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Sample records for alkali halide photocathodes

  1. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

    SciTech Connect

    Brendel', V M; Bukin, V V; Garnov, Sergei V; Bagdasarov, V Kh; Denisov, N N; Garanin, Sergey G; Terekhin, V A; Trutnev, Yurii A

    2012-12-31

    A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation. (laser technologies)

  2. Fabrication of alkali halide UV photocathodes by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Brendel', V. M.; Bukin, V. V.; Garnov, Sergei V.; Bagdasarov, V. Kh; Denisov, N. N.; Garanin, Sergey G.; Terekhin, V. A.; Trutnev, Yurii A.

    2012-12-01

    A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation.

  3. Quantum efficiencies of imaging detectors with alkali halide photocathodes. I - Microchannel plates with separate and integral CsI photocathodes

    NASA Technical Reports Server (NTRS)

    Carruthers, George R.

    1987-01-01

    Measurements and comparisons have been made of the quantum efficiencies of microchannel plate (MCP) detectors in the far-UV (below 2000-A) wavelength range using CsI photocathodes (a) deposited on the front surfaces of microchannel plates and (b) deposited on solid substrates as opaque photocathodes with the resulting photoelectrons input to microchannel plates. The efficiences were measured in both pulse-counting and photodiode modes of operation. Typical efficiencies are about 15 percent at 1216 A for a CsI-coated MCP compared with 65 percent for an opaque CsI photocathode MCP detector. Special processing has yielded an efficiency as high as 20 percent for a CsI-coated MCP. This may possibly be further improved by optimization of the tilt angle of the MCP channels relative to the front face of the MCP and incident radiation. However, at present there still remains a factor of at least 3 quantum efficiency advantage in the separate opaque CsI photocathode configuration.

  4. Extreme ultraviolet quantum efficiency of opaque alkali halide photocathodes on microchannel plates

    NASA Technical Reports Server (NTRS)

    Siegmund, O. H. W.; Everman, E.; Vallerga, J. V.; Lampton, M.

    1988-01-01

    Comprehensive measurements are presented for the quantum detection efficiency (QDE) of the microchannel plate materials CsI, KBr, KCl, and MgF2, over the 44-1800 A wavelength range. QDEs in excess of 40 percent are achieved by several materials in specific wavelength regions of the EUV. Structure is noted in the wavelength dependence of the QDE that is directly related to the valence-band/conduction-band gap energy and the onset of atomic-like resonant transitions. A simple photocathode model allows interpretation of these features, together with the QDE efficiency variation, as a function of illumination angle.

  5. Adsorption on Alkali Halides.

    NASA Astrophysics Data System (ADS)

    Urzua Duran, Gilberto Antonio

    1995-01-01

    Using a variety of interionic potentials, I have computed the configurations of adsorbed alkali halides monomers on the (001) surface of selected alkali halides crystals. In the majority of cases studied it is found that the monomer adsorbs perpendicular to the surface with the cation sitting nearly on top of the surface anion. In about ten percent of the cases though the monomer adsorbs tilted from the vertical. In these cases the ion that is closer to the surface can be the cation or the anion. The effect of polarization forces is found to be important. In order to discuss the effects of surface retaxation with adsorbates, I have evaluated the surface relaxation of the alkali halide crystals, using a shell model for the interionic forces. It is found that surface relaxation and rumpling are generally small, especially when the van der Waals forces are included. A theory of the effect of substrate vibrations on the binding of an adsorbed atom is developed. At T = 0 the binding energy is D_0-E, where D_0 is the surface well depth (classical binding energy) and E is the quantum correction. For several simple models, it is found that E is surprisingly model-independent. We compare D _0-E with the binding energies to a rigid substrate, D_0-E_{rs}, and to a vibrationally averaged substrate, D _0-E_{va}. We prove that E_{va}>=q E>=q E_ {rs} and that similar relations hold at finite temperature for the free energy of binding. In most cases E_{rs} is better than E_{va} as an approximation to E.

  6. Alkali metal and alkali earth metal gadolinium halide scintillators

    DOEpatents

    Bourret-Courchesne, Edith; Derenzo, Stephen E.; Parms, Shameka; Porter-Chapman, Yetta D.; Wiggins, Latoria K.

    2016-08-02

    The present invention provides for a composition comprising an inorganic scintillator comprising a gadolinium halide, optionally cerium-doped, having the formula A.sub.nGdX.sub.m:Ce; wherein A is nothing, an alkali metal, such as Li or Na, or an alkali earth metal, such as Ba; X is F, Br, Cl, or I; n is an integer from 1 to 2; m is an integer from 4 to 7; and the molar percent of cerium is 0% to 100%. The gadolinium halides or alkali earth metal gadolinium halides are scintillators and produce a bright luminescence upon irradiation by a suitable radiation.

  7. The Additive Coloration of Alkali Halides

    ERIC Educational Resources Information Center

    Jirgal, G. H.; and others

    1969-01-01

    Describes the construction and use of an inexpensive, vacuum furnace designed to produce F-centers in alkali halide crystals by additive coloration. The method described avoids corrosion or contamination during the coloration process. Examination of the resultant crystals is discussed and several experiments using additively colored crystals are…

  8. Ionic alkali halide XUV laser feasibility study

    SciTech Connect

    Yang, T.T.; Gylys, V.T.; Bower, R.D.; Harris, D.G.; Blauer, J.A.; Turner, C.E.; Hindy, R.N.

    1989-11-10

    The objective of this work is to assess the feasibility of a select set of ionic alkali halide XUV laser concepts by obtaining the relevant kinetic and spectroscopic parameters required for a proof-of-principle and conceptual design. The proposed lasers operate in the 80--200 nm spectral region and do not require input from outside radiation sources for their operation. Frequency up-conversion and frequency mixing techniques and therefore not considered in the work to be described. An experimental and theoretical study of a new type of laser operating in the extreme ultraviolet wavelength region has been conducted. The lasing species are singly ionized alkali halide molecules such as Rb{sup 2+}F{sub {minus}}, Rb{sup 2+}Br{sup {minus}} and Cs{sup 2+}F{sup {minus}}. These species are similar in electronic structure to the rare gas halide excimers, such as XeF and Krf, except that the ionic molecules emit at wavelengths of 80--200 nm, much shorter than the conventional rare-gas halide excimer laser. The radiative lifetime of these molecules are typically near 1 ns, which is about an order of magnitude shorter than that for rare-gas halide systems. The values of the cross section for stimulated emission are on the order of 1 {times} 10{sup {minus}16}cm{sup 2}. Because of the fundamental similarity to existing UV lasers, these systems show promise as a high power, efficient XUV lasers. 55 refs., 50 figs., 5 tabs.

  9. Enhanced quantum efficiency from hybrid cesium halide/copper photocathodes

    NASA Astrophysics Data System (ADS)

    Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Gong, Yu; Hess, Wayne P.

    2014-04-01

    The quantum efficiency (QE) of Cu is found to increase dramatically when coated by a CsI film and then irradiated by a UV laser. Over three orders of magnitude quantum efficiency enhancement at 266 nm is observed in CsI/Cu(100), indicating potential application in future photocathode devices. Upon laser irradiation, a large work function reduction to a value less than 2 eV is also observed, significantly greater than for similarly treated CsBr/Cu(100). The initial QE enhancement, prior to laser irradiation, is attributed to interface interaction and the intrinsic properties of the Cs halide film. Further QE enhancement following activation is attributed to formation of inter-band states and Cs metal accumulation at the interface induced by laser irradiation.

  10. Enhanced Quantum Efficiency From Hybrid Cesium Halide/Copper Photocathode

    SciTech Connect

    Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Gong, Yu; Hess, Wayne P.

    2014-04-28

    The quantum efficiency of Cu is found to increase dramatically when coated by a CsI film and then irradiated by a UV laser. Over three orders of magnitude quantum efficiency enhancement at 266 nm is observed in CsI/Cu(100), indicating potential application in future photocathode devices. Upon laser irradiation, a large work function reduction to a value less than 2 eV is also observed, significantly greater than for similarly treated CsBr/Cu(100). The initial QE enhancement, prior to laser irradiation, is attributed to interface interaction, surface cleanliness and the intrinsic properties of the Cs halide film. Further QE enhancement following activation is attributed to formation of inter-band states and Cs metal accumulation at the interface induced by laser irradiation.

  11. Enhanced quantum efficiency from hybrid cesium halide/copper photocathodes

    SciTech Connect

    Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Gong, Yu; Hess, Wayne P.

    2014-04-28

    The quantum efficiency (QE) of Cu is found to increase dramatically when coated by a CsI film and then irradiated by a UV laser. Over three orders of magnitude quantum efficiency enhancement at 266 nm is observed in CsI/Cu(100), indicating potential application in future photocathode devices. Upon laser irradiation, a large work function reduction to a value less than 2 eV is also observed, significantly greater than for similarly treated CsBr/Cu(100). The initial QE enhancement, prior to laser irradiation, is attributed to interface interaction and the intrinsic properties of the Cs halide film. Further QE enhancement following activation is attributed to formation of inter-band states and Cs metal accumulation at the interface induced by laser irradiation.

  12. Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

    SciTech Connect

    Bory, Benjamin F.; Wang, Jingxin; Janssen, René A. J.; Meskers, Stefan C. J.; Gomes, Henrique L.; De Leeuw, Dago M.

    2014-12-08

    Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron–hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 10{sup 25}/m{sup 3}. The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics.

  13. Ultra low emittance electron beams from multi-alkali antimonide photocathode operated with infrared light

    NASA Astrophysics Data System (ADS)

    Cultrera, L.; Gulliford, C.; Bartnik, A.; Lee, H.; Bazarov, I.

    2016-03-01

    The intrinsic emittance of electron beams generated from a multi-alkali photocathode operated in a high voltage DC gun is reported. The photocathode showed sensitivity extending to the infrared part of the spectrum up to 830 nm. The measured intrinsic emittances of electron beams generated with light having wavelength longer than 800 nm are approaching the limit imposed by the thermal energy of electrons at room temperature with quantum efficiencies comparable to metallic photocathodes used in operation of modern photoinjectors.

  14. Electro-optic contribution to Raman scattering from alkali halides

    SciTech Connect

    Mahan, G.D.; Subbaswamy, K.R.

    1986-06-15

    The electro-optic contributions to second-order Raman scattering and field-induced first-order scattering from alkali halides are calculated explicitly in terms of the ionic hyperpolarizability coefficients. The relevant local-field corrections are evaluated. Illustrative numerical results are presented.

  15. Cohesive Energy-Lattice Constant and Bulk Modulus-Lattice Constant Relationships: Alkali Halides, Ag Halides, Tl Halides

    NASA Technical Reports Server (NTRS)

    Schlosser, Herbert

    1992-01-01

    In this note we present two expressions relating the cohesive energy, E(sub coh), and the zero pressure isothermal bulk modulus, B(sub 0), of the alkali halides. Ag halides and TI halides, with the nearest neighbor distances, d(sub nn). First, we show that the product E(sub coh)d(sub 0) within families of halide crystals with common crystal structure is to a good approximation constant, with maximum rms deviation of plus or minus 2%. Secondly, we demonstrate that within families of halide crystals with a common cation and common crystal structure the product B(sub 0)d(sup 3.5)(sub nn) is a good approximation constant, with maximum rms deviation of plus or minus 1.36%.

  16. Interfacial tension in immiscible mixtures of alkali halides.

    PubMed

    Lockett, Vera; Rukavishnikova, Irina V; Stepanov, Victor P; Tkachev, Nikolai K

    2010-02-01

    The interfacial tension of the liquid-phase interface in seven immiscible reciprocal ternary mixtures of lithium fluoride with the following alkali halides: CsCl, KBr, RbBr, CsBr, KI, RbI, and CsI was measured using the cylinder weighing method over a wide temperature range. It was shown that for all mixtures the interfacial tension gradually decreases with growing temperature. The interfacial tension of the reciprocal ternary mixtures at a given temperature increases both with the alkali cation radius (K(+) < Rb(+) < Cs(+)) and with the radius of the halogen anion (Cl(-) < Br(-) < I(-)). PMID:20094678

  17. Alkali Halide Microstructured Optical Fiber for X-Ray Detection

    NASA Technical Reports Server (NTRS)

    DeHaven, S. L.; Wincheski, R. A.; Albin, S.

    2014-01-01

    Microstructured optical fibers containing alkali halide scintillation materials of CsI(Na), CsI(Tl), and NaI(Tl) are presented. The scintillation materials are grown inside the microstructured fibers using a modified Bridgman-Stockbarger technique. The x-ray photon counts of these fibers, with and without an aluminum film coating are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The photon count results show significant variations in the fiber output based on the materials. The alkali halide fiber output can exceed that of the CdTe detector, dependent upon photon counter efficiency and fiber configuration. The results and associated materials difference are discussed.

  18. Alkali halide microstructured optical fiber for X-ray detection

    SciTech Connect

    DeHaven, S. L. E-mail: russel.a.wincheski@nasa.gov; Wincheski, R. A. E-mail: russel.a.wincheski@nasa.gov; Albin, S.

    2015-03-31

    Microstructured optical fibers containing alkali halide scintillation materials of CsI(Na), CsI(Tl), and NaI(Tl) are presented. The scintillation materials are grown inside the microstructured fibers using a modified Bridgman-Stockbarger technique. The x-ray photon counts of these fibers, with and without an aluminum film coating are compared to the output of a collimated CdTe solid state detector over an energy range from 10 to 40 keV. The photon count results show significant variations in the fiber output based on the materials. The alkali halide fiber output can exceed that of the CdTe detector, dependent upon photon counter efficiency and fiber configuration. The results and associated materials difference are discussed.

  19. Volcanic Origin of Alkali Halides on Io

    NASA Technical Reports Server (NTRS)

    Schaefer, L.; Fegley, B., Jr.

    2003-01-01

    The recent observation of NaCl (gas) on Io confirms our earlier prediction that NaCl is produced volcanically. Here we extend our calculations by modeling thermochemical equilibrium of O, S, Li, Na, K, Rb, Cs, F, Cl, Br, and I as a function of temperature and pressure in a Pele-like volcanic gas with O/S/Na/Cl/K = 1.518/1/0.05/0.04/0.005 and CI chondritic ratios of the other (as yet unobserved) alkalis and halogens. For reference, the nominal temperature and pressure for Pele is 1760 plus or minus 210 K and 0.01 bars based on Galileo data and modeling.

  20. Electronic excitation in bulk and nanocrystalline alkali halides.

    PubMed

    Bichoutskaia, Elena; Pyper, Nicholas C

    2012-11-14

    The lowest energy excitations in bulk alkali halides are investigated by considering five different excited state descriptions. It is concluded that excitation transfers one outermost halide electron in the fully ionic ground state to the lowest energy vacant s orbital of one closest cation neighbour to produce the excited state termed dipolar. The excitation energies of seven salts were computed using shell model description of the lattice polarization produced by the effective dipole moment of the excited state neutral halogen-neutral metal pair. Ab initio uncorrelated short-range inter-ionic interactions computed from anion wavefunctions adapted to the in-crystal environment were augmented by short-range electron correlation contributions derived from uniform electron-gas density functional theory. Dispersive attractions including wavefunction overlap damping were introduced using reliable semi-empirical dispersion coefficients. The good agreement between the predicted excitation energies and experiment provides strong evidence that the excited state is dipolar. In alkali halide nanocrystals in which each ionic plane contains only four ions, the Madelung energies are significantly reduced compared with the bulk. This predicts that the corresponding intra-crystal excitation energies in the nanocrystals, where there are two excited states depending on whether the halide electron is transferred to a cation in the same or in the neighbouring plane, will be reduced by almost 2 eV. For such an encapsulated KI crystal, it has been shown that the greater polarization in the excited state of the bulk crystal causes these reductions to be lowered to a 1.1 eV-1.5 eV range for the case of charge transfer to a neighbouring plane. For intra-plane charge transfer the magnitude of the polarization energy is further reduced thus causing the excitation in these encapsulated materials to be only 0.2 eV less than in the bulk crystal. PMID:23163361

  1. A new mechanism for radiation damage processes in alkali halides

    NASA Astrophysics Data System (ADS)

    Dubinko, V. I.; Turkin, A. A.; Vainshtein, D. I.; den Hartog, H. W.

    1999-12-01

    We present a theory of radiation damage formation in alkali halides based on a new mechanism of dislocation climb, which involves the production of VF centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of H centers of dislocation lines. We consider the evolution of all experimentally observed extended defects: metal colloids, gas bubbles, and vacancy voids. Voids are shown to arise and grow large due to the reaction between F and VF centers at the surface of halogen bubbles. Voids can ignite a back reaction between the radiolytic products resulting in decomposition of the irradiated material.

  2. A new polarizable force field for alkali and halide ions

    SciTech Connect

    Kiss, Péter T.; Baranyai, András

    2014-09-21

    We developed transferable potentials for alkali and halide ions which are consistent with our recent model of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. Following the approach used for the water potential, we applied Gaussian charge distributions, exponential repulsion, and r{sup −6} attraction. One of the two charges of the ions is fixed to the center of the particle, while the other is connected to this charge by a harmonic spring to express polarization. Polarizability is taken from quantum chemical calculations. The repulsion between different species is expressed by the combining rule of Kong [J. Chem. Phys. 59, 2464 (1972)]. Our primary target was the hydration free energy of ions which is correct within the error of calculations. We calculated water-ion clusters up to 6 water molecules, and, as a crosscheck, we determined the density and internal energy of alkali-halide crystals at ambient conditions with acceptable accuracy. The structure of hydrated ions was also discussed.

  3. A new polarizable force field for alkali and halide ions

    NASA Astrophysics Data System (ADS)

    Kiss, Péter T.; Baranyai, András

    2014-09-01

    We developed transferable potentials for alkali and halide ions which are consistent with our recent model of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. Following the approach used for the water potential, we applied Gaussian charge distributions, exponential repulsion, and r-6 attraction. One of the two charges of the ions is fixed to the center of the particle, while the other is connected to this charge by a harmonic spring to express polarization. Polarizability is taken from quantum chemical calculations. The repulsion between different species is expressed by the combining rule of Kong [J. Chem. Phys. 59, 2464 (1972)]. Our primary target was the hydration free energy of ions which is correct within the error of calculations. We calculated water-ion clusters up to 6 water molecules, and, as a crosscheck, we determined the density and internal energy of alkali-halide crystals at ambient conditions with acceptable accuracy. The structure of hydrated ions was also discussed.

  4. Potential function and dissociation energy of alkali halide

    NASA Astrophysics Data System (ADS)

    Srivastava, Abhay P.; Pandey, Anjani K.; Pandey, Brijesh K.

    2016-05-01

    Dissociation energy of some alkali halides have been calculated by using different interaction potential function such as Born-Mayer, Varshani-Shukla and L5 potential model. The theoretical calculation is compared with experimental values. The Result shows that the values of dissociation energy as calculated by using different potential models have an equal amount of deviation with experimental values. The above said deviation with experimental values can be explained by consideration of rotational-vibrational coupling between the constituents of molecules in the limelight of molecular spectroscopy. Findings of present work suggest that the existing potential model need to be reviewed in view of the correction factors solely depending on the rotational, vibrational and electronic coupling between the constituents of molecules.

  5. Bi-alkali antimonide photocathode growth: An X-ray diffraction study

    NASA Astrophysics Data System (ADS)

    Schubert, Susanne; Wong, Jared; Feng, Jun; Karkare, Siddharth; Padmore, Howard; Ruiz-Osés, Miguel; Smedley, John; Muller, Erik; Ding, Zihao; Gaowei, Mengjia; Attenkofer, Klaus; Liang, Xue; Xie, Junqi; Kühn, Julius

    2016-07-01

    Bi-alkali antimonide photocathodes are one of the best known sources of electrons for high current and/or high bunch charge applications like Energy Recovery Linacs or Free Electron Lasers. Despite their high quantum efficiency in visible light and low intrinsic emittance, the surface roughness of these photocathodes prohibits their use as low emittance cathodes in high accelerating gradient superconducting and normal conducting radio frequency photoguns and limits the minimum possible intrinsic emittance near the threshold. Also, the growth process for these materials is largely based on recipes obtained by trial and error and is very unreliable. In this paper, using X-ray diffraction, we investigate the different structural and chemical changes that take place during the growth process of the bi-alkali antimonide material K2CsSb. Our measurements give us a deeper understanding of the growth process of alkali-antimonide photocathodes allowing us to optimize it with the goal of minimizing the surface roughness to preserve the intrinsic emittance at high electric fields and increasing its reproducibility.

  6. Solvent-averaged potentials for alkali-, earth alkali-, and alkylammonium halide aqueous solutions

    NASA Astrophysics Data System (ADS)

    Hess, Berk; van der Vegt, Nico F. A.

    2007-12-01

    We derive effective, solvent-free ion-ion potentials for alkali-, earth alkali-, and alkylammonium halide aqueous solutions. The implicit solvent potentials are parametrized to reproduce experimental osmotic coefficients. The modeling approach minimizes the amount of input required from atomistic (force field) models, which usually predict large variations in the effective ion-ion potentials at short distances. For the smaller ion species, the reported potentials are composed of a Coulomb and a Weeks-Chandler-Andersen term. For larger ions, we find that an additional, attractive potential is required at the contact minimum, which is related to solvent degrees of freedom that are usually not accounted for in standard electrostatics models. The reported potentials provide a simple and accurate force field for use in molecular dynamics and Monte Carlo simulations of (poly-)electrolyte systems.

  7. Efficient destruction of CF4 through in situ generation of alkali metals from heated alkali halide reducing mixtures.

    PubMed

    Lee, Myung Churl; Choi, Wonyong

    2002-03-15

    Perfluorocarbons (PFCs) are the most potent green house gases that are very recalcitrant at destruction. An effective way of converting PFCs using hot solid reagents into safe products has been recently introduced. By investigating the thermal reductive destruction of tetrafluoromethane (CF4) we provided new insight and more physicochemical consideration on this novel process. The complete destruction of CF4was successfully achieved by flowing the gas through a heated reagent bed (400-950 degrees C) that contained powder mixtures of alkali halides, CaO, and Si. The silicon acted as a reducing agent of alkali halides for the in-situ production of alkali metals, and the calcium oxide played the role of a halide ion acceptor. The absence of any single component in this ternary mixture drastically reduced the destruction efficiency of CF4. The CF4 destruction efficiencies with the solid reagent containing the alkali halide, MX, increased in the order of Li approximately Na < K < Cs for alkali cations and I < Br < Cl < F for halide anions. This trend agreed with the endothermicity of the alkali metal generation reaction: the higher the endothermicity, the lower the destruction efficiency. Alkali metal generation was indirectly detected by monitoring H2 production from its reaction with water. The production of alkali metals increased with NaF, KF, and CsF in this order. The CsF/CaO/Si system exhibited the complete destruction of CF4 at as low as 600 degrees C. The solid product analysis by X-ray diffraction (XRD) showed the formation of CaF2 and the depletion of Si with black carbon particles formed in the solid reagent residue. No CO/CO2 and toxic HF and SiF4 formation were detected in the exhaust gas. PMID:11944694

  8. Investigating Metallization in Shock-Compressed Alkali Halides

    NASA Astrophysics Data System (ADS)

    Diamond, M. R.; Ali, S. J.; Eggert, J.; Jeanloz, R.; Collins, G. W.; McWilliams, R. S.

    2014-12-01

    Laser-shock compression on four alkali halides has been used to probe the transition from insulating to metallic states, a high-pressure transition in chemical bonding that has fundamental implications for planetary formation and structure. Collectively, pressures up to 450 GPa were explored across a total of fourteen single-crystal samples of CsI, CsBr, KBr and NaCl. Velocity interferometry (VISAR) was used to record shock velocities and reflectivities at 532 nm during decaying shock compression. The data show up to three-fold increases in density as well as significant increases in optical reflectivity in response to high pressures and temperatures. Using a Drude model to estimate conductivities from the measured reflectivities, we investigate the onset of metallic conductivities for each compound. Ionic salts are simple model systems amenable to first-principles theory and serve as analog materials for predicting whether specific chemical constituents can reside in the rocky mantles or metallic cores of planets. A key objective is to disentangle the complementary roles of temperature and compression in transforming ionic into metallic bonding. Furthermore, at high pressures CsI becomes analogous to Xe: they are isoelectronic and follow matching equations of state. Therefore, studies on CsI can inform understanding of noble-gas geochemistry at conditions deep inside planets (e.g., the likelihood of Xe solubility in planetary mantles or cores). Our experiments were conducted using the Janus laser of the Jupiter Laser Facility at Lawrence Livermore National Laboratory.

  9. Strong Turbulence in Alkali Halide Negative Ion Plasmas

    NASA Astrophysics Data System (ADS)

    Sheehan, Daniel

    1999-11-01

    Negative ion plasmas (NIPs) are charge-neutral plasmas in which the negative charge is dominated by negative ions rather than electrons. They are found in laser discharges, combustion products, semiconductor manufacturing processes, stellar atmospheres, pulsar magnetospheres, and the Earth's ionosphere, both naturally and man-made. They often display signatures of strong turbulence^1. Development of a novel, compact, unmagnetized alkali halide (MX) NIP source will be discussed, it incorporating a ohmically-heated incandescent (2500K) tantulum solenoid (3cm dia, 15 cm long) with heat shields. The solenoid ionizes the MX vapor and confines contaminant electrons, allowing a very dry (electron-free) source. Plasma densities of 10^10 cm-3 and positive to negative ion mass ratios of 1 <= fracm_+m- <= 20 are achievable. The source will allow tests of strong turbulence theory^2. 1 Sheehan, D.P., et al., Phys. Fluids B5, 1593 (1993). 2 Tsytovich, V. and Wharton, C.W., Comm. Plasma Phys. Cont. Fusion 4, 91 (1978).

  10. Reflectivities of Four Shock-Compressed Alkali Halides

    NASA Astrophysics Data System (ADS)

    Diamond, M. R.; McWilliams, R. S.; Eggert, J.; Jeanloz, R.; Ali, S. J.; Collins, G. W.

    2015-12-01

    Laser-shock compression on four alkali halides has been used to probe the transition from insulating to metallic states, a high-pressure transition in chemical bonding that has fundamental implications for planetary formation and structure. Collectively, pressures up to 450 GPa and densities up to three-fold compression were explored across a total of fourteen single-crystal samples of CsI, CsBr, KBr and NaCl. Velocity interferometry was used to record shock velocities and reflectivities at 532 nm during decaying shock compression. The data show up to 40% (or higher) reflectivity, corresponding to notable electrical conductivities, in response to high pressures and temperatures. Furthermore, band-gap closure, dependent on density, can be examined from the reflectivity data. Ionic salts are simple model systems amenable to first-principles theory and serve as analog materials for predicting whether specific chemical constituents can reside in the rocky mantles or metallic cores of planets. A key objective is to disentangle the complementary roles of temperature and compression in transforming ionic into metallic bonding. Furthermore, at high pressures CsI becomes analogous to Xe: they are isoelectronic and follow matching equations of state. Therefore, studies on CsI could inform understanding of noble-gas geochemistry at conditions deep inside planets.

  11. Graphitic cage transformation by electron-beam-induced catalysis with alkali-halide nanocrystals

    NASA Astrophysics Data System (ADS)

    Fujita, Jun-ichi; Tachi, Masashi; Ito, Naoto; Murakami, Katsuhisa; Takeguchi, Masaki

    2016-05-01

    We found that alkali-halide nanocrystals, such as KCl and NaCl, have strong catalytic capability to form graphitic carbon cages from amorphous carbon shells under electron beam irradiation. In addition to the electron beam irradiation strongly inducing the decomposition of alkali-halide nanocrystals, graphene fragments were formed and linked together to form the final product of thin graphitic carbon cages after the evaporation of alkali-halide nanocrystals. The required electron dose was approximately 1 to 20 C/cm2 at 120 keV at room temperature, which was about two orders of magnitude smaller than that required for conventional beam-induced graphitization. The “knock-on” effect of primary electrons strongly induced the decomposition of the alkali-halide crystal inside the amorphous carbon shell. However, the strong ionic cohesion quickly reformed the crystal into thin layers inside the amorphous shell. The bond excitation induced by the electron beam irradiation seemed to enhance strongly the graphitization at the interface between the outer amorphous carbon shell and the inner alkali-halide crystal.

  12. Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

    NASA Astrophysics Data System (ADS)

    Ruiz-Osés, M.; Schubert, S.; Attenkofer, K.; Ben-Zvi, I.; Liang, X.; Muller, E.; Padmore, H.; Rao, T.; Vecchione, T.; Wong, J.; Xie, J.; Smedley, J.

    2014-12-01

    Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K2CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K2CsSb upon cesium deposition, is correlated with changes in the quantum efficiency.

  13. Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

    SciTech Connect

    Ruiz-Osés, M.; Ben-Zvi, I.; Liang, X.; Muller, E.; Schubert, S.; Attenkofer, K.; Rao, T.; Smedley, J.; Padmore, H.; Vecchione, T.; Wong, J.; Xie, J.

    2014-12-01

    Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K{sub 2}CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K{sub 2}CsSb upon cesium deposition, is correlated with changes in the quantum efficiency.

  14. Study of bi-alkali photocathode growth on glass by X-ray techniques for fast timing response photomultipliers

    NASA Astrophysics Data System (ADS)

    Xie, Junqi; Demarteau, Marcel; Wagner, Robert; Ruiz-Oses, Miguel; Liang, Xue; Ben-Zvi, Ilan; Attenkofer, Klaus; Schubert, Susanne; Smedley, John; Wong, Jared; Padmore, Howard; Woll, Arthur

    2014-03-01

    Bi-alkali antimonide photocathode is an essential component in fast timing response photomultipliers. Real-time in-situ grazing incidence x-ray diffraction and post-growth x-ray reflectivity measurement were performed to study the photocathode deposition process on glass substrate. Grazing incidence x-ray diffraction patterns show the formation of Sb crystalline, dissolution of crystalline phase Sb by the application of K vapor and reformation of refined crystal textures. XRR result exhibits that the film thickness increases ~ 4.5 times after K diffusion and almost have no change after Cs diffusion. Further investigation is expected to understand the photocathode growth process and provide guidelines for photocathode development.

  15. Theoretical and experimental investigation of force imaging at the atomic scale on alkali halide crystals

    NASA Astrophysics Data System (ADS)

    Shluger, A. L.; Wilson, R. Mark; Williams, R. T.

    1994-02-01

    Assuming a model tip (Si4O10H10) as a reasonable representation of the surface of a Si3N4 cantilever stylus having a hydrogen-terminated asperity and a broader load-bearing base, we investigate the interaction of an atomic force microscope (AFM) with an alkali halide crystal by quantum chemical methods. Structural relaxation of the sample during engagement is allowed, and defect formation is investigated. Force curves above cation and anion positions are calculated, determining maximum sustainable loads and indicating a basis for atomic contrast. Experiments using a Si3N4 cantilever for AFM imaging of 12 alkali halide and alkaline earth fluoride crystals in air and desiccated helium are reported, in the widest AFM survey of such materials to date. Adsorbed water is shown to significantly enhance the observation of atomic periodicity on ionic halide samples, and rapid surface diffusion on alkali halide crystals is illustrated as it affects prospects for defect investigations. Observations of step edges and point-defect candidates at atomic scale are reported. The theoretical and experimental results are discussed together in the effort to provide a quantum-mechanical model for observations of alkali halide samples at atomic resolution, and to examine a possible basis for atomic resolution in the presence of long-range attractive forces.

  16. Electro-optic contribution to field-induced Raman scattering in alkali halides

    SciTech Connect

    Subbaswamy, K.R.; Mahan, G.D.

    1985-10-15

    The electro-optic contribution to the field-induced first-order Raman scattering cross section in alkali halide crystals is calculated using measured values for hyperpolarizabilities. The electro-optic contribution is much larger than the previously reported atomic displacement contribution. The results cast some doubt on the accuracy of the reported hyperpolarizability values.

  17. Resonance-Raman-scattering spectroscopy for the halogen-molecular-ion centers in alkali halides

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Tanimura, K.; Itoh, N.

    1993-10-01

    We have measured the Raman scattering in resonance with the bonding-to-antibonding transitions of two types of dihalogen-molecular-ion centers in alkali halides, the VK and H centers; the molecular ion occupies two adjacent halogen sites in the former and a single halogen site in the latter. It is found that the stretching-vibration frequency of the molecular ion is higher by more than 30% for the H center than for the VK center. The hardening is ascribed to the bond tightening due to the Madelung potential. Although the Raman line due to the stretching vibration consists of a single line in most alkali halides, two closely lying lines are observed for the H centers in alkali halides with small alkali-metal to halogen radius ratio and also for the VK center in NaCl. The paired-line structure is ascribed to the coupling of the stretching vibration of the halogen molecular ion with the lattice.

  18. Refined potentials for rare gas atom adsorption on rare gas and alkali-halide surfaces

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

    1985-01-01

    The utilization of models of interatomic potential for physical interaction to estimate the long range attractive potential for rare gases and ions is discussed. The long range attractive force is calculated in terms of the atomic dispersion properties. A data base of atomic dispersion parameters for rare gas atoms, alkali ion, and halogen ions is applied to the study of the repulsive core; the procedure for evaluating the repulsive core of ion interactions is described. The interaction of rare gas atoms on ideal rare gas solid and alkali-halide surfaces is analyzed; zero coverage absorption potentials are derived.

  19. Theory of metal atom-water interactions and alkali halide dimers

    NASA Technical Reports Server (NTRS)

    Jordan, K. D.; Kurtz, H. A.

    1982-01-01

    Theoretical studies of the interactions of metal atoms with water and some of its isoelectronic analogs, and of the properties of alkali halides and their aggregates are discussed. Results are presented of ab initio calculations of the heats of reaction of the metal-water adducts and hydroxyhydrides of Li, Be, B, Na, Mg, and Al, and of the bond lengths and angles an; the heats of reaction for the insertion of Al into HF, H2O, NH3, H2S and CH3OH, and Be and Mg into H2O. Calculations of the electron affinities and dipole moments and polarizabilities of selected gas phase alkali halide monomers and dimers are discussed, with particular attention given to results of calculations of the polarizability of LiF taking into account electron correlation effects, and the polarizability of the dimer (LiF)2.

  20. Reactions between cold methyl halide molecules and alkali-metal atoms

    SciTech Connect

    Lutz, Jesse J.; Hutson, Jeremy M.

    2014-01-07

    We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH{sub 3}X (X = F, Cl, Br, I) and alkali-metal atoms A (A = Li, Na, K, Rb) using high-level ab initio calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, CH{sub 3}X + A → CH{sub 3} + AX. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

  1. Development of processes for the production of solar grade silicon from halides and alkali metals

    NASA Technical Reports Server (NTRS)

    Dickson, C. R.; Gould, R. K.

    1980-01-01

    High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost were studied. Experiments were performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process.

  2. Theoretical analysis of the kinetics of low-temperature defect recombination in alkali halide crystals

    NASA Astrophysics Data System (ADS)

    Kuzovkov, V. N.; Popov, A. I.; Kotomin, E. A.; Moskina, A. M.; Vasilchenko, E.; Lushchik, A.

    2016-07-01

    We analyzed carefully the experimental kinetics of the low-temperature diffusion-controlled F, H center recombination in a series of irradiated alkali halides and extracted the migration energies and pre-exponential parameters for the hole H centers. The migration energy for the complementary electronic F centers in NaCl was obtained from the colloid formation kinetics observed above room temperature. The obtained parameters were compared with data available from the literature.

  3. Temperature Dependence of Interatomic Separation and Bulk Modulus for Alkali Halides

    NASA Astrophysics Data System (ADS)

    Liu, Quan

    2016-07-01

    The values of interatomic separation r with the change of temperature T for seven alkali halides have been investigated with the help of an isobaric equation of state. The calculated results are used to predict the values of bulk modulus at different temperatures. The results are compared with the available experimental data and other theoretical results and are further discussed in view of recent research in the field of high temperature physics.

  4. Alkali metal/halide thermal energy storage systems performance evaluation

    NASA Technical Reports Server (NTRS)

    Phillips, W. M.; Stearns, J. W.

    1986-01-01

    A pseudoheat-pipe heat transfer mechanism has been demonstrated effective in terms of both total heat removal efficiency and rate, on the one hand, and system isothermal characteristics, on the other, for solar thermal energy storage systems of the kind being contemplated for spacecraft. The selection of appropriate salt and alkali metal substances for the system renders it applicable to a wide temperature range. The rapid heat transfer rate obtainable makes possible the placing of the thermal energy storage system around the solar receiver canister, and the immersing of heat transfer fluid tubes in the phase change salt to obtain an isothermal heat source.

  5. Metal Hydride and Alkali Halide Opacities in Extrasolar Giant Planets and Cool Stellar Atmospheres

    NASA Technical Reports Server (NTRS)

    Weck, Philippe F.; Stancil, Phillip C.; Kirby, Kate; Schweitzer, Andreas; Hauschildt, Peter H.

    2006-01-01

    The lack of accurate and complete molecular line and continuum opacity data has been a serious limitation to developing atmospheric models of cool stars and Extrasolar Giant Planets (EGPs). We report our recent calculations of molecular opacities resulting from the presence of metal hydrides and alkali halides. The resulting data have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state.

  6. Multi-Alkali Photocathode Development at Brookhaven National Lab for Application in Superconducting Photoinjectors

    SciTech Connect

    Burrill, A.; Ben-Zvi, I.; Pate, D.; Rao, T.; Segalov, Z.; Dowell, D.; /SLAC

    2006-02-15

    The development of a suitable photocathode for use in a high average current photoinjector at temperatures ranging from 273 K down to 2 K is a subject of considerable interest, and active research. The choice of photocathode material is often a trade-off made based on the quantum efficiency of the cathode material, the tolerance to adverse vacuum conditions, and the laser wavelength needed to produce photoelectrons. In this paper an overview of the BNL work to date on CsK{sub 2}Sb photocathodes on a variety of substrates, irradiated at multiple wavelengths, and at temperatures down to 170 K will be discussed. The application of this photocathode material into a SRF photoinjector will also be discussed.

  7. MULTI-ALKALI PHOTOCATHODE DEVELOPMENT AT BROOKHAVEN NATIONAL LAB FOR APPLICATION IN SUPERCONDUCTING PHOTOINJECTORS. KICKERS.

    SciTech Connect

    BURRILL, A.; BEN-ZVI, I.; RAO, T.; PATE, D.; SEGALOV, Z.

    2005-05-16

    The development of a suitable photocathode for use in a high average current photoinjector at temperatures ranging from 273 K down to 2 K is a subject of considerable interest, and active research. The choice of photocathode material is often a trade-off made based on the quantum efficiency of the cathode material, the tolerance to adverse vacuum conditions, and the laser wavelength needed to produce photoelectrons. In this paper an overview of the BNL work to date on CsK{sub 2}Sb photocathodes on a variety of substrates, irradiated at multiple wavelengths, and at temperatures down to 170 K will be discussed. The application of this photocathode material into a SRF photoinjector will also be discussed.

  8. Molecular dispersion energy parameters for alkali and halide ions in aqueous solution.

    PubMed

    Reiser, S; Deublein, S; Vrabec, J; Hasse, H

    2014-01-28

    Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li(+), Na(+), K(+), Rb(+), Cs(+), F(-), Cl(-), Br(-), and I(-). The employed ion force fields consist of one Lennard-Jones (LJ) site and one concentric point charge with a magnitude of ±1 e. The SPC/E model is used for water. The LJ size parameter of the ion models is taken from Deublein et al. [J. Chem. Phys. 136, 084501 (2012)], while the LJ energy parameter is determined in the present study based on experimental self-diffusion coefficient data of the alkali cations and the halide anions in aqueous solutions as well as the position of the first maximum of the radial distribution function of water around the ions. On the basis of these force field parameters, the electric conductivity, the hydration dynamics of water molecules around the ions, and the enthalpy of hydration is predicted. Considering a wide range of salinity, this study is conducted at temperatures of 293.15 and 298.15 K and a pressure of 1 bar. PMID:25669552

  9. Molecular dispersion energy parameters for alkali and halide ions in aqueous solution

    SciTech Connect

    Reiser, S.; Deublein, S.; Hasse, H.; Vrabec, J.

    2014-01-28

    Thermodynamic properties of aqueous solutions containing alkali and halide ions are determined by molecular simulation. The following ions are studied: Li{sup +}, Na{sup +}, K{sup +}, Rb{sup +}, Cs{sup +}, F{sup −}, Cl{sup −}, Br{sup −}, and I{sup −}. The employed ion force fields consist of one Lennard-Jones (LJ) site and one concentric point charge with a magnitude of ±1 e. The SPC/E model is used for water. The LJ size parameter of the ion models is taken from Deublein et al. [J. Chem. Phys. 136, 084501 (2012)], while the LJ energy parameter is determined in the present study based on experimental self-diffusion coefficient data of the alkali cations and the halide anions in aqueous solutions as well as the position of the first maximum of the radial distribution function of water around the ions. On the basis of these force field parameters, the electric conductivity, the hydration dynamics of water molecules around the ions, and the enthalpy of hydration is predicted. Considering a wide range of salinity, this study is conducted at temperatures of 293.15 and 298.15 K and a pressure of 1 bar.

  10. Photoelectron Spectroscopy of Alkali-Halide Cluster Anions Containing Excess Electrons

    NASA Astrophysics Data System (ADS)

    Fatemi, Darius James

    1995-01-01

    We have obtained photoelectron spectra for alkali -halide clusters containing excess electrons. These measurements demonstrate that the mode of electron accommodation and the cluster configuration depend on the sizes of the atomic ions comprising the aggregate. We also report on the role of the source temperature in determining the structures observed for a cluster. Photoelectron measurements of metal-rich alkali -halide clusters (MX)_{n}M _{m}^-(m >=q 2) suggest that the metallic and ionic components within each of these systems are separated from each other. This behavior is evident for n = 3,5 in clusters of cesium chloride and for n = 3,7,8,9 for sodium iodide clusters. We also studied the mixed species (NaI) _{n}Na_{m} OH^- and(NaI)_ {n}H_2O ^-. The (NaI)_{n} Na_{m}OH ^- clusters appear to contain the OH ^- ion in the same way a halogen anion would be accommodated. Photoelectron spectra of(NaI) _{n}H_2O ^- are consistent with adsorption of a water molecule on an edge of an ionic lattice.

  11. Alkali Halide Interfacial Behavior in a Sequence of Charged Slit Pores

    SciTech Connect

    Wander, Matthew C; Shuford, Kevin L

    2011-01-01

    In this paper, a variety of alkali halide, aqueous electrolyte solutions in contact with charged, planar-graphite slit-pores are simulated using classical molecular dynamics. Size trends in structure and transport properties are examined by varying the choice of ions among the alkali metal and halide series. As with the uncharged pores, system dynamics are driven by changes in water hydration behavior and specifically by variations in the number of hydrogen bonds per water molecule. Overall, the larger ions diffuse more rapidly under high surface charge conditions than the smaller ions. In particular, for the 1 nmslit, ion diffusivity increased by a factor of 4 compared to the uncharged case. Finally, a quantitative fit to the interfacial charge structure is presented, which confirms the presence of two distinct types of layers in an aqueous interface. This model indicates that the chemistry of the interface is able to create a small interfacial potential, and it shows how water molecules can rotate to increase charge separation in response to a surface potential.

  12. Multiple neutral alkali halide attachments onto oligosaccharides in electrospray ionization mass spectrometry

    NASA Astrophysics Data System (ADS)

    Striegel, André M.; Timpa, Judy D.; Piotrowiak, Piotr; Cole, Richard B.

    1997-03-01

    Oligosaccharides perform essential functions in a variety of biological and agricultural processes. Recent approaches to characterization of these molecules by mass spectrometry have utilized mainly soft-ionization methods such as electrospray ionization (ESI) and thermospray (TS), as well as fast atom bombardment (FAB). The behavior of a series of maltooligosaccharides with [alpha]-(1 --> 4) linkages, maltose (G2) through maltoheptaose (G7), under ESI conditions, has been investigated here. The oligosaccharides were dissolved in N,N-dimethylacetamide containing lithium chloride (DMAc/LiCl) prior to analysis by ESI-MS. A highly unusual feature, evident in all mass spectra obtained using this solvent system, was the presence of multiple [`]neutral' salt attachments onto lithium adducts of the sugars. Resultant ions took the form of [Gx + Li + nLiCl+, where n may reach a value as high as eight. Compared to LiCl, the propensity for alkali halide attachment using other alkali chlorides or lithium halides was greatly reduced. An investigation of this phenomenon is presented in which the organic and inorganic portions of the employed solvent were systematically varied, and semi-empirical computer modeling was performed to better understand lithium coordination by the sugars.

  13. Alkali Halide Interfacial Behavior in a Sequence of Charged Slit Pores

    SciTech Connect

    Wander, Matthew C. F.; Shuford, Kevin L.

    2011-12-01

    In this paper, a variety of alkali halide, aqueous electrolyte solutions in contact with charged, planar-graphite slit-pores are simulated using classical molecular dynamics. Size trends in structure and transport properties are examined by varying the choice of ions among the alkali metal and halide series. As with the uncharged pores, system dynamics are driven by changes in water hydration behavior and specifically by variations in the number of hydrogen bonds per water molecule. Overall, the larger ions diffuse more rapidly under high surface charge conditions than the smaller ions. In particular, for the 1 nm slit, ion diffusivity increased by a factor of 4 compared to the uncharged case. Finally, a quantitative fit to the interfacial charge structure is presented, which confirms the presence of two distinct types of layers in an aqueous interface. This model indicates that the chemistry of the interface is able to create a small interfacial potential, and it shows how water molecules can rotate to increase charge separation in response to a surface potential.

  14. Alkali Metal Halide Salts as Interface Additives to Fabricate Hysteresis-Free Hybrid Perovskite-Based Photovoltaic Devices.

    PubMed

    Wang, Lili; Moghe, Dhanashree; Hafezian, Soroush; Chen, Pei; Young, Margaret; Elinski, Mark; Martinu, Ludvik; Kéna-Cohen, Stéphane; Lunt, Richard R

    2016-09-01

    A new method was developed for doping and fabricating hysteresis-free hybrid perovskite-based photovoltaic devices by using alkali metal halide salts as interface layer additives. Such salt layers introduced at the perovskite interface can provide excessive halide ions to fill vacancies formed during the deposition and annealing process. A range of solution-processed halide salts were investigated. The highest performance of methylammonium lead mixed-halide perovskite device was achieved with a NaI interlayer and showed a power conversion efficiency of 12.6% and a hysteresis of less than 2%. This represents a 90% improvement compared to control devices without this salt layer. Through depth-resolved mass spectrometry, optical modeling, and photoluminescence spectroscopy, this enhancement is attributed to the reduction of iodide vacancies, passivation of grain boundaries, and improved hole extraction. Our approach ultimately provides an alternative and facile route to high-performance and hysteresis-free perovskite solar cells. PMID:27532662

  15. Silicon Halide-alkali Metal Flames as a Source of Solar Grade Silicon

    NASA Technical Reports Server (NTRS)

    Olson, D. B.; Gould, R. K.

    1979-01-01

    A program is presented which was aimed at determining the feasibility of using high temperature reactions of alkali metals and silicon halides to produce low cost solar-grade silicon. Experiments are being conducted to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, and determine the effects of the reactants and/or products on materials of reactor construction. During the current reporting period, the results of heat release experiments were used to design and construct a new type of thick-wall graphite reactor to produce larger quantities of silicon. A reactor test facility was constructed. Material compatibility tests were performed for Na in contact with graphite and several coated graphites. All samples were rapidly degraded at T = 1200K, while samples retained structural strength at 1700K. Pyrolytic graphite coatings cracked and separated from substances in all cases.

  16. Ion Segregation and Deliquescence of Alkali Halide Nanocrystals on SiO2

    NASA Astrophysics Data System (ADS)

    Arima, Kenta; Jiang, Peng; Lin, Deng-Sung; Verdaguer, Albert; Salmeron, Miquel

    2009-08-01

    The adsorption of water on alkali halide (KBr, KCl, KF, NaCl) nanocrystals on SiO2 and their deliquescence was investigated as a function of relative humidity (RH) from 8% to near saturation by scanning polarization force microscopy. At low humidity, water adsorption solvates ions at the surface of the crystals and increases their mobility. This results in a large increase in the dielectric constant, which is manifested in an increase in the electrostatic force and in an increase in the apparent height of the nanocrystals. Above 58% RH, the diffusion of ions leads to Ostwald ripening, where larger nanocrystals grow at the expense of the smaller ones. At the deliquescence point, droplets were formed. For KBr, KCl, and NaCl, the droplets exhibit a negative surface potential relative to the surrounding region, which is indicative of the preferential segregation of anions to the air/solution interface.

  17. Role of excitons in electron- and photon-stimulated desorption of neutrals from alkali halides.

    PubMed

    Alexandrov, A; Piacentini, M; Zema, N; Felici, A C; Orlando, T M

    2001-01-15

    Low-energy (5-15 eV) electron- and photon-stimulated desorption of KI(100) yields I2P3/2 and 2P1/2 with hyperthermal (0.3 eV) and thermal velocity components. The desorption threshold for both components is 5.3 eV and is correlated with the gamma3/2-exciton long-wavelength edge. Exciton decay at the surface directly produces I2P3/2 and 2P1/2 with hyperthermal velocity and is in competition with self-trapping. Spin memory of the gamma-exciton hole-component is also evident in the hyperthermal channel. An exciton mediated desorption mechanism is presented which is general in alkali halides. PMID:11177874

  18. Ab initio perspective on the Mollwo-Ivey relation for F centers in alkali halides

    NASA Astrophysics Data System (ADS)

    Tiwald, Paul; Karsai, Ferenc; Laskowski, Robert; Gräfe, Stefanie; Blaha, Peter; Burgdörfer, Joachim; Wirtz, Ludger

    2015-10-01

    We revisit the well-known Mollwo-Ivey relation that describes the "universal" dependence of the absorption energies of F-type color centers on the lattice constant a of alkali-halide crystals, Eabs∝a-n. We perform both state-of-the-art ab initio quantum chemistry and post-DFT calculations of F-center absorption spectra. By "tuning" independently the lattice constant and the atomic species we show that the scaling with the lattice constant alone (keeping the elements fixed) would yield n =2 in agreement with the "particle-in-the-box" model. Keeping the lattice constant fixed and changing the atomic species enables us to quantify the ion-size effects which are shown to be responsible for the exponent n ≈1.8 .

  19. Studies of Non-Proportionality in Alkali Halide and Strontium Iodide Scintillators Using SLYNCI

    SciTech Connect

    Ahle, L; Bizarri, G; Boatner, L; Cherepy, N J; Choong, W; Moses, W W; Payne, S A; Shah, K; Sheets, S; Sturm, B W

    2009-05-05

    Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators [1-3]. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

  20. Studies of non-proportionality in alkali halide and strontium iodide scintillators using SLYNCI

    SciTech Connect

    Ahle, Larry; Bizarri, Gregory; Boatner, Lynn; Cherepy, Nerine J.; Choong, Woon-Seng; Moses, William W.; Payne, Stephen A.; Shah, Kanai; Sheets, Steven; Sturm, Benjamin, W.

    2010-10-14

    Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

  1. Ion Segregation and Deliquescence of Alkali Halide Nanocrystals on SiO2

    SciTech Connect

    Arima, Kenta; Jiang, Peng; Lin, Deng-Sung; Verdaguer, Albert; Salmeron, Miquel

    2009-08-11

    The adsorption of water on alkali halide (KBr, KCl, KF, NaCl) nanocrystals on SiO{sub 2} and their deliquescence was investigated as a function of relative humidity (RH) from 8% to near saturation by scanning polarization force microscopy. At low humidity, water adsorption solvates ions at the surface of the crystals and increases their mobility. This results in a large increase in the dielectric constant, which is manifested in an increase in the electrostatic force and in an increase in the apparent height of the nanocrystals. Above 58% RH, the diffusion of ions leads to Ostwald ripening, where larger nanocrystals grow at the expense of the smaller ones. At the deliquescence point, droplets were formed. For KBr, KCl, and NaCl, the droplets exhibit a negative surface potential relative to the surrounding region, which is indicative of the preferential segregation of anions to the air/solution interface.

  2. Quantum Efficiency Enhancement in CsI/Metal Photocathodes

    SciTech Connect

    Kong, Lingmei; Joly, Alan G.; Droubay, Timothy C.; Hess, Wayne P.

    2015-02-01

    High quantum efficiency enhancement is found for hybrid metal-insulator photocathodes consisting of thin films of CsI deposited on Cu(100), Ag(100), Au(111) and Au films irradiated by 266 nm laser pulses. Low work functions (near or below 2 eV) are observed following ultraviolet laser activation. Work functions are reduced by roughly 3 eV from that of clean metal surfaces. We discuss various mechanisms of quantum efficiency enhancement for alkali halide/metal photocathode systems and conclude that the large change in work function, due to Cs accumulation of Cs metal at the metal-alkali halide interface, is the dominant mechanism for quantum efficiency enhancement

  3. Metal-encapsulated organolead halide perovskite photocathode for solar-driven hydrogen evolution in water.

    PubMed

    Crespo-Quesada, Micaela; Pazos-Outón, Luis M; Warnan, Julien; Kuehnel, Moritz F; Friend, Richard H; Reisner, Erwin

    2016-01-01

    Lead-halide perovskites have triggered the latest breakthrough in photovoltaic technology. Despite the great promise shown by these materials, their instability towards water even in the presence of low amounts of moisture makes them, a priori, unsuitable for their direct use as light harvesters in aqueous solution for the production of hydrogen through water splitting. Here, we present a simple method that enables their use in photoelectrocatalytic hydrogen evolution while immersed in an aqueous solution. Field's metal, a fusible InBiSn alloy, is used to efficiently protect the perovskite from water while simultaneously allowing the photogenerated electrons to reach a Pt hydrogen evolution catalyst. A record photocurrent density of -9.8 mA cm(-2) at 0 V versus RHE with an onset potential as positive as 0.95±0.03 V versus RHE is obtained. The photoelectrodes show remarkable stability retaining more than 80% of their initial photocurrent for ∼1 h under continuous illumination. PMID:27595974

  4. Silicon halide-alkali metal flames as a source of solar grade silicon

    NASA Technical Reports Server (NTRS)

    Olsen, D. B.; Miller, W. J.

    1979-01-01

    The feasibility of using alkali metal-silicon halide diffusion flames to produce solar-grade silicon in large quantities and at low cost is demonstrated. Prior work shows that these flames are stable and that relatively high purity silicon can be produced using Na + SiCl4 flames. Silicon of similar purity is obtained from Na + SiF4 flames although yields are lower and product separation and collection are less thermochemically favored. Continuous separation of silicon from the byproduct alkali salt was demonstrated in a heated graphite reactor. The process was scaled up to reduce heat losses and to produce larger samples of silicon. Reagent delivery systems, scaled by a factor of 25, were built and operated at a production rate of 0.5 kg Si/h. Very rapid reactor heating rates are observed with wall temperatures reaching greater than 2000 K. Heat release parameters were measured using a cooled stainless steel reactor tube. A new reactor was designed.

  5. Chemistry of alkali cation exchanged faujasite and mesoporous NaX using alkyl halides and phosphates

    NASA Astrophysics Data System (ADS)

    Lee, Min-Hong

    The purpose of this work was to increase the reactivity of Faujasite X (NaX) zeolite toward the reactive decontamination of materials subject to nucleophilic attack by means of zeolite cation optimization and by means of the synthesis of mesoporous Faujasite X. Primary alkyl halides and trialkyl phosphates have been the test materials on which the cation-optimized and mesoporous zeolites have been tested. In the alkali cation optimization work, reactions of methyl iodide and 1-chloropropane with alkali metal cation exchanged Faujasite zeolite X were investigated at room temperature. The reactivity of the framework and the product formation were shown to depend on zeolite framework counter-cation. A quantitative study of zeolite product formation has been carried out, primarily using solid-state NMR spectroscopy. Large alkali cations showed preference toward substitution chemistry. In contrast, alkyl halide exposed LiX and NaX zeolites underwent both substitution and elimination. Subsequently introduced water molecules led to hydrolysis of framework species that was sensitive to framework counter-cation. The mesoporous NaX zeolites work undertakes to test whether an improvement in surface chemical reactivity can be achieved by introducing mesopores into the already reactive nucleophilic microporous NaX zeolite. Incorporation of the polydiallyl dimethyl ammonium chloride (PDADMAC) template and the formation of mesopores in Faujasite X zeolite (NaX) were successful and well-characterized. The mesopores are proposed to have occurred from incorporation of the cationic PDADMAC polymer into the zeolite by compensating zeolite framework charge. Subsequent sodium cation exchange of calcined mesoporous NaX was shown to restore the chemical reactivity characteristic of as-synthesized NaX. Trialkyl organophosphorous compounds underwent substitution reactions. The reactivity of both microporous and mesoporous Faujasite zeolite X and the product formation was shown to depend on

  6. Physics of solid and liquid alkali halide surfaces near the melting point

    NASA Astrophysics Data System (ADS)

    Zykova-Timan, T.; Ceresoli, D.; Tartaglino, U.; Tosatti, E.

    2005-10-01

    This paper presents a broad theoretical and simulation study of the high-temperature behavior of crystalline alkali halide surfaces typified by NaCl(100), of the liquid NaCl surface near freezing, and of the very unusual partial wetting of the solid surface by the melt. Simulations are conducted using two-body rigid-ion Born-Mayer-Huggins-Fumi-Tosi (BMHFT) potentials, with full treatment of long-range Coulomb forces. After a preliminary check of the description of bulk NaCl provided by these potentials, which seems generally good even at the melting point, we carry out a new investigation of solid and liquid surfaces. Solid NaCl(100) is found in this model to be very anharmonic and yet exceptionally stable when hot. It is predicted by a thermodynamic integration calculation of the surface free energy that NaCl(100) should be a well-ordered, nonmelting surface, metastable even well above the melting point. By contrast, the simulated liquid NaCl surface is found to exhibit large thermal fluctuations and no layering order. In spite of that, it is shown to possess a relatively large surface free energy. The latter is traced to a surface entropy deficit, reflecting some kind of surface short-range order. We show that the surface short-range order is most likely caused by the continuous transition of the bulk ionic melt into the vapor, made of NaCl molecules and dimers rather than of single ions. Finally, the solid-liquid interface free energy is derived through Young's equation from direct simulation of partial wetting of NaCl(100) by a liquid droplet. The resulting interface free energy is large, in line with the conspicuous solid-liquid 27% density difference. A partial wetting angle near 50° close to the experimental value of 48° is obtained in the process. It is concluded that three elements, namely, the exceptional anharmonic stability of the solid (100) surface, the molecular short-range order at the liquid surface, and the costly solid-liquid interface, all

  7. Excess-electron and excess-hole states of charged alkali halide clusters

    NASA Astrophysics Data System (ADS)

    Honea, Eric C.; Homer, Margie L.; Whetten, R. L.

    1990-12-01

    Charged alkali halide clusters from a He-cooled laser vaporization source have been used to investigate two distinct cluster states corresponding to the excess-electron and excess-hole states of the crystal. The production method is UV-laser vaporization of an alkali metal rod into a halogen-containing He flow stream, resulting in variable cluster composition and cooling sufficient to stabilize weakly bound forms. Detection of charged clusters is accomplished without subsequent ionization by pulsed-field time-of-flight mass spectrometry of the skimmed cluster beam. Three types of positively charged sodium fluoride cluster are observed, each corresponding to a distinct physical situation: NanF+n-1 (purely ionic form), Nann+1F+n-1 (excess-electron form), and NanF+n (excess-hole form). The purely ionic clusters exhibit an abundance pattern similar to that observed in sputtering and fragmentation experiments and are explained by the stability of completed cubic microlattice structures. The excess-electron clusters, in contrast, exhibit very strong abundance maxima at n = 13 and 22, corresponding to the all-odd series (2n + 1 = jxkxl;j,k,l odd). Their high relative stability is explained by the ease of Na(0) loss except when the excess electron localizes in a lattice site to complete a cuboid structure. These may correspond to the internal F-center state predicted earlier. A localized electron model incorporating structural simulation results as account for the observed pattern. The excess-hole clusters, which had been proposed as intermediates in the ionization-induced fragmentation of neutral AHCs, exhibit a smaller variation in stability, indicating that the hole might not be well localized.

  8. Silicon halide-alkali metal flames as a source of solar grade silicon

    NASA Technical Reports Server (NTRS)

    Olson, D. B.; Miller, W. J.; Gould, R. K.

    1980-01-01

    The feasibility of using continuous high-temperature reactions of alkali metals and silicon halides to produce silicon in large quantities and of suitable purity for use in the production of photovoltaic solar cells was demonstrated. Low pressure experiments were performed demonstrating the production of free silicon and providing experience with the construction of reactant vapor generators. Further experiments at higher reagent flow rates were performed in a low temperature flow tube configuration with co-axial injection of reagents and relatively pure silicon was produced. A high temperature graphite flow tube was built and continuous separation of Si from NaCl was demonstrated. A larger scaled well stirred reactor was built. Experiments were performed to investigate the compatability of graphite based reactor materials of construction with sodium. At 1100 to 1200 K none of these materials were found to be suitable. At 1700 K the graphites performed well with little damage except to coatings of pyrolytic graphite and silicon carbide which were damaged.

  9. Physics of solid and liquid alkali halide surfaces near the melting point

    NASA Astrophysics Data System (ADS)

    Zykova-Timan, Tatyana; Ceresoli, Davide; Tartaglino, Ugo; Tosatti, Erio

    2006-03-01

    NaCl (and other alkali halide) crystal surfaces have the peculiar property of repelling their own melt. As a result they let themselves be wetted only partially by their own liquid at the melting point TM. We recently investigated the physical reasons for this unusual behavior. We found them through theory and molecular dynamics simulation to stem from the conspiracy of three factors. First, the solid NaCl(100) surface is exceptionally anharmonic,but also exceptionally stable. It can in fact survive even well above the melting point, for unlike most other surfaces it does not spontaneously melt. Second, the solid-liquid interface is very costly, due to a 27% density difference between solid and liquid. Third, the surface tension of liquid NaCl is relatively high. This last feature is due to an unexpected entropy deficit, that can in turn be traced to incipient molecular charge order in the outermost regions of the molten salt surface[1,2].[1] T. Zykova-Timan, D. Ceresoli, U. Tartaglino, E. Tosatti, Phys. Rev. Lett. 94, 176105 (2005) [2] T. Zykova-Timan, D. Ceresoli, U. Tartaglino, E. Tosatti, J. Chem. Phys. 123, 164701 (2005)

  10. UV laser-induced desorption mechanism analyzed through two-layer alkali halide samples.

    PubMed

    Fernández-Lima, F A; Ponciano, C R; da Silveira, E F

    2008-05-01

    Time of flight-mass spectrometry (TOF-MS) is used to analyze positive and negative desorbed ions generated by UV laser ablation of several alkali (X) halide (Y) salts. Most of the observed desorbed cluster ions have the structure (XY)(n)X(+) or (XY)(n)Y(-). Their desorption yields decrease as exp(-kn), where k approximately 2 for both series, suggesting that the neutral component (XY)(n) plays the dominant role in the desorption process. Mass spectrum measurements were performed for compound samples in which two salts (out of CsI, RbI, KBr, KCl and KI) are homogeneously mixed or disposed in two superposed layers. The detection of small new ion species and large cluster ions of the original salts supports the scenario that the uppermost layers are completely atomized while deep layers are emitted colder and fragmented: It is proposed that ns-pulsed laser induced desorption of ionic salts occurs via two sequential mechanisms: (1) ejection of cations and anions in the hot plume, followed by recombination into new cluster ions and (2) ejection of relatively cold preformed species originated from deep layers or from periphery of the irradiated region. PMID:18095386

  11. Dynamics of nuclear wave packets at the F center in alkali halides

    NASA Astrophysics Data System (ADS)

    Koyama, Takeshi; Suemoto, Tohru

    2011-07-01

    The F center in alkali halides is a well-known prototype of a strongly coupled localized electron-phonon system. This colour center is one of the long studied targets in the field of photophysics because it is simple but rich in variety. Steady-state spectroscopy, such as modulation spectroscopy and Raman scattering spectroscopy, has elucidated the strength of the electron-phonon coupling in the (meta-)stable state, i.e. the ground state and the relaxed excited state. Picosecond spectroscopy has improved understanding of the state mixing in the transient state. Owing to recent developments of ultrafast lasers with pulse widths shorter than oscillation periods of phonons, it has been possible to perform real-time observation of lattice vibration, and the understanding of the transient state has been remarkably expanded. In this paper, we review early and present studies on dynamics of electron-phonon coupling at the F center, especially recent real-time observations on the dynamics of nuclear wave packets in the excited state of the F center in KI, KBr, KCl and RbCl. These real-time observations reveal (i) spatial extension of the electronic wave function of a trapped electron, (ii) the difference between the coupled phonons in the ground state and the excited state, (iii) diabatic transition between the adiabatic potential energy surfaces and (iv) anharmonicity of the potential energy surface.

  12. Surface Spectroscopy Studies of the Reactive Uptake of Ozone on Alkali Halides

    NASA Astrophysics Data System (ADS)

    Newberg, J. T.; Hemminger, J. C.

    2003-12-01

    Heterogeneous reactions in the atmosphere have attracted a lot of attention. In particular, reactions involving sea-salt in the form of aerosol droplets, particles, and/or sea-ice have been implicated to significantly affect the chemistry and composition of the marine boundary layer. For example, highly reactive chlorine and bromine atoms resulting from the oxidation of sea-salt halides (Cl- and Br-) have been implicated in tropospheric ozone depletion in the arctic and in lower latitude marine regions, as well as the deposition of mercury. While the heterogeneous processing of sea-salt has been studied extensively in laboratory, field and model studies, the mechanistic details behind the release of gas-phase halogens remains unclear and has sparked some interests. Recently there has been attention focused on the interaction of important atmospheric oxidants (e.g., OH and O3) with halides that reside at the air-particle interface of sea-salt. Such chemical interactions at the surface of particles may lead to unique chemical transformations that can alter current views of known chemical processing of sea-salt particles. There are several laboratory investigations which have investigated the surface reactivity of salts by measuring the reactive loss and/or formation of gas-phase species, indicating that reactions at the interface likely play an important role in aerosol chemistry. The efficacy of such surface-phase chemistry has yet to be elucidated with surface spectroscopy studies. X-ray photoelectron spectroscopy (XPS) is a surface spectroscopy technique with submonolayer resolution. Using XPS, we have investigated changes in the surface chemistry of various alkali halide salts upon exposure to ozone in an ultra-high vacuum (UHV) instrument. Salt samples were either freshly cleaved single crystals which were prepared from a melt, or purified salt crystals/powders pressed into pellets. Upon exposure to ozone, oxygen on the salt surfaces was monitored by measuring

  13. Optical properties of alkali halide crystals from all-electron hybrid TD-DFT calculations

    SciTech Connect

    Webster, R. Harrison, N. M.; Bernasconi, L.

    2015-06-07

    We present a study of the electronic and optical properties of a series of alkali halide crystals AX, with A = Li, Na, K, Rb and X = F, Cl, Br based on a recent implementation of hybrid-exchange time-dependent density functional theory (TD-DFT) (TD-B3LYP) in the all-electron Gaussian basis set code CRYSTAL. We examine, in particular, the impact of basis set size and quality on the prediction of the optical gap and exciton binding energy. The formation of bound excitons by photoexcitation is observed in all the studied systems and this is shown to be correlated to specific features of the Hartree-Fock exchange component of the TD-DFT response kernel. All computed optical gaps and exciton binding energies are however markedly below estimated experimental and, where available, 2-particle Green’s function (GW-Bethe-Salpeter equation, GW-BSE) values. We attribute this reduced exciton binding to the incorrect asymptotics of the B3LYP exchange correlation ground state functional and of the TD-B3LYP response kernel, which lead to a large underestimation of the Coulomb interaction between the excited electron and hole wavefunctions. Considering LiF as an example, we correlate the asymptotic behaviour of the TD-B3LYP kernel to the fraction of Fock exchange admixed in the ground state functional c{sub HF} and show that there exists one value of c{sub HF} (∼0.32) that reproduces at least semi-quantitatively the optical gap of this material.

  14. Simple electrolyte solutions: Comparison of DRISM and molecular dynamics results for alkali halide solutions

    PubMed Central

    Joung, In Suk; Luchko, Tyler; Case, David A.

    2013-01-01

    Using the dielectrically consistent reference interaction site model (DRISM) of molecular solvation, we have calculated structural and thermodynamic information of alkali-halide salts in aqueous solution, as a function of salt concentration. The impact of varying the closure relation used with DRISM is investigated using the partial series expansion of order-n (PSE-n) family of closures, which includes the commonly used hypernetted-chain equation (HNC) and Kovalenko-Hirata closures. Results are compared to explicit molecular dynamics (MD) simulations, using the same force fields, and to experiment. The mean activity coefficients of ions predicted by DRISM agree well with experimental values at concentrations below 0.5 m, especially when using the HNC closure. As individual ion activities (and the corresponding solvation free energies) are not known from experiment, only DRISM and MD results are directly compared and found to have reasonably good agreement. The activity of water directly estimated from DRISM is nearly consistent with values derived from the DRISM ion activities and the Gibbs-Duhem equation, but the changes in the computed pressure as a function of salt concentration dominate these comparisons. Good agreement with experiment is obtained if these pressure changes are ignored. Radial distribution functions of NaCl solution at three concentrations were compared between DRISM and MD simulations. DRISM shows comparable water distribution around the cation, but water structures around the anion deviate from the MD results; this may also be related to the high pressure of the system. Despite some problems, DRISM-PSE-n is an effective tool for investigating thermodynamic properties of simple electrolytes. PMID:23387564

  15. a Study of Two Electron Defect Systems in Alkali Halide Crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Chang Gang

    1993-01-01

    The structures of two electron defect systems in alkali halide crystals are studied. The systems which have been studied include: two electrons localized at an anion vacancy (F^'-centre); positronium self-trapped at an anion vacancy (Fe ^+-centre); positron self-trapped at a cation vacancy (F_{rm anti} -centre); positronium self-trapped at an interstice; and positronium in a Bloch state. An improved version of the extended-ion method which is based on the one electron Hartree-Fock approximation is used to perform these calculations. Its main feature is the exclusive use of floating 1s Gaussian functions as basis. For the multi-electron defect systems, the calculation of matrix elements of two electron interaction terms is a most difficult problem. We developed an effective approach to treat this interaction approximately. The correlation effect of defect electrons is partly accounted for by properly arranged Gaussian basis. The binding energy, thermal dissociation energy, and transition energy between ground state and excited state are calculated for F ^'-centres. A defect model with negative-U properties was introduced to interpret the deeply bound F^'-centre. Calculations of positron binding energies are made for Fe^+ -centres and F_{rm anti }-centres. In addition, we evaluate the angular correlation and lifetime of an annihilated electron-positron pair for Fe^+-centres, localized positronium and Bloch state positronium. The observed phenomena such as the transition of positronium from Bloch state to localized state, and the crystallographic effect are examined theoretically. The calculated results regarding various properties of crystals are in reasonably good agreement with experiment.

  16. Liquid madelung energy and schottky defect energy related to liquid structure and melting temperature for alkali halides

    SciTech Connect

    March, N.H.; Tosi, M.P.

    1985-01-01

    Motivated by the work of Reiss et al. in which the melting temperature T /SUB m/ of alkali halides is correlated with Coulomb energy, we consider the cohesive energy W of ionic melts and Schottky defect energy E /SUB s/ in the hot crystal, relative to the thermal energy k /SUB B/ T /SUB m/ . It is shown here that is accurately approximated by the liquid Madelung energy and hence that W/k /SUB B/ T /SUB m/ relates to the charge-charg direct correlation function c /SUB QQ/ (r) at r = 0. The existence of a ''Madelung constant'' for the liquid at T /SUB m/ is thereby demonstrated through the alkali halide series. An estimate of the ratio E /SUB s/ /k /SUB B/ T /SUB m/ i then considered; the basic additional ingredient being argued to be the static dielectric constant of the solid. Th BarrDawson-Lidiard empirical correlation between E /SUB s/ and k /SUB B/ T /SUB m/ can be understood in this way.

  17. Universal scaling of potential energy functions describing intermolecular interactions. II. The halide-water and alkali metal-water interactions

    SciTech Connect

    Werhahn, Jasper C.; Akase, Dai; Xantheas, Sotiris S.

    2014-08-14

    The scaled versions of the newly introduced [S. S. Xantheas and J. C. Werhahn, J. Chem. Phys.141, 064117 (2014)] generalized forms of some popular potential energy functions (PEFs) describing intermolecular interactions – Mie, Lennard-Jones, Morse, and Buckingham exponential-6 – have been used to fit the ab initio relaxed approach paths and fixed approach paths for the halide-water, X-(H2O), X = F, Cl, Br, I, and alkali metal-water, M+(H2O), M = Li, Na, K, Rb, Cs, interactions. The generalized forms of those PEFs have an additional parameter with respect to the original forms and produce fits to the ab initio data that are between one and two orders of magnitude better in the χ2 than the original PEFs. They were found to describe both the long-range, minimum and repulsive wall of the respective potential energy surfaces quite accurately. Overall the 4-parameter extended Morse (eM) and generalized Buckingham exponential-6 (gBe-6) potentials were found to best fit the ab initio data for these two classes of ion-water interactions. Finally, the fitted values of the parameter of the (eM) and (gBe-6) PEFs that control the repulsive wall of the potential correlate remarkably well with the ionic radii of the halide and alkali metal ions.

  18. Low-Energy Grazing Ion-Scattering from Alkali-Halide Surfaces: A Novel Approach to C-14 Detection

    SciTech Connect

    Meyer, Fred W; Galutschek, Ernst; Hotchkis, Michael

    2009-01-01

    Carbon-14 labeled compounds are widely used in the pharmaceutical industry, e.g., as tracers to determine the fate of these compounds in vivo. Conventional accelerator mass spectrometry (AMS) is one approach that offers sufficiently high sensitivity to avoid radiological waste and contamination issues in such studies, but requires large, expensive facilities that are usually not solely dedicated to this task. At the ORNL Multicharged Ion Research Facility (MIRF) we are exploring a small size, low cost alternative to AMS for biomedical 14C tracer studies that utilizes ECR-ion-source-generated keV-energy-range multicharged C beams grazingly incident on an alkali halide target, where efficient negative ion production by multiple electron capture takes place. By using C ion charge states of +3 or higher, the molecular isobar interference at mass 14, e.g. 12CH2 and 13CH, is eliminated. The negatively charged ions in the beam scattered from the alkali halide surface are separated from other scattered charge states by two large acceptance ({approx}15 msr) stages of electrostatic analysis. The N-14 isobar interference is thus removed, since N does not support a stable negative ion. Initial results for C-14 detection obtained using C-14 enriched CO2 from ANSTO will be described.

  19. Integrating 2-D position sensitive X-ray detectors with low-density alkali halide storage targets

    NASA Astrophysics Data System (ADS)

    Haubold, H.-G.; Hoheisel, W.; Hiller, P.

    1986-05-01

    For the use in scattering experiments with synchrotron radiation, integrating position sensitive X-ray detectors are discussed. These detectors store the photon number equivalent charge (PNEC) in low-density alkali halide targets. Performance tests are given for a detector which uses a Gd 2O 2S fluorescence screen for X-ray detection and the low-density KCl storage target of a television SEC vidicon tube for photon integration. Rather than directly by X-rays, this target is charged by 6 keV electrons from the image intensifier section of the vidicon. Its excellent storage capability allows measurements of extremely high-contrast, high-flux X-ray patterns with the same accuracy as achieved with any single photon detection system if the discussed readout techniques are applied.

  20. Development of processes for the production of solar grade silicon from halides and alkali metals, phase 1 and phase 2

    NASA Technical Reports Server (NTRS)

    Dickson, C. R.; Gould, R. K.; Felder, W.

    1981-01-01

    High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon are described. Product separation and collection processes were evaluated, measure heat release parameters for scaling purposes and effects of reactants and/or products on materials of reactor construction were determined, and preliminary engineering and economic analysis of a scaled up process were made. The feasibility of the basic process to make and collect silicon was demonstrated. The jet impaction/separation process was demonstrated to be a purification process. The rate at which gas phase species from silicon particle precursors, the time required for silane decomposition to produce particles, and the competing rate of growth of silicon seed particles injected into a decomposing silane environment were determined. The extent of silane decomposition as a function of residence time, temperature, and pressure was measured by infrared absorption spectroscopy. A simplistic model is presented to explain the growth of silicon in a decomposing silane enviroment.

  1. Size distributions and geometries of alkali halide nanoclusters probed using ESI FT-ICR mass spectrometry and quantum chemistry

    NASA Astrophysics Data System (ADS)

    Lemke, K.; Sadjadi, S.; Seward, T.

    2010-12-01

    The structures and energetic properties of ionic alkali metal halide clusters play a significant role in our understanding of aqueous geochemical processes such as salt dissolution, precipitation and neutralization reactions. Mass spectrometric and quantum chemical studies of such systems offer new opportunities to study the size-dependent evolution of cluster structures, the occurrence of magic number species as well as their fundamental properties. The work here presents new results for the stability, abundance and structure of pure [Na(NaClm)]+ , [K(KCl)m]+ and mixed [Na(NaCl)p(KCl)q]+ metal halide clusters with m<23 and p+q<14, respectively, using ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS) in combination with the Gn and CBS-x multistep ab initio methods. Ion-cluster experiments were conducted on a modified 7T Bruker FT-ICR/MS equipped with electrospray ionization (ESI) sources and a custom-designed solvent gas inlet interface. In ESI FT-ICR/MS experiments performed with solutions containing NaCl and KCl salts (1mM; 80/20 CH3CN/H2O), singly and doubly charged salt clusters were generated up to a cluster size of [Na(NaCl)22]+, [K(KCl)17]+ and [K2(KCl)21,23]2+, respectively, including “magic number” clusters that correspond to the completed cluster cuboids with the dimensions 3x3x1 (m=4), 3x3x2+3 (m=10) 3x3x3 (m=13) and 3x3x5 (m=22) (see Figure). On the other hand, no pure clusters except [K(KCl)1-3]+ were generated when alkali halides were electrosprayed from 1mM NaCl/KCl solutions. Instead, mixed [Na(NaCl)p(KCl)q]+ clusters are generated up to p+q=14, which are the largest mixed alkali halide clusters yet generated in mass spectrometric experiments, including a suite of ionic species that are generated via CH3CN fragmentation and charge transfer in [Na(CH3CN)n]+ to yield the clusters [Na(NaCN)(CH3CN)n-1]+. We describe our ESI FT-ICR/MS experiments and discuss ion cluster abundances and extent of clustering

  2. Multi-alkali photocathode thermal performance analysis of image intensifier based on low-high temperature environment testing conditions

    NASA Astrophysics Data System (ADS)

    Gao, Youtang; Tian, Si; Chang, Benkang; Qiu, Yafeng; Qiao, Jianliang

    2008-03-01

    Low-level-light (LLL) weapon sight measurement technologies based on Low-high temperature environments testing conditions are always concerned by military equipments manufacturers. Because low-high temperature environment, etc. are under loaded function, the electric performance parameter change to make LLL weapon sight, causing the LLL weapon sight can't be worked and used normally while taking aim. Generally believed that many photocathode is n-type and p-type doping of the inner surface layer comprising more photocathode not light sensitive, but also sensitive to temperature. To image intensifier is non-working state at the temperature 70°C +/-2°C test boxes and thermostats time one hour, five minutes to image intensifier into -50°C+/-2°C Test Box temperature one hour, then five minutes again placed 70°C +/-2°C high temperature test box for three cycle question image intensifier restore normal temperature after the test. The experiments show that, when the temperature rises, the heat semiconductor photocathode current density, thermal current rise in the temperature range 0 to 70°C, 4°C temperature is increased, almost twice its current heat. Of course, image intensifier imported the equivalent background illumination will also increase, resulting in night vision systems observed at the scene image contrast and differential rates were lowered, target detection system performance last night caused the decline. A study of the reasons is the photo-cathode materials and fabrication of thermal electron emission standards restricting the ability.

  3. Solubility of alkali metal halides in the ionic liquid [C4C1im][OTf].

    PubMed

    Kuzmina, O; Bordes, E; Schmauck, J; Hunt, P A; Hallett, J P; Welton, T

    2016-06-28

    The solubilities of the metal halides LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbCl, CsCl, CsI, were measured at temperatures ranging from 298.15 to 378.15 K in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4C1im][OTf]). Li(+), Na(+) and K(+) salts with anions matching the ionic liquid have also been investigated to determine how well these cations dissolve in [C4C1im][OTf]. This study compares the influence of metal cation and halide anion on the solubility of salts within this ionic liquid. The highest solubility found was for iodide salts, and the lowest solubility for the three fluoride salts. There is no outstanding difference in the solubility of salts with matching anions in comparison to halide salts. The experimental data were correlated employing several phase equilibria models, including ideal mixtures, van't Hoff, the λh (Buchowski) equation, the modified Apelblat equation, and the non-random two-liquid model (NRTL). It was found that the van't Hoff model gave the best correlation results. On the basis of the experimental data the thermodynamic dissolution parameters (ΔH, ΔS, and ΔG) were determined for the studied systems together with computed gas phase metathesis parameters. Dissolution depends on the energy difference between enthalpies of fusion and dissolution of the solute salt. This demonstrates that overcoming the lattice energy of the solid matrix is the key to the solubility of inorganic salts in ionic liquids. PMID:27264676

  4. Low-frequency modes of aqueous alkali halide solutions: an ultrafast optical Kerr effect study.

    PubMed

    Heisler, Ismael A; Mazur, Kamila; Meech, Stephen R

    2011-03-01

    A detailed picture of aqueous solvation of ions is central to the understanding of diverse phenomena in chemistry and biology. In this work, we report polarization resolved THz time domain measurements of the Raman spectral density of a wide range of aqueous salt solutions. In particular, the isotropic Raman spectral density reveals the frequency of the hydrogen bond formed between the halide ion and water. The frequency of this mode is measured for the series Cl(-), Br(-), and I(-) as a function of concentration, cation size, and charge. The frequencies extrapolated to zero concentration permit an estimation of the force constant of the mode, which is found to decrease with increasing halide mass and to be similar to the force constant associated with the water-water hydrogen bond. This result is consistent with recent calculations. The extrapolation of the frequency of the chloride hydrogen bond to zero concentration reveals a dependence of the frequency on the nature of the cation. This is ascribed to an interaction between the solvated anion and cation even at the lowest concentration studied here (<0.15 M). It is suggested that this behavior reflects the influence of the electric field of the cation on the hydrogen bond of an adjacent anion. Such interactions should be taken into account when modeling experimental data recorded at concentrations of ions in excess of 0.1 M. These measurements of the isotropic Raman spectral density are compared with those for the anisotropic response, which reflects the frequencies of the full range of hydrogen bonds in aqueous salt solutions. The anisotropic spectral density recovered can be modeled in terms of a concentration-dependent population of water-water H-bonds with a frequency unaffected by the ions, the halide-water hydrogen bonds, and a low-frequency collision-induced contribution. PMID:21291185

  5. EPR study of electron bombarded alkali- and alkaline-earth halide crystal surfaces

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Lad, R. A.

    1975-01-01

    An EPR study of electron bombarded LiF, NaCl, KCl, CaF2 and BaF2 polycrystalline surfaces has shown that small metal particles are formed on the surfaces of the crystals. Identification was made from CESR signals. The symmetric line-shape of the signals, even at 77 K, indicated that the particles were less than 0.5 micron in diameter. Signals due to F centers were observed in LiF but not in the other halides. Implications to metal deposition are considered.

  6. Lattice model calculation of elastic and thermodynamic properties at high pressure and temperature. [for alkali halides in NaCl lattice

    NASA Technical Reports Server (NTRS)

    Demarest, H. H., Jr.

    1972-01-01

    The elastic constants and the entire frequency spectrum were calculated up to high pressure for the alkali halides in the NaCl lattice, based on an assumed functional form of the inter-atomic potential. The quasiharmonic approximation is used to calculate the vibrational contribution to the pressure and the elastic constants at arbitrary temperature. By explicitly accounting for the effect of thermal and zero point motion, the adjustable parameters in the potential are determined to a high degree of accuracy from the elastic constants and their pressure derivatives measured at zero pressure. The calculated Gruneisen parameter, the elastic constants and their pressure derivatives are in good agreement with experimental results up to about 600 K. The model predicts that for some alkali halides the Grunesen parameter may decrease monotonically with pressure, while for others it may increase with pressure, after an initial decrease.

  7. Ca-Fe and Alkali-Halide Alteration of an Allende Type B CAI: Aqueous Alteration in Nebular or Asteroidal Settings

    NASA Technical Reports Server (NTRS)

    Ross, D. K.; Simon, J. I.; Simon, S. B.; Grossman, L.

    2012-01-01

    Ca-Fe and alkali-halide alteration of CAIs is often attributed to aqueous alteration by fluids circulating on asteroidal parent bodies after the various chondritic components have been assembled, although debate continues about the roles of asteroidal vs. nebular modification processes [1-7]. Here we report de-tailed observations of alteration products in a large Type B2 CAI, TS4 from Allende, one of the oxidized subgroup of CV3s, and propose a speculative model for aqueous alteration of CAIs in a nebular setting. Ca-Fe alteration in this CAI consists predominantly of end-member hedenbergite, end-member andradite, and compositionally variable, magnesian high-Ca pyroxene. These phases are strongly concentrated in an unusual "nodule" enclosed within the interior of the CAI (Fig. 1). The Ca, Fe-rich nodule superficially resembles a clast that pre-dated and was engulfed by the CAI, but closer inspection shows that relic spinel grains are enclosed in the nodule, and corroded CAI primary phases interfinger with the Fe-rich phases at the nodule s margins. This CAI also contains abundant sodalite and nepheline (alkali-halide) alteration that occurs around the rims of the CAI, but also penetrates more deeply into the CAI. The two types of alteration (Ca-Fe and alkali-halide) are adjacent, and very fine-grained Fe-rich phases are associated with sodalite-rich regions. Both types of alteration appear to be replacive; if that is true, it would require substantial introduction of Fe, and transport of elements (Ti, Al and Mg) out of the nodule, and introduction of Na and Cl into alkali-halide rich zones. Parts of the CAI have been extensively metasomatized.

  8. Interaction of wide band gap single crystals with 248 nm excimer laser radiation. XII. The emission of negative atomic ions from alkali halides

    SciTech Connect

    Kimura, Kenichi; Langford, S. C.; Dickinson, J. T.

    2007-12-01

    Many wide band gap materials yield charged and neutral emissions when exposed to sub-band-gap laser radiation at power densities below the threshold for optical breakdown and plume formation. In this work, we report the observation of negative alkali ions from several alkali halides under comparable conditions. We observe no evidence for negative halogen ions, in spite of the high electron affinities of the halogens. Significantly, the positive and negative alkali ions show a high degree of spatial and temporal overlap. A detailed study of all the relevant particle emissions from potassium chloride (KCl) suggests that K{sup -} is formed by the sequential attachment of two electrons to K{sup +}.

  9. Shallow electron traps in alkali halide crystals: Mollwo-Ivey relations of the optical absorption bands

    NASA Astrophysics Data System (ADS)

    Ziraps, Valters

    2001-03-01

    Evidences are given that two classes of the transient IR- absorption bands: (a) with max. at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl (due to shallow electron traps according G. Jacobs or due to bound polarons according E.V. Korovkin and T.A. Lebedkina) and (b) with max. at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, RbCl:I and RbBr:I (due to on-center STE localized at iodine dimer according M. Hirai and collaborators) are caused by the same defect- atomic alkali impurity center [M+]c0e- (electron e- trapped by a substitutional smaller size alkali cation impurity [M+]c0). The Mollwo-Ivey plots (for the transient IR-absorption bands) of the zero-phonon line energy E0 (for NaCl, KCl, KBr, RbCl and NaBr, KCl:I) and/or the low-energy edge valued E0 (for NaI, RbCl:I, RbBr:I) versus anion-cation distance (d) evidence that two types of the [M+]c0e- centers are predominant: (a) [Na+]c0e- in the KX and RbX host crystals with the relation E0approximately equals 6.15/d2.74, (b) [Li+]c03- in the NaX host crystals - E0approximately equals 29.4/d4.72. The Mollwo-Ivey relation E0approximately equals 18.36/d(superscript 2.70 is fulfilled as well for the F' band in NaCl, KCl, KBr, KI, RbCl, RbI if we use the F' center optical binding energy values E0.

  10. Photocathodes for RF photoinjectors

    NASA Astrophysics Data System (ADS)

    Michelato, P.

    1997-02-01

    Over the past ten years photocathodes have been extensively used as high-brightness electron sources in RF guns. In this paper, I present a general review of the alkali-based high quantum efficiency (QE) photoemitters (e.g. Cs 3Sb, K 2CsSb and Cs 2Te), together with a comparative analysis of the different preparation procedures and the results obtained, both in the preparation chambers and in RF guns. The need to increase the photocathode reliability has provided the impetus to get an R&D activity to go over the alchemy of photocathode preparation procedure. In this paper, I will discuss the results so far obtained in different laboratories, both by using traditional investigation strategy (e.g. QE and RF behavior) and by means of surface science techniques as Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS). Alkali antimonides have been used at first in the RF gun due to the high QE response to the green light of the Nd:YLF second-harmonic radiation. Measurements have confirmed the high reactivity of the alkali antimonide photocathodes to the residual gases: this fact makes their use in RF guns not practical, mainly for short lifetimes. Further investigations have shown that the choice of the substratum preparation procedure and chemical composition plays a fundamental role in the photocathode performance, both from the point of view of the QE and the operative lifetime and ruggedness to gas exposition. Cesium telluride (Cs 2Te) prepared on a molybdenum substratum seems to be, nowadays, the best compromise, in terms of preparation procedure reliability and ruggedness, that now the characteristics and drawbacks of this material are well understood (e.g. the need of an UV laser source). Future possible developments will be discussed. In particular, the measurement and the control of the thermal emittance and the time response could be an important task.

  11. Temperature-dependent solubilities and mean ionic activity coefficients of alkali halides in water from molecular dynamics simulations.

    PubMed

    Mester, Zoltan; Panagiotopoulos, Athanassios Z

    2015-07-28

    The mean ionic activity coefficients of aqueous KCl, NaF, NaI, and NaCl solutions of varying concentrations have been obtained from molecular dynamics simulations following a recently developed methodology based on gradual insertions of salt molecules [Z. Mester and A. Z. Panagiotopoulos, J. Chem. Phys. 142, 044507 (2015)]. The non-polarizable ion models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)], Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)], Reiser et al. [J. Chem. Phys. 140, 044504 (2014)], and Joung and Cheatham [J. Phys. Chem. B 112, 9020 (2008)] were used along with the extended simple point charge (SPC/E) water model [Berendsen et al., J. Phys. Chem. 91, 6269 (1987)] in the simulations. In addition to the chemical potentials in solution used to obtain the activity coefficients, we also calculated the chemical potentials of salt crystals and used them to obtain the solubility of these alkali halide models in SPC/E water. The models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)] and Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)] provide excellent predictions of the mean ionic activity coefficients at 298.15 K and 1 bar, but significantly underpredict or overpredict the solubilities. The other two models generally predicted the mean ionic activity coefficients only qualitatively. With the exception of NaF for which the solubility is significantly overpredicted, the model of Joung and Cheatham predicts salt solubilities that are approximately 40%-60% of the experimental values. The models of Reiser et al. [J. Chem. Phys. 140, 044504 (2014)] make good predictions for the NaCl and NaI solubilities, but significantly underpredict the solubilities for KCl and NaF. We also tested the transferability of the models to temperatures much higher than were used to parametrize them by performing simulations for NaCl at 373.15 K and 1 bar, and at 473.15 K and 15.5 bar. All models overpredict the drop in the values of mean ionic

  12. Temperature-dependent solubilities and mean ionic activity coefficients of alkali halides in water from molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Mester, Zoltan; Panagiotopoulos, Athanassios Z.

    2015-07-01

    The mean ionic activity coefficients of aqueous KCl, NaF, NaI, and NaCl solutions of varying concentrations have been obtained from molecular dynamics simulations following a recently developed methodology based on gradual insertions of salt molecules [Z. Mester and A. Z. Panagiotopoulos, J. Chem. Phys. 142, 044507 (2015)]. The non-polarizable ion models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)], Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)], Reiser et al. [J. Chem. Phys. 140, 044504 (2014)], and Joung and Cheatham [J. Phys. Chem. B 112, 9020 (2008)] were used along with the extended simple point charge (SPC/E) water model [Berendsen et al., J. Phys. Chem. 91, 6269 (1987)] in the simulations. In addition to the chemical potentials in solution used to obtain the activity coefficients, we also calculated the chemical potentials of salt crystals and used them to obtain the solubility of these alkali halide models in SPC/E water. The models of Weerasinghe and Smith [J. Chem. Phys. 119, 11342 (2003)] and Gee et al. [J. Chem. Theory Comput. 7, 1369 (2011)] provide excellent predictions of the mean ionic activity coefficients at 298.15 K and 1 bar, but significantly underpredict or overpredict the solubilities. The other two models generally predicted the mean ionic activity coefficients only qualitatively. With the exception of NaF for which the solubility is significantly overpredicted, the model of Joung and Cheatham predicts salt solubilities that are approximately 40%-60% of the experimental values. The models of Reiser et al. [J. Chem. Phys. 140, 044504 (2014)] make good predictions for the NaCl and NaI solubilities, but significantly underpredict the solubilities for KCl and NaF. We also tested the transferability of the models to temperatures much higher than were used to parametrize them by performing simulations for NaCl at 373.15 K and 1 bar, and at 473.15 K and 15.5 bar. All models overpredict the drop in the values of mean ionic

  13. Intrinsic emittance reduction in transmission mode photocathodes

    NASA Astrophysics Data System (ADS)

    Lee, Hyeri; Cultrera, Luca; Bazarov, Ivan

    2016-03-01

    High quantum efficiency (QE) and low emittance electron beams provided by multi-alkali photocathodes make them of great interest for next generation high brightness photoinjectors. Spicer's three-step model well describes the photoemission process; however, some photocathode characteristics such as their thickness have not yet been completely exploited to further improve the brightness of the generated electron beams. In this work, we report on the emittance and QE of a multi-alkali photocathode grown onto a glass substrate operated in transmission and reflection modes at different photon energies. We observed a 20% reduction in the intrinsic emittance from the reflection to the transmission mode operation. This observation can be explained by inelastic electron-phonon scattering during electrons' transit towards the cathode surface. Due to this effect, we predict that thicker photocathode layers will further reduce the intrinsic emittance of electron beams generated by photocathodes operated in transmission mode.

  14. Study on influence of growth conditions on position and shape of crystal/melt interface of alkali lead halide crystals at Bridgman growth

    NASA Astrophysics Data System (ADS)

    Král, Robert

    2012-12-01

    Suitable conditions for growth of high quality single crystals of ternary alkali lead halides prepared by a Bridgman method were explored using direct observation of a crystal/melt interface when pulling an ampoule out of a furnace, deliberated striations' induction and measurement of a temperature field in the filled ampoule in the vertical Bridgman arrangement, as model compounds lead chloride and ternary rubidium lead bromide were used. By direct observation only position of the crystal/melt interface was markedly determined, while by induced striations both the position and the shape of the interface were visualized but their contrast had to be intensified by adding admixtures. Performed temperature measurements in the filled ampoule brought both a view of temperature field in the 3D radial symmetry and basic data for comparison of a real temperature field with those obtained by projected modeling.

  15. Theoretical study of mixed LiLnX4 (Ln = La, Dy; X = F, Cl, Br, I) rare earth/alkali halide complexes.

    PubMed

    Groen, C P; Oskam, A; Kovács, A

    2000-12-25

    The structure, bonding and vibrational properties of the mixed LiLnX4 (Ln = La, Dy; X = F, Cl, Br, I) rare earth/alkali halide complexes were studied using various quantum chemical methods (HF, MP2 and the Becke3-Lee-Yang-Parr exchange-correlation density functional) in conjunction with polarized triple-zeta valence basis sets and quasi-relativistic effective core potentials for the heavy atoms. Our comparative study indicated the superiority of MP2 theory while the HF and B3-LYP methods as well as less sophisticated basis sets failed for the correct energetic relations. In particular, f polarization functions on Li and X proved to be important for the Li...X interaction in the complexes. From the three characteristic structures of such complexes, possessing 1-(C3v), 2-(C2v), or 3-fold coordination (C3v) between the alkali metal and the bridging halide atoms, the bi- and tridentate forms are located considerably lower on the potential energy surface then the monodentate isomer. Therefore only the bi- and tridentate isomers have chemical relevance. The monodentate isomer is only a high-lying local minimum in the case of X = F. For X = Cl, Br, and I this structure is found to be a second-order saddle point. The bidentate structure was found to be the global minimum for the systems with X = F, Cl, and Br. However, the relative stability with respect to the tridentate structure is very small (1-5 kJ/mol) for the heavier halide derivatives and the relative order is reversed in the case of the iodides. The energy difference between the three structures and the dissociation energy decrease in the row F to I. The ionic bonding in the complexes was characterized by natural charges and a topological analysis of the electron density distribution according to Bader's theorem. Variation of the geometrical and bonding characteristics between the lanthanum and dysprosium complexes reflects the effect of "lanthanide contraction". The calculated vibrational data indicate that

  16. Mass spectrometry of oligopeptides in the presence of large amounts of alkali halides using desorption/ionization induced by neutral cluster impact.

    PubMed

    Portz, André; Baur, Markus; Gebhardt, Christoph R; Dürr, Michael

    2016-06-01

    Oligopeptides in the presence of large amounts of salt were desorbed and ionized using desorption/ionization induced by neutral clusters (DINeC) for further analysis by means of mass spectrometry (MS). Using oligopeptides in alkali halide solutions as a model system, DINeC was shown to yield clear and fragmentation free mass spectra of the biomolecules even from environments with a large excess of salt. The results were traced back to a phase separation between salt and biomolecules during sample preparation. The ratio between alkali metal complexes [M+A](+) and bare biomolecules [M+H](+) was controlled using different preparation schemes. DINeC was applied to the products of a tryptic digest of bovine serum albumin in the presence of sodium chloride; the results of a mass fingerprint analysis did not show a major difference for the spectra with and without salt in the original solution. The metal-ion/peptide interaction was further investigated by means of tandem-MS. PMID:26825286

  17. A different view of structure-making and structure-breaking in alkali halide aqueous solutions through x-ray absorption spectroscopy.

    PubMed

    Waluyo, Iradwikanari; Nordlund, Dennis; Bergmann, Uwe; Schlesinger, Daniel; Pettersson, Lars G M; Nilsson, Anders

    2014-06-28

    X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl(-) and Br(-) are shown to have insignificant effect on the structure of water while I(-) locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na(+) and the effect on the liquid as similar to an increase in temperature. PMID:24985653

  18. A different view of structure-making and structure-breaking in alkali halide aqueous solutions through x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Waluyo, Iradwikanari; Nordlund, Dennis; Bergmann, Uwe; Schlesinger, Daniel; Pettersson, Lars G. M.; Nilsson, Anders

    2014-06-01

    X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl- and Br- are shown to have insignificant effect on the structure of water while I- locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na+ and the effect on the liquid as similar to an increase in temperature.

  19. Complete-velocity-range description of negative-ion conversion of neutral atoms on an alkali-metal-halide surface under grazing geometry

    NASA Astrophysics Data System (ADS)

    Zhou, Hu; Zhou, Wang; Zhang, Meixiao; Zhou, Lihua; Ma, Yulong; Wang, Guangyi; Wu, Yong; Li, Bowen; Chen, Ximeng

    2016-06-01

    We propose a simple theoretical approach to consider negative-ion conversion of neutral atoms grazing on alkali-metal-halide crystal surfaces over the complete velocity range. The conversion process is viewed as a series of successive binary collisions between the projectile and the negatively charged sites on the surface along their trajectories due to localization of valence-band electrons at the anionic sites of the crystal. Conversion from F0 to F- via grazing scattering in LiF(100) and KI(100) is demonstrated with this model, which incorporates the key factors of image interaction and Mott-Littleton polarization interaction for electron capture. It also incorporates the decrease in the electron affinity due to Coulomb barrier tunneling of large-velocity negative ions to the vacuum level near surface anion sites. The pronounced differences in the efficiency of F- formation at LiF(100) and KI(100) surfaces are well explained by the proposed model. The relative efficiency and related saturation of the negative-ion formation for LiF and KI crystals compare well with experimental results.

  20. Band-structure calculations of noble-gas and alkali halide solids using accurate Kohn-Sham potentials with self-interaction correction

    SciTech Connect

    Li, Y.; Krieger, J.B. ); Norman, M.R. ); Iafrate, G.J. )

    1991-11-15

    The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP.

  1. Characterization of an Alkali- and Halide-Resistant Laccase Expressed in E. coli: CotA from Bacillus clausii

    PubMed Central

    Brander, Søren; Mikkelsen, Jørn D.; Kepp, Kasper P.

    2014-01-01

    The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ∼0.5–2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s−1 at pH 6 and 5 s−1 at pH 8 in contrast to 6 s−1 at pH 6 and 2 s−1 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher for B. subtilis cotA at pHopt. While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500–700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ∼20 minutes half-life at 80°C, less than the ∼50 minutes at 80°C for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH∼8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization. PMID:24915287

  2. Characterization of an alkali- and halide-resistant laccase expressed in E. coli: CotA from Bacillus clausii.

    PubMed

    Brander, Søren; Mikkelsen, Jørn D; Kepp, Kasper P

    2014-01-01

    The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ~0.5-2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (K(M)) but to pH dependence of catalytic turnover: The k(cat) of B. clausii cotA was 1 s⁻¹ at pH 6 and 5 s⁻¹ at pH 8 in contrast to 6 s⁻¹ at pH 6 and 2 s⁻¹ at pH 8 for of B. subtilis cotA. Overall, k(cat)/K(M) was 10-fold higher for B. subtilis cotA at pH(opt). While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500-700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ~20 minutes half-life at 80°C, less than the ~50 minutes at 80°C for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH~8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization. PMID:24915287

  3. Correlation of CsK{sub 2}Sb photocathode lifetime with antimony thickness

    SciTech Connect

    Mamun, M. A. Elmustafa, A. A.; Hernandez-Garcia, C.; Poelker, M.

    2015-06-01

    CsK{sub 2}Sb photocathodes with quantum efficiency on the order of 10% at 532 nm, and lifetime greater than 90 days at low voltage, were successfully manufactured via co-deposition of alkali species emanating from an effusion source. Photocathodes were characterized as a function of antimony layer thickness and alkali consumption, inside a vacuum chamber that was initially baked, but frequently vented without re-baking. Photocathode lifetime measured at low voltage is correlated with the antimony layer thickness. Photocathodes manufactured with comparatively thick antimony layers exhibited the best lifetime. We speculate that the antimony layer serves as a reservoir, or sponge, for the alkali.

  4. Correlation of CsK2Sb photocathode lifetime with antimony thickness

    SciTech Connect

    Mamun, M. A.; Hernandez-Garcia, C.; Poelker, M.; Elmustafa, A. A.

    2015-06-01

    CsK2Sb photocathodes with quantum efficiency on the order of 10% at 532 nm, and lifetime greater than 90 days at low voltage, were successfully manufactured via co-deposition of alkali species emanating from an effusion source. Photocathodes were characterized as a function of antimony layer thickness and alkali consumption, inside a vacuum chamber that was initially baked, but frequently vented without re-baking. Photocathode lifetime measured at low voltage is correlated with the antimony layer thickness. Photocathodes manufactured with comparatively thick antimony layers exhibited the best lifetime. We speculate that the antimony layer serves as a reservoir, or sponge, for the alkali.

  5. Pre- and initial stages of epitaxy in alkali halide systems. II. Interaction of molecular beams of CsCl with (100) surfaces of NaCl

    NASA Astrophysics Data System (ADS)

    Dabringhaus, H.; Haag, M.

    The interaction of molecular beams of CsCl with (100) surfaces of NaCl is studied for crystal temperatures between 560 and 620 K and for molecular beam fluxes between 2 × 10 7 and 2 × 10 13 cm -2 s -1 by measurements of transient and steady state desorption fluxes, by static SIMS, and by electron microscopy. Also for the large Cs + ions a fast cation exchange Cs + ⇌ Na + between CsCl molecules adsorbed on the terrace and the outermost surface layer of the NaCl crystal is observed. The results for undersaturation are interpreted by incorporation of Cs + ions in the outermost surface layer of the NaCl crystal and by adsorption of CsCl molecules at the monatomic steps on the surface. The outermost surface layer proves to have a maximum capacity for Cs + of 2.4 × 10 11 cm -2. The residence time of Cs + ions in the outermost surface layer is determined as τ0 = 1.6 × 10 -12 exp(1.49 (eV)/ kT), the time for desorption of CsCl molecules from the monatomic steps as τ1 = 2.9 × 10 -14 exp(1.60 (eV)/ kT). By experiments with an additional NaCl flux onto the surface it is shown that τ0 is the time for a back-exchange of Cs + ions from the outermost surface layer against Na + from NaCl admolecules. For supersaturation the growth of polymorphic CsCl islands is observed. In the first growth stages these islands show the NaCl-type structure, while for later growth stages the CsCl type structure is found. A comparative discussion of all studied alkali halide systems shows that the different results can be attributed to the different radii of guest and host cation and to lattice misfits, respectively.

  6. Alkali halide-assisted penetration of neostigmine across excised human skin: a combination of structured water disruption and a Donnan-like effect.

    PubMed

    Michael-Baruch, E; Shiri, Y; Cohen, S

    1994-08-01

    The penetration of neostigmine across excised human skin mounted in flow-through diffusion cells, delivered from a 0.28 M aqueous solution, was below detection limits. The presence of either NaCl or LiCl in the donor solution caused significant fluxes of neostigmine, with permeability coefficients (Kp's) in the range of 10(-6) cm min-1. Paradoxically, low concentrations of NaCl or LiCl (0.25 and 0.5 M) were more effective in this respect than the 1 M solution, which was the least effective concentration in the range of 0.25-3 M. Thus, the dependence of the experimental Kp values on inorganic ion concentration followed a biphasic course, suggesting the participation of two distinctive mechanisms in the penetration-enhancement process. The early phase corresponding to 0.25 and 0.5 M NaCl or LiCl is being partly ascribed to a decrease in the viscosity of lamellar water caused by the influx of the respective hydrated ions, hydration of LiCl or NaCl being more extensive at low alkali halide concentration that at higher ones (reference cited). The late phase corresponding to 2 and 3 M LiCl and NaCl is partly ascribed to a Donnan-like effect whereby the presence of a large excess of poorly diffusible common ion (Na+ or Li+) enhances the partitioning into the skin of the more diffusible ion, in this case neostigmine cation. The presence of inorganic ions at different concentrations had no effect on the partial molal volume of neostigmine bromide (Vi infinity = 223.5 cm3 mol-1), which was practically the same for all concentrations of either LiCl and NaCl.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7983588

  7. Structure and Dynamics of Tunneling and Laser - Defects in Alkali Halides as Studied by a Behavior Type Analysis of the Polarized Raman Scattering.

    NASA Astrophysics Data System (ADS)

    Joosen, Wim M. C.

    It is demonstrated that proper analysis of polarized Raman spectra of defects in alkali halides by means of the Behavior Type (BT) method allows a detailed description of defect dynamics. The recently developed BT method provides a systematic procedure to distinguish, among the 125 Raman -active modes of the 33 possible point groups of a defect in a cubic lattice, the Raman modes which are consistent with the polarized Raman data, from those which are not. The efficiency of the BT method was shown in the interpretation of the low frequency Raman mode at 43 cm ^{-1} of the Li ^+ off-center impurity in KCl, which was attributed to a collective motion of the surrounding chlorine ions. This experimental finding inspired us to calculate the time dependent phonon autocorrelation function of a coupled spin-phonon system, which explains the anomalous isotope shift of the low frequency mode. We also studied the hydrogen-tagged Li ^+ center in KCl, which performs a correlated tunneling motion and put forward a defect model, in which the Li^+ ion and the hydrogen atom are both accommodated on the same cation site and displaced along <111> in opposite directions. There is no preferential molecular bond of any consequence between them. Our picture modifies the model based on electron spin resonance measurements, in which the H^{0}Li ^+ center is considered as a (LiH) ^+ molecular system. The Tl^0(1) defect is the first laser-center of the atomic type investigated with the Raman technique. The polarized Raman spectra, were excited in the third optical band of Tl^0 (1) and show that this transition is broadened by A_1-modes of the C_ {rm 4v} defect symmetry. We distinguished an induced first order spectrum, shown to be characteristic for the KCl lattice, and a low frequency vibration at about 30 cm^{-1}, which reflects the motion of the thallium atom along the fourfold axis. The Tl^+Tl^0 (1) center provided a first test-case for the extended BT method for resonant Raman

  8. Electrolytic systems and methods for making metal halides and refining metals

    SciTech Connect

    Holland, Justin M.; Cecala, David M.

    2015-05-26

    Disclosed are electrochemical cells and methods for producing a halide of a non-alkali metal and for electrorefining the halide. The systems typically involve an electrochemical cell having a cathode structure configured for dissolving a hydrogen halide that forms the halide into a molten salt of the halogen and an alkali metal. Typically a direct current voltage is applied across the cathode and an anode that is fabricated with the non-alkali metal such that the halide of the non-alkali metal is formed adjacent the anode. Electrorefining cells and methods involve applying a direct current voltage across the anode where the halide of the non-alkali metal is formed and the cathode where the non-alkali metal is electro-deposited. In a representative embodiment the halogen is chlorine, the alkali metal is lithium and the non-alkali metal is uranium.

  9. Masked Photocathode for Photoinjector

    SciTech Connect

    Qiang, Ji

    2010-01-21

    In this research note, we propose a scheme to insert a photocathode inside a photoinjector for generating high brightness electron beam. Instead of mounting the photocathode onto the electrode, a masked electrode with small hole is used to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material very simple by rotating the photocathode behind the mask into the hole. This will significantly increase the usage lifetime of a photocathode. Furthermore, this also helps reduce the dark current or secondary electron emission from the photocathode. The hole on the mask also provides a transverse cut-off to the Gaussian laser profile which can be beneficial from the beam dynamics point of view.

  10. Photocathode device that replenishes photoemissive coating

    DOEpatents

    Moody, Nathan A.; Lizon, David C.

    2016-06-14

    A photocathode device may replenish its photoemissive coating to replace coating material that desorbs/evaporates during photoemission. A linear actuator system may regulate the release of a replenishment material vapor, such as an alkali metal, from a chamber inside the photocathode device to a porous cathode substrate. The replenishment material deposits on the inner surface of a porous membrane and effuses through the membrane to the outer surface, where it replenishes the photoemissive coating. The rate of replenishment of the photoemissive coating may be adjusted using the linear actuator system to regulate performance of the photocathode device during photoemission. Alternatively, the linear actuator system may adjust a plasma discharge gap between a cartridge containing replenishment material and a metal grid. A potential is applied between the cartridge and the grid, resulting in ejection of metal ions from the cartridge that similarly replenish the photoemissive coating.

  11. Prototype dispenser photocathode: Demonstration and comparison to theory

    NASA Astrophysics Data System (ADS)

    Moody, N. A.; Jensen, K. L.; Feldman, D. W.; O'Shea, P. G.; Montgomery, E. J.

    2007-03-01

    A method to significantly extend the operational lifetime of alkali-based photocathodes by diffusing cesium to the surface at moderate temperature is presented and shown to restore the quantum efficiency (QE) of cesiated tungsten. Experimental measurements of QE as a function of surface cesium coverage compare exceptionally well with a recent theoretical photoemission model, notably without the use of adjustable parameters. A prototype cesium dispenser cell is demonstrated and validates the concept upon which long-life dispenser photocathodes can be based.

  12. Activation Layer Stabilization of High Polarization Photocathodes in Sub-Optimal RF Gun Environments

    SciTech Connect

    Mulhollan, Gregory; /SLAC /Saxed Surface Science, Austin, TX

    2010-08-25

    We have developed an activation procedure by which the reactivity to CO{sub 2}, a principal cause of yield decay for GaAs photocathodes, is greatly reduced. The use of a second alkali in the activation process is responsible for the increased immunity of the activated surface. The best immunity was obtained by using a combination of Cs and Li without any loss in near bandgap yield. Optimally activated photocathodes have nearly equal quantities of both alkalis.

  13. A Masked Photocathode in Photoinjector

    SciTech Connect

    Qiang, Ji

    2010-12-14

    In this paper, we propose a masked photocathode inside the photoinjector for generating high brightness election beam. Instead of mounting the photocathode onto an electrode, an electrode with small hole is used as a mask to shield the photocathode from the accelerating vacuum chamber. Using such a masked photocathode will make the replacement of photocathode material easy by rotating the photocathode behind the electrode into the hole. Furthermore, this helps reduce the dark current or secondary electron emission from the photocathode material. The masked photocathode also provides transverse cut-off to a Gaussian laser beam that reduces electron beam emittance growth from nonlinear space-charge effects.

  14. Heat capacity of molten halides.

    PubMed

    Redkin, Alexander A; Zaikov, Yurii P; Korzun, Iraida V; Reznitskikh, Olga G; Yaroslavtseva, Tatiana V; Kumkov, Sergey I

    2015-01-15

    The heat capacities of molten salts are very important for their practical use. Experimental investigation of this property is challenging because of the high temperatures involved and the corrosive nature of these materials. It is preferable to combine experimental investigations with empirical relationships, which allows for the evaluation of the heat capacity of molten salt mixtures. The isobaric molar heat capacities of all molten alkali and alkaline-earth halides were found to be constant for each group of salts. The value depends on the number of atoms in the salt, and the molar heat capacity per atom is constant for all molten halide salts with the exception of the lithium halides. The molar heat capacities of molten halides do not change when the anions are changed. PMID:25530462

  15. Piezoelectrically Enhanced Photocathodes

    NASA Technical Reports Server (NTRS)

    Beach, Robert A.; Nikzad, Shouleh; Bell, Lloyd Douglas; Strittmatter, Robert

    2011-01-01

    Doping of photocathodes with materials that have large piezoelectric coefficients has been proposed as an alternative means of increasing the desired photoemission of electrons. Treating cathode materials to increase emission of electrons is called "activation" in the art. It has been common practice to activate photocathodes by depositing thin layers of suitable metals (usually, cesium). Because cesium is unstable in air, fabrication of cesiated photocathodes and devices that contain them must be performed in sealed tubes under vacuum. It is difficult and costly to perform fabrication processes in enclosed, evacuated spaces. The proposed piezoelectrically enhanced photocathodes would have electron-emission properties similar to those of cesiated photocathodes but would be stable in air, and therefore could be fabricated more easily and at lower cost. Candidate photocathodes include nitrides of elements in column III of the periodic table . especially compounds of the general formula Al(x)Ga(1.x)N (where 0< or = x < or =.1). These compounds have high piezoelectric coefficients and are suitable for obtaining response to ultraviolet light. Fabrication of a photocathode according to the proposal would include inducement of strain in cathode layers during growth of the layers on a substrate. The strain would be induced by exploiting structural mismatches among the various constituent materials of the cathode. Because of the piezoelectric effect in this material, the strain would give rise to strong electric fields that, in turn, would give rise to a high concentration of charge near the surface. Examples of devices in which piezoelectrically enhanced photocathodes could be used include microchannel plates, electron- bombarded charge-coupled devices, image tubes, and night-vision goggles. Piezoelectrically enhanced photocathode materials could also be used in making highly efficient monolithic photodetectors. Highly efficient and stable piezoelectrically enhanced

  16. Oxidation of hydrogen halides to elemental halogens

    DOEpatents

    Rohrmann, Charles A.; Fullam, Harold T.

    1985-01-01

    A process for oxidizing hydrogen halides having substantially no sulfur impurities by means of a catalytically active molten salt is disclosed. A mixture of the subject hydrogen halide and an oxygen bearing gas is contacted with a molten salt containing an oxidizing catalyst and alkali metal normal sulfates and pyrosulfates to produce an effluent gas stream rich in the elemental halogen and substantially free of sulfur oxide gases.

  17. Acicular photomultiplier photocathode structure

    DOEpatents

    Craig, Richard A.; Bliss, Mary

    2003-09-30

    A method and apparatus for increasing the quantum efficiency of a photomultiplier tube by providing a photocathode with an increased surface-to-volume ratio. The photocathode includes a transparent substrate, upon one major side of which is formed one or more large aspect-ratio structures, such as needles, cones, fibers, prisms, or pyramids. The large aspect-ratio structures are at least partially composed of a photoelectron emitting material, i.e., a material that emits a photoelectron upon absorption of an optical photon. The large aspect-ratio structures may be substantially composed of the photoelectron emitting material (i.e., formed as such upon the surface of a relatively flat substrate) or be only partially composed of a photoelectron emitting material (i.e., the photoelectron emitting material is coated over large aspect-ratio structures formed from the substrate material itself.) The large aspect-ratio nature of the photocathode surface allows for an effective increase in the thickness of the photocathode relative the absorption of optical photons, thereby increasing the absorption rate of incident photons, without substantially increasing the effective thickness of the photocathode relative the escape incidence of the photoelectrons.

  18. Carbon nanotube based photocathodes

    NASA Astrophysics Data System (ADS)

    Hudanski, Ludovic; Minoux, Eric; Gangloff, Laurent; Teo, Kenneth B. K.; Schnell, Jean-Philippe; Xavier, Stephane; Robertson, John; Milne, William I.; Pribat, Didier; Legagneux, Pierre

    2008-03-01

    This paper describes a novel photocathode which is an array of vertically aligned multi-walled carbon nanotubes (MWCNTs), each MWCNT being associated with one p-i-n photodiode. Unlike conventional photocathodes, the functions of photon-electron conversion and subsequent electron emission are physically separated. Photon-electron conversion is achieved with p-i-n photodiodes and the electron emission occurs from the MWCNTs. The current modulation is highly efficient as it uses an optically controlled reconfiguration of the electric field at the MWCNT locations. Such devices are compatible with high frequency and very large bandwidth operation and could lead to their application in compact, light and efficient microwave amplifiers for satellite telecommunication. To demonstrate this new photocathode concept, we have fabricated the first carbon nanotube based photocathode using silicon p-i-n photodiodes and MWCNT bunches. Using a green laser, this photocathode delivers 0.5 mA with an internal quantum efficiency of 10% and an ION/IOFF ratio of 30.

  19. Low-workfunction photocathodes based on acetylide compounds

    SciTech Connect

    Terdik, Joseph Z; Spentzouris, Linda; Terry, Jr., Jeffrey H; Harkay, Katherine C; Nemeth, Karoly; Srajer, George

    2014-05-20

    A low-workfunction photocathode includes a photoemissive material employed as a coating on the photocathode. The photoemissive material includes A.sub.nMC.sub.2, where A is a first metal element, the first element is an alkali metal, an alkali-earth element or the element Al; n is an integer that is 0, 1, 2, 3 or 4; M is a second metal element, the second metal element is a transition metal or a metal stand-in; and C.sub.2 is the acetylide ion C.sub.2.sup.2-. The photoemissive material includes a crystalline structure or non-crystalline structure of rod-like or curvy 1-dimensional polymeric substructures with MC.sub.2 repeating units embedded in a matrix of A.

  20. Molecular compressibility of some halides in alcohols

    NASA Technical Reports Server (NTRS)

    Serban, C.; Auslaender, D.

    1974-01-01

    After measuring ultrasonic velocity and density, the molecular compressibility values from Wada's formula were calculated, for alkali metal halide solutions in methyl, ethyl, butyl, and glycol alcohol. The temperature and concentration dependence were studied, finding deviations due to the hydrogen bonds of the solvent.

  1. Development of a CCD for ultraviolet imaging using a CCD photocathode combination

    NASA Technical Reports Server (NTRS)

    Collins, D. R.; Roberts, C. G.; Chan, W. W.; Rhines, W. C.; Barton, J. B.; Sobieski, S.

    1975-01-01

    CCD in the electron-in mode, coupled with a bi-alkali photocathode to produce UV photon conversion, provides the following desirable features: (1) high UV response of the bi-alkali photocathode; (2) excellent imaging quality of a CCD area array; and (3) high signal-to-noise ratio due to the EBS (electron bombarded silicon) gain of the CCD operating in a tube configuration. This paper describes the rationale and progress made in developing a CCD for use as an UV imager.

  2. Piezoelectrically enhanced photocathode

    NASA Technical Reports Server (NTRS)

    Beach, Robert A. (Inventor); Nikzad, Shouleh (Inventor); Strittmatter, Robert P. (Inventor); Bell, Lloyd Douglas (Inventor)

    2009-01-01

    A photocathode, for generating electrons in response to incident photons in a photodetector, includes a base layer having a first lattice structure and an active layer having a second lattice structure and epitaxially formed on the base layer, the first and second lattice structures being sufficiently different to create a strain in the active layer with a corresponding piezoelectrically induced polarization field in the active layer, the active layer having a band gap energy corresponding to a desired photon energy.

  3. Computation of methodology-independent single-ion solvation properties from molecular simulations. IV. Optimized Lennard-Jones interaction parameter sets for the alkali and halide ions in water

    SciTech Connect

    Reif, Maria M.; Huenenberger, Philippe H.

    2011-04-14

    The raw single-ion solvation free energies computed from atomistic (explicit-solvent) simulations are extremely sensitive to the boundary conditions and treatment of electrostatic interactions used during these simulations. However, as shown recently [M. A. Kastenholz and P. H. Huenenberger, J. Chem. Phys. 124, 224501 (2006); M. M. Reif and P. H. Huenenberger, J. Chem. Phys. 134, 144103 (2010)], the application of appropriate correction terms permits to obtain methodology-independent results. The corrected values are then exclusively characteristic of the underlying molecular model including in particular the ion-solvent van der Waals interaction parameters, determining the effective ion size and the magnitude of its dispersion interactions. In the present study, the comparison of calculated (corrected) hydration free energies with experimental data (along with the consideration of ionic polarizabilities) is used to calibrate new sets of ion-solvent van der Waals (Lennard-Jones) interaction parameters for the alkali (Li{sup +}, Na{sup +}, K{sup +}, Rb{sup +}, Cs{sup +}) and halide (F{sup -}, Cl{sup -}, Br{sup -}, I{sup -}) ions along with either the SPC or the SPC/E water models. The experimental dataset is defined by conventional single-ion hydration free energies [Tissandier et al., J. Phys. Chem. A 102, 7787 (1998); Fawcett, J. Phys. Chem. B 103, 11181] along with three plausible choices for the (experimentally elusive) value of the absolute (intrinsic) hydration free energy of the proton, namely, {Delta}G{sub hyd} {sup O-minus} [H{sup +}]=-1100, -1075 or -1050 kJ mol{sup -1}, resulting in three sets L, M, and H for the SPC water model and three sets L{sub E}, M{sub E}, and H{sub E} for the SPC/E water model (alternative sets can easily be interpolated to intermediate {Delta}G{sub hyd} {sup O-minus} [H{sup +}] values). The residual sensitivity of the calculated (corrected) hydration free energies on the volume-pressure boundary conditions and on the effective

  4. Robust activation method for negative electron affinity photocathodes

    DOEpatents

    Mulhollan, Gregory A.; Bierman, John C.

    2011-09-13

    A method by which photocathodes(201), single crystal, amorphous, or otherwise ordered, can be surface modified to a robust state of lowered and in best cases negative, electron affinity has been discovered. Conventional methods employ the use of Cs(203) and an oxidizing agent(207), typically carried by diatomic oxygen or by more complex molecules, for example nitrogen trifluoride, to achieve a lowered electron affinity(404). In the improved activation method, a second alkali, other than Cs(205), is introduced onto the surface during the activation process, either by co-deposition, yo-yo, or sporadic or intermittent application. Best effect for GaAs photocathodes has been found through the use of Li(402) as the second alkali, though nearly the same effect can be found by employing Na(406). Suitable photocathodes are those which are grown, cut from boules, implanted, rolled, deposited or otherwise fabricated in a fashion and shape desired for test or manufacture independently supported or atop a support structure or within a framework or otherwise affixed or suspended in the place and position required for use.

  5. Final Report, Photocathodes for High Repetition Rate Light Sources

    SciTech Connect

    Ben-Zvi, Ilan

    2014-04-20

    This proposal brought together teams at Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL) and Stony Brook University (SBU) to study photocathodes for high repetition rate light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). The work done under this grant comprises a comprehensive program on critical aspects of the production of the electron beams needed for future user facilities. Our program pioneered in situ and in operando diagnostics for alkali antimonide growth. The focus is on development of photocathodes for high repetition rate Free Electron Lasers (FELs) and Energy Recovery Linacs (ERLs), including testing SRF photoguns, both normal-conducting and superconducting. Teams from BNL, LBNL and Stony Brook University (SBU) led this research, and coordinated their work over a range of topics. The work leveraged a robust infrastructure of existing facilities and the support was used for carrying out the research at these facilities. The program concentrated in three areas: a) Physics and chemistry of alkali-antimonide cathodes b) Development and testing of a diamond amplifier for photocathodes c) Tests of both cathodes in superconducting RF photoguns and copper RF photoguns

  6. DIAMOND AMPLIFIER FOR PHOTOCATHODES.

    SciTech Connect

    RAO,T.; BEN-ZVI,I.; BURRILL,A.; CHANG,X.; HULBERT,S.; JOHNSON,P.D.; KEWISCH,J.

    2004-06-21

    We report a new approach to the generation of high-current, high-brightness electron beams. Primary electrons are produced by a photocathode (or other means) and are accelerated to a few thousand electron-volts, then strike a specially prepared diamond window. The large Secondary Electron Yield (SEY) provides a multiplication of the number of electrons by about two orders of magnitude. The secondary electrons drift through the diamond under an electric field and emerge into the accelerating proper of the ''gun'' through a Negative Electron Affinity surface of the diamond. The advantages of the new approach include the following: (1) Reduction of the number of primary electrons by the large SEY, i.e. a very low laser power in a photocathode producing the primaries. (2) Low thermal emittance due to the NEA surface and the rapid thermalization of the electrons. (3) Protection of the cathode from possible contamination from the gun, allowing the use of large quantum efficiency but sensitive cathodes. (4) Protection of the gun from possible contamination by the cathode, allowing the use of superconducting gun cavities. (5) Production of high average currents, up to ampere class. (6) Encapsulated design, making the ''load-lock'' systems unnecessary. This paper presents the criteria that need to be taken into account in designing the amplifier.

  7. Infrared-sensitive photocathode

    DOEpatents

    Mariella, Jr., Raymond P.; Cooper, Gregory A.

    1995-01-01

    A single-crystal, multi-layer device incorporating an IR absorbing layer that is compositionally different from the Ga.sub.x Al.sub.1-x Sb layer which acts as the electron emitter. Many different IR absorbing layers can be envisioned for use in this embodiment, limited only by the ability to grow quality material on a chosen substrate. A non-exclusive list of possible IR absorbing layers would include GaSb, InAs and InAs/Ga.sub.w In.sub.y Al.sub.1-y-w Sb superlattices. The absorption of the IR photon excites an electron into the conduction band of the IR absorber. An externally applied electric field then transports electrons from the conduction band of the absorber into the conduction band of the Ga.sub.x Al.sub.1-x Sb, from which they are ejected into vacuum. Because the band alignments of Ga.sub.x Al.sub.1-x Sb can be made the same as that of GaAs, emitting efficiencies comparable to GaAs photocathodes are obtainable. The present invention provides a photocathode that is responsive to wavelengths within the range of 0.9 .mu.m to at least 10 .mu.m.

  8. Infrared-sensitive photocathode

    DOEpatents

    Mariella, R.P. Jr.; Cooper, G.A.

    1995-04-04

    A single-crystal, multi-layer device is described incorporating an IR absorbing layer that is compositionally different from the Ga{sub x}Al{sub 1{minus}x}Sb layer which acts as the electron emitter. Many different IR absorbing layers can be envisioned for use in this embodiment, limited only by the ability to grow quality material on a chosen substrate. A non-exclusive list of possible IR absorbing layers would include GaSb, InAs and InAs/Ga{sub w}In{sub y}Al{sub 1{minus}y{minus}w}Sb superlattices. The absorption of the IR photon excites an electron into the conduction band of the IR absorber. An externally applied electric field then transports electrons from the conduction band of the absorber into the conduction band of the Ga{sub x}Al{sub 1{minus}x}Sb, from which they are ejected into vacuum. Because the band alignments of Ga{sub x}Al{sub 1{minus}x}Sb can be made the same as that of GaAs, emitting efficiencies comparable to GaAs photocathodes are obtainable. The present invention provides a photocathode that is responsive to wavelengths within the range of 0.9 {mu}m to at least 10 {mu}m. 9 figures.

  9. Dense-Pinch Photocathode

    NASA Astrophysics Data System (ADS)

    Asmus, John F.; Lovberg, Ralph H.

    1988-05-01

    A promising approach to the generation of low-emittance e-beams for particle beam and FEL application employs a photoelectron cathode. IF such an e-beam source is to be viable at high power, a high-performance hard-UV illuminator is needed. Toward this end, experiments have been performed by illuminating a metal photocathode with the VUV radiation from a laser-guided gas-embedded high-density high-Z pinch. Such a VUV source is interesting because the plasma is created at high density and is optically thick. Thus, it is both a stable and an efficient radiator. Coupled with a copper photocathode it has generated a-beam current densities up to 60 A/sq-cm. The test device has been modified to utilize a pinch formed from a liquid jet in vacuum, rather than the laser-guided discharge in high-pressure gas. This is more suitable for rep-rate operation as it dispenses with the VUV-absorbing interposed gas, the channel-forming laser, and gas transport at high average power. A decane-jet device has been tested at 10 Hz with a peak pulse VUV power of 100 MW.

  10. DIAMOND AMPLIFIED PHOTOCATHODES.

    SciTech Connect

    SMEDLEY,J.; BEN-ZVI, I.; BOHON, J.; CHANG, X.; GROVER, R.; ISAKOVIC, A.; RAO, T.; WU, Q.

    2007-11-26

    High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.

  11. The Silver Halides

    ERIC Educational Resources Information Center

    Sahyun, M. R. V.

    1977-01-01

    Illustrates the type of fractional bonding for solid silver halides. Treats the silver halides as electron excess compounds, and develops a model of a localized bonding unit that may be iterated in three dimensions to describe the bulk phase. (MLH)

  12. Metal-halide mixtures for latent heat energy storage

    NASA Technical Reports Server (NTRS)

    Chen, K.; Manvi, R.

    1981-01-01

    Alkali metal and alkali halide mixtures are identified which may be suitable for thermal energy storage at temperatures above 600 C. The use of metal-halides is appropriate because of their tendency to form two immiscible melts with a density difference, which reduces scale formation and solidification on heat transfer surfaces. Also, the accumulation of phase change material along the melt interface is avoided by the self-dispersing characteristic of some metal-halides, in particular Sr-SrCl2, Ba-BaCl2, and Ba-BaBr2 mixtures. Further advantages lie in their high thermal conductivities, ability to cope with thermal shock, corrosion inhibition, and possibly higher energy densities.

  13. Recent Progress toward Robust Photocathodes

    SciTech Connect

    Mulhollan, G. A.; Bierman, J. C.

    2009-08-04

    RF photoinjectors for next generation spin-polarized electron accelerators require photo-cathodes capable of surviving RF gun operation. Free electron laser photoinjectors can benefit from more robust visible light excited photoemitters. A negative electron affinity gallium arsenide activation recipe has been found that diminishes its background gas susceptibility without any loss of near bandgap photoyield. The highest degree of immunity to carbon dioxide exposure was achieved with a combination of cesium and lithium. Activated amorphous silicon photocathodes evince advantageous properties for high current photoinjectors including low cost, substrate flexibility, visible light excitation and greatly reduced gas reactivity compared to gallium arsenide.

  14. CsI and some new photocathodes

    SciTech Connect

    Anderson, D.F.; Kwan, S.; Peskov, V.

    1993-06-01

    A discussion of the possible sources of discrepancies in the measurements of the quantum efficiency of CsI photocathodes is presented. We propose that the major causes for disagreements in QE are due to the QE dependence on the current density extracted from the photocathode, on the electric field, and on the temperature of the photocathode. Preliminary results on TMAE enhanced GaAs and Si, plus TMAE protected CsTe and SbCs photocathodes, operated in gas, are also presented.

  15. Factors affecting performance of dispenser photocathodes

    NASA Astrophysics Data System (ADS)

    Moody, Nathan A.; Jensen, Kevin L.; Feldman, Donald W.; Montgomery, Eric J.; O'Shea, Patrick G.

    2007-11-01

    Usable lifetime has long been a limitation of high efficiency photocathodes in high average current accelerator applications such as free electron lasers, where poor vacuum conditions and high incident laser power contribute to early degradation in electron beam emission. Recent progress has been made in adapting well known thermionic dispenser techniques to photocathodes, resulting in a dispenser photocathode whose photosensitive surface coating of cesium can be periodically replenished to extend effective lifetime. This article details the design and fabrication process of a prototype cesium dispenser photocathode and describes in detail the dominant factors affecting its performance: activation procedure, surface cleanliness, temperature, and substrate microstructure.

  16. Alkali Bee

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The alkali bee, Nomia melanderi, is native to deserts and semi-arid desert basins of the western United States. It is a very effective and manageable pollinator for the production of seed in alfalfa (=lucerne) and some other crops, such as onion. It is the world’s only intensively managed ground-n...

  17. Oxidation of hydrogen halides to elemental halogens with catalytic molten salt mixtures

    DOEpatents

    Rohrmann, Charles A.

    1978-01-01

    A process for oxidizing hydrogen halides by means of a catalytically active molten salt is disclosed. The subject hydrogen halide is contacted with a molten salt containing an oxygen compound of vanadium and alkali metal sulfates and pyrosulfates to produce an effluent gas stream rich in the elemental halogen. The reduced vanadium which remains after this contacting is regenerated to the active higher valence state by contacting the spent molten salt with a stream of oxygen-bearing gas.

  18. S-20 photocathode research activity. Part I

    SciTech Connect

    Gex, F.; Huen, T.; Kalibjian, R.

    1983-11-22

    The goal of this activity has been to develop and implement S-20 photocathode processing techniques at Lawrence Livermore National Laboratory (LLNL) in order to study the physical properties of the photocathode films. The present work is the initial phase of a planned activity in understanding cathode fabrication techniques and the optical/electrical characterization of these films.

  19. Metal-halide mixtures for latent heat energy storage

    NASA Technical Reports Server (NTRS)

    Chen, K.; Manvi, R.

    1981-01-01

    Some candidates for alkali metal and alkali halide mixtures suitable for thermal energy storage at temperatures 600 C are identified. A solar thermal system application which offer advantages such as precipitation of salt crystals away from heat transfer surfaces, increased thermal conductivity of phase change materials, corrosion inhibition, and a constant monotectic temperature, independent of mixture concentrations. By using the lighters, metal rich phase as a heat transfer medium and the denser, salt rich phase as a phase change material for latent heat storage, undesirable solidification on the heat transfer surface may be prevented, is presented.

  20. Bio-conventional bleaching of kadam kraft-AQ pulp by thermo-alkali-tolerant xylanases from two strains of Coprinellus disseminatus for extenuating adsorbable organic halides and improving strength with optical properties and energy conservation.

    PubMed

    Lal, Mohan; Dutt, Dharm; Tyagi, C H

    2012-04-01

    Two novel thermo-alkali-tolerant crude xylanases namely MLK-01 (enzyme-A) and MLK-07 (enzyme-B) from Coprinellus disseminatus mitigated kappa numbers of Anthocephalus cadamba kraft-AQ pulps by 32.5 and 34.38%, improved brightness by 1.5 and 1.6% and viscosity by 5.75 and 6.47% after (A)XE(1) and (B)XE(1)-stages, respectively. The release of reducing sugars and chromophores was the highest during prebleaching of A. cadamba kraft-AQ pulp at enzyme doses of 5 and 10 IU/g, reaction times 90 and 120 min, reaction temperatures 75 and 65°C and consistency 10% for MLK-01 and MLK-07, respectively. MLK-07 was more efficient than MLK01 in terms of producing pulp brightness, improving mechanical strength properties and reducing pollution load. MLK-01 and MLK-07 reduced AOX by 19.51 and 42.77%, respectively at 4% chlorine demands with an increase in COD and colour due to removal of lignin carbohydrates complexes. A. cadamba kraft-AQ pulps treated with xylanases from MLK-01 to MLK-07 and followed by CEHH bleaching at half chlorine demand (2%) showed a drastic reduction in brightness with slight improvement in mechanical strength properties compared to pulp bleached at 4% chlorine demand. MLK-01 reduced AOX, COD and colour by 43.83, 39.03 and 27.71% and MLK-07 by 38.34, 40.48 and 30.77%, respectively at half chlorine demand compared to full chlorine demand (4%). pH variation during prebleaching of A. cadamba kraft-AQ pulps with strains MLK-01 and MLK-07 followed by CEHH bleaching sequences showed a decrease in pulp brightness, AOX, COD and colour with an increase in mechanical strength properties, pulp viscosity and PFI revolutions to get a beating level of 35 ± 1 °SR at full chlorine demand. PMID:22805918

  1. Vitrification of IFR and MSBR halide salt reprocessing wastes

    SciTech Connect

    Siemer, D.D.

    2013-07-01

    Both of the genuinely sustainable (breeder) nuclear fuel cycles (IFR - Integral Fast Reactor - and MSBR - Molten Salt Breeder Reactor -) studied by the USA's national laboratories would generate high level reprocessing waste (HLRW) streams consisting of a relatively small amount ( about 4 mole %) of fission product halide (chloride or fluoride) salts in a matrix comprised primarily (about 95 mole %) of non radioactive alkali metal halide salts. Because leach resistant glasses cannot accommodate much of any of the halides, most of the treatment scenarios previously envisioned for such HLRW have assumed a monolithic waste form comprised of a synthetic analog of an insoluble crystalline halide mineral. In practice, this translates to making a 'substituted' sodalite ('Ceramic Waste Form') of the IFR's chloride salt-based wastes and fluoroapatite of the MSBR's fluoride salt-based wastes. This paper discusses my experimental studies of an alternative waste management scenario for both fuel cycles that would separate/recycle the waste's halide and immobilize everything else in iron phosphate (Fe-P) glass. It will describe both how the work was done and what its results indicate about how a treatment process for both of those wastes should be implemented (fluoride and chloride behave differently). In either case, this scenario's primary advantages include much higher waste loadings, much lower overall cost, and the generation of a product (glass) that is more consistent with current waste management practices. (author)

  2. Process for oxidation of hydrogen halides to elemental halogens

    DOEpatents

    Lyke, Stephen E.

    1992-01-01

    An improved process for generating an elemental halogen selected from chlorine, bromine or iodine, from a corresponding hydrogen halide by absorbing a molten salt mixture, which includes sulfur, alkali metals and oxygen with a sulfur to metal molar ratio between 0.9 and 1.1 and includes a dissolved oxygen compound capable of reacting with hydrogen halide to produce elemental halogen, into a porous, relatively inert substrate to produce a substrate-supported salt mixture. Thereafter, the substrate-supported salt mixture is contacted (stage 1) with a hydrogen halide while maintaining the substrate-supported salt mixture during the contacting at an elevated temperature sufficient to sustain a reaction between the oxygen compound and the hydrogen halide to produce a gaseous elemental halogen product. This is followed by purging the substrate-supported salt mixture with steam (stage 2) thereby recovering any unreacted hydrogen halide and additional elemental halogen for recycle to stage 1. The dissolved oxygen compound is regenerated in a high temperature (stage 3) and an optical intermediate temperature stage (stage 4) by contacting the substrate-supported salt mixture with a gas containing oxygen whereby the dissolved oxygen compound in the substrate-supported salt mixture is regenerated by being oxidized to a higher valence state.

  3. Photocathodes for the energy recovery linacs

    SciTech Connect

    Rao, T; Burrill, A; Chang, X Y; Smedley, J; Nishitani, T; Garcia, C Hernandez; Poelker, M; Seddon, E; Hannon, F E; Sinclair, C K; Lewellen, J; Feldman, D

    2005-03-19

    This paper presents an overview of existing and emerging technologies on electron sources that can service various Energy Recovering Linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed.

  4. PHOTOCATHODES FOR THE ENERGY RECOVERY LINACS.

    SciTech Connect

    RAO, T.; BURRILL, A.; CHANG, X.Y.; SMEDLEY, J.; ET AL.

    2005-03-19

    This paper presents an overview of existing and emerging technologies on electron sources that can service various Energy Recovering Linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed.

  5. Photocathodes for the energy recovery linacs

    NASA Astrophysics Data System (ADS)

    Rao, T.; Burrill, A.; Chang, X. Y.; Smedley, J.; Nishitani, T.; Hernandez Garcia, C.; Poelker, M.; Seddon, E.; Hannon, F. E.; Sinclair, C. K.; Lewellen, J.; Feldman, D.

    2006-02-01

    This paper presents an overview of existing and emerging technologies on electron sources that can service various energy recovering linacs under consideration. Photocathodes that can deliver average currents from 1 mA to 1 A, the pros and cons associated with these cathodes are addressed. Status of emerging technologies such as secondary emitters, cesiated dispenser cathodes, field and photon assisted field emitters and super lattice photocathodes are also reviewed.

  6. Advanced photocathode simulation and theory

    NASA Astrophysics Data System (ADS)

    Jensen, K. L.; Feldman, D. W.; O'Shea, P. G.

    2003-07-01

    A low work function dispenser type photocathode that is self-annealing or repairing would have a substantial impact on Free Electron Lasers (FELs). On such a cathode, the emitting surface is constantly renewed by replenishment of low-work-function material. A photo-dispenser cathode should operate at a relatively low temperature compared to a conventional dispenser cathode and is anticipated to be robust and long-lived. Coatings cause a reduction in the transport barrier experienced by the electrons through a complex modification of the potential at the surface, e.g., a reduction in work function due to dipole effects. In this work, we describe our theoretical program to address such effects, as part of a program concurrent with experimental efforts to develop dispenser cathodes for use in high power RF photoinjectors. In particular, we discuss the development of a generalised Transmission Coefficient approach, its application to photoemission from metals, and progress towards developing a methodology for the determination of the general emission barrier profile.

  7. RF Gun Photocathode Research at SLAC

    SciTech Connect

    Jongewaard, E.; Akre, R.; Brachmann, A.; Corbett, J.; Gilevich, S.; Grouev, K.; Hering, P.; P.Krejcik,; Lewandowski, J.; Loos, H.; Montagne, T.; Sheppard, J.C.; Stefan, P.; Vlieks, A.; Weathersby, S.; Zhou, F.; /SLAC

    2012-05-16

    LCLS is presently operating with a third copper photocathode in the original rf gun, with a quantum efficiency (QE) of {approx}1 x 10{sup -4} and projected emittance {gamma}{var_epsilon}{sub x,y} = 0.45 {micro}m at 250 pC bunch charge. The spare LCLS gun is installed in the SLAC Accelerator Structure Test Area (ASTA), fully processed to high rf power. As part of a wider photocathode R and D program, a UV laser system and additional gun diagnostics are being installed at ASTA to measure QE, QE lifetime, and electron beam emittance under a variety of operating conditions. The near-term goals are to test and verify the spare photocathode production/installation sequence, including transfer from the final holding chamber to the rf gun. Mid- and longer-term goals include development of a rigorous understanding of plasma and laser-assisted surface conditioning and investigation of new, high-QE photocathode materials. In parallel, an x-ray photoemission spectroscopy station is nearing completion, to analyze Cu photocathode surface chemistry. In this paper we review the status and anticipated operating parameters of ASTA and the spectroscopy test chamber.

  8. Skylab experiments on semiconductors and alkali halides. [single crystal growth

    NASA Technical Reports Server (NTRS)

    Lundquist, C. A.

    1974-01-01

    The space processing experiments performed during the Skylab missions included one on single crystal growth of germanium selenide and telluride, one on pure and doped germanium crystals, two on pure and doped indium antimonide, one on gallium-indium-antimony systems, and one on a sodium chloride-sodium fluoride eutectic. In each experiment, three ampoules of sample were processed in the multipurpose electric furnace within the Skylab Materials Processing Facility. All were successful in varying degrees and gave important information about crystal growth removed from the effects of earth surface gravity.

  9. Cold ablation driven by localized forces in alkali halides.

    PubMed

    Hada, Masaki; Zhang, Dongfang; Pichugin, Kostyantyn; Hirscht, Julian; Kochman, Michał A; Hayes, Stuart A; Manz, Stephanie; Gengler, Regis Y N; Wann, Derek A; Seki, Toshio; Moriena, Gustavo; Morrison, Carole A; Matsuo, Jiro; Sciaini, Germán; Miller, R J Dwayne

    2014-01-01

    Laser ablation has been widely used for a variety of applications. Since the mechanisms for ablation are strongly dependent on the photoexcitation level, so called cold material processing has relied on the use of high-peak-power laser fluences for which nonthermal processes become dominant; often reaching the universal threshold for plasma formation of ~1 J cm(-2) in most solids. Here we show single-shot time-resolved femtosecond electron diffraction, femtosecond optical reflectivity and ion detection experiments to study the evolution of the ablation process that follows femtosecond 400 nm laser excitation in crystalline sodium chloride, caesium iodide and potassium iodide. The phenomenon in this class of materials occurs well below the threshold for plasma formation and even below the melting point. The results reveal fast electronic and localized structural changes that lead to the ejection of particulates and the formation of micron-deep craters, reflecting the very nature of the strong repulsive forces at play. PMID:24835317

  10. Calculations of hyper-Raman tensor components of alkali halides

    NASA Astrophysics Data System (ADS)

    de Landa Castillo-Alvarado, Fray; Kucharczyk, Wlotek

    1998-03-01

    Calculations of hyper-Raman tensor components of NaCl,KCl and KBr crystals based on the bond polizability approach are presented. The results obtained are in good agreement whit experimental data reported previously in literature. A week cubic anisotropy of the hyper-Raman tensor is found. For LO mode our results predict the lattice deformation contribution to hyper-Raman scattering to be comparable whit the electro-optic contribution.

  11. Calculations of hyper-Raman tensor components of alkali halides

    NASA Astrophysics Data System (ADS)

    Kucharczyk, W.; Castillo Alvarado, F. L.

    1999-01-01

    Calculations of hyper-Raman scattering by the zone-centre optical phonons in NaCl, KCl and KBr crystals based on the bond polarizability approach are presented. The results obtained for the hyper-Raman tensor components are in agreement with experimental data reported previously in literature. A weak cubic anisotropy of the hyper-Raman tensor is found. For the LO mode our results predict the lattice and electro-optic contributions to hyper-Raman scattering to be of the same order of magnitude.

  12. Alkali metal nitrate purification

    DOEpatents

    Fiorucci, Louis C.; Morgan, Michael J.

    1986-02-04

    A process is disclosed for removing contaminants from impure alkali metal nitrates containing them. The process comprises heating the impure alkali metal nitrates in solution form or molten form at a temperature and for a time sufficient to effect precipitation of solid impurities and separating the solid impurities from the resulting purified alkali metal nitrates. The resulting purified alkali metal nitrates in solution form may be heated to evaporate water therefrom to produce purified molten alkali metal nitrates suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of purified alkali metal nitrates.

  13. High Biomass Specific Methyl Halide Production Rates of Selected Coastal Marsh Plants and its Relationship to Halide Content

    NASA Astrophysics Data System (ADS)

    Manley, S. L.; Wang, N.; Cicerone, R. J.

    2002-12-01

    Salt tolerant coastal marsh plants (halophytes) have previously been shown to be globally significant producers of methyl chloride (MeCl) and methyl bromide (MeBr). While halophytes are known for their high salt content, there are few reports of their halide content. Our studies have attempted to quantify biomass specific methyl halide (MeX) production from these plants and relate it to tissue halide levels. MeCl, MeBr and MeI production rates and tissue chloride, bromide and iodide concentrations from selected coastal marsh plants were measured for nearly a year. Certain halophyte species (i.e. Batis and Frankenia) have very high summer biomass specific production rates for MeX (e.g. Frankenia: 1 ug MeCl /gfwt/hr; 80 ng MeBr/gfwt/hr; 8 ng MeI/gfwt/hr). These rates of MeCl and MeBr production are much higher than those from other coastal marsh plants or seaweeds. Plant halide levels remain high throughout the year, while MeX production peaks at a high level in mid summer falling to low winter rates. This implies a linkage to plant growth. Higher levels of chloride and bromide were seen in the fleshy marsh plants such as Batis (saltwort, approximately 20 percent dry wt chloride, 0.4 percent dry wt bromide) and Salicornia (pickleweed) than in the others such as Frankenia (alkali heath) approx 7 percent dry wt chloride, 0.1 percent dry wt bromide) or Spartina (cordgrass). No such trend was seen for iodide, which ranged from 4 - 10 ppm. Calculations show the daily halide losses from MeX production are far less than the variability in tissue halide content. MeX production removes a small fraction of the total tissue halide from these plants suggesting that MeX production is not a mechanism used by these species to control internal halide levels. Saltwort cell-free extracts incubated with bromide or iodide in the presence of S-adenosyl-L-methionine (SAM) produced the corresponding MeX. MeBr production was inhibited by caffeic acid the substrate of lignin-specific O

  14. Atomic hydrogen cleaning of semiconductor photocathodes

    SciTech Connect

    Sinclair, C.K.; Poelker, B.M.; Price, J.S.

    1997-06-01

    Negative Electron Affinity (NEA) semiconductor photocathodes are widely used for the production of polarized electron beams, and are also useful for the production of high brightness electron beams which can be modulated at very high frequencies. Preparation of an atomically clean semiconductor surface is an essential step in the fabrication of a NEA photocathode. This cleaning step is difficult for certain semiconductors, such as the very thin materials which produce the highest beam polarization, and those which have tightly bound oxides and carbides. Using a small RF dissociation atomic hydrogen source, the authors have reproducibly cleaned GaAs wafers which have been only degreased prior to installation in vacuum. They have consistently prepared very high quantum efficiency photocathodes following atomic hydrogen cleaning. Details of their apparatus and most recent results are presented.

  15. SSRL photocathode RF gun test stand

    SciTech Connect

    Hernandez, M.; Baltay, M.; Boyce, A.

    1995-12-31

    A photocathode RF gun test stand designed for the production and study of high brightness electron beams will be constructed at SSRL. The beam will be generated from a laser driven third generation photocathode RF gun being developed in collaboration with BNL, LBL, and UCLA. The 3-5 [MeV] beam from the gun will be accelerated using a SLAC three meter S-band accelerator section, in order to achieve the desired low emittance beam, emittance compensation with solenoidal focusing will be employed.

  16. An electron-lens for opaque photocathodes.

    NASA Technical Reports Server (NTRS)

    Johnson, C. B.; Hallam, K. L.

    1973-01-01

    It is possible to employ opaque photocathodes in image tubes having a special electromagnetic lens without the use of special internal image-forming optical lenses or mirrors. The special electron lens, having flat object and image planes, is found to provide excellent quality electron-optical image transfer. Stray light reflection inside the tube is expected to be less serious in this electron lens than in a conventional magnetically focused image tube lens due to the offset image plane, and due to the increased absorption of photons in opaque photocathode applications.

  17. Performance of the Brookhaven photocathode rf gun

    SciTech Connect

    Batchelor, K.; Ben-Zvi, I.; Fernow, R.C.; Fischer, J.; Fisher, A.S.; Gallardo, J.; Ingold, G.; Kirk, H.G.; Leung, K.P.; Malone, R.; Pogorelsky, I.; Srinivasan-Rao, T.; Rogers, J.; Tsang, T.; Sheehan, J.; Ulc, S.; Woodle, M.; Xie, J.; Zhang, R.S.; Lin, L.Y.; McDonald, K.T.; Russell, D.P.; Hung, C.M.; Wang, X.J.

    1991-12-31

    The Brookhaven Accelerator Test Facility (ATF) uses a photocathode rf gun to provide a high-brightness electron beam intended for FEL and laser-acceleration experiments. The rf gun consists of 1{1/2} cells driven at 2856 MHz in {pi}-mode with a maximum cathode field of 100 MV/m. To achieve long lifetimes, the photocathode development concentrates on robust metals such as copper, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. The results are compared to models.

  18. Performance of the Brookhaven photocathode rf gun

    SciTech Connect

    Batchelor, K.; Ben-Zvi, I.; Fernow, R.C.; Fischer, J.; Fisher, A.S.; Gallardo, J.; Ingold, G.; Kirk, H.G.; Leung, K.P.; Malone, R.; Pogorelsky, I.; Srinivasan-Rao, T.; Rogers, J.; Tsang, T.; Sheehan, J.; Ulc, S.; Woodle, M.; Xie, J.; Zhang, R.S. ); Lin, L.Y. . Dept. of Applied Physics); McDonald, K.T.; Russell, D.P. (Pr

    1991-01-01

    The Brookhaven Accelerator Test Facility (ATF) uses a photocathode rf gun to provide a high-brightness electron beam intended for FEL and laser-acceleration experiments. The rf gun consists of 1{1/2} cells driven at 2856 MHz in {pi}-mode with a maximum cathode field of 100 MV/m. To achieve long lifetimes, the photocathode development concentrates on robust metals such as copper, yttrium and samarium. We illuminate these cathodes with a 10-ps, frequency-quadrupled Nd:YAG laser. We describe the initial operation of the gun, including measurements of transverse and longitudinal emittance, quantum efficiencies, and peak current. The results are compared to models.

  19. Milk-alkali syndrome

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/000332.htm Milk-alkali syndrome To use the sharing features on this page, please enable JavaScript. Milk-alkali syndrome is a condition in which there ...

  20. Graphene shield enhanced photocathodes and methods for making the same

    DOEpatents

    Moody, Nathan Andrew

    2014-09-02

    Disclosed are graphene shield enhanced photocathodes, such as high QE photocathodes. In certain embodiments, a monolayer graphene shield membrane ruggedizes a high quantum efficiency photoemission electron source by protecting a photosensitive film of the photocathode, extending operational lifetime and simplifying its integration in practical electron sources. In certain embodiments of the disclosed graphene shield enhanced photocathodes, the graphene serves as a transparent shield that does not inhibit photon or electron transmission but isolates the photosensitive film of the photocathode from reactive gas species, preventing contamination and yielding longer lifetime.

  1. Wire ageing with the TEA photocathode

    SciTech Connect

    Va`vra, J.

    1996-06-01

    Recently several RICH protypes successfully tested a gaseous TEA photocathode. However, its wire ageing behavior is unknown. In principle, TEA is a more strongly bonded molecule than TMAE, and, as a result, one would expect better wire ageing behavior. This paper explores this question.

  2. High polarization photocathode R D at SLAC

    SciTech Connect

    Maruyama, Takashi; Garwin, E.L. ); Prepost, R.; Zaplac, G.H. . Dept. of Physics)

    1993-01-01

    This paper describes recent progress on the development of high polarization photocathodes for polarized electron sources. A strained InGaAs cathode has achieved a maximum electron-spin polarization of 71% and has demonstrated the strain enhancement of polarization for the first time. Strained GaAs cathodes have yielded polarizations as high as 90% with much higher quantum efficiency.

  3. PREPARATION OF HALIDES OF PLUTONIUM

    DOEpatents

    Garner, C.S.; Johns, I.B.

    1958-09-01

    A dry chemical method is described for preparing plutonium halides, which consists in contacting plutonyl nitrate with dry gaseous HCl or HF at an elevated temperature. The addition to the reaction gas of a small quantity of an oxidizing gas or a reducing gas will cause formation of the tetra- or tri-halide of plutonium as desired.

  4. Halide laser glasses

    SciTech Connect

    Weber, M.J.

    1982-01-14

    Energy storage and energy extraction are of prime importance for efficient laser action and are affected by the line strengths and linewidths of optical transitions, excited-state lifetimes, nonradiative decay processes, spectroscopic inhomogeneities, nonlinear refractive index, and damage threshold. These properties are all host dependent. To illustrate this, the spectroscopic properties of Nd/sup 3 +/ have been measured in numerous oxide, oxyhalide, and halide glasses. A table summarizes the reported ranges of stimulated emission cross sections, peak wavelengths, linewidths, and radiative lifetimes associated with the /sup 4/F/sub 3/2/ ..-->.. /sup 4/I/sub 11/2/ lasing transition.

  5. A Summary of the 2010 Photocathode Physics for Photoinjectors Workshop

    SciTech Connect

    Bazarov, I; Dowell, D; Hannon, Fay; Harkay, K; Garcia, C H; Padmore, H; Rao, T; Smedley, J

    2010-10-01

    This contribution contains a summary and some highlights from the Photocathode Physics for Photoinjectors (P3) Workshop [1]. This workshop, held at Brookhaven National Laboratory in Ocotber of 2010, was aimed at bringing the photocathode community together to discuss and explore the current state of the art in accelerator photocathodes, from both a theoretical and a materials science perspective. All types of photocathode materials were discussed, including metals, NEA and PEA semiconductors, and "designer" photocathodes with bespoke properties. Topics of the workshop included: Current status of photocathodes for accelerator applications Current fabrication methods Applications of modern materials science to the growth and analysis of cathodes Photoemission spectroscopy as a diagnostic of cathode performance Utilization of modern user facilities Photoemission theory Novel ideas in cathode development Discussion forum on future collaboration for cathode growth, analysis and testing

  6. PROGRESS ON LEAD PHOTOCATHODES FOR SUPERCONDUCTING INJECTORS.

    SciTech Connect

    SMEDLEY, J.; RAO, T.; SEKUTOWICZ, J.; KNEISEL, P.; LANGNER, J.; STRZYZEWSKI, P.; LEFFERTS, R.; LIPSKI, A.

    2005-05-16

    We present the results of our investigation of bulk lead, along with various types of lead films, as suitable photocathode materials for superconducting RF injectors. The quantum efficiency of each sample is presented as a function of the photon energy of the incident light, from 3.9 eV to 6.5 eV. Quantum efficiencies of 0.5% have been obtained. Production of a niobium cavity with a lead-plated cathode is underway.

  7. Progress on lead photocathodes for superconducting injectors

    SciTech Connect

    Smedley, John; Rao, Triveni; Sekutowicz, Jacek; Kneisel, Peter; Langner, J; Strzyzewski, P; Lefferts, Richard; Lipski, Andrzej

    2005-05-16

    We present the results of our investigation of bulk lead, along with various types of lead films, as suitable photocathode materials for superconducting RF injectors. The quantum efficiency of each sample is presented as a function of the photon energy of the incident light, from 3.9 eV to 6.5 eV. Quantum efficiencies of 0.5% have been obtained. Production of a niobium cavity with a lead plated cathode is underway.

  8. Activation Layer Stabilization of High Polarization Photocathodes in Sub-Optimal RF Gun Environments

    SciTech Connect

    Gregory A. Mulhollan

    2010-11-16

    Specific activation recipes for bulk, 100 nm thick MBE grown and high polarization III-V photocathode material have been developed which mitigate the effects of exposure to background gasses. Lifetime data using four representative gasses were acquired for bulk GaAs, 100 nm unstrained GaAs and strained superlattice GaAs/GaAsP, all activated both with Cs and then Cs and Li (bi-alkali). Each photoemitter showed marked resilience improvement when activated using the bi-alkali recipe compared to the standard single alkali recipe. A dual alkali activation system at SLAC was constructed, baked and commissioned with the purpose of performing spin-polarization measurements on electrons emitted from the bi-alkali activated surfaces. An end station at SSRL was configured with the required sources for energy resolved photoemission measurements on the bi-alkali activated and CO2 dosed surfaces. The bi-alkali recipes were successfully implemented at SLAC/SSRL. Measurements at SLAC of the photoelectron spin-polarization from the modified activation surface showed no sign of a change in value compared to the standard activated material, i.e., no ill effects. Analysis of photoemission data indicates that the addition of Li to the activation layer results in a multi-layer structure. The presence of Li in the activation layer also acts as an inhibitor to CO2 absorption, hence better lifetimes in worse vacuum were achieved. The bi-alkali activation has been tested on O2 activated GaAs for comparison with NF3 activated surfaces. Comparable resilience to CO2 exposure was achieved for the O2 activated surface. An RF PECVD amorphous silicon growth system was modified to allow high temperature heat cleaning of GaAs substrates prior to film deposition. Growth versus thickness data were collected. Very thin amorphous silicon germanium layers were optimized to exhibit good behavior as an electron emitter. Growth of the amorphous silicon germanium films on the above substrates was fine tuned

  9. METHOD OF PREPARING METAL HALIDES

    DOEpatents

    Hendrickson, A.V.

    1958-11-18

    The conversion of plutonium halides from plutonium peroxide can be done by washing the peroxide with hydrogen peroxide, drying the peroxide, passing a dry gaseous hydrohalide over the surface of the peroxide at a temperature of about lOO icient laborato C until the reaction rate has stabillzed, and then ralsing the reaction temperature to between 400 and 600 icient laborato C until the conversion to plutonium halide is substantially complete.

  10. A magnetically focused image tube employing an opaque photocathode

    NASA Technical Reports Server (NTRS)

    Johnson, C. B.; Hallam, K. L.

    1973-01-01

    Image converter has been developed which uses opaque photocathode for improved efficiency. Device is easier to fabricate than previous semi-transparent photocathode converters and uses compounds from Groups 3-5 that are responsive to wave-lengths between ultraviolet (approximately 100 nm) and near infrared region (approximately 1000 nm).

  11. Photoemission Spectroscopic Study of Cesium Telluride Thin Film Photocathode

    SciTech Connect

    Sugiyama, Harue; Ogawa, Koji; Azuma, Junpei; Takahashi, Kazutoshi; Kamada, Masao

    2009-08-04

    The photoemission spectroscopy using synchrotron radiation has been carried out to study the high quantum efficiency and long working lifetime of cesium telluride (Cs{sub x}Te{sub y}) thin film photocathode. The electron affinity derived from the observed energy-distribution curves provides an important hint for long persistency of the photocathode.

  12. Actinide halide complexes

    DOEpatents

    Avens, L.R.; Zwick, B.D.; Sattelberger, A.P.; Clark, D.L.; Watkin, J.G.

    1992-11-24

    A compound is described of the formula MX[sub n]L[sub m] wherein M is a metal atom selected from the group consisting of thorium, plutonium, neptunium or americium, X is a halide atom, n is an integer selected from the group of three or four, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is an integer selected from the group of three or four for monodentate ligands or is the integer two for bidentate ligands, where the sum of n+m equals seven or eight for monodentate ligands or five or six for bidentate ligands. A compound of the formula MX[sub n] wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds are described including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant.

  13. Actinide halide complexes

    DOEpatents

    Avens, Larry R.; Zwick, Bill D.; Sattelberger, Alfred P.; Clark, David L.; Watkin, John G.

    1992-01-01

    A compound of the formula MX.sub.n L.sub.m wherein M is a metal atom selected from the group consisting of thorium, plutonium, neptunium or americium, X is a halide atom, n is an integer selected from the group of three or four, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is an integer selected from the group of three or four for monodentate ligands or is the integer two for bidentate ligands, where the sum of n+m equals seven or eight for monodentate ligands or five or six for bidentate ligands, a compound of the formula MX.sub.n wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant, are provided.

  14. Development of Polarized Photocathodes for the Linear Collider

    SciTech Connect

    Richard Prepost

    2009-12-22

    In prior years a Wisconsin-SLAC collaboration developed polarized photocathodes which were used for the SLAC SLD and fixed target programs. Currently, the R&D program goal is the development of a polarized electron source (PES) which meets the ILC requirements for polarization, charge, lifetime, and pulse structure. There are two parts to this program. One part is the continued improvement of photocathode structures with higher polarization. The second part is the design and development of the laser system used to drive the photocathode. The long pulse train for the ILC introduces new challenges for the PES. More reliable and stable operation of the PES may be achievable if appropriate R&D is carried out for higher voltage operation and for a simpler photocathode load-lock system. The collaboration with SLAC is through the Polarized Photocathode Research Collaboration (PPRC). Senior SLAC personnel include T. Maruyama, J. Clendenin, R. Kirby, and A. Brachmann.

  15. Suppression of afterpulsing in photomultipliers by gating the photocathode.

    PubMed

    Bristow, Michael P

    2002-08-20

    A number of gating schemes to minimize the long-term afterpulse signal in photomultipliers have been evaluated. Blocking the excitation pulse by gating the photocathode was found to reduce the gate-on afterpulse background by a factor of 230 over that for nongated operation. This afterpulse or signal-induced background (SIB), which is particularly troublesome in stratospheric lidar measurements, appears as a weak exponentially decaying signal extending into the millisecond region after the photomultiplier tube (PMT) is exposed to an intense submicrosecond optical pulse. Photocathode gating is not feasible in PMTs with semitransparent bialkali photocathodes because of their slow gate response time, but is easily implemented in PMTs with opaque bialkali or semitransparent multialkali (S-20) photocathodes that can be gated with nanosecond response. In those PMTs with semitransparent bialkali photocathodes, a gated (adjacent) focus grid (if available) also produces a significant reduction in the SIB. PMID:12206204

  16. Advances in DC photocathode electron guns

    SciTech Connect

    Bruce M. Dunham; P. Heartmann; Reza Kazimi; Hongxiu Liu; B. M. Poelker; J. S. Price; P. M. Rutt; W. J. Schneider; Charles K. Sinclair

    1998-07-01

    At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides a source of polarized electrons for the main accelerator. The gun is required to produce high average current with long operational lifetimes and high system throughout. Recent work has shown that careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source operation. These conditions include vacuum and the related effect of ion backbombardment, and precise control of all of the electrons emitted from the cathode. In this paper, the authors will review recent results and discuss implications for future photocathode guns.

  17. STATUS OF DIAMOND SECONDARY EMISSION ENHANCED PHOTOCATHODE

    SciTech Connect

    RAO,T.; BEN-ZVI, I.; CHANG, X.; GRIMES, J.; GROVER, R.; ISAKOVIC, A.; SMEDLEY, J.; TODD, R.; WARREN, J.; WU, Q.

    2007-05-25

    The diamond secondary emission enhanced photocathode (SEEP) provides an attractive alternative for simple photo cathodes in high average current electron injectors. It reduces the laser power required to drive the cathode, simultaneously isolating the cathode and the FW cavity from each other, thereby protecting them from contamination and increasing their life time. In this paper, we present the latest results on the secondary electron yield using pulsed thermionic and photo cathodes as primary electron sources, shaping the diamond using laser ablation and reactive ion etching as well as the theoretical underpinning of secondary electron generation and preliminary results of modeling.

  18. Solid state cell with alkali metal halo-alkali thiocyanate electrolyte

    SciTech Connect

    Rao, B. M.; Silbernagel, B. G.

    1980-02-26

    A novel electrochemical cell is disclosed utilizing: (A) an anode which contains an alkali metal as an anode-active material; (B) a cathode and (C) an electrolyte comprising an electrolytically effective amount of one or more compounds having the formula: (Ax)ma'scn wherein a is an alkali metal, X is a halogen, a' is an alkali metal and 0.1 < or = N < or = 10. Preferred systems include lithium-containing anodes, lithium-containing electrolytes and cathodes which contain cathode-active material selected from the group consisting of cathode-active sulfurs, halogens, halides, chromates, phosphates, oxides and chalcogenides, especially those chalcogenides of the empirical formula mzm wherein M is one or more metals selected from the group consisting of iron, titanium, zirconium, hafnium, niobium, tantalum and vanadium, Z is one or more chalcogens selected from the group consisting of oxygen, sulfur, selenium and tellurium, and M is a numerical value between about 1.8 and about 3.2.

  19. Radiochemical synthesis of pure anhydrous metal halides

    NASA Technical Reports Server (NTRS)

    Philipp, W. H.; Marsik, S. J.; May, C. E.

    1973-01-01

    Method uses radiation chemistry as practical tool for inorganic preparations and in particular deposition of metals by irradiation of their aqueous metal salt solutions with high energy electrons. Higher valence metal halide is dissolved in organic liquid and exposed to high energy electrons. This causes metal halide to be reduced to a lower valence metal halide.

  20. Preparation of cerium halide solvate complexes

    DOEpatents

    Vasudevan, Kalyan V; Smith, Nickolaus A; Gordon, John C; McKigney, Edward A; Muenchaussen, Ross E

    2013-08-06

    Crystals of a solvated cerium(III) halide solvate complex resulted from a process of forming a paste of a cerium(III) halide in an ionic liquid, adding a solvent to the paste, removing any undissolved solid, and then cooling the liquid phase. Diffusing a solvent vapor into the liquid phase also resulted in crystals of a solvated cerium(III) halide complex.

  1. Modern theory and applications of photocathodes

    SciTech Connect

    Spicer, W.E.; Herrera-Gomez, A.

    1993-08-01

    Over the last thirty years, the Spicer Three-Step model has provided a very useful description of the process of photoemission for both fundamental and practical applications. By treating photoemission in terms of three successive steps-optical absorption, electron transport, and escape across the surface this theory allows photoemission to be related to parameters of the emitter, such as the optical absorption coefficient, electron scattering mechanisms, and the height of the potential barrier at the surface. Using simple equations and established parameters, the Three-Step model predicts the performance of cathodes and provides detailed understanding of the unexpected phenomena that appear when photocathodes are pushed into new practical domains. As an example, time responses are estimated for existing cathodes, and are found to cover a range of six orders of magnitude. Further, the time response is found to be directly related to the sensitivity (i.e., quantum efficiency) of the cathode. The quantum yield systematically decreases with the time response. Thus, metals are predicted to have the shortest time response (as little as 10{sup {minus}15} sec) and the smallest quantum efficiency (as little as 10{sup {minus}4} electrons per photon), whereas the negative affinity photocathodes have high yield (as high as 0.6 electrons per photon) but long response times (as long as 10{sup {minus}9} sec). Other applications of the Three-Step model are discussed.

  2. Performance of photocathode rf gun electron accelerators

    SciTech Connect

    Ben-Zvi, I.

    1993-07-01

    In Photo-Injectors (PI) electron guns, electrons are emitted from a photocathode by a short laser pulse and then accelerated by intense rf fields in a resonant cavity. The best known advantage of this technique is the high peak current with a good emittance (high brightness). This is important for short wavelength Free-Electron Lasers and linear colliders. PIs are in operation in many electron accelerator facilities and a large number of new guns are under construction. Some applications have emerged, providing, for example, very high pulse charges. PIs have been operated over a wide range of frequencies, from 144 to 3000 MHz (a 17 GHz gun is being developed). An exciting new possibility is the development of superconducting PIs. A significant body of experimental and theoretical work exists by now, indicating the criticality of the accelerator elements that follow the gun for the preservation of the PI`s performance as well as possible avenues of improvements in brightness. Considerable research is being done on the laser and photocathode material of the PI, and improvement is expected in this area.

  3. Performance of photocathode rf gun electron accelerators

    SciTech Connect

    Ben-Zvi, I.

    1993-01-01

    In Photo-Injectors (PI) electron guns, electrons are emitted from a photocathode by a short laser pulse and then accelerated by intense rf fields in a resonant cavity. The best known advantage of this technique is the high peak current with a good emittance (high brightness). This is important for short wavelength Free-Electron Lasers and linear colliders. PIs are in operation in many electron accelerator facilities and a large number of new guns are under construction. Some applications have emerged, providing, for example, very high pulse charges. PIs have been operated over a wide range of frequencies, from 144 to 3000 MHz (a 17 GHz gun is being developed). An exciting new possibility is the development of superconducting PIs. A significant body of experimental and theoretical work exists by now, indicating the criticality of the accelerator elements that follow the gun for the preservation of the PI's performance as well as possible avenues of improvements in brightness. Considerable research is being done on the laser and photocathode material of the PI, and improvement is expected in this area.

  4. Alkali metal ionization detector

    DOEpatents

    Bauerle, James E.; Reed, William H.; Berkey, Edgar

    1978-01-01

    Variations in the conventional filament and collector electrodes of an alkali metal ionization detector, including the substitution of helical electrode configurations for either the conventional wire filament or flat plate collector; or, the substitution of a plurality of discrete filament electrodes providing an in situ capability for transferring from an operationally defective filament electrode to a previously unused filament electrode without removing the alkali metal ionization detector from the monitored environment. In particular, the helical collector arrangement which is coaxially disposed about the filament electrode, i.e. the thermal ionizer, provides an improved collection of positive ions developed by the filament electrode. The helical filament design, on the other hand, provides the advantage of an increased surface area for ionization of alkali metal-bearing species in a monitored gas environment as well as providing a relatively strong electric field for collecting the ions at the collector electrode about which the helical filament electrode is coaxially positioned. Alternatively, both the filament and collector electrodes can be helical. Furthermore, the operation of the conventional alkali metal ionization detector as a leak detector can be simplified as to cost and complexity, by operating the detector at a reduced collector potential while maintaining the sensitivity of the alkali metal ionization detector adequate for the relatively low concentration of alkali vapor and aerosol typically encountered in leak detection applications.

  5. Observation of a charge limit for photocathode electron guns

    SciTech Connect

    Woods, M.; Clendenin, J.; Frisch, J.; Kulikov, A.; Saez, P.; Schultz, D.; Turner, J.; Witte, K.; Zolotorev, M.

    1992-12-01

    The Photocathode Electron Gun (PEG) at SLAC is required to produce bunch intensities of up to 10{sup 11} electrons within 2 ns (8 Amps). Operation of PEG has demonstrated a `Charge Limit` phenomenon, whereby the charge that can be extracted from the gun with an intense laser beam saturates at significantly less than 10{sup 11} electrons (the expected `Space Charge Limited` charge) when the photocathode Quantum Efficiency is low. We report studies of this Charge Limit phenomenon observed with a GaAs photocathode.

  6. Observation of a charge limit for photocathode electron guns

    SciTech Connect

    Woods, M.; Clendenin, J.; Frisch, J.; Kulikov, A.; Saez, P.; Schultz, D.; Turner, J.; Witte, K.; Zolotorev, M.

    1992-12-01

    The Photocathode Electron Gun (PEG) at SLAC is required to produce bunch intensities of up to 10[sup 11] electrons within 2 ns (8 Amps). Operation of PEG has demonstrated a 'Charge Limit' phenomenon, whereby the charge that can be extracted from the gun with an intense laser beam saturates at significantly less than 10[sup 11] electrons (the expected Space Charge Limited' charge) when the photocathode Quantum Efficiency is low. We report studies of this Charge Limit phenomenon observed with a GaAs photocathode.

  7. Atomic forces between noble gas atoms, alkali ions, and halogen ions for surface interactions

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Outlaw, R. A.; Heinbockel, J. H.

    1988-01-01

    The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base developed from analysis of the two-body potential data, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas surfaces and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

  8. Parallel Simulation of Underdense Plasma Photocathode Experiments

    NASA Astrophysics Data System (ADS)

    Bruhwiler, David; Hidding, Bernhard; Xi, Yunfeng; Andonian, Gerard; Rosenzweig, James; Cormier-Michel, Estelle

    2013-10-01

    The underdense plasma photocathode concept (aka Trojan horse) is a promising approach to achieving fs-scale electron bunches with pC-scale charge and transverse normalized emittance below 0.01 mm-mrad, yielding peak currents of order 100 A and beam brightness as high as 1019 A /m2 / rad2 , for a wide range of achievable beam energies up to 10 GeV. A proof-of-principle experiment will be conducted at the FACET user facility in early 2014. We present 2D and 3D simulations with physical parameters relevant to the planned experiment. Work supported by DOE under Contract Nos. DE-SC0009533, DE-FG02-07ER46272 and DEFG03-92ER40693, and by ONR under Contract No. N00014-06-1-0925. NERSC computing resources are supported by DOE.

  9. Jefferson Lab IR demo FEL photocathode quantum efficiency scanner

    NASA Astrophysics Data System (ADS)

    Gubeli, J.; Evans, R.; Grippo, A.; Jordan, K.; Shinn, M.; Siggins, T.

    2001-12-01

    Jefferson Laboratory's Free Electron Laser (FEL) incorporates a cesiated gallium arsenide (GaAs) DC photocathode gun as its electron source. By using a set of scanning mirrors, the surface of the GaAs wafer is illuminated with a 543.5nm helium-neon laser. Measuring the current flow across the biased photocathode generates a quantum efficiency (QE) map of the 1-in. diameter wafer surface. The resulting QE map provides a very detailed picture of the efficiency of the wafer surface. By generating a QE map in a matter of minutes, the photocathode scanner has proven to be an exceptional tool in quickly determining sensitivity and availability of the photocathode for operation.

  10. Apparatus enables accurate determination of alkali oxides in alkali metals

    NASA Technical Reports Server (NTRS)

    Dupraw, W. A.; Gahn, R. F.; Graab, J. W.; Maple, W. E.; Rosenblum, L.

    1966-01-01

    Evacuated apparatus determines the alkali oxide content of an alkali metal by separating the metal from the oxide by amalgamation with mercury. The apparatus prevents oxygen and moisture from inadvertently entering the system during the sampling and analytical procedure.

  11. High gradient rf gun studies of CsBr photocathodes

    SciTech Connect

    Vecchione, Theodore; Maldonado, Juan R.; Gierman, Stephen; Corbett, Jeff; Hartmann, Nick; Pianetta, Piero A.; Hesselink, Lambertus; Schmerge, John F.

    2015-04-03

    CsBr photocathodes have 10 times higher quantum efficiency with only 3 times larger intrinsic transverse emittance than copper. They are robust and can withstand 80 MV/m fields without breaking down or emitting dark current. They can operate in 2×10⁻⁹ torr vacuum and survive exposure to air. They are well suited for generating high pulse charge in rf guns without a photocathode transfer system.

  12. Advanced 3D Photocathode Modeling and Simulations Final Report

    SciTech Connect

    Dimitre A Dimitrov; David L Bruhwiler

    2005-06-06

    High brightness electron beams required by the proposed Next Linear Collider demand strong advances in photocathode electron gun performance. Significant improvement in the production of such beams with rf photocathode electron guns is hampered by the lack high-fidelity simulations. The critical missing piece in existing gun codes is a physics-based, detailed treatment of the very complex and highly nonlinear photoemission process.

  13. High gradient rf gun studies of CsBr photocathodes

    NASA Astrophysics Data System (ADS)

    Vecchione, Theodore; Maldonado, Juan R.; Gierman, Stephen; Corbett, Jeff; Hartmann, Nick; Pianetta, Piero A.; Hesselink, Lambertus; Schmerge, John F.

    2015-04-01

    CsBr photocathodes have 10 times higher quantum efficiency with only 3 times larger intrinsic transverse emittance than copper. They are robust and can withstand 80 MV /m fields without breaking down or emitting dark current. They can operate in 2 ×10-9 torr vacuum and survive exposure to air. They are well suited for generating high pulse charge in rf guns without a photocathode transfer system.

  14. Development of Halide and Oxy-Halides for Isotopic Separations

    SciTech Connect

    Leigh R. Martin; Aaron T. Johnson; Jana Pfeiffer; Martha R. Finck

    2014-10-01

    The goal of this project was to synthesize a volatile form of Np for introduction into mass spectrometers at INL. Volatile solids of the 5f elements are typically those of the halides (e.g. UF6), however fluorine is highly corrosive to the sensitive internal components of the mass separator, and the other volatile halides exist as several different stable isotopes in nature. However, iodide is both mono-isotopic and volatile, and as such presents an avenue for creation of a form of Np suitable for introduction into the mass separator. To accomplish this goal, the technical work in the project sought to establish a novel synthetic route for the conversion NpO2+ (dissolved in nitric acid) to NpI3 and NpI4.

  15. R&D ERL: Photocathode Deposition and Transport System

    SciTech Connect

    Pate, D.; Ben-Zvi, I.; Rao, T.; Burrill, R.; Todd, R.; Smedley, J.; Holmes, D.

    2010-01-01

    The purpose of the photocathode deposition and transport system is to (1) produce a robust, high yield multialkali photocathode and (2) have a method of transporting the multialkali photocathode for insertion into a super conducting RF electron gun. This process is only successful if a sufficient quantum efficiency lifetime of the cathode, which is inserted in the SRF electron gun, is maintained. One important element in producing a multialkali photocathode is the strict vacuum requirements of 10{sup -11} torr to assure success in the production of longlived photocathodes that will not have their QE or lifetime depleted due to residual gas poisoning in a poor vacuum. A cutaway view of our third generation deposition system is shown in figure 1. There are certain design criteria and principles required. One must be able to install, remove, rejuvenate and replace a cathode without exposing the source or cathode to atmosphere. The system must allow one to deposit Cs, K, and Sb on a cathode tip surface at pressures in the 10{sup -10} to 10{sup -9} torr range. The cathode needs to be heated to as high as 850 C for cleaning and maintained at 130 C to 150 C during deposition. There should also be the capability for in-situ QE measurements. In addition the preparation of dispenser photocathodes must be accounted for, thus requiring an ion source for cathode cleaning. Finally the transport cart must be mobile and be able to negotiate the ERL facility labyrinth.

  16. Alkalis and Skin.

    PubMed

    Greenwood, John E; Tan, Jin Lin; Ming, Justin Choong Tzen; Abell, Andrew D

    2016-01-01

    The aim of this editorial is to provide an overview of the chemical interactions occurring in the skin of our patients on contact with alkaline agents. Strongly basic alkali is highly aggressive and will readily hydrolyze (or cleave) key biological molecules such as lipids and proteins. This phenomenon is known as saponification in the case of lipids and liquefactive denaturation for peptides and proteins. A short section on current first-aid concepts is included. A better understanding of the basic science behind alkali burns will make us better teachers and provide an insight into the urgency needed in treating these common and dangerous chemical injuries. PMID:26182072

  17. Alkali metal ion battery with bimetallic electrode

    SciTech Connect

    Boysen, Dane A; Bradwell, David J; Jiang, Kai; Kim, Hojong; Ortiz, Luis A; Sadoway, Donald R; Tomaszowska, Alina A; Wei, Weifeng; Wang, Kangli

    2015-04-07

    Electrochemical cells having molten electrodes having an alkali metal provide receipt and delivery of power by transporting atoms of the alkali metal between electrode environments of disparate chemical potentials through an electrochemical pathway comprising a salt of the alkali metal. The chemical potential of the alkali metal is decreased when combined with one or more non-alkali metals, thus producing a voltage between an electrode comprising the molten the alkali metal and the electrode comprising the combined alkali/non-alkali metals.

  18. Methods of recovering alkali metals

    DOEpatents

    Krumhansl, James L; Rigali, Mark J

    2014-03-04

    Approaches for alkali metal extraction, sequestration and recovery are described. For example, a method of recovering alkali metals includes providing a CST or CST-like (e.g., small pore zeolite) material. The alkali metal species is scavenged from the liquid mixture by the CST or CST-like material. The alkali metal species is extracted from the CST or CST-like material.

  19. 40 CFR 721.4095 - Quaternary ammonium alkyltherpropyl trialkylamine halides.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... trialkylamine halides. 721.4095 Section 721.4095 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.4095 Quaternary ammonium alkyltherpropyl trialkylamine halides. (a... generically as quaternary ammonium alkyltherpropyl trialkylamine halides (PMNs...

  20. TRANSURANIC METAL HALIDES AND A PROCESS FOR THE PRODUCTION THEREOF

    DOEpatents

    Fried, S.

    1951-03-20

    Halides of transuranic elements are prepared by contacting with aluminum and a halogen, or with an aluminum halide, a transuranic metal oxide, oxyhalide, halide, or mixture thereof at an elevated temperature.

  1. Chlor-Alkali Technology.

    ERIC Educational Resources Information Center

    Venkatesh, S.; Tilak, B. V.

    1983-01-01

    Chlor-alkali technology is one of the largest electrochemical industries in the world, the main products being chlorine and caustic soda (sodium hydroxide) generated simultaneously by the electrolysis of sodium chloride. This technology is reviewed in terms of electrochemical principles and manufacturing processes involved. (Author/JN)

  2. Fabrication and measurement of regenerable low work function dispenser photocathodes

    NASA Astrophysics Data System (ADS)

    Moody, Nathan A.

    Laser-switched photoemitters are a source of electrons for high current applications such as free electron lasers. Laser-modulated photoemission permits rapid switching of the electron beam, far surpassing what can be achieved using electric-field gated emission. Photoinjector systems consist of a drive laser producing short bunches of photons and an efficient photocathode, which converts photon bunches into electron beam pulses. Development of both technologies is required, but the scope of this project is restricted to improvement of the photocathode. Most high-efficiency photocathodes employ cesium-based surface coatings to reduce work function and enable efficient electron emission in the visible range. Lifetime is severely limited by the loss of this delicate coating, which degrades rapidly in practical vacuum environments. More robust photocathodes exist, but have much lower efficiency, and place unrealistic demands on drive laser power and stability. This research proposes a novel dispenser concept that dramatically extends the lifetime of high efficiency cesium-based cathodes by continuously or periodically restoring the cesium surface monolayer during an in situ rejuvenation process. Sintered tungsten provides an interface between a cesium reservoir and the photoemitting surface. During temperature-controlled rejuvenation, cesium diffuses through and across the sintered tungsten to create and sustain a low-work function photocathode. The prototype dispenser cathode was fabricated and tested for two modes of operation: continuous and periodic near-room temperature rejuvenation. The data are compared with a photoemission model of partially covered surfaces under design for integration with existing beam simulations. Overall performance suggests that this cesium-delivery mechanism can significantly enhance the efficiency and operational lifetime of a wide variety of present and future cesium-based photocathodes. Also reported are surface characterization, ion

  3. Hydrothermal alkali metal recovery process

    DOEpatents

    Wolfs, Denise Y.; Clavenna, Le Roy R.; Eakman, James M.; Kalina, Theodore

    1980-01-01

    In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by treating them with a calcium or magnesium-containing compound in the presence of water at a temperature between about 250.degree. F. and about 700.degree. F. and in the presence of an added base to establish a pH during the treatment step that is higher than would otherwise be possible without the addition of the base. During the treating process the relatively high pH facilitates the conversion of water-insoluble alkali metal compounds in the alkali metal residues into water-soluble alkali metal constituents. The resultant aqueous solution containing water-soluble alkali metal constituents is then separated from the residue solids, which consist of the treated particles and any insoluble materials formed during the treatment step, and recycled to the gasification process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preferably, the base that is added during the treatment step is an alkali metal hydroxide obtained by water washing the residue solids produced during the treatment step.

  4. Progress on diamond amplified photo-cathode

    SciTech Connect

    Wang, E.; Ben-Zvi, I.; Burrill, A.; Kewisch, J.; Chang, X.; Rao, T.; Smedley, J.; Wu, Q.; Muller, E.; Xin, T.

    2011-03-28

    Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length. The diamond-amplified photocathode, that promises to support a high average current, low emittance, and a highly stable electron beam with a long lifetime, is under development for an electron source. The diamond, functioning as a secondary emitter amplifies the primary current, with a few KeV energy, that comes from the traditional cathode. Earlier, our group recorded a maximum gain of 40 in the secondary electron emission from a diamond amplifier. In this article, we detail our optimization of the hydrogenation process for a diamond amplifier that resulted in a stable emission gain of 140. We proved that these characteristics are reproducible. We now are designing a system to test the diamond amplifier cathode using an 112MHz SRF gun to measure the limits of the emission current's density, and on the bunch charge and bunch length.

  5. Polarization Possibilities of Small Spin-Orbit Interaction in Strained-Superlattice Photocathodes

    SciTech Connect

    Maruyama, T.; Brachmann, A.; Clendenin, J.E.; Garwin, E.L.; Ioakeimidi, K.; Kirby, R.E.; Prepost, R.; Moy, A.M.; /SVT Assoc., Eden Prairie

    2006-12-12

    Strained-superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important.

  6. Photocathode Optimization for a Dynamic Transmission Electron Microscope: Final Report

    SciTech Connect

    Ellis, P; Flom, Z; Heinselman, K; Nguyen, T; Tung, S; Haskell, R; Reed, B W; LaGrange, T

    2011-08-04

    The Dynamic Transmission Electron Microscope (DTEM) team at Harvey Mudd College has been sponsored by LLNL to design and build a test setup for optimizing the performance of the DTEM's electron source. Unlike a traditional TEM, the DTEM achieves much faster exposure times by using photoemission from a photocathode to produce electrons for imaging. The DTEM team's work is motivated by the need to improve the coherence and current density of the electron cloud produced by the electron gun in order to increase the image resolution and contrast achievable by DTEM. The photoemission test setup is nearly complete and the team will soon complete baseline tests of electron gun performance. The photoemission laser and high voltage power supply have been repaired; the optics path for relaying the laser to the photocathode has been finalized, assembled, and aligned; the internal setup of the vacuum chamber has been finalized and mostly implemented; and system control, synchronization, and data acquisition has been implemented in LabVIEW. Immediate future work includes determining a consistent alignment procedure to place the laser waist on the photocathode, and taking baseline performance measurements of the tantalum photocathode. Future research will examine the performance of the electron gun as a function of the photoemission laser profile, the photocathode material, and the geometry and voltages of the accelerating and focusing components in the electron gun. This report presents the team's progress and outlines the work that remains.

  7. Simple model potential and model wave functions for (H-alkali)+ and (alkali-alkali)+ ions

    NASA Astrophysics Data System (ADS)

    Patil, S. H.; Tang, K. T.

    2000-07-01

    A simple model potential is proposed to describe the interaction of a valence electron with the alkali core, which incorporates the correct asymptotic behavior in terms of dipolar polarizabilities, and the short-range exchange effects in terms of a hard core adjusted to give the correct energy for the valence electron. Based on this potential, simple wave functions are developed to describe the (H-alkali)+ and (alkali-alkali)+ ions. These wave functions exhibit some important structures of the ions, and provide a universal description of the properties of all (H-alkali)+ and (alkali-alkali)+ ions, in particular, the equilibrium separations of the nuclei and the corresponding dissociation energies. They also allow us to calculate the dipolar polarizabilities of Li2+, Na2+, K2+, Rb2+, and Cs2+.

  8. Multiple-Wavelength Metal/Halide Laser

    NASA Technical Reports Server (NTRS)

    Nerheim, N. M.

    1984-01-01

    Single device produces multiple lasing lines. Laser capable of producing many lasing lines has several reservoirs of halide lasant mixed with chlorides of copper, manganese and iron. Convection-control technique possible to rapidly change from one metal halide to another at maximum energy.

  9. Alkali-vapor lasers

    NASA Astrophysics Data System (ADS)

    Zweiback, J.; Komashko, A.; Krupke, W. F.

    2010-02-01

    We report on the results from several of our alkali laser systems. We show highly efficient performance from an alexandrite-pumped rubidium laser. Using a laser diode stack as a pump source, we demonstrate up to 145 W of average power from a CW system. We present a design for a transversely pumped demonstration system that will show all of the required laser physics for a high power system.

  10. The effects of dissolved halide anions on hydrogen bonding in liquid water.

    PubMed

    Smith, Jared D; Saykally, Richard J; Geissler, Phillip L

    2007-11-14

    It is widely believed that the addition of salts to water engenders structural changes in the hydrogen-bond network well beyond the adjacent shell of solvating molecules. Classification of many ions as "structure makers" and "structure breakers" has been based in part on corresponding changes in the vibrational spectra (Raman and IR). Here we show that changes in O-H vibrational spectra induced by the alkali halides in liquid water result instead from the actions of ions' electric fields on adjacent water molecules. Computer simulations that accurately reproduce our experimental measurements suggest that the statistics of hydrogen-bond strengths are only weakly modified beyond this first solvation shell. PMID:17958418

  11. Study of photoemission mechanism for varied doping GaN photocathode

    NASA Astrophysics Data System (ADS)

    Qiao, Jianliang; Xu, Yuan; Niu, Jun; Gao, Youtang; Chang, Benkang

    2015-10-01

    Negative electron affinity (NEA) GaN photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive threshold and so on. The quantum efficiency is an important parameter for the preparation and evaluation of NEA GaN photocathode. The varied doping GaN photocathode has the directional inside electric field within the material, so the higher quantum efficiency can be obtained. The varied doping NEA GaN photocathode has better photoemission performance. According to the photoemission theory of NEA GaN photocathode, the quantum efficiency formulas for uniform doping and varied doping NEA GaN photocathodes were given. In the certain condition, the quantum efficiency formula for varied doping GaN photocathode consists with the uniform doping. The activation experiment was finished for varied doping GaN photocathode. The cleaning method and technics for varied doping GaN photocathode were given in detail. To get an atom clean surface, the heat cleaning must be done after the chemical cleaning. Using the activation and evaluation system for NEA photocathode, the varied doping GaN photocathode was activated with Cs and O, and the photocurrent curve for varied doping GaN photocathode was gotten.

  12. Characterization of diamond film and bare metal photocathodes as a function of temperature and surface preparation

    SciTech Connect

    Shurter, R.P.; Moir, D.C.; Devlin, D.J.

    1996-07-01

    High current photocathodes using bare metal and polycrystalline diamond films illuminated by ultraviolet lasers are being developed at Los Alamos for use in a new generation of linear induction accelerators. These photocathodes must be able to produce multiple 60 ns pulses separated by several to tens of nanoseconds. The vacuum environment in which the photocathodes must operate is 10{sup -5} torr.

  13. Hygroscopicity Evaluation of Halide Scintillators

    SciTech Connect

    Zhuravleva, M; Stand, L; Wei, H; Hobbs, C. L.; Boatner, Lynn A; Ramey, Joanne Oxendine; Burger, Arnold; Rowe, E; Bhattacharya, P.; Tupitsyn, E; Melcher, Charles L

    2014-01-01

    A collaborative study of relative hygroscopicity of anhydrous halide scintillators grown at various laboratories is presented. We have developed a technique to evaluate moisture sensitivity of both raw materials and grown crystals, in which the moisture absorption rate is measured using a gravimetric analysis. Degradation of the scintillation performance was investigated by recording gamma-ray spectra and monitoring the photopeak position, count rate and energy resolution. The accompanying physical degradation of the samples exposed to ambient atmosphere was photographically recorded as well. The results were compared with ben

  14. Photoemission characteristics of thin GaAs-based heterojunction photocathodes

    SciTech Connect

    Feng, Cheng; Zhang, Yijun Qian, Yunsheng; Shi, Feng; Zou, Jijun; Zeng, Yugang

    2015-01-14

    To better understand the different photoemission mechanism of thin heterojunction photocathodes, the quantum efficiency models of reflection-mode and transmission-mode GaAs-based heterojunction photocathodes are revised based on one-dimensional continuity equations, wherein photoelectrons generated from both the emission layer and buffer layer are taken into account. By comparison of simulated results between the revised and conventional models, it is found that the electron contribution from the buffer layer to shortwave quantum efficiency is closely related to some factors, such as the thicknesses of emission layer and buffer layer and the interface recombination velocity. Besides, the experimental quantum efficiency data of reflection-mode and transmission-mode AlGaAs/GaAs photocathodes are well fitted to the revised models, which confirm the applicability of the revised quantum efficiency models.

  15. Intrinsic Emittance Reduction of an Electron Beam from Metal Photocathodes

    SciTech Connect

    Hauri, C. P.; Ganter, R.; Le Pimpec, F.; Trisorio, A.; Ruchert, C.; Braun, H. H.

    2010-06-11

    Electron beams in modern linear accelerators are now becoming limited in brightness by the intrinsic emittance of the photocathode electron source. Therefore it becomes important for large scale facilities such as free electron lasers to reduce this fundamental limit. In this Letter we present measurements of the intrinsic emittance for different laser wavelength (from 261 to 282 nm) and for different photocathode materials such as Mo, Nb, Al, Cu. Values as low as 0.41{+-}0.03 mm{center_dot}mrad/mm laser spot size (rms) were measured for a copper photocathode illuminated with a 282 nm laser wavelength. The key element for emittance reduction is a uv laser system which allows adjustment of the laser photon energy to match the effective work function of the cathode material and to emit photoelectrons with a lower initial kinetic energy. The quantum efficiency over the explored wavelength range varies by less than a factor of 3.

  16. Polarized Photocathode R&D for Future Linear Collliders

    SciTech Connect

    Zhou, F; Brachmann, A.; Maruyama, T.; Sheppard, J.C.; /SLAC

    2009-01-23

    It is a challenge to generate full charge electrons from the electron sources without compromising polarization for the proposed ILC and CLIC. It is essential to advance polarized photocathodes to meet the requirements. SLAC has worldwide unique dedicated test facilities, Cathode Test System and dc-Gun Test Laboratory, to fully characterize polarized photocathodes. Recent systematic measurements on a strained-well InAlGaAs/AlGaAs cathode at the facilities show that 87% polarization and 0.3% QE are achieved. The QE can be increased to {approx}1.0% with atomic hydrogen cleaning. The surface charge limit at a very low current intensity and the clear dependence of the polarization on the surface charge limit are observed for the first time. On-going programs to develop photocathodes for the ILC and CLIC are briefly introduced.

  17. FEMTO SECOND ELECTRON BEAM DIFFRACTION USING A PHOTOCATHODE RF GUN.

    SciTech Connect

    WANG,X.J.WU,Z.IHEE,H.

    2003-05-12

    One of the 21st century scientific frontiers is to explore the molecule structure transition on the femtosecond time scale. X-ray free electron laser (XFEL) is one of the tools now under development for investigating femto-second structure transition. We are proposing an alternative technique--femto-second electron diffraction based on a photocathode RF gun. We will present a design of a kHz femto-seconds electron diffraction system based on a photocathode RF gun. Our simulation shows that, the photocathode RF gun can produce 100 fs (FWHM) electron bunch with millions electrons at about 2 MeV. This is at least one order of magnitude reduction in bunch length, and two orders of magnitude increase in number of electrons comparing to present time-resolved electron diffraction system. We will also discuss various issues and limitations related to MeV electron diffraction.

  18. 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.

  19. High quantum efficiency S-20 photocathodes in photon counting detectors

    NASA Astrophysics Data System (ADS)

    Orlov, D. A.; DeFazio, J.; Duarte Pinto, S.; Glazenborg, R.; Kernen, E.

    2016-04-01

    Based on conventional S-20 processes, a new series of high quantum efficiency (QE) photocathodes has been developed that can be specifically tuned for use in the ultraviolet, blue or green regions of the spectrum. The QE values exceed 30% at maximum response, and the dark count rate is found to be as low as 30 Hz/cm2 at room temperature. This combination of properties along with a fast temporal response makes these photocathodes ideal for application in photon counting detectors, which is demonstrated with an MCP photomultiplier tube for single and multi-photoelectron detection.

  20. Analysis of Slice Transverse Emittance Evolution ina Photocathode RF Gun

    SciTech Connect

    Huang, Z.; Ding, Y.; Qiang, J.; /LBL, Berkeley

    2007-10-17

    The slice transverse emittance of an electron beam is of critical significance for an x-ray FEL. In a photocathode RF gun, the slice transverse emittance is not only determined by the emission process, but also influenced strongly by the non-linear space charge effect. In this paper, we study the slice transverse emittance evolution in a photocathode RF gun using a simple model that includes effects of RF acceleration, focusing, and space charge force. The results are compared with IMPACT-T space charge simulations and may be used to understand the development of the slice emittance in an RF gun.

  1. Emission properties of body-centered cubic elemental metal photocathodes

    SciTech Connect

    Li, Tuo; Rickman, Benjamin L. Schroeder, W. Andreas

    2015-04-07

    A first principles analysis of photoemission is developed to explain the lower than expected rms transverse electron momentum measured using the solenoid scan technique for the body-centered cubic Group Vb (V, Nb, and Ta) and Group VIb (Cr, Mo, and W) metallic photocathodes. The density functional theory based analysis elucidates the fundamental role that the electronic band structure (and its dispersion) plays in determining the emission properties of solid-state photocathodes and includes evaluation of work function anisotropy using a thin-slab method.

  2. Shallow halogen vacancies in halide optoelectronic materials

    DOE PAGESBeta

    Shi, Hongliang; Du, Mao -Hua

    2014-11-05

    Halogen vacancies (VH) are usually deep color centers (F centers) in halides and can act as major electron traps or recombination centers. The deep VH contributes to the typically poor carrier transport properties in halides. However, several halides have recently emerged as excellent optoelectronic materials, e.g., CH3NH3PbI3 and TlBr. Both CH3NH3PbI3 and TlBr have been found to have shallow VH, in contrast to commonly seen deep VH in halides. In this paper, several halide optoelectronic materials, i.e., CH3NH3PbI3, CH3NH3SnI3 (photovoltaic materials), TlBr, and CsPbBr3, (gamma-ray detection materials) are studied to understand the material chemistry and structure that determine whether VHmore » is a shallow or deep defect in a halide material. It is found that crystal structure and chemistry of ns2 ions both play important roles in creating shallow VH in halides such as CH3NH3PbI3, CH3NH3SnI3, and TlBr. The key to identifying halides with shallow VH is to find the right crystal structures and compounds that suppress cation orbital hybridization at VH, such as those with long cation-cation distances and low anion coordination numbers, and those with crystal symmetry that prevents strong hybridization of cation dangling bond orbitals at VH. Furthermore, the results of this paper provide insight and guidance to identifying halides with shallow VH as good electronic and optoelectronic materials.« less

  3. Shallow halogen vacancies in halide optoelectronic materials

    NASA Astrophysics Data System (ADS)

    Shi, Hongliang; Du, Mao-Hua

    2014-11-01

    Halogen vacancies (VH ) are usually deep color centers (F centers) in halides and can act as major electron traps or recombination centers. The deep VH contributes to the typically poor carrier transport properties in halides. However, several halides have recently emerged as excellent optoelectronic materials, e.g., C H3N H3Pb I3 and TlBr. Both C H3N H3Pb I3 and TlBr have been found to have shallow VH , in contrast to commonly seen deep VH in halides. In this paper, several halide optoelectronic materials, i.e., C H3N H3Pb I3 , C H3N H3Sn I3 (photovoltaic materials), TlBr, and CsPbB r3 (gamma-ray detection materials) are studied to understand the material chemistry and structure that determine whether VH is a shallow or deep defect in a halide material. It is found that crystal structure and chemistry of n s2 ions both play important roles in creating shallow VH in halides such as C H3N H3Pb I3 , C H3N H3Sn I3 , and TlBr. The key to identifying halides with shallow VH is to find the right crystal structures and compounds that suppress cation orbital hybridization at VH , such as those with large cation-cation distances and low anion coordination numbers and those with crystal symmetry that prevents strong hybridization of cation dangling bond orbitals at VH . The results of this paper provide insight and guidance to identifying halides with shallow VH as good electronic and optoelectronic materials.

  4. Cross-Electrophile Coupling of Vinyl Halides with Alkyl Halides.

    PubMed

    Johnson, Keywan A; Biswas, Soumik; Weix, Daniel J

    2016-05-23

    An improved method for the reductive coupling of aryl and vinyl bromides with alkyl halides that gave high yields for a variety of substrates at room temperature with a low (2.5 to 0.5 mol %) catalyst loading is presented. Under the optimized conditions, difficult substrates, such as unhindered alkenyl bromides, can be coupled to give the desired olefins with minimal diene formation and good stereoretention. These improved conditions also worked well for aryl bromides. For example, a gram-scale reaction was demonstrated with 0.5 mol % catalyst loading, whereas reactions at 10 mol % catalyst loading completed in as little as 20 minutes. Finally, a low-cost single-component pre-catalyst, (bpy)NiI2 (bpy=2,2'-bipyridine) that is both air- and moisture-stable over a period of months was introduced. PMID:27017436

  5. A photocathode RF gun for x-ray FEL

    SciTech Connect

    Wang, X.J.; Batchelor, K.; Ben-Zvi, I.

    1995-12-31

    A 1.6 cell photocathode RF gun was developed by a BNL/SLAC/UCLA collaboration for X-ray FEL and other applications. The objective of the collaboration is to develop a cost effective and more reliable photocathode RF gun based on the operational experience of the original BNL gun. The new photocathode RF gun is cable of producing 1 mm-mrad normalized rms emittance photocurrent with a peak current of 100 A. The half-cell length of the new RF gun was lengthened to reduce the peak field on the cavity surface, the side-coupled scheme for cavity and waveguide coupling was replaced by a symmetrized coupling to the full-cell. The cavity aperture was increased to improve the coupling between two cells and for flat beam application. The experimental results of cold testing the RF gun will be presented. We will also present an injector design based on the new photocathode RF gun and emittance compensation technique.

  6. New Photocathode materials for electron-ion-colliders

    SciTech Connect

    Lukaszew, Rosa A.

    2015-02-25

    Our aim has been to explore new photocathode materials and schemes to develop strategies and technologies for next generation nuclear physics accelerator capabilities, particularly for Electron Ion Colliders (EIC). Thus, we investigated thin film deposition and ensuing properties for several adequate magnetic materials applicable to spin-polarized photocathodes. We also implemented a full experimental setup for light incidence at an acute angle onto the photocathode surface in order to excite surface Plasmon resonance hence increasing light absorption by a metallic surface. We successfully tested the setup with a thermionic cathode as well as Plasmonic silver-MgO samples and obtained very encouraging results. Our first results are very encouraging since the photocurrent measured on this preliminary plasmonic Ag-MgO sample under low power (~ 1mW) cw red light from a HeNe laser was 256 pA, thus two orders magnitude larger than that reported by others following also plasmonic approaches. We extended our studies to shorter wavelengths and we also started preliminary work on chemically ordered MnAl thin films –a component of the tertiary Ag-Mn-Al (silmanal) alloy in order to develop spin-polarized photocathodes capable of sustaining surface Plasmon resonance. It is worthwhile mentioning that a graduate student has been directly involved during this project ensuring the training of next generation of scientists in this area of research.

  7. SUPPRESSION OF AFTERPULSING IN PHOTOMULTIPLIERS BY GATING THE PHOTOCATHODE

    EPA Science Inventory

    A number of gating schemes to minimize the long-term afterpulse signal in photomultipliers have been evaluated. Blocking the excitation pulse by gating the photocathode was found to reduce the gate-on afterpulse background by a factor of 230 over that for nongated operation. Thi...

  8. Metal-Insulator Photocathode Heterojunction for Directed Electron Emission

    SciTech Connect

    Droubay, Timothy C.; Chambers, Scott A.; Joly, Alan G.; Hess, Wayne P.; Nemeth, Karoly; Harkay, Katherine C.; Spentzouris, Linda

    2014-02-14

    New photocathode materials capable of producing intense and directed electron pulses are needed for development of next generation light sources and dynamic transmission electron microscopy. Ideal photocathodes should have high photoemission quantum efficiency (QE) and be capable of delivering collimated and well-shaped pulses of consistent charge under high-field operating conditions. High-brightness and low-intrinsic emittance electron pulses have been predicted for hybrid metal-insulator photocathode designs constructed from three to four monolayer MgO films on atomically flat silver. Here we use angle-resolved photoelectron spectroscopy to confirm directional photoemission and a large increase in QE under ultraviolet laser excitation of an ultrathin MgO film on Ag(001). We observe new low-binding energy photoemission, not seen for Ag(001), and greater electron emission in the normal direction. Under 4.66 eV laser excitation, the photoemission quantum efficiency of the MgO/Ag(001) hybrid photocathode is a factor of seven greater than that for clean Ag(001).

  9. PROCESS OF RECOVERING ALKALI METALS

    DOEpatents

    Wolkoff, J.

    1961-08-15

    A process is described of recovering alkali metal vapor by sorption on activated alumina, activated carbon, dehydrated zeolite, activated magnesia, or Fuller's earth preheated above the vaporization temperature of the alkali metal and subsequent desorption by heating the solvent under vacuum. (AEC)

  10. Preparation of alkali metal dispersions

    NASA Technical Reports Server (NTRS)

    Rembaum, A.; Landel, R. F. (Inventor)

    1968-01-01

    A method is described for producing alkali metal dispersions of high purity. The dispersions are prepared by varying the equilibrium solubility of the alkali metal in a suitable organic solvent in the presence of aromatic hydrocarbons. The equilibrium variation is produced by temperature change. The size of the particles is controlled by controlling the rate of temperature change.

  11. Purification of alkali metal nitrates

    DOEpatents

    Fiorucci, Louis C.; Gregory, Kevin M.

    1985-05-14

    A process is disclosed for removing heavy metal contaminants from impure alkali metal nitrates containing them. The process comprises mixing the impure nitrates with sufficient water to form a concentrated aqueous solution of the impure nitrates, adjusting the pH of the resulting solution to within the range of between about 2 and about 7, adding sufficient reducing agent to react with heavy metal contaminants within said solution, adjusting the pH of the solution containing reducing agent to effect precipitation of heavy metal impurities and separating the solid impurities from the resulting purified aqueous solution of alkali metal nitrates. The resulting purified solution of alkali metal nitrates may be heated to evaporate water therefrom to produce purified molten alkali metal nitrate suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of alkali metal nitrates.

  12. Toxicity of organometal halide perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Babayigit, Aslihan; Ethirajan, Anitha; Muller, Marc; Conings, Bert

    2016-03-01

    In the last few years, the advent of metal halide perovskite solar cells has revolutionized the prospects of next-generation photovoltaics. As this technology is maturing at an exceptional rate, research on its environmental impact is becoming increasingly relevant.

  13. Hydrogen Halides on Jupiter and Saturn

    NASA Astrophysics Data System (ADS)

    Showman, Adam P.

    2001-07-01

    The quest to detect gaseous HCl, HBr, and HF in the atmospheres of Jupiter and Saturn has led to a tentative detection of 1 ppb HCl near Saturn's cloud deck. The detection is puzzling because, while these hydrogen halides may be present several scale heights below the clouds, they are expected to react with ammonia to form solid ammonium halide salts in the upper troposphere. I show that the loss timescale for condensation of gaseous hydrogen halides onto particles is ˜10 3-10 5 s for realistic cloud densities and particle sizes, which is much less than the ˜10 8 s residence time of upper tropospheric air. The hydrogen halides can only survive transport up to the cloud layer if less than 1 in 10 6 of their collisions with particle surfaces leads to condensation, which is unlikely. Even in the absence of foreign particles, homogeneous nucleation would probably prevent supersaturations in excess of a few hundred, which is ˜10 20-10 40 times too low to explain the observation. These calculations therefore suggest that hydrogen halides cannot exist at part-per-billion levels in the upper troposphere. The interplanetary source of halogens is also too low to produce detectable quantities of hydrogen halides except perhaps at pressures less than 1 mbar. A possible detection of chlorine by the Galileo probe at pressures exceeding 9 bars on Jupiter may be consistent with the equilibrium abundance of gaseous HCl or NH 4Cl.

  14. Preliminary Results from a superconducting photocathode sample cavity

    SciTech Connect

    Peter Kneisel; Jacek Sekutowicz; R. Lefferts; A. Lipski

    2005-05-01

    Pure niobium has been proposed as a photocathode material to extract directly photo-currents from the surface of a RF-gun cavity [1]. However, the quantum efficiency of niobium is {approx}3 {center_dot} 10{sup -4}, whereas electro- or vacuum deposited lead has an {approx} 10 times higher quantum efficiency. We have designed and tested a photo-injector niobium cavity, which can be used to insert photo-cathodes made of different materials in the high electric field region of the cavity. Experiments have been conducted with niobium and lead, which show that neither the Q- values of the cavity nor the obtainable surface fields are significantly lowered. This paper reports about the results from these tests.

  15. Highly efficient and stable ultraviolet photocathode based on nanodiamond particles

    NASA Astrophysics Data System (ADS)

    Velardi, L.; Valentini, A.; Cicala, G.

    2016-02-01

    Nanodiamond (ND) layers on silicon substrate are deposited by the pulsed spray technique starting from nanoparticles of about 250 nm dispersed in 1,2-dichloroethane solvent. The aim of this letter is to investigate the quantum efficiency (QE) of photocathodes based on ND particles in the vacuum ultraviolet spectral range. Various ND layers are examined employing as-received and hydrogenated nanoparticles. As expected, the hydrogen plasma treatment improves strongly the photoemission of the layer giving a QE of 22% at 146 nm. Indeed, this efficiency value is achieved only if the particles are treated in H2 microwave plasma before the growth of the sprayed layer rather than to hydrogenate the already formed one. These QE values are higher than those of photocathodes based on plasma chemical vapor deposition diamond films, but with the advantage of being much stable, too. The highest QE values are explained to be due to the intrinsic chemical and structural features of utilized ND particles.

  16. Temporal Response Measurements of GaAs-Based Photocathodes

    NASA Astrophysics Data System (ADS)

    Honda, Yosuke; Matsuba, Shunya; Jin, Xiuguang; Miyajima, Tsukasa; Yamamoto, Masahiro; Uchiyama, Takashi; Kuwahara, Makoto; Takeda, Yoshikazu

    2013-08-01

    It is well known that a negative electron affinity GaAs photocathode shows a moderate temporal response when excited by a laser pulse of wavelength close to its band gap energy. We show here that the temporal response can be estimated using a diffusion model that describes the internal transport of the conduction electrons. Using a transverse deflection cavity system, we measured the temporal profile of the electron bunch generated by a DC photocathode gun illuminated by a ps pulsed laser. A systematic set of measurements of GaAs cathodes with various active layer thicknesses and boundary conditions confirmed that the observed temporal response is well understood by the diffusion model calculation.

  17. DC photogun vacuum characterization through photocathode lifetime studies

    SciTech Connect

    Marcy Stutzman; Joseph Grames; Matt Poelker; Kenneth Surles-Law; Philip Adderley

    2007-07-02

    Excellent vacuum is essential for long photocathode lifetimes in DC high voltage photoelectron guns. Vacuum Research at Thomas Jefferson National Accelerator Facility has focused on characterizing the existing vacuum systems at the CEBAF polarized photoinjector and on quantifying improvements for new systems. Vacuum chamber preprocessing, full activation of NEG pumps and NEG coating the chamber walls should improve the vacuum within the electron gun, however, pressure measurement is difficult at pressures approaching the extreme-high-vacuum (XHV) region and extractor gauge readings are not significantly different between the improved and original systems. The ultimate test of vacuum in a DC high voltage photogun is the photocathode lifetime, which is limited by the ionization and back-bombardment of residual gasses. Discussion will include our new load-locked gun design as well as lifetime measurements in both our operational and new photo-guns, and the correlations between measured vacuum and lifetimes will be investigated.

  18. The Quantum Efficiency and Thermal Emittance of Metal Photocathodes

    SciTech Connect

    Dowell, David H.; Schmerge, John F.; /SLAC

    2009-03-04

    Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths, with the principle improvements occurring since the invention of the photocathode gun. The state-of-the-art normalized emittance electron beams are now becoming limited by the thermal emittance of the cathode. In both DC and RF photocathode guns, details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance of metal cathodes using the Fermi-Dirac model for the electron distribution. We derive the thermal emittance and its relationship to the quantum efficiency, and compare our results to those of others.

  19. Extreme ultraviolet quantum detection efficiency of rubidium bromide opaque photocathodes

    NASA Technical Reports Server (NTRS)

    Siegmund, Oswald H. W.; Gaines, Geoffrey A.

    1990-01-01

    Measurements are presented of the quantum detection efficiency (QDE) of three samples of RbBr photocathode layers over the 44-150-A wavelength range. The QDE of RbBr-coated microchannel plate (MCP) was measured using a back-to-back Z-stack MCP configuration in a detector with a wedge and strip position-sensitive anode, of the type described by Siegmund et al. (1984). To assess the stability of RbBr layer, the RbBr photocathode was exposed to air at about 30 percent humidity for 20 hr. It was found that the QDE values for the aged cathode were within the QDE measurement errors of the original values. A simple QDE model was developed, and it was found that its predictions are in accord with the QDE measurements.

  20. Dimming of metal halide lamps

    NASA Technical Reports Server (NTRS)

    Schurer, Kees

    1994-01-01

    We ran some tests on the effect of dimming of metal halide (MH) lamps upon the stability and the spectral quality of the light output. Lamps used were a new Philips lamp HPI-T 250W, a similar Philips lamp with a few thousand burning hours and a new Osram lamp HQI-T 250W/D. The ballast was a BBC type DJ 250/2KS, the starter a BAS TORGI type MZN 250 SE and the dimmer an Elstrom Control System type ERHQ-T 250. Power was derived from a Philips stabilizer, type PE 1602. Lamp output was monitored with a PAR meter. Spectra were taken at 100% and at 50% output as measured with the PAR meter. Lamps were allowed to stabilize at any setting for 30 minutes before measurements were made. Lamp manufacturers advise against dimming for fear of poor stability and intolerable changes of the spectrum. However, none of the lamps showed a decrease in stability, no flicker or wandering of the discharge, and the changes of the spectrum were not negligible, but certainly not dramatic. Lamps of either manufacture retain their white color, relative peak heights of spectral lines did shift, but no gaps in the spectrum occurred. Spectra taken at 50% with 30 minutes intervals coincided. Differences between the new and the older Philips lamp were noticeable, but not really significant.

  1. Thermal emittance measurements of a cesium potassium antimonide photocathode

    NASA Astrophysics Data System (ADS)

    Bazarov, Ivan; Cultrera, Luca; Bartnik, Adam; Dunham, Bruce; Karkare, Siddharth; Li, Yulin; Liu, Xianghong; Maxson, Jared; Roussel, William

    2011-05-01

    Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56±0.03 mm mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.

  2. Applications of Laser and Synchrotron Based ARPES to Photocathode Research

    SciTech Connect

    Rameau J.; Smedley J.; Muller, E.; Kidd, T.; Johnson, P.; Allen, P.; Carr, L.; Valla, T.

    2010-10-12

    Laser angle resolved photoelectron spectroscopy (ARPES) provides unique information about angle and energy distribution of photoelectrons. Laser ARPES gives unique insight into how NEA materials work. ARPES combined with some ancillary measurements gives a very complete picture of system electronic physics. For H:C[100] there is now a clear program for engineering as well as development analogous systems. ARPES well suited for identifying 'ideal' photocathodes with intrinsically low emittance and high QE.

  3. High Brightness and high polarization electron source using transmission photocathode

    SciTech Connect

    Yamamoto, Naoto; Jin Xiuguang; Ujihara, Toru; Takeda, Yoshikazu; Mano, Atsushi; Nakagawa, Yasuhide; Nakanishi, Tsutomu; Okumi, Shoji; Yamamoto, Masahiro; Konomi, Taro; Ohshima, Takashi; Saka, Takashi; Kato, Toshihiro; Horinaka, Hiromichi; Yasue, Tsuneo; Koshikawa, Takanori

    2009-08-04

    A transmission photocathode was fabricated based on GaAs-GaAsP strained superlattice layers on a GaP substrate and a 20 kV-gun was built to generate the polarized electron beams with the diameter of a few micro-meter. As the results, the reduced brightness of 1.3x10{sup 7} A/cm{sup 2}/sr and the polarization of 90% were achieved.

  4. S-11 and S-20 photocathode research activity. Rev. 1

    SciTech Connect

    Gex, F.; Huen, T.; Kalibjian, R.

    1984-08-27

    The S-1 semi-transparent photocathode is the only one that can be used to study the 1.06 ..mu..m neodynium laser pulses of less than 10 ps duration. We first reviewed the recent results obtained at the Paris Observatory (research sponsored by the CEA), and then we tried to determine the role of the main constituents and their contributions in photoemission.

  5. Upgrading platform using alkali metals

    SciTech Connect

    Gordon, John Howard

    2014-09-09

    A process for removing sulfur, nitrogen or metals from an oil feedstock (such as heavy oil, bitumen, shale oil, etc.) The method involves reacting the oil feedstock with an alkali metal and a radical capping substance. The alkali metal reacts with the metal, sulfur or nitrogen content to form one or more inorganic products and the radical capping substance reacts with the carbon and hydrogen content to form a hydrocarbon phase. The inorganic products may then be separated out from the hydrocarbon phase.

  6. The Remarkable Reactivity of Aryl Halides with Nucleophiles

    ERIC Educational Resources Information Center

    Bunnett, Joseph F.

    1974-01-01

    Discusses the reactivity of aryl halides with nucleophilic or basic reagents, including nucleophilic attacks on carbon, hydrogen, halogen, and arynes. Suggestions are made concerning revisions of the sections on aryl halide chemistry courses and the corresponding chapters in textbooks. (CC)

  7. Shallow halogen vacancies in halide optoelectronic materials

    SciTech Connect

    Shi, Hongliang; Du, Mao -Hua

    2014-11-05

    Halogen vacancies (VH) are usually deep color centers (F centers) in halides and can act as major electron traps or recombination centers. The deep VH contributes to the typically poor carrier transport properties in halides. However, several halides have recently emerged as excellent optoelectronic materials, e.g., CH3NH3PbI3 and TlBr. Both CH3NH3PbI3 and TlBr have been found to have shallow VH, in contrast to commonly seen deep VH in halides. In this paper, several halide optoelectronic materials, i.e., CH3NH3PbI3, CH3NH3SnI3 (photovoltaic materials), TlBr, and CsPbBr3, (gamma-ray detection materials) are studied to understand the material chemistry and structure that determine whether VH is a shallow or deep defect in a halide material. It is found that crystal structure and chemistry of ns2 ions both play important roles in creating shallow VH in halides such as CH3NH3PbI3, CH3NH3SnI3, and TlBr. The key to identifying halides with shallow VH is to find the right crystal structures and compounds that suppress cation orbital hybridization at VH, such as those with long cation-cation distances and low anion coordination numbers, and those with crystal symmetry that prevents strong hybridization of cation dangling bond orbitals at VH. Furthermore, the results of this paper provide insight and guidance to identifying halides with shallow VH as good electronic and optoelectronic materials.

  8. Highly efficient photocathodes for dye-sensitized tandem solar cells.

    PubMed

    Nattestad, A; Mozer, A J; Fischer, M K R; Cheng, Y-B; Mishra, A; Bäuerle, P; Bach, U

    2010-01-01

    Thin-film dye-sensitized solar cells (DSCs) based on mesoporous semiconductor electrodes are low-cost alternatives to conventional silicon devices. High-efficiency DSCs typically operate as photoanodes (n-DSCs), where photocurrents result from dye-sensitized electron injection into n-type semiconductors. Dye-sensitized photocathodes (p-DSCs) operate in an inverse mode, where dye-excitation is followed by rapid electron transfer from a p-type semiconductor to the dye (dye-sensitized hole injection). Such p-DSCs and n-DSCs can be combined to construct tandem solar cells (pn-DSCs) with a theoretical efficiency limitation well beyond that of single-junction DSCs (ref. 4). Nevertheless, the efficiencies of such tandem pn-DSCs have so far been hampered by the poor performance of the available p-DSCs (refs 3, 5-15). Here we show for the first time that p-DSCs can convert absorbed photons to electrons with yields of up to 96%, resulting in a sevenfold increase in energy conversion efficiency compared with previously reported photocathodes. The donor-acceptor dyes, studied as photocathodic sensitizers, comprise a variable-length oligothiophene bridge, which provides control over the spatial separation of the photogenerated charge carriers. As a result, charge recombination is decelerated by several orders of magnitude and tandem pn-DSCs can be constructed that exceed the efficiency of their individual components. PMID:19946281

  9. Highly efficient photocathodes for dye-sensitized tandem solar cells

    NASA Astrophysics Data System (ADS)

    Nattestad, A.; Mozer, A. J.; Fischer, M. K. R.; Cheng, Y.-B.; Mishra, A.; Bäuerle, P.; Bach, U.

    2010-01-01

    Thin-film dye-sensitized solar cells (DSCs) based on mesoporous semiconductor electrodes are low-cost alternatives to conventional silicon devices. High-efficiency DSCs typically operate as photoanodes (n-DSCs), where photocurrents result from dye-sensitized electron injection into n-type semiconductors. Dye-sensitized photocathodes (p-DSCs) operate in an inverse mode, where dye-excitation is followed by rapid electron transfer from a p-type semiconductor to the dye (dye-sensitized hole injection). Such p-DSCs and n-DSCs can be combined to construct tandem solar cells (pn-DSCs) with a theoretical efficiency limitation well beyond that of single-junction DSCs (ref. 4). Nevertheless, the efficiencies of such tandem pn-DSCs have so far been hampered by the poor performance of the available p-DSCs (refs 3, 5-15). Here we show for the first time that p-DSCs can convert absorbed photons to electrons with yields of up to 96%, resulting in a sevenfold increase in energy conversion efficiency compared with previously reported photocathodes. The donor-acceptor dyes, studied as photocathodic sensitizers, comprise a variable-length oligothiophene bridge, which provides control over the spatial separation of the photogenerated charge carriers. As a result, charge recombination is decelerated by several orders of magnitude and tandem pn-DSCs can be constructed that exceed the efficiency of their individual components.

  10. 40 CFR 721.575 - Substituted alkyl halide.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Substituted alkyl halide. 721.575... Substances § 721.575 Substituted alkyl halide. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as substituted alkyl halide (PMN P-83-1222)...

  11. Method for recovering hydrocarbons from molten metal halides

    DOEpatents

    Pell, Melvyn B.

    1979-01-01

    In a process for hydrocracking heavy carbonaceous materials by contacting such carbonaceous materials with hydrogen in the presence of a molten metal halide catalyst to produce hydrocarbons having lower molecular weights and thereafter recovering the hydrocarbons so produced from the molten metal halide, an improvement comprising injecting into the spent molten metal halide, a liquid low-boiling hydrocarbon stream is disclosed.

  12. Recent advances in technetium halide chemistry.

    PubMed

    Poineau, Frederic; Johnstone, Erik V; Czerwinski, Kenneth R; Sattelberger, Alfred P

    2014-02-18

    Transition metal binary halides are fundamental compounds, and the study of their structure, bonding, and other properties gives chemists a better understanding of physicochemical trends across the periodic table. One transition metal whose halide chemistry is underdeveloped is technetium, the lightest radioelement. For half a century, the halide chemistry of technetium has been defined by three compounds: TcF6, TcF5, and TcCl4. The absence of Tc binary bromides and iodides in the literature was surprising considering the existence of such compounds for all of the elements surrounding technetium. The common synthetic routes that scientists use to obtain binary halides of the neighboring elements, such as sealed tube reactions between elements and flowing gas reactions between a molecular complex and HX gas (X = Cl, Br, or I), had not been reported for technetium. In this Account, we discuss how we used these routes to revisit the halide chemistry of technetium. We report seven new phases: TcBr4, TcBr3, α/β-TcCl3, α/β-TcCl2, and TcI3. Technetium tetrachloride and tetrabromide are isostructural to PtX4 (X = Cl or Br) and consist of infinite chains of edge-sharing TcX6 octahedra. Trivalent technetium halides are isostructural to ruthenium and molybdenum (β-TcCl3, TcBr3, and TcI3) and to rhenium (α-TcCl3). Technetium tribromide and triiodide exhibit the TiI3 structure-type and consist of infinite chains of face-sharing TcX6 (X = Br or I) octahedra. Concerning the trichlorides, β-TcCl3 crystallizes with the AlCl3 structure-type and consists of infinite layers of edge-sharing TcCl6 octahedra, while α-TcCl3 consists of infinite layers of Tc3Cl9 units. Both phases of technetium dichloride exhibit new structure-types that consist of infinite chains of [Tc2Cl8] units. For the technetium binary halides, we studied the metal-metal interaction by theoretical methods and magnetic measurements. The change of the electronic configuration of the metal atom from d(3) (Tc

  13. The electronic structure of alkali aurides. A four-component Dirac-Kohn-Sham study.

    PubMed

    Belpassi, Leonardo; Tarantelli, Francesco; Sgamellotti, Antonio; Quiney, Harry M

    2006-04-01

    Spectroscopic constants, including dissociation energies, harmonic and anharmonic vibrational frequencies, and dipole moments, are calculated for the complete alkali auride series (LiAu, NaAu, KAu, RbAu, CsAu). The four-component formulation of relativistic density functional theory has been employed in this study, using the G-spinor basis sets implemented recently in the program BERTHA. The performance of four standard nonrelativistic density functionals employed is investigated by comparing the results with the best available theoretical and experimental data. The present work provides the first theoretical predictions on the molecular properties of RbAu. The intermetallic bond that occurs in the alkali auride series is highly polar and is characterized by a large charge transfer from the alkali metals to gold. The extent of this electron transfer has been investigated using several different charge analysis methods, enabling us to reach some general conclusions on their relative performance. We further report a detailed analysis of the topological properties of relativistic electron density in the bonding region, discussing the features of this approach which characterize the nature of the chemical bond. We have also computed the fully relativistic density for the alkali halides MBr and MI (M = Li, Na, K, Rb, and Cs). The comparative study shows that, on the basis of several topological properties and the variation in bond lengths, the gold atom behaves similarly to a halogen intermediate between Br and I. PMID:16571062

  14. Technical memo on new results on CsI photocathodes: Enhancement and aging

    SciTech Connect

    Anderson, D.F.; Kwan, S. ); Hoeneisen, B. ); Peskov, V. . World Lab.)

    1991-09-01

    It appears that there are 4 processes involved in the enhancement and aging of a CsI or CsI-TMAE photocathode: water absorption, charging up of the photocathode, a self annealing aging, and a permanent aging. The evidence for these processes are presented. 9 refs., 6 figs.

  15. The Boeing photocathode accelerator magnetic pulse compression and energy recovery experiment

    SciTech Connect

    Dowell, D.H.; Adamski, J.L.; Hayward, T.D.

    1995-12-31

    An 18 MeV, photocathode accelerator operating at 433 MHz is being commissioned for FEL applications. The accelerator consists of a two-cell RF photocathode imjector followed by four new multicell cavities. The two cell injector has previously been operated at a micropulse repetition frequency of 27 MHz, a micropulse charge of 5 nC and 25% duty factor.

  16. Hydrothermal alkali metal catalyst recovery process

    DOEpatents

    Eakman, James M.; Clavenna, LeRoy R.

    1979-01-01

    In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles primarily in the form of water soluble alkali metal formates by treating the particles with a calcium or magnesium-containing compound in the presence of water at a temperature between about 250.degree. F. and about 700.degree. F. and in the presence of added carbon monoxide. During the treating process the water insoluble alkali metal compounds comprising the insoluble alkali metal residues are converted into water soluble alkali metal formates. The resultant aqueous solution containing water soluble alkali metal formates is then separated from the treated particles and any insoluble materials formed during the treatment process, and recycled to the gasification process where the alkali metal formates serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. This process permits increased recovery of alkali metal constituents, thereby decreasing the overall cost of the gasification process by reducing the amount of makeup alkali metal compounds necessary.

  17. Advanced Strained-Superlattice Photocathodes for Polarized Electron Sources

    SciTech Connect

    Dr. Aaron Moy

    2005-01-31

    Polarized electrons have been essential for high-energy parity-violating experiments and measurements of the nucleon spin structure. The availability of a polarized electron beam was crucial to the success of the Stanford Linear Collider (SLC) in achieving a precise measurement of the electroweak mixing angle, and polarized electron beams will be required for all future linear colliders. Polarized electrons are readily produced by GaAs photocathode sources. When a circularly polarized laser beam tuned to the bandgap minimum is directed to the negative-electron-affinity (NEA) surface of a GaAs crystal, longitudinally polarized electrons are emitted into vacuum. The electron polarization is easily reversed by reversing the laser polarization. The important properties of these photocathodes for accelerator applications are: degree of polarization of the extracted beam; ability to extract sufficient charge to meet accelerator pulse-structure requirements; efficiency and stability of operation; and absence of any asymmetries in the beam properties (charge, position, energy, etc.) upon polarization reversal. The performance of GaAs photocathodes has improved significantly since they were first introduced in 1978 [1]. The theoretical maximum polarization of 50% for natural GaAs was first exceeded in 1991 using the lattice mismatch of a thin InGaAs layer epitaxially grown over a GaAs substrate to generate a strain in the former that broke the natural degeneracy between the heavy- and light-hole valence bands [2]. Polarizations as high as 78% were produced for the SLC from photocathodes based on a thin GaAs epilayer grown on GaAsP [3,4]. After 10 years of experience with many cathode samples at several laboratories [5], the maximum polarization using the GaAs/GaAsP single strained-layer cathode remained limited to 80%, while the quantum efficiency (QE) for a 100-nm epilayer is only 0.3% or less. Two factors were known to limit the polarization of these cathodes: (1) the

  18. Alkali Halide Opacity in Brown Dwarf and Cool Stellar Atmospheres: A Study of Lithium Chloride

    NASA Astrophysics Data System (ADS)

    Kirby, K.; Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.

    2003-12-01

    Recent thermochemical equilibrium calculations have revealed the important role played by lithium chloride in the lithium chemistry of cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl appears to be the dominant Li-bearing gas over an extended domain of the (P,T) diagram, typically for temperatures below 1500 K. LiCl has a large dipole moment in its ground electronic state which can give rise to intense rovibrational line spectra. In addition, LiCl can make dipole transitions to several low-lying unbound excited states, causing dissociation of the molecule. For these reasons, LiCl may be a significant source of line and continuum opacity in brown dwarf and cool stellar atmospheres. In this work, we report calculations of complete lists of line oscillator strengths and photodissociation cross sections for the low-lying electronic states of LiCl. We have performed single- and double-excitation configuration interaction calculations using the ALCHEMY ab initio package (Mc Lean et al. 1991, MOTECC 91, Elsevier, Leiden) and obtained the potential curves and the corresponding dipole transition moment functions between the X 1Σ ^+ ground state and the B 1Σ ^+ and A 1Π excited states. The resulting line oscillator strengths and molecular photodissociation cross sections have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS). This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582.

  19. Elastic properties of alpha quartz and the alkali halides based on an interatomic force model.

    NASA Technical Reports Server (NTRS)

    Weidner, D. J.; Simmons, G.

    1972-01-01

    A two-body central-force atomic model can be used to describe accurately the elastic properties of alpha quartz if the nontetrahedral O:O forces are included. The strength of the Si:O interaction has little effect on the bulk modulus. The technique is sufficiently general to allow calculations of the elastic properties of a specified structure under arbitrary pressure from a complete description of the interatomic forces. The elastic constants for the NaCl structure and the CsCl structure are examined. Our model includes two-body, central, anion-anion, anion-cation, and electrostatic interactions.

  20. The aluminum electrode in AlCl3-alkali-halide melts

    NASA Technical Reports Server (NTRS)

    Holleck, G. L.; Giner, J.

    1972-01-01

    Passivation phenomena were observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and 1/sq root of 2 pi (rps). Upon cathodic polarization dentrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl (57.5-12.5-20 mol%) was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/cm2 at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/cm2 were measured.

  1. The aluminum electrode in AlCl3-alkali-halide melts.

    NASA Technical Reports Server (NTRS)

    Holleck, G. L.; Giner, J.

    1972-01-01

    Passivation phenomena have been observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and omega to the minus 1/2 power. Upon cathodic polarization, dendrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/sq cm at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/sq cm were measured.

  2. Is surface layering of aqueous alkali halides determined by ion pairing in the bulk solution?

    NASA Astrophysics Data System (ADS)

    Brandes, Eva; Stage, Christiane; Motschmann, Hubert; Rieder, Julian; Buchner, Richard

    2014-11-01

    This contribution aims to elucidate the connection between ion-ion-solvent interactions in the bulk of aqueous electrolyte solutions and the properties of their liquid-air interface. In particular, we were interested in the conditions under which ion pairs form at the surface and whether this is linked to ion pairing in the bulk. For this reason different combinations of hard (Cl-, Li+) and soft ions (I-, Cs+) were investigated. Ion hydration and possible ion association in the bulk was probed with dielectric relaxation spectroscopy. This technique monitors the cooperative reorientation of the dipolar solvent molecules and detects all ion-pair species possibly present in the solution. At the interface, the formation of contact ion pairs was investigated by infrared-visible-sum frequency spectroscopy (SFG). This nonlinear optical technique possesses an inherent surface specificity and can be used for the characterization of interfacial water. The intensity of the SFG-active vibrational stretching modes depends on the number of oriented water molecules. The electric field at the surface of a charged aqueous interface aligns the water dipoles, which in turn increases the SFG response. Hence, the enhancement of the oscillator strengths of the water vibrational modes can be used to draw some conclusions on the strengths and geometrical extension of the electric field. The formation of ion pairs at the interface reduces the intensity of the band associated with hydrogen-bonded water. The underlying theory is presented. The combined data show that there are no contact ion pairs in the bulk of the fluid and—at best—only small amounts of solvent shared ion pairs. On the other hand, the combination of hard/hard or soft/soft ions leads to the formation of ion pairs at the liquid-air interface.

  3. Properties of alkali-halide salt solutions about polarizable nanoparticle solutes for different ion models

    NASA Astrophysics Data System (ADS)

    Wynveen, Aaron; Bresme, Fernando

    2010-10-01

    We investigate the distributions of various salts about large hydrophobic polarizable solutes in aqueous electrolyte solutions. The solutes are modeled as nanometer-sized cylindrical objects, a scale relevant to biomolecules and nanomaterials, and particularly high aspect ratio nanoparticles. Interactions, including image charge forces arising from the finite polarizability of the solute, between explicit solvent/ions and the solute are computed explicitly using a molecular dynamics simulation methodology we have recently introduced. Comparisons are made between several salt species and different models of the force fields for each ionic component of the salt. We find evidence that both small cations, Li+, and large anions, I-, adsorb at hydrophobic interfaces. Our results indicate that the ion structure about the solute is strongly dependent on the force field investigated, suggesting that ion selectivity is quite sensitive to the respective parameters defining the ion's size and binding energy as well as to the polarizability of the solute.

  4. Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces.

    PubMed

    Nony, Laurent; Bocquet, Franck; Para, Franck; Chérioux, Frédéric; Duverger, Eric; Palmino, Frank; Luzet, Vincent; Loppacher, Christian

    2012-01-01

    We investigated the adsorption of 4-methoxy-4'-(3-sulfonatopropyl)stilbazolium (MSPS) on different ionic (001) crystal surfaces by means of noncontact atomic force microscopy. MSPS is a zwitterionic molecule with a strong electric dipole moment. When deposited onto the substrates at room temperature, MSPS diffuses to step edges and defect sites and forms disordered assemblies of molecules. Subsequent annealing induces two different processes: First, at high coverage, the molecules assemble into a well-organized quadratic lattice, which is perfectly aligned with the <110> directions of the substrate surface (i.e., rows of equal charges) and which produces a Moiré pattern due to coincidences with the substrate lattice constant. Second, at low coverage, we observe step edges decorated with MSPS molecules that run along the <110> direction. These polar steps most probably minimize the surface energy as they counterbalance the molecular dipole by presenting oppositely charged ions on the rearranged step edge. PMID:22497002

  5. Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces

    PubMed Central

    Nony, Laurent; Bocquet, Franck; Para, Franck; Chérioux, Frédéric; Duverger, Eric; Palmino, Frank; Luzet, Vincent

    2012-01-01

    Summary We investigated the adsorption of 4-methoxy-4′-(3-sulfonatopropyl)stilbazolium (MSPS) on different ionic (001) crystal surfaces by means of noncontact atomic force microscopy. MSPS is a zwitterionic molecule with a strong electric dipole moment. When deposited onto the substrates at room temperature, MSPS diffuses to step edges and defect sites and forms disordered assemblies of molecules. Subsequent annealing induces two different processes: First, at high coverage, the molecules assemble into a well-organized quadratic lattice, which is perfectly aligned with the <110> directions of the substrate surface (i.e., rows of equal charges) and which produces a Moiré pattern due to coincidences with the substrate lattice constant. Second, at low coverage, we observe step edges decorated with MSPS molecules that run along the <110> direction. These polar steps most probably minimize the surface energy as they counterbalance the molecular dipole by presenting oppositely charged ions on the rearranged step edge. PMID:22497002

  6. Electronic line-up in light-emitting diodes with alkali-halide/metal cathodes

    NASA Astrophysics Data System (ADS)

    Brown, T. M.; Friend, R. H.; Millard, I. S.; Lacey, D. J.; Butler, T.; Burroughes, J. H.; Cacialli, F.

    2003-05-01

    The electronic nature of metal-semiconductor contacts is a fundamental issue in the understanding of semiconductor device physics, because such contacts control charge injection, and therefore play a major role in determining the electron/hole population in the semiconductor itself. This role is particularly important for organic semiconductors as they are generally used in their pristine, undoped form. Here, we review our progress in the understanding of the energy level line-up in finished, blue-emitting, polyfluorene-based light-emitting diodes, which exploit LiF and CsF thin films in combination with Ca and Al to obtain cathodes with low injection barriers. We have used electroabsorption measurements, as they allow the noninvasive determination of the built-in potential when changing the cathode. This provides precious experimental information on the alteration of the polymer/cathode interfacial energy level line-up. The latter is found to depend strongly on the electrode work function. Thus, the Schottky-Mott model for the energy level alignment is found to be a better first-order approximation than those models where strong pinning or large interface dipoles determine the alignment (e.g., Bardeen model), except for electrodes that extensively react with the polymer, and introduce deep gap states. In addition, we show results that validate the approximation of rigid tilting of polymer energy levels with bias (for biases for which no significant injection of carriers occurs). To investigate further the consequences of the electronic line-up on device operation, we complemented the electroabsorption measurements with characterization of the emissive and transport properties of the light-emitting diodes, and confirmed that the cathodic barrier lowering in CsF/Ca/Al and LiF/Ca/Al electrodes leads to the best improvements in electron injection. We found that luminance and overall current are greatly affected by the barrier-reducing cathodes, indicating a truly bipolar transport, with comparable electron and hole currents. We also found significant indications of CsF/Ca/Al cathodes strongly reacting with the polymer, which is suggestive of CsF dissociation and diffusion in the bulk of the polymer.

  7. Vibration-Resistant Support for Halide Lamps

    NASA Technical Reports Server (NTRS)

    Kiss, J.

    1987-01-01

    Lamp envelope protected against breakage. Old and new mounts for halide arc lamp sealed in housing with parabolic refector and quartz window. New version supports lamp with compliant garters instead of rigid brazed joint at top and dimensionally unstable finger stock at bottom.

  8. Mean transverse energy and response time measurements of GaInP based photocathodes

    SciTech Connect

    Jin, Xiuguang; Yamamoto, Masahiro; Miyajima, Tsukasa; Honda, Yosuke; Uchiyama, Takashi; Tabuchi, Masao; Takeda, Yoshikazu

    2014-08-14

    GaInP, which has a wider band gap than GaAs, is introduced as a photocathode for energy recovery linac (ERL). The wide band gap of material is expected to reduce the heating effect in the thermal relaxation process after high energy excitation. GaInP photocathodes exhibited higher quantum efficiency than GaAs and low thermal emittance as the same as GaAs photocathodes under green laser light irradiation. A short picosecond electron pulse was also achieved with the GaInP photocathode under 532 nm pulse laser irradiation. These experimental results demonstrate that the GaInP photocathode is an important candidate for ERL.

  9. A mechanism of Cu work function reduction in CsBr/Cu photocathodes

    SciTech Connect

    Halliday, M. T. E.; Hess, W. P.; Shluger, A. L.

    2016-01-01

    Thin films of CsBr deposited on Cu(100) have been proposed as next-generation photocathode materials for applications in particle accelerators and free-electron lasers. However, the mechanisms underlying an improved photocathode performance remain poorly understood. We present density Functional Theory (DFT) calculations of the work function reduction following the application of CsBr thin film coatings to Cu photocathodes. The effects of structure and van der Waals forces are examined. Calculations suggest that CsBr films can reduce the work function by around 1.5 eV, which would explain the exponential increase in quantum efficiency (QE) of coated vs. uncoated photocathodes. A model explaining experimentally observed laser activation of photocathode is provided whereby the photo-induced creation of di-vacancies at the surface, and their subsequent diffusion throughout the lattice and segregation at the interface leads to a further increase in QE after a period of laser irradiation.

  10. Effects of atomic hydrogen and deuterium exposure on high polarization GaAs photocathodes

    SciTech Connect

    M. Baylac; P. Adderley; J. Brittian; J. Clark; T. Day; J. Grames; J. Hansknecht; M. Poelker; M. Stutzman; A. T. Wu; A. S. Terekhov

    2005-12-01

    Strained-layer GaAs and strained-superlattice GaAs photocathodes are used at Jefferson Laboratory to create high average current beams of highly spin-polarized electrons. High electron yield, or quantum efficiency (QE), is obtained only when the photocathode surface is atomically clean. For years, exposure to atomic hydrogen or deuterium has been the photocathode cleaning technique employed at Jefferson Laboratory. This work demonstrates that atomic hydrogen cleaning is not necessary when precautions are taken to ensure that clean photocathode material from the vendor is not inadvertently dirtied while samples are prepared for installation inside photoemission guns. Moreover, this work demonstrates that QE and beam polarization can be significantly reduced when clean high-polarization photocathode material is exposed to atomic hydrogen from an rf dissociator-style atomic hydrogen source. Surface analysis provides some insight into the mechanisms that degrade QE and polarization due to atomic hydrogen cleaning.

  11. Kelvin probe studies of cesium telluride photocathode for the AWA photoinjector

    SciTech Connect

    Velazquez, D.; Wisniewski, E. E.; Yusof, Z.; Harkay, K.; Spentzouris, L.; Terry, J.

    2012-12-21

    Cesium telluride is an important photocathode as an electron source for particle accelerators. It has a relatively high quantum efficiency (> 1%), is robust in a photoinjector, and long lifetime. This photocathode is fabricated in-house for a new Argonne Wakefield Accelerator (AWA) beamline to produce high charge per bunch ({approx}50 nC) in a long bunch train. We present some results from a study of the work function of cesium telluride photocathode using the Kelvin Probe technique. The study includes an investigation of the correlation between the quantum efficiency and the work function, the effect of photocathode aging, the effect of UV light exposure on the work function, and the evolution of the work function during and after photocathode rejuvenation via heating.

  12. Thermal emittance and response time of a cesium antimonide photocathode

    NASA Astrophysics Data System (ADS)

    Cultrera, Luca; Bazarov, Ivan; Bartnik, Adam; Dunham, Bruce; Karkare, Siddharth; Merluzzi, Richard; Nichols, Matthew

    2011-10-01

    Measurements of the intrinsic emittance and response time of a Cs3Sb photocathode are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. Photoemission response time is evaluated using a RF deflecting cavity synchronized to a picosecond laser pulse train. We find that Cs3Sb has both small mean transverse energy, 160 ± 10 meV at 532 nm laser wavelength, and a prompt response time (below the resolution of our measurement) making it a suitable material for high brightness electron photoinjectors.

  13. High power testing of a 17 GHz photocathode RF gun

    SciTech Connect

    Chen, S.C.; Danly, B.G.; Gonichon, J.

    1995-12-31

    The physics and technological issues involved in high gradient particle acceleration at high microwave (RF) frequencies are under study at MIT. The 17 GHz photocathode RF gun has a 1 1/2 cell ({pi} mode) room temperature cooper cavity. High power tests have been conducted at 5-10 MW levels with 100 ns pulses. A maximum surface electric field of 250 MV/m was achieved. This corresponds to an average on-axis gradient of 150 MeV/m. The gradient was also verified by a preliminary electron beam energy measurement. Even high gradients are expected in our next cavity design.

  14. A new chemical analysis system using a photocathode RF gun

    NASA Astrophysics Data System (ADS)

    Aoki, Yasushi; Yang, Jinfeng; Hirose, Masafumi; Sakai, Fumio; Tsunemi, Akira; Yorozu, Masafumi; Okada, Yasuhiro; Endo, Akira; Wang, Xijie; Ben-Zvi, Ilan

    2000-11-01

    A compact chemical analysis (pulse radiolysis) apparatus using a BNL-type s-band photocathode RF gun (GUN-IV) is now under development at Sumitomo Heavy Industries (SHI). Using the apparatus, fast chemical reactions induced by 3.5 ps pulse of electron beam can be analyzed by means of time-resolved photo-absorption spectroscopy with 10 ps laser pulses in the wavelength range of 210-2000 nm. The high-precision control of RF phase makes 10 ps of time-resolution possible for the analysis.

  15. Thermal limit to the intrinsic emittance from metal photocathodes

    SciTech Connect

    Feng, Jun Nasiatka, J.; Wan, Weishi; Karkare, Siddharth; Padmore, Howard A.; Smedley, John

    2015-09-28

    Measurements of the intrinsic emittance and transverse momentum distributions obtained from a metal (antimony thin film) photocathode near and below the photoemission threshold are presented. Measurements show that the intrinsic emittance is limited by the lattice temperature of the cathode as the incident photon energy approaches the photoemission threshold. A theoretical model to calculate the transverse momentum distributions near this photoemission threshold is presented. An excellent match between the experimental measurements and the theoretical calculations is demonstrated. These measurements are relevant to low emittance electron sources for Free Electron Lasers and Ultrafast Electron Diffraction experiments.

  16. RECENT PROGRESS ON THE DIAMOND AMPLIFIED PHOTO-CATHODE EXPERIMENT.

    SciTech Connect

    CHANG,X.; BEN-ZVI, I.; BURRILL, A.; GRIMES, J.; RAO, T.; SEGALOV, Z.; SMEDLEY, J.; WU, Q.

    2007-06-25

    We report recent progress on the Diamond Amplified Photo-cathode (DAP). The use of a pulsed electron gun provides detailed information about the DAP physics. The secondary electron gain has been measured under various electric fields. We have achieved gains of a few hundred in the transmission mode and observed evidence of emission of electrons from the surface. A model based on recombination of electrons and holes during generation well describes the field dependence of the gain. The emittance measurement system for the DAP has been designed, constructed and is ready for use. The capsule design of the DAP is also being studied in parallel.

  17. Laser Development for Future Photocathode Research at SLAC

    NASA Astrophysics Data System (ADS)

    Brachmann, A.; Cone, K.; Clendenin, J. E.; Garwin, E. L.; Kirby, R. E.; Luh, D.; Maruyama, T.; Prepost, R.; Prescott, C. Y.

    2005-08-01

    This report summarizes results of recent upgrades to SLAC's polarized source drive laser system. A Q-switching system has been incorporated into the flashlamp-pumped Ti:Sapphire laser system. The Q-switched laser provides energies up to 5 mJ for a 200 ns long pulse. Slow Q-switching provides control over length and shape of the laser pulse. A peak current of > 5.5 A has been demonstrated using a GaAs photocathode illuminated by this laser system.

  18. High voltage switch triggered by a laser-photocathode subsystem

    DOEpatents

    Chen, Ping; Lundquist, Martin L.; Yu, David U. L.

    2013-01-08

    A spark gap switch for controlling the output of a high voltage pulse from a high voltage source, for example, a capacitor bank or a pulse forming network, to an external load such as a high gradient electron gun, laser, pulsed power accelerator or wide band radar. The combination of a UV laser and a high vacuum quartz cell, in which a photocathode and an anode are installed, is utilized as triggering devices to switch the spark gap from a non-conducting state to a conducting state with low delay and low jitter.

  19. Characterization of quantum well structures using a photocathode electron microscope

    NASA Technical Reports Server (NTRS)

    Spencer, Michael G.; Scott, Craig J.

    1989-01-01

    Present day integrated circuits pose a challenge to conventional electronic and mechanical test methods. Feature sizes in the submicron and nanometric regime require radical approaches in order to facilitate electrical contact to circuits and devices being tested. In addition, microwave operating frequencies require careful attention to distributed effects when considering the electrical signal paths within and external to the device under test. An alternative testing approach which combines the best of electrical and optical time domain testing is presented, namely photocathode electron microscope quantitative voltage contrast (PEMQVC).

  20. Modeling the quantum efficiency of controlled porosity dispenser photocathodes

    NASA Astrophysics Data System (ADS)

    Pan, Z.; Jensen, K.; O'Shea, P.

    2012-01-01

    A theoretical model of diffusion, evaporation, and rejuvenation of cesium on the surface of a controlled porosity dispenser photocathode is developed. The model applies a novel hexagonal meshgrid for increased numerical accuracy. For activation temperatures within the range of 400 K-1000 K, simulation found differences of less than 5% between the quantum efficiency (QE) maximum and minimum over ideal homogenous surfaces. Simulations suggest more variation for real cases to include real surface non uniformity. Changes in the QE map across the surface suggest that the emittance can change depending on temperature. Extensions to the model as well as connections to experiment are discussed.

  1. Pulse Selection Control for the IR FEL Photocathode Drive Laser

    NASA Astrophysics Data System (ADS)

    Jordan, K.; Evans, R.; Garza, O.; Hill, R.; Shinn, M.; Song, J.; Venhaus, D.

    1997-05-01

    The method for current control of the photocathode source is described. This device allows remote control of drive laser output pulses for resulting beam currents of less than 1 microamp to full current of 5 milliamps. The low current modes are accomplished by counting discrete micropulses and gating electro-optical cells. The higher current modes are done by varying both the photons per pulse and the frequency of the laser output pulses. Programmable Logic Devices (PLDs) provide the choice in micropulses per macropulse and the macropulse frequency. All macropulses are line locked to 60 Hz and have the ability to be slewed through a line cycle in discrete steps.

  2. Characteristic of photocurrent decline of transmission-mode equally doped GaAs photocathode

    NASA Astrophysics Data System (ADS)

    Zhang, Dong Lian; Shi, Feng; Gao, Xiang; Cheng, Hong-Chang; Miao, Zhuang; Niu, Sen; Wang, Long; Chen, Chang

    2014-09-01

    Photocurrent of GaAs photocathode activated with Cs and O was tested by auto-activation monitor, the fitting curves of photocurrent showed that the photocurrent of the photocathode after the first activation declines exponentially, and then declines linearly with very small slope |k1|; the photocurrent after the second activation rises exponentially, and then declines linearly with a slope|k2| which is a bit larger than |k1|.Based on the mechanism difference between twice annealing of the photocathode, the degeneration behavior of the photocathode was analyzed by three-dipoles model and XPS test after the first activation and succedent thermal cleaning. It is indicated that Cs2O dipoles on the surface are saturated after the photocathode was activated for the first time, the remained Cs and Cs2O in the ultra-high vacuum chamber which deposited on the photocathode surface will prevent the emission of photoelectrons. The photocathode surface with Cs and O reconstructed when it was annealing for the second time, a lot of Cs2O dipoles changed into more stable GaAs-O-Cs dipoles, and this phenomenon would happened immediately as soon as the photocathode was activating for the second time. After the residual Cs and Cs2O dipoles depleted, the neutral gas CO2, H2O, O2, damaging the surface dipoles layer, are the main factors resulted in the decline of photocurrent. Due to the instable Cs2O dipoles on the surface of photocathode have greater chances of converting into stable GaAs-O-Cs dipoles when photocathode was activated for the first time, the photocurrent declines more slowly compared with the second activation. The discussion for the phenomenon is of great significance for exploring the photoemission mechanism of Ⅲ-Ⅴ semiconductors.

  3. Polarization and charge limit studies of strained GaAs photocathodes

    SciTech Connect

    Saez, P.J.

    1997-03-01

    This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of {approximately} 2.5 A/cm{sup 2} at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don`t have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes.

  4. Electrolytic method to make alkali alcoholates using ion conducting alkali electrolyte/separator

    DOEpatents

    Joshi, Ashok V.; Balagopal, Shekar; Pendelton, Justin

    2011-12-13

    Alkali alcoholates, also called alkali alkoxides, are produced from alkali metal salt solutions and alcohol using a three-compartment electrolytic cell. The electrolytic cell includes an anolyte compartment configured with an anode, a buffer compartment, and a catholyte compartment configured with a cathode. An alkali ion conducting solid electrolyte configured to selectively transport alkali ions is positioned between the anolyte compartment and the buffer compartment. An alkali ion permeable separator is positioned between the buffer compartment and the catholyte compartment. The catholyte solution may include an alkali alcoholate and alcohol. The anolyte solution may include at least one alkali salt. The buffer compartment solution may include a soluble alkali salt and an alkali alcoholate in alcohol.

  5. The calcium-alkali syndrome.

    PubMed

    Arroyo, Mariangeli; Fenves, Andrew Z; Emmett, Michael

    2013-04-01

    The milk-alkali syndrome was a common cause of hypercalcemia, metabolic alkalosis, and renal failure in the early 20th century. It was caused by the ingestion of large quantities of milk and absorbable alkali to treat peptic ulcer disease. The syndrome virtually vanished after introduction of histamine-2 blockers and proton pump inhibitors. More recently, a similar condition called the calcium-alkali syndrome has emerged as a common cause of hypercalcemia and alkalosis. It is usually caused by the ingestion of large amounts of calcium carbonate salts to prevent or treat osteoporosis and dyspepsia. We describe a 78-year-old woman who presented with weakness, malaise, and confusion. She was found to have hypercalcemia, acute renal failure, and metabolic alkalosis. Upon further questioning, she reported use of large amounts of calcium carbonate tablets to treat recent heartburn symptoms. Calcium supplements were discontinued, and she was treated with intravenous normal saline. After 5 days, the calcium and bicarbonate levels normalized and renal function returned to baseline. In this article, we review the pathogenesis of the calcium-alkali syndrome as well as the differences between the traditional and modern syndromes. PMID:23543983

  6. A Stable, Non-Cesiated III-Nitride Photocathode for Ultraviolet Astronomy Application

    NASA Astrophysics Data System (ADS)

    Bell, Lloyd

    In this effort, we propose to develop a new type of cesium-free photocathode using III-nitride (III-N) materials (GaN, AlN, and their alloys) and to achieve highly efficient, solar blind, and stable UV response. Currently, detectors used in UV instruments utilize a photocathode to convert UV photons into electrons that are subsequently detected by microchannel plate or CCD. The performance of these detectors critically depends on the efficiency and stability of their photocathodes. In particular, photocathode instability is responsible for many of the fabrication difficulties commonly experienced with this class of detectors. In recent years, III-N (in particular GaN) photocathodes have been demonstrated with very high QE (>50%) in parts of UV spectral range. Moreover, due to the wide bandgaps of III-nitride materials, photocathode response can be tailored to be intrinsically solar-blind. However, these photocathodes still rely on cesiation for activation, necessitating all-vacuum fabrication and sealed-tube operation. The proposed photocathode structure will achieve activation through methods for band structure engineering such as delta-doping and polarization field engineering. Compared to the current state-of-the-art in flight-ready microchannel plate sealed tubes, photocathodes based on III-N materials will yield high QE and significantly enhance both fabrication yield and reliability, since they do not require cesium or other highly reactive materials for activation. This performance will enable a ~4 meter medium class UV spectroscopic and imaging mission that is of high scientific priority for NASA. This work will build on the success of our previous APRA-funded effort. In that work, we demonstrated III-nitride photocathode operation without the use of cesium and stable response with respect to time. These accomplishments represent major improvements to the state-of-the-art for photocathode technologies. In the proposed effort, we will implement III

  7. Theoretical characterization of dihydrogen adducts with halide anions

    NASA Astrophysics Data System (ADS)

    Vitillo, Jenny G.; Damin, Alessandro; Zecchina, Adriano; Ricchiardi, Gabriele

    2006-06-01

    The interaction between a hydrogen molecule and the halide anions F-, Cl-, Br-, and I- has been studied at different levels of theory and with different basis sets. The most stable configurations of the complexes have a linear geometry, while the t-shaped complexes are saddle points on the potential energy surface, opposite to what is observed for alkali cations. An electrostatic analysis conducted on the resulting adducts has highlighted the predominance of the electrostatic term in the complexation energy and, in particular, of the quadrupole- and dipole-polarizability dependent contributions. Another striking difference with respect to the positive ions, is the fact that although the binding energies have similar values (ranging between 25 and 3kJ/mol for F- and I-, respectively), the vibrational shift of the ν˜H-H and in general the perturbation of the hydrogen molecule in complexes are much greater in the complexes with anions (Δν˜H-H ranges between -720 and -65cm-1). Another difference with respect to the interaction with cations is a larger charge transfer from the anion to the hydrogen molecule. The Δν˜ is the result of the cooperative role of the electrostatics and of the charge transfer in the interaction. The correlation between binding energies and vibrational shift is far from linear, contrary to what is observed for cation complexes, in accordance with the higher polarizability and dynamic polarizability of the molecule along the molecular axis. The observed correlation may be valuable in the interpretation of spectra and thermodynamic properties of adsorbed H2 in storage materials.

  8. Very high quantum efficiency PMTs with bialkali photo-cathode

    NASA Astrophysics Data System (ADS)

    Mirzoyan, R.; Laatiaoui, M.; Teshima, M.

    2006-11-01

    Since the mid-1960s and until today the classical PMTs with semitransparent bialkali photo-cathode provide peak Quantum Efficiency (QE) of ˜25%. About 2 years ago we started a program with the PMT manufacturers Hamamatsu, Photonis and Electron Tubes for boosting up the QE of bialkali PMTs. In the mean time we have obtained several batches of experimental PMTs from the above-mentioned manufacturers and measured few samples with QE values as high as 32-36% in the peak. Also, we want to report on the modest (5-7) % increase of the QE of the PMTs with flat input window after sandblasting. Earlier we have reported that by coating the hemi-spherical input window of bialkali PMTs with a milky layer we could enhance their QE by ˜10-20% for wavelengths ˜320 nm. Assuming that the industry can reliably produce PMTs with 32-35% QE in the peak, by applying the milky layer coating technique to the PMTs with hemi-spherical input window one shall be able to achieve peak QE values of ˜35-40%. Being by an order of magnitude cheaper and providing a matching level of QE such PMTs will become strong competitors for hybrid photo-diodes (HPD) with GaAsP photo-cathode.

  9. Magnetron Driven L Band RF Gun using a Photocathode Emitter

    NASA Astrophysics Data System (ADS)

    Evans, Kirk; Fisher, Amnon; Friedman, Moshe

    1996-11-01

    Magnetron Driven L Band RF Gun using a Photocathode Emitter A tunable 5 megawatt L-Band injection locked magnetron amplifier is used to drive a 1-1/2 cell RF cavity gun, to produce a 2.5 megavolt electron beam. A tunable RF source relaxes the precision of the cavity gun construction, and therefore simplifies the design and reduces the overall cost. The design of the L-Band ( 1.3 GHz) RF cavity linear accelerator is presented, along with Superfish, SOS computer simulations, and calculations of beam energy and temporal qualities. Measurements of a few robust photocathode materials as well as measurements of the beam qualities of the final accelerator are presented. Future work will utilize new semiconductor laser diodes that can be electrically driven in the gigahertz range. This makes possible an electron gun system which can run at the RF frequency used to accelerate the electron beam. Such a system produces a "lock to clock" and synchronized RF and electron beam source which can be run single shot or any rep rate up to the RF frequency.

  10. AlGaN/InGaN Photocathode Development

    SciTech Connect

    Buckley, J. H.; Leopold, D. J.

    2008-12-24

    An increase in quantum efficiency in photodetectors could result in a proportional reduction in the area of atmospheric Cherenkov telescopes and an even larger reduction in cost. We report on the development of high quantum efficiency, high gain, UV/blue photon-counting detectors based on AlGaN/InGaN photocathode heterostructures grown by molecular beam epitaxy. This research could eventually result in nearly ideal light detectors with a number of distinct advantages over existing technologies for numerous applications in high-energy physics and particle astrophysics. Potential advantages include much lower noise detection, better stability and radiation resistance than other cathode structures, high VUV sensitivity and very low radioactive background levels for deep underground experiments, and high detection efficiency for the detection of individual VUV-visible photons. We are also developing photocathodes with intrinsic gain, initially improving the detection efficiency of hybrid semiconductor-vacuum tube devices and eventually leading to a new type of all-solid-state photomultiplier device.

  11. Transport of Soil Halides through Rice Paddies: A Viable Mechanism for Rapid Dispersion of the Soil Halide Reservoir

    NASA Astrophysics Data System (ADS)

    Redeker, K. R.; Manley, S.; Wang, N.; Cicerone, R.

    2002-05-01

    On short time scales (1-10 years) soil halide concentrations have been assumed to be primarily driven by leaching and deposition processes. Recent results however, have shown that terrestrial plants volatilize soil halides in the form of methyl halides. Emissions of methyl chloride, methyl bromide and methyl iodide represent major pathways for delivery of inorganic halogen radicals to the atmosphere. Inorganic halogen radicals destroy ozone in the stratosphere and modify the oxidative capacity of the lower atmosphere. We have previously shown that rice paddies emit methyl halides and that emissions depend on growth stage of the rice plant as well as field water management. We show here that rice grown in a greenhouse at UCI is capable of volatilizing and/or storing up to 30%, 5%, and 10% of the available chloride, bromide and iodide within the top meter of soil. The percent of plant tissue halide volatilized as methyl halide over the course of the season is calculated to be 0.05%, 0.25% and 85.0% for chloride, bromide and iodide. We compare our greenhouse soil halide concentrations to other commercial rice fields around the world and estimate the e-folding time for soil halides within each region. We suggest that rice agriculture is the driving removal mechanism for halides within rice paddies and that terrestrial plants play a larger role in global cycling of halides than previously estimated.

  12. Observation of Significant Quantum Efficiency Enhancement from a Polarized Photocathode with Distributed Bragg Reflector

    SciTech Connect

    Zhang, Shukui; Poelker, Matthew; Stutzman, Marcy L.; Chen, Yiqiao; Moy, Aaron

    2015-09-01

    Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we present recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator.

  13. A high average current DC GaAs photocathode gun for ERLs and FELs

    SciTech Connect

    C. Hernandez-Garcia; T. Siggins; S. Benson; D. Bullard; H. F. Dylla; K. Jordan; C. Murray; G. R. Neil; Michelle D. Shinn; R. Walker

    2005-05-01

    The Jefferson Lab (JLab) 10 kW IR Upgrade FEL DC GaAs photocathode gun is presently the highest average current electron source operational in the U.S., delivering a record 9.1 mA CW, 350 kV electron beam with 122 pC/bunch at 75 MHz rep rate. Pulsed operation has also been demonstrated with 8 mA per pulse (110 pC/bunch) in 16 ms-long pulses at 2 Hz rep rate. Routinely the gun delivers 5 mA CW and pulse current at 135 pC/bunch for FEL operations. The Upgrade DC photocathode gun is a direct evolution of the DC photocathode gun used in the previous JLab 1 kW IR Demo FEL. Improvements in the vacuum conditions, incorporation of two UHV motion mechanisms (a retractable cathode and a photocathode shield door) and a new way to add cesium to the GaAs photocathode surface have extended its lifetime to over 450 Coulombs delivered between re-cesiations (quantum efficiency replenishment). With each photocathode activation quantum efficiencies above 6% are routinely achieved. The photocathode activation and performance will be described in detail.

  14. Surface Science Analysis of GaAs Photocathodes Following Sustained Electron Beam Delivery

    SciTech Connect

    Shutthanandan, V.; Zhu, Zihua; Stutzman, Marcy L.; Hannon, Fay; Hernandez-Garcia, Carlos; Nandasiri, Manjula I.; Kuchibhatla, Satyanarayana V N T; Thevuthasan, Suntharampillai; Hess, Wayne P.

    2012-06-12

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Several photocathode degradation processes are suspected, including defect formation by ion back bombardment, photochemistry of surface adsorbed species and irradiation-induced surface defect formation. To better understand the mechanisms of photocathode degradation, we have conducted surface and bulk analysis studies of two GaAs photocathodes removed from the FEL photoinjector after delivering electron beam for a few years. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, strained super-lattice GaAs photocathode samples, removed from the CEBAF photoinjector were analyzed using Transmission Electron Microscopy (TEM) and SIMS. This analysis of photocathode degradation during nominal photoinjector operating conditions represents first steps towards developing robust new photocathode designs necessary for generating sub-micron emittance electron beams required for both fourth generation light sources and intense polarized CW electron beams for nuclear and high energy physics facilities.

  15. Flame inhibition by hydrogen halides - Some spectroscopic measurements

    NASA Technical Reports Server (NTRS)

    Lerner, N. R.; Cagliostro, D. E.

    1973-01-01

    The far-ultraviolet absorption spectrum of an air-propane diffusion flame inhibited with hydrogen halides has been studied. Plots of the absorption of light by hydrogen halides as a function of position in the flame and also as a function of the amount of hydrogen halide added to the flame have been obtained. The hydrogen halides are shown to be more stable on the fuel side of the reaction zone than they are on the air side. Thermal diffusion is seen to be important in determining the concentration distribution of the heavier hydrogen halides in diffusion flames. The relationship between the concentration distribution of the hydrogen halides in the flame and the flame inhibition mechanism is discussed.

  16. Morphology-Controlled Synthesis of Organometal Halide Perovskite Inverse Opals.

    PubMed

    Chen, Kun; Tüysüz, Harun

    2015-11-01

    The booming development of organometal halide perovskites in recent years has prompted the exploration of morphology-control strategies to improve their performance in photovoltaic, photonic, and optoelectronic applications. However, the preparation of organometal halide perovskites with high hierarchical architecture is still highly challenging and a general morphology-control method for various organometal halide perovskites has not been achieved. A mild and scalable method to prepare organometal halide perovskites in inverse opal morphology is presented that uses a polystyrene-based artificial opal as hard template. Our method is flexible and compatible with different halides and organic ammonium compositions. Thus, the perovskite inverse opal maintains the advantage of straightforward structure and band gap engineering. Furthermore, optoelectronic investigations reveal that morphology exerted influence on the conducting nature of organometal halide perovskites. PMID:26376773

  17. Lanthanide-halide based humidity indicators

    DOEpatents

    Beitz, James V.; Williams, Clayton W.

    2008-01-01

    The present invention discloses a lanthanide-halide based humidity indicator and method of producing such indicator. The color of the present invention indicates the humidity of an atmosphere to which it is exposed. For example, impregnating an adsorbent support such as silica gel with an aqueous solution of the europium-containing reagent solution described herein, and dehydrating the support to dryness forms a substance with a yellow color. When this substance is exposed to a humid atmosphere the water vapor from the air is adsorbed into the coating on the pore surface of the silica gel. As the water content of the coating increases, the visual color of the coated silica gel changes from yellow to white. The color change is due to the water combining with the lanthanide-halide complex on the pores of the gel.

  18. EVALUATION OF METHODS FOR THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER AND WASTE

    EPA Science Inventory

    Various methods for the determination of total organic halides (TOX) in groundwater and in waste oil samples have been evaluated. Of three inorganic halide species generation approaches and three inorganic halide determinative techniques evaluated for groundwater analyses, one co...

  19. Progress in Understanding Alkali-Alkali Spin Relaxation

    NASA Astrophysics Data System (ADS)

    Erickson, Christopher J.; Happer, William; Chann, Bien; Kadlecek, Stephen; Anderson, L. W.; Walker, Thad G.

    2000-06-01

    In extensive experiments we have shown that a spin interaction with a relatively long correlation time causes much of the spin relaxation in very dense alkali-metal vapors. The spin relaxation is affected by the pressure of the helium or nitrogen buffer gas, although there is little dependence at pressures above one atmosphere. There are substantial differences in the relaxation rates for different isotopes of the same element, for example ^87Rb and ^85Rb. We have completed extensive modeling of how singlet and triplet dimers and doublet trimers of the alkali-metal atoms could cause spin relaxation in dense alkali-metal vapors. In the case of doublet trimers or triplet dimers, we assume the main coupling to the nuclear spins is through the Fermi Contact interaction with the unpaired electrons. Spin loss to the rotation of the molecule is assumed to occur through the electronic spin-rotation and spin-axis (dipole-dipole) interactions for the triplet dimers. For the singlet dimers, we assume that the nuclear spins couple directly to the rotational angular momentum of the molecule through the electric quadrupole interaction. We account for all of the total nuclear spin states that occur for the dimers and trimers. We have also considered the possibility that the collisional breakup and formation rates of the dimers or trimers could saturate with increasing buffer gas pressure. Such saturation occurs in many other unimolecular reactions and is often ascribed to breakup through activated states.

  20. Interpulse kinetics in copper and copper halide lasers

    NASA Technical Reports Server (NTRS)

    Harstad, K. G.

    1983-01-01

    The various rate processes that govern the interpulse relaxation in metal vapor and metal halide vapor lasers are considered. Computer calculations indicate that the rapid metastable levels relaxation observed in copper and copper halide laser experiments requires the existence of a relatively small resonance in the cross section for metastable excitation or deexcitation near threshold. The accurate calculation of interpulse relaxation requires knowledge of rate constants presently not well known; this is especially so for metal halide lasers.

  1. Process and composition for drying of gaseous hydrogen halides

    DOEpatents

    Tom, Glenn M.; Brown, Duncan W.

    1989-08-01

    A process for drying a gaseous hydrogen halide of the formula HX, wherein X is selected from the group consisting of bromine, chlorine, fluorine, and iodine, to remove water impurity therefrom, comprising: contacting the water impurity-containing gaseous hydrogen halide with a scavenger including a support having associated therewith one or more members of the group consisting of: (a) an active scavenging moiety selected from one or more members of the group consisting of: (i) metal halide compounds dispersed in the support, of the formula MX.sub.y ; and (ii) metal halide pendant functional groups of the formula -MX.sub.y-1 covalently bonded to the support, wherein M is a y-valent metal, and y is an integer whose value is from 1 to 3; (b) corresponding partially or fully alkylated compounds and/or pendant functional groups, of the metal halide compounds and/or pendant functional groups of (a); wherein the alkylated compounds and/or pendant functional groups, when present, are reactive with the gaseous hydrogen halide to form the corresponding halide compounds and/or pendant functional groups of (a); and M being selected such that the heat of formation, .DELTA.H.sub.f of its hydrated halide, MX.sub.y.(H.sub.2 O).sub.n, is governed by the relationship: .DELTA.H.sub.f .gtoreq.n.times.10.1 kilocalories/mole of such hydrated halide compound wherein n is the number of water molecules bound to the metal halide in the metal halide hydrate. Also disclosed is an appertaining scavenger composition and a contacting apparatus wherein the scavenger is deployed in a bed for contacting with the water impurity-containing gaseous hydrogen halide.

  2. Properties of CsI and CsI-TMAE photocathodes

    SciTech Connect

    Anderson, D.F.; Kwan, S.; Peskov, V. ); Hoeneisen, B. )

    1992-06-01

    The importance of heating the CsI or CsI-TMAE photocathodes during preparation, as well as the importance of the gas environment on the quantum efficiency is presented. The dependence of the aging characteristics of these photocathodes on the operating temperature, on the presence of gas, and on the charge amplification of the chamber is also discussed. For CsI photocathodes charges in excess of 2{times}10{sup 14} e{sup {minus}}/mm{sup 2} can be collected with little degradation of performance. A timing resolution of 0.55 ns is also achieved for single photoelectrons suggesting a possible time-of-flight detector.

  3. Photocathode non-uniformity contribution to the energy resolution of scintillators.

    PubMed

    Mottaghian, M; Koohi-Fayegh, R; Ghal-Eh, N; Etaati, G R

    2010-06-01

    This paper introduces the basics of the light transport simulation in scintillators and the wavelength-dependencies in the process. The non-uniformity measurement of the photocathode surface is undertaken, showing that for the photocathode used in this study the quantum efficiency falls to about 4 % of its maximum value, especially in areas far from the centre. The wavelength- and position-dependent quantum efficiency is implemented in the Monte Carlo light transport code, showing that, the contribution of the photocathode non-uniformity to the energy resolution is estimated to be around 18 %, when all position- and wavelength-dependencies are included. PMID:20167795

  4. Ion back-bombardment of GaAs photocathodes inside dc high voltage electron guns

    SciTech Connect

    Joseph Grames; Philip Adderley; Joshua Brittian; Daniel Charles; James Clark; John Hansknecht; Benard Poelker; Marcy Stutzman; Kenneth Surles-law

    2005-05-01

    DC high voltage GaAs photoguns are key components at accelerator facilities worldwide. New experiments and new accelerator facilities demand improved performance from these guns, in particular higher current operation and longer photocathode operating lifetime. This conference submission explores bulk GaAs photocathode lifetime as a function of beam current, active photocathode area, laser spot size and the vacuum of the gun and beam line. Lifetime measurements were made at 100 microamps, a beam current relevant for accelerators like CEBAF, and at beam currents of 1 milliamps and 5 milliamps, a regime that is interesting for high current Free Electron Laser (FEL) and Energy Recovery Linac (ERL) operation.

  5. Performance of the 8-in. R5912 photomultiplier tube with super bialkali photocathode

    NASA Astrophysics Data System (ADS)

    Wang, W.; Qian, S.; Xia, J.; Ning, Z.; Cheng, Y.; Qi, M.; Heng, Y.; Wang, Z.; Li, X.; Liu, S.; Lei, X.

    2015-08-01

    An enhanced R5912 family photomultiplier (8-inch.) model with super bialkali photocathode was developed by Hamamatsu. The spectral responses of the standard and enhanced photocathode were compared and a relative increase of 39% at 400 nm was found for the enhanced one. Additional measurements on the relative detection efficiency at a gain of 1E7 showed a consistent improvement of the quantum efficiency. Good uniformity was observed on the super bialkali photocathode. Additional tests proved that both the charge resolution and time properties were not affected by the new cathode technology. Dark count rate and dark current values were found larger in the super bialkali model compared to the standard one.

  6. Lanthanide doped strontium-barium cesium halide scintillators

    SciTech Connect

    Bizarri, Gregory; Bourret-Courchesne, Edith; Derenzo, Stephen E.; Borade, Ramesh B.; Gundiah, Gautam; Yan, Zewu; Hanrahan, Stephen M.; Chaudhry, Anurag; Canning, Andrew

    2015-06-09

    The present invention provides for a composition comprising an inorganic scintillator comprising an optionally lanthanide-doped strontium-barium, optionally cesium, halide, useful for detecting nuclear material.

  7. Positron-alkali atom scattering

    NASA Technical Reports Server (NTRS)

    Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.; Ward, S. J.

    1990-01-01

    Positron-alkali atom scattering was recently investigated both theoretically and experimentally in the energy range from a few eV up to 100 eV. On the theoretical side calculations of the integrated elastic and excitation cross sections as well as total cross sections for Li, Na and K were based upon either the close-coupling method or the modified Glauber approximation. These theoretical results are in good agreement with experimental measurements of the total cross section for both Na and K. Resonance structures were also found in the L = 0, 1 and 2 partial waves for positron scattering from the alkalis. The structure of these resonances appears to be quite complex and, as expected, they occur in conjunction with the atomic excitation thresholds. Currently both theoretical and experimental work is in progress on positron-Rb scattering in the same energy range.

  8. Alkali metal/sulfur battery

    DOEpatents

    Anand, Joginder N.

    1978-01-01

    Alkali metal/sulfur batteries in which the electrolyte-separator is a relatively fragile membrane are improved by providing means for separating the molten sulfur/sulfide catholyte from contact with the membrane prior to cooling the cell to temperatures at which the catholyte will solidify. If the catholyte is permitted to solidify while in contact with the membrane, the latter may be damaged. The improvement permits such batteries to be prefilled with catholyte and shipped, at ordinary temperatures.

  9. Superconductivity in alkali metal fullerides

    NASA Astrophysics Data System (ADS)

    Murphy, D. W.; Rosseinsky, M. J.; Haddon, R. C.; Ramirez, A. P.; Hebard, A. F.; Tycko, R.; Fleming, R. M.; Dabbagh, G.

    1991-12-01

    The recent synthesis of macroscopic quantities of spherical molecular carbon compounds, commonly called fullerenes, has stimulated a wide variety of studies of the chemical and physical properties of this novel class of compounds. We discovered that the smallest of the known fullerenes, C 60, could be made conducting and superconducting by reaction with alkali metals. In this paper, an overview of the motivation for these discoveries and some recent results are presented.

  10. Alkali metal sources for OLED devices

    NASA Astrophysics Data System (ADS)

    Cattaneo, Lorena; Longoni, Giorgio; Bonucci, Antonio; Tominetti, Stefano

    2005-07-01

    In OLED organic layers electron injection is improved by using alkali metals as cathodes, to lower work function or, as dopants of organic layer at cathode interface. The creation of an alkali metal layer can be accomplished through conventional physical vapor deposition from a heated dispenser. However alkali metals are very reactive and must be handled in inert atmosphere all through the entire process. If a contamination takes place, it reduces the lithium deposition rate and also the lithium total yield in a not controlled way. An innovative alkali metal dispensing technology has been developed to overcome these problems and ensure OLED alkali metal cathode reliability. The alkali Metal dispenser, called Alkamax, will be able to release up to a few grams of alkali metals (in particular Li and Cs) throughout the adoption of a very stable form of the alkali metal. Lithium, for example, can be evaporated "on demand": the evaporation could be stopped and re-activated without losing alkali metal yield because the metal not yet consumed remains in its stable form. A full characterization of dispensing material, dispenser configuration and dispensing process has been carried out in order to optimize the evaporation and deposition dynamics of alkali metals layers. The study has been performed applying also inside developed simulations tools.

  11. Atomic hydrogen cleaning of GaAS Photocathodes

    SciTech Connect

    M. Poelker; J. Price; C. Sinclair

    1997-01-01

    It is well known that surface contaminants on semiconductors can be removed when samples are exposed to atomic hydrogen. Atomic H reacts with oxides and carbides on the surface, forming compounds that are liberated and subsequently pumped away. Experiments at Jefferson lab with bulk GaAs in a low-voltage ultra-high vacuum H cleaning chamber have resulted in the production of photocathodes with high photoelectron yield (i.e., quantum efficiency) and long lifetime. A small, portable H cleaning apparatus also has been constructed to successfully clean GaAs samples that are later removed from the vacuum apparatus, transported through air and installed in a high-voltage laser-driven spin-polarized electron source. These results indicate that this method is a versatile and robust alternative to conventional wet chemical etching procedures usually employed to clean bulk GaAs.

  12. Enhanced lifetime hybrid-diffuser cesium reservoir photocathode

    NASA Astrophysics Data System (ADS)

    Montgomery, Eric J.; Pan, Zhigang; Riddick, Blake C.; O'Shea, Patrick G.; Feldman, Donald W.; Jensen, Kevin L.; Ives, R. Lawrence; Falce, Louis R.

    2013-01-01

    A novel self-healing hybrid-diffuser cesium reservoir photocathode is demonstrated. The model-driven design optimizes operating temperature to match diffusion and evaporation rates and maximize quantum efficiency of the cesiated tungsten surface. A sintered-wire tungsten emitter promotes surface uniformity. Cesium loss is less than 0.023 µg/cm2/hr at 125°C, and conservatively extrapolated reservoir lifetime exceeds 30,000 hours. Contamination robustness to a direct atmospheric leak with room-temperature contamination by over 200 Langmuirs of oxidizing gases is excellent, with 90% of maximum QE repeatedly restored via in situ self-healing recesiation under gentle 90°C heating.

  13. Enhanced lifetime hybrid-diffuser cesium reservoir photocathode

    NASA Astrophysics Data System (ADS)

    Montgomery, Eric J.; Pan, Zhigang; Riddick, Blake C.; O'Shea, Patrick G.; Feldman, Donald W.; Jensen, Kevin L.; Ives, R. Lawrence; Falce, Louis R.

    2012-12-01

    A novel self-healing hybrid-diffuser cesium reservoir photocathode is demonstrated. The model-driven design optimizes operating temperature to match diffusion and evaporation rates and maximize quantum efficiency of the cesiated tungsten surface. A sintered-wire tungsten emitter promotes surface uniformity. Cesium loss is less than 0.023 µg/cm2/hr at 125°C, and conservatively extrapolated reservoir lifetime exceeds 30,000 hours. Contamination robustness to a direct atmospheric leak with room-temperature contamination by over 200 Langmuirs of oxidizing gases is excellent, with 90% of maximum QE repeatedly restored via in situ self-healing recesiation under gentle 90°C heating.

  14. Making and Breaking of Lead Halide Perovskites.

    PubMed

    Manser, Joseph S; Saidaminov, Makhsud I; Christians, Jeffrey A; Bakr, Osman M; Kamat, Prashant V

    2016-02-16

    A new front-runner has emerged in the field of next-generation photovoltaics. A unique class of materials, known as organic metal halide perovskites, bridges the gap between low-cost fabrication and exceptional device performance. These compounds can be processed at low temperature (typically in the range 80-150 °C) and readily self-assemble from the solution phase into high-quality semiconductor thin films. The low energetic barrier for crystal formation has mixed consequences. On one hand, it enables inexpensive processing and both optical and electronic tunability. The caveat, however, is that many as-formed lead halide perovskite thin films lack chemical and structural stability, undergoing rapid degradation in the presence of moisture or heat. To date, improvements in perovskite solar cell efficiency have resulted primarily from better control over thin film morphology, manipulation of the stoichiometry and chemistry of lead halide and alkylammonium halide precursors, and the choice of solvent treatment. Proper characterization and tuning of processing parameters can aid in rational optimization of perovskite devices. Likewise, gaining a comprehensive understanding of the degradation mechanism and identifying components of the perovskite structure that may be particularly susceptible to attack by moisture are vital to mitigate device degradation under operating conditions. This Account provides insight into the lifecycle of organic-inorganic lead halide perovskites, including (i) the nature of the precursor solution, (ii) formation of solid-state perovskite thin films and single crystals, and (iii) transformation of perovskites into hydrated phases upon exposure to moisture. In particular, spectroscopic and structural characterization techniques shed light on the thermally driven evolution of the perovskite structure. By tuning precursor stoichiometry and chemistry, and thus the lead halide charge-transfer complexes present in solution, crystallization

  15. Mechanism and Selectivity in Nickel-Catalyzed Cross-Electrophile Coupling of Aryl Halides with Alkyl Halides

    PubMed Central

    Biswas, Soumik; Weix, Daniel J.

    2013-01-01

    The direct cross-coupling of two different electrophiles, such as an aryl halide with an alkyl halide, offers many advantages over conventional cross-coupling methods that require a carbon nucleophile. Despite its promise as a versatile synthetic strategy, a limited understanding of the mechanism and origin of cross selectivity has hindered progress in reaction development and design. Herein, we shed light on the mechanism for the nickel-catalyzed cross-electrophile coupling of aryl halides with alkyl halides and demonstrate that the selectivity arises from an unusual catalytic cycle that combines both polar and radical steps to form the new C-C bond. PMID:23952217

  16. High-speed photocathodes fabricated from metallic nanostructures

    NASA Astrophysics Data System (ADS)

    Nolle, Eduard L.; Khavin, Yuri B.; Schelev, Mikhail Y.

    2005-03-01

    Spectral dependences of photoemission (PE), absorption and reflection from Ag and Au granular films are studied experimentally together with their structure and physical properties using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPES). It is found that a new intensive PE band in the visible spectral range (l = 500 - 600 nm) appears when such films are activated with Cs and O and this PE band coincides with the absorption and reflection bands. Theoretical calculations of PE spectra based on absorption spectrum of metallic oblate spheroidal nanoparticles are also carried out. Such calculations indicate that the appearance of this PE band can be explained by excitation of the surface plasmons in spheroidal nanoparticles with the major axes approximately equal to 50 nm and minor axes approximately equal to 5 nm. Similar calculations carried out for an S-1 photocathode indicate that the shape and the position of the measured long wavelength PE band with the peak maximum at λ ~ 800 nm can also be explained by excitation of the surface plasmons in Ag spheroidal nanoparticles with the axes equal to 25 and 0.9 nm correspondingly. Degradation with time of PE from Ag and Au granular films is also studied and it is shown that while Ag nanoparticles degrade due to desorption of Cs, Au nanoparticles degrade due to its adsorption. Photoelectron emission in the studied metallic nanostructures can be explained by the surface photoeffect caused by excitation of the surface plasmons in nanoparticles. Therefore, photocathodes with subfemtosecond-range temporal resolution and quantum yield equal to several percent in the visible wavelength range can be fabricated from such nanostructures.

  17. Towards a Robust, Efficient Dispenser Photocathode: the Effect of Recesiation on Quantum Efficiency

    SciTech Connect

    Montgomery, Eric J.; Pan Zhigang; Leung, Jessica; Feldman, Donald W.; O'Shea, Patrick G.; Jensen, Kevin L.

    2009-01-22

    Future electron accelerators and Free Electron Lasers (FELs) require high brightness electron sources; photocathodes for such devices are challenged to maintain long life and high electron emission efficiency (high quantum efficiency, or QE). The UMD dispenser photocathode design addresses this tradeoff of robustness and QE. In such a dispenser, a cesium-based surface layer is deposited on a porous substrate. The surface layer can be replenished from a subsurface cesium reservoir under gentle heating, allowing cesium to diffuse controllably to the surface and providing demonstrably more robust photocathodes. In support of the premise that recesiation is able to restore contaminated photocathodes, we here report controlled contamination of cesium-based surface layers with subsequent recesiation and the resulting effect on QE. Contaminant gases investigated include examples known from the vacuum environment of typical electron guns.

  18. Towards a Robust, Efficient Dispenser Photocathode: the Effect of Recesiation on Quantum Efficiency

    NASA Astrophysics Data System (ADS)

    Montgomery, Eric J.; Pan, Zhigang; Leung, Jessica; Feldman, Donald W.; O'Shea, Patrick G.; Jensen, Kevin L.

    2009-01-01

    Future electron accelerators and Free Electron Lasers (FELs) require high brightness electron sources; photocathodes for such devices are challenged to maintain long life and high electron emission efficiency (high quantum efficiency, or QE). The UMD dispenser photocathode design addresses this tradeoff of robustness and QE. In such a dispenser, a cesium-based surface layer is deposited on a porous substrate. The surface layer can be replenished from a subsurface cesium reservoir under gentle heating, allowing cesium to diffuse controllably to the surface and providing demonstrably more robust photocathodes. In support of the premise that recesiation is able to restore contaminated photocathodes, we here report controlled contamination of cesium-based surface layers with subsequent recesiation and the resulting effect on QE. Contaminant gases investigated include examples known from the vacuum environment of typical electron guns.

  19. Ultraviolet response of InGaAsP photocathodes. [for ground based and space applications

    NASA Technical Reports Server (NTRS)

    Feibelman, W. A.

    1977-01-01

    Three type VPM 164 photomultiplier tubes with III-IV compound InGaAsP reflective photocathodes were developed for use in ground-based and space-borne astronomical detectors. Although the achieved response of about 0.02% quantum efficiency at 1.083 microns fell short of the goal of 1% quantum efficiency, the broadband characteristics are still considerably better than those of the S-1 photocathode.

  20. Regenerable activated bauxite adsorbent alkali monitor probe

    DOEpatents

    Lee, Sheldon H. D.

    1992-01-01

    A regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC exhaust gases.

  1. Regenerable activated bauxite adsorbent alkali monitor probe

    DOEpatents

    Lee, S.H.D.

    1992-12-22

    A regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC exhaust gases. 6 figs.

  2. Study on photoemission surface of varied doping GaN photocathode

    NASA Astrophysics Data System (ADS)

    Qiao, Jianliang; Du, Ruijuan; Ding, Huan; Gao, Youtang; Chang, Benkang

    2014-09-01

    For varied doping GaN photocathode, from bulk to surface the doping concentrations are distributed from high to low. The varied doping GaN photocathode may produce directional inside electric field within the material, so the higher quantum efficiency can be obtained. The photoemission surface of varied doping GaN photocathode is very important to the high quantum efficiency, but the forming process of the surface state after Cs activation or Cs/O activation has been not known completely. Encircling the photoemission mechanism of varied GaN photocathode, considering the experiment phenomena during the activation and the successful activation results, the varied GaN photocathode surface model [GaN(Mg):Cs]:O-Cs after activation with cesium and oxygen was given. According to GaN photocathode activation process and the change of electronic affinity, the comparatively ideal NEA property can be achieved by Cs or Cs/O activation, and higher quantum efficiency can be obtained. The results show: The effective NEA characteristic of GaN can be gotten only by Cs. [GaN(Mg):Cs] dipoles form the first dipole layer, the positive end is toward the vacuum side. In the activation processing with Cs/O, the second dipole layer is formed by O-Cs dipoles, A O-Cs dipole includes one oxygen atom and two Cs atoms, and the positive end is also toward the vacuum side thus the escape of electrons can be promoted.

  3. High stability of negative electron affinity gallium arsenide photocathodes activated with Cs and NF3

    NASA Astrophysics Data System (ADS)

    Chanlek, N.; Herbert, J. D.; Jones, R. M.; Jones, L. B.; Middleman, K. J.; Militsyn, B. L.

    2015-09-01

    In this paper we report the first time demonstration under extremely high vacuum (XHV) conditions of the influence of O2, CO2, CO, N2, H2 and CH4 on the quantum efficiency (QE) of negative electron affinity (NEA) gallium arsenide (GaAs) photocathodes activated with Cs and NF3. The photocathodes were exposed to a small quantity (<0.25 Langmuirs) of each gas species under test in a vacuum chamber with a typical base pressure of 1.5× {{10}-11} mbar, thereby minimising the influence of the residual gas in the photocathode response. It was found that exposure to N2, H2 and CH4 does not affect the QE of the photocathodes, whereas exposure to O2 and CO2 lead to a substantial reduction in the QE of the photocathodes. Only small degradation in the QE under CO exposure was observed. Compared to those activated with Cs and O2 in our previous study [1], photocathodes activated with Cs and NF3 are more stable, especially under exposure to CO.

  4. Optical Design Considerations Relevant to Reflective UV Launch Gratings for Photocathode Irradiation

    SciTech Connect

    Bolton, Paul

    2010-12-07

    The characteristics of photoelectron microbunches emitted from a photocathode in response to laser irradiation determine many of the incident laser pulse requirements. RF photocathode designs based on grazing incidence of the irradiation benefit from the removal of launch optics from the electron beamline and enhanced absorption at Brewster angles. However, this also introduces two well known complexities in the laser pulse 'launch' requirements: (i) a transverse spatial anamorphism to guarantee that the projected transverse spatial profile of the irradiation is circular (in the plane of the photocathode) and (ii) a 'time slew' or tilted amplitude front on the laser pulse that is incident on the photocathode to guarantee that the temporal (longitudinal) profiles are synchronous across the entire transverse irradiation profile in the photocathode plane. A single diffraction grating can be used to fulfill these combined requirements. This reported work focuses on grating behavior only. It does not address imaging requirements associated with relayed optical transport from the grating to the photocathode. Because the grating is a highly dispersive optical element by design, the dispersive aspects of all launch requirements are important.

  5. Controlling Metal-Halide Vapor Density in Lasers

    NASA Technical Reports Server (NTRS)

    Pivirotto, T. J.

    1984-01-01

    Streams of buffer gas convect and dilute metal-halide vapor. Technique uses flow of buffer gas through reservoir, which contains heated metal halide, to convect vapors into discharge tube. Second stream of buffer gas dilutes vapor. Final vapor density in laser tube controlled and changed by adjusting either one or both of buffer gas flow rates.

  6. [Emissions of methyl halides from coastal salt marshes: A review].

    PubMed

    Xie, Wen-xia; Zhao, Quan-sheng; Cui, Yu-qian; Du, Hui-na; Ye, Si-yuan

    2015-11-01

    Methyl halides are the major carrier of halogens in the atmosphere, and they play an important role in tropospheric and stratospheric ozone depletion. Meanwhile, methyl halides can act as greenhouse gases in the atmosphere, and they are also environmentally significant because of their toxicity. Coastal salt marshes, the important intertidal ecosystems at the land-ocean interface, have been considered to be a large potential natural source of methyl halides. In this paper, the research status of the natural source or sink of methyl halides, the mechanisms of their emission from coastal salt marshes and affecting factors were summarized. In view of this, the following research fields need to be strengthened in the future: 1) Long time-scale and large region-range researches about the emission of methyl halides and the evaluation of their source and sink function, 2) Accurate quantification of contribution rates of different plant species and various biological types to fluxes of methyl halides, 3) Further researches on effects of the tidal fluctuation process and flooding duration on methyl halides emission, 4) Effects of the global change and human activities on methyl halides emission. PMID:26915215

  7. Resolution characteristics of graded band-gap reflection-mode AlGaAs/GaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Deng, Wenjuan; Zhang, Daoli; Zou, Jijun; Peng, Xincun; Wang, Weilu; Zhang, Yijun; Chang, Benkang

    2015-12-01

    The modulation transfer function (MTF) of graded band-gap AlGaAs/GaAs reflection-mode photocathodes was determined using two-dimensional Poisson and continuity equations through numerical method. Based on the MTF model, we calculated the theoretical MTF of graded and uniform band-gap reflection-mode photocathodes. We then analyzed the effects of Al composition, wavelength of incident photon, and thicknesses of AlGaAs and GaAs layer on the resolution. Calculation results show that graded band-gap structures can increase the resolution of reflection-mode photocathodes. When the spatial frequency is 800 lp/mm and wavelength is 600 nm, the resolution of graded band-gap photocathodes generally increases by 15.4-29.6%. The resolution improvement of graded band-gap photocathodes is attributed to the fact that the built-in electric field in graded band-gap photocathodes reduces the lateral diffusion distance of photoelectrons.

  8. How specific halide adsorption varies hydrophobic interactions.

    PubMed

    Stock, Philipp; Müller, Melanie; Utzig, Thomas; Valtiner, Markus

    2016-03-01

    Hydrophobic interactions (HI) are driven by the water structure around hydrophobes in aqueous electrolytes. How water structures at hydrophobic interfaces and how this influences the HI was subject to numerous studies. However, the effect of specific ion adsorption on HI and hydrophobic interfaces remains largely unexplored or controversial. Here, the authors utilized atomic force microscopy force spectroscopy at well-defined nanoscopic hydrophobic interfaces to experimentally address how specific ion adsorption of halide ions as well as NH4 (+), Cs(+), and Na(+) cations alters interaction forces across hydrophobic interfaces. Our data demonstrate that iodide adsorption at hydrophobic interfaces profoundly varies the hydrophobic interaction potential. A long-range and strong hydration repulsion at distances D > 3 nm, is followed by an instability which could be explained by a subsequent rapid ejection of adsorbed iodides from approaching hydrophobic interfaces. In addition, the authors find only a weakly pronounced influence of bromide, and as expected no influence of chloride. Also, all tested cations do not have any significant influence on HI. Complementary, x-ray photoelectron spectroscopy and quartz-crystal-microbalance with dissipation monitoring showed a clear adsorption of large halide ions (Br(-)/I(-)) onto hydrophobic self-assembled monolayers (SAMs). Interestingly, iodide can even lead to a full disintegration of SAMs due to specific and strong interactions of iodide with gold. Our data suggest that hydrophobic surfaces are not intrinsically charged negatively by hydroxide adsorption, as it was generally believed. Hydrophobic surfaces rather interact strongly with negatively charged large halide ions, leading to a surface charging and significant variation of interaction forces. PMID:26753786

  9. Ultraviolet absorption spectra of mercuric halides.

    NASA Technical Reports Server (NTRS)

    Templet, P.; Mcdonald, J. R.; Mcglynn, S. P.; Kendrow, C. H.; Roebber, J. L.; Weiss, K.

    1972-01-01

    The gas phase transitions of the mercuric halides were observed in the UV region by operating at temperatures above 400 K and at vapor pressures on the order of 0.5 mm. Spectral features exhibited by the chloride, bromide, and iodide of mercury correlate energetically with bands previously designated as intermolecular charge transfer transitions. The solution spectra of mercuric iodide and deep color of the crystals (if not due to some solid state interactions) indicate that this molecule may also have longer wavelength transitions.

  10. Raman spectra of hydroxide-halide melts

    NASA Astrophysics Data System (ADS)

    Zakiriyanova, I. D.; Khokhlov, V. A.

    2012-08-01

    The Raman spectra of molten binary mixtures based on sodium hydroxide and containing (mol %) 35 NaCl, 30 NaBr, and 30 NaI have been recorded at various temperatures. An increase in the vibrational frequency and the force constant of the O-H bond is detected under isothermal conditions upon a variation of the anionic composition of a melt in the series I → Br → Cl. Based on the experimental data, the viscosity of the hydroxide-halide melts is estimated.

  11. Alkali-Metal Spin Maser.

    PubMed

    Chalupczak, W; Josephs-Franks, P

    2015-07-17

    Quantum measurement is a combination of a read-out and a perturbation of the quantum system. We explore the nonlinear spin dynamics generated by a linearly polarized probe beam in a continuous measurement of the collective spin state in a thermal alkali-metal atomic sample. We demonstrate that the probe-beam-driven perturbation leads, in the presence of indirect pumping, to complete polarization of the sample and macroscopic coherent spin oscillations. As a consequence of the former we report observation of spectral profiles free from collisional broadening. Nonlinear dynamics is studied through exploring its effect on radio frequency as well as spin noise spectra. PMID:26230788

  12. 10 CFR 429.54 - Metal halide lamp ballasts and fixtures.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 3 2012-01-01 2012-01-01 false Metal halide lamp ballasts and fixtures. 429.54 Section... CONSUMER PRODUCTS AND COMMERCIAL AND INDUSTRIAL EQUIPMENT Certification § 429.54 Metal halide lamp ballasts... are applicable to metal halide lamp ballasts; and (2) For each basic model of metal halide...

  13. 10 CFR 429.54 - Metal halide lamp ballasts and fixtures.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 3 2014-01-01 2014-01-01 false Metal halide lamp ballasts and fixtures. 429.54 Section... CONSUMER PRODUCTS AND COMMERCIAL AND INDUSTRIAL EQUIPMENT Certification § 429.54 Metal halide lamp ballasts... are applicable to metal halide lamp ballasts; and (2) For each basic model of metal halide...

  14. 10 CFR 429.54 - Metal halide lamp ballasts and fixtures.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 3 2013-01-01 2013-01-01 false Metal halide lamp ballasts and fixtures. 429.54 Section... CONSUMER PRODUCTS AND COMMERCIAL AND INDUSTRIAL EQUIPMENT Certification § 429.54 Metal halide lamp ballasts... are applicable to metal halide lamp ballasts; and (2) For each basic model of metal halide...

  15. Indium phosphide negative electron affinity photocathodes: Surface cleaning and activation

    NASA Astrophysics Data System (ADS)

    Sun, Yun

    InP(100) is a very important semi-conductor for many applications. When activated by Cs and oxygen, the InP surface achieves the state of Negative Electron Affinity (NEA) making the Cs+O/InP system a very efficient electron source. Despite many years of study, the chemical cleaning and activation of InP are still not well understood. In our work, we have established an understanding of the basic physics and chemistry for the chemical cleaning and activation of the InP(100) surface. Synchrotron Radiation Photoelectron Spectroscopy is the main technique used in this study because of its high surface sensitivity and ability to identify chemical species present on the surface at each stage of our process. A clean, stoichiometric InP(100) surface is crucial for obtaining high performance of NEA photocathodes. Therefore, the first part of our study focused on the chemical cleaning of InP(100). We found that hydrogen peroxide based solutions alone, originally developed to clean GaAs(100) surfaces and widely used for InP(100), do not result in clean InP(I00) surfaces because oxide is left on the surface. A second cleaning step, which uses acid solutions like HCl or H2SO4, can remove all the oxide and leave a 0.4 ML protective layer of elemental phosphorous on the surface. The elemental phosphorous can be removed by annealing at 330°C and a clean InP(100) surface can be obtained. Cs deposition on InP(100) surface shows clear charge transfer from the Cs ad-atoms to the substrate. When the Cs/InP(100) surface is dosed with oxygen, the charge transfer from the Cs to substrate is reduced and substrate is oxidized. The activation of InP as a NEA photocathode is carried out by an alternating series of steps consisting of Cs deposition and Cs+O co-deposition. Two types of oxygen are found after activation. The first is dissociated oxygen and the other is a di-oxygen species (peroxide or superoxide). The decay of quantum-yield with time and with annealing is studied and changes in

  16. Methyl halide production associated with kelp

    NASA Technical Reports Server (NTRS)

    Dastoor, Minoo N.; Manley, Steven L.

    1985-01-01

    Methyl halides (MeX) are important trace constituents of the atmosphere because they, mostly MeCl, have a major impact on the atmospheric ozone layer. Also, MeCl may account for 5 pct. of the total Cl budget and MeI may have a central role in the biogeochemical cycling of iodine. High MeI concentrations were found in seawater from kelp beds and it has been suggested that MeI is produced by kelps and that MeI and MeBr along with numerous other halocarbons were released by non-kelp marine macroalgae. The objective was to determine if kelps (and other seaweeds) are sources of MeX and to assess their contribution to the estimated global source strength (EGSS) of MeX. Although the production of MeX appears to be associated with kelp, microbes involved with kelp degradation also produce MeX. Microbial MeX production may be of global significance. The microbial MeX production potential, assuming annual kelp production equals kelp degradation and 100 pct. conversion of kelp halides to MeX, is approx. 2 x the EGSS. This is not achieved but indicates that microbial production of MeX may be of global significance.

  17. Finding new perovskite halides via machine learning

    DOE PAGESBeta

    Pilania, Ghanshyam; Balachandran, Prasanna V.; Kim, Chiho; Lookman, Turab

    2016-04-26

    Advanced materials with improved properties have the potential to fuel future technological advancements. However, identification and discovery of these optimal materials for a specific application is a non-trivial task, because of the vastness of the chemical search space with enormous compositional and configurational degrees of freedom. Materials informatics provides an efficient approach toward rational design of new materials, via learning from known data to make decisions on new and previously unexplored compounds in an accelerated manner. Here, we demonstrate the power and utility of such statistical learning (or machine learning, henceforth referred to as ML) via building a support vectormore » machine (SVM) based classifier that uses elemental features (or descriptors) to predict the formability of a given ABX3 halide composition (where A and B represent monovalent and divalent cations, respectively, and X is F, Cl, Br, or I anion) in the perovskite crystal structure. The classification model is built by learning from a dataset of 185 experimentally known ABX3 compounds. After exploring a wide range of features, we identify ionic radii, tolerance factor, and octahedral factor to be the most important factors for the classification, suggesting that steric and geometric packing effects govern the stability of these halides. As a result, the trained and validated models then predict, with a high degree of confidence, several novel ABX3 compositions with perovskite crystal structure.« less

  18. Finding New Perovskite Halides via Machine learning

    NASA Astrophysics Data System (ADS)

    Pilania, Ghanshyam; Balachandran, Prasanna V.; Kim, Chiho; Lookman, Turab

    2016-04-01

    Advanced materials with improved properties have the potential to fuel future technological advancements. However, identification and discovery of these optimal materials for a specific application is a non-trivial task, because of the vastness of the chemical search space with enormous compositional and configurational degrees of freedom. Materials informatics provides an efficient approach towards rational design of new materials, via learning from known data to make decisions on new and previously unexplored compounds in an accelerated manner. Here, we demonstrate the power and utility of such statistical learning (or machine learning) via building a support vector machine (SVM) based classifier that uses elemental features (or descriptors) to predict the formability of a given ABX3 halide composition (where A and B represent monovalent and divalent cations, respectively, and X is F, Cl, Br or I anion) in the perovskite crystal structure. The classification model is built by learning from a dataset of 181 experimentally known ABX3 compounds. After exploring a wide range of features, we identify ionic radii, tolerance factor and octahedral factor to be the most important factors for the classification, suggesting that steric and geometric packing effects govern the stability of these halides. The trained and validated models then predict, with a high degree of confidence, several novel ABX3 compositions with perovskite crystal structure.

  19. Process for the disposal of alkali metals

    DOEpatents

    Lewis, Leroy C.

    1977-01-01

    Large quantities of alkali metals may be safely reacted for ultimate disposal by contact with a hot concentrated caustic solution. The alkali metals react with water in the caustic solution in a controlled reaction while steam dilutes the hydrogen formed by the reaction to a safe level.

  20. The alkali metals: 200 years of surprises.

    PubMed

    Dye, James L

    2015-03-13

    Alkali metal compounds have been known since antiquity. In 1807, Sir Humphry Davy surprised everyone by electrolytically preparing (and naming) potassium and sodium metals. In 1808, he noted their interaction with ammonia, which, 100 years later, was attributed to solvated electrons. After 1960, pulse radiolysis of nearly any solvent produced solvated electrons, which became one of the most studied species in chemistry. In 1968, alkali metal solutions in amines and ethers were shown to contain alkali metal anions in addition to solvated electrons. The advent of crown ethers and cryptands as complexants for alkali cations greatly enhanced alkali metal solubilities. This permitted us to prepare a crystalline salt of Na(-) in 1974, followed by 30 other alkalides with Na(-), K(-), Rb(-) and Cs(-) anions. This firmly established the -1 oxidation state of alkali metals. The synthesis of alkalides led to the crystallization of electrides, with trapped electrons as the anions. Electrides have a variety of electronic and magnetic properties, depending on the geometries and connectivities of the trapping sites. In 2009, the final surprise was the experimental demonstration that alkali metals under high pressure lose their metallic character as the electrons are localized in voids between the alkali cations to become high-pressure electrides! PMID:25666067

  1. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    NASA Astrophysics Data System (ADS)

    Shutthanandan, V.; Zhu, Z.; Stutzman, M. L.; Hannon, F. E.; Hernandez-Garcia, C.; Nandasiri, M. I.; Kuchibhatla, S. V. N. T.; Thevuthasan, S.; Hess, W. P.

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL). Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS), atomic force microscopy, and secondary ion mass spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF) photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  2. Comparative research on the transmission-mode GaAs photocathodes of exponential-doping structures

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Qian, Yun-Sheng; Zhang, Yi-Jun; Chang, Ben-Kang

    2012-03-01

    Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have been proven to have a higher quantum efficiency than uniform doping structures. On the basis of our early research on the surface photovoltage of GaAs photocathodes, and comparative research before and after activation of reflection-mode GaAs photocathodes, we further the comparative research on transmission-mode GaAs photocathodes. An exponential doping structure is the typical varied doping structure that can form a uniform electric field in the active layer. By solving the one-dimensional diffusion equation for no equilibrium minority carriers of transmission-mode GaAs photocathodes of the exponential doping structure, we can obtain the equations for the surface photovoltage (SPV) curve before activation and the spectral response curve (SRC) after activation. Through experiments and fitting calculations for the designed material, the body-material parameters can be well fitted by the SPV before activation, and proven by the fitting calculation for SRC after activation. Through the comparative research before and after activation, the average surface escape probability (SEP) can also be well fitted. This comparative research method can measure the body parameters and the value of SEP for the transmission-mode GaAs photocathode more exactly than the early method, which only measures the body parameters by SRC after activation. It can also help us to deeply study and exactly measure the parameters of the varied doping structures for transmission-mode GaAs photocathodes, and optimize the Cs-O activation technique in the future.

  3. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    SciTech Connect

    Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  4. Tellurite glass as a waste form for mixed alkali-chloride waste streams: Candidate materials selection and initial testing

    NASA Astrophysics Data System (ADS)

    Riley, Brian J.; Rieck, Bennett T.; McCloy, John S.; Crum, Jarrod V.; Sundaram, S. K.; Vienna, John D.

    2012-05-01

    Tellurite glasses have historically been shown to host large concentrations of halides. They are here considered for the first time as a waste form for immobilizing chloride wastes, such as may be generated in the proposed molten alkali salt electrochemical separations step in nuclear fuel reprocessing. Key properties of several tellurite glasses are determined to assess acceptability as a chloride waste form. TeO2 glasses with other oxides (PbO, Al2O3 + B2O3, WO3, P2O5, or ZnO) were fabricated with and without 10 mass% of a simulated (non-radioactive) mixed alkali, alkaline-earth, and rare earth chloride waste. Measured chemical durability is compared for the glasses, as determined by the product consistency test (PCT), a common standardized chemical durability test often used to validate borosilicate glass waste forms. The glass with the most promise as a waste form is the TeO2-PbO system, as it offers good halide retention, a low sodium release (by PCT) comparable with high-level waste silicate glass waste forms, and a high storage density.

  5. Method of handling radioactive alkali metal waste

    DOEpatents

    Wolson, Raymond D.; McPheeters, Charles C.

    1980-01-01

    Radioactive alkali metal is mixed with particulate silica in a rotary drum reactor in which the alkali metal is converted to the monoxide during rotation of the reactor to produce particulate silica coated with the alkali metal monoxide suitable as a feed material to make a glass for storing radioactive material. Silica particles, the majority of which pass through a 95 mesh screen or preferably through a 200 mesh screen, are employed in this process, and the preferred weight ratio of silica to alkali metal is 7 to 1 in order to produce a feed material for the final glass product having a silica to alkali metal monoxide ratio of about 5 to 1.

  6. Method of handling radioactive alkali metal waste

    DOEpatents

    Wolson, R.D.; McPheeters, C.C.

    Radioactive alkali metal is mixed with particulate silica in a rotary drum reactor in which the alkali metal is converted to the monoxide during rotation of the reactor to produce particulate silica coated with the alkali metal monoxide suitable as a feed material to make a glass for storing radioactive material. Silica particles, the majority of which pass through a 95 mesh screen or preferably through a 200 mesh screen, are employed in this process, and the preferred weight ratio of silica to alkali metal is 7 to 1 in order to produce a feed material for the final glass product having a silica to alkali metal monoxide ratio of about 5 to 1.

  7. BEAM EXPOSURE DEPENDENCE AND MECHANISMS OF PHOTON-STIMULATED DESORPTION FROM ALKALI FLUORIDES

    SciTech Connect

    Parks, C.C.; Shirley, D.A.; Loubriel, G.

    1983-11-01

    Photon-stimulated desorption experiments were performed on the (001) face of LiF for photon energies near the F(2s) and Li(ls) edges (from 37 to 72 eV). There are structures in the F{sup +} yield above the F(2s) edge which are absent in the Li{sup +} spectrum, differences in detail in the Li{sup +} and F{sup +} yields near the Li(1s) edge, and considerable broadening of the desorption yields as compared to the bulk photoabsorption spectrum. The first observation of a strong x-ray, and visible, beam exposure dependence of ion yields from LiF and NaF is also presented. These results are discussed in terms of electronic and defect properties of alkali halides.

  8. Beyond injection: Trojan horse underdense photocathode plasma wakefield acceleration

    SciTech Connect

    Hidding, B.; Rosenzweig, J. B.; Xi, Y.; O'Shea, B.; Andonian, G.; Schiller, D.; Barber, S.; Williams, O.; Pretzler, G.; Koenigstein, T.; Kleeschulte, F.; Hogan, M. J.; Litos, M.; Corde, S.; White, W. W.; Muggli, P.; Bruhwiler, D. L.; Lotov, K.

    2012-12-21

    An overview on the underlying principles of the hybrid plasma wakefield acceleration scheme dubbed 'Trojan Horse' acceleration is given. The concept is based on laser-controlled release of electrons directly into a particle-beam-driven plasma blowout, paving the way for controlled, shapeable electron bunches with ultralow emittance and ultrahigh brightness. Combining the virtues of a low-ionization-threshold underdense photocathode with the GV/m-scale electric fields of a practically dephasing-free beam-driven plasma blowout, this constitutes a 4th generation electron acceleration scheme. It is applicable as a beam brightness transformer for electron bunches from LWFA and PWFA systems alike. At FACET, the proof-of-concept experiment 'E-210: Trojan Horse Plasma Wakefield Acceleration' has recently been approved and is in preparation. At the same time, various LWFA facilities are currently considered to host experiments aiming at stabilizing and boosting the electron bunch output quality via a trojan horse afterburner stage. Since normalized emittance and brightness can be improved by many orders of magnitude, the scheme is an ideal candidate for light sources such as free-electron-lasers and those based on Thomson scattering and betatron radiation alike.

  9. Oxidatively Stable Nanoporous Silicon Photocathodes for Photoelectrochemical Hydrogen Evolution

    SciTech Connect

    Neale, Nathan R.; Zhao, Yixin; Zhu, Kai; Oh, Jihun; van de Lagemaat, Jao; Yuan, Hao-Chih; Branz, Howard M.

    2014-06-02

    Stable and high-performance nanoporous 'black silicon' photoelectrodes with electrolessly deposited Pt nanoparticle (NP) catalysts are made with two metal-assisted etching steps. Doubly etched samples exhibit >20 mA/cm2 photocurrent density at +0.2 V vs. reversible hydrogen electrode (RHE) for photoelectrochemical hydrogen evolution under 1 sun illumination. We find that the photocurrent onset voltage of black Si photocathodes prepared from single-crystal planar Si wafers increases in oxidative environments (e.g., aqueous electrolyte) owing to a positive flat-band potential shift caused by surface oxidation. However, this beneficial oxide layer becomes a kinetic barrier to proton reduction that inhibits hydrogen production after just 24 h. To mitigate this problem, we developed a novel second Pt-assisted etch process that buries the Pt NPs deeper into the nanoporous Si surface. This second etch shifts the onset voltage positively, from +0.25 V to +0.4 V vs. RHE, and reduces the charge-transfer resistance with no performance decrease seen for at least two months.

  10. The III-V photocathode - A major detector development.

    NASA Technical Reports Server (NTRS)

    Spicer, W. E.; Bell, R. L.

    1972-01-01

    Description of new (III-V) photocathodes which show improvements in sensitivity of as much as ten to a hundred times over conventional cathodes in the near infrared and useful improvements at shorter wavelengths. The development stems from a combination of basic knowledge of the photoemission process, gained in the 1950s, and the advancing understanding of the technology of III-V materials, in the 1960s. The superior performance of these cathodes is due to the fact that the vacuum level at the surface lies below the bottom of the conduction band in the bulk of the material. Consequently, the threshold of response is set by the III-V bandgap. The bandgap (and the threshold of response) can be varied by alloying different III-V materials together. A reduction in thermionic emission is realized with these cathodes. At present no semitransparent III-V cathodes with comparably interesting performance are available. The problems hindering further improvements, as well as the problems of placing these cathodes in practical multipliers and image tubes, are discussed briefly.

  11. Fabrication of GaAs/GaAsP superlattice photocathode

    NASA Astrophysics Data System (ADS)

    Watanabe, O.; Nishitani, T.; Togawa, K.; Takashima, Y.; Nakanishi, T.; Takeda, Y.; Kobayakawa, H.

    2001-06-01

    Several samples of GaAs/GaAsP superlattice were fabricated using a method of the Metalorganic Chemical Vapor Deposition (MOCVD) growth for the purpose of investigating various properties as a photocathode of spin-polarized electron sources. The MOCVD growth is easy to control in comparison with the Molecular Beam Epitaxial (MBE) growth in the fabrication procedure of the GaAs/GaAsP superlattices. We used Tertiarybutylarsine (TBAs) and Tertiarybutylphophine (TBP) as V-group sources to make the samples. It is for this reason that the toxicity of TBAs and TBP is lower than that of arsine (AsH3) and phosphine (PH3) which are commonly used, and the pyrolysis temperature for TBAs and TBP is lower than that for AsH3 and PH3 [1]. A large spin-polarization exceeding 90% was observed using the sample made in this method. We also obtained large quantum efficiencies of approximately 0.4% in the wavelength range from 760 nm to 780 nm. .

  12. High brightness photocathode injector for BNL Accelerator Test Facility

    SciTech Connect

    Parsa, Z.; Young, L.

    1990-01-01

    An analysis of the BNL photocathode (1-1/2 cell) Gun'' operating at 2856 MHZ, is presented. The beam parameters including beam energy, and emittance are calculated. A review of the Gun parameters and full input and output of our analysis with program PARMELA, is given in Section 2, some of our results, are tabulated. The phase plots and the beam parameters, at downstream ends of the elements, from cathode through the cavity, first cell is labeled as element 2; and second cell is labeled as element to the exit of the GUN. The analysis was made for 3 cases, using three different initial values (EO) for the average accelerating gradient (MV/m), for comparison with previous works. For illustration, the field obtained with program SUPERFISH is given, and conclusion including shunt impedances obtained for the cells and the cavity are given in Section 6. PARMELA is used as a standard design program at ATF. At the request of some of the users of program PARMELA, this request of some of the users of program PARMELA, this report include and illustrates some of our data, in the input and output format of the program PARMELA. 5 refs., 7 figs., 3 tabs.

  13. Beyond injection: Trojan horse underdense photocathode plasma wakefield acceleration

    NASA Astrophysics Data System (ADS)

    Hidding, B.; Rosenzweig, J. B.; Xi, Y.; O'Shea, B.; Andonian, G.; Schiller, D.; Barber, S.; Williams, O.; Pretzler, G.; Königstein, T.; Kleeschulte, F.; Hogan, M. J.; Litos, M.; Corde, S.; White, W. W.; Muggli, P.; Bruhwiler, D. L.; Lotov, K.

    2012-12-01

    An overview on the underlying principles of the hybrid plasma wakefield acceleration scheme dubbed "Trojan Horse" acceleration is given. The concept is based on laser-controlled release of electrons directly into a particle-beam-driven plasma blowout, paving the way for controlled, shapeable electron bunches with ultralow emittance and ultrahigh brightness. Combining the virtues of a low-ionization-threshold underdense photocathode with the GV/m-scale electric fields of a practically dephasing-free beam-driven plasma blowout, this constitutes a 4th generation electron acceleration scheme. It is applicable as a beam brightness transformer for electron bunches from LWFA and PWFA systems alike. At FACET, the proof-of-concept experiment "E-210: Trojan Horse Plasma Wakefield Acceleration" has recently been approved and is in preparation. At the same time, various LWFA facilities are currently considered to host experiments aiming at stabilizing and boosting the electron bunch output quality via a trojan horse afterburner stage. Since normalized emittance and brightness can be improved by many orders of magnitude, the scheme is an ideal candidate for light sources such as free-electron-lasers and those based on Thomson scattering and betatron radiation alike.

  14. Adsorption of hydrated halide ions on charged electrodes: Molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Glosli, James N.; Philpott, Michael R.

    1993-04-01

    Constant temperature molecular dynamics has been used to simulate the adsorption of hydrated halide ion X(-) = F(-), Cl(-), Br(-), and I(-), and lithium ion Li(+) on a flat uniformly charged surfaces. The simulations were done with either 214 water molecules and two ions (Li(+) and X(-)) in a box 2.362 nm deep or with 430 water molecules and the two ions in a box 4.320 nm deep. The boxes were periodically replicated in the xy directions. The magnitude of the surface charge on the box end was + or - 0.11 c/nm(sup 2), corresponding to an electric field of 2 x 10(exp 7) V/cm. The lateral dimensions of the simulation cell were 1.862 nm x 1.862 nm (x times y) in each case. All of the water molecules and ions interacted with the end walls via a weak 9 - 3 potential. The ST2 water model and parameters optimized for alkali halides interacting with the model ST2 water molecule were used in the calculations. Common practices of truncating the interactions at a finite distance (0.82 nm) and switching off Coulomb interactions at small distances were followed. The temperature was set at T = 2.411 kJ/mole (290 K). Some of the properties calculated were: distribution density profiles for ions and water across the gap important for comparisons iwth Gouy-Chapman theory, adsorbed ion-water pair correlation functions, the number of water molecules in the first and second hydration shells of the ions as a function of time. The time spent by a water molecule in the hydration shell was calculated to be approximately ten times longer for lithium than any other ion. The correlation between distance from the electrode and hydration number was studied and generally found to be pronounced for the larger anions.

  15. Photoemission characteristics of graded band-gap AlGaAs/GaAs wire photocathode

    NASA Astrophysics Data System (ADS)

    Ding, Xiaojun; Ge, Xiaowan; Zou, Jijun; Zhang, Yijun; Peng, Xincun; Deng, Wenjuan; Chen, Zhaoping; Zhao, Wenjun; Chang, Benkang

    2016-05-01

    A photoemission model of graded band-gap AlGaAs/GaAs wire NEA photocathode is developed based on the numerical solution of coupled Poisson and continuity equations. The emission current density and integral sensitivity of graded band-gap AlGaAs/GaAs wire photocathode as a function of incident light wavelength, Al composition range, and wire length, are simulated according to the model. The simulation results show that, compared with the GaAs (Al composition 0) wire photocathode, the peak integral sensitivities for the photocathodes with wire width of 1 μm and linearly graded Al composition ranges of 0 to 0.1, 0.2, 0.3, and 0.4 increase by 29.5%, 38.5%, 42.1%, and 43.8%, respectively. The optimum wire lengths are 4.7, 5.9, 7.1, and 8.4 μm for the wire photocathodes with Al composition ranges of 0 to 0.1, 0.2, 0.3, and 0.4, respectively.

  16. A mechanism of Cu work function reduction in CsBr/Cu photocathodes.

    PubMed

    Halliday, M T E; Hess, W P; Shluger, A L

    2016-03-14

    Thin films of CsBr deposited on Cu(100) have been proposed as next-generation photocathode materials for applications in particle accelerators and free-electron lasers. However, the mechanisms underlying an improved photocathode performance as well as their long-term stability remain poorly understood. We present Density Functional Theory (DFT) calculations of the work function reduction following the application of CsBr thin film coatings to Cu photocathodes. The effects of both flat and rough interface and van der Waals forces are examined. Calculations suggest that CsBr films can reduce the Cu(100) work function by about 1.5 eV, which would explain the observed increase in quantum efficiency (QE) of coated vs. uncoated photocathodes. A model explaining the experimentally observed laser activation of photocathodes is provided whereby the photo-induced creation of Br vacancies and Cs-Br di-vacancies and their subsequent diffusion to the Cu/CsBr interface lead to a further increase in QE after a period of laser irradiation. PMID:26899524

  17. A mechanism of Cu work function reduction in CsBr/Cu photocathodes

    DOE PAGESBeta

    Halliday, M. T. E.; Hess, W. P.; Shluger, A. L.

    2016-02-15

    Thin films of CsBr deposited on Cu(100) have been proposed as next-generation photocathode materials for applications in particle accelerators and free-electron lasers. However, the mechanisms underlying an improved photocathode performance remain poorly understood. We present density Functional Theory (DFT) calculations of the work function reduction following the application of CsBr thin film coatings to Cu photocathodes. The effects of structure and van der Waals forces are examined. Calculations suggest that CsBr films can reduce the work function by around 1.5 eV, which would explain the exponential increase in quantum efficiency (QE) of coated vs. uncoated photocathodes. In conclusion, a modelmore » explaining experimentally observed laser activation of photocathode is provided whereby the photo-induced creation of di-vacancies at the surface, and their subsequent diffusion throughout the lattice and segregation at the interface leads to a further increase in QE after a period of laser irradiation.« less

  18. Growth and characterization of indium gallium arsenide photocathodes for extended near infrared imaging

    NASA Astrophysics Data System (ADS)

    Bourree, Loig Erwan Richard

    Near infrared InGaAs photocathodes were designed and grown using molecular beam epitaxy (MBE), a high quality semiconductor growth technique, for the purpose of expanding the current spectral range of generation 3 image intensifier tubes to a 1000nm wavelength while maintaining a high quantum efficiency. Previous authors who have attempted this task have reported low sensitivity compared to the standard GaAs photocathodes and associated this drawback with the compositional mismatch from growing InGaAs epilayers onto GaAs substrates. Our approach differed from these previous authors by using MBE for the semiconductor growth instead of a vapor phase epitaxy technique that had been employed. In addition, to reduce the inherent lattice mismatch between the InGaAs photoemissive layer and the substrate, structures deviating from standard GaAs photocathodes were created, to include lattice-mismatch reducing buffers. These buffers are composed of ternary alloys with graded composition. Utilizing a variety of characterization techniques to determine growth parameters (thickness, doping, composition, crystallinity) a high level of control and reproducibility was achieved on our photocathode structures. Overall, negative electron affinity activation performed on our InGaAs photocathodes showed improvements in their white light photoresponse (PR) resulting from the inclusion of these buffers. Studies performed using room temperature photoluminescence, Raman spectroscopy and atomic force microscopy were employed to attempt relating these increases in PR to changes in material parameters and are presented in this dissertation.

  19. Design of quantum efficiency measurement system for variable doping GaAs photocathode

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

    2008-03-01

    To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

  20. Spectral response variation of a negative-electron-affinity photocathode in the preparation process.

    PubMed

    Liu, Lei; Du, Yujie; Chang, Benkang; Yunsheng, Qian

    2006-08-20

    In order to research the spectral response variation of a negative electron affinity (NEA) photocathode in the preparation process, we have done two experiments on a transmission-type GaAs photocathode. First, an automatic spectral response recording system is described, which is used to take spectral response curves during the activation procedure of the photocathode. By this system, the spectral response curves of a GaAs:Cs-O photocathode measured in situ are presented. Then, after the cathode is sealed with a microchannel plate and a fluorescence screen into the image tube, we measure the spectral response of the tube by another measurement instrument. By way of comparing and analyzing these curves, we can find the typical variation in spectral-responses. The reasons for the variation are discussed. Based on these curves, spectral matching factors of a GaAs cathode for green vegetation and rough concrete are calculated. The visual ranges of night-vision goggles under specific circumstances are estimated. The results show that the spectral response of the NEA photocathode degraded in the sealing process, especially at long wavelengths. The variation has also influenced the whole performance of the intensifier tube. PMID:16892108

  1. FUV quantum efficiency degradation of cesium iodide photocathodes caused by exposure to thermal atomic oxygen

    NASA Astrophysics Data System (ADS)

    McPhate, Jason; Anne, Joshi; Bacinski, John; Banks, Bruce; Cates, Carey; Christensen, Paul; Cruden, Brett; Dunham, Larry; Graham, Eric; Hughes, David; Kimble, Randy; Lupie, Olivia; Niedner, Malcolm; Osterman, Steven; Penton, Steven; Proffitt, Charles; Pugel, Diane; Siegmund, Oswald; Wheeler, Thomas

    2011-09-01

    The color dependence of the measured decline of the on-orbit sensitivity of the FUV channel of the HST Cosmic Origins Spectrograph (HST-COS) indicated the principal loss mechanism to be degradation of the cesium iodide (CsI) photocathode of the open-faced FUV detector. A possible cause of this degradation is contamination by atomic oxygen (AO), prompting an investigation of the interaction of AO with CsI. To address this question, opaque CsI photocathodes were deposited on stainless steel substrates employing the same deposition techniques and parameters used for the photocathodes of the HST-COS FUV detector. The as-deposited FUV quantum efficiency of these photocathodes was measured in the 117-174 nm range. Several of the photocathodes were exposed to varying levels of thermalized, atomic oxygen (AO) fluence (produced via an RF plasma). The post AO exposure QE's were measured and the degradation of sensitivity versus wavelength and AO fluence are presented.

  2. Halide-Substituted Electronic Properties of Organometal Halide Perovskite Films: Direct and Inverse Photoemission Studies.

    PubMed

    Li, Chi; Wei, Jian; Sato, Mikio; Koike, Harunobu; Xie, Zhong-Zhi; Li, Yan-Qing; Kanai, Kaname; Kera, Satoshi; Ueno, Nobuo; Tang, Jian-Xin

    2016-05-11

    Solution-processed perovskite solar cells are attracting increasing interest due to their potential in next-generation hybrid photovoltaic devices. Despite the morphological control over the perovskite films, quantitative information on electronic structures and interface energetics is of paramount importance to the optimal photovoltaic performance. Here, direct and inverse photoemission spectroscopies are used to determine the electronic structures and chemical compositions of various methylammonium lead halide perovskite films (MAPbX3, X = Cl, Br, and I), revealing the strong influence of halide substitution on the electronic properties of perovskite films. Precise control over halide compositions in MAPbX3 films causes the manipulation of the electronic properties, with a qualitatively blue shift along the I → Br → Cl series and showing the increase in ionization potentials from 5.96 to 7.04 eV and the change of transport band gaps in the range from 1.70 to 3.09 eV. The resulting light absorption of MAPbX3 films can cover the entire visible region from 420 to 800 nm. The results presented here provide a quantitative guide for the analysis of perovskite-based solar cell performance and the selection of optimal carrier-extraction materials for photogenerated electrons and holes. PMID:27101940

  3. Unraveling the Role of Monovalent Halides in Mixed-Halide Organic-Inorganic Perovskites.

    PubMed

    Deepa, Melepurath; Ramos, F Javier; Shivaprasad, S M; Ahmad, Shahzada

    2016-03-16

    The performance of perovskite solar cells is strongly influenced by the composition and microstructure of the perovskite. A recent approach to improve the power conversion efficiencies utilized mixed-halide perovskites, but the halide ions and their roles were not directly studied. Unraveling their precise location in the perovskite layer is of paramount importance. Here, we investigated four different perovskites by using X-ray photoelectron spectroscopy, and found that among the three studied mixed-halide perovskites, CH3 NH3 Pb(I0.74 Br0.26 )3 and CH3 NH3 PbBr3-x Clx show peaks that unambiguously demonstrate the presence of iodide and bromide in the former, and bromide and chloride in the latter. The CH3 NH3 PbI3-x Clx perovskite shows anomalous behavior, the iodide content far outweighs that of the chloride; a small proportion of chloride, in all likelihood, resides deep within the TiO2 /absorber layer. Our study reveals that there are many distinguishable structural differences between these perovskites, and that these directly impact the photovoltaic performances. PMID:26717046

  4. Vibrational Spectroscopy of Sodium Halide and Hydrogen Halide Aqueous Solutions: Application to Atmospheric Aerosol Chemistry

    NASA Astrophysics Data System (ADS)

    Levering, L. M.; Liu, D.; Allen, H. C.

    2003-12-01

    Heterogeneous reactions on the surfaces of atmospheric aerosols play an important role in atmospheric chemistry. These reactions are capable of converting alkyl and hydrogen halides (common constituents of marine boundary aerosols) into active halogen compounds. Fundamental questions still remain concerning surface species and reaction mechanisms pertaining to marine boundary aerosols. The first step in beginning to understand these heterogeneous reactions is to determine how ions in solution affect the structure of water at the interface. Vibrational sum frequency generation spectroscopy is used to examine the air-liquid interface of sodium halide and hydrogen halide (i.e. strong acid) solutions. In addition, comparison of the bulk water structure to that of the interface is accomplished using Raman spectroscopy. The hydrogen-bonding environment at the surface of NaCl is found to be similar to that of the air-water interface. In contrast, the interfacial water structure of NaBr, HCl, and HBr solutions is significantly altered from that of neat water. In the bulk, NaCl, NaBr, HCl, and HBr solutions disturb the hydrogen-bonding network of neat water. A comparison between the corresponding salts and acids show that the salts produce greater disorder (i.e. less coupling of the water symmetric stretching modes) in the bulk water structure.

  5. Alkali burns from wet cement.

    PubMed Central

    Peters, W. J.

    1984-01-01

    When water is added to the dry materials of Portland cement calcium hydroxide is formed; the wet cement is caustic (with a pH as high as 12.9) and can produce third-degree alkali burns after 2 hours of contact. Unlike professional cement workers, amateurs are usually not aware of any danger and may stand or kneel in the cement for long periods. As illustrated in a case report, general physicians may recognize neither the seriousness of the injury in its early stages nor the significance of a history of prolonged contact with wet cement. All people working with cement should be warned about its dangers and advised to immediately wash and dry the skin if contact does occur. Images Fig. 1 PMID:6561052

  6. Aqueous Copper(II) Photoinduced Polymerization of Acrylates: Low Copper Concentration and the Importance of Sodium Halide Salts.

    PubMed

    Jones, Glen R; Whitfield, Richard; Anastasaki, Athina; Haddleton, David M

    2016-06-15

    Photoinduced metal-mediated radical polymerization is a rapidly developing technique which allows for the synthesis of macromolecules with defined molecular weight and narrow molecular weight distributions, although typically exhibiting significant limitations in aqueous media. Herein we demonstrate that the presence of alkali metal halide salts, in conjunction with low copper concentration and UV irradiation, allows for the controlled polymerization of water-soluble acrylates in aqueous media, yielding narrow molecular weight distributions and high conversions. Despite the aqueous environment which typically compromises polymer end group fidelity, chain extensions have also been successfully performed and different degrees of polymerization were targeted. Importantly, no conversion was observed in the absence of UV light and the polymerization could be switched "on" and "off" upon demand, as demonstrated by intermittent light and dark periods and thus allowing access to spatiotemporal control. PMID:27184213

  7. Passive particle dosimetry. [silver halide crystal growth

    NASA Technical Reports Server (NTRS)

    Childs, C. B.

    1977-01-01

    Present methods of dosimetry are reviewed with emphasis on the processes using silver chloride crystals for ionizing particle dosimetry. Differences between the ability of various crystals to record ionizing particle paths are directly related to impurities in the range of a few ppm (parts per million). To understand the roles of these impurities in the process, a method for consistent production of high purity silver chloride, and silver bromide was developed which yields silver halides with detectable impurity content less than 1 ppm. This high purity silver chloride was used in growing crystals with controlled doping. Crystals were grown by both the Czochalski method and the Bridgman method, and the Bridgman grown crystals were used for the experiments discussed. The distribution coefficients of ten divalent cations were determined for the Bridgman crystals. The best dosimeters were made with silver chloride crystals containing 5 to 10 ppm of lead; other impurities tested did not produce proper dosimeters.

  8. Metal halide perovskites for energy applications

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Eperon, Giles E.; Snaith, Henry J.

    2016-06-01

    Exploring prospective materials for energy production and storage is one of the biggest challenges of this century. Solar energy is one of the most important renewable energy resources, due to its wide availability and low environmental impact. Metal halide perovskites have emerged as a class of semiconductor materials with unique properties, including tunable bandgap, high absorption coefficient, broad absorption spectrum, high charge carrier mobility and long charge diffusion lengths, which enable a broad range of photovoltaic and optoelectronic applications. Since the first embodiment of perovskite solar cells showing a power conversion efficiency of 3.8%, the device performance has been boosted up to a certified 22.1% within a few years. In this Perspective, we discuss differing forms of perovskite materials produced via various deposition procedures. We focus on their energy-related applications and discuss current challenges and possible solutions, with the aim of stimulating potential new applications.

  9. Integrating Sphere Alkali-Metal Vapor Cells

    NASA Astrophysics Data System (ADS)

    McGuyer, Bart; Ben-Kish, Amit; Jau, Yuan-Yu; Happer, William

    2010-03-01

    An integrating sphere is an optical multi-pass cavity that uses diffuse reflection to increase the optical path length. Typically applied in photometry and radiometry, integrating spheres have previously been used to detect trace gases and to cool and trap alkali-metal atoms. Here, we investigate the potential for integrating spheres to enhance optical absorption in optically thin alkali-metal vapor cells. In particular, we consider the importance of dielectric effects due to a glass container for the alkali-metal vapor. Potential applications include miniature atomic clocks and magnetometers, where multi-passing could reduce the operating temperature and power consumption.

  10. Alkali Silicate Vehicle Forms Durable, Fireproof Paint

    NASA Technical Reports Server (NTRS)

    Schutt, John B.; Seindenberg, Benjamin

    1964-01-01

    The problem: To develop a paint for use on satellites or space vehicles that exhibits high resistance to cracking, peeling, or flaking when subjected to a wide range of temperatures. Organic coatings will partially meet the required specifications but have the inherent disadvantage of combustibility. Alkali-silicate binders, used in some industrial coatings and adhesives, show evidence of forming a fireproof paint, but the problem of high surface-tension, a characteristic of alkali silicates, has not been resolved. The solution: Use of a suitable non-ionic wetting agent combined with a paint incorporating alkali silicate as the binder.

  11. Diode pumped alkali vapor fiber laser

    DOEpatents

    Payne, Stephen A.; Beach, Raymond J.; Dawson, Jay W.; Krupke, William F.

    2007-10-23

    A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

  12. Diode pumped alkali vapor fiber laser

    DOEpatents

    Payne, Stephen A.; Beach, Raymond J.; Dawson, Jay W.; Krupke, William F.

    2006-07-26

    A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

  13. Advancements in flowing diode pumped alkali lasers

    NASA Astrophysics Data System (ADS)

    Pitz, Greg A.; Stalnaker, Donald M.; Guild, Eric M.; Oliker, Benjamin Q.; Moran, Paul J.; Townsend, Steven W.; Hostutler, David A.

    2016-03-01

    Multiple variants of the Diode Pumped Alkali Laser (DPAL) have recently been demonstrated at the Air Force Research Laboratory (AFRL). Highlights of this ongoing research effort include: a) a 571W rubidium (Rb) based Master Oscillator Power Amplifier (MOPA) with a gain (2α) of 0.48 cm-1, b) a rubidium-cesium (Cs) Multi-Alkali Multi-Line (MAML) laser that simultaneously lases at both 795 nm and 895 nm, and c) a 1.5 kW resonantly pumped potassium (K) DPAL with a slope efficiency of 50%. The common factor among these experiments is the use of a flowing alkali test bed.

  14. Electronic and Ionic Transport Dynamics in Organolead Halide Perovskites.

    PubMed

    Li, Dehui; Wu, Hao; Cheng, Hung-Chieh; Wang, Gongming; Huang, Yu; Duan, Xiangfeng

    2016-07-26

    Ion migration has been postulated as the underlying mechanism responsible for the hysteresis in organolead halide perovskite devices. However, the electronic and ionic transport dynamics and how they impact each other in organolead halide perovskites remain elusive to date. Here we report a systematic investigation of the electronic and ionic transport dynamics in organolead halide perovskite microplate crystals and thin films using temperature-dependent transient response measurements. Our study reveals that thermally activated ionic and electronic conduction coexist in perovskite devices. The extracted activation energies suggest that the electronic transport is easier, but ions migrate harder in microplates than in thin films, demonstrating that the crystalline quality and grain boundaries can fundamentally modify electronic and ionic transport in perovskites. These findings offer valuable insight on the electronic and ionic transport dynamics in organolead halide perovskites, which is critical for optimizing perovskite devices with reduced hysteresis and improved stability and efficiency. PMID:27315525

  15. Photoemission Study of Cs-NF3 Activated GaAs(100) Negative Electron Affinity Photocathodes

    SciTech Connect

    Liu, Z.; Sun, Y.; Peterson, S.; Pianetta, P.

    2008-05-28

    GaAs based negative electron affinity photocathodes activated with Cs and NF{sub 3} are used as polarized electron sources for linear accelerators. It is generally believed that the activation layer consists of CsF. The activation layers of Cs-NF{sub 3} on GaAs photocathodes are herein investigated using synchrotron radiation photoelectron spectroscopy (SR-PES). F1s, N1s and other core levels are recorded at photon energies ranging from 70eV to 820eV. Surprisingly, a significant amount of nitrogen is observed in the activation layers. Two distinct species of nitrogen are observed, one of which decreases along with the Fluorine signal as the yield of the photocathode decays with time.

  16. High quantum efficiency photocathode simulation for the investigation of novel structured designs

    SciTech Connect

    MacPhee, A. G.; Nagel, S. R.; Bell, P. M.; Bradley, D. K.; Landen, O. L.; Opachich, Y. P.; Ross, P. W.; Huffman, E.; Koch, J. A.; Hilsabeck, T. J.

    2014-09-02

    A computer model in CST Studio Suite has been developed to evaluate several novel geometrically enhanced photocathode designs. This work was aimed at identifying a structure that would increase the total electron yield by a factor of two or greater in the 1–30 keV range. The modeling software was used to simulate the electric field and generate particle tracking for several potential structures. The final photocathode structure has been tailored to meet a set of detector performance requirements, namely, a spatial resolution of <40 μm and a temporal spread of 1–10 ps. As a result, we present the details of the geometrically enhanced photocathode model and resulting static field and electron emission characteristics.

  17. High quantum efficiency photocathode simulation for the investigation of novel structured designs

    SciTech Connect

    Opachich, Y. P. Ross, P. W.; Huffman, E.; Koch, J. A.; MacPhee, A. G.; Nagel, S. R.; Bell, P. M.; Bradley, D. K.; Landen, O. L.; Hilsabeck, T. J.

    2014-11-15

    A computer model in CST Studio Suite has been developed to evaluate several novel geometrically enhanced photocathode designs. This work was aimed at identifying a structure that would increase the total electron yield by a factor of two or greater in the 1–30 keV range. The modeling software was used to simulate the electric field and generate particle tracking for several potential structures. The final photocathode structure has been tailored to meet a set of detector performance requirements, namely, a spatial resolution of <40 μm and a temporal spread of 1–10 ps. We present the details of the geometrically enhanced photocathode model and resulting static field and electron emission characteristics.

  18. High quantum efficiency photocathode simulation for the investigation of novel structured designs

    DOE PAGESBeta

    MacPhee, A. G.; Nagel, S. R.; Bell, P. M.; Bradley, D. K.; Landen, O. L.; Opachich, Y. P.; Ross, P. W.; Huffman, E.; Koch, J. A.; Hilsabeck, T. J.

    2014-09-02

    A computer model in CST Studio Suite has been developed to evaluate several novel geometrically enhanced photocathode designs. This work was aimed at identifying a structure that would increase the total electron yield by a factor of two or greater in the 1–30 keV range. The modeling software was used to simulate the electric field and generate particle tracking for several potential structures. The final photocathode structure has been tailored to meet a set of detector performance requirements, namely, a spatial resolution of <40 μm and a temporal spread of 1–10 ps. As a result, we present the details ofmore » the geometrically enhanced photocathode model and resulting static field and electron emission characteristics.« less

  19. Characterizing and Optimizing Photocathode Laser Distributions for Ultra-low Emittance Electron Beam Operations

    SciTech Connect

    Zhou, F.; Bohler, D.; Ding, Y.; Gilevich, S.; Huang, Z.; Loos, H.; Ratner, D.; Vetter, S.

    2015-12-07

    Photocathode RF gun has been widely used for generation of high-brightness electron beams for many different applications. We found that the drive laser distributions in such RF guns play important roles in minimizing the electron beam emittance. Characterizing the laser distributions with measurable parameters and optimizing beam emittance versus the laser distribution parameters in both spatial and temporal directions are highly desired for high-brightness electron beam operation. In this paper, we report systematic measurements and simulations of emittance dependence on the measurable parameters represented for spatial and temporal laser distributions at the photocathode RF gun systems of Linac Coherent Light Source. The tolerable parameter ranges for photocathode drive laser distributions in both directions are presented for ultra-low emittance beam operations.

  20. Comparative research on indium seal process for transmission-mode GaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Zhang, Shuqin; Jin, Shangzhong; Xu, Sunan; Jiao, Gangcheng

    2013-01-01

    For night vision devices and other applications, the transmission-mode photocathodes must be sealed to tube by indium seal process (ISP) in practical application. But in early research, the integral sensitivity has large drop to about 30% amplitude after ISP process than after activation process. In order to well study the influence of ISP on surface barriers of activated GaAs photocathodes, we used the comparative research method by surface photovoltage spectroscopy (SPS) and spectral response current (SRC). Through fitting calculation, we can find that the impurity gas sources by micro channel plate and fluorescent screen have deep influence on the amplitude and width of surface barriers which lead to the large drop on SRC curves before and after ISP process. This on-line comparative research method can help to optimize ISP technique and vacuum degree optimization for transmission-mode GaAs photocathodes in the future.

  1. Monte Carlo charge transport and photoemission from negative electron affinity GaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Karkare, Siddharth; Dimitrov, Dimitre; Schaff, William; Cultrera, Luca; Bartnik, Adam; Liu, Xianghong; Sawyer, Eric; Esposito, Teresa; Bazarov, Ivan

    2013-03-01

    High quantum yield, low transverse energy spread, and prompt response time make GaAs activated to negative electron affinity an ideal candidate for a photocathode in high brightness photoinjectors. Even after decades of investigation, the exact mechanism of electron emission from GaAs is not well understood. Here, photoemission from such photocathodes is modeled using detailed Monte Carlo electron transport simulations. Simulations show a quantitative agreement with the experimental results for quantum efficiency, energy distributions of emitted electrons, and response time without the assumption of any ad hoc parameters. This agreement between simulation and experiment sheds light on the mechanism of electron emission and provides an opportunity to design novel semiconductor photocathodes with optimized performance.

  2. Temporal resolution limit estimation of x-ray streak cameras using a CsI photocathode

    SciTech Connect

    Li, Xiang; Gu, Li; Zong, Fangke; Zhang, Jingjin; Yang, Qinlao

    2015-08-28

    A Monte Carlo model is developed and implemented to calculate the characteristics of x-ray induced secondary electron (SE) emission from a CsI photocathode used in an x-ray streak camera. Time distributions of emitted SEs are investigated with an incident x-ray energy range from 1 to 30 keV and a CsI thickness range from 100 to 1000 nm. Simulation results indicate that SE time distribution curves have little dependence on the incident x-ray energy and CsI thickness. The calculated time dispersion within the CsI photocathode is about 70 fs, which should be the temporal resolution limit of x-ray streak cameras that use CsI as the photocathode material.

  3. Significant Broadband Photocurrent Enhancement by Au-CZTS Core-Shell Nanostructured Photocathodes

    NASA Astrophysics Data System (ADS)

    Zhang, Xuemei; Wu, Xu; Centeno, Anthony; Ryan, Mary P.; Alford, Neil M.; Riley, D. Jason; Xie, Fang

    2016-03-01

    Copper zinc tin sulfide (CZTS) is a promising material for harvesting solar energy due to its abundance and non-toxicity. However, its poor performance hinders their wide application. In this paper gold (Au) nanoparticles are successfully incorporated into CZTS to form Au@CZTS core-shell nanostructures. The photocathode of Au@CZTS nanostructures exhibits enhanced optical absorption characteristics and improved incident photon-to-current efficiency (IPCE) performance. It is demonstrated that using this photocathode there is a significant increase of the power conversion efficiency (PCE) of a photoelectrochemical solar cell of 100% compared to using a CZTS without Au core. More importantly, the PCE of Au@CZTS photocathode improved by 15.8% compared to standard platinum (Pt) counter electrode. The increased efficiency is attributed to plasmon resonance energy transfer (PRET) between the Au nanoparticle core and the CZTS shell at wavelengths shorter than the localized surface plasmon resonance (LSPR) peak of the Au and the semiconductor bandgap.

  4. Photoelectrochemical water splitting: silicon photocathodes for hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Warren, Emily L.; Boettcher, Shannon W.; McKone, James R.; Lewis, Nathan S.

    2010-08-01

    The development of low cost, scalable, renewable energy technologies is one of today's most pressing scientific challenges. We report on progress towards the development of a photoelectrochemical water-splitting system that will use sunlight and water as the inputs to produce renewable hydrogen with oxygen as a by-product. This system is based on the design principle of incorporating two separate, photosensitive inorganic semiconductor/liquid junctions to collectively generate the 1.7-1.9 V at open circuit needed to support both the oxidation of H2O (or OH-) and the reduction of H+ (or H2O). Si microwire arrays are a promising photocathode material because the high aspect-ratio electrode architecture allows for the use of low cost, earth-abundant materials without sacrificing energy-conversion efficiency, due to the orthogonalization of light absorption and charge-carrier collection. Additionally, the high surfacearea design of the rod-based semiconductor array inherently lowers the flux of charge carriers over the rod array surface relative to the projected geometric surface of the photoelectrode, thus lowering the photocurrent density at the solid/liquid junction and thereby relaxing the demands on the activity (and cost) of any electrocatalysts. Arrays of Si microwires grown using the Vapor Liquid Solid (VLS) mechanism have been shown to have desirable electronic light absorption properties. We have demonstrated that these arrays can be coated with earth-abundant metallic catalysts and used for photoelectrochemical production of hydrogen. This development is a step towards the demonstration of a complete artificial photosynthetic system, composed of only inexpensive, earth-abundant materials, that is simultaneously efficient, durable, and scalable.

  5. Zintl cluster chemistry in the alkali-metal-gallium systems

    SciTech Connect

    Henning, R.

    1998-03-27

    Previous research into the alkali-metal-gallium systems has revealed a large variety of networked gallium deltahedra. The clusters are analogues to borane clusters and follow the same electronic requirements of 2n+2 skeletal electrons for closo-deltahedra. This work has focused on compounds that do not follow the typical electron counting rules. The first isolated gallium cluster was found in Cs{sub 8}Ga{sub 11}. The geometry of the Ga{sub 11}{sup 7{minus}} unit is not deltahedral but can be described as a penta-capped trigonal prism. The reduction of the charge from a closo-Ga{sub 11}{sup 13{minus}} to Ga{sub 11}{sup 7{minus}} is believed to be the driving force of the distortion. The compound is paramagnetic because of an extra electron but incorporation of a halide atom into the structure captures the unpaired electron and forms a diamagnetic compound. A second isolated cluster has been found in Na{sub 10}Ga{sub 10}Ni where the tetra-capped trigonal prismatic gallium is centered by nickel. Stabilization of the cluster occurs through Ni-Ga bonding. A simple two-dimensional network occurs in the binary K{sub 2}Ga{sub 3} Octahedra are connected through four waist atoms to form a layered structure with the potassium atoms sitting between the layers. Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x} is nonstoichiometric and needs only a small amount of silver to form (x {approximately} 2--6). The structure is composed of three different clusters which are interconnected to form a three-dimensional structure. The RbGa{sub 3{minus}x}Au{sub x} system is also nonstoichiometric with a three-dimensional structure composed of Ga{sub 8} dodecahedra and four-bonded gallium atoms. Unlike Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x}, the RbGa{sub 3} binary is also stable. The binary is formally a Zintl phase but the ternary is not. Some chemistry in the alkali-metal-indium system also has been explored. A new potassium-indium binary is discussed but the structure has not been completely

  6. Enhanced Photocathodes for Astrophysics using Atomic Layer Deposition Techniques Deposition Techniques

    NASA Astrophysics Data System (ADS)

    Siegmund, Oswald

    The objective of this program is to exploit the recent availability of atomic layer deposition techniques to provide a new generation of high performance photocathodes. We intend to work on the enhancement of photocathodes by atomic layer deposition, and on atomic layer deposited substrate structures, and assess their performance (gain, lifetime, stability, image fidelity) in microchannel plate based detectors. This would enable detection efficiency and bandpass improvements for microchannel plate based spaceflight detectors for imaging and spectroscopic instruments in small and large formats. Applications include the detection of soft X-ray, and UV through NUV. Recent work has achieved considerable success in development of borosilicate substrate microchannel plates functionalized by atomic layer deposited resistive and photoemissive materials. These could provide stable, compatible, substrates for high efficiency photocathodes, although very limited work has been done to date on this aspect. This development addresses detector technologies for SALSO, and impending proposals for a number of other NASA sub-orbital and satellite instruments. Results with borosilicate substrate microchannel plates functionalized by atomic layer deposited surface layers has been impressive, providing economical devices with long term stable gain and low background in formats up to 20 cm. Atomic layer deposition provides a surface layer that is smooth, clean, and chemically compatible with photocathode materials, and withstands high temperatures. The substrates can also be made with larger open area ratios, and the atomic layer deposition nanofabrication processes provides high secondary emission coefficients that will enhance photocathode efficiencies. Photocathodes (GaN, etc) deposited by MOCVD or MBE processes may also be deposited using atomic layer deposition, with potential advantages in layer structuring and selective area coverage and penetration over large areas.

  7. Alkali metal for ultraviolet band-pass filter

    NASA Technical Reports Server (NTRS)

    Mardesich, Nick (Inventor); Fraschetti, George A. (Inventor); Mccann, Timothy A. (Inventor); Mayall, Sherwood D. (Inventor); Dunn, Donald E. (Inventor); Trauger, John T. (Inventor)

    1993-01-01

    An alkali metal filter having a layer of metallic bismuth deposited onto the alkali metal is provided. The metallic bismuth acts to stabilize the surface of the alkali metal to prevent substantial surface migration from occurring on the alkali metal, which may degrade optical characteristics of the filter. To this end, a layer of metallic bismuth is deposited by vapor deposition over the alkali metal to a depth of approximately 5 to 10 A. A complete alkali metal filter is described along with a method for fabricating the alkali metal filter.

  8. Design and beam dynamics simulations of an S-band photocathode rf gun

    NASA Astrophysics Data System (ADS)

    Kumar, Arvind; Pant, K. K.; Krishnagopal, S.

    2002-10-01

    We are building an S-band photocathode rf gun as an injector to a 30MeV electron linac for FEL applications. Here we discuss details of design simulations performed using superfish and gdfidl and compare with results of cold tests performed on prototype cells of the photocathode rf gun. We also discuss beam dynamics simulations performed using parmela and report results from simulations to achieve a normalized transverse rms emittance of about 1π mm mrad for a 10ps pulse with 1nC charge in the presence of a solenoid magnetic field used for emittance compensation.

  9. III-V photocathode with nitrogen doping for increased quantum efficiency

    NASA Technical Reports Server (NTRS)

    James, L. W. (Inventor)

    1976-01-01

    An increase in the quantum efficiency of a 3-5 photocathode is achieved by doping its semiconductor material with an acceptor and nitrogen, a column-5 isoelectronic element, that introduces a spatially localized energy level just below the conduction band similar to a donor level to which optical transitions can occur. This increases the absorption coefficient, alpha without compensation of the acceptor dopant. A layer of a suitable 1-5, 1-6 or 1-7 compound is included as an activation layer on the electron emission side to lower the work function of the photocathode.

  10. Characterization of quantum efficiency and robustness of cesium-based photocathodes

    NASA Astrophysics Data System (ADS)

    Montgomery, Eric J.

    High quantum efficiency, robust photocathodes produce picosecond-pulsed, high-current electron beams for photoinjection applications like free electron lasers. In photoinjectors, a pulsed drive laser incident on the photocathode causes photoemission of short, dense bunches of electrons, which are then accelerated into a relativistic, high quality beam. Future free electron lasers demand reliable photocathodes with long-lived quantum efficiency at suitable drive laser wavelengths to maintain high current density. But faced with contamination, heating, and ion back-bombardment, the highest efficiency photocathodes find their delicate cesium-based coatings inexorably lost. In answer, the work herein presents careful, focused studies on cesium-based photocathodes, particularly motivated by the cesium dispenser photocathode. This is a novel device comprised of an efficiently photoemissive, cesium-based coating deposited onto a porous sintered tungsten substrate, beneath which is a reservoir of elemental cesium. Under controlled heating cesium diffuses from the reservoir through the porous substrate and across the surface to replace cesium lost to harsh conditions---recently shown to significantly extend the lifetime of cesium-coated metal cathodes. This work first reports experiments on coated metals to validate and refine an advanced theory of photoemission already finding application in beam simulation codes. Second, it describes a new theory of photoemission from much higher quantum efficiency cesium-based semiconductors and verifies its predictions with independent experiment. Third, it investigates causes of cesium loss from both coated metal and semiconductor photocathodes and reports remarkable rejuvenation of full quantum efficiency for contaminated cesium-coated surfaces, affirming the dispenser prescription of cesium resupply. And fourth, it details continued advances in cesium dispenser design with much-improved operating characteristics: lower temperature

  11. X-ray Photoemission Spectroscopy Studies of Cesium Antimonide Photocathodes for Photoinjector Applications

    NASA Astrophysics Data System (ADS)

    Martini, Irene; Chevallay, Eric; Fedosseev, Valentin; Hessler, Christoph; Neupert, Holger; Nistor, Valentin; Taborelli, Mauro

    Within the CLIC (Compact Linear Collider) project, feasibility studies of a photoinjector option for the drive beam as an alternative to its baseline design using a thermionic electron gun (Geschonke et al. [1]) are on-going. This R&D program covers both the laser and the photocathode side. Cesium antimonide cathodes were produced at CERN by co-deposition onto copper substrates and characterized by photoemission and by XPS (X-ray Photoemission Spectroscopy) analysis. A systematic study on newly produced and used photocathodes was conducted in order to correlate the surface composition to the photoemissive properties.

  12. Alkali Metal Handling Practices at NASA MSFC

    NASA Technical Reports Server (NTRS)

    Salvail, Patrick G.; Carter, Robert R.

    2002-01-01

    NASA Marshall Space Flight Center (MSFC) is NASA s principle propulsion development center. Research and development is coordinated and carried out on not only the existing transportation systems, but also those that may be flown in the near future. Heat pipe cooled fast fission cores are among several concepts being considered for the Nuclear Systems Initiative. Marshall Space Flight Center has developed a capability to handle high-purity alkali metals for use in heat pipes or liquid metal heat transfer loops. This capability is a low budget prototype of an alkali metal handling system that would allow the production of flight qualified heat pipe modules or alkali metal loops. The processing approach used to introduce pure alkali metal into heat pipe modules and other test articles are described in this paper.

  13. Alkali-metal intercalation in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Béguin, F.; Duclaux, L.; Méténier, K.; Frackowiak, E.; Salvetat, J. P.; Conard, J.; Bonnamy, S.; Lauginie, P.

    1999-09-01

    We report on successful intercalation of multiwall (MWNT) and single wall (SWNT) carbon nanotubes with alkali metals by electrochemical and vapor phase reactions. A LiC10 compound was produced by full electrochemical reduction of MWNT. KC8 and CsC8-MWNT first stage derivatives were synthesized in conditions of alkali vapor saturation. Their identity periods and the 2×2 R 0° alkali superlattice are comparable to their parent graphite compounds. The dysonian shape of KC8 EPR line and the temperature-independent Pauli susceptibility are both characteristic of a metallic behavior, which was confirmed by 13C NMR anisotropic shifts. Exposure of SWNT bundles to alkali vapor led to an increase of the pristine triangular lattice from 1.67 nm to 1.85 nm and 1.87 nm for potassium and rubidium, respectively.

  14. Alkali metal intercalates of molybdenum disulfide.

    NASA Technical Reports Server (NTRS)

    Somoano, R. B.; Hadek, V.; Rembaum, A.

    1973-01-01

    Study of some of the physicochemical properties of compounds obtained by subjecting natural molybdenite and single crystals of molybdenum disulfide grown by chemical vapor transport to intercalation with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Reported data and results include: (1) the intercalation of the entire alkali metal group, (2) stoichiometries and X-ray data on all of the compounds, and (3) superconductivity data for all the intercalation compounds.

  15. Superconductivity in alkali-doped C60

    NASA Astrophysics Data System (ADS)

    Ramirez, Arthur P.

    2015-07-01

    Superconductivity in alkali-doped C60 (A3C60, A = an alkali atom) is well described by an s-wave state produced by phonon mediated pairing. Moderate coupling of electrons to high-frequency shape-changing intra-molecular vibrational modes produces transition temperatures (Tc) up to 33 K in single-phase material. The good understanding of pairing in A3C60 offers a paradigm for the development of new superconducting materials.

  16. Desulfurizing Coal With an Alkali Treatment

    NASA Technical Reports Server (NTRS)

    Ravindram, M.; Kalvinskas, J. J.

    1987-01-01

    Experimental coal-desulfurization process uses alkalies and steam in fluidized-bed reactor. With highly volatile, high-sulfur bituminous coal, process removed 98 percent of pyritic sulfur and 47 percent of organic sulfur. Used in coal liquefaction and in production of clean solid fuels and synthetic liquid fuels. Nitrogen or steam flows through bed of coal in reactor. Alkalies react with sulfur, removing it from coal. Nitrogen flow fluidizes bed while heating or cooling; steam is fluidizing medium during reaction.

  17. Analysis of the physical atomic forces between noble gas atoms, alkali ions and halogen ions

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

    1986-01-01

    The physical forces between atoms and molecules are important in a number of processes of practical importance, including line broadening in radiative processes, gas and crystal properties, adhesion, and thin films. The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base for the dispersion forces is developed from the literature based on evaluations with the harmonic oscillator dispersion model for higher order coefficients. The Zener model of the repulsive core is used in the context of the recent asymptotic wave functions of Handler and Smith; and an effective ionization potential within the Handler and Smith wave functions is defined to analyze the two body potential data of Waldman and Gordon, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

  18. Density functional studies on hydrogen-bonded clusters of hydrogen halides and the interaction on halide anions

    NASA Astrophysics Data System (ADS)

    Nirmala, V.; Kolandaivel, P.

    Density functional theory (DFT) calculations have been performed to study the structures and stability of X-·(HX)n=2-5 clusters where X = F, Cl, Br at B3LYP/6-311++G** level of theory. The presence of halide ions in these clusters disintegrates the hydrogen halide clusters. All the hydrogen halides are then hydrogen bonded to the centrally placed halide ions, thereby forming multiple hydrogen bonds. The interaction energies have been corrected for the basis set superposition error (BSSE) using Boy's counterpoise correction method. Evidence for the destruction of hydrogen bonds in hydrogen halide clusters due to the presence of halide ions is further obtained from topological analysis and natural bond orbital analysis. The chemical hardness and chemical potential have been calculated for all the anion clusters. The above analysis reveals that hydrogen bonding in these systems is not an essentially electrostatic interaction. The nature of the stabilization interactions operative in these multiple hydrogen-bonded clusters has been explained in terms of many-body contribution to interaction energies. From these studies, an attempt has been made to understand the nature of the molecular properties resulting from different electronegativities of the halogens.

  19. Alkali metal crystalline polymer electrolytes.

    PubMed

    Zhang, Chuhong; Gamble, Stephen; Ainsworth, David; Slawin, Alexandra M Z; Andreev, Yuri G; Bruce, Peter G

    2009-07-01

    Polymer electrolytes have been studied extensively because uniquely they combine ionic conductivity with solid yet flexible mechanical properties, rendering them important for all-solid-state devices including batteries, electrochromic displays and smart windows. For some 30 years, ionic conductivity in polymers was considered to occur only in the amorphous state above Tg. Crystalline polymers were believed to be insulators. This changed with the discovery of Li(+) conductivity in crystalline poly(ethylene oxide)(6):LiAsF(6). However, new crystalline polymer electrolytes have proved elusive, questioning whether the 6:1 complex has particular structural features making it a unique exception to the rule that only amorphous polymers conduct. Here, we demonstrate that ionic conductivity in crystalline polymers is not unique to the 6:1 complex by reporting several new crystalline polymer electrolytes containing different alkali metal salts (Na(+), K(+) and Rb(+)), including the best conductor poly(ethylene oxide)(8):NaAsF(6) discovered so far, with a conductivity 1.5 orders of magnitude higher than poly(ethylene oxide)(6):LiAsF(6). These are the first crystalline polymer electrolytes with a different composition and structures to that of the 6:1 Li(+) complex. PMID:19543313

  20. Charge Lifetime Study of K2CsSb Photocathode Inside a JLAB DC High Voltage Gun

    SciTech Connect

    Mammei, R.; Rao, T.; Suleiman, R.; Poelker, M.; Smedley, J.; McCarter, J.L.

    2011-10-01

    Two photocathodes are frequently considered for generating high average current electron beams and/or beams with high brightness for current and future accelerator applications: GaAs:Cs and K2CsSb. Each photocathode has advantages and disadvantages, and need to demonstrate performance at 'production' accelerator facilities. To this end a K2CsSb photocathode was manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure {approx} 5 x 10{sup -11} Torr. This photocathode was installed inside a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at 440 or 532 nm, to generate beams up to 20 mA. Photocathode charge lifetime measurements indicate that under some conditions this cathode has exceptionally high charge lifetime, without measurable QE decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. These studies also suggest a complex QE decay mechanism likely related to chemistry and localized heating via the laser beam.

  1. Spectral response variation of a negative-electron-affinity photocathode in the preparation process

    SciTech Connect

    Liu Lei; Du Yujie; Chang Benkang; Yunsheng Qian

    2006-08-20

    In order to research the spectral response variation of a negative electron affinity (NEA) photocathode in the preparation process, we have done two experiments on a transmission-type GaAs photocathode.First, an automatic spectral response recording system is described, which is used to take spectral response curves during the activation procedure of the photocathode. By this system, the spectral response curves of a GaAs:Cs-Ophotocathode measured in situ are presented. Then, after the cathode is sealed with a microchannel plate and a fluorescence screen into the image tube, we measure the spectral response of the tube by another measurement instrument. By way of comparing and analyzing these curves, we can find the typical variation in spectral-responses.The reasons for the variation are discussed. Based on these curves, spectral matching factors of a GaAs cathode for green vegetation and rough concrete are calculated. The visual ranges of night-vision goggles under specific circumstances are estimated. The results show that the spectral response of the NEA photocathode degraded in the sealing process, especially at long wavelengths. The variation has also influenced the whole performance of the intensifier tube.

  2. Photocathode electron beam sources using GaN and InGaN with NEA surface

    NASA Astrophysics Data System (ADS)

    Nishitani, T.; Maekawa, T.; Tabuchi, M.; Meguro, T.; Honda, Y.; Amano, H.

    2015-03-01

    A photocathode electron source using p-type GaN and p-type InGaN semiconductors with a negative electron affinity (NEA) surface has been studied for its ability to maintain an extended NEA state. The key technology of NEA photocathodes is the formation of electric dipoles by atoms on the surface, which makes it possible for photo excited electrons in the conduction band minimum to escape into the vacuum. This means that in order to keep the electron energy spread as small as possible, the excitation photon energy should be tuned to the band gap energy. However, the NEA surface is damaged by the adsorption of residual gas and the back-bombardment of ionized residual gas by photoelectrons. The p-type GaN and InGaN semiconductors were measured a lifetime of quantum yield of excitation energy corresponding to the band gap energy in comparison to the p-type GaAs as the conventional NEA photocathode. Lifetime of NEA-photocathodes using the GaN and InGaN were 21 times and 7.7 times longer respectively than that using the GaAs.

  3. Engineering MoSx/Ti/InP Hybrid Photocathode for Improved Solar Hydrogen Production

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Zheng, Maojun; Zhong, Miao; Ma, Liguo; Wang, Faze; Ma, Li; Shen, Wenzhong

    2016-07-01

    Due to its direct band gap of ~1.35 eV, appropriate energy band-edge positions, and low surface-recombination velocity, p-type InP has attracted considerable attention as a promising photocathode material for solar hydrogen generation. However, challenges remain with p-type InP for achieving high and stable photoelectrochemical (PEC) performances. Here, we demonstrate that surface modifications of InP photocathodes with Ti thin layers and amorphous MoSx nanoparticles can remarkably improve their PEC performances. A high photocurrent density with an improved PEC onset potential is obtained. Electrochemical impedance analyses reveal that the largely improved PEC performance of MoSx/Ti/InP is attributed to the reduced charge-transfer resistance and the increased band bending at the MoSx/Ti/InP/electrolyte interface. In addition, the MoSx/Ti/InP photocathodes function stably for PEC water reduction under continuous light illumination over 2 h. Our study demonstrates an effective approach to develop high-PEC-performance InP photocathodes towards stable solar hydrogen production.

  4. Engineering MoSx/Ti/InP Hybrid Photocathode for Improved Solar Hydrogen Production

    PubMed Central

    Li, Qiang; Zheng, Maojun; Zhong, Miao; Ma, Liguo; Wang, Faze; Ma, Li; Shen, Wenzhong

    2016-01-01

    Due to its direct band gap of ~1.35 eV, appropriate energy band-edge positions, and low surface-recombination velocity, p-type InP has attracted considerable attention as a promising photocathode material for solar hydrogen generation. However, challenges remain with p-type InP for achieving high and stable photoelectrochemical (PEC) performances. Here, we demonstrate that surface modifications of InP photocathodes with Ti thin layers and amorphous MoSx nanoparticles can remarkably improve their PEC performances. A high photocurrent density with an improved PEC onset potential is obtained. Electrochemical impedance analyses reveal that the largely improved PEC performance of MoSx/Ti/InP is attributed to the reduced charge-transfer resistance and the increased band bending at the MoSx/Ti/InP/electrolyte interface. In addition, the MoSx/Ti/InP photocathodes function stably for PEC water reduction under continuous light illumination over 2 h. Our study demonstrates an effective approach to develop high-PEC-performance InP photocathodes towards stable solar hydrogen production. PMID:27431993

  5. NREL Improves Hole Transport in Sensitized CdS-NiO Nanoparticle Photocathodes (Fact Sheet)

    SciTech Connect

    Not Available

    2012-01-01

    Significantly improved charge-collection efficiencies result from a general chemical approach to synthesizing photocathodes. It has been reported that a dye-sensitized nickel oxide (NiO) photocathode, when coupled to a dye-sensitized photoanode, could significantly increase overall solar conversion efficiency. However, the conversion efficiencies of these cells are still low. There has been much effort to improve the conversion efficiency by fabricating films with improved properties and developing more effective sensitizing dyes for p-type NiO. One of the factors limiting the use of NiO for solar cell application is the low hole conductivity in p-NiO. A team of researchers from the National Renewable Energy Laboratory (NREL) developed a general chemical approach to synthesize NiO-cadmium sulfide (CdS) core-shell nanoparticle films as photocathodes for p-type semiconductor-sensitized solar cells. Compared to dye-sensitized NiO photocathodes, the CdS-sensitized NiO cathodes exhibited two orders of magnitude faster hole transport (attributable to the passivation of surface traps by the CdS) and almost 100% charge-collection efficiencies.

  6. Enhanced Raman scattering from cesium suboxides on silver particles and the structure of S-1 photocathodes

    NASA Technical Reports Server (NTRS)

    Bates, C. W., Jr.

    1984-01-01

    An explanation is given for the results of recent enhanced Raman scattering studies of photomultiplier tubes with S-1 photocathode surfaces which indicated the presence of Cs11O3 but not Cs2O. The reason for the discrepancy between the currently accepted model of the S-1 and this recent result is discussed.

  7. Engineering MoSx/Ti/InP Hybrid Photocathode for Improved Solar Hydrogen Production.

    PubMed

    Li, Qiang; Zheng, Maojun; Zhong, Miao; Ma, Liguo; Wang, Faze; Ma, Li; Shen, Wenzhong

    2016-01-01

    Due to its direct band gap of ~1.35 eV, appropriate energy band-edge positions, and low surface-recombination velocity, p-type InP has attracted considerable attention as a promising photocathode material for solar hydrogen generation. However, challenges remain with p-type InP for achieving high and stable photoelectrochemical (PEC) performances. Here, we demonstrate that surface modifications of InP photocathodes with Ti thin layers and amorphous MoSx nanoparticles can remarkably improve their PEC performances. A high photocurrent density with an improved PEC onset potential is obtained. Electrochemical impedance analyses reveal that the largely improved PEC performance of MoSx/Ti/InP is attributed to the reduced charge-transfer resistance and the increased band bending at the MoSx/Ti/InP/electrolyte interface. In addition, the MoSx/Ti/InP photocathodes function stably for PEC water reduction under continuous light illumination over 2 h. Our study demonstrates an effective approach to develop high-PEC-performance InP photocathodes towards stable solar hydrogen production. PMID:27431993

  8. Color silver halide hologram production and mastering

    NASA Astrophysics Data System (ADS)

    Bjelkhagen, Hans I.; Huang, Qiang

    1997-04-01

    Color reflection holograms recorded with the Denisyuk geometry have been demonstrated by the recently formed HOLOS Corporation in New Hampshire. The Slavich red-green-blue (RGB) sensitized ultra-high resolution silver halide emulsion was used for the hologram recording. The employed laser wavelengths were 647 nm, 532 nm, and 476 nm, generated by an argon ion, a frequency doubled Nd:YAG, and a krypton ion laser, respectively. A beam combination mechanism with dichroic filters enabled a simultaneous RGB exposure, which made the color balance and overall exposure energy easy to control as well as simplifying the recording procedure. HOLOS has been producing limited edition color holograms in various sizes from 4' X 5' to 12' X 16'. A 30 foot long optical table and high power lasers will enable HOLOS to record color holograms up to the size of one meter square in the near future. Various approaches have been investigated in generating color hologram masters which have sufficiently high diffraction efficiency to contact copy the color images onto photopolymer materials. A specially designed test object including the 1931 CIE chromaticity diagram, a rainbow ribbon cable, pure yellow dots, and a cloisonne elephant was used for color recording experiments. In addition, the Macbeth Color Checker chart was used. Both colorimetric evaluation and scattering noise measurements were performed using the PR-650 Photo Research SpectraScan SpectraCalorimeter.

  9. Charge carrier mobility in hybrid halide perovskites

    PubMed Central

    Motta, Carlo; El-Mellouhi, Fedwa; Sanvito, Stefano

    2015-01-01

    The charge transport properties of hybrid halide perovskites are investigated with a combination of density functional theory including van der Waals interaction and the Boltzmann theory for diffusive transport in the relaxation time approximation. We find the mobility of electrons to be in the range 5–10 cm2V−1s−1 and that for holes within 1–5 cm2V−1s−1, where the variations depend on the crystal structure investigated and the level of doping. Such results, in good agreement with recent experiments, set the relaxation time to about 1 ps, which is the time-scale for the molecular rotation at room temperature. For the room temperature tetragonal phase we explore two possible orientations of the organic cations and find that the mobility has a significant asymmetry depending on the direction of the current with respect to the molecular axis. This is due mostly to the way the PbI3 octahedral symmetry is broken. Interestingly we find that substituting I with Cl has minor effects on the mobilities. Our analysis suggests that the carrier mobility is probably not a key factor in determining the high solar-harvesting efficiency of this class of materials. PMID:26235910

  10. Genetic Control of Methyl Halide Production in Arabidopsis

    NASA Astrophysics Data System (ADS)

    Rhew, R. C.; Ostergaard, L.; Saltzman, E. S.; Yanofsky, M. F.

    2003-12-01

    Methyl chloride and methyl bromide are the primary carriers of natural chlorine and bromine to the stratosphere where they catalyze the destruction of ozone, whereas methyl iodide influences aerosol formation and ozone loss in the troposphere. Methyl bromide is also an agricultural fumigant whose use is scheduled to be phased out by international agreement. Despite the economic and environmental importance of these methyl halides, their natural sources and biological production mechanisms are poorly understood. Currently identified sources include oceans, biomass burning, industrial and agricultural use, fuel combustion, salt marshes, wetlands, rice paddies, certain terrestrial plants and fungi, and abiotic processes. We demonstrate that the model plant Arabidopsis thaliana produces and emits methyl halides and that the enzyme primarily responsible for the production is encoded by the HARMLESS TO OZONE LAYER (HOL) gene located on chromosome II. In mutant plants that have a disruption of the HOL gene, methyl halide production is largely eliminated. A phylogenetic analysis using the HOL gene suggests that the ability to produce methyl halides is widespread among vascular plants. This approach provides a genetic basis for understanding and predicting patterns of methyl halide production by plants.

  11. Halide Perovskites: Poor Man's High-Performance Semiconductors.

    PubMed

    Stoumpos, Constantinos C; Kanatzidis, Mercouri G

    2016-07-01

    Halide perovskites are a rapidly developing class of medium-bandgap semiconductors which, to date, have been popularized on account of their remarkable success in solid-state heterojunction solar cells raising the photovoltaic efficiency to 20% within the last 5 years. As the physical properties of the materials are being explored, it is becoming apparent that the photovoltaic performance of the halide perovskites is just but one aspect of the wealth of opportunities that these compounds offer as high-performance semiconductors. From unique optical and electrical properties stemming from their characteristic electronic structure to highly efficient real-life technological applications, halide perovskites constitute a brand new class of materials with exotic properties awaiting discovery. The nature of halide perovskites from the materials' viewpoint is discussed here, enlisting the most important classes of the compounds and describing their most exciting properties. The topics covered focus on the optical and electrical properties highlighting some of the milestone achievements reported to date but also addressing controversies in the vastly expanding halide perovskite literature. PMID:27174223

  12. Two Dimensional Organometal Halide Perovskite Nanorods with Tunable Optical Properties.

    PubMed

    Aharon, Sigalit; Etgar, Lioz

    2016-05-11

    Organo-metal halide perovskite is an efficient light harvester in photovoltaic solar cells. Organometal halide perovskite is used mainly in its "bulk" form in the solar cell. Confined perovskite nanostructures could be a promising candidate for efficient optoelectronic devices, taking advantage of the superior bulk properties of organo-metal halide perovskite, as well as the nanoscale properties. In this paper, we present facile low-temperature synthesis of two-dimensional (2D) lead halide perovskite nanorods (NRs). These NRs show a shift to higher energies in the absorbance and in the photoluminescence compared to the bulk material, which supports their 2D structure. X-ray diffraction (XRD) analysis of the NRs demonstrates their 2D nature combined with the tetragonal 3D perovskite structure. In addition, by alternating the halide composition, we were able to tune the optical properties of the NRs. Fast Fourier transform, and electron diffraction show the tetragonal structure of these NRs. By varying the ligands ratio (e.g., octylammonium to oleic acid) in the synthesis, we were able to provide the formation mechanism of these novel 2D perovskite NRs. The 2D perovskite NRs are promising candidates for a variety of optoelectronic applications, such as light-emitting diodes, lasing, solar cells, and sensors. PMID:27089497

  13. Regeneration of zinc halide catalyst used in the hydrocracking of polynuclear hydrocarbons

    DOEpatents

    Gorin, Everett

    1978-01-01

    Improved recovery of spent molten zinc halide hydro-cracking catalyst is achieved in the oxidative vapor phase regeneration thereof by selective treatment of the zinc oxide carried over by the effluent vapors from the regeneration zone with hydrogen halide gas under conditions favoring the reaction of the zinc oxide with the hydrogen halide, whereby regenerated zinc halide is recovered in a solids-free state with little loss of zinc values.

  14. 10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 3 2010-01-01 2010-01-01 false Definitions concerning metal halide lamp ballasts and... FOR CERTAIN COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide lamp ballasts and fixtures. Ballast efficiency means, in the case of...

  15. 10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 3 2012-01-01 2012-01-01 false Definitions concerning metal halide lamp ballasts and fixtures. 431.322 Section 431.322 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ENERGY EFFICIENCY PROGRAM FOR CERTAIN COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide...

  16. 10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 3 2013-01-01 2013-01-01 false Definitions concerning metal halide lamp ballasts and fixtures. 431.322 Section 431.322 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ENERGY EFFICIENCY PROGRAM FOR CERTAIN COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide...

  17. 10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 3 2011-01-01 2011-01-01 false Definitions concerning metal halide lamp ballasts and fixtures. 431.322 Section 431.322 Energy DEPARTMENT OF ENERGY ENERGY CONSERVATION ENERGY EFFICIENCY PROGRAM FOR CERTAIN COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide...

  18. 40 CFR 721.10181 - Halide salt of an alkylamine (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Halide salt of an alkylamine (generic... Specific Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halide salt...

  19. 40 CFR 721.10181 - Halide salt of an alkylamine (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Halide salt of an alkylamine (generic... Specific Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halide salt...

  20. 40 CFR 721.10181 - Halide salt of an alkylamine (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Halide salt of an alkylamine (generic... Specific Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halide salt...

  1. 40 CFR 721.10181 - Halide salt of an alkylamine (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Halide salt of an alkylamine (generic... Specific Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as halide salt...

  2. Alkali metal adsorption on Al(111)

    NASA Astrophysics Data System (ADS)

    Andersen, J. N.; Lundgren, E.; Nyholm, R.; Qvarford, M.

    1993-06-01

    The submonolayer adsorption of Na, K, Rb, and Cs on the Al(111) surface at 100 K and at room temperature is investigated by high resolution core level spectroscopy and low energy electron diffraction. It is found that the first alkali atoms on the surface adsorb at surface defects. At higher coverages, up to approximately one third of the maximum submonolayer coverage, alkali atoms adsorbed at defects coexist with a dispersed phase. At higher coverages island formation is found to occur for the majority of the systems. It is argued that all of the ordered structures formed at room temperature involve a disruption of the Al(111) surface in contrast to the situation at 100 K where the alkali atoms adsorb as adatoms.

  3. SAFE Alkali Metal Heat Pipe Reliability

    NASA Astrophysics Data System (ADS)

    Reid, Robert S.

    2003-01-01

    Alkali metal heat pipes are among the best understood and tested of components for first generation space fission reactors. A flight reactor will require production of a hundred or more heat pipes with assured reliability over a number of years. To date, alkali metal heat pipes have been built mostly in low budget development environments with little formal quality assurance. Despite this, heat pipe test samples suggest that high reliability can be achieved with the care justified for space flight qualification. Fabrication procedures have been established that, if consistently applied, ensure long-term trouble-free heat pipe operation. Alkali metal heat pipes have been successfully flight tested in micro gravity and also have been shown capable of multi-year operation with no evidence of sensitivity to fast neutron fluence up to 1023 n/cm2. This represents 50 times the fluence of the proposed Safe Affordable Fission Engine (SAFE-100) heat pipe reactor core.

  4. p-GaAs(Cs,O)-photocathodes: Demarcation of domains of validity for practical models of the activation layer

    SciTech Connect

    Bakin, V. V.; Toropetsky, K. V.; Scheibler, H. E.; Terekhov, A. S.; Jones, L. B.; Militsyn, B. L.; Noakes, T. C. Q.

    2015-05-04

    The (Cs,O)-activation procedure for p-GaAs(Cs,O)-photocathodes was studied with the aim of demarcating the domains of validity for the two practical models of the (Cs,O)-activation layer: The dipole layer (DL) model and the heterojunction (HJ) model. To do this, the photocathode was activated far beyond the normal maximum of quantum efficiency, and several photocathode parameters were measured periodically during this process. In doing so, the data obtained enabled us to determine the domains of validity for the DL- and HJ-models, to define more precisely the characteristic parameters of the photocathode within both of these domains and thus to reveal the peculiarities of the influence of the (Cs,O)-layer on the photoelectron escape probability.

  5. Design and fabrication of prototype 6×6 cm2 microchannel plate photodetector with bialkali photocathode for fast timing applications

    NASA Astrophysics Data System (ADS)

    Xie, Junqi; Byrum, Karen; Demarteau, Marcel; Gregar, Joseph; May, Edward; Virgo, Mathew; Wagner, Robert; Walters, Dean; Wang, Jingbo; Xia, Lei; Zhao, Huyue

    2015-06-01

    Planar microchannel plate-based photodetectors with a bialkali photocathode are able to achieve photon detection with very good time and position resolution. A 6×6 cm2 photodetector production facility was designed and built at Argonne National Laboratory. Small form-factor MCP-based photodetectors completely constructed out of glass were designed and prototypes were successfully fabricated. Knudsen effusion cells were incorporated in the photocathode growth chamber to achieve uniform and high quantum efficiency photocathodes. The thin film uniformity was simulated and measured for an antimony film deposition, showing uniformity of better than 10%. Several prototype devices with bialkali photocathodes have been fabricated with the described system and their characteristics were evaluated in the large signal (multi-PE) limit. A typical prototype device exhibits time-of-flight resolution of ~27 psec and differential time resolution of ~9 psec, corresponding to spatial resolution of ~0.65 mm.

  6. Diode pumped alkali lasers (DPALs): an overview

    NASA Astrophysics Data System (ADS)

    Krupke, William F.

    2008-05-01

    The concept of power-scalable, high beam-quality diode pumped alkali lasers was introduced in 2003 [Krupke, US Patent No. 6,643,311; Opt. Letters, 28, 2336 (2003)]. Since then several laboratory DPAL devices have been reported on, confirming many of the spectroscopic, kinetic, and laser characteristics projected from literature data. This talk will present an overview of the DPAL concept, summarize key relevant properties of the cesium, rubidium, and potassium alkali vapor gain media so-far examined, outline power scaling considerations, and highlight results of published DPAL laboratory experiments.

  7. Alkali metal vapors - Laser spectroscopy and applications

    NASA Technical Reports Server (NTRS)

    Stwalley, W. C.; Koch, M. E.

    1980-01-01

    The paper examines the rapidly expanding use of lasers for spectroscopic studies of alkali metal vapors. Since the alkali metals (lithium, sodium, potassium, rubidium and cesium) are theoretically simple ('visible hydrogen'), readily ionized, and strongly interacting with laser light, they represent ideal systems for quantitative understanding of microscopic interconversion mechanisms between photon (e.g., solar or laser), chemical, electrical and thermal energy. The possible implications of such understanding for a wide variety of practical applications (sodium lamps, thermionic converters, magnetohydrodynamic devices, new lasers, 'lithium waterfall' inertial confinement fusion reactors, etc.) are also discussed.

  8. Ultrafast time-resolved spectroscopy of lead halide perovskite films

    NASA Astrophysics Data System (ADS)

    Idowu, Mopelola A.; Yau, Sung H.; Varnavski, Oleg; Goodson, Theodore

    2015-09-01

    Recently, lead halide perovskites which are organic-inorganic hybrid structures, have been discovered to be highly efficient as light absorbers. Herein, we show the investigation of the excited state dynamics and emission properties of non-stoichiometric precursor formed lead halide perovskites grown by interdiffusion method using steady-state and time-resolved spectroscopic measurements. The influence of the different ratios of the non-stoichiometric precursor solution was examined. The observed photoluminescence properties were correlated with the femtosecond transient absorption measurements.

  9. Thermodynamic reactivity, growth and characterization of mercurous halide crystals

    NASA Technical Reports Server (NTRS)

    Singh, N. B.; Gottlieb, M.; Henningsen, T.; Hopkins, R. H.; Mazelsky, R.; Singh, M.; Glicksman, M. E.; Paradies, C.

    1992-01-01

    Thermodynamic calculations were carried out for the Hg-X-O system (X = Cl, Br, I) to identify the potential sources of contamination and relative stability of oxides and oxy-halide phases. The effect of excess mercury vapor pressure on the optical quality of mercurous halide crystal was studied by growing several mercurous chloride crystals from mercury-rich composition. The optical quality of crystals was examined by birefringence interferometry and laser scattering studies. Crystals grown in slightly mercury-rich composition showed improved optical quality relative to stoichiometric crystals.

  10. Thallous halide materials for use in cryogenic applications

    NASA Technical Reports Server (NTRS)

    Lawless, William N. (Inventor)

    1981-01-01

    Thallous halides, either alone or in combination with other ceramic materials, are used in cryogenic applications such as heat exchange material for the regenerator section of a closed-cycle cryogenic refrigeration section, as stabilizing coatings for superconducting wires, and as dielectric insulating materials. The thallous halides possess unusually large specific heats at low temperatures, have large thermal conductivities, are nonmagnetic, and are nonconductors of electricity. They can be formed into a variety of shapes such as spheres, bars, rods, or the like and can be coated onto substrates.

  11. Boron and aluminum halides under pressure - polymerization and chemical transformations

    NASA Astrophysics Data System (ADS)

    Yao, Yansun

    2013-06-01

    High-pressure phase transitions of boron and aluminum halides have been theoretically studied. At low pressure, crystals of the familiar monomers (BX3) and dimers (Al2X6) are the structures of choice. While the higher oligomers as well as three dimensional infinite polymers are unstable at ambient pressure, they are stabilized by application of external pressure, taking advantage of the extra orbitals made accessible by the increased coordination. Several new crystal structures of boron and aluminum halides have been predicted at high pressures. Calculated x-ray diffraction patterns and Raman spectra of these phases are in good agreement with available experimental data.

  12. Applications of Raman scattering spectroscopy to halide glasses

    NASA Astrophysics Data System (ADS)

    Bendow, B.; Banerjee, P. K.; Drexhage, M. G.

    1983-04-01

    Polarized Raman scattering spectroscopy is a useful tool for investigating fundamental vibrational properties, structure and bonding, origins of IR edge absorption, and dispersion of the IR refractive index. In this paper, the application of Raman spectroscopy to halide glasses and, in particular, heavy metal fluoride glasses, is described. The spectra of the latter differ substantially from those of simple oxide, halide or chalcogenide glasses and, moreover, display a wide range of vibrational characteristics, depending on composition. In combination with infrared spectroscopy, useful guidelines can be developed for tailoring glass compositions for specific applications.

  13. Alkali-aggregate reaction in concrete containing high-alkali cement and granite aggregate

    SciTech Connect

    Owsiak, Z

    2004-01-01

    The paper discusses results of the research into the influence of high-alkali Portland cement on granite aggregate. The deformation of the concrete structure occurred after 18 months. The research was carried out by means of a scanning electron microscope equipped with a high-energy dispersive X-ray analyzer that allowed observation of unpolished sections of concrete bars exhibiting the cracking pattern typical of the alkali-silica reaction. Both the microscopic observation and the X-ray elemental analysis confirm the presence of alkali-silica gel and secondary ettringite in the cracks.

  14. Recovery of alkali metal constituents from catalytic coal conversion residues

    DOEpatents

    Soung, W.Y.

    In a coal gasification operation (32) or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by contacting them with water or an aqueous solution to remove water-soluble alkali metal constituents and produce an aqueous solution enriched in said constituents. The aqueous solution thus produced is then contacted with carbon dioxide to precipitate silicon constituents, the pH of the resultant solution is increased, preferably to a value in the range between about 12.5 and about 15.0, and the solution of increased pH is evaporated to increase the alkali metal concentration. The concentrated aqueous solution is then recycled to the conversion process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst.

  15. A low emittance and high efficiency visible light photocathode for high brightness accelerator-based X-ray light sources

    SciTech Connect

    Vecchione, T.; Ben-Zvi, I.; Dowell, D.H.; Feng, J.; Rao, T.; Smedley, J.; Wan, W.; Padmore, H.A.

    2011-07-21

    Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are a critical performance-limiting component of these systems. Here, we describe the development of photocathodes based on potassium-cesium-antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light, and low transverse emittance.

  16. A low emittance and high efficiency visible light photocathode for high brightness accelerator-based X-ray light sources

    SciTech Connect

    Vecchione, T.; Feng, J.; Wan, W.; Padmore, H. A.; Ben-Zvi, I.; Dowell, D. H.; Rao, T.; Smedley, J.

    2011-07-18

    Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are a critical performance-limiting component of these systems. Here, we describe the development of photocathodes based on potassium-cesium-antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light, and low transverse emittance.

  17. Dynamic optical modulation of an electron beam on a photocathode RF gun: Toward intensity-modulated radiation therapy (IMRT)

    NASA Astrophysics Data System (ADS)

    Kondoh, Takafumi; Kashima, Hiroaki; Yang, Jinfeng; Yoshida, Yoichi; Tagawa, Seiichi

    2008-10-01

    In intensity-modulated radiation therapy (IMRT), the aim is to deliver reduced doses of radiation to normal tissue. As a step toward IMRT, we examined dynamic optical modulation of an electron beam produced by a photocathode RF gun. Images on photomasks were transferred onto a photocathode by relay imaging. The resulting beam was controlled by a remote mirror. The modulated electron beam maintained its shape on acceleration, had a fine spatial resolution, and could be moved dynamically by optical methods.

  18. Salts of alkali metal anions and process of preparing same

    DOEpatents

    Dye, James L.; Ceraso, Joseph M.; Tehan, Frederick J.; Lok, Mei Tak

    1978-01-01

    Compounds of alkali metal anion salts of alkali metal cations in bicyclic polyoxadiamines are disclosed. The salts are prepared by contacting an excess of alkali metal with an alkali metal dissolving solution consisting of a bicyclic polyoxadiamine in a suitable solvent, and recovered by precipitation. The salts have a gold-color crystalline appearance and are stable in a vacuum at -10.degree. C. and below.

  19. Cocrystallization of certain 4f and 5f elements in the bivalent state with alkali metal halides

    SciTech Connect

    Mikheev, N.B.; Kamenskaya, A.M.; Veleshko, I.E.; Kulyukhin, S.A.

    1987-01-01

    The cocrystallization of Fm/sup 2 +/, Es/sup 2 +/, Cf/sup 2 +/, Am/sup 2 +/, Yb/sup 2 +/, Eu/sup 2 +/ and Sr/sup 2 +/ with NaCl, KCl and KBr in tetrahydrofuran (THF), hexamethylphosphorotriamide (HMPA), and ethanol has been studied. It is shown that in water-ethanol medium An/sup 2 +/ cocrystallize with KCl by the formation of anomalous mixed crystals and Ln/sup 2 +/ do not cocrystallize. In HMPA neither Ln/sup 2 +/ nor An/sup 2 +/ are observed to transfer into the KBr solid phase, while in THF both Ln/sup 2 +/ and An/sup 2 +/ cocrystallize with NaCl. The change in the behavior on Ln/sup 2 +/ and An/sup 2 +/ cocrystallize with a change from one solvent to another is caused by the difference in the effective ionic radii of these elements, which arises from the large nephelauxetic effect for An/sup 2 +/ as well as by the different solvating power of these solvents.

  20. The interaction energies and polarizabilities of sodium fluoride, sodium chloride, and some alkali and halide ions pairs

    NASA Astrophysics Data System (ADS)

    Bounds, David G.; Hinchliffe, Alan

    1982-02-01

    Ab initio SCF pair potentials and polarizabilities for NaF, NaCl, F 2-2, Na 2-2, K 2-2, FCl 2-, LiNa 2+, LiK 2+, presented. Together with results reported previously, these values form a complete and consistent set of energy and polarizability data on the fluorides and chlorides of lithium, sodium and potassium.

  1. On the 2 s-like relaxed excited state of the F center in alkali halide crystals

    NASA Astrophysics Data System (ADS)

    Panov, V. G.; Varaksin, A. N.; Sobolev, A. B.

    2008-06-01

    The energy and spectroscopic characteristics of the first excited 2 s-like electron state of the F center are presented according to the calculations performed in the framework of the variational model proposed by Gourary and Adrian. The relaxation of the crystal lattice in the vicinity of the excited F center is described. The problem of the spatial propagation of the F center is discussed. The results obtained for the 2 p and 2 s states of the F center are compared with each other and with the relevant experimental data.

  2. Photocathodes based on semiconductor superlattices for streak tubes for IR region of 0.9-1.0 um

    NASA Astrophysics Data System (ADS)

    Nolle, Eduard L.

    1995-05-01

    A possibility of temporal analysis of picosecond light pulses in the IR region with the help of photocathodes based on semiconductor superlattices (SL) of type I (InP/InGaAs) with Schottky barrier is discussed. A new principle of avalanche photoelectron emission from such an SL at interband absorption of light is suggested. The principle is based on the electrons free length path increasing in a SL with narrow quantum wells under high electric field applied to the SL. The idea makes it possible to develop a new device - avalanche photocathode with internal amplification for the IR region of 0.9-2 micrometers and temporal resolution better than 30 ps. It is proposed to use doped as well as undoped SL as basis for photocathodes sensitive to the IR radiation in the range of up to 10 micrometers . The photoemission from such structures is caused by the intersubband absorption of light in quantum wells. The use of undoped SL greatly reduced the thermoemission current of the photocathode but requires additional excitation of the SL by light pulses with energy approximately corresponding to the band gap of the narrow band gap material of the SL. The temporal resolution of such photocathodes is supposed to be less than 30 ps. The conditions for the avalanche photoelectron emission obtaining are determined, and the SL parameters which meet the requirement of maximum quantum efficiency of the photocathode are calculated.

  3. Faraday rotation density measurements of optically thick alkali metal vapors

    NASA Astrophysics Data System (ADS)

    Vliegen, E.; Kadlecek, S.; Anderson, L. W.; Walker, T. G.; Erickson, C. J.; Happer, William

    2001-03-01

    We investigate the measurement of alkali number densities using the Faraday rotation of linearly polarized light. We find that the alkali number density may be reliably extracted even in regimes of very high buffer gas pressure, and very high alkali number density. We have directly verified our results in potassium using absorption spectroscopy on the second resonance (4 2S→5 2P).

  4. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  5. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  6. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  7. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  8. 40 CFR 721.4660 - Alcohol, alkali metal salt.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alcohol, alkali metal salt. 721.4660... Substances § 721.4660 Alcohol, alkali metal salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as alcohol, alkali metal salt (PMN P-91-151)...

  9. 40 CFR 721.4660 - Alcohol, alkali metal salt.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alcohol, alkali metal salt. 721.4660... Substances § 721.4660 Alcohol, alkali metal salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as alcohol, alkali metal salt (PMN P-91-151)...

  10. 40 CFR 721.4660 - Alcohol, alkali metal salt.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alcohol, alkali metal salt. 721.4660... Substances § 721.4660 Alcohol, alkali metal salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as alcohol, alkali metal salt (PMN P-91-151)...

  11. 40 CFR 721.4660 - Alcohol, alkali metal salt.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alcohol, alkali metal salt. 721.4660... Substances § 721.4660 Alcohol, alkali metal salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as alcohol, alkali metal salt (PMN P-91-151)...

  12. 40 CFR 721.4660 - Alcohol, alkali metal salt.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alcohol, alkali metal salt. 721.4660... Substances § 721.4660 Alcohol, alkali metal salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance generically identified as alcohol, alkali metal salt (PMN P-91-151)...

  13. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ..., alkali salt. 721.5278 Section 721.5278 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.5278 Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical... as a substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to reporting...

  14. 40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ..., alkali salt. 721.8900 Section 721.8900 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.8900 Substituted halogenated pyridinol, alkali salt. (a) Chemical... as substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and P-88-1272) are subject...

  15. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ..., alkali salt. 721.5278 Section 721.5278 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.5278 Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical... as a substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to reporting...

  16. 40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ..., alkali salt. 721.8900 Section 721.8900 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.8900 Substituted halogenated pyridinol, alkali salt. (a) Chemical... as substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and P-88-1272) are subject...

  17. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ..., alkali salt. 721.5278 Section 721.5278 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.5278 Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical... as a substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to reporting...

  18. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ..., alkali salt. 721.5278 Section 721.5278 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.5278 Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical... as a substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to reporting...

  19. 40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ..., alkali salt. 721.5278 Section 721.5278 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.5278 Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical... as a substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to reporting...

  20. Structural Characterization of Methanol Substituted Lanthanum Halides

    PubMed Central

    Boyle, Timothy J.; Ottley, Leigh Anna M.; Alam, Todd M.; Rodriguez, Mark A.; Yang, Pin; Mcintyre, Sarah K.

    2010-01-01

    The first study into the alcohol solvation of lanthanum halide [LaX3] derivatives as a means to lower the processing temperature for the production of the LaBr3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(µ-Br)(H2O)7](Br)2}2 (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H2O)7(MeOH)2](Br)3 (2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH2, crystals of [Ca(MeOH)6](Br)2 (3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr2.75•5.25(MeOH)]+0.25 [LaBr3.25•4.75(MeOH)]−0.25} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr3 in MeOH forming the 8-coordinated [LaBr3(MeOH)5] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX3 derivatives were isolated as [(MeOH)4(Cl)2La(µ-Cl)]2 (6) and [La(MeOH)9](I)3•MeOH (7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR (139La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4 – 6 were slightly higher in comparison to their hydrated counterparts. PMID:20514349

  1. Computational studies of solid-state alkali conduction in rechargeable alkali-ion batteries

    DOE PAGESBeta

    Deng, Zhi; Mo, Yifei; Ong, Shyue Ping

    2016-03-25

    The facile conduction of alkali ions in a crystal host is of crucial importance in rechargeable alkali-ion batteries, the dominant form of energy storage today. In this review, we provide a comprehensive survey of computational approaches to study solid-state alkali diffusion. We demonstrate how these methods have provided useful insights into the design of materials that form the main components of a rechargeable alkali-ion battery, namely the electrodes, superionic conductor solid electrolytes and interfaces. We will also provide a perspective on future challenges and directions. Here, the scope of this review includes the monovalent lithium- and sodium-ion chemistries that aremore » currently of the most commercial interest.« less

  2. Alkali resistant optical coatings for alkali lasers and methods of production thereof

    DOEpatents

    Soules, Thomas F; Beach, Raymond J; Mitchell, Scott C

    2014-11-18

    In one embodiment, a multilayer dielectric coating for use in an alkali laser includes two or more alternating layers of high and low refractive index materials, wherein an innermost layer includes a thicker, >500 nm, and dense, >97% of theoretical, layer of at least one of: alumina, zirconia, and hafnia for protecting subsequent layers of the two or more alternating layers of high and low index dielectric materials from alkali attack. In another embodiment, a method for forming an alkali resistant coating includes forming a first oxide material above a substrate and forming a second oxide material above the first oxide material to form a multilayer dielectric coating, wherein the second oxide material is on a side of the multilayer dielectric coating for contacting an alkali.

  3. Charge Lifetime Measurements at High Average Current Using a K{sub 2}CsSb Photocathode inside a DC High Voltage Photogun

    SciTech Connect

    Mammei, Russell; Feingold, Joshua; Adderley, Philip; Clark, James; Covert, Steven; Grames, Joseph; Hansknecht, John; Machie, Danny; Poelker, Benard; Rao, Triveni; Smedley, John; Walsh, John; McCarter, James; Ruiz-Oses, M

    2013-03-01

    Two K{sub 2}CsSb photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure ~ 10{sup -11} Torr. These photocathodes were evaluated using a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at wavelengths 440 or 532 nm, to generate dc electron beams at currents up to 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without measurable quantum efficiency (QE) decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. Under other conditions the charge lifetime was poor, suggesting a complex QE decay mechanism likely related to chemistry and localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope with energy dispersive x-ray spectroscopy capability, to determine surface morphology and chemical composition.

  4. Terahertz radiation in alkali vapor plasmas

    SciTech Connect

    Sun, Xuan; Zhang, X.-C.

    2014-05-12

    By taking advantage of low ionization potentials of alkali atoms, we demonstrate terahertz wave generation from cesium and rubidium vapor plasmas with an amplitude nearly one order of magnitude larger than that from nitrogen gas at low pressure (0.02–0.5 Torr). The observed phenomena are explained by the numerical modeling based upon electron tunneling ionization.

  5. Purification and Characterization of an Extracellular, Thermo-Alkali-Stable, Metal Tolerant Laccase from Bacillus tequilensis SN4

    PubMed Central

    Sondhi, Sonica; Sharma, Prince; Saini, Shilpa; Puri, Neena; Gupta, Naveen

    2014-01-01

    A novel extracellular thermo-alkali-stable laccase from Bacillus tequilensis SN4 (SN4LAC) was purified to homogeneity. The laccase was a monomeric protein of molecular weight 32 KDa. UV-visible spectrum and peptide mass fingerprinting results showed that SN4LAC is a multicopper oxidase. Laccase was active in broad range of phenolic and non-phenolic substrates. Catalytic efficiency (kcat/Km) showed that 2, 6-dimethoxyphenol was most efficiently oxidized by the enzyme. The enzyme was inhibited by conventional inhibitors of laccase like sodium azide, cysteine, dithiothreitol and β-mercaptoethanol. SN4LAC was found to be highly thermostable, having temperature optimum at 85°C and could retain more than 80% activity at 70°C for 24 h. The optimum pH of activity for 2, 6-dimethoxyphenol, 2, 2′-azino bis[3-ethylbenzthiazoline-6-sulfonate], syringaldazine and guaiacol was 8.0, 5.5, 6.5 and 8.0 respectively. Enzyme was alkali-stable as it retained more than 75% activity at pH 9.0 for 24 h. Activity of the enzyme was significantly enhanced by Cu2+, Co2+, SDS and CTAB, while it was stable in the presence of halides, most of the other metal ions and surfactants. The extracellular nature and stability of SN4LAC in extreme conditions such as high temperature, pH, heavy metals, halides and detergents makes it a highly suitable candidate for biotechnological and industrial applications. PMID:24871763

  6. Purification and characterization of an extracellular, thermo-alkali-stable, metal tolerant laccase from Bacillus tequilensis SN4.

    PubMed

    Sondhi, Sonica; Sharma, Prince; Saini, Shilpa; Puri, Neena; Gupta, Naveen

    2014-01-01

    A novel extracellular thermo-alkali-stable laccase from Bacillus tequilensis SN4 (SN4LAC) was purified to homogeneity. The laccase was a monomeric protein of molecular weight 32 KDa. UV-visible spectrum and peptide mass fingerprinting results showed that SN4LAC is a multicopper oxidase. Laccase was active in broad range of phenolic and non-phenolic substrates. Catalytic efficiency (kcat/Km) showed that 2, 6-dimethoxyphenol was most efficiently oxidized by the enzyme. The enzyme was inhibited by conventional inhibitors of laccase like sodium azide, cysteine, dithiothreitol and β-mercaptoethanol. SN4LAC was found to be highly thermostable, having temperature optimum at 85°C and could retain more than 80% activity at 70°C for 24 h. The optimum pH of activity for 2, 6-dimethoxyphenol, 2, 2'-azino bis[3-ethylbenzthiazoline-6-sulfonate], syringaldazine and guaiacol was 8.0, 5.5, 6.5 and 8.0 respectively. Enzyme was alkali-stable as it retained more than 75% activity at pH 9.0 for 24 h. Activity of the enzyme was significantly enhanced by Cu2+, Co2+, SDS and CTAB, while it was stable in the presence of halides, most of the other metal ions and surfactants. The extracellular nature and stability of SN4LAC in extreme conditions such as high temperature, pH, heavy metals, halides and detergents makes it a highly suitable candidate for biotechnological and industrial applications. PMID:24871763

  7. Hyaline membrane disease, alkali, and intraventricular haemorrhage.

    PubMed Central

    Wigglesworth, J S; Keith, I H; Girling, D J; Slade, S A

    1976-01-01

    The relation between intraventricular haemorrhage (IVH) and hyaline membrane disease (HMD) was studied in singletons that came to necropsy at Hammersmith Hospital over the years 1966-73. The incidence of IVH in singleton live births was 3-22/1000 and of HMD 4-44/1000. Although the high figures were partily due to the large number of low birthweight infants born at this hospital, the incidence of IVH in babies weighing 1001-1500 g was three times as great as that reported in the 1658 British Perinatal Mortality Survey. Most IVH deaths were in babies with HMD, but the higher frequency of IVH was not associated with any prolongation of survival time of babies who died with HMD as compared with the 1958 survey. IVH was seen frequently at gestations of up to 36 weeks in babies with HMD but was rare above 30 weeks' gestation in babies without HMD. This indicated that factors associated with HMD must cause most cases of IVH seen at gestations above 30 weeks. Comparison of clinical details in infants with HMD who died with or without IVH (at gestations of 30-37 weeks) showed no significant differences between the groups other than a high incidence of fits and greater use of alkali therapy in the babies with IVH. During the 12 hours when most alkali therapy was given, babies dying with IVD received a mean total alkali dosage of 10-21 mmol/kg and those dying without IVH 6-34 mmol/kg (P less than 0-001).There was no difference in severity of hypoxia or of metabolic acidosis between the 2 groups. Babies who died with HMD and germinal layer haemorrhage (GLH) without IVH had received significantly more alkali than those who died with HMD alone, whereas survivors of severe respiratory distress syndrome had received lower alkali doses than other groups. It is suggested that the greatly increased death rate from IVH in babies with HMD indicates some alteration of management of HMD (since 1958) as a causative factor. Liberal use of hypertonic alkali solutions is the common factor

  8. Change of the surface potential barrier of GaAs photocathode during two-step activation

    NASA Astrophysics Data System (ADS)

    Niu, Jun; Gao, Youtang; Qian, Yunsheng; Chang, Benkang

    2014-09-01

    High and low temperature activation experiments were carried out for a transmission-mode GaAs photocathode sample, and the activation photocurrent curves were recorded. The variety of the activation photocurrent curves between high and low temperatures was studied. By using fitting calculation, the surface potential barrier parameters of NEA photocathode after high and low temperature activations were obtained, respectively, and the change of the surface potential barriers between high and low -temperature activations is indicated. Besides, The NEA cathode surface after high-temperature activation and low temperature activation were analyzed respectively by using angle-dependent X-ray photoelectron spectroscopy (XPS). Above investigation results indicate that, with contrast to high-temperature activation, the thickness of surface potential barriers after low-temperature activation become thin and the vacuum level is reduced further. As a result, the cathode spectral sensitivity is improved remarkably.

  9. Robust CsBr/Cu Photocathodes for the Linac Coherent Light Source

    SciTech Connect

    Maldonado, Juan R.; Liu, Zhi; Dowell, D.H.; Kirby, Robert E.; Sun, Yun; Pianetta, Piero; Pease, Fabian; /Stanford U., Phys. Dept.

    2011-06-21

    The linac coherent light source (LCLS), an x-ray free-electron laser project presently under construction at SLAC, uses a 2.856 GHz rf photocathode gun with a copper cathode for its electron source. While the copper cathode is performing well for the LCLS project, a cathode material with higher quantum efficiency would reduce the drive laser requirements and allow a greater range of operating conditions. Therefore a robust CsBr/Cu photocathode with greater than 50 times the quantum yield at 257 nm relative to the present LCLS copper cathode has been investigated. Preliminary experiments using a dedicated electron source development test stand at SLAC/SSRL are encouraging and are presented in this paper.

  10. Experimental studies of the charge limit phenomenon in NEA GaAs photocathodes

    SciTech Connect

    Tang, H.; Alley, R.K.; Aoyagi, H.; Clendenin, J.E.; Frisch, J.C.; Mulhollan, G.A.; Saez, P.J.; Schultz, D.C.; Turner, J.L.

    1994-06-01

    Negative electron affinity GaAs photocathodes have been in continuous use at SLAC for generating polarized electron beams since early 1992. If the quantum efficiency of a GaAs cathode is below a critical value, the maximum photoemitted charge with photons of energies close to the band gap in a 2-ns pulse is found to be limited by the intrinsic properties of the cathode instead of by the space charge limit. We have studied this novel charge limit phenomenon in a variety of GaAs photocathodes of different structures and doping densities. We find that the charge limit is strongly dependent on the cathode`s quantum efficiency and the extraction electric field, and to a lesser degree on the excitation laser wavelength. In addition, we show that the temporal behavior of the charge limit depends critically on the doping density.

  11. Silicon photocathode behavior in acidic V(II)-V(III) solutions

    SciTech Connect

    Heller, A.; Lewerenz, H.J.; Miller, B.

    1981-01-01

    The photoelectrochemical cell: p-Si/VCl/sub 3/-VCl/sub 2/-HCl/C shows a 2.87% light-to-electrical conversion efficiency at 101 mW/cm/sup 2/ of natural sunlight. Over a 0.5 V range, the photovoltage follows the redox potential of the solution. Pinning of the p-Si surface Fermi level, previously proposed for this system, is ruled out. The advantages of photocathode-based semi-conductor-liquid junction solar cells (over photoanode-based systems) are demonstrated and discussed and comparisons made with the previously described p-InP photocathode (9.47% light-to-electrical conversion efficiency). Current-voltage characteristics of the cell are given at 101 mW/cm/sup 2/ sunlight. It is shown that the stability and efficiency of this cell is the best of any Si-based photoelectrochemical cell studied so far. (MJJ)

  12. Photo-cathode preparation system of the A0 photo-injector

    NASA Astrophysics Data System (ADS)

    Kuchnir, M.

    2002-08-01

    The A0 Photo-Injector is an electron accelerator located in the AZero high bay area of Fermilab. A pulsed laser system generates electron bunches by the photo-electric effect when hitting a photo-cathode in a 1.5-cell, 1.3 GHz RF gun. A 9-cell, 1.3 GHz superconducting resonant cavity then accelerates the electrons to 15 MeV. The 10 ps time resolved waveform of the laser pulses is transferred to the electron bunches. This report is focused on the first hardware component of this accelerator, the Photo-cathode Preparation System. The reason for its existence is in the nature of the photo-electric material film used: Cs2 > Te (Cesium Telluride), a very reactive compound that once coated on the cathode requires that it be transported and used in ultra high vacuum (UHV), i.e. < 10-9 Torr.

  13. Planar Field Emitters and High Efficiency Photocathodes Based on Ultrananocrystalline Diamond

    NASA Technical Reports Server (NTRS)

    Sumant, Anirudha V. (Inventor); Baryshev, Sergey V. (Inventor); Antipov, Sergey P. (Inventor)

    2016-01-01

    A method of forming a field emitter comprises disposing a first layer on a substrate. The first layer is seeded with nanodiamond particles. The substrate with the first layer disposed thereon is maintained at a first temperature and a first pressure in a mixture of gases which includes nitrogen. The first layer is exposed to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, which has a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %. The field emitter has about 10.sup.12 to about 10.sup.14 emitting sites per cm.sup.2. A photocathode can also be formed similarly by forming a nitrogen doped ultrananocrystalline diamond film on a substrate similar to the field emitter, and then hydrogen terminating the film. The photocathode is responsive to near ultraviolet light as well as to visible light.

  14. Photo-cathode preparation system of the A0 photo-injector

    SciTech Connect

    Moyses Kuchnir et al.

    2002-08-23

    The A0 Photo-Injector is an electron accelerator located in the AZero high bay area of Fermilab. A pulsed laser system generates electron bunches by the photo-electric effect when hitting a photo-cathode in a 1.5-cell, 1.3 GHz RF gun. A 9-cell, 1.3 GHz superconducting resonant cavity then accelerates the electrons to 15 MeV. The 10 ps time resolved waveform of the laser pulses is transferred to the electron bunches. This report is focused on the first hardware component of this accelerator, the Photo-cathode Preparation System. The reason for its existence is in the nature of the photo-electric material film used: Cs{sub 2}Te (Cesium Telluride), a very reactive compound that once coated on the cathode requires that it be transported and used in ultra high vacuum (UHV), i.e. < 10{sup -9} Torr.

  15. Planar field emitters and high efficiency photocathodes based on ultrananocrystalline diamond

    DOEpatents

    Sumant, Anirudha V.; Baryshev, Sergey V.; Antipov, Sergey P.

    2016-08-16

    A method of forming a field emitter comprises disposing a first layer on a substrate. The first layer is seeded with nanodiamond particles. The substrate with the first layer disposed thereon is maintained at a first temperature and a first pressure in a mixture of gases which includes nitrogen. The first layer is exposed to a microwave plasma to form a nitrogen doped ultrananocrystalline diamond film on the first layer, which has a percentage of nitrogen in the range of about 0.05 atom % to about 0.5 atom %. The field emitter has about 10.sup.12 to about 10.sup.14 emitting sites per cm.sup.2. A photocathode can also be formed similarly by forming a nitrogen doped ultrananocrystalline diamond film on a substrate similar to the field emitter, and then hydrogen terminating the film. The photocathode is responsive to near ultraviolet light as well as to visible light.

  16. A High-Gradient CW R Photo-Cathode Electron Gun for High Current Injectors

    SciTech Connect

    Robert Rimmer

    2005-05-01

    The paper describes the analysis and preliminary design of a high-gradient photo-cathode RF gun optimized for high current CW operation. The gun cell shape is optimized to provide maximum acceleration for the newly emitted beam while minimizing wall losses in the structure. The design is intended for use in future high-current high-power CW FELs but the shape optimization for low wall losses may be advantageous for other applications such as XFELs or Linear Colliders using high peak power low duty factor guns where pulse heating is a limitation. The concept allows for DC bias on the photocathode in order to repel ions and improve cathode lifetime.

  17. Photoemission Studies of Metallic Photocathodes Prepared by Pulsed Laser Ablation Deposition Technique

    SciTech Connect

    Fasano, V.; Lorusso, A.; Perrone, A.; De Rosa, H.; Cultrera, L.

    2010-11-10

    We present the results of our investigation on metallic films as suitable photocathodes for the production of intense electron beams in RF photoinjector guns. Pulsed laser ablation deposition technique was used for growing Mg and Y thin films onto Si and Cu substrates in high vacuum and at room temperature.Different diagnostic methods were used to characterize the thin films deposited on Si with the aim to optimize the deposition process. Photoelectron performances were investigated on samples deposited on Cu substrate in an ultra high vacuum photodiode chamber at 10{sup -7} Pa. Relatively high quantum efficiencies have been obtained for the deposited films, comparable to those of corresponding bulks. Samples could stay for several months in humid open air before being tested in a photodiode cell. The deposition process and the role of the photocathode surface contamination and its influence on the photoelectron performances are presented and discussed.

  18. In Situ Observation of Dark Current Emission in a High Gradient rf Photocathode Gun.

    PubMed

    Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P; Baryshev, Sergey V; Chen, Huaibi; Conde, Manoel; Gai, Wei; Ha, Gwanghui; Jing, Chunguang; Wang, Faya; Wisniewski, Eric

    2016-08-19

    Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (∼100  μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ∼100  MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. The postexaminations with scanning electron microscopy and white light interferometry reveal the origins of ∼75% strong emission areas overlap with the spots where rf breakdown has occurred. PMID:27588860

  19. In Situ Observation of Dark Current Emission in a High Gradient rf Photocathode Gun

    NASA Astrophysics Data System (ADS)

    Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.; Baryshev, Sergey V.; Chen, Huaibi; Conde, Manoel; Gai, Wei; Ha, Gwanghui; Jing, Chunguang; Wang, Faya; Wisniewski, Eric

    2016-08-01

    Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (˜100 μ m ) dark current imaging experiment has been performed in an L -band photocathode gun operating at ˜100 MV /m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. The postexaminations with scanning electron microscopy and white light interferometry reveal the origins of ˜75 % strong emission areas overlap with the spots where rf breakdown has occurred.

  20. Engineering Design and Fabrication of an Ampere-Class Superconducting Photocathode Electron Gun

    SciTech Connect

    Ben-Zvi,I.

    2008-11-17

    Over the past three years, Advanced Energy Systems and Brookhaven National Laboratory (BNL) have been collaborating on the design of an Ampere- class superconducting photocathode electron gun. BNL performed the physics design of the overall system and RF cavity under prior programs. Advanced Energy Systems (AES) is currently responsible for the engineering design and fabrication of the electron gun under contract to BNL. We will report on the engineering design and fabrication status of the superconducting photocathode electron gun. The overall configuration of the cryomodule will be reviewed. The layout of the hermitic string, space frame, shielding package, and cold mass will be discussed. The engineering design of the gun cavity and removable cathode will be presented in detail and areas of technical risk will be highlighted. Finally, the fabrication sequence and fabrication status of the gun cavity will be discussed.

  1. Method for resurrecting negative electron affinity photocathodes after exposure to an oxidizing gas

    DOEpatents

    Mulhollan, Gregory A; Bierman, John C

    2012-10-30

    A method by which negative electron affinity photocathodes (201), single crystal, amorphous, or otherwise ordered, can be made to recover their quantum yield following exposure to an oxidizing gas has been discovered. Conventional recovery methods employ the use of cesium as a positive acting agent (104). In the improved recovery method, an electron beam (205), sufficiently energetic to generate a secondary electron cloud (207), is applied to the photocathode in need of recovery. The energetic beam, through the high secondary electron yield of the negative electron affinity surface (203), creates sufficient numbers of low energy electrons which act on the reduced-yield surface so as to negate the effects of absorbed oxidizing atoms thereby recovering the quantum yield to a pre-decay value.

  2. Ultraviolet quantum detection efficiency of potassium bromide as an opaque photocathode applied to microchannel plates

    NASA Technical Reports Server (NTRS)

    Siegmund, Oswald H. W.; Everman, E.; Vallerga, J. V.; Sokolowski, J.; Lampton, M.

    1987-01-01

    The quantum detection efficiency (QDE) of potassium bromide as a photocathode applied directly to the surface of a microchannel plate over the 250-1600 A wavelength range has been measured. The contributions of the photocathode material in the channels and on the interchannel web to the QDE have been determined. Two broad peaks in the QDE centered at about 450 and about 1050 A are apparent, the former with about 50 percent peak QDE and the latter with about 40 percent peak QDE. The photoelectric threshold is observed at about 1600 A, and there is a narrow QDE minimum at about 750 A which correlates with 2X the band gap energy for KBr. The angular variation of the QDE from 0 to 40 deg to the channnel axis has also been examined. The stability of Kbr with time is shown to be good with no significant degradation of QDE at wavelengths below 1216 A over a 15-day period in air.

  3. Structural and morphological properties of metallic thin films grown by pulsed laser deposition for photocathode application

    NASA Astrophysics Data System (ADS)

    Lorusso, A.; Gontad, F.; Caricato, A. P.; Chiadroni, E.; Broitman, E.; Perrone, A.

    2016-03-01

    In this work yttrium and lead thin films have been deposited by pulsed laser deposition technique and characterized by ex situ different diagnostic methods. All the films were adherent to the substrates and revealed a polycrystalline structure. Y films were uniform with a very low roughness and droplet density, while Pb thin films were characterized by a grain morphology with a relatively high roughness and droplet density. Such metallic materials are studied because they are proposed as a good alternative to copper and niobium photocathodes which are generally used in radiofrequency and superconducting radiofrequency guns, respectively. The photoemission performances of the photocathodes based on Y and Pb thin films have been also studied and discussed.

  4. 40 CFR 721.10698 - Polyfluorinated alkyl halide (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Polyfluorinated alkyl halide (generic). 721.10698 Section 721.10698 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) TOXIC SUBSTANCES CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific Chemical Substances §...

  5. Kinetic Studies of the Solvolysis of Two Organic Halides

    ERIC Educational Resources Information Center

    Duncan, J. A.; Pasto, D. J.

    1975-01-01

    Describes an undergraduate organic chemistry laboratory experiment which utilizes the solvolysis of organic halides to demonstrate first and second order reaction kinetics. The experiment also investigates the effect of a change of solvent polarity on reaction rate, common-ion and noncommon-ion salt effects, and the activation parameters of a…

  6. Method for calcining nuclear waste solutions containing zirconium and halides

    DOEpatents

    Newby, Billie J.

    1979-01-01

    A reduction in the quantity of gelatinous solids which are formed in aqueous zirconium-fluoride nuclear reprocessing waste solutions by calcium nitrate added to suppress halide volatility during calcination of the solution while further suppressing chloride volatility is achieved by increasing the aluminum to fluoride mole ratio in the waste solution prior to adding the calcium nitrate.

  7. Methyl halide emission estimates from domestic biomass burning in Africa

    NASA Astrophysics Data System (ADS)

    Mead, M. I.; Khan, M. A. H.; White, I. R.; Nickless, G.; Shallcross, D. E.

    Inventories of methyl halide emissions from domestic burning of biomass in Africa, from 1950 to the present day and projected to 2030, have been constructed. By combining emission factors from Andreae and Merlet [2001. Emission of trace gases and aerosols from biomass burning. Global Biogeochemical Cycles 15, 955-966], the biomass burning estimates from Yevich and Logan [2003. An assessment of biofuel use and burning of agricultural waste in the developing world. Global Biogeochemical Cycles 17(4), 1095, doi:10.1029/2002GB001952] and the population data from the UN population division, the emission of methyl halides from domestic biomass usage in Africa has been estimated. Data from this study suggest that methyl halide emissions from domestic biomass burning have increased by a factor of 4-5 from 1950 to 2005 and based on the expected population growth could double over the next 25 years. This estimated change has a non-negligible impact on the atmospheric budgets of methyl halides.

  8. Students' Understanding of Alkyl Halide Reactions in Undergraduate Organic Chemistry

    ERIC Educational Resources Information Center

    Cruz-Ramirez de Arellano, Daniel

    2013-01-01

    Organic chemistry is an essential subject for many undergraduate students completing degrees in science, engineering, and pre-professional programs. However, students often struggle with the concepts and skills required to successfully solve organic chemistry exercises. Since alkyl halides are traditionally the first functional group that is…

  9. On the Boiling Points of the Alkyl Halides.

    ERIC Educational Resources Information Center

    Correia, John

    1988-01-01

    Discusses the variety of explanations in organic chemistry textbooks of a physical property of organic compounds. Focuses on those concepts explaining attractive forces between molecules. Concludes that induction interactions play a major role in alkyl halides and other polar organic molecules and should be given wider exposure in chemistry texts.…

  10. Semiempirical and DFT Investigations of the Dissociation of Alkyl Halides

    ERIC Educational Resources Information Center

    Waas, Jack R.

    2006-01-01

    Enthalpy changes corresponding to the gas phase heats of dissociation of 12 organic halides were calculated using two semiempirical methods, the Hartree-Fock method, and two DFT methods. These calculated values were compared to experimental values where possible. All five methods agreed generally with the expected empirically known trends in the…

  11. CO2 electrochemical reduction via adsorbed halide anions

    NASA Astrophysics Data System (ADS)

    Ogura, Kotaro; Salazar-Villalpando, Maria D.

    2011-01-01

    The electrochemical reduction of CO2 was studied utilizing halide ions as electrolytes, specifically, aqueous solutions of KCl, KBr, KI. Electrochemical experiments were carried out in a laboratory-made, divided H-type cell. The working electrode was a copper mesh, while the counter and reference electrodes were a Pt wire and an Ag/AgCl electrode, respectively. The results of our work suggest a reaction mechanism for the electrochemical reduction of CO2 where the presence of Cu-X as the catalytic layer facilitates the electron transfer from the electrode to CO2. Electron-transfer to CO2 may occur via the X- ad(Br-, Cl-, I-)-C bond, which is formed by the electron flow from the specifically adsorbed halide anion to the vacant orbital of CO2. The stronger the adsorption of the halide anion to the electrode, the more strongly CO2 is restrained, resulting in higher CO2 reduction current. Furthermore, it is suggested that specifically adsorbed halide anions could suppress the adsorption of protons; leading to a higher hydrogen overvoltage. These effects may synergistically mitigate the over potential necessary for CO2 reduction, and thus increase the rate of electrochemical CO2 reduction.

  12. The Argonne Wakefield Accelerator high current photocathode, gun and drive linac

    SciTech Connect

    Schoessow, P.; Chojnacki, E.; Cox, G.

    1995-06-01

    The Argonne Wakefield Accelerator (AWA) is a new facility for advanced accelerator research. A major component of the AWA is its drive linac, consisting of a unique high current short pulse L-Band photocathode based gun and special standing wave preaccelerator designed to produce 100 nC, 30 ps electron bunches at 20 MeV. Commissioning on the drive linac is now underway. We report on our initial operating experience with this novel machine, including bunch length and emittance measurements.

  13. Growth and characterization of rugged sodium potassium antimonide photocathodes for high brilliance photoinjector

    NASA Astrophysics Data System (ADS)

    Cultrera, L.; Karkare, S.; Lillard, B.; Bartnik, A.; Bazarov, I.; Dunham, B.; Schaff, W.; Smolenski, K.

    2013-09-01

    Sodium potassium antimonide photocathodes with Quantum Efficiency (QE) in the range of few percent have been grown, and their photoemission properties are measured. We report the intrinsic emittance and response time of electron bunches extracted from this material. It is possible to recover the QE of an overheated cathode by simple potassium addition, and the cathode is rugged enough to deliver tens of mA of average current with no or minimal degradation.

  14. Characterization and development of photocathodes using laser induced time-of-flight spectroscopy

    NASA Astrophysics Data System (ADS)

    Ramirez-Homs, E.; Velazquez, D.; Spentzouris, L.; Terry, J.

    2011-10-01

    The emittance of a beam generated for use in particle accelerators is a critical performance parameter. In order to achieve peak performance, intrinsic transverse emittance on the order of 0.1mm-mrad is required. This initial emittance is about an order of magnitude lower than provided by today's sources. Several important efforts are being made to reach this lower emittance with cathode design modifications. A photocathode design study and implementation of experimental techniques for the characterization is proposed and discussed.

  15. Porous copper zinc tin sulfide thin film as photocathode for double junction photoelectrochemical solar cells.

    PubMed

    Dai, Pengcheng; Zhang, Guan; Chen, Yuncheng; Jiang, Hechun; Feng, Zhenyu; Lin, Zhaojun; Zhan, Jinhua

    2012-03-21

    Porous copper zinc tin sulfide (CZTS) thin film was prepared via a solvothermal approach. Compared with conventional dye-sensitized solar cells (DSSCs), double junction photoelectrochemical cells using dye-sensitized n-type TiO(2) (DS-TiO(2)) as the photoanode and porous p-type CZTS film as the photocathode shows an increased short circuit current, external quantum efficiency and power conversion efficiency. PMID:22322239

  16. Instrumentation for Theory-Inspired Photocathode Development within the Large Area Picosecond Photodetector (LAPPD) Project

    NASA Astrophysics Data System (ADS)

    Xie, Junqi; Attenkofer, Klaus; Demarteau, Marcel W.; Frisch, Henry J.; Lee, Seon W.; Paramonov, Alexander; Wagner, Robert G.; Yusof, Zikri; Large Area Picosecond Photodetector Collaboration

    We have designed and are commissioning a laboratory for the growth and characterization of photocathodes at Argonne National Laboratory. Two growth facilities, a versatile ultra high vacuum growth chamber and an industrial photomultiplier production facility, allow the investigation of fundamental aspects of the cathode growth and the development, modification and implementation of recipes in an industrial production environment. The instrumentation allows the study of optical properties, electrical behaviors and spectral response of the cathode.

  17. Polarization Possibilities of Small Spin-Orbit Interaction in Strained-Superlattice Photocathodes

    SciTech Connect

    Not Available

    2010-08-25

    Strained-superlattice photocathodes based on InGaP/GaAs were investigated. The photocathode performance is found highly dependent on the superlattice parameters. The electron confinement energy in superlattice appears important. The strained-superlattice structure based on GaAsP/GaAs, with a maximum polarization as high as 90% and more than 1% quantum efficiency, is presently the prime candidate for the ILC polarized electron photocathodes. A recent systematic study shows, however, that the peak polarization seems saturated even though the heavy-hole (HH) and light-hole (LH) band splitting is increased significantly, indicating that there is a material specific spin relaxation mechanism. It is widely accepted that the D'yakonov-Perel mechanism is the dominant spin relaxation mechanism in the III-V compound superlattice structures with a low p-doping ({le} 10{sup 17} cm{sup -3}), and that the spin relaxation may be reduced by choosing a material with a smaller spin-orbit interaction. As the spin-orbit interaction in phosphides is much smaller than in arsenides, strained-superlattice structure based on InGaP/GaAs were investigated. The computer code SPECCODE developed by Subashiev and Gerchikov has been used for calculating the band structures in superlattice.

  18. Nonepitaxial Thin-Film InP for Scalable and Efficient Photocathodes.

    PubMed

    Hettick, Mark; Zheng, Maxwell; Lin, Yongjing; Sutter-Fella, Carolin M; Ager, Joel W; Javey, Ali

    2015-06-18

    To date, some of the highest performance photocathodes of a photoelectrochemical (PEC) cell have been shown with single-crystalline p-type InP wafers, exhibiting half-cell solar-to-hydrogen conversion efficiencies of over 14%. However, the high cost of single-crystalline InP wafers may present a challenge for future large-scale industrial deployment. Analogous to solar cells, a thin-film approach could address the cost challenges by utilizing the benefits of the InP material while decreasing the use of expensive materials and processes. Here, we demonstrate this approach, using the newly developed thin-film vapor-liquid-solid (TF-VLS) nonepitaxial growth method combined with an atomic-layer deposition protection process to create thin-film InP photocathodes with large grain size and high performance, in the first reported solar device configuration generated by materials grown with this technique. Current-voltage measurements show a photocurrent (29.4 mA/cm(2)) and onset potential (630 mV) approaching single-crystalline wafers and an overall power conversion efficiency of 11.6%, making TF-VLS InP a promising photocathode for scalable and efficient solar hydrogen generation. PMID:26266588

  19. Channel electron multipliers - Detection efficiencies with opaque MgF2 photocathodes at XUV wavelengths

    NASA Technical Reports Server (NTRS)

    Lapson, L. B.; Timothy, J. G.

    1976-01-01

    Detection efficiencies of channel electron multipliers (CEM) with opaque MgF2 photocathodes obtained in the extreme ultraviolet (XUV), 44 A to 990 A, are reported. A stable highly efficient response is reported for that interval, with no adverse effects on CEM performance. Efficiencies twice those of uncoated CEMs are obtained for 50 A to 350 A. The Mullard B419BL and Galileo 4510WL single-stage cone-cathode CEMs were used in the experiments. A rare-gas double ionization chamber was employed as absolute standard detector for 406 A to 990 A, and a flow Geiger counter filled with 96% argon and 4% isobutane for 44 A to 256 A. Absolute detection efficiencies are 10% higher from 67 A to 990 A when photocathodes are illuminated at an angle of incidence 45 deg. The photocathodes suffered no loss of response in storage (in vacuum or air) after an initial aging period. Effects of scattered UV radiation are greatly reduced when MgF2-coated CEMs are used in the XUV.

  20. Nonlinear response of the photocathode of an x-ray streak camera to UV light

    SciTech Connect

    Kyrala, G.A.; Oro, D.M.; Studebaker, J.K.; Wood, W.M.; Schappert, G.T.; Watts, S.; Fulton, R.D.

    1994-09-01

    We have found that a potassium-iodide photocathode of an x-ray streak camera responds to UV light at {lambda}=308 nm. The photocathode surface work function, 6.5 eV, is larger than the 4 eV energy of the UV photon, hence the source of the response is interesting. We will present results on the response of a transmission type potassium-iodide photocathode to the UV light from a {lambda}308 nm, subpicosecond XeCl laser and from a {lambda}=326 nm HeCd laser. We will test for the nonlinearity of the yield to measure of the number of photons that are needed to be absorbed before a signal is recorded. We will present data on the effect of the UV irradiance on the yield, as well as on the temporal width of the recorded signal. We will give an explanation of the observation and its effect on the dynamic-range response of the streak-camera. We will show that the response is linear with the incident irradiance, up to an incident irradiance of 10{sup 8} W/cm{sup 2} and we will explain the observation.