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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. Does offshore crustal taper control an onshore topographic displacement gradient in SE Brasil?

    NASA Astrophysics Data System (ADS)

    Redfield, Tim; Terje Osmundsen, Per; Peron-Pinvidic, Gwenn

    2015-04-01

    The SE Brasilian Serras da Mantiqueira and do Mar topographic envelopes exhibit coast-parallel displacement gradients typical of linked normal faults in extending terrain. Between southern Curitiba and Cabo Frio, coast-perpendicular profiles show the distance from the maximum escarpment elevation to the likely location of the extended margin's flexural/rheological coupling point (Taper Break, or TB) is inversely correlative to the height of the escarpment. The correlation is similar to previously-published scaling relationships derived from Scandinavian and global datasets. Although Precambrian ductile shear zones guided brittle phase faulting during Mesozoic extension and Cenozoic margin uplift, the primary control governing fault reactivation and source-to-sink evolution of the SE Brasilian rifted margin seems rooted in crustal thinning. We see two lines of interest for petroleum exploration: Preferential reactivation of high angle faults at sharply-tapered margin sectors is expected to guide onshore to offshore sediment routing along margin-parallel corridors, and (should the TB-escarpment correlation be better validated with proposed analyses of high-quality marine geophysical datasets) a partial constraint upon architectural end member interpretations of deep crustal structure may be contemplated.

  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. 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

  5. Fe distribution in GaSe and InSe

    SciTech Connect

    Kovalyuk, Z.D.; Feichuk, P.I.; Shcherbak, L.P.; Zbykovskaya, N.I.

    1985-06-01

    In this paper, the authors use tagged atoms to determine the effective coefficients of Fe distribution in GaSe and InSe during crystallization of a doped melt by the Bridgman method. The distribution of Fe in GaSe and InSe was studied with the aid of Fe tagged with the radiosotopes VVFe + VZFe. Doping of the material was combined with the processes of synthesis and crystallization. Equations are presented for the calculation of the real impurity distribution in GaSe and InSe crystals.

  6. Properties of Se/InSe Thin-Film Interface

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  7. Electron-impact ionization of Se2+ and Se3+

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    Electron-impact ionization cross sections for Se2+ and Se3+ are calculated using a semi-relativistic configuration-average distorted-wave (CADW) method. Good agreement between the CADW calculations and recent experimental measurements are found for the single ionization of Se2+ from threshold to 500 eV and for the double ionization of Se2+ from threshold to 225 eV. Good agreement between the CADW calculations and recent experimental measurements are also found for the single ionization of Se3+ from threshold to 200 eV and for the double ionization of Se3+ near the peak of the cross section at 350 eV. Disagreements at other incident electron energies may be due to the complexity of the ionization pathways for low charged Se atomic ions, the various theoretical approximations, and the difficulty in measuring relatively small double ionization events.

  8. 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.

  9. 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.

  10. 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

  11. Optical investigation of CdSe/ZnSe quantum nanostructures

    NASA Astrophysics Data System (ADS)

    Valakh, M. Ya; Ivanov, S. V.; Mestres, N.; Pascual, J.; Shubina, T. V.; Sorokin, S. V.; Streltchuk, V. V.; Pozina, G.; Monemar, B.

    2002-02-01

    We have used resonant and non-resonant Raman scattering as well as photoluminescence and cathodoluminescence experiments to study the structure and composition properties of CdxZn1-xSe formed by migration enhanced epitaxy of CdSe layers on ZnSe buffers. The spectral change of the photoluminescence maximum correlates with the increase of the Cd content, depending on the nominal CdSe thickness in the 1.5-3.0 ML range. The inhomogeneous broadening of the photoluminescence band is caused by the composition difference between the two-dimensional mixed CdxZn1-xSe layer and the inserted islands with larger Cd concentration. This is confirmed by phonon frequency changes in resonant Raman scattering for samples with different nominal CdSe thicknesses as well as in Stokes and anti-Stokes frequency changes observed in the 1.5 ML sample. Attention is paid to the role of defects on Raman scattering and photoluminescence for the 3.15 ML sample.

  12. Electrodeposition of In-Se, Cu-Se, and Cu-In-Se thin films

    SciTech Connect

    Bhattacharya, R.N.; Fernandez, A.M.; Contreras, M.A.; Keane, J.; Tennant, A.L.; Ramanathan, K.; Tuttle, J.R.; Noufi, R.N.; Hermann, A.M.

    1996-03-01

    Indium-selenium, copper-selenium, and copper-indium-selenium thin films have been prepared by electrodeposition techniques on molybdenum substrates. Electrodeposited precursors are prepared at varying potentials, pH, and deposition times. The adhesion and uniformity of indium selenide on molybdenum substrates are improved by electrodepositing an initial copper layer (500 {angstrom}) on molybdenum. The films (In-Se, Cu-Se, and Cu-In-Se) are annealed at 250 and 450 C in Ar for 15 min and are slow-cooled (3 C/min). The films are characterized by electron microprobe analysis, inductive-coupled plasma spectrometry, X-ray diffraction analysis, Auger electron spectroscopy, and scanning electron microscopy. The as-deposited precursor films are loaded in a physical evaporation chamber and addition In or Cu and Se are added to the film to adjust the final composition to CuInSe{sub 2}. The device fabricated using electrodeposited Cu-In-Se precursor layers resulted in a solar cell efficiency of 9.4%.

  13. 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.

  14. Negatively charged excitons in semimagnetic CdSe/ZnSe/ZnMnSe quantum dots

    SciTech Connect

    Brichkin, A. S. Chernenko, A. V.; Chekhovich, E. A.; Dorozhkin, P. S.; Kulakovskii, V. D.; Ivanov, S. V.; Toropov, A. A.

    2007-08-15

    Low-temperature (T = 1.6 K) photoluminescence (PL) of individual CdSe/ZnSe/ZnMnSe quantum dots (QDs) with different magnitudes of the sp-d exchange interaction between the magnetic impurity ions and charge carriers has been studied in a magnetic field up to 12 T applied in the Faraday and Voigt geometry. The magnitude of the interaction was controlled by changing the fraction ({eta}{sub e,h}) of the squared wave function of charge carriers in the semimagnetic barrier by means of variation of the nonmagnetic (ZnSe) layer thickness. It is established that the sp-d exchange interaction leads to a change in the sign of the effective hole g factor even for {eta}{sub e,h} {approx} 5%, while further increase in the interaction magnitude is accompanied by a rapid growth in the magnitude of spin splitting for both electrons and holes. The quantum yield of PL exhibits a significant decrease due to nonradiative Auger recombination with the excitation of Mn ions only for {eta}{sub e,h} {approx} 12%, while the rate of the holes spin relaxation starts growing only for still higher {eta}{sub e,h} values. In a strong magnetic field perpendicular to the sample plane, the alignment of Mn spins leads to suppression of the Auger recombination only in the excited spin state. For a small rate of the hole spin relaxation, this leads to a rather unusual result: the emission from an excited trion state predominates in strong magnetic fields.

  15. Shape Coexistence in ^72Se

    NASA Astrophysics Data System (ADS)

    Lister, C. J.; Fischer, S. M.; McCutchan, E. A.; Ahn, T.; Casperson, R. J.; Heinz, A.; Ilie, G.; Qian, J.; Williams, E.; Winkler, R.

    2009-10-01

    One of the original candidates for shape co-existence in nuclei was ^72Se [1,2]. We have collected extensive new data, both ``in-beam'' following the ^40Ca(^36Ar,4p)^72Se reaction using Gammasphere at Argonne's ATLAS accelerator, and from the decay of ^72Br populated in the ^58Ni(^16O,pn) reaction studied at WNSL Yale. A new J^π=0^+ state was found at 1876 keV, the published [2] decay scheme was corrected, and twenty-six new levels were established. This detailed spectroscopy of low-lying states helps to delineate the two shape minima. The mixing of prolate-deformed and near-spherical states can be now quantified, and the gamma decay path from high-spin can be followed. The inferred groundstate shape is consistent with trends in experiment and calculation of the selenium isotopes [3,4]. [4pt] [1] J.H. Hamilton, et al., Phys. Rev. Letts. 32 239 (1974)[0pt] [2] W.E. Collins, et al., Phys.Rev. C9, 1457 (1974)[0pt] [3] S.M. Fischer, et al., Phys.Rev.Lett. 84, 4064 (2000)[0pt] [4] J. Ljungvall, et al., Phys.Rev.Lett. 100, 102502 (2008)

  16. Improving weather modeling in South America through IDD-Brasil

    NASA Astrophysics Data System (ADS)

    Chagas, G. O.

    2007-05-01

    The IDD-Brasil constitutes of an international collaboration among Universidade Federal do Rio de Janeiro (LPM/UFRJ), Centro de Previsão de Tempo e Estudos Climáticos (CPTEC/INPE) and the Unidata Program Center (Unidata/UCAR), which connects several universities and research centers across the Americas in a network to share real-time hydro meteorological data. Using this network as a new path to deliver and acquire observational data, IDD-Brazil participants are capable of receiving observational data from GTS (Global Telecommunication System), locally ingested data from several automatic weather stations networks (mesonets) from INPE, the entire array of METAR and SYNOP observations, and several model outputs and satellite imagery. During recent years Numerical Models have been used constantly, especially in mesoscale research, but the lack of a dense observational network in South America leads to several constraints during the data assimilation and model validation. Since the IDD-Brasil offers an improved and simple method to have new datasets readily accessible, it has been used continuously as a new manner to distribute surface observations that are not currently available in GTS, such as several mesonets in Brazil that account for an increase in data density. Through the usage of data ingested in IDD-Brasil as guess fields it is possible to study how the assimilation in several global models frequently used as initial conditions for mesoscale simulations can be affected, since in certain areas in Brazil the density of data nearly doubles if compared to GTS. Therefore it is also possible to better validate the results generated in mesoscale simulations, in view of the fact that the network has an improved spatial distribution. It is expected that the increase of locally held numerical model output from South American institutions in IDD- Brasil leads to an increased awareness of the need to constantly validate these results with observational data, thus

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  18. Runoff generation in SE Spain

    NASA Astrophysics Data System (ADS)

    Dalen, E. N.; Kirkby, M. J.; Chapman, P. J.; Bracken, L. J.

    2007-12-01

    We are working to improve a hydrological model for prediction of runoff in medium-scale semi-arid catchments in SE Spain. The aim is to develop and improve understandings of runoff generation in semi-arid areas and to improve modelling of runoff. Objectives are to investigate the influence of geology, landuse and seasonality on infiltration rates and use remonte sensing (RS) and GIS to classify an area into Hydrologically Similar Surfaces (HYSS) categories. The research includes investigating the impact of different landscape elements on runoff within two 150 km2 catchments, the Rambla Nogalte and the Rambla de Torrealvilla. Most storms within these catchments are of short duration. HYSS are defined as areas with similar1-D (vertical) partitioning of net rainfall between infiltration and overland flow. HYSS are identified from field measurements of soils, micro and macro- topography and infiltration rates; then combined with analysis of multi-spectral airborne RS images. HYSS are selected to minimise internal variability in the relationship between rainfall and local runoff generation and are scaled up to cover larger areas. The overall sampling strategy for measurements has been to undertake constant intensity rainfall simulator measurements within provisional HYSS categories, and to augment this with a large number of minidisk infiltrometer measurements. This strategy captures as much of the variability in the landscape as possible. The wide variability within even small areas has led to the final adoption of only a few large classes that can be effectively distinguished. The final part of the research is to link the spatial partitioning of the two catchments into HYSS with the detailed rainfall records for the areas, and combine these two sets of data into a grid-based model for runoff generation across the area. The applied Green-Ampt modelling approach gave 63 possible combinations of surface properties (9 HYSS) and areas in the Rambla Nogalte each represented

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

    NASA Astrophysics Data System (ADS)

    Walter, J.; Shioyama, H.

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhang, Ruili; Yang, Ping

    2013-05-01

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

  1. CuInSe2/ZnSe solar cells using reactively sputter-deposited ZnSe

    NASA Technical Reports Server (NTRS)

    Nouhi, A.; Stirn, R. J.; Hermann, A.

    1987-01-01

    Results on CuInSe2/ZnSe thin-film heterojunction photovoltaic devices are presented. By the use of reactive magnetron cosputtering of Zn and In dopant in Ar/H2Se, ZnSe thin films have been deposited on glass and conducting SnO2-coated glass substrates with resistivity as low as 20 ohm-cm at deposition temperatures as low as 120 C. Preliminary ZnSe depositions onto CuInSe2 films supplied by industrial laboratories are encouraging. Reactive-sputter-deposition parameters for ZnSe have yet to be optimized for CuInSe2 substrates; however, open-circuit voltages as high as 430 mV were obtained. The highest short-circuit current density, as determined by spectral response weighted for AM1.5 global insulation, was 37.4 mA/sq cm. In all cases, a highly conductive ZnO film was overcoated onto the ZnSe to reduce the overall sheet resistance.

  2. Estimation of selenium (Se) intake from Se in serum, whole blood, toenails, or urine

    SciTech Connect

    Longnecker, M.P.; Taylor, P.R.; Levander, O.A.; Flack, V.; Veillon, C.; McAdam, P.A.; Patterson, K.Y.; Holden, J.; Stampfer, M.J.; Morris, J.S.; Willett, W.C. NCI, Rockville, MD USDA, Beltsville, MD Harvard Univ., Boston, MA Univ. of Missouri, Columbia )

    1991-03-11

    Because Se content of food varies widely, estimates of intake based on Se status are more accurate than those based on food composition tables. 77 free-living subjects from South Dakota and Wyoming, where the range of Se intake was large, provided blood, toenails, and 24-hour urines. Se intake, measured by chemical analysis of 4-8 days of duplicate-plate food composites from each subject, was estimated on the basis of the Se indices. To predict the natural logarithm of Se intake from serum Se the best fit was provided by : {minus}0.465 + 0.568{asterisk}SSe. Addition of lean body mass (LBM (kg)) and energy intake (EI (MJ)) to the model markedly improved the fit. Models based on Se in blood or urine gave slightly better estimates than those based on toenail Se. Consideration of data in addition to indices of Se status resulted in improved estimates of intake.

  3. Biopolymer-protected CdSe nanoparticles.

    PubMed

    Bozanić, D K; Djoković, V; Bibić, N; Sreekumari Nair, P; Georges, M K; Radhakrishnan, T

    2009-11-23

    A synthetic procedure for the encapsulation of cadmium selenide (CdSe) nanoparticles in a sago starch matrix is introduced. The nanocomposite was investigated using structural, spectroscopic, and thermal methods. TEM micrographs of the nanocomposite showed spherical CdSe particles of 4-5 nm in size coated with a biopolymer layer. The absorption edges of both the aqueous solution and the thin film of the CdSe-starch nanocomposite were shifted toward lower wavelengths in comparison to the value of the bulk semiconductor. Infrared measurements revealed that the interaction of CdSe nanoparticles and starch chains takes place via OH groups. Although the onset of the temperature of decomposition of CdSe-starch nanocomposite is lower than that of the pure matrix, thermogravimetric analysis also showed that introduction of CdSe nanoparticles significantly reduced starch degradation rate leading to high residual mass at the end of the degradation process. PMID:19772959

  4. 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.

  5. 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.

  6. Oxidation of ultrathin GaSe

    DOE PAGESBeta

    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.

  7. Strategic Use of Naturally Selenium (Se)-rich Milling Coproducts to Eliminate Se Deficiency and Create Se-enriched Foods.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Selenium (Se) is essential for sustaining a healthy life. When dietary Se was marginally deficient, populations experienced impaired reproduction and growth rates and increased disease rates. Selenium-rich grains, harvested from regions with seleniferous soils, were natural sources of bioavailable S...

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

    NASA Astrophysics Data System (ADS)

    Marple, Maxwell Adam Thomas

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

  9. Semiconductor-metal transition of Se in Ru-Se Catalyst Nanoparticles

    NASA Astrophysics Data System (ADS)

    Babu, P. K.; Lewera, Adam; Oldfield, Eric; Wieckowski, Andrzej

    2009-03-01

    Ru-Se composite nanoparticles are promising catalysts for the oxygen reduction reaction (ORR) in fuel cells. Though the role of Se in enhancing the chemical stability of Ru nanoparticles is well established, the microscopic nature of Ru-Se interaction was not clearly understood. We carried out a combined investigation of ^77Se NMR and XPS on Ru-Se nanoparticles and our results indicate that Se, a semiconductor in elemental form, becomes metallic when interacting with Ru. ^77Se spin-lattice relaxation rates are found to be proportional to T, the well-known Korringa behavior characteristic of metals. The NMR results are supported by the XPS binding energy shifts which suggest that a possible Ru->Se charge transfer could be responsible for the semiconductor->metal transition of Se which also makes Ru less susceptible to oxidation during ORR.

  10. 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

  11. 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.

  12. 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.

  13. Quasiparticle band structure of HgSe

    SciTech Connect

    Rohlfing, M.; Louie, S.G.

    1998-04-01

    Motivated by a recent discussion about the existence of a fundamental gap in HgSe [Phys. Rev. Lett. {bold 78}, 3165 (1997)], we calculate the quasiparticle band structure of HgSe within the GW approximation for the electron self-energy. The band-structure results show that HgSe is a semimetal, which is in agreement with most experimental data. We observe a strong wave-vector dependence of the self-energy of the lowest conduction band, leading to an increased dispersion and a small effective mass. This may help to interpret recent photoemission spectroscopy measurements. {copyright} {ital 1998} {ital The American Physical Society}

  14. 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

  15. 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.

  16. Double electron capture searches in 74Se

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  17. 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.

  18. Surface migration and volume diffusion in the AgGaSe2-Ag2Se system

    NASA Technical Reports Server (NTRS)

    Kim, N.-H.; Feigelson, R. S.; Route, R. K.

    1992-01-01

    Surface migration and volume diffusion in the Ag2Se-AgGaSe2 system were investigated using reactive diffusion couples which were analyzed by X-ray diffraction, optical microscopy, and electron probe microanalysis. The surface diffusivities of all mobile species are found to be much larger than volume diffusivities. The results of the study suggest that Se moves together with Ag and Ga to maintain binary (Ag2Se and Ga2Se3) stoichiometry and electroneutrality. The dominance of surface migration kinetics can account for the uniform annihilation of second-phase precipitates during heat treatments.

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

    SciTech Connect

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

    1984-02-15

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

  20. 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

  1. 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.

  2. Monoclinic Cu2Se3Sn.

    PubMed

    Gulay, L D; Daszkiewicz, M; Ostapyuk, T A; Klymovych, O S; Zmiy, O F

    2010-05-01

    A previously unknown modification of dicopper(I) triselenostannate(IV), Cu(2)Se(3)Sn, has been obtained from the Cu(2)Se-SnSe(2) quasi-binary system and investigated using X-ray single-crystal diffraction. The Se atoms are stacked in a closest-packed arrangement with the layers in the sequence ABC. The Cu atoms occupy one-third of the tetrahedral interstices, whereas the Sn atoms are located in one-sixth of the tetrahedral interstices. All the atoms occupy general positions. The structure possesses pseudo-inversion symmetry. The Cu(2)Se(3)Sn structure investigated in this paper (96 atoms per unit cell, ordered distribution of Cu and Sn over 12 cation positions) is a superstructure of the reported cubic (eight atoms per unit cell, random distribution of Cu and Sn over one cation position) and monoclinic (24 atoms per unit cell, ordered distribution of Cu and Sn over three cation positions) modifications. PMID:20442500

  3. Cs2UPd3Se6

    PubMed Central

    Oh, George N.; Ibers, James A.

    2011-01-01

    Dicaesium uranium(IV) tripalladium(II) hexa­selenide, Cs2UPd3Se6, crystallizes in the space group Fmmm in the Ba2NaCu3O6 structure type. The asymmetric unit comprises the following atoms with site symmetries as shown: U1 (mm2), Cs1 (222), Cs2 (m2m), Pd1 (.m.), Pd2 (2mm), Se1 (m..), and Se2 (1). This layered structure contains six edge-sharing square-planar [PdSe4] units that form a hexa­gon. These, in turn, edge-share with [USe6] trigonal–prismatic units, forming an extended layer parallel to (010). The layers are stacked along [010]. They are staggered, and are separated by the Cs atoms. The Cs atoms are either coordinated in a square anti­prism of Se atoms or are ten-coordinate, with one square face and the opposite face hexa­gonal. PMID:21522818

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  6. CdSe Nanoplatelets: Living Polymers.

    PubMed

    Jana, Santanu; Davidson, Patrick; Abécassis, Benjamin

    2016-08-01

    Colloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self-assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face-to-face self-assembly of CdSe nanoplatelets into micron-long polymer-like threads made of up to ∼1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re-dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1-dimensional structures are flexible and feature a "living polymer" character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends. PMID:27329047

  7. FeNb3Se10: A new structure type related to NbSe3

    NASA Astrophysics Data System (ADS)

    Cava, R. J.; Himes, V. L.; Mighell, A. D.; Roth, R. S.

    1981-09-01

    Employing single-crystal x-ray-diffraction techniques, the crystal structure of FeNb3Se10 was found to consist of two NbSe6 trigonal prismatic chains of the type found in NbSe3 and a double chain of edge-shared MSe6 octahedra, both running parallel to the monoclinic b axis. The metal-atom disorder, critical to the interpretation of previously observed electronic properties, is confined to the octahedral chains.

  8. 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%. PMID:24734747

  9. 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.

  10. Superlattices of Bi2Se3/In2Se3: Growth characteristics and structural properties

    NASA Astrophysics Data System (ADS)

    Wang, Z. Y.; Guo, X.; Li, H. D.; Wong, T. L.; Wang, N.; Xie, M. H.

    2011-07-01

    Superlattices (SLs) consisted of alternating Bi2Se3 and In2Se3 layers are grown on Si(111) by molecular-beam epitaxy. Bi2Se3, a three-dimensional topological insulator (TI), showed good chemical and structural compatibility with In2Se3, a normal band insulator with large energy bandgap. The individual layers in the SLs are very uniform, and the hetero-interfaces are sharp. Therefore, such SL structures are potential candidates for explorations of the quantum size effects of TIs.

  11. n -type doping of CuIn Se2 and CuGa Se2

    NASA Astrophysics Data System (ADS)

    Persson, Clas; Zhao, Yu-Jun; Lany, Stephan; Zunger, Alex

    2005-07-01

    The efficiency of CuInSe2 based solar cell devices could improve significantly if CuGaSe2 , a wider band gap chalcopyrite semiconductor, could be added to the CuInSe2 absorber layer. This is, however, limited by the difficulty of doping n -type CuGaSe2 and, hence, in its alloys with CuInSe2 . Indeed, wider-gap members of semiconductor series are often more difficult to dope than lower-gap members of the same series. We find that in chalcopyrites, there are three critical values of the Fermi energy EF that control n -type doping: (i) EFn,pin is the value of EF where the energy to form Cu vacancies is zero. At this point, the spontaneously formed vacancies ( = acceptors) kill all electrons. (ii) EFn,comp is the value of EF where the energy to form a Cu vacancy equals the energy to form an n -type dopant, e.g., CdCu . (iii) EFn,site is the value of EF where the formation of Cd-on-In is equal to the formation of Cd-on-Cu. For good n -type doping, EFn,pin , EFn,comp , and EFn,site need to be as high as possible in the gap. We find that these quantities are higher in the gap in CuInSe2 than in CuGaSe2 , so the latter is difficult to dope n -type. In this work, we calculate all three critical Fermi energies and study theoretically the best growth condition for n -type CuInSe2 and CuGaSe2 with possible cation and anion doping. We find that the intrinsic defects such as VCu and InCu or GaCu play significant roles in doping in both chalcopyrites. For group-II cation (Cd, Zn, or Mg) doping, the best n -type growth condition is In/Ga -rich, and maximal Se-poor, which is also the optimal condition for stabilizing the intrinsic InCu/GaCu donors. Bulk CuInSe2 can be doped at equilibrium n -type, but bulk CuGaSe2 cannot be due to the low formation energy of intrinsic Cu-vacancy. For halogen anion doping, the best n -type materials growth is still under In/Ga -rich, and maximal Se-poor conditions. These conditions are not best for halogen substitutional defects, but are optimal for

  12. 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…

  13. 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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    PubMed

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

    2016-01-27

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

  18. Identification of {sup 88}Se and new levels in {sup 84,86}Se

    SciTech Connect

    Jones, E.F.; Gore, P.M.; Hamilton, J.H.; Ramayya, A.V.; Hwang, J.K.; Beyer, C.J.; Lima, A.P. de; Zhu, S.J.; Luo, Y.X.; Ma, W.C.; Rasmussen, J.O.; Lee, I.Y.; Wu, S.C.; Ginter, T.N.; Stoyer, M.; Cole, J.D.; Daniel, A.V.; Ter-Akopian, G.M.; Donangelo, R.

    2006-01-15

    From the analysis of {gamma}-{gamma}-{gamma} coincidence data taken with Gammasphere of the prompt {gamma} rays in the spontaneous fission of {sup 252}Cf, the 2{sup +}{yields}0{sup +} transition in {sup 88}Se was identified for the first time. Also, the 4{sup +}{yields}2{sup +} and 6{sup +}{yields}4{sup +} transitions in {sup 86}Se were identified along with four new states above 4{sup +} in {sup 84}Se. Surprisingly, the 2{sup +} energy rises in {sup 88}Se compared to {sup 86}Se. This increase in energy could arise from the interaction of a low-lying excited 0{sup +} state with different deformation and the 0{sup +} ground state to depress the ground-state energy.

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

    PubMed

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

    2015-01-01

    'Cold' crystallization in 80GeSe2-20Ga2Se3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga2Se3 and/or GeGa4Se8 phases and prevalent GeSe2 phase extracted mainly at the surface of thermally treated samples with preceding nucleation and void agglomeration in the initial stage of annealing are characteristic features of cold crystallization. PMID:25852346

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  1. 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.

  2. [NiFeSe]-hydrogenase chemistry.

    PubMed

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

    2015-11-17

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

  3. Anisotropy in CdSe quantum rods

    SciTech Connect

    Li, Liang-shi

    2003-09-01

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

  4. 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.

  5. 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.

  6. 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.

  7. Structural and chemical analysis of CdSe/ZnSe nanostructures by transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Peranio, N.; Rosenauer, A.; Gerthsen, D.; Sorokin, S. V.; Sedova, I. V.; Ivanov, S. V.

    2000-06-01

    A transmission electron microscopy (TEM) study of the structure and chemical composition of 0.5 to 3.0 ML (monolayer) CdSe sheets that are buried in a ZnSe matrix is presented. The CdSe layers were grown by migration-enhanced epitaxy at a growth temperature of 280 °C. We find two-dimensional (2D) CdxZn1-xSe layers with a total thickness of approximately 3 nm for all samples independent of the nominal CdSe content that contain inclusions (islands) with an enlarged Cd concentration. Plan-view TEM revealed two types of islands: First, small 2D islands with a lateral size of less than 10 nm, and second, large 2D islands with a lateral size between 30 and 130 nm. The combination of two-beam dark-field imaging and the new composition evaluation by lattice fringe analysis (CELFA) procedure allow the precise measurement of the Cd-concentration profiles of the CdxZn1-xSe layers. The CELFA evaluation yields a full width at half maximum value of (10+/-1) ML. The most probable origin of the broadening is a strong interdiffusion of Cd and Zn with an additional contribution of the segregation of the Cd atoms. The diffusion length of the Cd diffusion in ZnSe during the growth of the ZnSe cap layer is LD=(3.6+/-0.8) ML and the segregation probability is estimated to be R=(0.6+/-0.2). It is shown that neither objective lens aberrations nor specimen tilt are the main sources for the observed enormous broadening of the CdSe interlayers.

  8. 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

  9. Magnetic ground state of FeSe.

    PubMed

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

    2016-01-01

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

  10. Quadrupolar Spin Orders in FeSe

    NASA Astrophysics Data System (ADS)

    Wang, Zhentao; Nevidomskyy, Andriy

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

  11. Magnetic ground state of FeSe

    NASA Astrophysics Data System (ADS)

    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

    2016-07-01

    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.

  12. 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. PMID:23035457

  13. 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.

  14. Growth of multilayers of Bi{sub 2}Se{sub 3}/ZnSe: Heteroepitaxial interface formation and strain

    SciTech Connect

    Li, H. D.; Wang, Z. Y.; Guo, X.; Xie, M. H.; Wong, Tai Lun; Wang, Ning

    2011-01-24

    Multilayers of Bi{sub 2}Se{sub 3}/ZnSe with the periodicity of a few nanometers were grown by molecular-beam epitaxy on Si(111). While epitaxial growth of Bi{sub 2}Se{sub 3} on ZnSe proceeded by two-dimensional nucleation, ZnSe growth on Bi{sub 2}Se{sub 3} showed the three-dimensional growth front. Therefore, the two complementary interfaces of Bi{sub 2}Se{sub 3}/ZnSe were asymmetric in morphological properties. Strain-relaxation rates were found to differ between epitaxial ZnSe and Bi{sub 2}Se{sub 3}, which could be attributed to the specific growth modes and the properties of Bi{sub 2}Se{sub 3} and ZnSe surfaces.

  15. 77Se nuclear magnetic resonance of topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  16. Dynamic structure of liquid Se, Te and Se-Te mixtures by neutron scattering measurements

    SciTech Connect

    Chiba, Ayano; Yao, Makoto; Ohmasa, Yoshinori; Taylor, Jon; Bennington, Stephen M.

    2004-04-30

    Inelastic neutron scattering measurements are performed to investigate the dynamic structure of liquid Se, Te, and Te50Se50. The bond-stretching modes for liquid Se and Te50Se50 (both are in the semiconducting phase) are clearly observed at higher-energy regions than that for their trigonal phase. This shift is a reflection of their pronounced molecular-like properties without prominent inter-molecular interactions, whereas the vibrational modes for liquid Te (in the metallic phase) show its metallic-like bonding character with remarkable inter-molecular interactions. We thus observed a change in dynamic structure that accompanies the semiconductor-to-metal transition; the change that would be related to the slow dynamics induced by the transition.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  19. 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.

  20. CdZnSe/ZnSe strained layer superlattices disordered by germanium diffusion

    SciTech Connect

    Yokogawa, T.; Floyd, P.D.; Merz, J.L.

    1994-03-01

    We have investigated the phenomenon of layer disordering in CdZnSe/ZnSe strained layer superlattices (SLSs) by Ge diffusion and have fabricated CdZnSe/ZnSe optical waveguides using the Ge-induced disordering. Both the as-grown sample and the sample annealed without a Ge layer showed several orders of well-resolved double crystal x-ray satellite peaks due to SLS periodic structure. However, the satellite peaks completely disappeared in the Ge-diffused sample, indicating that the SLS structure was disordered by the Ge diffusion and not caused by the annealing process. Photoluminescence (PL) measurements at 1.4K of both the as-grown and the annealed samples without Ge diffusion show intense, sharp excitonic emission around 483 nm in CdZnSe/ZnSe SLS. After Ge diffusion, the PL peaks shift to higher energy confirming the layer disordering of the SLS. The blue shift due to disordering was also observed in the PL at room temperature (RT). The optical guided mode in the SLS guiding layer confined by the disordered alloy was confirmed. Lateral optical confinement in the stripe geometry laser was also confirmed by observing the RT stimulated emission produced by optical pumping. 12 refs., 6 figs.

  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. 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.

  3. 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.

  4. 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.

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2013-04-01

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

  7. ZnSe-based white LEDs

    NASA Astrophysics Data System (ADS)

    Katayama, K.; Matsubara, H.; Nakanishi, F.; Nakamura, T.; Doi, H.; Saegusa, A.; Mitsui, T.; Matsuoka, T.; Irikura, M.; Takebe, T.; Nishine, S.; Shirakawa, T.

    2000-06-01

    The first phosphor-free white LED based on II-IV compound materials is demonstrated. Our device utilizes a phenomenon unique to ZnSe homoepitaxy, where a portion of the main greenish-blue emission from the active layer of a pn junction diode is absorbed by the conductive substrate which in turn gives off an intense broad-band yellow emission centered around 585 nm by photoluminescence. These two emission bands combine to give a spectrum which appears white to the naked eye. A typical ZnSe-based white LED lamp exhibits a color temperature of approximately 3400 K with a CRI (color rendering index) of 68. The optical output power and operating voltage of such a device at a forward current of 20 mA is 2.0 mW and 2.7 V, respectively. The luminous efficiency estimated from these results is 10.4l m/W, which is comparable to the incandescent lamp as well as the commercial InGaN-based white LED. Device lifetimes (half-life) have exceeded 800 h at 20°C.

  8. 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.

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

    SciTech Connect

    Tripathi, S.K.; Sharma, Mamta

    2013-05-15

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

  10. 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.

  11. Preparation and characterization of Bi2Se3(0001) and of epitaxial FeSe nanocrystals on Bi2Se3(0001)

    NASA Astrophysics Data System (ADS)

    Cavallin, Alberto; Sevriuk, Vasilii; Fischer, Kenia Novakoski; Manna, Sujit; Ouazi, Safia; Ellguth, Martin; Tusche, Christian; Meyerheim, Holger L.; Sander, Dirk; Kirschner, Jürgen

    2016-04-01

    Procedures to prepare clean Bi2Se3(0001) surfaces from bulk samples and epitaxial FeSe nanocrystals on Bi2Se3(0001) are reported. Bi2Se3(0001) substrates are prepared by in vacuo cleavage of bulk samples, followed by ion bombardment and annealing cycles. FeSe is prepared by Fe deposition onto Bi2Se3 at 303 K, followed by annealing at T ≈ 623 K. We use low-energy electron diffraction, surface X-ray diffraction, photoemission spectroscopy, scanning tunneling microscopy and spectroscopy, and stress measurements to elucidate the correlation between structural and electronic properties of the pristine Bi2Se3(0001) and FeSe covered surfaces. Our analysis reveals the formation of epitaxial FeSe nanocrystals with a thickness of three unit cells (1.5 nm). Electron diffraction experiments indicate an anisotropic epitaxial strain in FeSe. A negligible strain close to 0.0% and a tensile strain of + 2.1% are observed along the in-plane [ 01 1 bar 0 ] and [ 2 11 bar 0 ] Bi2Se3 directions, respectively. The out-of-plane strain is + 4.2%. The role of this strain state for the reported high-TC superconductivity in bulk FeSe is discussed.

  12. Saturating refractive nonlinearities and optical bistability in ZnSe/CdZnSe MQWs at room temperature

    NASA Astrophysics Data System (ADS)

    Li, Hongyu; Shen, De Z.; Zhang, Jiying; Wang, Shumei; Yang, Baojun; Yu, Guangyou

    1998-08-01

    The excitonic nonlinear refractive index was calculated by using Kramers-Kronig relation and the saturating absorption of ZnSe/CdZnSe multiple quantum wells (MQWs) was studied under different pump intensities. The maximum nonlinear refractive index change is about -6.19 X 10-3. Excitonic optical bistability in ZnSe/CdZnSe MQWs is investigated at room temperature. The result indicates that the threshold and contrast ratio for the optical bistability in ZnSe/CdZnSe MQWs are about 210Kw/cm2 and 2:1, respectively. On the basis of the excitonic nonlinear theories and excitonic absorption spectra in the ZnSe/CdZnSe MQWs, we attribute the major nonlinear mechanism of the optical bistability in the ZnSe/CdZnSe MQWs to the phase space filling of excitonic states and excitonic band broadening due to exciton-exciton interactions.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  16. 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

  17. Photocatalytic Hydrogen Generation by CdSe/CdS Nanoparticles.

    PubMed

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

    2016-09-14

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

  18. 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. PMID:25977046

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

    PubMed

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

    2011-09-01

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

  20. Hexagonal CoSe formation in mechanical alloyed Co 75Se 25 mixture

    NASA Astrophysics Data System (ADS)

    Campos, C. E. M.; de Lima, J. C.; Grandi, T. A.; Machado, K. D.; Drago, V.; Pizani, P. S.

    2004-07-01

    A hexagonal CoSe alloy with NiAs-type structure was obtained by mechanical alloying starting from a mixture of pure crystalline powders with nominal composition Co 75Se 25. X-ray diffraction (XRD), differential scanning calorimetry (DSC), Mössbauer spectroscopy (MS) and Raman scattering (RS) techniques were used to follow the structural, thermal, magnetic and optical properties of the binary mixture as a function of milling time. XRD results show the formation of a nanometric hexagonal CoSe phase between 3 and 70 h of milling coexisting with non-reacted Co phases, also in nanometric scale. DSC and RS results showed some changes in the thermal and optical properties of the crystalline phases when the milling time increases. The Raman active modes of the CoSe and Co oxide phases were observed. MS results showed practically no iron in the samples milled up to 15 h, while for extended milling times (70 h), they showed the presence of some α-Fe and the formation of other iron alloys due to the contamination by the milling media.

  1. ZnSe-ZnMnSe and CdTe-CdMnTe superlattices

    NASA Astrophysics Data System (ADS)

    Gunshor, R. L.; Kolodziejski, L. A.; Otsuka, N.; Datta, S.

    1986-08-01

    We report the growth and characterization of superiattices of a new wide-gap, zincblende material system, Zn 1 - xMn xSe. ZnSe exhibiting dominant free excitonic emission in photoluminescence (PL) is the well material, while wider-band-gap Zn 1 - xMn xSe (0.23 < x < 0.66) forms the barrier material. PL measurements show greatly enhanced quantum efficiency compared to films of the ZnSe well material, while transmission electron microscopy shows extremely abrupt interfaces by the presence of seventh-order satellite spots. Previously reported superiattices in the CdTe-CdMnTe material system were grown with the (111) orientation, and exhibit unique excitonic properties believed related to the (111) interfaces. Using various techniques to select (111) or (100) heteroepitaxy of CdTe on (100) GaAs, we report the first (100) superlattices of this material, and compare the optical properties to the previous (111) structures.

  2. Disordered La3Cu4.88Se7.

    PubMed

    Gulay, L D; Daszkiewicz, M; Strok, O M; Pietraszko, A

    2011-03-01

    The crystal structure of copper(I) lanthanum selenide, La(3)Cu(4.88)Se(7), obtained from the La(2)Se(3)-Cu(2)Se quasi-binary system, has been investigated using X-ray single-crystal diffraction. The positions of the La and Se atoms are ordered and lie on mirror planes, whereas all positions for the Cu atoms are partially occupied. The crystal is built from edge-sharing [LaSe(6)] and [LaSe(7)] polyhedra. The five positions for the Cu atoms determine an ionic diffusion pathway in the structure. PMID:21368401

  3. 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.

  4. Growth of CuInSe2 and In2Se3/CuInSe2 nano-heterostructures through solid state reactions.

    PubMed

    Hsin, Cheng-Lun; Lee, Wei-Fan; Huang, Chi-Te; Huang, Chun-Wei; Wu, Wen-Wei; Chen, Lih-Juann

    2011-10-12

    In(2)Se(3) is an essential phase change material and CuInSe(2) is the fundamental basis of the copper-indium-gallium-diselenide (CIGS) solar energy material. In this paper, we demonstrate the feasibility to transform the phase change material to the solar energy material via the solid state reaction. The In(2)Se(3) nanobelts (NBs) were synthesized via the vapor-liquid-solid mechanism. The chemical composition and the optical properties were investigated by energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and reflectance and photoluminescence spectra. In the in situ observation of the solid state reaction with Cu to form the CuInSe(2) NBs with ultrahigh vacuum transmission electron microscopy, we observed the In(2)Se(3)/CuInSe(2) transformation at atomic scale in real time. The progression of the atomic layer at the interface provided the pertinent information on the kinetic mechanism. In(2)Se(3)/CuInSe(2) nano-heterostructures were also obtained in the present investigation. The approach to the CIGS nanosolar cell was also proposed. This study shall be beneficial in the development of high-performance nanowire solar cells and nanodevices with In(2)Se(3)/CuInSe(2) nano-heterostructures. PMID:21859092

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    We propose here to investigate the non-equilibrium viscosity of Ge-Se glasses under and after light irradiation. Ge10Se90 and Ge20Se80 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 Ge10Se90 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 Ge20Se80 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.

  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. 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.

  8. Synthesis and Crystallographic Analysis of 5-Se-Thymidine DNAs

    SciTech Connect

    Hassan, A.; Sheng, J; Jiang, J; Zhanbg, W; Huang, Z

    2009-01-01

    We investigated the possibility of the interaction of 5-CH3 of thymidine and its 5?-phosphate backbone (C-H O-PO3 interaction) in DNA via the insertion of the atomic probe (a selenium atom) into the exo-5-position of thymidine (5-Se-T). 5-Se-T was synthesized for the first time, via Mn(OAc)3 assisted electrophilic addition of CH3SeSeCH3 to 3?,5?-di-O-benzoyl-2?-deoxyuridine. The 5-Se-T phosphoramidite was subsequently synthesized and incorporated into DNA in over 99% coupling yield. Biophysical and structural investigations of the 5-Se-T DNAs revealed that the Se-modified and nonmodified DNAs are virtually identical. In addition, the crystallographic analysis of a 5-Se-T DNA strongly suggests a hydrogen-bond formation between the 5-CH3 and 5?-phosphate groups (CH3 PO4- interaction).

  9. 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

  10. Preliminary results on CuInSe2/ZnSe solar cells using reactively sputter-deposited ZnSe

    NASA Technical Reports Server (NTRS)

    Nouhi, A.; Stirn, R. J.

    1987-01-01

    In this paper preliminary results on CuInSe2/ZnSe thin film heterojunction photovoltaic devices are presented. High-conductivity ZnSe films were reactively sutter-deposited onto CuInSe2 films and overcoated with ZnO to reduce the sheet resistance. The highest short-circuit current density, as determined from a spectral response weighted for air mass 1.5 global insolation, was 37.4 mA/sq cm. The highest pen-circuit voltage observed was 430 mV.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  12. Phototransistor based on single In2Se3 nanosheets

    NASA Astrophysics Data System (ADS)

    Li, Qin-Liang; Liu, Chang-Hai; Nie, Yu-Ting; Chen, Wen-Hua; Gao, Xu; Sun, Xu-Hui; Wang, Sui-Dong

    2014-11-01

    Micrometer-sized single-crystalline In2Se3 nanosheets are synthesized by epitaxial growth from In2Se3 nanowires. The In2Se3 nanosheets possess anisotropic structural configuration with intralayer covalent bonding and interlayer van der Waals bonding. Phototransistors based on the In2Se3 nanosheets are realized, and the devices show high photoresponsivity and high photo On/Off ratio up to two orders. The photo-gating effect can be modulated by the gate bias, indicating potential utility of the In2Se3 nanosheets in a variety of optoelectronic applications.Micrometer-sized single-crystalline In2Se3 nanosheets are synthesized by epitaxial growth from In2Se3 nanowires. The In2Se3 nanosheets possess anisotropic structural configuration with intralayer covalent bonding and interlayer van der Waals bonding. Phototransistors based on the In2Se3 nanosheets are realized, and the devices show high photoresponsivity and high photo On/Off ratio up to two orders. The photo-gating effect can be modulated by the gate bias, indicating potential utility of the In2Se3 nanosheets in a variety of optoelectronic applications. Electronic supplementary information (ESI) available: SEM images of typical In2Se3 nanosheets, TEM-EDX spectrum of single In2Se3 nanosheets, STEM image and elemental mapping of an In2Se3 nanosheet, Scherrer sizes of In2Se3 nanosheets derived from the XRD pattern, statistics of In2Se3 nanosheet thickness, and photoresponse of an In2Se3 nanosheet phototransistor. See DOI: 10.1039/c4nr04404e

  13. Medium Energy Ion Scattering investigation of In diffusion in In2Se3/Bi2Se3

    NASA Astrophysics Data System (ADS)

    Lee, H. D.; Xu, C.; Shubeita, S.; Brahlek, M.; Koirala, N.; Oh, S.; Gustafsson, T.

    2013-03-01

    In2Se3, a band insulator, and Bi2Se3, a three-dimensional topological insulator, have inherently good chemical and structural compatibility. This suggests possible promising applications of In2Se3/Bi2Se3 devices as tunnel barriers and gate dielectrics. Recently, it has been shown that the similar (Bi1-xInx)2 Se3 thin system undergoes a transition from topological insulator to band insulator as a function of In concentration. It is therefore important to understand the extent of In diffusion in In2Se3/Bi2Se3 and its consequences for the transport properties. We have grown In2Se3/Bi2Se3 thin films on sapphire by Molecular Beam Epitaxy at three different temperatures. Medium Energy Ion Scattering measurements of those films showed that the higher growth temperature resulted in more In diffusion while our transport measurements showed that the Bi2Se3 mobility increases as the growth temperature decreases. We found that the trend of the mobility change of In2Se3/Bi2Se3 depending on the diffusion of In is similar with the trend of the mobility of (Bi1-xInx)2 Se3 as a function of In concentration.

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

    DOEpatents

    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.

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

    SciTech Connect

    Dewberry, R.A.

    1991-08-11

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

  16. 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.

  17. 21 CFR 118.4 - Salmonella Enteritidis (SE) prevention measures.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    .... (c) Rodents, flies, and other pest control. As part of this program, you must: (1) Monitor for... conditions. “SE monitored” means the pullets are raised under SE control conditions that prevent SE... National Poultry Improvement Plan's standards for “U.S. S. Enteritidis Clean” status (9 CFR 145.23(d))...

  18. 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.

  19. Nanocomposite pyrite-greigite reactivity toward Se(IV)/Se(VI).

    PubMed

    Charlet, Laurent; Kang, Mingliang; Bardelli, Fabrizio; Kirsch, Regina; Géhin, Antoine; Grenèche, Jean-Marc; Chen, Fanrong

    2012-05-01

    A nanopyrite/greigite composite was synthesized by reacting FeCl(3) and NaHS in a ratio of 1:2 (Wei et al. 1996). Following this procedure, the obtained solid phases consisted of 30-50 nm sized particles containing 28% of greigite (Fe(2+)Fe(3+)(2)S(4)) and 72% pyrite (FeS(2)). Batch reactor experiments were performed with selenite or selenate by equilibrating suspensions containing the nanosized pyrite-greigite solid phase at different pH-values and with or without the addition of extra Fe(2+). XANES-EXAFS spectroscopic techniques revealed, for the first time, the formation of ferroselite (FeSe(2)) as the predominant reaction product, along with elemental Se. In the present experimental conditions, at pH 6 and in equilibrium with Se(0), the solution is oversaturated with respect to ferrosilite. Furthermore, thermodynamic computations show that reaction kinetics likely played a significant role in our experimental system. PMID:22424403

  20. Interface oxygen and heat sensitivity of Cu(In,Ga)Se2 and CuGaSe2 solar cells

    NASA Astrophysics Data System (ADS)

    Ishizuka, Shogo; Fons, Paul J.; Yamada, Akimasa; Kamikawa-Shimizu, Yukiko; Shibata, Hajime

    2016-05-01

    Combined oxygen and heat exposure processes after p-CuGaSe2/n-CdS junction formation degrade CuGaSe2 solar cell efficiency, whereas such annealing processes can improve high In content Cu(In,Ga)Se2 device performance. This result is chiefly attributable to different interface structures consisting of oxygen-sensitive CuGaSe2 or relatively oxygen-insensitive Cu(In,Ga)Se2. To reduce CuGaSe2 interfacial recombination, reduction of the process temperature of the front contact layer deposition process is found to be the key. In this work, fill factor values exceeding 0.7 are reproducibly obtained from CuGaSe2 solar cells, though such high fill factor values have been very challenging to demonstrate to date using CuGaSe2 photoabsorber layers.

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

    SciTech Connect

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

    2014-04-24

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

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

    DOE PAGESBeta

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

    2016-04-01

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

  3. 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

  4. Type I/type II band alignment transition in strained PbSe /PbEuSeTe multiquantum wells

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

    Investigation of the optical transitions in tensily strained PbSe /PbEuSeTe multiquantum wells by differential transmission spectroscopy reveals a type I/type II band alignment transition due to strain-induced lowering of the band edge energies of the quantum wells. From the measured shifts of the optical transitions the optical deformation potentials of PbSe are obtained. This is crucial for realistic modeling of the electronic properties of strained PbSe heterostructures.

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

    PubMed

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

    2016-04-01

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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  11. Preparation and Characteristics of MoSe2 Interlayer in Bifacial Cu(In,Ga)Se2 Solar Cells

    NASA Astrophysics Data System (ADS)

    Pang, J. B.; Cai, Y. A.; He, Q.; Wang, H.; Jiang, W. L.; He, J. J.; Yu, T.; Liu, W.; Zhang, Y.; Sun, Y.

    MoSe2 thin films were formed simply by the selenization of Mo on bare soda lime glass substrate and glass coated with ZnO:Ga. Preliminarily, the structural property of MoSe2 was studied on bare soda lime glass with X-ray diffraction and Raman spectra. Furthermore, the electrical property of MoSe2 was discussed as the interlayer between the Cu(In,Ga)Se2 /ZnO:Ga double layers. Finally, bifacial solar cells with MoSe2 interlayer were illustrated with current-voltage curve and quantum efficiency.

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

    PubMed

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

    2015-01-01

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

  13. 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.

  14. Structure of Se-rich As-Se glasses by high-resolution x-ray photoelectron spectroscopy

    SciTech Connect

    Golovchak, R.; Kovalskiy, A.; Miller, A. C.; Jain, H.; Shpotyuk, O.

    2007-09-15

    To establish the validity of various proposed structural models, we have investigated the structure of the binary As{sub x}Se{sub 100-x} chalcogenide glass family (x{<=}40) by high-resolution x-ray photoelectron spectroscopy. From the composition dependence of the valence band, the contributions to the density of states from the 4p lone pair electrons of Se and the 4p bonding states and 4s electrons of Se and As are identified in the top part of the band. The analysis of Se 3d and As 3d core-level spectra supports the so-called chain crossing model for the atomic structure of Se-rich As{sub x}Se{sub 100-x} bulk glasses. The results also indicate small deviations ({approx}3-8%) from this model, especially for glass compositions with short Se chains (25Se{sub 60} and of Se-Se-Se fragments in a glass with composition x=30 is established.

  15. Transport study on tunnel junction structures based on In2Se3/Bi2Se3 heterostructures

    NASA Astrophysics Data System (ADS)

    Koirala, Nikesh; Brahlek, Matthew; Bansal, Namrata; Oh, Seongshik

    2013-03-01

    Bi2Se3 is a 3D Topological Insulator (TI) candidate material with structural similarity to In2Se3, which is a band insulator with large band gap. This compatibility leads to possibility of epitaxial growth of In2Se3/Bi2Se3 heterostructure, which has various application potential. For example, by depositing Superconducting or Ferromagnetic materials on top of this heterostructure, tunnel junctions can be fabricated. We have studied device structures made up of such tunnel junctions. In2Se3 was grown on top of Bi2Se3 using molecular beam epitaxy on Al2O3(0001) substrates. Superconductor (Nb) or Ferromagnet (CoFe, Gd) was then sputtered on top of In2Se3 and photolithography was used to make the tunnel junctions. Transport measurement data obtained from such structures will be presented.

  16. [Cs6 Cl][Fe24 Se26 ]: A Host-Guest Compound with Unique Fe-Se Topology.

    PubMed

    Valldor, Martin; Böhme, Bodo; Prots, Yurii; Borrmann, Horst; Adler, Peter; Schnelle, Walter; Watier, Yves; Kuo, Chang Yang; Pi, Tun-Wen; Hu, Zhiwei; Felser, Claudia; Tjeng, Liu Hao

    2016-03-18

    The novel host-guest compound [Cs6 Cl][Fe24 Se26 ] (I4/mmm; a=11.0991(9), c=22.143(2) Å) was obtained by reacting Cs2 Se, CsCl, Fe, and Se in closed ampoules. This is the first member of a family of compounds with unique Fe-Se topology, which consists of edge-sharing, extended fused cubane [Fe8 Se6 Se8/3 ] blocks that host a guest complex ion, [Cs6 Cl](5+) . Thus Fe is tetrahedrally coordinated and divalent with strong exchange couplings, which results in an ordered antiferromagnetic state below TN =221 K. At low temperatures, a distribution of hyperfine fields in the Mössbauer spectra suggests a structural distortion or a complex spin structure. With its strong Fe-Se covalency, the compound is close to electronic itinerancy and is, therefore, prone to exhibit tunable properties. PMID:26879367

  17. 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.

  18. High resolution photoemission study of CdSe and CdSe/ZnS core-shell nanocrystals

    NASA Astrophysics Data System (ADS)

    Borchert, H.; Talapin, D. V.; McGinley, C.; Adam, S.; Lobo, A.; de Castro, A. R. B.; Möller, T.; Weller, H.

    2003-07-01

    Colloidally prepared CdSe and CdSe/ZnS core-shell nanocrystals passivated with trioctylphosphine/trioctylphosphine oxide and hexadecylamine have been studied by photoelectron spectroscopy with tuneable synchrotron radiation. High-resolution spectra of the Se 3d level in CdSe nanocrystals indicate the bonding of organic ligands not only to surface Cd but also to surface Se atoms. The investigation of the CdSe/ZnS core-shell nanocrystals allows us to determine the average thickness of the ZnS shell and to study the interface between the two semiconductor nanomaterials. The photoemission spectra indicate a rather well ordered interface. No evidence for interfacial bonds other than Cd-S and Se-Zn is found.

  19. 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.

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

    DOE PAGESBeta

    Klobes, B.; Hu, Michael; Beekman, Matt; Johnson, David C; Hermann, Raphael P

    2016-01-01

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

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

    DOE PAGESBeta

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

    2015-11-30

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

  3. 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.

  4. Magnetooptical properties of a single CdMnSe/CdMgSe quantum well

    SciTech Connect

    Reshina, I. I. Ivanov, S. V.

    2008-11-15

    The spectra of photoluminescence and reflectance in magnetic fields up to 7 T are studied for a 3.8 nm semimagnetic CdMnSe quantum well confined by two CdMgSe barriers. A noticeable magnetic shift in the {sigma}{sup +}-polarized emission line of the heavy exciton to low energies and a decrease in the halfwidth of the line by more than one-half are detected with increasing magnetic field. It is established that a localized magnetic polaron is formed, with the polaron energy of 19.8 meV determined from the change in the degree of circular polarization in magnetic field. A {sigma}{sup -}-polarized emission line is observed in magnetic fields ranging from 0.4 to 2 T. This line can be interpreted as being produced by the complex of two electrons, with oppositely directed spins, and a heavy hole, i.e., by the trion X{sup -} or the exciton localized at a donor, D{sup 0}X. The binding energy of such complex is 10 meV.

  5. Optical and Electronic Properties of Nonconcentric PbSe/CdSe Colloidal Quantum Dots.

    PubMed

    Zaiats, Gary; Shapiro, Arthur; Yanover, Diana; Kauffmann, Yaron; Sashchiuk, Aldona; Lifshitz, Efrat

    2015-07-01

    Lead chalcogenide colloidal quantum dots are attractive candidates for applications operating in the near infrared spectral range. However, their function is forestalled by limited stability under ambient conditions. Prolonged temperature-activated cation-exchange of Cd(2+) for Pb(2+) forms PbSe/CdSe core/shell heterostructures, unveiling a promising surface passivation route and a method to modify the dots' electronic properties. Here, we follow early stages of an-exchange process, using spectroscopic and structural characterization tools, as well as numerical calculations. We illustrate that preliminary-exchange stages involve the formation of nonconcentric heterostructures, presumably due to a facet selective reaction, showing a pronounced change in the optical properties upon the increase of the degree of nonconcentricity or/and plausible creation of core/shell interfacial alloying. However, progressive-exchange stages lead to rearrangement of the shell segment into uniform coverage, providing tolerance to oxygen exposure with a spectral steadiness already on the formation of a monolayer shell. PMID:26266716

  6. Highly conducting ZnSe films by reactive magnetron sputtering

    NASA Technical Reports Server (NTRS)

    Nouhi, A.; Stirn, R. J.

    1986-01-01

    This paper presents the results of an effort to deposit high-conductivity ZnSe on glass and conducting SnO2-coated glass substrates by reactive magnetron sputter deposition, using pure metal sputter targets of Zn and dopants such as In, Ga, and Al. Clear yellow ZnSe films were successfully obtained. By using substrate temperatures as low as 150 C, cosputtered dopants, and sputter parameters and H2Se injection rates which maximize the Zn-to-Se ratio in the films, ZnSe bulk resistivities have been lowered by up to seven orders of magnitude, reaching values as low as 20 ohm cm. The most effective dopant to data has been In, cosputtered with Zn in amounts leading to In atomic concentrations as high as 1.4 percent. Atomic-absorption measurements show an average 49.9/48.9 ratio of Zn to Se.

  7. 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.

  8. 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. PMID:26522247

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

    NASA Astrophysics Data System (ADS)

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

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

  10. Transmission Spectra and Generation of Terahertz Pulses in SiO2-GaSe, TiO2-GaSe, Ga2O3-GaSe, and GaSe:S Structures

    NASA Astrophysics Data System (ADS)

    Bereznaya, S. A.; Zarubin, A. N.; Korotchenko, Z. V.; Prudaev, I. A.; Red'kin, R. A.; Sarkisov, S. Yu.; Tolbanov, O. P.

    2015-12-01

    Thin amorphous SiO2, TiO2, and Ga2O3 films were deposited on the surface of GaSe crystals by thermal and magnetron sputtering. It was found that under different technological conditions, the SiO2 and TiO2 layers on the surface of GaSe crack, while the Ga2O3 compound forms perfect films. A comparison of the transmission spectra and generation efficiency of terahertz pulses was made for the SiO2-GaSe, TiO2-GaSe, and Ga2O3-GaSe structures and for the GaSe:S 0.9 wt % and GaSe:S 7 wt % crystals. It was found that an increase in the concentration of sulfur in the GaSe:S crystals results in a decrease in the efficiency of generation of terahertz radiation by optical rectification of femtosecond laser pulses. Among the films deposited on the surface of GaSe, the SiO2 film has the least impact on the efficiency of generation.

  11. High performance single In2Se3 nanowire photodetector

    NASA Astrophysics Data System (ADS)

    Li, Q. L.; Li, Y.; Gao, J.; Wang, S. D.; Sun, X. H.

    2011-12-01

    The single indium selenide (In2Se3) nanowire photodetectors were fabricated, and the performance characteristics of the nanowire devices were systematically investigated. The single In2Se3 nanowire photodetectors show high and stable photoresponse in wide light wavelength (254-800 nm) and temperature range (7-300 K). The spectra response indicates that the absorption coefficient of the In2Se3 nanowires at certain wavelength dominates the performance of the devices. The good linearity of the photocurrents with the incident irradiation over a wide wavelength range has been obtained, demonstrating that the In2Se3 nanowire photodetectors work in a typical light-dependent resistor mode.

  12. Strain compensated CdSe/ZnSe/ZnCdMgSe quantum wells as building blocks for near to mid-IR intersubband devices

    NASA Astrophysics Data System (ADS)

    De Jesus, Joel; Chen, Guopeng; Hernandez-Mainet, Luis C.; Shen, Aidong; Tamargo, Maria C.

    2015-09-01

    In order to increase the conduction band offset of the ZnCdMgSe-based material system we studied the incorporation of strained CdSe layers to obtain deeper quantum wells for shorter wavelength intersubband transitions than those obtained in lattice-matched structures. Five CdSe/ZnSe/ZnCdMgSe multi-quantum wells (QW) samples grown by molecular beam epitaxy are studied in detail by transmission electron microscopy (TEM), X-ray diffraction (XRD), cw-photoluminescence (PL), and Fourier Transform Infrared (FTIR) absorption experiments. TEM and XRD results confirmed good structural quality of the samples. All the multi-QW PL energies were below the ZnCdSe lattice-matched to InP alloy bandgap (2.1 eV), which serves as first evidence of having achieved deeper quantum wells. FTIR absorptions from 3.83 to 2.56 μm were measured, shorter than those achieved by the lattice matched system. Simulations based on these results predict that absorptions as low as 2.18 μm can be obtained with these materials.

  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. 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.

  15. 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. PMID:26808586

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

  17. 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

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

    PubMed

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

    2013-01-01

    Generally, in scanning electron microscopy (SEM) imaging, it is desirable that a high-resolution image be composed mainly of those secondary electrons (SEs) generated by the primary electron beam, denoted SE(I) . However, in conventional SEM imaging, other, often unwanted, signal components consisting of backscattered electrons (BSEs), and their associated SEs, denoted SE(II) , are present; these signal components contribute a random background signal that degrades contrast, and therefore signal-to-noise ratio and resolution. Ideally, the highest resolution SEM image would consist only of the SE(I) component. In SEMs that use conventional pinhole lenses and their associated Everhart-Thornley detectors, the image is composed of several components, including SE(I) , SE(II) , and some BSE, depending on the geometry of the detector. Modern snorkel lens systems eliminate the BSEs, but not the SE(II) s. We present a microfabricated diaphragm for minimizing the unwanted SE(II) signal components. We present evidence of improved imaging using a microlithographically generated pattern of Au, about 500 nm thick, that blocks most of the undesired signal components, leaving an image composed mostly of SE(I) s. We refer to this structure as a "spatial backscatter diaphragm." PMID:22589040

  19. 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)

  20. 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.

  1. 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}.

  2. 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.

  3. 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$^{-3}$.

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

    PubMed

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

    2017-02-01

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

  5. 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.

  6. 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. PMID:23557168

  7. Aerosol phase generation of In-Se nanoparticles.

    PubMed

    Geretovszky, Zs; Deppert, K; Karlsson, L S; Karlsson, M N A; Malm, l J O; Mühlberg, M

    2006-03-01

    Results on the generation and heat treatment of In-Se nanoparticles, made by heterogeneous condensation of selenium on indium nanoparticles synthesised via the evaporation/condensation route are reported. In-situ aerosol measurements are complemented with ex-situ analysis, to provide structural, morphological, and compositional information on the In-Se nanoparticles. Our results indicate that prior to heat treatment In-Se nanoparticles have a shape in the aerosol phase, similar to an asymmetric dumbbell. The bigger particle of the dumbbell structure is made up of amorphous Se, while the overall composition of the polycrystalline smaller particle is around InSe. The smaller particle has an intrinsic structure, and consists of different InSe-compounds, with a decreasing In content towards the shell. The shape of the In-Se nanoparticles is different in the aerosol phase and on the surface of the samples. The observed variety of particle sizes and shapes on the sample surface is shown to be partly due to the agglomeration of the aerosol phase binaries (i.e., dumbbells) via coalescence on the surface of the sample and wetting of the sample surface by the Se nanoparticles. These processes make the bigger particle of the dumbbell structure appear almost perfectly hemispherical on the sample surfaces. During heat treatment at lower temperatures mainly the evaporative removal of the big Se particle of the dumbbell structure will take place. Annealing of the smaller particles starts to dominate at temperatures above 240 degrees C and makes the composition of the small particles closer to that of the thermodynamically most favoured In2Se3. PMID:16573110

  8. Crystal cluster growth and physical properties of the EuSbSe3 and EuBiSe3 phases.

    PubMed

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

    2015-02-01

    Syntheses of europium metal, selenium powder, and the Sb(2)Se(3)/Bi(2)Se(3) binaries were observed to produce crystal clusters of the EuSbSe(3) and EuBiSe(3) phases. These phases crystallize with the P2(1)2(1)2(1) space group and can be easily identified based on their growth habits, forming large clusters of needles. Previous literature suggested that their structure is charge-balanced with all europium atoms in the divalent state and one-quarter of the selenium atoms forming trimers. Physical property measurements on a pure sample of EuSbSe(3) revealed typical Arrhenius-type electrical resistivity, being approximately 3 orders of magnitude too large for thermoelectric applications. Electronic structure calculations indicated that both EuSbSe(3) and EuBiSe(3) are narrow-band-gap semiconductors, in good agreement with the electrical resistivity data. The valence and conduction band states near the Fermi level are dominated by the Sb/Bi and Se p states, as expected given their small difference in electronegativity. PMID:25255124

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  10. 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. PMID:12402090

  11. 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.

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

    PubMed

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

    2015-07-15

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

  13. Ultra-thin crystalline films of CdSe and CuSe formed at the organic-aqueous interface.

    PubMed

    Kalyanikutty, K P; Gautam, Ujjal K; Rao, C N R

    2007-06-01

    Two-dimensional nanostructures in the form of ultra-thin crystalline films of CdSe and CuSe have been prepared at the organic-aqueous interface by reacting toluene solutions of metal cupferronates with an aqueous solution of N,N-dimethyl selenourea. The films have been examined using electron microscopy and optical spectroscopy. At lower concentrations of the reacting species, the CdSe films formed at the toluene-water interface at approximately 30 degrees C consisted mostly of nanocrystals. With increase in concentration as well as temperature, the interface reaction yielded thicker films which are mostly single-crystalline. We have studied the time-dependent growth of the CdSe film at the interface using UV-visible absorption spectroscopy. Ultra-thin films of CuSe formed at the toluene-water interface are generally single-crystalline. PMID:17654965

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

    PubMed

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

    2016-08-15

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

  15. Multilevel Ge-Se Film Based Resist Systems

    NASA Astrophysics Data System (ADS)

    Tai, K. L.; Vadimsky, R. G.; Ong, E.

    1982-06-01

    Multilevel resist systems based on Ge-Se films make possible the use of optical projection printers for printing 0.5-1.0μm features. The four multilevel resist systems considered employ either a photosensitive or a photopassive polymer layer for planarization. In bilevel schemes the surface of the Ge-Se film is reacted in a Ag(CN)i- containing solution to form a Ag2Se imaging layer. No reacted Ge-Se is used as a sacrificial layer in trilevel schemes. Ge-Se films are resistant to attack by oxygen plasma and therefore make good masks for pattern transfer by dry (reactive ion) etching, to a thick underlying photopassive polymer layer. Because of their high absorbance (a 105cm-1) in the ultraviolet and violet, Ge-Se patterns can also be used as exposure masks for transferring images to a thick underlying photosensitive polymer layer. The latter is "flood" exposed through the Ge-Se mask and wet developed. Both dry and wet processes provide steep wall-profile patterns in the polymer layer. The dry process provides superior feature size control while the wet process offers reduced processing cost. The exceptional lithographic performance exhibited by Ge-Se resist systems is attributed to a unique edge-sharpening effect; diffraction is compensated for by lateral silver diffusion in the Ag2Se layer. Patterns having 0.6μm lines and spaces are obtained over lcmXlcm fields with a defocus tolerance of 2.5μm using a standard Zeiss 10:1 reduction lens (N.A.=0.28, λ=436nm). Results indicate that optical lithography can practically print features in the size regime previously reserved for a-beam or x-ray based lithographic technologies.

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

    NASA Astrophysics Data System (ADS)

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

    2003-01-01

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

  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. 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.

  19. Photoconductivity in ZnSe under high electric fields

    SciTech Connect

    Cho, P.S.; Ho, P.T.; Goldhar, J.; Lee, C.H. . Dept. of Electrical Engineering)

    1994-06-01

    High voltage photoconductive switches utilizing polycrystalline ZnSe were investigated. Experiments have been performed on polycrystalline ZnSe switches in a longitudinal geometry. Electrodes of perforated metal films, a transparent liquid electrolyte, plasma, and ultraviolet-light-generated carriers were used. High-bias fields of up to 100 kV/cm and current densities over 100 kA/cm[sup 2] can be applied to the polycrystalline ZnSe switches. Nonlinear effects were observed at high fields with near band edge illumination. Applications of these effects are discussed.

  20. Hg and Se Speciation in Liver Tissue of Marine Birds

    NASA Astrophysics Data System (ADS)

    Karanfil, Cahit; Bischoff, Karyn; Bunker, Grant

    2013-04-01

    X-ray fluorescence microprobe maps of Hg and Se distribution were made on liver tissue slices from marine birds (Cormorants) from Florida's Everglades. The birds bio-concentrate these toxic pollutants that are ingested from their diet of fish. The fluorescence maps show strong localization of Mercury and Selenium into "hot spots" less than 100 microns in size. XAFS measurements were made on hot spots to demonstrate that the Hg and Se are indeed are chemically bound, supporting the idea that moderate levels of Se may have a protective effect against Hg through its complexation.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    PubMed

    Yadav, Sushma; Chowdhury, Apurba; Sapra, Sameer

    2016-03-01

    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. PMID:26511899

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

    NASA Astrophysics Data System (ADS)

    Sharma, J.; Kumar, S.

    2010-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    PubMed

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

    2016-09-01

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

  6. 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.

  7. 10. Photocopy of c. 1906 photograph looking SE at row ...

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

    10. Photocopy of c. 1906 photograph looking SE at row of double Creole quarters along Main Street. - Laurel Valley Sugar Plantation, Double Creole Quarters, 2 Miles South of Thibodaux on State Route 308, Thibodaux, Lafourche Parish, LA

  8. 9. Photocopy of c. 1906 photograph looking SE at row ...

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

    9. Photocopy of c. 1906 photograph looking SE at row of double Creole workers' houses along Main Street. - Laurel Valley Sugar Plantation, Double Creole Quarters, 2 Miles South of Thibodaux on State Route 308, Thibodaux, Lafourche Parish, LA

  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. 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

  11. BLDG 8, VIEW OF NE SIDE LOOKING THRU SE DRIVE ...

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

    BLDG 8, VIEW OF NE SIDE LOOKING THRU SE DRIVE THROUGH. - Naval Magazine Lualualei, West Loch Branch, Ammo Rework Building, North of Fourth Street near intersection with B Avenue, Pearl City, Honolulu County, HI

  12. 2. East wall of Lock 1 looking SE from top ...

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

    2. East wall of Lock 1 looking SE from top of lock showing tooled stonework in foreground where gate hardware fitted. 1971. - Potowmack Company: Great Falls Canal, Lock No. 1, Great Falls, Fairfax County, VA

  13. 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

  14. 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

  15. Optical Properties of CdSe Nanoparticle Assemblies

    SciTech Connect

    Huser, T; Gerion, D; Zaitseva, N; Krol, D M; Leon, F R

    2003-11-24

    We report on three-dimensional fluorescence imaging of micron-size faceted crystals precipitated from solutions of CdSe nanocrystals. Such crystals have previously been suggested to be superlattices of CdSe quantum dots [1,2]. Possible applications for these materials include their use in optical and optoelectronic devices. The micron-size crystals were grown by slow evaporation from toluene solutions of CdSe nanocrystals in the range of 3-6 nm, produced by traditional wet-chemistry techniques. By using a confocal microscope with laser illumination, three-dimensional raster-scanning and synchronized hyper-spectral detection, we have generated spatial profiles of the fluorescence emission intensity and spectrum. The fluorescence data of the micro-crystals were compared with spectra of individual nanocrystals obtained from the same solution. The results do not support the assertion that these microcrystals consist of CdSe superlattices.

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

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

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

  17. 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

  18. 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

  19. 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

  20. 1. Building No. 9980. East side and SE wing on ...

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

    1. Building No. 9980. East side and SE wing on left as viewed from roof of Corridor A. - Madigan Hospital, Patients' & Medical Detachments, Bounded by Wilson & McKinley Avenues & Garfield & Lincoln Streets, Tacoma, Pierce County, WA

  1. 9. First floor shop office, SE corner of E wing, ...

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

    9. First floor shop office, SE corner of E wing, showing entry vestibule at right; looking SSE. (Ryan and Harms) - Rock Island Arsenal, Building No. 66, Rodman Avenue between Third & Fourth Streets, Rock Island, Rock Island County, IL

  2. View downstream of timber guide wall downstream from SE corner ...

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

    View downstream of timber guide wall downstream from SE corner of lock, view towards east - St. Lucie Canal, St. Lucie Lock No. 1, St. Lucie, Cross State Canal, Okeechobee Intracoastal Waterway, Stuart, Martin County, FL

  3. 23. Detail view of fireplace, secondfloor SE bedroom; looking N. ...

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

    23. Detail view of fireplace, second-floor SE bedroom; looking N. (Ceronie) - Rock Island Arsenal, Building No. 1, Gillespie Avenue between Terrace Drive & Hedge Lane, Rock Island, Rock Island County, IL

  4. 7. Window and door in SE corner of office in ...

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

    7. Window and door in SE corner of office in Tender Frame Shop. - Central of Georgia Railway, Savannah Repair Shops & Terminal Facilities, Tender Frame Shop, Bounded by West Broad, Jones, West Boundary & Hull Streets, Savannah, Chatham County, GA

  5. Origin of the solid solution in the LiInSe2-In2Se3 system

    NASA Astrophysics Data System (ADS)

    Vasilyeva, I. G.; Pochtar, A. A.; Isaenko, L. I.

    2014-12-01

    Techniques of bulk and local analyses were used to characterize the melt-grown single crystals of LiInSe2, where yellow matrix coexists together with extended red areas distributed irregularly. Bulk chemical analysis showed that the average stoichiometry of yellow matrix is close to ideal 1:1:2, but red areas are enriched with In2Se3. An excess In2Se3 is incorporated coherently into the crystal lattice of LiInSe2, forming the substitution solid solution with the general formula (Li1-3xInx⎕2)InSe2 and changing the color from yellow to red. The test crystals with the 50-55% content of In2Se3 were found by the X-ray analysis to be single phase. The differential dissolution technique, measuring the spatial variation of the composition with high resolution, demonstrated that the single phase crystals in the LiInSe2-In2Se3 system might be grown only in a very narrow range close to stoichiometric. Being supersaturated, the heterovalent solid solution phases decompose in the course of cooling, and the concentration micro-heterogeneity occurs in the matrix as the coherent (or incoherent) inclusions of two different types, practically pure selenides of lithium and indium. The origin and scale of the micro-heterogeneity determining the physical properties of LiInSe2 are discussed as a starting point for the development of physicochemical foundations for growing high quality optical crystals.

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

    SciTech Connect

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

    2011-02-15

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

  7. Methanococcus vannielii selenium-binding protein (SeBP): Chemical reactivity of recombinant SeBP produced in Escherichia coli

    PubMed Central

    Patteson, Kemberly G.; Trivedi, Neel; Stadtman, Thressa C.

    2005-01-01

    A selenium-binding protein (SeBP) from Methanococcus vannielii was recently identified, and its gene was isolated and overexpressed in Escherichia coli [Self, W. T., Pierce, R. & Stadtman, T. C. (2004) IUBMB Life 56, 501–507]. SeBP and recombinant SeBP (rSeBP) migrated as ≈42-kDa species on native gels and as ≈33-kDa species on SDS gels. rSeBP consists of identical 8.8-kDa subunits, each containing a single cysteine residue. rSeBP isolated in the absence of reducing agents contained oxidized cysteine (89%) and very little bound selenium (0.05 eq or less per subunit). Complete reduction of the oxidized cysteine residues in rSeBP with Tris(2-carboxyethyl)phosphine required addition of a denaturant, such as 1 M guanidine-hydrochloride. With selenite as the selenium source and the isolated reduced protein as sole reductant, binding of one selenium per tetramer under anaerobic conditions required four cysteine thiol groups, one on each subunit. In the corresponding reaction, with reduced glutathione (GSH), equimolar amounts of selenodiglutathione (GSSeSG) and glutathione disulfide are formed from selenite and 4 GSH. At GSH-to-selenite ratios >4:1, conversion of GSSeSG to a perselenide derivative, GSSe–, occurs. However, with the reduced rSeBP as sole electron donor in the reaction with selenite, further conversion of the R-SSeS-R product apparently did not occur. Prior alkylation of the cysteine thiol groups in reduced rSeBP prevented selenite reduction and selenium binding under comparable conditions. PMID:16103372

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

    PubMed

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

    2015-11-01

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

  9. 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.

  10. Tunable Graphene-GaSe Dual Heterojunction Device.

    PubMed

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

    2016-03-01

    A field-effect device based on dual graphene-GaSe heterojunctions is demonstrated. Monolayer graphene is used as electrodes on a GaSe channel to form two opposing Schottky diodes controllable by local top gates. The device exhibits strong rectification with tunable threshold voltage. Detailed theoretical modeling is used to explain the device operation and to distinguish the differences compared to a single diode. PMID:26727653

  11. 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.

  12. 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

  13. Tin oxidation mechanism in the Sn-Se alloy

    NASA Astrophysics Data System (ADS)

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

    1988-06-01

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

  14. 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

  15. Visible light-driven CdSe nanotube array photocatalyst

    PubMed Central

    2013-01-01

    Large-scale CdSe nanotube arrays on indium tin oxide (ITO) glass have been synthesized using ZnO nanorod template. The strong visible light absorption in CdSe, its excellent photoresponse, and the large surface area associated with the tubular morphology lead to good visible light-driven photocatalytic capability of these nanotube arrays. Compared to freestanding nanoparticles, such one-piece nanotube arrays on ITO make it very convenient for catalyst recycling after their usage PMID:23680487

  16. Visible light-driven CdSe nanotube array photocatalyst

    NASA Astrophysics Data System (ADS)

    Zhu, Haojun; Li, Quan

    2013-05-01

    Large-scale CdSe nanotube arrays on indium tin oxide (ITO) glass have been synthesized using ZnO nanorod template. The strong visible light absorption in CdSe, its excellent photoresponse, and the large surface area associated with the tubular morphology lead to good visible light-driven photocatalytic capability of these nanotube arrays. Compared to freestanding nanoparticles, such one-piece nanotube arrays on ITO make it very convenient for catalyst recycling after their usage

  17. Visible light-driven CdSe nanotube array photocatalyst.

    PubMed

    Zhu, Haojun; Li, Quan

    2013-01-01

    Large-scale CdSe nanotube arrays on indium tin oxide (ITO) glass have been synthesized using ZnO nanorod template. The strong visible light absorption in CdSe, its excellent photoresponse, and the large surface area associated with the tubular morphology lead to good visible light-driven photocatalytic capability of these nanotube arrays. Compared to freestanding nanoparticles, such one-piece nanotube arrays on ITO make it very convenient for catalyst recycling after their usage. PMID:23680487

  18. 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

  19. Electrodeposition and growth mechanism of SnSe thin films

    NASA Astrophysics Data System (ADS)

    Biçer, Mustafa; Şişman, İlkay

    2011-01-01

    Tin selenide (SnSe) thin films were electrochemically deposited onto Au(1 1 1) substrates from an aqueous solution containing SnCl2, Na2SeO3, and EDTA at room temperature (25 °C). The electrochemical behaviors and the codeposition potentials of Sn and Se were explored by cyclic voltammetry. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and UV-vis absorption spectroscopy were employed to characterize the thin films. When the electrodeposition potential increased, the Se content in the films decreased. It was found that the stoichiometric SnSe thin films could be obtained at -0.50 V. The as-deposited films were crystallized in the preferential orientation along the (1 1 1) plane. The morphologies of SnSe films could be changed from spherical grains to platelet-like particles as the deposition potential increases. The SEM investigations show that the film growth proceeds via nucleation, growth of film layer and formation of needle-like particles on the overlayer of the film. The optical absorption study showed the film has direct transition with band gap energy of 1.3 eV.

  20. 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].

  1. Oxidation resistance of Pb-Te-Se optical recording film

    NASA Astrophysics Data System (ADS)

    Terao, Motoyasu; Horigome, Shinkichi; Shigematsu, Kazuo; Miyauchi, Yasushi; Nakazawa, Masatoshi

    1987-08-01

    The dependence of oxidation resistance of metal-Te-Se optical recording films on film composition is investigated, as well as the effects of oxidation on laser beam recorded hole shape. The films are deposited by vacuum evaporation on substrates with a glass/UV light curing resin/cellulose nitrate structure. The role of Se in the film is to inhibit the oxidation. With at least 14% Se addition, film oxidation is completely inhibited even at 60 °C, relative humidity 95%. Depth profiles of elements in the recording films are analyzed by Auger electron and x-ray photoelectron spectroscopy to clarify the mechanisms of oxidation inhibition by Se addition. A selenium condensed layer is found at the inner part of an oxidized surface layer. The surface Te oxide layer and the Se-rich layer should inhibit the film inside from oxidizing. The role of the metallic elements In, Pb, Sn, Bi, and Sb in the film is to inhibit cracking and to decrease noise in reproduced signals by decreasing the size of crystal grains. Lead is found to be the best among these metallic elements, because the recorded hole shape is clean even when recorded after 15 days accelerated oxidation at 60 °C, relative humidity 95%. A very long storage life is expected for the Pb-Te-Se optical recording film.

  2. 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.

  3. 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.

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

    PubMed

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

    2016-01-01

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

  5. 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

  6. 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.

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

    PubMed

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

    2015-04-30

    The mechanism of (77)Se nuclear spin-lattice relaxation is investigated in binary Ge-Se glasses. The (77)Se nuclides in Se-Se-Se chain sites relax faster via dipolar coupling fluctuation compared to those in Ge-Se-Ge sites shared by GeSe4 tetrahedra that relax slower via the fluctuation of the chemical shift anisotropy. The relaxation rate for the Se-Se-Se sites decreases markedly with increasing magnetic field, whereas that for the Ge-Se-Ge sites displays no appreciable dependence on the magnetic field such that the extent of differential relaxation between the two Se environments becomes small at high fields on the order of 19.6 T. The corresponding dynamical correlation time is three orders of magnitude shorter (∼10(-9) s) for the Se-Se-Se sites, compared to that for the Ge-Se-Ge sites (∼10(-6) s). The large decoupling in the time scale between these Se environments provides direct experimental support to the commonly made assumption that the selenium chains are mechanically floppy, and the interconnected GeSe4 tetrahedra form the rigid elements in the selenide glass structure. PMID:25848959

  8. 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.

  9. Optical properties of (In2Se3)1- x ·(CuIn5Se8) x solid solutions

    NASA Astrophysics Data System (ADS)

    Bodnar, I. V.

    2010-11-01

    Single crystals of In2Se3 and CuIn5Se8 compounds and (In2Se3)1-x·(CuIn5Se8)x solid solutions have been grown from the melt using the Bridgman method and their composition and structure determined. It is shown that the crystals have n-type conductivity. Their transmission spectra were studied in the self-absorption edge region at 80 and 295 K. Based on the spectral measurements, the band gap width (Eg) was determined and the band gap concentration dependences were plotted. It is found that Eg varies with the x composition nonlinearly. Using the dielectric model of Van Vechten-Bergstresser and the Hill-Richardson pseudo potential model, Eg(x) was calculated theoretically.

  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. PMID:19507900

  11. 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.

  12. 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.

  13. Epitaxial growth and photoluminescence excitation spectroscopy of CdSe quantum dots in (Zn,Cd)Se barrier

    NASA Astrophysics Data System (ADS)

    Piwowar, J.; Pacuski, W.; Smoleński, T.; Goryca, M.; Bogucki, A.; Golnik, A.; Nawrocki, M.; Kossacki, P.; Suffczyński, J.

    2016-05-01

    Design, epitaxial growth, and resonant spectroscopy of CdSe Quantum Dots (QDs) embedded in an innovative (Zn,Cd)Se barrier are presented. The (Zn,Cd)Se barrier enables shifting of QDs energy emission down to 1.87 eV, that is below the energy of Mn$^{2+}$ ions internal transition (2.1 eV). This opens a perspective for implementation of epitaxial CdSe QDs doped with several Mn ions as, e. g., the light sources in high quantum yield magnetooptical devices. Polarization resolved Photoluminescence Excitation measurements of individual QDs reveal sharp ($\\Gamma <$ 150 $\\mu$eV) maxima and transfer of optical polarization to QD confining charged exciton state with efficiency attaining 26 %. The QD doping with single Mn$^{2+}$ ions is achieved.

  14. Fe:ZnSe and Fe:ZnMgSe lasers pumped by Er:YSGG radiation

    NASA Astrophysics Data System (ADS)

    Jelínková, H.; Doroshenko, M. E.; Jelínek, M.; Å ulc, J.; Němec, M.; Kubeček, V.; Zagoruiko, Y. A.; Kovalenko, N. O.; Gerasimenko, A. S.; Puzikov, V. M.; Komar, V. K.

    2015-02-01

    The aim of the presented work was to design and characterize bulk Fe:ZnSe and Fe:Zn(1-x)Mg(x)Se (Mg content x = 0.19) lasers coherently pumped by electro-optically Q-switched Er:YSGG laser. This laser generated pumping radiation at 2.79 μm with the maximum energy of 50 mJ in 80 ns long pulse with the repetition-rate of 1 Hz. The 25 mm long optical resonator of Fe:ZnSe or Fe:ZnMgSe lasers was formed by a plan dichroic pumping mirror and a concave output coupler (r = 200 mm) with reflectivity 88 % @ 4-5 μm. Both lasers were operated at room temperature. Measured maximum output energy/slope efficiency in respect to the absorbed energy was ~ 3.8 mJ/42 % for the Fe:ZnSe laser and ~ 0.48 mJ/10 % for the Fe:ZnMgSe laser. The generated output pulse duration was 150 - 200 ns in both cases and the output beam spatial profile was approximately gaussian. The Fe:ZnSe and Fe:ZnMgSe lasers output spectra line-width was ~ 200 nm (FWHM) and their maxima were centered at 4.45 μm and 4.8 μm, respectively. The results were compared to pumping the same crystals by a Q-switched Er:YAG laser in similar conditions.

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

    PubMed

    Kim, Hyung-Bae; Jang, Du-Jeon

    2016-01-01

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

  16. Dirac cone shift and potential fluctuations in a passivated In2Se3/Bi2Se3 topological interface state

    NASA Astrophysics Data System (ADS)

    Jenkins, Gregory S.; Sushkov, A. B.; Schmadel, D. C.; Kim, M.-H.; Drew, H. D.; Koblmueller, G.; Bichler, M.; Bansal, N.; Brahlek, M.; Oh, S.

    2013-03-01

    The topological interface state of Bi2Se3 capped with In2Se3 is measured by gated THz cyclotron resonance. An observed shift of 70 meV in the position of the Dirac point towards mid-gap due to the physical properties of the trivial insulator In2Se3 on Bi2Se3 opens new possibilities in tailoring Dirac cone properties in topological insulators. Modulating and sweeping a semi-transparant gate while probing at terahertz frequencies in magnetic field enables characterization of the burried In2Se3/Bi2Se3 topological interface state, even in the presence of significant bulk conductivity. Near the Dirac point, the mobility is 3500 cm2/V .s with potential fluctuations of 60 meV. The scattering rate shows a precipitous drop with Fermi energy indicating decoupling of the surface states from bulk states. At Fermi energies above the conduction band edge, a plateau is observed in the real part of the Faraday angle that is 80 times flatter than the step size expected from a single Landau Level, quantized in units of the fine structure constant. The work at UMD is supported by NSF DMR-1104343 and DOE DE-SC0005436

  17. Growth and characterization of PbSe and Pb1-xSnxSe on Si (100)

    NASA Astrophysics Data System (ADS)

    Sachar, H. K.; Chao, I.; McCann, P. J.; Fang, X. M.

    1999-05-01

    PbSe and Pb1-xSnxSe layers, with thicknesses ranging from 1 to 5 μm, were grown by liquid phase epitaxy on Si (100) substrates using PbSe/BaF2/CaF2 buffer layers grown by molecular beam epitaxy. Optical Nomarski characterization revealed excellent surface morphologies and good growth solution wipeoffs. Although most PbSe layers were free of cracks over the entire 8×8 mm2 substrate area, ternary Pb1-xSnxSe layers exhibited varying crack densities ranging from zero in the center of samples to over 30 cracks/cm at the edges. High resolution x-ray diffraction (HRXRD) measurements of crack-free PbSe layers showed a residual in-plane tensile strain of 0.21% indicating that most of the 0.74% thermal expansion mismatch strain was absorbed by plastic deformation. HRXRD full width half maxima values of less than 200 arc sec showed that these layers also had high crystalline quality. Fourier transform infrared transmission measurements at room temperature and 110 K showed absorption edges in the range of 270-80 meV, depending on temperature and tin content. This work shows that these materials should be suitable for fabrication of mid-infrared devices covering the 4.6-16 μm spectral range.

  18. BIOAVAILABILITY OF SELENIUM FROM MEAT AND BROCCOLI AS DETERMINED BY RETENTION AND DISTRIBUTION OF SE75

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Meat is the single greatest source of selenium (Se) in the North American diet. Although not naturally enriched in Se, broccoli will accumulate Se when grown on high Se soils. Previous reports have demonstrated that Se from meat is highly bioavailable whereas Se from broccoli has poor bioavailabil...

  19. 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 .

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

    PubMed

    Alvarez, Vincent; Rossetti, Andrea O

    2016-02-01

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

  1. 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+) .

  2. Heterojunctions of model CdTe/CdSe mixtures

    DOE PAGESBeta

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

    2015-03-18

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

  3. 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.

  4. EMPaSE: an Extensible Multi-Paradigm Simulation Environment

    Energy Science and Technology Software Center (ESTSC)

    2010-08-05

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

  5. Anomalous ion damage behavior in ZnSe

    SciTech Connect

    Yu, K.M.; Bourret-Courchesne, E.D.

    1996-09-01

    The structural properties of ZnSe damaged by 180 keV Zn ions are studied for a wide range of ion dose (10{sup 13}{endash}10{sup 16}/cm{sup 2}) using ion channeling techniques. We found that ZnSe cannot be rendered amorphous by implantation at either room temperature (RT) or liquid nitrogen temperature (LNT) in the range of doses investigated. For lower ion doses (10{sup 13}{endash}10{sup 14}/cm{sup 2}), ZnSe samples implanted at LNT result in less damage than those implanted at RT by as much as an order of magnitude. Moreover, no simple point defect or amorphous clusters are found in the implanted ZnSe. For high implant doses ({approx_gt}10{sup 14}/cm{sup 2}), the samples are still monocrystalline but become highly defective with extended defects. Our results also suggests that point defects in the ZnSe created during implantation may be mobile at or below RT and that they may migrate rapidly under ion irradiation. {copyright} {ital 1996 American Institute of Physics}

  6. First-principles study of Se-intercalated graphite

    SciTech Connect

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

    2000-05-11

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

  7. EMPaSE: an Extensible Multi-Paradigm Simulation Environment

    SciTech Connect

    Siirola, John; Spotz, William; & Warrender, Christina

    2010-08-05

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

  8. 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).

  9. 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.

  10. 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.

  11. Optical and spin polarization dynamics in GaSe nanoslabs

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We report nearly complete preservation of "spin memory" between optical absorption and photoluminescence (PL) in nanometer slabs of GaSe pumped with up to 0.2 eV excess energy. At cryogenic temperatures, the initial degree of circular polarization (ρ0) of PL approaches unity, with the major fraction of the spin polarization decaying with a time constant >500 ps in sub-100-nm GaSe nanoslabs. Even at room temperature, ρ0 as large as 0.7 is observed, while pumping 1 eV above the band edge yields ρ0=0.15 . Angular momentum preservation for both electrons and holes is due to the separation of the nondegenerate conduction and valence bands from other bands. In contrast to valley polarization in atomically thin transition-metal dichalcogenides, here optical spin polarization is preserved in nanoslabs of 100 layers or more of GaSe.

  12. Pressure-induced phase transformation of In2Se3

    NASA Astrophysics Data System (ADS)

    Rasmussen, Anya M.; Teklemichael, Samuel T.; Mafi, Elham; Gu, Yi; McCluskey, Matthew D.

    2013-02-01

    In2Se3 has potential as a phase-change material for memory applications. Understanding its phase diagram is important to achieve controlled switching between phases. Using x-ray diffraction and a diamond-anvil cell, the pressure-dependent structural properties of In2Se3 powder were studied at room temperature. α-In2Se3 transforms into the β phase at 0.7 GPa, an order of magnitude lower than phase-transition critical pressures in typical semiconductors. The β phase persists upon decompression to ambient pressure. Raman spectroscopy experiments confirm this result. The bulk moduli are reported and the c/a ratio for the β phase is shown to have a highly nonlinear dependence on pressure.

  13. Pressure-induced phase transformation of In2Se3

    NASA Astrophysics Data System (ADS)

    Rasmussen, Anya; Teklemichael, Samuel; Mafi, Elham; Gu, Yi; McCluskey, Matthew

    2013-06-01

    Phase-change memory, with fast read-write speeds and small dimensions, will soon replace flash memory in our cell phones and tablets. This type of memory relies on phase change materials like indium selenide, In2Se3, a III-VI semiconductor that exists in multiple crystalline phases. To achieve controlled switching between phases, it is important to understand both the thermal and elastic properties of In2Se3. Using synchrotron x-ray diffraction and a diamond-anvil cell, a pressure-induced phase transition in powder In2Se3 from the α phase to β phase was discovered at 0.7 GPa. This pressure is an order of magnitude lower than phase-transition pressures in most semiconductors. Raman spectroscopy experiments confirm this result. The bulk moduli are reported for both α and β phases, and the c / a ratio for the β phase is shown to have a nonlinear dependence on pressure.

  14. 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.

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

    PubMed

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

    2016-04-20

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

  16. 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

  17. Li/MoSe/sub 3/S secondary battery

    SciTech Connect

    Abraham, K.M.; Pasquariello, D.M.; McAndrews, G.F.

    1987-11-01

    A new Li insertion cathode for ambient temperature secondary lithium batteries, namely, MoSe/sub 3/S, has been identified and characterized. It exhibits a specific capacity of approximately 4 Li per mole of the chalcogenide. The discharge behavior of Li/MoSe/sub 3/S cells at various temperatures and their rechargeability have been assessed utilizing THF:2Me-TH:F/LiAsF/sub 6/ and PC/LiClO/sub 4/ electrolyte solutions. The quasi-theoretical specific energy of 380 Wh/kg realized with a practical MoSe/sub 3/S electrode compares favorably with that in a Li/TiS/sub 2/ cell.

  18. 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.

  19. Room-temperature stabilization of nanoscale superionic Ag2Se

    NASA Astrophysics Data System (ADS)

    Hu, T.; Wittenberg, J. S.; Lindenberg, A. M.

    2014-10-01

    Superionic materials are multi-component solids in which one sub-lattice exhibits high ionic conductivity within a fixed crystalline structure. This is typically associated with a structural phase transition occurring significantly above room temperature. Here, through combined temperature-resolved x-ray diffraction and differential scanning calorimetry, we map out the nanoscale size-dependence of the Ag2Se tetragonal to superionic phase transition temperature and determine the threshold size for room-temperature stabilization of superionic Ag2Se. For the first time, clear experimental evidence for such stabilization of the highly ionic conducting phase at room temperature is obtained in ˜2 nm diameter spheres, which corresponds to a >100 °C suppression of the bulk phase transition temperature. This may enable technological applications of Ag2Se in devices where high ionic conductivity at room temperature is required.

  20. Room-temperature stabilization of nanoscale superionic Ag₂Se.

    PubMed

    Hu, T; Wittenberg, J S; Lindenberg, A M

    2014-10-17

    Superionic materials are multi-component solids in which one sub-lattice exhibits high ionic conductivity within a fixed crystalline structure. This is typically associated with a structural phase transition occurring significantly above room temperature. Here, through combined temperature-resolved x-ray diffraction and differential scanning calorimetry, we map out the nanoscale size-dependence of the Ag₂Se tetragonal to superionic phase transition temperature and determine the threshold size for room-temperature stabilization of superionic Ag2Se. For the first time, clear experimental evidence for such stabilization of the highly ionic conducting phase at room temperature is obtained in ∼2 nm diameter spheres, which corresponds to a >100 °C suppression of the bulk phase transition temperature. This may enable technological applications of Ag₂Se in devices where high ionic conductivity at room temperature is required. PMID:25249347

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

    PubMed Central

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

    2012-01-01

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

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

    SciTech Connect

    Elyukhin, Vyacheslav A.

    2014-02-21

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

  3. Hot Photoluminescence in γ-In2Se3 Nanorods

    PubMed Central

    2008-01-01

    The energy relaxation of electrons in γ-In2Se3nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature (Te) of the hot electrons. TheTevariation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In2Se3nanorods may be a promising material for the photovoltaic devices. PMID:21749734

  4. Hot Photoluminescence in γ-In2Se3 Nanorods

    NASA Astrophysics Data System (ADS)

    Yang, M. D.; Hu, C. H.; Shen, J. L.; Lan, S. M.; Huang, P. J.; Chi, G. C.; Chen, K. H.; Chen, L. C.; Lin, T. Y.

    2008-11-01

    The energy relaxation of electrons in γ-In2Se3 nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature ( T e) of the hot electrons. The T e variation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In2Se3 nanorods may be a promising material for the photovoltaic devices.

  5. 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. PMID:22887269

  6. S/Se In Sulfide Inclusion In Diamond

    NASA Astrophysics Data System (ADS)

    Thomassot, E.; Couffignal, F.; Lorand, J.; Bureau, H.; Cartigny, P.; Harris, J. W.

    2009-05-01

    Sulfides are among the most common minerals found as inclusions in diamonds. Being protected from any alteration after diamond formation, they likely represent the most pristine sulfide sample of mantle rocks. Their chemical composition in major and minor elements (mainly Ni, Cu and Cr), as determined using Electron Probe Micro Analyse (EPMA), is commonly used to determine the rock type in which the diamond formed. Here we propose to apply the same technique to the trace element abundance determination. We performed selenium (Se) on sulfide inclusion in diamonds. The S/Se value could help understanding whether the diamond formed in an eclogitic or peridotitic environment and may also constrain on the magmatic differentiation of diamonds host rock as well as provide a potential surface (hydrothermal) signature in diamond inclusions. A trace element measurement scheme has been developed by EPMA at the CAMPARIS centre (Paris). Se-abundance was obtained using a 30 kV accelerating voltage and 100nA probe current. Total counting time was 800s for peak (1.1 Å ) and 400s for background on both side of peak. Analyses were duplicated by μPIXE using the LPS nuclear microprobe facility (SIS2M CEA Saclay, France). Maps from 30x30 μm2 to 70x70 μm2 were obtained by scanning a 4x4 μm2 proton beam of 3MeV, 600 pA, (0.4 to 2 μC). The two techniques show good agreement and we conclude that EPMA is well suited for accurate and precise Se measurements. We analysed five samples; two monosulfide solid solution (MSS) (Ni>22wt%) typical of the peridotitic paragenesis (P-type), and three Ni-poor sulfides (Ni<7wt%) typical of the eclogitic paragenesis (E-type). In P-type sulfides, Se-content (260 ppm) is significantly higher than previously reported in sulfides from mantle-derived lherzolites (40-160 ppm), pyroxenites (25-45 ppm) or harzburgite. The value of S/Se in MSS is low (˜1400) compared to those of the primitive mantle reservoir (3,300; McDounough et al., 1995 Chemical Geology

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  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. PMID:25102289

  10. 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

  11. Synthesis of CdSe and CdSe/TiO2 nanoparticles under multibubble sonoluminescence condition.

    PubMed

    Wang, Jing; Guo, Wei; Liu, Shanhu; Li, Deliang

    2012-05-01

    CdSe and CdSe/TiO(2) nanoparticles were synthesized under multibubble sonoluminescence (MBSL) condition. The influences of TiO(2) introduced as the sensitizer on the morphology and crystal transformation were investigated. The morphology, phase and optical properties of the final products have been characterized by X-ray powder diffraction, transmission electron microscope, UV-vis absorption spectroscopy and photoluminescence spectroscopy. The results showed that as-prepared nanoparticles are well-crystallized, and the suppression of crystal pattern transition as well as the control of CdSe crystal growth can be implemented by coupling of TiO(2) semiconductor. Furthermore, the possible growth mechanism for different morphologies and crystal phases of the nanocrystals were also discussed. PMID:21982937

  12. New Gammas and Levels of 76Se Observed in the 76Br(β++EC)76Se Decay

    NASA Astrophysics Data System (ADS)

    Shen, S. F.; Yan, Y. P.

    The decay of bromine-76 is studied by means of γ-ray spectroscopy. Bromine-76 is produced via two reactions: 75As(α, 3n)76Br and 76Se(p, n)76Br. The results of these experiments verify the previously reported levels of 76Se. In addition to the previously described transitions and levels, 37 new γ-rays and 15 new energy levels are found for the first time. In addition, in order to study the deformation of 76Se which lies in transitional region between strongly deformed and spherical nuclei, we calculate the total Routhian surfaces (TRS) of positive-parity states by cranking shell model formalism.

  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. Low energy nuclear reactions with RIBRAS, Radioactive Ion Beam in Brasil, system

    NASA Astrophysics Data System (ADS)

    Guimarães, V.; Lépine-Szily, A.; Lichtenthäler, R.; de Faria, P. N.; Barioni, A.; Pires, K. C. C.; Morcelle, V.; Mendes, D. R.; Zamora, J. C.; Morais, M. C.; Condori, R. P.; Benjamim, E. A.; Monteiro, D. S.; Crema, E.; Moro, A. M.; Lubian, J.

    2011-09-01

    RIBRAS, Radioactive Ion beam in Brasil, is a system based on superconducting solenoids which can produce low energy RNB (Radioactive Nuclear Beams) at the University of São Paulo, Brazil. Secondary radioactive beams of light particles such as 6He, 7Be and 8Li have been produced and low energy elastic scattering and transfer reaction experiments have been performed. The recent scientific program using this facility includes elastic scattering and transfer reactions of 6He halo nucleus on 9Be, 27Al, 51V and 120Sn targets and 8Li on 9Be, 12C and 51V targets. The total reaction cross section as a function of energy has been extracted from the elastic scattering data and the role of breakup of weakly bound or exotic nuclei is discussed. Also spectroscopic factors have been obtained from the transfer reactions.

  15. Structural Changes in Vitreous GeSe4 under Pressure

    SciTech Connect

    Skinner L. B.; Parise J.; Benmore, C.J,; Antao, S.; Soignard, E.; Amin, S.A.; Bychkov, E.; Rissi, E. and Yarger, J.L.

    2011-11-21

    High-energy X-ray diffraction experiments have been performed on GeSe{sub 4} glass up to pressures of 8.6 GPa, and the equation of state has been measured up to 10 GPa. The X-ray structure factors reveal a decrease in the first sharp diffraction peak intensity and broadening with pressure, which signifies a break-up of the intermediate range order in the glass. In contrast, the principal peak in the structure factor shows an increase in intensity and a sharpening with pressure, which is attributed to an increase in extended range order and coherence of the compacted units. The average nearest neighbor coordination number is found to remain constant in GeSe{sub 4} glass (within experimental error) over the pressure range measured. This is in contrast with the gradual increase found in GeSe{sub 2} glass. Rather, in GeSe{sub 4} glass the densification mechanism is shown to be associated with large inward shifts of the second neighbor and higher coordination shells. These features appear as additional correlations at 3.3 and 5.3 {angstrom} in the differences taken between adjacent pair distribution functions with increasing pressure.

  16. 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

  17. 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

  18. Orbital characters and electronic correlations in KCo2Se2

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Zhao, Y. G.; Li, Y.; Jia, L. L.; Cai, Y. P.; Zhou, S.; Xia, T. L.; Büchner, B.; Borisenko, S. V.; Wang, S. C.

    2015-07-01

    We report a comprehensive study of the tridimensional nature and orbital characters of the low-energy electronic structure in KCo2Se2, using polarization- and photon energy-dependent angle-resolved photoemission spectroscopy. We observed one electron-like Fermi surface (FS) at the Brillouin zone (BZ) center, four electron-like FSs centered at the BZ corner, and one hole-like FS at the BZ boundary. The FSs show weak dispersion along the kz direction, indicating the near-two-dimensional nature of FSs in KCo2Se2. In combination with the local-density approximation calculations, we determined the orbital characters of the low-energy electronic bands, which are mainly derived from the Co 3d orbital, mixed with part of the Se 4p states. The {{d}{{x2}-{{y}2}}} orbital gives a significant contribution to the band crossing the Fermi level. A band renormalization of about 1.6 is needed to capture the essential dispersive features, which suggests that electronic correlations are much weaker than that in KyFe2-xSe2.

  19. Orbital characters and electronic correlations in KCo2Se2.

    PubMed

    Liu, Z H; Zhao, Y G; Li, Y; Jia, L L; Cai, Y P; Zhou, S; Xia, T L; Büchner, B; Borisenko, S V; Wang, S C

    2015-07-29

    We report a comprehensive study of the tridimensional nature and orbital characters of the low-energy electronic structure in KCo2Se2, using polarization- and photon energy-dependent angle-resolved photoemission spectroscopy. We observed one electron-like Fermi surface (FS) at the Brillouin zone (BZ) center, four electron-like FSs centered at the BZ corner, and one hole-like FS at the BZ boundary. The FSs show weak dispersion along the kz direction, indicating the near-two-dimensional nature of FSs in KCo2Se2. In combination with the local-density approximation calculations, we determined the orbital characters of the low-energy electronic bands, which are mainly derived from the Co 3d orbital, mixed with part of the Se 4p states. The [Formula: see text] orbital gives a significant contribution to the band crossing the Fermi level. A band renormalization of about 1.6 is needed to capture the essential dispersive features, which suggests that electronic correlations are much weaker than that in KyFe2-xSe2. PMID:26153922

  20. Thermoelectric transport properties of In2Se3 single crystal

    NASA Astrophysics Data System (ADS)

    Nguyen, Thi Huong; Duong, Van Thiet; Nguyen, Van Quang; Duong, Anh Tuan; Cho, Sunglae; Song, Jae Yong; Park, Hyun-Min

    In recent years the discovery and development of green energy source are one of the top concerns in science. The enormous efforts have been devoted to search for thermoelectric materials. Enhancement of thermoelectric figure of merit (ZT = (S2 σ / κ) T) is currently research goal of scientists. In2Se3 is one of semiconductors with layered structure, which is good for thermoelectric applications. In this study, we report on the transport and thermoelectric properties of In2Se3 single crystal. The layered crystal structure of In2Se3 was determined by XRD and FE-SEM measurements. Ellipsometry measurement illustrated the indirect band gap of In2Se3, about 1.61 eV. Transport properties have been studied in the temperature range from 20 to 400 K along axis which is parallel to the layers direction. Interestingly, Seebeck coefficient was n-type and increased with temperature and the electrical conductivity increased with temperature. Therefore, power factor increased up to 2.69 µWcm-1K-2at 400 K. In this talk, we will discuss more on transport properties.

  1. 2. VIEW OF SE SPANS FROM SOUTHINCLINED Copy photograph of ...

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

    2. VIEW OF SE SPANS FROM SOUTH--INCLINED Copy photograph of photogrammetric plate LC-HAER-GS05-B-1971-602L. - Philadelphia & Reading Railroad, Wissahickon Creek Viaduct, Spanning Wissahickon Creek, north of Ridge Avenue Bridge, Philadelphia, Philadelphia County, PA

  2. 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

  3. 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.

  4. Optical Properties of PbTe and PbSe

    SciTech Connect

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

    2012-01-01

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

  5. 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.

  6. Two terminal CuInSe2 based cascade cells

    NASA Astrophysics Data System (ADS)

    Baron, B. N.; Birkmire, R. W.; McCandless, B. E.; Phillips, J. E.

    1990-07-01

    This report presents results and conclusions of a two-year research program on multijunction thin-film solar cells using a CuInSe2 heterojunction for the low-band-gap bottom cell and either an a-Si:H (E(sub g) = 1.8 eV) or a CdTe (E(sub g) = 1.5 eV) heterojunction for the high-band-gap top cell in a monolithic two-terminal cascade structure. Photochemical vapor deposition was used to deposit a-Si cells. The presence of a CuInSe2/(CdZn)S cell in the a-Si deposition reactor did not introduce contaminants or adversely affect the performance of conventional p-i-n cells. Procedures were developed for fabricating monolithic cascade devices with the configuration ITO/a-Si(n-i-p)/ZnO/(CdZn)S/CuInSe2/Mo/glass. A prototype two-terminal a-Si/CuInSe2 cascade cell had an open-circuit voltage over IV and an efficiency of 5.8 percent. Physical vapor deposition with extrinsic doping was studied as a preparation technique for depositing low-resistivity p-type CdTe on transparent contact materials at low temperatures.

  7. 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.

  8. 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

  9. 8. Photocopy of c. 1906 photograph looking SE at row ...

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

    8. Photocopy of c. 1906 photograph looking SE at row of workers' housing along Main Street; bell calling workers to work is mounted on pole at left, corner of locomotive shed at right. - Laurel Valley Sugar Plantation, Double Creole Quarters, 2 Miles South of Thibodaux on State Route 308, Thibodaux, Lafourche Parish, LA

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  11. Orbitally-driven giant phonon anharmonicity in SnSe

    DOE PAGESBeta

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

    2015-10-19

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

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

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

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

  13. 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

  14. VIEW LOOKING NW FROM CATWALK OF SE TOWER, SHOWING INTERIOR ...

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

    VIEW LOOKING NW FROM CATWALK OF SE TOWER, SHOWING INTERIOR ELEVATION OF TOWER OPPOSITE. NOTE THAT CONCRETE PIERS DO NOT MATCH FOOTINGS PROJECTING SLIGHTLY ABOVE WATER. - Lake Shore & Michigan Southern Railway, Bridge No. 6, Spanning Calumet River, east of Chicago Skyway (I-90), Chicago, Cook County, IL

  15. 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

  16. 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.

  17. Photochemical electronic doping of colloidal CdSe nanocrystals.

    PubMed

    Rinehart, Jeffrey D; Schimpf, Alina M; Weaver, Amanda L; Cohn, Alicia W; Gamelin, Daniel R

    2013-12-18

    A method for electronic doping of colloidal CdSe nanocrystals (NCs) is reported. Anaerobic photoexcitation of CdSe NCs in the presence of a borohydride hole quencher, Li[Et3BH], yields colloidal n-type CdSe NCs possessing extra conduction-band electrons compensated by cations deposited by the hydride hole quencher. The photodoped NCs possess excellent optical quality and display the key spectroscopic signatures associated with NC n-doping, including a bleach at the absorption edge, appearance of a new IR absorption band, and Auger quenching of the excitonic photoluminescence. Although stable under anaerobic conditions, these spectroscopic changes are all reversed completely upon exposure of the n-doped NCs to air. Chemical titration of the added electrons confirms previous correlations between absorption bleach and electron accumulation and provides a means of quantifying the extent of electron trapping in some NCs. The generality of this photodoping method is demonstrated by initial results on colloidal CdE (E = S, Te) NCs as well as on CdSe quantum dot films. PMID:24289732

  18. 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.

  19. 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.

  20. Elevation, looking SE. Concrete and steel bridge with exposed steel ...

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

    Elevation, looking SE. Concrete and steel bridge with exposed steel frame is the central of three bridges crossing Brush Street between east Baltimore and Piquette. The bridge links Old Lake Shore and Michigan Central Main Line on the western side to a New York Central siding on the eastern side - Railroad Overpass, East Milwaukee & Hastings Avenues, Detroit, MI

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

    PubMed

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

    2015-08-18

    Selenium poisoning is a significant health problem in parts of Punjab, India, which is an area of intense agricultural productivity. To determine the complex soil dynamics that control distribution of Se in this area, we measured concentrations and δ(82/76)Se of bulk Se and individual Se pools in four soil profiles. This was compared against δ(82/76)Se of crops and groundwater used for irrigation. The isotopic composition of bulk Se and component Se pools reveal spatial heterogeneity. The bulk δ(82/76)Se show progressively lower values with increasing soil depth indicating the preferential migration of isotopically lighter Se downward through the soil profile. The δ(82/76)Se of water-soluble Se is isotopically heavier than δ(82/76)Se of adsorbed Se, suggesting Se isotope fractionation by reduction prior to scavenging by reactive minerals in the soil. The organically bound Se is isotopically lighter than water-soluble Se and correlates with the C/N ratio at different soil depths. Thus, Se immobilization by redox cycling controls the biogeochemical Se cycle in the soil. Se isotope ratios help to trace biochemical processes of Se in agricultural seleniferous soils and provide an important assessment for better soil management mitigating Se concentrations of ecotoxicological levels. PMID:26177307

  2. Growth and characterization of van der Waals heterostuctures formed by the topological insulator Bi2Se3 and the trivial insulator SnSe2

    NASA Astrophysics Data System (ADS)

    Matetskiy, A. V.; Kibirev, I. A.; Zotov, A. V.; Saranin, A. A.

    2016-07-01

    The formation, structure and electronic properties of SnSe2-Bi2Se3 van der Waals heterostructures were studied. Both heterostructures, SnSe2 on Bi2Se3 and Bi2Se3 on SnSe2, were grown epitaxially with high crystallinity and sharp interfaces. Their electron band structures are of trivial and topological insulators, respectively. The Dirac surface states of Bi2Se3 survive under the SnSe2 overlayer. One triple layer of SnSe2 was found to be an efficient spacer for separating a Bi2Se3 topological-insulator slab into two and creating the corresponding topological surface states.

  3. Electronic structure and exchange interactions in diluted semimagnetic semiconductors (Zn,Co)Se and (Zn,Mn)Se

    NASA Astrophysics Data System (ADS)

    Mašek, J.

    1991-05-01

    A comparative study of the electronic structure of (Zn,Co)Se and (Zn,Mn)Se is done by using a tight-binding version of the coherent potential approximation. The densities of states, relevant for a photoemission experiment, are calculated for a magnetically disordered phase. The exchange constant Jpd is obtained from the splitting of the valence band top in the ferromagnetic phase of the mixed crystal; Jdd is estimated from the energy of a spin reversal. We explain the large exchange constant in the Co-based systems as a result of efficient hybridization of the d-states with the valence band.

  4. Lewis Acid Induced Anomerization of Se-Glycosides. Application to Synthesis of α-Se-GalCer.

    PubMed

    McDonagh, Anthony W; Mahon, Mary F; Murphy, Paul V

    2016-02-01

    The TiCl4 induced anomerization of selenium glycosides of galacturonic acid derivatives is reported. The reaction was successful for galacturonic acid when various alkyl, alkenyl, alkynyl, saccharide, steroid, and lipid groups were attached to the anomeric Se atom. An increased amount of TiCl4 and/or higher temperature were needed to ensure completion of the reaction in some cases. Yields were higher for reactions carried out at higher dilution. The reaction was applied to the synthesis of Se-based mimics of the potent immunostimulant α-GalCer (KRN7000). PMID:26794638

  5. 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

  6. Reproductive biology of the characid dourado Salminus franciscanus from the São Francisco River, Brasil.

    PubMed

    Freitas, Leonardo J A; Prado, Paula S; Arantes, Fabio P; Santiago, Kleber B; Sato, Yoshimi; Bazzoli, Nilo; Rizzo, Elizete

    2013-06-01

    The neotropical characid Salminus franciscanus is an economically valuable migratory fish whose populations have been drastically reduced in recent decades due to industrial and economic development in Brasil. To study its reproduction, a total of 283 adult specimens were captured in the Upper São Francisco River, downstream from the Três Marias dam, Minas Gerais, south-eastern Brasil, from August 2009 to July 2010. The gonadal maturity stages were determined from histological features of the gonads and gonadosomatic index (GSI). Gametogenesis was assessed by light and electron microscopy. For analysis of the oocyte's surface and fecundity, mature females were subjected to hormonal induction and oocyte stripping. Fish in resting (Stage 1) were common in all samplings, ripening/ripe and spawning (Stages 2 and 3) were predominant in October-November and December-January and post-spawning (Stage 4) occurred from December-January extending until April-May. The GSI followed the morphological changes of gonadal maturation, with a peak in October-November, when maximum GSI (7.08 in females and 3.46 in males) was achieved. From scanning electron microscopy, stripped oocytes showed a funnel-shaped micropyle and a simple oocyte surface arrangement, which is typical for non-adhesive eggs. Fecundity ranged from 160 to 440×10(3) oocytes per female and 129 to 175×10(3)oocytes/kg. The results of this study indicate that S. franciscanus reproduces in the Upper São Francisco River from October to January, exhibiting a total spawning pattern, non-adhesive eggs and high fecundity, providing support for aquaculture and conservation biology of this important neotropical characid fish. PMID:23618945

  7. Variability in baseline laboratory measurements of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

    PubMed

    Ladwig, R; Vigo, A; Fedeli, L M G; Chambless, L E; Bensenor, I; Schmidt, M I; Vidigal, P G; Castilhos, C D; Duncan, B B

    2016-01-01

    Multi-center epidemiological studies must ascertain that their measurements are accurate and reliable. For laboratory measurements, reliability can be assessed through investigation of reproducibility of measurements in the same individual. In this paper, we present results from the quality control analysis of the baseline laboratory measurements from the ELSA-Brasil study. The study enrolled 15,105 civil servants at 6 research centers in 3 regions of Brazil between 2008-2010, with multiple biochemical analytes being measured at a central laboratory. Quality control was ascertained through standard laboratory evaluation of intra- and inter-assay variability and test-retest analysis in a subset of randomly chosen participants. An additional sample of urine or blood was collected from these participants, and these samples were handled in the same manner as the original ones, locally and at the central laboratory. Reliability was assessed with the intraclass correlation coefficient (ICC), estimated through a random effects model. Coefficients of variation (CV) and Bland-Altman plots were additionally used to assess measurement variability. Laboratory intra and inter-assay CVs varied from 0.86% to 7.77%. From test-retest analyses, the ICCs were high for the majority of the analytes. Notably lower ICCs were observed for serum sodium (ICC=0.50; 95%CI=0.31-0.65) and serum potassium (ICC=0.73; 95%CI=0.60-0.83), due to the small biological range of these analytes. The CVs ranged from 1 to 14%. The Bland-Altman plots confirmed these results. The quality control analyses showed that the collection, processing and measurement protocols utilized in the ELSA-Brasil produced reliable biochemical measurements. PMID:27533768

  8. Variability in baseline laboratory measurements of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

    PubMed Central

    Ladwig, R.; Vigo, A.; Fedeli, L.M.G.; Chambless, L.E.; Bensenor, I.; Schmidt, M.I.; Vidigal, P.G.; Castilhos, C.D.; Duncan, B.B.

    2016-01-01

    Multi-center epidemiological studies must ascertain that their measurements are accurate and reliable. For laboratory measurements, reliability can be assessed through investigation of reproducibility of measurements in the same individual. In this paper, we present results from the quality control analysis of the baseline laboratory measurements from the ELSA-Brasil study. The study enrolled 15,105 civil servants at 6 research centers in 3 regions of Brazil between 2008–2010, with multiple biochemical analytes being measured at a central laboratory. Quality control was ascertained through standard laboratory evaluation of intra- and inter-assay variability and test-retest analysis in a subset of randomly chosen participants. An additional sample of urine or blood was collected from these participants, and these samples were handled in the same manner as the original ones, locally and at the central laboratory. Reliability was assessed with the intraclass correlation coefficient (ICC), estimated through a random effects model. Coefficients of variation (CV) and Bland-Altman plots were additionally used to assess measurement variability. Laboratory intra and inter-assay CVs varied from 0.86% to 7.77%. From test-retest analyses, the ICCs were high for the majority of the analytes. Notably lower ICCs were observed for serum sodium (ICC=0.50; 95%CI=0.31–0.65) and serum potassium (ICC=0.73; 95%CI=0.60–0.83), due to the small biological range of these analytes. The CVs ranged from 1 to 14%. The Bland-Altman plots confirmed these results. The quality control analyses showed that the collection, processing and measurement protocols utilized in the ELSA-Brasil produced reliable biochemical measurements. PMID:27533768

  9. 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

  10. On nematicity, magnetism and superconductivity in FeSe

    NASA Astrophysics Data System (ADS)

    Böhmer, Anna

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

  11. 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. PMID:24151632

  12. 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.

  13. Tailoring Magnetic Doping in the Topological Insulator Bi2Se3

    SciTech Connect

    Zhang, Jian-Min; Zhu, Wenguang; Zhang, Ying; Xiao, Di; Yao, Yugui

    2012-01-01

    WetheoreticallyinvestigatethepossibilityofestablishingferromagnetisminthetopologicalinsulatorBi2Se3viamagneticdopingof3dtransitionmetalelements.Theformationenergies,chargestates,bandstructures,andmagneticpropertiesofdopedBi2Se3arestudiedusing rst-principlescalculationswithindensityfunctionaltheory.OurresultsshowthatBisubstitutionalsitesareenergeticallymorefavorablethaninterstitialsitesforsingleimpurities.DetailedelectronicstructureanalysisrevealsthatCrandFedopedmaterialsarestillinsulatinginthebulkbuttheintrinsicbandgapofBi2Se3issubstantiallyreducedduetothestronghybridizationbetweenthedstatesofthedopantsandthepstatesoftheneighboringSeatoms.ThecalculatedmagneticcouplingsuggeststhatCrdopedBi2Se3ispossibletobebothferromagneticandinsulating,whileFedopedBi2Se3tendstobeweaklyantiferromagnetic.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  15. 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. PMID:20079683

  16. 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.

  17. 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.

  18. 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.

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

    SciTech Connect

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

    2015-08-31

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

  20. Selenium Chain Length Distribution in GexSe100-x Glasses: Insights from (77)Se NMR Spectroscopy and Quantum Chemical Calculations.

    PubMed

    Kaseman, Derrick C; Oliveira, Karina Moreira; Palazzo, Teresa; Sen, Sabyasachi

    2016-05-19

    The statistics of selenium chain length distribution in GexSe100-x glasses with 5 ≤ x ≤ 20 are investigated using a combination of high-resolution, two-dimensional (77)Se nuclear magnetic resonance (NMR) spectroscopy and quantum chemical calculations. This combined approach allows for the distinction of various selenium chain environments on the basis of subtle but systematic effects of next-nearest neighbors of Se atoms in -Se-Se-Se- linkages on the (77)Se chemical shift tensor parameters. Simulation of the experimental (77)Se NMR spectral line shapes indicates that Se chain speciation in these chalcogenide glasses follows the Flory-Schulz distribution, originally developed for organic chain polymers. PMID:27129100

  1. Selenium speciation in Lower Cambrian Se-enriched strata in South China and its geological implications

    NASA Astrophysics Data System (ADS)

    Fan, Haifeng; Wen, Hanjie; Hu, Ruizhong; Zhao, Hui

    2011-12-01

    To understand the impact of Selenium (Se) into the biogeochemical cycle and implications for palaeo-redox environment, a sequential extraction method was utilized for samples including black shales, cherts, a Ni-Mo-Se sulfide layer, K-bentonite and phosphorite from Lower Cambrian Se-enriched strata in southern China. Seven species (water-soluble, phosphate exchangeable, base-soluble, acetic acid-soluble, sulfide/selenide associated, residual Se) and different oxidation states (selenate Se(VI), selenite Se(IV), organic Se, Se (0) and mineral Se(-II)) were determinated in this study. We found that the Ni-Mo-Se sulfide layer contained a significantly greater amount of Se(-II) associated with sulfides/selenides than those in host black shales and cherts. Furthermore, a positive correlation between the degree of sulfidation of iron (DOS) and the percentage of the sulfide/selenide-associated Se(-II) was observed for samples, which suggests the proportion of sulfide/selenide-associated Se(-II) could serve as a proxy for palaeo-redox conditions. In addition, the higher percentage of Se(IV) in K-bentonite and phosphorite was found and possibly attributed to the adsorption of Se by clay minerals, iron hydroxide surfaces and organic particles. Based on the negative correlations between the percentage of Se(IV) and that of Se(-II) in samples, we propose that the K-bentonite has been altered under the acid oxic conditions, and the most of black shale (and cherts) and the Ni-Mo-Se sulfide layer formed under the anoxic and euxinic environments, respectively. Concerning Se accumulation in the Ni-Mo-Se sulfide layer, the major mechanism can be described by (1) biotic and abiotic adsorption and further dissimilatory reduction from oxidized Se(VI) and Se(IV) to Se(-II), through elemental Se, (2) contribution of hydrothermal fluid with mineral Se(-II).

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

    SciTech Connect

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

    1983-02-01

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

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

    SciTech Connect

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

    2014-04-01

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

  4. High circular polarization in electroluminescence from MoSe2

    NASA Astrophysics Data System (ADS)

    Onga, Masaru; Zhang, Yijin; Suzuki, Ryuji; Iwasa, Yoshihiro

    2016-02-01

    The coupling between the valley degree of freedom and the optical helicity is one of the unique phenomena in transition metal dichalcogenides. The significant valley polarization evaluated from circularly polarized photoluminescence (PL) has been reported in many transition metal dichalcogenides, except in MoSe2. This compound is an anomalous material showing ultra-fast relaxation of the valley polarized states, which causes negligible polarization in the PL. Meanwhile, circularly polarized electroluminescence (EL) has been recently reported in a WSe2 light-emitting transistor, providing another method for using the valley degree of freedom. Here, we report the EL properties of MoSe2, demonstrating electrical switching of the optical helicity. Importantly, we observed high circular polarization reaching 66%. The results imply that the dominant mechanism of circularly polarized EL is robust against intervalley scattering, in marked contrast to the PL.

  5. CO2 laser beam propagation with ZnSe optics

    NASA Astrophysics Data System (ADS)

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

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

  6. 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.

  7. 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.

  8. 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

  9. Giant Seebeck effect in Ge-doped SnSe.

    PubMed

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

    2016-01-01

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

  10. Giant Seebeck effect in Ge-doped SnSe

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  11. Doping mechanism in pure CuInSe2

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  12. Lattice Instability of 2H-TaSe2

    NASA Astrophysics Data System (ADS)

    John Bosco Balaguru, R.; Lawrence, N.; Alfred Cecil Raj, S.

    The charge density wave (CDW) in the layered compound 2H-TaSe2 at low temperatures has a commensurate phase, which causes super lattice points to appear in the Brillöuin zone of the undistorted phase. A Born-von Karman formalism has been employed for the calculation of phonon frequency distribution curves of 2H-TaSe2 both in the normal and in the commensurate charge density wave (CCDW) phases. A folding technique has been adopted for the calculation in the CCDW phase. The phonon distribution for both the phases have been reported. With these distributions the thermal properties such as specific heat capacity, Debye Waller factor W(k) and thermal conductivity have been worked out, and compared with the available experimental results.

  13. 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.

  14. 140 W Cr:ZnSe laser system.

    PubMed

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

    2016-09-01

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

  15. 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..

  16. Quantum confined acceptors and donors in InSe nanosheets

    SciTech Connect

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

    2014-12-01

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

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

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

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

  18. Parametric amplification in AgGaSe2

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  19. Pressure dependence of Se absorption lines in AlSb

    SciTech Connect

    Hsu, L. |; Haller, E.E.; Ramdas, A.K.

    1996-09-01

    Using far infrared absorption spectroscopy, the authors have investigated electronic transition spectra of Se donors in AlSb as a function of hydrostatic pressure. At least two distinct ground to bound excited state transition lines, which depend quadratically on the pressure, can be seen. At pressures between 30 and 50 kbar, evidence of an anti-crossing between one of the electronic transitions and a peak which they attribute to the 2 zone center LO phonon mode can be seen.

  20. Nematic antiferromagnetic states in bulk FeSe

    NASA Astrophysics Data System (ADS)

    Liu, Kai; Lu, Zhong-Yi; Xiang, Tao

    2016-05-01

    The existence of nematic order, which breaks the lattice rotational symmetry with nonequivalent a and b axes in iron-based superconductors, is a well-established experimental fact. An antiferromagnetic (AFM) transition is accompanying this order, observed in nearly all parent compounds, except bulk FeSe. The absence of the AFM order in FeSe casts doubt on the magnetic mechanism of iron-based superconductivity, since the nematic order is believed to be driven by the same interaction that is responsible for the superconducting pairing in these materials. Here we show, through systematic first-principles electronic structure calculations, that the ground state of FeSe is in fact strongly AFM correlated but without developing a magnetic long-range order. Actually, there are a series of staggered n -mer AFM states with corresponding energies below that of the single stripe AFM state, which is the ground state for the parent compounds of most iron-based superconductors. Here, the staggered n -mer (n any integer >1 ) means a set of n adjacent parallel spins on a line along the b axis with antiparallel spins between n -mers along both a and b axes. Moreover, different n -mers can antiparallelly mix with each other to coexist. Among all the states, we find that the lowest energy states formed by the staggered dimer, staggered trimer, and their random antiparallel aligned spin states along the b axis are quasidegenerate. The thermal average of these states does not show any magnetic long-range order, but it does possess a hidden one-dimensional AFM order along the a axis, which can be detected by elastic neutron scattering measurements. Our finding gives a natural account for the absence of long-range magnetic order and suggests that the nematicity is driven predominantly by spin fluctuations even in bulk FeSe, providing a unified description on the phase diagram of iron-based superconductors.

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

    NASA Technical Reports Server (NTRS)

    1991-01-01

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

  2. Deep levels in AgGaSe{sub 2}

    SciTech Connect

    Choi, I.H.; Yu, P.Y.

    1994-08-01

    The photoluminescence spectra of AgGaSe{sub 2} obtained at 77 K is reported. Two emission peaks have been observed and their pressure dependence studied. One of these peaks has been identified with emission involving one of the two deep level peak D{sub 1} and D{sub 2} observed previously in absorption measurement [App. Phys. Lett. 64,1717 (1994)]. A simple model for the capture of carriers into these deep levels has been proposed.

  3. 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

  4. Complex band structure of topological insulator Bi2Se3.

    PubMed

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

    2016-10-01

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

  5. Chiral exciton in the topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Kung, Hsiang-Hsi; Salehi, Maryam; Wang, Xueyun; Koirala, Nikesh; Brahlek, Matthew; Lee, Alexander; Cheong, Sang-Wook; Oh, Seongshik; Blumberg, Girsh

    Materials with novel band structures can host ``chiral excitons'', where the exciton emission preserves the helicity of the excitation photon, as recently demonstrated in transition metal dichalcogenide monolayers. Here, we report the observation of a highly polarized photoluminescence peak, which is due to chiral exciton emission in the topological insulator Bi2Se3. Surprisingly, the energy of the emission is centered at 2.26 eV, much higher than the 0.3 eV bulk band gap of Bi2Se3. The excitation profile shows maximum polarization around 2.60 eV excitation, suggesting the chiral exciton is due to interband transition between the topological surface states and a bulk band. We demonstrate that the polarization of the exciton emission is insensitive to temperature and Bi2Se3 film thickness, providing a convenient and robust platform for optoelectronic applications. Gb, HHK and AL acknowledge support from NSF Award DMR-1104884. MS, NK, MB and SO are funded by Gordon and Betty Moore Foundation's EPiQS initiative (GBMF4418) and NSF(DMR-1308142). XYW and SWC acknowledge support from NSF Award DMREF-1233349.

  6. Luminescent gelatin nanospheres by encapsulating CdSe quantum dots.

    PubMed

    Chen, Longyan; Willoughby, Adrienne; Zhang, Jin

    2014-02-01

    Quantum dots (QDs) have been encapsulated within gelatin nanoparticles (GNPs), which gives GNPs fluorescent properties and improves the biocompatibility of QDs. Hydrophilic CdSe QDs were produced through thermodecomposition following the ligand-exchange method, and were then encapsulated in GNPs. The results of high-resolution transmission electron microscopy and transmission electron microscopy show that CdSe QDs and QDs-encapsulated GNPs (QDs-GNPs) have average diameters of 5 ± 1 and 150 ± 10 nm, respectively. Results of both high-resolution transmission electron microscopy and confocal laser scanning microscopy indicate that CdSe QDs are successfully encapsulated within GNPs. The QDs-GNPs have distinctive fluorescent properties with maximum emission at 654 nm, with a 24 nm red-shift compared with hydrophilic mercaptoundecanoic acid (MUA)-modified QDs. In addition, an in vitro cytotoxicity test shows that QDs-GNPs do not have any toxic effect on cells. It is expected that QDs-GNPs might be an excellent candidate as a contrast agent in bio-imaging. PMID:23533134

  7. Preparation and applications of ZnSe nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    SciTech Connect

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

    2015-05-15

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

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

    PubMed

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

    2016-07-14

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

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

    PubMed

    Wang, Yanhua; Hao, Hang; Zhang, Shengmin

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  13. Spontaneous emission enhancement of colloidal CdSe nanoplatelets

    NASA Astrophysics Data System (ADS)

    Yang, Zhili; Pelton, Matthew; Waks, Edo

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

  14. Kinetics of Ge-Se-In Film Growth

    SciTech Connect

    Stoilova, A.; Petkov, P.; Nedeva, Y.; Monchev, B.

    2010-01-21

    The processes of vacuum evaporation and condensation in the Ge-Se-In system were investigated. Thin amorphous films were deposited by modified thermal evaporation from previously synthesized non-crystalline (GeSe{sub y}){sub 1-x}In{sub x} ingots, where x = 0, 5, 10, 15, 20 and y = 4, 5 and 6. The specific evaporation rate was determined by measuring of the mass of evaporator before evaporation and the mass of empty evaporator after evaporation in temperature range of evaporation (500-800) K. The substrate temperature was varied in the range (300-430) K to study the condensation process and specific condensation rate was determined by measuring of the substrate mass before and after condensation. The condensation energy of the (GeSe{sub y}){sub 1-x}In{sub x} layers steady increases at indium addition.The thin films studied by transmission electron microscopy (TEM) and electron microdiffraction (EMD) reveal homogeneous and amorphous structure. The layer composition determined by Auger electron spectroscopy is close to that of the corresponded bulk samples.

  15. Radioactive decay of excitations in ZnSe (Te)

    NASA Astrophysics Data System (ADS)

    Gordeev, S. I.; Galkin, Sergey N.; Kostyukevich, S. A.; Lalayants, A. I.; Ryzhikov, Vladimir D.; Tolmachev, Alexander V.; Voronkin, E. F.; Lisetskaja, E. K.

    2003-11-01

    Electro optical characteristics of the semiconductor compounds has been researched from the discovery of the semiconductor materials. One of the perspective ideas in this field was the possibility to obtain "cool" phosphorescence"s by means of the relaxations of the energy by recombination of excited electroni -holder pairs. In this work the conditions of obtaining of the electro luminescent structures based ZnSe(Te), their characteristics and structure of optical - and electro-luminescence centers are investigated. The Structure Me|ZnSe(Te):Zn|ZnO|ITO has shown the characteristics of the led, having bands of the radiation in the field of 540, 640 and 740 nm. The branch of the direct mode had a negative nonmonotonic area, because the thickness of ZnO quantum-dimensioned. The resemblance o the spectrums of electroluminescence of the crystals in abundance of Zn and film structures, which were obtained using the method of vacuum condensation results in that surface, cathode, nature of luminescence of ZnSe(Te) is possible to b explained in account of injection of the carriers in semiconductor.

  16. Metal contacts on ZnSe and GaN

    SciTech Connect

    Duxstad, K J

    1997-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Nakamura, Satoshi; Maeda, Tsuyoshi; Wada, Takahiro

    2010-12-01

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

  18. ZnSe immersion grating in the short NIR region

    NASA Astrophysics Data System (ADS)

    Ikeda, Yuji; Kobayashi, Naoto; Kuzmenko, Paul; Little, Steve L.; Mirkarimi, Paul B.; Alameda, Jennifer B.; Kaji, Sayumi; Sarugaku, Yuki; Yasui, Chikako; Kondo, Sohei; Fukue, Kei; Kawakita, Hideyo

    2014-07-01

    ZnSe has a high refractive index (n~ 2.45) and low optical loss (< 0.1/cm) from 0.8 to 12 um. Therefore ZnSe immersion gratings can enable high-resolution spectroscopy over a wide wavelength range. We are developing ZnSe immersion gratings for a ground-based NIR high-resolution spectrograph WINERED. We previously produced a large prism-shaped ZnSe immersion grating with a grooved area 50 mm x 58 mm (Ikeda et al. 2010). However, we find two problems as NIR immersion grating: (i) serious chipping of the grooves, and (ii) inter-order ghosts in the diffraction pattern. We believed the chipping to be due to micro cracks just beneath surface present prior to diamond machining. Therefore we removed this damaged region, a few tens of microns thick, by etching the ZnSe grating blank with a mixture of HCl and HNO3. Ghosts appearing halfway between main diffraction orders originate from small differences in spacing between odd and even grooves. Apparently the blank shifts repeatably by about 120 nm in the direction orthogonal to the grooves depending on whether the translation stage holding the blank is moving right to left or left to right. Therefore we remachined the grating only cutting grooves with the stage moving from right to left. After re-cutting, we also deposit the Cu coating with an enhanced interface layer of SiO2 on the groove, which is developed in our previous study. We evaluated the optical performances of this immersion grating. It shows light scattering of 3.8 % at 1μm, no prominent ghosts, and a spectral resolution of 91,200 at 1 μm. However we measured an absolute diffraction efficiency of only 27.3% for TE and 25.9 % for TM waves at 1.55 μm. A non-immersed measurement of the diffraction efficiency of the facet blazed near 20º exceeded 60%, much closer to theoretical predictions. We plan to carry out more tests to resolve this discrepancy.

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

    PubMed

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

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  1. Determination of Mass Attenuation Coefficients for CuInSe2 and CuGaSe2 Semiconductors

    NASA Astrophysics Data System (ADS)

    Çelik, Ahmet; Çevik, Uǧur; Baltaş, Hasan; Bacaksiz, Emin

    2007-04-01

    This work presents mass attenuation coefficients values of CuInSe2 and CuGaSe2 semiconductor thin films commonly used in photovoltaic devices. The mass attenuation coefficients were measured at different energies from 11.9 to 37.3 keV by using the secondary excitation method. Monochromatic photons were obtained using the Br, Sr, Mo, Cd, Te, Ba and Nd secondary targets. 59.5 keV gamma rays emitted from an annular Am-241 radioactive source were used to excite secondary targets. Characteristic X-rays emitted from secondary target were counted by a Si(Li) detector with a resolution of 0.16 keV at 5.9 keV. The measured values were compared with theoretical values calculated using WinXCOM program.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  3. Magnetic Coupling in FeBi2Se4 and FeSb2Se4 from first principles

    NASA Astrophysics Data System (ADS)

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

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

  4. Improved Performance in CuInSe2 and Surface-Modified CuGaSe2 Solar Cells

    SciTech Connect

    AbuShama, J.; Noufi, R.; Johnston, S.

    2005-01-01

    In this paper, we present an update and review on the progress made in the development of low-bandgap CuInSe2 (CIS) and wide-bandgap CuGaSe2 (CGS) solar cells. Our research project is primarily concerned with the optimization of the bottom and top cells of the tandem solar cell. This past year, we achieved new world record total-area efficiencies of 15.0% and 10.2% for CIS and surface-modified CGS solar cells, respectively. These achievements were possible by modifying the growth process for CIS and CGS absorbers. We attempt to modify the surface region of the CGS absorber to be CIGS-like in composition. In the mean time, we are designing a mechanical-stacked tandem solar cell where the CIS cell serves as the bottom cell.

  5. Determination of Mass Attenuation Coefficients for CuInSe2 and CuGaSe2 Semiconductors

    SciTech Connect

    Celik, Ahmet; Cevik, Ugur; Baltas, Hasan; Bacaksiz, Emin

    2007-04-23

    This work presents mass attenuation coefficients values of CuInSe2 and CuGaSe2 semiconductor thin films commonly used in photovoltaic devices. The mass attenuation coefficients were measured at different energies from 11.9 to 37.3 keV by using the secondary excitation method. Monochromatic photons were obtained using the Br, Sr, Mo, Cd, Te, Ba and Nd secondary targets. 59.5 keV gamma rays emitted from an annular Am-241 radioactive source were used to excite secondary targets. Characteristic X-rays emitted from secondary target were counted by a Si(Li) detector with a resolution of 0.16 keV at 5.9 keV. The measured values were compared with theoretical values calculated using WinXCOM program.

  6. Se EXAFS study of the elevated wurtzite to rock salt structural phase transition in CdSe nanocrystals

    SciTech Connect

    Tolbert, S.H.; Alivisatos, A.P. |

    1993-09-01

    High pressure Se EXAFS data has been obtained on 2.7 nm radius CdSe semiconductor nanocrystals. This system is observed to undergo a solid-solid phase transition at 6.5 GPa which is approximately twice the reported value for bulk CdSe. In combination with high pressure optical absorption experiments, EXAFS data can be used to identify the high-pressure phase structure as rock salt. EXAFS data can be fit with equations of state to yield pressure volume curves. Resultant values of bulk modulus and its derivative with respect to pressure are B{sub o} = 37 {plus_minus} 5 GPa and B{sub o}{prime} = 11 {plus_minus} 3. A thermodynamic model for the data is presented in which the internal energy in each phase is modified by a surface energy term. Differences in surface energy are used to explain the elevation in phase transition pressure. The model can be used to estimate a value for the surface energy in the rock salt phase; 1.9 {plus_minus} 0.3 N/m is obtained in comparison to 0.9 {plus_minus} 0. 1 N/m for the wurtzite phase.

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

    SciTech Connect

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

    2014-02-21

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

  8. Optical properties of water-soluble L-cysteine-capped alloyed CdSeS quantum dot passivated with ZnSeTe and ZnSeTe/ZnS shells

    NASA Astrophysics Data System (ADS)

    Adegoke, Oluwasesan; Nyokong, Tebello; Forbes, Patricia B. C.

    2015-08-01

    Alloyed quantum dots (QDs) passivated with shell materials have valuable optical characteristics suitable for a wide array of applications. In this work, alloyed ternary CdSeS QDs passivated with ZnSeTe and ZnSeTe/ZnS shells have been synthesized via a hot-injection method and a ligand exchange reaction employing L-cysteine as a thiol ligand has been used to obtain these water-soluble nanocrystals for the first time. The photoluminescence (PL) quantum yield (QY) of alloyed L-cysteine-capped CdSeS was 71.2% but decreased significantly to 5.2% upon passivation with a ZnSeTe shell. The red shift in PL emission of the CdSeS/ZnSeTe QDs was attributed to be strain-induced whilst a lattice-induced process likely created defect states in the core/shell interface hence contributing to the decline in the PL QY. Nonetheless, the fluorescence stability of CdSeS/ZnSeTe QDs in aqueous solution was unperturbed. Further passivation with a ZnS shell (CdSeS/ZnSeTe/ZnS) improved the PL QY to a value of 58.7% and thus indicates that the defect state in the QDs core/shell/shell structure was reduced. PL lifetime exciton measurements indicated that the rates of decay of the QDs influenced their photophysical properties.

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

    PubMed

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

    2016-02-01

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

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

    PubMed

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

    2014-04-01

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

  11. High transition temperatures in molecular intercalates of FeSe

    NASA Astrophysics Data System (ADS)

    Blundell, Stephen

    2015-03-01

    Molecular groups can now be intercalated into iron-based superconductors with dramatic consequences on the superconducting properties. These species act as charge reservoirs, sources of electrical polarization, and also make subtle structural modifications to superconducting layers, all of which can make novel adjustments to the band structure that in turn can control superconducting properties. By synthesizing the compound Lix(NH2)y(NH3)1 -yFe2Se2 (x ~ 0.6; y ~ 0.2), in which lithium ions, lithium amide and ammonia (NH3) act as the spacer layer between FeSe layers, we have turned a 9 K superconductor into a 43 K superconductor. Further chemical modification allow us to produce a range of new superconducting materials which we have studied using a variety of techniques including muon-spin rotation. Recently, we have used hydrothermal reactions to produce layered lithium iron selenide hydroxides with chemical formula Li1-xFex(OH)Fe1-ySe and thereby producing compounds whose transition temperature can be tuned from zero up to about 40 K. Minimizing the concentration of iron vacancies in the iron selenide layer and simultaneously increasing the electron count on iron in the selenide layers enhance the superconducting properties in this family. Future prospects for new superconducting materials using these novel synthetic routes will be discussed, as will also our current understanding of the superconductivity in these materials. (Work performed in collaboration with S. J. Clarke and coworkers at Oxford, RAL and Durham, UK.) Work supported by EPSRC(UK).

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

    NASA Astrophysics Data System (ADS)

    Stolz, Andreas

    2004-10-01

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

  13. Fractal structures of dendrites in GaSe crystals

    NASA Astrophysics Data System (ADS)

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

    2008-07-01

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

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

    SciTech Connect

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

    2015-05-15

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

  15. Electronic Band Gap of SrSe at High Pressure

    SciTech Connect

    Atkinson,T.; Chynoweth, K.; Cervantes, P.

    2006-01-01

    The electronic band gap of SrSe, in the CsCl-stuctured phase, was measured to 42 GPa via optical absorption studies. The indirect electronic band gap was found to close monotonically with pressure for the range of pressures studied. The change in band gap with respect to pressure, dE{sub gap}/dP, was determined to be -6.1(5)x10{sup -3} eV/GPa. By extrapolation of our line fit, we estimate band gap closure to occur at 180(20) GPa.

  16. Coherent Electronic Coupling in Atomically Thin MoSe2

    NASA Astrophysics Data System (ADS)

    Singh, Akshay; Moody, Galan; Wu, Sanfeng; Wu, Yanwen; Ghimire, Nirmal J.; Yan, Jiaqiang; Mandrus, David G.; Xu, Xiaodong; Li, Xiaoqin

    2014-05-01

    We report the first direct spectroscopic evidence for coherent electronic coupling between excitons and trions in atomically thin transition metal dichalcogenides, specifically monolayer MoSe2. Signatures of coupling appear as isolated cross-peaks in two-color pump-probe spectra, and the line shape of the peaks reveals that the coherent coupling originates from many-body interactions. Excellent agreement between the experiment and density matrix calculations suggests that coherent exciton-trion coupling leads to the formation of a correlated state with a remarkably large binding energy.

  17. Normal state incoherent pseudogap in FeSe superconductor

    NASA Astrophysics Data System (ADS)

    Craco, Luis; Laad, Mukul S.

    2016-05-01

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

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

    SciTech Connect

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

    2013-08-20

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

  19. The JAVA-based DICOM query interface DicoSE.

    PubMed

    Prinz, Michael; Fischer, Georg; Schuster, Ernst

    2005-03-01

    DICOM 3 is a very elaborate standard for the communication between medical image devices. It is published in several parts by the National Electrical Manufacturers Association (NEMA). To adequately visualize the data structure defined in parts 3, 5 and 6 of the DICOM standard, we implemented the web based Dicom Search Engine (DicoSE). It allows for querying the DICOM standard data dictionary for defined data fields and visualizes the topology of the data which is inherently present in DICOM datasets. For the administration of the underlying data a web based administration interface is provided. The service is entirely based on freely available software. PMID:15694639

  20. Polarity continuation and frustration in ZnSe nanospirals

    PubMed Central

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

    2014-01-01

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

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

    SciTech Connect

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

    2015-08-28

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

  2. Refining the W1 and SE1 Facilities

    NASA Technical Reports Server (NTRS)

    Chambers, Rodney D.

    2004-01-01

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

  3. Flexible, High-Speed CdSe Nanocrystal Integrated Circuits.

    PubMed

    Stinner, F Scott; Lai, Yuming; Straus, Daniel B; Diroll, Benjamin T; Kim, David K; Murray, Christopher B; Kagan, Cherie R

    2015-10-14

    We report large-area, flexible, high-speed analog and digital colloidal CdSe nanocrystal integrated circuits operating at low voltages. Using photolithography and a newly developed process to fabricate vertical interconnect access holes, we scale down device dimensions, reducing parasitic capacitances and increasing the frequency of circuit operation, and scale up device fabrication over 4 in. flexible substrates. We demonstrate amplifiers with ∼7 kHz bandwidth, ring oscillators with <10 μs stage delays, and NAND and NOR logic gates. PMID:26407206

  4. Mantle structure and tectonic history of SE Asia

    NASA Astrophysics Data System (ADS)

    Hall, Robert; Spakman, Wim

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  6. Soluble precursors for CuInSe2, CuIn(1-x)Ga(x)Se2, and Cu2ZnSn(S,Se)4 based on colloidal nanocrystals and molecular metal chalcogenide surface ligands.

    PubMed

    Jiang, Chengyang; Lee, Jong-Soo; Talapin, Dmitri V

    2012-03-21

    We report a new platform for design of soluble precursors for CuInSe(2) (CIS), Cu(In(1-x)Ga(x))Se(2) (CIGS), and Cu(2)ZnSn(S,Se)(4) (CZTS) phases for thin-film potovoltaics. To form these complex phases, we used colloidal nanocrystals (NCs) with metal chalcogenide complexes (MCCs) as surface ligands. The MCC ligands both provided colloidal stability and represented essential components of target phase. To obtain soluble precursors for CuInSe(2), we used Cu(2-x)Se NCs capped with In(2)Se(4)(2-) MCC surface ligands or CuInSe(2) NCs capped with {In(2)Cu(2)Se(4)S(3)}(3-) MCCs. A mixture of Cu(2-x)Se and ZnS NCs, both capped with Sn(2)S(6)(4-) or Sn(2)Se(6)(4-) ligands was used for solution deposition of CZTS films. Upon thermal annealing, the inorganic ligands reacted with NC cores forming well-crystallized pure ternary and quaternary phases. Solution-processed CIS and CZTS films featured large grain size and high phase purity, confirming the prospects of this approach for practical applications. PMID:22329720

  7. Phase equilibria in the quasi-ternary system Ag2Se-Ga2Se3-In2Se3 and physical properties of (Ga0.6In0.4)2Se3, (Ga0.594In0.396Er0.01)2Se3 single crystals

    NASA Astrophysics Data System (ADS)

    Ivashchenko, I. A.; Danyliuk, I. V.; Olekseyuk, I. D.; Halyan, V. V.

    2014-02-01

    The quasi-ternary system Ag2Se-Ga2Se3-In2Se3 was investigated by differential thermal, X-ray phase, X-ray structure, microstructure analysis and microhardness measurements. Five quasi-binary phase diagrams, six polythermal sections, isothermal section at 820 K and the liquidus surface projection were constructed. The character and temperature of the invariant processes were determined. The specific resistance of the single crystals (Ga0.6In0.4)2Se3, (Ga0.594In0.396Er0.01)2Se3 was measured, 7.5×105 and 3.15×105 Ω m, respectively, optical absorption spectra in the 600-1050 nm range were recorded at room temperature, and the band gap energy was estimated which is 1.95±0. 01 eV for both samples.

  8. Extraction, preliminary characterization and antioxidant activity of Se-enriched Maitake polysaccharide.

    PubMed

    Mao, Guanghua; Zou, Ye; Feng, Weiwei; Wang, Wei; Zhao, Ting; Ye, Changwen; Zhu, Yang; Wu, Xueshan; Yang, Liuqing; Wu, Xiangyang

    2014-01-30

    A Se-enriched Grifola frondosa polysaccharide (Se-GP) was obtained from G. frondosa enriched with Se by spraying an Na2SeO3 solution during fruit body growth using a Box-Behnken design and compared to G. frondosa polysaccharide (GP) for preliminary characterization and determination of the antioxidant activity. Under optimal conditions, polysaccharide yields and both the Se-GP and GP contents do not differ; however, the Se content of Se-GP (17.52 μg/g) was 48.7 times that of GP. Three homogenous Se-GPs (Se-GP11, Se-GP22 and Se-GP33) or GPs (GP11, GP22 and GP33) were obtained via DEAE-52 and Sephacryl S-400 purification. Their molecular weight and polysaccharide content of these compounds were not obviously different, whereas the Se content of Se-GP11, Se-GP22 and Se-GP33 was 9.41, 6.59 and 16.25 times that of GP11, GP22 and GP33, respectively. The antioxidant activity of Se-GP for the DPPH, ABTS and hydroxyl radicals was higher than that of GP and was highest for the hydroxyl radical. PMID:24299767

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

    PubMed

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

    2016-01-01

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

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

    PubMed Central

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

    2016-01-01

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

  11. Long-term selenium biofortification in carrots and broccoli grown in soils amended with Se-enriched S. pinnata

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Selenium (Se) biofortification has been practiced in Se-deficient regions throughout the world primarily by adding inorganic sources of Se to the soil. Adding organic sources of Se could be useful as an alternative Se amendment for the production of Se-biofortified food crops needed in Se-deficient ...

  12. Charge-induced nematicity in FeSe.

    PubMed

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

    2016-08-16

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

  13. Ising pairing in superconducting NbSe2 atomic layers

    NASA Astrophysics Data System (ADS)

    Xi, Xiaoxiang; Wang, Zefang; Zhao, Weiwei; Park, Ju-Hyun; Law, Kam Tuen; Berger, Helmuth; Forró, László; Shan, Jie; Mak, Kin Fai

    2016-02-01

    The properties of two-dimensional transition metal dichalcogenides arising from strong spin-orbit interactions and valley-dependent Berry curvature effects have recently attracted considerable interest. Although single-particle and excitonic phenomena related to spin-valley coupling have been extensively studied, the effects of spin-valley coupling on collective quantum phenomena remain less well understood. Here we report the observation of superconducting monolayer NbSe2 with an in-plane upper critical field of more than six times the Pauli paramagnetic limit, by means of magnetotransport measurements. The effect can be interpreted in terms of the competing Zeeman effect and large intrinsic spin-orbit interactions in non-centrosymmetric NbSe2 monolayers, where the electron spin is locked to the out-of-plane direction. Our results provide strong evidence of unconventional Ising pairing protected by spin-momentum locking, and suggest further studies of non-centrosymmetric superconductivity with unique spin and valley degrees of freedom in the two-dimensional limit.

  14. Thermodynamic properties of model CdTe/CdSe mixtures

    SciTech Connect

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

    2015-02-20

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

  15. Thermodynamic properties of model CdTe/CdSe mixtures

    DOE PAGESBeta

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

    2015-02-20

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

  16. Plasmon dynamics in colloidal Cu₂-xSe nanocrystals.

    PubMed

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

    2011-11-01

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

  17. Neutron detection with LiInSe2

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  18. Carrier transport in Bi2Se3 topological insulator slab

    NASA Astrophysics Data System (ADS)

    Gupta, Gaurav; Lin, Hsin; Bansil, Arun; Jalil, Mansoor Bin Abdul; Liang, Gengchiau

    2015-11-01

    Electron transport in Bi2Se3 topological insulator slabs is investigated in the thermal activation regime (>50 K) both in the absence (ballistic) and presence of weak and strong acoustic phonon scattering using the non-equilibrium Green function approach. Resistance of the slab is simulated as a function of temperature for a range of slab thicknesses and effective doping in order to gain a handle on how various factors interact and compete to determine the overall resistance of the slab. If the Bi2Se3 slab is biased at the Dirac point, resistance is found to display an insulating trend even for strong electron-phonon coupling strength. However, when the Fermi-level lies close to the bulk conduction band (heavy electron doping), phonon scattering can dominate and result in a metallic behavior, although the insulating trend is retained in the limit of ballistic transport. Depending on values of the operating parameters, the temperature dependence of the slab is found to exhibit a remarkably complex behavior, which ranges from insulating to metallic, and includes cases where the resistance exhibits a local maximum, much like the contradictory behaviors seen experimentally in various experiments.

  19. Dangling Bond Magnetic Polaron in CdSe nanocrystals

    NASA Astrophysics Data System (ADS)

    Efros, Alexander; Rodina, Anna

    In this work we study theoretically the effect of the spins of the surface dangling bonds on the PL of CdSe nanocrystals (NCs). We show that spins of dangling bonds open new recombination channels for the dark exciton recombination which is connected with flip-flip and flip-flop spin-assisted recombination of the dark exciton. Calculations show that at low temperatures the interaction between dangling bonds and NC excitons leads to the dynamical polarization of the dangling bond spins along the anisotropic axis following by the formation of a dangling bond magnetic polaron. An increase of the temperature, or of the external magnetic field perpendicular to the anisotropic axis, destroys the polaron state. This results in a shift of the transition energy and an increase of its recombination rate. Thus thermal depolarization of the polaron state may explain the small activation energies observed in the temperature dependences of the exciton lifetimes in CdSe NCs. The exchange interaction of the electron spin with spins of the surface dangling bonds explains also radiative recombination of the dark excitons in nanowires, nanorods and nanoplatelets.

  20. Fast uncooled low density FPA of VPD PbSe

    NASA Astrophysics Data System (ADS)

    Vergara, G.; Gutiérrez, R.; Gómez, L. J.; Villamayor, V.; Álvarez, M.; Torquemada, M. C.; Rodrigo, M. T.; Verdú, M.; Sánchez, F. J.; Almazán, R. M.; Plaza del Olmo, J.; Rodríguez, P.; Catalán, I.; Fernández, D.; Heras, A.; Serra-Graells, F.; Margarit, J. M.; Terés, L.; de Arcas, G.; Ruiz, M.; López, J. M.

    2009-05-01

    Polycrystalline PbSe technology is today an emerging technology thanks to the method for processing monolithic detectors based on a Vapor Phase Deposition (VPD) technique developed at CIDA. The first monolithic device was successfully processed in 2007 (16x16 FPA, 200 μm pitch and Digital Pixel Sensor (DPS) concept). Remarkable progress has been made improving some technological steps and developing tools for processing high signal rates. In this work, low resolution IR images taken up to 20 Kfps with a real uncooled device are shown. These results represent an important milestone and allocate the VPD PbSe technology among the major players within the domain of uncooled IR detectors. It is a photonic detector suitable for being used in low cost IR imagers sensitive in the MWIR band and with frame rates above 10,000 Hz. The number of applications is therefore huge, some of them specific, such as sensor for Active Protection Systems or low cost seekers.

  1. Transport studies in topological insulator Bi2Te2Se

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  2. Phonon anharmonicity and negative thermal expansion in SnSe

    DOE PAGESBeta

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

    2016-08-09

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

  3. Linear magnetoresistance in Ag2+δSe thin films

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

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

  4. Chromium Diffusion Doping on ZnSe Crystals

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  5. Ion-implanted epitaxially grown ZnSe

    NASA Technical Reports Server (NTRS)

    Chernow, F.

    1975-01-01

    The use of ZnSe to obtain efficient, short wavelength injection luminescence was investigated. It was proposed that shorter wavelength emission and higher efficiency be achieved by employing a p-i-n diode structure rather than the normal p-n diode structure. The intervening i layer minimizes concentration quenching effects and the donor-acceptor pair states leading to long wavelength emission. The surface p layer was formed by ion implantation; implantation of the i layer rather than the n substrate permits higher, uncompensated p-type doping. An ion implanted p-n junction in ZnSe is efficiency-limited by high electron injection terminating in nonradiative recombination at the front surface, and by low hole injection resulting from the inability to obtain high conductivity p-type surface layers. While the injection ratio in p-n junctions was determined by the radio of majority carrier concentrations, the injection ratio in p-i-n structures was determined by the mobility ratios and/or space charge neutrality requirements in the i layer.

  6. Synthesis and applications of CdSe nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  7. Phonon anharmonicity and negative thermal expansion in SnSe

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  8. Field Emission Characteristics of Polyaniline/Se Nanocomposites.

    PubMed

    Shumaila; Parveen, S; Alam, Masood; Siddiqui, Azher M; Husain, M

    2015-04-01

    Polyaniline (PAni)/Se nanocomposites have been synthesized in different compositions employing chemical route and shown excellent field emission behaviour. Detailed studies on the field emission for all composites with different concentrations of dopant are performed in an indigenously fabricated set up in a vacuum chamber with a base pressure of 10(-6) Torr at room temperature and analysed with current density versus Electric field (J-E) and Fowler-Nordheim (FN) plots. Comparative field emission results showed that 10% (w/w) doped PAni/Se nanocomposite depicts highest emission characteristics, current density and field enhancement factor with turn-on field as low as 1.2 V/µm in comparison with other composites, while pure PAni shows no field emission characteristics. These composites have also been characterized by Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectrometry (FTIR). FTIR results supply the evidence for the occurrence of the polymer in its conducting state. The ease of synthesis route and interesting field emission properties recommend these composites as a promising material for field emission based applications in vacuum micro-nanoelectronic devices and also for plastic display industry. PMID:26353501

  9. Some properties of solid solutions of the TlInSe/sub 2/-TlNdSe/sub 2/

    SciTech Connect

    Godzhaev, E.M.; Rzaeva, K.M.

    1987-05-01

    Solid solutions of the title system are investigated. Schematic diffractograms of the alloys TlIn/sub 1-x/-Nd/sub x/Se/sub 2/ are represented. Tables show the results of indexing the x-ray diffractograms of alloys of the title system. Current-voltage characteristics of the alloys are investigated under static conditions and the variation in the band-gap width was calculated as a function of the composition of the title solution from temperature dependences of the electrical conductivity and Hall effect.

  10. Optical and EPR spectroscopy of Zn:Cr:ZnSe and Zn:Fe:ZnSe crystals

    NASA Astrophysics Data System (ADS)

    Fedorov, V. V.; Konak, T.; Dashdorj, J.; Zvanut, M. E.; Mirov, S. B.

    2014-11-01

    Optical and EPR characterization of Cr and Fe doped ZnSe crystals annealed in Zn vapor revealed a strong bleaching of the divalent state of transition metal ions. Photo induced EPR kinetics were studied in 20-80 K temperature range. Analysis of time-dependent data reveals Cr1+ signal rise time decreases with increasing temperature. The non-exponential decay of Cr1+ concentration were analyzed using Auger-type recombination process. The photoluminescence quantum yield of Cr2+ ions at 5E(D) → 5T2(D) mid-IR transition excited via chromium ionization process was measured to be close to 100%.

  11. Ocean to continent transfer of atmospheric Se as revealed by epiphytic lichens.

    PubMed

    Wen, Hanjie; Carignan, Jean

    2009-10-01

    There is still a long-term debate concerning the relative contributions of naturally emitted and anthropogenic Se at the regional and local scales. Here, Se and heavy metal concentrations are reported for epiphytic lichens collected in coastal and inland areas from the USA, Canada and France for assessing atmospheric Se source. Correlations found between Se and Cl in lichens confirmed the major marine biogenic source for atmospheric Se. Continental samples do not show systematic relationships between Se and other metal (Pb, Cu, In ...) contents, even for lichens collected in the vicinity of smelters or close to urban areas. Our results suggest that, although anthropogenic Se may be present, the marine biogenic Se source is a major contributor to atmospheric Se for our sampling locations. The contribution of naturally emitted atmospheric Se may be significant in urban and industrial areas and should be taken into account for further studies. PMID:19467747

  12. Assimilation of Aerosols from Biomass Burning by the Radiative Transfer Model Brasil-Sr

    NASA Astrophysics Data System (ADS)

    Costa, R. S.; Gonçalves, A. R.; Souza, J. G.; Martins, F. R.; Pereira, E. B.

    2015-12-01

    The radiative transfer model BRASIL-SR is the main tool used by the Earth System Science Centre from the National Institute for Space Research (CCST / INPE) for solar energy resource assessment. Due to large and frequent events of burning biomass in Brazil there is a need to improve the aerosol representation in this model, mainly during the dry season (September - November) in Northern and Central Brazil. The standard aerosol representation in this model is inadequate to capture these events. It is based on the mean monthly climatological horizontal visibility with latitudinal values based on coarse global observation data. To improve the aerosol representation, climatological data of daily horizontal visibility from National Institute of Meteorology (INMET) was used to generate monthly averages from 1999 to 2012. To do a better representation of aerosols from burning biomass events, from megacities aerosol generation, and from transport processes, horizontal visibility estimates performed using aerosol optical thickness at 550 nm data from MACC Project Reanalysis model were used to adjust the aerosol representation in regions were the simple horizontal visibility fails. A methodology to generate these new visibility data from the Reanalysis was made and the resulting data was compared with the average horizontal visibility to implement a new corrected database. The solar irradiation simulated by the model using this new aerosol representation proved to be better than the previous version of the model in all regions with high aerosol loading.

  13. Efficient NiSe-Ni3Se2/Graphene Electrocatalyst in Dye-Sensitized Solar Cells: The Role of Hollow Hybrid Nanostructure.

    PubMed

    Zhang, Xiao; Zhen, Mengmeng; Bai, Jinwu; Jin, Shaowei; Liu, Lu

    2016-07-13

    Hollow and hybrid nanomaterials are excellent electrocatalysts on account of their novel electrocatalytic properties compared with homogeneous solid nanostructures. In this report, NiSe-Ni3Se2 hybrid nanostructure with morphology of hollow hexagonal nanodisk was synthesized in situ on graphene. A series of NiSe-Ni3Se2/RGO with different phase constitutions and nanostructures were obtained by controlling the durations of solvothermal treatment. Because of their unique hollow and hybrid structure, NiSe-Ni3Se2/RGO hollow nanodisks exhibited higher electrocatalytic performance than NiSe/RGO and solid NiSe-Ni3Se2/RGO nanostructure for reducing I3(-) as counter cell (CE) of dye-sensitized solar cells (DSSCs). Additionally, NiSe-Ni3Se2/RGO hollow nanodisks achieved much lower charge transfer resistance (Rct = 0.68 Ω) and higher power conversion efficiency (PCE) (7.87%) than those of Pt (Rct = 1.41 Ω, PCE = 7.28%). PMID:27314283

  14. Facile synthesis of hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure for high performance photodetectors.

    PubMed

    Chen, Shuo; Qiao, Xvsheng; Wang, Fengxia; Luo, Qun; Zhang, Xianghua; Wan, Xia; Xu, Yang; Fan, Xianping

    2016-01-28

    An effective colloidal process involving the hot-injection method is developed to synthesize uniform single-crystalline Sb2Se3 nanorods in high yields. The photoconductive characteristics of the as-synthesized Sb2Se3 nanorods are investigated by developing a film-based photodetector and this device displays a remarkable response to visible light with an "ON/OFF" ratio as high as 50 (with an incident light density of 12.05 mW cm(-2)), short response/recovery times and long-term durability. To overcome the challenge of the intrinsic low electrical conductivity of Sb2Se3, hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure having a type-II band alignment are firstly prepared. The electric current of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film has been significantly increased both in the dark and under light illumination. The responsivity of the photodetector based on the Sb2Se3/AgSbSe2 hybrid nanorod film is about 4.2 times as much as that of the photodetector based on the Sb2Se3 nanorod film. This improvement can be considered as an important step to promote Sb2Se3 based semiconductors for applications in high performance photodetectors. PMID:26743461

  15. Synthesis of CuInSe2 nanoparticles by phase transformation of In2Se3 via wet chemical process in low temperature

    NASA Astrophysics Data System (ADS)

    Li, Shi-na; Ma, Rui-xin; Zhu, Hong-min

    2014-07-01

    Chalcopyrite-type CuInSe2 nanoparticles are successfully prepared by using In2Se3 nanoparticles as a precursor reacted with copper chloride (CuCl) solution via a phase transformation process in low temperature. The reaction time is a key parameter. After the reaction time increasing from 0.5 h to 8 h, In2Se3 and CuCl react with each other gradually via phase transformation into CuInSe2 without any intermediate phase. The crystalline structure and morphology of the CuInSe2 nanoparticles are characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The diameter of CuInSe2 nanoparticles with good dispersibility ranges from 10 nm to 20 nm. The band gap of the CuInSe2 nanoparticles is 1.04 eV calculated from the ultraviolet-visible (UV-VIS) spectrum.

  16. Highly efficient quantum dot-sensitized TiO2 solar cells based on multilayered semiconductors (ZnSe/CdS/CdSe)

    NASA Astrophysics Data System (ADS)

    Yang, Lin; McCue, Connor; Zhang, Qifeng; Uchaker, Evan; Mai, Yaohua; Cao, Guozhong

    2015-02-01

    A new approach by inserting a layer of ZnSe QDs was studied to enhance the adsorption of CdS/CdSe QDs resulting in much improved power conversion efficiency. ZnSe, CdS and CdSe QDs were sequentially assembled on a nanocrystalline TiO2 film to prepare a ZnSe/CdS/CdSe sensitized photoelectrode for QD-sensitized solar cell (QDSSC) applications. The results show that the performance of QDSSCs is strongly dependent on the order of the QDs with respect to TiO2. The pre-assembled ZnSe QD layer acts as a seed layer in the subsequent SILAR process, inducing both the nucleation and growth of CdS QDs, whereas CdS and CdSe QDs have a complementary effect in light harvesting. In the cascade structure of TiO2/ZnSe/CdS/CdSe electrode, a high efficiency of 4.94% and a long electron lifetime of 87.4 ms were achieved, which can be attributed to the following factors: the higher intensity and red shift of light absorption in 400-700 nm range increase the electron concentration in TiO2 substrate sensitized by ZnSe/CdS/CdSe compared to the others, which directly accelerate electron transport in TiO2 and their transfer to FTO glass; the re-organization of energy levels among ZnSe, CdS and CdSe forms a stepwise structure of band-edge levels, which is advantageous to the electron injection and hole recovery of QDs.A new approach by inserting a layer of ZnSe QDs was studied to enhance the adsorption of CdS/CdSe QDs resulting in much improved power conversion efficiency. ZnSe, CdS and CdSe QDs were sequentially assembled on a nanocrystalline TiO2 film to prepare a ZnSe/CdS/CdSe sensitized photoelectrode for QD-sensitized solar cell (QDSSC) applications. The results show that the performance of QDSSCs is strongly dependent on the order of the QDs with respect to TiO2. The pre-assembled ZnSe QD layer acts as a seed layer in the subsequent SILAR process, inducing both the nucleation and growth of CdS QDs, whereas CdS and CdSe QDs have a complementary effect in light harvesting. In the cascade

  17. The influence of Se pressure on the electronic properties of CuInSe{sub 2} grown under Cu-excess

    SciTech Connect

    Deprédurand, Valérie; Bertram, Tobias; Regesch, David; Henx, Benjamin; Siebentritt, Susanne

    2014-10-27

    Standard Cu-poor Cu(In,Ga)Se{sub 2} solar cell absorbers are usually prepared under high Se excess since the electronic properties of the absorbers are better if prepared under high Se pressure. However, in CuInSe{sub 2}, grown under Cu-excess, it was found that solar cell properties improve with lowering the Se pressure, mostly because of reduced tunnel contribution to the recombination path. Lower Se pressure during Cu-rich growth leads to increased (112) texture of the absorber films, to better optical film quality, as seen by increased excitonic luminescence and to lower net doping levels, which explains the reduced tunnelling effect. These findings show an opposite trend from the one observed in Cu-poor Cu(In,Ga)Se{sub 2}.

  18. Photoluminescence study of the substitution of Cd by Zn during the growth by atomic layer epitaxy of alternate CdSe and ZnSe monolayers

    SciTech Connect

    Hernández-Calderón, I.; Salcedo-Reyes, J. C.

    2014-05-15

    We present a study of the substitution of Cd atoms by Zn atoms during the growth of alternate ZnSe and CdSe compound monolayers (ML) by atomic layer epitaxy (ALE) as a function of substrate temperature. Samples contained two quantum wells (QWs), each one made of alternate CdSe and ZnSe monolayers with total thickness of 12 ML but different growth parameters. The QWs were studied by low temperature photoluminescence (PL) spectroscopy. We show that the Cd content of underlying CdSe layers is affected by the exposure of the quantum well film to the Zn flux during the growth of ZnSe monolayers. The amount of Cd of the quantum well film decreases with higher exposures to the Zn flux. A brief discussion about the difficulties to grow the Zn{sub 0.5}Cd{sub 0.5}Se ordered alloy (CuAu-I type) by ALE is presented.

  19. Properties of CuIn{sub 3}Se{sub 5} crystals and In/CuIn{sub 3}Se{sub 5} structures

    SciTech Connect

    Bodnar', I. V. Rud', V. Yu.; Rud', Yu. V.

    2007-11-15

    Using the method of planar crystallization from the melt with deviations from the stoichiometric composition, p-CuIn{sub 3}Se{sub 5} single crystals are grown. The electrical properties of the homogeneous crystals are studied. It is found that the resistivity of the p-CuIn{sub 3}Se{sub 5} crystals depends on the excess Se content in the melt. It is established that the voltaic photosensitivity of the In/CuIn{sub 3}Se{sub 5} structures is enhanced with an increasing excess of Se content in the melt. The energy spectrum and the character of interband transitions in the CuIn{sub 3}Se{sub 5} crystals are discussed. It is concluded that the CuIn{sub 3}Se{sub 5} ternary compound can be used in high efficiency photoelectric converters of solar radiation.

  20. Selenium-mercury interaction during intestinal absorption of /sup 75/Se compounds in chicks

    SciTech Connect

    Mykkaenen, H.M.M.; Metsaeniitty, L.

    1987-08-01

    The effects of inorganic (HgCl/sub 2/) and organic (CH/sub 3/HgCl) mercury on the intestinal absorption of Se compounds (Na/sub 2/(75)SeO/sub 3/, Na/sub 2/(75)SeO4, L-(/sup 75/Se)methionine ((/sup 75/Se)Met)) were determined in 3-wk-old White Leghorn cockerels by the in vivo ligated duodenal loop procedure. The intraduodenal dose contained 0.05 microCi /sup 75/Se, 0.01 mM Se, 150 mM NaCl and 0-1.0 mM Hg. In the presence of 1 mM inorganic Hg in the intraduodenal dose, the absorption of the inorganic /sup 75/Se compounds was only about 65% of that in the control group, whereas only a slight inhibitory effect on (/sup 75/Se)Met absorption was observed. Methylmercury had no effect on (/sup 75/Se)selenite absorption. Precipitation of the /sup 75/Se-selenite in the intestinal lumen partly explained the direct interaction between inorganic Hg and Se compounds. Absorption of (/sup 75/Se)Met and (/sup 75/Se)selenite was also determined in chicks fed after hatching a purified diet supplemented with varying amounts of Hg (0-500 mg/kg) and Se (0-4 mg/kg). Dietary Hg significantly reduced the transfer of (/sup 75/Se)selenite to body by enhancing the accumulation of the isotope in the intestinal tissue. Dietary Hg did not affect the absorption of (/sup 75/Se)Met, but altered the whole-body distribution of this Se compound. Because interaction between Se and Hg was observed mainly between the inorganic compounds and with use of a manyfold excess of Hg over Se, the data suggest that intestinal interaction between these metals is not of great nutritional importance.

  1. Enhancement of superconducting Tc (33 K) by entrapment of FeSe in carbon coated Au-Pd17Se15 nanoparticles.

    PubMed

    Mishra, Sukhada; Song, Kai; Ghosh, Kartik C; Nath, Manashi

    2014-03-25

    FeSe has been an interesting member of the Fe-based superconductor family ever since the discovery of superconductivity in this simple binary chalcogenide. Simplicity of composition and ease of synthesis has made FeSe, in particular, very lucrative as a test system to understand the unconventional nature of superconductivity, especially in low-dimensional models. In this article we report the synthesis of composite nanoparticles containing FeSe nanoislands entrapped within an ent-FeSe-Pd16Se15-Au nanoparticle and sharing an interface with Pd17Se15. This assembly exhibits a significant enhancement in the superconducting Tc (onset at 33 K) accompanied by a noticeable lattice compression of FeSe along the <001> and <101> directions. The Tc in FeSe is very sensitive to application of pressure and it has been shown that with increasing external pressure Tc can be increased almost 4-fold. In these composite nanoparticles reported here, immobilization of FeSe on the Pd17Se15 surface contributes to increasing the effect of interfacial pressure, thereby enhancing the Tc. The effect of interfacial pressure is also manifested in the contraction of the FeSe lattice (up to 3.8% in <001> direction) as observed through extensive high-resolution TEM imaging. The confined FeSe in these nanoparticles occupied a region of approximately 15-25 nm, where lattice compression was uniform over the entire FeSe region, thereby maximizing its effect in enhancing the Tc. The nanoparticles have been synthesized by a simple catalyst-aided vapor transport reaction at 800 °C where iron acetylacetonate and Se were used as precursors. Morphology and composition of these nanoparticles have been studied in details through extensive electron microscopy. PMID:24494773

  2. Managing flow, sediment, and hydropower regimes in the Sre Pok, Se San, and Se Kong Rivers of the Mekong basin

    NASA Astrophysics Data System (ADS)

    Wild, Thomas B.; Loucks, Daniel P.

    2014-06-01

    The Lancang/Mekong River Basin is presently undergoing a period of rapid hydropower development. In its natural undeveloped state, the river transports about 160 million metric tons of sediment per year, maintaining the geomorphologic features of the basin, sustaining habitats, and transporting the nutrients that support ecosystem productivity. Despite the importance of sediment in the river, currently little attention is being paid to reservoir sediment trapping. This study is devoted to assessing the potential for managing sediment and its impact on energy production in the Se San, Sre Pok, and Se Kong tributaries of the Mekong River. These tributaries drain a set of adjacent watersheds that are important with respect to biodiversity and ecological productivity, and serve as a significant source of flow and sediment to the mainstream Mekong River. A daily sediment transport model is used to assess tradeoffs among energy production and sediment and flow regime alteration in multiple reservoir systems. This study finds that eventually about 40%-80% of the annual suspended sediment load may be trapped in reservoirs. Clearly, these reservoirs will affect the rivers' sediment regimes. However, even after 100 years of simulated sedimentation, reservoir storage capacities and hydropower production at most reservoir sites are not significantly reduced. This suggests that the strongest motivation for implementing measures to reduce trapped sediment is their impact not on hydropower production but on fish migration and survival and on sediment-dependent ecosystems such as the Vietnam Delta and Cambodia's Tonle Sap Lake.

  3. Patterning two-dimensional chalcogenide crystals of Bi2Se3 and In2Se3 and efficient photodetectors.

    PubMed

    Zheng, Wenshan; Xie, Tian; Zhou, Yu; Chen, Y L; Jiang, Wei; Zhao, Shuli; Wu, Jinxiong; Jing, Yumei; Wu, Yue; Chen, Guanchu; Guo, Yunfan; Yin, Jianbo; Huang, Shaoyun; Xu, H Q; Liu, Zhongfan; Peng, Hailin

    2015-01-01

    Patterning of high-quality two-dimensional chalcogenide crystals with unique planar structures and various fascinating electronic properties offers great potential for batch fabrication and integration of electronic and optoelectronic devices. However, it remains a challenge that requires accurate control of the crystallization, thickness, position, orientation and layout. Here we develop a method that combines microintaglio printing with van der Waals epitaxy to efficiently pattern various single-crystal two-dimensional chalcogenides onto transparent insulating mica substrates. Using this approach, we have patterned large-area arrays of two-dimensional single-crystal Bi2Se3 topological insulator with a record high Hall mobility of ∼1,750 cm(2) V(-1) s(-1) at room temperature. Furthermore, our patterned two-dimensional In2Se3 crystal arrays have been integrated and packaged to flexible photodetectors, yielding an ultrahigh external photoresponsivity of ∼1,650 A W(-1) at 633 nm. The facile patterning, integration and packaging of high-quality two-dimensional chalcogenide crystals hold promise for innovations of next-generation photodetector arrays, wearable electronics and integrated optoelectronic circuits. PMID:25898022

  4. Patterning two-dimensional chalcogenide crystals of Bi2Se3 and In2Se3 and efficient photodetectors

    NASA Astrophysics Data System (ADS)

    Zheng, Wenshan; Xie, Tian; Zhou, Yu; Chen, Y. L.; Jiang, Wei; Zhao, Shuli; Wu, Jinxiong; Jing, Yumei; Wu, Yue; Chen, Guanchu; Guo, Yunfan; Yin, Jianbo; Huang, Shaoyun; Xu, H. Q.; Liu, Zhongfan; Peng, Hailin

    2015-04-01

    Patterning of high-quality two-dimensional chalcogenide crystals with unique planar structures and various fascinating electronic properties offers great potential for batch fabrication and integration of electronic and optoelectronic devices. However, it remains a challenge that requires accurate control of the crystallization, thickness, position, orientation and layout. Here we develop a method that combines microintaglio printing with van der Waals epitaxy to efficiently pattern various single-crystal two-dimensional chalcogenides onto transparent insulating mica substrates. Using this approach, we have patterned large-area arrays of two-dimensional single-crystal Bi2Se3 topological insulator with a record high Hall mobility of ~1,750 cm2 V-1 s-1 at room temperature. Furthermore, our patterned two-dimensional In2Se3 crystal arrays have been integrated and packaged to flexible photodetectors, yielding an ultrahigh external photoresponsivity of ~1,650 A W-1 at 633 nm. The facile patterning, integration and packaging of high-quality two-dimensional chalcogenide crystals hold promise for innovations of next-generation photodetector arrays, wearable electronics and integrated optoelectronic circuits.

  5. Patterning two-dimensional chalcogenide crystals of Bi2Se3 and In2Se3 and efficient photodetectors

    PubMed Central

    Zheng, Wenshan; Xie, Tian; Zhou, Yu; Chen, Y.L.; Jiang, Wei; Zhao, Shuli; Wu, Jinxiong; Jing, Yumei; Wu, Yue; Chen, Guanchu; Guo, Yunfan; Yin, Jianbo; Huang, Shaoyun; Xu, H.Q.; Liu, Zhongfan; Peng, Hailin

    2015-01-01

    Patterning of high-quality two-dimensional chalcogenide crystals with unique planar structures and various fascinating electronic properties offers great potential for batch fabrication and integration of electronic and optoelectronic devices. However, it remains a challenge that requires accurate control of the crystallization, thickness, position, orientation and layout. Here we develop a method that combines microintaglio printing with van der Waals epitaxy to efficiently pattern various single-crystal two-dimensional chalcogenides onto transparent insulating mica substrates. Using this approach, we have patterned large-area arrays of two-dimensional single-crystal Bi2Se3 topological insulator with a record high Hall mobility of ∼1,750 cm2 V−1 s−1 at room temperature. Furthermore, our patterned two-dimensional In2Se3 crystal arrays have been integrated and packaged to flexible photodetectors, yielding an ultrahigh external photoresponsivity of ∼1,650 A W−1 at 633 nm. The facile patterning, integration and packaging of high-quality two-dimensional chalcogenide crystals hold promise for innovations of next-generation photodetector arrays, wearable electronics and integrated optoelectronic circuits. PMID:25898022

  6. Short-range CDW correlations in CoxNbSe2 and MnxNbSe2

    NASA Astrophysics Data System (ADS)

    Lee, J.; di Capua, R.; Karapetrov, G.; Nishizaki, T.; Kobayashi, N.; Iavarone, M.

    2013-03-01

    Scanning tunneling microscopy and transport measurements were performed on NbSe2 and Co- and Mn-intercalated NbSe2 single crystals, to address the effect of disorder induced on the CDW structure by the effect of intercalation. We find that the CDW transition at TCDW=33 K in the pure compound is accompanied by a small anomaly in resistivity, a strong non linearity of the Hall effect, with a sign reversal occurring at CDW transition, and high magnetoresistance in agreement with previous reports. The system remains metallic below the CDW transition. Upon increase of disorder the anomaly in resistivity moves at a lower temperature and eventually disappears for higher doping levels. By increasing the disorder also the magnetoresistance decreases and the Hall effect does not show any sign reversal. STM measurements on a pure sample reveal that CDW phase is long-range ordered below TCDW. For doped samples short range CDW correlations dominate a large part of the phase diagram.

  7. Magnetooptical study of CdSe/ZnMnSe semimagnetic quantum-dot ensembles with n-type modulation doping

    SciTech Connect

    Reshina, I. I. Ivanov, S. V.

    2014-12-15

    Magnetic and polarization investigations of the photoluminescence and resonant electron spin-flip Raman scattering in ensembles of self-organized CdSe/ZnMnSe semimagnetic quantum dots with n-type modulation doping are carried out. It is demonstrated that exciton transitions contribute to the photoluminescence band intensity, along with the transitions of trions in the singlet state. In the Hanle-effect measurements, negative circular polarization in zero magnetic field is observed, which is related to the optical orientation of a trion heavy hole. The lifetime and spin-relaxation time of a heavy hole are estimated as ≤3 and ≤1 ps, respectively. Such short times are assumed to be due to Auger recombination with the excitation of an intrinsic transition in a Mn{sup 2+} ion. Investigations of the photoluminescence-maximum intensity and shift in a longitudinal magnetic field at the σ{sup −}σ{sup +} and σ{sup −}σ{sup −} polarizations reveal the pronounced spin polarization of electrons. Under resonant excitation conditions, a sharp increase in the photoluminescence-band maximum intensity at σ{sup −} excitation polarization over the σ{sup +} one is observed. The Raman scattering peak at the electron spin-flip transition is observed upon resonant excitation in a transverse magnetic field in crossed linear polarizations. This peak is shown to be a Brillouin function of a magnetic field.

  8. Calorimetric study of tellurium rich Se-Te-Sn glasses

    NASA Astrophysics Data System (ADS)

    Heera, Pawan; Kumar, Anup; Jharwal, Manish; Sharma, Raman

    2016-05-01

    We report the calorimetric study of amorphous Se30Te70-x Snx alloys for x= 0, 1.5, 2.5, 4.5 in terms of kinetic parameters. The DSC curves recorded at four different heating rates are analyzed to determine the transition temperatures, activation energy, thermal stability, glass forming ability. The crystallization process has been investigated using Kissinger, Matusita, Augis and Bennett, and Gao and Wang models. Various kinetic parameters have been calculated for a better understanding of the growth mechanism. The glass transition temperatures Tg, onset crystallization Tc, peak crystallization Tp, and melting temperature Tm are found to increase with the increase in Sn content. The system under investigation is found to be thermally stable for at lower at% of Sn. The values of parameters HR, Hw, and S indicate that Glass forming ability (GFA) decays with an increase in Sn content.

  9. Low Temperature Thermoelectric Characterization of Ag2Se

    NASA Astrophysics Data System (ADS)

    Drymiotis, Fivos; Neff, David; Coney, Michael; Bux, Sabah; Fleurial, Jean-Pierre

    Previous work on Ag2Se showed that this n-type material could have a dimensionless thermoelectric figure of merit (zT) ~1 at room temperature, due to its high mobility and low thermal conductivity. However, the results from the initial reports have not yet been reproduced. In this talk, I will summarize our efforts to replicate the aforementioned thermoelectric performance, and also discuss the experimental setup that we utilized in order to perform the low-temperature thermoelectric characterization of this material. This work was performed at the California Institute of Technology/Jet Propulsion Laboratory under contract with the National Aeronautics and Space Administration. This work was supported by JPL's Research and Technology Development Program.

  10. Investigations on the structure of Pb-Ge-Se glasses

    NASA Astrophysics Data System (ADS)

    Kalra, G.; Upadhyay, M.; Sharma, Y.; Abhaya, S.; Murugavel, S.; Amarendra, G.

    2016-05-01

    Chalcogenide glasses have attracted much attention because of their potential application in various solid state devices. In the present work, we report here the detailed thermal, structural, microstructural studies on PbxGe42-xSe58 with (0 ≤ x ≤ 20) glasses. The influence of Pb content on the glass transition temperature, specific heat, and non-reversing enthalphy is observed and discussed qualitatively The Raman spectroscopic studies on the all the glass compositions are carried out and deconvoluted into different structural units. The positron annihilation life-time spectroscopy (PALS) studies helped to understand the nature of defect states present in the glassy system and its variation with Pb content. The concentration of charged defect centers is found to increase, whereas the open volume defect concentration decreases with Pb content in these glasses.

  11. Fermi surface reconstruction in FeSe under high pressure

    NASA Astrophysics Data System (ADS)

    Terashima, Taichi; Kikugawa, Naoki; Kiswandhi, Andhika; Graf, David; Choi, Eun-Sang; Brooks, James S.; Kasahara, Shigeru; Watashige, Tatsuya; Matsuda, Yuji; Shibauchi, Takasada; Wolf, Thomas; Böhmer, Anna E.; Hardy, Frédéric; Meingast, Christoph; Löhneysen, Hilbert v.; Uji, Shinya

    2016-03-01

    We report Shubnikov-de Haas (SdH) oscillation measurements on FeSe under high pressure up to P =16.1 kbar. We find a sudden change in SdH oscillations at the onset of the pressure-induced antiferromagnetism at P ˜8 kbar. We argue that this change can be attributed to a reconstruction of the Fermi surface by the antiferromagnetic order. The negative d Tc /d P observed in a range between P ˜8 and 12 kbar may be explained by the reduction in the density of states due to the reconstruction. The ratio of the transition temperature to the effective Fermi energy remains high under high pressure: kBTc/EF˜0.1 even at P =16.1 kbar.

  12. Stress-optic coefficients of ZnSe.

    PubMed

    Goldstein, L F; Thompson, J S; Schroeder, J B; Slattery, J E

    1975-10-01

    The stress-optic coefficients of ZnSe have been measured at room temperature; Twyman-Green and Fizeau interferometers were used in conjunction with a four-point loading device. Test specimens were rectangular parallelepipeds of chemically vapor-deposited material prepared by Raytheon Corporation. Measurements were made with the optical propagation parallel to the deposition direction, and optical scanning and computer analysis were employed to determine fringe positions to an accuracy of better than 0.01 of a fringe spacing. The experimental values for pi(11) and pi(12) are -1.48 +/- 0.05 x 10(-12) m(2)/N and +0.22 +/- 0.05 x 10(-12) m(2)/N, respectively. PMID:20155036

  13. Laser modulation of optical absorption in ZnSe

    NASA Technical Reports Server (NTRS)

    Major, R. W.

    1971-01-01

    The possibility of producing and detecting laser induced modulation of absorption (LIMA) in ZnSe crystals using a moderate laser intensity of about 6 mw output was investigated. The modulation is smaller than that previously obtained with higher laser photon flux, but is not too difficult to detect. Modulation of the order of a few parts in 10 to the 5th power, up to one part in 10 to the 4th power appears typical at the present. LIMA pulse shapes were recorded with varying system resolutions at a half dozen wavelengths in the visible, from 4800 A to 6000 A. Detailed data were taken, particularly at 5000 A, for a range of time intervals following laser pulse turn-on. Quantitative study of the excitation and decay kinetics of these is underway, though analysis is not complete. Major features are discussed with attention centered upon the detailed measurements made most recently at 5000 A.

  14. Band Bending Inversion in Bi2Se3 Nanostructures.

    PubMed

    Veyrat, Louis; Iacovella, Fabrice; Dufouleur, Joseph; Nowka, Christian; Funke, Hannes; Yang, Ming; Escoffier, Walter; Goiran, Michel; Eichler, Barbara; Schmidt, Oliver G; Büchner, Bernd; Hampel, Silke; Giraud, Romain

    2015-11-11

    Shubnikov-de Haas oscillations were studied under high magnetic field in Bi2Se3 nanostructures grown by chemical vapor transport, for different bulk carrier densities ranging from 3 × 10(19) cm(-3) to 6 × 10(17) cm(-3). The contribution of topological surface states to electrical transport can be identified and separated from bulk carriers and massive two-dimensional electron gas. Band bending is investigated, and a crossover from upward to downward band bending is found at low bulk density as a result of a competition between bulk and interface doping. These results highlight the need to control electrical doping both in the bulk and at interfaces in order to study only topological surface states. PMID:26479681

  15. Enchanced methods of hydrophilized CdSe quantum dots synthesis

    NASA Astrophysics Data System (ADS)

    Potapkin, D. V.; Zharkova, I. S.; Goryacheva, I. Y.

    2015-03-01

    Quantum dots are bright and stable fluorescence signal sources, but for most of applications they need an additional hydrophilization step. Unfortunately, most of existing approaches lead to QD's fluorescence quenching, so there is a need for additional enhancing of hydrophilized QD's brightness like UV irradiation, which can be used both on water insoluble QD's with oleic acid ligands (in toluene) and on hydrophilized QD's covered with UV-stable polymer (in aqueous solution). For synthesis of bright water-soluble fluorescent labels CdSe/CdS/ZnS colloidal quantum dots were covered with PAMAM dendrimer and irradiated with UV lamp in quartz cuvettes for 3 hours at the room temperature and then compared with control sample.

  16. Fluorescence quenching of CdSe quantum dots on graphene

    SciTech Connect

    Guo, Xi Tao; Hua Ni, Zhen Yan Nan, Hai; Hui Wang, Wen; Yan Liao, Chun; Zhang, Yan; Wei Zhao, Wei

    2013-11-11

    We studied systematically the fluorescence quenching of CdSe quantum dots (QDs) on graphene and its multilayers, as well as graphene oxide (GO) and reduced graphene oxide (rGO). Raman intensity of QDs was used as a quantitatively measurement of its concentration in order to achieve a reliable quenching factor (QF). It was found that the QF of graphene (∼13.1) and its multilayers is much larger than rGO (∼4.4), while GO (∼1.5) has the lowest quenching efficiency, which suggests that the graphitic structure is an important factor for quenching the fluorescence of QDs. It was also revealed that the QF of graphene is not strongly dependent on its thicknesses.

  17. Structural and transport properties of CdSe nanorods

    SciTech Connect

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

    2015-06-24

    The nanorods of cadmium selenide (CdSe) have been synthesized by soft chemical route. The selected area electron diffraction pattern, high resolution TEM and X-ray diffraction pattern indicate the cubic structure of the sample. The band gap of the sample is obtained using Tauc relation to UV-visible spectrum and found to be 1.92 eV. 1{sup st} order and 2{sup nd} order Raman bands are followed to investigate the behaviour of the phonon modes of the materials which is considered to be important to predict the potential of the material to microwave applications. Thermal behaviour of the sample is investigated using differential scanning calorimeter. Kissinger equation is used to calculate the activation energy of the sample, which is found to be 1.67 eV.

  18. Exciton Fine Structure in Single CdSe Nanorods

    NASA Astrophysics Data System (ADS)

    Le Thomas, N.; Herz, E.; Schöps, O.; Woggon, U.; Artemyev, M. V.

    2005-01-01

    We study the optical properties of excitons in one-dimensional (1D) nanostructures at low temperatures. In single CdSe/ZnS core-shell nanorods we observe a fine structure splitting and explain it by exchange interaction. Two peaks are observed with different degrees of linear polarization of DLP<0.85 and DLP>0.95. For small nanorod radii R≤aB/2, an increase in the photoluminescence decay time is found when the temperature increases from 10 to 80K. The observations are explained by a radius-dependent change in the symmetry of the 1D-exciton ground state which transforms from a dark state into bright states below a critical radius of Rcrit≈3.7 nm.

  19. S-wave velocity structure in the SE Tibetan plateau

    NASA Astrophysics Data System (ADS)

    Cai, Yan; Wu, Jianping; Wang, Weilai; Fang, Lihua; Fan, Liping

    2016-05-01

    We use observations recorded by 23 permanent and 99 temporary stations in the SE Tibetan plateau to obtain the S-wave velocity structure along two profiles by applying joint inversion with receiver functions and surface waves. The two profiles cross West Yunnan block (WYB), the Central Yunnan sub-block (CYB), South China block (SCB), and Nanpanjiang basin (NPB). The profile at ~25°N shows that the Moho interface in the CYB is deeper than those in the WYB and the NPB, and the topography and Moho depth have clear correspondence. Beneath the Xiaojiang fault zone (XJF), there exists a crustal low-velocity zone (LVZ), crossing the XJF and expanding eastward into the SCB. The NPB is shown to be of relatively high velocity. We speculate that the eastward extrusion of the Tibetan plateau may pass through the XJF and affect its eastern region, and is resisted by the rigid NPB, which has high velocity. This may be the main cause of the crustal thickening and uplift of the topography. In the Tengchong volcanic area, the crust is shown to have alternate high- and low-velocity layers, and the upper mantle is shown to be of low velocity. We consider that the magma which exists in the crust is from the upper mantle and that the complex crustal velocity structure is related to magmatic differentiation. Between the Tengchong volcanic area and the XJF, the crustal velocity is relatively high. Combining these observations with other geophysical evidence, it is indicated that rock strength is high and deformation is weak in this area, which is why the level of seismicity is quite low. The profile at ~23°N shows that the variation of the Moho depth is small from the eastern rigid block to the western active block with a wide range of LVZs. We consider that deformation to the south of the SE Tibetan Plateau is weak.

  20. S-wave velocity structure in the SE Tibetan plateau

    NASA Astrophysics Data System (ADS)

    Cai, Yan; Wu, Jianping; Wang, Weilai; Fang, Lihua; Fan, Liping

    2016-06-01

    We use observations recorded by 23 permanent and 99 temporary stations in the SE Tibetan plateau to obtain the S-wave velocity structure along two profiles by applying joint inversion with receiver functions and surface waves. The two profiles cross West Yunnan block (WYB), the Central Yunnan sub-block (CYB), South China block (SCB), and Nanpanjiang basin (NPB). The profile at ~25°N shows that the Moho interface in the CYB is deeper than those in the WYB and the NPB, and the topography and Moho depth have clear correspondence. Beneath the Xiaojiang fault zone (XJF), there exists a crustal low-velocity zone (LVZ), crossing the XJF and expanding eastward into the SCB. The NPB is shown to be of relatively high velocity. We speculate that the eastward extrusion of the Tibetan plateau may pass through the XJF and affect its eastern region, and is resisted by the rigid NPB, which has high velocity. This may be the main cause of the crustal thickening and uplift of the topography. In the Tengchong volcanic area, the crust is shown to have alternate high- and low-velocity layers, and the upper mantle is shown to be of low velocity. We consider that the magma which exists in the crust is from the upper mantle and that the complex crustal velocity structure is related to magmatic differentiation. Between the Tengchong volcanic area and the XJF, the crustal velocity is relatively high. Combining these observations with other geophysical evidence, it is indicated that rock strength is high and deformation is weak in this area, which is why the level of seismicity is quite low. The profile at ~23°N shows that the variation of the Moho depth is small from the eastern rigid block to the western active block with a wide range of LVZs. We consider that deformation to the south of the SE Tibetan Plateau is weak.

  1. Synthesis, structural, optical and Raman studies of pure and lanthanum doped ZnSe nanoparticles

    SciTech Connect

    Kumar, Pushpendra; Singh, Jai; Pandey, Mukesh Kumar; Jeyanthi, C.E.; Siddheswaran, R.; Paulraj, M.; Hui, K.N.; Hui, K.S.

    2014-01-01

    Graphical abstract: - Highlights: • Template-free synthesis of ZnSe and ZnSe:La nanoparticles was developed at low temperature 100 °C. • Cubic ZnSe and ZnSe:La nanoparticles were obtained by chemical route. • As-synthesized ZnSe:La nanoparticles showed higher emission intensity than ZnSe nanoparticles. • Band gap (E{sub g}) of ZnSe nanoparticles was bigger than ZnSe nanoparticles due to nanosized effect. - Abstract: In this work, a simple, effective and reproducible chemical synthetic route for the production of high-quality, pure ZnSe nanoparticles (NPs), and lanthanum-doped ZnSe (ZnSe:La) NPs is presented. The wide bandgap, luminescent pure ZnSe and ZnSe:La NPs has been synthesized at a low temperature (100 °C) in a single template-free step. The size and optical bandgap of the NPs was analyzed from powder X-ray diffraction (XRD), UV–visible (UV–vis) spectroscopy, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). A broad photoluminescence (PL) emission across the visible spectrum has been demonstrated by a systematic blue-shift in emission due to the formation of small nanoparticles. Here, contribution to emission intensity from surface states of NPs increases with La doping. TEM data revealed that the average size of ZnSe and ZnSe:La NPs is 14 and 8 nm, respectively. On the other hand, band gap energy E{sub g} of ZnSe and ZnSe:La NPs were found to be 3.59 eV and 3.65 eV, respectively. Results showed that hydrazine hydrate played multiple roles in the formation of ZnSe and ZnSe:La NPs. A possible reaction mechanism for the growth of NPs is also discussed.

  2. Relation of Anxiety and Depressive Symptoms to Coronary Artery Calcium (from the ELSA-Brasil Baseline Data).

    PubMed

    Santos, Itamar S; Bittencourt, Marcio S; Rocco, Priscila T; Pereira, Alexandre C; Barreto, Sandhi M; Brunoni, André R; Goulart, Alessandra C; Blaha, Michael J; Lotufo, Paulo A; Bensenor, Isabela M

    2016-07-15

    Previous studies of the association between symptoms of anxiety or depression and coronary artery calcium (CAC) have produced heterogeneous results. Our aim was to investigate whether psychopathological symptoms were associated with CAC in a cross-sectional analysis of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) baseline. We analyzed data from 4,279 ELSA-Brasil subjects (aged 35 to 74 years) from the São Paulo site without previous cardiovascular disease who underwent CAC score assessment at baseline. Prevalent CAC was defined as a CAC score >0. Anxiety and depressive symptoms were assessed using the Clinical Interview Schedule-Revised (CIS-R). We built binary logistic regression models to determine whether CIS-R scores, anxiety, or depression were associated with prevalent CAC. Prevalent CAC was found in 1,211 subjects (28.3%). After adjustment for age and gender, a direct association between CIS-R scores and prevalent CAC was revealed (odds ratio for 1-SD increase: 1.12; 95% confidence interval [CI] 1.04 to 1.22). This association persisted after multivariate adjustment (odds ratio for 1-SD increase 1.11; 95% CI 1.02 to 1.20). No independent associations were found for specific diagnoses of anxiety or depression and prevalent CAC. In post hoc models, a significant interaction term (p = 0.019) suggested a stronger association in older subjects. In conclusion, psychopathological symptoms were directly associated with coronary atherosclerosis in the ELSA-Brasil baseline in adjusted models, and this association seems to be stronger in older subjects. PMID:27236256

  3. Effective mRNA Inhibition in PANC-1 Cells in Vitro Mediated via an mPEG-SeSe-PEI Delivery System.

    PubMed

    Zhang, Yuefeng; Yang, Bin; Liu, Yajie; Qin, Wenjie; Li, Chao; Wang, Lantian; Zheng, Wen; Wu, Yulian

    2016-05-01

    RNA interference (RNAi)-mediated gene therapy is a promising approach to cure various diseases. However, developing an effective, safe, specific RNAi delivery system remains a major challenge. In this study, a novel redox-responsive polyetherimide (PEI)-based nanovector, mPEG-SeSe-PEI, was developed and its efficacy evaluated. We prepared three mPEG-SeSe-PEI vector candidates for small interfering glyceraldehyde-3-phosphate dehydrogenase (siGADPH) and determined their physiochemical properties and transfection efficiency using flow cytometry and PEG11.6-SeSe-PEI polymer. We investigated the silencing efficacy of GADPH mRNA expression in PANC-1 cells and observed that PEG11.6-SeSe-PEI/siGADPH (N/P ratio=10) polyplexes possessed the appropriate size and zeta-potential and exhibited excellent in vitro gene silencing effects with the least cytotoxicity in PANC-1 cells. In conclusion, we present PEG11.6-SeSe-PEI as a potential therapeutic gene delivery system for small interfering RNA (siRNA). PMID:26948169

  4. Resonant Levels, Vacancies, and Doping in Bi2Te3, Bi2Te2Se, and Bi2Se3 Tetradymites

    NASA Astrophysics Data System (ADS)

    Wiendlocha, Bartlomiej

    2016-07-01

    The electronic structure of the tetradymites, Bi_2Te_3, Bi_2Te_2Se, and Bi_2Se_3, containing various dopants and vacancies, has been studied using first-principles calculations. We focus on the possibility of formation of resonant levels (RL), confirming the formation of RL by Sn in Bi_2Te_3 and predicting similar behavior of Sn in Bi_2Te_2Se and Bi_2Se_3. Vacancies, which are likely present on chalcogen atom sites in real samples of Bi_2Te_2Se and Bi_2Se_3, are also studied and their charged donor and resonant behavior discussed. Doping of vacancy-containing materials with regular acceptors, such as Ca or Mg, is shown to compensate the donor effect of vacancies, and n-p crossover, while increasing the dopant concentration, is observed. We verify that the RL on Sn is not disturbed by chalcogen vacancies in Bi_2Te_2Se or Bi_2Se_3, and for the Sn-doped materials with Se or Te vacancies, double doping, instead of heavy doping with Sn, is suggested as an effective way of obtaining the resonant level. This should help to avoid smearing of the RL, a possible reason for earlier unsuccessful experimental observation of the influence of the RL on the thermoelectric properties of Sn-doped Bi_2Te_2Se. Finally, we show that Al and Ga are possible new resonant impurities in tetradymites, hoping that this will stimulate further experimental studies.

  5. Resonant Levels, Vacancies, and Doping in Bi2Te3, Bi2Te2Se, and Bi2Se3 Tetradymites

    NASA Astrophysics Data System (ADS)

    Wiendlocha, Bartlomiej

    2016-04-01

    The electronic structure of the tetradymites, Bi_2 Te_3 , Bi_2 Te_2 Se, and Bi_2 Se_3 , containing various dopants and vacancies, has been studied using first-principles calculations. We focus on the possibility of formation of resonant levels (RL), confirming the formation of RL by Sn in Bi_2 Te_3 and predicting similar behavior of Sn in Bi_2 Te_2 Se and Bi_2 Se_3 . Vacancies, which are likely present on chalcogen atom sites in real samples of Bi_2 Te_2 Se and Bi_2 Se_3 , are also studied and their charged donor and resonant behavior discussed. Doping of vacancy-containing materials with regular acceptors, such as Ca or Mg, is shown to compensate the donor effect of vacancies, and n-p crossover, while increasing the dopant concentration, is observed. We verify that the RL on Sn is not disturbed by chalcogen vacancies in Bi_2 Te_2 Se or Bi_2 Se_3 , and for the Sn-doped materials with Se or Te vacancies, double doping, instead of heavy doping with Sn, is suggested as an effective way of obtaining the resonant level. This should help to avoid smearing of the RL, a possible reason for earlier unsuccessful experimental observation of the influence of the RL on the thermoelectric properties of Sn-doped Bi_2 Te_2 Se. Finally, we show that Al and Ga are possible new resonant impurities in tetradymites, hoping that this will stimulate further experimental studies.

  6. High-quality, large-area MoSe2 and MoSe2/Bi2Se3 heterostructures on AlN(0001)/Si(111) substrates by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Xenogiannopoulou, E.; Tsipas, P.; Aretouli, K. E.; Tsoutsou, D.; Giamini, S. A.; Bazioti, C.; Dimitrakopulos, G. P.; Komninou, Ph.; Brems, S.; Huyghebaert, C.; Radu, I. P.; Dimoulas, A.

    2015-04-01

    Atomically-thin, inherently 2D semiconductors offer thickness scaling of nanoelectronic devices and excellent response to light for low-power versatile applications. Using small exfoliated flakes, advanced devices and integrated circuits have already been realized, showing great potential to impact nanoelectronics. Here, high-quality single-crystal MoSe2 is grown by molecular beam epitaxy on AlN(0001)/Si(111), showing the potential for scaling up growth to low-cost, large-area substrates for mass production. The MoSe2 layers are epitaxially aligned with the aluminum nitride (AlN) lattice, showing a uniform, smooth surface and interfaces with no reaction or intermixing, and with sufficiently high band offsets. High-quality single-layer MoSe2 is obtained, with a direct gap evidenced by angle-resolved photoemission spectroscopy and further confirmed by Raman and intense room temperature photoluminescence. The successful growth of high-quality MoSe2/Bi2Se3 multilayers on AlN shows promise for novel devices exploiting the non-trivial topological properties of Bi2Se3.Atomically-thin, inherently 2D semiconductors offer thickness scaling of nanoelectronic devices and excellent response to light for low-power versatile applications. Using small exfoliated flakes, advanced devices and integrated circuits have already been realized, showing great potential to impact nanoelectronics. Here, high-quality single-crystal MoSe2 is grown by molecular beam epitaxy on AlN(0001)/Si(111), showing the potential for scaling up growth to low-cost, large-area substrates for mass production. The MoSe2 layers are epitaxially aligned with the aluminum nitride (AlN) lattice, showing a uniform, smooth surface and interfaces with no reaction or intermixing, and with sufficiently high band offsets. High-quality single-layer MoSe2 is obtained, with a direct gap evidenced by angle-resolved photoemission spectroscopy and further confirmed by Raman and intense room temperature photoluminescence. The

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

    SciTech Connect

    Trump, Benjamin A.; Livi, Kenneth J.T.; McQueen, Tyrel M.

    2014-01-15

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

  8. Detection of a MoSe{sub 2} secondary phase layer in CZTSe by spectroscopic ellipsometry

    SciTech Connect

    Demircioğlu, Özden; Riedel, Ingo; Gütay, Levent; Mousel, Marina; Redinger, Alex; Rey, Germain; Weiss, Thomas; Siebentritt, Susanne

    2015-11-14

    We demonstrate the application of Spectroscopic Ellipsometry (SE) for identification of secondary phase MoSe{sub 2} in polycrystalline Cu{sub 2}ZnSnSe{sub 4} (CZTSe) samples. A MoSe{sub 2} reference sample was analyzed, and its optical constants (ε{sub 1} and ε{sub 2}) were extracted by SE analysis. This dataset was implemented into an optical model for analyzing SE data from a glass/Mo/CZTSe sample containing MoSe{sub 2} at the back side of the absorber. We present results on the n and k values of CZTSe and show the extraction of the thickness of the secondary phase MoSe{sub 2} layer. Raman spectroscopy and scanning electron microscopy were applied to confirm the SE results.

  9. Tuning the emission of aqueous Cu:ZnSe quantum dots to yellow light window

    NASA Astrophysics Data System (ADS)

    Wang, Chunlei; Hu, Zhiyang; Xu, Shuhong; Wang, Yanbin; Zhao, Zengxia; Wang, Zhuyuan; Cui, Yiping

    2015-07-01

    Synthesis of internally doped Cu:ZnSe QDs in an aqueous solution still suffers from narrow tunable emissions from the blue to green light window. In this work, we extended the emission window of aqueous Cu:ZnSe QDs to the yellow light window. Our results show that high solution pH, multiple injections of Zn precursors, and nucleation doping strategy are three key factors for preparing yellow emitted Cu:ZnSe QDs. All these factors can depress the reactivity of CuSe nuclei and Zn monomers, promoting ZnSe growth outside CuSe nuclei rather than form ZnSe nuclei separately. With increased ZnSe QD size, the conduction band and nearby trap state energy levels shift to higher energy sites, causing Cu:ZnSe QDs to have a much longer emission.

  10. Comparing the anomalous phonons in Fe(Te,Se) and (Fe,Ni)(Te,Se) via neutron scattering

    NASA Astrophysics Data System (ADS)

    Schneeloch, John; Xu, Zhijun; Gu, Genda; Zaliznyak, Igor; Winn, Barry; Rodriguez-Rivera, Jose; Birgeneau, Robert; Xu, Guangyong; Tranquada, John

    We studied the anomalous acoustic-type phonons in the Fe(Te,Se) iron-based superconductor family that arise from the (100) Bragg peak, which is forbidden according to the reported crystal structure for these materials. Inelastic neutron scattering was performed on superconducting and non-superconducting crystals of various compositions. The (100) phonons were much weaker in a non-superconducting nickel-doped crystal than in a superconducting crystal with similar selenium fraction, but comparison with another non-superconducting crystal suggests the difference is not simply related to superconductivity. This composition dependence was observed for both transverse and longitudinal phonons. The temperature dependences of the (100) phonons resembled those of conventional phonons. We will discuss these results and possible explanations for the relation between composition and lattice dynamics in this system.

  11. Phase relationships and homogeneity region of alloys of Ag/sub 2/Se with Cu/sub 2/Se

    SciTech Connect

    Yakshibaev, R.A.; Konev, V.N.; Mukhamadeeva, N.N.; Balapanov, M.K.

    1988-08-01

    We investigated the phase relationships in (Ag/sub 1-x/Cu/sub x/)/sub 2/Se alloys and their unit-cell parameters as functions of the composition and width of the homogeneity region of the solid solutions. The phase analysis in the 290-720 K temperature range was carried out by recording diffraction patterns on a DRON-3 diffractometer. The width of the homogeneity region was found by a means of coulometric titrations. The width of the homogeneity region was determined from the character of the dependence of the emf on the composition. The structural features of binary chalcogenides, such as the broad homogeneity region and the disordering of part of the cationic sublattice, were maintained in the ternary systems. These properties vary monotonically in the region where the solid solutions exist.

  12. Critical role of CdSe nanoplatelets in color-converting CdSe/ZnS nanocrystals for InGaN/GaN light-emitting diodes.

    PubMed

    Hasanov, Namig; Sharma, Vijay Kumar; Hernandez Martinez, Pedro Ludwig; Tan, Swee Tiam; Demir, Hilmi Volkan

    2016-06-15

    Here we report CdSe nanoplatelets that are incorporated into color-converting CdSe/ZnS nanocrystals for InGaN/GaN light-emitting diodes. The critical role of CdSe nanoplatelets as an exciton donor for the color conversion was experimentally investigated. The power conversion efficiency of the hybrid light-emitting diode was found to increase by 23% with the incorporation of the CdSe nanoplatelets. The performance enhancement is ascribed to efficient exciton transfer from the donor CdSe nanoplatelet quantum wells to the acceptor CdSe/ZnS nanocrystal quantum dots through Förster-type nonradiative resonance energy transfer. PMID:27304313

  13. Magnetically Hard Fe3Se4 Embedded in Bi2Se3 Topological Insulator Thin Films Grown by Molecular Beam Epitaxy.

    PubMed

    Vasconcelos, Hugo Menezes do Nascimento; Eddrief, Mahmoud; Zheng, Yunlin; Demaille, Dominique; Hidki, Sarah; Fonda, Emiliano; Novikova, Anastasiia; Fujii, Jun; Torelli, Piero; Salles, Benjamin Rache; Vobornik, Ivana; Panaccione, Giancarlo; de Oliveira, Adilson Jesus Aparecido; Marangolo, Massimiliano; Vidal, Franck

    2016-01-26

    We investigated the structural, magnetic, and electronic properties of Bi2Se3 epilayers containing Fe grown on GaAs(111) by molecular beam epitaxy. It is shown that, in the window of growth parameters leading to Bi2Se3 epilayers with optimized quality, Fe atom clustering leads to the formation of FexSey inclusions. These objects have platelet shape and are embedded within Bi2Se3. Monoclinic Fe3Se4 is identified as the main secondary phase through detailed structural measurements. Due to the presence of the hard ferrimagnetic Fe3Se4 inclusions, the system exhibits a very large coercive field at low temperature and room temperature magnetic ordering. Despite this composite structure and the proximity of a magnetic phase, the surface electronic structure of Bi2Se3 is preserved, as shown by the persistence of a gapless Dirac cone at Γ. PMID:26653134

  14. Self-assembly of CdSe quantum dots and colloidal titanium dioxide on copolymer microspheres (PS) for CdSe/PS and TiO2/CdSe/PS sub-microspheres with yolk-shell structure

    NASA Astrophysics Data System (ADS)

    Zhao, Qingchun

    2015-07-01

    Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, chemical/biological sensors, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in nanostructures. In this paper, relying on the interaction including van der Waals forces and hydrogen bond, CdSe/PS sub-microspheres composite and TiO2/CdSe/PS sub-microspheres with yolk-shell structure were prepared via self-assembly of CdSe quantum dots and colloidal titanium dioxide on modified PS surface. The morphology, structure and composition obtained products were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy disperse X-ray spectroscopy (EDX). Transmission electron microscopy (TEM) investigations show the CdSe quantum dots and colloidal titanate were assembled on the surface of PS sub-microspheres. CdSe QD-polymer sub-microspheres composites in which the QDs retain their original emission efficiency can be obtained. TiO2/CdSe/PS sub-microspheres with yolk-shell structure can improve the efficiency of charge separation.

  15. First-principles study of carbon impurities in CuInSe2 and CuGaSe2, present in non-vacuum synthesis methods

    NASA Astrophysics Data System (ADS)

    Bekaert, J.; Saniz, R.; Partoens, B.; Lamoen, D.

    2015-01-01

    A first-principles study of the structural and electronic properties of carbon impurities in CuInSe2 and CuGaSe2 is presented. Carbon is present in organic molecules in the precursor solutions used in non-vacuum growth methods for CuInSe2 and CuGaSe2 based photovoltaic cells. These growth methods make more efficient use of material, time, and energy than traditional vacuum methods. The formation energies of several carbon impurities are calculated using the hybrid HSE06 functional. CCu acts as a shallow donor, CIn and interstitial C yield deep donor levels in CuInSe2, while in CuGaSe2 CGa and interstitial C act as deep amphoteric defects. So, these defects reduce the majority carrier (hole) concentration in p-type CuInSe2 and CuGaSe2 by compensating the acceptor levels. The deep defects are likely to act as recombination centers for the photogenerated charge carriers and are thus detrimental for the performance of the photovoltaic cells. On the other hand, the formation energies of the carbon impurities are high, even under C-rich growth conditions. Thus, few C impurities will form in CuInSe2 and CuGaSe2 in thermodynamic equilibrium. However, the deposition of the precursor solution in non-vacuum growth methods presents conditions far from thermodynamic equilibrium. In this case, our calculations show that C impurities formed in non-equilibrium tend to segregate from CuInSe2 and CuGaSe2 by approaching thermodynamic equilibrium, e.g., via thorough annealing.

  16. Hydrogen bonding in neutral and cation dimers of H2Se with H2O, H2S, and H2Se.

    PubMed

    Joshi, Ravi; Ghanty, Tapan K; Mukherjee, Tulsi; Naumov, Sergej

    2012-12-01

    Structures, hydrogen bonding, and binding energies of H(4)SeA (A = O, S, Se) dimers and their cation radicals have been studied using DFT-B3LYP, MP2, and CCSD methods with 6-31++G(d,p), cc-pVTZ, and aug-cc-pVTZ basis sets. The binding energy (BE) order of the most stable neutral and cationic dimers have been found to be (H(2)Se···HOH) > (H(2)Se···HSH) > (H(2)Se···HSeH), and (H(2)Se···SeH(2))(+) > (H(2)Se···SH(2))(+) > (HSe···HOH(2))(+), respectively, by B3LYP/6-31++G(d,p) and MP2/aug-cc-pVTZ methods. Higher electronegativity of the heteroatom has been found to result in more stability of the neutral dimer but less of the cationic dimer. Among neutral dimers, structure with more electronegative heteroatom acting as proton donor has been found to be more stable. However, the hemibonded structure has been found to be more stable for the dimer cation radical unless the ionization potentials of the involved heteroatoms are very different, e.g., H(4)SeO(+). Vibrational frequency calculation suggests that an increase in electronegativity of A-atom results in a decrease in Se-H bond strength in H(4)SeA and H(4)SeA(+) dimers. The calculated values of Mulliken atomic charge/spin and hydrogen bond lengths of the dimers and their radical cations have also been discussed. PMID:23134584

  17. First-principles study of carbon impurities in CuInSe{sub 2} and CuGaSe{sub 2}, present in non-vacuum synthesis methods

    SciTech Connect

    Bekaert, J. Saniz, R.; Partoens, B.; Lamoen, D.

    2015-01-07

    A first-principles study of the structural and electronic properties of carbon impurities in CuInSe{sub 2} and CuGaSe{sub 2} is presented. Carbon is present in organic molecules in the precursor solutions used in non-vacuum growth methods for CuInSe{sub 2} and CuGaSe{sub 2} based photovoltaic cells. These growth methods make more efficient use of material, time, and energy than traditional vacuum methods. The formation energies of several carbon impurities are calculated using the hybrid HSE06 functional. C{sub Cu} acts as a shallow donor, C{sub In} and interstitial C yield deep donor levels in CuInSe{sub 2}, while in CuGaSe{sub 2} C{sub Ga} and interstitial C act as deep amphoteric defects. So, these defects reduce the majority carrier (hole) concentration in p-type CuInSe{sub 2} and CuGaSe{sub 2} by compensating the acceptor levels. The deep defects are likely to act as recombination centers for the photogenerated charge carriers and are thus detrimental for the performance of the photovoltaic cells. On the other hand, the formation energies of the carbon impurities are high, even under C-rich growth conditions. Thus, few C impurities will form in CuInSe{sub 2} and CuGaSe{sub 2} in thermodynamic equilibrium. However, the deposition of the precursor solution in non-vacuum growth methods presents conditions far from thermodynamic equilibrium. In this case, our calculations show that C impurities formed in non-equilibrium tend to segregate from CuInSe{sub 2} and CuGaSe{sub 2} by approaching thermodynamic equilibrium, e.g., via thorough annealing.

  18. Deformation characteristics and history along the Ilkwang Fault, SE Korea

    NASA Astrophysics Data System (ADS)

    Jin, K.; Kim, Y.; Yang, S.; Choi, J.

    2009-12-01

    The NNE-SSW trending Ilkwang Fault is one of the major structural features around SE Korea. It is a high angle, right-lateral strike-slip fault with a displacement of about 1.2 km. The basement around the fault is Cretaceous sedimentary and volcanic rocks forming a part of the Gyeongsang Basin in SE Korea, and it is intruded by later igneous rocks. The fault has not been studied intensively due to poor exposure along the fault. However, understanding the characteristics of the Ilkwang Fault is important because three nuclear power plants and one nuclear waste disposal site are located around the fault. We have mainly investigated along the new road-cut sections of the Busan-Ulsan Highway. Many geologic structures such as dykes, folds, and faults are measured in several studied sites. The analyzed structural patterns indicate multi-deformation including reactivation of pre-existing faults. In this study, we analyzed variation patterns of attitude on the beddings and fractures around some parts of the Ilkwang Fault. The strike/dip variation from the general attitude of the structural elements (e.g. beddings) is here used as an indicator of deformation intensity across the fault. This analysis indicates that respect distances (highly deformed area affected by faulting) along the Ilkwang Fault is about 1 km in sedimentary rocks and 200 m in volcanic rocks, respectively. It indicates that the Ilkwang Fault is a relatively big fault, and layered sedimentary rock is relatively weaker than massive volcanic rock under brittle deformation. Deformation history in the studied area, based on kinematic analysis of faults, joints and dykes, is as follows: 1) NNE-SSW trending reverse fault and fold. 2) E-W trending reverse fault and N-S trending acidic dykes. 3) ENE-WSW trending left-lateral fault, NNE-SSW trending right-lateral fault, and NE-SW trending basic dykes. 4) E-W trending normal fault. 5) N-S or NNE-SSW trending reverse fault.

  19. Constraining the history of vertical surface motions in SE England.

    NASA Astrophysics Data System (ADS)

    Smith, Philip; England, Richard; Zalasiewicz, Jan

    2015-04-01

    Constraining the history of vertical surface motions in SE England. While there is considerable focus on the effects of rising sea level what is often not considered are ongoing long term changes in surface topography driven by regional tectonics. The London basin is an area at risk from global sea level rise which has a significant long term history of vertical surface motions. Outcrop and borehole sections taken from the onshore and offshore Cenozoic geological record of the UK are used to plot these regional tectonic vertical motions through time. The Cenozoic geological formations useful to the research are dominantly shallow marine sediments and the successions are thickest in the axial regions of the London and Hampshire basins found in the South East of England. Each successive geological formation through time records a component of the tectonic uplift/subsidence history that spans from the end of the Cretaceous, 65Ma through to the present day. Once this history is better understood it can be used to make predictions of the possible vertical tectonic motion in the future. In order to isolate the tectonic uplift or subsidence in a basin and the magnitude of the basement movement, the water depth at the time of deposition, the relative sea-level and the compaction history for the sediments of each formation needs to be constrained. Water depth has been determined so far using a variety of sedimentological, palaeontological and sequence stratigraphic evidence. Palaeo-bathymetry maps have then be contoured from the point data providing the relative palaeo-coastline for each geological formation. The relative sea-level curve will be used from previous work. The third parameter is the decompaction of a formation from its preserved thickness at the present day, to its water saturated and unconsolidated state at the time of deposition. Resolving these parameters and producing a comprehensive burial history for each geological formation in the UK will allow the

  20. One thousand year palaeohydrological record derived from SE Australian stalagmites

    NASA Astrophysics Data System (ADS)

    McDonald, Janece

    2009-04-01

    Essential to successful water management in SE Australia is a thorough understanding of current and past rainfall patterns. Historically rainfall records only span the last 150 years and terrestrial archives such as speleothems, flood plain and lake cores and pollen cores are being utilised to generate pre-instrumental flood and drought histories. In this paper we present a ~ 1,000 year palaeohydrological record based on two speleothems from the same chamber in Wollondilly Cave, Wombeyan Karst Conservation Reserve, SE Australia. Prior to this study the geochemical record of two active stalagmites from the same cave system was evaluated with respect to the instrumental record. Chronology was obtained using accelerator mass spectrometry (AMS) 14C measurements together with trace element cycle counting. The most reliable palaeohydrological proxies found were magnesium (Mg), phosphorus (P) and yttrium (Y) which were able to be confidently related to dry/wet periods (Mg) and high infiltration events (P and Y). Oxygen isotopes trended positively with documented Interdecadal Pacific Oscillation (IPO) phase changes where negative ^18O anomalies aligned with negative phases of IPO and conversely positive ^18O anomalies aligned with positive phases of IPO. During negative phase of the IPO there is a higher probability of La Niña events bringing above average rainfall to the region. Modern stalagmites recorded the negative IPO (1945-1977) by low Mg, phases of elevated P and Y, and negative ^18O anomalies. Chronology was obtained on the two ~ 1,000 year stalagmites by locating the bomb pulse using AMS14C at the top and paired U-series/14C measurements made on the basal sections. Basal ages were ~4 - 5ka, though only the top ~ 7 cm has been analysed thus far. Growth rate for each stalagmite is estimated at ~ 0.05 mm year-1. Ages are still being further refined. Preliminary ^18O values show clear changes in trends back to ~ 700 AD. Between AD 750- 850 and AD 1050 - 1300 there

  1. Physical Activity and Lipid Profile in the ELSA-Brasil Study

    PubMed Central

    da Silva, Raquel Caroline; Diniz, Maria de Fátima Haueisen Sander; Alvim, Sheila; Vidigal, Pedro Guatimosim; Fedeli, Ligia Maria Giongo; Barreto, Sandhi Maria

    2016-01-01

    Background Regular physical activity (PA) induces desirable changes in plasma levels of high- and low-density lipoproteins (HDL and LDL, respectively) and triglycerides (TG), important risk factors for cardiometabolic diseases. However, doubts whether intensity and duration have equivalent benefits remain. Objective To assess the association of PA intensity and duration with HDL, LDL and TG levels. Methods Cross-sectional study with 12,688 participants from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) baseline, who were not on lipid-lowering medication. After adjustment for important covariates, multiple linear regression was used to assess the association of PA intensity and duration with HDL, LDL and TG (natural logarithm) levels. Results Both moderate and vigorous PA and PA practice ≥ 150 min/week were significantly associated with higher HDL and lower TG levels. Vigorous PA was associated with lower LDL only on univariate analysis. After adjustments, moderate and vigorous PA increased mean HDL level by 0.89 mg/dL and 1.71 mg/dL, respectively, and reduced TG geometric mean by 0.98 mg/dL and 0.93 mg/dL, respectively. PA practice ≥ 150 min/week increased mean HDL level by 1.05 mg/dL, and decreased TG geometric mean by 0.98 mg/dL. Conclusion Our findings reinforce the benefits of both PA parameters studied on HDL and TG levels, with a slight advantage for vigorous PA as compared to the recommendation based only on PA duration. PMID:27355470

  2. Se(VI) Reduction and the Precipitation of Se(0) Precipitation by the Facultative Bacterium Enterobacter Cloacae SLD1a-1 is Regulated by FNR

    SciTech Connect

    Yee,N.; Ma, J.; Dalia, A.; Boonfueng, T.; Kobayashi, D.

    2007-01-01

    The fate of selenium in the environment is controlled, in part, by microbial selenium oxyanion reduction and Se(0) precipitation. In this study, we identified a genetic regulator that controls selenate reductase activity in the Se-reducing bacterium Enterobacter cloacae SLD1a-1. Heterologous expression of the global anaerobic regulatory gene fnr (fumarate nitrate reduction regulator) from E. cloacae in the non-Se-reducing strain Escherichia coli S17-1 activated the ability to reduce Se(VI) and precipitate insoluble Se(0) particles. Se(VI) reduction by E. coli S17-1 containing the fnr gene occurred at rates similar to those for E. cloacae, with first-order reaction constants of k = 2.07 x 10{sup -2} h{sup -1} and k = 3.36 x 10{sup -2} h{sup -1}, respectively, and produced elemental selenium particles with identical morphologies and short-range atomic orders. Mutation of the fnr gene in E. cloacae SLD1a-1 resulted in derivative strains that were deficient in selenate reductase activity and unable to precipitate elemental selenium. Complementation by the wild-type fnr sequence restored the ability of mutant strains to reduce Se(VI). Our findings suggest that Se(VI) reduction and the precipitation of Se(0) by facultative anaerobes are regulated by oxygen-sensing transcription factors and occur under suboxic conditions.

  3. Intersubband absorption in CdSe/Zn{sub x}Cd{sub y}Mg{sub 1-x-y}Se self-assembled quantum dot multilayers

    SciTech Connect

    Shen, A.; Lu, H.; Charles, W.; Yokomizo, I.; Tamargo, M. C.; Franz, K. J.; Gmachl, C.; Zhang, S. K.; Zhou, X.; Alfano, R. R.; Liu, H. C.

    2007-02-12

    The authors report the observation of intersubband absorption in multilayers of CdSe/Zn{sub x}Cd{sub y}Mg{sub 1-x-y}Se self-assembled quantum dots. The samples were grown by molecular beam epitaxy on InP substrates. For samples with the CdSe dot layers doped with Cl and with the deposited CdSe equivalent layer thickness between 5.2 and 6.9 ML, peak absorption between 2.5 and 3.5 {mu}m was observed. These materials are promising for intersubband devices operating in the mid- and near-infrared ranges.

  4. Second Harmonic Generation of Self-Mode-Locked СО2-Laser Radiation in GaSe and GaSeS Crystals

    NASA Astrophysics Data System (ADS)

    Genin, D. E.; Beloplotov, D. V.; Sitnikov, A. G.; Panchenko, A. N.; Sarkisov, S. Yu.; Chernyshov, A. I.

    2014-03-01

    A TEA CO2 laser generating at the wavelength λ = 10.6 μm in the modes of free lasing and self-mode-locking was used to obtain and compare second harmonic generation (SHG) in GaSe and GaSe0.7S0.3 crystals. With the self-mode-locked laser, a 5-times higher energy efficiency of SHG was obtained. The efficiency of SHG in the GaSe0.7S0.3 crystal and its second-order nonlinear susceptibility were estimated and compared with their values for undoped GaSe.

  5. Origin of the solid solution in the LiInSe{sub 2}–In{sub 2}Se{sub 3} system

    SciTech Connect

    Vasilyeva, I.G.; Pochtar, A.A.; Isaenko, L.I.

    2014-12-15

    Techniques of bulk and local analyses were used to characterize the melt-grown single crystals of LiInSe{sub 2}, where yellow matrix coexists together with extended red areas distributed irregularly. Bulk chemical analysis showed that the average stoichiometry of yellow matrix is close to ideal 1:1:2, but red areas are enriched with In{sub 2}Se{sub 3}. An excess In{sub 2}Se{sub 3} is incorporated coherently into the crystal lattice of LiInSe{sub 2}, forming the substitution solid solution with the general formula (Li{sub 1−3x}In{sub x}⎕{sub 2})InSe{sub 2} and changing the color from yellow to red. The test crystals with the 50–55% content of In{sub 2}Se{sub 3} were found by the X-ray analysis to be single phase. The differential dissolution technique, measuring the spatial variation of the composition with high resolution, demonstrated that the single phase crystals in the LiInSe{sub 2}–In{sub 2}Se{sub 3} system might be grown only in a very narrow range close to stoichiometric. Being supersaturated, the heterovalent solid solution phases decompose in the course of cooling, and the concentration micro-heterogeneity occurs in the matrix as the coherent (or incoherent) inclusions of two different types, practically pure selenides of lithium and indium. The origin and scale of the micro-heterogeneity determining the physical properties of LiInSe{sub 2} are discussed as a starting point for the development of physicochemical foundations for growing high quality optical crystals. - Graphical abstract: Differential dissolution technique applied for detection of dispersive precipitates in as-grown LiInSe{sub 2} single crystals: kinetic curves of the phase dissolution: F is the main phase Li{sub 0.96}In{sub 1.01}Se{sub 2} (98.9%), secondary minor phases Li{sub 2}Se (0.1%), In{sub 2}Se{sub 3} (0.9%). - Highlights: • Phase purity of crystals Li{sub 1−3x}In{sub 1+x}Se{sub 2} was examined by a new stoichiographic method. • Breakup of the metastable solid solution

  6. Formation of ZnSe/Bi{sub 2}Se{sub 3} QDs by surface cation exchange and high photothermal conversion

    SciTech Connect

    Jia, Guozhi; Wang, Peng; Zhang, Yanbang; Wu, Zengna; Li, Qiang; Yao, Jianghong; Chang, Kai

    2015-08-15

    Water-dispersed core/shell structure ZnSe/Bi{sub 2}Se{sub 3} quantum dots were synthesized by ultrasonicwave-assisted cation exchange reaction. Only surface Zn ion can be replaced by Bi ion in ZnSe quantum dots, which lead to the ultrathin Bi{sub 2}Se{sub 3} shell layer formed. It is significance to find to change the crystal of QDs due to the acting of ultrasonicwave. Cation exchange mechanism and excellent photothermal conversion properties are discussed in detail.

  7. Electrical and photoelectric characteristics of structures based on InSe and GaSe layered semiconductors irradiated with 12.5-MeV electrons

    SciTech Connect

    Kovalyuk, Z. D. Politanska, O. A.; Sydor, O. N.; Maslyuk, V. T.

    2008-11-15

    The effect of irradiation with 12.5-MeV electrons on the electrical and photoelectric parameters of layered photoconverters based on p-InSe-n-InSe and p-GaSe-n-InSe structures is studied. The observed variations in the current-voltage characteristics, photoresponse spectra, open-circuit voltage, and short-circuit current are caused by the formation of point defects. The absence of pronounced changes in the characteristics of the homojunctions and heterojunctions even after irradiation at the highest dose makes it possible to recommend these junctions for use in the fabrication of radiation-resistant photodetectors.

  8. Superlattices of Bi{sub 2}Se{sub 3}/In{sub 2}Se{sub 3}: Growth characteristics and structural properties

    SciTech Connect

    Wang, Z. Y.; Guo, X.; Xie, M. H.; Li, H. D.; Wong, T. L.; Wang, N.

    2011-07-11

    Superlattices (SLs) consisted of alternating Bi{sub 2}Se{sub 3} and In{sub 2}Se{sub 3} layers are grown on Si(111) by molecular-beam epitaxy. Bi{sub 2}Se{sub 3}, a three-dimensional topological insulator (TI), showed good chemical and structural compatibility with In{sub 2}Se{sub 3}, a normal band insulator with large energy bandgap. The individual layers in the SLs are very uniform, and the hetero-interfaces are sharp. Therefore, such SL structures are potential candidates for explorations of the quantum size effects of TIs.

  9. Optimization of barrier layer thickness in MgSe/CdSe quantum wells for intersubband devices in the near infrared region

    SciTech Connect

    Chen, Guopeng; Shen, Aidong; Tamargo, Maria C.

    2015-10-28

    The authors report the optimization of MgSe barrier thickness in CdSe/MgSe multiple quantum well structures and its effect on structural, optical qualities and intersubband (ISB) transition characteristics. Three samples with the MgSe thicknesses of 2 nm, 3 nm, and 4 nm were grown on InP substrates by molecular beam epitaxy. X-ray diffraction and photoluminescence measurements showed that the thinner the MgSe barrier thickness the better the structural quality. However, ISB absorption was only observed in the sample with a MgSe thickness of 3 nm. Failing to observe ISB absorption in the sample with a thicker MgSe barrier (≥4 nm) is due to the deteriorated material quality while the missing of ISB transition in the sample with thinner barrier (≤2 nm) is due to the tunneling of electrons out of the CdSe wells. The optimized MgSe barrier thickness of around 3 nm is found to be able to suppress the electron tunneling while maintaining a good material quality of the overall structure.

  10. Two-dimensional X-ray diffraction characterization of (Zn,Cd,Mg)Se wurtzite layers grown on Bi2Se3

    NASA Astrophysics Data System (ADS)

    Hernandez-Mainet, L. C.; Chen, Z.; Garcia, T. A.; Bykov, A. B.; Krusin-Elbaum, L.; Tamargo, M. C.

    2016-01-01

    ZnSe, Zn0.49Cd0.51Se and Zn0.23Cd0.25Mg0.52Se layers grown on Bi2Se3/sapphire (0001) by molecular beam epitaxy (MBE) are characterized by two-dimensional X-ray diffraction. Pole figures are calculated for cubic and hexagonal planes of the (Zn,Cd,Mg)Se family and compared to their expected values. The targeted wurtzite plane was (11-22), while the cubic ones were the (220) and (311). The results show that, under our MBE growth conditions, ZnSe, Zn0.49Cd0.51Se and Zn0.23Cd0.25Mg0.52Se layers prefer to form the hexagonal (wurtzite) phase rather than the cubic one when grown on Bi2Se3/sapphire in (0001) direction. These results have implications for the next generation devices combining semiconductors and topological insulator materials.

  11. Synthesis, crystal structure, resistivity, and electronic structure of the U(V) quaternary polyselenide Ba8PdU2Se12(Se2)2

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    A new quaternary uranium(V) selenide, Ba8PdU2Se12(Se2)2, has been synthesized by reaction of elements at 1173 K. A single-crystal X-ray diffraction study shows that the compound crystallizes in a new structure type with two formula units in space group D2h12 - Pnnm of the orthorhombic crystal system with cell constants of a=9.490(1), b=12.240(2), and c=13.780(3) Å. Its crystal structure consists of [PdU2 Se1212-] units where U atoms are coordinated to six Se atoms in octahedral geometry and Pd atoms are coordinated to four Se atoms in square-planar geometry. These [PdU2 Se1212-] units are separated by Ba to result in a salt-like crystal structure. This compound also contains Se22- dimers that are part of Ba coordination polyhedra. The formula charge balances as (Ba2+)8(Pd2+)(U5+)2(Se2-)12(Se22-)2. Theoretical calculations predict antiferromagnetic semiconducting behavior for this compound with a band gap of 1.6 eV. Temperature-dependent four-probe resistivity measurements on single crystal confirm the semiconducting nature with an activation energy of 0.18(1) eV.

  12. Li diffusion in NbSe/sub 2/ and Ag/sub 0. 25/NbSe/sub 2/ single crystals

    SciTech Connect

    Folinsbee, J.T.; Simpson, A.M.; Jericho, M.H.

    1986-08-01

    Measurements are reported of the diffusion of Lithium into NbSe/sub 2/ and into NbSe/sub 2/ preintercalated with silver. Diffusion parallel to the layers is found to be at least 2 orders of magnitude greater than perpendicular to the layers, but not to be greatly affected by the presence of intercalated silver. The activation energy for Li hopping in NbSe/sub 2/ is estimated to be 520 meV. The staging structure of Ag/sub x/NbSe/sub 2/ is also reported. These results have implications for the characterization of cathode materials in intercalation batteries.

  13. One-pot solvothermal synthesis of ZnSe·xN2H4/GS and ZnSe/N-GS and enhanced visible-light photocatalysis.

    PubMed

    Liu, Bitao; Tian, Liangliang; Wang, Yuhua

    2013-09-11

    Doped-graphene has attracted considerable attention in many fields because doping element can alter the electrical properties of graphene. In this paper, we synthesized ZnSe·xN2H4/graphene (ZnSe·xN2H4/GS) and ZnSe/nitrogen-doped graphene (ZnSe/N-GS) nanocomposites with p-n junctions via one-pot solvothermal process. The structure, morphologies and catalytic performance of the ZnSe·xN2H4/GS and ZnSe/N-GS are characterized by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and cathodoluminescence spectrum (CL), respectively. Our experiments show that the as-prepared nanocomposites ZnSe·xN2H4/GS and ZnSe/N-GS exhibit remarkably enhanced photocatalytic activities for methylene blue (MB) dye under visible light irradiation. Even importantly, ZnSe/N-GS would make this degradation process more effective. Overall, this facile and catalyst-free synthesize method in this work could provide new insights into the fabrication of other composites based on doped graphene with high performance photocatalysts, which show their potential applications in producing of hydrogen through water splitting, environmental protection issues. PMID:23945131

  14. Production of Se-methylselenocysteine in transgenic plants expressing selenocysteine methyltransferase

    PubMed Central

    Ellis, Danielle R; Sors, Thomas G; Brunk, Dennis G; Albrecht, Carrie; Orser, Cindy; Lahner, Brett; Wood, Karl V; Harris, Hugh H; Pickering, Ingrid J; Salt, David E

    2004-01-01

    Background It has become increasingly evident that dietary Se plays a significant role in reducing the incidence of lung, colorectal and prostate cancer in humans. Different forms of Se vary in their chemopreventative efficacy, with Se-methylselenocysteine being one of the most potent. Interestingly, the Se accumulating plant Astragalus bisulcatus (Two-grooved poison vetch) contains up to 0.6% of its shoot dry weight as Se-methylselenocysteine. The ability of this Se accumulator to biosynthesize Se-methylselenocysteine provides a critical metabolic shunt that prevents selenocysteine and selenomethionine from entering the protein biosynthetic machinery. Such a metabolic shunt has been proposed to be vital for Se tolerance in A. bisulcatus. Utilization of this mechanism in other plants may provide a possible avenue for the genetic engineering of Se tolerance in plants ideally suited for the phytoremediation of Se contaminated land. Here, we describe the overexpression of a selenocysteine methyltransferase from A. bisulcatus to engineer Se-methylselenocysteine metabolism in the Se non-accumulator Arabidopsis thaliana (Thale cress). Results By over producing the A. bisulcatus enzyme selenocysteine methyltransferase in A. thaliana, we have introduced a novel biosynthetic ability that allows the non-accumulator to accumulate Se-methylselenocysteine and γ-glutamylmethylselenocysteine in shoots. The biosynthesis of Se-methylselenocysteine in A. thaliana also confers significantly increased selenite tolerance and foliar Se accumulation. Conclusion These results demonstrate the feasibility of developing transgenic plant-based production of Se-methylselenocysteine, as well as bioengineering selenite resistance in plants. Selenite resistance is the first step in engineering plants that are resistant to selenate, the predominant form of Se in the environment. PMID:15005814

  15. First-principles study of formation of Se submonolayer structures on Ru surfaces

    NASA Astrophysics Data System (ADS)

    Stolbov, Sergey

    2010-10-01

    The Ru nanoparticles with Se submonolayer coverage (Se/Ru) demonstrate high electrocatalytic activity toward oxygen reduction reaction (ORR) on cathodes of proton exchange membrane fuel cells. To understand the mechanisms of formation of Se structures on Ru surfaces, the geometric and electronic structures and energetics have been calculated in the present work for various distributions of Se atoms on the Ru(0001) surface and in the vicinity of the edge between the (0001) and (1101) facets. The calculations were performed within the density-functional theory with plane-wave expansion for wave functions and the projector augmented wave potentials. It has been found that due to electronic charge transfer from Ru to Se upon selenium adsorption, Se atoms become negatively charged and repel each other. This repulsion makes compact Se islands on Ru(0001) unstable. Se atoms prefer to separate from each other by the distance of ˜5.47Å or larger, which is possible for all Se adsorbates if coverage is not exceeding 1/3 ML. Further increase in Se coverage weakens Se-Ru bonding. Three-dimensional Se structure such as 4- and 11-atom pyramids are found to decompose spontaneously with scattering of Se atoms over the Ru(0001) surface. The Se adsorbates are also found to repel in the vicinity of the edge between the Ru facets, and a small increase in Se bonding to undercoordinated Ru atom does not change the trend of Se adsorbates to separate from each other. The obtained most stable configurations of Se on Ru with 1/3 ML coverage or less may also be optimal for ORR because they provide Ru sites available for O and OH adsorption.

  16. Reaction Routes for the Synthesis of CuInSe2 Using Bilayer Compound Precursors

    SciTech Connect

    Krishnan, Rangarajan; Wood, David; Chaudhari, Vaibhav U.; Payzant, E Andrew; Noufi, Rommel; Rozeveld, Steve; Kim, Woo Kyoung; Anderson, Timothy J

    2012-01-01

    The reaction pathways and phase evolution during synthesis of CuInSe{sub 2} (CIS) by a novel bilayer approach were investigated using in situ high-temperature X-ray diffraction. Two bilayer precursor structures, glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se and glass/Mo/{gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se, were examined in this study. Temperature ramp experiments revealed that the phase transformation sequence for each bilayer precursor qualitatively follows that predicted by the phase diagram and that the onset temperatures for decomposition of the sub-binary compounds depend on the Se partial pressure. Measurement of the isothermal rate of formation of CuInSe{sub 2} at six temperatures in the range 260 to 310 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-CuSe + {beta}-Cu{sub 2}Se/Se bilayer suggests relatively slow nucleation followed by diffusion-limited reaction with estimated activation energy of 162({+-}7) and 225 ({+-}16) kJ/mol from Avrami and parabolic models, respectively. Interestingly, the measured activation energy for the same precursor in a 4 mol % H{sub 2}/He ambient (108 ({+-}8) kJ/mol) was lower than that observed in pure N{sub 2} (158 ({+-}16) kJ/mol). The results of isothermal measurements in the temperature range 250 to 300 C for the {gamma}-In{sub 2}Se{sub 3}/{beta}-Cu{sub 2}Se/Se precursor film in an inert ambient are consistent with one-dimensional diffusion-limited growth with estimated activation energy from the Avrami and parabolic models of 194 ({+-}10) and 203 ({+-}12) kJ/mol, respectively.

  17. Selenium biofortification of broccoli and carrots grown in soil amended with Se-enriched hyperaccumulator Stanleya pinnata

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Amending soils with Se-hyperaccumulator plant derived sources of selenium (Se) may be useful for increasing Se content in food crops in Se-deficient regions of the world. In this study, we evaluated total Se and the different chemical species of Se in broccoli and carrots grown in soils amended with...

  18. Thermal Processing Effects on Microstructure and Composition of Cu3SbSe3

    SciTech Connect

    Majsztrik, Paul W; Kirkham, Melanie J; Garcia Negron, Valerie; Lara-Curzio, Edgar; Skoug, Eric; Morelli, Donald

    2013-01-01

    We report on the effects of thermal processing on the microstructure and composition of a system with overall stoichiometry of 3Cu:1Sb:3Se with the aim of producing single-phase Cu3SbSe3. It was found that slowly cooling from the melt produced a multiphase material consisting of Cu2Se and CuSbSe2, but devoid of Cu3SbSe3. Cooling rapidly from the melt resulted in three-phase microstructures consisting of Cu2Se, CuSbSe2, and Cu3SbSe3. Subsequent annealing of the three-phase material between 325 C and 400 C shifted composition towards nearly pure Cu3SbSe3, the target compound of this work. The kinetics of the transformation into Cu3SbSe3 is successfully described using a modified Avrami model, which suggests that diffusion is the rate-controlling step. Values of Young s modulus and hardness, obtained by nanoindentation, are reported for Cu2Se, CuSbSe2, and Cu3SbSe3.

  19. First-principles study of native point defects in Bi2Se3

    NASA Astrophysics Data System (ADS)

    Xue, L.; Zhou, P.; Zhang, C. X.; He, C. Y.; Hao, G. L.; Sun, L. Z.; Zhong, J. X.

    2013-05-01

    Using first-principles method within the framework of the density functional theory, we study the influence of native point defect on the structural and electronic properties of Bi2Se3. Se vacancy in Bi2Se3 is a double donor, and Bi vacancy is a triple acceptor. Se antisite (SeBi) is always an active donor in the system because its donor level (ɛ(+1/0)) enters into the conduction band. Interestingly, Bi antisite (BiSe1) in Bi2Se3 is an amphoteric dopant, acting as a donor when μe < 0.119 eV (the material is typical p-type) and as an acceptor when μe > 0.251 eV (the material is typical n-type). The formation energies under different growth environments (such as Bi-rich or Se-rich) indicate that under Se-rich condition, SeBi is the most stable native defect independent of electron chemical potential μe. Under Bi-rich condition, Se vacancy is the most stable native defect except for under the growth window as μe > 0.262 eV (the material is typical n-type) and ΔμSe < -0.459 eV (Bi-rich), under such growth window BiSe1 carrying one negative charge is the most stable one.

  20. Gran Sabana fires (SE Venezuela): a paleoecological perspective

    NASA Astrophysics Data System (ADS)

    Montoya, Encarni; Rull, Valentí

    2011-11-01

    Fires are among the most important risks for tropical ecosystems in a future climatic change scenario. Recently, paleoecological research has been addressed to discern the role played by fire in neotropical landscapes. However, given the magnitude of the Neotropics, many studies are relegated to infer just local trends. Here we present the compilation of the paleo-fire records developed until now in the southern Gran Sabana (SE Venezuela) with the aim to describe the fire history as well as to infer the possible forcing factors implied. In this sense, southern Gran Sabana has been under fire perturbation since the Lateglacial, with the concomitant effects upon vegetation, and persisted during the Holocene. Around 2000 cal yr BP onwards, the fire activity highly increased promoting the expansion of pre-existing savannas, the decrease of forests and the appearance and establishment of Mauritia palm swamps. The continuous fire incidence registered for several thousands of years has likely promoted the supremacy of treeless savannas upon other vegetation types and the degradation to secondary landscapes. Based on the available evidence, the anthropogenic nature of this high fire activity has been postulated. If so, it could be hypothesized that the timing arrival of Pemón, the present-day indigenous culture in the Gran Sabana, would be ca 2000 cal yr BP onwards, rather than the last centuries, as it has been formerly assumed. The implications of these ancient practices in the area are also discussed for present Gran Sabana landscapes sustainability and future conservation strategies.

  1. Luminescence chronology of the inland sand dunes from SE India

    NASA Astrophysics Data System (ADS)

    Reddy, Dontireddy Venkat; Singaraju, Vuddaraju; Mishra, Rakesh; Kumar, Devender; Thomas, Puthusserry Joseph; Rao, Karra Kameshwa; Singhvi, Ashok Kumar

    2013-09-01

    Records of past climate changes have been preserved variously on the earth's surface. Sand dunes are one such prominent imprint, and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases. We report inland sand dunes from Andhra Pradesh (SE India) spread over an area of ~ 500 km2, ~ 75 km inland from the east coast. The dune sands are examined to understand their provenance, transportation, timing of sand aggradation and their relationship to past climates. The dune distribution, grain morphology and the grain-size studies on sands suggest an aeolian origin. Physiography of the study area, heavy mineral assemblage, and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first-order streams emanating from hills in the region and from weathering of the Nellore schist belt. It appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area. OSL dating of 47 dune samples ranged from the present to ~ 50 ka, thereby suggesting a long duration of sand-dune aggradation and/or reworking history.

  2. Simulation of Dynamics of PVT Growth: ZnSe

    NASA Technical Reports Server (NTRS)

    Worlikar, A.; Overholt, M.; Motakef, S.; Su, C.-H.; Ramachandran, N.

    1999-01-01

    An unsteady model for the simulation of PVT growth process has been developed and applied to growth of ZnSe. The model is capable of tracking the unsteady aspects of the growth process caused by, for example, changes in the system temperature associated with growth, source-depletion, translation of the charge, out-gassing at high temperatures, as well as changes in the source composition during growth. The model predicts the evolution of growth interface morphology as well as the shape of source-gas interface. Thermo-fluid transport in the gas phase is handled by a Low-Mach number unsteady compressible flow formulation. Heat transfer in the crystal, source, and the quartz housing is calculated by the Monte-Carlo technique to capture the variations in the spectral transmittance and index of refraction of the participating media. Simulation results are presented for the growth interface morphology, thermal stresses in the crystal, and growth rate at various stages of growth. The influence of impurity gases on the growth process is also discussed, The simulation results are compared with the experimental observations. The capabilities of the developed tool in addressing other PVT growth processes such as SiC are discussed.

  3. Digital Doping in Magic-Sized CdSe Clusters.

    PubMed

    Muckel, Franziska; Yang, Jiwoong; Lorenz, Severin; Baek, Woonhyuk; Chang, Hogeun; Hyeon, Taeghwan; Bacher, Gerd; Fainblat, Rachel

    2016-07-26

    Magic-sized semiconductor clusters represent an exciting class of materials located at the boundary between quantum dots and molecules. It is expected that replacing single atoms of the host crystal with individual dopants in a one-by-one fashion can lead to unique modifications of the material properties. Here, we demonstrate the dependence of the magneto-optical response of (CdSe)13 clusters on the discrete number of Mn(2+) ion dopants. Using time-of-flight mass spectrometry, we are able to distinguish undoped, monodoped, and bidoped cluster species, allowing for an extraction of the relative amount of each species for a specific average doping concentration. A giant magneto-optical response is observed up to room temperature with clear evidence that exclusively monodoped clusters are magneto-optically active, whereas the Mn(2+) ions in bidoped clusters couple antiferromagnetically and are magneto-optically passive. Mn(2+)-doped clusters therefore represent a system where magneto-optical functionality is caused by solitary dopants, which might be beneficial for future solotronic applications. PMID:27420556

  4. Seasonal nutrient dynamics in three stream types in SE Alaska

    NASA Astrophysics Data System (ADS)

    Edwards, R. T.; Norberg, E.; Fellman, J.

    2005-05-01

    The Tongass National Forest encompasses over 5,000 salmon streams draining a wide variety of lithologies, microclimates and landforms. To predict management outcomes and responses to climate change, managers need an understanding of how ecosystem processes in streams vary over large spatial scales and with major controlling landscape variables. We measured forms of N, P and DOM in three common stream types: glacial, brownwater and clearwater near Juneau, AK. Glacial and clearwater streams showed strong seasonal trends in nitrate and total nitrogen related to snow melt and summer uptake, whereas brownwater streams were variable but not highly seasonal. Total nitrogen concentrations were dominated by inorganic forms in clearwater streams, organic forms in brownwater streams and varied seasonally between organic and inorganic forms in glacial streams. DOC concentrations were low in clearwater and glacial streams and varied little seasonally. Brownwater stream DOC values were high, variable and varied with discharge, with an increasing trend during summer. The Tongass NF recently classified SE Alaska forest lands into ecological subsections based on large-scale geophysical factors such as lithology and surficial geology. Partitioning Tongass streams using this approach may lead to better management predictions by more accurately incorporating natural variation in baseline stream dynamics.

  5. Crystal structure and phase transition of thermoelectric SnSe.

    PubMed

    Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo

    2016-06-01

    Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed. PMID:27240762

  6. Optical Properties of CdSe/ZnS Nanocrystals

    PubMed Central

    Gaigalas, Adolfas K; DeRose, Paul; Wang, Lili; Zhang, Yu-Zhong

    2014-01-01

    Measurements are presented of the absorbance, fluorescence emission, fluorescence quantum yield, and fluorescence lifetime of CdSe/ZnS nanocrystals, also known as quantum dots (QDs). The study included three groups of nanocrystals whose surfaces were either passivated with organic molecules, modified further with carboxyl groups, or conjugated with CD14 mouse anti-human antibodies. The surface modifications had observable effects on the optical properties of the nanocrystals. The oscillator strength (OS) of the band edge transition was about 1.0 for the nanocrystals emitting at 565 nm, 605 nm, and 655 nm. The OS could not be determined for QDs with emission at 700 nm and 800 nm. The fluorescence lifetimes varied from 26 ns for nanocrystals emitting near 600 nm to 150 ns for nanocrystals emitting near 800 nm. The quantum yield ranged between 0.4 and 0.9 for the nanocrystals in this study. A brightness index (BI) was used to evaluate the suitability of the nanocrystal labels for flow cytometer measurements. Most QD labels are at least as bright as fluorescein for applications in flow cytometer assays with 488 nm excitation. For optimal brightness the QDs should be excited with 405 nm light. We observed a strong dependence of the QD absorbance at 250 nm on the surface modification of the QD. PMID:26601047

  7. Orbital-driven nematicity in FeSe.

    PubMed

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

    2015-02-01

    A fundamental and unconventional characteristic of superconductivity in iron-based materials is that it occurs in the vicinity of two other instabilities. In addition to a tendency towards magnetic order, these Fe-based systems have a propensity for nematic ordering: a lowering of the rotational symmetry while time-reversal invariance is preserved. Setting the stage for superconductivity, it is heavily debated whether the nematic symmetry breaking is driven by lattice, orbital or spin degrees of freedom. Here, we report a very clear splitting of NMR resonance lines in FeSe at Tnem = 91 K, far above the superconducting Tc of 9.3 K. The splitting occurs for magnetic fields perpendicular to the Fe planes and has the temperature dependence of a Landau-type order parameter. Spin-lattice relaxation rates are not affected at Tnem, which unequivocally establishes orbital degrees of freedom as driving the nematic order. We demonstrate that superconductivity competes with the emerging nematicity. PMID:25384167

  8. Superconductivity and spin excitations in orbitally ordered FeSe

    NASA Astrophysics Data System (ADS)

    Kreisel, Andreas; Mukherjee, Shantanu; Hirschfeld, P. J.; Andersen, B. M.

    We provide a band-structure with low-energy properties consistent with recent photoemission and quantum oscillations measurements on the Fe-based superconductor FeSe, including a mean-field like orbital ordering in the dxz /dyz channel, and show that this model also accounts for the temperature dependence of the measured Knight shift and the spin-relaxation rate. An RPA calculation of the dynamical spin susceptibility yields spin excitations which are peaked at wave vector (π , 0) in the 1-Fe Brillouin zone, with a broad maximum at energies of order a few meV. Furthermore, the superconducting gap structure obtained from spin fluctuation theory exhibits nodes on the electron pockets, consistent with the 'V'-shaped density of states measured by tunneling spectroscopy on this material. The redistribution of spectral weight in the superconducting state creates a (π , 0) ''neutron resonance'' as seen in recent experiments. Comparing to various experimental results, we give predictions for further studies A.K. and B.M.A. acknowledge financial support from a Lundbeckfond fellowship (Grant No. A9318). P.J.H. was partially supported by the Department of Energy under Grant No. DE-FG02-05ER46236.

  9. Excitation energy dependent Raman spectrum of MoSe2

    PubMed Central

    Nam, Dahyun; Lee, Jae-Ung; Cheong, Hyeonsik

    2015-01-01

    Raman investigation of MoSe2 was carried out with eight different excitation energies. Seven peaks, including E1g, A1g, E2g1, and A2u2 peaks are observed in the range of 100–400 cm−1. The phonon modes are assigned by comparing the peak positions with theoretical calculations. The intensities of the peaks are enhanced at different excitation energies through resonance with different optical transitions. The A1g mode is enhanced at 1.58 and 3.82 eV, which are near the A exciton energy and the band-to-band transition between higher energy bands, respectively. The E2g1 mode is strongly enhanced with respect to the A1g mode for the 2.71- and 2.81-eV excitations, which are close to the C exciton energy. The different enhancements of the A1g and E2g1 modes are explained in terms of the symmetries of the exciton states and the exciton-phonon coupling. Other smaller peaks including E1g and A2u2 are forbidden but appear due to the resonance effect near optical transition energies. PMID:26601614

  10. Structure and growth mechanism of ZnSe nanowires

    NASA Astrophysics Data System (ADS)

    Basu, Joysurya; Divakar, R.; Nowak, Julia; Hofmann, Stephan; Colli, Alan; Franciosi, A.; Carter, C. Barry

    2008-09-01

    ZnSe nanowires were grown onto Mo transmission electron microscopy (TEM) grids by MBE by suitably varying the growth parameters. In situ and high-resolution TEM studies were carried out to understand the structure, defects, and growth mechanism of this nanowire. The nanowire morphology is very sensitive to the growth parameters involved. Twin boundaries are the most commonly occurring defects in the nanowires grown under Zn-rich condition and catalytic gold particles of irregular shape are observed along the nanowire body. In the course of in situ heating the shape of the nanowire tip is observed to change at ˜178 °C. Definite growth of the nanowire starts at ˜235 °C. The diameter of the grown nanowire is almost equal to that of the catalyst gold particle present at the tip of the nanowire. In situ experimental observation and available phase-diagram information strongly suggests that nanowire growth should be possible with a solid catalyst particle though it does not rule out the possibility of the existence of a VLS mechanism.

  11. Latest Cretaceous and Paleocene extension in SE California

    SciTech Connect

    Tosdal, R.M.; Conrad, J.E.; Murphy, G.P. )

    1993-04-01

    Two ductile deformations formed the 3.5-km-thick, south dipping American Girl shear zone in the Cargo Muchancho Mountains, SE California. The older event (D1) imprints crystalloblastic fabrics that record contractional strains at midcrustal depths in the Middle( ) and Late Jurassic. The second event (D2) is marked by superposed mylonitic fabrics that are coplanar and colinear with fabrics of D1. Small mylonitic shear zones of D2 cut undeformed rocks in the hanging wall of the American Girl shear zone. Folded sheets of Jurassic granite geneiss and kinematic indicators in mylonites indicative southward directed transport down the present dip of the foliation during D2. [sup 40]Ar/[sup 39]Ar release spectrum on hornblende from undeformed upper-plate monzo-diorite (173 Ma, U-Pb zircon), about 2 km above the top of shear zone has a plateau age of 96.7[+-]0.9 Ma. In contrast, hornblende release spectra from granite gneiss about 200 m below the top of the shear zone and from hornblende gneiss about 3 km below the top of the shear zone are flat and have identical ages. Hornblende from monzodiorite at the base of the upper plate has a more complicated spectrum that is interpreted to indicate a cooling age of 60.4[+-]1.3 Ma.

  12. Synthesis of highly luminescent mercaptosuccinic acid-coated CdSe nanocrystals under atmospheric conditions.

    PubMed

    Dong, Meiting; Xu, Jingyi; Liu, Shuxian; Zhou, Ying; Huang, Chaobiao

    2014-11-01

    Here we report a facile one-pot method for the preparation of high-quality CdSe nanocrystals (NCs) in aqueous solution under an air atmosphere. Compared with the traditional use of NaHSe or H2 Se, the more stable sodium selenite is utilized as the Se source for preparing highly luminescent CdSe nanocrystals. By using mercaptosuccinic acid (MSA) as the capping agent and borate-citrate acid as the buffering solution, CdSe nanocrystals with high quantum yield (up to 70%) have been synthesized conveniently. The influence of different experimental parameters, such as the pH of the precursor solution, the molar ratio of Cd(2+) to Na2 SeO3 and Cd(2+) to MSA on the CdSe nanocrystals, has been systematically investigated. The prepared CdSe NCs were spherical with a size of ~ 5 nm. PMID:24639040

  13. Hybrid Au-CdSe and Ag-CdSe nanoflowers and core-shell nanocrystals via one-pot heterogeneous nucleation and growth.

    PubMed

    AbouZeid, Khaled M; Mohamed, Mona B; El-Shall, M Samy

    2011-12-01

    A general approach, based on heterogeneous nucleation and growth of CdSe nanostructures on Au or Ag nanocrystals, for the synthesis of Au-CdSe and Ag-CdSe hybrid nanostructures is developed. The new approach provides a versatile one-pot route for the synthesis of hybrid nanoflowers consisting of a gold or silver core and multipod CdSe rods or an intact CdSe shell with controlled thickness, depending on the nucleation and growth parameters. At lower growth temperatures such as 150 °C, the CdSe clusters are adsorbed on the surface of the metal cores in their surface defects, then multiple arms and branches form, resulting in nanoflower-shaped hybrid structures. Increasing the size of the metal core through the choice of the reducing and capping agents results in an improvement of the interface between the metal and CdSe domains, producing core-shell structures. The growth temperature appears to be the most important factor determining the nature of the interface between the metal and CdSe domains. At relatively high temperatures such as 300 °C, the formation of large, faceted Au cores creates preferential growth sites for the CdSe nanocrystalline shell, thus resulting in well-defined Au-CdSe core-shell structures with large interfaces between the Au and CdSe domains. The present approach is expected to foster systematic studies of the electronic structures and optical properties of the metal-semiconductor hybrid materials for potential applications in photovoltaic and nanoelectronic devices. PMID:21994186

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

    SciTech Connect

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

    2006-02-15

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

  15. Electronic structure and photoelectrical properties of Ag2In2SiSe6 and Ag2In2GeSe6

    NASA Astrophysics Data System (ADS)

    Khyzhun, O. Y.; Myronchuk, G. L.; Zamuruyeva, O. V.; Parasyuk, O. V.

    2014-12-01

    High-quality Ag2In2SiSe6 and Ag2In2GeSe6 single crystals have been successfully grown by the vertical Bridgman-Stockbarger method and the horizontal gradient freeze technique, respectively. For pristine and Ar+ ion-irradiated surfaces of the single crystals under study, X-ray photoelectron core-level and valence-band spectra have been measured. Results of these studies allow for concluding that the Ag2In2SiSe6 and Ag2In2GeSe6 single crystal surfaces are sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ ion-bombardment with energy of 3.0 keV during 5 min at an ion current density of 14 μA/cm2 has induced some modification in top surface layers leading to an increase of content of In atoms in the layers. Comparison on a common energy scale of the X-ray emission Se Kβ2 bands representing energy distribution of the Se 4p states and the X-ray photoelectron valence-band spectra reveal that the main contribution of the valence Se p states occur in the upper portion of the valence band, with also their significant contributions in other valence band regions of the Ag2In2SiSe6 and Ag2In2GeSe6 single crystals. In addition, for the single crystals under consideration, temperature dependences of specific dark conductivity and spectral distributions of photoconductivity have been explored. It has been established that the Ag2In2SiSe6 and Ag2In2GeSe6 single crystals are high-resistance semiconductors with value of the specific electrical conductivity σ ≈ 1.67 × 10-9 Ω-1 сm-1 (at Т = 300 K). The both compounds are materials with p-type conductivity.

  16. Formation of two-dimensional CuSe on Cu(111) at very low selenium coverage

    DOE PAGESBeta

    Walen, Holly; Liu, Da -Jiang; Oh, Junepyo; Yang, Hyun Jin; Kim, Yousoo; Thiel, Patricia A.

    2016-05-09

    Here, using scanning tunneling microscopy (STM), we observe that adsorption of Se on Cu(111) produces islands with (√3 x √3)R30° structure, at Se coverages far below the structure's ideal coverage of 1/3 ML. Based on density functional theory (DFT), these islands cannot form due to attractive interactions between chemisorbed Se atoms. DFT shows that incorporating Cu atoms into the √3-Se lattice stabilizes the structure, which provides a plausible explanation for the experimental observations.

  17. Enhanced photoelectric activity of CdSe nanostructures with mixed crystalline phases

    NASA Astrophysics Data System (ADS)

    Tao, Leiming; Pang, Shan; An, Yanqing; Xu, Hongtao; Wu, Sixin

    2010-05-01

    CdSe nanostructures were synthesized by the hydrothermal process. The morphology and structures of as-prepared CdSe were seriously affected by adding an ionic liquid, lithium bis((trifluoromethyl)- sulfonyl)amide. The results illustrated that when the ionic liquid is added, CdSe nanorod-chain assemblies with the mixed cubic and hexagonal phases are obtained. The surface photovoltaic and photocurrent measurements demonstrated that CdSe nanorod-chain assemblies show a photoelectric response.

  18. Raman spectra of haloselenate(IV) ions—the SeO 2Br - anion

    NASA Astrophysics Data System (ADS)

    Milne, John; Lahaie, Pierre

    Compounds of the bromoselenite ion, MSeO 2Br(M + = φ 4Sb +, n-Bu 4N +) have been prepared and their Raman spectra studied. The spectra are consistent with C s symmetry. A normal coordinate analysis of the spectra of SeO 2F -, SeO 2Cl - and SeO 2Br - has been done and force constants determined. The SeX bonds are shown to be remarkably weak.

  19. Controllable synthesis of metal selenide heterostructures mediated by Ag2Se nanocrystals acting as catalysts.

    PubMed

    Zhou, Jiangcong; Huang, Feng; Xu, Ju; Wang, Yuansheng

    2013-10-21

    Ag2Se nanocrystals were demonstrated to be novel semiconductor mediators, or in other word catalysts, for the growth of semiconductor heterostructures in solution. This is a result of the unique feature of Ag2Se as a fast ion conductor, allowing foreign cations to dissolve and then to heterogrow the second phase. Using Ag2Se nanocrystals as catalysts, dimeric metal selenide heterostructures such as Ag2Se-CdSe and Ag2Se-ZnSe, and even multi-segment heterostructures such as Ag2Se-CdSe-ZnSe and Ag2Se-ZnSe-CdSe, were successfully synthesized. Several interesting features were found in the Ag2Se based heterogrowth. At the initial stage of heterogrowth, a layer of the second phase forms on the surface of an Ag2Se nanosphere, with a curved junction interface between the two phases. With further growth of the second phase, the Ag2Se nanosphere tends to flatten the junction surface by modifying its shape from sphere to hemisphere in order to minimize the conjunct area and thus the interfacial energy. Notably, the crystallographic relationship of the two phases in the heterostructure varies with the lattice parameters of the second phase, in order to reduce the lattice mismatch at the interface. Furthermore, a small lattice mismatch at the interface results in a straight rod-like second phase, while a large lattice mismatch would induce a tortuous product. The reported results may provide a new route for developing novel selenide semiconductor heterostructures which are potentially applicable in optoelectronic, biomedical, photovoltaic and catalytic fields. PMID:24056899

  20. Microscale distribution and elemental associations of Se in seleniferous soils in Punjab, India.

    PubMed

    Eiche, Elisabeth

    2015-04-01

    Several regions around the globe are known to have soils highly enriched in Se. Usually, bulk samples are analysed when characterizing enrichment and mobility of Se in seleniferous soils. In this study, Se concentration and distribution were determined along with other elements on a microscale level in seleniferous soils from Punjab, India, using synchrotron-based X-ray fluorescence (XRF) analysis. Additionally, the mineralogical and geochemical composition of bulk soil material was investigated. Sequential extractions were carried out to gain further insight into preferential Se associations. The objective of this study was to investigate the microscale geochemistry of seleniferous soils in order to be able to deduce information about Se host phases, to characterize the distribution, extent and origin of Se enrichment and to possibly reveal the relevant enrichment processes. Selenium concentrations in the soils vary considerably within tens of micrometers. Thirty times the bulk concentration, the highest Se enrichment was found to be 350 mg/kg. Results show that the primary origin of Se in these soils is probably not from weathering of bedrock or alluvium but rather from an external Se source, like Se-rich irrigation water. Secondary processes like in situ formation of mineral phases, adsorption or transformation to organic species finally lead to an immobilization and fixation of Se in the soils. In this context, reduction of Se oxyanions to elemental Se or to selenide as part of sulfides probably leads to the highest Se enrichment which, however, is mainly spatially confined. Lower Se enrichments are indicated to be due to (co-)precipitation with or adsorption to calcite. Therefore, this extremely heterogeneous distribution of Se must be controlled by small-scale differences in redox and solution chemistry which can develop in small soil structure like micropores or soil aggregates. PMID:25342451