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Sample records for deep impurity levels

  1. The origin of deep-level impurity transitions in hexagonal boron nitride

    SciTech Connect

    Du, X. Z.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2015-01-12

    Deep ultraviolet photoluminescence (PL) emission spectroscopy has been employed to investigate the origin of the widely observed deep level impurity related donor-acceptor pair (DAP) transition with an emission peak near 4.1 eV in hexagonal boron nitride (h-BN). A set of h-BN epilayers were grown by metal-organic chemical vapor deposition (MOCVD) under different ammonia (NH{sub 3}) flow rates to explore the role of nitrogen vacancies (V{sub N}) in the deep-level transitions. The emission intensity of the DAP transition near 4.1 eV was found to decrease exponentially with an increase of the NH{sub 3} flow rate employed during the MOCVD growth, implying that impurities involved are V{sub N}. The temperature-dependent PL spectra were measured from 10 K up to 800 K, which provided activation energies of ∼0.1 eV for the shallow impurity. Based on the measured energy level of the shallow impurity (∼0.1 eV) and previously estimated bandgap value of about 6.5 eV for h-BN, we deduce a value of ∼2.3 eV for the deep impurity involved in this DAP transition. The measured energy levels together with calculation results and formation energies of the impurities and defects in h-BN suggest that V{sub N} and carbon impurities occupying the nitrogen sites, respectively, are the most probable shallow donor and deep acceptor impurities involved in this DAP transition.

  2. Theoretical Studies of Deep Impurity Levels in Ternary Semiconductor Alloys.

    DTIC Science & Technology

    2014-09-26

    the predictions for all sp -bonded (X,X) nearest - neighbor pair states in Si. One interesting result is that near- neighbor (P,P) and (As,As) pairs are...levels [120]. (The shallow levels are "attached" to band edges which depend on the nearest - neighbor overlap integrals - and these integrals change...Hess provided data in collaborative lnteractions). Some successes of the theory for nearest - neighbor pairs in GaAsl_xPx are: (i) It predicts which pairs

  3. Resonant and deep impurity levels under hydrostatic pressure in pure n-type InAs

    NASA Astrophysics Data System (ADS)

    Kadri, A.; Aulombard, R. L.; Zitouni, K.; Konczewicz, L.

    1986-05-01

    Hall coefficient ( RH) and electrical resistivity (ϱ 0) were measured as a function of hydrostatic pressure up to 18 kbar, in the 4.2 K-120 K temperature range, on nominally undopted n-type InAs with free carrier concentration ∼2 × 10 16 cm -3. In the 4.2-30 K range, RH and ϱ 0 versus pressure variations indicate the deionization of impurity states which are resonant in the Γ 1c band at normal pressure. The position and the pressure variation of the resonant impurity level are discussed. At T>30 K, evidence is made for the existence of a donor-like impurity level lying ∼10 meV below the Γ 1c band minimum and moving with pressure at the rate of -1.8 meV/kbar with respect to this band.

  4. Deep Impurity States in Gallium Arsenide.

    DTIC Science & Technology

    1981-10-01

    determinations using a level to conduction band) and the capture rates mercury Schottky barrier. mercry chotky arrer.(fr m conduction band to deep level) as a...heating. The luminescence is dispersed through a grating spectrometer and detected with a cooled lead- sulphide photoconduc- tor. An important feature in the

  5. Energy levels of isoelectronic impurities by large scale LDA calculations

    SciTech Connect

    Li, Jingbo; Wang, Lin-Wang

    2002-11-22

    Isoelectronic impurity states are localized states induced by stoichiometric single atom substitution in bulk semiconductor. Photoluminescence spectra indicate deep impurity levels of 0.5 to 0.9eV above the top of valence band for systems like: GaN:As, GaN:P, CdS:Te, ZnS:Te. Previous calculations based on small supercells seemingly confirmed these experimental results. However, the current ab initio calculations based on thousand atom supercells indicate that the impurity levels of the above systems are actually much shallower(0.04 to 0.23 eV), and these impurity levels should be compared with photoluminescence excitation spectra, not photoluminescence spectra.

  6. Deep impurity trapping concepts for power semiconductor devices

    NASA Technical Reports Server (NTRS)

    Sundberg, G. R.

    1982-01-01

    High voltage semiconductor switches using deep impurity doped silicon now appear feasible for high voltage (1-100 kV), high power (10 Kw) switching and protection functions for future space power applications. Recent discoveries have demonstrated several practical ways of gating deep impurity doped silicon devices in planar configurations and of electrically controlling their characteristics, leading to a vast array of possible circuit applications. A new family of semiconductor switching devices and transducers are possible based on this technology. New deep impurity devices could be simpler than conventional p-n junction devices and yet use the same basic materials and processing techniques. In addition, multiple functions may be possible on a single device as well as increased ratings.

  7. Double-injection, deep-impurity switch development

    NASA Technical Reports Server (NTRS)

    Selim, F. A.; Whitson, D. W.

    1983-01-01

    The overall objective of this program is the development of device design and process techniques for the fabrication of a double-injection, deep-impurity (DI)(2) silicon switch that operates in the 1-10 kV range with conduction current of 10 and 1A, respectively. Other major specifications include a holding voltage of 0 to 5 volts at 1 A anode current, 10 microsecond switching time, and power dissipation of 50 W at 75 C. This report describes work that shows how the results obtained at the University of Cincinnati under NASA Grant NSG-3022 have been applied to larger area and higher voltage devices. The investigations include theoretical, analytical, and experimental studies of device design and processing. Methods to introduce deep levels, such as Au diffusion and electron irradiation, have been carried out to "pin down' the Fermi level and control device-switching characteristics. Different anode, cathode, and gate configurations are presented. Techniques to control the surface electric field of planar structures used for (DI)(2) switches are examined. Various sections of this report describe the device design, wafer-processing techniques, and various measurements which include ac and dc characteristics, 4-point probe, and spreading resistance.

  8. A study of the dependence of electron-induced defects on the doping impurity density in n-type germanium by deep-level transient spectroscopy (DLTS)

    NASA Astrophysics Data System (ADS)

    Nyamhere, Cloud; Auret, F. D.; Das, A. G. M.; Chawanda, A.

    2007-12-01

    We have measured the electrical characteristics of electron irradiation-induced defects in n-type (1 1 0), (1 1 1) and (1 0 0) germanium doped with antimony (Sb) by deep-level transient spectroscopy (DLTS) and Laplace-DLTS. The following electron traps at 0.04, 0.15, 0.20, 0.21, 0.23, 0.31 and 0.38 eV below the conduction band were observed and two hole traps at 0.09 and 0.30 eV above the valence band were recorded in the low doping (10 14 cm -3) samples. In the higher doping (10 15 cm -3) samples, similar electron traps were observed but the electron trap at 0.04 eV below the conduction band and hole trap at 0.09 eV above the valence band was not observed. The electron trap at 0.38 eV is identified as the (V-Sb) --/- center and the hole trap at 0.30 eV assigned the (V-Sb) 0/- appeared in almost equal concentrations in the higher-doped samples but in the lowest-doped samples the hole trap (V-Sb) 0/- was more dominant. We have also presented the annealing behavior of these electron-induced defects.

  9. Double-injection, deep-impurity switch development

    NASA Technical Reports Server (NTRS)

    Whitson, D. W.

    1985-01-01

    The overall objective of this program was the development of device design and process techniques for the fabrication of a double-injection, deep-impurity (DI) sup 2 silicon switch that operates in the 2-10 kV range with conduction current values of 5 A at 2 kV and 1 A at 10 kV. Other major specifications include a holding voltage of 10 V with no gate current, 10 microsec switching time, and power dissipation of 50 W at 75 C. It was decided to concentrate on the lateral circular devices in order to optimize the gold diffusion. This resulted in devices that are much better switches (approx.1 micro sec switching time), and in a gold diffusion process that is much more controllable than those previously developed. Some results with injection-gated devices were also obtained. The current conduction for V less than VT was analyzed and seen to agree, for the most part, with Lampert's theory. Various sections of this report describe the device designs, wafer-processing techniques, and various measurements which include ac and dc characteristics and four-point probe.

  10. Advanced development of double-injection, deep-impurity semiconductor switches

    NASA Technical Reports Server (NTRS)

    Hanes, M. H.

    1987-01-01

    Deep-impurity, double-injection devices, commonly refered to as (DI) squared devices, represent a class of semiconductor switches possessing a very high degree of tolerance to electron and neutron irradiation and to elevated temperature operation. These properties have caused them to be considered as attractive candidates for space power applications. The design, fabrication, and testing of several varieties of (DI) squared devices intended for power switching are described. All of these designs were based upon gold-doped silicon material. Test results, along with results of computer simulations of device operation, other calculations based upon the assumed mode of operation of (DI) squared devices, and empirical information regarding power semiconductor device operation and limitations, have led to the conculsion that these devices are not well suited to high-power applications. When operated in power circuitry configurations, they exhibit high-power losses in both the off-state and on-state modes. These losses are caused by phenomena inherent to the physics and material of the devices and cannot be much reduced by device design optimizations. The (DI) squared technology may, however, find application in low-power functions such as sensing, logic, and memory, when tolerance to radiation and temperature are desirable (especially is device performance is improved by incorporation of deep-level impurities other than gold.

  11. Temperature and pressure coefficients of iron resonant impurity level in PbTe

    NASA Astrophysics Data System (ADS)

    Skipetrov, E. P.; Kruleveckaya, O. V.; Skipetrova, L. A.; Slynko, V. E.

    2017-01-01

    We investigate temperature dependences of galvanomagnetic parameters in weak magnetic fields (4.2 ≤ T ≤ 300 K, B ≤ 0.07 T) in the p-Pb1-yFeyTe alloy from the middle part of the single-crystal ingot, where the Fermi level is pinned by the resonant impurity level lying under the top of the valence band. Experiments are performed under hydrostatic compression up to 10 kbar. Using scanning electron microscopy, we find microscopic inclusions of the secondary phase enriched with iron and show that the main phase is characterized by a good uniformity of the spatial distribution of impurities. A monotonous increase of the free hole concentration at liquid-helium temperature under pressure and anomalous temperature dependences of the Hall coefficient in the whole investigated pressure range are revealed. Experimental results are explained by a model assuming pinning of the Fermi level by the impurity level and a redistribution of electrons between the valence band and impurity states with increasing temperature and under pressure. In the framework of the two-band Kane dispersion law, theoretical temperature dependences of the Hall coefficient under pressure, which are in satisfactory agreement with the experimental ones at low temperatures, are calculated and temperature and pressure coefficients of the iron deep level are determined. Diagrams of the electronic structure rearrangement with increasing temperature for Pb1-yFeyTe at pressures up to 10 kbar are proposed.

  12. Multi-level Algorithm for the Anderson Impurity Model

    NASA Astrophysics Data System (ADS)

    Chandrasekharan, S.; Yoo, J.; Baranger, H. U.

    2004-03-01

    We develop a new quantum Monte Carlo algorithm to solve the Anderson impurity model. Instead of integrating out the Fermions, we work in the Fermion occupation number basis and thus have direct access to the Fermionic physics. The sign problem that arises in this formulation can be solved by a multi-level technique developed by Luscher and Weisz in the context of lattice QCD [JHEP, 0109 (2001) 010]. We use the directed-loop algorithm to update the degrees of freedom. Further, this algorithm allows us to work directly in the Euclidean time continuum limit for arbitrary values of the interaction strength thus avoiding time discretization errors. We present results for the impurity susceptibility and the properties of the screening cloud obtained using the algorithm.

  13. Screening charged impurities and lifting the orbital degeneracy in graphene by populating Landau levels.

    PubMed

    Luican-Mayer, Adina; Kharitonov, Maxim; Li, Guohong; Lu, Chih-Pin; Skachko, Ivan; Gonçalves, Alem-Mar B; Watanabe, K; Taniguchi, T; Andrei, Eva Y

    2014-01-24

    We report the observation of an isolated charged impurity in graphene and present direct evidence of the close connection between the screening properties of a 2D electron system and the influence of the impurity on its electronic environment. Using scanning tunneling microscopy and Landau level spectroscopy, we demonstrate that in the presence of a magnetic field the strength of the impurity can be tuned by controlling the occupation of Landau-level states with a gate voltage. At low occupation the impurity is screened, becoming essentially invisible. Screening diminishes as states are filled until, for fully occupied Landau levels, the unscreened impurity significantly perturbs the spectrum in its vicinity. In this regime we report the first observation of Landau-level splitting into discrete states due to lifting the orbital degeneracy.

  14. Coulomb impurity effects on the zero-Landau level splitting of graphene on polar substrates

    NASA Astrophysics Data System (ADS)

    Xiao, Yao; Li, Wei-Ping; Li, Zhi-Qing; Wang, Zi-Wu

    2017-04-01

    We theoretically investigate the effects of the Coulomb impurity on the zero-Landau level splitting of graphene on different polar substrates basing on the Fröhlich polaron model, in which the polaron is formed due to the carriers-surface optical phonon coupling. We discuss the influence of Coulomb impurity on the zero-Landau level splitting in the case of weak and strong coupling limits. We find that the splitting energy can be varied in a large scale due to the Coulomb impurity, which provides the possible theoretical explanation for the experimental measurements regarding the energy gap opened and zero-Landau level splitting in Landau quantized graphene.

  15. Cryogenic Laser Calorimetry for Impurity Analysis

    NASA Technical Reports Server (NTRS)

    Swimm, R. T.

    1985-01-01

    The results of a one-year effort to determine the applicability of laser-calorimetric spectroscopy to the study of deep-level impurities in silicon are presented. Critical considerations for impurity analysis by laser-calorimetric spectroscopy are discussed, the design and performance of a cryogenic laser calorimeter is described, and measurements of background absorption in high-purity silicon are presented.

  16. Impurity levels and power loading in the PDX tokamak with high power neutral beam injection

    SciTech Connect

    Fonck, R.J.; Bell, M.; Bol, K.

    1982-10-01

    The PDX tokamak provides an experimental facility for the direct comparison of various impurity control techniques under reactor-like conditions. Four neutral beam lines can inject up to 6 MW for 300 ms. Carbon rail limiter discharges have been used to test the effectiveness of perpendicular injection, but non-disruptive full power operation for > 100 ms is difficult without extensive conditioning. Initial tests of a toroidal bumper limiter indicate reduced power loading and roughly similar impurity levels compared to the carbon rail limiter discharges. Poloidal divertor discharges with up to 5 MW of injected power are cleaner than similar circular discharges, and the power is deposited in a remote divertor chamber. High density divertor operation indicates a reduction of impurity flow velocity in the divertor and enhanced recycling in the divertor region during neutral injection.

  17. Pressure studies of deep levels in semiconductors

    SciTech Connect

    Samara, G.A.

    1989-01-01

    The effects of pressure on the energetics and kinetics of electron emission and capture processes by several important deep levels in Si are discussed. The results yield the first quantitative measures of the breathing mode lattice relaxations accompanying these processes. 2 refs., 1 fig.

  18. Effect of impurities and processing on silicon solar cells. Volume 1: Characterization methods for impurities in silicon and impurity effects data base

    NASA Technical Reports Server (NTRS)

    Hopkins, R. H.; Davis, J. R.; Rohatgi, A.; Campbell, R. B.; Blais, P. D.; Rai-Choudhury, P.; Stapleton, R. E.; Mollenkopf, H. C.; Mccormick, J. R.

    1980-01-01

    Two major topics are treated: methods to measure and evaluate impurity effects in silicon and comprehensive tabulations of data derived during the study. Discussions of deep level spectroscopy, detailed dark I-V measurements, recombination lifetime determination, scanned laser photo-response, conventional solar cell I-V techniques, and descriptions of silicon chemical analysis are presented and discussed. The tabulated data include lists of impurity segregation coefficients, ingot impurity analyses and estimated concentrations, typical deep level impurity spectra, photoconductive and open circuit decay lifetimes for individual metal-doped ingots, and a complete tabulation of the cell I-V characteristics of nearly 200 ingots.

  19. Impurities in silicon solar cells

    NASA Technical Reports Server (NTRS)

    Hopkins, R. H.

    1985-01-01

    Metallic impurities, both singly and in combinations, affect the performance of silicon solar cells. Czochralski silicon web crystals were grown with controlled additions of secondary impurities. The primary electrical dopants were boron and phosphorus. The silicon test ingots were grown under controlled and carefully monitored conditions from high-purity charge and dopant material to minimize unintentional contamination. Following growth, each crystal was characterized by chemical, microstructural, electrical, and solar cell tests to provide a detailed and internally consistent description of the relationships between silicon impurity concentration and solar cell performance. Deep-level spectroscopy measurements were used to measure impurity concentrations at levels below the detectability of other techniques and to study thermally-induced changes in impurity activity. For the majority of contaminants, impurity-induced performance loss is due to a reduction of the base diffusion length. From these observations, a semi-empirical model which predicts cell performance as a function of metal impurity concentration was formulated. The model was then used successfully to predict the behavior of solar cells bearing as many as 11 different impurities.

  20. DETECTING LOW-LEVEL SYNTHESIS IMPURITIES IN MODIFIED PHOSPHOROTHIOATE OLIGONUCLEOTIDES USING LIQUID CHROMATOGRAPHY – HIGH RESOLUTION MASS SPECTROMETRY

    PubMed Central

    Nikcevic, Irena; Wyrzykiewicz, Tadeusz K.; Limbach, Patrick A.

    2010-01-01

    Summary An LC-MS method based on the use of high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTIRCMS) for profiling oligonucleotides synthesis impurities is described. Oligonucleotide phosphorothioatediesters (phosphorothioate oligonucleotides), in which one of the non-bridging oxygen atoms at each phosphorus center is replaced by a sulfur atom, are now one of the most popular oligonucleotide modifications due to their ease of chemical synthesis and advantageous pharmacokinetic properties. Despite significant progress in the solid-phase oligomerization chemistry used in the manufacturing of these oligonucleotides, multiple classes of low-level impurities always accompany synthetic oligonucleotides. Liquid chromatography-mass spectrometry has emerged as a powerful technique for the identification of these synthesis impurities. However, impurity profiling, where the entire complement of low-level synthetic impurities is identified in a single analysis, is more challenging. Here we present an LC-MS method based the use of high resolution-mass spectrometry, specifically Fourier transform ion cyclotron resonance mass spectrometry (FTIRCMS or FTMS). The optimal LC-FTMS conditions, including the stationary phase and mobile phases for the separation and identification of phosphorothioate oligonucleotides, were found. The characteristics of FTMS enable charge state determination from single m/z values of low-level impurities. Charge state information then enables more accurate modeling of the detected isotopic distribution for identification of the chemical composition of the detected impurity. Using this approach, a number of phosphorothioate impurities can be detected by LC-FTMS including failure sequences carrying 3′-terminal phosphate monoester and 3′-terminal phosphorothioate monoester, incomplete backbone sulfurization and desulfurization products, high molecular weight impurities, and chloral, isobutyryl, and N3 (2-cyanoethyl) adducts

  1. Breathing mode lattice relaxation associated with carrier emission and capture by deep electronic levels in silicon

    SciTech Connect

    Samara, G.A.

    1987-01-01

    The breathing mode (volume) lattice relaxations associated with carrier emission and capture are evaluated for a variety of deep levels in silicon using a recently proposed method based on high pressure measurement of the emission rates and capture cross sections. Included are (1) the vacancy-like acceptor levels associated with the oxygen-vacancy pair (or A-center) and the gold, platinum and palladium impurities, (2) the chalcogenide donors in their singly- and doubly-charged states and (3) a number of 3d transition metal donors. The signs and magnitudes (which range from approx.0 to 5A/sup 3//emitted carrier) of these relaxations are discussed in terms of models for the impurities and defects responsible for the associated levels. The results on the chalcogenides are compared with recent theoretical calculations. 8 refs., 1 tab.

  2. Energy levels and far-infrared optical absorption of impurity doped semiconductor nanorings: Intense laser and electric fields effects

    NASA Astrophysics Data System (ADS)

    Barseghyan, M. G.

    2016-11-01

    The effects of electron-impurity interaction on energy levels and far-infrared absorption in semiconductor nanoring under the action of intense laser and lateral electric fields have been investigated. Numerical calculations are performed using exact diagonalization technique. It is found that the electron-impurity interaction and external fields change the energy spectrum dramatically, and also have significant influence on the absorption spectrum. Strong dependence on laser field intensity and electric field of lowest energy levels, also supported by the Coulomb interaction with impurity, is clearly revealed.

  3. Breathing-mode lattice relaxation accompanying emission and capture by deep electronic levels in silicon

    SciTech Connect

    Samara, G. A.

    1989-05-15

    The breathing-mode (volume) lattice relaxations associated with carrier emission and capture by a variety of deep electronic levels in silicon are evaluated from high-pressure measurements of the emission rates and capture cross sections. Included are (1) the vacancylike acceptor levels associated with the oxygen-vacancy pair (or /ital A/ center) and the gold, platinum, and palladium impurities, (2) the chalcogenide donors in their singly and doubly charged states, (3) a number of 3/ital d/ transition-metal donors, and (4) the phosphorus-vacancy pair (or /ital E/ center) acceptor. The signs and magnitudes (which range from /similar to/0 to 5 A/sup 3//emitted-carrier) of these relaxations are discussed in terms of models for the impurities and defects responsible for the associated levels. The results on the chalcogenides are compared with recent theoretical results. The experimental method used appears to be the only viable experimental method for determining these relaxations which are a direct manifestation of the effective electron-phonon coupling at deep levels and which are important to the understanding of many of the properties of deep levels.

  4. First principle prediction of shallow defect level binding energies and deep level nonradiative recombination rates

    NASA Astrophysics Data System (ADS)

    Wang, Linwang

    2014-03-01

    Accurate calculation of defect level energies in semiconductors and their carrier capturing rate is an important issue in ab initio prediction of semiconductor properties. In this talk, I will present our result work in ab initio shallow level calculation and deep level caused nonradiative recombination rate calculation. In the shallow acceptor level calculation, a large system up to 64,000 atoms needs to be used to properly describe the weakly bounded hole wave functions. The single particle Hamiltonian of that system is patched from bulk potential and central potential. Furthermore, GW calculation is used to correct the one site potential of the impurity atom. The resulting binding energy agrees excellently with the experiments within 10 meV. To calculate the nonradiative decay rate, the electron-phonon coupling constants in the defect system are calculated all at once using a new variational algorithm. Multiphonon process formalism is used to calculate the nonradiative decay rate. It is found that the transition is induced by the electron and the optical phonon coupling, but the energy conservation is mostly satisfied by the acoustic phonons. The new algorithm allows fast calculation of such nonradiative decay rate for any defect levels, as well as other multiphonon processes in nanostructures. This work was supported by the Director, Office of Science (SC), Basic Energy Science (BES)/Materials Science and Engineering Division (MSED) of the U.S. Department of Energy (DOE) under the contract No. DE-AC02-05CH11231.

  5. Thermal annealing behavior of deep levels in Rh-doped n-type MOVPE GaAs

    NASA Astrophysics Data System (ADS)

    Naz, Nazir A.; Qurashi, Umar S.; Zafar Iqbal, M.

    2009-12-01

    We report the results of isochronal annealing study of deep levels in Rh-doped n-type GaAs grown by metal-organic vapor phase epitaxy (MOVPE). Deep level transient spectroscopy (DLTS) technique has been employed to study the effects of annealing on deep levels in Rh-doped p+nn+ junction samples. A majority-carrier emitting band of deep levels along with a high temperature peak (RhE1), corresponding to deep level energy position Ec-0.92 eV and a minority-carrier emitting band of deep levels are identified with Rh-impurity prior to thermal annealing of our samples. In addition to these Rh-related deep levels, the well-known native defect EL2 at Ec-0.79 eV is observed in majority-carrier emission spectra and two inadvertent deep-level defects, H1 at Ev+0.09 eV and H3 at Ev+0.93 eV, usually observed in reference (without Rh) samples, are also detected in the minority-carrier emission spectra of Rh-doped samples. At least one level is found to be introduced at Ec-0.13 eV in Rh-doped samples at about the same temperature position as the level E(A)1, observed in reference samples, as a result of isochronal annealing, while the other two levels observed in reference samples could not be seen in annealed Rh-doped samples. Data on the annealing behavior and other characteristics of both Rh-related bands of deep levels observed in majority- and minority-carrier emission DLTS spectra, as well as for the high temperature Rh-related electron-emission peak, are presented. Possible interpretations of these results for the nature and structure of the different deep-level defects are discussed.

  6. Determination of trace level impurities in uranium compounds by ICP-AES after organic extraction.

    PubMed

    Marin, S; Cornejo, S; Jara, C; Duran, N

    1996-06-01

    The determination was studied of Al, B, Be, Cd, Ca, Co, Cu, Mg, Mn, Mo, Pb, Si, Sn, V, Cr, Ni, and Fe as trace level impurities in uranium compounds by ICP-AES after extraction of uranium with three different mixtures of di-(2-ethyl-hexyl) phosphate (D2EHP) and tri-(2-ethyl-hexyl)-phosphate (T2EHP) in solvents like toluene, carbon tetrachloride, hexane and cyclohexane. The study was carried out in presence of different concentrations of HCl and HNO(3). A single extraction with D2EHP in cyclohexane using nitric acid as matrix was sufficient to reduce the U(3)O(8) concentration from 100 g/l to 100 microg/ml. The ICP-AES instrumentation applied, allowed the determination of metal concentrations ten-times lower than those usually found in nuclear grade U(3)O(8). To check the efficiency of the extraction and the accuracy of the proposed method, Certified Reference Materials were used in the dissolution and extraction steps. The method described can be used for the determination of trace metals in nuclear grade U(3)O(8).

  7. Isothermal Capacitance Transient Spectroscopy for Determination of Deep Level Parameters

    NASA Astrophysics Data System (ADS)

    Okushi, Hideyo; Tokumaru, Yozo

    1980-06-01

    A new measurement method for deep levels in semiconductors is proposed, by which the measurement of the transient change of capacitance is performed under an isothermal condition (Isothermal Capacitance Transient Spectroscopy). The method allows us to construct a precise measurement and analysis system by a programmable calculator. Computer simulation and experiment by the method in the case of Au-doped Si are demonstrated. It is shown that the method is one of useful tools for spectroscopic analysis of deep levels in semiconductors.

  8. Deep-levels in gallium arsenide for device applications

    NASA Astrophysics Data System (ADS)

    McManis, Joseph Edward

    Defects in semiconductors have been studied for over 40 years as a diagnostic of the quality of crystal growth. In this thesis, we investigate GaAs deep-levels specifically intended for devices. This thesis summarizes our efforts to characterize the near-infrared photoluminescence from deep-levels, study optical transitions via absorption, and fabricate and characterize deep-level light-emitting diodes (LEDs). This thesis also describes the first tunnel diodes which explicitly make use of GaAs deep-levels. Photoluminescence measurements of GaAs deep-levels showed a broad peak around a wavelength extending from 1.0--1.7 mum, which includes important wavelengths for fiber-optic communications (1.3--1.55 mum). Transmission measurements show the new result that very little of the radiative emission is self-absorbed. We measured the deep-level photoluminescence at several temperatures. We are also the first to report the internal quantum efficiency associated with the deep-level transitions. We have fabricated LEDs that, utilize the optical transitions of GaAs deep-levels. The electroluminescence spectra showed a broad peak from 1.0--1.7 mum at low currents, but the spectrum exhibited a blue-shift as the current was increased. To improve device performance, we designed an AlGaAs layer into the structure of the LEDs. The AlGaAs barrier layer acts as a resistive barrier so that the holes in the p-GaAs layer are swept away from underneath the gold p-contact. The AlGaAs layer also reduces the blue-shift by acting as a potential barrier so that only higher-energy holes are injected. We found that the LEDs with AlGaAs were brighter at long wavelengths, which was a significant improvement. Photoluminescence measurements show that the spectral blue-shift is not due to sample heating. We have developed a new physical model to explain the blue-shift: it is caused by Coloumb charging of the deep-centers. We have achieved the first tunnel diodes with which specifically utilize deep-levels

  9. Impurity gettering

    SciTech Connect

    Picraux, S.T.

    1995-06-01

    Transition metal impurities are well known to cause detrimental effects when present in the active regions of Si devices. Their presence degrades minority carrier lifetime, provides recombination-generation centers, increases junction leakage current and reduces gate oxide integrity. Thus, gettering processes are used to reduce the available metal impurities from the active region of microelectronic circuits. Gettering processes are usually divided into intrinsic (or internal) and extrinsic (or external) categories. Intrinsic refers to processing the Si wafer in a way to make available internal gettering sites, whereas extrinsic implies externally introduced gettering sites. Special concerns have been raised for intrinsic gettering. Not only will the formation of the precipitated oxide and denuded zone be difficult to achieve with the lower thermal budgets, but another inherent limit may set in. In this or any process which relies on the precipitation of metal silicides the impurity concentration can only be reduced as low as the solid solubility limit. However, the solubilities of transition metals relative to silicide formation are typically found to be {approx_gt}10{sup 12}/cm{sup 3} at temperatures of 800 C and above, and thus inadequate to getter to the needed concentration levels. It is thus anticipated that future microelectronic device processing will require one or more of the following advances in gettering technology: (1) new and more effective gettering mechanisms; (2) quantitative models of gettering to allow process optimization at low process thermal budgets and metal impurity concentrations, and/or (3) development of front side gettering methods to allow for more efficient gettering close to device regions. These trend-driven needs provide a driving force for qualitatively new approaches to gettering and provide possible new opportunities for the use of ion implantation in microelectronics processing.

  10. Investigation of Deep Levels in GaInNas

    SciTech Connect

    Abulfotuh, F.; Balcioglu, A.; Friedman, D.; Geisz, J.; Kurtz, S.

    1998-11-12

    This paper presents and discusses the first Deep-Level transient spectroscopy (DLTS) data obtained from measurements carried out on both Schottky barriers and homojunction devices of GaInNAs. The effect of N and In doping on the electrical properties of the GaNInAs devices, which results in structural defects and interface states, has been investigated. Moreover, the location and densities of deep levels related to the presence of N, In, and N+In are identified and correlated with the device performance. The data confirmed that the presence of N alone creates a high density of shallow hole traps related to the N atom and structural defects in the device. Doping by In, if present alone, also creates low-density deep traps (related to the In atom and structural defects) and extremely deep interface states. On the other hand, the co-presence of In and N eliminates both the interface states and levels related to structural defects. However, the device still has a high density of the shallow and deep traps that are responsible for the photocurrent loss in the GaNInAs device, together with the possible short diffusion length.

  11. Characterization of a deep-level compensation ratio through picosecond four-wave mixing on a transient reflection grating

    NASA Astrophysics Data System (ADS)

    Kadys, A.; Delaye, Ph; Roosen, G.; Jarasiunas, K.

    2007-09-01

    We demonstrate a novel application of a time-resolved four-wave mixing technique for the determination of a deep-level compensation ratio in a semi-insulating crystal. The approach is based on photoexcitation of carriers from deep impurity levels, formation of a space-charge electric field in deep traps, and monitoring dynamics of photorefractive, free- carrier and absorption gratings by light diffraction. The analysis of anisotropic diffraction features on the reflection grating provided requirements for crystal orientation in order to discriminate contribution of amplitude grating from the photorefractive phase grating, both being related to deep-trap occupation. Contributions of these optical nonlinearities were studied experimentally in (0 0 1)-oriented GaAs wafers by using a transient reflection grating configuration with a very small grating period (150 nm). Comparison of the reflection grating picosecond kinetics and its diffraction efficiency with modeling curves allowed us to ascribe the slow decay component to amplitude grating in recharged deep traps and determine their compensation ratio. The proposed technique allowed the determination of the compensation ratio of a deep EL2 donor, equal to 0.6 ± 0.05 in the given GaAs crystal.

  12. Large impurity effects in rubrene crystals: First-principles calculations

    SciTech Connect

    Tsetseris, L.; Pantelides, Sokrates T.

    2008-01-01

    Carrier mobilities of rubrene films are among the highest values reported for any organic semiconductor. Here, we probe with first-principles calculations the sensitivity of rubrene crystals on impurities. We find that isolated oxygen impurities create distinct peaks in the electronic density of states consistent with observations of defect levels in rubrene and that increased O content changes the position and shape of rubrene energy bands significantly. We also establish a dual role of hydrogen as individual H species and H impurity pairs create and annihilate deep carrier traps, respectively. The results are relevant to the performance and reliability of rubrene-based devices.

  13. Deep borehole disposal of high-level radioactive waste.

    SciTech Connect

    Stein, Joshua S.; Freeze, Geoffrey A.; Brady, Patrick Vane; Swift, Peter N.; Rechard, Robert Paul; Arnold, Bill Walter; Kanney, Joseph F.; Bauer, Stephen J.

    2009-07-01

    Preliminary evaluation of deep borehole disposal of high-level radioactive waste and spent nuclear fuel indicates the potential for excellent long-term safety performance at costs competitive with mined repositories. Significant fluid flow through basement rock is prevented, in part, by low permeabilities, poorly connected transport pathways, and overburden self-sealing. Deep fluids also resist vertical movement because they are density stratified. Thermal hydrologic calculations estimate the thermal pulse from emplaced waste to be small (less than 20 C at 10 meters from the borehole, for less than a few hundred years), and to result in maximum total vertical fluid movement of {approx}100 m. Reducing conditions will sharply limit solubilities of most dose-critical radionuclides at depth, and high ionic strengths of deep fluids will prevent colloidal transport. For the bounding analysis of this report, waste is envisioned to be emplaced as fuel assemblies stacked inside drill casing that are lowered, and emplaced using off-the-shelf oilfield and geothermal drilling techniques, into the lower 1-2 km portion of a vertical borehole {approx}45 cm in diameter and 3-5 km deep, followed by borehole sealing. Deep borehole disposal of radioactive waste in the United States would require modifications to the Nuclear Waste Policy Act and to applicable regulatory standards for long-term performance set by the US Environmental Protection Agency (40 CFR part 191) and US Nuclear Regulatory Commission (10 CFR part 60). The performance analysis described here is based on the assumption that long-term standards for deep borehole disposal would be identical in the key regards to those prescribed for existing repositories (40 CFR part 197 and 10 CFR part 63).

  14. Gallium arsenide deep-level optical emitter for fibre optics.

    PubMed

    Pan, Janet L; McManis, Joseph E; Osadchy, Thomas; Grober, Louise; Woodall, Jerry M; Kindlmann, Peter J

    2003-06-01

    Fibre-optic components fabricated on the same substrate as integrated circuits are important for future high-speed communications. One industry response has been the costly push to develop indium phosphide (InP) electronics. However, for fabrication simplicity, reliability and cost, gallium arsenide (GaAs) remains the established technology for integrated optoelectronics. Unfortunately, the GaAs bandgap wavelength (0.85 microm) is far too short for fibre optics at 1.3-1.5 microm. This has led to work on materials that have a large lattice mismatch on GaAs. Here we demonstrate the first light-emitting diode (LED) that emits at 1.5 microm fibre-optic wavelengths in GaAs using optical transitions from arsenic antisite (As(Ga)) deep levels. This is an enabling technology for fibre-optic components that are lattice-matched to GaAs integrated circuits. We present experimental results showing significant internal optical power (24 mW) and speed (in terahertz) from GaAs optical emitters using deep-level transitions. Finally, we present theory showing the ultimate limit to the efficiency-bandwidth product of semiconductor deep-level optical emitters.

  15. Controlling the Curie temperature in (Ga,Mn)As through location of the Fermi level within the impurity band.

    PubMed

    Dobrowolska, M; Tivakornsasithorn, K; Liu, X; Furdyna, J K; Berciu, M; Yu, K M; Walukiewicz, W

    2012-02-19

    The ferromagnetic semiconductor (Ga,Mn)As has emerged as the most studied material for prototype applications in semiconductor spintronics. Because ferromagnetism in (Ga,Mn)As is hole-mediated, the nature of the hole states has direct and crucial bearing on its Curie temperature T(C). It is vigorously debated, however, whether holes in (Ga,Mn)As reside in the valence band or in an impurity band. Here we combine results of channelling experiments, which measure the concentrations both of Mn ions and of holes relevant to the ferromagnetic order, with magnetization, transport, and magneto-optical data to address this issue. Taken together, these measurements provide strong evidence that it is the location of the Fermi level within the impurity band that determines T(C) through determining the degree of hole localization. This finding differs drastically from the often accepted view that T(C) is controlled by valence band holes, thus opening new avenues for achieving higher values of T(C).

  16. Correlation between deep-level defects and turn-on recovery characteristics in AlGaN/GaN hetero-structures

    NASA Astrophysics Data System (ADS)

    Nakano, Yoshitaka; Irokawa, Yoshihiro; Sumida, Yasunobu; Yagi, Shuichi; Kawai, Hiroji

    2012-11-01

    We report on a correlation between deep-level defects and turn-on recovery characteristics in AlGaN/GaN hetero-structures, employing Schottky barrier diodes. Photo-capacitance spectroscopy measurements reveal three specific deep levels located at ˜2.07, ˜2.80, and ˜3.23 eV below the conduction band, presumably attributable to Ga vacancies and/or impurity C present in the GaN buffer layer. Additionally, from photo-assisted turn-on current recovery measurements, by using 390 and 370 nm long-pass filters, the recovery time becomes significantly faster due to inactivation of their corresponding deep-level traps. Therefore, the ˜2.80 and ˜3.23 eV levels are probably responsible for the carrier-trapping phenomena in the bulk region.

  17. Deep-level spectroscopy in metal-insulator-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Kurtz, A.; Muñoz, E.; Chauveau, J. M.; Hierro, A.

    2017-02-01

    In this study we present a method for measuring bulk traps using deep-level spectroscopy techniques in metal-insulator-semiconductor (MIS) structures. We will focus on deep-level transient spectroscopy (DLTS), although this can be extended to deep-level optical spectroscopy (DLOS) and similar techniques. These methods require the modulation of a depletion region either from a Schottky junction or from a highly asymmetric p-n junction, junctions that may not be realizable in many current material systems. This is the case of wide-bandgap semiconductor families that present a doping asymmetry or have a high residual carrier concentration or surface carrier accumulation, such as InGaN or ZnO. By adding a thin insulating layer and forming an MIS structure this problem can be circumvented and DLTS/DLOS can be performed under certain conditions. A model for the measurement of bulk traps in MIS structures is thus presented, focusing on the similarities with standard DLTS, maintaining when possible links to existing knowledge on DLTS and related techniques. The model will be presented from an equivalent circuit point of view. The effect of the insulating layer on DLTS is evaluated by a combination of simulations and experiments, developing methods for the measurement of these type of devices. As a validation, highly doped ZnO:Ga MIS devices have been successfully characterized and compared with a reference undoped sample using the methods described in this work, obtaining the same intrinsic levels previously reported in the literature but in material doped as high as 1× {{10}18} cm-3.

  18. Semiconductor steady state defect effective Fermi level and deep level transient spectroscopy depth profiling

    NASA Astrophysics Data System (ADS)

    Chin, Ken K.; Cheng, Zimeng

    2016-09-01

    The widely used deep level transient spectroscopy (DLTS) theory and data analysis usually assume that the defect level distribution is uniform through the depth of the depletion region of the n—p junction. In this work we introduce the concept of effective Fermi level of the steady state of semiconductor, by using which deep level transient spectroscopy depth profiling (DLTSDP) is proposed. Based on the relationship of its transition free energy level (TFEL) and the effective Fermi level, the rules of detectivity of the defect levels are listed. Computer simulation of DLTSDP is presented and compared with experimental data. The experimental DLTS data are compared with what the DLTSDP selection rules predicted. The agreement is satisfactory.

  19. Deep-level defects related to the emissive pits in thick InGaN films on GaN template and bulk substrates

    NASA Astrophysics Data System (ADS)

    Sumiya, Masatomo; Toyomitsu, Naoki; Nakano, Yoshitaka; Wang, Jianyu; Harada, Yoshitomo; Sang, Liwen; Sekiguchi, Takashi; Yamaguchi, Tomohiro; Honda, Tohru

    2017-01-01

    We studied the emissive pits in InGaN films grown on compressive and strain-free GaN underlying layers. Pit density decreased with the full width at half maximum of ω(0002) of InGaN. The films grew on compressive and strain-free GaN underlying layers with spiral and step-flow modes, respectively. Carbon impurities accumulated inside the pits. Comparison of cathodoluminescence inside the pits and steady-state photocapacitance spectra showed that the energy level of the carbon impurities appeared at ˜2.8 eV below the conduction band (Ec) for both types of pits. Deep-level defects at Ec -2.4 eV resulting in green fluorescence emission were considered to originate from pits related to screw dislocations.

  20. Human-level control through deep reinforcement learning

    NASA Astrophysics Data System (ADS)

    Mnih, Volodymyr; Kavukcuoglu, Koray; Silver, David; Rusu, Andrei A.; Veness, Joel; Bellemare, Marc G.; Graves, Alex; Riedmiller, Martin; Fidjeland, Andreas K.; Ostrovski, Georg; Petersen, Stig; Beattie, Charles; Sadik, Amir; Antonoglou, Ioannis; King, Helen; Kumaran, Dharshan; Wierstra, Daan; Legg, Shane; Hassabis, Demis

    2015-02-01

    The theory of reinforcement learning provides a normative account, deeply rooted in psychological and neuroscientific perspectives on animal behaviour, of how agents may optimize their control of an environment. To use reinforcement learning successfully in situations approaching real-world complexity, however, agents are confronted with a difficult task: they must derive efficient representations of the environment from high-dimensional sensory inputs, and use these to generalize past experience to new situations. Remarkably, humans and other animals seem to solve this problem through a harmonious combination of reinforcement learning and hierarchical sensory processing systems, the former evidenced by a wealth of neural data revealing notable parallels between the phasic signals emitted by dopaminergic neurons and temporal difference reinforcement learning algorithms. While reinforcement learning agents have achieved some successes in a variety of domains, their applicability has previously been limited to domains in which useful features can be handcrafted, or to domains with fully observed, low-dimensional state spaces. Here we use recent advances in training deep neural networks to develop a novel artificial agent, termed a deep Q-network, that can learn successful policies directly from high-dimensional sensory inputs using end-to-end reinforcement learning. We tested this agent on the challenging domain of classic Atari 2600 games. We demonstrate that the deep Q-network agent, receiving only the pixels and the game score as inputs, was able to surpass the performance of all previous algorithms and achieve a level comparable to that of a professional human games tester across a set of 49 games, using the same algorithm, network architecture and hyperparameters. This work bridges the divide between high-dimensional sensory inputs and actions, resulting in the first artificial agent that is capable of learning to excel at a diverse array of challenging tasks.

  1. Human-level control through deep reinforcement learning.

    PubMed

    Mnih, Volodymyr; Kavukcuoglu, Koray; Silver, David; Rusu, Andrei A; Veness, Joel; Bellemare, Marc G; Graves, Alex; Riedmiller, Martin; Fidjeland, Andreas K; Ostrovski, Georg; Petersen, Stig; Beattie, Charles; Sadik, Amir; Antonoglou, Ioannis; King, Helen; Kumaran, Dharshan; Wierstra, Daan; Legg, Shane; Hassabis, Demis

    2015-02-26

    The theory of reinforcement learning provides a normative account, deeply rooted in psychological and neuroscientific perspectives on animal behaviour, of how agents may optimize their control of an environment. To use reinforcement learning successfully in situations approaching real-world complexity, however, agents are confronted with a difficult task: they must derive efficient representations of the environment from high-dimensional sensory inputs, and use these to generalize past experience to new situations. Remarkably, humans and other animals seem to solve this problem through a harmonious combination of reinforcement learning and hierarchical sensory processing systems, the former evidenced by a wealth of neural data revealing notable parallels between the phasic signals emitted by dopaminergic neurons and temporal difference reinforcement learning algorithms. While reinforcement learning agents have achieved some successes in a variety of domains, their applicability has previously been limited to domains in which useful features can be handcrafted, or to domains with fully observed, low-dimensional state spaces. Here we use recent advances in training deep neural networks to develop a novel artificial agent, termed a deep Q-network, that can learn successful policies directly from high-dimensional sensory inputs using end-to-end reinforcement learning. We tested this agent on the challenging domain of classic Atari 2600 games. We demonstrate that the deep Q-network agent, receiving only the pixels and the game score as inputs, was able to surpass the performance of all previous algorithms and achieve a level comparable to that of a professional human games tester across a set of 49 games, using the same algorithm, network architecture and hyperparameters. This work bridges the divide between high-dimensional sensory inputs and actions, resulting in the first artificial agent that is capable of learning to excel at a diverse array of challenging tasks.

  2. A first-principles core-level XPS study on the boron impurities in germanium crystal

    SciTech Connect

    Yamauchi, Jun; Yoshimoto, Yoshihide; Suwa, Yuji

    2013-12-04

    We systematically investigated the x-ray photoelectron spectroscopy (XPS) core-level shifts and formation energies of boron defects in germanium crystals and compared the results to those in silicon crystals. Both for XPS core-level shifts and formation energies, relationship between defects in Si and Ge is roughly linear. From the similarity in the formation energy, it is expected that the exotic clusters like icosahedral B12 exist in Ge as well as in Si.

  3. A first-principles core-level XPS study on the boron impurities in germanium crystal

    NASA Astrophysics Data System (ADS)

    Yamauchi, Jun; Yoshimoto, Yoshihide; Suwa, Yuji

    2013-12-01

    We systematically investigated the x-ray photoelectron spectroscopy (XPS) core-level shifts and formation energies of boron defects in germanium crystals and compared the results to those in silicon crystals. Both for XPS core-level shifts and formation energies, relationship between defects in Si and Ge is roughly linear. From the similarity in the formation energy, it is expected that the exotic clusters like icosahedral B12 exist in Ge as well as in Si.

  4. Transient - Photoresistance Spectroscopy of Deep Levels in High Resistivity Semiconductors

    NASA Astrophysics Data System (ADS)

    Seabaugh, Alan Carter

    A new photoinduced transient-resistance technique is proposed and examined for use in characterizing high -resistivity, short-lifetime semiconductors. In this technique, termed photoresistance deep-level transient spectroscopy (PR-DLTS), an optical pulse is used to generate excess carriers which are trapped by deep levels in the material. The ac resistance of the specimen is monitored, and the resistance transient which occurs after the illumination ends is signal processed in the same way as the capacitance transient in DLTS. A phenomenological model of the phototransient is used to derive an expression for the decay transient. Two limiting forms for the transient are predicted depending upon whether the emitted carriers are collected at the device contacts, or recombine in the bulk before being collected. In order to test this model, several methods for distinguishing between the predicted decays of the form exp(-(lamda)t) and (lamda)exp(-(lamda)t) were developed ((lamda) is the reciprocal time constant for the decay). The measured results are consistent with the predictions of the model, but an 'ideal' sample has not been found to fully test the predictions. On Au-doped Si, excellent agreement between published emission rates for the Au-acceptor and the apparent emission rates measured by PR-DLTS is found. In addition, PR-DLTS data for the Cr-related deep level in semi-insulating GaAs is consistent with published DLTS results on conducting GaAs. Comparison of the PR-DLTS technique with the dc current-transient technique, photoinduced transient spectroscopy (PITS), shows that the two techniques are sensitive to the same trapping/detrapping phenomena. Finally, the results of a comparative study of commercial semi-insulating GaAs are reported. Nineteen specimens from ten suppliers were examined using the PR -DLTS technique, including material grown by the horizontal Bridgman (HB) and liquid-encapsulated Czochralski (LEC) technique, both with and without Cr

  5. Identification of a novel low-level impurity in fungicide pyraclostrobin by high-performance liquid chromatography/tandem mass spectrometry.

    PubMed

    Xia, Kaimin; Shen, ShanShan; Gao, Qun; Shang, Wei; Pan, Yuanjiang; Wu, Jun

    2017-05-10

    Pyraclostrobin is one kind of new type methoxy acrylate fungicides that has been widely used in agriculture at present, with a lot of advantages including broad spectrum, high efficiency and high selectivity. In this work, a novel low-level impurity in the pyraclostrobin at about 0.2% was separated and characterized by high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS). Firstly, the impurity was speculated to possess the same skeleton structure as the main product pyraclostrobin while the methyl group on the methyl ester was substituted to be CH2CH2Cl on the basis of the on-line multi-stage mass spectrometric behaviors compared with that of pyraclostrobin. Then the accurate molecular weight and element composition of target impurity was verified to be C20H19Cl2N3O4 by high resolution mass spectrometry. Finally, the proposed structure was further confirmed by the (1)H NMR data.

  6. Characterization of deep level defects present in mono-like, quasi-mono and multicrystalline silicon solar substrates

    NASA Astrophysics Data System (ADS)

    Pérez, E.; García, H.; Castán, H.; Dueñas, S.

    2015-03-01

    Defects on mono-like (ml-Si), quasi-mono (qm-Si) and multicrystalline silicon solar cell substrates are studied in depth. Using the thermal admittance spectroscopy technique we found a single deep level with an activation energy between 213 and 224 meV and a capture cross section in the order of 10-15-10-14 cm2, in the case of ml-Si samples. The 271, 291 and 373 meV levels were found in qm-Si samples. The first one is associated with a capture cross section in the order of 10-16 cm2, the second one in the order of 10-14, while the third one is associated, for the same magnitude, with a value in the order of 10-12 cm2. Multicrystalline samples showed two tendencies in the Arrhenius plot fit associated with a deep level in each one. The activation energy of the first one ranges from 336 meV to 342 meV, and the capture cross sections are in the order of 10-13-10-11 cm2. The values obtained for the second one are 251 and 171 meV, with the capture cross section values in the order of 10-15 and 10-18 cm2, respectively. The nature of these defects is probably due to iron-based impurities in different complexes. Segregation into extended defects of Fei or Fei-V is the most probable cause of the deep levels with higher capture cross section value. Punctual complexes such as Fei or Fei-V2 are probably the reason for the deep levels with lower capture cross section value.

  7. Deep levels and radiation effects in p-InP

    NASA Technical Reports Server (NTRS)

    Anderson, W. A.; Singh, A.; Jiao, K.; Lee, B.

    1989-01-01

    A survey was conducted on past studies of hole traps in InP. An experiment was designed to evaluate hole traps in Zn-doped InP after fabrication, after electron irradiation and after annealing using deep level transient spectroscopy. Data similar to that of Yamaguchi was seen with observation of both radiation-induced hole and electron traps at E sub A=0.45 eV and 0.03 eV, respectively. Both traps are altered by annealing. It is also shown that trap parameters for surface-barrier devices are influenced by many factors such as bias voltage, which probes traps at different depths below the surface. These devices require great care in data evaluation.

  8. Development of RP UPLC-TOF/MS, stability indicating method for omeprazole and its related substances by applying two level factorial design; and identification and synthesis of non-pharmacopoeial impurities.

    PubMed

    Jadhav, Sushant Bhimrao; Kumar, C Kiran; Bandichhor, Rakeshwar; Bhosale, P N

    2016-01-25

    A new UPLC-TOF/MS compatible, reverse phase-stability indicating method was developed for determination of Omeprazole (OMP) and its related substances in pharmaceutical dosage forms by implementing Design of Experiment (DoE) i.e. two level full factorial Design (2(3)+3 center points=11 experiments) to understand the Critical Method Parameters (CMP) and its relation with Critical Method Attribute (CMA); to ensure robustness of the method. The separation of eleven specified impurities including conversion product of OMP related compound F (13) and G (14) i.e. Impurity-I (1), OMP related compound-I (11) and OMP 4-chloro analog (12) was achieved in a single method on Acquity BEH shield RP18 100 × 2.1 mm, 1.7 μm column, with inlet filter (0.2 μm) using gradient elution and detector wavelength at 305 nm and validated in accordance with ICH guidelines and found to be accurate, precise, reproducible, robust and specific. The drug was found to degrade extensively in heat, humidity and acidic conditions and forms unknown degradation products during stability studies. The same method was used for LC-MS analysis to identify m/z and fragmentation of maximum unknown impurities (Non-Pharmacopoeial) i.e. Impurity-I (1), Impurity-III (3), Impurity-V (5) and Impurity-VIII (9) formed during stability studies. Based on the results, degradation pathway for the drug has been proposed and synthesis of identified impurities i.e. impurities (Impurity-I (1), Impurity-III (3), Impurity-V (5) and Impurity-VIII (9)) are discussed in detail to ensure in-depth understanding of OMP and its related impurities and optimum performance during lifetime of the product.

  9. Deep level study of Mg-doped GaN using deep level transient spectroscopy and minority carrier transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Duc, Tran Thien; Pozina, Galia; Amano, Hiroshi; Monemar, Bo; Janzén, Erik; Hemmingsson, Carl

    2016-07-01

    Deep levels in Mg-doped GaN grown by metal organic chemical vapor deposition (MOCVD), undoped GaN grown by MOCVD, and halide vapor phase epitaxy (HVPE)-grown GaN have been studied using deep level transient spectroscopy and minority charge carrier transient spectroscopy on Schottky diodes. One hole trap, labeled HT1, was detected in the Mg-doped sample. It is observed that the hole emission rate of the trap is enhanced by increasing electric field. By fitting four different theoretical models for field-assisted carrier emission processes, the three-dimensional Coulombic Poole-Frenkel (PF) effect, three-dimensional square well PF effect, phonon-assisted tunneling, and one-dimensional Coulombic PF effect including phonon-assisted tunneling, it is found that the one-dimensional Coulombic PF model, including phonon-assisted tunneling, is consistent with the experimental data. Since the trap exhibits the PF effect, we suggest it is acceptorlike. From the theoretical model, the zero field ionization energy of the trap and an estimate of the hole capture cross section have been determined. Depending on whether the charge state is -1 or -2 after hole emission, the zero field activation energy Ei 0 is 0.57 eV or 0.60 eV, respectively, and the hole capture cross section σp is 1.3 ×10-15c m2 or 1.6 ×10-16c m2 , respectively. Since the level was not observed in undoped GaN, it is suggested that the trap is associated with an Mg related defect.

  10. Influence of the copper impurity level on the irradiation response of reactor pressure vessel steels investigated by SANS

    NASA Astrophysics Data System (ADS)

    Wagner, Arne; Ulbricht, Andreas; Bergner, Frank; Altstadt, Eberhard

    2012-06-01

    Reactor pressure vessel (RPV) steel, when exposed to neutron irradiation, induces the formation of nano-sized features. Using small angle neutron scattering (SANS) we have studied the neutron fluence dependence of the precipitate volume fraction for high-Cu and low-Cu materials separately. Cu-rich precipitates have long been recognized to play the dominant role in embrittlement of Cu-bearing RPV steels. In contrast, Mn-Ni-rich precipitates seem to govern embrittlement in the case of low levels of impurity Cu. The objective is to work out the resulting differences from the microstructural point of view. For low-Cu materials, the volume fraction was found to be within the detection limit of SANS at fluences below an apparent threshold fluence, whereas the slope increases considerably beyond. The relationship between irradiation-induced yield stress increase and precipitate volume fraction was also considered. We have derived estimates of the obstacle strength for Cu-rich precipitates and for Mn-Ni-rich precipitates.

  11. Deep-level magma ascent rates at Mt. Etna (Italy)

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Perinelli, C.; Putirka, K. D.

    2012-12-01

    Deep-level ascent rates are related to the triggering mechanisms of volcanic eruptions. Recent models and experimental studies have focused on the very shallow parts of magma plumbing systems, mostly the upper few km, and have thus far emphasized that volatile contents and volatile exsolution, are key to understanding eruption dynamics and its fingerprint in the rock texture. Massive volatile loss induces a dramatic change in the liquidus temperature, thus producing observable effects on the rates of nucleation and growth of minerals . Volatile saturation, however, may well occur at greater depths, which means that initial stages of magma ascent may be triggered by events taking place at much greater depths than those recorded by melt inclusions, likely captured at shallow levels. We present a method to evaluate ascent rates deep in a volcano plumbing system, discussing the implications for magma dehydration and using Mt. Etna as case a study. We investigate the deeper levels of magma transport by presenting detailed P-T paths for Etnean magmas, and combining these with Crystal Size Distribution (CSD)-derived cooling rates. The key to this analysis is the recognition that the slope of a P-T path, as determined from mineral-melt thermobarometry, is a result of magma cooling rate, which is in turn a function of magma ascent via the effect of pressure on volatile solubility. We also rely on a thermodynamic treatment of exsolution of non-ideal H2O-CO2 mixtures, based on the Kerric & Jacobs (1981) model, and the simplified solubility model of CO2 (Spera & Bergman, 1980) and H2O (Nicholls, 1980), recalibrated with experimental and melt inclusions data from Mt. Etna. Our modeling is able to decipher magma ascent velocity, v (dH/dt; H = depth, t = time), from ascent rate (dP/dt), and rate of cooling (dT/dt), where ρ is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships

  12. Deep-level defect characteristics in pentacene organic thin films

    NASA Astrophysics Data System (ADS)

    Yang, Yong Suk; Kim, Seong Hyun; Lee, Jeong-Ik; Chu, Hye Yong; Do, Lee-Mi; Lee, Hyoyoung; Oh, Jiyoung; Zyung, Taehyoung; Ryu, Min Ki; Jang, Min Su

    2002-03-01

    Organic thin-film transistors using the pentacene as an active electronic material have shown the mobility of 0.8 cm2/V s and the grains larger than 1 μm. To study the characteristics of electronic charge concentrations and the interface traps of the pentacene thin films, the capacitance properties were measured in the metal/insulator/organic semiconductor structure device by employing the capacitance-voltage and deep-level transient spectroscopy (DLTS) measurements. Based on the DLTS measurements, the concentrations and the energy levels of hole and electron traps in the obtained pentacene films were formed to be approximately 4.2×1015 cm-3 at Ev+0.24 eV, 9.6×1014 cm-3 at Ev+1.08 eV, 6.5×1015 cm-3 at Ev+0.31 eV and 2.6×1014 cm-3 at Ec-0.69 eV.

  13. High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Iwamoto, Naoya; Azarov, Alexander; Ohshima, Takeshi; Moe, Anne Marie M.; Svensson, Bengt G.

    2015-07-01

    Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 1015 cm-3 range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ˜1014 cm-3). Schottky barrier diodes fabricated on substrates annealed at 1400-1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

  14. High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

    SciTech Connect

    Iwamoto, Naoya Azarov, Alexander; Svensson, Bengt G.; Ohshima, Takeshi; Moe, Anne Marie M.

    2015-07-28

    Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 10{sup 15 }cm{sup −3} range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ∼10{sup 14 }cm{sup −3}). Schottky barrier diodes fabricated on substrates annealed at 1400–1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

  15. Low level impurities in imported wheat are a likely source of feral transgenic oilseed rape (Brassica napus L.) in Switzerland.

    PubMed

    Schulze, Juerg; Brodmann, Peter; Oehen, Bernadette; Bagutti, Claudia

    2015-11-01

    In Switzerland, the cultivation of genetically modified (GM) oilseed rape (Brassica napus L.) and the use of its seeds for food and feed are not permitted. Nevertheless, the GM oilseed rape events GT73, MS8×RF3, MS8 and RF3 have recently been found in the Rhine port of Basel, Switzerland. The sources of GM oilseed rape seeds have been unknown. The main agricultural good being imported at the Rhine port of Basel is wheat and from 2010 to 2013, 19% of all Swiss wheat imports originated from Canada. As over 90% of all oilseed rape grown in Canada is GM, we hypothesised that imports of Canadian wheat may contain low level impurities of GM oilseed rape. Therefore, waste fraction samples gathered during the mechanical cleaning of Canadian wheat from two Swiss grain mills were analysed by separating oilseed rape seeds from waste fraction samples and testing DNA of pooled seeds for the presence of transgenes by real-time PCR. Furthermore, oilseed rape seeds from each grain mill were sown in a germination experiment, and seedling DNA was tested for the presence of transgenes by real-time PCR. GT73, MS8×RF3, MS8 and RF3 oilseed rape was detected among seed samples and seedlings of both grain mills. Based on this data, we projected a mean proportion of 0.005% of oilseed rape in wheat imported from Canada. Besides Canadian wheat, the Rhine port of Basel does not import any other significant amounts of agricultural products from GM oilseed rape producing countries. We therefore conclude that Canadian wheat is the major source of unintended introduction of GM oilseed rape seeds into Switzerland.

  16. Low energy electron irradiation induced deep level defects in 6H-SiC: the implication for the microstructure of the deep levels E1/E2.

    PubMed

    Chen, X D; Yang, C L; Gong, M; Ge, W K; Fung, S; Beling, C D; Wang, J N; Lui, M K; Ling, C C

    2004-03-26

    N-type 6H-SiC samples irradiated with electrons having energies of E(e)=0.2, 0.3, 0.5, and 1.7 were studied by deep level transient technique. No deep level was detected at below 0.2 MeV irradiation energy while for E(e)>/=0.3 MeV, deep levels ED1, E(1)/E(2), and E(i) appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E(1)/E(2), as well as ED1 and E(i), involves the displacement of the C atom in the SiC lattice.

  17. Low Energy Electron Irradiation Induced Deep Level Defects in 6H-SiC: The Implication for the Microstructure of the Deep Levels E1/E2

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Yang, C. L.; Gong, M.; Ge, W. K.; Fung, S.; Beling, C. D.; Wang, J. N.; Lui, M. K.; Ling, C. C.

    2004-03-01

    N-type 6H-SiC samples irradiated with electrons having energies of Ee=0.2, 0.3, 0.5, and 1.7 were studied by deep level transient technique. No deep level was detected at below 0.2MeV irradiation energy while for Ee≥0.3 MeV, deep levels ED1, E1/E2, and Ei appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E1/E2, as well as ED1 and Ei, involves the displacement of the C atom in the SiC lattice.

  18. DLTS Study of RIE-Induced Deep Levels in Si Using p+n Diode Arrays

    NASA Astrophysics Data System (ADS)

    Watanabe, Miyoko Oku; Taguchi, Minoru; Kanzaki, Koichi; Zohta, Yasuhito

    1983-02-01

    Deep levels in Si induced by reactive ion etching (RIE) of SiO2 film have been studied by DLTS. In order to detect the RIE-induced damage existing near the surface region, special device structures consisting of p+n diode arrays are used. It is found that the dominant deep levels produced by RIE are four hole traps. One level at Ev+0.40 eV exhibits the Poole-Frenkel effect, from which it is identified as an acceptor. Another level at Ev+0.46 eV is deduced to be an interstitial iron level from the emission rate. There is a strong decrease in the deep level concentrations upon annealing above 500°C. However, the deep levels do not completely disappear upon annealing at high temperatures. The deep level concentrations correlate well with the current-voltage characteristics of the devices.

  19. Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

    NASA Astrophysics Data System (ADS)

    Wang, Zhao; Li, Bing; Zheng, Xu; Xie, Jing; Huang, Zheng; Liu, Cai; Feng, Liang-Huan; Zheng, Jia-Gui

    2010-02-01

    Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at Ev + 0.128 eV, originates from the vacancy of Cd (VCd). The electron trap E1, found at Ec -0.178 eV, is considered to be correlated with the interstitial Cuj+ in CdTe.

  20. The electronic level structure of lanthanide impurities in REPO4, REBO3, REAlO3, and RE2O3 (RE = La, Gd, Y, Lu, Sc) compounds

    NASA Astrophysics Data System (ADS)

    Dorenbos, Pieter

    2013-06-01

    The vacuum referred binding energies of electrons in divalent and trivalent lanthanide impurity states and host band states in the rare earth (RE = La, Gd, Y, Lu, Sc) orthophosphates REPO4, orthoborates REBO3, aluminum perovskites REAlO3, and sesqui-oxides RE2O3 have been determined by combining the recently developed chemical shift model with spectroscopic data from the archival literature. The main trends in impurity and host band level locations with changing type of RE, which determines the site size, and with changing P, B, Al, or RE cation, which determines the strength of bonding with the oxygen ligands, are identified. Sc3+-based compounds are characterized by a relatively low energy for the conduction band bottom, or equivalently a high electron affinity, which is attributed to a relatively strong electron bonding in the 3d-shell of Sc2+.

  1. Matrix elimination ion chromatography method for the determination of trace levels of anionic impurities in high purity cesium iodide.

    PubMed

    Ayushi; Kumar, Sangita D; Reddy, A V R

    2012-01-01

    In the present study an ion chromatographic method based on matrix elimination has been developed for the determination of anionic impurities in high purity cesium iodide crystals. The presence of impurities has a detrimental effect on the characteristics of detectors based on cesium iodide crystals. In particular, oxygen-containing anions inhibit the resolving power of scintillators and decrease the optical absorption. The quantitative determination of anions (fluoride, chloride, bromide, nitrate, phosphate, and sulphate) simultaneously in the high-purity cesium iodide crystals has not been carried out before. The large concentration of iodide poses a challenge in the determination of anions (especially phosphate and sulphate); hence, matrix elimination is accomplished by adopting a sample pretreatment technique. The method is validated for linearity, accuracy, and precision. The limit of detection for different anions is in the range of 0.3-3 µg/g, and the relative standard deviation is in the range of 4-6% for the overall method.

  2. Impurities in Kevlar 49 fibers

    SciTech Connect

    Pruneda, C.O.; Morgan, R.J.; Lim, R.; Gregory, L.J.; Fischer, J.W.

    1984-12-11

    The impurities in Kevlar 49 fibers (poly(p-phenylene terephthalamide)PPTA) are reported and discussed in terms of the fiber fabrication processes. These impurities were monitored by inductively coupled plasma emission and optical emission spectroscopy. The principal impurities Na/sub 2/SO/sub 4/ and total S were analyzed chemically. From these chemical analyses together with C, N, H elemental analyses we show that there are 1.5 wt % impurities present in Kevlar 49 fibers of which approx. 50% are in the form of Na/sub 2/SO/sub 4/ and the remainder probably in the form of benzene sulfonic -SO/sub 3/H PPTA side groups. There are 3 of these acid groups per each PPTA macromolecule. Organic impurities, such as terephthalic acid are discussed in the light of degradation studies of PPTA-H/sub 2/SO/sub 4/ spinning dopes. Electron microprobe x-ray spectroscopy and laser-induced damage studies were utilized to investigate the distribution of impurities through the fiber cross-section. The distribution of impurities throughout the fiber are determined by the fiber fabrication processes and are discussed at the microscopic and molecular level. The defects caused by these impurities and their effect on the deformation and failure modes are also considered. 22 references, 3 tables.

  3. Improved Performance of the Alkaline-Side CSEX Process for Cesium Extraction from Alkaline High-Level Waste Obtained by Characterization of the Effect of Surfactant Impurities

    SciTech Connect

    Delmau, L.H.

    1999-11-04

    Improved understanding and performance of the alkaline-side CSEX process has been obtained through the characterization of impurity effects that hinder complete stripping of cesium from the solvent. It is shown in this report that tests of the alkaline-side CSEX process conducted in the summer and fall of 1998 were complicated by the presence of common surfactant anions, undecyl- and dodecylsulfonate, as trace impurities in the two simulants tested. This conclusion was drawn from the results of a series of systematic extraction tests followed by a definitive identification by electrospray mass spectrometry (ES-MS). Based on this understanding, a straightforward preventative measure involving the addition of a lipophilic tertiary amine extractant at a small concentration to the solvent is proposed and demonstrated. As part of the task ''Fission Product Solvent Extraction'' supported by the Efficient Separations and Processing Crosscutting Program within the USDOE Office of Environmental Management, the alkaline-side CSEX process has been developed for removal of radio-cesium ({sup 137}Cs) from alkaline high-level wastes stored in underground tanks at the Hanford Site and Savannah River Site (SRS). As described in a previous report, tests conducted in Fiscal Year 1998 generally demonstrated performance meeting the requirements for cesium removal from the waste to be treated at the SRS. However, discrepancies in stripping behavior were shown to arise from unidentified differences ''in the batches of waste simulant employed for testing. Various effects such as solvent impurities, kinetics, contacting method, and counting method were eliminated as possible causes of the observed discrepancies. Tests in Fiscal Year 1999 reported herein confirmed the earlier suspicion that the simulants contained lipophilic anionic impurities. Extraction tests demonstrated that the impurities could be concentrated in the solvent, and by ES-MS in the negative-ion mode it was possible to

  4. Deep Levels of Processing Elicit a Distinctiveness Heuristic: Evidence from the Criterial Recollection Task

    ERIC Educational Resources Information Center

    Gallo, David A.; Meadow, Nathaniel G.; Johnson, Elizabeth L.; Foster, Katherine T.

    2008-01-01

    Thinking about the meaning of studied words (deep processing) enhances memory on typical recognition tests, relative to focusing on perceptual features (shallow processing). One explanation for this levels-of-processing effect is that deep processing leads to the encoding of more distinctive representations (i.e., more unique semantic or…

  5. Matrix Elimination Ion Chromatography Method for the Determination of Trace Levels of Anionic Impurities in High Purity Cesium Iodide

    PubMed Central

    Ayushi; Kumar, Sangita D.; Reddy, A.V.R.

    2012-01-01

    In the present study an ion chromatographic method based on matrix elimination has been developed for the determination of anionic impurities in high purity cesium iodide crystals. The presence of impurities has a detrimental effect on the characteristics of detectors based on cesium iodide crystals. In particular, oxygen-containing anions inhibit the resolving power of scintillators and decrease the optical absorption. The quantitative determination of anions (fluoride, chloride, bromide, nitrate, phosphate, and sulphate) simultaneously in the high-purity cesium iodide crystals has not been carried out before. The large concentration of iodide poses a challenge in the determination of anions (especially phosphate and sulphate); hence, matrix elimination is accomplished by adopting a sample pretreatment technique. The method is validated for linearity, accuracy, and precision. The limit of detection for different anions is in the range of 0.3–3 µg/g, and the relative standard deviation is in the range of 4–6% for the overall method. PMID:22291061

  6. The effect of impurities on linear and nonlinear absorption coefficient and refractive index of the spherical quantum dot four-level M-model the phenomenon of electromagnetically induced transparency

    NASA Astrophysics Data System (ADS)

    Damiri, H.; Askari, H. R.

    2017-01-01

    In this paper, the effect of impurities on the phenomenon of electromagnetically induced transparency in a spherical quantum dot with parabolic potential is examined. It is assumed that spherical quantum dot has configuration four levels model M. First, consider the polarization Z for light; rotating wave approximation approach, rotating coordinate system, as well as the density matrix approach, we examine the phenomenon of electromagnetically induced transparency in spherical quantum dot. Finally, with regard to impurities of the disorder, we review electromagnetically induced transparency and Changes resulting from the presence of impurities.

  7. Dual-wavelength excited photoluminescence spectroscopy of deep-level hole traps in Ga(In)NP

    SciTech Connect

    Dagnelund, D.; Huang, Y. Q.; Buyanova, I. A.; Chen, W. M.; Tu, C. W.; Yonezu, H.

    2015-01-07

    By employing photoluminescence (PL) spectroscopy under dual-wavelength optical excitation, we uncover the presence of deep-level hole traps in Ga(In)NP alloys grown by molecular beam epitaxy (MBE). The energy level positions of the traps are determined to be at 0.56 eV and 0.78 eV above the top of the valance band. We show that photo-excitation of the holes from the traps, by a secondary light source with a photon energy below the bandgap energy, can lead to a strong enhancement (up to 25%) of the PL emissions from the alloys under a primary optical excitation above the bandgap energy. We further demonstrate that the same hole traps can be found in various MBE-grown Ga(In)NP alloys, regardless of their growth temperatures, chemical compositions, and strain. The extent of the PL enhancement induced by the hole de-trapping is shown to vary between different alloys, however, likely reflecting their different trap concentrations. The absence of theses traps in the GaNP alloy grown by vapor phase epitaxy suggests that their incorporation could be associated with a contaminant accompanied by the N plasma source employed in the MBE growth, possibly a Cu impurity.

  8. Deep level defects in sublimation-grown 6H silicon carbide investigated by DLTS and EPR

    NASA Astrophysics Data System (ADS)

    Irmscher, K.; Pintilie, I.; Pintilie, L.; Schulz, D.

    2001-12-01

    6H-SiC bulk single crystals grown by physical vapor transport (PVT) were investigated by deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). One of the observed deep level defects was identified as isolated tungsten on Si sites by EPR. The electron spin of {1}/{2} could be explained by W 5+ (5d 1). This is equivalent to the single positive charge state of a double donor when taking into account the Fermi level position in the n-type samples. The interpretation is also consistent with the DLTS detection of a W related deep level which showed a behavior of the capture of electrons and holes that hints at a double donor. In addition a tantalum related deep level is tentatively discussed. W and Ta were incorporated on electrically active sites in 6H-SiC only in low concentrations (2-4×10 14 cm -3) during crystal growth by PVT.

  9. The Impact of Glyphosate, Its Metabolites and Impurities on Viability, ATP Level and Morphological changes in Human Peripheral Blood Mononuclear Cells

    PubMed Central

    Kwiatkowska, Marta; Jarosiewicz, Paweł; Michałowicz, Jaromir; Koter-Michalak, Maria; Huras, Bogumiła; Bukowska, Bożena

    2016-01-01

    The toxicity of herbicides to animals and human is an issue of worldwide concern. The present study has been undertaken to assess toxic effect of widely used pesticide—glyphosate, its metabolites: aminomethylphosphonic acid (AMPA) and methylphosphonic acid and its impurities: N-(phosphonomethyl)iminodiacetic acid (PMIDA), N-methylglyphosate, hydroxymethylphosphonic acid and bis-(phosphonomethyl)amine on human peripheral blood mononuclear cells (PBMCs). We have evaluated the effect of those compounds on viability, ATP level, size (FSC-A parameter) and granulation (SSC-A parameter) of the cells studied. Human peripheral blood mononuclear cells were exposed to different concentrations of glyphosate, its metabolites and impurities (0.01–10 mM) for 4 and 24 h. It was found that investigated compounds caused statistically significant decrease in viability and ATP level of PBMCs. The strongest changes in cell viability and ATP level were observed after 24 h incubation of PBMCs with bis-(phosphonomethyl)amine, and particularly PMIDA. Moreover, all studied compounds changed cell granularity, while PMIDA and bis-(phosphonomethyl)amine altered PBMCs size. It may be concluded that bis-(phosphonomethyl)amine, and PMIDA caused a slightly stronger damage to PBMCs than did glyphosate. Changes in the parameters studied in PBMCs were observed only at high concentrations of the compounds examined, which clearly shows that they may occur in this cell type only as a result of acute poisoning of human organism with these substances. PMID:27280764

  10. Ruthenium related deep-level defects in n-type GaAs

    NASA Astrophysics Data System (ADS)

    Naz, Nazir A.; Qurashi, Umar S.; Majid, A.; Zafar Iqbal, M.

    2009-12-01

    Deep-level transient spectroscopy (DLTS) has been used to investigate deep levels in n-type Ru-doped GaAs grown by low-pressure metal-organic chemical-vapor deposition (LP-MOCVD). DLTS scans over a wide temperature range (12-470 K) reveal two prominent deep-level peaks associated with Ru, when compared with control samples with no deliberate Ru-doping. The well-known mid-gap defect EL2 is also observed in these scans. The Ru-related deep levels, Ru1 and Ru2, correspond to energy positions Ec-0.46 eV and Ec-0.57 eV in the upper-half-bandgap of GaAs. No prominent deep levels associated with Ru are observed in the lower half-bandgap in the injection DLTS spectra; only the three inadvertent levels already present in the as-grown, control material are observed in these spectra. Although a possible Ru-related peak may be present with a rather small concentration in these injection DLTS spectra, it is difficult to clearly identify this peak also present in the control (as-grown, without Ru) samples at a closely similar position. Interestingly, doping with Ru reveals an interesting significant suppression of the pre-existing deep levels, including EL2. Detailed emission rate signatures are presented for the Ru-related deep levels and analyzed to obtain the relevant deep-level characteristics. Both Ru1 and Ru2 are found to show strong dependence on electric field, as demonstrated by the shift in the corresponding DLTS peak positions with the applied reverse bias during electron emission.

  11. Density and energy level of a deep-level Mg acceptor in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Matsuura, Hideharu; Morine, Tatsuya; Nagamachi, Shinji

    2015-01-01

    Reliably determining the densities and energy levels of deep-level dominant acceptors in heavily doped wide-band-gap semiconductors has been a topic of recent discussion. In these discussions, the focus is on both Hall scattering factors for holes and distribution functions for acceptors. Mg acceptor levels in 4H-SiC seem to be deep, and so here the electrical properties of Mg-implanted 4H-SiC layers are studied by measuring Hall effects. The obtained Hall scattering factors are not reliable because they drop to less than 0.5 at high measurement temperatures. Moreover, the Fermi-Dirac distribution function is unsuitable for examining Mg acceptors because the obtained acceptor density is much higher than the concentration of implanted Mg atoms. However, by using a distribution function that includes the influence of the excited states of a deep-level acceptor, the density and energy level of Mg acceptors can be reliably determined.

  12. Potentially mutagenic impurities: analysis of structural classes and carcinogenic potencies of chemical intermediates in pharmaceutical syntheses supports alternative methods to the default TTC for calculating safe levels of impurities.

    PubMed

    Galloway, Sheila M; Vijayaraj Reddy, M; McGettigan, Katherine; Gealy, Robert; Bercu, Joel

    2013-08-01

    Potentially mutagenic impurities in new pharmaceuticals are controlled to levels with negligible risk, the TTC (threshold of toxicological concern, 1.5 μg/day for a lifetime). The TTC was based on the more potent rodent carcinogens, excluding the highly potent "cohort of concern" (COC; for mutagenic carcinogens these are N-nitroso, Aflatoxin-like, and azoxy structures). We compared molecules with DEREK "structural alerts" for mutagenicity used in drug syntheses with the mutagenic carcinogens in the Gold Carcinogenicity Potency Database. Data from 108 diverse synthetic routes from 13 companies confirm that many "alerting" or mutagenic chemicals are in structural classes with lower carcinogenic potency than those used to derive the TTC. Acceptable daily intakes can be established that are higher than the default TTC for many structural classes (e.g., mono-functional alkyl halides and certain aromatic amines). Examples of ADIs for lifetime and shorter-term exposure are given for chemicals of various potencies. The percentage of chemicals with DEREK alerts that proved mutagenic in the Ames test ranged from 36% to 83%, depending on structural class, demonstrating that such SAR analysis to "flag" potential mutagens is conservative. We also note that aromatic azoxy compounds need not be classed as COC, which was based on alkyl azoxy chemicals.

  13. Identification of deep levels in liquid-encapsulation Czochralski-grown Fe- and Zn-doped InP: A proof of the nonexistence of a Fe4 + /Fe3 + donor level

    NASA Astrophysics Data System (ADS)

    Wolf, T.; Drews, D.; Scheffler, H.; Bimberg, D.; Mosel, F.; Kipfer, P.; Müller, G.

    1993-01-01

    Deep levels in liquid-encapsulation Czochralski (LEC) grown p-type InP:Fe codoped with Zn have been investigated by means of temperature-dependent Hall-effect (TDH), deep-level transient spectroscopy (DLTS), calorimetric absorption spectroscopy, and electron spin resonance measurements. Although a dominant deep hole trap is revealed both by DLTS and TDH measurements in the vicinity of the valence band edge at EV+0.2 eV, the spectroscopic analysis unambiguously invalidates previous speculations on the existence of a second energy level of the isolated iron impurity in the band gap of InP, i.e., a Fe4+/Fe3+ donor level. From the axial concentration profile and a comparison with a LEC-grown p-type InP crystal doped with Zn only it seems that the trap is not even iron-related in contrast to tentative assignments often found in the literature. Native or Zn-related defects which depend on the particular growth conditions used are assumed to account for this level.

  14. The effectiveness and stability of impurity/defect interactions and their impact on minority carrier lifetime. Annual subcontract report, 1 August 1990--31 July 1991

    SciTech Connect

    Rozgonyi, G.A.; Shimura, F.; Buczkowski, A.; Zhon, T.Q.

    1991-12-01

    This report covers the investigation and understanding of electrical activity of ``clean`` and metallic impurity decorated defects. A heterostructure containing a controlled number of deliberately introduced misfit dislocations is used as a model system to simulate a variety of defect/impurity interactions in photovoltaic materials. In addition, a noncontact laser/microwave deep-level transient spectroscopy technique is applied to characterize the minority carrier lifetime and determine the energy levels of defects. 59 refs.

  15. Deep level defect studies in semi-insulating 4H- and 6H-silicon carbide using optical admittance spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Wonwoo

    The objective of this study is to determine the deep vanadium defect levels in semi-insulating 4H- and 6H- silicon carbide using optical admittance spectroscopy. Also infrared spectroscopy and electron paramagnetic resonance spectroscopy are conducted to support the evidence of vanadium donor and acceptor levels obtained from OAS measurements. Vanadium acts as an amphoteric impurity in silicon carbide with a V3+/4+ acceptor level and V4+/5+ donor level. Although the value for the donor level is well established, the V3+/4+ defect level remains controversial. OAS shows that the vanadium donor level is isolated near Ec-1.7 eV, and the vanadium acceptor level is located at Ec-0.75 eV at a cubic site and Ec-0.94 eV at a hexagonal site in 4H-SiC, while the vanadium donor level of 6H-SiC samples is about Ec-1.5 eV. The acceptor levels of 6H-SiC were assigned to Ec-0.67 eV, E c -0.70 eV at two cubic sites, and Ec-0.87 eV at a hexagonal site. IR spectra demonstrated that the signatures of the vanadium V 3+ and V4+ charge states are present in the samples. EPR and photo-induced EPR are used to identify the V3+/4+ and V4+/5+ levels as well as the V3+ and V 4+ charge states. EPR spectra represent both V3+ and V4+ in 4H- and 6H samples consistent with FTIR data. EPR and photo-induced EPR suggest that the va nadium acceptor level is between 0.7 eV and 0.86 eV, while the donor level is near Ec-1.5 eV in 6H-SiC. The donor level of 4H-SiC is located at Ec-1.6 eV. Thus, the data obtained from EPR and FTIR support the assignment of the vanadium defect levels determined by OAS. Vanadium complexes induced by other elements such as titanium, hydrogen, and nitrogen atoms are also observed in OAS spectra and will be discussed in the text.

  16. Methods of measuring water levels in deep wells

    USGS Publications Warehouse

    Garber, M.S.; Koopman, F. C.

    1968-01-01

    Accurate measurement of water levels deeper than 1,000 feet in wells requires specialized equipment. Corrections for stretch and thermal expansion of measuring tapes must be considered, and other measuring devices must be calibrated periodically. Bore-hole deviation corrections also must be made. Devices for recording fluctuation of fluid level usually require mechanical modification for use at these depths. A multichannel recording device utilizing pressure transducers has been constructed. This device was originally designed to record aquifer response to nearby underground nuclear explosions but can also be used for recording data from multi-well pumping tests. Bottom-hole recording devices designed for oil-field use have been utilized in a limited manner. These devices were generally found to lack the precision required, in ground-water investigations at the Nevada Test Site but may be applicable in other areas. A newly developed bottom-hole recording pressure gauge of improved accuracy has been used with satisfactory results.

  17. Deep levels in semi-insulating LEC GaAs before and after silicon implantation

    SciTech Connect

    Dindo, S.; Abdel-Motaleb, I.; Lowe, K.; Tang, W.; Young, L.

    1985-11-01

    The deep trapping levels present before ion implantation of silicon into the semi-insulating LEC GaAs starting material were investigated using optical transient current spectroscopy (OTCS). MESFET channel current deep level transient spectroscopy (DLTS) was used for the implanted material. With a silicon nitride layer used t encapsulate the GaAs for postimplantation annealing and with implantation directly into the GaAs, it was found tha of seven or more deep levels seen in the semi-insulating substrate prior to silicon implantation only the level believed to be EL12 remained. On implanting through a thin Si/sub 3/N/sub 4/ encapsulating layer and annealing under Si/sub 3/N/sub 4/, only EL2 was found. With a silicon dioxide layer as an encapsulant, two traps remained and two apparently unreported levels appeared.

  18. Effects of irradiation and annealing on deep levels in rhodium-doped p-GaAs grown by metal-organic chemical-vapor deposition

    SciTech Connect

    Naz, Nazir A.; Qurashi, Umar S.; Iqbal, M. Zafar

    2011-06-01

    This paper reports a detailed study of the effects of irradiation and thermal annealing on deep levels in Rh-doped p-type GaAs grown by low-pressure metal-organic chemical-vapor deposition, using deep level transient spectroscopy (DLTS) technique. It is found upon irradiation with alpha particles that, in addition to the radiation-induced defect peaks, all the Rh-related peaks observed in majority, as well as minority-carrier emission DLTS scans show an increase in their respective concentrations. The usually observed {alpha}-induced defects H{alpha}1, H{alpha}2, and H{alpha}3 are found to have lower introduction rates in Rh-doped samples, as compared to reference samples (not doped with Rh). Alpha-irradiation has been found to decompose the two minority carrier emitting bands (one at low temperature {approx}150 K and the other at {approx}380 K) observed prior to irradiation into distinct peaks corresponding to deep levels Rh1 and Rh2 and EL2 and Rh3, respectively. A similar effect is also observed for the majority-carrier emitting band composed of hole emission from deep levels RhA and RhB, which separate out well upon irradiation. Further, from the double-correlation DLTS measurements, the emission rates of carriers from the radiation-enhanced peaks corresponding to deep levels Rh1, Rh2, Rh3, and RhC were found to be dependent on junction electric field. For RhC, the field dependence data have been analyzed in terms of the Poole-Frenkel model employing a 3-dimensional Coulomb potential with q = 2e (electronic charge). Temperature dependence of the hole capture cross-sections of the levels RhA and RhC was also studied quantitatively. The observed dependence of the hole capture cross-section of RhC on temperature can be interpreted in terms of multiphonon capture model, yielding a capture barrier of 0.2 eV and {sigma}({infinity}) = 2.3 x 10{sup -14} cm{sup 2}. The results of irradiation and isochronal thermal annealing study, in combination with the theoretical

  19. Effects of irradiation and annealing on deep levels in rhodium-doped p-GaAs grown by metal-organic chemical-vapor deposition

    NASA Astrophysics Data System (ADS)

    Naz, Nazir A.; Qurashi, Umar S.; Iqbal, M. Zafar

    2011-06-01

    This paper reports a detailed study of the effects of irradiation and thermal annealing on deep levels in Rh-doped p-type GaAs grown by low-pressure metal-organic chemical-vapor deposition, using deep level transient spectroscopy (DLTS) technique. It is found upon irradiation with alpha particles that, in addition to the radiation-induced defect peaks, all the Rh-related peaks observed in majority, as well as minority-carrier emission DLTS scans show an increase in their respective concentrations. The usually observed α-induced defects Hα1, Hα2, and Hα3 are found to have lower introduction rates in Rh-doped samples, as compared to reference samples (not doped with Rh). Alpha-irradiation has been found to decompose the two minority carrier emitting bands (one at low temperature ˜150 K and the other at ˜380 K) observed prior to irradiation into distinct peaks corresponding to deep levels Rh1 and Rh2 and EL2 and Rh3, respectively. A similar effect is also observed for the majority-carrier emitting band composed of hole emission from deep levels RhA and RhB, which separate out well upon irradiation. Further, from the double-correlation DLTS measurements, the emission rates of carriers from the radiation-enhanced peaks corresponding to deep levels Rh1, Rh2, Rh3, and RhC were found to be dependent on junction electric field. For RhC, the field dependence data have been analyzed in terms of the Poole-Frenkel model employing a 3-dimensional Coulomb potential with q = 2e (electronic charge). Temperature dependence of the hole capture cross-sections of the levels RhA and RhC was also studied quantitatively. The observed dependence of the hole capture cross-section of RhC on temperature can be interpreted in terms of multiphonon capture model, yielding a capture barrier of 0.2 eV and σ(∞) = 2.3 × 10-14 cm2. The results of irradiation and isochronal thermal annealing study, in combination with the theoretical analysis of the field dependence of hole emission data

  20. Interactions of structural defects with metallic impurities in multicrystalline silicon

    SciTech Connect

    McHugo, S.A.; Thompson, A.C.; Hieslmair, H.

    1997-04-01

    Multicrystalline silicon is one of the most promising materials for terrestrial solar cells. It is critical to getter impurities from the material as well as inhibit contamination during growth and processing. Standard processing steps such as, phosphorus in-diffusion for p-n junction formation and aluminum sintering for backside ohmic contact fabrication, intrinsically possess gettering capabilities. These processes have been shown to improve L{sub n} values in regions of multicrystalline silicon with low structural defect densities but not in highly dislocated regions. Recent Deep Level Transient Spectroscopy (DLTS) results indirectly reveal higher concentrations of iron in highly dislocated regions while further work suggests that the release of impurities from structural defects, such as dislocations, is the rate limiting step for gettering in multicrystalline silicon. The work presented here directly demonstrates the relationship between metal impurities, structural defects and solar cell performance in multicrystalline silicon. Edge-defined Film-fed Growth (EFG) multicrystalline silicon in the as-grown state and after full solar cell processing was used in this study. Standard solar cell processing steps were carried out at ASE Americas Inc. Metal impurity concentrations and distributions were determined by use of the x-ray fluorescence microprobe (beamline 10.3.1) at the Advanced Light Source, Lawrence Berkeley National Laboratory. The sample was at atmosphere so only elements with Z greater than silicon could be detected, which includes all metal impurities of interest. Structural defect densities were determined by preferential etching and surface analysis using a Scanning Electron Microscope (SEM) in secondary electron mode. Mapped areas were exactly relocated between the XRF and SEM to allow for direct comparison of impurity and structural defect distributions.

  1. Comparative study of deep levels in HVPE and MOCVD GaN by combining O-DLTS and pulsed photo-ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Pavlov, J.; Čeponis, T.; Gaubas, E.; Meskauskaite, D.; Reklaitis, I.; Vaitkus, J.; Grigonis, R.; Sirutkaitis, V.

    2015-12-01

    Operational characteristics of sensors made of GaN significantly depend on technologically introduced defects acting as rapid traps of excess carriers which reduce charge collection efficiency of detectors. In order to reveal the prevailing defects in HVPE and MOCVD grown GaN, the carrier lifetime and photo-ionization spectra have been simultaneously measured by using microwave probed photo-conductivity transient technique. Several traps ascribed to impurities as well as vacancy and anti-site type defects have been identified in HVPE GaN material samples by combining photo-ionization and electron spin resonance spectroscopy. The optical deep level transient spectroscopy technique has been applied for spectroscopy of the parameters of thermal emission from the traps ascribed to technological defects in the Schottky barrier terrace structures fabricated on MOCVD GaN.

  2. Impure placebo is a useless concept.

    PubMed

    Louhiala, Pekka; Hemilä, Harri; Puustinen, Raimo

    2015-08-01

    Placebos are allegedly used widely in general practice. Surveys reporting high level usage, however, have combined two categories, 'pure' and 'impure' placebos. The wide use of placebos is explained by the high level usage of impure placebos. In contrast, the prevalence of the use of pure placebos has been low. Traditional pure placebos are clinically ineffective treatments, whereas impure placebos form an ambiguous group of diverse treatments that are not always ineffective. In this paper, we focus on the impure placebo concept and demonstrate problems related to it. We also show that the common examples of impure placebos are not meaningful from the point of view of clinical practice. We conclude that the impure placebo is a scientifically misleading concept and should not be used in scientific or medical literature. The issues behind the concept, however, deserve serious attention in future research.

  3. Elemental Impurities in Pharmaceutical Excipients.

    PubMed

    Li, Gang; Schoneker, Dave; Ulman, Katherine L; Sturm, Jason J; Thackery, Lisa M; Kauffman, John F

    2015-12-01

    Control of elemental impurities in pharmaceutical materials is currently undergoing a transition from control based on concentrations in components of drug products to control based on permitted daily exposures in drug products. Within the pharmaceutical community, there is uncertainty regarding the impact of these changes on manufactures of drug products. This uncertainty is fueled in part by a lack of publically available information on elemental impurity levels in common pharmaceutical excipients. This paper summarizes a recent survey of elemental impurity levels in common pharmaceutical excipients as well as some drug substances. A widely applicable analytical procedure was developed and was shown to be suitable for analysis of elements that are subject to United States Pharmacopoeia Chapter <232> and International Conference on Harmonization's Q3D Guideline on Elemental Impurities. The procedure utilizes microwave-assisted digestion of pharmaceutical materials and inductively coupled plasma mass spectrometry for quantitative analysis of these elements. The procedure was applied to 190 samples from 31 different excipients and 15 samples from eight drug substances provided through the International Pharmaceutical Excipient Council of the Americas. The results of the survey indicate that, for the materials included in the study, relatively low levels of elemental impurities are present.

  4. Deep Level Defects in Electron-Irradiated Aluminum Gallium Nitride Grown by Molecular Beam Epitaxy

    DTIC Science & Technology

    2005-03-01

    To date, these energy levels have not been systematically measured (i.e. temperature dependent Hall ( TDH ) and deep level transient spectroscopy...Material I.D. Ref. Donors 0.06 0.018 0.06 0.06 e- (1 MeV) TDH undoped HVPE n≈1017 VN SiGa 33 Acceptors deep e- (1 MeV) TDH " NI 33...qualitative agreement with the linear carrier removal model of equation II-33. More recently, TDH measurements were reported for the same type of GaN sample

  5. Origin of deep level defect related photoluminescence in annealed InP

    NASA Astrophysics Data System (ADS)

    Zhao, Youwen; Dong, Zhiyuan; Miao, Shanshan; Deng, Aihong; Yang, Jun; Wang, Bo

    2006-12-01

    Deep level defects in annealed InP have been studied by using photoluminescence spectroscopy (PL), thermally stimulated current (TSC), deep level transient spectroscopy (DLTS), and positron annihilation lifetime (PAL). A noticeable broad PL peak centered at 1.3eV has been observed in the InP sample annealed in iron phosphide ambient. Both the 1.3eV PL emission and a defect at EC-0.18eV correlate with a divacancy detected in the annealed InP sample. The results make a divacancy defect and related property identified in the annealed InP.

  6. Revised role for the Poole--Frenkel effect in deep-level characterization

    SciTech Connect

    Buchwald, W.R.; Johnson, N.M.

    1988-07-15

    The Poole--Frenkel effect is commonly used to decide between donorlike and acceptorlike electronic character for deep-level defects in semiconductors. However, there exists at least one defect, the EL2 center in GaAs, which is experimentally established to be a deep donor and yet does not exhibit the classical Poole--Frenkel effect for thermal emission of electrons. In this communication it is proposed that the existence of another well-documented deep-level phenomenon can suppress the Poole--Frenkel effect. Namely, a thermally activated capture cross section, which identifies an energy barrier to carrier capture and is commonly ascribed to a multiphonon emission process, introduces additional mechanisms which can alter the predominance of the Coulombic potential of the emitted carrier so as to suppress the electric-field-induced barrier lowering. A simple one-dimensional model is analyzed to qualitatively illustrate the combined phenomena.

  7. Correlation of a generation-recombination center with a deep level trap in GaN

    SciTech Connect

    Nguyen, X. S. E-mail: elecsj@nus.edu.sg; Lin, K.; Zhang, Z.; Arehart, A. R.; Ringel, S. A.; McSkimming, B.; Speck, J. S.; Fitzgerald, E. A.; Chua, S. J. E-mail: elecsj@nus.edu.sg

    2015-03-09

    We report on the identification of a deep level trap centre which contributes to generation-recombination noise. A n-GaN epilayer, grown by MOCVD on sapphire, was measured by deep level transient spectroscopy (DLTS) and noise spectroscopy. DLTS found 3 well documented deep levels at E{sub c} − 0.26 eV, E{sub c} − 0.59 eV, and E{sub c} − 0.71 eV. The noise spectroscopy identified a generation recombination centre at E{sub c} − 0.65 ± 0.1 eV with a recombination lifetime of 65 μs at 300 K. This level is considered to be the same as the one at E{sub c} − 0.59 eV measured from DLTS, as they have similar trap densities and capture cross section. This result shows that some deep levels contribute to noise generation in GaN materials.

  8. Method for detecting trace impurities in gases

    DOEpatents

    Freund, Samuel M.; Maier, II, William B.; Holland, Redus F.; Beattie, Willard H.

    1981-01-01

    A technique for considerably improving the sensitivity and specificity of infrared spectrometry as applied to quantitative determination of trace impurities in various carrier or solvent gases is presented. A gas to be examined for impurities is liquefied and infrared absorption spectra of the liquid are obtained. Spectral simplification and number densities of impurities in the optical path are substantially higher than are obtainable in similar gas-phase analyses. Carbon dioxide impurity (.about.2 ppm) present in commercial Xe and ppm levels of Freon 12 and vinyl chloride added to liquefied air are used to illustrate the method.

  9. Method for detecting trace impurities in gases

    DOEpatents

    Freund, S.M.; Maier, W.B. II; Holland, R.F.; Beattie, W.H.

    A technique for considerably improving the sensitivity and specificity of infrared spectrometry as applied to quantitative determination of trace impurities in various carrier or solvent gases is presented. A gas to be examined for impurities is liquefied and infrared absorption spectra of the liquid are obtained. Spectral simplification and number densities of impurities in the optical path are substantially higher than are obtainable in similar gas-phase analyses. Carbon dioxide impurity (approx. 2 ppM) present in commercial Xe and ppM levels of Freon 12 and vinyl chloride added to liquefied air are used to illustrate the method.

  10. DLTS study of deep level defects in Li-ion irradiated bipolar junction transistor

    NASA Astrophysics Data System (ADS)

    Madhu, K. V.; Kulkarni, S. R.; Ravindra, M.; Damle, R.

    2007-01-01

    Commercial npn transistor (2N 2219A) irradiated with 50 MeV Li 3+-ions with fluences ranging from 3.1 × 10 13 ions cm -2 to 12.5 × 10 13 ions cm -2, is studied for radiation induced gain degradation and minority carrier trap levels or recombination centers. The properties such as activation energy, trap concentration and capture cross section of induced deep levels are studied by deep level transient spectroscopy (DLTS) technique. Minority carrier trap levels with energies ranging from 0.237 eV to 0.591 eV were observed in the base-collector junction of the transistor. In situ I- V measurements were made to study the gain degradation as a function of ion fluence. Ion induced energy levels result in increase in the base current through Shockley Read Hall (SRH) or multi-phonon recombination and subsequent transistor gain degradation.

  11. Effects of EL2 deep level in GaAs photoconductive switch

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Liu, Rui; Wang, Jing-li

    2009-07-01

    The semi-insulating (SI) GaAs photoconductive switch is considered to be the higher efficient THz source recently. In order to make good use of the photoconductive switch to generate the more efficient THz wave, SI-GaAs photoconductive switch's working mechanism is discussed from the respect of EL2 deep level in this paper. It has three operation modes. The SI-GaAs material has many kinds of intrinsic-defects. One of the more notable defects is EL2 deep level. The EL2 level can become an impactful electron trap in the linear operation mode; The EL2 level is also the necessary condition of nonlinear (also known as Lock-on) operation mode emerging in III-V semiconductors such as GaAs and InP. At the same time, the compound operation mode is substantial related with the conversion from neutral energy level EL20 to metastable energy level EL2* and singly ionized energy level EL2+ in semiconductor under the light. So in this paper the effects of EL2 deep level are analyzed in photoconductive switch' there operation modes.

  12. Theoretical Explanation for Success of Deep-Level-Learning Study Tours

    ERIC Educational Resources Information Center

    Bergsteiner, Harald; Avery, Gayle C.

    2008-01-01

    Study tours can help internationalize curricula and prepare students for global workplaces. We examine benefits of tours providing deep-level learning experiences rather than industrial tourism using five main theoretical frameworks to highlight the diverse learning benefits associated with intensive study tours in particular. Relevant theoretical…

  13. Deep-level transient spectroscopy of InAs/GaAs quantum dot superlattices

    SciTech Connect

    Sobolev, M. M.; Nevedomskii, V. N.; Zolotareva, R. V.; Vasil'ev, A. P.; Ustinov, V. M.

    2014-02-21

    Deep level transient spectroscopy (DLTS) has been applied to study the carrier emission from states of a 10-layer system of tunnel-coupled vertically correlated quantum dots (VCQDs) in p-n InAs/GaAs heterostructures with different widths of GaAs spacers under varied reverse bias (U{sub r}) and filling voltage pulse U{sub f}.

  14. Identification of process related trace level impurities in the actinide decorpration agent 3,4,3-LI(1,2-HOPO): Nozzle-Skimmer fragmentation via ESI LC-QTOFMS

    PubMed Central

    Panyala, Nagender R.; Sturzbecher-Hoehne, Manuel; Abergel, Rebecca J.

    2014-01-01

    3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of Liquid Chromatography coupled with photo-diode array UV detection and Electrospray Ionization-Quadrupole Time of Flight Mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (Nozzle-Skimmer Fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Time of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling. PMID:25165012

  15. Identification of process related trace level impurities in the actinide decorporation agent 3,4,3-LI(1,2-HOPO): Nozzle-skimmer fragmentation via ESI LC-QTOFMS.

    PubMed

    Panyala, Nagender R; Sturzbecher-Hoehne, Manuel; Abergel, Rebecca J

    2014-11-01

    3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of liquid chromatography coupled with photo-diode array UV detection and electrospray ionization-quadrupole time of flight mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (nozzle-skimmer fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Time of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling.

  16. Identification of process related trace level impurities in the actinide decorporation agent 3,4,3-LI(1,2-HOPO): Nozzle–skimmer fragmentation via ESI LC–QTOFMS

    DOE PAGES

    Panyala, Nagender R.; Sturzbecher-Hoehne, Manuel; Abergel, Rebecca J.

    2014-08-12

    We report that 3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of Liquid Chromatography coupled with photo-diode array UV detection and Electrospray Ionization-Quadrupole Time of Flight Mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (Nozzle-Skimmer Fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Timemore » of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling.« less

  17. Identification of process related trace level impurities in the actinide decorporation agent 3,4,3-LI(1,2-HOPO): Nozzle–skimmer fragmentation via ESI LC–QTOFMS

    SciTech Connect

    Panyala, Nagender R.; Sturzbecher-Hoehne, Manuel; Abergel, Rebecca J.

    2014-08-12

    We report that 3,4,3-LI(1,2-HOPO) is a chelating ligand and decorporation agent that can remove radioactive lanthanides and actinides from the body. Identification of trace impurities in drug samples is gaining much interest due to their significant influence on drug activity. In this study, trace impurities were detected in manufactured lots of 3,4,3-LI(1,2-HOPO) by a developed method of Liquid Chromatography coupled with photo-diode array UV detection and Electrospray Ionization-Quadrupole Time of Flight Mass spectrometry (LC-QTOFMS), via induced-in-source or collision-induced mass fragmentation (Nozzle-Skimmer Fragmentation). Molecular ions were fragmented within the nozzle-skimmer region of electrospray ionization (ESI) mass spectrometer equipped with a Time of Flight detector. Eight major (detected at levels higher than a 0.1% threshold) and seven minor trace impurities were identified. The respective structures of these impurities were elucidated via analysis of the generated fragment ions using mass fragmentation and elemental composition software. Proposed structures of impurities were further confirmed via isotopic modeling.

  18. Deep levels in undoped horizontal Bridgman GaAs by Fourier transform photoconductivity and Hall effect

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Brown, Gail J.; Rea, Laura S.; Smith, S. R.

    1992-01-01

    Deep levels between 0.1 and 1.0 eV in semi-insulating and high resistivity undoped horizontal Bridgman GaAs have been studied by temperature-dependent Hall effect (TDH) and Fourier transform photoconductivity (FTPC). Activation energies at 0.77, 0.426, and 0.15 eV have been observed by TDH. Photoionization thresholds at 1.0, 0.8, 0.56, 0.44, and 0.25 are reported. The photoconductivity thresholds at 0.56 and 0.25 eV are reported for the first time. New features in the 0.44 eV threshold suggest that the defect responsible for this level has a small lattice relaxation and Frank-Condon shift. Possible associations of the FTPC and TDH energies with the deep-level transient spectroscopy levels EL2, EL3, and EL6 are presented.

  19. Deep level transient spectroscopy (DLTS) on colloidal-synthesized nanocrystal solids.

    PubMed

    Bozyigit, Deniz; Jakob, Michael; Yarema, Olesya; Wood, Vanessa

    2013-04-24

    We demonstrate current-based, deep level transient spectroscopy (DLTS) on semiconductor nanocrystal solids to obtain quantitative information on deep-lying trap states, which play an important role in the electronic transport properties of these novel solids and impact optoelectronic device performance. Here, we apply this purely electrical measurement to an ethanedithiol-treated, PbS nanocrystal solid and find a deep trap with an activation energy of 0.40 eV and a density of NT = 1.7 × 10(17) cm(-3). We use these findings to draw and interpret band structure models to gain insight into charge transport in PbS nanocrystal solids and the operation of PbS nanocrystal-based solar cells.

  20. Energy Levels of a Hydrogenic Impurity in Gallium ARSENIDE/GALLIUM(1-X) Aluminum(x) Arsenide Multiple-Quantum Structures in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Nguyen, Nghia Trong

    Energy levels of a hydrogenic impurity (Si) in the (GaAs/Ga_{1-x}Al_{x }As) quantum-well systems with and without an applied magnetic field perpendicular to the interfaces have been studied theoretically. A variational approach employing the envelope wavefunction approximation has been used. The envelope wavefunction is chosen to be a product of a combination (mixing) of one or more confined states of a free electron in the one dimensional quantum-well potential considered with Gaussian trial functions. First, the study is focused on a coupled double -quantum-well model which serves as a bridge between the single-, and multiple-quantum-well structures. It is found that the binding energies depend significantly upon the well width, the barrier width, the location of the impurity, and the magnetic field. A comparison with recent experiments demonstrates that intersubband mixing plus the difference in electron effective-masses in the two semiconductors should be included in the calculations. Next, the problem is extended to the cases of multiple-quantum-well model with narrow barriers. For the doped well at the center of the structure in zero field, the calculated binding energies do not change in any significant way beyond 15 periods for either of two structures investigated (with periodicities of 80A well-9A barrier and 40A well -9A barrier). Calculations are also performed for superlattices with 15 periods in the presence of the magnetic field. Very good agreement is obtained in comparing the results with recent measurements. For the doped well at various locations within the structure, the outer boundary of the finite superlattice (15 wells) has significant effect on the binding energies, especially when the doped well is less than 4 wells away from the boundary. Finally, in a departure from above approach, we have attempted to simplify the problem by subsumming the entire effect of the superlattice periodic potential in the electron effective-mass (miniband

  1. Deep level defects in dilute GaAsBi alloys grown under intense UV illumination

    SciTech Connect

    Mooney, P. M.; Tarun, Marianne; Beaton, D. A.; Mascarenhas, A.; Alberi, K.

    2016-07-21

    Dilute GaAs1-xBix alloys exhibiting narrow band edge photoluminescence (PL) were recently grown by molecular beam epitaxy (MBE) with the growth surface illuminated by intense UV radiation. To investigate whether the improved optical quality of these films results from a reduction in the concentration of deep level defects, p+/n and n+/p junction diodes were fabricated on both the illuminated and dark areas of several samples. Deep Level Transient Spectroscopy (DLTS) measurements show that the illuminated and dark areas of both the n- and p-type GaAs1-xBix epi-layers have similar concentrations of near mid-gap electron and hole traps, in the 1015 cm-3 range. Thus the improved PL spectra cannot be explained by a reduction in non-radiative recombination at deep level defects. We note that carrier freeze-out above 35 K is significantly reduced in the illuminated areas of the p-type GaAs1-xBix layers compared to the dark areas, allowing the first DLTS measurements of defect energy levels close to the valence band edge. These defect levels may account for differences in the PL spectra from the illuminated and dark areas of un-doped layers with a similar Bi fraction.

  2. Deep-level dominated electrical characteristics of Au contacts on beta-SiC

    NASA Technical Reports Server (NTRS)

    Das, K.; Kong, H. S.; Petit, J. B.; Bumgarner, J. W.; Davis, R. F.; Matus, L. G.

    1990-01-01

    Electrical characteristics of Au contacts on beta-SiC films, grown epitaxially on both nominal and off-axis (100) silicon substrates, are reported. An analysis of the logarithmic I-V plots of the Au/beta-SiC diodes revealed information pertaining to the deep states present in the materials. It was found that while the beta-SiC films grown on nominally (100) oriented substrates show the presence of two deep levels located between 0.26 and 0.38 eV below the conduction bandedge, the beta-SiC films deposited on off-axis substrates have only one deep level, located about 0.49 eV below the conduction bandedge for the 2-deg off (100) substrates and 0.57 eV for the 4-deg off (100) substrates. The presence of the shallower deep states in the beta-SiC films grown on nominal (100) substrates is attributed to the electrical activity of antiphase domain boundaries.

  3. Reference design and operations for deep borehole disposal of high-level radioactive waste.

    SciTech Connect

    Herrick, Courtney Grant; Brady, Patrick Vane; Pye, Steven; Arnold, Bill Walter; Finger, John Travis; Bauer, Stephen J.

    2011-10-01

    A reference design and operational procedures for the disposal of high-level radioactive waste in deep boreholes have been developed and documented. The design and operations are feasible with currently available technology and meet existing safety and anticipated regulatory requirements. Objectives of the reference design include providing a baseline for more detailed technical analyses of system performance and serving as a basis for comparing design alternatives. Numerous factors suggest that deep borehole disposal of high-level radioactive waste is inherently safe. Several lines of evidence indicate that groundwater at depths of several kilometers in continental crystalline basement rocks has long residence times and low velocity. High salinity fluids have limited potential for vertical flow because of density stratification and prevent colloidal transport of radionuclides. Geochemically reducing conditions in the deep subsurface limit the solubility and enhance the retardation of key radionuclides. A non-technical advantage that the deep borehole concept may offer over a repository concept is that of facilitating incremental construction and loading at multiple perhaps regional locations. The disposal borehole would be drilled to a depth of 5,000 m using a telescoping design and would be logged and tested prior to waste emplacement. Waste canisters would be constructed of carbon steel, sealed by welds, and connected into canister strings with high-strength connections. Waste canister strings of about 200 m length would be emplaced in the lower 2,000 m of the fully cased borehole and be separated by bridge and cement plugs. Sealing of the upper part of the borehole would be done with a series of compacted bentonite seals, cement plugs, cement seals, cement plus crushed rock backfill, and bridge plugs. Elements of the reference design meet technical requirements defined in the study. Testing and operational safety assurance requirements are also defined. Overall

  4. Investigation of deep level defects in CdTe thin films

    SciTech Connect

    Shankar, H.; Castaldini, A.; Dauksta, E.; Medvid, A.; Cavallini, A.

    2014-02-21

    In the past few years, a large body of work has been dedicated to CdTe thin film semiconductors, as the electronic and optical properties of CdTe nanostructures make them desirable for photovoltaic applications. The performance of semiconductor devices is greatly influenced by the deep levels. Knowledge of parameters of deep levels present in as-grown materials and the identification of their origin is the key factor in the development of photovoltaic device performance. Photo Induced Current Transient Spectroscopy technique (PICTS) has proven to be a very powerful method for the study of deep levels enabling us to identify the type of traps, their activation energy and apparent capture cross section. In the present work, we report the effect of growth parameters and LASER irradiation intensity on the photo-electric and transport properties of CdTe thin films prepared by Close-Space Sublimation method using SiC electrical heating element. CdTe thin films were grown at three different source temperatures (630, 650 and 700 °C). The grown films were irradiated with Nd:YAG LASER and characterized by Photo-Induced Current Transient Spectroscopy, Photocurrent measurementand Current Voltage measurements. The defect levels are found to be significantly influenced by the growth temperature.

  5. Formation of copper(I) from trace levels of copper(II) as an artifactual impurity in the HPLC analysis of olanzapine.

    PubMed

    Baertschi, Steven W; Olsen, Bernard A; Wozniak, Timothy J; Toltl, Nick; O'Shea, Colette; Jansen, Patrick J

    2016-06-05

    An analytical artifact peak appearing to be an impurity was observed intermittently among several laboratories performing HPLC analyses of olanzapine drug substance and formulation samples. The artifact peak was identified as Cu(I) that was formed from the reaction of trace amounts of Cu(II) with olanzapine in the sample solution. Unlike Cu(II), Cu(I) was retained under the ion-pairing HPLC conditions used for analysis. A reaction mechanism was postulated whereby Cu(II) present in the sample solution oxidizes olanzapine to a radical-cation, resulting in formation of Cu(I) and three oxidation products of olanzapine including a previously unknown oxidation product that was identified as hydroxy-olanzapine. Acetonitrile in the sample solution was necessary for the reaction to occur. As little as 100 ppb Cu(II) in the sample solution produced a Cu(I) peak, that by peak area, corresponded to about 0.1% relative to the olanzapine peak. The hydroxy-olanzapine oxidation product was also detectable, but the relative peak area was much smaller. To prevent formation of the Cu(I) artifact peak, EDTA was added to the sample solvent to complex any trace Cu(II) that might be present. The addition of EDTA was shown to prevent Cu(I) formation when Cu(II) was present at levels of 4ppm in the sample solution.

  6. Trace level impurity method development with high-field asymmetric waveform ion mobility spectrometry: systematic study of factors affecting the performance.

    PubMed

    Champarnaud, Elodie; Laures, Alice M-F; Borman, Phil J; Chatfield, Marion J; Kapron, James T; Harrison, Mark; Wolff, Jean-Claude

    2009-01-01

    For the determination of trace level impurities, analytical chemists are confronted with complex mixtures and difficult separations. New technologies such as high-field asymmetric waveform ion mobility spectrometry (FAIMS) have been developed to make their work easier; however, efficient method development and troubleshooting can be quite challenging if little prior knowledge of the factors or their settings is available. We present the results of an investigation performed in order to obtain a better understanding of the FAIMS technology. The influence of eight factors (polarity of dispersion voltage, outer bias voltage, total gas flow rate, composition of the carrier gas (e.g. %He), outer electrode temperature, ratio between the temperatures of the inner and outer electrodes, flow rate and composition of the make-up mobile phase) was assessed. Five types of responses were monitored: value of the compensation voltage (CV), intensity, width and asymmetry of the compensation voltage peak, and resolution between two peaks. Three types of studies were performed using different test mixtures and various ionisation modes to assess whether the same conclusions could be drawn across these conditions for a number of different types of compounds. To extract the maximum information from as few experiments as possible, a Design of Experiment (DoE) approach was used. The results presented in this work provide detailed information on the factors affecting FAIMS separations and therefore should enable the user to troubleshoot more effectively and to develop efficient methods.

  7. Radiation induced deep level defects in bipolar junction transistors under various bias conditions

    NASA Astrophysics Data System (ADS)

    Liu, Chaoming; Yang, Jianqun; Li, Xingji; Ma, Guoliang; Xiao, Liyi; Bollmann, Joachim

    2015-12-01

    Bipolar junction transistor (BJT) is sensitive to ionization and displacement radiation effects in space. In this paper, 35 MeV Si ions were used as irradiation source to research the radiation damage on NPN and PNP bipolar transistors. The changing of electrical parameters of transistors was in situ measured with increasing irradiation fluence of 35 MeV Si ions. Using deep level transient spectroscopy (DLTS), defects in the bipolar junction transistors under various bias conditions are measured after irradiation. Based on the in situ electrical measurement and DLTS spectra, it is clearly that the bias conditions can affect the concentration of deep level defects, and the radiation damage induced by heavy ions.

  8. Investigation of deep level transient spectroscopy (DLTS) of dopant ZnO-based varistors

    NASA Astrophysics Data System (ADS)

    Ammar, A. H.; Farag, A. A. M.

    2010-03-01

    This work shows that the use of conventional analytical procedures to investigate the deep centers from the deep levels transient spectroscopy (DLTS) for ZnO varistors doped with single, double and ternary dopants of Bi 2O 3, CoO and MnO 2. This is to clarify the effect of these doping atoms on the conductivity of ZnO varistors. The results showed that the doping with Bi 2O 3 +CoO leads to a decrease in the conductivity while doping with Bi 2O 3+MnO 2 increased the conductivity and the three dopants together showed a compensating effect. The DLTS characterizing parameters such as minority-carrier capture cross-section, σ, effective density of states in the minority-carrier band, N D, energy separation between the trap level and the minority-carrier band, Δ E t and electron trap density, N t for each doped varistor were also calculated.

  9. Effect of hydrostatic pressure and alloy composition on sulfur- and selenium-related impurity states in heavily doped n-type GaxIn1-xSb

    NASA Astrophysics Data System (ADS)

    Zitouni, K.; Kadri, A.; Aulombard, R. L.

    1986-08-01

    The properties of sulfur- and selenium-related impurity states have been studied as a function of pressure and composition in heavily doped GaxIn1-xSb. Hall-coefficient and electrical-resistivity measurements were made under hydrostatic pressures of up to 25 kbar, in the alloy composition range 0.30<~x<~0.78 and in the temperature range 77 K<~T<~300 K. In both S-doped and Se-doped samples, the results show the existence of an impurity level forming a localized resonance in the Γ1c band continuum. At x=0.78 and P=0 kbar, the resonance lay ~130+/-10 meV and ~180+/-10 meV above the Γ1c band edge in S-doped and Se-doped samples, respectively. As x decreased, the resonance remained almost fixed with respect to the top of the valence band. As the pressure increased, the impurity level was driven into the fundamental gap, independently of nearby band edges, thus demonstrating ``deep-level behavior.'' Furthermore, the pressure-induced occupation of this impurity level led to time-dependent effects at T<~110 K. The activated thermal electron emission over a potential barrier gave clear evidence for a large lattice relaxation around the impurity centers. These results show the dominant effect of the local non-Coulombic component of the impurity potential, suggesting the complex nature of the impurity centers.

  10. Relaxation spectroscopy of deep levels in semiconductors: Laplace-DLTS method

    NASA Astrophysics Data System (ADS)

    Levin, M. N.; Bormontov, A. E.; Akhkubekov, A. É.; Tatokhin, E. A.

    2010-11-01

    Deep level transient spectroscopy (DLTS) is among the main methods used to determine the parameters of electrically active centers of charge localization in semiconductors. In order to increase the accuracy and adequacy of DLTS data, we propose a modified approach based on the application of an inverse Laplace transform. Using the proposed Laplace-DLTS method, it is possible to determine the parameters of centers with close carrier emission coefficients, which cannot be done using the traditional DLTS technique.

  11. Albedo Neutron Dosimetry in a Deep Geological Disposal Repository for High-Level Nuclear Waste.

    PubMed

    Pang, Bo; Becker, Frank

    2016-06-24

    Albedo neutron dosemeter is the German official personal neutron dosemeter in mixed radiation fields where neutrons contribute to personal dose. In deep geological repositories for high-level nuclear waste, where neutrons can dominate the radiation field, it is of interest to investigate the performance of albedo neutron dosemeter in such facilities. In this study, the deep geological repository is represented by a shielding cask loaded with spent nuclear fuel placed inside a rock salt emplacement drift. Due to the backscattering of neutrons in the drift, issues concerning calibration of the dosemeter arise. Field-specific calibration of the albedo neutron dosemeter was hence performed with Monte Carlo simulations. In order to assess the applicability of the albedo neutron dosemeter in a deep geological repository over a long time scale, spent nuclear fuel with different ages of 50, 100 and 500 years were investigated. It was found out, that the neutron radiation field in a deep geological repository can be assigned to the application area 'N1' of the albedo neutron dosemeter, which is typical in reactors and accelerators with heavy shielding.

  12. Large lattice relaxation deep levels in neutron-irradiated GaN

    NASA Astrophysics Data System (ADS)

    Li, S.; Zhang, J. D.; Beling, C. D.; Wang, K.; Wang, R. X.; Gong, M.; Sarkar, C. K.

    2005-11-01

    Deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) measurements have been carried out in neutron-irradiated n-type hydride-vapor-phase-epitaxy-grown GaN. A defect center characterized by a DLTS line, labeled as N1, is observed at EC-ET=0.17 eV. Another line, labeled as N2, at EC-ET=0.23 eV, seems to be induced at the same rate as N1 under irradiation and may be identified with E1. Other defects native to wurtzite GaN such as the C and E2 lines appear to enhance under neutron irradiation. The DLOS results show that the defects N1 and N2 have large Frank-Condon shifts of 0.64 and 0.67 eV, respectively, and hence large lattice relaxations. The as-grown and neutron-irradiated samples all exhibit the persistent photoconductivity effect commonly seen in GaN that may be attributed to DX centers. The concentration of the DX centers increases significantly with neutron dosage and is helpful in sustaining sample conductivity at low temperatures, thus making possible DLTS measurements on N1 an N2 in the radiation-induced deep-donor defect compensated material which otherwise are prevented by carrier freeze-out.

  13. Increased soluble P-selectin levels following deep venous thrombosis: cause or effect?

    PubMed

    Blann, A D; Noteboom, W M; Rosendaal, F R

    2000-01-01

    Deep vein thrombosis (DVT) is associated with coagulation abnormalities, but evidence of excess platelet activity is scant. Soluble P-selectin is a marker of platelet activity, with high levels being found in patients with thrombotic disease. We measured soluble P-selectin by enzyme-linked immunosorbent assay (ELISA) in plasma from 89 patients with objectively confirmed DVT and in 126 healthy age- and sex-matched control subjects, and found higher levels in the patients (P = 0.011). Taking the risk of DVT with a level of soluble P-selectin < 238 ng/ml to be 1, the relative risk of DVT with a soluble P-selectin level >238 ng/ml was 2.1 (95% CI 1. 2-3.6). These high levels may be a reflection of a generalized hypercoagulable state that, with factors such as the presence of persistent thrombin generation, could be responsible for excess platelet activation.

  14. Deep trap levels in CdS solar cells observed by capacitance measurements

    NASA Astrophysics Data System (ADS)

    Hmurcik, L.; Ketelsen, L.; Serway, R. A.

    1982-05-01

    Capacitance measurements have been carried out as a function of reverse bias voltage and signal frequency on thin-film and single-crystal CdS solar cells. It is shown that such measurements can reveal abrupt changes in C-V plots which are attributed to the presence of deep trapping states. The anomalous change in capacitance occurs when the bias voltage raises a trapping state above the Fermi level; the strength of the anomalies depends on several factors including temperature, signal frequency, and junction properties. Measurements taken on the CdS cells indicate that at least two deep trapping states are present in the partially formed i layer of CdS, which is consistent with results reported by other workers.

  15. Investigation of the origin of deep levels in CdTe doped with Bi

    SciTech Connect

    Saucedo, E.; Franc, J.; Elhadidy, H.; Horodysky, P.; Ruiz, C. M.; Bermudez, V.; Sochinskii, N. V.

    2008-05-01

    Combining optical (low temperature photoluminescence), electrical (thermoelectric effect spectroscopy), and structural (synchrotron X-ray powder diffraction) methods, the defect structure of CdTe doped with Bi was studied in crystals with dopant concentration in the range of 10{sup 17}-10{sup 19} at./cm{sup 3}. The semi-insulating state observed in crystals with low Bi concentration is assigned to the formation of a shallow donor level and a deep donor recombination center. Studying the evolution of lattice parameter with temperature, we postulate that the deep center is formed by a Te-Te dimer and their formation is explained by a tetrahedral to octahedral distortion, due to the introduction of Bi in the CdTe lattice. We also shows that this model agrees with the electrical, optical, and transport charge properties of the samples.

  16. Minority-carrier emission effect in deep level transient spectroscopy measurements on Schottky diodes

    SciTech Connect

    Lee, W.I.; Borrego, J.M.

    1988-06-01

    One basic assumption underlying all the deep level transient spectroscopy derivations is the existence of a single dominant emission process during the transient. It is demonstrated in this paper that the use of conventional procedure could result in significant errors in all the calculated defect parameters when the concerned level has comparable emission rates for both carriers in the detected range. A simple verification method and an improved scheme are proposed to determine the accurate defect parameters. By using this scheme, it is confirmed that EL2 in GaAs is an electron trap with a dominant electron emission rate. A level, designated as E3, in Si shows similar electron and hole emission rates in detected range. It is proven for this level that the conventional Arrhenius plot will lead to large errors in all the calculated defect properties, while the improved scheme provides the accurate information.

  17. [Blood plasma level of endothelin in miners of a deep coal mine].

    PubMed

    Plotkin, V Ia; Rebrov, B A; Nikitina, I V

    2000-09-01

    In 60 miners working in a deep coal mine the blood plasma level of endoteline-1 (E-1) was measured by the immunoenzyme technique immediately after working shift. Those in the mining where the working conditions are especially harsh were found to have the highest level of E-1 exceeding the control values. In studying the age-related content of E-1 in blood plasma of coal miners the highest levels of E-1 were recordable in workers 20 to 30 years old, declining and differing in age groups 20-30 and 41-50 years old. The level of E-1 was at its greatest in those workers with minimum length of service in the underground conditions, declining with the service more than 10 years in duration.

  18. Pressure-dependent DLTS (Deep Level Transient Spectroscopy) experiments on Si-doped AlGaAs

    NASA Astrophysics Data System (ADS)

    Farmer, J. W.; Hjalmarson, H. P.; Samara, G. A.

    Pressure dependent Deep Level Transient Spectroscopy (DLTS) experiments are used to measure the properties of the deep donors (DX-centers) responsible for the persistent photoconductivity effect in Si-doped AlGaAs. The sample dependence of the DLTS spectra shows evidence for a defect complex involved in the DX-center.

  19. Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS2 layered semiconductor

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargın, Elif Orhan; Odrinsky, Andrei P.

    2015-06-01

    Lanthanum-doped high quality TlInS2 (TlInS2:La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS2:La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS2:La. Thermal treatments of TlInS2:La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T ≤ 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 × 10-14 cm2, corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS2:La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 × 10-16 cm2 were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the

  20. Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS{sub 2} layered semiconductor

    SciTech Connect

    Seyidov, MirHasan Yu. Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargın, Elif Orhan; Odrinsky, Andrei P.

    2015-06-14

    Lanthanum-doped high quality TlInS{sub 2} (TlInS{sub 2}:La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS{sub 2}:La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS{sub 2}:La. Thermal treatments of TlInS{sub 2}:La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T ≤ 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 × 10{sup −14} cm{sup 2}, corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS{sub 2}:La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 × 10{sup −16} cm{sup 2} were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles

  1. Analysis of the deep level responsible for the degradation of InGaN-based laser diodes by DLTS

    NASA Astrophysics Data System (ADS)

    Meneghini, M.; de Santi, C.; Trivellin, N.; Orita, K.; Takigawa, S.; Tanaka, T.; Ueda, D.; Meneghesso, G.; Zanoni, E.

    2012-03-01

    Recent studies demonstrated that degradation of InGaN-based laser diodes is due to an increase in non-radiative recombination rate within the active layer of the devices, due to the generation of defects. The aim of this paper is to show - by DLTS - that the degradation of InGaN-based laser diodes is strongly correlated to the increase in the concentration of a deep level located within the active region. The activation energy of the detected deep level is 0.35-0.45 eV. Hypothesis on the nature of this deep level are presented in the paper.

  2. Silicon materials task of the low cost solar array project (Phase III). Effects of impurities and processing on silicon solar cells. Phase III summary and seventeenth quarterly report, Volume 2: analysis of impurity behavior

    SciTech Connect

    Hopkins, R.H.; Davis, J.R.; Rohatgi, A.; Campbell, R.B.; Blais, P.D.; Rai-Choudhury, P.; Stapleton, R.E.; Mollenkopf, H.C.; McCormick, J.R.

    1980-01-23

    The object of this phase of the program has been to investigate the effects of various processes, metal contaminants and contaminant-process interactions on the properties of silicon and on the performance of terrestrial silicon solar cells. The study encompassed topics including thermochemical (gettering) treatments, base doping concentration, base doping type (n vs. p), grain boundary-impurity interaction, non-uniformity of impurity distribution, long term effects of impurities, as well as synergic and complexing phenomena. The program approach consists in: (1) the growth of doubly and multiply-doped silicon single crystals containing a baseline boron or phosphorus dopant and specific impurities which produce deep levels in the forbidden band gap; (2) assessment of these crystals by chemical, microstructural, electrical and solar cell tests; (3) correlation of the impurity type and concentration with crystal quality and device performance; and (4) delineation of the role of impurities and processing on subsequent silicon solar cell performance. The overall results reported are based on the assessment of nearly 200 silicon ingots. (WHK)

  3. Deep Impurity Band Silicon for Subbandgap Photodetection

    DTIC Science & Technology

    2014-05-02

    Our prior research had demonstrated an insulator-to-metal transition in silicon hyperdoped with sulfur or selenium when the chalcogen concentration...silicon hyperdoped with selenium , from [1]. Filled defect band broadens until it intersects conduction band at 0.4% Se caus- ing insulator-to-metal...Aziz, T. Buonassisi, and J.C. Grossman, "Insulator-to-Metal Transition in Selenium -Hyperdoped Silicon: Observation and Origin", Physical Review Letters

  4. Submonolayer epitaxy with impurities

    NASA Astrophysics Data System (ADS)

    Kotrla, Miroslav; Krug, Joachim; Smilauer, Pavel

    2000-03-01

    The effect of impurities on epitaxial growth in the submonolayer regime is studied using kinetic Monte Carlo simulations of a two-species solid-on-solid growth model. Both species are mobile, and attractive interactions among adatoms and between adatoms and impurities are incorporated. Impurities can be codeposited with the growing material or predeposited prior to growth. The activated exchange of impurities and adatoms is identified as the key kinetic process in the formation a growth morphology in which the impurities decorate the island edges. The dependence of the island density N on flux F and coverage θ is studied in detail. The impurities strongly increase the island density without appreciably changing the exponent \\chi in the power law relation N ~ F^\\chi, apart from a saturation of the flux dependence at large F and small θ. Within the present model, even completely decorated island edges do not provide efficient barriers to the attachment of adatoms, and therefore the mechanism for the increase of \\chi proposed by D. Kandel [Phys. Rev. Lett. 78, 499 (1997)] is not operative. A simple analytic theory taking into account only the dependence of the adatom diffusion constant on impurity coverage is shown to provide semi-quantitative agreement with many features observed in the simulations.

  5. Deep-level magma dehydration and ascent rates at Mt. Etna (Sicily, Italy)

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Perinelli, C.; Putirka, K.

    2012-04-01

    Magma ascent velocity, v (dH/dt; H = depth, t = time),can be determined from ascent rate (dP/dt), and rate of cooling (dT/dt): v= 1/(rgpg) (dP/dT)(dT/dt) where r is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships between initial ascent rate of magma and the depths of magma dehydration, and v can be calculated using pressure and temperature (P - PH2O - T) estimates from mineral-liquid thermobarometry, and cooling rates inferred from Crystal Size Distribution (CSD) theory. For recent Mt. Etna lava flows, both dP/dT and dT/dt have been well characterized based, respectively, on clinopyroxene thermobarometry, and clinopyroxene CSDs (the latter yields dT/dt = 2x10-6 °C/s). Deep-level (>20 km) magma ascent rates range from practically 0 (where clinopyroxene P - T estimates form a cluster, and so dP/dT ≈ 0), to about 10 m/hr for flows that yield very steep P - T trajectories. Many lava flows at Mt. Etna yield P - T paths that follow a hydrous (about 3% water) clinopyroxene saturation surface, which closely approximates water contents obtained from melt inclusions. Independent assessments of deep level water content yield ascent rates of ~1 m/hr, in agreement with the slowest rates derived for magma effusion or vapor-driven ascent (~0.001 to >0.2 m/s, or 3.6 to 720 m/hr). Changes in P - T slopes, as obtained by pyroxene thermobarometry, indicate an upward acceleration of magma, which may be due to the onset of deep-level magma dehydration linked to the non-ideal behavior of water and CO2 mixtures that induce a deep-level maximum of water loss at P ≈ 0.4 MPa at T ≈ 1200 ° C for a CO2 content >1000ppm. Melt inclusion data on CO2 and H2O contents are successfully reproduced and interpreted in a context of magma dehydration induced by a CO2 flux possibly deriving by decarbonation reaction of the carbonate fraction of the Capo D'Orlando flysch.

  6. Low rate deep level transient spectroscopy - a powerful tool for defect characterization in wide bandgap semiconductors

    NASA Astrophysics Data System (ADS)

    Schmidt, Florian; von Wenckstern, Holger; Breitenstein, Otwin; Pickenhain, Rainer; Grundmann, Marius

    2014-02-01

    We present an overview of implementation and application of low rate Deep-Level Transient Spectroscopy (LR-DLTS). In conventional DLTS the sensitivity of the capacitance meter must be chosen so low that the whole capacitance drift range between lowest and highest temperature can be measured. In LR-DLTS the bridge is automatically balanced (capacitance and conductivity) after each measured transient. Thus, the highest available sensitivity still avoiding an overload can be used. With LR-DLTS it is now possible to extend the rate windows to the mHz range while preserving highest possible sensitivity. This allows the detection of energetically close levels and levels with large thermal activation energy. Also low emission rates in optical DLTS can be detected this way.

  7. Impurities in snowpacks.

    PubMed

    Sommerfeld, R A

    1989-04-01

    Snow can be involved in the acquisition, transport, storage and release of atmospheric impurities. Because it can store impurities for periods of time ranging from hours to millenia, it provides a medium for monitoring atmospheric impurities for a wide range of time scales.In most climates, snow is involved in the precipitation process. It can acquire atmospheric impurities either as aerosols or as gases. The aereosols can be included in the body of the snow crystals or adhered to their surfaces. Gases may be included in bubbles, particularly in the case of rime, or adsorbed on the ice surfaces. The amount of ice surface in a small storm is about 10(10) m(2).Snow on the ground can store the impurities acquired in the precipitation process and can acquire additional impurities as dry deposition. The low temperatures and the fact that ice is a solid reduces biological activity and rates of inorganic reactions. However, the assumption that there is no activity in the winter is not well found. Exchange is possible between different layers of the snow and between the snow and the atmosphere, resulting in relocation of gases and aerosols. These processes also insure that the impurities reside on the exterior surfaces of the ice particles that form the snowpack. Biological activity is possible near the ground-snow interface in most climates.The seasonal snowpack releases its impurities when it melts. Because below freezing processes relocate any internal impurities to the ice surfaces within the snowpack, the impurities are available to the first melt water. Pulses of both acidic and alkalinic impurities have been observed with the initial snow melt water. However, the monitoring of such pulses is difficult and the measurements are inconsistent.Impurities are incorporated for longer periods of time in perennial snowpacks and finally in ice fields. These can be glaciers, or, at the largest scale, continental ice sheets. Coring such ice is expensive but provides data on

  8. Simplex Algorithm for Deep-Level Transient Spectroscopy: Simplex-DLTS

    NASA Astrophysics Data System (ADS)

    Benchenane-Mehor, Halima; Benzohra, Mohamed; Idrissi-Benzohra, Malika; Olivie, François; Saÿdane, Abdelkader

    2004-11-01

    The Nelder-Mead simplex algorithm improved by Lagarias for low-dimension functions is introduced for the first time on transient capacitance signal analysis to decrease noise sensitivity and increase the resolution of deep-level transient spectroscopy method (DLTS). The application of the resolution figure of merit in predetermining the success of DLTS analyses’ ability to resolve defects has shown that the performances of the simplex-DLTS developed in this work are significantly better than those of matrix pencil-DLTS method (MP-DLTS) published in 1998. Comparing experimentally the two methods in analyzing the signals generated by the same 150 keV germanium preamorphized p+n samples, we found that the simplex-DLTS method detects six defects in which some show very close activation energy values, while the MP-DLTS method found only two defects. Hence, the superiority of the simplex-DLTS method is proved; it reveals deep levels in which the emission process is carried out in the same temperature range.

  9. Automatic recognition of severity level for diagnosis of diabetic retinopathy using deep visual features.

    PubMed

    Abbas, Qaisar; Fondon, Irene; Sarmiento, Auxiliadora; Jiménez, Soledad; Alemany, Pedro

    2017-03-28

    Diabetic retinopathy (DR) is leading cause of blindness among diabetic patients. Recognition of severity level is required by ophthalmologists to early detect and diagnose the DR. However, it is a challenging task for both medical experts and computer-aided diagnosis systems due to requiring extensive domain expert knowledge. In this article, a novel automatic recognition system for the five severity level of diabetic retinopathy (SLDR) is developed without performing any pre- and post-processing steps on retinal fundus images through learning of deep visual features (DVFs). These DVF features are extracted from each image by using color dense in scale-invariant and gradient location-orientation histogram techniques. To learn these DVF features, a semi-supervised multilayer deep-learning algorithm is utilized along with a new compressed layer and fine-tuning steps. This SLDR system was evaluated and compared with state-of-the-art techniques using the measures of sensitivity (SE), specificity (SP) and area under the receiving operating curves (AUC). On 750 fundus images (150 per category), the SE of 92.18%, SP of 94.50% and AUC of 0.924 values were obtained on average. These results demonstrate that the SLDR system is appropriate for early detection of DR and provide an effective treatment for prediction type of diabetes.

  10. Influences of Nickel and Vanadium Impurities on Microstructure of Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Zhu, Suming; Yao, Ji-Yong; Sweet, Lisa; Easton, Mark; Taylor, John; Robinson, Paul; Parson, Nick

    2013-05-01

    In recent years, the deterioration in the available coke quality for anode production has led to increased levels of metal impurities such as nickel and vanadium in primary aluminum. There is growing concern from the industry with regard to the impact of increased Ni and V levels on the downstream properties of Al alloy products. This article presents a detailed investigation of the influences of Ni and V impurities on microstructure of three common Al alloys, i.e., AA6063, AA3102, and A356, in both as-cast and heat-treated conditions. The characterization techniques employed include scanning electron microscopy, electron backscattered diffraction, energy-dispersive x-ray spectroscopy, wavelength-dispersive spectroscopy, and transmission electron microscopy. It is shown that the phase constituents of AA6063 are not altered by Ni additions up to 0.05% or V additions up to 0.04%. Whereas there is no change in phase constituents with increasing Ni up to 0.015% for AA3102, the addition of 0.05% Ni seems to have significant influence on the microstructure. For A356, Ni additions up to 0.02% do not seem to have significant influence on the microstructure, but a new phase with significantly high Ni content is formed when the Ni impurity level is increased to 0.05%. The deep insight obtained in this work should be helpful to understand the influences of Ni and V impurities on properties of Al alloys.

  11. Sea-level and deep-sea-temperature variability over the past 5.3 million years.

    PubMed

    Rohling, E J; Foster, G L; Grant, K M; Marino, G; Roberts, A P; Tamisiea, M E; Williams, F

    2014-04-24

    Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years (Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ(18)O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0-1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature.

  12. Electron Traps Detected in p-type GaAsN Using Deep Level Transient Spectroscopy

    SciTech Connect

    Johnston, S.; Kurtz, S.; Friedman, D.; Ptak, A.; Ahrenkiel, R.; Crandall, R.

    2005-01-01

    The GaAsN alloy can have a band gap as small as 1.0 eV when the nitrogen composition is about 2%. Indium can also be added to the alloy to increase lattice matching to GaAs and Ge. These properties are advantageous for developing a highly-efficient, multi-junction solar cell. However, poor GaAsN cell properties, such as low open-circuit voltage, have led to inadequate performance. Deep-level transient spectroscopy of p-type GaAsN has identified an electron trap having an activation energy near 0.2 eV and a trap density of at least 1016 cm-3. This trap level appears with the addition of small amounts of nitrogen to GaAs, which also corresponds to an increased drop in open-circuit voltage.

  13. Phase Shift of the Asymmetric Friedel-Anderson Impurity

    NASA Astrophysics Data System (ADS)

    Bergmann, Gerd

    2013-04-01

    The ground state of the asymmetric Friedel-Anderson (aFA) impurity is calculated within the FAIR (Friedel artificially inserted resonance) theory. Its properties are investigated by means of the fidelity with different Friedel impurities and by its Friedel oscillations. Friedel impurities with a specific phase shift δ at the Fermi level possess a finite fidelity with the aFA impurity. This phase shift δ determines other properties of the aFA impurity such as the amplitude and displacement of its Friedel oscillations. One can find the parameters of a Friedel impurity which coincides in its Friedel oscillations almost perfectly with the aFA impurity, thereby avoiding an Anderson orthogonality catastrophe.

  14. Deep level transient spectroscopic study of neutron-irradiated n-type 6H-SiC

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Fung, S.; Ling, C. C.; Beling, C. D.; Gong, M.

    2003-09-01

    Deep level transient spectroscopy has been employed to study the deep level defects introduced in n-type 6H-SiC after neutron irradiation. Deep levels situated at EC-0.23, EC-0.36/0.44, EC-0.50, and EC-0.62/0.68 eV have been detected in the temperature range of 100-450 K, which have been identified with the previously reported deep levels ED1, E1/E2, Ei, and Z1/Z2, respectively. Thermal annealing studies of these deep levels reveal that ED1 and Ei anneal at a temperature below 350 °C, the Z1/Z2 levels anneal out at 900 °C, while the intensity of the E1/E2 peaks is increased with annealing temperature, reaching a maximum at about 500-750 °C, and finally annealing out at 1400 °C. The possible nature of the deep levels ED1, E1/E2, Ei, and Z1/Z2 are discussed in the context of their annealing behavior. Upon further annealing at 1600 °C, four deep levels labeled NE1 at EC-0.44 eV, NE2 EC-0.53 eV, NE3EC-0.64 eV, and NE4EC-0.68 eV are produced. Evidence is given that these levels are different in their origin to E1/E2 and Z1/Z2.

  15. Deep level transient spectroscopy study of particle irradiation induced defects in n-6H-SiC

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Gong, M.; Fung, S.; Beling, C. D.; Ling, C. C.

    2004-03-01

    Neutron and electron irradiation induced deep level defects in n-type 6H-SiC have been investigated using deep level transient spectroscopy (DLTS) combined with annealing experiments. Deep levels ED1, E1/E2, Ei, and Z1/Z2 were observed in n-type 6H-SiC material irradiated with neutron. Thermal annealing studies of these deep levels revealed that ED1 and Ei annealed at a temperature below 350^oC, Z1/Z2 levels annealed out at 900^oC, while the intensity of the E1/E2 peaks increased with annealing temperature, reached a maximum at about 500-750^oC, and finally annealed out at 1400^oC. Upon further annealing at 1600^oC, four deep levels labeled NE1 at EC-0.44eV, NE2 EC-0.53eV, NE3 EC-0.64eV, and NE4 EC-0.68eV are produced. Ionization energies of these levels are similar to E1/E2 and Z1/Z2 respectively, but their capture cross sections are different. Samples were irradiated with electrons with different energies ranging from 0.2MeV to 1.7MeV. No deep level was detected in samples irradiated with 0.2MeV electron and deep levels ED1, E1/E2, and Ei were induced with electron energy larger than 0.3MeV.

  16. Effects of Pressure on Optically Active Deep Levels in Phosphorus Doped ZnSe

    NASA Astrophysics Data System (ADS)

    Weinstein, B. A.; Iota, V.

    1998-03-01

    We report high pressure photoluminescence (PL) and PL-excitation (PLE) studies at 8K of the 'midgap' emission in P-doped ZnSe using a diamond-cell with He medium. The dominant emission at low pressure is due to donor-acceptor-pair (DAP) transitions between shallow donors and deep trigonally relaxed P_Se acceptors.(J. Davies, et al., J. Luminescence 18/19, 322 (1979)) Its PL and PLE peaks shift by 8.2meV/kbar and 5.9meV/kbar, respectively -- Stokes shift decreasing with pressure. At 35kbar a new PL band, shifting to lower energy (-5.4meV/kbar), emerges from above the absorption edge, and concurrently the original DAP PL quenches. This shows that a resonant level, a deep donor or possibly a P_Se antibonding state,(R. Watts, et al., Phys. Rev. B3), 404 (1971) crosses the conduction edge into the gap. A third PL band is seen only with internse UV excitation. It occurs initially as a high energy shoulder of the original DAP peak, but shifts more rapidly upward (9.4meV/kbar) until it crosses the edge and quenches at 40kbar. We discuss candidates for this band, including donor-P_Se complexes, and we compare our results to similar work on the Zn vacancy in ZnSe. (figures)

  17. Intrinsic deep hole trap levels in Cu2O with self-consistent repulsive Coulomb energy

    NASA Astrophysics Data System (ADS)

    Huang, Bolong

    2016-03-01

    The large error of the DFT+U method on full-filled shell metal oxides is due to the residue of self-energy from the localized d orbitals of cations and p orbitals of the anions. U parameters are selfconsistently found to achieve the analytical self-energy cancellation. The improved band structures based on relaxed lattices of Cu2O are shown based on minimization of self-energy error. The experimentally reported intrinsic p-type trap levels are contributed by both Cu-vacancy and the O-interstitial defects in Cu2O. The latter defect has the lowest formation energy but contributes a deep hole trap level while the Cuvacancy has higher energy cost but acting as a shallow acceptor. Both present single-particle levels spread over nearby the valence band edge, consistent to the trend of defects transition levels. By this calculation approach, we also elucidated the entanglement of strong p-d orbital coupling to unravel the screened Coulomb potential of fully filled shells.

  18. Promoting and Studying Deep-Level Discourse During Large-Lecture Introductory Physics

    NASA Astrophysics Data System (ADS)

    Li, Sissi; Demaree, Dedra

    2010-10-01

    At Oregon State University, the introductory calculus-based physics sequence utilizes social engagement as a learning tool. The reformed curriculum is modeled after the Interactive Science Learning Environment from Rutgers University, and makes use of Peer Instruction as a pedagogical tool to facilitate interactions. Over the past two years we have utilized a number of techniques to understand how to facilitate activities that promote productive discussion within the large lecture classroom. We specifically seek student discussion that goes beyond agreement on conceptual questions, encouraging deeper discussions such as what assumptions are appropriate, or how different assumptions would change the chosen answer to a given question. We have quantitative analysis of engagement based on video data, qualitative analysis of dialogue from audio data, and classroom observations by an external researcher. In this paper we share a subset of what we have learned about how to engage students in deep-level discussions during lecture.

  19. Thermally stimulated current studies on deep levels in hydrothermally grown single crystal ZnO bulk

    NASA Astrophysics Data System (ADS)

    Kuriyama, K.; Ooi, M.; Matsumoto, K.; Kushida, K.

    2006-12-01

    The evaluation of the deep levels in hydrothermally grown ZnO single crystal bulk is studied using a thermally stimulated current (TSC) method with excitation above (below) the band gap. Two broad TSC spectra are resolved by four traps, P1 (165meV), P2 (255meV), P3 (300meV), and P4 (375meV). P2, P3, and P4 traps are responsible for excitation by the blue and green lights, but P1 trap is weakly responsible. Possible origins of P1 and P2 are attributed to native point defects and Li acceptor, respectively. P3 is correlated to oxygen vacancy as an origin of the green luminescence.

  20. Using Deep Level Transient Spectroscopy (DLTS) to characterize defects in semiconductor devices

    NASA Astrophysics Data System (ADS)

    Lang, David

    2012-02-01

    Deep Level Transient Spectroscopy (DLTS) is a member of the class of instrumentation methods that utilizes the detection of trapped electronic charge to characterize defects in solids. Such methods detect this charge either directly, e.g. via capacitance measurements, or indirectly, e.g. via the current associated with the release of trapped charge. These types of instrumentation have been widely used since the dawn of solid-state physics, particularly for nonradiative defects in semiconductors and insulators. In the case of semiconductor devices, the highly sensitive capacitive detection of trapped charge in the junction depletion layer makes these methods particularly powerful. The DLTS method introduced the concept of time-domain filtering (the so-called ``rate window'') to create a defect spectrum from the transient response of the device versus temperature. This talk will give an overview of DLTS, with particular emphasis on the correlation between defects and device performance.

  1. Anomalous behaviors of E1/E2 deep level defects in 6H silicon carbide

    NASA Astrophysics Data System (ADS)

    Chen, X. D.; Ling, C. C.; Gong, M.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.

    2005-01-01

    Deep level defects E1/E2 were observed in He-implanted, 0.3 and 1.7MeV electron-irradiated n-type 6H-SiC. Similar to others' results, the behaviors of E1 and E2 (like the peak intensity ratio, the annealing behaviors or the introduction rates) often varied from sample to sample. This anomalous result is not expected of E1/E2 being usually considered arising from the same defect located at the cubic and hexagonal sites respectively. The present study shows that this anomaly is due to another DLTS peak overlapping with the E1/E2. The activation energy and the capture cross section of this defect are EC-0.31eV and σ ˜8×10-14cm2, respectively.

  2. Deep levels induced by high fluence proton irradiation in undoped GaAs diodes

    SciTech Connect

    Castaldini, A.; Cavallini, A.; Polenta, L.; Canali, C.; Nava, F.; Ferrini, R.; Galli, M.

    1998-12-31

    Semi-insulating liquid encapsulated Czochralski grown GaAs has been investigated after irradiation at high fluences of high-energy protons. Electron beam induced current observations of scanning electron microscopy evidenced a radiation stimulated ordering. An analysis has been carried out of the deep levels associated with defects as a function of the irradiation fluence, using complementary current transient spectroscopies. By increasing the irradiation fluence, the concentration of the native traps at 0.37 eV together with that of the EL2 defect significantly increases and, at the same time, two new electron traps at 0.15 eV and 0.18 eV arise and quickly increase in density.

  3. Inexpensive circuit for the measurement of capture cross section of deep level defects in semiconductors

    NASA Astrophysics Data System (ADS)

    Reddy, C. V.; Fung, S.; Beling, C. D.

    1996-12-01

    A simple and inexpensive circuit to facilitate the direct measurement of capture cross section, when synchronized with a deep level transient spectroscopy system, is described. It avoids the most commonly encountered problem of loading and distortion of the bias (trap filling) pulses of nanosecond duration in the capture cross-section measurement. The capacitance meter, whose internal circuitry is responsible for the distortion, is connected and disconnected from the rest of the apparatus with the help of simple and low-cost reed relay switches featuring high operating speed and low contact resistance. Sharp bias pulses as small as 30 ns can successfully be applied to the sample with no observable distortion. Finally, a representative measurement is shown to demonstrate the simplicity and high performance of the circuit.

  4. On the capability of deep level transient spectroscopy for characterizing multi-crystalline silicon

    SciTech Connect

    Mchedlidze, T.; Nacke, M.; Hieckmann, E.; Weber, J.

    2014-01-07

    The suitability of the deep level transient spectroscopy (DLTS) technique in exploring locations with high and degraded carrier lifetimes containing grain-boundaries (GBs) in multicrystalline silicon (mc-Si) wafers was studied. The types and locations of GBs were determined in mc-Si samples by electron backscatter diffraction. Mesa-type Schottky diodes were prepared at (along) GBs and at reference, GB-free locations. Detected DLTS signals varied strongly along the same GB. Experiments with dislocation networks, model structures for GBs, showed that GB-related traps may be explored only using special arrangement of a GB and the diode contacts. Iron-related carrier traps were detected in locations with degraded carrier lifetimes. Densities of the traps for near-GB and for GB free locations were compared to the lifetime measurement results.

  5. Impurity gettering in semiconductors

    DOEpatents

    Sopori, Bhushan L.

    1995-01-01

    A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500.degree. C. to about 700.degree. C. for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal.

  6. Impurity gettering in semiconductors

    DOEpatents

    Sopori, B.L.

    1995-06-20

    A process for impurity gettering in a semiconductor substrate or device such as a silicon substrate or device is disclosed. The process comprises hydrogenating the substrate or device at the back side thereof with sufficient intensity and for a time period sufficient to produce a damaged back side. Thereafter, the substrate or device is illuminated with electromagnetic radiation at an intensity and for a time period sufficient to cause the impurities to diffuse to the back side and alloy with a metal there present to form a contact and capture the impurities. The impurity gettering process also can function to simultaneously passivate defects within the substrate or device, with the defects likewise diffusing to the back side for simultaneous passivation. Simultaneously, substantially all hydrogen-induced damage on the back side of the substrate or device is likewise annihilated. Also taught is an alternate process comprising thermal treatment after hydrogenation of the substrate or device at a temperature of from about 500 C to about 700 C for a time period sufficient to cause the impurities to diffuse to the damaged back side thereof for subsequent capture by an alloying metal. 1 fig.

  7. Passivation of impurities in semiconductors by hydrogen and light metal ions

    NASA Astrophysics Data System (ADS)

    Gislason, Hafliði P.

    1997-01-01

    Books as well as numerous articles have been written about hydrogen passivation in classical semiconductors such as Si and GaAs. The subject has gained a renewed interest recently since hydrogen is widely considered to saturate the hole conductivity of the wide bandgap semiconductors GaN and ZnSe which are currently most promising for blue light emitting devices. Other group-I impurities are capable of compensating the electrical conductivity of semiconductors both through directly neutralising (passivating) the impurity or providing space charge of polarity opposite to that of the dominating one. The paper reviews the similarities and differences between hydrogen and its light metallic neighbour in the periodic table, lithium. Also we provide a comparison with the heavier interstitial copper which is known for its ability to passivate shallow acceptors. Finally fundamental differences between shallow-level and deep level passivation will be addressed.

  8. Effect of Z{sub 1/2}, EH{sub 5}, and Ci1 deep defects on the performance of n-type 4H-SiC epitaxial layers Schottky detectors: Alpha spectroscopy and deep level transient spectroscopy studies

    SciTech Connect

    Mannan, Mohammad A.; Chaudhuri, Sandeep K.; Nguyen, Khai V.; Mandal, Krishna C.

    2014-06-14

    Spectroscopic performance of Schottky barrier alpha particle detectors fabricated on 50 μm thick n-type 4H-SiC epitaxial layers containing Z{sub 1/2}, EH{sub 5}, and Ci1 deep levels were investigated. The device performance was evaluated on the basis of junction current/capacitance characterization and alpha pulse-height spectroscopy. Capacitance mode deep level transient spectroscopy revealed the presence of the above-mentioned deep levels along with two shallow level defects related to titanium impurities (Ti(h) and Ti(c)) and an unidentified deep electron trap located at 2.4 eV below the conduction band minimum, which is being reported for the first time. The concentration of the lifetime killer Z{sub 1/2} defects was found to be 1.7 × 10{sup 13} cm{sup −3}. The charge transport and collection efficiency results obtained from the alpha particle pulse-height spectroscopy were interpreted using a drift-diffusion charge transport model. Based on these investigations, the physics behind the correlation of the detector properties viz., energy resolution and charge collection efficiency, the junction properties like uniformity in barrier-height, leakage current, and effective doping concentration, and the presence of defects has been discussed in details. The studies also revealed that the dominating contribution to the charge collection efficiency was due to the diffusion of charge carriers generated in the neutral region of the detector. The 10 mm{sup 2} large area detectors demonstrated an impressive energy resolution of 1.8% for 5486 keV alpha particles at an optimized operating reverse bias of 130 V.

  9. High-temperature molecular beam epitaxial growth of AlGaN/GaN on GaN templates with reduced interface impurity levels

    NASA Astrophysics Data System (ADS)

    Koblmüller, G.; Chu, R. M.; Raman, A.; Mishra, U. K.; Speck, J. S.

    2010-02-01

    We present combined in situ thermal cleaning and intentional doping strategies near the substrate regrowth interface to produce high-quality AlGaN/GaN high electron mobility transistors on semi-insulating (0001) GaN templates with low interfacial impurity concentrations and low buffer leakage. By exposing the GaN templates to an optimized thermal dissociation step in the plasma-assisted molecular beam epitaxy environment, oxygen, carbon, and, to lesser extent, Si impurities were effectively removed from the regrowth interface under preservation of good interface quality. Residual Si was further compensated by C-doped GaN via CBr4 to yield highly resistive GaN buffer layers. Improved N-rich growth conditions at high growth temperatures were then utilized for subsequent growth of the AlGaN/GaN device structure, yielding smooth surface morphologies and low residual oxygen concentration with large insensitivity to the (Al+Ga)N flux ratio. Room temperature electron mobilities of the two-dimensional electron gas at the AlGaN/GaN interface exceeded >1750 cm2/V s and the dc drain current reached ˜1.1 A/mm at a +1 V bias, demonstrating the effectiveness of the applied methods.

  10. Dermatologist-level classification of skin cancer with deep neural networks.

    PubMed

    Esteva, Andre; Kuprel, Brett; Novoa, Roberto A; Ko, Justin; Swetter, Susan M; Blau, Helen M; Thrun, Sebastian

    2017-02-02

    Skin cancer, the most common human malignancy, is primarily diagnosed visually, beginning with an initial clinical screening and followed potentially by dermoscopic analysis, a biopsy and histopathological examination. Automated classification of skin lesions using images is a challenging task owing to the fine-grained variability in the appearance of skin lesions. Deep convolutional neural networks (CNNs) show potential for general and highly variable tasks across many fine-grained object categories. Here we demonstrate classification of skin lesions using a single CNN, trained end-to-end from images directly, using only pixels and disease labels as inputs. We train a CNN using a dataset of 129,450 clinical images-two orders of magnitude larger than previous datasets-consisting of 2,032 different diseases. We test its performance against 21 board-certified dermatologists on biopsy-proven clinical images with two critical binary classification use cases: keratinocyte carcinomas versus benign seborrheic keratoses; and malignant melanomas versus benign nevi. The first case represents the identification of the most common cancers, the second represents the identification of the deadliest skin cancer. The CNN achieves performance on par with all tested experts across both tasks, demonstrating an artificial intelligence capable of classifying skin cancer with a level of competence comparable to dermatologists. Outfitted with deep neural networks, mobile devices can potentially extend the reach of dermatologists outside of the clinic. It is projected that 6.3 billion smartphone subscriptions will exist by the year 2021 (ref. 13) and can therefore potentially provide low-cost universal access to vital diagnostic care.

  11. Analysis of the effects of impurities in silicon

    NASA Technical Reports Server (NTRS)

    Wohlgemuth, J.; Giuliano, M. N.

    1980-01-01

    A solar cell fabrication and analysis program was conducted to determine the effects on the resultant solar cell efficiency of impurities intentionally incorporated into silicon. It was found that certain impurities such as titanium, tantalum, and vanadium were bad, even in very small concentrations. Cell performance appeared relatively tolerable to impurities such as copper, carbon, calcium, chromium, iron and nickel (in the concentration levels which were considered).

  12. Deep-level transient spectroscopy studies of Ni- and Zn-diffused vapor-phase-epitaxy n-GaAs

    NASA Technical Reports Server (NTRS)

    Partin, D. L.; Chen, J. W.; Milnes, A. G.; Vassamillet, L. F.

    1979-01-01

    The paper presents deep-level transient spectroscopy studies of Ni- and Zn-diffused vapor-phase epitaxy n-GaAs. Nickel diffused into VPE n-GaAs reduces the hole diffusion length L sub p from 4.3 to 1.1 microns. Deep-level transient spectroscopy was used to identify energy levels in Ni-diffused GaAs; the as-grown VPE GaAs contains traces of these levels and an electron trap. Ni diffusion reduces the concentration of this level by an amount that matches the increase in concentration of each of the two Ni-related levels. A technique for measuring minority-carrier capture cross sections was developed, which indicates that L sub p in Ni-diffused VPE n-GaAs is controlled by the E sub c - 0.39 eV defect level.

  13. Deep level transient capacitance measurements of GaSb self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Magno, R.; Bennett, Brian R.; Glaser, E. R.

    2000-11-01

    Deep level transient spectroscopy (DLTS) measurements have been made on GaAs n+p diodes containing GaSb self-assembled quantum dots and control junctions without dots. The self-assembled dots were formed by molecular beam epitaxy using the Stranski-Krastanov growth mode. The dots are located in the depletion region on the p side of the junction where they act as a potential well that may capture and emit holes. Spectra recorded for temperatures between 77 and 440 K reveal several peaks in diodes containing dots. A control sample with a GaSb wetting layer was found to contain a single broad high temperature peak that is similar to a line found in the GaSb quantum dot samples. No lines were found in the spectra of a control sample prepared without GaSb. DLTS profiling procedures indicate that one of the peaks is due to a quantum-confined energy level associated with the GaSb dots while the others are due to defects in the GaAs around the dots. The peak identified as a quantum-confined energy level shifts to higher temperatures and its intensity decreases on increasing the reverse bias. The activation energy for the quantum-confined level increases from 400 meV when measured at a low reverse bias to 550 meV for a large reverse bias. Lines with activation energies of 400, 640, and 840 meV are associated with defects in the GaAs based on the bias dependence of their peak positions and amplitudes.

  14. Development of an LC-MS method for ultra trace-level determination of 2,2,6,6-tetramethylpiperidine-1-oxl (TEMPO), a potential genotoxic impurity within active pharmaceutical ingredients.

    PubMed

    Pennington, Justin; Cohen, Ryan D; Tian, Ye; Boulineau, Fabien

    2015-10-10

    TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) is a stable free radical which has been widely used for various research and industrial applications, including the manufacture of many active pharmaceutical ingredients. TEMPO has been identified as a potential genotoxic impurity resulting in the need for analytical methodology to accurately determine its level at several orders of magnitude less than typical impurity quantitation limits. TEMPO can undergo disproportionation to form both oxidized and reduced TEMPO, making individual determination unreliable. To overcome this challenge, all TEMPO related species were converted to the reduced form through reduction with sodium ascorbate. Given the ultra-trace (0.5 ppm) level requirements and the lack of UV response in the reduced form, a single quadrupole mass spectrometer (MS) was utilized. In order to implement a highly sensitive MS method in a GMP environment, several approaches were employed to optimize accuracy and robustness including: internal standard correction for drift elimination, six-level standard addition to reduce matrix effects, and weighted linear regression to cover a broad analytical range. The method was fully validated according to ICH guidelines. The method is specific, linear, accurate, precise, and robust within a range of 0.5-100 ppm.

  15. Dynamical impurity problems

    SciTech Connect

    Emery, V.J.; Kivelson, S.A.

    1993-12-31

    In the past few years there has been a resurgence of interest in dynamical impurity problems, as a result of developments in the theory of correlated electron systems. The general dynamical impurity problem is a set of conduction electrons interacting with an impurity which has internal degrees of freedom. The simplest and earliest example, the Kondo problem, has attracted interest since the mid-sixties not only because of its physical importance but also as an example of a model displaying logarithmic divergences order by order in perturbation theory. It provided one of the earliest applications of the renormalization group method, which is designed to deal with just such a situation. As we shall see, the antiferromagnetic Kondo model is controlled by a strong-coupling fixed point, and the essence of the renormalization group solution is to carry out the global renormalization numerically starting from the original (weak-coupling) Hamiltonian. In these lectures, we shall describe an alternative route in which we identify an exactly solvable model which renormalizes to the same fixed point as the original dynamical impurity problem. This approach is akin to determining the critical behavior at a second order phase transition point by solving any model in a given universality class.

  16. Identification, isolation and characterization of process related impurities in ezetimibe.

    PubMed

    Guntupalli, Srikanth; Ray, Uttam Kumar; Murali, N; Gupta, P Badrinadh; Kumar, Vundavilli Jagadeesh; Satheesh, D; Islam, Aminul

    2014-01-01

    During the synthesis of ezetimibe, two process related impurities were detected were HPLC analysis at levels ranging from 0.05 to 0.8%. These two impurities were isolated by column chromatography and co-injected with ezetimibe sample to confirm the retention times in HPLC. These two impurities were characterized as 2-(4-hydroxybenzyl)-N,5-bis(4-fluorophenyl) pentanamide (impurity-I) and 1-(4-fluorophenyl)-3(3-(4-fluorophenyl)propyl)-4-(4-hydroxyphenyl)azetidin-2-one (impurity-II). Isolation, structural elucidation of these impurities by spectral data ((1)H NMR, (13)C NMR, MS and IR) and probable mechanism of their formation have been discussed.

  17. Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

    NASA Astrophysics Data System (ADS)

    Pousset, J.; Farella, I.; Gambino, S.; Cola, A.

    2016-03-01

    We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.

  18. Effects of impurities on silicon solar-cell performance

    NASA Technical Reports Server (NTRS)

    Hopkins, R. H.

    1986-01-01

    Model analyses indicate that sophisticated solar cell designs (back surface fields, optical reflectors, surface passivation, and double layer antireflective coatings) can produce devices with conversion efficiencies above 20%. To realize this potential, the quality of the silicon from which the cells are made must be improved; and these excellent electrical properties must be maintained during device processing. As the cell efficiency rises, the sensitivity to trace contaminants also increases. For example, the threshold Ti impurity concentraion at which cell performance degrades is more than an order of magnitude lower for an 18% cell than for a 16% cell. Similar behavior occurs for numerous other metal species which introduce deep level traps that stimulate the recombination of photogenerated carriers in silicon. Purification via crystal growth in conjunction with gettering steps to preserve the large diffusion length of the as grown material can lead to the production of devices with efficiencies above 18%, as verified experimentally.

  19. Impurity effects in silicon for high efficiency solar cells

    NASA Technical Reports Server (NTRS)

    Hopkins, R. H.; Rohatgi, A.

    1986-01-01

    Model analyses indicate that sophisticated solar cell designs including, e.g., back surface fields, optical reflectors, surface passivation, and double layer antireflective coatings can produce devices with conversion efficiencies above 20 percent (AM1). To realize this potential, the quality of the silicon from which the cells are made must be improved; and these excellent electrical properties must be maintained during device processing. As the cell efficiency rises, the sensitivity to trace contaminants also increases. For example, the threshold Ti impurity concentration at which cell performance degrades is more than an order of magnitude lower for an 18-percent cell. Similar behavior occurs for numerous other metal species which introduce deep level traps that stimulate the recombination of photogenerated carriers in silicon. Purification via crystal growth in conjunction with gettering steps to preserve the large diffusion length of the as-grown material can lead to the production of devices with efficiencies aboved 18 percent, as has been verified experimentally.

  20. Challenges to Standardization: A Case Study Using Coastal and Deep-Ocean Water Level Data

    NASA Astrophysics Data System (ADS)

    Sweeney, A. D.; Stroker, K. J.; Mungov, G.; McLean, S. J.

    2015-12-01

    Sea levels recorded at coastal stations and inferred from deep-ocean pressure observations at the seafloor are submitted for archive in multiple data and metadata formats. These formats include two forms of schema-less XML and a custom binary format accompanied by metadata in a spreadsheet. The authors report on efforts to use existing standards to make this data more discoverable and more useful beyond their initial use in detecting tsunamis. An initial review of data formats for sea level data around the globe revealed heterogeneity in presentation and content. In the absence of a widely-used domain-specific format, we adopted the general model for structuring data and metadata expressed by the Network Common Data Form (netCDF). netCDF has been endorsed by the Open Geospatial Consortium and has the advantages of small size when compared to equivalent plain text representation and provides a standard way of embedding metadata in the same file. We followed the orthogonal time-series profile of the Climate and Forecast discrete sampling geometries as the convention for structuring the data and describing metadata relevant for use. We adhered to the Attribute Convention for Data Discovery for capturing metadata to support user search. Beyond making it possible to structure data and metadata in a standard way, netCDF is supported by multiple software tools in providing programmatic cataloging, access, subsetting, and transformation to other formats. We will describe our successes and failures in adhering to existing standards and provide requirements for either augmenting existing conventions or developing new ones. Some of these enhancements are specific to sea level data, while others are applicable to time-series data in general.

  1. Gas chromatographic analysis of trace gas impurities in tungsten hexafluoride.

    PubMed

    Laurens, J B; de Coning, J P; Swinley, J M

    2001-03-09

    Highly reactive fluorinated gaseous matrices require special equipment and techniques for the gas chromatographic analysis of trace impurities in these gases. The impurities that were analysed at the low-microg/l levels included oxygen, nitrogen, carbon dioxide, carbon monoxide, sulfur hexafluoride and hydrogen. This paper describes the use of a system utilising backflush column switching to protect the columns and detectors in the analysis of trace gas impurities in tungsten hexafluoride. Two separate channels were used for the analysis of H2, O2, N2, CO, CO2 and SF6 impurities with pulsed discharge helium ionisation detection.

  2. Detection of deep levels and compensation mechanism in undoped, liquid-encapsulated Czochralski n-type GaAs

    NASA Astrophysics Data System (ADS)

    Siegel, W.; Kühnel, G.; Schneider, H. A.; Witte, H.; Flade, T.

    1991-02-01

    Undoped n-GaAs with a 300 K resistivity between 10-1 and 108 Ω cm (electron concentration between 1×107 and 5×1015 cm-3 ) grown in quartz crucibles by the liquid-encapsulated Czochralski (LEC) technique was investigated by thermally stimulated current (TSC), temperature-dependent Hall effect (TDH), and deep-level transient spectroscopy (DLTS). Using Schottky contacts the TSC method could be extended to medium-resistivity samples. The strongly varying electron concentrations are correlated to varying TDH activation energies. The correlation between the donors dominating the electrical equilibrium properties and the electron traps detected by TSC and DLTS is discussed. Medium-deep and deep levels are present in this LEC material in such high concentrations that they must be taken into account in the compensation mechanism.

  3. High levels of natural radioactivity in biota from deep-sea hydrothermal vents: a preliminary communication.

    PubMed

    Charmasson, Sabine; Sarradin, Pierre-Marie; Le Faouder, Antoine; Agarande, Michèle; Loyen, Jeanne; Desbruyères, Daniel

    2009-06-01

    Hydrothermal deep-sea vent fauna is naturally exposed to a peculiar environment enriched in potentially toxic species such as sulphides, heavy metals and natural radionuclides. It is now well established that some of the organisms present in such an environment accumulate metals during their lifespan. Though only few radionuclide measurements are available, it seems likely that hydrothermal vent communities are exposed to high natural radiation doses. Various archived biological samples collected on the East Pacific Rise and the Mid-Atlantic Ridge in 1996, 2001 and 2002 were analysed by ICP-MS in order to determine their uranium contents ((238)U, (235)U and (234)U). In addition (210)Po-Pb were determined in 2 samples collected in 2002. Vent organisms are characterized by high U, and Po-Pb levels compared to what is generally encountered in organisms from outside hydrothermal vent ecosystems. Though the number of data is low, the results reveal various trends in relation to the site, the location within the mixing zone and/or the organisms' trophic regime.

  4. Thermal-Mechanical Modeling of Deep Borehole Disposal of High-Level Radioactive Waste

    NASA Astrophysics Data System (ADS)

    Arnold, B. W.; Clayton, D. J.; Herrick, C. G.; Hadgu, T.

    2010-12-01

    Disposal of high-level radioactive waste, including spent nuclear fuel, in deep (3 to 5 km) boreholes is a potential option for safely isolating these wastes from the surface and near-surface environment. Existing drilling technology permits reliable and cost-effective construction of such deep boreholes. Conditions favorable for deep borehole disposal in crystalline basement rocks, including low permeability, high salinity, and geochemically reducing conditions, exist at depth in many locations, particularly in geologically stable continental regions. Isolation of waste depends, in part, on the effectiveness of borehole seals and potential alteration of permeability in the disturbed host rock surrounding the borehole. Coupled thermal-mechanical-hydrologic processes induced by heat from the radioactive waste may impact the disturbed zone near the borehole and borehole wall stability. Numerical simulations of the coupled thermal-mechanical response in the host rock surrounding the borehole were conducted with three software codes or combinations of software codes. Software codes used in the simulations were FEHM, JAS3D, Aria, and Adagio. Simulations were conducted for disposal of spent nuclear fuel assemblies and for the higher heat output of vitrified waste from the reprocessing of fuel. Simulations were also conducted for both isotropic and anisotropic ambient horizontal stress in the host rock. Physical, thermal, and mechanical properties representative of granite host rock at a depth of 4 km were used in the models. Simulation results indicate peak temperature increases at the borehole wall of about 30 °C and 180 °C for disposal of fuel assemblies and vitrified waste, respectively. Peak temperatures near the borehole occur within about 10 years and decline rapidly within a few hundred years and with distance. The host rock near the borehole is placed under additional compression. Peak mechanical stress is increased by about 15 MPa (above the assumed ambient

  5. Thermal-mechanical modeling of deep borehole disposal of high-level radioactive waste.

    SciTech Connect

    Arnold, Bill Walter; Hadgu, Teklu

    2010-12-01

    Disposal of high-level radioactive waste, including spent nuclear fuel, in deep (3 to 5 km) boreholes is a potential option for safely isolating these wastes from the surface and near-surface environment. Existing drilling technology permits reliable and cost-effective construction of such deep boreholes. Conditions favorable for deep borehole disposal in crystalline basement rocks, including low permeability, high salinity, and geochemically reducing conditions, exist at depth in many locations, particularly in geologically stable continental regions. Isolation of waste depends, in part, on the effectiveness of borehole seals and potential alteration of permeability in the disturbed host rock surrounding the borehole. Coupled thermal-mechanical-hydrologic processes induced by heat from the radioactive waste may impact the disturbed zone near the borehole and borehole wall stability. Numerical simulations of the coupled thermal-mechanical response in the host rock surrounding the borehole were conducted with three software codes or combinations of software codes. Software codes used in the simulations were FEHM, JAS3D, Aria, and Adagio. Simulations were conducted for disposal of spent nuclear fuel assemblies and for the higher heat output of vitrified waste from the reprocessing of fuel. Simulations were also conducted for both isotropic and anisotropic ambient horizontal stress in the host rock. Physical, thermal, and mechanical properties representative of granite host rock at a depth of 4 km were used in the models. Simulation results indicate peak temperature increases at the borehole wall of about 30 C and 180 C for disposal of fuel assemblies and vitrified waste, respectively. Peak temperatures near the borehole occur within about 10 years and decline rapidly within a few hundred years and with distance. The host rock near the borehole is placed under additional compression. Peak mechanical stress is increased by about 15 MPa (above the assumed ambient

  6. Transforming Passive Receptivity of Knowledge into Deep Learning Experiences at the Undergraduate Level: An Example from Music Theory

    ERIC Educational Resources Information Center

    Ferenc, Anna

    2015-01-01

    This article discusses transformation of passive knowledge receptivity into experiences of deep learning in a lecture-based music theory course at the second-year undergraduate level through implementation of collaborative projects that evoke natural critical learning environments. It presents an example of such a project, addresses key features…

  7. Comparison of bladder segmentation using deep-learning convolutional neural network with and without level sets

    NASA Astrophysics Data System (ADS)

    Cha, Kenny H.; Hadjiiski, Lubomir M.; Samala, Ravi K.; Chan, Heang-Ping; Cohan, Richard H.; Caoili, Elaine M.

    2016-03-01

    We are developing a CAD system for detection of bladder cancer in CTU. In this study we investigated the application of deep-learning convolutional neural network (DL-CNN) to the segmentation of the bladder, which is a challenging problem because of the strong boundary between the non-contrast and contrast-filled regions in the bladder. We trained a DL-CNN to estimate the likelihood of a pixel being inside the bladder using neighborhood information. The segmented bladder was obtained from thresholding and hole-filling of the likelihood map. We compared the segmentation performance of the DL-CNN alone and with additional cascaded 3D and 2D level sets to refine the segmentation using 3D hand-segmented contours as reference standard. The segmentation accuracy was evaluated by five performance measures: average volume intersection %, average % volume error, average absolute % error, average minimum distance, and average Jaccard index for a data set of 81 training and 92 test cases. For the training set, DLCNN with level sets achieved performance measures of 87.2+/-6.1%, 6.0+/-9.1%, 8.7+/-6.1%, 3.0+/-1.2 mm, and 81.9+/-7.6%, respectively, while the DL-CNN alone obtained the values of 73.6+/-8.5%, 23.0+/-8.5%, 23.0+/-8.5%, 5.1+/-1.5 mm, and 71.5+/-9.2%, respectively. For the test set, the DL-CNN with level sets achieved performance measures of 81.9+/-12.1%, 10.2+/-16.2%, 14.0+/-13.0%, 3.6+/-2.0 mm, and 76.2+/-11.8%, respectively, while DL-CNN alone obtained 68.7+/-12.0%, 27.2+/-13.7%, 27.4+/-13.6%, 5.7+/-2.2 mm, and 66.2+/-11.8%, respectively. DL-CNN alone is effective in segmenting bladders but may not follow the details of the bladder wall. The combination of DL-CNN with level sets provides highly accurate bladder segmentation.

  8. 40 CFR 158.340 - Discussion of formation of impurities.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... require an expanded discussion of information on impurities: (1) From other possible chemical reactions... why they may be present. The discussion should be based on established chemical theory and on what the... range of levels) of these impurities. (iii) The intended reactions and side reactions which may occur...

  9. Pressure as a probe of deep levels and defects in semiconductors: GaAs, GaP and their alloys

    SciTech Connect

    Samara, G.A.

    1992-01-01

    Measurements of the effects of pressure on the thermal electron emission rate and capture cross section for a variety of deep electronic levels in GaAs, GaP and their alloys have yielded the pressure dependences of the energies of these levels in the bandgaps, allowed evaluation of the breathing mode lattice relaxations accompanying carrier emission or capture by these levels and revealed trends which lead to new insights into the nature of the responsible defects. Emphasis is on deep levels believed to be associated with simple defects. Specifically, results will be summarized for the donor levels of the dominant native defect known as EL2 in CAM, which is believed to be associated with the arsenic antisite, and on the radiation-induced El and E2 levels in GaAs, GaP and their alloys, which are believed to be due to arsenic (or phosphorous) vacancies. The results are discussed in terms of models for the defects responsible for these deep levels.

  10. Pressure as a probe of deep levels and defects in semiconductors: GaAs, GaP and their alloys

    SciTech Connect

    Samara, G.A.

    1992-10-01

    Measurements of the effects of pressure on the thermal electron emission rate and capture cross section for a variety of deep electronic levels in GaAs, GaP and their alloys have yielded the pressure dependences of the energies of these levels in the bandgaps, allowed evaluation of the breathing mode lattice relaxations accompanying carrier emission or capture by these levels and revealed trends which lead to new insights into the nature of the responsible defects. Emphasis is on deep levels believed to be associated with simple defects. Specifically, results will be summarized for the donor levels of the dominant native defect known as EL2 in CAM, which is believed to be associated with the arsenic antisite, and on the radiation-induced El and E2 levels in GaAs, GaP and their alloys, which are believed to be due to arsenic (or phosphorous) vacancies. The results are discussed in terms of models for the defects responsible for these deep levels.

  11. Trade Study of System Level Ranked Radiation Protection Concepts for Deep Space Exploration

    NASA Technical Reports Server (NTRS)

    Cerro, Jeffrey A

    2013-01-01

    A strategic focus area for NASA is to pursue the development of technologies which support exploration in space beyond the current inhabited region of low earth orbit. An unresolved issue for crewed deep space exploration involves limiting crew radiation exposure to below acceptable levels, considering both solar particle events and galactic cosmic ray contributions to dosage. Galactic cosmic ray mitigation is not addressed in this paper, but by addressing credible, easily implemented, and mass efficient solutions for the possibility of solar particle events, additional margin is provided that can be used for cosmic ray dose accumulation. As a result, NASA s Advanced Engineering Systems project office initiated this Radiation Storm Shelter design activity. This paper reports on the first year results of an expected 3 year Storm Shelter study effort which will mature concepts and operational scenarios that protect exploration astronauts from solar particle radiation events. Large trade space definition, candidate concept ranking, and a planned demonstration comprised the majority of FY12 activities. A system key performance parameter is minimization of the required increase in mass needed to provide a safe environment. Total system mass along with operational assessments and other defined protection system metrics provide the guiding metrics to proceed with concept developments. After a downselect to four primary methods, the concepts were analyzed for dosage severity and the amount of shielding mass necessary to bring dosage to acceptable values. Besides analytical assessments, subscale models of several concepts and one full scale concept demonstrator were created. FY12 work terminated with a plan to demonstrate test articles of two selected approaches. The process of arriving at these selections and their current envisioned implementation are presented in this paper.

  12. Increased Levels of NF-kB-Dependent Markers in Cancer-Associated Deep Venous Thrombosis.

    PubMed

    Malaponte, Grazia; Signorelli, Salvatore S; Bevelacqua, Valentina; Polesel, Jerry; Taborelli, Martina; Guarneri, Claudio; Fenga, Concettina; Umezawa, Kazou; Libra, Massimo

    2015-01-01

    Several studies highlight the role of inflammatory markers in thrombosis as well as in cancer. However, their combined role in cancer-associated deep vein thrombosis (DVT) and the molecular mechanisms, involved in its pathophysiology, needs further investigations. In the present study, C-reactive protein, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1β), matrix metalloproteases-9 (MMP-9), vascular endothelial growth factor (VEGF), tissue factor (TF), fibrinogen and soluble P-selectin, were analyzed in plasma and in monocyte samples from 385 cancer patients, of whom 64 were concomitantly affected by DVT (+). All these markers were higher in cancer patients DVT+ than in those DVT-. Accordingly, significantly higher NF-kB activity was observed in cancer patients DVT+ than DVT-. Significant correlation between data obtained in plasma and monocyte samples was observed. NF-kB inhibition was associated with decreased levels of all molecules in both cancer DVT+ and DVT-. To further demonstrate the involvement of NF-kB activation by the above mentioned molecules, we treated monocyte derived from healthy donors with a pool of sera from cancer patients with and without DVT. These set of experiments further suggest the significant role played by some molecules, regulated by NF-kB, and detected in cancer patients with DVT. Our data support the notion that NF-kB may be considered as a therapeutic target for cancer patients, especially those complicated by DVT. Treatment with NF-kB inhibitors may represent a possible strategy to prevent or reduce the risk of DVT in cancer patients.

  13. The relationship between the deep-level structure in crust and brewing of strong earthquakes in Xingtai area

    NASA Astrophysics Data System (ADS)

    Xiao, Lan-Xi; Zhu, Yuan-Qing; Zhang, Shao-Quan; Liu, Xu; Guo, Yu

    1999-11-01

    In this paper, crust medium is treated as Maxwell medium, and crust model includes hard inclusion, soft inclusion, deep-level fault. The stress concentration and its evolution with time are obtained by using three-dimensional finite element method and differential method. The conclusions are draw as follows: (1) The average stress concentration and maximum shear stress concentration caused by non-heterogeneous of crust are very high in hard inclusion and around the deep fault. With the time passing by, the concentration of average stress in the model gradually trends to uniform. At the same time, the concentration of maximum shear stress in hard inclusion increases gradually. This character is favorable to transfer shear strain energy from soft inclusion to hard inclusion. (2) When the upper mantle beneath the inclusion upheave at a certain velocity of 1 cm/a, the changes of average stress concentration with time become complex, and the boundary of the hard and soft inclusion become unconspicuous, but the maximum shear stress concentration increases much more in the hard inclusion with time at a higher velocity. This feature make for transformation of energy from the soft inclusion to the hard inclusion. (3) The changes of average stress concentration and maximum shear stress concentration with time around the deep-level fault result in further accumulation of maximum shear stress concentration and finally cause the deep-level fault instable and accelerated creep along fault direction. (4) The changes of vertical displacement on the surface of the model, which is caused by the accelerated creep of the deep-level fault, is similar to that of the observation data before Xingtai strong earthquake.

  14. Study of radiation induced deep-level defects in proton irradiated AlGaAs-GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.

    1980-01-01

    Radiation induced deep-level defects (both electron and hole traps) in proton irradiated AlGaAs-GaAs p-n junction solar cells are investigated along with the correlation between the measured defect parameters and the solar cell performance parameters. The range of proton energies studied was from 50 KeV to 10 MeV and the proton fluence was varied from 10 to the 10th power to 10 to the 13th power P/sq cm. Experimental tools employed include deep-level transient spectroscopy, capacitance-voltage, current voltage, and SEM-EBIC methods. Defect and recombination parameters such as defect density and energy level, capture cross section, carrier lifetimes and effective hole diffusion lengths in n-GaAs LPE layers were determined from these measurements.

  15. DeepStack: Expert-level artificial intelligence in heads-up no-limit poker.

    PubMed

    Moravčík, Matej; Schmid, Martin; Burch, Neil; Lisý, Viliam; Morrill, Dustin; Bard, Nolan; Davis, Trevor; Waugh, Kevin; Johanson, Michael; Bowling, Michael

    2017-03-02

    Artificial intelligence has seen several breakthroughs in recent years, with games often serving as milestones. A common feature of these games is that players have perfect information. Poker is the quintessential game of imperfect information, and a longstanding challenge problem in artificial intelligence. We introduce DeepStack, an algorithm for imperfect information settings. It combines recursive reasoning to handle information asymmetry, decomposition to focus computation on the relevant decision, and a form of intuition that is automatically learned from self-play using deep learning. In a study involving 44,000 hands of poker, DeepStack defeated with statistical significance professional poker players in heads-up no-limit Texas hold'em. The approach is theoretically sound and is shown to produce more difficult to exploit strategies than prior approaches.

  16. Trace Level Quantification of the (-)2-(2-amino-5-chlorophenyl)-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-ol Genotoxic Impurity in Efavirenz Drug Substance and Drug Product Using LC-MS/MS.

    PubMed

    Jaishetty, Nagadeep; Palanisamy, Kamaraj; Maruthapillai, Arthanareeswari; Jaishetty, Rajamanohar

    2015-10-18

    Efavirenz is a non-nucleoside reverse transcriptase inhibitor used in the treatment of human immunodeficiency virus type-1 (HIV). (2S)-(2-Amino-5-chlorophenyl)-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-ol (AMCOL), used as an intermediate in the synthesis of efavirenz and a degradation impurity, has an aminoaryl derivative which is a well-known alerting function for genotoxic activity. Upon request from a regulatory agency, a selective and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for trace level quantitative determination of AMCOL related compound of efavirenz, for a risk assessment and comparison of impurity levels with the commercially available innovator product (brand name: Sustiva). The method provided excellent sensitivity at a typical target analyte level of <2.5 ppm, an established threshold of toxicological concern (TTC), when the drug substance and drug product samples were prepared at 15.0 mg/mL. The AMCOL sample was analyzed on a Luna C18 (2) (100 mm × 4.6 mm, 3 µm) column interfaced with a triple quadrupole tandem mass spectrometer operated in a multiple reaction monitoring (MRM) mode. Positive electrospray ionization (ESI) was employed as the ionization source and the mobile phase used was 5.0 mM ammonium acetate-methanol (35:65, v/v). The calibration curve showed good linearity over the concentration range of 0.2-5.0 ppm with a correlation coefficient of >0.999. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.07 and 0.2 ppm, respectively. The developed method was validated as per international council on harmonization (ICH) guidelines in terms of LOD, LOQ, linearity, precision, accuracy, specificity, and robustness.

  17. Trace Level Quantification of the (−)2-(2-amino-5-chlorophenyl)-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-ol Genotoxic Impurity in Efavirenz Drug Substance and Drug Product Using LC–MS/MS

    PubMed Central

    Jaishetty, Nagadeep; Palanisamy, Kamaraj; Maruthapillai, Arthanareeswari; Jaishetty, Rajamanohar

    2015-01-01

    Efavirenz is a non-nucleoside reverse transcriptase inhibitor used in the treatment of human immunodeficiency virus type-1 (HIV). (2S)-(2-Amino-5-chlorophenyl)-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-ol (AMCOL), used as an intermediate in the synthesis of efavirenz and a degradation impurity, has an aminoaryl derivative which is a well-known alerting function for genotoxic activity. Upon request from a regulatory agency, a selective and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for trace level quantitative determination of AMCOL related compound of efavirenz, for a risk assessment and comparison of impurity levels with the commercially available innovator product (brand name: Sustiva). The method provided excellent sensitivity at a typical target analyte level of <2.5 ppm, an established threshold of toxicological concern (TTC), when the drug substance and drug product samples were prepared at 15.0 mg/mL. The AMCOL sample was analyzed on a Luna C18 (2) (100 mm × 4.6 mm, 3 µm) column interfaced with a triple quadrupole tandem mass spectrometer operated in a multiple reaction monitoring (MRM) mode. Positive electrospray ionization (ESI) was employed as the ionization source and the mobile phase used was 5.0 mM ammonium acetate-methanol (35:65, v/v). The calibration curve showed good linearity over the concentration range of 0.2–5.0 ppm with a correlation coefficient of >0.999. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.07 and 0.2 ppm, respectively. The developed method was validated as per international council on harmonization (ICH) guidelines in terms of LOD, LOQ, linearity, precision, accuracy, specificity, and robustness. PMID:28117312

  18. Impurities in nonlinear optical oxide crystals

    NASA Astrophysics Data System (ADS)

    Morris, Patricia A.

    1990-11-01

    Impurities in nonlinear optical oxide crystals can affect many of the properties for device applications. The structures of typical crystals are tolerant with respect to occupancy and are nonstoichiometric on the cation sublattices (e.g. the A sublattice in crystals with the general formula AMO 3). This may, at least in part, be due to the presence of the relatively strong covalent nature of the acentric oxide groups determining the nonlinear optical properties. These circumstances make the incorporation of impurities into the lattice relatively easy and result in large distribution coefficients for many impurities. Generally, little purification during growth will occur with respect to these impurities and therefore, it is usually necessary to purify the starting materials of any unwanted ions. Chemical or powder processing and firing procedures can be used to prevent any contamination of the crystal growth precursors by common impurities (e.g. Si, Al, Fe, Ca, Na, K, Mg, Cl, and S) at a level of <10 parts per million total concentration. A combination of analytical techniques, including those which require little or no sample preparation (e.g. secondary ion mass spectrometry, neutron activation analysis, or laser microprobe mass spectrometry), should be used to determine the impurities present in a material. For example, the effects of protons incorporated (OH -) in the lattice of these crystals can be very detrimental and can be detected using infrared spectroscopy. The growth of many of these crystals requires flux techniques, but the temperature dependence of any nonstoichiometry present and of the distribution coefficients make the use of slow cooling techniques generally not recommended when uniformity of properties is required.

  19. High water level impedes the adaptation of Polygonum hydropiper to deep burial: responses of biomass allocation and root morphology.

    PubMed

    Pan, Ying; Xie, Yong H; Deng, Zheng M; Tang, Yue; Pan, Dong D

    2014-07-08

    Many studies have investigated the individual effects of sedimentation or inundation on the performance of wetland plants, but few have examined the combined influence of these processes. Wetland plants might show greater morphological plasticity in response to inundation than to sedimentation when these processes occur simultaneously since inundation can negate the negative effects of burial on plant growth. Here, we evaluate this hypothesis by assessing growth of the emergent macrophyte Polygonum hydropiper under flooding (0 and 40 cm) and sedimentation (0, 5, and 10 cm), separately and in combination. Deep burial and high water level each led to low oxidation-reduction potential, biomass (except for 5-cm burial), and growth of thick, short roots. These characteristics were generally more significant under high water level than under deep burial conditions. More biomass was allocated to stems in the deep burial treatments, but more to leaves in the high water level treatments. Additionally, biomass accumulation was lower and leaf mass ratio was higher in the 40-cm water level + 10-cm burial depth treatment than both separate effects. Our data indicate that inundation plays a more important role than sedimentation in determining plant morphology, suggesting hierarchical effects of environmental stressors on plant growth.

  20. Analysis of the Effects of Impurities in Silicon. [to determine solar cell efficiency

    NASA Technical Reports Server (NTRS)

    Wohlgemuth, J. H.; Lafky, W. M.; Burkholder, J. H.

    1979-01-01

    A solar cell fabrication and analysis program to determine the effects on the resultant solar cell efficiency of impurities incorporated into silicon is conducted. Flight quality technologies and quality assurance are employed to assure that variations in cell performance are due to the impurities incorporated in the silicon. The type and level of impurity doping in each test lot is given and the mechanism responsible for the degradation of cell performance is identified and correlated to the doped impurities.

  1. Evidence of minority carrier traps contribution in deep level transient spectroscopy measurement in n-GaN Schottky diode

    NASA Astrophysics Data System (ADS)

    Amor, S.; Ahaitouf, A.; Ahaitouf, Az; Salvestrini, J. P.; Ougazzaden, A.

    2017-01-01

    It is shown that deep level transient spectroscopy can be carried out on Schottky diodes to investigate, in addition to majority carrier traps, minority carrier traps. This is possible thanks to the application of a large reverse bias to the device which allows minority carrier injection by lowering their corresponding effective Schottky barrier height. Indeed, when increasing the reverse bias voltage, the deep level transient spectroscopy signal, initially negative and thus showing only majority carrier traps signature, becomes positive, revealing minority carrier traps involvement. A careful analysis of the recorded spectra leads to the identification of four minority carrier traps which have been so far only evidenced using dedicated technique such as minority carrier transient spectroscopy.

  2. EL2 and related defects in GaAs - Challenges and pitfalls. [microdefect introducing a deep donor level

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The incorporation process of nonequilibrium vacancies in melt-grown GaAs is strongly complicated by deviations from stoichiometry and the presence of two sublattices. Many of the microdefects originating in these vacancies and their interactions introduce energy levels (shallow and deep) within the energy gap. The direct identification of the chemical or structural signature of these defects and its direct correlation to their electronic behavior is not generally possible. It is necessary, therefore, to rely on indirect methods and phenomenological models and deal with the associated pitfalls. EL2, a microdefect introducing a deep donor level, has been in the limelight in recent years because it is believed to be responsible for the semi-insulating behavior of undoped GaAs. Although much progress has been made towards understanding its origin and nature, some relevant questions remain unanswered. An attempt is made to assess the present status of understanding of EL2 in the light of most recent results.

  3. Influence of EL2 deep level on photoconduction of semi-insulating GaAs under ultrashort pulse photoinjection

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Xie, Guangyong

    2016-02-01

    To investigate the influence of EL2 deep level on photoconduction of in semi-insulating GaAs (SI-GaAs), a 3 mm-electrode-gap lateral SI-GaAs photoconductive chip was manufactured and tested by using ultrashort pulse laser with 1064 nm wavelength, 10 ns pulsewidth, 3.0 mm light spot diameter and single pulse energy mean of 3.0 mJ. Based on the experimental results and the theory of trapping effect, the photon absorption process of EL2 defects in SI-GaAs is analyzed. For the influence of EL2 deep level, the lifetime of the electron gets shorter and the persistent photoconductivity (PPC) is significant. With increasing of voltage, the decay time constant of photoconduction is reduced and the decay index gets bigger for the ultrashort pulse photoinjection.

  4. Deep level defects in n-type GaAsBi and GaAs grown at low temperatures

    SciTech Connect

    Mooney, P. M.; Watkins, K. P.; Jiang, Zenan; Basile, A. F.; Lewis, R. B.; Bahrami-Yekta, V.; Masnadi-Shirazi, M.; Beaton, D. A.; Tiedje, T.

    2013-04-07

    Deep level defects in n-type GaAs{sub 1-x}Bi{sub x} having 0 < x < 0.012 and GaAs grown by molecular beam epitaxy (MBE) at substrate temperatures between 300 and 400 Degree-Sign C have been investigated by Deep Level Capacitance Spectroscopy. Incorporating Bi suppresses the formation of an electron trap with activation energy 0.40 eV, thus reducing the total trap concentration in dilute GaAsBi layers by more than a factor of 20 compared to GaAs grown under the same conditions. We find that the dominant traps in dilute GaAsBi layers are defect complexes involving As{sub Ga}, as expected for MBE growth at these temperatures.

  5. The effect of secondary impurities on solar cell performance

    NASA Technical Reports Server (NTRS)

    Hill, D. E.; Gutsche, H. W.; Wang, M. S.; Gupta, K. P.; Tucker, W. F.; Dowdy, J. D.; Crepin, R. J.

    1976-01-01

    Czochralski and float zone sigle crystals of silicon were doped with the primary impurities B or P so that a resistivity of 0.5 ohm cm resulted, and in addition doped with certain secondary impurities including Al, C, Cr, Cu, Fe, Mg, Mn, Na, Ni, O, Ti, V, and Zr. The actual presence of these impurities was confirmed by analysis of the crystals. Solar cell performance was evaluated and found to be degraded most significantly by Ti, V, and Zr and to some extent by most of the secondary impurities considered. These results are of significance to the low cost silicon program, since any such process would have to yield at least tolerable levels of these impurities.

  6. Studies of deep level transient spectroscopy of DX centers in GaAlAs: Te under uniaxial stress

    SciTech Connect

    Li, Ming-Fu |; Yu, Y.P. |; Weber, E.R.; Haller, E.E. |; Hansen, W.L.; Bauser, E.

    1991-11-01

    DX centers in Al{sub 0.38}Ga{sub 0.62}As doped with Te have been studied by Deep Level Transient Spectroscopy (DLTS) as a function of uniaxial stress. No splitting nor broadening of the DLTS peaks were observed. However, the peak positions and heights depend on the stress and its directions. The results have been analyzed by comparison with existing models and hydrostatic pressure measurements.

  7. Nonradiative coherent carrier captures and defect reaction at deep-level defects via phonon-kick mechanism

    SciTech Connect

    Wakita, Masaki; Suzuki, Kei; Shinozuka, Yuzo

    2014-02-21

    We simulated the time evolution of electron-lattice coupling mode, and a series of nonradiative carrier captures by a deep-level defect in a semiconductor. For lattice relaxation energy of the order of the band gap, a series of coherent (athermal) electron and hole captures by a defect is possible for high carrier densities, which results in an inflation in the induced lattice vibration, which in turn enhances a defect reaction.

  8. Study of deep level characteristics in the neutrons irradiated Si structures by combining pulsed and steady-state spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Kalendra, V.; Ceponis, T.; Uleckas, A.; Tekorius, A.; Vaitkus, J.; Velicka, A.

    2012-11-01

    The standard methods, such as capacitance deep level transient spectroscopy (C-DLTS) and thermally stimulated current (TSC) techniques are unsuitable for the analysis of heavily irradiated devices. In this work, therefore, several steady-state and pulsed techniques have been combined to comprehensively evaluate parameters of radiation defects and functional characteristics of the irradiated Si pin detectors. In order to understand defects created by radiation and evaluate their evolution with fluence, C-DLTS and TSC techniques have been employed to make a baseline identification of the radiation induced traps after irradiation with a rather small neutron fluence of 1012 cm-2. The steady-state photo-ionization spectroscopy (PIS) technique has been involved to correlate thermal- and photo- activation energies for definite radiation defects. A contactless technique for simultaneous measurements of the carrier lifetime and the parameters of deep levels based on microwave probed pulsed photo-conductivity (MW-PC) spectroscopy has been applied to correlate carrier capture cross-sections and densities of the identified different radiation defects. A technique for spectroscopy of deep levels in junction structures (BELIV) based on measurements of barrier capacitance charging current transient changes due to additional spectrally resolved pulsed illumination has been applied to evaluate the functional characteristics of the irradiated diodes. Pulsed spectroscopic measurements were implemented by combining the analysis of generation current and of barrier capacitance charging transients modified by a single fs pulse of illumination generated by an optical parametric oscillator of varied wavelength in the range from 0.5 to 10 μm. Several deep levels with activation energy in the range of 0.18-0.8 eV have been resolved from spectral analysis in the samples of Si grown by magnetic field applied Czochralski (MCz) technology.

  9. Deep-level emission in ZnO nanowires and bulk crystals: Excitation-intensity dependence versus crystalline quality

    SciTech Connect

    Hou, Dongchao; Voss, Tobias; Ronning, Carsten; Menzel, Andreas; Zacharias, Margit

    2014-06-21

    The excitation-intensity dependence of the excitonic near-band-edge emission (NBE) and deep-level related emission (DLE) bands in ZnO nanowires and bulk crystals is studied, which show distinctly different power laws. The behavior can be well explained with a rate-equation model taking into account deep donor and acceptor levels with certain capture cross sections for electrons from the conduction band and different radiative lifetimes. In addition, a further crucial ingredient of this model is the background n-type doping concentration inherent in almost all ZnO single crystals. The interplay of the deep defects and the background free-electron concentration in the conduction band at room temperature reproduces the experimental results well over a wide range of excitation intensities (almost five orders of magnitude). The results demonstrate that for many ZnO bulk samples and nanostructures, the relative intensity R = I{sub NBE}/I{sub DLE} can be adjusted over a wide range by varying the excitation intensity, thus, showing that R should not be taken as an indicator for the crystalline quality of ZnO samples unless absolute photoluminescence intensities under calibrated excitation conditions are compared. On the other hand, the results establish an all-optical technique to determine the relative doping levels in different ZnO samples by measuring the excitation-intensity dependence of the UV and visible luminescence bands.

  10. Two-Step Inverse Modeling for Estimation of Channel Impurity Pile-up

    NASA Astrophysics Data System (ADS)

    Nagumo, Toshiharu; Takeuchi, Kiyoshi; Akiyama, Yutaka; Hane, Masami

    2008-04-01

    A scheme for estimating the amount of channel impurity pile-up using inverse modeling assuming a simplified effective impurity profile is proposed. Impurity profile is divided into deep and surface regions, and they are evaluated in two steps. In the first step, the impurity profile in the deep region is determined using the shift of threshold voltage, and then in the second step, the impurity profile in the surface region is determined using the threshold voltage. By taking drain-induced barrier lowering (DIBL) into account, this scheme can be used to estimate the effective impurity profile in short-channel devices, and thus, can be used to evaluate the gate length dependence of the channel impurity pile-up. Evaluated results on n-type metal-oxide-semiconductor field-effect transistors (MOSFETs) indicate that the impurity pile-up is strong and gate-length-dependent in spike-annealed MOSFETs, whereas laser-annealed MOSFETs show almost no impurity pile-up. The proposed scheme can be used to clearly detect such process condition dependence, and therefore, is helpful for process optimization.

  11. Silicon materials task of the Low-Cost Solar Array Project (Phase IV). Effects of impurities and processing on silicon solar cells. Nineteenth quarterly report, April 1980-June 1980

    SciTech Connect

    Hopkins, R.H.; Davis, J.R.; Rohatgi, A.; Campbell, R.B.; Rai-Choudhury, P.; Hanes, M.H.; Mollenkopf, H.C.; McCormick, J.R.

    1980-07-01

    The overall objective of this program is to define the effects of impurities, various thermochemical processes, and any impurity-process interactions upon the performance of terrestrial solar cells. The results of the study form a basis for silicon producers, wafer manufacturers, and cell fabricators to develop appropriate cost-benefit relationships for the use of less pure, less costly solar grade silicon. Nine 4 ohm-cm p type silicon ingots were grown and evaluated in support of the experimental program this quarter. Of these, three were polycrystalline ingots doped with Cr, Mo, and V, respectively, produced under conditions which successfully eliminated the metal-rich inclusions formed when growth of these heavily-doped specimens was attempted during the last quarter. Evaluation of polycrystalline ingots doped to the mid 10/sup 13/ cm/sup -3/ range with Ti or V showed little evidence for grain boundary segregation. Deep level spectroscopy on both as-grown wafers and solar cells showed little variation in impurity concentration from place to place across the ingot regardless of the presence of grain boundaries or other structural features. Deep level spectroscopy was also used to monitor the electrically active impurity concentrations in ingots to be used for process studies, aging experiments, and high efficiency cells. The basic aspects of a model to describe efficiency behavior in high efficiency cells have been formulated and a computer routine is being implemented for back field type devices to analyze the functional relationships between impurity concentrations and cell performance.

  12. Reducing production of taste and odor by deep-living cyanobacteria in drinking water reservoirs by regulation of water level.

    PubMed

    Su, Ming; Jia, Dongmin; Yu, Jianwei; Vogt, Rolf D; Wang, Jingshi; An, Wei; Yang, Min

    2017-01-01

    Abatement and control of algae, producing toxins and creating taste & odor (T&O) in drinking water sources, is a major challenge for water supply. In this study we proposed a strategy based on water level regulation for the control of odor-producing cyanobacteria in source water. Miyun Reservoir, the main surface water source for Beijing, has been suffering from 2-methylisoborneol (2-MIB) induced T&O problems caused by deep-living Planktothrix sp. since 2002. The biomass of deep-living Planktothrix in Miyun Reservoir was found to be mainly governed by the water depth above its sediment habitat. An algorithm for water level regulation aiming to minimize the risk for T&O in different types of reservoirs is proposed. The study demonstrates that risk for T&O can be minimized by increasing the water level in Miyun Reservoir. The high-risk area can be reduced by about 2.91% (0.61% to 5.76%) of surface area for each meter increase in the water level, when the water level is lower than 145m. More specifically, the water level needs to be raised to higher than 147.7ma.s.l. from 131.0m in order to obtain an acceptable risk level (ARL) of 10%. This management strategy to abate T&O problems is simpler and cheaper to implement compared to traditional physical, chemical and biological techniques. Moreover, it has no apparent negative impact on water quality and aquatic organisms.

  13. Long-range exchange interaction between magnetic impurities in graphene

    NASA Astrophysics Data System (ADS)

    Agarwal, M.; Mishchenko, E. G.

    2017-02-01

    The effective spin exchange RKKY coupling between impurities (adatoms) on graphene mediated by conduction electrons is studied as a function of the strength of the potential part of the on-site energy U of the electron-adatom interaction. With increasing U , the exchange coupling becomes long range, determined largely by the impurity levels with energies close to the Dirac points. When adatoms reside on opposite sublattices, their exchange coupling, normally antiferromagnetic, becomes ferromagnetic and resonantly enhanced at a specific distance where an impurity level crosses the Dirac point.

  14. Isolation and structural elucidation of two impurities from a diacerein bulk drug.

    PubMed

    Ashok, Chaudhari; Golak, Maikap; Adwait, Deo; Krishna, Vivek; Himani, Agrawal; Umesh, Peshawe; Amol, Gawande; Srinivas, Sompalli; Sharad, Mane; Deepali, Jadhav; Atul, Chaudhari

    2009-02-20

    Two impurities were found in the crude sample of diacerein. The level of these impurities 1.14% and 1.24% were detected by isocratic reverse-phase high performance liquid chromatography (HPLC). The molecular weights of the impurities were determined by liquid chromatography-mass spectroscopy (LC-MS) analysis. These impurities were isolated from crude sample of diacerein by reverse-phase preparative liquid chromatography. These impurities were characterized as 5-acetoxy-4-hydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxylic acid (Impurity-1) and 4-acetoxy-5-hydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxylic acid (Impurity-2) respectively. Structural elucidation of both the impurities were carried out by (1)H NMR, (13)C NMR, DEPT, 1D NOESY, MS and IR spectroscopy.

  15. Development of a Universal Canister for Disposal of High-Level Waste in Deep Boreholes.

    SciTech Connect

    Price, Laura L.; Gomberg, Steve

    2015-11-01

    The mission of the United States Department of Energy’s Office of Environmental Management is to complete the safe cleanup of the environmental legacy brought about from five decades of nuclear weapons development and government-sponsored nuclear energy research. Some of the wastes that must be managed have been identified as good candidates for disposal in a deep borehole in crystalline rock. In particular, wastes that can be disposed of in a small package are good candidates for this disposal concept. A canister-based system that can be used for handling these wastes during the disposition process (i.e., storage, transfer, transportation, and disposal) could facilitate the eventual disposal of these wastes. Development of specifications for the universal canister system will consider the regulatory requirements that apply to storage, transportation, and disposal of the capsules, as well as operational requirements and limits that could affect the design of the canister (e.g., deep borehole diameter). In addition, there are risks and technical challenges that need to be recognized and addressed as Universal Canister system specifications are developed. This paper provides an approach to developing specifications for such a canister system that is integrated with the overall efforts of the DOE’s Used Fuel Disposition Campaign's Deep Borehole Field Test and compatible with planned storage of potential borehole-candidate wastes.

  16. Relationship of deep defects to oxygen and hydrogen content in nanocrystalline silicon photovoltaic materials

    SciTech Connect

    Hugger, Peter G.; Cohen, J. David; Yan Baojie; Yue Guozhen; Yang, Jeffrey; Guha, Subhendu

    2010-12-20

    We report measurements of the structural and compositional properties of a range of hydrogenated nanocrystalline films. We employed Raman spectroscopy for crystallinity and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) for impurity characterizations. The crystalline volume fractions and impurity levels are correlated with the deep state densities determined by drive level capacitance profiling. Those defects were found to have a thermal emission energy of 0.65{+-}.05 eV. We found that the overall crystallinity correlated reasonably well with the density of such defect states and also found a strong correlation between the defect density and the levels of oxygen impurities. Possible origins of these defects are discussed.

  17. Studies of deep level centers determining the diffusion length in epitaxial layers and crystals of undoped n-GaN

    NASA Astrophysics Data System (ADS)

    Lee, In-Hwan; Polyakov, A. Y.; Smirnov, N. B.; Yakimov, E. B.; Tarelkin, S. A.; Turutin, A. V.; Shemerov, I. V.; Pearton, S. J.

    2016-05-01

    A wide variety of parameters were measured for undoped n-GaN grown by hydride vapor phase epitaxy and compared to n-GaN films grown by conventional and lateral overgrowth metalorganic chemical vapor deposition. The parameters included deep level electron and hole trap spectra, microcathodoluminescence, electron beam induced current, diffusion length, and electron capture cross section from the dependence of the low temperature persistent photocapacitance on forward bias injection pulse duration. The results show a prominent role of electron traps with levels near Ec-0.56 eV in limiting the lifetime and diffusion length values in all these materials.

  18. Dispersion retrieval from multi-level ultra-deep reactive-ion-etched microstructures for terahertz slow-wave circuits

    SciTech Connect

    Baik, Chan-Wook Young Ahn, Ho; Kim, Yongsung; Lee, Jooho; Hong, Seogwoo; Hee Choi, Jun; Kim, Sunil; Hun Lee, Sang; Min Kim, Jong; Hwang, Sungwoo; Yeon Jun, So; Yu, SeGi; Lawrence Ives, R.

    2014-01-13

    A multi-level microstructure is proposed for terahertz slow-wave circuits, with dispersion relation retrieved by scattering parameter measurements. The measured return loss shows strong resonances above the cutoff with negligible phase shifts compared with finite element analysis. Splitting the circuit into multi levels enables a low aspect ratio configuration that alleviates the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles. The dispersion retrieved from the measurement, therefore, corresponds well to the theoretical estimation. The result provides a straightforward way to the precise determination of dispersions in terahertz vacuum electronics.

  19. Effects of the impurity-host interactions on the nonradiative processes in ZnS:Cr

    NASA Astrophysics Data System (ADS)

    Tablero, C.

    2010-11-01

    There is a great deal of controversy about whether the behavior of an intermediate band in the gap of semiconductors is similar or not to the deep-gap levels. It can have significant consequences, for example, on the nonradiative recombination. In order to analyze the behavior of an intermediate band, we have considered the effect of the inward and outward displacements corresponding to breathing and longitudinal modes of Cr-doped ZnS and on the charge density for different processes involved in the nonradiative recombination using first-principles. This metal-doped zinc chalcogenide has a partially filled band within the host semiconductor gap. In contrast to the properties exhibited by deep-gap levels in other systems, we find small variations in the equilibrium configurations, forces, and electronic density around the Cr when the nonradiative recombination mechanisms modify the intermediate band charge. The charge density around the impurity is equilibrated in response to the perturbations in the equilibrium nuclear configuration and the charge of the intermediate band. The equilibration follows a Le Chatelier principle through the modification of the contribution from the impurity to the intermediate band and to the valence band. The intermediate band introduced by Cr in ZnS for the concentrations analyzed makes the electronic capture difficult and later multiphonon emission in the charge-transfer processes, in accordance with experimental results.

  20. Effect of impurity doping in gapped bilayer graphene

    SciTech Connect

    Han, Qi; Yan, Baoming; Jia, Zhenzhao; Niu, Jingjing; Yu, Dapeng; Wu, Xiaosong

    2015-10-19

    Impurity doping plays a pivotal role in semiconductor electronics. We study the doping effect in a two-dimensional semiconductor, gapped bilayer graphene. By employing in situ deposition of calcium on the bilayer graphene, dopants are controllably introduced. Low temperature transport results show a variable range hopping conduction near the charge neutrality point persisting up to 50 K, providing evidence for the impurity levels inside the gap. Our experiment confirms a predicted peculiar effect in the gapped bilayer graphene, i.e., formation of in-gap states even if the bare impurity level lies in the conduction band. The result provides perspective on the effect of doping and impurity levels in semiconducting bilayer graphene.

  1. Distribution Coefficients of Impurities in Metals

    NASA Astrophysics Data System (ADS)

    Pearce, J. V.

    2014-04-01

    Impurities dissolved in very pure metals at the level of parts per million often cause an elevation or depression of the freezing temperature of the order of millikelvins. This represents a significant contribution to the uncertainty of standard platinum resistance thermometer calibrations. An important parameter for characterizing the behavior of impurities is the distribution coefficient , which is the ratio of the solid solubility to liquid solubility. A knowledge of for a given binary system is essential for contemporary methods of evaluating or correcting for the effect of impurities, and it is therefore of universal interest to have the most complete set of values possible. A survey of equilibrium values of (in the low concentration limit) reported in the literature for the International Temperature Scale of 1990 fixed points of Hg, Ga, In, Sn, Zn, Al, Au, Ag, and Cu is presented. In addition, thermodynamic calculations of using MTDATA are presented for 170 binary systems. In total, the combined values of from all available sources for 430 binary systems are presented. In addition, by considering all available values of for impurities in 25 different metal solvents (1300 binary systems) enough data are available to characterize patterns in the value of for a given impurity as a function of its position in the periodic table. This enables prediction of for a significant number of binary systems for which data and calculations are unavailable. By combining data from many sources, values of for solutes (atomic number from 1 to 94) in ITS-90 fixed points from Hg to Cu are suggested, together with some tentative predicted values where literature data and calculations are unavailable.

  2. Exploring the Deep-Level Reasoning Questions Effect during Vicarious Learning among Eighth to Eleventh Graders in the Domains of Computer Literacy and Newtonian Physics

    ERIC Educational Resources Information Center

    Gholson, Barry; Witherspoon, Amy; Morgan, Brent; Brittingham, Joshua K.; Coles, Robert; Graesser, Arthur C.; Sullins, Jeremiah; Craig, Scotty D.

    2009-01-01

    This paper tested the deep-level reasoning questions effect in the domains of computer literacy between eighth and tenth graders and Newtonian physics for ninth and eleventh graders. This effect claims that learning is facilitated when the materials are organized around questions that invite deep-reasoning. The literature indicates that vicarious…

  3. Stabilization of the Particle-Hole Pfaffian Order by Landau-Level Mixing and Impurities That Break Particle-Hole Symmetry

    NASA Astrophysics Data System (ADS)

    Zucker, P. T.; Feldman, D. E.

    2016-08-01

    Numerical results suggest that the quantum Hall effect at ν =5 /2 is described by the Pfaffian or anti-Pfaffian state in the absence of disorder and Landau-level mixing. Those states are incompatible with the observed transport properties of GaAs heterostructures, where disorder and Landau-level mixing are strong. We show that the recent proposal of a particle-hole (PH)-Pfaffian topological order by Son is consistent with all experiments. The absence of particle-hole symmetry at ν =5 /2 is not an obstacle to the existence of the PH-Pfaffian order since the order is robust to symmetry breaking.

  4. Stretching and deep and superficial massage do not influence blood lactate levels after heavy-intensity cycle exercise.

    PubMed

    Cè, Emiliano; Limonta, Eloisa; Maggioni, Martina A; Rampichini, Susanna; Veicsteinas, Arsenio; Esposito, Fabio

    2013-01-01

    The study aimed to assess the role of deep and superficial massage and passive stretching recovery on blood lactate concentration ([La(-)]) kinetics after a fatiguing exercise compared to active and passive recovery. Nine participants (age 23 ± 1 years; stature 1.76 ± 0.02 m; body mass 74 ± 4 kg) performed on five occasions an 8-min fatiguing exercise at 90% of maximum oxygen uptake, followed by five different 10-min interventions in random order: passive and active recovery, deep and superficial massage and stretching. Interventions were followed by 1 hour of recovery. Throughout each session, maximum voluntary contraction (MVC) of the knee extensor muscles, [La(-)], cardiorespiratory and metabolic variables were determined. Electromyographic signal (EMG) from the quadriceps muscles was also recorded. At the end of the fatiguing exercise, [La(-)], MVC, EMG amplitude, and metabolic and cardiorespiratory parameters were similar among conditions. During intervention administration, [La(-)] was lower and metabolic and cardiorespiratory parameters were higher in active recovery compared to the other modalities (P < 0.05). Stretching and deep and superficial massage did not alter [La(-)] kinetics compared to passive recovery. These findings indicate that the pressure exerted during massage administration and stretching manoeuvres did not play a significant role on post-exercise blood La(-) levels.

  5. Related impurities in peptide medicines.

    PubMed

    D'Hondt, Matthias; Bracke, Nathalie; Taevernier, Lien; Gevaert, Bert; Verbeke, Frederick; Wynendaele, Evelien; De Spiegeleer, Bart

    2014-12-01

    Peptides are an increasingly important group of pharmaceuticals, positioned between classic small organic molecules and larger bio-molecules such as proteins. Currently, the peptide drug market is growing twice as fast as other drug markets, illustrating the increasing clinical as well as economical impact of this medicine group. Most peptides today are manufactured by solid-phase peptide synthesis (SPPS). This review will provide a structured overview of the most commonly observed peptide-related impurities in peptide medicines, encompassing the active pharmaceutical ingredients (API or drug substance) as well as the finished drug products. Not only is control of these peptide-related impurities and degradants critical for the already approved and clinically used peptide-drugs, these impurities also possess the capability of greatly influencing initial functionality studies during early drug discovery phases, possibly resulting in erroneous conclusions. The first group of peptide-related impurities is SPPS-related: deletion and insertion of amino acids are related to inefficient Fmoc-deprotection and excess use of amino acid reagents, respectively. Fmoc-deprotection can cause racemization of amino acid residues and thus diastereomeric impurities. Inefficient deprotection of amino acid side chains results into peptide-protection adducts. Furthermore, unprotected side chains can react with a variety of reagents used in the synthesis. Oxidation of amino acid side chains and dimeric-to-oligomeric impurities were also observed. Unwanted peptide counter ions such as trifluoroacetate, originating from the SPPS itself or from additional purification treatments, may also be present in the final peptide product. Contamination of the desired peptide product by other unrelated peptides was also seen, pointing out the lack of appropriate GMP. The second impurity group results from typical peptide degradation mechanisms such as β-elimination, diketopiperazine, pyroglutamate

  6. Multiregion ultra-deep sequencing reveals early intermixing and variable levels of intratumoral heterogeneity in colorectal cancer.

    PubMed

    Suzuki, Yuka; Ng, Sarah Boonhsi; Chua, Clarinda; Leow, Wei Qiang; Chng, Jermain; Liu, Shi Yang; Ramnarayanan, Kalpana; Gan, Anna; Ho, Dan Liang; Ten, Rachel; Su, Yan; Lezhava, Alexandar; Lai, Jiunn Herng; Koh, Dennis; Lim, Kiat Hon; Tan, Patrick; Rozen, Steven G; Tan, Iain Beehuat

    2017-02-01

    Intratumor heterogeneity (ITH) contributes to cancer progression and chemoresistance. We sought to comprehensively describe ITH of somatic mutations, copy number, and transcriptomic alterations involving clinically and biologically relevant gene pathways in colorectal cancer (CRC). We performed multiregion, high-depth (384× on average) sequencing of 799 cancer-associated genes in 24 spatially separated primary tumor and nonmalignant tissues from four treatment-naïve CRC patients. We then used ultra-deep sequencing (17 075× on average) to accurately verify the presence or absence of identified somatic mutations in each sector. We also digitally measured gene expression and copy number alterations using NanoString assays. We identified the subclonal point mutations and determined the mutational timing and phylogenetic relationships among spatially separated sectors of each tumor. Truncal mutations, those shared by all sectors in the tumor, affected the well-described driver genes such as APC, TP53, and KRAS. With sequencing at 17 075×, we found that mutations first detected at a sequencing depth of 384× were in fact more widely shared among sectors than originally assessed. Interestingly, ultra-deep sequencing also revealed some mutations that were present in all spatially dispersed sectors, but at subclonal levels. Ultra-high-depth validation sequencing, copy number analysis, and gene expression profiling provided a comprehensive and accurate genomic landscape of spatial heterogeneity in CRC. Ultra-deep sequencing allowed more sensitive detection of somatic mutations and a more accurate assessment of ITH. By detecting the subclonal mutations with ultra-deep sequencing, we traced the genomic histories of each tumor and the relative timing of mutational events. We found evidence of early mixing, in which the subclonal ancestral mutations intermixed across the sectors before the acquisition of subsequent nontruncal mutations. Our findings also indicate that

  7. Mobile impurities in ferromagnetic liquids

    NASA Astrophysics Data System (ADS)

    Kantian, Adrian; Schollwoeck, Ulrich; Giamarchi, Thierry

    2011-03-01

    Recent work has shown that mobile impurities in one dimensional interacting systems may exhibit behaviour that differs strongly from that predicted by standard Tomonaga-Luttinger liquid theory, with the appearance of power-law divergences in the spectral function signifying sublinear diffusion of the impurity. Using time-dependent matrix product states, we investigate a range of cases of mobile impurities in systems beyond the analytically accessible examples to assess the existence of a new universality class of low-energy physics in one-dimensional systems. Correspondence: Adrian.Kantian@unige.ch This work was supported in part by the Swiss SNF under MaNEP and division II.

  8. Metallic impurities in gallium nitride grown by molecular beam epitaxy

    SciTech Connect

    McHugo, S.A.; Krueger, J.; Kisielowski, C.

    1997-04-01

    Transition metals are often encountered in trace amounts in semiconductors. They have been extensively studied in most elemental and compound systems, since they form deep donor and/or acceptor levels which usually degrade the electronic and optical material properties. Only very little is known about transition metals in recent III-V semiconducting materials, such as GaN, AlN and InN. These few studies have been done exclusively on Metal-Organic Chemical Vapor Deposition (MOCVD) or Hybrid Vapor Phase Epitaxy HVPE-grown GaN. Preliminary x-ray fluorescence studies at the Advanced Light Source, beamline 10.3.1, Lawrence Berkeley National Laboratory have revealed that GaN materials grown by Molecular Beam Epitaxy (MBE) have Fe, Ni and Cr as the dominant transition metal contaminants. This finding is commensurate with the extremely high concentrations of hydrogen, carbon and oxygen (up to 10{sup 20} cm{sup {minus}3}) measured by Secondary Ion Mass Spectroscopy (SIMS). Preliminary work using the mapping capabilities of the x-ray fluorescence microprobe revealed the metal impurities were inhomogeneously distributed over the film. Future work of this collaboration will be to find a correlation between the existence of transition metals in MBE films, as revealed by x-ray fluorescence, and Photoluminescence (PL) spectra taken in the infrared region. Also, the authors will make use of the 1 {mu}m spatial resolution of x-ray microprobe to locate the contaminants in relation to structural defects in the GaN films. Because of the large strain caused by the lattice mismatch between the GaN films and the substrates, the films grow in a columnar order with high densities of grain boundaries and dislocations. These structural defects offer preferential sites for metal precipitation or agglomeration which could degrade the optical properties of this material more so than if the impurities were left dissolved in the GaN.

  9. Evaluation of hydraulic characteristics of a deep artesian aquifer from natural water-level fluctuations, Miami, Florida

    USGS Publications Warehouse

    Meyer, Frederick W.

    1974-01-01

    Knowledge of tho hydraulic characteristics of aquifer systems is fundamental to defining the vertical and horizontal controls on fluid movement, information which is needed for assessing the environmental impact of subsurface waste storage. To meet this objective, natural water-level fluctuations in the 2,947-foot deep Peninsula Utilities disposal well near Miami, Florida were analyzed to obtain estimates of the hydraulic diffusivity, hydraulic conductivity, specific storage, transmissivity, and the storage coefficient of the Boulder Zone. The fluctuations are caused chiefly by oceanic and earth tides, and by changes in atmospheric pressure. The oceanic tidal fluctuations probably result from loading due to tides in Biscayne Bay.

  10. Deep level transient spectroscopy studies of n-type ZnO single crystals grown by different techniques.

    PubMed

    Scheffler, L; Kolkovsky, Vl; Lavrov, E V; Weber, J

    2011-08-24

    In the present study single-crystalline ZnO samples grown from the vapor phase, the melt, and a high-temperature aqueous solution (hydrothermal growth) are investigated before and after hydrogen plasma treatments, by means of deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. Dominant DLTS peaks are found to appear in the range of 120-350 K for all materials. The DLTS spectra depend on the procedure of growth of the ZnO. The thermal stabilities of the defects in an oxygen atmosphere and in an oxygen-lean atmosphere are analyzed. The origin of the DLTS peaks is discussed.

  11. Deep electronic levels in high-pressure Bridgman Cd{sub 1-x}Zn{sub x}Te

    SciTech Connect

    Szeles, C.; Shan, Y.Y.; Lynn, K.G.; Eissler, E.E.

    1995-12-01

    The behavior of deep electronic levels was studied as a function of Zn concentration in CdZnTe crystals grown by the high-pressure Bridgman technique using thermoelectric effect spectroscopy. A significant increase of the thermal ionization energies of hole traps was observed with the increasing Zn content of the ternary compound. The effect explains the stronger hole trapping and the resulting much shorter hole lifetime usually observed in CdZnTe as compared to CdTe. The behavior also suggests increased carrier recombination and explains the strong deterioration of electron collection in detectors fabricated from CdZnTe of high Zn concentration.

  12. On the optical evaluation of the EL2 deep level concentration in semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Walukiewicz, W.; Lagowski, J.; Gatos, H. C.

    1983-01-01

    A practical procedure for the evaluation of the Fermi energy in semi-insulating (SI)GaAs from electrical measurements is presented. This procedure makes it possible to reliably extend the determination of the major deep level (EL2) concentration, by near-infrared absorption measurements, to SIGaAs. Employing this procedure, it is shown that the EL2 concentration in Czochralski-grown GaAs increases monotonically with increasing As/Ga ratio (throughout the conversion from SI n type to semiconducting p-type crystals) rather than abruptly as previously proposed.

  13. Electronic properties of deep-level defects in proton irradiated AlGaAs-GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.

    1981-01-01

    Deep level transient spectroscopy and capacitance voltage techniques as well as analysis of the forward current voltage (I-V) characteristics and SEM-EIC data were carried out for proton irradiated GaAs solar cells over a wide range of proton energies and proton fluences. Defect and recombination parameters such as defect energy levels and density, carrier capture cross sections and lifetimes as well as diffusion lengths in the undoped n-GaAs LPE layers were determined. Good correlation between these defect parameters and solar cell performance parameters was obtained for GaAs solar cells irradiated by 200 and 290 KeV protons. It was found that 200 to 290 KeV protons will produce the most defects and damages to the GaAs solar cell structure used. The influence of the low temperature (200 to 400 C) periodic thermal annealing on the deep level defects and the performance of the 200 KeV proton irradiated cells is discussed.

  14. Recent trends in the impurity profile of pharmaceuticals

    PubMed Central

    Pilaniya, Kavita; Chandrawanshi, Harish K.; Pilaniya, Urmila; Manchandani, Pooja; Jain, Pratishtha; Singh, Nitin

    2010-01-01

    Various regulatory authorities such as the International Conference on Harmonization (ICH), the United States Food and Drug administration (FDA), and the Canadian Drug and Health Agency (CDHA) are emphasizing on the purity requirements and the identification of impurities in Active Pharmaceutical Ingredients (APIs). The various sources of impurity in pharmaceutical products are — reagents, heavy metals, ligands, catalysts, other materials like filter aids, charcoal, and the like, degraded end products obtained during \\ after manufacturing of bulk drugs from hydrolysis, photolytic cleavage, oxidative degradation, decarboxylation, enantiomeric impurity, and so on. The different pharmacopoeias such as the British Pharmacopoeia, United State Pharmacopoeia, and Indian Pharmacopoeia are slowly incorporating limits to allowable levels of impurities present in APIs or formulations. Various methods are used to isolate and characterize impurities in pharmaceuticals, such as, capillary electrophoresis, electron paramagnetic resonance, gas–liquid chromatography, gravimetric analysis, high performance liquid chromatography, solid-phase extraction methods, liquid–liquid extraction method, Ultraviolet Spectrometry, infrared spectroscopy, supercritical fluid extraction column chromatography, mass spectrometry, Nuclear magnetic resonance (NMR) spectroscopy, and RAMAN spectroscopy. Among all hyphenated techniques, the most exploited techniques for impurity profiling of drugs are Liquid Chromatography (LC)-Mass Spectroscopy (MS), LC-NMR, LC-NMR-MS, GC-MS, and LC-MS. This reveals the need and scope of impurity profiling of drugs in pharmaceutical research. PMID:22247862

  15. Characterization of the deep levels responsible for non-radiative recombination in InGaN/GaN light-emitting diodes

    SciTech Connect

    Meneghini, M. La Grassa, M.; Vaccari, S.; Meneghesso, G.; Zanoni, E.

    2014-03-17

    This paper presents an extensive investigation of the deep levels related to non-radiative recombination in InGaN/GaN light-emitting diodes (LEDs). The study is based on combined optical and deep-level transient spectroscopy measurements, carried out on LEDs with identical structure and with different values of the non-radiative recombination coefficient. Experimental data lead to the following, relevant, results: (i) LEDs with a high non-radiative recombination coefficient have a higher concentration of a trap (labeled as “e{sub 2}”) with an activation energy of 0.7 eV, which is supposed to be located close to/within the active region; (ii) measurements carried out with varying filling pulse duration suggest that this deep level behaves as a point-defect/dislocation complex. The Arrhenius plot of this deep level is critically compared with the previous literature reports, to identify its physical origin.

  16. Late Pleistocene Sea level on the New Jersey Margin: Implications to eustasy and deep-sea temperature

    USGS Publications Warehouse

    Wright, J.D.; Sheridan, R.E.; Miller, K.G.; Uptegrove, J.; Cramer, B.S.; Browning, J.V.

    2009-01-01

    We assembled and dated a late Pleistocene sea-level record based on sequence stratigraphy from the New Jersey margin and compared it with published records from fossil uplifted coral reefs in New Guinea, Barbados, and Araki Island, as well as a composite sea-level estimate from scaling of Red Sea isotopic values. Radiocarbon dates, amino acid racemization data, and superposition constrain the ages of large (20-80??m) sea-level falls from New Jersey that correlate with Marine Isotope Chrons (MIC) 2, 3b, 4, 5b, and 6 (the past 130??kyr). The sea-level records for MIC 1, 2, 4, 5e, and 6 are similar to those reported from New Guinea, Barbados, Araki, and the Red Sea; some differences exist among records for MIC 3. Our record consistently provides the shallowest sea level estimates for MIC3 (??? 25-60??m below present); it agrees most closely with the New Guinea record of Chappell (2002; ??? 35-70??m), but contrasts with deeper estimates provided by Araki (??? 85-95??m) and the Red Sea (50-90??m). Comparison of eustatic estimates with benthic foraminiferal ??18O records shows that the deep sea cooled ??? 2.5????C between MIC 5e and 5d (??? 120-110??ka) and that near freezing conditions persisted until Termination 1a (14-15??ka). Sea-level variations between MIC 5b and 2 (ca. 90-20??ka) follow a well-accepted 0.1???/10??m linear variation predicted by ice-growth effects on foraminiferal ??18O values. The pattern of deep-sea cooling follows a previously established hysteresis loop between two stable modes of operation. Cold, near freezing deep-water conditions characterize most of the past 130??kyr punctuated only by two warm intervals (the Holocene/MIC 1 and MIC 5e). We link these variations to changes in Northern Component Water (NCW). ?? 2009 Elsevier B.V. All rights reserved.

  17. Development of benthic biological monitoring criteria for disposal of low-level radioactive waste in the abyssal deep sea. Final report

    SciTech Connect

    Smith, C.R.; Present, T.M.C.; Jumars, P.A.

    1988-09-01

    In order to develop recommendations for monitoring low-level radioactive waste dumpsites in the abyss, the report attempts a synthesis of information from three overlapping topical areas. First, U.S. Regulations governing the dumping and monitoring of wastes in the ocean are interpreted in a deep-sea context. Second, significant attention is given to experiences obtained from past dumping of low-level radioactive wastes in marine environments, both shallow-water and deep-sea. Third, the report attempts to apply the monitoring Requirements and conceptual approaches selected to the abyssal seafloor, based on present understandings of the deep-sea ecosystem.

  18. Mapping vaccinia virus DNA replication origins at nucleotide level by deep sequencing.

    PubMed

    Senkevich, Tatiana G; Bruno, Daniel; Martens, Craig; Porcella, Stephen F; Wolf, Yuri I; Moss, Bernard

    2015-09-01

    Poxviruses reproduce in the host cytoplasm and encode most or all of the enzymes and factors needed for expression and synthesis of their double-stranded DNA genomes. Nevertheless, the mode of poxvirus DNA replication and the nature and location of the replication origins remain unknown. A current but unsubstantiated model posits only leading strand synthesis starting at a nick near one covalently closed end of the genome and continuing around the other end to generate a concatemer that is subsequently resolved into unit genomes. The existence of specific origins has been questioned because any plasmid can replicate in cells infected by vaccinia virus (VACV), the prototype poxvirus. We applied directional deep sequencing of short single-stranded DNA fragments enriched for RNA-primed nascent strands isolated from the cytoplasm of VACV-infected cells to pinpoint replication origins. The origins were identified as the switching points of the fragment directions, which correspond to the transition from continuous to discontinuous DNA synthesis. Origins containing a prominent initiation point mapped to a sequence within the hairpin loop at one end of the VACV genome and to the same sequence within the concatemeric junction of replication intermediates. These findings support a model for poxvirus genome replication that involves leading and lagging strand synthesis and is consistent with the requirements for primase and ligase activities as well as earlier electron microscopic and biochemical studies implicating a replication origin at the end of the VACV genome.

  19. Effect of carrier capture by deep levels on lateral photoconductivity of InGaAs/GaAs quantum dot structures

    NASA Astrophysics Data System (ADS)

    Vakulenko, O. V.; Golovynskyi, S. L.; Kondratenko, S. V.

    2011-08-01

    Having used thermally stimulated conductivity (TSC) technique, we identified deep electron traps that produce strong effects on charge carrier transport and photoconductivity in InGaAs/GaAs quantum dot (QD) structures. The values of deep levels below the conduction band of GaAs at 0.16, 0.22, and 0.35 eV are obtained from the analysis of the shapes of TSC curves after the excitation with the quanta energy hv = 0.9, 1.2, and 1.6 eV. The level 0.16 eV in depth is an effective electron trap that provides crossing of lateral conductivity with a high-resistance mode and, therefore, causes a high photocurrent sensitivity of about 3 A/W at 77 K with excitation by interband transitions in QDs. We determined the charge density of electrons captured by the (Ec - 0.16 eV) level to be 2 × 10-6 C/cm2 at 77 K that induces electric field ˜ 105 V/cm in a vicinity of QDs. The state at Ec - 0.22 eV is shown to be related to the recombination center that can hold non-equilibrium holes over a long time under the condition that the non-equilibrium holes are localized by the quantum states of QDs. In the course of long-term electron storage in a vicinity of QDs, an electron trapped at the (Ec - 0.16) eV level can be recaptured by a deeper spatially remote (Ec - 0.22 eV) level that allows the TSC peak observation at 106 K.

  20. Community metabolism in a deep (stratified) tropical reservoir during a period of high water-level fluctuations.

    PubMed

    Valdespino-Castillo, Patricia M; Merino-Ibarra, Martín; Jiménez-Contreras, Jorge; Castillo-Sandoval, Fermín S; Ramírez-Zierold, Jorge A

    2014-10-01

    As long as lakes and reservoirs are an important component of the global carbon cycle, monitoring of their metabolism is required, especially in the tropics. In particular, the response of deep reservoirs to water-level fluctuations (WLF) is an understudied field. Here, we study community metabolism through oxygen dynamics in a deep monomictic reservoir where high WLF (~10 m) have recently occurred. Simultaneous monitoring of environmental variables and zooplankton dynamics was used to assess the effects of WLF on the metabolism of the eutrophic Valle de Bravo (VB) reservoir, where cyanobacteria blooms are frequent. Mean gross primary production (P g) was high (2.2 g C m(-2) day(-1)), but temporal variation of P g was low except for a drastic reduction during circulation attributed to zooplankton grazing. The trophogenic layer showed net autotrophy on an annual basis, but turned to net heterotrophy during mixing, and furthermore when the whole water-column oxygen balance was calculated, considering the aphotic respiration (Raphotic). The high total respiration resulting (3.1 g C m(-2) day(-1)) is considered to be partly due to mixing enhanced by WLF. Net ecosystem production was equivalent to a net export of 3.4 mg CO₂ m(-2) day(-1) to the atmosphere. Low water levels are posed to intensify boundary-mixing events driven by the wind during the stratification in VB. Long-term monitoring showed changes in the planktonic community and a strong silicon decrease that matched with low water-level periods. The effects of low water-level on metabolism and planktonic community in VB suggest that water-level manipulation could be a useful management tool to promote phytoplankton groups other than cyanobacteria.

  1. Decomposition of groundwater level fluctuations using transfer modelling in an area with shallow to deep unsaturated zones

    NASA Astrophysics Data System (ADS)

    Gehrels, J. C.; van Geer, F. C.; de Vries, J. J.

    1994-05-01

    Time series analysis of the fluctuations in shallow groundwater levels in the Netherlands lowlands have revealed a large-scale decline in head during recent decades as a result of an increase in land drainage and groundwater withdrawal. The situation is more ambiguous in large groundwater bodies located in the eastern part of the country, where the unsaturated zone increases from near zero along the edges to about 40 m in the centre of the area. As depth of the unsaturated zone increases, groundwater level reacts with an increasing delay to fluctuations in climate and influences of human activities. The aim of the present paper is to model groundwater level fluctuations in these areas using a linear stochastic transfer function model, relating groundwater levels to estimated precipitation excess, and to separate artificial components from the natural groundwater regime. In this way, the impact of groundwater withdrawal and the reclamation of a 1000 km 2 polder area on the groundwater levels in the adjoining higher ground could be assessed. It became evident that the linearity assumption of the transfer functions becomes a serious drawback in areas with the deepest groundwater levels, because of non-linear processes in the deep unsaturated zone and the non-synchronous arrival of recharge in the saturated zone. Comparison of the results from modelling the influence of reclamation with an analytical solution showed that the lowering of groundwater level is partly compensated by reduced discharge and therefore is less than expected.

  2. Investigation of deep levels and precipitates related to molybdenum in silicon by DLTS and scanning infrared microscopy

    NASA Astrophysics Data System (ADS)

    Sandhu, A.; Ogikubo, T.; Goto, H.; Csapo, V.; Pavelka, T.

    2000-03-01

    We report on the properties of Si diffused with molybdenum (Mo) investigated using experimental techniques that included Fourier transform deep-level transient spectroscopy (FT-DLTS) and scanning infrared microscopy (SIRM). Samples were prepared using boron-doped float zone (1 0 0)Si wafers (100-400 Ω cm) and Mo was diffused into them by placing Mo powder onto the Si surface and annealing in a vacuum (8×10 -6 Torr) at temperatures between 400 and 800°C for 1-10 h. FT-DLTS measurements revealed that deep levels due to Mo ( Ev+0.29 eV) were only formed in samples when Mo was diffused above a threshold temperature of 650°C. SIRM imaging showed the presence of Mo-related precipitates having a density of 2.3×10 7-5.8×10 9 cm -3 near the surface region and iron-related precipitates having a density of 1.2×10 7-1.1×10 8 at a depth of 30 μm. The precipitate size was found to be strongly dependent on diffusion temperature and ranged between 50 and 100 nm as calculated from the scattered light intensity. The minority carrier lifetime was found to decrease with increasing density of iron traps that were unintentionally incorporated during the diffusion process.

  3. Deep electronic levels at growth interrupted interfaces in low-temperature-grown GaAs and the pressure dependence of these levels

    SciTech Connect

    Samara, G.A. ); Vook, D.W.; Gibbons, J.F. )

    1992-02-15

    Deep electronic energy levels associated with defects confined to interrupted growth interfaces of thin GaAs layers grown by low-temperature (720 K) metalorganic chemical vapor deposition using tertiarybutylarsine and subsequently annealed at 920 K for about 2 min were investigated by transient capacitance spectroscopy at both atmospheric pressure (1 bar) and hydrostatic pressures to 8 kbar. Samples grown under widely different As/Ga ratios in the gas phase were compared, and this ratio was found to have a strong influence on the levels observed. Most of these levels are characteristic of levels seen in GaAs grown from the vapor phase. Analysis of the pressure dependencies of the electron emission rates and capture cross sections shows that most of the levels move higher in energy with pressure and yields the activation volume which accompanies electron emission or capture. These features are unique signatures of the levels and provide new insights into the physics involved. One of the levels is identified as the midgap donor EL2. Its energy exhibits a relatively large increase with pressure, and a large inward (outward) volume relaxation accompanies electron emission (capture) of electrons from (by) it.

  4. Reactive impurities in excipients: profiling, identification and mitigation of drug-excipient incompatibility.

    PubMed

    Wu, Yongmei; Levons, Jaquan; Narang, Ajit S; Raghavan, Krishnaswamy; Rao, Venkatramana M

    2011-12-01

    Reactive impurities in pharmaceutical excipients could cause drug product instability, leading to decreased product performance, loss in potency, and/or formation of potentially toxic degradants. The levels of reactive impurities in excipients may vary between lots and vendors. Screening of excipients for these impurities and a thorough understanding of their potential interaction with drug candidates during early formulation development ensure robust drug product development. In this review paper, excipient impurities are categorized into six major classes, including reducing sugars, aldehydes, peroxides, metals, nitrate/nitrite, and organic acids. The sources of generation, the analytical method for detection, the stability of impurities upon storage and processing, and the potential reactions with drug candidates of these impurities are reviewed. Specific examples of drug-excipient impurity interaction from internal research and literature are provided. Mitigation strategies and corrective measures are also discussed.

  5. Quantum interference on electron scattering in graphene by carbon impurities in underlying h -BN

    NASA Astrophysics Data System (ADS)

    Kaneko, Tomoaki; Koshino, Mikito; Saito, Riichiro

    2017-03-01

    Electronic structures and transport properties of graphene on h -BN with carbon impurities are investigated by first-principles calculation and the tight-binding model. We show that the coupling between the impurity level and the graphene's Dirac cone sensitively depends on the impurity position, and in particular, it nearly vanishes when the impurity is located right below the center of the six membered ring of graphene. The Bloch phase factor at the Brillouin zone edge plays a decisive role in the cancellation of the hopping integrals. The impurity position dependence on the electronic structures of graphene on h -BN is investigated by the first-principles calculation, and its qualitative feature is well explained by a tight-binding model with graphene and a single impurity site. We also propose a simple one-dimensional chain-impurity model to analytically describe the role of the quantum interference in the position-dependent coupling.

  6. Growth temperature dependence of Si doping efficiency and compensating deep level defect incorporation in Al{sub 0.7}Ga{sub 0.3}N

    SciTech Connect

    Armstrong, Andrew M. Moseley, Michael W.; Allerman, Andrew A.; Crawford, Mary H.; Wierer, Jonathan J.

    2015-05-14

    The growth temperature dependence of Si doping efficiency and deep level defect formation was investigated for n-type Al{sub 0.7}Ga{sub 0.3}N. It was observed that dopant compensation was greatly reduced with reduced growth temperature. Deep level optical spectroscopy and lighted capacitance-voltage were used to understand the role of acceptor-like deep level defects on doping efficiency. Deep level defects were observed at 2.34 eV, 3.56 eV, and 4.74 eV below the conduction band minimum. The latter two deep levels were identified as the major compensators because the reduction in their concentrations at reduced growth temperature correlated closely with the concomitant increase in free electron concentration. Possible mechanisms for the strong growth temperature dependence of deep level formation are considered, including thermodynamically driven compensating defect formation that can arise for a semiconductor with very large band gap energy, such as Al{sub 0.7}Ga{sub 0.3}N.

  7. Deep uncertainty about the modes and tails of sea-level projections

    NASA Astrophysics Data System (ADS)

    Ruckert, Kelsey; Guan, Yawen; Forest, Chris; Keller, Klaus

    2015-04-01

    Sea-levels are generally rising around the world, posing nontrivial risks. Managing these risks hinges on sea-level rise projections and their associated uncertainties. Deriving sea-level projections presents nontrivial methodological challenges. Previous studies projecting sea-level rise have broken new ground, but typically adopt a single calibration method. Here we use a simple sea-level rise model to analyze and quantify the structural uncertainties driven by the choice of calibration method. In particular, we analyze a frequentist bootstrap method and a Bayesian approach (one with and one without the consideration of heteroskedastic errors). We show that the Bayesian approach with a heteroskedastic likelihood function performs best in hindcast experiments with respect to producing credible intervals with appropriate coverage. The choice of calibration method has considerable impacts on the modes and tails of the projections. Specifically, the modes vary across methods by more than 0.5 meters, in the year 2100. Arguably more important, the projected sea-levels with 1 in 100 and 1 in 10,000 exceedance probabilities vary by 2.5 and 3.5 meters. This structural uncertainty introduced by the choice of the statistical method has considerable implications for the design of sea-level rise adaptation strategies.

  8. Effect of antimony on the deep-level traps in GaInNAsSb thin films

    SciTech Connect

    Islam, Muhammad Monirul Miyashita, Naoya; Ahsan, Nazmul; Okada, Yoshitaka; Sakurai, Takeaki; Akimoto, Katsuhiro

    2014-09-15

    Admittance spectroscopy has been performed to investigate the effect of antimony (Sb) on GaInNAs material in relation to the deep-level defects in this material. Two electron traps, E1 and E2 at an energy level 0.12 and 0.41 eV below the conduction band (E{sub C}), respectively, were found in undoped GaInNAs. Bias-voltage dependent admittance confirmed that E1 is an interface-type defect being spatially localized at the GaInNAs/GaAs interface, while E2 is a bulk-type defect located around mid-gap of GaInNAs layer. Introduction of Sb improved the material quality which was evident from the reduction of both the interface and bulk-type defects.

  9. Influence of deep level defects on carrier lifetime in CdZnTe:In

    SciTech Connect

    Guo, Rongrong; Jie, Wanqi Wang, Ning; Zha, Gangqiang; Xu, Yadong; Wang, Tao; Fu, Xu

    2015-03-07

    The defect levels and carrier lifetime in CdZnTe:In crystal were characterized with photoluminescence, thermally stimulated current measurements, as well as contactless microwave photoconductivity decay (MWPCD) technique. An evaluation equation to extract the recombination lifetime and the reemission time from MWPCD signal is developed based on Hornbeck-Haynes trapping model. An excellent agreement between defect level distribution and carrier reemission time in MWPCD signal reveals the tail of the photoconductivity decay is controlled by the defect level reemission effect. Combining {sup 241}Am gamma ray radiation response measurement and laser beam induced transient current measurement, it predicted that defect level with the reemission time shorter than the collection time could lead to better charge collection efficiency of CdZnTe detector.

  10. Deep brain stimulation of the nucleus accumbens shell increases impulsive behavior and tissue levels of dopamine and serotonin.

    PubMed

    Sesia, Thibaut; Bulthuis, Vincent; Tan, Sonny; Lim, Lee Wei; Vlamings, Rinske; Blokland, Arjan; Steinbusch, Harry W M; Sharp, Trevor; Visser-Vandewalle, Veerle; Temel, Yasin

    2010-10-01

    The nucleus accumbens (NAc) is gaining interest as a target for deep brain stimulation (DBS) in refractory neuropsychiatric disorders with impulsivity as core symptom. The nucleus accumbens is composed of two subterritories, core and shell, which have different anatomical connections. In animal models, it has been shown that DBS of the NAc changes impulsive action. Here, we tested the hypothesis that a change in impulsive action by DBS of the NAc is associated with changes in dopamine levels. Rats received stimulating electrodes either in the NAc core or shell, and underwent behavioral testing in a reaction time task. In addition, in a second experiment, the effect of DBS of the NAc core and shell on extracellular dopamine and serotonin levels was assessed in the NAc and medial prefrontal cortex. Control subjects received sham surgery. We have found that DBS of the NAc shell stimulation induced more impulsive action but less perseverative checking. These effects were associated with increased levels of dopamine and serotonin in the NAc, but not in the medial prefrontal cortex. DBS of the NAc core had no effect on impulsive action, but decreased perseverative responses indicative of a better impulse control. In these subjects, no effects were found on neurotransmitter levels. Our data point out that DBS of the NAc shell has negative effects on impulsive action which is accompanied by increases of dopamine and serotonin levels in the NAc, whereas DBS of the NAc core has beneficial behavioral effects.

  11. Influence of surface states on deep level transient spectroscopy in AlGaN/GaN heterostructure

    NASA Astrophysics Data System (ADS)

    Qing, Zhu; Xiao-Hua, Ma; Wei-Wei, Chen; Bin, Hou; Jie-Jie, Zhu; Meng, Zhang; Li-Xiang, Chen; Yan-Rong, Cao; Yue, Hao

    2016-06-01

    Deep level transient spectroscopy (DLTS) as a method to investigate deep traps in AlGaN/GaN heterostructure or high electron mobility transistors (HEMTs) has been widely utilized. The DLTS measurements under different bias conditions are carried out in this paper. Two hole-like traps with active energies of E v + 0.47 eV, and E v + 0.10 eV are observed, which are related to surface states. The electron traps with active energies of E c - 0.56 eV are located in the channel, those with E c - 0.33 eV and E c - 0.88 eV are located in the AlGaN layer. The presence of surface states has a strong influence on the detection of electron traps, especially when the electron traps are low in density. The DLTS signal peak height of the electron trap is reduced and even disappears due to the presence of plentiful surface state. Project supported by the National Key Basic Research Program of China (Grant No. 2011CBA00606), the Program for New Century Excellent Talents in University, China (Grant No. NCET-12-0915), and the National Natural Science Foundation of China (Grant Nos. 61334002 and 61404097).

  12. Deep levels of vacancy-hydrogen centers in silicon studied by Laplace DLTS

    NASA Astrophysics Data System (ADS)

    Bonde Nielsen, K.; Dobaczewski, L.; Goscinski, K.; Bendesen, R.; Andersen, Ole; Bech Nielsen, B.

    1999-12-01

    We identify the acceptor levels (-/0) of the VH and V2H defects in silicon from comparison of DLTS and EPR annealing data. The levels are very close to each other and close to the acceptor level of the PV defect (the E-center) as well. In order to separate them, we have applied the high-resolution technique of Laplace DLTS and compared the formation and annealing properties of defects generated by implantation of hydrogen or helium. We further applied Laplace DLTS in combination with uniaxial stress to study the acceptor level at Ec-Et=0.31 eV previously assigned to a vacancy-hydrogen-oxygen defect. We find, in accordance with recent EPR measurements, that the defect displays orthorhombic-I symmetry and rule out that it contains two hydrogen atoms. The defect can be understood as a single hydrogen atom bound inside the A-center, the well-known VO defect of silicon, and we denote it VOH accordingly. The observed orthorhombic-I symmetry arises because the hydrogen atom (at T=160 K) swiftly jumps among two equivalent sites across the (1 1 0) plane that contains the Si-O-Si bond. Previous studies have shown that hydrogenation of oxygen-rich electron-irradiated samples leads to the formation of VOH with simultaneous depletion of the A-center. Our structural data are in accordance with this dynamic behavior.

  13. Deep-level study of Ga(In)P(NAs) alloys grown on Si substrates

    NASA Astrophysics Data System (ADS)

    Baranov, A. I.; Kleider, J. P.; Gudovskikh, A. S.; Darga, A.; Nikitina, E. V.; Egorov, A. Yu

    2016-08-01

    Defect properties of Ga(In)P(NAs) layers with different composition were studied by admittance spectroscopy. For nitrogen content layers the defect level with energy of 0.44-0.47 eV, which related to nitrogen incorporation into GaP, was observed. Its concentration is lower for GaPNAs layers compared to GaPN/InP due to better compensation by arsenic than by indium in lattice of GaP. Other defect level with energy of 0.30 eV was detected in GaPAs and GaPN/InP layers. Likely, the both observed defects in GaPAs and GaPN/InP have the same nature.

  14. Absolute pressure derivatives of deep level defects in III-V semiconductors

    SciTech Connect

    Nolte, D.D.; Walukiewicz, W.; Haller, E.E.

    1987-11-01

    Based on transition metal reference levels, we present absolute pressure derivatives for band-edges in GaAs and InP and defects in GaAs. The defect deformation potentials are directly related to the electron-lattice coupling which drives lattice relaxation around the defects. We find an exceedingly large inward lattice relaxation of the EL2 defect in GaAs upon electron emission. 12 refs., 1 fig.

  15. Impurity bubbles in a BEC

    NASA Astrophysics Data System (ADS)

    Timmermans, Eddy; Blinova, Alina; Boshier, Malcolm

    2013-05-01

    Polarons (particles that interact with the self-consistent deformation of the host medium that contains them) self-localize when strongly coupled. Dilute Bose-Einstein condensates (BECs) doped with neutral distinguishable atoms (impurities) and armed with a Feshbach-tuned impurity-boson interaction provide a unique laboratory to study self-localized polarons. In nature, self-localized polarons come in two flavors that exhibit qualitatively different behavior: In lattice systems, the deformation is slight and the particle is accompanied by a cloud of collective excitations as in the case of the Landau-Pekar polarons of electrons in a dielectric lattice. In natural fluids and gases, the strongly coupled particle radically alters the medium, e.g. by expelling the host medium as in the case of the electron bubbles in superfluid helium. We show that BEC-impurities can self-localize in a bubble, as well as in a Landau-Pekar polaron state. The BEC-impurity system is fully characterized by only two dimensionless coupling constants. In the corresponding phase diagram the bubble and Landau-Pekar polaron limits correspond to large islands separated by a cross-over region. The same BEC-impurity species can be adiabatically Feshbach steered from the Landau-Pekar to the bubble regime. This work was funded by the Los Alamos LDRD program.

  16. Interactive Sea Level Rise App & Online Viewer Offers Deep Dive Into Climate

    NASA Astrophysics Data System (ADS)

    Turrin, M.; Porter, D. F.; Ryan, W. B. F.; Pfirman, S. L.

    2015-12-01

    Climate has captured the attention of the public but its complexity can cause interested individuals to turn to opinion pieces, news articles or blogs for information. These platforms often oversimplify or present heavily interpreted or personalized perspectives. Data interactives are an extremely effective way to explore complex geoscience topics like climate, opening windows of understanding for the user that have previously been closed. Layering data onto maps through programs like GeoMapApp and the Earth Observer App has allowed users to dig directly into science data, but with only limited scaffolding. The interactive 'Polar Explorer: Sea Level Explorer App' provides a richly layered introduction to a range of topics connected to sea level rise. Each map is supported with a pop up and a short audio file of supplementary material, and an information page that includes the data source and links for further reading. This type of learning platform works well for both the formal and informal learning environment. Through science data displayed as map visualizations the user is invited into topics through an introductory question, such as "Why does sea level change?" After clicking on that question the user moves to a second layer of questions exploring the role of the ocean, the atmosphere, the contribution from the world's glaciers, world's ice sheets and other less obvious considerations such as the role of post-glacial rebound, or the mining of groundwater. Each question ends in a data map, or series of maps, that offer opportunities to interact with the topic. Under the role of the ocean 'Internal Ocean Temperature' offers the user a chance to touch to see temperature values spatially over the world's ocean, or to click through a data series starting at the ocean surface and diving to 5000 meters of depth showing how temperature changes with depth. Other sections, like the role of deglaciation of North America, allow the user to click and see change through

  17. Point Defects in Pb-, Bi-, and In-Doped CdZnTe Detectors: Deep-Level Transient Spectroscopy (DLTS) Measurements

    NASA Astrophysics Data System (ADS)

    Gul, R.; Keeter, K.; Rodriguez, R.; Bolotnikov, A. E.; Hossain, A.; Camarda, G. S.; Kim, K. H.; Yang, G.; Cui, Y.; Carcelen, V.; Franc, J.; Li, Z.; James, R. B.

    2012-03-01

    We studied, by current deep-level transient spectroscopy (I-DLTS), point defects induced in CdZnTe detectors by three dopants: Pb, Bi, and In. Pb-doped CdZnTe detectors have a new acceptor trap at around 0.48 eV. The absence of a VCd trap suggests that all Cd vacancies are compensated by Pb interstitials after they form a deep-acceptor complex [[PbCd]+-V{Cd/2-}]-. Bi-doped CdZnTe detectors had two distinct traps: a shallow trap at around 36 meV and a deep donor trap at around 0.82 eV. In detectors doped with In, we noted three well-known traps: two acceptor levels at around 0.18 eV (A-centers) and 0.31 eV (VCd), and a deep trap at around 1.1 eV.

  18. I- V and deep level transient spectroscopy studies on 60 MeV oxygen ion irradiated NPN transistors

    NASA Astrophysics Data System (ADS)

    Gnana Prakash, A. P.; Ke, S. C.; Siddappa, K.

    2004-02-01

    NPN transistors have been irradiated by 60 MeV oxygen ions in a fluence ranging from 5 × 10 10 to 1 × 10 13 ions/cm 2. The DC current gain ( hFE), excess base current ( ΔI B=I B post -I B pre ), excess collector current ( ΔI C=I C post -I C pre ) and collector saturation current (I C Sat ) of the ion irradiated transistors were studied systematically. The hFE of the transistors were found to be decreased drastically after ion irradiation. A significant increase has been observed in the collector current ( IC) along with the increase in the base current ( IB) after ion irradiation. The I C Sat of the ion irradiated transistors were also decreased significantly after irradiation. The radiation induced trap levels in the collector base depletion region of NPN transistors were studied by deep level transient spectroscopy technique and different types of trap levels were observed. The results obtained on the activation energy, density of trap levels, apparent capture cross section, introduction rate and space charge layer lifetime of different defects for different total fluence are presented and discussed.

  19. Investigation of defect properties in Cu(In,Ga)Se 2 solar cells by deep-level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Kerr, L. L.; Li, Sheng S.; Johnston, S. W.; Anderson, T. J.; Crisalle, O. D.; Kim, W. K.; Abushama, J.; Noufi, R. N.

    2004-09-01

    The performance of the chalcopyrite material Cu(In,Ga)Se 2 (CIGS) used as an absorber layer in thin-film photovoltaic devices is significantly affected by the presence of native defects. The deep-level transient spectroscopy (DLTS) technique is used in this work to characterize the defect properties, yielding relevant information about the defect types, their capture cross-sections, and energy levels and densities in the CIGS cells. Three solar cells developed using different absorber growth technologies were analyzed using DLTS, capacitance-voltage ( C- V), and capacitance-temperature ( C- T) techniques. It was found that CIS cells grown at the University of Florida exhibits a middle-gap defect level that may relate to the cell's low fill factor and open-circuit voltage values observed. A high efficiency ( ηc>18%) CIGS cell produced by the National Renewable Energy Laboratory (NREL) was found to contain three minority-carrier (electron) traps and a 13% CIGS cell produced by the Energy Photovoltaics Inc. (EPV) exhibited one majority (hole) trap. The approach followed using the DLTS technique serves as a paradigm for revealing the presence of significant defect levels in absorber materials, and may be used to support the identification of remedial processing operations.

  20. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    SciTech Connect

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; Campbell, J. M.

    2015-07-02

    In this study, an improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy(DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.

  1. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    NASA Astrophysics Data System (ADS)

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; Campbell, J. M.

    2015-07-01

    An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.

  2. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    SciTech Connect

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; Campbell, J. M.

    2015-07-07

    An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V{sub 2}) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.

  3. Afterpulsing model based on the quasi-continuous distribution of deep levels in single-photon avalanche diodes

    NASA Astrophysics Data System (ADS)

    Horoshko, D. B.; Chizhevsky, V. N.; Kilin, S. Ya.

    2017-01-01

    We have performed a statistical characterization of the effect of afterpulsing in a free-running silicon single-photon detector by measuring the distribution of afterpulse waiting times in response to pulsed illumination and fitting it by a sum of exponentials. We show that a high degree of goodness of fit can be obtained for 5 exponentials, but the physical meaning of estimated characteristic times is dubious. We show that a continuous limit of the sum of exponentials with a uniform density between the limiting times gives excellent fitting results in the full range of the detector response function. This means that in certain detectors the afterpulsing is caused by a continuous band of deep levels in the active area of the photodetector.

  4. Site selection and characterization processes for deep geologic disposal of high level nuclear waste

    SciTech Connect

    Costin, L.S.

    1997-10-01

    In this paper, the major elements of the site selection and characterization processes used in the US high level waste program are discussed. While much of the evolution of the site selection and characterization processes have been driven by the unique nature of the US program, these processes, which are well defined and documented, could be used as an initial basis for developing site screening, selection, and characterization programs in other countries. Thus, this paper focuses more on the process elements than the specific details of the US program.

  5. On the behaviour and origin of the major deep level (EL2) in GaAs

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Parsey, J. M.; Kaminska, M.; Wada, K.; Gatos, H. C.

    1982-01-01

    In an extensive crystal growth and characterization study of Bridgman-grown GaAs it was established that the following factors affect the concentration of the EL2 level: (1) the As pressure during growth; (2) the partial pressure of Ga2O; (3) the concentration of shallow donors and acceptors; and (4) the post-growth cooling cycle. The role of these factors is qualitatively and quantitatively explained by attributing the 0.82 eV donor state to the antisite defect As-sub-Ga formed as a result of Ga-vacancy migration during the post-growth cooling of the crystals.

  6. Characterization of high fluence neutron induced defect levels in high resistivity silicon detectors using a laser deep level transient spectroscopy (L-DLTS)

    NASA Astrophysics Data System (ADS)

    Chengji, Li; Li, Zheng

    1994-03-01

    Neutron irradiated high resistivity (4-6 kΩ-cm) silicon detectors in the neutron fluence ( Φn) range of 5 × 10 11 n/cm 2 to 1 × 10 14 n/cm 2 have been studied using a laser deep level transient spectroscopy (L-DLTS). It has been found that the A-center (oxygen-vacancy, Ec = 0.17 eV) concentration increases with neutron fluence, reaching a maximum at Φn ≈ 5×10 12 n/cm 2 before decreasing with Φn. A broad peak has been found between 200 K and 300 K, which is the result of the overlap of three single levels: the V-V - ( Ec = 0.38 eV), the E-center (P-v, Ec = 0.44 eV), and a level at Ec = 0.56 eV that is probably V-V 0. At low neutron fluences ( Φn < 5 × 10 12 n/cm 2), this broad peak is dominated by V-V - and the E-centers. However, as the fluence increases ( Φn ≥ 5 × 10 12 n/cm 2), the peak becomes dominated by the level of Ec = 0.56 eV.

  7. Identification of intrinsic deep level defects responsible for electret behavior in TlGaSe2 layered semiconductor

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Mikailzade, Faik A.; Uzun, Talip; Odrinsky, Andrei P.; Yakar, Emin; Aliyeva, Vafa B.; Babayev, Sardar S.; Mammadov, Tofig G.

    2016-02-01

    Unusual behavior of pyroelectric current signal polarity near the Curie point (Tc) was observed for TlGaSe2 a ferroelectric-semiconductor. It has been revealed that the polarity of the spontaneous polarization near Tc depends on the sample poling prehistory. In particular, applying an external electric field only in the temperature range of the paraelectric state during cooling regime in darkness brought to the depolarization current at Tc with the sign opposite to the external field polarity. Otherwise, if the sample was poled in the temperature interval of the incommensurate phase, pyroelectric current exhibits a peak at Tc with the polarity that is the same as for the external poling electric field. These observations indicate that internal electric field is present in the bulk and near-surface layer regions of the electrically poled single crystal TlGaSe2. Possible mechanisms and origins responsible for the internal electric fields in TlGaSe2 are discussed. It is shown that the formation of internal electric fields in TlGaSe2 is due to charging of intrinsic native defects during the poling process. Characteristics of electrically active intrinsic defects in TlGaSe2 were investigated by using of Photo-Induced Current Transient Spectroscopy (PICTS) technique. Six deep defect levels in the band gap of TlGaSe2 were determined, which were localized both in the bulk and on the surface of the sample and could be electrically charged. The correlation between polarization effects and PICTS results has been established. It was shown that native deep defects (A3-A6) localized in the bulk of crystal are responsible for hetero-charge formation and negative sign of the pyroelectric current peak observed around the Curie temperature after poling the sample in the temperature intervals well above Tc. It was also shown that the positive sign pyrocurrent observed near the Curie point is attributed to the homo-charge formed by native A2-trapping centers which are localized near

  8. Individual and Partner-Level Factors Associated with Condom Non-Use Among African American STI Clinic Attendees in the Deep South: An Event-Level Analysis.

    PubMed

    Marshall, Brandon D L; Perez-Brumer, Amaya G; MacCarthy, Sarah; Mena, Leandro; Chan, Philip A; Towey, Caitlin; Barnett, Nancy; Parker, Sharon; Barnes, Arti; Brinkley-Rubinstein, Lauren; Rose, Jennifer S; Nunn, Amy S

    2016-06-01

    The US HIV/AIDS epidemic is concentrated in the Deep South, yet factors contributing to HIV transmission are not fully understood. We examined relationships between substance use, sexual partnership characteristics, and condom non-use in an African American sample of STI clinic attendees in Jackson, Mississippi. We assessed condom non-use at last intercourse with up to three recent sexual partners reported by participants between January and June 2011. Participant- and partner-level correlates of condom non-use were examined using generalized estimating equations. The 1295 participants reported 2880 intercourse events, of which 1490 (51.7 %) involved condom non-use. Older age, lower educational attainment, reporting financial or material dependence on a sex partner, sex with a primary partner, and higher frequency of sex were associated with increased odds of condomless sex. HIV prevention efforts in the South should address underlying socioeconomic disparities and structural determinants that result in partner dependency and sexual risk behavior.

  9. Modeling of concrete carbonation in deep geological disposal of intermediate level waste

    NASA Astrophysics Data System (ADS)

    Thouvenot, P.; Bildstein, O.; Munier, I.; Cochepin, B.; Poyet, S.; Bourbon, X.; Treille, E.

    2013-07-01

    Simulations of atmospheric carbonation of Intermediate-Level Long-lived radioactive Waste (ILLW) concrete packages were conducted to evaluate their possible chemical degradations. Two-phase liquid water-air flow is combined with gas component diffusion processes leading to a progressive drying of the concrete.Complete drying of the 11 cm thick waste disposal package wall occurs over a period ranging from 2 years for the low-performance concrete to 10 years for the high-performance concrete. The drying process slows down when transport characteristics of concretes are enhanced. Carbonation depths in the order of 2 to 3 cm in 100 years are predicted for this cementitious component. However, these values are slightly overestimated compared to experimental data. Also the kinetic model of mineral reactivity requires improvements with respect to the protective effect of secondary carbonates and to thermodynamic data.

  10. Dumping of low-level radioactive waste in the deep ocean

    SciTech Connect

    Templeton, W.L.

    1980-01-01

    Two international agreements relate to the dumping of packaged radioactive waste into the oceans - the Convention on the Prevention of Marine Pollution by Dumping Wastes and Other Matter of 1972 (London Convention) and the Multilateral Consultation and Surveillance Mechanism for Sea Dumping of Radioactive Waste of 1977 under the Organization for Economic Co-operation and Development (OECD). The International Atomic Energy Agency was given the responsibility to define high-level radioactive wastes which are unsuitable for dumping in the oceans and to make recommendations for the dumping of other radioactive wastes. A revised Definition and Recommendations was submitted and accepted by the London Convention. This paper reviews the technical basis for the Definition and describes how it has been applied to the radiological assessment of the only operational dumping site in the North East Atlantic.

  11. EFFECT OF FUEL IMPURITIES ON FUEL CELL PERFORMANCE AND DURABILITY

    SciTech Connect

    Colon-Mercado, H.

    2010-09-28

    A fuel cell is an electrochemical energy conversion device that produces electricity during the combination of hydrogen and oxygen to produce water. Proton exchange membranes fuel cells are favored for portable applications as well as stationary ones due to their high power density, low operating temperature, and low corrosion of components. In real life operation, the use of pure fuel and oxidant gases results in an impractical system. A more realistic and cost efficient approach is the use of air as an oxidant gas and hydrogen from hydrogen carriers (i.e., ammonia, hydrocarbons, hydrides). However, trace impurities arising from different hydrogen sources and production increases the degradation of the fuel cell. These impurities include carbon monoxide, ammonia, sulfur, hydrocarbons, and halogen compounds. The International Organization for Standardization (ISO) has set maximum limits for trace impurities in the hydrogen stream; however fuel cell data is needed to validate the assumption that at those levels the impurities will cause no degradation. This report summarizes the effect of selected contaminants tested at SRNL at ISO levels. Runs at ISO proposed concentration levels show that model hydrocarbon compound such as tetrahydrofuran can cause serious degradation. However, the degradation is only temporary as when the impurity is removed from the hydrogen stream the performance completely recovers. Other molecules at the ISO concentration levels such as ammonia don't show effects on the fuel cell performance. On the other hand carbon monoxide and perchloroethylene shows major degradation and the system can only be recovered by following recovery procedures.

  12. ALUMINUM IMPURITY DIFFUSION IN MAGNESIUM

    SciTech Connect

    Brennan, Sarah; Warren, Andrew; Coffey, Kevin; Kulkarni, Nagraj S; Todd, Peter J; Sohn, Yong Ho; Klimov, Mikhail

    2012-01-01

    The Al impurity diffusion in polycrystalline Mg (99.9%) via depth profiling with secondary ion mass spectrometry was studied in the temperature range of 673-573K, utilizing the thin film method and thin film solution to the diffusion equation. Multiple samples were utilized and multiple profiles were obtained to determine statistically confident coefficient with maximum standard deviation of 16%. Activation energy and pre-exponential factor of Al impurity diffusion in Mg was determined as 155 kJ/mole and 3.9 x 10-3 m2/sec.

  13. Low-cost, high-precision micro-lensed optical fiber providing deep-micrometer to deep-nanometer-level light focusing.

    PubMed

    Wen, Sy-Bor; Sundaram, Vijay M; McBride, Daniel; Yang, Yu

    2016-04-15

    A new type of micro-lensed optical fiber through stacking appropriate high-refractive microspheres at designed locations with respect to the cleaved end of an optical fiber is numerically and experimentally demonstrated. This new type of micro-lensed optical fiber can be precisely constructed with low cost and high speed. Deep micrometer-scale and submicrometer-scale far-field light spots can be achieved when the optical fibers are multimode and single mode, respectively. By placing an appropriate teardrop dielectric nanoscale scatterer at the far-field spot of this new type of micro-lensed optical fiber, a deep-nanometer near-field spot can also be generated with high intensity and minimum joule heating, which is valuable in high-speed, high-resolution, and high-power nanoscale detection compared with traditional near-field optical fibers containing a significant portion of metallic material.

  14. Forced diffusion of impurities in natural diamond and polycrystalline diamond films

    NASA Astrophysics Data System (ADS)

    Popovici, Galina; Sung, T.; Khasawinah, S.; Prelas, M. A.; Wilson, R. G.

    1995-06-01

    A method is proposed for the determination of the state of an impurity (donor, acceptor, or deep level) in semiconductor lattice. To demonstrate the method boron was diffused into type Ia natural diamond under a dc electric field. The concentration and diffusion profiles of boron were affected by the applied field. Boron diffuses as a negative ion since it is an acceptor shallow enough to be partially ionized at the temperature of diffusion. The drift velocity of boron ions at the temperature of diffusion was also estimated. The diffusion of lithium and oxygen from a Li2CO3 source in chemical vapor deposited diamond films was performed under bias at 1000 °C in an argon atmosphere. After diffusion, the concentrations of Li, O, and H in the diamond films were found to be around (3-4)×1019 cm-3. No dependence of these concentrations on the applied bias was observed. It was found that the diffusion of Li goes primarily through grain boundaries, which may explain why it does not depend on the applied voltage. Fluorine was present as an impurity in the dopant source. Its concentration in the films was around (1-2)×1017 cm-3 and did depend on the applied bias, indicating that fluorine may have formed a shallow level in the diamond band gap.

  15. Protein phylogenies robustly resolve the deep-level relationships within Euglenozoa.

    PubMed

    Simpson, Alastair G B; Roger, Andrew J

    2004-01-01

    The deepest-level relationships amongst Euglenozoa remain poorly resolved, despite a rich history of morphological examination and numerous molecular phylogenetic studies of small subunit ribosomal RNA (SSU rRNA) data. We address this question using two nuclear-encoded proteins, the cytosolic isoforms of heat shock protein 90 (hsp90) and heat shock protein 70 (hsp70). For both proteins we examined sequences from the three primary groups within Euglenozoa (euglenids, diplonemids, and kinetoplastids), and from their close relatives, Heterolobosea. Maximum likelihood (ML) and ML distance analyses of these proteins support a close relationship between diplonemids and kinetoplastids to the exclusion of the euglenid Euglena gracilis. In hsp90 and combined protein analyses bootstrap support is very strong and alternative topologies are generally rejected by 'approximately unbiased' (AU) tests. This result is consistent with recent molecular biological and morphological data, but contradicts early structural accounts and many SSU rRNA analyses that favour a closer relationship between diplonemids and euglenids. However, a re-examination of an important SSU rRNA data set highlights the instability of the inferences from this marker. The protein analyses also suggest that bodonids are paraphyletic, with trypanosomatids grouping with 'clade 2' and 'clade 3' bodonids to the exclusion of 'clade 1' bodonids.

  16. Precision liquid-level measurement in deep tanks using a swept-RF resonant cavity

    NASA Astrophysics Data System (ADS)

    Piper, T. C.

    1992-03-01

    The Idaho Chemical Processing Plant (ICPP) has several large, temporary-liquid-storage tanks (50 feet diameter and 30 feet height). The tanks are located in separate underground cells. Because of the huge tank storage capacity per inch (1225 gallons), extremely accurate liquid depth measurement is required to observe normal additions (or to become aware of other than large leaks). In roughly 1970, Glenn Booman, then the header of the advanced instrumentation group of ICPP, began a program to develop what in a few years became known as 'IRF tank probes'. The initial probe was installed in tank WM-189 in 1975 and ten more were installed in other tanks in 1976. Though the RF components were fairly costly at that time, they were readily available and the system has, in general, operated without incident. Three of the most desirable features of the system not found in most other continuous reading level systems are that it exhibits no hysteresis, no creep and requires no calibration. In the years since installation the RF distribution system has been upgraded and the method of data processing has been changed somewhat. Presently, the need for more probes for more tanks has renewed interest. The original development work was never fully documented. The present talk is taken from a report being written to comprehensively describe the theory and operation of the RF probe.

  17. High-barrier Schottky contact on n-type 4H-SiC epitaxial layer and studies of defect levels by deep level transient spectroscopy (DLTS)

    NASA Astrophysics Data System (ADS)

    Nguyen, Khai V.; Pak, Rahmi O.; Oner, Cihan; Mannan, Mohammad A.; Mandal, Krishna C.

    2015-08-01

    High barrier Schottky contact has been fabricated on 50 μm n-type 4H-SiC epitaxial layers grown on 350 μm thick substrate 8° off-cut towards the [11̅20] direction. The 4H-SiC epitaxial wafer was diced into 10 x 10 mm2 samples. The metal-semiconductor junctions were fabricated by photolithography and dc sputtering with ruthenium (Ru). The junction properties were characterized through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Detectors were characterized by alpha spectroscopy measurements in terms of energy resolution and charge collection efficiency using a 0.1 μCi 241Am radiation source. It was found that detectors fabricated from high work function rare transition metal Ru demonstrated very low leakage current and significant improvement of detector performance. Defect characterization of the epitaxial layers was conducted by deep level transient spectroscopy (DLTS) to thoroughly investigate the defect levels in the active region. The presence of a new defect level induced by this rare transition metal-semiconductor interface has been identified and characterized.

  18. Thermal evolution and exhumation of deep-level batholithic exposures, southernmost Sierra Nevada, California

    USGS Publications Warehouse

    Saleeby, J.; Farley, K.A.; Kistler, R.W.; Fleck, R.J.

    2007-01-01

    The Tehachapi complex lies at the southern end of the Sierra Nevada batholith adjacent to the Neogene-Quaternary Garlock fault. The complex is composed principally of high-pressure (8-10 kbar) Cretaceous batholithic rocks, and it represents the deepest exposed levels of a continuous oblique crustal section through the southern Sierra Nevada batholith. Over the southern ???100 km of this section, structural/petrologic continuity and geochronological data indicate that ???35 km of felsic to intermediate-composition crust was generated by copious arc magmatism primarily between 105 and 99 Ma. In the Tehachapi complex, these batholithic rocks intrude and are bounded to the west by similar-composition gneissic-textured high-pressure batholithic rocks emplaced at ca. 115-110 Ma. This lower crustal complex is bounded below by a regional thrust system, which in Late Cretaceous time tectonically eroded the underlying mantle lithosphere, and in series displaced and underplated the Rand Schist subduction assemblage by low-angle slip from the outboard Franciscan trench. Geophysical and mantle xenolith studies indicate that the remnants of this shallow subduction thrust descend northward through the crust and into the mantle, leaving the mantle lithosphere intact beneath the greater Sierra Nevada batholith. This north-dipping regional structure records an inflection in the Farallon plate, which was segmented into a shallow subduc-tion trajectory to the south and a normal steeper trajectory to the north. We combine new and published data from a broad spectrum of thermochronom-eters that together form a coherent data array constraining the thermal evolution of the complex. Integration of these data with published thermobarometric and petro-genetic data also constrains the tectonically driven decompression and exhumation history of the complex. The timing of arc magmatic construction of the complex, as denoted above, is resolved by a large body of U/Pb zircon ages. High

  19. Determination of localized trap parameters in organic semiconductors using charge based deep level transient spectroscopy (Q-DLTS)

    NASA Astrophysics Data System (ADS)

    Nguyen, T. P.; Ip, J.; Gaudin, O.; Jackman, R. B.

    2004-07-01

    In organic light emitting diodes (OLEDs), localized traps within the band gap of the organic semiconductor play a fundamental role in the light emission process. Trapped charge carriers cannot recombine efficiently and therefore do not contribute to the emission. The determination of the trap parameters in the emitting layer is especially important in the evaluation of the efficiency of such devices. We have investigated the trap parameters in some organic semiconductors using the Charge-Based Deep Level Transient Spectroscopy (Q-DLTS) technique. Examples are given in poly(p phenylene vinylene) or PPV and 4, 4'-bis(4-dimethylaminostryryl) or DMASB, for which the trap level, the trap density, and the capture cross section were determined. In addition, it was possible to identify the carrier type (minority and majority) traps in these semiconductors. The results were compared with those obtained in similar materials by other techniques such as conventional DLTS, thermally stimulated currents (TSC), impedance measurements. Q-DLTS appears to be a powerful tool for studying defects in organic semiconductors.

  20. Control of impurities in toroidal plasma devices

    DOEpatents

    Ohkawa, Tihiro

    1980-01-01

    A method and apparatus for plasma impurity control in closed flux plasma systems such as Tokamak reactors is disclosed. Local axisymmetrical injection of hydrogen gas is employed to reverse the normally inward flow of impurities into the plasma.

  1. Thermal stability of deep level defects induced by high energy proton irradiation in n-type GaN

    SciTech Connect

    Zhang, Z.; Farzana, E.; Sun, W. Y.; Arehart, A. R.; Ringel, S. A.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; McSkimming, B.; Kyle, E. C. H.; Speck, J. S.

    2015-10-21

    The impact of annealing of proton irradiation-induced defects in n-type GaN devices has been systematically investigated using deep level transient and optical spectroscopies. Moderate temperature annealing (>200–250 °C) causes significant reduction in the concentration of nearly all irradiation-induced traps. While the decreased concentration of previously identified N and Ga vacancy related levels at E{sub C} − 0.13 eV, 0.16 eV, and 2.50 eV generally followed a first-order reaction model with activation energies matching theoretical values for N{sub I} and V{sub Ga} diffusion, irradiation-induced traps at E{sub C} − 0.72 eV, 1.25 eV, and 3.28 eV all decrease in concentration in a gradual manner, suggesting a more complex reduction mechanism. Slight increases in concentration are observed for the N-vacancy related levels at E{sub C} − 0.20 eV and 0.25 eV, which may be due to the reconfiguration of other N-vacancy related defects. Finally, the observed reduction in concentrations of the states at E{sub C} − 1.25 and E{sub C} − 3.28 eV as a function of annealing temperature closely tracks the detailed recovery behavior of the background carrier concentration as a function of annealing temperature. As a result, it is suggested that these two levels are likely to be responsible for the underlying carrier compensation effect that causes the observation of carrier removal in proton-irradiated n-GaN.

  2. Entanglement in quantum impurity problems is nonperturbative

    NASA Astrophysics Data System (ADS)

    Saleur, H.; Schmitteckert, P.; Vasseur, R.

    2013-08-01

    We study the entanglement entropy of a region of length 2L with the remainder of an infinite one-dimensional gapless quantum system in the case where the region is centered on a quantum impurity. The coupling to this impurity is not scale invariant, and the physics involves a crossover between weak- and strong-coupling regimes. While the impurity contribution to the entanglement has been computed numerically in the past, little is known analytically about it, since in particular the methods of conformal invariance cannot be applied because of the presence of a crossover length. We show in this paper that the small coupling expansion of the entanglement entropy in this problem is quite generally plagued by strong infrared divergences, implying a nonperturbative dependence on the coupling. The large coupling expansion turns out to be better behaved, thanks to powerful results from the boundary CFT formulation and, in some cases, the underlying integrability of the problem. However, it is clear that this expansion does not capture well the crossover physics. In the integrable case—which includes problems such as an XXZ chain with a modified link, the interacting resonant level model or the anisotropic Kondo model—a nonperturbative approach is in principle possible using form factors. We adapt in this paper the ideas of Cardy [J. Stat. Phys.JSTPBS0022-471510.1007/s10955-007-9422-x 130, 129 (2008)] and Castro-Alvaredo and Doyon [J. Stat. Phys.JSTPBS0022-471510.1007/s10955-008-9664-2 134, 105 (2009)] to the gapless case and show that, in the rather simple case of the resonant level model, and after some additional renormalizations, the form-factors approach yields remarkably accurate results for the entanglement all the way from short to large distances. This is confirmed by detailed comparison with numerical simulations. Both our form factor and numerical results are compatible with a nonperturbative form at short distance.

  3. Space charge suppression induced by deep traps in polyethylene/zeolite nanocomposite

    NASA Astrophysics Data System (ADS)

    Han, Bai; Wang, Xuan; Sun, Zhi; Yang, Jiaming; Lei, Qingquan

    2013-01-01

    NaY zeolite nanoparticles doped in low-density polyethylene (LDPE) is investigated. The zeolite nanoparticles are uniformly distributed in LDPE. Space charge distribution from pulsed electro-acoustic method and trap level from thermally stimulated current test are obtained. The results indicate that zeolite doping enormously suppresses space charge accumulation and reduces the conduction current by importing abundant deep traps. It can be explained that the zeolite nanoparticles increase the interface regions and introduce small size cavity traps from the porous surface of zeolite. The deep traps greatly weaken impurity ionization and carrier mobility, and raise potential barrier for charge injection.

  4. Effect of deep trapping states on space charge suppression in polyethylene/ZnO nanocomposite

    NASA Astrophysics Data System (ADS)

    Tian, Fuqiang; Lei, Qingquan; Wang, Xuan; Wang, Yi

    2011-10-01

    This letter intends to reveal the mechanism of space charge suppression in low density polyethylene (LDPE)/ZnO nanocomposites. Trap level and space charge distributions were obtained from modified isothermal discharge current method and pulsed electro-acoustic (PEA) method, respectively. The results showed that ZnO nanoparticle doping introduced large amounts of deep trapping states, significantly reduced space charge accumulation and conduction current. The results can be explained in terms of deep trapping states resulted from the interface regions and morphology structure changes by nanoparticles doping, which greatly reduced the charge mobility, raised the charge injection potential at the contact and weakened impurity ionization.

  5. Interactions between impurities and breather-pairs in a nonlinear lattice

    NASA Astrophysics Data System (ADS)

    Lin, Han; Chen, Weizhong; Lu, Lei; Wei, Rongjue

    2003-09-01

    Based on the Frenkel-Kontorova (FK) model with a δ-impurity, this Letter investigates the interactions between impurities and breather-pairs in a nonlinear pendulum chain driven by a vertical vibration. The numerical results show that a long impurity in pendulum length can absorb more energy into the chain and upgrade the energy level of the breather-pair, when the driving frequency is slight lower than that of parametric resonance of the perfect pendulums, while a short one plays a counteractive role. As the chain is driven at a higher frequency, the effect of impurities turns reverse, which shows a clear symmetry and equivalency between long and short impurities. The main results including the effect and the symmetry of impurities generalize the conclusion on the single breather to the breather-pair.

  6. Correlation between barrier inhomogeneities of 4H-SiC 1 A/600 V Schottky rectifiers and deep-level defects revealed by DLTS and Laplace DLTS

    NASA Astrophysics Data System (ADS)

    Gelczuk, Ł.; Kamyczek, P.; Płaczek-Popko, E.; Dąbrowska-Szata, M.

    2014-09-01

    Electrical properties of commercial silicon carbide (SiC) Schottky rectifiers are investigated through the measurement and analysis of the forward current-voltage (I-V) and reverse capacitance-voltage (C-V) characteristics in a large temperature range. Some of devices show distinct discrepancies in specific ranges of their electrical characteristics, especially the excess current dominates at voltage <1 V and temperature <300 K. Standard deep level transient spectroscopy (DLTS) revealed the presence of a single deep-level defect with activation energy of about 0.3 eV, exhibiting the features characteristic for extended defects (e.g. dislocations), such as logarithmic capture kinetics. Furthermore, high-resolution Laplace DLTS showed that this deep level consists actually of three closely spaced levels with activation energies ranging from about 0.26 eV to 0.29 eV. A strong correlation between these two techniques implies that the revealed trap level is due to extended defects surrounded by point traps or clusters of defects. On the basis of obtained specific features of the deep-level defect, it was proposed that this defect is arguably responsible for the observed Schottky barrier inhomogeneities.

  7. Deep-level transient spectroscopy and electrical characterization of ion-implanted p-n junctions into undoped InP

    NASA Astrophysics Data System (ADS)

    Martin, Jaime M.; García, S.; Mártil, I.; González-Díaz, G.; Castán, E.; Dueñas, S.

    1995-11-01

    Current-voltage, small-signal measurements, and deep-level transient spectroscopy (DLTS) spectra of p-n junctions made by Mg implantation into undoped InP are described. The I-V characteristics show that the dominant conduction mechanism at forward bias is recombination in the space-charge zone, whereas a thermally activated tunneling mechanism involving a trap at 0.32 eV dominates at reverse bias. Five deep levels located in the upper-half of the band gap were detected in the junctions by DLTS measurements, three of which (at 0.6, 0.45, and 0.425 eV) were found to appear due to rapid thermal annealing. The origin of the other two levels, at 0.31 and 0.285 eV, can be ascribed to implantation damage. Admittance spectroscopy measurements showed the presence of three levels at 0.44, 0.415, and 0.30 eV, all in agreement with those found by DLTS. The DLTS measurements showed that the concentration of deep levels decreased after longer annealing times, and that the concentration of deep levels due to the implantation increased after additional P or Si implantations. This explains the influence of annealing time and additional implantations on the I-V characteristics of the junctions.

  8. Detection of surface impurity phases in high T.sub.C superconductors using thermally stimulated luminescence

    DOEpatents

    Cooke, D. Wayne; Jahan, Muhammad S.

    1989-01-01

    Detection of surface impurity phases in high-temperature superconducting materials. Thermally stimulated luminescence has been found to occur in insulating impurity phases which commonly exist in high-temperature superconducting materials. The present invention is sensitive to impurity phases occurring at a level of less than 1% with a probe depth of about 1 .mu.m which is the region of interest for many superconductivity applications. Spectroscopic and spatial resolution of the emitted light from a sample permits identification and location of the impurity species. Absence of luminescence, and thus of insulating phases, can be correlated with low values of rf surface resistance.

  9. Fundamental aspects of metallic impurities and impurity interactions in silicon during device processing

    SciTech Connect

    Graff, K.

    1995-08-01

    A review on the behavior of metallic impurities in silicon can be considerably simplified by a restriction on pure, dislocation-free, monocrystalline silicon. In this case interactions between different impurities and between impurities and grown-in lattice defects can be reduced. This restriction is observed in Chapter 1 for discussing the general behavior of metallic impurities in silicon.

  10. Impurity control studies using SOL flow in DIII-D

    SciTech Connect

    Wade, M.R.; Hogan, J.T.; Isler, R.C.

    1998-11-01

    Experiments on DIII-D have demonstrated the efficacy of using induced scrape-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL flow is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using a modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative ELMing H-mode plasmas have been produced that combine high radiation losses (P{sub rad}/P{sub input} > 70%), low core fuel dilution (Z{sub eff} < 1.9), and good core confinement ({tau}{sub E} > 1.0 {tau}{sub E},ITER93H).

  11. Study of the effects of impurities on the properties of silicon solar cell

    NASA Technical Reports Server (NTRS)

    Sah, C. T.

    1981-01-01

    The effect of defects across the back-surface-field junction on the performance of high efficiency and thin solar cells, using a developed-perimeter device model for the three-dimensional defects is investigated. Significant degradation of open-circuit voltage can occur even if there are only a few defects distributed in the bulk of the solar cell. Two features in the thickness dependences of the fill factor and efficiency in impurity-doped back-surface-field solar cells are discovered in the exact numerical solution which are associated with the high injection level effect in the base and not predicted by the low-level analytical theory. What are believed to be the most accurate recombination parameters at the Ti center to date are also given and a theory is developed which is capable of distinguishing an acceptor-like deep level from a donor-like deep level using the measured values of the thermal emission and capture cross sections.

  12. Impurity/defect interactions during MeV Si{sup +} ion implantation annealing

    SciTech Connect

    Agarwal, A.; Koveshnikov, S.; Christensen, K.

    1995-08-01

    Ion implantation of dopant atoms at MeV energies is currently being explored in several integrated circuit device manufacturing processes. MeV implantation offers immediate advantages such as vertical well modulation, latch-up protection, device structure isolation, and reduced temperature processing. Simultaneously, it presents an opportunity to achieve {open_quotes}proximity{close_quotes} gettering of impurities from the active device region by placing high impurity solubility and/or secondary defect gettering sites within microns of the surface. If the MeV implanted species is a dopant ion, all three gettering mechanisms, i.e, segregation, relaxation and injection, can be involved in the gettering process, complicating the analysis and optimization of the process. However, investigation of gettering using non-dopant Si{sup +} ion damage allows the relaxation component of the gettering process to be isolated and examined separately. In general, gettering is verified by a reduction in impurity concentration in the region of interest, usually the device region, and/or a build-up of concentration/precipitation in a non-device sink region. An alternate and more meaningful approach is to use simple devices as materials characterization probes via changes in the electrical activity of the gettering sites. Device space charge probes also allow the evolution of the defect sites upon contamination to be tracked. We report here results of the electrical, structural, and chemical characterization of MeV implanted Si{sup +} damage using Deep Level Transient Spectroscopy (DLTS), Transmission Electron Microscopy (TEM), and Secondary Ion Mass Spectroscopy (SIMS). The damage has been characterized both as a function of annealing from 600 to 1100{degrees}C for 1 hr, and after contamination with Fe followed by low temperature gettering annealing.

  13. Observation of impurity accumulation and concurrent impurity influx in PBX

    SciTech Connect

    Sesnic, S.S.; Fonck, R.J.; Ida, K.; Bol, K.; Couture, P.; Gammel, G.; Kaita, R.; Kaye, S.; Kugel, H.; LeBlanc, B.

    1986-07-01

    Impurity studies in L- and H-mode discharges in PBX have shown that both types of discharges can evolve into either an impurity accumulative or nonaccumulative case. In a typical accumulative discharge, Zeff peaks in the center to values of about 5. The central metallic densities can be high, n/sub met//n/sub e/ approx. = 0.01, resulting in central radiated power densities in excess of 1 W/cm/sup 3/, consistent with bolometric estimates. The radial profiles of metals obtained independently from the line radiation in the soft x-ray and the VUV regions are very peaked. Concurrent with the peaking, an increase in the impurity influx coming from the edge of the plasma is observed. At the beginning of the accumulation phase the inward particle flux for titanium has values of 6 x 10/sup 10/ and 10 x 10/sup 10/ particles/cm/sup 2/s at minor radii of 6 and 17 cm. At the end of the accumulation phase, this particle flux is strongly increased to values of 3 x 10/sup 12/ and 1 x 10/sup 12/ particles/cm/sup 2/s. This increased flux is mainly due to influx from the edge of the plasma and to a lesser extent due to increased convective transport. Using the measured particle flux, an estimate of the diffusion coefficient D and the convective velocity v is obtained.

  14. On the relation between deep level compensation, resistivity and electric field in semi-insulating CdTe:Cl radiation detectors

    NASA Astrophysics Data System (ADS)

    Cola, Adriano; Farella, Isabella; Pousset, Jeremy; Valletta, Antonio

    2016-12-01

    A compensation model for semi-insulating CdTe:Cl based on a single dominant deep level 0.725 eV above the valence band is proposed. The model is corroborated by experimental evidence: resistivity measurements as a function of temperature on bulk crystals and stationary electric field distributions in Ohmic/Schottky radiation detectors, obtained by the Pockels effect. The latter are in close agreement with the numerical solutions of transport equations when considering the deep centre concentration in the range 2 - 4 × 1012 cm-3, and a compensation ratio R = 2.1, this one being consistent with an original ambipolar analysis of resistivity. More generally, the approach elucidates the role of electrical contacts and deep levels in controlling the electric fields in devices based on compensated materials.

  15. Injection deep level transient spectroscopy: An improved method for measuring capture rates of hot carriers in semiconductors

    DOE PAGES

    Fleming, R. M.; Seager, C. H.; Lang, D. V.; ...

    2015-07-02

    In this study, an improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy(DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capturemore » cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices.« less

  16. Cost-effective enrichment hybridization capture of chloroplast genomes at deep multiplexing levels for population genetics and phylogeography studies.

    PubMed

    Mariac, Cédric; Scarcelli, Nora; Pouzadou, Juliette; Barnaud, Adeline; Billot, Claire; Faye, Adama; Kougbeadjo, Ayite; Maillol, Vincent; Martin, Guillaume; Sabot, François; Santoni, Sylvain; Vigouroux, Yves; Couvreur, Thomas L P

    2014-11-01

    Biodiversity, phylogeography and population genetic studies will be revolutionized by access to large data sets thanks to next-generation sequencing methods. In this study, we develop an easy and cost-effective protocol for in-solution enrichment hybridization capture of complete chloroplast genomes applicable at deep-multiplexed levels. The protocol uses cheap in-house species-specific probes developed via long-range PCR of the entire chloroplast. Barcoded libraries are constructed, and in-solution enrichment of the chloroplasts is carried out using the probes. This protocol was tested and validated on six economically important West African crop species, namely African rice, pearl millet, three African yam species and fonio. For pearl millet, we also demonstrate the effectiveness of this protocol to retrieve 95% of the sequence of the whole chloroplast on 95 multiplexed individuals in a single MiSeq run at a success rate of 95%. This new protocol allows whole chloroplast genomes to be retrieved at a modest cost and will allow unprecedented resolution for closely related species in phylogeography studies using plastomes.

  17. Deep level transient spectroscopy (DLTS) study of defects introduced in antimony doped Ge by 2 MeV proton irradiation

    NASA Astrophysics Data System (ADS)

    Nyamhere, C.; Das, A. G. M.; Auret, F. D.; Chawanda, A.; Pineda-Vargas, C. A.; Venter, A.

    2011-08-01

    Deep level transient spectroscopy (DLTS) and Laplace-DLTS have been used to investigate the defects created in Sb doped Ge after irradiation with 2 MeV protons having a fluence of 1×10 13 protons/cm 2. The results show that proton irradiation resulted in primary hole traps at E V +0.15 and E V +0.30 eV and electron traps at E C -0.38, E C -0.32, E C -0.31, E C -0.22, E C -0.20, E C -0.17, E C -0.15 and E C -0.04 eV. Defects observed in this study are compared with those introduced in similar samples after MeV electron irradiation reported earlier. E C -0.31, E C -0.17 and E C -0.04, and E V +0.15 eV were not observed previously in similar samples after high energy irradiation. Results from this study suggest that although similar defects are introduced by electron and proton irradiation, traps introduced by the latter are dose dependent.

  18. Deep level transient spectroscopy study of electron traps in n-type GaAs after pulsed electron beam irradiation

    SciTech Connect

    Marrakchi, G.; Barbier, D.; Guillot, G.; Nouailhat, A.

    1987-10-01

    Electrical and deep level transient spectroscopy measurements on Schottky barriers were performed in order to characterize electrically active defects in n-type GaAs (Bridgman substrates or liquid-phase epitaxial layers) after pulsed electron beam annealing. Both surface damage and bulk defects were observed in the Bridgman substrates depending on the pulse energy density. No electron traps were detected in the liquid-phase epitaxial layers before and after annealing for an energy density of 0.4 J/cm/sup 2/. The existence of an interfacial insulating layer at the metal-semiconductor interface, associated with As out-diffusion during the pulsed electron irradiation, was revealed by the abnormally high values of the Schottky barrier diffusion potential. Moreover, two new electron traps with activation energy of 0.35 and 0.43 eV, called EP1 and EP2, were introduced in the Bridgman substrates after pulsed electron beam annealing. The presence of these traps, related to the As evaporation, was tentatively attributed to the decrease of the EL2 electron trap signal after 0.4-J/cm/sup 2/ annealing. It is proposed that these new defects states are due to the decomposition of the As/sub Ga/-As/sub i/ complex recently considered as the most probable defect configuration for the dominant EL2 electron trap usually detected in as-grown GaAs substrates.

  19. Building a conceptual framework to culturally adapt health promotion and prevention programs at the deep structural level.

    PubMed

    Wang-Schweig, Meme; Kviz, Frederick J; Altfeld, Susan J; Miller, Arlene M; Miller, Brenda A

    2014-07-01

    The debate on the effectiveness and merit for the amount of time, effort, and resources to culturally adapt health promotion and prevention programs continues. This may be due, in large part, to the lack of theory in commonly used methods to match programmatic content and delivery to the culture of a population, particularly at the deep structural level. This paper asserts that prior to the cultural adaptation of prevention programs, it is necessary to first develop a conceptual framework. We propose a multiphase approach to address key challenges in the science of cultural adaptation by first identifying and exploring relevant cultural factors that may affect the targeted health-related behavior prior to proceeding through steps of a stage model. The first phase involves developing an underlying conceptual framework that integrates cultural factors to ground this process. The second phase employs the different steps of a stage model. For Phase I of our approach, we offer four key steps and use our research study as an example of how these steps were applied to build a framework for the cultural adaptation of a family-based intervention to prevent adolescent alcohol use, Guiding Good Choices (GGC), to Chinese American families. We then provide a summary of the preliminary evidence from a few key relationships that were tested among our sample with the greater purpose of discussing how these findings might be used to culturally adapt GGC.

  20. Interaction of deep levels and potential fluctuations in scattering and recombination phenomena in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Kažukauskas, V.; Storasta, J.; Vaitkus, J.-V.

    1996-08-01

    The complex influence of recombination centers and potential fluctuations of the band gap on the scattering and recombination phenomena in n-type semiinsulating liquid- encapsulated-Czochralski-grown GaAs were investigated by using the transient photoconductivity and photo-Hall effects. The inhomogeneities cause a hyperbolic decrease of nonequilibrium carrier concentration and the saturation of Hall mobility, while the exponential parts of the decay appear due to the recharge of deep levels. The mean recombination barrier heights of potential fluctuations were evaluated. We propose a complex ``island'' model of scattering and recombination centers, consisting of defect clusters and their associations around dislocations, surrounded by potential barriers. At low light intensities and at the temperatures below 330 K they are insulating for majority charge carriers, thus reducing an effective crystal volume and causing percolation transport effects. At the temperature higher than 330-360 K the main barrier of the island can be recharged or screened by nonequilibrium carriers and its fine barrier structure appears as an effective scatterer, causing a sharp decrease of the nonequilibrium Hall mobility. It was demonstrated that although doping with Sb reduce dislocation density, it can intensify the effect of smaller defects on transport phenomena.

  1. Three-Dimensional Geologic Modeling of a Prospective Deep Underground Laboratory Site for High-Level Radioactive Waste Disposal in Korea

    NASA Astrophysics Data System (ADS)

    Park, J. Y.; Lee, S.; Park, S. U.; Kim, J. M.; Kihm, J. H.

    2014-12-01

    A series of three-dimensional geologic modeling was performed using a geostatistical geologic model GOCAD (ASGA and Paradigm) to characterize quantitatively and to visualize realistically a prospective deep underground laboratory site for high-level radioactive waste disposal in Korea. The necessity of a deep underground laboratory arises from its in-situ conditions for related deep scientific experiments. However, the construction and operation of such a deep underground laboratory take great efforts and expenses owing to its larger depth and thus higher geologic uncertainty. For these reasons, quantitative characterization and realistic visualization of geologic formations and structures of a deep underground laboratory site is crucial before its construction and operation. The study area for the prospective deep underground laboratory site is mainly consists of Precambrian metamorphic rocks as a complex. First, various topographic and geologic data of the study area were collected from literature and boreholes and preliminarily analyzed. Based on the preliminary analysis results, a three-dimensional structural model, which consists of the boundaries between the geologic formations and structures, was established, and a three-dimensional grid model, which consists of hexahedral grid blocks, was produced. Three-dimensional geologic formation model was then established by polymerizing these two models. Finally, a series of three-dimensional lithofacies modeling was performed using the sequential indicator simulation (SIS) and truncated Gaussian simulation (TGS). The volume fractions of metamorphic rocks predicted using the TGS are more similar to the actual data observed in boreholes than those predicted using the SIS. These three-dimensional geologic modeling results can improve a quantitative and realistic understanding of geologic characteristics of the prospective deep underground laboratory site for high-level radioactive waste disposal and thus can provide

  2. A biosphere modeling methodology for dose assessments of the potential Yucca Mountain deep geological high level radioactive waste repository.

    PubMed

    Watkins, B M; Smith, G M; Little, R H; Kessler, J

    1999-04-01

    Recent developments in performance standards for proposed high level radioactive waste disposal at Yucca Mountain suggest that health risk or dose rate limits will likely be part of future standards. Approaches to the development of biosphere modeling and dose assessments for Yucca Mountain have been relatively lacking in previous performance assessments due to the absence of such a requirement. This paper describes a practical methodology used to develop a biosphere model appropriate for calculating doses from use of well water by hypothetical individuals due to discharges of contaminated groundwater into a deep well. The biosphere model methodology, developed in parallel with the BIOMOVS II international study, allows a transparent recording of the decisions at each step, from the specification of the biosphere assessment context through to model development and analysis of results. A list of features, events, and processes relevant to Yucca Mountain was recorded and an interaction matrix developed to help identify relationships between them. Special consideration was given to critical/potential exposure group issues and approaches. The conceptual model of the biosphere system was then developed, based on the interaction matrix, to show how radionuclides migrate and accumulate in the biosphere media and result in potential exposure pathways. A mathematical dose assessment model was specified using the flexible AMBER software application, which allows users to construct their own compartment models. The starting point for the biosphere calculations was a unit flux of each radionuclide from the groundwater in the geosphere into the drinking water in the well. For each of the 26 radionuclides considered, the most significant exposure pathways for hypothetical individuals were identified. For 14 of the radionuclides, the primary exposure pathways were identified as consumption of various crops and animal products following assumed agricultural use of the contaminated

  3. Studies of deep levels in high resistivity silicon detectors irradiated by high fluence fast neutrons using a thermally stimulated current spectrometer

    SciTech Connect

    Li, Z.; Kraner, H.W.; Chen, W.; Beuttenmuller, R.; Biggeri, U.; Bruzzi, M.; Borchi, E.; Baldini, A.; Spillantini, P. |

    1993-04-01

    Measurements of deep level spectrum of high resistivity silicon detectors irradiated by high fluence fast neutrons ({Phi}{sub n}: 2 {times} 10{sup 12}n/cm{sup 2}) have been made using a thermally stimulated current (TSC) spectrometer. It has been found that at least nine new defect levels, with peaking temperature of 19K, 27K, 36K, 44K, 49K, 83K, 93K, 105K, and 120K, begin to appear when {Phi}{sub n} {ge} 1 {times} 10{sup 13}n/cm. All peaks have strong dependences on the filling voltage (V{sub fill}, forward bias) or injection current especially for high fluence ({Phi}{sub n} {ge} 10{sup 13} n/cm{sup 2}) situations. The defect concentration, energy level in the band gap, and cross section of each deep level, totaling, at least 13, have been studied systematically and possible identifications of the levels have been discussed.

  4. Semi-preparative LC-SPE-cryoflow NMR for impurity identifications: use of mother liquor as a better source of impurities.

    PubMed

    Rinaldi, Frank; Fan, Junying; Pathirana, Charles; Palaniswamy, Venkatapurim

    2013-09-01

    Unambiguous structural elucidation of active pharmaceutical ingredients (API) impurities is a particularly challenging necessity of pharmaceutical development, particularly if the impurities are low level (0.1% level). In many cases, this requires acquiring high-quality NMR data on a pure sample of each impurity. High-quality, high signal-to-noise (S/N) one- and two-dimensional NMR data can be obtained using liquid chromatography-solid phase extraction-cryoflow NMR (LC-SPE-cryoflow NMR) with a combination of semi-preparative column for separation and mother liquor as a source of concentrated impurities. These NMR data, in conjunction with mass spectrometry data, allowed for quick and unambiguous structural elucidations of four impurities found at low level in the crystallized API but found at appreciable levels in the mother liquor that was used as the source for these impurities. These data show that semi-preparative columns can be used at lower than ideal flow rates to facilitate trapping of HPLC components for LC-SPE-cryoflow NMR analysis without compromising chromatographic resolution. Also, despite the complex chromatography encountered with the use of mother liquor as a source of impurities, acceptably pure analytes were obtained for acquiring NMR data for unambiguous structure elucidations.

  5. Impurity diffusion in transition-metal oxides

    SciTech Connect

    Peterson, N.L.

    1982-06-01

    Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe/sub 3/O/sub 4/. Tracer impurity diffusion in these materials and TiO/sub 2/, together with measurements of the effect of impurities on tracer diffusion (Co in NiO and Cr in CoO), are reviewed and discussed in terms of impurity-defect interactions and mechanisms of diffusion. Divalent impurities in divalent solvents seem to have a weak interaction with vacancies whereas trivalent impurities in divalent solvents strongly influence the vacancy concentrations and significantly reduce solvent jump frequencies near a trivalent impurity. Impurities with small ionic radii diffuse more slowly with a larger activation energy than impurities with larger ionic radii for all systems considered in this review. Cobalt ions (a moderate size impurity) diffuse rapidly along the open channels parallel to the c-axis in TiO/sub 2/ whereas chromium ions (a smaller-sized impurity) do not. 60 references, 11 figures.

  6. Gaseous trace impurity analyzer and method

    DOEpatents

    Edwards, Jr., David; Schneider, William

    1980-01-01

    Simple apparatus for analyzing trace impurities in a gas, such as helium or hydrogen, comprises means for drawing a measured volume of the gas as sample into a heated zone. A segregable portion of the zone is then chilled to condense trace impurities in the gas in the chilled portion. The gas sample is evacuated from the heated zone including the chilled portion. Finally, the chilled portion is warmed to vaporize the condensed impurities in the order of their boiling points. As the temperature of the chilled portion rises, pressure will develop in the evacuated, heated zone by the vaporization of an impurity. The temperature at which the pressure increase occurs identifies that impurity and the pressure increase attained until the vaporization of the next impurity causes a further pressure increase is a measure of the quantity of the preceding impurity.

  7. Self-pumping impurity control

    DOEpatents

    Brooks, J.N.; Mattas, R.F.

    1983-12-21

    It is an object of the present invention to provide an apparatus for removing impurities from the plasma in a fusion reactor without an external vacuum pumping system. It is also an object of the present invention to provide an apparatus for removing the helium ash from a fusion reactor. It is another object of the present invention to provide an apparatus which removes helium ash and minimizes tritium recycling and inventory.

  8. Revealing substructures of H4 and H5 hole traps in p-type InP using Laplace deep-level transient spectroscopy

    SciTech Connect

    Darwich, R.; Mani, A. A.

    2010-08-15

    New substructures of H4 and H5 hole traps have been revealed using Laplace deep-level transient spectroscopy. Our measurements show that the hole traps H4 and H5 can have at least three components for each. Moreover, the activation energies are deduced and the microscopic nature of these substructures is discussed.

  9. On exchange interaction between shallow impurity centers in diluted semiconductors.

    NASA Astrophysics Data System (ADS)

    Krotkov, Pavel; Gor'kov, Lev

    2003-03-01

    We generalize the method developed in [1,2] to obtain asymptotically exact expressions for the exchange splitting in semiconductors of the levels of carriers localized on shallow impurities at small impurity concentrations (large inter-center separations). Our approach takes into account degeneracy inherent to shallow centers in most semiconductors. We also consider the effects of spin-orbital interaction and of an external magnetic field. [1] L.P. Gor'kov and L.P. Pitaevskii, Dokl. Akad. Nauk SSSR 151, 822 (1963) [Sov. Phys. Dokl. 8, 788 (1964)]. [2] C. Herring and M. Flicker, Phys. Rev. 134, A362 (1964)].

  10. Stimulated emission on impurity – band optical transitions in semiconductors

    SciTech Connect

    Bekin, N A; Shastin, V N

    2015-02-28

    This paper examines conditions for population inversion and amplification in the terahertz range using impurity – band electron transitions in semiconductors and semiconductor structures. Our estimates indicate that stimulated emission on such transitions under optical excitation of impurities can be obtained in a semiconductor with a sufficiently high doping level if electron heating is restricted. At a CO{sub 2} laser pump power density near 0.2 MW cm{sup -2} (photon energy of 117 meV), the gain in n-GaAs may exceed the loss by 50 cm{sup -1} provided the electron gas temperature does not exceed 40 K. We analyse the influence of the carrier effective mass and doping compensation on the gain coefficient and briefly discuss the use of resonance tunnelling for obtaining stimulated emission on impurity – band transitions in quantum cascade heterostructures. (terahertz radiation)

  11. Macroscopic scattering of cracks initiated at single impurity atoms

    NASA Astrophysics Data System (ADS)

    Kermode, J. R.; Ben-Bashat, L.; Atrash, F.; Cilliers, J. J.; Sherman, D.; de Vita, A.

    2013-09-01

    Brittle crystals, such as coloured gems, have long been known to cleave with atomically smooth fracture surfaces, despite being impurity laden, suggesting that isolated atomic impurities do not generally cause cracks to deflect. Whether cracks can ever deviate when hitting an atomic defect, and if so how they can go straight in real brittle crystals, which always contain many such defects, is still an open question. Here we carry out multiscale molecular dynamics simulations and high-resolution experiments on boron-doped silicon, revealing that cracks can be deflected by individual boron atoms. The process, however, requires a characteristic minimum time, which must be less than the time spent by the crack front at the impurity site. Deflection therefore occurs at low crack speeds, leading to surface ridges which intensify when the boron-dopage level is increased, whereas fast-moving cracks are dynamically steered away from being deflected, yielding smooth cleavage surfaces.

  12. Macroscopic scattering of cracks initiated at single impurity atoms.

    PubMed

    Kermode, J R; Ben-Bashat, L; Atrash, F; Cilliers, J J; Sherman, D; De Vita, A

    2013-01-01

    Brittle crystals, such as coloured gems, have long been known to cleave with atomically smooth fracture surfaces, despite being impurity laden, suggesting that isolated atomic impurities do not generally cause cracks to deflect. Whether cracks can ever deviate when hitting an atomic defect, and if so how they can go straight in real brittle crystals, which always contain many such defects, is still an open question. Here we carry out multiscale molecular dynamics simulations and high-resolution experiments on boron-doped silicon, revealing that cracks can be deflected by individual boron atoms. The process, however, requires a characteristic minimum time, which must be less than the time spent by the crack front at the impurity site. Deflection therefore occurs at low crack speeds, leading to surface ridges which intensify when the boron-dopage level is increased, whereas fast-moving cracks are dynamically steered away from being deflected, yielding smooth cleavage surfaces.

  13. Deep learning.

    PubMed

    LeCun, Yann; Bengio, Yoshua; Hinton, Geoffrey

    2015-05-28

    Deep learning allows computational models that are composed of multiple processing layers to learn representations of data with multiple levels of abstraction. These methods have dramatically improved the state-of-the-art in speech recognition, visual object recognition, object detection and many other domains such as drug discovery and genomics. Deep learning discovers intricate structure in large data sets by using the backpropagation algorithm to indicate how a machine should change its internal parameters that are used to compute the representation in each layer from the representation in the previous layer. Deep convolutional nets have brought about breakthroughs in processing images, video, speech and audio, whereas recurrent nets have shone light on sequential data such as text and speech.

  14. Deep learning

    NASA Astrophysics Data System (ADS)

    Lecun, Yann; Bengio, Yoshua; Hinton, Geoffrey

    2015-05-01

    Deep learning allows computational models that are composed of multiple processing layers to learn representations of data with multiple levels of abstraction. These methods have dramatically improved the state-of-the-art in speech recognition, visual object recognition, object detection and many other domains such as drug discovery and genomics. Deep learning discovers intricate structure in large data sets by using the backpropagation algorithm to indicate how a machine should change its internal parameters that are used to compute the representation in each layer from the representation in the previous layer. Deep convolutional nets have brought about breakthroughs in processing images, video, speech and audio, whereas recurrent nets have shone light on sequential data such as text and speech.

  15. Terrestrial source to deep-sea sink sediment budgets at high and low sea levels: Insights from tectonically active Southern California

    USGS Publications Warehouse

    Covault, J.A.; Romans, B.W.; Graham, S.A.; Fildani, A.; Hilley, G.E.

    2011-01-01

    Sediment routing from terrestrial source areas to the deep sea influences landscapes and seascapes and supply and filling of sedimentary basins. However, a comprehensive assessment of land-to-deep-sea sediment budgets over millennia with significant climate change is lacking. We provide source to sink sediment budgets using cosmogenic radionuclide-derived terrestrial denudation rates and submarine-fan deposition rates through sea-level fluctuations since oxygen isotope stage 3 (younger than 40 ka) in tectonically active, spatially restricted sediment-routing systems of Southern California. We show that source-area denudation and deep-sea deposition are balanced during a period of generally falling and low sea level (40-13 ka), but that deep-sea deposition exceeds terrestrial denudation during the subsequent period of rising and high sea level (younger than 13 ka). This additional supply of sediment is likely owed to enhanced dispersal of sediment across the shelf caused by seacliff erosion during postglacial shoreline transgression and initiation of submarine mass wasting. During periods of both low and high sea level, land and deep-sea sediment fluxes do not show orders of magnitude imbalances that might be expected in the wake of major sea-level changes. Thus, sediment-routing processes in a globally significant class of small, tectonically active systems might be fundamentally different from those of larger systems that drain entire orogens, in which sediment storage in coastal plains and wide continental shelves can exceed millions of years. Furthermore, in such small systems, depositional changes offshore can reflect onshore changes when viewed over time scales of several thousand years to more than 10 k.y. ?? 2011 Geological Society of America.

  16. A study on the energy bands of multi-quantum wells in the quantum cascade laser structure by deep-level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Jin Soak; Kim, Eun Kyu; Han, Il Ki; Song, Jin Dong; Lee, Jung Il; Lee, Sejoon; Shon, Yoon; Kim, D. Y.

    2006-08-01

    We have investigated the defect states and confined energy levels of three quantum wells (QWs) in the quantum cascade laser (QCL) structure by capacitance-voltage and deep-level transient spectroscopy methods. Defect states with activation energies in the range of 0.49-0.88 eV were obtained in the GaAs capping layer, and their origins were considered as EL3 and EL2 families, which are well-known deep levels of GaAs materials. The densities of these defects in the GaAs capping layer of the QCL structure were about 3-12% of the donor concentration. The confined energy levels of QWs showed activation energies of about 130 meV and 230 meV from the top of the AlGaAs barrier, and their carrier confinement ability was measured to be about 0.5% of the donor concentration.

  17. Peculiarities of tunneling current in w-AlN/GaN(0001) two-barrier structures induced by deep-level defects

    NASA Astrophysics Data System (ADS)

    Grinyaev, S. N.; Razzhuvalov, A. N.

    2016-10-01

    The influence of deep-level defects localized in spacer layers on the tunneling current in a w-AlN/GaN (0001) double-barrier structure is studied. It is shown that the current value essentially depends on the nature and spatial distribution of defects. New effects (screening of built-in fields, negative feedback, fixing of current peaks at high temperature) and a new mechanism of formation of resonances and tunneling current hysteresis caused by deep centers are established. The results of calculation agree with a number of experimental data on the position and temperature dependence of the current peak. It is noted that the current bistability can be caused by multicharged deep centers localized near the heteroboundaries of a double-barrier structure. Due to the defects, electric field in the barriers can reach values, at which the Poole-Frenkel effect should be taken into account.

  18. Tuning of deep level emission in highly oriented electrodeposited ZnO nanorods by post growth annealing treatments

    SciTech Connect

    Simimol, A.; Manikandanath, N. T.; Chowdhury, Prasanta; Barshilia, Harish C.; Anappara, Aji A.

    2014-08-21

    Highly dense and c-axis oriented zinc oxide (ZnO) nanorods with hexagonal wurtzite facets were deposited on fluorine doped tin oxide coated glass substrates by a simple and cost-effective electrodeposition method at low bath temperature (80 °C). The as-grown samples were then annealed at various temperatures (T{sub A} = 100–500 °C) in different environments (e.g., zinc, oxygen, air, and vacuum) to understand their photoluminescence (PL) behavior in the ultra-violet (UV) and the visible regions. The PL results revealed that the as-deposited ZnO nanorods consisted of oxygen vacancy (V{sub O}), zinc interstitial (Zn{sub i}), and oxygen interstitial (O{sub i}) defects and these can be reduced significantly by annealing in different environments at optimal annealing temperatures. However, the intensity of deep level emission increased for T{sub A} greater than the optimized values for the respective environments due to the introduction of various defect centers. For example, for T{sub A} ≥ 450 °C in the oxygen and air environments, the density of O{sub i} defects increased, whereas, the green emission associated with V{sub O} is dominant in the vacuum annealed (T{sub A} = 500 °C) ZnO nanorods. The UV peak red shifted after the post-growth annealing treatments in all the environments and the vacuum annealed sample exhibited highest UV peak intensity. The observations from the PL data are supported by the micro-Raman spectroscopy. The present study gives new insight into the origin of different defects that exist in the electrodeposited ZnO nanorods and how these defects can be precisely controlled in order to get the desired emissions for the opto-electronic applications.

  19. The Effect of Hydrogen Annealing on the Impurity Content of Alumina-Forming Alloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2000-01-01

    Previously, the effect of hydrogen annealing on increasing the adhesion of Al2O3 scales had been related to the effective desulfurization that occurred during this process. The simultaneous reduction of other impurities has now been re-examined for up to 20 impurity elements in the case of five different alloys (NiCrAl, FeCrAl, PWA 1480, Rene'142, and Rene'N5). Hydrogen annealing produced measurable reductions in elemental concentration for B, C, Na, Mg, P, K, Sr, or Sn in varying degrees for at least one and up to three of these alloys. No single element was reduced by hydrogen annealing for all the alloys except sulfur. In many cases spalling occurred at low levels of these other impurities, while in other cases the scales were adherent at high levels of the impurities. No impurity besides sulfur was strongly correlated with adhesion.

  20. Impurity-induced divertor plasma oscillations

    SciTech Connect

    Smirnov, R. D. Krasheninnikov, S. I.; Pigarov, A. Yu.; Kukushkin, A. S.; Rognlien, T. D.

    2016-01-15

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. The implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.

  1. Impurity-induced divertor plasma oscillations

    NASA Astrophysics Data System (ADS)

    Smirnov, R. D.; Kukushkin, A. S.; Krasheninnikov, S. I.; Pigarov, A. Yu.; Rognlien, T. D.

    2016-01-01

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. The implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.

  2. Impurity-induced divertor plasma oscillations

    SciTech Connect

    Smirnov, R. D.; Kukushkin, A. S.; Krasheninnikov, S. I.; Pigarov, A. Yu.; Rognlien, T. D.

    2016-01-07

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. As a result, the implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.

  3. Impurity-induced divertor plasma oscillations

    DOE PAGES

    Smirnov, R. D.; Kukushkin, A. S.; Krasheninnikov, S. I.; ...

    2016-01-07

    Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ionmore » transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. As a result, the implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.« less

  4. A Multidisciplinary Investigation to Determine the Structure and Source of Dimeric Impurities in AMG 517 Drug Substance.

    PubMed

    Silva Elipe, Maria Victoria; Tan, Zhixin Jessica; Ronk, Michael; Bostick, Tracy

    2009-01-01

    In the initial scale-up batches of the experimental drug substance AMG 517, a pair of unexpected impurities was observed by HPLC. Analysis of data from initial LC-MS experiments indicated the presence of two dimer-like molecules. One impurity had an additional sulfur atom incorporated into its structure relative to the other impurity. Isolation of the impurities was performed, and further structural elucidation experiments were conducted with high-resolution LC-MS and 2D NMR. The dimeric structures were confirmed, with one of the impurities having an unexpected C-S-C linkage. Based on the synthetic route of AMG 517, it was unlikely that these impurities were generated during the last two steps of the process. Stress studies on the enriched impurities were carried out to further confirm the existence of the C-S-C linkage in the benzothiazole portion of AMG 517. Further investigation revealed that these two dimeric impurities originated from existing impurities in the AMG 517 starting material, N-acetyl benzothiazole. The characterization of these two dimeric impurities allowed for better quality control of new batches of the N-acetyl benzothiazole starting material. As a result, subsequent batches of AMG 517 contained no reportable levels of these two impurities.

  5. Temperature Dependent Capacitance-Voltage And Deep Level Transient Spectroscopy Study Of Self-Assembled Ge Quantum Dots Embedded In P-type Silicon

    SciTech Connect

    Rangel-Kuoppa, Victor-Tapio; Chen Gang; Jantsch, Wolfgang

    2011-12-23

    Temperature dependent Capacitance-Voltage (TCV) and Deep Level Transient Spectroscopy (DLTS) techniques were used to study how Ge Quantum Dots (QDs) embedded in Silicon trap charge. Atomic Force Microscopy (AFM) is used to obtain the density of QDs, which is in the order of 3x10{sup 11} cm{sup -2}. Three shallow levels, with activation energies of 40, 65 and 90 meV, and densities around 10{sup 16} cm{sup -3}, are found and are related to Boron. Four deep levels, with activation energies of 110, 150, 330 and 380 meV, and densities between 2x10{sup 15} cm{sup -3} and 5x10{sup 15} cm{sup -3}, are also found. TCV results suggest they are related to the Ge QDs.

  6. I-V and DLTS study of generation and annihilation of deep-level defects in an oxygen-ion irradiated bipolar junction transistor

    NASA Astrophysics Data System (ADS)

    Madhu, K. V.; Kulkarni, S. R.; Ravindra, M.; Damle, R.

    A commercial bipolar junction transistor (2N 2219A, npn) irradiated with 84 MeV O6+-ions with fluence of the order of 1013 ions cm-2 is studied for radiation-induced gain degradation and deep-level defects or recombination centers. I-V measurements are made to study the gain degradation as a function of ion fluence. Properties such as activation energy, trap concentration and capture cross section of deep levels are studied by deep-level transient spectroscopy. Minority carrier trap energy levels with energies ranging from EC -0.17 eV to EC -0.55 eV are observed in the base-collector junction of the transistor. Majority carrier defect levels are also observed with energies ranging from EV +0.26 eV to EV +0.44 eV. The irradiated device is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 250 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for an increase in base current through Shockley-Read-Hall or multi-phonon recombination and consequent transistor gain degradation.

  7. Some logistical considerations in designing a system of deep boreholes for disposal of high-level radioactive waste.

    SciTech Connect

    Gray, Genetha Anne; Brady, Patrick Vane; Arnold, Bill Walter

    2012-09-01

    Deep boreholes could be a relatively inexpensive, safe, and rapidly deployable strategy for disposing Americas nuclear waste. To study this approach, Sandia invested in a three year LDRD project entitled %E2%80%9CRadionuclide Transport from Deep Boreholes.%E2%80%9D In the first two years, the borehole reference design and backfill analysis were completed and the supporting modeling of borehole temperature and fluid transport profiles were done. In the third year, some of the logistics of implementing a deep borehole waste disposal system were considered. This report describes what was learned in the third year of the study and draws some conclusions about the potential bottlenecks of system implementation.

  8. Role of sea-level change in deep water deposition along a carbonate shelf margin, Early and Middle Permian, Delaware Basin: implications for reservoir characterization

    NASA Astrophysics Data System (ADS)

    Li, Shunli; Yu, Xinghe; Li, Shengli; Giles, Katherine A.

    2015-04-01

    The architecture and sedimentary characteristics of deep water deposition can reflect influences of sea-level change on depositional processes on the shelf edge, slope, and basin floor. Outcrops of the northern slope and basin floor of the Delaware Basin in west Texas are progressively exposed due to canyon incision and road cutting. The outcrops in the Delaware Basin were measured to characterize gravity flow deposits in deep water of the basin. Subsurface data from the East Ford and Red Tank fields in the central and northeastern Delaware Basin were used to study reservoir architectures and properties. Depositional models of deep water gravity flows at different stages of sea-level change were constructed on the basis of outcrop and subsurface data. In the falling-stage system tracts, sandy debris with collapses of reef carbonates are deposited on the slope, and high-density turbidites on the slope toe and basin floor. In the low-stand system tracts, deep water fans that consist of mixed sand/mud facies on the basin floor are comprised of high- to low-density turbidites. In the transgression and high-stand system tracts, channel-levee systems and elongate lobes of mud-rich calciturbidite deposits formed as a result of sea level rise and scarcity of sandy sediment supply. For the reservoir architecture, the fan-like debris and high-density turbidites show high net-to-gross ratio of 62 %, which indicates the sandiest reservoirs for hydrocarbon accumulation. Lobe-like deep water fans with net-to-gross ratio of 57 % facilitate the formation of high quality sandy reservoirs. The channel-levee systems with muddy calciturbidites have low net-to-gross ratio of 30 %.

  9. Impurity-induced moments in underdoped cuprates

    SciTech Connect

    Khaliullin, G. |; Kilian, R.; Krivenko, S.; Fulde, P.

    1997-11-01

    We examine the effect of a nonmagnetic impurity in a two-dimensional spin liquid in the spin-gap phase, employing a drone-fermion representation of spin-1/2 operators. The properties of the local moment induced in the vicinity of the impurity are investigated and an expression for the nuclear-magnetic-resonance Knight shift is derived, which we compare with experimental results. Introducing a second impurity into the spin liquid an antiferromagnetic interaction between the moments is found when the two impurities are located on different sublattices. The presence of many impurities leads to a screening of this interaction as is shown by means of a coherent-potential approximation. Further, the Kondo screening of an impurity-induced local spin by charge carriers is discussed. {copyright} {ital 1997} {ital The American Physical Society}

  10. Anisotropic inflation from vector impurity

    SciTech Connect

    Kanno, Sugumi; Kimura, Masashi; Soda, Jiro; Yokoyama, Shuichiro E-mail: mkimura@sci.osaka-cu.ac.jp E-mail: shu@a.phys.nagoya-u.ac.jp

    2008-08-15

    We study an inflationary scenario with a vector impurity. We show that the universe undergoes anisotropic inflationary expansion due to a preferred direction determined by the vector. Using the slow roll approximation, we find a formula for determining the anisotropy of the inflationary universe. We discuss possible observable predictions of this scenario. In particular, it is stressed that primordial gravitational waves can be induced from curvature perturbations. Hence, even in low scale inflation, a sizable amount of primordial gravitational waves may be produced during inflation.

  11. Instabilities and bifurcations of nonlinear impurity modes.

    PubMed

    Kevrekidis, Panayotis G; Kivshar, Yuri S; Kovalev, Alexander S

    2003-04-01

    We study the structure and stability of nonlinear impurity modes in the discrete nonlinear Schrödinger equation with a single on-site nonlinear impurity emphasizing the effects of interplay between discreteness, nonlinearity, and disorder. We show how the interaction of a nonlinear localized mode (a discrete soliton or discrete breather) with a repulsive impurity generates a family of stationary states near the impurity site, as well as examine both theoretical and numerical criteria for the transition between different localized states via a cascade of bifurcations.

  12. The Mg impurity in nitride alloys

    SciTech Connect

    Zvanut, M. E.; Willoughby, W. R.; Sunay, U. R.; Koleske, D. D.; Allerman, A. A.; Wang, Ke; Araki, Tsutomu; Nanishi, Yasushi

    2014-02-21

    Although several magnetic resonance studies address the Mg acceptor in GaN, there are few reports on Mg doping in the alloys, where hole production depends strongly on the Al or In content. Our electron paramagnetic resonance (EPR) measurements of the p-type alloys suggest that the Mg impurity retains the axial symmetry, characteristic of a p-type dopant in both alloys; however, In and Al produce additional, different characteristics of the acceptor. In InGaN, the behavior is consistent with a lowering of the acceptor level and increasing hole density as In concentration increases. For AlGaN, the amount of neutral Mg decreases with increasing Al content, which is attributed to different kinetics of hydrogen diffusion thought to occur in samples with higher Al mole fraction.

  13. Pressure dependence of the E 2 and E 1 deep levels in GaAs, GaP, and their alloys

    SciTech Connect

    Samara, G.A.; Biefeld, R.M.; Dawson, L.R.; Zipperian, T.E.; Barnes, C.E. )

    1991-03-15

    Measurements of the effects of pressure on the thermal-electron emission rate and capture cross section for the {ital E}2 and {ital E}1 deep levels in GaAs, GaP, and their alloys have yielded the pressure dependences of the energies of these levels, allowed evaluation of the breathing-mode lattice relaxations accompanying carrier emission or capture by these levels, and revealed trends that lead to new insights. The results are consistent with a model which associates {ital E}2 with the ({minus}/0) and {ital E}1 with the (2{minus}/{minus}) charge states of the As (or P) vacancy.

  14. Kinetic effects on geodesic acoustic mode from combined collisions and impurities

    SciTech Connect

    Yang, Shangchuan; Xie, Jinlin Liu, Wandong

    2015-04-15

    The dispersion relation for geodesic acoustic mode (GAM) is derived by applying a gyrokinetic model that accounts for the effects from both collisions and impurities. Based on the dispersion relation, an analysis is performed for the non-monotonic behavior of GAM damping versus the characteristic collision rate at various impurity levels. As the effective charge increases, the maximum damping rate is found to shift towards lower collision rates, nearer to the parameter range of a typical tokamak edge plasma. The relative strengths of ion-ion and impurity-induced collision effects, which are illustrated by numerical calculations, are found to be comparable. Impurity-induced collisions help decrease the frequency of GAM, while their effects on the damping rate are non-monotonic, resulting in a weaker total damping in the high collision regime. The results presented suggest considering collision effects as well as impurity effects in GAM analysis.

  15. Identification and characterization of potential impurities in raloxifene hydrochloride.

    PubMed

    Reddy, Reguri Buchi; Goud, Thirumani Venkateshwar; Nagamani, Nagabushanam; Kumar, Nutakki Pavan; Alagudurai, Anandan; Murugan, Raman; Parthasarathy, Kannabiran; Karthikeyan, Vinayagam; Balaji, Perumal

    2012-01-01

    During the synthesis of the bulk drug Raloxifene hydrochloride, eight impurities were observed, four of which were found to be new. All of the impurities were detected using the gradient high performance liquid chromatographic (HPLC) method, whose area percentages ranged from 0.05 to 0.1%. LCMS was performed to identify the mass number of these impurities, and a systematic study was carried out to characterize them. These impurities were synthesized and characterized by spectral data, subjected to co-injection in HPLC, and were found to be matching with the impurities present in the sample. Based on their spectral data (IR, NMR, and Mass), these impurities were characterized as Raloxifene-N-Oxide [Impurity: 1]; EP impurity A [Impurity: 2]; EP impurity B [Impurity: 3]; Raloxifene Dimer [Impurity: 4]; HABT (6-Acetoxy-2-[4-hydroxyphenyl]-1-benzothiophene or 6-Hydroxy-2-[4-acetoxyphenyl]-1-benzothiophene) [Impurity: 5]; PEBE (Methyl[4-[2-(piperidin-1-yl)ethoxy

  16. Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au /GaN Schottky contacts

    NASA Astrophysics Data System (ADS)

    Wang, R. X.; Xu, S. J.; Shi, S. L.; Beling, C. D.; Fung, S.; Zhao, D. G.; Yang, H.; Tao, X. M.

    2006-10-01

    Under identical preparation conditions, Au /GaN Schottky contacts were prepared on two kinds of GaN epilayers with significantly different background electron concentrations and mobility as well as yellow emission intensities. Current-voltage (I-V) and variable-frequency capacitance-voltage (C-V) characteristics show that the Schottky contacts on the GaN epilayer with a higher background carrier concentration and strong yellow emission exhibit anomalous reverse-bias I-V and C-V characteristics. This is attributed to the presence of deep level centers. Theoretical simulation of the low-frequency C-V curves leads to a determination of the density and energy level position of the deep centers.

  17. The influence of impurities on crystallization kinetics a case study on ammonium sulfate

    NASA Astrophysics Data System (ADS)

    Rauls, M.; Bartosch, K.; Kind, M.; Kuch, St.; Lacmann, R.; Mersmann, A.

    2000-05-01

    The influence of impurities on the crystallization kinetics of ammonium sulfate was investigated. MSMPR experiments were conducted with the impurities aluminum sulfate and the azo dyes amaranth and fuchsine. Nucleation and growth rates as well as mean crystal sizes were related to the supersaturation σ and-the width of the metastable zone. It was found that all impurity levels in the system reduce kinetic coefficients for crystal growth and suppress nucleation by adsorption on the crystal surfaces. An increase of supersaturation and metastable zone width compensates for this reduction at low impurity concentrations and allows the growth of larger crystals compared to the pure system. At high impurity concentrations and increasing surface coverage of the crystals, supersaturation rises faster than metastable zone width, causing an increase in nucleation rates and a higher fines content in the product compared to the pure system. A similar interdependence between impurity concentration, crystal size and supersaturation was found for other systems not reported here. The observations made can be explained in terms of adsorption equilibria of the impurities on the crystals. This seemingly general relationship allows the adjustment of crystal sizes in crystallization processes by control of impurity concentrations. A second paper will discuss the changes in crystal morphology in greater depth (Kuch et al., 2000).

  18. Harnessing intrinsic localized modes to identify impurities in nonlinear periodic systems

    NASA Astrophysics Data System (ADS)

    Thota, M.; Harne, R. L.; Wang, K. W.

    2015-02-01

    Intrinsic localized modes (ILMs) are concentrations of vibrational energy in periodic systems/lattices due to the combined influences of nonlinearity and discreteness. Moreover, ILMs can move within the system and may strongly interact with an impurity, such as a stiffness change, mass variation, etc. Numerous scientific fields have uncovered examples and evidence of ILMs, motivating a multidisciplinary pursuit to rigorously understand the underlying principles. In spite of the diverse technical studies, a characterization of ILM interaction behaviors with multiple impurities in dissipative lattices remains outstanding. The insights on such behaviors may be broadly useful when dynamic measurements are the only accessible features of the periodic system. For instance, one may guide an ILM within the lattice using a deliberately applied and steered impurity and harness the observed interaction behaviors with a second, static (immovable) impurity/defect to identify how the underlying lattice is different at the second, defected site, whether or not one knew the position of the defect a priori. In this spirit, this research studies, analyzes, and characterizes the interaction types amongst an ILM and multiple impurities, and devises a method to identify a static defect impurity using quantitatively and qualitatively distinct interaction phenomena. The method is found to be robust to moderate levels of lattice stiffness heterogeneity and is applicable to monitor various property changes that represent impurities. Finally, experimental studies verify that ILMs interact with multiple impurities in unique ways such that defect features may be effectively identified.

  19. Radiative mechanism and surface modification of four visible deep level defect states in ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Barbagiovanni, E. G.; Reitano, R.; Franzò, G.; Strano, V.; Terrasi, A.; Mirabella, S.

    2015-12-01

    Visible luminescence from ZnO nanorods (NRs) is attracting large scientific interest for light emission and sensing applications. We study visible luminescent defects in ZnO NRs as a function of post growth thermal treatments, and find four distinct visible deep level defect states (VDLSs): blue (2.52 eV), green (2.23 eV), orange (2.03 eV), and red (1.92 eV). Photoluminescence (PL) studies reveal a distinct modification in the UV (3.25 eV) emission intensity and a shift in the visible spectra after annealing. Annealing at 600 °C in Ar (Ar600) and O2 (O600) causes a blue and red-shift in the visible emission band, respectively. All samples demonstrate orange emission from the core of the NR, with an additional surface related green, blue, and red emission in the As-Prep, Ar600, and O600 samples, respectively. From PL excitation (PLE) measurements we determine the onset energy for population of the various VDLSs, and relate it to the presence of an Urbach tail below the conduction band due to a presence of ionized Zni or Zni complexes. We measured an onset energy of 3.25 eV for the as prepared sample. The onset energy red-shifts in the annealed samples by about 0.05 to 0.1 eV indicating a change in the defect structure, which we relate to the shift in the visible emission. We then used X-ray photoemission spectroscopy (XPS), and elastic recoil detection analysis (ERDA) to understand changes in the surface structure, and H content, respectively. The results of the XPS and ERDA analysis explain how the chemical states are modified due to annealing. We summarize our results by correlating our VDLSs with specific intrinsic defect states to build a model for PL emission in ZnO NRs. These results are important for understanding how to control defect related visible emission for sensing and electroluminescence applications.Visible luminescence from ZnO nanorods (NRs) is attracting large scientific interest for light emission and sensing applications. We study visible

  20. Operation of the Oxide Washer for Water-Washing Solubles out of Impure Pu Oxide

    SciTech Connect

    Dodson, K E; Close, W L; Krikorian, O H; Summers III, H V

    2006-01-30

    An evaluation has been made for using the Oxide Washer to wash water-soluble materials out of impure Pu oxide. It is found that multiple washes are needed to reduce the water-soluble materials to very low levels in the impure Pu oxides. The removal of the wash water from the Oxide Washer is accompanied by particulates of the impure Pu oxide, which subsequently need to be filtered out. In spite of the additional filtration needed, the overall level of manpower required for processing is still only about one third of that for an all-manual operation.

  1. Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

    SciTech Connect

    Alnoor, Hatim Chey, Chan Oeurn; Pozina, Galia; Willander, Magnus; Nur, Omer; Liu, Xianjie; Khranovskyy, Volodymyr

    2015-08-15

    Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

  2. Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

    NASA Astrophysics Data System (ADS)

    Alnoor, Hatim; Chey, Chan Oeurn; Pozina, Galia; Liu, Xianjie; Khranovskyy, Volodymyr; Willander, Magnus; Nur, Omer

    2015-08-01

    Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.

  3. Determining factors for the presence of impurities in selectively collected biowaste.

    PubMed

    Puig-Ventosa, Ignasi; Freire-González, Jaume; Jofra-Sora, Marta

    2013-05-01

    The presence of impurities in biodegradable waste (biowaste) causes problems with the management of waste, among which are additional costs derived from the need to improve pre-treatment of biowaste, loss of treatment capacity and the difficulty selling treated biowaste as compost owing to its low quality. When treated biowaste is used for soil conditioning it can also cause soil pollution. Understanding the reasons why impurities are in biowaste and the factors affecting the percentage of impurities present can be used to determine ways to minimise these negative effects. This article attempts to identify the main causes for the presence of impurities in biowaste. In order to do so, it carries out an empirical analysis of the level of impurities in biowaste from municipal waste collection in two steps. First, a bivariate analysis focuses on significant correlations between the presence of impurities and several variables. Second, the construction of an explanatory model based on the significant relations obtained in the first step, and on literature research, are used to check the stated hypothesis. The estimates demonstrate that the collection system, the global levels of separate collection, the urban density of the municipality and the requirement to use compostable bags may be the main drivers of impurity levels in biowaste.

  4. Detection of innate immune response modulating impurities in therapeutic proteins.

    PubMed

    Haile, Lydia Asrat; Puig, Montserrat; Kelley-Baker, Logan; Verthelyi, Daniela

    2015-01-01

    Therapeutic proteins can contain multiple impurities, some of which are variants of the product, while others are derived from the cell substrate and the manufacturing process. Such impurities, even when present at trace levels, have the potential to activate innate immune cells in peripheral blood or embedded in tissues causing expression of cytokines and chemokines, increasing antigen uptake, facilitating processing and presentation by antigen presenting cells, and fostering product immunogenicity. Currently, while products are tested for host cell protein content, assays to control innate immune response modulating impurities (IIRMIs) in products are focused mainly on endotoxin and nucleic acids, however, depending on the cell substrate and the manufacturing process, numerous other IIRMI could be present. In these studies we assess two approaches that allow for the detection of a broader subset of IIRMIs. In the first, we use commercial cell lines transfected with Toll like receptors (TLR) to detect receptor-specific agonists. This method is sensitive to trace levels of IIRMI and provides information of the type of IIRMIs present but is limited by the availability of stably transfected cell lines and requires pre-existing knowledge of the IIRMIs likely to be present in the product. Alternatively, the use of a combination of macrophage cell lines of human and mouse origin allows for the detection of a broader spectrum of impurities, but does not identify the source of the activation. Importantly, for either system the lower limit of detection (LLOD) of impurities was similar to that of PBMC and it was not modified by the therapeutic protein tested, even in settings where the product had inherent immune modulatory properties. Together these data indicate that a cell-based assay approach could be used to screen products for the presence of IIRMIs and inform immunogenicity risk assessments, particularly in the context of comparability exercises.

  5. Silicon materials task of the Low-Cost Solar Array Project: Phase IV. Effects of impurities and processing on silicon solar cells. Twenty-first quarterly report, October-December 1980

    SciTech Connect

    Hopkins, R.H.; Hanes, M.H.; Davis, J.R.; Rohatgi, A.; Rai-Choudhury, P.; Mollenkopf, H.C.

    1981-01-30

    The overall objective of this program is to define the effects of impurities, various thermochemical processes, and any impurity-process interactions upon the performance of terrestrial solar cells. The results of the study form a basis for silicon producers, wafer manufacturers, and cell fabricators to develop appropriate cost-benefit relationships for the use of less pure, less costly solar grade silicon. Cr is highly mobile in silicon even at temperatures as low as 600/sup 0/C. Contrasting with earlier data for Mo, Ti, and V, Cr concentrations vary from place to place in polycrystalline silicon wafers and the electrically-active Cr concentration in the polysilicon is more than an order of magnitude smaller than would be projected from single crystal impurity data. We hypothesize that Cr diffuses during ingot cooldown after groth, preferentially segregates to grain boundaries and becomes electrically deactivated. Both Al and Au introduce deep levels when grown into silicon crystals. Accelerated aging data from Ni-contaminated silicon imply that no significant impurity-induced cell performance reduction should be expected over a twenty-year device lifetime. Combined electrical bias and thermal stressing of silicon solar cells containing Nb, Fe, Cu, Ti, Cr, and Ag, respectively produces no performance loss after 100 hour exposures up to 225/sup 0/C. Ti and V, but not Mo, can be gettered from polycrystalline silicon by POCl/sub 3/ or HCl at temperatures of 1000 and 1100/sup 0/C.

  6. Controlled samples for silicon defect and impurity studies

    SciTech Connect

    Ciszek, T.F.

    1995-08-01

    Because of the diverse defects and impurities that are present in any given sample of silicon material, it can be extremely difficult to conduct a controlled experiment to study the influence of any particular defect or impurity on photovoltaic properties such as minority charge carrier lifetime {tau} or solar cell efficiency q. For example, the influence of iron may be different if boron is present, or the influence of silicon self interstitial clusters may be different if oxygen is present. It thus becomes important to conduct such studies on controlled samples where the influence of secondary effects is minimized. At NREL, over the past several years, we have focused on using the high-purity float-zone (FZ) growth method to obtain controlled samples. Because the silicon melt is not in contact with a container, and no heated components are in the growth region, very high purities and low defect levels can be achieved in baseline material. The baseline can be controllably perturbed by introduction of specific defects or impurities. The chart shown below lists some of the types of defect and impurity. combinations that can be studied in this way. The boxes marked with an {open_quotes}x{close_quotes} represent combinations we have studied to some extent.

  7. Substitutional 4d and 5d impurities in graphene.

    PubMed

    Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

    2016-08-21

    We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The adsorption energies and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which are also well-known characteristics of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar adsorption energies, distances and magnetic moments to the 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3 μB for manganese is reduced to 1 μB for technetium and rhenium. We find that compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree of hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different if 4d or 5d impurities are used instead of 3d impurities.

  8. Eliminating Impurity Traps in the Silane Process

    NASA Technical Reports Server (NTRS)

    Coleman, L. M.

    1982-01-01

    Redistribution reaction section of silane process progressively separates heavier parts of chlorosilane feedstock until light silane product is available for pyrolysis. Small amount of liquid containing impurities is withdrawn from processing stages in which trapping occurs and passed to earlier processing stage in which impurities tend to be removed via chemical reactions.

  9. Analysis of trace impurities in organometallic semiconductor grade reagent materials using electrothermal vaporization - inductively coupled plasma spectrometry

    SciTech Connect

    Argentine, M.D.

    1993-12-31

    Trace impurity determinations in volatile, pyrophoric organometallic materials is complicated owing to its chemical nature. Furthermore, trends toward high semiconductor circuit density demand that impurity determinations are performed at increasingly low levels. Volatility of the impurities is also desired as it plays a significant role in impurity incorporation in semiconductor products. Determination of both volatile and nonvolatile impurities in semiconductor-grade organometallic reagent materials has been accomplished using electrothermal vaporization-inductively coupled plasma spectrometry. Solid or liquid materials can be dispensed directly onto a graphite microboat, and application of an appropriate time-temperature ramp allows separation of impurities based on volatility. Temporal separation allows quantitative capabilities on both volatile and nonvolatile signals in a single ETV run. Calibration efforts for volatile impurities have been compared with results from exponential dilution and direct vapor sampling techniques. Nonvolatile impurity determinations can be reasonably performed with aqueous external standard calibration. Inductively coupled plasma-mass spectrometry provides an alternate and more sensitive, multielement detection method. Several spectroscopic and non-spectroscopic difficulties with volatile impurity detection remain. Nonetheless, qualitative and semiquantitative (<50% RSD) determination of most impurities may be performed in a single ETV run.

  10. Defect properties of Sb- and Bi-doped CuInSe{sub 2}: The effect of the deep lone-pair s states

    SciTech Connect

    Park, Ji-Sang; Yang, Ji-Hui; Ramanathan, Kannan; Wei, Su-Huai

    2014-12-15

    Bi or Sb doping has been used to make better material properties of polycrystalline Cu{sub 2}(In,Ga)Se{sub 2} as solar cell absorbers, including the experimentally observed improved electrical properties. However, the mechanism is still not clear. Using first-principles method, we investigate the stability and electronic structure of Bi- and Sb-related defects in CuInSe{sub 2} and study their effects on the doping efficiency. Contrary to previous thinking that Bi or Sb substituted on the anion site, we find that under anion-rich conditions, the impurities can substitute on cation sites and are isovalent to In because of the formation of the impurity lone pair s states. When the impurities substitute for Cu, the defects act as shallow double donors and help remove the deep In{sub Cu} level, thus resulting in the improved carrier life time. On the other hand, under anion-poor conditions, impurities at the Se site create amphoteric deep levels that are detrimental to the device performance.

  11. Analytical control of process impurities in Pazopanib hydrochloride by impurity fate mapping.

    PubMed

    Li, Yan; Liu, David Q; Yang, Shawn; Sudini, Ravinder; McGuire, Michael A; Bhanushali, Dharmesh S; Kord, Alireza S

    2010-08-01

    Understanding the origin and fate of organic impurities within the manufacturing process along with a good control strategy is an integral part of the quality control of drug substance. Following the underlying principles of quality by design (QbD), a systematic approach to analytical control of process impurities by impurity fate mapping (IFM) has been developed and applied to the investigation and control of impurities in the manufacturing process of Pazopanib hydrochloride, an anticancer drug approved recently by the U.S. FDA. This approach requires an aggressive chemical and analytical search for potential impurities in the starting materials, intermediates and drug substance, and experimental studies to track their fate through the manufacturing process in order to understand the process capability for rejecting such impurities. Comprehensive IFM can provide elements of control strategies for impurities. This paper highlights the critical roles that analytical sciences play in the IFM process and impurity control. The application of various analytical techniques (HPLC, LC-MS, NMR, etc.) and development of sensitive and selective methods for impurity detection, identification, separation and quantification are highlighted with illustrative examples. As an essential part of the entire control strategy for Pazopanib hydrochloride, analytical control of impurities with 'meaningful' specifications and the 'right' analytical methods is addressed. In particular, IFM provides scientific justification that can allow for control of process impurities up-stream at the starting materials or intermediates whenever possible.

  12. Deep levels in a-plane, high Mg-content Mg{sub x}Zn{sub 1-x}O epitaxial layers grown by molecular beam epitaxy

    SciTech Connect

    Guer, Emre; Tabares, G.; Hierro, A.; Chauveau, J. M.

    2012-12-15

    Deep level defects in n-type unintentionally doped a-plane Mg{sub x}Zn{sub 1-x}O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg{sub x}Zn{sub 1-x}O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E{sub c} - 1.4 eV, 2.1 eV, 2.6 V, and E{sub v} + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E{sub c} - 2.1 eV, E{sub v} + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E{sub v} + 0.3 eV and E{sub c} - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E{sub v} + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E{sub c} - 1.4 eV and E{sub c} - 2.6 eV levels in Mg alloyed samples.

  13. Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy

    SciTech Connect

    Zhang, Z.; Arehart, A. R.; Ringel, S. A.; Kyle, E. C. H.; Speck, J. S.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.

    2015-01-12

    The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 10{sup 13 }cm{sup −2} and 3 × 10{sup 13 }cm{sup −2} fluences not only introduces a trap with an E{sub V} + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at E{sub V} + 0.48 eV, E{sub V} + 2.42 eV, E{sub V} + 3.00 eV, and E{sub V} + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment.

  14. Electrical characterization of deep levels created by bombarding nitrogen-doped 4H-SiC with alpha-particle irradiation

    NASA Astrophysics Data System (ADS)

    Omotoso, Ezekiel; Meyer, Walter E.; Auret, F. Danie; Paradzah, Alexander T.; Legodi, Matshisa J.

    2016-03-01

    Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate the effect of alpha-particle irradiation on the electrical properties of nitrogen-doped 4H-SiC. The samples were bombarded with alpha-particles at room temperature (300 K) using an americium-241 (241Am) radionuclide source. DLTS revealed the presence of four deep levels in the as-grown samples, E0.09, E0.11, E0.16 and E0.65. After irradiation with a fluence of 4.1 × 1010 alpha-particles-cm-2, DLTS measurements indicated the presence of two new deep levels, E0.39 and E0.62 with energy levels, EC - 0.39 eV and EC - 0.62 eV, with an apparent capture cross sections of 2 × 10-16 and 2 × 10-14 cm2, respectively. Furthermore, irradiation with fluence of 8.9 × 1010 alpha-particles-cm-2 resulted in the disappearance of shallow defects due to a lowering of the Fermi level. These defects re-appeared after annealing at 300 °C for 20 min. Defects, E0.39 and E0.42 with close emission rates were attributed to silicon or carbon vacancy and could only be separated by using high resolution Laplace-DLTS. The DLTS peaks at EC - (0.55-0.70) eV (known as Z1/Z2) were attributed to an isolated carbon vacancy (VC).

  15. Tunneling spectroscopy of a phosphorus impurity atom on the Ge(111)-(2 × 1) surface

    SciTech Connect

    Savinov, S. V.; Oreshkin, A. I. E-mail: oreshkin@spmlab.ru; Oreshkin, S. I.; Haesendonck, C. van

    2015-06-15

    We numerically model the Ge(111)-(2 × 1) surface electronic properties in the vicinity of a P donor impurity atom located near the surface. We find a notable increase in the surface local density of states (LDOS) around the surface dopant near the bottom of the empty surface state band π*, which we call a split state due to its limited spatial extent and energetic position inside the band gap. We show that despite the well-established bulk donor impurity energy level position at the very bottom of the conduction band, a surface donor impurity on the Ge(111)-(2 × 1) surface might produce an energy level below the Fermi energy, depending on the impurity atom local environment. It is demonstrated that the impurity located in subsurface atomic layers is visible in a scanning tunneling microscope (STM) experiment on the Ge(111)-(2 × 1) surface. The quasi-1D character of the impurity image, observed in STM experiments, is confirmed by our computer simulations with a note that a few π-bonded dimer rows may be affected by the presence of the impurity atom. We elaborate a model that allows classifying atoms on the experimental low-temperature STM image. We show the presence of spatial oscillations of the LDOS by the density-functional theory method.

  16. EFFECT OF IMPURITIES ON THE PERFORMANCE OF A Pd-Ag DIFFUSER

    SciTech Connect

    Morgan, G.

    2010-12-16

    A commercially fabricated diffuser purchased from Johnson-Matthey, Inc. was evaluated for performance characterization testing at the Savannah River National Laboratory (SRNL). Different impurities are often present in the feed streams of the process diffusers, but the effect of these impurities on the diffuser performance is currently unknown. Various impurities were introduced into the feed stream of the diffuser at various levels ranging from 0.5% to 10% of the total flow in order to determine the effect that these impurities have on the permeation of hydrogen through the palladium-silver membrane. The introduction of various impurities into the feed stream of the diffuser had a minimal effect on the overall permeation of hydrogen through the Pd-Ag membrane. Of the four impurities introduced into the feed stream, carbon monoxide (CO) was the only impurity that showed any evidence of causing a reduction in the amount of hydrogen permeating through the Pd-Ag membrane. The hydrogen permeation returned to its baseline level after the CO was removed from the feed stream. There were no lasting effects of the CO exposure on the ability of the membrane to effectively separate hydrogen from the non-hydrogen species in the gas stream under the conditions tested.

  17. Platinum-related deep levels in silicon and their passivation by atomic hydrogen using a home-built automated DLTS system

    NASA Astrophysics Data System (ADS)

    Reddy, B. P. N.; Reddy, P. N.; Pandu Rangaiah, S. V.

    1996-09-01

    An inexpensive automated DLTS system has been developed in modular form consisting of modules such as a capacitance meter, pulse generator, DLTS system timing controller, data acquisition system, PID temperature controller, cryostat with LN2 flow control facility, etc. These modules, except the capacitance meter and pulse generator, have been designed and fabricated in the laboratory. Further they are integrated and interfaced to PC AT/386 computer. Software has been developed to run the spectrometer, collect data and off-line data processing for the deep level parameters such as activation energy, capture cross-section and density. The system has been used to study the deep levels of platinum in n-type silicon and their passivation by atomic hydrogen. The estimated activation energy of the two acceptor levels are Ec-0.280 eV and Ec-0.522 eV and their capture cross sections are 2.2E-15 cm-2 and 4.3E-15 cm-2 respectively. These levels are found to be reactivated when the hydrogenated samples are annealed in the temperature range 350 - 500 degrees Celsius. The mechanism of passivation and reactivation of these levels are discussed.

  18. Kinetics of local "magnetic" moment and non-stationary spin-polarized current in the single impurity Anderson-model

    NASA Astrophysics Data System (ADS)

    Maslova, N. S.; Mantsevich, V. N.; Arseyev, P. I.

    2017-02-01

    We perform theoretical investigation of the localized state dynamics in the presence of interaction with the reservoir and Coulomb correlations. We analyze kinetic equations for electron occupation numbers with different spins taking into account high order correlation functions for the localized electrons. We reveal that in the stationary state electron occupation numbers with the opposite spins always have the same value - the stationary state is a "paramagnetic" one. "Magnetic" properties can appear only in the non-stationary characteristics of the single-impurity Anderson model and in the dynamics of the localized electrons second order correlation functions. We found, that for deep energy levels and strong Coulomb correlations, relaxation time for initial "magnetic" state can be several orders larger than for "paramagnetic" one. So, long-living "magnetic" moment can exist in the system. We also found non-stationary spin polarized currents flowing in opposite directions for the different spins in the particular time interval.

  19. Segregation Coefficients of Impurities in Selenium by Zone Refining

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Sha, Yi-Gao

    1998-01-01

    The purification of Se by zone refining process was studied. The impurity solute levels along the length of a zone-refined Se sample were measured by spark source mass spectrographic analysis. By comparing the experimental concentration levels with theoretical curves the segregation coefficient, defined as the ratio of equilibrium concentration of a given solute in the solid to that in the liquid, k = x(sub s)/x(sub l) for most of the impurities in Se are found to be close to unity, i.e., between 0.85 and 1.15, with the k value for Si, Zn, Fe, Na and Al greater than 1 and that for S, Cl, Ca, P, As, Mn and Cr less than 1. This implies that a large number of passes is needed for the successful implementation of zone refining in the purification of Se.

  20. The beauty of impurities: Two revivals of Friedel's virtual bound-state concept

    NASA Astrophysics Data System (ADS)

    Georges, Antoine

    2016-03-01

    Jacques Friedel pioneered the theoretical study of impurities and magnetic impurities in metals. He discovered Friedel oscillations, introduced the concept of virtual bound-state, and demonstrated that the charge on the impurity is related to the scattering phase-shift at the Fermi level (Friedel sum-rule). After a brief review of some of these concepts, I describe how they proved useful in two new contexts. The first one concerns the Coulomb blockade in quantum dots, and its suppression by the Kondo effect. The second one is the dynamical mean-field theory of strong electronic correlations.

  1. Method and apparatus for detecting and measuring trace impurities in flowing gases

    DOEpatents

    Taylor, Gene W.; Dowdy, Edward J.

    1979-01-01

    Trace impurities in flowing gases may be detected and measured by a dynamic atomic molecular emission spectrograph utilizing as its energy source the energy transfer reactions of metastable species, atomic or molecular, with the impurities in the flowing gas. An electronically metastable species which maintains a stable afterglow is formed and mixed with the flowing gas in a region downstream from and separate from the region in which the metastable species is formed. Impurity levels are determined quantitatively by the measurement of line and/or band intensity as a function of concentration employing emission spectroscopic techniques.

  2. Effects of intermittent electrical stimulation on superficial pressure, tissue oxygenation, and discomfort levels for the prevention of deep tissue injury.

    PubMed

    Solis, Leandro R; Gyawali, Selina; Seres, Peter; Curtis, Cara A; Chong, Su Ling; Thompson, Richard B; Mushahwar, Vivian K

    2011-02-01

    The overall goal of this project is to develop effective methods for the prevention of deep tissue injury (DTI). DTI is a severe type of pressure ulcer that originates at deep bone-muscle interfaces as a result of the prolonged compression of tissue. It afflicts individuals with reduced mobility and sensation, particularly those with spinal cord injury. We previously proposed using a novel electrical stimulation paradigm called intermittent electrical stimulation (IES) for the prophylactic prevention of DTI. IES-induced contractions mimic the natural repositioning performed by intact individuals, who subconsciously reposition themselves as a result of discomfort due to prolonged sitting. In this study, we investigated the effectiveness of various IES paradigms in reducing pressure around the ischial tuberosities, increasing tissue oxygenation throughout the gluteus muscles, and reducing sitting discomfort in able-bodied volunteers. The results were compared to the effects of voluntary muscle contractions and conventional pressure relief maneuvers (wheelchair push-ups). IES significantly reduced pressure around the tuberosities, produced significant and long-lasting elevations in tissue oxygenation, and significantly reduced discomfort produced by prolonged sitting. IES performed as well or better than both voluntary contractions and chair push-ups. The results suggest that IES may be an effective means for the prevention of DTI.

  3. Paramagnetic Attraction of Impurity-Helium Solids

    NASA Technical Reports Server (NTRS)

    Bernard, E. P.; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

    2003-01-01

    Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals.

  4. Direct Visualization of an Impurity Depletion Zone

    NASA Technical Reports Server (NTRS)

    Chernov, Alex A.; Garcia-Ruiz, Juan Ma; Thomas, Bill R.

    2000-01-01

    When a crystal incorporates more impurity per unit of its volume than the impurity concentration in solution, the solution in vicinity of the growing crystal is depleted with respect to the impurity I,2. With a stagnant solution, e. g. in microgravity or gels, an impurity depletion zone expands as the crystal grows and results in greater purity in most of the outer portion of the crystal than in the core. Crystallization in gel provides an opportunity to mimic microgravity conditions and visualize the impurity depletion zone. Colorless, transparent apoferritin (M congruent to 450 KDa) crystals were grown in the presence of red holoferritin dimer as a microheterogeneous impurity (M congruent to 900 KDa) within agarose gel by counterdiffusion with Cd(2+) precipitant. Preferential trapping of dimers, (distribution coefficient K = 4 (exp 1,2)) results in weaker red color around the crystals grown in the left tube in the figure as compared to the control middle tube without crystals. The left and the middle tubes contain colored ferritin dimers, the right tube contains colored trimers. The meniscus in the left tube separate gel (below) and liquid solution containing Cd(2+) (above). Similar solutions, though without precipitants, were present on top of the middle and right tube allowing diffusion of dimers and trimers. The area of weaker color intensity around crystals directly demonstrates overlapped impurity depletion zones.

  5. Elemental impurity analysis of mercuric iodide by ICP/MS

    SciTech Connect

    Cross, E.S.; Mroz, E.; Olivares, J.A.

    1993-06-01

    A method has been developed to analyze mercuric iodide (HgI{sub 2}) for elemental contamination using Inductively Coupled Plasma/Mass Spectroscopy (ICP/MS). This paper will discuss the ICP/MS method, the effectiveness of purification schemes for removing impurities from HgI{sub 2}, as well as preliminary correlations between HgI{sub 2} detector performance and elemental contamination levels.

  6. Elemental impurity analysis of mercuric iodide by ICP/MS

    SciTech Connect

    Cross, E.S. . Santa Barbara Operations); Mroz, E.; Olivares, J.A. )

    1993-01-01

    A method has been developed to analyze mercuric iodide (HgI[sub 2]) for elemental contamination using Inductively Coupled Plasma/Mass Spectroscopy (ICP/MS). This paper will discuss the ICP/MS method, the effectiveness of purification schemes for removing impurities from HgI[sub 2], as well as preliminary correlations between HgI[sub 2] detector performance and elemental contamination levels.

  7. An introduction to blocked impurity band detectors

    NASA Technical Reports Server (NTRS)

    Geist, Jon

    1988-01-01

    Blocked impurity band detectors fabricated using standard silicon technologies offer the possibility of combining high sensitivity and high accuracy in a single detector operating in a low background environment. The solid state photomultiplier described by Petroff et al., which is a new type of blocked impurity band detector, offers even higher sensitivity as well as operation in the visible spectral region. The principle of operation and possible application of blocked impurity band detectors for stellar seismology and the search for extra-solar planets are described.

  8. Charge, quantum state, and energy distributions of impurities released in plasma-wall interaction processes

    SciTech Connect

    Gruen, D.M.

    1981-01-01

    Conventional wisdom has it that total sputtering yields correlate with high Z-impurity levels found in fusion plasmas. The charge, quantum states and energy distributions of sputtered atoms have been virtually ignored in these considerations. Impurity transport from the wall or limiter to the plasma is, however, strongly influenced by these factors which may play a crucial role in determining impurity levels in the deeper plasma regions. Preliminary calculations have shown that positively charged impurities would most likely be redeposited on their surfaces of origin. The conditions leading to charged or excited state atoms emission and the energy distributions of such species are reviewed. Techniques for measuring these quantities are discussed and the need for a wider data base in this field is pointed out.

  9. Identification, control strategies, and analytical approaches for the determination of potential genotoxic impurities in pharmaceuticals: a comprehensive review.

    PubMed

    Reddy, Ambavaram Vijaya Bhaskar; Jaafar, Jafariah; Umar, Khalid; Majid, Zaiton Abdul; Aris, Azmi Bin; Talib, Juhaizah; Madhavi, Gajulapalle

    2015-03-01

    Potential genotoxic impurities in pharmaceuticals at trace levels are of increasing concern to both pharmaceutical industries and regulatory agencies due to their possibility for human carcinogenesis. Molecular functional groups that render starting materials and synthetic intermediates as reactive building blocks for small molecules may also be responsible for their genotoxicity. Determination of these genotoxic impurities at trace levels requires highly sensitive and selective analytical methodologies, which poses tremendous challenges on analytical communities in pharmaceutical research and development. Experimental guidance for the analytical determination of some important classes of genotoxic impurities is still unavailable in the literature. Therefore, the present review explores the structural alerts of commonly encountered potential genotoxic impurities, draft guidance of various regulatory authorities in order to control the level of impurities in drug substances and to assess their toxicity. This review also describes the analytical considerations for the determination of potential genotoxic impurities at trace levels and finally few case studies are also discussed for the determination of some important classes of potential genotoxic impurities. It is the authors' intention to provide a complete strategy that helps analytical scientists for the analysis of such potential genotoxic impurities in pharmaceuticals.

  10. Study of radiation induced deep-level defects and annealing effects in the proton irradiated AlGaAs-GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.

    1981-01-01

    The radiation induced deep-level defects and the recombination parameters in the proton irradiated AlGaAs-GaAs p-n junction solar cells were investigated over a wide range of proton energies (from 50 KeV to 10 MeV) and proton fluences (from 10 to the 10th to 10 to the 13th P/sq cm), using DLTS, I-V, C-V, and SEM-EMIC measurement techniques. The measurements were used to determine the defect and recombination parameters such as defect density and energy level, carrier lifetimes, and the hole diffusion lengths in the GaAs LPE layers. Results show that a good correlation was obtained between the measured defect parameters and the dark recombination current as well as the performance parameters of the solar cells. The most damages to the cell were produced by the 200 KeV protons. In addition, the effects of low temperatures (200 to 400 C) thermal annealing on the deep-level defects and the dark current of the 200 KeV proton irradiated samples were examined.

  11. Effects of a key deep level and interface states on the performance of GaAsN solar cells: a simulation analysis

    NASA Astrophysics Data System (ADS)

    Han, Xiuxun; Hwang, Jong-Ha; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi

    2012-10-01

    To explore the origin of low conversion efficiency of GaAsN solar cells, the effects from a key deep level (E1) at about 0.3-0.4 eV below the conduction band and interface states between the GaAsN emitter and GaAs front surface field layer were investigated by numerical simulation. Our results show that a high deep level concentration in GaAsN layers and a large interface recombination velocity are necessary to fit the experimental data. Interface recombination plays an important role in reducing the quantum efficiency in the short-wavelength region. Its effect can be weakened by applying a thin emitter and a high doping level in the GaAs surface field layer. The abundant existence of E1 is responsible for the high contribution of Shockley-Read-Hall recombination from the space-charged region. Its density should be reduced to <1015 cm-3 for higher conversion efficiency.

  12. Oxidation-Induced Deep Levels in n - and p -Type 4 H - and 6 H -SiC and Their Influence on Carrier Lifetime

    NASA Astrophysics Data System (ADS)

    Booker, I. D.; Abdalla, H.; Hassan, J.; Karhu, R.; Lilja, L.; Janzén, E.; Sveinbjörnsson, E. Ö.

    2016-07-01

    We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4 H -SiC and their 6 H -SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n - and p -type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.

  13. A Rydberg impurity in a dense background gas (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Liebisch, Tara; Schlagmüller, Michael; Engel, Felix; Westphal, Karl; Kleinbach, Kathrin; Böttcher, Fabian; Loew, Robert; Hofferberth, Sebastian; Pfau, Tilman; Perez-Rios, Jesus; Greene, Chris

    2016-04-01

    A single Rydberg atom impurity excited in a BEC is a system that can be utilized to measure the quantum mechanical properties of electron - neutral scattering andthe electron probability density of a Rydberg atom. The Rydberg electron - neutral atom scattering process, is a fundamental scattering process, which can be described via Fermi's pseudopotential as V{ěc{r},ěc{R} )=2pi {a}[k(R)]&delta^{(3)}(ěc{r}-ěc{R}). The scattering length is dependent on the momentum of the Rydberg electron, and therefore is dependent on the separation of the Rydberg electron from the ion core. At the classical outermost turning point of the electron, it has the slowest momentum leading to s-wave dominated scattering potentials 10's of MHz in depth for n<40 (Greene et al. PRL 85 2458 (2000), Bendkowsky et al. PRL 105 163201 (2010)). In alkali atoms there is a shape resonance for p-wave scattering, which becomes relevant at ion-neutral separations of 75nm (I.I. Fabrikant J.Phys B 19, 1527 (1985)). This shape resonance potential is several GHz deep, spanning the energy level spacing between n and n-1 principal quantum numbers. At high BEC densities of 5x10^14cm-3 the nearest neighbor spacing is less than 70nm. A Rydberg atom excited within a BEC, is an excitation of the Rydberg atom and all N neutral atoms located within the Rydberg orbit, described as nS+N x 5S. The nS+N x 5S state is density shifted from the Rydberg resonance. Not only does the distribution of atoms within the Rydberg orbit lead to a density shift, but, at these high densities, atoms excited in the nS+N x 5S state near the shape resonance potential cause large perturbations to the density shift, leading to a line broadening. Therefore the spectroscopic line shape of a Rydberg atom in a BEC allows us to probe the theoretically calculated p-wave shape resonance potential. Furthermore, we can observe and measure the dynamics of neutrals excited in the nS+N x 5S state. In the ultracold regime of a BEC, the background

  14. Influence of impurities on the solid-solid phase transitions in zirconium

    SciTech Connect

    Rigg, Paulo A; Greeff, Carl W; Gray, George T., III; Knudson, Marcus D

    2009-08-04

    In an effort to better understand the influence of impurities on the solid-solid phase transitions in Group IVb metals, experiments have been carried out on polycrystalline zirconium samples using plate impact and isentropic loading techniques. Samples with three levels of impurities were shock-loaded using both gas and powder-driven guns and isentropically loaded using magnetic drive (Sandia's Z-Machine) to determine the properties and characteristics of both the {alpha} {yields} {omega} and {omega} {yields} {beta} transitions.

  15. Impurities and electronic localization in graphene bilayers

    NASA Astrophysics Data System (ADS)

    Ojeda Collado, H. P.; Usaj, Gonzalo; Balseiro, C. A.

    2015-01-01

    We analyze the electronic properties of bilayer graphene with Bernal stacking and a low concentration of adatoms. Assuming that the host bilayer lies on top of a substrate, we consider the case where impurities are adsorbed only on the upper layer. We describe nonmagnetic impurities as a single orbital hybridized with carbon's pz states. The effect of impurity doping on the local density of states with and without a gated electric field perpendicular to the layers is analyzed. We look for Anderson localization in the different regimes and estimate the localization length. In the biased system, the field-induced gap is partially filled by strongly localized impurity states. Interestingly, the structure, distribution, and localization length of these states depend on the field polarization.

  16. Numerical Studies of Impurities in Fusion Plasmas

    DOE R&D Accomplishments Database

    Hulse, R. A.

    1982-09-01

    The coupled partial differential equations used to describe the behavior of impurity ions in magnetically confined controlled fusion plasmas require numerical solution for cases of practical interest. Computer codes developed for impurity modeling at the Princeton Plasma Physics Laboratory are used as examples of the types of codes employed for this purpose. These codes solve for the impurity ionization state densities and associated radiation rates using atomic physics appropriate for these low-density, high-temperature plasmas. The simpler codes solve local equations in zero spatial dimensions while more complex cases require codes which explicitly include transport of the impurity ions simultaneously with the atomic processes of ionization and recombination. Typical applications are discussed and computational results are presented for selected cases of interest.

  17. Discovery of Lower Pleistocene Shallow-marine Deposits on Mayaguana Island, Bahamas. Implications for Eustatic Sea-Level Curves Derived From Deep-Sea Oxygen-Isotope Records

    NASA Astrophysics Data System (ADS)

    Godefroid, F.; Kindler, P.; Chiaradia, M.; Hasler, C.; Samankassou, E.

    2008-12-01

    87Sr/86Sr-dated marine and beach sediments exposed along the north shore of Mayaguana Island (Bahamas) provide new estimates of the elevation of high sea stands during the Early Pleistocene that will contribute to better calibrate eustatic sea-level curves derived from deep-sea oxygen-isotope records. A newly investigated sea cliff located to the west of Mount Misery Point on the northern coast of Mayaguana, in the SE part of the Bahamian archipelago, includes two vertically stacked sequences of shallow-marine carbonates separated and capped by paleosols and eolianites. The lower unit, reaching up to 5.5 m above modern sea level, consists of coarse laminated calcarenites containing numerous mollusk and red-algal fragments, and large in-situ coral specimens (Diploria strigosa). The second unit, exposed between 7.3 and 10 m, includes bioturbated, coral-rich limestones, overlain by thinly bedded calcarenites characterized by an early generation of fibrous rim cement. 87Sr/86Sr ratios measured from these carbonates range from 0.709123 at the base of the section to 0.709142 at its top. The first unit can be interpreted as a peri-reefal facies deposited when relative sea level was at least 5.5 m above present. The second unit corresponds to one shallowing-upward sequence of subtidal and beach deposits generated when sea level was around 9 m above its actual stand. Sr-isotope ratios indicate that both units were formed during the Early Pleistocene, likely between 1.6 and 1.0 Ma BP. Comparison with existing oxygen-isotope records from deep- sea sediments suggests that the identified sea-level highstands could correspond to negative δ18O peaks estimated at 1.45 and 1.50 Ma BP. Based on the elevation of fossil reefs dating from the last interglacial (Marine Isotope Stage 5e) and the occurrence of Upper Miocene shallow-marine deposits close to modern sea level, Mayaguana can be considered as tectonically stable. The elevation values obtained for these Early Pleistocene

  18. Transport of Impurity Ions in the Wendelstein 7-AS Stellarator Plasma

    SciTech Connect

    Burhenn, Rainer; Baldzuhn, Juergen; Beidler, Craig; Brakel, Rudolf; Ehmler, Hartmut; Giannone, Louis; Grigull, Peter; Hirsch, Matthias; Knauer, Jens; Krychowiak, Maciej; Maassberg, Henning; McCormick, Kent; Pasch, Ekkehard; Weller, Arthur; Ida, Katsumi

    2006-01-15

    The impact of global plasma parameters on impurity transport in the stellarator W7-AS was investigated by laser blow-off technique. Both, density and heating power were identified to have a strong influence on impurity confinement {tau}{sub I} {approx} n{sub e}{sup 1.2}/P{sub ECRH}{sup 0.8}. In spite of stationary conditions at lower densities, an increasing trend for accumulation was observed at plasma densities beyond 5{center_dot}1019 m-3 due to reduction of the diffusion coefficients. Up to densities of at least 9{center_dot}1019 m-3, launching of electron cyclotron resonance heating (ECRH) power of 1.2 MW is able to counteract the impurity accumulation by deterioration of the impurity confinement with heating power according to the scaling law as given above. In neutral beam injection (NBI) heated plasmas at densities higher than 1{center_dot}1020m-3, long confinement times were observed, often accompanied by loss of density control and degradation of plasma energy due to increasing radiation losses. The installation of island divertor allowed a general extension of the range of accessible densities up to 4{center_dot}1020m-3: beyond a certain power-dependent threshold density (1.5-2.1{center_dot}1020m-3), the plasma enters the High Density H-mode (HDH) regime and the impurity confinement time drops to values comparable to the energy confinement time. High density plasmas could be sustained quasi-stationary with a low level of impurity radiation. The favourable impurity behavior goes along with a reduction of the inward impurity convection in the core plasma and possible changes in the edge transport. For the characterization of the general impurity behavior in W7-AS plasmas the usual transport models for axisymmetric devices are not sufficient and additional stellarator specific processes have to be considered.

  19. Removal of some impurities from carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Feng, Yongcheng; Zhou, Gumin; Wang, Guoping; Qu, Meizhen; Yu, Zuolong

    2003-07-01

    A non-destructive mild oxidation method of removing some impurities from as-grown carbon nanotubes (CNTs), including single-wall carbon nanotubes (SWNTs) and multi-wall carbon nanotubes (MWNTs), by H 2O 2 oxidation and HCl treatment, has been investigated, and somewhat pure carbon nanotubes have been prepared. The CNTs from which some impurities were removed have been evaluated by transmission electron microscopy (TEM) and temperature programmed oxidation and gas chromatography (TPO-GC).

  20. Precipitating Chromium Impurities in Silicon Wafers

    NASA Technical Reports Server (NTRS)

    Salama, A. M.

    1982-01-01

    Two new treatments for silicon wafers improve solar-cell conversion efficiency by precipitating electrically-active chromium impurities. One method is simple heat treatment. Other involves laser-induced damage followed by similar heat treatment. Chromium is one impurity of concern in metallurgical-grade silicon for solar cells. In new treatment, chromium active centers are made electrically inactive by precipitating chromium from solid solution, enabling use of lower grade, lower cost silicon in cell manufacture.

  1. Effects of Impurities on Alumina-Niobium InterfacialMicrostructures

    SciTech Connect

    McKeown, Joseph T.; Sugar, Joshua D.; Gronsky, Ronald; Glaeser,Andreas M.

    2005-06-20

    Optical microscopy, scanning electron microscopy, and transmission electron microscopy were employed to examine the interfacial microstructural effects of impurities in alumina substrates used to fabricate alumina-niobium interfaces via liquid-film-assisted joining. Three types of alumina were used: undoped high-purity single-crystal sapphire; a high-purity, high-strength polycrystalline alumina; and a lower-purity, lower-strength polycrystalline alumina. Interfaces formed between niobium and both the sapphire and high-purity polycrystalline alumina were free of detectable levels of impurities. In the lower-purity alumina, niobium silicides were observed at the alumina-niobium interface and on alumina grain boundaries near the interface. These silicides formed in small-grained regions of the alumina and were found to grow from the interface into the alumina along grain boundaries. Smaller silicide precipitates found on grain boundaries are believed to form upon cooling from the bonding temperature.

  2. Elemental impurity analysis of mercuric iodide by ICP/MS

    SciTech Connect

    Cross, E.S.; Mroz, E.; Olivares, J.A.

    1994-06-01

    A method has been developed to analyze mercuric iodide (HgI{sub 2}) for elemental contamination using Inductively Coupled Plasma/Mass Spectroscopy (ICP/MS). This paper discusses the ICP/MS method, the effectiveness of purification schemes for removing impurities from HgI{sub 2}, as well as preliminary correlations between HgI{sub 2} detector performance and elemental contamination levels. The purified HgI{sub 2} is grown into a single crystal by physical vapor transport. The crystal are cut into slices and they are fabricated into room temperature radiation detectors and photocells. Crystals that produce good resolution gamma detector do not necessarily make good resolution photocells or x-ray detectors. Many factors other than elemental impurities may contribute to these differences in performance.

  3. Effect of impurity doping concentration on solar cell output

    NASA Technical Reports Server (NTRS)

    Iles, P. A.; Soclof, S. I.

    1975-01-01

    Experimental measurements were made of solar cell and related photovoltaic parameters for silicon with high concentrations of dopant impurities. The cell output peaked for doping levels around 10 to the 17th power per cu cm. Independent measurements of diffusion length and open circuit voltage at high doping levels showed severe reductions at concentrations above 10 to the 18th power per cu cm. Theoretical reasons are given to explain these reductions. Indication is given of the problems requiring solution before increased cell output can be achieved at high doping levels.

  4. In situ bacterial colonization of compacted bentonite under deep geological high-level radioactive waste repository conditions.

    PubMed

    Chi Fru, E; Athar, R

    2008-06-01

    Subsurface microorganisms are expected to invade, colonize, and influence the safety performance of deep geological spent nuclear fuel (SNF) repositories. An understanding of the interactions of subsurface dwelling microbial communities with the storage is thus essential. For this to be achieved, experiments must be conducted under in situ conditions. We investigated the presence of groundwater microorganisms in repository bentonite saturated with groundwater recovered from tests conducted at the Aspö underground Hard Rock Laboratory in Sweden. A 16S ribosomal RNA and dissimilatory bisulfite reductase gene distribution between the bentonite and groundwater samples suggested that the sulfate-reducing bacteria widespread in the aquifers were not common in the clay. Aerophilic bacteria could be cultured from samples run at or=67 degrees C. Generally, the largely gram-negative groundwater microorganisms were poorly represented in the bentonite while the gram-positive bacteria commonly found in the clay predominated. Thus, bentonite compacted to a density of approximately 2 g cm(-3) together with elevated temperatures might discourage the mass introduction of the predominantly mesophilic granitic aquifer bacteria into future SNF repositories in the long run.

  5. Investigation of deep-level defects in CuGaSe2 thin-film solar cells using photocapacitance methods.

    PubMed

    Hu, Xiaobo; Xue, Juanjuan; Tian, Jiao; Weng, Guoen; Chen, Shaoqiang

    2017-03-10

    Properties of deep-level defects in CuGaSe2 thin-film solar cells were investigated using photocapacitance methods. By measuring the transient photocapacitance spectra, a deep-level defect centered at around 0.8 eV above the valence band and a defect band located around 1.54 eV above the valence band were determined. A configuration coordinate model was used to explain the thermal quenching effect of the two defects. By measuring the steady-state photocapacitance, a fast increase, followed by a slow increase, was observed in the photocapacitance transient when the sample was illuminated by light with a photon energy of 0.8 eV at low temperature. Upon re-exposure by sub-bandgap light, an extra slow decrease in photocapacitance transient was observed. These observations were interpreted using a configuration coordinate model assuming two states for the 0.8 eV defect: a stable state D and a metastable state D* with a large lattice relaxation. The variation of the photocapacitance transients was attributed to the different optical transition processes of carriers between the two states of the 0.8 eV defect and the valence and conduction bands.

  6. Persistent photoconductivity in AlGaN/GaN heterojunction channels caused by the ionization of deep levels in the AlGaN barrier layer

    SciTech Connect

    Murayama, H.; Akiyama, Y.; Niwa, R.; Sakashita, H.; Sakaki, H.; Kachi, T.; Sugimoto, M.

    2013-12-04

    Time-dependent responses of drain current (I{sub d}) in an AlGaN/GaN HEMT under UV (3.3 eV) and red (2.0 eV) light illumination have been studied at 300 K and 250 K. UV illumination enhances I{sub d} by about 10 %, indicating that the density of two-dimensional electrons is raised by about 10{sup 12} cm{sup −2}. When UV light is turned off at 300 K, a part of increased I{sub d} decays quickly but the other part of increment is persistent, showing a slow decay. At 250 K, the majority of increment remains persistent. It is found that such a persistent increase of I{sub d} at 250 K can be partially erased by the illumination of red light. These photo-responses are explained by a simple band-bending model in which deep levels in the AlGaN barrier get positively charged by the UV light, resulting in a parabolic band bending in the AlGaN layer, while some potion of those deep levels are neutralized by the red light.

  7. Nonlocal effects in double fishnet metasurfaces nanostructured at deep subwavelength level as a path toward simultaneous sensing of multiple chemical analytes

    NASA Astrophysics Data System (ADS)

    Tanasković, Dragan; Obradov, Marko; Jakšić, Olga; Jakšić, Zoran

    2016-01-01

    Nanoplasmonic devices are among the most sensitive chemical sensors, with sensitivities reaching the single-molecule level. An especially convenient class of such sensors is that based on metasurfaces with subwavelength nanoholes, examples being extraordinary optical transmission arrays and double fishnet structures. Such structures ensure operation both in transmission and reflection mode and ensure high sensitivities and excellent coupling with external readout. In this paper we consider the possibility to tailor the response of aperture-based sensor structures by modifying the geometry of nanoholes at the deep subwavelength level through ensuring controlled use of nonlocal effects. We investigate the case where nonlocality is achieved by modifying the basic metamaterial fishnet structure (a metal-dielectric-metal sandwich with rectangular openings) by superposing additional subwavelength patterns, ensuring the appearance of new optical modes. The obtained unit cell superstructure will have multiple tailorable spectral peaks that will increase the selectivity at different wavelengths. The finite elements method was used for simulations of the proposed structures. As an example, we applied our results to the case of a benzene sensor, showing that its spectral properties and selectivity can be tuned by modifying geometry at a deep subwavelength scale. The obtained custom-designed spectral selectivity is convenient for multianalyte chemical sensing using a single structure.

  8. Investigation of deep-level defects in InGaAsN/GaAs 3xQWs structures grown by AP-MOVPE

    NASA Astrophysics Data System (ADS)

    Gelczuk, Ł.; Dabrowska-Szata, M.; Kamyczek, P.; Płaczek-Popko, E.; Kopalko, K.; Ściana, B.; Pucicki, D.; Radziewicz, D.; Tłaczała, M.

    2013-07-01

    We have investigated deep-level defects in InGaAsN/GaAs 3xQW structures by means of conventional as well as high-resolution deep level transient spectroscopy (DLTS). The three samples were grown by atmospheric pressure metalorganic vapour phase epitaxy (AP-MOVPE) in different growth temperatures (566°C, 575°C and 585°C). The DLTS measurements revealed four electron traps E1 (0.17-0.24 eV), E2 (0.36-0.38 eV), E3 (0.46-0.49 eV) and E4 (0.81-0.84 eV) and one hole trap H1(0.8 eV) in our structures. The electron trap E1 was associated with N-related complexes while the other electron traps with native defects, usually observed in GaAs-based structures EL6, EL3 and EL2, respectively. Finally, the trap E2 and H1, observed in the structure grown at lowest temperature, were associated with the same trap, which can act as both an electron and hole trap. It was thus concluded that E2/H1 may be a generation-recombination center.

  9. Combining deep learning and level set for the automated segmentation of the left ventricle of the heart from cardiac cine magnetic resonance.

    PubMed

    Ngo, Tuan Anh; Lu, Zhi; Carneiro, Gustavo

    2017-01-01

    We introduce a new methodology that combines deep learning and level set for the automated segmentation of the left ventricle of the heart from cardiac cine magnetic resonance (MR) data. This combination is relevant for segmentation problems, where the visual object of interest presents large shape and appearance variations, but the annotated training set is small, which is the case for various medical image analysis applications, including the one considered in this paper. In particular, level set methods are based on shape and appearance terms that use small training sets, but present limitations for modelling the visual object variations. Deep learning methods can model such variations using relatively small amounts of annotated training, but they often need to be regularised to produce good generalisation. Therefore, the combination of these methods brings together the advantages of both approaches, producing a methodology that needs small training sets and produces accurate segmentation results. We test our methodology on the MICCAI 2009 left ventricle segmentation challenge database (containing 15 sequences for training, 15 for validation and 15 for testing), where our approach achieves the most accurate results in the semi-automated problem and state-of-the-art results for the fully automated challenge.

  10. Lake-level history of Lake Michigan for the past 12,000 years: the record from deep lacustrine sediments

    USGS Publications Warehouse

    Colman, Steven M.; Forester, Richard M.; Reynolds, Richard L.; Sweetkind, Donald S.; King, John W.; Gangemi, Paul; Jones, Glenn A.; Keigwin, Loyd D.; Foster, David S.

    1994-01-01

    Collection and analysis of an extensive set of seismic-reflection profiles and cores from southern Lake Michigan have provided new data that document the history of the lake basin for the past 12,000 years. Analyses of the seismic data, together with radiocarbon dating, magnetic, sedimentologic, isotopic, and paleontologic studies of core samples, have allowed us to reconstruct lake-level changes during this recent part of the lake's history.The post-glacial history of lake-level changes in the Lake Michigan basin begins about 11.2 ka with the fall from the high Calumet level, caused by the retreat of the Two Rivers glacier, which had blocked the northern outlet of the lake. This lake-level fall was temporarily reversed by a major influx of water from glacial Lake Agassiz (about 10.6 ka), during which deposition of the distinctive gray Wilmette Bed of the Lake Michigan Formation interrupted deposition of red glaciolacustrine sediment. Lake level then continued to fall, culminating in the opening of the North Bay outlet at about 10.3 ka. During the resulting Chippewa low phase, lake level was about 80 m lower than it is today in the southern basin of Lake Michigan.The rise of the early Holocene lake level, controlled primarily by isostatic rebound of the North Bay outlet, resulted in a prominent, planar, transgressive unconformity that eroded most of the shoreline features below present lake level. Superimposed on this overall rise in lake level, a second influx of water from Lake Agassiz temporarily raised lake levels an unknown amount about 9.1 ka. At about 7 ka, lake level may have fallen below the level of the outlet because of sharply drier climate. Sometime between 6 and 5 ka, the character of the lake changed dramatically, probably due mostly to climatic causes, becoming highly undersaturated with respect to calcium carbonate and returning primary control of lake level to the isostatically rising North Bay outlet. Post-Nipissing (about 5 ka) lake level has

  11. Growth Temperature Dependence of Si Doping Efficiency and Compensating Deep Level Defect Incorporation in Al0.7Ga0.3N

    SciTech Connect

    Armstrong, Andrew; Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; Wierer, Jonathan

    2015-05-11

    The growth temperature dependence of Si doping efficiency and deep level defect formation was investigated for n-type Al0.7Ga0.3N. It was observed that dopant compensation was greatly reduced with reduced growth temperature. Furthermore, deep level optical spectroscopy and lighted capacitance-voltage were used to understand the role of acceptor-like deep level defects on doping efficiency. Deep level defects were observed at 2.34 eV, 3.56 eV, and 4.74 eV below the conduction band minimum. The latter two deep levels were identified as the major compensators because the reduction in their concentrations at reduced growth temperature correlated closely with the concomitant increase in free electron concentration. Possible mechanisms for the strong growth temperature dependence of deep level formation are considered, which includes thermodynamically driven compensating defect formation that can arise for a semiconductor with very large band gap energy, such as Al0.7Ga0.3N.

  12. Classification of illicit heroin by UPLC-Q-TOF analysis of acidic and neutral manufacturing impurities.

    PubMed

    Liu, Cuimei; Hua, Zhendong; Bai, Yanping

    2015-12-01

    The illicit manufacture of heroin results in the formation of trace levels of acidic and neutral manufacturing impurities that provide valuable information about the manufacturing process used. In this work, a new ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF) method; that features high resolution, mass accuracy and sensitivity for profiling neutral and acidic heroin manufacturing impurities was developed. After the UPLC-Q-TOF analysis, the retention times and m/z data pairs of acidic and neutral manufacturing impurities were detected, and 19 peaks were found to be evidently different between heroin samples from "Golden Triangle" and "Golden Crescent". Based on the data set of these 19 impurities in 150 authentic heroin samples, classification of heroin geographic origins was successfully achieved utilizing partial least squares discriminant analysis (PLS-DA). By analyzing another data set of 267 authentic heroin samples, the developed discrimiant model was validated and proved to be accurate and reliable.

  13. Impurity segregation in zone-refined precursors for crystalline halide scintillators

    NASA Astrophysics Data System (ADS)

    Swider, S.; Lam, S.; Motakef, S.; Donohoe, E.; Coers, L.; Taylor, S.; Spencer, S.

    2015-06-01

    Successful growth of halide scintillator crystals depends on a supply of ultra-high purity (UHP) precursor materials. Metallic interstitials and substitutions may provide traps that quench luminescence. Oxygen impurities can create competing compounds within a matrix, such as oxyhalides, that disrupt crystallinity and nucleate cracks. Using mass spectroscopy and oxygen combustion analysis, we analyzed impurities in SrI2, EuI2, and YCl3 precursors before and after zone refining. The data show most alkali and alkali earth impurities segregated easily. However, with the exception of iron, many transition metals were incorporated into the solid. Reliable oxygen measurements proved difficult to achieve. Additional oxygen was measured in nitrates and sulfates, via ion chromatography. Zone refining reduced the overall impurity content, but levels remained above a 10 ppm target.

  14. Deep level transient spectroscopy of hole traps related to CdTe self-assembled quantum dots embedded in ZnTe matrix

    NASA Astrophysics Data System (ADS)

    Zielony, E.; Placzek-Popko, E.; Dyba, P.; Gumienny, Z.; Dobaczewski, L.; Karczewski, G.

    2011-12-01

    The capacitance—voltage (C-V) and deep level transient spectroscopy (DLTS) measurements have been performed on a Schottky structure containing self-assembled CdTe quantum dots (QDs) embedded in ZnTe (p-type) matrix. A characteristic step on the C-V curve due to charge accumulation on QD states as well as QD related DLTS signal were found. Thermal activation energy of 0.1 eV was obtained from Arrhenius plot related to the signal. This energy level can be related either to the hole emission from the defects accompanying QD formation or to the hole emission from the QD states to the ZnTe valence band.

  15. On the Diurnal Cycle of Deep Convection, High-Level Cloud, and Upper Troposphere Water Vapor in the Multiscale Modeling Framework

    SciTech Connect

    Zhang, Yunyan; Klein, Stephen A.; Liu, Chuntao; Tian, Baijun; Marchand, Roger T.; Haynes, J. M.; McCoy, Renata; Zhang, Yuying; Ackerman, Thomas P.

    2008-08-22

    The Multiscale Modeling Framework (MMF), also called ‘‘superparameterization’’, embeds a cloud-resolving model (CRM) at each grid column of a general circulation model to replace traditional parameterizations of moist convection and large-scale condensation. This study evaluates the diurnal cycle of deep convection, high-level clouds, and upper troposphere water vapor by applying an infrared (IR) brightness temperature (Tb) and a precipitation radar (PR) simulator to the CRM column data. Simulator results are then compared with IR radiances from geostationary satellites and PR reflectivities from the Tropical Rainfall Measuring Mission (TRMM). While the actual surface precipitation rate in the MMF has a reasonable diurnal phase and amplitude when compared with TRMM observations, the IR simulator results indicate an inconsistency in the diurnal anomalies of high-level clouds between the model and the geostationary satellite data. Primarily because of its excessive high-level clouds, the MMF overestimates the simulated precipitation index (PI) and fails to reproduce the observed diurnal cycle phase relationships among PI, high-level clouds, and upper troposphere relative humidity. The PR simulator results show that over the tropical oceans, the occurrence fraction of reflectivity in excess of 20 dBZ is almost 1 order of magnitude larger than the TRMM data especially at altitudes above 6 km. Both results suggest that the MMF oceanic convection is overactive and possible reasons for this bias are discussed. However, the joint distribution of simulated IR Tb and PR reflectivity indicates that the most intense deep convection is found more often over tropical land than ocean, in agreement with previous observational studies.

  16. Intrinsic point defects and their interaction with impurities in mono-crystalline zinc oxide

    NASA Astrophysics Data System (ADS)

    Svensson, Bengt G.

    2015-03-01

    Zinc oxide (ZnO) is a direct and wide band-gap semiconductor with several attractive features, like an exciton binding energy of ~ 60 meV, for light emitting devices, photovoltaics and spintronics. In the past decade, ZnO has received tremendous attention by the semiconductor physics community and many challenging issues have been addressed, especially the ``native'' n-type conductivity, the role of intrinsic point defects, and the realization of reproducible p-type doping. The latter is, indeed, decisive for a true breakthrough of ZnO-based optoelectronics. In this contribution, recent progress in our understanding of the interaction between intrinsic point defects and impurities in ZnO will be discussed. Aluminum (Al) is often introduced intentionally to accomplish high n-type conductivity since Al on Zn-site (AlZn) acts as a shallow donor. However, AlZn was recently found to react strongly with Zn vacancies (VZn) and the resulting complex (AlZn-VZn) is energetically favorable. The AlZn-VZn complex is a deep acceptor limiting the n-type doping efficiency and this finding is expected to hold in general for complexes between VZn and group-III elements. Further, implantation of self-ions (Zn and O) has been demonstrated to affect radically the balance of intrinsic point defects where an excess of Zn interstitials gives rise to a dramatic depletion of residual Li impurities on Zn-site (LiZn) whilst the opposite holds for an excess of O interstitials. In fact, this behavior appears to be of general validity and Li depletion occurs for a wide variety of implanted elements incorporated into the Zn sub-lattice while Li pile-up occurs for elements residing on O-site. Finally, the most prominent deep-level defect in ZnO, labelled E3, will be shown to involve hydrogen. E3 exists in most ZnO materials, irrespective of the growth method used, and evidence for a center formed by reaction between interstitial hydrogen and primary defects on the Zn sub-lattice will be given.

  17. Nitrogen Impurity Gettering in Oxide Dispersion Ductilized Chromium

    SciTech Connect

    Brady, Michael P; Anderson, Ian M; Weaver, Mark; Meyer III, Harry M; Walker, Larry R; Miller, Michael K; Larson, David James; Wright, Ian G; Sikka, Vinod K; Rar, Andrei; Pharr, George Mathews; Keiser, James R; Walls, Claudia Alexandra

    2003-01-01

    Work by Scruggs in the 1960s demonstrated that tensile ductility could be achieved at room temperature in powder metallurgically-produced Cr alloyed with MgO. During consolidation, much of the MgO converted to the MgCr{sub 2}O{sub 4} spinel phase, which was hypothesized to getter nitrogen from the Cr, rendering it ductile. We have duplicated this effect, achieving room temperature tensile elongations of 4% for hot-pressed Cr-6MgO-(0-1)Ti (wt.%) and 10% for hot-pressed and extruded Cr-6MgO-0.75Ti. Direct incorporation of nitrogen into the MgCr{sub 2}O{sub 4} phase was not detected; however, impurities, particularly nitrogen and sulfur, were observed to segregate to and/or precipitate at interfaces between the MgO/MgCr{sub 2}O{sub 4} phases and the Cr matrix. Exploratory studies of other non-spinel forming oxide dispersions (La{sub 2}O{sub 3}, TiO{sub 2} and Y{sub 2}O{sub 3}) showed a similar pattern of impurity segregation/precipitation, suggesting that there is nothing unique about spinel dispersions in Cr with regards to impurities. However, none of these other dispersions resulted in similar levels of tensile elongation.

  18. Satellite Water Impurity Marker (SWIM) for predicting seasonal cholera outbreaks

    NASA Astrophysics Data System (ADS)

    Jutla, A. S.; Akanda, A. S.; Islam, S.

    2011-12-01

    Prediction of outbreaks of cholera, a deadly water related disease, remains elusive. Since coastal brackish water provides a natural ecological niche for cholera bacteria and because a powerful evidence of new biotypes is emerging, it is highly unlikely that cholera will be fully eradicated. Therefore, it is necessary to develop cholera prediction model with several months' of lead time. Satellite based estimates of chlorophyll, a surrogate for phytoplankton abundance, has been associated with proliferation of cholera bacteria. However, survival of cholera bacteria in a variety of coastal ecological environment put constraints on predictive abilities of chlorophyll algorithm since it only measures greenness in coastal waters. Here, we propose a new remote sensing reflectance based statistical index: Satellite Water Impurity Marker, or SWIM. This statistical index estimates impurity levels in the coastal waters and is based on the variability observed in the difference between the blue (412nm) and green (555nm) wavelengths in coastal waters. The developed index is bounded between clear and impure water and shows the ability to predict cholera outbreaks in the Bengal Delta with a predicted r2 of 78% with two months lead time. We anticipate that a predictive system based on SWIM will provide essential lead time allowing effective intervention and mitigation strategies to be developed for other cholera endemic regions of the world.

  19. Groundwater level changes in a deep well in response to a magma intrusion event on Kilauea Volcano, Hawai'i

    USGS Publications Warehouse

    Hurwitz, S.; Johnston, M.J.S.

    2003-01-01

    On May 21, 2001, an abrupt inflation of Kilauea Volcano's summit induced a rapid and large increase in compressional strain, with a maximum of 2 ??strain recorded by a borehole dilatometer. Water level (pressure) simultaneously dropped by 6 cm. This mode of water level change (drop) is in contrast to that expected for compressional strain from poroelastic theory, and therefore it is proposed that the stress applied by the intrusion has caused opening of fractures or interflows that drained water out of the well. Upon relaxation of the stress recorded by the dilatometer, water levels have recovered at a similar rate. The proposed model has implications for the analysis of ground surface deformation and for mechanisms that trigger phreatomagmatic eruptions.

  20. Subthalamic Nucleus Deep Brain Stimulation Modulate Catecholamine Levels with Significant Relations to Clinical Outcome after Surgery in Patients with Parkinson’s Disease

    PubMed Central

    Yamamoto, Tatsuya; Uchiyama, Tomoyuki; Higuchi, Yoshinori; Asahina, Masato; Hirano, Shigeki; Yamanaka, Yoshitaka; Kuwabara, Satoshi

    2015-01-01

    Aims Although subthalamic nucleus deep brain stimulation (STN-DBS) is effective in patients with advanced Parkinson’s disease (PD), its physiological mechanisms remain unclear. Because STN-DBS is effective in patients with PD whose motor symptoms are dramatically alleviated by L-3,4-dihydroxyphenylalanine (L-DOPA) treatment, the higher preoperative catecholamine levels might be related to the better clinical outcome after surgery. We aimed to examine the correlation between the preoperative catecholamine levels and postoperative clinical outcome after subthalamic nucleus deep brain stimulation. The effectiveness of STN-DBS in the patient who responded well to dopaminergic medication suggest the causal link between the dopaminergic system and STN-DBS. We also examined how catecholamine levels were modulated after subthalamic stimulation. Methods In total 25 patients with PD were enrolled (Mean age 66.2 ± 6.7 years, mean disease duration 11.6 ± 3.7 years). Mean levodopa equivalent doses were 1032 ± 34.6 mg before surgery. Cerebrospinal fluid and plasma catecholamine levels were measured an hour after oral administration of antiparkinsonian drugs before surgery. The mean Unified Parkinson’s Disease Rating Scale scores (UPDRS) and the Parkinson’s disease Questionnaire-39 (PDQ-39) were obtained before and after surgery. Of the 25 patients, postoperative cerebrospinal fluid and plasma were collected an hour after oral administration of antiparkinsonian drugs during on stimulation at follow up in 11 patients. Results Mean levodopa equivalent doses significantly decreased after surgery with improvement in motor functions and quality of life. The preoperative catecholamine levels had basically negative correlations with postoperative motor scores and quality of life, suggesting that higher preoperative catecholamine levels were related to better outcome after STN-DBS. The preoperative plasma levels of L-DOPA had significantly negative correlations with

  1. Non-linear optical response of an impurity in a cylindrical quantum dot under the action of a magnetic field

    NASA Astrophysics Data System (ADS)

    Portacio, Alfonso A.; Rodríguez, Boris A.; Villamil, Pablo

    2017-04-01

    The linear and nonlinear optical response in a cylindrical quantum dot (CQD) of GaAs / Ga0.6Al0.4 As with a donor impurity in a uniform magnetic field applied in the axial direction of the cylinder is studied theoretically. The calculations were carried out in approximations of effective mass and two-level quantum systems. Using the variational method, the binding energies and the wave functions of the 1s-like y 2pz-like states for different positions of the impurity inside the CQD were found. It was found that the binding energy is greatest in the center of the CQD and diminishes as the impurity moves radially and/or axially. The optical rectification, the change in the refractive index, and the optical absorption were studied as functions of the energy of a photon incident on the CQD and different intensities of the magnetic field, with an impurity located at various positions. It was found that in a CDQ with an impurity inside, the effect of the variation of the intensity of the magnetic field on the optical response is much less than the effect produced by the variation of the position of the impurity. The physical reason for this behavior is that in nanostructures with impurities the Coulomb confinement is stronger than the magnetic confinement. It was also found that when the impurity is in the center of the quantum dot, the optical rectification coefficient is zero, due to the symmetry that the wave function of the impurity exhibits at this geometric point. When the impurity moves in the axial direction, the symmetry is broken and the optical rectification coefficient is different from zero, and its value increases as the impurity moves away from the center of the CQD.

  2. Arthropod Phylogenetics in Light of Three Novel Millipede (Myriapoda: Diplopoda) Mitochondrial Genomes with Comments on the Appropriateness of Mitochondrial Genome Sequence Data for Inferring Deep Level Relationships

    PubMed Central

    Brewer, Michael S.; Swafford, Lynn; Spruill, Chad L.; Bond, Jason E.

    2013-01-01

    Background Arthropods are the most diverse group of eukaryotic organisms, but their phylogenetic relationships are poorly understood. Herein, we describe three mitochondrial genomes representing orders of millipedes for which complete genomes had not been characterized. Newly sequenced genomes are combined with existing data to characterize the protein coding regions of myriapods and to attempt to reconstruct the evolutionary relationships within the Myriapoda and Arthropoda. Results The newly sequenced genomes are similar to previously characterized millipede sequences in terms of synteny and length. Unique translocations occurred within the newly sequenced taxa, including one half of the Appalachioria falcifera genome, which is inverted with respect to other millipede genomes. Across myriapods, amino acid conservation levels are highly dependent on the gene region. Additionally, individual loci varied in the level of amino acid conservation. Overall, most gene regions showed low levels of conservation at many sites. Attempts to reconstruct the evolutionary relationships suffered from questionable relationships and low support values. Analyses of phylogenetic informativeness show the lack of signal deep in the trees (i.e., genes evolve too quickly). As a result, the myriapod tree resembles previously published results but lacks convincing support, and, within the arthropod tree, well established groups were recovered as polyphyletic. Conclusions The novel genome sequences described herein provide useful genomic information concerning millipede groups that had not been investigated. Taken together with existing sequences, the variety of compositions and evolution of myriapod mitochondrial genomes are shown to be more complex than previously thought. Unfortunately, the use of mitochondrial protein-coding regions in deep arthropod phylogenetics appears problematic, a result consistent with previously published studies. Lack of phylogenetic signal renders the

  3. Transport analysis of tungsten impurity in ITER

    NASA Astrophysics Data System (ADS)

    Murakami, Y.; Amano, T.; Shimizu, K.; Shimada, M.

    2003-03-01

    The radial distribution of tungsten impurity in ITER is calculated by using the 1.5D transport code TOTAL coupled with NCLASS, which can solve the neo-classical impurity flux considering arbitrary aspect ratio and collisionality. An impurity screening effect is observed when the density profile is flat and the line radiation power is smaller than in the case without impurity transport by a factor of 2. It is shown that 90 MW of line radiation power is possible without significant degradation of plasma performance ( HH98( y,2) ˜1) when the fusion power is 700 MW (fusion gain Q=10). The allowable tungsten density is about 7×10 15/m 3, which is 0.01% of the electron density and the increase of the effective ionic charge Zeff is about 0.39. In this case, the total radiation power is more than half of the total heating power 210 MW, and power to the divertor region is less than 100 MW. This operation regime gives an opportunity for high fusion power operation in ITER with acceptable divertor conditions. Simulations for the case with an internal transport barrier (ITB) are also performed and it is found that impurity shielding by an ITB is possible with density profile control.

  4. Gettering of metal impurities in silicon

    SciTech Connect

    Schroeter, W.; Spiecker, E.; Apel, M.

    1995-08-01

    Gettering means the removal of metallic impurities from the device-active area of the wafer by transport to a predesigned region-called gettering layer (GL). We introduce an interface at z = d{sub GL}, at which the effect of the gettering mechanism on the metal impurity distribution in the wafer is quantified, e.g. by specifying currents or by interfacial reactions of metal impurities, self interstitials etc. between GL and wafer. In response metal impurities will diffuse out of the wafer into the gettering layer. Following such a concept, in general three species of the metal impurity (M) are involved in gettering: M{sub p} {l_arrow} M{sub i} {l_arrow} M{sub GL}. M{sub p} denotes immobile species in the wafer, which are precipitated into suicides or segregated at extended defects or whose diffusivity is too small to contribute noticeably to transport during the gettering procedure - like many substitutional metal species.

  5. Magnetic impurity in a Weyl semimetal

    NASA Astrophysics Data System (ADS)

    Sun, Jin-Hua; Xu, Dong-Hui; Zhang, Fu-Chun; Zhou, Yi

    2015-11-01

    We utilize the variational method to study the Kondo screening of a spin-1 /2 magnetic impurity in a three-dimensional (3D) Weyl semimetal with two Weyl nodes along the kz axis. The model reduces to a 3D Dirac semimetal when the separation of the two Weyl nodes vanishes. When the chemical potential lies at the nodal point, μ =0 , the impurity spin is screened only if the coupling between the impurity and the conduction electron exceeds a critical value. For finite but small μ , the impurity spin is weakly bound due to the low density of states, which is proportional to μ2, contrary to that in a 2D Dirac metal such as graphene and 2D helical metal, where the density of states is proportional to |μ | . The spin-spin correlation function Ju v(r ) between the spin v component of the magnetic impurity at the origin and the spin u component of a conduction electron at spatial point r is found to be strongly anisotropic due to the spin-orbit coupling, and it decays in the power law. The main difference of the Kondo screening in 3D Weyl semimetals and in Dirac semimetals is in the spin x (y ) component of the correlation function in the spatial direction of the z axis.

  6. Donor and double-donor transitions of the carbon vacancy related EH6/7 deep level in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Booker, I. D.; Janzén, E.; Son, N. T.; Hassan, J.; Stenberg, P.; Sveinbjörnsson, E. Ö.

    2016-06-01

    Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6/7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (˜600 K) are σn2+(T) ≈ 1 × 10-14 cm2, σn+(T) ≈ 1 × 10-14 cm2, and σp0(T) ≈ 9 × 10-18 cm2 for EH6 and σn2+(T) ≈ 2 × 10-14 cm2, σn+(T) ≈ 2 × 10-14 cm2, σp0(T) ≈ 1 × 10-20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6/7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.

  7. Analysis of Radiation Damaged and Annealed Gallium Arsenide and Indium Phosphide Solar Cells Using Deep Level Transient Spectroscopy Techniques

    DTIC Science & Technology

    1991-03-01

    148 APPENDIX F EQUATIONS AN SAMPLE CALCULATIONS FOR DLTS ON InP CELL 1073 ALONG WITH ENERGY AND CAPTURE CROSS SECTION PLOTS...level fluctuation based on damage and recovery. C. EXPERIMENTAL PROCEDURE AND RESULTS Cells numbered 1073 and 1074 have been previously irradiated at IE15...electrons/cm . Cell number 1073 maintained 96.8% of the initial V value and 93.8% of its initial I,¢ value while cell 1074 maintained 91.6% of its

  8. Using statistical and artificial neural network models to forecast potentiometric levels at a deep well in South Texas

    NASA Astrophysics Data System (ADS)

    Uddameri, V.

    2007-01-01

    Reliable forecasts of monthly and quarterly fluctuations in groundwater levels are necessary for short- and medium-term planning and management of aquifers to ensure proper service of seasonal demands within a region. Development of physically based transient mathematical models at this time scale poses considerable challenges due to lack of suitable data and other uncertainties. Artificial neural networks (ANN) possess flexible mathematical structures and are capable of mapping highly nonlinear relationships. Feed-forward neural network models were constructed and trained using the back-percolation algorithm to forecast monthly and quarterly time-series water levels at a well that taps into the deeper Evangeline formation of the Gulf Coast aquifer in Victoria, TX. Unlike unconfined formations, no causal relationships exist between water levels and hydro-meteorological variables measured near the vicinity of the well. As such, an endogenous forecasting model using dummy variables to capture short-term seasonal fluctuations and longer-term (decadal) trends was constructed. The root mean square error, mean absolute deviation and correlation coefficient ( R) were noted to be 1.40, 0.33 and 0.77 m, respectively, for an evaluation dataset of quarterly measurements and 1.17, 0.46, and 0.88 m for an evaluative monthly dataset not used to train or test the model. These statistics were better for the ANN model than those developed using statistical regression techniques.

  9. The phylogeny of a species-level tendency: species heritability and possible deep origins of Bergmann's rule in tetrapods.

    PubMed

    De Queiroz, Alan; Ashton, Kyle G

    2004-08-01

    One of the most widely recognized generalizations in biology is Bergmann's rule, the observation that, within species of birds and mammals, body size tends to be inversely related to ambient temperature. Recent studies indicate that turtles and salamanders also tend to follow Bergmann's rule, which hints that this species-level tendency originated early in tetrapod history. Furthermore, exceptions to Bergmann's rule are concentrated within squamate reptiles (lizards and snakes), suggesting that the tendency to express a Bergmann's rule cline may be heritable at the species level. We evaluated species-level heritability and early origination of Bergmann's rule by mapping size-latitude relationships for 352 species onto a tetrapod phylogeny. When the largest available dataset is used, Bergmann's rule shows significant phylogenetic signal, indicating species-level heritability. This represents one of the few demonstrations of heritability for an emergent species-level property and the first for an ecogeographic rule. When species are discretely coded as showing either Bergmann's rule or its converse, parsimony reconstructions suggest that: (1) the tendency to follow Bergmann's rule is ancestral for tetrapods, and (2) most extant species that express the rule have retained this tendency from that ancient ancestor. The first inference also generally holds when the discrete data or size-latitude correlation coefficients are analyzed using maximum likelihood, although the results are only statistically significant for some versions of the discrete analyses. The best estimates of ancestral states suggest that the traditional adaptive explanation for Bergmann's rule-conservation of metabolic heat-was not involved in the origin of the trait since that origin predates the evolution of endothermy. A more general thermoregulatory hypothesis could apply to endotherms and some ectotherms, but fails to explain why salamanders have retained Bergmann's rule. Thus, if

  10. Comparison and Interpretation of Admittance Spectroscopy and Deep Level Transient Spectroscopy from Co-Evaporated and Solution-Deposited Cu2ZnSn(Sx, Se1-x)4 Solar Cells

    SciTech Connect

    Caruso, A. E.; Lund, E. A.; Kosyak, V.; Pruzan, D. S.; Miskin, C.; Agrawal, R.; Beall, Carolyn; Repins, Ingrid; Scarpulla, M. A.

    2016-11-21

    Cu2ZnSn(S, Se)4 (CZTSe) is an earth-abundant semiconductor with potential for economical thin-film photovoltaic devices. Short minority carrier lifetimes contribute to low open circuit voltage and efficiency. Deep level defects that may contribute to lower minority carrier lifetimes in kesterites have been theoretically predicted, however very little experimental characterization of these deep defects exists. In this work we use admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS) to characterize devices built using CZTSSe absorber layers deposited via both coevaporation and solution processing. AS reveals a band of widely-distributed activation energies for traps or energy barriers for transport, especially in the solution deposited case. DLTS reveals signatures of deep majority and minority traps within both types of samples.

  11. Quantitative assessment of cumulative carcinogenic risk for multiple genotoxic impurities in a new drug substance.

    PubMed

    Bercu, Joel P; Hoffman, Wherly P; Lee, Cindy; Ness, Daniel K

    2008-08-01

    In pharmaceutical development, significant effort is made to minimize the carcinogenic potential of new drug substances (NDS). This involves appropriate genotoxicity and carcinogenicity testing of the NDS, and understanding the genotoxic potential of its impurities. Current available guidance recommends the use of the threshold of toxicological concern (TTC) for a single impurity where mutagenicity but no carcinogenicity information exists. Despite best efforts, the presence of more than one genotoxic impurity in an NDS may occur at trace levels. This paper repeats the analysis performed by others for a single genotoxic compound, but also uses statistical simulations to assess the impact on cancer risk for a mixture of genotoxic compounds. In summary, with the addition of multiple impurities all controlled to the TTC, an increase in cancer risk was observed. This increase is relatively small when considering the conservative assumptions of the TTC. If structurally similar compounds had an assumed strong correlation (+/-10-fold from the first randomly selected impurity) in cancer potency, the resulting cancer risk was not negatively impacted. Findings based on probabilistic analysis here can be very useful in making appropriate decisions about risk management of multiple genotoxic impurities measured in the final drug substance.

  12. Some aspects of selection of impurities improving photoelectric characteristics of chalcogenide vitreous semiconductors

    SciTech Connect

    Burdiyan, I. I.; Cosiuc, V. V. Pynzar', R. A.

    2008-02-15

    The effect of low concentrations of two groups of doping impurities (one group includes Sn, Pb, Dy, Ho, Y and the other group includes In, Cs, and Al) on photoelectric properties of As{sub 2}Se{sub 3} and (As{sub 2}S{sub 3}){sub 0.3}(As{sub 2}Se{sub 3}){sub 0.7} was investigated. Studies of spectral distributions of photoconductivity and optical absorption showed that there is a distinct increase in photoconductivity if the level of doping with elements of the first group is as high as 0.015%. Elements of the second group of impurities did not exert any significant effect on photoconductivity. The effect of impurities of the first group is attributed to occupation of vacant sites (formed as a result of removal of highly volatile Se and S atoms) by low concentrations of impurity atoms. The observed effect is related to the fact that substitutional atoms can preserve covalent bonds and to the small difference between atomic sizes and electron affinity for doping impurities and S and Se. Atoms of the second group of impurities lack these features.

  13. Strong quantum scarring by local impurities

    NASA Astrophysics Data System (ADS)

    Luukko, Perttu J. J.; Drury, Byron; Klales, Anna; Kaplan, Lev; Heller, Eric J.; Räsänen, Esa

    2016-11-01

    We discover and characterise strong quantum scars, or quantum eigenstates resembling classical periodic orbits, in two-dimensional quantum wells perturbed by local impurities. These scars are not explained by ordinary scar theory, which would require the existence of short, moderately unstable periodic orbits in the perturbed system. Instead, they are supported by classical resonances in the unperturbed system and the resulting quantum near-degeneracy. Even in the case of a large number of randomly scattered impurities, the scars prefer distinct orientations that extremise the overlap with the impurities. We demonstrate that these preferred orientations can be used for highly efficient transport of quantum wave packets across the perturbed potential landscape. Assisted by the scars, wave-packet recurrences are significantly stronger than in the unperturbed system. Together with the controllability of the preferred orientations, this property may be very useful for quantum transport applications.

  14. Magnetic impurities in small metal clusters

    NASA Astrophysics Data System (ADS)

    Pastor, G. M.

    2005-09-01

    [Dedicated to Bernhard Mühlschlegel on the occasion of his 80th birthday]Magnetic impurities in small metallic clusters are investigated in the framework of the Anderson model by using exact diagonalization and geometry optimization methods.The singlet-triplet spin gap E shows a remarkable dependence as a function of band-filling, cluster structure, and impurity position that can be interpreted in terms of the environment-specific conduction-electron spectrum. The low-energy spin excitations involve similar energies as isomerizations. Interesting correlations between cluster structure and magnetic behavior are revealed. Finite-temperature properties such as specific heat, effective impurity moment, and magnetic susceptibility are calculated exactly in the canonical ensemble. A finite-size equivalent of the Kondo effect is identified and its structural dependence is discussed.

  15. Strong quantum scarring by local impurities

    PubMed Central

    Luukko, Perttu J. J.; Drury, Byron; Klales, Anna; Kaplan, Lev; Heller, Eric J.; Räsänen, Esa

    2016-01-01

    We discover and characterise strong quantum scars, or quantum eigenstates resembling classical periodic orbits, in two-dimensional quantum wells perturbed by local impurities. These scars are not explained by ordinary scar theory, which would require the existence of short, moderately unstable periodic orbits in the perturbed system. Instead, they are supported by classical resonances in the unperturbed system and the resulting quantum near-degeneracy. Even in the case of a large number of randomly scattered impurities, the scars prefer distinct orientations that extremise the overlap with the impurities. We demonstrate that these preferred orientations can be used for highly efficient transport of quantum wave packets across the perturbed potential landscape. Assisted by the scars, wave-packet recurrences are significantly stronger than in the unperturbed system. Together with the controllability of the preferred orientations, this property may be very useful for quantum transport applications. PMID:27892510

  16. Characteristics of impurity-induced pseudogap

    NASA Astrophysics Data System (ADS)

    Numata, Yoshinori; Uto, Tatsuro; Matuda, Azusa

    2016-05-01

    We have performed STM/STS measurements on a single crystal of Bi2.1Sr1.9Ca (Cu1-xCox) 2O8+δ (Co-Bi2212), to reveal impurity effects on the pseudogap in cuprate high-Tc superconductors. We report a drastic change in the temperature dependence of a pseudogap and in the density of states (DOS) modulation with a 4a period, in a certain doping range. In the Co 4% substituted samples, the pseudogap gradually closed like a gap of a BCS superconductor for slightly overdoped and overdoped regime, while their low temperature values were enhanced due to impurity. In addition, a disappearance of a 4a periodic modulation and a development of new modulation were observed in the DOS spatial distribution. These results indicate an intimate relation between the DOS modulation and the pseudogap, and qualitative difference in the impurity enhanced pseudogap and conventional one.

  17. Deep XMM observations of Draco rule out at the 99 per cent confidence level a dark matter decay origin for the 3.5 keV line

    NASA Astrophysics Data System (ADS)

    Jeltema, Tesla; Profumo, Stefano

    2016-06-01

    We searched for an X-ray line at energies around 3.5 keV in deep, ˜1.6 Ms XMM-Newton observations of the dwarf spheroidal galaxy Draco. No line was found in either the Metal Oxide Semi-conductor (MOS) or the p-type/n-type semiconductor (PN) detectors. The data in this energy range are completely consistent with a single, unfolded power-law modelling the particle background, which dominates at these energies, plus instrumental lines; the addition of a ˜3.5 keV line feature gives no improvement to the fit. The corresponding upper limit on the line flux rules out a dark matter decay origin for the 3.5 keV line found in observations of clusters of galaxies and in the Galactic Centre at greater than 99 per cent confidence level.

  18. Characterization of defects introduced in Sb doped Ge by 3 keV Ar sputtering using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS)

    NASA Astrophysics Data System (ADS)

    Nyamhere, C.; Das, A. G. M.; Auret, F. D.; Chawanda, A.; Mtangi, W.; Odendaal, Q.; Carr, A.

    2009-12-01

    We have used deep level transient spectroscopy (DLTS), and Laplace-DLTS to investigate the defects created in antimony doped germanium (Ge) by sputtering with 3 keV Ar ions. Hole traps at EV+0.09 eV and EV+0.31 eV and an electron trap at EC-0.38 eV ( E-center) were observed soon after the sputtering process. Room temperature annealing of the irradiated samples over a period of a month revealed a hole trap at EV+0.26 eV. Above room temperature annealing studies revealed new hole traps at EV+0.27 eV, EV+0.30 eV and EV+0.40 eV.

  19. Deep level defects E1/E2 in n-type 6H silicon carbide induced by electron radiation and He-implantation

    NASA Astrophysics Data System (ADS)

    Ling, C. C.; Chen, X. D.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.; Gong, M.

    2005-06-01

    6H-SiC samples subjected to He-implantation and e--irradiation (Ee=0.2MeV-1.7MeV) were investigated by deep level transient spectroscopy (DLTS). E1/E2 were identified in the He-implanted and the e--irradiated samples with Ee⩾0.3MeV. Considering the minimum e- energy required to displace the atoms in the lattice, the E1/E2 creation was related to the C-atom displacement. Similar to previous reports, the peak intensity and the capture cross sections of E1/E2 anomalously varies from samples to samples. It was shown that these anomalies were due to the presence of a DLTS peak overlapping with the E1/E2 signals.

  20. Theoretical Studies of the Interaction of Excitons with Charged Impurities in Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Tayo, Benjamin O.

    A fundamental theory of the electronic and optical properties of semiconductors shows the importance of impurities, which are often unavoidable and can alter intrinsic properties of semiconductor materials substantially. While the subject of impurity doping is well understood in bulk semiconductors, the role and impact of doping in low dimensional materials like carbon nanotubes is still under investigation and there exists significant debate on the exact nature of electronic impurity levels in single-walled carbon nanotubes associated with adatoms. In this work, we address the role of impurities in single-walled carbon nanotubes. A simple model is developed for studying the interaction of bright (singlet) excitons in semiconducting single-wall nanotubes with charged impurities. The model reveals a red shift in the energy of excitonic states in the presence of an impurity, thus indicating binding of excitons in the impurity potential well. Signatures of several bound states were found in the absorption spectrum below the onset of excitonic optical transitions in the bare nanotube. The dependence of the binding energy on the model parameters, such as impurity charge and position, was determined and analytical fits were derived for a number of tubes of different diameter. The nanotube family splitting is seen in the diameter dependence, gradually decreasing with the diameter. By calculating the partial absorption coefficient for a small segment of nanotube the local nature of the wave function of the bound states was derived. Our studies provide useful insights into the role of the physical environment (here, a charged impurity atom) in the manipulation of the excited states of carbon nanotubes. We performed very detailed calculations of the electronic and optical properties of carbon nanotubes in the presence of an immobile impurity atom, thus going beyond previous many-body perturbation theory (MBPT) studies in which the carbon nanotubes were considered in vacuum

  1. Magnetic impurities in spin-split superconductors

    NASA Astrophysics Data System (ADS)

    van Gerven Oei, W.-V.; Tanasković, D.; Žitko, R.

    2017-02-01

    Hybrid semiconductor-superconductor quantum dot devices are tunable physical realizations of quantum impurity models for a magnetic impurity in a superconducting host. The binding energy of the localized subgap Shiba states is set by the gate voltages and external magnetic field. In this work we discuss the effects of the Zeeman spin splitting, which is generically present both in the quantum dot and in the (thin-film) superconductor. The unequal g factors in semiconductor and superconductor materials result in respective Zeeman splittings of different magnitude. We consider both classical and quantum impurities. In the first case we analytically study the spectral function and the subgap states. The energy of bound states depends on the spin-splitting of the Bogoliubov quasiparticle bands as a simple rigid shift. For the case of collinear magnetization of impurity and host, the Shiba resonance of a given spin polarization remains unperturbed when it overlaps with the branch of the quasiparticle excitations of the opposite spin polarization. In the quantum case, we employ numerical renormalization group calculations to study the effect of the Zeeman field for different values of the g factors of the impurity and of the superconductor. We find that in general the critical magnetic field for the singlet-doublet transition changes nonmonotonically as a function of the superconducting gap, demonstrating the existence of two different transition mechanisms: Zeeman splitting of Shiba states or gap closure due to Zeeman splitting of Bogoliubov states. We also study how in the presence of spin-orbit coupling, modeled as an additional noncollinear component of the magnetic field at the impurity site, the Shiba resonance overlapping with the quasiparticle continuum of the opposite spin gradually broadens and then merges with the continuum.

  2. Changes in 63 Hz third-octave band sound levels over 42 months recorded at four deep-ocean observatories

    NASA Astrophysics Data System (ADS)

    van der Schaar, Mike; Ainslie, Michael A.; Robinson, Stephen P.; Prior, Mark K.; André, Michel

    2014-02-01

    The growing scientific and societal concerns about the effects of underwater sound on marine ecosystems have been recently recognised through the introduction of several international initiatives, like the International Quiet Ocean Experiment, aimed at measuring the environmental impact of ocean noise on large spatial and temporal scales. From a regulatory perspective, the European Marine Strategy Framework Directive includes noise (and other forms of energy) as one of eleven descriptors of good environmental status of Europe's seas. The directive requires member states to monitor trends in annually averaged sound. The Laboratory of Applied Bioacoustics has developed a software package that measures sound levels and monitors acoustic sources in real-time; this software was used for the LIDO project (www.listentothedeep.com), which originated from the European Seafloor Observatory Network of Excellence (ESONET-NoE; www.esonet-noe.org). The system is currently operating worldwide from several wired and radio-linked observatories. The CTBTO (Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization) has made available years of data from hydroacoustic stations to look for ambient sound trends and to detect cetacean presence. Here, we present the analysis of four CTBTO platforms (located in the Pacific, Atlantic and Indian oceans), covering 42 months of data, intended to detect annual and monthly changes or trends in the ambient sound levels.

  3. The Prediction of the Risk Level of Pulmonary Embolism and Deep Vein Thrombosis through Artificial Neural Network

    PubMed Central

    Agharezaei, Laleh; Agharezaei, Zhila; Nemati, Ali; Bahaadinbeigy, Kambiz; Keynia, Farshid; Baneshi, Mohammad Reza; Iranpour, Abedin; Agharezaei, Moslem

    2016-01-01

    Background: Venous thromboembolism is a common cause of mortality among hospitalized patients and yet it is preventable through detecting the precipitating factors and a prompt diagnosis by specialists. The present study has been carried out in order to assist specialists in the diagnosis and prediction of the risk level of pulmonary embolism in patients, by means of artificial neural network. Method: A number of 31 risk factors have been used in this study in order to evaluate the conditions of 294 patients hospitalized in 3 educational hospitals affiliated with Kerman University of Medical Sciences. Two types of artificial neural networks, namely Feed-Forward Back Propagation and Elman Back Propagation, were compared in this study. Results: Through an optimized artificial neural network model, an accuracy and risk level index of 93.23 percent was achieved and, subsequently, the results have been compared with those obtained from the perfusion scan of the patients. 86.61 percent of high risk patients diagnosed through perfusion scan diagnostic method were also diagnosed correctly through the method proposed in the present study. Conclusions: The results of this study can be a good resource for physicians, medical assistants, and healthcare staff to diagnose high risk patients more precisely and prevent the mortalities. Additionally, expenses and other unnecessary diagnostic methods such as perfusion scans can be efficiently reduced. PMID:28077893

  4. The physics of Kondo impurities in graphene.

    PubMed

    Fritz, Lars; Vojta, Matthias

    2013-03-01

    This article summarizes our understanding of the Kondo effect in graphene, primarily from a theoretical perspective. We shall describe different ways to create magnetic moments in graphene, either by adatom deposition or via defects. For dilute moments, the theoretical description is in terms of effective Anderson or Kondo impurity models coupled to graphene's Dirac electrons. We shall discuss in detail the physics of these models, including their quantum phase transitions and the effect of carrier doping, and confront this with existing experimental data. Finally, we will point out connections to other quantum impurity problems, e.g., in unconventional superconductors, topological insulators, and quantum spin liquids.

  5. Fractional impurity moments in two-dimensional noncollinear magnets.

    PubMed

    Wollny, Alexander; Fritz, Lars; Vojta, Matthias

    2011-09-23

    We study dilute magnetic impurities and vacancies in two-dimensional frustrated magnets with noncollinear order. Taking the triangular-lattice Heisenberg model as an example, we use quasiclassical methods to determine the impurity contributions to the magnetization and susceptibility. Most importantly, each impurity moment is not quantized but receives nonuniversal screening corrections due to local relief of frustration. At finite temperatures, where bulk long-range order is absent, this implies an impurity-induced magnetic response of Curie form, with a prefactor corresponding to a fractional moment per impurity. We also discuss the behavior in an applied magnetic field, where we find a singular linear-response limit for overcompensated impurities.

  6. Identification, Characterization, and Quantification of Impurities of Safinamide Mesilate: Process-Related Impurities and Degradation Products.

    PubMed

    Zou, Liang; Sun, Lili; Zhang, Hui; Hui, Wenkai; Zou, Qiaogen; Zhu, Zheying

    2017-02-02

    The characterization of process-related impurities and degradation products of safinamide mesilate (SAFM) in bulk drugand a stability-indicating HPLC method for the separation and quantification of all the impurities were investigated. Four process-related impurities (Imp-B, Imp-C, Imp-D, and Imp-E) were found in the SAFM bulk drug. Five degradation products (Imp-A, Imp-C, Imp-D, Imp-E, and Imp-F) were observed in SAFM under oxidative conditions. Imp-C, Imp-D, and Imp-E were also degradation products and process-related impurities. Remarkably, one new compound, identified as (S)-2-[4-(3-fluoro-benzyloxy) benzamido] propanamide (i.e., Imp-D), is being reported here as an impurity for the first time. Furthermore, the structures of the aforementioned impurities were characterized and confirmed via IR, NMR, and MS techniques, and the most probable formation mechanisms of all impurities proposed according to the synthesis route. Optimum separation was achieved on an Inertsil ODS-3 column (250 × 4.6 mm, 5 μm), using 0.1% formic acid in water (pH adjusted to 5.0) and acetonitrile as the mobile phase in gradient mode. The proposed method was found to be stability-indicating, precise, linear, accurate, sensitive, and robust for the quantitation of SAFM and its process-related substances, including its degradation products.

  7. Revised shallow and deep water-level and storage-volume changes in the Equus Beds Aquifer near Wichita, Kansas, predevelopment to 1993

    USGS Publications Warehouse

    Hansen, Cristi V.; Lanning-Rush, Jennifer L.; Ziegler, Andrew C.

    2013-01-01

    credits from the Equus Beds aquifer by the city of Wichita. The 1993 water levels correspond to the lowest recorded levels and largest storage declines since 1940. Revised and new water-level maps of shallow and deep layers were developed to better represent the general condition of the aquifer. Only static water levels were used to better represent the general condition of the aquifer and comply with Wichita’s ASR permits. To ensure adequate data density, the January 1993 period was expanded to October 1992 through February 1993. Static 1993 water levels from the deep aquifer layer of the Equus Beds aquifer possibly could be used as the lower baseline for regulatory purposes. Previously, maps of water-level changes used to estimate the storage-volume changes included a combination of static (unaffected by pumping or nearby pumping) and stressed (affected by pumping or nearby pumping) water levels from wells. Some of these wells were open to the shallow aquifer layer and some were open to the deep aquifer layer of the Equus Beds aquifer. In this report, only static water levels in the shallow aquifer layer were used to determine storage-volume changes. The effects on average water-level and storage-volume change from the use of mixed, stressed water levels and a specific yield of 0.20 were compared to the use of static water levels in the shallow aquifer and a specific yield of 0.15. This comparison indicates that the change in specific yield causes storage-volume changes to decrease about 25 percent, whereas the use of static water levels in the shallow aquifer layer causes an increase of less than 4 percent. Use of a specific yield of 0.15 will result in substantial decreases in the amount of storage-volume change compared to those reported previously that were calculated using a specific yield of 0.20. Based on these revised water-level maps and computations, the overall decline and change in storage from predevelopment to 1993 represented a loss in storage of about

  8. Climate change and ocean acidification impacts on lower trophic levels and the export of organic carbon to the deep ocean

    NASA Astrophysics Data System (ADS)

    Yool, A.; Popova, E. E.; Coward, A. C.; Bernie, D.; Anderson, T. R.

    2013-02-01

    Most future projections forecast significant and ongoing climate change during the 21st century, but with the severity of impacts dependent on efforts to restrain or reorganise human activity to limit carbon dioxide (CO2) emissions. A major sink for atmospheric CO2, and a key source of biological resources, the World Ocean is widely anticipated to undergo profound physical and - via ocean acidification - chemical changes as direct and indirect results of these emissions. Given strong biophysical coupling, the marine biota is also expected to experience strong changes in response to this anthropogenic forcing. Here we examine the large-scale response of ocean biogeochemistry to climate and acidification impacts during the 21st century for Representative Concentration Pathways (RCPs) 2.6 and 8.5 using an intermediate complexity global ecosystem model, Medusa-2.0. The primary impact of future change lies in stratification-led declines in the availability of key nutrients in surface waters, which in turn leads to a global decrease (1990s vs. 2090s) in ocean productivity (-6.3%). This impact has knock-on consequences for the abundances of the low trophic level biogeochemical actors modelled by Medusa-2.0 (-5.8%), and these would be expected to similarly impact higher trophic level elements such as fisheries. Related impacts are found in the flux of organic material to seafloor communities (-40.7% at 1000 m), and in the volume of ocean suboxic zones (+12.5%). A sensitivity analysis removing an acidification feedback on calcification finds that change in this process significantly impacts benthic communities, suggesting that a better understanding of the OA-sensitivity of calcifying organisms, and their role in ballasting sinking organic carbon, may significantly improve forecasting of these ecosystems. For all processes, there is geographical variability in change, and changes are much more pronounced under RCP 8.5 than the RCP 2.6 scenario.

  9. An investigation of impurity centers in semiconductors of variable composition. Part 1: General theory and some applications

    NASA Technical Reports Server (NTRS)

    Vonroos, O. H.

    1982-01-01

    A theory of deep point defects imbedded in otherwise perfect semiconductor crystals is developed with the aid of pseudopotentials. The dominant short-range forces engendered by the impurity are sufficiently weakened in all cases where the cancellation theorem of the pseudopotential formalism is operative. Thus, effective-mass-like equations exhibiting local effective potentials derived from nonlocal pseudopotentials are shown to be valid for a large class of defects. A two-band secular determinant for the energy eigenvalues of deep defects is also derived from the set of integral equations which corresponds to the set of differential equations of the effective-mass type. Subsequently, the theory in its simplest form, is applied to the system Al(x)Ga(1-x)As:Se. It is shown that the one-electron donor level of Se within the forbidden gap of Al(x)Ga(1-x)As as a function of the AlAs mole fraction x reaches its maximum of about 300 meV (as measured from the conduction band edge) at the cross-over from the direct to the indirect band-gap at x = 0.44 in agreement with experiments.

  10. Deep-level transient spectroscopy of interfacial states in ``buffer-free'' p-i-n GaSb/GaAs devices

    NASA Astrophysics Data System (ADS)

    Aziz, Mohsin; Ferrandis, Philippe; Mesli, Abdelmadjid; Hussain Mari, Riaz; Francisco Felix, Jorlandio; Sellai, Azzouz; Jameel, Dler; Al Saqri, Noor; Khatab, Almontaser; Taylor, David; Henini, Mohamed

    2013-10-01

    A systematic study was carried out on defect states in Interfacial Misfit (IMF) unpassivated and Te-passivated IMF in p-i-n GaSb/GaAs devices using Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS. Additionally, Current-Voltage (I-V) measurements were performed, which showed that the turn-on voltage (Von) of passivated samples is lower than that for unpassivated samples; an effect which can be explained by the introduction of new defects states near to the interface of GaSb/GaAs, where Te was incorporated to passivate the IMF. The Capacitance-Voltage (C-V) analysis demonstrates that these new states are the consequence of adding Te at the misfit of GaSb/GaAs. Furthermore, DLTS measurements reveal a distribution of states including a main midgap energy level, namely the well documented EL2 trap, with some peculiar behaviour. Most of these levels are related to interface states that are generated by the mismatch between GaAs and GaSb. Originally, the addition of Te atoms was thought to passivate these interface states. On the contrary, this paper, which attempts at correlating the current-voltage and capacitance-voltage characteristics to the DLTS results, shows clearly that Te atoms increase the density of interface states.

  11. Climate change and ocean acidification impacts on lower trophic levels and the export of organic carbon to the deep ocean

    NASA Astrophysics Data System (ADS)

    Yool, A.; Popova, E. E.; Coward, A. C.; Bernie, D.; Anderson, T. R.

    2013-09-01

    Most future projections forecast significant and ongoing climate change during the 21st century, but with the severity of impacts dependent on efforts to restrain or reorganise human activity to limit carbon dioxide (CO2) emissions. A major sink for atmospheric CO2, and a key source of biological resources, the World Ocean is widely anticipated to undergo profound physical and - via ocean acidification - chemical changes as direct and indirect results of these emissions. Given strong biophysical coupling, the marine biota is also expected to experience strong changes in response to this anthropogenic forcing. Here we examine the large-scale response of ocean biogeochemistry to climate and acidification impacts during the 21st century for Representative Concentration Pathways (RCPs) 2.6 and 8.5 using an intermediate complexity global ecosystem model, MEDUSA-2.0. The primary impact of future change lies in stratification-led declines in the availability of key nutrients in surface waters, which in turn leads to a global decrease (1990s vs. 2090s) in ocean productivity (-6.3%). This impact has knock-on consequences for the abundance of the low trophic level biogeochemical actors modelled by MEDUSA-2.0 (-5.8%), and these would be expected to similarly impact higher trophic level elements such as fisheries. Related impacts are found in the flux of organic material to seafloor communities (-40.7% at 1000 m), and in the volume of ocean suboxic zones (+12.5%). A sensitivity analysis removing an acidification feedback on calcification finds that change in this process significantly impacts benthic communities, suggesting that a~better understanding of the OA-sensitivity of calcifying organisms, and their role in ballasting sinking organic carbon, may significantly improve forecasting of these ecosystems. For all processes, there is geographical variability in change - for instance, productivity declines -21% in the Atlantic and increases +59% in the Arctic - and changes are

  12. Mitigation of Effects of Occlusion on Object Recognition with Deep Neural Networks through Low-Level Image Completion.

    PubMed

    Chandler, Benjamin; Mingolla, Ennio

    2016-01-01

    Heavily occluded objects are more difficult for classification algorithms to identify correctly than unoccluded objects. This effect is rare and thus hard to measure with datasets like ImageNet and PASCAL VOC, however, owing to biases in human-generated image pose selection. We introduce a dataset that emphasizes occlusion and additions to a standard convolutional neural network aimed at increasing invariance to occlusion. An unmodified convolutional neural network trained and tested on the new dataset rapidly degrades to chance-level accuracy as occlusion increases. Training with occluded data slows this decline but still yields poor performance with high occlusion. Integrating novel preprocessing stages to segment the input and inpaint occlusions is an effective mitigation. A convolutional network so modified is nearly as effective with more than 81% of pixels occluded as it is with no occlusion. Such a network is also more accurate on unoccluded images than an otherwise identical network that has been trained with only unoccluded images. These results depend on successful segmentation. The occlusions in our dataset are deliberately easy to segment from the figure and background. Achieving similar results on a more challenging dataset would require finding a method to split figure, background, and occluding pixels in the input.

  13. Mitigation of Effects of Occlusion on Object Recognition with Deep Neural Networks through Low-Level Image Completion

    PubMed Central

    Mingolla, Ennio

    2016-01-01

    Heavily occluded objects are more difficult for classification algorithms to identify correctly than unoccluded objects. This effect is rare and thus hard to measure with datasets like ImageNet and PASCAL VOC, however, owing to biases in human-generated image pose selection. We introduce a dataset that emphasizes occlusion and additions to a standard convolutional neural network aimed at increasing invariance to occlusion. An unmodified convolutional neural network trained and tested on the new dataset rapidly degrades to chance-level accuracy as occlusion increases. Training with occluded data slows this decline but still yields poor performance with high occlusion. Integrating novel preprocessing stages to segment the input and inpaint occlusions is an effective mitigation. A convolutional network so modified is nearly as effective with more than 81% of pixels occluded as it is with no occlusion. Such a network is also more accurate on unoccluded images than an otherwise identical network that has been trained with only unoccluded images. These results depend on successful segmentation. The occlusions in our dataset are deliberately easy to segment from the figure and background. Achieving similar results on a more challenging dataset would require finding a method to split figure, background, and occluding pixels in the input. PMID:27340396

  14. Identification, characterization and quantification of new impurities by LC-ESI/MS/MS and LC-UV methods in rivastigmine tartrate active pharmaceutical ingredient.

    PubMed

    Thomas, Saji; Shandilya, Sanjeev; Bharati, Amber; Paul, Saroj Kumar; Agarwal, Ashutosh; Mathela, Chandra S

    2012-01-05

    Six impurities were detected at trace level in rivastigmine tartrate drug substance by a newly developed high performance liquid chromatography method. Three impurities were characterized rapidly and three impurities were found to be unknown. The unknown impurities were enriched and identified with a combination of semi-preparative HPLC and LC/MS/MS techniques. Proposed structures were further confirmed by characterization using NMR, FT-IR, and EA techniques of impurity standards. Based on the spectroscopic, spectrometric and elemental analysis data unknown impurities were characterized as 3-[1-(dimethylamino)ethyl]phenyl N-ethyl-N-methyl carbamate N-oxide, ethyl-methyl-carbamic acid 4-(1-dimethylamino-ethyl)-phenyl ester and ethyl-methyl-carbamic acid 2-(1-dimethylamino-ethyl)-phenyl ester. A plausible mechanism for the formation of these impurities is also proposed. The method was validated according to ICH guidelines for fourteen impurities to demonstrate specificity, precision, linearity, accuracy and stability indicating nature of the method. Regression analysis showed correlation coefficient value greater than 0.999 for rivastigmine tartrate and its impurities. Accuracy of the method was established based on the recovery obtained between 93.41 and 113.33% for all impurities.

  15. Impurity content of reduced-activation ferritic steels and a vanadium alloy

    SciTech Connect

    Klueh, R.L.; Grossbeck, M.L.; Bloom, E.E.

    1997-04-01

    Inductively coupled plasma mass spectrometry was used to analyze a reduced-activation ferritic/martensitic steel and a vanadium alloy for low-level impurities that would compromise the reduced-activation characteristics of these materials. The ferritic steel was from the 5-ton IEA heat of modified F82H, and the vanadium alloy was from a 500-kg heat of V-4Cr-4Ti. To compare techniques for analysis of low concentrations of impurities, the vanadium alloy was also examined by glow discharge mass spectrometry. Two other reduced-activation steels and two commercial ferritic steels were also analyzed to determine the difference in the level of the detrimental impurities in the IEA heat and steels for which no extra effort was made to restrict some of the tramp impurities. Silver, cobalt, molybdenum, and niobium proved to be the tramp impurities of most importance. The levels observed in these two materials produced with present technology exceeded the limits for low activation for either shallow land burial or recycling. The chemical analyses provide a benchmark for the improvement in production technology required to achieve reduced activation; they also provide a set of concentrations for calculating decay characteristics for reduced-activation materials. The results indicate the progress that has been made and give an indication of what must still be done before the reduced-activation criteria can be achieved.

  16. Li-FSI Impurity Impact Study: Final CRADA Report

    SciTech Connect

    Pupek, Krzysztof; Dzwiniel, Trevor; Krumdick, Gregory

    2017-01-01

    There is growing interest in lithium bis(fluorosulfonyl)imide (LiFSI ) as an alternative to LiPF6 and as an additive to electrolytes used in lithium-ion cells. LiFSI has attracted attention because it is reported to have higher ionic conductivity, better high temperature stability, and enhanced stability toward hydrolysis, Also, LiFSI additive to electrolytes can bring benefits of improved storage properties and reduced gas evolution in the cells. Different levels of different electrochemically active impurities could affect the performance of LiFSI as an electrolyte salt for Li-ion batteries, generating inconsistent and conflicting interpretations of the experimental data.

  17. Coulomb impurities in two-dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Zhu, Jia-Lin; Li, Guo; Yang, Ning

    2017-03-01

    Introducing a powerful method, we obtain the exact solutions for a Coulomb impurity in two-dimensional infinite and finite topological insulators. The level order and zero-energy degeneracy of the spectra are found to be quite different between topological trivial and nontrivial phases. For quantum dots of topological insulator, the variation of the edge and Coulomb states with dot size, Coulomb potential, and magnetic field are clearly shown. It is found that for small dots the edge states can be strongly coupled with the Coulomb states and for large dots the edge states are insensitive to the Coulomb fields but sensitive to the magnetic fields.

  18. Deep sequencing of Brachypodium small RNAs at the global genome level identifies microRNAs involved in cold stress response

    PubMed Central

    Zhang, Jingyu; Xu, Yunyuan; Huan, Qing; Chong, Kang

    2009-01-01

    Background MicroRNAs (miRNAs) are endogenous small RNAs having large-scale regulatory effects on plant development and stress responses. Extensive studies of miRNAs have only been performed in a few model plants. Although miRNAs are proved to be involved in plant cold stress responses, little is known for winter-habit monocots. Brachypodium distachyon, with close evolutionary relationship to cool-season cereals, has recently emerged as a novel model plant. There are few reports of Brachypodium miRNAs. Results High-throughput sequencing and whole-genome-wide data mining led to the identification of 27 conserved miRNAs, as well as 129 predicted miRNAs in Brachypodium. For multiple-member conserved miRNA families, their sizes in Brachypodium were much smaller than those in rice and Populus. The genome organization of miR395 family in Brachypodium was quite different from that in rice. The expression of 3 conserved miRNAs and 25 predicted miRNAs showed significant changes in response to cold stress. Among these miRNAs, some were cold-induced and some were cold-suppressed, but all the conserved miRNAs were up-regulated under cold stress condition. Conclusion Our results suggest that Brachypodium miRNAs are composed of a set of conserved miRNAs and a large proportion of non-conserved miRNAs with low expression levels. Both kinds of miRNAs were involved in cold stress response, but all the conserved miRNAs were up-regulated, implying an important role for cold-induced miRNAs. The different size and genome organization of miRNA families in Brachypodium and rice suggest that the frequency of duplication events or the selection pressure on duplicated miRNAs are different between these two closely related plant species. PMID:19772667

  19. The excited state dynamics of KLa(MoO{sub 4}){sub 2}:Pr{sup 3+}: From a case study to the determination of the energy levels of rare earth impurities relative to the bandgap in oxidising host lattices

    SciTech Connect

    Cavalli, Enrico Boutinaud, Philippe; Bettinelli, Marco; Dorenbos, Pieter

    2008-05-15

    The luminescence properties of KLa(MoO{sub 4}){sub 2} (KLM) single crystals doped with Pr{sup 3+} have been measured in the 10-600 K temperature range in order to investigate the mechanisms involved in the radiationless processes. At variance with previously studied scheelite-like molybdates activated with Pr{sup 3+}, no effects attributed to the formation of intervalence charge transfer states have been observed. The model proposed in order to account for this behaviour allows the determination of the energy of the Pr{sup 3+} levels relative to the valence and conduction bands of the host. This model has firstly been confirmed for Tb{sup 3+}-doped KLM, for which suitable experimental data are available, and then extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties. The obtained conclusions are finally supported in the light of the comparison with some other representative cases. - Graphical abstract: The study of the excited state dynamics of KLa(MoO{sub 4}){sub 2} single crystals doped with Pr{sup 3+} allows to determine the energies of the levels of the active ion relative to the valence and conduction bands of the host. This model has then been extended to the other rare earth ions on the basis of the systematic nature of the lanthanide energy levels properties.

  20. Defects and impurities in mercuric iodine processing

    SciTech Connect

    van Scyoc, J.M.; James, R.B.; Schlesinger, T.E.; Gilbert, T.S.

    1996-03-01

    In the fabrication of mercuric iodide HgI{sub 2} room temperature radiation detectors, as in any semiconductor process, the quality of the final device is very sensitive to the impurities and defects present. Each process step can change the effects of existing defects, reduce the number of defects, or introduce new defects. In HgI{sub 2} detectors these defects act as trapping and recombination centers, thereby degrading immediate performance and leading to unstable devices. In this work we characterized some of the defects believed to strongly affect detector operation. Specifically, we studied impurities that are known to be present in typical HgI{sub 2} materials. Leakage current measurements were used to study the introduction and characteristics of these impurities, as such experiments reveal the mobile nature of these defects. In particular, we found that copper, which acts as a hole trap, introduces a positively charged center that diffuses and drifts readily in typical device environments. These measurements suggest that Cu, and related impurities like silver, may be one of the leading causes of HgI{sub 2} detector failures.

  1. Impurities in a lyophilized formulation of BMS-204352: identification and role of sanitizing agents.

    PubMed

    Nassar, Munir N; Nesarikar, Vishwas V; Khaselev, Nona; Lozano, Ruben

    2006-01-01

    The purpose of this study was to identify two impurities in the parenteral lyophilized formulation of BMS-204352, investigate the role of sanitizing agents as their potential source, evaluate their effect on drug product stability, and develop a strategy to prevent their contamination of the drug product. The two impurities were identified as o-phenylphenol and 4-t-amylphenol based on liquid chromatography/mass spectroscopy (LC/MS) and chromatographic comparison to authentic samples. The LC/MS spectra of commercially available o-phenylphenol and 4-t-amylphenol showed identical patterns of fragmentation and the same retention times as the impurities identified in the BMS-204352 lyophilized product. Levels of these impurities were low and ranged between 0.2-0.3 microg/vial as determined by HPLC and using an authentic external reference standard. To confirm the hypothesis that the commercial sanitizing agents used in the sterile area were the source of these phenolic impurities, several product samples were spiked with the sanitizing agents. Both o-phenylphenol and 4-t-amylphenol were detected in the spiked samples. Further investigation revealed that o-phenylphenol and 4-t-amylphenol are active ingredients of these commercial sanitizing agents. Drug product samples containing the phenolic impurities showed no potency loss following storage at 30, 50, and 70 degrees C indicating these impurities had no adverse effect on product stability. These studies suggest that sanitizing agents used in the sterile area, although may be present at trace levels below typical cleaning procedure detection methods, need to be properly controlled and closely monitored during the manufacturing of injectable products, particularly highly potent drugs. Sanitizing agents, even though not used on product contact surfaces, may potentially contaminate a product through vapor transfer in an open environment.

  2. Pharmaceutical impurities and degradation products: uses and applications of NMR techniques.

    PubMed

    Maggio, Rubén M; Calvo, Natalia L; Vignaduzzo, Silvana E; Kaufman, Teodoro S

    2014-12-01

    Current standards and regulations demand the pharmaceutical industry not only to produce highly pure drug substances, but to achieve a thorough understanding of the impurities accompanying their manufactured drug substances and products. These challenges have become important goals of process chemistry and have steadily stimulated the search of impurities after accelerated or forced degradation procedures. As a result, impurity profiling is one of the most attractive, active and relevant fields of modern pharmaceutical analysis. This activity includes the identification, structural elucidation and quantitative determination of impurities and degradation products in bulk drugs and their pharmaceutical formulations. Nuclear magnetic resonance (NMR) spectroscopy has evolved into an irreplaceable approach for pharmaceutical quality assessment, currently playing a critical role in unequivocal structure identification as well as structural confirmation (qualitative detection), enabling the understanding of the underlying mechanisms of the formation of process and/or degradation impurities. NMR is able to provide qualitative information without the need of standards of the unknown compounds and multiple components can be quantified in a complex sample without previous separation. When coupled to separative techniques, the resulting hyphenated methodologies enhance the analytical power of this spectroscopy to previously unknown levels. As a result, and by enabling the implementation of rational decisions regarding the identity and level of impurities, NMR contributes to the goal of making better and safer medicines. Herein are discussed the applications of NMR spectroscopy and its hyphenated derivate techniques to the study of a wide range pharmaceutical impurities. Details on the advantages and disadvantages of the methodology and well as specific challenges with regards to the different analytical problems are also presented.

  3. Study of impurity distribution in mechanically polished, chemically treated and high vacuum degassed pure niobium samples using the TOFSIMS technique

    NASA Astrophysics Data System (ADS)

    Bose, A.; Joshi, S. C.

    2015-07-01

    The performance of superconducting radio frequency (SRF) cavities is strongly influenced by various impurities within the penetration depth (∼50 nm) of niobium (Nb), which in turn depends on the applied surface treatments. The effect of these surface treatments on the impurities of Nb has been explored using various surface analytical techniques. However, the results are still inadequate in many aspects and the effect of sequential SRF treatments on the impurity distribution has not been explored. The present study analyzes various impurities within the penetration depth of Nb samples, treated by SRF cavity processing techniques such as colloidal silica polishing (simulating centrifugal barrel polishing), buffer chemical polishing (BCP), high pressure rinsing (HPR) and degassing under a high vacuum (HV) condition at 600 °C for 10 h. Static, dynamic and slow sputtering modes of the time of flight secondary ion mass spectrometry (TOFSIMS) technique were employed to study the effect of the above treatments on interstitial impurities, hydrocarbons, oxides, acidic residues, reaction products and metallic contaminations. The study confirms that the impurity distribution in Nb is not only sensitive to the surface treatments, but also to their sequence. Varying the treatment sequence prior to HV degassing treatments affected the final impurity levels in HV degassed bulk Nb samples. The HV degassing treatment was capable of reducing hydrogen contamination, but oxygen, carbon and metallic impurities were introduced into bulk Nb due to poor isolation from furnace contamination. On the other hand, BCP treated samples exhibited minimum hydrocarbon and metallic contamination along with the thinnest oxide layer at ∼2.8 nm, but led to extensive contamination of the oxide layer with residuals and reaction products of acids used in the BCP solution. HPR treatment, on the other hand, was effective in reducing the acidic impurities on the top surface. Variability of the

  4. Process and system for removing impurities from a gas

    SciTech Connect

    Henningsen, Gunnar; Knowlton, Teddy Merrill; Findlay, John George; Schlather, Jerry Neal; Turk, Brian S

    2014-04-15

    A fluidized reactor system for removing impurities from a gas and an associated process are provided. The system includes a fluidized absorber for contacting a feed gas with a sorbent stream to reduce the impurity content of the feed gas; a fluidized solids regenerator for contacting an impurity loaded sorbent stream with a regeneration gas to reduce the impurity content of the sorbent stream; a first non-mechanical gas seal forming solids transfer device adapted to receive an impurity loaded sorbent stream from the absorber and transport the impurity loaded sorbent stream to the regenerator at a controllable flow rate in response to an aeration gas; and a second non-mechanical gas seal forming solids transfer device adapted to receive a sorbent stream of reduced impurity content from the regenerator and transfer the sorbent stream of reduced impurity content to the absorber without changing the flow rate of the sorbent stream.

  5. Development of Impurity Profiling Methods Using Modern Analytical Techniques.

    PubMed

    Ramachandra, Bondigalla

    2017-01-02

    This review gives a brief introduction about the process- and product-related impurities and emphasizes on the development of novel analytical methods for their determination. It describes the application of modern analytical techniques, particularly the ultra-performance liquid chromatography (UPLC), liquid chromatography-mass spectrometry (LC-MS), high-resolution mass spectrometry (HRMS), gas chromatography-mass spectrometry (GC-MS) and high-performance thin layer chromatography (HPTLC). In addition to that, the application of nuclear magnetic resonance (NMR) spectroscopy was also discussed for the characterization of impurities and degradation products. The significance of the quality, efficacy and safety of drug substances/products, including the source of impurities, kinds of impurities, adverse effects by the presence of impurities, quality control of impurities, necessity for the development of impurity profiling methods, identification of impurities and regulatory aspects has been discussed. Other important aspects that have been discussed are forced degradation studies and the development of stability indicating assay methods.

  6. 40 CFR 158.340 - Discussion of formation of impurities.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... and products produced by an integrated system. (1) Each impurity associated with the active ingredient...) Products not produced by an integrated system. Each impurity associated with the active ingredient...

  7. Resonant impurities and their electronic behavior in single-layer graphene

    NASA Astrophysics Data System (ADS)

    Wang, Lin

    The electronic behavior of single-layer graphene (SLG) containing resonant impurities wasinvestigated, particularly by quantum capacitance measurements. Before introducing resonant impurities into SLG, the properties of pristine SLG devices top-gated using ultra-thin Y2O3 dielectric layers were systematically studied by structure characterization, DC transport measurements and AC quantum capacitance measurements. Y2O 3 is an ideal candidate of dielectric materials for SLG top-gated devices by introducing very few short-range impurities. This facilitates us to probe the quantum capacitance and the density of states (D = Cq/e 2) of pristine and disordered graphene due to its very large capacitance. A new type of resonant impurities of Ag adatoms deposited on SLG was successfully detected through quantum capacitance measurements. The midgap states induced by Ag-adatoms are visible at room temperature and more evident at cryogenic temperatures. Theintensity of Ag-adatom-induced resonances becomes stronger at higher impurity concentration and higher magnetic fields, which agrees fairly well with theoretical calculations based on the density functional theory (DFT) and tight-binding model (TB). We elucidated that the appearance of the robust resonant peak near the charge neutrality point (CNP) and the splitting of zero Landau level (LL) for Ag-adsorbed graphene are manifestations of the hybridization effect of electrons from graphene bands and the resonant impurity bands. With a very high density of Ag adatoms, SLG capacitors show unconventional negative quantum capacitance behavior. The Ag adatoms act as resonant impurities and form nearly dispersionless resonant impurity bands near the CNP. Resonant impurities quench the kinetic energy and drive the electrons to the Coulomb energy dominated regime with negative compressibility. In the absence of a magnetic field, negative quantum capacitance is observed near the CNP. In the quantum Hall regime, negative quantum

  8. Parallel Impurity Spreading During Massive Gas Injection

    NASA Astrophysics Data System (ADS)

    Izzo, V. A.

    2016-10-01

    Extended-MHD simulations of disruption mitigation in DIII-D demonstrate that both pre-existing islands (locked-modes) and plasma rotation can significantly influence toroidal spreading of impurities following massive gas injection (MGI). Given the importance of successful disruption mitigation in ITER and the large disparity in device parameters, empirical demonstrations of disruption mitigation strategies in present tokamaks are insufficient to inspire unreserved confidence for ITER. Here, MHD simulations elucidate how impurities injected as a localized jet spread toroidally and poloidally. Simulations with large pre-existing islands at the q = 2 surface reveal that the magnetic topology strongly influences the rate of impurity spreading parallel to the field lines. Parallel spreading is largely driven by rapid parallel heat conduction, and is much faster at low order rational surfaces, where a short parallel connection length leads to faster thermal equilibration. Consequently, the presence of large islands, which alter the connection length, can slow impurity transport; but the simulations also show that the appearance of a 4/2 harmonic of the 2/1 mode, which breaks up the large islands, can increase the rate of spreading. This effect is seen both for simulations with spontaneously growing and directly imposed 4/2 modes. Given the prevalence of locked-modes as a cause of disruptions, understanding the effect of large islands is of particular importance. Simulations with and without islands also show that rotation can alter impurity spreading, even reversing the predominant direction of spreading, which is toward the high-field-side in the absence of rotation. Given expected differences in rotation for ITER vs. DIII-D, rotation effects are another important consideration when extrapolating experimental results. Work supported by US DOE under DE-FG02-95ER54309.

  9. Deciphering the role of impurities in methylammonium iodide and their impact on the performance of perovskite solar cells (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Levchuk, Levgen; Hou, Yi; Gruber, Marco; Herre, Patrick; Brandl, Marco; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Tykwinski, Rik R.; Batentschuk, Miroslaw; Brabec, Christoph J.

    2016-09-01

    Solution based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, we have investigated the purity levels of common perovskite precursor solutions and found a number of impurities which are most critically controlling the crystallization of perovskites. Moreover, we identified these impurities at different level of concentrations is all commercially available precursors. In detail, we present a detailed chemical study on the nature of the various impurities in CH3NH3I and explored their impact on the crystal formation. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity free precursors vs precursors containing different concentrations of impurities. Most interestingly, we revealed that a certain concentration of impurities is detrimental to facilitate the growth of large grained crystals. This study gives valuable insight into the rate determining steps of perovskite crystal growth and provides the basis for developing reliable and reproducible high performance recipes for Perovskite solar cell processing.

  10. The Potts model on a Bethe lattice with nonmagnetic impurities

    SciTech Connect

    Semkin, S. V. Smagin, V. P.

    2015-10-15

    We have obtained a solution for the Potts model on a Bethe lattice with mobile nonmagnetic impurities. A method is proposed for constructing a “pseudochaotic” impurity distribution by a vanishing correlation in the arrangement of impurity atoms for the nearest sites. For a pseudochaotic impurity distribution, we obtained the phase-transition temperature, magnetization, and spontaneous magnetization jumps at the phase-transition temperature.

  11. Divertor impurity sources; effects of hot surfaces and thin films on impurity production

    NASA Astrophysics Data System (ADS)

    Stamp, M. F.; Andrew, P.; Brezinsek, S.; Huber, A.; JET EFDA Contributors

    2005-03-01

    Strong continuum emission has been observed from divertor tiles at visible wavelengths and identified as Planck radiation from surfaces with temperatures of typically ˜ 2600 K. Such hot spots (which are not tile edges) can persist for several seconds and are more common at the inner divertor, than the outer. Surprisingly, these hot spots do not usually produce significant impurity fluxes. In contrast, ELMs may produce a significant enhancement of impurity fluxes, depending on strike point location and ELM size.

  12. As-grown deep-level defects in n-GaN grown by metal-organic chemical vapor deposition on freestanding GaN

    SciTech Connect

    Chen Shang; Ishikawa, Kenji; Hori, Masaru; Honda, Unhi; Shibata, Tatsunari; Matsumura, Toshiya; Tokuda, Yutaka; Ueda, Hiroyuki; Uesugi, Tsutomu; Kachi, Tetsu

    2012-09-01

    Traps of energy levels E{sub c}-0.26 and E{sub c}-0.61 eV have been identified as as-grown traps in n-GaN grown by metal-organic chemical vapor deposition by using deep level transient spectroscopy of the Schottky contacts fabricated by resistive evaporation. The additional traps of E{sub c}-0.13 and E{sub c}-0.65 eV have been observed in samples whose contacts are deposited by electron-beam evaporation. An increase in concentration of the E{sub c}-0.13 and E{sub c}-0.65 eV traps when approaching the interface between the contact and the GaN film supports our argument that these traps are induced by electron-beam irradiation. Conversely, the depth profiles of as-grown traps show different profiles between several samples with increased or uniform distribution in the near surface below 50 nm. Similar profiles are observed in GaN grown on a sapphire substrate. We conclude that the growth process causes these large concentrations of as-grown traps in the near-surface region. It is speculated that the finishing step in the growth process should be an essential issue in the investigation of the surface state of GaN.

  13. Deep levels in high resistive CdTe and CdZnTe explored by photo-Hall effect and photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Musiienko, Artem; Grill, Roman; Hlídek, Pavel; Moravec, Pavel; Belas, Eduard; Zázvorka, Jakub; Korcsmáros, Gabriel; Franc, Jan; Vasylchenko, Igor

    2017-01-01

    High resistive CdTe and CdZnTe single crystals were measured by photo-Hall effect spectroscopy (PHES) and photoluminescence spectroscopy (PL) with the aim of discovering the position of deep levels (DLs) in the band gap. Illumination in the range of 0.65-1.77 eV, room temperature, and DC electrical measurements were used in the case of PHES. Low temperature (4 K) photoluminescence spectra were recorded in the spectral range above 0.47 eV. Eight samples, both n-type and p-type, were studied and typical shapes of spectra were collected, compared and interpreted for both spectroscopy methods. It was shown that a simple single-level model of PHES often fails in the interpretation of DLs distant from the midgap. Eight DLs with the energy E c - 0.65 eV, E c - 0.8 eV, E c - 0.9 eV, E c - (1.10-1.15) eV, E v + 0.70 eV, E v + 0.85 eV, E v + 1.0 eV, and E c - 1.25 eV were interpreted. A memory effect characterized by a relaxation time of about 60 s was observed at the 0.8 eV level and allowed us to determine the 1.7 × 10-17 cm2 capture cross-section of electrons on this level. It is argued that PHES is a convenient complementary method to identify and characterize DLs, including DLs inaccessible by thermal emission techniques. DLs observed by PHES were consistently verified by PL.

  14. Low-temperature effects of resonance electronic states at transition-element impurities in the kinetic, magnetic, and acoustic properties of semiconductors

    NASA Astrophysics Data System (ADS)

    Okulov, V. I.; Govorkova, T. E.; Gudkov, V. V.; Zhevstovskikh, I. V.; Korolyev, A. V.; Lonchakov, A. T.; Okulova, K. A.; Pamyatnykh, E. A.; Paranchich, S. Yu.

    2007-02-01

    New research results on phenomena due to the existence of electronic resonance energy levels and hybridized states at impurities of transition elements in semiconductors are presented. The data show that the thermal conductivity and ultrasonic parameters of mercury selenide containing iron impurities have resonance anomalies due to the influence of these impurities. A consistent and detailed interpretation is offered for the set of observed effects of hybridized states in mercury selenide with iron impurities. The proposed interpretation of the data obtained on other systems is discussed.

  15. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters.

    PubMed

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M

    2017-03-10

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id'-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id'-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id'-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry.

  16. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters

    PubMed Central

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M.

    2017-01-01

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id′-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id′-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id′-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry. PMID:28281570

  17. Caprylic acid precipitation method for impurity reduction: an alternative to conventional chromatography for monoclonal antibody purification.

    PubMed

    Brodsky, Yan; Zhang, Cheng; Yigzaw, Yinges; Vedantham, Ganesh

    2012-10-01

    We report the use of caprylic acid based impurity precipitation as (1) an alternative method to polishing chromatography techniques commonly used for monoclonal antibody purification and (2) an impurity reduction step prior to harvesting the bioreactor. This impurity reduction method was tested with protein A purified antibodies and with cell culture fluid. First, the operational parameters influencing precipitation of host cell proteins and high molecular weight aggregate in protein A pools were investigated. When used as a polishing step, the primary factor affecting purification and yield was determined to be pH. Caprylic acid precipitation was comparable to polishing IEX chromatography in reducing host cell protein and aggregate levels. A virus reduction study showed complete clearance of a model retrovirus during caprylic acid precipitation of protein A purified antibody. Caprylic acid mediated impurity precipitation in cell culture showed that the impurity clearance was generally insensitive to pH and caprylic acid concentration whereas yield was a function of caprylic acid concentration. Protein A purification of caprylic acid precipitated cell culture fluid generated less turbid product pool with reduced levels of host cell proteins and high molecular weight aggregate. The results of this study show caprylic acid precipitation to be an effective purification method that can be incorporated into a production facility with minimal cost as it utilizes existing tanks and process flow. Eliminating flow through chromatography polishing step can provide process intensification by avoiding the process tank volume constraints for high titer processes.

  18. Impurity bound states in fully gapped d-wave superconductors with subdominant order parameters

    NASA Astrophysics Data System (ADS)

    Mashkoori, Mahdi; Björnson, Kristofer; Black-Schaffer, Annica M.

    2017-03-01

    Impurities in superconductors and their induced bound states are important both for engineering novel states such as Majorana zero-energy modes and for probing bulk properties of the superconducting state. The high-temperature cuprates offer a clear advantage in a much larger superconducting order parameter, but the nodal energy spectrum of a pure d-wave superconductor only allows virtual bound states. Fully gapped d-wave superconducting states have, however, been proposed in several cuprate systems thanks to subdominant order parameters producing d + is- or d + id‧-wave superconducting states. Here we study both magnetic and potential impurities in these fully gapped d-wave superconductors. Using analytical T-matrix and complementary numerical tight-binding lattice calculations, we show that magnetic and potential impurities behave fundamentally different in d + is- and d + id‧-wave superconductors. In a d + is-wave superconductor, there are no bound states for potential impurities, while a magnetic impurity produces one pair of bound states, with a zero-energy level crossing at a finite scattering strength. On the other hand, a d + id‧-wave symmetry always gives rise to two pairs of bound states and only produce a reachable zero-energy level crossing if the normal state has a strong particle-hole asymmetry.

  19. Impurity enrichment and radiative enhancement using induced SOL flow in DIII-D

    SciTech Connect

    Wade, M.R.; West, W.P.; Wood, R.D.

    1998-07-01

    Experiments on DIII-D have demonstrated the efficacy of using induced scrap-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL floe is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative plasmas have been produced that combine high radiation losses (P{sub rad}/P{sub input} > 70%), low core fuel dilution (Z{sub eff} < 1.9), and good core confinement ({tau}{sub E} > 1.0 {tau}{sub E,ITER93H}).

  20. Monte Carlo method for magnetic impurities in metals

    NASA Technical Reports Server (NTRS)

    Hirsch, J. E.; Fye, R. M.

    1986-01-01

    The paper discusses a Monte Carlo algorithm to study properties of dilute magnetic alloys; the method can treat a small number of magnetic impurities interacting wiith the conduction electrons in a metal. Results for the susceptibility of a single Anderson impurity in the symmetric case show the expected universal behavior at low temperatures. Some results for two Anderson impurities are also discussed.

  1. Shape of impurity electronic absorption bands in nematic liquid crystal

    SciTech Connect

    Aver`yanov, E.M.

    1994-11-01

    The impurity-matrix anisotropic static intermolecular interactions, orientation-statistical properties, and electronic structure of uniaxial impurity molecules are shown to have a significant influence on spectral moments of the electronic absorption bands of impurities in the nematic liquid crystal. 14 refs., 3 figs.

  2. Impact of Pharmaceutical Impurities in Ecstasy Tablets: Gas Chromatography-Mass Spectrometry Study.

    PubMed

    Jalali, Amir; Hatamie, Amir; Saferpour, Tahere; Khajeamiri, Alireza; Safa, Tahere; Buazar, Foad

    2016-01-01

    In this study, a simple and reliable method by gas chromatograph-mass spectrometry (GC-MS) was developed for the fast and regular identification of 3, 4-MDMA impurities in ecstasy tablets. In so doing, 8 samples of impurities were extracted by diethyl ether under alkaline condition and then analyzed by GC-MS. The results revealed high MDMA levels ranging from 37.6% to 57.7%. The GC-MS method showed that unambiguous identification can be achieved for MDMA from 3, 4-methylenedioxyamphetamine (MDA), Amphetamine (AM), methamphetamine (MA) and ketamine (Keta) compounds, respectively. The experimental results indicated the acceptable time window without interfering peaks. It is found that GC-MS was provided a suitable and rapid identification approach for MDMA (Ecstacy) tablets, particularly in the Forensic labs. Consequently, the intense MDMA levels would support the police to develop a simple quantification of impurity in Ecstasy tablets.

  3. Impact of Pharmaceutical Impurities in Ecstasy Tablets: Gas Chromatography-Mass Spectrometry Study

    PubMed Central

    Jalali, Amir; Hatamie, Amir; Saferpour, Tahere; Khajeamiri, Alireza; Safa, Tahere; Buazar, Foad

    2016-01-01

    In this study, a simple and reliable method by gas chromatograph–mass spectrometry (GC–MS) was developed for the fast and regular identification of 3, 4-MDMA impurities in ecstasy tablets. In so doing, 8 samples of impurities were extracted by diethyl ether under alkaline condition and then analyzed by GC–MS. The results revealed high MDMA levels ranging from 37.6% to 57.7%. The GC-MS method showed that unambiguous identification can be achieved for MDMA from 3, 4-methylenedioxyamphetamine (MDA), Amphetamine (AM), methamphetamine (MA) and ketamine (Keta) compounds, respectively. The experimental results indicated the acceptable time window without interfering peaks. It is found that GC-MS was provided a suitable and rapid identification approach for MDMA (Ecstacy) tablets, particularly in the Forensic labs. Consequently, the intense MDMA levels would support the police to develop a simple quantification of impurity in Ecstasy tablets. PMID:27610162

  4. Photoionization and electrostatic multipoles properties of spherical core/shell/shell quantum nanolayer with off-center impurity

    NASA Astrophysics Data System (ADS)

    Baghdasaryan, D. A.; Kazaryan, E. M.; Sarkisyan, H. A.

    2017-04-01

    The electronic, optical and electrostatic properties of the spherical core/shell/shell quantum nanolayer with an off-centered impurity have been studied. Spherical nanolayers of both "small" and "large" radii have been considered in the framework of perturbation theory and the variational method. Photoionization cross-section that corresponds to the electron transitions from the impurity ground state to the size-quantized levels have been studied. The dependence of the photoionization cross section on the photon energy, impurity position and the geometrical parameters of the spherical nanolayer have been obtained. The electrostatic multipoles of the considered system have been investigated.

  5. EVALUATION OF IMPURITY EXTREMES IN A PLUTONIUM-LOADED BOROSILICATE GLASS

    SciTech Connect

    Marra, J; Kevin Fox, K; Charles Crawford, C; Ned Bibler, N; Elizabeth Hoffman, E; Tommy Edwards, T

    2007-11-12

    A vitrification technology utilizing a lanthanide borosilicate (LaBS) glass appears to be a viable option for the disposition of excess weapons-useable plutonium that is not suitable for processing into mixed oxide (MOX) fuel. A significant effort to develop a glass formulation and vitrification process to immobilize plutonium was completed in the mid-1990s. The LaBS glass formulation was found to be capable of immobilizing in excess of 10 wt % Pu and to be tolerant of a range of impurities. To confirm the results of previous testing with surrogate Pu feeds containing impurities, four glass compositions were selected for fabrication with actual plutonium oxide and impurities. The four compositions represented extremes in impurity type and concentration. The homogeneity and durability of these four compositions were measured. The homogeneity of the glasses was evaluated using x-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS). The XRD results indicated that the glasses were amorphous with no evidence of crystalline species in the glass. The SEM/EDS analyses did show the presence of some undissolved PuO{sub 2} material. The EDS spectra indicated that some of the PuO{sub 2} crystals also contained hafnium oxide. The SEM/EDS analyses showed that there were no heterogeneities in the glass due to the feed impurities. The durability of the glasses was measured using the Product Consistency Test (PCT). The PCT results indicated that the durability of Pu impurity glasses was comparable with Pu glasses without impurities and significantly more durable than the Environmental Assessment (EA) glass used as the benchmark for repository disposition of high-level waste (HLW) glasses.

  6. An Experimental Design Approach for Impurity Profiling of Valacyclovir-Related Products by RP-HPLC

    PubMed Central

    Katakam, Prakash; Dey, Baishakhi; Hwisa, Nagiat T; Assaleh, Fathi H; Chandu, Babu R; Singla, Rajeev K; Mitra, Analava

    2014-01-01

    Abstract Impurity profiling has become an important phase of pharmaceutical research where both spectroscopic and chromatographic methods find applications. The analytical methodology needs to be very sensitive, specific, and precise which will separate and determine the impurity of interest at the 0.1% level. Current research reports a validated RP-HPLC method to detect and separate valacyclovir-related impurities (Imp-E and Imp-G) using the Box-Behnken design approach of response surface methodology. A gradient mobile phase (buffer: acetonitrile as mobile phase A and acetonitrile: methanol as mobile phase B) was used. Linearity was found in the concentration range of 50–150 μg/mL. The mean recovery of impurities was 99.9% and 103.2%, respectively. The %RSD for the peak areas of Imp-E and Imp-G were 0.9 and 0.1, respectively. No blank interferences at the retention times of the impurities suggest the specificity of the method. The LOD values were 0.0024 μg/mL for Imp-E and 0.04 μg/mL for Imp-G and the LOQ values were obtained as 0.0082 μg/mL and 0.136 μg/mL, respectively, for the impurities. The S/N ratios in both cases were within the specification limits. Proper peak shapes and satisfactory resolution with good retention times suggested the suitability of the method for impurity profiling of valacyclovir-related drug substances. PMID:25853072

  7. The development of a potassium-sulfide glass fiber cell and studies on impurities in alkali metal-sulfur cells

    NASA Technical Reports Server (NTRS)

    Tsang, F. Y.

    1977-01-01

    Potassium sulfur rechargeable cells, having as the electrolyte the thin walls of hollow glass fibers made from permeable glass, were developed. The cells had short lives, probably due to the construction materials and impurities in the potassium. The effect of the impurities in the analogous NA-S system was studied. Calcium, potassium, and NaOH/oxide impurities caused increased resistance or corrosion of the glass fibers. For long lived cell operation, the Na must contain less than 1 ppm Ca and less than a few ppm of hydroxide/oxide. Up to 150 ppm K can be tolerated. After purification of the Na anolyte, cell lifetimes in excess of 1000 deep charge-discharge cycles or over 8 months on continuous cycling at 10-30 percent depth of discharge were obtained.

  8. Quantification of active pharmaceutical ingredient and impurities in sildenafil citrate obtained from the Internet

    PubMed Central

    Nutan, Mohammad T.; Dodla, Uday Krishna Reddy

    2014-01-01

    Background: The accessibility of prescription drugs produced outside of the United States, most notably sildenafil citrate (innovator product, Viagra®), has been made much easier by the Internet. Of greatest concern to clinicians and policymakers is product quality and patient safety. The US Food and Drug Administration (FDA) has issued warnings to potential buyers that the safety of drugs purchased from the Internet cannot be guaranteed, and may present a health risk to consumers from substandard products. Objective: The objective of this study was to determine whether generic sildenafil citrate tablets from international markets obtained via the Internet are equivalent to the US innovator product regarding major aspects of pharmaceutical quality: potency, accuracy of labeling, and presence and level of impurities. This will help identify aspects of drug quality that may impact public health risks. Methods: A total of 15 sildenafil citrate tablets were obtained for pharmaceutical analysis: 14 generic samples from international Internet pharmacy websites and the US innovator product. According to US Pharmacopeial guidelines, tablet samples were tested using high-performance liquid chromatography for potency of active pharmaceutical ingredient (API) and levels of impurities (impurities A, B, C, and D). Impurity levels were compared with International Conference on Harmonisation (ICH) limits. Results: Among the 15 samples, 4 samples possessed higher impurity B levels than the ICH qualification threshold, 8 samples possessed higher impurity C levels than the ICH qualification threshold, and 4 samples possessed more than 1% impurity quantity of maximum daily dose (MDD). For API, 6 of the samples failed to fall within the 5% assay limit. Conclusions: Quality assurance tests are often used to detect formulation defects of drug products during the manufacturing and/or storage process. Results suggest that manufacturing standards for sildenafil citrate generic drug

  9. Protein Crystal Growth Dynamics and Impurity Incorporation

    NASA Technical Reports Server (NTRS)

    Chernov, Alex A.; Thomas, Bill

    2000-01-01

    The general concepts and theories of crystal growth are proven to work for biomolecular crystallization. This allowed us to extract basic parameters controlling growth kinetics - free surface energy, alpha, and kinetic coefficient, beta, for steps. Surface energy per molecular site in thermal units, alpha(omega)(sup 2/3)/kT approx. = 1, is close to the one for inorganic crystals in solution (omega is the specific molecular volume, T is the temperature). Entropic restrictions on incorporation of biomolecules into the lattice reduce the incorporation rate, beta, by a factor of 10(exp 2) - 10(exp 3) relative to inorganic crystals. A dehydration barrier of approx. 18kcal/mol may explain approx. 10(exp -6) times difference between frequencies of adding a molecule to the lattice and Brownian attempts to do so. The latter was obtained from AFM measurements of step and kink growth rates on orthorhombic lysozyme. Protein and many inorganic crystals typically do not belong to the Kossel type, thus requiring a theory to account for inequivalent molecular positions within its unit cell. Orthorhombic lysozyme will serve as an example of how to develop such a theory. Factors deteriorating crystal quality - stress and strain, mosaicity, molecular disorder - will be reviewed with emphasis on impurities. Dimers in ferritin and lysozyme and acetylated lysozyme, are microheterogeneous i.e. nearly isomorphic impurities that are shown to be preferentially trapped by tetragonal lysozyme and ferritin crystals, respectively. The distribution coefficient, K defined as a ratio of the (impurity/protein) ratios in crystal and in solution is a measure of trapping. For acetylated lysoyzme, K = 2.15 or, 3.42 for differently acetylated forms, is independent of both the impurity and the crystallizing protein concentration. The reason is that impurity flux to the surface is constant while the growth rate rises with supersaturation. About 3 times lower dimer concentration in space grown ferritin and

  10. Human adipocytes from the subcutaneous superficial layer have greater adipogenic potential and lower PPAR-γ DNA methylation levels than deep layer adipocytes.

    PubMed

    Kosaka, Kentaro; Kubota, Yoshitaka; Adachi, Naoki; Akita, Shinsuke; Sasahara, Yoshitaro; Kira, Tomoe; Kuroda, Masayuki; Mitsukawa, Nobuyuki; Bujo, Hideaki; Satoh, Kaneshige

    2016-08-01

    Human subcutaneous fat tissue consists of two layers, superficial adipose tissue (SAT) and deep adipose tissue (DAT). Some recent reports suggest that a disproportionate accumulation of DAT is related to obesity-associated metabolic complications. However, the differences in adipocyte function between SAT and DAT are unclear. To clarify the differences in human adipocyte characteristics between SAT and DAT, human ceiling culture-derived proliferative adipocytes (ccdPAs) were primary cultured from SAT and DAT of three lean female patients. Differences in adipogenic differentiation potential and sensitivity to exogenous adipogenic factors were examined. Epigenetic modification of the CpG island DNA methylation levels of genes related to adipogenesis was measured. In histological analyses, the mean adipocyte size in SAT was significantly larger than that in DAT (8,741 ± 416 vs. 7,732 ± 213 μm(2), P < 0.05). Primary cultured adipocytes from SAT showed significantly greater adipogenesis than did those of DAT. Sensitivity to partial adipogenic stimulation was significantly different between ccdPAs of SAT and DAT. Peroxisome proliferator-activated receptor-γ (PPAR-γ) protein expression and leptin protein secretion from ccdPAs were significantly higher in SAT than DAT. DNA methylation levels of PPAR-γ were significantly lower in ccdPAs of SAT than DAT. Adipocyte size was larger in SAT than DAT in vivo. This is consistent with the findings of an in vitro study that, compared with ccdPAs in DAT, ccdPAs in SAT have higher adipogenic potential and lower DNA methylation levels of PPAR-γ.

  11. Electrical properties of grain boundaries and dislocations in crystalline silicon: Influence of impurity incorporation and hydrogenation

    NASA Astrophysics Data System (ADS)

    Park, Yongkook

    potential energy barrier in thermal equilibrium was reduced by 70 meV. Whereas the clean sample had a density of GB states of ˜6x1012 cm-2eV-1 in the range of Ev+0.54˜0.64 eV, hydrogenation reduced the density of GB states to ˜9x1011 cm-2eV -1 in the range of Ev+0.56˜0.61 eV, which is about a seven-fold reduction from that of the clean sample. Segregation and thermal dissociation kinetics of hydrogen at a large-angle general GB in crystalline silicon have been investigated using deuterium as a readily identifiable isotope which duplicates hydrogen chemistry. Segregation or trapping of deuterium (hydrogen) introduced was found to take place at (110)/(001) Si GB. The segregation coefficient (k) of deuterium (hydrogen) at GB was determined as k≈24+/-3 at 100°C. Thermal dissociation of deuterium (hydrogen) from GB obeyed first-order kinetics with an activation energy of ˜1.62 eV. The electrical activities of dislocations in a SiGe/Si heterostructure were examined by deep level transient spectroscopy (DLTS) after iron contamination and phosphorous diffusion gettering. DLTS of iron contaminated samples revealed a peak at 210 K, which was assigned to individual iron atoms or very small (<2 nm) precipitates decorated along dislocations. Arrhenius plot of the 210 K peak yielded a hole capture cross section of 2.4x10-14 cm2 and an energy level of 0.42 eV above the valance band. DLTS of the iron contaminated sample revealed that 6x10 14 cm-3 of boron can more effectively trap interstitial iron at room temperature than the strain field/defect sites at 107 ˜108 cm-2 dislocations. Phosphorous diffusion experiments revealed that the gettering efficiency of iron impurities depends on the dislocation density. For regions of high dislocation density, phosphorous diffusion cannot remove all iron impurities decorated at dislocations, suggesting a strong binding of iron impurities at dislocation core defects.

  12. When small is big: the role of impurities in electrocatalysis.

    SciTech Connect

    Strmcnik, Dusan; Li, Dongguo; Lopes, Pietro P.; Tripkovic, Dusan; Kodama, Kensaku; Stamenkovic, Vojislav R.; Markovic, Nenad M.

    2015-11-01

    Improvements in the fundamental understanding of electrocatalysis have started to revolutionize the development of electrochemical interfaces for the efficient conversion of chemical energy into electricity, as well as for the utilization of electrons to produce new chemicals that then can be re-used in energy conversion systems. Here, some facets of the role of trace level of impurities (from 10-7 to 10-6 M) in electrocatalysis of the oxygen reduction reaction, hydrogen oxidation and evolution reactions, and CO oxidation reactions are explored on well-characterized platinum single crystal surfaces and high surface area materials in alkaline and acidic environments. Of particular interest is the effect of anions (e.g., Cl-, NO3-) and cations (i.e., Cu2+) present in the supporting electrolytes as well as surface defects (i.e., ad-islands) that are present on metal surfaces. The examples presented are chosen to demonstrate that a small level of impurities may play a crucial role in governing the reactivity of electrochemical interfaces.

  13. Power Radiated from ITER and CIT by Impurities

    DOE R&D Accomplishments Database

    Cummings, J.; Cohen, S. A.; Hulse, R.; Post, D. E.; Redi, M. H.; Perkins, J.

    1990-07-01

    The MIST code has been used to model impurity radiation from the edge and core plasmas in ITER and CIT. A broad range of parameters have been varied, including Z{sub eff}, impurity species, impurity transport coefficients, and plasma temperature and density profiles, especially at the edge. For a set of these parameters representative of the baseline ITER ignition scenario, it is seen that impurity radiation, which is produced in roughly equal amounts by the edge and core regions, can make a major improvement in divertor operation without compromising core energy confinement. Scalings of impurity radiation with atomic number and machine size are also discussed.

  14. Incorporation of impurity to a tetragonal lysozyme crystal

    NASA Astrophysics Data System (ADS)

    Kurihara, Kazuo; Miyashita, Satoru; Sazaki, Gen; Nakada, Toshitaka; Durbin, Stephen D.; Komatsu, Hiroshi; Ohba, Tetsuhiko; Ohki, Kazuo

    1999-01-01

    Concentration of a phosphor-labeled impurity (ovalbumin) incorporated into protein (hen egg white lysozyme) crystals during growth was measured by fluorescence.This technique enabled us to measure the local impurity concentration in a crystal quantitatively. Impurity concentration increased with growth rate, which could not be explained by two conventional models (equilibrium adsorption model and Burton-Prim-Slichter model); a modified model is proposed. Impurity concentration also increased with the pH of the solution. This result is discussed considering the electrostatic interaction between the impurity and the crystallizing species.

  15. Characterization and validation of an in silico toxicology model to predict the mutagenic potential of drug impurities.

    PubMed

    Valerio, Luis G; Cross, Kevin P

    2012-05-01

    Control and minimization of human exposure to potential genotoxic impurities found in drug substances and products is an important part of preclinical safety assessments of new drug products. The FDA's 2008 draft guidance on genotoxic and carcinogenic impurities in drug substances and products allows use of computational quantitative structure-activity relationships (QSAR) to identify structural alerts for known and expected impurities present at levels below qualified thresholds. This study provides the information necessary to establish the practical use of a new in silico toxicology model for predicting Salmonella t. mutagenicity (Ames assay outcome) of drug impurities and other chemicals. We describe the model's chemical content and toxicity fingerprint in terms of compound space, molecular and structural toxicophores, and have rigorously tested its predictive power using both cross-validation and external validation experiments, as well as case studies. Consistent with desired regulatory use, the model performs with high sensitivity (81%) and high negative predictivity (81%) based on external validation with 2368 compounds foreign to the model and having known mutagenicity. A database of drug impurities was created from proprietary FDA submissions and the public literature which found significant overlap between the structural features of drug impurities and training set chemicals in the QSAR model. Overall, the model's predictive performance was found to be acceptable for screening drug impurities for Salmonella mutagenicity.

  16. Characterization of impurities of HIV NNRTI Doravirine by UHPLC-high resolution MS and tandem MS analysis.

    PubMed

    Zhang, Li-Kang; Yang, Ross; Sheng, Huaming; Helmy, Roy; Zheng, Jinjian; Cao, Yang; Gauthier, Donald R

    2016-10-01

    World Health Organization estimates that 34 million individuals globally are living with Human Immunodeficiency Virus (HIV). Doravirine is a non-nucleoside reverse transcriptase inhibitors (NNRTI) being evaluated by Merck for the treatment of HIV-1 infection. Drug regulation authorities require the purity of a pharmaceutical to be fully defined. This is important to ensure that the pharmacological and toxicological effects are truly those of the drug substances and not because of the impurities. Thus, understanding the drug impurity profiles is critical to the safety and potency assessment of the drug candidate for clinical trials. The impurity characterization can also provide useful information for critical assessment of pharmaceutical processes. Advances in mass spectrometry instrumentation and methods allow the identification of impurities in pharmaceuticals with a minimum of sample material and increased sensitivity. In this study, a rapid and sensitive method was developed for the structural determination of the major impurities of doravirine. The study utilizes ultra performance liquid chromatography-high-resolution-tandem mass spectrometry (UHPLC-HRMS/MS) techniques to perform structure elucidation of the unknown structures. This approach has significant impact on impurity structural elucidation, and a total of five trace-level impurities of doravirine were characterized using the developed method. Copyright © 2016 John Wiley & Sons, Ltd.

  17. Overcoming the Limitations of the SIE and OME Methods in Assessing the Effects of Impurities in Temperature Fixed Points

    NASA Astrophysics Data System (ADS)

    Fahr, M.; Cundy, D. S.

    2015-08-01

    Impurities are still among the primary concerns regarding the realization of many fixed points of the International Temperature Scale (ITS-90). Several methods have been suggested to correct for these effects. The most promising strategy, with regard to the achievable uncertainty level, is the `sum of the individual estimates' (SIE) method. It involves a chemical analysis of the material and a calculation of each of the detected chemical species' effect on the phase-transition temperature of the fixed-point substance. This correction can be accurate only if all the detected impurities are completely dissolved. Given the recent evidence for insoluble impurities in metal fixed points, this strategy needs to be modified; otherwise, it may lead to an inaccurate estimation of the impurity-related effect on the fixed-point temperature. In this article, a correction method is set out that reflects the crucial distinction between soluble, insoluble, and partially soluble impurities. This `sum of the individual estimates for the dissolved species' (SIEDS) method starts from a chemical analysis but takes into account only the dissolved particles. For this purpose, different types of substances are considered as possible dissolved impurities and are discussed from a chemical point of view. For those impurities where data are insufficient, only an uncertainty estimation is possible. For this purpose, the `overall maximum estimate of the dissolved species' (OMEDS) method is derived from the SIEDS method as the new counterpart to the well-known `overall maximum estimate' (OME) method.

  18. Systematic analysis of neuronal wiring of the rodent deep cerebellar nuclei reveals differences reflecting adaptations at the neuronal circuit and internuclear levels.

    PubMed

    Hamodeh, Salah; Baizer, Joan; Sugihara, Izumi; Sultan, Fahad

    2014-08-01

    A common view of the architecture of different brain regions is that, despite their heterogeneity, they have optimized their wiring schemes to make maximal use of space. Based on experimental findings, computational models have delineated how about two-thirds of the neuropil is filled out with dendrites and axons optimizing cable costs and conduction time while keeping the connectivity at the highest level. However, whether this assumption can be generalized to all brain regions has not yet been tested. Here we quantified and charted the components of the neuropil in the four deep cerebellar nuclei (DCN) of the rat's brain. We segmented and traced the neuropil stained with one of two antibodies, one antibody against dendritic microtubule-associated proteins (MAP2a,b) and the second against the Purkinje cell axons (PCP2). We compared fiber length density, average fiber diameter, and volume fraction within different components of the DCN in a random, systematic fashion. We observed differences in dendritic and axonal fiber length density, average fiber diameters, and volume fraction within the four different nuclei that make up the DCN. We observe a relative increase in the length density of dendrites and Purkinje cell axons in two of the DCN, namely, the posterior interposed nucleus and the lateral nucleus. Furthermore, the DCN have a surprisingly low volume fraction of their dendritic length density, which we propose is related to their special circuitry. In summary, our results show previously unappreciated functional adaptations among these nuclei.

  19. Effects of low temperature periodic annealing on the deep-level defects in 200 keV proton irradiated AlGaAs-GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.; Chiu, T. T.; Loo, R. Y.

    1981-01-01

    The GaAs solar cell has shown good potential for space applications. However, degradation in performance occurred when the cells were irradiated by high energy electrons and protons in the space environment. The considered investigation is concerned with the effect of periodic thermal annealing on the deep-level defects induced by the 200 keV protons in the AlGaAs-GaAs solar cells. Protons at a fluence of 10 to the 11th P/sq cm were used in the irradiation cycle, while annealing temperatures of 200 C (for 24 hours), 300 C (six hours), and 400 C (six hours) were employed. The most likely candidate for the E(c) -0.71 eV electron trap observed in the 200 keV proton irradiated samples may be due to GaAs antisite, while the observed E(v) +0.18 eV hole trap has been attributed to the gallium vacancy related defect. The obtained results show that periodic annealing in the considered case does not offer any advantages over the one time annealing process.

  20. Earth system modelling on system-level heterogeneous architectures: EMAC (version 2.42) on the Dynamical Exascale Entry Platform (DEEP)

    NASA Astrophysics Data System (ADS)

    Christou, Michalis; Christoudias, Theodoros; Morillo, Julián; Alvarez, Damian; Merx, Hendrik

    2016-09-01

    We examine an alternative approach to heterogeneous cluster-computing in the many-core era for Earth system models, using the European Centre for Medium-Range Weather Forecasts Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model as a pilot application on the Dynamical Exascale Entry Platform (DEEP). A set of autonomous coprocessors interconnected together, called Booster, complements a conventional HPC Cluster and increases its computing performance, offering extra flexibility to expose multiple levels of parallelism and achieve better scalability. The EMAC model atmospheric chemistry code (Module Efficiently Calculating the Chemistry of the Atmosphere (MECCA)) was taskified with an offload mechanism implemented using OmpSs directives. The model was ported to the MareNostrum 3 supercomputer to allow testing with Intel Xeon Phi accelerators on a production-size machine. The changes proposed in this paper are expected to contribute to the eventual adoption of Cluster-Booster division and Many Integrated Core (MIC) accelerated architectures in presently available implementations of Earth system models, towards exploiting the potential of a fully Exascale-capable platform.

  1. Investigation of electrically active defects in InGaAs quantum wire intermediate-band solar cells using deep-level transient spectroscopy technique

    NASA Astrophysics Data System (ADS)

    Saqri, Noor alhuda Al; Felix, Jorlandio F.; Aziz, Mohsin; Kunets, Vasyl P.; Jameel, Dler; Taylor, David; Henini, Mohamed; Abd El-sadek, Mahmmoud S.; Furrow, Colin; Ware, Morgan E.; Benamara, Mourad; Mortazavi, Mansour; Salamo, Gregory

    2017-01-01

    InGaAs quantum wire (QWr) intermediate-band solar cell-based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current-voltage (I-V) and capacitance-voltage (C-V) techniques, were found to change with temperature over a wide range of 20-340 K. The electron and hole traps present in these devices have been investigated using deep-level transient spectroscopy (DLTS). The DLTS results showed that the traps detected in the QWr-doped devices are directly or indirectly related to the insertion of the Si δ-layer used to dope the wires. In addition, in the QWr-doped devices, the decrease of the solar conversion efficiencies at low temperatures and the associated decrease of the integrated external quantum efficiency through InGaAs could be attributed to detected traps E1QWR_D, E2QWR_D, and E3QWR_D with activation energies of 0.0037, 0.0053, and 0.041 eV, respectively.

  2. Defects in virgin and N+ -implanted ZnO single crystals studied by positron annihilation, Hall effect, and deep-level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Brauer, G.; Anwand, W.; Skorupa, W.; Kuriplach, J.; Melikhova, O.; Moisson, C.; von Wenckstern, H.; Schmidt, H.; Lorenz, M.; Grundmann, M.

    2006-07-01

    High-quality single crystals of ZnO in the as-grown and N+ ion-implanted states have been investigated using a combination of three experimental techniques—namely, positron lifetime/slow positron implantation spectroscopy accompanied by theoretical calculations of the positron lifetime for selected defects, temperature-dependent Hall (TDH) measurements, and deep level transient spectroscopy (DLTS). The positron lifetime in bulk ZnO is measured to be (151±2)ps and that for positrons trapped in defects (257±2)ps . On the basis of theoretical calculations the latter is attributed to Zn+O divacancies, existing in the sample in neutral charge state, and not to the Zn vacancy proposed in previous experimental work. Their concentration is estimated to be 3.7×1017cm-3 . From TDH measurements the existence of negatively charged intrinsic defects acting as compensating acceptors is concluded which are invisible to positrons—maybe interstitial oxygen. This view is supported from TDH results in combination with DLTS which revealed the creation of the defect E1 , and an increase in concentration of the defect E3 after N+ ion implantation, and peculiarities in the observation of the defect E4 .

  3. Investigation of electrically active defects in InGaAs quantum wire intermediate-band solar cells using deep-level transient spectroscopy technique.

    PubMed

    Al Saqri, Noor Alhuda; Felix, Jorlandio F; Aziz, Mohsin; Kunets, Vasyl P; Jameel, Dler; Taylor, David; Henini, Mohamed; Abd El-Sadek, Mahmmoud S; Furrow, Colin; Ware, Morgan E; Benamara, Mourad; Mortazavi, Mansour; Salamo, Gregory

    2017-01-27

    InGaAs quantum wire (QWr) intermediate-band solar cell-based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current-voltage (I-V) and capacitance-voltage (C-V) techniques, were found to change with temperature over a wide range of 20-340 K. The electron and hole traps present in these devices have been investigated using deep-level transient spectroscopy (DLTS). The DLTS results showed that the traps detected in the QWr-doped devices are directly or indirectly related to the insertion of the Si δ-layer used to dope the wires. In addition, in the QWr-doped devices, the decrease of the solar conversion efficiencies at low temperatures and the associated decrease of the integrated external quantum efficiency through InGaAs could be attributed to detected traps E1QWR_D, E2QWR_D, and E3QWR_D with activation energies of 0.0037, 0.0053, and 0.041 eV, respectively.

  4. Nondestructive characterization of dislocations and micropipes in high-resistivity 6H-SiC wafers by deep-level photoluminescence mapping

    NASA Astrophysics Data System (ADS)

    Tajima, M.; Higashi, E.; Hayashi, T.; Kinoshita, H.; Shiomi, H.

    2005-02-01

    We demonstrated the effectiveness of deep-level photoluminescence (PL) mapping for nondestructive detection of dislocations and micropipes in high-resistivity 6H-SiC wafers. PL spectra of the wafers at room temperature were dominated by a broad band with a peak at 1.3eV, which was traceable to the Si vacancy-related V1, V2, and V3 lines at 4.2K. The intensity-mapping pattern agreed closely with the etch-pit pattern both on a wafer scale and on a microscopic scale. Large dark spots with one or two bright cores, small dark spots, and dark lines corresponded to micropipes, threading screw dislocations, and edge dislocations forming small angle grain boundaries, respectively. The intensity reduction around dislocations and micropipes was attributed to a decrease of the radiative centers for the 1.3eV band, which occurred as a result either of the interaction between vacancies and dislocations or of the gettering effect of vacancy-related defects.

  5. Hydrophilic Conjugated Polymers with Large Bandgaps and Deep-Lying HOMO Levels as an Efficient Cathode Interlayer in Inverted Polymer Solar Cells.

    PubMed

    Kan, Yuanyuan; Zhu, Yongxiang; Liu, Zhulin; Zhang, Lianjie; Chen, Junwu; Cao, Yong

    2015-08-01

    Two hydrophilic conjugated polymers, PmP-NOH and PmP36F-NOH, with polar diethanol-amine on the side chains and main chain structures of poly(meta-phenylene) and poly(meta-phenylene-alt-3,6-fluorene), respectively, are successfully synthesized. The films of PmP-NOH and PmP36F-NOH show absorption edges at 340 and 343 nm, respectively. The calculated optical bandgaps of the two polymers are 3.65 and 3.62 eV, respectively, the largest ones so far reported for hydrophilic conjugated polymers. PmP-NOH and PmP36F-NOH also possess deep-lying highest occupied molecular orbital levels of -6.19 and -6.15 eV, respectively. Inserting PmP-NOH and PmP36F-NOH as a cathode interlayer in inverted polymer solar cells with a PTB7/PC71 BM blend as the active layer, high power conversion efficiencies of 8.58% and 8.33%, respectively, are achieved, demonstrating that the two hydrophilic polymers are excellent interlayers for efficient inverted polymer solar cells.

  6. Kinetic neoclassical calculations of impurity radiation profiles

    SciTech Connect

    Stotler, D. P.; Battaglia, D. J.; Hager, R.; Kim, K.; Koskela, T.; Park, G.; Reinke, M. L.

    2016-12-30

    Modifications of the drift-kinetic transport code XGC0 to include the transport, ionization, and recombination of individual charge states, as well as the associated radiation, are described. The code is first applied to a simulation of an NSTX H-mode discharge with carbon impurity to demonstrate the approach to coronal equilibrium. The effects of neoclassical phenomena on the radiated power profile are examined sequentially through the activation of individual physics modules in the code. Orbit squeezing and the neoclassical inward pinch result in increased radiation for temperatures above a few hundred eV and changes to the ratios of charge state emissions at a given electron temperature. As a result, analogous simulations with a neon impurity yield qualitatively similar results.

  7. Kinetic neoclassical calculations of impurity radiation profiles

    DOE PAGES

    Stotler, D. P.; Battaglia, D. J.; Hager, R.; ...

    2016-12-30

    Modifications of the drift-kinetic transport code XGC0 to include the transport, ionization, and recombination of individual charge states, as well as the associated radiation, are described. The code is first applied to a simulation of an NSTX H-mode discharge with carbon impurity to demonstrate the approach to coronal equilibrium. The effects of neoclassical phenomena on the radiated power profile are examined sequentially through the activation of individual physics modules in the code. Orbit squeezing and the neoclassical inward pinch result in increased radiation for temperatures above a few hundred eV and changes to the ratios of charge state emissions atmore » a given electron temperature. As a result, analogous simulations with a neon impurity yield qualitatively similar results.« less

  8. Global migration of impurities in tokamaks

    NASA Astrophysics Data System (ADS)

    Hakola, A.; Airila, M. I.; Björkas, C.; Borodin, D.; Brezinsek, S.; Coad, J. P.; Groth, M.; Järvinen, A.; Kirschner, A.; Koivuranta, S.; Krieger, K.; Kurki-Suonio, T.; Likonen, J.; Lindholm, V.; Makkonen, T.; Mayer, M.; Miettunen, J.; Müller, H. W.; Neu, R.; Petersson, P.; Rohde, V.; Rubel, M.; Widdowson, A.; the ASDEX Upgrade Team; Contributors, JET-EFDA

    2013-12-01

    The migration of impurities in tokamaks has been studied with the help of tracer-injection (13C and 15N) experiments in JET and ASDEX Upgrade since 2001. We have identified a common pattern for the migrating particles: scrape-off layer flows drive impurities from the low-field side towards the high-field side of the vessel. Migration is also sensitive to the density and magnetic configuration of the plasma, and strong local variations in the resulting deposition patterns require 3D treatment of the migration process. Moreover, re-erosion of the deposited particles has to be taken into account to properly describe the migration process during steady-state operation of the tokamak.

  9. Spin pumping through magnetic impurity effect

    NASA Astrophysics Data System (ADS)

    Deng, Wei-Yin; Sheng, Li; Xing, Ding-Yu

    2015-08-01

    We propose a simple adiabatic quantum spin pump to generate pure spin current. The spin pump is driven by an ac gate voltage and a time-dependent magnetic impurity potential. It is found that the total pumped spin per cycle exhibits oscillations, whose magnitude decays exponentially with changing strength of the impurity potential. The proposed method may be useful for spintronic applications. Project supported by the State Key Program for Basic Research of China (Grant Nos. 2015CB921202, 2014CB921103, 2011CB922103, and 2010CB923400), the National Natural Science Foundation of China (Grant Nos. 11225420, 11174125, and 91021003), and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

  10. Spectroscopic investigation of heavy impurity behaviour during ICRH with the JET ITER-like wall

    SciTech Connect

    Czarnecka, A.; Bobkov, V.; Maggi, C.; Pütterich, T.; Coffey, I. H.; Colas, L.; Jacquet, P.; Lawson, K. D.; Mayoral, M.-L. [Euratom Collaboration: JET-EFDA Contributors

    2014-02-12

    Magnetically confined plasmas, such as those produced in the tokamak JET, contain measurable amounts of impurity ions produced during plasma-wall interactions (PWI) from the plasma-facing components and recessed wall areas. The impurities, including high- and mid-Z elements such as tungsten (W) from first wall tiles and nickel (Ni) from Inconel structure material, need to be controlled within tolerable limits, to ensure they do not significantly affect the performance of the plasma. This contribution focuses on documenting W and Ni impurity behavior during Ion Cyclotron Resonance Heating (ICRH) operation with the new ITER-Like Wall (ILW). Ni- and W-concentration were derived from VUV spectroscopy and the impact of applied power level, relative phasing of the antenna straps, plasma separatrix - antenna strap distance, IC resonance position, edge density and different plasma configuration, on the impurity release during ICRH are presented. For the same ICRH power the Ni and W concentration was lower with dipole phasing than in the case of −π/2 phasing. The Ni concentration was found to increase with ICRH power and for the same NBI power level, ICRH-heated plasmas were characterized by two times higher Ni impurity content. Both W and Ni concentrations increased strongly with decreasing edge density which is equivalent to higher edge electron temperatures and more energetic ions responsible for the sputtering. In either case higher levels were found in ICRH than in NBI heated discharges. When the central plasma temperature was similar, ICRH on-axis heating resulted in higher core Ni impurity concentration in comparison to off-axis ICRH in L-mode. It was also found that the main core radiation during ICRH came from W.

  11. Impurities contained in antifungal drug ketoconazole are potent activators of human aryl hydrocarbon receptor.

    PubMed

    Grycová, Aneta; Dořičáková, Aneta; Dvořák, Zdeněk

    2015-12-03

    Antifungal drug ketoconazole is a mixture of (+)/(-) cis-enantiomers, which also contains several impurities. Ketoconazole was identified as an activator of aryl hydrocarbon receptor AhR by three independent research teams. In the current paper we demonstrate that impurities contained in ketoconazole preparations are strong activators of human AhR and inducers of CYP1A1. Impurity IMP-C had similar potency (EC50), but 10-15 times higher efficacy (magnitude of induction) towards AhR, comparing to (+)-ketoconazole, as revealed by gene reporter assay in AZ-AHR stably transfected cells. Impurities IMP-B and IMP-C, and in lesser extent IMP-E, induced a formation of AhR-DNA complex, as demonstrated by electromobility shift assay EMSA. Impurities IMP-C and IMP-E dose-dependently induced CYP1A1 mRNA after 24 h, and their effects were comparable to those by (+)-ketoconazole. The level of CYP1A1 protein in HepG2 cells was strongly increased by IMP-C after 48h. In conclusion, our data further elucidated molecular effects of ketoconazole towards AhR signaling pathway, with possible implications in ketoconazole role in skin chemoprevention and/or damage, involving AhR.

  12. Assembly and Study of Different Mercury Cells with Known Impurity Content and Isotopic Composition

    NASA Astrophysics Data System (ADS)

    Del Campo, D.; Chimenti, V.; Reyes, J.; Castrillón, J. A. Rodríguez; Moldovan, M.; Alonso, J. I. García

    2008-02-01

    The “Centro Español de Metrología” is carrying out a project to improve the knowledge of the influence of impurities and isotopic composition on the temperature of the mercury triple point. High-purity mercury from the Almaden mine (stated purity of 99.9998%) was further purified by vacuum distillation. Three mercury fractions, the original mercury from Almaden and two distilled fractions, were characterized in terms of both impurities and isotopic composition and used to measure the mercury triple point. The original mercury sample contained silver at 560 ng · g-1 as the main impurity while the impurity levels were much lower (silver < 1 ng · g-1) in the two distilled fractions. The isotopic composition of the distilled fractions showed delta values, expressed as 1,000×(^{198/202}Hg_sample-^{198/202} Hg_reference)/^{198/202}Hg_reference, of 1.37±0.07 (1 σ) for the first distilled sample and -1.55±0.03 (1 σ) for the second distilled sample with reference to the original Almaden mercury. For the measurement of the mercury triple point, an alcohol stirred bath was used that allowed two cells to be compared nearly simultaneously. It was observed that the presence of the silver impurities in the high-purity mercury modified slightly the mercury triple point while the effect of variations in the isotopic composition can be considered negligible.

  13. Development of Hydrophilic Interaction Liquid Chromatography Method for the Analysis of Moxonidine and Its Impurities

    PubMed Central

    2016-01-01

    Fast and simple hydrophilic interaction liquid chromatography (HILIC) method was developed and validated for the analysis of moxonidine and its four impurities (A, B, C, and D) in pharmaceutical dosage form. All experiments were performed on the Agilent Technologies 1200 high-performance liquid chromatography (HPLC) system using Zorbax RX-SIL, 250 mm × 4.6 mm, 5 μm column as stationary phase (T = 25°C, F = 1 mL/min, and λ = 255 nm), and mixture of acetonitrile and 40 mM ammonium formate buffer (pH 2.8) 80 : 20 (v/v) as mobile phase. Under the optimal chromatographic conditions, selected by central composite design, separation and analysis of moxonidine and its four impurities are enabled within 12 minutes. Validation of the method was conducted in accordance with ICH guidelines. Based on the obtained results selectivity, linearity (r ≥ 0.9976), accuracy (recovery: 93.66%–114.08%), precision (RSD: 0.56%–2.55%), and robustness of the method were confirmed. The obtained values of the limit of detection and quantification revealed that the method can be used for determination of impurities levels below 0.1%. Validated method was applied for determination of moxonidine and its impurities in commercially available tablet formulation. Obtained results confirmed that validated method is fast, simple, and reliable for analysis of moxonidine and its impurities in tablets. PMID:27847672

  14. Electrophobic interaction induced impurity clustering in metals

    SciTech Connect

    Zhou, Hong-Bo; Wang, Jin-Long; Jiang, W.; Lu, Guang-Hong; Aguiar, J. A.; Liu, Feng

    2016-10-01

    We introduce the concept of electrophobic interaction, analogous to hydrophobic interaction, for describing the behavior of impurity atoms in a metal, a 'solvent of electrons'. We demonstrate that there exists a form of electrophobic interaction between impurities with closed electron shell structure, which governs their dissolution behavior in a metal. Using He, Be and Ar as examples, we predict by first-principles calculations that the electrophobic interaction drives He, Be or Ar to form a close-packed cluster with a clustering energy that follows a universal power-law scaling with the number of atoms (N) dissolved in a free electron gas, as well as W or Al lattice, as Ec is proportional to (N2/3-N). This new concept unifies the explanation for a series of experimental observations of close-packed inert-gas bubble formation in metals, and significantly advances our fundamental understanding and capacity to predict the solute behavior of impurities in metals, a useful contribution to be considered in future material design of metals for nuclear, metallurgical, and energy applications.

  15. Deep Earthquakes.

    ERIC Educational Resources Information Center

    Frohlich, Cliff

    1989-01-01

    Summarizes research to find the nature of deep earthquakes occurring hundreds of kilometers down in the earth's mantle. Describes further research problems in this area. Presents several illustrations and four references. (YP)

  16. Potential interactions between different levels of cosmic radiation and their influence on the assessment of radiation risk during a manned deep space mission

    NASA Astrophysics Data System (ADS)

    Mortazavi, S.

    Despite the fact that galactic cosmic rays is believed to be isotropic throughout interstellar space, solar flares and coronal mass ejections can produce sudden and dramatic increase in flux of particles and expose the astronauts to transient high levels of ionizing radiation Furthermore, astronauts receive extra doses in the course of their extravehicular activities. It has been estimated that exposure to unpredictable extremely large solar particle events would kill the astronauts without massive shielding in interplanetary space. It is also generally believed that the biological effects of small doses of ionizing radiation may lie below the detection limits. However, potential interactions between a small dose and a subsequent high dose are still a black box that its output may be much different from the effect of a high dose alone. Potential interactions from low and high doses can either be a simple additivity, adaptive responses or synergistic effects. Significant adaptive response has been demonstrated in humans after exposure to high levels of natural radiation. Furthermore, non-linear behavior has been observed for cosmic radiation. Recent long-term follow-up studies as well as studies performed on twins show that in contrast to early reports, the type of interaction is determined by intrinsic factors such as genetic constitution of each individual. Despite that these responses for low- LET radiations (mainly photons and beta particles) are documented to some extent, there are no data on possible interactions of high-energy protons or high-LET heavy ions. The assessment of potential interactions between chronic low doses and acute high doses of high energy protons and heavy ions will be of importance in practical radiation protection of cosmonauts during a deep space mission.

  17. Synthesis of the impurities during the manufacture of bulk drug midazolam and separation of these impurities by HPLC.

    PubMed

    Sati, Bhawana; Sati, Hemlata; Saklani, Sarla; Bhatt, Prakash Chandra; Mishra, Ravinesh

    2013-09-01

    During the manufacture of bulk drug midazolam various impurities arised that can be the related products or degradation products. Structures of eight impurities that can arise during the manufacture of bulk drug midazolam were proposed. In the present work, synthesis of these impurities and their characterization by different spectroscopic techniques have been done. HPLC method was developed for the separation of impurities from the bulk drug. The developed method separates midazolam from its eight impurities/degradation products within a run time of 45 min.

  18. Incorporation and redistribution of impurities into silicon nanowires during metal-particle-assisted growth.

    PubMed

    Chen, Wanghua; Yu, Linwei; Misra, Soumyadeep; Fan, Zheng; Pareige, Philippe; Patriarche, Gilles; Bouchoule, Sophie; Roca i Cabarrocas, Pere

    2014-06-12

    The incorporation of metal atoms into silicon nanowires during metal-particle-assisted growth is a critical issue for various nanowire-based applications. Here we have been able to access directly the incorporation and redistribution of metal atoms into silicon nanowires produced by two different processes at growth rates ranging from 3 to 40 nm s(-1), by using laser-assisted atom probe tomography and scanning transmission electron microscopy. We find that the concentration of metal impurities in crystalline silicon nanowires increases with the growth rate and can reach a level of two orders of magnitude higher than that in their equilibrium solubility. Moreover, we demonstrate that the impurities are first incorporated into nanowire volume and then segregate at defects such as the twin planes. A dimer-atom-insertion kinetic model is proposed to account for the impurity incorporation into nanowires.

  19. Devolution and grant-in-aid design for the provision of impure public goods.

    PubMed

    Levaggi, Laura; Levaggi, Rosella

    2016-01-01

    Traditional fiscal federalism theory postulates that devolution for the provision of local public goods increases welfare. However, most of the services offered at local level are local impure public goods whose characteristics may prevent devolution from being efficient. Our paper shows that devolution is the optimal choice only for local impure public goods. For an environment characterised by coordination and asymmetry of information problems, we propose the optimal grants-in-aid formula that Central Government should use to reduce welfare losses and we compare it with what suggested by the mainstream literature. Finally, we show under which conditions devolution should be preferred to a centralised solution. From a policy point of view, our paper may explain the heterogeneity in the choices made by countries in terms of devolution in the provision of merit and impure public goods.

  20. Synergistic effect of hydrogen and impurity segregations on the grain boundary embrittlement in Nb

    NASA Astrophysics Data System (ADS)

    Ilyin, A. M.; Shestakov, V. P.; Tazhibaeva, I. L.

    2000-12-01

    Niobium and its alloys are the candidate materials for fusion reactors and can be used at high-temperatures. This paper was intended to study embrittlement of niobium by high-concentrations of hydrogen and impurity segregation at grain boundaries. Specimens of commercial Nb were subjected to heat treatment at 1100°C and 500°C and subsequently charged with deuterium in an electrolytic cell. The charged specimens were placed into the high-vacuum chamber of a special self-made Auger electron spectrometer. They were then fractured under high-vacuum conditions and the chemistry of grain boundaries was analysed. Carbon and oxygen were found as the main impurities on the grain boundaries and effective energies for hydrogen-impurity-grain boundary interaction have been estimated. It was found that there is a noticeable reduction of fracture strength corresponding to the grain boundary oxygen and carbon segregation levels.

  1. Theory of Electronic Structures of Selenium and Tellurium with and without Impurities

    NASA Astrophysics Data System (ADS)

    Cho, Hwa-Suck; Scheicher, R. H.; Jeong, Junho; Das, T. P.; Paudyal, D. D.; Maharjan, N. B.; Mishra, D. R.; Byahut, S. P.

    2003-03-01

    As part of our program to understand at an electronic level the mechanism for influence of impurity ions on glass transition temperatures in chalcogen glasses we are carrying out electronic structure investigations of pure Se and Te and with Te and Se impurities respectively, to examine how well one can explain available nuclear quadrupole interaction (NQI) tensors for ^77Se and ^125Te nuclei in the latter four systems(See for instance, P. Boolchand et al., Phys. Rev. Lett. 30, 1292 (1973); Solid State Commun. 13, 1619 (1973).) and thus obtain an assessment of the accuracy of the electronic structures of these systems. Our results on the chains of selenium and tellurium show good agreement with NQI data for the pure and impurity systems. Investigations are in progress on Se and Te rings that occur in amorphous systems.

  2. Interstitial impurity-induced magnetism in α-PbO surface.

    PubMed

    Arguelles, E; Amino, S; Aspera, S; Nakanishi, H; Kasai, H

    2015-01-14

    We have investigated the effects of 3d transition metal (TM) and non-magnetic interstitial impurities in α-PbO (0 0 1) surface using ab-initio calculations. The calculated impurity-induced magnetic moments are 2.25 μB, 3.11 μB and 0.94 μB for Fe, Mn and Pb interstitials respectively. In the bonding process, TM's lower energy lying d(z2) states form overlaps with nearest neighbour oxygen atoms' p(z) states, with other non-bonding spin split d states situated near or at the Fermi level. These spin split orbitals introduce spin polarised p impurity states of oxygen atoms near the surface.

  3. Effect of weak impurities on electronic properties of graphene: Functional renormalization-group analysis

    NASA Astrophysics Data System (ADS)

    Katanin, A.

    2013-12-01

    We consider an effect of weak impurities on the electronic properties of graphene within the functional renormalization-group approach. The energy dependences of the electronic self-energy and density of states near the neutrality point are discussed. Depending on the symmetry of the impurities, the electronic damping Γ and density of states ρ can deviate substantially from those given by the self-consistent Born approximation. We investigate the crossover from the results of the self-consistent Born approximation, which are valid far from the neutrality point to the strong-coupling (diffusive) regime near the neutrality point. For impurities, which are diagonal in both valley and sublattice indices, we obtain a finite density of states at the Fermi level with values which are much bigger than the result of the self-consistent Born approximation.

  4. Characterization and validation of an in silico toxicology model to predict the mutagenic potential of drug impurities*

    SciTech Connect

    Valerio, Luis G.; Cross, Kevin P.

    2012-05-01

    Control and minimization of human exposure to potential genotoxic impurities found in drug substances and products is an important part of preclinical safety assessments of new drug products. The FDA's 2008 draft guidance on genotoxic and carcinogenic impurities in drug substances and products allows use of computational quantitative structure–activity relationships (QSAR) to identify structural alerts for known and expected impurities present at levels below qualified thresholds. This study provides the information necessary to establish the practical use of a new in silico toxicology model for predicting Salmonella t. mutagenicity (Ames assay outcome) of drug impurities and other chemicals. We describe the model's chemical content and toxicity fingerprint in terms of compound space, molecular and structural toxicophores, and have rigorously tested its predictive power using both cross-validation and external validation experiments, as well as case studies. Consistent with desired regulatory use, the model performs with high sensitivity (81%) and high negative predictivity (81%) based on external validation with 2368 compounds foreign to the model and having known mutagenicity. A database of drug impurities was created from proprietary FDA submissions and the public literature which found significant overlap between the structural features of drug impurities and training set chemicals in the QSAR model. Overall, the model's predictive performance was found to be acceptable for screening drug impurities for Salmonella mutagenicity. -- Highlights: ► We characterize a new in silico model to predict mutagenicity of drug impurities. ► The model predicts Salmonella mutagenicity and will be useful for safety assessment. ► We examine toxicity fingerprints and toxicophores of this Ames assay model. ► We compare these attributes to those found in drug impurities known to FDA/CDER. ► We validate the model and find it has a desired predictive performance.

  5. Estimated Tissue and Blood N(2) Levels and Risk of Decompression Sickness in Deep-, Intermediate-, and Shallow-Diving Toothed Whales during Exposure to Naval Sonar.

    PubMed

    Kvadsheim, P H; Miller, P J O; Tyack, P L; Sivle, L D; Lam, F P A; Fahlman, A

    2012-01-01

    Naval sonar has been accused of causing whale stranding by a mechanism which increases formation of tissue N(2) gas bubbles. Increased tissue and blood N(2) levels, and thereby increased risk of decompression sickness (DCS), is thought to result from changes in behavior or physiological responses during diving. Previous theoretical studies have used hypothetical sonar-induced changes in both behavior and physiology to model blood and tissue N(2) tension [Formula: see text], but this is the first attempt to estimate the changes during actual behavioral responses to sonar. We used an existing mathematical model to estimate blood and tissue N(2) tension [Formula: see text] from dive data recorded from sperm, killer, long-finned pilot, Blainville's beaked, and Cuvier's beaked whales before and during exposure to Low- (1-2 kHz) and Mid- (2-7 kHz) frequency active sonar. Our objectives were: (1) to determine if differences in dive behavior affects risk of bubble formation, and if (2) behavioral- or (3) physiological responses to sonar are plausible risk factors. Our results suggest that all species have natural high N(2) levels, with deep diving generally resulting in higher end-dive [Formula: see text] as compared with shallow diving. Sonar exposure caused some changes in dive behavior in both killer whales, pilot whales and beaked whales, but this did not lead to any increased risk of DCS. However, in three of eight exposure session with sperm whales, the animal changed to shallower diving, and in all these cases this seem to result in an increased risk of DCS, although risk was still within the normal risk range of this species. When a hypothetical removal of the normal dive response (bradycardia and peripheral vasoconstriction), was added to the behavioral response during model simulations, this led to an increased variance in the estimated end-dive N(2) levels, but no consistent change of risk. In conclusion, we cannot rule out the possibility that a combination

  6. Estimated Tissue and Blood N2 Levels and Risk of Decompression Sickness in Deep-, Intermediate-, and Shallow-Diving Toothed Whales during Exposure to Naval Sonar

    PubMed Central

    Kvadsheim, P. H.; Miller, P. J. O.; Tyack, P. L.; Sivle, L. D.; Lam, F. P. A.; Fahlman, A.

    2012-01-01

    Naval sonar has been accused of causing whale stranding by a mechanism which increases formation of tissue N2 gas bubbles. Increased tissue and blood N2 levels, and thereby increased risk of decompression sickness (DCS), is thought to result from changes in behavior or physiological responses during diving. Previous theoretical studies have used hypothetical sonar-induced changes in both behavior and physiology to model blood and tissue N2 tension PN2, but this is the first attempt to estimate the changes during actual behavioral responses to sonar. We used an existing mathematical model to estimate blood and tissue N2 tension PN2 from dive data recorded from sperm, killer, long-finned pilot, Blainville’s beaked, and Cuvier’s beaked whales before and during exposure to Low- (1–2 kHz) and Mid- (2–7 kHz) frequency active sonar. Our objectives were: (1) to determine if differences in dive behavior affects risk of bubble formation, and if (2) behavioral- or (3) physiological responses to sonar are plausible risk factors. Our results suggest that all species have natural high N2 levels, with deep diving generally resulting in higher end-dive PN2 as compared with shallow diving. Sonar exposure caused some changes in dive behavior in both killer whales, pilot whales and beaked whales, but this did not lead to any increased risk of DCS. However, in three of eight exposure session with sperm whales, the animal changed to shallower diving, and in all these cases this seem to result in an increased risk of DCS, although risk was still within the normal risk range of this species. When a hypothetical removal of the normal dive response (bradycardia and peripheral vasoconstriction), was added to the behavioral response during model simulations, this led to an increased variance in the estimated end-dive N2 levels, but no consistent change of risk. In conclusion, we cannot rule out the possibility that a combination of behavioral and physiological responses to sonar

  7. High Plasma Levels of D-Dimer Are Independently Associated with a Heightened Risk of Deep Vein Thrombosis in Patients with Intracerebral Hemorrhage.

    PubMed

    Cheng, Xuan; Zhang, Lu; Xie, Nan-Chang; Ma, Yun-Qing; Lian, Ya-Jun

    2016-10-01

    Deep venous thrombosis (DVT) is a complication of stroke. Our aim was to determine whether D-dimer plasma levels at admission could be a risk factor for DVT in Chinese patients with acute intracerebral hemorrhage (ICH). From December 2012 to November 2014, all patients with first-ever acute ICH were included. At baseline, the demographical and clinical data were taken. These patients were assessed for DVT using color Doppler ultrasonography (CDUS) on 15 days after ICH and whenever clinically requested. Multivariate analyses were performed using logistic regression models. Receiver operating characteristic (ROC) curves were used to test the overall predictive accuracy of D-dimer and other markers. In our study, acute ICH was diagnosed in 265 patients and 210 completed a 15-day follow-up and were included in the analysis. Fifty-four (25.7 %) out of the 210 patients were diagnosed as DVT. Plasma D-dimer levels were significantly higher in ICH patients with DVT as compared to those without DVT (P < 0.0001). Multivariate logistic regression analysis adjusted for common risk factors showed that plasma D-dimer levels ≥1.20 mg/L were an independent predictor of DVT [odds ratio (OR) = 12.99, 95 % confidence interval (CI) = 3.17-32.98; P < 0.0001]. With an area under the curve (AUC) of 0.91 (95 % CI = 0.86-0.94), D-dimer showed a significantly greater discriminatory ability to predict DVT as compared with high-sensitivity C-reactive protein (Hs-CRP) (AUC = 0.77, 95 % CI = 0.70-0.82; P < 0.01), homocysteine (HCY) (AUC = 0.75, 95 % CI = 0.70-0.81; P < 0.01), and National Institutes of Health Stroke Scale (NIHSS) score (AUC = 0.80, 95 % CI = 0.72-0.85; P < 0.01). The present study suggested that elevated D-dimer plasma levels were independent predictors for DVT in Chinese patients with ICH.

  8. Observation and Calculation of the ECRH Effect on the Tracer Impurity Accumulation in LHD

    NASA Astrophysics Data System (ADS)

    Tamura, Naoki

    2016-10-01

    In a magnetic confinement fusion reactor various Z impurities will exist inside the plasma. When the amount of the impurities exceeds the acceptable level by an accumulation, this will lead to impermissible plasma performance degradation due to the radiation losses and plasma dilution. Therefore, it is crucially important to develop effective schemes for controlling the impurities in the core plasma and to understand the underlying physical mechanisms of such schemes. Recent LHD experiments show the ability of ECRH to control the impurity accumulation. Experiments on the LHD have used a tracer-encapsulated solid pellet (TESPEL), which is embedded with vanadium, to introduce the extrinsic and non-recycling impurity directly inside the last-closed flux surface (LCFS) region. Therefore, the confinement time of the vanadium impurity can be directly evaluated from the time history of highly ionized vanadium ion. In cases where the collisionality between the impurity ions and the bulk ion is in the Banana-Plateau regime (but close to the collisional Pfirsch-Schlüter (PS) regime), the impurities in the LHD plasma are strongly accumulated into the core plasma. When the 1.5 MW 154 GHz ECRH is applied for such plasma just after the TESPEL injection, the accumulation of the vanadium ions was almost completely suppressed. This result indicates that applying ECRH changes the direction of the radial vanadium particle flux from the inward to the outward. Although the neoclassical ambipolar radial electric field in stellarators has a stronger impact on the transport, particularly on the impurity transport, than in tokamaks, there is no conclusive data regarding a radial electric field measured with a charge exchange spectroscopy diagnostic to support the view that the change in the radial electric field would be attributed to the outward flow of the vanadium ions in the LHD plasma. In this contribution, the results of ongoing evaluations of the neoclassical (e.g., PENTA/DKES that

  9. Theoretical Study of Radiation from a Broad Range of Impurity Ions for Magnetic Fusion Diagnostics

    SciTech Connect

    Safronova, Alla

    2014-03-14

    Spectroscopy of radiation emitted by impurities plays an important role in the study of magnetically confined fusion plasmas. The measurements of these impurities are crucial for the control of the general machine conditions, for the monitoring of the impurity levels, and for the detection of various possible fault conditions. Low-Z impurities, typically present in concentrations of 1%, are lithium, beryllium, boron, carbon, and oxygen. Some of the common medium-Z impurities are metals such as iron, nickel, and copper, and high-Z impurities, such as tungsten, are present in smaller concentrations of 0.1% or less. Despite the relatively small concentration numbers, the aforementioned impurities might make a substantial contribution to radiated power, and also influence both plasma conditions and instruments. A detailed theoretical study of line radiation from impurities that covers a very broad spectral range from less than 1 Å to more than 1000 Å has been accomplished and the results were applied to the LLNL Electron Beam Ion Trap (EBIT) and the Sustained Spheromak Physics Experiment (SSPX) and to the National Spherical Torus Experiment (NSTX) at Princeton. Though low- and medium-Z impurities were also studied, the main emphasis was made on the comprehensive theoretical study of radiation from tungsten using different state-of-the-art atomic structure codes such as Relativistic Many-Body Perturbation Theory (RMBPT). The important component of this research was a comparison of the results from the RMBPT code with other codes such as the Multiconfigurational Hartree–Fock developed by Cowan (COWAN code) and the Multiconfiguration Relativistic Hebrew University Lawrence Atomic Code (HULLAC code), and estimation of accuracy of calculations. We also have studied dielectronic recombination, an important recombination process for fusion plasma, for variety of highly and low charged tungsten ions using COWAN and HULLAC codes. Accurate DR rate coefficients are needed for

  10. Motion of a distinguishable Impurity in the Bose gas: Arrested expansion without a lattice and impurity snaking

    SciTech Connect

    Neil J. Robinson; Caux, Jean -Sebastien; Konik, Robert M.

    2016-04-07

    We consider the real-time dynamics of an initially localized distinguishable impurity injected into the ground state of the Lieb-Liniger model. Focusing on the case where integrability is preserved, we numerically compute the time evolution of the impurity density operator in regimes far from analytically tractable limits. We find that the injected impurity undergoes a stuttering motion as it moves and expands. For an initially stationary impurity, the interaction-driven formation of a quasibound state with a hole in the background gas leads to arrested expansion—a period of quasistationary behavior. In conclusion, when the impurity is injected with a finite center-of-mass momentum, the impurity moves through the background gas in a snaking manner, arising from a quantum Newton’s cradlelike scenario where momentum is exchanged back and forth between the impurity and the background gas.

  11. Motion of a distinguishable Impurity in the Bose gas: Arrested expansion without a lattice and impurity snaking

    DOE PAGES

    Neil J. Robinson; Caux, Jean -Sebastien; Konik, Robert M.

    2016-04-07

    We consider the real-time dynamics of an initially localized distinguishable impurity injected into the ground state of the Lieb-Liniger model. Focusing on the case where integrability is preserved, we numerically compute the time evolution of the impurity density operator in regimes far from analytically tractable limits. We find that the injected impurity undergoes a stuttering motion as it moves and expands. For an initially stationary impurity, the interaction-driven formation of a quasibound state with a hole in the background gas leads to arrested expansion—a period of quasistationary behavior. In conclusion, when the impurity is injected with a finite center-of-mass momentum,more » the impurity moves through the background gas in a snaking manner, arising from a quantum Newton’s cradlelike scenario where momentum is exchanged back and forth between the impurity and the background gas.« less

  12. Motion of a Distinguishable Impurity in the Bose Gas: Arrested Expansion Without a Lattice and Impurity Snaking

    NASA Astrophysics Data System (ADS)

    Robinson, Neil J.; Caux, Jean-Sébastien; Konik, Robert M.

    2016-04-01

    We consider the real-time dynamics of an initially localized distinguishable impurity injected into the ground state of the Lieb-Liniger model. Focusing on the case where integrability is preserved, we numerically compute the time evolution of the impurity density operator in regimes far from analytically tractable limits. We find that the injected impurity undergoes a stuttering motion as it moves and expands. For an initially stationary impurity, the interaction-driven formation of a quasibound state with a hole in the background gas leads to arrested expansion—a period of quasistationary behavior. When the impurity is injected with a finite center-of-mass momentum, the impurity moves through the background gas in a snaking manner, arising from a quantum Newton's cradlelike scenario where momentum is exchanged back and forth between the impurity and the background gas.

  13. Spectroscopic methods for detection of impurities in water

    NASA Astrophysics Data System (ADS)

    Strashnikova, Natalia V.; Papiashvili, Nona; Cohen-Luria, Rivka; Mark, Shlomo; Shilon, Guy; Khankin, Daniel; Kalisky, Yehoshua; Kalisky, Ofra; Parola, Abraham H.

    2011-11-01

    Optical photoluminescence spectroscopic method for detection of impurities, hazardous materials, pesticides, and pollutants in water resources, both qualitatively and quantitatively, is presented. The method is based on synchronous fluorescence spectroscopy (SFS) of organic aromatic compounds, or poly-aromatic hydrocarbons (PAH), and is carried out by following simultaneously their excitation and emission spectra. The full excitation emission matrix (EEM) generated in this way provides a 2-D and 3-D fluorescence map of the tested sample and the diagonals through the axes origin provide the synchronous fluorescence spectra at a constant wavelengths differences between the emission and excitation wavelengths, thus enabling multitude components identification. This map contains all the relevant spectroscopic information of the tested sample, and serves as a unique "fingerprint" with a very specific and accurate identification. When compared with pre-determined spectra and calibration curves from a "databank", there is a one-toone correspondence between the image and the specific compound, and it can be identified accurately both qualitatively and quantitatively. This method offers several significant advantages, and it provides a sensitive (ppm detection level), accurate and simple spectroscopic tool to monitor impurities and pollutants in water. The design and performance of the spectrofluorimeter prototype, as well as the software development and analysis of chemical organic compounds and mixtures in water will be discussed in this paper.

  14. A mechanistic study of impurity segregation at silicon grain boundaries

    SciTech Connect

    Käshammer, Peter; Sinno, Talid

    2015-09-07

    The segregation behavior of carbon and oxygen atoms at various silicon grain boundaries was studied using a combination of atomistic simulation and analytical modeling. First, quasi-lattice Grand Canonical Monte Carlo simulations were used to compute segregation isotherms as a function of grain boundary type, impurity atom loading level, and temperature. Next, the atomistic results were employed to regress different analytical segregation models and extract thermodynamic and structural properties. The multilayer Brunauer–Emmett–Teller (BET) isotherm was found to quantitatively capture all the simulation conditions probed in this work, while simpler, single layer models such as the Langmuir-McLean model did not. Some of the BET parameters, namely, the binding free energy of the first adsorption layer and the impurity holding capacity of each layer, were tested for correlation with various measures of grain boundary structure and/or mechanical properties. It was found that certain measures of the atomistic stress distribution correlate strongly with the first-layer binding free energy for substitutional carbon atoms, while common grain boundary identifiers such as sigma value and energy density are not useful in this regard. Preliminary analysis of the more complex case of interstitial oxygen segregation showed that similar measures based on atomistic stress also may be useful here, but more systematic correlative studies are needed to develop a comprehensive picture.

  15. Valency configuration of transition metal impurities in ZnO

    SciTech Connect

    Petit, Leon; Schulthess, Thomas C; Svane, Axel; Temmerman, Walter M; Szotek, Zdzislawa; Janotti, Anderson

    2006-01-01

    We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to the valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.

  16. Study of radioactive impurities in neutron transmutation doped germanium

    NASA Astrophysics Data System (ADS)

    Mathimalar, S.; Dokania, N.; Singh, V.; Nanal, V.; Pillay, R. G.; Shrivastava, A.; Jagadeesan, K. C.; Thakare, S. V.

    2015-02-01

    A program to develop low temperature (mK) sensors with neutron transmutation doped Ge for rare event studies with a cryogenic bolometer has been initiated. For this purpose, semiconductor grade Ge wafers are irradiated with thermal neutron flux from Dhruva reactor at Bhabha Atomic Research Centre (BARC), Mumbai. Spectroscopic studies of irradiated samples have revealed that the environment of the capsule used for irradiating the sample leads to significant levels of 65Zn, 110mAg and 182Ta impurities, which can be reduced by chemical etching of approximately 50 μm thick surface layer. From measurements of the etched samples in the low background counting setup, activity due to trace impurities of 123Sb in bulk Ge is estimated to be 1 Bq / g after irradiation. These estimates indicate that in order to use the NTD Ge sensors for rare event studies, a cooldown period of 2 years would be necessary to reduce the radioactive background to ≤ 1 mBq / g.

  17. Oxygen and carbon impurities and related defects in silicon

    NASA Technical Reports Server (NTRS)

    Pearce, C. W.

    1985-01-01

    Oxygen and carbon are the predominant impurities in Czochralski-grown silicon. The incorporation of oxygen and carbon during crystal growth is reviewed and device effects are discussed. Methods for controlling oxygen and carbon incorporation during crystal growth are discussed and results supporting a segregation coefficient of k=0.5 for oxygen are presented. The nucleation and precipitation behavior of oxygen is complex. Temperature and doping level effects which add insight into the role of point defects in the nucleation process are highlighted. In general, precipitation is found to be retarded in N+ and P+ silicon. The types and quantities of defects resulting from the oxygen precipitates is of interest as they are technologically useful in the process called intrinsic gettering. A comparison is made between the available defect sites and the quantities of metallic impurities present in a typical wafer which need to be gettered. Finally, a discussion of the denuded-zone, intrinsic-gettered (DZ-IG) structure on device properties is presented.

  18. A mechanistic study of impurity segregation at silicon grain boundaries

    NASA Astrophysics Data System (ADS)

    Käshammer, Peter; Sinno, Talid

    2015-09-01

    The segregation behavior of carbon and oxygen atoms at various silicon grain boundaries was studied using a combination of atomistic simulation and analytical modeling. First, quasi-lattice Grand Canonical Monte Carlo simulations were used to compute segregation isotherms as a function of grain boundary type, impurity atom loading level, and temperature. Next, the atomistic results were employed to regress different analytical segregation models and extract thermodynamic and structural properties. The multilayer Brunauer-Emmett-Teller (BET) isotherm was found to quantitatively capture all the simulation conditions probed in this work, while simpler, single layer models such as the Langmuir-McLean model did not. Some of the BET parameters, namely, the binding free energy of the first adsorption layer and the impurity holding capacity of each layer, were tested for correlation with various measures of grain boundary structure and/or mechanical properties. It was found that certain measures of the atomistic stress distribution correlate strongly with the first-layer binding free energy for substitutional carbon atoms, while common grain boundary identifiers such as sigma value and energy density are not useful in this regard. Preliminary analysis of the more complex case of interstitial oxygen segregation showed that similar measures based on atomistic stress also may be useful here, but more systematic correlative studies are needed to develop a comprehensive picture.

  19. Capillary electrophoresis determination of loratadine and related impurities.

    PubMed

    Fernández, H; Rupérez, F J; Barbas, C

    2003-03-10

    While HPLC has traditionally been the method of choice for purity determination of pharmaceutical substances, capillary electrophoresis (CE) offers a different selectivity and hence it is a complementary technique to HPLC. Loratadine, an antihistamine, could include in its raw material seven impurities that ought to be separated, identified and quantified for drug development and quality control. As a complementary tool for undoubtful identification, a CE method has been developed. The separation was carried out with an uncoated fused-silica capillary (57 cm x 50 microm ID) and was operated at 20 kV potential. Temperature was maintained at 25 degrees C. The final separation buffer was prepared with 100 mM H(3)PO(4) made up to pH 2.5 with NaOH and with 10% acetonitrile added (v/v). Impurities can be detected at the 0.1% level of the active and validation parameters for linearity accuracy and precision are adequate for all the analytes and that permits to consider the method reliable and suitable for application to long-term stability and purity studies.

  20. Theoretical explanation for strong poloidal impurity asymmetry in tokamak pedestals

    NASA Astrophysics Data System (ADS)

    Espinosa, Silvia

    2016-10-01

    Stronger impurity density in-out poloidal asymmetries than predicted by the most comprehensive neoclassical models have been measured in H-mode tokamak pedestals during the last decade. However, these pioneering theories neglect the impurity diamagnetic drift, while recent measurements indicate that it can be of the same order as the ExB drift that is retained. In order to keep both drifts self-consistently, stronger radial gradients of the impurity density must be allowed. As a result, radial impurity flow effects need to be included for the first time. These effects substantially alter the parallel impurity flow. The resulting modification in the impurity friction with the banana regime background ions then allows stronger poloidal variation of the impurity density, temperature and potential. Even the six-fold high field side accumulation of boron density measured on Alcator C-Mod can be explained without invoking anomalous transport. Moreover, the potential can no longer be assumed to be a flux function since the impurity density variation gives a poloidally varying potential that results in strong poloidal variation of the radial electric field. The fact that the magnitude of the negative radial electric field and the impurity temperature are both larger on the low field side is also correctly predicted. Finally, this pedestal neoclassical model with radial flows may provide insight on how to control impurity accumulation in JET. Supported by DOE Grant DE-FG0291ER54109 and La Caixa Fellowship.