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1

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

NASA Technical Reports Server (NTRS)

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.

Carruthers, George R.

1987-01-01

2

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

3

Synthetic Alkali Halides  

NSDL National Science Digital Library

This complex experimental investigation uses alkali halides (NaCl, KCl, and mixtures of both) to simulate the melting of alkali feldspars which melt at too high of temperatures to work with in lab. Three hypotheses are tested: It is possible to crystallize alkali-chloride salts from a magma with any composition between NaCl and KCl. Because K+ and Na+ do not have the same ionic size, the atomic spacing in alkali chlorides will vary systematically with composition. Alkali chlorides are equally stable at high (just below liquidus) and low (subsolidus)temperatures. This project takes more than one class period, depending on how many students are in the class, because there will be lines at the scales, oven, and XRD. It is advisable to introduce the lab in class and have students complete various parts on their own time. There are three main parts. Part one: Synthesize all alkali halide compositions at high temperature (hopefully above the solvus. Part two: Put grown crystals back in an oven at lower temperature to see if they will unmix. Part three: Write a report evaluating and interpreting all results, relevant graphs, and the above three hypothesis.

Dexter Perkins

4

Adsorption on Alkali Halides.  

NASA Astrophysics Data System (ADS)

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.

Urzua Duran, Gilberto Antonio

1995-01-01

5

The Additive Coloration of Alkali Halides  

ERIC Educational Resources Information Center

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…

Jirgal, G. H.; and others

1969-01-01

6

Elastic constants of alkali halides: Multipole expansion  

NASA Astrophysics Data System (ADS)

The elastic constants at zero temperature are calculated for the alkali-halide crystals. Two new terms are included: the induced quadrupole and induced octupole polarizabilities of the ions. These terms are significant, and affect the final result by 5-50%. The elastic constants are a good quantity for testing theories of ionic bonding.

Mahan, G. D.

1984-05-01

7

Solvation at nanoscale: Alkali-halides in water clusters  

SciTech Connect

The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.

Partanen, Leena [Department of Physics, Tampere University of Technology, Box 692, 33101 Tampere (Finland); Mikkelae, Mikko-Heikki; Huttula, Marko [Department of Physics, University of Oulu, Box 3000, 90014 University of Oulu (Finland); Tchaplyguine, Maxim [MAX-lab, Lund University, Box 118, 22100 Lund (Sweden); Zhang Chaofan; Andersson, Tomas; Bjoerneholm, Olle [Department of Physics and Astronomy, University of Uppsala, Box 516, 75120 Uppsala (Sweden)

2013-01-28

8

Enhanced Quantum Efficiency From Hybrid Cesium Halide/Copper Photocathode  

SciTech Connect

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.

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

2014-04-28

9

Ionic alkali halide XUV laser feasibility study  

SciTech Connect

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.

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

1989-11-10

10

Anion polarizability functions in alkali halide crystals  

NASA Astrophysics Data System (ADS)

Anion polarizabilities in alkali halide crystals are analysed as a function of interionic separation R . The anion polarizability is treated as a function of the anion and cation radii, with its partial derivatives approximated by those with respect to R for fixed cation and anion, respectively. With pressure derivatives of the ionic radii deduced from the crystal compressibility, assuming transferability among crystals, the polarizability derivatives with respect to ionic radius yield pressure derivatives of the polarizability that agree with experiment to within a factor of two. These results offer a useful means of predicting the pressure dependence of dielectric data.

Batana, A.; Bruno, J.; Munn, R. W.

11

Alkali Halide Nanotubes: Structure and Stability  

PubMed Central

Accurate density functional theory (DFT) and coupled-cluster (CCSD) calculations on a series of (LiF)n=2,36 neutral clusters suggest that nanotube structures with hexagonal and octagonal transversal cross sections show stability equal to or greater than that of the typical cubic form of large LiF crystals. The nanotube stability was further corroborated by quantum dynamic calculations at room temperature. The fact that stable nanotube structures were also found for other alkali halides (e.g., NaCl and KBr) suggests that this geometry may be widely implemented in material sciences. PMID:24376901

Fernandez-Lima, Francisco A.; Henkes, Aline Verônica; da Silveira, Enio F.; Nascimento, Marco Antonio Chaer

2013-01-01

12

Thermoluminescence of alkali halides and its implications  

NASA Astrophysics Data System (ADS)

Trapping levels present in some alkali halides namely NaCl, KCl, KBr, and KI are determined by deconvolution of the thermoluminescence (TL) curves. Unlike most of the studies undertaken over the last few decades, we have presented a comprehensive picture of the phenomenon of TL as an analytical technique capable of revealing the position of the trapping levels present in the materials. We show that for all practical purposes, TL can be described involving only the three key trapping parameters, namely, the activation energy (E), the frequency factor (s), and the order of kinetics (b) even for complex glow curves having a number of TL peaks. Finally, based on these, we logically infer the importance of TL in development and characterization of materials used in dosimetry, dating and scintillation.

Gartia, R. K.; Rey, L.; Tejkumar Singh, Th.; Basanta Singh, Th.

2012-03-01

13

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

NASA Astrophysics Data System (ADS)

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 1025/m3. The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics.

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

2014-12-01

14

Magnetic polarizations of electrons at dislocations in alkali halides  

E-print Network

interval. 25 NAGNETIC POLARIZATIONS OF ELECTRONS AT DISLOCATIONS IN ALKALI HALIDES 1. INTRODUCTION. The new magnetic effects observed in our laboratory on a number of single crystals of alkali halides are thought to be caused by electrons trapped... on d1slocations. The magnet1c properties are perhaps more interesting as a bas1c contribution to the sc1ence of magnetism than to a knowledge of d. islocations 1n these very pure, optically clear, s1ngle crystals of alkal1 halides. The gross magnet...

McClurg, Gene Roark

2012-06-07

15

Structured alkali halides for medical applications  

NASA Astrophysics Data System (ADS)

Image plates based on storage phosphors are a major application of radiation defects in insulators. Storage phosphors absorb X-ray quanta creating trapped electron-hole pairs in the material. Optical stimulation of the electron causes recombination leading to light emission. Application of image plates requires an optimal compromise between resolution (represented by the modulation transfer function (MTF)) and sensitivity. In our paper we present a new solution of the problem of combining a high MTF with a high sensitivity by structuring the image plates in form of thin needles acting as light guides. This suppresses the lateral spread of light which is detrimental to resolution. As doped CsBr, e.g. CsBr:Ga [Physica Medica XV (1999) 301], can pose a good storage phosphor evaporated layers are of interest in computed radiography. Needle structured CsI:Tl is used as scintillator in direct radiography [IEEE Trans. Nucl. Sci. 45 (3) (1998)]. CsBr layers have been produced by evaporation in vacuum and in inert gas atmosphere varying pressure and temperature. The resulting structures are of fibrous or columnar nature being in good agreement with the zone model of Thornton [Ann. Rev. Mater. Sci. 7 (1977) 239]. A zone model for CsBr has been developed. Measurements on doped alkali halide image plates having needle structure show good MTF at high sensitivity making a significant progress in image plate technology.

Schmitt, B.; Fuchs, M.; Hell, E.; Knüpfer, W.; Hackenschmied, P.; Winnacker, A.

2002-05-01

16

Infrared Laser-Induced Breakdown Spectroscopy of Alkali Metal Halides  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) is a powerful diagnostic tool for detection of trace elements by monitoring the atomic and ionic emission from laser-induced plasmas. LIBS is a relatively simple technique and has been successfully employed in applications such as environmental monitoring, materials analysis, medical diagnostics, industrial process control, and homeland security. Most LIBS applications are limited to emission features in the ultraviolet-visible-near infrared (UV-VIS-NIR) region arising from atoms and simple molecular fragments. In the present work, we report on the observation of mid- infrared emission lines from alkali metal halides due to laser-induced breakdown processes. The studied alkali metal halides included LiCl, NaCl, NaBr, KCl, KBr, KF, RbCl, and RbBr. The laser-induced plasma was produced by focusing a 16 mJ pulsed Nd:YAG laser (1064 nm) on the target. The LIBS infrared emission from alkali halides showed intense and narrow bands located in the region from 2-8 ?m. The observed emission features were assigned to atomic transitions between higher-lying Rydberg states of neutral alkali atoms. More detailed results of the performed IR LIBS studies on alkali metal halides will be discussed at the conference.

Brown, Ei; Hommerich, Uwe; Yang, Clayton; Trivedi, Sudhir; Samuels, Alan; Snyder, Peter

2008-10-01

17

Interfacial tension in immiscible mixtures of alkali halides.  

PubMed

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

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

2010-02-01

18

Refractive indices, electronic polarizabilities and dielectric constants of alkali halides  

NASA Astrophysics Data System (ADS)

New relations are proposed for the evaluation of refractive indices, electronic polarizabilities and optical dielectric constants of alkali halides. Refractive indices and optical dielectronic constants for alkali halides have been estimated based on the following relations: E ge 1.4n = 63.8 + 0.03? eE ge 1.4n = 68.5 + 3.9? ex e and ? = {E 2g}/{83.1}-0.5E g + 5.9 where Eg, n, ? e, ? exe and ? are the energy gap (in eV), refractive index, equilibrium vibrational frequency (in cm -1), vibrational anharmonicity constant term (in cm -1) and optical dielectric constant, respectively. Strain derivative values of the electronic dielectric constant in ionic crystals are also evaluated using the energy gap. In all cases the calculated and the literature values are in good agreement with each other.

Reddy, R. R.; Anjaneyulu, S.; Rao, T. V. R.

1992-09-01

19

Volcanic Origin of Alkali Halides on Io  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

20

Electronic excitation in bulk and nanocrystalline alkali halides  

NASA Astrophysics Data System (ADS)

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.

Bichoutskaia, Elena; Pyper, Nicholas C.

2012-11-01

21

Morphology transitions during the growth of alkali halides from solution  

NASA Astrophysics Data System (ADS)

Four alkali-halide salt compounds were prepared by the evaporation of aqueous solutions on mica substrates. Growth runs were carried out over a wide range of conditions by varying the substrate temperature and the evaporation rate independently. During RbI growth, where the misfit between salt and mica lattices is small, the morphology of the deposited salt crystals tends to be faceted, except under extreme conditions. For salts with a larger misfit relative to the substrate (KI, RbBr, and CsBr), faceted growth is no longer the most common form. Despite the differences among the various compounds, in all cases we find sets of growth conditions which can favor faceted, dendritic, directional-array, and seaweed morphologies. While many previous experiments have focused upon a single morphology transition, these experiments show that at least four distinct morphologies can be produced in a single material system when growth conditions are varied sufficiently.

Lamelas, F. J.; Seader, S.; Zunic, M.; Sloane, C. V.; Xiong, May

2003-01-01

22

Comparison of CsBr and KBr coated Cu photocathodes: Effects of laser irradiation and work function changes  

SciTech Connect

Thin films (7 nm layers) of CsBr and KBr were deposited on Cu(100) to investigate photoemission properties of these potential photocathode materials. After thin film deposition and prolonged laser ultraviolet (UV) irradiation (266 nm picosecond laser) photoemission quantum efficiency increases by factors of 26 and 77 for KBr/Cu(100) and CsBr/Cu(100) photocathodes, respectively. Immediately following thin film deposition, a decrease in work function is observed, compared to bare Cu, in both cases. Quantum efficiency enhancements are attributed to the decrease in photocathode work function, due to the deposition of alkali halide thin films, and photo-induced processes, that introduce defect states into the alkali halide bandgap, induced by UV laser irradiation. It is possible that alkali metal formation occurs during UV irradiation and that this further contributes to photoemission enhancement. Our results suggest that KBr, a relatively stable alkali-halide, has potential for photocathode applications.

He, Weidong; VilayurGanapathy, Subramanian; Joly, Alan G.; Droubay, Timothy C.; Chambers, Scott A.; Maldonado, Juan R.; Hess, Wayne P.

2013-02-20

23

Two types of epitaxial orientations for the growth of alkali halide on fcc metal substrates  

NASA Astrophysics Data System (ADS)

Thin-film growth of alkali halides on (001) surfaces of fcc transition metals was studied using reflection high-energy electron diffraction. Alkali halide grew with its [100] axis rotated by 45° from that of the metal substrate ([100]film//[110]substrate) for LiCl/Cu(001) and LiCl/Ni(001). On the contrary, alkali halide grew without azimuthal rotation ([100]film//[100]substrate) for LiCl/Ag(001), NaCl/Cu(001), NaCl/Ag(001), and NaCl0.6Br0.4/Ag(001). The former growth mode ([100]film//[110]substrate) occurred only with a small difference in the first-nearest neighbor (first-NN) interatomic distance between alkali halide and metal. The latter growth mode ([100]film//[100]substrate) occurred even with a large difference in the first-NN interatomic distance. The mechanism of the latter growth was explained by the preferential direction of steps on (001) surfaces of fcc metals and the migration of alkali halide molecules to the steps.

Kiguchi, Manabu; Entani, Shiro; Saiki, Koichiro; Inoue, Hiroaki; Koma, Atsushi

2002-10-01

24

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

NASA Astrophysics Data System (ADS)

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.

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

25

Thermally stimulated depolarization of Eu 2+-cation vacancy dipoles in alkali halide single crystals  

NASA Astrophysics Data System (ADS)

Ionic thermocurrent (ITC) measurements have been performed on eight alkali halide single crystals doped with divalent europium. In all cases, the observed ITC peaks were fitted with a mono-energetic model without to appeal to any dipole-dipole interaction. Values for the reorientation parameters have been calculated. The relationship T M1n? -1 ? E previously found for I-V complexes in alkali halides has been found to be very well obeyed for the experimental data obtained in this investigation. It is also reported that the logarithm of the experimentally determined energies for free dipole reorientation shows a linear dependence on the interaction distance between the Eu 2+ ion and the surrounding halogen ions in the distorted cubic site occupied by this impurity in the alkali halides.

Hernández, J. A.; Murrieta, H. S.; Jaque, F.; Rubio, J. O.

1981-09-01

26

A mass-spectrometric determination of the work function of alkali metal halide crystals  

NASA Astrophysics Data System (ADS)

Thermochemical cycles including experimentally measured enthalpies of sublimation of alkali metal halides in the form of M2X+ and MX{2/?} ionic clusters and MX molecules were used to calculate work functions for NaCl, NaBr, NaI, KCl, KBr, KI, RbCl, and RbI.

Kudin, L. S.; Dunaev, A. M.; Butman, M. F.; Kryuchkov, A. S.

2011-02-01

27

COLOUR CENTRES IN DOPED ALKALI HALIDES. THE ROLE OF OXYGEN AND TITANIUM  

E-print Network

COLOUR CENTRES IN DOPED ALKALI HALIDES. THE ROLE OF OXYGEN AND TITANIUM IN THE LUMINESCENCE OF Li that the luminescence occurs by hole capture at a titanium defect site. However electron spin resonance has shown that the titanium is incorporated in the crystal as Ti3+ and Ti4+ ions with the possibility of charge compensa- tion

Paris-Sud XI, Université de

28

Ordering of alkali halide salts dissolved in bacteriophage Pf1 solutions: A nuclear magnetic resonance study  

E-print Network

Ordering of alkali halide salts dissolved in bacteriophage Pf1 solutions: A nuclear magnetic into filamentous bacteriophage Pf1 solutions display line splittings and shifts consistent with an interaction phospholipid bicelles1 and filamen- tous virus2 and bacteriophage3 particles partially restores an- isotropic

Augustine, Mathew P.

29

On the interionic potentials and polarization models in alkali halide crystals  

NASA Astrophysics Data System (ADS)

It is shown that the modified Szigeti relation can be used to make a critical assessment of various polarization models and interionic potentials in alkali halides. Various sets of interionic potentials derived recently are critically discussed. The importance of three body interactions in developing a potential model as well as a polarization model is demonstrated.

Shanker, J.; Sinha, R. K.; Hans, D.

1987-06-01

30

The role of halide ions on the electrochemical behaviour of iron in alkali solutions  

NASA Astrophysics Data System (ADS)

Active dissolution and passivation of transition metals in alkali solutions is of technological importance in batteries. The performance of alkaline batteries is decided by the presence of halides as they influence passivation. Cyclic voltammetric studies were carried out on iron in different sodium hydroxide solutions in presence of halides. In alkali solutions iron formed hydroxo complexes and their polymers in the interfacial diffusion layer. With progress of time they formed a cation selective layer. The diffusion layer turned into bipolar ion selective layer consisted of halides, a selective inner sublayer to the metal side and cation selective outer layer to the solution side. At very high anodic potentials, dehydration and deprotonation led to the conversion of salt layer into an oxide.

Begum, S. Nathira; Muralidharan, V. S.; Basha, C. Ahmed

2008-02-01

31

An overlap model for exchange-induction: application to alkali halides  

NASA Astrophysics Data System (ADS)

An existing method for estimating intermolecular exchange energies in weak Van der Waals interactions, based on the overlap between their ground-state charge densities, is extended to ionic interactions using the overlap between the polarised charge density of a negative ion and the ground-state charge density of surrounding positive ions. This enables the exchange-induction energy to be included in the model. One adjustable parameter for each ion pair is fitted to the dimer interaction energy. The prediction of in-crystal anion polarizabilities is excellent for the five alkali halides tested, and polarizabilities of anions in ionic dimers and trimers are reasonably well reproduced for lithium halides.

Wheatley, Richard J.

1998-09-01

32

Aluminum bromide fused-salt battery. [Al\\/Al+ alkali halides\\/C, 50 to 250° operating temp  

Microsoft Academic Search

A battery which operates at lower temperatures (50 to 250°) than other molten salt batteries is described. It has an aluminum anode, a carbon cathode, and an electrolyte of aluminum and alkali metal halides. (RWR)

Buzzelli

1972-01-01

33

Reactions between cold methyl halide molecules and alkali-metal atoms  

NASA Astrophysics Data System (ADS)

We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH3X (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, CH3X + A ? CH3 + 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.

Lutz, Jesse J.; Hutson, Jeremy M.

2014-01-01

34

Reactions between cold methyl halide molecules and alkali-metal atoms  

SciTech Connect

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.

Lutz, Jesse J.; Hutson, Jeremy M. [Joint Quantum Centre (JQC) Durham-Newcastle, Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom)] [Joint Quantum Centre (JQC) Durham-Newcastle, Department of Chemistry, Durham University, South Road, Durham DH1 3LE (United Kingdom)

2014-01-07

35

Relaxation of the rocksalt (001) surface: Alkali halides, MgO, and PbS  

NASA Astrophysics Data System (ADS)

We evaluate the static relaxation of the (001) face of rocksalt-structured ionic crystals, using shell models. The results for moderately polarizable compounds, namely, the alkali halides and MgO, are in qualitative agreement with those of earlier calculations but overall somewhat smaller. PbS is treated as an example of highly polarizable substances close to an instability. The results for PbS show a larger and deeper penetrating relaxation than in the case of the alkali halides. Preliminary results for PbTe, which has a large (T-dependent) anion polarizability, show a precursor of a total crystal reconstruction. It is conjectured that in such cases the lowered symmetry at the surface can act as a trigger for a structural phase transition.

de Wette, F. W.; Kress, W.; Schröder, U.

1985-09-01

36

Anomalous high-field electron injection and photoconduction in thin-film alkali halides  

Microsoft Academic Search

Transient ion currents in thin-film alkali halides at ca. <2 V, which may exceed 10-4 A cm-2 at 1 ms, decay rapidly according to I~t-m with 0

Michael N. Pisanias; William H. Hamill

1980-01-01

37

Anomalous high-field electron injection and photoconduction in thin-film alkali halides  

Microsoft Academic Search

Transient ion currents in thin-film alkali halides at ca. <2 V, which may exceed 10?4 A cm?2 at 1 ms, decay rapidly according to I?t?m with 0

Michael N. Pisanias; William H. Hamill

1980-01-01

38

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

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

39

Ionic sizes and strain derivative of electronic susceptibility in alkali halides  

NASA Astrophysics Data System (ADS)

An analysis of the electronic susceptibility of alkali halides related to ionic sizes is performed. The model based on the decomposition of the optical susceptibility into contributions of valence and core electrons is applied to obtain ionic radii, photoelastic constants p11 + 2 p12, the strain derivative of electronic dieletric constants, and changes in the refractive index with density and strain polarizability constants. An attempt is made to predict p11 and p12 in some alkali halides. The relationship between the ratio of electronic polarizabilities of alkali and halide ions and the ratio of cation to anion radii {r c}/{r a} is observed. The photoelastic and strain polarizability constants are found to be nearly linearly dependent on {r c}/{r a}. Correlations between crystal ionicity and effective ionic charge and their dependences on {r c}/{r a} are discussed. The approach relates photoelastic constants to the volume dependence of the effective ionic charge. The contribution of second- neighbour interactions is considered and the failure of the Cauchy relationis correlated with {r c}/{r a}.

Kucharczyk, W.

1991-07-01

40

Protection of cesium-antimony photocathodes  

NASA Astrophysics Data System (ADS)

In order to operate gaseous photomultipliers in the visible range it was suggested to protect sensitive photocathodes against contact to air and counting gases by their coating with a thin solid dielectric film. We present data on coating of cesium-antimony photocathodes with alkali-halide (NaI, CsI, CsF, NaF), oxide (SiO) and organic (hexatriacontane, calcium stearate) films. The photoelectron transmission through these films and their protection capability have been studied in detail. Cesium-antinomy photocathodes are shown to withstand exposure to considerable doses of oxygen and dry air when coated with NaI films. This opens ways to their operation in gas media.

Buzulutskov, A.; Breskin, A.; Chechik, R.; Prager, M.; Shefer, E.

1997-02-01

41

Atomic and molecular spectra of vapours evolved in a graphite furnace. Part 1. Alkali halides  

NASA Astrophysics Data System (ADS)

Molecular Absorption Spectrometry (MAS) with electrothermal vaporization was applied to the measurement of absorption by alkali halides. The MAS system, consisting of a deuterium lamp primary source, a tubular graphite furnace, a grating polychromator and a linear array of Charge-Coupled-Device (CCD) detectors, allowed the simultaneous determination of atomic and molecular absorption in the range 200-400 nm. Vaporization was carried out in a pyrocoated graphite tube and absorption was measured during the heating of the furnace from 500°C to 2000°C in 100 s. Alkali halides vaporize as molecular compounds which absorb radiation in the whole ultraviolet range. The complexity of the molecular bands as well as the extent of the absorption increases from fluorides to iodides. The limit of absorption at long wavelengths is 254 nm for NaF, 287 nm for NaCl, 320 nm for NaBr and 370 nm for NaI. The appearance of vapors was observed between 680°C (RbI) and 1220°C (LiF), while the maximum absorption was reached between 800°C (CsI) and 1440°C (LiF); the characteristic temperatures of the vaporization peak were shifted towards lower values going from fluorides to iodides.

Daminelli, G.; Katskov, D. A.; Mofolo, R. M.; Tittarelli, P.

1999-05-01

42

Nanometer-scale patterning of alkali halide surfaces by ion bombardment  

NASA Astrophysics Data System (ADS)

Structural properties of alkali halide surfaces (KBr, KI, and RbI) have been modified by low energy Ar + ion beam bombardment. The morphology developed on the irradiated surfaces was investigated by the atomic-force microscopy (contact mode) under UHV conditions. The results indicate that for the incidence angles between 30° and 40° a periodic ripple morphology is developed with the ripple vector parallel to the beam direction, whereas for the angles larger than 60° the vector is perpendicular to the beam. The average surface roughness and the wavelength of the ion-induced periodic structures were measured as a function of the ion fluence (10 13-10 18 ions/cm 2), the beam energy (1-5 keV), and the sample temperature (from 300 K to 600 K). The results are explained in terms of a new atomic-scale model taking into account the fact that ion sputtering of alkali halides in the investigated energy range is dominated by electronic processes rather than ballistic collisions.

Saeed, S. R.; Sinha, O. P.; Krok, F.; Szymonski, M.

2008-12-01

43

Desorption and surface topography changes induced by He + ion bombardment of alkali halides  

NASA Astrophysics Data System (ADS)

Desorption fluxes from alkali halide (RbI, KBr) crystals under 5 keV He + bombardment and the corresponding surface topography evolution were investigated by means of quadruple mass spectroscopy (QMS) and dynamic force microscopy (DFM) in UHV. Although, for the energy range of He + ions used, desorption of alkali halides occurs predominantly via electronic processes, there are significant differences between the ion-stimulated desorption (ISD) and the electron-stimulated desorption (ESD). The latter proceeds in a layer-by-layer mode and, as a result, oscillating desorption fluxes are observed. For ISD the DFM images show that the surface erosion does not follow the layer-by-layer scheme and no oscillation in desorption fluxes are found but they exhibit monotonic decrease to some saturation level. We suggest that these differences between electron- and ion-stimulated desorption are caused by ballistic processes disturbing the perfect lattice and introducing defects in the bulk and at the surface. Such lattice defects can act as recombination centres for diffusing Frenkel defects and inhibit the desorption process. Additionally, projectiles colliding violently with top-layer ions introduce additional nucleation centres for vacancies on the surface which lead to the surface erosion in the multi-layer mode.

Krok, F.; Kolodziej, J. J.; Such, B.; Czuba, P.; Piatkowski, P.; Struski, P.; Szymonski, M.

2004-12-01

44

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

SciTech Connect

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.

Reiser, S.; Deublein, S.; Hasse, H., E-mail: hans.hasse@mv.uni-kl.de [Laboratory of Engineering Thermodynamics, University of Kaiserslautern, 67663 Kaiserslautern (Germany); Vrabec, J. [Thermodynamics and Energy Technology, University of Paderborn, 33098 Paderborn (Germany)] [Thermodynamics and Energy Technology, University of Paderborn, 33098 Paderborn (Germany)

2014-01-28

45

Alkali Halide Interfacial Behavior in a Sequence of Charged Slit Pores  

SciTech Connect

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.

Wander, Matthew C [ORNL; Shuford, Kevin L [ORNL

2011-01-01

46

Microscopic model for the two-phonon Raman spectra of alkali halides  

NASA Astrophysics Data System (ADS)

The second-order Raman-scattering (SORS) cross section of alkali halides has been evaluated by using the Buckingham expansion for the induced polarizability. This ab initio approach leads to a microscopic expression of the SORS cross section without free parameters. The first two nonzero contributions of the expansion, namely, the dipole-induced dipole (DID) coming from the first-order dressed polarizability and the BTQ (second-dipole hyperpolarizability × dipole propagator × effective charge) coming from the second-dipole-quadrupole polarizability, have been considered. The short-range contribution to the induced polarizability coming from the electronic overlap has not been included in the present work. The SORS spectra are expressed in terms of the dynamical quantities of the crystal (eigenvectors and eigenfrequencies) and in terms of some bare ionic susceptibilities, namely, the ions' bare polarizabilities ?+ and ?- and the second-dipole-quadrupole bare polarizabilities B+ and B-. As an example the results are shown in the case of KBr. Considerations on the long-range nature of the DID spectrum and on the short-range nature of the BTQ spectrum are made. The relative weights of the two contributions to the SORS in the whole class of alkali halides are also discussed.

Gallo, P.; Mazzacurati, V.; Ruocco, G.; Signorelli, G.

1993-05-01

47

Molecular Simulation of Aqueous Electrolyte Solubility. 3. Alkali-Halide Salts and Their Mixtures in Water and in Hydrochloric Acid  

E-print Network

Molecular Simulation of Aqueous Electrolyte Solubility. 3. Alkali- Halide Salts and Their Mixtures. Phys Chem. B 2011, 115, 7849-7861) for directly calculating the aqueous solubility of electrolytes and are of reasonable accuracy. The accuracy of the calculated solubility is highly dependent on the solid chemical

Lisal, Martin

48

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

SciTech Connect

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.

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

49

Determination Factor of Lattice Structure in Hexadecafluorovanadylphthalocyanine Epitaxially Grown on Alkali-Halide Substrates  

NASA Astrophysics Data System (ADS)

The epitaxial growth of fluorine-substituted vanadylphtalocyanine (FxVOPc; x = 15.4) on KBr, KI, and RbI was studied. The lattice structure of F15.4VOPc changes from (\\sqrt{10} × \\sqrt{10})R ± 27° to (\\sqrt{8} × \\sqrt{8})R0° as the lattice constants of the substrates increase. This sequence is different from that of other shuttlecock-shaped phthalocyanines(Pcs) such as VOPc, TiOPc and AlPcCl, in which the structure changes from (\\sqrt{10} × \\sqrt{10})R ± 27° to (3 × 3)R45°. The difference suggests that the orientation of molecules on the substrates plays an important role in the determination of the lattice structure of F15.4VOPc on alkali-halide substrates.

Uno, So-ichiro; Hoshi, Hajime; Takezoe, Hideo; Ishikawa, Ken

2005-03-01

50

Ion Segregation and Deliquescence of Alkali Halide Nanocrystals on SiO2  

SciTech Connect

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.

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

2009-08-11

51

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

SciTech Connect

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.

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

52

Dynamics of the defect-mediated desorption of alkali halide surfaces  

NASA Astrophysics Data System (ADS)

Dynamic processes leading to desorption of Rb and I atoms from the RbI (100) surface co-irradiated with 1 keV electrons and visible light (with a wavelength corresponding to the F-center absorption band) have been studied by means of mass-selected time-of-flight (TOF) spectroscopy. Depending on the sample temperature, substantial enhancement of the desorption yield as well as pronounced changes in the TOF spectra of the emitted atoms have been found. The TOF spectra of halogen atoms consist of two components: the thermal (which can be fitted with Maxwellian distribution) and the non-thermal one. The non-thermal peak is temperature-independent. There is no non-thermal component for alkali atoms. The comparison of TOF spectra for I atoms emitted from electron bombarded sample with and without simultaneous light irradiation indicates that the yield increase is caused by thermally desorbed atoms, while the non-thermal peak remains unchanged. Presented results confirm well the predictions of the theoretical model of desorption proposed earlier, known as the defect-mediated (F and H center) desorption of alkali halide.

Szymonski, M.; Droba, A.; Struski, P.; Krok, F.

2012-08-01

53

GaN photocathodes for UV detection and imaging  

NASA Astrophysics Data System (ADS)

The nitride-III semiconductors, in particular GaN (band gap energy 3.5 eV), AlN (band gap 6.2 eV) and their alloys AlxGa1-xN are attractive as UV photo-convertors with applications as photocathodes for position sensitive detector systems. These can "fill the gap" in the 150-400nm wavelength regime between alkali halide photocathodes (<2000Å), and the various optical photocathodes (>4000Å, mutlialkali & GaAs). Currently CsTe photocathodes have fairly low efficiency (Fig. 1) in the 100nm to 300nm regime are sensitive to contamination and have no tolerance to gas exposure. We have prepared and measured a number of GaN photocathodes in opaque and semitransparent modes, achieving >50% quantum efficiency in opaque mode and ~35% in semitransparent mode (Fig. 2). The GaN photocathodes are stable over periods of >1 year and are robust enough to be re-activated many times. The cutoff wavelength is sharp, with a rapid decline in quantum efficiency at ~380-400nm. Application of GaN photocathodes in imaging devices should be feasible in the near future. Further performance improvements are also expected as GaN fabrication and processing techniques are refined.

Siegmund, Oswald H. W.; Tremsin, Anton S.; Martin, Adrian; Malloy, James; Ulmer, Melville P.; Wessels, Bruce

2003-12-01

54

Calculation of electronic, structural, and vibrational properties in alkali halides using a density-functional method with localized densities  

NASA Astrophysics Data System (ADS)

A recently developed density-functional method based on localized densities is applied to calculate electronic, structural, and vibrational properties of 20 alkali halides with elements lithium through cesium and fluorine through iodine. Properties calculated include dissociation energy, lattice parameter, dielectric constant, elastic moduli, and phonon frequencies for the high-symmetry points of the Brillouin zone. Results are discussed and compared with experiment and other calculations.

Mei, W. N.; Boyer, L. L.; Mehl, M. J.; Ossowski, M. M.; Stokes, H. T.

2000-05-01

55

Molecular Modeling and Monte Carlo Simulation of Concentrated Aqueous Alkali Halide Solutions at 25 C.  

NASA Astrophysics Data System (ADS)

A study of concentrated aqueous alkali halide solutions is made at the molecular level, through modeling and computer simulation of their structural and thermodynamic properties. It is found that the HNC approximation is the best integral equation theory to predict such properties within the framework of the primitive model (PM). The intrinsic limitations of the PM in describing ionic association and hydration effects are addressed and discussed in order to emphasize the need for explicitly including the water molecules in the treatment of aqueous electrolyte solutions by means of a civilized model (CM). As a step toward developing a CM as simple as possible, it is shown that a modified version of the SPC model of liquid water in which the Lennard-Jones interaction between intermolecular oxygen sites is replaced by a hard core interaction, is still successful enough to predict the degree of hydrogen bonding of real water. A simple civilized model (SCM) (in which the ions are treated as hard spheres interacting through Coulombic potentials and the water molecules are simulated using the simplified SPC model) is introduced in order to study the changes in the structural features of various aqueous alkali halide solutions upon varying both the concentration and the size of the ions. Both cations and anions are found to be solvated by the water molecules at expense of a breakdown in the hydrogen-bonded water network. Hydration numbers are reported for the first time for NaBr and KBr, and the first simulation -based estimates for LiBr, NaI and KI are also obtained. In several cases, values of the hydration numbers based on the SCM are found to be in excellent agreement with available experimental results obtained from x-ray diffraction measurements. Finally, it is shown that a neoprimitive model (NPM) can be developed by incorporating some of the structural features seen in the SCM into the short-range part of the PM interionic potential via a shielded square well whose width and depth's temperature coefficient can be determined from a fit of experimental data for the osmotic coefficient and heat of dilution, respectively.

Llano-Restrepo, Mario Andres

56

a Behavior-Type Raman Study of Orientationally Degenerate Defects in Doped Alkali Halides.  

NASA Astrophysics Data System (ADS)

Localized defects with unusual rotational or translational motion in alkali halides are investigated by polarized Raman scattering. Molecular impurities reorient between several equivalent equilibrium orientations. The KI:Ag ^{+} system occupies a regular lattice site at 2K and goes off-center, when the temperature is raised to 25K. The free electron in the heavy-metal dimer centers is moving between two equivalent configurations. These motions influence the composition of the Raman spectra, their temperature dependence, and their polarization properties. Raman data represented for several diatomic (CN^{-}, SH^{-}, O_sp {2}{-}, and OD^ {-}) and triatomic (NCO^ {-}) linear molecules, and for the bent triatomic NO_sp{2}{-} molecular ion in KCl, KBr, KI, and NaBr. Preliminary results for KI_{1-x}(NH _4)I are also reported. The symmetry assignment by polarized Raman scattering is in agreement with previous results for the diatomic systems. The C _{3v} symmetry of the static NCO^{-} in KBr is established for the first time. Surprising and new results are obtained for the symmetries of NO_sp{2} {-} and NH_sp{4} {+}. The influence of rotational motion and polarizability of the surrounding ions on the polarized Raman data is discussed. New and different polarized Raman behavior is established for mixed molecular crystals of higher concentrations, reflecting electric/elastic dipole interactions. The on- to off-center transition of the KI:Ag^+ system is tracked by the temperature dependence of the Raman scattering data in the range between 2 and 25K. Calculations for the on-center configuration indicate that the temperature behavior is in contrast with that of 'soft-mode' systems. A possible mechanism, involving localized anharmonic modes trapped at the impurity site, is discussed and correlated with the unusual polarization properties of the Raman scattering. Thermally activated reorientation and superionic motion are compared. The resonant Raman data for Tl^+Tl ^0(1)-like dimer centers in Ga^+ - and In^+-doped alkali halides are presented. The Ga^+Ga ^0(1) (In^+In ^0(1)) defects in KCl and RbCl are identified. The correspondence with previously suggested models is discussed. The Raman response of the dimer centers is determined by the non-adiabatic motion of the unpaired electron. The non -atomic behavior of the third excited state of Tl ^0(1)-like defects is shown to be reflected in the Raman data.

Fleurent, Hilde Berthe

57

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

PubMed

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

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

2008-05-01

58

A re-investigation of the quadratic electrostriction of alkali halides of rocksalt type  

NASA Astrophysics Data System (ADS)

In order to clarify the reasons for the contradictory results regarding quadratic electrostriction in alkali halides reported by various authors, we developed an improved capacitive dilatometer. Employing the frequency-modulation technique, the resolution of the experimental set-up reaches icons/Journals/Common/Delta" ALT="Delta" ALIGN="TOP"/> licons/Journals/Common/approx" ALT="approx" ALIGN="TOP"/> 2×10-13 m. Various possible sources of errors could be detected, including sample mounting, calibration faults and, in particular, electro-mechanical resonances caused by strong Coulomb interactions between certain components of the dilatometer. From frequency-dependent measurements in the range 60-1200 Hz we determined the complete tensors of the quadratic electrostriction of LiF, NaCl, NaBr, KCl, KBr, KI, RbCl, RbBr and RbI at room temperature. The results are in reasonable agreement with values derived from sophisticated lattice-theoretical models. Furthermore, we studied the influence of the real structure of Li-doped KCl crystals on their electrostrictive properties.

Schreuer, J.; Haussühl, S.

1999-06-01

59

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

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

60

First-principles study on the energetics and vibrational properties of the S-2 impurity in alkali-halide crystals  

NASA Astrophysics Data System (ADS)

We have performed first-principles electronic structure calculations for the S2 and S-2 molecules in the vacuum and found that the calculated equilibrium bond lengths and vibrational spectroscopic constants are in good agreement with the experiments as well as the previous calculations. Based on this conformation we extended these calculations to the substitutional S-2 molecule in the alkali halides, such as NaCl, NaBr, NaI, KCl, KBr, KI, RbCl, RbBr, and RbI. It is found from these calculations that the S-2 center aligned to [110] direction is generally favorable over those with the [100] and [111] orientations, in agreement with the experiments. We also found that the vibrational frequencies of the S-2 anion in the alkali halides shift to higher energies with decreasing lattice parameters. These results suggest that the change in the bond length of the S-2 anion in the matrices depends on the species of halogen atom, while the frequencies are influenced by the species of alkali atom.

Nishidate, Kazume; Baba, Mamoru; Sarjono; Hasegawa, Masayuki; Nishikawa, Kiyoshi; Sokolska, I.; Ryba-Romanowski, W.

2003-12-01

61

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

PubMed Central

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

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

2013-01-01

62

IR spectroscopy of aqueous alkali halide solutions: Pure salt-solvated water spectra and hydration numbers  

NASA Astrophysics Data System (ADS)

Extrapolation techniques were used to obtain pure salt-solvated water spectra from the attenuated total reflection infrared spectra (ATR-IR) of aqueous solutions of the nine alkali halide salts LiCl, NaCl, KCl, CsCl, NaBr, KBr, NaI, KI, and CsI and the alkaline-earth chloride salt MgCl2. These salts ionize completely in water. The ions by themselves do not absorb in the IR, but their interactions with water can be observed and analyzed. A pure salt-solvated water spectrum is easier to analyze than that of a combined solution of pure water and salt-solvated water. Although the salt-solvated water spectra examined have distinctive signatures, they can be classified in three categories: those similar to NaCl; those not similar to NaCl; and MgCl2, in a class by itself. Each of the pure salt-solvated water spectra differs from that of liquid water, though the number of bands is the same. From the Gaussian band fitting, we found that the positions of the bands were fairly constant, whereas their intensities differed. The salt hydration numbers were determined: for NaCl, KCl, NaBr, KBr, and CsI solutions it is 5; for KI and MgCL2 it is 4; for NaI it is 3.5; for CsCl it is 3; and for LiCl it is 2. From these results we found that each pair of ions (monoatomic ions) of the ten salt solutions studied are close bound and form a complex in a cluster organization with a fixed number of water molecules.

Max, Jean-Joseph; Chapados, Camille

2001-08-01

63

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

NASA Astrophysics Data System (ADS)

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 ?2 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. 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.

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

2014-08-01

64

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)

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.

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

1981-01-01

65

Specific features of the temperature quenching of luminescence of self-trapped excitons in alkali halide crystals under low-temperature deformation  

NASA Astrophysics Data System (ADS)

The activation energy of temperature quenching of luminescence of self-trapped excitons in alkali halide crystals subjected to low-temperature uniaxial deformation is evaluated experimentally. It is found that an increase in the activation energy is observed in the following series of crystals: KBr ? NaCl ? KI ? NaBr ? CsBr ? RbI. The effect of enhancement of intrinsic luminescence of alkali halide crystals due to the lowering of the symmetry of the crystal lattice under low-temperature uniaxial deformation is interpreted by analyzing the observed increase in the activation energy that characterizes the height of the potential barrier separating channels of radiative and nonradiative decay (with the formation of radiation defects) of self-trapped excitons.

Shunkeev, K.; Sarmukhanov, E.; Barmina, A.; Myasnikova, L.; Sagimbaeva, Sh.; Shunkeev, S.

2008-10-01

66

An Investigation of Ion-Pairing of Alkali Metal Halides in Aqueous Solutions Using the Electrical Conductivity and the Monte Carlo Computer Simulation Methods  

PubMed Central

The ion pairing is, in very dilute aqueous solutions, of rather small importance for solutions’ properties, which renders its precise quantification quite a laborious task. Here we studied the ion pairing of alkali halides in water by using the precise electric conductivity measurements in dilute solutions, and in a wide temperature range. The low-concentration chemical model was used to analyze the results, and to estimate the association constant of different alkali halide salts. It has been shown that the association constant is related to the solubility of salts in water and produces a ’volcano relationship’, when plotted against the difference between the free energy of hydration of the corresponding individual ions. The computer simulation, using the simple MB+dipole water model, were used to interprete the results, to find a microscopic basis for Collins’ law of matching water affinities. PMID:24526801

Gujt, Jure; Bešter-Roga?, Marija; Hribar-Lee, Barbara

2013-01-01

67

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

PubMed

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

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

2011-03-01

68

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

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

69

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

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

70

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

SciTech Connect

The scaled forms of the newly introduced generalized potential energy functions (PEFs) describing intermolecular interactions [J. Chem. Phys. xx, yyyyy (2011)] have been used to fit the ab-initio minimum energy paths (MEPs) for the halide- and alkali metal-water systems X-(H2O), X=F, Cl, Br, I, and M+(H2O), M=Li, Na, K, Rb, Cs. These generalized forms produce fits to the ab-initio data that are between one and two orders of magnitude better in the ?2 than the original forms of the PEFs. They were found to describe both the long-range, minimum and repulsive wall of the potential energy surface quite well. Overall the 4-parameter extended Morse (eM) and generalized Buckingham exponential-6 (gB-e6) potentials were found to best fit the ab-initio data. Furthermore, a single set of parameters of the reduced form was found to describe all candidates within each class of interactions. The fact that in reduced coordinates a whole class of interactions can be represented by a single PEF, yields the simple relationship between the molecular parameters associated with energy (well depth, ?), structure (equilibrium distance, rm) and spectroscopy (anharmonic frequency, ?):€? = A? (? /?)1/ 2 /rm + B?? /rm 3 , where A and B are constants depending on the underlying PEF. This more general case of Badger’s rule has been validated using the experimentally measured frequencies of the hydrogen bonded OH stretching vibrations in the halide-water series.

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

2014-08-14

71

Electron- and photon-stimulated desorption of atomic hydrogen from radiation-modified alkali halide surfaces  

NASA Astrophysics Data System (ADS)

The desorption yields of excited hydrogen atoms from the surfaces of KCl, KBr, NaCl, NaF, and LiF have been measured as a function of incident photon and electron energy and flux, time of irradiation, dosing pressure of H2 and sample temperature. As these surfaces are exposed to H2 gas during electron or photon bombardment, the fluorescence from excited hydrogen atoms ejected from the surface is monitored. The desorption yields are found to be contingent upon surface damage induced by the incident particle radiation, leading to dissociative adsorption at surface sites containing an excess of alkali metal. A desorption mechanism is presented in which incident electrons or photons induce a valence excitation to a neutral, antibonding state of the surface alkali hydride molecule complex, leading to the desorption of hydrogen atoms possessing several eV of kinetic energy.

Hudson, L. T.; Tolk, N. H.; Bao, C.; Nordlander, P.; Russell, D. P.; Xu, J.

2000-10-01

72

N ,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) on alkali halide (001) surfaces  

NASA Astrophysics Data System (ADS)

The growth of N ,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) (DiMe-PTCDI) on KBr(001) and NaCl(001) surfaces has been studied. Experimental results have been achieved using frequency modulation atomic force microscopy at room temperature under ultrahigh vacuum conditions. On both substrates, DiMe-PTCDI forms molecular wires with a width of 10nm, typically, and a length of up to 600nm at low coverages. All wires grow along either the [110] direction (or [11¯0] direction, respectively) of the alkali halide (001) substrates. There is no wetting layer of molecules: atomic resolution of the substrates can be achieved between the wires. The wires are mobile on KBr but substantially more stable on NaCl. A p(2×2) superstructure in a brickwall arrangement on the ionic crystal surfaces is proposed based on electrostatic considerations. Calculations and Monte Carlo simulations using empirical potentials reveal possible growth mechanisms for molecules within the first layer for both substrates, also showing a significantly higher binding energy for NaCl(001). For KBr, the p(2×2) superstructure is confirmed by the simulations; for NaCl, a less dense, incommensurate superstructure is predicted.

Fendrich, Markus; Lange, Manfred; Weiss, Christian; Kunstmann, Tobias; Möller, Rolf

2009-05-01

73

Characterization of alkali halides doped 1-(2-methoxy benzyloxy)-8- hydroxy-9,10-anthraquinone films for photovoltaic applications  

NASA Astrophysics Data System (ADS)

Thin films of 1-(2-methoxy benzyloxy)-8-hydroxy-9, 10-anthraquinone (AQ) have been prepared by hot wall technique onto glass substrates kept at 348 K in a vacuum of 10-5 Torr. Chemical modifications of films have been performed by their treatment with different alkali halides. The films so obtained are systematically studied for their electrical and optical properties. The electrical conductivities of the resulting films exhibited semiconductor-like temperature dependence in the experimental range studied. LiCl and LiBr doped films exhibit almost three orders of magnitude higher conductivity, than untreated films, whereas NaCl, NaBr and KBr do not show any remarkable change in the conductivity. Analysis of optical absorption measurements indicate that the interband transition energies of films lie in the range of 2.57-2.66 eV. Keeping in view the electrical and optical properties of films, ITO/AQ/Al solar cells have been fabricated and characterized. The J-V characteristics of these devices are found to be in good agreement with standard diode equation. Power conversion efficiency of Li doped AQ based devices are found to increase by an order of two as compared to undoped AQ based devices.

Mahajan, Aman; Singh, Mandeep; Gupta, Himani; Bedi, R. K.; Kumar, S.; Aswal, D. K.

2012-06-01

74

Thermodynamics of small alkali metal halide cluster ions: comparison of classical molecular simulations with experiment and quantum chemistry.  

PubMed

We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali metal halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge nonpolarizable SPC/E, (ii) Drude point charge polarizable SWM4-DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ion hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas-phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties. PMID:25513841

Vlcek, Lukas; Uhlik, Filip; Moucka, Filip; Nezbeda, Ivo; Chialvo, Ariel A

2015-01-22

75

Model calculation of the pressure derivative of the low-frequency dielectric constant of alkali halide crystals  

NASA Astrophysics Data System (ADS)

The mechanism of polarization of insulators in a static electric field is still not clearly understood. The current situation presents an anomaly. The model which describes the high-frequency dielectric behavior quite well is found to be inadequate for the static case. In fact, with the same set of parameters within any single phenomenological model, it has not been possible to describe satisfactorily both the dielectric constants and their pressure derivatives. In search of a suitable model which can achieve this we have, in the present work, tried to analyze the mechanism of polarization from first principles. The interesting finding of this analysis is that there are two types of short-range polarization effects having entirely different origins: One of which (the second-order exchange interaction) contributes both to the static and high-frequency dielectric properties and the other (the first-order exchange interaction) to the static one only. We have suggested a model based on this analysis. The present calculation of the pressure derivative of the static dielectric constant of alkali halide crystals within a simplified version of this model together with our earlier calculation of the same for the high-frequency dielectric constant provides a fair overall description of the entire dielectric behavior of insulators. In addition, the present investigation also discusses the approximations which yield the well-known models for ionic solids which include polarization.

Banerjee, Lalit K.; Basu, A. N.; Sengupta, S.

1982-07-01

76

Photocathodes for RF photoinjectors  

NASA Astrophysics Data System (ADS)

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.

Michelato, P.

1997-02-01

77

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

NASA Astrophysics Data System (ADS)

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.

Ziraps, Valters

2001-03-01

78

Thermal diffusivity of alkali and silver halide crystals as a function of temperature  

NASA Astrophysics Data System (ADS)

The phonon component of thermal diffusivity (D) for ten synthetic single-crystals (LiF, NaCl, NaI, NaI:Tl, KCl, KBr, CsI, CsI:Tl, AgCl, and AgBr) with the B1 and B2 structures was measured from ambient temperature (T) up to ˜1093 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. We investigated optical flats from different manufacturers as well as pellets made from compressed powders of most of the above chemical compositions plus LiI, NaBr, KI, RbCl, RbBr, RbI, CsCl, CsBr, and AgI. Impurities were characterized using various spectroscopic methods. With increasing T ,D decreases such that near melting the derivatives ?D/?T are low, -0.0006±0.0004 mm2 s-1 K-1. Our results are ˜16% lower than D298 previously obtained with contact methods, which are elevated by ballistic radiative transfer for these infrared (IR) windows, and are well described by either D-1 following a low order polynomial in T, or by D-1?T+n, where n ranges from 1.0294 to 1.9429. Inverse correlations were found between D298 and both density and thermal expansivity (?). Primitive lattice constant times compressional velocity correlates directly with D but changes much more slowly with temperature. Instead, D(T ) is proportional to (T?L)-1 from ˜0 K up to the limit of measurements, in accord with these physical properties being anharmonic. On average, the damped harmonic oscillator-phonon gas model reproduces D298 based on two physical properties: compressional velocity and the damping coefficient (? ) from analysis of IR reflectivity data. Given large uncertainties in ?(T ), D-1(T) is reproduced for LiF, NaCl, MgO, and the silver halides, for which IR reflectivity data are available. Our correlations show that optical phonons largely govern heat transport of insulators, and permit prediction of D and thus thermal conductivity for simple, diatomic solids.

Yu, Xueyang; Hofmeister, Anne M.

2011-02-01

79

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Optical surface breakdown of alkali halide crystals by microsecond pulses from a wide-aperture CO2 laser  

NASA Astrophysics Data System (ADS)

A study was made of the dynamics of temporal and spatial changes in the spectral characteristics of plasmas. A three-stage mechanism of the damage to surfaces of alkali halide crystals by microsecond pulses from a TEA CO2 laser was proposed: breakdown initiation (at a distance of 3-5 mm from the surface with a time delay up to 1 ?s relative to the leading edge of a laser pulse), evaporation (after a further delay of 3-5 ?s), and interaction of the adsorbates with a plasma jet and with the laser radiation, as well as heating and cracking of a crystal by the UV plasma radiation.

Kazantsev, S. G.

1998-04-01

80

Fourier Transform Infrared Studies of Isolated Cyanide Ion Defects and Cyanide ION:LITHIUM Ion Defect Pairs in Alkali-Halides  

NASA Astrophysics Data System (ADS)

FTIR absorption--and partially Raman scattering --measurements of the CN^- stretching -mode response have been used to study the vibrational and rotational properties of this diatomic molecular ion as a substitutional defect under a wide variation of alkali -halide host crystal, temperature, and other physical conditions. As a basis of this study, the existent theoretical and experimental material on the electric multipole character of free rm CN^- ions and its binding potential U(R, theta) to alkali-ions (forming free alkali-cyanide molecules) has been critically reviewed. This potential was used to construct the weakly hindered rotational potential of the rm CN^- ion as a substitutional defect in a cavity of 6 surrounding alkali-ions. In the first experimental part, earlier studies of isolated CN^- defects have been extended in two important directions. By measurements of the three lowest harmonic transitions in terms of their frequencies and absorption intensities, the mechanical potential rm U_{M}(r) and electrical dipole moment function p(r) have been determined for rm CN^- ions in KCl and KBr hosts. The rm U_{M}(r) can be well approximated to be an anharmonic Morse function, but the derived p(r) must be close to a linear function to produce only small electrical anharmonicity for rm CN^- (in strong contrast to the very large electrical anharmonicity for rm OH^- and rm OD^ - defects). The second extension, production and studies of isolated rm CN^- defects in Li-halide and alkali-fluoride host crystals, has mostly succeeded. In spite of strong "size-mismatch" between rm CN^- and rm F^- host ions, small isolated rm CN^- concentrations can be substituted into KF, RbF, and CsF hosts, however, not into LiF and NaF. The first time observed isolated rm CN^- stretching-mode absorption in Li-halides shows by its temperature broadening (~ rm T^2) strong rotational localization similar as in Na-halide hosts. Based on the Born-Mayer -Huggins repulsive potential, an empirical relation for the rm CN^- stretching-mode frequency has been derived to be a function of host interionic distance d. The measured frequencies of 16 hosts can be fitted to this relation very well, which predicts by extrapolation of rm dtoinfty the not yet measured free gas rm CN^- frequency to be 2027 rm cm^{ -1}.. In the second experimental part, Li^+ {-}CN^- defect pairs formed in 12 double-doped alkali-halide hosts have been studied with FTIR and polarized Raman techniques. The observation of two sharp stretching-mode transitions (A and rm A^') confirms the existence of two <100> oriented linear pair configurations rm Li^+ {-}CN^- and rm Li ^+{-}NC^- of slightly different energy, which change their relative populations under temperature variation. In most hosts, the rm Li^+ {-}CN^- configuration is found to be the lower energy one, which is opposite to the behavior of free LiNC molecules. By thermal quenching the pairs can be partially converted into isolated defects, and their recovery can be observed by the increases of the A and rm A^' absorption. This allows to study "spectroscopically" the diffusion behavior of rm Li^+ ions near room temperature.

An, Chong Pyung

1995-01-01

81

Monte Carlo simulation of the structural properties of concentrated aqueous alkali halide solutions at 25 °C using a simple civilized model  

NASA Astrophysics Data System (ADS)

In this paper we present the results of a Monte Carlo (MC) simulation study of the structural properties of concentrated aqueous solutions of various alkali halides at 25 °C using a simple civilized model (SCM). A simplified version of the rigid nonpolarizable SPC model of liquid water, in which the Lennard-Jones interaction between intermolecular oxygen sites is changed into a hard-core repulsion, is combined in our SCM with a treatment of the ions as charged hard spheres. Changes in the structure of the solvent, and the behavior of ionic solvation and ion pairing upon varying the concentration and size of the ions, are determined by computing the corresponding ten radial distribution functions from sufficiently long MC simulation runs for various aqueous alkali halide solutions at concentrations above 1 M. Hydration numbers are reported for the first time for NaBr and KBr, and the first simulation-based estimates for LiBr, NaI, and KI are also obtained. Whenever possible, results for the hydration numbers are compared with available experimental data and also with other simulation studies. The excellent predictive capability and simplicity of the SCM proposed here, should lead to the development of tractable theoretical approaches to aqueous 1:1 electrolyte solutions in the near future.

Llano-Restrepo, Mario; Chapman, Walter G.

1994-06-01

82

Development of processes for the production of solar grade silicon from halides and alkali metals. Second quarterly report, 1 January-31 March 1980  

SciTech Connect

This program is directed toward the development of processes involving high temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost. Experiments are being 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. Samples of the silicon product will be delivered to JPL for evaluation of solar cell performance. During this reporting period, the program efforts were directed toward the measurement of reagent flow rates and silicon collection efficiencies, the construction of a new sodium heat pipe to permit one to two hour runs, and the completion of the economic and engineering analyses of the AeroChem process to make solar grade silicon. Progress is reported.

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

1980-04-01

83

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

84

Biological photocathodes.  

PubMed Central

Biological surfaces emit electrons when subjected to UV light. This emission is increased greatly after exposure to cesium vapor. Increases from 2 to 3 orders of magnitude are observed, depending on the biochemicals present. Heme and chlorophyll exhibit unusually high photoemission currents, which are increased further after cesiation. Photoemission from proteins and lipids is much less but also is increased by exposure to cesium. The formation of photocathodes with cesium greatly increases the practical magnifications attainable in photoelectron microscopy of organic and biological specimens. Photoelectron micrographs taken at magnifications greater than or equal to X 100,000 of chlorophyll-rich thylakoid membranes and of colloidal gold-labeled cytoskeleton preparations of cultured epithelial cells demonstrate the improvement in magnification. The selectivity and stability of the photocathodes suggest the possibility of detecting chromophore binding proteins in membranes and the design of photoelectron labels for tagging specific sites on biological surfaces. Images PMID:2928305

Griffith, O H; Habliston, D L; Birrell, G B; Skoczylas, W P; Hedberg, K K

1989-01-01

85

Alkali reduction of graphene oxide in molten halide salts: production of corrugated graphene derivatives for high-performance supercapacitors.  

PubMed

Herein we present a green and facile approach to the successful reduction of graphene oxide (GO) materials using molten halide flux at 370 °C. GO materials have been synthesized using a modified Hummers method and subsequently reduced for periods of up to 8 h. Reduced GO (rGO) flakes have been characterized using X-ray-diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR), all indicating a significantly reduced amount of oxygen-containing functionalities on the rGO materials. Furthermore, impressive electrical conductivities and electrochemical capacitances have been measured for the rGO flakes, which, along with the morphology determined from scanning electron microscopy, highlight the role of surface corrugation in these rGO materials. PMID:25337832

Abdelkader, Amr M; Vallés, Cristina; Cooper, Adam J; Kinloch, Ian A; Dryfe, Robert A W

2014-11-25

86

Role of polarization effects in the prediction of an orthorhombic pressure-induced phase in alkali halides  

NASA Astrophysics Data System (ADS)

Ab initio static atomistic simulations including semiempirical polarization energy corrections are performed to investigate the stability under pressure of cubic (B1 and B2) and orthorhombic (B33) structures of NaBr, NaI, and LiBr crystals. The calculated unit-cell geometries, equations of state parameters, and phase-transition properties show systematic trends controlled by the ionic sizes and compare successfully with available experimental data. A microscopic analysis of the crystal energy identifies the anionic polarization contribution as essential to explain: (i) the preference of the recently observed B1?B33 transformation over the B1?B2 one in NaBr and NaI and (ii) the potential appearance of the orthorhombic phase at high pressures in lithium halide crystals.

Marqués, M.; Flórez, M.; Blanco, M.; Recio, J.

2003-07-01

87

Complete basis set extrapolated potential energy, dipole, and polarizability surfaces of alkali halide ion-neutral weakly avoided crossings with and without applied electric fields  

NASA Astrophysics Data System (ADS)

Complete basis set extrapolations of alkali halide (LiF, LiCl, NaF, NaCl) energy, dipole, and polarizability surfaces are performed with and without applied fields along the internuclear axis using state-averaged multireference configuration interaction. Comparison between properties (equilibrium separation, dissociation energy, crossing distance, diabatic coupling constant, dipole, and polarizability) derived from the extrapolated potential energy (or dipole) surfaces are made with those obtained from direct extrapolation from the basis set trends. The two extrapolation procedures are generally found to agree well for these systems. Crossing distances from this work are compared to those of previous work and values obtained from the Rittner potential. Complete basis set extrapolated crossing distances agree well with those derived from the Rittner potential for LiF, but were significantly larger for LiCl, NaF, and NaCl. The results presented here serve as an important set of benchmark data for the development of new-generation many-body force fields that are able to model charge transfer.

Giese, Timothy J.; York, Darrin M.

2004-05-01

88

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

SciTech Connect

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.

Li, Y.; Krieger, J.B. (Department of Physics, Brooklyn College, City University of New York, Brooklyn, New York 11210 (United States)); Norman, M.R. (Material Sciences Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Iafrate, G.J. (U.S. Army Research Office, Research Triangle Park, North Carolina 27709-2211 (United States))

1991-11-15

89

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

PubMed

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

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

2014-01-01

90

Superlattice Photocathode Damage Analysis  

NASA Astrophysics Data System (ADS)

Jefferson Lab uses 100 kV DC high voltage photoguns with high polarization strained superlattice GaAs photocathodes to achieve electron beam polarization over 80%. The photocathode is subjected to back-bombardment from ionized residual gasses during operation. We present surface analyses using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) to characterize photocathode damage.

Stutzman, Marcy L.; Grames, Joseph

2009-08-01

91

Drive laser Photocathode  

E-print Network

The electron beam passes through a "wiggler" magnet #12;Prototype Dispenser Photocathode direction of diffusion. · Cs diffuses at the same rate out of each pore of the dispenser. #12;Time Snapshot · Direct experimental data for Cs density over time on a dispenser photocathode is soon to be obtained

Anlage, Steven

92

Piezoelectrically Enhanced Photocathodes  

NASA Technical Reports Server (NTRS)

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, ultraviolet-sensitive photocathodes and photodetectors could be fabricated by use of novel techniques for growing piezoelectrically enhanced layers, in conjunction with thinning and dopant-selective etching techniques.

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

2011-01-01

93

Heat capacity of molten halides.  

PubMed

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

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

2015-01-15

94

White X-ray pulse emission of alkali halide aqueous solutions irradiated by focused femtosecond laser pulses: a spectroscopic study on electron temperatures as functions of laser intensity, solute concentration, and solute atomic number  

NASA Astrophysics Data System (ADS)

Aqueous solutions of alkali halides were irradiated with focused femtosecond laser pulses (130 fs, 780 nm, 1 kHz) in air, and X-ray emission spectra were measured. The laser power density at the focus was estimated to be 2 PW/cm 2 when the laser intensity was 0.65 mJ/pulse. Broad X-ray emission spectra having tails to the higher energy were commonly observed, often accompanied by characteristic K and L lines of solutes. Electron temperatures ( Te) were obtained from the slopes of the broad X-ray spectra on the basis of the assumption of Maxwell-Boltzmann distribution of electron energy. The value of Te was 1.90 keV in the case of distilled water irradiated with laser pulses of 0.53 mJ/pulse laser pulses, while two components of Te (2.67 and 9.83 keV) were observed in the case of saturated cesium chloride aqueous solution (6.5 mol/dm 3). These two components may be related to different electron acceleration processes such as inverse-bremsstrahlung and resonance absorption.

Hatanaka, Koji; Miura, Toshifumi; Fukumura, Hiroshi

2004-04-01

95

Oxidation of hydrogen halides to elemental halogens  

DOEpatents

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.

Rohrmann, Charles A. (Kennewick, WA); Fullam, Harold T. (Richland, WA)

1985-01-01

96

Low-workfunction photocathodes based on acetylide compounds  

DOEpatents

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.

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

2014-05-20

97

Piezoelectrically enhanced photocathode  

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

98

Gaseous photodetectors with solid photocathodes  

Microsoft Academic Search

Remarkable properties of gas photodetectors make them attractive for application in high energy physics, astrophysics, and\\u000a medical imaging. This review presents the results of research and development of gaseous photodetectors with solid photocathodes\\u000a (GPDs). In particular, efficient photocathodes for the ultraviolet (mainly CsI) and the visible ranges, including photocathodes\\u000a with protective dielectric nanofilms, are described. Some problems of the physics

A. F. Buzulutskov

2008-01-01

99

Molecular compressibility of some halides in alcohols  

NASA Technical Reports Server (NTRS)

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.

Serban, C.; Auslaender, D.

1974-01-01

100

Photocathodes in accelerator applications  

SciTech Connect

Some electron accelerator applications require bursts of short pulses at high microscopic repetition rates and high peak brightness. A photocathode, illuminated by a mode-locked laser, is well suited to filling this need. The intrinsic brightness of a photoemitter beam is high; experiments are under way at Los Alamos to study the brightness of short bunches with high space charge after acceleration. A laser-illuminated Cs/sub 3/Sb photoemitter is located in the first rf cavity of an injector linac. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a streak camera.

Fraser, J.S.; Sheffield, R.L.; Gray, E.R.; Giles, P.M.; Springer, R.W.; Loebs, V.A.

1987-01-01

101

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  

NASA Astrophysics Data System (ADS)

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. Hünenberger, J. Chem. Phys. 124, 224501 (2006), 10.1529/biophysj.106.083667; M. M. Reif and P. H. Hünenberger, 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+, Na+, K+, Rb+, Cs+) and halide (F-, Cl-, Br-, I-) 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), 10.1021/jp982638r; 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, ? G_hyd^{ominus }[H+] = -1100, -1075 or -1050 kJ mol-1, resulting in three sets L, M, and H for the SPC water model and three sets LE, ME, and HE for the SPC/E water model (alternative sets can easily be interpolated to intermediate ? G_hyd^{ominus }[H+] values). The residual sensitivity of the calculated (corrected) hydration free energies on the volume-pressure boundary conditions and on the effective ionic radius entering into the calculation of the correction terms is also evaluated and found to be very limited. Ultimately, it is expected that comparison with other experimental ionic properties (e.g., derivative single-ion solvation properties, as well as data concerning ionic crystals, melts, solutions at finite concentrations, or nonaqueous solutions) will permit to validate one specific set and thus, the associated ? G_hyd^{ominus }[H+] value (atomistic consistency assumption). Preliminary results (first-peak positions in the ion-water radial distribution functions, partial molar volumes of ionic salts in water, and structural properties of ionic crystals) support a value of ? G_hyd^{ominus }[H+] close to -1100 kJ.mol-1.

Reif, Maria M.; Hünenberger, Philippe H.

2011-04-01

102

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.  

PubMed

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. Hu?nenberger, J. Chem. Phys. 124, 224501 (2006); M. M. Reif and P. H. Hu?nenberger, 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(+), Na(+), K(+), Rb(+), Cs(+)) and halide (F(-), Cl(-), Br(-), I(-)) 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, ?G(hyd)(?)[H(+)] = -1100, -1075 or -1050 kJ mol(-1), resulting in three sets L, M, and H for the SPC water model and three sets L(E), M(E), and H(E) for the SPC/E water model (alternative sets can easily be interpolated to intermediate ?G(hyd)(?)[H(+)] values). The residual sensitivity of the calculated (corrected) hydration free energies on the volume-pressure boundary conditions and on the effective ionic radius entering into the calculation of the correction terms is also evaluated and found to be very limited. Ultimately, it is expected that comparison with other experimental ionic properties (e.g., derivative single-ion solvation properties, as well as data concerning ionic crystals, melts, solutions at finite concentrations, or nonaqueous solutions) will permit to validate one specific set and thus, the associated ?G(hyd)(?)[H(+)] value (atomistic consistency assumption). Preliminary results (first-peak positions in the ion-water radial distribution functions, partial molar volumes of ionic salts in water, and structural properties of ionic crystals) support a value of ?G(hyd)(?)[H(+)] close to -1100 kJ·mol(-1). PMID:21495739

Reif, Maria M; Hünenberger, Philippe H

2011-04-14

103

Infrared-sensitive photocathode  

DOEpatents

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.

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

1995-04-04

104

Infrared-sensitive photocathode  

DOEpatents

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.

Mariella, Jr., Raymond P. (Danville, CA); Cooper, Gregory A. (Pleasant Hill, CA)

1995-01-01

105

Final Report, Photocathodes for High Repetition Rate Light Sources  

SciTech Connect

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

Ben-Zvi, Ilan [Stony Brook University

2014-04-20

106

1st Workshop on Photo-cathodes: 300nm-500nm July 20-21, 2009: University of Chicago  

E-print Network

1st Workshop on Photo-cathodes: 300nm-500nm July 20-21, 2009: University of Chicago 3rd Floor-of-the-Art John Smedley (BNL) 10:15 - 10:30 Coffee Session 2: Transparent Bialkali/Multi-alkali Photo to Be More Red Jerry Vavra (SLAC) 3:30 - 3:45 Coffee Session 4: Opaque Photo-cathodes: What QE Can We Get? 4

107

Photocathodes for free electron lasers  

SciTech Connect

Many different photocathodes have been used as electron sources for FELs and other electron accelerator systems. In choosing one, a compromise between lifetime and quantum efficiency have been unavoidable. High quantum efficiency photocathodes such as CsK{sub 2}Sb, Cs{sub 3}Sb, and cesiated GaAs have short operational lifetimes and require an ultrahigh-vacuum environment. Long lifetime photocathodes such as LaB{sub 6}, Cu, and Y have relatively low quantum efficiencies. However, recently, cesium telluride was found to be an exception. Initial results from CERN and now at Los Alamos have shown that Cs{sub 2}Te is reasonably rugged with a high quantum efficiency below 270 nm. Further studies were carried out at Los Alamos in determining its performance as an electron source for the Los Alamos Advanced FEL. The Los Alamos Advanced FEL was successfully operated at 5-6 microns with a Cs{sub 2}Te photocathode driven by a frequency quadrupled Nd:YLF laser as the electron source. Cs{sub 2}Te photocathodes with quantum efficiencies of 12-18% at 254 mn were fabricated in an ultrahigh-vacuum chamber and transferred under high vacuum to the FEL. The authors estimated that the operational lifetime of Cs{sub 2}Te photocathodes to be at least 20 times that for K{sub 2}CsSb photocathodes. Furthermore, experiments in the fabrication chamber have shown that heating to 150-200{degrees}C photocathodes exposed for one hour at 2{times}10{sup {minus}4} torr of air was sufficient to revive the quantum efficiency from below 1% to about 10%. The electron beam for the FEL extracted from a cesium telluride target was also characterized. The emittance, response time, saturation level and dark current of cesium telluride photocathodes was determined to be sufficient for FEL applications.

Kong, S.H.; Kinross-Wright, J.; Nuguyen, D.C.; Sheffield, R.L.

1994-09-01

108

Surface topography dependent desorption of alkali halides  

PubMed

Electron-stimulated desorption of the (100)KBr surface has been investigated in vacuum with noncontact atomic force microscopy and mass spectroscopy. It has been found that both desorption components (K and Br) show oscillatory dependence on the electron dose with the oscillation amplitude decaying gradually. These results correspond with periodically varying, as a result of a layer-by-layer desorption, surface topography. It is proposed that the surface terrace edges act as traps for excited F centers diffusing in the crystal. The oscillating density of terrace edges varies surface recombination/reflection rates for the F centers and modulates the balance between surface and bulk deexcitation of the crystal. PMID:10978122

Such; Kolodziej; Czuba; Piatkowski; Struski; Krok; Szymonski

2000-09-18

109

Spectroscopic predictions for alkali-atom-alkali-halide reaction intermediates  

NASA Astrophysics Data System (ADS)

The semi-empirical Roach-Child model is used to predict ionisation potentials, rotational constants, vibrational frequencies and the first three electronic absorption bands for the reaction intermediates Na 2Cl, K 2Cl and NaKCl, which are known to be isolatable by supersonic beam techniques.

Thompson, J. W.; Child, M. S.

1989-05-01

110

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

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 ionic radius entering into the calculation of the correction terms is also evaluated and found to be very limited. Ultimately, it is expected that comparison with other experimental ionic properties (e.g., derivative single-ion solvation properties, as well as data concerning ionic crystals, melts, solutions at finite concentrations, or nonaqueous solutions) will permit to validate one specific set and thus, the associated {Delta}G{sub hyd} {sup O-minus} [H{sup +}] value (atomistic consistency assumption). Preliminary results (first-peak positions in the ion-water radial distribution functions, partial molar volumes of ionic salts in water, and structural properties of ionic crystals) support a value of {Delta}G{sub hyd} {sup O-minus} [H{sup +}] close to -1100 kJ{center_dot}mol{sup -1}.

Reif, Maria M.; Huenenberger, Philippe H. [Laboratory of Physical Chemistry, ETH Zuerich, CH-8093 Zuerich (Switzerland)

2011-04-14

111

Cs based photocathodes for gaseous detectors  

SciTech Connect

We demonstrated that some standard photocathodes SbCs, GaAs(Cs), Au(Cs) can easily be manufactured for use inside gaseous detectors. When filed with clean quenched gases such detectors have a quantum efficiency of a few percent in the visible region of the spectra and can operate at a gain >10{sup 3}. We tried to make these photocathodes more air stable by protecting their surfaces with a thin layer of CsI or liquid TMAE. The most air stable were photocathodes with a CsI protective layer. A wavelengths {le}185 nm such photocathodes have the highest quantum efficiency among all known air stable photocathodes, including CsI. Gaseous detectors with such photocathodes can operate at a gain of 10{sup 5}. Results of first tests of doped CsI photocathode are also presented. Possible fields of application of new photocathodes are discussed.

Borovick-Romanov, A. [Inst. for Physical Problems (Russian Federation); Peskov, V. [Fermi National Accelerator Lab., Batavia, IL (United States)

1993-08-01

112

Optical and Spectral Studies on ? Alanine Metal Halide Hybrid Crystals  

NASA Astrophysics Data System (ADS)

We have synthesized and grown ? alanine metal halide hybrid crystals viz. ? alanine cadmium chloride (BACC), an amino acid transition metal halide complex crystal and ? alanine potassium chloride (BAPC), an amino acid alkali metal halide complex crystal by slow evaporation method. The grown crystals were found to be transparent and have well defined morphology. The optical characteristics of the grown crystals were carried out with the help of UV-Vis Spectroscopy. The optical transmittances of the spectrums show that BAPC is more transparent than BACC. The Photoluminescence of the materials were determined by the Photoluminescent Spectroscopy

Sweetlin, M. Daniel; Selvarajan, P.; Perumal, S.; Ramalingom, S.

2011-10-01

113

Alkali Metal/Salt Thermal-Energy-Storage Systems  

NASA Technical Reports Server (NTRS)

Proposed thermal-energy-storage system based on mixture of alkali metal and one of its halide salts; metal and salt form slurry of two immiscible melts. Use of slurry expected to prevent incrustations of solidified salts on heat-transfer surfaces that occur where salts alone used. Since incrustations impede heat transfer, system performance improved. In system, charging heat-exchanger surface immersed in lower liquid, rich in halide-salt, phase-charge material. Discharging heat exchanger surface immersed in upper liquid, rich in alkali metal.

Phillips, Wayne W.; Stearns, John W.

1987-01-01

114

PHOTOCATHODES FOR THE ENERGY RECOVERY LINACS.  

SciTech Connect

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.

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

2005-03-19

115

Photocathodes for the energy recovery linacs  

SciTech Connect

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.

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

2005-03-19

116

Binary technetium halides  

NASA Astrophysics Data System (ADS)

In this work, the synthetic and coordination chemistry as well as the physico-chemical properties of binary technetium (Tc) chlorides, bromides, and iodides were investigated. Resulting from these studies was the discovery of five new binary Tc halide phases: alpha/beta-TcCl3, alpha/beta-TcCl 2, and TcI3, and the reinvestigation of the chemistries of TcBr3 and TcX4 (X = Cl, Br). Prior to 2009, the chemistry of binary Tc halides was poorly studied and defined by only three compounds, i.e., TcF6, TcF5, and TcCl4. Today, ten phases are known (i.e., TcF6, TcF5, TcCl4, TcBr 4, TcBr3, TcI3, alpha/beta-TcCl3 and alpha/beta-TcCl2) making the binary halide system of Tc comparable to those of its neighboring elements. Technetium binary halides were synthesized using three methods: reactions of the elements in sealed tubes, reactions of flowing HX(g) (X = Cl, Br, and I) with Tc2(O2CCH3)4Cl2, and thermal decompositions of TcX4 (X = Cl, Br) and alpha-TcCl 3 in sealed tubes under vacuum. Binary Tc halides can be found in various dimensionalities such as molecular solids (TcF6), extended chains (TcF5, TcCl4, alpha/beta-TcCl2, TcBr 3, TcI3), infinite layers (beta-TcCl3), and bidimensional networks of clusters (alpha-TcCl3); eight structure-types with varying degrees of metal-metal interactions are now known. The coordination chemistry of Tc binary halides can resemble that of the adjacent elements: molybdenum and ruthenium (beta-TcCl3, TcBr3, TcI 3), rhenium (TcF5, alpha-TcCl3), platinum (TcCl 4, TcBr4), or can be unique (alpha-TcCl2 and beta-TcCl 2) in respect to other known transition metal binary halides. Technetium binary halides display a range of interesting physical properties that are manifested from their electronic and structural configurations. The thermochemistry of binary Tc halides is extensive. These compounds can selectively volatilize, decompose, disproportionate, or convert to other phases. Ultimately, binary Tc halides may find application in the nuclear fuel cycle and as precursors in inorganic and organometallic chemistry.

Johnstone, Erik Vaughan

117

Vitrification of IFR and MSBR halide salt reprocessing wastes  

SciTech Connect

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)

Siemer, D.D. [Idaho National Laboratory, 12N 3167E, Idaho Falls, ID 83402 (United States)

2013-07-01

118

Process for oxidation of hydrogen halides to elemental halogens  

DOEpatents

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.

Lyke, Stephen E. (Middleton, WI)

1992-01-01

119

High Efficiency Visible Photocathode Development  

SciTech Connect

The alkali antimonides are of significant interest to the accelerator community, as they have a high quantum efficiency (QE) under illumination by green light. These cathodes are attractive for high-average-current photoinjector applications and understanding their fundamental properties are critical to the production of long lived, reliable cathodes. We report on ongoing work to characterize cathode formation during growth. In-situ X-ray Diffraction (XRD) has been used to compare grain size and texture in antimony layers, and X-ray Photoelectron Spectroscopy (XPS) has been used to investigate the solid-state chemistry of cathode formation.

Smedley J.; Rao T.; Mueller, K.; Ben-Zvi, I.; Ruiz-Oses, M.; Liang, X.; Muller, E.M.; Lee, S.; Attenkofer, K.; Padmore, H.; Vecchione, T.

2011-09-30

120

RF Gun Photocathode Research at SLAC  

SciTech Connect

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.

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

121

Graphene shield enhanced photocathodes and methods for making the same  

DOEpatents

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.

Moody, Nathan Andrew

2014-09-02

122

Diamond Amplified Photocathodes John Smedley1  

E-print Network

acting as a barrier between the primary cathode and the cavity. Synthetic diamond has exhibited secondaryDiamond Amplified Photocathodes John Smedley1 , Ilan Ben-Zvi1 , Jen Bohon2 , Xiangyun Chang1 protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic

123

Making Solid Solutions with Alkali Halides (and Breaking Them)  

NSDL National Science Digital Library

In this exercise, the class will grow a variety of crystals of the same mineral, but with different chemical compositions. These crystals will be made from mixtures of halite (NaCl)and sylvite (KCl) that are melted and cooled. Because K+1 is significantly larger than Na+1,the unit cell is larger in sylvite than in halite. Intermediate compositions have intermediate unit cell sizes. Thus, a measurement of the lattice spacing of the crystalline products of your experiments can be used to determine their chemical composition. The principle goal of these experiments is to demonstrate that solid solutions do occur and that their physical properties vary with their chemical composition. Additional goals include studying the effect of composition on melting, exploring the process of exsolution as a function of temperature, and seeing the effect of fluids and deformation on crystallization kinetics.

John Brady

124

Linkage Isomerism of CO Adsorbed on Alkali Halides.  

PubMed

Variable-temperature FTIR spectra of CO adsorbed on NaCl and KBr films are shown to reveal linkage isomerism, that is, formation of C- and O-bonded adsorption complexes with the same cationic sites. Not all of the sites can be involved in that, only the three- or four-coordinated cations located on kinks, edges, or steps of microcrystals. For NaCl, these adsorption complexes account for the high-frequency (HF) C-O stretching bands at 2175 and 2160 cm(-1). Coresponding LF bands of O-bonded CO were found at 2115 and 2124 cm(-1). In the spectrum of KBr, the HF band is poorly resolved, and only one LF band can be clearly seen, near 2124 cm(-1). The value of the isomerization enthalpy for complexes that account for the bands at 2160 and 2124 cm(-1) of CO adsorbed on NaCl, estimated from the experiment, is 4.0 ± 0.2 kJ/mol. Quantum mechanical calculations by DFT methods applied to NaCl model clusters interacting with the CO molecule confirm the existence of two potential wells with adsorption and isomerization energies close to the experimentally measured values, and enable us to estimate the height of the potential barrier between the two adsorption states. PMID:25222795

Belykh, Roman; Maevskaya, Maria; Krauklis, Irina; Tsyganenko, Alexey

2014-09-29

125

Ionic Thermocurrents in Alkali Halide Crystals Containing Substitutional Beryllium Ions  

Microsoft Academic Search

The dielectric relaxations of NaCl and KCl single crystals containing beryllium ions have been studied using the technique of the ionic thermocurrents (ITC) in the range of temperatures between 1.2 and 300°K. The ITC spectra are characterized by three types of relaxations in both host crystals. The analysis of such relaxations and the observed temperature dependence of their relaxation times

Cesare Bucci

1967-01-01

126

Comment on ``lattice energy in alkali halide crystals''  

NASA Astrophysics Data System (ADS)

Recently Yadav has proposed a new repulsive term in the ionic interaction potential which has three unknown parameters. In order to determine uniquely the model parameters he proposed a condition which is found to be physically unconsistent.

Shukla, M. M.

1985-02-01

127

Cold ablation driven by localized forces in alkali halides  

NASA Astrophysics Data System (ADS)

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.

Hada, Masaki; Zhang, Dongfang; Pichugin, Kostyantyn; Hirscht, Julian; Kochman, Micha? 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

2014-05-01

128

Multialkali photocathodes grown by molecular beam epitaxy technique  

NASA Astrophysics Data System (ADS)

A new technique of bialkali photocathodes growth by molecular beam epitaxy (MI3E) has been developed. The photocathode film was deposited onto the substrate from molecular beams produced by simultaneously operating molecular sources of Sb, Na and K. Thus suggested procedure is noticeably differed from the classical one. Growth rate was about 1 A/sec and complete cycle of photocathode fabrication was 15-20 minutes. A special ultra high vacuum (UHV) chamber for MBE of multialkali photocathodes has been designed. The chamber is a part of UHV system consisting of an analysis vessel supplied with Auger and ESCA electron spectrometer and low energy electron diffractometer (LEED), the MBE chamber itself and a chamber for cold sealing of photocathodes with device body through indium ring. The system gives a possibility to carry out investigations of multialkali photocathode physics and to produce commercial devices. Developed technique can be used for fabrication of vacuum devices including streak tubes.

Dubovoi, I. A.; Chernikov, A. S.; Prokhorov, Alexander M.; Schelev, Mikhail Y.; Ushakov, Victor N.

1991-04-01

129

Characterization of Cesiated Tungsten Dispenser Photocathodes  

E-print Network

Characterization of Cesiated Tungsten Dispenser Photocathodes Anne Balter Collaborators: Eric;· +· +· + · +· +· +· +· +· +· +· +· +· + Cesium Ions Sintered Tungsten Metal Desorbed Cesium Cesium Reservoir 3 Dispenser Cathode Introduction;#12;5 Dispenser Characterization 2 Bk T I AT e - = 2 ln I T 1 3 10T- � -22 -21 -20 -19 -18 -17 2.1 2.15 2

Anlage, Steven

130

Activation and evaluation of GaN photocathodes  

Microsoft Academic Search

Gallium Nitride (GaN) photocathodes are potentially attractive as UV detective materials and electron sources. Based on the activation and evaluation system for GaAs photocathode, which consists of ultra-high vacuum (UHV) activation chamber, multi-information measurement system, X-ray photoelectron spectroscopy (XPS), and ultraviolet ray photoelectron spectroscopy (UPS), the control and measurement system for the activation of UV photocathodes was developed. The developed

Yunsheng Qian; Benkang Chang; Jiangliang Qiao; Yijun Zhang; Rongguo Fu; Yafeng Qiu

2009-01-01

131

Alkali metal nitrate purification  

DOEpatents

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.

Fiorucci, Louis C. (Hamden, CT); Morgan, Michael J. (Guilford, CT)

1986-02-04

132

Freezing in Halide Salts  

NASA Astrophysics Data System (ADS)

The static criterion that the amplitude of the principal peak of the liquid structure factor has a constant value along the freezing line and the onset of freezing are studied from the structure factors and the static dielectric functions of halide salts interacting via the effective pair potentials through the hypernetted-chain approximation. It is observed that the criterion above is restricted to the effective charge difference. The critical value of plasma parameter at freezing is affected by the mobility and number concentration of anions and cations. The distribution of the value of the static dielectric function closest to the wave number axis in the negative region is also determined by the charge difference and the ordering of ions and related to the onset of freezing.

Akdere, ?.; Y?lmaz, M.; Kavanoz, H. B.; Ta?seven, Ç.

2008-06-01

133

CANDELA PHOTO-INJECTOR EXPERIMENTAL RESULTS WITH A DISPENSER PHOTOCATHODE  

E-print Network

CANDELA PHOTO-INJECTOR EXPERIMENTAL RESULTS WITH A DISPENSER PHOTOCATHODE C. Travier, B. Leblond, M- injector. The dispenser photocathode is illuminated by a 500 fs pulse from a frequency-tripled Ti:sapphire laser. In this paper we report charge measurements showing that the dispenser pho- tocathode has

Paris-Sud XI, Université de

134

Enhancement of photoemission from and postprocessing of K2CsSb photocathode using excimer laser  

NASA Astrophysics Data System (ADS)

The high quantum efficiency at visible wavelengths of alkali-antimonide photoemissive materials, such as K2CsSb, makes them excellent potential photocathodes for high-current applications. We have developed a technique of using an ultraviolet laser to clean the cathode's substrate and thus enhance the photoyield of a K2CsSb photocathode subsequently deposited on the substrate. We have shown that the quantum efficiency of the cathode from the laser-exposed substrate can be at least 50% higher than that of an unexposed surface. We have also formulated a nonthermal technique for completely removing the cathode from the substrate while preserving an ultrahigh vacuum to assure the regrowth of the cathode. The bialkali cathode is dissociated and then removed completely upon 10 s exposure to a 248 nm laser beam with 3.5 mJ/mm2 of energy density at a 30 Hz repetition frequency. Here, we discuss these experimental results and their potential applications. We also describe applications of this technique to reduce the beam's halo and its emittance.

Wang, Erdong; Rao, Triveni; Ben-zvi, Ilan

2014-02-01

135

Microwave-assisted hydrothermal hydrolysis of cellobiose and effects of additions of halide salts.  

PubMed

Microwave irradiation was compared with induction heating for hydrothermal hydrolysis of cellobiose. Microwave heating improved glucose selectivity and resulted in a pH of the hydrolyzates that was ?0.57 units lower than those from conventional heating, which suggests that fewer side-reactions occurred. Halide salts of alkali and alkali earth metals improved microwave-assisted hydrothermal saccharification of cellobiose at lower reaction severity by around 0.3 of logR(0). NaCl addition of ?10mM reduced the required microwave output to 58.6-66.2% as compared to conventional microwave-hydrothermal hydrolysis without halide salts. Kinetic analyses revealed that the addition of salt increased the hydrolysis rate by increasing the frequency factor of the reaction. The results showed that microwave irradiation in the presence of microwave-absorbing salts is effective for hydrothermal hydrolysis of carbohydrates. PMID:22939594

Tsubaki, Shuntaro; Oono, Kiriyo; Onda, Ayumu; Yanagisawa, Kazumichi; Azuma, Jun-Ichi

2012-11-01

136

Development of Polarized Photocathodes for the Linear Collider  

SciTech Connect

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.

Richard Prepost

2009-12-22

137

Silver nanorod arrays for photocathode applications  

SciTech Connect

In this study, we explore the possibility of using plasmonic Ag nanorod arrays featuring enhanced photoemission as high-brightness photocathode material. Silver nanorod arrays are synthesized by the DC electrodeposition method and their dimensionality, uniformity, crystallinity and oxide/impurity content are characterized. These Ag nanorod arrays exhibit greatly enhanced two-photon photoemission under 400 nm femtosecond pulsed laser excitation. Plasmonic field enhancement in the array produces photoemission hot spots that are mapped using photoemission electron microscopy (PEEM). The relative photoemission enhancement of nanorod array hot spots relative to that of a flat Ag thin film is found to range between 102 and 3 x 103.

Vilayur Ganapathy, Subramanian; Nandasiri, Manjula I.; Joly, Alan G.; El-Khoury, Patrick Z.; Varga, Tamas; Coffey, Greg W.; Schwenzer, Birgit; Pandey, Archana; Kayani, Asghar N.; Hess, Wayne P.; Thevuthasan, Suntharampillai

2013-10-14

138

A multi-frequency RF photocathode gun  

NASA Astrophysics Data System (ADS)

The concept of a photocathode injection gun driven by several harmonically related phase-locked RF sources is considered. This concept is aimed at providing electron bunches with parameters as follows: charge/bunch ?1 nC, bunch energy 5-10 MeV, bunch width 20-40 ps, and fundamental frequency = 1.3 GHz. In comparison with a conventional single mode 1.5 cell injection gun, multi-harmonic excitation can allow operation with lower RF power input, lower Ohmic losses, and lower beam emittance (for a given cathode field).

Kuzikov, S. V.; Hirshfield, J. L.; Jiang, Y.; Vikharev, A. A.; Vogel, V.

2013-01-01

139

STATUS OF DIAMOND SECONDARY EMISSION ENHANCED PHOTOCATHODE  

SciTech Connect

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.

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

2007-05-25

140

Performance of photocathode rf gun electron accelerators  

SciTech Connect

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.

Ben-Zvi, I.

1993-07-01

141

Performance of photocathode rf gun electron accelerators  

SciTech Connect

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.

Ben-Zvi, I.

1993-01-01

142

Methyl Halide Production by Fungi  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl), methyl bromide (CH3Br) and methyl iodide (CH3I) are methyl halide gases that contribute significant amounts of halogen radicals to the atmosphere. In an effort to better understand the global budget of methyl halides and their impact on the atmosphere, we need to identify the natural sources in addition to the known anthropogenic sources of these compounds. We are investigating the role of fungi in the production of methyl halides in the soils and wetlands in southern New Hampshire, USA. Previous research has shown that wood decay fungi and ectomycorrhizal fungi, which are within a group of fungi called basidiomycetes, emit methyl halides. In our study, measurements of headspace gas extracted from flasks containing fungi grown in culture demonstrate that a variety of fungi, including basidiomycetes and non-basidiomycetes, emit methyl halides. Our research sites include four ecosystems: an agricultural field, a temperate forest, a fresh water wetland, and coastal salt marshes. We have collected and isolated fungi at each site by culturing tissue samples of fruiting bodies and plant material, by using wood baits, and from the direct culture of soil. We compared the rates of methyl halide emissions from the fungi in the four ecosystems. In addition, we measured emissions from previously assayed fungal isolates after reintroducing them to sterilized soils that were collected from their original environments. Fungal biomass was determined by substrate-induced respiration (SIR). The emission rate by the fungus was determined by a linear regression of the concentration of methyl halide in the sample headspace over time divided by the fungal biomass.

Dailey, G. D.; Varner, R. K.; Blanchard, R. O.; Sive, B. C.; Crill, P. M.

2005-12-01

143

Actinide halide complexes  

DOEpatents

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.

Avens, Larry R. (Los Alamos, NM); Zwick, Bill D. (Santa Fe, NM); Sattelberger, Alfred P. (Los Alamos, NM); Clark, David L. (Los Alamos, NM); Watkin, John G. (Los Alamos, NM)

1992-01-01

144

Radiochemical synthesis of pure anhydrous metal halides  

NASA Technical Reports Server (NTRS)

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.

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

1973-01-01

145

Development of femtosecond photocathode RF gun  

NASA Astrophysics Data System (ADS)

Femtosecond electron bunches are essential for the observation of ultrafast reactions and phenomena in materials. To improve the time resolution of pulse radiolysis and ultrafast electron diffraction (UED), which involve the use of ultrashort electron bunches and ultrashort light, a femtosecond photocathode RF gun driven by a femtosecond laser was investigated experimentally. Bunch charge generated in the RF gun was studied based on the Schottky effect. Thermal emittance was estimated as 0.26 mm mrad at an rms laser spot size of 0.21 mm. Bunch length and longitudinal emittance were obtained as 180 fs and 0.87 deg keV, respectively, at a bunch charge of 3.5 pC and rms laser spot size of 0.38 mm.

Kan, K.; Yang, J.; Kondoh, T.; Yoshida, Y.

2011-12-01

146

Advanced 3D Photocathode Modeling and Simulations Final Report  

SciTech Connect

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.

Dimitre A Dimitrov; David L Bruhwiler

2005-06-06

147

R&D ERL: Photocathode Deposition and Transport System  

SciTech Connect

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.

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

2010-01-01

148

Metal Photocathodes for Free Electron Laser Applications  

NASA Astrophysics Data System (ADS)

Synchrotron x-ray radiation sources have revolutionized many areas of science from elucidating the atomic structure of proteins to understanding the electronic structure of complex materials such as the cuprate superconductors. In a Free Electron Laser (FEL), the main difference to the synchrotron radiation mechanism is that the light field acts on the electron beam, over a long distance in an undulator, and causes electron bunching at the optical wavelength. Electrons in different parts of the electron bunch are therefore correlated, and so emit coherently, with a brightness that scales as the square of the number of electrons. In order to lase, the electron beam in a FEL must have a transverse geometric emittance less than the wavelength of the light to be produced. For the generation of x-ray wavelengths, this is one of the most difficult challenges in the design and construction of a FEL. The geometric emittance can be "compressed" by acceleration to very high energy, but with the penalty of very large physical size and very large cost. The motivation for this work was provided by the desire to investigate the fundamental origin of the emittance of an electron beam as it is born at a photocathode. If this initial, or "thermal" emittance can be reduced, the energy, scale and cost of accelerators potentially would be reduced. As the LCLS used copper as its photocathode, this material was the one studied in this work. Copper was used in the LCLS as it represented a "robust" material that could stand the very high accelerating gradients used in the photoinjector of the FEL. Metals are also prompt photoemitters, and so can be used to produce very short electron bunches. This can be a useful property for creation of extremely short FEL pulses, and also for creation of beams that are allowed to expand under space charge forces, but in a way that results in linear fields, allowing subsequent recompression. An ideal photocathode for FEL photoinjector should have high quantum efficiency (QE), small emittance, fast temporal response, long lifetime, and minimal complexity. High QE of cathodes require less power for driving laser and also reduce the risk of damaging the cathode materials. Small emittance reduce the scale of the accelerator, therefore, the cost. Metal photocathodes such as copper exhibit long lifetime and fast response, but have quite low quantum efficiency ( < 10-4). The aim in this work was to understand the quantum yield of the metal, and the transverse momentum spectrum, as the product of the latter and the cathode beam spot size gives the transverse emittance. Initial x-ray diffraction work provided evidence that the LCLS photocathode consisted of large low index single crystal grains, and so work focused on the study of single crystals that could be produced with atomically ordered surfaces, rather than a polycrystalline material. Present theories of quantum yield and transverse emittance assume the basic premise that the metal is entirely disordered, and work here shows that this is fundamentally incorrect, and that the order of the surface plays a critical role in determining the characteristics of emission. In order to investigate these surfaces, I constructed a laser-based ultra-low energy angle resolved photoemission system, capable of measuring the momentum spectrum of the emission and wavelength and angle dependent electron yield. This system has been commissioned, and data taken on low index surfaces of copper. Results from this work on single crystal copper demonstrates that emitted electrons from the band structure of a material can exhibit small emittance and high quantum efficiency. We show that the emission from the Cu(111) surface state is highly correlated between angle of incidence and excitation energy. This manifests itself in the form of a truncated emission cone, rather than the isotropic emission predicted from the normal model. This clearly then reduces the emittance from the normal values. It also results in extremely strong polarization dependence, wi

Greaves, Corin Michael Ricardo

149

Mixed Alkali Effect in Alkali Metasilicate Glasses  

NASA Astrophysics Data System (ADS)

Molecular dynamics (MD) simulation was performed for LiKSiO3 glass to clarify the mechanism of the ``mixed alkali effect". In LiKSiO3 glass at 800 K (near Tg), jump paths of Li and K ion are visualized. Each kind of alkali metal ions clearly shows an independent path. Each jump path has a low dimensional structure in (short) localized regions, while each path forms percolation clusters of various sizes. The larger probability of the back-correlation in the mixture than that in the pure salts contributes to the mixed alkali effect. Cooperative jumps of like ions are found to play an important role in the high conductivity of the pure Li containing glass and decreased contribution of the cooperative jumps to bulk diffusion coefficients explains the anomalous increase in the Haven ratio in the mixed alkali system. Namely, the interception of the jump paths in the mixture affects a collective motion more than a single ion motion.

Habasaki, J.; Okada, I.; Hiwatari, Y.

150

Diode pumped alkali lasers  

NASA Astrophysics Data System (ADS)

Diode pumped alkali lasers attract growing attention during the past several years because they have demonstrated potential to compete and, possibly, replace the best existing high power laser systems. In spite of the fact that an optically pumped alkali (potassium) vapor laser was first proposed by A.L. Schawlow and C.H. Townes in 1958, the intensive research and development of alkali vapor started only in 2003, when really efficient lasing in Rb and Cs vapors was demonstrated. The interest to this research was stimulated by the possibility of using efficient diode lasers for optical pumping of the alkali gain medium that promises high overall efficiency of the device. A variety of experiments on alkali lasers, including the demonstration of efficient Rb, Cs and K vapor lasers, power scaling experiments with multiple diode laser pumping sources and experiments on diode pumped alkali vapor amplifiers were performed during the past several years. In this paper we present a review of the most important achievements in high power alkali lasers research and development, discuss some problems existing in this field and future perspectives in DPAL development.

Zhdanov, B. V.; Knize, R. J.

2011-11-01

151

Progress on diamond amplified photo-cathode  

SciTech Connect

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.

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

2011-03-28

152

Photocathode Optimization for a Dynamic Transmission Electron Microscope: Final Report  

SciTech Connect

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.

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

2011-08-04

153

Activation and evaluation of GaN photocathodes  

NASA Astrophysics Data System (ADS)

Gallium Nitride (GaN) photocathodes are potentially attractive as UV detective materials and electron sources. Based on the activation and evaluation system for GaAs photocathode, which consists of ultra-high vacuum (UHV) activation chamber, multi-information measurement system, X-ray photoelectron spectroscopy (XPS), and ultraviolet ray photoelectron spectroscopy (UPS), the control and measurement system for the activation of UV photocathodes was developed. The developed system, which consists of Xenon lamp, monochromator with scanner, signal-processing module, power control unit of Cs and O source, A/D adapter, digital I/O card, computer and software, can control the activation of GaN photocathodes and measure on-line the spectral response curves of GaN photocathodes. GaN materials on sapphire substrate were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) with p-type Mg doping. The GaN materials were activated by Cs-O. The spectral response and quantum efficiency (QE) were measured and calculated. The experiment results are discussed.

Qian, Yunsheng; Chang, Benkang; Qiao, Jiangliang; Zhang, Yijun; Fu, Rongguo; Qiu, Yafeng

2009-09-01

154

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

155

FEMTO SECOND ELECTRON BEAM DIFFRACTION USING A PHOTOCATHODE RF GUN.  

SciTech Connect

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.

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

2003-05-12

156

Polarized Photocathode R&D for Future Linear Collliders  

SciTech Connect

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.

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

2009-01-23

157

Intrinsic emittance reduction of an electron beam from metal photocathodes.  

PubMed

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·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. PMID:20867245

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

2010-06-11

158

Alkalis in alternative fuels  

SciTech Connect

The alkali content of annually produced biofuels severely limits their use for energy. When fired in conventional boilers the alkali reacts with other inorganic elements to agglomerate fluidized beds, forms slag on grates and creates flyash that sticks to refractory and deposits on convection surfaces. This paper describes results from a cooperative project between the biomass industry and the National Renewable Energy Laboratory to investigate the extent and nature of these alkali deposits and look for potential solutions. The chemistry and firing characteristics of more than 26 fuels were investigated in the laboratory and in full scale industrial firing tests. Many different analytical methods were used to characterize the fuels and deposits. Urban wood fuels, agricultural residues, energy crops were included in a database. Effects of alkali are described which may influence fuel selection and boiler operation. While the transformation of inorganics and mechanisms of deposit information can be explained, the use of some energy crops with high alkali will require special furnace designs.

Miles, T.R.; MIles, T.R. Jr. [Consulting Design Engineer, Portland, OR (United States)

1994-12-31

159

SLAC rf photocathode gun test facility  

NASA Astrophysics Data System (ADS)

A high brightness electron injector is a necessary component for x-ray FELs. A dedicated rf gun test facility is being developed at SLAC to measure the phase space distribution from a photocathode rf gun generated electron beam. This Gun Test Facility will allow optimization of the beam brightness by independently adjusting parameters such as accelerating field, laser pulse shape and total charge. The test facility is comprised of a single S-band klystron, 3 m SLAC linac section, analyzing magnet, diagnostic section, a cathode drive laser and the gun under test. The laser is comprised of a Nd:YLF oscillator and a Nd:glass regenerative amplifier. The light incident on the cathode is capable of both normal and near grazing incidence and is currently frequency quadrupled into the UV. In the near future a Nd:glass oscillator will be installed which will be capable of generating pulses as short as 200 fs. This oscillator will be used to make emittance measurements as a function of the laser pulse width and shape. Both oscillators will be phase-locked to the 24th sub-harmonic of the linac frequency. Emittance measurements will be made downstream of the linac at an electron beam energy of approximately 30 - 50 MeV using a quad scan with a beam profile screen and/or a wire scanner to measure the spot size. A current transformer and a Faraday cup will be used to measure the charge while a streak camera or a transition radiator can be used to measure the micropulse width. The first gun to undergo testing will be the BNL/SLAC/UCLA 1.6 cell symmetrized cavity gun with a copper cathode. With field gradients in the gun as high as 150 MV/m, using solenoidal emittance compensation and spatial and temporal flat top laser pulses, PARMELA simulations predict normalized emittances of less than 1.5 pi mm-mrad with 10 ps long pulses and 1 nC of charge after acceleration in a 3 meter linac section to about 30 MeV. Appropriate additional acceleration can further reduce the emittance below 1 pi mm-mrad.

Schmerge, John F.; Reis, David A.; Hernandez, Mike; Meyerhofer, David D.; Miller, Roger H.; Palmer, Dennis T.; Weaver, Jim N.; Winick, Herman; Yeremian, A. D.

1997-05-01

160

Halide transport in Xenopus oocytes.  

PubMed

1. Radioisotopes and intracellular microelectrodes were used to characterize the permeability of Xenopus oocytes to chloride and other halides. 2. Uptake of 36Cl had a half-time for equilibration of approximately 3 h, with an initial rate of Cl- entry corresponding to a permeability coefficient of 3.9 x 10(-7) cm/s, and an equilibrium uptake of 36Cl of 33 mM. 3. Replacement of bathing Na+ by K+ depolarized the oocytes from -46 to -7 mV and stimulated influx approximately 3-fold. 4. Influx was linearly dependent on bathing [Cl-] and was temperature dependent with an activation energy of 46 kJ/mol. Influx of 125I of 36Cl was not affected by the presence of equal concentrations of other halides or thiocyanate. These results are consistent with a channel-mediated entry mechanism. 5. Diphenylamine-2-carboxylate (DPAC) and 9-anthracene carboxylate (9-AC), blockers of Cl- channels in other cells, inhibited Cl- entry with dissociation constants (Kds) of approximately 5 x 10(-4) and approximately 10(-3) M, respectively. Inhibitors of Cl(-)-HCO3- exchange or Na(+)-K(+)-2Cl- co-transport did not affect Cl- influx. 6. Attempts to lower or raise intracellular Ca2+ with BAPTA or A23187, respectively, were also without effect on Cl- influx. 7. The halide selectivity sequence determined with isotopes was I- (3.2) greater than Br- (1.3) greater than Cl- (1.0). However, DPAC inhibited almost all of the 36Cl influx but only a small fraction of 125I influx. 8. Replacement of bathing Cl- by I- or Br-resulted in hyperpolarizations, from which the same selectivity sequence was determined. 9. Replacement of bathing Cl- by gluconate caused a marked depolarization, which was inhibited by DPAC and, less potently, by 9-AC. PMID:1822540

Katayama, Y; Widdicombe, J H

1991-11-01

161

Fluorination of the cyanogen halides  

E-print Network

copper caps which were sliver soldered ln place. Copper tubing entrance and exit tubes were silver soldered to the top of the pot. The pipe union formed a leak proof system which could be assembled with reactants, and disassembled after reaction.... The fluorine tube ran down the outside of ths reaction tube and entered at the bottom of the tube. The fluorine hsd to pass through the cyanogen halide before emerging at the top of the reaction tube. The copper exit tube was silver soldered to the metal...

Ward, Raymond Anthony

2012-06-07

162

Hygroscopicity Evaluation of Halide Scintillators  

SciTech Connect

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

Zhuravleva, M [The University of Tennessee] [The University of Tennessee; Stand, L [The University of Tennessee] [The University of Tennessee; Wei, H [The University of Tennessee] [The University of Tennessee; Hobbs, C. L. [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK); Boatner, Lynn A [ORNL] [ORNL; Ramey, Joanne Oxendine [ORNL] [ORNL; Burger, Arnold [Fisk University, Nashville] [Fisk University, Nashville; Rowe, E [Fisk University, Nashville] [Fisk University, Nashville; Bhattacharya, P. [Fisk University, Nashville] [Fisk University, Nashville; Tupitsyn, E [Fisk University, Nashville] [Fisk University, Nashville; Melcher, Charles L [University of Tennessee, Knoxville (UTK)] [University of Tennessee, Knoxville (UTK)

2014-01-01

163

High gradient acceleration in a 17 GHz photocathode RF gun  

Microsoft Academic Search

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 1½ cell room temperature copper cavity with a peak accelerating gradient of about 250 MV\\/m. The anticipated beam parameters, when operating with a photoemission cathode, are: energy 2 MeV, normalized emittance

S. C. Chen; J. Gonichon; L. C.-L. Lin; R. J. Temkin; S. Trotz; B. G. Danly; J. S. Wurtele

1993-01-01

164

Metal-Insulator Photocathode Heterojunction for Directed Electron Emission  

SciTech Connect

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).

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

2014-02-14

165

Methods of recovering alkali metals  

DOEpatents

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.

Krumhansl, James L; Rigali, Mark J

2014-03-04

166

Chlor-Alkali Technology.  

ERIC Educational Resources Information Center

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)

Venkatesh, S.; Tilak, B. V.

1983-01-01

167

Milk-Alkali Syndrome  

PubMed Central

Milk-alkali syndrome (MAS) consists of hypercalcemia, various degrees of renal failure, and metabolic alkalosis due to ingestion of large amounts of calcium and absorbable alkali. This syndrome was first identified after medical treatment of peptic ulcer disease with milk and alkali was widely adopted at the beginning of the 20th century. With the introduction of histamine2 blockers and proton pump inhibitors, the occurrence of MAS became rare; however, a resurgence of MAS has been witnessed because of the wide availability and increasing use of calcium carbonate, mostly for osteoporosis prevention. The aim of this review was to determine the incidence, pathogenesis, histologic findings, diagnosis, and clinical course of MAS. A MEDLINE search was performed with the keyword milk-alkali syndrome using the PubMed search engine. All relevant English language articles were reviewed. The exact pathomechanism of MAS remains uncertain, but a unique interplay between hypercalcemia and alkalosis in the kidneys seems to lead to a self-reinforcing cycle, resulting in the clinical picture of MAS. Treatment is supportive and involves hydration and withdrawal of the offending agents. Physicians and the public need to be aware of the potential adverse effects of ingesting excessive amounts of calcium carbonate. PMID:19252114

Medarov, Boris I.

2009-01-01

168

Shallow halogen vacancies in halide optoelectronic materials  

NASA Astrophysics Data System (ADS)

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.

Shi, Hongliang; Du, Mao-Hua

2014-11-01

169

Alkali and halogen chemistry in volcanic gases on Io  

NASA Astrophysics Data System (ADS)

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10 -6 to 10 +1 bars) ranges, which overlap the nominal conditions at Pele ( T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I 2 (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F.

Schaefer, Laura; Fegley, Bruce

2005-02-01

170

Equilibrium coverage of halides on metal electrodes  

NASA Astrophysics Data System (ADS)

The adsorption of halides on Cu(111) and Pt(111) has been studied using periodic density functional theory calculations. The equilibrium coverage of the halides as a function of the electrode potential was determined using a thermodynamic approach in which the electrochemical environment is not explicitly taken into account. For all considered systems, halide coverages between 1/3 and 3/8 should be stable over a wide potential range. Although some quantitative discrepancies with experiment are obtained, the qualitative trends derived from the calculations are consistent with experimental observations. The reasons for the remaining discrepancies with the experiment are discussed.

Gossenberger, Florian; Roman, Tanglaw; Groß, Axel

2015-01-01

171

Hydrothermal alkali metal recovery process  

DOEpatents

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.

Wolfs, Denise Y. (Houston, TX); Clavenna, Le Roy R. (Baytown, TX); Eakman, James M. (Houston, TX); Kalina, Theodore (Morris Plains, NJ)

1980-01-01

172

Transfer of aryl halide to alkyl halide: reductive elimination of alkylhalide from alkylpalladium halides containing syn-?-hydrogen atoms.  

PubMed

?-Hydride abstraction is a well-accepted elementary step for catalytic cycles in organometallic chemistry. It is usually anticipated that alkylpalladium halides containing syn-?-hydrogen atoms will undergo ?-hydride abstraction to afford the Heck-type products. However, this study discloses that the above general knowledge is only conditionally correct. Our experimental results demonstrate that the reductive elimination of alkylhalides from alkylpalladium halides containing syn-?-hydrogen atoms may surpass the ?-hydride abstraction or even become exclusive in certain cases. PMID:25367776

Hao, Wei; Wei, Junnian; Geng, Weizhi; Zhang, Wen-Xiong; Xi, Zhenfeng

2014-12-22

173

Inhibition of palmito polyphenoloxidase by halide salts.  

PubMed

The inhibitory properties of halide salts on palmito polyphenoloxidase (PPO) are described. Halide salts have the same inhibitory effect on the two forms of palmito PPO separated by hydrophobic chromatography. Fluoride and chloride ions showed a non-competitive, mixed type inhibition while bromide and iodide ions were found to be non-competitive inhibitors. A study of the Ki for the different halide salts showed that the smaller F- ion is a stronger inhibitor than I- and Br- and that Cl- has the highest Ki value. This suggests that the active site of the palmito PPO is not easily accessible. The inhibition by chloride and fluoride ion was found to be pH-dependent. The inhibitory effects of these ions increased with a decrease in pH. It is suggested that halide ions (X) could bind to either the protonated enzyme (EH) or the protonated substrate-enzyme complex (EHS) to yield inactive forms EHX and EHSX, respectively. PMID:9795866

Robert, C; Rouch, C; Cadet, F

1998-07-01

174

The effect of surface cleaning on quantum efficiency in AlGaN photocathode  

NASA Astrophysics Data System (ADS)

To improve the quantum efficiency of AlGaN photocathode, various surfaces cleaning techniques for the removal of alumina and carbon from AlGaN photocathode surface were investigated. The atomic compositions of AlGaN photocathode structure and surface were measured by the X-ray photoelectron spectroscopy and Ar+ ion sputtering. It is found that the boiling KOH solution and the mixture of sulfuric acid and hydrogen peroxide, coupled with the thermal cleaning at 850 °C can effectively remove the alumina and carbon from the AlGaN photocathode surface. The quantum efficiency of AlGaN photocathode is improved to 35.1% at 240 nm, an increase of 50% over the AlGaN photocathode chemically cleaned by only the mixed solution of sulfuric acid and hydrogen peroxide and thermally cleaned at 710 °C.

Hao, Guanghui; Zhang, Yijun; Jin, Muchun; Feng, Cheng; Chen, Xinlong; Chang, Benkang

2015-01-01

175

Preparation of graphene/polymer composite photocathode for QDSSC  

NASA Astrophysics Data System (ADS)

Graphene (rGO) was fabricated by modified Hummers method and a reducing process. Conductive polymer/graphene films were obtained by scalpel technology and used as photocathode in CdS quantum dot-sensitized solar cell (QDSSC). Polymers used in this paper were ethyl cellulose (EC), polyphenyl vinyl (PPV) and polyvinyl butyral (PVB), respectively. The obtained composite films were investigated by X-ray diffraction, Raman spectroscopy technology and scanning electron microscope (SEM). The photoelectric properties of QDSSCs were tested under AM 1.5 irradiation. Test results show that the film performance of the EC/rGO and PPV/rGO photocathode have been improved effectively. Power conversion efficiency (PCE) of the relative QDSSCs under AM 1.5 irradiation were 0.81% and 0.86%, respectively.

Wang, Qiandi; Shen, Yue; Tan, Jie; Xu, Kai; Shen, Tan; Cao, Meng; Gu, Feng; Wang, Linjun

2013-12-01

176

Advanced Laser Technologies for High-brightness Photocathode Electron Gun  

NASA Astrophysics Data System (ADS)

A laser-excited photocathode RF gun is one of the most reliable high-brightness electron beam sources for XFELs. Several 3D laser shaping methods have been developed as ideal photocathode illumination sources at SPring-8 since 2001. To suppress the emittance growth caused by nonlinear space-charge forces, the 3D cylindrical UV-pulse was optimized spatially as a flattop and temporally as squarely stacked chirped pulses. This shaping system is a serial combination of a deformable mirror that adaptively shapes the spatial profile with a genetic algorithm and a UV-pulse stacker that consists of four birefringent ?-BBO crystal rods for temporal shaping. Using this 3D-shaped pulse, a normalized emittance of 1.4 ? mm mrad was obtained in 2006. Utilizing laser's Z-polarization, Schottky-effect-gated photocathode gun was proposed in 2006. The cathode work functions are reduced by a laser-induced Schottky effect. As a result of focusing a radially polarized laser pulse with a hollow lens in vacuum, the Z-field (Z-polarization) is generated at the cathode.

Tomizawa, Hiromitsu

177

Performance of Au transmission photocathode on a microchannel plate detector  

SciTech Connect

X-ray framing cameras, employing microchannel plates (MCPs) for detection and signal amplification, play a key role in research in high-energy-density physics. These instruments convert radiographic x-rays into electrons produced by plasma during such experiments into electrons that are amplified in the channels and then detected by a phosphor material. The separation of detection from signal amplification offers potential improvements in sensitivity and noise properties. We have implemented a suspended Au transmission photocathode (160 A thick) on a MCP and are evaluating it using a 1.5 keV Al K{alpha} x-ray source. We find an approximately twofold increase in the ratio of detected events to incident photons when the photocathode-to-MCP voltage difference is sufficiently large. Our calculations indicate that this increase is probably caused by a combination of signal produced by the photocathode and an increase in the efficiency of detection of x-rays that reach the MCP surface through modification of the local electric field.

Lowenstern, M. E.; Harding, E. C.; Huntington, C. M.; Visco, A. J.; Rathore, G.; Drake, R. P. [University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109 (United States)

2008-10-15

178

A method for the selective hydrogenation of alkenyl halides to alkyl halides.  

PubMed

A general method for the selective hydrogenation of alkenyl halides to alkyl halides is described. Fluoro, chloro, bromo, iodo, and gem-dihaloalkenes are viable substrates for the transformation. The selectivity of the hydrogenation is consistent with reduction by a hydrogen atom transfer pathway. PMID:24824195

King, Sandra M; Ma, Xiaoshen; Herzon, Seth B

2014-05-14

179

Dimming of metal halide lamps  

NASA Technical Reports Server (NTRS)

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.

Schurer, Kees

1994-01-01

180

40 CFR 721.4095 - Quaternary ammonium alkyltherpropyl trialkylamine halides.  

Code of Federal Regulations, 2010 CFR

... 2010-07-01 false Quaternary ammonium alkyltherpropyl trialkylamine halides...Substances § 721.4095 Quaternary ammonium alkyltherpropyl trialkylamine halides...substances identified generically as quaternary ammonium alkyltherpropyl trialkylamine...

2010-07-01

181

The Remarkable Reactivity of Aryl Halides with Nucleophiles  

ERIC Educational Resources Information Center

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)

Bunnett, Joseph F.

1974-01-01

182

Spectroscopy on Metal-Halide Lamps under Varying Gravity Conditions  

E-print Network

Spectroscopy on Metal-Halide Lamps under Varying Gravity Conditions PROEFSCHRIFT ter verkrijging the Eindhoven University of Technology Library Flikweert, Adriaan Jan Spectroscopy on Metal-Halide Lamps under / metaalhalogenidelampen / lichtbronnen / plasmadiagnostiek / spectroscopie / microzwaartekracht / hyperzwaartekracht

Eindhoven, Technische Universiteit

183

Significantly improved charge-collection efficiencies result from a general chemical approach to synthesizing photocathodes.  

E-print Network

Significantly improved charge-collection efficiencies result from a general chemical approach in sensitized CdS­NiO nanoparticle photocathodes,"Chem. Commun. 47, 10419 (2011). Key Research Results Achievement Researchers developed a chemical approach that resulted in CdS-sensitized photocathodes

184

Studies of TTF RF Photocathode Gun using acoustic sensors J. Nelson and M. Ross  

E-print Network

1 Studies of TTF RF Photocathode Gun using acoustic sensors J. Nelson and M. Ross SLAC November 27 RF high voltage breakdown locations in the photocathode gun system. It is not known if the acoustic gun [4] to locate its breakdown events during operation with a pulse length of 300µs and a pulse

185

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

SciTech Connect

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.

Anderson, D.F.; Kwan, S. (Fermi National Accelerator Lab., Batavia, IL (United States)); Hoeneisen, B. (Universidad San Francisco de Quito (Ecuador)); Peskov, V. (European Organization for Nuclear Research, Geneva (Switzerland). World Lab.)

1991-09-01

186

Research on mechanical shock impact of GaAs photocathode photoemission performance  

NASA Astrophysics Data System (ADS)

The GaAs photocathode has been widely used in optoelectronic devices such as image intensifiers and photomultiplier tubes, but it is inevitable for these devices to withstand a variety of mechanical shock. In order to study the impact on the GaAs photocathode's photoemission performance caused by mechanical shock, GaAs photocathode image intensifier is researched in this paper . The spectral response of the GaAs photocathode was tested respectively before and after several value of mechanical shock?the value of mechanical shock:55g?65g?75g?85g and 95g?.The parameter of the GaAs photocathode can be calculated and the quantum efficiency curve can be fitted as well using the MATLAB software. The results show that surface escape probability is increased after photocathode is subjected to mechanical shock, so that its photoemission performance will be improved. We think this phenomenon is due to the GaAs photocathode surface Cs-O reconstruction. This finding provided a new method to enhance the photoemission performance of photocathode.

Shi, Feng; Cheng, Hong-chang; Bai, Xiao-feng; Yan, Lei; Jiao, Gang-cheng

2013-08-01

187

Preparation of alkali metal dispersions  

NASA Technical Reports Server (NTRS)

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.

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

1968-01-01

188

Purification of alkali metal nitrates  

DOEpatents

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.

Fiorucci, Louis C. (Hamden, CT); Gregory, Kevin M. (Woodridge, IL)

1985-05-14

189

Recent advances in technetium halide chemistry.  

PubMed

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, ?/?-TcCl3, ?/?-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 (?-TcCl3, TcBr3, and TcI3) and to rhenium (?-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, ?-TcCl3 crystallizes with the AlCl3 structure-type and consists of infinite layers of edge-sharing TcCl6 octahedra, while ?-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(IV)) to d(5) (Tc(II)) is accompanied by the formation of metal-metal bonds in the coordination polyhedra. There is no metal-metal interaction in TcX4, a Tc?Tc double bond is present in ?/?-TcCl3, and a Tc?Tc triple bond is present in ?/?-TcCl2. We investigated the thermal behavior of these binary halides in sealed tubes under vacuum at elevated temperature. Technetium tetrachloride decomposes stepwise to ?-TcCl3 and ?-TcCl2 at 450 °C, while ?-TcCl3 converts to ?-TcCl3 at 280 °C. The technetium dichlorides disproportionate to Tc metal and TcCl4 above ?600 °C. At 450 °C in a sealed Pyrex tube, TcBr3 decomposes to Na{[Tc6Br12]2Br}, while TcI3 decomposes to Tc metal. We have used technetium tribromide in the preparation of new divalent complexes; we expect that the other halides will also serve as starting materials for the synthesis of new compounds (e.g., complexes with a Tc3(9+) core, divalent iodide complexes, binary carbides, nitrides, and phosphides, etc.). Technetium halides may also find applications in the nuclear fuel cycle; their thermal properties could be utilized in separation processes using halide volatility. In summary, we hope that these new insights on technetium binary halides will contribute to a better understanding of the chemistry of this fascinating element. PMID:24393028

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

2014-02-18

190

Kelvin probe studies of cesium telluride photocathode for the AWA photoinjector  

SciTech Connect

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.

Velazquez, D.; Wisniewski, E. E.; Yusof, Z.; Harkay, K.; Spentzouris, L.; Terry, J. [Physics Department at Illinois Institute of Technology, Chicago, IL 60616 and High Energy Physics Division at Argonne National Laboratory, Lemont, IL 60439 (United States); High Energy Physics Division at Argonne National Laboratory, Lemont, IL 60439 (United States); Accelerator Science Division at Argonne National Laboratory, Lemont, IL 60439 (United States); Physics Department at Illinois Institute of Technology, Chicago, IL 60616 (United States)

2012-12-21

191

Compact THz radiation source based on photocathode RF gun  

NASA Astrophysics Data System (ADS)

Terahertz (THz) science and technology have already become the research highlight at present. In this paper, we put forward a proposal to generate THz radiation at tens of MW peak power. As a result of the ultrafast laser and the high accelerating field of photocathode RF gun, we can generate and accelerate an electron beam to several MeV, of which the bunch length is less than sub-ps. When the short electron bunches are injected into the wiggler, THz radiation based on Coherent Synchrotron Radiation could be achieved with tens of MW peak power. The whole THz FEL facility can be scaled to the size of a tabletop.

Liu, ShengGuang; Urakawa, JunJi

2011-12-01

192

A new chemical analysis system using a photocathode RF gun  

NASA Astrophysics Data System (ADS)

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.

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

2000-11-01

193

RECENT PROGRESS ON THE DIAMOND AMPLIFIED PHOTO-CATHODE EXPERIMENT.  

SciTech Connect

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.

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

2007-06-25

194

Polarization and charge limit studies of strained GaAs photocathodes  

SciTech Connect

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.

Saez, P.J.

1997-03-01

195

Influence of air exposure on CsI photocathodes  

NASA Astrophysics Data System (ADS)

We investigate the influence of air exposure on the quantum efficiency (QE) and surface morphology of CsI photocathodes (PCs), at relative humidities (RH) higher than 80% down to nearly 3% (both at room temperature) and a 60 °C baking condition. By atomic force microscopy (AFM) surface analysis, it is clearly seen that RH >60% speeds up water film formation and CsI dissolution on the surface of the photocathode at the minute scale, while both grain size and QE change slowly at RH <30% at the hour scale. In the baking environment, the peak QE decreases less than 1.5% (absolute) within one week, and a stainless steel substrate and electron beam evaporation technique tend to effectively weaken the influence of air. With an Au-coated FR-4 substrate, the QE degradation is found to strongly depend on wavelength in the range of 120-210 nm. According to spectra of X-ray photoelectron spectroscopy (XPS), an excess of cesium was observed and the chemical reaction between water and CsI when exposed to humid air is proved. It is found that carbon, and not H2O or O2, is the main pollutant in the baking condition.

Xie, Yuguang; Zhang, Aiwu; Liu, Yingbiao; Liu, Hongbang; Hu, Tao; Zhou, Li; Cai, Xiao; Fang, Jian; Yu, Boxiang; Ge, Yongshuai; Lü, Qiwen; Sun, Xilei; Sun, Lijun; Xue, Zheng; Xie, Yigang; Zheng, Yangheng; Lü, Junguang

2012-10-01

196

Large charge extraction from metallic multifilamentary Nb3Sn photocathode.  

PubMed

The current density limit for photoemission from metals was measured in an rf photogun to be below 10(9)??A/m2. We have achieved 1.6×10(11)??A/m2 by photofield emission from a new type of photocathode made from a metallic-composite, multifilamentary Nb3Sn wire driven by a 266 nm picosecond laser pulse and a 2 ns, 50 kV accelerating voltage. This cathode has a micrometer arrayed structure with tens of thousands of Nb/Nb3Sn filaments embedded in a bronze matrix. Our measurements revealed the existence of a new electron emission regime at high laser fluence (100??mJ/cm2). We have extracted stably, and without any surface ablation, up to 4800 pC of charge. This corresponds to 0.9% quantum efficiency, 100 times larger than what is measured from conventional metallic photocathodes. The unexpected large and stable charge extraction cannot be explained by the 3-step model. Thanks to the small emitting area, the measured emittance (0.6??mm·mrad) is low in spite of the high current density and space charge effects. This cathode will be of benefit for many applications based on short and bright electron bunches. PMID:23003048

Anghel, A; Ardana-Lamas, F; Le Pimpec, F; Hauri, C P

2012-05-11

197

Large Charge Extraction from Metallic Multifilamentary Nb3Sn Photocathode  

NASA Astrophysics Data System (ADS)

The current density limit for photoemission from metals was measured in an rf photogun to be below 109A/m2. We have achieved 1.6×1011A/m2 by photofield emission from a new type of photocathode made from a metallic-composite, multifilamentary Nb3Sn wire driven by a 266 nm picosecond laser pulse and a 2 ns, 50 kV accelerating voltage. This cathode has a micrometer arrayed structure with tens of thousands of Nb/Nb3Sn filaments embedded in a bronze matrix. Our measurements revealed the existence of a new electron emission regime at high laser fluence (100mJ/cm2). We have extracted stably, and without any surface ablation, up to 4800 pC of charge. This corresponds to 0.9% quantum efficiency, 100 times larger than what is measured from conventional metallic photocathodes. The unexpected large and stable charge extraction cannot be explained by the 3-step model. Thanks to the small emitting area, the measured emittance (0.6mm·mrad) is low in spite of the high current density and space charge effects. This cathode will be of benefit for many applications based on short and bright electron bunches.

Anghel, A.; Ardana-Lamas, F.; Le Pimpec, F.; Hauri, C. P.

2012-05-01

198

Unraveling halide hydration: A high dilution approach  

NASA Astrophysics Data System (ADS)

The hydration properties of halide aqua ions have been investigated combining classical Molecular Dynamics (MD) with Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Three halide-water interaction potentials recently developed [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)], along with three plausible choices for the value of the absolute hydration free energy of the proton (? G^{ominus }_{hyd}[H^+]), have been checked for their capability to properly describe the structural properties of halide aqueous solutions, by comparing the MD structural results with EXAFS experimental data. A very good agreement between theory and experiment has been obtained with one parameter set, namely LE, thus strengthening preliminary evidences for a ? G^{ominus }_{hyd}[H^+] value of -1100 kJ mol-1 [M. M. Reif and P. H. Hünenberger, J. Chem. Phys. 134, 144104 (2011)]. The Cl-, Br-, and I- ions have been found to form an unstructured and disordered first hydration shell in aqueous solution, with a broad distribution of instantaneous coordination numbers. Conversely, the F- ion shows more ordered and defined first solvation shell, with only two statistically relevant coordination geometries (six and sevenfold complexes). Our thorough investigation on the effect of halide ions on the microscopic structure of water highlights that the perturbation induced by the Cl-, Br-, and I- ions does not extend beyond the ion first hydration shell, and the structure of water in the F- second shell is also substantially unaffected by the ion.

Migliorati, Valentina; Sessa, Francesco; Aquilanti, Giuliana; D'Angelo, Paola

2014-07-01

199

Kerr Constants of the Hydrogen Halide Gases  

Microsoft Academic Search

ON the basis of a recent note dealing with the polarization ellipsoids of the hydrogen halide gases1, it becomes possible to calculate their Kerr constants (Na-D line, 20° C, 760 mm.), numbers which should be directly capable of experimental verification.

C. H. Douglas Clark; E. C. Humphries

1936-01-01

200

Opaque gallium nitride photocathodes in UV imaging detectors with microchannel plates  

NASA Astrophysics Data System (ADS)

The optimization and performance of opaque Galium Nitride (GaN) photocathodes deposited directly on novel Microchannel Plates (MCPs) are presented in this paper. The novel borosilicate glass MCPs, which are manufactured with the help of Atomic Layer Deposition, can withstand higher temperatures enabling direct deposition of GaN films on their surfaces. The quantum efficiency of MBE-grown GaN photocathodes of various thickness and buffer layers was studied in the spectral range of ~200-400 nm for the films grown on different surface layers (such as Al2O3 or buffer AlN layer) in order to determine the optimal opaque photocathode configuration. The MCPs with the GaN photocathodes were activated with surface cesiation in order to achieve the negative Electron Affinity for the efficient photon detection. The opaque photocathodes enable substantial broadening of the spectral sensitivity range compared to the semitransparent configuration when the photocathodes are deposited on the input window. The design of currently processed sealed tube event counting detector with an opaque GaN photocathode are also described in this paper. Our experiments demonstrate that although there is still development work required the detection quantum efficiencies exceeding 20% level should be achievable in 200-400 nm range and <50% in 100-200 nm range for the event counting MCP detectors with high spatial resolution (better than 50 ?m) and timing resolution of <100 ps and very low background levels of only few events cm-2 s-1.

Tremsin, Anton S.; Hull, Jeffrey S.; Siegmund, Oswald H. W.; McPhate, Jason B.; Vallerga, John V.; Dabiran, Amir M.; Mane, Anil; Elam, Jeff

2013-09-01

201

Upgrading platform using alkali metals  

DOEpatents

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.

Gordon, John Howard

2014-09-09

202

A novel system for measurement of the transverse electron momentum distribution from photocathodes.  

PubMed

The transverse momentum of electrons produced by a photocathode contributes significantly to the performance of several different types of accelerator-based light sources, such as Free Electron Lasers, as well as systems designed for ultrafast electron diffraction and dynamic transmission electron microscopy. Minimization of the transverse emittance from photocathodes is the subject of intensive research, and therefore measurement of this parameter is of great importance. Here, we describe a simple system that offers real time measurements of transverse emittance and can be easily integrated into the photocathode fabrication process. PMID:25638118

Feng, J; Nasiatka, J; Wan, W; Vecchione, T; Padmore, H A

2015-01-01

203

A novel system for measurement of the transverse electron momentum distribution from photocathodes  

NASA Astrophysics Data System (ADS)

The transverse momentum of electrons produced by a photocathode contributes significantly to the performance of several different types of accelerator-based light sources, such as Free Electron Lasers, as well as systems designed for ultrafast electron diffraction and dynamic transmission electron microscopy. Minimization of the transverse emittance from photocathodes is the subject of intensive research, and therefore measurement of this parameter is of great importance. Here, we describe a simple system that offers real time measurements of transverse emittance and can be easily integrated into the photocathode fabrication process.

Feng, J.; Nasiatka, J.; Wan, W.; Vecchione, T.; Padmore, H. A.

2015-01-01

204

High-power fiber lasers for photocathode electron injectors  

NASA Astrophysics Data System (ADS)

Many new applications for electron accelerators require high-brightness, high-average power beams, and most rely on photocathode-based electron injectors as a source of electrons. To achieve such a photoinjector, one requires both a high-power laser system to produce the high average current beam, and also a system at reduced repetition rate for electron beam diagnostics to verify high beam brightness. Here we report on two fiber laser systems designed to meet these specific needs, at 50 MHz and 1.3 GHz repetition rate, together with pulse pickers, second harmonic generation, spatiotemporal beam shaping, intensity feedback, and laser beam transport. The performance and flexibility of these laser systems have allowed us to demonstrate electron beam with both low emittance and high average current for the Cornell energy recovery linac.

Zhao, Zhi; Bartnik, Adam; Wise, Frank W.; Bazarov, Ivan V.; Dunham, Bruce M.

2014-05-01

205

Atomic hydrogen cleaning of GaAS Photocathodes  

SciTech Connect

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.

M. Poelker; J. Price; C. Sinclair

1997-01-01

206

Silicon based tandem cells: novel photocathodes for hydrogen production.  

PubMed

A photovoltaic tandem cell made of amorphous silicon (a-Si) and microcrystalline silicon (?c-Si) was investigated as a photocathode for hydrogen evolution in a photoelectrochemical device. The electronic and electrochemical properties of the samples were characterized using X-ray photoemission spectroscopy (XPS) and cyclic voltammetry (CV), whereas the morphology of the surface in contact with the electrolyte was investigated by scanning electron microscopy (SEM). The electric efficiency of the tandem cell was determined to be 5.2% in a photoelectrochemical (PEC) setup in acidic solution which is only about half of the photovoltaic efficiency of the tandem cell. A significant improvement in efficiency was achieved with platinum as a catalyst which was deposited by physical vapour deposition (PVD) under ultra-high vacuum (UHV) conditions. PMID:24710175

Calvet, W; Murugasen, E; Klett, J; Kaiser, B; Jaegermann, W; Finger, F; Hoch, S; Blug, M; Busse, J

2014-06-28

207

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

NASA Astrophysics Data System (ADS)

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 1? ^+ ground state and the B 1? ^+ and A 1? 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.

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

2003-12-01

208

The aluminum electrode in AlCl3-alkali-halide melts  

NASA Technical Reports Server (NTRS)

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.

Holleck, G. L.; Giner, J.

1972-01-01

209

Electronic and phonon processes of MnO4 - molecular impurities in alkali halide crystals  

NASA Astrophysics Data System (ADS)

We present the results of a detailed study of the near-infrared photoluminescence and the luminescence excitation spectra of iodide (KI and RbI) and bromide (KBr and RbBr) crystals doped with MnO-4, MnO42- and MnO43- molecular ions. The experimental and the theoretical study of the NIRL integral intensity temperature dependence in a wide temperature interval 4-300 K shows unusual thermoactivation behavior of the intensity for MnO4- doped crystals. The thermo-photo-induced transformation of MnO-4 into MnO42- was observed for both types of crystals doped by the MnO4- ions.

Maksimova, T. I.; Hermanovich, K.; Hanuza, J.; Happek, U.

2005-01-01

210

Surface Structure and Lattice Dynamics of Alkali Halide Crystals Studied by High-Resolution Ion Scattering  

NASA Astrophysics Data System (ADS)

The rumpled surface structure and thermal lattice vibrations of KI(001) and RbI(001) were measured directly by high-resolution medium energy ion scattering (MEIS). The relaxation of interlayer distance between the top and second layer and the rumpling of the top and second layers were determined using the ion shadowing effect with an accuracy of 0.01 Å. From the displaced lattice positions determined above, we derived the dipole moments of the top- and second-layer ions self-consistently employing the polarizabilities estimated from the optical refractive index combined with the Clausius Mossotti relation. The balance between a short-range force and a long-range Coulombic one made it possible to judge the applicability of the short-range pair potentials proposed so far. We also determined the root-mean-square (rms) thermal vibration amplitudes of the bulk and the top-layer ions together with the correlations of the ions in the [001] and [101] strings by taking various kinds of scattering geometries. The results obtained were compared with those calculated from the molecular dynamics (MD) simulations based on a classical model using the dipole moments determined above and the Born Mayer type pair potential. The present MEIS results are in overall agreement with the MD simulations.

Kido, Yoshiaki; Okazawa, Tetsuaki

211

Non-melting and self-wetting of alkali halide surfaces at high temperatures  

NASA Astrophysics Data System (ADS)

We investigated theoretically the high temperature thermodynamic properties and the (lack of) self-wetting of ionic crystal surfaces, with NaCl(100) as a prototype case. We found by classical molecular dynamics simulations that NaCl(100) is a non-melting crystal surface and can be overheated to a spinodal temperature TS 150 K above the bulk melting temperature (T_M). While surface non-melting is in itself well known, and is observed on semiconductors as well as on close packed metal surfaces, the basic mechanism for NaCl appears to be different from either of them. Moreover, there appear to be two distinct metastability regimes of solid NaCl(100) above T_M. The first regime TM < T < T_1, (T1 - TM = 60 K) the metastable solid surface is strongly protected by a nucleation barrier of large thickness. This thickness decreases with temperature, until it drops to a lattice spacing a at T_1. In the second regime T1 < T < TS is characterized by a ``fragile'' metastability, with a nucleation barrier one lattice spacing thick. Here, the smallest seed is able to cause melting, i.e., it is enough to melt the first monolayer for the liquid to break through and melt the whole system. A basic explanation of these facts and of the two regimes is given, based on a short-range oscillatory interaction between the solid-liquid and the liquid-vapor interfaces. In addition, we also simulated a liquid NaCl nanodroplet, deposited on a solid NaCl surface in the vicinity of the bulk melting point. The anomalously large contact angle measured long ago by Mutaftschiev [1] is well reproduced by this realistic molecular dynamics droplet simulation. Based on these results, and on independent determinations of the liquid-vapor (?_LV) and the solid-vapor interface free energy (?_SV) an estimate of the solid-liquid interface free energy (?_SL) is extracted. The solid-vapor surface free energy turns out to be anomalously small and similar to the liquid-vapor one, providing a direct thermodynamic explanation of the reduced wetting ability of the ionic melt. G. Grange and B. Mutaftschiev, Surf. Sci. 47, 723 (1975).

Ceresoli, Davide; Zykova-Timan, Tania; Tartaglino, Ugo; Sekkal, Wassila; Jagla, Edoardo; Tosatti, Erio

2004-03-01

212

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

PubMed

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. PMID:25399174

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

2014-11-14

213

Building foundations for molecular electronics: Growth of organic molecules on alkali halides as prototypical insulating substrates  

NASA Astrophysics Data System (ADS)

The epitaxy and growth of a series of organic molecules deposited on insulating surfaces were investigated by noncontact atomic force microscopy (nc-AFM). The molecules studied, C60, 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylene tetracarboxlylic diimide (PTCDI), and copper (II) phthalocyanine (CuPc), were selected to investigate the effect of different molecular geometries, charge distributions and intermolecular interactions and as interesting candidates in molecular electronic applications. As it is known that the properties of molecules are influenced by their structural arrangements, an understanding of the interactions of molecules with substrates of interest as well as the dominant processes involved in growth are of great interest. Model insulating substrates KBr and NaCl were used for growth studies, due to the necessity of insulators in electrically isolating device regions. Dewetting processes were observed in several of these systems: C 60 on KBr and NaCl, PTCDA on NaCl and PTCDI on NaCl. The specific influences of de- wetting are discussed for each system, in particular the morphological impact of dewetting and the driving of dewetting by strained metastable monolayers. For C60 deposits, interesting branched structures are formed in the process of dewetting which are remarkably stable once formed, yet do not represent the equilibrium growth morphology. A determination of the large cell coincident epitaxy reveals a small, yet significant discrepancy between the observed overlayer and calculated stable adsorption sites indicating a dominance of the intermolecular interaction over the molecule---substrate interaction. For both PTCDA and PTCDI on NaCl, strained metastable monolayer epitaxies were observed giving rise to a transition in both interface structure and morphology: a dewetting transition. A comparison of the observed molecular scale structures and growth modalities is made in order to build a framework for understanding the prevalence of dewetting for molecules on ionic surfaces. Finally, in order to better understand the connection between molecular scale structures and interesting opto-electronic properties, the application of a hybrid-electrostatic characterization technique by nc-AFM is discussed. Using this technique, the opto-electrostatic response of three different PTCDA arrangements on a nanotemplated NaCl surface are shown to differ according to the degree of intermolecular interaction permitted by the structure.

Burke, Sarah A.

214

Building foundations for molecular electronics: Growth of organic molecules on alkali halides as prototypical insulating substrates  

Microsoft Academic Search

The epitaxy and growth of a series of organic molecules deposited on insulating surfaces were investigated by noncontact atomic force microscopy (nc-AFM). The molecules studied, C60, 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylene tetracarboxlylic diimide (PTCDI), and copper (II) phthalocyanine (CuPc), were selected to investigate the effect of different molecular geometries, charge distributions and intermolecular interactions and as interesting candidates in molecular

Sarah A. Burke

2009-01-01

215

Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy.  

PubMed

In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces. We have found that, together with molecular islands of upright standing pentacene, a new phase of tilted molecules appears near step edges on KBr. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density functional theory calculations. Our images reveal that differently oriented molecules display different LCPD and that their value is independent of the number of molecular layers. These results point to the formation of an interface dipole, which may be explained by a partial charge transfer from the pentacene to the surface. Moreover, the monitoring of the evolution of the pentacene islands shows that they are strongly affected by dewetting: Multilayers build up at the expense of monolayers, and in the Kelvin images, previously unknown line defects appear, which reveal the epitaxial growth of pentacene crystals. PMID:24601525

Neff, Julia L; Milde, Peter; León, Carmen Pérez; Kundrat, Matthew D; Eng, Lukas M; Jacob, Christoph R; Hoffmann-Vogel, Regina

2014-04-22

216

Vibrational entropy of polyatomic solids: Metal carbides, metal borides, and alkali halides  

Microsoft Academic Search

It is shown that in the high temperature vibrational entropy of polyatomic solids, the influence of the atomic masses is described by an effective mass \\u000a$$M_e = M_1^{C_1 } M_1^{C_2 } .{\\\\text{ }}.{\\\\text{ }}.{\\\\text{ }}M_j^{C_j } $$\\u000a, where ci is the concentration of mass Mi. This mass effect explains almost all of the differences between TiC, ZrC, and HfC

G. Grimvall; J. Rosén

1983-01-01

217

Temperature Dependence of Auger-Free Luminescence in Alkali and Alkaline-Earth Halides  

NASA Astrophysics Data System (ADS)

Auger-free luminescence (AFL) resulting from a radiative transition between theoutermost-core bands and the valence bands in BaF2, RbF, CsF, CsCl and CsBrhas been studied in a wide range of temperatures from 10 to 300 K. The AFLspectra are separated from those originating from the valence-band excitationwith use of time-resolved luminescence spectroscopy. It is found that the decayprofile of AFL in each crystal is essentially the same throughout the spectrum. The remarkable thermal broadening of the linewidth is verified for all systems. This strongly suggests that the core hole generated on a positive ion inducesconsiderable displacement of the surrounding ions within its lifetime. Based onthe present results, the spectral shape of AFL is discussed in terms of acluster model and a two-band model, requiring further development of theinvestigations in theory and experiment.

Itoh, Minoru; Kamada, Masao; Ohno, Nobuhito

1997-08-01

218

Thermal conductivity of molten alkali halides from equilibrium molecular dynamics simulations.  

PubMed

The thermal conductivity of molten sodium chloride and potassium chloride has been computed through equilibrium molecular dynamics Green-Kubo simulations in the microcanonical ensemble (N,V,E). In order to access the temperature dependence of the thermal conductivity coefficient of these materials, the simulations were performed at five different state points. The form of the microscopic energy flux for ionic systems whose Coulombic interactions are calculated through the Ewald method is discussed in detail and an efficient formula is used by analogy with the methods used to evaluate the stress tensor in Coulombic systems. The results show that the Born-Mayer-Huggins-Tosi-Fumi potential predicts a weak negative temperature dependence for the thermal conductivity of NaCl and KCl. The simulation results are in agreement with part of the experimental data available in the literature with simulation values generally overpredicting the thermal conductivity by 10%-20%. PMID:15267797

Galamba, N; Nieto de Castro, C A; Ely, J F

2004-05-01

219

Long-lived submicrometric bubbles in very diluted alkali halide water solutions.  

PubMed

Solutions of LiCl and of NaCl in ultrapure water were studied through Rayleigh/Brillouin scattering as a function of the concentration (molarity, M) of dissolved salt from 0.2 M to extremely low concentration (2 × 10(-17) M). The Landau-Placzek ratio, R/B, of the Rayleigh scattering intensity over the total Brillouin was measured thanks to the dynamically controlled stability of the used Fabry-Perot interferometer. It was observed that the R/B ratio follows two stages as a function of increasing dilution rate: after a strong decrease between 0.2 M and 2 × 10(-5) M, it increases to reach a maximum between 10(-9) M and 10(-16) M. The first stage corresponds to the decrease of the Rayleigh scattering by the ion concentration fluctuations with the decrease of salt concentration. The second stage, at lower concentrations, is consistent with the increase of the Rayleigh scattering by long-lived sub-microscopic bubbles with the decrease of ion concentration. The origin of these sub-microscopic bubbles is the shaking of the solutions, which was carried out after each centesimal dilution. The very long lifetime of the sub-microscopic bubbles and the effects of aging originate in the electric charge of bubbles. The increase of R/B with the decrease of the low salt concentration corresponds to the increase of the sub-microscopic bubble size with the decrease of concentration, which is imposed by the bubble stability due to the covering of the surface bubble by negative ions. PMID:22337122

Duval, Eugène; Adichtchev, Sergey; Sirotkin, Sergey; Mermet, Alain

2012-03-28

220

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

221

Theory of negative-ion conversion of neutral atoms in grazing scattering from alkali halide surfaces  

NASA Astrophysics Data System (ADS)

The theoretical approach proposed by Borisov et al. [Phys. Rev. Lett. 77, 1893 (1996)] to treat negative-ion conversion of neutral atoms at ionic crystal surfaces is described in detail. Due to the localization of the valence-band electrons at the anionic sites of the crystal, the conversion process is viewed as a result of successive binary collisions between the projectile and the negatively charged sites at the surface. Parameter-free calculations of F- formation in grazing scattering from LiF(100) and KI(100) are performed using a model in which all sites of the crystal lattice but one, the active site, are represented by eventually polarizable point charges. Parallel velocity thresholds for negative-ion formation, relative efficiency of the negative-ion formation for LiF and KI crystals, and dependences of this efficiency on the scattering angle correspond well to the experimental results.

Borisov, A. G.; Sidis, V.

1997-10-01

222

Calculation of energies of radiative tunneling transitions between defects in alkali halides  

NASA Astrophysics Data System (ADS)

The procedure for calculating the energies of radiative tunneling transition between spatially separated electron and hole centres in ionic crystals based on semiempirical INDO calculation of a pair of close defects and on a further account of electronic polarization of a crystal due to defects has been presented. Pairs of an electron, F, and hole ( H, Vk, V2) centres in KCl and LiF crystals are studied. The influence of close defect interaction and of polarization upon emitted photon energy has also been considered. It is shown that due to polarization this energy varies with a distance between defects in a more complicated way than {e 2}/{?R} shown in semiconductors.

Shluger, A.; Kotomin, E.; Kantorovich, L.

1982-06-01

223

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

PubMed Central

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

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

2012-01-01

224

Effect of impurities on the hardness of alkali halide single crystals  

NASA Astrophysics Data System (ADS)

Micro hardness number of KCl, KBr and KCl-Br grown by Czocharlski technique, in the presence of homovalent and aliovalent ions of different ionic radii were measured in the indentation load range from 5 to 80*10-3 N. The measured data showed that there is an indentation size effect and classical Meyer's law was used for the characterization of crystal hardness of these crystals. The Meyer's index was also found to be smaller than 2 indicating brittle material characteristic. The P.R.S. model was used for the determination of the load independent micro hardness value. Result can be explained on the basis of interaction between created dislocation and point defect. It was found that hardness of these crystals is depending on the type of impurity.

Verma, Ashok K.; Ojha, Chaturbhuj; Shrivastava, A. K.

2014-04-01

225

Zeeman Effect of the A Absorption Bands in Tl and Pb-Doped Alkali Halides  

Microsoft Academic Search

Zeeman effects of the A absorption bands in KBr:Tl, KI:Tl, KCl:Pb and KBr:Pb are studied by means of circular dichroism, and g-factors of the excited states relevant to these absorption bands are found to be 0.6˜0.8.

Ryumyo Onaka; Teruhiko Mabuchi; Akira Yoshikawa

1967-01-01

226

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

SciTech Connect

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.

Montgomery, Eric J.; Pan Zhigang; Leung, Jessica; Feldman, Donald W.; O'Shea, Patrick G. [Institute for Research in Electronics and Applied Physics, University of MD, College Park, MD 20742 (United States); Jensen, Kevin L. [Code 6843, ESTD, Naval Research Laboratory, Washington D.C. 20375-5347 (United States)

2009-01-22

227

Lanthanide-halide based humidity indicators  

DOEpatents

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.

Beitz, James V. (Hinsdale, IL); Williams, Clayton W. (Chicago, IL)

2008-01-01

228

Flame inhibition by hydrogen halides - Some spectroscopic measurements  

NASA Technical Reports Server (NTRS)

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.

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

1973-01-01

229

Electron extraction from a CsI photocathode into condensed Xe, Kr, and Ar  

Microsoft Academic Search

We have studied the electron extraction from a CsI photocathode into gaseous (0-55 atm) and liquid Xe, Kr, and Ar. Two experimental setups were used. In the first one the photocathode was irradiated with a UV lamp and the photocurrent was directly measured. In the liquid phase, the QE was 2-3 times higher than that in vacuum for LXe and

E. Aprile; A. Bolotnikov; D. Chen; R. Mukherjee; F. Xu; D. F. Anderson; V. Peskov

1994-01-01

230

Characterization of a superconducting Pb photocathode in a superconducting rf photoinjector cavity  

NASA Astrophysics Data System (ADS)

Photocathodes are a limiting factor for the next generation of ultrahigh brightness photoinjectors. We studied the behavior of a superconducting Pb cathode in the cryogenic environment of a superconducting rf gun cavity to measure the quantum efficiency, its spatial distribution, and the work function. We will also discuss how the cathode surface contaminants modify the performance of the photocathode as well as the gun cavity and we discuss the possibilities to remove these contaminants.

Barday, R.; Burrill, A.; Jankowiak, A.; Kamps, T.; Knobloch, J.; Kugeler, O.; Matveenko, A.; Neumann, A.; Schmeißer, M.; Völker, J.; Kneisel, P.; Nietubyc, R.; Schubert, S.; Smedley, J.; Sekutowicz, J.; Will, I.

2013-12-01

231

Position-Sensitive Detector with GaAs photocathode and high time resolution  

SciTech Connect

The Position-Sensitive Detector (PSD) on base of GaAs photocathode and microchannel plate set has been developed. PSD consists of thick semi-conductor photocathode with quantum efficiency about 48% in the range of 4000-7500 A, two micro-channel plates, and 16-electrode collector. The detector has spatial resolution of 20-40 microns for about 5{center_dot}10{sup 2} pixels, time resolution of 1 {mu}s and effective sensitivity up to 35%.

De-Bur, Vjacheslav; Beskin, Grigory; Karpov, Sergey; Plokhotnichenko, Vladimir [Special Astropysical Observatory, Nizhnij Arkhyz, 369167 (Russian Federation); Terekhov, Alexander; Kosolobov, Sergey; Sheibler, Heinrich [Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation)

2008-02-22

232

Blue-green reflection-mode GaAlAs photocathodes  

NASA Astrophysics Data System (ADS)

In order to obtain the suitable photocathode which could be applicable for the field of ocean exploration, the p-type zinc (Zn)-doped reflection-mode GaAlAs photocathode sample using exponential-doping technique is grown by metal organic chemical vapor deposition, the Al component of GaAlAs emission layer is designed to be 0.63. After the chemical etching, the photocathode samples are heated in vacuum at high-temperature of 650°C and 600°C respectively, the vacuum variation curves during the heat cleaning are measured, which correspond to the desorption of oxides in the surface of GaAlAs emission layer. The (Cs, O) activation for the photocathodes is executed after heat cleaning. Different proportion of Cs and O is performed on the different photocathode samples. The activation photocurrent curves of two samples with different heat cleaning temperature show that the GaAlAs surface treated by higher heat cleaning temperature is more sensitive to the Cs-O adsorption. The photocathode activated with the larger Cs current has a shorter time to reach the first photocurrent peak, and also obtains a bigger final photocurrent peak. According to the measured spectral response curves, it could be found that a suitable heat cleaning temperature and a moderate Cs/O current ratio are very important to prepare high performance GaAlAs photocathode. The prepared reflection-mode GaAlAs photocathodes are response to the blue-green light, and the cut-off wavelength is at about 580 nm.

Chen, Xinlong; Zhao, Jing; Chang, Benkang; Jin, Muchun; Hao, Guanghui; Xu, Yuan

2012-11-01

233

40 CFR 721.10181 - Halide salt of an alkylamine (generic).  

Code of Federal Regulations, 2011 CFR

...2011-07-01 2011-07-01 false Halide salt of an alkylamine (generic). 721...Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a...substance identified generically as halide salt of an alkylamine (PMN...

2011-07-01

234

40 CFR 721.10181 - Halide salt of an alkylamine (generic).  

Code of Federal Regulations, 2012 CFR

...2012-07-01 2012-07-01 false Halide salt of an alkylamine (generic). 721...Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a...substance identified generically as halide salt of an alkylamine (PMN...

2012-07-01

235

40 CFR 721.10181 - Halide salt of an alkylamine (generic).  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Halide salt of an alkylamine (generic). 721...Chemical Substances § 721.10181 Halide salt of an alkylamine (generic). (a...substance identified generically as halide salt of an alkylamine (PMN...

2010-07-01

236

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...

237

76 FR 18127 - Energy Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and Availability of...  

Federal Register 2010, 2011, 2012, 2013, 2014

...1904-AC00 Energy Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and...establishing energy conservation standards for metal halide lamp fixtures (MHLFs); the analytical...appliance_standards/commercial/metal_halide_lamp_fixtures.html....

2011-04-01

238

10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 false Definitions concerning metal halide lamp ballasts and fixtures...COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide lamp ballasts and fixtures....

2010-01-01

239

75 FR 5544 - Energy Conservation Program: Energy Conservation Standards for Metal Halide Lamp Fixtures: Public...  

Federal Register 2010, 2011, 2012, 2013, 2014

...Program: Energy Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and...energy conservation standards for certain metal halide lamp fixtures. This document announces...Document for energy conservation standards for metal halide lamp fixtures and provide...

2010-02-03

240

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

DOEpatents

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.

Joshi, Ashok V. (Salt Lake City, UT); Balagopal, Shekar (Sandy, UT); Pendelton, Justin (Salt Lake City, UT)

2011-12-13

241

Surface science analysis of GaAs photocathodes following sustained electron beam delivery  

NASA Astrophysics Data System (ADS)

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.

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

242

Regioselective Heck reaction of aliphatic olefins and aryl halides.  

PubMed

A regioselective Heck reaction of aliphatic olefins and aryl bromides is realized at internal carbons of olefins. Methanol solvent promoted halide ionization from neutral arylpalladium halide complexes via hydrogen bonding, so as to create cationic aryl-Pd species for regioselective olefin insertion. PMID:24060852

Qin, Liena; Hirao, Hajime; Zhou, Jianrong Steve

2013-11-11

243

Ionization on Platinum and Tungsten Surfaces. II. The Potassium Halides  

Microsoft Academic Search

The ionization of the potassium halides on tungsten follows the Saha-Langmuir equation and indicates the formation of stable partial films of halide. On platinum, however, reflection occurs amounting to more than 99% for KCl, KBr, and KI, and about 75% for KF.

Sheldon Datz; Ellison H. Taylor

1956-01-01

244

Laser driver for a photocathode of an electron linear accelerator  

SciTech Connect

A laser system is designed for operation with a photocathode electron gun for a linear accelerator with the following parameters of radiation at a wavelength of 262 nm (the fourth harmonic of a Nd:YLF laser). The pulse trains (macropulses) with a repetition rate of 5 Hz and a duration of 900 {mu}s consist of 8-ps micropulses with an energy of 1.4 {mu}J and a repetition rate of 2.708 MHz. This repetition rate is variable within {+-}32 kHz and is stabilised by an external signal with an accuracy of 10 Hz. Due to the use of a feedback-controlled acousto-optic modulator, the root-mean-square deviation of the micropulse energy in the first and second harmonics is 2.5% and 3.6%, respectively. Using the decaying branch of the dependence of the second-to-fourth harmonic conversion efficiency on the second harmonic intensity, we decreased the root-mean-square deviation of the energy of the fourth-harmonic micropulses to 2.3% at the first-to-fourth harmonic conversion efficiency of 27%. (lasers and amplifiers)

Potemkin, A K; Gacheva, E I; Zelenogorskii, V V; Katin, E V; Kozhevatov, I E; Lozhkarev, V V; Luchinin, G A; Silin, D E; Khazanov, Efim A [Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation); Trubnikov, D V; Shirkov, G D [Joint Institute for Nuclear Research, Dubna, Moscow region (Russian Federation); Kuriki, M [Hiroshima University, Higashi-Hiroshima, Hiroshima (Japan); Urakava, J [High Energy Accelerator Research Organisation, KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

2011-01-24

245

Beyond injection: Trojan horse underdense photocathode plasma wakefield acceleration  

NASA Astrophysics Data System (ADS)

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.

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

246

Spectroscopic Studies of Diatomic Indium Halides  

NASA Astrophysics Data System (ADS)

A critical review of the available spectroscopic information about diatomic indium halides has been performed. The literature was surveyed till early 2002 and the data on the molecular constants for the ground state, as well as excited states of these molecules has been presented. A brief discussion on the dissociation energies, ionization potentials, and the nature of the bonding in the ground state is given. The energy level diagram and Rydberg-Klein-Rees potential curves for the different electronic states of these molecules are also presented. Mechanism of laser emission/fluorescence due to atomic indium in the ultraviolet photodissociation of indium monohalides has also been discussed.

Mishra, S. K.; Yadav, Raj K. S.; Singh, V. B.; Rai, S. B.

2004-06-01

247

Lifetime test of photoemission from Cs3Sb photocathode coated with W or Cr film  

NASA Astrophysics Data System (ADS)

Cs3Sb photocathodes were fabricated at 8-16 °C with sandwiched layers of Sb, Cs, and Sb deposited onto the fine tips of three cathodes at 15 °C. After examining the influence of the cathode tip temperature on the changes in the quantum efficiencies of the Cs3Sb photocathodes during and after additional Cs depositions, we performed lifetime tests of the three Cs3Sb photocathodes using a 405-nm semiconductor laser and 488-nm Ar ion laser. The decrease in the photocurrent with time was more rapid with the 488-nm laser irradiation than with the 405-nm laser irradiation, and continuous laser irradiation caused a much more rapid decrease in photoelectrons with time than intermittent laser irradiation did. We deposited a 0.32-0.64-nm-thick W film or a 0.43-nm-thick Cr film onto the Cs3Sb photocathode during the lifetime test at 0.9-1.0 × 10-7 Pa. We found that the passive WO3 or Cr2O3 film, which was formed at a reduced vacuum level of 1.6 × 10-7 Pa or during the continuous 405-nm laser irradiation, increased the lifetime of the Cs3Sb photocathode by effectively protecting its surface against oxidation and evaporation of Cs. This protection effect was most effective at approximately 90 °C.

Kimoto, Takayoshi; Arai, Yoshihiro; Ren, Xiaobing

2013-11-01

248

A Hybrid Laser-driven E-beam Injector Using Photo-cathode Electron Gun and superconducting Cavity*  

E-print Network

A Hybrid Laser-driven E-beam Injector Using Photo-cathode Electron Gun and superconducting Cavity, Beijing 100871, China * Work supported by NNSF of China Abstract A laser-driven photo-cathode electron gun constructed and tested. As the next step, a hybrid photo-injector, using a DC laser-driven electron gun

Geng, Rong-Li

249

Photoemission characteristics of (Cs, O) activation exponential-doping Ga0.37Al0.63As photocathodes  

NASA Astrophysics Data System (ADS)

Based on the studies of the GaAs photocathode, the surface model of the Ga0.37Al0.63As photocathode is investigated and the energy distributions of electrons reaching the surface charge region, reaching the surface and emitting into vacuum are calculated. The (Cs, O) adsorption and photoemission characteristics of the Ga0.37Al0.63As photocathode are studied according to the experiments. We use the quantum efficiency formula to fit the experimental curve, and obtain the performance parameters of the photocathode and the surface barrier parameters. The results show that the surface barrier of the Ga0.37Al0.63As photocathode is similar to that of the GaAs photocathode. The prepared reflection-mode Ga0.37Al0.63As photocathode responds to the blue-green light, while the transmission-mode Ga0.37Al0.63As photocathode is sensitive to the 532 nm light.

Chen, Xinlong; Zhao, Jing; Chang, Benkang; Yu, Xiaohua; Hao, Guanghui; Xu, Yuan; Cheng, Hongchang

2013-06-01

250

Cesium Evaporation Rate on Tungsten Photocathodes Ameerah Jabr-Hamdan, Dr. Eric Montgomery, Dr. Patrick O' Shea, Blake Riddick, and Peter Zhigang Pan  

E-print Network

Cesium Evaporation Rate on Tungsten Photocathodes Ameerah Jabr-Hamdan, Dr. Eric Montgomery, Dr into a vacuum chamber. Experimentally found the evaporation rate of Cesium on a Tungsten Photocathode Photocathode) More accurate model of Cesium evaporation. The Free Electron Laser and Needed Improvements

Anlage, Steven

251

High quantum efficiency photocathode simulation for the investigation of novel structured designs  

SciTech Connect

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 ?m 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.

Opachich, Y. P., E-mail: opachiyp@nv.doe.gov; Ross, P. W.; Huffman, E.; Koch, J. A. [National Security Technologies LLC, Livermore, California 94550 (United States); MacPhee, A. G.; Nagel, S. R.; Bell, P. M.; Bradley, D. K.; Landen, O. L. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Hilsabeck, T. J. [General Atomics, San Diego, California 92121 (United States)

2014-11-15

252

High quantum efficiency photocathode simulation for the investigation of novel structured designs.  

PubMed

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 ?m 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. PMID:25430201

Opachich, Y P; Ross, P W; MacPhee, A G; Hilsabeck, T J; Nagel, S R; Huffman, E; Bell, P M; Bradley, D K; Koch, J A; Landen, O L

2014-11-01

253

Comparative research on indium seal process for transmission-mode GaAs photocathodes  

NASA Astrophysics Data System (ADS)

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.

Chen, Liang; Zhang, Shuqin; Jin, Shangzhong; Xu, Sunan; Jiao, Gangcheng

2013-01-01

254

Quantum efficiency of technical metal photocathodes under laser irradiation of various wavelengths  

NASA Astrophysics Data System (ADS)

Quantum efficiency studies for various laser wavelengths and various technical metal surfaces were carried out in a dedicated unbaked vacuum chamber in the absence of a significant electrical field. Copper, magnesium, aluminum, and aluminum-lithium photocathodes were irradiated by two different high power, high repetition rate, laser systems. We have observed an emission of electrons for photon energies below the work function of the material. This is explained by multiple photon absorption by the photocathode. We have not observed any degradation of the QE for these materials, but an improvement when irradiating them over a long period of time. This is contrary to observations made in RF photoguns.

Le Pimpec, F.; Milne, C. J.; Hauri, C. P.; Ardana-Lamas, F.

2013-09-01

255

Compact narrow-band THz radiation source based on photocathode rf gun  

NASA Astrophysics Data System (ADS)

Narrow-band THz coherent Cherenkov radiation can be driven by a subpicosecond electron bunch traveling along the axis of a hollow cylindrical dielectric-lined waveguide. We present a scheme of compact THz radiation source based on the photocathode rf gun. On the basis of our analytic result, the subpicosecond electron bunch with high charge (800 pC) can be generated directly in the photocathode rf gun. According to the analytical and simulated results, a narrow emission spectrum peaked at 0.24 THz with 2 megawatt (MW) peak power is expected to gain in the proposed scheme (the length of the facility is about 1.2 m).

Li, Wei-Wei; He, Zhi-Gang; Jia, Qi-Ka

2014-04-01

256

Regenerable activated bauxite adsorbent alkali monitor probe  

DOEpatents

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.

Lee, S.H.D.

1992-12-22

257

Regenerable activated bauxite adsorbent alkali monitor probe  

DOEpatents

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.

Lee, Sheldon H. D. (Willowbrook, IL)

1992-01-01

258

Passive particle dosimetry. [silver halide crystal growth  

NASA Technical Reports Server (NTRS)

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.

Childs, C. B.

1977-01-01

259

Cross-coupling reactions of unactivated alkyl halides  

E-print Network

My graduate research at MIT has been focused on the development of palladium- or nickel-catalyzed cross-coupling reactions using unactivated alkyl electrophiles (e.g., halides and sulfonates). Although aryl and alkenyl ...

Zhou, Jianrong (Jianrong Steve)

2005-01-01

260

Palladium-catalyzed carboxylative coupling of allylstannanes and allyl halides  

SciTech Connect

A three-component carboxylative coupling between allyl halides, allylstannanes, and CO{sub 2} to produce allyl esters is catalyzed by Pd and Pt phosphine complexes. Tentative mechanistic pathways for the catalytic reaction are proposed.

Franks, R.J.; Nicholas, K.M.

2000-04-17

261

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2014 CFR

...Substituted naphthalenesulfonic acid, alkali salt. 721.5278 Section 721.5278 ...Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical substance and significant...substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to...

2014-07-01

262

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Code of Federal Regulations, 2011 CFR

...Substituted naphthalenesulfonic acid, alkali salt. 721.5278 Section 721.5278 ...Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical substance and significant...substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is subject to...

2011-07-01

263

40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.  

Code of Federal Regulations, 2010 CFR

...Substituted halogenated pyridinol, alkali salt. 721.8900 Section 721.8900 ...Substituted halogenated pyridinol, alkali salt. (a) Chemical substances and significant...substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and...

2010-07-01

264

40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.  

Code of Federal Regulations, 2013 CFR

...Substituted halogenated pyridinol, alkali salt. 721.8900 Section 721.8900 ...Substituted halogenated pyridinol, alkali salt. (a) Chemical substances and significant...substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and...

2013-07-01

265

Purification and Characterization of an Extracellular, Thermo-Alkali-Stable, Metal Tolerant Laccase from Bacillus tequilensis SN4  

PubMed Central

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 ?-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

Sondhi, Sonica; Sharma, Prince; Saini, Shilpa; Puri, Neena; Gupta, Naveen

2014-01-01

266

Quantum efficiency study of the sensitive to blue-green light transmission-mode GaAlAs photocathode  

NASA Astrophysics Data System (ADS)

The quantum efficiency of the blue-green transmission-mode GaAlAs photocathode has been studied. Two transmission-mode GaAlAs photocathodes with different structures are prepared, and the quantum efficiency curves are measured. We use the quantum efficiency formula to fit the experimental curves, and obtain the performance parameters of photocathodes such as the electron diffusion length, the back interface recombination velocity, and the surface electron escape probability. The effects of the Al compositions, the thickness of emission layer, and the electron diffusion length on quantum efficiency are investigated. The results show that both of transmission-mode GaAlAs photocathodes are sensitive to the blue-green light. The peak quantum efficiency of one photocathode appears at about 565 nm, while that of another photocathode appears at about 535 nm. The Al composition of emission layer plays a major role on the peak position of quantum efficiency of transmission-mode GaAlAs photocathode. Besides, the thickness of emission layer and the Al composition of window layer also have a large influence on the quantum efficiency.

Chen, Xinlong; Jin, Muchun; Xu, Yuan; Chang, Benkang; Shi, Feng; Cheng, Hongchang

2015-01-01

267

Variable doping narrow-band response GaAlAs photocathode the preparation method of the research  

NASA Astrophysics Data System (ADS)

In order to avoid the low sensitivity common problem of 532nm sensitive narrow-band response photocathode, variable doping narrow-band response GaAlAs photocathode structure is designed. The photocathode is composed of GaAs substrates, Ga1-x1Alx1As buffer layer, Ga1-x2Alx2As doping concentration gradient emissive layer and GaAs protection layer from bottom to top. Among them, exponential doping method is applied to Ga1-x2Alx2As unit layer from the bottom to the top. And a preparation methods of GaAlAs photocathode is developed. For the GaAlAs photocathode components which grow well, chemical cleaning, heating purification and (Cs, O) activation are operated, and ultimately Cs / O activation layer is formed on the surface of Ga1-x2Alx2As doping concentration gradient emissive layer. The highest sensitivity of the photocathode peak response is at 532nm, and the photocathode quantum efficiency in 532nm peaks at 36%.

Xu, Yuan; Chen, XinLong; Zhao, Jing; Wang, Honggang; Chang, BenKang

2012-11-01

268

The degradation of quantum efficiency in negative electron affinity GaAs photocathodes under gas exposure  

NASA Astrophysics Data System (ADS)

The influence of O2, CO2, CO, N2, H2 and CH4 on the stability of the quantum efficiency (QE) of a negative electron affinity gallium arsenide (GaAs) photocathode activated with caesium (Cs) and oxygen (O) has been demonstrated for the first time under an extremely high vacuum condition, a base pressure of 1.5 × 10-11 mbar, where the influence of the background gas is minimized. It was found that exposure of a GaAs photocathode to N2, H2 and CH4 does not affect the QE, whereas exposure to O2, CO2 and CO leads to a substantial reduction in photocathode QE. It was also found that the QE of photocathodes which have been degraded under O2 exposure can be recovered to 95% of their initial QE level by the re-caesiation process, while those which have been degraded under exposure to CO and CO2 can only be partly restored to 60-70% of their initial QE levels.

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

2014-02-01

269

Studies in Laser Photo-cathode RF Guns A Dissertation Presented  

E-print Network

Studies in Laser Photo-cathode RF Guns A Dissertation Presented by Xiangyun Chang to The Graduate-cathode RF Guns by Xiangyun Chang Doctor of Philosophy in Physics Stony Brook University 2005 The emittance compensation mechanics of a "non-magnetized" (the magnetic field on cathode is zero) beam in a compact RF gun

270

OPTIMAL PARAMETERS OF THE PHOTOCATHODE GUN SPACE CHARGE TO IMPROVE BEAM QUALITY  

E-print Network

at Brookhaven national Laboratory will be described. INTRODUCTION On present BNL ATF operates copper cathode 1.5 cell photocathode RF gun. Laser cleaning used to enhance cathode surface properties improving Quantum Efficiency (QE) of electron emission. In the past cathode cleaning was enhanced by certain level of RF power

Brookhaven National Laboratory

271

Diamond Amplified Photocathode Ilan Ben-Zvi, Andrew Burrill, Xiangyun Chang, Peter D.  

E-print Network

Diamond Amplified Photocathode R&D Plans Ilan Ben-Zvi, Andrew Burrill, Xiangyun Chang, Peter D;The basic idea Photon in Primary electrons Secondary electrons CsK2Sb Diamond #12;Motivation · Capable& assembly · Low thermal emittance · Prompt emission #12;Schematic Arrangement of the System #12;· Diamond

272

Highlights on photocathodes based on thin films prepared by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

We review the current status of metallic photocathodes based on thin films prepared by pulsed laser deposition (PLD) and we explore ways to improve the performance of these devices. PLD seems to be a very efficient and suitable technique for producing adherent and uniform thin films. Time-resolved mass spectrometric investigations definitively suggest that the deposition of high-purity metallic thin films should be carried out in ultrahigh vacuum systems and after a deep and careful laser cleaning of the target surface. Moreover, the laser cleaning of the target surface is highly recommended not only to remove the first contaminated layers but also to improve the quality of the vacuum by reducing the partial pressure of reactive chemical species as H2O, H2, and O2 molecules. The challenge to realize high-purity Mg and Y thin films is very interesting for the photocathode R&D due to the good photoemission properties of these metals. Photocathodes based on Mg and Y thin films have been characterized by scanning electron microscopy and x-ray diffraction techniques to derive the morphological and structural features, respectively. They were also tested in a photodiode cell to deduce the photoelectron properties. The quantum efficiency of such photocathodes was systematically improved by in situ laser cleaning treatments of the surface in order to remove the contaminated layers reaching, in this way, the quantum efficiency of the corresponding bulk materials.

Lorusso, A.; Gontad, F.; Perrone, A.; Stankova, N.

2011-09-01

273

Halide and proton binding kinetics of yellow fluorescent protein variants.  

PubMed

A T203Y substitution in green fluorescent protein causes a red shift in emission to yield a class of mutants known as yellow fluorescent protein (YFP). Many of these YFP mutants bind halides with affinities in the millimolar range, which often results in the chromophore pK values being shifted into the physiological range. While such sensitivities may be exploited for halide and pH sensors, it is desirable to reduce such environmental sensitivities in other studies, such as in Förster resonance energy transfer probes to measure conformational changes within fusion proteins. Venus and Citrine are two such variants that have been developed with much reduced halide sensitivities. Here we compare the kinetics of halide binding, and the coupled protonation reaction, for several YFP variants and detect slow kinetics (dissociation rate constants in the range of 0.1-1 s(-1)), indicative of binding to an internal site, in all cases. The effective halide affinity for Venus and Citrine is much reduced compared with that of the original YFP 10C construct, primarily through a reduced association rate constant. Nuclear magnetic resonance studies of YFP 10C confirm halide binding occurs on a slow time scale (<4 s(-1)) and that perturbations in the chemical shift occur throughout the sequence and structure. PMID:23514090

Seward, Harriet E; Basran, Jaswir; Denton, Roanne; Pfuhl, Mark; Muskett, Frederick W; Bagshaw, Clive R

2013-04-01

274

Arsenic volatilization of GaAs photocathode at low temperature during thermal cleaning  

NASA Astrophysics Data System (ADS)

The gallium arsenide (GaAs) photocathode was generally cleaned by radiant heating, direct heating, ion bombardment annealing, and so on. In this paper, the radiant heating method, namely thermal cleaning method, was adopted for GaAs photocathode surface purification. Using this method could obtain an atomic clean surface, ensure the integrity of the GaAs surface lattice, and guarantee the uniformity of surface cleaning effect at the same time. But because the accurate measurement of the GaAs photocathode surface temperature in the vacuum system was very difficult, the residual gas analyzer (RGA) was used in this experiment to monitor the residual gas composition in ultrahigh vacuum during the thermal cleaning process and determine the thermal cleaning temperature by the partial pressure curves of As and Ga. It was found that the first peaks of As and Ga elements both appeared after heating about one hour, accompanied with H2O, N2/CO, CO2 and other common gas. According to partial pressure curves of H2O, N2/CO, CO2 and the heating time, it could be judged that the temperature at that time was not high, which should be under 150°C.After thermal cleaning experiment of three GaAs photocathodes, it was found that the peak value of As partial pressure at low temperature was generally within 10-11mbar~10-10mbar, and the peak value was at 10-10mbar at high temperature. Sometimes it was appeared that the peak value of As partial pressure at low temperature was even higher than the peak value at high temperature. The As volatilization phenomenon occurred at low temperature indicated that the elemental As exist on the GaAs photocathode surface or near surface after the chemical etching process, and the As could volatilize from GaAs photocathode at low temperature in the beginning of thermal cleaning. This research has guiding significance for further understanding the thermal cleaning mechanism of GaAs photocathode and improving the thermal cleaning technology.

Liu, Hui; Shi, Feng; Miao, Zhuang; Gao, Xiang; Cheng, Hong-chang; Niu, Sen; Wang, Long; Chen, Chang

2014-09-01

275

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

SciTech Connect

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.

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

1983-11-01

276

Mixed valency and anionogenic magnetism in alkali metal oxides.  

E-print Network

??Magnetische eigenschappen alkali metaaloxides In zijn proefschrift beschrijft Shirakumara Giriyapura een onderzoek naar de magnetische eigenschappen van alkali metaaloxides. Het magnetisme in deze materialen is… (more)

Giriyapura Parameshwarappa, Shivakumara

2012-01-01

277

Developments in Alkali-Metal Atomic Magnetometry  

E-print Network

Developments in Alkali-Metal Atomic Magnetometry Scott Jeffrey Seltzer A DISSERTATION PRESENTED by Scott Jeffrey Seltzer. All rights reserved. #12;Abstract Alkali-metal magnetometers use the coherent find use in a variety of areas ranging from medicine and NMR to explosives detec- tion and fundamental

Romalis, Mike

278

Density functional studies on hydrogen-bonded clusters of hydrogen halides and the interaction on halide anions  

NASA Astrophysics Data System (ADS)

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.

Nirmala, V.; Kolandaivel, P.

279

10 CFR 431.324 - Uniform test method for the measurement of energy efficiency of metal halide ballasts.  

Code of Federal Regulations, 2010 CFR

...the measurement of energy efficiency of metal halide ballasts. 431.324 Section...CERTAIN COMMERCIAL AND INDUSTRIAL EQUIPMENT Metal Halide Lamp Ballasts and Fixtures Test...the measurement of energy efficiency of metal halide ballasts. (a) Scope....

2010-01-01

280

Water in the hydration shell of halide ions has significantly reduced Fermi resonance and moderately enhanced Raman cross section in the OH stretch regions.  

PubMed

Water in the presence of electrolytes plays an important role in biological and industrial processes. The properties of water, such as the intermolecular coupling, Fermi resonance (FR), hydrogen-bonding, and Raman cross section were investigated by measuring the Raman spectra in the OD and OH stretch regions in presence of alkali halides (NaX; X = F, Cl, Br, I). It is observed that the changes in spectral characteristics by the addition of NaX in D2O are similar to those obtained by the addition of H2O in D2O. The spectral width decreases significantly by the addition of NaX in D2O (H2O) than that in the isotopically diluted water. Quantitative estimation, on the basis of integrated Raman intensity, revealed that the relative Raman cross section, ?(H)/?(b) (?(H) and ?(b) are the average Raman cross section of water in the first hydration shell of X(-) and in bulk, respectively), in D2O and H2O is higher than those in the respective isotopically diluted water. These results suggest that water in the hydration shell has reduced FR and intermolecular coupling compared to those in bulk. In the isotopically diluted water, the relative Raman cross section increases with increase in size of the halide ions (?(H)/?(b) = 0.6, 1.1, 1.5, and 1.9 for F(-), Cl(-), Br(-), and I(-), respectively), which is assignable to the enhancement of Raman cross section by charge transfer from halide ions to the hydrating water. Nevertheless, the experimentally determined ?(H)/?(b) is lower than the calculated values obtained on the basis of the energy of the charge transfer state of water. The weak enhancement of ?(H)/?(b) signifies that the charge transfer transition in the hydration shell of halide ions causes little change in the OD (OH) bond lengths of hydrating water. PMID:23895453

Ahmed, Mohammed; Singh, Ajay K; Mondal, Jahur A; Sarkar, Sisir K

2013-08-22

281

Comparison of boron halide, decaborane and B implants in Si from Molecular Dynamics simulations  

E-print Network

Comparison of boron halide, decaborane and B implants in Si from Molecular Dynamics simulations R are becoming too low. The investigation here is to look at the alternative heavier halides and decaborane

Webb, Roger P.

282

Hemibonding of hydroxyl radical and halide anion in aqueous solution.  

PubMed

Molecular geometries and properties of the possible reaction products between the hydroxyl radical and the halide anions in aqueous solution were investigated. The formation of two-center three-electron bonding (hemibonding) between the hydroxyl radical and halide anions (Cl, Br, I) was examined by density functional theory (DFT) calculation with a range-separated hybrid (RSH) exchange-correlation functional. The long-range corrected hybrid functional (LC-?PBE), which have given quantitatively satisfactory results for odd electron systems and excited states, was examined by test calculations for dihalogen radical anions (X(2)(-); X = Cl, Br, I) and hydroxyl radical-water clusters. Equilibrium geometries with hemibonding between the hydroxyl radical and halide anions were located by including four hydrogen-bonded water molecules. Excitation energies and oscillator strengths of ?-?* transitions calculated by the time-dependent DFT method showed good agreement with observed values. Calculated values of the free energy of reaction on the formation of hydroxyl halide radical anion from the hydroxyl radical and halide anion were endothermic for chloride but exothermic for bromide and iodide, which is consistent with experimental values of equilibrium constants. PMID:22136588

Yamaguchi, Makoto

2011-12-29

283

Analysis of Alkali Surface Ionization on Porous Substrates  

Microsoft Academic Search

The evaporation of alkali atoms and ions from porous substrates is analyzed, making the basic assumption that the transport of alkali material occurs only by surface flow of densely packed alkali atoms close to the emitter surface. The alkali efflux velocity to the emitter surface depends on the flow rate per pore and the minimum pore radius within the surface-flow

Otto K. Husmann

1968-01-01

284

Alkali Silicate Vehicle Forms Durable, Fireproof Paint  

NASA Technical Reports Server (NTRS)

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.

Schutt, John B.; Seindenberg, Benjamin

1964-01-01

285

Nanosized alkali-metal-doped ethoxotitanate clusters.  

PubMed

The synthesis and crystallographic characterization of alkali-metal-doped ethoxotitanate clusters with 28 and 29 Ti atoms as well as a new dopant-free Ti28 cluster are presented. The light-metal-doped polyoxotitanate clusters in which the alkali-metal atom is the critical structure-determining component are the largest synthesized so far. Calculations show that doping with light alkali atoms narrows the band gap compared with the nondoped crystals but does not introduce additional energy levels within the band gap. PMID:23587091

Chen, Yang; Trzop, Elzbieta; Makal, Anna; Sokolow, Jesse D; Coppens, Philip

2013-05-01

286

Diode pumped alkali vapor fiber laser  

DOEpatents

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.

Payne, Stephen A. (Castro Valley, CA); Beach, Raymond J. (Livermore, CA); Dawson, Jay W. (Livermore, CA); Krupke, William F. (Pleasanton, CA)

2007-10-23

287

Diode pumped alkali vapor fiber laser  

DOEpatents

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.

Payne, Stephen A. (Castro Valley, CA); Beach, Raymond J. (Livermore, CA); Dawson, Jay W. (Livermore, CA); Krupke, William F. (Pleasanton, CA)

2006-07-26

288

Analysis of the physical atomic forces between noble gas atoms, alkali ions and halogen ions  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

289

Simulation study of sub-femtosecond electron bunch generation using photocathode RF gun linac  

NASA Astrophysics Data System (ADS)

Pulse radiolysis, a stroboscopic method involving the use of an ultrashort electron bunch and ultrashort light, is essential for the observation of ultrafast reactions. The time resolution of pulse radiolysis depends on the electron bunch length. At Osaka University, a 98-fs electron bunch was generated using a photocathode RF gun linac for the development of femtosecond pulse radiolysis. In order to improve the time resolution of pulse radiolysis, the feasibility of sub-femtosecond electron bunch generation using a photocathode RF gun linac and a magnetic bunch compressor was studied in a simulation. Increase in bunch length due to higher-order effects and bunch charge was investigated using the simulation codes PARMELA and ELEGANT.

Kan, K.; Yang, J.; Kondoh, T.; Norizawa, K.; Ogata, A.; Kozawa, T.; Yoshida, Y.

2010-10-01

290

Operating techniques for high-temperature mercury halide lasers  

NASA Astrophysics Data System (ADS)

A comparative analysis of the existing static gas fill techniques and the proposed flowing gas techniques for producing three-component mixtures of a rare gas, nitrogen, and mercury halide vapor within a heated mercury halide laser discharge tube is presented. The technique developed involves passing flow-mixed nitrogen and rare gas through an evaporator consisting of a Pyrex tube with tightly packed glass wool impregnated with finely divided mercury halide powder. The technique allows higher accuracy of the gas-vapor mixture introduction into the discharge tube to be achieved and provides high-temperature gas purging, thereby eliminating the need for high-vacuum processing. Finally, the system is noted to be capable of rapid flow direction reversal and recirculation of the buffer gas.

Baker, H. J.; Seddon, N.

1985-04-01

291

Intrinsic Electron Beam Emittance from Metal Photocathodes: The Effect of the Electron Effective Mass  

NASA Astrophysics Data System (ADS)

A theoretical development of prior analyses, together with our solenoid scan measurements on eight planar metal photocathodes (Ag, Be, Cr, Cu, Mo, Sn, Ta, and W) and previous data on Mg [X. J. Wang, M. Babzien, R. Malone, and Z. Wu, in Proceedings of LINAC2002, Gyeongju, Korea, 2002 (Pohang Accelerator Laboratory, Pohang, Korea, 2002), pp. 142-144.] indicate that the transverse momentum (and hence intrinsic emittance) of an electron beam is fundamentally dependent on the electron effective mass in the metal.

Rickman, B. L.; Berger, Joel A.; Nicholls, A. W.; Schroeder, W. Andreas

2013-12-01

292

A 100MW, electron-beam-pumped, argon fluoride laser for driving metal photo-cathodes  

Microsoft Academic Search

Summary form only given, as follows. A reliable and repeatable electron beam pumped ArF laser system to drive bare aluminum metal photo-cathodes is described. The system consists of a seven stage Marx generator charged to 65 kV\\/stage that in-turn pulse charges a 150-ns-long, 5.5-ohmm water PFL to voltages as high as 750 kV. The PFL utilizes a low-jitter, self-breaking SF6

R. L. Carlson; J. R. Quicksilver; R. N. Ridlon; T. P. Hughes

2001-01-01

293

Alkali Metal Handling Practices at NASA MSFC  

NASA Technical Reports Server (NTRS)

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.

Salvail, Patrick G.; Carter, Robert R.

2002-01-01

294

Alkali Metal Handling Practices at NASA MSFC  

NASA Astrophysics Data System (ADS)

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.

Salvail, Patrick G.; Carter, Robert R.

2003-01-01

295

Alkali metal propellants for MPD thrusters  

NASA Technical Reports Server (NTRS)

Experiments performed in the United States in the 1960s and early 1970s and in the Soviet Union with alkali metal-fuelled MPD thrusters indicate performance levels substantially better than those achieved with gaseous propellants. Cathode wear appears to be less in engines with alkali metal propellants also. A critical review of the available data indicates that the data are consistent and reliable. An analysis of testing and systems-level considerations shows that pumping requirements for testing are substantially decreased and reductions in tankage fraction can be expected. In addition, while care must be exercised in handling the alkali metals, it is not prohibitively difficult or hazardous. The greatest disadvantage seems to be the potential for spacecraft contamination, but there appear to be viable strategies for minimizing the impact of propellant deposition on spacecraft surfaces. Renewed examination of alkali metal-fuelled MPD thrusters for ambitious SEI missions is recommended.

Polk, J. E.; Pivirotto, T. J.

1991-01-01

296

Milk Alkali and Hydrochlorothiazide: A Case Report  

PubMed Central

Hypercalcemia is a relatively common clinical problem in both outpatient and inpatient settings. Primary pathophysiology is the entry of calcium that exceeds its excretion into urine or deposition in bone into circulation. Among a wide array of causes of hypercalcemia, hyperparathyroidism and malignancy are the most common, accounting for greater than 90 percent of cases. Concordantly, there has been a resurgence of milk-alkali syndrome associated with the ingestion of large amounts of calcium and absorbable alkali, making it the third leading cause of hypercalcemia (Beall and Scofield, 1995 and Picolos et al., 2005). This paper centers on a case of over-the-counter calcium and alkali ingestion for acid reflux leading to milk alkali with concordant use of thiazide diuretic for hypertension. PMID:21738535

Parvez, Babar; Emuwa, Chinenye; Faulkner, Marquetta L.; Murray, John J.

2011-01-01

297

Cs-Te photocathode RF electron gun for applied research at the Waseda University  

NASA Astrophysics Data System (ADS)

A compact electron accelerator based on photo-cathode RF electron gun is under development for applied research at the Waseda University. Higher charge and higher energy are key issues for applications such as pulse radiolysis experiment and laser-Compton X-ray generation. The new RF-gun cavity with cesium telluride (Cs-Te) photo-cathode which has higher quantum efficiency (Q.E.) compared with metal cathodes has been installed. The evaluation of Q.E. of the photo-cathode has been performed and the value obtained is more than 5% at the preparation stage. For understanding the Cs-Te cathode properties and the higher Q.E. operation, fundamental studies by single bunch beam operation have been performed resulting in more than 6 nC bunch charge with a high Q.E. of 2.9%. Additionally, the new RF-gun cavity was improved for obtaining a higher Q value. Higher beam energy, i.e. shunt impedance compared with old type cavity, was observed. The shunt impedance increased by about 20%. These successful results will considerably contribute to the applied research.

Sakaue, Kazuyuki; Hayano, Hitoshi; Kashiwagi, Shigeru; Kuroda, Ryunosuke; Masuda, Akihiko; Suzuki, Tatsuya; Takatomi, Toshikazu; Terunuma, Nobuhiro; Urakawa, Junji; Washio, Masakazu

2011-12-01

298

Dilute phosphide nitride materials as photocathodes for electrochemical solar energy conversion  

NASA Astrophysics Data System (ADS)

Dilute nitride materials have been used in a variety of III-V photonic devices, but have not been significantly explored in photoelectrochemical applications. This work focuses on using dilute phosphide nitride materials of the form (Al,In)P1-xNx as photocathodes for the generation of hydrogen fuel from solar energy. Heteroepitaxial MOCVD growth of AlPN thin films on GaP yields high quality material with a direct bandgap energy of 2.218 eV. Aligned epitaxial growth of InP and GaP nanowires on InP and Si substrates, respectively, provides a template for designing nanostructured photocathodes over a large area. Electrochemical testing of a AlPN/GaP heterostructure electrode yields up to a sixfold increase in photocurrent enhancement under blue light illumination as compared to a GaP electrode. Additionally, the AlPN/GaP electrodes exhibit no degradation in performance after galvanostatic biasing over time. These results show that (Al,In)P1-xNx is a promising materials system for use in nanoscale photocathode structures.

Parameshwaran, Vijay; Xu, Xiaoqing; Kang, Yangsen; Harris, James; Wong, H.-S. Philip; Clemens, Bruce

2013-03-01

299

Nonlinear response of the photocathode of an x-ray streak camera to UV light  

SciTech Connect

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.

Kyrala, G.A.; Oro, D.M.; Studebaker, J.K.; Wood, W.M.; Schappert, G.T.; Watts, S.; Fulton, R.D.

1994-09-01

300

Modeling the resupply, diffusion, and evaporation of cesium on the surface of controlled porosity dispenser photocathodes  

NASA Astrophysics Data System (ADS)

A controlled porosity dispenser (CPD) photocathode is currently being explored and developed to replace the Cs during operation and increase photocathode lifetime. Experimental results from cesium (Cs) emission of a sintered-wire tungsten CPD are presented and are used to inform a theoretical model of Cs resupply, diffusion, and evaporation on the surface of the photocathode. The evaporation of Cs from a tungsten surface is modeled using an effective one-dimensional potential well representation of the binding energy. The model accounts for both local and global interactions of Cs with the surface metal as well as with other Cs atoms. It is found that for typical activation temperatures within the range of 500 K-750 K, differences of less than 5% between the quantum efficiency (QE) maximum and minimum over ideal homogenous surfaces occur, even when variations to mimic surface non-uniformity due to pore blockage are included. The theoretical evaporation rates of sub-monolayer surface coverage of Cs compare well to the data of Taylor and Langmuir [I. Langmuir and J. B. Taylor, Phys. Rev. 40, 463-464 (1932)] and reproduce the nonlinear behavior of evaporation with varying coverage and temperature.

Pan, Zhigang; Jensen, Kevin L.; Montgomery, Eric J.

2013-09-01

301

GaAs photocathode cleaning by atomic hydrogen from a plasma source  

NASA Astrophysics Data System (ADS)

A clean GaAs surface is required in order to fabricate negative-electron-affinity photocathodes. Surface preparation is routinely performed by chemical cleaning and heating in ultra-high vacuum. These processes could damage the surface and produce photocathodes with low quantum efficiencies. Here an alternative technique which overcomes these problems, namely chemical cleaning and heating in ultra-high vacuum, is used. A helical resonator discharge produces hydrogen plasma which is used in a down-flow configuration to clean the GaAs(100) surface of a bulk crystal and strained layer GaAs prior to activation to negative electron affinity. Atomic hydrogen reacts with the oxides and hydrocarbons on the surface, forming volatile compounds. The photocathodes are prepared by depositing caesium onto the clean semiconductor surface. The photoemission current increases with surface cleaning. The reflection high-energy electron-diffraction pattern after atomic hydrogen cleaning reveals a clean 2×4 reconstructed GaAs(100) surface compared with a halo before cleaning.

Elamrawi, K. A.; Elsayed-Ali, H. E.

1999-02-01

302

Metal on metal oxide nanowire Co-catalyzed Si photocathode for solar water splitting.  

PubMed

We report a systematic study of Si|ZnO and Si|ZnO| metal photocathodes for effective photoelectrochemical cells and hydrogen generation. Both ZnO nanocrystalline thin films and vertical nanowire arrays were studied. Si|ZnO electrodes showed increased cathodic photocurrents due to improved charge separation by the formation of a p/n junction, and Si|ZnO:Al (n(+)-ZnO) and Si|ZnO(N(2)) (thin films prepared in N(2)/Ar gas) lead to a further increase in cathodic photocurrents. Si|ZnONW (nanowire array) photocathodes dramatically increased the photocurrents and thus photoelectrochemical conversion efficiency due to the enhanced light absorption and enlarged surface area. The ZnO film thickness and ZnO nanowire length were important to the enhancements. A thin metal coating on ZnO showed increased photocurrent due to a catalyzed hydrogen evolution reaction and Ni metal showed comparable catalytic activities to those of Pt and Pd. Moreover, photoelectrochemical instability of Si|ZnO electrodes was minimized by metal co-catalysts. Our results indicate that the metal and ZnO on p-type Si serve as co-catalysts for photoelectrochemical water splitting, which can provide a possible low-cost and scalable method to fabricate high efficiency photocathodes for practical applications in clean solar energy harvesting. PMID:22539234

Sun, Ke; Madsen, Kristian; Andersen, Pål; Bao, Weining; Sun, Zhelin; Wang, Deli

2012-05-17

303

Heat load of a GaAs photocathode in an SRF electron gun  

NASA Astrophysics Data System (ADS)

A great deal of effort has been made over the last decades to develop a better polarized electron source for high energy physics. Several laboratories operate DC guns with a gallium arsenide photocathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved by using a superconducting radio frequency (SRF) electron gun, which delivers beams of a higher brightness than that from DC guns because the field gradient at the cathode is higher. SRF guns with metal and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since a bulk gallium arsenide (GaAs) photocathode is normal conducting, a problem arises from the heat load stemming from the cathode. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and verification by measuring the quality factor of the gun with and without the cathode at 2 K. We simulate heat generation and flow from the GaAs cathode using the ANSYS program. By following the findings with the heat load model, we designed and fabricated a new cathode holder (plug) to decrease the heat load from GaAs.

Wang, Er-Dong; Jörg, Kewisch; Ilan, Ben-Zvi; Andrew, Burrill; Trivini, Rao; Wu, Qiong; Animesh, Jain; Ramesh, Gupta; Doug, Holmes; Zhao, Kui

2011-04-01

304

Thallous halide materials for use in cryogenic applications  

NASA Technical Reports Server (NTRS)

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.

Lawless, William N. (Inventor)

1981-01-01

305

Thermodynamic reactivity, growth and characterization of mercurous halide crystals  

NASA Technical Reports Server (NTRS)

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.

Singh, N. B.; Gottlieb, M.; Henningsen, T.; Hopkins, R. H.; Mazelsky, R.; Singh, M.; Glicksman, M. E.; Paradies, C.

1992-01-01

306

Desulfurizing Coal With an Alkali Treatment  

NASA Technical Reports Server (NTRS)

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.

Ravindram, M.; Kalvinskas, J. J.

1987-01-01

307

Alkali metal intercalates of molybdenum disulfide.  

NASA Technical Reports Server (NTRS)

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.

Somoano, R. B.; Hadek, V.; Rembaum, A.

1973-01-01

308

Halide Effects in the Synthesis of Mixed Uranium(IV) Aryloxide-Halide Compounds.  

PubMed

Several uranium(IV) aryloxide and mixed aryloxide-halide compounds of the formula UX(4)(-)(z)()(OAr)(z)() (X = Cl, Br, I; OAr = 2,6-di-tert-butylphenoxide; z = 2, 3, 4) have been prepared by the reaction of KOAr with the appropriate uranium tetrahalide in tetrahydrofuran (THF). The complex UI(4)(CH(3)CN)(4) reacts with 2 equiv of KOAr in THF to yield the compound I(2)U(OAr)(2) (1). The utility of this reaction is limited by the instability of UI(4)(CH(3)CN)(4) in THF, however, and isolated yields of the THF adduct of 1 do not exceed 50%. In contrast, UBr(4)(CH(3)CN)(4) is stable in THF solution and reacts with 2 equiv of KOAr to yield the dibromide, Br(2)U(OAr)(2)(THF) (4.THF), in 77% yield. Under identical reaction conditions, UCl(4) reacts to yield the complex [K(THF)(4)][UCl(3)(OAr)(2)] (5) in 68% yield. The uranium center in compound 5 is coordinated by two trans aryloxide ligands and three chloride ligands in a trigonal bipyramidal arrangement. Two chloride ligands of each unit are also coordinated to a potassium ion, forming an infinite chain in the lattice. Compounds 1 and 5 will further react with 1 equiv of KOAr to yield the compounds XU(OAr)(3) (2, X = I; 6, X = Cl). Both UI(4)(CH(3)CN)(4) and UCl(4) will react with a 4.2 equiv of KOAr to yield the previously characterized compound U(OAr)(4) (3). The stability of the mixed aryloxide-halide uranium complexes toward ligand redistribution reactions has been investigated. PMID:11670521

McKee, Steven D.; Burns, Carol J.; Avens, Larry R.

1998-08-10

309

Absorption spectra of alkali-C?? nanoclusters.  

PubMed

We investigate the absorption spectra of alkali-doped C60 nanoclusters, namely C60Nan, C60Kn, and C60Lin, with n = 1, 2, 6, 12, in the framework of the time-dependent density-functional theory (TDDFT). We study the dependence of the absorption spectra on the nature of the alkali. We show that in few cases the absorption spectra depend on the arrangement of the alkali atoms over the fullerene, though sometimes the absorption spectra do not allow us to distinguish between different configurations. When only one or two alkali atoms are adsorbed on the fullerene, the optical response of alkali-doped C60 is similar to that of the anion C60(-) with a strong response in the UV domain. In contrast, for higher concentration of alkali, a strong optical response is predicted in the visible range, particularly when metal-metal bonds are formed. The weak optical response of the I(h)-symmetry C60Li12 is proposed to be used as a signature of its structure. PMID:25223347

Rabilloud, Franck

2014-10-28

310

Methyl halide emissions from savanna fires in southern Africa  

NASA Astrophysics Data System (ADS)

The methyl halides, methyl chloride (CH3Cl), methyl bromide (CH3Br), and methyl iodide (CH3I), were measured in regional air samples and smoke from savanna fires in southern Africa during the Southern Africa Fire-Atmosphere Research Initiative-92 (SAFARI-92) experiment (August-October 1992). All three species were significantly enhanced in the smoke plumes relative to the regional background. Good correlations were found between the methyl halides and carbon monoxide, suggesting that emission was predominantly associated with the smoldering phase of the fires. About 90% of the halogen content of the fuel burned was released to the atmosphere, mostly as halide species, but a significant fraction (3-38%) was emitted in methylated form. On the basis of comparison with the composition of the regional background atmosphere, emission ratios to carbon dioxide and carbon monoxide were determined for the methyl halide species. The emission ratios decreased in the sequence CH3Cl > CH3Br > CH3I. Extrapolation of these results in combination with data from other types of biomass burning, e.g. forest fires, suggests that vegetation fires make a significant contribution to the atmospheric budget of CH3Cl and CH3Br. For tropospheric CH3I, on the other hand, fires appear to be a minor source. Our results suggest that pyrogenic emissions of CH3Cl and CH3Br need to be considered as significant contributors to stratospheric ozone destruction.

Andreae, M. O.; Atlas, E.; Harris, G. W.; Helas, G.; de Kock, A.; Koppmann, R.; Maenhaut, W.; Manø, S.; Pollock, W. H.; Rudolph, J.; Scharffe, D.; Schebeske, G.; Welling, M.

1996-10-01

311

Formation of autocomplexes in halide melts of trivalent metals  

NASA Astrophysics Data System (ADS)

Chemical equilibrium with respect to the dissociation of charged autocomplexes (MX6)3- in ionic melts of the MX3 type is analyzed. The chemical equilibrium M3+ + 6X- = (MX6)3- in salt melts of trivalent metal halides shifts strongly toward dissociation, due to the electrostatic interactions between charged particles in the melts.

Peshkina, K. G.; Tkachev, N. K.

2014-09-01

312

Chemical form effects on the surface ionization of lithium halides  

Microsoft Academic Search

The surface ionization of lithium halides, i.e. fluoride, chloride, bromide and iodide, was studied using a mass spectrometer. In the measurements of ionization using rhenium filaments, it was found that the ionization efficiencies depend on the chemical forms of the samples. To analyze the mechanism of ionization, direct ionization by dissociative ionization is introduced in the present work. The ionization

Tatsuya Suzuki; Hideki Iwabuchi; Kazuko Takahashi; Masao Nomura; Makoto Okamoto; Yasuhiko Fujii

1995-01-01

313

Bright Light-Emitting Diodes based on Organometal Halide Perovskite  

E-print Network

1 Bright Light-Emitting Diodes based on Organometal Halide Perovskite Zhi-Kuang Tan1, Reza Saberi Moghaddam1, May Ling Lai1, Pablo Docampo2, Ruben Higler1, Felix Deschler1, Michael Price1, Aditya Sadhanala1, Luis M. Pazos1, Dan Credgington1...

Tan, Zhi-Kuang; Moghaddam, Reza Saberi; Lai, May Ling; Docampo, Pablo; Higler, Ruben; Deschler, Felix; Price, Michael; Sadhanala, Aditya; Pazos, Luis M.; Credgington, Dan; Hanusch, Fabian; Bein, Thomas; Snaith, Henry J.; Friend, Richard H.

2014-08-03

314

Metal halide lamps in the international space station ISS  

Microsoft Academic Search

Optical emission spectroscopy was performed on a metal-halide lamp under micro-gravity conditions of the international space station. Several transitions of atomic and ionic Dy and atomic Hg have been measured at different lateral positions from which we obtained atomic and ionic Dy and atomic Hg intensity profiles. After Abel inversion, the calibrated radial intensity profile of Hg was used to

T. Nimalasuriya; A. J. Flikweert; M. Haverlag; P. C. M. Kemps; G. M. W. Kroesen; W. W. Stoffels; J. J. A. M. van der Mullen

2006-01-01

315

Cooled Transmission-Mode NEA-Photocathode with a Band-Graded Active Layer for High Brightness Electron Source  

SciTech Connect

A Free-Electron Laser (FEL) places many exacting demands on a Negative Electron Affinity (NEA) photocathode, such as the need for an ultra-fast response time, low energy spread for emitted electrons, high quantum efficiency (Q.E.) and a high average photocurrent. However, these key requirements are conflicting, and cannot be fulfilled by conventional photocathode design. For example, to achieve {approx}10 ps response time, the photocathode active layer should be thinned to {approx}100-150 nm, but this thickness is insufficient to provide near-complete absorption of light with hv{approx_equal}{epsilon}{sub g} so high Q.E. cannot be achieved. Complete optical absorption and high Q.E. can be obtained using a thin active layer at higher photon energies, but this generates photoelectrons with excess kinetic energy within the semiconductor. These photoelectrons do not thermalise in a thin active layer, so yield a broad energy distribution in the emitted electrons. Moreover, cooling of the conventional semiconductor photocathode structure is ineffective due to its fragility, so it cannot be pressed firmly to a heat sink to attain good thermal contact. Consequently, the maximum CW photocurrent is limited to a few miiliamps. The goal of our work is to develop a new design of NEA-photocathode which is optimised for FEL applications.

Jones, L. B.; Militsyn, B. L.; Smith, S. L. [STFC Daresbury Laboratory, Warrington, WA4 4AD (United Kingdom); Rozhkov, S. A. [Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); Bakin, V. V.; Kosolobov, S. N.; Scheibler, H. E. [Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation); Terekhov, A. S. [Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); Institute of Semiconductor Physics, Novosibirsk, 630090 (Russian Federation)

2009-08-04

316

ture peculiar to each compound. The advantage of alkali halide salts in this respect is that they are readily available  

E-print Network

of Chromatograms: Sub-Nanogram Detection of Aflatoxins Sir: The presence of carcinogenic mold metabolites, par- ticularly aflatoxins, in food and feed products has become increasingly recognized as a serious health only nanogram levels of, for example, aflatoxin B1 although as little as 0.1-0.2 ng has been reported

Zare, Richard N.

317

Intensity distributions of reflected surface channeling protons scattered on surfaces of electron-bombarded alkali halide crystals  

NASA Astrophysics Data System (ADS)

We have examined the surface-channeling of 550 keV protons on electron-bombarded KBr(0 0 1) surfaces at grazing incidence. On the surface, electron-stimulated desorption (ESD) resulting from the irradiation of 5 keV electrons changes the surface morphology. In order to investigate the change of the surface morphology, the luminous intensity distributions observed on a fluorescent screen (scattering patterns) of the reflected protons under the surface-channeling conditions are measured. Normalized specular intensity of the protons oscillates, and the results of computer simulations show that the period of the intensity oscillation agrees with the period of layer-by-layer desorption. The measured period of the oscillation is comparable to the simulated one, i.e., the period of the desorption, however, the measured amplitude of the oscillation is weak. This shows that the layer-by-layer desorption of the experimental surface is observed but is not as remarkable as that of the perfect surface introduced in the simulation.

Fukazawa, Y.; Kihara, K.; Iwamoto, K.; Susuki, Y.

2013-11-01

318

Erratum: The Structure of Alkali Halide Dimers: A Critical Test of Ionic Models and New Ab Initio Results  

Microsoft Academic Search

It has come to our attention that some of the ab initio results presented are incorrect due to errors in the Cs and C1 basis sets, and a small error in the binding energy of Rb2F2. The corrected results are presented below for the species that were affected, modifying the results in Table III of the original paper. Only those

Robert J. Cave

2006-01-01

319

Observation of interatomic radiative transition of valence electrons to outermost-core-hole states in alkali halides  

NASA Astrophysics Data System (ADS)

Excitation spectra of visible luminescence in CsF (2.5-5.6 eV), CsCl (3.9-6.0 eV), CsBr (4.4-6.2 eV), and RbF (2.6-6.2 eV) have been measured at room temperature with use of synchrotron radiation for the energy range up to 40 eV. It is shown that the excitation thresholds of these luminescence bands are located at the transition energies from the outermost-core band to the conduction band. This fact provides direct evidence for the radiative decay of valence electrons into outermost-core holes in which the Auger decay process is energetically impossible in these materials.

Kubota, Shinzou; Itoh, Minoru; Ruan(Gen), Jian-Zhi; Sakuragi, Shiro; Hashimoto, Satoshi

1988-05-01

320

The structure of alkali halide dimers: A critical test of ionic models and new ab initio results  

NASA Astrophysics Data System (ADS)

In semiempirical ionic models a number of adjustable parameters have to be fitted to experimental data of either monomer molecules or crystals. This leads to strong correlations between these constants and prevents a unique test and a clear physical interpretation of the fit parameters. Moreover, it is not clear whether these constants remain unchanged when the model is applied to dimers or larger clusters. It is shown that these correlations can be substantially reduced when reliable information about dimers is available from experiments or ab initio calculations. Starting with Dunham coefficients of the monomer potential determined from microwave measurements, we have calculated the monomer to dimer bond expansion and the bond angle without any additional adjustable parameter. Assuming that the overlap repulsion between nearest neighbors remains unchanged, the bond expansion is mainly determined by the simple Coulomb repulsion between equally charged ions and depends only very little on the effective ion polarizabilities. Deviation of the bond angle from 90° sensitively tests the difference of effective polarizabilities of the two ions. A comparison with previously available data and new ab initio MP2 results presented here for the heavy-atom containing dimers shows that bond angles can be modeled reasonably well with Seitz-Ruffa corrected Pauling polarizabilities while calculated bond expansions are much too long. This shows that changes of the overlap repulsion term must be considered for reliable predictions of the structure of dimers and larger clusters.

Törring, T.; Biermann, S.; Hoeft, J.; Mawhorter, R.; Cave, R. J.; Szemenyei, C.

1996-05-01

321

Evaluation of the amperex 56 TVP photomultiplier. [characteristics: photoelectron time spread, anode pulse amplitude and photocathode sensing area  

NASA Technical Reports Server (NTRS)

Characteristics were measured for the Amperex 56 TVP 42 mm-diameter photomultiplier. Some typical photomultiplier characteristics-such as gain, dark current, transit and rise times-are compared with data provided. Photomultiplier characteristics generally not available such as the single photoelectron time spread, the relative collection efficiency, the relative anode pulse amplitude as a function of the voltage between the photocathode and focusing electrode, and the position of the photocathode sensing area were measured and are discussed for two 56 TVP's. The single photoelectron time spread, the relative collection efficiency, and the transit time difference as a function of the voltage between photocathode and focusing electrode were also measured and are discussed, particularly with respect to the optimization of photomultiplier operating conditions for timing applications.

Lo, C. C.; Leskovar, B.

1976-01-01

322

A H2-evolving photocathode based on direct sensitization of MoS3 with an organic photovoltaic cell.  

PubMed

An organic solar cell based on a poly-3-hexylthiophene (P3HT): phenyl-C61-butyric acid (PCBM) bulk hetero-junction was directly coupled with molybdenum sulfide resulting in the design of a new type of photocathode for the production of hydrogen. Both the light-harvesting system and the catalyst were deposited by low-cost solution-processed methods, i.e. spin coating and spray coating respectively. Spray-coated MoS3 films are catalytically active in strongly acidic aqueous solutions with the best efficiencies for thicknesses of 40 to 90 nm. The photocathodes display photocurrents higher than reference samples, without catalyst or without coupling with a solar cell. Analysis by gas chromatography confirms the light-induced hydrogen evolution. The addition of titanium dioxide in the MoS3 film enhances electron transport and collection within thick films and therefore the performance of the photocathode. PMID:24404434

Bourgeteau, Tiphaine; Tondelier, Denis; Geffroy, Bernard; Brisse, Romain; Laberty-Robert, Christel; Campidelli, Stéphane; de Bettignies, Rémi; Artero, Vincent; Palacin, Serge; Jousselme, Bruno

2013-01-01

323

High time resolution beam-based measurement of the rf-to-laser jitter in a photocathode rf gun  

NASA Astrophysics Data System (ADS)

Characterizing the rf-to-laser jitter in the photocathode rf gun and its possible origins is important for improving the synchronization and beam quality of the linac based on the photocathode rf gun. A new method based on the rf compression effect in the photocathode rf gun is proposed to measure the rf-to-laser jitter in the gun. By taking advantage of the correlation between the rf compression and the laser injection phase, the error caused by the jitter of the accelerating field in the gun is minimized and thus 10fs time resolution is expected. Experimental demonstration at the Tsinghua Thomson scattering x-ray source with a time resolution better than 35 fs is reported in this paper. The experimental results are successfully used to obtain information on the possible cause of the jitter and the accompanying drifts.

Zhang, Zhen; Du, Yingchao; Yan, Lixin; Du, Qiang; Hua, Jianfei; Shi, Jiaru; Yang, Jin; Wang, Dan; Huang, Wenhui; Chen, Huaibi; Tang, Chuanxiang

2014-03-01

324

A H2-evolving photocathode based on direct sensitization of MoS3 with an organic photovoltaic cell  

PubMed Central

An organic solar cell based on a poly-3-hexylthiophene (P3HT): phenyl-C61-butyric acid (PCBM) bulk hetero-junction was directly coupled with molybdenum sulfide resulting in the design of a new type of photocathode for the production of hydrogen. Both the light-harvesting system and the catalyst were deposited by low-cost solution-processed methods, i.e. spin coating and spray coating respectively. Spray-coated MoS3 films are catalytically active in strongly acidic aqueous solutions with the best efficiencies for thicknesses of 40 to 90 nm. The photocathodes display photocurrents higher than reference samples, without catalyst or without coupling with a solar cell. Analysis by gas chromatography confirms the light-induced hydrogen evolution. The addition of titanium dioxide in the MoS3 film enhances electron transport and collection within thick films and therefore the performance of the photocathode. PMID:24404434

Bourgeteau, Tiphaine; Tondelier, Denis; Geffroy, Bernard; Brisse, Romain; Laberty-Robert, Christel; Campidelli, Stéphane; de Bettignies, Rémi; Artero, Vincent; Palacin, Serge; Jousselme, Bruno

2013-01-01

325

ChemTeacher: Alkali Metals - Group 1 (IA)  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Alkali Metals page includes resources for teaching students about the discovery, properties, and uses of the alkali metals.

2011-01-01

326

Matrix isolation infrared spectra of hydrogen halide and halogen complexes with nitrosyl halides  

NASA Technical Reports Server (NTRS)

Matrix isolation infrared spectra of nitrosyl halide (XNO) complexes with HX and X2 (X = Cl, Br) are presented. The relative frequency shifts of the HX mode are modest (ClNO H-Cl, delta-nu/nu = -0.045; BrNO H-Br, delta-nu/nu = -0.026), indicating weak hydrogen bonds 1-3 kcal/mol. These shifts are accompanied by significant shifts to higher frequencies in the XN-O stretching mode (CIN-O HCl, delta-nu/nu = +0.016; BrN-O HBr, delta-nu/nu = +0.011). Similar shifts were observed for the XN-O X2 complexes (ClN-O Cl2, delta-nu/nu = +0.009; BrN-O-Br2, delta-nu/nu = +0.013). In all four complexes, the X-NO stretching mode relative shift is opposite in sign and about 1.6 times that of the NO stretching mode. These four complexes are considered to be similar in structure and charge distribution. The XN-O frequency shift suggests that complex formation is accompanied by charge withdrawal from the NO bond ranging from about .04 to .07 electron charges. The HX and X2 molecules act as electron acceptors, drawing electrons out of the antibonding orbital of NO and strengthening the XN-O bond. The implications of the pattern of vibrational shifts concerning the structure of the complexes are discussed.

Allamandola, Louis J.; Lucas, Donald; Pimentel, George C.

1982-01-01

327

Spectroscopic effects of disorder and vibrational localization in mixed-halide metal-halide chain solids  

SciTech Connect

Resonance Raman techniques, together with lattice-dynamics and Peierls-Hubbard modelling, are used to explore the electronic and vibrational dynamics of the quasi-one-dimensional metal-halogen chain solids [Pt(en){sub 2}][R(en){sub 2}X{sub 2}](ClO{sub 4}){sub 4}, (en = C{sub 2}H{sub 8}N{sub 2} and X=Cl, Br), abbreviated ``PLX.`` The mixed-halide materials PtCl{sub 1-x}Br{sub x} and PtCl{sub 1-x}I{sub x} consist of long mixed chains with heterojunctions between segments of the two constituent materials. Thus, in addition to providing mesoscale modulation of the chain electronic states, they serve as prototypes for elucidating the properties to be expected for macroscopic heterojunctions of these highly nonlinear materials. Once a detailed understanding of the various local vibrational modes occurring in these disordered solids is developed, the electronic structure of the chain segments and junctions can be probed by tuning the Raman excitation through their various electronic resonances.

Love, S.P.; Scott, B.; Worl, L.A.; Huckett, S.C.; Saxena, A.; Huang, X.Z.; Bishop, A.R.; Swanson, B.I.

1993-02-01

328

Quantum Efficiency and Topography of Heated and Plasma-Cleaned Copper Photocathode Surfaces  

SciTech Connect

We present measurements of photoemission quantum efficiency (QE) for copper photocathodes heated and cleaned by low energy argon and hydrogen ion plasma. The QE and surface roughness parameters were measured before and after processing and surface chemical composition was tracked in-situ with x-ray photoelectron spectroscopy (XPS). Thermal annealing at 230 C was sufficient to improve the QE by 3-4 orders of magnitude, depending on the initial QE. Exposure to residual gas slowly reduced the QE but it was easily restored by argon ion cleaning for a few minutes. XPS showed that the annealing or ion bombardment removed surface water and hydrocarbons.

Palmer, Dennis T.; /Titan PSD; Kirby, R.E.; King, F.K.; /SLAC

2005-08-04

329

Generation and measurement of sub-picosecond electron bunch in photocathode rf gun  

NASA Astrophysics Data System (ADS)

We consider a scheme to generate a sub-picosecond electron bunch in the photocathode rf gun by improving the acceleration gradient in the gun, suitably tuning the bunch charge, the laser spot size and the acceleration phase, and reducing the growth of transverse emittance by laser shaping. A nondestructive technique is also reported to measure the electron bunch length, by measuring the high-frequency spectrum of wakefield radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric.

Li, Wei-Wei; He, Zhi-Gang; Jia, Qi-Ka

2013-12-01

330

Slice emittance measurement for photocathode RF gun with solenoid scanning and RF deflecting cavity  

NASA Astrophysics Data System (ADS)

The radiation of high-gain short-wavelength free-electron laser depends on the slice transverse emittance of the electron bunch. This essay introduces the method of slice emittance measurement, and shows the brief setup of this experiment using the solenoid scanning and RF deflecting cavity at Tsinghua University. The preliminary experimental results show that the slice rms emittance of the electron bunch generated by photocathode RF gun has considerable variations along the bunch and is typically less than 0.55 mm mrad for the laser rms radius of 0.4 mm.

Li, Chen; Huang, WenHui; Du, YingChao; Yan, LiXin; Tang, ChuanXiang

2011-12-01

331

Intrinsic electron beam emittance from metal photocathodes: the effect of the electron effective mass.  

PubMed

A theoretical development of prior analyses, together with our solenoid scan measurements on eight planar metal photocathodes (Ag, Be, Cr, Cu, Mo, Sn, Ta, and W) and previous data on Mg [X.?J. Wang, M. Babzien, R. Malone, and Z. Wu, in Proceedings of LINAC2002, Gyeongju, Korea, 2002 (Pohang Accelerator Laboratory, Pohang, Korea, 2002), pp. 142-144.] indicate that the transverse momentum (and hence intrinsic emittance) of an electron beam is fundamentally dependent on the electron effective mass in the metal. PMID:24476300

Rickman, B L; Berger, Joel A; Nicholls, A W; Schroeder, W Andreas

2013-12-01

332

A novel scaling law relating the geometrical dimensions of a photocathode radio frequency gun to its radio frequency properties.  

PubMed

Developing a photocathode RF gun with the desired RF properties of the ?-mode, such as field balance (e(b)) ~1, resonant frequency f(?) = 2856 MHz, and waveguide-to-cavity coupling coefficient ?(?) ~1, requires precise tuning of the resonant frequencies of the independent full- and half-cells (f(f) and f(h)), and of the waveguide-to-full-cell coupling coefficient (?(f)). While contemporary electromagnetic codes and precision machining capability have made it possible to design and tune independent cells of a photocathode RF gun for desired RF properties, thereby eliminating the need for tuning, access to such computational resources and quality of machining is not very widespread. Therefore, many such structures require tuning after machining by employing conventional tuning techniques that are iterative in nature. Any procedure that improves understanding of the tuning process and consequently reduces the number of iterations and the associated risks in tuning a photocathode gun would, therefore, be useful. In this paper, we discuss a method devised by us to tune a photocathode RF gun for desired RF properties under operating conditions. We develop and employ a simple scaling law that accounts for inter-dependence between frequency of independent cells and waveguide-to-cavity coupling coefficient, and the effect of brazing clearance for joining of the two cells. The method has been employed to successfully develop multiple 1.6 cell BNL?SLAC/UCLA type S-band photocathode RF guns with the desired RF properties, without the need to tune them by a tiresome cut-and-measure process. Our analysis also provides a physical insight into how the geometrical dimensions affect the RF properties of the photo-cathode RF gun. PMID:22225212

Lal, Shankar; Pant, K K; Krishnagopal, S

2011-12-01

333

Alkali-aggregate reaction in concrete containing high-alkali cement and granite aggregate  

SciTech Connect

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.

Owsiak, Z

2004-01-01

334

Membrane Cells in Chlor Alkali Application  

E-print Network

MEMBRANE CELLS IN COLOR ALKALI APPLICATION Dr. K. Lesker, UHDE GmbH ABSTRACT The worldwide chlorine/caustic soda production has reached approximately 40 million tpy. Despite the stagnation of the chlorine demand in thc wcstcrn world, e... lias t:spl:cially proVt:1I ils vt:rsalilily in oruer lo tultill all reqUirements tor the conversion of an existing chlor alkali plant. The worldwide chlorine/causlic soda production has reached approximately 40 milhon tpv. The United States...

Lesker, K.

335

Alkali metal vapors - Laser spectroscopy and applications  

NASA Technical Reports Server (NTRS)

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.

Stwalley, W. C.; Koch, M. E.

1980-01-01

336

Raman spectra of ionic liquids: A simulation study of LaCl3 and its mixtures with alkali chlorides  

NASA Astrophysics Data System (ADS)

Theoretical Raman spectra of the elpasolite-structured crystal Cs2NaLaCl6 and of molten mixtures of LaCl6 with NaCl and CsCl have been obtained from computer simulations in order to examine how the Raman spectra reflect the coordination structure around the La3+ ions. This system is a model for many other trivalent metal halides and for examining how the network structure of the pure melts is broken down by the addition of alkali halides with different structure-breaking powers. The results suggest a way of reconciling the conclusions of Raman studies about the structures of the melts with those of neutron and x-ray-diffraction studies, which have already been examined with the same simulation methods. The Raman spectra, both polarized and depolarized, are calculated from a model for the dependence of the polarizability of the system on the ionic coordinates which was inspired by electronic structure calculations of the polarizabilities of ions in a condensed phase environment. Some results on the lifetimes of the coordination complexes responsible for the appearance of the discrete Raman bands are discussed.

Glover, William J.; Madden, Paul A.

2004-10-01

337

Band filling with free charge carriers in organometal halide perovskites  

NASA Astrophysics Data System (ADS)

The unique and promising properties of semiconducting organometal halide perovskites have brought these materials to the forefront of solar energy research. Here, we present new insights into the excited-state properties of CH3NH3PbI3 thin films through femtosecond transient absorption spectroscopy measurements. The photoinduced bleach recovery at 760?nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via recombination of free electrons and holes. Additionally, charge accumulation in the perovskite films leads to an increase in the intrinsic bandgap that follows the Burstein-Moss band filling model. Both the recombination mechanism and the band-edge shift are studied as a function of the photogenerated carrier density and serve to elucidate the behaviour of charge carriers in hybrid perovskites. These results offer insights into the intrinsic photophysics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications.

Manser, Joseph S.; Kamat, Prashant V.

2014-09-01

338

Investigating the proteome reactivity and selectivity of aryl halides.  

PubMed

Protein-reactive electrophiles are critical to chemical proteomic applications including activity-based protein profiling, site-selective protein modification, and covalent inhibitor development. Here, we explore the protein reactivity of a panel of aryl halides that function through a nucleophilic aromatic substitution (S(N)Ar) mechanism. We show that the reactivity of these electrophiles can be finely tuned by varying the substituents on the aryl ring. We identify p-chloro- and fluoronitrobenzenes and dichlorotriazines as covalent protein modifiers at low micromolar concentrations. Interestingly, investigating the site of labeling of these electrophiles within complex proteomes identified p-chloronitrobenzene as highly cysteine selective, whereas the dichlorotriazine favored reactivity with lysines. These studies illustrate the diverse reactivity and amino-acid selectivity of aryl halides and enable the future application of this class of electrophiles in chemical proteomics. PMID:24548313

Shannon, D Alexander; Banerjee, Ranjan; Webster, Elizabeth R; Bak, Daniel W; Wang, Chu; Weerapana, Eranthie

2014-03-01

339

Large methyl halide emissions from south Texas salt marshes  

NASA Astrophysics Data System (ADS)

Coastal salt marshes are natural sources of methyl chloride (CH3Cl) and methyl bromide (CH3Br) to the atmosphere, but measured emission rates vary widely by geography. Here we report large methyl halide fluxes from subtropical salt marshes of south Texas. Sites with the halophytic plant, Batis maritima, emitted methyl halides at rates that are orders of magnitude greater than sites containing other vascular plants or macroalgae. B. maritima emissions were generally highest at midday; however, diurnal variability was more pronounced for CH3Br than CH3Cl, and surprisingly high nighttime CH3Cl fluxes were observed in July. Seasonal and intra-site variability were large, even taking into account biomass differences. Overall, these subtropical salt marsh sites show much higher emission rates than temperate salt marshes at similar times of the year, supporting the contention that low-latitude salt marshes are significant sources of CH3Cl and CH3Br.

Rhew, R. C.; Whelan, M. E.; Min, D.-H.

2014-11-01

340

Large methyl halide emissions from south Texas salt marshes  

NASA Astrophysics Data System (ADS)

Coastal salt marshes are natural sources of methyl chloride (CH3Cl) and methyl bromide (CH3Br) to the atmosphere, but measured emission rates vary widely by geography. Here we report large methyl halide fluxes from subtropical salt marshes of south Texas. Sites with the halophytic plant, Batis maritima, emitted methyl halides at rates that are orders of magnitude greater than sites containing other vascular plants or macroalgae. B. maritima emissions were generally highest at midday; however, diurnal variability was more pronounced for CH3Br than CH3Cl, and surprisingly high nighttime CH3Cl fluxes were observed in July. Seasonal and intra-site variability were large, even taking into account biomass differences. Overall, these subtropical salt marsh sites show much higher emission rates than temperate salt marshes at similar times of the year, supporting the contention that low-latitude salt marshes are significant sources of CH3Cl and CH3Br.

Rhew, R. C.; Whelan, M. E.; Min, D.-H.

2014-06-01

341

Chemical form effects on the surface ionization of lithium halides  

NASA Astrophysics Data System (ADS)

The surface ionization of lithium halides, i.e. fluoride, chloride, bromide and iodide, was studied using a mass spectrometer. In the measurements of ionization using rhenium filaments, it was found that the ionization efficiencies depend on the chemical forms of the samples. To analyze the mechanism of ionization, direct ionization by dissociative ionization is introduced in the present work. The ionization parameter [var epsilon] has been experimentally shown to be [var epsilon] = [phi]DI-W, where [phi]DI is the dissociative ionization energy, and W is the work function. In conclusion, a Saha-Langmuir-type equation is applicable to the surface ionization of lithium halides using the dissociative ionization energy term instead of the ionization potential of atoms.

Suzuki, Tatsuya; Iwabuchi, Hideki; Takahashi, Kazuko; Nomura, Masao; Okamoto, Makoto; Fujii, Yasuhiko

1995-07-01

342

Perfluorooctanesulfonic Acid Catalyzed Friedel-Crafts Alkylation with Alkyl Halides  

Microsoft Academic Search

A New procedure to prepare superacid perfluorooctanesulfonic acid (POSA) is reported. POSA catalyzed Friedel-Crafts alkylation of aromatic compounds with alkyl halides in liquid-phase reactions. Alkylation gave higher total yields than the corresponding reactions with Nafion-H, without the need of any complex decomposition or work-up. The reactions do not need to be carried out under absolutely anhydrous condition. The catalyst POSA

Xiangkai Fu; Mingqian He; Qingying Lei; Bikuei Luo

1991-01-01

343

Methyl halide emissions from savanna fires in southern Africa  

Microsoft Academic Search

The methyl halides, methyl chloride (CH3Cl), methyl bromide (CH3Br), and methyl iodide (CH3I), were measured in regional air samples and smoke from savanna fires in southern Africa during the Southern Africa Fire-Atmosphere Research Initiative-92 (SAFARI-92) experiment (August-October 1992). All three species were significantly enhanced in the smoke plumes relative to the regional background. Good correlations were found between the methyl

M. O. Andreae; E. Atlas; G. W. Harris; G. Helas; A. de Kock; R. Koppmann; W. Maenhaut; S. Manø; W. H. Pollock; J. Rudolph; D. Scharffe; G. Schebeske; M. Welling

1996-01-01

344

Alkali resistant optical coatings for alkali lasers and methods of production thereof  

DOEpatents

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.

Soules, Thomas F; Beach, Raymond J; Mitchell, Scott C

2014-11-18

345

A halide sensor based on the quenching of fluorescence of an immobilised indolium salt  

Microsoft Academic Search

A halide sensitive indolium salt has been produced by the quaternisation of Harmane with 1,3-propane sultone. The product, 1-methyl-2(sulfonatopropyl)-9H-pyrido[3,4-b] indolium (SPI), is readily water soluble and in the presence of aqueous halide ions is fluorescence quenched, enabling halide concentrations to be determined using Stern–Volmer kinetics. The fluorophore has been immobilised within a hydrophilic Quattro copolymer, so-called due to its four

Chris D. Geddes

2000-01-01

346

Extensive and Highly Accurate Line Lists for Hydrogen Halides  

NASA Astrophysics Data System (ADS)

New dipole moment functions (DMF) for the ground X 1?+ electronic states of the hydrogen halides (HF, HCl, HBr, HI) have been obtained using a direct fit approach that fits the best available and appropriately weighted experimental line intensity data for individual ro-vibrational transitions. Combining the newly developed (taking into account the most recent experiments) empirical potential energy functions and the DMFs, line positions and line intensities of the hydrogen halides and their isotopologues have been calculated numerically using program LEVEL. In addition, new semi-empirical algorithms for assigning line-shape parameters for these species have been developed. Using these improvements, new line lists for hydrogen halides were created to update the HITRAN spectroscopic database. These new lists are more accurate and significantly more extensive than those included in the current version of the database (HITRAN2008). R.J. Le Roy, ``LEVEL 8.0, 2007'', University of Waterloo Chemical Physics Research Report CP-663 (2007); see http://leroy.uwaterloo.ca/programs/. L.S. Rothman, I.E. Gordon, A. Barbe, D.C. Benner, P.F. Bernath, et al., ``The HITRAN 2008 Molecular Spectroscopic Database,'' JQSRT 110, 532-572 (2009).

Li, G.; Bernath, P. F.; Gordon, I. E.; Rothman, L. S.; Richard, C.; Le Roy, R. J.; Coxon, J. A.; Hajigeorgiou, P.

2011-06-01

347

Will Lanthanum Halide Scintillators Make NaI(Tl) Obsolete?  

NASA Astrophysics Data System (ADS)

The commercial availability of lanthanum halide scintillators (LaCl3:Ce and LaBr3:Ce) has been much anticipated due to their significantly better resolution (3-4% at 662 keV) relative to NaI(Tl). Unfortunately, our initial investigation of these scintillators revealed significant alpha contamination quite apparent in background spectra. Using measurements of the detector in coincidence with a HPGe detector, we identified the alpha-contaminant as Ac-227. Since this time, the alpha contamination has been substantially reduced so that a second contaminant, La-138 (a beta, gamma, and x-ray source) has become the dominant contaminant in the material. Commercially-available sizes of lanthanum halide scintillators have now reached sizes suitable for handheld Radioactive Isotope Identification Devices (RIIDs). To study the potential of this new material for RIIDs we performed a series of measurements comparing a 1.5'' x 1.5'' LaBr3 detector with an Exploranium GR-135 RIID, which contains a 1.5'' x 2.2'' NaI(Tl) detector. Measurements were taken for short timeframes of seconds to minutes, as typifies RIID usage. Measurements included examples of naturally occurring radioactive material (NORM) typically found in cargo. Of particular interest was the extent to which interference between the La-138 contaminant and K-40, a radioisotope commonly found in NORM, compromise the lanthanum halide performance. Example spectra, detector comparisons and results will be shown.

Milbrath, Brian

2006-05-01

348

Terahertz radiation in alkali vapor plasmas  

SciTech Connect

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.

Sun, Xuan; Zhang, X.-C., E-mail: Xi-Cheng.Zhang@rochester.edu [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States)

2014-05-12

349

Photoionization of Alkali-Doped Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

Superfluid helium droplets (He_N) provide a cold, weakly-interacting environment for the investigation of weakly bound molecules. Whereas the host-dopant interaction is weak for neutral molecules, ion impurities may be surrounded by frozen shells of polarized helium atoms. An extreme example of the different behavior is given by alkali metal impurities that stay at the surface of the droplet as neutrals but immerse into the droplet as cations releasing a considerable amount of binding energy. We report measurements of the photoionization efficiency for the rubidium-He_N and cesium-He_N systems and find that the ionization threshold is lowered compared with the free atoms and is in good agreement with Rydberg state spectroscopy of these systems. The corresponding energy shift increases when going from heavy to light alkali metals and from small to large helium droplets. Both effects can be explained by the difference in polarization energies associated with submerged alkali metal cations. The findings agree qualitatively well with recent calculations of helium snowball formation around alkali metal cations. M. Theisen, F. Lackner, G. Krois, and W. E. Ernst, J. Phys. Chem. Lett. 2, 2778 (2011). F. Lackner, G. Krois, M. Theisen, M. Koch, and W. E. Ernst, Phys. Chem. Chem. Phys. 13, 18781 (2011). D. E. Galli, D. M. Ceperley, and L. Reatto, J. Phys. Chem. A 115, 7300 (2011).

Theisen, Moritz; Lackner, Florian; Krois, Günter; Koch, Markus; Ernst, Wolfgang E.

2012-06-01

350

Water Content of Lunar Alkali Feldspar  

NASA Astrophysics Data System (ADS)

A report of the first estimate of lunar water from alkali feldspar, which is ~2–3 orders of magnitude higher than that estimated from apatite in similar rocks. We estimate the minimum water content of urKREEP (+bulk Moon) of 100–1000 ppm.

Mills, R. D.; Simon, J. I.; Wang, J.; Hauri, E. H.; Alexander, C. M. O'D.

2014-09-01

351

SO2 REMOVAL BY LIMESTONE DUAL ALKALI  

EPA Science Inventory

The article gives results of testing (between February 1982 and March 1983) on a pilot-scale, limestone, dual-alkali, flue gas desulfurization (FGD) system at IERL-RTP, where testing started in 1979. These results that significant improvement in soda ash consumption and filter ca...

352

Use of non evaporable getter pumps to ensure long term performances of high quantum efficiency photocathodes  

SciTech Connect

High quantum efficiency photocathodes are routinely used as laser triggered emitters in the advanced high brightness electron sources based on radio frequency guns. The sensitivity of “semiconductor” type photocathodes to vacuum levels and gas composition requires special care during preparation and handling. This paper will discuss the results obtained using a novel pumping approach based on coupling a 20?l s{sup ?1} sputter ion getter pump with a CapaciTorr® D100 non evaporable getter (NEG) pump. A pressure of 8?10{sup ?8}?Pa was achieved using only a sputter ion pump after a 6?day bake-out. With the addition of a NEG pump, a pressure of 2?10{sup ?9}?Pa was achieved after a 2?day bake-out. These pressure values were maintained without power due to the ability of the NEG to pump gases by chemical reaction. Long term monitoring of cathodes quantum efficiencies was also carried out at different photon wavelengths for more than two years, showing no degradation of the photoemissive film properties.

Sertore, Daniele, E-mail: daniele.sertore@mi.infn.it; Michelato, Paolo; Monaco, Laura [Istituto Nazionale di Fisica Nucleare Sez. Milano – LASA, Via Fratelli Cervi 201, I-20090 Segrate (Italy); Manini, Paolo; Siviero, Fabrizio [SAES Getters S.p.A., Viale Italia 77, 20020 Lainate (Italy)

2014-05-15

353

Heat load of a P-doped GaAs photocathode in SRF electron gun  

SciTech Connect

Many efforts were made over the last decades to develop a better polarized electron source for the high energy physics. Several laboratories operate DC guns with the Gallium-Arsenide photo-cathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved using a Superconducting RF electron gun, which delivers beams of higher brightness than DC guns does, because the field gradient at the cathode is higher. SRF guns with metal cathodes and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since the cathode will be normal conducting, the problem about the heat load stemming from the cathode arises. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and the verification by measuring the quality factor of the gun with and without cathode.

Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Jain, A.; Gupta, R.; Holmes, D.

2010-05-23

354

Quantum efficiency measurement of CsI photocathodes using synchrotron radiation at BSRF  

NASA Astrophysics Data System (ADS)

A quantum efficiency(QE) measurement system has been established for CsI photocathodes in the wavelength range of 120-210 nm by using the synchrotron radiation light source at Beijing Synchrotron Radiation Laboratory (BSRF). An AXUV100G photodiode calibrated by Physikalisch-Technische Bundesanstalt (PTB) was used as the transfer detector standard to ensure the accuracy and reliability of the QE measurement. The dependencies of QE measurement on beam energy, vacuum pressure and bias voltage were studied in detail. The influence of photoionization in gas on the QE measurement was observed and is described. The surface morphological characteristics of both substrate and CsI film were analyzed by atomic force microscopy (AFM). The QE results of differently prepared CsI photocathodes were compared, including: the printed circuit board (PCB) of FR-4 (Woven glass and epoxy)+Cu, FR-4+Cu/Ni/Au, and stainless steel substrates; a series of thickness from 60 to 600 nm; and the resistive and electron beam evaporation techniques.

Xie, Yuguang; Liu, Hongbang; Zhang, Aiwu; Liu, Yingbiao; Hu, Tao; Zhou, Li; An, Zhenghua; Cai, Xiao; Fang, Jian; Ge, Yongshuai; Lü, Qiwen; Shi, Feng; Sun, Xilei; Sun, Lijun; Xue, Zheng; Yu, Boxiang; Zheng, Yangheng; Lü, Junguang

2012-02-01

355

Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst  

NASA Astrophysics Data System (ADS)

Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7mAcm-2 at 0V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production.

Morales-Guio, Carlos G.; Tilley, S. David; Vrubel, Heron; Grätzel, Michael; Hu, Xile

2014-01-01

356

Hydrogen evolution from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst.  

PubMed

Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7?mA?cm(-2) at 0?V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production. PMID:24402352

Morales-Guio, Carlos G; Tilley, S David; Vrubel, Heron; Grätzel, Michael; Hu, Xile

2014-01-01

357

Improved Ion Resistance for III-V Photocathodes in High Current Guns  

SciTech Connect

The two photocathode test systems were modified, baked and recommissioned. The first system was dedicated to ion studies and the second to electron stimulated recovery (ESR) work. The demonstration system for the electron beam rejuvenation was set up, tested and demonstrated to one of the SSRL team (Dr. Kirby) during a site visit. The requisite subsystems were transferred to SSRL, installed and photoemission studies conducted on activated surfaces following electron beam exposure. Little surface chemistry change was detected in the photoemission spectra following the ESR process. The yield mapping system for the ion (and later, the electron beam rejuvenation) studies was implemented and use made routine. Ion species and flux measurements were performed for H, He, Ne, Ar, Kr and Xe ions at energies of 0.5, 1.0 and 2.0 kV. Gas induced photoyield measurements followed each ion exposure measurement. These data permit the extraction of photoyield induced change per ion (by species) at the measured energies. Electron beam induced rejuvenation was first demonstrated in the second chamber with primary electron beam energy and dependency investigations following. A Hiden quadrupole mass spectrometer for the electron stimulated desorption (ESD) measurements was procured. The UHV test systems needed for subsequent measurements were configured, baked, commissioned and utilized for their intended purposes. Measurements characterizing the desorption products from the ESD process and secondary electron (SE) yield at the surfaces of negative electron affinity GaAs photocathodes have been performed. One US Utility Patent was granted covering the ESR process.

Mulhollan, Gregory, A.

2012-11-16

358

Graphene incorporated nanocrystalline TiO2 films for the photocathodic protection of 304 stainless steel  

NASA Astrophysics Data System (ADS)

Composite films of TiO2 and graphene (GR) were prepared on 304 stainless steel (304SS) by the sol-gel method and heat treatment. The morphology, crystalline phase, and composition of the GR/TiO2 films were characterized systematically by X-ray diffraction, Raman spectroscopy and scanning electron microscopy, respectively. The photocathodic protection performances of the composite film under illumination and dark conditions in 3.0% NaCl solution were evaluated through the electrochemical measurements. It is indicated that the incorporation of GR in TiO2 film can improve effectively the photocathodic protection effect for 304SS under the UV illumination. Compared to 350 mV of pure TiO2 film, the electrode potentials can be negatively shifted to about -600 mV under UV light irradiation by incorporating GR into TiO2 films. At the same time, a 14-fold photocurrent density can be obtained for the GR/TiO2 film. This indicates that GR can play an excellent enhancing effect on the photogenerated cathodic protection of TiO2 films.

Guo, Xiangqin; Liu, Wei; Cao, Lixin; Su, Ge; Xu, Hongmei; Liu, Binhao

2013-10-01

359

New EBCCD with transferred electron photocathode for range-gated active imaging system  

NASA Astrophysics Data System (ADS)

A detailed comparison between conventional image intensifiers and electron bombarded CCD (EBCCD) is conducted. These sensors' advantages and drawbacks are analyzed. EBCCD with transferred electron (TE) photocathode and its application in Laser Illuminated Viewing and Ranging (LIVAR) system are shown in details. The TE Photocathode (TEP) developed by Intevac in 1996 has a demonstrated quantum efficiency of 20% or higher over the spectral range between 0.95 and 1.7 ?m. The TEP is coupled directly with a CCD chip in an electron bombarded CCD (EBCCD) configuration. The overall noise figure of the EBCCD camera is close to one, approximately half that of a standard Generation-III image intensifier. The EBCCD eliminates the micro-channel plate (MCP), phosphor screen, and fiber optics, and as a result both improved image quality and increased sensitivity can be obtained in a smaller sized camera. Because of the reduction in the number of image conversions and the significantly greater signal-to-noise performance, an EBCCD has higher contrast and resolution than an ICCD. These characteristics make the EBCCD a good candidate for military, helmet-mounted night-vision systems as well as for covert surveillance applications.

Xu, Xiaowen; Guo, Jin

2002-09-01

360

Calcium-Alkali Syndrome in the Modern Era  

PubMed Central

The ingestion of calcium, along with alkali, results in a well-described triad of hypercalcemia, metabolic alkalosis, and renal insufficiency. Over time, the epidemiology and root cause of the syndrome have shifted, such that the disorder, originally called the milk-alkali syndrome, is now better described as the calcium-alkali syndrome. The calcium-alkali syndrome is an important cause of morbidity that may be on the rise, an unintended consequence of shifts in calcium and vitamin D intake in segments of the population. We review the pathophysiology of the calcium-alkali syndrome. PMID:24288027

Patel, Ami M.; Adeseun, Gbemisola A.; Goldfarb, Stanley

2013-01-01

361

Abiotic Formation of Methyl Halides in the Terrestrial Environment  

NASA Astrophysics Data System (ADS)

Methyl chloride and methyl bromide are the most abundant chlorine and bromine containing organic compounds in the atmosphere. Since both compounds have relatively long tropospheric lifetimes they can effectively transport halogen atoms from the Earth's surface, where they are released, to the stratosphere and following photolytic oxidation form reactive halogen gases that lead to the chemical destruction of ozone. Methyl chloride and methyl bromide account for more than 20% of the ozone-depleting halogens delivered to the stratosphere and are predicted to grow in importance as the chlorine contribution to the stratosphere from anthropogenic CFCs decline. Today methyl chloride and methyl bromide originate mainly from natural sources with only a minor fraction considered to be of anthropogenic origin. However, until as recently as 2000 most of the methyl chloride and methyl bromide input to the atmosphere was considered to originate from the oceans, but investigations in recent years have clearly demonstrated that terrestrial sources such as biomass burning, wood-rotting fungi, coastal salt marshes, tropical vegetation and organic matter degradation must dominate the atmospheric budgets of these trace gases. However, many uncertainties still exist regarding strengths of both sources and sinks, as well as the mechanisms of formation of these naturally occurring halogenated gases. A better understanding of the atmospheric budget of both methyl chloride and methyl bromide is therefore required for reliable prediction of future ozone depletion. Biotic and abiotic methylation processes of chloride and bromide ion are considered to be the dominant pathways of formation of these methyl halides in nature. In this presentation I will focus on abiotic formation processes in the terrestrial environment and the potential parameters that control their emissions. Recent advances in our understanding of the abiotic formation pathway of methyl halides will be discussed. This will include a consideration on how stable isotope studies assisted advancements in this subject area. For example, it has been shown that the methoxyl groups of lignin and pectin which together constitute the bulk of the C1 plant pool have a carbon isotope signature significantly depleted in 13C. Plant-derived C1 volatile organic compounds (VOCs) are also highly depleted in 13C compared with Cn+1 VOCs. These observations suggest that the plant methoxyl pool is the predominant source of methyl halides released from senescent and dead plant litter. The distinct 13C depletion of plant methoxyl groups and naturally produced methyl halides may provide a helpful tool in constraining complex environmental processes and therefore improve our understanding of the global cycles of atmospheric methyl halides.

Keppler, F.

2011-12-01

362

THE OPERATION OF THE BNL/ATF GUN-IV PHOTOCATHODE RF GUN AT THE ADVANCED PHOTON SOURCE  

E-print Network

THE OPERATION OF THE BNL/ATF GUN-IV PHOTOCATHODE RF GUN AT THE ADVANCED PHOTON SOURCE * S (SASE) process is nearing completion. Recently, an rf photoinjector gun system was made available, and integration of this gun with the APS will be discussed. 1 INTRODUCTION The Advanced Photon Source (APS

Brookhaven National Laboratory

363

Hydrogen production using a molybdenum sulfide catalyst on a titanium-protected n(+)p-silicon photocathode.  

PubMed

A low-cost substitute: A titanium protection layer on silicon made it possible to use silicon under highly oxidizing conditions without oxidation of the silicon. Molybdenum sulfide was electrodeposited on the Ti-protected n(+)p-silicon electrode. This electrode was applied as a photocathode for water splitting and showed a greatly enhanced efficiency. PMID:22887979

Seger, Brian; Laursen, Anders B; Vesborg, Peter C K; Pedersen, Thomas; Hansen, Ole; Dahl, Søren; Chorkendorff, Ib

2012-09-01

364

Removal of Retired Alkali Metal Test Systems  

SciTech Connect

This paper describes the successful effort to remove alkali metals, alkali metal residues, and piping and structures from retired non-radioactive test systems on the Hanford Site. These test systems were used between 1965 and 1982 to support the Fast Flux Test Facility and the Liquid Metal Fast Breeder Reactor Program. A considerable volume of sodium and sodium-potassium alloy (NaK) was successfully recycled to the commercial sector; structural material and electrical material such as wiring was also recycled. Innovative techniques were used to safely remove NaK and its residues from a test system that could not be gravity-drained. The work was done safely, with no environmental issues or significant schedule delays.

Brehm, W. F.; Church, W. R.; Biglin, J. W.

2003-02-26

365

35 Cl, 79 Br, 81 Br, and 127 I NQR spectra of organomercury halides  

Microsoft Academic Search

A study of the NQR spectra of some halides disclosed that in the crystals of organomercury halides the behavior of the quadrupole constants is determined to a greater degree by the effect of the nature of the substituants on the intermolecular coordination reactions of Hg... Hal than by the usual transfer of the influence of the electronic effects along the

E. V. Bryukhova; A. K. Prokof'ev; T. Ya. Mel'nikova; O. Yu. Okhlobystia; G. K. Semin

1974-01-01

366

Iron-Exchanged Zeolite as Effective Catalysts for Friedel–Crafts Alkylation with Alkyl Halides  

Microsoft Academic Search

Friedel–Crafts alkylation of benzene and ethylbenzene with butyl halides has been investigated in the presence of iron-exchanged zeolites. The catalysts showed high conversions and selectivity for monoalkylated products with tertiary and secondary halides under mild reaction conditions (45–60°C). Alkylation of ethylbenzene with 2-chlorobutane can be achieved in 99% yield and 100% selectivity to the monoalkylated product.

Antônio M. F. Bidart; Ana P. S. Borges; Leonardo Nogueira; Elizabeth R. Lachter; Claudio J. A. Mota

2001-01-01

367

Hydrogen bond radii for the hydrogen halides and van der Waals radius of hydrogen  

Microsoft Academic Search

In this article, the effective size of hydrogen in the hydrogen halides forming hydrogen bonded complexes is estimated. The scheme proposed by Bhadane and Gadre [J. Chem. Phys. 107, 5625 (1997)] for estimating the size of hydrogen in HF is extended to the other hydrogen halides (HCl and HBr) and HCN. It is noted that the radius of H atom

Pankaj K. Mandal; E. Arunan

2001-01-01

368

THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER: AN INTERLABORATORY COMPARATIVE STUDY OF TWO METHODS  

EPA Science Inventory

Total organic halide (TOX) analyzers are commonly used to measure the amount of dissolved halogenated organic byproducts in disinfected waters. Because of the lack of information on the identity of disinfection byproducts, rigorous testing of the dissolved organic halide (DOX) pr...

369

THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER: A COMPARATIVE STUDY OF TWO INSTRUMENTS  

EPA Science Inventory

Total organic halide (TOX) analyzers are commonly used to measure the amount of dissolved halogenated organic byproducts in disinfected waters. ecause of the lack of information on the identity of disinfection byproducts, rigorous testing of the dissolved organic halide (DOX) pro...

370

Methyl halide emissions from greenhouse-grown mangroves Steven L. Manley,1  

E-print Network

Methyl halide emissions from greenhouse-grown mangroves Steven L. Manley,1 Nun-Yii Wang,2 Maggie L 2006; published 6 January 2007. [1] Two mangrove species, Avicennia germinans and Rhizophora mangle of methyl halide emissions from mangrove forests. Citation: Manley, S. L., N.-Y. Wang, M. L. Walser, and R

Manley, Steven L.

371

Cyclic carbonate formation from carbon dioxide and oxiranes in tetrabutylammonium halides as solvents and catalysts.  

PubMed

[reaction: see text] Epoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation. PMID:12123376

Caló, Vincenzo; Nacci, Angelo; Monopoli, Antonio; Fanizzi, Antonello

2002-07-25

372

Alkali-activated cements Opportunities and challenges  

Microsoft Academic Search

Alkali-activated cements as discussed here are those with compositions falling in the Me2O-MeO-Me2O3-SiO2-H2O system. This paper reviews their history of development and discusses their present status. Currently, there are major opportunities for such cements based upon (a) substantial knowledge of properties and mechanisms; (b) good track record of field performance in various applications and; (c) future orientation as environmentally friendly

Della M Roy

1999-01-01

373

Thermionic emission of alkali ions from zeolites  

Microsoft Academic Search

The thermionic emission of positive alkali ions from zeolites has been investigated in the high-voltage pulsed regime. Current densities of up to 1 A cm-2 have been obtained using 2-mus-long 30-kV pulses. This is about two orders of magnitude larger than currents obtained in the low-voltage dc regime. There are two major reasons for this difference. First, the currents have

A. N. Pargellis; M. Seidl

1978-01-01

374

Emittance studies of the BNL/SLAC/UCLA 1.6 cell photocathode rf gun  

SciTech Connect

The symmetrized 1.6 cell S-band photocathode gun developed by the BNL/SLAC/UCLA collaboration is in operation at the Brookhaven Accelerator Test Facility (ATF). A novel emittance compensation solenoid magnet has also been designed, built and is in operation at the ATF. These two subsystems form an emittance compensated photoinjector used for beam dynamics, advanced acceleration and free electron laser experiments at the ATF. The highest acceleration field achieved on the copper cathode is 150 MV/m, and the guns normal operating field is 130 MV/m. The maximum rf pulse length is 3 {micro}s. The transverse emittance of the photoelectron beam were measured for various injection parameters. The 1 nC emittance results are presented along with electron bunch length measurements that indicated that at above the 400 pC, space charge bunch lengthening is occurring. The thermal emittance, {epsilon}{sub o}, of the copper cathode has been measured.

Palmer, D.T.; Miller, R.H. [Stanford Linear Accelerator Center, Menlo Park, CA (United States); Wang, X.J. [Brookhaven National Lab., Upton, NY (United States). Accelerator Test Facility] [and others

1997-07-01

375

A photocathode rf gun design for a mm-wave linac-based FEL  

SciTech Connect

In recent years, advances in the rf gun technology have made it possible to produce small beam emittances suitable for short period microundulators which take advantage of the low emittance beam to reduce the wavelength of FELs. At the Advanced Photon Source, we are studying the design of a compact 50-MeV superconducting mm-wave linac-based FEL for the production of short wavelengths ({approximately}300 nm) to carry out FEL demonstration experiments. The electron source considered for the linac is a 30- GHz, 3 1/2-cell {pi}-mode photocathode rf gun. For cold model rf measurements a 15-GHz prototype structure was fabricated. Here we report on the design, numerical modelling and the initial cold-model rf measurement results on the 15-GHz prototype structure.

Nassiri, A.; Berenc, T,; Foster, J.; Waldschmidt, G.; Zhou, J.

1995-07-01

376

Emittance Studies of the BNL/SLAC/UCLA 1.6 Cell Photocathode RF Gun  

SciTech Connect

The symmetrized 1.6 cell S-band photocathode gun developed by the BNL/SLAC/UCLA collaboration is in operation at the Brookhaven Accelerator Test Facility (ATF). A novel emittance compensation solenoid magnet has also been designed, built and is in operation at the ATF. These two subsystems form an emittance compensated photoinjector used for beam dynamics, advanced acceleration and free electron laser experiments at the ATF. The highest acceleration field achieved on the copper cathode is 150 MV/m, and the guns normal operating field is 130 MV/m. The maximum rf pulse length is 3 {mu}s. The transverse emittance of the photoelectron beam were measured for various injection parameters. The 1 nC emittance results are presented along with electron bunch length measurements that indicated that at above the 400 pC, space charge bunch lengthening is occurring. The thermal emittance, {epsilon}{sub o}, of the copper cathode has been measured.

Palmer, D.T.; /SLAC; Wang, X.J.; /Brookhaven; Miller, R.H.; /SLAC; Babzien, M.; Ben-Zvi, I.; /Brookhaven; Pellegrini, C.; /UCLA; Sheehan, J.; Skaritka, J.; /Brookhaven; Winick, H.; /SLAC; Woodle, M.; Yakimenko, V.; /Brookhaven

2011-09-09

377

Evolution of surface potential barrier for negative-electron-affinity GaAs photocathodes  

NASA Astrophysics Data System (ADS)

The evolution of surface potential barrier for reflection-mode GaAs photocathodes in an ultrahigh vacuum system has been investigated by using spectral response and angle-dependent x-ray photoelectron spectroscopy (ADXPS) measurements at room temperature. The escape probabilities of electrons emitted into vacuum are obtained as a function of the incident electron energy, surface barrier height, and thickness. Based on the new escape probability expressions, we obtain the surface barrier parameters of the reflection-mode negative-electron-affinity (NEA) cathodes from the fit of the spectral response curves by using quantum-efficiency equations. These parameters reveal the evolution of the NEA cathode surface during the degradation process. In addition, the surface layer structure of both the freshly activated and degraded cathodes is calculated from the ADXPS spectra. The calculated results are in fair agreement with the fitted barrier parameters.

Zou, Jijun; Chang, Benkang; Yang, Zhi; Zhang, Yijun; Qiao, Jianliang

2009-01-01

378

Low-energy collisions with atomic and molecular ions in a photocathode electron target  

NASA Astrophysics Data System (ADS)

Dielectronic recombination of highly charged atomic ions and dissociative recombination of molecular ions have been investigated using fast ion beams merged with cold intense electron beams (down to <1meV beam temperature) from a GaAs photocathode. For beryllium-like germanium ions (Ge28+) isolated fine structure Rydberg resonances (n = 9 and 14) were observed at <0.2eV revealing configuration interaction with triply excited resonances and appearing as candidates for deriving radiative shifts of the 2s2-2s2p(3P0) excitation energy. For hydrogen fluoride ions (HF+) dissociative recombination with the cold electrons, producing n = 2 hydrogen atoms, was seen to occur for specific excited initial rotational levels. These levels were identified by their fragment energies down to about 4meV and it is envisaged to measure these energies with sub-meV accuracy.

Wolf, A.; Orlov, D. A.; Krantz, C.; Lestinsky, M.; Shornikov, A.; Novotný, O.; Stützel, J.; Buhr, H.; Mendes, M.; Petrignani, A.; Grieser, M.; Schippers, S.; Müller, A.; Ferro, F.; Lindroth, E.

2009-11-01

379

Comparative research on Cs/O activation source ratio for GaAs photocathodes  

NASA Astrophysics Data System (ADS)

Through the comparative research on cathode material by surface photovoltage spectroscopy (SPS) before activation and spectral response current (SRC) after activation, the value of surface escape probability (SEP) can be well measured. By the experiments and calculations for the designed cathode material, the influence of Cs/O activation source ratio on SRC and SEP can be well fitted. The lower and excessive source ratio can not get well SEP value and only the appropriate source ratio can get the better SEP value. Through the analysis of surface barrier layer model, the influence of Cs/O source ratio on the formation of surface barrier layer were well discussed. The appropriate source ratio can help to form the best double dipole arrange structure and better depth of Cs-O layer. This comparative research method can help to well study and optimize the Cs/O activation technique and varied doping structure design for GaAs photocathodes in the future.

Jiao, Gangcheng; Hu, Canglu; Chen, Liang; Qian, Yunsheng

2013-04-01

380

Biopolymer-Activated Graphitic Carbon Nitride towards a Sustainable Photocathode Material  

PubMed Central

Photoelectrochemical (PEC) conversion of solar light into chemical fuels is one of the most promising solutions to the challenge of sustainable energy. Graphitic carbon (IV) nitride polymer (g-CN) is an interesting sustainable photocathode material due to low-cost, visible-light sensitivity, and chemical stability up to 500°C in air. However, grain boundary effects and limited active sites greatly hamper g-CN activity. Here, we demonstrate biopolymer-activation of g-CN through simultaneous soft-templating of a sponge-like structure and incorporation of active carbon-dopant sites. This facile approach results in an almost 300% increase in the cathodic PEC activity of g-CN under simulated solar-irradiation. PMID:23831846

Zhang, Yuanjian; Schnepp, Zoë; Cao, Junyu; Ouyang, Shuxin; Li, Ying; Ye, Jinhua; Liu, Songqin

2013-01-01

381

An Approximate Analytic Expression for the Flux Density of Scintillation Light at the Photocathode  

SciTech Connect

The flux density of light exiting scintillator crystals is an important factor affecting the performance of radiation detectors, and is of particular importance for position sensitive instruments. Recent work by T. Woldemichael developed an analytic expression for the shape of the light spot at the bottom of a single crystal [1]. However, the results are of limited utility because there is generally a light pipe and photomultiplier entrance window between the bottom of the crystal and the photocathode. In this study, we expand Woldemichael s theory to include materials each with different indices of refraction and compare the adjusted light spot shape theory to GEANT 4 simulations [2]. Additionally, light reflection losses from index of refraction changes were also taken into account. We found that the simulations closely agree with the adjusted theory.

Braverman, Joshua B [ORNL; Harrison, Mark J [ORNL; Ziock, Klaus-Peter [ORNL

2012-01-01

382

Low energy Mott polarimetry of electrons from negative electron affinity photocathodes  

SciTech Connect

We present data on the spin polarization {ital P} and quantum yield {ital Y} of electrons photoemitted from negative electron affinity semiconductors, including GaAs(100), GaAsP(100) alloy, and strained GaAs layer epitaxially grown on a GaAsP(100) buffer. Near photothreshold the following values for {ital P}({ital Y}) are, respectively, obtained: 26% (2.5{times}10{sup {minus}2}), 40% (1{times}10{sup {minus}3}), and 60% (1.5{times}10{sup {minus}4}). We describe in detail the apparatus used containing a low energy (10--25 keV) Mott polarimeter. The system, completely fitted in a small volume ({similar_to}10{sup 4} cm{sup 3}) ultrahigh vacuum chamber, is intended as a test facility for characterizing candidate photocathode materials for spin polarized electron sources. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Ciccacci, F.; De Rossi, S. [INFM, Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, I-20133 Milano (Italy)] [INFM, Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, I-20133 Milano (Italy); Campbell, D.M. [Department of Physics, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ (United Kingdom)] [Department of Physics, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ (United Kingdom)

1995-08-01

383

Crossed-Beam Reactions of Barium with Hydrogen Halides Measurement of Internal State Distributions by Laser-Induced Fluorescence  

E-print Network

Crossed-Beam Reactions of Barium with Hydrogen Halides Measurement of Internal State Distributions is presented and applied to the reactions of barium with the hydrogen halides. It is found that most-inducedfluorescenceas a molecular beam detector and apply it to the reactions of barium atoms with hydrogen halides, Reactions (1

Zare, Richard N.

384

Metal-halide lamp design: atomic and molecular data needed  

NASA Astrophysics Data System (ADS)

Metal-halide lamps are a subset of high intensity discharge (HID) lamps so named because of their high radiance. These lamps are low temperature (~0.5 eV), weakly ionized plasmas sustained in refractory but light transmissive envelopes by the passage of electric current through atomic and molecular vapors. For commercial applications, the conversion of electric power to light must occur with good efficiency and with sufficient spectral content throughout the visible (380-780 nm) to permit the light so generated to render colors comparable to natural sunlight. This is achieved by adding multiple metals to a basic mercury discharge. Because the vapor pressure of most metals is very much lower than mercury itself, metal-halide salts of the desired metals, having higher vapor pressures, are used to introduce the material into the basic discharge. The metal compounds are usually polyatomic iodides, which vaporize and subsequently dissociate as they diffuse into the bulk plasma. Metals with multiple visible transitions are necessary to achieve high photometric efficiency (efficacy) and good color. Compounds of Sc, Dy, Ho, Tm, Ce, Pr, Yb and Nd are commonly used. The electrons, atoms and radicals are in local thermodynamic equilibrium (LTE), but not with the radiation field. Strong thermal (106 K m-1) and density gradients are sustained in the discharge. Atomic radiation produced in the high-temperature core transits through colder gas regions where it interacts with cold atoms and un-dissociated molecules before exiting the lamp. Power balance and spectral output of the lamp are directly affected by the strength of atomic transitions. Attempts to simulate the radiative output of functional metal-halide lamps have been successful only in very simple cases. More data (e.g. the atomic transition probabilities of Ce i) are necessary to improve lamp performance, to select appropriate radiators and in scaling the lamp geometry to various wattages for specific applications.

Lapatovich, Walter P.

2009-05-01

385

CFTR-mediated halide transport in phagosomes of human neutrophils  

PubMed Central

Chloride serves as a critical component of innate host defense against infection, providing the substrate for MPO-catalyzed production of HOCl in the phagosome of human neutrophils. Here, we used halide-specific fluorescent sensors covalently coupled to zymosan particles to investigate the kinetics of chloride and iodide transport in phagosomes of human neutrophils. Using the self-ratioable fluorescent probe specific for chloride anion, we measured chloride dynamics within phagosomes in response to extracellular chloride changes by quantitative fluorescence microscopy. Under the experimental conditions used, normal neutrophils showed rapid phagosomal chloride uptake with an initial influx rate of 0.31 ± 0.04 mM/s (n=5). GlyH-101, a CFTRinh, decreased the rate of uptake in a dose-dependent manner. Neutrophils isolated from CF patients showed a significantly slower rate of chloride uptake by phagosomes, having an initial influx rate of 0.043 ± 0.012 mM/s (n=5). Interestingly, the steady-state level of chloride in CF phagosomes was ?26 mM, significantly lower than that of the control (?68 mM). As CFTR transports chloride as well as other halides, we conjugated an iodide-sensitive probe as an independent approach to confirm the results. The dynamics of iodide uptake by neutrophil phagosomes were monitored by flow cytometry. CFTRinh172 blocked 40–50% of the overall iodide uptake by phagosomes in normal neutrophils. In a parallel manner, the level of iodide uptake by CF phagosomes was only 20–30% of that of the control. Taken together, these results implicate CFTR in transporting halides into the phagosomal lumen. PMID:20089668

Painter, Richard G.; Marrero, Luis; Lombard, Gisele A.; Valentine, Vincent G.; Nauseef, William M.; Wang, Guoshun

2010-01-01

386

Chemically induced fracturing in alkali feldspar  

NASA Astrophysics Data System (ADS)

Fracturing in alkali feldspar during Na+-K+ cation exchange with a NaCl-KCl salt melt was studied experimentally. Due to a marked composition dependence of the lattice parameters of alkali feldspar, any composition gradient arising from cation exchange causes coherency stress. If this stress exceeds a critical level fracturing occurs. Experiments were performed on potassium-rich gem-quality alkali feldspars with polished (010) and (001) surfaces. When the feldspar was shifted toward more sodium-rich compositions over more than about 10 mole %, a system of parallel cracks with regular crack spacing formed. The cracks have a general (h0l) orientation and do not correspond to any of the feldspar cleavages. The cracks are rather oriented (sub)-perpendicular to the direction of maximum tensile stress. The critical stress needed to initiate fracturing is about 325 MPa. The critical stress intensity factor for the propagation of mode I cracks, K Ic, is estimated as 2.30-2.72 MPa m1/2 (73-86 MPa mm1/2) from a systematic relation between characteristic crack spacing and coherency stress. An orientation mismatch of 18° between the crack normal and the direction of maximum tensile stress is ascribed to the anisotropy of the longitudinal elastic stiffness which has pronounced maxima in the crack plane and a minimum in the direction of the crack normal.

Scheidl, K. S.; Schaeffer, A.-K.; Petrishcheva, E.; Habler, G.; Fischer, F. D.; Schreuer, J.; Abart, R.

2014-01-01

387

Dye sensitised solar cells with nickel oxide photocathodes prepared via scalable microwave sintering.  

PubMed

Photoactive NiO electrodes for cathodic dye-sensitised solar cells (p-DSCs) have been prepared with thicknesses ranging between 0.4 and 3.0 ?m by spray-depositing pre-formed NiO nanoparticles on fluorine-doped tin oxide (FTO) coated glass substrates. The larger thicknesses were obtained in sequential sintering steps using a conventional furnace (CS) and a newly developed rapid discharge sintering (RDS) method. The latter procedure is employed for the first time for the preparation of p-DSCs. In particular, RDS represents a scalable procedure that is based on microwave-assisted plasma formation that allows the production in series of mesoporous NiO electrodes with large surface areas for p-type cell photocathodes. RDS possesses the unique feature of transmitting heat from the bulk of the system towards its outer interfaces with controlled confinement of the heating zone. The use of RDS results in a drastic reduction of processing times with respect to other deposition methods that involve heating/calcination steps with associated reduced costs in terms of energy. P1-dye sensitized NiO electrodes obtained via the RDS procedure have been tested in DSC devices and their performances have been analysed and compared with those of cathodic DSCs derived from CS-deposited samples. The largest conversion efficiencies (0.12%) and incident photon-to-current conversion efficiencies, IPCEs (50%), were obtained with sintered NiO electrodes having thicknesses of ~1.5-2.0 ?m. In all the devices, the photogenerated holes in NiO live significantly longer (?(h) ~ 1 s) than have previously been reported for P1-sensitized NiO photocathodes. In addition, P1-sensitised sintered electrodes give rise to relatively high photovoltages (up to 135 mV) when the triiodide-iodide redox couple is used. PMID:23301246

Gibson, Elizabeth A; Awais, Muhammad; Dini, Danilo; Dowling, Denis P; Pryce, Mary T; Vos, Johannes G; Boschloo, Gerrit; Hagfeldt, Anders

2013-02-21

388

Electronic, vibrational, and ODMR studies of solid oxalyl halides  

NASA Astrophysics Data System (ADS)

The lowest excited singlet and triplet states of the oxalyl halides, (COX)2 with X = F, Cl, and Br, have been investigated at ?- 4 K by optical and ODMR spectroscopy. The observed excited states are assigned as the 1, 3Au(n?*) states of the planar trans isomers. A partial reassignment of the ground state fundamentals is presented, based on the ODMR activities in the vibronically resolved emission spectra. Variations seen in the kinetic parameters and fine structure splittings of the 3Au state in the series are interpreted in terms of oxygen- and halogen-centred spin-orbit interactions.

Möller, G.; Tinti, D. S.

389

Selective Cross-Coupling of Organic Halides with Allylic Acetates  

PubMed Central

A general protocol for the coupling of haloarenes with a variety of allylic acetates is presented. Strengths of the method are a tolerance for electrophilic (ketone, aldehyde) and acidic (sulfonamide, trifluoroacetamide) substrates and the ability to couple with a variety of substituted allylic acetates. Secondary alkyl bromides can also be allylated under slightly modified conditions, demonstrating the generality of the approach. Finally, the coupling of a reactive vinyl halide could be achieved by the use of a very hindered ligand and more reactive, branched allylic acetates. PMID:23095043

Anka-Lufford, Lukiana L.; Prinsell, Michael R.

2012-01-01

390

Pressure Dependence of the Effective Charge in Copper Halides  

NASA Astrophysics Data System (ADS)

After showing how the effective charges are related to the superionic properties, the pressure dependence of the localized effective charges in copper halides is focused, where interesting material dependence has been reported, Namely, the localized effective charges in Cul, CuBr and CuCl increases, remains almost constant and decreases with pressure, respectively. By using the results of an ab initio simulation, it is found that in Cul, the Cu d-electrons contribute largely to the localized effective charge. For CuCl this contribution is diminished when compared with Cul.

Aniya, Masaru; Shimojo, Fuyuki

2007-01-01

391

Thermal conductivity of halide solid solutions: measurement and prediction.  

PubMed

The composition dependence of the lattice thermal conductivity in NaCl-KCl solid solutions has been measured as a function of composition and temperature. Samples with systematically varied compositions were prepared and the laser flash technique was used to determine the thermal diffusivity from 373 K to 823 K. A theoretical model, based on the Debye approximation of phonon density of state (which contains no adjustable parameters) was used to predict the thermal conductivity of both stoichiometric compounds and fully disordered solid solutions. The predictions obtained with the model agree very well with our measurement. A general method for predicting the thermal conductivity of different halide systems is discussed. PMID:25217938

Gheribi, Aïmen E; Poncsák, Sándor; St-Pierre, Rémi; Kiss, László I; Chartrand, Patrice

2014-09-14

392

Thermal conductivity of halide solid solutions: Measurement and prediction  

NASA Astrophysics Data System (ADS)

The composition dependence of the lattice thermal conductivity in NaCl-KCl solid solutions has been measured as a function of composition and temperature. Samples with systematically varied compositions were prepared and the laser flash technique was used to determine the thermal diffusivity from 373 K to 823 K. A theoretical model, based on the Debye approximation of phonon density of state (which contains no adjustable parameters) was used to predict the thermal conductivity of both stoichiometric compounds and fully disordered solid solutions. The predictions obtained with the model agree very well with our measurement. A general method for predicting the thermal conductivity of different halide systems is discussed.

Gheribi, Aïmen E.; Poncsák, Sándor; St-Pierre, Rémi; Kiss, László I.; Chartrand, Patrice

2014-09-01

393

Heavy ion passive dosimetry with silver halide single crystals  

NASA Technical Reports Server (NTRS)

A method of detecting radiation damage tracks due to heavy particles in large single crystals of the silver halides is described. The tracks, when made visible with a simple electrical apparatus, appear similar to tracks in emulsions. The properties of the crystals, the technique of printing out the tracks, and evidence concerning the threshold energy for registering particles indicates that this method may find application in heavy ion dosimetry. The method has been found to be sensitive to stopping He nuclei and relativistic M group cosmic rays. Some impurities strongly influence the printout of the tracks, and the effects of these impurities are discussed.

Childs, C. B.; Parnell, T. A.

1972-01-01

394

Selective cross-coupling of organic halides with allylic acetates.  

PubMed

A general protocol for the coupling of haloarenes with a variety of allylic acetates is presented. Strengths of the method are a tolerance for electrophilic (ketone, aldehyde) and acidic (sulfonamide, trifluoroacetamide) substrates and the ability to couple with a variety of substituted allylic acetates. Secondary alkyl bromides can also be allylated under slightly modified conditions, demonstrating the generality of the approach. Finally, the coupling of a reactive vinyl halide could be achieved by the use of a very hindered ligand and more reactive, branched allylic acetates. PMID:23095043

Anka-Lufford, Lukiana L; Prinsell, Michael R; Weix, Daniel J

2012-11-16

395

Impact of the organic halide salt on final perovskite composition for photovoltaic applications  

NASA Astrophysics Data System (ADS)

The methylammonium lead halide perovskites have shown significant promise as a low-cost, second generation, photovoltaic material. Despite recent advances, however, there are still a number of fundamental aspects of their formation as well as their physical and electronic behavior that are not well understood. In this letter we explore the mechanism by which these materials crystallize by testing the outcome of each of the reagent halide salts. We find that components of both salts, lead halide and methylammonium halide, are relatively mobile and can be readily exchanged during the crystallization process when the reaction is carried out in solution or in the solid state. We exploit this fact by showing that the perovskite structure is formed even when the lead salt's anion is a non-halide, leading to lower annealing temperature and time requirements for film formation. Studies into these behaviors may ultimately lead to improved processing conditions for photovoltaic films.

Moore, David T.; Sai, Hiroaki; Wee Tan, Kwan; Estroff, Lara A.; Wiesner, Ulrich

2014-08-01

396

ESCA study of alkali-treated coal surfaces  

SciTech Connect

The surface interactions of alkali with coal and mineral matter have been studied by ESCA to establish a basis for predicting the relative reactivity of alkali with sulfur during coal beneficiation processes. The speciation of sulfur in several coals doped with various alkali salts was determined and quantified following heating of the samples to 375/degree/C in air or N/sub 2/ and after washing them with water. Organic and pyritic sulfur react with the alkali cation when heated, after which the sulfide or oxidized sulfur product can be washed from the coal. The extent of reaction between the alkali salt and sulfur is governed by the size of the cation and the electronic properties of the anion; larger alkali cations are more reactive, as are anions with stronger nucleophilic properties.

Baltrus, J.P.; Diehl, J.R.; D'Este, J.R.

1988-01-01

397

Environmental mercury contamination around a chlor-alkali plant  

SciTech Connect

The chlor-alkali industry is one of the most important emitters of mercury. This metal is effectively spread from chlor-alkali plants into the atmosphere and it has been reported that only a few percent of the mercury emissions are deposited locally the major part spreading over very large areas. The purpose of this investigation was to study the spreading of mercury up to 100 km from a chlor-alkali plant using three different biological indicators.

Lodenius, M.; Tulisalo, E.

1984-04-01

398

Determination of the common and rare alkalies in mineral analysis  

USGS Publications Warehouse

Methods are described which afford a determination of each member of the alkali group and are successful in dealing with the quantities of the rare alkalies found in rocks and minerals. The procedures are relatively rapid and based chiefly on the use of chloroplatinic acid, absolute alcohol and ether, and ammonium sulfate. The percentages of all the alkalies found in a number of minerals are given.

Wells, R.C.; Stevens, R.E.

1934-01-01

399

Vacuum Ultraviolet Absorption in Alkali-Nitrites and Alkali-Nitrates  

Microsoft Academic Search

Vacuum ultraviolet absorption in alkali-nitrites (NaNO2 and KNO2) and alkali-nitrates (LiNO3, NaNO3, KNO3, RbNO3 and CsNO3) has been investigated in the region from 5 to 23 eV at room and liquid nitrogen temperatures. Two types of absorption bands are observed for each of these salts with polyatomic anions. One of them appears at about 6 eV and is relatively insensitive

Hiroshi Yamashita; Riso Kato

1970-01-01

400

High temperature alkali corrosion of ceramics in coal gas  

SciTech Connect

High temperature alkali corrosion has been known to cause premature failure of ceramic components used in advanced high temperature coal combustion systems such as coal gasification and clean-up, coal fired gas turbines, and high efficiency heat engines. The objective of this research is to systematically evaluate the alkali corrosion resistance of the most commonly used structural ceramics including silicon carbide, silicon nitride, cordierite, mullite, alumina, aluminum titanate, zirconia, and fireclay glass. The study consists of identification of the alkali reaction products (phase equilibria) and the kinetics of the alkali reactions as a function of temperature and time.

Pickrell, G.R.; Sun, T.; Brown, J.J.

1992-08-29

401

Electrochemical devices utilizing molten alkali metal electrode-reactant  

DOEpatents

Electrochemical cells are provided with a reactive metal to reduce the oxide of the alkali metal electrode-reactant. Cells employing a molten alkali metal electrode, e.g., sodium, in contact with a ceramic electrolyte, which is a conductor of the ions of the alkali metal forming the electrode, exhibit a lower resistance when a reactive metal, e.g., vanadium, is allowed to react with and reduce the alkali metal oxide. Such cells exhibit less degradation of the electrolyte and of the glass seals often used to joining the electrolyte to the other components of the cell under cycling conditions.

Hitchcock, David C. (Omaha, NE); Mailhe, Catherine C. (Berkeley, CA); De Jonghe, Lutgard C. (Oakland, CA)

1986-01-01

402

Electrochemical devices utilizing molten alkali metal electrode-reactant  

DOEpatents

Electrochemical cells are provided with a reactive metal to reduce the oxide of the alkali metal electrode-reactant. Cells employing a molten alkali metal electrode, e.g., sodium, in contact with a ceramic electrolyte, which is a conductor of the ions of the alkali metal forming the electrode, exhibit a lower resistance when a reactive metal, e.g., vanadium, is allowed to react with and reduce the alkali metal oxide. Such cells exhibit less degradation of the electrolyte and of the glass seals often used to joining the electrolyte to the other components of the cell under cycling conditions.

Hitchcock, D.C.; Mailhe, C.C.; De Jonghe, L.C.

1985-07-10

403

Oxide Film Aging on Alloy 22 in Halide Containing Solutions  

SciTech Connect

Passive and corrosion behaviors of Alloy 22 in chloride and fluoride containing solutions, changing the heat treatment of the alloy, the halide concentration and the pH of the solutions at 90 deg. C, was investigated. The study was implemented using electrochemical techniques, which included open circuit potential monitoring over time, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements carried out at open circuit and at passivity potentials. Corrosion rates obtained by EIS measurements after 24 h immersion in naturally aerated solutions were below 0.5 {mu}m/year. The corrosion rates were practically independent of solution pH, alloy heat treatment and halide ion nature and concentration. EIS low frequency resistance values increased with applied potential in the passive domain and with polarization time in pH 6 - 1 M NaCl at 90 deg. C. This effect was attributed to an increase in the oxide film thickness and oxide film aging. High frequency capacitance measurements indicated that passive oxide on Alloy 22 presented a double n-type/p-type semiconductor behavior in the passive potential range. (authors)

Rodriguez, Martin A.; Carranza, Ricardo M. [Dept. Materiales, Comision Nacional de Energia Atomica, Av. Gral. Paz 1499, Villa Maipu, 1650 (Argentina); Rebak, Raul B. [Lawrence Livermore National Laboratory, 7000 East Ave, L-631, Livermore, CA, 94550-9698 (United States)

2007-07-01

404

40 CFR 721.10098 - Disubstituted benzoic acid, alkali metal salt (generic).  

Code of Federal Regulations, 2013 CFR

...Disubstituted benzoic acid, alkali metal salt (generic). 721.10098 Section 721...Disubstituted benzoic acid, alkali metal salt (generic). (a) Chemical substance...disubstituted benzoic acid, alkali metal salt (PMN P-03-643) is subject to...

2013-07-01

405

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2014 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2014-07-01

406

40 CFR 721.5452 - Alkali metal salt of halogenated organoborate (generic).  

Code of Federal Regulations, 2010 CFR

... 2010-07-01 false Alkali metal salt of halogenated organoborate (generic...Substances § 721.5452 Alkali metal salt of halogenated organoborate (generic...substances identified generically as alkali metal salt of halogenated organoborate (PMN...

2010-07-01

407

40 CFR 721.5985 - Fatty alkyl phosphate, alkali metal salt (generic).  

Code of Federal Regulations, 2012 CFR

... Fatty alkyl phosphate, alkali metal salt (generic). 721.5985 Section 721... Fatty alkyl phosphate, alkali metal salt (generic). (a) Chemical substance...as a fatty alkyl phosphate, alkali metal salt (PMN P-99-0385) is subject to...

2012-07-01

408

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2013 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2013-07-01

409

40 CFR 721.10098 - Disubstituted benzoic acid, alkali metal salt (generic).  

Code of Federal Regulations, 2011 CFR

...Disubstituted benzoic acid, alkali metal salt (generic). 721.10098 Section 721...Disubstituted benzoic acid, alkali metal salt (generic). (a) Chemical substance...disubstituted benzoic acid, alkali metal salt (PMN P-03-643) is subject to...

2011-07-01

410

40 CFR 721.10630 - Amino acid, carboxyalkyl, alkylsulfonate, alkali salt (generic).  

Code of Federal Regulations, 2013 CFR

...carboxyalkyl, alkylsulfonate, alkali salt (generic). 721.10630 Section 721...carboxyalkyl, alkylsulfonate, alkali salt (generic). (a) Chemical substances...carboxyalkyl, alkylsulfonate, alkali salts (PMNs P-11-619 and...

2013-07-01

411

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2012 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2012-07-01

412

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2011 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2011-07-01

413

40 CFR 721.5452 - Alkali metal salt of halogenated organoborate (generic).  

Code of Federal Regulations, 2013 CFR

... 2013-07-01 false Alkali metal salt of halogenated organoborate (generic...Substances § 721.5452 Alkali metal salt of halogenated organoborate (generic...substances identified generically as alkali metal salt of halogenated organoborate (PMN...

2013-07-01

414

40 CFR 721.2565 - Alkylated sulfonated diphenyl oxide, alkali and amine salts.  

Code of Federal Regulations, 2010 CFR

...sulfonated diphenyl oxide, alkali and amine salts. 721.2565 Section 721.2565 ...sulfonated diphenyl oxide, alkali and amine salts. (a) Chemical substances and significant...alkylated sulfonated diphenyl oxide, alkali salt (PMN P-93-352) and alkylated...

2010-07-01

415

Insight into the photoelectron angular dependent energy distribution of negative-electron-affinity InP photocathodes  

SciTech Connect

Energy distribution and angular distribution of the photoelectrons from InP photocathodes are investigated using a precise Monte Carlo model. It is found that ?-valley electrons contribute to the first peak of the energy distribution curve, but the second peak is contributed by both ?-valley and L-valley electrons rather than only L-valley electrons. L valley electrons are shown to have a smaller angular spread than ?-valley electrons, which is attributed to the much higher potential energy of L-valley minimum. The further simulation indicates that the performance of InP photocathodes can be improved by increasing the hole concentration or decreasing the temperature, but the activation layer thickness variation only has very slight influence on either energy or angular distribution.

Chen, Zhanghui; Jiang, Xiangwei; Dong, Shan; Li, Jingbo, E-mail: jbli@semi.ac.cn; Li, Shushen [State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Wang, Linwang [Materials Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Mail Stop 50F, Berkeley, California 94720 (United States)

2014-01-13

416

Formability of ABX3 (X = F, Cl, Br, I) halide perovskites.  

PubMed

In this study a total of 186 complex halide systems were collected; the formabilities of ABX3 (X = F, Cl, Br and I) halide perovskites were investigated using the empirical structure map, which was constructed by Goldschmidt's tolerance factor and the octahedral factor. A model for halide perovskite formability was built up. In this model obtained, for all 186 complex halides systems, only one system (CsF-MnF2) without perovskite structure and six systems (RbF-PbF2, CsF-BeF2, KCl-FeCl2, TlI-MnI2, RbI-SnI2, TlI-PbI2) with perovskite structure were wrongly classified, so its predicting accuracy reaches 96%. It is also indicated that both the tolerance factor and the octahedral factor are a necessary but not sufficient condition for ABX3 halide perovskite formability, and a lowest limit of the octahedral factor exists for halide perovskite formation. This result is consistent with our previous report for ABO3 oxide perovskite, and may be helpful to design novel halide materials with the perovskite structure. PMID:19029699

Li, Chonghea; Lu, Xionggang; Ding, Weizhong; Feng, Liming; Gao, Yonghui; Guo, Ziming

2008-12-01

417

First Demonstration Of A Free-electron Laser Driven By Electrons From A Laser-Irradiated Photocathode  

Microsoft Academic Search

Results are reported from the first observation of a free-electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne\\/Stanford FEL achieved sustained oscillations lasting over three hours and driven by photoelectrons accelerated by the Stanford Mark III radio-frequency linac. A LaB6 cathode, irradiated by a tripled Nd:YAG mode-locked drive laser, is the source of the photoelectrons.

Mark Curtin; Glenn Bennett; Robert Burke; A. Bhowmik; P. Metty; S. Benson; J. M. J. Madey

1989-01-01

418

First demonstration of a free-electron laser driven by electrons from a laser-irradiated photocathode  

Microsoft Academic Search

We report the results from the first operation of a free electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne\\/Stanford FEL achieved sustained oscillations, lasting in excess of three hours, driven by photoelectrons accelerated by the Stanford Mark III radiofrequency linac. A LaB6 cathode, irradiated by a tripled Nd: Yag mode-locked drive laser was the

Mark Curtin; Glenn Bennett; Robert Burke; Anup Bhowmik; Phillip Metty; Stephen Benson; J. M. J. Madey

1990-01-01

419

Canadian Micro-Mineral Association: ALKALI - NUTS  

NSDL National Science Digital Library

This website, created by the Canadian Micro-Mineral Association, furnishes information on the minerals and environments near Mont Saint-Hilaire (MSH) in Quebec, Canada. Students and educators can discover the physical characteristics, fluorescence, and the distribution and rarity of the hundreds of species of minerals found around MSH. Each description includes helpful images of the amazing minerals and environments. Users can learn about the two classification systems: Dana and Strunz. The site presents MSH-related current news, articles, and announcements. Users can also discover the meaning and origin of the term, ALKALI-NUTS.

420

Alkali solution treatment on sandstone cores  

E-print Network

' or 12 hours and then the cores were dried in an oven maintained at 212 F to remove any 0 remaining water or solvent. The dried samples were weighed and the physical dimensions were measured with a caliper. Each core was placed in a desiccator...ALKALI SOLUTION TREATMENT ON SANDSTONE CORES A Thesis by S UK J IN LEE Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE May 1978 Major Subject: Petroleum...

Lee, Suk Jin

1978-01-01

421

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

SciTech Connect

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW{sub 12}O{sub 40}]{sub 2}[Cu{sub 2}(Phen){sub 4}Cl](H{sub 2}4, 4 Prime -bpy){sub 4}{center_dot}H{sub 3}O{center_dot}5H{sub 2}O (1) and [HPW{sub 12}O{sub 40}][Cd{sub 2}(Phen){sub 4}Cl{sub 2}](4, 4 Prime -bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW{sub 12}O{sub 40}]{sup 5-}, metal halide clusters [Cu{sub 2}(Phen){sub 4}Cl]{sup +}and 4, 4 Prime -bpy ligands, while compound 2 is constructed from [PW{sub 12}O{sub 40}]{sup 3-}, metal halide cluster [Cd{sub 2}(Phen){sub 4}Cl{sub 2}]{sup 2+} and 4, 4 Prime -bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. - Graphical Abstract: Two new compounds have been synthesized and characterized. Structure analyses revealed that the two compounds are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Highlights: Black-Right-Pointing-Pointer First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Two different kinds of metal halide clusters. Black-Right-Pointing-Pointer Supramolecular structures based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Hybridization of three different of building blocks.

Wang Lamei; Fan Yong; Wang Yan; Xiao Lina; Hu Yangyang; Peng Yu; Wang Tiegang; Gao Zhongmin; Zheng Dafang [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Cui Xiaobing, E-mail: cuixb@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Xu Jiqing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China)

2012-07-15

422

Mild Palladium-Catalyzed Cyanation of (Hetero)aryl Halides and Triflates in Aqueous Media.  

PubMed

A mild, efficient, and low-temperature palladium-catalyzed cyanation of (hetero)aryl halides and triflates is reported. Previous palladium-catalyzed cyanations of (hetero)aryl halides have required higher temperatures to achieve good catalytic activity. This current reaction allows the cyanation of a general scope of (hetero)aryl halides and triflates at 2-5 mol % catalyst loadings with temperatures ranging from rt to 40 °C. This mild method was applied to the synthesis of lersivirine, a reverse transcriptase inhibitor. PMID:25555140

Cohen, Daniel T; Buchwald, Stephen L

2015-01-16

423

Vaporisation and thermal decomposition of dialkylimidazolium halide ion ionic liquids.  

PubMed

Vaporisation and liquid phase thermal decomposition, TD, of two halide ion ionic liquids, 1-octyl-3-methylimidazolium chloride, [C8C1Im]Cl, and 1-octyl-3-methylimidazolium iodide, [C8C1Im]I, are investigated using temperature programmed desorption (TPD) line of sight mass spectrometry (LOSMS) at ultra-high vacuum (UHV). The ability to use MS to distinguish between vaporisation and TD allows the thermodynamics/kinetics of both vaporisation and TD to be investigated within the same experiments. Vaporisation of both halide ion ionic liquids is demonstrated. For both [C8C1Im]Cl and [C8C1Im]I the vapour is shown to be composed of neutral ion pairs (NIPs). The enthalpy of vaporisation at temperature T, ?vapHT, was experimentally determined as ?vapH455 = 151 ± 10 kJ mol(-1) for [C8C1Im]Cl and ?vapH480 = 149 ± 8 kJ mol(-1) for [C8C1Im]I. Extrapolation of ?vapHT to the reference temperature, 298 K, gave ?vapH298 = 166 ± 10 kJ mol(-1) for [C8C1Im]Cl and ?vapH298 = 167 ± 8 kJ mol(-1) for [C8C1Im]I, higher than most ?vapH298 values measured to date for other [C8C1Im](+)-containing ionic liquids. In addition, predictions of ?vapH298 for other halide ion ionic liquids are made. Liquid phase TD is shown to proceed via nucleophilic substitution to give two sets of products: 1-octylimidazole and methylhalide, and 1-methylimidazole and 1-octylhalide. The activation energy of TD at a temperature T, Ea,TD,T, is measured for the nucleophilic substitution of [C8C1Im]I to give methyliodide; Ea,TD,480 = 136 ± 15 kJ mol(-1). Ea,TD,T is measured for the nucleophilic substitution of [C8C1Im]Cl to give methylchloride; Ea,TD,455 = 132 ± 10 kJ mol(-1). The fact that ?vapHT and Ea,TD,T are the same (within error) for both ionic liquids is commented upon, and conclusions are drawn as to the thermal stability of these ionic liquids. PMID:24105256

Lovelock, Kevin R J; Armstrong, James P; Licence, Peter; Jones, Robert G

2014-01-28

424

Recovery of alkali metal constituents from catalytic coal conversion residues  

DOEpatents

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 (46, 53, 61, 69) 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 (63) to precipitate silicon constituents, the pH of the resultant solution is increased (81), preferably to a value in the range between about 12.5 and about 15.0, and the solution of increased pH is evaporated (84) to increase the alkali metal concentration. The concentrated aqueous solution is then recycled to the conversion process (86, 18, 17) where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst.

Soung, Wen Y. (Houston, TX)

1984-01-01

425

Alkali Activated Geopolymeric Binder Using Tungsten Mine Waste: Preliminary Investigation  

Microsoft Academic Search

This paper reports preliminary results of a PhD research project related to the development of an alkali- activated geopolymeric binder using mineral waste mud from the Portuguese tungsten mine Panasqueira which is still operating. Mineralogical analysis indicates that the waste mud is compose mainly of muscovite and quartz with a high content of iron and alkali metals. Results of the

F. Pacheco-Torgal; J. P. Castro-Gomes; S. Jalali

426

The effect of alkali charge on Eucalyptus spp. kraft pulping  

Microsoft Academic Search

The objective of this study was to evaluate the behavior of the pulping process in industrial Eucalyptus spp chips under different alkali charges. The alkali charge applied varied between 10 and 20%, at 1% intervals. The parameters analyzed were: total yield, screened yield, kappa number, pH, viscosity and hexenuronic acids content. For all these parameters variations in the results were

Gabriela Monnerat; Carvalho Bassa; Francismara A. Sanches Duarte; Vera M. Sacon

427

Self-discharge in bimetallic cells containing alkali metal  

NASA Technical Reports Server (NTRS)

Theoretical analysis of thermally regenerative bimetallic cells with alkali metal anodes shows a relation between the current drawn and the rate of discharge under open-circuit conditions. The self-discharge rate of the cell is due to the dissolution and ionization of alkali metal atoms in the fused-salt electrolyte

Foster, M. S.; Hesson, J. C.; Shimotake, H.

1969-01-01

428

Intermetallic generators of alkali metal with a seal  

Microsoft Academic Search

A design of an alkali metal generator with a working substance in the form of intermetallic compound AnMem the surface of which is covered by a protective layer Me (A — alkali metal, Me — an element, the vapour pressure of which under the deposition temperatures is ?- 108 and more times lower than the vapour pressure of the component

KA Chuntonov; VV Mansurov

1996-01-01

429

Method of assembling and sealing an alkali metal battery  

Microsoft Academic Search

A method of initially assembling and then subsequently hermetically sealing a container portion of an alkali metal battery to a ceramic portion of such a battery is disclosed. Sealing surfaces are formed respectively on a container portion and a ceramic portion of an alkali metal battery. These sealing surfaces are brought into juxtaposition and a material is interposed there between.

P. E. Elkins; J. E. Bell; R. A. Harlow; G. G. Chase

1983-01-01

430

Method of assembling and sealing an alkali metal battery  

Microsoft Academic Search

A method of initially assembling and then subsequently hermetically sealing a container portion of an alkali metal battery to a ceramic portion of such a battery is disclosed. Sealing surfaces are formed respectively on a container portion and a ceramic portion of an alkali metal battery. These sealing surfaces are brought into juxtaposition and a material is interposed therebetween. This

Perry E. Elkins; Jerry E. Bell; Richard A. Harlow; Gordon G. Chase

1983-01-01

431

Application of inorganic membranes in the alkali recovery process  

Microsoft Academic Search

In the mills with wheat straw as raw material in China, the high silica content of raw material resulted in a low ratio of alkali recovery and high maintenance cost for equipment. However, till now, little progress has been made on removal of silica in the alkali recovery process of wheat straw pulping. Many researchers have investigated the feasibility of

Guangli Liu; Yangsheng Liu; Hanchang Shi; Yi Qian

2004-01-01

432

Venus: Halide cloud condensation and volatile element inventories  

NASA Technical Reports Server (NTRS)

Several Venus cloud condensates, including A12C16 as well as halides, oxides and sulfides of arsenic and antimony, are assessed for their thermodynamic and geochemical plausibility. Aluminum chloride can confidently be ruled out, and condensation of arsenic sulfides on the surface will cause arsenic compounds to be too rare to produce the observed clouds. Antimony may conceivably be sufficiently volatile, but the expected molecular form is gaseous SbS, not the chloride. Arsenic and antimony compounds in the atmosphere will be regulated at very low levels by sulfide precipitation, irrespective of the planetary inventory of As and Sb. Thus the arguments for a volatile-deficient origin for Venus based on the depletion of water and mercury (relative to Earth) cannot be tested by a search for atmospheric arsenic or antimony.

Lewis, J. S.; Fegley, B., Jr.

1982-01-01

433

Electric field effects on alanine tripeptide in sodium halide solutions.  

PubMed

Abstract The electric field effects on conformational properties of trialanine in different halide solutions were explored with long-scale molecular dynamics simulations. NaF, NaCl, NaBr and NaI solutions of low (0.2?M) and high (2?M) concentrations were exposed to a constant electric field of 1000?V/m. Generally, the electric field does not disturb trialanine's structure. Large structural changes appear only in the case of the supersaturated 2.0?M NaF solution containing NaF crystals. Although the electric field affects in a complex way, all the ions-water-peptide interactions, it predominantly affects the electroselectivity effect, which describes specific interactions such as the ion-pair formation. PMID:25006865

Astrakas, Loukas G; Gousias, Christos; Tzaphlidou, Margaret

2014-07-01

434

Interactions between halide anions and a molecular hydrophobic interface.  

PubMed

Interactions between halide ions (fluoride and iodide) and t-butyl alcohol (TBA) dissolved in water are probed using a recently developed hydration-shell spectroscopic technique and theoretical cluster and liquid calculations. High ignal-to-noise Raman spectroscopic measurements are combined with multivariate curve resolution (Raman-MCR) to reveal that while there is little interaction between aqueous fluoride ions and TBA, iodide ions break down the tetrahedral hydration-shell structure of TBA and produce a red-shift in its CH stretch frequency, in good agreement with the theoretical effective fragment potential (EFP) molecular dynamics simulations and hybrid quantum/EFP frequency calculations. The results imply that there is a significantly larger probability of finding iodide than fluoride in the first hydration shell of TBA, although the local iodide concentration is apparently not as high as in the surrounding bulk aqueous NaI solution. PMID:23795504

Rankin, Blake M; Hands, Michael D; Wilcox, David S; Fega, K Rebecca; Slipchenko, Lyudmila V; Ben-Amotz, Dor

2013-01-01

435

Halide and nitrite recognizing hexanuclear metallacycle copper(II) pyrazolates.  

PubMed

Halide-centered hexanuclear, anionic copper(II) pyrazolate complexes [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)X](-), X = Cl, Br, I are isolated in a good yield from the redox reaction of the trinuclear copper(I) pyrazolate complex [?-Cu(3)((3,5-CF(3))(2)pz)(3)] with a halide source such as PPh(3)AuCl or [Bu(4)N]X, X = Cl, Br, or I, in air. X-ray structures of the anion-centered hexanuclear complexes show that the six copper atoms are bridged by bis(3,5-trifluoromethyl)pyrazolate and hydroxyl ligands above and below the six copper atom plane. The anions are located at the center of the cavity and weakly bound to the six copper atoms in a ?(6)-arrangement, Cu-X = ~3.1 Å. A nitrite-centered hexanuclear copper(II) pyrazolate complex [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))](-) was obtained when a solution of [PPN]NO(2) in CH(3)CN was added dropwise to the trinuclear copper(I) pyrazolate complex [?-Cu(3)((3,5-CF(3))(2)pz)(3)] dissolved in CH(3)CN, in air. Blue crystals are produced by slow evaporation of the acetonitrile solvent. The X-ray structure of [PPN][trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))] complex shows the nitrite anion sits in the hexanuclear cavity and is perpendicular to the copper plane with a O-N-O angle of 118.3(7)°. The (19)F and (1)H NMR of the pyrazolate ring atoms are sensitive to the anion present in the ring. Anion exchange of the NO(2)(-) by Cl(-) can be observed easily by (1)H NMR. PMID:21190383

Mohamed, Ahmed A; Ricci, Simone; Burini, Alfredo; Galassi, Rossana; Santini, Carlo; Chiarella, Gina M; Melgarejo, Doris Y; Fackler, John P

2011-02-01

436

Comparison of elemental boron and boron halide implants into silicon  

NASA Astrophysics Data System (ADS)

This paper investigates the electrical activation of boron halide molecular implants into silicon and compares them to boron implants at the same effective energy. The implanted species: B +, BF2+, BCl2+ and BBr2+ were implanted to doses of 2 × 10 14 and 1 × 10 15 B cm -2 the energy of the molecular implants was calculated to give an effective boron implant energy of 5 keV. Samples cut from the wafers were annealed for 30 s at temperatures ranging from 800 °C to 1100 °C. Hall effect measurements were used to compare and contrast the electrical activation of the boron between the different halide species and doses. It was found that molecular implants of BBr2+ and BCl2+ do not enhance the electrical activation of boron to the same extent that BF2+ implants do. The BBr2+ implants are only comparable with boron after annealing at high temperatures (above 1000 °C). The BF2+ implants show enhanced electrical activation with respect to boron for all the annealing temperatures and doses studied. Rutherford backscattering spectroscopy (RBS) of silicon implanted with BBr2+ to a dose of 1 × 10 15 boron atoms cm -2, shows that an amorphous region is created during the implantation. This region fully re-grows after annealing at 1100 °C; lower temperature anneals remove only part of the amorphous layer. RBS channelling shows that a fraction of the bromine takes up substitutional lattice sites upon implantation, and that this fraction increases as the samples are annealed at temperatures above 600 °C with 40% of the B being in substitutional sites after annealing at 1050 °C.

Sharp, J. A.; Gwilliam, R. M.; Sealy, B. J.; Jeynes, C.; Hamilton, J. J.; Kirkby, K. J.

2005-08-01

437

Bright light-emitting diodes based on organometal halide perovskite.  

PubMed

Solid-state light-emitting devices based on direct-bandgap semiconductors have, over the past two decades, been utilized as energy-efficient sources of lighting. However, fabrication of these devices typically relies on expensive high-temperature and high-vacuum processes, rendering them uneconomical for use in large-area displays. Here, we report high-brightness light-emitting diodes based on solution-processed organometal halide perovskites. We demonstrate electroluminescence in the near-infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15?nm layer of CH3NH3PbI(3-x)Cl(x) perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9'-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2?W?sr(-1)?m(-2) at a current density of 363?mA?cm(-2), with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. In our green light-emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364?cd?m(-2) at a current density of 123?mA?cm(-2), giving external and internal quantum efficiencies of 0.1% and 0.4%, respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour-tunable light emitters for low-cost display, lighting and optical communication applications. PMID:25086602

Tan, Zhi-Kuang; Moghaddam, Reza Saberi; Lai, May Ling; Docampo, Pablo; Higler, Ruben; Deschler, Felix; Price, Michael; Sadhanala, Aditya; Pazos, Luis M; Credgington, Dan; Hanusch, Fabian; Bein, Thomas; Snaith, Henry J; Friend, Richard H

2014-09-01

438

A study on the dynamic interfacial tension of acidic crude oil/alkali (alkali-polymer) systems--  

SciTech Connect

This paper describes the investigation of dynamic interfacial tension (DIFT) between the acidic Liao-He crude oil and two types of brine: a simple alkali system and a combined alkali-polymer system. It was found that interfacial tension (IFT) changed markedly with time and that the history of DIFT depended upon the concentration of alkali in the brine. The experimental results also showed that the IFT dropped dramatically as soon as the fresh oil contacted brine causing spontaneous emulsification to occur. The steady-state value of DIFT {gamma} st can be lower with the combined alkali-polymer system than with the simple alkali system. The results indicate that biopolymer is more effective than partially hydrolyzed polyacrylamide (PHPAM) for lowering {gamma} st and that Na{sub 2}Co{sub 1} causes a lower {gamma} st than NaOH in the combined alkali-polymer system. Optimized formulations containing Na{sub 2}CO{sub 3} added biopolymer can reduce {gamma} st by two orders of magnitude, and PHPAM can reduce {gamma} st by one order of magnitude. The interaction between alkali and polymer in the combined alkali-polymer system is discussed.

Huang, Y.; Yang, P.; Qin, T. (Research Institute of Petroleum Exploration and Development, Beijing (CN))

1989-01-01

439

Plasmon-enhanced photocathode for high brightness and high repetition rate x-ray sources  

SciTech Connect

High brightness electron sources are at the heart of anew generation of x-ray sources based on the Free ElectronLaser (FEL) as well as in Energy Recovery Linac (ERL) and Inverse Compton Scattering (ICS) sources.The source of electrons consists of a photoinjector, comprised of a laser-driven photocathode in a high gradient electric field produced by an rf cavity. The function of the rf cavity is to provide a field sufficient for acceleration of electrons to relativistic velocity over a small distance, thus minimizing effects of the space-charge. Even so, the dense electron beam required for high brightness suffers from a space charge field that chirps and reshapes the electron pulse increasing beam emittance and thus reducing the overall brightness. This emittance growth can be avoided if the initial distribution of electrons is pancake shaped, with a semicircular transverse intensity profile. In this case, the electron distribution develops under its space charge field from a pancake into a uniformly filled ellipsoidal beam. This condition, referred to as the blowout regime, requires ultrashort pulses less than 100 fs long and has been successfully demonstrated recently in a high gradient photoinjector.

Polyakov, Aleksandr; Senft, Christoph; Thompson, K. F.; Feng, J.; Cabrini, S.; Schuck, P. J.; Padmore, Howard; Peppernick, Samuel J.; Hess, Wayne P.

2013-02-11

440

Non-conventional photocathodes based on Cu thin films deposited on Y substrate by sputtering  

NASA Astrophysics Data System (ADS)

Copper (Cu) thin films were deposited on yttrium (Y) substrate by sputtering. During the deposition, a small central area of the Y substrate was shielded to avoid the film deposition and was successively used to study its photoemissive properties. This configuration has two advantages: the cathode presents (i) the quantum efficiency and the work function of Y and (ii) high electrical compatibility when inserted into the conventional radio-frequency gun built with Cu bulk. The photocathode was investigated by scanning electron microscopy to determine surface morphology. X-ray diffraction and atomic force microscopy studies were performed to compare the structure and surface properties of the deposited film. The measured electrical resistivity value of the Cu film was similar to that of high purity Cu bulk. Film to substrate adhesion was also evaluated using the Daimler-Benz Rockwell-C adhesion test method. Finally, the photoelectron performance in terms of quantum efficiency was obtained in a high vacuum photodiode cell before and after laser cleaning procedures. A comparison with the results obtained with a twin sample prepared by pulsed laser deposition is presented and discussed.

Perrone, A.; D'Elia, M.; Gontad, F.; Di Giulio, M.; Maruccio, G.; Cola, A.; Stankova, N. E.; Kovacheva, D. G.; Broitman, E.

2014-07-01

441

Software Tools for the Analysis of the Photocathode Response of Photomultiplier Vacuum Tubes  

E-print Network

The central institute of electronics (ZEA-2) in the Forschungszentrum Juelich (FZJ) has developed a system to scan the response of the photocathode of photomultiplier tubes (PMT). The PMT sits tight on a supporting structure, while a blue light emitting diode is moved along its surface by two stepper motors, spanning both the x and y coordinates. All the system is located in a light-tight box made by wood. A graphical software was developed in-situ to perform the scan operations under different configurations (e.g., the step size of the scan and the number of measurements per point). During each point measurement the current output generated in the vacuum photomultiplier is processed in sequence by a pre-amplifier (mainly to convert the current signal into a voltage signal), an amplifier, and by an ADC module (typically a CAEN N957). The information of the measurement is saved in files at the end of the scan. Recently, software based on the CERN ROOT and on the Qt libraries was developed to help the user anal...

Fabbri, R

2013-01-01

442

1 ms Pulse Beam Generation and Acceleration by Photocathode Radio Frequency Gun and Superconducting Accelerator  

NASA Astrophysics Data System (ADS)

We report the successful generation and acceleration of a 1-ms-long pulse and multibunch electron beam by a normal conducting photocathode RF gun and a super conducting accelerator at the KEK Superconducting Test Facility (STF). A 1.3 GHz normal conducting RF gun generates a 1 ms and 10 mA macropulse that fully satisfies the designed parameters. This is the longest macropulse generated by a normal conducting RF gun with a frequency of more than 1 GHz. A beam acceleration of up to 40 MeV was demonstrated with more than 60% of the designed average current. The accelerated beam properties were evaluated: the intensity and energy fluctuations were 3.8% and less than 0.08%, respectively. These beam properties are sufficient for the requirement of the STF operation including that in the quantum beam project, which is high-brightness-X-ray generation by inverse laser Compton scattering. The intensity fluctuation should be improved toward the International Linear Collider (ILC) for uniform acceleration.

Kuriki, Masao; Iijima, Hokuto; Hosoda, Seiichi; Watanabe, Ken; Hayano, Hitoshi; Urakawa, Junji; Isoyama, Goro; Kato, Ryukou; Kawase, Keigo; Kuramoto, Ayaka; Kashiwagi, Shigeru; Sakaue, Kazuyuki

2013-05-01

443

First demonstration of a free-electron laser driven by electrons from a laser irradiated photocathode  

NASA Astrophysics Data System (ADS)

Results are reported from the first observation of a free-electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne/Stanford FEL achieved sustained oscillations lasting over three hours and driven by photoelectrons accelerated by the Stanford Mark III radio-frequency linac. A LaB6 cathode, irradiated by a tripled Nd:YAG mode-locked drive laser, is the source of the photoelectrons. The drive laser, operating at 95.2 MHz, is phase-locked to the 30th subharmonic of the S-band linac. Peak currents in excess of 125 amps are observed and delivered to the Rocketdyne two-meter undulator, which is operated as a stand-alone oscillator. The electron beam has an energy spread of 0.8 percent (FWHM) at 38.5 MeV and an emittance, at the undulator, comparable to that observed for thermionic operation of the electron source. Small signal gain in excess of 150 percent is observed. Preliminary estimates of the electron beam brightness deliverable to the undulator range from 3.5 to 5.0 x 10 to the 11 amps/sq m.

Curtin, Mark; Bennett, Glenn; Burke, Robert; Benson, Stephen; Madey, J. M. J.

444

A low-voltage retarding-field Mott polarimeter for photocathode characterization  

SciTech Connect

Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2)×10?4, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1)×10?5. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type.

J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, T.J. Gay

2010-06-01

445

Stepwise Halide-Triggered Double and Triple Catenation of Self-Assembled Coordination Cages.  

PubMed

A simple self-assembled [Pd2 L4 ] coordination cage consisting of four carbazole-based ligands was found to dimerize into the interpenetrated double cage [3?X@Pd4 L8 ] upon the addition of 1.5 equivalents of halide anions (X=Cl(-) , Br(-) ). The halide anions serve as templates, as they are sandwiched by four Pd(II) cations and occupy the three pockets of the entangled cage structure. The subsequent addition of larger amounts of the same halide triggers another structural conversion, now yielding a triply catenated link structure in which each Pd(II) node is trans-coordinated by two pyridine donors and two halide ligands. This simple system demonstrates how molecular complexity can increase upon a gradual change of the relative concentrations of reaction partners that are able to serve different structural roles. PMID:25395277

Zhu, Rongmei; Lübben, Jens; Dittrich, Birger; Clever, Guido H

2014-11-13

446

10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2014 CFR

...purpose of controlling the ballast and putting the ballast in standby mode. Electronic ballast means a device that uses semiconductors as the primary means to control lamp starting and operation. Metal halide ballast means a ballast used to start...

2014-01-01

447

10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2013 CFR

...purpose of controlling the ballast and putting the ballast in standby mode. Electronic ballast means a device that uses semiconductors as the primary means to control lamp starting and operation. Metal halide ballast means a ballast used to start...

2013-01-01

448

10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.  

Code of Federal Regulations, 2012 CFR

...purpose of controlling the ballast and putting the ballast in standby mode. Electronic ballast means a device that uses semiconductors as the primary means to control lamp starting and operation. Metal halide ballast means a ballast used to start...

2012-01-01

449

Synthesis and characterization of cerium-doped lanthanum halide colloidal nanocrystals.  

E-print Network

??Cerium-doped bulk lanthanum halide compounds are attractive in the field of high-energy radiation detection due to their interesting properties that include efficient radiation absorption, highly… (more)

Sankar, Krishnaprasad

2009-01-01

450

Methods for synthesizing alane without the formation of adducts and free of halides  

DOEpatents

A process is provided to synthesize an alane without the formation of alane adducts as a precursor. The resulting product is a crystallized .alpha.-alane and is a highly stable product and is free of halides.

Zidan, Ragaiy; Knight, Douglas A; Dinh, Long V

2013-02-19

451

A combined metal-halide/metal flux synthetic route towards type-I clathrates: crystal structures and thermoelectric properties of A8Al8Si38 (A = K, Rb, and Cs).  

PubMed

Single-phase samples of the compounds K8Al8Si38 (1), Rb8Al8Si38 (2), and Cs7.9Al7.9Si38.1 (3) were obtained with high crystallinity and in good quantities by using a novel flux method with two different flux materials, such as Al and the respective alkali-metal halide salt (KBr, RbCl, and CsCl). This approach facilitates the removal of the product mixture from the container and also allows convenient extraction of the flux media due to the good solubility of the halide salts in water. The products were analyzed by means of single-crystal X-ray structure determination, powder X-ray and neutron diffraction experiments, (27)Al-MAS NMR spectroscopy measurements, quantum chemical calculations, as well as magnetic and transport measurements (thermal conductivity, electrical resistivity, and Seebeck coefficient). Due to the excellent quality of the neutron diffraction data, the difference between the nuclear scattering factors of silicon and aluminum atoms was sufficient to refine their mixed occupancy at specific sites. The role of variable-range hopping for the interpretation of the resistivity and the Seebeck coefficient is discussed. PMID:25267571

Baran, Volodymyr; Senyshyn, Anatoliy; Karttunen, Antti J; Fischer, Andreas; Scherer, Wolfgang; Raudaschl-Sieber, Gabriele; Fässler, Thomas F

2014-11-10

452

Unique properties of halide perovskites as possible origins of the superior solar cell performance.  

PubMed

Halide perovskites solar cells have the potential to exhibit higher energy conversion efficiencies with ultrathin films than conventional thin-film solar cells based on CdTe, CuInSe2 , and Cu2 ZnSnSe4 . The superior solar-cell performance of halide perovskites may originate from its high optical absorption, comparable electron and hole effective mass, and electrically clean defect properties, including point defects and grain boundaries. PMID:24827122

Yin, Wan-Jian; Shi, Tingting; Yan, Yanfa

2014-07-16

453

Elastic properties of alkali-feldspars  

NASA Astrophysics Data System (ADS)

New measurements of single crystal elastic moduli for a suite of the alkali feldspars are reported. In order to interpret Earth's seismic structure, knowledge of the elastic properties of constituent minerals is essential. The elasticity of feldspar minerals, despite being the most abundant phase in Earth's crust (estimated to be more than 60%), were previously poorly characterized. All prior seismic and petrologic studies have utilized 50-year-old results, of questionable quality, based on 1-bar measurements on pseudo-single crystals. Alkali-feldspars present a large experimental challenge associated with their structural complexity. In the K-end member (KAlSi3O8) the symmetry is governed by Al/Si ordering, in the Na-end member (NaAlSi3O8) the symmetry is governed by whether or not there is a displacive collapse of the framework independent of the Al/Si ordering. K-feldspars exhibit monoclinic (C2/m) symmetry (necessitating determination of 13 elastic moduli) if disordered and triclinic (C-1) symmetry (21 elastic moduli) if ordered. Exsolution of Na-rich and K-rich phases is ubiquitous in natural samples, making it difficult to find suitable single phase and untwinned samples for study. The small single domain samples selected for this study were previously characterized by x-ray diffraction and microprobe analysis to ensure adequate sample quality. Surface wave velocities were measured on oriented surfaces of natural and synthetic single crystals using impulsively stimulated light scattering. A surface corrugation with a spacing of about 2 microns was impulsively created by the overlap of 100 ps infrared light pulses. The time evolution of the stimulated standing elastic waves was detected by measuring the intensity of diffraction from the surface corrugation of a variably delayed probe pulse. This method allows accurate (better than 0.2%) determination of velocities on samples smaller than 100 microns. The combination of measured surface wave velocities and separately determined compressibilities, based on high-pressure x-ray studies, allowed determination of the full elastic tensor for alkali-feldspars as a function of composition and structure.

Waeselmann, N.; Brown, J.; Angel, R. J.; Ross, N.; Kaminsky, W.

2013-12-01

454

Alkali oxide-tantalum oxide and alkali oxide-niobium oxide ionic conductors  

NASA Technical Reports Server (NTRS)

A search was made for new cationic conducting phases in alkali-tantalate and niobate systems. The phase equilibrium diagrams were constructed for the six binary systems Nb2O5-LiNbO3, Nb2O5-NaNbO3, Nb2O5-KNbO3, Ta2O5-NaTaO3, Ta2O5-LiTaO3, and Ta2O5-KTaO3. Various other binary and ternary systems were also examined. Pellets of nineteen phases were evaluated (by the sponsoring agency) by dielectric loss measurements. Attempts were made to grow large crystals of eight different phases. The system Ta2O5-KTaO3 contains at least three phases which showed peaks in dielectric loss vs. temperature. All three contain structures related to the tungsten bronzes with alkali ions in non-stoichiometric crystallographic positions.

Roth, R. S.; Parker, H. S.; Brower, W. S.; Minor, D.

1974-01-01

455

Alkali elemental and potassium isotopic compositions of Semarkona chondrules  

USGS Publications Warehouse

We report measurements of K isotope ratios in 28 Semarkona chondrules with a wide range of petrologic types and bulk compositions as well as the compositions of CPX-mesostasis pairs in 17 type I Semarkona chondrules, including two chondrules with radial alkali zonation and 19 type II chondrules. Despite the wide range in K/Al ratios, no systematic variations in K isotopic compositions were found. Semarkona chondrules do not record a simple history of Rayleigh-type loss of K. Experimentally determined evaporation rates suggest that considerable alkali evaporation would have occurred during chondrule formation. Nevertheless, based on Na CPX-mesostasis distribution coefficients, the alkali contents of the cores of most chondrules in Semarkona were probably established at the time of final crystallization. However, Na CPX-mesostasis distribution coefficients also show that alkali zonation in type I Semarkona chondrules was produced by entry of alkalis after solidification, probably during parent body alteration. This alkali metasomatism may have gone to completion in some chondrules. Our preferred explanation for the lack of systematic isotopic enrichments, even in alkali depleted type I chondrule cores, is that they exchanged with the ambient gas as they cooled. ?? The Meteoritical Society, 2005.

Alexander, C.M. O'D.; Grossman, J.N.

2005-01-01

456

Observation of vapor pressure enhancement of rare-earth metal-halide salts in the temperature range relevant to metal-halide lamps  

SciTech Connect

Total vapor-phase densities of Dy in equilibrium with a DyI{sub 3}/InI condensate and Tm in equilibrium with a TmI{sub 3}/TlI condensate have been measured for temperatures between 900 K and 1400 K. The measurements show strong enhancements in rare-earth vapor densities compared to vapors in equilibrium with the pure rare-earth metal-halides. The measurements were made with x-ray induced fluorescence on the sector 1-ID beam line at the Advanced Photon Source. The temperature range and salt mixtures are relevant to the operation of metal-halide high-intensity discharge lamps.

Curry, J. J.; Henins, A.; Hardis, J. E. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Estupinan, E. G. [Osram Sylvania Inc., Beverly, Massachusetts 01915 (United States); Lapatovich, W. P. [Independent Consultant, 51 Pye Brook Lane, Boxford, Massachusetts 01921 (United States); Shastri, S. D. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2012-02-20

457

Influence of halide flux on the crystallinity, microstructure and thermoluminescence properties of CdSiO{sub 3}:Co{sup 2+} nanophosphor  

SciTech Connect

Graphical abstract: TL glow curves of CdSiO{sub 3}:Co{sup 2+} different alkali flux (inset without adding flux). Display Omitted Highlights: ? CdSiO{sub 3}:Co{sup 2+} (1–7 mol%) nanocrystalline phosphors synthesized by combustion route. ? Flux effect on thermoluminescence behavior of CdSiO{sub 3}:Co{sup 2+} reported for first time. ? Addition of 2 wt% of flux would drastically enhance the TL properties. ? Well resolved single glow peak at ?170 °C was recorded for all the samples. ? Among all the alkali flux, NaCl shows highest TL peak intensity. -- Abstract: CdSiO{sub 3}:Co{sup 2+} (1–7 mol %) nanophosphors have been prepared via solution combustion method with post calcination at 800 °C for 2 h for the first time. The formation of expected monoclinic phase was investigated by Powder X-ray diffraction (PXRD) measurements. The effect of different fluxes like NaF, NaCl, NH{sub 4}F and NH{sub 4}Cl on the crystallinity, phase and morphology of CdSiO{sub 3} was investigated in detail. The crystallinity of the samples can be greatly enhanced by using fluxes rather than increasing the calcination temperature. Scanning electronic micrograph (SEM) image shows that the powder morphologies are highly influenced by flux addition. The addition of 2 wt% of fluxes would drastically enhance the crystallinity when NaCl, NH{sub 4}F and NH{sub 4}Cl fluxes are used. A well resolved single thermoluminescent glow peak at ?170 °C was recorded for all the samples. Among all the halide fluxes, NaCl flux was found to be the potential one in enhancing the TL peak intensity along with crystallinity.

Manjunatha, C. [Department of Chemistry, M.S. Ramaiah Institute of Technology, Bangalore 560054 (India) [Department of Chemistry, M.S. Ramaiah Institute of Technology, Bangalore 560054 (India); Visvesvaraya Technological University, Belgaum, Karnataka 590018 (India); Department of Chemistry, R.V. College of Engineering, Bangalore 560059 (India); Nagabhushana, B.M., E-mail: bmnshan@yahoo.com [Department of Chemistry, M.S. Ramaiah Institute of Technology, Bangalore 560054 (India); Visvesvaraya Technological University, Belgaum, Karnataka 590018 (India); Sunitha, D.V.; Nagabhushana, H.; Sharma, S.C. [Prof. C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumkur 572103 (India)] [Prof. C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumkur 572103 (India); Chakradhar, R.P.S., E-mail: chakra72@physics.iisc.ernet.in [CSIR-National Aerospace Laboratories, Bangalore 560017 (India)] [CSIR-National Aerospace Laboratories, Bangalore 560017 (India)

2013-01-15

458

Structure and Chemistry in Halide Lead-Tellurite Glasses  

SciTech Connect

A series of TeO2-PbO glasses were fabricated with increasing fractions of mixed alkali, alkaline earth, and lanthanide chlorides. The glass and crystal structure was studied with Raman spectroscopy, nuclear magnetic resonance (NMR), X-ray diffraction, and electron microscopy. As the chloride fraction increased, the medium-range order in the glass decreased up to a critical point (~14 mass% of mixed chlorides), above which the glasses became phase-separated. Resulting phases are a TeO2/PbO-rich phase and a crystalline phase rich in alkali chlorides. The 125Te NMR indicates, contrary to previous studies, that Te site distribution did not change with increased concentrations of M+, M2+, and M3+ cations, but rather is controlled by the Te/Pb molar ratio. The 207Pb NMR shows that two Pb species exist and their relative concentration changes nearly linearly with addition of the mixed chlorides, indicating that the additives to the TeO2-PbO glass are accommodated by changing the Pb species. The 23Na and 35Cl NMR indicate that Na and Cl are distributed in the single-phase glass phase up to the critical point, and at higher concentrations partition to crystalline phases. Transmission electron microscopy shows that the sample at the critical point contains ~10 nm seed nuclei that increase in size and concentration with exposure to the electron beam.

McCloy, John S.; Riley, Brian J.; Lipton, Andrew S.; Windisch, Charles F.; Washton, Nancy M.; Olszta, Matthew J.; Rodriguez, Carmen P.

2013-02-11

459

Heat pipes containing alkali metal working fluid  

NASA Technical Reports Server (NTRS)

A technique for improving high temperature evaporation-condensation heat-transfer devices which have important and unique advantage in terrestrial and space energy processing is described. The device is in the form of a heat pipe comprising a sealed container or envelope which contains a capillary wick. The temperature of one end of the heat pipe is raised by the input of heat from an external heat source which is extremely hot and corrosive. A working fluid of a corrosive alkali metal, such as lithium, sodium, or potassium transfers this heat to a heat receiver remote from the heat source. The container and wick are fabricated from a superalloy containing a small percentage of a corrosion inhibiting or gettering element. Lanthanum, scandium, yttrium, thorium, and hafnium are utilized as the alloying metal.

Morris, J. F. (inventor)

1981-01-01

460

Cells having cathodes derived from alkali salts of chromium dichalcogenides  

SciTech Connect

The present invention is directed to rechargeable current-producing cell comprising: (a) an anode made by an alkali or an earth-alkali metal; (b) a non-aqueous electrolyte solution; (c) a cathode formed by alkali metal salts of chromium dichalcogenides of general formula M' /SUB x/ M'' /SUB y/ CrB/sub 2/, wherein M' and M'' are metals of group I A of the Periodic Table, B is a chalcogen and x and y have values between zero and one.

Moshtev, R.; Manev, V.; Nasalevska, A.; Pistoia, G.

1983-09-20

461

Planting six tree species on soda-saline-alkali soil  

Microsoft Academic Search

Populus simonigra, Salix matsudana, Ulmus pumila, Populus nigra, Acer negundo, Fraxinus mandshurica. Tamarix chinensis, Hippophae\\u000a rhammoldes, Syriga onlata were planted on the soda-saline-alkali. The soil had pH 8.5–9.6, salinity 0.1%–0.3%, sodiumionized\\u000a ratio 16%–51% and normality ratio of saline base Na+\\/(Ca+++Mg++)>4. Populus simonigra grows very well on the all kinds of soda-saline-alkali soils except on the alkali sport with the worst

Zhang Yujiang; Liu Peng; Yang Dewei; Ma Chenghui; Liu Gang

1998-01-01

462

Electrochemical cell utilizing molten alkali metal electrode-reactant  

DOEpatents

An improved electrochemical cell comprising an additive-modified molten alkali metal electrode-reactant and/or electrolyte is disclosed. Various electrochemical cells employing a molten alkali metal, e.g., sodium, electrode in contact with a cationically conductive ceramic membrane experience a lower resistance and a lower temperature coefficient of resistance whenever small amounts of selenium are present at the interface of the electrolyte and the molten alkali metal. Further, cells having small amounts of selenium present at the electrolyte-molten metal interface exhibit less degradation of the electrolyte under long term cycling conditions.

Virkar, Anil V. (Sandy, UT); Miller, Gerald R. (Salt Lake City, UT)

1983-11-04

463

Increasing Class C fly ash reduces alkali silica reactivity  

SciTech Connect

Contrary to earlier studies, it has been found that incremental additions of Class C fly ash do reduce alkali silica reactivity (ASR), in highly reactive, high alkali concrete mixes. AST can be further reduced by substituting 5% metakaolin or silica fume for the aggregate in concrete mixes with high (more than 30%) Class C fly ash substitution. The paper reports results of studies using Class C fly ash from the Labadie Station plant in Missouri which typically has between 1.3 and 1.45% available alkalis by ASTM C311. 7 figs.

Hicks, J.K. [Mineral Resources Technologies, Inc. (United States)

2007-07-01