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Sample records for hot atom chemical

  1. Molecular Beam Studies of Hot Atom Chemical Reactions: Reactive Scattering of Energetic Deuterium Atoms

    DOE R&D Accomplishments Database

    Continetti, R. E.; Balko, B. A.; Lee, Y. T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H{sub 2} -> DH + H and the substitution reaction D + C{sub 2}H{sub 2} -> C{sub 2}HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible.

  2. Hot atom chemistry and radiopharmaceuticals

    SciTech Connect

    Krohn, Kenneth A.; Moerlein, Stephen M.; Link, Jeanne M.; Welch, Michael J.

    2012-12-19

    The chemical products made in a cyclotron target are a combined result of the chemical effects of the nuclear transformation that made the radioactive atom and the bulk radiolysis in the target. This review uses some well-known examples to understand how hot atom chemistry explains the primary products from a nuclear reaction and then how radiation chemistry is exploited to set up the optimal product for radiosynthesis. It also addresses the chemical effects of nuclear decay. There are important principles that are common to hot atom chemistry and radiopharmaceutical chemistry. Both emphasize short-lived radionuclides and manipulation of high specific activity nuclides. Furthermore, they both rely on radiochromatographic separation for identification of no-carrieradded products.

  3. Hot atoms in cosmic chemistry.

    PubMed

    Rossler, K; Jung, H J; Nebeling, B

    1984-01-01

    High energy chemical reactions and atom molecule interactions might be important for cosmic chemistry with respect to the accelerated species in solar wind, cosmic rays, colliding gas and dust clouds and secondary knock-on particles in solids. "Hot" atoms with energies ranging from a few eV to some MeV can be generated via nuclear reactions and consequent recoil processes. The chemical fate of the radioactive atoms can be followed by radiochemical methods (radio GC or HPLC). Hot atom chemistry may serve for laboratory simulation of the reactions of energetic species with gaseous or solid interstellar matter. Due to the effective measurement of 10(8)-10(10) atoms only it covers a low to medium dose regime and may add to the studies of ion implantation which due to the optical methods applied are necessarily in the high dose regime. Experimental results are given for the systems: C/H2O (gas), C/H2O (solid, 77 K), N/CH4 (solid, 77K) and C/NH3 (solid, 77 K). Nuclear reactions used for the generation of 2 to 3 MeV atoms are: N(p,alpha) 11C, 16O(p,alpha pn) 11C and 12C(d,n) 13N with 8 to 45 MeV protons or deuterons from a cyclotron. Typical reactions products are: CO, CO2, CH4, CH2O, CH3OH, HCOOH, NH3, CH3NH2, cyanamide, formamidine, guanidine etc. Products of hot reactions in solids are more complex than in corresponding gaseous systems, which underlines the importance of solid state reactions for the build-up of precursors for biomolecules in space. As one of the major mechanisms for product formation, the simultaneous or fast consecutive reactions of a hot carbon with two target molecules (reaction complex) is discussed.

  4. Characterization of atomic-layer MoS2 synthesized using a hot filament chemical vapor deposition method

    NASA Astrophysics Data System (ADS)

    Ying-Zi, Peng; Yang, Song; Xiao-Qiang, Xie; Yuan, Li; Zheng-Hong, Qian; Ru, Bai

    2016-05-01

    Atomic-layer MoS2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy (AFM), x-ray diffraction (XRD), high-resolution transition electron microscopy (HRTEM), photoluminescence (PL), and x-ray photoelectron spectroscopy (XPS) characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation (002). The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasi-honeycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS2. The stoichiometric mole ratio of S/Mo is about 2.0–2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS2 under our experimental conditions. Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant Nos. LY16F040003 and LY16A040007) and the National Natural Science Foundation of China (Grant Nos. 51401069 and 11574067).

  5. Semiempirical hot atom theory. I - Initialization and application

    NASA Technical Reports Server (NTRS)

    Aronowitz, S.; Chang, S.; Scattergood, T.

    1981-01-01

    A semiempirical approach to the modeling of the kinetics of reaction systems containing both hot and nonhot atoms is proposed. The approach is based on the probabilistic kinetic theory of hot-atom reactions formulated by Wolfgang (1963), with transmission probabilities estimated for a rectangular potential barrier for hot-atom and nonhot-atom reactions. A computational scheme for determining product concentrations following hot and nonhot reactions in a system containing photolytically produced hot atoms is then applied to the DBr + CH4 and HBr + CD4 hot hydrogen atom systems studied by Martin and Willard (1964), and good agreement is obtained between theoretical and experimental results.

  6. Liquid-metal atomization for hot working preforms

    NASA Technical Reports Server (NTRS)

    Grant, N. J.; Pelloux, R. M.

    1974-01-01

    Rapid quenching of a liquid metal by atomization or splat cooling overcomes the major limitation of most solidification processes, namely, the segregation of alloying elements, impurities, and constituent phases. The cooling rates of different atomizing processes are related to the dendrite arm spacings and to the microstructure of the atomized powders. The increased solubility limits and the formation of metastable compounds in splat-cooled alloys are discussed. Consolidation of the powders by hot isostatic compaction, hot extrusion, or hot forging and rolling processes yields billets with properties equivalent to or better than those of the wrought alloys. The application of this powder processing technology to high-performance alloys is reviewed.

  7. Bichromatic electromagnetically induced transparency in hot atomic vapors

    NASA Astrophysics Data System (ADS)

    Yan, Hui; Liao, Kai-Yu; Li, Jian-Feng; Du, Yan-Xiong; Zhang, Zhi-Ming; Zhu, Shi-Liang

    2013-05-01

    In a three-level Λ atomic system coupled by a symmetrical bichromatic laser field, a weak probe laser field shows multiple absorption peaks in the case of cold atoms. As for hot atomic vapors, we experimentally observe double symmetrical electromagnetically induced transparency windows instead of multiple absorption peaks. This abnormal spectrum is due to the Doppler averaging. The electromagnetically induced transparency windows observed here are useful for obtaining slow photons at different frequencies.

  8. TOWARD CHEMICAL CONSTRAINTS ON HOT JUPITER MIGRATION

    SciTech Connect

    Madhusudhan, Nikku; Amin, Mustafa A.; Kennedy, Grant M.

    2014-10-10

    The origin of hot Jupiters—gas giant exoplanets orbiting very close to their host stars—is a long-standing puzzle. Planet formation theories suggest that such planets are unlikely to have formed in situ but instead may have formed at large orbital separations beyond the snow line and migrated inward to their present orbits. Two competing hypotheses suggest that the planets migrated either through interaction with the protoplanetary disk during their formation, or by disk-free mechanisms such as gravitational interactions with a third body. Observations of eccentricities and spin-orbit misalignments of hot Jupiter systems have been unable to differentiate between the two hypotheses. In the present work, we suggest that chemical depletions in hot Jupiter atmospheres might be able to constrain their migration mechanisms. We find that sub-solar carbon and oxygen abundances in Jovian-mass hot Jupiters around Sun-like stars are hard to explain by disk migration. Instead, such abundances are more readily explained by giant planets forming at large orbital separations, either by core accretion or gravitational instability, and migrating to close-in orbits via disk-free mechanisms involving dynamical encounters. Such planets also contain solar or super-solar C/O ratios. On the contrary, hot Jupiters with super-solar O and C abundances can be explained by a variety of formation-migration pathways which, however, lead to solar or sub-solar C/O ratios. Current estimates of low oxygen abundances in hot Jupiter atmospheres may be indicative of disk-free migration mechanisms. We discuss open questions in this area which future studies will need to investigate.

  9. Cold Light from Hot Atoms and Molecules

    SciTech Connect

    Lister, Graeme; Curry, John J.

    2011-05-11

    The introduction of rare earth atoms and molecules into lighting discharges led to great advances in efficacy of these lamps. Atoms such as Dy, Ho and Ce provide excellent radiation sources for lighting applications, with rich visible spectra, such that a suitable combination of these elements can provide high quality white light. Rare earth molecules have also proved important in enhancing the radiation spectrum from phosphors in fluorescent lamps. This paper reviews some of the current aspects of lighting research, particularly rare earth chemistry and radiation, and the associated fundamental atomic and molecular data.

  10. Chemical uncertainties in modeling hot Jupiters atmospheres

    NASA Astrophysics Data System (ADS)

    Hebrard, Eric; Domagal-Goldman, Shawn

    2015-11-01

    Most predictions and interpretations of observations in beyond our Solar System have occurred through the use of 1D photo-thermo-chemical models. Their predicted atmospheric compositions are highly dependent on model parameters. Chemical reactions are based on empirical parameters that must be known at temperatures ranging from 100 K to above 2500 K and at pressures from millibars to hundreds of bars. Obtained from experiments, calculations and educated-guessed estimations, these parameters are always evaluated with substantial uncertainties. However, although of practical use, few models of exoplanetary atmospheres have considered these underlying chemical uncertainties and their consequences. Recent progress has been made recently that allow us to (1) evaluate the accuracy and precision of 1D models of planetary atmospheres, with quantifiable uncertainties on their predictions for the atmospheric composition and associated spectral features, (2) identify the ‘key parameters’ that contribute the most to the models predictivity and should therefore require further experimental or theoretical analysis, (3) reduce and optimize complex chemical networks for their inclusion in multidimensional atmospheric models.First, a global sampling approach based on low discrepancy sequences has been applied in order to propose error bars on simulations of the atmospheres HD 209458b and HD 189733b, using a detailed kinetic model derived from applied combustion models that was methodically validated over a range of temperatures and pressures typical for these hot Jupiters. A two-parameters temperature-dependent uncertainty factor has been assigned to each considered rate constant. Second, a global sensitivity approach based on high dimensional model representations (HDMR) has been applied in order to identify those reactions which make the largest contributions to the overall uncertainty of the simulated results. The HDMR analysis has been restricted to the most important

  11. Hot hydrogen atom reactions moderated by H2 and He

    NASA Technical Reports Server (NTRS)

    Aronowitz, S.; Scattergood, T.; Flores, J.; Chang, S.

    1986-01-01

    Photolysis experiments were performed on the H2-CD4-NH3 and He-CD4-NH3 systems. The photolysis (1849 A) involved only NH3. Mixtures of H2:CD4:NH3 included all combinations of the ratios (200,400,800):(10,20,40):4. Two He:CD4:NH3 mixtures were examined where the ratios equalled the combinations 100:(10,20):4. Abstraction of a D from CD4 by the photolytically produced hot hydrogen from ammonia was monitored by mass spectrometric determination of HD. Both experiment and semiempirical hot-atom theory show that H2 is a very poor thermalizer of hot hydrogens with excess kinetic energy of about 2 eV. Applications of the hard-sphere collision model to the H2-CD4-NH3 system resulted in predicted ratios of net HD production to NH3 decomposition that were two orders of magnitude smaller than the experimental ratios. On the other hand, helium is found to be a very efficient thermalizer; here, the classical model yields reasonable agreement with experiments. Application of a semiempirical hot-atom program gave quantitative agreement with experiment for either system.

  12. On the role of 'hot' atoms in plasma-assisted ignition.

    PubMed

    Starikovskiy, Andrey Yu

    2015-08-13

    This paper discusses the processes leading to the formation of 'hot' atoms and radicals possessing excessive translational energy in high-voltage NS pulse discharges. It is shown that the formation of such 'hot' atoms occurs efficiently both in the dissociation of molecules by direct electron impact, and in the collisional quenching of electronically excited states. Depending on the magnitude of the reduced electric field in the discharge, reactions of these 'hot' atoms increase the initial concentration of radicals in the discharge afterglow two to three times when compared with the values calculated without effects of translational non-equilibrium. The role of thermally non-equilibrium excitation has been demonstrated in the formation of the initial distribution of the chemically active components in the mixture and its influence on the kinetics of ignition initiation at low and high temperatures. It was found that in undiluted mixtures the presence of 'hot' atoms can significantly decrease an ignition threshold and accelerate a low-temperature oxidation.

  13. Exploring Chemical Equilibrium in Hot Jovians

    NASA Astrophysics Data System (ADS)

    Blumenthal, Sarah; Harrington, Joseph; Mandell, Avi; Hébrard, Eric; Venot, Olivia; Cubillos, Patricio; Blecic, Jasmina; Challener, Ryan

    2016-01-01

    It has been established that equilibrium chemistry is usually achieved deep in the atmosphere of hot Jovians where timescales are short (Line and Yung 2013). Thus, equilibrium chemistry has been used as a starting point (setting initial conditions) for evaluating disequilibrium processes. We explore parameters of setting these initial conditions including departures from solar metallicity, the number of species allowed in a system, the types of species allowed in a system, and different thermodynamic libraries in an attempt to create a standard for evaluating equilibrium chemistry. NASA's open source code Chemical Equilibrium and Applications (CEA) is used to calculate model planet abundances by varying the metallicity, in the pressure regime 0.1 to 1 bar. These results are compared to a variety of exoplanets(Teq between 600 and 2100K) qualitatively by color maps of the dayside with different temperature redistributions. Additionally, CEA (with an up-dated thermodynamic library) is compared with the thermochemical model presented in Venotet al. (2012) for HD 209458b and HD 189733b. This same analysis is then applied to the cooler planet HD 97658b. Spectra are generated and we compare both models' outputs using the open source codetransit (https://github.com/exosports/transit) using the opacities of 15 molecules. We make the updated CEA thermodyanamic library and supporting Python scripts to do the CEA analyses available open source. Thiswork was supported by NASA Planetary Atmospheres grant NNX12AI69G.

  14. Hot-atom synthesis of organic compounds on Jupiter

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    Results of recent laboratory 'simulations' of photochemical processes on Jupiter are combined with available data on mixing rates and exposure times in the Jovian atmosphere to give quantitative predictions of the rate at which hot-atom reactions produce organic molecules. It is shown that abstraction reactions on methane by hot H atoms from solar UV photolysis of H2S will produce no more than 4 times 10 to the -17th power g/sq cm/sec for a steady-state mole fraction of total organics of approximately 10 to the -16th power. This is roughly 10 to the 7th power times less than the limit of detection of the most sensitive gas analysis experiments ever flown on a spacecraft. By far the most common organic molecule produced by this mechanism is CH3SH, methyl mercaptan, which is produced at a rate at least 600 times smaller than the rate of production of ethane by direct photolysis of CH4 at high altitudes.

  15. Novel Infrared Dynamics of Cold Atoms on Hot Graphene

    NASA Astrophysics Data System (ADS)

    Sengupta, Sanghita; Kotov, Valeri; Clougherty, Dennis

    The low-energy dynamics of cold atoms interacting with macroscopic graphene membranes exhibits severe infrared divergences when treated perturbatively. These infrared problems are even more pronounced at finite temperature due to the (infinitely) many flexural phonons excited in graphene. We have devised a technique to take account (resummation) of such processes in the spirit of the well-known exact solution of the independent boson model. Remarkably, there is also similarity to the infrared problems and their treatment (via the Bloch-Nordsieck scheme) in finite temperature ``hot'' quantum electrodynamics and chromodynamics due to the long-range, unscreened nature of gauge interactions. The method takes into account correctly the strong damping provided by the many emitted phonons at finite temperature. In our case, the inverse membrane size plays the role of an effective low-energy scale, and, unlike the above mentioned field theories, there remains an unusual, highly nontrivial dependence on that scale due to the 2D nature of the problem. We present detailed results for the sticking (atomic damping rate) rate of cold atomic hydrogen as a function of the membrane temperature and size. We find that the rate is very strongly dependent on both quantities.

  16. Extended Characterization of Chemical Processes in Hot Cells Using Environmental Swipe Samples

    SciTech Connect

    Olsen, Khris B.; Mitroshkov, Alexandre V.; Thomas, M-L; Lepel, Elwood A.; Brunson, Ronald R.; Ladd-Lively, Jennifer

    2012-09-15

    Environmental sampling is used extensively by the International Atomic Energy Agency (IAEA) for verification of information from State declarations or a facility’s design regarding nuclear activities occurring within the country or a specific facility. Environmental sampling of hot cells within a facility under safeguards is conducted using 10.2 cm x 10.2 cm cotton swipe material or cellulose swipes. Traditional target analytes used by the IAEA to verify operations within a facility include a select list of gamma-emitting radionuclides and total and isotopic U and Pu. Analysis of environmental swipe samples collected within a hot-cell facility where chemical processing occurs may also provide information regarding specific chemicals used in fuel processing. However, using swipe material to elucidate what specific chemical processes were/are being used within a hot cell has not been previously evaluated. Staff from Pacific Northwest National Laboratory (PNNL) and Oak Ridge National Laboratory (ORNL) teamed to evaluate the potential use of environmental swipe samples as collection media for volatile and semivolatile organic compounds. This evaluation was initiated with sample collection during a series of Coupled End-to-End (CETE) reprocessing runs at ORNL. The study included measurement of gamma emitting radionuclides, total and isotopic U and Pu, and volatile and semivolatile organic compounds. These results allowed us to elucidate what chemical processes used in the hot cells during reprocessing of power reactor and identify other legacy chemicals used in hot cell operations which predate the CETE process.

  17. Dry soldering with hot filament produced atomic hydrogen

    DOEpatents

    Panitz, J.K.G.; Jellison, J.L.; Staley, D.J.

    1995-04-25

    A system is disclosed for chemically transforming metal surface oxides to metal that is especially, but not exclusively, suitable for preparing metal surfaces for dry soldering and solder reflow processes. The system employs one or more hot, refractory metal filaments, grids or surfaces to thermally dissociate molecular species in a low pressure of working gas such as a hydrogen-containing gas to produce reactive species in a reactive plasma that can chemically reduce metal oxides and form volatile compounds that are removed in the working gas flow. Dry soldering and solder reflow processes are especially applicable to the manufacture of printed circuit boards, semiconductor chip lead attachment and packaging multichip modules. The system can be retrofitted onto existing metal treatment ovens, furnaces, welding systems and wave soldering system designs. 1 fig.

  18. Dry soldering with hot filament produced atomic hydrogen

    DOEpatents

    Panitz, Janda K. G.; Jellison, James L.; Staley, David J.

    1995-01-01

    A system for chemically transforming metal surface oxides to metal that is especially, but not exclusively, suitable for preparing metal surfaces for dry soldering and solder reflow processes. The system employs one or more hot, refractory metal filaments, grids or surfaces to thermally dissociate molecular species in a low pressure of working gas such as a hydrogen-containing gas to produce reactive species in a reactive plasma that can chemically reduce metal oxides and form volatile compounds that are removed in the working gas flow. Dry soldering and solder reflow processes are especially applicable to the manufacture of printed circuit boards, semiconductor chip lead attachment and packaging multichip modules. The system can be retrofitted onto existing metal treatment ovens, furnaces, welding systems and wave soldering system designs.

  19. Synthesis of silicon nanowires using tin catalyst by hot wire chemical vapor processing

    SciTech Connect

    Meshram, Nagsen; Kumbhar, Alka; Dusane, R.O.

    2013-06-01

    Highlights: ► Silicon nanowires are grown by hot wire chemical vapor processing at 400 °C using Sn as catalyst material via VLS. ► For nanowire synthesis Sn nanotemplates are formed with hot wire generated atomic hydrogen. ► The TEM image reveals the crystalline nature of nanowire. - Abstract: Silicon nanowires (SiNWs) have been synthesized at temperatures in the range 300–400 °C by the hot wire chemical vapor processing (HWCVP) using tin nanotemplate. The tin nano-template is formed by hot wire atomic hydrogen treatment of thermally evaporated Sn films (∼300 nm thick) on glass substrates. Silicon nanowires are then grown using hot wire induced dissociation of SiH{sub 4} gas over the nanotemplate. Growth conditions like growth time and temperature were varied to study their effect on the tin nanoparticle size and on the silicon nanowire dimensions thereafter. From the observations, it is clear that the nanowire diameters and lengths depend on the size of nanoparticles and the growth time respectively. Though SiNWs were observed to grow at temperatures as low as 300 °C, nanowires with a narrow diameter distribution were achieved at 400 °C. Raman spectra and transmission electron microscope (TEM) reveal the crystalline nature of the silicon nanowires.

  20. Graphene-Semiconductor Catalytic Nanodiodes for Quantitative Detection of Hot Electrons Induced by a Chemical Reaction.

    PubMed

    Lee, Hyosun; Nedrygailov, Ievgen I; Lee, Young Keun; Lee, Changhwan; Choi, Hongkyw; Choi, Jin Sik; Choi, Choon-Gi; Park, Jeong Young

    2016-03-01

    Direct detection of hot electrons generated by exothermic surface reactions on nanocatalysts is an effective strategy to obtain insight into electronic excitation during chemical reactions. For this purpose, we fabricated a novel catalytic nanodiode based on a Schottky junction between a single layer of graphene and an n-type TiO2 layer that enables the detection of hot electron flows produced by hydrogen oxidation on Pt nanoparticles. By making a comparative analysis of data obtained from measuring the hot electron current (chemicurrent) and turnover frequency, we demonstrate that graphene's unique electronic structure and extraordinary material properties, including its atomically thin nature and ballistic electron transport, allow improved conductivity at the interface between the catalytic Pt nanoparticles and the support. Thereby, graphene-based nanodiodes offer an effective and facile way to approach the study of chemical energy conversion mechanisms in composite catalysts with carbon-based supports.

  1. RADIOACTIVE CHEMICAL ELEMENTS IN THE ATOMIC TABLE.

    SciTech Connect

    HOLDEN, N.E.

    2005-08-13

    In the 1949 Report of the Atomic Weights Commission, a series of new elements were added to the Atomic Weights Table. Since these elements had been produced in the laboratory and were not discovered in nature, the atomic weight value of these artificial products would depend upon the production method. Since atomic weight is a property of an element as it occurs in nature, it would be incorrect to assign an atomic weight value to that element. As a result of that discussion, the Commission decided to provide only the mass number of the most stable (longest-lived) known isotope as the number to be associated with these entries in the Atomic Weights Table. As a function of time, the mass number associated with various elements has changed as longer-lived isotopes of a particular elements has been found in nature, or as improved half-life values of an element's isotopes might cause a shift in the longest-lived isotope from one mass number to another. In the 1957 Report of the Atomic Weights Commission, it was decided to discontinue the listing of the mass number in the Atomic Weights Table on the grounds that the kind of information supplied by the mass number is inconsistent with the primary purpose of the Table, i.e., to provide accurate values of ''these constants'' for use in chemical calculations. In addition to the Table of Atomic Weights, the Commission included an auxiliary Table of Radioactive Elements for the first time, where the entry would be the isotope of that element which was most stable, i.e., it had the longest known half-life. In their 1973 report, the Commission noted that the users of the Atomic Weights Table were dissatisfied with the omission of values in the Table for some elements and it was decided to reintroduce the mass number for elements. In their 1983 report, the Commission decided that radioactive elements were considered to lack a characteristic terrestrial isotopic composition, from which an atomic weight value could be calculated to

  2. 25. Wood quench tower, chemical tank on right, hot gas ...

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

    25. Wood quench tower, chemical tank on right, hot gas pipes between coke ovens and compressor building XX), coal conveyor to pulverizer building on right, water tank to left of quench tower. Looking north/northwest - Rouge Steel Company, 3001 Miller Road, Dearborn, MI

  3. The status of chemical sensors for hot-dip galvanization

    NASA Astrophysics Data System (ADS)

    Fergus, Jeffrey W.

    1996-09-01

    Alloying elements are added to the zinc used in the hot-dip galvanization of sheet steel to control the properties and appearance of the resulting coating. For example, aluminum is added to improve the corrosion resistance and adherence of the coating. Other additions, such as antimony, are added to control the grain size and, thus, the appearance of the coating. The concentrations of these alloying elements may change during the process, either deliberately according to product specifications or due to factors such as preferential oxidation. These changes may require replenishment of a depleted alloying element or adjustments in other processing parameters to maintain optimal efficiency. Intelligent adjustments require knowledge of the alloy composition, which requires inline measurement of the concentrations of alloying elements. This article presents recent developments in chemical sensors for use in hot-dip galvanization. In particular, electrochemical sensors for measuring the concentrations of aluminum and antimony in molten zinc are reviewed.

  4. Intermolecular atom-atom bonds in crystals - a chemical perspective.

    PubMed

    Thakur, Tejender S; Dubey, Ritesh; Desiraju, Gautam R

    2015-03-01

    Short atom-atom distances between molecules are almost always indicative of specific intermolecular bonding. These distances may be used to assess the significance of all hydrogen bonds, including the C-H⋯O and even weaker C-H⋯F varieties.

  5. Coherent anti-Stokes Raman scattering (CARS) detection or hot atom reaction product internal energy distributions

    SciTech Connect

    Quick, C.R. Jr.; Moore, D.S.

    1983-01-01

    Coherent anti-Stokes Raman spectroscopy (CARS) is being utilized to investigate the rovibrational energy distributions produced by reactive and nonreactive collisions of translationally hot atoms with simple molecules. Translationally hot H atoms are produced by ArF laser photolysis of HBr. Using CARS we have monitored, in a state-specific and time-resolved manner, rotational excitation of HBr (v = 0), vibrational excitation of HBr and H/sub 2/, rovibrational excitation of H/sub 2/ produced by the reaction H + HBr ..-->.. H/sub 2/ + Br, and Br atom production by photolysis of HBr.

  6. Muon transfer from hot muonic hydrogen atoms to neon

    SciTech Connect

    Jacot-Guillarmod, R. . Inst. de Physique); Bailey, J.M. ); Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A. ); Beveridge, J.L.; Marshall, G.M.; Brewer, J.H.; Forster, B.M. ); Huber, T.M. ); Kammel, P.; Zmeskal, J.

    1992-01-01

    A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of [mu][sup [minus]p] atoms in each target. The rates [lambda][sub pp[mu

  7. Infrared dynamics of cold atoms on hot graphene membranes

    NASA Astrophysics Data System (ADS)

    Sengupta, Sanghita; Kotov, Valeri N.; Clougherty, Dennis P.

    2016-06-01

    We study the infrared dynamics of low-energy atoms interacting with a sample of suspended graphene at finite temperature. The dynamics exhibits severe infrared divergences order by order in perturbation theory as a result of the singular nature of low-energy flexural phonon emission. Our model can be viewed as a two-channel generalization of the independent boson model with asymmetric atom-phonon coupling. This allows us to take advantage of the exact nonperturbative solution of the independent boson model in the stronger channel while treating the weaker one perturbatively. In the low-energy limit, the exact solution can be viewed as a resummation (exponentiation) of the most divergent diagrams in the perturbative expansion. As a result of this procedure, we obtain the atom's Green function which we use to calculate the atom damping rate, a quantity equal to the quantum sticking rate. A characteristic feature of our results is that the Green's function retains a weak, infrared cutoff dependence that reflects the reduced dimensionality of the problem. As a consequence, we predict a measurable dependence of the sticking rate on graphene sample size. We provide detailed predictions for the sticking rate of atomic hydrogen as a function of temperature and sample size. The resummation yields an enhanced sticking rate relative to the conventional Fermi golden rule result (equivalent to the one-loop atom self-energy), as higher-order processes increase damping at finite temperature.

  8. Atomically resolved real-space imaging of hot electron dynamics

    PubMed Central

    Lock, D.; Rusimova, K. R.; Pan, T. L.; Palmer, R. E.; Sloan, P. A.

    2015-01-01

    The dynamics of hot electrons are central to understanding the properties of many electronic devices. But their ultra-short lifetime, typically 100 fs or less, and correspondingly short transport length-scale in the nanometre range constrain real-space investigations. Here we report variable temperature and voltage measurements of the nonlocal manipulation of adsorbed molecules on the Si(111)-7 × 7 surface in the scanning tunnelling microscope. The range of the nonlocal effect increases with temperature and, at constant temperature, is invariant over a wide range of electron energies. The measurements probe, in real space, the underlying hot electron dynamics on the 10 nm scale and are well described by a two-dimensional diffusive model with a single decay channel, consistent with 2-photon photo-emission (2PPE) measurements of the real time dynamics. PMID:26387703

  9. Atomically resolved real-space imaging of hot electron dynamics.

    PubMed

    Lock, D; Rusimova, K R; Pan, T L; Palmer, R E; Sloan, P A

    2015-09-21

    The dynamics of hot electrons are central to understanding the properties of many electronic devices. But their ultra-short lifetime, typically 100 fs or less, and correspondingly short transport length-scale in the nanometre range constrain real-space investigations. Here we report variable temperature and voltage measurements of the nonlocal manipulation of adsorbed molecules on the Si(111)-7 × 7 surface in the scanning tunnelling microscope. The range of the nonlocal effect increases with temperature and, at constant temperature, is invariant over a wide range of electron energies. The measurements probe, in real space, the underlying hot electron dynamics on the 10 nm scale and are well described by a two-dimensional diffusive model with a single decay channel, consistent with 2-photon photo-emission (2PPE) measurements of the real time dynamics.

  10. Co-Occurring Atomic Contacts for the Characterization of Protein Binding Hot Spots.

    PubMed

    Liu, Qian; Ren, Jing; Song, Jiangning; Li, Jinyan

    2015-01-01

    A binding hot spot is a small area at a protein-protein interface that can make significant contribution to binding free energy. This work investigates the substantial contribution made by some special co-occurring atomic contacts at a binding hot spot. A co-occurring atomic contact is a pair of atomic contacts that are close to each other with no more than three covalent-bond steps. We found that two kinds of co-occurring atomic contacts can play an important part in the accurate prediction of binding hot spot residues. One is the co-occurrence of two nearby hydrogen bonds. For example, mutations of any residue in a hydrogen bond network consisting of multiple co-occurring hydrogen bonds could disrupt the interaction considerably. The other kind of co-occurring atomic contact is the co-occurrence of a hydrophobic carbon contact and a contact between a hydrophobic carbon atom and a π ring. In fact, this co-occurrence signifies the collective effect of hydrophobic contacts. We also found that the B-factor measurements of several specific groups of amino acids are useful for the prediction of hot spots. Taking the B-factor, individual atomic contacts and the co-occurring contacts as features, we developed a new prediction method and thoroughly assessed its performance via cross-validation and independent dataset test. The results show that our method achieves higher prediction performance than well-known methods such as Robetta, FoldX and Hotpoint. We conclude that these contact descriptors, in particular the novel co-occurring atomic contacts, can be used to facilitate accurate and interpretable characterization of protein binding hot spots.

  11. Muon transfer from hot muonic hydrogen atoms to neon

    SciTech Connect

    Jacot-Guillarmod, R.; Bailey, J.M.; Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A.; Beveridge, J.L.; Marshall, G.M.; Brewer, J.H.; Forster, B.M.; Huber, T.M.; Kammel, P.; Zmeskal, J.; Kunselman, A.R.; Petitjean, C.

    1992-12-31

    A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of {mu}{sup {minus}p} atoms in each target. The rates {lambda}{sub pp{mu}} and {lambda}{sub pd} can be extracted.

  12. Development of a chemical oxygen - iodine laser with production of atomic iodine in a chemical reaction

    SciTech Connect

    Censky, M; Spalek, O; Jirasek, V; Kodymova, J; Jakubec, I

    2009-11-30

    The alternative method of atomic iodine generation for a chemical oxygen - iodine laser (COIL) in chemical reactions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied. (lasers)

  13. Quantum Chemical Topology: Knowledgeable atoms in peptides

    NASA Astrophysics Data System (ADS)

    Popelier, Paul L. A.

    2012-06-01

    The need to improve atomistic biomolecular force fields remains acute. Fortunately, the abundance of contemporary computing power enables an overhaul of the architecture of current force fields, which typically base their electrostatics on fixed atomic partial charges. We discuss the principles behind the electrostatics of a more realistic force field under construction, called QCTFF. At the heart of QCTFF lies the so-called topological atom, which is a malleable box, whose shape and electrostatics changes in response to a changing environment. This response is captured by a machine learning method called Kriging. Kriging directly predicts each multipole moment of a given atom (i.e. the output) from the coordinates of the nuclei surrounding this atom (i.e. the input). This procedure yields accurate interatomic electrostatic energies, which form the basis for future-proof progress in force field design.

  14. Electromagnetically induced photonic bandgap in hot Cs atoms

    SciTech Connect

    Li, D. W.; Zhang, L.; Su, X. M.; Zhuo, Z. C.; Kim, J. B

    2010-04-15

    Three-level {Lambda}-type thermal Cs atoms are used to demonstrate the phenomenon of a photonic bandgap induced by quantum coherence with a standing wave (SW). We observed the transmitted signals of probe field driven by several kinds of SW, which are formed by a strong forward-traveling field and a backward-traveling field when a mirror reflects the forward-traveling beam. Considering Doppler inhomogeneous broadenings with a SW drive, we employ Fourier transformation to solve density-matrix equations for simulation results. The simulation results are found to be consistent with the experimental results.

  15. A Thermo-Chemical Reactor for analytical atomic spectrometry

    NASA Astrophysics Data System (ADS)

    Gilmutdinov, A. Kh.; Nagulin, K. Yu.

    2009-01-01

    A novel atomization/vaporization system for analytical atomic spectrometry is developed. It consists of two electrically and thermally separated parts that can be heated separately. Unlike conventional electrothermal atomizers in which atomization occurs immediately above the vaporization site and at the same instant of time, the proposed system allows analyte atomization via an intermediate stage of fractional condensation as a two stage process: Vaporization → Condensation → Atomization. The condensation step is selective since vaporized matrix constituents are mainly non-condensable gases and leave the system by diffusion while analyte species are trapped on the cold surface of a condenser. This kind of sample distillation keeps all the advantages of traditional electrothermal atomization and allows significant reduction of matrix interferences. Integration into one design a vaporizer, condenser and atomizer gives much more flexibility for in situ sample treatment and thus the system is called a Thermo-Chemical Reactor (TCR). Details of the design, temperature measurements, vaporization-condensation-atomization mechanisms of various elements in variety of matrices are investigated in the TCR with spectral, temporal and spatial resolution. The ability of the TCR to significantly reduce interferences and to conduct sample pyrolysis at much higher temperatures as compared to conventional electrothermal atomizers is demonstrated. The analytical potential of the system is shown when atomic absorption determination of Cd and Pb in citrus leaves and milk powder without the use of any chemical modification.

  16. Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation

    NASA Astrophysics Data System (ADS)

    Gonçalves, Gil; Vila, Mercedes; Bdikin, Igor; de Andrés, Alicia; Emami, Nazanin; Ferreira, Rute A. S.; Carlos, Luís D.; Grácio, José; Marques, Paula A. A. P.

    2014-10-01

    Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform.

  17. Correlation between molecular recoil and molecular orientation in collisions of symmetric top molecules with hot hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Ni, C. K.; Flynn, G. W.

    1992-05-01

    Nascent Doppler profiles are measured for hot H-atom—molecule collisions in numerous rotational sublevels of two symmetric tops. Linewidths for CDF 3 molecules due to hot H-atom collisions increase with the quantum number K. In contrast, linewidths for CD 3F molecules due to hot H-atom collisions decrease with the quantum number K. A simple model is proposed to explain the K dependent linewidths.

  18. Comparative Study on Hot Atom Coronae of Solar and Extrasolar Planets

    NASA Astrophysics Data System (ADS)

    Shematovich, Valery

    Solar/stellar forcing on the upper atmospheres of the solar and extrasolar planets via both absorption of the XUV (soft X-rays and extreme ultraviolet) radiation and atmospheric sputtering results in the formation of an extended neutral corona populated by the suprathermal (hot) H, C, N, and O atoms (see, e.g., Johnson et al., 2008). The hot corona, in turn, is altered by an inflow of the solar wind/magnetospheric plasma and local pick-up ions onto the planetary exosphere. Such inflow results in the formation of the superthermal atoms (energetic neutral atoms - ENAs) due to the charge exchange with the high-energy precipitating ions and can affect the long-term evolution of the atmosphere due to the atmospheric escape. The origin, kinetics and transport of the suprathermal H, C, N, and O atoms in the transition regions (from thermosphere to exosphere) of the planetary atmospheres are discussed. Reactions of dissociative recombination of the ionospheric ions CO _{2} (+) , CO (+) , O _{2} (+) , and N _{2} (+) with thermal electrons are the main photochemical sources of hot atoms. The dissociation of atmospheric molecules by the solar/stellar XUV radiation and accompanying photoelectron fluxes and the induced exothermic photochemistry are also the important sources of the suprathermal atoms. Such kinetic systems with the non-thermal processes are usually investigated with the different (test particles, DSMC, and hybrid) versions of the kinetic Monte Carlo method. In our studies the kinetic energy distribution functions of suprathermal and superthermal atoms were calculated using the stochastic model of the hot planetary corona (Shematovich, 2004, 2010; Groeller et al., 2014), and the Monte Carlo model (Shematovich et al., 2011, 2013) of the high-energy proton and hydrogen atom precipitation into the atmosphere respectively. These functions allowed us to estimate the space distribution of suprathermals in the planetary transition regions. An application of these

  19. Scattering of cold-atom coherences by hot atoms: frequency shifts from background-gas collisions.

    PubMed

    Gibble, Kurt

    2013-05-01

    Frequency shifts from background-gas collisions currently contribute significantly to the inaccuracy of atomic clocks. Because nearly all collisions with room-temperature background gases that transfer momentum eject the cold atoms from the clock, the interference between the scattered and unscattered waves in the forward direction dominates these frequency shifts. We show they are ≈ 10 times smaller than in room-temperature clocks and that van der Waals interactions produce the cold-atom background-gas shift. General considerations allow the loss of the Ramsey fringe amplitude to bound this frequency shift. PMID:23683186

  20. Ultra fast cooling of hot steel plate by air atomized spray with salt solution

    NASA Astrophysics Data System (ADS)

    Mohapatra, Soumya S.; Ravikumar, Satya V.; Jha, Jay M.; Singh, Akhilendra K.; Bhattacharya, Chandrima; Pal, Surjya K.; Chakraborty, Sudipto

    2014-05-01

    In the present study, the applicability of air atomized spray with the salt added water has been studied for ultra fast cooling (UFC) of a 6 mm thick AISI-304 hot steel plate. The investigation includes the effect of salt (NaCl and MgSO4) concentration and spray mass flux on the cooling rate. The initial temperature of the steel plate before the commencement of cooling is kept at 900 °C or above, which is usually observed as the "finish rolling temperature" in the hot strip mill of a steel plant. The heat transfer analysis shows that air atomized spray with the MgSO4 salt produces 1.5 times higher cooling rate than atomized spray with the pure water, whereas air atomized spray with NaCl produces only 1.2 times higher cooling rate. In transition boiling regime, the salt deposition occurs which causes enhancement in heat transfer rate by conduction. Moreover, surface tension is the governing parameter behind the vapour film instability and this length scale increases with increase in surface tension of coolant. Overall, the achieved cooling rates produced by both types of salt added air atomized spray are found to be in the UFC regime.

  1. Two-color ghost interference with photon pairs generated in hot atoms

    SciTech Connect

    Ding Dongsheng; Zhou Zhiyuan; Shi Baosen; Zou Xubo; Guo Guangcan

    2012-09-15

    We report on an experimental observation of a two-photon ghost interference experiment. A distinguishing feature of our experiment is that the photons are generated via a non-degenerated spontaneous four-wave mixing process in a hot atomic ensemble; therefore the photon has narrow bandwidth. Besides, there is a large difference in frequency between two photons in a pair. Our works may be important to achieve more secure, large transmission capacity long-distance quantum communication.

  2. Subnatural-linewidth biphotons from a Doppler-broadened hot atomic vapour cell

    PubMed Central

    Shu, Chi; Chen, Peng; Chow, Tsz Kiu Aaron; Zhu, Lingbang; Xiao, Yanhong; Loy, M.M.T.; Du, Shengwang

    2016-01-01

    Entangled photon pairs, termed as biphotons, have been the benchmark tool for experimental quantum optics. The quantum-network protocols based on photon–atom interfaces have stimulated a great demand for single photons with bandwidth comparable to or narrower than the atomic natural linewidth. In the past decade, laser-cooled atoms have often been used for producing such biphotons, but the apparatus is too large and complicated for engineering. Here we report the generation of subnatural-linewidth (<6 MHz) biphotons from a Doppler-broadened (530 MHz) hot atomic vapour cell. We use on-resonance spontaneous four-wave mixing in a hot paraffin-coated 87Rb vapour cell at 63 °C to produce biphotons with controllable bandwidth (1.9–3.2 MHz) and coherence time (47–94 ns). Our backward phase-matching scheme with spatially separated optical pumping is the key to suppress uncorrelated photons from resonance fluorescence. The result may lead towards miniature narrowband biphoton sources. PMID:27658721

  3. Geologic setting and chemical characteristics of hot springs in central and western Alaska

    USGS Publications Warehouse

    Miller, Thomas P.; Barnes, Ivan; Pattan, William Wallace

    1973-01-01

    The geologic and chemical data are too preliminary to make an estimate of the potential of the hot springs as a geothermal resource. The data suggest, however, that most of the hot springs of central and western Alaska have relatively low subsurface temperatures and limited reservoir capacities in comparison with geothermal areas presently being utilized for electrical power generation.

  4. Hot-wire detector for chemically active materials used in gas chromatography

    NASA Technical Reports Server (NTRS)

    1966-01-01

    Hot-filament detector analyzes chemically active materials used in gas chromatography. The detector reacts chemically with the effluent vapors in the gas chromatographic apparatus to change the electrical resistance of the filament as a function of the affluent composition. Due to the changes produced by chemical action on the filament, the system is often calibrated.

  5. Infrared light emission from nano hot electron gas created in atomic point contacts

    NASA Astrophysics Data System (ADS)

    Malinowski, T.; Klein, H. R.; Iazykov, M.; Dumas, Ph.

    2016-06-01

    Gold atomic point contacts are prototype systems to evidence ballistic electron transport. The typical dimension of the nanojunction being smaller than the electron-phonon interaction length, even at room temperature, electrons transfer their excess energy to the lattice only far from the contact. At the contact however, favored by huge current densities, electron-electron interactions result in a nano hot electron gas acting as a source of photons. Using a home built Mechanically Controlled Break Junction, it is reported here, for the first time, that this nano hot electron gas also radiates in the infrared range (0.2 eV to 1.2 eV). Moreover, following the description introduced by Tomchuk et al. (Sov. Phys.-Solid State, 8 (1966) 2510), we show that this radiation is compatible with a black-body-like spectrum emitted from an electron gas at temperatures of several thousands of kelvins.

  6. Infrared light emission from nano hot electron gas created in atomic point contacts

    NASA Astrophysics Data System (ADS)

    Malinowski, T.; Klein, H. R.; Iazykov, M.; Dumas, Ph.

    2016-06-01

    Gold atomic point contacts are prototype systems to evidence ballistic electron transport. The typical dimension of the nanojunction being smaller than the electron-phonon interaction length, even at room temperature, electrons transfer their excess energy to the lattice only far from the contact. At the contact however, favored by huge current densities, electron-electron interactions result in a nano hot electron gas acting as a source of photons. Using a home built Mechanically Controlled Break Junction, it is reported here, for the first time, that this nano hot electron gas also radiates in the infrared range (0.2 eV to 1.2 eV). Moreover, following the description introduced by Tomchuk et al. (Sov. Phys.-Solid State, 8 (1966) 2510), we show that this radiation is compatible with a black-body–like spectrum emitted from an electron gas at temperatures of several thousands of kelvins.

  7. Electrohydrodynamic atomization (EHDA) assisted wet chemical synthesis of nickel nanoparticles

    SciTech Connect

    Barzegar Vishlaghi, M.; Farzalipour Tabriz, M.; Mohammad Moradi, O.

    2012-07-15

    Highlights: ► Electrohydrodynamic atomization (EHDA) assisted chemical synthesis of nickel nanoparticles is reported. ► Substituting water with non-aqueous media prevents the formation of nickel hydroxide. ► Size of particles decreased from 10 to 20 nm down to 2–4 nm by using multi-jet mode. ► Synthesized nanoparticles have diffraction patterns similar to amorphous materials. -- Abstract: In this study nickel nanoparticles were prepared via chemical reduction of nickel acetate using sodium borohydride using electrohydrodynamic atomization (EHDA) technique. This technique was used to spray a finely dispersed aerosol of nickel precursor solution into the reductive bath. Obtained particles were characterized by means of X-ray diffraction (XRD), UV–Visible spectroscopy, and transmission electron microscopy (TEM). Results confirmed the formation of nickel nanoparticles and showed that applying EHDA technique to chemical reduction method results in producing smaller particles with narrower size distribution in comparison with conventional reductive precipitation method.

  8. Global Dynamics of Hot Atomic Oxygen in Mars' Upper Atmosphere and Comparison with Recent Observation

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Combi, M. R.; Tenishev, V.; Bougher, S. W.

    2012-12-01

    The production of energetic particles in Mars's upper thermosphere and exosphere results in the formation of hot atom coronae. Dissociative recombination (DR) of O2+ ion is the dominant source of the production of hot atomic oxygen and the most important reaction for the exosphere on Mars, which occurs mostly deep in the dayside thermosphere of Mars. In this investigation, we have carried out the study of the global dynamics of energetic particles in Mars' upper atmosphere using our newly developed self-consistent Monte-Carlo model. The calculated total global escapes of hot oxygen are presented for different solar activities (solar maximum and minimum) and Martian seasons (aphelion, equinox, and perihelion). To describe self-consistently the exosphere and the upper thermosphere, a combination of our 3D Direct Simulation Monte Carlo (DSMC) model [Valeille, A., Combi, M., Bougher, S., Tenishev, V., Nagy, A., 2009. J. Geophys. Res. 114, E11006. doi:10.1029/2009JE003389] and the 3D Mars Thermosphere General Circulation Model (MTGCM) [Bougher, S.W., Bell, J.M., Murphy, J.R., Lopez-Valverde, M.A., Withers, P.G., 2006. Geophys. Res. Lett. 32, doi: 10.1029/2005GL024059. L02203] is used. Profiles of density and temperature, atmospheric loss rates, and return fluxes are studied using the model for the cases considered. Progress in updating the model physics is also described. Along with comparisons of our DSMC model outputs with those from other recent exosphere model studies, we present a comparison of our model results with the derived neutral oxygen density from atomic oxygen emission at 1304Å that was detected by Alice instrument on board European Space Agency's Rosetta spacecraft [Feldman, P., Steffl, A., Parker, J, A'Hearn, M., Bertaux, J., Stern, S., Weaver, H., Slater, D., Versteeg, M., Throop, H., Cunningham, N., Feaga, L., 2011. Icarus. 214, 2, 394-399, doi:10.1016/j.icarus.2011.06.013].

  9. Growth and characterization of boron doped graphene by Hot Filament Chemical Vapor Deposition Technique (HFCVD)

    NASA Astrophysics Data System (ADS)

    Jafari, A.; Ghoranneviss, M.; Salar Elahi, A.

    2016-03-01

    Large-area boron doped graphene was synthesized on Cu foil (as a catalyst) by Hot Filament Chemical Vapor Deposition (HFCVD) using boron oxide powder and ethanol vapor. To investigate the effect of different boron percentages, grow time and the growth mechanism of boron-doped graphene, scanning electron microscopy (SEM), Raman scattering and X-ray photoelectron spectroscopy (XPS) were applied. Also in this experiment, the I-V characteristic carried out for study of electrical property of graphene with keithley 2361 system. Nucleation of graphene domains with an average domain size of ~20 μm was observed when the growth time is 9 min that has full covered on the Cu surface. The Raman spectroscopy show that the frequency of the 2D band down-shifts with B doping, consistent with the increase of the in-plane lattice constant, and a weakening of the B-C in-plane bond strength relative to that of C-C bond. Also the shifts of the G-band frequencies can be interpreted in terms of the size of the C-C ring and the changes in the electronic structure of graphene in the presence of boron atoms. The study of electrical property shows that by increasing the grow time the conductance increases which this result in agree with SEM images and graphene grain boundary. Also by increasing the boron percentage in gas mixer the conductance decreases since doping graphene with boron creates a band-gap in graphene band structure. The XPS results of B doped graphene confirm the existence of boron in doped graphene, which indicates the boron atoms doped in the graphene lattice are mainly in the form of BC3. The results showed that boron-doped graphene can be successfully synthesized using boron oxide powder and ethanol vapor via a HFCVD method and also chemical boron doping can be change the electrical conductivity of the graphene.

  10. Chemically induced magnetism in atomically precise gold clusters.

    PubMed

    Krishna, Katla Sai; Tarakeshwar, Pilarisetty; Mujica, Vladimiro; Kumar, Challa S S R

    2014-03-12

    Comparative theoretical and experimental investigations are reported into chemically induced magnetism in atomically-precise, ligand-stabilized gold clusters Au25 , Au38 and Au55 . The results indicate that [Au25 (PPh3 )10 (SC12 H25 )5 Cl2 ](2+) and Au38 (SC12 H25 )24 are diamagnetic, Au25 (SC2 H4 Ph)18 is paramagnetic, and Au55 (PPh3 )12 Cl6 , is ferromagnetic at room temperature. Understanding the magnetic properties resulting from quantum size effects in such atomically precise gold clusters could lead to new fundamental discoveries and applications.

  11. Direct Atom Imaging by Chemical-Sensitive Holography.

    PubMed

    Lühr, Tobias; Winkelmann, Aimo; Nolze, Gert; Krull, Dominique; Westphal, Carsten

    2016-05-11

    In order to understand the physical and chemical properties of advanced materials, functional molecular adsorbates, and protein structures, a detailed knowledge of the atomic arrangement is essential. Up to now, if subsurface structures are under investigation, only indirect methods revealed reliable results of the atoms' spatial arrangement. An alternative and direct method is three-dimensional imaging by means of holography. Holography was in fact proposed for electron waves, because of the electrons' short wavelength at easily accessible energies. Further, electron waves are ideal structure probes on an atomic length scale, because electrons have a high scattering probability even for light elements. However, holographic reconstructions of electron diffraction patterns have in the past contained severe image artifacts and were limited to at most a few tens of atoms. Here, we present a general reconstruction algorithm that leads to high-quality atomic images showing thousands of atoms. Additionally, we show that different elements can be identified by electron holography for the example of FeS2.

  12. Generating Molecular Rovibrational Coherence by Two-Photon Femtosecond Photoassociation of Thermally Hot Atoms

    SciTech Connect

    Rybak, Leonid; Levin, Liat; Amitay, Zohar; Amaran, Saieswari; Kosloff, Ronnie; Tomza, Michal; Moszynski, Robert; Koch, Christiane P.

    2011-12-30

    The formation of diatomic molecules with rotational and vibrational coherence is demonstrated experimentally in free-to-bound two-photon femtosecond photoassociation of hot atoms. In a thermal gas at a temperature of 1000 K, pairs of magnesium atoms, colliding in their electronic ground state, are excited into coherent superpositions of bound rovibrational levels in an electronically excited state. The rovibrational coherence is probed by a time-delayed third photon, resulting in quantum beats in the UV fluorescence. A comprehensive theoretical model based on ab initio calculations rationalizes the generation of coherence by Franck-Condon filtering of collision energies and partial waves, quantifying it in terms of an increase in quantum purity of the thermal ensemble. Our results open the way to coherent control of a binary reaction.

  13. Generating Molecular Rovibrational Coherence by Two-Photon Femtosecond Photoassociation of Thermally Hot Atoms

    NASA Astrophysics Data System (ADS)

    Rybak, Leonid; Amaran, Saieswari; Levin, Liat; Tomza, Michał; Moszynski, Robert; Kosloff, Ronnie; Koch, Christiane P.; Amitay, Zohar

    2011-12-01

    The formation of diatomic molecules with rotational and vibrational coherence is demonstrated experimentally in free-to-bound two-photon femtosecond photoassociation of hot atoms. In a thermal gas at a temperature of 1000 K, pairs of magnesium atoms, colliding in their electronic ground state, are excited into coherent superpositions of bound rovibrational levels in an electronically excited state. The rovibrational coherence is probed by a time-delayed third photon, resulting in quantum beats in the UV fluorescence. A comprehensive theoretical model based on ab initio calculations rationalizes the generation of coherence by Franck-Condon filtering of collision energies and partial waves, quantifying it in terms of an increase in quantum purity of the thermal ensemble. Our results open the way to coherent control of a binary reaction.

  14. Chemical domain of QSAR models from atom-centered fragments.

    PubMed

    Kühne, Ralph; Ebert, Ralf-Uwe; Schüürmann, Gerrit

    2009-12-01

    A methodology to characterize the chemical domain of qualitative and quantitative structure-activity relationship (QSAR) models based on the atom-centered fragment (ACF) approach is introduced. ACFs decompose the molecule into structural pieces, with each non-hydrogen atom of the molecule acting as an ACF center. ACFs vary with respect to their size in terms of the path length covered in each bonding direction starting from a given central atom and how comprehensively the neighbor atoms (including hydrogen) are described in terms of element type and bonding environment. In addition to these different levels of ACF definitions, the ACF match mode as degree of strictness of the ACF comparison between a test compound and a given ACF pool (such as from a training set) has to be specified. Analyses of the prediction statistics of three QSAR models with their training sets as well as with external test sets and associated subsets demonstrate a clear relationship between the prediction performance and the levels of ACF definition and match mode. The findings suggest that second-order ACFs combined with a borderline match mode may serve as a generic and at the same time a mechanistically sound tool to define and evaluate the chemical domain of QSAR models. Moreover, four standard categories of the ACF-based membership to a given chemical domain (outside, borderline outside, borderline inside, inside) are introduced that provide more specific information about the expected QSAR prediction performance. As such, the ACF-based characterization of the chemical domain appears to be particularly useful for QSAR applications in the context of REACH and other regulatory schemes addressing the safety evaluation of chemical compounds.

  15. Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random phase wavefunctions

    SciTech Connect

    Amaran, Saieswari; Kosloff, Ronnie; Tomza, Michał; Skomorowski, Wojciech; Pawłowski, Filip; Moszynski, Robert; Rybak, Leonid; Levin, Liat; Amitay, Zohar; Berglund, J. Martin; Reich, Daniel M.; Koch, Christiane P.

    2013-10-28

    Two-photon photoassociation of hot magnesium atoms by femtosecond laser pulses, creating electronically excited magnesium dimer molecules, is studied from first principles, combining ab initio quantum chemistry and molecular quantum dynamics. This theoretical framework allows for rationalizing the generation of molecular rovibrational coherence from thermally hot atoms [L. Rybak, S. Amaran, L. Levin, M. Tomza, R. Moszynski, R. Kosloff, C. P. Koch, and Z. Amitay, Phys. Rev. Lett. 107, 273001 (2011)]. Random phase thermal wavefunctions are employed to model the thermal ensemble of hot colliding atoms. Comparing two different choices of basis functions, random phase wavefunctions built from eigenstates are found to have the fastest convergence for the photoassociation yield. The interaction of the colliding atoms with a femtosecond laser pulse is modeled non-perturbatively to account for strong-field effects.

  16. RAPID COMMUNICATION: High silicon etch rates by hot filament generated atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Wanka, H. N.; Schubert, M. B.

    1997-04-01

    The etching of hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon by hot tungsten filament generated atomic hydrogen has been investigated. Room-temperature etch rates of 27 Å 0022-3727/30/8/002/img1 for amorphous and 20 Å 0022-3727/30/8/002/img1 for microcrystalline silicon have been achieved. Boron doping decreases the etch rate, whereas phosphorus doping does not affect it. No surface roughening occurs, even for the highest a-Si:H etch rates. In the initial phase of the etch process, however, a bond structure modification arises close to the surface. An increase of microcrystalline silicon etch rates towards the substrate/film interface reflects the coalescence of the microcrystalline nuclei. Hot filament atomic hydrogen etching provides high etch rates of amorphous and polycrystalline silicon with a high selectivity against metals and thermal oxide. Due to its simple setup and control, this kind of hydrogen etching is very interesting for applications in semiconductor technology where F- or Cl-etchants are to be avoided.

  17. Kinetic study on hot-wire-assisted atomic layer deposition of nickel thin films

    SciTech Connect

    Yuan, Guangjie Shimizu, Hideharu; Momose, Takeshi; Shimogaki, Yukihiro

    2014-01-15

    High-purity Ni films were deposited using hot-wire-assisted atomic layer deposition (HW-ALD) at deposition temperatures of 175, 250, and 350 °C. Negligible amount of nitrogen or carbon contamination was detected, even though the authors used NH{sub 2} radical as the reducing agent and nickelocene as the precursor. NH{sub 2} radicals were generated by the thermal decomposition of NH{sub 3} with the assist of HW and used to reduce the adsorbed metal growth precursors. To understand and improve the deposition process, the kinetics of HW-ALD were analyzed using a Langmuir-type model. Unlike remote-plasma-enhanced atomic layer deposition, HW-ALD does not lead to plasma-induced damage. This is a significant advantage, because the authors can supply sufficient NH{sub 2} radicals to deposit high-purity metallic films by adjusting the distance between the hot wire and the substrate. NH{sub 2} radicals have a short lifetime, and it was important to use a short distance between the radical generation site and substrate. Furthermore, the impurity content of the nickel films was independent of the deposition temperature, which is evidence of the temperature-independent nature of the NH{sub 2} radical flux and the reactivity of the NH{sub 2} radicals.

  18. Atomic Resolution Imaging and Quantification of Chemical Functionality of Surfaces

    SciTech Connect

    Schwarz, Udo

    2014-12-10

    The work carried out from 2006-2014 under DoE support was targeted at developing new approaches to the atomic-scale characterization of surfaces that include species-selective imaging and an ability to quantify chemical surface interactions with site-specific accuracy. The newly established methods were subsequently applied to gain insight into the local chemical interactions that govern the catalytic properties of model catalysts of interest to DoE. The foundation of our work was the development of three-dimensional atomic force microscopy (3D-AFM), a new measurement mode that allows the mapping of the complete surface force and energy fields with picometer resolution in space (x, y, and z) and piconewton/millielectron volts in force/energy. From this experimental platform, we further expanded by adding the simultaneous recording of tunneling current (3D-AFM/STM) using chemically well-defined tips. Through comparison with simulations, we were able to achieve precise quantification and assignment of local chemical interactions to exact positions within the lattice. During the course of the project, the novel techniques were applied to surface-oxidized copper, titanium dioxide, and silicon oxide. On these materials, defect-induced changes to the chemical surface reactivity and electronic charge density were characterized with site-specific accuracy.

  19. Doping of vanadium to nanocrystalline diamond films by hot filament chemical vapor deposition.

    PubMed

    Zhang, Yaozhong; Zhang, Liying; Zhao, Jiang; Wang, Liang; Zhao, Gang; Zhang, Yafei

    2012-01-01

    Doping an impure element with a larger atomic volume into crystalline structure of buck crystals is normally blocked because the rigid crystalline structure could not tolerate a larger distortion. However, this difficulty may be weakened for nanocrystalline structures. Diamonds, as well as many semiconductors, have a difficulty in effective doping. Theoretical calculations carried out by DFT indicate that vanadium (V) is a dopant element for the n-type diamond semiconductor, and their several donor state levels are distributed between the conduction band and middle bandgap position in the V-doped band structure of diamond. Experimental investigation of doping vanadium into nanocrystalline diamond films (NDFs) was first attempted by hot filament chemical vapor deposition technique. Acetone/H2 gas mixtures and vanadium oxytripropoxide (VO(OCH2CH2CH3)3) solutions of acetone with V and C elemental ratios of 1:5,000, 1:2,000, and 1:1,000 were used as carbon and vanadium sources, respectively. The resistivity of the V-doped NDFs decreased two orders with the increasing V/C ratios.

  20. Hot spot formation and chemical reaction initiation in shocked HMX crystals with nanovoids: a large-scale reactive molecular dynamics study.

    PubMed

    Zhou, Tingting; Lou, Jianfeng; Zhang, Yangeng; Song, Huajie; Huang, Fenglei

    2016-07-14

    We report million-atom reactive molecular dynamic simulations of shock initiation of β-cyclotetramethylene tetranitramine (β-HMX) single crystals containing nanometer-scale spherical voids. Shock induced void collapse and subsequent hot spot formation as well as chemical reaction initiation are observed which depend on the void size and impact strength. For an impact velocity of 1 km s(-1) and a void radius of 4 nm, the void collapse process includes three stages; the dominant mechanism is the convergence of upstream molecules toward the centerline and the downstream surface of the void forming flowing molecules. Hot spot formation also undergoes three stages, and the principal mechanism is kinetic energy transforming to thermal energy due to the collision of flowing molecules on the downstream surface. The high temperature of the hot spot initiates a local chemical reaction, and the breakage of the N-NO2 bond plays the key role in the initial reaction mechanism. The impact strength and void size have noticeable effects on the shock dynamical process, resulting in a variation of the predominant mechanisms leading to void collapse and hot spot formation. Larger voids or stronger shocks result in more intense hot spots and, thus, more violent chemical reactions, promoting more reaction channels and generating more reaction products in a shorter duration. The reaction products are mainly concentrated in the developed hot spot, indicating that the chemical reactivity of the hmx crystal is greatly enhanced by void collapse. The detailed information derived from this study can aid a thorough understanding of the role of void collapse in hot spot formation and the chemical reaction initiation of explosives. PMID:27307079

  1. Hot spot formation and chemical reaction initiation in shocked HMX crystals with nanovoids: a large-scale reactive molecular dynamics study.

    PubMed

    Zhou, Tingting; Lou, Jianfeng; Zhang, Yangeng; Song, Huajie; Huang, Fenglei

    2016-07-14

    We report million-atom reactive molecular dynamic simulations of shock initiation of β-cyclotetramethylene tetranitramine (β-HMX) single crystals containing nanometer-scale spherical voids. Shock induced void collapse and subsequent hot spot formation as well as chemical reaction initiation are observed which depend on the void size and impact strength. For an impact velocity of 1 km s(-1) and a void radius of 4 nm, the void collapse process includes three stages; the dominant mechanism is the convergence of upstream molecules toward the centerline and the downstream surface of the void forming flowing molecules. Hot spot formation also undergoes three stages, and the principal mechanism is kinetic energy transforming to thermal energy due to the collision of flowing molecules on the downstream surface. The high temperature of the hot spot initiates a local chemical reaction, and the breakage of the N-NO2 bond plays the key role in the initial reaction mechanism. The impact strength and void size have noticeable effects on the shock dynamical process, resulting in a variation of the predominant mechanisms leading to void collapse and hot spot formation. Larger voids or stronger shocks result in more intense hot spots and, thus, more violent chemical reactions, promoting more reaction channels and generating more reaction products in a shorter duration. The reaction products are mainly concentrated in the developed hot spot, indicating that the chemical reactivity of the hmx crystal is greatly enhanced by void collapse. The detailed information derived from this study can aid a thorough understanding of the role of void collapse in hot spot formation and the chemical reaction initiation of explosives.

  2. Chemical control of electrical contact to sp2 carbon atoms

    PubMed Central

    Frederiksen, Thomas; Foti, Giuseppe; Scheurer, Fabrice; Speisser, Virginie; Schull, Guillaume

    2014-01-01

    Carbon-based nanostructures are attracting tremendous interest as components in ultrafast electronics and optoelectronics. The electrical interfaces to these structures play a crucial role for the electron transport, but the lack of control at the atomic scale can hamper device functionality and integration into operating circuitry. Here we study a prototype carbon-based molecular junction consisting of a single C60 molecule and probe how the electric current through the junction depends on the chemical nature of the foremost electrode atom in contact with the molecule. We find that the efficiency of charge injection to a C60 molecule varies substantially for the considered metallic species, and demonstrate that the relative strength of the metal-C bond can be extracted from our transport measurements. Our study further suggests that a single-C60 junction is a basic model to explore the properties of electrical contacts to meso- and macroscopic sp2 carbon structures. PMID:24736561

  3. Plasmonic hot carrier dynamics in solid-state and chemical systems for energy conversion

    NASA Astrophysics Data System (ADS)

    Narang, Prineha; Sundararaman, Ravishankar; Atwater, Harry A.

    2016-06-01

    Surface plasmons provide a pathway to efficiently absorb and confine light in metallic nanostructures, thereby bridging photonics to the nano scale. The decay of surface plasmons generates energetic `hot' carriers, which can drive chemical reactions or be injected into semiconductors for nano-scale photochemical or photovoltaic energy conversion. Novel plasmonic hot carrier devices and architectures continue to be demonstrated, but the complexity of the underlying processes make a complete microscopic understanding of all the mechanisms and design considerations for such devices extremely challenging.Here,we review the theoretical and computational efforts to understand and model plasmonic hot carrier devices.We split the problem into three steps: hot carrier generation, transport and collection, and review theoretical approaches with the appropriate level of detail for each step along with their predictions.We identify the key advances necessary to complete the microscopic mechanistic picture and facilitate the design of the next generation of devices and materials for plasmonic energy conversion.

  4. Chemical erosion of atomically dispersed doped hydrocarbon layers by deuterium

    NASA Astrophysics Data System (ADS)

    Balden, M.; Roth, J.; Pardo, E. de Juan; Wiltner, A.

    2003-03-01

    The chemical erosion of atomically dispersed Ti-doped (˜10 at.%) amorphous hydrocarbon layers (a-C:H:Ti) was investigated in the temperature range of 300-800 K for 30 eV deuterium impact. Compared to pyrolytic graphite, the methane production yield is strongly reduced at elevated temperatures. This reduction starts from temperatures just above room temperature and is even larger than for B-doped graphite. The reduction of the activation energy for hydrogen release may be the dominant interpretation for the decreased hydrocarbon formation. The ratio of emitted CD 3 to CD 4 increases with temperature for pyrolytic graphite and even stronger for the doped layers. The fluence dependence of the chemical erosion yield was determined, which is explained by enrichment of the dopant due to the preferential erosion of C.

  5. All-Hot-Wire Chemical Vapor Deposition a-Si:H Solar Cells

    SciTech Connect

    Iwaniczko, E.; Wang, Q.; Xu, Y.; Nelson, B. P.; Mahan, A. H.; Crandall, R. S.; Branz, H. M.

    2000-01-01

    Efficient hydrogenated amorphous silicon (a-Si:H) nip solar cells have been fabricated with all doped and undoped a-Si:H layers deposited by hot-wire chemical vapor deposition (HWCVD). The total deposition time of all layers, except the top ITO-contact, is less than 4 minutes.

  6. Low temperature junction growth using hot-wire chemical vapor deposition

    DOEpatents

    Wang, Qi; Page, Matthew; Iwaniczko, Eugene; Wang, Tihu; Yan, Yanfa

    2014-02-04

    A system and a process for forming a semi-conductor device, and solar cells (10) formed thereby. The process includes preparing a substrate (12) for deposition of a junction layer (14); forming the junction layer (14) on the substrate (12) using hot wire chemical vapor deposition; and, finishing the semi-conductor device.

  7. Chemical hydrofracturing of the Hot Dry Rock reservoir

    SciTech Connect

    Yakovlev, Leonid

    1996-01-24

    The experimental study of the water-rock interaction shows that the secondary mineral assemblage depends on the water composition. For example, granite-pure water interaction produces zeolites (relatively low-dense, Mg-poor minerals), whereas seawater yields chlorites (high-dense, Mg-rich minerals). The reactions have volumetric effects from several % to 20 % in magnitude. Volume deformations in the heterogeneous matrix cause uneven mechanical strains. Reactions with the effect of about 0,1 vol.% may cause strains of the order of 100-1000 bars being enough for destruction of rocks. Signs and magnitudes of local volume changes depend on the mineral composition of the secondary assemblage. Hence, one can provide either healing or cracking of primary fractures, as desired, by changing the composition of water in the water-felsic rock system where some elements (Mg, Fe) are in lack. The techniques of "chemical hydrofracturing" looks promising as applied to a granite HDR massif. One can regulate the permeability of fractured flow paths by changing in concord the composition and pressure of the injected water. This approach should promote efficient extraction of the petrothermal energy.

  8. Chemical and isotopic characteristics of hot springs along the along the Neogene Malawi rift.

    NASA Astrophysics Data System (ADS)

    Atekwana, E. A.; Tsokonombwe, G. W.; Elsenbeck, J.; Wanless, V. D.; Atekwana, E. A.

    2015-12-01

    We measured the concentrations of major ions and dissolved inorganic carbon (DIC) and the stable isotopes of carbon (δ13CDIC), hydrogen (δD) and oxygen (δ18O) of hot springs along the Neogene Malawi rift. We compared the results with those of streams and a cold spring. We aimed to assess the hot springs for evidence of addition of mantle mass, specifically water and carbon and (2) determine the processes that control the chemical and isotopic evolution of the hot springs. Understanding the source(s) of heat for the springs and if the chemical and isotopic characteristics show evidence of mantle processes is an important goal of the Project for Rift Initiation, Development and Evolution (PRIDE). The temperature of the hot springs ranged from 35 to 80 ºC. High temperature anomalies are observed between latitudes 10 to 11, 12 to 13 and 15 to 16 degrees south along the rift axis. The δD and δ18O for the cold spring, hot springs and streams had a similar range, were positively correlated and lie on the trend of the local meteoric water line. We suggest negligible contribution of water from a connate or magmatic source and limited oxygen exchange from water-rock interaction or CO2 exchange from deep sedimentary carbonates. The DIC concentrations of the hot springs are higher (5 to 61 mg C/L) than those of streams (2 to 28 mg C/L) indicating addition of carbon to the DIC pool during the circulation of some springs. The range in the δ13CDIC of the hot springs (-17 to -8‰) is broader and lower compared to streams (-12 to -5‰) due to addition of carbon with a δ13CDIC of -15‰ to the spring water during circulation. Our results indicate that (1) the source of water for the hot springs is meteoric, (2) the hot springs have not experienced extensive water-rock interaction due to fast circulation suggesting highly permeable fault zones, (3) the source of carbon in the DIC of the hot springs is mostly CO2(g) from the soil zone and (4) the springs are heated by normal

  9. Room-temperature photoluminescence from nitrogenated carbon nanotips grown by plasma-enhanced hot filament chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wang, B. B.; Cheng, Q. J.; Chen, Y. A.; Ostrikov, K.

    2011-09-01

    Nitrogenated carbon nanotips with a low atomic concentration of nitrogen have been synthesized by using a custom-designed plasma-enhanced hot-filament plasma chemical vapor deposition system. The properties (including morphology, structure, composition, photoluminescence, etc.) of the synthesized nitrogenated carbon nanotips are investigated using advanced characterization tools. The room-temperature photoluminescence measurements show that the nitrogenated carbon nanotips can generate two distinct broad emissions located at ˜405 and ˜507 nm, respectively. Through the detailed analysis, it is shown that these two emission bands are attributed to the transition between the lone pair valence and σ* bands, which are related to the sp3 and sp2 C-N bonds, respectively. These results are highly relevant to advanced applications of nitrogenated carbon nanotips in light emitting optoelectronic devices.

  10. Theory of rotational transition in atom-diatom chemical reaction

    NASA Astrophysics Data System (ADS)

    Nakamura, Masato; Nakamura, Hiroki

    1989-05-01

    Rotational transition in atom-diatom chemical reaction is theoretically studied. A new approximate theory (which we call IOS-DW approximation) is proposed on the basis of the physical idea that rotational transition in reaction is induced by the following two different mechanisms: rotationally inelastic half collision in both initial and final arrangement channels, and coordinate transformation in the reaction zone. This theory gives a fairy compact expression for the state-to-state transition probability. Introducing the additional physically reasonable assumption that reaction (particle rearrangement) takes place in a spatially localized region, we have reduced this expression into a simpler analytical form which can explicitly give overall rotational state distribution in reaction. Numerical application was made to the H+H2 reaction and demonstrated its effectiveness for the simplicity. A further simplified most naive approximation, i.e., independent events approximation was also proposed and demonstrated to work well in the test calculation of H+H2. The overall rotational state distribution is expressed simply by a product sum of the transition probabilities for the three consecutive processes in reaction: inelastic transition in the initial half collision, transition due to particle rearrangement, and inelastic transition in the final half collision.

  11. Deposition of thermal and hot-wire chemical vapor deposition copper thin films on patterned substrates.

    PubMed

    Papadimitropoulos, G; Davazoglou, D

    2011-09-01

    In this work we study the hot-wire chemical vapor deposition (HWCVD) of copper films on blanket and patterned substrates at high filament temperatures. A vertical chemical vapor deposition reactor was used in which the chemical reactions were assisted by a tungsten filament heated at 650 degrees C. Hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (CupraSelect) vapors were used, directly injected into the reactor with the aid of a liquid injection system using N2 as carrier gas. Copper thin films grown also by thermal and hot-wire CVD. The substrates used were oxidized silicon wafers on which trenches with dimensions of the order of 500 nm were formed and subsequently covered with LPCVD W. HWCVD copper thin films grown at filament temperature of 650 degrees C showed higher growth rates compared to the thermally ones. They also exhibited higher resistivities than thermal and HWCVD films grown at lower filament temperatures. Thermally grown Cu films have very uniform deposition leading to full coverage of the patterned substrates while the HWCVD films exhibited a tendency to vertical growth, thereby creating gaps and incomplete step coverage. PMID:22097561

  12. Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

    NASA Astrophysics Data System (ADS)

    Marchal, F.; Yousfi, M.; Merbahi, N.; Wattieaux, G.; Piquemal, A.

    2016-03-01

    Two experimental techniques have been used to quantify the atomic oxygen density in the case of hot air plasma generated by a microwave (MW) resonant cavity. The latter operates at a frequency of 2.45 GHz inside a cell of gas conditioning at a pressure of 600 mbar, an injected air flow of 12 L/min and an input MW power of 1 kW. The first technique is based on the standard two photon absorption laser induced fluorescence (TALIF) using xenon for calibration but applied for the first time in the present post discharge hot air plasma column having a temperature of about 4500 K near the axis of the nozzle. The second diagnostic technique is an actinometry method based on optical emission spectroscopy (OES). In this case, we compared the spectra intensities of a specific atomic oxygen line (844 nm) and the closest wavelength xenon line (823 nm). The two lines need to be collected under absolutely the same spectroscopic parameters. The xenon emission is due to the addition of a small proportion of xenon (1% Xe) of this chemically inert gas inside the air while a further small quantity of H2 (2%) is also added in the mixture in order to collect OH(A-X) and NH(A-X) spectra without noise. The latter molecular spectra are required to estimate gas and excitation temperatures. Optical emission spectroscopy measurements, at for instance the position z=12 mm on the axis plasma column that leads to a gas measured temperature equal to 3500 K, an excitation temperature of about 9500 K and an atomic oxygen density 2.09×1017±0.2×1017 cm-3. This is in very good agreement with the TALIF measurement, which is equal to 2.0×1017 cm-3.

  13. A THREE-PHASE CHEMICAL MODEL OF HOT CORES: THE FORMATION OF GLYCINE

    SciTech Connect

    Garrod, Robin T.

    2013-03-01

    A new chemical model is presented that simulates fully coupled gas-phase, grain-surface, and bulk-ice chemistry in hot cores. Glycine (NH{sub 2}CH{sub 2}COOH), the simplest amino acid, and related molecules such as glycinal, propionic acid, and propanal, are included in the chemical network. Glycine is found to form in moderate abundance within and upon dust-grain ices via three radical-addition mechanisms, with no single mechanism strongly dominant. Glycine production in the ice occurs over temperatures {approx}40-120 K. Peak gas-phase glycine fractional abundances lie in the range 8 Multiplication-Sign 10{sup -11}-8 Multiplication-Sign 10{sup -9}, occurring at {approx}200 K, the evaporation temperature of glycine. A gas-phase mechanism for glycine production is tested and found insignificant, even under optimal conditions. A new spectroscopic radiative-transfer model is used, allowing the translation and comparison of the chemical-model results with observations of specific sources. Comparison with the nearby hot-core source NGC 6334 IRS1 shows excellent agreement with integrated line intensities of observed species, including methyl formate. The results for glycine are consistent with the current lack of a detection of this molecule toward other sources; the high evaporation temperature of glycine renders the emission region extremely compact. Glycine detection with ALMA is predicted to be highly plausible, for bright, nearby sources with narrow emission lines. Photodissociation of water and subsequent hydrogen abstraction from organic molecules by OH, and NH{sub 2}, are crucial to the buildup of complex organic species in the ice. The inclusion of alternative branches within the network of radical-addition reactions appears important to the abundances of hot-core molecules; less favorable branching ratios may remedy the anomalously high abundance of glycolaldehyde predicted by this and previous models.

  14. Plasmonic hot carrier dynamics in solid-state and chemical systems for energy conversion

    DOE PAGES

    Narang, Prineha; Sundararaman, Ravishankar; Atwater, Harry A.

    2016-06-11

    Surface plasmons provide a pathway to efficiently absorb and confine light in metallic nanostructures, thereby bridging photonics to the nano scale. The decay of surface plasmons generates energetic ‘hot’ carriers, which can drive chemical reactions or be injected into semiconductors for nano-scale photochemical or photovoltaic energy conversion. Novel plasmonic hot carrier devices and architectures continue to be demonstrated, but the complexity of the underlying processes make a complete microscopic understanding of all the mechanisms and design considerations for such devices extremely challenging.Here,we review the theoretical and computational efforts to understand and model plasmonic hot carrier devices.We split the problem intomore » three steps: hot carrier generation, transport and collection, and review theoretical approaches with the appropriate level of detail for each step along with their predictions. As a result, we identify the key advances necessary to complete the microscopic mechanistic picture and facilitate the design of the next generation of devices and materials for plasmonic energy conversion.« less

  15. Extracting chemical information from plane wave calculations by a 3D 'fuzzy atoms' analysis

    NASA Astrophysics Data System (ADS)

    Bakó, I.; Stirling, A.; Seitsonen, A. P.; Mayer, I.

    2013-03-01

    Bond order and valence indices have been calculated by the method of the three-dimensional 'fuzzy atoms' analysis, using the numerical molecular orbitals obtained from plane wave DFT calculations, i.e., without introducing any external atom-centered functions. Weight functions of both Hirshfeld and Becke types have been applied. The results are rather close to the similar 'fuzzy atoms' ones obtained by using atom-centered basis sets and agree well with the chemical expectations, stressing the power of the genuine chemical concepts.

  16. Chemical Principles Revisited: Updating the Atomic Theory in General Chemistry.

    ERIC Educational Resources Information Center

    Whitman, Mark

    1984-01-01

    Presents a descriptive overview of recent achievements in atomic structure to provide instructors with the background necessary to enhance their classroom presentations. Topics considered include hadrons, quarks, leptons, forces, and the unified fields theory. (JN)

  17. Cheminoes: A Didactic Game to Learn Chemical Relationships between Valence, Atomic Number, and Symbol

    ERIC Educational Resources Information Center

    Moreno, Luis F.; Hincapié, Gina; Alzate, María Victoria

    2014-01-01

    Cheminoes is a didactic game that enables the meaningful learning of some relations between concepts such as chemical element, valence, atomic number, and chemical symbol for the first 36 chemical elements of the periodic system. Among the students who have played the game, their opinions of the activity were positive, considering the game to be a…

  18. Ion-atom charge-transfer reactions and a hot intercloud medium. [in interstellar space

    NASA Technical Reports Server (NTRS)

    Steigman, G.

    1975-01-01

    An investigation is conducted concerning the ionization equilibrium of carbon in a hot intercloud medium (ICM), taking into account various charge-transfer reactions. Attention is given to problems related to observations of carbon along the lines of sight to several unreddened stars. It is pointed out that the observed underabundance of C III and overabundance of C I can be consistent with the presence of a hot, partially ionized ICM, provided that two of the charge-transfer reactions considered are rapid at thermal energies.

  19. Internal and external atomic steps in graphite exhibit dramatically different physical and chemical properties.

    PubMed

    Lee, Hyunsoo; Lee, Han-Bo-Ram; Kwon, Sangku; Salmeron, Miquel; Park, Jeong Young

    2015-04-28

    We report on the physical and chemical properties of atomic steps on the surface of highly oriented pyrolytic graphite (HOPG) investigated using atomic force microscopy. Two types of step edges are identified: internal (formed during crystal growth) and external (formed by mechanical cleavage of bulk HOPG). The external steps exhibit higher friction than the internal steps due to the broken bonds of the exposed edge C atoms, while carbon atoms in the internal steps are not exposed. The reactivity of the atomic steps is manifested in a variety of ways, including the preferential attachment of Pt nanoparticles deposited on HOPG when using atomic layer deposition and KOH clusters formed during drop casting from aqueous solutions. These phenomena imply that only external atomic steps can be used for selective electrodeposition for nanoscale electronic devices.

  20. Chemical and physical degradation of glass fiber reinforced cross-linked polyester immersed in hot water

    SciTech Connect

    Hamada, H.; Maekawa, Z.I.; Ikuta, N.; Kiyosumi, K.; Tanimoto, T.; Morii, T.

    1994-12-31

    This study deals with chemical and physical degradation behavior of randomly oriented E-glass fiber continuous strand mat reinforced cross-linked polyester immersed in hot water at 80 and 95 C. The specimens were immersed in hot water for 3, 10, 30, 100, 300, 1000, 3000 and 4000h. Weight change measurement, three-point bending and infrared measurement were performed for the specimens after the immersion. Changes of the weight gain indicated the Fickian diffusion at early immersion time, and after that, it indicated the non-Fickian diffusion with a gradual progress of debonding between fiber and matrix. This degradation of the interface caused a remarkable increase of the weight loss, which was never observed in neat resin. The bending modulus decreased with increase of the weight gain at early immersion time, however, it kept constant at longer immersion time both at 80 C and at 95 C. The constant modulus level at 80C was higher than that at 95 C. At longer immersion time at 80 C, the modulus decreased again to the same level at 95C. The results of infrared measurement suggested the difference of degradation mechanism between early immersion time and longer immersion time. At early immersion time, the resin changed physically by swelling and extraction of polymer with water penetration. Such differences of degradation affected the reduction of modulus. Moreover, the effect of the debonding at the interface on the modulus was discussed by the finite element analysis by introducing the damage mechanics.

  1. SELECTED CHEMICAL ANALYSES AND GEOTHERMOMETRY OF HOT SPRING WATERS FROM THE CALABOZOS CALDERA, CENTRAL CHILE.

    USGS Publications Warehouse

    Thompson, J.M.; Grunder, A.L.; Hildreth, Wes

    1983-01-01

    Hot springs discharging from the active hydrothermal system associated with the Calabozos caldera, Chile, have measured orifice temperatures as high as 98. 5 degree C and calculated geothermometer temperatures as high as 250 degree C. Three types of spring waters can be identified from the chemical analyses: a Na-Cl type, a Na-HCO//3 type and a Na-mixed anion type. Chloride-enthalpy relations indicate that the hydrothermal reservoir water may attain temperatures near 342 degree C and that most spring waters are mixed with cold meteoric water. Despite the proximity of Mesozoic marine gypsum deposits, the Cl/Br weight ratio of the Calabozos spring waters does not appear to indicate that these waters have a significant 'marine' signature. Refs.

  2. Template assisted synthesis of photocatalytic titanium dioxide nanotubes by hot filament chemical vapor deposition method

    NASA Astrophysics Data System (ADS)

    Karaman, Mustafa; Sarıipek, Fatma; Köysüren, Özcan; Yıldız, H. Bekir

    2013-10-01

    Titanium dioxide thin films were deposited conformally over electrospun polymethyl methacrylate (PMMA) fibers by hot filament chemical vapor deposition method. Deposition rates were observed to be very high to allow for rapid coatings. Thermal annealing of as deposited materials leads the clean decomposition of the polymeric inner layer and formation of randomly distributed anatase TiO2 nanotubes. Nanotubular TiO2 structure was clearly identified by SEM and that structure is ideal for good photocatalytic activity because of its high surface area per unit volume ratio. FTIR and XPS results show the formation of stoichiometric TiO2, and the crystalline form of the final nanotubes was found to be anatase (1 0 1) after XRD analysis. High photocatalytic activity of TiO2 nanotubes under UV irradiation was observed with an apparent rate constant of 0.74 h-1 for methyl orange decomposition.

  3. Fabrication of commercial-scale fiber-reinforced hot-gas filters by chemical vapor deposition

    SciTech Connect

    White, L.R.

    1992-11-01

    Goal was to fabricate a filter for removing particulates from hot gases; principal applications would be in advanced utility processes such as pressurized fluidized bed combustion or coal gasification combined cycle systems. Filters were made in two steps: make a ceramic fiber preform and coat it with SiC by chemical vapor infiltration (CVD). The most promising construction was felt/filament wound. Light, tough ceramic composite filters can be made; reinforcement by continuous fibers is needed to avoid brittleness. Direct metal to filter contact does not damage the top which simplifies installation. However, much of the filter surface of felt/filament wound structures is closed over by the CVD coating, and the surface is rough and subject to delamination. Recommendations are given for improving the filters.

  4. Chemical Analysis of Impurity Boron Atoms in Diamond Using Soft X-ray Emission Spectroscopy

    SciTech Connect

    Muramatsu, Yasuji; Iihara, Junji; Takebe, Toshihiko; Denlinger, Jonathan D.

    2008-03-29

    To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

  5. Environmental Assessment for decontaminating and decommissioning the General Atomics Hot Cell Facility. Final [report

    SciTech Connect

    1995-08-01

    This EA evaluates the proposed action to decontaminate and decommission GA`s hot cell facility in northern San Diego, CA. This facility has been used for DOE and commercial nuclear R&D for > 30 years. About 30,000 cubic feet of decontamination debris and up to 50,000 cubic feet of contaminated soil are to be removed. Low-level radioactive waste would be shipped for disposal. It was determined that the proposal does not constitute a major federal action significantly affecting the human environment according to NEPA; therefore, a finding of no significant impact is made, and an environmental impact statement is not required.

  6. In situ observation of thermomigration of Sn atoms to the hot end of 96.5Sn-3Ag-0.5Cu flip chip solder joints

    NASA Astrophysics Data System (ADS)

    Ouyang, Fan-Yi; Kao, C.-L.

    2011-12-01

    In this study, we investigated the phenomenon of thermomigration in 96.5Sn-3Ag-0.5Cu flip chip solder joints at an ambient temperature of 150 °C. We observed mass protrusion on the chip side (hot end), indicating that Sn atoms moved to the hot end, and void formation on the substrate side (cold end). The diffusion markers also moved to the substrate side, in the same direction of the vacancy flux, indicating that the latter played a dominant role during the thermomigration process. The molar heat of transport (Q*) of the Sn atoms was 3.38 kJ/mol.

  7. On a new method for chemical production of iodine atoms in a chemical oxygen-iodine laser

    SciTech Connect

    Andreeva, Tamara L; Kuznetsova, S V; Maslov, A I; Sorokin, Vadim N

    2004-11-30

    A new method is proposed for generating iodine atoms in a chemical oxygen-iodine laser. The method is based on a branched chain reaction of dissociation of the alkyl iodide CH{sub 3}I in a medium of singlet oxygen and chlorine. (active media)

  8. Chemical mechanisms and reaction rates for the initiation of hot corrosion of IN-738

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1984-01-01

    Sodium-sulfate-induced hot corrosion of preoxidized IN-738 was studied at 975 C with special emphasis placed on the processes occurring during the long induction period. Thermogravimetric tests were run for predetermined periods of time, and then one set of specimens was washed with water. Chemical analysis of the wash solutions yielded information about water soluble metal salts and residual sulfate. A second set of samples was cross sectioned dry and polished in a nonaqueous medium. Element distributions within the oxide scale were obtained from electron microprobe X-ray micrographs. Evolution of SO was monitored throughout the thermogravimetric tests. Kinetic rate studies were performed for several pertinent processes; appropriate rate constants were obtained from the following chemical reactions: Cr2O3 + 2 Na2SO4(1) + 3/2 O2 yields 2 Na2CrO4(1) + 2 SO3(g)n TiO2 + Na2SO4(1) yields Na2O(TiO2)n + SO3(g)n TiO2 + Na2CrO4(1) yields Na2O(TiO2)n + CrO3(g).

  9. Chemical reactions involved in the initiation of hot corrosion of IN-738

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1984-01-01

    Sodium-sulfate-induced hot corrosion of preoxidized IN-738 was studied at 975 C with special emphasis placed on the processes occurring during the long induction period. Thermogravimetric tests were run for predetermined periods of time, and then one set of specimens was washed with water. Chemical analysis of the wash solutions yielded information about water soluble metal salts and residual sulfate. A second set of samples was cross sectioned dry and polished in a nonaqueous medium. Element distributions within the oxide scale were obtained from electron microprobe X-ray micrographs. Evolution of SO was monitored throughout the thermogravimetric tests. Kinetic rate studies were performed for several pertinent processes; appropriate rate constants were obtained from the following chemical reactions; Cr203 + 2 Na2S04(1) + 3/2 02 yields 2 Na2Cr04(1) + 2 S03(g)n TiO2 + Na2S04(1) yields Na20(T102)n + 503(g)n T102 + Na2Cro4(1) yields Na2(T102)n + Cr03(g).

  10. Comparison of laser-ablation and hot-wall chemical vapour deposition techniques for nanowire fabrication

    NASA Astrophysics Data System (ADS)

    Stern, E.; Cheng, G.; Guthrie, S.; Turner-Evans, D.; Broomfield, E.; Lei, B.; Li, C.; Zhang, D.; Zhou, C.; Reed, M. A.

    2006-06-01

    A comparison of the transport properties of populations of single-crystal, In2O3 nanowires (NWs) grown by unassisted hot-wall chemical vapour deposition (CVD) versus NWs grown by laser-ablation-assisted chemical vapour deposition (LA-CVD) is presented. For nominally identical growth conditions across the two systems, NWs fabricated at 850 °C with laser-ablation had significantly higher average mobilities at the 99.9% confidence level, 53.3 ± 5.8 cm2 V-1 s-1 versus 10.2 ± 1.9 cm2 V-1 s-1. It is also observed that increasing growth temperature decreases mobility for LA-CVD NWs. Transmission electron microscopy studies of CVD-fabricated samples indicate the presence of an amorphous In2O3 region surrounding the single-crystal core. Further, low-temperature measurements verify the presence of ionized impurity scattering in low-mobility CVD-grown NWs.

  11. Gas temperature measurements inside a hot wall chemical vapor synthesis reactor.

    PubMed

    Notthoff, Christian; Schilling, Carolin; Winterer, Markus

    2012-11-01

    One key but complex parameter in the chemical vapor synthesis (CVS) of nanoparticles is the time temperature profile of the gas phase, which determines particle characteristics such as size (distribution), morphology, microstructure, crystal, and local structure. Relevant for the CVS process and for the corresponding particle characteristics is, however, not the T(t)-profile generated by an external energy source such as a hot wall or microwave reactor but the temperature of the gas carrying reactants and products (particles). Due to a complex feedback of the thermodynamic and chemical processes in the reaction volume with the external energy source, it is very difficult to predict the real gas phase temperature field from the externally applied T(t)-profile. Therefore, a measurement technique capable to determine the temperature distribution of the gas phase under process conditions is needed. In this contribution, we demonstrate with three proof of principle experiments the use of laser induced fluorescence thermometry to investigate the CVS process under realistic conditions.

  12. Translationally and rotationally resolved excitation of CO2(00 0 2) by collisions with hot hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Khan, Farooq A.; Kreutz, Thomas G.; Flynn, George W.; Weston, Ralph E., Jr.

    1993-04-01

    Time domain tunable diode laser absorption spectroscopy has been used to measure rotationally resolved transient absorption line shapes and nascent rotational populations for CO2 molecules excited into the (00 0 2) vibrational state by collisions with translationally hot hydrogen atoms. The 00 0 2 rotational population distribution and rotationally resolved linewidths are remarkably similar to those previously obtained for 00 0 1. Within the context of a simple physical model used to interpret the data, the similar rotational distributions and translational recoils for 00 0 1 and 00 0 2 suggest that these two states are excited by similar collision trajectories, wherein asymmetric stretching excitation is optimized when H strikes near the end of the O-C-O molecule. The magnitude of population scattered into 00 0 2 is about 21 times smaller than that scattered into 00 0 1.

  13. Hydrogen atom initiated chemistry. [chemical evolution in planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Hong, J. H.; Becker, R. S.

    1979-01-01

    H Atoms have been created by the photolysis of H2S. These then initiated reactions in mixtures involving acetylene-ammonia-water and ethylene-ammonia-water. In the case of the acetylene system, the products consisted of two amino acids, ethylene and a group of primarily cyclic thio-compounds, but no free sulfur. In the case of the ethylene systems, seven amino acids, including an aromatic one, ethane, free sulfur, and a group of solely linear thio-compounds were produced. Total quantum yields for the production of amino acids were about 3 x 10 to the -5th and about 2 x 10 to the -4th with ethylene and acetylene respectively as carbon substrates. Consideration is given of the mechanism for the formation of some of the products and implications regarding planetary atmosphere chemistry, particularly that of Jupiter, are explored.

  14. Deducing chemical structure from crystallographically determined atomic coordinates

    PubMed Central

    Bruno, Ian J.; Shields, Gregory P.; Taylor, Robin

    2011-01-01

    An improved algorithm has been developed for assigning chemical structures to incoming entries to the Cambridge Structural Database, using only the information available in the deposited CIF. Steps in the algorithm include detection of bonds, selection of polymer unit, resolution of disorder, and assignment of bond types and formal charges. The chief difficulty is posed by the large number of metallo-organic crystal structures that must be processed, given our aspiration that assigned chemical structures should accurately reflect properties such as the oxidation states of metals and redox-active ligands, metal coordination numbers and hapticities, and the aromaticity or otherwise of metal ligands. Other complications arise from disorder, especially when it is symmetry imposed or modelled with the SQUEEZE algorithm. Each assigned structure is accompanied by an estimate of reliability and, where necessary, diagnostic information indicating probable points of error. Although the algorithm was written to aid building of the Cambridge Structural Database, it has the potential to develop into a general-purpose tool for adding chemical information to newly determined crystal structures. PMID:21775812

  15. Interaction of hot swirling air and liquid film flow in airblast atomizers

    NASA Astrophysics Data System (ADS)

    Baumann, Wolfgang W.; Bendisch, Holger; Eickhoff, Heinrich; Thiele, Frank

    The flowfield in an airblast atomizer of the prefilming type is studied numerically. Special attention is drawn to the flow near the liquid film surface, which is calculated using a boundary-layer method. Thereby near-wall effects (e.g., evaporation) are exactly accounted for. The main nozzle flow is calculated using the Navier-Stokes equations. Both systems are linked by the boundary conditions. The results for an airblast atomizer with adjacent combustion chamber show significant differences between coupled and uncoupled calculations. It is shown that the detailed modeling of the film and the coupled calculation, which accounts exactly for boundary-layer effects including evaporation, is essential for accurate simulations.

  16. GHz Rabi Flopping to Rydberg States in Hot Atomic Vapor Cells

    SciTech Connect

    Huber, B.; Baluktsian, T.; Schlagmueller, M.; Koelle, A.; Kuebler, H.; Loew, R.; Pfau, T.

    2011-12-09

    We report on the observation of Rabi oscillations to a Rydberg state on a time scale below 1 ns in thermal rubidium vapor. We use a bandwidth-limited pulsed excitation and observe up to 6 full Rabi cycles within a pulse duration of {approx}4 ns. We find good agreement between the experiment and numerical simulations based on a surprisingly simple model. This result shows that fully coherent dynamics with Rydberg states can be achieved even in thermal atomic vapor, thus suggesting small vapor cells as a platform for room-temperature quantum devices. Furthermore, the result implies that previous coherent dynamics in single-atom Rydberg gates can be accelerated by 3 orders of magnitude.

  17. Epitaxial Thin Film Silicon Solar Cells Fabricated by Hot Wire Chemical Vapor Deposition Below 750 ..deg..C: Preprint

    SciTech Connect

    Alberi, K.; Martin, I. T.; Shub, M.; Teplin, C. W.; Iwaniczko, E.; Xu, Y.; duda, A.; Stradin, P.; Johnston, S. W.; Romero, M. J.; Branz, H. M.; Young, D. L.

    2009-06-01

    We report on fabricating film c-Si solar cells on Si wafer templates by hot-wire chemical vapor deposition. These devices, grown at glass-compatible temperatures < 750..deg..C, demonstrate open-circuit voltages > 500 mV and efficiencies > 5%.

  18. Single molecule and single atom sensors for atomic resolution imaging of chemically complex surfaces.

    PubMed

    Kichin, Georgy; Weiss, Christian; Wagner, Christian; Tautz, F Stefan; Temirov, Ruslan

    2011-10-26

    Individual Xe atoms as well as single CO and CH(4) molecules adsorbed at the tip apex of a scanning tunneling microscope (STM) function as microscopic force sensors that change the tunneling current in response to the forces acting from the surface. An STM equipped with any of these sensors is able to image the short-range Pauli repulsion and thus resolve the inner structure of large organic adsorbate molecules. Differences in the performance of the three studied sensors suggest that the sensor functionality can be tailored by tuning the interaction between the sensor particle and the STM tip.

  19. Photon pair production from a hot atomic ensemble in the diamond configuration

    NASA Astrophysics Data System (ADS)

    Willis, Richard Thomas

    This thesis discusses four-wave mixing (4WM) in a warm ensemble of rubidium using the diamond configuration level structure. Both classical 4WM and nonclassical photon-pair production are investigated. Quantum information science has spawned a great amount of experimental work on the interaction of light with collective modes of excitation in atomic ensembles. Plans to build quantum networks and quantum repeaters with atom ensembles take advantage of nonlinear interactions to produce and store non-classical states of light. These technologies will require photon sources that not only generate nonclassical light, but also resonant, narrow band light. Here we investigate a system which could be used as such a source. We take advantage of the 4WM interaction in a warm ensemble of Rubidium atoms. Our scheme utilizes the diamond energy level configuration which, in rubidium, allows for correlated pairs at telecommunications wavelengths. We start by examining the properties of classical 4WM in the system. We measure the resonance structure and see that it can be understood in terms of velocity class selective resonant enhancement and power splitting effects. The efficiency of the process is low and limited by linear absorption of the pumps. Our observations agree with a semi-classical Maxwell-Bloch theoretical treatment. Next we observe pair generation by spontaneous 4WM from the warm ensemble. The temporal profile of the cross-correlation function (CCF) for the photons depends on pump-laser power and detuning. This allows us to produce biphotons with controllable spectra. A simple quantum optical theoretical treatment based on linear filtering gives qualitative agreement with the data. We show that the photon pairs are polarization entangled, clearly violating Bell's Inequality. A perturbative quantum optical treatment predicts the polarization state of the pairs and agrees with our measurements. We analyze the photon statistics of the source and find the largest

  20. Following Ostwald ripening in nanoalloys by high-resolution imaging with single-atom chemical sensitivity

    NASA Astrophysics Data System (ADS)

    Alloyeau, D.; Oikawa, T.; Nelayah, J.; Wang, G.; Ricolleau, C.

    2012-09-01

    Several studies have shown that substantial compositional changes can occur during the coarsening of bimetallic nanoparticles (CoPt, AuPd). To explain this phenomenon that could dramatically impacts all the technologically relevant properties of nanoalloys, we have exploited the sensitivity of the latest generation of electron microscope to prove that during the beam-induced coarsening of CoPt nanoparticles, the dynamic of atom exchanges between the particles is different for Co and Pt. By distinguishing the chemical nature of individual atoms of Co and Pt, while they are diffusing on a carbon film, we have clearly shown that Co atoms have a higher mobility than Pt atoms because of their higher evaporation rate from the particles. These atomic-scale observations bring the experimental evidence on the origin of the compositional changes in nanoalloys induced by Ostwald ripening mechanisms.

  1. Determining Chemically and Spatially Resolved Atomic Profile of Low Contrast Interface Structure with High Resolution

    PubMed Central

    Nayak, Maheswar; Pradhan, P. C.; Lodha, G. S.

    2015-01-01

    We present precise measurements of atomic distributions of low electron density contrast at a buried interface using soft x-ray resonant scattering. This approach allows one to construct chemically and spatially highly resolved atomic distribution profile upto several tens of nanometer in a non-destructive and quantitative manner. We demonstrate that the method is sensitive enough to resolve compositional differences of few atomic percent in nano-scaled layered structures of elements with poor electron density differences (0.05%). The present study near the edge of potential impurities in soft x-ray range for low-Z system will stimulate the activity in that field. PMID:25726866

  2. Chemical, isotopic, and dissolved gas compositions of the hot springs of the Owyhee Uplands, Malheur County, Oregon

    USGS Publications Warehouse

    Mariner, R.H.; Young, H.W.; Evans, William C.; Nielson, Dennis L.

    1994-01-01

    Hot springs along the Owyhee River in southeastern Oregon between Three Forks and Lake Owyhee could be part of a north flowing regional system or a series of small separate geothermal systems Heat for the waters could be from a very young (Holocene) volcanic activity (basalt flows) of the Owyhee Uplands or the regional heat flow. The springs discharge warm to hot, dilute, slightly alkaline, sodium bicarbonate water. Chemically they are similar to the dilute thermal water at Bruneau Grand View and Twin Falls, Idaho. Maximum aquifer temperatures in the Owyhee Uplands, estimated from chemical geothermometry, are about 100°C. Dissolved helium concentrations, carbon 14 activity, and chemical and isotope data are examined fro systematic trends which would indicate a geothermal system of regional extent.

  3. Synthesis of SiO{sub 2}/β-SiC/graphite hybrid composite by low temperature hot filament chemical vapor deposition

    SciTech Connect

    Zhang, Zhikun; Bi, Kaifeng; Liu, Yanhong; Qin, Fuwen; Liu, Hongzhu; Bian, Jiming; Zhang, Dong; Miao, Lihua

    2013-11-18

    β-SiC thin films were synthesized directly on graphite by hot filament chemical vapor deposition at low temperature. SiH{sub 4} diluted in hydrogen was employed as the silicon source, while graphite was functioned as both substrate and carbon source for the as-grown β-SiC films. X-ray diffraction and Fourier transform infrared analysis indicate that SiO{sub 2}/β-SiC/graphite hybrid composite was formed after post annealing treatment, and its crystalline quality can be remarkably improved under optimized annealing conditions. The possible growth mechanism was proposed based on in situ etching of graphite by reactive hydrogen radicals at the atomic level.

  4. Anomalously high thermal conductivity of amorphous Si deposited by hot-wire chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Yang, Ho-Soon; Cahill, David G.; Liu, X.; Feldman, J. L.; Crandall, R. S.; Sperling, B. A.; Abelson, J. R.

    2010-03-01

    The thermal conductivities of thin films of amorphous Si (a-Si) deposited by hot-wire chemical vapor deposition (HWCVD) are measured by time-domain thermoreflectance (TDTR). Amorphous Si samples prepared at the National Renewable Energy Laboratory (NREL) show an anomalous enhancement in thermal conductivity compared to other forms of a-Si and compared to the prediction of the model of the minimum thermal conductivity. The thermal conductivity of the NREL HWCVD a-Si samples also decreases with increasing frequency of the temperature fields used in the experiment. This frequency dependence of the thermal conductivity is nearly identical to the results of our previous studies of crystalline semiconductor alloys; a comparison of the frequency dependence to a phonon-scattering model suggests that Rayleigh-type scattering controls the mean-free path of ˜5meV phonons in this material. Amorphous Si films prepared at University of Illinois (U. Illinois) do not show an enhanced thermal conductivity even though Raman vibrational spectra of the U. Illinois and NREL samples are nearly identical. Thus, the thermal conductivity of a-Si depends on details of the microstructure that are not revealed by vibrational spectroscopy and measurements by TDTR provide a convenient method of identifying novel microstructures in amorphous materials.

  5. Controlled growth of high-quality graphene using hot-filament chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Selvakumar, N.; Vadivel, B.; Rao, D. V. Sridhara; Krupanidhi, S. B.; Barshilia, Harish C.

    2016-11-01

    High-quality graphene was grown on polycrystalline copper (Cu) foils (1 cm × 1 cm) using hot-filament chemical vapor deposition method. The role of process parameters such as gas flow rates (methane and hydrogen), growth temperatures (filament and substrate) and durations on the growth of graphene was studied. The process parameters were also optimized to grow monolayer, bilayer and multilayer graphene in a controlled manner, and a growth mechanism was deduced from the experimental results. The presence of graphene on Cu foils was confirmed using X-ray photoelectron spectroscopy, micro-Raman spectroscopy, field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. FESEM micrographs clearly showed that the graphene starts nucleating as hexagonal islands and later evolves as dendritic lobe-shaped islands with an increase in supersaturation. The TEM images substantiate the growth of monolayer, bilayer and multilayer graphene. The I 2D/ I G ratio = 2 confirmed the presence of the monolayer graphene and the absence of `D' peak in the Raman spectrum indicated the high purity of graphene grown on Cu foils. These results also show that the polycrystalline copper foil morphology has negligible effect on the growth of monolayer graphene.

  6. Hot atom reactions involving multivalent and univalent species. Progress report, February 1980-January 1981

    SciTech Connect

    Tang, Y.N.

    1981-01-01

    Major progress was made in the study of recoil /sup 31/Si reactions. The most significant discovery is that monomeric /sup 31/SiF/sub 2/ adds to two molecules of C/sub 2/H/sub 4/ to give 1,1-difluorosilacyclopentane as a final product. When radical scavengers were added, the yield of this product was not altered. When 1,3-butadiene was added to the above recoil /sup 31/Si system to compete with C/sub 2/H/sub 4/ for the available /sup 31/SiF/sub 2/, a nearly complementary relationship was found between 1,1-difluorosilacyclopent-3-ene-/sup 31/Si, the butadiene product, and 1,1-difluorosilacyclopentane-/sup 31/Si. Quantitatively, it was deduced that butadiene is about ten times more reactive than C/sub 2/H/sub 4/ for the trapping of /sup 31/SiF/sub 2/. When Ne was added as a moderator to the 5:1 C/sub 2/H/sub 4/:butadiene competition system, the two product ratio shifts from 1:2 in favor of butadiene to 10:1 in favor of C/sub 2/H/sub 4/. This indicates that it is the lower energy /sup 31/SiF/sub 2/ species which is captured by C/sub 2/H/sub 4/, while it is favorable for the more energetic /sup 31/SiF/sub 2/ to be captured by butadiene. In the systems reacting recoil /sup 31/Si atoms with C/sub 2/H/sub 4/ in the presence of PF/sub 3/, four unidentified products with yields less than that of 1,1-difluorosilacyclopentane were also observed. Two of them were also formed when either PH/sub 3/ or (CH/sub 3/)/sub 3/P were used as the /sup 31/Si precursor. This means that they are likely to be direct /sup 31/Si atom reaction products. When recoil /sup 31/Si atoms reacted with C/sub 2/H/sub 4/ in the presence of (CH/sub 3/)/sub 3/P, the main product was identified as /sup 31/SiH(CH/sub 3/)/sub 2/CH = CH/sub 2/. This might mean the formation of dimethylsilene, /sup 31/Si(CH/sub 3/)/sub 2/, and the addition of it to CH/sub 2/ = CH/sub 2/ to give the product. In addition, catalytic C-F hydrogenolysis of CH/sub 2/ = CHF, CH/sub 3/CH/sub 2/F, CHF = CHF, CH/sub 2/ = CF/sub 2/, CH

  7. Ultrafast formation of interlayer hot excitons in atomically thin MoS2/WS2 heterostructures.

    PubMed

    Chen, Hailong; Wen, Xiewen; Zhang, Jing; Wu, Tianmin; Gong, Yongji; Zhang, Xiang; Yuan, Jiangtan; Yi, Chongyue; Lou, Jun; Ajayan, Pulickel M; Zhuang, Wei; Zhang, Guangyu; Zheng, Junrong

    2016-01-01

    Van der Waals heterostructures composed of two-dimensional transition-metal dichalcogenides layers have recently emerged as a new family of materials, with great potential for atomically thin opto-electronic and photovoltaic applications. It is puzzling, however, that the photocurrent is yielded so efficiently in these structures, despite the apparent momentum mismatch between the intralayer/interlayer excitons during the charge transfer, as well as the tightly bound nature of the excitons in 2D geometry. Using the energy-state-resolved ultrafast visible/infrared microspectroscopy, we herein obtain unambiguous experimental evidence of the charge transfer intermediate state with excess energy, during the transition from an intralayer exciton to an interlayer exciton at the interface of a WS2/MoS2 heterostructure, and free carriers moving across the interface much faster than recombining into the intralayer excitons. The observations therefore explain how the remarkable charge transfer rate and photocurrent generation are achieved even with the aforementioned momentum mismatch and excitonic localization in 2D heterostructures and devices. PMID:27539942

  8. Ultrafast formation of interlayer hot excitons in atomically thin MoS2/WS2 heterostructures

    NASA Astrophysics Data System (ADS)

    Chen, Hailong; Wen, Xiewen; Zhang, Jing; Wu, Tianmin; Gong, Yongji; Zhang, Xiang; Yuan, Jiangtan; Yi, Chongyue; Lou, Jun; Ajayan, Pulickel M.; Zhuang, Wei; Zhang, Guangyu; Zheng, Junrong

    2016-08-01

    Van der Waals heterostructures composed of two-dimensional transition-metal dichalcogenides layers have recently emerged as a new family of materials, with great potential for atomically thin opto-electronic and photovoltaic applications. It is puzzling, however, that the photocurrent is yielded so efficiently in these structures, despite the apparent momentum mismatch between the intralayer/interlayer excitons during the charge transfer, as well as the tightly bound nature of the excitons in 2D geometry. Using the energy-state-resolved ultrafast visible/infrared microspectroscopy, we herein obtain unambiguous experimental evidence of the charge transfer intermediate state with excess energy, during the transition from an intralayer exciton to an interlayer exciton at the interface of a WS2/MoS2 heterostructure, and free carriers moving across the interface much faster than recombining into the intralayer excitons. The observations therefore explain how the remarkable charge transfer rate and photocurrent generation are achieved even with the aforementioned momentum mismatch and excitonic localization in 2D heterostructures and devices.

  9. Ultrafast formation of interlayer hot excitons in atomically thin MoS2/WS2 heterostructures.

    PubMed

    Chen, Hailong; Wen, Xiewen; Zhang, Jing; Wu, Tianmin; Gong, Yongji; Zhang, Xiang; Yuan, Jiangtan; Yi, Chongyue; Lou, Jun; Ajayan, Pulickel M; Zhuang, Wei; Zhang, Guangyu; Zheng, Junrong

    2016-08-19

    Van der Waals heterostructures composed of two-dimensional transition-metal dichalcogenides layers have recently emerged as a new family of materials, with great potential for atomically thin opto-electronic and photovoltaic applications. It is puzzling, however, that the photocurrent is yielded so efficiently in these structures, despite the apparent momentum mismatch between the intralayer/interlayer excitons during the charge transfer, as well as the tightly bound nature of the excitons in 2D geometry. Using the energy-state-resolved ultrafast visible/infrared microspectroscopy, we herein obtain unambiguous experimental evidence of the charge transfer intermediate state with excess energy, during the transition from an intralayer exciton to an interlayer exciton at the interface of a WS2/MoS2 heterostructure, and free carriers moving across the interface much faster than recombining into the intralayer excitons. The observations therefore explain how the remarkable charge transfer rate and photocurrent generation are achieved even with the aforementioned momentum mismatch and excitonic localization in 2D heterostructures and devices.

  10. Ultrafast formation of interlayer hot excitons in atomically thin MoS2/WS2 heterostructures

    PubMed Central

    Chen, Hailong; Wen, Xiewen; Zhang, Jing; Wu, Tianmin; Gong, Yongji; Zhang, Xiang; Yuan, Jiangtan; Yi, Chongyue; Lou, Jun; Ajayan, Pulickel M.; Zhuang, Wei; Zhang, Guangyu; Zheng, Junrong

    2016-01-01

    Van der Waals heterostructures composed of two-dimensional transition-metal dichalcogenides layers have recently emerged as a new family of materials, with great potential for atomically thin opto-electronic and photovoltaic applications. It is puzzling, however, that the photocurrent is yielded so efficiently in these structures, despite the apparent momentum mismatch between the intralayer/interlayer excitons during the charge transfer, as well as the tightly bound nature of the excitons in 2D geometry. Using the energy-state-resolved ultrafast visible/infrared microspectroscopy, we herein obtain unambiguous experimental evidence of the charge transfer intermediate state with excess energy, during the transition from an intralayer exciton to an interlayer exciton at the interface of a WS2/MoS2 heterostructure, and free carriers moving across the interface much faster than recombining into the intralayer excitons. The observations therefore explain how the remarkable charge transfer rate and photocurrent generation are achieved even with the aforementioned momentum mismatch and excitonic localization in 2D heterostructures and devices. PMID:27539942

  11. Fast Atomic-Scale Chemical Imaging of Crystalline Materials and Dynamic Phase Transformations.

    PubMed

    Lu, Ping; Yuan, Ren Liang; Ihlefeld, Jon F; Spoerke, Erik David; Pan, Wei; Zuo, Jian Min

    2016-04-13

    Atomic-scale phenomena fundamentally influence materials form and function that makes the ability to locally probe and study these processes critical to advancing our understanding and development of materials. Atomic-scale chemical imaging by scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) is a powerful approach to investigate solid crystal structures. Inefficient X-ray emission and collection, however, require long acquisition times (typically hundreds of seconds), making the technique incompatible with electron-beam sensitive materials and study of dynamic material phenomena. Here we describe an atomic-scale STEM-EDS chemical imaging technique that decreases the acquisition time to as little as one second, a reduction of more than 100 times. We demonstrate this new approach using LaAlO3 single crystal and study dynamic phase transformation in beam-sensitive Li[Li0.2Ni0.2Mn0.6]O2 (LNMO) lithium ion battery cathode material. By capturing a series of time-lapsed chemical maps, we show for the first time clear atomic-scale evidence of preferred Ni-mobility in LNMO transformation, revealing new kinetic mechanisms. These examples highlight the potential of this approach toward temporal, atomic-scale mapping of crystal structure and chemistry for investigating dynamic material phenomena.

  12. Atomic Force Tomography of a Nonplanar Molecule: Role of Lateral and Chemical Sample-Tip Interactions

    NASA Astrophysics Data System (ADS)

    Kong, Xianghua; Ji, Wei; Physics department, McGill Team; Physics department, Renmin University of China Team

    Atomically identification of the molecular geometric structures is an important prerequisite to understand their chemical and electrical properties. TiOPc, a steric structure, gives rise to two adsorption configurations of TiOPc on Cu(111), namely O-dn and O-up. The roles of chemical specific interactions of different intramolecular atoms with the AFM tips were discussed at the submolecular level. For O-up, the molecular backbone of TiOPc is only visible out of a certain range from the center of the molecule, accompanied with significant dissipation signal. Theoretical calculation identifies such dissipation signal as the chemical attraction between the out-of-plane O in TiOPc and the Cu atoms behind the CO of a tip at a certain range of lateral distance between them. When they approach closer, the sample O repulses another O in the CO tip making it tilting strongly, which softens the tip and thus leads to even stronger O (sample) - Cu (tip) attraction. A direct demonstration of sample-tip electronic hybridization was manifested in the simpler O-dn case where an explicit wavefunction overlap between the tip O atom and the sample Ti atom. Given these results presented here, we anticipate that this method might be developed further generally useful in single-molecule chemistry and physics. X.K. thanks the Chinese Scholarship Council for support.

  13. Metal oxide nanoparticle growth on graphene via chemical activation with atomic oxygen.

    PubMed

    Johns, James E; Alaboson, Justice M P; Patwardhan, Sameer; Ryder, Christopher R; Schatz, George C; Hersam, Mark C

    2013-12-01

    Chemically interfacing the inert basal plane of graphene with other materials has limited the development of graphene-based catalysts, composite materials, and devices. Here, we overcome this limitation by chemically activating epitaxial graphene on SiC(0001) using atomic oxygen. Atomic oxygen produces epoxide groups on graphene, which act as reactive nucleation sites for zinc oxide nanoparticle growth using the atomic layer deposition precursor diethyl zinc. In particular, exposure of epoxidized graphene to diethyl zinc abstracts oxygen, creating mobile species that diffuse on the surface to form metal oxide clusters. This mechanism is corroborated with a combination of scanning probe microscopy, Raman spectroscopy, and density functional theory and can likely be generalized to a wide variety of related surface reactions on graphene.

  14. Revealing the angular symmetry of chemical bonds by atomic force microscopy.

    PubMed

    Welker, Joachim; Giessibl, Franz J

    2012-04-27

    We have measured the angular dependence of chemical bonding forces between a carbon monoxide molecule that is adsorbed to a copper surface and the terminal atom of the metallic tip of a combined scanning tunneling microscope and atomic force microscope. We provide tomographic maps of force and current as a function of distance that revealed the emergence of strongly directional chemical bonds as tip and sample approach. The force maps show pronounced single, dual, or triple minima depending on the orientation of the tip atom, whereas tunneling current maps showed a single minimum for all three tip conditions. We introduce an angular dependent model for the bonding energy that maps the observed experimental data for all observed orientations and distances.

  15. Development Of Hot Surface Polysilicon-Based Chemical Sensor And Actuator With Integrated Catalytic Micropatterns For Gas Sensing Applications

    NASA Astrophysics Data System (ADS)

    Vereshchagina, E.; Gardeniers, J. G. E.

    2009-05-01

    Over the last twenty years, we have followed a rapid expansion in the development of chemical sensors and microreactors for detection and analysis of volatile organic compounds. However, for many of the developed gas sensors poor sensitivity and selectivity, and high-power consumption remain among one of the main drawbacks. One promising approach to increase selectivity at lower power consumption is calorimetric sensing, performed in a pulsed regime and using specific catalytic materials. In this work, we study kinetics of various catalytic oxidation reactions using micromachined hot surface polysilicon-based sensor containing sensitive and selective catalysts. The sensor acts as both thermal actuator of chemical and biochemical reactions on hot-surfaces and detector of heats (enthalpies) associated with these reactions. Using novel deposition techniques we integrated selective catalysts in an array of hot plates such that they can be thermally actuated and sensed individually. This allows selective detection and analysis of dangerous gas compounds in a mixture, specifically hydrocarbons at concentrations down to low ppm level. In this contribution we compare various techniques for the local immobilization of catalytic material on hot spots of the sensor in terms of process compatibility, mechanical stress, stability and cost.

  16. Atomic force microscopy of DNA on mica and chemically modified mica.

    PubMed

    Thundat, T; Allison, D P; Warmack, R J; Brown, G M; Jacobson, K B; Schrick, J J; Ferrell, T L

    1992-12-01

    Atomic force microscopy (AFM) was used to image circular DNA adsorbed on freshly cleaved mica and mica chemically modified with Mg(II), Co(II), La(III), and Zr(IV). Images obtained on unmodified mica show coiling of DNA due to forces involved during the drying process. The coiling or super twisting appeared to be right handed and the extent of super twisting could be controlled by the drying conditions. Images of DNA observed on chemically modified surfaces show isolated open circular DNA that is free from super twisting, presumably due to strong binding of DNA on chemically modified surfaces.

  17. Very thin and stable thin-film silicon alloy triple junction solar cells by hot wire chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Veldhuizen, L. W.; Schropp, R. E. I.

    2016-08-01

    We present a silicon-based triple junction solar cell that requires a deposition time of less than 15 min for all photoactive layers. As a low-bandgap material, we used thin layers of hydrogenated amorphous silicon germanium with lower band gap than commonly used, which is possible due to the application of hot wire chemical vapor deposition. The triple junction cell shows an initial energy conversion efficiency exceeding 10%, and with a relative performance stability within 6%, the cell shows a high tolerance to light-induced degradation. With these results, we help to demonstrate that hot wire chemical vapor deposition is a viable deposition method for the fabrication of low-cost solar cells.

  18. Chemical processes involved in the initiation of hot corrosion of B-1900 and NASA-TRW VIA

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1979-01-01

    Sodium sulfate induced hot corrosion of B-1900 and NASA-TRW VIA at 900 C was studied with special emphasis on the chemical reactions occurring during and immediately after the induction period. Thermogravimetric tests were run for set periods of time after which the samples were washed with water and water soluable metal salts and/or residual sulfates were analyzed chemically. Element distributions within the oxide layer were obtained from electron microprobe X-ray micrographs. A third set of samples were subjected to surface analysis by X-ray photoelectron spectroscopy. Evolution of SO2 was monitored throughout many of the hot corrosion tests. Results are interpreted in terms of acid-base fluxing mechanisms.

  19. The H + OCS hot atom reaction - CO state distributions and translational energy from time-resolved infrared absorption spectroscopy

    NASA Technical Reports Server (NTRS)

    Nickolaisen, Scott L.; Cartland, Harry E.

    1993-01-01

    Time-resolved infrared diode laser spectroscopy has been used to probe CO internal and translational excitation from the reaction of hot H atoms with OCS. Product distributions should be strongly biased toward the maximum 1.4 eV collision energy obtained from 278 nm pulsed photolysis of HI. Rotations and vibrations are both colder than predicted by statistical density of states theory, as evidenced by large positive surprisal parameters. The bias against rotation is stronger than that against vibration, with measurable population as high as v = 4. The average CO internal excitation is 1920/cm, accounting for only 13 percent of the available energy. Of the energy balance, time-resolved sub-Doppler line shape measurements show that more than 38 percent appears as relative translation of the separating CO and SH fragments. Studies of the relaxation kinetics indicate that some rotational energy transfer occurs on the time scale of our measurements, but the distributions do not relax sufficiently to alter our conclusions. Vibrational distributions are nascent, though vibrational relaxation of excited CO is unusually fast in the OCS bath, with rates approaching 3 percent of gas kinetic for v = 1.

  20. Determination of hot and cool burning residential wood combustion source strengths using chemical mass balance modeling

    SciTech Connect

    Rau, J.A.; Huntzicker, J.J.; Khalil, M.A.K. )

    1987-01-01

    This paper compares CMB results using separate hot and cool RWC source composition profiles, a composite of hot and cool composition profiles weighted according reported stove usage patterns, and the conventional EPA RWC source composition profile. These profiles are shown. Since the composition of hot and cool burn particles is dramatically different, hot and cool burn composition profiles can be used as separate sources in the same CMB model. Hot burning RWC particles are black, have a mild acrid smell and contain from 20 to 60% carbon (up to 80% of the carbon can be in the form of elemental carbon) and high levels of trace elements (5-25%K, 2-5% S and 2-4% Cl). In contrast, cool or smoldering burn smoke particles are tan, have a strong pleasant wood smoke smell, and contain 55-60% carbon which is mostly in the form of organic carbon with only a few percent of elemental carbon. The concentrations of trace elements in cool burning emissions are generally less than 0.1%. During hot burning the RWC smoke plume is practically invisible, while during cool burning the plume is very visible and has the typical blue-gray color associated with wood burning. For similar amounts of fuel burning in a stove, emission levels for cool burning are an average of 4.8 times higher than for hot burning.

  1. Hot-wire chemical vapour deposition at low substrate temperatures for optoelectronic applications

    NASA Astrophysics Data System (ADS)

    Bakker, R.

    2010-09-01

    The need for large quantities of rapidly and cheaply produced electronic devices has increased rapidly over the past decades. The transistors and diodes that are used to build these devices are predominantly made of crystalline silicon. Since crystalline silicon is very expensive to produce on a large scale and cannot be directly deposited on plastic substrates, much research is being done on thin film amorphous or nanocrystalline semiconductors and insulators. Hot-wire chemical vapour deposition (HWCVD) is a novel, low cost, and convenient way to deposit these materials. The process can be controlled in such a way that specific chemical reactions take place and unwanted side reactions are minimized. It can easily be scaled up to produce large-area thin film electronics. Conventionally, plasma enhanced chemical vapour deposition (PECVD) is used to deposit semiconductors and inorganic dielectrics. Recently, HWCVD has been explored for fast deposition of such materials. An adaptation of HWCVD, initiated chemical vapour deposition (iCVD), offers the unique possibility of producing organic materials and polymers in a vacuum reactor, without the use of solvents. This technique was originally proposed at the Massachusetts institute of technology (MIT) by Prof. Karen Gleason. The iCVD process involves the creation of radicals by dissociation of a peroxide (a molecule with a ~O-O~ bond) by a heated wire in a vacuum reactor. This radical initiates a polymerization reaction of a vinyl (a molecule with a double carbon-carbon bond, ~C=C~) monomer at a substrate held at room temperature. This thesis describes a dedicated iCVD reactor for polymer deposition, installed at Utrecht University, along with a reactor with a cooled substrate holder in an existing HWCVD multi-chamber setup for low-temperature silicon nitride (SiNx) depositions. The most important features of these reactors are described and the characterization techniques are explained. This thesis contains four new

  2. The effects of consistent chemical kinetics calculations on the pressure-temperature profiles and emission spectra of hot Jupiters

    NASA Astrophysics Data System (ADS)

    Drummond, B.; Tremblin, P.; Baraffe, I.; Amundsen, D. S.; Mayne, N. J.; Venot, O.; Goyal, J.

    2016-10-01

    In this work we investigate the impact of calculating non-equilibrium chemical abundances consistently with the temperature structure for the atmospheres of highly-irradiated, close-in gas giant exoplanets. Chemical kinetics models have been widely used in the literature to investigate the chemical compositions of hot Jupiter atmospheres which are expected to be driven away from chemical equilibrium via processes such as vertical mixing and photochemistry. All of these models have so far used pressure-temperature (P-T) profiles as fixed model input. This results in a decoupling of the chemistry from the radiative and thermal properties of the atmosphere, despite the fact that in nature they are intricately linked. We use a one-dimensional radiative-convective equilibrium model, ATMO, which includes a sophisticated chemistry scheme to calculate P-T profiles which are fully consistent with non-equilibrium chemical abundances, including vertical mixing and photochemistry. Our primary conclusion is that, in cases of strong chemical disequilibrium, consistent calculations can lead to differences in the P-T profile of up to 100 K compared to the P-T profile derived assuming chemical equilibrium. This temperature change can, in turn, have important consequences for the chemical abundances themselves as well as for the simulated emission spectra. In particular, we find that performing the chemical kinetics calculation consistently can reduce the overall impact of non-equilibrium chemistry on the observable emission spectrum of hot Jupiters. Simulated observations derived from non-consistent models could thus yield the wrong interpretation. We show that this behaviour is due to the non-consistent models violating the energy budget balance of the atmosphere.

  3. Chemical quantification of atomic-scale EDS maps under thin specimen conditions.

    PubMed

    Lu, Ping; Romero, Eric; Lee, Shinbuhm; MacManus-Driscoll, Judith L; Jia, Quanxi

    2014-12-01

    We report our effort to quantify atomic-scale chemical maps obtained by collecting energy-dispersive X-ray spectra (EDS) using scanning transmission electron microscopy (STEM) (STEM-EDS). With thin specimen conditions and localized EDS scattering potential, the X-ray counts from atomic columns can be properly counted by fitting Gaussian peaks at the atomic columns, and can then be used for site-by-site chemical quantification. The effects of specimen thickness and X-ray energy on the Gaussian peak width are investigated using SrTiO3 (STO) as a model specimen. The relationship between the peak width and spatial resolution of an EDS map is also studied. Furthermore, the method developed by this work is applied to study cation occupancy in a Sm-doped STO thin film and antiphase boundaries (APBs) present within the STO film. We find that Sm atoms occupy both Sr and Ti sites but preferably the Sr sites, and Sm atoms are relatively depleted at the APBs likely owing to the effect of strain.

  4. Chemical Quantification of Atomic-Scale EDS Maps under Thin Specimen Conditions

    DOE PAGES

    Lu, Ping; Romero, Eric; Lee, Shinbuhm; MacManus-Driscoll, Judith L.; Jia, Quanxi

    2014-10-13

    We report our effort to quantify atomic-scale chemical maps obtained by collecting energy-dispersive X-ray spectra (EDS) using scanning transmission electron microscopy (STEM) (STEM-EDS). Under a thin specimen condition and when the EDS scattering potential is localized, the X-ray counts from atomic columns can be properly counted by fitting Gaussian peaks at the atomic columns, and can then be used for site-by-site chemical quantification. The effects of specimen thickness and X-ray energy on the Gaussian peak-width are investigated by using SrTiO3 (STO) as a model specimen. The relationship between the peak-width and spatial-resolution of an EDS map is also studied. Furthermore,more » the method developed by this work is applied to study a Sm-doped STO thin film and antiphase boundaries present within the STO film. We find that Sm atoms occupy both Sr and Ti sites but preferably the Sr sites, and Sm atoms are relatively depleted at the antiphase boundaries likely due to the effect of strain.« less

  5. Chemical Quantification of Atomic-Scale EDS Maps under Thin Specimen Conditions

    SciTech Connect

    Lu, Ping; Romero, Eric; Lee, Shinbuhm; MacManus-Driscoll, Judith L.; Jia, Quanxi

    2014-10-13

    We report our effort to quantify atomic-scale chemical maps obtained by collecting energy-dispersive X-ray spectra (EDS) using scanning transmission electron microscopy (STEM) (STEM-EDS). Under a thin specimen condition and when the EDS scattering potential is localized, the X-ray counts from atomic columns can be properly counted by fitting Gaussian peaks at the atomic columns, and can then be used for site-by-site chemical quantification. The effects of specimen thickness and X-ray energy on the Gaussian peak-width are investigated by using SrTiO3 (STO) as a model specimen. The relationship between the peak-width and spatial-resolution of an EDS map is also studied. Furthermore, the method developed by this work is applied to study a Sm-doped STO thin film and antiphase boundaries present within the STO film. We find that Sm atoms occupy both Sr and Ti sites but preferably the Sr sites, and Sm atoms are relatively depleted at the antiphase boundaries likely due to the effect of strain.

  6. ReactionMap: an efficient atom-mapping algorithm for chemical reactions.

    PubMed

    Fooshee, David; Andronico, Alessio; Baldi, Pierre

    2013-11-25

    Large databases of chemical reactions provide new data-mining opportunities and challenges. Key challenges result from the imperfect quality of the data and the fact that many of these reactions are not properly balanced or atom-mapped. Here, we describe ReactionMap, an efficient atom-mapping algorithm. Our approach uses a combination of maximum common chemical subgraph search and minimization of an assignment cost function derived empirically from training data. We use a set of over 259,000 balanced atom-mapped reactions from the SPRESI commercial database to train the system, and we validate it on random sets of 1000 and 17,996 reactions sampled from this pool. These large test sets represent a broad range of chemical reaction types, and ReactionMap correctly maps about 99% of the atoms and about 96% of the reactions, with a mean time per mapping of 2 s. Most correctly mapped reactions are mapped with high confidence. Mapping accuracy compares favorably with ChemAxon's AutoMapper, versions 5 and 6.1, and the DREAM Web tool. These approaches correctly map 60.7%, 86.5%, and 90.3% of the reactions, respectively, on the same data set. A ReactionMap server is available on the ChemDB Web portal at http://cdb.ics.uci.edu .

  7. Chemical mapping and quantification at the atomic scale by scanning transmission electron microscopy.

    PubMed

    Chu, Ming-Wen; Chen, Cheng Hsuan

    2013-06-25

    With innovative modern material-growth methods, a broad spectrum of fascinating materials with reduced dimensions-ranging from single-atom catalysts, nanoplasmonic and nanophotonic materials to two-dimensional heterostructural interfaces-is continually emerging and extending the new frontiers of materials research. A persistent central challenge in this grand scientific context has been the detailed characterization of the individual objects in these materials with the highest spatial resolution, a problem prompting the need for experimental techniques that integrate both microscopic and spectroscopic capabilities. To date, several representative microscopy-spectroscopy combinations have become available, such as scanning tunneling microscopy, tip-enhanced scanning optical microscopy, atom probe tomography, scanning transmission X-ray microscopy, and scanning transmission electron microscopy (STEM). Among these tools, STEM boasts unique chemical and electronic sensitivity at unparalleled resolution. In this Perspective, we elucidate the advances in STEM and chemical mapping applications at the atomic scale by energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy with a focus on the ultimate challenge of chemical quantification with atomic accuracy.

  8. Radical and Atom Transfer Halogenation (RATH): A Facile Route for Chemical and Polymer Functionalization.

    PubMed

    Han, Yi-Jen; Lin, Chia-Yu; Liang, Mong; Liu, Ying-Ling

    2016-05-01

    This work demonstrates a new halogenation reaction through sequential radical and halogen transfer reactions, named as "radical and atom transfer halogenation" (RATH). Both benzoxazine compounds and poly(2,6-dimethyl-1,4-phenylene oxide) have been demonstrated as active species for RATH. Consequently, the halogenated compound becomes an active initiator of atom transfer radical polymerization. Combination of RATH and sequential ATRP provides an convenient and effective approach to prepare reactive and crosslinkable polymers. The RATH reaction opens a new window both to chemical synthesis and molecular design and preparation of polymeric materials.

  9. Chemical processes involved in the initiation of hot corrosion of B-1900 and NASA-TRW VIA. [high temperature tests of superalloys

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1979-01-01

    Sodium surface-induced hot corrosion of B-1900 and NASA-TRW VIA alloys at 900 C has been studied, with special attention to the chemical reactions during and immediately after the induction period. Thermogravimetric tests were run and data were obtained by chemical analysis of water soluble metal salts and of residual sulfate. Surface analyses of hot corroded samples were obtained by spectroscopic techniques (ESCA). A chemical mechanism for elucidating Na2SO4-induced hot corrosion is proposed indicating that hot corrosion is initiated by basic fluxing of the protective Al2O3 scale. The sequential, catastrophic corrosion results from molybdenum content. The self-sustaining feature is a consequence of the cyclic nature of the acidic fluxing. It is believed that the mechanism is applicable not only to laboratory results, but also to the practical problem of hot corrosion encountered in gas turbine engines.

  10. Expanding the Scope of Density Derived Electrostatic and Chemical Charge Partitioning to Thousands of Atoms.

    PubMed

    Lee, Louis P; Limas, Nidia Gabaldon; Cole, Daniel J; Payne, Mike C; Skylaris, Chris-Kriton; Manz, Thomas A

    2014-12-01

    The density derived electrostatic and chemical (DDEC/c3) method is implemented into the onetep program to compute net atomic charges (NACs), as well as higher-order atomic multipole moments, of molecules, dense solids, nanoclusters, liquids, and biomolecules using linear-scaling density functional theory (DFT) in a distributed memory parallel computing environment. For a >1000 atom model of the oxygenated myoglobin protein, the DDEC/c3 net charge of the adsorbed oxygen molecule is approximately -1e (in agreement with the Weiss model) using a dynamical mean field theory treatment of the iron atom, but much smaller in magnitude when using the generalized gradient approximation. For GaAs semiconducting nanorods, the system dipole moment using the DDEC/c3 NACs is about 5% higher in magnitude than the dipole computed directly from the quantum mechanical electron density distribution, and the DDEC/c3 NACs reproduce the electrostatic potential to within approximately 0.1 V on the nanorod's solvent-accessible surface. As examples of conducting materials, we study (i) a 55-atom Pt cluster with an adsorbed CO molecule and (ii) the dense solids Mo2C and Pd3V. Our results for solid Mo2C and Pd3V confirm the necessity of a constraint enforcing exponentially decaying electron density in the tails of buried atoms. PMID:26583221

  11. Direct electrothermal atomic absorption spectrometry determination of nickel in sea water using multiple hot injection and Zeeman correction.

    PubMed

    Bermejo-Barrera, P; Moreda-Piñeiro, J; Moreda-Piñeiro, A; Bermejo-Barrera, A

    1998-03-01

    Methods for the direct determination of Ni in sea water samples by ETAAS were developed using Zeeman effect background correction system (ZEBC) and a multi-injection technique. A mass of palladium nitrate of 2.5 mug (for an injection volume of 100 mul) was used as chemical modifier. The optimum pyrolysis and atomization temperatures were 1700 and 2100 degrees C, respectively. The characteristic mass (m(0)) and characteristic concentration (C(0)), precision and accuracy were studied for different injection volumes (20, 100 and 200 mul). For an injection volume of 100 mul (five 20 mul aliquot) of sample the accuracy analysis of different certified materials (saline and non saline water) was agreeable. The total time of the proposed procedure is 6 min. A m(0) and C(0) of 34.5 pg and 0.3 mug l(-1), respectively were obtained for this injection volume (100 mul). Finally, interferences from major and minor components of sea water was studied.

  12. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    NASA Technical Reports Server (NTRS)

    Kahn, L. R.

    1981-01-01

    A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.

  13. A collaboration of labs: The Institute for Atom-Efficient Chemical Transformations (IACT)

    ScienceCinema

    Lobo, Rodrigo; Marshall, Chris; Cheng, Lei; Stair, Peter; Wu, Tianpan; Ray, Natalie; O'Neil, Brandon; Dietrich, Paul

    2016-07-12

    The Institute for Atom-Efficient Chemical Transformations (IACT) is an Energy Frontier Research Center funded by the U.S. Department of Energy. IACT focuses on advancing the science of catalysis to improve the efficiency of producing fuels from biomass and coal. IACT is a collaborative effort that brings together a diverse team of scientists from Argonne National Laboratory, Brookhaven National Laboratory, Northwestern University, Purdue University and the University of Wisconsin. For more information, visit www.iact.anl.gov

  14. Calculation of the Relative Chemical Stabilities of Proteins as a Function of Temperature and Redox Chemistry in a Hot Spring

    PubMed Central

    Dick, Jeffrey M.; Shock, Everett L.

    2011-01-01

    Uncovering the chemical and physical links between natural environments and microbial communities is becoming increasingly amenable owing to geochemical observations and metagenomic sequencing. At the hot spring known as Bison Pool in Yellowstone National Park, the cooling of the water in the outflow channel is associated with an increase in oxidation potential estimated from multiple field-based measurements. Representative groups of proteins whose sequences were derived from metagenomic data also exhibit an increase in average oxidation state of carbon in the protein molecules with distance from the hot-spring source. The energetic requirements of reactions to form selected proteins used in the model were computed using amino-acid group additivity for the standard molal thermodynamic properties of the proteins, and the relative chemical stabilities of the proteins were investigated by varying temperature, pH and oxidation state, expressed as activity of dissolved hydrogen. The relative stabilities of the proteins were found to track the locations of the sampling sites when the calculations included a function for hydrogen activity that increases with temperature and is higher, or more reducing, than values consistent with measurements of dissolved oxygen, sulfide and oxidation-reduction potential in the field. These findings imply that spatial patterns in the amino acid compositions of proteins can be linked, through energetics of overall chemical reactions representing the formation of the proteins, to the environmental conditions at this hot spring, even if microbial cells maintain considerably different internal conditions. Further applications of the thermodynamic calculations are possible for other natural microbial ecosystems. PMID:21853048

  15. Assembly of Complex Nano-Structure from Single Atoms
    Chemical Identification, Manipulation and Assembly by AFM—

    NASA Astrophysics Data System (ADS)

    Morita, Seizo; Sugimoto, Yoshiaki; Ooyabu, Noriaki; Custance, Óscar; Abe, Masayuki; Pou, Pablo; Jelinek, Pavel; Pérez, Rubén

    An atomic force microscope (AFM) under noncontact and nearcontact regions operated at room-temperature (RT) in ultrahigh vacuum, is used as a tool for topography-based atomic discrimination and atomic-interchange manipulations of two intermixed atomic species on semiconductor surfaces. Noncontact AFM topography based site-specific force curves provide the chemical covalent bonding forces between the tip apex and the atoms at the surface. Here, we introduced an example related to topography-based atomic discrimination using selected Sn and Si adatoms in Sn/Si(111)-(√3 ×√3 ) surface. Recently, under nearcontact region, we found a lateral atom-interchange manipulation phenomenon at RT in Sn/Ge(111)-c(2×8) intermixed sample. This phenomenon can interchange an embedded Sn atom with a neighbor Ge atom at RT. Using the vector scan method under nearcontact region, we constructed “Atom Inlay”, that is, atom letters “Sn” consisted of 19 Sn atoms embedded in Ge(111)-c(2×8) substrate. Using these methods, now we can assemble compound semiconductor nanostructures atom-by-atom.

  16. Chemical vapor deposition of atomically thin materials for membrane dialysis applications

    NASA Astrophysics Data System (ADS)

    Kidambi, Piran; Mok, Alexander; Jang, Doojoon; Boutilier, Michael; Wang, Luda; Karnik, Rohit; Microfluidics; Nanofluidics Research Lab Team

    2015-11-01

    Atomically thin 2D materials like graphene and h-BN represent a new class of membranes materials. They offer the possibility of minimum theoretical membrane transport resistance along with the opportunity to tune pore sizes at the nanometer scale. Chemical vapor deposition has emerged as the preferable route towards scalable, cost effective synthesis of 2D materials. Here we show selective molecular transport through sub-nanometer diameter pores in graphene grown via chemical vapor deposition processes. A combination of pressure driven and diffusive transport measurements shows evidence for size selective transport behavior which can be used for separation by dialysis for applications such as desalting of biomolecular or chemical solutions. Principal Investigator

  17. Chemical structure imaging of a single molecule by atomic force microscopy at room temperature

    PubMed Central

    Iwata, Kota; Yamazaki, Shiro; Mutombo, Pingo; Hapala, Prokop; Ondráček, Martin; Jelínek, Pavel; Sugimoto, Yoshiaki

    2015-01-01

    Atomic force microscopy is capable of resolving the chemical structure of a single molecule on a surface. In previous research, such high resolution has only been obtained at low temperatures. Here we demonstrate that the chemical structure of a single molecule can be clearly revealed even at room temperature. 3,4,9,10-perylene tetracarboxylic dianhydride, which is strongly adsorbed onto a corner-hole site of a Si(111)–(7 × 7) surface in a bridge-like configuration is used for demonstration. Force spectroscopy combined with first-principle calculations clarifies that chemical structures can be resolved independent of tip reactivity. We show that the submolecular contrast over a central part of the molecule is achieved in the repulsive regime due to differences in the attractive van der Waals interaction and the Pauli repulsive interaction between different sites of the molecule. PMID:26178193

  18. Intrinsic Atomic Orbitals: An Unbiased Bridge between Quantum Theory and Chemical Concepts.

    PubMed

    Knizia, Gerald

    2013-11-12

    Modern quantum chemistry can make quantitative predictions on an immense array of chemical systems. However, the interpretation of those predictions is often complicated by the complex wave function expansions used. Here we show that an exceptionally simple algebraic construction allows for defining atomic core and valence orbitals, polarized by the molecular environment, which can exactly represent self-consistent field wave functions. This construction provides an unbiased and direct connection between quantum chemistry and empirical chemical concepts, and can be used, for example, to calculate the nature of bonding in molecules, in chemical terms, from first principles. In particular, we find consistency with electronegativities (χ), C 1s core-level shifts, resonance substituent parameters (σR), Lewis structures, and oxidation states of transition-metal complexes.

  19. Fabrication of high density, adherent films of five-fold symmetric diamond crystals by hot filament chemical vapour deposition

    NASA Astrophysics Data System (ADS)

    Wei, Qiuping; Ashfold, M. N. R.; Yu, Z. M.; Ma, Li; Yin, D. F.

    2011-12-01

    Five-fold symmetric diamond crystals (FSDCs) have been grown on a large variety of substrates by hot filament chemical vapour deposition (CVD) methods. High density, adherent films of FSDCs have been prepared on carbon steel with a thermal sprayed WC-Co interlayer, and their quality, adhesion and tribological behaviour were investigated. The diamond films show excellent adhesion under Rockwell indentation testing and when subjected to high-speed, high-load, long-time reciprocating dry sliding ball-on-flat wear tests against a Si 3N 4 counter-face in ambient air.

  20. Method and apparatus for fabricating a thin-film solar cell utilizing a hot wire chemical vapor deposition technique

    DOEpatents

    Wang, Qi; Iwaniczko, Eugene

    2006-10-17

    A thin-film solar cell is provided. The thin-film solar cell comprises an a-SiGe:H (1.6 eV) n-i-p solar cell having a deposition rate of at least ten (10) .ANG./second for the a-SiGe:H intrinsic layer by hot wire chemical vapor deposition. A method for fabricating a thin film solar cell is also provided. The method comprises depositing a n-i-p layer at a deposition rate of at least ten (10) .ANG./second for the a-SiGe:H intrinsic layer.

  1. Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns

    PubMed Central

    Chang, Tzu-Hsuan; Xiong, Shisheng; Jacobberger, Robert M.; Mikael, Solomon; Suh, Hyo Seon; Liu, Chi-Chun; Geng, Dalong; Wang, Xudong; Arnold, Michael S.; Ma, Zhenqiang; Nealey, Paul F.

    2016-01-01

    Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyrene-block-poly(methyl methacrylate). Faster assembly kinetics are observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. The rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces. PMID:27528258

  2. Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns.

    PubMed

    Chang, Tzu-Hsuan; Xiong, Shisheng; Jacobberger, Robert M; Mikael, Solomon; Suh, Hyo Seon; Liu, Chi-Chun; Geng, Dalong; Wang, Xudong; Arnold, Michael S; Ma, Zhenqiang; Nealey, Paul F

    2016-01-01

    Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyrene-block-poly(methyl methacrylate). Faster assembly kinetics are observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. The rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces.

  3. Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns

    NASA Astrophysics Data System (ADS)

    Chang, Tzu-Hsuan; Xiong, Shisheng; Jacobberger, Robert M.; Mikael, Solomon; Suh, Hyo Seon; Liu, Chi-Chun; Geng, Dalong; Wang, Xudong; Arnold, Michael S.; Ma, Zhenqiang; Nealey, Paul F.

    2016-08-01

    Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyrene-block-poly(methyl methacrylate). Faster assembly kinetics are observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. The rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces.

  4. Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns.

    PubMed

    Chang, Tzu-Hsuan; Xiong, Shisheng; Jacobberger, Robert M; Mikael, Solomon; Suh, Hyo Seon; Liu, Chi-Chun; Geng, Dalong; Wang, Xudong; Arnold, Michael S; Ma, Zhenqiang; Nealey, Paul F

    2016-01-01

    Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyrene-block-poly(methyl methacrylate). Faster assembly kinetics are observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. The rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces. PMID:27528258

  5. Physico-chemical evolution of groundwater in tectonically active areas. Application to the Leana hot spring (Murcia Region, SE Spain)

    NASA Astrophysics Data System (ADS)

    Martínez, M.; Hornero, J.; Trujillo, C.

    2016-09-01

    Seismic events can affect the physico-chemical characteristics of groundwater. These anomalies are of a pre-seismic, co-seismic and post-seismic nature and correspond to pulse variations, sudden increases and decreases without return to initial values and upward or downward changes in trend. Continuous and in situ conductivity and temperature monitoring and periodic water sampling at a hot spring associated with neotectonic activity are of great interest for establishing predictive methods. This method is limited to the seismic activity affecting the fracturing system with which the hot spring is associated. The Region of Murcia and surroundings (southeast Spain) was selected as the study area for exploring the nature of these influences on groundwater. A hot spring in the Leana spa (Murcia) was equipped and monitored during the period 2006-2008, allowing for the in situ determination of conductivity and temperature as well as of major and minor constituents at the laboratory. Due to its proximity and related with fault network, we suggest that 86 % of earthquakes located between 0 and 10 km may affect in situ parameters of groundwater, and 75 % may affect laboratory determinations. This percentage drops in more distant zones. Of all earthquakes that seem to influence groundwater, 55 % of the in situ parameter anomalies and 53 % of laboratory were of a pre-seismic nature.

  6. Quantum chemical simulations of atomic layer deposition of metal oxides and metal nitrides

    NASA Astrophysics Data System (ADS)

    Xu, Ye

    Scaling of SiO2 gate dielectrics to extend the miniaturization of complementary metal oxide semiconductor (CMOS) devices in accordance with Moore's Law has resulted in unacceptable tunneling current leakage levels. The projection that this challenge could significantly limit CMOS performance has prompted the intense search for alternative gate dielectric materials that can achieve high capacitances with physically thicker films which minimize tunneling leakage current. Atomic layer deposition is an ideal deposition method for high-k films because it controls the film thickness with atomic layer precision and can achieve high film conformality and uniformity. We use density functional theory (DFT) to explore chemical reactions involved in ALD processes at the atomic level. We have investigated different metal precursors for ALD process. Compared to halides, metal alkylamides are more favorable on nitrided silicon surfaces and subsequent film growth. Likewise, hafnium alkylamide is more favorable than water to initiate the nucleation on hydrogen terminated silicon surfaces. For deposition on organic self-assembled monolayers, different end groups significantly affect the selectivity towards ALD reactions. The chemical mechanisms involved in ALD of hafnium nitride, aluminum nitride are developed which provide an understanding to the difficulty in producing oxygen free metal nitrides by ALD. By combining ALD of metal oxide and metal nitride, a new method for incorporating nitrogen into oxide films is proposed. In TMA and ozone reaction, it's found that by-product water can be a catalyzer for this reaction.

  7. Physico-Chemical and Structural Interpretation of Discrete Derivative Indices on N-Tuples Atoms.

    PubMed

    Martínez-Santiago, Oscar; Marrero-Ponce, Yovani; Barigye, Stephen J; Le Thi Thu, Huong; Torres, F Javier; Zambrano, Cesar H; Muñiz Olite, Jorge L; Cruz-Monteagudo, Maykel; Vivas-Reyes, Ricardo; Vázquez Infante, Liliana; Artiles Martínez, Luis M

    2016-01-01

    This report examines the interpretation of the Graph Derivative Indices (GDIs) from three different perspectives (i.e., in structural, steric and electronic terms). It is found that the individual vertex frequencies may be expressed in terms of the geometrical and electronic reactivity of the atoms and bonds, respectively. On the other hand, it is demonstrated that the GDIs are sensitive to progressive structural modifications in terms of: size, ramifications, electronic richness, conjugation effects and molecular symmetry. Moreover, it is observed that the GDIs quantify the interaction capacity among molecules and codify information on the activation entropy. A structure property relationship study reveals that there exists a direct correspondence between the individual frequencies of atoms and Hückel's Free Valence, as well as between the atomic GDIs and the chemical shift in NMR, which collectively validates the theory that these indices codify steric and electronic information of the atoms in a molecule. Taking in consideration the regularity and coherence found in experiments performed with the GDIs, it is possible to say that GDIs possess plausible interpretation in structural and physicochemical terms. PMID:27240357

  8. Physico-Chemical and Structural Interpretation of Discrete Derivative Indices on N-Tuples Atoms

    PubMed Central

    Martínez-Santiago, Oscar; Marrero-Ponce, Yovani; Barigye, Stephen J.; Le Thi Thu, Huong; Torres, F. Javier; Zambrano, Cesar H.; Muñiz Olite, Jorge L.; Cruz-Monteagudo, Maykel; Vivas-Reyes, Ricardo; Vázquez Infante, Liliana; Artiles Martínez, Luis M.

    2016-01-01

    This report examines the interpretation of the Graph Derivative Indices (GDIs) from three different perspectives (i.e., in structural, steric and electronic terms). It is found that the individual vertex frequencies may be expressed in terms of the geometrical and electronic reactivity of the atoms and bonds, respectively. On the other hand, it is demonstrated that the GDIs are sensitive to progressive structural modifications in terms of: size, ramifications, electronic richness, conjugation effects and molecular symmetry. Moreover, it is observed that the GDIs quantify the interaction capacity among molecules and codify information on the activation entropy. A structure property relationship study reveals that there exists a direct correspondence between the individual frequencies of atoms and Hückel’s Free Valence, as well as between the atomic GDIs and the chemical shift in NMR, which collectively validates the theory that these indices codify steric and electronic information of the atoms in a molecule. Taking in consideration the regularity and coherence found in experiments performed with the GDIs, it is possible to say that GDIs possess plausible interpretation in structural and physicochemical terms. PMID:27240357

  9. Physico-Chemical and Structural Interpretation of Discrete Derivative Indices on N-Tuples Atoms.

    PubMed

    Martínez-Santiago, Oscar; Marrero-Ponce, Yovani; Barigye, Stephen J; Le Thi Thu, Huong; Torres, F Javier; Zambrano, Cesar H; Muñiz Olite, Jorge L; Cruz-Monteagudo, Maykel; Vivas-Reyes, Ricardo; Vázquez Infante, Liliana; Artiles Martínez, Luis M

    2016-05-27

    This report examines the interpretation of the Graph Derivative Indices (GDIs) from three different perspectives (i.e., in structural, steric and electronic terms). It is found that the individual vertex frequencies may be expressed in terms of the geometrical and electronic reactivity of the atoms and bonds, respectively. On the other hand, it is demonstrated that the GDIs are sensitive to progressive structural modifications in terms of: size, ramifications, electronic richness, conjugation effects and molecular symmetry. Moreover, it is observed that the GDIs quantify the interaction capacity among molecules and codify information on the activation entropy. A structure property relationship study reveals that there exists a direct correspondence between the individual frequencies of atoms and Hückel's Free Valence, as well as between the atomic GDIs and the chemical shift in NMR, which collectively validates the theory that these indices codify steric and electronic information of the atoms in a molecule. Taking in consideration the regularity and coherence found in experiments performed with the GDIs, it is possible to say that GDIs possess plausible interpretation in structural and physicochemical terms.

  10. Hot-filament chemical vapor deposition chamber and process with multiple gas inlets

    DOEpatents

    Deng, Xunming; Povolny, Henry S.

    2004-06-29

    A thin film deposition method uses a vacuum confinement cup that employs a dense hot filament and multiple gas inlets. At least one reactant gas is introduced into the confinement cup both near and spaced apart from the heated filament. An electrode inside the confinement cup is used to generate plasma for film deposition. The method is used to deposit advanced thin films (such as silicon based thin films) at a high quality and at a high deposition rate.

  11. Chemical control of electrical contact to sp² carbon atoms.

    PubMed

    Frederiksen, Thomas; Foti, Giuseppe; Scheurer, Fabrice; Speisser, Virginie; Schull, Guillaume

    2014-01-01

    Carbon-based nanostructures are attracting tremendous interest as components in ultrafast electronics and optoelectronics. The electrical interfaces to these structures play a crucial role for the electron transport, but the lack of control at the atomic scale can hamper device functionality and integration into operating circuitry. Here we study a prototype carbon-based molecular junction consisting of a single C60 molecule and probe how the electric current through the junction depends on the chemical nature of the foremost electrode atom in contact with the molecule. We find that the efficiency of charge injection to a C60 molecule varies substantially for the considered metallic species, and demonstrate that the relative strength of the metal-C bond can be extracted from our transport measurements. Our study further suggests that a single-C60 junction is a basic model to explore the properties of electrical contacts to meso- and macroscopic sp(2) carbon structures.

  12. Nuclear Quadrupole Coupling Constants of Two Chemically Distinct Nitrogen Atoms in 4-Aminobenzonitrile

    PubMed Central

    2014-01-01

    The rotational spectrum of 4-aminobenzonitrile in the gas phase between 2 and 8.5 GHz is reported. Due to the two chemically distinct nitrogen atoms, the observed transitions showed a rich hyperfine structure. From the determination of the nuclear quadrupole coupling constants, information about the electronic environment of these atoms could be inferred. The results are compared to data for related molecules, especially with respect to the absence of dual fluorescence in 4-aminobenzonitrile. In addition, the two-photon ionization spectrum of this molecule was recorded using a time-of-flight mass spectrometer integrated into the setup. This new experimental apparatus is presented here for the first time. PMID:24911139

  13. Synthesis of multiferroic Er-Fe-O thin films by atomic layer and chemical vapor deposition

    SciTech Connect

    Mantovan, R. Vangelista, S.; Wiemer, C.; Lamperti, A.; Tallarida, G.; Chikoidze, E.; Dumont, Y.; Fanciulli, M.

    2014-05-07

    R-Fe-O (R = rare earth) compounds have recently attracted high interest as potential new multiferroic materials. Here, we report a method based on the solid-state reaction between Er{sub 2}O{sub 3} and Fe layers, respectively grown by atomic layer deposition and chemical vapor deposition, to synthesize Er-Fe-O thin films. The reaction is induced by thermal annealing and evolution of the formed phases is followed by in situ grazing incidence X-ray diffraction. Dominant ErFeO{sub 3} and ErFe{sub 2}O{sub 4} phases develop following subsequent thermal annealing processes at 850 °C in air and N{sub 2}. Structural, chemical, and morphological characterization of the layers are conducted through X-ray diffraction and reflectivity, time-of-flight secondary ion-mass spectrometry, and atomic force microscopy. Magnetic properties are evaluated by magnetic force microscopy, conversion electron Mössbauer spectroscopy, and vibrating sample magnetometer, being consistent with the presence of the phases identified by X-ray diffraction. Our results constitute a first step toward the use of cost-effective chemical methods for the synthesis of this class of multiferroic thin films.

  14. Theory of quasicrystal surfaces: Probing the chemical reactivity by atomic and molecular adsorption

    NASA Astrophysics Data System (ADS)

    Krajčí, M.; Hafner, J.

    The adsorption of oxygen and carbon atoms and of carbon monoxide molecules on a fivefold surface of icosahedral Al-Pd-Mn quasicrystals has been investigated using ab initio density-functional calculations. The quasicrystalline surface has been modeled by periodically repeated slabs cut from rational approximants to the quasicrystalline structure. Atomic and molecular adsorption have been studied for a large number of possible adsorption sites by performing three-dimensional static relaxations of the adsorbate/substrate complex. Four different scenarios for the dissociative adsorption of the CO molecule have been investigated via nudged-elastic band calculations of the transition states. Al and Mn-metal atoms present at the surface bind C and O atoms rather strongly, while Pd atoms are unstable adsorption sites: during relaxation, the adsorbate drifts to the nearest strong-binding site. The chemical reactivity with respect to a CO molecule varies very strongly across the surface. The adsorption close to Mn sites is promoted by rather strong covalent effects, but CO is only physisorbed at Al sites via weak polarization forces. On the basis of the observed local variations of the adsorption strength, we develop scenarios for dissociation and determine the potential energy barriers for this processes. We find that CO adsorbed close to a transition-metal atom can dissociate via an activated process, but the dissociation rate is expected to be rather low because of a high dissociation barrier and a "late" transition state. CO adsorbed close to Al atoms will desorb before dissociation. Surface vacancies present as a consequence of the irregular coordination of the Mackay cluster in the quasiperiodic structure will act as strongly attractive traps for diffusing molecules. Mn surface atoms are located in the center of truncated Mackay clusters. In scanning tunneling electron microscopy (STM) these truncated clusters are imaged as "white flowers". Surface vacancies are

  15. Mathematical modeling of chemical composition modification and etching of polymers under the atomic oxygen influence

    NASA Astrophysics Data System (ADS)

    Chirskaia, Natalia; Novikov, Lev; Voronina, Ekaterina

    2016-07-01

    Atomic oxygen (AO) of the upper atmosphere is one of the most important space factors that can cause degradation of spacecraft surface. In our previous mathematical model the Monte Carlo method and the "large particles" approximation were used for simulating processes of polymer etching under the influence of AO [1]. The interaction of enlarged AO particles with the polymer was described in terms of probabilities of reactions such as etching of polymer and specular and diffuse scattering of the AO particles on polymer. The effects of atomic oxygen on protected polymers and microfiller containing composites were simulated. The simulation results were in quite good agreement with the results of laboratory experiments on magnetoplasmadynamic accelerator of the oxygen plasma of SINP MSU [2]. In this paper we present a new model that describes the reactions of AO interactions with polymeric materials in more detail. Reactions of formation and further emission of chemical compounds such as CO, CO _{2}, H _{2}O, etc. cause the modification of the chemical composition of the polymer and change the probabilities of its consequent interaction with the AO. The simulation results are compared with the results of previous simulation and with the results of laboratory experiments. The reasons for the differences between the results of natural experiments on spacecraft, laboratory experiments and simulations are discussed. N. Chirskaya, M. Samokhina, Computer modeling of polymer structures degradation under the atomic oxygen exposure, WDS'12 Proceedings of Contributed Papers: Part III - Physics, Matfyzpress Prague, 2012, pp. 30-35. E. Voronina, L. Novikov, V. Chernik, N. Chirskaya, K. Vernigorov, G. Bondarenko, and A. Gaidar, Mathematical and experimental simulation of impact of atomic oxygen of the earth's upper atmosphere on nanostructures and polymer composites, Inorganic Materials: Applied Research, 2012, vol. 3, no. 2, pp. 95-101.

  16. Hot Canyon

    ScienceCinema

    None

    2016-07-12

    This historical film footage, originally produced in the early 1950s as part of a series by WOI-TV, shows atomic research at Ames Laboratory. The work was conducted in a special area of the Laboratory known as the "Hot Canyon."

  17. Hot Canyon

    SciTech Connect

    2012-01-01

    This historical film footage, originally produced in the early 1950s as part of a series by WOI-TV, shows atomic research at Ames Laboratory. The work was conducted in a special area of the Laboratory known as the "Hot Canyon."

  18. Deposition of microcrystalline silicon prepared by hot-wire chemical-vapor deposition: The influence of the deposition parameters on the material properties and solar cell performance

    NASA Astrophysics Data System (ADS)

    Klein, Stefan; Finger, Friedhelm; Carius, Reinhard; Stutzmann, Martin

    2005-07-01

    Microcrystalline silicon (μc-Si:H) of superior quality can be prepared using the hot-wire chemical-vapor deposition method (HWCVD). At a low substrate temperature (TS) of 185 °C excellent material properties and solar cell performance were obtained with spin densities of 6×1015cm-3 and solar cell efficiencies up to 9.4%, respectively. In this study we have systematically investigated the influence of various deposition parameters on the deposition rate and the material properties. For this purpose, thin films and solar cells were prepared at specific substrate and filament temperatures and deposition pressures (pD), covering the complete range from amorphous to highly crystalline material by adjusting the silane concentration. The influence of these deposition parameters on the chemical reactions at the filament and in the gas phase qualitatively explains the behavior of the structural composition and the formation of defects. In particular, we propose that the deposition rate is determined by the production of reactive species at the filament and a particular atomic-hydrogen-to-silicon ratio is found at the microcrystalline/amorphous transition. The structural, optical, and electronic properties were studied using Raman and infrared spectroscopies, optical-absorption measurements, electron-spin resonance, and dark and photoconductivities. These experiments show that higher TS and pD lead to a deterioration of the material quality, i.e., much higher defect densities, oxygen contaminations, and SiH absorption at 2100cm-1. Similar to plasma enhanced chemical-vapor deposition material, μc-Si:H solar cells prepared with HW i layers show increasing open circuit voltages (Voc) with increasing silane concentration and best performance is achieved near the transition to amorphous growth. Such solar cells prepared at low TS exhibit very high Voc up to 600 mV and fill factors above 70% with i layers prepared by HWCVD.

  19. The hot core towards the intermediate-mass protostar NGC 7129 FIRS 2. Chemical similarities with Orion KL

    NASA Astrophysics Data System (ADS)

    Fuente, A.; Cernicharo, J.; Caselli, P.; McCoey, C.; Johnstone, D.; Fich, M.; van Kempen, T.; Palau, Aina; Yıldız, U. A.; Tercero, B.; López, A.

    2014-08-01

    Context. This paper is dedicated to the study of the chemistry of the intermediate-mass (IM) hot core NGC 7129 FIRS 2, probably the most compact warm core found in the 2-8 M⊙ stellar mass range. Aims: Our aim is to determine the chemical composition of the IM hot core NGC 7129 FIRS 2, and to provide new insights on the chemistry of hot cores in a more general context. Methods: NGC 7129 FIRS 2 (hereafter, FIRS 2) is located at a distance of 1250 pc and high spatial resolution observations are required to resolve the hot core at its center. We present a molecular survey from 218 200 MHz to 221 800 MHz carried out with the IRAM Plateau de Bure Interferometer (PdBI). These observations were complemented with a long integration single-dish spectrum taken with the IRAM 30 m telescope in Pico de Veleta (Spain). We used a local thermodynamic equilibrium (LTE) single temperature code to model the whole dataset. Results: The interferometric spectrum is crowded with a total of ≈300 lines from which a few dozen remain unidentified. The spectrum has been modeled with a total of 20 species and their isomers, isotopologues, and deuterated compounds. Complex molecules like methyl formate (CH3OCHO), ethanol (CH3CH2OH), glycolaldehyde (CH2OHCHO), acetone (CH3COCH3), dimethyl ether (CH3OCH3), ethyl cyanide (CH3CH2CN), and the aGg' conformer of ethylene glycol (aGg'-(CH2OH)2) are among the detected species. The detection of vibrationally excited lines of CH3CN, CH3OCHO, CH3OH, OCS, HC3N, and CH3CHO proves the existence of gas and dust at high temperatures. The gas kinetic temperature estimated from the vibrational lines of CH3CN, ~405-67+100 K, is similar to that measured in massive hot cores. Our data allow an extensive comparison of the chemistry in FIRS 2 and the Orion hot core. Conclusions: We find a quite similar chemistry in FIRS 2 and Orion. Most of the studied fractional molecular abundances agree within a factor of 5. Larger differences are only found for the deuterated

  20. KFC2: a knowledge-based hot spot prediction method based on interface solvation, atomic density, and plasticity features.

    PubMed

    Zhu, Xiaolei; Mitchell, Julie C

    2011-09-01

    Hot spots constitute a small fraction of protein-protein interface residues, yet they account for a large fraction of the binding affinity. Based on our previous method (KFC), we present two new methods (KFC2a and KFC2b) that outperform other methods at hot spot prediction. A number of improvements were made in developing these new methods. First, we created a training data set that contained a similar number of hot spot and non-hot spot residues. In addition, we generated 47 different features, and different numbers of features were used to train the models to avoid over-fitting. Finally, two feature combinations were selected: One (used in KFC2a) is composed of eight features that are mainly related to solvent accessible surface area and local plasticity; the other (KFC2b) is composed of seven features, only two of which are identical to those used in KFC2a. The two models were built using support vector machines (SVM). The two KFC2 models were then tested on a mixed independent test set, and compared with other methods such as Robetta, FOLDEF, HotPoint, MINERVA, and KFC. KFC2a showed the highest predictive accuracy for hot spot residues (True Positive Rate: TPR = 0.85); however, the false positive rate was somewhat higher than for other models. KFC2b showed the best predictive accuracy for hot spot residues (True Positive Rate: TPR = 0.62) among all methods other than KFC2a, and the False Positive Rate (FPR = 0.15) was comparable with other highly predictive methods.

  1. Hot subluminous stars: On the Search for Chemical Signatures of their Genesis

    NASA Astrophysics Data System (ADS)

    Hirsch, Heiko Andreas

    2009-10-01

    This thesis deals with the hot subluminous stars of spectral class O. Although the name suggests otherwise, these stars are still 10 to 1000 times more luminous than the sun, they emit most of their radiation energy in the ultraviolet range. First stars of this type have been categorized in the 1950ies. Since they are blue objects like Quasars they often are discovered in surveys at high Galactic latitudes aiming at Quasars and other extragalactic objects. The hot subluminous stars can be divided into two classes, the subluminous O and subluminous B stars, or short sdO and sdB. The sdOs and sdBs play an important role in astronomy, as many old stellar populations, e.g. globular clusters and elliptical galaxies, have strong UV fluxes. UV bright regions often are "stellar nurseries", where new stars are born. Globular clusters and elliptical galaxies, however, do not experience star formation. This UV excess can be explained by population models that include the hot subluminous stars. Many sdB stars show short-period, multiperiodic light variations, which are due to radial and nonradial pulsations. Asteroseismology can explore the inner structure of stars and estimate e.g. the stellar mass, a variable that can only determine in very lucky circumstances (eclipsing binaries). These stars are also important for cosmology because they qualify as supernova Ia progenitors. The nature of the sdO stars is less well understood than that of their cooler and more numerous siblings, the sdBs. The connection of the sdBs to the horizontal branch is established for many years now, accordingly they are old helium core burning objects after their red giant phase. More precisely, they are on the extended horizontal branch (EHB), the hot end of the horizontal branch. EHB stars are characterized by a very low envelope mass, i.e. we see more or less directly the hot helium burning core. Strong mass loss in the RGB phase is regarded as responsible for this phenomenon, the exact mechanism

  2. Characterization of pressurized hot water extracts of grape pomace: chemical and biological antioxidant activity.

    PubMed

    Vergara-Salinas, J R; Vergara, Mauricio; Altamirano, Claudia; Gonzalez, Álvaro; Pérez-Correa, J R

    2015-03-15

    Pressurized hot water extracts obtained at different temperatures possess different compositions and antioxidant activities and, consequently, different bioactivities. We characterized two pressurized hot water extracts from grape pomace obtained at 100°C (GPE100) and 200°C (GPE200) in terms of antioxidant activity and composition, as well as protective effect on cell growth and mitochondrial membrane potential (Δψm) in a HL-60 cell culture under oxidative conditions. GPE100 extracts were richer in polyphenols and poorer in Maillard reaction products (MRPs) than were GPE200 extracts. Moreover, hydroxymethylfurfural was detected only in GPE200. Both extracts exhibited similar protective effects on cell growth (comparable to the effect of trolox). In addition, GPE100 strongly decreased the Δψm loss, reaching values even lower than those of the control culture. This protective effect may be related to its high polyphenols content. At the highest concentration assessed, both extracts showed strong cytotoxicity, especially GPE200. This cytotoxicity could be related to their MRPs content.

  3. Chemical indicators of subsurface temperature applied to hot spring waters of Yellowstone National Park, Wyoming, U.S.A.

    USGS Publications Warehouse

    Fournier, R.O.; Truesdell, A.H.

    1970-01-01

    Under favorable conditions the chemistry of hot springs may give reliable indications of subsurface temperatures and circulation patterns. These chemical indicators can be classified by the type of process involved: {A table is presented}. All these indicators have certain limitations. The silica geothermometer gives results independent of the local mineral suite and gas partial pressures, but may be affected by dilution. Alkali ratios are strongly affected by the local mineral suite and the formation of complex ions. Carbonate-chloride ratios are strongly affected by subsurface PCO2. The relative concentration of volatiles can be very misleading in high-pressure liquid systems. In Yellowstone National Park most thermal waters issue from hot, shallow aquifers with pressures in excess of hydrostatic by 2 to 6 bars and with large flows (the flow of hot spring water from the Park is greater than 4000 liters per second). These conditions should be ideal for the use of chemical indicators to estimate aquifer temperatures. In five drill holes aquifer temperatures were within 2??C of that predicted from the silica content of nearby hot springs; the temperature level off at a lower value than predicted in only one hole, and in four other holes drilling was terminated before the predicted aquifer temperature was reached. The temperature-Na/K ratio relationship does not follow any published experimental or empirical curve for water-feldspar or water-clay reactions. We suspect that ion exchange reactions involving zeolites in the Yellowstone rocks result in higher Na/K ratios at given temperatures than result from feldspar or clay reactions. Comparison of SiO2 and Cl/(HCO3 + CO3) suggest that because of higher subsurface PCO2 in Upper Geyser Basin a given Cl/(HCO3 + CO3) ratio there means a higher temperature than in Lower Geyser Basin. No correlation was found in Yellowstone Park between the subsurface regions of highest temperature and the relative concentration of volatile

  4. LASER ABLATION-INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROSCOPY STUDY AT THE 222-S LABORATORY USING HOT-CELL GLOVE BOX PROTOTYPE SYSTEM

    SciTech Connect

    SEIDEL CM; JAIN J; OWENS JW

    2009-02-23

    This report describes the installation, testing, and acceptance of the Waste Treatment and Immobilization Plant (WTP) procured laser ablation-inductively coupled plasma-atomic emission spectroscopy (LA-ICP-AES) system for remotely analyzing high-level waste (HLW) samples in a hot cell environment. The work was completed by the Analytical Process Development (APD) group in accordance with Task Order 2005-003; ATS MP 1027, Management Plan for Waste Treatment Plant Project Work Performed by Analytical Technical Services. The APD group at the 222-S Laboratory demonstrated acceptable turnaround time (TAT) and provide sufficient data to assess sensitivity, accuracy, and precision of the LA-ICP-AES method.

  5. LASER ABLATION-INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION SPECTROSCOPY STUDY AT THE 222-S LABORATORY USING HOT-CELL GLOVE BOX PROTOTYPE SYSTEM

    SciTech Connect

    LOCKREM LL; OWENS JW; SEIDEL CM

    2009-03-26

    This report describes the installation, testing and acceptance of the Waste Treatment and Immobilization Plant procured laser ablation-inductively coupled plasma-atomic emission spectroscopy (LA-ICP-AES) system for remotely analyzing high-level waste samples in a hot cell environment. The 2005-003; ATS MP 1027, Management Plan for Waste Treatment Plant Project Work Performed by Analytical Technical Services. The APD group at the 222-S laboratory demonstrated acceptable turnaround time (TAT) and provide sufficient data to assess sensitivity, accuracy, and precision of the LA-ICP-AES method.

  6. Progress in Visualizing Atomic Size Effects with DFT-Chemical Pressure Analysis: From Isolated Atoms to Trends in AB5 Intermetallics.

    PubMed

    Berns, Veronica M; Engelkemier, Joshua; Guo, Yiming; Kilduff, Brandon J; Fredrickson, Daniel C

    2014-08-12

    The notion of atomic size poses an important challenge to chemical theory: empirical evidence has long established that atoms have spatial requirements, which are summarized in tables of covalent, ionic, metallic, and van der Waals radii. Considerations based on these radii play a central role in the design and interpretation of experiments, but few methods are available to directly support arguments based on atomic size using electronic structure methods. Recently, we described an approach to elucidating atomic size effects using theoretical calculations: the DFT-Chemical Pressure analysis, which visualizes the local pressures arising in crystal structures from the interactions of atomic size and electronic effects. Using this approach, a variety of structural phenomena in intermetallic phases have already been understood in terms that provide guidance to new synthetic experiments. However, the applicability of the DFT-CP method to the broad range of the structures encountered in the solid state is limited by two issues: (1) the difficulty of interpreting the intense pressure features that appear in atomic core regions and (2) the need to divide space among pairs of interacting atoms in a meaningful way. In this article, we describe general solutions to these issues. In addressing the first issue, we explore the CP analysis of a test case in which no core pressures would be expected to arise: isolated atoms in large boxes. Our calculations reveal that intense core pressures do indeed arise in these virtually pressure-less model systems and allow us to trace the issue to the shifts in the voxel positions relative to atomic centers upon expanding and contracting the unit cell. A compensatory grid unwarping procedure is introduced to remedy this artifact. The second issue revolves around the difficulty of interpreting the pressure map in terms of interatomic interactions in a way that respects the size differences of the atoms and avoids artificial geometrical

  7. Chemical assembly of atomically thin transistors and circuits in a large scale

    NASA Astrophysics Data System (ADS)

    Zhao, Mervin; Ye, Yu; Han, Yimo; Xia, Yang; Zhu, Hanyu; Wang, Yuan; Muller, David; Zhang, Xiang

    Next-generation electronics calls for new materials beyond silicon for increased functionality, performance, and scaling in integrated circuits. 2D gapless graphene and semiconducting TMDCs have emerged as promising electronic materials due to their atomic thickness, chemical stability and scalability. However, difficulties in the assembly of 2D electronic structures arise in the precise spatial control over the conducting and semiconducting crystals, typically relying on physically transferring them. Ultimately, this renders them unsuitable for an industrial scale and impedes the maturity of integrating atomic elements in modern electronics. Here, we report the large-scale spatially controlled synthesis of the single-layer MoS2 laterally in electrical contact with graphene using a seeded growth method. TEM studies reveal that the single-layer MoS2 nucleates at the edge of the graphene, creating a lateral van der Waals heterostructure. The graphene allows for electrical injection into MoS2, creating 2D atomic transistors with high transconductance, on-off ratios, and mobility. In addition, we assemble 2D logic circuits, such as a heterostructure NMOS inverter with a high voltage gain, up to 70.

  8. Intermolecular and intramolecular hydrogen bonds involving fluorine atoms: implications for recognition, selectivity, and chemical properties.

    PubMed

    Dalvit, Claudio; Vulpetti, Anna

    2012-02-01

    A correlation between 19F NMR isotropic chemical shift and close intermolecular F⋅⋅⋅H-X contacts (with X=N or O) has been identified upon analysis of the X-ray crystal structures of fluorinated molecules listed in the Cambridge Structural Database (CSD). An optimal F⋅⋅⋅X distance involving primary and shielded secondary fluorine atoms in hydrogen-bond formation along with a correlation between F⋅⋅⋅H distance and F⋅⋅⋅H-X angle were also derived from the analysis. The hydrogen bonds involving fluorine are relevant, not only for the recognition mechanism and stabilization of a preferred conformation, but also for improvement in the permeability of the molecules, as shown with examples taken from a proprietary database. Results of an analysis of the small number of fluorine-containing natural products listed in the Protein Data Bank (PDB) appear to strengthen the derived correlation between 19F NMR isotropic chemical shift and interactions involving fluorine (also known as the "rule of shielding") and provides a hypothesis for the recognition mechanism and catalytic activity of specific enzymes. Novel chemical scaffolds, based on the rule of shielding, have been designed for recognizing distinct structural motifs present in proteins. It is envisaged that this approach could find useful applications in drug design for the efficient optimization of chemical fragments or promising compounds by increasing potency and selectivity against the desired biomolecular target.

  9. Chemical Stability of Titania and Alumina Thin Films Formed by Atomic Layer Deposition.

    PubMed

    Correa, Gabriela C; Bao, Bo; Strandwitz, Nicholas C

    2015-07-15

    Thin films formed by atomic layer deposition (ALD) are being examined for a variety of chemical protection and diffusion barrier applications, yet their stability in various fluid environments is not well characterized. The chemical stability of titania and alumina thin films in air, 18 MΩ water, 1 M KCl, 1 M HNO3, 1 M H2SO4, 1 M HCl, 1 M KOH, and mercury was studied. Films were deposited at 150 °C using trimethylaluminum-H2O and tetrakis(dimethylamido)titanium-H2O chemistries for alumina and titania, respectively. A subset of samples were heated to 450 and 900 °C in inert atmosphere. Films were examined using spectroscopic ellipsometry, atomic force microscopy, optical microscopy, scanning electron microscopy, and X-ray diffraction. Notably, alumina samples were found to be unstable in pure water, acid, and basic environments in the as-synthesized state and after 450 °C thermal treatment. In pure water, a dissolution-precipitation mechanism is hypothesized to cause surface roughening. The stability of alumina films was greatly enhanced after annealing at 900 °C in acidic and basic solutions. Titania films were found to be stable in acid after annealing at or above 450 °C. All films showed a composition-independent increase in measured thickness when immersed in mercury. These results provide stability-processing relationships that are important for controlled etching and protective barrier layers.

  10. Characterizing intra and inter annual variability of storm events based on very high frequency monitoring of hydrological and chemical variables: what can we learn about hot spots and hot moments from continuous hydro-chemical sensors ?

    NASA Astrophysics Data System (ADS)

    Fovet, O.; Thelusma, G.; Humbert, G.; Dupas, R.; Jaffrezic, A.; Grimaldi, C.; Faucheux, M.; Gilliet, N.; Hamon, Y.; Gruau, G.

    2015-12-01

    Storm events are hot moments of emission for several dissolved and particulate chemical species at major stake for water quality (e.g. dissolved organic carbon DOC, suspended sediments, phosphorus, NH4). During such events, the solutes or particles are exported from heterogeneous sources through various pathways to stream or are possibly stored in retention hot spots temporary. This leads to specific integrated signals at the outlet at the scale of storm events. The dynamics of such events are also very short especially in headwater catchments where their total duration ranges over 10h to 3 days, with very quick variations in stream flow and concentrations at the outlet occurring in a few hours. Thus for investigating properly event processes, high frequency monitoring of flow and water quality is required. We analysed 103 storm events in a 5 km2 agricultural headwater catchment, part of the AgrHys Observatory, on the basis of a 3-year-long data set which combined meterological (Rainfall), hydrological (flow and piezometry), and water quality (turbidity, conductivity, DOC and NO3 concentrations) data recorded at very high frequencies (from 1 to 20 min) thanks to dedicated sensors. We described the storm events using simple (1 variable) and combined (2 variables) descriptors for characterizing level and dynamics of flow (Q), groundwater levels, and concentrations (C) but also the C-Q relationships. Three intra annual periods have been previously defined for base flow dynamic according to shallow groundwater table variations so that they correspond to different connectivity status in the catchment. The seasonal and inter-annual variability of the storm events have been analysed using the descriptors and based on these predefined periods. Principal component analysis based on storm chemical descriptors led to discriminate these three seasons while storm hydrological descriptors are less variable between them. Finally we used a clustering method to build a typology of

  11. Quantitative Statistical Analysis of Atomic Scale Structural and Chemical Variations in Complex Oxides Interfaces

    NASA Astrophysics Data System (ADS)

    Yang, Hao

    Grain boundaries (GBs) are known to have far-reaching effects on the electrical and mechanical properties of materials. Understanding the atomic scale mechanisms behind these effects requires an accurate determination of the interplay between GB structure and composition. Based on the analysis of a range of grain boundaries using aberration corrected scanning transmission electron microscopy (STEM), a general structural units model has been derived for the structure of grain boundaries in various dense packing cubic materials including FCC metals, perovskites and fluorites. The similarities in the observed grain boundary structures of these materials originate from related space (and point) group symmetries of the parent structures. The presence of structural variations away from the general structural units model may be caused by frustrations of certain symmetry operations that result from the incorporation of point defects (vacancies and impurities). A clear understanding of the similarity and variation in grain boundary atomic structures will not only provide a means to infer the structure-property relationships in broad classes of materials, but also enables us eventually to effectively manipulate the GB structures to achieve better materials properties. To understand these chemical induced variations, and further quantify exactly how atomic scale variations at the boundary plane extend to the practical mesoscale operating length of the system, statistical analysis has been applied to the aberration corrected STEM Z-contrast images acquired from a series of undoped and doped SrTiO3 GBs. In order to understand the effects of oxygen vacancies incorporation, in-situ characterization of GB atomic structures were performed using the Environmental TEM under the reduced gas and heating environment. This analysis of GB similarity and variation provides insights into the structure-composition relationship in GBs to understand the influence of nonstoichiometry and dopant

  12. On the possibility to grow zinc oxide-based transparent conducting oxide films by hot-wire chemical vapor deposition

    SciTech Connect

    Abrutis, Adulfas Silimavicus, Laimis; Kubilius, Virgaudas; Murauskas, Tomas; Saltyte, Zita; Kuprenaite, Sabina; Plausinaitiene, Valentina

    2014-03-15

    Hot-wire chemical vapor deposition (HW-CVD) was applied to grow zinc oxide (ZnO)-based transparent conducting oxide (TCO) films. Indium (In)-doped ZnO films were deposited using a cold wall pulsed liquid injection CVD system with three nichrome wires installed at a distance of 2 cm from the substrate holder. The wires were heated by an AC current in the range of 0–10 A. Zn and In 2,2,6,6-tetramethyl-3,5-heptanedionates dissolved in 1,2-dimethoxyethane were used as precursors. The hot wires had a marked effect on the growth rates of ZnO, In-doped ZnO, and In{sub 2}O{sub 3} films; at a current of 6–10 A, growth rates were increased by a factor of ≈10–20 compared with those of traditional CVD at the same substrate temperature (400 °C). In-doped ZnO films with thickness of ≈150 nm deposited on sapphire-R grown at a wire current of 9 A exhibited a resistivity of ≈2 × 10{sup −3} Ωcm and transparency of >90% in the visible spectral range. These initial results reveal the potential of HW-CVD for the growth of TCOs.

  13. Boron nitride phosphide thin films grown on quartz substrate by hot-filament and plasma-assisted chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Zhang, X. W.; Xu, S. Y.; Han, G. R.

    2004-10-01

    Boron nitride phosphide films are, for the first time, grown on transparent quartz substrate by hot filament and radio-frequency plasma co-assisted chemical vapor deposition technique. XPS, XRD, SEM, and UV measurements are performed to study the chemical composition, crystallization, microstructure, and optical absorption, respectively. A centipede-like microstructure and undulating ground morphology on the film surface are observed, and their growth mechanism is speculated upon. The chemical composition is determined as BN1-xPx, whose characteristic XRD peak is preliminarily identified. The optical band gap can be modulated between 5.52 eV and 3.74 eV, simply by adjusting the phosphorus content in BN1-xPx through modifying the PH3 flux during the film-deposition process. The merits of the BN1-xPx film, such as high ultraviolet photoelectric sensitivity with negligible sensitivity in the visible region, modifiable wide optical band gap, and good adhesion on transparent substrate, suggest potential applications for ultraviolet photo-electronics.

  14. Chemical and Physical Weathering in a Hot-arid, Tectonically Active Alluvial System (Anza-Borrego Desert, CA)

    NASA Astrophysics Data System (ADS)

    Joo, Y. J.; Elwood Madden, M.; Soreghan, G. S.

    2014-12-01

    Climate and tectonics are primary controls on bedrock erosion, and sediment production, transport, and deposition. Additionally, silicate weathering in tectonically active regions is known to play a significant role in global climate owing to the high rates of physical erosion and exposure of unweathered bedrock to chemical weathering, which removes CO2 from the atmosphere. Therefore, the feedback between weathering and climate is key to understanding climate change through Earth history. This study investigates chemical and physical weathering of alluvial sediments in the Anza-Borrego Desert, California, located in the southern part of the San Andreas Fault System. This setting provides an ideal opportunity to study weathering in a hot and arid climate with mean annual temperatures of ~23 °C and mean annual precipitation of ~160 mm in the basin. Samples were collected along a proximal-to-distal transect of an alluvial-fan system sourced exclusively from Cretaceous tonalite of the Peninsular Range. The single bedrock lithology enables exploration of the effects of other variables — climate, transport distance, drainage area, and tectonics— on the physical and chemical properties of the sediments. Although minimal overall (CIA = 56-61), the degree of chemical weathering increases down transect, dominated by plagioclase dissolution. BET surface area of the mud (<63µm) fraction decreases distally, which is consistent with coarsening grain-size. Chemical alteration and BET surface area both increase in a distal region, within the active Elsinore Fault zone. Extensive fracturing here, together with a more-humid Pleistocene climate likely facilitated in-situ bedrock weathering; specifically, dissolution of primary minerals (e.g. plagioclase), preceding the arid alluvial erosion, transport, and deposition in the Holocene. This study further seeks to disentangle the complex record of the climate and tectonic signals imprinted in these sediments.

  15. TEM investigation on the growth mechanism of carbon nanotubes synthesized by hot-filament chemical vapor deposition.

    PubMed

    Chen, Xihong; Wang, Rongming; Xu, Jun; Yu, Dapeng

    2004-01-01

    Carbon nanotubes (CNTs) were synthesized using hot-filament chemical vapor deposition on Ni film-coated Si substrate. The CNTs were well-aligned perpendicular to the substrate. The as-grown CNTs were bamboo-like in their morphology, and were investigated using SEM and high-resolution transmission electron microscopy (HRTEM). The SEM and HRTEM studies show that the both ends of a CNT contain metallic catalytic particles, which is different from results previously reported. Our analysis results provide strong evidence that the metallic catalyst remains in a liquid state during nanotube growth. The upward-growth pulling force of the CNT layer elongates the liquid nanoparticles, which are finally broken into two parts. One part remains at the substrate surface (base of the CNTs) and is responsible for the catalytic growth of the CNTs. The other part is enclosed at the tip of the CNTs and is inactive during CNT growth.

  16. Atomic scale dynamics of a solid state chemical reaction directly determined by annular dark-field electron microscopy.

    PubMed

    Pennycook, Timothy J; Jones, Lewys; Pettersson, Henrik; Coelho, João; Canavan, Megan; Mendoza-Sanchez, Beatriz; Nicolosi, Valeria; Nellist, Peter D

    2014-12-22

    Dynamic processes, such as solid-state chemical reactions and phase changes, are ubiquitous in materials science, and developing a capability to observe the mechanisms of such processes on the atomic scale can offer new insights across a wide range of materials systems. Aberration correction in scanning transmission electron microscopy (STEM) has enabled atomic resolution imaging at significantly reduced beam energies and electron doses. It has also made possible the quantitative determination of the composition and occupancy of atomic columns using the atomic number (Z)-contrast annular dark-field (ADF) imaging available in STEM. Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides. These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors. We employ rapid scanning in STEM to both drive and directly observe the atomic scale dynamics behind the transformation of Mn3O4 into MnO. The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

  17. Role of hydrogen in the chemical vapor deposition growth of MoS2 atomic layers

    NASA Astrophysics Data System (ADS)

    Li, Xiao; Li, Xinming; Zang, Xiaobei; Zhu, Miao; He, Yijia; Wang, Kunlin; Xie, Dan; Zhu, Hongwei

    2015-04-01

    Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials.Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials. Electronic supplementary

  18. Interlayer Potassium And Its Neighboring Atoms in Micas: Crystal-Chemical Modeling And Xanes Spectroscopy

    SciTech Connect

    Brigatti, M.F.; Malferrari, D.; Poppi, M.; Mottana, A.; Cibin, G.; Marcelli, A.; Cinque, G.

    2009-05-12

    A detailed description of the interlayer site in trioctahedral true micas is presented based on a statistical appraisal of crystal-chemical, structural, and spectroscopic data determined on two sets of trioctahedral micas extensively studied by both X-ray diffraction refinement on single crystals (SC-XRD) and X-ray absorption fine spectroscopy (XAFS) at the potassium K-edge. Spectroscopy was carried out on both random powders and oriented cleavage flakes, the latter setting taking advantage of the polarized character of synchrotron radiation. Such an approach (AXANES) is shown to be complementary to crystal-chemical investigation based on SC-XRD refinement. However, the results are not definitive as they focus on few samples having extreme features only (e.g., end-members, unusual compositions, and samples with extreme and well-identified substitution mechanisms). The experimental absorption K-edge (XANES) for potassium was decomposed by calculation and extrapolated into a full in-plane absorption component ({sigma}{parallel}) and a full out-of-plane absorption component ({sigma}{perpendicular}). These two patterns reflect different structural features: {sigma}{parallel}represents the arrangement of the atoms located in the mica interlayer space and facing tetrahedral sheets; {sigma}{perpendicular} is associated with multiple-scattering interactions entering deep into the mica structure, thus also reflecting interactions with the heavy atoms (essentially Fe) located in the octahedral sheet. The out-of-plane patterns also provide insights into the electronic properties of the octahedral cations, such as their oxidation states (e.g., Fe{sup 2+} and Fe{sup 3+}) and their ordering (e.g., trans- vs. cis-setting). It is also possible to distinguish between F- and OH-rich micas due to peculiar absorption features originating from the F vs. OH occupancy of the O4 octahedral site. Thus, combining crystal-chemical, structural, and spectroscopic information is shown to be a

  19. Quantifying net microbial metabolism in the sub-seafloor using the chemical composition of adjacent hot and warm vent fluids

    NASA Astrophysics Data System (ADS)

    Butterfield, D. A.; Holden, J. F.; Roe, K. K.; Lilley, M. D.; Olson, E. J.; Ver Eecke, H. C.; Opatkiewicz, A. D.; Huber, J. A.

    2009-12-01

    Myriad evidence points to the existence and activity of diverse microbial communities living in the sub-seafloor where hot hydrothermal fluids (T>300°C) mix with cold seawater to create thermal and chemical gradients that can support many different metabolic types. When the hot source composition is well characterized, chemical mixing models can be used to compare the expected and actual composition of warm diffuse vents. The differences are attributed to sub-seafloor reactions. In some cases, e.g. for methanogenesis and methanotrophy, the sub-seafloor reactions can be unambiguously attributed to microbial activity. In other cases, e.g. sulfide oxidation, the effects of competing abiotic reactions may sometimes be constrained or simplifying assumptions made to estimate the role of microbial activity. The mixing model concept has been applied before, but there have been very few systematic surveys to quantify sub-seafloor mixing zone reactions on a vent field scale. During two recent expeditions to the Endeavour Integrated Studies Site and Axial Volcano on the Juan de Fuca ridge, NE Pacific, the Hydrothermal Fluid and Particle Sampler was used to collect 6-10 paired samples of adjacent focused and diffuse fluids. Chemical mixing model results show evidence of variable, site-specific sulfide oxidation (loss of 25-94%), methane oxidation (loss of 20-66%), and methanogenesis (3 to 5-fold gain) in the sub-seafloor mixing zone. Laboratory experiments on microbial cultures of Methanocaldococcus jannaschii grew optimally at 82°C with H2 concentrations near 100µM, and showed no measurable growth when H2 concentrations were below 20 µM. Most of the high-temperature sources at Endeavour in 2008/9 have too little hydrogen to provide this concentration range when mixed with enough seawater to bring the temperature below 100°C, producing sub-optimal conditions for methanogens. In many Endeavour vents, we find evidence for loss of methane in the sub-seafloor mixing zone

  20. Chemical studies of selected trace elements in hot-spring drainages of Yellowstone National Park

    SciTech Connect

    Stauffer, R.E.; Jenne, E.A.; Ball, J.W.

    1980-01-01

    Intensive chemical studies were made of S(-II), O/sub 2/, Al, Fe, Mn, P, As(III), As(V), and Li in waters from two high-Cl, low Ca-Mg hotspring drainages in the Lower Geyser Basin, a warm spring system rich in Ca and Mg in the Yellowstone Canyon area, and the Madison River system above Hebgen Lake. Analyses were also made of other representative thermal waters from the Park.

  1. Survey of reproductive hazards among oil, chemical, and atomic workers exposed to halogenated hydrocarbons

    SciTech Connect

    Savitz, D.A.; Harley, B.; Krekel, S.; Marshall, J.; Bondy, J.; Orleans, M.

    1984-01-01

    Several halogenated hydrocarbons are suspected of causing adverse reproductive effects. Because of such concerns, the Oil, Chemical, and Atomic Workers International Union surveyed the reproductive histories of two groups of workers. One group worked at plants engaged in the production or use of halogenated hydrocarbons (exposed) whereas the others had no such opportunity for exposure (nonexposed). Although a low response rate precludes firm conclusions, the 1,280 completed questionnaires provide useful data for generating hypotheses in this developing field of interest. A history of diagnosed cancer was reported more frequently among exposed workers. The infant mortality rate was also significantly elevated among the offspring of exposed workers. No risk gradient was observed for episodes of infertility, fetal loss, congenital defects, or low-birthweight offspring. Concerns with nonresponse, exposure characterization, possible confounding factors, and limited statistical power are addressed. The results provide further suggestions which help to direct studies of occupational reproductive risks.

  2. Surface Modification and Chemical Sputtering of Graphite Induced by Low Energy Atomic and Molecular Deuterium Ions

    SciTech Connect

    Zhang, Hengda; Meyer, Fred W; Meyer III, Harry M; Lance, Michael J

    2008-01-01

    The surface morphology, and chemical/structural modifications induced during chemical sputtering of ATJ graphite by low-energy (<200 eV/D) deuterium atomic and molecular ions are explored by Scanning Electron Microscopy (SEM), Raman and Auger Electron Spectroscopy (AES) diagnostics. At the lowest impact energies, the ion range may become less than the probe depth of Raman and AES spectroscopy diagnostics. We show that such diagnostics are still useful probes at these energies. As demonstration, we used these surface diagnostics to confirm the characteristic changes of surface texture, increased amorphization, enhanced surface reactivity to impurity species, and increased sp{sup 3} content that low-energy deuterium ion bombardment to steady-state chemical sputtering conditions produces. To put these studies into proper context, we also present new chemical sputtering yields for methane production of ATJ graphite at room temperature by impact of D{sub 2}{sup +} in the energy range 10-250 eV/D, and by impact of D{sup +} and D{sub 3}{sup +} at 30 eV/D and 125 eV/D, obtained using a Quadrupole Mass Spectroscopy (QMS) approach. Below 100 eV/D, the methane production in ATJ graphite is larger than that in HOPG by a factor of {approx} 2. In the energy range 10-60 eV/D, the methane production yield is almost independent of energy and then decreases with increasing ion energies. The results are in good agreement with recent molecular dynamics simulations.

  3. Multi-element analysis of manganese nodules by atomic absorption spectrometry without chemical separation

    USGS Publications Warehouse

    Kane, J.S.; Harnly, J.M.

    1982-01-01

    Five manganese nodules, including the USGS reference nodules A-1 and P-1, were analyzed for Co, Cu, Fe, K, Mg, Mn, Na, Ni and Zn without prior chemical separation by using a simultaneous multi-element atomic absorption spectrometer with an air-cetylene flame. The nodules were prepared in three digestion matrices. One of these solutions was measured using sixteen different combinations of burner height and air/acetylene ratios. Results for A-1 and P-1 are compared to recommended values and results for all nodules are compared to those obtained with an inductively coupled plasma. The elements Co, Cu, Fe, K, Mg, Mn, Na, Ni, and Zn are simultaneously determined with a composite recovery for all elements of 100 ?? 7%, independent of the digestion matrices, heights in the flame, or flame stoichiometries examined. Individual recoveries for Co, K, and Ni are considerably poorer in two digests than this composite figure, however. The optimum individual recoveries of 100 ?? 5% and imprecisions of 1-4%, except for zinc, are obtained when Co, K, Mn, Na and Ni are determined simultaneously in a concentrated digest, and in another analytical sequence, when Cu, Fe, Mg, Mn and Zn are measured simultaneously after dilution. Determination of manganese is equally accurate in the two sequences; its measurement in both assures internal consistency between the two measurement sequences. This approach improves analytical efficiency over that for conventional atomic absorption methods, while minimizing loss of accuracy or precision for individual elements. ?? 1982.

  4. Design and implementation of a novel portable atomic layer deposition/chemical vapor deposition hybrid reactor.

    PubMed

    Selvaraj, Sathees Kannan; Jursich, Gregory; Takoudis, Christos G

    2013-09-01

    We report the development of a novel portable atomic layer deposition chemical vapor deposition (ALD/CVD) hybrid reactor setup. Unique feature of this reactor is the use of ALD/CVD mode in a single portable deposition system to fabricate multi-layer thin films over a broad range from "bulk-like" multi-micrometer to nanometer atomic dimensions. The precursor delivery system and control-architecture are designed so that continuous reactant flows for CVD and cyclic pulsating flows for ALD mode are facilitated. A custom-written LabVIEW program controls the valve sequencing to allow synthesis of different kinds of film structures under either ALD or CVD mode or both. The entire reactor setup weighs less than 40 lb and has a relatively small footprint of 8 × 9 in., making it compact and easy for transportation. The reactor is tested in the ALD mode with titanium oxide (TiO2) ALD using tetrakis(diethylamino)titanium and water vapor. The resulting growth rate of 0.04 nm/cycle and purity of the films are in good agreement with literature values. The ALD/CVD hybrid mode is demonstrated with ALD of TiO2 and CVD of tin oxide (SnOx). Transmission electron microscopy images of the resulting films confirm the formation of successive distinct TiO2-ALD and SnO(x)-CVD layers. PMID:24089868

  5. Design and implementation of a novel portable atomic layer deposition/chemical vapor deposition hybrid reactor.

    PubMed

    Selvaraj, Sathees Kannan; Jursich, Gregory; Takoudis, Christos G

    2013-09-01

    We report the development of a novel portable atomic layer deposition chemical vapor deposition (ALD/CVD) hybrid reactor setup. Unique feature of this reactor is the use of ALD/CVD mode in a single portable deposition system to fabricate multi-layer thin films over a broad range from "bulk-like" multi-micrometer to nanometer atomic dimensions. The precursor delivery system and control-architecture are designed so that continuous reactant flows for CVD and cyclic pulsating flows for ALD mode are facilitated. A custom-written LabVIEW program controls the valve sequencing to allow synthesis of different kinds of film structures under either ALD or CVD mode or both. The entire reactor setup weighs less than 40 lb and has a relatively small footprint of 8 × 9 in., making it compact and easy for transportation. The reactor is tested in the ALD mode with titanium oxide (TiO2) ALD using tetrakis(diethylamino)titanium and water vapor. The resulting growth rate of 0.04 nm/cycle and purity of the films are in good agreement with literature values. The ALD/CVD hybrid mode is demonstrated with ALD of TiO2 and CVD of tin oxide (SnOx). Transmission electron microscopy images of the resulting films confirm the formation of successive distinct TiO2-ALD and SnO(x)-CVD layers.

  6. Chemical nature of boron and nitrogen dopant atoms in graphene strongly influences its electronic properties.

    PubMed

    Lazar, Petr; Zbořil, Radek; Pumera, Martin; Otyepka, Michal

    2014-07-21

    Boron and nitrogen doped graphenes are highly promising materials for electrochemical applications, such as energy storage, generation and sensing. The doped graphenes can be prepared by a broad variety of chemical approaches. The substitution of a carbon atom should induce n-type behavior in the case of nitrogen and p-type behavior in the case of boron-doped graphene; however, the real situation is more complex. The electrochemical experiments show that boron-doped graphene prepared by hydroboration reaction exhibits similar properties as the nitrogen doped graphene; according to theory, the electrochemical behavior of B and N doped graphenes should be opposite. Here we analyze the electronic structure of N/B-doped graphene (at ∼5% coverage) by theoretical calculations. We consider graphene doped by both substitution and addition reactions. The density of states (DOS) plots show that graphene doped by substitution of the carbon atom by N/B behaves as expected, i.e., as an n/p-doped material. N-doped graphene also has a lower value of the workfunction (3.10 eV) with respect to that of the pristine graphene (4.31 eV), whereas the workfunction of B-doped graphene is increased to the value of 5.57 eV. On the other hand, the workfunctions of graphene doped by addition of -NH2 (4.77 eV) and -BH2 (4.54 eV) groups are both slightly increased and therefore the chemical nature of the dopant is less distinguishable. This shows that mode of doping depends significantly on the synthesis method used, as it leads to different types of behaviour, and, in turn, different electronic and electrochemical properties of doped graphene, as observed in electrocatalytic experiments. This study has a tremendous impact on the design of doped graphene systems from the point of view of synthetic chemistry.

  7. Atom-specific look at the surface chemical bond using x-ray emission spectroscopy

    SciTech Connect

    Nilsson, A.; Wassdahl, N.; Weinelt, M.

    1997-04-01

    CO and N{sub 2} adsorbed on the late transition metals have become prototype systems regarding the general understanding of molecular adsorption. It is in general assumed that the bonding of molecules to transition metals can be explained in terms of the interaction of the frontier HOMO and LUMO molecular orbitals with the d-orbitals. In such a picture the other molecular orbitals should remain essentially the same as in the free molecule. For the adsorption of the isoelectronic molecules CO and N{sub 2} this has led to the so called Blyholder model i.e., a synergetic {sigma} (HOMO) donor and {pi} (LUMO) backdonation bond. The authors results at the ALS show that such a picture is oversimplified. The direct observation and identification of the states related to the surface chemical bond is an experimental challenge. For noble and transition metal surfaces, the adsorption induced states overlap with the metal d valence band. Their signature is therefore often obscured by bulk substrate states. This complication has made it difficult for techniques such as photoemission and inverse photoemission to provide reliable information on the energy of chemisorption induced states and has left questions unanswered regarding the validity of the frontier orbitals concept. Here the authors show how x-ray emission spectroscopy (XES), in spite of its inherent bulk sensitivity, can be used to investigate adsorbed molecules. Due to the localization of the core-excited intermediate state, XE spectroscopy allows an atomic specific separation of the valence electronic states. Thus the molecular contributions to the surface measurements make it possible to determine the symmetry of the molecular states, i.e., the separation of {pi} and {sigma} type states. In all the authors can obtain an atomic view of the electronic states involved in the formation of the chemical bond to the surface.

  8. Thin film solar cells with Si nanocrystallites embedded in amorphous intrinsic layers by hot-wire chemical vapor deposition.

    PubMed

    Park, Seungil; Parida, Bhaskar; Kim, Keunjoo

    2013-05-01

    We investigated the thin film growths of hydrogenated silicon by hot-wire chemical vapor deposition with different flow rates of SiH4 and H2 mixture ambient and fabricated thin film solar cells by implementing the intrinsic layers to SiC/Si heterojunction p-i-n structures. The film samples showed the different infrared absorption spectra of 2,000 and 2,100 cm(-1), which are corresponding to the chemical bonds of SiH and SiH2, respectively. The a-Si:H sample with the relatively high silane concentration provides the absorption peak of SiH bond, but the microc-Si:H sample with the relatively low silane concentration provides the absorption peak of SiH2 bond as well as SiH bond. Furthermore, the microc-Si:H sample showed the Raman spectral shift of 520 cm(-1) for crystalline phase Si bonds as well as the 480 cm(-1) for the amorphous phase Si bonds. These bonding structures are very consistent with the further analysis of the long-wavelength photoconduction tail and the formation of nanocrystalline Si structures. The microc-Si:H thin film solar cell has the photovoltaic behavior of open circuit voltage similar to crystalline silicon thin film solar cell, indicating that microc-Si:H thin film with the mixed phase of amorphous and nanocrystalline structures show the carrier transportation through the channel of nanocrystallites.

  9. Synthesis of carbon nanotubes on diamond-like carbon by the hot filament plasma-enhanced chemical vapor deposition method.

    PubMed

    Choi, Eun Chang; Park, Yong Seob; Hong, Byungyou

    2009-01-01

    Carbon nanotubes (CNTs) have attracted considerable attention as possible routes to device miniaturization due to their excellent mechanical, thermal, and electronic properties. These properties show great potential for devices such as field emission displays, transistors, and sensors. The growth of CNTs can be explained by interaction between small carbon patches and the metal catalyst. The metals such as nickel, cobalt, gold, iron, platinum, and palladium are used as the catalysts for the CNT growth. In this study, diamond-like carbon (DLC) was used for CNT growth as a nonmetallic catalyst layer. DLC films were deposited by a radio frequency (RF) plasma-enhanced chemical vapor deposition (RF-PECVD) method with a mixture of methane and hydrogen gases. CNTs were synthesized by a hot filament plasma-enhanced chemical vapor deposition (HF-PECVD) method with ammonia (NH3) as a pretreatment gas and acetylene (C2H2) as a carbon source gas. The grown CNTs and the pretreated DLC films were observed using field emission scanning electron microscopy (FE-SEM) measurement, and the structure of the grown CNTs was analyzed by high resolution transmission scanning electron microscopy (HR-TEM). Also, using energy dispersive spectroscopy (EDS) measurement, we confirmed that only the carbon component remained on the substrate. PMID:19318258

  10. Study of the roles of chemical modifiers in determining boron using graphite furnace atomic absorption spectrometry and optimization of the temperature profile during atomization.

    PubMed

    Yamamoto, Yuhei; Shirasaki, Toshihiro; Yonetani, Akira; Imai, Shoji

    2015-01-01

    The measurement conditions for determining boron using graphite furnace-atomic absorption spectrometry (GF-AAS) were investigated. Differences in the boron absorbance profiles were found using three different commercially available GF-AAS instruments when the graphite atomizers in them were not tuned. The boron absorbances found with and without adjusting the graphite atomizers suggested that achieving an adequate absorbance for the determination of boron requires a sharp temperature profile that overshoots the target temperature during the atomization process. Chemical modifiers that could improve the boron absorbance without the need for using coating agents were tested. Calcium carbonate improved the boron absorbance but did not suppress variability in the peak height. Improvement of boron absorbance was comparatively less using iron nitrate or copper nitrate than using calcium carbonate, but variability in the peak height was clearly suppressed using iron nitrate or copper nitrate. The limit of detection was 0.0026 mg L(-1) when iron nitrate was used. It appears that iron nitrate is a useful new chemical modifier for the quick and simple determination of boron using GF-AAS.

  11. Computer Modeling Of Atomization

    NASA Technical Reports Server (NTRS)

    Giridharan, M.; Ibrahim, E.; Przekwas, A.; Cheuch, S.; Krishnan, A.; Yang, H.; Lee, J.

    1994-01-01

    Improved mathematical models based on fundamental principles of conservation of mass, energy, and momentum developed for use in computer simulation of atomization of jets of liquid fuel in rocket engines. Models also used to study atomization in terrestrial applications; prove especially useful in designing improved industrial sprays - humidifier water sprays, chemical process sprays, and sprays of molten metal. Because present improved mathematical models based on first principles, they are minimally dependent on empirical correlations and better able to represent hot-flow conditions that prevail in rocket engines and are too severe to be accessible for detailed experimentation.

  12. Hot spot initiation and chemical reaction in shocked polymeric bonded explosives

    NASA Astrophysics Data System (ADS)

    An, Qi; Zybin, Sergey; Jaramillo-Botero, Andres; Goddard, William; Materials; Process Simulation Center, Caltech Team

    2011-06-01

    A polymer bonded explosive (PBX) model based on PBXN-106 is studied via molecular dynamics (MD) simulations using reactive force field (ReaxFF) under shock loading conditions. Hotspot is observed when shock waves pass through the non-planar interface of explosives and elastomers. Adiabatic shear localization is proposed as the main mechanism of hotspot ignition in PBX for high velocity impact. Our simulation also shows that the coupling of shear localization and chemical reactions at hotspot region play important rules at stress relaxtion for explosives. The phenomenon that shock waves are obsorbed by elastomers is also observed in the MD simulations. This research received supports from ARO (W911NF-05-1-0345; W911NF-08-1-0124), ONR (N00014-05-1-0778), and Los Alamos National Laboratory (LANL).

  13. Chemical enrichment in the hot intra-cluster medium seen with XMM-Newton/EPIC

    NASA Astrophysics Data System (ADS)

    Mernier, F.; de Plaa, J.; Pinto, C.; Kaastra, J.; Kosec, P.; Zhang, Y.; Mao, J.; Werner, N.

    2016-06-01

    The intra-cluster medium (ICM), permeating the large gravitational potential well of galaxy clusters and groups, is rich in metals, which can be detected via their emission lines in the soft X-ray band. These heavy elements (typically from O to Ni) have been synthesized by Type Ia (SNIa) and core-collapse (SNcc) supernovae within the galaxy members, and continuously enrich the ICM since the cosmic star formation peak (z ≃ 2-3). Because the predicted chemical yields of supernovae depend on either their explosion mechanisms (SNIa) or the initial mass and metallicity of their progenitors (SNcc), measuring the abundances in the ICM can help to constrain supernovae models. In this study, we use XMM-Newton/EPIC to measure the abundances of 9 elements (Mg, Si, S, Ar, Ca, Cr, Mn, Fe and Ni) in a sample of 44 cool-core galaxy clusters, groups and ellipticals (the CHEERS catalog). Combining these results with the O and Ne abundances measured using RGS, we establish an average X/Fe abundance pattern in the ICM, and we determine the best-fit SNIa and SNcc models, as well as the relative fraction of SNIa/SNcc responsible for the enrichment.

  14. Examinations of Chemical Resistance and Thermal Behaviour of Ceramic Filter Materials for Hot-Gas Cleaning

    SciTech Connect

    Angermann, J.; Meyer, B.; Horlbeck, W.

    2002-09-19

    Increasing prosperity and the steady growth of the world population lead to a strongly rising energy requirement. Therefore the saving of the available resources as well as the limitation of CO{sub 2}-emission are the main reasons for developing highly efficient power stations. The use of combined cycle technology for advanced coal fired power plants allow a significantly higher conversion efficiency than it is possible in an only steam power plant. In order to increase the gas turbine inlet temperature, the filtration of fine particles is necessary. Therefore the filtration unit is one of the key components of the circulating pressurized fluidized bed combustion technology (PFBC). To use this technology more effectively, gas cleaning at high temperatures or in an reducing atmosphere is necessary. A possibility of the effective gas cleaning at high temperatures is the use of porous ceramic candle filters. The structure of such filter elements usually consists of a highly porous sup port which ensures the mechanical strength and a layer which operates as the functional part for the particle removal. To ensure a guaranteed lifetime of about 16000 h the effect of combustion or gasification atmosphere and temperature on the thermal and mechanical properties of the filter material has to be studied. The examinations and results, described in this article, are part of some previous work. This paper focuses especially on the chemical resistance and the thermal behaviour of the used ceramic filter materials.

  15. Quantitative spectroscopy of hot stars: accurate atomic data applied on a large scale as driver of recent breakthroughs

    NASA Astrophysics Data System (ADS)

    Przybilla, Norbert; Schaffenroth, Veronika; Nieva, Maria-Fernanda

    2015-08-01

    OB-type stars present hotbeds for non-LTE physics because of their strong radiation fields that drive the atmospheric plasma out of local thermodynamic equilibrium. We report on recent breakthroughs in the quantitative analysis of the optical and UV-spectra of OB-type stars that were facilitated by application of accurate and precise atomic data on a large scale. An astophysicist's dream has come true, by bringing observed and model spectra into close match over wide parts of the observed wavelength ranges. This facilitates tight observational constraints to be derived from OB-type stars for wide applications in astrophysics. However, despite the progress made, many details of the modelling may be improved further. We discuss atomic data needs in terms of laboratory measurements and also ab-initio calculations. Particular emphasis is given to quantitative spectroscopy in the near-IR, which will be in focus in the era of the upcoming extremely large telescopes.

  16. Atomic layer deposition and chemical vapor deposition precursor selection method application to strontium and barium precursors.

    PubMed

    Holme, Timothy P; Prinz, Fritz B

    2007-08-23

    A new selection method for atomic layer deposition (ALD) or chemical vapor deposition (CVD) precursors is proposed and tested. Density functional theory was used to simulate Sr and Ba precursors, and several precursors were selected and used to grow films via ALD as test cases for the precursor selection method. The precursors studied were M(x)2 (M = Sr, Ba; x = tetramethylheptanedionate (tmhd), acetylacetonate (acac), hexafluoroacetylacetonate (hfac), cyclopentadienyl (H(5)C(5)), pentamethylcyclopentadienyl (Me(5)C(5)), n-propyltetramethylcyclopentadienyl (PrMe(4)C(5)), tris(isopropylcyclopentadienyl) (Pr(3)(i)H(2)C(5)), tris(isopropylcyclopentadienyl)(THF) (Pr(3)(i)H(2)C(5))(OC(4)H(8)), tris(isopropylcyclopentadienyl)(THF)2 (Pr(3)(i)H(2)C(5))(OC(4)H(8))2, tris(tert-butylcyclopentadienyl) (Bu(3)(t)H(2)C(5)), tris(tert-butylcyclopentadienyl)(THF) (Bu(3)(t)H(2)C(5))(OC(4)H(8)), heptafluoro-2,2-dimethyl-3,5-octanedionate (fod)). The energy required to break bonds between the metal atom and the ligands was calculated to find which precursors react most readily. In the case of tmhd and Cp precursors, the energy required to break bonds in the precursor ligand was studied to evaluate the most likely mechanism of carbon incorporation into the film. Trends for Ba and Sr followed each other closely, reflecting the similar chemistry among alkaline earth metals. The diketonate precursors have stronger bonds to the metals than the Cp precursors, but weaker bonds within the ligand, explaining the carbon contamination found in experimentally grown films. Atomic layer deposition of SrO was tested with Sr(tmhd)2 and Sr(PrMe(4)Cp)2 and oxygen, ozone, and water as oxygen sources. No deposition was measured with tmhd precursors, and SrO films were deposited with PrMe(4)Cp with a source temperature of 200 degrees C and at substrate temperatures between 250 and 350 degrees C with growth rates increasing for oxygen sources in this order: O2 < H2O < O2 + H2O. The experimental results

  17. Learning about Atoms, Molecules, and Chemical Bonds: A Case Study of Multiple-Model Use in Grade 11 Chemistry.

    ERIC Educational Resources Information Center

    Harrison, Allan G.; Treagust, David F.

    2000-01-01

    Reports in detail on a year-long case study of multiple-model use at grade 11. Suggests that students who socially negotiated the shared and unshared attributes of common analogical models for atoms, molecules, and chemical bonds used these models more consistently in their explanations. (Author/CCM)

  18. Hot wire chemical vapor deposition chemistry in the gas phase and on the catalyst surface with organosilicon compounds.

    PubMed

    Shi, Yujun

    2015-02-17

    CONSPECTUS: Hot wire chemical vapor deposition (HWCVD), also referred to as catalytic CVD (Cat-CVD), has been used to produce Si-containing thin films, nanomaterials, and functional polymer coatings that have found wide applications in microelectronic and photovoltaic devices, in automobiles, and in biotechnology. The success of HWCVD is largely due to its various advantages, including high deposition rate, low substrate temperatures, lack of plasma-induced damage, and large-area uniformity. Film growth in HWCVD is induced by reactive species generated from primary decomposition on the metal wire or from secondary reactions in the gas phase. In order to achieve a rational and efficient optimization of the process, it is essential to identify the reactive species and to understand the chemical kinetics that govern the production of these precursor species for film growth. In this Account, we report recent progress in unraveling the complex gas-phase reaction chemistry in the HWCVD growth of silicon carbide thin films using organosilicon compounds as single-source precursors. We have demonstrated that laser ionization mass spectrometry is a powerful diagnostic tool for studying the gas-phase reaction chemistry when combined with the methods of isotope labeling and chemical trapping. The four methyl-substituted silane molecules, belonging to open-chain alkylsilanes, dissociatively adsorb on W and Ta filaments to produce methyl radical and H2 molecule. Under the typical deposition pressures, with increasing number of methyl substitution, the dominant chemistry occurring in the gas phase switches from silylene/silene reactions to free-radical short chain reactions. This change in dominant reaction intermediates from silylene/silene to methyl radicals explains the observation from thin film deposition that silicon carbide films become more C-rich with a decreasing number of Si-H bonds in the four precursor molecules. In the case of cyclic monosilacyclobutanes, we have

  19. Hot bubbles of planetary nebulae with hydrogen-deficient winds. I. Heat conduction in a chemically stratified plasma

    NASA Astrophysics Data System (ADS)

    Sandin, C.; Steffen, M.; Schönberner, D.; Rühling, U.

    2016-02-01

    Heat conduction has been found a plausible solution to explain discrepancies between expected and measured temperatures in hot bubbles of planetary nebulae (PNe). While the heat conduction process depends on the chemical composition, to date it has been exclusively studied for pure hydrogen plasmas in PNe. A smaller population of PNe show hydrogen-deficient and helium- and carbon-enriched surfaces surrounded by bubbles of the same composition; considerable differences are expected in physical properties of these objects in comparison to the pure hydrogen case. The aim of this study is to explore how a chemistry-dependent formulation of the heat conduction affects physical properties and how it affects the X-ray emission from PN bubbles of hydrogen-deficient stars. We extend the description of heat conduction in our radiation hydrodynamics code to work with any chemical composition. We then compare the bubble-formation process with a representative PN model using both the new and the old descriptions. We also compare differences in the resulting X-ray temperature and luminosity observables of the two descriptions. The improved equations show that the heat conduction in our representative model of a hydrogen-deficient PN is nearly as efficient with the chemistry-dependent description; a lower value on the diffusion coefficient is compensated by a slightly steeper temperature gradient. The bubble becomes somewhat hotter with the improved equations, but differences are otherwise minute. The observable properties of the bubble in terms of the X-ray temperature and luminosity are seemingly unaffected.

  20. High-angle tilt boundary graphene domain recrystallized from mobile hot-wire-assisted chemical vapor deposition system.

    PubMed

    Lee, Jinsup; Baek, Jinwook; Ryu, Gyeong Hee; Lee, Mi Jin; Oh, Seran; Hong, Seul Ki; Kim, Bo-Hyun; Lee, Seok-Hee; Cho, Byung Jin; Lee, Zonghoon; Jeon, Seokwoo

    2014-08-13

    Crystallization of materials has attracted research interest for a long time, and its mechanisms in three-dimensional materials have been well studied. However, crystallization of two-dimensional (2D) materials is yet to be challenged. Clarifying the dynamics underlying growth of 2D materials will provide the insight for the potential route to synthesize large and highly crystallized 2D domains with low defects. Here, we present the growth dynamics and recrystallization of 2D material graphene under a mobile hot-wire assisted chemical vapor deposition (MHW-CVD) system. Under local but sequential heating by MHW-CVD system, the initial nucleation of nanocrystalline graphenes, which was not extended into the growth stage due to the insufficient thermal energy, took a recrystallization and converted into a grand single crystal domain. During this process, the stitching-like healing of graphene was also observed. The local but sequential endowing thermal energy to nanocrystalline graphenes enabled us to simultaneously reveal the recrystallization and healing dynamics in graphene growth, which suggests an alternative route to synthesize a highly crystalline and large domain size graphene. Also, this recrystallization and healing of 2D nanocrystalline graphenes offers an interesting insight on the growth mechanism of 2D materials.

  1. Advances in chemical and physical properties of electric arc furnace carbon steel slag by hot stage processing and mineral mixing.

    PubMed

    Liapis, Ioannis; Papayianni, Ioanna

    2015-01-01

    Slags are recognised as a highly efficient, cost effective tool in the metal processing industry, by minimising heat losses, reducing metal oxidation through contact with air, removing metal impurities and protecting refractories and graphite electrodes. When compared to natural aggregates for use in the construction industry, slags have higher specific weight that acts as an economic deterrent. A method of altering the specific weight of EAFC slag by hot stage processing and mineral mixing, during steel production is presented in this article. The method has minimal interference with the production process of steel, even by limited additions of appropriate minerals at high temperatures. Five minerals are examined, namely perlite, ladle furnace slag, bauxite, diatomite and olivine. Measurements of specific weight are accompanied by X-ray diffraction (XRD) and fluorescence (XRF) analysis and scanning electron microscopy spectral images. It is also shown how altering the chemical composition is expected to affect the furnace refractory lining. Additionally, the process has been repeated for the most suitable mix in gas furnace and physical properties (FI, SI, LA, PSV, AAV, volume stability) examined. Alteration of the specific weight can result in tailoring slag properties for specific applications in the construction sector. PMID:25261762

  2. High-angle tilt boundary graphene domain recrystallized from mobile hot-wire-assisted chemical vapor deposition system.

    PubMed

    Lee, Jinsup; Baek, Jinwook; Ryu, Gyeong Hee; Lee, Mi Jin; Oh, Seran; Hong, Seul Ki; Kim, Bo-Hyun; Lee, Seok-Hee; Cho, Byung Jin; Lee, Zonghoon; Jeon, Seokwoo

    2014-08-13

    Crystallization of materials has attracted research interest for a long time, and its mechanisms in three-dimensional materials have been well studied. However, crystallization of two-dimensional (2D) materials is yet to be challenged. Clarifying the dynamics underlying growth of 2D materials will provide the insight for the potential route to synthesize large and highly crystallized 2D domains with low defects. Here, we present the growth dynamics and recrystallization of 2D material graphene under a mobile hot-wire assisted chemical vapor deposition (MHW-CVD) system. Under local but sequential heating by MHW-CVD system, the initial nucleation of nanocrystalline graphenes, which was not extended into the growth stage due to the insufficient thermal energy, took a recrystallization and converted into a grand single crystal domain. During this process, the stitching-like healing of graphene was also observed. The local but sequential endowing thermal energy to nanocrystalline graphenes enabled us to simultaneously reveal the recrystallization and healing dynamics in graphene growth, which suggests an alternative route to synthesize a highly crystalline and large domain size graphene. Also, this recrystallization and healing of 2D nanocrystalline graphenes offers an interesting insight on the growth mechanism of 2D materials. PMID:24978293

  3. Advances in chemical and physical properties of electric arc furnace carbon steel slag by hot stage processing and mineral mixing.

    PubMed

    Liapis, Ioannis; Papayianni, Ioanna

    2015-01-01

    Slags are recognised as a highly efficient, cost effective tool in the metal processing industry, by minimising heat losses, reducing metal oxidation through contact with air, removing metal impurities and protecting refractories and graphite electrodes. When compared to natural aggregates for use in the construction industry, slags have higher specific weight that acts as an economic deterrent. A method of altering the specific weight of EAFC slag by hot stage processing and mineral mixing, during steel production is presented in this article. The method has minimal interference with the production process of steel, even by limited additions of appropriate minerals at high temperatures. Five minerals are examined, namely perlite, ladle furnace slag, bauxite, diatomite and olivine. Measurements of specific weight are accompanied by X-ray diffraction (XRD) and fluorescence (XRF) analysis and scanning electron microscopy spectral images. It is also shown how altering the chemical composition is expected to affect the furnace refractory lining. Additionally, the process has been repeated for the most suitable mix in gas furnace and physical properties (FI, SI, LA, PSV, AAV, volume stability) examined. Alteration of the specific weight can result in tailoring slag properties for specific applications in the construction sector.

  4. Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

    NASA Astrophysics Data System (ADS)

    Chaudhari, Pradip; Singh, Arvind; Topkar, Anita; Dusane, Rajiv

    2015-04-01

    In order to utilize the well established silicon detector technology for neutron detection application, a silicon based thermal neutron detector was fabricated by integrating a thin boron carbide layer as a neutron converter with a silicon PIN detector. Hot wire chemical vapor deposition (HWCVD), which is a low cost, low temperature process for deposition of thin films with precise thickness was explored as a technique for direct deposition of a boron carbide layer over the metalized front surface of the detector chip. The presence of B-C bonding and 10B isotope in the boron carbide film were confirmed by Fourier transform infrared spectroscopy and secondary ion mass spectrometry respectively. The deposition of HWCVD boron carbide layer being a low temperature process was observed not to cause degradation of the PIN detector. The response of the detector with 0.2 μm and 0.5 μm thick boron carbide layer was examined in a nuclear reactor. The pulse height spectrum shows evidence of thermal neutron response with signature of (n, α) reaction. The results presented in this article indicate that HWCVD boron carbide deposition technique would be suitable for low cost industrial fabrication of PIN based single element or 1D/2D position sensitive thermal neutron detectors.

  5. Low temperature deposition of polycrystalline silicon thin films on a flexible polymer substrate by hot wire chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Sang-hoon; Jung, Jae-soo; Lee, Sung-soo; Lee, Sung-bo; Hwang, Nong-moon

    2016-11-01

    For the applications such as flexible displays and solar cells, the direct deposition of crystalline silicon films on a flexible polymer substrate has been a great issue. Here, we investigated the direct deposition of polycrystalline silicon films on a polyimide film at the substrate temperature of 200 °C. The low temperature deposition of crystalline silicon on a flexible substrate has been successfully made based on two ideas. One is that the Si-Cl-H system has a retrograde solubility of silicon in the gas phase near the substrate temperature. The other is the new concept of non-classical crystallization, where films grow by the building block of nanoparticles formed in the gas phase during hot-wire chemical vapor deposition (HWCVD). The total amount of precipitation of silicon nanoparticles decreased with increasing HCl concentration. By adding HCl, the amount and the size of silicon nanoparticles were reduced remarkably, which is related with the low temperature deposition of silicon films of highly crystalline fraction with a very thin amorphous incubation layer. The dark conductivity of the intrinsic film prepared at the flow rate ratio of RHCl=[HCl]/[SiH4]=3.61 was 1.84×10-6 Scm-1 at room temperature. The Hall mobility of the n-type silicon film prepared at RHCl=3.61 was 5.72 cm2 V-1s-1. These electrical properties of silicon films are high enough and could be used in flexible electric devices.

  6. Characterization of chemically and enzymatically treated hemp fibres using atomic force microscopy and spectroscopy

    NASA Astrophysics Data System (ADS)

    George, Michael; Mussone, Paolo G.; Abboud, Zeinab; Bressler, David C.

    2014-09-01

    The mechanical and moisture resistance properties of natural fibre reinforced composites are dependent on the adhesion between the matrix of choice and the fibre. The main goal of this study was to investigate the effect of NaOH swelling of hemp fibres prior to enzymatic treatment and a novel chemical sulfonic acid method on the physical properties of hemp fibres. The colloidal properties of treated hemp fibres were studied exclusively using an atomic force microscope. AFM imaging in tapping mode revealed that each treatment rendered the surface topography of the hemp fibres clean and exposed the individual fibre bundles. Hemp fibres treated with laccase had no effect on the surface adhesion forces measured. Interestingly, mercerization prior to xylanase + cellulase and laccase treatments resulted in greater enzyme access evident in the increased adhesion force measurements. Hemp fibres treated with sulfonic acid showed an increase in surface de-fibrillation and smoothness. A decrease in adhesion forces for 4-aminotoulene-3-sulfonic acid (AT3S) treated fibres suggested a reduction in surface polarity. This work demonstrated that AFM can be used as a tool to estimate the surface forces and roughness for modified fibres and that enzymatic coupled with chemical methods can be used to improve the surface properties of natural fibres for composite applications. Further, this work is one of the first that offers some insight into the effect of mercerization prior to enzymes and the effect on the surface topography. AFM will be used to selectively screen treated fibres for composite applications based on the adhesion forces associated with the colloidal interface between the AFM tip and the fibre surfaces.

  7. Average atom transport properties for pure and mixed species in the hot and warm dense matter regimes

    SciTech Connect

    Starrett, C. E.; Kress, J. D.; Collins, L. A.; Hanson, D. E.; Clerouin, J.; Recoules, V.

    2012-10-15

    The Kubo-Greenwood formulation for calculation of optical conductivities with an average atom model is extended to calculate thermal conductivities. The method is applied to species and conditions of interest for inertial confinement fusion. For the mixed species studied, the partial pressure mixing rule is used. Results including pressures, dc, and thermal conductivities are compared to ab initio calculations. Agreement for pressures is good, for both the pure and mixed species. For conductivities, it is found that the ad hoc renormalization method with line broadening, described in the text, gives best agreement with the ab initio results. However, some disagreement is found and the possible reasons for this are discussed.

  8. Atom-scale depth localization of biologically important chemical elements in molecular layers.

    PubMed

    Schneck, Emanuel; Scoppola, Ernesto; Drnec, Jakub; Mocuta, Cristian; Felici, Roberto; Novikov, Dmitri; Fragneto, Giovanna; Daillant, Jean

    2016-08-23

    In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces. PMID:27503887

  9. Increase in the power of lasing on atomic and ion transitions in chemical elements

    SciTech Connect

    Klimkin, V M; Sokovikov, V G

    2007-02-28

    A method for increasing the power of pulsed lasing on atomic and ion transitions in chemical elements obtained by the conversion of the UV radiation of excimer lasers in cells with metal vapours is studied. A part of UV radiation transmitted through a cell with metal vapour is used for pumping a dye solution in such a way that the cell converter with metal vapour represents a master oscillator, while the dye cell represents an amplifier. The study is performed by the example of amplification of weak spectral components of radiation from a XeCl* laser converted in mercury and barium vapours. In the amplifying stage the longitudinal pumping of the dye is used and a scheme for suppressing self-excitation is employed. It is found by selecting dyes that the alcohol solution of uranin is nearly optimal for amplification of the 546.1-nm laser line of mercury, while the best results in amplification of the 533-nm and 648.2-nm laser lines of barium were obtained by using alcohol solutions of rhodamine 6G and oxazine 17, respectively. The power of the 546.1-nm mercury line was increased by an order of magnitude, while the power of the 533-nm and 648.2-nm lines of barium - almost by a factor of twenty-five. (lasers)

  10. Atom-scale depth localization of biologically important chemical elements in molecular layers

    PubMed Central

    Schneck, Emanuel; Scoppola, Ernesto; Drnec, Jakub; Mocuta, Cristian; Felici, Roberto; Novikov, Dmitri; Fragneto, Giovanna; Daillant, Jean

    2016-01-01

    In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers’ global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces. PMID:27503887

  11. Reaction of atomically clean aluminum and chemically modified aluminum with alkyl halides

    SciTech Connect

    Chen, J.G.; Beebe, T.P. Jr.; Crowell, J.E.; Yates, J.T. Jr.

    1987-03-18

    The interaction of methyl halides with an atomically clean A(111) surface has been investigated using high-resolution electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES), and temperature programmed desorption (TPD). CH/sub 3/I adsorbs on A(111) both molecularly and dissociatively at 150 K; adsorbed CH/sub 3/I decomposes to CH/sub (a)/ and I/sub (a)/ in the temperature range of 250-450 K. No surface reaction of CH/sub 3/Cl or CH/sub 3/Br with clean or chemically modified Al(111) was observed, and a reactive sticking coefficient of < 10/sup -5/ was estimated in the temperature range of 135-500 K (CH/sub 3/Cl) or at 150 K (CH/sub 3/Br). Reasons for the reactivity differences of the methyl halides toward the Al(111) surface are discussed. These findings on Al, and their implication in Grignard reaction mechanisms, are compared with recent studies by another group on a Mg surface.

  12. Atom-scale depth localization of biologically important chemical elements in molecular layers.

    PubMed

    Schneck, Emanuel; Scoppola, Ernesto; Drnec, Jakub; Mocuta, Cristian; Felici, Roberto; Novikov, Dmitri; Fragneto, Giovanna; Daillant, Jean

    2016-08-23

    In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.

  13. Determination of cadmium in water samples by fast pyrolysis-chemical vapor generation atomic fluorescence spectrometry

    NASA Astrophysics Data System (ADS)

    Zhang, Jingya; Fang, Jinliang; Duan, Xuchuan

    2016-08-01

    A pyrolysis-vapor generation procedure to determine cadmium by atomic fluorescence spectrometry has been established. Under fast pyrolysis, cadmium ion can be reduced to volatile cadmium species by sodium formate. The presence of thiourea enhanced the efficiency of cadmium vapor generation and eliminated the interference of copper. The possible mechanism of vapor generation of cadmium was discussed. The optimization of the parameters for pyrolysis-chemical vapor generation, including pyrolysis temperature, amount of sodium formate, concentration of hydrochloric acid, and carrier argon flow rate were carried out. Under the optimized conditions, the absolute and concentration detection limits were 0.38 ng and 2.2 ng ml- 1, respectively, assuming that 0.17 ml of sample was injected. The generation efficiency of was 28-37%. The method was successfully applied to determine trace amounts of cadmium in two certified reference materials of Environmental Water (GSB07-1185-2000 and GSBZ 50009-88). The results were in good agreement with the certified reference values.

  14. Nanoscale fabrication and characterization of chemically modified silicon surfaces using conductive atomic force microscopy in liquids

    NASA Astrophysics Data System (ADS)

    Kinser, Christopher Reagan

    This dissertation examines the modification and characterization of hydrogen-terminated silicon surfaces in organic liquids. Conductive atomic force microscope (cAFM) lithography is used to fabricate structures with sub-100 nm line width on H:Si(111) in n-alkanes, 1-alkenes, and 1-alkanes. Nanopatterning is accomplished by applying a positive (n-alkanes and 1-alkenes) or a negative (1-alkanes) voltage pulse to the silicon substrate with the cAFM tip connected to ground. The chemical and kinetic behavior of the patterned features is characterized using AFM, lateral force microscopy, time-of-flight secondary ion mass spectroscopy (TOF SIMS), and chemical etching. Features patterned in hexadecane, 1-octadecene, and undecylenic acid methyl ester exhibited chemical and kinetic behavior consistent with AFM field induced oxidation. The oxide features are formed due to capillary condensation of a water meniscus at the AFM tip-sample junction. A space-charge limited growth model is proposed to explain the observed growth kinetics. Surface modifications produced in the presence of neat 1-dodecyne and 1-octadecyne exhibited a reduced lateral force compared to the background H:Si(111) substrate and were resistant to a hydrofluoric acid etch, characteristics which indicate that the patterned features are not due to field induced oxidation and which are consistent with the presence of the methyl-terminated 1-alkyne bound directly to the silicon surface through silicon-carbon bonds. In addition to the cAFM patterned surfaces, full monolayers of undecylenic acid methyl ester (SAM-1) and undec-10-enoic acid 2-bromoethyl ester (SAM-2) were grown on H:Si(111) substrates using ultraviolet light. The structure and chemistry of the monolayers were characterized using AFM, TOF SIMS, X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), X-ray standing waves (XSW), and X-ray fluorescence (XRF). These combined analyses provide evidence that SAM-1 and SAM-2 form dense monolayers

  15. Realization of atomically flat steps and terraces like surface of SrTiO3 (001) single crystal by hot water etching and high temperature annealing

    NASA Astrophysics Data System (ADS)

    Prakash, Bhanu; Chakraverty, S.

    2015-07-01

    We have successfully prepared atomically flat single-terminated SrTiO3(001) surface using a mild and reproducible etching technique combined with high temperature annealing. To achieve single terminated surface, deionised water at 60 °C was used to selectively etch SrO composites from the substrate surface. A clear step-and-terrace like surface morphology is observed by subsequent air annealing at 1000 °C. Atomic Force Microscopy suggests the step height (~0.4 nm) corresponding to the lattice parameter of SrTiO3, which confirms the formation of single-terminated surface. This chemical-free mild etching technique might be useful to prepare single-terminated surface, especially for the perovskites containing reactive elements.

  16. Use of a CO{sub 2} pellet non-destructive cleaning system to decontaminate radiological waste and equipment in shielded hot cells at the Bettis Atomic Power Laboratory

    SciTech Connect

    Bench, T.R.

    1997-05-01

    This paper details how the Bettis Atomic Power Laboratory modified and utilized a commercially available, solid carbon dioxide (CO{sub 2}) pellet, non-destructive cleaning system to support the disposition and disposal of radioactive waste from shielded hot cells. Some waste materials and equipment accumulated in the shielded hot cells cannot be disposed directly because they are contaminated with transuranic materials (elements with atomic numbers greater than that of uranium) above waste disposal site regulatory limits. A commercially available CO{sub 2} pellet non-destructive cleaning system was extensively modified for remote operation inside a shielded hot cell to remove the transuranic contaminants from the waste and equipment without generating any secondary waste in the process. The removed transuranic contaminants are simultaneously captured, consolidated, and retained for later disposal at a transuranic waste facility.

  17. In-Situ Hot Stage Atomic Force Microscopy Study of Poly(E-Caprolactone) Crystal Growth in Ultrathin Films

    NASA Astrophysics Data System (ADS)

    Prud'Homme, Robert E.; Mareau, Vincent H.

    2005-03-01

    Morphologies, growth rates and melting of isothermally crystallized ultrathin (200 to 1 nm) poly(e-caprolactone) (PCL) films have been investigated in real-time by atomic force microscopy. The flat-on orientation of the lamellar crystals relative to the substrate was determined by electron diffraction. The truncated lozenge shape PCL crystals observed at low undercooling become distorted for films of thicknesses equal or thinner than the lamellar thickness, which depends on the crystallization temperature but not on the initial film thickness. The melting behavior of distorted crystals differs from that of undistorted ones, and their growth is slower and non-linear. The crystal growth rate decreases greatly with the film thickness. All these observations are discussed in terms of the diffusion of the polymer chains from the melt to the crystal growth front.

  18. Chemical vapor deposition and atomic layer deposition of metal oxide and nitride thin films

    NASA Astrophysics Data System (ADS)

    Barton, Jeffrey Thomas

    Processes for depositing thin films with various electronic, optical, mechanical, and chemical properties are indispensable in many industries today. Of the many deposition methods available, chemical vapor deposition (CVD) has proved over time to be one of the most flexible, efficient, and cost-effective. Atomic layer deposition (ALD) is a newer process that is gaining favor as a method for depositing films with excellent properties and unparalleled precision. This work describes the development of novel CVD and ALD processes to deposit a variety of materials. Hafnium oxide and zirconium oxide show promise as replacements for SiO 2 as gate dielectrics in future-generation transistors. These high-k materials would provide sufficient capacitance with layers thick enough to avoid leakage from tunneling. An ALD method is presented here for depositing conformal hafnium oxide from tetrakis-(diethylamido)hafnium and oxygen gas. A CVD method for depositing zirconium oxide from tetrakis-(dialkylamido)zirconium and either oxygen gas or water vapor is also described. The use of copper for interconnects in integrated circuits requires improved diffusion barrier materials, given its high diffusivity compared to the previously-used aluminum and tungsten. Tungsten nitride has a low resistivity among barrier materials, and can be deposited in amorphous films that are effective diffusion barriers in layers as thin as a few nanometers. Here we demonstrate CVD and plasma-enhanced CVD methods to deposit tungsten nitride films from bis-(dialkylamido)bis-( tert-butylimido)tungsten precursors and ammonia gas. Recent findings had shown uniform copper growth on tantalum silicate films, without the dewetting that usually occurs on oxide surfaces. Tantalum and tungsten silicates were deposited by a CVD reaction from the reaction of either tris-(diethylamido)ethylimido tantalum or bis-(ethylmethylamido)-bis-( tert-butylimido)tungsten with tris-(tert-butoxy)silanol. The ability of evaporated

  19. Chemical Vapor Deposition Synthesized Atomically Thin Molybdenum Disulfide with Optoelectronic-Grade Crystalline Quality.

    PubMed

    Bilgin, Ismail; Liu, Fangze; Vargas, Anthony; Winchester, Andrew; Man, Michael K L; Upmanyu, Moneesh; Dani, Keshav M; Gupta, Gautam; Talapatra, Saikat; Mohite, Aditya D; Kar, Swastik

    2015-09-22

    The ability to synthesize high-quality samples over large areas and at low cost is one of the biggest challenges during the developmental stage of any novel material. While chemical vapor deposition (CVD) methods provide a promising low-cost route for CMOS compatible, large-scale growth of materials, it often falls short of the high-quality demands in nanoelectronics and optoelectronics. We present large-scale CVD synthesis of single- and few-layered MoS2 using direct vapor-phase sulfurization of MoO2, which enables us to obtain extremely high-quality single-crystal monolayer MoS2 samples with field-effect mobility exceeding 30 cm(2)/(V s) in monolayers. These samples can be readily synthesized on a variety of substrates, and demonstrate a high-degree of optoelectronic uniformity in Raman and photoluminescence mapping over entire crystals with areas exceeding hundreds of square micrometers. Because of their high crystalline quality, Raman spectroscopy on these samples reveal a range of multiphonon processes through peaks with equal or better clarity compared to past reports on mechanically exfoliated samples. This enables us to investigate the layer thickness and substrate dependence of the extremely weak phonon processes at 285 and 487 cm(-1) in 2D-MoS2. The ultrahigh, optoelectronic-grade crystalline quality of these samples could be further established through photocurrent spectroscopy, which clearly reveal excitonic states at room temperature, a feat that has been previously demonstrated only on samples which were fabricated by micro-mechanical exfoliation and then artificially suspended across trenches. Our method reflects a big step in the development of atomically thin, 2D-MoS2 for scalable, high-quality optoelectronics. PMID:26256639

  20. Chemical Vapor Deposition Synthesized Atomically Thin Molybdenum Disulfide with Optoelectronic-Grade Crystalline Quality.

    PubMed

    Bilgin, Ismail; Liu, Fangze; Vargas, Anthony; Winchester, Andrew; Man, Michael K L; Upmanyu, Moneesh; Dani, Keshav M; Gupta, Gautam; Talapatra, Saikat; Mohite, Aditya D; Kar, Swastik

    2015-09-22

    The ability to synthesize high-quality samples over large areas and at low cost is one of the biggest challenges during the developmental stage of any novel material. While chemical vapor deposition (CVD) methods provide a promising low-cost route for CMOS compatible, large-scale growth of materials, it often falls short of the high-quality demands in nanoelectronics and optoelectronics. We present large-scale CVD synthesis of single- and few-layered MoS2 using direct vapor-phase sulfurization of MoO2, which enables us to obtain extremely high-quality single-crystal monolayer MoS2 samples with field-effect mobility exceeding 30 cm(2)/(V s) in monolayers. These samples can be readily synthesized on a variety of substrates, and demonstrate a high-degree of optoelectronic uniformity in Raman and photoluminescence mapping over entire crystals with areas exceeding hundreds of square micrometers. Because of their high crystalline quality, Raman spectroscopy on these samples reveal a range of multiphonon processes through peaks with equal or better clarity compared to past reports on mechanically exfoliated samples. This enables us to investigate the layer thickness and substrate dependence of the extremely weak phonon processes at 285 and 487 cm(-1) in 2D-MoS2. The ultrahigh, optoelectronic-grade crystalline quality of these samples could be further established through photocurrent spectroscopy, which clearly reveal excitonic states at room temperature, a feat that has been previously demonstrated only on samples which were fabricated by micro-mechanical exfoliation and then artificially suspended across trenches. Our method reflects a big step in the development of atomically thin, 2D-MoS2 for scalable, high-quality optoelectronics.

  1. Physical Construction of the Chemical Atom: Is It Convenient to Go All the Way Back?

    ERIC Educational Resources Information Center

    Izquierdo-Aymerich, Merce; Aduriz-Bravo, Agustin

    2009-01-01

    In this paper we present an analysis of chemistry texts (mainly textbooks) published during the first half of the 20th century. We show the evolution of the explanations therein in terms of atoms and of atomic structure, when scientists were interpreting phenomena as evidence of the discontinuous, corpuscular structure of matter. In this process…

  2. Determination of bismuth in environmental samples by slurry sampling graphite furnace atomic absorption spectrometry using combined chemical modifiers.

    PubMed

    Dobrowolski, Ryszard; Dobrzyńska, Joanna; Gawrońska, Barbara

    2015-01-01

    Slurry sampling graphite furnace atomic absorption spectrometry technique was applied for the determination of Bi in environmental samples. The study focused on the effect of Zr, Ti, Nb and W carbides, as permanent modifiers, on the Bi signal. Because of its highest thermal and chemical stability and ability to substantially increase Bi signal, NbC was chosen as the most effective modifier. The temperature programme applied for Bi determination was optimized based on the pyrolysis and atomization curves obtained for slurries prepared from certified reference materials (CRMs) of the soil and sediments. To overcome interferences caused by sulfur compounds, Ba(NO₃)₂ was used as a chemical modifier. Calibration was performed using the aqueous standard solutions. The analysis of the CRMs confirmed the reliability of the proposed analytical method. The characteristic mass for Bi was determined to be 16 pg with the detection limit of 50 ng/g for the optimized procedure at the 5% (w/v) slurry concentration.

  3. Correlating STM Contrast and Atomic-Scale Structure by Chemical Modification: Vacancy Dislocation Loops on FeO/Pt(111)

    SciTech Connect

    Merte, L. R.; Knudsen, Jan; Grabow, Lars C.; Vang, Ronnie T.; Laegsgaard, E.; Mavrikakis, Manos; Besenbacher, Fleming

    2008-11-28

    By chemically modifying the FeO(111) thin film on Pt(111), we show that it is possible to unambiguously correlate its STM morphology with its underlying structure without recourse to STM simulations. Partial reduction of the oxide surface leads to the formation of triangularly-shaped oxygen vacancy dislocation loops at specific sites in the moiré structure of the film. Their presence allows unambiguous identification of the high-symmetry domains of the moiré structure, whose differing chemical properties govern the templating effect on adsorbed metal atoms, clusters and molecules.

  4. Atomic-scale Chemical Imaging and Quantification of Metallic Alloy Structures by Energy-Dispersive X-ray Spectroscopy

    PubMed Central

    Lu, Ping; Zhou, Lin; Kramer, M. J.; Smith, David J.

    2014-01-01

    Determination of atomic-scale crystal structure for nanostructured intermetallic alloys, such as magnetic alloys containing Al, Ni, Co (alnico) and Fe, is crucial for understanding physical properties such as magnetism, but technically challenging due to the small interatomic distances and the similar atomic numbers. By applying energy-dispersive X-ray spectroscopy (EDS) mapping to the study of two intermetallic phases of an alnico alloy resulting from spinodal decomposition, we have determined atomic-scale chemical composition at individual lattice sites for the two phases: one is the B2 phase with Fe0.76Co0.24 -Fe0.40Co0.60 ordering and the other is the L21 phase with Ni0.48Co0.52 at A-sites, Al at BΙ-sites and Fe0.20Ti0.80 at BΙΙ-sites, respectively. The technique developed through this study represents a powerful real-space approach to investigate structure chemically at the atomic scale for a wide range of materials systems. PMID:24492747

  5. Three-photon resonance ionization of atomic Mn in a hot-cavity laser ion source using Ti:sapphire lasers

    SciTech Connect

    Liu, Y.; Gottwald, T.; Mattolat, C.; Wendt, K.

    2015-05-08

    We have demonstrated three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti: sapphire lasers. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d54s5s f6S5/2 level at 49 415.35 cm-1, while Rydberg transitions were reached from the 3d54s4d e 6D9/2,7/2,5/2) levels at around 47 210 cm-1. Analyses of the strong Rydberg transitions associated with the 3d54s4d e 6D7/2 lower level indicate that they belong to the dipole-allowed 4d → nf69/2,7/2,5/2 series converging to the 3d54s 7S3 ground state of Mn II. From this series, an ionization potential of 59 959.56 ± 0.01 cm-1 is obtained for Mn. At high ion source temperatures the semi-forbidden 4d → nf8F°9/2,7/2,5/2 series was also observed. The overall ionization efficiency for Mn has been measured to be about 0.9% when using the strong AI transition in the third excitation step and 0.3% when employing an intense Rydberg transition. Experimental data indicate that the ionization efficiency was limited by the interaction of Mn atoms with ion source materials at high temperatures.

  6. Three-photon resonance ionization of atomic Mn in a hot-cavity laser ion source using Ti:sapphire lasers

    DOE PAGES

    Liu, Y.; Gottwald, T.; Mattolat, C.; Wendt, K.

    2015-05-08

    We have demonstrated three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti: sapphire lasers. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d54s5s f6S5/2 level at 49 415.35 cm-1, while Rydberg transitions were reached from the 3d54s4d e 6D9/2,7/2,5/2) levels at around 47 210 cm-1. Analyses of the strong Rydberg transitions associated with the 3d54s4d e 6D7/2 lower level indicate that they belong to the dipole-allowed 4d → nf6F°9/2,7/2,5/2 series converging to the 3d54s 7S3 groundmore » state of Mn II. From this series, an ionization potential of 59 959.56 ± 0.01 cm-1 is obtained for Mn. At high ion source temperatures the semi-forbidden 4d → nf8F°9/2,7/2,5/2 series was also observed. The overall ionization efficiency for Mn has been measured to be about 0.9% when using the strong AI transition in the third excitation step and 0.3% when employing an intense Rydberg transition. Experimental data indicate that the ionization efficiency was limited by the interaction of Mn atoms with ion source materials at high temperatures.« less

  7. Geochemistry, Comparative Analysis, and Physical and Chemical Characteristics of the Thermal Waters East of Hot Springs National Park, Arkansas, 2006-09

    USGS Publications Warehouse

    Kresse, Timothy M.; Hays, Phillip D.

    2009-01-01

    rock collapse for uncased wells completed in highly fractured rock. However, the propagation of newly formed large fractures that potentially could damage well structures or result in pirating of water from production wells appears to be of limited possibility based on review of relevant studies. Characteristics of hydraulic conductivity, storage, and fracture porosity were interpreted from flow rates observed in individual wells completed in the Bigfork Chert and Stanley Shale; from hydrographs produced from continuous measurements of water levels in wells completed in the Arkansas Novaculite, the Bigfork Chert, and Stanley Shale; and from a potentiometric-surface map constructed using water levels in wells throughout the study area. Data gathered from these three separate exercises showed that fracture porosity is much greater in the Bigfork Chert relative to that in the Stanley Shale, shallow groundwater flows from elevated recharge areas with exposures of Bigfork Chert along and into streams within the valleys formed on exposures of the Stanley Shale, and there was no evidence of interbasin transfer of groundwater within the shallow flow system. Fifteen shallow wells and two cold-water springs were sampled from the various exposed formations in the study area to characterize the water quality and geochemistry for the shallow groundwater system and for comparison to the geochemistry of the hot springs in Hot Springs National Park. For the quartz formations (novaculite, chert, and sandstone formations), total dissolved solids concentrations were very low with a median concentration of 23 milligrams per liter, whereas the median concentration for groundwater from the shale formations was 184 milligrams per liter. Ten hot springs in Hot Springs National Park were sampled for the study. Several chemical constituents for the hot springs, including pH, total dissolved solids, major cations and anions, and trace metals, show similarity with the shale formations

  8. Ultracold Chemical Reactions of a Single Rydberg Atom in a Dense Gas

    NASA Astrophysics Data System (ADS)

    Schlagmüller, Michael; Liebisch, Tara Cubel; Engel, Felix; Kleinbach, Kathrin S.; Böttcher, Fabian; Hermann, Udo; Westphal, Karl M.; Gaj, Anita; Löw, Robert; Hofferberth, Sebastian; Pfau, Tilman; Pérez-Ríos, Jesús; Greene, Chris H.

    2016-07-01

    Within a dense environment (ρ ≈1014 atoms /cm3 ) at ultracold temperatures (T <1 μ K ), a single atom excited to a Rydberg state acts as a reaction center for surrounding neutral atoms. At these temperatures, almost all neutral atoms within the Rydberg orbit are bound to the Rydberg core and interact with the Rydberg atom. We have studied the reaction rate and products for n S 87Rb Rydberg states, and we mainly observe a state change of the Rydberg electron to a high orbital angular momentum l , with the released energy being converted into kinetic energy of the Rydberg atom. Unexpectedly, the measurements show a threshold behavior at n ≈100 for the inelastic collision time leading to increased lifetimes of the Rydberg state independent of the densities investigated. Even at very high densities (ρ ≈4.8 ×1014 cm-3 ), the lifetime of a Rydberg atom exceeds 10 μ s at n >140 compared to 1 μ s at n =90 . In addition, a second observed reaction mechanism, namely, Rb2+ molecule formation, was studied. Both reaction products are equally probable for n =40 , but the fraction of Rb2+ created drops to below 10% for n ≥90 .

  9. Atom probe study of the carbon distribution in a hardened martensitic hot-work tool steel X38CrMoV5-1.

    PubMed

    Lerchbacher, Christoph; Zinner, Silvia; Leitner, Harald

    2012-07-01

    The microstructure of the hardened common hot-work tool steel X38CrMoV5-1 has been characterized by atom probe tomography with the focus on the carbon distribution. Samples quenched with technically relevant cooling parameters λ from 0.1 (30 K/s) to 12 (0.25 K/s) have been investigated. The parameter λ is an industrially commonly used exponential cooling parameter, representing the cooling time from 800 to 500 °C in seconds divided with hundred. In all samples pronounced carbon segregation to dislocations and cluster formation could be observed after quenching. Carbon enriched interlath films with peak carbon levels of 6-10 at.%, which have been identified to be retained austenite by TEM, show a thickness increase with increasing λ. Therefore, the fraction of total carbon staying in the austenite grows. This carbon is not available for the tempering induced precipitation of secondary carbides in the bulk. Through all samples no segregation of any substitutional elements takes place. Charpy impact testing and fracture surface analysis of the hardened samples reveal the cooling rate induced microstructural distinctions.

  10. Atomic layer chemical vapor deposition of ZrO2-based dielectric films: Nanostructure and nanochemistry

    NASA Astrophysics Data System (ADS)

    Dey, S. K.; Wang, C.-G.; Tang, D.; Kim, M. J.; Carpenter, R. W.; Werkhoven, C.; Shero, E.

    2003-04-01

    A 4 nm layer of ZrOx (targeted x˜2) was deposited on an interfacial layer (IL) of native oxide (SiO, t˜1.2 nm) surface on 200 mm Si wafers by a manufacturable atomic layer chemical vapor deposition technique at 300 °C. Some as-deposited layers were subjected to a postdeposition, rapid thermal annealing at 700 °C for 5 min in flowing oxygen at atmospheric pressure. The experimental x-ray diffraction, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and high-resolution parallel electron energy loss spectroscopy results showed that a multiphase and heterogeneous structure evolved, which we call the Zr-O/IL/Si stack. The as-deposited Zr-O layer was amorphous ZrO2-rich Zr silicate containing about 15% by volume of embedded ZrO2 nanocrystals, which transformed to a glass nanoceramic (with over 90% by volume of predominantly tetragonal-ZrO2 (t-ZrO2) and monoclinic-ZrO2 (m-ZrO2) nanocrystals) upon annealing. The formation of disordered amorphous regions within some of the nanocrystals, as well as crystalline regions with defects, probably gave rise to lattice strains and deformations. The interfacial layer (IL) was partitioned into an upper SiO2-rich Zr silicate and the lower SiOx. The latter was substoichiometric and the average oxidation state increased from Si0.86+ in SiO0.43 (as-deposited) to Si1.32+ in SiO0.66 (annealed). This high oxygen deficiency in SiOx was indicative of the low mobility of oxidizing specie in the Zr-O layer. The stacks were characterized for their dielectric properties in the Pt/{Zr-O/IL}/Si metal oxide-semiconductor capacitor (MOSCAP) configuration. The measured equivalent oxide thickness (EOT) was not consistent with the calculated EOT using a bilayer model of ZrO2 and SiO2, and the capacitance in accumulation (and therefore, EOT and kZr-O) was frequency dispersive, trends well documented in literature. This behavior is qualitatively explained in terms of the multilayer nanostructure and nanochemistry that

  11. Flow injection-chemical vapor generation atomic fluorescence spectrometry hyphenated system for organic mercury determination: A step forward

    NASA Astrophysics Data System (ADS)

    Angeli, Valeria; Biagi, Simona; Ghimenti, Silvia; Onor, Massimo; D'Ulivo, Alessandro; Bramanti, Emilia

    2011-11-01

    Monomethylmercury and ethylmercury were determined on line using flow injection-chemical vapor generation atomic fluorescence spectrometry without neither requiring a pre-treatment with chemical oxidants, nor UV/MW additional post column interface, nor organic solvents, nor complexing agents, such as cysteine. Inorganic mercury, monomethylmercury and ethylmercury were detected by atomic fluorescence spectrometry in an Ar/H 2 miniaturized flame after sodium borohydride reduction to Hg 0, monomethylmercury hydride and ethylmercury hydride, respectively. The effect of mercury complexing agent such as cysteine, ethylendiaminotetracetic acid and HCl with respect to water and Ar/H 2 microflame was investigated. The behavior of inorganic mercury, monomethylmercury and ethylmercury and their cysteine-complexes was also studied by continuous flow-chemical vapor generation atomic fluorescence spectrometry in order to characterize the reduction reaction with tetrahydroborate. When complexed with cysteine, inorganic mercury, monomethylmercury and ethylmercury cannot be separately quantified varying tetrahydroborate concentration due to a lack of selectivity, and their speciation requires a pre-separation stage (e.g. a chromatographic separation). If not complexed with cysteine, monomethylmercury and ethylmercury cannot be separated, as well, but their sum can be quantified separately with respect to inorganic mercury choosing a suitable concentration of tetrahydroborate (e.g. 10 - 5 mol L - 1 ), thus allowing the organic/inorganic mercury speciation. The detection limits of the flow injection-chemical vapor generation atomic fluorescence spectrometry method were about 45 nmol L - 1 (as mercury) for all the species considered, a relative standard deviation ranging between 1.8 and 2.9% and a linear dynamic range between 0.1 and 5 μmol L - 1 were obtained. Recoveries of monomethylmercury and ethylmercury with respect to inorganic mercury were never less than 91%. Flow injection-chemical

  12. New horizons in chemical propulsion. [processes using free radicals, atomic hydrogen, excited species, etc

    NASA Technical Reports Server (NTRS)

    Cohen, W.

    1973-01-01

    After a review of the work of the late-Fifties on free radicals for propulsion, it is concluded that atomic hydrogen would provide a potentially large increase in specific impulse. Work conducted to find an approach for isolating atomic hydrogen is considered. Other possibilities for obtaining propellants of greatly increased capability might be connected with the technology for the generation of activated states of gases, metallic hydrogen, fuels obtained from other planets, and laser transfer of energy.

  13. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    NASA Technical Reports Server (NTRS)

    Kahn, L. R.

    1982-01-01

    Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.

  14. The effect of different chemical agents on human enamel: an atomic force and scanning electron microscopy study

    NASA Astrophysics Data System (ADS)

    Rominu, Roxana O.; Rominu, Mihai; Negrutiu, Meda Lavinia; Sinescu, Cosmin; Pop, Daniela; Petrescu, Emanuela

    2010-12-01

    PURPOSE: The goal of our study was to investigate the changes in enamel surface roughess induced by the application of different chemical substances by atomic force microscopy and scanning electron microscopy. METHOD: Five sound human first upper premolar teeth were chosen for the study. The buccal surface of each tooth was treated with a different chemical agent as follows: Sample 1 - 38% phosphoric acid etching (30s) , sample 2 - no surface treatment (control sample), 3 - bleaching with 37.5 % hydrogen peroxide (according to the manufacturer's instructions), 4 - conditioning with a self-etching primer (15 s), 5 - 9.6 % hydrofluoric acid etching (30s). All samples were investigated by atomic force microscopy in a non-contact mode and by scanning electron microscopy. Several images were obtained for each sample, showing evident differences regarding enamel surface morphology. The mean surface roughness and the mean square roughness were calculated and compared. RESULTS: All chemical substances led to an increased surface roughness. Phosphoric acid led to the highest roughness while the control sample showed the lowest. Hydrofluoric acid also led to an increase in surface roughness but its effects have yet to be investigated due to its potential toxicity. CONCLUSIONS: By treating the human enamel with the above mentioned chemical compounds a negative microretentive surface is obtained, with a morphology depending on the applied substance.

  15. Similarity searching of chemical databases using atom environment descriptors (MOLPRINT 2D): evaluation of performance.

    PubMed

    Bender, Andreas; Mussa, Hamse Y; Glen, Robert C; Reiling, Stephan

    2004-01-01

    A molecular similarity searching technique based on atom environments, information-gain-based feature selection, and the naive Bayesian classifier has been applied to a series of diverse datasets and its performance compared to those of alternative searching methods. Atom environments are count vectors of heavy atoms present at a topological distance from each heavy atom of a molecular structure. In this application, using a recently published dataset of more than 100000 molecules from the MDL Drug Data Report database, the atom environment approach appears to outperform fusion of ranking scores as well as binary kernel discrimination, which are both used in combination with Unity fingerprints. Overall retrieval rates among the top 5% of the sorted library are nearly 10% better (more than 14% better in relative numbers) than those of the second best method, Unity fingerprints and binary kernel discrimination. In 10 out of 11 sets of active compounds the combination of atom environments and the naive Bayesian classifier appears to be the superior method, while in the remaining dataset, data fusion and binary kernel discrimination in combination with Unity fingerprints is the method of choice. Binary kernel discrimination in combination with Unity fingerprints generally comes second in performance overall. The difference in performance can largely be attributed to the different molecular descriptors used. Atom environments outperform Unity fingerprints by a large margin if the combination of these descriptors with the Tanimoto coefficient is compared. The naive Bayesian classifier in combination with information-gain-based feature selection and selection of a sensible number of features performs about as well as binary kernel discrimination in experiments where these classification methods are compared. When used on a monoaminooxidase dataset, atom environments and the naive Bayesian classifier perform as well as binary kernel discrimination in the case of a 50

  16. Catalyst-free growth of mono- and few-atomic-layer boron nitride sheets by chemical vapor deposition.

    PubMed

    Qin, Li; Yu, Jie; Li, Mingyu; Liu, Fei; Bai, Xuedong

    2011-05-27

    Boron nitride (BN) is a wide bandgap semiconductor with a structure analogous to graphite. Mono- and few-atomic-layer BN sheets have been grown on silicon substrates by microwave plasma chemical vapor deposition from a gas mixture of BF(3)-H(2)-N(2) without using any catalysts. Growth of the BN sheets can be ascribed to the etching effects of the fluorine-containing gases and the thickness control down to mono- and few-atomic-layers was realized by decreasing the concentrations of BF(3) and H(2) in N(2). A large decrease of the BF(3) and H(2) concentrations was achieved by increasing the gas flow rate of N(2) and keeping the BF(3) and H(2) flow rates constant and the mono- and few-atomic-layered BN sheets were obtained at the BF(3), H(2) and N(2) flow rates of 3, 10, and 1200 sccm. The present mono- and few-atomic-layer BN sheets are promising for applications in catalyst supports, composites, gas adsorption, nanoelectronics, etc. PMID:21451227

  17. On the physical and chemical details of alumina atomic layer deposition: A combined experimental and numerical approach

    SciTech Connect

    Pan, Dongqing; Ma, Lulu; Xie, Yuanyuan; Yuan, Chris; Jen, Tien Chien

    2015-03-15

    Alumina thin film is typically studied as a model atomic layer deposition (ALD) process due to its high dielectric constant, high thermal stability, and good adhesion on various wafer surfaces. Despite extensive applications of alumina ALD in microelectronics industries, details on the physical and chemical processes are not yet well understood. ALD experiments are not able to shed adequate light on the detailed information regarding the transient ALD process. Most of current numerical approaches lack detailed surface reaction mechanisms, and their results are not well correlated with experimental observations. In this paper, the authors present a combined experimental and numerical study on the details of flow and surface reactions in alumina ALD using trimethylaluminum and water as precursors. Results obtained from experiments and simulations are compared and correlated. By experiments, growth rate on five samples under different deposition conditions is characterized. The deposition rate from numerical simulation agrees well with the experimental results. Details of precursor distributions in a full cycle of ALD are studied numerically to bridge between experimental observations and simulations. The 3D transient numerical model adopts surface reaction kinetics and mechanisms based on atomic-level studies to investigate the surface deposition process. Surface deposition is shown as a strictly self-limited process in our numerical studies. ALD is a complex strong-coupled fluid, thermal and chemical process, which is not only heavily dependent on the chemical kinetics and surface conditions but also on the flow and material distributions.

  18. Evaluating and interpreting the chemical relevance of the linear response kernel for atoms II: open shell.

    PubMed

    Boisdenghien, Zino; Fias, Stijn; Van Alsenoy, Christian; De Proft, Frank; Geerlings, Paul

    2014-07-28

    Most of the work done on the linear response kernel χ(r,r') has focussed on its atom-atom condensed form χAB. Our previous work [Boisdenghien et al., J. Chem. Theory Comput., 2013, 9, 1007] was the first effort to truly focus on the non-condensed form of this function for closed (sub)shell atoms in a systematic fashion. In this work, we extend our method to the open shell case. To simplify the plotting of our results, we average our results to a symmetrical quantity χ(r,r'). This allows us to plot the linear response kernel for all elements up to and including argon and to investigate the periodicity throughout the first three rows in the periodic table and in the different representations of χ(r,r'). Within the context of Spin Polarized Conceptual Density Functional Theory, the first two-dimensional plots of spin polarized linear response functions are presented and commented on for some selected cases on the basis of the atomic ground state electronic configurations. Using the relation between the linear response kernel and the polarizability we compare the values of the polarizability tensor calculated using our method to high-level values. PMID:24837234

  19. Chemical Structure and Properties: A Modified Atoms-First, One-Semester Introductory Chemistry Course

    ERIC Educational Resources Information Center

    Schaller, Chris P.; Graham, Kate J.; Johnson, Brian J.; Jakubowski, Henry V.; McKenna, Anna G.; McIntee, Edward J.; Jones, T. Nicholas; Fazal, M. A.; Peterson, Alicia A.

    2015-01-01

    A one-semester, introductory chemistry course is described that develops a primarily qualitative understanding of structure-property relationships. Starting from an atoms-first approach, the course examines the properties and three-dimensional structure of metallic and ionic solids before expanding into a thorough investigation of molecules. In…

  20. An x ray scatter approach for non-destructive chemical analysis of low atomic numbered elements

    NASA Technical Reports Server (NTRS)

    Ross, H. Richard

    1993-01-01

    A non-destructive x-ray scatter (XRS) approach has been developed, along with a rapid atomic scatter algorithm for the detection and analysis of low atomic-numbered elements in solids, powders, and liquids. The present method of energy dispersive x-ray fluorescence spectroscopy (EDXRF) makes the analysis of light elements (i.e., less than sodium; less than 11) extremely difficult. Detection and measurement become progressively worse as atomic numbers become smaller, due to a competing process called 'Auger Emission', which reduces fluorescent intensity, coupled with the high mass absorption coefficients exhibited by low energy x-rays, the detection and determination of low atomic-numbered elements by x-ray spectrometry is limited. However, an indirect approach based on the intensity ratio of Compton and Rayleigh scattered has been used to define light element components in alloys, plastics and other materials. This XRS technique provides qualitative and quantitative information about the overall constituents of a variety of samples.

  1. Atomic and Molecular Structure in Chemical Education: A Critical Analysis from Various Perspectives of Science Education.

    ERIC Educational Resources Information Center

    Tsaparlis, Georgios

    1997-01-01

    Provides a critical analysis of the role that atomic theory plays in the science curriculum from elementary through secondary school. Examines structural concepts from the perspective of the theory of meaningful learning, information processing theory, and the alternative conceptions movement. Contains 54 references. (DDR)

  2. Cobalt as chemical modifier to improve chromium sensitivity and minimize matrix effects in tungsten coil atomic emission spectrometry.

    PubMed

    Silva, Sidnei G; Donati, George L; Santos, Luana N; Jones, Bradley T; Nóbrega, Joaquim A

    2013-05-30

    Cobalt is used as chemical modifier to improve sensitivity and minimize matrix effects in Cr determinations by tungsten coil atomic emission spectrometry (WCAES). The atomizer is a tungsten filament extracted from microscope light bulbs. A solid-state power supply and a handheld CCD-based spectrometer are also used in the instrumental setup. In the presence of 1000 mg L(-1) Co, WCAES limit of detection for Cr (λ=425.4 nm) is calculated as 0.070 mg L(-1); a 10-fold improvement compared to determinations without Co modifier. The mechanism involved in such signal enhancement is similar to the one observed in ICP OES and ICP-MS determinations of As and Se in the presence of C. Cobalt increases the population of Cr(+) by charge transfer reactions. In a second step, Cr(+)/e(-) recombination takes place, which results in a larger population of excited-state Cr atoms. This alternative excitation route is energetically more efficient than heat transfer from atomizer and gas phase to analyte atoms. A linear dynamic range of 0.25-10 mg L(-1) and repeatability of 3.8% (RSD, n=10) for a 2.0 mg L(-1) Cr solution are obtained with this strategy. The modifier high concentration also contributes to improving accuracy due to a matrix-matching effect. The method was applied to a certified reference material of Dogfish Muscle (DORM-2) and no statistically significant difference was observed between determined and certified Cr values at a 95% confidence level. Spike experiments with bottled water samples resulted in recoveries between 93% and 112%.

  3. Large-area high-throughput synthesis of monolayer graphene sheet by Hot Filament Thermal Chemical Vapor Deposition

    PubMed Central

    Hawaldar, Ranjit; Merino, P.; Correia, M. R.; Bdikin, Igor; Grácio, José; Méndez, J.; Martín-Gago, J. A.; Singh, Manoj Kumar

    2012-01-01

    We report hot filament thermal CVD (HFTCVD) as a new hybrid of hot filament and thermal CVD and demonstrate its feasibility by producing high quality large area strictly monolayer graphene films on Cu substrates. Gradient in gas composition and flow rate that arises due to smart placement of the substrate inside the Ta filament wound alumina tube accompanied by radical formation on Ta due to precracking coupled with substrate mediated physicochemical processes like diffusion, polymerization etc., led to graphene growth. We further confirmed our mechanistic hypothesis by depositing graphene on Ni and SiO2/Si substrates. HFTCVD can be further extended to dope graphene with various heteroatoms (H, N, and B, etc.,), combine with functional materials (diamond, carbon nanotubes etc.,) and can be extended to all other materials (Si, SiO2, SiC etc.,) and processes (initiator polymerization, TFT processing) possible by HFCVD and thermal CVD. PMID:23002423

  4. Hot-electron-mediated surface chemistry: toward electronic control of catalytic activity.

    PubMed

    Park, Jeong Young; Kim, Sun Mi; Lee, Hyosun; Nedrygailov, Ievgen I

    2015-08-18

    Energy dissipation at surfaces and interfaces is mediated by excitation of elementary processes, including phonons and electronic excitation, once external energy is deposited to the surface during exothermic chemical processes. Nonadiabatic electronic excitation in exothermic catalytic reactions results in the flow of energetic electrons with an energy of 1-3 eV when chemical energy is converted to electron flow on a short (femtosecond) time scale before atomic vibration adiabatically dissipates the energy (in picoseconds). These energetic electrons that are not in thermal equilibrium with the metal atoms are called "hot electrons". The detection of hot electron flow under atomic or molecular processes and understanding its role in chemical reactions have been major topics in surface chemistry. Recent studies have demonstrated electronic excitation produced during atomic or molecular processes on surfaces, and the influence of hot electrons on atomic and molecular processes. We outline research efforts aimed at identification of the intrinsic relation between the flow of hot electrons and catalytic reactions. We show various strategies for detection and use of hot electrons generated by the energy dissipation processes in surface chemical reactions and photon absorption. A Schottky barrier localized at the metal-oxide interface of either catalytic nanodiodes or hybrid nanocatalysts allows hot electrons to irreversibly transport through the interface. We show that the chemicurrent, composed of hot electrons excited by the surface reaction of CO oxidation or hydrogen oxidation, correlates well with the turnover rate measured separately by gas chromatography. Furthermore, we show that hot electron flows generated on a gold thin film by photon absorption (or internal photoemission) can be amplified by localized surface plasmon resonance. The influence of hot charge carriers on the chemistry at the metal-oxide interface are discussed for the cases of Au, Ag, and Pt

  5. Hot-electron-mediated surface chemistry: toward electronic control of catalytic activity.

    PubMed

    Park, Jeong Young; Kim, Sun Mi; Lee, Hyosun; Nedrygailov, Ievgen I

    2015-08-18

    Energy dissipation at surfaces and interfaces is mediated by excitation of elementary processes, including phonons and electronic excitation, once external energy is deposited to the surface during exothermic chemical processes. Nonadiabatic electronic excitation in exothermic catalytic reactions results in the flow of energetic electrons with an energy of 1-3 eV when chemical energy is converted to electron flow on a short (femtosecond) time scale before atomic vibration adiabatically dissipates the energy (in picoseconds). These energetic electrons that are not in thermal equilibrium with the metal atoms are called "hot electrons". The detection of hot electron flow under atomic or molecular processes and understanding its role in chemical reactions have been major topics in surface chemistry. Recent studies have demonstrated electronic excitation produced during atomic or molecular processes on surfaces, and the influence of hot electrons on atomic and molecular processes. We outline research efforts aimed at identification of the intrinsic relation between the flow of hot electrons and catalytic reactions. We show various strategies for detection and use of hot electrons generated by the energy dissipation processes in surface chemical reactions and photon absorption. A Schottky barrier localized at the metal-oxide interface of either catalytic nanodiodes or hybrid nanocatalysts allows hot electrons to irreversibly transport through the interface. We show that the chemicurrent, composed of hot electrons excited by the surface reaction of CO oxidation or hydrogen oxidation, correlates well with the turnover rate measured separately by gas chromatography. Furthermore, we show that hot electron flows generated on a gold thin film by photon absorption (or internal photoemission) can be amplified by localized surface plasmon resonance. The influence of hot charge carriers on the chemistry at the metal-oxide interface are discussed for the cases of Au, Ag, and Pt

  6. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    NASA Technical Reports Server (NTRS)

    Kahn, L. R.

    1981-01-01

    The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.

  7. Chemical reaction of atomic oxygen with evaporated films of copper, part 4

    NASA Technical Reports Server (NTRS)

    Fromhold, A. T.; Williams, J. R.

    1990-01-01

    Evaporated copper films were exposed to an atomic oxygen flux of 1.4 x 10(exp 17) atoms/sq cm per sec at temperatures in the range 285 to 375 F (140 to 191 C) for time intervals between 2 and 50 minutes. Rutherford backscattering spectroscopy (RBS) was used to determine the thickness of the oxide layers formed and the ratio of the number of copper to oxygen atoms in the layers. Oxide film thicknesses ranged from 50 to 3000 A (0.005 to 0.3 microns, or equivalently, 5 x 10(exp -9) to 3 x 10(exp -7); it was determined that the primary oxide phase was Cu2O. The growth law was found to be parabolic (L(t) varies as t(exp 1/2)), in which the oxide thickness L(t) increases as the square root of the exposure time t. The analysis of the data is consistent with either of the two parabolic growth laws. (The thin-film parabolic growth law is based on the assumption that the process is diffusion controlled, with the space charge within the growing oxide layer being negligible. The thick-film parabolic growth law is also based on a diffusion controlled process, but space-charge neutrality prevails locally within very thick oxides.) In the absence of a voltage measurement across the growing oxide, a distinction between the two mechanisms cannot be made, nor can growth by the diffusion of neutral atomic oxygen be entirely ruled out. The activation energy for the reaction is on the order of 1.1 eV (1.76 x 10(exp -19) joule, or equivalently, 25.3 kcal/mole).

  8. Atomic Data for Zn II: Improving Spectral Diagnostics of Chemical Evolution in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Kisielius, Romas; Kulkarni, Varsha P.; Ferland, Gary J.; Bogdanovich, Pavel; Som, Debopam; Lykins, Matt L.

    2015-05-01

    Damped Lyα (DLA) and sub-DLA absorbers in quasar spectra provide the most sensitive tools for measuring the element abundances of distant galaxies. The estimation of abundances from absorption lines depends sensitively on the accuracy of the atomic data used. We have started a project to produce new atomic spectroscopic parameters for optical and UV spectral lines using state-of-the-art computer codes employing a very broad configuration interaction (CI) basis. Here we report our results for Zn ii, an ion used widely in studies of the interstellar medium (ISM) as well as DLAs and sub-DLAs. We report new calculations of many energy levels of Zn ii and the line strengths of the resulting radiative transitions. Our calculations use the CI approach within a numerical Hartree-Fock framework. We use both nonrelativistic and quasi-relativistic one-electron radial orbitals. We have incorporated the results of these atomic calculations into the plasma simulation code Cloudy and applied them to a lab plasma and examples of a DLA and a sub-DLA. Our values of the Zn ii λ λ 2026, 2062 oscillator strengths are higher than previous values by 0.10 dex. The Cloudy calculations for representative absorbers with the revised Zn atomic data imply ionization corrections lower than calculated earlier by 0.05 dex. The new results imply that Zn metallicities should be lower by 0.1 dex for DLAs and by 0.13-0.15 dex for sub-DLAs than in past studies. Our results can be applied to other studies of Zn ii in the Galactic and extragalactic ISM.

  9. Influence of ultrasonic pretreatment on the yield of bio-oil prepared by thermo-chemical conversion of rice husk in hot-compressed water.

    PubMed

    Shi, Wen; Jia, Jingfu; Gao, Yahui; Zhao, Yaping

    2013-10-01

    The aim of the current study is to investigate the feasibility of thermo-chemical conversion of rice husk in hot-compressed water via ultrasonic pretreatment to increase the bio-oil yield. The results show that ultrasonic pretreatment remarkably changes the structures of the rice husk, such as enhancing swelling and surface area, eroding lignin structure, and resulting in more exposure of the cellulose and hemicellulose. The highest bio-oil yield of 42.8% was obtained from the thermo-chemical conversion at 300 °C and 0 min of the residence time for the 1 h pretreated rice husk. GC-MS analysis indicates that the relative contents of phenols, 5-Hydroxymethylfurfural, and lactic acid are higher in bio-oils obtained from the pretreated rice husks than that from the raw rice husk. PMID:23948273

  10. Most probable distance between the nucleus and HOMO electron: the latent meaning of atomic radius from the product of chemical hardness and polarizability.

    PubMed

    Szarek, Paweł; Grochala, Wojciech

    2014-11-01

    The simple relationship between size of an atom, the Pearson hardness, and electronic polarizability is described. The estimated atomic radius correlates well with experimental as well as theoretical covalent radii reported in the literature. Furthermore, the direct connection of atomic radius to HOMO electron density and important notions of conceptual DFT (such as frontier molecular orbitals and Fukui function) has been shown and interpreted. The radial maximum of HOMO density distribution at (αη)(1/2) minimizes the system energy. Eventually, the knowledge of the Fukui function of an atom is sufficient to estimate its electronic polarizability, chemical potential, and hardness.

  11. Descriptions and Implementations of DL_F Notation: A Natural Chemical Expression System of Atom Types for Molecular Simulations.

    PubMed

    Yong, Chin W

    2016-08-22

    DL_F Notation is an easy-to-understand, standardized atom typesetting expression for molecular simulations for a range of organic force field (FF) schemes such as OPLSAA, PCFF, and CVFF. It is implemented within DL_FIELD, a software program that facilitates the setting up of molecular FF models for DL_POLY molecular dynamics simulation software. By making use of the Notation, a single core conversion module (the DL_F conversion Engine) implemented within DL_FIELD can be used to analyze a molecular structure and determine the types of atoms for a given FF scheme. Users only need to provide the molecular input structure in a simple xyz format and DL_FIELD can produce the necessary force field file for DL_POLY automatically. In commensurate with the development concept of DL_FIELD, which placed emphasis on robustness and user friendliness, the Engine provides a single-step solution to setup complex FF models. This allows users to switch from one of the above-mentioned FF seamlessly to another while at the same time provides a consistent atom typing that is expressed in a natural chemical sense. PMID:27455451

  12. The atomic structure and chemical composition of HfOx (x < 2) films prepared by ion-beam sputtering deposition

    NASA Astrophysics Data System (ADS)

    Aliev, V. S.; Gerasimova, A. K.; Kruchinin, V. N.; Gritsenko, V. A.; Prosvirin, I. P.; Badmaeva, I. A.

    2016-08-01

    Non-stoichiometric HfOx films of different chemical composition (x < 2) were fabricated by ion-beam sputtering deposition (IBSD) at room temperature. The ratio of O and Hf atoms in films x was varied by setting the O2 partial pressure in a chamber. An effect of chemical composition on the atomic structure of the films was studied by reflection high-energy electron diffraction, x-ray photoelectron spectroscopy and field emission scanning electron microscopy methods. The films were found to be amorphous, consisting only of three components: Hf-metal clusters, Hf4O7 suboxide and stoichiometric HfO2. The relative concentration of these components varies with changing x. The surface of the films contains the increased oxygen content compared to the bulk. It was found that the Hf4O7 suboxide concentration is maximal at x = 1.8. The concept of hafnium oxide film growth by the IBSD method is proposed to explain the lack of suboxides variety in the films and the instability of HfO2, when annealed at high temperature.

  13. Atomic-Scale Chemical Imaging of Composition and Bonding at Perovskite Oxide Interfaces

    NASA Astrophysics Data System (ADS)

    Fitting Kourkoutis, L.

    2010-03-01

    Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) has proven to be a powerful technique to study buried perovskite oxide heterointerfaces. With the recent addition of 3^rd order and now 5^th order aberration correction, which provides a factor of 100x increase in signal over an uncorrected system, we are now able to record 2D maps of composition and bonding of oxide interfaces at atomic resolution [1]. Here, we present studies of the microscopic structure of oxide/oxide multilayers and heterostructures by STEM in combination with EELS and its effect on the properties of the film. Using atomic-resolution spectroscopic imaging we show that the degradation of the magnetic and transport properties of La0.7Sr0.3MnO3/SrTiO3 multilayers correlates with atomic intermixing at the interfaces and the presence of extended defects in the La0.7Sr0.3MnO3 layers. When these defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in 5 unit cell thick manganite layers, almost 40% thinner than the previously reported critical thickness of 3-5 nm for sustaining metallic ferromagnetism below Tc in La0.7Sr0.3MnO3 thin films grown on SrTiO3.[4pt] [1] D.A. Muller, L. Fitting Kourkoutis, M. Murfitt, J.H. Song, H.Y. Hwang, J. Silcox, N. Dellby, O.L. Krivanek, Science 319, 1073-1076 (2008).

  14. Physical and chemical nature of the scaling relations between adsorption energies of atoms on metal surfaces.

    PubMed

    Calle-Vallejo, F; Martínez, J I; García-Lastra, J M; Rossmeisl, J; Koper, M T M

    2012-03-16

    Despite their importance in physics and chemistry, the origin and extent of the scaling relations between the energetics of adsorbed species on surfaces remain elusive. We demonstrate here that scalability is not exclusive to adsorbed atoms and their hydrogenated species but rather a general phenomenon between any set of adsorbates bound similarly to the surface. On the example of the near-surface alloys of Pt, we show that scalability is a result of identical variations of adsorption energies with respect to the valence configuration of both the surface components and the adsorbates. PMID:22540492

  15. The Formation of Glycine in Hot Cores: New Gas-grain Chemical Simulations of Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Garrod, Robin

    2012-07-01

    Organic molecules of increasing complexity have been detected in the warm envelopes of star-forming cores, commonly referred to as "hot cores". Spectroscopic searches at mm/sub-mm wavelengths have uncovered both amines and carboxylic acids in these regions, as well as a range of other compounds including alcohols, ethers, esters, and nitriles. However, the simplest amino acid, glycine (NH2CH2COOH), has not yet been reliably detected in the ISM. There has been much interest in this molecule, due to its importance to the formation of proteins, and to life, while the positive identification of interstellar molecules of similar or greater complexity suggests that its existence in star-forming regions is plausible. I will present the results of recent models of hot-core chemistry that simulate the formation of both simple and complex molecules on the surfaces or within the ice mantles of dust grains. I will also present results from the first gas-grain astrochemical model to approach the question of amino-acid formation in hot cores. The formation of glycine in moderate abundance is found to be as efficient as that for similarly complex species, while its sublimation from the grains occurs at somewhat higher temperatures. However, simulated emission spectra based on the model results show that the degree of compactness of high-abundance regions, and the density and temperature profiles of the cores may be the key variables affecting the future detection of glycine, as well as other amino acids, and may explain its non-detection to date.

  16. Method for quantitative determination and separation of trace amounts of chemical elements in the presence of large quantities of other elements having the same atomic mass

    DOEpatents

    Miller, C.M.; Nogar, N.S.

    1982-09-02

    Photoionization via autoionizing atomic levels combined with conventional mass spectroscopy provides a technique for quantitative analysis of trace quantities of chemical elements in the presence of much larger amounts of other elements with substantially the same atomic mass. Ytterbium samples smaller than 10 ng have been detected using an ArF* excimer laser which provides the atomic ions for a time-of-flight mass spectrometer. Elemental selectivity of greater than 5:1 with respect to lutetium impurity has been obtained. Autoionization via a single photon process permits greater photon utilization efficiency because of its greater absorption cross section than bound-free transitions, while maintaining sufficient spectroscopic structure to allow significant photoionization selectivity between different atomic species. Separation of atomic species from others of substantially the same atomic mass is also described.

  17. Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s.

    PubMed

    Kurnosov, Arkady A; Rubtsov, Igor V; Maksymov, Andrii O; Burin, Alexander L

    2016-07-21

    We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so that they can participate only in the transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to the atomic mass. For the same reason, the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Theory predictions are consistent with the time-dependent density functional theory calculations. Molecular systems for experimental evaluation of the predictions are proposed. PMID:27448902

  18. Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s.

    PubMed

    Kurnosov, Arkady A; Rubtsov, Igor V; Maksymov, Andrii O; Burin, Alexander L

    2016-07-21

    We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so that they can participate only in the transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to the atomic mass. For the same reason, the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Theory predictions are consistent with the time-dependent density functional theory calculations. Molecular systems for experimental evaluation of the predictions are proposed.

  19. Electronic torsional sound in linear atomic chains: Chemical energy transport at 1000 km/s

    NASA Astrophysics Data System (ADS)

    Kurnosov, Arkady A.; Rubtsov, Igor V.; Maksymov, Andrii O.; Burin, Alexander L.

    2016-07-01

    We investigate entirely electronic torsional vibrational modes in linear cumulene chains. The carbon nuclei of a cumulene are positioned along the primary axis so that they can participate only in the transverse and longitudinal motions. However, the interatomic electronic clouds behave as a torsion spring with remarkable torsional stiffness. The collective dynamics of these clouds can be described in terms of electronic vibrational quanta, which we name torsitons. It is shown that the group velocity of the wavepacket of torsitons is much higher than the typical speed of sound, because of the small mass of participating electrons compared to the atomic mass. For the same reason, the maximum energy of the torsitons in cumulenes is as high as a few electronvolts, while the minimum possible energy is evaluated as a few hundred wavenumbers and this minimum is associated with asymmetry of zero point atomic vibrations. Theory predictions are consistent with the time-dependent density functional theory calculations. Molecular systems for experimental evaluation of the predictions are proposed.

  20. Simulation of hydration/dehydration of CaO/Ca(OH){sub 2} chemical heat pump reactor for cold/hot heat generation

    SciTech Connect

    Ogura, Hironao; Shimojyo, Rui; Kage, Hiroyuki; Matsuno, Yoshizo; Mujumdar, A.S.

    1999-09-01

    A chemical heat pump (CHP) utilizes reversible reactions involving significant endothermic and exothermic heats of reaction in order to develop a heat pump effect by storing and releasing energy while transforming it from chemical to thermal energy and vice versa. In this paper, the authors present a mathematical model and its numerical solution for the heat and mass transport phenomena occurring in the reactant particle bed of the CHP for heat storage and cold/hot heat generation based on the CaO/Ca(OH){sub 2} reversible hydration/dehydration reaction. Transient conservation equations of mass and energy transport including chemical kinetics are solved numerically subject to appropriate boundary and initial conditions to examine the influence of the mass transfer resistance on the overall performance of this CHP configuration. These results are presented and discussed with the aim of enhancing the CHP performance in the next generation reactor designs. The CHP can store thermal energy in industrial waste heat, solar heat, terrestrial heat, etc. in the form of chemical energy, and release it at various temperature levels during the heat-demand period.

  1. [Erytrocyte membrane change due to the chemical treatment studied with atomic force microscopy].

    PubMed

    Targosz-Korecka, Marta; Sułowicz, Władysław; Czuba, Paweł; Szymoński, Marek; Miklaszewska, Monika; Pietrzyk, Jacek A; Rumian, Roman; Krawentek, Lidia

    2009-01-01

    The influence of some selected pharmacological compounds on the structure of human erythrocytes (red blood cells, RBCs) has been studied by means of an atomic force microscopy (AFM). The imaging has been done both in the air environment on the fixed cells, and in the liquid (physiological conditions). It was shown that RBCs are very sensitive to osmotic changes in the solution. Increased NaCl concentration in the solution to a value higher than 0.9% leads to the characteristic changes of the erythrocyte from a discoid-like shape to a very irregular one, the so-called "echinocyte", with a lot of ledges. After exposition on nifedipin the modification of the erythrocyte surface morphology was observed. Based on the contact and non-contact AFMs study the consecutive stages of RBCs surface modification were observed. Scanning electron microscopy pictures of erythrocytes were presented for comparison. PMID:20514900

  2. Three-dimensional chemical imaging of embedded nanoparticles using atom probe tomography.

    PubMed

    Kuchibhatla, Satyanarayana V N T; Shutthanandan, V; Prosa, T J; Adusumilli, P; Arey, B; Buxbaum, A; Wang, Y C; Tessner, T; Ulfig, R; Wang, C M; Thevuthasan, S

    2012-06-01

    Analysis of nanoparticles is often challenging especially when they are embedded in a matrix. Hence, we have used laser-assisted atom probe tomography (APT) to analyze the Au nanoclusters synthesized in situ using ion-beam implantation in a single crystal MgO matrix. APT analysis along with scanning transmission electron microscopy and energy dispersive spectroscopy (STEM-EDX) indicated that the nanoparticles have an average size ~8-12 nm. While it is difficult to analyze the composition of individual nanoparticles using STEM, APT analysis can give three-dimensional compositions of the same. It was shown that the maximum Au concentration in the nanoparticles increases with increasing particle size, with a maximum Au concentration of up to 50%.

  3. Chemical reactivity of hydrogen, nitrogen, and oxygen atoms at temperatures below 100 k

    NASA Technical Reports Server (NTRS)

    Mcgee, H. A., Jr.

    1973-01-01

    The synthesis of unusual compounds by techniques employing cryogenic cooling to retard their very extreme reactivity was investigated. Examples of such species that were studied are diimide (N2H2), cyclobutadiene (C4H4), cyclopropanone (C3H4O), oxirene (C2H2O), and many others. Special purpose cryogenically cooled inlet arrangements were designed such that the analyses incurred no warm-up of the cold, and frequently explosively unstable, compounds. Controlled energy electron impact techniques were used to measure critical potentials and to develop the molecular energetics and thermodynamics of these molecules and to gain some insight into their kinetic characteristics as well. Three and four carbon strained ring molecules were studied. Several reactions of oxygen and hydrogen atoms with simple molecules of H, N, C, and O in hard quench configurations were studied. And the quench stabilization of BH3 was explored as a model system in cryochemistry.

  4. Three-dimensional Chemical Imaging of Embedded Nanoparticles using Atom Probe Tomography

    SciTech Connect

    Kuchibhatla, Satyanarayana V N T; Shutthanandan, V.; Prosa, Ty J.; Adusumilli, Praneet; Arey, Bruce W.; Buxbaum, Alex; Wang, Y. C.; Tessner, Ted; Ulfig, Robert M.; Wang, Chong M.; Thevuthasan, Suntharampillai

    2012-05-03

    Analysis of nanoparticles is often challenging especially when they are embedded in a matrix. Hence, we have used laser-assisted atom probe tomography (APT) to analyze the Au-nanoclusters synthesized in situ using ion beam implantation in single crystal MgO matrix. APT analysis along with scanning transmission electron microscopy and energy dispersive spectroscopy (STEM-EDS) indicated that the nanoparticles have an average size ~ 8 - 12 nm. While it is difficult to analyze the composition of individual nanoparticles using STEM, APT analysis can give three dimensional compositions of the same. It was shown that the maximum Au-concentration in the nanoparticles increases with increasing particle size, with a maximum Au-concentration of up to 50%.

  5. Two-Dimensional Atomic-Layered Alloy Junctions for High-Performance Wearable Chemical Sensor.

    PubMed

    Cho, Byungjin; Kim, Ah Ra; Kim, Dong Jae; Chung, Hee-Suk; Choi, Sun Young; Kwon, Jung-Dae; Park, Sang Won; Kim, Yonghun; Lee, Byoung Hun; Lee, Kyu Hwan; Kim, Dong-Ho; Nam, Jaewook; Hahm, Myung Gwan

    2016-08-01

    We first report that two-dimensional (2D) metal (NbSe2)-semiconductor (WSe2)-based flexible, wearable, and launderable gas sensors can be prepared through simple one-step chemical vapor deposition of prepatterned WO3 and Nb2O5. Compared to a control device with a Au/WSe2 junction, gas-sensing performance of the 2D NbSe2/WSe2 device was significantly enhanced, which might have resulted from the formation of a NbxW1-xSe2 transition alloy junction lowering the Schottky barrier height. This would make it easier to collect charges of channels induced by molecule adsorption, improving gas response characteristics toward chemical species including NO2 and NH3. 2D NbSe2/WSe2 devices on a flexible substrate provide gas-sensing properties with excellent durability under harsh bending. Furthermore, the device stitched on a T-shirt still performed well even after conventional cleaning with a laundry machine, enabling wearable and launderable chemical sensors. These results could pave a road toward futuristic gas-sensing platforms based on only 2D materials.

  6. Two-Dimensional Atomic-Layered Alloy Junctions for High-Performance Wearable Chemical Sensor.

    PubMed

    Cho, Byungjin; Kim, Ah Ra; Kim, Dong Jae; Chung, Hee-Suk; Choi, Sun Young; Kwon, Jung-Dae; Park, Sang Won; Kim, Yonghun; Lee, Byoung Hun; Lee, Kyu Hwan; Kim, Dong-Ho; Nam, Jaewook; Hahm, Myung Gwan

    2016-08-01

    We first report that two-dimensional (2D) metal (NbSe2)-semiconductor (WSe2)-based flexible, wearable, and launderable gas sensors can be prepared through simple one-step chemical vapor deposition of prepatterned WO3 and Nb2O5. Compared to a control device with a Au/WSe2 junction, gas-sensing performance of the 2D NbSe2/WSe2 device was significantly enhanced, which might have resulted from the formation of a NbxW1-xSe2 transition alloy junction lowering the Schottky barrier height. This would make it easier to collect charges of channels induced by molecule adsorption, improving gas response characteristics toward chemical species including NO2 and NH3. 2D NbSe2/WSe2 devices on a flexible substrate provide gas-sensing properties with excellent durability under harsh bending. Furthermore, the device stitched on a T-shirt still performed well even after conventional cleaning with a laundry machine, enabling wearable and launderable chemical sensors. These results could pave a road toward futuristic gas-sensing platforms based on only 2D materials. PMID:27388231

  7. Liquid hot water pretreatment of energy grasses and its influence of physico-chemical changes on enzymatic digestibility.

    PubMed

    Yu, Qiang; Liu, Jing; Zhuang, Xinshu; Yuan, Zhenhong; Wang, Wen; Qi, Wei; Wang, Qiong; Tan, Xuesong; Kong, Xiaoying

    2016-01-01

    Pennisetum hybrid I, II and switchgrass were pretreated with liquid hot water to enhance the release of sugars. The optimum hydrolysis factor for three energy grasses was 5.98, and the total xylose yield was 88.4%, 98.1% and 83.6% for grass I, II and S. It was indicated that the ratio of syringyl and guaiacyl units of lignin played an important role on the hemicellulose hydrolysis in LHW than branch degree, but latter contributed more on the characterization of xylooligomers degree of polymerization. Moreover, the analysis of multi-scale changes of substrate suggested that cellulose crystallinity index and degree of polymerization seemed no direct relationships for increase of enzymatic digestibility. While lignin barrier was the main factor limiting efficiency of sugar release, and Pennisetum hybrid with low lignin content and high sugar recovery was proved to be a prospective plant feedstock for cellulosic ethanol production. PMID:26233251

  8. Quantum Chemical Evaluation of the Astrochemical Significance of Reactions between S Atom and Acetylene or Ethylene

    NASA Technical Reports Server (NTRS)

    Woon, David E.

    2007-01-01

    Addition-elimination reactions of S atom in its P-3 ground state with acetylene (C2H2) and ethylene (C2H4) were characterized with both molecular orbital and density functional theory calculations employing correlation consistent basis sets in order to assess the likelihood either reaction might play a general role in astrochemistry or a specific role in the formation of S2 (X (sup 3 SIGMA (sub g) (sup -)) via a mechanism proposed by Saxena and Misra (Mon. Not. R. Astron. Soc. 1995, 272, 89). The acetylene and ethylene reactions proceed through C2H2S ((sup 3)A")) and C2H4S ((sup 3)A")) intermediates, respectively, to yield HCCS ((sup 2)II)) and C2H3S ((sup 2)A')). Substantial barriers were found in the exit channels for every combination of method and basis set considered in this work, which effectively precludes hydrogen elimination pathways for both S + C2H2 and S + C2H4 in the ultracold interstellar medium where only very modest barriers can be surmounted and processes without barriers tend to predominate. However, if one or both intermediates is formed and stabilized efficiently under cometary or dense interstellar cloud conditions, they could serve as temporary reservoirs for S atom and participate in reactions such as S + C2H2S (right arrow) S2 = C2H2 or S + C2H4S (right arrow) S2 + C2H4. For formation and stabilization to be efficient, the reaction must possess a barrier height small enough to be surmountable at low temperatures yet large enough to prevent redissociation to reactants. Barrier heights computed with B3LYP and large basis sets are very low, but more rigorous QCISD(T) and RCCSD(T) results indicate that the barrier heights are closer to 3-4 kcal/mol. The calculations therefore indicate that S + C2H2 or S + C2H4 could contribute to the formation of S2 in comets and may serve as a means to gauge coma temperature. The energetics of the ethylene reaction are more favorable.

  9. Combined Chemical and Topographic Imaging at Atmospheric Pressure via Microprobe Laser Desorption/Ionization Mass Spectrometry-Atomic Force Microscopy

    SciTech Connect

    Bradshaw, James A; Ovchinnikova, Olga S; Meyer, Kent A; Goeringer, Doug

    2009-01-01

    The operational characteristics and imaging performance are described for a new instrument comprising an atomic force microscope (AFM) coupled with a pulsed laser and a linear ion trap mass spectrometer. The AFM operating mode is used to produce topographic surface images having nanometer-scale spatial and height resolution. Spatially resolved mass spectra of ions, produced from the same surface via microprobe-mode laser desorption/ionization at atmospheric pressure, are then used to create a 100 x 100 m chemical image. The effective spatial resolution of the image (~2 m) was constrained by the limit of detection (estimated to be 109 1010 ions) rather than by the diameter of the focused laser spot or the step size of the AFM sample stage. Thus, it is expected that improvements in imaging performance can be realized by implementation of post-ionization methods.

  10. Inner-shell electron spectroscopy and chemical properties of atoms and small molecules

    SciTech Connect

    T. Darrah Thomas

    2009-01-21

    The program has been concerned with gas-phase carbon 1s photoelectron spectroscopy of a number of molecules of potential chemical interest. The primary goals have been to determine carbon 1s ionization energies with a view of relating these to other chemical properties such as electronegativity, acidity, basicity, and reactivity, in order to provide a better understanding of these fundamental properties. The role of electron-donating (methyl) and electron-withdrawing (fluoro) substituents on the carbon 1s ionization energies of substituted benzenes has been studied., and these results have been related to measurements of the reactivities of the same molecule as well as to their affinities for protons (basicity). Opportunities for investigation in unplanned areas have arisen, and the program has been modified to take advantage of these. One has been the realization that, under certain circumstances, inner-shell ionization energies may depend on the molecular conformation. Several examples of this phenomenon have been investigated and it has been shown that this technique provides a tool for the measurement of the energy differences between different conformers of the same substance. The other has been the demonstration that photoelectron recoil can lead to the excitation of vibrational modes that are forbidden in the normal view of photoemission and to rotational heating of the molecule that increases with the energy of the exciting radiation.

  11. Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition.

    PubMed

    Liu, Zheng; Amani, Matin; Najmaei, Sina; Xu, Quan; Zou, Xiaolong; Zhou, Wu; Yu, Ting; Qiu, Caiyu; Birdwell, A Glen; Crowne, Frank J; Vajtai, Robert; Yakobson, Boris I; Xia, Zhenhai; Dubey, Madan; Ajayan, Pulickel M; Lou, Jun

    2014-11-18

    Monolayer molybdenum disulfide (MoS2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS2. Recently, large-size monolayer MoS2 has been produced by chemical vapour deposition, but has not yet been fully explored. Here we systematically characterize chemical vapour deposition-grown MoS2 by photoluminescence spectroscopy and mapping and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced bandgap engineering. We also evaluate the effective strain transferred from polymer substrates to MoS2 by three-dimensional finite element analysis. Furthermore, our work demonstrates that photoluminescence mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS2.

  12. Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

    DOE PAGES

    Liu, Zheng; Amani, Matin; Najmaei, Sina; Xu, Quan; Zou, Xiaolong; Zhou, Wu; Yu, Ting; Qiu, Caiyu; Birdwell, A. Glen; Crowne, Frank J.; et al

    2014-11-18

    Monolayer molybdenum disulfide (MoS2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices, and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS2. Recently, large-size monolayer MoS2 has been produced by chemical vapor deposition but has not yet been fully explored. Here we systematically characterize chemical vapor deposition grown MoS2 by PL spectroscopy and mapping, and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced band gap engineering. We also evaluate the effective strain transferred from polymermore » substrates to MoS2 by three-dimensional finite element analysis. In addition, our work demonstrates that PL mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS2.« less

  13. Magnetic isotope effect and theory of atomic orbital hybridization to predict a mechanism of chemical exchange reactions.

    PubMed

    Epov, Vladimir N

    2011-08-01

    A novel approach is suggested to investigate the mechanisms of chemical complexation reactions based on the results of Fujii with co-workers; they have experimentally observed that several metals and metalloids demonstrate mass-independent isotope fractionation during the reactions with the DC18C6 crown ether using solvent-solvent extraction. In this manuscript, the isotope fractionation caused by the magnetic isotope effect is used to understand the mechanisms of chemical exchange reactions. Due to the rule that reactions are allowed for certain electron spin states, and forbidden for others, magnetic isotopes show chemical anomalies during these reactions. Mass-independent fractionation is suggested to take place due to the hyperfine interaction of the nuclear spin with the electron spin of the intermediate product. Moreover, the sign of the mass-independent fractionation is found to be dependent on the element and its species, which is also explained by the magnetic isotope effect. For example, highly negative mass-independent isotope fractionation of magnetic isotopes was observed for reactions of DC18C6 with SnCl(2) species and with several Ru(III) chloro-species, and highly positive for reactions of this ether with TeCl(6)(2-), and with several Cd(II) and Pd(II) species. The atomic radius of an element is also a critical parameter for the reaction with crown ether, particularly the element ions with [Kr]4d(n)5s(m) electron shell fits the best with the DC18C6 crown ring. It is demonstrated that the magnetic isotope effect in combination with the theory of orbital hybridization can help to understand the mechanism of complexation reactions. The suggested approach is also applied to explain previously published mass-independent fractionation of Hg isotopes in other types of chemical exchange reactions.

  14. Spectacular enhancement of thermoelectric phenomena in chemically synthesized graphene nanoribbons with substitution atoms.

    PubMed

    Zberecki, K; Swirkowicz, R; Wierzbicki, M; Barnaś, J

    2016-07-21

    We analyze theoretically the transport and thermoelectric properties of graphene nanoribbons of a specific geometry, which have been synthesized recently from polymers [Cai, et al., Nature, 2011, 466, 470]. When such nanoribbons are modified at one of the two edges by Al or N substitutions, they acquire a ferromagnetic moment localized at the modified edge. We present numerical results on the electronic structure and thermoelectric properties (including also spin thermoelectricity) of the modified nanoribbons. The results show that such nanoribbons can display large thermoelectric efficiency in certain regions of chemical potential, where the corresponding electric and spin figures of merit achieve unusually large values. The enhancement of thermoelectric efficiency follows from a reduced phonon heat conductance of the nanoribbons and from their peculiar electronic band structure. Thus, such nanoribbons are promising for practical applications in nanoelectronic and spintronic devices. PMID:27331357

  15. Spectacular enhancement of thermoelectric phenomena in chemically synthesized graphene nanoribbons with substitution atoms.

    PubMed

    Zberecki, K; Swirkowicz, R; Wierzbicki, M; Barnaś, J

    2016-07-21

    We analyze theoretically the transport and thermoelectric properties of graphene nanoribbons of a specific geometry, which have been synthesized recently from polymers [Cai, et al., Nature, 2011, 466, 470]. When such nanoribbons are modified at one of the two edges by Al or N substitutions, they acquire a ferromagnetic moment localized at the modified edge. We present numerical results on the electronic structure and thermoelectric properties (including also spin thermoelectricity) of the modified nanoribbons. The results show that such nanoribbons can display large thermoelectric efficiency in certain regions of chemical potential, where the corresponding electric and spin figures of merit achieve unusually large values. The enhancement of thermoelectric efficiency follows from a reduced phonon heat conductance of the nanoribbons and from their peculiar electronic band structure. Thus, such nanoribbons are promising for practical applications in nanoelectronic and spintronic devices.

  16. The role of radial nodes of atomic orbitals for chemical bonding and the periodic table.

    PubMed

    Kaupp, Martin

    2007-01-15

    The role of radial nodes, or of their absence, in valence orbitals for chemical bonding and periodic trends is discussed from a unified viewpoint. In particular, we emphasize the special role of the absence of a radial node whenever a shell with angular quantum number l is occupied for the first time (lack of "primogenic repulsion"), as with the 1s, 2p, 3d, and 4f shells. Although the consequences of the very compact 2p shell (e.g. good isovalent hybridization, multiple bonding, high electronegativity, lone-pair repulsion, octet rule) are relatively well known, it seems that some of the aspects of the very compact 3d shell in transition-metal chemistry are less well appreciated, e.g., the often weakened and stretched bonds at equilibrium structure, the frequently colored complexes, and the importance of nondynamical electron-correlation effects in bonding.

  17. Fluorescence Concentric Triangles: A Case of Chemical Heterogeneity in WS2 Atomic Monolayer.

    PubMed

    Liu, Hongwei; Lu, Junpeng; Ho, Kenneth; Hu, Zhenliang; Dang, Zhiya; Carvalho, Alexandra; Tan, Hui Ru; Tok, Eng Soon; Sow, Chorng Haur

    2016-09-14

    We report a novel optical property in WS2 monolayer. The monolayer naturally exhibits beautiful in-plane periodical and lateral homojunctions by way of alternate dark and bright band in the fluorescence images of these monolayers. The interface between different fluorescence species within the sample is distinct and sharp. This gives rise to intriguing concentric triangular fluorescence patterns in the monolayer. The novel optical property of this special WS2 monolayer is facilitated by chemical heterogeneity. The photoluminescence of the bright band is dominated by emissions from trion and biexciton while the emission from defect-bound exciton dominates the photoluminescence at the dark band. The discovery of such concentric fluorescence patterns represents a potentially new form of optoelectronic or photonic functionality. PMID:27479127

  18. Use of radiation effects for a controlled change in the chemical composition and properties of materials by intentional addition or substitution of atoms of a certain kind

    SciTech Connect

    Gurovich, B. A.; Prikhod'ko, K. E. Kuleshova, E. A.; Maslakov, K. I.; Komarov, D. A.

    2013-06-15

    This study is a continuation of works [1-12] dealing with the field developed by the authors, namely, to widen the possibilities of radiation methods for a controlled change in the atomic composition and properties of thin-film materials. The effects under study serve as the basis for the following two methods: selective atom binding and selective atom substitution. Such changes in the atomic composition are induced by irradiation by mixed beams consisting of protons and other ions, the energy of which is sufficient for target atom displacements. The obtained experimental data demonstrate that the changes in the chemical composition of thin-film materials during irradiation by an ion beam of a complex composition take place according to mechanisms that differ radically from the well-known mechanisms controlling the corresponding chemical reactions in these materials. These radical changes are shown to be mainly caused by the accelerated ioninduced atomic displacements in an irradiated material during irradiation; that is, they have a purely radiation nature. The possibilities of the new methods for creating composite structures consisting of regions with a locally changed chemical composition and properties are demonstrated for a wide class of materials.

  19. The Local Atomic Structure and Chemical Bonding in Sodium Tin Phases

    DOE PAGES

    Baggetto, Loic; Bridges, Craig A.; Jumas, Dr. Jean-Claude; Mullins, David R.; Carroll, Kyler J.; Meisner, Roberta; Crumlin, Ethan; Liu, Xiason; Yang, Wanli; Veith, Gabriel M.

    2014-09-25

    To understand these electrochemically-derived materials we have reinvestigated the formation of Na-Sn alloys to identify all the phases which form when x ≥ 1 (NaxSn) and characterized the local bonding around the Sn atoms with X-ray diffraction, 119Sn M ssbauer spectroscopy, and X-ray absorption spectroscopies. The results from the well-defined crystallographic materials were compared to the spectroscopic measurements of the local Sn structures in the electrochemically prepared materials. The reinvestigation of the Na-Sn compounds yields a number of new results: (i) Na7Sn3 is a new thermodynamically-stable phase with a rhombohedral structure and R-3m space group; (ii) orthorhombic Na9Sn4 (Cmcm) hasmore » relatively slow formation kinetics suggesting why it does not form at room temperature during the electrochemical reaction; (iii) orthorhombic Na14.78Sn4 (Pnma), better described as Na16-xSn4, is Na-richer than cubic Na15Sn4 (I-43d). Characterization of electrochemically prepared Na-Sn alloys indicate that, at the exception of Na7Sn3 and Na15Sn4, different crystal structures than similar Na-Sn compositions prepared via classic solid state reactions are formed. These phases are composed of disordered structures characteristic of kinetic-driven solid-state amorphization reactions. In these structures, Sn coordinates in asymmetric environments, which differ significantly from the environments present in Na-Sn model compounds.« less

  20. The Local Atomic Structure and Chemical Bonding in Sodium Tin Phases

    SciTech Connect

    Baggetto, Loic; Bridges, Craig A.; Jumas, Dr. Jean-Claude; Mullins, David R.; Carroll, Kyler J.; Meisner, Roberta; Crumlin, Ethan; Liu, Xiason; Yang, Wanli; Veith, Gabriel M.

    2014-09-25

    To understand these electrochemically-derived materials we have reinvestigated the formation of Na-Sn alloys to identify all the phases which form when x ≥ 1 (NaxSn) and characterized the local bonding around the Sn atoms with X-ray diffraction, 119Sn M ssbauer spectroscopy, and X-ray absorption spectroscopies. The results from the well-defined crystallographic materials were compared to the spectroscopic measurements of the local Sn structures in the electrochemically prepared materials. The reinvestigation of the Na-Sn compounds yields a number of new results: (i) Na7Sn3 is a new thermodynamically-stable phase with a rhombohedral structure and R-3m space group; (ii) orthorhombic Na9Sn4 (Cmcm) has relatively slow formation kinetics suggesting why it does not form at room temperature during the electrochemical reaction; (iii) orthorhombic Na14.78Sn4 (Pnma), better described as Na16-xSn4, is Na-richer than cubic Na15Sn4 (I-43d). Characterization of electrochemically prepared Na-Sn alloys indicate that, at the exception of Na7Sn3 and Na15Sn4, different crystal structures than similar Na-Sn compositions prepared via classic solid state reactions are formed. These phases are composed of disordered structures characteristic of kinetic-driven solid-state amorphization reactions. In these structures, Sn coordinates in asymmetric environments, which differ significantly from the environments present in Na-Sn model compounds.

  1. O(3P) atoms as a chemical probe of surface ordering in ionic liquids.

    PubMed

    Waring, Carla; Bagot, Paul A J; Slattery, John M; Costen, Matthew L; McKendrick, Kenneth G

    2010-04-15

    The reactivity of photolytically generated, gas-phase, ground-state atomic oxygen, O((3)P), with the surfaces of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([NTf(2)]) ionic liquids has been investigated. The liquids differ only in the length of the linear C(n)H(2n+1) alkyl side chain on the cation, with n = 2, 4, 5, 8, and 12. Laser-induced fluorescence was used to detect gas-phase OH v' = 0 radicals formed at the gas-liquid interface. The reactivity of the ionic liquids increases nonlinearly with n, in a way that cannot simply be explained by stoichiometry. We infer that the alkyl chains must be preferentially exposed at the interface to a degree that is dependent on chain length. A relatively sharp onset of surface segregation is apparent in the region of n = 4. The surface specificity of the method is confirmed through the nonthermal characteristics of both the translational and rotational distributions of the OH v' = 0. These reveal that the dynamics are dominated by a direct, impulsive scattering mechanism at the outer layers of the liquid. The OH v' = 0 yield is effectively independent of the bulk temperature of the longest-chain ionic liquid in the range 298-343 K, also consistent with a predominantly direct mechanism. These product attributes are broadly similar to those of the benchmark pure hydrocarbon liquid, squalane, but a more detailed analysis suggests that the interface may be microscopically smoother for the ionic liquids.

  2. Elucidation of the dynamics for hot-spot initiation at nonuniform interfaces of highly shocked materials

    NASA Astrophysics Data System (ADS)

    An, Qi; Zybin, Sergey V.; Goddard, William A., III; Jaramillo-Botero, Andres; Blanco, Mario; Luo, Sheng-Nian

    2011-12-01

    The fundamental processes in shock-induced instabilities of materials remain obscure, particularly for detonation of energetic materials. We simulated these processes at the atomic scale on a realistic model of a polymer-bonded explosive (3,695,375 atoms/cell) and observed that a hot spot forms at the nonuniform interface, arising from shear relaxation that results in shear along the interface that leads to a large temperature increase that persists long after the shock front has passed the interface. For energetic materials this temperature increase is coupled to chemical reactions that lead to detonation. We show that decreasing the density of the binder eliminates the hot spot.

  3. Novel chemical route for atomic layer deposition of MoS₂ thin film on SiO₂/Si substrate.

    PubMed

    Jin, Zhenyu; Shin, Seokhee; Kwon, Do Hyun; Han, Seung-Joo; Min, Yo-Sep

    2014-11-01

    Recently MoS₂ with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS₂ due to a lack of suitable chemistry. Here we report MoS₂ growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS₂ can be directly grown on a SiO₂/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E(1)₂g and A₁g) of 2H-MoS₂ with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS₂ layers to be aligned with its basal plane parallel to the substrate.

  4. Structural and chemical characterization of novel NixZn1-xGa2O4 nanocatalysts at atomic resolution

    NASA Astrophysics Data System (ADS)

    Xu, Qian; Wu, Zhaochun; Hong, Jinhua; Chang, Xiaofeng; Li, Xueji; Yan, Shicheng; Wang, Peng

    2015-10-01

    NixZn1-xGa2O4 has already been demonstrated as a noteworthy example of potentially useful catalytic properties such as NOx reduction. In our previous work, it was interesting to find out that the operating temperature of NiGa2O4 catalyst in NOx reduction can be tuned by simple chemical substitution of Ni2+ by Zn2+. It is believed that the mechanism behind such stoichiometry-dependence on operating temperature should be strongly correlated with microstructure, surface morphology as well as the local composition of the nanocatalysts. In the present investigation, NixZn1-xGa2O4 solid solution was synthesized via a hydrothermal ion-exchange reaction, using NaGaO2 and the corresponding acetic salts as the starting materials. By means of a state-of-the-art aberration corrected STEM and high resolution TEM, the structural and chemical characterization at the atomic scale on the NixZn1-xGa2O4 nanocatalyst was carried out, including the crystal structure, size, morphology, surface structure and local composition. It is found that the catalyst was solid solution and most possible exposed facets may be (1 1 1).

  5. Chemical analyses of hot springs, pools, geysers, and surface waters from Yellowstone National Park, Wyoming, and vicinity, 1974-1975

    USGS Publications Warehouse

    Ball, James W.; Nordstrom, D. Kirk; Jenne, Everett A.; Vivit, Davison V.

    1998-01-01

    This report presents all analytical determinations for samples collected from Yellowstone National Park and vicinity during 1974 and 1975. Water temperature, pH, Eh, and dissolved O2 were determined on-site. Total alkalinity and F were determined on the day of sample collection. Flame atomic-absorption spectrometry was used to determine concentrations of Li, Na, K, Ca, and Mg. Ultraviolet/visible spectrophotometry was used to determine concentrations of Fe(II), Fe(III), As(III), and As(V). Direct-current plasma-optical-emission spectrometry was used to determine the concentrations of B, Ba, Cd, Cs, Cu, Mn, Ni, Pb, Rb, Sr, and Zn. Two samples collected from Yellowstone Park in June 1974 were used as reference samples for testing the plasma analytical method. Results of these tests demonstrate acceptable precision for all detectable elements. Charge imbalance calculations revealed a small number of samples that may have been subject to measurement errors in pH or alkalinity. These data represent some of the most complete analyses of Yellowstone waters available.

  6. Topographical and Chemical Imaging of a Phase Separated Polymer Using a Combined Atomic Force Microscopy/Infrared Spectroscopy/Mass Spectrometry Platform

    DOE PAGES

    Tai, Tamin; Karácsony, Orsolya; Bocharova, Vera; Van Berkel, Gary J.; Kertesz, Vilmos

    2016-02-18

    This article describes how the use of a hybrid atomic force microscopy/infrared spectroscopy/mass spectrometry imaging platform was demonstrated for the acquisition and correlation of nanoscale sample surface topography and chemical images based on infrared spectroscopy and mass spectrometry.

  7. An integrated chemical and stable-isotope model of the origin of Midocean Ridge Hot Spring Systems

    NASA Astrophysics Data System (ADS)

    Bowers, Teresa Suter; Taylor, Hugh P., Jr.

    1985-12-01

    Chemical and isotopic changes accompanying seawater-basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs, incorporating provision for addition and subtraction of a wide-range of reactant and product minerals, as well as cation and oxygen and hydrogen isotopic exchange equilibria. The models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100° to 350°C, with an overall water-rock ratio of about 0.5 being constrained by an assumed δ18OH2O at 350°C of +2.0 per mil (H. Craig, personal communication, 1984). This is a realistic model because: (1) the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust; (2) the water-rock ratio is high (>50) at low temperatures and low (<0.5) at high temperatures; and (3) it allows for back-reaction of earlier-formed minerals during the course of reaction progress. The results closely match the major-element chemistry (Von Damm et al., 1985) and isotopic compositions (Craig et al., 1980) of the hydrothermal solutions presently emanating from vents at 21°N on the East Pacific Rise. The calculated solution chemistry, for example, correctly predicts complete loss of Mg and SO4 and substantial increases in Si and Fe; however, discrepancies exist in the predicted pH (5.5 versus 3.5 measured) and state of saturation of the solution with respect to greenschist-facies minerals. The calculated δDH2O is +2.6 per mil, in excellent agreement with analytical determinations. The calculated chemical, mineralogic, and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges (Humphris and Thompson, 1978; Stakes and O'Neil, 1982), as well as with data from ophiolites (Gregory and Taylor, 1981). Predicted alteration products include anhydrite and clay minerals at low temperatures and a typical

  8. Numerical study of He/CF{sub 3}I pulsed discharge used to produce iodine atom in chemical oxygen-iodine laser

    SciTech Connect

    Zhang Jiao; Wang Yanhui; Wang Dezhen; Duo Liping; Li Guofu

    2013-04-15

    The pulsed discharge for producing iodine atoms from the alkyl and perfluoroalky iodides (CH{sub 3}I, CF{sub 3}I, etc.) is the most efficient method for achieving the pulse operating mode of a chemical oxygen-iodine laser. In this paper, a one-dimensional fluid model is developed to study the characteristics of pulsed discharge in CF{sub 3}I-He mixture. By solving continuity equation, momentum equation, Poisson equation, Boltzmann equation, and an electric circuit equation, the temporal evolution of discharge current density and various discharge products, especially the atomic iodine, are investigated. The dependence of iodine atom density on discharge parameters is also studied. The results show that iodine atom density increases with the pulsed width and pulsed voltage amplitude. The mixture ratio of CF{sub 3}I and helium plays a more significant role in iodine atom production. For a constant voltage amplitude, there exists an optimal mixture ratio under which the maximum iodine atom concentration is achieved. The bigger the applied voltage amplitude is, the higher partial pressure of CF{sub 3}I is needed to obtain the maximum iodine atom concentration.

  9. Indium-Based Interface Chemical Engineering by Electrochemistry and Atomic Layer Deposition for Copper Indium Diselenide Solar Cells

    NASA Astrophysics Data System (ADS)

    Guillemoles, Jean-François; Canava, Bruno; Yousfi, El Bekkaye; Cowache, Pierre; Galtayries, Anouk; Asikainen, Timo; Powalla, Michael; Hariskos, Dimitri; Schock, Hans-Werner; Lincot, Daniel

    2001-10-01

    The key to achieve better Cu(In, Ga)Se2 (CIGS) cells is through the improvement of the CIGS/ZnO interface. In this work, we illustrate various approaches, wet and dry, to engineer that interface with processes that avoid the use of Cd containing compounds. Wet chemical treatments have been performed so as to test the possibility to improve that interface by surface doping of CIGS@. X-ray photoelectron spectroscopy (XPS) and Kelvin probe studies show that such doping is not achieved in the conditions leading to best devices. Rather, the most desirable feature of the surface treatments appears to be surface passivation. We show that this can be achieved via CIGS surface reaction with In(III) ions, leading to 12.5% efficient devices. A well passivated interface can also be achieved directly, using an all dry process, by Atomic Layer Deposition (ALD) of In2S3 buffer layer, yielding to 13.5% efficient devices. The ALD growth of the buffer layers have been studied in situ with the help of a quartz crystal microgravimetry.

  10. Insights From Atomic-Resolution X-Ray Structures Of Chemically-Synthesized Hiv-1 Protease In Complex With Inhibitors

    PubMed Central

    Johnson, Erik C.B.; Malito, Enrico; Shen, Yuequan; Pentelute, Brad; Rich, Dan; Florián, Jan; Tang, Wei-Jen; Kent, Stephen B.H.

    2007-01-01

    Summary The HIV-1 protease is an aspartyl protease essential for HIV-1 viral infectivity. HIV-1 protease has one catalytic site formed by the homodimeric enzyme. We have chemically synthesized fully active HIV-1 protease using modern ligation methods. When complexed with the classic substrate-derived inhibitors JG-365 and MVT-101, the synthetic HIV-1 protease formed crystals that diffracted to 1.04 and 1.2Å resolution, respectively. These atomic resolution structures revealed additional structural details of the HIV-1 protease interactions with its active site ligands. Heptapeptide inhibitor JG-365, which has a hydroxyethylamine moiety in place of the scissile bond, binds in two equivalent antiparallel orientations within the catalytic groove, whereas the reduced isostere hexapeptide MVT-101 binds in a single orientation. When JG-365 was converted into the natural peptide substrate for molecular dynamic simulations, we found putative catalytically competent reactant states for both lytic water and direct nucleophilic attack mechanisms. Moreover, free energy perturbation calculations indicated that the insertion of catalytic water into the catalytic site is an energetically favorable process. PMID:17869270

  11. Insights from atomic-resolution X-ray structures of chemically synthesized HIV-1 protease in complex with inhibitors.

    PubMed

    Johnson, Erik C B; Malito, Enrico; Shen, Yuequan; Pentelute, Brad; Rich, Dan; Florián, Jan; Tang, Wei-Jen; Kent, Stephen B H

    2007-10-26

    The human immunodeficiency virus 1 (HIV-1) protease (PR) is an aspartyl protease essential for HIV-1 viral infectivity. HIV-1 PR has one catalytic site formed by the homodimeric enzyme. We chemically synthesized fully active HIV-1 PR using modern ligation methods. When complexed with the classic substrate-derived inhibitors JG-365 and MVT-101, the synthetic HIV-1 PR formed crystals that diffracted to 1.04- and 1.2-A resolution, respectively. These atomic-resolution structures revealed additional structural details of the HIV-1 PR's interactions with its active site ligands. Heptapeptide inhibitor JG-365, which has a hydroxyethylamine moiety in place of the scissile bond, binds in two equivalent antiparallel orientations within the catalytic groove, whereas the reduced isostere hexapeptide MVT-101 binds in a single orientation. When JG-365 was converted into the natural peptide substrate for molecular dynamic simulations, we found putative catalytically competent reactant states for both lytic water and direct nucleophilic attack mechanisms. Moreover, free energy perturbation calculations indicated that the insertion of catalytic water into the catalytic site is an energetically favorable process.

  12. Measurement of a Large Chemical Reaction Rate between Ultracold Closed-Shell {sup 40}Ca Atoms and Open-Shell {sup 174}Yb{sup +} Ions Held in a Hybrid Atom-Ion Trap

    SciTech Connect

    Rellergert, Wade G.; Sullivan, Scott T.; Chen Kuang; Schowalter, Steven J.; Hudson, Eric R.; Kotochigova, Svetlana; Petrov, Alexander

    2011-12-09

    Ultracold {sup 174}Yb{sup +} ions and {sup 40}Ca atoms are confined in a hybrid trap. The charge exchange chemical reaction rate constant between these two species is measured and found to be 4 orders of magnitude larger than recent measurements in other heteronuclear systems. The structure of the CaYb{sup +} molecule is determined and used in a calculation that explains the fast chemical reaction as a consequence of strong radiative charge transfer. A possible explanation is offered for the apparent contradiction between typical theoretical predictions and measurements of the radiative association process in this and other recent experiments.

  13. Development of hot-pressed and chemical-vapor-deposited zinc sulfide and zinc selenide in the United States for optical windows

    NASA Astrophysics Data System (ADS)

    Harris, Daniel C.

    2007-04-01

    By the mid 1950s, there was a need for infrared-transmitting materials with improved optical and mechanical characteristics for military and commercial instruments. The newly invented "heat-seeking" missile also required a more durable infrared-transmitting dome. Some properties of ZnS were known from studies of natural minerals. More properties of pure ZnS and ZnSe were measured with single crystals grown in Air Force and industrial laboratories in the 1950s. In 1956, a team led by William Parsons at the Eastman Kodak Hawk-Eye Works in Rochester, New York began to apply the technique of hot pressing to make infrared-transmitting ceramics from powders. This work led to commercial production of six materials, including ZnS (IRTRAN® 2) and ZnSe (IRTRAN® 4) in the 1960s. Because the hot pressed materials could not be made in very large sizes and suffered from undesirable optical losses, the Air Force began to look for alternative manufacturing methods around 1970. Almost immediately, highly successful materials were produced by chemical vapor deposition under Air Force sponsorship by a team led by James Pappis at the Raytheon Research Division in Waltham, Massachusetts. Chemical-vapor-deposited materials replaced hot pressed materials in most applications within a few years. From a stream of Air Force contracts in the 1970s and early 1980s, Raytheon produced two different grades of ZnS for windows and domes, one grade of ZnSe for high-energy CO II laser windows, and a composite ZnS/ZnSe window for aircraft sensor pods. In 1980, a competitor called CVD, Inc., was formed by Robert Donadio, who came from the Raytheon Research Division. CVD began with a license from Raytheon, but soon sued Raytheon, arguing that the license violated the Sherman Antitrust Act. Raytheon countersued for breach of employment contracts and misappropriation of trade secrets. In 1984, a jury ruled in favor of CVD, which went on to build a lucrative business in ZnSe and ZnS. CVD was eventually

  14. Investigation of thermal and hot-wire chemical vapor deposition copper thin films on TiN substrates using CupraSelect as precursor.

    PubMed

    Papadimitropoulos, G; Davazoglou, D

    2011-09-01

    Copper films were deposited on oxidized Si substrates covered with TiN using a novel chemical vapor deposition reactor in which reactions were assisted by a heated tungsten filament (hot-wire CVD, HWCVD). Liquid at room temperature hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (CupraSelect) was directly injected into the reactor with the aid of a direct-liquid injection (DLI) system using N2 as carrier gas. The deposition rates of HWCVD Cu films obtained on TiN covered substrates were found to increase with filament temperature (65 and 170 degrees C were tested). The resistivities of HWCVD Cu films were found to be higher than for thermally grown films due to the possible presence of impurities into the Cu films from the incomplete dissociation of the precursor and W impurities caused by the presence of the filament. For HWCVD films grown at a filament temperature of 170 degrees C, smaller grains are formed than at 65 degrees C as shown from the taken SEM micrographs. XRD diffractograms taken on Cu films deposited on TiN could not reveal the presence of W compounds originating from the filament because the relative peak was masked by the TiN [112] peak. PMID:22097549

  15. Nanocrystalline Si/SiO{sub 2} core-shell network with intense white light emission fabricated by hot-wire chemical vapor deposition

    SciTech Connect

    Matsumoto, Y. Dutt, A.; Santana-Rodríguez, G.; Santoyo-Salazar, J.; Aceves-Mijares, M.

    2015-04-27

    We report the fabrication of a stable Si/SiO{sub 2} core-shell network using hot-wire chemical vapor deposition on a silicon substrate at a relatively low substrate temperature of 200 °C. Structural investigations using transmission electron microscopy and X-ray diffraction confirm the presence of nanocrystalline silicon and silicon dioxide quantum dots in the form of a core-shell network embedded in the amorphous SiO{sub x} matrix, while selected area electron diffraction confirms the formation of a core-shell structure. The core-shell structure exhibits a bright white emission that can be seen with the unaided eye at room temperature without any post-annealing treatments, and the observed photoemission does not alter in color or intensity after prolonged laser exposure. Additional measurements are performed while varying the laser power and optical gain is found in the as-deposited material. Intense stable white luminescence is observed and shows the prospective for various optical and biological applications in the future.

  16. The influence of charge effect on the growth of hydrogenated amorphous silicon by the hot-wire chemical vapor deposition technique

    SciTech Connect

    Wang, Q.; Nelson, B.P.; Iwaniczko, E.; Mahan, A.H.; Crandall, R.S.; Benner, J.

    1998-09-01

    The authors observe at lower substrate temperatures that the scatter in the dark conductivity on hydrogenated amorphous silicon (a-Si:H) films grown on insulating substrates (e.g., Corning 7059 glass) by the hot-wire chemical vapor deposition technique (HWCVD) can be five orders of magnitude or more. This is especially true at deposition temperatures below 350 C. However, when the authors grow the same materials on substrates with a conductive grid, virtually all of their films have acceptable dark conductivity (< 5 {times} 10{sup {minus}10} S/cm) at all deposition temperatures below 425 C. This is in contrast to only about 20% of the materials grown in this same temperature range on insulating substrates having an acceptable dark conductivity. The authors estimated an average energy of 5 eV electrons reaching the growing surface in vacuum, and did additional experiments to see the influence of both the electron flux and the energy of the electrons on the film growth. Although these effects do not seem to be important for growing a-Si:H by HWCVD on conductive substrates, they help better understand the important parameters for a-Si:H growth, and thus, to optimize these parameters in other applications of HWCVD technology.

  17. Physical and chemical parameter correlations with technical and technological characteristics of heating systems and the presence of Legionella spp. in the hot water supply.

    PubMed

    Rakić, Anita; Štambuk-Giljanović, Nives

    2016-02-01

    The purpose of this study was to evaluate the prevalence of Legionella spp. and compare the quality of hot water between four facilities for accommodation located in Southern Croatia (the Split-Dalmatian County). The research included data collection on the technical and technological characteristics in the period from 2009 to 2012. The survey included a type of construction material for the distribution and internal networks, heating system water heater type, and water consumption. Changes in water quality were monitored by determination of the physical and chemical parameters (temperature, pH, free chlorine residual concentrations, iron, zinc, copper and manganese) in the samples, as well as the presence and concentration of bacteria Legionella spp. The temperature is an important factor for the development of biofilms, and it is in negative correlation with the appearance of Legionella spp. Positive correlations between the Fe and Zn concentrations and Legionella spp. were established, while the inhibitory effect of a higher Cu concentration on the Legionella spp. concentration was proven. Legionella spp. were identified in 38/126 (30.2%) of the water samples from the heating system with zinc-coated pipes, as well as in 78/299 (26.1%) of the samples from systems with plastic pipes. A similar number of Legionella spp. positive samples were established regardless of the type of the water heating system (central or independent). The study confirms the necessity of regular microbial contamination monitoring of the drinking water distribution systems (DWDSs).

  18. Physical and chemical parameter correlations with technical and technological characteristics of heating systems and the presence of Legionella spp. in the hot water supply.

    PubMed

    Rakić, Anita; Štambuk-Giljanović, Nives

    2016-02-01

    The purpose of this study was to evaluate the prevalence of Legionella spp. and compare the quality of hot water between four facilities for accommodation located in Southern Croatia (the Split-Dalmatian County). The research included data collection on the technical and technological characteristics in the period from 2009 to 2012. The survey included a type of construction material for the distribution and internal networks, heating system water heater type, and water consumption. Changes in water quality were monitored by determination of the physical and chemical parameters (temperature, pH, free chlorine residual concentrations, iron, zinc, copper and manganese) in the samples, as well as the presence and concentration of bacteria Legionella spp. The temperature is an important factor for the development of biofilms, and it is in negative correlation with the appearance of Legionella spp. Positive correlations between the Fe and Zn concentrations and Legionella spp. were established, while the inhibitory effect of a higher Cu concentration on the Legionella spp. concentration was proven. Legionella spp. were identified in 38/126 (30.2%) of the water samples from the heating system with zinc-coated pipes, as well as in 78/299 (26.1%) of the samples from systems with plastic pipes. A similar number of Legionella spp. positive samples were established regardless of the type of the water heating system (central or independent). The study confirms the necessity of regular microbial contamination monitoring of the drinking water distribution systems (DWDSs). PMID:26733467

  19. Topographical and Chemical Imaging of a Phase Separated Polymer Using a Combined Atomic Force Microscopy/Infrared Spectroscopy/Mass Spectrometry Platform.

    PubMed

    Tai, Tamin; Karácsony, Orsolya; Bocharova, Vera; Van Berkel, Gary J; Kertesz, Vilmos

    2016-03-01

    In this paper, the use of a hybrid atomic force microscopy/infrared spectroscopy/mass spectrometry imaging platform was demonstrated for the acquisition and correlation of nanoscale sample surface topography and chemical images based on infrared spectroscopy and mass spectrometry. The infrared chemical imaging component of the system utilized photothermal expansion of the sample at the tip of the atomic force microscopy probe recorded at infrared wave numbers specific to the different surface constituents. The mass spectrometry-based chemical imaging component of the system utilized nanothermal analysis probes for thermolytic surface sampling followed by atmospheric pressure chemical ionization of the gas phase species produced with subsequent mass analysis. The basic instrumental setup, operation, and image correlation procedures are discussed, and the multimodal imaging capability and utility are demonstrated using a phase separated poly(2-vinylpyridine)/poly(methyl methacrylate) polymer thin film. The topography and both the infrared and mass spectral chemical images showed that the valley regions of the thin film surface were comprised primarily of poly(2-vinylpyridine) and hill or plateau regions were primarily poly(methyl methacrylate). The spatial resolution of the mass spectral chemical images was estimated to be 1.6 μm based on the ability to distinguish surface features in those images that were also observed in the topography and infrared images of the same surface.

  20. Characterizing seasonal variability of storm events based on very high frequency monitoring of hydrological and chemical variables: comparing patterns in hot spots and hot moments for nutrient and sediment export

    NASA Astrophysics Data System (ADS)

    Fovet, Ophelie; Thelusma, Gilbert; Humbert, Guillaume; Dupas, Rémi; Faucheux, Mikael; Gilliet, Nicolas; Hamon, Yannick; Jaffrezic, Anne; Grimaldi, Catherine; Gruau, Gerard

    2016-04-01

    Storm events are critical hot moments of emission for several dissolved and particulate chemical species at major stake for water quality (e.g. dissolved organic carbon DOC, suspended sediments, phosphorus). During such events, the solutes or particles are exported from heterogeneous sources through various pathways to stream leading to specific integrated signals at the outlet characterized by very short dynamics. This is merely true in headwater catchments where the total duration of such events ranges over 10h to 3 days, with very quick variations in stream flow and concentrations at the outlet occurring in a few hours. Thus for investigating properly event processes, high frequency monitoring of flow and water quality is required. We analysed 103 storm events in a 5 km2 agricultural headwater catchment, part of the AgrHys Observatory, on the basis of a 3-year-long data set which combined meterological (Rainfall), hydrological (flow and piezometry), and water quality (turbidity, conductivity, DOC and NO3 concentrations) data recorded at very high frequencies (from 1 to 20 min) thanks to dedicated sensors. We proposed a range of quantitative storm descriptors for characterizing input (rainfall), antecedent and initial conditions (groundwater levels and saturated area), and stream response in terms of level and dynamics of flow (Q), groundwater levels, and concentrations (C) but also the C-Q relationships. Three intra annual periods have been previously defined for base flow dynamic according to shallow groundwater table variations so that they correspond to different connectivity status in the catchment. The seasonal and inter-annual variability of the storm events have been analysed using the descriptors and based on these predefined periods. Results show that the hydrological flowpaths and the consequent storm chemistry were controlled by the hydrological base flow regime rather than by the rain input characteristics. This highlights that the exports of NO3

  1. Determination of copper in airborne particulate matter using slurry sampling and chemical vapor generation atomic absorption spectrometry.

    PubMed

    Silva, Laiana O B; Leao, Danilo J; dos Santos, Debora C; Matos, Geraldo D; de Andrade, Jailson B; Ferreira, Sergio L C

    2014-09-01

    The present paper describes the development of a method for the determination of copper in airborne particulate matter using slurry sampling and chemical vapor generation atomic absorption spectrometry (CVG AAS). Chemometric tools were employed to characterize the influence of several factors on the generation of volatile copper species. First, a two-level full factorial design was performed that included the following chemical variables: hydrochloric acid concentration, tetrahydroborate concentration, sulfanilamide concentration and tetrahydroborate volume, using absorbance as the response. Under the established experimental conditions, the hydrochloric acid concentration had the greatest influence on the generation of volatile copper species. Subsequently, a Box-Behnken design was performed to determine the optimum conditions for these parameters. A second chemometric study employing a two-level full factorial design was performed to evaluate the following physical factors: tetrahydroborate flow rate, flame composition, alcohol volume and sample volume. The results of this study demonstrated that the tetrahydroborate flow rate was critical for the process. The chemometric experiments determined the following experimental conditions for the method: hydrochloric acid concentration, 0.208 M; tetrahydroborate concentration, 4.59%; sulfanilamide concentration, 0.79%; tetrahydroborate volume, 2.50 mL; tetrahydroborate flow rate, 6.50 mL min(-1); alcohol volume, 200 µL; and sample volume, 7.0 mL. Thus, this method, using a slurry volume of 500 µL and a final dilution of 7 mL, allowed for the determination of copper with limits of detection and quantification of 0.30 and 0.99 µg L(-1), respectively. Precisions, expressed as RSD%, of 4.6 and 2.8% were obtained using copper solutions at concentrations of 5.0 and 50.0 µg L(-1), respectively. The accuracy was evaluated by the analysis of a certified reference material of urban particulate matter. The copper concentration

  2. Determination of copper in airborne particulate matter using slurry sampling and chemical vapor generation atomic absorption spectrometry.

    PubMed

    Silva, Laiana O B; Leao, Danilo J; dos Santos, Debora C; Matos, Geraldo D; de Andrade, Jailson B; Ferreira, Sergio L C

    2014-09-01

    The present paper describes the development of a method for the determination of copper in airborne particulate matter using slurry sampling and chemical vapor generation atomic absorption spectrometry (CVG AAS). Chemometric tools were employed to characterize the influence of several factors on the generation of volatile copper species. First, a two-level full factorial design was performed that included the following chemical variables: hydrochloric acid concentration, tetrahydroborate concentration, sulfanilamide concentration and tetrahydroborate volume, using absorbance as the response. Under the established experimental conditions, the hydrochloric acid concentration had the greatest influence on the generation of volatile copper species. Subsequently, a Box-Behnken design was performed to determine the optimum conditions for these parameters. A second chemometric study employing a two-level full factorial design was performed to evaluate the following physical factors: tetrahydroborate flow rate, flame composition, alcohol volume and sample volume. The results of this study demonstrated that the tetrahydroborate flow rate was critical for the process. The chemometric experiments determined the following experimental conditions for the method: hydrochloric acid concentration, 0.208 M; tetrahydroborate concentration, 4.59%; sulfanilamide concentration, 0.79%; tetrahydroborate volume, 2.50 mL; tetrahydroborate flow rate, 6.50 mL min(-1); alcohol volume, 200 µL; and sample volume, 7.0 mL. Thus, this method, using a slurry volume of 500 µL and a final dilution of 7 mL, allowed for the determination of copper with limits of detection and quantification of 0.30 and 0.99 µg L(-1), respectively. Precisions, expressed as RSD%, of 4.6 and 2.8% were obtained using copper solutions at concentrations of 5.0 and 50.0 µg L(-1), respectively. The accuracy was evaluated by the analysis of a certified reference material of urban particulate matter. The copper concentration

  3. Direct observation of electron emission from the grain boundaries of chemical vapour deposition diamond films by tunneling atomic force microscopy

    SciTech Connect

    Chatterjee, Vijay; Harniman, Robert; May, Paul W.; Barhai, P. K.

    2014-04-28

    The emission of electrons from diamond in vacuum occurs readily as a result of the negative electron affinity of the hydrogenated surface due to features with nanoscale dimensions, which can concentrate electric fields high enough to induce electron emission from them. Electrons can be emitted as a result of an applied electric field (field emission) with possible uses in displays or cold-cathode devices. Alternatively, electrons can be emitted simply by heating the diamond in vacuum to temperatures as low as 350 °C (thermionic emission), and this may find applications in solar energy generation or energy harvesting devices. Electron emission studies usually use doped polycrystalline diamond films deposited onto Si or metallic substrates by chemical vapor deposition, and these films have a rough, faceted morphology on the micron or nanometer scale. Electron emission is often improved by patterning the diamond surface into sharp points or needles, the idea being that the field lines concentrate at the points lowering the barrier for electron emission. However, there is little direct evidence that electrons are emitted from these sharp tips. The few reports in the literature that have studied the emission sites suggested that emission came from the grain boundaries and not the protruding regions. We now present direct observation of the emission sites over a large area of polycrystalline diamond using tunneling atomic force microscopy. We confirm that the emission current comes mostly from the grain boundaries, which is consistent with a model for emission in which the non-diamond phase is the source of electrons with a threshold that is determined by the surrounding hydrogenated diamond surface.

  4. Modelling of non-LTE atomic physics processes in hot dense plasmas during the interaction with an intense short pulse laser

    NASA Astrophysics Data System (ADS)

    Davis, J.; Petrov, G. M.

    2014-05-01

    The implicit 2D3V particle-in-cell (PIC) code developed to study the interaction of intense lasers with matter (Petrov and Davis 2008 Comput. Phys. Commun. 179 868-80 2011 Phys. Plasmas 18 073102) has been extended to include atomic physics under extreme energy density conditions. The atomic physics model is applied to aluminium. Each ionization stage contains two levels: one ground and one lumped excited state, for which various atomic physics processes such as optical field ionization, collisional ionization, excitation, de-excitation and radiative decay describe the population density. Two-dimensional PIC simulations have been carried out for laser pulses with peak intensity 1 × 1020 W cm-2, pulse duration 60 fs, spot size 3 µm and energy 0.75 J interacting with ultrathin (0.2 µm) Al foil. Radiation emitted during the laser-target interaction is computed by accounting for both bound-bound transitions and bremsstrahlung radiation. We demonstrate that the radiation signature of laser-produced plasma can be used as a complementary tool to other diagnostic techniques used in laser-plasma interactions. Finally, results from the PIC model are compared to equilibrium calculations (Maxwell-Boltzmann and Saha). In the early stages of laser-plasma interactions (<100 fs) the plasma is far from equilibrium and equilibrium models can not be applied with confidence to model the plasma.

  5. Hot Groups.

    ERIC Educational Resources Information Center

    Vail, Kathleen

    1996-01-01

    Collaborators sparked by creative ideas and obsessed by a common task may not realize they're part of a "hot group"--a term coined by business professors Harold J. Leavitt and Jean Lipman-Blumen. Spawned by group decision making and employee empowerment, hot groups can flourish in education settings. They're typically small, short lived, and goal…

  6. TiO2-Coated Transparent Conductive Oxide (SnO2:F) Films Prepared by Atmospheric Pressure Chemical Vapor Deposition with High Durability against Atomic Hydrogen

    NASA Astrophysics Data System (ADS)

    Kambe, Mika; Sato, Kazuo; Kobayashi, Daisuke; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Fukawa, Makoto; Taneda, Naoki; Yamada, Akira; Konagai, Makoto

    2006-03-01

    The durability of textured transparent conductive oxide (TCO) thin films against atomic hydrogen was investigated. An ultrathin TiO2 layer of 2 nm thickness was deposited on textured fluorine-doped tin oxide (SnO2:F) films, successively by atmospheric pressure chemical vapor deposition (AP-CVD). TCO films with a TiO2 layer showed a higher optical transmittance and a lower resistivity after exposure to atomic hydrogen excited by very high frequency (VHF) plasma, while TCO films without a TiO2 layer showed a lower optical transmittance and a higher resistivity after the exposure. These TCO films were characterized by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) before and after the exposure to atomic hydrogen.

  7. Organic, inorganic and total mercury determination in fish by chemical vapor generation with collection on a gold gauze and electrothermal atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Duarte, Fábio Andrei; Bizzi, Cezar Augusto; Antes, Fabiane Goldschmidt; Dressler, Valderi Luiz; Flores, Érico Marlon de Moraes

    2009-06-01

    A method for organic, inorganic and total mercury determination in fish tissue has been developed using chemical vapor generation and collection of mercury vapor on a gold gauze inside a graphite tube and further atomization by electrothermal atomic absorption spectrometry. After drying and cryogenic grinding, potassium bromide and hydrochloric acid solution (1 mol L - 1 KBr in 6 mol L - 1 HCl) was added to the samples. After centrifugation, total mercury was determined in the supernatant. Organomercury compounds were selectively extracted from KBr solution using chloroform and the resultant solution was back extracted with 1% m/v L-cysteine. This solution was used for organic Hg determination. Inorganic Hg remaining in KBr solution was directly determined by chemical vapor generation electrothermal atomic absorption spectrometry. Mercury vapor generation from extracts was performed using 1 mol L - 1 HCl and 2.5% m/v NaBH 4 solutions and a batch chemical vapor generation system. Mercury vapor was collected on the gold gauze heated resistively at 80 °C and the atomization temperature was set at 650 °C. The selectivity of extraction was evaluated using liquid chromatography coupled to chemical vapor generation and determination by inductively coupled plasma mass spectrometry. The proposed method was applied for mercury analysis in shark, croaker and tuna fish tissues. Certified reference materials were used to check accuracy and the agreement was better than 95%. The characteristic mass was 60 pg and method limits of detection were 5, 1 and 1 ng g - 1 for organic, inorganic and total mercury, respectively. With the proposed method it was possible to analyze up to 2, 2 and 6 samples per hour for organic, inorganic and total Hg determination, respectively.

  8. Atomic-level robustness of the Si(100)-2×1:H surface following liquid phase chemical treatments in atmospheric pressure environments

    NASA Astrophysics Data System (ADS)

    Baluch, A. S.; Guisinger, N. P.; Basu, R.; Foley, E. T.; Hersam, M. C.

    2004-05-01

    The UHV-prepared Si(100)-2×1:H surface is studied at atomic resolution following liquid phase chemical processing under atmospheric pressure conditions. A custom experimental setup, consisting of an UHV scanning tunneling microscope (STM) chamber that is directly interfaced to an inert atmosphere glovebox, facilitates liquid phase chemical processing without exposing the pristine H-passivated surface to ambient air. While in the inert atmosphere, the Si(100)-2×1:H surface is treated with a variety of organic and aqueous solvents. Atomic resolution STM images reveal that the hydrogen passivation remains largely intact after treatments in toluene and dichloromethane. In addition, by minimizing oxygen levels during processing, perturbation to the Si(100)-2×1:H surface can be significantly reduced following exposure to water. These results are potentially useful in the fields of microelectronics and molecular-beam epitaxy, where liquid phase chemical processing is often avoided in an effort to preserve atomically pristine Si(100) surfaces. Furthermore, this study delineates the conditions under which various organic and biological molecules can be delivered to nanopatterned Si(100)-2×1:H surfaces via liquid phase solvents. .

  9. IR Hot Wave

    SciTech Connect

    Graham, T. B.

    2010-04-01

    The IR Hot Wave{trademark} furnace is a breakthrough heat treatment system for manufacturing metal components. Near-infrared (IR) radiant energy combines with IR convective heating for heat treating. Heat treatment is an essential process in the manufacture of most components. The controlled heating and cooling of a metal or metal alloy alters its physical, mechanical, and sometimes chemical properties without changing the object's shape. The IR Hot Wave{trademark} furnace offers the simplest, quickest, most efficient, and cost-effective heat treatment option for metals and metal alloys. Compared with other heat treatment alternatives, the IR Hot Wave{trademark} system: (1) is 3 to 15 times faster; (2) is 2 to 3 times more energy efficient; (3) is 20% to 50% more cost-effective; (4) has a {+-}1 C thermal profile compared to a {+-}10 C thermal profile for conventional gas furnaces; and (5) has a 25% to 50% smaller footprint.

  10. Polytype stability, microstructural evolution, and impurities at the interface of homoepitaxial 4H-silicon carbide(1120) thin films grown via hot-wall chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Bishop, Seann M. G.

    The electronic properties of 4H-SiC make it a leading semiconductor material for high-power applications. Despite advances in SiC crystal growth, devices fabricated in 4H-SiC(0001) continue to be limited by defects like micropipes, dislocations and stacking faults. Investigations performed here on non-basal 4H-SiC have demonstrated micropipe-free, 4H-SiC(112¯0) films comparable with conventional 4H-SiC(0001). Improved device performance has been achieved for p-i-n rectifiers fabricated in 4H-SiC(112¯0). Hot-wall chemical vapor deposition (CVD) is the most widely used growth process employed to meet the material demands for 4H-SiC-based high-power electronics; however, the suitability of this technique for the growth of thin films (<10 mum) is not well established. A detailed analysis of the epitaxial growth of 4H-SiC(112¯0) thin films by vertical, hot-wall CVD has been performed in this work. Two growth regimes were identified and termed sublimation growth and precursor growth. In the former, the SiC coating decomposes and results in the in-situ (sublimation) growth of epitaxial SiC films. It is proposed that in-situ layer aids in subsequent thin film growth from reactant gases. Transmission electron microscopy revealed areas without observable defects and an indistinguishable interface between the substrate and sublimation grown layer. Aluminum impurity concentrations to 3x10 18 cm-3 were identified near the interface with the substrate. The influence of these impurities on the cathodoluminescence spectrum of 4H-SiC was studied. A model based on boundary layer theory was developed to explain the origin and the profile of the aluminum impurities. Secondary ion mass spectrometry revealed the SiC coating to be the major source of aluminum impurities. An argon diluent reduced the concentration of aluminum at the interface to 2x1017 cm-3. Films deposited via precursor growth exhibited specular surfaces. Optical and structural characterization showed the films

  11. Quantum Chemical Insight into the LiF Interlayer Effects in Organic Electronics: Reactions between Al Atom and LiF Clusters.

    PubMed

    Wu, Shui-Xing; Kan, Yu-He; Li, Hai-Bin; Zhao, Liang; Wu, Yong; Su, Zhong-Min

    2015-08-01

    It is well known that the aluminum cathode performs dramatically better when a thin lithium fluoride (LiF) layer inserted in organic electronic devices. The doping effect induced by the librated Li atom via the chemical reactions producing AlF3 as byproduct was previously proposed as one of possible mechanisms. However, the underlying mechanism discussion is quite complicated and not fully understood so far, although the LiF interlayer is widely used. In this paper, we perform theoretical calculations to consider the reactions between an aluminum atom and distinct LiF clusters. The reaction pathways of the Al-(LiF)n (n = 2, 4, 16) systems were discovered and the energetics were theoretically evaluated. The release of Li atom and the formation of AlF3 were found in two different chemical reaction routes. The undissociated Al-(LiF)n systems have chances to change to some structures with loosely bound electrons. Our findings about the interacted Al-(LiF)n systems reveal new insights into the LiF interlayer effects in organic electronics applications.

  12. Chemical stabilization and improved thermal resilience of molecular arrangements: possible formation of a surface network of bonds by multiple pulse atomic layer deposition.

    PubMed

    de Pauli, Muriel; Matos, Matheus J S; Siles, Pablo F; Prado, Mariana C; Neves, Bernardo R A; Ferreira, Sukarno O; Mazzoni, Mário S C; Malachias, Angelo

    2014-08-14

    In this work, we make use of an atomic layer deposition (ALD) surface reaction based on trimethyl-aluminum (TMA) and water to modify O-H terminated self-assembled layers of octadecylphosphonic acid (OPA). The structural modifications were investigated by X-ray reflectivity, X-ray diffraction, and atomic force microscopy. We observed a significant improvement in the thermal stability of ALD-modified molecules, with the existence of a supramolecular packing structure up to 500 °C. Following the experimental observations, density functional theory (DFT) calculations indicate the possibility of formation of a covalent network with aluminum atoms connecting OPA molecules at terrace surfaces. Chemical stability is also achieved on top of such a composite surface, inhibiting further ALD oxide deposition. On the other hand, in the terrace edges, where the covalent array is discontinued, the chemical conditions allow for oxide growth. Analysis of the DFT results on band structure and density of states of modified OPA molecules suggests that besides the observed thermal resilience, the dielectric character of OPA layers is preserved. This new ALD-modified OPA composite is potentially suitable for applications such as dielectric layers in organic devices, where better thermal performance is required.

  13. Chemical stabilization and improved thermal resilience of molecular arrangements: possible formation of a surface network of bonds by multiple pulse atomic layer deposition.

    PubMed

    de Pauli, Muriel; Matos, Matheus J S; Siles, Pablo F; Prado, Mariana C; Neves, Bernardo R A; Ferreira, Sukarno O; Mazzoni, Mário S C; Malachias, Angelo

    2014-08-14

    In this work, we make use of an atomic layer deposition (ALD) surface reaction based on trimethyl-aluminum (TMA) and water to modify O-H terminated self-assembled layers of octadecylphosphonic acid (OPA). The structural modifications were investigated by X-ray reflectivity, X-ray diffraction, and atomic force microscopy. We observed a significant improvement in the thermal stability of ALD-modified molecules, with the existence of a supramolecular packing structure up to 500 °C. Following the experimental observations, density functional theory (DFT) calculations indicate the possibility of formation of a covalent network with aluminum atoms connecting OPA molecules at terrace surfaces. Chemical stability is also achieved on top of such a composite surface, inhibiting further ALD oxide deposition. On the other hand, in the terrace edges, where the covalent array is discontinued, the chemical conditions allow for oxide growth. Analysis of the DFT results on band structure and density of states of modified OPA molecules suggests that besides the observed thermal resilience, the dielectric character of OPA layers is preserved. This new ALD-modified OPA composite is potentially suitable for applications such as dielectric layers in organic devices, where better thermal performance is required. PMID:25055162

  14. Rayleigh scattering in the atmospheres of hot stars

    NASA Astrophysics Data System (ADS)

    Fišák, J.; Krtička, J.; Munzar, D.; Kubát, J.

    2016-05-01

    Context. Rayleigh scattering is a result of an interaction of photons with bound electrons. Rayleigh scattering is mostly neglected in calculations of hot star model atmospheres because most of the hydrogen atoms are ionized and the heavier elements have a lower abundance than hydrogen. In atmospheres of some chemically peculiar stars, helium overabundant regions containing singly ionized helium are present and Rayleigh scattering can be a significant opacity source. Aims: We evaluate the contribution of Rayleigh scattering by neutral hydrogen and singly ionized helium in the atmospheres of hot stars with solar composition and in the atmospheres of helium overabundant stars. Methods: We computed several series of model atmospheres using the TLUSTY code and emergent fluxes using the SYNSPEC code. These models describe atmospheres of main sequence B-type stars with different helium abundance. We used an existing grid of models for atmospheres with solar chemical composition and we calculated an additional grid for helium-rich stars with N(He)/N(H) = 10. Results: Rayleigh scattering by neutral hydrogen can be neglected in atmospheres of hot stars, while Rayleigh scattering by singly ionized helium can be a non-negligible opacity source in some hot stars, especially in helium-rich stars.

  15. A contribution to non-equilibrium chemical kinetics. III. Some high-energy strongly non-equilibrium processes in solids and liquids

    NASA Astrophysics Data System (ADS)

    Temkin, A. Ya.

    1989-10-01

    The present work is the continuation of the previous works of the author on the non-equilibrium chemical kinetics. The consideration of direct and hot spot reactions provoked by the passage of fast particles through a liquid or solid medium is continued. It is shown that the model of quasi-particles permits us to detect and to consider a kinetic effect of primary fast particle reactions caused by the distribution of target molecules with respect to distance from the primary particle trajectory. It has been found what kinds of chemical kinetic experiments allow us to get rid of this effect to obtain correct values of the reaction elementary act parameters in the condensed phase. Spherical hot spot chemical kinetics of the reaction of two hot diatomic molecules is considered and compared with the one in cylindrical hot spots. It is shown that the creation of spherical hot spots can be stimulated by the addition of atoms having the mass close to that of the primary fast particle. In particular, this can be used to increase the selectivity of the radiation therapy by injection of such atoms to the tumor. Hot atom-polymer segment reaction kinetics in a cylindrical hot spot is considered. The obtained expressions for reaction product yields represent the hot spot contribution to polymer transformations by heavy fast ions. Their possible application to the DNA destruction by hot hydrogen atoms in a hot spot is discussed. Expressions for macroscopic yields of direct and hot spot reactions have been obtained. The hot spot evolution in the presence of laser radiation is considered. Various possibilities of fast particle and laser beams combining irradiation use are considered, especially for the laser material processing and metalworking as well as for the laser medicine.

  16. Parameters of an electric-discharge generator of iodine atoms for a chemical oxygen-iodine laser

    SciTech Connect

    Azyazov, V N; Vorob'ev, M V; Voronov, A I; Kupryaev, Nikolai V; Mikheev, P A; Ufimtsev, N I

    2009-01-31

    Laser-induced fluorescence is used for measuring the concentration of iodine molecules at the output of an electric-discharge generator of atomic iodine. Methyl iodide CH{sub 3}I is used as the donor of atomic iodine. The fraction of iodine extracted from CH{sub 3}I in the generator is {approx}50%. The optimal operation regimes are found in which 80%-90% of iodine contained in the output flow of the generator was in the atomic state. This fraction decreased during the iodine transport due to recombination and was 20%-30% at the place where iodine was injected into the oxygen flow. The fraction of the discharge power spent for dissociation was {approx}3%. (elements of laser setups)

  17. Quantitative chemical-structure evaluation using atom probe tomography: Short-range order analysis of Fe-Al.

    PubMed

    Marceau, R K W; Ceguerra, A V; Breen, A J; Raabe, D; Ringer, S P

    2015-10-01

    Short-range-order (SRO) has been quantitatively evaluated in an Fe-18Al (at%) alloy using atom probe tomography (APT) data and by calculation of the generalised multicomponent short-range order (GM-SRO) parameters, which have been determined by shell-based analysis of the three-dimensional atomic positions. The accuracy of this method with respect to limited detector efficiency and spatial resolution is tested against simulated D03 ordered data. Whilst there is minimal adverse effect from limited atom probe instrument detector efficiency, the combination of this with imperfect spatial resolution has the effect of making the data appear more randomised. The value of lattice rectification of the experimental APT data prior to GM-SRO analysis is demonstrated through improved information sensitivity.

  18. Role of preferential weak hybridization between the surface-state of a metal and the oxygen atom in the chemical adsorption mechanism.

    PubMed

    Kim, Yong Su; Jeon, Sang Ho; Bostwick, Aaron; Rotenberg, Eli; Ross, Philip N; Walter, Andrew L; Chang, Young Jun; Stamenkovic, Vojislav R; Markovic, Nenad M; Noh, Tae Won; Han, Seungwu; Mun, Bongjin Simon

    2013-11-21

    We report on the chemical adsorption mechanism of atomic oxygen on the Pt(111) surface using angle-resolved-photoemission spectroscopy (ARPES) and density functional calculations. The detailed band structure of Pt(111) from ARPES reveals that most of the bands near the Fermi level are surface-states. By comparing band maps of Pt and O/Pt, we identify that dxz (dyz) and dz(2) orbitals are strongly correlated in the surface-states around the symmetry point M and K, respectively. Additionally, we demonstrate that the s- or p-orbital of oxygen atoms hybridizes preferentially with the dxz (dyz) orbital near the M symmetry point. This weak hybridization occurs with minimal charge transfer. PMID:24097254

  19. Spectroscopy and reactions of molecules important in chemical evolution

    NASA Technical Reports Server (NTRS)

    Becker, R. S.

    1974-01-01

    The research includes: (1) hot hydrogen atom reactions in terms of the nature of products produced, mechanism of the reactions and the implication and application of such reactions for molecules existing in interstellar clouds, in planetary atmospheres, and in chemical evolution; (2) photochemical reactions that can lead to molecules important in chemical evolution, interstellar clouds and as constituents in planetary atmospheres; and (3) spectroscopic and theoretical properties of biomolecules and their precursors and where possible, use these to understand their photochemical behavior.

  20. Chemical activation through super energy transfer collisions.

    PubMed

    Smith, Jonathan M; Nikow, Matthew; Ma, Jianqiang; Wilhelm, Michael J; Han, Yong-Chang; Sharma, Amit R; Bowman, Joel M; Dai, Hai-Lung

    2014-02-01

    Can a molecule be efficiently activated with a large amount of energy in a single collision with a fast atom? If so, this type of collision will greatly affect molecular reactivity and equilibrium in systems where abundant hot atoms exist. Conventional expectation of molecular energy transfer (ET) is that the probability decreases exponentially with the amount of energy transferred, hence the probability of what we label "super energy transfer" is negligible. We show, however, that in collisions between an atom and a molecule for which chemical reactions may occur, such as those between a translationally hot H atom and an ambient acetylene (HCCH) or sulfur dioxide, ET of chemically significant amounts of energy commences with surprisingly high efficiency through chemical complex formation. Time-resolved infrared emission observations are supported by quasi-classical trajectory calculations on a global ab initio potential energy surface. Results show that ∼10% of collisions between H atoms moving with ∼60 kcal/mol energy and HCCH result in transfer of up to 70% of this energy to activate internal degrees of freedom.

  1. Computer modeling of a hot filament diamond deposition reactor

    NASA Technical Reports Server (NTRS)

    Kuczmarski, Maria A.; Washlock, Paul A.; Angus, John C.

    1991-01-01

    A commercial fluid mechanics program, FLUENT, has been applied to the modeling of a hot-filament diamond deposition reactor. Streamlines and contours of constant temperature and species concentrations are obtained for practical reactor geometries and conditions. The modeling is presently restricted to two-dimensional simulations and to a chemical mechanism of ten independent homogeneous and surface reactions. Comparisons are made between predicted power consumption, substrate temperature, and concentrations of atomic hydrogen and methyl-radical with values taken from the literature. The results to date indicate that the modeling can aid in the rational design and analysis of practical reactor configurations.

  2. An informational approach about energy and temperature in atoms

    NASA Astrophysics Data System (ADS)

    Flores-Gallegos, N.

    2016-08-01

    In this letter, we introduce new definitions of energy and temperature based on the information theory model, and we show that our definition of informational energy is related to the kinetic energy of the Thomas-Fermi model, meanwhile the definition of informational temperature proposed, permit identify 'hot' and 'cold' zones of an atom, such zones are related to the changes in the local electron energy wherein the chemical and physical changes can occur; informational temperature also can reproduce the shell structure of an atom.

  3. Hot Tickets

    ERIC Educational Resources Information Center

    Fox, Bette-Lee; Hoffert, Barbara; Kuzyk, Raya; McCormack, Heather; Williams, Wilda

    2008-01-01

    This article describes the highlights of this year's BookExpo America (BEA) held at the Los Angeles Convention Center. The attendees at BEA had not minded that the air was recycled, the lighting was fluorescent, and the food was bad. The first hot book sighting came courtesy of Anne Rice. Michelle Moran, author of newly published novel, "The…

  4. Practical hot oiling and hot watering for paraffin control

    SciTech Connect

    Mansure, A.J.; Barker, K.M.

    1994-03-01

    One of the common oil-field wellbore problems is paraffin deposition. Even though hot oiling or hot watering is usually the first method tried for removing paraffin, few operators appreciate the limitations of ``hot oiling`` and the potential for the fluid to aggravate well problems and cause formation damage. Field tests have shown that the chemical and thermal processes that occur during ``hot oiling`` are very complex and that there are significant variations in practices among operators. Key issues include: (1) During a typical hot oiling job, a significant amount of the fluid injected into the well goes into the formation, and hence, particulates and chemicals in the fluid have the potential to damage the formation. (2) Hot oiling can vaporize oil in the tubing faster than the pump lifts oil. This interrupts paraffin removal from the well, and thus the wax is refined into harder deposits, goes deeper into the well, and can stick rods. These insights have been used to determine good ``hot oiling`` practices designed to maximize wax removal and minimize formation damage.

  5. Local atomic structure analysis of SiC interface with oxide using chemical-state-selective X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Isomura, Noritake; Murai, Takaaki; Oji, Hiroshi; Nomoto, Toyokazu; Watanabe, Yukihiko; Kimoto, Yasuji

    2016-10-01

    A local atomic structure analysis of the interface between chemical vapor-deposited SiO2 and 4H-SiC was achieved via a combination of chemical-state-selective X-ray absorption spectroscopy and the use of a sample with a very thin oxide film. The Si K-edge spectrum, which monitors the SiC-assigned Auger peak, allows the SiC side of the SiO2/SiC interface to be selectively measured through the SiO2 film. We estimate the coordination number of the first nearest neighbor to be reduced by 17% with respect to the SiC bulk. This suggests that C vacancy defects exist at the SiC side of the interface.

  6. Atomic-Scale Observations of (010) LiFePO4 Surfaces Before and After Chemical Delithiation.

    PubMed

    Kobayashi, Shunsuke; Fisher, Craig A J; Kato, Takeharu; Ukyo, Yoshio; Hirayama, Tsukasa; Ikuhara, Yuichi

    2016-09-14

    The ability to view directly the surface structures of battery materials with atomic resolution promises to dramatically improve our understanding of lithium (de)intercalation and related processes. Here we report the use of state-of-the-art scanning transmission electron microscopy techniques to probe the (010) surface of commercially important material LiFePO4 and compare the results with theoretical models. The surface structure is noticeably different depending on whether Li ions are present in the topmost surface layer or not. Li ions are also found to migrate back to surface regions from within the crystal relatively quickly after partial delithiation, demonstrating the facile nature of Li transport in the [010] direction. The results are consistent with phase transformation models involving metastable phase formation and relaxation, providing atomic-level insights into these fundamental processes. PMID:27472440

  7. Atom trap loss, elastic collisions, and technology

    NASA Astrophysics Data System (ADS)

    Booth, James

    2012-10-01

    The study of collisions and scattering has been one of the most productive approaches for modern physics, illuminating the fundamental structure of crystals, surfaces, atoms, and sub-atomic particles. In the field of cold atoms, this is no less true: studies of cold atom collisions were essential to the production of quantum degenerate matter, the formation of cold molecules, and so on. Over the past few years it has been my delight to investigate elastic collisions between cold atoms trapped in either a magneto-optical trap (MOT) or a magnetic trap with hot, background gas in the vacuum environment through the measurement of the loss of atoms from the trap. Motivated by the goal of creating cold atom-based technology, we are deciphering what the trapped atoms are communicating about their environment through the observed loss rate. These measurements have the advantages of being straightforward to implement and they provide information about the underlying, fundamental inter-atomic processes. In this talk I will present some of our recent work, including the observation of the trap depth dependence on loss rate for argon-rubidium collisions. The data follow the computed loss rate curve based on the long-range Van der Waals interaction between the two species. The implications of these findings are exciting: trap depths can be determined from the trap loss measurement under controlled background density conditions; observation of trap loss rate in comparison to models for elastic, inelastic, and chemical processes can lead to improved understanding and characterization of these fundamental interactions; finally the marriage of cold atoms with collision modeling offers the promise of creating a novel pressure sensor and pressure standard for the high and ultra-high vacuum regime.

  8. Atomic layer chemical vapor deposition of AlxGa1-xN for solar blind UV-detectors

    NASA Astrophysics Data System (ADS)

    Khan, M. A.

    1988-05-01

    APA Optics completed a program aimed at developing aluminum gallium nitride materials technology using atomic layer epitaxy. The key objective of the Phase I work was to study the nitrogen vacancy problem using a unique switched atomic layer MOCVD approach as the growth technique. These nitrogen vacancies result in extremely high carrier densities in single crystal epitaxial layers of GaN thereby rendering the material unusable for emitters (such as electroluminescent devices) or detectors (such as photoconductors or Schottky barriers). Four tasks were completed under Phase 1 program. Under the first task we designed and incorporated a unique silicon carbide coated graphic substrate in our low procures MOCVD system. This susceptor was designed to implement the switched atomic layer epitaxy approach. Program Task 2 focussed at growing single Layers of AlxGa1-xN (over entire x) using a standard low pressure MOCVD approach. We were successful in growing high quality single crystal layers. These layers were checked for single crystal nature (using Laue and RHEED), carrier concentrations and mobilities (using Van der Pauw and Hall measurements) and optical transmissions. These data as shown indicate material growth matching some of the best reported values in literature.

  9. Atomic data for S II—toward better diagnostics of chemical evolution in high-redshift galaxies

    SciTech Connect

    Kisielius, Romas; Bogdanovich, Pavel; Kulkarni, Varsha P.; Ferland, Gary J.; Lykins, Matt L.

    2014-01-01

    Absorption-line spectroscopy is a powerful tool used to estimate element abundances in both the nearby and distant universe. The accuracy of the abundances thus derived is naturally limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state of the art quantal calculations. Here, we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the spectra of quasars and gamma-ray bursts. We report new extensive calculations of a large number of energy levels of S II, and the line strengths of the resulting radiative transitions. Our calculations are based on the configuration interaction approach within a numerical Hartree-Fock framework, and utilize both non-relativistic and quasirelativistic one-electron radial orbitals. The results of these new atomic calculations are then incorporated into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative purposes. The new results imply relatively modest changes (≈0.04 dex) to the metallicities estimated from S II in past studies. These results will be readily applicable to other studies of S II in the Milky Way and other galaxies.

  10. Theoretical Modelling of Hot Stars

    NASA Astrophysics Data System (ADS)

    Najarro, F.; Hillier, D. J.; Figer, D. F.; Geballe, T. R.

    1999-06-01

    Recent progress towards model atmospheres for hot stars is discussed. A new generation of NLTE wind blanketed models, together with high S/N spectra of the hot star population in the central parsec, which are currently being obtained, will allow metal abundance determinations (Fe, Si, Mg, Na, etc). Metallicity studies of hot stars in the IR will provide major constraints not only on the theory of evolution of massive stars but also on our efforts to solve the puzzle of the central parsecs of the Galaxy. Preliminary results suggest that the metallicity of the Pistol Star is 3 times solar, thus indicating strong chemical enrichment of the gas in the Galactic Center.

  11. Toward the Development of a Fundamentally Based Chemical Model for Cyclopentanone: High-Pressure-Limit Rate Constants for H Atom Abstraction and Fuel Radical Decomposition.

    PubMed

    Zhou, Chong-Wen; Simmie, John M; Pitz, William J; Curran, Henry J

    2016-09-15

    Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. Calculated thermodynamic and kinetic data are presented for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. These radicals can be formed via H atom abstraction reactions by Ḣ and Ö atoms and ȮH, HȮ2, and ĊH3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when ȮH is involved, but the reverse holds true for HȮ2 radicals. The subsequent β-scission of the radicals formed is also determined, and it is shown that recent tunable VUV photoionization mass spectrometry experiments can be interpreted in this light. The bulk of the calculations used the composite model chemistry G4, which was benchmarked in the simplest case with a coupled cluster treatment, CCSD(T), in the complete basis set limit. PMID:27558073

  12. Effect of surface pretreatment on interfacial chemical bonding states of atomic layer deposited ZrO{sub 2} on AlGaN

    SciTech Connect

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Liu, Zhi Hong

    2015-09-15

    Atomic layer deposition (ALD) of ZrO{sub 2} on native oxide covered (untreated) and buffered oxide etchant (BOE) treated AlGaN surface was analyzed by utilizing x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy. Evidenced by Ga–O and Al–O chemical bonds by XPS, parasitic oxidation during deposition is largely enhanced on BOE treated AlGaN surface. Due to the high reactivity of Al atoms, more prominent oxidation of Al atoms is observed, which leads to thicker interfacial layer formed on BOE treated surface. The results suggest that native oxide on AlGaN surface may serve as a protecting layer to inhibit the surface from further parasitic oxidation during ALD. The findings provide important process guidelines for the use of ALD ZrO{sub 2} and its pre-ALD surface treatments for high-k AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors and other related device applications.

  13. Confocal absorption spectral imaging of MoS2: optical transitions depending on the atomic thickness of intrinsic and chemically doped MoS2.

    PubMed

    Dhakal, Krishna P; Duong, Dinh Loc; Lee, Jubok; Nam, Honggi; Kim, Minsu; Kan, Min; Lee, Young Hee; Kim, Jeongyong

    2014-11-01

    We performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra (over the range 1.5-3.2 eV) within regions having different numbers of layers and studied the variation of optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to the bulk MoS2 and this shift was attributed to the reduction of the gap energy in the Brillouin zone at the K-point as the atomic thickness increased. We also performed n-type chemical doping of MoS2 films using reduced benzyl viologen (BV) and the confocal absorption spectra modified by the doping showed a strong dependence on the atomic thickness: A and B exciton peaks were greatly quenched in the monolayer MoS2 while much less effect was shown in larger thickness and the BG peak either showed very small quenching for 1 L MoS2 or remained constant for larger thicknesses. Our results indicate that confocal absorption spectral imaging can provide comprehensive information on optical transitions of microscopic size intrinsic and doped two-dimensional layered materials.

  14. Impact of post-deposition annealing on interfacial chemical bonding states between AlGaN and ZrO{sub 2} grown by atomic layer deposition

    SciTech Connect

    Ye, Gang; Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Wang, Hong; Liu, Zhi Hong

    2015-03-02

    The effect of post-deposition annealing on chemical bonding states at interface between Al{sub 0.5}Ga{sub 0.5}N and ZrO{sub 2} grown by atomic layer deposition (ALD) is studied by angle-resolved x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been found that both of Al-O/Al 2p and Ga-O/Ga 3d area ratio decrease at annealing temperatures lower than 500 °C, which could be attributed to “clean up” effect of ALD-ZrO{sub 2} on AlGaN. Compared to Ga spectra, a much larger decrease in Al-O/Al 2p ratio at a smaller take-off angle θ is observed, which indicates higher effectiveness of the passivation of Al-O bond than Ga-O bond through “clean up” effect near the interface. However, degradation of ZrO{sub 2}/AlGaN interface quality due to re-oxidation at higher annealing temperature (>500 °C) is also found. The XPS spectra clearly reveal that Al atoms at ZrO{sub 2}/AlGaN interface are easier to get oxidized as compared with Ga atoms.

  15. Toward the Development of a Fundamentally Based Chemical Model for Cyclopentanone: High-Pressure-Limit Rate Constants for H Atom Abstraction and Fuel Radical Decomposition.

    PubMed

    Zhou, Chong-Wen; Simmie, John M; Pitz, William J; Curran, Henry J

    2016-09-15

    Theoretical aspects of the development of a chemical kinetic model for the pyrolysis and combustion of a cyclic ketone, cyclopentanone, are considered. Calculated thermodynamic and kinetic data are presented for the first time for the principal species including 2- and 3-oxo-cyclopentyl radicals, which are in reasonable agreement with the literature. These radicals can be formed via H atom abstraction reactions by Ḣ and Ö atoms and ȮH, HȮ2, and ĊH3 radicals, the rate constants of which have been calculated. Abstraction from the β-hydrogen atom is the dominant process when ȮH is involved, but the reverse holds true for HȮ2 radicals. The subsequent β-scission of the radicals formed is also determined, and it is shown that recent tunable VUV photoionization mass spectrometry experiments can be interpreted in this light. The bulk of the calculations used the composite model chemistry G4, which was benchmarked in the simplest case with a coupled cluster treatment, CCSD(T), in the complete basis set limit.

  16. Using magnetic levitation to distinguish atomic-level differences in chemical composition of polymers, and to monitor chemical reactions on solid supports.

    PubMed

    Mirica, Katherine A; Phillips, Scott T; Shevkoplyas, Sergey S; Whitesides, George M

    2008-12-31

    This communication describes a density-based method that uses magnetic levitation for monitoring solid-supported reactions and for distinguishing differences in chemical composition of polymers. The method is simple, rapid, and inexpensive and is similar to thin-layer chromatography (TLC; for solution-phase chemistry) in its potential for monitoring reactions in solid-phase chemistry. The technique involves levitating a sample of beads (taken from a reaction mixture) in a cuvette containing a paramagnetic solution (e.g., GdCl(3) dissolved in H(2)O) positioned between two NdFeB magnets. The vertical position at which the beads levitate corresponds to the density of the beads and correlates with the progress of a chemical reaction on a solid support. The method is particularly useful for monitoring the kinetics of reactions occurring on polymer beads. PMID:19063630

  17. The atomic structure and chemical composition of HfOx (x < 2) films prepared by ion-beam sputtering deposition

    NASA Astrophysics Data System (ADS)

    Aliev, V. S.; Gerasimova, A. K.; Kruchinin, V. N.; Gritsenko, V. A.; Prosvirin, I. P.; Badmaeva, I. A.

    2016-08-01

    Non-stoichiometric HfOx films of different chemical composition (x < 2) were fabricated by ion-beam sputtering deposition (IBSD) at room temperature. The ratio of O and Hf atoms in films x was varied by setting the O2 partial pressure in a chamber. An effect of chemical composition on the atomic structure of the films was studied by reflection high-energy electron diffraction, x-ray photoelectron spectroscopy and field emission scanning electron microscopy methods. The films were found to be amorphous, consisting only of three components: Hf-metal clusters, Hf4O7 suboxide and stoichiometric HfO2. The relative concentration of these components varies with changing x. The surface of the films contains the increased oxygen content compared to the bulk. It was found that the Hf4O7 suboxide concentration is maximal at x = 1.8. The concept of hafnium oxide film growth by the IBSD method is proposed to explain the lack of suboxides variety in the films and the instability of HfO2, when annealed at high temperature.

  18. Composition and conductance distributions of single GeSi quantum rings studied by conductive atomic force microscopy combined with selective chemical etching

    NASA Astrophysics Data System (ADS)

    Lv, Y.; Cui, J.; Jiang, Z. M.; Yang, X. J.

    2013-02-01

    Atomic force microscopy imaging combined with selective chemical etching is employed to quantitatively investigate three-dimensional (3D) composition distributions of single GeSi quantum rings (QRs). In addition, the 3D quantitative composition distributions and the corresponding conductance distributions are simultaneously obtained on the same single GeSi QRs by conductive atomic force microscopy combined with selective chemical etching, allowing us to investigate the correlations between the conductance and composition distributions of single QRs. The results show that the QRs’ central holes have higher Ge content, but exhibit lower conductance, indicating that the QRs’ conductance distribution is not consistent with their composition distribution. By comparing the topography, composition and conductance profiles of the same single QRs before and after different etching processes, it is found that the conductance distributions of GeSi QRs do not vary with the change of composition distribution. Instead, the QRs’ conductance distributions are found to be consistent with their topographic shapes, which can be supposed to be due to the shape determined electronic structures.

  19. Composition and conductance distributions of single GeSi quantum rings studied by conductive atomic force microscopy combined with selective chemical etching.

    PubMed

    Lv, Y; Cui, J; Jiang, Z M; Yang, X J

    2013-02-15

    Atomic force microscopy imaging combined with selective chemical etching is employed to quantitatively investigate three-dimensional (3D) composition distributions of single GeSi quantum rings (QRs). In addition, the 3D quantitative composition distributions and the corresponding conductance distributions are simultaneously obtained on the same single GeSi QRs by conductive atomic force microscopy combined with selective chemical etching, allowing us to investigate the correlations between the conductance and composition distributions of single QRs. The results show that the QRs' central holes have higher Ge content, but exhibit lower conductance, indicating that the QRs' conductance distribution is not consistent with their composition distribution. By comparing the topography, composition and conductance profiles of the same single QRs before and after different etching processes, it is found that the conductance distributions of GeSi QRs do not vary with the change of composition distribution. Instead, the QRs' conductance distributions are found to be consistent with their topographic shapes, which can be supposed to be due to the shape determined electronic structures.

  20. Exploring Conceptual Frameworks of Models of Atomic Structures and Periodic Variations, Chemical Bonding, and Molecular Shape and Polarity: A Comparison of Undergraduate General Chemistry Students with High and Low Levels of Content Knowledge

    ERIC Educational Resources Information Center

    Wang, Chia-Yu; Barrow, Lloyd H.

    2013-01-01

    The purpose of the study was to explore students' conceptual frameworks of models of atomic structure and periodic variations, chemical bonding, and molecular shape and polarity, and how these conceptual frameworks influence their quality of explanations and ability to shift among chemical representations. This study employed a purposeful sampling…

  1. The Nature of Atoms.

    ERIC Educational Resources Information Center

    Holden, Alan

    This monograph was written for the purpose of presenting physics to college students who are not preparing for careers in physics. It deals with the nature of atoms, and treats the following topics: (1) the atomic hypothesis, (2) the chemical elements, (3) models of an atom, (4) a particle in a one-dimensional well, (5) a particle in a central…

  2. Images of Atoms.

    ERIC Educational Resources Information Center

    Wright, Tony

    2003-01-01

    Recommends using a simple image, such as the fuzzy atom ball to help students develop a useful understanding of the molecular world. Explains that the image helps students easily grasp ideas about atoms and molecules and leads naturally to more advanced ideas of atomic structure, chemical bonding, and quantum physics. (Author/NB)

  3. Chemical, mechanical and sensory monitoring of hot air- and infrared-roasted hazelnuts (Corylus avellana L.) during nine months of storage.

    PubMed

    Belviso, Simona; Dal Bello, Barbara; Giacosa, Simone; Bertolino, Marta; Ghirardello, Daniela; Giordano, Manuela; Rolle, Luca; Gerbi, Vincenzo; Zeppa, Giuseppe

    2017-02-15

    Roasted hazelnuts can be consumed as whole nuts, or as an ingredient in the confectionary and bakery industries and are highly appreciated for their typical taste, aroma and crunchy texture. In this work, two hazelnut types (TGT, Ordu) from two harvests were roasted using two different systems (hot air, infrared) at different time/temperature combinations, and the evolution of oxidative stability, the total phenolic content (TPC), the antioxidant capacity, the mechanical and acoustic properties and the sensory perception were determined during storage. The results showed that the oxidative stability was increased by roasting hazelnuts at 120°C for 40min with hot air system. Similar overall trends were not found for the TPC, the antioxidant capacity and the mechanical-acoustic properties. However, for the maintenance of high antioxidant activity, a storage time of 6months at 4°C is recommended. The two roasting systems gave hazelnuts with significant sensory differences only at high roasting temperature.

  4. Chemical, mechanical and sensory monitoring of hot air- and infrared-roasted hazelnuts (Corylus avellana L.) during nine months of storage.

    PubMed

    Belviso, Simona; Dal Bello, Barbara; Giacosa, Simone; Bertolino, Marta; Ghirardello, Daniela; Giordano, Manuela; Rolle, Luca; Gerbi, Vincenzo; Zeppa, Giuseppe

    2017-02-15

    Roasted hazelnuts can be consumed as whole nuts, or as an ingredient in the confectionary and bakery industries and are highly appreciated for their typical taste, aroma and crunchy texture. In this work, two hazelnut types (TGT, Ordu) from two harvests were roasted using two different systems (hot air, infrared) at different time/temperature combinations, and the evolution of oxidative stability, the total phenolic content (TPC), the antioxidant capacity, the mechanical and acoustic properties and the sensory perception were determined during storage. The results showed that the oxidative stability was increased by roasting hazelnuts at 120°C for 40min with hot air system. Similar overall trends were not found for the TPC, the antioxidant capacity and the mechanical-acoustic properties. However, for the maintenance of high antioxidant activity, a storage time of 6months at 4°C is recommended. The two roasting systems gave hazelnuts with significant sensory differences only at high roasting temperature. PMID:27664651

  5. Determination and characterization of phytochelatins by liquid chromatography coupled with on line chemical vapour generation and atomic fluorescence spectrometric detection.

    PubMed

    Bramanti, Emilia; Toncelli, Daniel; Morelli, Elisabetta; Lampugnani, Leonardo; Zamboni, Roberto; Miller, Keith E; Zemetra, Joseph; D'Ulivo, Alessandro

    2006-11-10

    Liquid chromatography (LC) coupled on line with UV/visible diode array detector (DAD) and cold vapour generation atomic fluorescence spectrometry (CVGAFS) has been developed for the speciation, determination and characterization of phytochelatins (PCs). The method is based on a bidimensional approach, e.g. on the analysis of synthetic PC solutions (apo-PCs and Cd(2+)-complexed PCs) (i) by size exclusion chromatography coupled to UV diode array detector (SEC-DAD); (ii) by the derivatization of PC -SH groups in SEC fractions by p-hydroxymercurybenzoate (PHMB) and the indirect detection of PC-PHMB complexes by reversed phase liquid chromatography coupled to atomic fluorescence detector (RPLC-CVGAFS). MALDI-TOF/MS (matrix assisted laser desorption ionization time of flight mass spectrometry) analysis of underivatized synthetic PC samples was performed in order have a qualitative information of their composition. Quantitative analysis of synthetic PC solutions has been performed on the basis of peak area of PC-PHMB complexes of the mercury specific chromatogram and calibration curve of standard solution of glutathione (GSH) complexed to PHMB (GS-PHMB). The limit of quantitation (LOQ) in terms of GS-PHMB complex was 90 nM (CV 5%) with an injection volume of 35 microL, corresponding to 3.2 pmol (0.97 ng) of GSH. The method has been applied to analysis of extracts of cell cultures from Phaeodactylum tricornutum grown in Cd-containing nutrient solutions, analysed by SEC-DAD-CVGAFS and RPLC-DAD-CVGAFS.

  6. When Atoms Want

    ERIC Educational Resources Information Center

    Talanquer, Vicente

    2013-01-01

    Chemistry students and teachers often explain the chemical reactivity of atoms, molecules, and chemical substances in terms of purposes or needs (e.g., atoms want or need to gain, lose, or share electrons in order to become more stable). These teleological explanations seem to have pedagogical value as they help students understand and use…

  7. Influence of citric acid as chemical modifier for lead determination in dietary calcium supplement samples by graphite furnace atomic absorption spectrometry

    NASA Astrophysics Data System (ADS)

    Cezar Paz de Mattos, Julio; Medeiros Nunes, Adriane; Figueiredo Martins, Ayrton; Luiz Dressler, Valderi; Marlon de Moraes Flores, Érico

    2005-06-01

    Citric acid was used as a chemical modifier for Pb determination by graphite furnace atomic absorption spectrometry in dietary supplement samples (calcium carbonate, dolomite and oyster shell samples) and its efficiency was compared to the use of palladium. Pyrolysis and atomization curves were established without use of chemical modifier, with the addition of 20, 100 and 200 μg of citric acid, and with 3 μg of palladium. The citric acid modifier made possible the interference-free Pb determination in the presence of high concentrations of Ca and Mg nitrates. Acid sample digestion involving closed vessels (microwave-assisted and conventional heating) and acid attack using polypropylene vessels at room temperature were compared. All digestion procedures presented similar results for calcium carbonate and dolomite samples. However, for oyster shell samples accurate results were obtained only with the use of closed vessel systems. Analyte addition and matrix-matched standards were used for calibration. The characteristic mass for Pb using citric acid and palladium were 16 and 25 pg, respectively. The relative standard deviation (RSD) was always less than 5% when citric acid was used. The relative and absolute limits of detection were 0.02 μg g - 1 and 8 pg with citric acid and 0.1 μg g - 1 and 44 pg with the Pd modifier, respectively ( n = 10, 3σ). The recovery of Pb in spiked calcium supplement samples (10 μg l - 1 ) was between 98% and 105%. With the use of 100 μg of citric acid as chemical modifier, problems such as high background absorption and high RSD values were minimized in comparison to the addition of 3 μg of palladium.

  8. Search for methylamine in high mass hot cores

    NASA Astrophysics Data System (ADS)

    Ligterink, N. F. W.; Tenenbaum, E. D.; van Dishoeck, E. F.

    2015-04-01

    Aims: We aim to detect methylamine, CH3NH2, in a variety of hot cores and use it as a test for the importance of photon-induced chemistry in ice mantles and mobility of radicals. Specifically, CH3NH2 cannot be formed from atom addition to CO whereas other NH2-containing molecules such as formamide, NH2CHO, can. Methods: Submillimeter spectra of several massive hot core regions were taken with the James Clerk Maxwell Telescope (JCMT). Abundances are determined with the rotational diagram method where possible. Results: Methylamine is not detected, giving upper limit column densities between 1.9-6.4 × 1016 cm-2 for source sizes corresponding to the 100 K envelope radius. Combined with previously obtained JCMT data analysed in the same way, abundance ratios of CH3NH2, NH2CHO and CH3CN with respect to each other and to CH3OH are determined. These ratios are compared with Sagittarius B2 observations, where all species are detected, and to hot core models. Conclusions: The observed ratios suggest that both methylamine and formamide are overproduced by up to an order of magnitude in hot core models. Acetonitrile is however underproduced. The proposed chemical schemes leading to these molecules are discussed and reactions that need further laboratory studies are identified. The upper limits obtained in this paper can be used to guide future observations, especially with ALMA. Appendices are available in electronic form at http://www.aanda.org

  9. Atomic Layer Deposition of Chemical Passivation Layers and High Performance Anti-Reflection Coatings on Back-Illuminated Detectors

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E. (Inventor); Greer, Frank (Inventor); Nikzad, Shouleh (Inventor)

    2014-01-01

    A back-illuminated silicon photodetector has a layer of Al2O3 deposited on a silicon oxide surface that receives electromagnetic radiation to be detected. The Al2O3 layer has an antireflection coating deposited thereon. The Al2O3 layer provides a chemically resistant separation layer between the silicon oxide surface and the antireflection coating. The Al2O3 layer is thin enough that it is optically innocuous. Under deep ultraviolet radiation, the silicon oxide layer and the antireflection coating do not interact chemically. In one embodiment, the silicon photodetector has a delta-doped layer near (within a few nanometers of) the silicon oxide surface. The Al2O3 layer is expected to provide similar protection for doped layers fabricated using other methods, such as MBE, ion implantation and CVD deposition.

  10. Nonequilibrium electronic phenomena and the chemical energy accommodation during heterogeneous recombination of atomic hydrogen on the manganese doped willemite

    NASA Astrophysics Data System (ADS)

    Grankin, D. V.; Grankin, V. P.; Styrov, V. V.; Sushchikh, M.

    2016-03-01

    The surface chemiluminescence of Zn2SiO4-Mn phosphor (λmax = 525 nm) has been studied under excitation by exoergic interaction of H-atoms with its surface. We have found that the pre-irradiation of the Zn2SiO4-Mn by UV light results in the transient increase in the luminescence intensity by two orders of magnitude. On the other hand, deposition of Pd-nanoparticles on the surface leads to luminescence quenching. These two effects are associated with the energy accommodation in the gas-surface interaction via electronic channel by the filled electron traps of the insulating phosphor or by metallic electrons of the Pd-nanoparticles.

  11. Rocket-borne instrumentation for the measurement of atomic oxygen based on chemical release in the lower thermosphere

    NASA Astrophysics Data System (ADS)

    Vanhemelrijk, E.; Vanransbeek, E.

    Rocket-borne instrumentation, which determines atomic oxygen density as a function of altitude, was tested. A technique where NO gas is ejected in the backward direction of the flight is outlined. A 6.8 g explosive charge punches a 40 mm hole in the gas bottles. At 80 to 105 km altitude 99% of the gas is ejected within 0.07 sec over a 60 m release interval, assuming rocket velocity = 100 m/sec. The initial Gaussian radius of the cloud is 60 to 70 m, satisfying the point release principle. Cloud altitudes, and wind speeds are derived from ground based photographs. Oxygen concentration is determined by analyzing the chemiluminescence of the point releases. Rocket flights confirm the usefulness of the system.

  12. Physical/chemical properties of tin oxide thin film transistors prepared using plasma-enhanced atomic layer deposition

    SciTech Connect

    Lee, Byung Kook; Jung, Eunae; Kim, Seok Hwan; Moon, Dae Chul; Lee, Sun Sook; Park, Bo Keun; Hwang, Jin Ha; Chung, Taek-Mo; Kim, Chang Gyoun; An, Ki-Seok

    2012-10-15

    Thin film transistors (TFTs) with tin oxide films as the channel layer were fabricated by means of plasma enhanced atomic layer deposition (PE-ALD). The as-deposited tin oxide films show n-type conductivity and a nano-crystalline structure of SnO{sub 2}. Notwithstanding the relatively low deposition temperatures of 70, 100, and 130 °C, the bottom gate tin oxide TFTs show an on/off drain current ratio of 10{sup 6} while the device mobility values were increased from 2.31 cm{sup 2}/V s to 6.24 cm{sup 2}/V s upon increasing the deposition temperature of the tin oxide films.

  13. Low-Temperature Process for Atomic Layer Chemical Vapor Deposition of an Al2O3 Passivation Layer for Organic Photovoltaic Cells.

    PubMed

    Kim, Hoonbae; Lee, Jihye; Sohn, Sunyoung; Jung, Donggeun

    2016-05-01

    Flexible organic photovoltaic (OPV) cells have drawn extensive attention due to their light weight, cost efficiency, portability, and so on. However, OPV cells degrade quickly due to organic damage by water vapor or oxygen penetration when the devices are driven in the atmosphere without a passivation layer. In order to prevent damage due to water vapor or oxygen permeation into the devices, passivation layers have been introduced through methods such as sputtering, plasma enhanced chemical vapor deposition, and atomic layer chemical vapor deposition (ALCVD). In this work, the structural and chemical properties of Al2O3 films, deposited via ALCVD at relatively low temperatures of 109 degrees C, 200 degrees C, and 300 degrees C, are analyzed. In our experiment, trimethylaluminum (TMA) and H2O were used as precursors for Al2O3 film deposition via ALCVD. All of the Al2O3 films showed very smooth, featureless surfaces without notable defects. However, we found that the plastic flexible substrate of an OPV device passivated with 300 degrees C deposition temperature was partially bended and melted, indicating that passivation layers for OPV cells on plastic flexible substrates need to be formed at temperatures lower than 300 degrees C. The OPV cells on plastic flexible substrates were passivated by the Al2O3 film deposited at the temperature of 109 degrees C. Thereafter, the photovoltaic properties of passivated OPV cells were investigated as a function of exposure time under the atmosphere. PMID:27483916

  14. How Iron-Containing Proteins Control Dioxygen Chemistry: A Detailed Atomic Level Description Via Accurate Quantum Chemical and Mixed Quantum Mechanics/Molecular Mechanics Calculations.

    SciTech Connect

    Friesner, Richard A.; Baik, Mu-Hyun; Gherman, Benjamin F.; Guallar, Victor; Wirstam, Maria E.; Murphy, Robert B.; Lippard, Stephen J.

    2003-03-01

    Over the past several years, rapid advances in computational hardware, quantum chemical methods, and mixed quantum mechanics/molecular mechanics (QM/MM) techniques have made it possible to model accurately the interaction of ligands with metal-containing proteins at an atomic level of detail. In this paper, we describe the application of our computational methodology, based on density functional (DFT) quantum chemical methods, to two diiron-containing proteins that interact with dioxygen: methane monooxygenase (MMO) and hemerythrin (Hr). Although the active sites are structurally related, the biological function differs substantially. MMO is an enzyme found in methanotrophic bacteria and hydroxylates aliphatic C-H bonds, whereas Hr is a carrier protein for dioxygen used by a number of marine invertebrates. Quantitative descriptions of the structures and energetics of key intermediates and transition states involved in the reaction with dioxygen are provided, allowing their mechanisms to be compared and contrasted in detail. An in-depth understanding of how the chemical identity of the first ligand coordination shell, structural features, electrostatic and van der Waals interactions of more distant shells control ligand binding and reactive chemistry is provided, affording a systematic analysis of how iron-containing proteins process dioxygen. Extensive contact with experiment is made in both systems, and a remarkable degree of accuracy and robustness of the calculations is obtained from both a qualitative and quantitative perspective.

  15. Low-Temperature Process for Atomic Layer Chemical Vapor Deposition of an Al2O3 Passivation Layer for Organic Photovoltaic Cells.

    PubMed

    Kim, Hoonbae; Lee, Jihye; Sohn, Sunyoung; Jung, Donggeun

    2016-05-01

    Flexible organic photovoltaic (OPV) cells have drawn extensive attention due to their light weight, cost efficiency, portability, and so on. However, OPV cells degrade quickly due to organic damage by water vapor or oxygen penetration when the devices are driven in the atmosphere without a passivation layer. In order to prevent damage due to water vapor or oxygen permeation into the devices, passivation layers have been introduced through methods such as sputtering, plasma enhanced chemical vapor deposition, and atomic layer chemical vapor deposition (ALCVD). In this work, the structural and chemical properties of Al2O3 films, deposited via ALCVD at relatively low temperatures of 109 degrees C, 200 degrees C, and 300 degrees C, are analyzed. In our experiment, trimethylaluminum (TMA) and H2O were used as precursors for Al2O3 film deposition via ALCVD. All of the Al2O3 films showed very smooth, featureless surfaces without notable defects. However, we found that the plastic flexible substrate of an OPV device passivated with 300 degrees C deposition temperature was partially bended and melted, indicating that passivation layers for OPV cells on plastic flexible substrates need to be formed at temperatures lower than 300 degrees C. The OPV cells on plastic flexible substrates were passivated by the Al2O3 film deposited at the temperature of 109 degrees C. Thereafter, the photovoltaic properties of passivated OPV cells were investigated as a function of exposure time under the atmosphere.

  16. Integral equation model for warm and hot dense mixtures.

    PubMed

    Starrett, C E; Saumon, D; Daligault, J; Hamel, S

    2014-09-01

    In a previous work [C. E. Starrett and D. Saumon, Phys. Rev. E 87, 013104 (2013)] a model for the calculation of electronic and ionic structures of warm and hot dense matter was described and validated. In that model the electronic structure of one atom in a plasma is determined using a density-functional-theory-based average-atom (AA) model and the ionic structure is determined by coupling the AA model to integral equations governing the fluid structure. That model was for plasmas with one nuclear species only. Here we extend it to treat plasmas with many nuclear species, i.e., mixtures, and apply it to a carbon-hydrogen mixture relevant to inertial confinement fusion experiments. Comparison of the predicted electronic and ionic structures with orbital-free and Kohn-Sham molecular dynamics simulations reveals excellent agreement wherever chemical bonding is not significant.

  17. Precisely detecting atomic position of atomic intensity images.

    PubMed

    Wang, Zhijun; Guo, Yaolin; Tang, Sai; Li, Junjie; Wang, Jincheng; Zhou, Yaohe

    2015-03-01

    We proposed a quantitative method to detect atomic position in atomic intensity images from experiments such as high-resolution transmission electron microscopy, atomic force microscopy, and simulation such as phase field crystal modeling. The evaluation of detection accuracy proves the excellent performance of the method. This method provides a chance to precisely determine atomic interactions based on the detected atomic positions from the atomic intensity image, and hence to investigate the related physical, chemical and electrical properties.

  18. Theoretical studies of atomic properties and chemical stabilities in acid solutions of element Uus (Z=117) and Astatine

    NASA Astrophysics Data System (ADS)

    Chang, Z. W.; Li, J. G.; Dong, C. Z.

    2012-11-01

    Multi-configuration Dirac-Fock (MCDF) method was employed to calculate the first five ionization potentials, electron affinities, resonance excitation energies, oscillator strengths and radii for the element Uus and its homologue At. Main valence correlation effects were taken into account. The Breit interaction and QED effects were also estimated. The uncertainties of calculated IPs, EAs and IR for Uus and At were reduced through an extrapolation procedure. The good consistency with available experimental and other theoretical values demonstrates the validity of the present results. These theoretical data were further used to predict the chemical stabilities of element Uus and At in acid solutions.

  19. Hot Meetings

    NASA Technical Reports Server (NTRS)

    Chiu, Mary

    2002-01-01

    A colleague walked by my office one time as I was conducting a meeting. There were about five or six members of my team present. The colleague, a man who had been with our institution (The Johns Hopkins Applied Physics Lab, a.k.a. APL) for many years, could not help eavesdropping. He said later it sounded like we we re having a raucous argument, and he wondered whether he should stand by the door in case things got out of hand and someone threw a punch. Our Advanced Composition Explorer (ACE) team was a hot group, to invoke the language that is fashionable today, although we never thought of ourselves in those terms. It was just our modus operandi. The tenor of the discussion got loud and volatile at times, but I prefer to think of it as animated, robust, or just plain collaborative. Mary Chiu and her "hot" team from the Johns Hopkins Applied Physics Laboratory built the Advanced Composition Explorer spacecraft for NASA. Instruments on the spacecraft continue to collect data that inform us about what's happening on our most important star, the Sun.

  20. Mapping chemical disorder and ferroelectric distortions in the double perovskite compound Sr 2-x Gd x MnTiO6 by atomic resolution electron microscopy and spectroscopy.

    PubMed

    Biškup, Neven; Álvarez-Serrano, Inmaculada; Veiga, Maria; Rivera-Calzada, Alberto; Garcia-Hernandez, Mar; Pennycook, Stephen J; Varela, Maria

    2014-06-01

    In this work we report a study of the chemical and structural order of the double perovskite compound Sr 2-x Gd x MnTiO6 for compositions x=0, 0.25, 0.5, 0.75, and 1. A noticeable disorder at the B-site in the Mn and Ti sublattice is detected at the atomic scale by electron energy-loss spectroscopy for all x values, resulting in Mn-rich and Ti-rich regions. For x ≥ 0.75, the cubic unit cell doubles and lowers its symmetry because of structural rearrangements associated with a giant ferroelectric displacement of the perovskite B-site cation. We discuss this finding in the light of the large electroresistance observed in Sr 2-x Gd x MnTiO6, x ≥ 0.75.

  1. Small Atomic Orbital Basis Set First-Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources.

    PubMed

    Sure, Rebecca; Brandenburg, Jan Gerit; Grimme, Stefan

    2016-04-01

    In quantum chemical computations the combination of Hartree-Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double-zeta quality is still widely used, for example, in the popular B3LYP/6-31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean-field methods. PMID:27308221

  2. Small Atomic Orbital Basis Set First-Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources.

    PubMed

    Sure, Rebecca; Brandenburg, Jan Gerit; Grimme, Stefan

    2016-04-01

    In quantum chemical computations the combination of Hartree-Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double-zeta quality is still widely used, for example, in the popular B3LYP/6-31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean-field methods.

  3. Small Atomic Orbital Basis Set First‐Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources

    PubMed Central

    Sure, Rebecca; Brandenburg, Jan Gerit

    2015-01-01

    Abstract In quantum chemical computations the combination of Hartree–Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double‐zeta quality is still widely used, for example, in the popular B3LYP/6‐31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean‐field methods. PMID:27308221

  4. Atomic layer deposition of Al{sub 2}O{sub 3} on germanium-tin (GeSn) and impact of wet chemical surface pre-treatment

    SciTech Connect

    Gupta, Suyog Chen, Robert; Harris, James S.; Saraswat, Krishna C.

    2013-12-09

    GeSn is quickly emerging as a potential candidate for high performance Si-compatible transistor technology. Fabrication of high-ĸ gate stacks on GeSn with good interface properties is essential for realizing high performance field effect transistors based on this material system. We demonstrate an effective surface passivation scheme for n-Ge{sub 0.97}Sn{sub 0.03} alloy using atomic layer deposition (ALD) of Al{sub 2}O{sub 3}. The effect of pre-ALD wet chemical surface treatment is analyzed and shown to be critical in obtaining a good quality interface between GeSn and Al{sub 2}O{sub 3}. Using proper surface pre-treatment, mid-gap trap density for the Al{sub 2}O{sub 3}/GeSn interface of the order of 10{sup 12} cm{sup −2} has been achieved.

  5. Novel chemical route for atomic layer deposition of MoS2 thin film on SiO2/Si substrate

    NASA Astrophysics Data System (ADS)

    JinThese Authors Equally Contributed To This Work., Zhenyu; Shin, Seokhee; Kwon, Do Hyun; Han, Seung-Joo; Min, Yo-Sep

    2014-11-01

    Recently MoS2 with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS2 due to a lack of suitable chemistry. Here we report MoS2 growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS2 can be directly grown on a SiO2/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E12g and A1g) of 2H-MoS2 with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS2 layers to be aligned with its basal plane parallel to the substrate.Recently MoS2 with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS2 due to a lack of suitable chemistry. Here we report MoS2 growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS2 can be directly grown on a SiO2/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E12g and A1g) of 2H-MoS2 with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS2 layers to be aligned with its basal plane parallel to the substrate. Electronic supplementary

  6. Energy partitioning in polyatomic chemical reactions: Quantum state resolved studies of highly exothermic atom abstraction reactions from molecules in the gas phase and at the gas-liquid interface

    NASA Astrophysics Data System (ADS)

    Zolot, Alexander M.

    This thesis recounts a series of experiments that interrogate the dynamics of elementary chemical reactions using quantum state resolved measurements of gas-phase products. The gas-phase reactions F + HCl → HF + Cl and F + H2O → HF + OH are studied using crossed supersonic jets under single collision conditions. Infrared (IR) laser absorption probes HF product with near shot-noise limited sensitivity and high resolution, capable of resolving rovibrational states and Doppler lineshapes. Both reactions yield inverted vibrational populations. For the HCl reaction, strongly bimodal rotational distributions are observed, suggesting microscopic branching of the reaction mechanism. Alternatively, such structure may result from a quantum-resonance mediated reaction similar to those found in the well-characterized F + HD system. For the H2O reaction, a small, but significant, branching into v = 2 is particularly remarkable because this manifold is accessible only via the additional center of mass collision energy in the crossed jets. Rotationally hyperthermal HF is also observed. Ab initio calculations of the transition state geometry suggest mechanisms for both rotational and vibrational excitation. Exothermic chemical reaction dynamics at the gas-liquid interface have been investigated by colliding a supersonic jet of F atoms with liquid squalane (C30H62), a low vapor pressure hydrocarbon compatible with the high vacuum environment. IR spectroscopy provides absolute HF( v,J) product densities and Doppler resolved velocity component distributions perpendicular to the surface normal. Compared to analogous gas-phase F + hydrocarbon reactions, the liquid surface is a more effective "heat sink," yet vibrationally excited populations reveal incomplete thermal accommodation with the surface. Non-Boltzmann J-state populations and hot Doppler lineshapes that broaden with HF excitation indicate two competing scattering mechanisms: (i) a direct reactive scattering channel

  7. Universal Transfer and Stacking of Chemical Vapor Deposition Grown Two-Dimensional Atomic Layers with Water-Soluble Polymer Mediator.

    PubMed

    Lu, Zhixing; Sun, Lifei; Xu, Guanchen; Zheng, Jingying; Zhang, Qi; Wang, Jingyi; Jiao, Liying

    2016-05-24

    Chemical vapor deposition (CVD) has shown great potential in synthesizing various high-quality two-dimensional (2D) transition metal dichalcogenides (TMDCs). However, the nondestruction transfer of these CVD-grown 2D TMDCs at a high yield remains a key challenge for applying these emerging materials in various aspects. To address this challenge, we designed a water-soluble transfer mediator consisting of two polymers, polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA), which can form strong interactions with CVD-grown 2D TMDCs for the nondestruction transfer of these materials. With this mediator, we realized the physical transfer of CVD-grown MoS2 flakes and several other 2D TMDCs, including 2D alloys and heterostructures to a wide range of substrates at a high yield of >90% with well-retained properties as evidenced by various microscopic, spectroscopic, and electrical measurements. Field-effect transistors (FETs) made on thus-transferred CVD-grown MoS2 monolayers exhibited obviously higher mobility than those transferred by chemical method. We also constructed several artificial 2D crystals showing very strong interlayer coupling by the multiple transfer of CVD-grown 2D TMDCs monolayers with this approach. This transfer approach will make versatile CVD-grown 2D materials and their artificial stacks with pristine qualities easily accessible for both fundamental studies and practical applications. PMID:27158832

  8. Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition

    SciTech Connect

    Liu, Zheng; Amani, Matin; Najmaei, Sina; Xu, Quan; Zou, Xiaolong; Zhou, Wu; Yu, Ting; Qiu, Caiyu; Birdwell, A. Glen; Crowne, Frank J.; Vajtai, Robert; Yakobson, Boris I.; Xia, Zhenhai; Dubey, Madan; Ajayan, Pulickel M.; Lou, Jun

    2014-11-18

    Monolayer molybdenum disulfide (MoS2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices, and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS2. Recently, large-size monolayer MoS2 has been produced by chemical vapor deposition but has not yet been fully explored. Here we systematically characterize chemical vapor deposition grown MoS2 by PL spectroscopy and mapping, and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced band gap engineering. We also evaluate the effective strain transferred from polymer substrates to MoS2 by three-dimensional finite element analysis. In addition, our work demonstrates that PL mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS2.

  9. Atomic MoS2 monolayers synthesized from a metal-organic complex by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Liu, Lina; Qiu, Hailong; Wang, Jingyi; Xu, Guanchen; Jiao, Liying

    2016-02-01

    The controllable synthesis of MoS2 monolayers is the key challenge for their practical applications. Here we report the chemical vapor deposition (CVD) growth of single layered MoS2 by utilizing a bifunctional precursor. This precursor is a metal-organic complex which supplies both Mo sources and organic seeding promoters for the efficient CVD growth of MoS2 monolayers. The successful growth of high quality MoS2 flakes indicates that the rational design of bifunctional precursors will open up a new way for the controllable CVD growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs).The controllable synthesis of MoS2 monolayers is the key challenge for their practical applications. Here we report the chemical vapor deposition (CVD) growth of single layered MoS2 by utilizing a bifunctional precursor. This precursor is a metal-organic complex which supplies both Mo sources and organic seeding promoters for the efficient CVD growth of MoS2 monolayers. The successful growth of high quality MoS2 flakes indicates that the rational design of bifunctional precursors will open up a new way for the controllable CVD growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs). Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr09089j

  10. Universal Transfer and Stacking of Chemical Vapor Deposition Grown Two-Dimensional Atomic Layers with Water-Soluble Polymer Mediator.

    PubMed

    Lu, Zhixing; Sun, Lifei; Xu, Guanchen; Zheng, Jingying; Zhang, Qi; Wang, Jingyi; Jiao, Liying

    2016-05-24

    Chemical vapor deposition (CVD) has shown great potential in synthesizing various high-quality two-dimensional (2D) transition metal dichalcogenides (TMDCs). However, the nondestruction transfer of these CVD-grown 2D TMDCs at a high yield remains a key challenge for applying these emerging materials in various aspects. To address this challenge, we designed a water-soluble transfer mediator consisting of two polymers, polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA), which can form strong interactions with CVD-grown 2D TMDCs for the nondestruction transfer of these materials. With this mediator, we realized the physical transfer of CVD-grown MoS2 flakes and several other 2D TMDCs, including 2D alloys and heterostructures to a wide range of substrates at a high yield of >90% with well-retained properties as evidenced by various microscopic, spectroscopic, and electrical measurements. Field-effect transistors (FETs) made on thus-transferred CVD-grown MoS2 monolayers exhibited obviously higher mobility than those transferred by chemical method. We also constructed several artificial 2D crystals showing very strong interlayer coupling by the multiple transfer of CVD-grown 2D TMDCs monolayers with this approach. This transfer approach will make versatile CVD-grown 2D materials and their artificial stacks with pristine qualities easily accessible for both fundamental studies and practical applications.

  11. Investigation of chemical modifiers for the direct determination of arsenic in fish oil using high-resolution continuum source graphite furnace atomic absorption spectrometry.

    PubMed

    Pereira, Éderson R; de Almeida, Tarcísio S; Borges, Daniel L G; Carasek, Eduardo; Welz, Bernhard; Feldmann, Jörg; Campo Menoyo, Javier Del

    2016-04-01

    High-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) has been applied for the development of a method for the determination of total As in fish oil samples using direct analysis. The method does not use any sample pretreatment, besides dilution with 1-propanole, in order to decrease the oil viscosity. The stability and sensitivity of As were evaluated using ruthenium and iridium as permanent chemical modifiers and palladium added in solution over the sample. The best results were obtained with ruthenium as the permanent modifier and palladium in solution added to samples and standard solutions. Under these conditions, aqueous standard solutions could be used for calibration for the fish oil samples diluted with 1-propanole. The pyrolysis and atomization temperatures were 1400 °C and 2300 °C, respectively, and the limit of detection and characteristic mass were 30 pg and 43 pg, respectively. Accuracy and precision of the method have been evaluated using microwave-assisted acid digestion of the samples with subsequent determination by HR-CS GF AAS and ICP-MS; the results were in agreement (95% confidence level) with those of the proposed method.

  12. Reactions of laser-ablated U atoms with HF: infrared spectra and quantum chemical calculations of HUF, UH, and UF in noble gas solids.

    PubMed

    Vent-Schmidt, Thomas; Andrews, Lester; Riedel, Sebastian

    2015-03-19

    Reactions of laser-ablated U atoms with HF produce HUF as the major product and UH and UF as minor products, which are identified from their argon and neon matrix infrared spectra. Our assignment of HUF is confirmed by the observation of DUF and close agreement with observed and calculated vibrational frequencies and deuterium shifts in the vibrational frequencies. Our previous observation of the UH diatomic molecule from argon matrix experiments with H2, HD, and D2 as reagents is confirmed through its present observation with HF and DF, and with recent higher level quantum chemical calculations. The HF reaction provides a lower concentration of F in the system and thus simplifies the fluorine chemistry relative to similar U atom reactions with F2, and the new matrix identification of UF here is consistent with recent high level calculations on UF. In addition, we find evidence for the higher oxidation state secondary reaction products UHF2, UHF3, and UH2F2. PMID:25080179

  13. Atomic-scale and pit-free flattening of GaN by combination of plasma pretreatment and time-controlled chemical mechanical polishing

    SciTech Connect

    Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya

    2015-08-03

    Chemical mechanical polishing (CMP) combined with atmospheric-pressure plasma pretreatment was applied to a GaN (0001) substrate. The irradiation of a CF{sub 4}-containing plasma was proven to be very useful for modifying the surface of GaN. When CMP was conducted on a plasma-irradiated surface, a modified layer of GaF{sub 3} acted as a protective layer on GaN by preventing the formation of etch pits. Within a short duration (8 min) of CMP using a commercially available CeO{sub 2} slurry, an atomically flat surface with a root mean square (rms) roughness of 0.11 nm was obtained. Moreover, etch pits, which are inevitably introduced in conventional CMP, could not be observed at the dislocation sites on the polished GaN surface. It was revealed that CMP combined with the plasma pretreatment was very effective for obtaining a pit-free and atomically flat GaN surface.

  14. From gas-phase to liquid-water chemical reactions: the fluorine atom plus water trimer system.

    PubMed

    Li, Guoliang; Li, Qian-Shu; Xie, Yaoming; Schaefer, Henry F

    2015-09-14

    The potential energy profile for the F+(H2 O)3 →HF+(H2 O)2 OH reaction has been investigated using the "gold standard" CCSD(T) method with correlation-consistent basis sets up to cc-pVQZ. Four different reaction pathways have been found and these are related, both geometrically and energetically. The entrance complexes F⋅⋅⋅(H2 O)3 for all four reaction pathways are found lying ca. 7 kcal mol(-1) below the separated reactants F+(H2 O)3 . The four reaction barriers on their respective reaction coordinates lie ca. 4 kcal mol(-1) below the reactants. There are also corresponding exit complexes HF⋅⋅⋅(H2 O)2 OH, lying about 13 kcal mol(-1) below the separated products HF+(H2 O)2 OH. Compared with analogous F+(H2 O)2 and F+H2 O reactions, the F+(H2 O)3 reaction is somewhat similar to the former but qualitatively different from the latter. It may be reasonable to predict that the reactions between atomic fluorine and water tetramer (or even larger water clusters) may be similar to the F+(H2 O)3 reaction.

  15. Encapsulation of redox polysulphides via chemical interaction with nitrogen atoms in the organic linkers of metal-organic framework nanocrystals

    PubMed Central

    Park, Jung Hyo; Choi, Kyung Min; Lee, Dong Ki; Moon, Byeong Cheul; Shin, Sang Rim; Song, Min-Kyu; Kang, Jeung Ku

    2016-01-01

    Lithium polysulphides generated during discharge in the cathode of a lithium-sulphur redox cell are important, but their dissolution into the electrolyte from the cathode during each redox cycle leads to a shortened cycle life. Herein, we use in situ spectroelectrochemical measurements to demonstrate that sp2 nitrogen atoms in the organic linkers of nanocrystalline metal-organic framework-867 (nMOF-867) are able to encapsulate lithium polysulphides inside the microcages of nMOF-867, thus helping to prevent their dissolution into the electrolyte during discharge/charge cycles. This encapsulation mechanism of lithiated/delithiated polysulphides was further confirmed by observations of shifted FTIR spectra for the C = N and C-N bonds, the XPS spectra for the Li-N bonds from nMOF-867, and a visualization method, demonstrating that nMOF-867 prevents lithium polysulphides from being dissolved in the electrolyte. Indeed, a cathode fabricated using nMOF-867 exhibited excellent capacity retention over a long cycle life of 500 discharge/charge cycles, with a capacity loss of approximately 0.027% per cycle from a discharge capacity of 788 mAh/g at a high current rate of 835 mA/g. PMID:27149405

  16. Determination of nickel in saliva by electrothermal atomic absorption spectrometry using various chemical modifiers with Zeeman-effect background correction.

    PubMed

    Burguera, E; Sanchez de Briceño, A; Rondon, C E; Burguera, J L; Burguera, M; Carrero, P

    1998-07-01

    The profile of nickel signal using electrothermal atomic absorption spectrometry with deuterium and Zeeman-effect background correction is presented. The Zeeman effect system of background correction offered definitive advantages and therefore was used for the determination of nickel in saliva in the presence of various isomorphous metals. The highest nickel absorbance values corresponded at 200, 300, 300, 300, 600, and 200 ng of Tb, Mg, Sm, Lu, Tm, and Pd, respectively. On the other hand, the addition of Eu, Er, and Ho decreased the nickel signal. The presence on each modifier alone does not eliminate the matrix interference. However, the use of 200 ng of Pd in conjuction with 300 ng of Lu has a higher sensitivity, offers an advantage against interference from the background of saliva matrix and produces good recoveries (98 to 102% from unspiked and spiked saliva samples). The limit of detection was 0.11 micrograms/L for a characteristic mass of 16.6 pg of nickel using Pd-Lu as modifier. The within-batch precision varied between 0.8 and 1.5% relative standard deviations. The analysis of thirty samples of whole saliva gave an average of 0.81 +/- 0.30 of micrograms/L of Ni (range from 0.5 to 2.0 micrograms/L of Ni). The agreement between the observed and certified values obtained from a Seronorm Blood Serum Standard Reference Material was good.

  17. Encapsulation of redox polysulphides via chemical interaction with nitrogen atoms in the organic linkers of metal-organic framework nanocrystals

    NASA Astrophysics Data System (ADS)

    Park, Jung Hyo; Choi, Kyung Min; Lee, Dong Ki; Moon, Byeong Cheul; Shin, Sang Rim; Song, Min-Kyu; Kang, Jeung Ku

    2016-05-01

    Lithium polysulphides generated during discharge in the cathode of a lithium-sulphur redox cell are important, but their dissolution into the electrolyte from the cathode during each redox cycle leads to a shortened cycle life. Herein, we use in situ spectroelectrochemical measurements to demonstrate that sp2 nitrogen atoms in the organic linkers of nanocrystalline metal-organic framework-867 (nMOF-867) are able to encapsulate lithium polysulphides inside the microcages of nMOF-867, thus helping to prevent their dissolution into the electrolyte during discharge/charge cycles. This encapsulation mechanism of lithiated/delithiated polysulphides was further confirmed by observations of shifted FTIR spectra for the C = N and C-N bonds, the XPS spectra for the Li-N bonds from nMOF-867, and a visualization method, demonstrating that nMOF-867 prevents lithium polysulphides from being dissolved in the electrolyte. Indeed, a cathode fabricated using nMOF-867 exhibited excellent capacity retention over a long cycle life of 500 discharge/charge cycles, with a capacity loss of approximately 0.027% per cycle from a discharge capacity of 788 mAh/g at a high current rate of 835 mA/g.

  18. Encapsulation of redox polysulphides via chemical interaction with nitrogen atoms in the organic linkers of metal-organic framework nanocrystals.

    PubMed

    Park, Jung Hyo; Choi, Kyung Min; Lee, Dong Ki; Moon, Byeong Cheul; Shin, Sang Rim; Song, Min-Kyu; Kang, Jeung Ku

    2016-01-01

    Lithium polysulphides generated during discharge in the cathode of a lithium-sulphur redox cell are important, but their dissolution into the electrolyte from the cathode during each redox cycle leads to a shortened cycle life. Herein, we use in situ spectroelectrochemical measurements to demonstrate that sp(2) nitrogen atoms in the organic linkers of nanocrystalline metal-organic framework-867 (nMOF-867) are able to encapsulate lithium polysulphides inside the microcages of nMOF-867, thus helping to prevent their dissolution into the electrolyte during discharge/charge cycles. This encapsulation mechanism of lithiated/delithiated polysulphides was further confirmed by observations of shifted FTIR spectra for the C = N and C-N bonds, the XPS spectra for the Li-N bonds from nMOF-867, and a visualization method, demonstrating that nMOF-867 prevents lithium polysulphides from being dissolved in the electrolyte. Indeed, a cathode fabricated using nMOF-867 exhibited excellent capacity retention over a long cycle life of 500 discharge/charge cycles, with a capacity loss of approximately 0.027% per cycle from a discharge capacity of 788 mAh/g at a high current rate of 835 mA/g. PMID:27149405

  19. Chemical ordering of Co and Ni in a W-(AlCoNi) crystalline approximant related to Al-Co-Ni decagonal quasicrystals studied by atomic resolution energy-dispersive X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Yasuhara, Akira; Hiraga, Kenji

    2015-01-01

    A W-(AlCoNi) crystalline approximant, which is closely related to Al-Co-Ni decagonal quasicrystals, in an Al72.5Co20Ni7.5 alloy has been studied by atomic resolution energy-dispersive X-ray spectroscopy (EDS), in an instrument attached to a spherical aberration (Cs)-corrected scanning transmission electron microscope. On high-resolution EDS maps of Co and Ni elements, obtained by integrating many sets of EDS data taken from undamaged areas, chemical ordering of Co and Ni is clearly detected. In the structure of the W-(AlCoNi) phase, consisting of arrangements of transition-metal (TM) atoms located at vertices of pentagonal tilings and pentagonal arrangements of mixed sites (MSs) of TM and Al atoms, Co atoms occupy the TM atom positions with the pentagonal tiling and Ni is enriched in part of the pentagonal arrangements of MSs.

  20. Photocurrent detection of chemically tuned hierarchical ZnO nanostructures grown on seed layers formed by atomic layer deposition

    PubMed Central

    2012-01-01

    We demonstrate the morphological control method of ZnO nanostructures by atomic layer deposition (ALD) on an Al2O3/ZnO seed layer surface and the application of a hierarchical ZnO nanostructure for a photodetector. Two layers of ZnO and Al2O3 prepared using ALD with different pH values in solution coexisted on the alloy film surface, leading to deactivation of the surface hydroxyl groups. This surface complex decreased the ZnO nucleation on the seed layer surface, and thereby effectively screened the inherent surface polarity of ZnO. As a result, a 2-D zinc hydroxyl compound nanosheet was produced. With increasing ALD cycles of ZnO in the seed layer, the nanostructure morphology changes from 2-D nanosheet to 1-D nanorod due to the recovery of the natural crystallinity and polarity of ZnO. The thin ALD ZnO seed layer conformally covers the complex nanosheet structure to produce a nanorod, then a 3-D, hierarchical ZnO nanostructure was synthesized using a combined hydrothermal and ALD method. During the deposition of the ALD ZnO seed layer, the zinc hydroxyl compound nanosheets underwent a self-annealing process at 150 °C, resulting in structural transformation to pure ZnO 3-D nanosheets without collapse of the intrinsic morphology. The investigation on band electronic properties of ZnO 2-D nanosheet and 3-D hierarchical structure revealed noticeable variations depending on the richness of Zn-OH in each morphology. The improved visible and ultraviolet photocurrent characteristics of a photodetector with the active region using 3-D hierarchical structure against those of 2-D nanosheet structure were achieved. PMID:22672780

  1. Metallorganic chemical vapor deposition and atomic layer deposition approaches for the growth of hafnium-based thin films from dialkylamide precursors for advanced CMOS gate stack applications

    NASA Astrophysics Data System (ADS)

    Consiglio, Steven P.

    To continue the rapid progress of the semiconductor industry as described by Moore's Law, the feasibility of new material systems for front end of the line (FEOL) process technologies needs to be investigated, since the currently employed polysilicon/SiO2-based transistor system is reaching its fundamental scaling limits. Revolutionary breakthroughs in complementary-metal-oxide-semiconductor (CMOS) technology were recently announced by Intel Corporation and International Business Machines Corporation (IBM), with both organizations revealing significant progress in the implementation of hafnium-based high-k dielectrics along with metal gates. This announcement was heralded by Gordon Moore as "...the biggest change in transistor technology since the introduction of polysilicon gate MOS transistors in the late 1960s." Accordingly, the study described herein focuses on the growth of Hf-based dielectrics and Hf-based metal gates using chemical vapor-based deposition methods, specifically metallorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD). A family of Hf source complexes that has received much attention recently due to their desirable properties for implementation in wafer scale manufacturing is the Hf dialkylamide precursors. These precursors are room temperature liquids and possess sufficient volatility and desirable decomposition characteristics for both MOCVD and ALD processing. Another benefit of using these sources is the existence of chemically compatible Si dialkylamide sources as co-precursors for use in Hf silicate growth. The first part of this study investigates properties of MOCVD-deposited HfO2 and HfSixOy using dimethylamido Hf and Si precursor sources using a customized MOCVD reactor. The second part of this study involves a study of wet and dry surface pre-treatments for ALD growth of HfO2 using tetrakis(ethylmethylamido)hafnium in a wafer scale manufacturing environment. The third part of this study is an investigation of

  2. An improved high performance liquid chromatography-photodiode array detection-atmospheric pressure chemical ionization-mass spectrometry method for determination of chlorophylls and their derivatives in freeze-dried and hot-air-dried Rhinacanthus nasutus (L.) Kurz.

    PubMed

    Kao, Tsai Hua; Chen, Chia Ju; Chen, Bing Huei

    2011-10-30

    Rhinacanthus nasutus (L.) Kurz, a traditional Chinese herb possessing antioxidant and anti-cancer activities, has been reported to contain functional components like carotenoids and chlorophylls. However, the variety and amount of chlorophylls remain uncertain. The objectives of this study were to develop a high performance liquid chromatography-photodiode array detection-atmospheric pressure chemical ionization-mass spectrometry (HPLC-DAD-APCI-MS) method for determination of chlorophylls and their derivatives in hot-air-dried and freeze-dried R. nasutus. An Agilent Eclipse XDB-C18 column and a gradient mobile phase composed of methanol/N,N-dimethylformamide (97:3, v/v), acetonitrile and acetone were employed to separate internal standard zinc-phthalocyanine plus 12 cholorophylls and their derivatives within 21 min, including chlorophyll a, chlorophyll a', hydroxychlorophyll a, 15-OH-lactone chlorophyll a, chlorophyll b, chlorophyll b', hydroxychlorophyll b, pheophytin a, pheophytin a', hydroxypheophytin a, hydroxypheophytin a' and pheophytin b in hot-air-dried R. nasutus with flow rate at 1 mL/min and detection at 660 nm. But, in freeze-dried R. nasutus, only 4 chlorophylls and their derivatives, including chlorophyll a, chlorophyll a', chlorophyll b and pheophytin a were detected. Zinc-phthalocyanine was found to be an appropriate internal standard to quantify all the chlorophyll compounds. After quantification by HPLC-DAD, both chlorophyll a and pheophytin a were the most abundant in hot-air-dried R. nasutus, while in freeze-dried R. nasutus, chlorophyll a and chlorophyll b dominated. PMID:22063550

  3. Influence of krypton atoms on the structure of hydrogenated amorphous carbon deposited by plasma enhanced chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Oliveira, M. H.; Viana, G. A.; de Lima, M. M.; Cros, A.; Cantarero, A.; Marques, F. C.

    2010-12-01

    Hydrogenated amorphous carbon (a-C:H) films were prepared by plasma enhanced chemical vapor deposition using methane (CH4) plus krypton (Kr) mixed atmosphere. The depositions were performed as function of the bias voltage and krypton partial pressure. The goal of this work was to study the influence of krypton gas on the physical properties of a-C:H films deposited on the cathode electrode. Krypton concentration up to 1.6 at. %, determined by Rutherford Back-Scattering, was obtained at high Kr partial pressure and bias of -120 V. The structure of the films was analyzed by means of optical transmission spectroscopy, multi-wavelength Raman scattering and Fourier Transform Infrared spectroscopy. It was verified that the structure of the films remains unchanged up to a concentration of Kr of about 1.0 at. %. A slight graphitization of the films occurs for higher concentration. The observed variation in the film structure, optical band gap, stress, and hydrogen concentration were associated mainly with the subplantation process of hydrocarbons radicals, rather than the krypton ion energy.

  4. Influence of krypton atoms on the structure of hydrogenated amorphous carbon deposited by plasma enhanced chemical vapor deposition

    SciTech Connect

    Oliveira, M. H. Jr.; Viana, G. A.; Marques, F. C.; Lima, M. M. Jr. de; Cros, A.; Cantarero, A.

    2010-12-15

    Hydrogenated amorphous carbon (a-C:H) films were prepared by plasma enhanced chemical vapor deposition using methane (CH{sub 4}) plus krypton (Kr) mixed atmosphere. The depositions were performed as function of the bias voltage and krypton partial pressure. The goal of this work was to study the influence of krypton gas on the physical properties of a-C:H films deposited on the cathode electrode. Krypton concentration up to 1.6 at. %, determined by Rutherford Back-Scattering, was obtained at high Kr partial pressure and bias of -120 V. The structure of the films was analyzed by means of optical transmission spectroscopy, multi-wavelength Raman scattering and Fourier Transform Infrared spectroscopy. It was verified that the structure of the films remains unchanged up to a concentration of Kr of about 1.0 at. %. A slight graphitization of the films occurs for higher concentration. The observed variation in the film structure, optical band gap, stress, and hydrogen concentration were associated mainly with the subplantation process of hydrocarbons radicals, rather than the krypton ion energy.

  5. Probabilistic human health risk assessment of degradation-related chemical mixtures in heterogeneous aquifers: Risk statistics, hot spots, and preferential channels

    NASA Astrophysics Data System (ADS)

    Henri, Christopher V.; Fernández-Garcia, Daniel; Barros, Felipe P. J.

    2015-06-01

    The increasing presence of toxic chemicals released in the subsurface has led to a rapid growth of social concerns and the need to develop and employ models that can predict the impact of groundwater contamination on human health risk under uncertainty. Monitored natural attenuation is a common remediation action in many contamination cases. However, natural attenuation can lead to the production of daughter species of distinct toxicity that may pose challenges in pollution management strategies. The actual threat that these contaminants pose to human health depends on the interplay between the complex structure of the geological media and the toxicity of each pollutant byproduct. This work addresses human health risk for chemical mixtures resulting from the sequential degradation of a contaminant (such as a chlorinated solvent) under uncertainty through high-resolution three-dimensional numerical simulations. We systematically investigate the interaction between aquifer heterogeneity, flow connectivity, contaminant injection model, and chemical toxicity in the probabilistic characterization of health risk. We illustrate how chemical-specific travel times control the regime of the expected risk and its corresponding uncertainties. Results indicate conditions where preferential flow paths can favor the reduction of the overall risk of the chemical mixture. The overall human risk response to aquifer connectivity is shown to be nontrivial for multispecies transport. This nontriviality is a result of the interaction between aquifer heterogeneity and chemical toxicity. To quantify the joint effect of connectivity and toxicity in health risk, we propose a toxicity-based Damköhler number. Furthermore, we provide a statistical characterization in terms of low-order moments and the probability density function of the individual and total risks.

  6. A batch study on the bio-fixation of carbon dioxide in the absorbed solution from a chemical wet scrubber by hot spring and marine algae.

    PubMed

    Hsueh, H T; Chu, H; Yu, S T

    2007-01-01

    Carbon dioxide mass transfer is a key factor in cultivating micro-algae except for the light limitation of photosynthesis. It is a novel idea to enhance mass transfer with the cyclic procedure of absorbing CO(2) with a high performance alkaline abosorber such as a packed tower and regenerating the alkaline solution with algal photosynthesis. Hence, the algae with high affinity for alkaline condition must be purified. In this study, a hot spring alga (HSA) was purified from an alkaline hot spring (pH 9.3, 62 degrees C) in Taiwan and grows well over pH 11.5 and 50 degrees C. For performance of HSA, CO(2) removal efficiencies in the packed tower increase about 5-fold in a suitable growth condition compared to that without adding any potassium hydroxide. But ammonia solution was not a good choice for this system with regard to carbon dioxide removal efficiency because of its toxicity on HSA. In addition, HSA also exhibits a high growth rate under the controlled pHs from 7 to 11. Besides, a well mass balance of carbon and nitrogen made sure that less other byproducts formed in the procedure of carboxylation. For analysis of some metals in HSA, such as Mg, Mn, Fe, Zn, related to the photosynthesis increased by a rising cultivated pH and revealed that those metals might be accumulated under alkaline conditions but the growth rate was still limited by the ratio of bicarbonate (useful carbon source) and carbonate. Meanwhile, Nannochlopsis oculta (NAO) was also tested under different additional carbon sources. The results revealed that solutions of sodium/potassium carbonate are better carbon sources than ammonia carbonate/bicarbonate for the growth of NAO. However, pH 9.6 of growth limitation based on sodium was lower than one of HSA. The integrated system is, therefore, more feasible to treat CO(2) in the flue gases using the algae with higher alkaline affinity such as HSA in small volume bioreactors.

  7. Moisture barrier and chemical corrosion protection of silver-based telescope mirrors using aluminum oxide films by plasma-enhanced atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Fryauf, David M.; Phillips, Andrew C.; Kobayashi, Nobuhiko P.

    2013-09-01

    An urgent demand remains in astronomy for high-reflectivity silver mirrors that can withstand years of exposure in observatory environments. The University of California Observatories Astronomical Coatings Lab has undertaken development of protected silver coatings suitable for telescope mirrors that maintain high reflectivity at wavelengths from 340 nm through the mid-infrared spectrum. We present initial results of an investigation into whether plasma-enhanced atomic layer deposition (PEALD) can produce superior protective layers of transparent dielectrics. Several novel coating recipes have been developed with ion-assisted electron beam deposition (IAEBD) of materials including yttrium fluoride, and oxides of yttrium, hafnium, and titanium. Samples of these mirror coatings were covered with conformal layers of aluminum oxide (AlOx) deposited by PEALD using trimethylaluminum as a metal precursor and oxygen as an oxidant gas activated by remote plasma. Samples of coating recipes with and without PEALD oxide undergo aggressive environmental testing, including high temperature/high humidity (HTHH), in which samples were exposed to an environment of 80% humidity at 80°C for ten days in a simple test set-up. HTHH testing show visible results suggesting that the PEALD oxide offers enhanced robust protection against chemical corrosion and moisture from an accelerated aging environment. Mirror samples are further characterized by reflectivity/absorption and atomic force microscopy before and after deposition of oxide coatings. AlOx is suitable for many applications and has been the initial material choice for this study, although we also tried TiOx and HfOx. Further experimentation based on these initial results is on-going.

  8. Non-chromatographic speciation analysis of mercury by flow injection on-line preconcentration in combination with chemical vapor generation atomic fluorescence spectrometry

    NASA Astrophysics Data System (ADS)

    Wu, Hong; Jin, Yan; Han, Weiying; Miao, Qiang; Bi, Shuping

    2006-07-01

    A novel non-chromatographic approach for direct speciation of mercury, based on the selective retention inorganic mercury and methylmercury on the inner wall of a knotted reactor by using ammonium diethyl dithiophosphate and dithizone as complexing agents respectively, was developed for flow injection on-line sorption preconcentration coupled with chemical vapor generation non-dispersive atomic fluorescence spectrometry. With the sample pH kept at 2.0, the preconcentration of inorganic mercury on the inner walls of the knotted reactor was carried out based on the exclusive retention of Hg-DDP complex in the presence of methylmercury via on-line merging the sample solution with ammonium diethyl dithiophosphate solution, and selective preconcentration methylmercury was achieved with dithizone instead of ammonium diethyl dithiophosphate. A 15% (v/v) HCl was introduced to elute the retained mercury species and merge with KBH 4 solution for atomic fluorescence spectrometry detection. Under the optimal experimental conditions, the sample throughputs of inorganic mercury and methylmercury were 30 and 20 h - 1 with the enhancement factors of 13 and 24. The detection limits were found to be 3.6 ng l - 1 for Hg 2+ and 2.0 ng l - 1 for CH 3Hg +. The precisions (RSD) for the 11 replicate measurements of each 0.2 μg l - 1 of Hg 2+ and CH 3Hg + were 2.2% and 2.8%, respectively. The developed method was validated by the analysis of certified reference materials (simulated natural water, rice flour and pork) and by recovery measurements on spiked samples, and was applied to the determination of inorganic mercury and methylmercury in biological and environmental water samples.

  9. Chemical vapor generation for atomic spectrometry. A contribution to the comprehension of reaction mechanisms in the generation of volatile hydrides using borane complexes

    NASA Astrophysics Data System (ADS)

    D'Ulivo, Alessandro; Baiocchi, Cristiano; Pitzalis, Emanuela; Onor, Massimo; Zamboni, Roberto

    2004-04-01

    A systematic study has been developed in order to clarify the mechanism of hydride generation using different borane complexes [sodium tetrahydroborate(III), NaBH 4 (THB); borane-ammonia complex, H 3B-NH 3 (AB); borane- tert-Butylamine complex, H 3B-NH 2C(CH 3) 3 (TBAB)], as derivatizing reagents. Stannane, stibine and bismuthine were generated in a continuous flow reaction system at different acidities in the pH range of 1.38-12.7. The pH of sample solution was pre-equilibrated on-line in a mixing loop by the addition of appropriate solution before the reaction with the derivatizing reagent in a reaction loop. The generated hydrides were delivered to a miniature argon hydrogen flame atomizer and free atoms detected by atomic absorption spectrometry (AAS). The effect of pH on the relative sensitivity has been investigated by varying both the mixing loop volume (4, 15 and 50 μl) and reaction loop volume (100 and 500 μl). The mixing rates of the solutions have been also tested to avoid any undesired effect arising from the incomplete mixing of the solution in the flow reaction system. The generation of hydrides using on-line pre-equilibration of pH can be observed also in alkaline or neutral conditions, while the generation of the same hydrides is observed only in acidic solution if the equilibration of pH was performed off-line. Stannane generation using amineboranes has never been reported before. Kinetic calculations were performed in order to estimate the concentration of nascent hydrogen arising from the decomposition of the derivatizing agents in the flow reaction system. It has been found that in many cases, the mechanism of nascent hydrogen failed to explain the generation of the hydrides. The direct action of BH 4- and H 3B-X species (X=ammonia or amino group) on the analyte element, present in solution in a suitable chemical form, is the only possible mechanism of hydride formation in a wide range of solution acidities, from pH 4.5 up to pH 12.7. The

  10. Relationships among equivalent oxide thickness, nanochemistry, and nanostructure in atomic layer chemical-vapor-deposited Hf-O films on Si

    NASA Astrophysics Data System (ADS)

    Dey, S. K.; Das, A.; Tsai, M.; Gu, D.; Floyd, M.; Carpenter, R. W.; De Waard, H.; Werkhoven, C.; Marcus, S.

    2004-05-01

    The relationships among the equivalent oxide thickness (EOT), nanochemistry, and nanostructure of atomic layer chemical-vapor-deposited (ALCVD) Hf-O-based films, with oxide and nitrided oxide interlayers on Si substrates, were studied using x-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) in annular dark-field imaging (ADF), and parallel electron energy-loss spectroscopy (PEELS), capacitance-voltage, and leakage-current-voltage measurements. The XPS (Hf 4f binding energy shift) studies indicated the formation of Hf-O-Si bonds in as-deposited amorphous films, the amount of which was influenced by the interlayer composition and annealing conditions. After post-deposition annealing in N2 and O2, the Hf-O layers were nanocrystalline. Although HRTEM images showed a structurally sharp interface between the Hf-O layer and the interlayer, angle-resolved XPS, ADF imaging, and PEELS in the STEM revealed a chemically diffused HfSiOx region in between. This interdiffusion was observed by the detection of Si (using Si L edge) and Hf (using Hf O2,3 edge) in the Hf-O layer and the interlayer. For an annealed Hf-O/interlayer stack, with an ALCVD target thickness of 4.0 nm for the Hf-O layer on 1.2 nm of nitrided chemical oxide, the experimentally measured EOT and leakage current (at -1 V) were 1.52 nm and ˜10-8 A/cm2. A three-layer (1.2 nm interlayer of nitrided chemical oxide/compositionally graded, 2 nm region of HfSiOx/2 nm HfO2 layer) capacitor model was used to determine the respective contributions to the measured EOT, and the dielectric permittivity of the interlayer was found to be 6.06. These studies clearly indicate that a total EOT of 1 nm and below is attainable in the Hf-N-O-Si/Si-N-O system.

  11. Liquid hot water pretreatment of sugarcane bagasse and its comparison with chemical pretreatment methods for the sugar recovery and structural changes.

    PubMed

    Yu, Qiang; Zhuang, Xinshu; Lv, Shuangliang; He, Minchao; Zhang, Yu; Yuan, Zhenhong; Qi, Wei; Wang, Qiong; Wang, Wen; Tan, Xuesong

    2013-02-01

    Liquid hot water (LHW), dilute hydrochloric acid (HCl) and dilute sodium hydroxide (NaOH) were applied to sugarcane bagasse (SB). Application of the same analytical methods and material balance approaches facilitated meaningful comparisons of glucose and xylose yields from combined pretreatment and enzymatic hydrolysis. All pretreatments enhanced sugar recovery from pretreatment and subsequent enzymatic hydrolysis substantially compared to untreated sugarcane bagasse. Adding Tween80 in the enzymatic hydrolysis process increased the conversion level of glucan/xylan by 0.3-fold, especially for the low pH pretreatment where more lignin was left in the solids. The total sugar recovery from sugarcane bagasse with the coupled operations of pretreatment and 72 h enzymatic digestion reached 71.6% for LHW process, 76.6% for HCl pretreatment and 77.3% for NaOH pretreatment. Different structural changes at the plant tissue, cellular, and cell wall levels might be responsible for the different enzymatic digestibility. Furthermore, a combined LHW and aqueous ammonia pretreatment was proposed to reduce energy input and enhance the sugar recovery.

  12. Are hot Neptunes partially evaporated hot Jupiters?

    NASA Astrophysics Data System (ADS)

    Boué, G.; Figueira, P.; Correia, A. C. M.; Santos, N. C.

    2011-10-01

    The detection of short period planets (hot Jupiters and their lower mass counterparts, hot Neptunes and super-Earths) still defies the models of planet formation and evolution. Several possibilities have been proposed to explain the nature and formation process of the lower mass population, including in situ formation, disk migration, planet-planet scattering and kozai evolution, and the evaporation of a higher mass hot Jupiter. Using dynamical models and the best estimates for evaporation velocities, we show that under reasonable (and observed) physical conditions, hot Jupiter evaporation may explain the observed population of hot Neptunes/super-Earths.

  13. Are Hot Neptunes Partialy Evaporated Hot Jupiters?

    NASA Astrophysics Data System (ADS)

    Santos, Nuno; Boue, G.; Figueira, P.; Correia, A.

    2011-09-01

    The detection of short period planets (hot Jupiters and their lower mass counterparts, hot neptunes and super-earths) still defies the models of planet formation and evolution. Several possibilities have been proposed to explain the nature and formation process of the lower mass population, including in situ formation, disk migration, planet-planet scattering and kozai evolution, and the evaporation of a higher mass hot Jupiter. Using dynamical models and the best estimates for evaporation velocities, we show that under reasonable (and observed) physical conditions, hot Jupiter evaporation can explain the observed population of hot Neptunes/super-Earths.

  14. Atomic Oxygen Effects

    NASA Technical Reports Server (NTRS)

    Miller, Sharon K. R.

    2014-01-01

    Atomic oxygen, which is the most predominant species in low Earth orbit, is highly reactive and can break chemical bonds on the surface of a wide variety of materials leading to volatilization or surface oxidation which can result in failure of spacecraft materials and components. This presentation will give an overview of how atomic oxygen reacts with spacecraft materials, results of space exposure testing of a variety of materials, and examples of failures caused by atomic oxygen.

  15. Metal atom oxidation laser

    DOEpatents

    Jensen, R.J.; Rice, W.W.; Beattie, W.H.

    1975-10-28

    A chemical laser which operates by formation of metal or carbon atoms and reaction of such atoms with a gaseous oxidizer in an optical resonant cavity is described. The lasing species are diatomic or polyatomic in nature and are readily produced by exchange or other abstraction reactions between the metal or carbon atoms and the oxidizer. The lasing molecules may be metal or carbon monohalides or monoxides. (auth)

  16. Metal atom oxidation laser

    DOEpatents

    Jensen, R.J.; Rice, W.W.; Beattie, W.H.

    1975-10-28

    A chemical laser which operates by formation of metal or carbon atoms and reaction of such atoms with a gaseous oxidizer in an optical resonant cavity is described. The lasing species are diatomic or polyatomic in nature and are readily produced by exchange or other abstraction reactions between the metal or carbon atoms and the oxidizer. The lasing molecules may be metal or carbon monohalides or monoxides.

  17. Insights into good hot oiling practices

    SciTech Connect

    Mansure, A.J. ); Barker, K.M. )

    1992-01-01

    One of the common oil-field wellbore problems is paraffin deposition. Even though hot oiling is usually the first method tried for removing paraffin, few operators appreciate the limitations of hot oiling and the potential for hot oiling to aggravate well problems and cause formation damage. Several hot oiling jobs were monitored to understand old pumpers tales'' and the dynamics of hot oiling. The field work was supported with laboratory analyses of the oil and calculations of thermal effectiveness. This limited study has shown that the chemical and thermal processes that occur during hot oiling are very complex and that there are significant variations in practices among operators. Key findings of this work include: (1) During a typical hot oiling job, a significant amount of the oil injected into the annulus goes into the formation, and hence, has the potential to damage the formation. (2) Organic particulates in stock tank oil may not completely dissolve/met as the oil passes through the hot-oiling-truck heat exchanger, hence, these particulates may plug the formation. (3) Hot oiling can vaporize oil in the tubing faster than the pump lifts oil. This interrupts paraffin removal from the well, and thus, since the wax is not removed from the well the wax is refined into harder deposits, can go deeper into the well, and can stick rods. These insights have been used to determine good hot oiling practices designed to maximize wax removal and minimize formation damage.

  18. Fabrication of full-scale fiber-reinforced hot-gas filters by chemical vapor depostion. Final report, November 1, 1994 -- December 32, 1995

    SciTech Connect

    Smith, R.G.; Eaton, J.H.; Pysher, D.J.; Leitheiser, M.A.

    1996-01-01

    The overall goal of this contract and its extensions has been to develop a hot gas candle filter which is light weight, has a thin wall, resists mechanical and thermal shock, and is resistive to alkali attack. A ceramic fiber reinforced, ceramic matrix composite approach has been followed to fabricate this new candle filter. Past reports covered the first test results of two ceramic composite candle filters at the Westinghouse Science and Technology Center in March of 1993, subsequent improvements made in the filters construction and fabrication processing, and the testing of six improved full size, 60 mm diameter by 1575 mm length, filters that met or exceeded performance requirements set for them. Completion of the 172 hours of simulated PFBC testing and thermal transients plus maintaining less than 4 ppm clean side ash concentration provided a basis for moving to the next step of testing in the Tidd PFBCC Demonstration Project. In this contract extension 3M fabricated 110 filters to be used for tests in demonstration power plant facilities and other tests that become available. The filters were tested to meet all quality assurance specifications and inventoried for Oak Ridge National Laboratory, ORNL. The filters are being shipped to various industrial, university, and national laboratory test facilities as requested by ORNL. Ten ceramic composite filters were installed in December, 1994 in the Tidd PFBC Demonstration Project filter vessel for their test period No. 5. Five filters were installed in a top cluster and five in a bottom cluster. The filters were removed in May 1995 after operating for 1 1 1 0 hours in a temperature range of 760{degrees}C to 843{degrees}C, with 80% of the run above 815{degrees}C.

  19. Control of thickness and chemical properties of atomic layer deposition overcoats for stabilizing Cu/γ-Al2 O3 catalysts.

    PubMed

    O'Neill, Brandon J; Sener, Canan; Jackson, David H K; Kuech, Thomas F; Dumesic, James A

    2014-12-01

    Whereas sintering and leaching of copper nanoparticles during liquid-phase catalytic processing can be prevented by using atomic layer deposition (ALD) to overcoat the nanoparticles with AlOx , this acidic overcoat leads to reversible deactivation of the catalyst by resinification and blocking of the pores within the overcoat during hydrogenation of furfural. We demonstrate that decreasing the overcoat thickness from 45 to 5 ALD cycles is an effective method to increase the rate per gram of catalyst and to decrease the rate of deactivation for catalysts pretreated at 673 K, and a fully regenerable copper catalyst can be produced with only five ALD cycles of AlOx . Moreover, although an overcoat of MgOx does not lead to stabilization of copper nanoparticles against sintering and leaching during liquid-phase hydrogenation reactions, the AlOx overcoat can be chemically modified to decrease acidity and deactivation through the addition of MgOx , while maintaining stability of the copper nanoparticles.

  20. Direct determination of arsenic in soil samples by fast pyrolysis-chemical vapor generation using sodium formate as a reductant followed by nondispersive atomic fluorescence spectrometry

    NASA Astrophysics Data System (ADS)

    Duan, Xuchuan; Zhang, Jingya; Bu, Fanlong

    2015-09-01

    This new study shows for the first time that sodium formate can react with trace arsenic to form volatile species via fast pyrolysis - chemical vapor generation. We found that the presence of thiourea greatly enhanced the generation efficiency and eliminated the interference of copper. We studied the reaction temperature, the volume of sodium formate, the reaction acidity, and the carried argon rate using nondispersive atomic fluorescence spectrometry. Under optimal conditions of T = 500 °C, the volumes of 30% sodium formate and 10% thiourea were 0.2 ml and 0.05 ml, respectively. The carrier argon rate was 300 ml min- 1 and the detection limit and precision of arsenic were 0.39 ng and 3.25%, respectively. The amount of arsenic in soil can be directly determined by adding trace amount of hydrochloric acid as a decomposition reagent without any sample pretreatment. The method was successfully applied to determine trace amount of arsenic in two soil-certified reference materials (GBW07453 and GBW07450), and the results were found to be in agreement with certified reference values.

  1. The hydrogen peroxide-rare gas systems: quantum chemical calculations and hyperspherical harmonic representation of the potential energy surface for atom-floppy molecule interactions.

    PubMed

    Barreto, Patricia R P; Vilela, Alessandra F A; Lombardi, Andrea; Maciel, Glauciete S; Palazzetti, Federico; Aquilanti, Vincenzo

    2007-12-13

    A quantum chemical exploration is reported on the interaction potentials of H2O2 with the rare gases, He, Ne, Ar, Kr, and Xe. Hydrogen peroxide (the simplest example of chiral molecule in its equilibrium geometry) is modeled as rigid except for the torsional mode around the O-O bond. However, on the basis of previous work (Maciel, G. S.; et al. Chem. Phys. Lett. 2006 432, 383), the internal mode description is based, rather than on the vectors of the usual valence picture, on the orthogonal local representation, which was demonstrated useful for molecular dynamics simulations, because the torsion around the vector joining the center-of-mass of the two OH radicals mimics accurately the adiabatic reaction path for chirality changing isomerization, following the torsional potential energy profile from equilibrium through the barriers for the trans and cis geometries. The basic motivation of this work is the determination of potential energy surfaces for the interactions to be used in classical and quantum simulations of molecular collisions, specifically those leading to chirality changes of possible relevance in the modeling of prebiotic phenomena. Particular attention is devoted to the definition of coordinates and expansion formulas for the potentials, allowing for a faithful representation of geometrical and symmetry properties of these systems, prototypical of the interaction of an atom with a floppy molecule.

  2. A pseudo-atomic model for the capsid shell of bacteriophage lambda using chemical cross-linking/mass spectrometry and molecular modeling.

    PubMed

    Singh, Pragya; Nakatani, Eri; Goodlett, David R; Catalano, Carlos Enrique

    2013-09-23

    Bacteriophage lambda is one of the most exhaustively studied of the double-stranded DNA viruses. Its assembly pathway is highly conserved among the herpesviruses and many of the bacteriophages, making it an excellent model system. Despite extensive genetic and biophysical characterization of many of the lambda proteins and the assembly pathways in which they are implicated, there is a relative dearth of structural information on many of the most critical proteins involved in lambda assembly and maturation, including that of the lambda major capsid protein. Toward this end, we have utilized a combination of chemical cross-linking/mass spectrometry and computational modeling to construct a pseudo-atomic model of the lambda major capsid protein as a monomer, as well as in the context of the assembled procapsid shell. The approach described here is generalizable and can be used to provide structural models for any biological complex of interest. The procapsid structural model is in good agreement with published biochemical data indicating that procapsid expansion exposes hydrophobic surface area and that this serves to nucleate assembly of capsid decoration protein, gpD. The model further implicates additional molecular interactions that may be critical to the assembly of the capsid shell and for the stabilization of the structure by the gpD decoration protein.

  3. Work function variation of MoS{sub 2} atomic layers grown with chemical vapor deposition: The effects of thickness and the adsorption of water/oxygen molecules

    SciTech Connect

    Kim, Jong Hun; Kim, Jae Hyeon; Park, Jeong Young E-mail: jeongypark@kaist.ac.kr; Lee, Jinhwan; Hwang, C. C.; Lee, Changgu E-mail: jeongypark@kaist.ac.kr

    2015-06-22

    The electrical properties of two-dimensional atomic sheets exhibit remarkable dependences on layer thickness and surface chemistry. Here, we investigated the variation of the work function properties of MoS{sub 2} films prepared with chemical vapor deposition (CVD) on SiO{sub 2} substrates with the number of film layers. Wafer-scale CVD MoS{sub 2} films with 2, 4, and 12 layers were fabricated on SiO{sub 2}, and their properties were evaluated by using Raman and photoluminescence spectroscopies. In accordance with our X-ray photoelectron spectroscopy results, our Kelvin probe force microscopy investigation found that the surface potential of the MoS{sub 2} films increases by ∼0.15 eV when the number of layers is increased from 2 to 12. Photoemission spectroscopy (PES) with in-situ annealing under ultra high vacuum conditions was used to directly demonstrate that this work function shift is associated with the screening effects of oxygen or water molecules adsorbed on the film surface. After annealing, it was found with PES that the surface potential decreases by ∼0.2 eV upon the removal of the adsorbed layers, which confirms that adsorbed species have a role in the variation in the work function.

  4. 3-Dimensional atomic scale structure of the ionic liquid-graphite interface elucidated by AM-AFM and quantum chemical simulations.

    PubMed

    Page, Alister J; Elbourne, Aaron; Stefanovic, Ryan; Addicoat, Matthew A; Warr, Gregory G; Voïtchovsky, Kislon; Atkin, Rob

    2014-07-21

    In situ amplitude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition.

  5. Atomic-Resolution Visualization of Distinctive Chemical Mixing Behavior of Ni, Co and Mn with Li in Layered Lithium Transition-Metal Oxide Cathode Materials

    SciTech Connect

    Yan, Pengfei; Zheng, Jianming; Lv, Dongping; Wei, Yi; Zheng, Jiaxin; Wang, Zhiguo; Kuppan, Saravanan; Yu, Jianguo; Luo, Langli; Edwards, Danny J.; Olszta, Matthew J.; Amine, Khalil; Liu, Jun; Xiao, Jie; Pan, Feng; Chen, Guoying; Zhang, Jiguang; Wang, Chong M.

    2015-07-06

    Capacity and voltage fading of layer structured cathode based on lithium transition metal oxide is closely related to the lattice position and migration behavior of the transition metal ions. However, it is scarcely clear about the behavior of each of these transition metal ions. We report direct atomic resolution visualization of interatomic layer mixing of transition metal (Ni, Co, Mn) and lithium ions in layer structured oxide cathodes for lithium ion batteries. Using chemical imaging with aberration corrected scanning transmission electron microscope (STEM) and DFT calculations, we discovered that in the layered cathodes, Mn and Co tend to reside almost exclusively at the lattice site of transition metal (TM) layer in the structure or little interlayer mixing with Li. In contrast, Ni shows high degree of interlayer mixing with Li. The fraction of Ni ions reside in the Li layer followed a near linear dependence on total Ni concentration before reaching saturation. The observed distinctively different behavior of Ni with respect to Co and Mn provides new insights on both capacity and voltage fade in this class of cathode materials based on lithium and TM oxides, therefore providing scientific basis for selective tailoring of oxide cathode materials for enhanced performance.

  6. Heavy Halogen Atom Effect on (13)C NMR Chemical Shifts in Monohalo Derivatives of Cyclohexane and Pyran. Experimental and Theoretical Study.

    PubMed

    Neto, Alvaro Cunha; Ducati, Lucas C; Rittner, Roberto; Tormena, Cláudio F; Contreras, Rubén H; Frenking, Gernot

    2009-09-01

    As a first step, a qualitative analysis of the spin-orbit operator was performed to predict the kind of organic compounds, where it could be expected that the SO/FC (spin-orbit/Fermi contact) and SO/SD (spin-orbit/spin dipolar) yield unusually small contributions to the "heavy atom effect" on (13)C SCSs (substituent chemical shifts). This analysis led to the conclusion that compounds presenting strong hyperconjugative interactions involving the σ*C-X orbital (X = halogen) are good examples where such effects can be expected to take place. On the basis of such results, the following set of model compounds was chosen: 2-eq-halocyclohexane (2-eq), 2-ax-halocyclohexane (2-ax), and 2-ax-halopyran (3), to measure (13)C SCSs. Such experimental values, as well as those of methane and halomethanes taken from the literature, were compared to calculated values at a nonrelativistic approach using B3LYP, and at a relativistic approach with BP86 using scalar ZORA, spin-orbit ZORA, scalar PAULI, and spin-orbit PAULI. Results from relativistic calculations are in agreement with the trends predicted by the qualitative model discussed in this work.

  7. Control of thickness and chemical properties of atomic layer deposition overcoats for stabilizing Cu/γ-Al2 O3 catalysts.

    PubMed

    O'Neill, Brandon J; Sener, Canan; Jackson, David H K; Kuech, Thomas F; Dumesic, James A

    2014-12-01

    Whereas sintering and leaching of copper nanoparticles during liquid-phase catalytic processing can be prevented by using atomic layer deposition (ALD) to overcoat the nanoparticles with AlOx , this acidic overcoat leads to reversible deactivation of the catalyst by resinification and blocking of the pores within the overcoat during hydrogenation of furfural. We demonstrate that decreasing the overcoat thickness from 45 to 5 ALD cycles is an effective method to increase the rate per gram of catalyst and to decrease the rate of deactivation for catalysts pretreated at 673 K, and a fully regenerable copper catalyst can be produced with only five ALD cycles of AlOx . Moreover, although an overcoat of MgOx does not lead to stabilization of copper nanoparticles against sintering and leaching during liquid-phase hydrogenation reactions, the AlOx overcoat can be chemically modified to decrease acidity and deactivation through the addition of MgOx , while maintaining stability of the copper nanoparticles. PMID:25257472

  8. Optimisation of Direct Copper Determination in Human Breast Milk Without Digestion by Zeeman Graphite Furnace Atomic Absorption Spectrophotometry with Two Chemical Modifiers.

    PubMed

    Pineau, Alain; Fauconneau, Bernard; Marrauld, Annie; Lebeau, Alexandra; Hankard, Regis; Guillard, Olivier

    2015-08-01

    Milk is an important food in the human diet, and copper (Cu) in human milk is indispensable to children's normal growth and development. It is consequently important that Cu deficiency, occurring in malnourished women or in malabsorption following bariatric surgery, be prevented. The objective of this work is to provide hospital-based paediatricians with a tool enabling rapid measurement of Cu in human breast milk through a technique that biology laboratories can easily apply. Using electrothermal atomic absorption spectrophotometry with Zeeman correction, we have optimized this method with two chemical modifiers and without digestion for analytical procedure. Detection limits and quantification limits for Cu in human milk were found to be 0.077 and 0.26 μmol/L, respectively. Within-run (n = 30) and between-run (n = 15) variations in a pool of human milk samples were 1.50 and 3.62%, respectively. Average recoveries ranged from 98.67 to 100.61%. The reliability of this method was also confirmed by analysing certified reference material (10%). In breast milk samples collected from 100 lactating mothers, Cu mean (±1 SD) was 7.09 ± 1.60 μmol/L. In conclusion, with minimal preparation and quick determination, the method proposed is suitable for measurement of Cu in human breast milk.

  9. Atomically resolved force microscopy at room temperature

    SciTech Connect

    Morita, Seizo

    2014-04-24

    Atomic force microscopy (AFM) can now not only image individual atoms but also construct atom letters using atom manipulation method even at room temperature (RT). Therefore, the AFM is the second generation atomic tool following the scanning tunneling microscopy (STM). However the AFM can image even insulating atoms, and also directly measure/map the atomic force and potential at the atomic scale. Noting these advantages, we have been developing a bottom-up nanostructuring system at RT based on the AFM. It can identify chemical species of individual atoms and then manipulate selected atom species to the predesigned site one-by-one to assemble complex nanostructures consisted of multi atom species at RT. Here we introduce our results toward atom-by-atom assembly of composite nanostructures based on the AFM at RT including the latest result on atom gating of nano-space for atom-by-atom creation of atom clusters at RT for semiconductor surfaces.

  10. Thermal stress in seven types of chemical defense ensembles during moderate exercise in hot environments. Final report, May 1991-July 1992

    SciTech Connect

    Bomalaski, S.H.; Hengst, R.; Constable, S.H.

    1993-08-01

    United States Air Force -(USAF) personnel must perform their duties in many operational environments, including those with the potential for contamination with toxic chemical warfare (CW) agents. This study evaluated the physiological response to thermal stress in subjects performing moderate work in current and prototype chemical protective garments including the Battle Dress Overgarment (BDO)+BDU, BDO without BDU, United Kingdom (UK) undercoverall+BDU, Gore-Tex rainsuit+PJ-7 undercoverall, Marine Light Fighter Suit (MLFS), CWU77P, PJ-7 alone, and the BDU alone. Experimental conditions were dry bulb temperature of 40 deg C (104 deg F), a wet bulb temperature of 270C (80.6 deg F), and a black globe temperature of 450C (113 deg F). Eleven subjects walked on a treadmill at 3 mph with a 5% grade incline until rectal temperature (Tre) rose 1.5 deg C (2.7 deg F) above the starting value. Heart rate, rectal and mean skin temperature, and body heat storage were monitored continuously. Sweat evaporation and production were determined from the differences between pre- and postexperiment clothed and nude weights. Significantly longer work times, lower heart rates, lower Tmsk, and lower heat storage, were seen in the group comprised of the BDU, MLFS, CWU-77P, and PJ-7 compared to the Gore-Tex with PJ-7, UK plus BD BDO+BDU, and BDO no BDU ensembles. Suits which resulted in shorter tolerance times also caused rates of sweat production and lower % sweat evaporation than the less physiologically burdensome suits. Chemical protective ensembles, Thermal stress, Clothing, Exercise.

  11. Recrystallization and reactivation of dopant atoms in ion-implanted silicon nanowires.

    PubMed

    Fukata, Naoki; Takiguchi, Ryo; Ishida, Shinya; Yokono, Shigeki; Hishita, Shunichi; Murakami, Kouichi

    2012-04-24

    Recrystallization of silicon nanowires (SiNWs) after ion implantation strongly depends on the ion doses and species. Full amorphization by high-dose implantation induces polycrystal structures in SiNWs even after high-temperature annealing, with this tendency more pronounced for heavy ions. Hot-implantation techniques dramatically suppress polycrystallization in SiNWs, resulting in reversion to the original single-crystal structures and consequently high reactivation rate of dopant atoms. In this study, the chemical bonding states and electrical activities of implanted boron and phosphorus atoms were evaluated by Raman scattering and electron spin resonance, demonstrating the formation of p- and n-type SiNWs.

  12. Hot electron-induced reduction of small molecules on photorecycling metal surfaces

    NASA Astrophysics Data System (ADS)

    Xie, Wei; Schlücker, Sebastian

    2015-07-01

    Noble metals are important photocatalysts due to their ability to convert light into chemical energy. Hot electrons, generated via the non-radiative decay of localized surface plasmons, can be transferred to reactants on the metal surface. Unfortunately, the number of hot electrons per molecule is limited due to charge-carrier recombination. In addition to the reduction half-reaction with hot electrons, also the corresponding oxidation counter-half-reaction must take place since otherwise the overall redox reaction cannot proceed. Here we report on the conceptual importance of promoting the oxidation counter-half-reaction in plasmon-mediated catalysis by photorecycling in order to overcome this general limitation. A six-electron photocatalytic reaction occurs even in the absence of conventional chemical reducing agents due to the photoinduced recycling of Ag atoms from hot holes in the oxidation half-reaction. This concept of multi-electron, counter-half-reaction-promoted photocatalysis provides exciting new opportunities for driving efficient light-to-energy conversion processes.

  13. Single atom electrochemical and atomic analytics

    NASA Astrophysics Data System (ADS)

    Vasudevan, Rama

    In the past decade, advances in electron and scanning-probe based microscopies have led to a wealth of imaging and spectroscopic data with atomic resolution, yielding substantial insight into local physics and chemistry in a diverse range of systems such as oxide catalysts, multiferroics, manganites, and 2D materials. However, typical analysis of atomically resolved images is limited, despite the fact that image intensities and distortions of the atoms from their idealized positions contain unique information on the physical and chemical properties inherent to the system. Here, we present approaches to data mine atomically resolved images in oxides, specifically in the hole-doped manganite La5/8Ca3/8MnO3, on epitaxial films studied by in-situ scanning tunnelling microscopy (STM). Through application of bias to the STM tip, atomic-scale electrochemistry is demonstrated on the manganite surface. STM images are then further analyzed through a suite of algorithms including 2D autocorrelations, sliding window Fourier transforms, and others, and can be combined with basic thermodynamic modelling to reveal relevant physical and chemical descriptors including segregation energies, existence and strength of atomic-scale diffusion barriers, surface energies and sub-surface chemical species identification. These approaches promise to provide tremendous insights from atomically resolved functional imaging, can provide relevant thermodynamic parameters, and auger well for use with first-principles calculations to yield quantitative atomic-level chemical identification and structure-property relations. This research was sponsored by the Division of Materials Sciences and Engineering, BES, DOE. Research was conducted at the Center for Nanophase Materials Sciences, which also provided support and is a DOE Office of Science User Facility.

  14. Remelting of cumulates as a process for producing chemical zoning in silicic tuffs: A comparison of cool, wet and hot, dry rhyolitic magma systems

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ellis, B. S.; Ramos, F. C.; Starkel, W. A.; Boroughs, S.; Olin, P. H.; Bachmann, O.

    2015-11-01

    We review petrological and geochemical features of silicic pyroclastic deposits of dominantly low to moderate (0-25%) crystallinity, and volumes in the range of 5-1000 km3, erupted from caldera volcanoes. Chemical gradients in zoned deposits with compositions near the water-saturated granite minimum, for example the Bishop and Bandelier Tuffs, are consistent with mineral/melt partitioning predicted from the observed phenocryst assemblages, and are inconsistent with mixing with more mafic magma. Smaller volume alkaline (phonolite and pantellerite) systems show similar behavior. In contrast, high-temperature ignimbrites of the 'Snake River'-type typically lack compositional zoning. Internal isotopic variations are weak or absent from whole rocks in both types of rhyolite, even in systems where associated volcanic rocks exhibit wide isotopic variation and strong contrasts exist between the isotopic compositions of mantle and crust. An exception to this is 87Sr/86Sr variations in high-silica rhyolite systems, where Sr has been depleted to subchondritic concentrations and is exceptionally sensitive to open-system processes. Both types of ignimbrite commonly contain crystal aggregates, interpreted as fragments of cumulate mush. In zoned systems, these aggregates exhibit evidence for partial resorption of early-formed crystals. We infer that chemical zoning is a near closed-system process and propose that it arises through melting of cognate cumulate mush beneath a crystal-poor body of melt due to heating by invading mafic or intermediate magma with little mass transfer to the eruptible magma. If the crystal mush is fusible (e.g. dominated by sanidine + quartz), part of it melts to yield mobile, water-poor rhyolite that pools at the interface between the mush and overlying rhyolitic liquid. This new, eruptible melt has a cumulate composition and is thus less evolved than the original supernatant melt lens. The result is a chemically zoned crystal-poor rhyolitic magma

  15. Investigation of the influence of the chemical composition of HSLA steel grades on the microstructure homogeneity during hot rolling in continuous rolling mills using a fast layer model

    NASA Astrophysics Data System (ADS)

    Schmidtchen, M.; Rimnac, A.; Warczok, P.; Kozeschnik, E.; Bernhard, C.; Bragin, S.; Kawalla, R.; Linzer, B.

    2016-03-01

    The newly developed LaySiMS simulation tool provides new insight for inhomogeneous material flow and microstructure evolution in an endless strip production (ESP) plant. A deepened understanding of the influence of inhomogeneities in initial material state, temperature profile and material flow and their impact on the finished product can be reached e.g. by allowing for variable layer thickness distributions in the roll gap. Coupling temperature, deformation work and work hardening/recrystallization phenomena accounts for covering important effects in the roll gap. The underlying concept of the LaySiMS approach will be outlined and new insight gained regarding microstructural evolution, shear and inhomogeneous stress and strain states in the roll gap as well as local residual stresses will be presented. For the case of thin slab casting and direct rolling (TSDR) the interrelation of inhomogeneous initial state, micro structure evolution and dissolution state of micro alloying elements within the roughing section of an ESP line will be discussed. Special emphasis is put on the influence of the local chemical composition arising from direct charging on throughthickness homogeneity of the final product. It is concluded that, due to the specific combination of large reductions in the high reduction mills (HRM) and the highly inhomogeneous inverse temperature profile, the ESP-concept provides great opportunities for homogenizing the microstructure across the strip thickness.

  16. Quantum chemical study on influence of intermolecular hydrogen bonding on the geometry, the atomic charges and the vibrational dynamics of 2,6-dichlorobenzonitrile.

    PubMed

    Agarwal, Parag; Bee, Saba; Gupta, Archana; Tandon, Poonam; Rastogi, V K; Mishra, Soni; Rawat, Poonam

    2014-01-01

    FT-IR (4000-400 cm(-1)) and FT-Raman (4000-200 cm(-1)) spectral measurements on solid 2,6-dichlorobenzonitrile (2,6-DCBN) have been done. The molecular geometry, harmonic vibrational frequencies and bonding features in the ground state have been calculated by density functional theory at the B3LYP/6-311++G (d,p) level. A comparison between the calculated and the experimental results covering the molecular structure has been made. The assignments of the fundamental vibrational modes have been done on the basis of the potential energy distribution (PED). To investigate the influence of intermolecular hydrogen bonding on the geometry, the charge distribution and the vibrational spectrum of 2,6-DCBN; calculations have been done for the monomer as well as the tetramer. The intermolecular interaction energies corrected for basis set superposition error (BSSE) have been calculated using counterpoise method. Based on these results, the correlations between the vibrational modes and the structure of the tetramer have been discussed. Molecular electrostatic potential (MEP) contour map has been plotted in order to predict how different geometries could interact. The Natural Bond Orbital (NBO) analysis has been done for the chemical interpretation of hyperconjugative interactions and electron density transfer between occupied (bonding or lone pair) orbitals to unoccupied (antibonding or Rydberg) orbitals. UV spectrum was measured in methanol solution. The energies and oscillator strengths were calculated by Time Dependent Density Functional Theory (TD-DFT) and matched to the experimental findings. TD-DFT method has also been used for theoretically studying the hydrogen bonding dynamics by monitoring the spectral shifts of some characteristic vibrational modes involved in the formation of hydrogen bonds in the ground and the first excited state. The (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge independent atomic orbital

  17. Chemical noise produced by equilibrium adsorption/desorption of surface pyridine at Au-Ag-Au bimetallic atom-scale junctions studied by fluctuation spectroscopy.

    PubMed

    Hwang, Tai-Wei; Branagan, Sean P; Bohn, Paul W

    2013-03-20

    The chemical noise contained in conductance fluctuations resulting from adsorption and desorption of pyridine at Au-Ag-Au bimetallic atom-scale junctions (ASJs) exhibiting ballistic electron transport is studied using fluctuation spectroscopy. ASJs are fabricated by electrochemical Ag deposition in a Au nanogap to produce a high-conductance Ag quantum wire, followed by electromigration-induced thinning in pyridine solution to create stable ASJs. The conductance behavior of the resulting ASJs is analyzed by sequential autocorrelation and Fourier transform of the current-time data to yield the power spectral density (PSD). In these experiments the PSDs from Ag ASJs in pyridine exhibit two main frequency regions: 1/f noise originating from resistance fluctuations of the junction itself at low frequencies, and a Lorentzian noise component arising from molecular adsorption/desorption fluctuations at higher frequencies. The characteristic cutoff frequency of the Lorentzian noise component determines the relaxation time of molecular fluctuations, which, in turn, is sensitive to the kinetics of the adsorption/desorption process. The kinetics are found to depend on concentration and on the adsorption binding energy. The junction size (<5G0), on the other hand, does not affect the kinetics, as the cutoff frequency remains unchanged. Concentration-dependent adsorption free energies are interpreted as arising from a distribution of binding energies, N(E(b)), on the Ag ASJ. Other observations, such as long lifetime ASJs and two-level fluctuations in conductance, provide additional evidence for the integral role of the adsorbate in determining ASJ reorganization dynamics.

  18. Single atom microscopy.

    PubMed

    Zhou, Wu; Oxley, Mark P; Lupini, Andrew R; Krivanek, Ondrej L; Pennycook, Stephen J; Idrobo, Juan-Carlos

    2012-12-01

    We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity.

  19. Single atom microscopy.

    PubMed

    Zhou, Wu; Oxley, Mark P; Lupini, Andrew R; Krivanek, Ondrej L; Pennycook, Stephen J; Idrobo, Juan-Carlos

    2012-12-01

    We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity. PMID:23146658

  20. Hot oxygen corona of Mars

    SciTech Connect

    Ip, W.H.

    1988-10-01

    Electron dissociative recombination of O2(+) ions in the Venus ionosphere, which may be an important source of suprathermal atomic oxygen, is presently considered as a factor in the Mars exosphere; due to the weaker surface gravitational attraction of Mars, a hot oxygen corona thus formed would be denser than that of Venus at altitudes greater than 2000 km despite Mars' lower ionospheric content. If such an extended oxygen corona does exist on Mars, its collisional interaction with Phobos would lead to the formation of an oxygen gas torus whose average number density is of the order of only 1-2/cu cm along the Phobos orbit. 51 references.

  1. Hot Flow Anomalies at Venus

    NASA Technical Reports Server (NTRS)

    Collinson, G. A.; Sibeck, David Gary; Boardsen, Scott A.; Moore, Tom; Barabash, S.; Masters, A.; Shane, N.; Slavin, J.A.; Coates, A.J.; Zhang, T. L.; Sarantos, M.

    2012-01-01

    We present a multi-instrument study of a hot flow anomaly (HFA) observed by the Venus Express spacecraft in the Venusian foreshock, on 22 March 2008, incorporating both Venus Express Magnetometer and Analyzer of Space Plasmas and Energetic Atoms (ASPERA) plasma observations. Centered on an interplanetary magnetic field discontinuity with inward convective motional electric fields on both sides, with a decreased core field strength, ion observations consistent with a flow deflection, and bounded by compressive heated edges, the properties of this event are consistent with those of HFAs observed at other planets within the solar system.

  2. Hot Subluminous Stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  3. Hot Subluminous Stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung–Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  4. Atom mapping with constraint programming.

    PubMed

    Mann, Martin; Nahar, Feras; Schnorr, Norah; Backofen, Rolf; Stadler, Peter F; Flamm, Christoph

    2014-01-01

    Chemical reactions are rearrangements of chemical bonds. Each atom in an educt molecule thus appears again in a specific position of one of the reaction products. This bijection between educt and product atoms is not reported by chemical reaction databases, however, so that the "Atom Mapping Problem" of finding this bijection is left as an important computational task for many practical applications in computational chemistry and systems biology. Elementary chemical reactions feature a cyclic imaginary transition state (ITS) that imposes additional restrictions on the bijection between educt and product atoms that are not taken into account by previous approaches. We demonstrate that Constraint Programming is well-suited to solving the Atom Mapping Problem in this setting. The performance of our approach is evaluated for a manually curated subset of chemical reactions from the KEGG database featuring various ITS cycle layouts and reaction mechanisms.

  5. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Liège (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99

  6. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Liège (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99

  7. Hot Spot Removal System: System description

    SciTech Connect

    1997-09-01

    Hazardous wastes contaminated with radionuclides, chemicals, and explosives exist across the Department of Energy complex and need to be remediated due to environmental concerns. Currently, an opportunity is being developed to dramatically reduce remediation costs and to assist in the acceleration of schedules associated with these wastes by deploying a Hot Spot Removal System. Removing the hot spot from the waste site will remove risk driver(s) and enable another, more cost effective process/option/remedial alternative (i.e., capping) to be applied to the remainder of the site. The Hot Spot Removal System consists of a suite of technologies that will be utilized to locate and remove source terms. Components of the system can also be used in a variety of other cleanup activities. This Hot Spot Removal System Description document presents technologies that were considered for possible inclusion in the Hot Spot Removal System, technologies made available to the Hot Spot Removal System, industrial interest in the Hot Spot Removal System`s subsystems, the schedule required for the Hot Spot Removal System, the evaluation of the relevant technologies, and the recommendations for equipment and technologies as stated in the Plan section.

  8. Reviews Book: Sustainable Energy—Without the Hot Air Equipment: Doppler Effect Unit Book: The Physics of Rugby Book: Plastic Fantastic: How the Biggest Fraud in Physics Shook the Scientific World Equipment: Brunel Eyecam Equipment: 200x Digital Microscope Book: The Atom and the Apple: Twelve Tales from Contemporary Physics Book: Physics 2 for OCR Web Watch

    NASA Astrophysics Data System (ADS)

    2009-09-01

    WE RECOMMEND Sustainable Energy—Without the Hot Air This excellent book makes sense of energy facts and figures Doppler Effect Unit Another simple, effective piece of kit from SEP Plastic Fantastic: How the Biggest Fraud in Physics Shook the Scientific World Intriguing and unique write-up of an intellectual fraud case Brunel Eyecam An affordable digital eyepiece for your microscope 200x Digital Microscope An adjustable digital flexcam for classroom use The Atom and the Apple: Twelve Tales from Contemporary Physics A fascinating round-up of the recent history of physics WORTH A LOOK The Physics of Rugby Book uses sport analogy and context to teach physics concepts Physics 2 for OCR Essential textbook for the course but otherwise pointless WEB WATCH Some free teaching materials are better than those you'd pay for

  9. Atomic and molecular supernovae

    NASA Technical Reports Server (NTRS)

    Liu, Weihong

    1997-01-01

    Atomic and molecular physics of supernovae is discussed with an emphasis on the importance of detailed treatments of the critical atomic and molecular processes with the best available atomic and molecular data. The observations of molecules in SN 1987A are interpreted through a combination of spectral and chemical modelings, leading to strong constraints on the mixing and nucleosynthesis of the supernova. The non-equilibrium chemistry is used to argue that carbon dust can form in the oxygen-rich clumps where the efficient molecular cooling makes the nucleation of dust grains possible. For Type Ia supernovae, the analyses of their nebular spectra lead to strong constraints on the supernova explosion models.

  10. Atom Tunneling in Chemistry.

    PubMed

    Meisner, Jan; Kästner, Johannes

    2016-04-25

    Quantum mechanical tunneling of atoms is increasingly found to play an important role in many chemical transformations. Experimentally, atom tunneling can be indirectly detected by temperature-independent rate constants at low temperature or by enhanced kinetic isotope effects. In contrast, the influence of tunneling on the reaction rates can be monitored directly through computational investigations. The tunnel effect, for example, changes reaction paths and branching ratios, enables chemical reactions in an astrochemical environment that would be impossible by thermal transition, and influences biochemical processes. PMID:26990917

  11. Chemical vapor deposition and atomic layer deposition of Ta-based diffusion barriers using tert-butylimido tris(diethylamido) tantalum metal organic precursor

    NASA Astrophysics Data System (ADS)

    Kim, Keechan

    Ta-N and Ta-Al-N Cu diffusion barriers were deposited by chemical vapor deposition (CVD) and atomic layer deposition (ALD) using tert-butylimido tris(diethylamido) tantalum (TBTDET)/tri-ethyl aluminum (TEA) metal organic precursors. The effect of NH3 addition on film properties during TaN CVD from TBTDET was examined. As the NH3 flow was increased at constant TBTDET flow, the film density, nitrogen content, and grain size increased, while resistivity and carbon content decreased as compared to films deposited with TBTDET alone. These property changes are attributed, in part, to transamination reaction between the diethylamido ligands in TBTDET and NH3. The higher film density and nitrogen content produced TaN films that exhibited superior diffusion barrier performance compared to those deposited without NH3 addition. TaN was also successfully deposited by ALD with alternating exposure to TBTDET and NH3. TBTDET adsorption was shown to be self-limiting with a single monolayer growth rate of 2.6 A/cycle over the process temperature window of 200 to 300°C. An incubation period exists during the initial cycles as evidenced by a non-linear relationship between film thickness and cycle number. Ultra-thin ALD-TaN layers, as thin as 38 A, effectively blocked Cu diffusion during a 30 min anneal at 500°C. Ternary Ta-Al-N films were deposited from TBTDET and TEA to promote formation of an amorphous film and increasing the recrystallization temperature. The Al mole fraction was linearly dependent on the TEA exposure time suggesting growth was self-limiting. Although Al insertion into TaN promoted an amorphous structure, it also lowered the overall film density. A comparative study of the diffusion barrier performance showed that failure occurred for both TaN and Ta-Al-N films at the same thickness, suggesting the increased amorphous content by adding Al was offset by the lower film density. Selecting a different reactant exposure sequence produced different film properties. A

  12. Solutions for Hot Situations

    NASA Technical Reports Server (NTRS)

    2003-01-01

    From the company that brought the world an integral heating and cooling food service system after originally developing it for NASA's Apollo Program, comes yet another orbital offshoot: a product that can be as thin as paper and as strong as steel. Nextel Ceramic Textiles and Composites from 3M Company offer space-age protection and innovative solutions for hot situations, ranging from NASA to NASCAR. With superior thermal protection, Nextel fabrics, tape, and sleevings outperform other high temperature textiles such as aramids, carbon, glass, and quartz, permitting engineers and manufacturers to handle applications up to 2,500 F (1,371 C). The stiffness and strength of Nextel Continuous Ceramic Fibers make them a great match for improving the rigidity of aluminum in metal matrix composites. Moreover, the fibers demonstrate low shrinkage at operating temperatures, which allow for the manufacturing of a dimensionally stable product. These novel fibers also offer excellent chemical resistance, low thermal conductivity, thermal shock resistance, low porosity, and unique electrical properties.

  13. High-resolution electron spin resonance spectroscopy of XeF* in solid argon. The hyperfine structure constants as a probe of relativistic effects in the chemical bonding properties of a heavy noble gas atom.

    PubMed

    Misochko, Eugenii Ya; Akimov, Alexander V; Goldschleger, Ilya U; Tyurin, Danil A; Laikov, Dimitri N

    2005-01-15

    Xenon fluoride radicals were generated by solid-state chemical reactions of mobile fluorine atoms with xenon atoms trapped in Ar matrix. Highly resolved electron spin resonance spectra of XeF* were obtained in the temperature range of 5-25 K and the anisotropic hyperfine parameters were determined for magnetic nuclei 19F, 129Xe, and 131Xe using naturally occurring and isotopically enriched xenon. Signs of parallel and perpendicular hyperfine components were established from analysis of temperature changes in the spectra and from numerical solutions of the spin Hamiltonian for two nonequivalent magnetic nuclei. Thus, the complete set of components of hyperfine- and g-factor tensors of XeF* were obtained: 19F (Aiso=435, Adip=1249 MHz) and 129Xe (Aiso=-1340, Adip=-485 MHz); g(parallel)=1.9822 and g(perpendicular)=2.0570. Comparison of the measured hyperfine parameters with those predicted by density-functional theory (DFT) calculations indicates, that relativistic DFT gives true electron spin distribution in the 2Sigma+ ground-state, whereas nonrelativistic theory underestimates dramatically the electron-nuclear contact Fermi interaction (Aiso) on the Xe atom. Analysis of the obtained magnetic-dipole interaction constants (Adip) shows that fluorine 2p and xenon 5p atomic orbitals make a major contribution to the spin density distribution in XeF*. Both relativistic and nonrelativistic calculations give close magnetic-dipole interaction constants, which are in agreement with the measured values. The other relativistic feature is considerable anisotropy of g-tensor, which results from spin-orbit interaction. The orbital contribution appears due to mixing of the ionic 2Pi states with the 2Sigma+ ground state, and the spin-orbit interaction plays a significant role in the chemical bonding of XeF*.

  14. New sources for the hot oxygen geocorona

    NASA Technical Reports Server (NTRS)

    Richards, P. G.; Hickey, M. P.; Torr, D. G.

    1994-01-01

    This paper investigates new sources of thermospheric non thermal (hot) oxygen due to exothermic reactions involving numerous minor (ion and neutral) and metastable species. Numerical calculations are performed for low altitude, daytime, winter conditions, with moderately high solar activity and low magnetic activity. Under these conditions we find that the quenching of metastable species are a significant source of hot oxygen, with kinetic energy production rates a factor of ten higher than those due to previously considered O2(+) and NO(+) dissociative recombination reactions. Some of the most significant new sources of hot oxygen are reactions involving quenching of O(+)((sup 2)D), O((sup 1)D), N((sup 2)D), O(+)((sup 2)P) and vibrationally excited N2 by atomic oxygen.

  15. Atomic polarizabilities

    SciTech Connect

    Safronova, M. S.; Mitroy, J.; Clark, Charles W.; Kozlov, M. G.

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  16. Plasmon-induced dynamics of H{sub 2} splitting on a silver atomic chain

    SciTech Connect

    Yan, Lei; Ding, Zijing; Song, Peng; Wang, Fangwei; Meng, Sheng

    2015-08-24

    Localized surface plasmon resonances (LSPR) supported in metal nanostructures can be efficiently harnessed to drive photocatalytic reactions, whose atomic scale mechanism remains a challenge. Here, real-time dynamics of H{sub 2} photosplitting on a linear silver atomic chain, upon exposure to femtosecond laser pulses, has been investigated using time-dependent density functional theory. The wavelength dependent H{sub 2} splitting process is strongly coupled to LSPR excitation in silver chain. We identify that hot electrons produced in the silver chain by plasmon excitation are transferred to the antibonding state of the adsorbed H{sub 2} and trigger H{sub 2} dissociation, consistent with experimental observations. Increasing illumination intensity and the length of atomic chain promote H{sub 2} splitting, thanks to stronger LSPR. Dynamic electronic response can be quantitatively described within the present approach, providing insights towards a complete fundamental understanding on plasmon-induced chemical reactions at the microscopic scale.

  17. ADVANCED HOT GAS FILTER DEVELOPMENT

    SciTech Connect

    E.S. Connolly; G.D. Forsythe

    1998-12-22

    Advanced, coal-based power plants will require durable and reliable hot gas filtration systems to remove particulate contaminants from the gas streams to protect downstream components such as turbine blades from erosion damage. It is expected that the filter elements in these systems will have to be made of ceramic materials to withstand goal service temperatures of 1600 F or higher. Recent demonstration projects and pilot plant tests have indicated that the current generation of ceramic hot gas filters (cross-flow and candle configurations) are failing prematurely. Two of the most promising materials that have been extensively evaluated are clay-bonded silicon carbide and alumina-mullite porous monoliths. These candidates, however, have been found to suffer progressive thermal shock fatigue damage, as a result of rapid cooling/heating cycles. Such temperature changes occur when the hot filters are back-pulsed with cooler gas to clean them, or in process upset conditions, where even larger gas temperature changes may occur quickly and unpredictably. In addition, the clay-bonded silicon carbide materials are susceptible to chemical attack of the glassy binder phase that holds the SiC particles together, resulting in softening, strength loss, creep, and eventual failure.

  18. Computational tests of quantum chemical models for structures, vibrational frequencies, and heats of formation of molecules with phosphorus and sulfur atoms.

    PubMed

    Hahn, David K; RaghuVeer, Krishans S; Ortiz, J V

    2010-08-12

    The Gaussian-n, complete basis set, and Weizmann-1 quantum chemical models for heats of formation are applied to a set of molecules with relevance to the combustion or pyrolysis of chemical warfare materials. Most of these models generate standard deviations from experiment that are less than 2 kcal/mol. The structures and vibrational frequencies that are generated in the course of these calculations are in good agreement with experimental data. Detailed comparisons with respect to structural types indicate that the present computational models are likely to generate useful data for complex models of combustion and pyrolysis of chemical warfare materials.

  19. Use of low temperature blowers for recirculation of hot gases

    DOEpatents

    Maru, H.C.; Forooque, M.

    1982-08-19

    An apparatus is described for maintaining motors at low operating temperatures during recirculation of hot gases in fuel cell operations and chemical processes such as fluidized bed coal gasification. The apparatus includes a means for separating the hot process gas from the motor using a secondary lower temperature gas, thereby minimizing the temperature increase of the motor and associated accessories.

  20. The Earth's Hot Spots.

    ERIC Educational Resources Information Center

    Vink, Gregory E.; And Others

    1985-01-01

    Hot spots are isolated areas of geologic activity where volcanic eruptions, earthquakes, and upwelling currents occur far from plate boundaries. These mantle plumes are relatively stable and crustal plates drift over them. The nature and location of hot spots (with particular attention to the Hawaiian Islands and Iceland) are discussed. (DH)

  1. Hot Spot at Yellowstone

    ERIC Educational Resources Information Center

    Dress, Abby

    2005-01-01

    Within this huge national park (over two million acres spread across Wyoming, Montana, and Idaho) are steaming geysers, hot springs, bubbling mudpots, and fumaroles, or steam vents. Drives on the main roads of Yellowstone take tourists through the major hot attractions, which also include Norris Geyser Basin, Upper and Lower Geyser Basin, West…

  2. Analytic study of the chain dark decomposition reaction of iodides - atomic iodine donors - in the active medium of a pulsed chemical oxygen-iodine laser: 1. Criteria for the development of the branching chain dark decomposition reaction of iodides

    SciTech Connect

    Andreeva, Tamara L; Kuznetsova, S V; Maslov, Aleksandr I; Sorokin, Vadim N

    2009-02-28

    The scheme of chemical processes proceeding in the active medium of a pulsed chemical oxygen-iodine laser (COIL) is analysed. Based on the analysis performed, the complete system of differential equations corresponding to this scheme is replaced by a simplified system of equations describing in dimensionless variables the chain dark decomposition of iodides - atomic iodine donors, in the COIL active medium. The procedure solving this system is described, the basic parameters determining the development of the chain reaction are found and its specific time intervals are determined. The initial stage of the reaction is analysed and criteria for the development of the branching chain decomposition reaction of iodide in the COIL active medium are determined. (active media)

  3. Microscale Effects from Global Hot Plasma Imagery

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Fok, M.-C.; Perez, J. D.; Keady, J. P.

    1995-01-01

    We have used a three-dimensional model of recovery phase storm hot plasmas to explore the signatures of pitch angle distributions (PADS) in global fast atom imagery of the magnetosphere. The model computes mass, energy, and position-dependent PADs based on drift effects, charge exchange losses, and Coulomb drag. The hot plasma PAD strongly influences both the storm current system carried by the hot plasma and its time evolution. In turn, the PAD is strongly influenced by plasma waves through pitch angle diffusion, a microscale effect. We report the first simulated neutral atom images that account for anisotropic PADs within the hot plasma. They exhibit spatial distribution features that correspond directly to the PADs along the lines of sight. We investigate the use of image brightness distributions along tangent-shell field lines to infer equatorial PADS. In tangent-shell regions with minimal spatial gradients, reasonably accurate PADs are inferred from simulated images. They demonstrate the importance of modeling PADs for image inversion and show that comparisons of models with real storm plasma images will reveal the global effects of these microscale processes.

  4. Cavity enhanced atomic magnetometry

    PubMed Central

    Crepaz, Herbert; Ley, Li Yuan; Dumke, Rainer

    2015-01-01

    Atom sensing based on Faraday rotation is an indispensable method for precision measurements, universally suitable for both hot and cold atomic systems. Here we demonstrate an all-optical magnetometer where the optical cell for Faraday rotation spectroscopy is augmented with a low finesse cavity. Unlike in previous experiments, where specifically designed multipass cells had been employed, our scheme allows to use conventional, spherical vapour cells. Spherical shaped cells have the advantage that they can be effectively coated inside with a spin relaxation suppressing layer providing long spin coherence times without addition of a buffer gas. Cavity enhancement shows in an increase in optical polarization rotation and sensitivity compared to single-pass configurations. PMID:26481853

  5. 6. HOT AIR PORTION OF DAMPERS. Hot Springs National ...

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

    6. HOT AIR PORTION OF DAMPERS. - Hot Springs National Park, Bathhouse Row, Lamar Bathhouse: Mechanical & Piping Systems, State Highway 7, 1 mile north of U.S. Highway 70, Hot Springs, Garland County, AR

  6. Characterization of the physico-chemical properties of polymeric materials for aerospace flight. [differential thermal and atomic absorption spectroscopic analysis of nickel cadmium batteries

    NASA Technical Reports Server (NTRS)

    Rock, M.

    1981-01-01

    Electrodes and electrolytes of nickel cadmium sealed batteries were analyzed. Different thermal analysis of negative and positive battery electrodes was conducted and the temperature ranges of occurrence of endotherms indicating decomposition of cadmium hydroxide and nickel hydroxide are identified. Atomic absorption spectroscopy was used to analyze electrodes and electrolytes for traces of nickel, cadmium, cobalt, and potassium. Calibration curves and data are given for each sample analyzed. Instrumentation and analytical procedures used for each method are described.

  7. Atomic branching in molecules

    NASA Astrophysics Data System (ADS)

    Estrada, Ernesto; Rodríguez-Velázquez, Juan A.; Randić, Milan

    A graph theoretic measure of extended atomic branching is defined that accounts for the effects of all atoms in the molecule, giving higher weight to the nearest neighbors. It is based on the counting of all substructures in which an atom takes part in a molecule. We prove a theorem that permits the exact calculation of this measure based on the eigenvalues and eigenvectors of the adjacency matrix of the graph representing a molecule. The definition of this measure within the context of the Hückel molecular orbital (HMO) and its calculation for benzenoid hydrocarbons are also studied. We show that the extended atomic branching can be defined using any real symmetric matrix, as well as any Hermitian (self-adjoint) matrix, which permits its calculation in topological, geometrical, and quantum chemical contexts.

  8. Atomic Chain Electronics

    NASA Technical Reports Server (NTRS)

    Yamada, Toshishige; Saini, Subhash (Technical Monitor)

    1998-01-01

    Adatom chains, precise structures artificially created on an atomically regulated surface, are the smallest possible candidates for future nanoelectronics. Since all the devices are created by combining adatom chains precisely prepared with atomic precision, device characteristics are predictable, and free from deviations due to accidental structural defects. In this atomic dimension, however, an analogy to the current semiconductor devices may not work. For example, Si structures are not always semiconducting. Adatom states do not always localize at the substrate surface when adatoms form chemical bonds to the substrate atoms. Transport properties are often determined for the entire system of the chain and electrodes, and not for chains only. These fundamental issues are discussed, which will be useful for future device considerations.

  9. Resonance Radiation and Excited Atoms

    NASA Astrophysics Data System (ADS)

    Mitchell, Allan C. G.; Zemansky, Mark W.

    2009-06-01

    1. Introduction; 2. Physical and chemical effects connected with resonance radiation; 3. Absorption lines and measurements of the lifetime of the resonance state; 4. Collision processes involving excited atoms; 5. The polarization of resonance radiation; Appendix; Index.

  10. Pyridazine-based Schiff base ligands with N 4O xS 2 ( x = 2, 4) donor set atoms: Synthesis, characterization, spectral studies and 13C chemical shifts computed by the GIAO-DFT and CSGT-DFT methodologies

    NASA Astrophysics Data System (ADS)

    Khanmohammadi, Hamid; Erfantalab, Malihe

    2010-01-01

    Six pyridazine-based Schiff base ligands, H 2L n ( n = 1-5) and H 4L, with N 4O 2S 2 and N 4O 4S 2 donor set atoms, respectively, were prepared by condensation reaction of 3,6-bis-((2-aminoethyl)thio)pyridazine with various salicyladehyde derivatives in ethanol and under solvent-free polyphosphate ester catalyzed conditions. The acid-base properties of H 2L 2 and H 2L 3 in DMSO/water (1:1) solution have been studied by spectrophotometric method at 25 °C. Optimized geometries of all compounds were also obtained at the B3LYP level of theory. Additionally, the 13C chemical shielding of gas phase H 2L 1 and H 2L 2 were studied by the gauge independent atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods at the level of density functional theory (DFT). The 6-311++G* basis set was utilized for all of the atoms.

  11. Contact mechanics modeling of pull-off measurements: effect of solvent, probe radius, and chemical binding probability on the detection of single-bond rupture forces by atomic force microscopy.

    PubMed

    Skulason, Hjalti; Frisbie, C Daniel

    2002-07-01

    Pull-off forces for chemically modified atomic force microscopy tips in contact with flat substrates coated with receptor molecules are calculated using a Johnson, Kendall, and Roberts contact mechanics model. The expression for the work of adhesion is modified to account for the formation of discrete numbers of chemical bonds (nBonds) between the tip and substrate. The model predicts that the pull-off force scales as nBonds(1/2), which differs from a common assumption that the pull-off force scales linearly with nBonds. Periodic peak progressions are observed in histograms generated from hundreds of computed pull-off forces. The histogram periodicity is the signature of discrete chemical interactions between the tip and substrate and allows estimation of single-bond rupture forces. The effects of solvent, probe tip radius, and chemical binding probability on the detection of single-bond forces are examined systematically. A dimensionless parameter, the effective force resolution, is introduced that serves as a quantitative predictor for determining when periodicity in force histograms can occur. The output of model is compared to recent experimental results involving tips and substrates modified with self-assembled monolayers. An advantage of this contact mechanics approach is that it allows straightforward estimation of solvent effects on pull-off forces.

  12. Spin-polarized lithium diffusion in a glass hot-vapor cell

    NASA Astrophysics Data System (ADS)

    Ishikawa, Kiyoshi

    2016-08-01

    We report diffusion coefficients of optically pumped lithium atoms in helium buffer gas. The free-induction decay and the spin-echo signals of ground-state atoms were optically detected in an external magnetic field with the addition of field gradient. Lithium hot vapor was produced in a borosilicate-glass cell at a temperature between 290 and 360°C. The simple setup using the glass cells enabled lithium atomic spectroscopy in a similar way to other alkali-metal atoms and study of the collisional properties of lithium atoms in a hot-vapor phase.

  13. Micro-topography creates biogeochemical hot spots in wetlands

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Atreyee

    2012-10-01

    Interventions in wetlands could improve water quality, as wetlands regulate not only nutrients such as nitrogen and sulfur but also pollutants in the waters that flow through them. Biological and chemical processes maintain conditions for redox reactions in the wetlands that control the concentration of certain solutes, including nutrients and pollutants. But such biogeochemical processes are not evenly distributed and often are localized in “hot spots” or take place in bouts known as “hot moments.” How these hot spots or hot moments arise remains poorly understood and is often explained by simply evoking variations in soil properties in the wetlands.

  14. Atomic collisions, inelastic indeed

    NASA Astrophysics Data System (ADS)

    Bercegol, Herve; Ferrando, Gwenael; Lehoucq, Roland

    At the turn of the twentieth century, a hot controversy raged about the ability of Boltzmann's framework to take care of irreversibility. The so-called Loschmidt's paradox progressively faded with time during the last hundred years, due to the predictive efficiency of statistical mechanics. However, one detail at the origin of the controversy - the elasticity of atomic collisions - was not completely challenged. A semi-classical treatment of two atoms interacting with the vacuum zero-point field permits to predict a friction force acting against the rotation of the pair of atoms. By its form and its level, the calculated torque is a candidate as a physical cause for diffusion of energy and angular momentum, and consequently for entropy growth. It opens the way to a revision of the standard vision of irreversibility. This presentation will focus on two points. First we will discuss the recent result in a broader context of electromagnetic interactions during microscopic collisions. The predicted friction phenomenon can be compared to and distinguished from Collision-Induced Emission and other types of inelastic collisions. Second we will investigate the consequences of the friction torque on calculated trajectories of colliding atoms, quantifying the generation of dimers linked by dispersion forces.

  15. Probing cis-trans isomerization in the S{sub 1} state of C{sub 2}H{sub 2} via H-atom action and hot band-pumped IR-UV double resonance spectroscopies

    SciTech Connect

    Changala, P. Bryan; Baraban, Joshua H.; Field, Robert W.; Merer, Anthony J.

    2015-08-28

    We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S{sub 1} state of acetylene, C{sub 2}H{sub 2}, in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm{sup −1} below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C{sub 2}H + H sets in roughly 1100 cm{sup −1} below the barrier; the resulting quenching of laser-induced fluorescence (LIF) reduces its value for recording spectra in this region. The other difficulty is that tunneling through the barrier causes a staggering in the K-rotational structure of isomerizing vibrational levels. The assignment of these levels requires data for K values up to at least 3. Given the rotational selection rule K′ − ℓ{sup ′′} = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ{sup ′′} > 0. In this paper, high resolution H-atom resonance-enhanced multiphoton ionization spectra are demonstrated to contain predissociated bands which are almost invisible in LIF spectra, while preliminary data using a hyperthermal pulsed nozzle show that ℓ{sup ′′} = 2 states can be selectively populated in a jet, giving access to K′ = 3 states in IR-UV double resonance.

  16. An In-Depth Study of the Abundance Pattern in the Hot Interstellar Medium in NGC 4649

    NASA Technical Reports Server (NTRS)

    Loewenstein, Michael; Davis, David S.

    2012-01-01

    We present our X-ray imaging spectroscopic analysis of data from deep Suzaku and XMM-Newton Observatory exposures of the Virgo Cluster elliptical galaxy NGC 4649 (M60), focusing on the abundance pattern in the hot interstellar medium (ISM). All measured elements show a radial decline in abundance, with the possible exception of Oxygen. We construct steady state solutions to the chemical evolution equations that include infall in addition to stellar mass return and Type Ia supernovae (SNIa) enrichment, and consider recently published SNIa yields. By adjusting a single model parameter to obtain a match to the global abundance pattern in NGC 4649 we infer that introduction of subsolar metallicity external gas has reduced the overall ISM metallicity and diluted the effectiveness of SNIa to skew the pattern towards low alpha/Fe ratios, and estimate the combination of SNIa rate and level of dilution. Evidently, newly-introduced gas is heated as it is integrated into, and interacts with, the hot gas that is already present. These results indicate a complex flow and enrichment history for NGC 4649, reflecting the continual evolution of elliptical galaxies beyond the formation epoch. The heating and circulation of accreted gas may help reconcile this dynamic history with the mostly passive evolution of elliptical stellar populations. In an appendix we examine the effects of the recent updated atomic database AtomDB in spectral fitting of thermal plasmas with hot ISM temperatures in the elliptical galaxy range.

  17. AN IN-DEPTH STUDY OF THE ABUNDANCE PATTERN IN THE HOT INTERSTELLAR MEDIUM IN NGC 4649

    SciTech Connect

    Loewenstein, Michael; Davis, David S. E-mail: David.S.Davis@nasa.gov

    2012-10-01

    We present our X-ray imaging spectroscopic analysis of data from deep Suzaku and XMM-Newton Observatory exposures of the Virgo Cluster elliptical galaxy NGC 4649 (M60), focusing on the abundance pattern in the hot interstellar medium (ISM). All measured elements show a radial decline in abundance, with the possible exception of O. We construct steady-state solutions to the chemical evolution equations that include infall in addition to stellar mass return and Type Ia supernova (SNIa) enrichment, and consider recently published SNIa yields. By adjusting a single model parameter to obtain a match to the global abundance pattern in NGC 4649, we infer that introduction of subsolar metallicity external gas has reduced the overall ISM metallicity and diluted the effectiveness of SNIa to skew the pattern toward low {alpha}/Fe ratios, and estimate the combination of SNIa rate and level of dilution. Evidently, newly introduced gas is heated as it is integrated into, and interacts with, the hot gas that is already present. These results indicate a complex flow and enrichment history for NGC 4649, reflecting the continual evolution of elliptical galaxies beyond the formation epoch. The heating and circulation of accreted gas may help reconcile this dynamic history with the mostly passive evolution of elliptical stellar populations. In an Appendix, we examine the effects of the recent updated atomic database AtomDB in spectral fitting of thermal plasmas with hot ISM temperatures in the elliptical galaxy range.

  18. A Qualitative Report of the Ways High School Chemistry Students Attempt to Represent a Chemical Reaction at the Atomic/Molecular Level

    ERIC Educational Resources Information Center

    Kern, Anne L.; Wood, Nathan B.; Roehrig, Gillian H.; Nyachwaya, James

    2010-01-01

    We report the findings of a large-scale (n = 1,337) qualitative descriptive analysis of U.S. high schools students' particulate representations of a chemical reaction, specifically, the combustion of methane. Data were collected as part of an end of course exam. Student representations were coded into 17 distinct subcategories under one of five…

  19. Tracking Changes in Absorptivity, Stiffness, and Organic Chemical Composition in Laboratory Generated HULIS SOA using Atomic Force Microscopy and X-ray Microscopy

    NASA Astrophysics Data System (ADS)

    Hawkins, L. N.; Lemire, A.; Kong, W.

    2014-12-01

    Light absorbing organic compounds are among the many products of aqueous phase secondary organic aerosol formation. Once formed, these compounds can alter the optical and material properties of SOA in ways that impact their ability to scatter and absorb solar radiation, deliquesce and evaporate quickly during cloud cycling, and react with gas phase species such as oxidants. To quantify these effects, we have characterized the changes in UV-visible absorption, stiffness, and particle shape that occur when aqueous SOA is exposed to repeated wet-dry cycles and photooxidation. Material properties were measured with Atomic Force Microscopy of atomized laboratory generated SOA; this material was created by combining glyoxal, methylglyoxal, or glycolaldehyde with ammonium sulfate, glycine, or methylamine in solution and either spray drying or evaporating the bulk solution. In addition to optical and material properties, changes in organic functional groups were tracked using scanning transmission x-ray microscopy (STXM) of the near carbon edge x-ray absorption fine structure (NEXAFS). Photooxidation experiments of the same aqueous SOA revealed concomitant changes in the organic functional groups and light absorption spectra, along with measurable changes in particle stiffness.

  20. Direct determination of phosphorus in different food samples by means of solid sampling electrothermal atomic absorption spectrometry using Pd+Ca chemical modifier

    NASA Astrophysics Data System (ADS)

    Coşkun, Nihat; Akman, Süleyman

    2005-03-01

    In this study, direct determination of phosphorus in different food samples (milk powder, banana, and dried banana) and in various standard reference materials (apple leaves, bovine liver, pine needles) using solid sampling electrothermal atomic absorption spectrometry was investigated. Aqueous standards were used for all determinations. 5 μg Pd+5 μg Ca modifier mixture was used in all experiments. Pyrolysis temperature and atomization temperature were 1100 °C and 2500 °C, respectively. High background was reduced by applying a cool-down step in the furnace program. The accuracy of solid sampling results was checked by determination of the phosphorus content after dissolving samples. There was no significant error between results found by solid sampling and solution techniques. In addition solid certified materials were investigated. There were no significant differences between the phosphorus content of CRM and results obtained. The limit of detection, based on three times the standard deviation was 0.018 μg P.

  1. Chemical networks

    NASA Astrophysics Data System (ADS)

    Thi, Wing-Fai

    2015-09-01

    This chapter discusses the fundamental ideas of how chemical networks are build, their strengths and limitations. The chemical reactions that occur in disks combine the cold phase reactions used to model cold molecular clouds with the hot chemistry applied to planetary atmosphere models. With a general understanding of the different types of reactions that can occur, one can proceed in building a network of chemical reactions and use it to explain the abundance of species seen in disks. One on-going research subject is finding new paths to synthesize species either in the gas-phase or on grain surfaces. Specific formation routes for water or carbon monoxide are discussed in more details. 13th Lecture of the Summer School "Protoplanetary Disks: Theory and Modelling Meet Observations"

  2. Atomic supersymmetry

    NASA Technical Reports Server (NTRS)

    Kostelecky, V. Alan

    1993-01-01

    Atomic supersymmetry is a quantum-mechanical supersymmetry connecting the properties of different atoms and ions. A short description of some established results in the subject are provided and a few recent developments are discussed including the extension to parabolic coordinates and the calculation of Stark maps using supersymmetry-based models.

  3. Atomic Calligraphy

    NASA Astrophysics Data System (ADS)

    Imboden, Matthias; Pardo, Flavio; Bolle, Cristian; Han, Han; Tareen, Ammar; Chang, Jackson; Christopher, Jason; Corman, Benjamin; Bishop, David

    2013-03-01

    Here we present a MEMS based method to fabricate devices with a small number of atoms. In standard semiconductor fabrication, a large amount of material is deposited, after which etching removes what is not wanted. This technique breaks down for structures that approach the single atom limit, as it is inconceivable to etch away all but one atom. What is needed is a bottom up method with single or near single atom precision. We demonstrate a MEMS device that enables nanometer position controlled deposition of gold atoms. A digitally driven plate is swept as a flux of gold atoms passes through an aperture. Appling voltages on four comb capacitors connected to the central plate by tethers enable nanometer lateral precision in the xy plane over 15x15 sq. microns. Typical MEMS structures have manufacturing resolutions on the order of a micron. Using a FIB it is possible to mill apertures as small as 10 nm in diameter. Assuming a low incident atomic flux, as well as an integrated MEMS based shutter with microsecond response time, it becomes possible to deposit single atoms. Due to their small size and low power consumption, such nano-printers can be mounted directly in a cryogenic system at ultrahigh vacuum to deposit clean quench condensed metallic structures.

  4. Hot Accretion Disks Revisited

    NASA Astrophysics Data System (ADS)

    Bjoernsson, Gunnlaugur; Abramowicz, Marek A.; Chen, Xingming; Lasota, Jean-Pierre

    1996-08-01

    All previous studies of hot (Tp 1010-1012 K), optically thin accretion disks have neglected either the presence of e+ e- pairs or advective cooling. Thus all hot disk models constructed previously have not been self-consistent. In this paper we calculate local disk models including pair physics, relevant radiative processes in the hot plasma, and the effect of advective cooling. We use a modification of the Björnsson & Svensson mapping method. We find that the role of e+ e- pairs in the structure of hot, optically thin accretion disks is far less significant than was previously thought. The improved description of the radiation-matter interactions provided in the present paper modify the previously obtained values of the critical parameters characterizing advectively dominated flows.

  5. Saturn's Hot Plasma Explosions

    NASA Video Gallery

    This animation based on data obtained by NASA's Cassini Spacecraft shows how the "explosions" of hot plasma on the night side (orange and white) periodically inflate Saturn's magnetic field (white ...

  6. Hot Oiling Spreadsheet

    1993-10-22

    One of the most common oil-field treatments is hot oiling to remove paraffin from wells. Even though the practice is common, the thermal effectiveness of the process is not commonly understood. In order for producers to easily understand the thermodynamics of hot oiling, a simple tool is needed for estimating downhole temperatures. Such a tool has been developed that can be distributed as a compiled spreadsheet.

  7. Geothermal hot water system

    SciTech Connect

    Dittell, E.W.

    1983-05-10

    Geothermal hot water system including a hot water tank and a warm water tank which are heated independently of each other by a close loop freon system. The closed loop freon system includes a main condenser which heats water for the warm water tank and a super-heated condenser which heats water for the hot water tank, and where the freon passes through a water evaporator which is heated by water such as from a well or other suitable source. The water evaporator in the closed loop freon system passes the water through but no environmental change to the water. An electrical circuit including aquastats in the warm water tank connected therethrough controls operation of the closed loop freon system including respective pumps on the super-heated condenser and main condenser for pumping water. Pumps pump water through the main condenser for the warm tank and through the super-heated condenser for the hot tank. The system provides for energy conservation in that the head pressure of the compressor is kept in the lower operating ranges as determined by the discharge flow of the main condenser which varies by the head pressure and temperature flow control which varies by temperature. The geothermal hot water system uses a least amount of energy in heating the water in the hot tank as well as the warm tank.

  8. Energy partitioning for ``fuzzy'' atoms

    NASA Astrophysics Data System (ADS)

    Salvador, P.; Mayer, I.

    2004-03-01

    The total energy of a molecule is presented as a sum of one- and two-atomic energy components in terms of "fuzzy" atoms, i.e., such divisions of the three-dimensional physical space into atomic regions in which the regions assigned to the individual atoms have no sharp boundaries but exhibit a continuous transition from one to another. By proper definitions the energy components are on the chemical energy scale. The method is realized by using Becke's integration scheme and weight function permitting very effective numerical integrations.

  9. Surface and interfacial reaction study of half cycle atomic layer deposited HfO{sub 2} on chemically treated GaSb surfaces

    SciTech Connect

    Zhernokletov, D. M.; Dong, H.; Brennan, B.; Kim, J.; Yakimov, M.; Tokranov, V.; Oktyabrsky, S.; Wallace, R. M.

    2013-04-01

    An in situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (XPS) study was conducted in order to investigate the evolution of the HfO{sub 2} dielectric interface with GaSb(100) surfaces after sulfur passivation and HCl etching, designed to remove the native oxides. With the first pulses of tetrakis(dimethylamido)hafnium(IV) and water, a decrease in the concentration of antimony oxide states present on the HCl-etched surface is observed, while antimony sulfur states diminished below the XPS detection limit on sulfur passivated surface. An increase in the amount of gallium oxide/sulfide is seen, suggesting oxygen or sulfur transfers from antimony to gallium during antimony oxides/sulfides decomposition.

  10. Effects of rapid thermal annealing on structural, chemical, and electrical characteristics of atomic-layer deposited lanthanum doped zirconium dioxide thin film on 4H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Lim, Way Foong; Quah, Hock Jin; Lu, Qifeng; Mu, Yifei; Ismail, Wan Azli Wan; Rahim, Bazura Abdul; Esa, Siti Rahmah; Kee, Yeh Yee; Zhao, Ce Zhou; Hassan, Zainuriah; Cheong, Kuan Yew

    2016-03-01

    Effects of rapid thermal annealing at different temperatures (700-900 °C) on structural, chemical, and electrical characteristics of lanthanum (La) doped zirconium oxide (ZrO2) atomic layer deposited on 4H-SiC substrates have been investigated. Chemical composition depth profiling analysis using X-ray photoelectron spectroscopy (XPS) and cross-sectional studies using high resolution transmission electron microscopy equipped with energy dispersive X-ray spectroscopy line scan analysis were insufficient to justify the presence of La in the investigated samples. The minute amount of La present in the bulk oxide was confirmed by chemical depth profiles of time-of-flight secondary ion mass spectrometry. The presence of La in the ZrO2 lattice led to the formation of oxygen vacancies, which was revealed through binding energy shift for XPS O 1s core level spectra of Zrsbnd O. The highest amount of oxygen vacancies in the sample annealed at 700 °C has yielded the acquisition of the highest electric breakdown field (∼ 6.3 MV/cm) and dielectric constant value (k = 23) as well as the highest current-time (I-t) sensor response towards oxygen gas. The attainment of both the insulating and catalytic properties in the La doped ZrO2 signified the potential of the doped ZrO2 as a metal reactive oxide on 4H-SiC substrate.

  11. How Good Are the Standard Atomic Weights?

    ERIC Educational Resources Information Center

    Peiser, H. Steffen

    1985-01-01

    This review of standard atomic weights is written chiefly for chemical analysts who may place too much confidence in the accuracy of these values. Topics considered include Frank Clarke's atomic weights, effects of radioactivity and other anomalies in isotopic abundance, atomic weight limitations from experimental uncertainties, and others. (JN)

  12. Kinetic Atom.

    ERIC Educational Resources Information Center

    Wilson, David B.

    1981-01-01

    Surveys the research of scientists like Joule, Kelvin, Maxwell, Clausius, and Boltzmann as it comments on the basic conceptual issues involved in the development of a more precise kinetic theory and the idea of a kinetic atom. (Author/SK)

  13. Acting Atoms.

    ERIC Educational Resources Information Center

    Farin, Susan Archie

    1997-01-01

    Describes a fun game in which students act as electrons, protons, and neutrons. This activity is designed to help students develop a concrete understanding of the abstract concept of atomic structure. (DKM)

  14. Chemical reactions during plasma-enhanced atomic layer deposition of SiO2 films employing aminosilane and O2/Ar plasma at 50 °C

    NASA Astrophysics Data System (ADS)

    Lu, Yi; Kobayashi, Akiko; Kondo, Hiroki; Ishikawa, Kenji; Sekine, Makoto; Hori, Masaru

    2014-01-01

    We report the temporal evolution of surface species observed in situ using attenuated total reflection Fourier transform infrared absorption spectroscopy (ATR-FTIR) during plasma-enhanced atomic layer deposition (PE-ALD) of SiO2 films employing aminosilane and an O2/Ar plasma at a temperature of 50 °C. Reversals in the appearance of IR absorbance features associated with SiO-H, C-Hx, and Si-H proved to coincide with the self-limiting reaction property in ALD. Our IR results indicate that an O2/Ar plasma can both removed CHx groups and transform SiH surface species to SiOH. In addition, SiO2 deposition was confirmed by a continuous increase in Si-O absorbance with each PE-ALD step, which becomes stable after several cycles. On the basis of our results, the mechanism of low temperature SiO2 PE-ALD was discussed.

  15. Matrix Infrared Spectroscopic and Quantum Chemical Investigations of the Group 5 Transition Metal Atom and CX4 Molecule (X = H, F, and Cl) Reaction Products.

    PubMed

    Lyon, Jonathan T; Cho, Han-Gook; Andrews, Lester

    2015-12-24

    Laser-ablated vanadium, niobium, and tantalum atoms were reacted with CH2X2, CHX3, and CX4 (X = F and Cl) molecules in condensing argon, and the products were investigated by matrix isolation infrared spectroscopy. The major reaction products are new CH2-MX2, CHX-MX2, HC-MX3, and XC-MX3 complexes. These reactive species were identified by comparing their matrix infrared spectra with frequencies, intensities, and isotopic shifts from density functional theory calculations. Product structures and energies from these calculations are also presented. Results from previously studied Group 4 and 6 metal reaction products are compared. Little change is found in the calculated metal-carbon bond lengths in the early first row CH2═MF2 methylidene σ(2)π(2) series; however, the methylidyne complexes HC{}MF3 show considerable increase in bond strength for the nominally σ(2)π(1)π(1)(Ti), σ(2)π(2)π(1)(V), and σ(2)π(2)π(2)(Cr) carbon{}metal bonds left to right. The Group 5 HC{}MF3 complexes have only a plane of symmetry whereas the Group 4 and 6 analogues have 3-fold symmetry. PMID:26601564

  16. Ceramic hot-gas filter

    DOEpatents

    Connolly, E.S.; Forsythe, G.D.; Domanski, D.M.; Chambers, J.A.; Rajendran, G.P.

    1999-05-11

    A ceramic hot-gas candle filter is described having a porous support of filament-wound oxide ceramic yarn at least partially surrounded by a porous refractory oxide ceramic matrix, and a membrane layer on at least one surface thereof. The membrane layer may be on the outer surface, the inner surface, or both the outer and inner surface of the porous support. The membrane layer may be formed of an ordered arrangement of circularly wound, continuous filament oxide ceramic yarn, a ceramic filler material which is less permeable than the filament-wound support structure, or some combination of continuous filament and filler material. A particularly effective membrane layer features circularly wound filament with gaps intentionally placed between adjacent windings, and a filler material of ceramic particulates uniformly distributed throughout the gap region. The filter can withstand thermal cycling during back pulse cleaning and is resistant to chemical degradation at high temperatures.

  17. Ceramic hot-gas filter

    DOEpatents

    Connolly, Elizabeth Sokolinski; Forsythe, George Daniel; Domanski, Daniel Matthew; Chambers, Jeffrey Allen; Rajendran, Govindasamy Paramasivam

    1999-01-01

    A ceramic hot-gas candle filter having a porous support of filament-wound oxide ceramic yarn at least partially surrounded by a porous refractory oxide ceramic matrix, and a membrane layer on at least one surface thereof. The membrane layer may be on the outer surface, the inner surface, or both the outer and inner surface of the porous support. The membrane layer may be formed of an ordered arrangement of circularly wound, continuous filament oxide ceramic yarn, a ceramic filler material which is less permeable than the filament-wound support structure, or some combination of continuous filament and filler material. A particularly effective membrane layer features circularly wound filament with gaps intentionally placed between adjacent windings, and a filler material of ceramic particulates uniformly distributed throughout the gap region. The filter can withstand thermal cycling during backpulse cleaning and is resistant to chemical degradation at high temperatures.

  18. Mechanical gate control for atom-by-atom cluster assembly with scanning probe microscopy.

    PubMed

    Sugimoto, Yoshiaki; Yurtsever, Ayhan; Hirayama, Naoki; Abe, Masayuki; Morita, Seizo

    2014-07-11

    Nanoclusters supported on substrates are of great importance in physics and chemistry as well as in technical applications, such as single-electron transistors and nanocatalysts. The properties of nanoclusters differ significantly from those of either the constituent atoms or the bulk solid, and are highly sensitive to size and chemical composition. Here we propose a novel atom gating technique to assemble various atom clusters composed of a defined number of atoms at room temperature. The present gating operation is based on the transfer of single diffusing atoms among nanospaces governed by gates, which can be opened in response to the chemical interaction force with a scanning probe microscope tip. This method provides an alternative way to create pre-designed atom clusters with different chemical compositions and to evaluate their chemical stabilities, thus enabling investigation into the influence that a single dopant atom incorporated into the host clusters has on a given cluster stability.

  19. PMMA-Etching-Free Transfer of Wafer-scale Chemical Vapor Deposition Two-dimensional Atomic Crystal by a Water Soluble Polyvinyl Alcohol Polymer Method.

    PubMed

    Van Ngoc, Huynh; Qian, Yongteng; Han, Suk Kil; Kang, Dae Joon

    2016-01-01

    We have explored a facile technique to transfer large area 2-Dimensional (2D) materials grown by chemical vapor deposition method onto various substrates by adding a water-soluble Polyvinyl Alcohol (PVA) layer between the polymethyl-methacrylate (PMMA) and the 2D material film. This technique not only allows the effective transfer to an arbitrary target substrate with a high degree of freedom, but also avoids PMMA etching thereby maintaining the high quality of the transferred 2D materials with minimum contamination. We applied this method to transfer various 2D materials grown on different rigid substrates of general interest, such as graphene on copper foil, h-BN on platinum and MoS2 on SiO2/Si. This facile transfer technique has great potential for future research towards the application of 2D materials in high performance optical, mechanical and electronic devices. PMID:27616038

  20. PMMA-Etching-Free Transfer of Wafer-scale Chemical Vapor Deposition Two-dimensional Atomic Crystal by a Water Soluble Polyvinyl Alcohol Polymer Method

    NASA Astrophysics Data System (ADS)

    van Ngoc, Huynh; Qian, Yongteng; Han, Suk Kil; Kang, Dae Joon

    2016-09-01

    We have explored a facile technique to transfer large area 2-Dimensional (2D) materials grown by chemical vapor deposition method onto various substrates by adding a water-soluble Polyvinyl Alcohol (PVA) layer between the polymethyl-methacrylate (PMMA) and the 2D material film. This technique not only allows the effective transfer to an arbitrary target substrate with a high degree of freedom, but also avoids PMMA etching thereby maintaining the high quality of the transferred 2D materials with minimum contamination. We applied this method to transfer various 2D materials grown on different rigid substrates of general interest, such as graphene on copper foil, h-BN on platinum and MoS2 on SiO2/Si. This facile transfer technique has great potential for future research towards the application of 2D materials in high performance optical, mechanical and electronic devices.

  1. PMMA-Etching-Free Transfer of Wafer-scale Chemical Vapor Deposition Two-dimensional Atomic Crystal by a Water Soluble Polyvinyl Alcohol Polymer Method

    PubMed Central

    Van Ngoc, Huynh; Qian, Yongteng; Han, Suk Kil; Kang, Dae Joon

    2016-01-01

    We have explored a facile technique to transfer large area 2-Dimensional (2D) materials grown by chemical vapor deposition method onto various substrates by adding a water-soluble Polyvinyl Alcohol (PVA) layer between the polymethyl-methacrylate (PMMA) and the 2D material film. This technique not only allows the effective transfer to an arbitrary target substrate with a high degree of freedom, but also avoids PMMA etching thereby maintaining the high quality of the transferred 2D materials with minimum contamination. We applied this method to transfer various 2D materials grown on different rigid substrates of general interest, such as graphene on copper foil, h-BN on platinum and MoS2 on SiO2/Si. This facile transfer technique has great potential for future research towards the application of 2D materials in high performance optical, mechanical and electronic devices. PMID:27616038

  2. PMMA-Etching-Free Transfer of Wafer-scale Chemical Vapor Deposition Two-dimensional Atomic Crystal by a Water Soluble Polyvinyl Alcohol Polymer Method.

    PubMed

    Van Ngoc, Huynh; Qian, Yongteng; Han, Suk Kil; Kang, Dae Joon

    2016-09-12

    We have explored a facile technique to transfer large area 2-Dimensional (2D) materials grown by chemical vapor deposition method onto various substrates by adding a water-soluble Polyvinyl Alcohol (PVA) layer between the polymethyl-methacrylate (PMMA) and the 2D material film. This technique not only allows the effective transfer to an arbitrary target substrate with a high degree of freedom, but also avoids PMMA etching thereby maintaining the high quality of the transferred 2D materials with minimum contamination. We applied this method to transfer various 2D materials grown on different rigid substrates of general interest, such as graphene on copper foil, h-BN on platinum and MoS2 on SiO2/Si. This facile transfer technique has great potential for future research towards the application of 2D materials in high performance optical, mechanical and electronic devices.

  3. Hot Topic Talk 4

    NASA Astrophysics Data System (ADS)

    Hosten, Onur

    2016-05-01

    I will focus on our experiments with cold atoms highlighting some of the most recent developments in the prospect of using quantum entanglement to improve the precision of atomic and optical sensors. The first part of the talk will describe the generation of 20 dB spin-squeezed states of half a million 87Rb atoms inside of an optical cavity. The second part will describe the experimental demonstration of a new concept we call quantum phase magnification. The demonstrated 20 dB squeezing enables a 100-fold reduction in averaging time or a 100-fold reduction in atom numbers to achieve a given sensing precision. As part of this work we show an atomic clock operating 10 dB beyond the classical limit. Some of the states prepared in these experiments possess in excess of 680 atom entanglement. The quantum phase magnification experiment shows that detection noise levels below the standard quantum limit is in fact not a requirement to realize the benefits of the intrinsic sensitivity provided by exotic quantum states. Here, optical cavity-aided effective interactions between atoms magnify signals to-be-measured to levels that can easily be detected with a rather inefficient fluorescence imaging system. The method relaxes stringent detection requirements which have been the main bottleneck in quantum metrology experiments, and can also be implemented in physical platforms other than cold atom-cavity systems.

  4. Dispersants displace hot oiling

    SciTech Connect

    Wash, R.

    1984-02-01

    Laboratory experiments and field testing of dispersants in producing wells have resulted in development of 2 inexpensive paraffin dispersant packages with a broad application range, potential for significant savings over hot oiling, and that can be applied effectively by both continuous and batch treating techniques. The 2 dispersants are soluble in the carrier solvent (one soluble in oil, one in water); are able to readily disperse the wax during a hot flask test conducted in a laboratory; and leave the producing interval water wet. Field data on the 2 dispersants are tabulated, demonstrating their efficacy.

  5. Hot Oil Removes Wax

    NASA Technical Reports Server (NTRS)

    Herzstock, James J.

    1991-01-01

    Mineral oil heated to temperature of 250 degrees F (121 degrees C) found effective in removing wax from workpieces after fabrication. Depending upon size and shape of part to be cleaned of wax, part immersed in tank of hot oil, and/or interior of part flushed with hot oil. Pump, fittings, and ancillary tooling built easily for this purpose. After cleaning, innocuous oil residue washed off part by alkaline aqueous degreasing process. Serves as relatively safe alternative to carcinogenic and environmentally hazardous solvent perchloroethylene.

  6. Oxidation and hot corrosion of hot-pressed Si3N4 at 1000 deg C

    NASA Technical Reports Server (NTRS)

    Fielder, W. L.

    1985-01-01

    The oxidation and hot corrosion of a commercial, hot-pressed Si3N4 were investigated at 1000 C under an atmosphere of flowing O2. For the hot corrosion studies, thin films of Na2SO4 were airbrushed on the Si3N4 surface. The hot corrosion attack was monitored by the following techniques: continuous weight measurements, SO2 evolution, film morphology, and chemical analyses. Even though the hot corrosion weight changes after 25 hr were relatively small, the formation of SiO2 from oxidation of Si3N4 was an order of magnitude greater in the presence of molten Na2SO4. The formation of a protective SiO2 phase at the Si3N4 surface is minimized by the fluxing action of the molten Na2SO4 thereby allowing the oxidation of the Si3N4 to proceed more rapidly. A simple process is proposed to account for the hot corrosion process.

  7. Some Like It Hot, Some like It Cold

    ERIC Educational Resources Information Center

    Silberman, Robert G.

    2004-01-01

    In order to find the right combination to construct a cold pack for athletic injuries, students mix liquids and solids in a calorimeter, and use a thermometer to ascertain whether the chemical reaction is hot or cold. Many formulae for chemical reactions are given, the first of which is used for commercial cold packs.

  8. Energy partitioning in elementary chemical processes

    SciTech Connect

    Bersohn, R.

    1993-12-01

    In the past year research has centered on the decomposition of hot molecules, the reaction of ethynyl radicals with hydrogen molecules and the reaction of oxygen atoms with acetylene. Reaction kinetics studies are reported for each of these systems.

  9. Atomic research

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.; Connatser, Robert; Cothren, Bobby; Johnson, R. B.

    1993-01-01

    Work performed by the University of Alabama in Huntsville's (UAH) Center for Applied Optics (CAO) entitled Atomic Research is documented. Atomic oxygen (AO) effects on materials have long been a critical concern in designing spacecraft to withstand exposure to the Low Earth Orbit (LEO) environment. The objective of this research effort was to provide technical expertise in the design of instrumentation and experimental techniques for analyzing materials exposed to atomic oxygen in accelerated testing at NASA/MSFC. Such testing was required to answer fundamental questions concerning Space Station Freedom (SSF) candidate materials and materials exposed to atomic oxygen aboard the Long-Duration Exposure Facility (LDEF). The primary UAH task was to provide technical design, review, and analysis to MSFC in the development of a state-of-the-art 5eV atomic oxygen beam facility required to simulate the RAM-induced low earth orbit (LEO) AO environment. This development was to be accomplished primarily at NASA/MSFC. In support of this task, contamination effects and ultraviolet (UV) simulation testing was also to be carried out using NASA/MSFC facilities. Any materials analysis of LDEF samples was to be accomplished at UAH.

  10. Actuated atomizer

    NASA Technical Reports Server (NTRS)

    Tilton, Charles (Inventor); Weiler, Jeff (Inventor); Palmer, Randall (Inventor); Appel, Philip (Inventor)

    2008-01-01

    An actuated atomizer is adapted for spray cooling or other applications wherein a well-developed, homogeneous and generally conical spray mist is required. The actuated atomizer includes an outer shell formed by an inner ring; an outer ring; an actuator insert and a cap. A nozzle framework is positioned within the actuator insert. A base of the nozzle framework defines swirl inlets, a swirl chamber and a swirl chamber. A nozzle insert defines a center inlet and feed ports. A spool is positioned within the coil housing, and carries the coil windings having a number of turns calculated to result in a magnetic field of sufficient strength to overcome the bias of the spring. A plunger moves in response to the magnetic field of the windings. A stop prevents the pintle from being withdrawn excessively. A pintle, positioned by the plunger, moves between first and second positions. In the first position, the head of the pintle blocks the discharge passage of the nozzle framework, thereby preventing the atomizer from discharging fluid. In the second position, the pintle is withdrawn from the swirl chamber, allowing the atomizer to release atomized fluid. A spring biases the pintle to block the discharge passage. The strength of the spring is overcome, however, by the magnetic field created by the windings positioned on the spool, which withdraws the plunger into the spool and further compresses the spring.

  11. Preparation of LWBR (Light Water Breeder Reactor) spent fuel for shipment to ICPP (Idaho Chemical Processing Plant) for long term storage (LWBR Development Program). [Shippingport Atomic Power Station

    SciTech Connect

    Hodges, B.W.

    1987-10-01

    After successfully operating for 29,047 effective full power hours, the Light Water Breeder Reactor (LWBR) core was defueled prior to total decommissioning of the Shippingport facility. All nuclear fuel and much of the reactor internal hardware was removed from the reactor vessel. Non-fuel components were prepared for shipment to disposal sites, and the fuel assemblies were partially disassembled and shipped to the Expended Core Facility (ECF) in Idaho. At ECF, the fuel modules underwent further disassembly to provide fuel rods for nondestructive testing to establish the core's breeding efficiency and to provide core components for examinations to assess their performance characteristics. This report presents a basic description of the processes and equipment used to prepare and to ship all LWBR nuclear fuel to the Idaho Chemical Processing Plant (ICPP) for long-term storage. Preparation processes included the underwater loading of LWBR fuel into storage liners, the sealing, dewatering and drying of the storage liners, and the final pressurization of the storage liners with inert neon gas. Shipping operations included the underwater installation of the fuel loaded storage liner into the Peach Bottom shipping cask, cask removal from the waterpit, cask preparations for shipping, and cask shipment by tractor trailer to the ICPP facility for long-term storage. The ICPP facility preparations for LWBR fuel storage and the ICPP process for discharge of the fuel into underground silos are presented. 10 refs., 42 figs.

  12. Effect of the Chemical State of the Surface on the Relaxation of the Surface Shell Atoms in SiC and GaN Nanocrystals

    NASA Technical Reports Server (NTRS)

    Palosz, B.; Grzanka, E.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H. P.; Janik, J. F.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-surface layer was examined using the concept of the apparent lattice parameter (alp) determined for different diffraction vectors Q. The apparent lattice parameter is a lattice parameter determined either from an individual Bragg reflection, or from a selected region of the diffraction pattern. At low diffraction vectors the Bragg peak positions are affected mainly by the structure of the near-surface layer, while at high Q-values only the interior of the nano-grain contributes to the diffraction pattern. Following the measurements on raw (as prepared) powders we investigated powders cleaned by annealing at 400C under vacuum, and the same powders wetted with water. Theoretical alp-Q plots showed that the structure of the surface layer depends on the sample treatment. Semi-quantitative analysis based on the comparison of the experimental and theoretical alp-Q plots was performed. Theoretical alp-Q relations were obtained from the diffraction patterns calculated for models of nanocrystals with a strained surface layer using the Debye functions.

  13. Atom Interferometry

    SciTech Connect

    Kasevich, Mark

    2008-05-08

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton's constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gyroscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be used to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  14. Atom Interferometry

    SciTech Connect

    Mark Kasevich

    2008-05-07

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  15. Atom Interferometry

    ScienceCinema

    Mark Kasevich

    2016-07-12

    Atom de Broglie wave interferometry has emerged as a tool capable of addressing a diverse set of questions in gravitational and condensed matter physics, and as an enabling technology for advanced sensors in geodesy and navigation. This talk will review basic principles, then discuss recent applications and future directions. Scientific applications to be discussed include measurement of G (Newton’s constant), tests of the Equivalence Principle and post-Newtonian gravity, and study of the Kosterlitz-Thouless phase transition in layered superfluids. Technology applications include development of precision gryoscopes and gravity gradiometers. The talk will conclude with speculative remarks looking to the future: Can atom interference methods be sued to detect gravity waves? Can non-classical (entangled/squeezed state) atom sources lead to meaningful sensor performance improvements?

  16. Hot Wall Epitaxy And Characterization Of Bismuth And Antimony Thin Films On Barium Fluoride Substrates

    NASA Astrophysics Data System (ADS)

    Collazo, Ramon; Dalmau, Rafael; Martinez, Antonio

    1998-03-01

    We have grown thin films of bismuth and antimony using hot wall epitaxy. The epitaxial films were grown on (111)-BaF2 substrates. The chemical integrity of the films was established using Auger electron spectroscopy and X ray Photoelectron Spectroscopy. The thickness of the films was measured using an atomic force microscope to establish their growth rate. The crystallographic properties of the films were assessed using x-ray diffraction techniques. Both bismuth and antimony thin films were found to be oriented with the [003] direction perpendicular to the plane of the films. Pole figures of both types of films indicate the epitaxial nature of the films. Bi/Sb multilayer structures were grown using the same growth technique. We will report on the results of the characterization of these films as well as on the growth apparatus and process. Work supported in part by EPSCoR-NSF Grant EHR-9108775 and NCRADA-NSWCDD-92-01.

  17. Hot-hole photodetectors

    NASA Astrophysics Data System (ADS)

    2014-05-01

    By injecting high-energy charge carriers (dubbed 'hot holes') into a semiconductor, scientists have succeeded in realizing photodetectors capable of detecting ultralong wavelengths. Unil Perera from Georgia State University in the USA explains how the devices work and how they can be improved.

  18. Hot off the Press

    ERIC Educational Resources Information Center

    Brisco, Nicole D.

    2007-01-01

    In the past, the newspaper was one of the world's most used sources of information. Recently, however, its use has declined due to the popularity of cable television and the Internet. Yet the idea of reading the morning paper with a hot cup of coffee holds many warm memories for children who watched their parents in this daily ritual. In this…

  19. Zen Hot Dog Molecules

    ERIC Educational Resources Information Center

    Ryan, Dennis

    2009-01-01

    Substituted cycloalkanes with one branch illustrating each topic in an instructional unit can serve as summaries or reviews in courses of organic chemistry. The hungry Zen master told the hot dog vendor to make him one with everything. You can do the same for your students.

  20. Hot piston ring tests

    NASA Astrophysics Data System (ADS)

    Allen, David J.; Tomazic, William A.

    1987-12-01

    As part of the DOE/NASA Automotive Stirling Engine Project, tests were made at NASA Lewis Research Center to determine whether appendix gap losses could be reduced and Stirling engine performance increased by installing an additional piston ring near the top of each piston dome. An MTI-designed upgraded Mod I Automotive Stirling Engine was used. Unlike the conventional rings at the bottom of the piston, these hot rings operated in a high temperature environment (700 C). They were made of a high temperature alloy (Stellite 6B) and a high temperature solid lubricant coating (NASA Lewis-developed PS-200) was applied to the cylinder walls. Engine tests were run at 5, 10, and 15 MPa operating pressure over a range of operating speeds. Tests were run both with hot rings and without to provide a baseline for comparison. Minimum data to assess the potential of both the hot rings and high temperature low friction coating was obtained. Results indicated a slight increase in power and efficiency, an increase over and above the friction loss introduced by the hot rings. Seal leakage measurements showed a significant reduction. Wear on both rings and coating was low.