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Sample records for itabaiana se brasil

  1. Paleomagnetism of Early Cambrian Itabaiana mafic dikes (NE Brazil) and the final assembly of Gondwana

    NASA Astrophysics Data System (ADS)

    Trindade, Ricardo I. F.; D'Agrella-Filho, Manoel S.; Epof, Igor; Brito Neves, Benjamim B.

    2006-04-01

    Paleomagnetic analysis on 15 early Cambrian mafic dikes from Itabaiana (Paraíba State) yielded a southern (northwestern) direction with steep upward (downward) inclination ( Dm = 167.5°, Im = - 63.7°, α95 = 7.3°). AF and Thermal demagnetization, thermomagnetic curves, and hysteresis results suggest that this component is dominantly carried by fine-grained SD magnetite. The high stability of this component and positive baked contact tests on three dikes indicate it represents a primary thermoremanent magnetization. Ar-Ar analysis on whole-rock samples from two sites provides a strong constraint on the age of the Itabaiana paleomagnetic pole (134.6° E, 34.9° S; A95 = 7.3, K = 28) defined by plateau ages of 525 ± 5 and 526 ± 4 Ma. This pole completely satisfies six out of the seven quality criteria proposed by Van der Voo [R. Van der Voo, The reliability of paleomagnetic data, Tectonophysics 184 (1990) 1-9.] and permits a tight constraint on the Early Cambrian sector of the Gondwana apparent polar wander path. Paleogeographic reconstructions consistent with the available paleomagnetic and geological record show that Gondwana was sutured along three major orogenies, the Mozambique (Brasilano/Pan-African) Orogeny (800-650 Ma), the Kuunga Orogeny (570-530 Ma) and the Pampean-Araguaia Orogeny (540-520 Ma). We suggest that after rifting away from Laurentia at the end of the Neoproterozoic, opening the Iapetus ocean, the Amazonian craton and minor adjoining blocks, such as Rio Apa and Pampia, collided with the proto-Gondwana by Cambrian times at ca. 530-520 Ma. Unless for small adjustments, Gondwana was completely formed by 525 Ma whose paleogeography is defined by the Itabaiana pole.

  2. Interaction of aqueous Se(IV)/Se(VI) with FeSe/FeSe2: implication to Se redox process.

    PubMed

    Kang, Mingliang; Ma, Bin; Bardelli, Fabrizio; Chen, Fanrong; Liu, Chunli; Zheng, Zhong; Wu, Shijun; Charlet, Laurent

    2013-03-15

    Since reductive precipitation is considered as the most effective way to immobilize (79)Se, interaction of aqueous Se(IV)/Se(VI) with Fe(II)-bearing minerals has received extensive attention. In contrast to the thermodynamic calculations, as well as the prevalence of iron selenide phases observed in soil, sediments and ore deposits, most laboratory experiments have found that Se(0) was the reaction product. In this study, the interaction of Se(IV)/Se(VI) with FeSe/FeSe2 were investigated. The results demonstrate that FeSe and FeSe2 can be oxidized to Se(0) by Se(IV) with relatively fast kinetics, while reaction between Se(VI) and FeSe/FeSe2 only occurs under limited conditions (i.e. in the presence of high ferrous content and higher pH) with much slower kinetics, and there is no evident reaction in most case. Therefore, reduction of Se(IV) by Fe(II)-bearing minerals, in particular by natural occurring minerals, is envisioned to produce Se(0) at the early stage of experiments, rather than FeSe or FeSe2. Due to the formation of bulk Se(0) and its low solubility, the Fe-Se-O-H2O system will maintain redox disequilibrium in laboratory time-scale. This study also reveals that iron selenides, like iron sulfides, have strong reactivity toward Fe(3+). The findings in this study give insight into possible controls on Se redox process. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. 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

  4. Photosensitive anisotype n-ZnSe/ p-InSe and n-ZnSe/ p-GaSe heterojunctions

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    Anisotype n-ZnSe/ p-InSe and n-ZnSe/ p-GaSe heterojunctions are obtained for the first time. They are grown on layered crystalline GaSe and InSe substrates by annealing in Zn vapor. It is found that these heterojunctions are sensitive to light in the near-infrared and visible spectral ranges.

  5. ZnSe/ZnSeTe Superlattice Nanotips

    PubMed Central

    2010-01-01

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

  6. 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.

  7. Electronic states of InSe/GaSe superlattice

    NASA Astrophysics Data System (ADS)

    Erkoç, Ş.; Allahverdi, K.; Ibrahim, Z.

    1994-06-01

    Analysis of recent publications revealed an increasing interest in epitaxial growth of InSe/GaSe superlattice. Within the effective mass theory we carried out self-consistent calculations of the confined and itinerant electronic states, potential profile and charge density distribution of InSe/GaSe superlattice, where the InSe layers are the well and the GaSe layers the barrier. Calculations were performed for three types of doping: uniform, modulated in the well, and modulated in the barrier. It has been found that the Coulomb interaction in the well and barrier forces the formation of localized states in the barrier region. The possibility of an insulator-metal transition in InSe/GaSe superlattice is predicted for modulation doping in the barrier and for a doping level n = 10 19cm-3. A decrease of the barrier height has been found for modulation doping in the well.

  8. TEST CELLS SE-5 - SE-8 - SE-10 IN THE ENGINE RESEARCH BUILDING ERB AND 117 HIGH ENERGY FUELS LABORAT

    NASA Technical Reports Server (NTRS)

    1963-01-01

    TEST CELLS SE-5 - SE-8 - SE-10 IN THE ENGINE RESEARCH BUILDING ERB AND 117 HIGH ENERGY FUELS LABORATORY HEFL - TRANSDUCER INSTRUMENTATION CONSOLE SE-10 - TEMPERATURE INSTRUMENTATION CONSOLE SE-10 - MODULE FUEL CELL EXPERIMENT SE-8 -

  9. TEST CELLS SE-5 - SE-8 - SE-10 IN THE ENGINE RESEARCH BUILDING ERB AND 117 HIGH ENERGY FUELS LABORAT

    NASA Technical Reports Server (NTRS)

    1963-01-01

    TEST CELLS SE-5 - SE-8 - SE-10 IN THE ENGINE RESEARCH BUILDING ERB AND 117 HIGH ENERGY FUELS LABORATORY HEFL - TRANSDUCER INSTRUMENTATION CONSOLE SE-10 - TEMPERATURE INSTRUMENTATION CONSOLE SE-10 - MODULE FUEL CELL EXPERIMENT SE-8

  10. TEST CELLS SE-5 - SE-8 - SE-10 IN THE ENGINE RESEARCH BUILDING ERB AND 117 HIGH ENERGY FUELS LABORAT

    NASA Technical Reports Server (NTRS)

    1963-01-01

    TEST CELLS SE-5 - SE-8 - SE-10 IN THE ENGINE RESEARCH BUILDING ERB AND 117 HIGH ENERGY FUELS LABORATORY HEFL - TRANSDUCER INSTRUMENTATION CONSOLE SE-10 - TEMPERATURE INSTRUMENTATION CONSOLE SE-10 - MODUEL FUEL CELL EXPERIMENT SE-8

  11. Intraband Spectroscopy of GaSe Nanoparticles and InSe/GaSe Nanoparticle Heterojunctions

    NASA Astrophysics Data System (ADS)

    Kelley, David F.; Tu, Haohua; Chen, Xiang-Bai

    The spectroscopic and dynamical characteristics of electron and hole intraband transitions in several sizes of GaSe nanoparticles have been studied using polarized femtosecond transient absorption spectroscopy. Assignments of the observed absorptions are made in terms of the known GaSe band structure and a model in which the electron and hole states are described by particle-in-a-cylinder states. The results indicate that the transient absorption spectrum is due to a size-independent, z-polarized hole intraband transition, and in the smaller particles, an x,y-polarized electron transition. In InSe/GaSe mixed aggregates, direct electron transfer from InSe to GaSe nanoparticles occurs upon photoexcitation of a charge transfer band. An exciton on GaSe nanoparticles can undergo diffusion and charge separation the an InSe/GaSe heterojunction.

  12. Study of the heterointerfaces InSe on GaSe and GaSe on InSe

    NASA Astrophysics Data System (ADS)

    Fargues, D.; Brahim-Otsmane, L.; Eddrief, M.; Sébenne, C.; Balkanski, M.

    1993-03-01

    InSe and GaSe thin films are grown on freshly cleaved (00.1) substrates of GaSe and InSe, respectively, by molecular beam epitaxy. They are studied in situ by X-ray photoelectron spectroscopy (XPS) and reflection high energy electron diffraction (RHEED). From the attenuation curves of the XPS substrate core level peaks, the quasi layer-by-layer growth is shown during the first stages of deposition in agreement with RHEED results. But both interfaces are not totally symmetrical. For InSe on GaSe(00.1), the sharpness of the interface is shown and the conditions of growth are well established. For GaSe on InSe(00.1), the sharpness of the interface can also be suggested although it is less clear; this is related to the growth conditions.

  13. IDD-BRASIL: Implementation and Progress

    NASA Astrophysics Data System (ADS)

    Chagas, G. O.; Almeida, W. G.; Yoksas, T.; Cutrim, E. M.; Garrana, D.

    2007-05-01

    In response to the academic meteorological community's demand for real-time weather data, and access to datasets not readily available, the Unidata Program of the University Corporation for Atmospheric Research (UCAR) developed the Internet Data Distribution, IDD system. With a modest beginning in the early 1990's, IDD has grown to become the leading Internet2 advanced-application by delivering over 20 terabytes of data per week to over 160 institutions in the US and around the world. Meteorological and related real-time data, model output, and a vast amount of experimental products are delivered at no cost to the Unidata participating institutions. In 2004, through a collaboration among three leading universities and research centers in Brazil, the Centro de Previsão de Tempo e Estudos Climáticos (CPTEC/INPE), the Universidade Federal do Rio de Janeiro (UFRJ), and the Universidade de São Paulo (USP), the Unidata IDD has expanded into Brazil creating a data sharing peer, the IDD-Brasil. Throughout a series of outreach initiatives, the IDD-Brasil is extending its reach, providing data to universities in Argentina, Chile, Africa and Portugal. By lowering the barrier between distant institutions, participants are now cooperating and sharing many datasets that were not generally available outside their organizations. Future plans include the deployment of a new data-relay node in cooperation with Universidade de Aveiro, Portugal in order to provide a local source of data for institutions in Portugal and Africa, and the distribution of products derived from the GOES-10 satellite, which covers mainly South America, through IDD in real-time. Jointly, the IDD and IDD-Brasil are fostering new collaborations among universities, WMO Regional Meteorological Training Centers, and national meteorological agencies, empowering the Atmospheric Sciences across several countries.

  14. Photophysics of GaSe/InSe nanoparticle heterojunctions.

    PubMed

    Chen, Xiang-Bai; Kelley, David F

    2006-12-21

    The photophysics of mixed aggregates of GaSe/InSe nanoparticles have been studied using static and time-resolved absorption and emission spectroscopies. The results indicate that the GaSe/InSe interfaces form heterojunctions and exhibit photoinduced direct charge transfer from the GaSe valence band to the InSe conduction band. This results in the electrons and holes being localized separately in these two types of nanoparticles. The energy diagram of the nanoparticle heterojunction can be constructed from the static spectra, known bulk band offsets, and quantum confinement effects. These considerations accurately predict the energy of the observed charge-transfer band. Photoexcitation also produces excitons in the aggregates, away from the heterojunctions. These excitons can undergo diffusion and quench upon reaching a heterojunction. Time-resolved fluorescence kinetics can be modeled to extract an exciton diffusion coefficient. A value of 2.0 nm2/ns is obtained, which is in good agreement with values obtained from previous fluorescence anisotropy decay measurements.

  15. Spin-polarized transport through ZnMnSe/ZnSe/ZnBeSe heterostructures

    NASA Astrophysics Data System (ADS)

    Ming, Y.; Gong, J.; Zhang, R. Q.

    2011-11-01

    Using the transfer matrix method and Airy function, the spin-dependent tunneling through the ZnMnSe/ZnSe/ZnBeSe structure was investigated theoretically. The electron tunneling determined by the applied bias, external magnetic field, and spin orientations exhibited some interesting and complex features. It was found that the magnetic field could suppress the spin-up current, but enhance the spin-down current. Furthermore the spin-flip of current could be realized by changing the applied bias slightly. Therefore, it can be believed that our structure could behave as a good spin-filter.

  16. Explicación de las disparidades raciales en la salud neonatal en Brasil*

    PubMed Central

    Nyarko, Kwame A.; López-Camelo, Jorge; Castilla, Eduardo E.; Wehby, George L.

    2015-01-01

    Objetivos. Buscamos cuantificar la manera en que los efectos socioeconómicos, demográficos, geográficos y de atención de salud explican las disparidades raciales en las tasas de bajo peso al nacer y prematuridad en Brasil. Métodos. Utilizamos una muestra de 8 949 niños nacidos entre 1995 y el 2009 en 15 ciudades y 7 provincias de Brasil. Nos centramos en las disparidades en la prevalencia de bajo peso al nacer (< 2 500 g) y prematuridad (< 37 semanas de gestación) en recién nacidos de ascendencia solo africana o mezclada con otras ascendencias y de ascendencia solo europea. Usamos un modelo de descomposición para cuantificar la contribución de los factores conceptualmente pertinentes a esas disparidades. Resultados. El modelo permitió explicar entre 45% y 94% de las disparidades en cuanto al bajo peso al nacer y entre 64% y 94% de las disparidades en cuanto a la prematuridad entre los grupos de ascendencia africana y de ascendencia europea. Las diferencias en el uso de atención prenatal y en la ubicación geográfica fueron los factores más importantes, seguidos por las diferencias socioeconómicas. El modelo permitió explicar la mayoría de las disparidades en los recién nacidos de ascendencia africana mezclada y parte de las disparidades en los de ascendencia solo africana. Conclusiones. En las políticas públicas para mejorar la salud infantil se deben abordar las diferencias en cuanto a la atención prenatal y la ubicación geográfica a fin de reducir las disparidades en materia de salud entre los recién nacidos de ascendencia africana y los de ascendencia europea en Brasil.

  17. Validation of NOViSE.

    PubMed

    Korzeniowski, Przemyslaw; Brown, Daniel C; Sodergren, Mikael H; Barrow, Alastair; Bello, Fernando

    2017-02-01

    The goal of this study was to establish face, content, and construct validity of NOViSE-the first force-feedback enabled virtual reality (VR) simulator for natural orifice transluminal endoscopic surgery (NOTES). Fourteen surgeons and surgical trainees performed 3 simulated hybrid transgastric cholecystectomies using a flexible endoscope on NOViSE. Four of them were classified as "NOTES experts" who had independently performed 10 or more simulated or human NOTES procedures. Seven participants were classified as "Novices" and 3 as "Gastroenterologists" with no or minimal NOTES experience. A standardized 5-point Likert-type scale questionnaire was administered to assess the face and content validity. NOViSE showed good overall face and content validity. In 14 out of 15 statements pertaining to face validity (graphical appearance, endoscope and tissue behavior, overall realism), ≥50% of responses were "agree" or "strongly agree." In terms of content validity, 85.7% of participants agreed or strongly agreed that NOViSE is a useful training tool for NOTES and 71.4% that they would recommend it to others. Construct validity was established by comparing a number of performance metrics such as task completion times, path lengths, applied forces, and so on. NOViSE demonstrated early signs of construct validity. Experts were faster and used a shorter endoscopic path length than novices in all but one task. The results indicate that NOViSE authentically recreates a transgastric hybrid cholecystectomy and sets promising foundations for the further development of a VR training curriculum for NOTES without compromising patient safety or requiring expensive animal facilities.

  18. Respostas religiosas à aids no Brasil: impressões de pesquisa.

    PubMed

    Seffner, Fernando; da Silva, Cristiane Gonçalves Meireles; Maksud, Ivia; Garcia, Jonathan; Rios, Luís Felipe; Natividade, Marcelo; Borges, Priscila Rodrigues; Parker, Richard; Terto, Veriano

    2008-01-01

    O texto encontra-se estruturado em quatro partes. Na primeira delas, apresentamos um conjunto de considerações e informações acerca da situação da aids no Brasil, das relações entre religião, sexualidade, aids e estado laico, bem como uma descrição mais clara do Projeto Respostas Religiosas ao HIV/Aids no Brasil, do qual este texto apresenta algumas impressões de pesquisa preliminares. A seguir, dedicamos um item a apresentação da Pastoral de DST/Aids, sua história, estrutura e objetivos. No item seguinte problematizamos diversas questões em particular no âmbito das relações Estado e Igreja, relações entre agentes de pastoral e hierarquia da Igreja, e questões ligadas mais diretamente à sexualidade e aids, todas referenciadas ao trabalho da Pastoral de DST/Aids. Ao final, apresentamos a bibliografia e fontes consultadas.

  19. Respostas religiosas à aids no Brasil: impressões de pesquisa1

    PubMed Central

    Seffner, Fernando; da Silva, Cristiane Gonçalves Meireles; Maksud, Ívia; Garcia, Jonathan; Rios, Luís Felipe; Natividade, Marcelo; Borges, Priscila Rodrigues; Parker, Richard; Terto, Veriano

    2009-01-01

    Resumo O texto encontra-se estruturado em quatro partes. Na primeira delas, apresentamos um conjunto de considerações e informações acerca da situação da aids no Brasil, das relações entre religião, sexualidade, aids e estado laico, bem como uma descrição mais clara do Projeto Respostas Religiosas ao HIV/Aids no Brasil, do qual este texto apresenta algumas impressões de pesquisa preliminares. A seguir, dedicamos um item a apresentação da Pastoral de DST/Aids, sua história, estrutura e objetivos. No item seguinte problematizamos diversas questões em particular no âmbito das relações Estado e Igreja, relações entre agentes de pastoral e hierarquia da Igreja, e questões ligadas mais diretamente à sexualidade e aids, todas referenciadas ao trabalho da Pastoral de DST/Aids. Ao final, apresentamos a bibliografia e fontes consultadas. PMID:20428503

  20. Bond dissociation energies of diatomic transition metal selenides: TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe

    NASA Astrophysics Data System (ADS)

    Sorensen, Jason J.; Persinger, Thomas D.; Sevy, Andrew; Franchina, Jordan A.; Johnson, Eric L.; Morse, Michael D.

    2016-12-01

    Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe. It is argued that the sharp onset of predissociation corresponds to the bond dissociation energy in each of these molecules due to their high density of states as the ground separated atom limit is approached. The bond dissociation energies obtained are D0(TiSe) = 3.998(6) eV, D0(ZrSe) = 4.902(3) eV, D0(HfSe) = 5.154(4) eV, D0(VSe) = 3.884(3) eV, D0(NbSe) = 4.834(3) eV, and D0(TaSe) = 4.705(3) eV. Using these dissociation energies, the enthalpies of formation were found to be Δf,0 KHo(TiSe(g)) = 320.6 ± 16.8 kJ mol-1, Δf,0 KHo(ZrSe(g)) = 371.1 ± 8.5 kJ mol-1, Δf,0 KHo(HfSe(g)) = 356.1 ± 6.5 kJ mol-1, Δf,0 KHo(VSe(g)) = 372.9 ± 8.1 kJ mol-1, Δf,0 KHo(NbSe(g)) = 498.9 ± 8.1 kJ mol-1, and Δf,0 KHo(TaSe(g) ) = 562.9 ± 1.5 kJ mol-1. Comparisons are made to previous work, when available. Also reported are calculated ground state electronic configurations and terms, dipole moments, vibrational frequencies, bond lengths, and bond dissociation energies for each molecule. A strong correlation of the measured bond dissociation energy with the radial expectation value, ⟨r⟩nd, for the metal atom is found.

  1. Validation of NOViSE

    PubMed Central

    Korzeniowski, Przemyslaw; Brown, Daniel C.; Sodergren, Mikael H.; Barrow, Alastair; Bello, Fernando

    2016-01-01

    The goal of this study was to establish face, content, and construct validity of NOViSE—the first force-feedback enabled virtual reality (VR) simulator for natural orifice transluminal endoscopic surgery (NOTES). Fourteen surgeons and surgical trainees performed 3 simulated hybrid transgastric cholecystectomies using a flexible endoscope on NOViSE. Four of them were classified as “NOTES experts” who had independently performed 10 or more simulated or human NOTES procedures. Seven participants were classified as “Novices” and 3 as “Gastroenterologists” with no or minimal NOTES experience. A standardized 5-point Likert-type scale questionnaire was administered to assess the face and content validity. NOViSE showed good overall face and content validity. In 14 out of 15 statements pertaining to face validity (graphical appearance, endoscope and tissue behavior, overall realism), ≥50% of responses were “agree” or “strongly agree.” In terms of content validity, 85.7% of participants agreed or strongly agreed that NOViSE is a useful training tool for NOTES and 71.4% that they would recommend it to others. Construct validity was established by comparing a number of performance metrics such as task completion times, path lengths, applied forces, and so on. NOViSE demonstrated early signs of construct validity. Experts were faster and used a shorter endoscopic path length than novices in all but one task. The results indicate that NOViSE authentically recreates a transgastric hybrid cholecystectomy and sets promising foundations for the further development of a VR training curriculum for NOTES without compromising patient safety or requiring expensive animal facilities. PMID:27671036

  2. Metabolism of 76Se-methylselenocysteine compared with that of 77Se-selenomethionine and 82Se-selenite.

    PubMed

    Suzuki, Kazuo T; Doi, Chiaki; Suzuki, Noriyuki

    2006-12-01

    Se-Methylated selenoamino acids, Se-methylselenocysteine (MeSeCys) and selenomethionine (SeMet), are chemically inert storage forms of selenium in selenium-accumulators, and a nutritional and supplemental source. The metabolic pathway for MeSeCys was precisely traced by referring to those for SeMet and selenite by applying a new tracer method involving multiple homo-elemental stable isotopes. Male Wistar rats were depleted of endogenous natural abundance selenium with a single (80)Se-enriched isotope, and then (76)Se-MeSeCys, (77)Se-SeMet and (82)Se-selenite were orally administered simultaneously at 25 microg Se/kg body weight each. Organs and body fluids were obtained at 3, 6, 9 and 12 h, and 1 and 2 days later, and subjected to speciation analysis. The main characteristics of the metabolism were as follows; MeSeCys was incorporated into selenoprotein P slightly more than or at a comparable level to that of SeMet but less than that of selenite. MeSeCys and SeMet but not selenite was taken up by organs in their intact forms. MeSeCys and SeMet were delivered specifically to the pancreas and present in a form bound to an identical or similar protein. Trimethylselenonium (TMSe) was only produced from MeSeCys, i.e., not from SeMet or selenite, in the kidneys. Both selenosugars A and B of MeSeCys, SeMet and selenite origin were detected in the liver but only selenosugar B in the kidneys. These results suggest that MeSeCys can be a similar or better selenium source than SeMet, and supplies methylselenol much more efficiently in organs than SeMet and selenite. TMSe was produced much efficiently from MeSeCys than from SeMet and selenite, suggesting a role of methylselenol through the beta-lyase reaction in the metabolism of Se-methylated selenoamino acids.

  3. Tracing cytotoxic effects of small organic Se species in human liver cells back to total cellular Se and Se metabolites.

    PubMed

    Marschall, T A; Kroepfl, N; Jensen, K B; Bornhorst, J; Meermann, B; Kuehnelt, D; Schwerdtle, T

    2017-03-22

    Small selenium (Se) species play a major role in the metabolism, excretion and dietary supply of the essential trace element selenium. Human cells provide a valuable tool for investigating currently unresolved issues on the cellular mechanisms of Se toxicity and metabolism. In this study, we developed two isotope dilution inductively coupled plasma tandem-mass spectrometry based methods and applied them to human hepatoma cells (HepG2) in order to quantitatively elucidate total cellular Se concentrations and cellular Se species transformations in relation to the cytotoxic effects of four small organic Se species. Species- and incubation time-dependent results were obtained: the two major urinary excretion metabolites trimethylselenonium (TMSe) and methyl-2-acetamido-2-deoxy-1-seleno-β-d-galactopyranoside (SeSugar 1) were taken up by the HepG2 cells in an unmodified manner and did not considerably contribute to the Se pool. In contrast, Se-methylselenocysteine (MeSeCys) and selenomethionine (SeMet) were taken up in higher amounts, they were largely incorporated by the cells (most likely into proteins) and metabolized to other small Se species. Two new metabolites of MeSeCys, namely γ-glutamyl-Se-methylselenocysteine and Se-methylselenoglutathione, were identified by means of HPLC-electrospray-ionization-Orbitrap-MS. They are certainly involved in the (de-)toxification modes of Se metabolism and require further investigation.

  4. Overview and prospects of Se phytoremediation approaches

    USDA-ARS?s Scientific Manuscript database

    Evidence is lacking on whether selenium (Se) is essential for vegetation growth, but plants can absorb, assimilate, and accumulate Se in leaves and roots. The capability of plants to take up substantial amount of Se is now being utilized to remove excess Se from contaminated soils. This process has ...

  5. Structural models of FeSe(x).

    PubMed

    Kurmaev, E Z; McLeod, J A; Skorikov, N A; Finkelstein, L D; Moewes, A; Korotin, M A; Izyumov, Yu A; Xie, Y L; Wu, G; Chen, X H

    2009-10-28

    Two different structural models for non-stoichiometric FeSe(x) are examined and compared with soft x-ray spectroscopy findings for FeSe(x) (x = 0.85, 0.50). A structural model of tetragonal FeSe with excess interstitial Fe gives better agreement with experiment than a structural model of tetragonal FeSe with Se vacancies. This interstitial Fe increases the number of 3d states at the Fermi level. We find evidence that large non-stoichiometric ratios of Fe:Se, such as that of FeSe(0.50), yield clusters of pure Fe in the crystal structure.

  6. 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.

  7. Electrical and photovoltaic properties of Cu-doped p-GaSe/n-InSe heterojunction

    NASA Astrophysics Data System (ADS)

    Shigetomi, S.; Ikari, T.

    2000-08-01

    GaSe(Cu)/InSe heterojunctions have been formed by bringing the cleavage surface of undoped n-InSe and Cu-doped p-GaSe into direct contact. Transport and phototransport properties are studied by the measurements of capacitance-voltage, current-voltage, and the spectral response of short-circuit current. Moreover, the efficiency parameters under illumination are estimated by using the open-circuit voltage and short-circuit current. These characteristics of GaSe(Cu)/InSe heterojunctions are compared with those of GaSe(Un)/InSe heterojunctions fabricated by undoped p-GaSe and n-InSe. The series resistance of GaSe(Cu)/InSe heterojunctions is found, the value of which is about 103 times lower than the corresponding value of GaSe(Un)/InSe heterojunctions. A short-circuit current density of 9.0 mA/cm2 and an open-circuit voltage of 0.42 V on GaSe(Cu)/InSe heterojunctions are obtained under illumination of 120 mW/cm2 of a halogen lamp. The short-circuit current of GaSe(Cu)/InSe heterojunctions is about one order of magnitude lager than that of GaSe(Un)/InSe heterojunctions. These experimental results indicate that the low-resistivity of Cu-doped GaSe is effective for the electrical and photovoltaic properties of GaSe/InSe heterojunctions.

  8. [Medical assessments and measurements in ELSA-Brasil].

    PubMed

    Mill, Jose Geraldo; Pinto, Karina; Griep, Rosane Härter; Goulart, Alessandra; Foppa, Murilo; Lotufo, Paulo A; Maestri, Marcelo K; Ribeiro, Antonio Luiz; Andreão, Rodrigo Varejão; Dantas, Eduardo Miranda; Oliveira, Ilka; Fuchs, Sandra C; Cunha, Roberto de Sá; Bensenor, Isabela M

    2013-06-01

    The article describes assessments and measurements performed in the Brazilian Longitudinal Study for Adult Health (ELSA-Brasil). Some assessments including anthropometric assessment, casual blood pressure measurement, and ankle-brachial index have an established clinical application while others including pulse wave velocity, heart rate variability, and carotid intima-media thickness have no established application and do not have reference values for healthy Brazilian population but may be important predictors of cardiovascular outcomes. Blood pressure measurement following postural change maneuver was included in the ELSA-Brasil because it has not been much tested in epidemiological studies. Innovative approaches were developed for assessing the ankle-brachial index using an automatic device instead of the mercury column to measure blood pressure and for assessing the anterior-posterior diameter of the right lobe of the liver by ultrasound for quantitative assessment of nonalcoholic fatty liver disease. All ELSA-Brasil subjects were younger (35 years or more) than those included in other cohorts studying subclinical atherosclerosis. The inclusion of younger individuals and a variety of assessments make the ELSA-Brasil a relevant epidemiology study nationwide and worldwide.

  9. Tendências de teses e dissertações sobre ensino de astronomia no Brasil

    NASA Astrophysics Data System (ADS)

    Bretones, P. S.; Megid Neto, J.

    2003-08-01

    Neste trabalho são apresentados os resultados de uma pesquisa do tipo estado da arte sobre teses e dissertações defendidas no Brasil e relativas ao ensino de Astronomia. Teve por objetivo identificar essa produção e conhecer as principais tendências da pesquisa nesse campo. O procedimento inicial consistiu de um levantamento bibliográfico junto ao Centro de Documentação em Ensino de Ciências (CEDOC) da Faculdade de Educação da UNICAMP e ao Banco de Teses da CAPES disponível na Internet. Foram localizadas 13 dissertações de mestrado e 3 teses de doutorado, as quais foram estudadas em função dos seguintes aspectos: instituição, ano de defesa, nível escolar abrangido no estudo, foco temático do estudo e gênero de trabalho acadêmico. Deste conjunto de pesquisas, 13 (81,3%) delas foram defendidas a partir da segunda metade dos anos 90, indicando uma preocupação mais recente com temas relativos ao ensino de Astronomia no conjunto da produção acadêmica em programas de pós-graduação no Brasil. Verificou-se que 43,7% dos trabalhos foram produzidas na USP e 18,8% na UNICAMP. Quanto ao nível escolar abrangido nos estudos, predominaram os estudos direcionados ao Ensino Fundamental de 5a a 8a séries (62,5%). No que diz respeito ao foco temático das pesquisas, as principais tendências voltaram-se: 56,3% para Conteúdo e Método; 43,8% para Concepções do Professor; 37,5% para Currículo e Programas; 37,5% para Recursos Didáticos. Quanto ao gênero de trabalho acadêmico, verificou-se que 43,8% são de Pesquisa Experimental e 31,3% de Pesquisa de Análise de Conteúdo. Estudos de revisão bibliográfica como este visam colaborar com a divulgação ampla da produção acadêmica em determinada área, traçando algumas de suas tendências. Ao mesmo tempo possibilita, a partir de investigações decorrentes, apontar as suas contribuições para o ensino e sinalizar com necessidades a serem supridas por futuras pesquisas.

  10. Heteroepitaxy of Layered Compound InSe and InSe/GaSe onto GaAs Substrates

    NASA Astrophysics Data System (ADS)

    Budiman, Maman; Yamada, Akira; Konagai, Makoto

    1998-07-01

    The van der Waals epitaxy of InSe films was performed on (111)GaAs surface at the growth temperature of 350°C. A spiral trigonal structure was observed on the surface of the InSe films. To improve crystal quality of the InSe films, their orientation control was investigated. The growth rate decreased rapidly as the growth temperature increased and no InSe films were obtained at growth temperatures higher than 480°C. At growth temperatures of 450°C and higher, a double-domain structure was observed, probably due to the coexistence of In4Se3 phase in the films. Therefore, the InSe film was directly grown on c-axis inclined GaSe, and it was revealed that InSe films were more easily grown on GaSe than on (001)GaAs surface, due to the same crystal structure. Furthermore, for fabrication of the quantum well structure, heteroepitaxial growth of GaSe/InSe/GaSe films on (001)GaAs substrate was investigated.

  11. 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

    2016-12-01

    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.

  12. Electron and hole dynamics in GaSe nanoparticles and GaSe-InSe nanoparticle heterojunctions.

    NASA Astrophysics Data System (ADS)

    Kelley, David F.; Tu, Haohua; Mogyorosi, Karoly; Chen, Xiang-Bai

    2006-08-01

    Femtosecond polarized transient absorption results are obtained for InSe and GaSe nanoparticles. The results indicate that the transient absorption spectrum of large GaSe particles is dominated by a size-independent, z-polarized hole intraband transition. The small particle spectra exhibit the same z-polarized hole transition and a much more intense x,y-polarized absorption that is assigned to a charge transfer transition from the conduction band to particle surface (edge) states. The intensity of this transition depends on the momentum state (Γ or M) of the electron, and Γ to M electron momentum relaxation results in a 15 ps absorption decay. These results are used to interpret analogous results obtained for mixed GaSe-InSe nanoparticle aggregates, also in the solution phase. The static absorption spectrum of the mixed aggregates exhibits a strong interparticle charge transfer absorption band at an energy slightly higher than the InSe bandgap. Photoexcitation of this band results in a polarized transient absorption spectrum and transient absorption kinetics characteristic of InSe valence band holes and GaSe conduction band electrons. This result indicates that with small GaSe particles, direct InSe to GaSe electron transfer occurs upon photoexcitation.

  13. 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.

  14. Estimation of Se(VI)/Se(IV) ratio in water by the ratio recorded in barite

    NASA Astrophysics Data System (ADS)

    Tokunaga, Kohei; Yokoyama, Yuka; Takahashi, Yoshio

    2013-11-01

    It is possible that the distribution behaviors of redox-sensitive elements such as selenium (Se) between authigenic minerals and water can provide information on the oxidation state of the element in the coexistent water during mineral deposition. Considering the similar chemical characteristics of Se(IV) and Se(VI) oxyanions, we propose that the Se(VI)/Se(IV) ratio in a particular precipitate, such as barite, may enable us to estimate the Se(VI)/Se(IV) ratio in the coexistent water. The coprecipitation experiments of Se with barite coupled with the determination of the oxidation state of Se both in the aqueous phase and in barite were conducted by Se K-edge X-ray absorption near-edge structure and high-performance liquid chromatography connected to inductively coupled plasma-mass spectrometry, respectively, to investigate the influence of the oxidation state of Se on its immobilization into barite at pH 4.0 and 8.0. The results showed that the Se(VI)/Se(IV) ratio in barite was correlated with the Se(VI)/Se(IV) ratio in water, which in turn can provide physicochemical and biogeochemical information related to the Se(VI)/Se(IV) ratio in water in the environment where barite precipitated.

  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. [ELSA-Brasil strategies for outcome identification, investigation and ascertainment].

    PubMed

    Barreto, Sandhi Maria; Ladeira, Roberto Marini; Bastos, Maria do Socorro Castelo Branco de Oliveira; Diniz, Maria de Fátima Haueisen Sander; Jesus, Elcimara Amorim de; Kelles, Silvana Márcia Bruschi; Luft, Vivian Cristine; Melo, Enirtes Caetano Prates; Oliveira, Elizabete Regina Araújo de

    2013-06-01

    The article describes the strategies adopted by the Brazilian Longitudinal Study for Adult Health (ELSA-Brasil) for participation and retention of subjects. This is key to ensure internal validity of longitudinal studies, and to identify, investigate, and ascertain outcomes of interest. The follow-up strategies include annual telephone contacts with new assessments and interviews every three to four years this approach aims to identify transient outcomes (reversible or not), permanent outcomes as well as complications related to the progression of major diseases--cardiovascular diseases and diabetes--to be studied. Telephone interviews are designed to monitor subjects' health status and to identify potential health-related events such as hospital admissions, medical visits or pre-selected medical procedures. Subjects are also encouraged to report to the ELSA-Brasil team any new health-related events. When a potential event is identified, a thorough investigation is carried out to collect relevant information about that event from medical records. All data are blinded and reviewed and analyzed by a medical expert committee. Incident outcome ascertainment follows well-established international criteria to ensure data comparability and avoid misclassification. In addition to these strategies, the occurrence of health-related events is also investigated through linkage of secondary databases, such as national mortality and hospital admission databases. Accurate identification of outcomes will allow to estimating their incidence in the study cohort and to investigate the effect of the exposures studied in the ELSA-Brasil at baseline and at its subsequent waves.

  17. Scanning tunneling microscopy of interface properties of Bi2Se3 on FeSe.

    PubMed

    Wang, Yilin; Jiang, Yeping; Chen, Mu; Li, Zhi; Song, Canli; Wang, Lili; He, Ke; Chen, Xi; Ma, Xucun; Xue, Qi-Kun

    2012-11-28

    We investigate the heteroepitaxial growth of Bi(2)Se(3) films on FeSe substrates by low-temperature scanning tunneling microscopy/spectroscopy. The growth of Bi(2)Se(3) on FeSe proceeds via van der Waals epitaxy with atomically flat morphology. A striped moiré pattern originating from the lattice mismatch between Bi(2)Se(3) and FeSe is observed. Tunneling spectra reveal the spatially inhomogeneous electronic structure of the Bi(2)Se(3) thin films, which can be ascribed to the charge transfer at the interface.

  18. Strain Compensation in Single ZnSe/CdSe Quantum Wells: Analytical Model and Experimental Evidence.

    PubMed

    Rieger, Torsten; Riedl, Thomas; Neumann, Elmar; Grützmacher, Detlev; Lindner, Jörg K N; Pawlis, Alexander

    2017-03-08

    The lattice mismatch between CdSe and ZnSe is known to limit the thickness of ZnSe/CdSe quantum wells on GaAs (001) substrates to about 2-3 monolayers. We demonstrate that this thickness can be enhanced significantly by using In0.12Ga0.88As pseudo substrates, which generate alternating tensile and compressive strains in the ZnSe/CdSe/ZnSe layers resulting in an efficient strain compensation. This method enables to design CdSe/ZnSe quantum wells with CdSe thicknesses ranging from 1 to 6 monolayers, covering the whole visible spectrum. The strain compensation effect is investigated by high resolution transmission electron microscopy and supported by molecular statics simulations. The model approach with the supporting experimental measurements is sufficiently general to be also applied to other highly mismatched material combinations for the design of advanced strained heterostructures.

  19. Oxidation of ultrathin GaSe

    DOE PAGES

    Thomas Edwin Beechem; McDonald, Anthony E.; Ohta, Taisuke; ...

    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.

  20. 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.

  1. 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.

  2. CuInSe2 phase formation during Cu2Se/In2Se3 interdiffusion reaction

    NASA Astrophysics Data System (ADS)

    Park, J. S.; Dong, Z.; Kim, Sungtae; Perepezko, J. H.

    2000-04-01

    Diffusion couples based upon Cu2Se/In2Se3 pairings have been examined in order to identify the kinetics of intermediate phase development and the associated phase equilibria. For the diffusion couples annealed at 550 °C for 1.5 h, all phases included in the Cu2Se-In2Se3 pseudobinary phase diagram section developed including the CuInSe2 (CIS) phase. Also, the In6Se7 phase formed for annealing times in excess of 1.5 h at 550 °C, indicating a modification of the diffusion pathway outside the pseudobinary phase diagram section. The growth of the CIS phase formed by reactive diffusion follows parabolic kinetics (x2=kt) with the k value of 3.3×10-8 cm2/s. CIS phase precipitates with a dendritic morphology are also produced within the Cu2Se side of the diffusion couple far from the initial interface, indicating that In is the fast component during interdiffusion. Based upon electron diffraction analysis and simulation of electron diffraction patterns, the dendritic shaped CIS precipitate structure was uniquely determined to be the metastable zinc blende type rather than the stable chalcopyrite-type structure. The structure and orientation relationship between the metastable CIS phase and the Cu2Se matrix satisfy the conditions established for the development of a solid state dendritic morphology.

  3. The fractionation of selenium isotopic exchange between Se (0) and Se (IV)

    NASA Astrophysics Data System (ADS)

    Can, T. D.; Jianming, Z.; Qin, H.; Xu, W.

    2016-12-01

    Selenium (Se) has six naturally stable isotopes, 74Se, 76Se, 77Se, 78Se, 80Se, and 82Se; with the relative abundance of 0.89%, 9.37%, 7.64%, 23.77%, 49.61%, and 8.73%, respectively. According to the previous work, the variations in δ82/76Se suggested that biogeochemical cycling in earth surface can lead to significant Se isotopic fractionation [1]. It was now believed that the abiotic and biotic reduction for Se (IV) and Se (VI) oxyanion was the main processes for Se isotope fractionation in natural systems. However, recently, the theoretical calculation by first-principles shows that equilibrium Se isotope fractionation between SeO32-and SeO42- can reach Δ82/76Se =13.3‰ at the 25 °, and have a trend of heavy Se isotopes enrichment as SeO42- > SeO3 2- > HSeO3- > SeO2 > selenoamino acids > alkylselenides > Se (0) or H2Se >HSe-[2]. So we take a new idea that the significant isotopic fractionation of Se may be caused by the combined role of Se reduction and isotopic exchange. In the past years, the study of the mechanism of Se isotope fractionation was mainly focused on the reduction of Se oxyanion, but for the fractionation by the isotope exchange between different Se speciation is poorly studied. Therefore, we take the isotope exchange between Se (0) and Se (IV) as an example, to compare the isotope fractionation of Se under the different reaction conditions. Experiment was conducted using 10 mg Se (0) particles mixed with 2 mg/L Se (IV) solution in different medium (MQ-water, 0.1mol/L and 1mol / L NaOH), and the time lasted for 96 days. The value of δ82/76Se in Se (IV) solution from the initial -1.20 ‰ to 2.22‰, 4.20‰ and 6.69‰, respectively. From this experiment we can know, with the increasement of alkalinity in medium solution, the rate for oxidation of Se (0) oxidized by the dissolved oxygen is gradually to increase, and can gain more free electrons for the reaction of the isotopic exchange between Se (0) and Se (IV), and make the rate of isotopic

  4. Cs(3)Sm(7)Se(12).

    PubMed

    Schneck, Christof; Elbe, Andreas; Schurz, Christian M; Schleid, Thomas

    2012-01-01

    The title compound, tricaesium hepta-samarium(III) dodeca-selenide, is setting a new starting point for realization of the channel structure of the Cs(3)M(7)Se(12) series, now with M = Sm, Gd-Er. This Cs(3)Y(7)Se(12)-type arrangement is structurally based on the Z-type sesquiselenides M(2)Se(3) adopting the Sc(2)S(3) structure. Thus, the structural set-up of Cs(3)Sm(7)Se(12) consists of edge- and vertex-connected [SmSe(6)](9-) octa-hedra [d(Ø)(Sm(3+) - Se(2-)) = 2.931 Å], forming a rock-salt-related network [Sm(7)Se(12)](3-) with channels along [001] that are apt to take up monovalent cations (here Cs(+)) with coordination numbers of 7 + 1 for one and of 6 for the second cation. The latter cation has a trigonal-prismatic coordination and shows half-occupancy, resulting in an impossible short distance [2.394 (4) Å] between symmetrically coupled Cs(+) cations of the same kind. While one Sm atom occupies Wyckoff position 2b with site symmetry ..2/m, all other 11 crystallographically different atoms (namely 2 × Cs, 3 × Sm and 6 × Se) are located at Wyckoff positions 4g with site symmetry ..m.

  5. 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

  6. One-step synthesis of PbSe-ZnSe composite thin film

    PubMed Central

    2011-01-01

    This study investigates the preparation of PbSe-ZnSe composite thin films by simultaneous hot-wall deposition (HWD) from multiple resources. The XRD result reveals that the solubility limit of Pb in ZnSe is quite narrow, less than 1 mol%, with obvious phase-separation in the composite thin films. A nanoscale elemental mapping of the film containing 5 mol% PbSe indicates that isolated PbSe nanocrystals are dispersed in the ZnSe matrix. The optical absorption edge of the composite thin films shifts toward the low-photon-energy region as the PbSe content increases. The use of a phase-separating PbSe-ZnSe system and HWD techniques enables simple production of the composite package. PMID:21711822

  7. Ultrastable Amorphous Sb2Se3 Film.

    PubMed

    Zhang, Kai; Li, Yang; Huang, Quan; Wang, Bihan; Zheng, Xuerong; Ren, Yang; Yang, Wenge

    2017-08-31

    Increasing the thermostability of amorphous materials has been a long journey to improve their properties. The metastable nature of chalcogenide glasses limits their practical applications as an amorphous semiconductor in photovoltaic performance. Here, we report the formation and physical properties of ultrastable amorphous Sb2Se3 with an enhanced thermal stability compared to ordinary amorphous Sb2Se3 (ΔTx= 17 K). By in situ high temperature-high energy synchrotron X-ray diffraction, the difference in structure relaxation between ordinary and ultrastable amorphous Sb2Se3 was manifested by local structure evolution. Ultrastable amorphous Sb2Se3 showed the smallest surface roughness and highest refractive index, the mechanism behind was further discussed in terms of fast molecular mobility and molecular orientation during vapor deposition. Formation of ultrastable amorphous Sb2Se3 demonstrated a promising avenue to obtain novel functional amorphous semiconductor with modulated structure and property.

  8. Properties and Bibliography of GaSe

    DTIC Science & Technology

    1994-02-01

    covered by (Nitsche 1961), (Boelsterli 1962), (Terhell 1972,1975), (van Egmond 1974) and (Wiedemeier 1992). Crystals grown by the Bridgman method have...8217 ± 10’ 9(•.=5.31gm) = 10010’ ± 20’ e(0(=10.6gm) = 12040’ ± 20’. Also for SHG of 10.61m, they measured d22(GaSe)/d 3l ( CdSe ) = 3 ± 0.6, taking d31( CdSe ...proustite) = 4.9 ± 0.7 which yields d22(GaSe) = 180 x 10-9 esu when taking d-(proustite) = 37 x 10-9 esu and d31 ( CdSe ) = 53 x 10-9 esu. Also, they summed YAG

  9. Glass formation and the third harmonic generation of Cu2Se-GeSe2-As2Se3 glasses

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Klymovych, O. S.; Myronchuk, G. L.; Zamuruyeva, O. V.; Zmiy, O. F.; Alahmed, Z. A.; Chyský, J.; Bila, Jiri; Kamarudin, H.

    2014-10-01

    We have performed the investigation of the nonlinear optical properties namely the third harmonic generation (THG) of the glass-formation region in the Cu2Se-GeSe2-As2Se3 system. The samples were synthesized by direct single-temperature method from high-purity elementary substances. We have found that the value of disorder parameter Δ depends on the composition of the glassy alloys. The measurements show that increasing the Cu2Se concentration leads to increased slope of the absorption edge, which may be explained by the decrease of the height of random potential relief for the electrons in the tails of the state density which border the band edges. A very sharp increase in the THG at low temperature was observed. Significant enhancement in THG was obtained with decreasing the energy gap, which agreed well with the nonlinear optical susceptibilities obtained from other glasses.

  10. Al/CdSe/GaSe/C resonant tunneling thin film transistors

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    An Al/CdSe/GaSe/C thin film transistor device was prepared by the physical vapor deposition technique at a vacuum pressure of 10-5 mbar. The x-ray diffraction measurements demonstrated the polycrystalline nature of the surface of the device. The dc current-voltage characteristics recorded for the Al/CdSe/C and Al/CdSe/GaSe/C channels displayed a resonant tunneling diode features during the forward and reverse voltage biasing, respectively. In addition, the switching current ratio of the Al/CdSe/C increased from 18.6 to 9.62×103 as a result of the GaSe deposition on the CdSe surface. Moreover, the alternating electrical signal analyses in the frequency range of 1.0 MHz to 1.8 GHz, showed some remarkable properties of negative resistance and negative capacitance spectra of the Al/CdSe/GaSe/C thin film transistors. Two distinct resonance-antiresonance phenomena in the resistance spectra and one in the capacitance spectra were observed at 0.53, 1.04 and 1.40 GHz for the Al/CdSe/C channel, respectively. The respective resonating peak positions of the resistance spectra shift to 0.38 and 0.95 GHz when GaSe is interfaced with CdSe. These features of the thin film transistors are promising for use in high quality microwave filtering circuits and also for use as ultrafast switches.

  11. Reaction kinetics of CuInSe2 thin films grown from bilayer InSe/CuSe precursors

    NASA Astrophysics Data System (ADS)

    Kim, S.; Kim, W. K.; Kaczynski, R. M.; Acher, R. D.; Yoon, S.; Anderson, T. J.; Crisalle, O. D.; Payzant, E. A.; Li, S. S.

    2005-03-01

    The reaction kinetics for the formation of CuInSe2 thin films from a stacked bilayer precursor consisting of InSe and CuSe was studied by means of in situ high-temperature x-ray diffraction. In particular, the isothermal phase evolution of the glass/InSe/CuSe precursor was observed at different temperatures. The pathway produces a CuInSe2 diffusion barrier layer that also functions as a nucleation barrier. Hence, amorphous and crystalline phases simultaneously grow during isothermal processing. The shape of the time-resolved fractional reaction curve exhibits a deceleratory behavior, consistent with the presence of a diffusion-controlled reaction mechanism. Analyses based on Avrami and parabolic-rate laws were conducted. The Avrami exponent for each isothermal reaction is in the range 0.5-0.8, which indicates that the growth reaction is dominantly one-dimensional diffusion controlled. The estimated apparent activation energy for this reaction is 66.0 kJ/mol. The results based on the parabolic rate model are consistent with the Avrami analysis, yielding a similar apparent activation energy value, and thus supporting the conclusion that the process is one-dimensional diffusion controlled.

  12. Lattice dynamics of a simple GaSe-InSe superlattice

    NASA Astrophysics Data System (ADS)

    Schwarcz, R.; Kanehisa, M. A.

    1994-11-01

    A simple linear chain model is used to calculate the phonon dispersion curves for a superlattice composed of one layer of GaSe and one layer of InSe alternatively stacked along the c-axis. The resultant acoustic modes are essentially averages of the two constituents. Most optical modes are found to be confined in either GaSe layers of InSe layers. However, some low energy-optical modes have contributions from the two constituents.

  13. Nanoindentation of GaSe thin films

    NASA Astrophysics Data System (ADS)

    Jian, Sheng-Rui; Ku, Shin-An; Luo, Chih-Wei; Juang, Jenh-Yih

    2012-07-01

    The structural and nanomechanical properties of GaSe thin films were investigated by means of X-ray diffraction (XRD) and nanoindentation techniques. The GaSe thin films were deposited on Si(111) substrates by pulsed laser deposition. XRD patterns reveal only the pure (000 l)-oriented reflections originating from the hexagonal GaSe phase and no trace of any impurity or additional phases. Nanoindentation results exhibit discontinuities (so-called multiple `pop-in' events) in the loading segments of the load-displacement curves, and the continuous stiffness measurements indicate that the hardness and Young's modulus of the hexagonal GaSe films are 1.8 ± 0.2 and 65.8 ± 5.6 GPa, respectively.

  14. Thermal transport in monolayer InSe

    NASA Astrophysics Data System (ADS)

    Nissimagoudar, Arun S.; Ma, Jinlong; Chen, Yani; Li, Wu

    2017-08-01

    Two-dimensional InSe, a recently synthesized semiconductor having a moderate band gap, has gained attention due to its ultra high mobility and high photo-responsivity. In this work, we calculate the lattice thermal conductivity (κ) of monolayer InSe by solving the phonon Boltzmann transport equation (BTE) with first-principles calculated inter atomic force constants. κ of monolayer InSe is isotropic and found to be around 27.6 W m K-1 at room temperature along the in-plane direction. The size dependence of κ shows the size effect can persist up to 20 μm. Further, κ can be reduced to half by tuning the sample size to 300 nm. This low value suggests that κ might be a limiting factor for emerging nanoelectronic applications of monolayer InSe.

  15. Nanoindentation of GaSe thin films

    PubMed Central

    2012-01-01

    The structural and nanomechanical properties of GaSe thin films were investigated by means of X-ray diffraction (XRD) and nanoindentation techniques. The GaSe thin films were deposited on Si(111) substrates by pulsed laser deposition. XRD patterns reveal only the pure (000 l)-oriented reflections originating from the hexagonal GaSe phase and no trace of any impurity or additional phases. Nanoindentation results exhibit discontinuities (so-called multiple ‘pop-in’ events) in the loading segments of the load–displacement curves, and the continuous stiffness measurements indicate that the hardness and Young’s modulus of the hexagonal GaSe films are 1.8 ± 0.2 and 65.8 ± 5.6 GPa, respectively. PMID:22804961

  16. Lustre filesystem for CMS storage element (SE)

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Kim, B.; Avery, P.; Fu, Y.; Bourilkov, D.; Taylor, C.; Prescott, C.; Rodriguez, J.

    2011-12-01

    This paper presents our effort to integrate the Lustre filesystem with BeStMan, GridFTP and Ganglia to make it a fully functional WLCG SE (Storage Element). We first describe the configuration of our Lustre filesystem at the University of Florida and our integration process. We then present benchmark performance figures and IO rates from the CMS analysis jobs and the WAN data transfer performance that are conducted on the Lustre SE.

  17. Dynamics of vitreous Ag-Ge-Se

    NASA Astrophysics Data System (ADS)

    Dejus, R. J.; Lepoire, D. J.; Susman, S.; Volin, K. J.; Price, D. L.

    1991-12-01

    The dynamic scattering function S(Q,E) for vitreous g-Ag4Ge3Se9 at T=15 K has been measured by time-of-flight inelastic neutron scattering using an incident energy of ~60 meV. The neutron measurements have been complemented by room-temperature Raman-scattering measurements. The data are presented and discussed in terms of the elastic structure factor Sel(Q), the total structure factor S(Q), the neutron-weighted generalized one-phonon vibrational density of states (GVDOS), and the Q dependence of the dynamic structure factor S(Q,E) at selected energy excitations. Comparisons are made with experimental results for pure GeSe2 glass, and with calculations based on the method of normal-mode analysis to interpret the data. The introduction of Ag into the Ge-Se glassy network has a profound effect on the vibrational spectrum and the intermediate-range order. The GeSe4/2 tetrahedron, however, generally accepted as the local structural element of pure GeSe2 glass, remains a valid structural component also in the heavily Ag-doped glass. We find that the so-called companion line in the Raman spectrum for g-GeSe2 disappears upon doping with Ag, indicating a change of the intermediate-range order. Moreover, there is a large increase in the population of vibrational modes below ~200 cm-1 in both the GVDOS and the Raman spectrum. These modes can be associated with vibrational modes of Ag atoms interacting with three Se in a nearly planar pyramidal arrangement. We derive 30 kdyn/cm for the Ag-Se stretching constant.

  18. The system SnTe-InSe

    SciTech Connect

    Gurshumov, A.P.; Alidzhanov, M.A.; Aliev, A.S.; Gadzhiev, T.G.; Mamedov, N.A.

    1986-03-01

    This paper discusses the nature of the interaction and physicochemical properties of the alloys of the system SnTe-InSe. The DTA was performed on an NTR-74 pyrometer, XPA on a Dron-2.0 diffractometer and MSA on an MIM-7 metallographic microscope. The microhardness of the samples was determined on a PMT-3 microhardness tester. The congruently melting compound SnInTeSe and solid solutions based on the starting components are formed in the system.

  19. Compression of klockmannite, CuSe

    NASA Astrophysics Data System (ADS)

    Peiris, Suhithi M.; Pearson, Tania T.; Heinz, Dion L.

    1998-07-01

    Copper selenide (CuSe) was compressed in a diamond anvil cell at room temperature up to a pressure of 52 GPa and studied using energy dispersive x-ray diffraction and Raman spectroscopy. CuSe is nearly isostructural with copper sulfide (CuS), and a previous study indicates that copper sulfide undergoes reversible pressure-induced amorphization at 18 GPa. The intensity of the x-ray diffraction peaks for CuSe decrease slowly, however, they never completely disappear up to a pressure of 52 GPa. The third-order Birch-Murnaghan equation of state fit to the data yields K0=96.9±5.3 GPa and K0'=4.1±0.5. Vinet's universal equation of state yields essentially identical parameters. Raman spectroscopy demonstrates that upon compression, the S-S bond in CuS compresses differently than the Se-Se bond in CuSe, possibly accounting for the different high pressure behavior of these two very similar compounds.

  20. 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.

  1. 77Se solid-state NMR of As2Se3, As4Se4 and As4Se3 crystals: a combined experimental and computational study.

    PubMed

    Sykina, Kateryna; Yang, Guang; Roiland, Claire; Le Pollès, Laurent; Le Fur, Eric; Pickard, Chris J; Bureau, Bruno; Furet, Eric

    2013-05-07

    (77)Se NMR parameters for three prototypical crystalline compounds (As2Se3, As4Se4 and As4Se3) have been determined from solid-state NMR spectra in the framework of an investigation concerning AsxSe(1-x) glass structure understanding. Density functional NMR calculations using the gauge including projector augmented wave methodology have been performed on X-ray and optimized crystal structures for a set of selenium-based crystals. These theoretical results have been combined with the experimental data in order to achieve a precise assignment of the spectral lines. This work and the high sensitivity of solid-state NMR to local order show that the structure of As4Se3 should be reinvestigated using state-of-the-art diffraction techniques. Calculations performed on several molecules derived from the crystal structures have demonstrated the limited effect of interlayer or intermolecular interactions on the isotropic chemical shifts. These interactions are therefore not responsible for the unexpected large chemical shift difference observed between these three systems that could mostly be attributed to the presence of short rings.

  2. Sb2Se3 under pressure

    PubMed Central

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

    2013-01-01

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

  3. Photoinduced direct electron transfer from InSe to GaSe semiconductor nanoparticles.

    PubMed

    Tu, Haohua; Kelley, David F

    2006-01-01

    Direct electron transfer from InSe nanoparticles to GaSe nanoparticles in mixed solution-phase aggregates has been found to occur upon photoexcitation. Mixed aggregates exhibit a strong charge-transfer absorption band at an energy slightly higher than the InSe band gap. Photoexcitation of this band results in a polarized transient absorption spectrum and transient absorption kinetics characteristic of InSe valence-band holes and GaSe conduction-band electrons. The kinetics indicate that charge separation persists for at least several hundred picoseconds.

  4. 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.

  5. Structural elucidation and antioxidant activity a novel Se-polysaccharide from Se-enriched Grifola frondosa.

    PubMed

    Li, Qian; Wang, Wei; Zhu, Yun; Chen, Yao; Zhang, Weijie; Yu, Ping; Mao, Guanghua; Zhao, Ting; Feng, Weiwei; Yang, Liuqing; Wu, Xiangyang

    2017-04-01

    Se-GFP-22, a heteropolysaccharide, with a weight-average Mw of 4.13×10(6)Da, was purified from the crude Se-polysaccharide (Se-GFP) isolated from fruit bodies of Se-enriched Grifola frondosa. Selenium was accumulated efficiently in Grifola frondosa during cultivation with Na2SeO3. The structure was investigated through FT-IR, GC, GC-MS, NMR, HPSEC-MALL-RI, particle size, Conge-red test, CD, AFM and SEM. Se-GFP-22 was deduced as a backbone chain of 1,4-α-d-Glcp units with a branched point at C6 of both 1,3,6-β-d-Manp and 1,4,6-α-d-Galp units. A typical absorption for selenium ester was existed in Se-GFP-22. Se-GFP-22 adopted as a spherical conformation with random coils. A novel Se-polysaccharide of different monosaccharide constituents, molecular weight, linkage types and high content of selenium has been isolated from G. frondosa. The antioxidant effect of Se-GFP-22 was more potent than that of G. frondosa polysaccharide (GFP-22), which may be influenced by the co-effect of polysaccharide and Se, molecular weight, degree of branching and configuration. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Structural Characterization Of CdSe and ZnSe Nanostructures

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, B.; Kalita, P. K.; Datta, P.

    2010-10-01

    Chemically bath deposited CdSe and ZnSe powder possesses mixed type structures whereas it is hexagonal wurtzite type in thin film form. SEM images of CdSe symmetrically exhibit the growth of spherical, rod and the rose(flower) type microstructures. ZnSe shows fine grain structures. The growth of microstructures in these selenides according to the growth direction along c-axis of hexagonal wurtzite crystal. Photoluminescence shows strong blue luminescence at 414 and 437 nm in CdSe nanoparticles. ZnSe shows strong PL at 650 nm that is attributed to the strong d-native traps. The blue shifted band gap luminescence at 392 nm shows the quantum confinement in ZnSe nanoparticles.

  7. {sup 80}Se({gamma},n){sup 79}Se cross section and s-process branching at {sup 79}Se

    SciTech Connect

    Makinaga, A.; Utsunomiya, H.; Kaihori, T.; Yamagata, T.; Akimune, H.; Goriely, S.; Toyokawa, H.; Matsumoto, T.; Harano, H.; Harada, H.; Goko, S.; Kitatani, F.; Hara, K. Y.; Hohara, S.; Lui, Y.-W.

    2008-05-21

    Photoneutron cross sections were measured for {sup 80}Se near the neutron separation energy with laser Compton-backscattered {gamma}-ray beams at AIST. Neutron capture rates are evaluated for {sup 79}Se with the photoreaction data as experimental constraints on the El {gamma}-strength function, a key parameter in the Hauser-Feshbach statistical model calculation. Solving the set of differential equations under a single neutron exposure, we analyzed the solar abundance ratio of the weak components of {sup 80}Kr and {sup 82}Kr in terms of the s-process branching at {sup 79}Se. We discuss the region of temperature and neutron density allowed for the weak s-process nucleosynthesis.

  8. Substitutional doping of ZnSe films

    NASA Astrophysics Data System (ADS)

    Ren, J.; Bowers, K. A.; Hwang, S.; Cook, J. W.; Schetzina, J. F.

    1991-05-01

    Molecular beam epitaxy has been successfully employed to grow n-type ZnSe:Cl epilayers on (100) GaAs substrates at 275°C. The ZnSe:Cl epilayers are highly conducting and exhibit bright blue-violet edge luminescence at room temperature. A Hall mobility of 2480 cm 2/V⋯s at 40 K was measured for an n-type ZnSe:Cl film doped to a level of ˜3×10 17 cm -3 and for which a compensation ratio NA/ ND ˜ 4% was calculated. Carrier concentrations as large as 7×10 18 cm -3 were obtained by increasing the temperature of the MBE oven containing the Cl dopant. p-Type ZnSe films were prepared using Li as a substitutional dopant. The ZnSe:Li films exhibit photoluminescence spectra at 4 K dominated by an acceptor-bound exciton peak at 2.791 eV, providing clear evidence of p-type doping.

  9. Maternal selenium (Se) nutrition affects both milk Se and lipid patterns

    SciTech Connect

    Dotson, K.D.; Picciano, M.F.; Perrel, J.P.; Perkins, E.G. Univ. of Illinois, Urbana )

    1991-03-15

    In this study relationships between patterns of Se and lipid secretion in milk of women on self-selected diets were assessed. Milk samples were collected from 10 women at 4, 6 and 8 wks postpartum and blood samples at 4 to 8 wks. Milk samples were extracted and analyzed for tiacylglycerols and fatty acids. Activity of glutathione peroxidase (GSH-Px) and contents of Se in milk, plasma and erythrocytes were also measured. Two groups were found: one displaying an increase in plasma Se and the other, a decrease from 4 to 8 wks. Milk Se significantly decreased only in women whose plasma Se also decreased. Milk Se was negatively correlated with myristic and stearic acids in women whose plasma Se increased and with arachidonic, eicosapentaenoic and docosahexaenoic acids in women whose plasma Se decreased. Results of this study show that maternal Se nutrition relates not only to the quantity of Se secreted in milk but also to the quantities of individual fatty acids.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  11. 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.

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

    PubMed

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

    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.

  13. Superparamagnetism of Cu2Se nanoparticles.

    PubMed

    Kim, Soo-Whan; Lee, Kyu Joon; Jung, Myung-Hwa; Li, Yan; Seo, Won Seek

    2012-07-01

    Cu2Se nanoparticles were synthesized using the standard Schlenk line and glove box techniques, with the hot-injection method. The X-ray diffraction (XRD) analysis showed that the initial nanoparticles were formed in a stoichiometric Cu2Se phase with a cubic structure. When the nanoparticles are exposed to air, the diffraction peaks shift to higher angles. This suggests that the nanoparticles are changed to a nonstoichiometric Cu2-deltaSe phase with copper vacancies. The mean size of the nanoparticles was about 7 nm. The magnetic results show that the initial nanoparticles were diamagnetic, and after 1-week air exposure, they became paramagnetic. This dramatic change from diamagnetic to paramagnetic can be explained by the oxidation of Cu+ into Cu2+ at the nanoparticle surface. In addition, the superparamagnetic properties were observed to have a blocking temperature of 150 K. The coercive field decreased as the temperature approached the blocking temperature, and eventually vanished above the blocking temperature.

  14. 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).

  15. Growth and structural characterizations of GaSe and GaSe:Cd single crystals

    NASA Astrophysics Data System (ADS)

    Ashkhasi, Afsoun; Gürbulak, Bekir; Şata, Mehmet; Turgut, Güven; Duman, Songül

    2017-02-01

    GaSe and GaSe:Cd single crystals used in this research were grown by using the Bridgman/Stockbarger method. All of the samples were freshly and gently cleaved with a razor blade from the grown ingots and no further polishing and cleaning treatments were required because of the natural mirror-like cleavage faces. The Samples were cleaved along the cleavage planes (001). The structure and lattice parameters of the undoped GaSe and GaSe:Cd semiconductors have been analyzed using a X-ray diffractometer (XRD), Scanning electron microscopy (SEM) and energy dispersive X-rays (EDX) techniques. It is found that GaSe and GaSe:Cd crystals have hexagonal structure, quite close 2θ peak values. XRD measurements indicate that there is an increase in peak intensities at specific annealing temperatures (500°C). Cd doping causes a significant decrease in the XRD peak intensity.

  16. Microstructure of Cu(In,Ga)Se2 Films Deposited in Low Se Vapor Pressure

    NASA Astrophysics Data System (ADS)

    Nishiwaki, Shiro; Kohara, Naoki; Negami, Takayuki; Miyake, Hideo; Wada, Takahiro

    1999-05-01

    The microstructure of Cu(In,Ga)Se2 (CIGS) films deposited under low Se flux was studied using scanning electron microscopy, scanning Auger electron spectroscopy and high resolution and analytical electron microscopy. CIGS films were deposited on Mo coated soda-lime glass substrate using the “3-stage” process in which the Se flux used during the third stage was restricted to a forth of standard value. In the as-grown CIGS films, voids were observed along the grain boundaries and a Cu2Se phase was identified at the surface and the grain boundaries. The voids and Cu2Se layer were produced by vaporization of an In Se compound from the films during the third stage of deposition. A reaction model on the CIGS grain surface is proposed based on the microstructure observations.

  17. {InSe}/{GaSe} heterointerfaces prepared by Van der Waals epitaxy

    NASA Astrophysics Data System (ADS)

    Lang, O.; Klein, A.; Schlaf, R.; Löher, T.; Pettenkofer, C.; Jaegermann, W.; Chevy, A.

    1995-01-01

    Epitaxial films of layered substrates can be prepared onto layered substrates even for large lattice mismatch, when the growth is attempted with the Van der Waals surfaces opposing each other (Van der Waals epitaxy). Thin epitaxial InSe(GaSe) films are prepared onto ultrahigh vacuum (UHV) cleaved GaSe(InSe) Van der Waals (0001) surfaces. The films and the heterointerface are characterized by photoelectron spectroscopy, electron diffraction and scanning tunneling microscopy (STM). High quality and stoichiometric films are obtained by direct InSe(GaSe) evaporation from a Knudsen cell at sample temperatures between 520 and 620 K. Despite a 6% lattice mismatch the deposited films are oriented with their c- and α-axis to the hexagonal substrate. The growth mostly follows the Frank-Van der Merwe mode. This rather ideal growth behaviour is related to the specific properties of the Van der Waals plane which contains no dangling bonds.

  18. Current transport characteristics of pSe-nMoSe2 heterojunction diode

    NASA Astrophysics Data System (ADS)

    Sumesh, C. K.; Patel, K. D.; Pathak, V. M.; Srivastava, R.

    2010-12-01

    The characteristics of heterojunction diode pSe-nMoSe2 fabricated from thermally evaporated p-Se films on n-type Molybdenum diselenide (MoSe2) grown by direct vapour transport (DVT) technique have been examined by using current-voltage measurements. To investigate the dark current transport mechanism in pSe-nMoSe2 heterojunctions the current-voltage characteristics were measured in the temperature range 100-300 K. The prepared diode shows a rectification ratio of the order of 103 within the range -2 to 2 V. A multi-step tunnelling model was used to analyze the I-V-T characteristics of the prepared device. The activation energy determined from the saturation current was about 1.16 eV.

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

    PubMed

    Yang, Ping

    2014-04-01

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

  20. High voltage ZnSe/CuInSe[sub 2] solar cells

    SciTech Connect

    Olsen, L.C.; Addis, F.W. )

    1994-06-30

    This paper describes investigations of CIS solar cells based on ZnSe window layers deposited by MOCVD. Investigations of ZnSe/CIS solar cells are being carried out to determine if ZnSe is a viable alternative to CdS as a window material. MOCVD growth of ZnSe is accomplished in a SPIRE 500XT reactor and conductive n-type ZnSe is grown by using iodine as a dopant. ZnSe films have been grown on CIS substrates at 200 [degree]C to 250 [degree]C. ZnO is also being deposited by MOCVD by reacting tetrahydrofuran (THF) with a zinc adduct. ZnSe/CIS heterojunctions have been studied by growing n-ZnSe films onto 2 cm [times] 2 cm CIS substrates diced from materials supplied by Siemens. Test cells are fabricated by depositing thin, transparent Al contacts 2.8 mm in diameter on top of the ZnSe to serve as contacts. These test devices typically exhibit open circuit voltages [gt]500 mV and estimated active area efficiencies [gt]13%. Efforts to deposit ZnO onto ZnSe/CIS structures for top contact layers have usually resulted in photocurrent suppression, apparently due to interaction of the ZnO deposition process with the ZnSe layer. One approach used for cell fabrication involves the use of a protective layer between ZnO and ZnSe. A cell with a total area efficiency of 9.3% and a Voc of 509 mV has been fabricated.

  1. Tendências De Teses e Dissertações Sobre Educação em Astronomia No Brasil

    NASA Astrophysics Data System (ADS)

    Bretones, Paulo Sergio; Megid Neto, Jorge

    2005-07-01

    Apresentam-se os resultados de uma pesquisa do tipo estado da arte sobre teses e dissertações defendidas no Brasil e relativas ao ensino de Astronomia, com objetivo de identificar essa produção e conhecer as principais tendências da pesquisa nesse campo. Foram localizadas 13 dissertações de mestrado e 3 teses de doutorado, as quais foram estudadas em função dos seguintes aspectos: isntituição, ano de defesa, nível escolar abrangido no estudo, foco temático do estudo e gênero de trabalho acadêmico. Pretende-se assim colaborar com a divulgação ampla da produção acadêmica na área. Ao mesmo tempo o estudo possibilita, a partir de investigações decorrentes, apontar as contribuições dessa produção para o ensino e sinalizar com necessidades a serem supridas por futuras pesquisas.

  2. 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.

  3. Inverse-photoemission spectroscopy of GaSe and InSe

    NASA Astrophysics Data System (ADS)

    Sporken, R.; Hafsi, R.; Coletti, F.; Debever, J. M.; Thiry, P. A.; Chevy, A.

    1994-04-01

    The lamellar semiconductors GaSe and InSe have been studied with k-resolved inverse-photoemission spectroscopy along two major symmetry directions (Γ¯ K¯ and Γ¯ M¯) of the surface Brillouin zone. Three bands with well-resolved features are observed from which the dispersion of the conduction bands can be determined with good precision. The minimum of the conduction band is found at M¯ in GaSe and at Γ¯ in InSe. These results are compared with theoretical studies using pseudopotential and tight-binding calculations.

  4. Optical studies of pure Te90Se10 and Se90Te10 chalcogenide

    NASA Astrophysics Data System (ADS)

    Verma, Arvind Kumar; Kumar, Nishant; Srivastava, Anchal; Shukla, R. K.

    2016-05-01

    In this paper Te90Se10 and Se90Te10 Chalcogenide glasses are prepared by melt quenching method at 1000 °C for 8 and half hours at the pressure of 10-2 Torr. Absorbance spectra are recorded in the spectral range of 200-1200 nm of pure glassy SeTe in normal wavelength scanning mode. Shift in Absorption for Se90Te10 to Te90Se10 is 239 to 258 nm.Optical constants such as extinction coefficient (k), band gap (Eg) are calculated by JASCO, Model-V670; UV/VIS/NIR spectrophotometer. Optical band gap for S1 (Te90Se10) and for S2 (Se90Te10) are 1.03eV, 2.60eV respectively. Luminescence spectra recorded by (LS 55) Perkin-Elmer at excitation wavelength with 300 to 330 nm. Luminescence Intensity of Se90Te10 (S2) is more than Te90Se10 (S1).

  5. Atomic scale microstructure and properties of Se-deficient two-dimensional MoSe2.

    PubMed

    Lehtinen, Ossi; Komsa, Hannu-Pekka; Pulkin, Artem; Whitwick, Michael Brian; Chen, Ming-Wei; Lehnert, Tibor; Mohn, Michael J; Yazyev, Oleg V; Kis, Andras; Kaiser, Ute; Krasheninnikov, Arkady V

    2015-03-24

    We study the atomic scale microstructure of nonstoichiometric two-dimensional (2D) transition metal dichalcogenide MoSe2-x by employing aberration-corrected high-resolution transmission electron microscopy. We show that a Se-deficit in single layers of MoSe2 grown by molecular beam epitaxy gives rise to a dense network of mirror-twin-boundaries (MTBs) decorating the 2D-grains. With the use of density functional theory calculations, we further demonstrate that MTBs are thermodynamically stable structures in Se-deficient sheets. These line defects host spatially localized states with energies close to the valence band minimum, thus giving rise to enhanced conductance along straight MTBs. However, electronic transport calculations show that the transmission of hole charge carriers across MTBs is strongly suppressed due to band bending effects. We further observe formation of MTBs during in situ removal of Se atoms by the electron beam of the microscope, thus confirming that MTBs appear due to Se-deficit, and not coalescence of individual grains during growth. At a very high local Se-deficit, the 2D sheet becomes unstable and transforms to a nanowire. Our results on Se-deficient MoSe2 suggest routes toward engineering the properties of 2D transition metal dichalcogenides by deviations from the stoichiometric composition.

  6. 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…

  7. 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.

  8. 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…

  9. VerSeDa: vertebrate secretome database

    PubMed Central

    Cortazar, Ana R.; Oguiza, José A.

    2017-01-01

    Based on the current tools, de novo secretome (full set of proteins secreted by an organism) prediction is a time consuming bioinformatic task that requires a multifactorial analysis in order to obtain reliable in silico predictions. Hence, to accelerate this process and offer researchers a reliable repository where secretome information can be obtained for vertebrates and model organisms, we have developed VerSeDa (Vertebrate Secretome Database). This freely available database stores information about proteins that are predicted to be secreted through the classical and non-classical mechanisms, for the wide range of vertebrate species deposited at the NCBI, UCSC and ENSEMBL sites. To our knowledge, VerSeDa is the only state-of-the-art database designed to store secretome data from multiple vertebrate genomes, thus, saving an important amount of time spent in the prediction of protein features that can be retrieved from this repository directly. Database URL: VerSeDa is freely available at http://genomics.cicbiogune.es/VerSeDa/index.php PMID:28365718

  10. VerSeDa: vertebrate secretome database.

    PubMed

    Cortazar, Ana R; Oguiza, José A; Aransay, Ana M; Lavín, José L

    2017-01-01

    Based on the current tools, de novo secretome (full set of proteins secreted by an organism) prediction is a time consuming bioinformatic task that requires a multifactorial analysis in order to obtain reliable in silico predictions. Hence, to accelerate this process and offer researchers a reliable repository where secretome information can be obtained for vertebrates and model organisms, we have developed VerSeDa (Vertebrate Secretome Database). This freely available database stores information about proteins that are predicted to be secreted through the classical and non-classical mechanisms, for the wide range of vertebrate species deposited at the NCBI, UCSC and ENSEMBL sites. To our knowledge, VerSeDa is the only state-of-the-art database designed to store secretome data from multiple vertebrate genomes, thus, saving an important amount of time spent in the prediction of protein features that can be retrieved from this repository directly. VerSeDa is freely available at http://genomics.cicbiogune.es/VerSeDa/index.php.

  11. Preparing CAM-SE for Multi-Tracer Applications: CAM-SE-Cslam

    NASA Astrophysics Data System (ADS)

    Lauritzen, P. H.; Taylor, M.; Goldhaber, S.

    2014-12-01

    The NCAR-DOE spectral element (SE) dynamical core comes from the HOMME (High-Order Modeling Environment; Dennis et al., 2012) and it is available in CAM. The CAM-SE dynamical core is designed with intrinsic mimetic properties guaranteeing total energy conservation (to time-truncation errors) and mass-conservation, and has demonstrated excellent scalability on massively parallel compute platforms (Taylor, 2011). For applications involving many tracers such as chemistry and biochemistry modeling, CAM-SE has been found to be significantly more computationally costly than the current "workhorse" model CAM-FV (Finite-Volume; Lin 2004). Hence a multi-tracer efficient scheme, called the CSLAM (Conservative Semi-Lagrangian Multi-tracer; Lauritzen et al., 2011) scheme, has been implemented in the HOMME (Erath et al., 2012). The CSLAM scheme has recently been cast in flux-form in HOMME so that it can be coupled to the SE dynamical core through conventional flux-coupling methods where the SE dynamical core provides background air mass fluxes to CSLAM. Since the CSLAM scheme makes use of a finite-volume gnomonic cubed-sphere grid and hence does not operate on the SE quadrature grid, the capability of running tracer advection, the physical parameterization suite and dynamics on separate grids has been implemented in CAM-SE. The default CAM-SE-CSLAM setup is to run physics on the quasi-equal area CSLAM grid. The capability of running physics on a different grid than the SE dynamical core may provide a more consistent coupling since the physics grid option operates with quasi-equal-area cell average values rather than non-equi-distant grid-point (SE quadrature point) values. Preliminary results on the performance of CAM-SE-CSLAM will be presented.

  12. Physical activity in Brazil: lessons from ELSA-Brasil. Narrative review.

    PubMed

    Pitanga, Francisco José Gondim; Almeida, Maria Conceição Chagas; Queiroz, Ciro Oliveira; Aquino, Estela Maria Leão de; Matos, Sheila Maria Alvim

    2017-01-01

    The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) was conducted among civil servants at six higher education institutions located in six Brazilian state capitals. The objective of this review was to identify the publications produced within the scope of ELSA-Brasil that analyzed the participants' physical activity. Review study using baseline data from ELSA-Brasil. Narrative review of Brazilian studies on physical activity produced using data from ELSA-Brasil participants. The prevalence of leisure-time physical activity (LTPA) among ELSA-Brasil participants was low (44.1% among men and 33.8% among women). The main factors associated were social (higher schooling and family income), environmental (living in places with conditions and opportunities for physical activity) and individual (not being obese, being retired, not smoking and positive perception of body image). The perception of facilities for walking in the neighborhood was positively associated with both LTPA and commuting-related physical activity. An active lifestyle was a protective factor against several cardiometa-bolic variables (hypertension, diabetes, lipid abnormalities and cardiovascular risk over the next 10 years). Comparison between LTPA and commuting-related physical activity showed that only LTPA had a protective effect against arterial hypertension. The prevalence of physical activity among ELSA-Brasil participants was low. The main determinants were social, environmental and personal. LTPA had a greater protective efect on cardio-metabolic outcomes than did commuting-related physical activity.

  13. 31P to 77Se cross polarization in beta-P4Se3.

    PubMed

    Pietrass, T; Seydoux, R; Roth, R E; Eckert, H; Pines, A

    1997-08-01

    Cross polarization from 31P to 77Se is demonstrated in beta-P4Se3. This material, an inorganic glass, is readily synthesized from the elements and serves as a convenient sample for setting the Hartmann-Hahn condition.

  14. 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.

  15. Optical detectors on GaSe and InSe layered crystals

    NASA Astrophysics Data System (ADS)

    Kyazym-Zade, A. G.; Agaeva, A. A.; Salmanov, V. M.; Mokhtari, A. G.

    2007-12-01

    Fast uncooled GaSe and InSe detectors that can record ultrashort (10-12 10-9 s) laser pulses in the visual and near-IR ranges are developed. The quick response of the detectors is due to rapid recombination channels with a high capture cross section present in the crystals.

  16. Comparative Transcriptome Analysis of SE initial dedifferentiation in cotton of different SE capability.

    PubMed

    Cao, Aiping; Zheng, Yinying; Yu, Yu; Wang, Xuwen; Shao, Dongnan; Sun, Jie; Cui, Baiming

    2017-08-17

    Somatic embryogenesis (SE) is a critical transition from vegetative to embryogenic growth in higher plants; however, few studies have investigated the mechanism that regulates SE initial differentiation. Most cotton varieties have not undergone regeneration by SE, so only a few varieties can be used in genetic engineering. Here, two varieties of cotton with different SE capabilities (HD, higher differentiation and LD, lower differentiation) were analyzed by high throughout RNA-Seq at the pre-induction stage (0h) and two induction stages (3h and 3d) under callus-induction medium (CIM). About 1150 million clean reads were obtained from 98.21% raw data. Transcriptomic analysis revealed that "protein kinase activity" and "oxidoreductase activity" were highly represented GO terms during the same and different treatment stages among HD and LD. Moreover, several stress-related transcription factors might play important roles in SE initiation. The SE-related regulation genes (SERKs) showed different expression patterns between HD and LD. Furthermore, the complex auxin and ethylene signaling pathway contributes to initiation of differentiation in SE. Thus, our RNA-sequencing of comparative transcriptome analysis will lay a foundation for future studies to better define early somatic formation in cotton with different SE capabilities.

  17. Ab initio calculations of optical constants of GaSe and InSe layered crystals

    NASA Astrophysics Data System (ADS)

    Sarkisov, S. Yu.; Kosobutsky, A. V.; Brudnyi, V. N.; Zhuravlev, Yu. N.

    2015-09-01

    The dielectric functions, refractive indices, and extinction coefficients of GaSe and InSe layered crystals have been calculated within the density functional theory. The calculations have been performed for the values of theoretical structural parameters optimized using the exchange-correlation functional, which allows one to take into account the dispersion interactions. It has been found that optical functions are characterized by the most pronounced polarization anisotropy in the range of photon energies of ˜4-7 eV. The frequency dependences for InSe compound in the range up to 4 eV demonstrate the more pronounced anisotropy as compared to GaSe. The results obtained for GaSe crystal agree better with the experimental data as compared to the previous calculations.

  18. Ultrafast carrier dynamics in type II ZnSe/CdS/ZnSe nanobarbells.

    PubMed

    Hewa-Kasakarage, Nishshanka N; El-Khoury, Patrick Z; Tarnovsky, Alexander N; Kirsanova, Maria; Nemitz, Ian; Nemchinov, Alexander; Zamkov, Mikhail

    2010-04-27

    We employ femtosecond transient absorption spectroscopy to get an insight into ultrafast processes occurring at the interface of type II ZnSe/CdS heterostructured nanocrystals fabricated via colloidal routes and comprising a barbell-like arrangement of ZnSe tips and CdS nanorods. Our study shows that resonant excitation of ZnSe tips results in an unprecedently fast transfer of excited electrons into CdS domains of nanobarbells (<0.35 ps), whereas selective pumping of CdS components leads to a relatively slow injection of photoinduced holes into ZnSe tips (tau(h)= 95 ps). A qualitative thermodynamic description of observed electron processes within the classical limit of Marcus theory was used to identify a specific charge transfer regime associated with the ultrafast electron injection into CdS. Potential photocatalytic applications of the observed fast separation of carriers along the main axis of ZnSe/CdS barbells are discussed.

  19. Morphology of ultrathin CdSe quantum confinement layers in ZnSe matrices

    NASA Astrophysics Data System (ADS)

    Chinyama, K. G.; O'Donnell, K. P.; Rosenauer, A.; Gerthsen, D.

    1999-06-01

    Using a combination of transmission electron microscopy (TEM), high resolution TEM (HRTEM), digital analysis of lattice images (DALI), and correspondence analysis (CA) we present at near-atomic resolution the morphology of a nominal 2 monolayer (ML) cadmium selenide (CdSe) quantum well (QW) between ZnSe barriers. We reveal the presence of ˜10 ML zinc cadmium selenide (Zn xCd 1- xSe) alloy insertion layer of varying composition in a ZnSe matrix. A spotty pattern in the plane of the layer indicates the presence of self-assembled clusters or islands similar to the structures commonly referred to as quantum dots. Further analysis indicates that these clusters, of less than 10 nm in lateral extent, themselves contain sites highly saturated with CdSe. Analysis of photoluminescence (PL) spectra suggests that the emission originates predominantly from excitons trapped in these islands.

  20. Exciton dynamics in cation-exchanged CdSe/PbSe nanorods: The role of defects

    NASA Astrophysics Data System (ADS)

    Lee, Sooho; Wang, Yimeng; Liu, Yawei; Lee, Dongkyu; Lee, Kangha; Lee, Doh C.; Lian, Tianquan

    2017-09-01

    Cation exchange occurs via defect initiated solid-state diffusion, a process that can lead to defect formations. The effect of such inherent defect formation on carrier dynamics of cation-exchanged heterostructures remains poorly understood. Herein, we report exciton dynamics in type II CdSe/PbSe heterostructure nanorods formed via cation exchange. The majority of electrons in CdSe domains decays in 5 ps due to ultrafast carrier trapping. The defect generated by cation exchange can be healed by annealing the as-synthesized CdSe/PbSe heterostructure nanorods. This study suggests a strategy for improving properties of heteronanostructures prepared by cation exchange for applications in photovoltaics and photocatalysis.

  1. 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.

  2. Respostas religiosas à aids no Brasil: impressões de pesquisa acerca da Pastoral de DST/Aids da Igreja Católica1

    PubMed Central

    Seffner, Fernando; Silva, Cristiane Gonçalves Meireles da; Maksud, Ívia; Garcia, Jonathan; Rios, Luís Felipe; Natividade, Marcelo; Borges, Priscila Rodrigues; Parker, Richard; Terto, Veriano

    2009-01-01

    O texto encontra-se estruturado em quatro partes. Na primeira delas, apresentamos um conjunto de considerações e informações acerca da situação da aids no Brasil, das relações entre religião, sexualidade, aids e estado laico, bem como uma descrição mais clara do Projeto Respostas Religiosas ao HIV/Aids no Brasil, do qual este texto apresenta algumas impressões de pesquisa preliminares. A seguir, dedicamos um item a apresentação da Pastoral de DST/Aids, sua história, estrutura e objetivos. No item seguinte problematizamos diversas questões em particular no âmbito das relações Estado e Igreja, relações entre agentes de pastoral e hierarquia da Igreja, e questões ligadas mais diretamente à sexualidade e aids, todas referenciadas ao trabalho da Pastoral de DST/Aids. Ao final, apresentamos a bibliografia e fontes consultadas. PMID:20442806

  3. Metabolism of {sup 76}Se-methylselenocysteine compared with that of {sup 77}Se-selenomethionine and {sup 82}Se-selenite

    SciTech Connect

    Suzuki, Kazuo T. . E-mail: ktsuzuki@p.chiba-u.ac.jp; Doi, Chiaki; Suzuki, Noriyuki

    2006-12-01

    Se-Methylated selenoamino acids, Se-methylselenocysteine (MeSeCys) and selenomethionine (SeMet), are chemically inert storage forms of selenium in selenium-accumulators, and a nutritional and supplemental source. The metabolic pathway for MeSeCys was precisely traced by referring to those for SeMet and selenite by applying a new tracer method involving multiple homo-elemental stable isotopes. Male Wistar rats were depleted of endogenous natural abundance selenium with a single {sup 8}Se-enriched isotope, and then {sup 76}Se-MeSeCys, {sup 77}Se-SeMet and {sup 82}Se-selenite were orally administered simultaneously at 25 {mu}g Se/kg body weight each. Organs and body fluids were obtained at 3, 6, 9 and 12 h, and 1 and 2 days later, and subjected to speciation analysis. The main characteristics of the metabolism were as follows; MeSeCys was incorporated into selenoprotein P slightly more than or at a comparable level to that of SeMet but less than that of selenite. MeSeCys and SeMet but not selenite was taken up by organs in their intact forms. MeSeCys and SeMet were delivered specifically to the pancreas and present in a form bound to an identical or similar protein. Trimethylselenonium (TMSe) was only produced from MeSeCys, i.e., not from SeMet or selenite, in the kidneys. Both selenosugars A and B of MeSeCys, SeMet and selenite origin were detected in the liver but only selenosugar B in the kidneys. These results suggest that MeSeCys can be a similar or better selenium source than SeMet, and supplies methylselenol much more efficiently in organs than SeMet and selenite. TMSe was produced much efficiently from MeSeCys than from SeMet and selenite, suggesting a role of methylselenol through the {beta}-lyase reaction in the metabolism of Se-methylated selenoamino acids.

  4. Anisotropy in CdSe quantum rods

    SciTech Connect

    Li, Liang-shi

    2003-01-01

    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

  5. 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.

  6. Superconducting gap structure of FeSe.

    PubMed

    Jiao, Lin; Huang, Chien-Lung; Rößler, Sahana; Koz, Cevriye; Rößler, Ulrich K; Schwarz, Ulrich; Wirth, Steffen

    2017-03-07

    The microscopic mechanism governing the zero-resistance flow of current in some iron-based, high-temperature superconducting materials is not well understood up to now. A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure. Here we present a combined study of low-temperature specific heat and scanning tunnelling microscopy measurements on single crystalline FeSe. The results reveal the existence of at least two superconducting gaps which can be represented by a phenomenological two-band model. The analysis of the specific heat suggests significant anisotropy in the gap magnitude with deep gap minima. The tunneling spectra display an overall "U"-shaped gap close to the Fermi level away as well as on top of twin boundaries. These results are compatible with the anisotropic nodeless models describing superconductivity in FeSe.

  7. Superconducting gap structure of FeSe

    NASA Astrophysics Data System (ADS)

    Jiao, Lin; Huang, Chien-Lung; Rößler, Sahana; Koz, Cevriye; Rößler, Ulrich K.; Schwarz, Ulrich; Wirth, Steffen

    2017-03-01

    The microscopic mechanism governing the zero-resistance flow of current in some iron-based, high-temperature superconducting materials is not well understood up to now. A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure. Here we present a combined study of low-temperature specific heat and scanning tunnelling microscopy measurements on single crystalline FeSe. The results reveal the existence of at least two superconducting gaps which can be represented by a phenomenological two-band model. The analysis of the specific heat suggests significant anisotropy in the gap magnitude with deep gap minima. The tunneling spectra display an overall “U”-shaped gap close to the Fermi level away as well as on top of twin boundaries. These results are compatible with the anisotropic nodeless models describing superconductivity in FeSe.

  8. Superconducting gap structure of FeSe

    PubMed Central

    Jiao, Lin; Huang, Chien-Lung; Rößler, Sahana; Koz, Cevriye; Rößler, Ulrich K.; Schwarz, Ulrich; Wirth, Steffen

    2017-01-01

    The microscopic mechanism governing the zero-resistance flow of current in some iron-based, high-temperature superconducting materials is not well understood up to now. A central issue concerning the investigation of these materials is their superconducting gap symmetry and structure. Here we present a combined study of low-temperature specific heat and scanning tunnelling microscopy measurements on single crystalline FeSe. The results reveal the existence of at least two superconducting gaps which can be represented by a phenomenological two-band model. The analysis of the specific heat suggests significant anisotropy in the gap magnitude with deep gap minima. The tunneling spectra display an overall “U”-shaped gap close to the Fermi level away as well as on top of twin boundaries. These results are compatible with the anisotropic nodeless models describing superconductivity in FeSe. PMID:28266654

  9. Chemical beam epitaxy of ZnSe

    NASA Astrophysics Data System (ADS)

    Kolodziejski, Leslie A.

    1990-10-01

    ZnSe, ZnTe, and ZnSe/ZnTe layered quantum well structures have room temperature direct energy bandgaps which span the blue/blue-green optical spectrum. These II-VI semiconductors possess significant technological potential for visible optoelectronic device applications. Both military and commercial applications are envisioned. Blue/blue-green semiconductor injection lasers for underwater to satellite communications, visible flat panel electroluminescent displays, optical disc recording using blue wavelengths to increase the density of recorded information, color laser printers, and short range domestic or industrial communications via polymer fibers are examples of frequently quoted potential markets. The magnitude in U.S. dollars offered by these varied and large commercial markets warrants substantial investment in both research time and funds to push these materials to their ultimate potential for optoelectronic device fabrication testing, and marketing. Substantial effort is currently underway in Japan and Europe with major investment in funds and manpower.

  10. The GeTe-PbSe system

    SciTech Connect

    Abrikosov, N.Kh.; Avilov, E.S.; Karpinskii, O.G.; Radkevich, O.V.; Shelimova, L.E.

    1986-03-01

    Phase equilibria are investigated in the GeTe-PbSe system and also the effect of cation-anion substitution in the structural state, phase-transformation temperatures, and electrophysical properties of the solution alloys based on alpha-GeTe are studied. After annealing at 570 K, the alloys were investigated by thermal, microstructural, x-ray-phase, and dilatometric analyses. Electrical conductivity and Hall coefficient were measured at 300 K by an R 56/2 ac potentiometer with precision of 3 and 10% respectively. The precision in the thermo-emf-coefficient measurements was 3% and in thermal-conductivity measurements was 10%. It was established that the Ge /SUB 0.9/ Te-PbSe section is quasibinary only at temperatures near th solidus, where a continuous series of solid solutions exist.

  11. 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.

  12. Chemical Beam Epitaxy of ZnSe

    DTIC Science & Technology

    1990-10-17

    is curren:ly underway in Japan and Europe with major investment in funds and manpower. However, the problems which remain are largely still an issue...of availability of suitable materials, specifically availability of p-type ZnSe with sufficient useable hole carrier concentrations. The problem ...contract provided essential seed funding necessary to accumulate sufficient funds to build and equip a state-or-the-art chemical beam epitaxy facility at

  13. 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.

  14. 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

  15. 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

    2016-07-19

    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.

  16. In-beam Spectroscopy of ^68Se.

    NASA Astrophysics Data System (ADS)

    Fischer, S. M.; Balamuth, D. P.; Hausladen, P.; Lister, C. J.; Blumenthal, D. J.; Schwartz, J.; Leddy, M. J.; Sarantites, D. G.; Devlin, M.

    1998-04-01

    Nuclei with N≈Z in the A=70 mass region exhibit rapid changes in shape with the addition or subtraction of one or two particles; shape coexistence has been demonstrated in slightly lighter systems. Experimental investigation of these N=Z nuclei has proven to be quite difficult, principally due to very low cross sections for relevant fusion-evaporation reactions. To date only three transitions have been reported (C.J. Lister et al.), Phys. Rev. C42, R1191 (1990). in ^68Se. In the present work, ^68Se was produced via the ^40Ca(^36Ar,2α) reaction at a beam energy of 140 MeV. The Gammasphere and Microball arrays were used to detect γ-rays of fold 3 and higher in coincidence with evaporated charged particles. Doppler corrections were applied on an event-by-event basis to γ-rays in coincidence with 2 α particles, and a careful subtraction of feedthrough channels was performed. Two previously identified transitions in ^68Se have been confirmed and at least seven new transitions have been observed. The proposed level scheme, based on coincidence relationships and γ-ray angular distributions, will be discussed.

  17. Forming glasses from Se and Te.

    PubMed

    Bureau, Bruno; Boussard-Pledel, Catherine; Lucas, Pierre; Zhang, Xianghua; Lucas, Jacques

    2009-10-26

    Despite being close neighbors on the Periodic Table, selenium and tellurium present a totally different abilities to form glasses. Se is a very good glass former, and gives rise to numerous glass compositions which are popular for their transparency in the infrared range and their stability against crystallization. These glasses can be shaped into sophisticated optical devices such as optical fibers, planar guides or lenses. Nevertheless, their transparencies are limited at about 12 microm (depending on the thickness of the optical systems) due to the relatively small mass of the Se element. On the other hand, tellurium is heavier and its use in substitution for Se permits to shift the IR cutoff beyond 20 microm. However, the semimetallic nature of Te limits its glass formation ability and this glass family is known to be unstable and consequently has found application as phase change material in the Digital Versatile Disk (DVD) technology. In this paper, after a review of selenide glasses and their applications, it will be shown how, in a recent past, it has been possible to stabilize tellurium glasses by introducing new elements like Ga or I in their compositions.

  18. Low Temperature Photoluminescence of PVT Grown ZnSe and ZnSeTe

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

  19. One-pot synthesis of multicolor MnSe:ZnSe nanocrystals for optical coding.

    PubMed

    Wang, Yanbin; Wang, Chunlei; Xu, Shuhong; Shao, Haibao; Jiang, Yuan; Bo, Fan; Wang, Zhuyuan; Cui, Yiping

    2014-02-01

    Though the investigation on controlling the fluorescence properties of nanocrystals (NCs) with single emission has been widely reported, few efforts were spent on adjusting the fluorescence properties of NCs with multiple emission peaks. In this work, we successfully synthesized multicolor MnSe:ZnSe NCs with multiple emission peaks and developed a simple and accurate method to realize photoluminescence (PL) spectra (or color) adjustment. The PL of MnSe:ZnSe NCs has two distinct emission peaks, the trap emission of ZnSe at 475nm and Mn(2+)-induced emission at 585nm. By adjusting the nucleation temperature, the emission color of the NCs can be encoded according to the ratio of the emission intensities at 475 and 585nm. With the nucleation temperature rising from 0 to 70°C, the PL ratio between trap emission and Mn(2+)-induced emission can be consecutively changed from (1, 3) to (1, 0.5). In addition, the trap state is deeply inside the NCs rather than on NCs surface so that the trap emission is stable during environment change. Thus, these MnSe:ZnSe NCs hold great promise as novel single-particle coding labels for biomedical imaging. Copyright © 2013 Elsevier Inc. All rights reserved.

  20. Designed Formulation of Se-Impregnated N-Containing Hollow Core Mesoporous Shell Carbon Spheres: Multifunctional Potential Cathode for Li-Se and Na-Se Batteries.

    PubMed

    Kalimuthu, Balakumar; Nallathamby, Kalaiselvi

    2017-08-16

    Nitrogen-containing carbon spheres with hollow core and mesoporous shell (NHCS), capable of confining Se at levels as high as 72 wt % has been demonstrated to exhibit appreciable electrochemical behavior with 52 and 61 wt % Se loading. In particular, 52 wt % Se confined NHCS cathode exhibits 265 mAh/g at 10C rate and retains 75% of initial capacity at 2C rate up to 10 000 cycles with an insignificant decay of 0.0025% per cycle, which is an ever first report on the extended cycle life of Li-Se batteries. Due to the negligible difference found between the transport kinetics of Se and that of Li2Se, irrespective of the cycling rate, 52 wt % Se @ NHCS performs better at high rates. Furthermore, capacity is governed by the extent of utilization of confined Se and cycle life by the extent of mitigation of volume expansion. Accordingly, rate capability studies recommend 52 wt % Se loaded cathode above 2C rate and 61 wt % Se loading up to 2C rate. Furthermore, NHCS/Se-52 cathode demonstrates suitability for Na-Se batteries by exhibiting 339 and 219 mAh/g of capacity at rates of C/5 and 2C rates, respectively. NHCS with select Se concentration could thus be exploited for multifunctional cathode behavior in Li-Se and Na-Se systems.

  1. ZnCdSe/ZnSe quantum-dot semiconductor optical amplifiers

    NASA Astrophysics Data System (ADS)

    Al-Mossawi, Muwaffaq Abdullah

    2017-02-01

    Gain of CdZnSe quantum dot (QD) semiconductor optical amplifiers (SOAs) is studied theoretically using non-Markovian gain model including many-body effects. The calculations are done at three mole fractions. Spontaneous emission and noise figure of the amplifier are studied. The effect of shot noise is included. High gain, polarization independence, and low noise figure are characterize these QD-SOAs. A multi-mode gain appears for Zn0.69Cd0.31Se structure while the structure Zn0.6Cd0.4Se give a low noise.

  2. Optical nonlinearities in GaSe and InSe crystals upon laser excitation

    NASA Astrophysics Data System (ADS)

    Kyazym-zade, A. G.; Salmanov, V. M.; Guseinov, A. G.; Gasanova, L. G.; Mamedov, R. M.

    2014-04-01

    The nonlinear absorption of light and its temporal evolution in the vicinity of exciton resonance in layered GaSe and InSe crystals under high optical excitation have been experimentally investigated. The decisive factor for the observed temporal dependence of the absorption coefficient and its dependence on the excitation intensity is screening excitons by nonequilibrium-carrier plasma. It is shown that the increase in the transmittance in the absorption-band edge in GaSe with a simultaneous blue shift of the band edge is caused by filling the energy bands under high optical excitation.

  3. (BiSe)1.23CrSe2 and (BiSe)1.22(Cr1.2Se2)2: magnetic anisotropy in the first structurally characterized Bi-Se-Cr ternary compounds.

    PubMed

    Clarke, Samantha M; Freedman, Danna E

    2015-03-16

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

  4. BeTe/ZnSe graded band gap ohmic contacts to p-ZnSe

    NASA Astrophysics Data System (ADS)

    Mensz, P. M.

    1994-04-01

    BeTe is not a very well known wide-band semiconductor. Due to the close lattice match to GaAs and ZnSe and p-type as-grown character, BexZn1-xTexSe1-x graded band-gap layers appear an ideal candidate for ohmic contact to p-type ZnSe based semiconductors. These contacts allow for an implementation of epitaxial structures of II-VI compound diode lasers entirely lattice matched to the GaAs substrate. The numerical calculations predict contact resistivity of BexZn1-xTexSe1-x graded gap contacts lower than ρc=10-4 Ω cm2 at acceptor doping level 1×1018 cm-3, which corresponds to a voltage drop across the contact layer of less than 0.1 V during lasing operation.

  5. Nota sobre el "Se" como Sujeto Indefinido (A Note on "Se" as an Indefinite Subject)

    ERIC Educational Resources Information Center

    Lujan, Marta

    1975-01-01

    Contradicts Pablo Jordan's theory that certain "se" constructions in Spanish are neither passive nor reflexive. It is claimed that syntactic evidence reveals two types of impersonal structures, the impersonal active and the passive reflexive. (Text is in Spanish.) (CK)

  6. Energy spectrum and effective mass of carriers in the InSe/GaSe superlattice

    NASA Astrophysics Data System (ADS)

    Gashimzade, F. M.; Mustafaev, N. B.

    1995-03-01

    Within an effective mass approximation the energy spectrum and mass of carriers in the InSe/GaSe superlattice have been calculated. The superlattice belongs to type II: electrons are primarily confined to the InSe layers whereas the holes are mosfly confined to the GaSe layers. The characteristic feature of electronic structure of the superlattice is the existence of minibands of light carriers at the θ point of the Brillouin zone and minibands of heavy carriers at the M point. The dependence of the miniband structure on thickness of layers has been computed. It is shown that the minibands of light and heavy carriers compete with one another in energy. A general conclusion is made concerning the influence of the competition between the minibands on optic and kinetic properties of the superlattice.

  7. Growth of II-VI ZnSe/CdSe nanowires for quantum dot luminescence

    NASA Astrophysics Data System (ADS)

    Bellet-Amalric, E.; Elouneg-Jamroz, M.; Rueda-Fonseca, P.; Bounouar, S.; Hertog, M. Den; Bougerol, C.; André, R.; Genuist, Y.; Poizat, J. P.; Kheng, K.; Cibert, J.; Tatarenko, S.

    2013-09-01

    The growth of gold catalyzed ZnSe nanowires, with CdSe insertions, by molecular beam epitaxy is investigated. In situ reflection high energy electron diffraction and ex-situ transmission electron diffraction reveal that both during, the gold dewetting and the nanowire growth, the gold particles remain always in the solid phase. The nanowire growth proceeds by ledge flow at the gold/nanowire interface as observed ex-situ by the presence of two monolayers high steps at the interface. The nanowire diameters present a high homogeneity corresponding to the low dispersion of the gold droplets. Finally, a rather abrupt interface, of less than 1 nm thick, is observed between the ZnSe barrier and the CdSe quantum dot allowing a high confinement of the excitons. All the above observations are compatible with a Vapor-Solid-Solid growth mode.

  8. Photodisintegration of {sup 80}Se: Implications for the s-process branching at {sup 79}Se

    SciTech Connect

    Makinaga, A.; Utsunomiya, H.; Kaihori, T.; Akimune, H.; Yamagata, T.; Goriely, S.; Goko, S.; Harada, H.; Kitatani, F.; Hara, Y. K.; Toyokawa, H.; Matsumoto, T.; Harano, H.; Hohara, S.; Lui, Y.-W.

    2009-02-15

    Photoneutron cross sections were measured for {sup 80}Se immediately above the neutron separation energy with quasimonochromatic {gamma}-ray beams to experimentally constrain the E1 {gamma} strength function for {sup 80}Se. Two sets of the {gamma} strength function and the level density that equally meet the experimental constraint predict largely different neutron capture cross sections for {sup 79}Se. Based on the Maxwellian-averaged cross sections of the latest compilation complemented with the predicted cross sections for {sup 79}Se, we calculated {sigma}N values of the main s-process component using a phenomenological model and deduced empirical abundances of the weak s-process component. An attempt is made of considering the implications of the abundance ratios of {sup 80}Kr and {sup 82}Kr within the framework of phenomenological models for the weak s process.

  9. A novel synthesis of a CuInSe2 thin film from electrodeposited Cu-Se-In-Se precursors with three steps annealing.

    PubMed

    Hu, Shao-Yu; Lee, Wen-Hsi; Chang, Shih-Chieh; Wang, Ying-Lang

    2012-09-01

    In this study, copper indium diselenide (CIS) films were synthesized from electrodeposited Cu-Se-In-Se precursors by three step annealing. The Se layer between Cu and In layer was grown to prevent the formation of Cu/In compound. The Cu-Se precursors were first annealed to grow uniform and conductive Cu2Se surface. After deposition of the four layers precursors, two steps annealing was employed to form Cu2Se-In2Se3 precursors. Transforming Cu2Se-In2Se3 to CIS required less thermal energy. Therefore, high quality CIS film can be synthesized by two steps annealing due to its high crystallinity. The properties of the CIS films were characterized by scanning electron microscopy (SEM), X-ray Diffraction (XRD), and Raman Spectra.

  10. Composition and submicron structure of chemically deposited Cu2Se-In2Se3 films

    NASA Astrophysics Data System (ADS)

    Markov, V. F.; Tulenin, S. S.; Maskaeva, L. N.; Kuznetsov, M. V.; Barbin, N. M.

    2012-03-01

    Films of substitutional solid solutions of the Cu2Se-In2Se3 system containing up to 7.5 at. % In have been obtained by chemical deposition from aqueous media. The composition, structure, and morphology of the films have been studied. Data of X-ray diffraction and X-ray photoelectron spectroscopy showed that copper in the solid solution occurs in a single-valence state (Cu+). The deposited layers possess a globular morphology and are nanostructured.

  11. Power dependent phonon frequency within CdSe and CdMnSe nanosheets

    NASA Astrophysics Data System (ADS)

    Halder, Oindrila; Rath, S.

    2017-05-01

    The trend of tuning transitional materials in semiconductors is advancing everyday research. The composite behavior exhibited by doped nanoparticles is governed by many factors. These can either improve or adversely affect the desired electronic properties. In this work we have compared the Raman Scattering study of different power dependent excitations on CdSe nanosheets and manganese doped CdSe nanosheets and delved into the possibilities of their different electronic structures due to the phonon contribution.

  12. Atmospheric Pressure Synthesis of In2Se3, Cu2Se, and CuInSe2 without External Selenization from Solution Precursors

    SciTech Connect

    Nekuda Malik, J. A.; van Hest, M. F. A. M.; Miedaner, A.; Curtis, C. J.; Leisch, J. E.; Parilla, P. A.; Kaufman, M.; Taylor, M.; Stanbery, B. J.; O'Hayre, R. P.; Ginley, D. S.

    2009-04-01

    In{sub 2}Se{sub 3}, Cu{sub 2}Se, and CuInSe{sub 2} thin films have been successfully fabricated using novel metal organic decomposition (MOD) precursors and atmospheric pressure-based deposition and processing. The phase evolution of the binary (In-Se and Cu-Se) and ternary (Cu-In-Se) MOD precursor films was examined during processing to evaluate the nature of the phase and composition changes. The In-Se binary precursor exhibits two specific phase regimes: (i) a cubic-InxSey phase at processing temperatures between 300 and 400 C and (ii) the {gamma}-In{sub 2}Se{sub 3} phase for films annealed above 450 C. Both phases exhibit a composition of 40 at.% indium and 60 at.% selenium. The binary Cu-Se precursor films show more diverse phase behavior, and within a narrow temperature processing range a number of Cu-Se phases, including CuSe{sub 2}, CuSe, and Cu{sub 2}Se, can be produced and stabilized. The ternary Cu-In-Se precursor can be used to produce relatively dense CuInSe{sub 2} films at temperatures between 300 and 500 C. Layering the binary precursors together has provided an approach to producing CuInSe{sub 2} thin films; however, the morphology of the layered binary structure exhibits a significant degree of porosity. An alternative method of layering was explored where the Cu-Se binary was layered on top of an existing indium-gallium-selenide layer and processed. This method produced highly dense and large-grained (>3 {micro}m) CuInSe{sub 2} thin films. This has significant potential as a manufacturable route to CIGS-based solar cells.

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

    NASA Astrophysics Data System (ADS)

    Rangel-Kuoppa, Victor-Tapio

    2013-12-01

    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.

  15. 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.

  16. Ion implanted epitaxially grown ZnSe

    NASA Technical Reports Server (NTRS)

    1974-01-01

    The epitaxial growth of ZnSe on (100) Ge using the close-spaced transport process is described. Substrate temperature of 575 C and source temperatures of 675 C yield 10 micron, single crystal layers in 10 hours. The Ge substrates provides a nonreplenishable chemical transport agent and the epitaxial layer thickness is limited to approximately 10 microns. Grown epitaxial layers show excellent photoluminescence structure at 77 K. Grown layers exhibit high resistivity, and annealing in Zn vapor at 575 C reduces the resistivity to 10-100 ohms-cm. Zinc vapor annealing quenches the visible photoluminescence.

  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. 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.

  19. Impact fracture of ZnSe ceramics

    NASA Astrophysics Data System (ADS)

    Shcherbakov, I. P.; Dunaev, A. A.; Kadomtsev, A. G.; Chmel', A. E.

    2016-10-01

    Structurally different ZnSe ceramics prepared by various techniques were subjected to fallingweight impact fracture. Mechanoluminescence (ML) pulses generated during the motion and multiplication of dislocations were detected, as well as acoustic emission (AE) pulses produced predominantly during the growth of macroscopic (on the specimen scale) cracks. The luminescence began immediately at the moment of contact of a striker with the surface of the specimen, whereas the emission of sound occurred within 50-100 μs after the impact. The emission maxima in the ML and AE time series coincided with each other. The signal series were used to construct energy distributions upon the emission of light and the generation of sound. It was established that the ML amplitude (the number of emitted photons) is proportional to the energy released due to dislocation rearrangements, and the intensity (the square of the amplitude) of AE pulses is proportional to the energy released due to discontinuities of the material. It was found that the ML energy distribution follows a power law, which indicates the self-organization of an ensemble of dislocations during rapid plastic deformation. The AE energy distribution, on the contrary, was found to be random, i.e., typical of the growth of non-interacting cracks. It was shown that the efficiency of the interaction of dislocations depends, to a certain extent, on the technological prehistory of ZnSe ceramics.

  20. Carvacrol after status epilepticus (SE) prevents recurrent SE, early seizures, cell death, and cognitive decline.

    PubMed

    Khalil, Aytakin; Kovac, Stjepana; Morris, Gareth; Walker, Matthew C

    2017-02-01

    Carvacrol is a naturally occurring monoterpenic phenol that has been suggested to have an action at transient receptor potential cation subfamily M7 (TRPM7) channels, γ-aminobutyric acid (GABAA receptors, and sodium channels, and has been shown to be antiinflammatory. Carvacrol is neuroprotective in models of cerebral ischemia in vivo and in vitro, probably through its action at TRPM7 channels. We therefore aimed to determine the effect of carvacrol on status epilepticus (SE), chronic epilepsy, cell death, and post-SE cognitive decline. We performed long-term, continuous wireless electroencephalography (EEG) monitoring in vivo in rats who underwent perforant path stimulation (PPS) to induce SE and were then randomized to treatment with carvacrol or saline. We also evaluated TRPM7 receptor expression and quantified seizure-induced cell death. The alternating T-maze paradigm was used to assess memory function. Immunostaining showed that TRPM7 channels are widely expressed in neurons within the hippocampus. We found that carvacrol inhibited recurrent SE and early seizures in vivo, but had no detectable effect in the hippocampus on paired-pulse inhibition or the fiber volley, indicating that it was not acting through sodium channel inhibition or GABA receptors. Although the development and severity of chronic epilepsy were not altered by carvacrol, cognitive decline was significantly improved in animals treated with carvacrol. In keeping with preserved memory functions in animals treated with carvacrol, carvacrol had a protective effect against SE-induced cell death in CA1 and hilus, the hippocampal regions most affected by cell loss in the PPS epilepsy model. Carvacrol, a naturally occurring inhibitor of TRPM7 channels, is a novel, promising treatment to prevent early recurrence of SE, SE-related neuronal damage, and cognitive decline. Wiley Periodicals, Inc. © 2017 International League Against Epilepsy.

  1. Metabolism of selenium (Se) in rats chronically poisoned with D- or L-selenomethionine (SeMet), selenite or selenate

    SciTech Connect

    McAdam, P.A.; Levander, O.A.

    1986-03-01

    L-SeMet is a potential cancer chemoprevention agent for humans. Little difference was seen in the acute toxicity of L vs. D-SeMet in rats. To study chronic toxicity, weanling male rats were fed purified diets containing 2.5, 5.0 or 10 ppm Se as L-SeMet, D-SeMet, Na/sub 2/SeO/sub 3/ or Na/sub 2/SeO/sub 4/ for 6 weeks. Controls received 0.1 ppm Se as selenite. All rats fed 10 ppm Se died within 29 days. Se fed as D-SeMet was retained in the tissues as strongly as L-SeMet. Rats fed D or L-SeMet deposited large amounts of Se in muscle not reflected by proportionate increases in either plasma or RBC Se. Therefore, attempts to follow increases in Se body burden in individuals supplemented with large doses of L-SeMet by monitoring plasma or whole blood Se levels should be interpreted with caution.

  2. Chemical excision of tetrahedral FeSe(2) chains from the superconductor FeSe: synthesis, crystal structure, and magnetism of Fe(3)Se(4)(en)(2).

    PubMed

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

    2013-12-26

    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.

  3. Depth resolved cathodoluminescence and microanalysis of ZnCdSe/ZnSe quantum well heterostructures

    NASA Astrophysics Data System (ADS)

    Shakhmin, Alexey A.; Sedova, Irina V.; Sorokin, Sergey V.; Zamoryanskaya, Maria V.

    2013-04-01

    The novel approaches to study the II-VI-based laser heterostructures using cathodoluminescence and electron probe microanalysis techniques are described in detail. The heterostructures were grown by molecular beam epitaxy on GaAs (0 0 1) substrates and consist of bottom and top ZnMgSSe cladding layers and ZnCdSe/ZnSe quantum well embedded in Zn(Mg)SSe/ZnSe graded index waveguide. The microanalysis technique based on the intensity measurements of characteristic X-rays has been applied to determine both the composition of ZnCdSe quantum well layer and its position within heterostructure. The depth resolved cathodoluminescence technique has been applied for the transport studies of electron beam generated carriers in heterostructure. The cathodoluminescence intensity of ZnCdSe quantum well has been measured as a function of electron beam energy. The Monte-Carlo simulations of carrier generation distribution within the heterostructure under electron beam irradiation have been used for fitting of experimental results. It made possible the nondestructive characterization of the multilayer heterostructure to estimate both deficiency and carrier transport length.

  4. Preparation, characterization, and antiproliferative activities of the Se-containing polysaccharide SeGLP-2B-1 from Se-enriched Ganoderma lucidum.

    PubMed

    Shang, Dejing; Zhang, Jianing; Wen, Lei; Li, Yang; Cui, Qiao

    2009-09-09

    Inorganic selenite can be transformed into organic forms and bind to proteins and polysaccharides in Se-enriched submerged Ganoderma lucidum cultures. In the present study, a novel Se-containing polysaccharide, SeGLP-2B-1, was purified from the Se-enriched mycelia of G. lucidum and the antiproliferative activities against six human cancer cell lines were investigated. The Se content of SeGLP-2B-1 was 186.7 microg/g, which was 150-fold larger than that of the regular polysaccharide GLP-2B-1 (1.3 microg/g). SeGLP-2B-1 (1.06 x 10(6) Da) was composed of glucose, rhamnose, xylose, and galactose with a molar ratio of 1.000:0.652:0.443:0.227. SeGLP-2B-1 exhibited an approximately 10-fold stronger antiproliferative activity against six human cancer cell lines as compared to GLP-2B-1. Thus, Se is believed to play an important role in increasing the antiproliferative property of SeGLP-2B-1. These findings indicate that SeGLP-2B-1 may serve as a dietary Se supplement.

  5. 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.

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

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 2 2011-04-01 2011-04-01 false Salmonella Enteritidis (SE) prevention measures....4 Salmonella Enteritidis (SE) prevention measures. You must follow the SE prevention measures set forth in this section. In addition, you must have and implement a written SE prevention plan that is...

  7. 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....4 Salmonella Enteritidis (SE) prevention measures. You must follow the SE prevention measures set forth in this section. In addition, you must have and implement a written SE prevention plan that is...

  8. 21 CFR 118.4 - Salmonella Enteritidis (SE) prevention measures.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 2 2013-04-01 2013-04-01 false Salmonella Enteritidis (SE) prevention measures....4 Salmonella Enteritidis (SE) prevention measures. You must follow the SE prevention measures set forth in this section. In addition, you must have and implement a written SE prevention plan that is...

  9. Models of GexSe1-x

    NASA Astrophysics Data System (ADS)

    Malouin, Marc-André.; Mousseau, Normand

    2008-03-01

    We present numerical models of chalcogenide glasses constructed using the effective two and three body interaction potential developed by Mauro and Varshneya [1] combined with the activation-relaxation technique (ART nouveau) [2]. Structures are prepared starting from a random distribution, avoiding biases and crystalline remnants. Structural properties are studied mainly via characteristic system measurements including partial and total radial distribution functions, bond angle distributions, mean coordinations and bonds population. Results are shown for GexSe1-x for various x concentrations and compared to both experimental measurements and ab initio simulation results. [1] J.C. Mauro and A.K. Varshneya, J. Am. Ceram. Soc., 89 [7] 2323-6 (2006). [2] R. Malek and N. Mousseau, Phys. Rev. E 62, 7723 (2000).

  10. Upconversion luminescence from CdSe nanoparticles.

    PubMed

    Chen, Wei; Joly, Alan G; McCready, David E

    2005-06-08

    Efficient upconversion luminescence has been observed from CdSe nanoparticles ranging in size from 2.5 to 6 nm. The upconversion luminescence exhibits a near-quadratic laser power dependence. Emissions from both excitons and trap states are observed in the upconversion and photoluminescence spectra, and in the upconversion luminescence the emission from the trap states is enhanced relative to the trap-state emission in the photoluminescence. The upconversion decay lifetimes are slightly longer than the photoluminescence decay lifetimes. Time-resolved spectral measurements indicate that this is due to the involvement of long decay components from surface or trap states. Both the photoluminescence and upconversion luminescence decrease in intensity with increasing temperature due mainly to thermal quenching. All the observations indicate that trap states work as emitters rather than as intermediate states for upconversion luminescence and that two-photon absorption is the likely excitation mechanism.

  11. Coulomb Excitation of 78,80Se and the radioactive 84Se (N = 50) isotopes

    NASA Astrophysics Data System (ADS)

    Galindo-Uribarri, A.; Padilla-Rodal, E.; Garcia-Ruiz, R. F.; Allmond, J. M.; Batchelder, J. C.; Beene, J. R.; Lagergren, K. B.; Mueller, P. E.; Radford, D. C.; Stracener, D. W.; Urrego-Blanco, J. P.; Varner, R. L.; Yu, C.-H.

    2011-10-01

    Coulomb excitation is a purely electromagnetic excitation process of nuclear states due to the Coulomb field of two colliding nuclei. It is a very precise tool to measure excitation probabilities and provide insight on the collectivity of nuclear excitations and in particular on nuclear shapes. We have measured the B(E2) value of various nuclei in the mass A ~ 80 region using particle-gamma coincidences with the HyBall and Clarion arrays at HRIBF. The Coulomb excitation of various projectile-target combinations (ASe on 12C, 24Mg, 27Al and 50Ti) allow the use of consistency cross checks and the systematic study of isotopic and isotonic chains using both stable and radioactive nuclei under almost identical experimental conditions.We present new results for 78Se, 80Se and the radioactive nucleus 84Se (N = 50). Research sponsored by the Office of Nuclear Physics, U.S. Department of Energy and CONACyT Grant 103366.

  12. Phonons in bulk CdSe and CdSe nanowires.

    PubMed

    Mohr, Marcel; Thomsen, Christian

    2009-03-18

    We present first-principles calculations for bulk CdSe and CdSe nanowires with diameters of up to 22 A. Their electronic and structural properties are presented and discussed. The vibrational properties of bulk CdSe and the zone-center vibrations of the nanowires are calculated and analyzed. An iterative, symmetry-based relaxation method is used that yields improved results for phonon frequencies. We find that the band gap varies with the surface termination and that strongly size-dependent and nearly constant vibrational modes exist in the nanowires, depending on the displacement directions. A strong shift in frequency for specific modes is found, stemming from surface contributions to the polarization, similar to that reported for thin slabs. A comparison with experimental data from Raman measurements is given.

  13. Purcell effect for CdSe /ZnSe quantum dots placed into hybrid micropillars

    NASA Astrophysics Data System (ADS)

    Robin, I. C.; André, R.; Balocchi, A.; Carayon, S.; Moehl, S.; Gérard, J. M.; Ferlazzo, L.

    2005-12-01

    This letter reports the observation of the Purcell effect for CdSe /ZnSe quantum dots located in a hybrid micropillar. The sample consist of a λ /2-ZnSe cavity sandwiched between two SiO2/TiO2 Bragg reflectors. Time-resolved photoluminescence (PL) measurements on a series of single-quantum dots were used to probe the Purcell effect in a 1.1μm diameter pillar. A three-fold enhancement of quantum-dot spontaneous emission rate is observed for quantum dots in resonance with excited degenerated modes of the pillar. The variation of the PL decay shortening from dot to dot is interpreted calculating the theoretical maximal Purcell factor for the different modes resonant with the dots.

  14. 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.

  15. Cohort Profile: Longitudinal Study of Adult Health (ELSA-Brasil)

    PubMed Central

    Schmidt, Maria Inês; Duncan, Bruce B; Mill, José Geraldo; Lotufo, Paulo A; Chor, Dóra; Barreto, Sandhi Maria; Aquino, Estela ML; Passos, Valéria Maria Azeredo; Matos, Sheila MA; Molina, Maria del Carmen B; Carvalho, Marilia S; Bensenor, Isabela M

    2015-01-01

    Chronic diseases are a global problem, yet information on their determinants is generally scant in low- and middle-income countries. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) aims to contribute relevant information regarding the development and progression of clinical and subclinical chronic diseases, particularly cardiovascular diseases and diabetes, in one such setting. At Visit 1, we enrolled 15 105 civil servants from predefined universities or research institutes. Baseline assessment (2008–10) included detailed interviews and measurements to assess social and biological determinants of health, as well as various clinical and subclinical conditions related to diabetes, cardiovascular diseases and mental health. A second visit of interviews and examinations is under way (2012–14) to enrich the assessment of cohort exposures and to detect initial incident events. Annual surveillance has been conducted since 2009 for the ascertainment of incident events. Biological samples (sera, plasma, urine and DNA) obtained at both visits have been placed in long-term storage. Baseline data are available for analyses, and collaboration via specific research proposals directed to study investigators is welcome. PMID:24585730

  16. Determination of dispersive optical constants of nanocrystalline CdSe (nc-CdSe) thin films

    SciTech Connect

    Sharma, Kriti; Al-Kabbi, Alaa S.; Saini, G.S.S.; Tripathi, S.K.

    2012-06-15

    Highlights: ► nc-CdSe thin films are prepared by thermal vacuum evaporation technique. ► TEM analysis shows NCs are spherical in shape. ► XRD reveals the hexagonal (wurtzite) crystal structure of nc-CdSe thin films. ► The direct optical bandgap of nc-CdSe is 2.25 eV in contrast to bulk (1.7 eV). ► Dispersion of refractive index is discussed in terms of Wemple–DiDomenico single oscillator model. -- Abstract: The nanocrystalline thin films of CdSe are prepared by thermal evaporation technique at room temperature. These thin films are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). The transmission spectra are recorded in the transmission range 400–3300 nm for nc-CdSe thin films. Transmittance measurements are used to calculate the refractive index (n) and absorption coefficient (α) using Swanepoel's method. The optical band gap (E{sub g}{sup opt}) has been determined from the absorption coefficient values using Tauc's procedure. The optical constants such as extinction coefficient (k), real (ε{sub 1}) and imaginary (ε{sub 2}) dielectric constants, dielectric loss (tan δ), optical conductivity (σ{sub opt}), Urbach energy (E{sub u}) and steepness parameter (σ) are also calculated for nc-CdSe thin films. The normal dispersion of refractive index is described using Wemple–DiDomenico single-oscillator model. Refractive index dispersion is further analysed to calculate lattice dielectric constant (ε{sub L}).

  17. Phosphine-free synthesis of high quality ZnSe, ZnSe/ZnS, and Cu-, Mn-doped ZnSe nanocrystals.

    PubMed

    Shen, Huaibin; Wang, Hongzhe; Li, Xiaomin; Niu, Jin Zhong; Wang, Hua; Chen, Xia; Li, Lin Song

    2009-12-21

    High quality zinc blende ZnSe and ZnSe/ZnS core/shell nanocrystals have been synthesized by two converse injection methods (i.e. zinc precursor injection or selenium precursor injection) when Se-ODE complex was chosen as the phosphine-free selenium precursor. Absorption spectroscopy, fluorescence spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to characterize the as-synthesized ZnSe and ZnSe/ZnS nanocrystals. The quality of the as-prepared ZnSe nanocrystals reached the same high level compared with the method using phosphine selenium precursors since the quantum yields were between 40 and 60% and photoluminescence (PL) full width at half-maximum (FWHM) was well controlled between 14 and 17 nm. The parameter window for the growth of high quality ZnSe nanocrystals was found to be much broader and monodisperse ZnSe nanocrystals were synthesized successfully even when the reaction temperature was set as low as 240 degrees C. As cores, such zinc blende ZnSe nanocrystals were also used to synthesize ZnSe/ZnS core/shell nanocrystals with high fluorescence quantum yields of 70%. Cu(2+) or Mn(2+) doped ZnSe nanocrystals were also synthesized by simply modifying this phosphine-free method. The emission range has been extended to 500 and 600 nm with the use of Cu(2+) and Mn(2+) dopants compared with the emission coverage of ZnSe at around 400 nm. This is the first totally "green approach" (i.e. phosphine-free synthesis) for the synthesis of high quality ZnSe, ZnSe/ZnS, and Cu(2+) or Mn(2+) doped ZnSe nanocrystals.

  18. Relaxation of hot excitons in CdZnSe/ZnSe quantum wells and quantum dots

    NASA Astrophysics Data System (ADS)

    Spiegel, R.; Bacher, G.; Breitwieser, O.; Forchel, A.; Jobst, B.; Hommel, D.; Landwehr, G.

    1998-05-01

    The relaxation dynamics of hot excitons was studied in (Zn,Cd)Se/ZnSe quantum wells and quantum dots. A fast population of the radiative excitonic ground state occurs for an excitation excess energy corresponding to an integer number of optical phonon energies. This is indicated by a spectrally narrow photoluminescence peak observed immediately after the exciting laser pulse. Spatial diffusion of excitons, controlled by the interaction between excitons and acoustic phonons, causes a distinct linewidth broadening with increasing delay time in quantum wells. In contrast, this process is found to be strongly suppressed in quantum dots.

  19. 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.

  20. 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.

  1. Spectroscopic Properties of Se 2-2and Se -2in Cancrinite

    NASA Astrophysics Data System (ADS)

    Lindner, Gottlieb-Georg; Hoffmann, Katrin; Witke, Klaus; Reinen, Dirk; Heinemann, Christoph; Koch, Wolfram

    1996-10-01

    Selenium has been introduced into the cancrinite matrix by hydrothermal methods. Hereby uniform red-brown hexagonal crystals of very good quality up to 4 × 1 × 1 mm in size have been obtained. Selenium was found to be homogeneously distributed in cancrinite-in contrast to post-synthesis loading. UV/VIS and Raman investigations identify Se2-2as the predominating coloring species besides Se-2. Because of the high optical anisotropy of cancrinite (⊥c, ∥c) strong polarization effects were detected.

  2. [Design and implementation of the ELSA-Brasil biobank: a prospective study in a Brazilian population].

    PubMed

    Pereira, Alexandre C; Bensenor, Isabela M; Fedeli, Ligia M; Castilhos, Cristina; Vidigal, Pedro G; Maniero, Viviane; Leite, Claudia M; Pimentel, Robercia A; Duncan, Bruce B; Mill, Jose Geraldo; Lotufo, Paulo A

    2013-06-01

    The Brazilian Longitudinal Study for Adult Health (ELSA-Brasil) is a multicenter prospective cohort of civil servants designed to assess the determinants of chronic diseases, especially cardiovascular diseases and type 2 diabetes. The present article describes the main design and implementation points of the ELSA-Brasil biobank project. Economic, political, logistical and technological aspects of this study are characterized. Additionally, it discusses the final biorepository protocol and the facilities implemented to achieve this objective. The design and implementation process of the ELSA-Brasil biobank took three years to be performed. Both the central and local biobanks were built according to the best biorepository techniques, using different technological solutions for the distinct needs expected in this study.

  3. Improvement of dispersion stability and optical properties of CdSe/ZnSe structured quantum dots by polymer coating.

    PubMed

    Kwon, Young-Tae; Eom, Nu Si A; Choi, Yo-Min; Kim, Bum-Sung; Kim, Taek-Soo; Lee, Chan-Gi; Lee, Kun-Jae; Choa, Yong-Ho

    2014-10-01

    In this study, CdSe core and CdSe/ZnSe core/shell quantum dots with a narrow size distribution were synthesized in a micro-reactor. A PMMA coating applied to the surface of CdSe/ZnSe core/shell QDs to prevent degradation gave improved dispersion stability compared to the CdSe core and CdSe/ZnSe core/shell. Many previous approaches to dispersion stability have not been quantitatively assessed. The dispersion stability was confirmed by multiple light scattering measurement. Additionally, the PMMA-coated CdSe/ZnSe QDs showed greatly improved optical properties with a photoluminescence quantum yield up to 80%. This structural motif is expected to prevent the degradation of QDs.

  4. Annealing tunes interlayer coupling and optoelectronic property of bilayer SnSe2/MoSe2 heterostructures

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Shang, Jimin; Yang, Yang; Wang, Rumei; Cheng, Xuerui

    2017-10-01

    By assembling two isolated monolayers, the vertical stacking heterostructure of SnSe2/MoSe2 is designed. The morphology of the SnSe2/MoSe2 vertical heterostructures is observed by optical microscope and atomic force microscope. Furthermore, through controlling different annealing time at the temperature 150 °C, the promoted field-effect performance of the SnSe2/MoSe2 heterostructures is observed. The underlying mechanism can be attributed to the increasing interlayer coupling along with the extended annealing time. On the other hand, due to the type-II band alignment, the electron will transfer from the MoSe2 to SnSe2, leading to the weaker photoluminescence intensity. The results show that the field-effect performance can be greatly improved via appropriate annealing time, exhibiting great potential application of the SnSe2/MoSe2 heterostructure in optoelectronic devices.

  5. Structural, optical and electrical properties of vacuum evaporated PbSe/ZnSe multilayer thin films

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    Multilayer thin films structures have received wide-spread attention due to their fast response and high efficiency. In this paper, we report the properties of PbSe/ZnSe multilayer thin films prepared by vacuum evaporation technique by sequential deposition of individual compounds. The prominent peak corresponding to (2 0 0) plane was observed in the Xray diffractogram with cubic crystal structure. The size of the crystallites are found to be 8 nm and 14 nm for the three-layer and five-layer films respectively. The absorption edge starts at 430 nm for the three-layer structures while that for the fivelayer film starts at 480 nm. The calculated optical band gaps of the three-layer and five-layer PbSe/ZnSe multilayer films are found to be 1.7 eV and 1.9 eV respectively. The electrical resitivities are found to be 2.8 × 107 Ω-cm for the three-layer film and 1.02 Ω cm for the five-layer film. The various electrical properties of the films such as mobility, carrier concentration and sheet resistance also are discussed in this paper.

  6. 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.

  7. Heteroepitaxial growth of SnSe films by pulsed laser deposition using Se-rich targets

    NASA Astrophysics Data System (ADS)

    Inoue, Takeshi; Hiramatsu, Hidenori; Hosono, Hideo; Kamiya, Toshio

    2015-11-01

    Epitaxial growth of SnSe was studied using pulsed laser deposition on three kinds of single-crystalline substrates, MgO (100), NaCl (100), and SrF2 (100), along with silica glass. For polycrystalline SnSe grown on glass, we found that a 20% Se-rich polycrystalline target is effective for obtaining stoichiometric SnSe films. The crystal structure of all the obtained films was the same as that of bulk SnSe, and the optimum temperatures for epitaxial growth were 400-500 °C, where the highest temperature was limited by re-evaporation. All the epitaxial films exhibited an a-axis orientation. For in-plane epitaxial structures, a quasi cube-on-cube heteroepitaxy was observed for MgO, whereas a 45°-rotated heteroepitaxy was observed for NaCl and SrF2, which can be explained by in-plane lattice matching. The anisotropic lattice mismatching and thermal expansion explain the compressive strain induced along the in-plane c-axis and the tensile strains along the in-plane b-axis and the out-of-plane a-axis. The epitaxial films on NaCl exhibited the best crystallinity, but the highest hole mobility of 60 cm2/(V s) was obtained on MgO. The indirect optical gap of the best films was determined to be 0.8 eV. Plausible interface models were proposed based on density functional calculations.

  8. 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. Copyright © 2011 Elsevier Ltd. All rights reserved.

  9. Purification and identification of Se-containing antioxidative peptides from enzymatic hydrolysates of Se-enriched brown rice protein.

    PubMed

    Liu, Kunlun; Zhao, Yan; Chen, Fusheng; Fang, Yong

    2015-11-15

    As a further study of Se-containing proteins (Se-Pro) derived from Se-enriched brown rice (Se-BR), this paper aimed to purify and identify Se-containing antioxidative peptides (Se-antioxi-Peps) from Se-Pro hydrolysates. The total Se content in Se-BR was 6.26μg/g DW, and selenocystine, Se-methylselenocysteine, and selenomethionine were identified as the main organic Se species by high-performance liquid chromatography-inductively coupled plasma mass spectrometry. Se-Pro was extracted and hydrolyzed by four types of proteases, and Alcalase was chosen as the optimum enzyme according to the degree of hydrolysis (DH). The hydrolysate with 17.08% DH possessing the highest DPPH radical scavenging activity was separated into five fractions (F1 to F5). Fractions F3 to F5, which had high antioxidative activities, were further separated. Sub-fractions F3-3, F4-2, and F5-1 were chosen to evaluate antioxidative activities and analyze Se species. The Se-antioxi-Pep with the sequence SeMet-Pro-Ser was identified by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Copyright © 2015 Elsevier Ltd. All rights reserved.

  10. Dielectric relaxation of CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Das, Sayantani; Dutta, Alo; Ghosh, Binita; Banerjee, Sourish; Sinha, T. P.

    2014-11-01

    Nanoparticles of cadmium selenide (CdSe) have been synthesized by soft chemical route using mercaptoethanol as a capping agent. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to sphalerite structure with the average particle size of 25 nm. The band gap of the material is found to be 2.1 eV. The photoluminescence (PL) emission spectra of the sample are measured at various excitation wavelengths. The PL spectra appear in the visible region, and the emission feature depends on the wavelength of the excitation. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 323 to 473 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). The dielectric relaxation of the sample is investigated in the electric modulus formalism. The temperature dependent relaxation times obey the Arrhenius law. The Havriliak-Negami model is used to investigate the dielectric relaxation mechanism in the sample. The frequency dependent conductivity spectra are found to obey the power law.

  11. 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.

  12. 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.

  13. Substitution for petroleum products in Brasil: Urgent issues

    SciTech Connect

    de Araujo, J.L.; Ghirardi, A.

    1986-06-01

    Brazililan energy policy during the last decade has focused on the replacement of imported petroleum with domestic energy sources, combined with efforts at conservation. The substitution results, however, have been more spectacular by far. The strategy of replacement is based on two elements. first, to increase domestic petroleum exploration and production. Second, to promote non-petroleum fuels as alternatives to the industrial and transportation sectors, for the substitution of fuel oil and gasoline, respectively. A combination of the substitution strategy, the country's petroleum refining structure, and the composition of the substitution strategy, the country's petroleum refining structure, and the composition of demand, has resulted in large surpluses of both gasoline and fuel oil, while diesel has become the most used among petroleum products. The surpluses are not easily exportable because there is ample availability of fuel oil in the world market, and because the low octane number of the gasoline produced in Brasil is not compatible with the engines of cars elsewhere in the region and in the world. Furthermore, although gasoline might be upgraded, the question remains that prospects for the world market are not encouraging, and an export-based strategy does not seem justified in view of the growing surpluses. The objective of this analysis is to review the mechanisms of themajor petroleum-substitution programs currently in existence, identifying their past impact on the energy market and the possible consequences of changes in the goals and operating conditions of these programs, in the light of the new prospects for increased domestic oil production and self-sufficiency. 23 refs., 2 figs., 1 tab.

  14. Atomic structure of the two intermediate phase glasses SiSe4 and GeSe4

    NASA Astrophysics Data System (ADS)

    Massobrio, Carlo; Celino, Massimo; Salmon, Philip S.; Martin, Richard A.; Micoulaut, Matthieu; Pasquarello, Alfredo

    2009-05-01

    The microscopic origin of the intermediate phase in two prototypical covalently bonded AxB1-x network glass forming systems, where A=Ge or Si, B=Se , and 0≤x≤1 , was investigated by combining neutron diffraction with first-principles molecular-dynamics methods. Specifically, the structure of glassy GeSe4 and SiSe4 was examined, and the calculated total structure factor and total pair-correlation function for both materials are in good agreement with experiment. The structure of both glasses differs markedly from a simple model comprising undefective AB4 corner-sharing tetrahedra in which all A atoms are linked by B2 dimers. Instead, edge-sharing tetrahedra occur and the twofold coordinated Se atoms form three distinct structural motifs, namely, Se-Se2 , Se-SeGe (or Se-SeSi), and Se-Ge2 (or Se-Si2 ). This identifies several of the conformations that are responsible for the structural variability in GexSe1-x and SixSe1-x glasses, a quantity that is linked to the finite width of the intermediate phase window.

  15. Se Isotopes as groundwater redox indicators: Detecting natural attenuation of Se at an in situ recovery U mine

    SciTech Connect

    Anirban, Basu; Schilling, Kathrin; Brown, Shaun T.; Johnson, Thomas M.; Christensen, John N.; Hartmann, Matt; Reimus, Paul William; Heikoop, Jeffrey Martin; Woldegabriel, Giday; DePaolo, Donald J.

    2016-08-22

    One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. Here in this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradient wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of $-$2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Moreover, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.

  16. Se Isotopes as groundwater redox indicators: Detecting natural attenuation of Se at an in situ recovery U mine

    SciTech Connect

    Anirban, Basu; Schilling, Kathrin; Brown, Shaun T.; Johnson, Thomas M.; Christensen, John N.; Hartmann, Matt; Reimus, Paul William; Heikoop, Jeffrey Martin; Woldegabriel, Giday; DePaolo, Donald J.

    2016-08-22

    One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. Here in this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradient wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of $-$2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Moreover, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.

  17. Se Isotopes as groundwater redox indicators: Detecting natural attenuation of Se at an in situ recovery U mine

    DOE PAGES

    Anirban, Basu; Schilling, Kathrin; Brown, Shaun T.; ...

    2016-08-22

    One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. Here in this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradientmore » wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of $-$2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Moreover, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.« less

  18. Se Isotopes as Groundwater Redox Indicators: Detecting Natural Attenuation of Se at an in Situ Recovery U Mine.

    PubMed

    Basu, Anirban; Schilling, Kathrin; Brown, Shaun T; Johnson, Thomas M; Christensen, John N; Hartmann, Matt; Reimus, Paul W; Heikoop, Jeffrey M; Woldegabriel, Giday; DePaolo, Donald J

    2016-10-04

    One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. In this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradient wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ(82)SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ(82)Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of -2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Furthermore, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.

  19. Cu2ZnSnSe4 thin-film solar cells fabricated using Cu2SnSe3 and ZnSe bilayers

    NASA Astrophysics Data System (ADS)

    Kim, Kang Min; Liao, Kuang Hsiang; Tampo, Hitoshi; Shibata, Hajime; Niki, Shigeru

    2015-04-01

    Evaporated Cu2SnSe3 (CTSe) and ZnSe bilayers are used as precursors for the fabrication of Cu2ZnSnSe4 (CZTSe) thin films. Large grains (i.e., >1 µm) in CZTSe were obtained at a relatively low annealing temperature of 500 °C. The stacking order of precursors strongly affected the chemical composition of CZTSe thin films even under identical growth conditions. Zn loss in CTSe/ZnSe/Mo precursors occurred during CTSe deposition, whereas ZnSe/CTSe/Mo precursors showed improved stability in composition. The CZTSe solar cells fabricated using ZnSe/CTSe bilayer precursors with annealing showed a conversion efficiency of over 7%.

  20. Tailoring ZnSe-CdSe colloidal quantum dots via cation exchange: from core/shell to alloy nanocrystals.

    PubMed

    Groeneveld, Esther; Witteman, Leon; Lefferts, Merel; Ke, Xiaoxing; Bals, Sara; Van Tendeloo, Gustaaf; Donega, Celso de Mello

    2013-09-24

    We report a study of Zn(2+) by Cd(2+) cation exchange (CE) in colloidal ZnSe nanocrystals (NCs). Our results reveal that CE in ZnSe NCs is a thermally activated isotropic process. The CE efficiency (i.e., fraction of Cd(2+) ions originally in solution, Cdsol, that is incorporated in the ZnSe NC) increases with temperature and depends also on the Cdsol/ZnSe ratio. Interestingly, the reaction temperature can be used as a sensitive parameter to tailor both the composition and the elemental distribution profile of the product (Zn,Cd)Se NCs. At 150 °C ZnSe/CdSe core/shell hetero-NCs (HNCs) are obtained, while higher temperatures (200 and 220 °C) produce (Zn1-xCdx)Se gradient alloy NCs, with increasingly smoother gradients as the temperature increases, until homogeneous alloy NCs are obtained at T ≥ 240 °C. Remarkably, sequential heating (150 °C followed by 220 °C) leads to ZnSe/CdSe core/shell HNCs with thicker shells, rather than (Zn1-xCdx)Se gradient alloy NCs. Thermal treatment at 250 °C converts the ZnSe/CdSe core/shell HNCs into (Zn1-xCdx)Se homogeneous alloy NCs, while preserving the NC shape. A mechanism for the cation exchange in ZnSe NCs is proposed, in which fast CE takes place at the NC surface, and is followed by relatively slower thermally activated solid-state cation diffusion, which is mediated by Frenkel defects. The findings presented here demonstrate that cation exchange in colloidal ZnSe NCs provides a very sensitive tool to tailor the nature and localization regime of the electron and hole wave functions and the optoelectronic properties of colloidal ZnSe-CdSe NCs.

  1. Optical band gap study of a-Se and Se-Sb thin films

    NASA Astrophysics Data System (ADS)

    Kaur, Ramandeep; Singh, Palwinder; Thakur, Anup

    2016-05-01

    Amorphous selenium (a-Se) and a-Se95Sb5 alloy were prepared using melt quenching technique. X-ray diffraction (XRD) pattern confirmed the amorphous nature of the prepared samples. Composition of the prepared samples has been determined using Energy dispersive X-ray fluorescence (EDXRF) technique. Differential thermal analysis (DTA) confirmed the glassy nature of the prepared samples. Thin films of the prepared samples were deposited on glass substrate using thermal evaporation method. Amorphous nature of the deposited films was confirmed using XRD. Optical properties of these films were obtained from the UV-VIS transmission spectra, at normal incidence, over 200-1100 nm spectral range. The optical absorption edge was described by using the model given by the Tauc. Optical band gap of the deposited films was calculated using Tauc plot. Optical characterization showed that average transmission and optical band gap decreased with the addition of antinomy.

  2. 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.

  3. Mechanical properties of layered InSe and GaSe single crystals

    NASA Astrophysics Data System (ADS)

    Mosca, D. H.; Mattoso, N.; Lepienski, C. M.; Veiga, W.; Mazzaro, I.; Etgens, V. H.; Eddrief, M.

    2002-01-01

    The mechanical properties of InSe and GaSe single crystals have been studied by means of nanoindentation tests. Both bulk crystals are well ordered and present a predominant γ-type interlayer stacking sequence as determined by x-ray diffraction and transmission electron microscopy measurements. The course of plastic deformation induced in the crystals by application of a definite shear stress through the penetration of a Berkovich tip indicates that the deformation occurs predominantly by pop-in events along easy slip directions having a fairly elastic character between displacements. Hardness anisotropy along crystal axes is clearly seen and the measured elastic modulus presents a discrepancy smaller than 5% in comparison with theoretical calculations performed using previous experimental values of the elastic constants.

  4. CdSe nanorods dominate photocurrent of hybrid CdSe-P3HT photovoltaic cell.

    PubMed

    Schierhorn, Martin; Boettcher, Shannon W; Peet, Jeffrey H; Matioli, Elison; Bazan, Guillermo C; Stucky, Galen D; Moskovits, Martin

    2010-10-26

    Photovoltaic devices based on organic semiconductors require charge-separating networks (bulk heterojunctions) for optimal performance. Here we report on the fabrication of organic-inorganic photovoltaic devices with tailored (n-type) CdSe nanorod arrays aligned perpendicularly to the substrate. The nanorod lengths varied from 58 ± 12 to 721 ± 15 nm, while the diameters and inter-rod spacings were kept constant at 89.5 ± 7.5 and 41.3 ± 9.9 nm, respectively. Short-circuit densities improved linearly with nanorod length, resulting in power conversion efficiencies of up to 1.38% for cells with nanorods 612 ± 46 nm long. Notably, the cell's efficiency was dominated by exciton generation in the CdSe nanorods.

  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. ZnCdSe/ZnCdMgSe quantum well infrared photodetector.

    PubMed

    Ravikumar, Arvind P; Alfaro-Martinez, Adrian; Chen, Guopeng; Zhao, Kuaile; Tamargo, Maria C; Gmachl, Claire F; Shen, Aidong

    2012-09-24

    We report the design, fabrication and characterization of a II-VI Zn(0.51)Cd(0.49)Se / Zn0.45(Cd)0.42(Mg)(0.13)Se-based quantum well infrared photodetector (QWIP) with a bound to quasi-bound transition centered at 8.7 µm. The good growth quality of the epitaxial layers was verified by x-ray diffraction measurements. Absorption and photocurrent measurements yield results consistent with conventional III-V QWIPs. Photocurrent measurements reveal an exponential decrease with temperature. In addition, we also observe more than 4 orders of magnitude increase in photocurrent with applied bias. By compensating the drop in temperature performance with an increase in applied bias, we achieve an operating temperature of up to 140K and a responsivity of 1-10 µA/W.

  7. Optical band gap study of a-Se and Se-Sb thin films

    SciTech Connect

    Kaur, Ramandeep; Singh, Palwinder; Thakur, Anup

    2016-05-06

    Amorphous selenium (a-Se) and a-Se{sub 95}Sb{sub 5} alloy were prepared using melt quenching technique. X-ray diffraction (XRD) pattern confirmed the amorphous nature of the prepared samples. Composition of the prepared samples has been determined using Energy dispersive X-ray fluorescence (EDXRF) technique. Differential thermal analysis (DTA) confirmed the glassy nature of the prepared samples. Thin films of the prepared samples were deposited on glass substrate using thermal evaporation method. Amorphous nature of the deposited films was confirmed using XRD. Optical properties of these films were obtained from the UV-VIS transmission spectra, at normal incidence, over 200-1100 nm spectral range. The optical absorption edge was described by using the model given by the Tauc. Optical band gap of the deposited films was calculated using Tauc plot. Optical characterization showed that average transmission and optical band gap decreased with the addition of antinomy.

  8. Highly efficient multifunctional MnSe/ZnSeS quantum dots for biomedical applications

    NASA Astrophysics Data System (ADS)

    Armijo, Leisha M.; Akins, Brian A.; Plumley, John B.; Rivera, Antonio C.; Withers, Nathan J.; Cook, Nathaniel C.; Smolyakov, Gennady A.; Huber, Dale L.; Smyth, Hugh D. C.; Osińki, Marek

    2013-03-01

    Colloidal quantum dots (QDs) are of interest for a variety of biomedical applications, including bioimaging, drug targeting, and photodynamic therapy. However, a significant limitation is that highly efficient photoluminescent QDs available commercially contain cadmium. Recent research has focused on cadmium-free QDs, which are anticipated to exhibit significantly lower cytotoxicity. Previous work has focused on InP and ZnO as alternative semiconductor materials for QDs. However, these nanoparticles have been shown to be cytotoxic. Recently, we have synthesized high quantum efficiency (exceeding 90%), color tunable MnSe/ZnSeS nanoparticles, as potentially attractive QDs for biomedical applications. Additionally, the manganese imparts magnetic properties on the QDs, which are important for magnetic field-guided transport, hyperthermia, and potentially magnetic resonance imaging (MRI). The QDs can be further biofunctionalized via conjugation to a ligand or a biomarker of disease, allowing combination of drug delivery with visual verification and colocalization due to the color tunability of the QDs.

  9. LETTER TO THE EDITOR: Raman investigation of InSe and GaSe single-crystals oxidation

    NASA Astrophysics Data System (ADS)

    Balitskii, O. A.; Savchyn, V. P.; Yukhymchuk, V. O.

    2002-02-01

    We discuss the Raman scattering of thermally oxidized gallium selenide (GaSe) and indium selenide (InSe) single crystals. It has been established that the oxidation mechanisms of these compounds are rather different. For InSe, an increase of the oxidation temperature leads to the formation of (SeO4) complexes. For GaSe, it is characteristic that only Ga2O3 is formed as an oxygen-containing phase during the oxidation. The presence of the Me2Se3 phase (where Me is Ga or In) in its own oxide is common for both of the semiconductors.

  10. 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.

  11. 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

  12. Photoelectric processes in CdSe thin film solar cells

    SciTech Connect

    Rickus, E.

    1984-05-01

    Efficiencies exceeding 7 percent have been achieved with CdSe/ZnSe/Au thin film solar cells. The collection efficiency of carriers in highly oriented CdSe films is near unity, resulting in short circuit current densities comparable to values observed on single crystalline cells. Recombination of carriers at the CdSe/ZnSe interface plays a minor role. CdSe /SUB x/ Te /SUB 1-x/ cells show the potential of enhanced short circuit current densities. Crystallographic and chemical inhomogeneities have a major influence on their performance. The comparison of photoelectrochemical cells based on CdSe single crystals and on polycrystalline layers demonstrates the photovoltaic quality of our CdSe films.

  13. Electronic structure of the GaSe/Si(111) and InSe/Si(111) heterojunctions

    NASA Astrophysics Data System (ADS)

    Camara, M. O.; Mauger, A.; Devos, I.

    2002-05-01

    A tight-binding calculation of the electronic properties of the semiconductor GaSe/Si(111) and InSe/Si(111) heterojunctions is performed in a charge-dependent tight binding approach where the only Coulomb effect is a shift of all the pseudoatomic levels of a given atom at site i by the same quantity Ui. The fitting parameters Ui are determined in the framework of constrained optimization techniques using the conjugate gradient method. The band offsets at the interfaces are determined and found to be in quantitative agreement with recent experiments on both heterojunctions. In addition, this optimization technique allows us to give more insight in the charge transfer between atomic planes at the heterojunction. As a result of the the strain induced by the lattice mismatch of the III-VI half layer grafted to the Si(111) surface the charge distribution does not match the simple charge neutrality condition in the case of InSe/Si(111).

  14. 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.

  15. 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.

  16. Deposition of stoichiometric Bi2Se3 film by vacuum-thermal treatment of Se/Bi heterostructure

    NASA Astrophysics Data System (ADS)

    Kogai, V. Ya.; Mikheev, K. G.; Mikheev, G. M.

    2017-08-01

    The possibility of obtaining a stoichiometric Bi2Se3 film by vacuum-thermal treatment of a Se/Bi heterostructure is demonstrated for the first time. It was found that a stoichiometric Bi2Se3 film can be only produced at a certain ratio of the Se and Bi film thicknesses ( d Se/ d Bi = 3.13). X-ray-diffraction analysis and Raman spectroscopy were used to study the phase transformations in a Se(141 nm)/Bi(45 nm) heterostructure upon its thermal treatment in a vacuum. The phase transition temperatures at which various crystalline phases are formed were determined. It is shown that Bi2Se3 crystallizes in the Se(141 nm)/Bi(45 nm) heterostructure heated to 493 K in conformity with an exponential law, with a characteristic time in which the equilibrium state is attained equal to 20 min.

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

    DOE PAGES

    Li, Xufan; Lin, Ming-Wei; Lin, Junhao; ...

    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

  18. Spectral anisotropy of a photoresponse from heterojunctions based on GaSe and InSe layered crystals

    NASA Astrophysics Data System (ADS)

    Katerinchuk, V. N.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.

    2014-03-01

    The object of investigation is photoresponse spectra taken from the cleaved end face of heterojunctions formed by GaSe and InSe anisotropic crystals. Spectra taken from the as-prepared and chemically processed faces of the heterojunctions are compared. A modified method of growing GaSe crystals with a virgin end face is suggested, and the surface of GaSe crystals thus grown is examined by atomic force microscopy.

  19. 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.

  20. 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

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

    SciTech Connect

    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 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 the 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.

  2. Molecular and biochemical characterization of the selenocysteine Se-methyltransferase gene and Se-methylselenocysteine synthesis in broccoli.

    PubMed

    Lyi, Sangbom M; Heller, Laurence I; Rutzke, Michael; Welch, Ross M; Kochian, Leon V; Li, Li

    2005-05-01

    Selenium (Se) plays an indispensable role in human nutrition and has been implicated to have important health benefits, including being a cancer preventative agent. While different forms of Se vary in their anticarcinogenic efficacy, Se-methylselenocysteine (SeMSC) has been demonstrated to be one of the most effective chemopreventative compounds. Broccoli (Brassica oleracea var. italica) is known for its ability to accumulate high levels of Se with the majority of the selenoamino acids in the form of Se-methylselenocysteine. Therefore, it serves as a good model to study the regulation of SeMSC accumulation in plants. A cDNA encoding selenocysteine Se-methyltransferase, the key enzyme responsible for SeMSC formation, was cloned from broccoli using a homocysteine S-methyltransferase gene probe from Arabidopsis (Arabidopsis thaliana). This clone, designated as BoSMT, was functionally expressed in Escherichia coli, and its identity was confirmed by its substrate specificity in the methylation of selenocysteine. The BoSMT gene represents a single copy sequence in the broccoli genome. Examination of BoSMT gene expression and SeMSC accumulation in response to selenate, selenite, and sulfate treatments showed that the BoSMT transcript and SeMSC synthesis were significantly up-regulated in plants exposed to selenate but were low in plants supplied with selenite. Simultaneous treatment of selenate with selenite significantly reduced SeMSC production. In addition, high levels of sulfate suppressed selenate uptake, resulting in a dramatic reduction of BoSMT mRNA level and SeMSC accumulation. Our results reveal that SeMSC accumulation closely correlated with the BoSMT gene expression and the total Se status in tissues and provide important information for maximizing the SeMSC production in this beneficial vegetable plant.

  3. 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.

  4. 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.

  5. 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.

  6. Impact of ⁷⁷Te on the structure and Se NMR spectra of Se-rich Ge-Te-Se glasses: a combined experimental and computational investigation.

    PubMed

    Bouëssel du Bourg, Lila; Roiland, Claire; le Pollès, Laurent; Deschamps, Michaël; Boussard-Plédel, Catherine; Bureau, Bruno; Pickard, Chris J; Furet, Eric

    2015-11-21

    Selenium-rich Ge-Te-Se glasses have been synthesized along the GeSe4-GeTe4 pseudo-composition line and acquired by (77)Se Hahn echo magic-angle spinning NMR. The comparison with the GeSe4 spectrum shows a drastic modification of the typical double-resonance lineshape even at low Te concentrations (<10%). In order to rationalize this feature and to understand the effect of Te on the structure of our glasses, first-principles molecular dynamics simulations and gauge including projector augmented wave NMR parameter calculations have been performed. The distribution of the tellurium atoms in the selenium phase was shown to be mainly responsible for the (77)Se lineshape changes. Another possible factor related to the perturbation of the δiso value due to Te proximity appears to be much more limited in the bulk, while the results obtained using molecular models suggest shifts of several hundreds of ppm.

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

    SciTech Connect

    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%.

  8. DEZ ANOS DE EXPERIÊNCIA DO COMITÊ DE ÉTICA EM PESQUISA DA SECRETARIA DE SAÚDE DO DISTRITO FEDERAL, BRASIL

    PubMed Central

    Novaes, Maria Rita C. G.; Guilhem, Dirce; Lolas, Fernando

    2009-01-01

    O objetivo deste artigo é relatar a experiência do Comitê de Ética em Pesquisa da Secretaria de Estado de Saúde do Distrito Federal (CEP/SES/DF) Brasil, durante o período de 10 anos a partir de sua fundação. Trata-se de uma avaliação descritiva e documental, na modalidade estudo de caso, utilizando-se a totalidade de projetos protocolados no CEP/SES/DF (N° 052/08) nesse período. As pendências mais freqüentes dos projetos foram: termo de consentimento livre e esclarecido (30%), folha de rosto (25%), metodologia (20%), curriculum vitae (12%), planilha de orçamento (9%), outros (4%). O relato das atividades do CEP/SES/DF no período de 10 anos revelou, através de sua produtividade, a legitimidade do processo de análise ética dos protocolos visando à proteção dos participantes da pesquisa. PMID:19888441

  9. Tracing biogeochemical Se cycling in seleniferous reclaimed mine soils

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    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 soil and natural water ecosystems. Specifically in southeastern Idaho, historic and on-going phosphate mining have resulted in Se-enriched soils throughout the region. Previous work has shown that different Se oxidation states (i.e. Se(IV) and Se(VI)) impact fungal growth and aerobic Se reduction(to Se(0)) very differently, though in practice Se speciation is rarely measured in soils. We have utilized multiple methods to analyze both total Se and identify chemical forms of Se contained in the soil. Reclaimed mine soils at this site range from relatively low Se content (1 ppm) to enriched (70 ppm) with a wide range of chemical forms. Selenium content in the rhizosphere of several enriched locations is also enriched compared to the bulk soil in the same location. We have isolated a wide variety of aerobic selenium transforming and tolerant microorganisms ( 175 bacteria and 75 fungi), from across the many mine-locations and undisturbed reference locations, indicating that selenium transformation is likely a widespread trait in soil organisms residing in Se-contaminated environments. Currently, we are also working to establish the overall microbial community in these soils, and comparing solid-state and wet-chemical measurements of Se chemical forms. This will help to provide reliable methods for practitioners to understand Se cycling, mobility and bioavailability in selenium-contaminated areas.

  10. Shell deposition of CdSe nano dots and rods

    NASA Astrophysics Data System (ADS)

    Yang, Ping; Chen, Hsueh Shin; Zhang, Qiang; Shi, Ruixia; Wang, Junpeng; Che, Quande

    2014-08-01

    To investigate the shell deposited kinetics, CdSe quantum dots (QDs) and nanorods (NRs) with a maximum length of 17 nm were fabricated via organic synthesis routes. CdSe with a hexagonal crystal structure (wurtzite) favors epitaxial growth on the {002} surfaces when well-controlled conditions were used. The morphologies and sizes of CdSe samples depended strongly on chemicals and temperature. In the case of 320 °C, CdSe NRs with adjusted length of 7-17 nm were obtained from trioctylphosphine oxide (TOPO) and tetradecylphosphonic acid (TDPA). In contrast, short CdSe NRs (less than 10 nm) were created from octadecylphosphonic acid (ODPA) and trioctylamine (TOA). Spherical CdSe QDs were further fabricated using stearic acid (SA) and TOPO at 300 °C. CdSe cores were coated with Cd0.5Zn0.5S and CdTe shells. Anisotropic growth occurred during shell deposition because CdS shells grown preferentially on the {001} facet of the CdSe core. In the case of CdSe core prepared from TOPO and TDPA, CdSe/Cd0.5Zn0.5S core/shell samples prepared from long CdSe NRs (more than 10 nm) revealed a peanut morphology while the core/shell samples created from short ones (less than 10 nm) exhibited a spherical morphology. All of the CdSe/Cd0.5Zn0.5S core/shell samples revealed a similar length to that of the CdSe cores. This phenomenon was also observed for the core/shell samples fabricated using CdSe NRs prepared by ODPA and TOA. This is ascribed to the well-developed crystal structure of CdSe NRs fabricated using an organic synthesis at high temperature. In contrast, this anisotropic growth did not occur when spherical CdSe QDs prepared from SA and TOPO and the shell (Cd0.5Zn0.5S) coating carried out using SA and TOA. To indicate the shell depositing process, CdSe NRs fabricated using TDPA and TOPO were coated with a CdTe shell. CdTe monomers were deposited on the middle and tip parts of the CdSe NRs to form a tetrapod-like morphology at 220 °C. This is ascribed to the large difference of

  11. Luminescence and photoelectric spectra of ZnSe/Cd xZn 1- xSe superlattices

    NASA Astrophysics Data System (ADS)

    Agafonov, E. N.; Georgobiani, A. N.; Lepnev, L. S.; Sadofyev, Yu. G.

    2003-11-01

    The electroluminescence and photovoltage spectra of the ZnSe/Cd xZn 1- xSe superlattices with non-doping layers, grown by molecular beam epitaxy, have been measured. Narrow lines in the range 500-560 nm have been observed in electroluminescence measurements at 77 and 293 K. Well-resolved peaks attributed to carrier excitation, as well as photosensitivity bands corresponding to the Cd xZn 1- xSe/ZnSe superlattice region and the ZnSe buffer layer, have been observed in photovoltaic measurements.

  12. Synthesis and Properties of ZnSe Precursor and ZnSe Nanoribbon Arrays on Zn Substrates

    SciTech Connect

    Zhao, L. J.; Pang, Q.; Cai, Y.; Luo, X. D.; Wang, N.; Ge, W. K.; Wang, J. N.; Fang, Y. P.; Wen, X. G.; Yang, S. H.

    2007-04-10

    Well-aligned ZnSe precursor nanoribbon arrays on zinc surface were fabricated via a solvothermal method using Zn foil as Zn source, Se powder as Se source and ethylenediamine (en) as solvent. The ZnSe nanoribbon arrays can be easily obtained by heating the ZnSe precursors in N2 at 300 deg. C for 5 hours. The as-prepared precursors as well as the annealed products are characterized by scanning electron microscopy and powder X-ray diffraction. Field emission (FE) experiments on annealed sample are also carried out.

  13. Bent Polytypic ZnSe and CdSe Nanowires Probed by Photoluminescence.

    PubMed

    Kim, Yejin; Im, Hyung Soon; Park, Kidong; Kim, Jundong; Ahn, Jae-Pyoung; Yoo, Seung Jo; Kim, Jin-Gyu; Park, Jeunghee

    2017-03-15

    Nanowires (NWs) have witnessed tremendous development over the past two decades owing to their varying potential applications. Semiconductor NWs often contain stacking faults due to the presence of coexisting phases, which frequently hampers their use. Herein, it is investigated how stacking faults affect the optical properties of bent ZnSe and CdSe NWs, which are synthesized using the vapor transport method. Polytypic zinc blende-wurtzite structures are produced for both these NWs by altering the growth conditions. The NWs are bent by the mechanical buckling of poly(dimethylsilioxane), and micro-photoluminescence (PL) spectra were then collected for individual NWs with various bending strains (0-2%). The PL measurements show peak broadening and red shifts of the near-band-edge emission as the bending strain increases, indicating that the bandgap decreases with increasing the bending strain. Remarkably, the bandgap decrease is more significant for the polytypic NWs than for the single phase NWs. This work provides insights into flexible electronic devices of 1D nanostructures by engineering the polytypic structures.

  14. Growth, structural and optical characterization of MBE {ZnCdSe}/{ZnSe} quantum wells

    NASA Astrophysics Data System (ADS)

    Reisinger, T.; Lankes, S.; Kastner, M. J.; Rosenauer, A.; Franzen, F.; Meier, M.; Gebhardt, W.

    1996-02-01

    {ZnCdSe}/{ZnSe} quantum wells (QW) were grown with molecular beam epitaxy (MBE) on GaAs(001) substrates cleaned with hydrogen plasma. Reflection high-energy electron diffraction (RHEED) was used for in-situ growth control of the QW structures. A quantitative evaluation of the RHEED oscillations yields an exact value of the growth rate. Furthermore, in comparing the growth rate of the barrier and the well a reasonable estimate of the Cd content is possible. The in-situ RHEED measurements were supplemented by ex-situ HRXRD and HRTEM investigations. The latter method was found to be especially useful to evaluate the Cd-concentration profile of the QWs by digital analysis of lattice images (DALI). X-ray rocking curves of MQWs were recorded which show well-resolved satellite peaks. A comparison with simulations based on dynamical diffraction theory yields the structural parameters such as well width, barrier width and composition of the QWs. The XRD and TEM results are compared with the parameters determined by RHEED. In addition, we performed photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy for optical characterization of the samples. The PLE spectra show an interference pattern which is explained by standing polariton waves.

  15. Evidence of thermally activated transfer of excited carriers between CdSe/ZnSe quantum dots

    NASA Astrophysics Data System (ADS)

    Zhang, X. B.; Ha, K. L.; Hark, S. K.

    2001-10-01

    Temperature dependent photoluminescence and cathodoluminescence of selfassembled CdSe/ZnSe quantum dots grown by metalorganic vapor phase deposition were investigated. We found an unusual large red shift and a narrowing of the photoluminescence peak with temperature increases. Cathodoluminescence studies of a small number of quantum dots showed that the broad peak observed in the photoluminescence spectra is, in fact, made up of a series of narrower peaks, coming from quantum dots of different sizes. While the intensity of luminescence from small dots drops monotonously with temperature rises, that from the large dots displays a peculiar behavior. It actually increases within the temperature range of 140 170 K, the same range in which the photoluminescence peak shows narrowing. The simultaneous increase of luminescence from some quantum dots and decrease from others are believed to be responsible for the red shift and narrowing of the observed photoluminescence peak. A simple analytically solvable rate equation model was used to understand the spectral data. We suggest that the unusual behaviors observed can be understood as resulting from a transfer of thermally activated carriers from small to large quantum dots.

  16. Investigation of biocompatible and protein sensitive highly luminescent quantum dots/nanocrystals of CdSe, CdSe/ZnS and CdSe/CdS

    NASA Astrophysics Data System (ADS)

    Ratnesh, R. K.; Mehata, Mohan Singh

    2017-05-01

    The size and shape dependent semiconductor quantum dots (0D nanoparticles) with color tunability demonstrating significant influence in a biological system and considered as ideal probes. Here, a non-coordinated colloidal approach was used for the synthesis of CdSe, CdSe/ZnS and CdSe/CdS core-shell quantum dots (QDs) of 3-4 nm. The synthesized nanocrystals show a high crystallinity, examined by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The core-shell semiconductor QDs exhibit stronger photoluminescence (PL) as compared to the core QDs. The strong PL with small full-width half maximum (FWHM) indicates that the prepared QDs have a nearly uniform size distribution and well dispersibility. The quantum yield (QY) of core-shell QDs increases due to the surface passivation. Further, the PL of BSA is quenched strongly by the presence of core-shell QDs and follows the well-known Stern-Volmer (S-V) relation, whereas the PL lifetime does not follow the S-V relation, demonstrating that the observed quenching is predominantly static in nature. Among CdSe core, CdSe/ZnS and CdSe/CdS core-shell QDs, the CdSe/ZnS QDs shows the least cytotoxicity and most biocompatibility. Thus, the prepared core-shell QDs are biocompatible and exhibit strong sensing ability.

  17. 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; ...

    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

  18. CuInSe/sub 2/-based photoelectrochemical cells: their use in characterization of thin CuInSe/sub 2/ films, and as photovoltaic cells per se

    SciTech Connect

    Cahen, D; Chen, Y W; Ireland, P J; Noufi, R; Turner, J A; Rincon, C; Bachmann, K J

    1984-05-01

    Photoelectrochemistry has been employed to characterize the p-CuInSe/sub 2/ component of the CdS/CuInSe/sub 2/ on-metal and a nonaqueous electrolyte containing a redox couple not specifically adsorbed onto the semiconductor, we can test the films for photovoltaic activity and obtain effective electronic properties of them, before CdS deposition, in a nondestructive manner. Electrochemical decomposition of CuInSe/sub 2/ was investigated in acetonitrile solutions to determine the mechanism of decomposition (n and p) in the dark and under illumination. Electrochemical, solution chemical and surface analyses confirmed at the light-assisted decomposition of CuInSe/sub 2/ resulted in metal ions and elemental chalcogen. On the basis of the results from the electrochemical decomposition, and studies on the solid state chemistry of the (Cu/sub 2/Se)/sub x/(In/sub 2/Se/sub 3/)/sub 1-x/ system and surface analyses, the CuInSe/sub 2//polyiodide interface was stabilized and up to 11.7% conversion efficiencies were obtained.

  19. Resonant tunneling transport in ZnxBe1-xSe/ZnSe/ZnyBe1-ySe asymmetric quantum structures

    NASA Astrophysics Data System (ADS)

    Sirkeli, Vadim P.; Yilmazoglu, Oktay; Al-Daffaie, Shihab; Oprea, Ion; Ong, Duu Sheng; Küppers, Franko; Hartnagel, Hans L.

    2017-05-01

    II-VI compounds are promising materials for the fabrication of room-temperature terahertz devices due to their beneficial properties like as type-I conduction band alignment, high breakdown field strength ( 331 kV/cm for ZnSe vs. 80 kV/cm for GaAs), and higher values of the conduction band offset (1.5 eV for BeSe/ZnSe vs. 0.7 eV for AlAs/GaAs). In this paper we report on numerical study of the resonant tunneling transport in ZnBeSe/ZnSe/ZnBeSe symmetric and asymmetric resonant tunneling diodes (RTDs). The negative differential resistance feature is observed in the current-voltage characteristics of the ZnSe-based RTDs. It is found that the maximum of peak-to-valley ratio (PVR) of the current density is equal to 6.025 and 7.144 at 150 K, and to 1.120 and 1.105 at 300 K for the symmetric and asymmetric RTDs, respectively. The effect of barrier heights on the frequency and output power performance of RTD devices are studied and discussed.

  20. Investigation of biocompatible and protein sensitive highly luminescent quantum dots/nanocrystals of CdSe, CdSe/ZnS and CdSe/CdS.

    PubMed

    Ratnesh, R K; Mehata, Mohan Singh

    2017-02-16

    The size and shape dependent semiconductor quantum dots (0D nanoparticles) with color tunability demonstrating significant influence in a biological system and considered as ideal probes. Here, a non-coordinated colloidal approach was used for the synthesis of CdSe, CdSe/ZnS and CdSe/CdS core-shell quantum dots (QDs) of 3-4nm. The synthesized nanocrystals show a high crystallinity, examined by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The core-shell semiconductor QDs exhibit stronger photoluminescence (PL) as compared to the core QDs. The strong PL with small full-width half maximum (FWHM) indicates that the prepared QDs have a nearly uniform size distribution and well dispersibility. The quantum yield (QY) of core-shell QDs increases due to the surface passivation. Further, the PL of BSA is quenched strongly by the presence of core-shell QDs and follows the well-known Stern-Volmer (S-V) relation, whereas the PL lifetime does not follow the S-V relation, demonstrating that the observed quenching is predominantly static in nature. Among CdSe core, CdSe/ZnS and CdSe/CdS core-shell QDs, the CdSe/ZnS QDs shows the least cytotoxicity and most biocompatibility. Thus, the prepared core-shell QDs are biocompatible and exhibit strong sensing ability.

  1. 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.

  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.

  3. 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

    2015-01-09

    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.

  4. 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.

  5. Effect of ZnSe/GaAs interface treatment in ZnSe quality control for optoelectronic device applications

    NASA Astrophysics Data System (ADS)

    Park, Kwangwook; Beaton, Daniel; Steirer, Kenneth X.; Alberi, Kirstin

    2017-05-01

    We investigate the role of interface initiation conditions on the growth of ZnSe/GaAs heterovalent heterostructures. ZnSe epilayers were grown on a GaAs surface with various degrees of As-termination and the application of either a Zn or Se pre-treatment. Structural analysis revealed that Zn pre-treatment of an As-rich GaAs surface suppresses Ga2Se3 formation at the interface and promotes the growth of high crystal quality ZnSe. This is confirmed with low-temperature photoluminescence. However, moderation of Ga-Se bonding through a Se pre-treatment of an As-rich GaAs surface can prevent excessive intermixing at the interface and promote excitonic emission in the underlying GaAs layer. These results provide guidance on how best to prepare heterovalent interfaces for various applications.

  6. 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.

  7. Effect of ZnSe/GaAs interface treatment in ZnSe quality control for optoelectronic device applications

    DOE PAGES

    Park, Kwangwook; Beaton, Daniel; Steirer, Kenneth X.; ...

    2017-01-27

    Here, we investigate the role of interface initiation conditions on the growth of ZnSe/GaAs heterovalent heterostructures. ZnSe epilayers were grown on a GaAs surface with various degrees of As-termination and the application of either a Zn or Se pre-treatment. Structural analysis revealed that Zn pre-treatment of an As-rich GaAs surface suppresses Ga2Se3 formation at the interface and promotes the growth of high crystal quality ZnSe. This is confirmed with low-temperature photoluminescence. However, moderation of Ga-Se bonding through a Se pre-treatment of an As-rich GaAs surface can prevent excessive intermixing at the interface and promote excitonic emission in the underlying GaAsmore » layer. These results provide guidance on how best to prepare heterovalent interfaces for various applications.« less

  8. Synthesis of CdSe Quantum Dots Using Fusarium oxysporum.

    PubMed

    Yamaguchi, Takaaki; Tsuruda, Yoshijiro; Furukawa, Tomohiro; Negishi, Lumi; Imura, Yuki; Sakuda, Shohei; Yoshimura, Etsuro; Suzuki, Michio

    2016-10-20

    CdSe quantum dots are often used in industry as fluorescent materials. In this study, CdSe quantum dots were synthesized using Fusarium oxysporum. The cadmium and selenium concentration, pH, and temperature for the culture of F. oxysporum (Fusarium oxysporum) were optimized for the synthesis, and the CdSe quantum dots obtained from the mycelial cells of F. oxysporum were observed by transmission electron microscopy. Ultra-thin sections of F. oxysporum showed that the CdSe quantum dots were precipitated in the intracellular space, indicating that cadmium and selenium ions were incorporated into the cell and that the quantum dots were synthesized with intracellular metabolites. To reveal differences in F. oxysporum metabolism, cell extracts of F. oxysporum, before and after CdSe synthesis, were compared using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results suggested that the amount of superoxide dismutase (SOD) decreased after CdSe synthesis. Fluorescence microscopy revealed that cytoplasmic superoxide increased significantly after CdSe synthesis. The accumulation of superoxide may increase the expression of various metabolites that play a role in reducing Se(4+) to Se(2-) and inhibit the aggregation of CdSe to make nanoparticles.

  9. 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.

  10. PREVALENCE AND FACTORS ASSOCIATED WITH VITAMIN B12 DEFICIENCY IN ELDERLY FROM VIÇOSA/MG, BRASIL.

    PubMed

    Oliveira Martinho, Karina; Luiz Araújo Tinôco, Adelson; Queiroz Ribeiro, Andréia

    2015-11-01

    La prevalencia de deficiencia nutricional de vitamina B12 aumenta con la edad y es especialmente común en la población mayor. El objetivo de este estudio consistió en determinar su prevalencia y los factores asociados a esta carencia en mayores no institucionalizados de Viçosa, Estado de Minas Gerais, Brasil. Métodos: estudio poblacional interseccional, realizado para identificar la prevalencia y los factores asociados a deficiencia de vitamina B12 entre la población de mayores en Viçosa (MG). Los datos fueron recopilados desde agosto de 2011 hasta junio de 2012 mediante una encuesta en los hogares y pruebas hematológicas y bioquímicas realizadas en 340 mayores. Resultados: la prevalencia de deficiencia de vitamina B12 en este grupo fue del 17,4% (95% CI, 13,4% - 21,4%). La deficiencia cognitiva se presenta como un factor importante relacionado con la deficiencia de vitamina B12. Conclusiones: el informe actual contribuye a los estudios que destacan ciertos factores que podrían afectar al rendimiento de las personas mayores en su proceso de envejecimiento natural, especialmente cuando estos factores están asociados con deficiencia cognitiva y dan lugar a una discapacidad significativa así como pérdida de calidad de vida. Así, los resultados aquí presentados han servido para aportar un conocimiento más comprensivo sobre la relación entre deficiencia de B12 y su impacto sobre este grupo de población. También han demostrado su relevancia de cara a la planificación de programas e iniciativas de salud pública centrados en este grupo de población.

  11. Atomic Defects and Doping of Monolayer NbSe2.

    PubMed

    Nguyen, Lan; Komsa, Hannu-Pekka; Khestanova, Ekaterina; Kashtiban, Reza J; Peters, Jonathan J P; Lawlor, Sean; Sanchez, Ana M; Sloan, Jeremy; Gorbachev, Roman V; Grigorieva, Irina V; Krasheninnikov, Arkady V; Haigh, Sarah J

    2017-03-28

    We have investigated the structure of atomic defects within monolayer NbSe2 encapsulated in graphene by combining atomic resolution transmission electron microscope imaging, density functional theory (DFT) calculations, and strain mapping using geometric phase analysis. We demonstrate the presence of stable Nb and Se monovacancies in monolayer material and reveal that Se monovacancies are the most frequently observed defects, consistent with DFT calculations of their formation energy. We reveal that adventitious impurities of C, N, and O can substitute into the NbSe2 lattice stabilizing Se divacancies. We further observe evidence of Pt substitution into both Se and Nb vacancy sites. This knowledge of the character and relative frequency of different atomic defects provides the potential to better understand and control the unusual electronic and magnetic properties of this exciting two-dimensional material.

  12. 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.

  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. The synthesis and photocatalytic activity of ZnSe microspheres

    NASA Astrophysics Data System (ADS)

    Cao, Huaqiang; Xiao, Yujiang; Zhang, Sichun

    2011-01-01

    This paper reports the synthesis of semiconductor ZnSe microspheres composed of nanoparticles via a solvothermal route between the organic molecule selenophene (C4H4 Se) and ZnCl2 without adding any surfactant. The ZnSe microspheres were characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), specific surface area measurement, and photoluminescence (PL) spectra. A strong and broad blue PL emission at 443 nm in wavelength (~2.79 eV in photon energy) is attributed to the near-band-edge (NBE) emission of ZnSe, while the 530 nm peak is a defect-related (DL) emission. The photocatalytic activity of the as-prepared ZnSe microspheres was evaluated by photodegradation of methyl orange (MO) dye under ultraviolet (UV) light and visible light irradiation. The degradations of MO reach 94% or 95.1%, close to 100%, in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 7 or 10 h under UV irradiation, respectively. Meanwhile the degradations of MO reach 94.3% or 60.6% in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 12 h, respectively. The degradation rate of ZnSe microspheres is twice that of ZnSe commercial powder under UV light irradiation, and three times under visible light irradiation. The degradation process of MO dye on ZnSe microspheres under UV or visible light is also discussed.

  15. The synthesis and photocatalytic activity of ZnSe microspheres.

    PubMed

    Cao, Huaqiang; Xiao, Yujiang; Zhang, Sichun

    2011-01-07

    This paper reports the synthesis of semiconductor ZnSe microspheres composed of nanoparticles via a solvothermal route between the organic molecule selenophene (C(4)H(4) Se) and ZnCl(2) without adding any surfactant. The ZnSe microspheres were characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), specific surface area measurement, and photoluminescence (PL) spectra. A strong and broad blue PL emission at 443 nm in wavelength (∼2.79 eV in photon energy) is attributed to the near-band-edge (NBE) emission of ZnSe, while the 530 nm peak is a defect-related (DL) emission. The photocatalytic activity of the as-prepared ZnSe microspheres was evaluated by photodegradation of methyl orange (MO) dye under ultraviolet (UV) light and visible light irradiation. The degradations of MO reach 94% or 95.1%, close to 100%, in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 7 or 10 h under UV irradiation, respectively. Meanwhile the degradations of MO reach 94.3% or 60.6% in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 12 h, respectively. The degradation rate of ZnSe microspheres is twice that of ZnSe commercial powder under UV light irradiation, and three times under visible light irradiation. The degradation process of MO dye on ZnSe microspheres under UV or visible light is also discussed.

  16. Cr:ZnSe guided wave lasers and materials

    NASA Astrophysics Data System (ADS)

    McDaniel, Sean; Lancaster, Adam; Stites, Ronald; Thorburn, Fiona; Kar, Ajoy; Cook, Gary

    2017-02-01

    We describe a variety of technological advances in the development of efficient, powerful, and continuously tunable Cr:ZnSe lasers operating in the 2.3-2.7 μm spectral region. This includes the development of compact "single chip" waveguide Cr:ZnSe lasers, waveguide mode-locked Cr:ZnSe lasers, and the creation of homogeneously broadened laser material.

  17. Ab initio phonon thermal transport in monolayer InSe, GaSe, GaS, and alloys.

    PubMed

    Pandey, Tribhuwan; Parker, David; Lindsay, Lucas

    2017-09-08

    We compare vibrational properties and phonon thermal conductivities (κ) of monolayer InSe, GaSe, and GaS systems using density functional theory and Peierls-Boltzmann transport methods. In going from InSe to GaSe to GaS, system mass decreases giving both increasing acoustic phonon velocities and decreasing scattering of these heat-carrying modes with optic phonons, ultimately giving κ<sub>InSe</sub> < κ<sub>GaSe</sub> < κ<sub>GaS</sub>. This behavior is demonstrated by correlating the scattering phase space limited by fundamental conservation conditions with mode scattering rates and phonon dispersions for each material. We also show that, unlike flat monolayer systems such as graphene, in InSe, GaSe and GaS thermal transport is governed by in-plane vibrations. Alloying of InSe, GaSe, and GaS systems provides an effective method for modulating their κ through intrinsic vibrational modifications and phonon scattering from mass disorder giving reductions ~ 2-3.5 times. This disorder also suppresses phonon mean free paths in the alloy systems compared to those in their crystalline counterparts. This work provides fundamental insights of lattice thermal transport from basic vibrational properties for an interesting set of two-dimensional materials. © 2017 IOP Publishing Ltd.

  18. Anti-tumor and immunomodulatory activity of selenium (Se)-polysaccharide from Se-enriched Grifola frondosa.

    PubMed

    Mao, Guang-Hua; Ren, Yi; Li, Qian; Wu, Hui-Yu; Jin, Dun; Zhao, Ting; Xu, Cai-Quan; Zhang, Deng-Hong; Jia, Qing-Dong; Bai, Yan-Peng; Yang, Liu-Qing; Wu, Xiang-Yang

    2016-01-01

    A polysaccharide termed Se-GP11 was extracted and purified from Se-enriched Grifola frondosa in our previous study. This study investigated the characterization, anti-tumor and immunomodulatory activity of Se-GP11. The results showed that Se-GP11 was composed of mannose, glucose and galactose with a molar ratio of 1:4.91:2.41. The weight-average molecular weight (Mw) and weight-average mean square radius (Rw) of Se-GP11 in 0.1M sodium chloride solution were 3.3×10(4)Da and 32.8 nm. Se-GP11 existed as a globular conformation with random coil structure. Se-GP11 had no anti-tumor activity against HepG-2 cells in vitro, and it significantly inhibited the growth of Heps tumor in vivo. Se-GP11 increased the relatively thymus and spleen weights as well as serum necrosis factor-alpha (TNF-α) and interleukin-2 (IL-2) levels. In addition, Se-GP11 promoted the phagocytosis and NO production of RAW264.7 as compared with that of the normal control group. The results revealed that the Se-GP11 may exhibit the anti-tumor through improving immunologic function of the tumor bearing mice. Copyright © 2015 Elsevier B.V. All rights reserved.

  19. Synthesis and Characterization of Cu 3NbSe 4 and KCu 2TaSe 4

    NASA Astrophysics Data System (ADS)

    Lu, Ying-Jie; Ibers, James A.

    1993-11-01

    Cu 3NbSe 4 has been synthesized from a stoichiometric reaction of the elements at 950°C. The material, which has the sulvanite (Cu 3VS 4) structure, crystallizes in space group T 1d- P4¯3 m of the cubic system with one formula unit in a cell with a = 5.638(1) Å at - 165°C. Cu 3NbSe 4 has a three-dimensional structure with edge-sharing of CuSe 4 and NbSe 4 tetrahedra and corner-sharing among CuSe 4 tetrahedra extending equally in all directions. KCu 2TaSe 4 was prepared from a reaction of K 2Se 5, Cu, Ta, and Se in the ratio 1:4:2:3 at 850°C. KCu 2TaSe 4 crystallizes in space group C43 - Cc of the monoclinic system with four formula units in a cell of dimensions a = 5.660(1), b = 18.829(4), c = 7.662(2) Å, β = 90.04(3)° at - 165°C. In this structure the Ta and two independent Cu atoms are in tetrahedral sites. The CuSe 4 and TaSe 4 tetrahedra share edges and corners to make up two-dimensional layers. These layers are separated from one another by K + ions. KCu 2TaSe 4 is not isostructural with KCu 2NbSe 4, although the structures are similar.

  20. Early Identification of SE-Related Program Risks: Opportunities for DoD Systems Engineering (SE) Transformation via SE Effectiveness Measures (EMs) and Evidence-Based Reviews

    DTIC Science & Technology

    2009-09-30

    producing a negative return on investment. In such cases, agile methods such as rapid prototyping, Scrum [27] and eXtreme Programming [3] will be...more detailed SE personnel competency frameworks that focus more on SE personnel certification or organizational skills coverage. The general design...redone, producing a negative return on investment. In such cases, agile methods such as rapid prototyping, Scrum and eXtreme Programming will be

  1. Defects and oxidation resilience in InSe

    NASA Astrophysics Data System (ADS)

    Xiao, K. J.; Carvalho, A.; Castro Neto, A. H.

    2017-08-01

    We use density functional theory to study intrinsic defects and oxygen related defects in indium selenide. We find that InSe is prone to oxidation, but however not reacting with oxygen as strongly as phosphorene. The dominant intrinsic defects in In-rich material are the In interstitial, a shallow donor, and the Se vacancy, which introduces deep traps. The latter can be passivated by oxygen, which is isoelectronic with Se. The dominant intrinsic defects in Se-rich material have comparatively higher formation energies.

  2. Ultraviolet-blue photoluminescence of ZnSe quantum dots.

    PubMed

    Peng, Ling Ling; Wang, Yu Hua; Li, Cheng Yan

    2010-03-01

    Zinc blende, sphericity, monodisperse, high luminescence ZnSe quantum dots (QDs) were synthesized by a one-step mild hydrothermal route with Zn and Se dissolved in aqueous NaOH as the source material. The structure and the morphology of the sample were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicated that the products were cubic blende ZnSe ranging from 3.2 to 4.5 nm in size. TEM images showed that the QDs have very good dispersibility and distribution. The characteristic features of the absorption and photoluminescence spectra of ZnSe quantum dots were studied at room temperature. Compared with the bulk ZnSe, the absorption edges and luminescent peaks of ZnSe QDs were blue shifted to higher energies due to the quantum confinement effect. Photoluminescence at ultraviolet excitation showed the strong emission at 390 nm related to the higher excitonic states. ZnSe QDs exhibiting photoluminescence line widths as narrow as 40-60 nm. Meanwhile, we simply explored the theoretical mechanism of luminescence in ZnSe QDs and analogized the relation of various point defect concentrations of ZnSe.

  3. Dynamic Conversion Between Se-N Covalent and Noncovalent Interactions.

    PubMed

    Xie, Meng; Wang, Lili; Liu, Fang; Zhang, Dongju; Gao, Jun

    2016-11-17

    Se-N dynamic covalent bond is a new dynamic covalent bond which has applications in the fabrication of stimuli responsive and self-healing functional materials. Although recent advances have been achieved in the experimental aspect, little is known about the formation mechanism of Se-N dynamic covalent bond. Here the structures and nature of Se-N dynamic covalent bond between three kinds of pyridine derivatives R-C5H4N, [pyridine (R = H), 4-methylpyridine (R = CH3), 4-dimethylamino-pyridine (R = N(CH3)2)] and phenylselenyl bromine (PhSeBr) have been analyzed using density functional theory. The interactions between Se atom in PhSeBr and N atom in pyridine or pyridine derivatives can be divided into three models: dissociation, nonbonding interaction and covalent bond interaction. Quantum chemical calculations on three series compounds show that these three models can convert mutually, which results in the generation of Se-N dynamic covalent bond. Solvent effects produced in polar solvents such as CH2Cl2 can make the conversion between Se-N covalent bond and Se···N nonbonding interactions easier. The kind of the substituents in pyridine ring can affect the conversion process: the stronger the electron-donating ability of the substituent, the easier the structure transformation.

  4. Cohort profile: Epidemiological Clinicopathological studies in Europe (EClipSE).

    PubMed

    2009-01-01

    Epidemiological Clinicopathological Studies in Europe (EClipSE) is the harmonization of neuropathological and longitudinal clinical data from three population-based prospective longitudinal studies of aging. The EClipSE database (Version 1.0) comprises data from the first 970 people who donated their brain at death and this number will increase. EClipSE enables sociodemographic, health, cognitive, and genetic measures collected during life to be related to neuropathology at death, testing hypotheses which require more power than has been previously possible. EClipSE aims to help throw light on relationships between biological, health and psychological factors underlying ageing and the manifestation of clinical dementia.

  5. 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.

  6. Elucidation of two giants: challenges to thick-shell synthesis in CdSe/ZnSe and ZnSe/CdS core/shell quantum dots.

    PubMed

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

    2015-03-25

    Core/thick-shell giant quantum dots (gQDs) possessing type II electronic structures exhibit suppressed blinking and diminished nonradiative Auger recombination. 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.

  7. 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.

  8. 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; ...

    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

  9. Heavy p-type doping of ZnSe thin films using Cu2Se in pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaojun; Man Yu, Kin; Kronawitter, Coleman X.; Ma, Zhixun; Yu, Peter Y.; Mao, Samuel S.

    2012-07-01

    Undoped, Cu-doped, Se-enriched, and Cu2Se-doped ZnSe films have been grown on fused quartz substrates by pulsed laser deposition. While the other films are highly resistive, Cu2Se-doped ZnSe films are p-type conducting with hole concentrations of ˜1.1 × 1019 cm-3 and resistivities of ˜0.098 Ω cm (compared with previous reports of ˜1×1018 cm-3 and ˜0.75 Ω cm). The exceptional heavy p-type doping of ZnSe films can be attributed to substitution of Zn atoms with Cu while limiting selenium-vacancy-associated compensating defects with additional selenium. This work is of importance to solve doping difficulties and contact problems of wide-bandgap semiconductors.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  11. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  13. Chemical bath deposition of ZnSe and CuSe thin films using n,n-dimethylselenourea

    SciTech Connect

    Estrada, C.A.; Zingaro, R.A.; Meyers, E.A. . Dept. of Chemistry); Nair, P.K.; Nair, M.T.S. . Lab. de Energia Solar)

    1994-03-01

    Chemical bath deposition techniques for ZnSe and CuSe thin films using N,N-dimethylselenourea as the source of selenide ion are presented. Films of 0.1 to 0.3 [mu]m in thickness of ZnSe and CuSe are obtained in 2 to 10 h depositions at 50 C. The ZnSe films possess optical bandgap [approximately]2.63 eV and suffer thermal degradation at temperatures >350 C. They are very resistive, with sheet resistance [approximately]10[sup 12] [Omega]/[open square] ([approximately]0.3 [mu]m film, 10 h deposition). The CuSe films have sheet resistance [approximately]10[sup 3] [Omega]/[open square] ([approximately]0.13 [mu]m, 3 h deposition) but undergo thermal degradation at temperature >200 C. Structure, composition, optical, and electrical characteristics of the films are discussed.

  14. Preparation of colloidal CdSe and CdS/CdSe nanoparticles from sodium selenosulfate in aqueous polymers solutions.

    PubMed

    Raevskaya, Alexandra E; Stroyuk, Alexander L; Kuchmiy, Stephan Ya

    2006-10-01

    Cadmium selenide nanoparticles formation at the interaction between CdCl2 and Na2SeSO3 in aqueous solutions of sodium polyphosphate and gelatin has been studied. Structural and optical properties of CdSe nanoparticles have been characterized. It has been shown that the temperature and the ratio of reagents concentrations are the basic parameters, controlling the size of CdSe nanoparticles. Photocatalytic activity of CdS nanoparticles in Na2SeSO3 reduction has been found and investigated; structural and optical properties of binary CdS/CdSe nanoparticles have been characterized. This photoreaction, when carried out in the presence of CdCl2, results in the formation of composite CdS/CdSe nanoparticles. It has been shown that slow interaction of adsorbed selenosulfate with surface-trapped CdS conduction band electrons is the limiting stage of the photocatalytic reaction.

  15. Resultados do desenvolvimento de um propulsor à plasma no Brasil

    NASA Astrophysics Data System (ADS)

    Ferreira, I. S.; Ferreira, J. L.

    2003-08-01

    Uma das partes mais importantes de um satélite é o controle de atitude do mesmo. E se tratando de um satélite científico, a atenção para este sistema deve ser redobrada. Uma possibilidade atraente para executar esta tarefa é a propulsão elétrica. Aqui, mostraremos resultados obtidos pelo propulsor à plasma PHALL-01, desenvolvido na Universidade de Brasília entre 2000 e 2003. Este é derivado do propulsor russo SPT-100 (Stationary Plasma Thruster), mas com o emprego inovador de um arranjo de imãs permanentes como fonte do campo magnético, este último o agente da aceleração do plasma. Esta alteração foi motivada pelo objetivo de que o mesmo operasse com o mínimo de potência elétrica. A partir da formulação teórica do mecanismo de aceleração, tendo como base as equações da magnetohidrodinâmica, pode-se obter vínculos sob os quais o propulsor pudesse ser construído. O mais forte destes é o que dita a topologia do campo magnético. Sendo assim, foram realizadas simulações computacionais, que definiram a geometria do propulsor. Após construído, este foi diagnosticado usando-se sondas de Langmuir e analisadores de energia. Como resultados, obtivemos a distribuição espacial da temperatura, densidade e potencial do plasma, bem como a distribuição angular do feixe produzido pelo mesmo em vários regimes de operação. O espectro de energia do feixe de plasma também foi medido, indicando íons de até 560eV. Combinando estes resultados, calculou-se o empuxo do propulsor: 84mN; e o impulso específico: 1083s. Estes demonstram que o mesmo estará qualificado, num futuro próximo, para o emprego no controle de atitude de satélites científicos, ou até mesmo como parte do conjunto propulsor primário, responsáveis pela transferência de órbitas.

  16. 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.

  17. Seismic waether over Brasil during the Chile earthquake/tsunami of September 2015

    NASA Astrophysics Data System (ADS)

    Kherani, Esfhan; Klausner, Virginia

    2016-07-01

    During an earthquake and tsunami, the Earth's atmosphere and ionosphere hosts varieities of disturbances. We refer, this phenomena, as seismic weather, drawing anology from the space weather. In this work, we study the seismic weather over Brasil, associated with the September Chile eqarthquake/tsunami. We aim to simulate this seismic weather for which the seismogenic magnetic and airglow disturbances over Brasil are already reported. We employ the Seismic-Atmsopheric-Ionospheric coupling model (SAI) developed by us, to study this seismic weather. The Earth's surface displacement obtained from seismometer is consisdered as an input to the model which them trigger the Acoustic-Gravity waves (AGWs) in the atmosphere and subsequent magnetic and airglow disturbances in the atmosphere-ionosphere coupled system. The results provide better understanding of coupling arising from the Rayleigh wave forcing.

  18. [Routines of organization of clinical tests and interviews in the ELSA-Brasil investigation center].

    PubMed

    Bensenor, Isabela M; Griep, Rosane H; Pinto, Karina Araújo; Faria, Carolina Perim de; Felisbino-Mendes, Mariana; Caetano, Edna I; Albuquerque, Liliane da Silva; Schmidt, Maria Inês

    2013-06-01

    The ELSA-Brasil (Estudo Longitudinal de Saúde do Adulto - Brazilian Longitudinal Study for Adult Health) is a prospective cohort study with extensive assessments throughout time. This article describes the routine of clinical tests and interviews performed with participants and the structuring of the Research Center physical space and teams. The ELSA-Brasil assumes that participants will be present at the Research Center to have the tests and interviews performed, according to standard protocols developed by this study. Considering the multiplicity of activities involved, each with specific needs for standardization, several predetermined orders of clinical tests and interviews were created. This ensured a high standard of quality in data collection without harm to participants' comfort. Each participant was previously assigned to a specific sequence of clinical tests and interviews with a predefined arrival time, mean length of stay of five to six hours and departure time.

  19. 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.

  20. Flexible one-dimensional carbon-selenium composite nanofibers with superior electrochemical performance for Li-Se/Na-Se batteries

    NASA Astrophysics Data System (ADS)

    Zeng, Linchao; Wei, Xiang; Wang, Jiaqing; Jiang, Yu; Li, Weihan; Yu, Yan

    2015-05-01

    A facile strategy is developed to synthesis selenium/carbon composites (Se@CNFs-CNT) by co-heating Se powder and electrospun Polyacrylonitrile (PAN)-CNT nanofibers at 600°Cin a sealed vessel. The Se molecules are chemically bonded and physical encapsulated by carbonized PAN-CNT composite (CNFs-CNT), which leads to prevent the dissolution of polyselenide intermediates in carbonate based electrolyte. When directly used as flexible free-standing cathode material for Li-Se batteries in low cost carbonate-based electrolyte, the Se@CNFs-CNT electrode exhibits improved cyclability (517 mAh g-1 after 500 cycles at 0.5 A g-1) and rate capability (485 mAh g-1 at 1 A g-1). Moreover, when tested as sodium batteries, it maintains a reversible capacity of 410 mAh g-1 after 240 cycles at 0.5 A g-1. The superior electrochemical performance (especially at high rates) of Se@CNFs-CNT is attributed to synergistic effect of the additive of CNT, the well confine of Se in the CNFs-CNT matrix through chemical bonding and the 3D interconnected carbon nanofibers (CNFs). This simple yet efficient process thus provides a promising route towards fabrication of a variety of high performance flexible Li-Se and Na-Se batteries.

  1. Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid–Solid–Vapor Growth

    PubMed Central

    2014-01-01

    Here, we show a novel solid–solid–vapor (SSV) growth mechanism whereby epitaxial growth of heterogeneous semiconductor nanowires takes place by evaporation-induced cation exchange. During heating of PbSe-CdSe nanodumbbells inside a transmission electron microscope (TEM), we observed that PbSe nanocrystals grew epitaxially at the expense of CdSe nanodomains driven by evaporation of Cd. Analysis of atomic-resolution TEM observations and detailed atomistic simulations reveals that the growth process is mediated by vacancies. PMID:24844280

  2. 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.

  3. Origin of low thermal conductivity in SnSe

    NASA Astrophysics Data System (ADS)

    Xiao, Yu; Chang, Cheng; Pei, Yanling; Wu, Di; Peng, Kunling; Zhou, Xiaoyuan; Gong, Shengkai; He, Jiaqing; Zhang, Yongsheng; Zeng, Zhi; Zhao, Li-Dong

    2016-09-01

    We provide direct evidence to understand the origin of low thermal conductivity of SnSe using elastic measurements. Compared to state-of-the-art lead chalcogenides Pb Q (Q =Te , Se, S), SnSe exhibits low values of sound velocity (˜1420 m /s ) , Young's modulus (E ˜27.7 GPa ) , and shear modulus (G ˜9.6 GPa ) , which are ascribed to the extremely weak Sn-Se atomic interactions (or bonds between layers); meanwhile, the deduced average Grüneisen parameter γ of SnSe is as large as ˜3.13, originating from the strong anharmonicity of the bonding arrangement. The calculated phonon mean free path (l ˜ 0.84 nm) at 300 K is comparable to the lattice parameters of SnSe, indicating little room is left for further reduction of the thermal conductivity through introducing nanoscale microstructures and microscale grain boundaries. The low elastic properties indicate that the weak chemical bonding stiffness of SnSe generally causes phonon modes softening which eventually slows down phonon propagation. This work provides insightful data to understand the low lattice thermal conductivity of SnSe.

  4. New occurrences of ferroselite (FeSe2)

    USGS Publications Warehouse

    Coleman, R.G.

    1959-01-01

    Iron selenide from the uranium-vanadium ores of the Colorado Plateau was under investigation when ferroselite was described as a new mineral in Russia by Bur'yanova and Komkov (1955). Association of ferroselite with selenian pyrite and marcasite within discrete areas of these uranium-vanadium deposits suggests an unusual environment of formation. Its association with apparent low temperature assemblages in the United States and Bussia indicates that its minimum temperature of formation is quite low. Chemical analyses of ferroselite agree well with the theoretical formula FeSe2; material from the Virgin no. 3 mine, Montrose County, Colorado, gives the formula FeSe2.07 and that from the A.E.C. no. 8 mine, Temple Mountain, Utah, gives the formula (Fe, Co)Se2.08. The similarity of hastite and ferroselite suggests that a complete series FeSe2-CoSe2 may exist. In contrast to this, pyrite associated with ferroselite apparently will camouflage only 4 per cent (molecular) FeSe2 within its structure. Ferroselite cannot be distinguished from rammelsbergite (FeAs2) by X-ray or in polished section; therefore, the exact identification of these two minerals can be made only by specific tests for As or Se. As hastite (CoSe2) and marcasite are in the same structure group as ferroselite and rammelsbergite, identification of these minerals should include qualitative chemical determinations. ?? 1959.

  5. On the Use of "Por" Plus Agent with "Se" Construction

    ERIC Educational Resources Information Center

    De Mello, George

    1978-01-01

    Two explanations for the role of "se" in such constructions as "Se construyen casas" are given by grammarians; one states that it is a passive interpretation ("Houses are built"), the other advocates an impersonal interpretation ("One builds houses"). Different views are presented and analyzed. (Author/NCR)

  6. Cr:ZnSe planar waveguide mid-IR laser

    NASA Astrophysics Data System (ADS)

    Willimas, J. E.; Martyshkin, D. V.; Fedorov, V. V.; Moskalev, I. S.; Camata, R. P.; Mirov, S. B.

    2011-02-01

    Middle infrared (mid-IR) chromium-doped zinc selenide (Cr:ZnSe) bulk lasers have attracted a lot of attention due to their unique combination of optical and laser properties facilitating a wide range of potential scientific, industrial, and medical applications. Utilization of thin film waveguide geometry enabling good thermal management and control of beam quality is a viable pathway for compact chip-integrated optical laser design. Cr:ZnSe thin films are also promising as saturable absorbers and mode-lockers of the cavities of solid state lasers operating over 1.3-2.1 μm. We recently reported the first successful demonstration of mid-IR Cr:ZnSe planar waveguide lasing at 2.6 μm under gain-switched short-pulse (5 ns) 1.56 μm excitation as well as the passive Q-switching of the cavity of a fiber-pumped Er:YAG laser operating at 1645 nm using a highly doped Cr:ZnSe thin film. PLD grown Cr:ZnSe waveguide were fabricated on sapphire substrates (Cr:ZnSe/sapphire) with chromium concentration of 1018-1019 cm-3. Further development of mid-IR lasing in the Cr:ZnSe planar waveguide under continuous wave excitation were investigated. In addition, deposition of Cr:ZnSe-based thin film structures on n-type GaAs substrates were also investigated for possible mid-IR electroluminescence.

  7. Simulating far infrared spectra of Zn1-xMnxSe/GaAs epifilms, MnSe/ZnSe superlattices and predicting impurity modes of N, P defects in Zn1-xMnxSe

    PubMed Central

    Talwar, Devki N.; Yang, Tzuen-Rong; Chou, Wu-Ching

    2016-01-01

    Abstract A comprehensive lattice dynamical study is reported to emphasize the vibrational behavior of perfect/imperfect zinc-blende (zb) ZnSe, MnSe and Zn1−xMnxSe alloys. Low temperature far-infrared (FIR) reflectivity measurements performed on a series of molecular beam epitaxy grown Zn1−xMnxSe/GaAs (001) epilayers have a typical ‘intermediate-phonon-mode’ behavior. Besides perceiving ZnSe- and MnSe-like TO-phonon resonances, the study also revealed a weak Mn alloy-disorder mode below MnSe band. A classical effective-medium theory of multilayer optics is used to evaluate dielectric tensors of both epilayers and substrate for simulating reflectivity and transmission spectra of ultrathin epifilms and superlattices at near normal and/or oblique incidence. In the framework of a realistic rigid-ion model and exploiting an average t-matrix Greens function (ATM-GF) theory we appraised the vibrational properties of nitrogen and phosphorous doped Zn-Mn chalcogenides. Lattice relaxations around isolated NSe (PSe) defects in ZnSe and zb MnSe are evaluated by first principles bond-orbital model that helped construct perturbation models for simulating the localized vibrational modes (LVMs). Calculated shift of impurity modes for isotopic 14NSe (15NSe) defects in ZnSe offered a strong revelation of an inflexible defect–host interaction. By retaining force constant change parameter of 14NSe (15NSe) in heavily N-doped ZnSe, the ATM-GF theory predicted (a) three non-degenerate LVMs for the photoluminescence defect center V Se-Zn-14NSe (V Se-Zn-15NSe) of C s symmetry, and (b) six impurity modes for the second nearest-neighbor NSe-Zn-NSe pair defect of C 2v symmetry. From the range of simulated defect modes, we have ruled out the possibility of N-pairs and justified the presence of VSe-Zn-NSe complex centers – likely to be responsible for the observed large absorption bandwidth in highly N-doped ZnSe. High resolution measurements of FIR absorption and/or Raman scattering

  8. Simulating far infrared spectra of Zn1-xMnxSe/GaAs epifilms, MnSe/ZnSe superlattices and predicting impurity modes of N, P defects in Zn1-xMnxSe.

    PubMed

    Talwar, Devki N; Yang, Tzuen-Rong; Chou, Wu-Ching

    2016-01-01

    A comprehensive lattice dynamical study is reported to emphasize the vibrational behavior of perfect/imperfect zinc-blende (zb) ZnSe, MnSe and Zn1-xMnxSe alloys. Low temperature far-infrared (FIR) reflectivity measurements performed on a series of molecular beam epitaxy grown Zn1-xMnxSe/GaAs (001) epilayers have a typical 'intermediate-phonon-mode' behavior. Besides perceiving ZnSe- and MnSe-like TO-phonon resonances, the study also revealed a weak Mn alloy-disorder mode below MnSe band. A classical effective-medium theory of multilayer optics is used to evaluate dielectric tensors of both epilayers and substrate for simulating reflectivity and transmission spectra of ultrathin epifilms and superlattices at near normal and/or oblique incidence. In the framework of a realistic rigid-ion model and exploiting an average t-matrix Greens function (ATM-GF) theory we appraised the vibrational properties of nitrogen and phosphorous doped Zn-Mn chalcogenides. Lattice relaxations around isolated NSe (PSe) defects in ZnSe and zb MnSe are evaluated by first principles bond-orbital model that helped construct perturbation models for simulating the localized vibrational modes (LVMs). Calculated shift of impurity modes for isotopic (14)NSe ((15)NSe) defects in ZnSe offered a strong revelation of an inflexible defect-host interaction. By retaining force constant change parameter of (14)NSe ((15)NSe) in heavily N-doped ZnSe, the ATM-GF theory predicted (a) three non-degenerate LVMs for the photoluminescence defect center (V)Se-Zn-(14)NSe ((V)Se-Zn-(15)NSe) of Cs symmetry, and (b) six impurity modes for the second nearest-neighbor NSe-Zn-NSe pair defect of C2v symmetry. From the range of simulated defect modes, we have ruled out the possibility of N-pairs and justified the presence of VSe-Zn-NSe complex centers - likely to be responsible for the observed large absorption bandwidth in highly N-doped ZnSe. High resolution measurements of FIR absorption and/or Raman scattering

  9. 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.

  10. 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}.

  11. Biomolecular recognition in DNA tagged CdSe nanowires.

    PubMed

    Sarangi, S N; Goswami, K; Sahu, S N

    2007-06-15

    DNA template driven CdSe nanobeads (NBs) and nanowires (NWs) have been synthesized by an electrodeposition technique. The synthesis protocol has yielded randomly oriented cubic CdSe NBs with mean size approximately 3.0 nm in presence of single stranded DNA, poly G(30). Monocrystalline cubic CdSe NWs of width approximately 4.0 nm with string-like morphology have been achieved when synthesized in presence of both poly G(30) and its conjugate, poly C(30). Optical absorption of CdSe NBs show a blue shift of 0.8 eV and long wavelength tailing where as NWs show steep increase of absorption in shorter wavelength regime accompanied by a further blue shift. DNA tags to the NBs or NWs have been confirmed from Fourier transform infrared spectroscopy measurements. Biomolecular recognition with CdSe NWs have been established by photoluminescence measurements.

  12. Synthesis and Thermoelectric Properties of Bi2Se3 Nanostructures

    PubMed Central

    2011-01-01

    Bismuth selenide (Bi2Se3) nanostructures were synthesized via solvothermal method. The crystallinity of the as-synthesized sample has been analyzed by X-ray diffraction, which shows the formation of rhombohedral Bi2Se3. Electron microscopy examination indicates that the Bi2Se3 nanoparticles have hexagonal flake-like shape. The effect of the synthesis temperature on the morphology of the Bi2Se3 nanostructures has also been investigated. It is found that the particle size increases with the synthesis temperature. Thermoelectric properties of the Bi2Se3 nanostructures were also measured, and the maximum value of dimensionless figure of merit (ZT) of 0.096 was obtained at 523 K. PMID:27502679

  13. 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$^{-3}$.

  14. NQR study of chalcogenide glasses Ge-As-Se.

    PubMed

    Glotova, Olga; Korneva, Irina; Sinyavsky, Nikolay; Ostafin, Michal; Nogaj, Boleslaw

    2011-07-01

    A three-component Ge-As-Se system is studied by the nuclear quadrupole resonance (NQR) method on (75)As nuclei and by the nutation NQR spectroscopy. The NQR (75)As spectra of the glasses Ge(0.021) As(0.375) Se(0.604), Ge(0.043) As(0.348) Se(0.609) and Ge(0.068) As(0.318) Se(0.614) reveal broad lines with two peaks assigned to the main structural unit of As(2)Se(3). With increasing average coordination number ( ̅r), the spectrum signals are shifted towards higher frequencies. At ̅r > 2.54, the spectrum becomes complex, which is a consequence of formation of more complex molecular structures in the glasses of high content of germanium. At fixed frequencies the asymmetry parameter η of the samples studied is determined. Copyright © 2011 John Wiley & Sons, Ltd.

  15. Anisotropic Differential Reflectance Spectroscopy of Thin GeSe

    NASA Astrophysics Data System (ADS)

    Matson, Joseph; Woods, Grace; Churchill, Hugh

    2017-01-01

    Atomically thin monochalcogenides are predicted to exhibit a two-dimensional structural phase transition. This phase transition could be useful for designing new phase change memory devices. The critical temperature is dependent on the material as well as the thickness, and is predicted to occur just above room temperature for monolayer GeSe. We used differential reflectance spectroscopy on thin samples of GeSe to measure changes in the optical anisotropy with temperature as a signature of this phase transition. We constructed an apparatus for temperature-depedendent spectroscopy of micro-scale GeSe samples, and measured anisotropic optical absorption of thin GeSe. We observed a decrease in optical anisotropy of GeSe at elevated temperatures, which may be a first indication of the continuous transition from a rectangular to a square lattice in that material. This work was supported by NSF REU Grant #EEC-1359306.

  16. Spectroscopy of 76Se: Prolate-to-oblate shape transition

    NASA Astrophysics Data System (ADS)

    Xu, C.; Li, X. Q.; Meng, J.; Zhang, S. Q.; Hua, H.; Wang, S. Y.; Qi, B.; Liu, C.; Xiao, Z. G.; Li, H. J.; Zhu, L. H.; Shi, Z.; Li, Z. H.; Ye, Y. L.; Jiang, D. X.; Sun, J. J.; Zhang, Z. H.; Shi, Y.; Zhao, P. W.; Chen, Q. B.; Liang, W. Y.; Han, R.; Niu, C. Y.; Li, C. G.; Wang, C. G.; Li, Z. H.; Wyngaardt, S. M.; Bark, R. A.; Papka, P.; Bucher, T. D.; Kamblawe, A.; Khaleel, E.; Khumalo, N.; Lawrie, E. A.; Lawrie, J. J.; Jones, P.; Mullins, S. M.; Murray, S.; Wiedeking, M.; Sharpey-Schafer, J. F.; Majola, S. N. T.; Ndayishimye, J.; Negi, D.; Noncolela, S. P.; Ntshangase, S. S.; Shirinda, O.; Sithole, P.; Stankiewicz, M. A.; Orce, J. N.; Dinoko, T.; Easton, J.; Nyakó, B. M.; Juhász, K.

    2015-06-01

    The spectroscopy of 76Se has been studied using the 70Zn (12C , α 2 n) 76Se fusion evaporation reaction. The yrast band of 76Se has been extended to substantially higher spin, allowing observation of the second band crossing. The much-delayed g9 /2 proton-pair alignment is discussed in terms of the cranked shell model and most likely is caused by a shape transition from prolate to oblate along the yrast line occurring in 76Se . Based on the systematic investigation of the band crossings associated with the g9 /2 quasiparticle alignments and their relationships with the shape evolutions in the even-A Se and Kr isotopes, a comprehensive picture of shape evolution along with spin and isospin in these nuclei is obtained.

  17. Carrier Relaxation of ZnCdSe/ZnSe Quantum Wells

    NASA Astrophysics Data System (ADS)

    Jang, Der-Jun; Lee, Meng-En; Chung, Yung-Hsien; Yang, Chu-Shou; Chou, Wu-Ching

    2008-09-01

    The energy relaxations of Zn0.91Cd0.09Se multiquantum wells and epilayer structures were studied with an ultrafast time-resolved photoluminescence apparatus. The increase in the rise time of photoluminescence with decreasing photon energy and the redshift of the peak energy of time-resolved photoluminescence spectra with the delay time are attributed to the band-filling effect and energy relaxation of hot carriers. The derived carrier temperature decreases rapidly within the first 10 ps after photoexcitation and at a much slower rate thereafter. The fast carrier cooling can be explained by the longitudinal optical (LO) phonon emissions by carriers through the Fröhlich interaction. The obtained effective scattering times of carrier and LO phonons are comparable to the theoretical prediction of 20 fs for multi-quantum well (MQW) of 20 nm well thickness and the epilayer. The slow carrier capture process may account for the long effective scattering time of 35 fs for the MQWs of 5 nm well thickness.

  18. Colloidal CdSe/Cu3P/CdSe nanocrystal heterostructures and their evolution upon thermal annealing.

    PubMed

    De Trizio, Luca; De Donato, Francesco; Casu, Alberto; Genovese, Alessandro; Falqui, Andrea; Povia, Mauro; Manna, Liberato

    2013-05-28

    We report the synthesis of colloidal CdSe/Cu(3)P/CdSe nanocrystal heterostructures grown from hexagonal Cu(3)P platelets as templates. One type of heterostructure was a sort of "coral", formed by vertical pillars of CdSe grown preferentially on both basal facets of a Cu(3)P platelet and at its edges. Another type of heterostructure had a "sandwich" type of architecture, formed by two thick, epitaxial CdSe layers encasing the original Cu(3)P platelet. When the sandwiches were annealed under vacuum up to 450 °C, sublimation of P and Cd species with concomitant interdiffusion of Cu and Se species was observed by in situ HR- and EFTEM analyses. These processes transformed the starting sandwiches into Cu2Se nanoplatelets. Under the same conditions, both the pristine (uncoated) Cu(3)P platelets and a control sample made of isolated CdSe nanocrystals were stable. Therefore, the thermal instability of the sandwiches under vacuum might be explained by the diffusion of Cu species from Cu(3)P cores into CdSe domains, which triggered sublimation of Cd, as well as out-diffusion of P species and their partial sublimation, together with the overall transformation of the sandwiches into Cu(2)Se nanocrystals. A similar fate was followed by the coral-like structures. These CdSe/Cu(3)P/CdSe nanocrystals are therefore an example of a nanostructure that is thermally unstable, despite its separate components showing to be stable under the same conditions.

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

    PubMed

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

    2015-11-20

    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 Ga(2)O(3) 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 (∼10(8) 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Atkins, Ryan Elliot

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

  2. Sonochemical synthesis and mechanistic study of copper selenides Cu(2-x)Se, beta-CuSe, and Cu(3)Se(2).

    PubMed

    Xie, Yi; Zheng, Xiuwen; Jiang, Xuchuan; Lu, Jun; Zhu, Liying

    2002-01-28

    Nanocrystallites of nonstoichiometric copper selenide (Cu(2-x)Se) and stoichiometric copper selenides (beta-CuSe and Cu(3)Se(2)) were synthesized in different solutions via sonochemical irradiation at room temperature. The influence of solvents, surfactants, and ultrasonic irradiation on the morphology and phase of products has been investigated. The morphological difference of the products was mainly affected by the solvents and surfactants, which can self-aggregate into lamellar structures or microemulsions, and then these unique structures can act as both supramolecular template and microreactor to direct the growth of copper selenides. On the other hand, it was also found that the sonochemical irradiation and solvents played an important role in the formation of different phases of copper selenides. The proposed formation mechanism of copper selenides is discussed.

  3. CuInSe2 formation through Cu2Se-In3Se2 multilayer structures prepared by thermal evaporation technique

    NASA Astrophysics Data System (ADS)

    Mohan, A.; Rajesh, S.; Srikesh, G.

    2016-05-01

    The current study investigates the Cu2Se/In3Se2 multilayer structure deposited by thermal evaporation technique for CIS solar cells with different number of layers. The X-ray diffraction pattern reveals that the layer thickness improves the crystallinity and the formation of CIS for the 30 layer films through photoluminescence (PL) emission. The optical band gap values are found to be 2.87 eV and 2.79 eV for 5 and 10 period films respectively. The splitted band gap ranging 1.30 and 2.25 eV for 15 periods and decrease in the band gap values are due to large grains. This splitting is due to quantum size effect and CIS composite formation. The vibration frequency at 174.54 cm-1 is evident for formation of CuInSe2 Chalcopyrite phase.

  4. Employment of Recent Science and Engineering (S/E) Graduates in S/E Fields Increased. Science Resources Studies Highlights.

    ERIC Educational Resources Information Center

    National Science Foundation, Washington, DC. Div. of Science Resources Studies.

    Major findings are presented of the 1980 New Entrants Survey, which was conducted to assess the early experience of 1978 and 1979 recipients of bachelor's and master's degrees in science and engineering (S/E) fields. The results of earlier surveys of recent S/E graduates conducted in 1976, 1978, and 1979 and a 1981 rapid-response survey of…

  5. Dependence of energy levels and optical transitions on layer thicknesses in InSe/GaSe superlattices

    NASA Astrophysics Data System (ADS)

    Erkoç, Şakir; Katırcıoğlu, Şenay

    1998-01-01

    We have investigated the dependence of energy levels and optical transition matrix elements in InSe/GaSe superlattices on well and/or barrier widths. Self-consistent-field calculations have been performed within the effective-mass theory approximation.

  6. Production of 82Se enriched Zinc Selenide (ZnSe) crystals for the study of neutrinoless double beta decay

    NASA Astrophysics Data System (ADS)

    Dafinei, I.; Nagorny, S.; Pirro, S.; Cardani, L.; Clemenza, M.; Ferroni, F.; Laubenstein, M.; Nisi, S.; Pattavina, L.; Schaeffner, K.; di Vacri, M. L.; Boyarintsev, A.; Breslavskii, I.; Galkin, S.; Lalayants, A.; Rybalka, I.; Zvereva, V.; Enculescu, M.

    2017-10-01

    High purity Zinc Selenide (ZnSe) crystals are produced starting from elemental Zn and Se to be used for the search of the neutrinoless double beta decay (0νDBD) of 82Se. In order to increase the number of emitting nuclides, enriched 82Se is used. Dedicated production lines for the synthesis and conditioning of the Zn82Se powder in order to make it suitable for crystal growth were assembled compliant with radio-purity constraints specific to rare event physics experiments. Besides routine check of impurities concentration, high sensitivity measurements are made for radio-isotope concentrations in raw materials, reactants, consumables, ancillaries and intermediary products used for ZnSe crystals production. Indications are given on the crystals perfection and how it is achieved. Since very expensive isotopically enriched material (82Se) is used, a special attention is given for acquiring the maximum yield in the mass balance of all production stages. Production and certification protocols are presented and resulting ready-to-use Zn82Se crystals are described.

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

    USDA-ARS?s Scientific Manuscript database

    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...

  8. Insertion of CdSe quantum dots in ZnSe nanowires: MBE growth and microstructure analysis

    NASA Astrophysics Data System (ADS)

    den Hertog, M.; Elouneg-Jamroz, M.; Bellet-Amalric, E.; Bounouar, S.; Bougerol, C.; André, R.; Genuist, Y.; Poizat, J. P.; Kheng, K.; Tatarenko, S.

    2011-05-01

    ZnSe nanowire growth has been successfully achieved on ZnSe (1 0 0) and (1 1 1)B buffer layers deposited on GaAs substrates. Cubic [1 0 0] oriented ZnSe nanowires or [0 0 0 1] oriented hexagonal NWs are obtained on (1 0 0) substrates while [1 1 1] oriented cubic mixed with [0 0 0 1] oriented hexagonal regions are obtained on (1 1 1)B substrates. Most of the NWs are perpendicular to the surface in the last case. CdSe quantum dots were successfully incorporated in the ZnSe NWs as demonstrated by transmission electron microscopy, energy filtered TEM and high angle annular dark field scanning TEM measurements.

  9. Uncovering Hot Hole Dynamics in CdSe Nanocrystals.

    PubMed

    Liu, Cunming; Peterson, Jeffrey J; Krauss, Todd D

    2014-09-04

    Single and multiple exciton relaxation dynamics of CdSe/CdZnS nanocrystal quantum dots (QDs) monitored at the two lowest optical transitions, 1Se-1S3/2 and 1Se-2S3/2, have been examined using ultrafast transient absorption (TA) spectroscopy. For the CdSe/CdZnS QDs studied, the 1Se-1S3/2 and 1Se-2S3/2 transitions are widely separated (∼180 meV) compared to bare CdSe QDs (∼50-100 meV), allowing for clearly distinguishable TA signals attributable to hot hole relaxation. Holes depopulate from the 2S3/2 state with a lifetime of 7 ± 2 ps, which is consistent with the predictions for hole relaxation via a phonon coupling pathway to lower-energy hole states, with possible contributions from hole trapping as well. These results suggest that tuning the surface chemistry of semiconductor QDs is a viable route to measure and possibly control their hot hole relaxation dynamics.

  10. Novel mechanical behaviors of wurtzite CdSe nanowires

    NASA Astrophysics Data System (ADS)

    Fu, Bing; Chen, Li; Xie, Yiqun; Feng, Jie; Ye, Xiang

    2015-09-01

    As an important semiconducting nanomaterial, CdSe nanowires have attracted much attention. Although many studies have been conducted in the electronic and optical properties of CdSe NWs, the mechanical properties of Wurtzite (WZ) CdSe nanowires remain unclear. Using molecular dynamics simulations, we have studied the tensile mechanical properties and behaviors of [0001]-oriented Wurtzite CdSe nanowires. By monitoring the stretching processes of CdSe nanowires, three distinct structures are found: the WZ wire, a body-centered tetragonal structure with four-atom rings (denoted as BCT-4), and a structure that consists of ten-atom rings with two four-atom rings (denoted as TAR-4) which is observed for the first time. Not only the elastic tensile characteristics are highly reversible under unloading, but a reverse transition between TAR-4 and BCT-4 is also observed. The stretching processes also have a strong dependence on temperature. A tubular structure similar to carbon nanotubes is observed at 150 K, a single-atom chain is formed at 300, 350 and 450 K, and a double-atom chain is found at 600 K. Our findings on tensile mechanical properties of WZ CdSe nanowires does not only provide inspiration to future study on other properties of CdSe nanomaterials but also help design and build efficient nanoscale devices.

  11. GaSe oxidation in air: from bulk to monolayers

    NASA Astrophysics Data System (ADS)

    Rahaman, Mahfujur; Rodriguez, Raul D.; Monecke, Manuel; Lopez-Rivera, Santos A.; Zahn, Dietrich R. T.

    2017-10-01

    Two-dimensional (2D) van derWaals semiconductors have been the subject of intense research due to their low dimensionality and tunable optoelectronic properties. However, the stability of these materials in air is one of the important issues that needs to be clarified, especially for technological applications. Here the time evolution of GaSe oxidation from monolayer to bulk is investigated by Raman spectroscopy, photoluminescence emission, and x-ray photoelectron spectroscopy. The Raman spectroscopy study reveals that GaSe monolayers become oxidized almost immediately after exposure to air. However, the oxidation is a self-limiting process taking roughly 5 h to penetrate up to 3 layers of GaSe. After oxidation, GaSe single-layers decompose into amorphous Se which has a strong Raman cross section under red excitation. The present study provides a clear picture of the stability of GaSe in air and will guide future research of GaSe from single- to few-layers for the appropriate development of novel technological applications for this promising 2D material.

  12. Synthesis of ZnSe and ZnSe:Cu quantum dots by a room temperature photochemical (UV-assisted) approach using Na2 SeO3 as Se source and investigating optical properties.

    PubMed

    Khafajeh, R; Molaei, M; Karimipour, M

    2017-06-01

    In this study, ZnSe and ZnSe:Cu quantum dots (QDs) were synthesized using Na2 SeO3 as the Se source by a rapid and room temperature photochemical (UV-assisted) approach. Thioglycolic acid (TGA) was employed as the capping agent and UV illumination activated the chemical reactions. Synthesized QDs were successfully characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and UV-visible (UV-vis) spectroscopy, Fourier transform-infrared (FT-IR), and energy dispersive X-ray spectroscopy (EDX). XRD analysis demonstrated the cubic zinc blend phase QDs. TEM images indicated that round-shaped particles were formed, most of which had a diameter of about 4 nm. The band gap of the ZnSe QDs was higher than that for ZnSe in bulk. PL spectra indicated an emission with three peaks related to the excitonic, surface trap states and deep level (DL) states. The band gap and QD emission were tunable only by UV illumination time during synthesis. ZnSe:Cu showed green emission due to transition of electrons from the Conduction band (CB) or surface trap states to the (2) T2 acceptor levels of Cu(2)(+) . The emission was increased by increasing the Cu(2)(+) ion concentration, such that the optimal value of PL intensity was obtained for the nominal mole ratio of Cu:Zn 1.5%. Copyright © 2016 John Wiley & Sons, Ltd.

  13. 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.

  14. Investigation of Kinetics of crystallization Processes of S15-Se85, S15-Se81-Cu4 Chalcogenide glasses

    NASA Astrophysics Data System (ADS)

    Samudrala, Kavitha; Babu Devarasetty, Suresh

    2016-09-01

    In the present work, S15-Se85, S15-Se81-Cu4 chalcogenide glasses are prepared by using conventional melt quenching technique. The as-prepared samples are studied by experimental techniques like X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC). XRD studies have confirmed that the as-prepared samples are amorphous in nature. It is clear from DSC studies that the as-prepared samples are glassy in nature. Kinetic analysis of the crystallization process of as-prepared glasses is carried using DSC curves. Activation energy for glass transition and Activation energy for crystallization are determined using Kissinger method. Activation energy for glass transition of S15-Se85 and S15-Se81-Cu4 glasses is found to be 84.5076 and 275.801 KJ/Mole respectively. Activation energy for crystallization of S15-Se85 glass is found to be 106.2622 KJ/Mole for 1st peak while Activation energy for crystallization of S15-Se81-Cu4 glasses is found to be 97.93 KJ/Mole for 1st peak and 84.20 KJ/Mole for 2nd peak. Kauzmann temperature (Tk) is determined from the heating rate dependent glass transition and crystallization temperatures. Tk value for S15-Se85 glass sample is 236.680K (1st peak) and for S15-Se81-Cu4 is 283.530K (1st peak) and 286.330K (2n peak). Avrami Index (n) is also determined for as-prepared glasses. Avrami Index (n) value for S15-Se85 glass sample is 1.8 (1st peak) and for S15-Se81-Cu4 is 2.9 (1st peak) and 1.4 (2nd peak). The crystalline phases by thermal treatment of as-prepared glasses are identified using XRD patterns.

  15. 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.

  16. Synthesis and characterization of Cr doped CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

    Majid, Abdul; Arshad, Humaira; Murtaza, Shahzad

    2015-09-01

    Chromium doped cadmium selenide (CdSe) nanoparticles were prepared via Chemical Co-precipitation Method. The effects of doping and doping concentration on structural and optical properties of the materials were studied. The structural characterization of samples carried out by using X-ray diffraction (XRD) indicated the formation of CdSe nanoparticles of zinc blend (cubic) polytype. It was also noted that lattice parameter decreases with increase in doping concentration. Fourier Transform Infrared Spectroscopy (FTIR) analysis of the samples shows the presence of several modes of vibration related to CdSe nanoparticles and the dopant.

  17. 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.

  18. Laser cooling of CdSe quantum dots

    NASA Astrophysics Data System (ADS)

    Nemova, Galina; Kashyap, Raman

    2014-05-01

    We present a theoretical scheme for laser cooling of the colloidal cadmium selenide (CbSe) QDs. The laser cooling process is based on the anti-Stokes fluorescence observed in QDs. We have considered laser cooling in the system of identical CdSe QDs laser pumped with energy of photons less than mean fluorescence energy. The dependences of all parameters of the system on the temperature have been taken into account. Following to our simulation the laser cooling with temperature drop ~100K can be realised with well technologically developed today passivated CdSe QDs.

  19. Magnetic study of Fe-doped CdSe nanomaterials

    SciTech Connect

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

    2016-05-06

    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.

  20. Reversible ultrafast melting in bulk CdSe

    SciTech Connect

    Wu, Wenzhi; He, Feng; Wang, Yaguo

    2016-02-07

    In this work, transient reflectivity changes in bulk CdSe have been measured with two-color femtosecond pump-probe spectroscopy under a wide range of pump fluences. Three regions of reflectivity change with pump fluences have been consistently revealed for excited carrier density, coherent phonon amplitude, and lattice temperature. For laser fluences from 13 to 19.3 mJ/cm{sup 2}, ultrafast melting happens in first several picoseconds. This melting process is purely thermal and reversible. A complete phase transformation in bulk CdSe may be reached when the absorbed laser energy is localized long enough, as observed in nanocrystalline CdSe.

  1. Controlling the assembly of chalcogenide anions in ionic liquids: from binary Ge/Se through ternary Ge/Sn/Se to binary Sn/Se frameworks.

    PubMed

    Lin, Yumei; Massa, Werner; Dehnen, Stefanie

    2012-10-15

    Seven compounds with binary or ternary Ge/Se, Ge/Sn/Se, or Sn/Se anionic substructures crystallized upon the ionothermal reactions of [K(4)(H(2)O)(3)][Ge(4)Se(10)] with SnCl(4)·5H(2)O or SnCl(2) in [BMMIm][BF(4)] or [BMIm][BF(4)] (BMMIm=1-butyl-2,3-dimethyl-imidazolium, BMIm=1-butyl-3-methyl-imidazolium). The products were obtained by subtly varying the reaction conditions; the nature and amount of an additional amine was the most important parameter in the product selection and in determining the Sn/Ge ratio in the isolated products. The crystal structures of these chalcogenides were based on complex anions with unprecedented topologies that varied from discrete clusters (0D) through 1D chain structures or 2D layers to 3D frameworks. The architecture and composition of the title compounds were well reflected by their optical absorption behavior. Herein, we report a convenient approach for the generation of chalcogenidometallate phases with fine-tunable electronic properties in ionic liquids, which have been inaccessible by traditional methods.

  2. Temperature induced CuInSe2 nanocrystal formation in the Cu2Se-In3Se2 multilayer thin films

    NASA Astrophysics Data System (ADS)

    A, Mohan; S, Rajesh

    2017-04-01

    The paper deals with the impact of annealing on Cu2Se-In3Se2 multilayer structure and discusses the quantum confinements. Thermal evaporation technique was used to prepare multilayer films over the glass substrates. The films were annealed at different temperatures (150 °C-350 °C) under vacuum atmosphere. The XRD pattern reveals that the films exhibit (112) peaks with CuInSe2 Chalcopyrite structure and upon annealing crystallinity improved. The grain size comes around 13-19 nm. The optical band gap value was found to be 2.21 to 2.09 eV and band gap splitting was observed for higher annealing temperatures. The increase in the band gap is related to quantum confinement effect. SEM image shows nano crystals spread over the entire surface for higher annealing temperatures. Optical absorption and PL spectra shows the blue shift during annealing. The HR-TEM shows the particle size in the nano range and which confirms the CuInSe2 nanocrystal formation. AFM image shows the rough surface with homogenous grains for the as deposited films and smooth surface for annealed films.

  3. Thickness-Dependent Charge Carrier Dynamics in CdSe/ZnSe/CdS Core/Barrier/Shell Nanoheterostructures.

    PubMed

    Yadav, Sushma; Chowdhury, Apurba; Sapra, Sameer

    2016-03-03

    We report the synthesis of CdSe/ZnSe/CdS heterostructures composed of type I and type II band alignments, where ZnSe acts as a barrier for charge carriers between the CdSe core and the CdS shell as well as being an active component of the type I (CdSe/ZnSe) and type II (ZnSe/CdS) structure simultaneously. We investigated the effect of the thickness of the barrier and the shell on the charge carrier dynamics by using UV/Vis absorbance, photoluminescence (PL), and time-resolved fluorescence techniques. The experimental data are supported by simple theoretical calculations based on effective mass approximation (EMA). PL results indicate the emission from both type I and type II structures. Time-resolved fluorescence studies show that the lifetime of the core emission decreases with increasing barrier width, owing to a greater confinement of the exciton to the core, whereas it increases with shell width because of the tunneling of charge carriers, primarily electrons, delaying the recombination of the exciton. The lifetime of the shell emission decreases with shell width as well as barrier width and height, with a larger effect being observed for the barrier width and negligible for the associated changes in the barrier height. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. 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

    2016-09-09

    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.

  5. High Efficiency CdS/CdSe Quantum Dot Sensitized Solar Cells with Two ZnSe Layers.

    PubMed

    Huang, Fei; Zhang, Lisha; Zhang, Qifeng; Hou, Juan; Wang, Hongen; Wang, Huanli; Peng, Shanglong; Liu, Jianshe; Cao, Guozhong

    2016-12-21

    CdS/CdSe quantum dot sensitized solar cells (QDSCs) have been intensively investigated; however, most of the reported power conversion efficiency (PCE) is still lower than 7% due to serious charge recombination and a low loading amount of QDs. Therefore, suppressing charge recombination and enhancing light absorption are required to improve the performance of QDSCs. The present study demonstrated successful design and fabrication of QDSCs with a high efficiency of 7.24% based on CdS/CdSe QDs with two ZnSe layers inserted at the interfaces between QDs and TiO2 and electrolyte. The effects of two ZnSe layers on the performance of the QDSCs were systematically investigated. The results indicated that the inner ZnSe buffer layer located between QDs and TiO2 serves as a seed layer to enhance the subsequent deposition of CdS/CdSe QDs, which leads to higher loading amount and covering ratio of QDs on the TiO2 photoanode. The outer ZnSe layer located between QDs and electrolyte behaves as an effective passivation layer, which not only reduces the surface charge recombination, but also enhances the light harvesting.

  6. Dipole strength in 80Se below the neutron-separation energy for the nuclear transmutation of 79Se

    NASA Astrophysics Data System (ADS)

    Makinaga, Ayano; Massarczyk, Ralph; Beard, Mary; Schwengner, Ronald; Otsu, Hideaki; Müller, Stefan; Röder, Marko; Schmidt, Konrad; Wagner, Andreas

    2017-09-01

    The γ-ray strength function (γSF) in 80Se is an important parameter to estimate the neutron-capture cross section of 79Se which is one of the long-lived fission products (LLFPs). Until now, the γSF method was applied for 80Se only above the neutron-separation energy (Sn) and the evaluated 79Se(n,γ) cross section has an instability caused by the GSF below Sn. We studied the dipole-strength distribution of 80Se in a photon-scattering experiment using bremsstrahlung produced by an electron beam of an energy of 11.5 MeV at the linear accelerator ELBE at HZDR. The present photoabsorption cross section of 80Se was combined with results of (γ,n) experiments and are compared with predictions usinmg the TALYS code. We also estimated the 79Se(n,γ) cross sections and compare them with TALYS predictionms and earlier work by other groups.

  7. 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.

  8. 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

  9. 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

  10. BLDG 6, NE END AND SE SIDE WITH BLDG 7 ...

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

    BLDG 6, NE END AND SE SIDE WITH BLDG 7 ON LEFT. - Naval Magazine Lualualei, West Loch Branch, Inert Storehouse Type, Northeast of Fourth Street & D Avenue intersection, Pearl City, Honolulu County, HI

  11. BLDG 7, SE SIDE OF CENTER PORTION OF BLDG WITH ...

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

    BLDG 7, SE SIDE OF CENTER PORTION OF BLDG WITH POLE. - Naval Magazine Lualualei, West Loch Branch, Inert Storehouse Type, Northeast of Fourth Street & D Avenue intersection, Pearl City, Honolulu County, HI

  12. 3. LOOKING SE AT EASTERN ABUTMENT PIER, SHOWING PIN CONNECTION ...

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

    3. LOOKING SE AT EASTERN ABUTMENT PIER, SHOWING PIN CONNECTION AND UNDERSIDE OF ARCH RIBS. - Passerelle in Lincoln Park, Spanning North Lake Shore Drive (U.S. Route 41) on axis of East Menomonee Street, Chicago, Cook County, IL

  13. 3. Peeler Shed, SE side, with blower assembly. This structure ...

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

    3. Peeler Shed, SE side, with blower assembly. This structure was need to move back to the Chipper Building for processing. - Pacific Creosoting Plant, Log Peeling Operation, 5350 Creosote Place, Northeast, Bremerton, Kitsap County, WA

  14. Optical Properties of Multilayer CdSe/POLYMER Structures

    NASA Astrophysics Data System (ADS)

    Red'Ko, V. P.; Voitenkov, A. I.; Kovalenko, O. E.

    The effects of preparation condition, concentration and size of particles upon optical and photoelectrical characteristics of multilayer structures CdSe/polyethylene terephthalate obtained by electron-beam evaporation were investigated.

  15. 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

  16. Structural and optical properties of homogeneous Cu(In,Ga)Se2 thin films prepared by thermal reaction of InSe/Cu/GaSe alloys with elemental Se vapour

    NASA Astrophysics Data System (ADS)

    Dejene, F. B.; Alberts, V.

    2005-01-01

    In this study, thin films of Cu(In,Ga)Se2 were prepared by the controlled reaction of thermally evaporated InSe/Cu/GaSe precursors with elemental Se vapour in vacuum. We indicate that this classical two-step growth process can be utilized to produce homogeneous single-phase chalcopyrite absorber films with superior structural properties. X-ray diffraction studies indicated that the interplanar spacing d(112) decreases linearly with an increase in the Ga/[In + Ga] atomic ratio due to homogeneous incorporation of gallium into the chalcopyrite lattice. Optical studies revealed the expected systematic increase in the band gap with increasing gallium concentration, once again confirming the monophasic nature of the alloys.

  17. 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

  18. 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

  19. 2. PERSPECTIVE VIEW OF WESTERN PORTAL, LOOKING SE. Philadelphia ...

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

    2. PERSPECTIVE VIEW OF WESTERN PORTAL, LOOKING SE. - Philadelphia & Reading Railroad, Flat Rock Tunnel, Beneath Flat Rock Hill, west of Schuylkill Expressway (I-76), West Manayunk, Montgomery County, PA

  20. 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

  1. CdSe nanocrystals formation in silica sonogels

    SciTech Connect

    Hummel, D.C.; Torriani, I.L.; Ramos, A.Y.; Craievich, A.F.; Rosa-Fox, N. De La; Esquivias, L.

    1994-12-31

    Host-matrix gels were prepared by hydrolysis of TEOS with the addition of cadmium nitrate, formamide as DCCA (drying control chemical additive) and submitted to a preselected dose of high power ultrasound. The impregnation of the dry ``sonogel`` with KSeCN solution under vacuum conditions promoted the formation of the CdSe nanocrystals and enhanced the mechanical properties of the matrix. A transparent red xerogel was obtained and characterized by optical spectroscopy, TEM and SAXS measurements. The results support a structural model of a porous matrix containing CdSe nanocrystals exhibiting a bimodal size distribution that depends on the Se content of the impregnating solutions. The blue shift of the optical absorption bands reveal the quantum-size confinement effects of CdSe nanocrystals.

  2. 3. View looking SE showing S elevation. Central of ...

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

    3. View looking SE showing S elevation. - 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

  3. View looking SE inside Electrical Shop Central of Georgia ...

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

    View looking SE inside Electrical Shop - Central of Georgia Railway, Savannah Repair Shops & Terminal Facilities, Electrical Shop, Bounded by West Broad, Jones, West Boundary & Hull Streets, Savannah, Chatham County, GA

  4. 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

  5. Comparison of diffusivity data derived from electrochemical and NMR investigations of the SeCN¯/(SeCN)2/(SeCN)3¯ system in ionic liquids.

    PubMed

    Solangi, Amber; Bond, Alan M; Burgar, Iko; Hollenkamp, Anthony F; Horne, Michael D; Rüther, Thomas; Zhao, Chuan

    2011-06-02

    Electrochemical studies in room temperature ionic liquids are often hampered by their relatively high viscosity. However, in some circumstances, fast exchange between participating electroactive species has provided beneficial enhancement of charge transport. The iodide (I¯)/iodine (I(2))/triiodide (I(3)¯) redox system that introduces exchange via the I¯ + I(2) ⇌ I(3)¯ process is a well documented example because it is used as a redox mediator in dye-sensitized solar cells. To provide enhanced understanding of ion movement in RTIL media, a combined electrochemical and NMR study of diffusion in the {SeCN¯-(SeCN)(2)-(SeCN)(3)¯} system has been undertaken in a selection of commonly used RTILs. In this system, each of the Se, C and N nuclei is NMR active. The electrochemical behavior of the pure ionic liquid, [C(4)mim][SeCN], which is synthesized and characterized here for the first time, also has been investigated. Voltammetric studies, which yield readily interpreted diffusion-limited responses under steady-state conditions by means of a Random Assembly of Microdisks (RAM) microelectrode array, have been used to measure electrochemically based diffusion coefficients, while self-diffusion coefficients were measured by pulsed field gradient NMR methods. The diffusivity data, derived from concentration and field gradients respectively, are in good agreement. The NMR data reveal that exchange processes occur between selenocyanate species, but the voltammetric data show the rates of exchange are too slow to enhance charge transfer. Thus, a comparison of the iodide and selenocyanate systems is somewhat paradoxical in that while the latter give RTILs of low viscosity, sluggish exchange kinetics prevent any significant enhancement of charge transfer through direct electron exchange. In contrast, faster exchange between iodide and its oxidation products leads to substantial electron exchange but this effect does not compensate sufficiently for mass transport

  6. Enhancement of hole mobility in InSe monolayer via an InSe and black phosphorus heterostructure.

    PubMed

    Ding, Yi-Min; Shi, Jun-Jie; Xia, Congxin; Zhang, Min; Du, Juan; Huang, Pu; Wu, Meng; Wang, Hui; Cen, Yu-Lang; Pan, Shu-Hang

    2017-10-05

    To enhance the low hole mobility (∼40 cm(2) V(-1) s(-1)) of InSe monolayer, a novel two-dimensional (2D) van der Waals heterostructure made of InSe and black phosphorus (BP) monolayers with high hole mobility (∼10(3) cm(2) V(-1) s(-1)) has been constructed and its structural and electronic properties are investigated using first-principles calculations. We find that the InSe/BP heterostructure exhibits a direct band gap of 1.39 eV and type-II band alignment with electrons (holes) located in the InSe (BP) layer. The band offsets of InSe and BP are 0.78 eV for the conduction band minimum and 0.86 eV for the valence band maximum, respectively. Surprisingly, the hole mobility in the InSe/BP heterostructure exceeds 10(4) cm(2) V(-1) s(-1), which is one order of magnitude larger than the hole mobility of BP and three orders larger than that of the InSe monolayer. The electron mobility is also increased to 3 × 10(3) cm(2) V(-1) s(-1). The physical reason has been analyzed deeply, and a universal method is proposed to improve the carrier mobility of 2D materials by forming heterostructures with them and other 2D materials with complementary properties. The InSe/BP heterostructure can thus be widely used in nanoscale InSe-based field-effect transistors, photodetectors and photovoltaic devices due to its type-II band alignment and high carrier mobility.

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. Extension of the yrast band in 74Se

    NASA Astrophysics Data System (ADS)

    Gross, C. J.; Cottle, P. D.; Headly, D. M.; Hüttmeier, U. J.; Moore, E. F.; Tabor, S. L.

    1987-11-01

    New states in the yrast band of 74Se have been seen with the reaction 52Cr(28Si,α2p)74Se at 98 MeV. The new states extend the known level scheme up to Jπ=(22+). For the states Jπ>=6+ the spectrum shows a relatively constant moment of inertia parameter ħ2/2θ=27.8+/-0.5 keV.

  12. 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

  13. Etude du diagramme ternaire CuInSe 2ZnSeIn 2Se 3

    NASA Astrophysics Data System (ADS)

    Chippaux, Daniel; Deschanvres, Alfred

    1982-11-01

    The system CuInSe 2ZnSeIn 2Se 3 has been investigated. A large domain of thiogallate-type compounds was found with a number of cation vacancies less or equal to that of ZnIn 2Se 4 compound. A study with a least-squares method was performed on the experimental parameters a and c and relations with the compositions are given. The blende-structure model with cation vacancies was used for evaluation of the vacancy radius [ r1 = (0.97 ± 0.05) Å] in the thiogallate compounds.

  14. 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

  15. Electron transport in stepped Bi2Se3 thin films

    NASA Astrophysics Data System (ADS)

    Bauer, S.; Bobisch, C. A.

    2017-08-01

    We analyse the electron transport in a 16 quintuple layer thick stepped Bi2Se3 film grown on Si(1 1 1) by means of scanning tunnelling potentiometry (STP) and multi-point probe measurements. Scanning tunnelling microscopy images reveal that the local structure of the Bi2Se3 film is dominated by terrace steps and domain boundaries. From a microscopic study on the nm scale by STP, we find a mostly linear gradient of the voltage on the Bi2Se3 terraces which is interrupted by voltage drops at the position of the domain boundaries. The voltage drops indicate that the domain boundaries are scatterers for the electron transport. Macroscopic resistance measurements (2PP and in-line 4PP measurement) on the µm scale support the microscopic results. An additional rotational square 4PP measurement shows an electrical anisotropy of the sheet conductance parallel and perpendicular to the Bi2Se3 steps of about 10%. This is a result of the anisotropic step distribution at the stepped Bi2Se3 surface while domain boundaries are distributed isotropically. The determined value of the conductivity of the Bi2Se3 steps of about 1000 S cm-1 verifies the value of an earlier STP study.

  16. 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].

  17. Pseudodynamic imaging of the temporomandibular joint: SE versus GE sequences

    SciTech Connect

    Masui, Takayuki; Isoda, Haruo; Mochizuki, Takao

    1996-05-01

    Pseudodynamic MR imaging of the temporomandibular joints (TMJs) has been used for the evaluation of the functional aspects of the TMJs. To evaluate the value of T1-weighted spin-echo (SE) and gradient-echo (GE) techniques, both techniques were performed in 9 asymptomatic (mean 25.7 years, 22-32 years), and 25 symptomatic (mean 44.9 years, 20-71 years) subjects with signs and symptoms of internal derangement or osteoarthrosis of the TMJs. The imaging time for the SE (180 ms / 15 ms / 110{degrees} repetition time / echo time /flip angle) and GE (fast low angle shot; FLASH, 90 ms / 12 ms / 40{degrees}) sequences was 27 and 28 s, respectively. In asymptomatic and symptomatic subjects, the confidence of the identification of the meniscal position was better on SE than GE images (3.6 {+-} 0.6 vs. 2.9 {+-} 0.9, p < 0.01, 3.2 {+-} 0.8 vs. 2.8 {+-} 0.8, p < 0.05), respectively and the sizes of the menisci were bigger on SE than GE images. The delineation of the condylar cortex was better on GE than SE images. For pseudodynamic imaging display of the TMJs, the SE images might be better than GE images to provide the stable recognition of the menisci. 17 refs., 7 figs., 5 tabs.

  18. Structural manifestations of aging in Se-rich glasses

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    We examine weakly cross-linked GexSe100-x (0%Se. The 5-fold reduction of W(x) with a decrease of Ge content is accompanied by a 2-fold increase in the non-reversing enthalpy. Rejuvenation of the aged glasses changes W(x) from 15C at 7% Ge to 7C for pure Se. Tg is found to decrease upon rejuvenation with the difference (Tg(aged)-Tg(rejuv)) showing a maximum near 3% Ge and vanishing for pure Se and 6% of Ge, which are topological thresholds. These results in Se-rich glasses are consistent with aging induced decoupling of Se8 crowns and growth of extended range structural correlations between polymeric Sen chains due to lone pair interactions. At higher x, near 8-10% of Ge, eutectic effects are manifested. Work supported by NSF Grant DMR 08-53957.

  19. Electron transport in stepped Bi2Se3 thin films.

    PubMed

    Bauer, S; Bobisch, C A

    2017-08-23

    We analyse the electron transport in a 16 quintuple layer thick stepped Bi2Se3 film grown on Si(1 1 1) by means of scanning tunnelling potentiometry (STP) and multi-point probe measurements. Scanning tunnelling microscopy images reveal that the local structure of the Bi2Se3 film is dominated by terrace steps and domain boundaries. From a microscopic study on the nm scale by STP, we find a mostly linear gradient of the voltage on the Bi2Se3 terraces which is interrupted by voltage drops at the position of the domain boundaries. The voltage drops indicate that the domain boundaries are scatterers for the electron transport. Macroscopic resistance measurements (2PP and in-line 4PP measurement) on the µm scale support the microscopic results. An additional rotational square 4PP measurement shows an electrical anisotropy of the sheet conductance parallel and perpendicular to the Bi2Se3 steps of about 10%. This is a result of the anisotropic step distribution at the stepped Bi2Se3 surface while domain boundaries are distributed isotropically. The determined value of the conductivity of the Bi2Se3 steps of about 1000 S cm(-1) verifies the value of an earlier STP study.

  20. 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.

  1. 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.

  2. 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.

  3. Microwave Conductivity Spectroscopy for Fe(Se,Te) Thin Films

    NASA Astrophysics Data System (ADS)

    Nabeshima, Fuyuki; Nagasawa, Kosuke; Asami, Daisuke; Sawada, Yuichi; Imai, Yoshinori; Maeda, Atsutaka

    Iron chalcogenide superconductors Fe(Se,Te) have very small ɛF and are considered to be in the BCS-BEC crossover regime. Since Ginzburg number, Gi =(kBTc /ɛF) 4 , which is the relative temperature width of the superconducting fluctuation region, is large for materials in the BCS-BEC crossover regime, large superconducting fluctuations are expected in Fe(Se,Te). In order to investigate superconducting fluctuations in these materials we have performed microwave conductivity spectroscopy on Fe(Se,Te) thin films. Superfluid density of an Fe(Se,Te) film with Tczero =17 K took finite values above 25 K. This temperature is much higher than Tc estimated by the dc measurement, suggesting strong superconducting fluctuations in Fe(Se,Te). A dynamic scaling analysis of complex fluctuation conductivity revealed that the superconducting fluctuations of Fe(Se,Te) exhibit a 2-dimensional behavior, while BKT transition was not observed. We will also report on the thickness dependence and the Te content dependence of the superconducting fluctuation Partially supported by the Japan Society for the Promotion of Science (JSPS) Research Fellowship for Young Scientists and by JSPS KAKENHI Grant Numbers 15K17697.

  4. NaviSE: superenhancer navigator integrating epigenomics signal algebra.

    PubMed

    Ascensión, Alex M; Arrospide-Elgarresta, Mikel; Izeta, Ander; Araúzo-Bravo, Marcos J

    2017-06-06

    Superenhancers are crucial structural genomic elements determining cell fate, and they are also involved in the determination of several diseases, such as cancer or neurodegeneration. Although there are pipelines which use independent pieces of software to predict the presence of superenhancers from genome-wide chromatin marks or DNA-interaction protein binding sites, there is not yet an integrated software tool that processes automatically algebra combinations of raw data sequencing into a comprehensive final annotated report of predicted superenhancers. We have developed NaviSE, a user-friendly streamlined tool which performs a fully-automated parallel processing of genome-wide epigenomics data from sequencing files into a final report, built with a comprehensive set of annotated files that are navigated through a graphic user interface dynamically generated by NaviSE. NaviSE also implements an 'epigenomics signal algebra' that allows the combination of multiple activation and repression epigenomics signals. NaviSE provides an interactive chromosomal landscaping of the locations of superenhancers, which can be navigated to obtain annotated information about superenhancer signal profile, associated genes, gene ontology enrichment analysis, motifs of transcription factor binding sites enriched in superenhancers, graphs of the metrics evaluating the superenhancers quality, protein-protein interaction networks and enriched metabolic pathways among other features. We have parallelised the most time-consuming tasks achieving a reduction up to 30% for a 15 CPUs machine. We have optimized the default parameters of NaviSE to facilitate its use. NaviSE allows different entry levels of data processing, from sra-fastq files to bed files; and unifies the processing of multiple replicates. NaviSE outperforms the more time-consuming processes required in a non-integrated pipeline. Alongside its high performance, NaviSE is able to provide biological insights, predicting cell

  5. Thermoelectric properties of single-layered SnSe sheet

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.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

  6. Relaxation of hot excitons in inhomogeneously broadened CdxZn1-xSe/ZnSe nanostructures

    NASA Astrophysics Data System (ADS)

    Bacher, G.; Spiegel, R.; Kümmell, T.; Breitwieser, O.; Forchel, A.; Jobst, B.; Hommel, D.; Landwehr, G.

    1997-09-01

    The dimensionality dependence of hot exciton relaxation was studied by means of photoluminescence (PL) spectroscopy comparing CdxZn1-xSe/ZnSe quantum wells and quantum dots. In both systems, an efficient population of radiative excitonic ground states via longitudinal-optical (LO) phonon scattering is observed for an excess energy of the exciting laser corresponding to an integer number of LO-phonon energies. Thus, only selected areas of the inhomogeneously broadened systems contribute to the PL spectrum immediately after the exciting laser pulse. This results in a drastical reduction of the PL linewidth. In quantum wells, the redistribution of excitons occurs due to acoustic phonon assisted migration within the CdxZn1-xSe/ZnSe layer. In contrast, this process is found to be substantially suppressed in quantum dots due to the three-dimensional exciton confinement.

  7. 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.

  8. Existence and removal of Cu2Se second phase in coevaporated Cu2ZnSnSe4 thin films

    NASA Astrophysics Data System (ADS)

    Tanaka, Tooru; Sueishi, Tatsuya; Saito, Katsuhiko; Guo, Qixin; Nishio, Mitsuhiro; Yu, Kin M.; Walukiewicz, Wladek

    2012-03-01

    The composition dependence of the electrical properties of Cu2ZnSnSe4 thin films synthesized by coevaporation and the results of phase analyses are reported. We found that the hole concentration depends on the Cu/(Zn + Sn) ratio and is on the order of 1017 cm-3 for the ratio of 0.7 and increases to over 1020 cm-3 when the ratio exceeds 0.9. Raman spectra indicate the coexistence of semimetallic Cu2Se second phase in the thin films with Cu/(Zn + Sn) ratio above 0.9. In order to remove the Cu2Se phase selectively, we attempted a KCN etching. After the KCN etching for 30 min, the Raman peak attributed to the Cu2Se phase disappeared, and the hole concentration decreased to about 1018 cm-3.

  9. Photoluminescence brightening via electrochemical trap passivation in ZnSe and Mn(2+)-doped ZnSe quantum dots.

    PubMed

    Weaver, Amanda L; Gamelin, Daniel R

    2012-04-18

    Spectroelectrochemical experiments on wide-gap semiconductor nanocrystals (ZnSe and Mn(2+)-doped ZnSe) have allowed the influence of trap electrochemistry on nanocrystal photoluminescence to be examined in the absence of semiconductor band filling. Large photoluminescence electrobrightening is observed in both materials upon application of a reducing potential and is reversed upon return to the equilibrium potential. Electrobrightening is correlated with the transfer of electrons into nanocrystal films, implicating reductive passivation of midgap surface electron traps. Analysis indicates that the electrobrightening magnitude is determined by competition between electron trapping and photoluminescence (ZnSe) or energy transfer (Mn(2+)-doped ZnSe) dynamics within the excitonic excited state, and that electron trapping is extremely fast (k(trap) ≈ 10(11) s(-1)). These results shed new light on the complex surface chemistries of semiconductor nanocrystals. © 2012 American Chemical Society

  10. Anisotropy of chemical transformation from In2Se3 to CuInSe2 nanowires through solid state reaction.

    PubMed

    Schoen, David T; Peng, Hailin; Cui, Yi

    2009-06-17

    In(2)Se(3) nanowires synthesized by the VLS technique are transformed by solid-state reaction with copper into high-quality single-crystalline CuInSe(2) nanowires. The process is studied by in situ transmission electron microscopy. The transformation temperature exhibits a surprising anisotropy, with In(2)Se(3) nanowires grown along their [0001] direction transforming at a surprisingly low temperature of 225 degrees C, while nanowires in a [11(2)0] orientation require a much higher temperature of 585 degrees C. These results offer a route to the synthesis of CuInSe(2) nanowires at a relatively low temperature as well as insight into the details of a transformation commonly used in the fabrication of thin-film solar cells.

  11. Optical properties study in As50Se50 and As50Se40Te10 chalcogenide thin films

    NASA Astrophysics Data System (ADS)

    Behera, M.; Naik, Parbati; Panda, R.; Naik, R.

    2017-05-01

    Amorphous As50Se50 and As50Se40Te10 thin films were prepared by thermal evaporation technique. The amorphous nature of these films were confirmed from the XRD study. The optical transmission spectra of these films were measured in the wavelength range of 400-1200 nm. The transmittance power is found to be decreased with Te incorporation into As50Se50 while the absorption value is increased. The mechanism of the optical absorption follows the rule of allowed non-direct transition. The optical band gap value is found to be decreased while the width of localized states (urbach energy) Ee increases with Te addition. Addition of Te into As50Se50 is found to affect the refractive index and extinction coefficient. The Raman shift observed in the two films clearly supports the optical changes due to Te addition. The chemical bond approach has been applied to interpret the decrease in optical band gap.

  12. 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.

  13. Electronic structure and optical absorption spectra of CdSe covered with ZnSe and ZnS epilayers

    NASA Astrophysics Data System (ADS)

    Yun, So Jeong; Lee, Geunsik; Kim, Jai Sam; Shin, Seung Koo; Yoon, Young-Gui

    2006-02-01

    Using the first-principles methods we compute the electronic structure and the absorption spectra for a wurtzite CdSe (0001) slab covered with zincblende ZnSe and ZnS epilayers. For each structure we compute the DOS and the imaginary part of the dielectric function. We find that the semiconductor passivation shifts the 'near Fermi-level' states of the bare CdSe slab down to lower energy levels. The migration suggests the decrease of surface effects and energy loss. We observe the substantial reduction of the abnormal peaks in the absorption spectra of the bare CdSe slab, which seems to be a consequence of the DOS migration. This is consistent with the experimental results that a proper passivation enhance the luminescence efficiency. We also study the case that the epilayer surface is terminated with PH 3 and find the PH 3 passivation also reduces the surface state to some extent.

  14. Optical properties of Se2- and Se2 color centers in the red selenium ultramarine with the sodalite structure.

    PubMed

    Schlaich, H; Lindner, G G; Felmann, J; Göbel, E O; Reinen, D

    2000-06-26

    The unique optical properties of Se2- radicals located in the cages of the sodalite structure are reported. By means of luminescence, photoluminescence excitation, and absorption spectroscopy, three different centers are identified. Two of them are Se2- anions in sites with presumably a tetrahedral Na4(4+) coordination and a Na3(3+) environment with cation deficiency, respectively, giving rise to a red luminescence band with two different progressions. The third center is the intermediate Se2 molecule, created photochemically by UV laser excitation. It induces an additional blue luminescence. The electronic properties of the Se2- centers, particularly in the excited states, are significantly influenced by steric constraints imposed by the limited space in the sodalite host polyhedra. Thus, the sodalite structure can be viewed as a model system for studying effects of this kind on chromophores imbedded in the cages of the zeolite-type lattice.

  15. Detection of a ZnSe secondary phase in coevaporated Cu2ZnSnSe4 thin films

    NASA Astrophysics Data System (ADS)

    Redinger, Alex; Hönes, Katja; Fontané, Xavier; Izquierdo-Roca, Victor; Saucedo, Edgardo; Valle, Nathalie; Pérez-Rodríguez, Alejandro; Siebentritt, Susanne

    2011-03-01

    Cu2ZnSnSe4 (CZTSe) thin films are grown by coevaporation. Composition depth profiles reveal that a Zn rich phase is present at the CZTSe/Mo interface. Raman measurements on the as grown films are used to study the near surface region and the CZTSe/Mo interface, after mechanically removing the thin film from the Mo coated glass. These measurements provide direct experimental evidence of the formation of a ZnSe phase at the CZTSe/Mo interface. While the Raman spectra at the surface region are dominated by CZTSe modes, those measured at the CZTSe/Mo interface are dominated by ZnSe and MoSe2 modes.

  16. 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.

  17. Tunable Magnetic Exchange Interactions in Manganese-Doped Inverted Core-Shell ZnSe-CdSe Nanocrystals

    DTIC Science & Technology

    2009-01-01

    interaction. c, A diagram showing the relative energies of quantum -confined electron and hole levels in the nanocrystal (Ee and Eh) and the occupied...Nano Lett. 4, 1485–1488 (2004). 8. Bacher, G. et al. Optical spectroscopy on individual CdSe/ZnMnSe quantum dots . Appl. Phys. Lett. 79, 524–527 (2001...route towards magnetically active quantum dots . With a view towards enhancing carrier/paramagnetic ion spin interactions, colloidal nanocrystals

  18. Nonuniform Excitonic Charge Distribution Enhances Exciton-Phonon Coupling in ZnSe/CdSe Alloyed Quantum Dots.

    PubMed

    Gong, Ke; Kelley, David F; Kelley, Anne Myers

    2017-02-02

    Zinc to cadmium cation exchange of ZnSe quantum dots has been used to produce a series of alloyed Zn1-xCdxSe quantum dots. As x increases and the lowest-energy exciton shifts to the red, the peak initially broadens and then sharpens as x approaches 1. Resonance Raman spectra obtained with excitation near the lowest excitonic absorption peak show a gradual shift of the longitudinal optical phonon peak from 251 cm(-1) in pure ZnSe to 210 cm(-1) in nearly pure CdSe with strong broadening at intermediate compositions. The LO overtone to fundamental intensity ratio, a rough gauge of exciton-phonon coupling strength, increases considerably for intermediate compositions compared with those of either pure ZnSe or pure CdSe. The results indicate that partial localization of the hole in locally Cd-rich regions of the alloyed particles increases the strengths of local internal electric fields, increasing the coupling between the exciton and polar optical phonons.

  19. Tunable Se vacancy defects and the unconventional charge density wave in 1 T -TiSe2 -δ

    NASA Astrophysics Data System (ADS)

    Huang, S. H.; Shu, G. J.; Pai, Woei Wu; Liu, H. L.; Chou, F. C.

    2017-01-01

    A systematic study of polycrystalline 1 T -TiSe2 -δ with controlled Se loss indicates that the unconventional charge density wave (CDW) phase is found to be most pronounced in samples with δ ˜0.12 , instead of being Se vacancy free. The level of Se vacancy defects and temperature determines whether 1 T -TiSe2 -δ should be categorized as a semiconductor, a semimetal, or an excitonic insulator. An interpretation using a general band picture of p -type doped narrow-band-gap semiconductor with an impurity band (IB) in proximity to the valence band (VB) is proposed to explain the evolution of electronic structures for 1 T -TiSe2 -δ , from the intermediate doping of δ ˜0.08 , to the critical doping of δ ˜0.12 showing an anomalous resistivity peak between ˜100 -200 K , and to the heavily doped of δ ˜0.17 as an n -type degenerate semiconductor. Integrated chemical analysis and physical property characterization, including electron probe microanalysis (EPMA), synchrotron x-ray diffraction, resistivity, and Seebeck coefficient measurement results are provided for the polycrystalline samples prepared via vacuum-sealed high temperature annealing route.

  20. Novel Pd2Se3 Two-Dimensional Phase Driven by Interlayer Fusion in Layered PdSe2

    NASA Astrophysics Data System (ADS)

    Lin, Junhao; Zuluaga, Sebastian; Yu, Peng; Liu, Zheng; Pantelides, Sokrates T.; Suenaga, Kazu

    2017-07-01

    Two-dimensional (2D) materials are easily fabricated when their bulk form has a layered structure. The monolayer form in layered transition-metal dichalcogenides is typically the same as a single layer of the bulk material. However, PdSe2 presents a puzzle. Its monolayer form has been theoretically shown to be stable, but there have been no reports that monolayer PdSe2 has been fabricated. Here, combining atomic-scale imaging in a scanning transmission electron microscope and density functional theory, we demonstrate that the preferred monolayer form of this material amounts to a melding of two bulk monolayers accompanied by the emission of Se atoms so that the resulting stoichiometry is Pd2Se3 . We further verify the interlayer melding mechanism by creating Se vacancies in situ in the layered PdSe2 matrix using electron irradiation. The discovery that strong interlayer interactions can be induced by defects and lead to the formation of new 2D materials opens a new venue for the exploration of defect engineering and novel 2D structures.

  1. Spin Dynamics and Optical Nonlinearities in Layered GaSe and Colloidal CdSe Nanocrystal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tang, Yanhao

    In this thesis, we studied spin dynamics, optical nonlinearity and the optical Stark effect in bulk GaSe, mono- and few-layer GaSe, and colloidal CdSe nanocrystal quantum dots (NQDs), respectively. Control of the spin has been a long-term goal due to its potential applications in quantum information processing. Candidates for spintronics should have a long spin lifetime and allow for generation of a high initial spin polarization. GaSe caught our attention due to its orbitally nondegenerate valence bands, which are in contrast to the degenerate heavy and light hole valence bands in conventional III-V and II-VI semiconductors, like GaAs and CdSe. With time- and polarization-resolved photoluminescence, we demonstrated the generation of initial spin polarization as high as 0.9 followed by bi-exponential spin relaxation at 10 K (˜30 ps and ≥300 ps), owing to such orbitally nondegenerate valence bands in GaSe. We also directly revealed the initial spin and population relaxation as transitions from triplet excitons to singlet excitions via spin-flip of the electron or hole. Contrary to semiconductor transition metal dichalcogenides, MX2 (M=Mo,W; X=S,Se,Te), GaSe is a direct band gap semiconductor in bulk, but transforms to an indirect band gap semiconductor in a monolayer as the maximum of the valence band is shifted away from the Gamma point. Associated with such a valence band in monolayer GaSe, ferromagnetism has been predicted upon hole doping due to a strong electronic exchange field. To study the electronic structure of GaSe in mono- and few-layer GaSe, we measured layer- and frequency-dependent second-harmonic generation (SHG) in GaSe from monolayer to ≥100 layers and determined a second-order optical nonlinearity chi(2) in the multi-slab system. We found reduced a chi(2) in GaSe with thickness < 7 layers, tentatively attributed to the predicted increase in the band gap. How quantum confinement affects the light-matter interaction in colloidal CdSe

  2. Fixed-flexion knee radiography using a new positioning device produced highly repeatable measurements of joint space width: ELSA-Brasil Musculoskeletal Study (ELSA-Brasil MSK).

    PubMed

    Telles, Rosa Weiss; Costa-Silva, Luciana; Machado, Luciana A C; Reis, Rodrigo Citton Padilha Dos; Barreto, Sandhi Maria

    To describe the performance of a non-fluoroscopic fixed-flexion PA radiographic protocol with a new positioning device, developed for the assessment of knee osteoarthritis (OA) in Brazilian Longitudinal Study of Adult Health Musculoskeletal Study (ELSA-Brasil MSK). A test-retest design including 19 adults (38 knee images) was conducted. Feasibility of the radiographic protocol was assessed by image quality parameters and presence of radioanatomic alignment according to intermargin distance (IMD) values. Repeatability was assessed for IMD and joint space width (JSW) measured at three different locations. Approximately 90% of knee images presented excellent quality. Frequencies of nearly perfect radioanatomic alignment (IMD ≤1mm) ranged from 29% to 50%, and satisfactory alignment was found in up to 71% and 76% of the images (IMD ≤1.5mm and ≤1.7mm, respectively). Repeatability analyses yielded the following results: IMD [SD of mean difference=1.08; coefficient of variation (%CV)=54.68%; intraclass correlation coefficient (ICC) (95%CI)=0.59 (0.34-0.77)]; JSW [SD of mean difference=0.34-0.61; %CV=4.48%-9.80%; ICC (95%CI)=0.74 (0.55-0.85)-0.94 (0.87-0.97)]. Adequately reproducible measurements of IMD and JSW were found in 68% and 87% of the images, respectively. Despite the difficulty in achieving consistent radioanatomic alignment between subsequent radiographs in terms of IMD, the protocol produced highly repeatable JSW measurements when these were taken at midpoint and 10mm from the medial extremity of the medial tibial plateau. Therefore, measurements of JSW at these locations can be considered adequate for the assessment of knee OA in ELSA-Brasil MSK. Copyright © 2016. Published by Elsevier Editora Ltda.

  3. Fixed-flexion knee radiography using a new positioning device produced highly repeatable measurements of joint space width: ELSA-Brasil Musculoskeletal Study (ELSA-Brasil MSK).

    PubMed

    Telles, Rosa Weiss; Costa-Silva, Luciana; Machado, Luciana A C; Reis, Rodrigo Citton Padilha Dos; Barreto, Sandhi Maria

    2016-11-26

    To describe the performance of a non-fluoroscopic fixed-flexion PA radiographic protocol with a new positioning device, developed for the assessment of knee osteoarthritis (OA) in ELSA-Brasil MSK. A test-retest design including 19 adults (38 knee images) was conducted. Feasibility of the radiographic protocol was assessed by image quality parameters and presence of radioanatomic alignment according to intermargin distance (IMD) values. Repeatability was assessed for IMD and joint space width (JSW) measured at three different locations. Approximately 90% of knee images presented excellent quality. Frequencies of nearly perfect radioanatomic alignment (IMD ≤1mm) ranged from 29% to 50%, and satisfactory alignment was found in up to 71% and 76% of the images (IMD ≤1.5mm and ≤1.7mm, respectively). Repeatability analyses yielded the following results: IMD [SD of mean difference=1.08; coefficient of variation (%CV)=54.68%; intraclass correlation coefficient (ICC) (95%CI)=0.59 (0.34-0.77)]; JSW [SD of mean difference=0.34 - 0.61; %CV=4.48% - 9.80%; ICC (95%CI)=0.74 (0.55-0.85) - 0.94 (0.87-0.97)]. Adequately reproducible measurements of IMD and JSW were found in 68% and 87% of the images, respectively. Despite the difficulty in achieving consistent radioanatomic alignment between subsequent radiographs in terms of IMD, the protocol produced highly repeatable JSW measurements when these were taken at midpoint and 10mm from the medial extremity of the medial tibial plateu. Therefore, measurements of JSW at these locations can be considered adequate for the assessment of knee OA in ELSA-Brasil MSK. Copyright © 2016. Published by Elsevier Editora Ltda.

  4. Avança Brasil: environmental and social consequences of Brazil's planned infrastructure in Amazonia.

    PubMed

    Fearnside, Philip M

    2002-12-01

    "Avança Brasil" (Forward Brazil) is a package of 338 projects throughout Brazil; the portion of the plan to be carried out in Brazil's Legal Amazon region totals US$43 billion over 8 years, US$20 billion of which would be for infrastructure causing environmental damage. Brazil's environmental impact assessment system is not yet capable of coping with the challenge presented by Avança Brasil. Generic problems with the licensing process include stimulation of a lobby in favor of construction before decisions are made on the advisability of the projects, the "dragging effect" of third parties, whereby economic activity is attracted to the infrastructure but escapes the environmental impact assessment system, a tendency for consulting firms to produce favorable reports, a bureaucratic emphasis on the existence of steps without regard to the content of what is said, and the inability to take account of the chain of events unleashed when a given project is undertaken. The environmental and social costs of forest loss are high; among them is loss of opportunities for sustainable use of the forest, including loss of environmental services such as biodiversity maintenance, water cycling, and carbon storage. The benefits of export infrastructure are meager, especially from the point of view of generating employment. Much of the transportation infrastructure is for soybeans, while the hydroelectric dams contribute to processing aluminum. The example of Avança Brasil makes clear the need to rethink how major development decisions are made and to reconsider a number of the plan's component projects.

  5. Ab Initio Study on Atomic Structures and Physical Properties of CdSe Quantum Nanodots

    DTIC Science & Technology

    2009-11-25

    CdSe quantum dots , with magic number (( CdSe )13, ( CdSe )19, ( CdSe )33 and ( CdSe )34 ). Effects of organic ligand binding on the stability of CdSe as well...calculations of optical absorption spectra for CdSe quantum dots , with magic number (( CdSe )13, ( CdSe )19, ( CdSe )33 and ( CdSe )34 ), have been calculated in...1 AOARD-08-4037 Title of Proposed Project: Ab initio study on atomic structures and physical

  6. 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 .

  7. 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+) .

  8. Anomalous magnetotransport behaviours in PtSe2 microflakes

    NASA Astrophysics Data System (ADS)

    Li, Zhaoguo; Zhang, Jicheng; Zeng, Yong; Meng, Lingbiao; Zhou, Minjie; Wu, Weidong

    2017-06-01

    Platinum diselenide (PtSe2) is a newly discovered 2D transition metal dichalcogenide, and is further theoretically identified as a candidate of type-II Dirac semimetals. The electrical transport study of PtSe2 microflakes may provide great potential not only in fundamental physics, but also for future electronic applications. We report the anomalous magnetotransport properties of PtSe2 microflakes. The anisotropic magnetoresistance of PtSe2 microflakes can be normalized by introducing a 3D scaling factor {{\\varepsilon}θ}={≤ft({{\\cos}2}θ +{{γ-2}{{\\sin}2}θ \\right)}1/2} , where θ is the magnetic field angle with respect to the c axis of the crystal and γ is the mass anisotropic constant of electrons. Additionally, the non-monotonic temperature-dependent magnetoresistance of PtSe2 microflakes is observed both in the perpendicular and in-plane magnetic field orientations. This anomalous magnetotransport behaviour may be ascribed to the novel features of type-II Dirac fermions; however, the exact physical mechanism deserves further investigation.

  9. Heterojunctions of model CdTe/CdSe mixtures

    DOE PAGES

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

    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

  10. Nanocrystalline Cr(2+)-doped ZnSe nanowires laser.

    PubMed

    Feng, Guoying; Yang, Chao; Zhou, Shouhuan

    2013-01-09

    By using femtosecond laser pulses to ablate microsized targets that are dispersed in liquid media, nanocrystalline Cr(2+)-doped ZnSe nanowires have been successfully fabricated for the first time. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 30-120 nm for these nanowires. X-ray diffraction results show that the products are nanocrystalline ZnSe with cubic sphalerite structure. Scanning electron microscope results indicate that the products be ZnSe nanowires. The nanowires are usually 30-120 nm in diameter and several tens of micrometers in length. Photoluminescence of the nanocrystalline Cr(2+)-doped ZnSe nanowires shows strong emission at around 2000-2500 nm under excitation of 1300-2250 nm wavelength at room temperature. By using the Cr(2+)-doped ZnSe multiple nanowires as the gain medium, mid-infrared oscillation at 2194 nm has been established. The oscillation wavelength of the multiple nanowires laser is 150 nm shifted to shorter wavelengths in comparison with that of microsized powder random laser.

  11. 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.

  12. 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. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. 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.

  14. Optics of colloidal quantum-confined CdSe nanoscrolls

    SciTech Connect

    Vasiliev, R B; Sokolikova, M S; Vitukhnovskii, A G; Ambrozevich, S A; Selyukov, A S; Lebedev, V S

    2015-09-30

    Nanostructures in the form of 1.2-nm-thick colloidal CdSe nanoplatelets rolled into scrolls are investigated. The morphology of these scrolls is analysed and their basic geometric parameters are determined (diameter 29 nm, longitudinal size 100 – 150 nm) by TEM microscopy. Absorption and photoluminescence spectra of these objects are recorded, and the luminescence decay kinetics is studied. It is shown that the optical properties of CdSe nanoscrolls differ significantly from the properties of CdSe quantum dots and that these nanoscrolls are attractive for nanophotonic devices due to large oscillator strengths of the transition, small widths of excitonic peaks and short luminescence decay times. Nanoscrolls can be used to design hybrid organic–inorganic pure-color LEDs with a high luminescence quantum yield and low operating voltages. (optics and technology of nanostructures)

  15. Data-driven initialization of SParSE

    NASA Astrophysics Data System (ADS)

    Roh, Min K.; Proctor, Joshua L.

    2017-07-01

    Despite the ever-increasing affordability and availability of high performance computing platforms, computational analysis of stochastic biochemical systems remains an open problem. A recently developed event-based parameter estimation method, the stochastic parameter search for events (SParSE), is able to efficiently sample reaction rate parameter values that confer a user-specified target event with a given probability and error tolerance. Despite the substantial computational savings, the efficiency of SParSE can be further improved by intelligently generating new initial parameter sets based on previously computed trajectories. In this article, we propose a principled method which combines the efficiencies of SParSE with these geometric machine-learning methods to generate new initial parameters based on the previously collected data.

  16. Mössbauer measurements on SnSe2

    NASA Astrophysics Data System (ADS)

    Bibicu, I.; Lőrinczi, A.; Popescu, M.

    2010-11-01

    Tin chalcogenides SnX2 and SnX, where X = S, Se and Te present a particularly interest for their electronic properties and applications in gas sensors. The state of tin in these materials is important for understanding of the sensing effect and improvement of the sensor performances. Mössbauer spectroscopy is a widely used technique for the analysis of the local electronic structure or chemical bonding in solids. In this paper we applied Mössbauer technique for the investigation of bulk and thin films of SnSe2 chalcogenide. The films of SnSe2 chalcogenide were obtained by the methods: PLD ("Pulsed laser deposition") and PED ("Pulsed electron deposition"). Mössbauer measurements were performed by transmission (TMS), respectively conversion electron spectroscopy (CEMS). By CEMS spectroscopy surfaces, coatings and thin films containing Sn can be studied on substrates and to various depths up to 1000 nanometers.

  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. Monolayer FeSe on SrTiO3

    NASA Astrophysics Data System (ADS)

    Huang, Dennis; Hoffman, Jennifer E.

    2017-03-01

    Epitaxial engineering of solid state heterointerfaces is a leading avenue to realizing enhanced or novel electronic states of matter. As a recent example, bulk FeSe is an unconventional superconductor with a modest transition temperature (Tc) of 9 K. However, when a single atomic layer of FeSe is grown on SrTiO3, its Tc can skyrocket by an order of magnitude to 65 K or 109 K. Since this discovery in 2012, efforts to reproduce, understand, and extend these findings continue to draw both excitement and scrutiny. In this review, we first present a critical survey of experimental measurements performed using a wide range of techniques. We then turn to the open question of microscopic mechanisms of superconductivity. We examine contrasting indications for both phononic (conventional) and magnetic/orbital (unconventional) means of electron pairing, as well as speculations about whether they could work cooperatively to boost Tc in a monolayer of FeSe.

  19. Quasiparticle dynamics and phonon softening in FeSe superconductors.

    PubMed

    Luo, C W; Wu, I H; Cheng, P C; Lin, J-Y; Wu, K H; Uen, T M; Juang, J Y; Kobayashi, T; Chareev, D A; Volkova, O S; Vasiliev, A N

    2012-06-22

    Quasiparticle dynamics of FeSe single crystals revealed by dual-color transient reflectivity measurements (ΔR/R) provides unprecedented information on Fe-based superconductors. The amplitude of the fast component in ΔR/R clearly gives a competing scenario between spin fluctuations and superconductivity. Together with the transport measurements, the relaxation time analysis further exhibits anomalous changes at 90 and 230 K. The former manifests a structure phase transition as well as the associated phonon softening. The latter suggests a previously overlooked phase transition or crossover in FeSe. The electron-phonon coupling constant λ is found to be 0.16, identical to the value of theoretical calculations. Such a small λ demonstrates an unconventional origin of superconductivity in FeSe.

  20. Single-photon emitters in GaSe

    NASA Astrophysics Data System (ADS)

    Tonndorf, Philipp; Schwarz, Stefan; Kern, Johannes; Niehues, Iris; Del Pozo-Zamudio, Osvaldo; Dmitriev, Alexander I.; Bakhtinov, Anatoly P.; Borisenko, Dmitry N.; Kolesnikov, Nikolai N.; Tartakovskii, Alexander I.; Michaelis de Vasconcellos, Steffen; Bratschitsch, Rudolf

    2017-06-01

    Single-photon sources are important building blocks for quantum information technology. Emitters based on solid-state systems provide a viable route to integration in photonic devices. Here, we report on single-photon emitters in the layered semiconductor GaSe. We identify the exciton and biexciton transition of the quantum emitters with power-dependent photoluminescence and photon statistics measurements. We find evidence that the localization of the excitons is related to deformations of the GaSe crystal, caused by nanoscale selenium inclusions, which are incorporated in the crystal. These deformations give rise to local strain fields, which induce confinement potentials for the excitons. This mechanism lights the way for the controlled positioning of single-photon emitters in GaSe on the nanoscale.

  1. 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.

  2. Topological Superconductivity in CuxBi2Se3

    NASA Astrophysics Data System (ADS)

    Sasaki, Satoshi; Kriener, M.; Segawa, Kouji; Yada, Keiji; Tanaka, Yukio; Sato, Masatoshi; Ando, Yoichi

    2011-11-01

    A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator CuxBi2Se3, which superconducts below ˜3K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting CuxBi2Se3 present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in CuxBi2Se3. In addition, we found an unusual pseudogap that develops below ˜20K and coexists with the topological superconducting state.

  3. A Quaternary ZnCdSeTe Nanotip Photodetector

    PubMed Central

    2009-01-01

    The authors report the growth of needle-like high density quaternary Zn0.87Cd0.13Se0.98Te0.02nanotips on oxidized Si(100) substrate. It was found that average length and average diameter of the nanotips were 1.3 μm and 91 nm, respectively. It was also found that the as-grown ZnCdSeTe nanotips exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. Furthermore, it was found that the operation speeds of the fabricated ZnCdSeTe nanotip photodetector were fast with turn-on and turn-off time constants both less than 2 s. PMID:20652144

  4. 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.

  5. 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.

  6. Electrodeposition and characterization of CdSe semiconducting nanowires.

    PubMed

    Yu-Zhang, K; Guo, D Z; Mallet, J; Molinari, M; Loualiche, A; Troyon, M

    2008-04-01

    In this paper, we present our work on the electrodeposited CdSe semiconducting nanowires. Using a low cost and low temperature approach by electrochemistry, CdSe nanowires were successfully grown using polycarbonate template. Depending on the host pore dimension of the substrate, wire diameter can be varied from 400 nm down to 30 nm and wire length from a few microns to tens microns. The as-deposited nanowires exhibit predominantly metastable zinc blende (ZB) structure but after the heat treatment they become wurtzite (W) structure. A combination of different characterization techniques, such as X-ray diffraction, SEM, TEM-HRTEM and EDXS, was used to investigate the growth morphology, crystalline structure and defects in the nanowires. The luminescent properties of CdSe nanowires have also been studied by means of photoluminescence.

  7. Self-Assembled PbSe Nanowire:Perovskite Hybrids.

    PubMed

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

    2015-12-02

    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.

  8. Effect of doping on electronic properties of HgSe

    SciTech Connect

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

    2016-05-23

    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 Γ. 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.

  9. Topological Superconductivity in Cu(x)Bi(2)Se(3).

    PubMed

    Sasaki, Satoshi; Kriener, M; Segawa, Kouji; Yada, Keiji; Tanaka, Yukio; Sato, Masatoshi; Ando, Yoichi

    2011-11-18

    A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator Cu(x)Bi(2)Se(3), which superconducts below ∼3 K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting Cu(x)Bi(2)Se(3) present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in Cu(x)Bi(2)Se(3). In addition, we found an unusual pseudogap that develops below ∼20 K and coexists with the topological superconducting state.

  10. Crystallographic and optical properties and band structures of CuInSe2, CuIn3Se5, and CuIn5Se8 phases in Cu-poor Cu2Se-In2Se3 pseudo-binary system

    NASA Astrophysics Data System (ADS)

    Maeda, Tsuyoshi; Gong, Weiyan; Wada, Takahiro

    2016-04-01

    We prepared CuInSe2 and Cu-poor Cu-In-Se (CIS) phases such as CuIn3Se5 and CuIn5Se8 in the composition of (1 - x)Cu2Se-(x)In2Se3 with 0.5 ≤ x ≤ 1.0. The crystal structure of the sample changed from chalcopyrite-type CuInSe2 to hexagonal CuIn5Se8 through stannite-type CuIn3Se5 with increasing x (decreasing Cu/In ratio). The band-gap energies of Cu-poor CIS samples, i.e., CuIn3Se5 (1.17 eV) and CuIn5Se8 (1.22-1.24 eV), are larger than that of chalcopyrite-type CuInSe2 (0.99 eV). The energy levels of the valence band maxima (VBMs) were estimated from the ionization energy by photoemission yield spectroscopy (PYS) measurements. The energy levels of the VBMs of the Cu-poor CIS samples decrease rapidly with decreasing Cu/In ratio. The ionization energy of stannite-type CuIn3Se5 is 0.4 eV larger than that of chalcopyrite-type CuInSe2. The ionization energy of CuIn5Se8 is 0.1-0.3 eV larger than that of CuIn3Se5. These results show that the energy position of the VBM from the vacuum level of Cu-poor CIS phases, such as CuIn3Se5 and CuIn5Se8, is deeper than that of CuInSe2. To understand the electronic structure of Cu-poor CIS compounds, we performed first-principles band structure calculations on stannite-type CuIn5Se8 and a reference compound, tetragonal chalcopyrite-type CuInSe2, using the HSE06 nonlocal screened hybrid density functional. The calculated band-gap energy of tetragonal stannite-type CuIn5Se8 (1.19 eV) is larger than that of chalcopyrite-type CuInSe2 (0.94 eV).

  11. 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})

  12. High-temperature superconductivity in FeSe monolayers

    NASA Astrophysics Data System (ADS)

    Sadovskii, M. V.

    2016-10-01

    This paper reviews the basic experimental and theoretical aspects of high-temperature superconductivity in intercalated FeSe compounds and FeSe monolayer films on SrTiO_3 and similar substrates. The paper examines in detail the electronic structure of these systems, how it is calculated, and how the calculated results compare with ARPES experiments. It is emphasized that the reviewed systems have qualitatively different electronic spectra from the typical pattern of well-studied FeAs superconductors and explores the implications of these differences for a theoretical description of how these spectra form. Possible mechanisms of Cooper pairing in FeSe monolayers are discussed and the associated problems are examined. Because FeSe monolayer films on SrTiO_3 are typical Ginzburg 'sandwiches', the possibility of increasing their T_c via 'excitonic' superconductivity mechanisms is considered. It is shown that, while the classical version of this mechanism (as proposed for such systems by Allender, Bray, and Bardeen) fails to explain the observed values of T_c, the situation changes when optical phonons in SrTiO_3 (with energy of about 100 meV) are considered to be 'excitons'. Both the simplest possible model of T_c enhancement due to interaction with such phonons and more complex ones with dominant 'forward' scattering that explain successfully the increase in T_c compared to bulk FeSe and intercalated FeSe systems are verified. Problems related to the antiadiabatic nature of this superconductivity mechanism are also discussed.

  13. 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

  14. Fabrication and photoluminescence properties of porous CdSe

    SciTech Connect

    Tiginyanu, I.M.; Monaico, E.; Ursaki, V.V.; Tezlevan, V.E.; Boyd, Robert W.

    2005-02-07

    We report the results of a study of the growth of pores in n-CdSe single crystals using anodic etching techniques. Upon anodization in dark, a nonuniform distribution of pores was produced. However, anodic dissolution of the material under in situ UV illumination proves to result in uniform distribution of pores stretching perpendicularly to the initial surface of the specimen. The porous structures exhibit less luminescence than the bulk samples. These results pave the way for cost-effective manufacturing of CdSe-based semiconductor nanotemplates for nanofabrication.

  15. 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.

  16. Scanning tunneling luminescence of individual CdSe nanowires.

    PubMed

    Lutz, Theresa; Kabakchiev, Alexander; Dufaux, Thomas; Wolpert, Christian; Wang, Zhe; Burghard, Marko; Kuhnke, Klaus; Kern, Klaus

    2011-08-22

    The local luminescence properties of individual CdSe nanowires composed of segments of zinc blende and wurtzite crystal structures are investigated by low-temperature scanning tunneling luminescence spectroscopy. Light emission from the wires is achieved by the direct injection of holes and electrons, without the need for coupling to tip-induced plasmons in the underlying metal substrate. The photon energy is found to increase with decreasing wire diameter due to exciton confinement. The bulk bandgap extrapolated from the energy versus diameter dependence is consistent with photon emission from the zinc blende-type CdSe sections.

  17. Polytypic phase transitions in metal intercalated Bi2Se3

    NASA Astrophysics Data System (ADS)

    Wang, Mengjing; Koski, Kristie J.

    2016-12-01

    The temperature and concentration dependent phase diagrams of zero-valent copper, cobalt, and iron intercalated bismuth selenide are investigated using in situ transmission electron microscopy. Polytypic phase transitions associated with superlattice formation along with order-disorder transitions of the guest intercalant are determined. Dual-element intercalants of CuCo, CuFe, and CoFe-Bi2Se3 are also investigated. Hexagonal and striped domain formation consistent with two-dimensional ordering of the intercalant and Pokrovksy-Talapov theory is identified as a function of concentration. These studies provide a complete picture of the structural behavior of zero-valent metal intercalated Bi2Se3.

  18. Exotic topological insulator states and topological phase transitions in Sb2Se3-Bi2Se3 heterostructures.

    PubMed

    Zhang, Qianfan; Zhang, Zhiyong; Zhu, Zhiyong; Schwingenschlögl, Udo; Cui, Yi

    2012-03-27

    Topological insulator is a new state of matter attracting tremendous interest due to its gapless linear dispersion and spin momentum locking topological states located near the surface. Heterostructures, which have traditionally been powerful in controlling the electronic properties of semiconductor devices, are interesting for topological insulators. Here, we studied the spatial distribution of the topological state in Sb(2)Se(3)-Bi(2)Se(3) heterostructures by first-principle simulation and discovered that an exotic topological state exists. Surprisingly, the state migrates from the nontrivial Bi(2)Se(3) into the trivial Sb(2)Se(3) region and spreads across the entire Sb(2)Se(3) slab, extending beyond the concept of "surface" state while preserving all of the topological surface state characteristics. This unusual topological state arises from the coupling between different materials and the modification of electronic structure near Fermi energy. Our study demonstrates that heterostructures can open up opportunities for controlling the real-space distribution of the topological state and inducing quantum phase transitions between topologically trivial and nontrivial states.

  19. The Se effect on the oxygen reduction reaction on the Se/Ru electro-catalysts. Insight from first principles.

    NASA Astrophysics Data System (ADS)

    Stolbov, Sergey

    2011-03-01

    Rational search for new efficient low-cost electrocatalysts for oxygen reduction reaction (ORR) on the hydrogen fuel cell cathodes focuses on varying the material composition to modify the local densities of electronic states (LDOS) of the surface atoms, in order to tune the surface-adsorbate electronic state hybridization and hence binding energies of the ORR intermediates. My calculation results for the Se/Ru electrocatalysts suggest an alternative way of tuning the binding energies. The Se atoms deposited on the Ru surface are found not to change Ru LDOS noticeably, however, Se atoms are negatively charged due to ionic Se-Ru bonding. As a result, they repeal electrostatically the adsorbed negatively charged O and OH intermediates, and this way reduce their binding energies. Since for the Ru case, reduction of the O and OH binding energies makes ORR energetically favorable, Se deposition dramatically improve the ORR rate on Ru. The ORR rate can thus be enhanced by changing coverage of the deposited halchogen atoms or by tuning the charge transfer to those by modifying the substrate composition.

  20. Linear and NLO spectroscopy of GaSe and InSe nanoparticles formed via laser ablation

    NASA Astrophysics Data System (ADS)

    Pashayev, A.; Tunaboylu, B.; Allahverdiyev, K.; Salayev, E.; Tagiyev, B.

    2015-12-01

    Nanoparticles of layered GaSe, InSe were fabricated by laser ablation (LA) method (KrF laser, λ = 248 nm, 50 Hz, maximum energy 200 mJ, τ = 4 ns) and characterized by: •XRF •GDOES •SEM and TEM; •UV-, VIS-, and IRabsorption; •Raman and PL spectroscopy (also in confocal geometry). Results are discussed in relation to the particle size. Absorption spectra of particles with diameter 20 nm and less turned out to be blue shifted and is consisted with a weak confinement effect on Wannier-Mott type excitons. It is shown, that with decreasing the particle size the energy position of the low-frequency Raman active phonons in both compounds are shifted to lower frequencies (21 and 18 cm-1 in bulk GaSe and InSe and 8 and 7 cm-1 in particles with sizes 5 and 7 nm, respectively). From the low frequency Raman data, decrease of the force constants ca. 25 % (for GaSe) due to the formation of the nanoparticles are estimated, and the origin is suggested. Second harmonic generation (SHG) with 1064 nm line of a mode locked Nd : YAG laser was observed for nanoparticles ablated on different substrates. Potential for using these structures for laser light visualizators are discussed.

  1. HPVB and HPVZM shaped growth of CdZnTe, CdSe, and ZnSe crystals

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Nikolai N.; James, Ralph B.; Berzigiarova, Nadejda S.; Kulakov, Mihail P.

    2003-01-01

    High-pressure Bridgman (HPVB) and vertical zone melting (HPVZM) growth has been applied for manufacturing Cd1-xZnxTe (x = 0.04 - 0.2), CdSe and ZnSe crystal tapes with sizes up to 120×120×12 mm. The influence of the technological parameters of the growth process on the crystal quality and some properties is discussed. The dependence of the inclusion (bubbles) content on deviation from the melt stoichiometry is determined. The method for growing plates with low content of the inclusions is described. High-resistivity crystal tapes of undoped CdZnTe (1010 Ohm×cm), CdSe (1011 Ohm×cm) and ZnSe (>1011 Ohm×cm) were prepared. Possibility of the tape growth on the oriented seed is shown on example of CdSe. The difference between HPVB and HPVZM results is described. Main HPVZM advantage for II-VI compound crystal growth is possibility of obtaining crystals with stoichiometric composition or with controlled deviation from stoichiometry. Hence HPVZM is preferable for growing high-resistivity II-VI crystals with low inclusion content.

  2. Fabrication of the CdSeTe alloyed and CdSeTe/ZnS core-shell quantum dots

    NASA Astrophysics Data System (ADS)

    Liang, Guo-Xi; Zhu, Jun-Jie

    2011-02-01

    The near-infrared (NIR)-emitting quantum dots (Qdots) have great potential for the use in biological imaging and diagnostic applications. In our work, a facile method was developed for the preparation of high quality, water-soluble, and NIR-emitting CdSeTe alloyed Qdots (A-Qdots) with L-cysteine (L-cys) as capping agent. By changing the size and the composition of the A-Qdots, the photoluminescent quantum yields (QYs) can reach as high as 53% and the emission color can be tuned between visible and NIR regions. Based on the fluorescence of the A-Qdots selectively quenched in the presence of Cu2+, the NIR-emitting CdSeTe A-Qdots were applied in ultrasensitive Cu2+ sensing. Furthermore, the prepared CdSeTe A-Qdots have been successfully applied for cell imaging, glucose and cholesterol assay, which demonstrates the great potential of the Qdots for biological applications. In order to improve the biocompatibility of the CdSeTe A-Qdots, new water-soluble CdSeTe/ZnS core-shell Qdots (CS-Qdots) with excellent NIR emission were synthesized in aqueous solution. The prepared CS-Qdots not only possessed high QYs but also exhibited excellent photobstability and favorable biocompatibility. Moreover, the CS-Qdots showed high electrogenerated chemiluminescence (ECL) signal. These characteristics showed their potential applications in cell imaging and biosensing with high sensitivity.

  3. [{Cp2(tBuSe)Nb}2E] (E = O and Se) with bridging oxide or selenide ligands.

    PubMed

    Hector, Andrew L; Jura, Marek; Levason, William; Reid, Gillian; Reid, Stuart D; Webster, Michael

    2008-10-01

    The title compounds, mu-oxido-bis[(tert-butylselenolato)bis(eta(5)-cyclopentadienyl)niobium(IV)] toluene solvate, [Nb(2)(C(5)H(5))(4)(C(4)H(9)Se)(2)O] x C(7)H(8), and mu-selenido-bis[(tert-butylselenolato)bis(eta(5)-cyclopentadienyl)niobium(IV)], [Nb(2)(C(5)H(5))(4)(C(4)H(9)Se)(2)Se], consist of niobium(IV) centres each bonded to two eta(5)-coordinated cyclopentadienyl groups and one tert-butylselenolate ligand and are the first organometallic niobium selenolates to be structurally characterized. A bridging oxide or selenide completes the niobium coordination spheres of the discrete dinuclear molecules. In the oxide, the O atom lies on an inversion centre, resulting in a linear Nb-O-Nb linkage, whereas the selenide has a bent bridging group [Nb-Se-Nb = 139.76 (2) degrees]. The difference is attributable to strong pi bonding in the oxide case, although the effects on the Nb-C and Nb-Se(t)Bu bond lengths are small.

  4. 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.

  5. 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.

  6. Preparation of clean surfaces and Se vacancy formation in Bi2Se3 by ion bombardment and annealing

    NASA Astrophysics Data System (ADS)

    Zhou, Weimin; Zhu, Haoshan; Valles, Connie M.; Yarmoff, Jory A.

    2017-08-01

    Bismuth Selenide (Bi2Se3) is a topological insulator (TI) with a structure consisting of stacked quintuple layers. Single crystal surfaces are commonly prepared by mechanical cleaving. This work explores the use of low energy Ar+ ion bombardment and annealing (IBA) as an alternative method to produce reproducible and stable Bi2Se3 surfaces under ultra-high vacuum (UHV). It is found that a clean and well-ordered surface can be prepared by a single cycle of 1 keV Ar+ ion bombardment and 30 min of annealing. Low energy electron diffraction (LEED) and detailed low energy ion scattering (LEIS) measurements show no differences between IBA-prepared surfaces and those prepared by in situ cleaving in UHV. Analysis of the LEED patterns shows that the optimal annealing temperature is 450 °C. Angular LEIS scans reveal the formation of surface Se vacancies when the annealing temperature exceeds 520 °C.

  7. Zinc diffusion in polycrystalline Cu(In,Ga)Se2 and single-crystal CuInSe2 layers

    NASA Astrophysics Data System (ADS)

    Bastek, J.; Stolwijk, N. A.; Wuerz, R.; Eicke, A.; Albert, J.; Sadewasser, S.

    2012-08-01

    The diffusion behavior of Zn in solar-grade Cu(In,Ga)Se2 (CIGSe) is found to be similar to that in epitaxial CuInSe2 (CISe), which indicates that grain boundaries only play a minor role as segregation sites and fast-transport pathways. The diffusivity obeys the Arrhenius equation DZn = 3.8 × 10-3exp(-1.24 eV/kBT) cm2 s-1. Surprisingly, the Zn65 diffusion profiles obtained by the radiotracer technique exhibit anomalous shapes with a second maximum near the CI(G)Se-substrate interface. The observations may be indicative of an interstitial-substitutional diffusion mechanism.

  8. Crossover from 3D to 2D Quantum Transport in Bi2Se3/In2Se3 Superlattices

    NASA Astrophysics Data System (ADS)

    Yanfei, Zhao; Haiwen, Liu; Xin, Guo; Ying, Jiang; Yi, Sun; Huichao, Wang; Yong, Wang; Handong, Li; Maohai, Xie; Xincheng, Xie; Jian, Wang

    2015-03-01

    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.

  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. VLS synthesis of disordered CdSe nanowires and optical properties of an individual CdSe nanowire

    NASA Astrophysics Data System (ADS)

    Xiao, Bin-bin; Xu, Yue-bing

    2011-12-01

    Disordered CdSe nanowires have been successfully grown on silicon substrates by Au-catalyzed vapor-liquid-solid (VLS) mechanism. Scanning electron microscopy (SEM) reveals that the as-prepared products consist of a large quantity of 1D nanowire disordered predominantly perpendicular to the surface of the substrate. A plausible formation mechanism of disordered CdSe nanowires is proposed here. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) confirm on their hexagonal wurtzite crystallite structure. An intense red near-band edge emission (702 nm) is observed based on room temperature photoluminescence measurements of individual nanowire. This kind of CdSe nanostructures may be used in optoelectronics devices in the near future.

  11. Investigation of CuGaSe2/CuInSe2 double heterojunction interfaces grown by molecular beam epitaxy.

    PubMed

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

    2015-02-01

    In-situ reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001) using migration-enhanced epitaxy. The streaky RHEED pattern and persistent RHEED intensity oscillations caused by the alternate deposition of migration-enhanced epitaxy sequence are observed and the growths of smooth surfaces are confirmed. RHEED observation results also confirmed constituent material interdiffusion at the heterointerface. Cross-sectional transmission electron microscopy showed a flat and abrupt heterointerface when the substrate temperature is as low as 400 °C. These have been confirmed even by X-ray diffraction and photoluminescence measurements.

  12. Investigation of CuGaSe2/CuInSe2 double heterojunction interfaces grown by molecular beam epitaxy

    PubMed Central

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

    2015-01-01

    In-situ reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001) using migration-enhanced epitaxy. The streaky RHEED pattern and persistent RHEED intensity oscillations caused by the alternate deposition of migration-enhanced epitaxy sequence are observed and the growths of smooth surfaces are confirmed. RHEED observation results also confirmed constituent material interdiffusion at the heterointerface. Cross-sectional transmission electron microscopy showed a flat and abrupt heterointerface when the substrate temperature is as low as 400 °C. These have been confirmed even by X-ray diffraction and photoluminescence measurements. PMID:25874158

  13. 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.

  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.; ...

    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. 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

  17. 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

  18. Art deco railing detail on SE side. Partial segment in ...

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

    Art deco railing detail on SE side. Partial segment in left foreground is same as center segment in photo WA-141-5. - Raging River Bridge No. 234A, Preston-Fall City Road & Southeast Forty-fourth Place, Fall City, King County, WA

  19. Chemistry in CESM-SE: Evaluation, Performance and Optimization

    SciTech Connect

    Lamarque, Jean-Francois; Conley, Andrew; Vitt, Francis; Drake, John; Sun, Jian

    2016-01-06

    The purpose of the proposed work focused on development of chemistry representation within the Spectral Element (SE) dynamical core as implemented in the Community Earth System Model (CESM). More specifically, a main focus was on the ability of SE to accurately represent tracer transport. The proposed approach was to incrementally increase the complexity of the problem, starting from specified two-dimensional flow and tracers to simulations using specified dynamics and full chemistry. As demonstrated below, we have successfully studied all aspects of the proposed work, although only part of the work has been published in the refereed literature so far. Furthermore, because the SE dynamical core has been found to have several deficiencies that are still being investigated for solution, not all proposed tasks were finalized. In addition to the tests for SE performance, in an effort to decrease the computational burden of interactive chemistry, especially in the case of a large number of chemical species and chemical reactions, development on a faster chemical solver and implementation on GPUs has been implemented in CESM under the leadership of John Drake (U. Tennessee).

  20. Brittle Fracture of 2D MoSe2

    DOE PAGES

    Yang, Yingchao; Li, Xing; Wen, Minru; ...

    2016-11-03

    An in situ quantitative tensile testing platform is developed in this paper to enable the uniform in-plane loading of a freestanding membrane of 2D materials inside a scanning electron microscope. The in situ tensile testing reveals the brittle fracture of large-area MoSe2 crystals and measures their fracture strength for the first time.

  1. 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

  2. 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

  3. 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.

  4. 7. PORTAL ELEVATION, LOOKING SE. SINGLE BRIDGE IS PITTSBURGH, FORT ...

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

    7. PORTAL ELEVATION, LOOKING SE. SINGLE BRIDGE IS PITTSBURGH, FORT WAYNE & CHICAGO RAILWAY; PAIR OF BRIDGES ARE ABANDONED LAKE SHORE AND MICHIGAN SOUTHERN RAILROAD (HAER No. IL-161). - Pittsburgh, Fort Wayne & Chicago Railway, Calumet River Bridge, Spanning Calumet River, east of Chicago Skyway (I-90), Chicago, Cook County, IL

  5. PORTAL ELEVATION, LOOKING SE. SINGLE BRIDGE IS PITTSBURGH, FORT WAYNE ...

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

    PORTAL ELEVATION, LOOKING SE. SINGLE BRIDGE IS PITTSBURGH, FORT WAYNE & CHICAGO RAILWAY; PAIR OF BRIDGES ARE ABANDONED LAKE SHORE AND MICHIGAN SOUTHERN RAILROAD (HAER No. IL-161). - Pittsburgh, Fort Wayne & Chicago Railway, Calumet River Bridge, Spanning Calumet River, east of Chicago Skyway (I-90), Chicago, Cook County, IL

  6. Thermoelectric properties of SnSe2 monolayer

    NASA Astrophysics Data System (ADS)

    Li, Guanpeng; Ding, Guangqian; Gao, Guoying

    2017-01-01

    The 2H (MoS2-type) phase of 2D transition metal dichalcogenides (TMDCs) has been extensively studied and exhibits excellent electronic and optoelectronic properties, but the high phonon thermal conductivity is detrimental to the thermoelectric performances. Here, we use first-principles methods combined with Boltzmann transport theory to calculate the electronic and phononic transport properties of 1T (CdI2-type) SnSe2 monolayer, a recently realized 2D metal dichalcogenide semiconductor. The calculated band gap is 0.85 eV, which is a little larger than the bulk value. Lower phonon thermal conductivity and higher power factor are obtained in 1T-SnSe2 monolayer compared to 2H-TMDCs monolayers. The low phonon thermal conductivity (3.27 W mK-1 at room temperature) is mainly due to the low phonon frequency of acoustic modes and the coupling of acoustic modes with optical modes. We also find that the p-type has better thermoelectric performance than the n-type, and the figure of merit within p-type can reach 0.94 at 600 K for 1T-SnSe2 monolayer, which is higher than those of most 2H-TMDCs monolayers, making 1T-SnSe2 monolayer a promising candidate for thermoelectric applications.

  7. A revised climatology of SE Australia at the LGM

    NASA Astrophysics Data System (ADS)

    Shulmeister, James; Cohen, Tim; Kiernan, Kevin; Woodward, Craig; Clark, Doug; Fitzsimmons, Kat; Kemp, Justine; Gontz, Allen; Haworth, Robert; Moss, Patrick; Chang, Jie; Mueller, Daniela; Slee, Adrian; Ellerton, Dan

    2015-04-01

    This paper summarises some of the results of a recently completed project aimed at defining climate conditions at the LGM in south eastern Australia. We conclude that overall cooling on the SE mainland was 8-10°C but that cooling along the eastern coastal strip and in Tasmania was somewhat less (4-7°C). The persistence of a humid climate along the east coast and in the adjacent highlands allowed rivers to flow more strongly than during the Holocene. We suggest that onshore flow on the northern limbs of east coast high pressure cells, supplemented by moisture from east coast lows maintained this humid fringe. The processes were enhanced by increased sea-land temperature contrasts especially in winter and by reduced evapotranspiration under lower temperatures and altered vegetation cover. We can explain most of the paleoenvironmental observations in SE Australia at the LGM by invoking an enhanced high pressure cell over the modern SE mainland while westerly flow continued to dominate in Tasmania. At the true LGM westerly penetration of the SE mainland was reduced but east coast systems were either unaffected or enhanced.

  8. 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.

  9. CdSe nanowires grown by using chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Gubur, H. Metin; Septekin, F.; Alpdogan, S.

    2015-10-01

    The Cadmium-selenide (CdSe) nanowire thin films were prepared on glass substrates by using chemical bath deposition (CBD) at 70 °C. Cadmium sulfate and sodium selenosulphate were used as Cd2+ and Se2- ion sources, respectively. The CdSe nanowire film was annealed in an air atmosphere at 573 K for 1 hour. X-ray diffraction (XRD) results showed that the nanowire films as-deposited and annealed had mixed cubic and hexagonal phase. Scanning electron microscopy (SEM) indicated that the CdSe nanowires had lengths ranging from 642 nm to 2.5 μm and diameters ranging from 46 nm to 211 nm. The optical properties of the as-deposited and the annealed nanowire films, an investigated by recording the transmission spectra by using an UV-visible spectrophotometer revealed that the energy band gap decreased (from 1.78 eV to 1.50 eV) upon annealing. The conductivity measurements made by using four-probe methods for both the annealed and the as-deposited films showed that the resistivity, conductivity and activation energy changed upon annealing.

  10. Characterization of p-type ZnSe

    NASA Astrophysics Data System (ADS)

    Haase, M. A.; Cheng, H.; DePuydt, J. M.; Potts, J. E.

    1990-01-01

    Lithium-doped ZnSe has been grown on (100) GaAs by molecular beam epitaxy. The epitaxial layers are p-type with net acceptor concentrations (NA-ND) as high as 8×1016 cm-3— the highest ever reported for molecular beam epitaxial ZnSe. Room temperature ac measurements show resistivities as low as 2.9 Ω cm. Higher Li concentrations give rise to self-compensation and a decrease in NA-ND. The details of the electrical and optical characterization of these layers are presented. Rudimentary blue light emitting pn junction diodes have been fabricated. While these devices show dominant blue emission (463 nm) at room temperature, large turn-on voltages indicate that the p-ZnSe/p-GaAs interface presents a large barrier to hole transport. Moreover, we find that difficulty in making device-quality ohmic contacts to p-ZnSe is the next major obstacle to the fabrication of efficient blue light emitting diodes.

  11. Ohmic contact in monolayer InSe-metal interface

    NASA Astrophysics Data System (ADS)

    Jin, Hao; Li, Jianwei; Wan, Langhui; Dai, Ying; Wei, Yadong; Guo, Hong

    2017-06-01

    As conventional Si-based devices approach their scaling limit, it is of great significance to find new materials for future electronic logic devices. The emerging two-dimensional (2D) materials with atomic thickness have attracted intense interests for their exotic properties. However, the presence of the Schottky barrier limits their applications, which is difficult to control over due to the Fermi level pinning effect. Therefore, searching for low resistance metal contact to 2D semiconductors becomes one of the most important topics. Here, we report that Ohmic contact can be realized in a monolayer InSe-Cu system. Based on the density functional theory combined with the nonequilibrium Green’s functions, the geometry, overlapping states, tunneling barrier, Schottky barrier, and band alignment at the interface of group-IB (Cu, Ag, and Au) with InSe monolayer are discussed in details. Our results reveal that Cu, the most common electrode used in the industry, shows great potential to form favorable contact with single layer InSe due to the strong interaction and high orbital overlapping. The calculated drain-source current versus bias voltage (I  -  V) curve exhibits linear behavior, indicating good Ohmic contact between the Cu electrodes and InSe channel. Our work may pave the way for design of next-generation ultrathin and flexible devices.

  12. Current Oscillations in Doped Thin Films of CdSe.

    DTIC Science & Technology

    The previously unreported phenomenon of current oscillations in doped thin films of cadmium selenide was explored. It was concluded that, with...appropriate processing, devices made with thin films of CdSe will exhibit current oscillations when high electric fields and illumination are applied, and that these oscillations have frequencies of 5 to 8000 Hz. (Author)

  13. Multifunctional "Se": Course of Development in Spanish Children.

    ERIC Educational Resources Information Center

    Gathercole, Virginia C.

    A study explored the acquisition of "se" by Spanish-speaking children in Madrid, Spain, looking at: (1) acquisition of multifunctional forms; and (2) the course of acquisition for a linguistic expression that has both anaphoric and non-anaphoric functions, and its relevance to Binding Theory approaches to the acquisition of reflexives.…

  14. 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.

  15. 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

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

    PubMed

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

    2015-09-02

    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.

  17. Mobility in single crystal Bi2Se3.

    NASA Technical Reports Server (NTRS)

    Woollam, j. A.; Beale, H.; Spain, I. L.

    1972-01-01

    Galvanomagnetic effects are measured in p-type Bi2Se3 in magnetic fields to 8 tesla. Both Hall and conductivity mobilities are determined between 4.2 and 300 K. Carrier compensation, as well as nearly equal electron and hole mobilities are found in samples with approximately 10 to the 25th power per cu m 3 total carrier concentration.

  18. 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.

  19. Superconductivity and hybrid soft modes in TiSe2

    DOE PAGES

    Maschek, M.; Rosenkranz, S.; Hott, R.; ...

    2016-12-12

    The interplay between superconductivity and charge-density-wave (CDW) order plays a central role in the layered transition-metal dichalcogenides. 1T-TiSe2 forms a prime example, featuring superconducting domes on intercalation as well as under applied pressure. Here, we present high energy-resolution inelastic x-ray scattering measurements of the CDW soft phonon mode in intercalated CuxTiSe2 and pressurized 1T-TiSe2 along with detailed ab-initio calculations for the lattice dynamical properties and phonon-mediated superconductivity. We find that the intercalation-induced superconductivity can be explained by a solely phonon-mediated pairing mechanism, while this is not possible for the superconducting phase under pressure. We argue that a hybridization of phononmore » and exciton modes in the pairing mechanism is necessary to explain the full observed temperature-pressure-intercalation phase diagram. Finally, these results indicate that 1T-TiSe2 under pressure is close to the elusive state of the excitonic insulator.« less

  20. NbSe3 Cathodes For Li Rechargeable Cells

    NASA Technical Reports Server (NTRS)

    Bugga, Ratnakumar V.; Ni, Ching-Ion; Distefano, Salvador; Somoano, Robert B.; Bankston, C. Perry

    1990-01-01

    Report describes experimental studies involving preparation, characterization, and measurements of performance of NbSe3, intended for use as cathode material in lithium rechargeable electrochemical cells. Characteristics superior to those of other intercalating cathode materials, including high volumetric and gravimetric energy densities and ability to sustain discharges at high rates.

  1. Brazilian Longitudinal Study of Adult Health (ELSA-Brasil): objectives and design.

    PubMed

    Aquino, Estela M L; Barreto, Sandhi Maria; Bensenor, Isabela M; Carvalho, Marilia S; Chor, Dóra; Duncan, Bruce B; Lotufo, Paulo A; Mill, José Geraldo; Molina, Maria Del Carmen; Mota, Eduardo L A; Passos, Valéria Maria Azeredo; Schmidt, Maria Inês; Szklo, Moyses

    2012-02-15

    Although low- and middle-income countries still bear the burden of major infectious diseases, chronic noncommunicable diseases are becoming increasingly common due to rapid demographic, epidemiologic, and nutritional transitions. However, information is generally scant in these countries regarding chronic disease incidence, social determinants, and risk factors. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) aims to contribute relevant information with respect to the development and progression of clinical and subclinical chronic diseases, particularly cardiovascular diseases and diabetes. In this report, the authors delineate the study's objectives, principal methodological features, and timeline. At baseline, ELSA-Brasil enrolled 15,105 civil servants from 5 universities and 1 research institute. The baseline examination (2008-2010) included detailed interviews, clinical and anthropometric examinations, an oral glucose tolerance test, overnight urine collection, a 12-lead resting electrocardiogram, measurement of carotid intima-media thickness, echocardiography, measurement of pulse wave velocity, hepatic ultrasonography, retinal fundus photography, and an analysis of heart rate variability. Long-term biologic sample storage will allow investigation of biomarkers that may predict cardiovascular diseases and diabetes. Annual telephone surveillance, initiated in 2009, will continue for the duration of the study. A follow-up examination is scheduled for 2012-2013.

  2. Migraine and subclinical atherosclerosis in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

    PubMed

    Goulart, Alessandra C; Santos, Itamar S; Bittencourt, Márcio S; Lotufo, Paulo A; Benseñor, Isabela M

    2016-08-01

    The relationship between migraine and coronary heart disease (CHD) remains controversial. We aimed to investigate the association of subclinical atherosclerosis and migraine with or without aura compared to a non-migraine subgroup (reference) in a large Brazilian multicentric cohort study, the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). Migraine diagnostic was based on International Headache Society criteria, and aura symptoms were validated by a medical doctor in a sub-sample of the ELSA-Brasil, who also underwent coronary artery calcium score (CAC) and carotid intima-media thickness (C-IMT) evaluations. Subclinical atherosclerosis indexes (CAC and C-IMT) were analyzed as dependent variables and migraine (all, with aura, without aura) as an independent variable in the linear and multinomial logistic regression models adjusted for possible confounders. Of 3217 ELSA participants free from CVD at baseline, we found a migraine frequency of 11.9% (5.1% with aura and 6.8% without aura). Overall, migraineurs were mostly women, younger and had lower frequency of CV risk factors, such as hypertension, diabetes and low HDL-cholesterol, compared to non-migraineurs. The strongest inverse correlation between migraine and subclinical atherosclerosis was verified with CAC score. However, all associations lost their significance after multivariate adjustment. In this cross-sectional evaluation of the ELSA study, migraine was not associated with subclinical atherosclerosis, regardless of aura symptoms. © International Headache Society 2015.

  3. Quantum chemistry of the minimal CdSe clusters

    NASA Astrophysics Data System (ADS)

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

    2008-08-01

    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 Cd2Se2, which is also used to benchmark different computational methods versus high level ab initio techniques. Full geometry optimization of Cd2Se2 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 Cd/Se 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 binding

  4. Electronic structure of the layer compounds GaSe and InSe in a tight-binding approach

    NASA Astrophysics Data System (ADS)

    Camara, M. O.; Mauger, A.; Devos, I.

    2002-03-01

    The three-dimensional band structure of the III-VI layer compounds GaSe and InSe has been investigated in the tight-binding approach. The pseudo-Hamiltonian matrix elements in the sp3s* basis are fit in order to reproduce the nonlocal pseudopotential band structure, in the framework of constrained optimization techniques using the conjugate gradient method. The results are in good agreement with the optical and photoemission experimental data. The scaling laws appropriate to the covalent bonding are violated by a fraction of eV only, which suggests that the interlayer interactions are not solely of the van der Waals type.

  5. Photon guiding characteristics of waveguide membranes coupled to a microdisk of ZnSe/(Zn,Mg)Se quantum well structures

    NASA Astrophysics Data System (ADS)

    Schmidt, G.; Rieger, T.; Trellenkamp, S.; Grützmacher, D.; Pawlis, A.

    2017-07-01

    Integrated optical devices composed of waveguides and microdisks emitting blue light were fabricated from ZnSe/(Zn,Mg)Se quantum well structures. Here we study the optical properties and photon guiding characteristics of such devices. The structures were fabricated by multi-step electron beam lithography and subsequent wet chemical etching. The transfer characteristic of photons through the waveguide was analyzed via spatial-resolved μ-photoluminescence spectroscopy. Spatial excitation of the microdisk revealed substantial overcoupling of photons from the microdisk into the waveguide.

  6. Effect of deformation on the valence shell occupancies of 74Ge, 76Ge, 76Se and 78Se

    NASA Astrophysics Data System (ADS)

    Elsharkawy, H. M.; Saleh Yousef, M.

    2017-03-01

    The set of BCS equations have been solved using both realistic and schematic separable forces to calculate the occupation probability amplitudes for protons and neutrons in the valence shells of 74Ge, 76Ge, 76Se and 78Se deformed nuclei. A comparison between the calculated occupation probabilities with the experimental measured values is introduced. A big difference is found between the occupation probabilities of protons with the experimental values, while for neutrons the agreement with the experimental values at high deformations is satisfactory.

  7. 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

  8. Diffusion behavior for Se and Zr in sodium-bentonite

    SciTech Connect

    Sato, Haruo; Yui, Mikazu; Yoshikawa, Hideki

    1995-12-31

    Apparent diffusion coefficients for Se and Zr in bentonite were measured by in-diffusion method at room temperature using water-saturated sodium-bentonite, Kunigel V1{reg_sign} containing 50wt% Na-smectite as a major mineral was used as the bentonite material. The experiments were carried out in the dry density range of 400--1,800 kg/m{sup 3}. Bentonite samples were immersed with distilled water and saturated before the experiments. The experiments for Se were carried out under N{sub 2} atmospheric condition (O{sub 2}: 2.5ppm). Those for Zr were carried out under aerobic condition. The apparent diffusion coefficients decrease with increasing density of the bentonite. Since dominant species of Se in the pore water is predicted to be SeO{sub 3}{sup 2{minus}}, Se may be retarded by anion-exclusion because of negative charge on the surface of the bentonite and little sorption. The dominant species of Zr in the porewater is predicted to be Zr(OH){sub 5}{sup {minus}} or HZrO{sub 3}{sup {minus}}. Distribution coefficient measured for Zr on the bentonite was about 1.0 m{sup 3}/kg from batch experiments. Therefore, the retardation may be caused by combination of the sorption and the anion-exclusion. A modeling for the diffusion mechanisms in the bentonite were discussed based on an electric double layer theory. Comparison between the apparent diffusion coefficients predicted by the model and the measured ones shows a good agreement.

  9. High-conjugation-efficiency aqueous CdSe quantum dots.

    PubMed

    Au, Giang H T; Shih, Wan Y; Shih, Wei-Heng

    2013-11-12

    Quantum dots (QDs) are photoluminescent nanoparticles that can be directly or indirectly coupled with a receptor such as an antibody to specifically image a target biomolecule such as an antigen. Recent studies have shown that QDs can be directly made at room temperature and in an aqueous environment (AQDs) with 3-mercaptopropionic acid (MPA) as the capping ligand without solvent and ligand exchange typically required by QDs made by the organic solvent routes (OQDs). In this study, we have synthesized CdSe AQDs and compared their conjugation efficiency and imaging efficacy with commercial carboxylated OQDs in HT29 colon cancer cells using a primary antibody-biotinylated secondary antibody-streptavidin (SA) sandwich. We showed that the best imaging condition for AQDs occurred when one AQD was bound with 3 ± 0.3 SA with a nominal SA/AQD ratio of 4 corresponding to an SA conjugation efficiency of 75 ± 7.5%. In comparison, for commercial CdSe-ZnS OQDs to achieve 2.7 ± 0.4 bound SAs per OQD for comparable imaging efficacy a nominal SA/OQD ratio of 80 was needed corresponding to an SA conjugation efficiency of 3.4 ± 0.5% for CdSe-ZnS OQDs. The more than 10 times better SA conjugation efficiency of the CdSe AQDs as compared to that of the CdSe-ZnS OQDs was attributed to more capping molecules on the AQD surface as a result of the direct aqueous synthesis. More capping molecules on the AQD surface also allowed the SA-AQD conjugate to be stable in cell culture medium for more than three days without losing their staining capability in a flowing cell culture medium. In contrast, SA-OQD conjugates aggregated in cell culture medium and in phosphate buffer saline solution over time.

  10. 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.

  11. Synthesis, crystal structure, optical, and electronic study of the new ternary thorium selenide Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2}

    SciTech Connect

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

    2015-11-15

    The compound Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. Its crystal structure features one-dimensional chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} 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 Th{sup 4+} and hence charge balance of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is achieved as 3×Ba{sup 2+}, 1×Th{sup 4+}, 3×Se{sup 2−}, and 2×Se{sub 2}{sup 2−}. From optical measurements the band gap of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is 1.96(2) eV. DFT calculations indicate that the compound is a semiconductor. - Graphical abstract: Local coordination environment of Th atoms in the Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} structure. - Highlights: • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. • The structure features chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} cations. • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is a semiconductor with a band gap of 1.96(2) eV.

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

    USDA-ARS?s Scientific Manuscript database

    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 ...

  13. Efectos combinados de la ampliación de la atención primaria de salud y de las transferencias condicionadas de dinero en efectivo sobre la mortalidad infantil en Brasil, 1998–2010*

    PubMed Central

    Guanais, Frederico C.

    2015-01-01

    Objetivos. Examiné los efectos combinados del acceso a la atención primaria mediante el Programa de Salud Familiar (PSF) y las transferencias condicionadas de dinero en efectivo del Programa Bolsa Familia (PBF) sobre la mortalidad infantil posneonatal (MIPN) en Brasil. Métodos. Empleé un análisis ecológico longitudinal usando datos en panel de 4 583 municipios brasileños de 1998 al 2010, con 54 253 observaciones en total. Estimé modelos de regresión de efectos fijos por mínimos cuadrados ordinarios, con la tasa de MIPN como la variable dependiente y el PSF, el PBF y sus interacciones como las principales variables independientes de interés. Resultados. La asociación de una mayor cobertura del PSF con una menor tasa de MIPN se volvió más fuerte conforme aumentaba la cobertura del PBF. En los promedios de todas las demás variables, cuando la cobertura de PBF era 25%, la MIPN predicha fue 5,24 (intervalo de confianza [IC] de 95% = 4,95, 5,53) para una cobertura del PSF de 0%, y de 3,54 (IC de 95% = 2,77, 4,31) para una cobertura del PSF de 100%. Cuando la cobertura del PBF era de 60%, la MIPN predicha fue 4,65 (IC de 95% = 4,36, 4,94) para una cobertura del PSF de 0%, y de 1,38 (IC de 95% = 0,88, 1,89) para una cobertura del PSF de 100%. Conclusiones. El efecto del PSF depende de la ampliación del PBF. Para las poblaciones empobrecidas y subatendidas, la combinación de intervenciones tanto del lado de la oferta como del lado de la demanda podría ser necesaria para mejorar los resultados en salud.

  14. Micro-Raman Study of Orientation Effects of CuxSe-Crystallites on Cu-rich CuGaSe2 Thin Films

    NASA Astrophysics Data System (ADS)

    Xue, C.; Papadimitriou, D.; Raptis, Y. S.; Richter, W.; Esser, N.; Siebentritt, S.; Lux-Steiner, M. Ch.

    2004-08-01

    The structural properties of copper selenide (CuxSe), formed as a secondary phase on the surface of CuGaSe2 films grown under Cu-rich conditions on GaAs (100) substrates, were studied by micro-Raman spectroscopy. Raman bands at 45 and 263cm-1, observed on crystallites dispersed on the CuGaSe2 film, are in agreement with the Raman modes of CuSe and Cu2Se. Polarization- and angular-dependent micro-Raman measurements reveal that the CuxSe-crystallites are grown with a preferential orientation on the CuGaSe2 surface.

  15. Origin of the enhancement in transport properties on polycrystalline SnSe with compositing two-dimensional material MoSe2

    NASA Astrophysics Data System (ADS)

    Huang, Xue-Qin; Chen, Yue-Xing; Yin, Meijie; Feng, Dan; He, Jiaqing

    2017-03-01

    P-type SnSe compositing with 2D MoSe2 materials have been prepared by the solid solution method followed by the spark plasma sintering technique. The total thermal conductivities of SnSe/MoSe2 composites were found to be higher than for pristineSnSe at room temperature; and the disparity between them becomes smaller at higher temperatures, where the low thermal conductivities remained. Both the carrier concentration and the carrier mobility were significantly improved after MoSe2 was introduced into the SnSe matrix along the direction perpendicular to the pressing direction, leading to an extraordinary enhancement in electrical transport performance. The maximum ZT of 0.5 was obtained at 773 K for SnSe + 1.5%MoSe2 along the direction perpendicular to the pressing direction; this value is 1.5 times as large as that of the pristine SnSe.

  16. Origin of the enhancement in transport properties on polycrystalline SnSe with compositing two-dimensional material MoSe2.

    PubMed

    Huang, Xue-Qin; Chen, Yue-Xing; Yin, Meijie; Dan Feng; He, Jiaqing

    2017-03-10

    P-type SnSe compositing with 2D MoSe2 materials have been prepared by the solid solution method followed by the spark plasma sintering technique. The total thermal conductivities of SnSe/MoSe2 composites were found to be higher than for pristineSnSe at room temperature; and the disparity between them becomes smaller at higher temperatures, where the low thermal conductivities remained. Both the carrier concentration and the carrier mobility were significantly improved after MoSe2 was introduced into the SnSe matrix along the direction perpendicular to the pressing direction, leading to an extraordinary enhancement in electrical transport performance. The maximum ZT of 0.5 was obtained at 773 K for SnSe + 1.5%MoSe2 along the direction perpendicular to the pressing direction; this value is 1.5 times as large as that of the pristine SnSe.

  17. Influence of the stacking order on structural features of the Cu-In-Ga-Se precursors for formation of Cu(In,Ga)Se2 thin films prepared by thermal reaction of InSe/Cu/GaSe alloys to elemental Se vapor and diethylselenide gas

    NASA Astrophysics Data System (ADS)

    Dejene, F. B.; Sugiyama, M.; Nakanishi, H.; Alberts, V.; Chichibu, S. F.

    2006-09-01

    A novel partway for the fabrication of copper-indium (gallium) diselenide has been developed. This two-stage process consists of the formation of Cu-In-(Ga)-Se precursors and subsequent selenization to form CuIn(Ga)Se2. In this work, we have investigated and compared the possible interactions in Cu-In-Ga-Se systems, using sequentially stacked precursors premixed with Se, in order to get a better understanding of the Cu(In,Ga)Se2 thin film formation. Comparison of these SEM micrographs clearly revealed that the surface morphologies and hence surface roughness of the resulting Cu(In,Ga)Se2 absorber films were significantly influenced by the structure of the precursor films prior to selenization. XRD analyses revealed the presence of a graded CuIn1-xGaxSe structure, irrespective of the stacking order during the precursor formation step for samples selenized using elemental Se vapor. It was established that distinct from the case of using Se vapor, a single-phase Cu(In,Ga)Se2 films were obtained by diethylselenide (DESe) selenization from Cu-In-Ga metal precursors premixed Se irrespective of the stacking order during the precursor formation step.

  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. High-efficiency CuInSe2 and CuInGaSe2 based cells and materials research

    NASA Astrophysics Data System (ADS)

    Devaney, W. E.; Chen, W. S.; Stewart, J. M.

    1989-06-01

    The results of the first year of a two-year research program are presented. A 1 sq cm ZnO/CdZnS/CuInGaSe(sub 2) solar cell with total-area efficiency of 12.5 percent (AM1.5, 100mW/sq cm) was fabricated. The quantum efficiency of this device at 400 nm exceeds 0.7 as a result of the improved transmission of the ZnO/thin CdZnS window layers. The fabrication and characteristics of each of the three layers and of the complete devices are discussed. Results on gallium doping of CdZnS window layers are presented. Three-layer antireflection coatings for CdZnS/CuInSe2 cells are single-layer coatings for ZnO/CdZnS/CuInGaSe2 structures were designed and deposited. Results on devices made using high-gallium-content CuInGaSe2 are discussed.

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

    PubMed

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

    2011-07-29

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

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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 MoS2 and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique "puckered" C2v 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.

  3. 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.

  4. Research on optical band gap of the novel GeSe2-In2Se3-KI chalcohalide glasses.

    PubMed

    Wang, Guoxiang; Nie, Qiuhua; Wang, Xunsi; Dai, Shixun; Zhu, Mingxing; Shen, Xiang; Bai, Kun; Zhang, Xianghua

    2010-03-01

    The glass-forming region of the GeSe(2)-In(2)Se(3)-KI system was reported firstly. The dependence of physical, thermal and optical properties on compositions as formula of (1-x)(0.8GeSe(2)-0.2In(2)Se(3))-xKI (x=0, 0.1, 0.2, 0.3) chalcohalide glasses was investigated. The allowed direct transition and indirect transition, and Urbach energy of samples were calculated according to the classical Tauc equation. The results show that the glass system has good thermal stability and that there is an obvious blue-shift at the visible absorbing cutting-off edge. When the dissolved amount of KI increased from 0 to 30mol%, the direct optical band gap and the indirect optical band gap were in the range from 1.617 to 1.893eV and 1.573 to 1.857eV. With the decrease of the molar refraction the refractive index decreases, optical band gap and metallization criterion increase. The relationship between energy band gap and metallization criterion was analyzed and the optical properties of chalcohalide glasses were summarized.

  5. Efficiency limiting factors in Cu(In,Ga)Se2 thin film solar cells prepared by Se-free rapid thermal annealing of sputter-deposited Cu-In-Ga-Se precursors

    NASA Astrophysics Data System (ADS)

    Young Park, Ha; Gwon Moon, Dong; Ho Yun, Jae; Ahn, Seoung Kyu; Yoon, Kyung Hoon; Ahn, SeJin

    2013-12-01

    We report an efficiency limiting factor of CuInGaSe2 (CIGS) thin film solar cells fabricated by rapid thermal annealing (RTA) of sputter-deposited Cu-In-Ga-Se films without an additional supply of Se vapor. The CIGS thin films show a single-phase chalcopyrite structure without Ga segregation, and there is no apparent Se deficiency in overall composition measured by routine compositional analysis. However, detailed investigation on properties of the CIGS films and devices reveals that the formation of Se vacancies on the CIGS film surface during Se-free RTA is a main limiting factor of the device efficiency.

  6. Synthesis and Magnetic Properties of NiSe, NiTe, CoSe, and CoTe

    NASA Astrophysics Data System (ADS)

    Umeyama, Norio; Tokumoto, Madoka; Yagi, Shota; Tomura, Masatoshi; Tokiwa, Kazuyasu; Fujii, Takenori; Toda, Ryo; Miyakawa, Nobuaki; Ikeda, Shin-Ichi

    2012-05-01

    Polycrystalline NiSe, NiTe, CoSe, and CoTe have been synthesized by two methods, i.e., (1) the solid-state reaction in an evacuated quartz ampoule (QA) and (2) the high-pressure (HP) technique (HP) in a Au capsule using a cubic anvil cell. All the obtained samples have the nickel arsenide-type hexagonal crystal structure, except CoTe (HP), and their estimated lattice parameters, a and c, show almost the same values within 0.8% in comparison between samples prepared by the QA method and those by the HP method. On the other hand, a distinct difference between samples prepared by QA and HP processes is found in the magnetization of NiSe and NiTe. In particular, for NiTe, the temperature dependence of magnetization indicates two transition temperatures at about 20 and 130 K in samples prepared by the HP process. However, samples of NiTex (x = 0.5, 0.66, 0.82, 1, 1.22, and 2) and NiTe containing Au prepared by QA process do not show similar magnetic orders in the temperature range between 2 and 300 K. Also, samples of NiSe (HP) show magnetic transition at ˜20 K, while those of NiSe (QA) show a magnetic inflection point at ˜10 K. To the best of our knowledge the remarkable difference in magnetic properties caused by the method of synthesis has not been reported. In this paper, we present comparative experimental results of magnetic, electric, and specific heat measurements of samples prepared by the two methods. A possible explanation for such a substantial difference in magnetic interaction will be discussed.

  7. Influence of Se concentrations and species in hydroponic cultures on Se uptake, translocation and assimilation in non-accumulator ryegrass.

    PubMed

    Versini, Antoine; Di Tullo, Pamela; Aubry, Emmanuel; Bueno, Maïté; Thiry, Yves; Pannier, Florence; Castrec-Rouelle, Maryse

    2016-11-01

    The success of biofortification and phytoremediation practices, addressing Se deficiency and Se pollution issues, hinges crucially on the fate of selenium in the plant media in response to uptake, translocation and assimilation processes. We investigate the fate of selenium in root and shoot compartments after 3 and 6 weeks of experiment using a total of 128 plants grown in hydroponic solution supplied with 0.2, 2, 5, 20 and 100 mg L(-1) of selenium in the form of selenite, selenate and a mixture of both species. Selenate-treated plants exhibited higher root-to-shoot Se translocation and total Se uptake than selenite-treated plants. Plants took advantage of the selenate mobility and presumably of the storage capacity of leaf vacuoles to circumvent selenium toxicity within the plant. Surprisingly, 28% of selenate was found in shoots of selenite-treated plants, questioning the ability of plants to oxidize selenite into selenate. Selenomethionine and methylated organo-selenium amounted to 30% and 8% respectively in shoots and 35% and 9% in roots of the identified Se, suggesting that selenium metabolization occurred concomitantly in root and shoot plant compartments and demonstrating that non-accumulator plants can synthesize notable quantities of precursor compound for volatilization. The present study demonstrated that non-accumulator plants can develop the same strategies as hyper-accumulator plants to limit selenium toxicity. When both selenate and selenite were supplied together, plants used selenate in a storage pathway and selenite in an assimilation pathway. Plants might thereby benefit from mixed supplies of selenite and selenate by saving enzymes and energy required for selenate reduction.

  8. Structure and properties of ZnSxSe1-x thin films deposited by thermal evaporation of ZnS and ZnSe powder mixtures

    NASA Astrophysics Data System (ADS)

    Valeev, R. G.; Romanov, E. A.; Vorobiev, V. L.; Mukhgalin, V. V.; Kriventsov, V. V.; Chukavin, A. I.; Robouch, B. V.

    2015-02-01

    Interest to ZnSxSe1-x alloys is due to their band-gap tunability varying S and Se content. Films of ZnSxSe1-x were grown evaporating ZnS and ZnSe powder mixtures onto SiO2, NaCl, Si and ITO substrates using an original low-cost method. X-ray diffraction patterns and Raman spectroscopy, show that the lattice structure of these films is cubic ZnSe-like, as S atoms replace Se and film compositions have their initial S/Se ratio. Optical absorption spectra show that band gap values increase from 2.25 to 3 eV as x increases, in agreement with the literature. Because S atomic radii are smaller than Se, EXAFS spectra confirm that bond distances and Se coordination numbers decrease as the Se content decreases. The strong deviation from linearity of ZnSe coordination numbers in the ZnSxSe1-x indicate that within this ordered crystal structure strong site occupation preferences occur in the distribution of Se and S ions. The behavior is quantitatively confirmed by the strong deviation from the random Bernoulli distribution of the three sight occupation preference coefficients of the strained tetrahedron model. Actually, the ternary ZnSxSe1-x system is a bi-binary (ZnS+ZnSe) alloy with evanescent formation of ternary configurations throughout the x-range.

  9. 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

    2013-07-03

    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.

  10. CiSE and Computational Physics: Undergraduate Physics Challenge

    NASA Astrophysics Data System (ADS)

    Donnelly, Denis

    2008-04-01

    The role of Computing in Science and Engineering (CiSE) in support of computational physics is discussed with emphasis on CiSE's computational physics challenge. Winners awards are 1500, 1000, and 500. Each winner also receives a copy of Mathematica plus modest travel support. The challenge was for undergraduates at any accredited educational institution. Applicants were to select a physically and computationally interesting problem of their own choosing. Awards are presented at this session. Student winners discuss their work in papers that follow. First prize winner is Yevgeny Binder, of Loyola University in Chicago -``PartonKit: A C Program for Fast Parton Evolution with the Rossi Method.'' Second prize winner is John Barrett, of the University of Massachusetts, Amherst - ``Analysis of Photon Transport in 3 Polarized Scintillating Target Proto-types.'' Third prize winner is Steven Anton, of the University of Delaware - ``Electron Wave Packet Propagation in Graphene Nanoribbons.''

  11. 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

  12. 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..

  13. 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.

  14. 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.

  15. Superconductivity and ferromagnetism in nanomaterial NbSe2

    NASA Astrophysics Data System (ADS)

    Gill, Raminder

    2017-07-01

    Finding of superconductivity (SC) in ultra thin layer of Niobium diselenide (NbSe2) caught the attention of each condensed matter physicist in the era of nanotechnology. The coexistence of SC and magnetism have been a topic of interesting research in solid-state physics since the discovery of superconductivity. Ferromagnetism induced in any compound could destroy superconductivity by disturbing the cooper pairing of electrons of the atoms. The interplay between ferromagnetism (FM) and SC in nanomaterial NBSe2 impressed to study and to know the exact mechanism behind this coexistence which can lead to a very interesting research: superconductivity at room temperature. In this paper, I have theoretically studied the coexistence of SC and FM in NbSe2 and how this material could be useful in finding many high Tc nanomaterials.

  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. Valley trion dynamics in monolayer MoSe2

    NASA Astrophysics Data System (ADS)

    Gao, Feng; Gong, Yongji; Titze, Michael; Almeida, Raybel; Ajayan, Pulickel M.; Li, Hebin

    2016-12-01

    Charged excitons called trions play an important role in the fundamental valley dynamics in newly emerging two-dimensional semiconductor materials. We use ultrafast pump-probe spectroscopy to study the valley trion dynamics in a MoSe2 monolayer grown by using chemical vapor deposition. The dynamics displays an ultrafast trion formation followed by a nonexponential decay. The measurements at different pump fluences show that the trion decay dynamics becomes slower as the excitation density increases. The observed trion dynamics and the associated density dependence are a result of the trapping by two defect states as being the dominating decay mechanism. The simulation based on a set of rate equations reproduces the experimental data for different pump fluences. Our results reveal the important trion dynamics and identify the trapping by defect states as the primary trion decay mechanism in monolayer MoSe2 under the excitation densities used in our experiment.

  18. High temperature XRD of Cu2GeSe3

    NASA Astrophysics Data System (ADS)

    Premkumar D., S.; Chetty, Raju; Malar, P.; Mallik, Ramesh Chandra

    2015-06-01

    The Cu2GeSe3 is prepared by solid state synthesis method. The high temperature XRD has been done at different temperature from 30 °C to 450 °C. The reitveld refinement confirms Cu2GeSe3 phase and orthorhombic crystal structure. The lattice constants are increasing with increase in the temperature and their rate of increase with respect to temperature are used for finding the thermal expansion coefficient. The calculation of the linear and volume coefficient of thermal expansion is done from 30 °C to 400 °C. Decrease in the values of linear expansion coefficients with temperature are observed along a and c axis. Since thermal expansion coefficient is the consequence of the distortion of atoms in the lattice; this can be further used to find the minimum lattice thermal conductivity at given temperature.

  19. Electron-Phonon Coupling in a CdSe Nanowire

    NASA Astrophysics Data System (ADS)

    Barrett, Christopher; Wang, Lin-Wang

    2012-02-01

    It is important to calculate the coupling between phonons and electrons in realistic nanostructures, e.g. to understand carrier cooling and dynamics in a nanowire. In this talk, we will present results of phonon spectrum calculations using a customized valence force field (VFF) method. This customized VFF method is developed to be fittable to the results of any ab-initio calculations, with density functional theory (DFT) results being used in this work. By fitting many different DFT calculations on different motifs and their perturbations, we have obtained in the custom VFF a very efficient method that closely reproduces DFT phonons for CdSe nanowires with (10-10) surfaces having Cd-Se dimerization. We have also combined the results of these phonon spectrum calculations with electronic structure calculations to obtain the electron-phonon coupling. We will present this result and and show how the electron-phonon coupling affects the carrier dynamics in the nanowire.

  20. Phonon spectrum in a CdSe nanowire

    NASA Astrophysics Data System (ADS)

    Barrett, Chris; Wang, Lin-Wang

    2011-03-01

    It is important to calculate the phonon spectrum of realistic nanowires, e.g. to understand its thermo conductivity or to calculate the electron-phonon interaction. In this talk, we will present results of phonon spectrum calculation using valence force field (VFF) method. An important issue is to construct the VFF to describe the surface atomic displacement. We have developed a general VFF formalism to fit our VFF result with the density functional theory (DFT) calculated surface atom displacement energies. In particular, the (10-10) CdSe surface is modelled with Cd-Se dimerization. We will discuss the quality of such VFF model. The phonon spectrum of the nanowire will be presented, and its implication on the phonon transport and electron-phonon coupling will also be discussed. This work is supported by U.S. Department of Energy BES, office of science, under Contract No. DE-AC02-05CH11231.

  1. 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.

  2. [P3Se4](+): A Binary Phosphorus-Selenium Cation.

    PubMed

    Feldmann, Kai-Oliver; Wiegand, Thomas; Ren, Jinjun; Eckert, Hellmut; Breternitz, Joachim; Groh, Matthias F; Müller, Ulrike; Ruck, Michael; Maryasin, Boris; Ochsenfeld, Christian; Schön, Oliver; Karaghiosoff, Konstantin; Weigand, Jan J

    2015-06-26

    Although a fairly large number of binary group 15/16 element cations have been reported, no example involving phosphorus in combination with a group 16 element has been synthesized and characterized to date. In this contribution is reported the synthesis and structural characterization of the first example of such a cation, namely a nortricyclane-type [P3Se4](+). This cation has been independently discovered by three groups through three different synthetic routes, as described herein. The molecular and electronic structure of the [P3Se4](+) cage and its crystal properties in the solid state have been characterized comprehensively by using X-ray diffraction, Raman, and nuclear magnetic resonance spectroscopies, as well as quantum chemical calculations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Mass Study of the Neutron Deficient Nulceus ^68Se

    NASA Astrophysics Data System (ADS)

    Brown, T.; Davids, C.; Penttila, H.; Blumenthal, D.; Lister, C.; Busse, B.; Batchelder, J.; Walters, W.; Conticchio, L.; Mustillo, D.; Ramayya, A. V.

    1998-10-01

    For the last few decades, many groups have made innovative attempts to study the properties of the neutron deficient nucleus ^68Se. Due to the small production cross section and the inability to quickly and definitely separate ^68Se from other reaction products, the search has thus far been incomplete. With the Fragment Mass Analyzer at Argonne National Lab, the halflife and β+ decay scheme were measured and found to agree with that of a previous work (P. Baumann et al., Phys. Rev. C50 R1180(1994)). A mass measurement was also performed. The latter piece of information is critical for nuclear synthesis models in regard to the rp process. This work was supported by the US Department of Energy, Nuclear Physics Division, under contract W-31-109-ENG-38 and by the NSF.

  4. 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.

  5. Suppression of superconductivity by twin boundaries in FeSe.

    PubMed

    Song, Can-Li; Wang, Yi-Lin; Jiang, Ye-Ping; Wang, Lili; He, Ke; Chen, Xi; Hoffman, Jennifer E; Ma, Xu-Cun; Xue, Qi-Kun

    2012-09-28

    Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate twin boundaries in stoichiometric FeSe films grown by molecular beam epitaxy. Twin boundaries can be unambiguously identified by imaging the 90° change in the orientation of local electronic dimers from Fe site impurities on either side. Twin boundaries run at approximately 45° to the Fe-Fe bond directions, and noticeably suppress the superconducting gap, in contrast with the recent experimental and theoretical findings in other iron pnictides. Furthermore, vortices appear to accumulate on twin boundaries, consistent with the degraded superconductivity there. The variation in superconductivity is likely caused by the increased Se height in the vicinity of twin boundaries, providing the first local evidence for the importance of this height to the mechanism of superconductivity.

  6. Doping mechanism in pure CuInSe{sub 2}

    SciTech Connect

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

    2016-05-07

    We investigate the dopant concentration and majority carrier mobility in epitaxial CuInSe{sub 2} 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 CuInSe{sub 2} solar cell absorbers.

  7. 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

    2016-06-02

    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.

  8. Electronically-driven orthorhombic distortion in FeSe

    NASA Astrophysics Data System (ADS)

    Watson, Matthew; Davies, Nathaniel; Haghighirad, Amir; Narayanan, Arjun; Kim, Timur; Hoersch, Moritz; Blake, Samuel; Coldea, Amalia

    2015-03-01

    FeSe is structurally the simplest of Fe-based superconductors, and exhibits a tetragonal-to-orthorhombic structural transition at ~ 90 K, but no long-range magnetism at any temperature. We report measurements of the resistivity anisotropy in FeSe above Ts finding a large and divergent response to an applied strain, with a comparable magnitude and temperature-dependence to measurements in Ba(Fe1-xCox)2As2, but opposite sign. We compare this data with literature reports on NMR and our own ARPES data, which taken together indicate that the structural transition is electronically-driven with orbital degrees of freedom playing a central role. This work was supported by EPSRC, UK (EP/I004475/1) and Diamond Light Source.

  9. Low Dimensional Properties Manifested in NbSe3

    NASA Astrophysics Data System (ADS)

    Rocha, Matthew P.; Kevan, S. D.; Rossnagel, K.; Rotenberg, Eli

    2003-05-01

    We have recently completed a comprehensive angle resolved photoemission (ARP) study of the quasi-one-dimensional conductor NbSe_3. While this compound has been known about for some three decades, photoemission has not previously been possible due to the sample structure; high quality single crystals grow as long, wide, flat ribbons (typical dimensions in our experiments are 10×100×104 μm). Using the spectromicroscopy beamline at the Advanced Light Source, the valence band structure of NbSe3 has been directly mapped. We report on systematic measurements taken across the T1 charge-density wave (CDW) transition and in multiple geometries. Modifications of the band dispersions with the onset of the CDW are discussed. Fermi contours have also been plotted, and our results are compared to a density-functional calculation.

  10. MoSe2 Nanolabels for Electrochemical Immunoassays.

    PubMed

    Toh, Rou Jun; Mayorga-Martinez, Carmen C; Sofer, Zdeněk; Pumera, Martin

    2016-12-20

    There is huge interest in biosensors as a result of the demand for personalized medicine. In biomolecular detection, transition-metal dichalcogenides (TMDs) can be used as signal-enhancing elements. Herein, we utilize a solution-based electrochemical exfoliation technique with bipolar electrodes to manufacture MoSe2 nanolabels for biomolecular detection. Prepared MoSe2 nanoparticles (NPs) exhibit electrocatalytic activity toward the hydrogen evolution reaction (HER), and such a property allows it to act as a robust label for magneto-immunoassays toward protein detection. The magneto-immunoassay also displayed good selectivity, a wide linear range of 2 to 500 ng mL(-1), high sensitivity (LOD = 1.23 ng mL(-1)) and reproducibility (RSD = 9.7%). These findings establish the viability and reproducibility of such an exfoliation technique for TMD nanolabels for the development of low costs and efficient biosensing systems.

  11. Trap levels in layered semiconductor Ga 2SeS

    NASA Astrophysics Data System (ADS)

    Aydinli, A.; Gasanly, N. M.; Aytekin, S.

    2004-12-01

    Trap levels in nominally undoped Ga 2SeS layered crystals have been characterized by thermally stimulated current (TSC) measurements. During the measurements, current was allowed to flow along the c-axis of the crystals in the temperature range of 10-300 K. Two distinct TSC peaks were observed in the spectra, deconvolution of which yielded three peaks. The results are analyzed by curve fitting, peak shape and initial rise methods. They all seem to be in good agreement with each other. The activation energies of three trapping centers in Ga 2SeS are found to be 72, 100 and 150 meV. The capture cross section of these traps are 6.7×10 -23, 1.8×10 -23 and 2.8×10 -22 cm 2 with concentrations of 1.3×10 12, 5.4×10 12 and 4.2×10 12 cm -3, respectively.

  12. 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.

  13. Small-core As-Se fiber for Raman amplification.

    PubMed

    Thielen, P A; Shaw, L B; Pureza, P C; Nguyen, V Q; Sanghera, J S; Aggarwal, I D

    2003-08-15

    We have demonstrated Raman small-core As-Se fiber. More than 20-dB of gain was observed in a 1.1-m length of fiber pumped by a nanosecond pulse of approximately 10.8-W peak power at 1.50 microm. The peak of the Raman gain occurred at a shift of approximately 240 cm(-1). The Raman gain coefficient is estimated to be approximately 2.3 x 10(-11) m/W, which is more than 300 times greater than that of silica. The large Raman gain coefficient coupled with the large IR transparency window of these fibers shows promise for development of As-Se Raman fiber lasers and amplifiers in the near-, mid-, and long-IR spectral regions.

  14. Critical analysis of the thermodynamic properties of the In-Se gaseous and solid phases

    NASA Astrophysics Data System (ADS)

    Chatillon, Christian

    1993-03-01

    The thermodynamic properties of the In4Se3(s), InSe(s), In6Se7(s), In2Se3(s) compounds and of the In2Se(g), InSe(g) and In2Se2(g) molecules are established from literature data after a critical analysis of primary data. Using the congruent vaporization property of the In2Se3(s) compound, the discrepancies between data are analysed and new values are proposed that allow the calculation of vaporization processes in the In-Se system to be carried out.

  15. Deformation potentials of CdSe quantum dots

    SciTech Connect

    Li, Jingbo; Wang, Lin-Wang

    2004-06-02

    The size dependent deformation potentials of CdSe quantum dots are studied by first principle and semi-empirical pseudopotentials calculations. They find that the amplitude of the quantum dot deformation potential is only slightly larger than the bulk value, and this increase is mostly caused by the off {Lambda} point deformation potentials in the bulk, which are larger in amplitude than the {Lambda} point deformation potential.

  16. Electrochemical synthesis and characterization of Cu2Se nanowires

    NASA Astrophysics Data System (ADS)

    Kaur, Harmanmeet; Kaur, Jaskiran; Singh, Lakhwant; Singh, Surinder

    2013-12-01

    Copper Selenide (Cu2Se) nanowires were successfully fabricated via potentiostatic electrodeposition using polycarbonate membranes (Whatmann, USA) with nominal pore diameter of 100 nm. The morphology of the so fabricated nanowires was examined by field emission scanning electron microscopy (FE-SEM). Later the samples were characterized for their structural, optical and electrical properties by XRD, UV-visible spectroscopy and I-V respectively.

  17. SE Tools Overview & Advanced Systems Engineering Lab (ASEL)

    DTIC Science & Technology

    2011-06-02

    Unclassified/FOUO SE Tools Overview & Advanced Systems Engineering Lab ( ASEL ) Pradeep Mendonza TARDEC Systems Engineering Group pradeep.mendonza...Lab ( ASEL ) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Pradeep Mendonza 5d. PROJECT NUMBER 5e. TASK NUMBER...AGENDA Systems Engineering Capabilities Interactive Reference Guide (IRG) SEG COTS Tools What is ASEL ? Snapshots of the Decision Management Tool

  18. 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.

  19. On Debye temperature anomaly observed in Ge Se Ag glasses

    NASA Astrophysics Data System (ADS)

    Razdan, Ashok

    2008-09-01

    Anomalous values of Debye temperature have been obtained from recoil free factor measurements Ge-Se-Ag glasses recently [B. Arcondo, M.A. Urena, A. Piarristeguy, A. Pradel, M. Fontana, Physica B 389 (2007) 77]. In the present paper we show that this anomaly may arise due to the presence of anharmonic potential at the high spin ferrous site. We use q Lamb Mossbauer factor and anharmonic Lamb Mossbauer factor to study this anharmonicity.

  20. 1. AERIAL VIEW, LOOKING SE. CHICAGO SKYWAY TOLL BRIDGE (HAER ...

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

    1. AERIAL VIEW, LOOKING SE. CHICAGO SKYWAY TOLL BRIDGE (HAER No. IL-145) IS TOWARD RIGHT OF FRAME; PITTSBURGH, FORT WAYNE & CHICAGO RAILWAY BRIDGE IS JUST LEFT OF GRAIN ELEVATOR; PAIR OF LAKE SHORE & MICHIGAN SOUTHERN RAILWAY BRIDGES (HAER No. IL-161) ARE TOWARD LEFT OF FRAME. - Pittsburgh, Fort Wayne & Chicago Railway, Calumet River Bridge, Spanning Calumet River, east of Chicago Skyway (I-90), Chicago, Cook County, IL