have been made by SPS at different temperatures of 230, 250, 280, and 350 °C. The X-ray diffraction, transmission electron microscopy, thermoelectric, and thermal transport measurements illustrate that the pellet sintered at 250 °C shows a minimum grain growth and an optimal number of interfaces for efficient TE figure of merit, ZT?0.55. For the high temperature (350 °C) pelletized nanoplatelet composites, the concurrent rise in electrical and thermal conductivities with a deleterious decrease in thermoelectric power have been observed, which results because of the grain growth and rearrangements of the interfaces and grain boundaries. Cross section electron microscopy investigations indeed show significant grain growth. Our study highlights an optimized temperature range for the pelletization of the nanoplatelet composites for TE applications. The results provide a subtle understanding of the grain growth mechanism and the filtering of low energy electrons and phonons with thermoelectric interfaces. PMID:22823516

Soni, Ajay; Shen, Yiqiang; Yin, Ming; Zhao, Yanyuan; Yu, Ligen; Hu, Xiao; Dong, Zhili; Khor, Khiam Aik; Dresselhaus, Mildred S; Xiong, Qihua

2012-08-01

294

Homo- and heterovalent substitutions in the new clathrates I Si30P16Te(8-x)Se(x) and Si(30+x)P(16-x)Te(8-x)Br(x): synthesis, crystal structure, and thermoelectric properties.  

PubMed

The new cationic clathrates I Si(30)P(16)Te(8-x)Se(x) and Si(30+x)P(16-x)Te(8-x)Br(x) were synthesized by the standard ampule technique. The Si(30)P(16)Te(8-x)Se(x) (x = 0-2.3) clathrates crystallize in the cubic space group Pm3?n with the unit cell parameter a ranging from 9.9382(2) to 9.9696(1) Å. In the case of the Si(30+x)P(16-x)Te(8-x)Br(x) (x = 1-6.4) clathrates, the lattice parameter varies from 9.9720(8) to 10.0405(1) Å; at lower Si/P ratios (x = 1-3) the ordering of bromine atoms induces the splitting of the guest positions and causes the transformation from the space group Pm3n to Pm3. Irrespective of the structure peculiarities, the normal temperature motion of the guest atoms inside the oversized cages of the framework is observed. The title clathrates possess very low thermal expansion coefficients ranging from 6.6 × 10(-6) to 1.0 × 10(-5) K(-1) in the temperature range of 298-1100 K. The characteristic Debye temperature is about 490 K. Measurements of the electrical resistivity and thermopower showed typical behavior of p-type thermally activated semiconductors, whereas the temperature behavior of the thermal conductivity is glasslike and in general consistent with the PGEC concept. The highest value of the thermoelectric figure of merit (ZT = 0.1) was achieved for the Br-bearing clathrate Si(32.1(2))P(13.9(2))Te(6.6(2))Br(1.0(1)) at 750 K. PMID:23072375

Abramchuk, Nikolay S; Carrillo-Cabrera, Wilder; Veremchuk, Igor; Oeschler, Niels; Olenev, Andrei V; Prots, Yurii; Burkhardt, Ulrich; Dikarev, Evgeny V; Grin, Juri; Shevelkov, Andrei V

2012-11-01

295

Syntheses, Vibrational Spectra, and Theoretical Studies of the Adamantanoid Sn(4)Ch(10)(4-) (Ch= Se, Te) Anions: X-ray Crystal Structures of[18-crown-6-K](4)[Sn4Se10]?5en and[18-crown-6-K](4)[Sn4Te10]?3en?2THF  

SciTech Connect

The salts[18-crown-6-K]4[Sn4Se10]?5en and[18-crown-6-K]4[Sn4Te10]?5en?2THF were isolated by extracting the alloys KSn0.90Se1.93 and K4Sn4Te10 in ethylenediamine (en) in the presence of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane). The Sn4Te104- anion has been structurally characterized for the first time by a single-crystal X-ray diffraction study of[18-crown-6-K]4[Sn4Te10]?5en?2THF: P21/n, a= 22.420(5)?, b= 19.570(4)?, c= 24.680(5)?,?= 96.90(3)o, V= 10750.2(37)?3, Z= 4 and R1= 0.0468 at -183 C and, in addition to Si4Te104- and Ge4Te104-, represents the only other known group 14 adamantanoid telluride. The crystal structure determination of the related[18-crown-6-K]4[Sn4Se10]?5en salt has also been determined: P21/n, a= 22.003(2)?, b= 18.966(2)?, c= 24.393(2)?,?= 97.548(8)o, V= 10091.0(17)?3, Z= 4 and R1= 0.0843 at -123 C. The anion geometries are of the adamantanoid type where the SnIV atoms occupy the bridgehead positions and the chalcogen atoms occupy the bridging and terminal sites. The energy minimized geometries of Sn4Ch104- have also been determined using density functional theory (DFT). Mayer bond order analyses, Mayer valencies and empirical bond valencies reveal that the terminal Sn-Ch bonds have significant multiple bond character, with the terminal Sn-Se bond having more multiple bond character than Sn-Te. The vibrational frequencies of the Sn4Se104- and Sn4Te104- anions have been calculated using DFT methods, allowing the Raman spectrum of Sn4Se104- to be fully assigned.

Pirani, A M. (McMaster University); Mercier, Helene P.A. (McMaster University); Dixon, David A. (BATTELLE (PACIFIC NW LAB)); Borrmann, Horst (Max-Planck-Institut fur Festkorperforschung); Schrobilgen, Gary J. (McMaster University)

2000-12-01

296

Urbach-Martienssen's tail in the absorption spectra of the ordered vacancy compound CuIn3Se5  

NASA Astrophysics Data System (ADS)

The presence of Urbach-Martienssen's tail in the absorption coefficient spectra just below the fundamental absorption edge is observed in several samples of the ordered vacancy compound CuIn3Se5 at different temperatures below 300 K. An empirical relation that takes into account the effect of structural disorder and modification in the contribution of the thermal term, caused due to the deviation from the ideal stoichiometry 1:3:5, is proposed to explain the change of Urbach's energy KT/? with temperature. The phonon energy involved in the electron-phonon interaction, in the absence of structural disorder, is estimated to be around 23 meV.

Wasim, S. M.; Marín, G.; Rincón, C.; Sánchez Pérez, G.

1998-11-01

297

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

298

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

299

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

300

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 400°C for more than 1?hour. Superconductivity was witnessed to evolve mainly from the edge of the crystal to the central part. After the optimal annealing, the complete removal of excess Fe was demonstrated via STM measurements. Some fundamental properties were recharacterized and compared with those of as-grown crystals to discuss the influence of excess Fe. PMID:24695095

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

2014-01-01

301

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

NASA Astrophysics Data System (ADS)

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

2014-06-01

302

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

303

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

SciTech Connect

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

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

2012-01-01

304

Thermoelectric properties of p-type Bi0.5Sb1.5Te2.7Se0.3 fabricated by high pressure sintering method  

NASA Astrophysics Data System (ADS)

Bi0.5Sb1.5Te2.7Se0.3 doped with 4 wt. % Te was prepared by high pressure (1.89-5.98 GPa) sintering (HPS) method. The phase composition, crystal structure and morphology were analyzed by x-ray diffraction method and scanning electron microscopy. The dependences of thermoelectric properties and microstructures of the samples on high pressure and temperature were studied. The results show that high pressure sintering has a great effect on the crystal structure and the thermoelectric properties of the samples. The HPS can decrease the thermal conductivity by nanostructure and increase the figure of merit. The ZTmax is 1.16. It deserves our special attention that this nanostructure has good stability at high temperature. Besides, the conditions for the Seebeck coefficient is equal to zero or it increases with the electric conductivity synchronously were discussed.

Xu, Gui-Ying; Niu, Si-Tong; Wu, Xiao-Feng

2012-10-01

305

Chemical and Structural Evolution in the Th-SeO3(2-)/SeO4(2-) System: from Simple Selenites to Cluster-Based Selenate Compounds.  

PubMed

While extensive success has been gained in the structural chemistry of the U-Se system, the synthesis and characterization of Th-based Se structures are widely unexplored. Here, four new Th-Se compounds, ?-Th(SeO3)2, ?-Th(SeO3)2, Th(Se2O5)2, and Th3O2(OH)2(SeO4)3, have been obtained from mild hydrothermal or low-temperature (180-220 °C) flux conditions and were subsequently structurally and spectroscopically characterized. The crystal structures of ?-Th(SeO3)2 and ?-Th(SeO3)2 are based on ThO8 and SeO3 polyhedra, respectively, featuring a three-dimensional (3D) network with selenite anions filling in the Th channels along the a axis. Th(Se2O5)2 is a 3D framework composed of isolated ThO8 polyhedra interconnected by [Se2O5](2-) dimers. Th3O2(OH)2(SeO4)3 is also a 3D framework constructed by octahedral hexathorium clusters [Th6(?3-O)4(?3-OH)4](12+), which are interlinked by selenate groups SeO4(2-). The positions of the vibrational modes associated with both Se(IV)O3(2-) and Se(VI)O4(2-) units, respectively, were determined for four compounds, and the Raman spectra of ?- and ?-Th(SeO3)2 are compared and discussed in detail. PMID:25719971

Xiao, Bin; Langer, Eike; Dellen, Jakob; Schlenz, Hartmut; Bosbach, Dirk; Suleimanov, Evgeny V; Alekseev, Evgeny V

2015-03-16

306

Analysis of heavily tailed size distributions of ZnTe/ZnSe quantum dot structures by using the bootstrap methodology  

NASA Astrophysics Data System (ADS)

We have used the bootstrap methodology to analyze dot size distributions of ZnTe quantum dot (QD) structures. The photoluminescence (PL) spectrum indicates that the ZnTe QD structure belongs to a type-II band alignment. The broadness with small fluctuations in the PL represents the spatial inhomogeneity of the QD sizes. The Schrodinger equation together with the first-order perturbation correction was numerically solved to correlate the dot size and the photon energy. Using the bootstrap "loess" curve fitting method, the PL spectrum was determined to be a normal distribution with a high significance level of 46% tested by a null hypothesis H0. By examining the slope of the complementary cumulative distribution function, we found that the size distribution is heavy tailed.

Lee, Johnson; Chou, W. C.; Jan, G. J.

2002-09-01

307

Electronic correlations and unusual superconducting response in the optical properties of the iron chalcogenide FeTe0.55Se0.45  

E-print Network

.55Se0.45 have been determined above and below the critical temperature Tc=14 K. At room temperatureElectronic correlations and unusual superconducting response in the optical properties of the iron of superconductivity in the iron- arsenic LaFeAsO1-xFx 1111 pnictide compound has prompted an intense investigation

Johnson, Peter D.

308

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

NASA Astrophysics Data System (ADS)

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

Chang, Jiwon

2015-04-01

309

Pressure induced phase transition (B1–B2) and elastic properties in alkaline earth BaX (X?=?S, Se and Te) chalcogenides  

Microsoft Academic Search

Pressure induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in alkaline-earth-chalcogenides (BaX; X?=?S, Se and Te) are presented. An effective interionic interaction potential (EIoIP) with long-range Coulomb and three-body interactions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbour ions and the van der Waals (vdW) interaction is developed. Emphasis has been given

Dinesh Varshney; N. Kaurav; R. Kinge; R. K. Singh

2008-01-01

310

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

311

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

312

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

313

Development of a computer model for polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells. Annual subcontract report, 1 January 1990--31 December 1990  

SciTech Connect

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

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

1992-04-01

314

Reinvestigation of the influence of Se impurity on the structural and thermoelectric properties of AgSbTe2  

NASA Astrophysics Data System (ADS)

The samples with the nominal composition of AgSbTe2-xSex (x = 0.0? 0.1) were prepared. The structural properties were investigated by X-ray diffraction and SEM microscopy. The electrical conductivity, thermal conductivity and Seebeck coefficient have been measured within the temperature range from 300 to 675K. Heat capacity and phase transitions were studied by DSC method. We have confirmed that prolonged annealing leads to decomposition of materials and degradation of their thermoelectric properties.

Schmidt, M.; Wojciechowski, K. T.

2012-06-01

315

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

316

Impact of In Situ Generated Ag2Te Nanoparticles on the Microstructure and Thermoelectric Properties of AgSbTe2 Compounds  

NASA Astrophysics Data System (ADS)

A series of ternary (Ag2Te) x (Sb2Te3)100- x ( x = 44 to 54) bulk materials with in situ generated Ag2Te nanoparticles were prepared from high-purity elements by combining the melt-quench technique with the spark plasma sintering technique. The influence of the Ag2Te nanoparticles on the thermoelectric transport properties, and the mechanism of nanoparticle formation were investigated. With increasing x, the concentration of the Ag2Te nanoparticles increased monotonically, but their diameter remained nearly unchanged. Due to the possible carrier energy filtering effect caused by the Ag2Te nanoparticle inclusions, the Seebeck coefficient of the sample with x = 50 was two times higher than that of the sample prepared by the melting method. Moreover, notable scattering of mid-to-long wavelength phonons arising from the evenly distributed Ag2Te nanoparticles led to a large reduction of the lattice thermal conductivity. All these effects led to the enhancement of the ZT value of the x = 50 sample (AgSbTe2) compared with the single-phase sample ( x = 44).

Du, B.; Xu, J.; Zhang, W.; Tang, X.

2011-05-01

317

Photosensitivity of thin-film structures based on CuIn3Se5 and CuIn5Se8 ternary semiconductor compounds  

NASA Astrophysics Data System (ADS)

Polycrystalline n-type CuIn3Se5 and CuIn5Se8 films with thicknesses from 0.4 to 1 ?m have been grown by pulsed laser ablation of bulk p-CuIn3Se5 and n-CuIn5Se8 crystals in vacuum. The temperature dependences of the resistivities of these crystals are determined by deep donor levels with energies E D ? 0.2 0.3 eV. Photosensitive thin-film structures based on these films have been created for the first time and their photosensitivity spectra have been measured. The possibility of using thin CuIn3Se5 and CuIn5Se8 films in broadband photoconverters is demonstrated.

Bodnar', I. V.; Gremenok, V. F.; Nikolaev, Yu. A.; Rud', V. Yu.; Rud', Yu. V.; Terukov, E. I.

2007-02-01

318

Heterostructures based on the CuIn3Se5, CuGa3Se5, CuGa5Se8, CuGa3Te5 and CuGa5Te8 ternary compounds  

NASA Astrophysics Data System (ADS)

AIBIII2n+1CVI3n+2 single crystals were prepared by directional solidification of the stoichiometric melt. We have created new photosensitive surface-barrier structures. The photovoltaic effect of these structures have been investigated. We conclude that the new class photosensitive structures can be utilized as photoconvertors of an optical radiation.

Bodnar, Ivan; Victorov, Ivan; Leon, Maximo; Bairamov, Bakhish; Rud, Vasilii; Rud, Yury

2006-09-01

319

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

320

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 Gómez, J. A.; Douda, J.; Gazarian, K.

2013-06-01

321

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 Å 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

322

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

323

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

324

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

325

Superconductivity in the misfit compound of (LaSe)1.14(NbSe2): STM/S, calorimetric and magnetization studies  

NASA Astrophysics Data System (ADS)

(LaSe)1.14(NbSe2) is a low temperature superconductor with Tc around 1.2 K belonging to the family of the lamellar chalcogenides. Electron transfer from the LaSe to the NbSe2 slab results in a natural layered system of the insulating LaSe and (super) conducting NbSe2 sheets. In our previous investigations of the anisotropic transport [P. Szabó et al., Phys. Rev. Lett. 86, 5990 (2001)] indications have been found that this system behaves as a stack of Josephson-coupled superconducting NbSe2 sheets separated by insulating LaSe layers. We test this hypothesis by STM/S measurements at subkelvin temperatures and in magnetic fields. Superconducting energy gap obtained by STM opens at the same temperature and field where the interlayer resistivity starts to increase before drop to zero value. Before any conclusions are made homogeneity of the superconducting parameters is to be tested. STM indicates large areas without any gap but calorimetric measurements have shown the bulk superconductivity and magnetization revealed extremely low pinning.

Samuely, P.; Szabo, P.; Kacmarcik, J.; Pribulova, Z.; Samuely, T.; Rodrigo, J. G.; Marcenat, C.; Klein, T.; Cario, L.

2013-03-01

326

Influence of nanoscale Ag2Te precipitates on the thermoelectric properties of the Sn doped P-type AgSbTe2 compound  

NASA Astrophysics Data System (ADS)

We report a maximal figure of merit (ZT) value of 1.1 at 600 K was obtained for the sample of which x = 0.03, representing an enhancement greater than 20% compared with a pristine AgSbTe2 sample. This favorable thermoelectric performance originated from the optimal Sn2+ substitution for Sb3+ in AgSbTe2, which not only increased electrical conductivity but also led to a substantial reduction in thermal conductivity that was likely caused by an enhanced phonon-scattering mechanism through the combined effects of lattice defects and the presence of Ag2Te nanoprecipitates dispersed in the matrix.

Mohanraman, Rajeshkumar; Sankar, Raman; Chou, Fang-Cheng; Lee, Chih-Hao; Iizuka, Yoshiyuki; Muthuselvam, I. Panneer; Chen, Yang-Yuan

2014-09-01

327

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

328

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

E-print Network

of mercury chalcogenides in the zinc-blende structure have been calculated within the LDA, GW (G0W0, "one, 71.30.+h I. INTRODUCTION For many years it has been believed that the cubic mercury chalcogenides Hg enough to allow a firm determination of the 6, 7, 8 level sequence. In fact HgSe is probably the Hg

Svane, Axel Torstein

2011-01-01

329

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

NASA Astrophysics Data System (ADS)

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

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

1994-09-01

330

Effect of Te doping on superconductivity and charge-density wave in dichalcogenides 2H-NbSe2-xTex (x = 0, 0.1, 0.2)  

NASA Astrophysics Data System (ADS)

Single crystals of Te-doped dichalcogenides 2H-NbSe2-xTex (x = 0,0.10,0.20) were grown by vapour transport method. The effect of Te doping on the superconducting and charge-density wave (CDW) transitions has been investigated. The sharp decrease of residual resistance ratio, RRR = R(300K)/R(8K), with increasing Te content was observed, indicating that the disorder in the conducting plane is induced by Te doping. Meanwhile the superconducting transition temperature, Tc, decreases monotonically with Te content. However, the CDW transition temperature, TCDW, shown by a small jump in the temperature dependence of the resistivity near 30 K, increases slightly. The results show that the suppression of superconductivity might be caused by the enhancement of CDW ordering. The disorder has little influence on the CDW ordering.

Wang, Hong-Tao; Li, Lin-Jun; Ye, De-Shu; Cheng, Xin-Hong; Xu, Zhu-An

2007-08-01

331

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

332

Experimental detection of a Majorana mode in the core of a magnetic vortex inside a topological insulator-superconductor Bi(2)Te(3)/NbSe(2) heterostructure.  

PubMed

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 Bi(2)Te(3) films grown on a superconductor NbSe(2). 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 Bi(2)Te(3). 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. PMID:25615497

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

333

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.

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

2014-05-19

334

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

PubMed Central

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

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

2013-01-01

335

Crystal structure of {approx}RCu{sub 3}S{sub 3} and {approx}RCuTe{sub 2} (R=Gd-Lu) compounds  

SciTech Connect

The crystal structures of ternary compounds TbCu{sub 3}S{sub 3}, Dy{sub 1.06}Cu{sub 2.84}S{sub 3} (space group R3-bar), Ho{sub 0.67}Cu{sub 2}S{sub 2} (space group P3-bar m1), ErCu{sub 3}S{sub 3} (space group P3-bar 1c), Yb{sub 0.80}Cu{sub 1.60}S{sub 2}, Lu{sub 0.67}Cu{sub 2}S{sub 2}, TbCuTe{sub 2}, DyCuTe{sub 2}, Tm{sub 1.07}Cu{sub 0.78}Te{sub 2}, LuCuTe{sub 2} (space group P3-bar m1), Gd{sub 0.75}Cu{sub 1.74}Te{sub 2} (space group P3-bar 1m) were determined by means of X-ray single crystal diffraction. The S(Te) atoms are stacked in a close packed arrangement with the layers in the sequence AB. The R atoms are distributed over octahedral interstices whereas Cu atoms are located in tetrahedral interstices. Disorder of R and Cu atoms in studied chalcogenides is found. Crystal structure comparison showed that TbCuTe{sub 2} and DyCuTe{sub 2} crystallize as superstructure 2a Multiplication-Sign 2a Multiplication-Sign {sub 2}c to CaAl{sub 2}Si{sub 2} structure type, whereas Gd{sub 0.75}Cu{sub 1.74}Te{sub 2}, ErCu{sub 3}S{sub 3} and TbCu{sub 3}S{sub 3} (Dy{sub 1.06}Cu{sub 2.84}S{sub 3}) have superstructure {radical}3a Multiplication-Sign {radical}3a Multiplication-Sign nc with n=1, 2, 3. - Graphical abstract: In the series of the {approx}RCu{sub 3}S{sub 3} and {approx}RCuTe{sub 2} compounds the R and Cu atoms occupy disordered positions. The S(Te) atoms are stacked in a close packed arrangement with the layers in the sequence AB. Highlights: Black-Right-Pointing-Pointer The {approx}RCu{sub 3}S{sub 3} and {approx}RCuTe{sub 2} (R=Gd-Lu) crystallize with layered structure. Black-Right-Pointing-Pointer Superstructure {radical}3a Multiplication-Sign {radical}3a Multiplication-Sign nc (n=1, 2, 3) to CaAl{sub 2}Si{sub 2} structure type is found. Black-Right-Pointing-Pointer TbCuTe{sub 2} and DyCuTe{sub 2} crystallize as superstructure 2a Multiplication-Sign 2a Multiplication-Sign 2c. Black-Right-Pointing-Pointer Disorder of R and Cu atoms in studied chalcogenides is found.

Gulay, L.D. [Department of Ecology and Protection of Environment, Volyn National University, Voli Ave 13, 43009 Lutsk (Ukraine); Daszkiewicz, M., E-mail: m.daszkiewicz@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P. O. Box 1410, 50-950 WrocLaw (Poland); Shemet, V.Ya. [Department of Chemistry, Lutsk National Technical University, L'vivska str. 75, 43018 Lutsk (Ukraine)

2012-02-15

336

Two-dimensional universal conductance fluctuations and the electron-phonon interaction of surface states in Bi2Te2Se microflakes  

PubMed Central

The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs). Even if one delicately suppresses the bulk conductance by improving the quality of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se microflakes. The solely-B?-dependent UCF is achieved and its temperature dependence is investigated. The surface transport is further revealed by weak antilocalizations. Such survived UCFs of the surface states result from the limited dephasing length of the bulk carriers in ternary crystals. The electron-phonon interaction is addressed as a secondary source of the surface state dephasing based on the temperature-dependent scaling behavior. PMID:22916331

Li, Zhaoguo; Chen, Taishi; Pan, Haiyang; Song, Fengqi; Wang, Baigeng; Han, Junhao; Qin, Yuyuan; Wang, Xuefeng; Zhang, Rong; Wan, Jianguo; Xing, Dingyu; Wang, Guanghou

2012-01-01

337

Synthesis of Direct Printable CdS Nanoparticles for Cu(In,Ga)Se2/CdTe Thin-Film Solar Cell  

NASA Astrophysics Data System (ADS)

CdS nanoparticles were synthesized for the application in direct write technology. Various parameters such as deposition time, pH, and cadmium ion concentration, were varied in order to observe optimum conditions for the synthesis of CdS nanoparticles. As a result of this study, it was confirmed that the optimum conditions for synthesis of CdS nanoparticles were pH 11, 70 °C, and 3 mmol/dm3 cadmium. CdS nanoparticles, synthesized under these conditions, were under-filled between two glass substrates, and the elements, cadmium and sulphur, on glass substrates were observed with an energy-dispersive X-ray spectrometer (EDX). This indicates that the deposition of CdS nanoparticles by a direct printing process into two substrates is possible, and CdS nanoparticles can be applied to the fabrication of a Cu(In,Ga)Se2/CdTe thin-film solar cell.

Hwang, Se-Yeon; Kim, Nam-Soo

2010-05-01

338

Effect of pressure-driven local structural rearrangement on the superconducting properties of FeSe0.5Te0.5  

NASA Astrophysics Data System (ADS)

The pressure dependence of the superconducting transition temperature Tc, the local structure, and the electronic properties of the iron chalcogenide superconductor FeSe0.5Te0.5 was investigated by means of SQUID magnetometry and site-selective polarized x-ray absorption spectroscopy at the iron and selenium K -edges. The measurements reveal a discontinuous decrease of the local bond distances by crossing a tetragonal to monoclinic structural phase transition at pS˜2.7 GPa. The electronic structure, however, evolves evenly, but the superconducting properties are highly affected by changes in the local structure. These results underline the close connection of the lattice and the superconductivity in the iron-based superconductors.

Bendele, M.; Guguchia, Z.; von Rohr, F.; Irifune, T.; Shinmei, T.; Kantor, I.; Pascarelli, S.; Joseph, B.; Marini, C.

2014-11-01

339

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

PubMed

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

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

2012-11-29

340

Shubnikov-de Haas oscillations from topological surface states of metallic Bi2Se2.1Te0.9  

NASA Astrophysics Data System (ADS)

We have studied the quantum oscillations in the conductivity of metallic, p -type Bi2Se2.1Te0.9 . The dependence of the oscillations on the angle of the magnetic field with the surface as well as the Berry phase determined from the Landau level fan plot indicate that the observed oscillations arise from surface carriers with a characteristic Dirac dispersion. Several quantities characterizing the surface conduction are calculated employing the Lifshitz-Kosevich theory. The low value of the Fermi energy with respect to the Dirac point is consistent with the metallic character of the bulk hole carriers. We conclude that, due to the peculiar shape of the valence band, the Shubnikov-de Haas oscillations of the bulk carriers are shifted to higher magnetic fields, which allows for the detection of the quantum oscillations from the topological surface states at a lower field.

Shrestha, Keshav; Marinova, Vera; Lorenz, Bernd; Chu, Paul C. W.

2014-12-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

342

Cathodic Deposition of Components in BiSbTe Ternary Compounds as Thermoelectric Films Using Choline-Chloride-Based Ionic Liquids  

NASA Astrophysics Data System (ADS)

This paper reports electrodeposition of BiTe, SbTe, and BiSbTe films using ionic liquids based on choline chloride (ChCl) and malonic acid mixtures (1:1 moles) at 80°C to 85°C. The electrolyte contained bismuth and/or antinomy species and tellurium species with 1.5 mM to 50 mM concentrations; Pt sheet, Pt mesh, and Pt wire were used for working, auxiliary, and quasireference electrodes, respectively. Cyclic voltammograms revealed the beginning and cathodic peak of pure Te deposition; at more negative potentials simultaneous codeposition of binary or ternary compounds as limiting currents or a series of peaks were observed. Correspondingly, two or three dissolution (stripping) anodic peaks were observed. Nyquist and Bode impedance spectra show differences in Pt behavior due to its polarization at various cathodic potentials. Equivalent-circuit components providing the best fit to the data were calculated. Deposition of BiSbTe films on copper plates was also performed by electrolysis at controlled potentials or current pulses. Some measurements of Seebeck coefficients of the obtained films were carried out.

Golgovici, Florentina; Cojocaru, Anca; Nedelcu, Marin; Visan, Teodor

2010-09-01

343

Structural, Electronic, Magnetic and Optical Properties of Ferromagnetic Pb1-xEuxSe and Pb1-xEuxTe Alloys (x = 0, 0.25, 0.50, 0.75 and 1)  

NASA Astrophysics Data System (ADS)

First-principles total energy calculations have been performed using full potential linear-augmented-plane-wave method within the framework of density functional theory to study the structural, electronic, magnetic and optical properties of the Pb1-xEux Se and Pb1-xEuxTe(0 ? x ?1) alloys in the ferromagnetic (FM) ordering. The calculations have been extended to treat the strongly localized f electrons of Eu atom by the self-interaction correction (SIC) approach. For structural optimization, the Wu and Cohen generalized gradient approximation (GGA) functional has been used, whereas for calculating electronic properties, the GGA parameterization scheme formulated by Engel and Vosko (EV) has also been utilized. It has been observed that the use of experimental value of Coulomb parameter (Uf-expt.) within the SIC does not yield an accurate EuSe and EuTe energy band structure. The improvement in the electronic band structures of nonmagnetic PbSe/PbTe and ferromagnetic EuSe/EuTe have been achieved by considering the effects of spin-orbit coupling for Pb atoms, by a suitable choice of U and by treating the U values for Eu atom's f and d electrons as parameters. The electronic and optical properties of FM Pb1-xEuxSe in agreement with experiments can be achieved by combining EV GGA with a Hubbard U < Uf-expt., however, a stronger and stable AFM coupling in EuTe leaves the above scheme unable to provide good electronic structure of FM Pb1-xEuxTe. In case of Pb1-xEuxSe the nonlinear behaviour of electronic structure is reflected in the optical properties of Eu-doped PbSe that have been studied in terms of incident photons' energy dependent complex dielectric function.

Alay-E-Abbas, S. M.; Younas, S.; Hanif, S.; Sharif, M.; Hussain, Iqbal; Ghulam Abbas, S. M.; Shaukat, A.

2013-07-01

344

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

345

Syntheses and structures of the infinite chain compounds Cs(4)Ti(3)Se(13), Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14).  

PubMed

The alkali metal/group 4 metal/polychalcogenides Cs(4)Ti(3)Se(13), Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14) have been synthesized by means of the reactive flux method at 823 or 873 K. Cs(4)Ti(3)Se(13) crystallizes in a new structure type in space group C(2)(2)-P2(1) with eight formula units in a monoclinic cell at T = 153 K of dimensions a = 10.2524(6) A, b = 32.468(2) A, c = 14.6747(8) A, beta = 100.008(1) degrees. Cs(4)Ti(3)Se(13) is composed of four independent one-dimensional [Ti(3)Se(13)(4-)] chains separated by Cs(+) cations. These chains adopt hexagonal closest packing along the [100] direction. The [Ti(3)Se(13)(4-)] chains are built from the face- and edge-sharing of pentagonal pyramids and pentagonal bipyramids. Formal oxidation states cannot be assigned in Cs(4)Ti(3)Se(13). The compounds Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14) crystallize in the K(4)Ti(3)S(14) structure type with four formula units in space group C(2)(h)()(6)-C2/c of the monoclinic system at T = 153 K in cells of dimensions a = 21.085(1) A, b = 8.1169(5) A, c = 13.1992(8) A, beta = 112.835(1) degrees for Rb(4)Ti(3)S(14);a = 21.329(3) A, b = 8.415(1) A, c = 13.678(2) A, beta = 113.801(2) degrees for Cs(4)Ti(3)S(14); a = 21.643(2) A, b = 8.1848(8) A, c = 13.331(1) A, beta = 111.762(2) degrees for Rb(4)Hf(3)S(14); a = 22.605(7) A, b = 8.552(3) A, c = 13.880(4) A, beta = 110.919(9) degrees for Rb(4)Zr(3)Se(14); a = 22.826(5) A, b = 8.841(2) A, c = 14.278(3) A, beta = 111.456(4) degrees for Cs(4)Zr(3)Se(14); and a = 22.758(5) A, b = 8.844(2) A, c = 14.276(3) A, beta = 111.88(3) degrees for Cs(4)Hf(3)Se(14). These A(4)M(3)Q(14) compounds (A = alkali metal; M = group 4 metal; Q = chalcogen) contain hexagonally closest-packed [M(3)Q(14)(4-)] chains that run in the [101] direction and are separated by A(+) cations. Each [M(3)Q(14)(4-)] chain is built from a [M(3)Q(14)] unit that consists of two MQ(7) pentagonal bipyramids or one distorted MQ(8) bicapped octahedron bonded together by edge- or face-sharing. Each [M(3)Q(14)] unit contains six Q(2)(2-) dimers, with Q-Q distances in the normal single-bond range 2.0616(9)-2.095(2) A for S-S and 2.367(1)-2.391(2) A for Se-Se. The A(4)M(3)Q(14) compounds can be formulated as (A(+))(4)(M(4+))(3)(Q(2)(2-))(6)(Q(2-))(2). PMID:11327911

Huang, F Q; Ibers, J A

2001-05-01

346

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

347

Cs 4P 2Se 10: A new compound discovered with the application of solid-state and high temperature NMR  

NASA Astrophysics Data System (ADS)

The new compound Cs 4P 2Se 10 was serendipitously produced in high purity during a high-temperature synthesis done in a nuclear magnetic resonance (NMR) spectrometer. 31P magic angle spinning (MAS) NMR of the products of the synthesis revealed that the dominant phosphorus-containing product had a chemical shift of -52.8 ppm that could not be assigned to any known compound. Deep reddish brown well-formed plate-like crystals were isolated from the NMR reaction ampoule and the structure was solved with X-ray diffraction. Cs 4P 2Se 10 has the triclinic space group P-1 with a=7.3587(11) Å, b=7.4546(11) Å, c=10.1420(15) Å, ?=85.938(2)°, ?=88.055(2)°, and ?=85.609(2)° and contains the [P 2Se 10] 4- anion. To our knowledge, this is the first compound containing this anion that is composed of two tetrahedral (PSe 4) units connected by a diselenide linkage. It was also possible to form a glass by quenching the melt in ice water, and Cs 4P 2Se 10 was recovered upon annealing. The static 31P NMR spectrum at 350 °C contained a single peak with a -35 ppm chemical shift and a ˜7 ppm peak width. This study highlights the potential of solid-state and high-temperature NMR for aiding discovery of new compounds and for probing the species that exist at high temperature.

Gave, Matthew A.; Canlas, Christian G.; Chung, In; Iyer, Ratnasabapathy G.; Kanatzidis, Mercouri G.; Weliky, David P.

2007-10-01

348

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

349

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

350

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 1–10??.cm and greater contrast between the bulk and surface resistivities compared to other Bi-based topological insulators. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we present complex conductivity of BSTS single crystals, disentangling the surface and bulk contributions. We find that the Drude spectral weight is 1–2 orders of magnitude smaller than in other Bi-based topological insulators, and similar to that of Bi2Se3 thin films, suggesting a significant contribution of the topological surface states to the conductivity of the BSTS sample. Moreover, an impurity band is present about 30?meV below the Fermi level, and the surface and bulk carrier densities agree with those obtained from transport data. Furthermore, from the surface Drude contribution, we obtain a ~98% transmission through one surface layer — this is consistent with the transmission through single-layer or bilayer graphene, which shares a common Dirac-cone feature in the band structure. PMID:24343202

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

351

Effect of carrier density and valence states on superconductivity of oxygen annealed Fe{sub 1.06}Te{sub 0.6}Se{sub 0.4} single crystals  

SciTech Connect

The variations of carrier density and valence states in oxygen annealed Fe{sub 1.06}Te{sub 0.6}Se{sub 0.4} single crystals were studied systematically. It was found that the carrier density n{sub H} increases after oxygen annealing by Hall coefficient measurements. The X-ray photoelectron spectroscopy experiments reveal that the oxygen annealing changes Fe{sup 0} and Te{sup 0} states to Fe{sup 2+/3+} and Te{sup 4+}, respectively, while the valence variation of Se is negligible. Our results indicate that the improvement of superconductivity, such as the zero resistance transition temperature T{sub c}{sup zero}, shielding and Meissner fraction value 4?? and upper critical field H{sub c2}, could be closely related to the proper manipulation of n{sub H} and the valence states by oxygen annealing in the system.

Su, T. S.; Yin, Y. W., E-mail: yyw@ustc.edu.cn, E-mail: lixg@ustc.edu.cn; Teng, M. L.; Gong, Z. Z.; Zhang, M. J.; Li, X. G., E-mail: yyw@ustc.edu.cn, E-mail: lixg@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at Microscale, Department of Physics, University of Science and Technology of China, Hefei 230026 (China)

2013-11-14

352

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

353

Anion substitution effects on structure and magnetism of the chromium chalcogenide Cr{sub 5}Te{sub 8}-Part II: Cluster-glass and spin-glass behavior in trigonal Cr{sub (1+x)}Q{sub 2} with basic cells and trigonal Cr{sub (5+x)}Q{sub 8} with superstructures (Q=Te, Se; Te:Se=6:2)  

SciTech Connect

The effect of substitution of up to two Te atoms by Se atoms on the crystal structure, the magnetic and electronic properties has been studied in the system Cr{sub (5+x)}Te{sub 8-y}Se{sub y}. Trigonal basic cells with space group P-3m1 for Cr{sub (1+x)}Q{sub 2} and trigonal supercells (doubling of the unit cell in all directions) with space group P-3m1 for Cr{sub (5+x)}Q{sub 8} ((1+x)=1.27, 1.32, 1.36; (5+x)=5.08, 5.28, 5.44; Q=Te, Se; Te:Se=6:2) have been identified in X-ray powder diffraction patterns and Rietveld refinements as high-temperature and low-temperature phases, respectively. The crystal structures are related to the hexagonal NiAs-type structure with metal vacancies in every second metal layer. The magnetic properties are closely related to the Cr content and the structure type. Cluster-glass and spin-glass behavior at low temperatures are observed for high and low Cr contents, respectively. For the same Cr content, the phases with trigonal basic cells have higher values for the Curie temperature T{sub c} and the freezing temperature T{sub f}, and larger magnetization than those for the phases with trigonal supercells. For the same structure type, the values for T{sub c}/T{sub f} do not show a linear relationship with the change of Cr content but exhibit a V-shape fashion. Our experimental investigations were accompanied by spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) electronic structure calculations. Cr deficiencies as well as atomic disorder on the chalcogen sites was accounted for using the coherent potential approximation (CPA) alloy theory. Calculation of the exchange coupling parameters J{sub ij} provided the basis for subsequent Monte Carlo simulations of the magnetic properties at finite temperatures.

Huang Zhongle [Institute of Inorganic Chemistry, Christian-Albrechts-University Kiel, Olshausenstr.40, D-24098 Kiel (Germany)]. E-mail: zlhuang@ac.uni-kiel.de; Bensch, Wolfgang [Institute of Inorganic Chemistry, Christian-Albrechts-University Kiel, Olshausenstr.40, D-24098 Kiel (Germany); Mankovsky, Sergiy [Department of Chemistry, LMU-Munich, Butenandstr. 5-13, D-81377 Munich (Germany); Polesya, Svitlana [Department of Chemistry, LMU-Munich, Butenandstr. 5-13, D-81377 Munich (Germany); Ebert, Hubert [Department of Chemistry, LMU-Munich, Butenandstr. 5-13, D-81377 Munich (Germany); Kremer, Reinhard K. [Max-Planck Institut fuer Festkoerperforschung, Heisenbergstr. 1, D-70506 Stuttgart (Germany)

2006-07-15

354

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

355

On the bad metallicity and phase diagrams of Fe1+?X (X =Te, Se, S, solid solutions): an electrical resistivity study  

NASA Astrophysics Data System (ADS)

Based on a systematic analysis of the thermal evolution of the resistivities of Fe-based chalcogenides Fe1+?Te1-xXx (X = Se, S), it is inferred that their often observed nonmetallic resistivities are related to a presence of two resistive channels: one is a high- temperature thermally-activated process while the other is a low-temperature log-in-T process. On lowering temperature, there are often two metal-to-nonmetall crossover events: one from the high-T thermally-activated nonmetallic regime into a metal-like phase and the other from the log-in-T regime into a second metal-like phase. Based on these events, together with the magnetic and superconducting transitions, a phase diagram is constructed for each series. We discuss the origin of both processes as well as the associated crossover events. We also discuss how these resistive processes are being influenced by pressure, intercalation, disorder, doping, or sample condition and, in turn, how these modifications are shaping the associated phase diagrams.

El Massalami, M.; Deguchi, K.; Machida, T.; Takeya, H.; Takano, Y.

2014-12-01

356

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

357

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

SciTech Connect

We present an analysis of the spin–rotation 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 spin–rotation 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 spin–rotation 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 spin–rotation and absolute shielding constants were determined combining ab initio and relativistic DFT calculations. For the heavy nuclei, the breakdown of the relationship between the spin–rotation 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 Tromsø—The Arctic University of Norway, N-9037 Tromsø (Norway)] [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø—The Arctic University of Norway, N-9037 Tromsø (Norway); Demissie, Taye B. [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø—The Arctic University of Norway, N-9037 Tromsø (Norway) [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø—The Arctic University of Norway, N-9037 Tromsø (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

358

Effect of copper doping on kinetic phenomena in n-Bi{sub 2}Te{sub 2.85}Se{sub 0.15}  

SciTech Connect

In single crystals of copper-doped and undoped Bi{sub 2}Te{sub 2.85}Se{sub 0.15} solid solutions with an electron concentration close to 1 x 10{sup 19} cm{sup -3}, the temperature dependences are investigated for the Hall (R{sub 123}, R{sub 321}) and Seebeck (S{sub 11}) kinetic coefficients, the electrical-conductivity ({sigma}{sub 11}), Nernst-Ettingshausen (Q{sub 123}), and thermal conductivity (k{sub 11}) coefficients in the temperature range of 77-400 K. The absence of noticeable anomalies in the temperature dependences of the kinetic coefficients makes it possible to use the one-band model when analyzing the experimental results. Within the framework of the one-band model, the effective mass of density of states (m{sub d} {approx} 0.8m{sub 0}), the energy gap ({epsilon}{sub g} {approx} 0.2 eV), and the effective scattering parameter (r{sub eff} {approx} 0.2) are estimated. The obtained value of the parameter r{sub eff} is indicative of the mixed electron-scattering mechanism with the dominant scattering by acoustic phonons. Data on the thermal conductivity and the lattice resistivity obtained by subtracting the electron contribution according to the Wiedemann-Franz law are presented.

Zhitinskaya, M. K.; Nemov, S. A. [St. Petersburg State Technical University (Russian Federation)], E-mail: nemov_s@mail.ru; Svechnikova, T. E. [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation)

2007-10-15

359

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

PubMed Central

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

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

2014-01-01

360

Magnetic hourglass dispersion and its relation to high-temperature superconductivity in iron-tuned Fe1+yTe0.7Se0.3  

NASA Astrophysics Data System (ADS)

High-temperature superconductivity remains arguably the greatest enigma of condensed matter physics. The discovery of iron-based high-temperature superconductors [1, 2] has renewed the importance of understanding superconductivity in materials susceptible to magnetic order and fluctuations. Intriguingly, they show magnetic fluctuations reminiscent of superconducting (SC) cuprates [3], including a ‘resonance’ and an ‘hourglass’-shaped dispersion [4], which provides an opportunity to gain new insights into the coupling between spin fluctuations and superconductivity. In this paper, we report inelastic neutron scattering data on Fe1+yTe0.7Se0.3 using excess iron concentration to tune between an SC (y = 0.02) and a non-SC (y = 0.05) ground state. We find incommensurate spectra in both the samples but discover that in the one that becomes SC, a constriction toward a commensurate hourglass-shape develops well above Tc. Conversely, a spin gap and a concomitant spectral weight shift happen below Tc. Our results imply that the hourglass-shaped dispersion is most likely a prerequisite for superconductivity, whereas the spin gap and shift of spectral weight are the consequences of superconductivity. We explain this observation by pointing out that an inward dispersion toward the commensurate wave vector is needed for the opening of a spin gap to lower the magnetic exchange energy and hence provide the necessary condensation energy for the SC state to emerge.

Tsyrulin, N.; Viennois, R.; Giannini, E.; Boehm, M.; Jimenez-Ruiz, M.; Omrani, A. A.; Dalla Piazza, B.; Rønnow, H. M.

2012-07-01

361

The effect of bio-conjugation on aging of the photoluminescence in CdSeTe-ZnS core-shell quantum dots  

NASA Astrophysics Data System (ADS)

The aging of the photoluminescence (PL) in bio-conjugated and non-conjugated CdSeTe-ZnS core-shell quantum dots (QDs) is studied by the micro-PL, micro-Raman and X-ray diffraction (XRD) in the samples of buffered QD solution dried on a crystalline Si wafer and stored in the atmospheric ambience for about 2 years. The aging of the PL consists in a "blue" spectral shift of the PL band, an increase in PL band half-width and the decrease in the PL intensity. These changes are more pronounced in the conjugated QD samples. The XRD analysis of the aged samples revealed that the QD core diameter is reduced by ˜1.5 nm in the conjugated QDs as compared to the non-conjugated ones. The possible mechanism of PL spectrum aging is the oxidation that decreases the QD core dimension. It is concluded that the bio-conjugation promotes QD oxidation and the mechanism of the effect is proposed.

Kryshtab, T. G.; Borkovska, L. V.; Kolomys, O. F.; Korsunska, N. O.; Strelchuk, V. V.; Germash, L. P.; Pechers'ka, ?. Yu.; Chornokur, G.; Ostapenko, S. S.; Phelan, C. M.; Stroyuk, O. L.

2012-03-01

362

Doping- and pressure-induced change of electrical and magnetic properties in the Fe-based spin-ladder compound BaFe2Se3  

NASA Astrophysics Data System (ADS)

We have investigated the evolution of electronic structure in the Fe-based ladder compound Ba(Fe1-xCox)2Se3 (0?x ?0.15) by means of resistivity, magnetic susceptibility, and reflectivity measurements. Although the Co substitution into BaFe2Se3 greatly decreases the resistivity, the compound still shows an insulating behavior at x =0.15. Moreover, the insulating state at x =0.15 is robust even under the high pressure of 8 GPa. The antiferromagnetic transition temperatures are gradually suppressed by substituting Co atoms at x ?0.10, while the spin glass state is observed at x ?0.125. Our finding revealed that the substituted Co atoms play a dual effect: electron-carrier dopant and localized moment, providing a supplemental insight into the doping effect in the Fe-based superconductors.

Du, Fei; Hirata, Yasuyuki; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Ueda, Yutaka; Ohgushi, Kenya

2014-08-01

363

Chromatographic speciation of anionic and neutral selenium compounds in Se-accumulating Brassica juncea (Indian mustard) and in selenized yeast  

Microsoft Academic Search

Selenium-accumulating plants such as Brassica juncea (Indian mustard) concentrate the element in plant shoots and roots. Such behavior may provide a cost-effective technology to clean up contaminated soils and waters that pose major environmental and human health problems (phytoremediation). Such ability to transform selenium into bioactive compounds has important implications for human nutrition and health. Element selective characterization of B.

Chethaka Kahakachchi; Harriet Totoe Boakye; Peter C. Uden; Julian F. Tyson

2004-01-01

364

Te-Te and Te-C bond cleavage reactions using a monovalent gallanediyl.  

PubMed

LGa (L = [(2,6-i-Pr2-C6H3)NC(Me)]2CH) reacts with elemental tellurium with formation of the Te-bridged compound [LGa-?-Te]2, whereas the reactions with Ph2Te2 and i-Pr2Te occurred with cleavage of the Te-Te and Te-C bond, respectively, and subsequent formation of LGa(TePh)2 and LGa(i-Pr)Tei-Pr . were characterized by heteronuclear NMR ((1)H, (13)C, (125)Te) and IR spectroscopy and their solid state structures were determined by single crystal X-ray analyses. PMID:25680084

Ganesamoorthy, Chelladurai; Bendt, Georg; Bläser, Dieter; Wölper, Christoph; Schulz, Stephan

2015-03-01

365

Dispersion of the linear and nonlinear optical susceptibilities of the CuAl(S{sub 1?x}Se{sub x}){sub 2} mixed chaclcopyrite compounds  

SciTech Connect

Based on the electronic band structure, we have calculated the dispersion of the linear and nonlinear optical susceptibilities for the mixed CuAl(S{sub 1?x}Se{sub x}){sub 2} chaclcopyrite compounds with x?=?0.0, 0.25, 0.5, 0.75, and 1.0. Calculations are performed within the Perdew-Becke-Ernzerhof general gradient approximation. The investigated compounds possess a direct band gap of about 2.2?eV (CuAlS{sub 2}), 1.9?eV (CuAl(S{sub 0.75}Se{sub 0.25}){sub 2}), 1.7?eV (CuAl(S{sub 0.5}Se{sub 0.5}){sub 2}), 1.5?eV (CuAl(S{sub 0.25}Se{sub 0.75}){sub 2}), and 1.4?eV (CuAlSe{sub 2}) which tuned to make them optically active for the optoelectronics and photovoltaic applications. These results confirm that substituting S by Se causes significant band gaps' reduction. The optical function's dispersion ?{sub 2}{sup xx}(?) and ?{sub 2}{sup zz}(?)/?{sub 2}{sup xx}(?), ?{sub 2}{sup yy}(?), and ?{sub 2}{sup zz}(?) was calculated and discussed in detail. To demonstrate the effect of substituting S by Se on the complex second-order nonlinear optical susceptibility tensors, we performed detailed calculations for the complex second-order nonlinear optical susceptibility tensors, which show that the neat parents compounds CuAlS{sub 2} and CuAlSe{sub 2} exhibit | ?{sub 123}{sup (2)}(?2?;?;?) | as the dominant component, while the mixed alloys exhibit | ?{sub 111}{sup (2)}(?2?;?;?) | as the dominant component. The features of | ?{sub 123}{sup (2)}(?2?;?;?) | and | ?{sub 111}{sup (2)}(?2?;?;?) | spectra were analyzed on the basis of the absorptive part of the corresponding dielectric function ?{sub 2}(?) as a function of both ?/2 and ?.

Reshak, A. H., E-mail: maalidph@yahoo.com [New Technologies - Research Centre, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Brik, M. G. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Institute of Physics, University of Tartu, Ravila 14C, Tartu 50411 (Estonia); Auluck, S. [Council of Scientific and Industrial Research—National Physical Laboratory Dr. K S Krishnan Marg, New Delhi 110012 (India)

2014-09-14

366

Shuttle Mission STS-50: Orbital Processing of High-Quality CdTe Compound Semiconductors Experiment: Final Flight Sample Characterization Report  

NASA Technical Reports Server (NTRS)

The Orbital Processing of High-Quality Doped and Alloyed CdTe Compound Semiconductors program was initiated to investigate, quantitatively, the influences of gravitationally dependent phenomena on the growth and quality of bulk compound semiconductors. The objective was to improve crystal quality (both structural and compositional) and to better understand and control the variables within the crystal growth production process. The empirical effort entailed the development of a terrestrial (one-g) experiment baseline for quantitative comparison with microgravity (mu-g) results. This effort was supported by the development of high-fidelity process models of heat transfer, fluid flow and solute redistribution, and thermo-mechanical stress occurring in the furnace, safety cartridge, ampoule, and crystal throughout the melting, seeding, crystal growth, and post-solidification processing. In addition, the sensitivity of the orbital experiments was analyzed with respect to the residual microgravity (mu-g) environment, both steady state and g-jitter. CdZnTe crystals were grown in one-g and in mu-g. Crystals processed terrestrially were grown at the NASA Ground Control Experiments Laboratory (GCEL) and at Grumman Aerospace Corporation (now Northrop Grumman Corporation). Two mu-g crystals were grown in the Crystal Growth Furnace (CGF) during the First United States Microgravity Laboratory Mission (USML-1), STS-50, June 24 - July 9, 1992.

Larson, David J.; Casagrande, Luis G.; DiMarzio, Don; Alexander, J. Iwan D.; Carlson, Fred; Lee, Taipo; Dudley, Michael; Raghathamachar, Balaji

1998-01-01

367

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 Kohlrausch–Williams–Watts stretched exponential function. The stretched exponential function describes the recombination processes of the LEMPs formed in the crystal regions of the finite clusters as well as the infinite cluster. This reflects the appearance of spatially heterogeneous dynamics in Cd{sub 0.70}Mn{sub 0.30}Te SG compound below T{sub f} which is due to the disorder in the spin distribution caused by the formation of different MMSSs.

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

368

Electrical Conductivity and Dielectric Properties of Se85Te15- x Sb x ( x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) Thin Films  

NASA Astrophysics Data System (ADS)

The alternating-current (ac) conductivity and dielectric properties of Se85Te15- x Sb x ( x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) films are reported in this work. Thin films were deposited by thermal evaporation under base pressure of 10-5 Torr. The films were well characterized by x-ray diffraction, differential scanning calorimetry, and energy-dispersive x-ray spectroscopy. The ac conductivity and dielectric properties have been investigated for the studied films in the temperature range from 297 K to 333 K and over the frequency range from 102 Hz to 105 Hz. The experimental results indicate that the ac conductivity and the dielectric constant depend on temperature, frequency, and Sb content. The frequency dependence of was found to be linear with a slope lying very close to unity and is independent of temperature. This behavior can be explained in terms of correlated barrier hopping between centers forming intimate valence-alternation pairs. The density of localized states N( E F) at the Fermi level is estimated. The activation energy was found to decrease with increasing frequency. The dielectric constant ? 1 and dielectric loss ? 2 were found to decrease with increasing frequency and increased with increasing temperature over the ranges studied. The maximum barrier height W m for the studied films was calculated from an analysis of the dielectric loss ? 2 according to the Guintini equation. The values agree with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The variation of the studied properties with Sb content was also investigated.

Hegab, N. A.; Fadel, M.; Yahia, I. S.; Salem, A. M.; Farid, A. S.

2013-12-01

369

Preparation of a diphosphine with persistent phosphinyl radical character in solution: characterization, reactivity with O2, S8, Se, Te, and P4, and electronic structure calculations.  

PubMed

A new, easily synthesized diphosphine based on a heterocyclic 1,3,2-diazaphospholidine framework has been prepared. Due to the large, sterically encumbering Dipp groups (Dipp = 2,6-diisopropylphenyl) on the heterocyclic ring, the diphosphine undergoes homolytic cleavage of the P-P bond in solution to form two phosphinyl radicals. The diphosphine has been reacted with O(2), S(8), Se, Te, and P(4), giving products that involve insertion of elements between the P-P bond to yield the related phosphinic acid anhydride, sulfide/disulfide, selenide, telluride, and a butterfly-type perphospha-bicyclobutadiene structure with a trans,trans-geometry. All molecules have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Variable-temperature EPR spectroscopy was utilized to study the nature of the phosphinyl radical in solution. Electronic structure calculations were performed on a number of systems from the parent diphosphine [H(2)P](2) to amino-substituted [(H(2)N)(2)P](2) and cyclic amino-substituted [(H(2)C)(2)(NH)(2)P](2); then, bulky substituents (Ph or Dipp) were attached to the cyclic amino systems. Calculations on the isolated diphosphine at the B3LYP/6-31+G* level show that the homolytic cleavage of the P-P bond to form two phosphinyl radicals is favored over the diphosphine by ~11 kJ/mol. Furthermore, there is a significant amount of relaxation energy stored in the ligands (52.3 kJ/mol), providing a major driving force behind the homolytic cleavage of the central P-P bond. PMID:23098074

Giffin, Nick A; Hendsbee, Arthur D; Roemmele, Tracey L; Lumsden, Michael D; Pye, Cory C; Masuda, Jason D

2012-11-01

370

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

371

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

372

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

373

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

374

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

375

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

NASA Astrophysics Data System (ADS)

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

Kashi, Siamak

376

Synthesis, characterization, and structure-property relationships in two new polar oxides: Zn2(MoO4)(SeO3) and Zn2(MoO4)(TeO3).  

PubMed

Two new noncentrosymmetric (NCS) polar oxide materials, Zn(2)(MoO(4))(AO(3)) (A = Se(4+) or Te(4+)), have been synthesized by hydrothermal and solid-state techniques. Their crystal structures have been determined, and characterization of their functional properties (second-harmonic generation, piezoelectricity, and polarization) has been performed. The isostructural materials exhibit a three-dimensional network consisting of ZnO(4), ZnO(6), MoO(4), and AO(3) polyhedra that share edges and corners. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation indicate the materials exhibit moderate SHG efficiencies of 100 × and 80 × ?-SiO(2) for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively. Particle size vs SHG efficiency measurements indicate the materials are type 1 non-phase-matchable. Converse piezoelectric measurements resulted in d(33) values of ?14 and ?30 pm/V for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively, whereas pyroelectric measurements revealed coefficients of -0.31 and -0.64 ?C/m(2) K at 55 °C for Zn(2)(MoO(4))(SeO(3)) and Zn(2)(MoO(4))(TeO(3)), respectively. Frequency-dependent polarization measurements confirmed that all of the materials are nonferroelectric; that is, the macroscopic polarization is not reversible, or "switchable". Infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements were also performed. First-principles density functional theory (DFT) electronic structure calculations were also done. Crystal data: Zn(2)(MoO(4))(SeO(3)), monoclinic, space group P2(1) (No. 4), a = 5.1809(4) Å, b = 8.3238(7) Å, c = 7.1541(6) Å, ? = 99.413(1)°, V = 305.2(1) Å(3), Z = 2; Zn(2)(MoO(4))(TeO(3)), monoclinic, space group P2(1) (No. 4), a = 5.178(4) Å, b = 8.409(6) Å, c = 7.241(5) Å, ? = 99.351(8)°, V = 311.1(4) Å(3), Z = 2. PMID:21557565

Nguyen, Sau Doan; Kim, Sang-Hwan; Halasyamani, P Shiv

2011-06-01

377

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

378

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

379

Synthesis and Characterization of Mid-Infrared Transparency Compounds: Acentric BaHgS2 and Centric Ba8Hg4S5Se7.  

PubMed

Two mid-IR transparency compounds, namely, acentric BaHgS2 (BHS) and centric Ba8Hg4S5Se7 (BHSSe), were successfully synthesized by a conventional solid-state reaction method. The space group of BHS is orthorhombic Pmc21 with [HgS4] tetrahedra and isolated dumbbell-shaped [HgS2] units, while BHSSe belongs to the orthorhombic space group Pnma with infinite isolated ?[HgSe2(S/Se)2](4-) chains. Raman spectra and thermal analysis of the titled materials were measured. In addition, their band gaps are found to be 1.93 (BHS) and 1.98 eV (BHSSe) from the measured diffuse reflectance spectra. Significantly, the powder BHS sample exhibits a good second harmonic generation (SHG) response of ?6.5 times compared with that of reference AgGaS2 at a fundamental wavelength (2.09 ?m). The calculated SHG coefficients of BHS are also reported, and the maximum result agrees well with the test observation. PMID:25742293

Wu, Kui; Su, Xin; Pan, Shilie; Yang, Zhihua

2015-03-16

380

Thermodynamic Modeling of the Pt-Te and Pt-Sb-Te Systems  

NASA Astrophysics Data System (ADS)

The Pt-Te and the Pt-Sb-Te systems are modeled using the calculation of phase diagram (CALPHAD) technique. In the Pt-Te system, the liquid phase is modeled as (Pt, PtTe2, Te) using the associate model, and four intermediates, PtTe2, Pt2Te3, Pt3Te4 and PtTe, are treated as stoichiometric compounds and their enthalpies of formation are obtained by means of first-principles calculations. The solution phases, fcc(Pt) and hex(Te), are described as substitutional solutions. Combined with the thermodynamic models of the liquid phase in the Pt-Sb and Sb-Te systems in the literature, the liquid phase of the Pt-Sb-Te ternary system is modeled as (Pt, Sb, Te, Sb2Te3, PtTe2) also using the associate model. The compounds, PtTe2, Pt2Te3, Pt3Te4 and PtTe in the Pt-Te system and PtSb2, PtSb, Pt3Sb2 and Pt7Sb in the Pt-Sb system are treated as line compounds Pt m (Sb,Te) n in the Pt-Sb-Te system, and the compound Pt5Sb is treated as (Pt,Sb)5(Pt,Sb,Te). A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Pt-Te phase diagram, the experimental heat capacities of PtTe and PtTe2, the enthalpies of formation from first-principles calculations for PtTe2, Pt2Te3, Pt3Te4, and PtTe, and the ternary isothermal sections at 873 K, 923 K, 1073 K and 1273 K are well reproduced.

Guo, Cuiping; Huang, Liang; Li, Changrong; Shang, Shunli; Du, Zhenmin

2015-02-01

381

Magnetic behavior of Fe(Se,Te) systems: First-principles calculations Hongliang Shi, Zhong-Bing Huang, John S. Tse, and Hai-Qing Lin  

E-print Network

) The effect of electrostatic shielding using invisibility cloak AIP Advances 1, 042126 (2011) Probing the superconductivity. It is found that the double stripe order in FeTe1Ã?xSex changes to the single stripe order when x

382

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

383

X-ray characterization, electronic band structure, and thermoelectric properties of the cluster compound Ag2Tl2Mo9Se11.  

PubMed

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

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

2014-11-01

384

Te nanowires  

NASA Astrophysics Data System (ADS)

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.

Schönherr, Piet; Collins-McIntyre, Liam J.; Zhang, ShiLei; Kusch, Patryk; Reich, Stephanie; Giles, Terence; Daisenberger, Dominik; Prabhakaran, Dharmalingam; Hesjedal, Thorsten

2014-03-01

385

Magnetic behaviour of some I2.Mn.IV.VI4 compounds  

Microsoft Academic Search

Polycrystalline samples of quaternary compounds I2.Mn.IV.VI4, with I = Cu, Ag, IV = Si, Ge, Sn and Vi = Se, Te, were prepared from the elements using the melt and anneal technique. The majority of these compounds can take more than one structure, depending upon heat treatment, with subcell symmetry of orthorhombic, tetragonal or cubic form, so that a total

X. L. Chen; A.-M. Lamarche; G. Lamarche; J. C. Woolley

1993-01-01

386

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

PubMed

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

Gu, Junsi; Fahrenkrug, Eli; Maldonado, Stephen

2014-09-01

387

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

NASA Astrophysics Data System (ADS)

Room temperature synthesis of ordered-vacancy-compounds (OVCs) and copper indium diselenide (CuInSe2, CIS) by cation and anion exchange reactions of solid CdS thin films with CIS ionic solution in an alkaline chemical bath is reported. The growth parameters such as pH, deposition time and concentration of the solutions were optimized to achieve uniform thin films. Nanostructured CdS thin films (150 nm thick) prepared by chemical bath deposition are used for the deposition of OVC and CIS thin films. The ion exchange reaction between the CdS thin film and the CIS ionic solutions transforms the yellow colour CdS film into faint black, indicating the formation of OVC and CIS film. The resultant films were annealed in air at 200 °C for 1 h and further subjected to characterization using the x-ray diffraction, transmission electron microscopy, energy dispersive x-ray analysis, x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, optical absorption and electrical measurement techniques. The OVC and CuIn3Se5 nanodomains are observed in chalcopyrite CIS thin films and these films have nanostructured morphology onto amorphous/nanocrystalline phase of CdS. The OVC-CIS films are p-type with a band gap energy of 1.453 eV.

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

2009-03-01

388

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

389

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

PubMed

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

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

2014-09-11

390

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

391

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

392

Structural study of a Ag3.4In3.7Sb76.4Te16.5 quadruple compound utilized for phase-change optical disks  

Microsoft Academic Search

The behavior of a quadruple compound, Ag3.4In3.7Sb76.4Te16.5, is investigated at various temperatures using the large Debye-Sherrer camera installed in BL02B2 at SPring-8, to elucidate its crystal structure. The low-temperature phase of this crystal has an A7 structure with atoms of Ag, In, Sb, or Te randomly occupying the 6(c) site in the R3¯m space group. The crystal lattice thermally expands

Toshiyuki Matsunaga; Yukihiro Umetani; Noboru Yamada

2001-01-01

393

High vacuum molecular beam epitaxy for the growth of IV VI compounds  

NASA Astrophysics Data System (ADS)

The molecular beam epitaxy growth of IV-VI compounds using background pressures of about 10 -7 Torr (during growth) instead of ultra-high vacuum background conditions is investigated. A simple high vacuum molecular beam epitaxy system is described. Calculations of the growth rate for the binary and pseudobinary compounds are compared with experimental data. Results on the growth of PbTe, PbSe and dilute magnetic Pb 1- xMn xSe and Pb 1- xMn xSe epitaxial films as well as on PbTe/Pb 1- xMn xTe and PbSe/Pb 1- xMn xSe multi-quantum-well structures are presented. Structural properties have been checked by X-ray diffraction. The electronic properties are investigated by conductivity and Hall effect measurements. These data are compared with that of samples grown under ultra-high vacuum conditions.

Frank, N.; Voitecek, A.; Clemens, H.; Holzinger, A.; Bauer, G.

1993-01-01

394

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

395

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

396

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

397

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, Jörg; Bernasconi, Marco

2015-01-01

398

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

399

Synthesis of CdIn2Se4 and Cu0.5Ag1.5InSe3 Compounds via Chemical and Solid-State Methods  

NASA Astrophysics Data System (ADS)

CdIn2Se4 and Cu0.5Ag1.5InSe3 are high-performance thermoelectric materials. In this study, both CdIn2Se4 and Cu0.5Ag1.5InSe3 powders were synthesized using a microwave and solution method followed by annealing in nitrogen atmosphere. CdIn2Se4 was synthesized by two routes. First, CdSe was prepared using a microwave method. Second, In metal was prepared using a solution method. The prepared metals were annealed in nitrogen atmosphere. From the x-ray diffraction (XRD) results, CdIn2Se4 was observed as the main phase with CdSe and In2O3 as contaminant phases. The synthesis of Cu0.5Ag1.5InSe3 was also divided into two steps. First, CuAg and Se were prepared using a microwave method. Second, In metal was prepared using a solution method. The prepared metals were annealed in nitrogen atmosphere. From the XRD results, Cu0.5Ag1.5InSe3 was observed as the main phase with Cu0.5- x Ag1.5- y In x+ y Se and Se as contaminant phases.

Laokawee, Viratchara; Sarakonsri, Thapanee; Thanachayanont, Chanchana

2014-04-01

400

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

PubMed

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

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

2013-12-01

401

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

402

Condensed rare-earth metal-rich tellurides. Extension of layered Sc 6PdTe 2-type compounds to yttrium and lutetium analogues and to Y 7Te 2, the limiting binary member  

NASA Astrophysics Data System (ADS)

Six isotypic R6ZTe 2 phases have been synthesized in Ta at elevated temperatures and characterized by single crystal X-ray refinements for R=Y, Z=Rh, Pd, Ag, Y and for R=Lu, Z=Cu, Ag. All crystallize in the Sc 6PdTe 2-type structure, Pnma, Z=4, a˜21.5 Å, b˜4.1 Å, c˜11.4 Å. The results can be viewed as the replacement of Te3 atoms in the parent isotypic Sc 2Te (or in the hypothetical Y 2Te or Lu 2Te analogues) by the above the Z, the Y example giving the new binary phase Y 7Te 2. The shorter (and stronger) metal-metal bonds concentrate in the region of metal ( Z, Y) substitution, as revealed by larger integrated crystal orbital Hamilton population (ICOHP) values derived from linear muffin-tin-orbital (LMTO) calculations. Partial densities-of-states data for Y 7Te 2 reflect a similar behavior. Individual R- R bond distances are seen to deviate appreciably from the more fundamental overlap population measures for each.

Castro-Castro, Laura M.; Chen, Ling; Corbett, John D.

2007-11-01

403

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

PubMed

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

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

2005-03-23

404

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

405

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

406

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

SciTech Connect

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

Ji, Haojie; Dhomkar, Siddharth; Roy, Bidisha; Kuskovsky, Igor L. [Department of Physics, Queens College of CUNY, Queens, New York 11367 (United States); The Graduate Center of CUNY, New York, New York 10016 (United States); Shuvayev, Vladimir [Department of Physics, Queens College of CUNY, Queens, New York 11367 (United States); Deligiannakis, Vasilios; Tamargo, Maria C. [The Graduate Center of CUNY, New York, New York 10016 (United States); Department of Chemistry, City College of CUNY, New York, New York 10031 (United States); Ludwig, Jonathan [National High Magnetic Field Laboratory, Tallahassee, Florida 32310 (United States); Department of Physics, Florida State University, Tallahassee, Florida 32306 (United States); Smirnov, Dmitry [National High Magnetic Field Laboratory, Tallahassee, Florida 32310 (United States); Wang, Alice [Evans Analytical Group, Sunnyvale, California 94086 (United States)

2014-10-28

407

Temperature-dependent transformation of the magnetic excitation spectrum on approaching superconductivity in Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5).  

PubMed

Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, T(c), for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe(1+y-x)(Ni/Cu)(x)Te(0.5)Se(0.5) that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T?T(c) to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperatures up to ~3T(c). If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to T(c) demonstrates that strong interactions are involved. PMID:23368150

Xu, Zhijun; Wen, Jinsheng; Zhao, Yang; Matsuda, Masaaki; Ku, Wei; Liu, Xuerong; Gu, Genda; Lee, D-H; Birgeneau, R J; Tranquada, J M; Xu, Guangyong

2012-11-30

408

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

409

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

410

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

411

Advanced processing technology for high-efficiency, thin-film CuInSe{sub 2} and CdTe solar cells. Final subcontract report, March 1, 1992--April 30, 1995  

SciTech Connect

This report describes work performed by the University of South Florida to develop a manufacturing-friendly fabrication process for CuInSe{sub 2} (CIS) solar cells. The process developed under this project uses conventional deposition processes and equipment, does not require stringent process control, and uses elemental Se as the selenium source. The authors believe it can be readily scaled up using off-the-shelf processing equipment and that it will meet the low manufacturing-cost objectives. Another significant achievement under this project was the development of a reactive sputtering deposition technology for ZnO. ZnO is used in many solar cell devices, and sputtering is a desirable manufacturing technology. The application of sputtering has been limited because conventional deposition uses ceramic targets that result in low sputtering rates. The use of Zn metal as the target in reactive sputtering overcomes this limitation. The authors have demonstrated that ZnO deposited by reactive sputtering has state-of-the-art opto-electronic properties. These developments result in large-area uniformity and optimized performance and provide a significant opportunity for applying and commercializing the technology. The second objective of this project was to fabricate high-efficiency CdTe solar cells using manufacturing-friendly processes. Three deposition processes were used to deposit CdS films: chemical bath deposition, rf sputtering, and close-spaced sublimation (CSS). The CdTe films were deposited by CSS. A cell with a record efficiency of 15.8% was obtained.

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

1996-01-01