Science.gov

Sample records for mundial se profundiza

  1. Centro para la Salud Mundial (CGH) del NCI

    Cancer.gov

    El Centro para la Salud Mundial (CGH) del NCI coordina actividades de investigación y trabaja con socios nacionales e internacionales para comprender y enfrentar la carga que representa el cáncer a nivel mundial.

  2. SE-FIT

    NASA Technical Reports Server (NTRS)

    Chen, Yongkang; Weislogel, Mark; Schaeffer, Ben; Semerjian, Ben; Yang, Lihong; Zimmerli, Gregory

    2012-01-01

    The mathematical theory of capillary surfaces has developed steadily over the centuries, but it was not until the last few decades that new technologies have put a more urgent demand on a substantially more qualitative and quantitative understanding of phenomena relating to capillarity in general. So far, the new theory development successfully predicts the behavior of capillary surfaces for special cases. However, an efficient quantitative mathematical prediction of capillary phenomena related to the shape and stability of geometrically complex equilibrium capillary surfaces remains a significant challenge. As one of many numerical tools, the open-source Surface Evolver (SE) algorithm has played an important role over the last two decades. The current effort was undertaken to provide a front-end to enhance the accessibility of SE for the purposes of design and analysis. Like SE, the new code is open-source and will remain under development for the foreseeable future. The ultimate goal of the current Surface Evolver Fluid Interface Tool (SEFIT) development is to build a fully integrated front-end with a set of graphical user interface (GUI) elements. Such a front-end enables the access to functionalities that are developed along with the GUIs to deal with pre-processing, convergence computation operation, and post-processing. In other words, SE-FIT is not just a GUI front-end, but an integrated environment that can perform sophisticated computational tasks, e.g. importing industry standard file formats and employing parameter sweep functions, which are both lacking in SE, and require minimal interaction by the user. These functions are created using a mixture of Visual Basic and the SE script language. These form the foundation for a high-performance front-end that substantially simplifies use without sacrificing the proven capabilities of SE. The real power of SE-FIT lies in its automated pre-processing, pre-defined geometries, convergence computation operation

  3. Centro para la Salud Mundial del NCI anuncia becas de investigación para tecnologías portátiles

    Cancer.gov

    El Centro para la Salud Mundial del NCI (CGH) anunció el otorgamiento de subvenciones que apoyarán el desarrollo y la validación de tecnologías portátiles y de bajo costo para mejorar la detección temprana, el diagnóstico y el tratamiento del cáncer.

  4. Absorption and optical conduction in InSe/ZnSe/InSe thin film transistors

    NASA Astrophysics Data System (ADS)

    Al Garni, S. E.; Qasrawi, A. F.

    2016-01-01

    In this work, (n)InSe/(p)ZnSe and (n)InSe/(p)ZnSe/(n)InSe heterojunction thin film transistor (TFT) devices are produced by the thermal evaporation technique. They are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy and optical spectroscopy techniques. While the InSe films are found to be amorphous, the ZnSe and InSe/ZnSe films exhibited polycrystalline nature of crystallization. The optical analysis has shown that these devices exhibit a conduction band offsets of 0.47 and valence band offsets of 0.67 and 0.74eV, respectively. In addition, while the dielectric spectra of the InSe and ZnSe displayed resonance peaks at 416 and 528THz, the dielectric spectra of InSe/ZnSe and InSe/ZnSe/InSe layers indicated two additional peaks at 305 and 350THz, respectively. On the other hand, the optical conductivity analysis and modeling in the light of free carrier absorption theory reflected low values of drift mobilities associated with incident alternating electric fields at terahertz frequencies. The drift mobility of the charge carrier particles at femtoseconds scattering times increased as a result of the ZnSe sandwiching between two InSe layers. The valence band offsets, the dielectric resonance at 305 and 350THz and the optical conductivity values nominate TFT devices for use in optoelectronics.

  5. Properties of Se/InSe Thin-Film Interface

    NASA Astrophysics Data System (ADS)

    Qasrawi, A. F.; Kayed, T. S.; Elsayed, Khaled A.

    2016-06-01

    Se, InSe, and Se/InSe thin films have been prepared by the physical vapor deposition technique at pressure of ˜10-5 torr. The structural, optical, and electrical properties of the films and Se/InSe interface were investigated by means of x-ray diffraction (XRD) analysis, ultraviolet-visible spectroscopy, and current-voltage ( I- V) characteristics. XRD analysis indicated that the prepared InSe films were amorphous while the Se films were polycrystalline having hexagonal structure with unit cell parameters of a = 4.3544 Å and c = 4.9494 Å. Spectral reflectance and transmittance analysis showed that both Se and InSe films exhibited indirect allowed transitions with energy bandgaps of 1.92 eV and 1.34 eV, respectively. The Se/InSe interface exhibited two energy bandgaps of 0.98 eV and 1.73 eV above and below 2.2 eV, respectively. Dielectric constant values were also calculated from reflectance spectra for the three layers in the frequency range of 500 THz to 272 THz. The dielectric constant exhibited a promising feature suggesting use of the Se/InSe interface as an optical resonator. Moreover, the Au/Se/InSe/Ag heterojunction showed some rectifying properties that could be used in standard optoelectronic devices. The ideality factor and height of the energy barrier to charge carrier motion in this device were found to be 1.72 and 0.66 eV, respectively.

  6. Pressure stabilized Se-Se dimer formation in PbSe 2

    NASA Astrophysics Data System (ADS)

    Bremholm, M.; Hor, Y. S.; Cava, R. J.

    2011-01-01

    The preparation of PbSe 2 through the reaction of PbSe with excess Se at 4.5 GPa and 650 °C is reported. The crystal structure, determined from X-ray powder diffraction data (CuAl 2 structure type, I4/mcm (#140), a = 6.42695(11) Å, c = 7.70254(13) Å, Z = 4), consists of layers of [Se 2] 2- dimers with Pb 2+ in square antiprismatic coordination with Se. This is a rare crystal structure for divalent metal chalcogenides, previously only identified for SrS 2 and BaTe 2. Undoped PbSe 2 as well as Bi 3+- and Ag +-doped samples (10% Pb substitution) show semi-metallic resistivity down to 0.4 K. Magnetic susceptibility measurement of PbSe 2 shows no magnetic ordering above 1.8 K. The Seebeck coefficients show nearly linear behavior from 35 to 400 K and the largest numerical values are found in the case of undoped PbSe 2, + 99 μVK -1, and Bi 3+-doped PbSe 2, - 146 μVK -1, at the highest temperature measured, 400 K.

  7. Se metallomics during lactic fermentation of Se-enriched yogurt.

    PubMed

    Palomo, María; Gutiérrez, Ana M; Pérez-Conde, M Concepción; Cámara, Carmen; Madrid, Yolanda

    2014-12-01

    Selenium biotransformation by lactic acid bacteria during the preparation of Se-enriched yogurt was evaluated. The study focused on the distribution of selenium in the aqueous soluble protein fraction and the detection of selenoamino acids. Screening of selenium in Tris-buffer-urea soluble fraction was carried out by sodium dodecyl sulphate polyacrylamide gel electrophoresis after pre-fractionating with asymmetric field flow fractionation using inductively coupled plasma-mass spectrometry as the detector. Selenium-containing fractions were identified by peptide mapping using nano LC-ESI/LTQMS. Proteins such as thioredoxin, glutaredoxin, albumin, β-lactoglobulin, and lactoperoxidase were identified in the selenium-containing fraction. All these proteins were detected in both the control and the selenium-enriched yogurt except chaperones, which were only detected in the control samples. Chaperones are heat-shock proteins expressed in response to elevated temperature or other cellular stresses. Selenium may have an effect on chaperones expression in Lactobacillus. For the amino acids analysis, selenocysteine was the primary seleno-containing species.

  8. Liquidus Projections of Bi-Se-Ga and Bi-Se-Te Ternary Systems

    NASA Astrophysics Data System (ADS)

    Lin, Po-han; Chen, Sinn-wen; Hwang, Jenn-dong; Chu, Hsu-shen

    2016-06-01

    This study determines the liquidus projections of both Bi-Se-Ga and Bi-Se-Te ternary systems which are constituent ternary systems of promising Bi-Se-Te-Ga thermoelectric materials. Ternary Bi-Se-Ga and Bi-Se-Te alloys are prepared. Their primary solidification phases are experimentally determined, and thermal analysis experiments are carried out. The liquidus projections are determined based on the ternary experimental results and phase diagrams of constituent binary systems. The Bi-Se-Ga system includes seven primary solidification phases, Bi, Ga, GaSe, Ga2Se3, Se, Bi2Se3, and (Bi2)n(Bi2Se3)m. In the Bi-Se-Te system, there are five primary solidification phases, Bi, (Bi2)n(Bi2Te3)m, Bi2(Se,Te)3, (Se,Te), and (Bi2)n(Bi2Se3)m. Both the (Bi2)n(Bi2Te3)m and (Bi2)n(Bi2Se3)m phases are not a single phase, but a collection of series undetermined phases. Large miscibility gaps are observed in the Bi-Se-Ga system. The temperatures of the invariant reactions, Liquid + Bi + GaSe = Ga and Liquid + Ga2Se3 = Bi + GaSe, are at 495 K (222 °C) and 533 K (260 °C), respectively.

  9. ZnSe/CdSe Superlattice Nanowires by Catalyst-assisted Molecular Beam Epitaxy

    SciTech Connect

    Karczewski, G.; Dluzewski, P.; Kret, S.; Klopotowski, L.; Wojtowicz, T.

    2007-04-10

    We report on Au catalyst-assisted molecular beam epitaxy growth and properties of pure ZnSe and ZnSe/CdSe superlattice nanowires. In particular, we concentrate our attention on the morphological characterization by transmission and scanning electron microscopy of pure ZnSe NWs and we compare their optical properties with those of ZnSe/CdSe superlattice NWs fabricated at the same technological conditions.

  10. Formation of highly luminescent Zn1-xCdxSe nanocrystals using CdSe and ZnSe seeds

    NASA Astrophysics Data System (ADS)

    Zhang, Ruili; Yang, Ping

    2013-05-01

    High-quality colloidal Zn1-xCdxSe nanocrystals (NCs) with tunable photoluminescence (PL) from blue to orange were synthesized using oleic acid as a capping agent. The Zn1-xCdxSe NCs were prepared through two approaches: using CdSe or ZnSe seeds. In the case of CdSe NCs as seeds, Zn1-xCdxSe NCs were fabricated by the reaction of Zn, Cd, and Se precursors in the coordinating solvent system at high temperature. The Zn1-xCdxSe NCs revealed orange emitting. A significant blue-shift of absorption and PL spectra were observed with time, indicating the formation of ternary NCs. In contrast, Zn1-xCdxSe NCs revealed blue to green PL for ZnSe NCs as seeds. This is ascribed to an embryonic nuclei-induced alloying process. With increasing time, the Zn1-xCdxSe NCs exhibited a red-shift both in their absorption and PL spectra. This is attributed to the engineering in band gap energy via the control of NC composition. The PL properties of as-prepared alloyed NCs are comparable or even better than those for the parent binary systems. The PL peak wavelength of the Zn1-xCdxSe NCs depended strongly on reaction time and the molar ratio of Cd/Zn. The Zn1-xCdxSe NCs revealed a spherical morphology and exhibited a wurtzite structure according to transmission electron microscopy observation and an X-ray diffraction analysis.

  11. Se atoms and Se6 molecules as guests in Se-carbons - prepared by reduction of a SeCl4-graphite precursor

    NASA Astrophysics Data System (ADS)

    Walter, J.; Shioyama, H.

    2000-01-01

    A SeCl4 -graphite intercalation compound precursor was reduced by a solution of lithium diphenylide in tetrahydrofuran at room temperature. X-ray diffraction measurements gave two distinguishable stages. One stage represented a Se-atom intercalation the other represented an intercalation of Se6 molecules. The in-plane diffraction patterns were estimated by selected-area electron diffraction, the existence of two different guest species (atoms and molecules) could be proved. The Se6 -molecule phase shows an incommensurate lattice with regard to the host lattice, but they are in the same orientation. The lattice parameter of intercalated Se6 is a Se 6-guest = 1158+/-36 pm, c Se 6-guest = 483+/-38 pm, which fits with the lattice parameter of non-intercalated Se6 molecules. Se atom domains show a 2 × agraphite superlattice with respect to the host lattice, which is a commensurate superstructure. Raman scattering data showed the occurrence of an acceptor-type graphite intercalation compound. Three different types of spectra could be obtained, two kinds of spectra consists of doublets at 1588 cm-1 and 1608 cm-1 , with different intensity ratios. These two kinds of spectra are certainly attributed to Se-atom domains, with different stages. A third type of spectrum show bands at higher wavenumbers (1646 cm-1 and 1653 cm-1 ). These bands are probably correlated to Se6 -molecule domains. They represent maybe very early stages of nanoparticle formation.

  12. Low temperature solution-phase growth of ZnSe and ZnSe/CdSe core/shell nanowires.

    PubMed

    Petchsang, Nattasamon; Shapoval, Liubov; Vietmeyer, Felix; Yu, Yanghai; Hodak, Jose H; Tang, I-Ming; Kosel, Thomas H; Kuno, Masaru

    2011-08-01

    High quality ZnSe nanowires (NWs) and complementary ZnSe/CdSe core/shell species have been synthesized using a recently developed solution-liquid-solid (SLS) growth technique. In particular, bismuth salts as opposed to pre-synthesized Bi or Au/Bi nanoparticles have been used to grow NWs at low temperatures in solution. Resulting wires are characterized using transmission electron microscopy and possess mean ensemble diameters between 15 and 28 nm with accompanying lengths ranging from 4-10 μm. Subsequent solution-based overcoating chemistry results in ZnSe wires covered with CdSe nanocrystals. By varying the shell's growth time, different thicknesses can be obtained and range from 8 to 21 nm. More interestingly, the mean constituent CdSe nanocrystal diameter can be varied and results in size-dependent shell emission spectra.

  13. Turnover of Se in adequately fed chickens using Se-75 as a tracer.

    PubMed

    Brandt-Kjelsen, A; Govasmark, E; Haug, A; Salbu, B

    2014-06-01

    Inorganic selenium (Se) in the form of selenite is applied to livestock to avoid Se deficiency. Selenite is, however, an artificial Se source in diets of unsupplemented chickens. It is therefore hypothesized that organic Se sources, such as Se-enriched yeast and wheat, could be a more suitable Se supply in animal nutrition, although information on the transition of Se from organic Se sources in fast-growing chickens is scarce. In this work, chickens were fed a low Se diet (0.27 ± 0.01 mg Se/kg, Se-enriched yeast) until 20 days of age, after which the Se concentration was increased to maximum concentration allowed by the poultry industry in Europe (0.5 p.p.m. Se). At the same time, a daily contribution of carrier-free (75)Se tracer from labelled wheat was administered from day 20 to 27. The chickens showed S and Se homeostasis, as the concentration of S and Se in liver, blood or kidney remained about constant, and steady state of S and Se in the other organs was reached 1 day after the diet shift. The uptake of (75)Se was readily seen in all organs. After 1 week, the depuration of the (75)Se tracer was followed, and biological half-lives and retention in individual organs were determined. The shortest biological half-lives were observed in major metabolic organs, the liver, kidney and pancreas with half-lives close to 4 days. There was a significant (p < 0.05) uptake in lung, brain and muscle that reached steady state when the administration of (75)Se was terminated. The half-life of (75)Se in heart was 9 days and 7 days in blood. The longest half-lives were observed in muscle (12 days), brain and lungs (13 days). All half-lives were shorter than in Se deplete animals.

  14. Low temperature solution-phase growth of ZnSe and ZnSe/CdSe core/shell nanowires

    NASA Astrophysics Data System (ADS)

    Petchsang, Nattasamon; Shapoval, Liubov; Vietmeyer, Felix; Yu, Yanghai; Hodak, Jose H.; Tang, I.-Ming; Kosel, Thomas H.; Kuno, Masaru

    2011-08-01

    High quality ZnSe nanowires (NWs) and complementary ZnSe/CdSe core/shell species have been synthesized using a recently developed solution-liquid-solid (SLS) growth technique. In particular, bismuth salts as opposed to pre-synthesized Bi or Au/Bi nanoparticles have been used to grow NWs at low temperatures in solution. Resulting wires are characterized using transmission electron microscopy and possess mean ensemble diameters between 15 and 28 nm with accompanying lengths ranging from 4-10 μm. Subsequent solution-based overcoating chemistry results in ZnSe wires covered with CdSe nanocrystals. By varying the shell's growth time, different thicknesses can be obtained and range from 8 to 21 nm. More interestingly, the mean constituent CdSe nanocrystal diameter can be varied and results in size-dependent shell emission spectra.High quality ZnSe nanowires (NWs) and complementary ZnSe/CdSe core/shell species have been synthesized using a recently developed solution-liquid-solid (SLS) growth technique. In particular, bismuth salts as opposed to pre-synthesized Bi or Au/Bi nanoparticles have been used to grow NWs at low temperatures in solution. Resulting wires are characterized using transmission electron microscopy and possess mean ensemble diameters between 15 and 28 nm with accompanying lengths ranging from 4-10 μm. Subsequent solution-based overcoating chemistry results in ZnSe wires covered with CdSe nanocrystals. By varying the shell's growth time, different thicknesses can be obtained and range from 8 to 21 nm. More interestingly, the mean constituent CdSe nanocrystal diameter can be varied and results in size-dependent shell emission spectra. Electronic supplementary information (ESI) available. See DOI: 10.1039/c1nr10176e

  15. The reactivity of [PhP(Se)(mu-Se)]2 and (PhP)3Se2 towards acetylenes and cyanamides: X-ray crystal structures of some P-Se-C and P-Se-C-N heterocycles.

    PubMed

    Bhattacharyya, Pravat; Slawin, Alexandra M Z; Woollins, J Derek

    2002-06-17

    Several unusual P-Se-C and P-Se-C-N heterocycles are formed by the reaction of [PhP(Se)(mu-Se)]2 or (PhP)3Se2 with alkynes or cyanamides, generated by the fragmentation of the organophosphorus-selenium compound and addition across the C identical to C or C identical to N triple bond of the organic substrate. X-ray crystallographic analysis reveals an unexpected diversity of structural motifs within these heterocyclic systems, including P2SeCN, P2C2Se and PC2Se2 rings.

  16. Oxidation of ultrathin GaSe

    SciTech Connect

    Thomas Edwin Beechem; McDonald, Anthony E.; Ohta, Taisuke; Howell, Stephen W.; Kalugin, Nikolai G.; Kowalski, Brian M.; Brumbach, Michael T.; Spataru, Catalin D.; Pask, Jesse A.

    2015-10-26

    Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga2Se3 and amorphous Se. Furthermore, photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

  17. Oxidation of ultrathin GaSe

    DOE PAGES

    Thomas Edwin Beechem; McDonald, Anthony E.; Ohta, Taisuke; Howell, Stephen W.; Kalugin, Nikolai G.; Kowalski, Brian M.; Brumbach, Michael T.; Spataru, Catalin D.; Pask, Jesse A.

    2015-10-26

    Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga2Se3 and amorphous Se. Furthermore, photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

  18. Oxidation of ultrathin GaSe

    SciTech Connect

    Beechem, Thomas E. Brumbach, Michael T.; McDonald, Anthony E.; Howell, Stephen W.; Ohta, Taisuke; Kowalski, Brian M.; Pask, Jesse A.; Kalugin, Nikolai G.; Spataru, Catalin D.

    2015-10-26

    Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga{sub 2}Se{sub 3} and amorphous Se. Photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

  19. Metabolism of sup 75 Se from ( sup 75 Se) selenate into selenoproteins in rats

    SciTech Connect

    Evenson, J.K.; Thompson, K.M.; Weiss, S.L.; Sunde, R.A. )

    1991-03-11

    Since the metabolism and nutritional biochemistry of selenate has not been studied extensively, the authors used our SDS/PAGE procedure to study ({sup 75}Se) selenate distribution, retention and incorporation into selenoproteins. The authors hypothesis was that the distribution of ({sup 75}Se) selenate among tissues would differ compared to selenite, but that {sup 75}Se incorporation into selenoproteins would follow the same pattern as selenite. To test this hypothesis, male weanling rats were fed a torula yeast-based diet supplemented with 0, 0.2, or 2 {mu}g Se/g diet for 7 wk. Rats were injected iv with 50 {mu}Ci ({sup 75}Se) selenate, and killed 1, 3, 24, and 72 h later. Total {sup 75}Se retention decreased with increasing dietary Se, and was less than previously observed for ({sup 75}Se) selenite at each level of Se. Tissue {sup 75}Se recoveries for ({sup 75}Se) selenite were 22-88% of the values previously measured for ({sup 75}Se) selenite. {sup 75}Se incorporation profiles for selenate were virtually identical to those observed for selenite in all tissues, except in Se-deficient kidney cytosol where the 60 kDa {sup 75}Se selenoprotein was not the major selenoprotein. This study shows that the chemical form of selenium can affect distribution and retention, but that the form of selenium has little effect on incorporation into selenoproteins.

  20. The Structure and Electrical Properties of the Ag2Se + Ga2Se3 + GeSe2 Glass System

    NASA Astrophysics Data System (ADS)

    Marple, Maxwell Adam Thomas

    Silver containing homogeneous chalcogenide glasses in the ternary system Ag2Se-Ga2Se3-GeSe2 (AGGS) are synthesized and their atomic structure-property relationships are investigated. Structural studies are carried out using Raman, 77Se, 71Ga, 69Ga, and 109Ag nuclear magnetic resonance (NMR) spectroscopy. The structure of these glasses consists primarily of a network of corner sharing (Ga/Ge)Se4/2 tetrahedra with a small fraction of homopolar Se-Se bonds. Compositional modification of the atomic structure follows the charge compensated network model developed in the literature for aluminosilicate glasses. Ag2Se acts as a network modifier, forming non-bridging Se in glasses with Ag/Ga >1, while Ga 2Se3 plays the role of a network intermediate similar to Al2O3 in oxide glasses. The network favors the formation of homopolar Ge-Ge bonding in glasses with Ag/Ga <1, to accommodate the Se deficiency brought by the incorporation of Ga2Se3 with Ga being tetrahedrally coordinated to Se. This structural model is consistent with the variation in the glass transition temperatures and molar volume. Electrical Impedance Spectroscopy (EIS) reveals the ionic conductivity of the AGGS glasses to be quite high at ambient temperature, reaching up to 10 --4 S/cm for glasses with the highest Ag content. Increasing Se deficiency with respect to stoichiometry can enhance the conductivity further to ˜3x10--4 S/cm . Transference number measurements using the electromotive force (EMF) method as well as variable temperature 109Ag NMR line shape studies indicate that the conductivity is predominantly ionic in nature and results from fast hopping dynamics of Ag ions. The high ionic conductivity can be related to a heavily modified structural network that results in a potential energy landscape with many suitable hopping sites for the Ag ions. These structural characteristics and electrical properties of the glasses in the AGGS system may guide in the development of next generation fast ion

  1. Unrecognized hemoglobin SE disease as microcytosis

    PubMed Central

    Cooper, Barry; Guileyardo, Joseph; Mora, Adan

    2016-01-01

    Hemoglobin SE disease was first described during the 1950s as a relatively benign microcytosis, but increasing prevalence has revealed a predisposition towards vasoocclusive sickling. Recognition of SE hemoglobinopathies’ potential complications is crucial so medical measures can be utilized to avoid multiorgan injury. PMID:27365881

  2. Se passivation and re-growth on ZnSe and (Zn,Mn)Se (001) epilayer surfaces

    NASA Astrophysics Data System (ADS)

    Jonker, B. T.; Krebs, J. J.; Prinz, G. A.

    1988-09-01

    We report the use of a thin Se coating to passivate and protect the surface of ZnSe and Zn1-xMnxSe (001) epilayers on GaAs(001) prior to removal from the molecular beam epitaxy (MBE) system and exposure to atmosphere. After prolonged exposure to the laboratory ambient, the samples are returned to the MBE system and the Se is thermally desorbed. The resultant surface is clean and well-ordered as demonstrated by Auger electron spectroscopy and reflection high energy electron diffraction (RHEED), and either homo- or hetero-epitaxial growth is continued. For ZnSe epilayers grown in two equal stages of a total thickness of 1 μm with an intervening passivation and 24 hour air exposure, the (004) x-ray double crystal rocking curve exhibits no increase in linewidth relative to continuously grown reference samples of the same thickness. In the case of heteroepitaxial growth of Fe films on Zn0.8Mn0.2Se, RHEED shows well-ordered single crystal growth of α-Fe(001) even at very low coverages. Ferromagnetic resonances and vibrating sample magnetometry data show these films to be of excellent magnetic quality. This Se passivation technique thus offers a ready means of transferring these II-VI epilayers from the growth system to other facilities.

  3. Cs(2)UPd(3)Se(6).

    PubMed

    Oh, George N; Ibers, James A

    2011-01-12

    Dicaesium uranium(IV) tripalladium(II) hexa-selenide, Cs(2)UPd(3)Se(6), crystallizes in the space group Fmmm in the Ba(2)NaCu(3)O(6) structure type. The asymmetric unit comprises the following atoms with site symmetries as shown: U1 (mm2), Cs1 (222), Cs2 (m2m), Pd1 (.m.), Pd2 (2mm), Se1 (m..), and Se2 (1). This layered structure contains six edge-sharing square-planar [PdSe(4)] units that form a hexa-gon. These, in turn, edge-share with [USe(6)] trigonal-prismatic units, forming an extended layer parallel to (010). The layers are stacked along [010]. They are staggered, and are separated by the Cs atoms. The Cs atoms are either coordinated in a square anti-prism of Se atoms or are ten-coordinate, with one square face and the opposite face hexa-gonal.

  4. Neutron-capture resonances for 82Se

    NASA Astrophysics Data System (ADS)

    Browne, J. C.; Berman, B. L.

    1982-09-01

    Strong neturon-capture resonances for 82Se have been found at 3.63, 7.1, and 9.51 keV and weaker ones have been found at 0.58, 1.15, and possibly 13.54 and 16.5 keV. None was found at lower neutron energies; this absence of strong epithermal capture resonances invalidates the hypothesis that the depth dependence of the abundance ratio of 78Kr to 83Kr found in meteoritic studies owes its origin to anomalous 83Kr production by neutron capture on 82Se. Precise energies have been assigned to neutron-capture resonances up to 40 keV for all the other selenium isotopes as well. NUCLEAR REACTIONS 82Se, natSe(n, γ) neutron time of flight; resonance energies; abundance ratio of 78Kr to 83Kr.

  5. Double electron capture searches in 74Se

    NASA Astrophysics Data System (ADS)

    Lehnert, B.; Wester, T.; Degering, D.; Sommer, D.; Wagner, L.; Zuber, K.

    2016-08-01

    A search for various double electron capture modes of 74Se has been performed using an ultralow background Ge-detector in the Felsenkeller laboratory, Germany. Especially for the potentially resonant transition into the 1204.2 keV excited state of 74Ge a lower half-life limit of 0.70× {10}19 yr (90% credibility) has been obtained. Serious concerns are raised about the validity of obtained 74Se limits in some recent publications.

  6. Synthesis of (/sup 75/Se)trimethylselenonium iodide from (/sup 75/Se)selenocystine

    SciTech Connect

    Foster, S.J.; Ganther, H.E.

    1984-02-15

    The synthesis of (/sup 75/Se)trimethylselenonium iodide from (/sup 75/)selenocystine is described. The starting compound is reduced to (/sup 75/Se)selenocysteine with borohydride and reacted with methyl iodide to form (/sup 75/Se)Se-methyl-selenocysteine, then treated with methyl iodide in formic acid solution to form Se-dimethyl-selenocysteine selenonium iodide. Over a period of days, the selenonium intermediate undergoes spontaneous elimination to form alanine and dimethyl selenide, which reacts with methyl iodide to give the trimethylselenonium product in over 90% yield. 15 references.

  7. Atomistic Model of Physical Ageing in Se-rich As-Se Glasses

    SciTech Connect

    Golovchak,R.; Shpotyuk, O.; Kozdras, A.; Bureau, B.; Vlcek, M.; Ganjoo, A.; Jain, H.

    2007-01-01

    Thermal, optical, X-ray excited and magnetic methods were used to develop a microstructural model of physical ageing in Se-rich glasses. The glass composition As10Se90, possessing a typical cross-linked chain structure, was chosen as a model object for the investigations. The effect of physical ageing in this glass was revealed by differential scanning calorimetry, whereas the corresponding changes in its atomic arrangement were studied by extended X-ray absorption fine structure, Raman and solid-state 77Se nuclear magnetic resonance spectroscopy. Straightening-shrinkage processes are shown to be responsible for the physical ageing in this Se-rich As-Se glass.

  8. Amphoteric CdSe nanocrystalline quantum dots.

    PubMed

    Islam, Mohammad A

    2008-06-25

    The nanocrystal quantum dot (NQD) charge states strongly influence their electrical transport properties in photovoltaic and electroluminescent devices, optical gains in NQD lasers, and the stability of the dots in thin films. We report a unique electrostatic nature of CdSe NQDs, studied by electrophoretic methods. When we submerged a pair of metal electrodes, in a parallel plate capacitor configuration, into a dilute solution of CdSe NQDs in hexane, and applied a DC voltage across the pair, thin films of CdSe NQDs were deposited on both the positive and the negative electrodes. Extensive characterizations including scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman studies revealed that the films on both the positive and the negative electrodes were identical in every respect, clearly indicating that: (1) a fraction (<1%) of the CdSe NQDs in free form in hexane solution are charged and, more importantly, (2) there are equal numbers of positive and negative CdSe NQDs in the hexane solution. Experiments also show that the number of deposited dots is at least an order of magnitude higher than the number of initially charged dots, indicating regeneration. We used simple thermodynamics to explain such amphoteric nature and the charging/regeneration of the CdSe NQDs.

  9. A transferable force field for CdS-CdSe-PbS-PbSe solid systems

    SciTech Connect

    Fan, Zhaochuan; Vlugt, Thijs J. H.; Koster, Rik S.; Fang, Changming; Huis, Marijn A. van; Wang, Shuaiwei; Yalcin, Anil O.; Tichelaar, Frans D.; Zandbergen, Henny W.

    2014-12-28

    A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., “Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth,” Nano Lett. 14, 3661–3667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and CdS, and provide detailed information on the validation of this force field. The parameterization combines Bader charge analysis, empirical fitting, and ab initio energy surface fitting. When compared with experimental data and density functional theory calculations, it is shown that a wide range of physical properties of bulk PbS, PbSe, CdS, CdSe, and their mixed phases can be accurately reproduced using this force field. The choice of functional forms and parameterization strategy is demonstrated to be rational and effective. This transferable force field can be used in various studies on II-VI and IV-VI semiconductor materials consisting of CdS, CdSe, PbS, and PbSe. Here, we demonstrate the applicability of the force field model by molecular dynamics simulations whereby transformations are initiated by cation exchange.

  10. One-pot synthesis of hollow NiSe-CoSe nanoparticles with improved performance for hybrid supercapacitors

    NASA Astrophysics Data System (ADS)

    Chen, Haichao; Fan, Meiqiang; Li, Chao; Tian, Guanglei; Lv, Chunju; Chen, Da; Shu, Kangying; Jiang, Jianjun

    2016-10-01

    Hollow NiSe-CoSe samples have been synthesized for the first time via a one-pot solvothermal approach. The strategy is robust enough to synthesize NiSe-CoSe nanoparticles with different NiSe to CoSe ratios but with a similar hollow structure. Co ions in the NiSe-CoSe nanoparticles play decisive role for formation of the hollow structure; otherwise, the nanoparticles become solid for the NiSe sample. When used as the positive electroactive materials for energy storage, the NiSe-CoSe samples show excellent electrochemical activity in alkaline electrolyte. Using the synergistic effect between NiSe and CoSe, the electrochemical performance of NiSe-CoSe can be tuned by varying the NiSe to CoSe ratios. The NiSe-CoSe sample with a NiSe to CoSe ratio of 4:2 shows the best electrochemical performance in terms of superior specific capacity, improved rate capability and excellent cycling stability. In addition, the electrochemical performance of NiSe-CoSe sample with a NiSe to CoSe ratio of 4:2 is also evaluated via assembling hybrid supercapacitors with RGO, and the hybrid supercapacitor delivers both high power and energy densities (41.8 Wh kg-1 at 750 W kg-1 and 20.3 Wh kg-1 at 30 kW kg-1).

  11. Improved photoluminescence quantum yield and stability of CdSe-TOP, CdSe-ODA-TOPO, CdSe/CdS and CdSe/EP nanocomposites

    NASA Astrophysics Data System (ADS)

    Wei, Shutian; Zhu, Zhilin; Wang, Zhixiao; Wei, Gugangfen; Wang, Pingjian; Li, Hai; Hua, Zhen; Lin, Zhonghai

    2016-07-01

    Size-controllable monodisperse CdSe nanocrystals with different organic capping were prepared based on the hot-injection method. The effective separation of nucleation and growth was achieved by rapidly mixing two highly reactive precursors. As a contrast, we prepared CdSe/CdS nanocrystals (NCs) successfully based on the selective ion layer adsorption and reaction (SILAR) technique. This inorganic capping obtained higher photoluminescence quantum yield (PLQY) of 59.3% compared with organic capping of 40.8%. Furthermore, the CdSe-epoxy resin (EP) composites were prepared by adopting a flexible ex situ method, and showed excellent stability in the ambient environment for one year. So the composites with both high PLQY of nanocrystals and excellent stability are very promising to device application.

  12. Se status in normal and pathological human individuals before and after Se supplementation

    NASA Astrophysics Data System (ADS)

    Bellisola, G.; Cinque, G.; Galassini, S.; Guidi, G. C.; Liu, N. Q.; Moschini, G.

    1996-04-01

    The determination of selenium in plasma and in urine samples has been suggested for the assessment of Se status in human individuals. The kidney is of fundamental importance in Se homeostasis: with low Se intake its excretion will be decreased and with high Se intake it will be increased. In 21 patients with kidney disease (8 with normal kidney function and 13 with moderate renal failure) Se was measured in 1 ml of urine by PIXE after preconcentration of the sample. The total urine volume was measured to calculate total daily Se excretion. The same procedure was applied to 14 normal individuals for comparison. All individuals were then supplemented orally with selenite for 8 weeks (Se = 600 μg/day) and the procedure was repeated. The behaviour of the major selenoproteins was also investigated by measuring glutathione peroxidase activities in plasma, in platelets and in erythrocyte samples. For renal function, serum and urine creatinine concentrations were utilised and creatinine clearances were calculated. Results obtained were compared before and after Se treatment and between groups. Some correlation studies were carried out between Se and kidney functions and/or selenoperoxidase activities.

  13. Electroreflectance study of RuSe 2

    NASA Astrophysics Data System (ADS)

    Huang, Y. S.; Lin, S. S.; Sheu, J. S.; Shen, W. M.; Pollak, Fred H.

    1990-12-01

    We report the first electrolyte-electroreflectance (EER) study of a RuSe 2 single crystal in the photon energy region of 0.9-5.5 eV. The EER spectrum exhibits differential like structure in the vicinity of interband transitions. The transition energies are determined accurately. A probable energy-band structure is constructed.

  14. Y Se Repite = And It Repeats Itself

    ERIC Educational Resources Information Center

    Katzew, Adriana

    2010-01-01

    In this article, the author discusses Y Se Repite [And It Repeats Itself], a project she conceptualized due to the growing number of Latino/a Mexican migrant workers in dairy farms in the state of Vermont. In 2006, approximately 2,000 Latinos/as--most of them undocumented Mexican migrant workers--worked throughout the state's dairy farms, yet…

  15. SE Great Basin Play Fairway Analysis

    DOE Data Explorer

    Adam Brandt

    2015-11-15

    Within this submission are multiple .tif images with accompanying metadata of magnetotelluric conductor occurrence, fault critical stress composite risk segment (CRS), permeability CRS, Quaternary mafic extrusions, Quaternary fault density, and Quaternary rhyolite maps. Each of these contributed to a final play fairway analysis (PFA) for the SE Great Basin study area.

  16. Effect of alcohol consumption on selenium (Se) bioavailability in rats

    SciTech Connect

    Cho, H.K.; Snook, J.T.; Yang, F.L.

    1986-03-01

    This study was done to determine the effects of alcohol ingestion on Se bioavailability in initially Se-depleted rats. Weanling male rats were fed a Se deficient (0.012 mg/kg) basal diet for 4 weeks and then for the subsequent 4 weeks were supplemented at 0.031 mg Se/kg or at 0.085 mg Se/kg of diet in the form of high Se yeast. During the Se repletion period alcohol replaced medium chain triglycerides in the diet at 3 levels: 0%, 10%, and 20% of calories. Dietary Se level significantly (P < .0001) affected urinary Se, fecal Se, Se absorption, Se balance, whole blood Se, whole blood glutathione peroxidase activity, and liver Se. In rats fed the higher Se diet total liver Se increased 50% when 20% rather than 0% alcohol was given. In rats fed the lower Se diet total liver Se decreased 12% as dietary alcohol increased from 0 to 20%. There was a significant (P < .0015) interaction between alcohol and Se level. All the other parameters for Se bioavailability were not affected by alcohol consumption. However, alcohol consumption significantly reduced growth rate at both Se levels.

  17. Ba4Ga2Se8: A ternary selenide containing chains and discrete Se22- units

    NASA Astrophysics Data System (ADS)

    Yin, Wenlong; Iyer, Abishek K.; Lin, Xinsong; Mar, Arthur

    2016-05-01

    The ternary selenide Ba4Ga2Se8 has been synthesized by reaction of BaSe, Ga2Se3, and Se at 1023 K. Single-crystal X-ray diffraction analysis revealed a monoclinic structure (space group P21/c, Z=4, a=13.2393(5) Å, b=6.4305(2) Å, c=20.6432(8) Å, β=104.3148(6)°) featuring one-dimensional chains of corner-sharing Ga-centered tetrahedra and discrete Se22- anionic units, with charge-compensating Ba2+ cations located between them. The UV/vis/NIR diffuse reflectance spectrum reveals an optical band gap of 1.63(2) eV, which is consistent with the black color of the crystals and agrees with a calculated gap of 1.51 eV obtained from band structure calculations. The presence of the Se22- units narrows the band gap in Ba4Ga2Se8 relative to other Ba-Ga-Se phases.

  18. Ultra-Fast Synthesis for Ag2Se and CuAgSe Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    DUAN, H. Z.; LI, Y. L.; ZHAO, K. P.; QIU, P. F.; SHI, X.; CHEN, L. D.

    2016-10-01

    Ag2Se and CuAgSe have been recently reported as promising thermoelectric materials at room temperature. The traditional melting-annealing-sintering processes are used to grow Ag2Se and CuAgSe materials with the disadvantages of high costs of energy and time. In this work, phase-pure polycrystalline Ag2Se and CuAgSe compounds were synthesized from raw elemental powders directly by manual mixing followed by spark plasma sintering (MM-SPS) in a few minutes. The influence of SPS heating rate on the phase composition, microstructure, and thermoelectric properties, including Seebeck coefficient, electrical conductivity, and thermal conductivity, were investigated. The zTs of 0.8 at 390 K and 0.6 at 450 K are obtained for Ag2Se and CuAgSe, respectively, which is comparable with the values in the materials prepared by the traditional method. Furthermore, this ultrafast sample synthesis can significantly save material synthesis time and thus has the obvious advantage for large-scale production.

  19. Ultra-Fast Synthesis for Ag2Se and CuAgSe Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    DUAN, H. Z.; LI, Y. L.; ZHAO, K. P.; QIU, P. F.; SHI, X.; CHEN, L. D.

    2016-06-01

    Ag2Se and CuAgSe have been recently reported as promising thermoelectric materials at room temperature. The traditional melting-annealing-sintering processes are used to grow Ag2Se and CuAgSe materials with the disadvantages of high costs of energy and time. In this work, phase-pure polycrystalline Ag2Se and CuAgSe compounds were synthesized from raw elemental powders directly by manual mixing followed by spark plasma sintering (MM-SPS) in a few minutes. The influence of SPS heating rate on the phase composition, microstructure, and thermoelectric properties, including Seebeck coefficient, electrical conductivity, and thermal conductivity, were investigated. The zTs of 0.8 at 390 K and 0.6 at 450 K are obtained for Ag2Se and CuAgSe, respectively, which is comparable with the values in the materials prepared by the traditional method. Furthermore, this ultrafast sample synthesis can significantly save material synthesis time and thus has the obvious advantage for large-scale production.

  20. Epitaxial 2D MoSe2 (HfSe2) Semiconductor/2D TaSe2 Metal van der Waals Heterostructures.

    PubMed

    Tsoutsou, Dimitra; Aretouli, Kleopatra E; Tsipas, Polychronis; Marquez-Velasco, Jose; Xenogiannopoulou, Evangelia; Kelaidis, Nikolaos; Aminalragia Giamini, Sigiava; Dimoulas, Athanasios

    2016-01-27

    Molecular beam epitaxy of 2D metal TaSe2/2D MoSe2 (HfSe2) semiconductor heterostructures on epi-AlN(0001)/Si(111) substrates is reported. Electron diffraction reveals an in-plane orientation indicative of van der Waals epitaxy, whereas electronic band imaging supported by first-principles calculations and X-ray photoelectron spectroscopy indicate the presence of a dominant trigonal prismatic 2H-TaSe2 phase and a minor contribution from octahedrally coordinated TaSe2, which is present in TaSe2/AlN and TaSe2/HfSe2/AlN but notably absent in the TaSe2/MoSe2/AlN, indicating superior structural quality of TaSe2 grown on MoSe2. Apart from its structural and chemical compatibility with the selenide semiconductors, TaSe2 has a workfunction of 5.5 eV as measured by ultraviolet photoelectron spectroscopy, which matches very well with the semiconductor workfunctions, implying that epi-TaSe2 can be used for low-resistivity contacts to MoSe2 and HfSe2. PMID:26727305

  1. 'Cold' crystallization in nanostructurized 80GeSe2-20Ga2Se3 glass.

    PubMed

    Klym, Halyna; Ingram, Adam; Shpotyuk, Oleh; Calvez, Laurent; Petracovschi, Elena; Kulyk, Bohdan; Serkiz, Roman; Szatanik, Roman

    2015-01-01

    'Cold' crystallization in 80GeSe2-20Ga2Se3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga2Se3 and/or GeGa4Se8 phases and prevalent GeSe2 phase extracted mainly at the surface of thermally treated samples with preceding nucleation and void agglomeration in the initial stage of annealing are characteristic features of cold crystallization.

  2. Superconductivity enhanced by Se doping in Eu3Bi2(S,Se)4F4

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Zhai, H. F.; Tang, Z. J.; Li, L.; Li, Y. K.; Chen, Q.; Chen, J.; Wang, Z.; Feng, C. M.; Cao, G. H.; Xu, Z. A.

    2015-07-01

    We investigated the negative-chemical-pressure effect of Eu3Bi2S4-x Se x F4 (0 ≤ x ≤ 2.0) by the partial substitution of S with Se. The crystalline lattice substantially expands as Se is doped, suggesting an effective negative chemical pressure. With Se/S doping, the charge-density-wave-like anomaly is suppressed, and meanwhile the superconducting transition temperature (T_c) is enhanced. For x = 2.0 , T c reaches 3.35 K and bulk superconductivity is confirmed by the strong diamagnetic signal, with shielding volume fraction over 90%. Magnetic-susceptibility, specific-heat and Hall-effect measurements reveal that the Se/S doping increases the carrier density, corresponding to the increase of the average Eu valence. Our work provides a rare paradigm of negative-chemical-pressure effect.

  3. 'Cold' crystallization in nanostructurized 80GeSe2-20Ga2Se3 glass

    NASA Astrophysics Data System (ADS)

    Klym, Halyna; Ingram, Adam; Shpotyuk, Oleh; Calvez, Laurent; Petracovschi, Elena; Kulyk, Bohdan; Serkiz, Roman; Szatanik, Roman

    2015-02-01

    'Cold' crystallization in 80GeSe2-20Ga2Se3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga2Se3 and/or GeGa4Se8 phases and prevalent GeSe2 phase extracted mainly at the surface of thermally treated samples with preceding nucleation and void agglomeration in the initial stage of annealing are characteristic features of cold crystallization.

  4. [NiFeSe]-hydrogenase chemistry.

    PubMed

    Wombwell, Claire; Caputo, Christine A; Reisner, Erwin

    2015-11-17

    The development of technology for the inexpensive generation of the renewable energy vector H2 through water splitting is of immediate economic, ecological, and humanitarian interest. Recent interest in hydrogenases has been fueled by their exceptionally high catalytic rates for H2 production at a marginal overpotential, which is presently only matched by the nonscalable noble metal platinum. The mechanistic understanding of hydrogenase function guides the design of synthetic catalysts, and selection of a suitable hydrogenase enables direct applications in electro- and photocatalysis. [FeFe]-hydrogenases display excellent H2 evolution activity, but they are irreversibly damaged upon exposure to O2, which currently prevents their use in full water splitting systems. O2-tolerant [NiFe]-hydrogenases are known, but they are typically strongly biased toward H2 oxidation, while H2 production by [NiFe]-hydrogenases is often product (H2) inhibited. [NiFeSe]-hydrogenases are a subclass of [NiFe]-hydrogenases with a selenocysteine residue coordinated to the active site nickel center in place of a cysteine. They exhibit a combination of unique properties that are highly advantageous for applications in water splitting compared with other hydrogenases. They display a high H2 evolution rate with marginal inhibition by H2 and tolerance to O2. [NiFeSe]-hydrogenases are therefore one of the most active molecular H2 evolution catalysts applicable in water splitting. Herein, we summarize our recent progress in exploring the unique chemistry of [NiFeSe]-hydrogenases through biomimetic model chemistry and the chemistry with [NiFeSe]-hydrogenases in semiartificial photosynthetic systems. We gain perspective from the structural, spectroscopic, and electrochemical properties of the [NiFeSe]-hydrogenases and compare them with the chemistry of synthetic models of this hydrogenase active site. Our synthetic models give insight into the effects on the electronic properties and reactivity of

  5. [NiFeSe]-hydrogenase chemistry.

    PubMed

    Wombwell, Claire; Caputo, Christine A; Reisner, Erwin

    2015-11-17

    The development of technology for the inexpensive generation of the renewable energy vector H2 through water splitting is of immediate economic, ecological, and humanitarian interest. Recent interest in hydrogenases has been fueled by their exceptionally high catalytic rates for H2 production at a marginal overpotential, which is presently only matched by the nonscalable noble metal platinum. The mechanistic understanding of hydrogenase function guides the design of synthetic catalysts, and selection of a suitable hydrogenase enables direct applications in electro- and photocatalysis. [FeFe]-hydrogenases display excellent H2 evolution activity, but they are irreversibly damaged upon exposure to O2, which currently prevents their use in full water splitting systems. O2-tolerant [NiFe]-hydrogenases are known, but they are typically strongly biased toward H2 oxidation, while H2 production by [NiFe]-hydrogenases is often product (H2) inhibited. [NiFeSe]-hydrogenases are a subclass of [NiFe]-hydrogenases with a selenocysteine residue coordinated to the active site nickel center in place of a cysteine. They exhibit a combination of unique properties that are highly advantageous for applications in water splitting compared with other hydrogenases. They display a high H2 evolution rate with marginal inhibition by H2 and tolerance to O2. [NiFeSe]-hydrogenases are therefore one of the most active molecular H2 evolution catalysts applicable in water splitting. Herein, we summarize our recent progress in exploring the unique chemistry of [NiFeSe]-hydrogenases through biomimetic model chemistry and the chemistry with [NiFeSe]-hydrogenases in semiartificial photosynthetic systems. We gain perspective from the structural, spectroscopic, and electrochemical properties of the [NiFeSe]-hydrogenases and compare them with the chemistry of synthetic models of this hydrogenase active site. Our synthetic models give insight into the effects on the electronic properties and reactivity of

  6. Two-dimensional semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures by molecular beam epitaxy

    SciTech Connect

    Aretouli, K. E.; Tsipas, P.; Tsoutsou, D.; Marquez-Velasco, J.; Xenogiannopoulou, E.; Giamini, S. A.; Vassalou, E.; Kelaidis, N.; Dimoulas, A.

    2015-04-06

    Using molecular beam epitaxy, atomically thin 2D semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures are grown on AlN(0001)/Si(111) substrates. Details of the electronic band structure of HfSe{sub 2} are imaged by in-situ angle resolved photoelectron spectroscopy indicating a high quality epitaxial layer. High-resolution surface tunneling microscopy supported by first principles calculations provides evidence of an ordered Se adlayer, which may be responsible for a reduction of the measured workfunction of HfSe{sub 2} compared to theoretical predictions. The latter reduction minimizes the workfunction difference between the HfSe{sub 2} and MoSe{sub 2} layers resulting in a small valence band offset of only 0.13 eV at the MoSe{sub 2}/HfSe{sub 2} heterointerface and a weak type II band alignment.

  7. Anisotropy in CdSe quantum rods

    SciTech Connect

    Li, Liang-shi

    2003-09-01

    The size-dependent optical and electronic properties of semiconductor nanocrystals have drawn much attention in the past decade, and have been very well understood for spherical ones. The advent of the synthetic methods to make rod-like CdSe nanocrystals with wurtzite structure has offered us a new opportunity to study their properties as functions of their shape. This dissertation includes three main parts: synthesis of CdSe nanorods with tightly controlled widths and lengths, their optical and dielectric properties, and their large-scale assembly, all of which are either directly or indirectly caused by the uniaxial crystallographic structure of wurtzite CdSe. The hexagonal wurtzite structure is believed to be the primary reason for the growth of CdSe nanorods. It represents itself in the kinetic stabilization of the rod-like particles over the spherical ones in the presence of phosphonic acids. By varying the composition of the surfactant mixture used for synthesis we have achieved tight control of the widths and lengths of the nanorods. The synthesis of monodisperse CdSe nanorods enables us to systematically study their size-dependent properties. For example, room temperature single particle fluorescence spectroscopy has shown that nanorods emit linearly polarized photoluminescence. Theoretical calculations have shown that it is due to the crossing between the two highest occupied electronic levels with increasing aspect ratio. We also measured the permanent electric dipole moment of the nanorods with transient electric birefringence technique. Experimental results on nanorods with different sizes show that the dipole moment is linear to the particle volume, indicating that it originates from the non-centrosymmetric hexagonal lattice. The elongation of the nanocrystals also results in the anisotropic inter-particle interaction. One of the consequences is the formation of liquid crystalline phases when the nanorods are dispersed in solvent to a high enough

  8. SE Great Basin Play Fairway Analysis

    SciTech Connect

    Adam Brandt

    2015-11-15

    This submission includes a Na/K geothermometer probability greater than 200 deg C map, as well as two play fairway analysis (PFA) models. The probability map acts as a composite risk segment for the PFA models. The PFA models differ in their application of magnetotelluric conductors as composite risk segments. These PFA models map out the geothermal potential in the region of SE Great Basin, Utah.

  9. Magnetic ground state of FeSe

    PubMed Central

    Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K.; Iida, K.; Christianson, A. D.; Walker, H. C.; Adroja, D. T.; Abdel-Hafiez, M.; Chen, Xiaojia; Chareev, D. A.; Vasiliev, A. N.; Zhao, Jun

    2016-01-01

    Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities. PMID:27431986

  10. Magnetic ground state of FeSe.

    PubMed

    Wang, Qisi; Shen, Yao; Pan, Bingying; Zhang, Xiaowen; Ikeuchi, K; Iida, K; Christianson, A D; Walker, H C; Adroja, D T; Abdel-Hafiez, M; Chen, Xiaojia; Chareev, D A; Vasiliev, A N; Zhao, Jun

    2016-01-01

    Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit Néel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts=90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here we report inelastic neutron-scattering experiments that reveal both stripe and Néel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the Néel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ∼60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S=1 nematic quantum-disordered paramagnet interpolating between the Néel and stripe magnetic instabilities. PMID:27431986

  11. Quadrupolar Spin Orders in FeSe

    NASA Astrophysics Data System (ADS)

    Wang, Zhentao; Nevidomskyy, Andriy

    Motivated by the absence of long-range magnetic order and the strong spin fluctuations observed in the Fe-based superconductor FeSe, we study spin-1 model on a square lattice up to next-nearest neighbor Heisenberg and biquadratic spin exchanges. The zero-temperature variational phase diagram gives the conventional antiferromagnetic order and also more exotic quadrupolar spin phases. These quadrupolar phases do not host long-range magnetic order and preserve time-reversal symmetry, but break the spin SU(2) symmetry. In particular, we observe a robust ferroquadrupolar order (FQ) in immediate proximity to the columnar AFM phase. We envision that FeSe may be positioned within the FQ phase close to the phase boundary. Using the flavor-wave technique, we calculate the structure factor inside the FQ phase and find a Goldstone mode emerging from Q = (0 , 0) , which however bears zero spectral weight at ω = 0 due to time reversal symmetry. At the same time, we observe strong spin fluctuations near (π , 0) / (0 , π) , which agrees with the recent neutron scattering experiments. Further, we calculate the higher order interactions between the (π , 0) and (0 , π) spin fluctuations inside the FQ phase, which may shed light on the C4 symmetry breaking in the nematic phase of FeSe.

  12. 77Se nuclear magnetic resonance of topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Georgieva, Nataliya M.; Rybicki, Damian; Guehne, Robin; Williams, Grant V. M.; Chong, Shen V.; Kadowaki, Kazuo; Garate, Ion; Haase, Jürgen

    2016-05-01

    Topological insulators constitute a new class of materials with an energy gap in the bulk and peculiar metallic states on the surface. We report on new features resulting from the bulk electronic structure, based on a comprehensive nuclear magnetic resonance (NMR) study of 77Se on Bi2Se3 and Cu0.15Bi2Se3 single crystals. First, we find two resonance lines and show that they originate from the two inequivalent Se lattice sites. Second, we observe unusual field-independent linewidths and attribute them to an unexpectedly strong internuclear coupling mediated by bulk electrons. In order to support this interpretation, we present a model calculation of the indirect internuclear coupling and show that the Bloembergen-Rowland coupling is much stronger than the Ruderman-Kittel-Kasuya-Yosida coupling. Our results call for a revision of earlier NMR studies and add information concerning the bulk electronic properties.

  13. Conduction band offset determination between strained CdSe and ZnSe layers using DLTS

    SciTech Connect

    Rangel-Kuoppa, Victor-Tapio

    2013-12-04

    The conduction band offset between strained CdSe layers embedded in unintentionally n-type doped ZnSe is measured and reported. Two samples, consisting of thirty Ultra Thin Quantum Wells (UTQWs) of CdSe embedded in ZnSe, grown by Atomic Layer Epitaxy, are used for this study. The thicknesses of the UTQWs are one and three monolayers (MLs) in each sample, respectively. As expected, the sample with one ML UTQWs does not show any energy level in the UTQWs due to the small thickness of the UTQWs, while the thickness of the sample with 3 ML UTQWs is large enough to form an energy level inside the UTQWs. This energy level appears as a majority trap with an activation energy of 223.58 ± 9.54 meV. This corresponds to UTQWs with barrier heights (the conduction band offset) between 742 meV and 784 meV. These values suggest that the band gap misfit between strained CdSe and ZnSe is around 70.5 to 74 % in the conduction band.

  14. Homopolar bonds in Se-rich Ge‒As‒Se chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Si-Wei, Xu; Rong-Ping, Wang; Zhi-Yong, Yang; Li, Wang; Luther-Davies, Barry

    2016-05-01

    We have prepared three groups of Ge-As-Se glasses in which the Se content is 5.5 mol%, 10 mol%, and 20 mol% rich, respectively. We explored the possibility of suppressing the formation of the Ge-Ge and As-As homopolar bonds in the glasses. Thermal kinetics analysis indicated that the 5.5 mol% Se-rich Ge11.5As24Se64.5 glass exhibits the minimum fragility and thus is most stable against structural relaxation. Analysis of the Raman spectra of the glasses indicated that the Ge-Ge and As-As homopolar bonds could be almost completely suppressed in 20 mol% Se-rich Ge15As14Se71 glass. Project supported by the Australian Research Council (ARC) Centre of Excellence for Ultrahigh Bandwidth Device for Optical System (Project CE110001018), Australian Research Council Discovery Programs (Project DP110102753), and the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions, China.

  15. Electronic Structure and Characteristics of Chemical Bonds in CuInSe2, CuGaSe2, and CuAlSe2

    NASA Astrophysics Data System (ADS)

    Maeda, Tsuyoshi; Wada, Takahiro

    2010-04-01

    Electronic structural calculations of chalcopyrite-type CuInSe2 and its related compounds, CuGaSe2 and CuAlSe2, were performed by a recently proposed screened-exchange local density approximation (sX-LDA) method. The theoretical band gaps of CuInSe2, CuGaSe2, and CuAlSe2, obtained by the conventional calculation method using a generalized gradient approximation (GGA) functional, were 0.04, 0.14, and 1.11 eV, respectively. These values were considerably underestimated in comparison with their experimental values of 1.04, 1.68, and 2.67 eV because the exchange-correlation energy was not precisely calculated. Therefore, electronic structural calculations of chalcopyrite-type CuInSe2 and related compounds were performed with an sX-LDA functional to obtain accurate electronic structure. The present sX-LDA calculation successfully reproduced the band gaps of CuInSe2 (0.96 eV), CuGaSe2 (1.36 eV), and CuAlSe2 (2.22 eV). The obtained electronic structures and band gap energies of CuInSe2, CuGaSe2, and CuAlSe2 are discussed on the basis of schematic molecular orbital diagrams of tetrahedral CuSe47-, InSe45-, GaSe45-, and AlSe45- clusters.

  16. Exciton spin dynamics in GaSe

    SciTech Connect

    Tang, Yanhao; Xie, Wei; McGuire, John A. Lai, Chih Wei; Mandal, Krishna C.

    2015-09-21

    We analyze exciton spin dynamics in GaSe under nonresonant circularly polarized optical pumping with an exciton spin-flip rate-equation model. The model reproduces polarized time-dependent photoluminescence measurements in which the initial circular polarization approaches unity even when pumping with 0.15 eV excess energy. At T = 10 K, the exciton spin relaxation exhibits a biexponential decay with sub-20 ps and >500 ps time constants, which are also reproduced by the rate-equation model assuming distinct spin-relaxation rates for hot (nonequilibrium) and cold band-edge excitons.

  17. Spectrum of sodiumlike selenium - Se XXIV

    NASA Technical Reports Server (NTRS)

    Brown, C. M.; Seely, J. F.; Feldman, U.; Richardson, M. C.; Behring, W. E.; Cohen, L.

    1986-01-01

    High-resolution spectra of Se XXIV have been obtained with a 3-m grazing-incidence spectrograph. Thin plastic foils coated with selenium were irradiated with four or eight beams of the OMEGA laser in a line-focus configuration. Spectrograms were obtained by viewing the plasma axially. Prominent in the spectra were the 3s-3p and 3p-3d transitions in the 150-240-A region and the transitions nl-(n + 1)l-prime with n = 3, 4 in the 24-80-A region. The energy levels and ionization limit derived from the measured wavelengths are also presented.

  18. Colloidal CdSe Quantum Rings.

    PubMed

    Fedin, Igor; Talapin, Dmitri V

    2016-08-10

    Semiconductor quantum rings are of great fundamental interest because their non-trivial topology creates novel physical properties. At the same time, toroidal topology is difficult to achieve for colloidal nanocrystals and epitaxially grown semiconductor nanostructures. In this work, we introduce the synthesis of luminescent colloidal CdSe nanorings and nanostructures with double and triple toroidal topology. The nanorings form during controlled etching and rearrangement of two-dimensional nanoplatelets. We discuss a possible mechanism of the transformation of nanoplatelets into nanorings and potential utility of colloidal nanorings for magneto-optical (e.g., Aharonov-Bohm effect) and other applications.

  19. Chemical Excision of Tetrahedral FeSe2 Chains from the Superconductor FeSe: Synthesis, Crystal Structure, and Magnetism of Fe3Se4(en)2

    PubMed Central

    Pak, Chongin; Kamali, Saeed; Pham, Joyce; Lee, Kathleen; Greenfield, Joshua T.; Kovnir, Kirill

    2014-01-01

    Fragments of the superconducting FeSe layer, FeSe2 tetrahedral chains, were stabilized in the crystal structure of a new mixed-valent compound Fe3Se4(en)2 (en = ethylenediamine) synthesized from elemental Fe and Se. The FeSe2 chains are separated from each other by means of Fe(en)2 linkers. Mössbauer spectroscopy and magnetometry reveal strong magnetic interactions within the FeSe2 chains which result in antiferromagnetic ordering below 170 K. According to DFT calculations, anisotropic transport and magnetic properties are expected for Fe3Se4(en)2. This compound offers a unique way to manipulate the properties of the Fe-Se infinite fragments by varying the topology and charge of the Fe-amino linkers. PMID:24299423

  20. Stretched Exponential relaxation in pure Se glass

    NASA Astrophysics Data System (ADS)

    Dash, S.; Ravindren, S.; Boolchand, P.

    A universal feature of glasses is the stretched exponential relaxation, f (t) = exp[ - t / τ ] β . The model of diffusion of excitations to randomly distributed traps in a glass by Phillips1 yields the stretched exponent β = d[d +2] where d, the effective dimensionality. We have measured the enthalpy of relaxation ΔHnr (tw) at Tg of Se glass in modulated DSC experiments as glasses age at 300K and find β = 0.43(2) for tw in the 0 Se100-x glasses as x increases to 20%, the length of the polymeric Sen chains between the Ge-crosslinks decreases to n = 2. and the striking relaxation effects nearly vanish. J.C. Phillips, Rep.Prog.Phys. 59 , 1133 (1996). Supported by NSF Grant DMR 08-53957.

  1. Selenium bioaccessibility and bioavailability in Se-enriched food supplements.

    PubMed

    Thiry, Celine; Schneider, Yves-Jacques; Pussemier, Luc; De Temmerman, Ludwig; Ruttens, Ann

    2013-04-01

    Most European people have selenium (Se) intake inferior to recommended values that are considered necessary to ensure the beneficial action of antioxidant selenoproteins. People could therefore tend to have recourse to Se-enriched food supplements (FS) aiming to increase their Se body level. On the Belgian market, three main types of Se-rich FS are available: Se-enriched yeast, selenate-based FS, and selenite-based FS. In the present work, in vitro tests imitating gastrointestinal digestion and intestinal absorption were used to determine the bioaccessible and bioavailable fractions of Se present in one specimen of each category of FS. The aim of the study was to verify to which extent the difference in Se speciation could influence the efficiency of FS for enhancing the human Se status. Results indicated that differences exist in both bioaccessibility and bioavailability between the three types of FS, and that these differences could be related, at least partially, to the Se species profile. Overall bioavailability of the three FS was low (maximum 14 % of the original Se content). Among the three samples, the selenate-based FS produced the highest fraction of bioavailable Se, followed by Se-yeast, and finally by the selenite-based FS for which Se was almost not available at all. These results confirm the low availability of inorganic Se but were somewhat unexpected regarding the yeast-based FS since Se-rich yeasts are usually reported to contain an important fraction of available Se. PMID:23397356

  2. Synthesis and optical study of green light emitting polymer coated CdSe/ZnSe core/shell nanocrystals

    SciTech Connect

    Tripathi, S.K.; Sharma, Mamta

    2013-05-15

    Highlights: ► Synthesis of Polymer coated core CdSe and CdSe/ZnSe core/shell NCs. ► From TEM image, the spherical nature of CdSe and CdSe/ZnSe is obtained. ► Exhibiting green band photoemission peak at 541 nm and 549 nm for CdSe core and CdSe/ZnSe core/shell NCs. ► The shell thickness has been calculated by using superposition of quantum confinement energy model. - Abstract: CdSe/ZnSe Core/Shell NCs dispersed in PVA are synthesized by chemical method at room temperature. This is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV/Vis spectra and photoluminescence spectroscopy (PL). TEM image shows the spherical nature of CdSe/ZnSe core/shell NCs. The red shift of absorption and emission peak of CdSe/ZnSe core/shell NCs as compared to CdSe core confirmed the formation of core/shell. The superposition of quantum confinement energy model is used for calculation of thickness of ZnSe shell.

  3. Microstructure and phase transformations in FeSe superconductor

    NASA Astrophysics Data System (ADS)

    Diko, P.; Antal, V.; Kavečansky, V.; Yang, Ch.; Chen, I.

    2012-06-01

    It is shown that a FeSe bulk superconductor prepared by solidification in an inert atmosphere contains an acicular β(Fe1-xSe) phase with a residual δ(Fe1-xSe) high temperature phase. Four different crystal orientations of the β(Fe1-xSe) phase formed from one δ(Fe1-xSe) grain were detected by polarised light microscopy. This behaviour is typical for diffusion-less transformations. The diffusion-less character of δ(Fe1-xSe) to β(Fe1-xSe) transformation was confirmed by thermal analysis.

  4. Valence changes in TmSe by alloying with TmTe and EuSe

    NASA Astrophysics Data System (ADS)

    Batlogg, B.

    1981-01-01

    The valence of the Tm ions in mixed-valent TmSe has been influenced by alloying with TmTe and EuSe in order to study the interaction between intermediate-valent rare-earth ions as a function of the degree of valence mixing. Magnetic, elastic, electrical, and optical properties have been measured on TmSe1-xTex crystals for seven distinct compositions. The degree of valence mixing is increased as Se is replaced by Te up to ~ 20% and the material remains metallic. Whereas TmSe orders metamagnetically (TN=3 K), the Te-containing samples are spontaneously magnetized below 3-5 K. This increasing strength of the ferromagnetic interactions, accompanying the increase of valence mixing, is consistent with the model of a double exchange coupling of mixed-valent Tm ions. TmSe1-xTex with x>=0.5 is semiconducting, the Tm ions are divalent and the overall electronic structure is similar to the ones of the Sm, Eu, and Yb monochalcogenides. The only peculiarities are the narrow energy gaps (0.2 to 0.35 eV) which require pressures of some 20 to 30 kbar to be closed. The magnetic properties are dominated by the crystal-field-split 2F72 ground state, leading to ordering temperatures well below 1 K. As Eu replaces Tm in TmSe, it is divalent because of its highly stable 4f7 shell, whereas the Tm2+ 4f13 and Tm3+ 4f12 5d configurations are nearly degenerate: in Tm0.5Eu0.5Se they are separated by an energy gap of only 0.1 eV, which can be driven to zero with moderate external pressure (15 kbar). In the metallic Tm0.83Eu0.17Se, the Tm ions are of predominantly inhomogeneously mixed-valent character since the Eu ions, being larger in volume are thought to give rise to local deformations of the lattice.

  5. 2-Selenouridine triphosphate synthesis and Se-RNA transcription.

    PubMed

    Sun, Huiyan; Jiang, Sibo; Caton-Williams, Julianne; Liu, Hehua; Huang, Zhen

    2013-09-01

    2-Selenouridine ((Se)U) is one of the naturally occurring modifications of Se-tRNAs ((Se)U-RNA) at the wobble position of the anticodon loop. Its role in the RNA-RNA interaction, especially during the mRNA decoding, is elusive. To assist the research exploration, herein we report the enzymatic synthesis of the (Se)U-RNA via 2-selenouridine triphosphate ((Se)UTP) synthesis and RNA transcription. Moreover, we have demonstrated that the synthesized (Se)UTP is stable and recognizable by T7 RNA polymerase. Under the optimized conditions, the transcription yield of (Se)U-RNA can reach up to 85% of the corresponding native RNA. Furthermore, the transcribed (Se)U-hammerhead ribozyme has the similar activity as the corresponding native, which suggests usefulness of (Se)U-RNAs in function and structure studies of noncoding RNAs, including the Se-tRNAs.

  6. Photo and electroluminescence of ZnSe: Sn and ZnSe:(Sn, Pr) phosphors

    NASA Astrophysics Data System (ADS)

    Mishra, A. K.; Mishra, S. K.; Pandey, S. P.; Lakshmi Mishra, Kshama

    2016-09-01

    We have prepared ZnSe (luminescent grade) phosphor doped with Sn and (Sn,Pr) with varying concentration in an inert atmosphere in a silica tubular furnace at temperature of (780 ± 20) °C for 1 hr to obtain ZnSe:Sn and ZnSe: (Sn,Pr) phosphors. The photo luminescence (PL) and electroluminescence (EL) spectra of these phosphors have been studied at room temperature and results were discussed in the light of existing models. Dependence of EL emission on the voltage frequency has also been carried out. It is found that the plot between the integrated light intensity versus 1/√Vrms is a straight line suggesting the existence of Mott-Schottky type barrier on the metal semiconductor interface.

  7. Coexistence of planar and three-dimensional quantum dots in CdSe/ZnSe structures

    NASA Astrophysics Data System (ADS)

    Strassburg, M.; Deniozou, Th.; Hoffmann, A.; Heitz, R.; Pohl, U. W.; Bimberg, D.; Litvinov, D.; Rosenauer, A.; Gerthsen, D.; Schwedhelm, S.; Lischka, K.; Schikora, D.

    2000-02-01

    Two well distinguishable classes of nanoscale islands were identified in CdSe/ZnSe quantum dot structures by optical spectroscopy and transmission electron microscopy. For 2.1 to 3.1 monolayer CdSe deposition, coherent three-dimensional (3D) islands, formed in the Stranski-Krastanow (SK) mode, are found with typical diameters of ˜16 nm and a coverage-dependent density of up to 3×1010cm-2. Simultaneously, small islands with lateral extensions below 10 nm and a density of ˜5×1011cm-2 are formed by strain-modified island growth. Whereas the 3D SK islands dominate the emission properties at room temperature, the latter smaller islands determine the optical properties at temperatures below 120 K.

  8. Resource Letter SE-2: Solar Energy

    NASA Astrophysics Data System (ADS)

    Hodges, Laurent

    1982-10-01

    This resource letter provides a source of information about the main types of solar energy and their uses, updating Resource Letter SE-1 issued seven years ago. It is intended for the use of high school and college teachers both in developing courses and in guiding students to the literature of solar energy applications. Articles marked with an asterisk have been selected for publication in an accompanying reprint book. The letter E after the reference number denotes a relatively elementary item, useful for high school and introductory college use and the educated public; the letter I denotes intermediate level references, sophomore to senior level; and the letter A denotes advanced material, principally for senior and graduate-level courses.

  9. 76Se(t,p)78Se reaction at 17 MeV

    NASA Astrophysics Data System (ADS)

    Watson, D. L.; Fortune, H. T.

    1987-02-01

    The 76Se(t,p)78Se reaction has been studied at an incident energy of 17 MeV. Excitation energies for 80 states (or groups of states) up to 6.16 MeV have been measured. Angular distributions have been obtained for 61 of them, below Ex=5.03 MeV. Comparison of the data with distorted-wave Born approximation calculations, using pure configurations for the transfer amplitudes, have enabled the L transfer (and hence Jπ value) to be determined for 58 of these states. Of these assignments, 52 are new.

  10. Dipolar structures in colloidal dispersions of PbSe and CdSe quantum dots.

    PubMed

    Klokkenburg, Mark; Houtepen, Arjan J; Koole, Rolf; de Folter, Julius W J; Erné, Ben H; van Faassen, Ernst; Vanmaekelbergh, Daniël

    2007-09-01

    We show by cryogenic transmission electron microscopy that PbSe and CdSe nanocrystals of various shapes in a liquid colloidal dispersion self-assemble into equilibrium structures that have a pronounced dipolar character, to an extent that depends on particle concentration and size. Analyzing the cluster-size distributions with a one-dimensional (1D) aggregation model yields a dipolar pair attraction of 8-10 kBT at room temperature. This accounts for the long-range alignment of the crystal planes of individual nanocrystals in self-assembled superstructures and for anisotropic nanostructures grown via oriented attachment. PMID:17713960

  11. Energy transfer processes in ZnSe/(Zn,Mn)Se double quantum wells

    NASA Astrophysics Data System (ADS)

    Jankowski, Stephanie; Horst, Swantje; Chernikov, Alexej; Chatterjee, Sangam; Heimbrodt, Wolfram

    2009-10-01

    The complex interplay of energy transfer and tunneling processes in a series of asymmetric ZnSe/(Zn,Mn)Se double quantum-well (DQW) structures is investigated. Steady-state and time-resolved photoluminescence at low temperatures and external magnetic fields up to 7 T in this system show remarkable differences to earlier studies on CdTe/(Cd,Mn)Te DQWs. The pure quantum-mechanical tunneling process is only a minor contribution to the magnetic field dependence of the emission even in case of small barriers and strong QW coupling. The experimental results are supported by quantum-well calculations.

  12. Temperature dependent band offsets in PbSe/PbEuSe quantum well heterostructures

    SciTech Connect

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

    2012-10-22

    The band offsets of PbSe/Pb{sub 1-x}Eu{sub x}Se multi-quantum wells grown by molecular beam epitaxy are determined as a function of temperature and europium content using temperature-modulated differential transmission spectroscopy. The confined quantum well states in the valence and conduction bands are analyzed using a k{center_dot}p model with envelope function approximation. From the fit of the experimental data, the normalized conduction band offset is determined as 0.45{+-}0.15 of the band gap difference, independently of Eu content up to 14% and temperature from 20 to 300 K.

  13. Electron-impact ionization of the Se2+ and Se3+ atomic ions

    NASA Astrophysics Data System (ADS)

    Loch, S. D.; Pindzola, M. S.

    2016-05-01

    Semi-relativistic configuration-average distorted-wave (CADW) calculations are made for the electron-impact ionization of the Se2+ and Se3+ atomic ions. The CADW calculations are found to be in reasonable agreement with recent measurements made at the Multicharged Ion Research Facility at the University of Nevada in Reno. The CADW calculations for configurations near ionization thresholds are checked against level to level distorted-wave (LLDW) calculations. Work supported in part by Grants from NASA, NSF, and DOE.

  14. Monodispersed spherical colloids of Se@CdSe: synthesis and use as building blocks in fabricating photonic crystals.

    PubMed

    Jeong, Unyong; Kim, Jong-Uk; Xia, Younan; Li, Zhi-Yuan

    2005-05-01

    Monodispersed spherical core-shell colloids of Se@Ag(2)Se have been exploited as a chemical template to synthesize Se@CdSe core-shell particles using a cation-exchange reaction. A small amount of tributylphosphine could facilitate the replacement of Ag(+) by Cd(2+) in methanol at 50 degrees C to complete the conversion within 150 min. The orthorhombic structure of beta-Ag(2)Se changed to a well-defined wurtzite lattice for CdSe. The CdSe shells could be converted back to beta-Ag(2)Se by reacting with AgNO(3) in methanol at room temperature. Because of the uniformity in size and high refractive index associated with the Se@CdSe core-shell colloids, they could serve as a new class of building blocks to fabricate photonic crystals with wide and strong stop bands.

  15. Photocatalytic Hydrogen Generation by CdSe/CdS Nanoparticles.

    PubMed

    Qiu, Fen; Han, Zhiji; Peterson, Jeffrey J; Odoi, Michael Y; Sowers, Kelly L; Krauss, Todd D

    2016-09-14

    The photocatalytic hydrogen (H2) production activity of various CdSe semiconductor nanoparticles was compared including CdSe and CdSe/CdS quantum dots (QDs), CdSe quantum rods (QRs), and CdSe/CdS dot-in-rods (DIRs). With equivalent photons absorbed, the H2 generation activity orders as CdSe QDs ≫ CdSe QRs > CdSe/CdS QDs > CdSe/CdS DIRs, which is surprisingly the opposite of the electron-hole separation efficiency. Calculations of photoexcited surface charge densities are positively correlated with the H2 production rate and suggest the size of the nanoparticle plays a critical role in determining the relative efficiency of H2 production. PMID:27478995

  16. Distribution of Se and its species in Myriophyllum spicatum and Ceratophyllum demersum growing in water containing Se (VI).

    PubMed

    Mechora, Spela; Cuderman, Petra; Stibilj, Vekoslava; Germ, Mateja

    2011-09-01

    The uptake of Se (VI) by two aquatic plants, Myriophyllum spicatum L. and Ceratophyllum demersum L., and its effects on their physiological characteristics have been studied. Plants were cultivated outdoors under semi-controlled conditions and in two concentrations of Na selenate solution (20 μg Se L(-1) and 10 mg Se L(-1)). The higher dose of Se reduced the photochemical efficiency of PSII in both species, while the lower dose had no effect on PSII. Addition of Se had no effect on the amounts of chlorophyll a and b. The concentration of Se in plants grown in 10 mg Se L(-1), averaged 212 ± 12 μg Seg(-1) DM in M. spicatum (grown from 8-13 d), and 492 ± 85 μg Se g(-1) DM in C. demersum (grown for 31 d). Both species could take up a large amount of Se. The amount of soluble Se compounds in enzyme extracts ranged from 16% to 26% in control, and in high Se solution from 48% to 36% in M. spicatum and C. demersum, respectively. Se-species were determined using HPLC-ICP-MS. The main soluble species in both plants was selenate (∼37%), while SeMet and SeMeSeCys were detected at trace levels. PMID:21703659

  17. Growth and characterization of ZnSe nanoparticles

    SciTech Connect

    Sharma, Shail Malik, Mukhtar Ah. Chandel, Tarun Thakur, Vikas Rajaram, P.

    2014-04-24

    ZnSe nanoparticles were prepared using a chemical bath deposition technique. X-ray diffraction study shows that the ZnSe crystallizes in the cubic phase. The crystallite size of the ZnSe samples calculated using the Scherrer’s formula was found to be slightly smaller than the Bohr exciton radius of bulk ZnSe. SEM studies show the growth of a mixture of nanorods and spherical nanoparticles. EDAX analysis confirms that the synthesized ZnSe nanoparticles are of good stiochiometry. Optical studies show the blue shift in the absorption edge for ZnSe nanoparticles caused by quantum confinement.

  18. Photoinduced aging and viscosity evolution in Se-rich Ge-Se glasses

    SciTech Connect

    Gueguen, Yann; Sangleboeuf, Jean-Christophe; Rouxel, Tanguy; King, Ellyn A.; Lucas, Pierre; Keryvin, Vincent; Bureau, Bruno

    2013-08-21

    We propose here to investigate the non-equilibrium viscosity of Ge-Se glasses under and after light irradiation. Ge{sub 10}Se{sub 90} and Ge{sub 20}Se{sub 80} fibers have been aged in the dark and under ambient light, over months. During aging, both the relaxation of enthalpy and the viscosity have been investigated. The viscosity was measured by shear relaxation-recovery tests allowing the measurement of non-equilibrium viscosity. When Ge{sub 10}Se{sub 90} glass fibers are aged under irradiation, a relatively fast fictive temperature decrease is observed. Concomitantly, during aging under irradiation, the non-equilibrium viscosity increases and reaches an equilibrium after two months of aging. This viscosity increase is also observed in Ge{sub 20}Se{sub 80} fibers. Nevertheless, this equilibrium viscosity is far below the viscosity expected at the configurational equilibrium. As soon as the irradiation ceases, the viscosity increases almost instantaneously by about one order of magnitude. Then, if the fibers are kept in the dark, their viscosity slowly increases over months. The analysis of the shear relaxation functions shows that the aging is thermorheologically simple. On the other side, there is no simple relaxation between the shear relaxation functions measured under irradiation and those measured in the dark. These results clearly suggest that a very specific photoinduced aging process occurs under irradiation. This aging is due to photorelaxation. Nevertheless, the viscosity changes are not solely correlated to photoaging and photorelaxation. A scenario is proposed to explain all the observed viscosity evolutions under and after irradiation, on the basis of photoinduced transient defects.

  19. Taconic collision in SE Penna and Delaware

    SciTech Connect

    Crawford, M.L.; Crawford, W.A.; Hoersch, A.L.; Srogi, L.A.; Wagner, M.E.

    1985-01-01

    Taconic metamorphism and tectonism in SE Pennsylvania and northern Delaware were a result of the collision of a volcanic arc with North America. The Wilmington Complex, the infrastructure of the arc, is presently the highest structural unit. It consists of granulite facies volcanogenic sediments intruded by gabbro and a ca. 500 Ma gabbronorite-charnockite suite. Latest Precambrian-earliest Paleozoic sediments of the Glenarm series were metamorphosed to conditions above the second sillimanite isograd beneath the overthrust hot (700-800/sup 0/C) Wilmington Complex. As the edge of the continent was depressed and heated under the advancing thrust complex, basement-involved nappes of Grenville age rocks (Avondale anticline, Woodville dome) with the Glenarm sedimentary cover were thrust over still rigid autochthonous basement (West Chester Prong). On the NW flank of the orogen, Grenville age gneiss-cored massifs (Honey Brook Upland, Mine Ridge, Trenton Prong), unconformably overlain by lower Paleozoic continental shelf sediments, were involved in the thrusting but metamorphosed only to the greenschist facies. Steep anticlines developed later in the Paleozoic, contributing to the present pattern of northeast trending Grenville basement massifs mantled by overlying units.

  20. 23. Interior view of SE corner of first floor of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    23. Interior view of SE corner of first floor of 1896 south section of building, showing windows and column. Camera pointed SE. - Puget Sound Naval Shipyard, Pattern Shop, Farragut Avenue, Bremerton, Kitsap County, WA

  1. MgSe/ZnSe/CdSe coupled quantum wells grown on InP substrate with intersubband absorption covering 1.55 μm

    SciTech Connect

    Chen, Guopeng; Shen, Aidong; De Jesus, Joel; Tamargo, Maria C.

    2014-12-08

    The authors report the observation of intersubband (ISB) transitions in the optical communication wavelength region in MgSe/ZnSe/CdSe coupled quantum wells (QWs). The coupled QWs were grown on InP substrates by molecular beam epitaxy. By inserting ZnSe layers to compensate the strain, samples with high structural quality were obtained, as indicated by well resolved satellite peaks in high-resolution x-ray diffraction. The observed ISB transition energies agree well with the calculated values.

  2. Efficiency enhancement of Sb2Se3 thin-film solar cells by the co-evaporation of Se and Sb2Se3

    NASA Astrophysics Data System (ADS)

    Li, Zhiqiang; Zhu, Hongbing; Guo, Yuting; Niu, Xiaona; Chen, Xu; Zhang, Chong; Zhang, Wen; Liang, Xiaoyang; Zhou, Dong; Chen, Jingwei; Mai, Yaohua

    2016-05-01

    In this work, we present an alternative route to supply excessive selenium (Se) for the deposition of Sb2Se3 thin films by the co-evaporation of Se and Sb2Se3. Scanning electron microscopy (SEM) images showed that additional Se modified the growth process and surface morphology of Sb2Se3 thin films. X-ray diffraction (XRD) patterns confirmed that this co-evaporation process enhanced the beneficiary preferred orientations, and capacitance-voltage (C-V) measurement showed that the carrier concentration of the Sb2Se3 absorber increased with the additional evaporation of Se. Accordingly, the efficiency of the devices employing co-evaporated Sb2Se3 absorber layers increased significantly from 2.1 to 3.47% with a open-circuit voltage (V OC) of 364 mV, a short-circuit current density (J SC) of 23.14 mA/cm2, and a fill factor (FF) of 41.26%.

  3. Procedure for separation of Se and determination of Se-79 by liquid scintillation

    SciTech Connect

    Dewberry, R.A.

    1991-08-11

    This report describes the development work and demonstration of a technique for separation of selenium suitable for determination of Se-79 by liquid scintillation counting. The technique has been demonstrated on actual DWPF (Defense Waste Processing Facility) sludge samples which contain very large loads of Sr-90 activity. The separation required a decontamination of selenium from Sr by a factor of over 10{sup 6}, from Co and Cs by factor of 10{sup 4}, and from Tc-99 by a factor of 100, while still maintaining a selenium recovery of about 50%. Using this technique the author has determined Se-79 in five actual DWPF samples with a precision of about 70% relative standard deviation. This separation has not been demonstrated on actual DWPF samples which have the largest Cs-137 loads. He does not anticipate that these untested samples will present a difficult problem.

  4. Dipole strength in 80Se for s process and nuclear transmutation of 79Se

    NASA Astrophysics Data System (ADS)

    Makinaga, A.; Massarczyk, R.; Beard, M.; Schwengner, R.; Otsu, H.; Al-Abdullah, T.; Anders, M.; Bemmerer, D.; Hannaske, R.; John, R.; Junghans, A. R.; Müller, S. E.; Röder, M.; Schmidt, K.; Wagner, A.

    2016-10-01

    The dipole strength distribution of 80Se was studied in a photon-scattering experiment by using bremsstrahlung produced with an electron beam of energy 11.5 MeV at the linear accelerator ELBE. We identified 180 γ transitions up to an energy of 9.6 MeV, and analyzed the strength in the quasicontinuum of the spectrum. Simulations of statistical γ -ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section below the neutron-separation energy derived in this way was combined with the photoabsorption cross section obtained from an earlier (γ ,n ) experiment and used as an input for the calculation of 79Se(n ,γ ) reaction rates on the basis of the statistical reaction model.

  5. SE-72/AS-72 generator system based on Se extraction/ As reextraction

    SciTech Connect

    Fassbender, Michael Ernst; Ballard, Beau D

    2013-09-10

    The preparation of a .sup.72Se/.sup.72As radioisotope generator involves forming an acidic aqueous solution of an irradiated alkali bromide target such as a NaBr target, oxidizing soluble bromide in the solution to elemental bromine, removing the elemental bromine, evaporating the resulting solution to a residue, removing hydrogen chloride from the residue, forming an acidic aqueous solution of the residue, adding a chelator that selectively forms a chelation complex with selenium, and extracting the chelation complex from the acidic aqueous solution into an organic phase. As the .sup.72Se generates .sup.72As in the organic phase, the .sup.72As may be extracted repeatedly from the organic phase with an aqueous acid solution.

  6. 21 CFR 118.4 - Salmonella Enteritidis (SE) prevention measures.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... National Poultry Improvement Plan's standards for “U.S. S. Enteritidis Clean” status (9 CFR 145.23(d)) or... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Salmonella Enteritidis (SE) prevention measures....4 Salmonella Enteritidis (SE) prevention measures. You must follow the SE prevention measures...

  7. Local Structure of CuIn3Se5

    SciTech Connect

    Chang, C. H.; Wei, S. H.; Leyarovska, N.; Johnson, J. W.; Zhang, S. B.; Stanbery, B. J.; Anderson, T. J.

    2000-01-01

    The results of a detailed EXAFS study of the Cu-K, In-K, and Se-K edges CuIn3Se5 are reported. The Cu and In first nearest neighbor local structures were found to be almost identical to those in CuInSe2.

  8. Fluorescence relaxation dynamics of CdSe and CdSe/CdS core/shell quantum dots

    SciTech Connect

    Kaur, Gurvir; Kaur, Harmandeep; Tripathi, S. K.

    2014-04-24

    Time-resolved fluorescence spectra for colloidal CdSe and CdSe/CdS core/shell quantum dots have been investigated to know their electron relaxation dynamics at the maximum steady state fluorescence intensity. CdSe core and CdSe/CdS type I core-shell materials with different shell (CdS) thicknesses have been synthesized using mercaptoacetic acid as a capping agent. Steady state absorption and emission studies confirmed successful synthesis of CdSe and CdSe/CdS core-shell quantum dots. The fluorescence shows a tri-exponential decay with lifetimes 57.39, 7.82 and 0.96 ns for CdSe quantum dots. The lifetime of each recombination decreased with growth of CdS shell over the CdSe core, with maximum contribution to fluorescence by the fastest transition.

  9. Two-dimensional GaSe/MoSe2 misfit bilayer heterojunctions by van der Waals epitaxy.

    PubMed

    Li, Xufan; Lin, Ming-Wei; Lin, Junhao; Huang, Bing; Puretzky, Alexander A; Ma, Cheng; Wang, Kai; Zhou, Wu; Pantelides, Sokrates T; Chi, Miaofang; Kravchenko, Ivan; Fowlkes, Jason; Rouleau, Christopher M; Geohegan, David B; Xiao, Kai

    2016-04-01

    Two-dimensional (2D) heterostructures hold the promise for future atomically thin electronics and optoelectronics because of their diverse functionalities. Although heterostructures consisting of different 2D materials with well-matched lattices and novel physical properties have been successfully fabricated via van der Waals (vdW) epitaxy, constructing heterostructures from layered semiconductors with large lattice misfits remains challenging. We report the growth of 2D GaSe/MoSe2 heterostructures with a large lattice misfit using two-step chemical vapor deposition (CVD). Both vertically stacked and lateral heterostructures are demonstrated. The vertically stacked GaSe/MoSe2 heterostructures exhibit vdW epitaxy with well-aligned lattice orientation between the two layers, forming a periodic superlattice. However, the lateral heterostructures exhibit no lateral epitaxial alignment at the interface between GaSe and MoSe2 crystalline domains. Instead of a direct lateral connection at the boundary region where the same lattice orientation is observed between GaSe and MoSe2 monolayer domains in lateral GaSe/MoSe2 heterostructures, GaSe monolayers are found to overgrow MoSe2 during CVD, forming a stripe of vertically stacked vdW heterostructures at the crystal interface. Such vertically stacked vdW GaSe/MoSe2 heterostructures are shown to form p-n junctions with effective transport and separation of photogenerated charge carriers between layers, resulting in a gate-tunable photovoltaic response. These GaSe/MoSe2 vdW heterostructures should have applications as gate-tunable field-effect transistors, photodetectors, and solar cells. PMID:27152356

  10. Two-dimensional GaSe/MoSe2 misfit bilayer heterojunctions by van der Waals epitaxy

    DOE PAGES

    Li, Xufan; Lin, Ming-Wei; Lin, Junhao; Huang, Bing; Puretzky, Alexander A.; Ma, Cheng; Wang, Kai; Zhou, Wu; Pantelides, Sokrates T.; Chi, Miaofang; et al

    2016-04-01

    Two-dimensional (2D) heterostructures hold the promise for future atomically-thin electronics and optoelectronics due to their diverse functionalities. While heterostructures consisting of different transition metal dichacolgenide monolayers with well-matched lattices and novel physical properties have been successfully fabricated via van der Waals (vdW) or edge epitaxy, constructing heterostructures from monolayers of layered semiconductors with large lattice misfits still remains challenging. Here, we report the growth of monolayer GaSe/MoSe2 heterostructures with large lattice misfit by two-step chemical vapor deposition (CVD). Both vertically stacked and lateral heterostructures are demonstrated. The vertically stacked GaSe/MoSe2 heterostructures exhibit vdW epitaxy with well-aligned lattice orientation between themore » two layers, forming an incommensurate vdW heterostructure. However, the lateral heterostructures exhibit no lateral epitaxial alignment at the interface between GaSe and MoSe2 crystalline domains. Instead of a direct lateral connection at the boundary region where the same lattice orientation is observed between GaSe and MoSe2 monolayer domains in lateral GaSe/MoSe2 heterostructures, GaSe monolayers are found to overgrow MoSe2 during CVD, forming a stripe of vertically stacked vdW heterostructure at the crystal interface. Such vertically-stacked vdW GaSe/MoSe2 heterostructures are shown to form p-n junctions with effective transport and separation of photo-generated charge carriers between layers, resulting in a gate-tunable photovoltaic response. In conclusion, these GaSe/MoSe2 vdW heterostructures should have applications as gate-tunable field-effect transistors, photodetectors, and solar cells.« less

  11. Two-dimensional GaSe/MoSe2 misfit bilayer heterojunctions by van der Waals epitaxy.

    PubMed

    Li, Xufan; Lin, Ming-Wei; Lin, Junhao; Huang, Bing; Puretzky, Alexander A; Ma, Cheng; Wang, Kai; Zhou, Wu; Pantelides, Sokrates T; Chi, Miaofang; Kravchenko, Ivan; Fowlkes, Jason; Rouleau, Christopher M; Geohegan, David B; Xiao, Kai

    2016-04-01

    Two-dimensional (2D) heterostructures hold the promise for future atomically thin electronics and optoelectronics because of their diverse functionalities. Although heterostructures consisting of different 2D materials with well-matched lattices and novel physical properties have been successfully fabricated via van der Waals (vdW) epitaxy, constructing heterostructures from layered semiconductors with large lattice misfits remains challenging. We report the growth of 2D GaSe/MoSe2 heterostructures with a large lattice misfit using two-step chemical vapor deposition (CVD). Both vertically stacked and lateral heterostructures are demonstrated. The vertically stacked GaSe/MoSe2 heterostructures exhibit vdW epitaxy with well-aligned lattice orientation between the two layers, forming a periodic superlattice. However, the lateral heterostructures exhibit no lateral epitaxial alignment at the interface between GaSe and MoSe2 crystalline domains. Instead of a direct lateral connection at the boundary region where the same lattice orientation is observed between GaSe and MoSe2 monolayer domains in lateral GaSe/MoSe2 heterostructures, GaSe monolayers are found to overgrow MoSe2 during CVD, forming a stripe of vertically stacked vdW heterostructures at the crystal interface. Such vertically stacked vdW GaSe/MoSe2 heterostructures are shown to form p-n junctions with effective transport and separation of photogenerated charge carriers between layers, resulting in a gate-tunable photovoltaic response. These GaSe/MoSe2 vdW heterostructures should have applications as gate-tunable field-effect transistors, photodetectors, and solar cells.

  12. Two-dimensional GaSe/MoSe2 misfit bilayer heterojunctions by van der Waals epitaxy

    PubMed Central

    Li, Xufan; Lin, Ming-Wei; Lin, Junhao; Huang, Bing; Puretzky, Alexander A.; Ma, Cheng; Wang, Kai; Zhou, Wu; Pantelides, Sokrates T.; Chi, Miaofang; Kravchenko, Ivan; Fowlkes, Jason; Rouleau, Christopher M.; Geohegan, David B.; Xiao, Kai

    2016-01-01

    Two-dimensional (2D) heterostructures hold the promise for future atomically thin electronics and optoelectronics because of their diverse functionalities. Although heterostructures consisting of different 2D materials with well-matched lattices and novel physical properties have been successfully fabricated via van der Waals (vdW) epitaxy, constructing heterostructures from layered semiconductors with large lattice misfits remains challenging. We report the growth of 2D GaSe/MoSe2 heterostructures with a large lattice misfit using two-step chemical vapor deposition (CVD). Both vertically stacked and lateral heterostructures are demonstrated. The vertically stacked GaSe/MoSe2 heterostructures exhibit vdW epitaxy with well-aligned lattice orientation between the two layers, forming a periodic superlattice. However, the lateral heterostructures exhibit no lateral epitaxial alignment at the interface between GaSe and MoSe2 crystalline domains. Instead of a direct lateral connection at the boundary region where the same lattice orientation is observed between GaSe and MoSe2 monolayer domains in lateral GaSe/MoSe2 heterostructures, GaSe monolayers are found to overgrow MoSe2 during CVD, forming a stripe of vertically stacked vdW heterostructures at the crystal interface. Such vertically stacked vdW GaSe/MoSe2 heterostructures are shown to form p-n junctions with effective transport and separation of photogenerated charge carriers between layers, resulting in a gate-tunable photovoltaic response. These GaSe/MoSe2 vdW heterostructures should have applications as gate-tunable field-effect transistors, photodetectors, and solar cells. PMID:27152356

  13. The Intraplate Earthquakes of SE Africa

    NASA Astrophysics Data System (ADS)

    Fonseca, J. F. B. D.; Domingues, A.

    2014-12-01

    Southeast Africa is a region of complex tectonic inheritance, combining early Archean cratonic blocks - the Zimbabwe and Kaapvaal cratons - and several collision belts ranging in age from ~2.6Ga (Limpopo Belt) to the Pan-African Orogeny, 800-500 Ma ago (Zambezi Belt, Mozambique Belt). Mesozoic rifting was the last tectonic event to leave an imprint in the lithosphere of the region. Tertiary deformation is mild and related to the extensional regime of the East African Rift System (EARS) further north. Instrumental seismology started in Johannesburg in 1910 (Saunders et al., 2008). Ambraseys and Adams (1991) conducted a reappraisal of the seismicity of Sub-Saharan Africa from 1900 to 1930, and the compilations by Krige and Maree (1948) and Gutenberg and F. Richter (1949) are main sources for the two subsequent decades. The available data can be considered complete since 1900 for magnitudes above M6 (Ambraseys and Adams, 1991), although major epicentral errors are likely to affect the early decades. Earthquakes above this threshold in the region to the south of Lake Malawi and to the east of the Okavango Rift are reported in 1919 (MS6.5, NE South Africa), 1932 (MS6.8, Natal Bay), 1940 (MS6.2, SE Mozambique), 1951 (MS6.0, Central Mozambique), 1957 (M6.0, Central Mozambique), again in 1957 (M6.2, Central Mozambique), 1958 (M6.0, Southern Zimbabwe), 1959 (M6.1, Southern Zambia) and 2006 (M7.0, Central Mozambique). The four M>6 earthquakes from 1957 to 1959 configure a cluster in time, followed by a shutdown (at M>6) that was to last nearly five decades. While a coincidence is unlikely, a causal link is challenged by the large spatial scatter of about 500 km. However, the fact that the four earthquakes occurred on the border of the Zimbabwe craton may provide a clue to the mechanism promoting the clustering. We combine these data with recent seismicity results (Fonseca et al., 2014) to discuss possible factors controlling the seismotectonics of the region.

  14. Twinning effect on photoluminescence spectra of ZnSe nanowires

    SciTech Connect

    Xu, Jing; Wang, Chunrui Wu, Binhe; Xu, Xiaofeng; Chen, Xiaoshuang; Oh, Hongseok; Baek, Hyeonjun; Yi, Gyu-Chul

    2014-11-07

    Bandgap engineering in a single material along the axial length of nanowires may be realized by arranging periodic twinning, whose twin plane is vertical to the axial length of nanowires. In this paper, we report the effect of twin on photoluminescence of ZnSe nanowires, which refers to the bandgap of it. The exciton-related emission peaks of transverse twinning ZnSe nanowires manifest a 10-meV-blue-shift in comparison with those of longitudinal twinning ZnSe nanowires. The blue-shift is attributed to quantum confinement effect, which is influenced severely by the proportion of wurtzite ZnSe layers in ZnSe nanowires.

  15. Crystal Growth of Undoped and Doped ZnSe

    NASA Technical Reports Server (NTRS)

    Davis, Swanson L.; Chen, K.-T.; George, M. A.; Shi, D. T.; Collins, W. E.; Burger, Arnold

    1997-01-01

    The surface morphology of freshly cleaved ZnSe single crystal grown by the physical vapor transport (PVT) method was investigated by Atomic Force Microscopy (AFM) and the results were correlated with Differential Scanning Calorimetry (DSC) data. Selenium precipitates have been revealed in undoped doped ZnSe crystals having a size of about 50 nm. A transition temperature around 221 C in the DSC measurements is interpreted as the eutectic temperature of Se-saturated ZnSe. The AFM images of doped ZnSe also show that possible Cr clusters are uniformly distributed and they have an estimated size of about 6 nm.

  16. The phase evolution mechanism in Fe(Se, Te) system

    NASA Astrophysics Data System (ADS)

    Liu, Jixing; Li, Chengshan; Zhang, Shengnan; Feng, Jianqing; Zhang, Pingxiang; Zhou, Lian

    2016-08-01

    The phase evolution mechanism in Fe(Se, Te) system during sintering was investigated with step-by-step heat treatment process. It was noticed that the diffusion processes between Fe and Se (Te) as well as that between Se and Te were both very important to the formation of superconducting Fe(Se, Te) phase with very uniform chemical composition. During heat treatment, solid solutions of (Se, Te)ss with different chemical composition were formed with the diffusion of Se atoms into Te solids and Te atoms into Se melts, simultaneously. Then with the increasing temperature, Fe atoms diffused into (Se, Te)ss, Fe(Se, Te)2 and Fe(Se, Te) phases were formed in sequence with the increasing Fe content. The chemical composition in melts became more and more uniform with the further increasing of sintering temperature and dwell time. Therefore, it was suggested that in order to achieve Fe(Se, Te) phase with high superconducting properties, it was necessary to enhance the diffusion process during sintering. The critical temperature of the sample, which was sintered at 700 °C for 12 h with slow cooling process and an O2-annealing process for 24 h, was above 14.0 K. This Tc value proved that a good superconducting β phase could be obtained under this sintering condition.

  17. Air-Stable and Efficient PbSe Quantum-Dot Solar Cells Based upon ZnSe to PbSe Cation-Exchanged Quantum Dots.

    PubMed

    Kim, Sungwoo; Marshall, Ashley R; Kroupa, Daniel M; Miller, Elisa M; Luther, Joseph M; Jeong, Sohee; Beard, Matthew C

    2015-08-25

    We developed a single step, cation-exchange reaction that produces air-stable PbSe quantum dots (QDs) from ZnSe QDs and PbX2 (X = Cl, Br, or I) precursors. The resulting PbSe QDs are terminated with halide anions and contain residual Zn cations. We characterized the PbSe QDs using UV-vis-NIR absorption, photoluminescence quantum yield spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Solar cells fabricated from these PbSe QDs obtained an overall best power conversion efficiency of 6.47% at one sun illumination. The solar cell performance without encapsulation remains unchanged for over 50 days in ambient conditions; and after 50 days, the National Renewable Energy Laboratory certification team certified the device at 5.9%.

  18. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films.

    PubMed

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-01

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates. PMID:25483981

  19. A dry method to synthesize dendritic Ag2Se nanostructures utilizing CdSe quantum dots and Ag thin films

    NASA Astrophysics Data System (ADS)

    Hu, Lian; Zhang, Bingpo; Xu, Tianning; Li, Ruifeng; Wu, Huizhen

    2015-01-01

    Dendritic Ag2Se nanostructures are synthesized in a dry environment by UV irradiating the hybrids composed of CdSe quantum dots (QDs) and silver (Ag). UV irradiation on CdSe QDs induces a photooxidation effect on the QD surface and leads to the formation of SeO2 components. Then SeO2 reacts with the Ag atoms in either Ag film or QD layer to produce the Ag2Se. The growth mechanism of Ag2Se dendrites on solid Ag films is explored and explained by a diffusion limited aggregation model in which the QD layer provides enough freedom for Ag2Se motion. Since the oxidation of the CdSe QDs is the critical step for the Ag2Se dendrites formation this dry chemical interaction between QDs and Ag film can be applied in the study of the QD surface chemical properties. With this dry synthesis method, the Ag2Se dendrites can also be facilely formed at the designed area on Ag substrates.

  20. Preparation and characterization of wire-like Sb 2Se 3 and flake-like Bi 2Se 3 nanocrystals

    NASA Astrophysics Data System (ADS)

    Wang, Debao; Yu, Dabin; Mo, Maosong; Liu, Xianming; Qian, Yitai

    2003-06-01

    Crystalline Sb 2Se 3 and Bi 2Se 3 have been prepared through the reaction between SbCl 3 (or BiCl 3) and elemental selenium using sodium sulfite as a reducing reagent. TEM images show that the as-prepared Sb 2Se 3 comprise uniform nanowires, while Bi 2Se 3 crystals exhibit a hexagonal flake-like morphology. The optical absorption of the products has been investigated, and the optical band gap energy for direct transition in Sb 2Se 3 nanowires is found to be 1.46 eV. The composition of the as-prepared products has been identified by XPS. The reaction mechanism is discussed in detail, and it is proposed that the oriented growth behavior of Sb 2Se 3 and Bi 2Se 3 crystals is determined by their cleavage nature. The chain-like arrangement of Sb and Se atoms parallel to the c-axis in the orthorhombic lattice and the two-dimensional assembly of Bi and Se atoms perpendicular to the c-axis in the hexagonal cell contribute to the formation of wire-like Sb 2Se 3 and flake-like hexagonal Bi 2Se 3 crystals, respectively. These arguments can also be applied to explain the growth behavior of other V 2VI 3-type crystals.

  1. Effect of long-term phosphorus fertilization on soil Se and transfer of soil Se to crops in northern Japan.

    PubMed

    Altansuvd, Javkhlantuya; Nakamaru, Yasuo M; Kasajima, Shinya; Ito, Hirotake; Yoshida, Hozumi

    2014-07-01

    Phosphorus (P) fertilizer can potentially serve as a source for Se accumulation in croplands. Furthermore, it has been reported that the addition of P fertilizer to soil may enhance Se availability. Japanese agricultural soils are typically enriched in P as a result of long-term, excessive P fertilization. Therefore, we conducted a three-year field experiment in order to evaluate the effect of P fertilization on the Se content of soils and crops. Potato, wheat and barley were cultivated with and without P fertilization at two field sites in Hokkaido (northern Japan) with different levels of historical P accumulation. The first field site consisted of an Andosol soil with low available P and the second site, a Cambisol soil with high available P. The three years of continuous P fertilization over the course of the experiment did not result in a significant increase in the Se content of soils or plants. The Se content of soils and plants, however, was higher in soil samples from the Cambisol field site than from the Andosol field site, and total soil Se was significantly correlated with available soil P. Soluble soil Se and the soil-plant transfer factor for Se were not affected by P fertilization. Thus, we concluded that the higher plant Se content at the Cambisol field site was primarily due to the higher levels of accumulated Se in the soil at the site and that historical excess P fertilization typical of agricultural soils in Japan contributes to increased Se uptake by crops.

  2. SeP, ApoER2 and megalin as necessary factors to maintain Se homeostasis in mammals.

    PubMed

    Krol, Magdalena Beata; Gromadzinska, Jolanta; Wasowicz, Wojciech

    2012-10-01

    Selenoprotein P (SeP) is an extracellular protein containing ten selenium atoms in the form of selenocysteine, secreted mainly from the liver. About 60% of the whole plasma selenium level is present in SeP, which makes it a useful biomarker of selenium nutritional status. The main functions of SeP are transport and storage of selenium in plasma. It is especially an important protein for the brain, testes and kidneys where the supplementation of the proper amount of Se ensures the synthesis of selenoenzymes with antioxidant properties.Recently, it has been found that SeP uptake in kidneys, testes and brain depends on the apolipoprotein receptor 2 (ApoER2) and lipoprotein megalin receptor (Lrp2). Megalin receptor represents a physiological SeP receptor in kidneys, mediating the re-uptake of secreted SeP from the primary urine. The absence of a functional megalin receptor causes a significant reduction of plasma selenium and the SeP levels as a result of Se excretion. ApoER2 is a SeP receptor in the brain and testes which uptakes Se from the extracellular fluid. Deletion of ApoER2 in mice leads to a lowered selenium level in the brain and testes, neurological dysfunction, production of abnormal spermatozoa, infertility and even death when the subjects are fed a low-selenium diet. PMID:22683052

  3. Thermoelectric transport of Se-rich Ag{sub 2}Se in normal phases and phase transitions

    SciTech Connect

    Mi, Wenlong; Lv, Yanhong; Qiu, Pengfei; Shi, Xun E-mail: cld@mail.sic.ac.cn; Chen, Lidong E-mail: cld@mail.sic.ac.cn; Zhang, Tiansong

    2014-03-31

    Small amount of Se atoms are used to tune the carrier concentrations (n{sub H}) and electrical transport in Ag{sub 2}Se. Significant enhancements in power factor and thermoelectric figure of merit (zT) are observed in the compositions of Ag{sub 2}Se{sub 1.06} and Ag{sub 2}Se{sub 1.08}. The excessive Se atoms do not change the intrinsically electron-conducting character in Ag{sub 2}Se. The detailed analysis reveals the experiment optimum carrier concentration in Ag{sub 2}Se is around 5 × 10{sup 18} cm{sup −3}. We also investigate the temperature of maximum zT and the thermoelectric transport during the first order phase transitions using the recently developed measurement system.

  4. Confined lattice dynamics of single and quadruple SnSe bilayers in [(SnSe)1.04]m[MoSe2]n ferecrystals

    NASA Astrophysics Data System (ADS)

    Klobes, Benedikt; Hu, Michael Y.; Beekman, Matt; Johnson, David C.; Hermann, Raphaël P.

    2015-12-01

    The Sn specific densities of phonon states in the SnSe subunits of [(SnSe)1.04]m[MoSe2]n ferecrystals with (m,n) = (1,1), (4,1) and in bulk SnSe were derived from nuclear inelastic scattering by the 119Sn Mössbauer resonance. Using different measurement configurations, phonons with polarization parallel and perpendicular to the ferecrystal plane were specifically probed. Vibrational properties and phonon spectral weight are found to strongly depend on the phonon polarization and layer count m. A highly peculiar feature of these ferecrystal densities of phonon states is the emergence of rather sharp high energy vibrational modes polarized perpendicular to the ferecrystal plane, which contrasts with usual findings in thin layered structures and nanostructured materials in general, and a depletion of modes with a gap appearing between acoustic and high energy modes. The spectral weight of these phonons depends on the overall SnSe content, m, but cannot be unambiguously attributed to SnSe-MoSe2 interfaces. Considering the low energy part of lattice dynamics, ferecrystals exhibit rather low average phonon group velocities as compared to the speed of sound in the long wavelength limit. For the (1,1) ferecrystal, this effect is most pronounced for vibrations polarized in the ferecrystal plane. Thus, an experimental microscopic origin for the vibrational and bonding anisotropy in subunits of ferecrystals is provided.

  5. Composition and structure of ZnxCd1-xSe single layers prepared by thermal evaporation of ZnSe and CdSe

    NASA Astrophysics Data System (ADS)

    Nesheva, D.; Aneva, Z.; Šćepanović, M. J.; Bineva, I.; Levi, Z.; Popović, Z. V.; Pejova, B.

    2010-11-01

    Single layers of ZnxCd1-xSe with five different compositions and thickness of 400 nm have been prepared by thermal vacuum evaporation, through alloying of ultra thin ZnSe and CdSe films with equivalent thickness of 0.12, 0.25 or 0.37 nm. The deposition was carried out on rotating substrates kept at room temperature. The layer composition was varied by alloying ZnSe and CdSe films with different equivalent thicknesses. The film composition x = 0.39, 0.52, 0.59, 0.69 and 0.8 has been determined by Energy-Dispersive Spectroscopy and confirmed with Raman scattering data. The microstructure of ZnxCd1-xSe has been investigated by Atomic Force Microscopy and Raman scattering measurement. The Atomic Force Microscopy results have revealed that the layers are nanocrystalline and the grain size is <= 20 nm. The Raman scattering data have shown four replicas of the longitudinal optical phonons, thus confirming the conclusion for the layer crystallinity. The obtained results have shown that the applied deposition technique makes possible preparation of ternary nanocrystalline ZnxCd1-xSe layers with desired compositions..

  6. Confined lattice dynamics of single and quadruple SnSe bilayers in [(SnSe) 1.04 ] m [MoSe 2 ] n ferecrystals

    DOE PAGES

    Klobes, Benedikt; Hu, Michael Y.; Beekman, Matt; Johnson, David C.; Hermann, Raphaël P.

    2015-11-30

    The Sn specific densities of phonon states in the SnSe subunits of [(SnSe)1.04]m[MoSe2]n ferecrystals with (m,n) = (1,1), (4,1) and in bulk SnSe were derived from nuclear inelastic scattering by the 119Sn M ssbauer resonance. When using different measurement configurations, phonons with polarization parallel and perpendicular to the ferecrystal plane were specifically probed. Vibrational properties and phonon spectral weight are found to strongly depend on the phonon polarization and layer count m. Moreover, a highly peculiar feature of these ferecrystal densities of phonon states is the emergence of rather sharp high energy vibrational modes polarized perpendicular to the ferecrystal plane,more » which contrasts with usual findings in thin layered structures and nanostructured materials in general, and a depletion of modes with a gap appearing between acoustic and high energy modes. The spectral weight of these phonons depends on the overall SnSe content, m, but cannot be unambiguously attributed to SnSe MoSe2 interfaces. Considering the low energy part of lattice dynamics, ferecrystals exhibit rather low average phonon group velocities as compared to the speed of sound in the long wavelength limit. For the (1,1) ferecrystal, this effect is most pronounced for vibrations polarized in the ferecrystal plane. Therefore, an experimental microscopic origin for the vibrational and bonding anisotropy in subunits of ferecrystals is provided.« less

  7. RNA adducts with Na 2SeO 4 and Na 2SeO 3 - Stability and structural features

    NASA Astrophysics Data System (ADS)

    Nafisi, Shohreh; Manouchehri, Firouzeh; Montazeri, Maryam

    2011-12-01

    Selenium compounds are widely available in dietary supplements and have been extensively studied for their antioxidant and anticancer properties. Low blood Se levels were found to be associated with an increased incidence and mortality from various types of cancers. Although many in vivo and clinical trials have been conducted using these compounds, their biochemical and chemical mechanisms of efficacy are the focus of much current research. This study was designed to examine the interaction of Na 2SeO 4 and Na 2SeO 3 with RNA in aqueous solution at physiological conditions, using a constant RNA concentration (6.25 mM) and various sodium selenate and sodium selenite/polynucleotide (phosphate) ratios of 1/80, 1/40, 1/20, 1/10, 1/5, 1/2 and 1/1. Fourier transform infrared, UV-Visible spectroscopic methods were used to determine the drug binding modes, the binding constants, and the stability of Na 2SeO 4 and Na 2SeO 3-RNA complexes in aqueous solution. Spectroscopic evidence showed that Na 2SeO 4 and Na 2SeO 3 bind to the major and minor grooves of RNA ( via G, A and U bases) with some degree of the Se-phosphate (PO 2) interaction for both compounds with overall binding constants of K(Na 2SeO 4-RNA) = 8.34 × 10 3 and K(Na 2SeO 3-RNA) = 4.57 × 10 3 M -1. The order of selenium salts-biopolymer stability was Na 2SeO 4-RNA > Na 2SeO 3-RNA. RNA aggregations occurred at higher selenium concentrations. No biopolymer conformational changes were observed upon Na 2SeO 4 and Na 2SeO 3 interactions, while RNA remains in the A-family structure.

  8. First Reported Case of Proliferative Retinopathy in Hemoglobin SE Disease

    PubMed Central

    Yang, Christopher; Fantin, Aldo; Darnley-Fisch, Deborah; Desai, Uday

    2014-01-01

    We report the first case of proliferative sickle cell retinopathy in a patient with hemoglobin SE (Hb SE) disease. Only a few dozen cases of Hb SE disease have been reported previously, and none had evidence of proliferative retinopathy. A 56-year-old African American man presented to our clinic for routine examination and was found to have sea-fan peripheral neovascularization bilaterally without maculopathy. Hemoglobin analysis revealed Hb SE heterozygosity. Sector laser photocoagulation to areas of nonperfusion in both eyes resulted in regression of the peripheral neovascularization over a period of 6 months. Although Hb SE disease is rare, the incidence of Hb SE disease is postulated to rise in the future. Awareness of its potential ocular complications is needed to appropriately refer these patients for screening. PMID:25210638

  9. ZnCdMgSe-Based Semiconductors for Intersubband Devices

    SciTech Connect

    Tamargo, Maria C.

    2008-11-13

    This paper presents a review of recent results on the application of ZnCdMgSe-based wide bandgap II-VI compounds to intersubband devices such as quantum cascade lasers and quantum well infrared photodetectors operating in the mid-infrared region. The conduction band offset of ZnCdSe/ZnCdMgSe quantum well structures was determined from contactless electroreflectance measurements to be as high as 1.12 eV. FT-IR was used to measure intersubband absorption in multi-quantum well structures in the mid-IR range. Electroluminescence at 4.8 {mu}m was observed from a quantum cascade emitter structure made from these materials. Preliminary results are also presented on self assembled quantum dots of CdSe on ZnCdMgSe, and novel quantum well structures with metastable binary MgSe barriers.

  10. Highly luminescent ultranarrow Mn doped ZnSe nanowires.

    PubMed

    Chin, Patrick T K; Stouwdam, Jan W; Janssen, René A J

    2009-02-01

    Colloidal Mn-doped ZnSe nanowires with diameters of 1-3 nm and lengths up to 200 nm were prepared from Li(4)[Zn(10)Se(4)(SPh)(16)] clusters and manganese stearate. The nanowires exhibit optical properties that depend on size, shape, and doping level. The manganese photoluminescence is slightly polarized perpendicular to the long axis and reaches a quantum yield of 40% after passivating the crystals with a CdSe shell.

  11. First-principles study of topological surface states in Bi2Se3/ZnSe superlattices

    NASA Astrophysics Data System (ADS)

    Park, Kyungwha; Chen, Zhiyi; Zhao, Lukas; Garcia, Thor Axtmann; Tamargo, Maria; Krusin-Elbaum, Lia

    Topological insulators (TIs) are interesting due to robustness of surface states within a bulk band gap in the presence of time reversal symmetry. Various TI heterostructures are based on the robustness of the topological surface states. Thus, it is crucial to understand how the topological surface states are influenced by interfaces. Recently Bi2Se3/ZnxCd1-xSe superlattices grown by molecular beam epitaxy showed interesting magneto-transport properties such as a single two-dimensional conducting channel per TI layer with the Berry phase of π. Intrigued by this experiment, we investigate topological surface states of the Bi2Se3/ZnSe superlattice by using density-functional theory. Based on the stoichiometry and the charge balance of the ZnSe layer, when one side of the ZnSe layer is terminated with Zn in the superlattice, the other side must be terminated with Se. Using the superlattice model and two slab models with either a Zn-terminated or Se-terminated interface, we calculate the effect of the inherent asymmetry of the ZnSe layer on the topological surface states of Bi2Se3, and compare our result to the experiment. Funding from NSF DMR-1206354, DMR-1312483, DMR-1420634, HRD-0833180, and DOD-W911NF-13-1-0159, and Computer resources from SDSC Trestles under DMR060009N and VT ARC.

  12. XAS Studies of Se Speciation in Selenite-Fed Rats

    PubMed Central

    Weekley, Claire M.; Aitken, Jade B.; Witting, Paul K.; Harris, Hugh H.

    2014-01-01

    The biological activity of selenium is dependent on its chemical form. Therefore, knowledge of Se chemistry in vivo is required for efficacious use of selenium compounds in disease prevention and treatment. Using X-ray absorption spectroscopy, Se speciation in the kidney, liver, heart, spleen, testis and red blood cells of rats fed control (~0.3 ppm Se) or selenite-supplemented (1 ppm or 5 ppm Se) diets for 3 or 6 weeks, was investigated. X-ray absorption spectroscopy revealed the presence of Se–Se and Se–C species in the kidney and liver, and Se–S species in the kidney, but not the liver. X-ray absorption near edge structure (XANES) spectra showed that there was variation in speciation in the liver and kidneys, but Se speciation was much more uniform in the remaining organs. Using principal component analysis (PCA) to interpret the Se K-edge X-ray absorption spectra, we were able to directly compare the speciation of Se in two different models of selenite metabolism – human lung cancer cells and rat tissues. The effects of Se dose, tissue type and duration of diet on selenium speciation in rat tissues were investigated, and a relationship between the duration of the diet (3 weeks versus 6 weeks) and selenium speciation was observed. PMID:25363824

  13. Rocketdyne - SE-7 and SE-8 Engines. Chapter 4, Appendix F

    NASA Technical Reports Server (NTRS)

    Harmon, Tim

    2009-01-01

    The 70-pound SE-7 engine is very similar with its two valves, ablative material, a silicon carbide liner, a silicon carbide throat, and overall configuration. There were different wraps. One had a ninety-degree ablative material orientation. That is important because it caused problems with the SE-8, but not for this application. It was not overly stressed. It was a validation of the off-the-shelf application approach. There were two SE-7 engines located on the stage near the bottom. They had their own propellant tanks. That was the application. All it did was give a little bit of gravity by firing to push the propellants to the bottom of the tanks for start or restart. It was not a particularly complicated setup. (See Slides 6 and 7, Appendix F) What had we learned? This was a proven engine in a space environment. There weren't any development issues. Off-the-shelf seemed to work. There were no operational issues, which made the SE-7 very cost-effective. Besides NASA, the customer for this application was the Douglas Aircraft Company. Douglas decided the off-the-shelf idea was cost-effective. With the Gemini Program, the company was McDonnell Aircraft Corporation, which was part of the reason the off-the-shelf idea was applied to the Apollo. (See Slide 8, Appendix F) However, here are some differences between Apollo and Gemini vehicles. For one thing, the Apollo vehicle was really moving at high speed when it re-entered the atmosphere. Instead of a mere 17,000 miles per hour, it was going 24,000 miles per hour. That meant the heat load was four times as high on the Apollo vehicle as on the Gemini craft. Things were vibrating a little more. We had two redundant systems. Apollo was redundant where it could be as much as possible. That was really a keystone or maybe an anchor point for Apollo. We decided to pursue the off-the-shelf approach. However, the prime contractor was a different entity - the North American Space Division. They thought they ought to tune up

  14. Small-polaron transport and thermoelectric properties of the misfit-layer composite (BiSe)109TaSe2 / TaSe2

    NASA Astrophysics Data System (ADS)

    Kim, Jin-Hee; Song, Yoo Jang; Rhyee, Jong-Soo; Kim, Bong-Seo; Park, Su-Dong; Lee, Hyeung Jin; Shin, Jae-Wook

    2014-03-01

    We studied the thermoelectric properties of the composite of misfit-layered compounds (BiSe)109TaSe2 and TaSe2. The x-ray diffraction pattern on the cross-sectional plane of the sintered body shows a preferred orientation of the (00 l) direction for (BiSe)109TaSe2 / TaSe2 indicating anisotropic alignment during hot pressing. Because of the crystallographic alignment, the temperature-dependent electrical resistivity ρ (T) , Seebeck coefficient S (T) , and the thermal conductivity κ (T) exhibit in-plane and out-of-plane anisotropic transport behavior. The Seebeck coefficient is very low because of the coexistence of electron and hole mixing, as confirmed by the two-carrier model. The lattice thermal conductivity κLof the covalent bonding layer (in-plane) is lower than those of the layer with van der Waals bonding (out-of-plane) implying the existence of a charge density wave along the in-plane. We observed a sign anomaly of the positive Hall coefficient RH and negative Seebeck coefficient S. According to Holstein's small-polaron model, the sign anomaly may come from the odd number of small-polaron hopping sites.

  15. Preparation of multiband structure with Cu2Se/Ga3Se2/In3Se2 thin films by thermal evaporation technique for maximal solar spectrum utilization

    NASA Astrophysics Data System (ADS)

    Mohan, A.; Rajesh, S.; Gopalakrishnan, M.

    2016-10-01

    The paper investigates and discusses the formation of multiband structure through the Cu2Se-Ga3Se-In3Se2 thin films for maximal solar spectrum utilization. Stacking different semiconductor materials with various band gaps were done by successive evaporation method. Based on the band gap values the layers are arranged (low to high bandgap from the substrate). The XRD results exhibits the formation of CIGS composites through this successive evaporation of Cu2Se/Ga3Se/In3Se2 and treating then with temperature. Scanning Electron Microscope images shows improved crystallinity with the reduction in the larger grain boundary scattering after annealing. Optical spectra shows the stronger absorption in an UV-Visible region and higher transmission in the infrared and near infrared region. The optical band gap values calculated for as prepared films is 2.20 eV and the band gap was split into 1.62, 1.92 eV and 2.27eV for annealed samples. This multiband structures are much needed to utilize the full solar spectrum.

  16. Elucidation of Two Giants: Challenges to Thick-shell Synthesis in CdSe/ZnSe and ZnSe/CdS Core/Shell Quantum Dots

    SciTech Connect

    Acharya, Krishna P.; Nguyen, Hue M.; Paulite, Melissa; Piryatinski, Andrei; Zhang, Jun; Casson, Joanna Lee; Xu, Hongwu; Htoon, Han; Hollingsworth, Jennifer Ann

    2015-03-06

    Core/thick-shell "giant" quantum dots (gQDs) possessing type II electronic structures exhibit suppressed blinking and diminished nonradiative Auger recombination. Here we investigate CdSe/ZnSe and ZnSe/CdS as potential new gQDs. We show theoretically and experimentally that both can exhibit partial or complete spatial separation of an excited-state electron–hole pair (i.e., type II behavior). However, we reveal that thick-shell growth is challenged by competing processes: alloying and cation exchange. We demonstrate that these can be largely avoided by choice of shelling conditions (e.g., time, temperature, and QD core identity). The resulting CdSe/ZnSe gQDs exhibit unusual single-QD properties, principally emitting from dim gray states but having high two-exciton (biexciton) emission efficiencies, whereas ZnSe/CdS gQDs show characteristic gQD blinking suppression, though only if shelling is accompanied by partial cation exchange.

  17. Elucidation of Two Giants: Challenges to Thick-shell Synthesis in CdSe/ZnSe and ZnSe/CdS Core/Shell Quantum Dots

    DOE PAGES

    Acharya, Krishna P.; Nguyen, Hue M.; Paulite, Melissa; Piryatinski, Andrei; Zhang, Jun; Casson, Joanna Lee; Xu, Hongwu; Htoon, Han; Hollingsworth, Jennifer Ann

    2015-03-06

    Core/thick-shell "giant" quantum dots (gQDs) possessing type II electronic structures exhibit suppressed blinking and diminished nonradiative Auger recombination. Here we investigate CdSe/ZnSe and ZnSe/CdS as potential new gQDs. We show theoretically and experimentally that both can exhibit partial or complete spatial separation of an excited-state electron–hole pair (i.e., type II behavior). However, we reveal that thick-shell growth is challenged by competing processes: alloying and cation exchange. We demonstrate that these can be largely avoided by choice of shelling conditions (e.g., time, temperature, and QD core identity). The resulting CdSe/ZnSe gQDs exhibit unusual single-QD properties, principally emitting from dim gray statesmore » but having high two-exciton (biexciton) emission efficiencies, whereas ZnSe/CdS gQDs show characteristic gQD blinking suppression, though only if shelling is accompanied by partial cation exchange.« less

  18. Nanoclusters of CaSe in calcium-doped Bi2Se3 grown by molecular-beam epitaxy.

    PubMed

    Shang, Panju; Guo, Xin; Zhao, Bao; Dai, Xianqi; Bin, Li; Jia, Jinfeng; Li, Quan; Xie, Maohai

    2016-02-26

    In calcium (Ca) doped Bi2Se3 films grown by molecular beam epitaxy, nanoclusters of CaSe are revealed by high-angle annular dark field imaging and energy dispersive x-ray spectroscopy analysis using a scanning transmission electron microscope. As the interface between the ordinary insulator CaSe and topological insulator, Bi2Se3, can host topological nontrivial interface state, this represents an interesting material system for further studies. We show by first principles total energy calculations that aggregation of Ca atoms in Bi2Se3 is driven by energy minimization and a preferential intercalation of Ca in the van der Waals gap between quintuple layers of Bi2Se3 induces reordering of atomic stacking and causes an increasing amount of stacking faults in film. The above findings also provide an explanation of less-than-expected electrical carrier (hole) concentrations in Ca-doped samples.

  19. Electronic structure and superconductivity of FeSe-related superconductors.

    PubMed

    Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J

    2015-05-13

    FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films.

  20. Electronic structure and superconductivity of FeSe-related superconductors.

    PubMed

    Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J

    2015-05-13

    FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films. PMID:25879999

  1. Phase transformation and quantum confinement effect in CdSe/Se multilayer thin films prepared by physical vapour deposition

    NASA Astrophysics Data System (ADS)

    Kumar, M. Melvin David; Devadason, Suganthi

    2013-12-01

    CdSe/Se multilayer (ML) thin films with different thickness ratios of Se and CdSe sublayers were prepared by using a thermal evaporation method. Prepared samples were annealed at temperature 300 K. From X-ray diffraction (XRD) studies, samples prepared at room temperature showed a (100) plane of CdSe with wurtzite structure, whereas the annealed samples confirmed the cubic structure. Stress created in ML systems was calculated from XRD data and found that it increases with decreasing particle size. The energy band gap value of a CdSe/Se ML thin film is shifted to a value higher than that of the bulk CdSe (1.74 eV) semiconductor. This is due to decrease in the crystallite size smaller than the Bohr exciton diameter of CdSe (11.2 nm). Crystallite sizes (≈5 nm) were calculated from UV-VIS data with the predictions of an effective mass approximation model. The photoluminescence peak of the ML samples is split into two bands having nearest values due to the emissions from spin-orbit split-up of the excited energy state.

  2. n-type doping and passivation of CuInSe2 and CuGaSe2 by hydrogen

    NASA Astrophysics Data System (ADS)

    Kılıç, Çetin; Zunger, Alex

    2003-08-01

    An impurity in a semiconductor can have either amphoteric behavior (no net production of electron or holes), or be an energetically deep center (carriers produced only at high temperature), or a shallow center (carriers produced even at low temperature). In most semiconductors (e.g., Si, GaAs, GaP, InP, and ZnSe) hydrogen impurities do not produce free carriers, being instead an amphoretic center; yet hydrogen does dope n-type some oxides such as SnO2 and ZnO. We studied theoretically whether or not H could dope chalcopyrite I-III-VI2 compounds, CuInSe2 and CuGaSe2. Based on the first-principles calculations, we find that nonsubstitutionally incorporated hydrogen forms a deep donor in CuGaSe2, but a relatively shallow donor in CuInSe2. The interaction of hydrogen with the abundant defect complex (2VCu+InCu)0 yields an even shallower donor, making CuInSe2 n type. In addition, our results show that hydrogen passivates the acceptorlike copper vacancies in both CuInSe2 and CuGaSe2, thus eliminating p type behavior. These findings, in conjunction with typical conditions under which CuInSe2 and CuGaSe2 are grown, indicate that CuInSe2 could be doped n type via hydrogen incorporation, whereas CuGaSe2 could not. The reason for the different behavior of CuInSe2 and CuGaSe2 towards hydrogen is that in the latter case the conduction-band minimum is at a considerably higher energy than in the former case. Despite this difference in electrical properties, it is predicted that hydrogen can be stored in both CuInSe2 and CuGaSe2 via implantation since the implanted hydrogens decorate copper atoms as well as preexisting copper vacancies.

  3. Investigation of the behaviour of electronic resistive switching memory based on MoSe2-doped ultralong Se microwires

    NASA Astrophysics Data System (ADS)

    Zhou, Guangdong; Sun, Bai; Yao, Yanqing; Zhang, Huihui; Zhou, Ankun; Alameh, Kamal; Ding, Baofu; Song, Qunliang

    2016-10-01

    MoSe2-doped ultralong Se microwires of length/diameter ratio in the order of ˜240 are synthesized by hydrothermal method. An electronic resistive switching memory (ERSM) device using a single MoSe2-doped ultralong Se microwire is attained. The ERSM exhibits stable resistance ratio of ˜102 for 5000 s, highly stable performance during 500 stressing cycles, and excellent immunity to the frequency of the driving voltage. By investigating the dynamic processes of trap filling, de-trapping, and free-charge migration, trap-controlled space-charge-limited current mechanism is found to dominate the observed ERSM behaviour.

  4. Do SE(II) electrons really degrade SEM image quality?

    PubMed

    Bernstein, Gary H; Carter, Andrew D; Joy, David C

    2013-01-01

    Generally, in scanning electron microscopy (SEM) imaging, it is desirable that a high-resolution image be composed mainly of those secondary electrons (SEs) generated by the primary electron beam, denoted SE(I) . However, in conventional SEM imaging, other, often unwanted, signal components consisting of backscattered electrons (BSEs), and their associated SEs, denoted SE(II) , are present; these signal components contribute a random background signal that degrades contrast, and therefore signal-to-noise ratio and resolution. Ideally, the highest resolution SEM image would consist only of the SE(I) component. In SEMs that use conventional pinhole lenses and their associated Everhart-Thornley detectors, the image is composed of several components, including SE(I) , SE(II) , and some BSE, depending on the geometry of the detector. Modern snorkel lens systems eliminate the BSEs, but not the SE(II) s. We present a microfabricated diaphragm for minimizing the unwanted SE(II) signal components. We present evidence of improved imaging using a microlithographically generated pattern of Au, about 500 nm thick, that blocks most of the undesired signal components, leaving an image composed mostly of SE(I) s. We refer to this structure as a "spatial backscatter diaphragm."

  5. ZnSe Films in GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Kachare, Ram H.

    1987-01-01

    ZnSe increases efficiency and conserves material. Two proposed uses of zinc selenide films promise to boost performance and reduce cost of gallium arsenide solar cells. Accordingly ZnSe serves as surface-passivation layer and as sacrificial layer enabling repeated use of costly GaAs substrate in fabrication.

  6. Effect of Se treatment on the volatile compounds in broccoli.

    PubMed

    Lv, Jiayu; Wu, Jie; Zuo, Jinhua; Fan, Linlin; Shi, Junyan; Gao, Lipu; Li, Miao; Wang, Qing

    2017-02-01

    Broccoli contains high levels of bioactive compounds but deteriorates and senesces easily. In the present study, freshly harvested broccoli was treated with selenite and stored at two different temperatures. The effect of selenite treatment on sensory quality and postharvest physiology were analyzed. Volatile components were assessed by HS-SPME combined with GC-MS and EN. The metabolism of Se and S was also examined. Results indicated that Se treatment had a significant effect on maintaining the sensory quality, suppressing the respiration intensity and ethylene production, as well as increasing the content of Se and decreasing the content of S. In particular, significant differences in the composition of volatile compounds were present between control and Se-treated. The differences were mainly due to differences in alcohols and sulfide compounds. These results demonstrate that Se treatment can have a positive effect on maintaining quality and enhancing its sensory quality through the release of volatile compounds. PMID:27596413

  7. Study of thermal stability of Cu2Se thermoelectric material

    NASA Astrophysics Data System (ADS)

    Bohra, Anil; Bhatt, Ranu; Bhattacharya, Shovit; Basu, Ranita; Ahmad, Sajid; Singh, Ajay; Aswal, D. K.; Gupta, S. K.

    2016-05-01

    Sustainability of thermoelectric parameter in operating temperature range is a key consideration factor for fabricating thermoelectric generator or cooler. In present work, we have studied the stability of thermoelectric parameter of Cu2Se within the temperature range of 50-800°C. Temperature dependent Seebeck coefficients and electrical resistivity measurement are performed under three continuous thermal cycles. X-ray diffraction pattern shows the presence of mixed cubic-monoclinic Cu2Se phase in bare pellet which transforms to pure α-Cu2Se phase with repeating thermal cycle. Significant enhancement in Seebeck coefficient and electrical resistivity is observed which may be attributed to (i) Se loss observed in EDS and (ii) the phase transformation from mixed cubic-monoclinic structure to pure monoclinic α-Cu2Se phase.

  8. Thermoelectric properties of n-type PbSe revisited

    SciTech Connect

    Parker, David S; Singh, David J; Ren, Zhifeng; Zhang, Qinyong

    2012-01-01

    It was recently predicted \\cite{parker} and experimentally confirmed \\cite{sny_PbSe} that $p$-type PbSe would be a good thermoelectric material. Recent experimental work \\cite{pers2} now suggests that $n$-type PbSe can also be a good thermoelectric material. We now re-examine the thermoelectric performance of PbSe with a revised approximation which improves band gap accuracy. We now find that $n$-type PbSe {\\it can} be a high performance material, with thermopowers as high in magnitude as 250 $\\mu$V/K at 1000 K and 300 $\\mu$V/K at 800 K. Optimal 1000 K $n$-type doping ranges are between 2 $\\times 10^{19}$cm$^{-3}$ and 8 $\\times 10^{19}$cm$^{-3}$, while at 800 K the corresponding range is from 7 $\\times$10$^{18}$ to 4 $\\times $10$^{19}$ cm$^{-3}$.

  9. Crystal structure of kappa-In2Se3

    SciTech Connect

    Jasinski, J.; Swider, W.; Washburn, J.; Liliental-Weber, Z.; Chaiken, A.; Nauka, K.; Gibson, G.A.; Yang, C.C.

    2002-10-24

    Structural properties of single-phase films of {kappa}-In{sub 2}Se{sub 3} and {gamma}-In{sub 2}Se{sub 3} were investigated. Both films were polycrystalline but their microstructure differed considerably. The a-lattice parameter of {kappa}-In{sub 2}Se{sub 3} has been measured. Comparison between these two materials indicates that {kappa}-In{sub 2}Se{sub 3} has a significantly larger unit cell ({Delta}c = 2.5 {+-} 0.2 % and {Delta}a = 13.5 {+-} 0.5%) and a structure more similar to the {alpha}-phase of In{sub 2}Se{sub 3}.

  10. Fabrication and characterization of PbSe nanostructures on van der Waals surfaces of GaSe layered semiconductor crystals

    NASA Astrophysics Data System (ADS)

    Kudrynskyi, Z. R.; Bakhtinov, A. P.; Vodopyanov, V. N.; Kovalyuk, Z. D.; Tovarnitskii, M. V.; Lytvyn, O. S.

    2015-11-01

    The growth morphology, composition and structure of PbSe nanostructures grown on the atomically smooth, clean, nanoporous and oxidized van der Waals (0001) surfaces of GaSe layered crystals were studied by means of atomic force microscopy, x-ray diffractometry, photoelectron spectroscopy and Raman spectroscopy. Semiconductor heterostructures were grown by the hot-wall technique in vacuum. Nanoporous GaSe substrates were fabricated by the thermal annealing of layered crystals in a molecular hydrogen atmosphere. The irradiation of the GaSe(0001) surface by UV radiation was used to fabricate thin Ga2O3 layers with thickness < 2 nm. It was found that the narrow gap semiconductor PbSe shows a tendency to form clusters with a square or rectangular symmetry on the clean low-energy (0001) GaSe surface, and (001)-oriented growth of PbSe thin films takes place on this surface. Using this growth technique it is possible to grow PbSe nanostructures with different morphologies: continuous epitaxial layers with thickness < 10 nm on the uncontaminated p-GaSe(0001) surfaces, homogeneous arrays of quantum dots with a high lateral density (more than 1011 cm-2) on the oxidized van der Waals (0001) surfaces and faceted square pillar-like nanostructures with a low lateral density (˜108 cm-2) on the nanoporous GaSe substrates. We exploit the ‘vapor-liquid-solid’ growth with low-melting metal (Ga) catalyst of PbSe crystalline branched nanostructures via a surface-defect-assisted mechanism.

  11. Detection of Salmonella enterica serovar Enteritidis (SE) Antibodies in Serum Using A Polystyrene Bead/SE Flagella Agglutination Assay

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Serologic screening of flocks can be an important method to detect Salmonella enteritidis (SE) infections but can be labor intensive or lack specificity. Our goal was to develop a rapid agglutination assay using SE flagella adsorbed to polystyrene beads as a simple, relatively specific test to dete...

  12. Synthesis and optical properties of core/shell ternary/ternary CdZnSe/ZnSeS quantum dots

    NASA Astrophysics Data System (ADS)

    Nguyen, Hai Yen; de Marcillac, Willy Daney; Lethiec, Clotilde; Phan, Ngoc Hong; Schwob, Catherine; Maître, Agnès; Nguyen, Quang Liem; Le, Van Vu; Bénalloul, Paul; Coolen, Laurent; Thu Nga, Pham

    2014-07-01

    In this paper we report on the synthesis of ternary/ternary alloyed CdZnSe/ZnSeS core/shell quantum dots (QDs) by embryonic nuclei-induced alloying process. We synthesized CdZnSe core QDs emitting in the spectral range of 530-607 nm with various Cd/Zn ratios, depending on the core synthesis temperature. By shelling ZnSeS on the CdZnSe core QDs, the average luminescence quantum yield is increased by a typical factor of 2 up to 17, which we attribute to the reduction of number of non-emitting QDs. The single-photon emitter micro-photoluminescence study showed that the CdZnSe/ZnSeS core/shell QDs are good single-photon emitters and their blinking properties were improved compared to the CdZnSe core QDs. Quantum yields up to 25% were measured for the core/shell samples, demonstrating the potential for high-quality ternary/ternary QDs fabrication.

  13. Synthesis, crystal structure, optical, and electronic study of the new ternary thorium selenide Ba3ThSe3(Se2)2

    NASA Astrophysics Data System (ADS)

    Prakash, Jai; Mesbah, Adel; Beard, Jessica; Lebègue, Sébastien; Malliakas, Christos D.; Ibers, James A.

    2015-11-01

    The compound Ba3ThSe3(Se2)2 has been synthesized by solid-state methods at 1173 K. Its crystal structure features one-dimensional chains of 1∞[Th(Se)3(Se2)26-] separated by Ba2+ cations. Each Th atom in these chains is coordinated to two Se-Se single-bonded pairs and four Se atoms to give rise to a pseudooctahedral geometry around Th. The Th-Se distances are consistent with Th4+ and hence charge balance of Ba3ThSe3(Se2)2 is achieved as 3×Ba2+, 1×Th4+, 3×Se2-, and 2×Se22-. From optical measurements the band gap of Ba3ThSe3(Se2)2 is 1.96(2) eV. DFT calculations indicate that the compound is a semiconductor.

  14. Improving tRNAscan-SE Annotation Results via Ensemble Classifiers.

    PubMed

    Zou, Quan; Guo, Jiasheng; Ju, Ying; Wu, Meihong; Zeng, Xiangxiang; Hong, Zhiling

    2015-11-01

    tRNAScan-SE is a tRNA detection program that is widely used for tRNA annotation; however, the false positive rate of tRNAScan-SE is unacceptable for large sequences. Here, we used a machine learning method to try to improve the tRNAScan-SE results. A new predictor, tRNA-Predict, was designed. We obtained real and pseudo-tRNA sequences as training data sets using tRNAScan-SE and constructed three different tRNA feature sets. We then set up an ensemble classifier, LibMutil, to predict tRNAs from the training data. The positive data set of 623 tRNA sequences was obtained from tRNAdb 2009 and the negative data set was the false positive tRNAs predicted by tRNAscan-SE. Our in silico experiments revealed a prediction accuracy rate of 95.1 % for tRNA-Predict using 10-fold cross-validation. tRNA-Predict was developed to distinguish functional tRNAs from pseudo-tRNAs rather than to predict tRNAs from a genome-wide scan. However, tRNA-Predict can work with the output of tRNAscan-SE, which is a genome-wide scanning method, to improve the tRNAscan-SE annotation results. The tRNA-Predict web server is accessible at http://datamining.xmu.edu.cn/∼gjs/tRNA-Predict. PMID:27491037

  15. Synthesis and Thermal Properties of Solid-State Structural Isomers: Ordered Intergrowths of SnSe and MoSe2.

    PubMed

    Gunning, Noel S; Feser, Joseph; Beekman, Matt; Cahill, David G; Johnson, David C

    2015-07-15

    A family of structural isomers [(SnSe)1.05]m(MoSe2)n were prepared using the modulated elemental reactant method by varying the layer sequence and layer thicknesses in the precursor. By varying the sequence of Sn-Se and Mo-Se layer pairs deposited and annealing the precursors to self-assemble the targeted compound, all six possible isomers [(SnSe)1.05]4(MoSe2)4, [(SnSe)1.05]3(MoSe2)3[(SnSe)1.05]1(MoSe2)1, [(SnSe)1.05]3(MoSe2)2[(SnSe)1.05]1(MoSe2)2, [(SnSe)1.05]2(MoSe2)3[(SnSe)1.05]2(MoSe2)1, [(SnSe)1.05]2(MoSe2)1[(SnSe)1.05]1(MoSe2)2[(SnSe)1.05]1(MoSe2)1, and [(SnSe)1.05]2(MoSe2)2[(SnSe)1.05]1(MoSe2)1[(SnSe)1.05]1(MoSe2)1 were prepared. The structures were characterized by X-ray diffraction and electron microscopy which showed that all of the compounds have very similar c-axis lattice parameters and in-plane constituent lattice parameters yet distinct isomeric structures. These studies confirm that the structure, order, and thickness of the constituent layers match that of the precursors. The cross-plane thermal conductivity is found to be very low (∼0.08 Wm(-1) K(-1)) and independent of the number of SnSe-MoSe2 interfaces within uncertainty. The poor thermal transport in these layered isomers is attributed to a large cross-plane thermal resistance created by SnSe-MoSe2 and MoSe2-MoSe2 turbostratically disordered van der Waals interfaces, the density of which has less variation among the different compounds than the SnSe-MoSe2 interface density alone. PMID:26086400

  16. Copper Selenidophosphates Cu4P2Se6, Cu4P3Se4, Cu4P4Se3, and CuP2Se, Featuring Zero-, One-, and Two-Dimensional Anions.

    PubMed

    Kuhn, Alexander; Schoop, Leslie M; Eger, Roland; Moudrakovski, Igor; Schwarzmüller, Stefan; Duppel, Viola; Kremer, Reinhard K; Oeckler, Oliver; Lotsch, Bettina V

    2016-08-15

    Five new compounds in the Cu/P/Se phase diagram have been synthesized, and their crystal structures have been determined. The crystal structures of these compounds comprise four previously unreported zero-, one-, and two-dimensional selenidophosphate anions containing low-valent phosphorus. In addition to two new modifications of Cu4P2Se6 featuring the well-known hexaselenidohypodiphosphate(IV) ion, there are three copper selenidophosphates with low-valent P: Cu4P3Se4 contains two different new anions, (i) a monomeric (zero-dimensional) selenidophosphate anion [P2Se4](4-) and (ii) a one-dimensional selenidophosphate anion [Formula: see text], which is related to the well-known gray-Se-like [Formula: see text] Zintl anion. Cu4P4Se3 contains one-dimensional [Formula: see text] polyanions, whereas CuP2Se contains the 2D selenidophosphate [Formula: see text] polyanion. It consists of charge-neutral CuP2Se layers separated by a van der Waals gap which is very rare for a Zintl-type phase. Hence, besides black P, CuP2Se constitutes a new possible source of 2D oxidized phosphorus containing layers for intercalation or exfoliation experiments. Additionally, the electronic structures and some fundamental physical properties of the new compounds are reported. All compounds are semiconducting with indirect band gaps of the orders of around 1 eV. The phases reported here add to the structural diversity of chalcogenido phosphates. The structural variety of this family of compounds may translate into a variety of tunable physical properties. PMID:27447868

  17. Optical Probing of metamagnetic phases in epitaxial EuSe

    SciTech Connect

    Galgano, G. D.; Henriques, A. B.; Bauer, G.; Springholz, G.

    2011-12-23

    EuSe is a wide gap magnetic semiconductors with a potential for applications in proof-of-concept spintronic devices. When the temperature is lowered, EuSe goes through sharp transitions between a variety of magnetic phases and is thus described as metamagnetic. The purpose of the present investigation is to correlate the magnetic order to the sharp dichroic doublet, discovered recently in high quality thin epitaxial layers of EuSe, grown by molecular beam epitaxy. We report detailed measurements of the doublet positions and intensities as a function of magnetic field in low temperatures, covering several magnetic phases.

  18. Magnetic study of Fe-doped CdSe nanomaterials

    NASA Astrophysics Data System (ADS)

    Das, Sayantani; Banerjee, Sourish; Sinha, T. P.

    2016-05-01

    Nanoparticles of pure and iron (50 %) doped cadmium selenide (CdSe) have been synthesized by soft chemical route. EDAX analysis supports the inclusion of Fe into CdSe nanoparticles. The average particle size of pure and doped CdSe is found to be ˜50 nm from scanning electron microscopy (SEM). Magnetization of the samples are measured under the field cooled (FC) and zero field cooled (ZFC) modes in the temperature range from 5K to 300K applying a magnetic field of 500Oe. Field dependent magnetization (M-H) measurement indicates presence of room temperature (RT) paramagnetism and low temperature (5K) ferromagnetism of the sample.

  19. Solid state 77Se NMR investigations on arsenic-selenium glasses and crystals

    NASA Astrophysics Data System (ADS)

    Bureau, Bruno; Troles, Johann; LeFloch, Marie; Smektala, Frédéric; Silly, Gilles; Lucas, Jacques

    2003-01-01

    Some resolved solid state 77Se NMR spectra are presented in the As xSe 1- x glass family at ambient temperature. They exhibit three different kinds of Se environments. A comparison with the parent crystalline phases permits to assign the lines to Se- Se-Se, Se- Se-As and As- Se-As Se atom neighborhoods. The measurements of the relative intensities of the lines prove the validity of the intermediate range order structural model known as the "chains crossing model" which is based on AsSe 3 pyramids homogeneously distributed among the divalent Se atoms network. In particular, any scenario involving a selenium clustering process is refuted.

  20. ZnSe hollow nanospheres in mechanically stable near-IR antireflection coatings for ZnSe substrates

    NASA Astrophysics Data System (ADS)

    Li, Chao; Luo, Rui-Chun; Mao, Yong-Qiang; Du, Xi-Wen; Yang, Jing

    2016-09-01

    Though possessing low absorption throughout a wide infrared (IR) spectral regime, owing to a high refractive index, zinc selenide substrates are generally covered by antireflection coatings (ARCs) for practical optical uses. However, achieving a high transmission of ZnSe substrates in the near-IR (NIR) region is still challenging. Herein, for the first time, colloidal ZnSe hollow nanospheres (HNSs) smaller than 100 nm were prepared and adopted to assemble ARCs for ZnSe substrates. The voiding kinetics of the HNSs was found to agree well with the nanoscale Kirkendall effect, and the self-diffusion of the Zn ion in the core was faster than its diffusion through the ZnSe shell. With single-index ARCs, the transmission of ZnSe substrates was remarkably enhanced in the NIR region, with up to an 18% increase at 840 nm. Besides, the ZnSe HNS-based ARCs showed superior mechanical stability even under violent ultrasonication in organic solutions. We expect that ZnSe HNSs will make it possible to construct graded-index ARCs to realize omnidirectional and broadband antireflection in IR, through further tuning of HNSs’ void fraction.

  1. ZnSe hollow nanospheres in mechanically stable near-IR antireflection coatings for ZnSe substrates.

    PubMed

    Li, Chao; Luo, Rui-Chun; Mao, Yong-Qiang; Du, Xi-Wen; Yang, Jing

    2016-09-01

    Though possessing low absorption throughout a wide infrared (IR) spectral regime, owing to a high refractive index, zinc selenide substrates are generally covered by antireflection coatings (ARCs) for practical optical uses. However, achieving a high transmission of ZnSe substrates in the near-IR (NIR) region is still challenging. Herein, for the first time, colloidal ZnSe hollow nanospheres (HNSs) smaller than 100 nm were prepared and adopted to assemble ARCs for ZnSe substrates. The voiding kinetics of the HNSs was found to agree well with the nanoscale Kirkendall effect, and the self-diffusion of the Zn ion in the core was faster than its diffusion through the ZnSe shell. With single-index ARCs, the transmission of ZnSe substrates was remarkably enhanced in the NIR region, with up to an 18% increase at 840 nm. Besides, the ZnSe HNS-based ARCs showed superior mechanical stability even under violent ultrasonication in organic solutions. We expect that ZnSe HNSs will make it possible to construct graded-index ARCs to realize omnidirectional and broadband antireflection in IR, through further tuning of HNSs' void fraction.

  2. Structural and optical properties of CuSe2 nanocrystals formed in thin solid Cu-Se film

    NASA Astrophysics Data System (ADS)

    Gilić, M.; Petrović, M.; Kostić, R.; Stojanović, D.; Barudžija, T.; Mitrić, M.; Romčević, N.; Ralević, U.; Trajić, J.; Romčević, M.; Yahia, I. S.

    2016-05-01

    This paper describes the structural and optical properties of Cu-Se thin films. The surface morphology of thin films was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Formation of Cu-Se thin films is concluded to proceed unevenly, in the form of islands which later grew into agglomerates. The structural characterization of Cu-Se thin film was investigated using X-ray diffraction pattern (XRD). The presence of two-phase system is observed. One is the solid solution of Cu in Se and the other is low-pressure modification of CuSe2. The Raman spectroscopy was used to identify and quantify the individual phases present in the Cu-Se films. Red shift and asymmetry of Raman mode characteristic for CuSe2 enable us to estimate nanocrystal dimension. In the analysis of the far-infrared reflection spectra, numerical model for calculating the reflectivity coefficient of layered system, which includes film with nanocrystalite inclusions (modeled by Maxwell-Garnett approximation) and substrate, has been applied.

  3. ZnSe hollow nanospheres in mechanically stable near-IR antireflection coatings for ZnSe substrates.

    PubMed

    Li, Chao; Luo, Rui-Chun; Mao, Yong-Qiang; Du, Xi-Wen; Yang, Jing

    2016-09-01

    Though possessing low absorption throughout a wide infrared (IR) spectral regime, owing to a high refractive index, zinc selenide substrates are generally covered by antireflection coatings (ARCs) for practical optical uses. However, achieving a high transmission of ZnSe substrates in the near-IR (NIR) region is still challenging. Herein, for the first time, colloidal ZnSe hollow nanospheres (HNSs) smaller than 100 nm were prepared and adopted to assemble ARCs for ZnSe substrates. The voiding kinetics of the HNSs was found to agree well with the nanoscale Kirkendall effect, and the self-diffusion of the Zn ion in the core was faster than its diffusion through the ZnSe shell. With single-index ARCs, the transmission of ZnSe substrates was remarkably enhanced in the NIR region, with up to an 18% increase at 840 nm. Besides, the ZnSe HNS-based ARCs showed superior mechanical stability even under violent ultrasonication in organic solutions. We expect that ZnSe HNSs will make it possible to construct graded-index ARCs to realize omnidirectional and broadband antireflection in IR, through further tuning of HNSs' void fraction. PMID:27482737

  4. Observation of a charge delocalization from Se vacancies in Bi2Se3 : A positron annihilation study of native defects

    NASA Astrophysics Data System (ADS)

    Unzueta, I.; Zabala, N.; Marín-Borrás, V.; Muñoz-Sanjosé, V.; García, J. A.; Plazaola, F.

    2016-07-01

    By means of positron annihilation lifetime spectroscopy, we have investigated the native defects present in Bi2Se3 , which belongs to the family of topological insulators. We experimentally demonstrate that selenium vacancy defects (VSe1) are present in Bi2Se3 as-grown samples, and that their charge is delocalized as temperature increases. At least from 100 K up to room temperature both VSe10 and VSe1+ charge states coexist. The observed charge delocalization determines the contribution of VSe1 defects to the n -type conductivity of Bi2Se3 . These findings are supported by theoretical calculations, which show that vacancies of nonequivalent Se1 and Se2 selenium atoms are clearly differentiated by positron annihilation lifetime spectroscopy, enabling us to directly detect and quantify the most favorable type of selenium vacancy. In addition to open-volume defects, experimental data indicate the presence of defects that act as shallow traps, suggesting that more than one type of native defects coexist in Bi2Se3 . As will be discussed, the presence of a dislocation density around 1010cm-2 could be the source of the detected shallow traps. Understanding the one-dimensional defects and the origin of the charge delocalization that leads Bi2Se3 to be an n -type semiconductor will help in the development of high-quality topological insulators based on this material.

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

    NASA Astrophysics Data System (ADS)

    Sharma, J.; Kumar, S.

    2010-07-01

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

  6. 8. Water treatment plant, view to SE, berm in foreground ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Water treatment plant, view to SE, berm in foreground covering settling tank - Fort Benton Water Treatment Plant, Filtration Plant, Lots 9-13 of Block 7, Fort Benton Original Townsite at Missouri River, Fort Benton, Chouteau County, MT

  7. 3. Partial view of SE sides of Boiler Building (left), ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Partial view of SE sides of Boiler Building (left), Incineration Building (to right of stack) and Machine Shop (right). - Pacific Creosoting Plant, Boiler Building, 5350 Creosote Place, Northeast, Bremerton, Kitsap County, WA

  8. 73. View looking SE down Promenade towards Brooklyn with Brooklyn ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    73. View looking SE down Promenade towards Brooklyn with Brooklyn Tower and bicyclist in background. Jet Lowe, photographer, 1982. - Brooklyn Bridge, Spanning East River between Park Row, Manhattan and Sands Street, Brooklyn, New York County, NY

  9. 43. View from top of Brooklyn Tower looking SE towards ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    43. View from top of Brooklyn Tower looking SE towards Brooklyn showing approach span suspension system and approach roads. Jet Lowe, photograher, 1982. - Brooklyn Bridge, Spanning East River between Park Row, Manhattan and Sands Street, Brooklyn, New York County, NY

  10. 72. View looking SE down pedestrian walking away from bridge ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    72. View looking SE down pedestrian walking away from bridge towards Brooklyn. Jet Lowe, photographer, 1982. - Brooklyn Bridge, Spanning East River between Park Row, Manhattan and Sands Street, Brooklyn, New York County, NY

  11. 30. Aerial view looking SE at Brooklyn Tower and the ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    30. Aerial view looking SE at Brooklyn Tower and the intersection of Water Street and Camden Plaza. Jet Lowe, photographer, 1982. - Brooklyn Bridge, Spanning East River between Park Row, Manhattan and Sands Street, Brooklyn, New York County, NY

  12. 62. Ground level, angled view looking SE at Brooklyn anchorage ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    62. Ground level, angled view looking SE at Brooklyn anchorage and side span superstructure. Jet Lowe, photographer, 1982. - Brooklyn Bridge, Spanning East River between Park Row, Manhattan and Sands Street, Brooklyn, New York County, NY

  13. View of viaduct, looking SE from roof of adjacent parking ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of viaduct, looking SE from roof of adjacent parking garage. - Mulberry Street Viaduct, Spanning Paxton Creek & Cameron Street (State Route 230) at Mulberry Street (State Route 3012), Harrisburg, Dauphin County, PA

  14. 1. AERIAL VIEW FROM SE LOOKING NW, SHOWING BRIDGE AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. AERIAL VIEW FROM SE LOOKING NW, SHOWING BRIDGE AND SITE CONTEXT - Slates' Mill Bridge, Township Road 439 spanning South Branch of Tunkhannock Creek in Benton Township, Dalton, Lackawanna County, PA

  15. Overview of north elevation, looking SE from west bank of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Overview of north elevation, looking SE from west bank of Beaver River. - Pittsburgh, Youngstown & Ashtabula Railroad, Bridge No. 13, Spanning Beaver River, South of State Route 288 Bridge, Wampum, Lawrence County, PA

  16. Overview of north elevation, looking SE from west bank of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Overview of north elevation, looking SE from west bank of Beaver River, with train on bridge. - Pittsburgh, Youngstown & Ashtabula Railroad, Bridge No. 13, Spanning Beaver River, South of State Route 288 Bridge, Wampum, Lawrence County, PA

  17. A new determination of 79Se half-life.

    PubMed

    Bienvenu, Philippe; Cassette, Philippe; Andreoletti, Gilbert; Bé, Marie-Martine; Comte, Jérôme; Lépy, Marie-Christine

    2007-03-01

    A new value of (79)Se half-life was determined by the means of inductively coupled plasma mass spectrometry (ICP-MS) and liquid scintillation counting (LSC) on a sample source isolated from a nuclear reprocessing solution. The procedure used to extract Se from the complex sample solution consisted in liquid-liquid extraction and ion exchange chromatographic methods. The concentration of (79)Se was measured using ICP-MS coupled with electro-thermal vaporisation to eliminate potential isobaric interferences. The activity was measured using LSC after gamma-ray spectrometry to check the contribution of residual radioactive contaminants. From these results, the half-life of (79)Se was found to be 3.77 (19) x 10(5) a.

  18. 8. Interior view looking SE on second floor of Paint ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Interior view looking SE on second floor of Paint Shop. - Central of Georgia Railway, Savannah Repair Shops & Terminal Facilities, Paint & Coach Barn, Bounded by West Broad, Jones, West Boundary & Hull Streets, Savannah, Chatham County, GA

  19. 158. View looking SE showing 'Centennial Anniversary of the Declaration ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    158. View looking SE showing 'Centennial Anniversary of the Declaration of Independence' fountain on Aquarium Drive with north facade of Art Museum in right background. - Fairmount Waterworks, East bank of Schuylkill River, Aquarium Drive, Philadelphia, Philadelphia County, PA

  20. Synthesis and properties of new CdSe-AgI-As{sub 2}Se{sub 3} chalcogenide glasses

    SciTech Connect

    Kassem, M.; Le Coq, D.; Fourmentin, M.; Hindle, F.; Bokova, M.; Cuisset, A.; Masselin, P.; Bychkov, E.

    2011-02-15

    Research highlights: {yields} Determination of the glass-forming region in the pseudo-ternary CdSe-AgI-As{sub 2}Se{sub 3} system. {yields} Characterization of macroscopic properties of the new CdSe-AgI-As{sub 2}Se{sub 3} glasses. {yields} Far infrared transmission of chalcogenide glasses. {yields} Characterization of the total conductivity of CdSe-AgI-As{sub 2}Se{sub 3} glasses. -- Abstract: The glass-forming region in the pseudo-ternary CdSe-AgI-As{sub 2}Se{sub 3} system was determined. Measurements including differential scanning calorimetry (DSC), density, and X-ray diffraction were performed. The effect resulting from the addition of CdSe or AgI has been highlighted by examining three series of different base glasses. The characteristic temperatures of the glass samples, including glass transition (T{sub g}), crystallisation (T{sub x}), and melting (T{sub m}) temperatures are reported and used to calculate their {Delta}T = T{sub x} - T{sub g} and their Hruby, H{sub r} = (T{sub x} - T{sub g})/(T{sub m} - T{sub x}), criteria. Evolution of the total electrical conductivity {sigma} and the room temperature conductivity {sigma}{sub 298} was also studied. The terahertz transparency domain in the 50-600 cm{sup -1} region was pointed for different chalcogenide glasses (ChGs) and the potential of the THz spectroscopy was suggested to obtain structural information on ChGs.

  1. Antiphase Boundaries in the Turbostratically Disordered Misfit Compound (BiSe)(1+δ)NbSe2.

    PubMed

    Mitchson, Gavin; Falmbigl, Matthias; Ditto, Jeffrey; Johnson, David C

    2015-11-01

    (BiSe)(1+δ)NbSe2 ferecrystals were synthesized in order to determine whether structural modulation in BiSe layers, characterized by periodic antiphase boundaries and Bi-Bi bonding, occurs. Specular X-ray diffraction revealed the formation of the desired compound with a c-axis lattice parameter of 1.21 nm from precursors with a range of initial compositions and initial periodicities. In-plane X-ray diffraction scans could be indexed as hk0 reflections of the constituents, with a rectangular basal BiSe lattice and a trigonal basal NbSe2 lattice. Electron micrographs showed extensive turbostratic disorder in the samples and the presence of periodic antiphase boundaries (approximately 1.5 nm periodicity) in BiSe layers oriented with the [110] direction parallel to the zone axis of the microscope. This indicates that the structural modulation in the BiSe layers is not due to coherency strain resulting from commensurate in-plane lattices. Electrical transport measurements indicate that holes are the dominant charge carrying species, that there is a weak decrease in resistivity as temperature decreases, and that minimal charge transfer occurs from the BiSe to NbSe2 layers. This is consistent with the lack of charge transfer from the BiX to the TX2 layers reported in misfit layer compounds where antiphase boundaries were observed. This suggests that electronic considerations, i.e., localization of electrons in the Bi-Bi pairs at the antiphase boundaries, play a dominant role in stabilizing the structural modulation. PMID:26465820

  2. Flux free growth of superconducting FeSe single crystals

    NASA Astrophysics Data System (ADS)

    Maheshwari, P. K.; Joshi, L. M.; Gahtori, Bhasker; Srivastava, A. K.; Gupta, Anurag; Patnaik, S. P.; Awana, V. P. S.

    2016-07-01

    We report flux free growth of superconducting FeSe single crystals by an easy and versatile high temperature melt and slow cooling method for first time. The room temperature x-ray diffraction (XRD) on the surface of the piece of such obtained crystals showed single [101] plane of β-FeSe tetragonal phase. The bulk powder XRD, being obtained by crushing the part of crystal chunk showed majority (∼87%) β-FeSe tetragonal (space group P4/nmm) and minority (∼13%) δ-FeSe hexagonal (space group P63/mmc) crystalline phases. Detailed high resolution transmission electron microscope images along with selected area electron diffraction showed the abundance of both majority β-FeSe and minority δ-FeSe phases. Both transport (ρ-T) and magnetization exhibited superconductivity at below around 10 K. Interestingly, the magnetization signal of these crystals is dominated by the magnetism of minority δ-FeSe magnetic phase, and hence the isothermal magnetization at 4 K was seen to be ferromagnetic like. Transport (ρ-T) measurements under magnetic field showed superconductivity onset at below 12 K, and ρ = 0 (T c) at 9 K. Superconducting transition temperature (T c) decreases with applied field to around 6 K at 7 T, with dT c/dH of ∼0.4 K T‑1, giving rise to an H c2(0) value of around 50 , 30 and 20 T for normal resistivity ρ n = 90%, 50% and 10% respectively, which are calculated from conventional one band Werthamer–Helfand–Hohenberg equation. FeSe single crystal activation energy is calculated from thermally activated flux flow model which is found to decreases with field from 12.1 meV for 0.2 T to 3.77 meV for 7 T.

  3. Tin oxidation mechanism in the Sn-Se alloy

    NASA Astrophysics Data System (ADS)

    Duhalde, S.; Arcondo, B.; Nassif, E.; Sirkin, H.

    1988-06-01

    Mössbauer spectroscopy and X-ray diffraction studies performed on powdered samples of Sn-Se alloys allowed us to determine the influence of the chalcogenide bonds in the tin oxidation mechanism. The weak bonds present in the SnSe2 compound increase the tin oxidation kinetics, an effect which is not found in pure tin samples maintained in the same conditions.

  4. Processing ambiguous Spanish se in a minimal chain.

    PubMed

    Meseguer, Enrique; Acuña-Fariña, Carlos; Carreiras, Manuel

    2009-04-01

    The recovery of pieces of information that are not linguistically expressed is a constant feature of the process of language comprehension. In the processing literature, such missing information is generally referred to as "gaps". Usually, one resolves gaps by finding "fillers" in either the sentence or the context. For instance, in Peter seemed to be upset, Peter is really the subject of being upset but appears as surface subject of seems. Sometimes constituents move, leaving gaps behind. Various Romance languages such as Spanish or Italian have a grammatical particle se/si, which, as it is extremely ambiguous, licenses different sorts of gaps. In Spanish, se can encode at least reflexive, impersonal, and passive meanings. In an eye-tracking experiment we contrast reflexive structures containing postverbal subjects with impersonal structures with no subjects (GAP se vendó apresuradamente el corredor/"the runner bandaged himself hurriedly" vs. GAP se vendó apresuradamente al corridor/"(someone) bandaged the runner hurriedly"). In a second manipulation we contrast the presence of an extra argument with se-passives (GAP se vendó el tobillo el corredor/"the runner bandaged his ankle" vs. GAP se vendó el tobillo al corridor/"the runner's ankle was bandaged"). Our comparisons involve contrasting standard transitive structures with nonstandard word order (postverbal subject and a preverbal subject gap) against inherently complex and less habitual structures such as impersonals (with no subject) or se-passives (with subjects in canonical object position). We evaluate the minimal chain principle (de Vincenzi, 1991), according to which displacement is costly because it entails complex (derivational) "chains" that must be undone before phrasal packaging can commence. We show the minimal chain principle to be essentially correct when contrasting more complex but more frequent structures with less complex but less frequent structures. A noteworthy feature of this research

  5. Genetic Identification of an Enzymatic Se(VI) Reduction Pathway

    NASA Astrophysics Data System (ADS)

    Yee, N.; Kobayashi, D. Y.

    2006-12-01

    Enterobacter cloacae is a biofilm-forming organism that colonizes the subterranean portions of plants. Because of its ability to catalyze the reduction of selenium oxyanions, this bacterium plays an important role in Se(0) biomineralization and Se cycling in soils. Identification of the genes that regulate selenate reductase activity is needed to elucidate the mechanisms employed by this organism to reduce Se(VI). However, the genes in E. cloacae involved in selenium reduction are currently unknown. In this study, transposon mutagenesis and direct cloning techniques were used to identify genetic regions in E. cloacae SLD1a-1 associated with selenate reductase activity. The mini-Tn5 transposon system was used to produce mutants that have lost the ability to reduce selenate. E. cloacae mutants and genomic library clones heterologously expressed in E. coli S17-1 were screened for activity on LB agar supplemented with sodium selenate. The rate of selenate reduction by the clones was measured in liquid minimal media, and the Se(0) minerals formed by the clones were examined using EXAFS, TEM, and XRD. The transposon mutagenesis experiments revealed that mutation of menaquinone biosynthesis genes inhibits selenate reduction. The direct cloning experiments showed that heterologous expression of the global anaerobic regulatory gene fnr from Enterobacter cloacae in the non Se-reducing strain E. coli S17-1 activated selenate reductase activity and the ability to precipitate Se(0) particles. Se(VI) reduction by E. coli S17-1 containing the fnr gene occurred at similar rates as E. cloacae and produced elemental selenium particles with identical morphologies and short range atomic order. These findings indicate that Se(VI) reduction by facultative anaerobes is regulated by anaerobic electron carriers and oxygen sensing transcription factors.

  6. Template free-solvothermaly synthesized copper selenide (CuSe, Cu 2- xSe, β-Cu 2Se and Cu 2Se) hexagonal nanoplates from different precursors at low temperature

    NASA Astrophysics Data System (ADS)

    Kumar, Pushpendra; Singh, Kedar; Srivastava, O. N.

    2010-09-01

    Nonstoichiometric (Cu 2- xSe) and stoichiometric (CuSe, β-Cu 2Se and Cu 2Se) copper selenide hexagonal nanoplates have been synthesized using different general and convenient copper sources, e.g. copper chloride, copper sulphate, copper nitrate, copper acetate, elemental copper with elemental selenium, friendly ethylene glycol and hydrazine hydrate in a defined amount of water at 100 °C within 12 h adopting the solvothermal method. Phase analysis, purity and morphology of the product have been well studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray diffraction (EDAX) techniques. The structural and compositional analysis revealed that the products were of pure phase with corresponding atomic ratios. SEM, TEM and HRTEM analyses revealed that the nanoplates were in the range 200-450 nm and the as-prepared products were uniform and highly crystallized. The nanoplates consisted of {0 0 1} facets of top-bottom surfaces and {1 1 0} facets of the other six side surfaces. This new approach encompasses many advantages over the conventional solvothermal method in terms of product quality (better morphology control with high yield) and reaction conditions (lower temperatures). Copper selenide hexagonal nanoplates obtained by the described method could be potential building blocks to construct functional devices and solar cell. This work may open up a new rationale on designing the solution synthesis of nanostructures for materials possessing similar intrinsic crystal symmetry. On the basis of the carefully controlled experiments mentioned herein, a plausible formation mechanism of the hexagonal nanoplates was suggested and discussed. To the best of our knowledge, this is the first report on nonstoichiometric (Cu 2- xSe) as well as stoichiometric (CuSe, β-Cu 2Se and Cu 2Se) copper selenide hexagonal nanoplates with

  7. Tunable Graphene-GaSe Dual Heterojunction Device.

    PubMed

    Kim, Wonjae; Li, Changfeng; Chaves, Ferney A; Jiménez, David; Rodriguez, Raul D; Susoma, Jannatul; Fenner, Matthias A; Lipsanen, Harri; Riikonen, Juha

    2016-03-01

    A field-effect device based on dual graphene-GaSe heterojunctions is demonstrated. Monolayer graphene is used as electrodes on a GaSe channel to form two opposing Schottky diodes controllable by local top gates. The device exhibits strong rectification with tunable threshold voltage. Detailed theoretical modeling is used to explain the device operation and to distinguish the differences compared to a single diode.

  8. Direct evidence of current blocking by ZnSe in Cu2ZnSnSe4 solar cells

    NASA Astrophysics Data System (ADS)

    Timo Wätjen, Jörn; Engman, Jessica; Edoff, Marika; Platzer-Björkman, Charlotte

    2012-04-01

    Thin films of polycrystalline Cu2ZnSnSe4 were made by selenization of co-sputtered metallic precursors and processed to solar cells. Electron beam induced current (EBIC) in combination with microscopic scale IV characterization is used to investigate lateral inhomogeneities in electrical performance across the solar cell area. Transmission electron microscopy relates areas with low EBIC response to the formation of a ZnSe phase at the absorber surface resulting in a current blocking behavior and a reduced short-circuit current density for the solar cells. Areas without ZnSe have a high EBIC response and result in high quality diodes well suited for solar cells.

  9. Dislocation-driven growth of porous CdSe nanorods from CdSe.(ethylenediamine)0.5 nanorods

    NASA Astrophysics Data System (ADS)

    Kim, Hyung-Bae; Jang, Du-Jeon

    2015-12-01

    Porous CdSe nanorods having a novel flute-like morphology have been prepared facilely via the hydrothermal treatment of CdSe.(en)0.5 (en = ethylenediamine) nanorods as sacrificial templates. During the hydrothermal process, various crystalline imperfections such as stacking faults and twinning planes appear due to lattice mismatches between orthorhombic CdSe.(en)0.5 and hexagonal wurtzite porous CdSe nanorods and subsequently disappear to release mismatched strains. In the self-healing process of defects, due to the imbalance of in-and-out atomic diffusion, point defects of atomic vacancies are heavily generated in CdSe nanorods to produce volume defects of voids eventually. The photoluminescence of CdSe nanorods shifts to the red region and decreases in intensity with the increase of the hydrolysis time as surface states and selenium vacancies increase. The mean lifetime of photoluminescence increases with the increase of the hydrothermal-treatment time as the fractional amplitude of the surface-state-related component increases.Porous CdSe nanorods having a novel flute-like morphology have been prepared facilely via the hydrothermal treatment of CdSe.(en)0.5 (en = ethylenediamine) nanorods as sacrificial templates. During the hydrothermal process, various crystalline imperfections such as stacking faults and twinning planes appear due to lattice mismatches between orthorhombic CdSe.(en)0.5 and hexagonal wurtzite porous CdSe nanorods and subsequently disappear to release mismatched strains. In the self-healing process of defects, due to the imbalance of in-and-out atomic diffusion, point defects of atomic vacancies are heavily generated in CdSe nanorods to produce volume defects of voids eventually. The photoluminescence of CdSe nanorods shifts to the red region and decreases in intensity with the increase of the hydrolysis time as surface states and selenium vacancies increase. The mean lifetime of photoluminescence increases with the increase of the hydrothermal

  10. STM study on the structures of SnSe surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Tae Hoon; Kim, Sang-Ui; Thi Ly, Trinh; Duong, Anh Tuan; Cho, Sunglae; Rhim, S. H.; Kim, Jungdae

    SnSe is a 2 dimensional layered material, and each layer is coupled by van deer Waals forces allowing very easy cleaving though the layer surfaces. SnSe has been studied for various potential applications because of its high stability and elemental abundance in earth. Recently, it was also reported that bulk SnSe has an excellent thermoelectric property of ZT =2.6 at 923 K along the b axis (Zhao et al., Nature 508 373 (2014)). The surface of a single crystal SnSe was studied via a home-built low temperature scanning tunneling microscopy (STM). Clear atomic images of SnSe surfaces were observed at the filled and empty state measurements, and detail atomic structures were analyzed by comparing with DFT simulations. We found that the atomic image of SnSe surfaces measured by STM is not trivial to understand. Only Sn atoms were visible on STM topographic images for the both of filled and empty state probing. This work was supported by the National Research Foundation of Korea(NRF) [Nos. NRF-2013R1A1A1008724, NRF-2009-0093818, and NRF-2014R1A4A1071686].

  11. Identification QTLs Controlling Genes for Se Uptake in Lentil Seeds

    PubMed Central

    Ates, Duygu; Sever, Tugce; Aldemir, Secil; Yagmur, Bulent; Temel, Hulya Yilmaz; Kaya, Hilal Betul; Alsaleh, Ahmad; Kahraman, Abdullah; Ozkan, Hakan; Vandenberg, Albert; Tanyolac, Bahattin

    2016-01-01

    Lentil (Lens culinaris Medik.) is an excellent source of protein and carbohydrates and is also rich in essential trace elements for the human diet. Selenium (Se) is an essential micronutrient for human health and nutrition, providing protection against several diseases and regulating important biological systems. Dietary intake of 55 μg of Se per day is recommended for adults, with inadequate Se intake causing significant health problems. The objective of this study was to identify and map quantitative trait loci (QTL) of genes controlling Se accumulation in lentil seeds using a population of 96 recombinant inbred lines (RILs) developed from the cross “PI 320937” × “Eston” grown in three different environments for two years (2012 and 2013). Se concentration in seed varied between 119 and 883 μg/kg. A linkage map consisting of 1,784 markers (4 SSRs, and 1,780 SNPs) was developed. The map spanned a total length of 4,060.6 cM, consisting of 7 linkage groups (LGs) with an average distance of 2.3 cM between adjacent markers. Four QTL regions and 36 putative QTL markers, with LOD scores ranging from 3.00 to 4.97, distributed across two linkage groups (LG2 and LG5) were associated with seed Se concentration, explaining 6.3–16.9% of the phenotypic variation. PMID:26978666

  12. Identification QTLs Controlling Genes for Se Uptake in Lentil Seeds.

    PubMed

    Ates, Duygu; Sever, Tugce; Aldemir, Secil; Yagmur, Bulent; Temel, Hulya Yilmaz; Kaya, Hilal Betul; Alsaleh, Ahmad; Kahraman, Abdullah; Ozkan, Hakan; Vandenberg, Albert; Tanyolac, Bahattin

    2016-01-01

    Lentil (Lens culinaris Medik.) is an excellent source of protein and carbohydrates and is also rich in essential trace elements for the human diet. Selenium (Se) is an essential micronutrient for human health and nutrition, providing protection against several diseases and regulating important biological systems. Dietary intake of 55 μg of Se per day is recommended for adults, with inadequate Se intake causing significant health problems. The objective of this study was to identify and map quantitative trait loci (QTL) of genes controlling Se accumulation in lentil seeds using a population of 96 recombinant inbred lines (RILs) developed from the cross "PI 320937" × "Eston" grown in three different environments for two years (2012 and 2013). Se concentration in seed varied between 119 and 883 μg/kg. A linkage map consisting of 1,784 markers (4 SSRs, and 1,780 SNPs) was developed. The map spanned a total length of 4,060.6 cM, consisting of 7 linkage groups (LGs) with an average distance of 2.3 cM between adjacent markers. Four QTL regions and 36 putative QTL markers, with LOD scores ranging from 3.00 to 4.97, distributed across two linkage groups (LG2 and LG5) were associated with seed Se concentration, explaining 6.3-16.9% of the phenotypic variation.

  13. Optical Characterization of Bulk ZnSeTe Solid Solutions

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  14. Identification QTLs Controlling Genes for Se Uptake in Lentil Seeds.

    PubMed

    Ates, Duygu; Sever, Tugce; Aldemir, Secil; Yagmur, Bulent; Temel, Hulya Yilmaz; Kaya, Hilal Betul; Alsaleh, Ahmad; Kahraman, Abdullah; Ozkan, Hakan; Vandenberg, Albert; Tanyolac, Bahattin

    2016-01-01

    Lentil (Lens culinaris Medik.) is an excellent source of protein and carbohydrates and is also rich in essential trace elements for the human diet. Selenium (Se) is an essential micronutrient for human health and nutrition, providing protection against several diseases and regulating important biological systems. Dietary intake of 55 μg of Se per day is recommended for adults, with inadequate Se intake causing significant health problems. The objective of this study was to identify and map quantitative trait loci (QTL) of genes controlling Se accumulation in lentil seeds using a population of 96 recombinant inbred lines (RILs) developed from the cross "PI 320937" × "Eston" grown in three different environments for two years (2012 and 2013). Se concentration in seed varied between 119 and 883 μg/kg. A linkage map consisting of 1,784 markers (4 SSRs, and 1,780 SNPs) was developed. The map spanned a total length of 4,060.6 cM, consisting of 7 linkage groups (LGs) with an average distance of 2.3 cM between adjacent markers. Four QTL regions and 36 putative QTL markers, with LOD scores ranging from 3.00 to 4.97, distributed across two linkage groups (LG2 and LG5) were associated with seed Se concentration, explaining 6.3-16.9% of the phenotypic variation. PMID:26978666

  15. (77)Se nuclear spin-lattice relaxation in binary Ge-Se glasses: insights into floppy versus rigid behavior of structural units.

    PubMed

    Sen, Sabyasachi; Kaseman, Derrick C; Hung, Ivan; Gan, Zhehong

    2015-04-30

    The mechanism of (77)Se nuclear spin-lattice relaxation is investigated in binary Ge-Se glasses. The (77)Se nuclides in Se-Se-Se chain sites relax faster via dipolar coupling fluctuation compared to those in Ge-Se-Ge sites shared by GeSe4 tetrahedra that relax slower via the fluctuation of the chemical shift anisotropy. The relaxation rate for the Se-Se-Se sites decreases markedly with increasing magnetic field, whereas that for the Ge-Se-Ge sites displays no appreciable dependence on the magnetic field such that the extent of differential relaxation between the two Se environments becomes small at high fields on the order of 19.6 T. The corresponding dynamical correlation time is three orders of magnitude shorter (∼10(-9) s) for the Se-Se-Se sites, compared to that for the Ge-Se-Ge sites (∼10(-6) s). The large decoupling in the time scale between these Se environments provides direct experimental support to the commonly made assumption that the selenium chains are mechanically floppy, and the interconnected GeSe4 tetrahedra form the rigid elements in the selenide glass structure.

  16. Sulfur gradient-driven Se diffusion at the CdS/CuIn(S,Se){sub 2} solar cell interface

    SciTech Connect

    Weinhardt, L.; Morkel, M.; Baer, M.; Pookpanratana, S.; Heske, C.; Niesen, T. P.; Karg, F.; Ramanathan, K.; Contreras, M. A.; Noufi, R.; Umbach, E.

    2010-05-03

    The diffusion behavior of Se at the CdS/Cu(In,Ga)(S,Se){sub 2} thin film solar cell interface was investigated by x-ray photoelectron spectroscopy and x-ray excited Auger electron spectroscopy. Buffer/absorber structures with S/Se ratios between zero and three at the initial Cu(In,Ga)(S,Se){sub 2} surface were analyzed. Samples from a high-efficiency laboratory process (NREL) as well as from an industrial large-area process (AVANCIS) were investigated. We find selenium diffusion into the CdS buffer layer, the magnitude of which strongly depends on the S content at the absorber surface. The associated modification of the heterojunction partners has significant impact on the electronic structure at the interface.

  17. Magneto-optical studies of ensembles of semimagnetic self-organized Cd(Mn)Se/Zn(Mn)Se Quantum Dots

    SciTech Connect

    Reshina, I. I.; Ivanov, S. V.; Toropov, A. A.

    2013-12-04

    Ensembles of Cd(Mn)Se/ZnSe and CdSe/Zn(Mn)Se semimagnetic self-organized quantum dots with different Mn content have been studied by photoluminescence and resonant Raman scattering under strong magnetic fields in Faraday and Voigt geometries and with spectral and polarization selective excitation. Electron spin-flip Raman scattering has been observed in Voigt geometry in the structures with large Mn content. Narrow exciton peaks completely σ{sup −}σ{sup +} polarized have been observed under selective excitation in Faraday geometry in the structures with medium and small Mn content. A number of specific effects manifested themselves in the structures with a smallest Mn content where no Zeeman shift of the photoluminescence bands was observed.

  18. Photoelectrochemical Characterization of Polycrystalline CdSe, CdTe and CuInSe2 Semiconductor Films

    NASA Astrophysics Data System (ADS)

    Koutsikou, R.; Bouroushian, M.

    2010-01-01

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

  19. Enhanced lateral photovoltaic effect observed in CdSe quantum dots embedded structure of Zn/CdSe/Si.

    PubMed

    Lan, Tian; Liu, Shuai; Wang, Hui

    2011-01-01

    The quantum dots (QDs) system has been intensively studied for decades owing to its huge potential for applications. In this Letter, we report a lateral photovoltaic effect (LPE) with a large sensitivity observed in CdSe QDs embedded structure of Zn/CdSe/Si. This result not only enriches applications of the QDs system but also opens a new window to study the carrier dynamics of the QDs system.

  20. Dislocation-driven growth of porous CdSe nanorods from CdSe·(ethylenediamine)(0.5) nanorods.

    PubMed

    Kim, Hyung-Bae; Jang, Du-Jeon

    2016-01-01

    Porous CdSe nanorods having a novel flute-like morphology have been prepared facilely via the hydrothermal treatment of CdSe·(en)0.5 (en = ethylenediamine) nanorods as sacrificial templates. During the hydrothermal process, various crystalline imperfections such as stacking faults and twinning planes appear due to lattice mismatches between orthorhombic CdSe·(en)0.5 and hexagonal wurtzite porous CdSe nanorods and subsequently disappear to release mismatched strains. In the self-healing process of defects, due to the imbalance of in-and-out atomic diffusion, point defects of atomic vacancies are heavily generated in CdSe nanorods to produce volume defects of voids eventually. The photoluminescence of CdSe nanorods shifts to the red region and decreases in intensity with the increase of the hydrolysis time as surface states and selenium vacancies increase. The mean lifetime of photoluminescence increases with the increase of the hydrothermal-treatment time as the fractional amplitude of the surface-state-related component increases. PMID:26615794

  1. Crystallization of In-Se/CuInSe 2 thin-film stack by sequential electrodeposition and annealing

    NASA Astrophysics Data System (ADS)

    Oda, Y.; Matsubayashi, M.; Minemoto, T.; Takakura, H.

    2009-01-01

    CuInSe 2 (CIS) films with large grain sizes and slightly In-rich composition ratios were realized by a sequential electrodeposition (ED) and annealing of In-Se/CIS bilayers. In general, ED-CIS films needed to be crystallized by annealing and the Cu/In ratios needed adjustment by KCN etching because they were amorphous with Cu-rich compositional ratios. KCN etchings cause pits and crevasses as defects by removal of Cu 2-xSe compounds formed on the surface and in the grain boundary in the annealing process. These defects should work as shunt paths for solar cells with ED-CIS films. In this study, we attempted to fabricate In-Se/CIS bilayers by sequential ED and annealing to solve this serial issue. ED-In-Se films could be realized not on ED-CIS films but on the annealed CIS films by the difference in each oxidation potential. At the electric charges of 1.5-1.8 C for In-Se with a coulomb meter, Cu/In ratios of bilayers annealed at 600 °C for 10 min under Ar atmosphere could be adjusted to 0.9-1.0. At the same annealing condition, the complete intermixing of bilayers and the crystal grain growth were realized. As a result, the best solar cell fabricated with the film resulted in around 2% efficiency.

  2. Transition probabilities in neutron-rich Se,8684

    NASA Astrophysics Data System (ADS)

    Litzinger, J.; Blazhev, A.; Dewald, A.; Didierjean, F.; Duchêne, G.; Fransen, C.; Lozeva, R.; Sieja, K.; Verney, D.; de Angelis, G.; Bazzacco, D.; Birkenbach, B.; Bottoni, S.; Bracco, A.; Braunroth, T.; Cederwall, B.; Corradi, L.; Crespi, F. C. L.; Désesquelles, P.; Eberth, J.; Ellinger, E.; Farnea, E.; Fioretto, E.; Gernhäuser, R.; Goasduff, A.; Görgen, A.; Gottardo, A.; Grebosz, J.; Hackstein, M.; Hess, H.; Ibrahim, F.; Jolie, J.; Jungclaus, A.; Kolos, K.; Korten, W.; Leoni, S.; Lunardi, S.; Maj, A.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Mijatovic, T.; Million, B.; Möller, O.; Modamio, V.; Montagnoli, G.; Montanari, D.; Morales, A. I.; Napoli, D. R.; Niikura, M.; Pollarolo, G.; Pullia, A.; Quintana, B.; Recchia, F.; Reiter, P.; Rosso, D.; Sahin, E.; Salsac, M. D.; Scarlassara, F.; Söderström, P.-A.; Stefanini, A. M.; Stezowski, O.; Szilner, S.; Theisen, Ch.; Valiente Dobón, J. J.; Vandone, V.; Vogt, A.

    2015-12-01

    Reduced quadrupole transition probabilities for low-lying transitions in neutron-rich Se,8684 are investigated with a recoil distance Doppler shift (RDDS) experiment. The experiment was performed at the Istituto Nazionale di Fisica Nucleare (INFN) Laboratori Nazionali di Legnaro using the Cologne Plunger device for the RDDS technique and the AGATA Demonstrator array for the γ -ray detection coupled to the PRISMA magnetic spectrometer for an event-by-event particle identification. In 86Se the level lifetime of the yrast 21+ state and an upper limit for the lifetime of the 41+ state are determined for the first time. The results of 86Se are in agreement with previously reported predictions of large-scale shell-model calculations using Ni78-I and Ni78-II effective interactions. In addition, intrinsic shape parameters of lowest yrast states in 86Se are calculated. In semimagic 84Se level lifetimes of the yrast 41+ and 61+ states are determined for the first time. Large-scale shell-model calculations using effective interactions Ni78-II, JUN45, jj4b, and jj4pna are performed. The calculations describe B (E 2 ;21+→01+) and B (E 2 ;61+→41+) fairly well and point out problems in reproducing the experimental B (E 2 ;41+→21+) .

  3. Monotherapy or Polytherapy for First-Line Treatment of SE?

    PubMed

    Alvarez, Vincent; Rossetti, Andrea O

    2016-02-01

    Status epilepticus (SE) is one of the most frequent neurologic emergencies, and a rapid and effective treatment is warranted. Current guidelines recommend a stepwise approach using a sequence of different antiepileptic drugs with benzodiazepines (BZD) being the first treatment proposed. To provide the more effective treatment as soon as possible, some authors have suggested using a combined polytherapy as first-line treatment. Strong evidence supports the use of benzodiazepines, mostly lorazepam and midazolam as initial monotherapy treatment for SE. Insufficient data are available to support the use of nonsedating antiepileptic drugs as phenytoin, valproic acid, or levetiracetam without a previous benzodiazepine administration. Studies assessing the role of a combined initial therapy are rare, if not missing. Moreover, owing the wide range of SE etiologies, a "one fits all" initial polytherapy seems difficult to achieve. After reviewing the available evidence, guidelines, and current practices regarding monotherapy and polytherapy as first-line treatment in SE in adults, the authors propose a rational algorithm for early antiseizure treatment in SE. PMID:26840871

  4. Heterojunctions of model CdTe/CdSe mixtures

    SciTech Connect

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

    2015-03-18

    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 also 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 further 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. We thus 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.

  5. Heterojunctions of model CdTe/CdSe mixtures

    DOE PAGES

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

    2015-03-18

    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 also 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 further analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization tomore » 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. We thus 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.« less

  6. Thermoelectric properties of single-layered SnSe sheet.

    PubMed

    Wang, Fancy Qian; Zhang, Shunhong; Yu, Jiabing; Wang, Qian

    2015-10-14

    Motivated by the recent study of inspiring thermoelectric properties in bulk SnSe [Zhao et al., Nature, 2014, 508, 373] and the experimental synthesis of SnSe sheets [Chen et al., J. Am. Chem. Soc., 2013, 135, 1213], we have carried out systematic calculations for a single-layered SnSe sheet focusing on its stability, electronic structure and thermoelectric properties by using density functional theory combined with Boltzmann transport theory. We have found that the sheet is dynamically and thermally stable with a band gap of 1.28 eV, and the figure of merit (ZT) reaches 3.27 (2.76) along the armchair (zigzag) direction with optimal n-type carrier concentration, which is enhanced nearly 7 times compared to its bulk counterpart at 700 K due to quantum confinement effect. Furthermore, we designed four types of thermoelectric couples by assembling single-layered SnSe sheets with different transport directions and doping types, and found that their efficiencies are all above 13%, which are higher than those of thermoelectric couples made of commercial bulk Bi2Te3 (7%-8%), suggesting the great potential of single-layered SnSe sheets for heat-electricity conversion.

  7. Electrodeposition and characterization of HgSe thin films

    SciTech Connect

    Mahalingam, T. . E-mail: maha51@rediffmail.com; Kathalingam, A.; Sanjeeviraja, C.; Chandramohan, R.; Chu, J.P.; Kim, Yong Deak; Velumani, S.

    2007-08-15

    In this article we present the results on the electrochemical synthesis of mercury selenide (HgSe), an interesting II-VI material. HgSe thin films were deposited potentiostatically on conducting glass substrates from an aqueous bath containing HgCl{sub 2} and SeO{sub 2}. The prepared films were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscope (SEM) and optical absorption techniques. Stoichiometric polycrystalline HgSe films were obtained at a deposition potential around - 0.7 V vs SCE, at a temperature 60 deg. C and a pH value of 3.5. The as-grown films exhibited a direct optical band gap of 0.78 eV. This report deals with the growth mechanism and a study related to the influence of electrolyte bath composition, deposition potential, temperature and pH on the properties of HgSe thin films.

  8. Superconductivity and wire fabrication of FeSe family

    NASA Astrophysics Data System (ADS)

    Ozaki, Toshinori; Deguchi, Keita; Mizuguchi, Yoshikazu; Kumakura, Hiroaki; Takano, Yoshihiko; National InstituteMaterials Science Team

    2011-03-01

    The 11 family is an fascinating iron-based superconducting system for not only elucidation of superconducting mechanism but also technological applications because of the simplest crystal structures, the less toxic and high critical field. Recently, we found that the superconductivity appears in the specimen immersed in alcoholic beverages. Focused on the pressure dependence of Se height from Fe layer in FeSe, we found that the Tc is correlated to Se height. Moreover, the anion height dependence of Tc for all FeAs-based superconductor obeyed a universal curve with a peak around 1.38 AA}. We succeeded in observing the transport Jc in the single- and 7-core wires of FeTe x Se 1-x superconductor using an in-situ powder-in-tube (PIT) method. The Jc values in single- and 7-core wire are as high as 159 A/cm2 and 100 A/cm2 at 4.2 K, respectively. It is considered that the optimization of the composition, together with the improvement of the grain boundary in FeTe x Se 1-x superconducting wires, will lead to higher Jc .

  9. n-ZnSe/p-GaAs heterojunction solar cells

    SciTech Connect

    Blieske, U.; Kampschulte, T.; Bauknecht, A.; Saad, M.; Lux-Steiner, M.C.; Soellner, J.; Krost, A.; Schatke, K.

    1997-12-31

    For PV applications epitaxial layers of n-ZnSe were grown by metal-organic vapor phase epitaxy (MOVPE) at 340 C on GaAs(001) substrates. n-type net carrier concentration in the range between 10{sup 17}--10{sup 19} cm{sup {minus}3} was demonstrated. By increasing the doping concentration the double crystal x-ray diffraction full width at half maximum of 1.2 {micro}m thick ZnSe-layers increased. A first n-ZnSe/p-GaAs solar cell achieved an open circuit voltage of 706 mV, a fill factor of 65% and a short circuit current density of 10mACm{sup {minus}2} (total area, ELH-lamp, 100mW/cm{sup 2}, no AR-coating). J{sub sc} was increased by 4mA/cm{sup 2} by depositing sputtered n{sup +}-ZnO on the n-ZnSe layer. In order to further improve the PV performance n-ZnSe will be grown on GaAs buffer layers, the doping profile will be optimized systematically and MgF{sub 2} will be deposited on the ZnO layer.

  10. Preparation of CuInSe2 film with electrodeposition

    NASA Astrophysics Data System (ADS)

    Li, Wenyi; Yu, Jian; Yu, Xuebin; Chen, Qiulong; Cai, Xun

    2000-11-01

    CuInSe2(CIS) films directly electrodeposited on sputtered Mo-glass, sprayed SnO2-glass substrates had been accomplished at room temperature in the potentiostatic mode from a bath containing CuCl, InCl3(DOT)4H2O and SeO2. The acidity of bath was adjusted to 1PH. Energy dispersive spectrometry, atomic force microscopy (AFM), x- ray diffraction and hot-probe method was utilized to characterize the CIS films. The key factor for preparing single-phase CuInSe2 is the proportion of CuCl, InCl3(DOT)4H2O and SeO2. The CIS films are nearly stoichiometry of CuInSe2 and polycrystalline on Mo- glass. The Cu excess films are p-type semiconductor, and the In excess films n-type. The deposition potential obviously affects the surface morphology of CIS films. AFM results had indicated that the CIS films on Mo-glass grow in layer and on SnO2 glass in island.

  11. First-principles study of Se-intercalated graphite

    SciTech Connect

    BARTKOWIAK,M.; MODINE,NORMAND A.; SOFO,J.O.; MAHAN,G.D.

    2000-05-11

    Se-intercalated graphite compounds (Se-GICs) are considered as promising candidates for room-temperature thermoelectric cooling devices. Here the authors analyze the crystallographic structure and electronic properties of these materials within the framework of density-functional theory. First, the Adaptive-Coordinate Real-space Electronic Structure (ACRES) code is used to determine the stable structure of a representative stage-2 Se-GIC by relaxing atomic positions. The stable configuration is found to be a pendant-type structure, in which each selenium is bonded covalently to two atoms within the same carbon layer, causing a local distortion of the in-plane conjugation of the graphite. Then, they use the full potential linearized augmented plane wave (FP-LAPW) method to calculate the electronic band structure of the material and discuss its properties. Near the Fermi energy E{sub F}, there are wide bands originating from the host graphitic electronic structure and a few very narrow bands mainly of Se 4p character. The latter bands contribute to high peaks in the density of states close to E{sub F}. They show that this feature, although typical of many good thermoelectrics, does not necessarily imply high thermopower in the case of Se-GICs.

  12. EMPaSE: an Extensible Multi-Paradigm Simulation Environment

    2010-08-05

    EMPaSE is a hierarchical, extensible, modular modeling environment for developing and running hybrid simulations of sequential-modular, systems dynamics, discrete-event, and agent-based paradigms. It contains two principle components: a multi-paradigm simulation engine and a graphical user interface. EMPaSE models are defined through a hierarchically-defined set of computational modules that define the simulation logic. Inter-module communication occurs through two complimentary systems: pull-based "ports" for general computation patterns and push-based "plugs" for event processing. Entities (i.e. agents) withinmore » the simulation operate within an abstract multi-network environment. The EMPaSE simulation engine is designed around a flexible plug-in architecture, allowing simulations to import computational modules, engine customizations, and interfaces to external applications from independent plug-in libraries. The EMPaSE GUI environment provides an environment for graphically constructing, executing, and debugging EMPaSE models. As with the simulation engine, the GUI is constructed on top of an extensible architecture that supports rapid customization of the user experience through external plug-in libraries.« less

  13. Deposition of CdSe by EC-ALE

    NASA Astrophysics Data System (ADS)

    Mathe, Mkhulu K.; Cox, Stephen M.; Flowers, Billy H.; Vaidyanathan, R.; Pham, Long; Srisook, Nattapong; Happek, Uwe; Stickney, John L.

    2004-10-01

    The optimization of a program for CdSe thin film deposition using electrochemical atomic layer epitaxy (EC-ALE) is reported. EC-ALE uses surface limited reactions, underpotential deposition, to form compound thin film deposits one atomic layer at a time on Au substrates. Cyclic voltammograms showing deposition of Cd and Se on the Au substrate were first performed to identify cycle potentials. CdSe thin films were formed using an automated flow deposition system, by alternately depositing Se and Cd atomic layers, forming a compound monolayer each cycle. In total, 200 cycle deposits were formed using a series of different potentials, to better optimize the deposition conditions. Electron probe microanalysis of the deposits showed Cd/Se ratio between 1.01 and 1.13. X-ray diffraction indicated the deposits were zinc blende, with a (1 1 1) preferred orientation. The thickness of the deposits were determined using ellipsometry, and found to be around 70 nm. AFM studies of the morphology of substrates and deposits indicated that conformal films were formed. The band gaps of the deposits was determined using UV-VIS absorption measurements, photoconductivity and reflection adsorption FTIR, and all suggested a value of 1.74 eV, consistent with literature values.

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

    SciTech Connect

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

    2013-12-16

    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.

  15. Self-Assembled PbSe Nanowire:Perovskite Hybrids.

    PubMed

    Yang, Zhenyu; Yassitepe, Emre; Voznyy, Oleksandr; Janmohamed, Alyf; Lan, Xinzheng; Levina, Larissa; Comin, Riccardo; Sargent, Edward H

    2015-12-01

    Inorganic semiconductor nanowires are of interest in nano- and microscale photonic and electronic applications. Here we report the formation of PbSe nanowires based on directional quantum dot alignment and fusion regulated by hybrid organic-inorganic perovskite surface ligands. All material synthesis is carried out at mild temperatures. Passivation of PbSe quantum dots was achieved via a new perovskite ligand exchange. Subsequent in situ ammonium/amine substitution by butylamine enables quantum dots to be capped by butylammonium lead iodide, and this further drives the formation of a PbSe nanowire superlattice in a two-dimensional (2D) perovskite matrix. The average spacing between two adjacent nanowires agrees well with the thickness of single atomic layer of 2D perovskite, consistent with the formation of a new self-assembled semiconductor nanowire:perovskite heterocrystal hybrid.

  16. Surface Morphology of Undoped and Doped ZnSe Films

    NASA Technical Reports Server (NTRS)

    George, T.; Hayes, M.; Chen, H.; Chattopadhyay, K.; Thomas E.; Morgan, S.; Burger, A.

    1998-01-01

    Rare-earth doped ions in polar II-VI semiconductors have recently played an important role in the optical properties of materials and devices. In this study, undoped ZnSe and erbium doped ZnSe films were grown by radio frequency (RF) magnetron sputtering method. Atomic Force Microscopy (AFM) was used together with optical microscopy and UV-Vis spectroscopy to characterize the films. Doped samples were found to have higher surface roughness and quite different surface morphology compared to that of undoped samples. The grown films generally show a relatively smooth and uniform surface indicating that they are of overall good quality. The impact of plasma etching on ZnSe:Er film examined under AFM is also discussed.

  17. Effect of doping on electronic properties of HgSe

    NASA Astrophysics Data System (ADS)

    Nag, Abhinav; Sastri, O. S. K. S.; Kumar, Jagdish

    2016-05-01

    First principle study of electronic properties of pure and doped HgSe have been performed using all electron Full Potential Linearized Augmented Plane Wave (FP-LAPW) method using ELK code. The electronic exchange and co-relations are considered using Generalized Gradient Approach (GGA). Lattice parameter, Density of States (DOS) and Band structure calculations have been performed. The total energy curve (Energy vs Lattice parameter), DOS and band structure calculations are in good agreement with the experimental values and those obtained using other DFT codes. The doped material is studied within the Virtual Crystal Approximation (VCA) with doping levels of 10% to 25% of electrons (hole) per unit cell. Results predict zero band gap in undopedHgSe and bands meet at Fermi level near the symmetry point D. For doped HgSe, we found that by electron (hole) doping, the point where conduction and valence bands meet can be shifted below (above) the fermi level.

  18. Structural changes in thermoelectric SnSe at high pressures.

    PubMed

    Loa, I; Husband, R J; Downie, R A; Popuri, S R; Bos, J-W G

    2015-02-25

    The crystal structure of the thermoelectric material tin selenide has been investigated with angle-dispersive synchrotron x-ray powder diffraction under hydrostatic pressure up to 27 GPa. With increasing pressure, a continuous evolution of the crystal structure from the GeS type to the higher-symmetry TlI type was observed, with a critical pressure of 10.5(3) GPa. The orthorhombic high-pressure modification, β'-SnSe, is closely related to the pseudo-tetragonal high-temperature modification at ambient pressure. The similarity between the changes of the crystal structure at elevated temperatures and at high pressures suggests the possibility that strained thin films of SnSe may provide a route to overcoming the problem of the limited thermal stability of β-SnSe at high temperatures.

  19. Solvothermal synthesis of well-dispersed ZnSe microspheres.

    PubMed

    Ren, Xiaolei; Li, Qiuyu; Xue, Yannan; Zhai, Xuefeng; Yu, Min

    2013-01-01

    Well-defined crystalline ZnSe microspheres have been fabricated successfully via a simple solvothermal route under mild conditions in the presence of ethylenediamine tetraacetic acid disodium salt (Na(2)EDTA) and octadecylamine (ODA). X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrum (EDS), X-ray photoelectron spectra (XPS), Fourier transform-infrared spectroscopy (FT-IR), and photoluminescence spectra (PL) were used to characterize the phase structures, morphologies, and properties of the products. The result of XRD demonstrated that we obtained ZnSe products crystallized well with a stilleite structure. The influencing elements such as reaction time, sodium hydroxide (NaOH), addition of chelating reagent Na(2)EDTA, and the water/ethanol volume ratio were investigated, and the possible formation mechanism was also proposed. Furthermore, the experimental result indicated that ZnSe microspheres showed blue emission under ultraviolet excitation.

  20. Optical properties of ZnSe(Te) with ytterbium impurity.

    PubMed

    Makhniy, Viktor P; Horley, Paul P; Vorobiev, Yuri V; Kinzerska, Oksana V

    2016-04-20

    We report the results on infrared transmission measurements of non-doped and tellurium-doped crystals of zinc selenide grown from the melt. It was found that non-doped samples feature high transmission (50%-60%) for the wavelengths of 1-22 μm. The efficient scintillating crystals of ZnSe(Te) are almost opaque for λ>7  μm. Doping these samples with ytterbium from the gas phase does not achieve any significant transmission increase for non-doped ZnSe samples in the spectral range of 1-22 μm. However, it considerably increases (up to 50%) transmission for doped ZnSe(Te) at the wavelengths λ>10  μm. These optical peculiarities were analyzed taking into account restructurization of point defect ensembles created by Te and Yb impurities. PMID:27140112

  1. Electroded avalanche amorphous selenium (a-Se) photosensor

    PubMed Central

    Bubon, Oleksandr; DeCrescenzo, Giovanni; Zhao, Wei; Ohkawa, Yuji; Miyakawa, Kazunori; Matsubara, Tomoki; Kikuchi, Kenji; Tanioka, Kenkichi; Kubota, Misao; Rowlands, John A.; Reznik, Alla

    2012-01-01

    Although avalanche amorphous selenium (a-Se) is a very promising photoconductor for a variety of imaging applications, it is currently restricted to applications with electron beam readout in vacuum pick-up tube called a High-gain Avalanche Rushing Photoconductor (HARP). The electron beam readout is compatible with high definition television (HDTV) applications, but for use in solid-state medical imaging devices it should be replaced by an electronic readout with a two-dimensional array of metal pixel electrodes. However, due to the high electric field required for avalanche multiplication, it is a technological challenge to avoid possible dielectric breakdown at the edges, where electric field experiences local enhancement. It has been shown recently that this problem can be overcome by the use of a Resistive Interface Layer (RIL) deposited between a-Se and the metal electrode, however, at that time, at a sacrifice in transport properties. Here we show that optimization of RIL deposition technique allows for electroded avalanche a-Se with transport properties and time performance previously not achievable with any other a-Se structures. We have demonstrated this by detailed analysis of transport properties performed by Time-of-Flight (TOF) technique. Our results showed that a stable gain of 200 is reached at 104 V/μm for a 15-μm thick a-Se layer, which is the maximum theoretical gain for this thickness. We conclude that RIL is an enabling technology for practical implementation of solid-state avalanche a-Se image sensors. PMID:23115545

  2. Nanoscale order in ZnSe:(Mg, O)

    SciTech Connect

    Elyukhin, Vyacheslav A.

    2014-02-21

    Self-assembling of 1O4Mg identical tetrahedral clusters resulting in the nanoscale order in ZnSe:(Mg, O) is presented. Co-doping transforms ZnSe into Mg{sub x}Zn{sub 1−x}O{sub y}Se{sub 1−y} alloy of MgO, MgSe, ZnO and ZnSe. The decrease of a sum of the enthalpies of the constituent compounds and diminution of the strain energy are the causes of this phenomenon. The self-assembling conditions are obtained from the free energy minimum when magnesium and oxygen are in the dilute and ultra dilute limits, correspondingly. The occurrence of 1O4Mg clusters and completion of self-assembling when all oxygen atoms are in clusters are results of the continuous phase transitions. The self-assembling occurrence temperature does not depend on the oxygen content and it is a function of magnesium concentration. Mg{sub x}Zn{sub 1−x}O{sub y}Se{sub 1−y} with all oxygen atoms in clusters can be obtained in temperature ranges from T = 206 °C (x = 0.001, y = 1×10{sup −4}) to T = 456 °C (x = 0.01, y = 1×10{sup −4}) and from T = 237 °C (x = 0.001, y = 1×10{sup −6}) to T = 462 °C (x = 0.01, y = 1×10{sup −6})

  3. La biogenèse des mélanosomes

    PubMed Central

    Delevoye, Cédric; Giordano, Francesca; van Niel, Guillaume; Raposo, Graça

    2012-01-01

    Les mélanocytes situés à la base de l’épiderme produisent des mélanosomes qui sont transférés aux kératinocytes pour assurer la pigmentation de l’épiderme et sa photoprotection contre les rayons ultraviolets. Les mélanosomes, organites apparentés aux lysosomes, sont le lieu de synthèse et de stockage d’un pigment, la mélanine. Leur formation dépend de protéines mélanosomales qui transitent par les voies de biosynthèse et d’endocytose et exploitent les mécanismes moléculaires du trafic intracellulaire. Les acteurs moléculaires impliqués dans le transport des protéines mélanosomales et la biogenèse des mélanosomes sont la cible de mutations dans des maladies génétiques accompagnées d’hypopigmentation comme l’albinisme et les maladies lysosomales. Les études menées sur les mélanocytes issus de souris modèles de ces maladies permettent de comprendre certaines des étapes-clés de la mélanogenèse ainsi que les dysfonctionnements associés à ces pathologies. De plus, décrypter la mélanogenèse facilite également la compréhension d’autres processus physiologiques, comme l’illustrent les similitudes inattendues avec l’amyloïdogenèse dans les maladies neurodégénératives. PMID:21382323

  4. Surface half-metallicity of half-Heusler compound FeCrSe and interface half-metallicity of FeCrSe/GaP

    NASA Astrophysics Data System (ADS)

    Khalaf Al-zyadi, Jabbar M.; Jolan, Mudhahir H.; Yao, Kai-Lun

    2016-04-01

    Recent studies showed that half-Heusler FeCrSe exhibits half-metallic ferromagnetism (Huang et al. [20]). In this paper, we investigate extensively the electronic, magnetic, and half-metallic properties of the half-Heusler alloy FeCrSe (111) and (001) surfaces and the interface with GaP (111) substrate by using the first-principles calculations within the density functional theory. The atomic density of states demonstrates that the half-me tallicity verified in the bulk FeCrSe is maintained at the CrSe-terminated (001) and Se-terminated (111) surfaces, but lost at both Cr- and Fe-terminated (111) surfaces and the Fe-terminated (001) surface. Alternatively, for the interface of FeCrSe/GaP (111), the bulk half-metallicity is destroyed at Se-P configuration while Se-Ga interface and subinterface show nearly 100% spin polarization. Moreover, the calculated interfacial adhesion energies exhibit that Se-Ga shape is more stable than the Se-P one. The calculated magnetic moments of Se, Ga at the Se-Ga (111) interface and P at the Se-P (111) interface increase with respect to the corresponding bulk values while the atomic magnetic moment of Se atom at the Se-P (111) interface decreases. We also notice that the magnetic moments of subinterface Fe at both Se-Ga and Se-P (111) interfaces decrease compared to the bulk values.

  5. Thermoelectric properties of PbTe/PbSe mesomaterials

    NASA Astrophysics Data System (ADS)

    Chen, Feng; Wang, Yaqi; Xue, Yuyi; Chu, C. W.; Zhang, Jun; Fang, Jiye; Tan, Chunhu; Lin, Zhigang; Liu, Bob

    2008-03-01

    Ball milled PbTe mixed with PbSe nano-wires (PTSW) or with PbSe nano-crystals (PTSC) are sintered under high pressure. Different sintering conditions are tested to preserve the mesostructures. Thermoelectric properties (resistivity, Seebeck coefficient and thermal conductivity) are measured at various temperatures. Pure ball milled PbTe are also sintered and measured for comparison. In this talk, we will present these data and compare with various PbTe data from the literature. Our results show that this mesostructure approach is promising and the sintering condition is the key factor for further improvement.

  6. GaSe damage threshold under IR pulse pumping

    NASA Astrophysics Data System (ADS)

    Guo, Jin; Xie, Ji-Jiang; Zhang, Laiming; Chen, Fei; Jiang, Ke; Alexeev, Sergei V.; Andreev, Yury M.; Kokh, Konstantin A.; Lanskii, Gregory V.; Losev, Valery F.; Lubenko, Dmitry M.; Shaiduko, Anna V.; Svetlichnyi, Valeriy A.

    2012-01-01

    Damage threshold of non-linear GaSe crystals under IR fs (Ti:Sapphiere 800 nm laser and 1.1-2.9μm OPG) and ns (2. 79 Er3+:YSGG and 10.6μm CO2 laser) pulse pumping is studded in details. Local micro defects and field induced effects (GaSe dissociation, multiphoton absorptions and transient transparency origin effects) are identified as responsible for damage threshold in this case. Local (including nano scaled) defects and thermal effects are identified as reason of damage threshold under ns pulse pumping.

  7. Piezo-phototronic effect of CdSe nanowires.

    PubMed

    Dong, Lin; Niu, Simiao; Pan, Caofeng; Yu, Ruomeng; Zhang, Yan; Wang, Zhong Lin

    2012-10-23

    The piezo-phototronic effect on transport properties of flexible CdSe NW devices is investigated. An optimum sensitivity of the flexible CdSe NW devices can be achieved by adjusting the applied strain and illumination intensity. The piezo-phototronic effect under compressive strain increases the internal electric field of the Schottky barrier, and assists the separation of the photo-excited electron-hole pairs, resulting in the increase of photocurrent. A trap-mediated mechanism is responsible for the decreased hole separation when the strain is larger than the critical strain.

  8. Electronic structure and thermoelectric properties of (PbSe)m/(SnSe)n superlattice: A first principles study

    NASA Astrophysics Data System (ADS)

    Do, Duc Cuong; Rhim, S. H.; Hong, Soon Cheol

    2015-03-01

    Figure of merit (ZT) of thermoelectric materials can be enhanced by lowering thermal conductivity or/and increasing electrical conductivity. The extremely high ZT of layered structure SnSe opened up a new direction in study of thermoelectricity due to its low thermal conductivity, which, however, is limited to high temperature. Here, we performed first principles density functional calculations to explore room-temperature thermoelectricity. We consider (PbSe)m/(SnSe)n superlattices with different period, whose quantum well structure is expected to increase electrical conductivity by modulation of charge doping at interface. Calculations of Seebeck coefficients for the superlattices are presented. Supported by the Ministry of Trade, Industry & Energy, Korea (20132020000110) and Priority Research Centers Program (2009-0093818) through National Research Foundation of Korea.

  9. Crossover from 3D to 2D quantum transport in Bi2Se3/In2Se3 superlattices.

    PubMed

    Zhao, Yanfei; Liu, Haiwen; Guo, Xin; Jiang, Ying; Sun, Yi; Wang, Huichao; Wang, Yong; Li, Han-Dong; Xie, Mao-Hai; Xie, Xin-Cheng; Wang, Jian

    2014-09-10

    The topological insulator/normal insulator (TI/NI) superlattices (SLs) with multiple Dirac channels are predicted to offer great opportunity to design novel materials and investigate new quantum phenomena. Here, we report first transport studies on the SLs composed of TI Bi2Se3 layers sandwiched by NI In2Se3 layers artificially grown by molecular beam epitaxy (MBE). The transport properties of two kinds of SL samples show convincing evidence that the transport dimensionality changes from three-dimensional (3D) to two-dimensional (2D) when decreasing the thickness of building block Bi2Se3 layers, corresponding to the crossover from coherent TI transport to separated TI channels. Our findings provide the possibility to realizing "3D surface states" in TI/NI SLs.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  11. Mechanical Properties of ZnSe for the FEANICS Module

    NASA Technical Reports Server (NTRS)

    Salem, Jon

    2006-01-01

    Mechanical and physical properties of ZnSe windows to be used with the FEANICS (Flow Enclosure Accommodating Novel Investigations in Combustion of Solids) experiments were measured in order to determine design allowables. In addition, the literature on crack growth properties was summarized. The average Young's modulus, Poisson's ratio, equibiaxial fracture strength, flaw size, grain size, Knoop hardness, Vicker's hardness, and branching constant were 74.3 +/- 0.1 GPa, 0.31, 57.8 +/- 6.5 MPa, 21 4 mm, 43 +/- 9 micron, 0.97 +/- 0.02 GPa, 0.97 +/- 0.02 GPa, and 1.0 +/- 0.1 MPam(exp 0.5), respectively. The properties of current ZnSe made by chemical vapor deposition are in good agreement with those measured in the 1970's. The hardness of CVD ZnSe windows is about one twentieth of the sapphire window being replaced, and about one-sixth of that of window glass. Thus the ZnSe window must be handled with great care. The large grain size relative to the inherent crack size implies the need to use single crystal crack growth properties in the design process. In order to determine the local failure stresses in one of the test specimens, a solution for the stresses between the support ring and the edge of a circular plate load between concentric rings was derived.

  12. General view, looking SE during repainting, restoration, and rebuilding of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    General view, looking SE during repainting, restoration, and rebuilding of roadway and bridge truss system. Scaffolding designed to minimize environmental damage from paint chips, paint vapors, and dirt. - Schenley Park Bridge over Panther Hollow, Spanning Panther Hollow at Panther Hollow Road, Pittsburgh, Allegheny County, PA

  13. Optical Properties of PbTe and PbSe

    SciTech Connect

    Ekuma, Chinedu E; Singh, David J; Moreno, Juana; Jarrell, Mark

    2012-01-01

    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.

  14. Orbitally-driven giant phonon anharmonicity in SnSe

    SciTech Connect

    Li, Chen W.; Hong, Jiawang; May, Andrew F.; Bansal, Dipanshu; Chi, Songxue; Hong, Tao; Ehlers, Georg; Delaire, Olivier A.

    2015-10-19

    We understand that elementary excitations and their couplings in condensed matter systems is critical to develop better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The material with the current record for thermoelectric conversion efficiency, SnSe, achieves an ultra-low thermal conductivity, but the mechanism enabling this strong phonon scattering remains largely unknown. Using inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and revealed the origin of ionic-potential anharmonicity responsible for the unique properties of SnSe. We show that the giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. Our results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers precious insights on how electron-phonon and phononphonon interactions may lead to the realization of ultra-low thermal conductivity.

  15. Orbitally-driven giant phonon anharmonicity in SnSe

    DOE PAGES

    Li, Chen W.; Hong, Jiawang; May, Andrew F.; Bansal, Dipanshu; Chi, Songxue; Hong, Tao; Ehlers, Georg; Delaire, Olivier A.

    2015-10-19

    We understand that elementary excitations and their couplings in condensed matter systems is critical to develop better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The material with the current record for thermoelectric conversion efficiency, SnSe, achieves an ultra-low thermal conductivity, but the mechanism enabling this strong phonon scattering remains largely unknown. Using inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and revealed the origin of ionic-potential anharmonicity responsible for the unique properties of SnSe. Wemore » show that the giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. Our results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers precious insights on how electron-phonon and phononphonon interactions may lead to the realization of ultra-low thermal conductivity.« less

  16. Mass Flux of ZnSe by Physical Vapor Transport

    NASA Technical Reports Server (NTRS)

    Sha, Yi-Gao; Su, Ching-Hua; Palosz, W.; Volz, M. P.; Gillies, D. C.; Szofran, F. R.; Lehoczky, S. L.; Liu, Hao-Chieh; Brebrick, R. F.

    1995-01-01

    Mass fluxes of ZnSe by physical vapor transport (PVT) were measured in the temperature range of 1050 to 1160 C using an in-situ dynamic technique. The starting materials were either baked out or distilled under vacuum to obtain near-congruently subliming compositions. Using an optical absorption technique Zn and Se, were found to be the dominant vapor species. Partial pressures of Zn and Se, over the starting materials at temperatures between 960 and 1140 C were obtained by measuring the optical densities of the vapor phase at the wavelengths of 2138, 3405, 3508, 3613, and 3792 A. The amount and composition of the residual gas inside the experimental ampoules were measured after the run using a total pressure gauge. For the first time, the experimentally determined partial pressures of Zn and Se, and the amount and composition of the residual gas were used in a one-dimensional diffusion limited analysis of the mass transport rates for a PVT system. Reasonable agreement between the experimental and theoretical results was observed.

  17. Novel thin-film CuInSe2 fabrication

    NASA Astrophysics Data System (ADS)

    Mooney, G. D.; Hermann, A. M.

    1989-06-01

    This work studies the feasibility of fabricating CuInSe sub 2 (CIS) solar cells by laser annealing sandwiched layers of elemental Cu, In, and Se. The chalcopyrite phase of CIS is now obtained by thermal annealing elemental Cu and In layers in H sub 2 Se. This process is hazardous because the H sub 2 Se gas is highly toxic. The ability to form the desired chalcopyrite structure by laser annealing would be safer and more conductive to large-scale production. Initial studies of the feasibility of laser annealing the elemental layered structures were performed using a CW argon laser on films fabricated by means of electrodeposition. Characterization of the post-annealed films by X-ray diffraction analysis has shown encouraging results. The laser annealed films have all contained the chalcopyrite phase of CIS. The percentage of the chalcopyrite phase has been small however. Undesirable binary oxides have also formed. To produce higher quality films, future work will concentrate on increasing the percentage of the desirable phase and eliminating all binary compounds.

  18. Novel thin-film CuInSe2 fabrication

    NASA Astrophysics Data System (ADS)

    Gabor, A.; Hermann, A.

    1992-09-01

    This report describes the formation of thin films of CuInSe2 (CIS) by annealing precursor films containing Cu, In, and Se in a rapid thermal processor. This involves two steps: (1) a precursor containing Cu, In, and Se is deposited on unheated substrates such that CIS does not form during this deposition step; and (2) the precursor is annealed in a rapid thermal processor to crystallize the CIS. Advantages of this process are as follows: (1) no H2Se is used; (2) concentration gradients can potentially be built into the film due to the rapid annealing; and (3) the precursor can potentially be deposited using scalable methods such as sputtering, solution growth, and electrodeposition. The deposition method used was three-source, elemental physical vapor deposition. At room temperature, such a method was considered to be a flexible way to deposit a precursor that would be fairly typical of precursors deposited by more scalable techniques. Precursors were made both by the stacked elemental layer approach, where one element at a time was evaporated, as well as by a co-evaporation method. Adhesion problems limited device performance, and the co-evaporated precursors displayed unintended segregation of Cu and I in a direction normal to the film plane. The best cell efficiency was 3.5 percent.

  19. GAP Noise Computation By The CE/SE Method

    NASA Technical Reports Server (NTRS)

    Loh, Ching Y.; Chang, Sin-Chung; Wang, Xiao Y.; Jorgenson, Philip C. E.

    2001-01-01

    A typical gap noise problem is considered in this paper using the new space-time conservation element and solution element (CE/SE) method. Implementation of the computation is straightforward. No turbulence model, LES (large eddy simulation) or a preset boundary layer profile is used, yet the computed frequency agrees well with the experimental one.

  20. Bayer Electrofilter Fines as Potential Se(VI) Adsorbents

    NASA Astrophysics Data System (ADS)

    Ayala, Julia; Fernández, Begoña

    2015-11-01

    Removal of Se(VI) from an aqueous solution under different conditions was investigated using Bayer electrofilter fines (BEFs), a waste from alumina production, as an adsorbent. Adsorption selenate was studied using batch adsorption experiments as a function of pH (2-12), contact time (0.08-30 h), adsorbent concentration (4-80 g/L), initial selenium concentration (5-203 mg/L), and ionic strength (0-0.1 M NaCl). The results showed that adsorption was significantly affected by pH Se(VI) having the highest affinity for BEFs at pH 3. Sorption Se(VI) reached equilibrium in 4 h. Increasing ionic strength decreased selenate sorption. The adsorption of Se(VI) onto BEFs was found to fit the Langmuir isotherm. Maximum selenium uptake values were calculated as 2.3613 mg/g and 1.5608 mg/g when using adsorbent concentrations of 20 g/L and 40 g/L, respectively.

  1. Photoacoustic characterization of n-RuSe2 semiconductor pellets

    NASA Astrophysics Data System (ADS)

    Bernal-Alvarado, J.; Vargas-Luna, M.; Solorza-Feria, O.; Mondragón, R.; Alonso-Vante, N.

    2000-09-01

    Using the open photoacoustic cell technique, a set of physical properties for a semiconductor (n-RuSe2) in powder form was measured. According to the Dramicanin theoretical model, charge carriers transport parameters (bulk and surface) and the effective thermal diffusivity were obtained.

  2. 21 CFR 118.4 - Salmonella Enteritidis (SE) prevention measures.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 2 2012-04-01 2012-04-01 false Salmonella Enteritidis (SE) prevention measures... National Poultry Improvement Plan's standards for “U.S. S. Enteritidis Clean” status (9 CFR 145.23(d)) or... environmental test required in paragraph (a)(2)(i) of this section is positive, you must begin egg testing,...

  3. Diverse lattice dynamics in ternary Cu-Sb-Se compounds

    PubMed Central

    Qiu, Wujie; Wu, Lihua; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2015-01-01

    Searching and designing materials with extremely low lattice thermal conductivity (LTC) has attracted considerable attention in material sciences. Here we systematically demonstrate the diverse lattice dynamics of the ternary Cu-Sb-Se compounds due to the different chemical-bond environments. For Cu3SbSe4 and CuSbSe2, the chemical bond strength is nearly equally distributed in crystalline bulk, and all the atoms are constrained to be around their equilibrium positions. Their thermal transport behaviors are well interpreted by the perturbative phonon-phonon interactions. While for Cu3SbSe3 with obvious chemical-bond hierarchy, one type of atoms is weakly bonded with surrounding atoms, which leads the structure to the part-crystalline state. The part-crystalline state makes a great contribution to the reduction of thermal conductivity that can only be effectively described by including a rattling-like scattering process in addition to the perturbative method. Current results may inspire new approaches to designing materials with low lattice thermal conductivities for high-performance thermoelectric conversion and thermal barrier coatings. PMID:26328765

  4. 10. Interior view looking SE showing reinforced concrete structural system ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    10. Interior view looking SE showing reinforced concrete structural system at ground floor of Paint Shop. - Central of Georgia Railway, Savannah Repair Shops & Terminal Facilities, Paint & Coach Barn, Bounded by West Broad, Jones, West Boundary & Hull Streets, Savannah, Chatham County, GA

  5. General view looking SE at corridor and Pennsylvania Station. Baltimore, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    General view looking SE at corridor and Pennsylvania Station. Baltimore, Baltimore City, MD. Sec. 1201, MP 93.23. - Northeast Railroad Corridor, Amtrak route between District of Columbia/Maryland state line & Maryland/Delaware state line, Baltimore, Independent City, MD

  6. 21 CFR 118.4 - Salmonella Enteritidis (SE) prevention measures.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... environmental test required in paragraph (a)(2)(i) of this section is positive, you must begin egg testing, as... National Poultry Improvement Plan's standards for “U.S. S. Enteritidis Clean” status (9 CFR 145.23(d)) or equivalent standard; (2) Environmental testing. (i) The pullet environment is tested for SE when pullets...

  7. 21 CFR 118.4 - Salmonella Enteritidis (SE) prevention measures.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... environmental test required in paragraph (a)(2)(i) of this section is positive, you must begin egg testing, as... National Poultry Improvement Plan's standards for “U.S. S. Enteritidis Clean” status (9 CFR 145.23(d)) or equivalent standard; (2) Environmental testing. (i) The pullet environment is tested for SE when pullets...

  8. 5. Perspective view of SE corner of Building 59. In ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Perspective view of SE corner of Building 59. In distance, note change in the roff line where the 1896 south section of building ends and the 1904 middle section begins. - Puget Sound Naval Shipyard, Pattern Shop, Farragut Avenue, Bremerton, Kitsap County, WA

  9. 491-nm ZnCeSe/ZnSe/ZnMgSSe SCH Laser Diode with a Low Operating Voltage

    NASA Astrophysics Data System (ADS)

    Itoh, Satoshi; Nakayama, Norikazu; Ohata, Toyoharu; Ozawa, Masafumi; Okuyama, Hiroyuki; Nakano, Kazushi; Ishibashi, Akira; Ikeda, Masao; Mori, Yoshifumi

    1993-10-01

    Room temperature pulsed operation of ZnCdSe/ZnSe/ZnMgSSe separate-confinement heterostructure lasers has been achieved at a wavelength of 491 nm, which is the shortest wavelength at room temperature ever reported. The laser structure was made by molecular beam epitaxy on n-GaAs substrate. The operating current density was 3.8 kA/cm2 for a diode with a 720 μm long and 10 μm wide stripe. An operating voltage of 9 V has been obtained at the threshold current using improved contact layers and ohmic metals.

  10. Quantum chemistry of the minimal CdSe clusters.

    PubMed

    Yang, Ping; Tretiak, Sergei; Masunov, Artëm E; Ivanov, Sergei

    2008-08-21

    Colloidal quantum dots are semiconductor nanocrystals (NCs) which have stimulated a great deal of research and have attracted technical interest in recent years due to their chemical stability and the tunability of photophysical properties. While internal structure of large quantum dots is similar to bulk, their surface structure and passivating role of capping ligands (surfactants) are not fully understood to date. We apply ab initio wavefunction methods, density functional theory, and semiempirical approaches to study the passivation effects of substituted phosphine and amine ligands on the minimal cluster Cd(2)Se(2), which is also used to benchmark different computational methods versus high level ab initio techniques. Full geometry optimization of Cd(2)Se(2) at different theory levels and ligand coverage is used to understand the affinities of various ligands and the impact of ligands on cluster structure. Most possible bonding patterns between ligands and surface CdSe atoms are considered, including a ligand coordinated to Se atoms. The degree of passivation of Cd and Se atoms (one or two ligands attached to one atom) is also studied. The results suggest that B3LYP/LANL2DZ level of theory is appropriate for the system modeling, whereas frequently used semiempirical methods (such as AM1 and PM3) produce unphysical results. The use of hydrogen atom for modeling of the cluster passivating ligands is found to yield unphysical results as well. Hence, the surface termination of II-VI semiconductor NCs with hydrogen atoms often used in computational models should probably be avoided. Basis set superposition error, zero-point energy, and thermal corrections, as well as solvent effects simulated with polarized continuum model are found to produce minor variations on the ligand binding energies. The effects of Cd-Se complex structure on both the electronic band gap (highest occupied molecular orbital-lowest unoccupied molecular orbital energy difference) and ligand

  11. Fate of Selenium in Soils at a Seleniferous Site Recorded by High Precision Se Isotope Measurements.

    PubMed

    Schilling, Kathrin; Johnson, Thomas M; Dhillon, Karaj S; Mason, Paul R D

    2015-08-18

    Selenium poisoning is a significant health problem in parts of Punjab, India, which is an area of intense agricultural productivity. To determine the complex soil dynamics that control distribution of Se in this area, we measured concentrations and δ(82/76)Se of bulk Se and individual Se pools in four soil profiles. This was compared against δ(82/76)Se of crops and groundwater used for irrigation. The isotopic composition of bulk Se and component Se pools reveal spatial heterogeneity. The bulk δ(82/76)Se show progressively lower values with increasing soil depth indicating the preferential migration of isotopically lighter Se downward through the soil profile. The δ(82/76)Se of water-soluble Se is isotopically heavier than δ(82/76)Se of adsorbed Se, suggesting Se isotope fractionation by reduction prior to scavenging by reactive minerals in the soil. The organically bound Se is isotopically lighter than water-soluble Se and correlates with the C/N ratio at different soil depths. Thus, Se immobilization by redox cycling controls the biogeochemical Se cycle in the soil. Se isotope ratios help to trace biochemical processes of Se in agricultural seleniferous soils and provide an important assessment for better soil management mitigating Se concentrations of ecotoxicological levels.

  12. Sensor Exposure, Exploitation, and Experimentation Environment (SE4)

    NASA Astrophysics Data System (ADS)

    Buell, D.; Duff, F.; Goding, J.; Bankston, M.; McLaughlin, T.; Six, S.; Taylor, S.; Wootton, S.

    2011-09-01

    As the resident space object population increases from new launches and events such as the COSMOS/IRIDIUM collision, the maintenance of high-level Space Situational Awareness (SSA) has become increasingly difficult. To maintain situational awareness of the changing environment, new systems and methods must be developed. The Sensor Exposure, Exploitation and Experimentation Environment (SE4) provides a platform to illustrate “The Art of the Possible” that shows the potential benefit of enriched sensor data collections and real-time data sharing. Through modeling and simulation, and a net-centric architecture, SE4 shows the added value of sharing data in real-time and exposing new types of sensor data. The objective of SE4 is to develop an experimentation and innovation environment for sensor data exposure, composable sensor capabilities, reuse, and exploitation that accelerates the delivery of needed Command and Control, Intelligence, Surveillance, and Reconnaissance capabilities to the warfighter. Through modeling, simulation and rapid prototyping, the art of the possible for a fully-connected, net-centric space Command and Control (C2) and sensor enterprise can be demonstrated. This paper provides results that demonstrate the potential for faster cataloging of breakup events and additional event monitoring that are possible with data available today in the Space Surveillance Network (SSN). Demonstrating the art of the possible for the enterprise will guide net-centric requirements definition and facilitate discussions with stakeholder organizations on the Concept of Operations (CONOPS), policy, and Tactics, Techniques, and Procedures (TTP) evolution necessary to take full advantage of net-centric operations. SE4 aligns with direction from Secretary Gates and the Chairman Joint Chief of Staff that emphasizes the need to get the most out of our existing systems. Continuing to utilize SE4 will enable the enterprise by demonstrating the benefits of applying

  13. On nematicity, magnetism and superconductivity in FeSe

    NASA Astrophysics Data System (ADS)

    Böhmer, Anna

    FeSe is unique among iron-based superconductors, notably regarding the interrelationships of structure, magnetism, and superconductivity. At ambient pressure, FeSe exhibits a tetragonal-to-orthorhombic (nematic) phase transition at Ts = 90 K, similar to other iron-based materials, but unlike them, no long-range magnetic order. One consequence is the unique possibility to study the in-plane resistivity anisotropy, arguably the most investigated 'nematic property', without interfering effects from the Fermi surface reconstruction induced by antiferromagnetic order. Recent findings pose the question whether nematicity in FeSe is driven by magnetic fluctuations, as often assumed in other iron-based systems. In particular, magnetic fluctuations, which are prominent at low temperatures, are not observed above Ts in FeSe by NMR, even though indicated by inelastic neutron scattering. The pressure-temperature phase diagram, recently obtained in new comprehensiveness using vapor-grown single crystals, shows that the structural transition is suppressed at 2 GPa and a new, likely magnetic phase is stabilized above 0.8 GPa, where Tc has a local maximum. Various theoretical scenarios have been proposed to explain this nematic transition far away from the magnetic order. Surprisingly, the degree of the orthorhombic distortion does not decrease below the superconducting transition at Tc = 8 K, suggesting that nematic and superconducting ``channels'' do not compete. Our new results on the superconducting state under pressure, show a non-monotonic pressure dependence of the upper critical field, which is well explained by the Fermi surface evolution. Further, we have successfully detwinned FeSe crystals and measured the in-plane resistivity anisotropy and elastoresistivity coefficients and compared them with model calculations of inelastic scattering from spin fluctuations. This work was supported by the Ames Laboratory, US DOE, under Contract No. DE-AC02-07CH11358.

  14. Optical Characterization of Bulk ZnSeTe Solid Solutions

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

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

    PubMed

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

    2013-07-01

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

  16. Giant piezoelectricity of monolayer group IV monochalcogenides: SnSe, SnS, GeSe, and GeS

    SciTech Connect

    Fei, Ruixiang; Yang, Li; Li, Wenbin; Li, Ju

    2015-10-26

    We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS{sub 2} and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique “puckered” C{sub 2v} symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.

  17. Elastic and thermal properties of the layered thermoelectrics BiOCuSe and LaOCuSe

    NASA Astrophysics Data System (ADS)

    Saha, S. K.; Dutta, G.

    2016-09-01

    We determine the elastic properties of the layered thermoelectrics BiOCuSe and LaOCuSe using first-principles density functional theory calculations. To predict their stability, we calculate six distinct elastic constants, where all of them are positive, and suggest mechanically stable tetragonal crystals. As elastic properties relate to the nature and the strength of the chemical bond, the latter is analyzed by means of real-space descriptors, such as the electron localization function (ELF) and Bader charge. From elastic constants, a set of related properties, namely, bulk modulus, shear modulus, Young's modulus, sound velocity, Debye temperature, Grüneisen parameter, and thermal conductivity, are evaluated. Both materials are found to be ductile in nature and not brittle. We find BiOCuSe to have a smaller sound velocity and, hence, within the accuracy of the used Slack's model, a smaller thermal conductivity than LaOCuSe. Our calculations also reveal that the elastic properties and the related lattice thermal transport of both materials exhibit a much larger anisotropy than their electronic band properties that are known to be moderately anisotropic because of a moderate effective-electron-mass anisotropy. Finally, we determine the lattice dynamical properties, such as phonon dispersion, atomic displacement, and mode Grüneisen parameters, in order to correlate the elastic response, chemical bonding, and lattice dynamics.

  18. Temperature dependence of Raman shifts in layered ReSe{sub 2} and SnSe{sub 2} semiconductor nanosheets

    SciTech Connect

    Taube, A.; Łapińska, A.; Judek, J.; Zdrojek, M.

    2015-07-06

    Transition metal dichalcogenides (TMDCs) are attractive for variety of nanoscale electronics and optoelectronics devices due to their unique properties. Despite growing progress in the research field of TMDCs, many of their properties are still unknown. In this letter, we report measurements of Raman spectra of rhenium diselenide (ReSe{sub 2}) and tin diselenide (SnSe{sub 2}) layered semiconductor nanosheets as a function of temperature (70–400 K). We analyze the temperature dependence of the positions of eight ReSe{sub 2} modes and SnSe{sub 2} A{sub 1g} mode. All observed Raman mode shifts exhibit nonlinear temperature dependence at low temperatures which is explained by optical phonon decay process into two or three acoustics phonons. The first order temperature coefficients (χ), determined for high temperatures, of rhenium diselenide Raman modes are in the range between −0.0033 and −0.0118 cm{sup −1}/K, whereas χ of tin diselenide A{sub 1g} mode was −0.0129 cm{sup −1}/K. Our findings are useful for further analysis of phonon and thermal properties of these dichalcogenide layered semiconductors.

  19. Identification and characterization of the heme-binding proteins SeShp and SeHtsA of Streptococcus equi subspecies equi

    PubMed Central

    Nygaard, Tyler K; Liu, Mengyao; McClure, Michael J; Lei, Benfang

    2006-01-01

    Background Heme is a preferred iron source of bacterial pathogens. Streptococcus equi subspecies equi is a bacterial pathogen that causes strangles in horses. Whether S. equi has a heme acquisition transporter is unknown. Results An S. equi genome database was blasted with the heme binding proteins Shp and HtsA of Streptococcus pyogenes, and found that S. equi has the homologue of Shp (designated SeShp) and HtsA (designated SeHtsA). Tag-free recombinant SeShp and SeHtsA and 6xHis-tagged SeHtsA (SeHtsAHis) were prepared and characterized. Purified holoSeShp and holoSeHtsA bind Fe(II)-protoporphyrin IX (heme) and Fe(III)-protoporphyrin IX (hemin) in a 1:1 stoichiometry, respectively, and are designated hemoSeShp and hemiSeHtsA. HemiSeShp and hemiSeHtsAHis can be reconstituted from apoSeShp and apoSeHtsAHis and hemin. HemoSeShp is stable in air and can be oxidized to hemiSeShp by ferricyanide. HemiSeHtsA can be reduced into hemoSeHtsA, which autoxidizes readily. HemoSeShp rapidly transfers its heme to apoSeHtsAHis. In addition, hemoSeShp can also transfer its heme to apoHtsA, and hemoShp is able to donate heme to apoSeHtsAHis. Conclusion The primary structures, optical properties, oxidative stability, and in vitro heme transfer reaction of SeShp and SeHtsA are very similar to those of S. pyogenes Shp and HtsA. The data suggest that the putative cell surface protein SeShp and lipoprotein SeHtsA are part of the machinery to acquire heme in S. equi. The results also imply that the structure, function, and functional mechanism of the heme acquisition machinery are conserved in S. equi and S. pyogenes. PMID:17007644

  20. Study of single crystal CuInSe2 thin films and CuGaSe2/CuInSe2 single quantum well grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Thiru, Sathiabama; Asakawa, Masaki; Honda, Kazuki; Kawaharazuka, Atsushi; Tackeuchi, Atsushi; Makimoto, Toshiki; Horikoshi, Yoshiji

    2015-09-01

    High quality CuGaSe2 and CuInSe2 single crystalline layers are grown on GaAs (001) by employing the deposition sequence of migration enhanced epitaxy using a solid source molecular beam epitaxy system. When CuGaSe2 is grown on CuInSe2 at moderate temperatures, severe interdiffusion takes place at the heterojunction of CuGaSe2/CuInSe2. This problem has been solved by optimizing the growth temperature and deposition rates of the constituent elements. Thus, we have successfully grown CuGaSe2/CuInSe2 single quantum well with sharp interfaces on GaAs (001) for the first time. Intense photoluminescence from the single quantum well with 10 nm well width is demonstrated.

  1. Direct observation of a gap opening in topological interface states of MnSe/Bi{sub 2}Se{sub 3} heterostructure

    SciTech Connect

    Matetskiy, A. V. Kibirev, I. A.; Saranin, A. A.; Hirahara, T.; Hasegawa, S.; Zotov, A. V.

    2015-08-31

    High-quality MnSe(111) film was bilayer-by-bilayer grown epitaxially onto the Bi{sub 2}Se{sub 3}(111) surface using molecular beam epitaxy. Reversal scenario with quintuple layer-by-layer growth of Bi{sub 2}Se{sub 3} onto the MnSe film was also realized. Angle-resolved photoemission spectroscopy measurements of Bi{sub 2}Se{sub 3} capped with two bi-layers of MnSe revealed that an energy gap of about 90 meV appears at the Dirac point of the original Bi{sub 2}Se{sub 3} surface, possibly due to breaking the time-reversal symmetry on the Bi{sub 2}Se{sub 3} surface by magnetic proximity effect from MnSe.

  2. Doping mechanism in pure CuInSe2

    NASA Astrophysics Data System (ADS)

    Werner, F.; Colombara, D.; Melchiorre, M.; Valle, N.; El Adib, B.; Spindler, C.; Siebentritt, S.

    2016-05-01

    We investigate the dopant concentration and majority carrier mobility in epitaxial CuInSe2 thin films for different copper-to-indium ratios and selenium excess during growth. We find that all copper-poor samples are n-type, and that hopping conduction in a shallow donor state plays a significant role for carrier transport. Annealing in sodium ambient enhances gallium in-diffusion from the substrate wafer and changes the net doping of the previously n-type samples to p-type. We suggest that sodium incorporation from the glass might be responsible for the observed p-type doping in polycrystalline Cu-poor CuInSe2 solar cell absorbers.

  3. Low-energy Coulomb excitation of radioactive ^70Se

    NASA Astrophysics Data System (ADS)

    Hurst, Aaron

    2007-10-01

    An isobarically pure beam of ^70Se ions was post accelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording de-excitation γ rays in the highly segmented MINIBALL γ-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the 2^+1 state in ^70Se is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for this state, using an earlier published lifetime measurement, reopening the question over whether there are deformed oblate shapes close to the ground state in the neutron-deficient selenium isotopes.

  4. Synthesis and photoresponse of large GaSe atomic layers.

    PubMed

    Lei, Sidong; Ge, Liehui; Liu, Zheng; Najmaei, Sina; Shi, Gang; You, Ge; Lou, Jun; Vajtai, Robert; Ajayan, Pulickel M

    2013-06-12

    We report the direct growth of large, atomically thin GaSe single crystals on insulating substrates by vapor phase mass transport. A correlation is identified between the number of layers and a Raman shift and intensity change. We found obvious contrast of the resistance of the material in the dark and when illuminated with visible light. In the photoconductivity measurement we observed a low dark current. The on-off ratio measured with a 405 nm at 0.5 mW/mm(2) light source is in the order of 10(3); the photoresponsivity is 17 mA/W, and the quantum efficiency is 5.2%, suggesting possibility for photodetector and sensor applications. The photocurrent spectrum of few-layer GaSe shows an intense blue shift of the excitation edge and expanded band gap compared with bulk material.

  5. CO2 laser beam propagation with ZnSe optics

    NASA Astrophysics Data System (ADS)

    Leong, K. H.; Liu, Yi; Holdridge, D. J.

    Beam propagation characteristics of ZnSe optics used in kiloWatt power CO2 laser aided material processing applications are determined using the Prometec Laser Beam Analyzer. The laser used was a Rofin Sinar RS6000 CO2 laser with mode aperturing. Beam power varied from 500W to 6300W and beam modes used were TEM(sub 00), TEM(sub 01), TEM(sub 10), and TEM(sub 20). Both transmissive and reflective optics were examined. The ZnSe lenses tested included meniscus, diffractive, and cylindrical lenses of 5 in. focal length and a 10 in. focal length integrating lens. Reflective optics included an integrator and a 5 in. focal length parabolic mirror for welding. Parameters obtained included beam propagation profiles, intensity profiles, depth of focus, spot size, and back focal length. A subset of the data obtained is presented here. Details of the work will appear in a full length paper.

  6. Structure and optical properties of CdSe chalcogenide semiconductors

    NASA Astrophysics Data System (ADS)

    Ganaie, Mohsin; Prince, Zulfequar, M.

    2015-08-01

    CdSe bulk sample has been prepared by melt-quenching technique and were characterized with XRD, SEM, FTIR, and electrical measurements. Thin films were deposited by thermal evaporation technique on ultra clean glass substrates under a high vacuum of 10-6 Torr. An XRD measurement reveals the coexistence of glassy and crystalline phase in bulk sample. SEM studies shows single phase, porous, and granular surface morphology of powder CdSe alloy. Optical properties (optical gap, absorption coefficient, extinction coefficient, refractive index) are calculated in the range of 190-1100nm. Analysis of the optical measurement shows that the non-direct transition is predominant and the band gap come outs to be 1.751eV. Dc conductivity measurement is thermally activated process which shows the semiconducting nature of the sample having activation energy 0.31eV.

  7. Total absorption spectroscopy of N = 51 nucleus 85Se

    NASA Astrophysics Data System (ADS)

    Goetz, K. C.; Grzywacz, R. K.; Rykaczewski, K. P.; Karny, M.; Fialkowska, A.; Wolinska-Cichocka, M.; Rasco, B. C.; Zganjar, E. F.; Johnson, J. W.; Gross, C. J.

    2014-09-01

    An experimental campaign utilizing the Modular Total Absorption Spectrometer (MTAS) was conducted at the HRIBF facility in January of 2012. The campaign studied 22 isotopes, many of which were identified as the highest priority for decay heat analysis during a nuclear fuel cycle, see the report by the OECD-IAEA Nuclear Energy Agency in 2007. The case of 85Se will be discussed. 85Se is a Z = 34, N = 51 nucleus with the valence neutron located in the positive parity sd single particle state. Therefore, its decay properties are determined by interplay between first forbidden decays of the valence neutron and Gamow-Teller decay of a 78Ni core. Analysis of the data obtained during the January 2012 run indicates a significant increase of the beta strength function when compared with previous measurements, see Ref..

  8. Giant Seebeck effect in Ge-doped SnSe.

    PubMed

    Gharsallah, M; Serrano-Sánchez, F; Nemes, N M; Mompeán, F J; Martínez, J L; Fernández-Díaz, M T; Elhalouani, F; Alonso, J A

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  9. 140 W Cr:ZnSe laser system.

    PubMed

    Moskalev, Igor; Mirov, Sergey; Mirov, Mike; Vasilyev, Sergey; Smolski, Viktor; Zakrevskiy, Andrey; Gapontsev, Valentin

    2016-09-01

    We report a significant breakthrough in the development of fiber-pumped high-power CW laser systems based on Cr2+:ZnS and Cr2+:ZnSe gain media. We demonstrate output power levels of up to 140 W near 2500 nm, and 32 W at 2940 nm with corresponding optical efficiencies of 62% and 29%. Our novel approach is based on rapid simultaneous scanning of the collinear laser mode and pump beam across the Cr:ZnS/Se gain element which allows us to virtually eliminate thermal lensing effects and obtain unprecedented levels of output power with very high optical-to-optical efficiency. PMID:27607712

  10. Giant Seebeck effect in Ge-doped SnSe

    NASA Astrophysics Data System (ADS)

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-06-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit.

  11. Cr(+2) Diffusion Doping in ZnSe

    NASA Technical Reports Server (NTRS)

    Journigan, Troy D.; Chen, K.-T.; Chen, H.; Burger, A.; Schaffers, K.; Page, R. H.; Payne, S. A.

    1997-01-01

    Chromium doped zinc selenides crystals have recently been demonstrated to be a promising material for near-IR room temperature tunable lasers which has an emission range of 2-3 pm. In this study, a new diffusion doping process has been developed for incorporation of Cr(+2) ion into ZnSe wafers. This process has been successfully performed under isothermal conditions, at temperatures above 800 degrees Celsius. Concentrations in excess of 10(exp 19) Cr(+2) ions/cu cm, an order of magnitude larger than previously reported in melt grown ZnSe material, have been obtained. The diffusivity was estimated to be about 10-* sq cm/sec using a classical diffusion model. Resistivity was derived from current-voltage measurements and in the 107-10(exp 16) Ohms-cm and increased as function of Cr concentration.

  12. {sup 67}As-{sup 67}Se mirror pair spectroscopy

    SciTech Connect

    Wiedemann, K. T.; Medina, N. H.; De Angelis, G.; Orlandi, R.; Vedova, F. Della; Gadea, A.; Marginean, N.; Napoli, D. R.; Sahin, E.; Tonev, D.; Bracco, A.; Leoni, S.; Carpenter, M.; Greene, J.; Lister, C. J.; Seweryniak, D.; Zhu, S.; Chiara, C. J.; Pechenaya, O. L.; Reviol, W.

    2009-06-03

    This work focus on the electromagnetic decay properties of the heaviest known mirror pair {sup 67}As and {sup 67}Se, produced in the fusion evaporation reaction {sup 32}S+{sup 40}Ca, with a E = 90 MeV beam provided by the ATLAS accelerator at Argonne National Laboratory. The high selectivity required to investigate these proton-rich nuclei was achieved with the concurrent employment of Gammasphere, Neutron-Shell, and Microball. The full array allowed to obtain the level scheme of the {sup 67}Se nucleus up to 5.56 MeV, and 5 new transitions were assigned to the known {sup 67}As level-scheme. The level spin and parities were assigned using the ADO analysis and symmetry arguments.

  13. Giant Seebeck effect in Ge-doped SnSe

    PubMed Central

    Gharsallah, M.; Serrano-Sánchez, F.; Nemes, N. M.; Mompeán, F. J.; Martínez, J. L.; Fernández-Díaz, M. T.; Elhalouani, F.; Alonso, J. A.

    2016-01-01

    Thermoelectric materials may contribute in the near future as new alternative sources of sustainable energy. Unprecedented thermoelectric properties in p-type SnSe single crystals have been recently reported, accompanied by extremely low thermal conductivity in polycrystalline samples. In order to enhance thermoelectric efficiency through proper tuning of this material we report a full structural characterization and evaluation of the thermoelectric properties of novel Ge-doped SnSe prepared by a straightforward arc-melting method, which yields nanostructured polycrystalline samples. Ge does not dope the system in the sense of donating carriers, yet the electrical properties show a semiconductor behavior with resistivity values higher than that of the parent compound, as a consequence of nanostructuration, whereas the Seebeck coefficient is higher and thermal conductivity lower, favorable to a better ZT figure of merit. PMID:27251233

  14. Epitaxial growth of CZT(S,Se) on silicon

    DOEpatents

    Bojarczuk, Nestor A.; Gershon, Talia S.; Guha, Supratik; Shin, Byungha; Zhu, Yu

    2016-03-15

    Techniques for epitaxial growth of CZT(S,Se) materials on Si are provided. In one aspect, a method of forming an epitaxial kesterite material is provided which includes the steps of: selecting a Si substrate based on a crystallographic orientation of the Si substrate; forming an epitaxial oxide interlayer on the Si substrate to enhance wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial oxide interlayer is formed from a material that is lattice-matched to Si; and forming the epitaxial kesterite material on a side of the epitaxial oxide interlayer opposite the Si substrate, wherein the epitaxial kesterite material includes Cu, Zn, Sn, and at least one of S and Se, and wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate. A method of forming an epitaxial kesterite-based photovoltaic device and an epitaxial kesterite-based device are also provided.

  15. Superconductivity in cubic noncentrosymmetric PdBiSe Crystal

    NASA Astrophysics Data System (ADS)

    Joshi, B.; Thamizhavel, A.; Ramakrishnan, S.

    2015-03-01

    Mixing of spin singlet and spin triplet superconducting pairing state is expected in noncentrosymmetric superconductors (NCS) due to the inherent presence of Rashba-type antisymmetric spin-orbit coupling. Unlike low symmetry (tetragonal or monoclinic) NCS, parity is isotropicaly broken in space for cubic NCS and can additionally lead to the coexistence of magnetic and superconducting state under certain conditions. Motivated with such enriched possibility of unconventional superconducting phases in cubic NCS we are reporting successful formation of single crystalline cubic noncentrosymmetric PdBiSe with lattice parameter a = 6.4316 Å and space group P21 3 (space group no. 198) which undergoes to superconducting transition state below 1.8 K as measured by electrical transport and AC susceptibility measurements. Significant strength of Rashba-type antisymmetric spin-orbit coupling can be expected for PdBiSe due to the presence of high Z (atomic number) elements consequently making it potential candidate for unconventional superconductivity.

  16. Computation of Pressurized Gas Bearings Using CE/SE Method

    NASA Technical Reports Server (NTRS)

    Cioc, Sorin; Dimofte, Florin; Keith, Theo G., Jr.; Fleming, David P.

    2003-01-01

    The space-time conservation element and solution element (CE/SE) method is extended to compute compressible viscous flows in pressurized thin fluid films. This numerical scheme has previously been used successfully to solve a wide variety of compressible flow problems, including flows with large and small discontinuities. In this paper, the method is applied to calculate the pressure distribution in a hybrid gas journal bearing. The formulation of the problem is presented, including the modeling of the feeding system. the numerical results obtained are compared with experimental data. Good agreement between the computed results and the test data were obtained, and thus validate the CE/SE method to solve such problems.

  17. Urinary trimethylselenonium excretion by the rat: effect of level and source of /sup 75/Se

    SciTech Connect

    Nahapetian, A.T.; Janghorbani, M.; Young, V.R.

    1983-02-01

    The purpose of this study was to explore in rats the urinary metabolites of selenium (Se), by using (/sup 75/Se)selenomethionine, (/sup 75/Se)selenocystine, and (/sup 75/Se)selenite, and to assess the effects of low and high levels of Se intake on trimethylselenonium ion (TMSe) excretion in urine. Male adult rats were adapted for 6 weeks to a commercial rat laboratory stock diet (0.25 ppm Se). They were then starved for 24 hours and given an oral dose of either low (16 micrograms Se/kg body weight) or high (1500 micrograms Se/kg body weight) Se as the test Se compounds. Appearance of radioactivity in TMSe and non-TMSe Se metabolites in urine was monitored for 48 hours. About 40% of the /sup 75/Se dose was excreted in urine. TMSe was the major urinary Se metabolite (57-69% of urinary /sup 75/Se and 16-25% of oral /sup 75/Se dose) at high, and a minor urinary Se metabolite (10% of urinary /sup 75/Se and 3-4% of oral /sup 75/Se dose) at low dose levels of Se and for all three Se test compounds. At least 80% of urinary /sup 75/Se and 26-42% of the orally administered /sup 75/Se were excreted as non-TMSe Se metabolites in urine under the latter condition. It is hypothesized that at a requirement intake of Se either a trace or no TMSe is excreted in urine, and it becomes a major excretory metabolite of Se when the dietary trace mineral intake exceeds a requirement level, probably serving as a means of detoxification.

  18. Quantum confined acceptors and donors in InSe nanosheets

    SciTech Connect

    Mudd, G. W.; Patanè, A. Makarovsky, O.; Eaves, L.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Fay, M. W.; Zólyomi, V.; Falko, V.

    2014-12-01

    We report on the radiative recombination of photo-excited carriers bound at native donors and acceptors in exfoliated nanoflakes of nominally undoped rhombohedral γ-polytype InSe. The binding energies of these states are found to increase with the decrease in flake thickness, L. We model their dependence on L using a two-dimensional hydrogenic model for impurities and show that they are strongly sensitive to the position of the impurities within the nanolayer.

  19. Parametric amplification in AgGaSe2

    NASA Technical Reports Server (NTRS)

    Barnes, Norman P.; Gettemy, Donald J.; Hietanen, Jack R.; Iannini, Rebecca A.

    1989-01-01

    AgGaSe2 has been grown, annealed, and characterized for the mid-IR. Characterization includes measurement of the average power-limiting factors including absorption and the variation of the refractive indices with temperature. Using specially annealed crystals 20 mm long and a Ho:YAG pump, parametric amplification at 3.39 microns has achieved a gain of 2.9 with a peak power input of only 8 MW/sq cm.

  20. Parallel CE/SE Computations via Domain Decomposition

    NASA Technical Reports Server (NTRS)

    Himansu, Ananda; Jorgenson, Philip C. E.; Wang, Xiao-Yen; Chang, Sin-Chung

    2000-01-01

    This paper describes the parallelization strategy and achieved parallel efficiency of an explicit time-marching algorithm for solving conservation laws. The Space-Time Conservation Element and Solution Element (CE/SE) algorithm for solving the 2D and 3D Euler equations is parallelized with the aid of domain decomposition. The parallel efficiency of the resultant algorithm on a Silicon Graphics Origin 2000 parallel computer is checked.

  1. View SE of threestory steel and brick building. Part of ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View SE of three-story steel and brick building. Part of large complex of buildings along Milwaukee Ave. (1920, 1950, & 1960 Milwaukee Ave. E) that is attached to the back of 1891 Trombly Ave. Openings on first floor are bricked up; second floor rectangular widows on the street facade are framed by an arched brick pattern. One brick course protrudes to form a cornice line between the second and third floors - 1900 East Milwaukee (Industrial Building), Detroit, MI

  2. Lake Powell, SE Utah and NE Arizona, USA

    NASA Technical Reports Server (NTRS)

    1991-01-01

    The Glen Canyon National Recreation Area with Lake Powell and Monument Valley in both SE Utah and NE Arizona (36.5N, 110.0W) are well known tourist areas in the southwest. Water from Lake Powell feeds the Colorado River before it rages through the Grand Canyon. The darker green areas indicate the high forested country of Navajo Mountain and Black Mesa in Arizona. Shadows from the many steep sided hills add a near three dimensional effect to the scene.

  3. Time-resolved photoconductivity of PbSe nanocrystal arrays.

    PubMed

    Murphy, James E; Beard, Matthew C; Nozik, Arthur J

    2006-12-21

    We report the sub-picosecond photoconductivity dynamics of chemically treated PbSe nanocrystal arrays utilizing time-resolved terahertz spectroscopy (TRTS). TRTS allows both the degree of interdot electronic coupling and the carrier dynamics to be extracted simultaneously. The following capping ligands bonded to the quantum dot surface were studied: hydrazine, ethylenediamine, butlyamine, and aniline. In addition, the arrays were treated with NaOH. We find that the treatments affect both the degree of electronic coupling and the carrier dynamics.

  4. Syntheses, structures, and optical properties of the indium/germanium selenides Cs{sub 4}In{sub 8}GeSe{sub 16}, CsInSe{sub 2}, and CsInGeSe{sub 4}

    SciTech Connect

    Ward, Matthew D.; Pozzi, Eric A.; Van Duyne, Richard P.; Ibers, James A.

    2014-04-01

    The three solid-state indium/germanium selenides Cs{sub 4}In{sub 8}GeSe{sub 16}, CsInSe{sub 2}, and CsInGeSe{sub 4} have been synthesized at 1173 K. The structure of Cs{sub 4}In{sub 8}GeSe{sub 16} is a three-dimensional framework whereas those of CsInSe{sub 2} and CsInGeSe{sub 4} comprise sheets separated by Cs cations. Both Cs{sub 4}In{sub 8}GeSe{sub 16} and CsInGeSe{sub 4} display In/Ge disorder. From optical absorption measurements these compounds have band gaps of 2.20 and 2.32 eV, respectively. All three compounds are charge balanced. - Graphical abstract: Structure of Cs{sub 4}In{sub 8}GeSe{sub 16}. - Highlights: • The solid-state In/Ge selenides Cs{sub 4}In{sub 8}GeSe{sub 16}, CsInSe{sub 2}, and CsInGeSe{sub 4} have been synthesized. • Both Cs{sub 4}In{sub 8}GeSe{sub 16} and CsInGeSe{sub 4} display In/Ge disorder. • Cs{sub 4}In{sub 8}GeSe{sub 16} and CsInGeSe{sub 4} have band gaps of 2.20 eV and 2.32 eV, respectively.

  5. Electron microscopy of iron chalcogenide FeTe(Se) films

    NASA Astrophysics Data System (ADS)

    Shchichko, I. O.; Presnyakov, M. Yu.; Stepantsov, E. A.; Kazakov, S. M.; Antipov, E. V.; Makarova, I. P.; Vasil'ev, A. L.

    2015-05-01

    The structure of Fe1 + δTe1 - x Se x films ( x = 0; 0.05) grown on single-crystal MgO and LaAlO3 substrates has been investigated by transmission and scanning transmission electron microscopy. The study of Fe1.11Te/MgO structures has revealed two crystallographic orientation relationships between the film and substrate. It is shown that the lattice mismatch between the film and substrate is compensated for by the formation of misfit dislocations. The Burgers vector projection is determined. The stresses in the film can partially be compensated for due to the formation of an intermediate disordered layer. It is shown that a FeTe0.5Se0.5 film grown on a LaAlO3 substrate is single-crystal and that the FeTe0.5Se0.5/LaAlO3 interface in a selected region is coherent. The orientation relationships between the film and substrate are also determined for this case.

  6. Lysozyme loading and release from Se doped hydroxyapatite nanoparticles.

    PubMed

    Wang, Yanhua; Hao, Hang; Zhang, Shengmin

    2016-04-01

    Element-substituted hydroxyapatite (HA) based nanocomposites have become a promising therapeutic material for improving bone defect repair. Selenium substituted HA nanoparticles can both induce apoptosis of bone tumor cells and enhance osteointegration. However, the effect of selenite ions on the proteins in combination with the HA nanoparticles remains to be elucidated. Here, we investigated the influence of selenium doping concentration on the loading and release of lysozyme (LSM) as a model protein drug. The selenium substituted HA-LSM composites with different doping concentrations were synthesized and characterized. The subsequent delivery of lysozyme was studied in a phosphate buffer solution (PBS). We found that selenium substituted HA-LSM composites with Se:P=10% showed the highest amount of lysozyme loading (41.7%), whereas the amount of lysozyme loaded in undoped HA nanoparticles was the lowest (34.1%). The doped selenium interacts with lysozyme molecules, which leads to the increase of β-sheet and unordered, and the decrease of self-association, α-helix and β-turns in protein structures. Moreover, selenium addition significantly slows the protein release from HA-LSM composites. The composites with Se:P=10% release lysozyme at the slightly slower rate among the samples with different Se doping concentrations. It also shows that the released lysozyme retains most of its enzymatic activity.

  7. Lysozyme loading and release from Se doped hydroxyapatite nanoparticles.

    PubMed

    Wang, Yanhua; Hao, Hang; Zhang, Shengmin

    2016-04-01

    Element-substituted hydroxyapatite (HA) based nanocomposites have become a promising therapeutic material for improving bone defect repair. Selenium substituted HA nanoparticles can both induce apoptosis of bone tumor cells and enhance osteointegration. However, the effect of selenite ions on the proteins in combination with the HA nanoparticles remains to be elucidated. Here, we investigated the influence of selenium doping concentration on the loading and release of lysozyme (LSM) as a model protein drug. The selenium substituted HA-LSM composites with different doping concentrations were synthesized and characterized. The subsequent delivery of lysozyme was studied in a phosphate buffer solution (PBS). We found that selenium substituted HA-LSM composites with Se:P=10% showed the highest amount of lysozyme loading (41.7%), whereas the amount of lysozyme loaded in undoped HA nanoparticles was the lowest (34.1%). The doped selenium interacts with lysozyme molecules, which leads to the increase of β-sheet and unordered, and the decrease of self-association, α-helix and β-turns in protein structures. Moreover, selenium addition significantly slows the protein release from HA-LSM composites. The composites with Se:P=10% release lysozyme at the slightly slower rate among the samples with different Se doping concentrations. It also shows that the released lysozyme retains most of its enzymatic activity. PMID:26838882

  8. Spontaneous emission enhancement of colloidal CdSe nanoplatelets

    NASA Astrophysics Data System (ADS)

    Yang, Zhili; Pelton, Matthew; Waks, Edo

    Colloidal CdS /CdSe/CdS nanoplatelets synthesized recently are high efficient nano-emitters and gain media for nanoscale lasers and other nonlinear optical devices. They are characterized as quantum well structure due to energy gap difference between core CdSe and shell CdS, of which the luminescent wavelength could be tuned precisely by their thickness of growth. However, the influence of environment on the material's optical properties and further enhancement of the emission to implement nanoscale systems remains to be investigated. Here we demonstrate spontaneous emission rate enhancement of these CdSe nanoplatelets coupled to a photonic crystal cavity. We show clearly the photoluminescent spectrum modification of the nanoplatelets emission and an averaged Purcell enhancement factor of 3.1 is achieved when they are coupled to carefully-designed nanobeam photonic crystal cavities compared to the ones on unpatterned surface in our experiment of lifetime measurement. Also the phenomenon of cavity quality factor increasing is observed when increasing intensity of pumping, which attributes to saturable absorption of the nanoplatelets. Our success in enhancement of emission from these nanoplatelets here paves the road to realize actual nanoscale integrated systems such as ultra-low threshold micro-cavity lasers.

  9. Near-infrared electronic spectra of BiSe

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Breidohr, R.; Meinecke, F.; Fink, E. H.

    2009-11-01

    NIR/VIS emission spectra of BiSe were measured in the 5800-20,000 cm -1 region with a Fourier-transform spectrometer. BiSe was produced by reaction of bismuth and selenium vapors and excited by energy transfer from metastable oxygen O 2( a1Δ g) in a fast-flow system. The spectrum of BiSe was found to be closely related to those of the previously studied BiO and BiS radicals. Four band systems were unambiguously assigned to the transitions X22Π 3/2 → X12Π 1/2, A24Π 1/2 → X12Π 1/2, C14Σ -1/2 → X12Π 1/2 and C14Σ -1/2 → A24Π 1/2 and the electronic energies and vibrational constants of the states X12Π 1/2, X22Π 3/2, A24Π 1/2 and C14Σ -1/2 were derived.

  10. Superconducting Gap Anisotropy in Monolayer FeSe Thin Film.

    PubMed

    Zhang, Y; Lee, J J; Moore, R G; Li, W; Yi, M; Hashimoto, M; Lu, D H; Devereaux, T P; Lee, D-H; Shen, Z-X

    2016-09-01

    Superconductivity originates from pairing of electrons near the Fermi energy. The Fermi surface topology and pairing symmetry are thus two pivotal characteristics of a superconductor. Superconductivity in one monolayer (1 ML) FeSe thin film has attracted great interest recently due to its intriguing interfacial properties and possibly high superconducting transition temperature over 65 K. Here, we report high-resolution measurements of the Fermi surface and superconducting gaps in 1 ML FeSe using angle-resolved photoemission spectroscopy. Two ellipselike electron pockets are clearly resolved overlapping with each other at the Brillouin zone corner. The superconducting gap is nodeless but moderately anisotropic, which puts strong constraint on determining the pairing symmetry. The gap maxima locate on the d_{xy} bands along the major axis of the ellipse and four gap minima are observed at the intersections of electron pockets. The gap maximum location combined with the Fermi surface geometry deviate from a single d-wave, extended s-wave or s_{±} gap function, suggesting an important role of the multiorbital nature of Fermi surface and orbital-dependent pairing in 1 ML FeSe. The gap minima location may be explained by a sign change on the electron pockets, or a competition between intra- and interorbital pairing. PMID:27661715

  11. The synthesis of [(PbSe)1+δ]m(TiSe2)n[(SnSe2)1+γ]m(TiSe2)n heterostructures with designed nanoarchitectures by self assembly of amorphous precursors

    NASA Astrophysics Data System (ADS)

    Merrill, Devin R.; Sutherland, Duncan R.; Ditto, Jeffrey J.; Moore, Daniel B.; Falmbigl, Matthias; Medlin, Douglas L.; Johnson, David C.

    2016-07-01

    Targeted heterostructures containing intergrown two dimensional (2D) layers of 3 different constituent layers, SnSe2, PbSe and TiSe2, were prepared by controlling the composition and sequence of elemental bilayers within a designed precursor. Varying the structure of the precursor enabled the number of structural units of each constituent and the sequence of crystalline 2D layers to be precisely controlled. The stacking of the 2D layers, their structures, and the segregation of the elements between them were determined using X-ray diffraction and electron microscopy techniques, with the observed sequence of the 2D layers consistent with the targeted intergrowth. This ability to prepare targeted heterostructures is critical, since the number of possible configurations in the final compound increases rapidly as the number of constituents increases, from almost 60 000 with two constituents to over 130 million with three constituents and to over 35 billion with four constituents for 20 or fewer distinct layers in the unit cell. This general route for synthesizing specific multiple component heterostructures will accelerate the feedback loop in this growing research area, permitting theorists to assume specific structures in the search for enhanced properties and providing experimentalists with crystallographically aligned samples to test these predictions.

  12. Superconducting Gap Anisotropy in Monolayer FeSe Thin Film

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Lee, J. J.; Moore, R. G.; Li, W.; Yi, M.; Hashimoto, M.; Lu, D. H.; Devereaux, T. P.; Lee, D.-H.; Shen, Z.-X.

    2016-09-01

    Superconductivity originates from pairing of electrons near the Fermi energy. The Fermi surface topology and pairing symmetry are thus two pivotal characteristics of a superconductor. Superconductivity in one monolayer (1 ML) FeSe thin film has attracted great interest recently due to its intriguing interfacial properties and possibly high superconducting transition temperature over 65 K. Here, we report high-resolution measurements of the Fermi surface and superconducting gaps in 1 ML FeSe using angle-resolved photoemission spectroscopy. Two ellipselike electron pockets are clearly resolved overlapping with each other at the Brillouin zone corner. The superconducting gap is nodeless but moderately anisotropic, which puts strong constraint on determining the pairing symmetry. The gap maxima locate on the dx y bands along the major axis of the ellipse and four gap minima are observed at the intersections of electron pockets. The gap maximum location combined with the Fermi surface geometry deviate from a single d -wave, extended s -wave or s± gap function, suggesting an important role of the multiorbital nature of Fermi surface and orbital-dependent pairing in 1 ML FeSe. The gap minima location may be explained by a sign change on the electron pockets, or a competition between intra- and interorbital pairing.

  13. Metal contacts on ZnSe and GaN

    SciTech Connect

    Duxstad, K J

    1997-05-01

    Recently, considerable interest has been focused on the development of blue light emitting materials and devices. The focus has been on GaN and ZnSe, direct band gap semiconductors with bands gaps of 3.4 and 2.6 eV, respectively. To have efficient, reliable devices it is necessary to have thermally and electrically stable Ohmic contacts. This requires knowledge of the metal-semiconductor reaction behavior. To date few studies have investigated this behavior. Much information has accumulated over the years on the behavior of metals on Si and GaAs. This thesis provides new knowledge for the more ionic wide band gap semiconductors. The initial reaction temperatures, first phases formed, and phase stability of Pt, Pd, and Ni on both semiconductors were investigated. The reactions of these metals on ZnSe and GaN are discussed in detail and correlated with predicted behavior. In addition, comparisons are made between these highly ionic semiconductors and Si and GaAs. The trends observed here should also be applicable to other II-VI and III-Nitride semiconductor systems, while the information on phase formation and stability should be useful in the development of contacts for ZnSe and GaN devices.

  14. Complex band structure of topological insulator Bi2Se3.

    PubMed

    Betancourt, J; Li, S; Dang, X; Burton, J D; Tsymbal, E Y; Velev, J P

    2016-10-01

    Topological insulators are very interesting from a fundamental point of view, and their unique properties may be useful for electronic and spintronic device applications. From the point of view of applications it is important to understand the decay behavior of carriers injected in the band gap of the topological insulator, which is determined by its complex band structure (CBS). Using first-principles calculations, we investigate the dispersion and symmetry of the complex bands of Bi2Se3 family of three-dimensional topological insulators. We compare the CBS of a band insulator and a topological insulator and follow the CBS evolution in both when the spin-orbit interaction is turned on. We find significant differences in the CBS linked to the topological band structure. In particular, our results demonstrate that the evanescent states in Bi2Se3 are non-trivially complex, i.e. contain both the real and imaginary contributions. This explains quantitatively the oscillatory behavior of the band gap obtained from Bi2Se3 (0 0 0 1) slab calculations. PMID:27485021

  15. Nematic quantum paramagnet and possible application to FeSe

    NASA Astrophysics Data System (ADS)

    Wang, Fa; Kivelson, Steven A.; Lee, Dung-Hai

    The nematic phases in iron pnictides are in close proximity to the stripe antiferromagnetic order, suggesting that magnetism is the driving force for the spontaneous 4-fold crystal rotation symmetry breaking. In contrast, bulk FeSe shows a nematic phase below 90K at ambient pressure, but has no magnetic long range order down to very low temperature. This prompts suggestions that the nematicity in FeSe is driven by some other mechanism. We argue that magnetic correlation can still drive nematic order in the absence of magnetic order. By field theoretical considerations and exact diagonalization results on finite size lattices, we conclude that the paramagnetic phase in frustrated spin-1 J1-J2 models on square lattice is such a ''nematic quantum paramagnet'', which breaks only the crystal 4-fold rotation symmetry. The prototype wavefunctions of such quantum ground states are horizontal(vertical) aligned spin-1 AKLT chains. We suggest that the local spins in FeSe may form this phase due to strong frustration. One unique consequence of this proposal is that the nematic paramagnetic phase will be close to both stripe and Neel antiferromagnetic order, and will thus host low but finite energy spin fluctuations at both ordering wavevectors.

  16. Complex band structure of topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Betancourt, J.; Li, S.; Dang, X.; Burton, J. D.; Tsymbal, E. Y.; Velev, J. P.

    2016-10-01

    Topological insulators are very interesting from a fundamental point of view, and their unique properties may be useful for electronic and spintronic device applications. From the point of view of applications it is important to understand the decay behavior of carriers injected in the band gap of the topological insulator, which is determined by its complex band structure (CBS). Using first-principles calculations, we investigate the dispersion and symmetry of the complex bands of Bi2Se3 family of three-dimensional topological insulators. We compare the CBS of a band insulator and a topological insulator and follow the CBS evolution in both when the spin-orbit interaction is turned on. We find significant differences in the CBS linked to the topological band structure. In particular, our results demonstrate that the evanescent states in Bi2Se3 are non-trivially complex, i.e. contain both the real and imaginary contributions. This explains quantitatively the oscillatory behavior of the band gap obtained from Bi2Se3 (0 0 0 1) slab calculations.

  17. An Atomically Layered InSe Avalanche Photodetector.

    PubMed

    Lei, Sidong; Wen, Fangfang; Ge, Liehui; Najmaei, Sina; George, Antony; Gong, Yongji; Gao, Weilu; Jin, Zehua; Li, Bo; Lou, Jun; Kono, Junichiro; Vajtai, Robert; Ajayan, Pulickel; Halas, Naomi J

    2015-05-13

    Atomically thin photodetectors based on 2D materials have attracted great interest due to their potential as highly energy-efficient integrated devices. However, photoinduced carrier generation in these media is relatively poor due to low optical absorption, limiting device performance. Current methods for overcoming this problem, such as reducing contact resistances or back gating, tend to increase dark current and suffer slow response times. Here, we realize the avalanche effect in a 2D material-based photodetector and show that avalanche multiplication can greatly enhance the device response of an ultrathin InSe-based photodetector. This is achieved by exploiting the large Schottky barrier formed between InSe and Al electrodes, enabling the application of a large bias voltage. Plasmonic enhancement of the photosensitivity, achieved by patterning arrays of Al nanodisks onto the InSe layer, further improves device efficiency. With an external quantum efficiency approaching 866%, a dark current in the picoamp range, and a fast response time of 87 μs, this atomic layer device exhibits multiple significant advances in overall performance for this class of devices.

  18. Electron microscopy of iron chalcogenide FeTe(Se) films

    SciTech Connect

    Shchichko, I. O.; Presnyakov, M. Yu.; Stepantsov, E. A.; Kazakov, S. M.; Antipov, E. V.; Makarova, I. P.; Vasil’ev, A. L.

    2015-05-15

    The structure of Fe{sub 1+δ}Te{sub 1−x}Se{sub x} films (x = 0; 0.05) grown on single-crystal MgO and LaAlO{sub 3} substrates has been investigated by transmission and scanning transmission electron microscopy. The study of Fe{sub 1.11}Te/MgO structures has revealed two crystallographic orientation relationships between the film and substrate. It is shown that the lattice mismatch between the film and substrate is compensated for by the formation of misfit dislocations. The Burgers vector projection is determined. The stresses in the film can partially be compensated for due to the formation of an intermediate disordered layer. It is shown that a FeTe{sub 0.5}Se{sub 0.5} film grown on a LaAlO{sub 3} substrate is single-crystal and that the FeTe{sub 0.5}Se{sub 0.5}/LaAlO{sub 3} interface in a selected region is coherent. The orientation relationships between the film and substrate are also determined for this case.

  19. Preparation and applications of ZnSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Ravindranadh, K.; Shekhawat, M. S.; Rao, M. C.

    2013-06-01

    Semiconductor nanoparticles have been attracting widespread scientific and technological interest due to their unique size-tunable optical and electronic properties. The ZnSe nanoparticles have wide-ranging applications in laser, optical instruments, etc. because it has a wide band gap and transmittance range, high luminescence efficiency, low absorption coefficient, and excellent transparency to infrared. ZnSe nanoparticles have been prepared at room temperature. Zinc chloride 99 mM of 4 mL is added to 2.2g PVA. Volume of the solution is made up to 50 mL by bidistilled water. The Solution is left for 24 h at room temperature to swell. After that the solution is warmed up to 60°C and stirred for 4 h until viscous transparent solution was obtained. One milliliter of Sodium Hydrogen Selenide was dropped into the solution with gentle stirring. Solution is casted on flat glass plate dishes. After the solvent evaporation, a thin film containing ZnSe nanoparticles are obtained. The film is washed with de-ionized water to remove other soluble salts before measurements.

  20. The synthesis of [(PbSe)1+δ]m(TiSe2)n[(SnSe2)1+γ]m(TiSe2)n heterostructures with designed nanoarchitectures by self assembly of amorphous precursors.

    PubMed

    Merrill, Devin R; Sutherland, Duncan R; Ditto, Jeffrey J; Moore, Daniel B; Falmbigl, Matthias; Medlin, Douglas L; Johnson, David C

    2016-07-14

    Targeted heterostructures containing intergrown two dimensional (2D) layers of 3 different constituent layers, SnSe2, PbSe and TiSe2, were prepared by controlling the composition and sequence of elemental bilayers within a designed precursor. Varying the structure of the precursor enabled the number of structural units of each constituent and the sequence of crystalline 2D layers to be precisely controlled. The stacking of the 2D layers, their structures, and the segregation of the elements between them were determined using X-ray diffraction and electron microscopy techniques, with the observed sequence of the 2D layers consistent with the targeted intergrowth. This ability to prepare targeted heterostructures is critical, since the number of possible configurations in the final compound increases rapidly as the number of constituents increases, from almost 60 000 with two constituents to over 130 million with three constituents and to over 35 billion with four constituents for 20 or fewer distinct layers in the unit cell. This general route for synthesizing specific multiple component heterostructures will accelerate the feedback loop in this growing research area, permitting theorists to assume specific structures in the search for enhanced properties and providing experimentalists with crystallographically aligned samples to test these predictions. PMID:27363315

  1. The Antiphagocytic Activity of SeM of Streptococcus equi Requires Capsule.

    PubMed

    Timoney, John F; Suther, Pranav; Velineni, Sridhar; Artiushin, Sergey C

    2014-01-01

    Resistance to phagocytosis is a crucial virulence property of Streptococcus equi (Streptococcus equi subsp. equi; Se), the cause of equine strangles. The contribution and interdependence of capsule and SeM to killing in equine blood and neutrophils were investigated in naturally occurring strains of Se. Strains CF32, SF463 were capsule and SeM positive, strains Lex90, Lex93 were capsule negative and SeM positive and strains Se19, Se1-8 were capsule positive and SeM deficient. Phagocytosis and killing of Se19, Se1-8, Lex90 and Lex93 in equine blood and by neutrophils suspended in serum were significantly (P ≤ 0.02) greater compared to CF32 and SF463. The results indicate capsule and SeM are both required for resistance to phagocytosis and killing and that the anti-phagocytic property of SeM is greatly reduced in the absence of capsule.

  2. Phase Stability and Electronic Structure of In-Free Photovoltaic Materials: Cu2ZnSiSe4, Cu2ZnGeSe4, and Cu2ZnSnSe4

    NASA Astrophysics Data System (ADS)

    Nakamura, Satoshi; Maeda, Tsuyoshi; Wada, Takahiro

    2010-12-01

    We have theoretically evaluated phase stability and electronic structure of Cu2ZnSiSe4 and Cu2ZnGeSe4 and compared the results with those of Cu2ZnSnSe4. The enthalpies of formation for kesterite (KS), stannite (ST), and wurtz-stannite (WST) phases of Cu2ZnSiSe4, Cu2ZnGeSe4, and Cu2ZnSnSe4 (CZTSe) were calculated by first-principles calculations. In these three compounds, the KS phase is more stable than the ST and WST phases. The theoretical band gaps of KS-type Cu2ZnSiSe4 (1.48 eV) and Cu2ZnGeSe4 (1.10 eV) are wider than that of KS-type Cu2ZnSnSe4 (0.63 eV). The valence band maximum (VBM) of KS-type Cu2ZnIVSe4 consists of antibonding orbital of Cu 3d and Se 4p, while the conduction band minimum (CBM) consist of antibonding orbital of IV ns and Se 4p. The VBMs of Cu 3d + Se 4p in Cu2ZnSiSe4 and Cu2ZnGeSe4 are similar to that in Cu2ZnSnSe4. Therefore, the energy levels of VBMs in Cu2ZnIVSe4 (IV = Si, Ge) do not change so much compared with that of CZTSe. On the other hand, the energy levels of CBMs of IV ns + Se 4p in Cu2ZnSiSe4 and Cu2ZnGeSe4 become higher than that in Cu2ZnSnSe4. These trends in the electronic structures are explained by the schematic molecular orbital diagrams of tetrahedral CuSe47-, ZnSe46-, and IVSe44- (IV = Si, Ge, Sn) clusters.

  3. Continental crustal history in SE Asia: Insights from zircon geochronology

    NASA Astrophysics Data System (ADS)

    Sevastjanova, I.; Hall, R.; Gunawan, I.; Ferdian, F.; Decker, J.

    2012-12-01

    It is well known that SE Asia is underlain mostly by continental crust derived from Gondwana. However, there are still many uncertainties about the ages of protoliths, origin, arrival ages and history of different blocks, because much of the basement is unexposed. We have compiled previously published and new zircon U-Pb age and Hf isotope data from SE Asia. Our data set currently contains over 8400 U-Pb ages and over 600 Hf isotope analyses from sedimentary, metamorphic and igneous rocks and work is continuing to increase its size and the area covered. Zircons range in age from 3.4 Ga to near-zero. Archean zircons (>2.5 Ga) are rare in SE Asia and significant Archean populations (particularly zircons >2.8 Ga) are found only in East Java and the Sibumasu block of the Malay Peninsula. The presence of Archean zircons strongly suggests that the East Java and Sibumasu blocks were once situated near present-day Western Australia. Detrital Paleoproterozoic (ca. 1.9-1.8 Ga) zircons are abundant in many parts of SE Asia. In Sundaland (Malay Peninsula, Sumatra, West Java, Borneo) the most likely source for these zircons is the tin belt basement, but a north Australian source is more likely for eastern Indonesian samples. An early Mesoproterozoic (ca. 1.6-1.5 Ga) zircon population, particularly common in eastern Indonesia, is interpreted to be derived from central or northern Australia. Mesoproterozoic zircons, ca. 1.4 Ga, are common only on fragments that are now attached to or were previously part of the north Australian margin, such as the Bird's Head of New Guinea, Timor, Seram, Sulawesi and SW Borneo. Hf isotope characteristics of zircons from Seram are similar to those of zircons from eastern Australia. This supports the suggestion that Seram was part of the Australian margin. Late Meso- and early Neoproterozoic zircons (ca. 1.2-1.1 Ga, 900 Ma, and 600 Ma) are present, but not abundant, in SE Asia. Dominant Phanerozoic populations are Permian-Triassic, Cretaceous, and

  4. K2Sn2ZnSe6, Na2Ge2ZnSe6, and Na2In2GeSe6: a new series of quaternary selenides with intriguing structural diversity and nonlinear optical properties.

    PubMed

    Zhou, Molin; Li, Chao; Li, Xiaoshuang; Yao, Jiyong; Wu, Yicheng

    2016-05-01

    Three new compounds (i.e., K2Sn2ZnSe6, Na2Ge2ZnSe6, and Na2In2GeSe6) with intriguing structural diversity and nonlinear optical properties were discovered for the first time. They crystallize in space groups P4/ncc, I4/mcm and Cc, respectively. In K2Sn2ZnSe6 and Na2Ge2ZnSe6, the [Sn(Ge)Se4] tetrahedra and [ZnSe4] tetrahedra are linked via edge-sharing to build up a 1D [Sn2ZnSe6] infinite chain separated by K(+)(Na(+)) cations along the c direction, while the structure of Na2In2GeSe6 is an interesting three-dimensional framework composed of [InSe4] and [GeSe4] tetrahedra via corner-sharing with Na(+) cations in the cavities. The experimental optical band gaps of these compounds were determined as 1.71(2) eV, 2.36(4) eV and 2.47(2) eV, respectively, according to UV-vis-NIR diffuse reflectance spectroscopy. Interestingly, in addition to the large band gap (1.80 eV for AgGaSe2, as a comparison), Na2In2GeSe6 exhibits phase-matchable nonlinear optical (NLO) properties with a powder second harmonic generation signal about 0.8 times that of AgGaS2. Moreover, Na2In2GeSe6 melts congruently at a rather low temperature of 671 °C, which suggests that bulk crystals can be easily obtained by the Bridgman-Stockbarger method. Our preliminary results indicate that Na2In2GeSe6 has promising applications in IR nonlinear optics. PMID:27049006

  5. Growth and characterization of ZnIn 2Se 4 buffer layer on CuInSe 2 thin films

    NASA Astrophysics Data System (ADS)

    Sun, Xianzhong; He, Yue; Feng, Jiayou

    2009-12-01

    The p-type CuInSe 2 (CIS) films were prepared by electrodeposition following the vacuum annealing process. Zn element was diffused into the CIS film samples at 350 °C by heating Zn grains in vacuum. Then, ZnIn 2Se 4 (ZIS) buffer layer was fabricated on CIS thin film by this thermal diffusion process. The formation of ZIS phase was confirmed by X-ray diffraction pattern (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Dark I- V measurement shows that the Zn-doped CIS (0.89 at%)/Mo structure reveals the rectifying property, which indicates that a p-n junction was formed.

  6. Band alignment in ZnSe/Zn1-x-y Cdx Mny Se quantum-well structures

    NASA Astrophysics Data System (ADS)

    Yu, W. Y.; Salib, M. S.; Petrou, A.; Jonker, B. T.; Warnock, J.

    1997-01-01

    We present a magneto-optical study of ZnSe/Zn1-x-y Cdx Mny Se quantum-well structures in which a suitable choice of the Cd composition leads to a system that is type I at zero magnetic field. When a magnetic field is applied perpendicular to the layers of the structure, the band edges split in such a way as to make the upper σ- (+, +) exciton transition type II, while the ground state σ+ (-, -) exciton component remains type I at all field values. This alignment reduces the probability for carrier relaxation from the higher-energy exciton component and opens the possibility of hole-spin population inversion via optical pumping.

  7. Nematicity and in-plane anisotropy of superconductivity in β -FeSe detected by 77Se nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Efremov, D. V.; Ok, J. M.; Kim, J. S.; van den Brink, Jeroen; Büchner, B.

    2016-05-01

    The recent study of 77Se nuclear magnetic resonance (NMR) in a β -FeSe single crystal proposed that ferro-orbital order breaks the 90∘ C4 rotational symmetry, driving nematic ordering. Here, we report an NMR study of the impact of small strains generated by gluing on nematic state and spin fluctuations. We observe that the local strains strongly affect the nematic transition, considerably enhancing its onset temperature. On the contrary, no effect on low-energy spin fluctuations was found. Furthermore we investigate the interplay of the nematic phase and superconductivity. Our study demonstrates that the twinned nematic domains respond unequivalently to superconductivity, evidencing the twofold C2 symmetry of superconductivity in this material. The obtained results are well understood in terms of the proposed ferro-orbital order.

  8. Magnetic Coupling in FeBi2Se4 and FeSb2Se4 from first principles

    NASA Astrophysics Data System (ADS)

    Williams, Logan; Kioupakis, Emmanouil; Lopez, Juan; Poudeu, Pierre Ferdinand P.

    Spintronic devices offer benefits in power efficiency and size reduction over current electronics, but require the development of semiconductor materials with favorable magnetic properties. Specifically, a high ferromagnetic-to-paramagnetic Curie transition temperature is required for spintronics operation at room temperature. FeBi2Se4 and FeSb2Se4 are two n and p-type magnetic semiconductors, respectively, with Curie transition temperatures of 450K. We employ first-principles calculations based on density functional theory to examine the magnetic coupling mechanisms in these materials. Our results indicate that antisite defects of Fe upon the Bi/Sb sites are crucial to the ferromagnetic coupling of the Fe magnetic moments in the crystals. This research was supported by the National Science Foundation CAREER award through Grant No. DMR-1254314. Computational Resources were provided by the DOE NERSC facility.

  9. Mass spectroscopic characterization of the GeSe:GeI4 vapor transport system

    NASA Technical Reports Server (NTRS)

    Buchan, Nicholas I.; Rosenberger, Franz

    1987-01-01

    The GeSe:GeI4 vapor crystal growth system was characterized mass spectroscopically. A steady-state Knudsen effusion technique was developed to simulate the equilibrium conditions at one end of a vapor transport ampoule. It was found that the previously neglected equilibrium GeSe2(s) = GeSe(v) + 1/2Se2(v) reduces the Se2(v) concentration to an extent that sublimation/condensation of GeSe becomes the dominant transport mechanism. At total pressures near 1 atm the concentration of an additional Ge-Se-I vapor species becomes comparable to that of GeSe(v).

  10. Absorbed dose to man from the Se-75 labeled conjugated bile salt SeHCAT: concise communication

    SciTech Connect

    Soundy, R.G.; Simpson, J.D.; Ross, H.M.; Merrick, M.V.

    1982-02-01

    The absorbed radiation dose that would result from the oral or intravenous administration of SeHCAT (23-(75Se)selena-25-homotaurocholate) has been calculated using the MIRD tables and formulas and data from measurements of whole-body distribution and from long-term whole-body counting in rats, mice, and man. When SeHCAT is administered to normal subjects, the gallbladder is the critical organ, receiving 12 mrad (oral dose) or 22 mrad (i.v.) per microcurie. The whole-body dose is 1 mrad/microCi, whatever the route of administration. In severe hepatic failure the liver might receive 200 mrad/microCi. The activity likely to be used in routine clinical practice is 10 microCi. Where a whole-body counter is used, an activity of 1 microCi has proved adequate. Even at an administered activity of 25 microCi, the absorbed dose is small compared with established techniques of investigating the gastrointestinal tract.

  11. Absorbed dose to man from the Se-75 labeled conjugated bile salt SeHCAT: concise communication

    SciTech Connect

    Soundy, R.G.; Simpson, J.D.; Ross, H.M.; Merrick, M.V.

    1982-02-01

    The absorbed radiation dose that would result from the oral or intravenous administration of SeHCAT (23-(/sup 75/Se)selena-25-homotaurocholate) has been calculated using the MIRD tables and formulas and data from measurements of whole-body distribution and from long-term whole-body counting in rats, mice, and man. When SeHCAT is administered to normal subjects, the gallbladder is the critical organ, receiving 12 mrad (oral dose) or 22 mrad (i.v.) per microcurie. The whole-body dose is 1 mrad/..mu..Ci, whatever the route of administration. In severe hepatic failure the liver might receive 200 mrad/..mu..Ci. The activity likely to be used in routine clinical practice is 10 ..mu..Ci. Where a whole-body counter is used, an activity of 1 ..mu..Ci has proved adequate. Even at an administered activity of 25 ..mu..Ci, the absorbed dose is small compared with established techniques of investigating the gastrointestinal tract.

  12. Reassignment of the O{sub Se}−V{sub Cd} complex in CdSe

    SciTech Connect

    Bastin, Dirk; Lavrov, E. V.; Weber, J.

    2014-02-21

    An IR absorption study of CdSe single crystals is presented. The as-received material revealed three absorption lines at 1094.2, 1107.5, and 1126.3 cm{sup −1}, which were previously assigned to the O{sub Se}−V{sub Cd} complex [G. Chen et al., Phys. Rev. Lett. 101, 195502 (2008)] We show that each of the lines is accompanied by a number of weaker satellites with intensities which match the natural abundances of sulfur isotopes. In contrast to the original identification it is suggested that these peaks are local vibrational modes of a SO{sub n} complex. The three modes correspond to different orientations of the complex in the CdSe lattice. Arguments are presented in favor of 2 oxygen atoms (n = 2) in the complex. Measurements with uniaxial stress applied to the samples revealed defect symmetries and activation energies for the defect reorientation. The complex was found to be stable up to 750 °C.

  13. Aqueous synthesis of high bright and tunable near-infrared AgInSe2-ZnSe quantum dots for bioimaging.

    PubMed

    Che, Dongchen; Zhu, Xiaoxu; Wang, Hongzhi; Duan, Yourong; Zhang, Qinghong; Li, Yaogang

    2016-02-01

    Efficient synthetic methods for near-infrared quantum dots with good biophysical properties as bioimaging agents are urgently required. In this work, a simple and fast synthesis of highly luminescent, near-infrared AgInSe2-ZnSe quantum dots (QDs) with tunable emissions in aqueous media is reported. This method avoids high temperature and pressure and organic solvents to directly generate water-dispersible AgInSe2-ZnSe QDs. The photoluminescence emission peak of the AgInSe2-ZnSe QDs ranged from 625 to 940nm, with quantum yields up to 31%. The AgInSe2-ZnSe QDs with high quantum yield, near-infrared and low cytotoxic could be used as good cell labels, showing great potential applications in bio-imaging.

  14. Aqueous synthesis of high bright and tunable near-infrared AgInSe2-ZnSe quantum dots for bioimaging.

    PubMed

    Che, Dongchen; Zhu, Xiaoxu; Wang, Hongzhi; Duan, Yourong; Zhang, Qinghong; Li, Yaogang

    2016-02-01

    Efficient synthetic methods for near-infrared quantum dots with good biophysical properties as bioimaging agents are urgently required. In this work, a simple and fast synthesis of highly luminescent, near-infrared AgInSe2-ZnSe quantum dots (QDs) with tunable emissions in aqueous media is reported. This method avoids high temperature and pressure and organic solvents to directly generate water-dispersible AgInSe2-ZnSe QDs. The photoluminescence emission peak of the AgInSe2-ZnSe QDs ranged from 625 to 940nm, with quantum yields up to 31%. The AgInSe2-ZnSe QDs with high quantum yield, near-infrared and low cytotoxic could be used as good cell labels, showing great potential applications in bio-imaging. PMID:26513730

  15. Investigation of the physical properties of specimens of the system La/sub 2/Se/sub 3/-PbSe

    SciTech Connect

    Nasibov, I.O.; Sultanov, T.I.; Shafagatova, G.G.; Abilov, C.I.

    1987-08-01

    The authors have investigated the temperature dependences of the electrical conductivity and coefficient of thermoemf of La/sub 2/PbSe/sub 4/, La/sub 2/Pb/sub 4/Se/sub 7/, and (La/sub 2/Se/sub 3/)/sub x/(PbSe)/sub 1-x/ (x = 0.02, 0.03) over a wide range of temperatures. It is established that the ternary compounds La/sub 2/PbSe/sub 4/ and La/sub 2/Pb/sub 4/Se/sub 7/ are p-type semiconductors with forbidden-band widths of 1.26 and 0.88 eV respectively. The solid solutions (La/sub 2/Se/sub 3/)/sub x/(PbSe)/sub 1-x/ are also semiconductors with donor and acceptor levels, the positions of which in the forbidden band do not depend on the composition.

  16. Template-engaged synthesis of RuSe 2 and Pd 17Se 15 nanotubes by reacting precursor salts with selenium nanowires

    NASA Astrophysics Data System (ADS)

    Jiang, Xuchuan; Mayers, Brian; Wang, Yuliang; Cattle, Bryan; Xia, Younan

    2004-02-01

    In the present work, nanowires of trigonal selenium ( t-Se) were reacted with Ru(acac) 3 and Pd(acac) 2 (or PdCl 2) to generate RuSe 2 and Pd 17Se 15 on the surface of each t-Se nanowire as a uniform, conformal sheath. The unreacted cores of selenium could be evaporated by heating the as-synthesized Se@RuSe 2 and Se@Pd 17Se 15 nanocables to yield selenide nanotubes with their typical wall-thickness around 6 nm. This template-engaged approach allowed for the production of both nanocables and nanotubes in a relatively large scale, and is believed to be able to get extended to synthesize other chalcogenides as tubular nanostructures.

  17. Long-wave phonons in ZnSe-BeSe mixed crystals: Raman scattering and percolation model

    NASA Astrophysics Data System (ADS)

    Pagès, O.; Ajjoun, M.; Tite, T.; Bormann, D.; Tournié, E.; Rustagi, K. C.

    2004-10-01

    We extend to longitudinal-optical (LO) phonons the percolation model set for the basic understanding of the atypical transverse-optical (TO) one-bond→two-mode behavior observed by Raman scattering in the Be-Se spectral range of the random Zn1-xBexSe alloy (0⩽x⩽1) , which opens the class of mixed crystals with contrast in the bond stiffness. The study is supported by contour modeling of the TO and LO Raman line shapes. This is achieved via application of the Hon and Faust treatment to a version of the modified-random-element-isodisplacement model generalized to multioscillators. While the TO signal clearly discriminates between Be-Se vibrations within the hard Be -rich region and the soft Zn -rich one, complexity arises in the LO symmetry due to vibration coupling via the 1ong-range longitudinal polarization field. In particular this generates a massive transfer of oscillator strength from the low-frequency (LO-) (hard, soft)-mixed mode to the high-frequency (LO+) one, which results in an apparent LO+ single-mode behavior. Moreover the contrasts between the Zn-Se and Be-Se bond lengths and bond stiffness are proposed to force a Verleur and Barker-like (VB) discrete multimode Raman response from each region. Accordingly LO- and LO+ intramode transfers of oscillator strength superimpose to the LO-→LO+ intermode one. This accounts for the spectacular distortions of the LO+ line shape. On the whole, the puzzling LO behavior can be regarded as the result of a cooperative phenomenon between two discrete assemblies of polar LO phonons, driven by the long-range longitudinal polarization field. Also, the Verleur and Barker description accounts for subtle unexplained behaviors in the TO symmetry. More generally it appears to provide a much attractive area for the discussion of the asymmetries of the TO and LO Raman line shapes in random alloys, as a possible alternative to the much debated spatial correlation model or to internal/external strain effects.

  18. SE Asian-West Pacific Tectonics and Mantle Structure

    NASA Astrophysics Data System (ADS)

    Hall, Robert

    2010-05-01

    It is probably impossible to interpret mantle structure without having a tectonic model first - which immediately raises some difficult questions. Particularly problematic is a reference frame. For Eurasia it is common, and probably reasonable, to assume little Cenozoic movement of the lithosphere relative to the underlying mantle, but can this assumption be justified for the Mesozoic? Even for the Cenozoic a small drift could mean significant misinterpretation of cause and consequence. Bearing this caveat in mind, for SE Asia and the adjacent West Pacific the upper mantle contains a record of little more than the last 15 Ma, with a few exceptions. The obvious features of subduction are recorded, with some interesting details, but some convincing subduction zones are not seen. The upper mantle structure shows us that we cannot yet see such details, such as multiple nearby subduction systems, tearing slabs, or rollback, deeper in the mantle or in parts of the region where resolution of tomographic models is poor. The lower mantle therefore displays only a crude record of tectonic history and probably nothing older than Mesozoic. On the other hand, the tectonic history we find recorded at the surface at the boundaries of SE Asia with the Indian-Australian and Pacific plates is also incomplete and problematical. In many areas the major plates have no clear-cut boundaries, the structure of the upper crust is much more complex than the deeper lithosphere, and for the continental regions it seems that the upper parts of the deforming lithosphere may be completely decoupled, within the crust, from what is beneath. SE Asia is not a plate in any meaningful sense, but is a heterogeneous region of weak and strong parts. There has been a long history of subduction beneath SE Asia. The deep high velocity anomaly in the lower mantle beneath the region appears to be a composite entity that formed by subduction in the Mesozoic and then influenced the position of later subduction

  19. Fractal structures of dendrites in GaSe crystals

    NASA Astrophysics Data System (ADS)

    Kolesnikov, N. N.; Borisenko, E. B.; Borisenko, D. N.; Bozhko, S. I.

    2008-07-01

    Solidification of melts at substantial supercooling is associated with instability on the growth front. This causes growth of dendrites, which form as a branched tree in a crystal. In the layered melt-grown GaSe crystals dendrites are observed, if growth rates are rather high [N.N. Kolesnikov, E.B. Borisenko, D.N. Borisenko, V.K. Gartman, Influence of growth conditions on microstructure and properties of GaSe crystals, J. Crystal Growth 300 (2) (2007) 294-298]. Models based on solution of the thermal diffusion problem are traditionally used to describe dendrite growth. Solution of this problem requires information about several physical parameters, such as diffusion coefficient, heat conductivity coefficient and supercooling at the solid/liquid interface. The study of scale invariance of dendrites formed in a crystal provides a new approach to solution of the dynamic growth problem. The calculated fractal dimensionality of the experimentally observed dendrites in GaSe crystals is D=1.7. It coincides with dimensionality of the clusters obtained through computer simulation in terms of the model of diffusion-limited aggregation (DLA). This result provides a new approach to description of the dynamics of dendrite growth. We have shown that the dendrite growth mechanism in the layered semiconductor crystals can be described by a two-dimensional DLA model. It is shown that probabilistic simulation can be used to show the development of a dendrite in any material. In contrast to the classical theories of dendrite growth, this approach does not require information on physical parameters.

  20. First Observation of ^60Ge and ^64Se

    NASA Astrophysics Data System (ADS)

    Stolz, Andreas

    2004-10-01

    The neutron-deficient nuclei ^60Ge and ^64Se were observed for the first time following the fragmentation of ^78Kr. This is the first observation of new proton-rich nuclei below Z=50 in over three years. A primary beam of 140-MeV/nucleon ^78Kr was produced using the Coupled Cyclotron Facility and fragmented in a Be target. The secondary neutron-deficient fragments were separated by the A1900 fragment separator [1] and stopped in a stack of silicon PIN diodes. The fragments were identified by a measurement of energy loss, total energy, and time-of-flight. ^60Ge is the last nucleus along the proton dripline lighter than cadmium which is predicted to be bound (S_2p = 50 ± 240 keV) by the latest atomic mass evaluation [2] and which has not yet been observed. Theoretical calculations predict ^60Ge to be bound with respect to two-proton emission by 167(141) keV [3] and 630 keV [4], while ^64Se is predicted not to be bound [2]. >From the number of observed events of ^60Ge and ^64Se the production cross section and lifetime will be estimated. No events of ^59Ga and ^63As were observed confirming that these nuclei are unbound with respect to proton emission and upper limits of the lifetime can be established. [1] D. J. Morrissey, B. M. Sherrill, M. Steiner, A. Stolz, and I. Wiedenhover, Nucl. Instrum. Methods Phys. Res. B 204, 90 (2003). [2] G. Audi, A. H. Wapstra, and C. Thibault, Nucl. Phys. A729, 337 (2003). [3] W. E. Ormand, Phys. Rev. C 55, 2407 (1997). [4] M.V. Stoitsov, J. Dobaczewski, W. Nazarewicz, S. Pittel, and D. J. Dean, Phys. Rev. C 68, 054312 (2003).

  1. Theoretical and experimental investigation of stability and spectra of doped Ag:ZnSe nanocrystals.

    PubMed

    Xu, Shuhong; Wang, Chunlei; Wang, Zhuyuan; Cui, Yiping

    2014-04-01

    In experiment, doped Ag:ZnSe nanocrystals (NCs) had better stability than that of ZnSe nanocrystals under ambient atmospheres in the presence of air and light illumination. However, it is difficult to explain the mechanism of better stability of Ag:ZnSe nanocrystals from the experiment perspective for doped nanocrystals are more unstable than corresponding pure nanocrystals in general. Using B3LYP/LANL2DZ method, we have investigated the geometrical structures, bonding characters, and molecular orbitals (MOs) of hexagonal and tetrahedral Ag doped ZnSe structures in theory. The results showed that the good stability of Ag:ZnSe nanocrystals can be attributed to the stronger binding between Ag and Se. Moreover, we have proved that Ag doped ZnSe nanocrystals synthesized in experiment should be substituting doped but not vacuity doped. Substituting Ag doped ZnSe molecules have the same configuration as that of the ZnSe structure, but vacuity doped Ag:ZnSe have completely different configuration than ZnSe structure due to the big size of Ag atom. In addition, through contrast of MO of ZnSe and Ag doped ZnSe, we have testified that Ag easily formed bonds with Se. The high binding energy and high probability of forming bonds with Se atom make Ag doped ZnSe nanocrystals have better stability than that of ZnSe nanocrystals. PMID:24633779

  2. Refining the W1 and SE1 Facilities

    NASA Technical Reports Server (NTRS)

    Chambers, Rodney D.

    2004-01-01

    The Engine Research Building (ERB) houses more than 60 test rigs that study all aspects of engine development. By working with Mary Gibson in the SE1 and W1A Turbine Facilities, I became aware of her responsibilities and better acquainted with the inner workings of the ERB. The SE1 Supersonic/Subsonic Wind Tunnel Facility contains 2 small wind tunnels. The first tunnel uses an atmospheric inlet, while the second uses treated 40-psig air. Both of the tunnels are capable of subsonic and supersonic operation. An auxiliary air supply and exhaust piping providing both test sections with suction, blowing, and crossfire capabilities. The current configuration of SE1 consists of a curved diffuser that studies the blockage along the endwalls. The W1A Low Speed Compressor Facility provides insight for the complex flow phenomena within its 4-stage axial compressor, sand the data obtained from W 1A is used to develop advanced models for fluid dynamic assessment. W1A is based off of a low speed research compressor developed by GE in the 1950's. This compressor has a removable casing treatment under rotor 1, which allows for various tip treatment studies. The increased size and low speed allows instrumentation to be located in the compressor s complex flow paths. Air enters the facility through a filtered roof vent, conditioned for temperature and turbulence, and then passed through the compressor W1A is described as a dynamic facility with many projects taking place simultaneously. This current environment makes it challenging to follow the various affairs that are taking place within the area. During my first 4 weeks at the NASA Glenn Research Center, I have assisted Mary Gibson in multiple tasks such as facility documents, record keeping, maintenance and upgrades. The facility has lube systems for its gearbox and compressor. These systems are critical in the successful operation of the facility. I was assigned the task of creating a facility estimate list, which included the

  3. Polarity continuation and frustration in ZnSe nanospirals

    PubMed Central

    Li, Luying; Tu, Fanfan; Jin, Lei; Choy, Wallace C. H.; Gao, Yihua; Wang, Jianbo

    2014-01-01

    ZnSe nanospirals including structures with polarity continuation and polarity frustration are simultaneously observed at atomic resolution. Through careful analysis of polarity within each dumbbell based on aberration-corrected high-angle annular-dark-field imaging, polarity continuation across parallel polytype interfaces as well as the surrounding Z-shape faulted dipoles is verified. Moreover, polarity frustration across regions with different stacking sequence, which would lead to accumulations of boundary interface charges in the triangular-shaped mixed regions with potential optoelectronic applications, is carefully studied. PMID:25502957

  4. Actinic reticuloid imitating Sézary syndrome.

    PubMed

    Pacheco, David; Fraga, Ana; Travassos, Ana Rita; Antunes, Joana; Freitas, Joaao; Soares de Almeida, Luis; Filipe, Paulo

    2012-09-01

    Actinic reticuloid is a rare chronic idiopathic photosensitive dermatosis belonging to the spectrum of chronic actinic dermatitis and may be mistaken for cutaneous T-cell lymphoma. We report the case of an erythrodermic patient, initially diagnosed with Sézary syndrome, treated with chlorambucil and prednisolone. Later on, a photobiological study demonstrated photosensitivity to UVB, UVA, and visible light. The clinical picture, histological findings resembling lymphoma, and the results of the photobiological study established the diagnosis of actinic reticuloid. Currently the patient is avoiding sun exposure and being medicated with azathioprine and prednisolone, and is showing sustained improvement. PMID:23267873

  5. Fano q reversal in topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Dordevic, S. V.; Foster, G. M.; Wolf, M. S.; Stojilovic, N.; Lei, H.; Petrovic, C.; Chen, Z.; Li, Z. Q.; Tung, L. C.

    We studied magneto-optical response of a canonical topological insulator Bi2Se3 with the goal of addressing a controversial issue of electron-phonon coupling. Magnetic-field induced modifications of reflectance are very pronounced in the infrared part of the spectrum, indicating strong electron-phonon coupling. This coupling causes an asymmetric line-shape of the 60 cm-1 phonon mode, and is analyzed within the Fano formalism. The analysis reveals that the Fano asymmetry parameter (q) changes sign when the cyclotron resonance is degenerate with the phonon mode. To the best of our knowledge this is the first example of magnetic field driven q-reversal.

  6. Normal state incoherent pseudogap in FeSe superconductor

    NASA Astrophysics Data System (ADS)

    Craco, Luis; Laad, Mukul S.

    2016-05-01

    The normal state of Iron chalcogenide superconductors show a range of unconventional features. Bad-metallic resistivity and proximity to insulating state manifest themselves in spectral and transport responses. In particular, obervation of low-energy pseudogap feature in the normal state raises the issue of the nature of processes underpinning its emergence as well as its relation to unconventional superconductivity. Here, using the LDA+DMFT method, we show how correlation-induced orbital-selective pseudogap-like physics underpin these incoherent features in stoichimetric and electron-doped FeSe superconductor. We discuss the pseudogap regime microscopically, along with implications for the superconductive instability.

  7. The sublimation kinetics of GeSe single crystals

    NASA Technical Reports Server (NTRS)

    Irene, E. A.; Wiedemeier, H.

    1975-01-01

    The sublimation kinetics of (001) oriented GeSe single crystal platelets was studied by high-temperature mass spectroscopy, quantitative vacuum microbalance techniques, and hot stage optical microscopy. For a mean experimental temperature of 563 K, the activation enthalpy and entropy are found to equal 32.3 kcal/mole and 19.1 eu, respectively. The vaporization coefficient is less than unity for the range of test temperatures, and decreases with increasing temperature. The combined experimental data are correlated by means of a multistep surface adsorption mechanism.

  8. Synthesis and characterization of Bi-Te-Se thermoelectric materials

    SciTech Connect

    Tripathi, S. K.; Kumari, Ankita; Ridhi, R.; Kaur, Jagdish

    2015-08-28

    Bismuth Telluride (Bi{sub 2}Te{sub 3}) and its related alloys act as a promising thermoelectric material and preferred over other thermoelectric materials due to their high stability and efficiency under ambient conditions. In the present work, we have reported economical, environment friendly and low-temperature aqueous chemical method for the synthesis of Bi-Se-Te alloy. The prepared samples are characterized by X-Ray Diffraction to investigate the structural properties and UV-Visible spectroscopy for the spectroscopic analysis. The absorption spectrum reveals the sensitivity in the ultraviolet as well as in visible region.

  9. Mantle structure and tectonic history of SE Asia

    NASA Astrophysics Data System (ADS)

    Hall, Robert; Spakman, Wim

    2015-09-01

    Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia and including Malaysia, parts of the Philippines, New Guinea and northern Australia. We begin with an explanation of seismic tomography and causes of velocity anomalies in the mantle, and discuss assessment of model quality for tomographic models created from P-wave travel times. We then introduce the global P-wave velocity anomaly model UU-P07 and the tectonic model used in this paper and give an overview of previous interpretations of mantle structure. The slab-related velocity anomalies we identify in the upper and lower mantle based on the UU-P07 model are interpreted in terms of the tectonic model and illustrated with figures and movies. Finally, we discuss where tomographic and tectonic models for SE Asia converge or diverge, and identify the most important conclusions concerning the history of the region. The tomographic images of the mantle record subduction beneath the SE Asian region to depths of approximately 1600 km. In the upper mantle anomalies mainly record subduction during the last 10 to 25 Ma, depending on the region considered. We interpret a vertical slab tear crossing the entire upper mantle north of west Sumatra where there is a strong lateral kink in slab morphology, slab holes between c.200-400 km below East Java and Sumbawa, and offer a new three-slab explanation for subduction in the North Sulawesi region. There is a different structure in the lower mantle compared to the upper mantle and the deep structure changes from west to east. What was imaged in earlier models as a broad and deep anomaly below SE Asia has a clear internal structure and we argue that many features can be identified as older subduction zones. We identify remnants of slabs

  10. Bi-Se doped with Cu, p-type semiconductor

    DOEpatents

    Bhattacharya, Raghu Nath; Phok, Sovannary; Parilla, Philip Anthony

    2013-08-20

    A Bi--Se doped with Cu, p-type semiconductor, preferably used as an absorber material in a photovoltaic device. Preferably the semiconductor has at least 20 molar percent Cu. In a preferred embodiment, the semiconductor comprises at least 28 molar percent of Cu. In one embodiment, the semiconductor comprises a molar percentage of Cu and Bi whereby the molar percentage of Cu divided by the molar percentage of Bi is greater than 1.2. In a preferred embodiment, the semiconductor is manufactured as a thin film having a thickness less than 600 nm.

  11. CdSe quantum dot formation: alternative paths to relaxation of a strained CdSe layer and influence of the capping conditions.

    PubMed

    Robin, I C; Aichele, T; Bougerol, C; André, R; Tatarenko, S; Bellet-Amalric, E; Van Daele, B; Van Tendeloo, G

    2007-07-01

    CdSe/ZnSe quantum dot formation is investigated by studying different steps of the growth. To precisely control the critical thickness of CdSe grown on a ZnSe buffer layer, the CdSe self-regulated growth rate in atomic layer epitaxy growth mode is determined by reflection high-energy electron diffraction (RHEED) measurements for a temperature range between 180 and 280 °C. Then, the two-dimensional-three-dimensional (2D-3D) transition of a strained CdSe layer on (001)-ZnSe induced by the use of amorphous selenium is studied. The formation of CdSe islands is found when 3 monolayers (ML) of CdSe are deposited. When only 2.5 ML of CdSe are deposited, another relaxation mechanism is observed, leading to the appearance of strong undulations on the surface. We also studied the evolution of the surface morphology when 2.7 ML are deposited, to study the boundary between those two phenomena. The influence of capping on quantum dot morphology is investigated. It is found that cadmium is redistributed within the layer during capping. Our results show that the cadmium distribution after capping depends on the capping temperature and on the strain of the CdSe layer. Cadmium incorporation after capping is also studied. It is found that the amount of incorporated cadmium depends on the strain of the CdSe layer before capping.

  12. Wide emission-tunable CdTeSe/ZnSe/ZnS core–shell quantum dots and their conjugation with E. coli O-157

    SciTech Connect

    Zhou, Haifeng; Zhou, Guangjun; Zhou, Juan; Xu, Dong; Zhang, Xingshuang; Kong, Peng; Yang, Zhongsen

    2015-05-15

    Highlights: • QDs with variety morphology were obtained via an injection controlled process. • 3-D PL spectra of core–shell QDs show different excitation wavelength dependence. • The PL intensity of QDs with ZnSe transition layer increases dramatically. • Core–shell QDs were processed into aqueous phase and conjugated with E. coli O-157. - Abstract: Wide emission-tunable and different morphological alloyed CdTeSe quantum dots (QDs), CdTeSe/ZnS and CdTeSe/ZnSe/ZnS core–shell QDs were successfully synthesized via an injection controlled process. The effect of injection procedure and reaction temperature were systematically discussed and the growth mechanism was proposed. Most efficient PL wavelength was correlated with reaction time and temperature. The 3-D PL spectra of spherical bare CdTeSe and core–shell QDs with different passivation showed different excitation wavelength dependency. The PL intensity of CdTeSe/ZnSe/ZnS core–shell QDs increased greatly in comparison with that of CdTeSe and CdTeSe/ZnSe QDs. ZnSe transition layer played an important role in improving the PL intensity by providing a smoothened interface and gradient band offsets. The core–shell QDs were transferred into aqueous phase and successfully conjugated with Escherichia coli O-157. The proposed phase-transfer and bio-labeling strategy may be applicable to various QDs with different compositions.

  13. Selenium bioaccessibility in stomach, small intestine and colon: Comparison between pure Se compounds, Se-enriched food crops and food supplements.

    PubMed

    Lavu, Rama V Srikanth; Van De Wiele, Tom; Pratti, Varalakshmi L; Tack, Filip; Du Laing, Gijs

    2016-04-15

    Selenium (Se) is an essential nutrient for humans as it plays an important role in glutathione peroxidase (GPx) activity. Moreover, it may reduce cancer risks. The objective of this work was to examine in vitro the bioaccessibility of Se in three different Se-enriched food supplements and two different Se-enriched food crops, with reference to two pure Se standards, and changes in its speciation during intestinal digestion. Selenate was found to be stable throughout the entire digestion, whereas incubation of selenomethionine resulted in the chemical and microbial production of minor metabolites. The bioaccessibility of Se in Se-enriched food supplements and food crops was found to be highest in the small intestine. Compared to SelenoPrecise and Se-ACE tablets, a yoghurt-based supplement exhibited a much lower Se bioaccessibility, possibly due to the presence of nano- or microparticles of elemental Se. Colon microbiota were found to primarily affect Se bioaccessibility in the colon environment, with the presence of inactivated microbiota resulting in a higher bioaccessibility. A higher potential of Se to reach the colon and become accessible in this phase may result in beneficial effects on the colon health.

  14. Selenium hyperaccumulator plants Stanleya pinnata and Astragalus bisulcatus are colonized by Se-resistant, Se-excluding wasp and beetle seed herbivores.

    PubMed

    Freeman, John L; Marcus, Matthew A; Fakra, Sirine C; Devonshire, Jean; McGrath, Steve P; Quinn, Colin F; Pilon-Smits, Elizabeth A H

    2012-01-01

    Selenium (Se) hyperaccumulator plants can concentrate the toxic element Se up to 1% of shoot (DW) which is known to protect hyperaccumulator plants from generalist herbivores. There is evidence for Se-resistant insect herbivores capable of feeding upon hyperaccumulators. In this study, resistance to Se was investigated in seed chalcids and seed beetles found consuming seeds inside pods of Se-hyperaccumulator species Astragalus bisulcatus and Stanleya pinnata. Selenium accumulation, localization and speciation were determined in seeds collected from hyperaccumulators in a seleniferous habitat and in seed herbivores. Astragalus bisulcatus seeds were consumed by seed beetle larvae (Acanthoscelides fraterculus Horn, Coleoptera: Bruchidae) and seed chalcid larvae (Bruchophagus mexicanus, Hymenoptera: Eurytomidae). Stanleya pinnata seeds were consumed by an unidentified seed chalcid larva. Micro X-ray absorption near-edge structure (µXANES) and micro-X-Ray Fluorescence mapping (µXRF) demonstrated Se was mostly organic C-Se-C forms in seeds of both hyperaccumulators, and S. pinnata seeds contained ∼24% elemental Se. Liquid chromatography-mass spectrometry of Se-compounds in S. pinnata seeds detected the C-Se-C compound seleno-cystathionine while previous studies of A. bisulcatus seeds detected the C-Se-C compounds methyl-selenocysteine and γ-glutamyl-methyl-selenocysteine. Micro-XRF and µXANES revealed Se ingested from hyperaccumulator seeds redistributed throughout seed herbivore tissues, and portions of seed C-Se-C were biotransformed into selenocysteine, selenocystine, selenodiglutathione, selenate and selenite. Astragalus bisulcatus seeds contained on average 5,750 µg Se g(-1), however adult beetles and adult chalcid wasps emerging from A. bisulcatus seed pods contained 4-6 µg Se g(-1). Stanleya pinnata seeds contained 1,329 µg Se g(-1) on average; however chalcid wasp larvae and adults emerging from S. pinnata seed pods contained 9 and 47 µg Se g(-1). The

  15. Environmental Selenium Transformations: Distinguishing Abiotic and Biotic Factors Influencing Se Redox Transformations

    NASA Astrophysics Data System (ADS)

    Rosenfeld, C.; Kenyon, J.; James, B. R.; Santelli, C. M.

    2014-12-01

    Worldwide, selenium (Se) is proving to be a significant environmental concern, with many anthropogenic activities (e.g. coal mining and combustion, phosphate mining and agricultural irrigation) releasing potentially hazardous concentrations into surface and subsurface ecosystems. The US EPA is currently considering aquatic Se regulations, however no guidelines exist for excess soil Se, despite its ability to act as a persistent Se source. Various abiotic and biological processes mediate Se oxidation/reduction (redox) transformations in soils, thus influencing its solubility and bioavailability. In this research we assess (1) the ability of metal-transforming fungal species to aerobically reduce Se (Se (IV and/or VI) to Se(0)), and (2) the relative contribution of biotic and abiotic pathways for aerobic Se transformation. The primary objective of this research is to determine what abiotic and biotic factors enhance or restrict Se bioavailability. Results indicate that fungal-mediated Se reduction may be quite widespread, with at least 7 out of 10 species of known Mn(II)-oxidizing fungi isolated from metal impacted environments also identified as capable of aerobically reducing Se(IV) and/or Se(VI) to Se(0). Increasing concentrations of selenite (SeO32-; Se(IV)) and selenate (SeO42-; Se(VI)) generally reduced fungal growth rates, although selenate was more likely to inhibit fungal growth than selenite. To study oxidation, Se(0) was combined with Mn(III/IV) (hydr)oxides (henceforth referred to as Mn oxides), Se-transforming fungi (Alternaria alternata), and oxalic acid to mimic Se biogeochemistry at the plant-soil interface. Increased pH in the presence of fungi (7.2 with fungi, 6.8 without fungi after 24 days) was observed. Additionally, a slight decrease in redox potential was measured for incubations without Mn oxides (236 mV with Mn oxides, 205 mV without Mn oxides after 24 days), indicating that Mn oxides may enhance Se oxidation. Elemental Se oxidation rates to

  16. Controlled synthesis of ferromagnetic MnSe x particles

    NASA Astrophysics Data System (ADS)

    Sun, Junjie; Li, Chao; Chen, Duo; Kang, Shishou; Liu, Guolei; Yu, Shuyun; Han, Guangbing; Mei, Liangmo

    2016-10-01

    The MnSe x (x = 1,2) nanoparticles were synthesized under hydrothermal condition, by reaction of the reduced selenium and Mn2+ ion in the presence of hydrazine and acetic acid. By precisely controlling the pH value of the solution, a series of MnSe x particles were synthesized. The structure and morphology of as-prepared particles were examined with x-ray diffractometer (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The average sizes of as-prepared particles varied from nanoscale to microscale with pH value increase. Furthermore, the nucleation and growth mechanism associated with pH values were discussed, which can be applied to the hydrothermal synthesis of metal chalcogenide in general. Finally, the optical and magnetic properties of as-prepared particles were measured. All as-made particles exhibit a ferromagnetic behavior with low coercivity and remanence at room temperature. Project supported by the National Basic Research Program of China (Grant No. 2015CB921502), the National Natural Science Foundation of China (Grant Nos. 11474184 and 11627805), the 111 Project (Grant No. B13029), and the Fundamental Research Funds of Shandong University, China.

  17. Charge-induced nematicity in FeSe.

    PubMed

    Massat, Pierre; Farina, Donato; Paul, Indranil; Karlsson, Sandra; Strobel, Pierre; Toulemonde, Pierre; Méasson, Marie-Aude; Cazayous, Maximilien; Sacuto, Alain; Kasahara, Shigeru; Shibauchi, Takasada; Matsuda, Yuji; Gallais, Yann

    2016-08-16

    The spontaneous appearance of nematicity, a state of matter that breaks rotation but not translation symmetry, is one of the most intriguing properties of the iron-based superconductors (Fe SC), and has relevance for the cuprates as well. Establishing the critical electronic modes behind nematicity remains a challenge, however, because their associated susceptibilities are not easily accessible by conventional probes. Here, using FeSe as a model system, and symmetry-resolved electronic Raman scattering as a probe, we unravel the presence of critical charge nematic fluctuations near the structural/nematic transition temperature, [Formula: see text] 90 K. The diverging behavior of the associated nematic susceptibility foretells the presence of a Pomeranchuk instability of the Fermi surface with d-wave symmetry. The excellent scaling between the observed nematic susceptibility and elastic modulus data demonstrates that the structural distortion is driven by this d-wave Pomeranchuk transition. Our results make a strong case for charge-induced nematicity in FeSe. PMID:27482118

  18. Plasmon dynamics in colloidal Cu₂-xSe nanocrystals.

    PubMed

    Scotognella, Francesco; Della Valle, Giuseppe; Srimath Kandada, Ajay Ram; Dorfs, Dirk; Zavelani-Rossi, Margherita; Conforti, Matteo; Miszta, Karol; Comin, Alberto; Korobchevskaya, Kseniya; Lanzani, Guglielmo; Manna, Liberato; Tassone, Francesco

    2011-11-01

    The optical response of metallic nanostructures after intense excitation with femtosecond-laser pulses has recently attracted increasing attention: such response is dominated by ultrafast electron-phonon coupling and offers the possibility to achieve optical modulation with unprecedented terahertz bandwidth. In addition to noble metal nanoparticles, efforts have been made in recent years to synthesize heavily doped semiconductor nanocrystals so as to achieve a plasmonic behavior with spectrally tunable features. In this work, we studied the dynamics of the localized plasmon resonance exhibited by colloidal Cu(2-x)Se nanocrystals of 13 nm in diameter and with x around 0.15, upon excitation by ultrafast laser pulses via pump-probe experiments in the near-infrared, with ∼200 fs resolution time. The experimental results were interpreted according to the two-temperature model and revealed the existence of strong nonlinearities in the plasmonic absorption due to the much lower carrier density of Cu(2-x)Se compared to noble metals, which led to ultrafast control of the probe signal with modulation depth exceeding 40% in transmission. PMID:21939261

  19. Chromium Diffusion Doping on ZnSe Crystals

    NASA Technical Reports Server (NTRS)

    Journigan, Troy D.; Chen, K.-T.; Chen, H.; Burger, A.; Schaffers, K.; Page, R. H.; Payne, S. A.

    1997-01-01

    Chromium doped zinc selenide crystal have recently been demonstrated to be a promising material for near-IR room temperature tunable lasers which have an emission range of 2-3 micrometers. In this study a new diffusion doping process has been developed for incorporation of Cr(+2) ion into ZnSe wafers. This process has been successfully performed under isothermal conditions, at temperatures above 800 C. Concentrations in excess of 10(exp 19) Cr(+2) ions/cu cm, an order of magnitude larger than previously reported in melt grown ZnSe material, have been obtained by diffusion doping, as estimated from optical absorption measurements. The diffusivity was estimated to be about 10(exp -8) sq cm/sec using a thin film diffusion model. Resistivity was derived from current-voltage measurements and in the range of 10(exp 13) and 10(exp 16) omega-cm. The emission spectra and temperature dependent lifetime data will also be presented and discussed.

  20. Phonon anharmonicity and negative thermal expansion in SnSe

    DOE PAGES

    Bansal, Dipanshu; Hong, Jiawang; Li, Chen W.; May, Andrew F.; Porter, Wallace; Hu, Michael Y.; Abernathy, Douglas L.; Delaire, Olivier

    2016-08-09

    In this paper, the anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy,more » in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. Finally, the origin of the anharmonic phonon thermodynamics is linked to the electronic structure.« less

  1. Transport studies in topological insulator Bi2Te2Se

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    Recently, 3D topological insulators, featuring spin helical topological surface states (SS), have attracted strong attention in condensed matter physics. Although the SS have been directly revealed and intensively studied by surface sensitive measurements, such as ARPES and STM, transport measurements remain challenging due to coexistence of the surface and bulk conduction channels and the sensitivity of sample surfaces to ambient exposure. We have grown high quality Bi2Te2Se crystals by the Bridgeman method. Resistance showed an insulating behavior followed by saturation at low temperature, indicating surface conduction. Through magnetotransport measurements, we demonstrated high mobility SS on freshly cleaved crystals. The transport signatures of surface Dirac fermions were uncovered from 2D SdH oscillations and non-linear Hall effect. We have also compared transport properties of the samples before and after exposure to air. A giant cusp in magnetoresistance at zero B field was observed after exposure. Our studies may help understand the interplay between the surface and the bulk conduction channels and the degradation of SS due to environmental exposure. We will also present some experimental results of gate tuning and thermoelectric measurements on Bi2Te2Se. We acknowledge support from DARPA MESO program (Grant N66001-11-1-4107).

  2. Thermodynamic properties of model CdTe/CdSe mixtures

    DOE PAGES

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

    2015-02-20

    We report on the thermodynamic properties of binary compound mixtures of model groups II–VI semiconductors. We use the recently introduced Stillinger–Weber Hamiltonian to model binary mixtures of CdTe and CdSe. We use molecular dynamics simulations to calculate the volume and enthalpy of mixing as a function of mole fraction. The lattice parameter of the mixture closely follows Vegard's law: a linear relation. This implies that the excess volume is a cubic function of mole fraction. A connection is made with hard sphere models of mixed fcc and zincblende structures. We found that the potential energy exhibits a positive deviation frommore » ideal soluton behaviour; the excess enthalpy is nearly independent of temperatures studied (300 and 533 K) and is well described by a simple cubic function of the mole fraction. Using a regular solution approach (combining non-ideal behaviour for the enthalpy with ideal solution behaviour for the entropy of mixing), we arrive at the Gibbs free energy of the mixture. The Gibbs free energy results indicate that the CdTe and CdSe mixtures exhibit phase separation. The upper consolute temperature is found to be 335 K. Finally, we provide the surface energy as a function of composition. Moreover, it roughly follows ideal solution theory, but with a negative deviation (negative excess surface energy). This indicates that alloying increases the stability, even for nano-particles.« less

  3. Plasmon dynamics in colloidal Cu₂-xSe nanocrystals.

    PubMed

    Scotognella, Francesco; Della Valle, Giuseppe; Srimath Kandada, Ajay Ram; Dorfs, Dirk; Zavelani-Rossi, Margherita; Conforti, Matteo; Miszta, Karol; Comin, Alberto; Korobchevskaya, Kseniya; Lanzani, Guglielmo; Manna, Liberato; Tassone, Francesco

    2011-11-01

    The optical response of metallic nanostructures after intense excitation with femtosecond-laser pulses has recently attracted increasing attention: such response is dominated by ultrafast electron-phonon coupling and offers the possibility to achieve optical modulation with unprecedented terahertz bandwidth. In addition to noble metal nanoparticles, efforts have been made in recent years to synthesize heavily doped semiconductor nanocrystals so as to achieve a plasmonic behavior with spectrally tunable features. In this work, we studied the dynamics of the localized plasmon resonance exhibited by colloidal Cu(2-x)Se nanocrystals of 13 nm in diameter and with x around 0.15, upon excitation by ultrafast laser pulses via pump-probe experiments in the near-infrared, with ∼200 fs resolution time. The experimental results were interpreted according to the two-temperature model and revealed the existence of strong nonlinearities in the plasmonic absorption due to the much lower carrier density of Cu(2-x)Se compared to noble metals, which led to ultrafast control of the probe signal with modulation depth exceeding 40% in transmission.

  4. Linear magnetoresistance in Ag2+δSe thin films

    NASA Astrophysics Data System (ADS)

    von Kreutzbruck, M.; Lembke, G.; Mogwitz, B.; Korte, C.; Janek, J.

    2009-01-01

    In the nonstoichiometric low-temperature phase of silver selenide a very small silver excess within the semiconducting silver selenide matrix in the order of 0.01% is sufficient to generate a linear magnetoresistance (LMR) of more than 300% at 5 T, which does not saturate at fields up to 60 T. Different theoretical models have been proposed to explain this unusual magnetoresistance (MR) behavior, among them a random resistor network consisting of four-terminal resistor units. According to this model the LMR and the crossover field from linear to quadratic behavior are primarily controlled by both the spatial distribution of the charge-carrier mobility and its average value, being essentially functions of the local and average compositions. Here we report measurements on silver-rich thin AgxSe films with a thickness between 20 nm and 2μm , which show an increasing average mobility in conjunction with an enhanced MR for increasing film thickness. We found a linear scaling between the size of the transverse LMR and the crossover field, as predicted by the theory. For films thinner than about 100 nm the MR with field directed in the sample plane shows a breakdown of the LMR, revealing the physical length scale of the inhomegeneities in thin AgxSe devices.

  5. Thermodynamic properties of model CdTe/CdSe mixtures

    SciTech Connect

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

    2015-02-20

    We report on the thermodynamic properties of binary compound mixtures of model groups II–VI semiconductors. We use the recently introduced Stillinger–Weber Hamiltonian to model binary mixtures of CdTe and CdSe. We use molecular dynamics simulations to calculate the volume and enthalpy of mixing as a function of mole fraction. The lattice parameter of the mixture closely follows Vegard's law: a linear relation. This implies that the excess volume is a cubic function of mole fraction. A connection is made with hard sphere models of mixed fcc and zincblende structures. We found that the potential energy exhibits a positive deviation from ideal soluton behaviour; the excess enthalpy is nearly independent of temperatures studied (300 and 533 K) and is well described by a simple cubic function of the mole fraction. Using a regular solution approach (combining non-ideal behaviour for the enthalpy with ideal solution behaviour for the entropy of mixing), we arrive at the Gibbs free energy of the mixture. The Gibbs free energy results indicate that the CdTe and CdSe mixtures exhibit phase separation. The upper consolute temperature is found to be 335 K. Finally, we provide the surface energy as a function of composition. Moreover, it roughly follows ideal solution theory, but with a negative deviation (negative excess surface energy). This indicates that alloying increases the stability, even for nano-particles.

  6. Two-Photon Photochemistry of CdSe Quantum Dots.

    PubMed

    Zeng, Youhong; Kelley, David F

    2015-10-27

    The two-photon photochemistry of CdSe quantum dots (QDs) has been systematically studied. We find that upon intense irradiation CdSe quantum dots that absorb two or more visible photons undergo photodarkening. The quantum yield for this process is on the order of 6% in chloroform and much smaller in nonpolar solvents, such as octane. An analysis of the energetics indicates that, following two-photon excitation, the biexciton undergoes an Auger process producing a hot hole. This hot hole is ejected to a surface-bound TOP ligand, forming a QD(-)/TOP(+) contact ion pair that separates in chloroform, but not in octane. The charged and deligated QD is dark, resulting in the overall photodarkening. This photodarkening reaction may or may not be reversible, depending on what other chemical components are in the irradiated solution. The quantum dot concentration dependence and PL decay kinetics indicate that charge recombination occurs rapidly, followed by ligand reattachment and reorganization on a longer (tens of minutes) time scale. The relation of this mechanism to one-photon photochemistry is also discussed.

  7. Neutron detection with LiInSe2

    NASA Astrophysics Data System (ADS)

    Bell, Zane W.; Burger, A.; Matei, Liviu; Groza, Michael; Stowe, Ashley; Tower, Joshua; Kargar, Alireza; Hong, Huicong

    2015-08-01

    The detection of thermal neutrons has traditionally been accomplished with 3He-tubes, but with the recent shortage of 3He, much research has gone into finding suitable replacements. Both relatively inefficient 10B- and 6LiF-coated silicon diodes and HgI2 have been known for many years, and engineered structures in Si that have been filled with 10B and 6LiF have shown promise. These devices are intended to realize an optimal juxtaposition of neutron-sensitive material and semiconductor and thereby simulate a semiconductor containing B or Li. Such material has been realized for the first time in the form of 6LiInSe2 in which collectable charge from the 6Li(n,t) reaction indicates a neutron event. In this paper we report neutron and gamma responses of 6LiInSe2, we show pulse height spectra from pure gamma sources and from a thermal neutron source, and we derive the μτ product from the position of spectral features as a function of bias voltage. In addition, we demonstrate the observation of the beta decay of 116mIn in samples exposed to thermal neutrons. This feature of the response serves as an additional confirmation of exposure to neutrons.

  8. Phonon anharmonicity and negative thermal expansion in SnSe

    NASA Astrophysics Data System (ADS)

    Bansal, Dipanshu; Hong, Jiawang; Li, Chen W.; May, Andrew F.; Porter, Wallace; Hu, Michael Y.; Abernathy, Douglas L.; Delaire, Olivier

    2016-08-01

    The anharmonic phonon properties of SnSe in the P n m a phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy, in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. The origin of the anharmonic phonon thermodynamics is linked to the electronic structure.

  9. Synthesis and applications of CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Rao, M. C.; Ravindranadh, K.; Shekhawat, M. S.

    2013-06-01

    Polymer nanoparticle composite materials have attracted the interest of a number of researchers, due to their synergistic and hybrid properties derived from several components. Whether in solution or in bulk, these materials offer unique mechanical, electrical, optical and thermal properties. CdSe nanoparticles have been prepared at room temperature. Cadmium chloride 99 mM of 4 mL is added to 2.2g Poly vinyl alcohol. The volume of solution is made up to 50 mL by bi-distilled water and the solution is left for 24 hours at room temperature to swell. After that the solution is warmed up to 60°C and stirred for 4 hours until viscous transparent solution is obtained. One milliliter of Sodium Hydrogen Selenide is dropped into the solution with gentle stirring. Solution is casted on flat glass plate dishes. After the solvent evaporation, a thin film containing CdSe nanoparticles are obtained. The film is washed with de-ionized water to remove other soluble salts before measurements.

  10. Tracking Se Assimilation and Speciation through the Rice Plant - Nutrient Competition, Toxicity and Distribution.

    PubMed

    Nothstein, Alexandra K; Eiche, Elisabeth; Riemann, Michael; Nick, Peter; Winkel, Lenny H E; Göttlicher, Jörg; Steininger, Ralph; Brendel, Rita; von Brasch, Matthias; Konrad, Gabriele; Neumann, Thomas

    2016-01-01

    Up to 1 billion people are affected by low intakes of the essential nutrient selenium (Se) due to low concentrations in crops. Biofortification of this micronutrient in plants is an attractive way of increasing dietary Se levels. We investigated a promising method of Se biofortification of rice seedlings, as rice is the primary staple for 3 billion people, but naturally contains low Se concentrations. We studied hydroponic Se uptake for 0-2500 ppb Se, potential phyto-toxicological effects of Se and the speciation of Se along the shoots and roots as a function of added Se species, concentrations and other nutrients supplied. We found that rice germinating directly in a Se environment increased plant-Se by factor 2-16, but that nutrient supplementation is required to prevent phyto-toxicity. XANES data showed that selenite uptake mainly resulted in the accumulation of organic Se in roots, but that selenate uptake resulted in accumulation of selenate in the higher part of the shoot, which is an essential requirement for Se to be transported to the grain. The amount of organic Se in the plant was positively correlated with applied Se concentration. Our results indicate that biofortification of seedlings with selenate is a successful method to increase Se levels in rice. PMID:27116220

  11. 21 CFR 118.8 - Testing methodology for Salmonella Enteritidis (SE).

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ....8 Testing methodology for Salmonella Enteritidis (SE). (a) Testing of environmental samples for SE. Testing to detect SE in environmental samples must be conducted by the method entitled “Environmental..., precision, and sensitivity in detecting SE. The April 2008 Environmental Sampling and Detection...

  12. Tracking Se Assimilation and Speciation through the Rice Plant – Nutrient Competition, Toxicity and Distribution

    PubMed Central

    Eiche, Elisabeth; Riemann, Michael; Nick, Peter; Winkel, Lenny H. E.; Göttlicher, Jörg; Steininger, Ralph; Brendel, Rita; von Brasch, Matthias; Konrad, Gabriele; Neumann, Thomas

    2016-01-01

    Up to 1 billion people are affected by low intakes of the essential nutrient selenium (Se) due to low concentrations in crops. Biofortification of this micronutrient in plants is an attractive way of increasing dietary Se levels. We investigated a promising method of Se biofortification of rice seedlings, as rice is the primary staple for 3 billion people, but naturally contains low Se concentrations. We studied hydroponic Se uptake for 0–2500 ppb Se, potential phyto-toxicological effects of Se and the speciation of Se along the shoots and roots as a function of added Se species, concentrations and other nutrients supplied. We found that rice germinating directly in a Se environment increased plant-Se by factor 2–16, but that nutrient supplementation is required to prevent phyto-toxicity. XANES data showed that selenite uptake mainly resulted in the accumulation of organic Se in roots, but that selenate uptake resulted in accumulation of selenate in the higher part of the shoot, which is an essential requirement for Se to be transported to the grain. The amount of organic Se in the plant was positively correlated with applied Se concentration. Our results indicate that biofortification of seedlings with selenate is a successful method to increase Se levels in rice. PMID:27116220

  13. Long-term selenium biofortification in carrots and broccoli grown in soils amended with Se-enriched S. pinnata

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Selenium (Se) biofortification has been practiced in Se-deficient regions throughout the world primarily by adding inorganic sources of Se to the soil. Adding organic sources of Se could be useful as an alternative Se amendment for the production of Se-biofortified food crops needed in Se-deficient ...

  14. Ocean to continent transfer of atmospheric Se as revealed by epiphytic lichens.

    PubMed

    Wen, Hanjie; Carignan, Jean

    2009-10-01

    There is still a long-term debate concerning the relative contributions of naturally emitted and anthropogenic Se at the regional and local scales. Here, Se and heavy metal concentrations are reported for epiphytic lichens collected in coastal and inland areas from the USA, Canada and France for assessing atmospheric Se source. Correlations found between Se and Cl in lichens confirmed the major marine biogenic source for atmospheric Se. Continental samples do not show systematic relationships between Se and other metal (Pb, Cu, In ...) contents, even for lichens collected in the vicinity of smelters or close to urban areas. Our results suggest that, although anthropogenic Se may be present, the marine biogenic Se source is a major contributor to atmospheric Se for our sampling locations. The contribution of naturally emitted atmospheric Se may be significant in urban and industrial areas and should be taken into account for further studies.

  15. Efficient NiSe-Ni3Se2/Graphene Electrocatalyst in Dye-Sensitized Solar Cells: The Role of Hollow Hybrid Nanostructure.

    PubMed

    Zhang, Xiao; Zhen, Mengmeng; Bai, Jinwu; Jin, Shaowei; Liu, Lu

    2016-07-13

    Hollow and hybrid nanomaterials are excellent electrocatalysts on account of their novel electrocatalytic properties compared with homogeneous solid nanostructures. In this report, NiSe-Ni3Se2 hybrid nanostructure with morphology of hollow hexagonal nanodisk was synthesized in situ on graphene. A series of NiSe-Ni3Se2/RGO with different phase constitutions and nanostructures were obtained by controlling the durations of solvothermal treatment. Because of their unique hollow and hybrid structure, NiSe-Ni3Se2/RGO hollow nanodisks exhibited higher electrocatalytic performance than NiSe/RGO and solid NiSe-Ni3Se2/RGO nanostructure for reducing I3(-) as counter cell (CE) of dye-sensitized solar cells (DSSCs). Additionally, NiSe-Ni3Se2/RGO hollow nanodisks achieved much lower charge transfer resistance (Rct = 0.68 Ω) and higher power conversion efficiency (PCE) (7.87%) than those of Pt (Rct = 1.41 Ω, PCE = 7.28%).

  16. Facile synthesis of hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure for high performance photodetectors.

    PubMed

    Chen, Shuo; Qiao, Xvsheng; Wang, Fengxia; Luo, Qun; Zhang, Xianghua; Wan, Xia; Xu, Yang; Fan, Xianping

    2016-01-28

    An effective colloidal process involving the hot-injection method is developed to synthesize uniform single-crystalline Sb2Se3 nanorods in high yields. The photoconductive characteristics of the as-synthesized Sb2Se3 nanorods are investigated by developing a film-based photodetector and this device displays a remarkable response to visible light with an "ON/OFF" ratio as high as 50 (with an incident light density of 12.05 mW cm(-2)), short response/recovery times and long-term durability. To overcome the challenge of the intrinsic low electrical conductivity of Sb2Se3, hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure having a type-II band alignment are firstly prepared. The electric current of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film has been significantly increased both in the dark and under light illumination. The responsivity of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film is about 4.2 times as much as that of the photodetector based on the Sb2Se3 nanorod film. This improvement can be considered as an important step to promote Sb2Se3 based semiconductors for applications in high performance photodetectors.

  17. The influence of Se pressure on the electronic properties of CuInSe{sub 2} grown under Cu-excess

    SciTech Connect

    Deprédurand, Valérie; Bertram, Tobias; Regesch, David; Henx, Benjamin; Siebentritt, Susanne

    2014-10-27

    Standard Cu-poor Cu(In,Ga)Se{sub 2} solar cell absorbers are usually prepared under high Se excess since the electronic properties of the absorbers are better if prepared under high Se pressure. However, in CuInSe{sub 2}, grown under Cu-excess, it was found that solar cell properties improve with lowering the Se pressure, mostly because of reduced tunnel contribution to the recombination path. Lower Se pressure during Cu-rich growth leads to increased (112) texture of the absorber films, to better optical film quality, as seen by increased excitonic luminescence and to lower net doping levels, which explains the reduced tunnelling effect. These findings show an opposite trend from the one observed in Cu-poor Cu(In,Ga)Se{sub 2}.

  18. [Selenium uptake and transport of rice under different Se-enriched natural soils].

    PubMed

    Jiang, Chao-qiang; Shen, Jia; Zu, Chao-long

    2015-03-01

    In this study, a pot experiment was conducted with "Wandao 205" as test materials to investigate Se uptake and translocation in rice under different Se concentrations (0.5, 1.0, and 1.5 mg . kg-1). Results showed that there was no significant change in rice yield when Se concentration in soil was lower than 1.5 mg . kg-1. Significant linear correlations existed between Se concentration in soil and different rice plant tissues. Se concentration in rice plant followed the order of root > straw > grain. Se concentration in different rice grain fractions followed the order of bran > polished rice > hull. The root absorption index of Se was more than 1.86, suggest that the rice could absorpt Se from soil effectively. However, the transport and accumulation of Se in seeds from Se-enriched soil was relatively constant. The Se transport index in seeds was between 0.53 and 0.59. Soil Se concentration within the range of 0.5 to 1.0 mg . kg-1 could produce Se-enriched rice, which might be enough for human requirement of 60-80 µg . d-1 Se. However, polished rice at high-Se treatment (1.5 mg . kg-1) exceeded the maximum standard limit of Se (0.3 mg . kg-1) for cereals in China. These results suggested that we could produce Se-enriched rice under soil Se concentration in the range of 0.5 to 1.0 mg . kg-1 without spraying Se fertilizer, thus reducing the cost and avoiding soil and water pollution caused by exogenous Se.

  19. Enhancement of superconducting Tc (33 K) by entrapment of FeSe in carbon coated Au-Pd17Se15 nanoparticles.

    PubMed

    Mishra, Sukhada; Song, Kai; Ghosh, Kartik C; Nath, Manashi

    2014-03-25

    FeSe has been an interesting member of the Fe-based superconductor family ever since the discovery of superconductivity in this simple binary chalcogenide. Simplicity of composition and ease of synthesis has made FeSe, in particular, very lucrative as a test system to understand the unconventional nature of superconductivity, especially in low-dimensional models. In this article we report the synthesis of composite nanoparticles containing FeSe nanoislands entrapped within an ent-FeSe-Pd16Se15-Au nanoparticle and sharing an interface with Pd17Se15. This assembly exhibits a significant enhancement in the superconducting Tc (onset at 33 K) accompanied by a noticeable lattice compression of FeSe along the <001> and <101> directions. The Tc in FeSe is very sensitive to application of pressure and it has been shown that with increasing external pressure Tc can be increased almost 4-fold. In these composite nanoparticles reported here, immobilization of FeSe on the Pd17Se15 surface contributes to increasing the effect of interfacial pressure, thereby enhancing the Tc. The effect of interfacial pressure is also manifested in the contraction of the FeSe lattice (up to 3.8% in <001> direction) as observed through extensive high-resolution TEM imaging. The confined FeSe in these nanoparticles occupied a region of approximately 15-25 nm, where lattice compression was uniform over the entire FeSe region, thereby maximizing its effect in enhancing the Tc. The nanoparticles have been synthesized by a simple catalyst-aided vapor transport reaction at 800 °C where iron acetylacetonate and Se were used as precursors. Morphology and composition of these nanoparticles have been studied in details through extensive electron microscopy. PMID:24494773

  20. Patterning two-dimensional chalcogenide crystals of Bi2Se3 and In2Se3 and efficient photodetectors.

    PubMed

    Zheng, Wenshan; Xie, Tian; Zhou, Yu; Chen, Y L; Jiang, Wei; Zhao, Shuli; Wu, Jinxiong; Jing, Yumei; Wu, Yue; Chen, Guanchu; Guo, Yunfan; Yin, Jianbo; Huang, Shaoyun; Xu, H Q; Liu, Zhongfan; Peng, Hailin

    2015-01-01

    Patterning of high-quality two-dimensional chalcogenide crystals with unique planar structures and various fascinating electronic properties offers great potential for batch fabrication and integration of electronic and optoelectronic devices. However, it remains a challenge that requires accurate control of the crystallization, thickness, position, orientation and layout. Here we develop a method that combines microintaglio printing with van der Waals epitaxy to efficiently pattern various single-crystal two-dimensional chalcogenides onto transparent insulating mica substrates. Using this approach, we have patterned large-area arrays of two-dimensional single-crystal Bi2Se3 topological insulator with a record high Hall mobility of ∼1,750 cm(2) V(-1) s(-1) at room temperature. Furthermore, our patterned two-dimensional In2Se3 crystal arrays have been integrated and packaged to flexible photodetectors, yielding an ultrahigh external photoresponsivity of ∼1,650 A W(-1) at 633 nm. The facile patterning, integration and packaging of high-quality two-dimensional chalcogenide crystals hold promise for innovations of next-generation photodetector arrays, wearable electronics and integrated optoelectronic circuits.

  1. Magnetooptical study of CdSe/ZnMnSe semimagnetic quantum-dot ensembles with n-type modulation doping

    SciTech Connect

    Reshina, I. I. Ivanov, S. V.

    2014-12-15

    Magnetic and polarization investigations of the photoluminescence and resonant electron spin-flip Raman scattering in ensembles of self-organized CdSe/ZnMnSe semimagnetic quantum dots with n-type modulation doping are carried out. It is demonstrated that exciton transitions contribute to the photoluminescence band intensity, along with the transitions of trions in the singlet state. In the Hanle-effect measurements, negative circular polarization in zero magnetic field is observed, which is related to the optical orientation of a trion heavy hole. The lifetime and spin-relaxation time of a heavy hole are estimated as ≤3 and ≤1 ps, respectively. Such short times are assumed to be due to Auger recombination with the excitation of an intrinsic transition in a Mn{sup 2+} ion. Investigations of the photoluminescence-maximum intensity and shift in a longitudinal magnetic field at the σ{sup −}σ{sup +} and σ{sup −}σ{sup −} polarizations reveal the pronounced spin polarization of electrons. Under resonant excitation conditions, a sharp increase in the photoluminescence-band maximum intensity at σ{sup −} excitation polarization over the σ{sup +} one is observed. The Raman scattering peak at the electron spin-flip transition is observed upon resonant excitation in a transverse magnetic field in crossed linear polarizations. This peak is shown to be a Brillouin function of a magnetic field.

  2. Patterning two-dimensional chalcogenide crystals of Bi2Se3 and In2Se3 and efficient photodetectors

    PubMed Central

    Zheng, Wenshan; Xie, Tian; Zhou, Yu; Chen, Y.L.; Jiang, Wei; Zhao, Shuli; Wu, Jinxiong; Jing, Yumei; Wu, Yue; Chen, Guanchu; Guo, Yunfan; Yin, Jianbo; Huang, Shaoyun; Xu, H.Q.; Liu, Zhongfan; Peng, Hailin

    2015-01-01

    Patterning of high-quality two-dimensional chalcogenide crystals with unique planar structures and various fascinating electronic properties offers great potential for batch fabrication and integration of electronic and optoelectronic devices. However, it remains a challenge that requires accurate control of the crystallization, thickness, position, orientation and layout. Here we develop a method that combines microintaglio printing with van der Waals epitaxy to efficiently pattern various single-crystal two-dimensional chalcogenides onto transparent insulating mica substrates. Using this approach, we have patterned large-area arrays of two-dimensional single-crystal Bi2Se3 topological insulator with a record high Hall mobility of ∼1,750 cm2 V−1 s−1 at room temperature. Furthermore, our patterned two-dimensional In2Se3 crystal arrays have been integrated and packaged to flexible photodetectors, yielding an ultrahigh external photoresponsivity of ∼1,650 A W−1 at 633 nm. The facile patterning, integration and packaging of high-quality two-dimensional chalcogenide crystals hold promise for innovations of next-generation photodetector arrays, wearable electronics and integrated optoelectronic circuits. PMID:25898022

  3. Managing flow, sediment, and hydropower regimes in the Sre Pok, Se San, and Se Kong Rivers of the Mekong basin

    NASA Astrophysics Data System (ADS)

    Wild, Thomas B.; Loucks, Daniel P.

    2014-06-01

    The Lancang/Mekong River Basin is presently undergoing a period of rapid hydropower development. In its natural undeveloped state, the river transports about 160 million metric tons of sediment per year, maintaining the geomorphologic features of the basin, sustaining habitats, and transporting the nutrients that support ecosystem productivity. Despite the importance of sediment in the river, currently little attention is being paid to reservoir sediment trapping. This study is devoted to assessing the potential for managing sediment and its impact on energy production in the Se San, Sre Pok, and Se Kong tributaries of the Mekong River. These tributaries drain a set of adjacent watersheds that are important with respect to biodiversity and ecological productivity, and serve as a significant source of flow and sediment to the mainstream Mekong River. A daily sediment transport model is used to assess tradeoffs among energy production and sediment and flow regime alteration in multiple reservoir systems. This study finds that eventually about 40%-80% of the annual suspended sediment load may be trapped in reservoirs. Clearly, these reservoirs will affect the rivers' sediment regimes. However, even after 100 years of simulated sedimentation, reservoir storage capacities and hydropower production at most reservoir sites are not significantly reduced. This suggests that the strongest motivation for implementing measures to reduce trapped sediment is their impact not on hydropower production but on fish migration and survival and on sediment-dependent ecosystems such as the Vietnam Delta and Cambodia's Tonle Sap Lake.

  4. Plate break-up geometry in SE-Afar

    NASA Astrophysics Data System (ADS)

    Geoffroy, Laurent; Le Gall, Bernard; Daoud, Mohamed

    2014-05-01

    New structural data acquired in Djibouti strongly support the view of a magma-rich to magma-poor pair of conjugate margins developed in SE Afar since at least 9 Ma. Our model is illustrated by a crustal-scale transect that emphasizes the role of a two-stage extensional detachment fault system, with opposing senses of motion through time. The geometry and kinematics of this detachment fault pattern are mainly documented from lavas and fault dip data extracted from remote sensing imagery (Landsat ETM+, and corresponding DEM), further calibrated by field observations. Although expressed by opposite fault geometries, the two successive extensional events evidenced here are part of a two-stage continental extensional tear-system associated with the ongoing propagation of the Aden-Tadjoura oceanic axis to the NW. A flip-flop evolution of detachment faults accommodating lithosphere divergence has recently been proposed for the development of the Indian Ocean and continental margins (Sauter et al., 2013). However, the SE Afar evolution further suggests a radical and sudden change in lithosphere behavior during extension, from a long-term and widespread magmatic stage to a syn-sedimentary break-up stage where mantle melting concentrates along the future oceanic axis. Of special interest is the fact that a late and rapid stage of non-magmatic extension led to break-up, whose geometry triggered the location of the break-up axis and earliest oceanic accretion. New structural data acquired in Djibouti strongly support the view of a magma-rich to magma-poor pair of conjugate margins developed in SE Afar since at least 9 Ma. Our model is illustrated by a crustal-scale transect that emphasizes the role of a two-stage extensional detachment fault system, with opposing senses of motion through time. The geometry and kinematics of this detachment fault pattern are mainly documented from lavas and fault dip data extracted from remote sensing imagery (Landsat ETM+, and corresponding

  5. Stress-optic coefficients of ZnSe.

    PubMed

    Goldstein, L F; Thompson, J S; Schroeder, J B; Slattery, J E

    1975-10-01

    The stress-optic coefficients of ZnSe have been measured at room temperature; Twyman-Green and Fizeau interferometers were used in conjunction with a four-point loading device. Test specimens were rectangular parallelepipeds of chemically vapor-deposited material prepared by Raytheon Corporation. Measurements were made with the optical propagation parallel to the deposition direction, and optical scanning and computer analysis were employed to determine fringe positions to an accuracy of better than 0.01 of a fringe spacing. The experimental values for pi(11) and pi(12) are -1.48 +/- 0.05 x 10(-12) m(2)/N and +0.22 +/- 0.05 x 10(-12) m(2)/N, respectively. PMID:20155036

  6. Structural and transport properties of CdSe nanorods

    SciTech Connect

    Das, Sayantani Banerjee, Sourish; Dutta, Alo; Ghosh, Binita; Sinha, T. P.

    2015-06-24

    The nanorods of cadmium selenide (CdSe) have been synthesized by soft chemical route. The selected area electron diffraction pattern, high resolution TEM and X-ray diffraction pattern indicate the cubic structure of the sample. The band gap of the sample is obtained using Tauc relation to UV-visible spectrum and found to be 1.92 eV. 1{sup st} order and 2{sup nd} order Raman bands are followed to investigate the behaviour of the phonon modes of the materials which is considered to be important to predict the potential of the material to microwave applications. Thermal behaviour of the sample is investigated using differential scanning calorimeter. Kissinger equation is used to calculate the activation energy of the sample, which is found to be 1.67 eV.

  7. High pressure differential conductance measurements of (Pb,Sn)Se

    NASA Astrophysics Data System (ADS)

    Paul, Tiffany; Vangennep, Derrick; Jackson, Daniel; Biswas, Amlan; Hamlin, James

    Topological transitions have been recognized as a new type of quantum phase transition. Recently, a number of papers have reported scanning tunneling microscope (STM) measurements of the Landau level spectra of topologically non-trivial materials. Such measurements can offer substantial insight into the nature of the transition between topologically distinct phases. Although applied pressure represents an attractive means to drive a topological quantum phase transition, STM measurements can not be performed under high pressure conditions. In this talk, I will discuss our recent attempts to observe Landau level spectra in compressed (Pb,Sn)Se using differential conductance measurements. Acknowledgements: TAP supported by REU NSF DMR-1461019. Pressure cell development and measurements at high magnetic fields supported by the National High Magnetic Field Laboratory User Collaboration Grants Program. Synthesis, characterization, and high pressure measurements supported by NSF DMR-1453752.

  8. Enchanced methods of hydrophilized CdSe quantum dots synthesis

    NASA Astrophysics Data System (ADS)

    Potapkin, D. V.; Zharkova, I. S.; Goryacheva, I. Y.

    2015-03-01

    Quantum dots are bright and stable fluorescence signal sources, but for most of applications they need an additional hydrophilization step. Unfortunately, most of existing approaches lead to QD's fluorescence quenching, so there is a need for additional enhancing of hydrophilized QD's brightness like UV irradiation, which can be used both on water insoluble QD's with oleic acid ligands (in toluene) and on hydrophilized QD's covered with UV-stable polymer (in aqueous solution). For synthesis of bright water-soluble fluorescent labels CdSe/CdS/ZnS colloidal quantum dots were covered with PAMAM dendrimer and irradiated with UV lamp in quartz cuvettes for 3 hours at the room temperature and then compared with control sample.

  9. STM imaging of impurity resonances on Bi2Se3.

    PubMed

    Alpichshev, Zhanybek; Biswas, Rudro R; Balatsky, Alexander V; Analytis, J G; Chu, J-H; Fisher, I R; Kapitulnik, A

    2012-05-18

    In this Letter we present detailed study of the density of states near defects in Bi2Se3. In particular, we present data on the commonly found triangular defects in this system. While we do not find any measurable quasiparticle scattering interference effects, we do find localized resonances, which can be well fitted by theory [R. R. Biswas and A. V. Balatsky, Phys. Rev. B 81, 233405(R) (2010)] once the potential is taken to be extended to properly account for the observed defects. The data together with the fits confirm that while the local density of states around the Dirac point of the electronic spectrum at the surface is significantly disrupted near the impurity by the creation of low-energy resonance state, the Dirac point is not locally destroyed. We discuss our results in terms of the expected protected surface state of topological insulators.

  10. Fluorescence quenching of CdSe quantum dots on graphene

    SciTech Connect

    Guo, Xi Tao; Hua Ni, Zhen Yan Nan, Hai; Hui Wang, Wen; Yan Liao, Chun; Zhang, Yan; Wei Zhao, Wei

    2013-11-11

    We studied systematically the fluorescence quenching of CdSe quantum dots (QDs) on graphene and its multilayers, as well as graphene oxide (GO) and reduced graphene oxide (rGO). Raman intensity of QDs was used as a quantitatively measurement of its concentration in order to achieve a reliable quenching factor (QF). It was found that the QF of graphene (∼13.1) and its multilayers is much larger than rGO (∼4.4), while GO (∼1.5) has the lowest quenching efficiency, which suggests that the graphitic structure is an important factor for quenching the fluorescence of QDs. It was also revealed that the QF of graphene is not strongly dependent on its thicknesses.

  11. Low Temperature Thermoelectric Characterization of Ag2Se

    NASA Astrophysics Data System (ADS)

    Drymiotis, Fivos; Neff, David; Coney, Michael; Bux, Sabah; Fleurial, Jean-Pierre

    Previous work on Ag2Se showed that this n-type material could have a dimensionless thermoelectric figure of merit (zT) ~1 at room temperature, due to its high mobility and low thermal conductivity. However, the results from the initial reports have not yet been reproduced. In this talk, I will summarize our efforts to replicate the aforementioned thermoelectric performance, and also discuss the experimental setup that we utilized in order to perform the low-temperature thermoelectric characterization of this material. This work was performed at the California Institute of Technology/Jet Propulsion Laboratory under contract with the National Aeronautics and Space Administration. This work was supported by JPL's Research and Technology Development Program.

  12. Laser modulation of optical absorption in ZnSe

    NASA Technical Reports Server (NTRS)

    Major, R. W.

    1971-01-01

    The possibility of producing and detecting laser induced modulation of absorption (LIMA) in ZnSe crystals using a moderate laser intensity of about 6 mw output was investigated. The modulation is smaller than that previously obtained with higher laser photon flux, but is not too difficult to detect. Modulation of the order of a few parts in 10 to the 5th power, up to one part in 10 to the 4th power appears typical at the present. LIMA pulse shapes were recorded with varying system resolutions at a half dozen wavelengths in the visible, from 4800 A to 6000 A. Detailed data were taken, particularly at 5000 A, for a range of time intervals following laser pulse turn-on. Quantitative study of the excitation and decay kinetics of these is underway, though analysis is not complete. Major features are discussed with attention centered upon the detailed measurements made most recently at 5000 A.

  13. Total energies in Se. II. Vacancy in the crystal

    NASA Astrophysics Data System (ADS)

    Vanderbilt, David; Joannopoulos, J. D.

    1983-05-01

    Ab initio total-energy calculations are used to determine theoretically the structural configuration of the vacancy in trigonal Se. The method consists of calculating the forces, as well as the total energies, within the local-density and frozen-core approximations, for a superlattice structure containing a vacancy. In this way, relaxations at the vacancy can be fully taken into account, including a possible self-healing of the vacancy. A slightly relaxed symmetric version of the ideal vacancy is the lowest-energy structure found; neither asymmetric relaxation nor valence alternation appears to occur. A simple Hubbard Hamiltonian is used to analyze the spin configuration of the lowest-energy structure.

  14. Imaging Charge Density Wave Nucleation in NbSe2

    NASA Astrophysics Data System (ADS)

    Rosenthal, Ethan; Arguello, Carlos; Chockalingam, Subbaiah; Chung, Woo Chang; Zhao, Liuyan; Gutierrez, Christopher; Kang, Joon Ho; Pasupathy, Abhay; Jia, Shuang; Cava, Robert

    2012-02-01

    Understanding the effects of spatial inhomogeneity in complex materials is necessary to achieve a fundamental understanding of their quantum states. NbSe2 serves as a clean and relatively simple system for understanding the emergence of one such state -- the charge density wave (CDW) phase. Using variable temperature scanning tunneling microscopy (STM), we visualize the nucleation of CDWs about crystal defects at temperatures well above TCDW. The CDW correlation length increases with decreasing temperature, until global order is reached below TCDW. We also employ scanning tunneling spectroscopy in order to visualize the energy-dependent, spatial phase of the CDW state. With both topographic and spectroscopic data, we will provide a clear picture of the CDW transition and insight into the microscopic mechanisms at work.

  15. Calorimetric study of tellurium rich Se-Te-Sn glasses

    NASA Astrophysics Data System (ADS)

    Heera, Pawan; Kumar, Anup; Jharwal, Manish; Sharma, Raman

    2016-05-01

    We report the calorimetric study of amorphous Se30Te70-x Snx alloys for x= 0, 1.5, 2.5, 4.5 in terms of kinetic parameters. The DSC curves recorded at four different heating rates are analyzed to determine the transition temperatures, activation energy, thermal stability, glass forming ability. The crystallization process has been investigated using Kissinger, Matusita, Augis and Bennett, and Gao and Wang models. Various kinetic parameters have been calculated for a better understanding of the growth mechanism. The glass transition temperatures Tg, onset crystallization Tc, peak crystallization Tp, and melting temperature Tm are found to increase with the increase in Sn content. The system under investigation is found to be thermally stable for at lower at% of Sn. The values of parameters HR, Hw, and S indicate that Glass forming ability (GFA) decays with an increase in Sn content.

  16. Hydroacoustic seafloor classification in the SE North Sea

    NASA Astrophysics Data System (ADS)

    Hass, H. C.; Bartholomä, A.; Bürk, D.; Holler, P.; Mielck, F.; Reimers, H.-C.

    2012-04-01

    Over the last years hydoacoustic investigations of the seafloor became a strong tool for habitat mapping. Directives of the European Union emphasize the need for reliable, high resolution and at the same time cost-effective methods to map the ecologic status of coastal marine areas which are highly dynamic and vulnerable to disturbances. Aside from the difficulties that arise from monitoring extended areas, standardized methods are still not existing. This results in habitat maps that cannot easily be brought together over larger areas. We present here initial results of the project WIMO ("Scientific concepts for monitoring the German Bight, SE North Sea") that aims at testing different hydroacoustic mapping tools in order to work out a standard routine for habitat mapping purposes. We studied five areas using an IMAGENEX YellowFin sidescan sonar, a BENTHOS 1624 sidescan sonar, a SONAVISION RoxAnn seafloor classification system among other seafloor classification systems, and a Kongsberg EM710 multibeam system. Sediment samples for groundtruthing were taken with a HELCOM grab sampler. The working areas are all in the coastal zone of the SE North Sea with water depth between 10 and 40 m. The parameters measured include depth and backscatter (multibeam), hardness and roughness (RoxAnn), seafloor sonographic imagery, and granulometry (grab samples). We present classification methods that implement selected parameters and all of the parameters, partly based on self-programmed routines. The results reveal that all methods are capable to gather information important for habitat assessment. However, the information provided by the different systems is not always the same and simply merging the data is no solution. We show different approaches to take advantage of the data and suggest combinations of instruments and parameters for efficient mapping standards.

  17. S-wave velocity structure in the SE Tibetan plateau

    NASA Astrophysics Data System (ADS)

    Cai, Yan; Wu, Jianping; Wang, Weilai; Fang, Lihua; Fan, Liping

    2016-06-01

    We use observations recorded by 23 permanent and 99 temporary stations in the SE Tibetan plateau to obtain the S-wave velocity structure along two profiles by applying joint inversion with receiver functions and surface waves. The two profiles cross West Yunnan block (WYB), the Central Yunnan sub-block (CYB), South China block (SCB), and Nanpanjiang basin (NPB). The profile at ~25°N shows that the Moho interface in the CYB is deeper than those in the WYB and the NPB, and the topography and Moho depth have clear correspondence. Beneath the Xiaojiang fault zone (XJF), there exists a crustal low-velocity zone (LVZ), crossing the XJF and expanding eastward into the SCB. The NPB is shown to be of relatively high velocity. We speculate that the eastward extrusion of the Tibetan plateau may pass through the XJF and affect its eastern region, and is resisted by the rigid NPB, which has high velocity. This may be the main cause of the crustal thickening and uplift of the topography. In the Tengchong volcanic area, the crust is shown to have alternate high- and low-velocity layers, and the upper mantle is shown to be of low velocity. We consider that the magma which exists in the crust is from the upper mantle and that the complex crustal velocity structure is related to magmatic differentiation. Between the Tengchong volcanic area and the XJF, the crustal velocity is relatively high. Combining these observations with other geophysical evidence, it is indicated that rock strength is high and deformation is weak in this area, which is why the level of seismicity is quite low. The profile at ~23°N shows that the variation of the Moho depth is small from the eastern rigid block to the western active block with a wide range of LVZs. We consider that deformation to the south of the SE Tibetan Plateau is weak.

  18. Differential effects of sodium selenite and nano-Se on growth performance, tissue se distribution, and glutathione peroxidase activity of avian broiler.

    PubMed

    Wang, Yanbo

    2009-05-01

    The present research evaluated differential effects of sodium selenite and nano-Se on growth performance, tissue Se distribution, and glutathione peroxidase (GSH-Px) activity of avian broiler. Broilers were randomly segregated into 12 groups so that three replicates were available for each of the three treatments (T-1, T-2, and T-3) and control groups. The control groups were fed basal diets without Se addition. T-1, T-2, and T-3 were fed with diets containing 0.2 mg kg(-1) sodium selenite, 0.2 mg kg(-1) nano-Se, and 0.5 mg kg(-1) nano-Se, respectively. Compared with the control, Se supplementation remarkably improved daily weight gain and survival rate and decreased feed conversion ratio (P < 0.05). However, no significant difference was observed between T-1, T-2, and T-3. The tissue Se content was significantly higher (P < 0.05) in Se-supplemented groups than the control, and T-3 showed the highest. Furthermore, higher Se content was observed in liver, and there was a significant difference (P < 0.05) compared with that in muscle. As for serum and hepatic GSH-Px activities, Se supplementation remarkably improved GSH-Px activity (P < 0.05), and there was no significant difference (P > 0.05) between treatments (T-1, T-2, and T-3). PMID:18972070

  19. Resonant Levels, Vacancies, and Doping in Bi2Te3, Bi2Te2Se, and Bi2Se3 Tetradymites

    NASA Astrophysics Data System (ADS)

    Wiendlocha, Bartlomiej

    2016-07-01

    The electronic structure of the tetradymites, Bi_2Te_3, Bi_2Te_2Se, and Bi_2Se_3, containing various dopants and vacancies, has been studied using first-principles calculations. We focus on the possibility of formation of resonant levels (RL), confirming the formation of RL by Sn in Bi_2Te_3 and predicting similar behavior of Sn in Bi_2Te_2Se and Bi_2Se_3. Vacancies, which are likely present on chalcogen atom sites in real samples of Bi_2Te_2Se and Bi_2Se_3, are also studied and their charged donor and resonant behavior discussed. Doping of vacancy-containing materials with regular acceptors, such as Ca or Mg, is shown to compensate the donor effect of vacancies, and n-p crossover, while increasing the dopant concentration, is observed. We verify that the RL on Sn is not disturbed by chalcogen vacancies in Bi_2Te_2Se or Bi_2Se_3, and for the Sn-doped materials with Se or Te vacancies, double doping, instead of heavy doping with Sn, is suggested as an effective way of obtaining the resonant level. This should help to avoid smearing of the RL, a possible reason for earlier unsuccessful experimental observation of the influence of the RL on the thermoelectric properties of Sn-doped Bi_2Te_2Se. Finally, we show that Al and Ga are possible new resonant impurities in tetradymites, hoping that this will stimulate further experimental studies.

  20. High-quality, large-area MoSe2 and MoSe2/Bi2Se3 heterostructures on AlN(0001)/Si(111) substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Xenogiannopoulou, E.; Tsipas, P.; Aretouli, K. E.; Tsoutsou, D.; Giamini, S. A.; Bazioti, C.; Dimitrakopulos, G. P.; Komninou, Ph.; Brems, S.; Huyghebaert, C.; Radu, I. P.; Dimoulas, A.

    2015-04-01

    Atomically-thin, inherently 2D semiconductors offer thickness scaling of nanoelectronic devices and excellent response to light for low-power versatile applications. Using small exfoliated flakes, advanced devices and integrated circuits have already been realized, showing great potential to impact nanoelectronics. Here, high-quality single-crystal MoSe2 is grown by molecular beam epitaxy on AlN(0001)/Si(111), showing the potential for scaling up growth to low-cost, large-area substrates for mass production. The MoSe2 layers are epitaxially aligned with the aluminum nitride (AlN) lattice, showing a uniform, smooth surface and interfaces with no reaction or intermixing, and with sufficiently high band offsets. High-quality single-layer MoSe2 is obtained, with a direct gap evidenced by angle-resolved photoemission spectroscopy and further confirmed by Raman and intense room temperature photoluminescence. The successful growth of high-quality MoSe2/Bi2Se3 multilayers on AlN shows promise for novel devices exploiting the non-trivial topological properties of Bi2Se3.Atomically-thin, inherently 2D semiconductors offer thickness scaling of nanoelectronic devices and excellent response to light for low-power versatile applications. Using small exfoliated flakes, advanced devices and integrated circuits have already been realized, showing great potential to impact nanoelectronics. Here, high-quality single-crystal MoSe2 is grown by molecular beam epitaxy on AlN(0001)/Si(111), showing the potential for scaling up growth to low-cost, large-area substrates for mass production. The MoSe2 layers are epitaxially aligned with the aluminum nitride (AlN) lattice, showing a uniform, smooth surface and interfaces with no reaction or intermixing, and with sufficiently high band offsets. High-quality single-layer MoSe2 is obtained, with a direct gap evidenced by angle-resolved photoemission spectroscopy and further confirmed by Raman and intense room temperature photoluminescence. The

  1. Simultaneous speciation of arsenic (As(III), MMA, DMA, and As(V)) and selenium (Se(IV), Se(VI), and SeCN-) in petroleum refinery aqueous streams.

    PubMed

    Tonietto, Gisele B; Godoy, José M; Oliveira, Ana Cristina; de Souza, Marcia V

    2010-07-01

    High-performance liquid chromatography (HPLC) coupled to an ICP-MS with an octapole reaction system (ORS) has been used to carry out quantitative speciation of selenium (Se) and arsenic (As) in the stream waters of a refining process. The argon dimers interfering with the (78)Se and (80)Se isotopes were suppressed by pressurizing the octapole chamber with 3.1 mL min(-1) H(2) and 0.5 mL min(-1) He. Four arsenic species arsenite--As(III), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)--and three inorganic Se species--selenite Se(IV), selenate Se(VI), and selenocyanate (SeCN(-))--were separated in a single run by ion chromatography (IC) using gradient elution with 100 mmol L(-1) NH(4)NO(3), pH 8.5, adjusted by addition of NH(3), as eluent. Repeatabilities of peak position and of peak area evaluation were better than 1% and about 3%, respectively. Detection limits (as 3sigma of the baseline noise) were 81, 56, and 75 ng L(-1) for Se(IV), Se(VI), and SeCN(-), respectively, and 22, 19, 25, and 16 ng L(-1) for As(III), As(V), MMA, and DMA, respectively. Calibration curve R (2) values ranged between 0.996 and 0.999 for the arsenic and selenium species. Column recovery for ion chromatography was calculated to be 97 +/- 6% for combined arsenic species and 98 +/- 3% for combined selenium species. Because certified reference materials for As and Se speciation studies are still not commercially available, in order to check accuracy and precision the method was applied to certified reference materials, BCR 714, BCR 1714, and BCR 715 and to two different refinery samples--inlet and outlet wastewater. The method was successfully used to study the quantitative speciation of selenium and arsenic in petroleum refinery wastewaters.

  2. Tuning the emission of aqueous Cu:ZnSe quantum dots to yellow light window

    NASA Astrophysics Data System (ADS)

    Wang, Chunlei; Hu, Zhiyang; Xu, Shuhong; Wang, Yanbin; Zhao, Zengxia; Wang, Zhuyuan; Cui, Yiping

    2015-07-01

    Synthesis of internally doped Cu:ZnSe QDs in an aqueous solution still suffers from narrow tunable emissions from the blue to green light window. In this work, we extended the emission window of aqueous Cu:ZnSe QDs to the yellow light window. Our results show that high solution pH, multiple injections of Zn precursors, and nucleation doping strategy are three key factors for preparing yellow emitted Cu:ZnSe QDs. All these factors can depress the reactivity of CuSe nuclei and Zn monomers, promoting ZnSe growth outside CuSe nuclei rather than form ZnSe nuclei separately. With increased ZnSe QD size, the conduction band and nearby trap state energy levels shift to higher energy sites, causing Cu:ZnSe QDs to have a much longer emission.

  3. Detection of a MoSe{sub 2} secondary phase layer in CZTSe by spectroscopic ellipsometry

    SciTech Connect

    Demircioğlu, Özden; Riedel, Ingo; Gütay, Levent; Mousel, Marina; Redinger, Alex; Rey, Germain; Weiss, Thomas; Siebentritt, Susanne

    2015-11-14

    We demonstrate the application of Spectroscopic Ellipsometry (SE) for identification of secondary phase MoSe{sub 2} in polycrystalline Cu{sub 2}ZnSnSe{sub 4} (CZTSe) samples. A MoSe{sub 2} reference sample was analyzed, and its optical constants (ε{sub 1} and ε{sub 2}) were extracted by SE analysis. This dataset was implemented into an optical model for analyzing SE data from a glass/Mo/CZTSe sample containing MoSe{sub 2} at the back side of the absorber. We present results on the n and k values of CZTSe and show the extraction of the thickness of the secondary phase MoSe{sub 2} layer. Raman spectroscopy and scanning electron microscopy were applied to confirm the SE results.

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

    SciTech Connect

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

    2014-01-15

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

  5. Multi-terminal Two-color ZnCdSe/ZnCdMgSe Based Quantum-well Infrared Photodetector

    NASA Astrophysics Data System (ADS)

    Kaya, Yasin; Ravikumar, Arvind; Chen, Guopeng; Tamargo, Maria C.; Shen, Aidong; Gmachl, Claire

    Target recognition and identification applications benefits from two-color infrared (IR) detectors in the mid and long-wavelength IR regions. Currently, InGaAs/AlGaAs and GaAs/AlGaAs multiple quantum wells (QWs) grown on GaAs substrate are the most commonly used two-color QW IR photodetectors (QWIPs). However, the lattice-mismatch and the buildup of strain limit the number of QWs that can be grown, in turn increasing the dark current noise, and limiting the device detectivity.In this work, we report on two-color QWIPs based on the large conduction band offset (~1.12ev) ZnCdSe/ZnCdMgSe material system lattice matched to InP. QWIPs were designed based on a bound to quasi-bound transition, centered at 4 μm and 7 μm and each QW is repeated 50 times to eliminate the high dark current and a contact layer is inserted between the two stacks of QWs for independent electrical contacts. Wafers are processed into two step rectangular mesas by lithography and wet etching. Experiments showed absorption spectra centered at 4.9 μm and 7.6 μm at 80 K and the full width at half maximums were Δλ / λ = 21 % and Δλ / λ = 23 % , respectively. Current work studies the Johnson and the background noise limited detectivities of these QWIPs. Current address: School of Earth, Energy and Environmental Sciences, Stanford, CA 94305, USA.

  6. Compounds in the system Cu 2SeAs 2Se 3

    NASA Astrophysics Data System (ADS)

    Blachnik, R.; Kurz, G.

    1984-11-01

    The phase diagram Cu 2SeAs 2Se 3 was investigated by thermal and X-ray methods. Cu 2Se has a limited solubility for As 2Se 3 (5 mole% at 769 K). The stoichiometric compound Cu 3AsSe 3 exists between 696 and 769 K. Cu 4As 2Se 5, a phase at 66.6 mole% Cu 2Se, decomposes peritectically at 746 K. The narrow homogeneity range (4 mole% at 683 K) extends far into the ternary space. CuAsSe 2 also decomposes peritectically at 683 K. A degenerated eutectic between CuAsSe 2 and As 2Se 3 was found at 641 K. Single crystals of Cu 4As 2Se 5 were grown in a salt melt. A metastable modification of the high-temperature phase Cu 3AsSe 3 can be obtained by quenching. Cu 4As 2Se 5 (space group R3, lattice constants a = 1404.0(1) pm, c = 960.2(1) pm), Cu 6As 4Se 9, obtained by Cambi and Elli, and Cu 7As 6Se 13 of Takeuchi and Horiuchi are different versions of a sphalerite-type compound with a broad homogeneity range in the system CuAsSe. CuAsSe 2 is possibly monoclinic with lattice parameters of a = 946.5(1) pm, b = 1229.3(1) pm, c = 511.7(1) pm, and β = 98.546(4)°. The enthalpy of mixing of Cu 2Se and As 2Se 3 in the liquid state is endothermic.

  7. Magnetically Hard Fe3Se4 Embedded in Bi2Se3 Topological Insulator Thin Films Grown by Molecular Beam Epitaxy.

    PubMed

    Vasconcelos, Hugo Menezes do Nascimento; Eddrief, Mahmoud; Zheng, Yunlin; Demaille, Dominique; Hidki, Sarah; Fonda, Emiliano; Novikova, Anastasiia; Fujii, Jun; Torelli, Piero; Salles, Benjamin Rache; Vobornik, Ivana; Panaccione, Giancarlo; de Oliveira, Adilson Jesus Aparecido; Marangolo, Massimiliano; Vidal, Franck

    2016-01-26

    We investigated the structural, magnetic, and electronic properties of Bi2Se3 epilayers containing Fe grown on GaAs(111) by molecular beam epitaxy. It is shown that, in the window of growth parameters leading to Bi2Se3 epilayers with optimized quality, Fe atom clustering leads to the formation of FexSey inclusions. These objects have platelet shape and are embedded within Bi2Se3. Monoclinic Fe3Se4 is identified as the main secondary phase through detailed structural measurements. Due to the presence of the hard ferrimagnetic Fe3Se4 inclusions, the system exhibits a very large coercive field at low temperature and room temperature magnetic ordering. Despite this composite structure and the proximity of a magnetic phase, the surface electronic structure of Bi2Se3 is preserved, as shown by the persistence of a gapless Dirac cone at Γ.

  8. Synthesis and Optical Properties of Colloidal CdS/CdSe/CdS Quantum Wells

    NASA Astrophysics Data System (ADS)

    Hai, Le Ba; Nghia, Nguyen Xuan; Nga, Pham Thu; Chinh, Vu Duc; Linh, Pham Thuy; Trang, Nguyen Thi Thu

    Colloidal CdS/CdSe/CdS quantum wells were synthesized from TOPSe and cadmium oleate in octadecene, a non-coordinating solvent. Absorption, emission, and Raman scattering spectra of colloidal CdS/CdSe/CdS quantum wells with different thickness of CdSe well were investigated. The effect of thickness of CdSe well on the optical and vibrational properties of colloidal CdS/CdSe/CdS quantum wells was discussed. The expri-mental results provide further evidence for the existence of quantum dot-quantum well structures in CdS/CdSe/CdS type materials.

  9. First-principles study of carbon impurities in CuInSe{sub 2} and CuGaSe{sub 2}, present in non-vacuum synthesis methods

    SciTech Connect

    Bekaert, J. Saniz, R.; Partoens, B.; Lamoen, D.

    2015-01-07

    A first-principles study of the structural and electronic properties of carbon impurities in CuInSe{sub 2} and CuGaSe{sub 2} is presented. Carbon is present in organic molecules in the precursor solutions used in non-vacuum growth methods for CuInSe{sub 2} and CuGaSe{sub 2} based photovoltaic cells. These growth methods make more efficient use of material, time, and energy than traditional vacuum methods. The formation energies of several carbon impurities are calculated using the hybrid HSE06 functional. C{sub Cu} acts as a shallow donor, C{sub In} and interstitial C yield deep donor levels in CuInSe{sub 2}, while in CuGaSe{sub 2} C{sub Ga} and interstitial C act as deep amphoteric defects. So, these defects reduce the majority carrier (hole) concentration in p-type CuInSe{sub 2} and CuGaSe{sub 2} by compensating the acceptor levels. The deep defects are likely to act as recombination centers for the photogenerated charge carriers and are thus detrimental for the performance of the photovoltaic cells. On the other hand, the formation energies of the carbon impurities are high, even under C-rich growth conditions. Thus, few C impurities will form in CuInSe{sub 2} and CuGaSe{sub 2} in thermodynamic equilibrium. However, the deposition of the precursor solution in non-vacuum growth methods presents conditions far from thermodynamic equilibrium. In this case, our calculations show that C impurities formed in non-equilibrium tend to segregate from CuInSe{sub 2} and CuGaSe{sub 2} by approaching thermodynamic equilibrium, e.g., via thorough annealing.

  10. Optimization of barrier layer thickness in MgSe/CdSe quantum wells for intersubband devices in the near infrared region

    SciTech Connect

    Chen, Guopeng; Shen, Aidong; Tamargo, Maria C.

    2015-10-28

    The authors report the optimization of MgSe barrier thickness in CdSe/MgSe multiple quantum well structures and its effect on structural, optical qualities and intersubband (ISB) transition characteristics. Three samples with the MgSe thicknesses of 2 nm, 3 nm, and 4 nm were grown on InP substrates by molecular beam epitaxy. X-ray diffraction and photoluminescence measurements showed that the thinner the MgSe barrier thickness the better the structural quality. However, ISB absorption was only observed in the sample with a MgSe thickness of 3 nm. Failing to observe ISB absorption in the sample with a thicker MgSe barrier (≥4 nm) is due to the deteriorated material quality while the missing of ISB transition in the sample with thinner barrier (≤2 nm) is due to the tunneling of electrons out of the CdSe wells. The optimized MgSe barrier thickness of around 3 nm is found to be able to suppress the electron tunneling while maintaining a good material quality of the overall structure.

  11. Electrical and photoelectric characteristics of structures based on InSe and GaSe layered semiconductors irradiated with 12.5-MeV electrons

    SciTech Connect

    Kovalyuk, Z. D. Politanska, O. A.; Sydor, O. N.; Maslyuk, V. T.

    2008-11-15

    The effect of irradiation with 12.5-MeV electrons on the electrical and photoelectric parameters of layered photoconverters based on p-InSe-n-InSe and p-GaSe-n-InSe structures is studied. The observed variations in the current-voltage characteristics, photoresponse spectra, open-circuit voltage, and short-circuit current are caused by the formation of point defects. The absence of pronounced changes in the characteristics of the homojunctions and heterojunctions even after irradiation at the highest dose makes it possible to recommend these junctions for use in the fabrication of radiation-resistant photodetectors.

  12. Origin of the solid solution in the LiInSe{sub 2}–In{sub 2}Se{sub 3} system

    SciTech Connect

    Vasilyeva, I.G.; Pochtar, A.A.; Isaenko, L.I.

    2014-12-15

    Techniques of bulk and local analyses were used to characterize the melt-grown single crystals of LiInSe{sub 2}, where yellow matrix coexists together with extended red areas distributed irregularly. Bulk chemical analysis showed that the average stoichiometry of yellow matrix is close to ideal 1:1:2, but red areas are enriched with In{sub 2}Se{sub 3}. An excess In{sub 2}Se{sub 3} is incorporated coherently into the crystal lattice of LiInSe{sub 2}, forming the substitution solid solution with the general formula (Li{sub 1−3x}In{sub x}⎕{sub 2})InSe{sub 2} and changing the color from yellow to red. The test crystals with the 50–55% content of In{sub 2}Se{sub 3} were found by the X-ray analysis to be single phase. The differential dissolution technique, measuring the spatial variation of the composition with high resolution, demonstrated that the single phase crystals in the LiInSe{sub 2}–In{sub 2}Se{sub 3} system might be grown only in a very narrow range close to stoichiometric. Being supersaturated, the heterovalent solid solution phases decompose in the course of cooling, and the concentration micro-heterogeneity occurs in the matrix as the coherent (or incoherent) inclusions of two different types, practically pure selenides of lithium and indium. The origin and scale of the micro-heterogeneity determining the physical properties of LiInSe{sub 2} are discussed as a starting point for the development of physicochemical foundations for growing high quality optical crystals. - Graphical abstract: Differential dissolution technique applied for detection of dispersive precipitates in as-grown LiInSe{sub 2} single crystals: kinetic curves of the phase dissolution: F is the main phase Li{sub 0.96}In{sub 1.01}Se{sub 2} (98.9%), secondary minor phases Li{sub 2}Se (0.1%), In{sub 2}Se{sub 3} (0.9%). - Highlights: • Phase purity of crystals Li{sub 1−3x}In{sub 1+x}Se{sub 2} was examined by a new stoichiographic method. • Breakup of the metastable solid solution

  13. Formation of ZnSe/Bi{sub 2}Se{sub 3} QDs by surface cation exchange and high photothermal conversion

    SciTech Connect

    Jia, Guozhi; Wang, Peng; Zhang, Yanbang; Wu, Zengna; Li, Qiang; Yao, Jianghong; Chang, Kai

    2015-08-15

    Water-dispersed core/shell structure ZnSe/Bi{sub 2}Se{sub 3} quantum dots were synthesized by ultrasonicwave-assisted cation exchange reaction. Only surface Zn ion can be replaced by Bi ion in ZnSe quantum dots, which lead to the ultrathin Bi{sub 2}Se{sub 3} shell layer formed. It is significance to find to change the crystal of QDs due to the acting of ultrasonicwave. Cation exchange mechanism and excellent photothermal conversion properties are discussed in detail.

  14. Second Harmonic Generation of Self-Mode-Locked СО2-Laser Radiation in GaSe and GaSeS Crystals

    NASA Astrophysics Data System (ADS)

    Genin, D. E.; Beloplotov, D. V.; Sitnikov, A. G.; Panchenko, A. N.; Sarkisov, S. Yu.; Chernyshov, A. I.

    2014-03-01

    A TEA CO2 laser generating at the wavelength λ = 10.6 μm in the modes of free lasing and self-mode-locking was used to obtain and compare second harmonic generation (SHG) in GaSe and GaSe0.7S0.3 crystals. With the self-mode-locked laser, a 5-times higher energy efficiency of SHG was obtained. The efficiency of SHG in the GaSe0.7S0.3 crystal and its second-order nonlinear susceptibility were estimated and compared with their values for undoped GaSe.

  15. X-ray-absorption near-edge structure of CuGaSe2 and ZnSe: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Šipr, O.; Machek, P.; Šimůnek, A.; Vackář, J.; Horák, J.

    1997-11-01

    X-ray-absorption near-edge structure (XANES) spectra of a ternary semiconductor CuGaSe2 at the Cu, Ga, and Se edges were measured and compared with Zn and Se spectra of ZnSe, taken from the literature. Having all five absorbing atoms in nearly identical coordination environments, we investigate the influence of the electronic structure on the XANES spectra. The spectra of CuGaSe2 and of ZnSe were calculated using a real-space multiple-scattering approach and using a pseudopotential band-structure technique. Both computational methods yield spectra that are in a good agreement with experiment. The effect of the size of the cluster involved in the real-space calculation on the calculated XANES spectra is investigated. Using self-consistent muffin-tin potentials does not lead to significantly different CuGaSe2 spectra than using non-self-consistent potentials. Real-space multiple-scattering spectra calculated without core holes exhibit only minor differences with respect to those obtained for relaxed screened core holes, the largest effect being found for Zn spectrum of ZnSe. Employing unrelaxed or unscreened core hole potentials resulted in spectra that did not agree with experiment. Contrary to earlier reports, no effect of charge transfer on the calculated XANES spectra of ZnSe was found.

  16. Differences in soil mobility and degradability between water-dispersible CdSe and CdSe/ZnS quantum dots.

    PubMed

    Navarro, Divina A; Banerjee, Sarbajit; Watson, David F; Aga, Diana S

    2011-08-01

    The relative leaching potential and degradation of water-dispersible CdSe and CdSe/ZnS quantum dots (QDs) were evaluated using small-scale soil columns. The potential of QDs to release toxic Cd(2+) and/or Se(2-)/SeO(3)(2-) ions upon degradation is of environmental concern and warrants investigation. Both classes of QDs exhibited limited soil mobility in CaCl(2), with more than 70% of the total Cd and Se species from QDs retained in the top soil after passing 10 column volumes of solution through the soil column. However, mobilization of Cd- and Se-species was observed when EDTA was used as the leaching solution. Approximately 98% of the total Cd(2+) loaded leached out from the Cd(2+)-spiked soil, while only 30% and 60% leached out from the CdSe and CdSe/ZnS QD-spiked soils, respectively. Soil column profiles and analysis of leachates suggest that intact QDs leached through the soil. Longer incubation (15 days) in soil prior to leaching indicated some degradation and/or surface modification of both QDs. These results suggest that chelating agents in the environment can enhance the soil mobility of intact and degraded QDs. It is apparent that QDs in soil, including the polymer-coated CdSe/ZnS QDs that are generally assumed to possess a higher degree of environmental stability, can undergo chemical transformations, which subsequently dictate their overall mobility.

  17. Coherent Electronic Coupling in Monolayer MoSe2

    NASA Astrophysics Data System (ADS)

    Moody, Galan; Singh, Akshay; Wu, Sanfeng; Wu, Yanwen; Ghimire, Nirmal; Yan, Jiaqiang; Mandrus, David; Xu, Xiaodong; Li, Xiaoqin

    2014-03-01

    Monolayer transition metal dichalcogenides (TMDs) have emerged as an interesting class of two-dimensional materials due to their unique optical properties, such as a crossover from an indirect-to-direct bandgap as well as valley-specific optical selection rules. A striking feature in the linear optical spectra of TMDs is pronounced neutral and charged excitons (trions), with significantly larger binding energies than conventional semiconductors due to reduced screening. Using ultrafast two-color pump-probe spectroscopy, we demonstrate that Coulomb interactions responsible for the large binding energies in monolayer MoSe2 also lead to strong coherent coupling between excitons and trions. Signatures for coherent coupling appear as isolated cross-peaks in a 2D spectrum obtained by tuning the pump and probe wavelengths through the resonances. While incoherent population transfer may partially contribute to one of the peaks, density matrix calculations reveal that the unique peak lineshapes arise from coherent exciton-trion many-body interactions, whose strength is significantly larger compared to conventional semiconductor quantum wells. Strong exciton-trion coherent coupling demonstrated here makes TMDs an excellent platform for future coherent opto-electronic devices. Currently at: National Institute of Standards & Technology, Boulder.

  18. Excitation energy dependent Raman spectrum of MoSe2

    PubMed Central

    Nam, Dahyun; Lee, Jae-Ung; Cheong, Hyeonsik

    2015-01-01

    Raman investigation of MoSe2 was carried out with eight different excitation energies. Seven peaks, including E1g, A1g, E2g1, and A2u2 peaks are observed in the range of 100–400 cm−1. The phonon modes are assigned by comparing the peak positions with theoretical calculations. The intensities of the peaks are enhanced at different excitation energies through resonance with different optical transitions. The A1g mode is enhanced at 1.58 and 3.82 eV, which are near the A exciton energy and the band-to-band transition between higher energy bands, respectively. The E2g1 mode is strongly enhanced with respect to the A1g mode for the 2.71- and 2.81-eV excitations, which are close to the C exciton energy. The different enhancements of the A1g and E2g1 modes are explained in terms of the symmetries of the exciton states and the exciton-phonon coupling. Other smaller peaks including E1g and A2u2 are forbidden but appear due to the resonance effect near optical transition energies. PMID:26601614

  19. Crystal structure and phase transition of thermoelectric SnSe.

    PubMed

    Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo

    2016-06-01

    Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.

  20. Serotonin-Labeled CdSe Nanocrystals: Applications for Neuroscience

    NASA Astrophysics Data System (ADS)

    Kippeny, Tadd; Adkins, Erika; Adams, Scott; Thomlinson, Ian; Schroeter, Sally; Defelice, Louis; Blakely, Randy; Rosenthal, Sandra

    2000-03-01

    Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter which has been linked to the regulation of critical behaviors including sleep, appetite, and mood. The serotonin transporter (SERT) is a 12-transmembrane domain protein responsible for clearance of serotonin from extracellular spaces following release. In order to assess the potential for use of ligand-conjugated nanocrystals to target cell surface receptors, ion channels, and transporters we have measured the ability of serotonin-labeled CdSe nanocrystals (SNACs) to block the uptake of tritiated serotonin by the human and Drosophila serotonin transporters (hSERT and dSERT). Estimated Ki values, the SNAC concentration at which half of the serotonin transport activity is blocked, were determined by nonlinear regression to be Ki (hSERT ) = 74uM and Ki (dSERT ) = 29uM. These values and our inability to detect free serotonin indicate that SNACs selectively interact with the serotonin recognition site of the transporter. We have also exposed the SNACs to cells containing ionotropic serotonin receptors and have measured the electrical response of the cell using a two microelectrode voltage clamp. We find that serotonin receptors do respond to the SNACs and we measure currents similar to the free serotonin response. These results indicate that ligand-conjugated nanocrystals can be used to label both receptor and transporter proteins. Initial fluorescence labeling experiments will be discussed.

  1. Optical properties of liquid Se-Te alloys

    NASA Astrophysics Data System (ADS)

    Silva, Larry A.; Cutler, Melvin

    1990-10-01

    Thin films have been used to determine the optical properties of the liquid-alloy system SexTe100-x in the photon energy range of 0.4 to 5.0 eV, and at temperatures from the melting point to 500 °C. These liquids are semiconductors at Se-rich compositions, and undergo a transition to metallic behavior at high Te concentrations. The effects of this transition first appear in the optical data at 80 at. % Te. Possible forms for the electronic band structure in the semiconducting phase of the liquid are derived from the nondirect transition model for optical absorption. The optical properties of liquid Te (metallic phase) are separated into intraband and interband components, modeling the intraband component by Drude behavior, to test previously proposed mechanisms for the semiconductor-metal transition. Our results are consistent with the preservation of two-fold covalent bonding across this transition, and predict a ~0.4 eV gap between a Fermi level within the valence-band and the conduction-band edge. We have also measured the sub-band-gap absorption coefficient in semiconducting liquids containing 0, 20, and 40 at. % Te, and find that the extent of the exponential absorption edge decreases with increasing Te concentration.

  2. Superconductivity and spin excitations in orbitally ordered FeSe

    NASA Astrophysics Data System (ADS)

    Kreisel, Andreas; Mukherjee, Shantanu; Hirschfeld, P. J.; Andersen, B. M.

    We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the dxz /dyz channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π , 0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π , 0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies A.K. and B.M.A. acknowledge financial support from a Lundbeckfond fellowship (Grant No. A9318). P.J.H. was partially supported by the Department of Energy under Grant No. DE-FG02-05ER46236.

  3. Is gall bladder cancer a bad cancer per se?

    PubMed

    Kapoor, Vinay K

    2015-07-27

    Gall bladder cancer (GBC) has one of the poorest outcomes of all cancers. Early GBC is difficult to diagnose on even computed tomography. GB has no submucosa and the cancer infiltrates directly into the muscularis propria. GB wall is thin and important adjacent organs viz. liver, duodenum and pancreas get easily infiltrated. Tumor in the GB neck often needs extended right hepatectomy. Infiltration of duodenum/pancreas may necessitate pancreato-duodenectomy or even hepato-pancreato-duodenectomy. Mortality of surgical procedures, when performed for GBC, is higher than when performed for other cancers. Survival in GBC, even after R0 resection, is poor. There is no proven role of neo-adjuvant or adjuvant therapy for loco-regionally advanced GBC. There is no role of palliative surgery in metastatic GBC. Early GBC is diagnosed incidentally after cholecystectomy for stones and requires reoperation for completion extended cholecystectomy but unfortunately, most surgeons are not aware of this. GBC has a peculiar epidemiology and is uncommon in the West and has, therefore, not received much attention. Preventive cholecystectomy for asymptomatic stones is not recommended and there is no serum marker for screening. With all factors pitched against it, it does appear that GBC is a bad cancer per se! PMID:26225192

  4. Gran Sabana fires (SE Venezuela): a paleoecological perspective

    NASA Astrophysics Data System (ADS)

    Montoya, Encarni; Rull, Valentí

    2011-11-01

    Fires are among the most important risks for tropical ecosystems in a future climatic change scenario. Recently, paleoecological research has been addressed to discern the role played by fire in neotropical landscapes. However, given the magnitude of the Neotropics, many studies are relegated to infer just local trends. Here we present the compilation of the paleo-fire records developed until now in the southern Gran Sabana (SE Venezuela) with the aim to describe the fire history as well as to infer the possible forcing factors implied. In this sense, southern Gran Sabana has been under fire perturbation since the Lateglacial, with the concomitant effects upon vegetation, and persisted during the Holocene. Around 2000 cal yr BP onwards, the fire activity highly increased promoting the expansion of pre-existing savannas, the decrease of forests and the appearance and establishment of Mauritia palm swamps. The continuous fire incidence registered for several thousands of years has likely promoted the supremacy of treeless savannas upon other vegetation types and the degradation to secondary landscapes. Based on the available evidence, the anthropogenic nature of this high fire activity has been postulated. If so, it could be hypothesized that the timing arrival of Pemón, the present-day indigenous culture in the Gran Sabana, would be ca 2000 cal yr BP onwards, rather than the last centuries, as it has been formerly assumed. The implications of these ancient practices in the area are also discussed for present Gran Sabana landscapes sustainability and future conservation strategies.

  5. Digital Doping in Magic-Sized CdSe Clusters.

    PubMed

    Muckel, Franziska; Yang, Jiwoong; Lorenz, Severin; Baek, Woonhyuk; Chang, Hogeun; Hyeon, Taeghwan; Bacher, Gerd; Fainblat, Rachel

    2016-07-26

    Magic-sized semiconductor clusters represent an exciting class of materials located at the boundary between quantum dots and molecules. It is expected that replacing single atoms of the host crystal with individual dopants in a one-by-one fashion can lead to unique modifications of the material properties. Here, we demonstrate the dependence of the magneto-optical response of (CdSe)13 clusters on the discrete number of Mn(2+) ion dopants. Using time-of-flight mass spectrometry, we are able to distinguish undoped, monodoped, and bidoped cluster species, allowing for an extraction of the relative amount of each species for a specific average doping concentration. A giant magneto-optical response is observed up to room temperature with clear evidence that exclusively monodoped clusters are magneto-optically active, whereas the Mn(2+) ions in bidoped clusters couple antiferromagnetically and are magneto-optically passive. Mn(2+)-doped clusters therefore represent a system where magneto-optical functionality is caused by solitary dopants, which might be beneficial for future solotronic applications. PMID:27420556

  6. Two-Step Photoexcitation Mechanism in Amorphous Se

    NASA Astrophysics Data System (ADS)

    Berashevich, J.; Mishchenko, A.; Reznik, A.

    2014-04-01

    The first-principles simulations are applied to study a photoinduced metastability in amorphous selenium and contribution of the valence-alteration pair (VAP) defects in this process. The VAP defect is confirmed to be the equilibrium defect; it minimizes the destabilizing interaction induced by disorientation of the lone-pair (LP) electrons along the Se chains, and, thus, relieves tension in a system. The photoexcitation involves the LP electrons, and it is proposed to be described by two coexisting processes, namely, single- and double-electron excitations. Both processes are found to induce the defect states in the band gap and cause experimentally observed photodarkening; however, only double-electron excitation is capable of triggering bond rearrangement and structural transformation. Lattice relaxation, which follows bond rearrangement, occurs with characteristic energy of -0.9±0.3 eV. It is found to promote formation of energetically favorable VAP defects and to trigger the ringlike to helixlike transformations, thus, ultimately stimulating the photoinduced crystallization. The photoinduced crystallization is directly simulated in a system characterized by increased crystalline order.

  7. Digital Doping in Magic-Sized CdSe Clusters.

    PubMed

    Muckel, Franziska; Yang, Jiwoong; Lorenz, Severin; Baek, Woonhyuk; Chang, Hogeun; Hyeon, Taeghwan; Bacher, Gerd; Fainblat, Rachel

    2016-07-26

    Magic-sized semiconductor clusters represent an exciting class of materials located at the boundary between quantum dots and molecules. It is expected that replacing single atoms of the host crystal with individual dopants in a one-by-one fashion can lead to unique modifications of the material properties. Here, we demonstrate the dependence of the magneto-optical response of (CdSe)13 clusters on the discrete number of Mn(2+) ion dopants. Using time-of-flight mass spectrometry, we are able to distinguish undoped, monodoped, and bidoped cluster species, allowing for an extraction of the relative amount of each species for a specific average doping concentration. A giant magneto-optical response is observed up to room temperature with clear evidence that exclusively monodoped clusters are magneto-optically active, whereas the Mn(2+) ions in bidoped clusters couple antiferromagnetically and are magneto-optically passive. Mn(2+)-doped clusters therefore represent a system where magneto-optical functionality is caused by solitary dopants, which might be beneficial for future solotronic applications.

  8. Crystal structure and phase transition of thermoelectric SnSe.

    PubMed

    Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo

    2016-06-01

    Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed. PMID:27240762

  9. Latest Cretaceous and Paleocene extension in SE California

    SciTech Connect

    Tosdal, R.M.; Conrad, J.E.; Murphy, G.P. )

    1993-04-01

    Two ductile deformations formed the 3.5-km-thick, south dipping American Girl shear zone in the Cargo Muchancho Mountains, SE California. The older event (D1) imprints crystalloblastic fabrics that record contractional strains at midcrustal depths in the Middle( ) and Late Jurassic. The second event (D2) is marked by superposed mylonitic fabrics that are coplanar and colinear with fabrics of D1. Small mylonitic shear zones of D2 cut undeformed rocks in the hanging wall of the American Girl shear zone. Folded sheets of Jurassic granite geneiss and kinematic indicators in mylonites indicative southward directed transport down the present dip of the foliation during D2. [sup 40]Ar/[sup 39]Ar release spectrum on hornblende from undeformed upper-plate monzo-diorite (173 Ma, U-Pb zircon), about 2 km above the top of shear zone has a plateau age of 96.7[+-]0.9 Ma. In contrast, hornblende release spectra from granite gneiss about 200 m below the top of the shear zone and from hornblende gneiss about 3 km below the top of the shear zone are flat and have identical ages. Hornblende from monzodiorite at the base of the upper plate has a more complicated spectrum that is interpreted to indicate a cooling age of 60.4[+-]1.3 Ma.

  10. CdSe nanocrystal based chem-/bio- sensors.

    PubMed

    Somers, Rebecca C; Bawendi, Moungi G; Nocera, Daniel G

    2007-04-01

    Semiconductor nanocrystals (NCs) have found application in biology mostly as optical imaging agents where the photophysical properties of the NCs are insensitive to species in their environment. This tutorial review examines the application of CdSe NCs as optical sensing agents where the NC's photophysical properties are sensitive to species in their environment. For this case, the NC is modified at the surface with a conjugate, which interacts with an external agent by physical (i.e. recognition) or chemical means. Signal transduction in these chem-bio (CB) sensitive NCs is derived primarily from energy transfer between the NC and the external agent, which functions as the energy transfer acceptor or donor. Signaling may be obtained by directly detecting luminescence from the NC and/or the conjugate. New developments for the use of NCs as gain materials in micro-lasing cavities (distributed feedback gratings and spherical resonators) opens the way to designing CB-sensitive NCs for high-gain sensing applications. PMID:17387407

  11. Structure and growth mechanism of ZnSe nanowires

    NASA Astrophysics Data System (ADS)

    Basu, Joysurya; Divakar, R.; Nowak, Julia; Hofmann, Stephan; Colli, Alan; Franciosi, A.; Carter, C. Barry

    2008-09-01

    ZnSe nanowires were grown onto Mo transmission electron microscopy (TEM) grids by MBE by suitably varying the growth parameters. In situ and high-resolution TEM studies were carried out to understand the structure, defects, and growth mechanism of this nanowire. The nanowire morphology is very sensitive to the growth parameters involved. Twin boundaries are the most commonly occurring defects in the nanowires grown under Zn-rich condition and catalytic gold particles of irregular shape are observed along the nanowire body. In the course of in situ heating the shape of the nanowire tip is observed to change at ˜178 °C. Definite growth of the nanowire starts at ˜235 °C. The diameter of the grown nanowire is almost equal to that of the catalyst gold particle present at the tip of the nanowire. In situ experimental observation and available phase-diagram information strongly suggests that nanowire growth should be possible with a solid catalyst particle though it does not rule out the possibility of the existence of a VLS mechanism.

  12. Reaction Routes for the Synthesis of CuInSe2 Using Bilayer Compound Precursors

    SciTech Connect

    Krishnan, Rangarajan; Wood, David; Chaudhari, Vaibhav U.; Payzant, E Andrew; Noufi, Rommel; Rozeveld, Steve; Kim, Woo Kyoung; Anderson, Timothy J

    2012-01-01

    The reaction pathways and phase evolution during synthesis of CuInSe{sub 2} (CIS) by a novel bilayer approach were investigated using in situ high-temperature X-ray diffraction. Two bilayer precursor structures, glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se and glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se, were examined in this study. Temperature ramp experiments revealed that the phase transformation sequence for each bilayer precursor qualitatively follows that predicted by the phase diagram and that the onset temperatures for decomposition of the sub-binary compounds depend on the Se partial pressure. Measurement of the isothermal rate of formation of CuInSe{sub 2} at six temperatures in the range 260 to 310 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se bilayer suggests relatively slow nucleation followed by diffusion-limited reaction with estimated activation energy of 162({+-}7) and 225 ({+-}16) kJ/mol from Avrami and parabolic models, respectively. Interestingly, the measured activation energy for the same precursor in a 4 mol % H{sub 2}/He ambient (108 ({+-}8) kJ/mol) was lower than that observed in pure N{sub 2} (158 ({+-}16) kJ/mol). The results of isothermal measurements in the temperature range 250 to 300 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se precursor film in an inert ambient are consistent with one-dimensional diffusion-limited growth with estimated activation energy from the Avrami and parabolic models of 194 ({+-}10) and 203 ({+-}12) kJ/mol, respectively.

  13. Thermal Processing Effects on Microstructure and Composition of Cu3SbSe3

    SciTech Connect

    Majsztrik, Paul W; Kirkham, Melanie J; Garcia Negron, Valerie; Lara-Curzio, Edgar; Skoug, Eric; Morelli, Donald

    2013-01-01

    We report on the effects of thermal processing on the microstructure and composition of a system with overall stoichiometry of 3Cu:1Sb:3Se with the aim of producing single-phase Cu3SbSe3. It was found that slowly cooling from the melt produced a multiphase material consisting of Cu2Se and CuSbSe2, but devoid of Cu3SbSe3. Cooling rapidly from the melt resulted in three-phase microstructures consisting of Cu2Se, CuSbSe2, and Cu3SbSe3. Subsequent annealing of the three-phase material between 325 C and 400 C shifted composition towards nearly pure Cu3SbSe3, the target compound of this work. The kinetics of the transformation into Cu3SbSe3 is successfully described using a modified Avrami model, which suggests that diffusion is the rate-controlling step. Values of Young s modulus and hardness, obtained by nanoindentation, are reported for Cu2Se, CuSbSe2, and Cu3SbSe3.

  14. Structure, dynamics, and electronic structure of liquid Ag-Se alloys investigated by ab initio simulation

    NASA Astrophysics Data System (ADS)

    Kirchhoff, F.; Holender, J. M.; Gillan, M. J.

    1996-07-01

    Ab initio molecular-dynamics simulations have been used to investigate the structure, dynamics, and electronic properties of the liquid alloy Ag1-xSex at 1350 K and at the three compositions x=0.33, 0.42, and 0.65. To provide a point of reference, calculations are also presented for the equilibrium structure and the electronic structure of the α-Ag2Se crystal. The calculations are based on density-functional theory in the local-density approximation and on the pseudopotential plane-wave method. For the solid, we find excellent agreement with experiment for the equilibrium lattice parameters and the atomic coordinates of the 12-atom orthorhombic unit cell, and we present an analysis of the electronic density of states and density distribution. The reliability of the liquid simulations is confirmed by detailed comparisons with very recent neutron-diffraction results for the partial structure factors and radial distribution functions (RDF) of the stoichiometric liquid Ag2Se. Comparison with the predictions of an empirical interaction model due to Rino et al. is also given for l-Ag2Se. The ab initio simulations show a dramatic change of the Se-Se RDF with increasing Se content. This change is due to the formation of Se clusters bound by covalent bonds, the Se-Se bond length being almost the same as in pure c-Se and l-Se. The clusters are predominantly chainlike, but for higher x there is a significant fraction of threefold coordinated Se atoms. It is shown that the equilibrium fractions of Se present as isolated atoms and in clusters can be understood on a simple charge-balance model based on an ionic interpretation. The Ag diffusion coefficient in the simulated stoichiometric liquid is consistent with experimental values measured in the high-temperature superionic solid. The Ag and Se diffusion coefficients both increase with Se content, in spite of the Se clustering. An analysis of the Se-Se bond dynamics reveals surprisingly short bond lifetimes of less than 1 ps

  15. Selenium biofortification of broccoli and carrots grown in soil amended with Se-enriched hyperaccumulator Stanleya pinnata

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Amending soils with Se-hyperaccumulator plant derived sources of selenium (Se) may be useful for increasing Se content in food crops in Se-deficient regions of the world. In this study, we evaluated total Se and the different chemical species of Se in broccoli and carrots grown in soils amended with...

  16. Electronic structure and photoelectrical properties of Ag2In2SiSe6 and Ag2In2GeSe6

    NASA Astrophysics Data System (ADS)

    Khyzhun, O. Y.; Myronchuk, G. L.; Zamuruyeva, O. V.; Parasyuk, O. V.

    2014-12-01

    High-quality Ag2In2SiSe6 and Ag2In2GeSe6 single crystals have been successfully grown by the vertical Bridgman-Stockbarger method and the horizontal gradient freeze technique, respectively. For pristine and Ar+ ion-irradiated surfaces of the single crystals under study, X-ray photoelectron core-level and valence-band spectra have been measured. Results of these studies allow for concluding that the Ag2In2SiSe6 and Ag2In2GeSe6 single crystal surfaces are sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ ion-bombardment with energy of 3.0 keV during 5 min at an ion current density of 14 μA/cm2 has induced some modification in top surface layers leading to an increase of content of In atoms in the layers. Comparison on a common energy scale of the X-ray emission Se Kβ2 bands representing energy distribution of the Se 4p states and the X-ray photoelectron valence-band spectra reveal that the main contribution of the valence Se p states occur in the upper portion of the valence band, with also their significant contributions in other valence band regions of the Ag2In2SiSe6 and Ag2In2GeSe6 single crystals. In addition, for the single crystals under consideration, temperature dependences of specific dark conductivity and spectral distributions of photoconductivity have been explored. It has been established that the Ag2In2SiSe6 and Ag2In2GeSe6 single crystals are high-resistance semiconductors with value of the specific electrical conductivity σ ≈ 1.67 × 10-9 Ω-1 сm-1 (at Т = 300 K). The both compounds are materials with p-type conductivity.

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

    SciTech Connect

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

    2006-02-15

    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.

  18. Controllable synthesis of metal selenide heterostructures mediated by Ag2Se nanocrystals acting as catalysts

    NASA Astrophysics Data System (ADS)

    Zhou, Jiangcong; Huang, Feng; Xu, Ju; Wang, Yuansheng

    2013-09-01

    Ag2Se nanocrystals were demonstrated to be novel semiconductor mediators, or in other word catalysts, for the growth of semiconductor heterostructures in solution. This is a result of the unique feature of Ag2Se as a fast ion conductor, allowing foreign cations to dissolve and then to heterogrow the second phase. Using Ag2Se nanocrystals as catalysts, dimeric metal selenide heterostructures such as Ag2Se-CdSe and Ag2Se-ZnSe, and even multi-segment heterostructures such as Ag2Se-CdSe-ZnSe and Ag2Se-ZnSe-CdSe, were successfully synthesized. Several interesting features were found in the Ag2Se based heterogrowth. At the initial stage of heterogrowth, a layer of the second phase forms on the surface of an Ag2Se nanosphere, with a curved junction interface between the two phases. With further growth of the second phase, the Ag2Se nanosphere tends to flatten the junction surface by modifying its shape from sphere to hemisphere in order to minimize the conjunct area and thus the interfacial energy. Notably, the crystallographic relationship of the two phases in the heterostructure varies with the lattice parameters of the second phase, in order to reduce the lattice mismatch at the interface. Furthermore, a small lattice mismatch at the interface results in a straight rod-like second phase, while a large lattice mismatch would induce a tortuous product. The reported results may provide a new route for developing novel selenide semiconductor heterostructures which are potentially applicable in optoelectronic, biomedical, photovoltaic and catalytic fields.Ag2Se nanocrystals were demonstrated to be novel semiconductor mediators, or in other word catalysts, for the growth of semiconductor heterostructures in solution. This is a result of the unique feature of Ag2Se as a fast ion conductor, allowing foreign cations to dissolve and then to heterogrow the second phase. Using Ag2Se nanocrystals as catalysts, dimeric metal selenide heterostructures such as Ag2Se-CdSe and Ag2Se-ZnSe

  19. {μ-PbSe}: a heavy CO homologue as an unexpected ligand.

    PubMed

    Thiele, Günther; Franzke, Yannick; Weigend, Florian; Dehnen, Stefanie

    2015-09-14

    Reactions of [K(18-crown-6)]2 [Pb2 Se3 ] and [K([2.2.2]crypt)]2 [Pb2 Se3 ] with [Rh(PPh3 )3 Cl] in en (ethane-1,2-diamine) afforded ionic compounds with [Rh3 (PPh3 )6 (μ3 -Se)2 ](-) and [Rh3 (CN)2 (PPh3 )4 (μ3 -Se)2 (μ-PbSe)](3-) anions, respectively. The latter contains a PbSe ligand, a rather uncommon homologue of CO that acts as a μ-bridge between two Rh atoms. Quantum chemical calculations yield a significantly higher bond energy for PbSe than for CO, since the size of the ligand orbitals better matches the comparably rigid Rh-Se-Rh angles and the resulting Rh⋅⋅⋅Rh distance. To rationalize the bent coordination of the ligand, orbitals with significant ligand contributions and their dependence on the bonding angle were investigated in detail.

  20. Confined lattice dynamics of single and quadruple SnSe bilayers in [(SnSe) 1.04 ] m [MoSe 2 ] n ferecrystals

    SciTech Connect

    Klobes, Benedikt; Hu, Michael Y.; Beekman, Matt; Johnson, David C.; Hermann, Raphaël P.

    2015-11-30

    The Sn specific densities of phonon states in the SnSe subunits of [(SnSe)1.04]m[MoSe2]n ferecrystals with (m,n) = (1,1), (4,1) and in bulk SnSe were derived from nuclear inelastic scattering by the 119Sn M ssbauer resonance. When using different measurement configurations, phonons with polarization parallel and perpendicular to the ferecrystal plane were specifically probed. Vibrational properties and phonon spectral weight are found to strongly depend on the phonon polarization and layer count m. Moreover, a highly peculiar feature of these ferecrystal densities of phonon states is the emergence of rather sharp high energy vibrational modes polarized perpendicular to the ferecrystal plane, which contrasts with usual findings in thin layered structures and nanostructured materials in general, and a depletion of modes with a gap appearing between acoustic and high energy modes. The spectral weight of these phonons depends on the overall SnSe content, m, but cannot be unambiguously attributed to SnSe MoSe2 interfaces. Considering the low energy part of lattice dynamics, ferecrystals exhibit rather low average phonon group velocities as compared to the speed of sound in the long wavelength limit. For the (1,1) ferecrystal, this effect is most pronounced for vibrations polarized in the ferecrystal plane. Therefore, an experimental microscopic origin for the vibrational and bonding anisotropy in subunits of ferecrystals is provided.

  1. Formation of two-dimensional CuSe on Cu(111) at very low selenium coverage

    DOE PAGES

    Walen, Holly; Liu, Da -Jiang; Oh, Junepyo; Yang, Hyun Jin; Kim, Yousoo; Thiel, Patricia A.

    2016-05-09

    Here, using scanning tunneling microscopy (STM), we observe that adsorption of Se on Cu(111) produces islands with (√3 x √3)R30° structure, at Se coverages far below the structure's ideal coverage of 1/3 ML. Based on density functional theory (DFT), these islands cannot form due to attractive interactions between chemisorbed Se atoms. DFT shows that incorporating Cu atoms into the √3-Se lattice stabilizes the structure, which provides a plausible explanation for the experimental observations.

  2. Late Cretaceous-Early Palaeogene tectonic development of SE Asia

    NASA Astrophysics Data System (ADS)

    Morley, C. K.

    2012-10-01

    The Late Cretaceous-Early Palaeogene history of the continental core of SE Asia (Sundaland) marks the time prior to collision of India with Asia when SE Asia, from the Tethys in the west to the Palaeo-Pacific in the east, lay in the upper plate of subduction zones. In Myanmar and Sumatra, subduction was interrupted in the Aptian-Albian by a phase of arc accretion (Woyla and Mawgyi arcs) and in Java, eastern Borneo and Western Sulawesi by collision of continental fragments rifted from northern Australia. Subsequent resumption of subduction in the Myanmar-Thailand sector explains: 1) early creation of oceanic crust in the Andaman Sea in a supra-subduction zone setting ~ 95 Ma, 2) the belt of granite plutons of Late Cretaceous-Early Palaeogene age (starting ~ 88 Ma) in western Thailand and central Myanmar, and 3) amphibolite grade metamorphism between 70 and 80 Ma seen in gneissic outcrops in western and central Thailand, and 4) accretionary prism development in the Western Belt of Myanmar, until glancing collision with the NE corner of Greater India promoted ophiolite obduction, deformation and exhumation of marine sediments in the early Palaeogene. The Ranong strike-slip fault and other less well documented faults, were episodically active during the Late Cretaceous-Palaeogene time. N to NW directed subduction of the Palaeo-Pacific ocean below Southern China, Vietnam and Borneo created a major magmatic arc, associated with rift basins, metamorphic core complexes and strike-slip deformation which continued into the Late Cretaceous. The origin and timing of termination of subduction has recently been explained by collision of a large Luconia continental fragment either during the Late Cretaceous or Palaeogene. Evidence for such a collision is absent from the South China Sea well and seismic reflection record and here collision is discounted. Instead relocation of the subducting margin further west, possibly in response of back-arc extension (which created the Proto

  3. Paleoseismological study on stone cultural sites in Gyeongju, SE Korea

    NASA Astrophysics Data System (ADS)

    Lee, M.; Jin, K.; Kim, Y.

    2008-12-01

    The Korean peninsular, located within the Eurasian intracontinental region, is presently considered to be tectonically safe compared with neighboring countries such as Japan and Taiwan. However, historical records for the Gyeongju area, which is an old capital city with many ancient stone buildings, demonstrate that seismic events have significantly affected lives and properties in this town. For example, one reported earthquake in 779 AD had an inferred magnitude of M=6.7 and resulted in the deaths of over a hundred people and the destruction of many buildings. This study examines the affects of paleoseismological events recorded by stone constructions in Gyeongju. The study area contains mostly granite and is located near the junction between the Yangsan and Ulsan faults, which represent two of the major faults in SE Korea. In May of 2007, a statue of Buddha that was previously attached to and carved from a vertical granite cliff was discovered resting on the 45° slope of the Yeolam valley. Based on the artistic style of the granite statue, it was estimated to be during the late 8th century; it has a weight of about 70 tons and dimensions of 250x190x620 cm. Four main joint directions exist in the statue and in granite exposed in the cliff at its original location. These joint sets match if the statue were rotated 15° clockwise back from present position. Another evidence for damages also occurs at ChumSungDae astronomical observatory. One possible cause for these destructions and damages is paleoseismicity in this area.

  4. Comparative oxygen barometry in granulites, Bamble sector, SE Norway

    SciTech Connect

    Harlov, D.E. )

    1992-07-01

    Oxygen fugacities have been estimated for the high-grade portion of the Bamble granulite facies terrane, SE Norway, using both titaniferous magnetite-ilmenite and orthopyroxene-titaniferous magnetite-quartz oxygen barometers. The two oxygen barometers show good agreement, for samples indicating high titaniferous magnetite-ilmenite temperatures whereas agreement is poor for low-temperature samples. Oxygen fugacities estimated from titaniferous magnetite-ilmenite are considerably lower than those estimated from orthopyroxene-titaniferous magnetite-quartz. This discrepancy increases with a decrease in temperature, which appears to reflect preferential resetting of the hematite content in the ilmenite grains, without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains. The mean temperature for non-reset samples, 795 {plus minus} 60C (1{sigma}), agrees well with temperatures obtained from garnet-orthopyroxene K{sub D} exchange thermometry in the same region, 785 {plus minus} 60C (1{sigma}). The non-reset oxygen fugacities also agree well with an independent study of the Bamble granulites by Cameron. The QUIlP equilibrium (Quartz-Ulvospinel-Ilmenite-Pyroxene) is used to project self-consistent equilibrium temperatures and oxygen fugacities for samples reset due to hematite loss from the ilmenite grains. These projected temperatures and oxygen fugacities agree reasonably well with non-reset samples. The mean projected temperature is 830 {plus minus} 40C (1{sigma}). This agreement strongly supports the conclusion that low titaniferous magnetite-ilmenite temperatures (down to 485C) and accompanying low-oxygen fugacities are the result of hematite loss from the ilmenite grains at some time after granulite-facies metamorphism.

  5. An investigation of new infrared nonlinear optical material: BaCdSnSe4, and three new related centrosymmetric compounds: Ba2SnSe4, Mg2GeSe4, and Ba2Ge2S6.

    PubMed

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

    2015-12-14

    A series of new metal chalcongenides, BaCdSnSe4 (1), Ba2SnSe4 (2), Mg2GeSe4 (3), and Ba2Ge2S6 (4), were successfully synthesized for the first time. Among them, compounds 2 and 4 were prepared by a molten flux method with Zn as the flux. In their structures, all of them have MQ4 (M = Sn, Ge; Q = S, Se) units. For compound 1, the CdSe4 and SnSe4 groups are connected to form CdSnSe6 layers and these layers are linked together by the Ba atoms. Compounds 2 and 3 are composed of isolated MSe4 (M = Sn, Ge) units and charge-balanced by the Ba or Mg atoms, respectively, while compound 4 has infinite ∞(GeS3)n chains, which is different from the structures of the other three compounds that only have isolated MSe4 (M = Sn, Ge) units. The measured IR and Raman data of the title compounds show wide infrared transmission ranges. The experimental band gaps of compounds 1, 2, 3 and were determined to be 1.79, 1.90, and 2.02 eV, respectively. Band structures were also calculated and indicate that their tetrahedral units, such as [SnSe4], [GeS4] and [GeSe4], determine the energy band gaps of the title compounds, respectively. As for compound 1, based on fundamental light at 2.09 μm, the experimental second harmonic generation (SHG) response is about 1.6 times that of the benchmark AgGaS2, which is also consistent with the calculated value. Based on the above results, compound 1 has promising applications in the IR field as a NLO material. PMID:26509847

  6. The Mesoproterozoic Kibaride belt (Katanga, SE D.R. Congo)

    NASA Astrophysics Data System (ADS)

    Kokonyangi, J. W.; Kampunzu, A. B.; Armstrong, R.; Yoshida, M.; Okudaira, T.; Arima, M.; Ngulube, D. A.

    2006-09-01

    Five representative key regions from the NE-SW-trending Mesoproterozoic Kibaride belt of SE Congo are described. Although the present database is still insufficient for a definitive reconstruction of the tectonic setting, available data suggest that the investigated areas experienced a similar geological history. The Kibaran Supergroup comprises four major lithostratigraphic units in SE Congo. The Kiaora Group is the oldest unit. It starts with a basal conglomerate which is overlain by siliciclastic rocks deposited in fluviatile and possibly lacustrine environments. The conglomerate is overlain by abundant metapelites (predominantly black schist) with calc-silicate, volcano-sedimentary rocks and minor metachert deposited in shallow marine environments. These units are cut by 1.38 Ga granitoids. The overlying Nzilo Group is composed of coarse-grained, siliciclastic metasedimentary rocks including metaconglomerates, quartzites and minor metapelites and metamorphosed ironstones. Frequent herringbone and wavy ripples suggest tidal flat deposition. The maximum depositional age of this group is given by the 1.38 Ga granitoids on which it rests disconformably and by detrital zircons from a quartzite, which yields a concordant age of 1360 ± 27 Ma. The above two groups are separated by a disconformity along with the matrix-supported Kataba Conglomerate occurs at the base of the Nzilo Group. Higher in the succession, the Hakansson Group is essentially pelitic with minor quartzites. At the top of the succession, the Lubudi Group is made of (stromatolitic) carbonates, black schists and minor black quartzites and is inferred to record shallow marine deposition. All these metasedimentary rocks were deposited before the emplacement of ca. 1.0-0.95 Ga tin granites and are older than 1.08 Ga, which is the age of the climax of Kibaran deformation in the Mitwaba area. Two major deformational events have been recognized in the study areas. The earliest (D 1) is characterized by ENE

  7. Growth process and magnetic properties of α-FeSe nanostructures

    NASA Astrophysics Data System (ADS)

    Li, S. J.; Li, D.; Jiang, J. J.; Liu, G. B.; Ma, S.; Liu, W.; Zhang, Z. D.

    2014-05-01

    Growth process and magnetic properties of PbO-type α-FexSe nanostructures with shape changing from nanocacti to nanopetals and then to nanosheets are investigated. With iron acetylacetonate [Fe(acac)3] and Se powder as raw materials, the diffusion process of Fe atoms dominates the synthesis of α-FexSe nanocacti following phase transitions from FeSe2 to Fe3Se4 and finally to α-FexSe. When a mixed solution containing Se precursor and Fe(acac)3 was used as the raw material, the formation of FeSe2 and Fe3Se4 can be avoided and, bended α-FexSe nanopetals can be prepared at 345 °C, which became flat nanosheets with a [001] preferred orientation as extending the reaction time from 1 to 4 h. No superconducting transition occurs in the α-FexSe (0.84 ≤ x ≤ 1.05) nanostructures due to composition heterogeneity or size effect. Magnetic measurements indicate that an antiferromagnetic component with a Néel point at about 45 K dominates the magnetic properties of the α-Fe0.87Se nanosheets.

  8. The effects of Selenocysteine Se-Methyltransferase on Selenium metabolism in Broccoli

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Selenium (Se) plays an indispensable role in human nutrition and has suggested to have important health benefits, including as a cancer preventative agent. Se-methylselenocysteine, a monomethylated form of Se, has been shown to be one of the most effective chemopreventative compounds. Broccoli is ...

  9. Temperature dependence of Raman scattering in amorphous films of In 1- xSe x alloys

    NASA Astrophysics Data System (ADS)

    Weszka, J.; Daniel, Ph.; Burian, A. M.; Burian, A.; Żelechower, M.

    2001-08-01

    Raman scattering (RS) in amorphous films of In 1- xSe x with 0.70≥ x≥0.38 has been studied in backscattering geometry with the use of a single channel Raman spectrometer at room and 10 K temperatures. The recorded RS spectra reveal dominant vibrational density-of-states character. They exhibit a continuum, spanning the Rayleigh line up to a shoulder at about 250 cm -1, that moves towards lower frequencies as x decreases from 0.70 to 0.38. The bands at about 104, 125 and at 143 and 237 cm -1 are attributed to In-In, Se 8 ring molecules and Se-chain oscillations, respectively. The structure of In 1- xSe x alloys is deduced to be a continuous random network based on InSe 4/2 tetrahedral clusters interconnected by Se atoms at the shared corners or local Se-chain fragments or Se 8 rings. With growing In content, some Se atoms in such clusters are replaced by In atoms to an extent dependent on In content. The disappearance of the 143 and 237 cm -1 bands in the low temperature spectra taken on the In 0.30Se 0.70 film is attributed to the contraction of interatomic bonds, making conditions favorable for breaking Se polymer chains and Se 8 ring molecule formation.

  10. Selenium speciation in soil and rice: influence of water management and Se fertilization.

    PubMed

    Li, Hua-Fen; Lombi, Enzo; Stroud, Jacqueline L; McGrath, Steve P; Zhao, Fang-Jie

    2010-11-24

    Rice (Oryza sativa) is the staple food for half of the world's population, but the selenium (Se) concentrations in rice grain are low in many rice-growing regions. This study investigated the effects of water management on the Se speciation dynamics in the soil solution and Se uptake and speciation in rice in a pot experiment. A control containing no Se or 0.5 mg kg(-1) of soil of selenite or selenate was added to the soil, and plants were grown under aerobic or flooded conditions. Flooding soil increased soluble Se concentration when no Se or selenite was added to the soil, but decreased it markedly when selenate was added. Selenate was the main species in the +selenate treatment, whereas selenite and selenomethionine selenium oxide were detected in the flooded soil solutions of the control and +selenite treatments. Grain Se concentration was 49% higher in the flooded than in the aerobic treatments without Se addition. In contrast, when selenate or selenite was added, the aerobically grown rice contained 25- and 2-fold, respectively, more Se in grain than the anaerobically grown rice. Analysis of Se in rice grain using enzymatic hydrolysis followed by HPLC-ICP-MS and in situ X-ray absorption near-edge structure (XANES) showed selenomethionine to be the predominant Se species. The study showed that selenate addition to aerobic soil was the most effective way to increase Se concentration in rice grain. PMID:20964343

  11. The Antiphagocytic Activity of SeM of Streptococcus equi Requires Capsule

    PubMed Central

    TIMONEY, John F.; SUTHER, Pranav; VELINENI, Sridhar; ARTIUSHIN, Sergey C.

    2014-01-01

    ABSTRACT Resistance to phagocytosis is a crucial virulence property of Streptococcus equi (Streptococcus equi subsp. equi; Se), the cause of equine strangles. The contribution and interdependence of capsule and SeM to killing in equine blood and neutrophils were investigated in naturally occurring strains of Se. Strains CF32, SF463 were capsule and SeM positive, strains Lex90, Lex93 were capsule negative and SeM positive and strains Se19, Se1-8 were capsule positive and SeM deficient. Phagocytosis and killing of Se19, Se1-8, Lex90 and Lex93 in equine blood and by neutrophils suspended in serum were significantly (P ≤ 0.02) greater compared to CF32 and SF463. The results indicate capsule and SeM are both required for resistance to phagocytosis and killing and that the anti-phagocytic property of SeM is greatly reduced in the absence of capsule. PMID:25013359

  12. A Safer, Easier, Faster Synthesis for CdSe Quantum Dot Nanocrystals

    ERIC Educational Resources Information Center

    Boatman, Elizabeth M.; Lisensky, George C.; Nordell, Karen J.

    2005-01-01

    The synthesis for CdSe quantum dot nanocrystals that vary in color and are a visually engaging way to demonstrate quantum effects in chemistry is presented. CdSe nanocrystals are synthesized from CdO and elemental Se using a kinetic growth method where particle size depends on reaction time.

  13. Growth process and magnetic properties of α-FeSe nanostructures

    SciTech Connect

    Li, S. J.; Li, D. Jiang, J. J.; Liu, G. B.; Ma, S.; Liu, W.; Zhang, Z. D.

    2014-05-07

    Growth process and magnetic properties of PbO-type α-Fe{sub x}Se nanostructures with shape changing from nanocacti to nanopetals and then to nanosheets are investigated. With iron acetylacetonate [Fe(acac){sub 3}] and Se powder as raw materials, the diffusion process of Fe atoms dominates the synthesis of α-Fe{sub x}Se nanocacti following phase transitions from FeSe{sub 2} to Fe{sub 3}Se{sub 4} and finally to α-Fe{sub x}Se. When a mixed solution containing Se precursor and Fe(acac){sub 3} was used as the raw material, the formation of FeSe{sub 2} and Fe{sub 3}Se{sub 4} can be avoided and, bended α-Fe{sub x}Se nanopetals can be prepared at 345 °C, which became flat nanosheets with a [001] preferred orientation as extending the reaction time from 1 to 4 h. No superconducting transition occurs in the α-Fe{sub x}Se (0.84 ≤ x ≤ 1.05) nanostructures due to composition heterogeneity or size effect. Magnetic measurements indicate that an antiferromagnetic component with a Néel point at about 45 K dominates the magnetic properties of the α-Fe{sub 0.87}Se nanosheets.

  14. Nanocrystal growth and morphology of PbTeSe-ZnSe composite thin films prepared by one-step synthesis method

    NASA Astrophysics Data System (ADS)

    Sato, Kazuhisa; Abe, Seishi

    2016-10-01

    The microstructure of polycrystalline PbTe1-xSex-ZnSe composite thin films has been studied by scanning transmission electron microscopy and electron diffraction. The films were prepared by the one-step synthesis method using simultaneous evaporation of PbTe and ZnSe. The nanocrystals of PbTe1-xSex are formed in a ZnSe matrix. Tellurium concentration can be tuned by controlling the PbTe evaporation source temperatures between 753 K and 793 K. Binary PbSe nanocrystals were formed at 753 K, while ternary PbTe1-xSex nanocrystals were formed at 793 K. The nanocrystals grow in a granular shape at the initial stage of film growth, and the morphology changes to nanowire-shape as the film grows, irrespective of the Te concentration. The ternary PbTe1-xSex nanocrystals were composed of two phases with different Te concentration; Te-rich (Se-poor) granular crystals were formed near the bottom half parts of the film and Te-poor (Se-rich) nanowires were formed at the upper half parts of the film. Columnar ZnSe crystals contain high-density {111} stacking faults due to the low stacking fault energy of ZnSe. A balance of deposition and re-evaporation on the substrate during the film growth will be responsible for the resultant nanocrystal morphology.

  15. Optical properties of amorphous Ge1- x Se x and Ge1- x- y Se x As y thin films — optical gap bowing and phonon modes

    NASA Astrophysics Data System (ADS)

    Lee, Hosuk; So, Hyeon Seob; Lee, Hosun; Shin, Hae-Young; Yoon, Seokhyun; Ahn, Hyung-Woo; Kim, Su-Dong; Lee, Suyoun; Jeong, Doo-Seok; Cheong, Byung-ki

    2014-06-01

    We investigated the optical properties of Ge1- x Se x and Ge1- x- y Se x As y amorphous films by using spectroscopic ellipsometry and Raman spectroscopy. The dielectric functions and absorption coefficients ( α) of the amorphous films were determined from the measured ellipsometric angles (Ψ,Δ). We obtained the optical gap energies and the Urbach energies from the absorption coefficients and found a strong bowing effect in the optical gap energy of Ge1- x- y Se x As y , where the endpoint binaries were Ge0.50Se0.50 and Ge0.31As0.69. Based on the correlation between the optical gap energies and the Urbach energies, we attributed the large bowing parameter to electronic disorder. Using Raman spectroscopy, we measured the phonon modes and discussed the composition dependence of the phonon peak frequencies and lineshapes in terms of structural units. Based on the composition dependence of the phonons in Ge1- x- y Se x As y , we identified the phonon modes of Ge0.31As0.69. A resonant Raman phenomenon was observed in Ge0.40Se0.60 at a laser excitation of 514 nm (2.41 eV). We verified that this laser energy corresponded to the transition energy of Ge0.40Se0.60 by using the second derivative of the dielectric function of Ge0.40Se0.60.

  16. Thermal stability and photoconductive properties of photosensors with an alternating multilayer structure of amorphous Se and As{sub x}Se{sub 1−x}

    SciTech Connect

    Yu, Tung-Yuan; Pan, Fu-Ming Chang, Cheng-Yi; Lin, Jian-Siang; Huang, Wen-Hsien

    2015-07-28

    In this study, we fabricated a-Se based photosensors with an alternating multilayer structure of a-Se and As{sub x}Se{sub 1−x} by rotational thermal evaporation deposition. During the deposition of the amorphous As{sub x}Se{sub 1−x} layers, As diffuses into the underlying a-Se component layers, thereby improving the thermal stability of the multilayer photosensor and thus increasing the breakdown electric field. Although the As doping introduces carrier traps in the a-Se layers, the multilayer photosensors demonstrate an effective quantum efficiency comparable to the single-layered a-Se sensor under the blue light illumination but are with a lower dark current density by two orders of magnitude. In addition to the top As{sub x}Se{sub 1−x} layer being functioning as an electron blocking layer, carrier traps present in the multilayer structure may decrease the drift mobility of charge carriers and disturb electric field distribution in the photosensors, thereby suppressing the dark current.

  17. New insights into the Mo/Cu(In,Ga)Se2 interface in thin film solar cells: Formation and properties of the MoSe2 interfacial layer

    NASA Astrophysics Data System (ADS)

    Klinkert, T.; Theys, B.; Patriarche, G.; Jubault, M.; Donsanti, F.; Guillemoles, J.-F.; Lincot, D.

    2016-10-01

    Being at the origin of an ohmic contact, the MoSe2 interfacial layer at the Mo/Cu(In,Ga)Se2 interface in CIGS (Cu(In,Ga)Se2 and related compounds) based solar cells has allowed for very high light-to-electricity conversion efficiencies up to 22.3%. This article gives new insights into the formation and the structural properties of this interfacial layer. Different selenization-steps of a Mo covered glass substrate prior to the CIGS deposition by co-evaporation led to MoSe2 interfacial layers with varying thickness and orientation, as observed by x-ray diffraction and atomic resolution transmission electron microscopy. A novel model based on the anisotropy of the Se diffusion coefficient in MoSe2 is proposed to explain the results. While the series resistance of finished CIGS solar cells is found to correlate with the MoSe2 orientation, the adhesion forces between the CIGS absorber layer and the Mo substrate stay constant. Their counter-intuitive non-correlation with the configuration of the MoSe2 interfacial layer is discussed and related to work from the literature.

  18. Metal Ions Mediated Morphology and Phase Transformation of Chalcogenide Semiconductor: From CuClSe2 Microribbon to CuSe Nanosheet.

    PubMed

    Liu, Yong-Qiang; Wu, Hao-Di; Zhao, Yu; Pan, Ge-Bo

    2015-05-01

    Foreign ions are of significant importance in controlling and modulating the morphology of semiconductor nanocrystals during the colloidal synthesis process. Herein, we demonstrate the potential of foreign metal ions to simultaneously control the morphology and crystal phase of chalcogenide semiconductors. The results indicate that the introduction of Al(3+) ions can induce the structural transformation from monoclinic CuClSe2 microribbons (MRs) to klockmannite CuSe nanosheets (NSs) and the growth of large-sized CuSe NSs. The as-prepared micrometer-sized CuSe NSs exhibit a high-conducting behavior, long-term durability, and environment stability. The novel properties enable CuSe NSs to open up a bright prospect for printable electrical interconnects and flexible electronic devices.

  19. A simple and facile synthesis of MPA capped CdSe and CdSe/CdS core/shell nanoparticles

    SciTech Connect

    Sukanya, D.; Sagayaraj, P.

    2015-06-24

    II-VI semiconductor nanostructures, in particular, CdSe quantum dots have drawn a lot of attention because of their promising potential applications in biological tagging, photovoltaic, display devices etc. due to their excellent optical properties, high emission quantum yield, size dependent emission wavelength and high photostability. In this paper, we describe the synthesis and properties of mercaptopropionic acid capped CdSe and CdSe/CdS nanoparticles through a simple and efficient co-precipitation method followed by hydrothermal treatment. The growth process, characterization and the optical absorption as a function of wavelength for the synthesized MPA capped CdSe and CdSe/CdS nanoparticles have been determined using X-ray diffraction study (XRD), Ultraviolet-Visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and High Resolution Transmission Electron Microscopy (HRTEM)

  20. Bioavailability of particle-associated Se to the bivalve Potamocorbula amurensis

    USGS Publications Warehouse

    Schlekat, C.E.; Dowdle, P.R.; Lee, B.-G.; Luoma, S.N.; Oremland, R.S.

    2000-01-01

    Elemental selenium, Se(0), is a prevalent chemical form in sediments, but little is known about its bioavailability. We evaluated the bioavailability of two forms of Se(0) by generating radioisotopic 75Se(0) through bacterial dissimilatory reduction of 75SeO32- by pure bacterial cultures (SES) and by an anaerobic sediment microbial consortium (SED). A third form was generated by reducing 75SeO32- with ascorbic acid (AA). Speciation determinations showed that AA and SES were >90% Se(0), but SED showed a mixture of Se(0), selenoanions, and a residual fraction. Pulse-chase techniques were used to measure assimilation efficiencies (AE) of these particulate Se forms by the bivalve Potamocorbula amurensis. Mean AE values were 3 ?? 2% for AA, 7 ?? 1% for SES, and 28 ?? 15% for SED, showing that the bioavailability of reduced, particle-associated Se is dependent upon its origin. To determine if oxidative microbial processes increased Se transfer, SES 75Se(0) was incubated with an aerobic sediment microbial consortium. After 113 d of incubation, 36% of SES Se(0) was oxidized to SeO32-. Assimilation of total particulate Se was unaffected however (mean AE = 5.5%). The mean AE from the diatom Phaeodactylum tricornutum was 58 ?? 8%, verifying the importance of Se associated with biogenic particles. Speciation and AE results from SED suggest that selenoanion reduction in wetlands and estuaries produces biologically available reduced selenium.Elemental selenium, Se(0), is a prevalent chemical form in sediments, but little is known about its bioavailability. We evaluated the bioavailability of two forms of Se(0) by generating radioisotopic 75Se(0) through bacterial dissimilatory reduction of 75SeO32- by pure bacterial cultures (SES) and by an anaerobic sediment microbial consortium (SED). A third form was generated by reducing 75SeO32 with ascorbic acid (AA). Speciation determinations showed that AA and SES were > 90% Se(0), but SED showed a mixture of Se(0), selenoanions, and a

  1. Phase relations in KxFe2-ySe2 and the structure of superconducting KxFe2Se2 via high-resolution synchrotron diffraction

    NASA Astrophysics Data System (ADS)

    Shoemaker, Daniel P.; Chung, Duck Young; Claus, Helmut; Francisco, Melanie C.; Avci, Sevda; Llobet, Anna; Kanatzidis, Mercouri G.

    2012-11-01

    Superconductivity in iron selenides has experienced a rapid growth, but not without major inconsistencies in the reported properties. For alkali-intercalated iron selenides, even the structure of the superconducting phase is a subject of debate, in part because the onset of superconductivity is affected much more delicately by stoichiometry and preparation than in cuprate or pnictide superconductors. If high-quality, pure, superconducting intercalated iron selenides are ever to be made, the intertwined physics and chemistry must be explained by systematic studies of how these materials form and by and identifying the many coexisting phases. To that end, we prepared pure K2Fe4Se5 powder and superconductors in the KxFe2-ySe2 system, and examined differences in their structures by high-resolution synchrotron and single-crystal x-ray diffraction. We found four distinct phases: semiconducting K2Fe4Se5, a metallic superconducting phase KxFe2Se2 with x ranging from 0.38 to 0.58, the phase KFe1.6Se2 with full K occupancy and no Fe vacancy ordering, and a oxidized phase K0.51(5)Fe0.70(2)Se that forms the PbClF structure upon exposure to moisture. We find that the vacancy-ordered phase K2Fe4Se5 does not become superconducting by doping, but the distinct iron-rich minority phase KxFe2Se2 precipitates from single crystals upon cooling from above the vacancy ordering temperature. This coexistence of separate metallic and semiconducting phases explains a broad maximum in resistivity around 100 K. Further studies to understand the solubility of excess Fe in the KxFe2-ySe2 structure will shed light on the maximum fraction of superconducting KxFe2Se2 that can be obtained by solid state synthesis.

  2. Effects of high selenomethionine (L-SeMet) intakes on female long-tailed macaques and their offspring

    SciTech Connect

    Hawkes, W.C.; Craig, K.A.; Omaye, S.T.; Willhite, C.C. Letterman Army Inst. of Research, San Francisco, CA Department of Health Services, Berkeley, CA )

    1991-03-11

    Pregnant females were treated daily for 30 days with 0, 25, 150 or 300 {mu}g Se as L-SeMet per kg body weight. Maternal Se toxicity was evident in the 150 and 300 {mu}g/kg-d groups. There were no effects of L-SeMet on pregnancy outcome, fetal morphology or neonatal development. Erythrocyte (RBC) glutathione peroxidase (GPx), RBC Se, plasma (PL) Se, PL GPx, hair (HR) Se, fecal Se and daily urinary Se excretion (UR Se) in dams were significantly correlated to L-SeMet intake. HR Se and UR Se showed the greatest responses to L-SeMet intake. RBC GPx increased 2.5-fold in the 150 {mu}g/kg-d group, casting doubt on use of RBC GPx saturation as a criterion of nutritional adequacy. Neonatal RBC and PL and fetal RBC, PL, liver, kidney, muscle and placental Se were significantly correlated to L-SeMet intake and maternal Se status, but GPx was not. There was no effect of L-SeMet on milk Se or milk GPx, showing the dominant effect of intrauterine exposure on neonatal Se status. PL Se was 3-fold higher in dams than in fetuses, suggesting a role of the placenta in regulating fetal Se. In control RBC and PL, fetal GPx {gt} neonatal GPx {gt} maternal GPx, suggesting an effect of development on GPx.

  3. Detrital zircon study along the Tsangpo River, SE Tibet

    NASA Astrophysics Data System (ADS)

    Liang, Y.; Chung, S.; Liu, D.; O'Reilly, S. Y.; Chu, M.; Ji, J.; Song, B.; Pearson, N. J.

    2004-12-01

    The interactions among tectonic uplift, river erosion and alluvial deposition are fundamental processes that shape the landscape of the Himalayan-Tibetan orogen since its creation from early Cenozoic time. To better understand these processes around the eastern Himalayan Syntaxis, we conducted a study by systematic sampling riverbank sediments along the Tsangpo River, SE Tibet. Detrital zircons separated from the sediments were subjected to U-Pb dating by the SHRIMP II at the Beijing SHRIMP Center and then in-situ measurements of Hf isotope ratios using LA-MC-ICPMS at GEMOC. These results, together with U-Pb ages and Hf isotope data that we recently obtained for the Transhimalayan plutonic and surrounding basement rocks, allow a more quantitative examination of the provenance or protosource areas for the river sediments. Consequently, the percentage inputs from these source areas can be estimated. Our study indicates that, before the Tsangpo River flows into the Namche Barwa Syntaxis of the eastern Himalayas where the River forms a 180° Big Bend gorge and crosscuts the Himalayan sequences, the Gangdese batholith that crops out just north of the River appear to be an overwhelming source accounting for ˜50 % of the bank sediments. The Tethyan Himalayan sequences south of the River are the second important source, with an input of ˜25 %. The proportion of sediment supply changes after the River enters the Big Bend gorge and turns to south: ˜25 % of detrital zircons are derived from the Greater Himalayas so that the input from the Tethyan Himalayas decreases (< 10 %) despite those from the Gangdese batholith remains high ( ˜40 %). Comparing with the sediment budget of the Brahmaputra River in the downstream based on literature Sr, Nd and Os isotope information, which suggests dominant ( ˜90-60 %) but subordinate ( ˜10-40 %) contributions by the (Greater and Lesser) Himalayan and Tibetan (including Tethyan Himalayan) rocks, respectively, the change is interpreted

  4. Open hydrological data at hypeweb.smhi.se

    NASA Astrophysics Data System (ADS)

    Arheimer, Berit; Strömbäck, Lena; Andersson, Jafet; Donnelly, Chantal; Gustafsson, David; Pechlivianidis, Ilias; Strömqvist, Johan

    2016-04-01

    Following the EU open data strategy the Swedish Meteorological and Hydrological Institute (SMHI) is providing large parts of the databases openly available. These data are ranging from historical observations to climate predictions in various areas such as weather, oceanography and hydrology. For the Water Service called Hypeweb (www.hypeweb.smhi.se), we provide data for water management. So far, the data has been used in: (i) Climate change impact assessments on water resources and dynamics; (ii) The European Water Framework Directive (WFD) for characterization and development of measure programs to improve the ecological status of water bodies; (iii) Design variables for infrastructure constructions; (iv) Spatial water-resource mapping; (v) Operational forecasts (1-10 days and seasonal) on floods and droughts; (vi) Input to oceanographic models for operational forecasts and marine status assessments; and (vii) Research. The data of Hypeweb is based on other open data sources that has been merged and re-purposed by using the Hydrological Predictions for the Environment (HYPE) model in world-wide applications with high resolution. HYPE is a dynamic, semi-distributed, process-based, and integrated catchment model. So far, the following regional domains have been modelled with different resolutions (number of subbasins within brackets): Sweden (37 000), Europe (35 000), Arctic basin (30 000), La Plata River (6 000), Niger River (800), Middle-East North-Africa (31 000), and the Indian subcontinent (6 000). The web site provides several interactive applications for exploring results from the models. The user can explore an overview of various water variables for historical and future conditions. Moreover the user can explore and download historical time series of discharge for each basin and explore the performance of the model towards observed river flow. The presentation will give an overview of the functionality of the web site and the available hydrological

  5. Geomorphological impacts of an extreme flood in SE Spain

    NASA Astrophysics Data System (ADS)

    Hooke, J. M.

    2016-06-01

    Long-term field studies in semiarid ephemeral streams are rare. These geomorphic data are essential for understanding the nature of the processes in order to develop modelling for risk assessments and management. An extreme flood event on 28 September 2012 affected the Murcia region of SE Spain, including long-tem monitoring sites on two fluvial systems in the Guadalentín basin, the Nogalte and Torrealvilla. Detailed morphological data were collected before and immediately after the event; and the amount of morphological change, erosion, and deposition have been related to peak flow conditions at the sites. On the Nogalte channel, peak flow reached 2500 m3 s- 1 at the downstream end of the catchment in less than 1 h. The event had a recurrence interval of > 50 years based on rainfall records and damage to old irrigation structures. The major effect in the braided, gravel channel of the Nogalte was net aggradation, with massive deposition in large flat bars. The measured changes in bankfull capacity were highly correlated with most hydraulic variables. Net changes in cut-and-fill in cross sections on the Nogalte were highly related to peak discharge and stream power but much less so to measures of hydraulic force (velocity, shear stress, unit stream power). Relationships of amount of erosion to hydraulic variables were much weaker than for amount of deposition, which was largely scaled to channel size and flow energy. Changes on the Torrealvilla were much less than on the Nogalte, and net erosion occurred at all sites. Sites on the Nogalte channel in schist exhibited higher deposition than those of the Torrealvilla sites on marl for the same hydraulic values. Overall, less morphological change took place in the extreme event on the Nogalte than predicted from some published hydraulic relations, probably reflecting the high sediment supply and the hydrological characteristics of the event. The results demonstrate the high degree of adjustment of these channels to

  6. Coeval Tibet uplift and shortening of SE Asia basins (Invited)

    NASA Astrophysics Data System (ADS)

    Pubellier, M.; Robert, A.; de Sigoyer, J.; Zuo, X.; Chamot-Rooke, N. R.; Chan, L. S.

    2010-12-01

    The SE Asian region has been the site of two mega events during the Tertiary; the formation of the Tibet-Himalayan structure and the continuous opening of basins at the rear of the Sunda subduction zone. The area covered by the Tibet plateau is the result of an accretion period which started by Jurassic times, and shed clastics in the Sichuan basin. Evidences of uplift of the plateau exist since 35 My, but the important motion also exist mostly on the edges around 14-8 My depending on the area and the method of dating. In front of the South China Block, the Longmen Shan thick-skin tectonics and uplift is also dated by the late Middle Miocene. Besides, the opening of the marginal basins of the present Sunda plate started early by the end of Cretaceous times and continued until the Pliocene. If a correlation between the mechanisms and timing of thickening of the Plateau and the opening of the basins still needs to be demonstrated, on the other hand, the beginning of basin shortening in the Sunda Plate, which started in the Mid Miocene, is marked by the final stage of the Proto South China Sea (PSCS) subduction and the end of the opening of the South China Sea. Around the basin system which fringes the India-Eurasia continental subduction, the stratigraphic series are marked by the classical MMU (Mid Miocene Unconformity) which is ubiquitous although suffering from slight variations in age. We propose that the E-W extrusion of crustal material from the Tibet area was possible because of the free edge and traction of the Sunda subduction until the end of the Middle Miocene. The early arrival of Australian crustal blocks (E Sulawesi) into the subduction was accommodated first by the subduction of the PSCS which acted as a buffer. The end of the PSCS consumption is coeval to the MMU, the uplift of Tibet, and the thick-skin deformation and exhumation observed in the Longmen Shan.

  7. Ferromagnetism in (Mn,Li) co-doped CdSe

    NASA Astrophysics Data System (ADS)

    Nabi, Z.; Ahuja, R.

    2008-12-01

    Ab initio calculations based on the density functional theory are reported for the Mn-doped CdSe for 5.5% and 12.5% Mn on a Cd sublattice. It is found that Mn-doped CdSe is antiferromagnetic. An essential ingredient to stabilize the ferromagnetism in bulk Cd1-xMnxSe can be realized by the co-doping of Li. We demonstrate that CdSe co-doped with Mn and Li has a stable ferromagnetic ground state and we show that the electronic structure of Cd1-2xMnxLixSe has a nearly metallic character.

  8. Synthesis, Structural and Optical Characterization of CdTeSe/ZnSe and CdTeSe/ZnTe Core/Shell Ternary Quantum Dots for Potential Application in Solar Cells

    NASA Astrophysics Data System (ADS)

    Hung, Le Xuan; Thang, Pham Nam; Van Nong, Hoang; Yen, Nguyen Hai; Chinh, Vu Đuc; Van Vu, Le; Hien, Nguyen Thi Thuc; de Marcillac, Willy Daney; Hong, Phan Ngoc; Loan, Nguyen Thu; Schwob, Catherine; Maître, Agnès; Liem, Nguyen Quang; Bénalloul, Paul; Coolen, Laurent; Nga, Pham Thu

    2016-08-01

    This work presents the results on the fabrication, structural and optical properties of CdTeSe/ZnTe and CdTeSe/ZnSe n monolayers (ML) (with n = 0,1,2,4 and 6 being the nominal shell monolayer thickness) ternary alloyed core/shell quantum dots (QDs). Transmission electron microscopy has been used to observe the shape and size of the QDs. These QDs crystallize at the zinc-blende phase. Raman scattering has been used to characterize the CdTeSe QDs' alloy composition in the fabrication and coating processes. The Raman spectrum of CdTeSe QDs, in the frequency range from 100 cm-1 to 300 cm-1, is a composite band with two peaks at 160 cm-1 and 192 cm-1. When the thickness of the ZnTe shell is 4 ML, the peak of the Raman spectrum only appears at 160 cm-1. For the ZnSe 4 ML shell, the peak only appears at ˜200 cm-1. This shows that the nature of the CdTeSe QDs is either CdTe-rich or CdSe-rich depending on the shell of each sample. The shell thickness of 2 ML does not change the ternary core QDs' crystalline phase. The absorption and photoluminescence spectra show that the absorption and emission bands can be shifted to 900 nm, depending on each ternary alloyed QD core/shell sample. This near-infrared spectrum region is suitable for applications in solar cells.

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

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    1993-01-01

    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.

  10. High-quality, large-area MoSe2 and MoSe2/Bi2Se3 heterostructures on AlN(0001)/Si(111) substrates by molecular beam epitaxy.

    PubMed

    Xenogiannopoulou, E; Tsipas, P; Aretouli, K E; Tsoutsou, D; Giamini, S A; Bazioti, C; Dimitrakopulos, G P; Komninou, Ph; Brems, S; Huyghebaert, C; Radu, I P; Dimoulas, A

    2015-05-01

    Atomically-thin, inherently 2D semiconductors offer thickness scaling of nanoelectronic devices and excellent response to light for low-power versatile applications. Using small exfoliated flakes, advanced devices and integrated circuits have already been realized, showing great potential to impact nanoelectronics. Here, high-quality single-crystal MoSe2 is grown by molecular beam epitaxy on AlN(0001)/Si(111), showing the potential for scaling up growth to low-cost, large-area substrates for mass production. The MoSe2 layers are epitaxially aligned with the aluminum nitride (AlN) lattice, showing a uniform, smooth surface and interfaces with no reaction or intermixing, and with sufficiently high band offsets. High-quality single-layer MoSe2 is obtained, with a direct gap evidenced by angle-resolved photoemission spectroscopy and further confirmed by Raman and intense room temperature photoluminescence. The successful growth of high-quality MoSe2/Bi2Se3 multilayers on AlN shows promise for novel devices exploiting the non-trivial topological properties of Bi2Se3.

  11. Effect of polymer matrix on structure of Se particles formed in aqueous solutions during redox process

    SciTech Connect

    Suvorova, E. I. Klechkovskaya, V. V.

    2010-12-15

    Transmission electron microscopy and X-ray energy dispersive microanalysis study of the structure of particles formed during the reduction of Se(IV) to Se(0) in aqueous solutions in the presence of amphiphilic polymers showed the formation of Se/polymer composite particles. The content of carbon inside the particles can be as large as 80 at %. Polymers deeply influence the structure of particles. Depending on polymers, the composite particles may be unstable with time and they spontaneously evolve from Se/polymer composite particles to crystalline particles of monoclinic Se. For the stable ones, addition of bacterial cellulose Acetobacter xylinum gel-film can induce crystallization in the particles which expel the polymeric material. The Se/polymer composite particles and Se crystalline particles exhibit different sensitivity to electron irradiation and stiffness.

  12. Partial Pressures for Several In-Se Compositions from Optical Absorbance of the Vapor

    NASA Technical Reports Server (NTRS)

    Brebrick, R. F.; Su, Ching-Hua

    2001-01-01

    The optical absorbance of the vapor phase over various In-Se compositions between 33.3-60.99 at.% Se and 673-1418 K was measured and used to obtain the partial pressures of Se2(g) and In2Se(g). The results are in agreement with silica Bourdon gauge measurements for compositions between 50-61 at.%, but significantly higher than those from Knudsen cell and simultaneous Knudsen-torsion cell measurements. It is found that 60.99 at.% Se lies outside the sesquiselenide homogeneity range and 59.98 at.% Se lies inside and is the congruently melting composition. The Gibbs energy of formation of the liquid from its pure liquid elements between 1000-1300 K is essentially independent of temperature and falls between -36 to -38 kJ per g atomic weight for 50 and 56% Se at 1200 and 1300 K.

  13. Phosphine-free synthesis of Ag-In-Se alloy nanocrystals with visible emissions

    NASA Astrophysics Data System (ADS)

    Yao, Dong; Liu, Huiwen; Liu, Yi; Dong, Chunwei; Zhang, Kai; Sheng, Yu; Cui, Jianli; Zhang, Hao; Yang, Bai

    2015-11-01

    As promising heavy metal-free emitting materials, Ag-In-Se nanocrystals (NCs) are conventionally synthesized using organic phosphine agents and exhibit near-infrared emissions. In this work, we demonstrate a rapid phosphine-free approach for synthesizing Ag-In-Se alloy NCs with the emissions tunable to the visible region on the basis of the phosphine-free dissolution of Se powder. At room temperature, Se powder is reduced by dodecanethiol and dissolved in oleylamine to produce a Se precursor. The resultant Se precursor is highly active, which permits rapid synthesis at a relatively low temperature, such as at 90 °C for 150 s. By optimizing the size, structure, and composition, the photoluminescence quantum yield of the as-synthesized Ag-In-Se NCs is enhanced to up to 10%. The growth of the Ag-In-Se NCs involves composition and phase transition, which strongly depend on the reaction temperature. The Ag2Se nuclei form first, and the Ag-In-Se NCs are produced by doping In3+ into the preformed Ag2Se nuclei. Tetragonal phase Ag-In-Se is obtained below 170 °C, while the orthorhombic phase appears over 190 °C. The potential of Ag-In-Se NCs as red emitting phosphors for lighting-emitting diodes is further demonstrated.As promising heavy metal-free emitting materials, Ag-In-Se nanocrystals (NCs) are conventionally synthesized using organic phosphine agents and exhibit near-infrared emissions. In this work, we demonstrate a rapid phosphine-free approach for synthesizing Ag-In-Se alloy NCs with the emissions tunable to the visible region on the basis of the phosphine-free dissolution of Se powder. At room temperature, Se powder is reduced by dodecanethiol and dissolved in oleylamine to produce a Se precursor. The resultant Se precursor is highly active, which permits rapid synthesis at a relatively low temperature, such as at 90 °C for 150 s. By optimizing the size, structure, and composition, the photoluminescence quantum yield of the as-synthesized Ag-In-Se NCs is

  14. Method of synthesizing and growing copper-indium-diselenide (CuInSe.sub.2) crystals

    DOEpatents

    Ciszek, Theodore F.

    1987-01-01

    A process for preparing CuInSe.sub.2 crystals includes melting a sufficient quantity of B.sub.2 O.sub.3 along with stoichiometric quantities of Cu, In, and Se in a crucible in a high pressure atmosphere of inert gas to encapsulate the CuInSe.sub.2 melt and confine the Se to the crucible. Additional Se in the range of 1.8 to 2.2 percent over the stoichiometric quantity is preferred to make up for small amounts of Se lost in the process. The crystal is grown by inserting a seed crystal through the B.sub.2 O.sub.3 encapsulate into contact with the CuInSe.sub.2 melt and withdrawing the seed upwardly to grow the crystal thereon from the melt.

  15. Method of synthesizing and growing copper-indium-diselenide (CuInSe/sub 2/) crystals

    DOEpatents

    Ciszek, T.F.

    1984-11-29

    A process for preparing CuInSe/sub 2/ crystals includes melting a sufficient quantity of B/sub 2/O/sub 2/ along with stochiometric quantities of Cu, In, and Se in a crucible in a high-pressure atmosphere of inert gas to encapsulate the CuInSe/sub 2/ melt and confine the Se to the crucible. Additional Se in the range of 1.8 to 2.2% over the stochiometric quantity is preferred to make up for small amounts of Se lost in the process. The melt can then be cooled slowly to form the crystal as direct solidification, or the crystal can be grown by inserting a seed crystal through the B/sub 2/O/sub 3/ encapsulate into contact with the CuInSe/sub 2/ melt and withdrawing the seed upwardly to grow the crystal thereon from the melt.

  16. Optical and Structural Properties of Zn-Cd-Mn-Se Double Quantum Well Systems

    NASA Astrophysics Data System (ADS)

    Matsumoto, Takashi; Ohmori, Kenta; Kodama, Kazuki; Hishikawa, Masao; Fukasawa, Sakyo; Iwasaki, Fumiaki; Muranaka, Tsutomu; Nabetani, Yoichi

    2011-05-01

    Double quantum well (DQW) structures consisting of a ZnCdSe well and a ZnCdMnSe well separated by a ZnSe barrier are grown with molecular beam epitaxy (MBE). The DQW structures are characterized by using X-ray diffraction measurement and simulation. Thickness of each well layer is designed so that the lowest energy level of ZnCdMnSe well is close to the excited level of the ZnCdSe well. Optical properties of the DQWs are studied with photoluminescence (PL) and reflection spectra in external magnetic fields up to 8 T in the Faraday geometry. Exciton transfer from ZnCdMnSe well to ZnCdSe well is observed in magneto PL with energy selective photoexcitation. Exciton energies in ground and excited states are estimated from PL excitation spectra and reflection spectra.

  17. Ligand Effects on Synthesis and Post-Synthetic Stability of PbSe Nanocrystals

    SciTech Connect

    Dai, Quanqin; Zhang, Yu; Wang, Yingnan; Hu, Michael Z.

    2010-01-01

    This paper reports the effect of ligands including oleic acid (OA), trioctylphosphine (TOP), and tributylphosphine (TBP) on the PbSe nanocrystal growth during synthesis, as well as the effect of OA ligands on the nanocrystal stability after synthesis. These ligands play important roles in the nucleation and growth mechanism of nanocrystals. We have discovered that the ligand effect on the growth of PbSe nanocrystals can differ from that on the mostly studied CdSe nanocrystals. Also, we present a method for producing relatively smaller and more monodisperse PbSe nanocrystals based on our new understanding that the use of TBP, instead of the generally reported TOP, can slow down the growth of PbSe nanocrystals. In addition, our postsynthetic investigation of OA ligand effects demonstrate the dominant desorption of OA-bonded Pb atoms, causing the shrinkage of PbSe nanocrystals. This provides some insight into stabilization strategies for labile PbSe nanocrystals.

  18. LEED and AES characterization of the GaAs(110)-ZnSe interface

    NASA Technical Reports Server (NTRS)

    Tu, D.-W.; Kahn, A.

    1984-01-01

    In this paper, a study is conducted of the composition and structure of epitaxial ZnSe films grown by congruent evaporation on GaAs(110) at a rate of 2 A/min. It is found that the films grown on 300 C GaAs are nearly stoichiometric and form an abrupt interface with the substrate. Films grown at higher temperature (T greater than 350-400 C) are Se rich. The crystallinity of films grown at 300 C is good and their surface atomic geometry is identical to that of a ZnSe crystal. The GaAs-ZnSe interface geometry seems to be dominated by the Se-substrate bonds. The adsorption of Se, during the formation of very thin ZnSe films (2-3 A), produces a (1 x 2) LEED pattern and modifications of the LEED I-V profiles, which probably indicate a change in the substrate atomic relaxation.

  19. XANES-EXAFS analysis of se solid-phase reaction products formed upon contacting Se(IV) with FeS2 and FeS.

    PubMed

    Breynaert, E; Bruggeman, C; Maes, A

    2008-05-15

    The solid-phase Se speciation after short-term (3 weeks) contact of selenite [Se(IV)] oxyanions with pyrite (FeS2) and troilite (FeS) was investigated using X-ray absorption spectroscopy (XAS; X-ray absorption near-edge spectroscopy-extended X-ray absorption fine structure (XANES-EXAFS)). It was found that the nature of the sulfide mineral dictates the final speciation since respectively Se(0) and FeSe(x) were formed, meaning that the reaction mechanism is different and that these phases cannot be regarded as geochemically similar. The experimental results support the previously proposed sorption/ reduction mechanism for the reaction of selenite with pyrite. In the presence of troilite the reduction proceeds through the intermediate formation of Se(0) by reduction of selenite with dissolved sulfide. XAS data recorded for the FeS2 and FeS were compared with different Se reference phases, ranging in oxidation state from -II to +IV, used for validation of the XAS analysis methodology. This methodology can in principle be used to analyze Se phases formed in "in situ" geochemical conditions such as high-level radioactive waste disposal facilities.

  20. Suppressed Formation of Conductive Phases in One-Pot Electrodeposited CuInSe2 by Tuning Se Concentration in Aqueous Electrolyte.

    PubMed

    Lee, Byung-Seok; Park, Sung-Yul L; Lee, Jang Mi; Jeong, Jeung-Hyun; Kim, Jin Young; Chung, Choong-Heui; Lee, Doh-Kwon

    2016-09-21

    The single-bath electrochemical deposition of CuInSe2 often leads to short-circuit behavior of the resulting solar cells due to the high shunt conductance. In this study, in an attempt to resolve this problem, the influence of the Se precursor concentration (CSe) on electrodeposited CuInSe2 films and solar cell devices is examined in the CSe range of 4.8 to 12.0 mM in selenite-based aqueous solutions containing Cu and In chlorides along with sulfamic acid (H3NSO3) and potassium hydrogen phthalate (C8H5KO4) additives. As CSe increases, the CuInSe2 layers become porous, and the grain growth of the CuInSe2 phase is restricted, while the parasitic shunting problem was markedly alleviated, as unambiguously demonstrated by measurements of the local current distribution. Due to these ambivalent influences, an optimal value of CSe that achieves the best quality of the films for high-efficiency solar cells is identified. Thus, the device prepared with 5.2 mM Se exhibits a power-conversion efficiency exceeding 10% with greatly improved device parameters, such as the shunt conductance and the reverse saturation current. The rationale of the present approach along with the physicochemical origin of its conspicuous impact on the resulting devices is discussed in conjunction with the electro-crystallization mechanism of the CuInSe2 compound.

  1. Air sensitivity of MoS2, MoSe2, MoTe2, HfS2, and HfSe2

    NASA Astrophysics Data System (ADS)

    Mirabelli, Gioele; McGeough, Conor; Schmidt, Michael; McCarthy, Eoin K.; Monaghan, Scott; Povey, Ian M.; McCarthy, Melissa; Gity, Farzan; Nagle, Roger; Hughes, Greg; Cafolla, Attilio; Hurley, Paul K.; Duffy, Ray

    2016-09-01

    A surface sensitivity study was performed on different transition-metal dichalcogenides (TMDs) under ambient conditions in order to understand which material is the most suitable for future device applications. Initially, Atomic Force Microscopy and Scanning Electron Microscopy studies were carried out over a period of 27 days on mechanically exfoliated flakes of 5 different TMDs, namely, MoS2, MoSe2, MoTe2, HfS2, and HfSe2. The most reactive were MoTe2 and HfSe2. HfSe2, in particular, showed surface protrusions after ambient exposure, reaching a height and width of approximately 60 nm after a single day. This study was later supplemented by Transmission Electron Microscopy (TEM) cross-sectional analysis, which showed hemispherical-shaped surface blisters that are amorphous in nature, approximately 180-240 nm tall and 420-540 nm wide, after 5 months of air exposure, as well as surface deformation in regions between these structures, related to surface oxidation. An X-ray photoelectron spectroscopy study of atmosphere exposed HfSe2 was conducted over various time scales, which indicated that the Hf undergoes a preferential reaction with oxygen as compared to the Se. Energy-Dispersive X-Ray Spectroscopy showed that the blisters are Se-rich; thus, it is theorised that HfO2 forms when the HfSe2 reacts in ambient, which in turn causes the Se atoms to be aggregated at the surface in the form of blisters. Overall, it is evident that air contact drastically affects the structural properties of TMD materials. This issue poses one of the biggest challenges for future TMD-based devices and technologies.

  2. GaSe1-xSx and GaSe1-xTex thick crystals for broadband terahertz pulses generation

    NASA Astrophysics Data System (ADS)

    Nazarov, M. M.; Yu. Sarkisov, S.; Shkurinov, A. P.; Tolbanov, O. P.

    2011-08-01

    We demonstrate the possibility of broadband THz pulse generation in mixed GaSe1-xSx and GaSe1-xTex crystals. The ordinary and extraordinary refractive indices of the crystals have been measured by the terahertz time-domain spectroscopy method, those values strongly influence the efficiency of THz generation process. The high birefringence and transparency of pure GaSe and mixed crystals allow optical rectification of femtosecond laser pulses in the several millimeters thick crystal using the еее interaction process (with two pumping waves and generated THz wave all having extraordinary polarization in the crystal).

  3. Formation of Se (0) Nanoparticles by Duganella sp. andAgrobacterium sp. isolated from Se-laden soil of North-East Punjab, India

    PubMed Central

    2012-01-01

    Background Selenium (Se) is an essential trace element, but is toxic at high concentrations. Depending upon the geological background, the land use or on anthropogenic pollution, different amounts of Se may be present in soil. Its toxicity is related to the oxyanions selenate and selenite as they are water soluble and bioavailable. Microorganisms play an important role in Se transformations in soil and its cycling in the environment by transforming water-soluble oxyanions into water insoluble, non-toxic elemental Se (0). For this study, soil samples were collected from selenium-contaminated agricultural soils of Punjab/India to enrich and isolate microbes that interacted with the Se cycle. Results A mixed microbial culture enriched from the arable soil of Punjab could reduce 230 mg/l of water soluble selenite to spherical Se (0) nanoparticles during aerobic growth as confirmed by SEM-EDX. Four pure cultures (C 1, C 4, C 6, C 7) of Gram negative, oxidase and catalase positive, aerobic bacteria were isolated from this mixed microbial consortium and identified by 16 S rDNA gene sequence alignment as two strains of Duganella sp. (C 1, C 4) and two strains of Agrobacterium sp.(C 6, C 7). SEM/TEM-EDX analyses of the culture broth of the four strains revealed excretion of uniformly round sharply contoured Se (0) nanoparticles by all cultures. Their size ranged from 140–200 nm in cultures of strains C 1 and C 4, and from 185–190 nm in cultures of strains C 6 and C 7. Both Duganella sp. revealed better selenite reduction efficiencies than the two Agrobacterium sp. Conclusions This is the first study reporting the capability of newly isolated, aerobically growing Duganella sp. and Agrobacterium sp. from soils of Punjab/India to form spherical, regularly formed Se (0) nanoparticles from water soluble selenite. Among others, the four strains may significantly contribute to the biogeochemical cycling of Se in soil. Bioconversion of toxic selenite to non-toxic Se (0

  4. Stability of Se species in plant extracts rich in phenolic substances.

    PubMed

    Cuderman, Petra; Stibilj, Vekoslava

    2010-02-01

    Since there is growing awareness of the strong dependence of the antioxidative function of selenium (Se) upon its chemical form, the stability of Se species during sample preparation is an important factor in obtaining qualitative and quantitative results. Many plant samples are rich in phenolic compounds (antioxidants), but data about their effect on specific Se species in extracts of plant samples are scarce. Therefore, the aim of this study was to investigate the effect of the most common phenolic substances in plant parts, namely tannin and the flavonoid rutin, on the concentration and/or transformation of several Se species (SeMet, SeCys(2), SeMeSeCys, Se(VI) and Se(IV)) during sample preparation (24 h incubation at 37 degrees C) and storage (4 days at 4 degrees C). Moreover, the effect observed was then studied in a real sample, buckwheat, because this plant is known as a rich source of phenolics, especially tannin and rutin. Se speciation was carried out by on-line coupling of ion-exchange HPLC-ICP-MS after water and enzymatic (protease) hydrolysis. The results showed that the ratio between the two antioxidants has an important role. When the antioxidants were present together, the response for Se(IV) was observed to start to decrease only at a ratio of rutin to tannin of 1:100 (w/w), indicating the ratio between antioxidants in buckwheat seeds. After water extraction, only 40% and after enzymatic extraction 80% of Se(IV) remained, but no other Se compound was detected with the system used. Furthermore, the extracts were not stable during storage at 4 degrees C. Signals for other Se species were stable. The results obtained for buckwheat seeds showed a decrease in Se(IV) response during sample preparation and storage, comparable to the one obtained with the experiments performed in vitro. However, Se species in extracts of other buckwheat parts (leaves, stems and sprouts) were stable. These results indicate that reactions in the extraction process and during

  5. Evaluation of the respiratory elimination kinetics of selenate and Se-methylselenocysteine after oral administration in lambs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sheep can be acutely poisoned by selenium (Se) accumulating forages which often contain selenate or Se-methylselenocysteine as their predominant forms. Excess Se can be eliminated via respiration. Sheep were given a single oral dose of 0, 1, 2, 3, 4, or 6 mg Se/kg BW as sodium selenate and Se-meth...

  6. First principles studies of the oxygen reduction reaction on Se-Ru nanostructures

    NASA Astrophysics Data System (ADS)

    Zuluaga, Sebastian; Stolbov, Sergey

    2011-03-01

    Experiments show an enhanced rate of the oxygen reduction reaction (ORR) on Se-Ru nanostructures (NS) in hydrogen fuel cell cathodes. We use first principles methods to study Ru and Se-Ru NS of approximate 1.2 nm size and shine some light on how the Se affects the O and OH adsorption, which is the bottle neck of the power delivered by the fuel cell. Experiments shows that the Se-Ru NS have a Ru core but is not clear how the Se is distributed on the surface. Our calculation shows that the Se atom adsorbs on the Ru surface with a binding energies in the range 5.7 to 7.1 eV with electronic charge transfer from the Ru atoms. Due to repulsion between negatively charged Se atoms, they tend to spread uniformly over the the Ru NS rather than form islands on its surface. We have also found that, in contrast to the flat Ru surface, the Se bond to the low coordinated Ru atoms have significant covalent component. Our calculation shows how the presence of Se atoms affects the adsorption of the ORR intermediates on the NS. In particular, we show that the electrostatic repulsion between charged Se and O or OH reduces the binding energy of the latters.

  7. Cation Exchange Synthesis and Unusual Resistive Switching Behaviors of Ag2Se Nanobelts.

    PubMed

    Guo, Zheng; Li, Min-Qiang; Liu, Jin-Huai; Huang, Xing-Jiu

    2015-12-16

    Ag2Se nanobelts are prepared through employing ZnSe nanobelts as templates via a facile cation exchange approach. The templates are derived from precursor ZnSe·0.5N2 H4 nanobelts, which are synthesized by a simple hydrothermal method. As-synthesized precursor nanobelts are with 200 nm in width and several hundreds of micrometers in length. Annealed in N2 , they are transformed into ZnSe nanobelts with preserving their initial morphology. Following with a complete replacement of Zn(2+) by Ag(+), Ag2Se nanobelts with single crystalline are obtained via a cation-exchange reaction. Combined with the Langmuir-Blodgett assembly technique, regular films of ZnSe nanobelts can be achieved on transparent glass substrates and Si wafers with interdigital Au electrode arrays. Further, the optical and electrical evolutions are investigated from ZnSe nanobelts to Ag2 Se nanobelts. Finally, the resistive switching characteristic are carefully explored for Ag2Se nanobelts regularly arranged on interdigital Au microelectrodes. The results indicate that it is analogous to complementary resistive switching behaviors, which is different from that of traditional two terminal devices about previously reported Ag2Se. In order to clarify this phenomenon, a possible mechanism has been proposed and indirectly demonstrated through in situ SEM (scanning electron microscropy) observation.

  8. Influence of diet on selenium (Se) toxicosis and oxidative stress in mallard ducklings

    SciTech Connect

    Hoffman, D.J.; Heinz, G.; Eisemann, J.; Pendleton, G.

    1995-12-31

    High concentrations of Se have been found in aquatic food chains associated with irrigation drainwater and result in toxicity to fish and wildlife. Both quality and composition of diet including protein for wild ducklings may vary in Se-contaminated environments. The authors compared the effects of Se (as seleno-DL-methionine) at different concentrations of dietary protein and methionine supplementation in mallard (Anas platvrhynchos) ducklings. Further comparisons were made among different forms of Se, including seleno-L-methionine (L), selenized yeast (Y) and selenized wheat (W) using a wheat-based diet and a non-wheat diet. All forms of selenium with different diets caused significant increases in plasma and hepatic glutathione peroxidase activities. Antagonistic interactive effects occurred between supplementary protein or methionine and Se. These included partial to complete alleviation of the following Se effects: mortality, hepatic lesions, and altered glutathione and thiol status. Se as L with the wheat-based diet was the most toxic, resulting in high mortality (64%) at 30 ppm and impaired growth (> 50%) and increased ratio of oxidized to reduced glutathione, Se as Y accumulated the least in liver compared to other forms. In a subsequent experiment with a non-wheat diet, Se as L was less toxic, These findings suggest the potential for antagonistic interactions between Se and dietary protein and methionine.

  9. Structural and Spectral Features of Selenium Nanospheres Produced by Se-Respiring Bacteria

    USGS Publications Warehouse

    Oremland, R.S.; Herbel, M.J.; Blum, J.S.; Langley, S.; Beveridge, T.J.; Ajayan, P.M.; Sutto, T.; Ellis, A.V.; Curran, S.

    2004-01-01

    Certain anaerobic bacteria respire toxic selenium oxyanions and in doing so produce extracellular accumulations of elemental selenium [Se(0)]. We examined three physiologically and phylogenetically diverse species of selenate- and selenite-respiring bacteria, Sulfurospirillum barnesii, Bacillus selenitireducens, and Selenihalanaerobacter shriftii, for the occurrence of this phenomenon. When grown with selenium oxyanions as the electron acceptor, all of these organisms formed extracellular granules consisting of stable, uniform nanospheres (diameter, ???300 nm) of Se(0) having monoclinic crystalline structures. Intracellular packets of Se(0) were also noted. The number of intracellular Se(0) packets could be reduced by first growing cells with nitrate as the electron acceptor and then adding selenite ions to washed suspensions of the nitrate-grown cells. This resulted in the formation of primarily extracellular Se nanospheres. After harvesting and cleansing of cellular debris, we observed large differences in the optical properties (UV-visible absorption and Raman spectra) of purified extracellular nanospheres produced in this manner by the three different bacterial species. The spectral properties in turn differed substantially from those of amorphous Se(0) formed by chemical oxidation of H2Se and of black, vitreous Se(0) formed chemically by reduction of selenite with ascorbate. The microbial synthesis of Se(0) nanospheres results in unique, complex, compacted nanostructural arrangements of Se atoms. These arrangements probably reflect a diversity of enzymes involved in the dissimilatory reduction that are subtly different in different microbes. Remarkably, these conditions cannot be achieved by current methods of chemical synthesis.

  10. CdSeS/ZnS alloyed nanocrystal lifetime and blinking studies under electrochemical control.

    PubMed

    Qin, Wei; Shah, Raman A; Guyot-Sionnest, Philippe

    2012-01-24

    Alloyed CdSeS nanocrystals allow tuning between the CdSe and CdS band edges while remaining relatively small. The CdSeS cores also lead to a reduced electron confinement energy and a slower biexciton decay rate compared to CdSe cores of similar sizes. A ZnS shell synthesis procedure allows stable CdSeS/ZnS colloidal quantum dots (QDs) suitable for single dot imaging. These are compared to CdSe/ZnS of similar core size. The blinking off-exponents of the CdSeS/ZnS dots in air and on a glass substrate were slightly larger. Using electrochemistry with ensemble and single dot measurements, the trion lifetime of CdSeS/ZnS dot is resolved to be ~0.75 ns, while it is about 0.15 ns for CdSe/ZnS. In addition, the blinking behavior of single CdSeS/ZnS QDs is largely suppressed when in the trion state.

  11. Isothermal sections of the quasi-ternary systems Ag2S(Se)-Ga2S(Se)3-In2S(Se)3 at 820 K and the physical properties of the ternary phases Ga5.5In4.5S15, Ga6In4Se15 and Ga5.5In4.5S15:Er3+, Ga6In4Se15:Er3+

    NASA Astrophysics Data System (ADS)

    Ivashchenko, I. A.; Danyliuk, I. V.; Gulay, L. D.; Halyan, V. V.; Olekseyuk, I. D.

    2016-05-01

    Isothermal sections of the quasi-ternary systems Ag2S(Se)-Ga2S(Se)3-In2S(Se)3 at 820 K were compared. Along the 50 mol% Ag2S(Se), both systems feature continuous solid solutions with the chalcopyrite structure. Along the 17 mol% Ag2S(Se), the interactions at the AgIn5S(Se)8-"AgGa5S(Se)8" sections are different. In the Ag2S-Ga2S3-In2S3 system the existence of the layered phase AgGaxIn5-xS8, 2.25≤x≤2.85, was confirmed (S.G. P63mc). The Ag2Se-Ga2Se3-In2Se3 system features the formation of solid solution (up to 53 mol% Ga2Se3) based on AgIn5Se8 (S.G. P-42m). Crystal structure, atomic coordinates were determined by powder diffraction method for samples from the homogeneity region of AgIn5Se8. Specific conductivities of the crystals Ga6In4Se15 (1.33·10-6 Ω-1 m-1), Ga5.94In3.96Er0.1Se15 (3.17·10-6 Ω-1 m-1), Ga5.5In4.5S15 (7.94·10-6 Ω-1 m-1), Ga5.46In4.47Er0.07S15 (1·10-9 Ω-1 m-1) were measured at room temperature. Optical absorption and photoconductivity spectra were recorded in the range 400-760 nm. The introduction of erbium leads to an increase in the absorption coefficient and to the appearance of absorption bands at 530, 660, 810, 980, 1530 nm.

  12. Phase Separation in As_2-xGe_xSe_1-2x Glasses^*

    NASA Astrophysics Data System (ADS)

    Georgiev, Daniel; Mamedov, Sergey; Qu, Tao; Boolchand, Punit

    2003-03-01

    The global maximum in Tg near stoichiometric compositions(GeSe_2, As_2Se_3) in binary (Ge-Se, As-Se) selenide glasses is evidence for nanoscale phase separation [1]. The connection between Tg and network connectivity has thus opened new possibilities to address glass structure issues using scanning calorimetry. Eleven compositions spanning the two end members of the titled ternary are examined in MDSC [2] and FT-Raman scattering measurements. T_g(x) are found to increase with x in the 0 < x < 1.2 range, to display a global maximum in the 1.2 < xt < 1.8 range, and to decrease thereafter. FT-Raman scattering reveals lineshapes that smoothly evolve from As_2Se3 glass to Ge_2Se3 glass. Addition of Ge_2Se3 to As_2Se3 glass results in formation of Ge(Se_1/2)4 tetrahedra as Tg increases since increases. At x =1, the glass can be described as a random network of polymeric As2 (Se_1/2)4 units mixed with Ge(Se_1/2)4 tetrahedra. At x > x_t, the Ge/Se ratio > 1/2 , as ethanelike Ge_2Se3 nanophase nucleates, and Tg decline as decreases [1]. ^* Supported by NSF grant DMR 01-010808 [1] P.Boolchand and W.J.Bresser Phil. Mag. B 80,1757(2000). [2] D.G.Georgiev et al. Phys.Rev B 62,R9228(2000).

  13. Chemical synthesis of Cu{sub 2}Se nanoparticles at room temperature

    SciTech Connect

    Rong, Fengxia; Bai, Yan; Chen, Tianfeng; Zheng, Wenjie

    2012-01-15

    Graphical abstract: The Cu{sub 2}Se nanoparticles were synthesized by a simple and rapid method at room temperature. The TEM and SEM images show that the Cu{sub 2}Se nanoparticles were spherical. Highlights: Black-Right-Pointing-Pointer Cu{sub 2}Se nanoparticles were synthesized by the reaction of nanoSe{sup 0} sol with Cu{sup +} ions. Black-Right-Pointing-Pointer The Cu{sub 2}Se nanoparticles were spherical with cubic structure and well crystallized. Black-Right-Pointing-Pointer Optical and electrochemical properties of Cu{sub 2}Se nanoparticles were observed. Black-Right-Pointing-Pointer The formation mechanism of Cu{sub 2}Se nanoparticles was proposed. -- Abstract: A simple and rapid method has been developed to synthesize cuprous selenide (Cu{sub 2}Se) nanoparticles by the reaction of selenium nanoparticles sol with copper sulfate solution containing ascorbic acid at room temperature. Cu{sub 2}Se nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray analysis (EDX). The results indicated that Cu{sub 2}Se nanoparticles were cubic crystal structure and spherical with the diameter about 75 nm. The ultraviolet-visible absorption spectrum (UV-vis) and cyclic voltammetry of Cu{sub 2}Se nanoparticles were also investigated. The optical band gap energy of Cu{sub 2}Se nanoparticles was 1.94 eV. On the basis of a series of experiments and characterizations, the formation mechanism of Cu{sub 2}Se nanoparticles was discussed.

  14. Quality improvements of ZnxCdyMg1-x-ySe layers grown on InP substrates by a thin ZnCdSe interfacial layer

    NASA Astrophysics Data System (ADS)

    Zeng, L.; Yang, B. X.; Tamargo, M. C.; Snoeks, E.; Zhao, L.

    1998-03-01

    The quality of lattice-matched ZnxCdyMg1-x-ySe epitaxial layers grown on (001) InP substrates with a III-V buffer layer has been improved by initially growing a ZnCdSe interfacial layer (50 Å) at low temperature. The widths of double crystal x-ray rocking curves for ZnxCdyMg1-x-ySe epilayers with band gaps as high as 3.05 eV were reduced to about 70 arcsec. The defect density evaluated from etch pit density and plan-view transmission electron microscopy measurements was reduced by two orders of magnitude, to 106-107cm-2. The photoluminescence band edge emission became more symmetric and slightly narrower. It is proposed that an initial two-dimensional growth mode has been achieved by incorporating such a lattice-matched ZnCdSe layer.

  15. Coexpression of CdSe and CdSe/CdS quantum dots in live cells using molecular hyperspectral imaging technology.

    PubMed

    Li, Qingli; Peng, Hui; Wang, Jing; Wang, Yiting; Guo, Fangmin

    2015-11-01

    A direct spatial and spectral observation of CdSe and CdSe/CdS quantum dots (QDs) as probes in live cells is performed by using a custom molecular hyperspectral imaging (MHI) system. Water-soluble CdSe and CdSe/CdS QDs are synthesized in aqueous solution under the assistance of high-intensity ultrasonic irradiation and incubated with colon cancer cells for bioimaging. Unlike the traditional fluorescence microscopy methods, MHI technology can identify QD probes according to their spectral signatures and generate coexpression and stain titer maps by a clustering method. The experimental results show that the MHI method has potential to unmix biomarkers by their spectral information, which opens up a pathway of optical multiplexing with many different QD probes. PMID:26588112

  16. Study of optical nonlinearity of CdSe and CdSe@ZnO core-shell quantum dots in nanosecond regime

    NASA Astrophysics Data System (ADS)

    Deepika; Dhar, Rakesh; Mohan, Devendra

    2015-12-01

    Thioglycolic acid capped cadmium selenide (CdSe) and CdSe@ZnO core-shell quantum dots have been synthesized in aqueous phase. The sample was characterized by UV-vis spectrophotometer, TEM and Z-scan technique. The nonlinear optical parameters viz. nonlinear absorption coefficient (β), nonlinear refractive index (n2) and third-order nonlinear susceptibilities (χ3) of quantum dots have been estimated using second harmonic of Nd:YAG laser. The study predicts that CdSe@ZnO quantum dots exhibits strong nonlinearity as compared to core CdSe quantum dots. The nonlinearity in quantum dots is attributed to the presence of resonant excitation and free optical processes. The presence of RSA in these nanoparticles makes them a potential material for the development of optical limiter.

  17. Set of Sellmeier equations for GaS and GaSe and its applications to the nonlinear optics in GaS(x)Se(1-x).

    PubMed

    Kato, Kiyoshi; Mikami, Takuya

    2014-04-01

    This paper reports a set of Sellmeier equations for GaS and GaSe that provide excellent reproduction of the phase-matching conditions for second- to sixth-harmonic generation of CO₂ laser radiation at 10.5910 μm in GaS(0.4)Se(0.6) at 20°C. In addition, this set of Sellmeier equations is found to reproduce well the phase-matching angles for second-harmonic generation of a Ti:Al₂O₃ laser-pumped BaB₂O₄ optical parametric generator at 2.14-2.9 μm and CO₂ laser radiation at 9.2(9.2007)-10.7(10.6746)  μm measured by Kang et al. [Appl. Phys. B 108, 545 (2012)] in GaS(0.09)Se(0.91) and GaS(0.41)Se(0.59).

  18. Coexpression of CdSe and CdSe/CdS quantum dots in live cells using molecular hyperspectral imaging technology

    NASA Astrophysics Data System (ADS)

    Li, Qingli; Peng, Hui; Wang, Jing; Wang, Yiting; Guo, Fangmin

    2015-11-01

    A direct spatial and spectral observation of CdSe and CdSe/CdS quantum dots (QDs) as probes in live cells is performed by using a custom molecular hyperspectral imaging (MHI) system. Water-soluble CdSe and CdSe/CdS QDs are synthesized in aqueous solution under the assistance of high-intensity ultrasonic irradiation and incubated with colon cancer cells for bioimaging. Unlike the traditional fluorescence microscopy methods, MHI technology can identify QD probes according to their spectral signatures and generate coexpression and stain titer maps by a clustering method. The experimental results show that the MHI method has potential to unmix biomarkers by their spectral information, which opens up a pathway of optical multiplexing with many different QD probes.

  19. Electrical properties of In{sub 2}Se{sub 3} single crystals and photosensitivity of Al/In{sub 2}Se{sub 3} Schottky barriers

    SciTech Connect

    Bodnar, I. V.; Ilchuk, G. A.; Petrus', R. Yu.; Rud', V. Yu.; Rud', Yu. V.; Serginov, M.

    2009-09-15

    In{sub 2}Se{sub 3} single crystals {approx}40 mm long and 14 mm in diameter were grown by the Bridgman method. The composition of grown single crystals and their crystal structure were determined. The conductivity ({sigma}) and Hall constant (R) of grown single crystals were measured and the first Schottky barriers Al/n-In{sub 2}Se{sub 3} were fabricated. Rectification and photovoltaic effect were detected in the new structures. Based on the study of the photosensitivity spectra of Al/n-In{sub 2}Se{sub 3} structures, the nature of the interband transitions and band gap of In{sub 2}Se{sub 3} crystals were determined. It was concluded that the new structures can be applied to develop broadband photoconverters of optical radiation.

  20. High-Pressure Synthesis and Structure Determination of K6(SeO4)(SeO5), The First Potassium Orthoselenate(VI)

    SciTech Connect

    Orosel,D.; Dinnebeier, R.; Jansen, M.

    2006-01-01

    The authors report on the first synthesis of a potassium orthoselenate(VI), K{sub 6}(SeO{sub 4})(SeO{sub 5}), and the structure determination from synchrotron powder diffraction data. The title compound crystallizes in the tetragonal space group P4{sub 1}2{sub 1}2 with a = 8.1259(1) {angstrom}, c = 17.4953(2) {angstrom}, V = 1155.21(2) {angstrom}{sup 3}, and Z = 4. Selenium displays two different complex anions, tetrahedral SeO{sub 4}{sup 2-} and trigonal-bipyramidal SeO{sub 5}{sup 4-}. When the formula is reduced to A{sub 3}B, the spatial arrangement of the constituting building units can be derived from the Li{sub 3}Bi type of structure.

  1. Crystal Structures and Electronic Absorption Spectra of Two Modifications of Cr(SeO 2OH)(Se 2O 5)

    NASA Astrophysics Data System (ADS)

    Wildner, M.; Andrut, M.

    1998-01-01

    Single crystals of two modifications (I and II) of Cr(SeO2OH)(Se2O5) have been synthesized under low-hydrothermal conditions. Their structures have been investigated using single-crystal X-ray diffraction data up to sinθ/λ=0.76 Å-1[I: monoclinic, space groupP21/n,a=7.517(2) Å,b=12.516(3) Å,c=7.381(2) Å,β=91.46(1)°,Z=4,R1=0.030 for 1562Fo>4σ(Fo) and 114 variables; II: orthorhombic, space groupPnma,a=8.782(2) Å,b=11.172(3) Å,c=7.545(2) Å,Z=4,R1=0.031 for 752Fo>4σ(Fo) and 65 variables]. In Cr(SeO2OH)(Se2O5)-I, sheets-built up from isolated CrO6octahedra and Se2O5groups-are linked via the SeO2OH groups and rather strong hydrogen bonds. This structure is isotypic with the corresponding compounds of Mn(III) and Fe(III). Cr(SeO2OH)(Se2O5)-II represents a new framework structure type, also composed of isolated CrO6octahedra and Se2O5and SeO2OH groups, but with very weak hydrogen bonds. The hydrogen-bonding schemes of both compounds were further investigated by FTIR microscope spectrometry in the range 7000-1000 cm-1, yielding a typical AB-band spectrum for phase I. Furthermore, polarized electronic absorption spectra were measured in the range 33,000-12,500 cm-1using UV-VIS microscope spectrometric techniques. According to the weak distortions of the CrO6octahedra in both compounds, the observed band splittings and polarization effects are rather weak. Hence, crystal field calculations were performed assumingOhsymmetry, resulting in the following crystal field parameter sets; I,Dq=1558,B35=653,B55=760,C=2920 cm-1; II,Dq=1641,B35=647,B55=730,C=2815 cm-1. TheseDqvalues are slightly below average compared to octahedral Cr(III) in other oxygen-based structures, a tendency that was already observed for other 3dtransition elements in crystal fields of selenite compounds. This might indicate a rather low position of the [SeO3]2-anion within the range of oxygen-based ligands in the spectrochemical series.

  2. Heating of the magnetic-ion spin system in modulation doped ZnMnSe/ZnBeSe quantum wells by means of photoexcitation.

    SciTech Connect

    Keller, D.; Astakhov, G. V.; Yakovlev, D. R.; Barrick, T.; Crooker, S. A.; Hansen, L.; Ossau, W.; Molenkamp, L. W.

    2002-01-01

    Heating of the spin system of magnetic ions by means of photoexcited carriers has been studied in modulation-doped (Zn,Mn)Se/(Zn,Be)Se quantum well structures with different electron densities varying from about 10{sup 9} to 5.5 x 10{sup 11} cm{sup -2}. The elevated temperature of the magnetic ions manifests in a reduced Zeeman splitting of the carriers already for low excitation densities. The efficiency of the heating decreases with increasing electron concentration.

  3. Photovoltaic Properties of CdSe/CdS and CdS/CdSe Core-Shell Particles Synthesized by Use of Uninterrupted Precipitation Procedures

    NASA Astrophysics Data System (ADS)

    Selene Coria-Monroy, C.; Sotelo-Lerma, M.; Martínez-Alonso, Claudia; Moreno-Romero, Paola M.; Rodríguez-Castañeda, Carlos A.; Corona-Corona, Israel; Hu, Hailin

    2015-10-01

    Cadmium Selenide (CdSe) and cadmium sulfide (CdS) are good electron acceptors for hybrid solar cells. CdSe and CdS nanoparticles can be prepared at low temperatures (60-80°C) from alkaline aqueous solutions of a cadmium salt, sodium citrate, and thiourea, as sulfur source, or sodium selenosulfate, as selenium source. Under the same experimental conditions, the reaction kinetics for CdS were faster than for CdSe. Formation of CdSe/CdS core-shell particles (type I: CdSe as core and CdS as shell) could be achieved by use of an uninterrupted one-step process by setting high and low solution temperatures for the core and shell compounds, respectively. The yield of the CdSe product was higher at a pH 8.5-9.5 whereas that of the CdS product was higher at higher pH (10-11). Therefore, formation of the "inverse" CdS/CdSe structure (type II: CdS as core and CdSe as shell) was possible in a one-step solution process by choosing a high solution pH for the core and a lower pH for the shell. Photoluminescence spectra and electron micrographs confirmed formation of the two types of core-shell particle. The photovoltaic performance of heterojunctions prepared with core-shell particles and poly(3-hexylthiophene) (P3HT), also suggested formation of core-shell particles. Both the photovoltage and photocurrent density of hybrid solar cells depended on the shell compound and not on the core. It was shown that the interface of the heterojunctions plays is important in solar cell applications, and its modification could be realized by incorporating different shell compounds on core particles.

  4. Core-Shell MnSe@Bi2 Se3 Fabricated via a Cation Exchange Method as Novel Nanotheranostics for Multimodal Imaging and Synergistic Thermoradiotherapy.

    PubMed

    Song, Guosheng; Liang, Chao; Gong, Hua; Li, Meifang; Zheng, Xianchuang; Cheng, Liang; Yang, Kai; Jiang, Xiqun; Liu, Zhuang

    2015-10-28

    MnSe@Bi2 Se3 core-shell nanostructures with highly integrated imaging and therapy functions are fabricated by a simple cation exchange method. Using those nanoparticles as a theranostic agent, a promise concept is further demonstrated to enhance conventional radiotherapy by: i) using X-ray absorbing agents to locally concentrate radiation energy and ii) employing near-infrared-light-triggered photothermal therapy to overcome hypoxia-associated radioresistance. PMID:26331476

  5. Biogeochemical and hydrological controls in mobilizing Se in a saline wetland environment

    NASA Astrophysics Data System (ADS)

    Datta, S.; Hettiarachchi, G. M.; Crawford, M.; Karna, R.; Allmendinger, N. E.; Khatiwada, R.

    2010-12-01

    Selenium (Se) contamination in watersheds remains a challenge to water and land and wildlife managers throughout the west and mid west of US. In that sense, understanding the fundamentals of Se mobilization, fixation and bioconcentration is the current research endeavor. The challenge for Se research is developing watershed-geochemical models that are well founded in Se geochemical/biologcial principles that can be applied in a wide range of situations to inform decisions. Pariette Wetlands, a 9000 acre Bureau of Land Management controlled wetland system composed of 20 ponds located at the confluence of Pariette Draw and the Green River is the present location of this study. The agricultural and irrigation practices and the water-rock interactions leading to salinization can be associated with changes in Se chemistry in the rivers. Since its inception Pariette Wetlands has been home to a rich and diverse wetland ecosystem located in the arid Uintah Basin of Northeastern Utah. Detailed sampling of surficial sediments (0-1 m) from stream banks, channel beds and for water sampling have been undergone in 2 separate field trips throughout the entire reach of the wetland. To establish Pariette Draw’s contribution of Se to the Green river, water and sediments were also sampled from the Green River up and downstream of its confluence with Pariette Draw. In situ measurements of water parameters within the wetland suggest a clear trend of increased pH from upstream, 8, to downstream, 9.2 and combined with TDS suggest a pH controlled saline environment system. The headwaters near Flood Control Dam have an added input of Se from a possible irrigation source upstream in Pleasant Valley area while Se drastically decreases downstream towards the Red Head Pond. Se fractionation in sediments is being analyzed via a sequential extraction procedure to locate the labile fractions of mostly inorganic bound Se. Solid state speciation of Se via μ-XRF aided μ-XANES is being combined

  6. Control of point defects in the Cu(In,Ga)Se2 film synthesized at low temperature from a Cu/In2Se3 stacked precursor

    NASA Astrophysics Data System (ADS)

    Jung, Gwang Sun; Kim, Seungtae; Ko, Young Min; Moon, Sun Hong; Choi, Yong Woo; Ahn, Byung Tae

    2016-07-01

    Low-temperature fabrication of Cu(In,Ga)Se2 (CIGS) film is essential for flexible CIGS solar cells. A large-grained CIGS film was synthesized with a Se-deficient Cu/In,Ga)2Se3 stacked precursor by reacting at 500 °C in a vacuum and was then subsequently annealing in Se environment. The CIGS solar cell with the as-prepared CIGS film had a poor cell performance due to a very low Ga composition at the CIGS surface. The surface Ga composition was controlled to 0.2 by supplying In, Ga, and Se in a temperature range of 350 to 500 °C. From an analysis of the photoluminescence spectra, we found that the point defects, Se vacancy and In-in-Cu antisite, in the CIGS film were greatly reduced by annealing below 450 °C. The short-circuit current was pronouncedly increased in the CIGS cells. The open-circuit voltage depended on both the Ga composition and Cu composition at the CIGS surface. In particular, a low Cu composition at the CIGS surface was essential for the higher performance solar cells. Our results indicated that CIGSs film synthesized at high temperature must be annealed at 350 °C or below to reduce undesirable point defects. [Figure not available: see fulltext.

  7. Core-Shell Zn x Cd1- x Se/Zn y Cd1- y Se Quantum Dots for Nonvolatile Memory and Electroluminescent Device Applications

    NASA Astrophysics Data System (ADS)

    Al-Amoody, Fuad; Suarez, Ernesto; Rodriguez, Angel; Heller, E.; Huang, Wenli; Jain, F.

    2011-08-01

    This paper presents a floating quantum dot (QD) gate nonvolatile memory device using high-energy-gap Zn y Cd1- y Se-cladded Zn x Cd1- x Se quantum dots ( y > x) with tunneling layers comprising nearly lattice-matched semiconductors (e.g., ZnS/ZnMgS) on Si channels. Also presented is the fabrication of an electroluminescent (EL) device with embedded cladded ZnCdSe quantum dots. These ZnCdSe quantum dots were embedded between indium tin oxide (ITO) on glass and a top Schottky metal electrode deposited on a thin CsF barrier. These QDs, which were nucleated in a photo-assisted microwave plasma (PMP) metalorganic chemical vapor deposition (MOCVD) reactor, were grown between the source and drain regions on a p-type silicon substrate of the nonvolatile memory device. The composition of QD cladding, which relates to the value of y in Zn y Cd1- y Se, was engineered by the intensity of ultraviolet light, which controlled the incorporation of zinc in ZnCdSe. The QD quality is comparable to those deposited by other methods. Characteristics and modeling of the II-VI quantum dots as well as two diverse types of devices are presented in this paper.

  8. Magnesium effects on CdSe self-assembled quantum dot formation on Zn xCd yMg 1-x-ySe layers

    NASA Astrophysics Data System (ADS)

    Noemi Perez-Paz, M.; Lu, Hong; Shen, Aidong; Jean Mary, F.; Akins, Daniel; Tamargo, Maria C.

    2006-09-01

    Optical and morphological studies are used to investigate the effects of chemical composition and, in particular, the magnesium content of the Zn xCd yMg 1-x-ySe barrier layers on the size, density and uniformity of CdSe self-assembled quantum dots (QDs). A reduction of the uncapped QD size, as well as a blue shift of the capped QD photoluminescence peak position by increasing Mg concentration in the Zn xCd yMg 1-x-ySe barrier has been demonstrated by changing the Mg cell temperature during growth. In addition, a more uniform and more densely packed QD layer has been observed with an increase of the MgSe fraction in the Zn xCd yMg 1-x-ySe barrier layer using three-dimensional topographic atomic force microscopy images of the surface of uncapped QDs. Results point to Mg as a chemical factor that induces QD formation, either by increasing the density of atomic steps or/and by changing the energy of the Zn xCd yMg 1-x-ySe surface.

  9. Mapping the 3D distribution of CdSe nanocrystals in highly oriented and nanostructured hybrid P3HT-CdSe films grown by directional epitaxial crystallization.

    PubMed

    Roiban, L; Hartmann, L; Fiore, A; Djurado, D; Chandezon, F; Reiss, P; Legrand, J-F; Doyle, S; Brinkmann, M; Ersen, O

    2012-11-21

    Highly oriented and nanostructured hybrid thin films made of regioregular poly(3-hexylthiophene) and colloidal CdSe nanocrystals are prepared by a zone melting method using epitaxial growth on 1,3,5-trichlorobenzene oriented crystals. The structure of the films has been analyzed by X-ray diffraction using synchrotron radiation, electron diffraction and 3D electron tomography to afford a multi-scale structural and morphological description of the highly structured hybrid films. A quantitative analysis of the reconstructed volumes based on electron tomography is used to establish a 3D map of the distribution of the CdSe nanocrystals in the bulk of the films. In particular, the influence of the P3HT-CdSe ratio on the 3D structure of the hybrid layers has been analyzed. In all cases, a bi-layer structure was observed. It is made of a first layer of pure oriented semi-crystalline P3HT grown epitaxially on the TCB substrate and a second P3HT layer containing CdSe nanocrystals uniformly distributed in the amorphous interlamellar zones of the polymer. The thickness of the P3HT layer containing CdSe nanoparticles increases gradually with increasing content of NCs in the films. A growth model is proposed to explain this original transversal organization of CdSe NCs in the oriented matrix of P3HT.

  10. Construction of coaxial ZnSe/ZnO p-n junctions and their photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Zhang, Xiwei; Meng, Dan; Hu, Dan; Tang, Zhenjie; Niu, Xiaoping; Yu, Fengjun; Ju, Lin

    2016-02-01

    Coaxial ZnSe/ZnO nanostructures were fabricated by coating a ZnO thin film on the surface of presynthesized p-type ZnSe 1D nanostructures by a sputtering method. Owing to the n-type behavior of ZnO resulting from intrinsic defects, coaxial ZnSe/ZnO p-n junctions were realized and showed a pronounced rectifying behavior. Photovoltaic devices based on the coaxial ZnSe/ZnO p-n junction showed a power conversion efficiency of 1.24% and a large open-circuit voltage of 0.87 V under UV light. The large bandgaps of ZnSe and ZnO and the high quality of the ZnSe/ZnO interface were considered to be related to the high performance of the devices.

  11. Epitaxy and photoresponse of two-dimensional GaSe crystals on flexible transparent mica sheets.

    PubMed

    Zhou, Yubing; Nie, Yufeng; Liu, Yujing; Yan, Kai; Hong, Jinhua; Jin, Chuanhong; Zhou, Yu; Yin, Jianbo; Liu, Zhongfan; Peng, Hailin

    2014-02-25

    We present the controlled synthesis of high-quality two-dimensional (2D) GaSe crystals on flexible transparent mica substrates via a facile van der Waals epitaxy method. Single- and few-layer GaSe nanoplates with the lateral size of up to tens of micrometers were produced. The orientation and nucleation sites of GaSe nanoplates were well-controlled. The 2D GaSe crystal-based photodetectors were demonstrated on both mechanically rigid SiO2/Si and flexible mica substrates. Efficient photoresponse was observed in 2D GaSe crystal devices on transparent flexible mica substrates, regardless of repeated bending with different radii. The controlled growth of 2D GaSe crystals with efficient photoresponsivity opens up opportunities for both fundamental aspects and new applications in photodetectors.

  12. ADVANCES IN SE-79 ANALYSES ON SAVANNAH RIVER SITE RADIOACTIVE WASTE MATRICES

    SciTech Connect

    Diprete, D; C Diprete, C; Ned Bibler, N; Cj Bannochie, C; Michael Hay, M

    2009-03-16

    Waste cleanup efforts underway at the United States Department of Energy's (DOE) Savannah River Site (SRS) in South Carolina, as well as other DOE nuclear sites, have created a need to characterize {sup 79}Se in radioactive waste inventories. Successful analysis of {sup 79}Se in high activity waste matrices is challenging for a variety of reasons. As a result of these unique challenges, the successful quantification of {sup 79}Se in the types of matrices present at SRS requires an extremely efficient and selective separation of {sup 79}Se from high levels of interfering radionuclides. A robust {sup 79}Se radiochemical separation method has been developed at the Savannah River National Laboratory (SRNL) which is routinely capable of successfully purifying {sup 79}Se from a wide range of interfering radioactive species. In addition to a dramatic improvements in the Kd, ease, and reproducibility of the analysis, the laboratory time has been reduced from several days to only 6 hours.

  13. Luminescence properties of MgxZn1-xSe prepared by Mg diffusion

    NASA Astrophysics Data System (ADS)

    Łożykowski, H. J.; Holtz, P. O.; Monemar, B.

    1983-07-01

    The photoluminescence of ZnSe doped with the isoelectronic substituent Mg with a simple diffusion procedure has been studied. It was found that Mg easily enters substitutionally on Zn-site to form MgxZn1-xSe. The diffused samples therefore show a graded bandgap due to a composition gradient in the surface region. In contrast to ZnSe the photoluminescence spectrum of MgxZn1-xSe is dominated by a near bandgap emission at all temperatures between 1.5 and 300 K. The bandgap shift compared with “pure” ZnSe is estimated from photoluminescence excitation spectra. The luminous efficiency of MgxZn1-xSe makes the material promising for future applications as light emitting diodes with a well defined narrow emission band at a wavelength determined by the Mg content x.

  14. A microscopic study investigating the structure of SnSe surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Sang-ui; Duong, Anh-Tuan; Cho, Sunglae; Rhim, S. H.; Kim, Jungdae

    2016-09-01

    SnSe has been widely studied due to its many potential applications that take advantage of its excellent thermoelectric, photovoltaic, and optoelectronic properties. However, experimental investigations into the microscopic structure of SnSe remain largely unexplored. Herein, for the first time, the atomic and electronic structures of SnSe surfaces are studied by a home-built low temperature scanning tunneling microscope (STM) and density functional theory (DFT) calculations. The cleaved surface of SnSe is comprised of covalently bonded Se and Sn atoms in zigzag patterns. However, rectangular periodicity was observed in the atomic images of SnSe surfaces for filled and empty state probing. Detailed atomic structures are analyzed by DFT calculations, indicating that the bright extrusions of both filled and empty state images are mostly located at the positions of Sn atoms.

  15. Pulsed laser deposition of Mn doped CdSe quantum dots for improved solar cell performance

    SciTech Connect

    Dai, Qilin; Wang, Wenyong E-mail: jtang2@uwyo.edu; Tang, Jinke E-mail: jtang2@uwyo.edu; Sabio, Erwin M.

    2014-05-05

    In this work, we demonstrate (1) a facile method to prepare Mn doped CdSe quantum dots (QDs) on Zn{sub 2}SnO{sub 4} photoanodes by pulsed laser deposition and (2) improved device performance of quantum dot sensitized solar cells of the Mn doped QDs (CdSe:Mn) compared to the undoped QDs (CdSe). The band diagram of photoanode Zn{sub 2}SnO{sub 4} and sensitizer CdSe:Mn QD is proposed based on the incident-photon-to-electron conversion efficiency (IPCE) data. Mn-modified band structure leads to absorption at longer wavelengths than the undoped CdSe QDs, which is due to the exchange splitting of the CdSe:Mn conduction band by the Mn dopant. Three-fold increase in the IPCE efficiency has also been observed for the Mn doped samples.

  16. Optimization of p-CuInSe sub 2/n-CdZnS solar cells

    NASA Astrophysics Data System (ADS)

    Birkmire, R. W.

    1986-05-01

    This research was conducted to fabricate CuInSe2/CdS solar cells on well-characterized CuInSe2 single-crystal wafers in order to improve our understanding of thin-film polycrystalline devices. CuInSe2 wafers were supplied to the Institute of Energy by K. Bachmann of North Carolina State University. CdS was deposited onto the wafers to make CuInSe2/CdS heterojunctions. Some wafers were treated in a Se atmosphere to lower the resistivity and to homogenize properties through the wafer. Not all wafers were single-crystal. The wafers were characterized in terms of resistivity, carrier type, composition and crystallographic structure. The CuInSe2/CdS cells had efficiencies over 4% and open-circuit voltages over 0.45 V. The number of wafers and their quality limited the device performance achievable in this work.

  17. Multi-orbits observed in superconducting Nb-doped Bi2Se3

    NASA Astrophysics Data System (ADS)

    Lawson, Benjamin; Corbae, Paul; Li, Gang; Yu, Fan; Asaba, Tomoya; Tinsman, Colin; Qiu, Yunsheng; Hor, Yew San; Li, Lu

    Recently discovered superconducting niobium doped Bi2Se3 shows promise to realize new physical phenomenon including the coexistence of superconductivity and magnetic ordering and possibly topological superconductivity. To understand the new physics showcased in this system, a detailed knowledge of the electronic structure is needed. We present the first observation of quantum oscillations in the magnetization (the de Haas-van Alphen effect) of Nb-doped Bi2Se3. In the fully superconducting crystal, two distinct orbits are observed, in sharp contrast to Bi2Se3, Cu-doped Bi2Se3, and Sr-doped Bi2Se3. The multiple frequencies observed in our quantum oscillations, combined with our electrical transport studies, indicate the multi-orbit nature of the electronic state of Nb-doped Bi2Se3.

  18. Energetics and electronic properties of Pt wires of different topologies on monolayer MoSe2

    NASA Astrophysics Data System (ADS)

    Jamdagni, Pooja; Kumar, Ashok; Thakur, Anil; Pandey, Ravindra; Ahluwalia, P. K.

    2016-05-01

    The energetics and electronic properties of different topology of Pt wires including linear, zigzag and ladder structures on MoSe2 monolayer have been investigated in the framework of density functional theory (DFT). The predicted order of stability of Pt wire on MoSe2 monolayer is found to be: linear > ladder > zigzag. Pt wires induce states near the Fermi level of MoSe2 that results into metallic characteristics of Pt-wire/MoSe2 assembled system. Valence band charge density signifies most of the contribution from Pt atoms near the Fermi energy of assembled wire/MoSe2 system. These findings are expected to be important for the fabrication of devices based on MoSe2 layers for flexible nanoelectronics.

  19. MoSeS: Modelling and Simulation for e-Social Science.

    PubMed

    Townend, Paul; Xu, Jie; Birkin, Mark; Turner, Andy; Wu, Belinda

    2009-07-13

    MoSeS (Modelling and Simulation for e-Social Science) is a research node of the National Centre for e-Social Science. MoSeS uses e-Science techniques to execute an events-driven model that simulates discrete demographic processes; this allows us to project the UK population 25 years into the future. This paper describes the architecture, simulation methodology and latest results obtained by MoSeS.

  20. Laser generation in polycrystalline Cr{sup 2+}:ZnSe with undoped faces

    SciTech Connect

    Savin, D V; Gavrishchuk, E M; Ikonnikov, V B; Eremeykin, O N; Egorov, A S

    2015-01-31

    An original method has been suggested for producing polycrystalline Cr{sup 2+}:ZnSe samples with undoped faces. Generation characteristics of a Cr{sup 2+}:ZnSe laser are studied under pulse-periodic pumping by a Tm{sup 3+}:YLF-laser. The efficiency of converting the pump radiation into laser generation at a wavelength of 2350 nm is 20%. Cr{sup 2+}:ZnSe samples exhibit high resistance to surface breakdown. (lasers)

  1. Cd and Te-based ohmic contact materials to p-Type ZnSe

    NASA Astrophysics Data System (ADS)

    Hashimoto, K.; Koide, Y.; Tadanaga, O.; Oku, T.; Teraguchi, N.; Tomomuea, Y.; Suzuki, A.; Murakami, Masanori

    1996-12-01

    In order to explore a possibility of forming an intermediate semiconductor layer with low Schottky barrier by the conventional deposition and annealing technique, the electrical properties of Cd and Te-based contacts on the nitrogendoped ZnSe substrates have been investigated. Cd in the Cd/W contact reacted with the ZnSe substrate after annealing at temperatures above 250°C and formed epitaxial Ccx}Zn1-xSe layers, leading to reduction of the “turn-on” voltage (VT) from about 11 to 6 V (here, a slash “/” between Cd and W means the deposition sequence). The reduction of the Vn} value by annealing at elevated temperatures was also observed for the Bi-Cd/W and In-Cd/W contacts. The average Cd composition (x) in the Cdn}Zn1-xSe layers was measured to be larger than 0.9, which agreed with the values estimated from the calculated Cd-Zn-Se phase diagrams. The ohmic behavior was strongly influenced by the thickness of the CdxZn1-xSe layer, the density of misfit dislocations formed at the interface between the Cdx Zn1-x Se and the ZnSe, and/or the total area of the Cd Zn. Se layers covering the ZnSe surface. The present result suggests that formation of the large-areal CcxZn1-xSe layers with thin thickness is crucial to achieve further reduction of the VT value by the conventional deposition and annealing technique. Also, the VT reduction was not obtained for the Te/W contact even after annealing at temperatures close to 300°C, which was explained to be due to absence of ternary ZnSe1-xTen intermediate layers.

  2. Photovoltaic Devices Employing Ternary PbSxSe1-x Nanocrystals

    SciTech Connect

    Ma, Wanli; Luther, Joseph; Zheng, Haimei; Wu, Yue; Alivisatos, A. Paul

    2009-02-05

    We report solar cells based on highly confined nanocrystals of the ternary compound PbSxSe1-x. Crystalline, monodisperse alloyed nanocrystals are obtained using a one-pot, hot injection reaction. Rutherford back scattering and energy filtered transmission electron microscopy suggest that the S and Se anions are uniformly distributed in the alloy nanoparticles. Photovoltaic devices made using ternary nanoparticles are more efficient than either pure PbS or pure PbSe based nanocrystal devices.

  3. Photoluminescence properties of MgxZn1-xSe single crystals

    NASA Astrophysics Data System (ADS)

    Park, Sang-An; Song, Ho-Jun; Kim, Wha-Tek; Kim, Hyung-Gon; Jin, Moon-Seog; Kim, Chang-Dae; Yoon, Chang-Sun

    1998-03-01

    MgxZn1-xSe single crystals were grown by the closed tube sublimation method. The MgxZn1-xSe single crystals crystallized into zincblende and wurtzite structures in the composition ranges of x=0.0-0.1 and x=0.2-0.6, respectively. Blue and violet emissions with LO phonon replica and self-activated emissions in the MgxZn1-xSe single crystals were observed at 10 K.

  4. Effect of 3d-metal doping on magnetic properties of Fe3 Se4

    NASA Astrophysics Data System (ADS)

    Sabirianov, Renat; Al-Aqtash, Nabil; Sengupta, Debasis

    2015-03-01

    Fe3Se4 exhibits large magnetocrystalline anisotropy (MAE) and coercivity up 40kOe. The large anisotropy of Fe3Se4 should be accompanied by large magnetization for permanent magnet applications. The magnetization of Fe3Se4 suffers from antiferromagnetic (AFM) superexchange coupling of Fe across the Se planes. We present density functional theory study of the magnetic properties of Fe3Se4 doped with TM (Co, Cr, Ni and Mn), TM ions doped in Fe sites, Fe3-x(TM)xSe4 (x = 0.5), to examine a potential increase of the magnetization and Curie temperature of Fe3Se4. We performed screening of the exchange interactions and magnetization modifications upon the substitution of Fe by 3d-transition metals at various Fe sites in the Fe3Se4 We find that the doping of Fe3Se4 with 3d-elements does not remove AFM coupling across layers. The increase in the strength of exchange interactions on doping with Cr should increase the Curie temperature of the system. We compare the results of doped alloy with the ones for Cr3Te4. This compound is analogous to Fe3Se4 because Te has same electron configuration as Se, but Cr has only four d-electrons. We find that Cr3Te4 has ferromagnetic coupling and magnetization larger than one possible in Fe3Se4. Magnetization per unit cell is 18.24μB. MAE of this material is large (MAE =1.67 MJ/m3)

  5. van der Waals epitaxy and photoresponse of two-dimensional CdSe plates

    NASA Astrophysics Data System (ADS)

    Zhu, Dan-Dan; Xia, Jing; Wang, Lei; Li, Xuan-Ze; Tian, Li-Feng; Meng, Xiang-Min

    2016-06-01

    Here we demonstrate the first growth of two-dimensional (2D) single-crystalline CdSe plates on mica substrates via van der Waals epitaxy. The as-synthesized 2D plates exhibit hexagonal, truncated triangular and triangular shapes with the lateral size around several microns. Photodetectors based on 2D CdSe plates present a fast response time of 24 ms, revealing that 2D CdSe is a promising building block for ultrathin optoelectronic devices.

  6. First principles study of oxygen adsorption on Se-modified Ru nanoparticles

    NASA Astrophysics Data System (ADS)

    Zuluaga, Sebastian; Stolbov, Sergey

    2012-08-01

    We present here the results of our density-functional-theory-based calculations of the electronic and geometric structures and energetics of Se and O adsorption on Ru 93- and 105-atom nanoparticles. These studies have been inspired by the fact that Se/Ru nanoparticles are considered promising electrocatalysts for the oxygen reduction reaction (ORR) on direct methanol fuel cell cathodes and the oxygen binding energy is a descriptor for the catalyst activity toward this reaction. We find the character of chemical bonding of Se on a flat nanoparticle facet to be ionic, similar to that obtained earlier for the Se/Ru(0001) surface, while in the case of a low-coordinated Ru configuration there is an indication of some covalent contribution to the bonding leading to an increase in Se binding energy. Se and O co-adsorbed on the flat facet both accept electronic charge from Ru, whereas the adsorption on low-coordinated sites causes more complicated valence charge redistribution. The Se modification of the Ru particles leads to weakening of the oxygen bonding to the particles. However, overall, O binding energies are found to be higher for the particles than for Se/Ru(0001). The high reactivity of the Se/Ru nanoparticles found in this work is not favorable for ORR. We thus expect that larger particles with well-developed flat facets will be more efficient ORR catalysts than small nanoparticles with a large fraction of under-coordinated adsorption sites.

  7. Enhancement in the photorefractive performance of organic composites photosensitized with functionalized CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Liang, Yichen; Wang, Wei; Moon, Jong-Sik; Winiarz, Jeffrey G.

    2016-08-01

    Enhancement in the photorefractive (PR) performance of organic composites photosensitized by CdSe quantum dots (QCdSe) passivated with the charge-transport ligands, sulfonated triphenyldiamine (STPD), is reported. This enhancement is primarily attributed to the ability of the passivating ligand, STPD, to facilitate the charge-transfer process between the QCdSe and the triphenyldiamine (TPD) charge-transport matrix. The PR composites exhibited a maximum photocharge-generation efficiency of 0.9% and two-beam coupling gain coefficient of 110 cm-1. These figures of merit represent a significant improvement over similar composites photosensitized with more conventional trioctylphosphine oxide-passivated QCdSe (TQCdSe). Moreover, composites photosensitized with SQCdSe had a faster response time of τ = 128 ms at an electric field of 60 V/μm compared with τ = 982 ms for those containing TQCdSe. Because of the molecular similarity between the STPD passivating groups and the TPD-based charge-transport matrix, concentrations of up to 1.4 wt% of SQCdSe are achieved in PR composites without any detectable phase separation, a considerable improvement over the 0.7 wt% for TQCdSe.

  8. Effects of Se and Zn supplementation on the antagonism against Pb and Cd in vegetables.

    PubMed

    He, P P; Lv, X Z; Wang, G Y

    2004-04-01

    The antagonistic effects of supplementation of Zn and Se to the soil on vegetables were studied in this work. In the pot experiment, Se (Se4+) and Zn (Zn2+) were applied, respectively, to the soil, in which the Chinese cabbage (Brassica rapa) and the lettuce (Lactuca sativa L.) were planted. As a result, Se and Zn were enriched evidently in the two vegetables. The contents of Pb and Cd in the two vegetables were decreased markedly while contents of some healthy mineral elements, like Mn and Mg, were increased to some extent when Se and Zn were applied. The antagonism of Se and Zn against Pb and Cd in plants was suggested. The farmland experiment on the lettuce was conducted to explore further the effect of supplementation of Zn and Se under the actual field conditions. Result came out to be that the enrichment of Zn and Se restrained the accumulation of Pb and Cd in the lettuce remarkably, as well as enhanced the absorption of some other nutritional elements, like Fe, Mn, Cu, Ca and Mg. Therefore, application of Se and Zn was proved to be an effective and feasible method to improve trace elements nutrition in the vegetables.

  9. Distribution and reuse of {sup 76}Se-selenosugar in selenium-deficient rats

    SciTech Connect

    Suzuki, Kazuo T. . E-mail: ktsuzuki@p.chiba-u.ac.jp; Somekawa, Layla; Suzuki, Noriyuki

    2006-10-15

    Nutritional selenium compounds are transformed to the common intermediate selenide and then utilized for selenoprotein synthesis or excreted in urine mostly as 1{beta}-methylseleno-N-acetyl-DD-galactosamine (selenosugar). Since the biological significance of selenosugar formation is unknown, we investigated their role in the formation of selenoenzymes in selenium deficiency. Rats were depleted of endogenous natural abundance selenium with a single stable isotope ({sup 82}Se) and then made Se-deficient. {sup 76}Se-Selenosugar was administered intravenously to the rats and their urine, serum, liver, kidneys and testes were subjected to speciation analysis with HPLC inductively coupled argon plasma mass spectrometry. Most {sup 76}Se was recovered in its intact form (approximately 80% of dose) in urine within 1 h. Speciation analysis revealed that residual endogenous natural abundance selenium estimated by {sup 77}Se and {sup 78}Se was negligible and distinct distributions of the labeled {sup 76}Se were detected in the body fluids and organs without interference from the endogenous natural abundance stable isotope. Namely, intact {sup 76}Se-selenosugar was distributed to organs after the injection, and {sup 76}Se was used for selenoprotein synthesis. Oxidation to methylseleninic acid and/or hydrolysis of the selenoacetal group to methylselenol were proposed to the transformation of selenosugar for the reuse. Effective use of an enriched stable isotope as an absolute label in hosts depleted of natural abundance isotopes was discussed for application in tracer experiments.

  10. Electrochemical preparation and structural characterization of CuGaSe2 thin films

    NASA Astrophysics Data System (ADS)

    Manfredy, L.; Marquez, O. P.; Lopez-Rivera, S. A.; Marquez, J.; Martínez, Y.; Miranda, D. A.

    2016-02-01

    CuGaSe2 thin films have been synthesized by one-step electrodeposition on titanium and SnO2/glass substrates from aqueous solutions that contain thiocyanate ion as a complexing agent. According to composition, and morphology analysis at deposition potential of -0.55V vs SCE (Standard Calomel Electrode) for 20 minutes from aqueous solutions of 4.6mM CuCl, 25.0mM GaCl3 y 9.2mM SeO2 in 2.0M de KSCN at pH 2.5 was found the optimum condition for obtain the CuGaSe2 thin films with good morphology and good stoichiometric. The samples were annealed at temperature of 520°C in inert atmosphere for 30 minutes to improve their crystallinity. The obtained CuGaSe2 thin film has a direct band gap (Eg) of 1.65eV. In addition, the cyclic voltammetry (CV) studies were performed in order to elucidate the electrodic processes that occur for the formation of semiconductor CuGaSe2. Therefore, the electrochemical behaviour for each ion (Cu+, Ga3+ and Se4+), for binary (Cu-Se, Ga-Se, and Cu- Ga) and for ternary (Cu-Ga-Se) systems are described. This material has potential application in solar cells.

  11. Phonons in the ternary phase ZrS 3-xSe x

    NASA Astrophysics Data System (ADS)

    Zwick, A.; Landa, G.; Carles, R.; Renucci, M. A.; Kjekshus, A.

    1983-03-01

    The mode behaviour of long wavelength optical phonons in the ternary phase ZrS 3-xSe x has been investigated by means of Raman spectroscopy through the whole composition range 0 ⩽ x ⩽ 3. A mixed one-, two- and three-mode behaviour is observed, depending respectively on modes of group I (quasi- rigid chain modes), II (internal deformation chain modes) and III (diatomic X-X [ X = S, Se] stretching mode). Three-mode behaviour of diatomic X-X mode is explained in terms of vibrations of S-S, Se-Se and S-Se pairs, practically insensitive to metal atoms as shown by comparison with the HfS 3-xSe x system. The analysis of integrated intensities of peaks assigned to vibrations of S-S, Se-Se and S-Se pairs on the basis of a statistical model concludes in favour of higher Raman efficiency of selenium pairs compared to sulfur pairs. On the other hand, one-mode behaviour of quasi-rigid chain modes establishes unambiguously a one-to-one mode correspondence between the two binary compounds, confirming thus our previous assignments. Spectral features of the ternary phase suggest contributions from the density of vibrational states due to relaxation of Raman selection rules resulting from configurational disorder.

  12. Toward the Intrinsic Limit of the Topological Insulator Bi_{2}Se_{3}.

    PubMed

    Dai, Jixia; West, Damien; Wang, Xueyun; Wang, Yazhong; Kwok, Daniel; Cheong, S-W; Zhang, S B; Wu, Weida

    2016-09-01

    Combining high resolution scanning tunneling microscopy and first principles calculations, we identified the major native defects, in particular the Se vacancies and Se interstitial defects, that are responsible for the bulk conduction and nanoscale potential fluctuations in single crystals of archetypal topological insulator Bi_{2}Se_{3}. Here it is established that the defect concentrations in Bi_{2}Se_{3} are far above the thermodynamic limit, and that the growth kinetics dominate the observed defect concentrations. Furthermore, through careful control of the synthesis, our tunneling spectroscopy suggests that our best samples are approaching the intrinsic limit with the Fermi level inside the band gap without introducing extrinsic dopants. PMID:27636482

  13. Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots

    PubMed Central

    Tohgha, Urice; Deol, Kirandeep K.; Porter, Ashlin G.; Bartko, Samuel G.; Choi, Jung Kyu; Leonard, Brian M.; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

    2014-01-01

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by post-synthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Density functional theory (DFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The chirality was induced by the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand. PMID:24200288

  14. Ligand induced circular dichroism and circularly polarized luminescence in CdSe quantum dots.

    PubMed

    Tohgha, Urice; Deol, Kirandeep K; Porter, Ashlin G; Bartko, Samuel G; Choi, Jung Kyu; Leonard, Brian M; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

    2013-12-23

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by postsynthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Time Dependent Density Functional Theory (TDDFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The origin of the induced chirality is consistent with the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand.

  15. Rutherford Backscattering Spectrometry analysis of iron-containing Bi2Se3 topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Alarcon-Diez, V.; Eddrief, M.; Vickridge, I.

    2016-03-01

    Fe-containing Bi2Se3 topological insulators (TI) thin films have been grown to investigate the intricate interplay between topological order and the incorporation of ferromagnetic atoms. Here we present the quantitative characterisation of the Bi2Se3 thin films with up to 16 at% Fe incorporated during the growth process on GaAs (1 1 1) substrate by Molecular Beam Epitaxy. We report the elemental composition and depth profiles of the Bi2Se3:Fe films obtained using Rutherford Backscattering Spectrometry (RBS) and their formed crystalline phase obtained by X-ray diffraction (XRD). Resistance of the TI to beam-induced damage was investigated by channelling RBS. Using the elemental composition from RBS and the thickness from XRD measurements the Fe-free film density was deduced. For Fe-containing samples, the diffraction reveals the formation of two distinct crystalline phases, as well as their intergrowth pattern, in which the basal planes of Bi2Se3 coexist with an additional Fe-Se phase. This intergrown composite, with chemical compatibility of the Fe-Se phase with the crystalline Bi2Se3 structure, preserves the intrinsic topological surface states of the TI component despite the inhomogeneous distribution of the constituent phases. RBS analysis gives the stoichiometry of the Bi2Se3, and Bi2Se3:Fe samples (estimated between 0 and 16 at% Fe) and gives insights into the composition of FeSex phases present.

  16. Room-temperature synthesis, hydrothermal recrystallization, and properties of metastable stoichiometric FeSe.

    PubMed

    Nitsche, F; Goltz, T; Klauss, H-H; Isaeva, A; Müller, U; Schnelle, W; Simon, P; Doert, Th; Ruck, M

    2012-07-01

    Room-temperature precipitation from aqueous solutions yields the hitherto unknown metastable stoichiometric iron selenide (ms-FeSe) with tetragonal anti-PbO type structure. Samples with improved crystallinity are obtained by diffusion-controlled precipitation or hydrothermal recrystallization. The relations of ms-FeSe to superconducting β-FeSe(1-x) and other neighbor phases of the iron-selenium system are established by high-temperature X-ray diffraction, DSC/TG/MS (differential scanning calorimetry/thermogravimetry/mass spectroscopy), (57)Fe Mössbauer spectroscopy, magnetization measurements, and transmission electron microscopy. Above 300 °C, ms-FeSe decomposes irreversibly to β-FeSe(1-x) and Fe(7)Se(8). The structural parameters of ms-FeSe (P4/nmm, a = 377.90(1) pm, c = 551.11(3) pm, Z = 2), obtained by Rietveld refinement, differ significantly from literature data for β-FeSe(1-x). The Mössbauer spectrum rules out interstitial iron atoms or additional phases. Magnetization data suggest canted antiferromagnetism below T(N) = 50 K. Stoichiometric non-superconducting ms-FeSe can be regarded as the true "parent" compound for the "11" iron-chalcogenide superconductors and may serve as starting point for new chemical modifications.

  17. Direct Patterning of CdSe Quantum Dots into Sub-100 nm Structures

    SciTech Connect

    Hampton, Meredith J.; Templeton, Joseph L.; DeSimone, Joseph M.

    2010-03-02

    Ordered, two-dimensional cadmium selenide (CdSe) arrays have been fabricated on indium-doped tin oxide (ITO) electrodes using the pattern replication in nonwetting templates (PRINT) process. CdSe quantum dots (QDs) with an average diameter of 2.7 nm and a pyridine surface ligand were used for patterning. The PRINT technique utilizes a perfluoropolyether (PFPE) elastomeric mold that is tolerant of most organic solvents, thus allowing solutions of CdSe QDs in 4-picoline to be used for patterning without significant deformation of the mold. Nanometer-scale diffraction gratings have been successfully replicated with CdSe QDs.

  18. Multi-branched CdSe nanocrystals stabilized by weak ligand for hybrid solar cell application.

    PubMed

    Liu, Jincheng; Tao, Hong; Cao, Yong; Ackermann, Jorg

    2014-04-01

    In this article, multi-branched CdSe nanocrystals were produced by a facile colloidal approach stabilized by oleylamine at a relative low temperature. The as-prepared multi-branched CdSe nanocrystals after simple washing process were used in the fabrication of poly(3-hexylthiophene)/CdSe bulk heterojunction photovoltaic device. The effective charge separation in the poly(3-hexylthiophene)/ CdSe nanocomposites have been confirmed by the strong photoluminescence quenching. The films of the blends of P3HT and simply-washed CdSe nanocrystals show more uniform morphology and flatter surface than the film of the bends of P3HT and pyridine-refluxed CdSe nanocrystals. The corresponding power conversion efficiency under 1 sun is about 0.66% for the P3HT/pyridine-washed CdSe hybrid device. Our work did a preliminary study in the hybrid solar cell application of branched blenze CdSe nanocrystals prepared by an easier way, and will be interesting and helpful for making the high-efficiency hybrid solar cells with branched CdSe acceptors.

  19. Spectroscopic study of Se(IV) removal from water by reductive precipitation using sulfide.

    PubMed

    Jung, Bahngmi; Safan, Aya; Batchelor, Bill; Abdel-Wahab, Ahmed

    2016-11-01

    This study investigates the removal of selenium (IV) from water by reductive precipitation using sodium sulfide at neutral pH. Also, it examines the application of UV light as an activating method to enhance reductive precipitation. Furthermore, this work evaluates the effects of sulfide dose and solution pH on behavior of Se(IV) reduction. Selenium was effectively removed in sulfide solution at both neutral and acidic pH. UV irradiation did not enhance removal efficiency of Se(IV) at conditions tested, but it affected solids morphology and composition. SEM/EDS and XPS results showed that selenite was reduced to elemental Se or Se-S precipitates (e.g. SenS8-n) in sulfide solution. High resolution S 2p XPS spectra suggested the presence of sulfur-containing anions (e.g. S2O3(2-), HSO3(-), etc.) or elemental S (S(0)), monosulfide (S(2-)), and polysulfides (Sn(2-)), which could be produced from sulfide photolysis or reaction with Se. In addition, large aggregates of irregular shape, which suggest Se-S precipitates or elemental sulfur, were found more prominently at pH 4 than at pH 7, and they were more noticeable in the presence of UV with longer reaction times. In addition, XRD patterns showed that gray elemental Se solids were dominant in experiments without UV, whereas Se-S precipitates (Se3S5) with an orange color were found in those with UV. PMID:27552695

  20. Contrasting Food Web Factor and Body Size Relationships with Hg and Se Concentrations in Marine Biota

    PubMed Central

    Karimi, Roxanne; Frisk, Michael; Fisher, Nicholas S.

    2013-01-01

    Marine fish and shellfish are primary sources of human exposure to mercury, a potentially toxic metal, and selenium, an essential element that may protect against mercury bioaccumulation and toxicity. Yet we lack a thorough understanding of Hg and Se patterns in common marine taxa, particularly those that are commercially important, and how food web and body size factors differ in their influence on Hg and Se patterns. We compared Hg and Se content among marine fish and invertebrate taxa collected from Long Island, NY, and examined associations between Hg, Se, body length, trophic level (measured by δ15N) and degree of pelagic feeding (measured by δ13C). Finfish, particularly shark, had high Hg content whereas bivalves generally had high Se content. Both taxonomic differences and variability were larger for Hg than Se, and Hg content explained most of the variation in Hg:Se molar ratios among taxa. Finally, Hg was more strongly associated with length and trophic level across taxa than Se, consistent with a greater degree of Hg bioaccumulation in the body over time, and biomagnification through the food web, respectively. Overall, our findings indicate distinct taxonomic and ecological Hg and Se patterns in commercially important marine biota, and these patterns have nutritional and toxicological implications for seafood-consuming wildlife and humans. PMID:24019976