Science.gov

Sample records for adjacent metal atoms

  1. Metal content of biopsies adjacent to dental cast alloys.

    PubMed

    Garhammer, Pauline; Schmalz, G; Hiller, K-A; Reitinger, T

    2003-06-01

    Single case reports indicate that components of dental alloys accumulate in the adjacent soft tissue of the oral cavity. However, data on a wider range of dental alloys and patient groups are scarce. Therefore, the aim of the present study was to examine the metal content of oral tissues adjacent to dental alloys showing persisting signs of inflammation or other discoloration (affected sites) and of healthy control sites with no adjacent metal restoration in 28 patients. The composition of the adjacent alloys was analyzed and compared to the alloy components in the affected sites. Tissue analysis was performed using atomic absorption spectroscopy. Alloy analysis was performed with energy-dispersive X-ray analysis. In the affected sites, the metals Ag, Au, Cu, and Pd prevailed compared to control sites, reflecting the frequency distribution of single metals in the adjacent alloys. In most cases (84%), at least one of the analyzed metals was a component of the alloy and also detected in the tissue. Metal components from almost all dental cast alloys can be detected in adjacent tissue.

  2. 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)

  3. 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.

  4. Metal atomization spray nozzle

    DOEpatents

    Huxford, T.J.

    1993-11-16

    A spray nozzle for a magnetohydrodynamic atomization apparatus has a feed passage for molten metal and a pair of spray electrodes mounted in the feed passage. The electrodes, diverging surfaces which define a nozzle throat and diverge at an acute angle from the throat. Current passes through molten metal when fed through the throat which creates the Lorentz force necessary to provide atomization of the molten metal. 6 figures.

  5. Metal atomization spray nozzle

    DOEpatents

    Huxford, Theodore J.

    1993-01-01

    A spray nozzle for a magnetohydrodynamic atomization apparatus has a feed passage for molten metal and a pair of spray electrodes mounted in the feed passage. The electrodes, diverging surfaces which define a nozzle throat and diverge at an acute angle from the throat. Current passes through molten metal when fed through the throat which creates the Lorentz force necessary to provide atomization of the molten metal.

  6. Thermoelastic response of thin metal films and their adjacent materials

    SciTech Connect

    Kang, S.; Yoon, Y.; Kim, J.; Kim, W.

    2013-01-14

    A pulsed laser beam applied to a thin metal film is capable of launching an acoustic wave due to thermal expansion. Heat transfer from the thin metal film to adjacent materials can also induce thermal expansion; thus, the properties of these adjacent materials (as well as the thin metal film) should be considered for a complete description of the thermoelastic response. Here, we show that adjacent materials with a small specific heat and large thermal expansion coefficient can generate an enhanced acoustic wave and we demonstrate a three-fold increase in the peak pressure of the generated acoustic wave on substitution of parylene for polydimethylsiloxane.

  7. The Thermomagnetic Instability in Superconducting Films with Adjacent Metal Layer

    NASA Astrophysics Data System (ADS)

    Vestgården, J. I.; Galperin, Y. M.; Johansen, T. H.

    2013-12-01

    Dendritic flux avalanches is a frequently encountered consequence of the thermomagnetic instability in type-II superconducting films. The avalanches, which are potentially harmful for superconductor-based devices, can be suppressed by an adjacent normal metal layer, even when the two layers are not in thermal contact. The suppression of the avalanches in this case is due to so-called magnetic braking, caused by eddy currents generated in the metal layer by propagating magnetic flux. We develop a theory of magnetic braking by analyzing coupled electrodynamics and heat flow in a superconductor-normal metal bilayer. The equations are solved by linearization and by numerical simulation of the avalanche dynamics. We find that in an uncoated superconductor, even a uniform thermomagnetic instability can develop into a dendritic flux avalanche. The mechanism is that a small non-uniformity caused by the electromagnetic non-locality induces a flux-flow hot spot at a random position. The hot spot quickly develops into a finger, which at high speeds penetrates into the superconductor, forming a branching structure. Magnetic braking slows the avalanches, and if the normal metal conductivity is sufficiently high, it can suppress the formation of the dendritic structure. During avalanches, the braking by the normal metal layer prevents the temperature from exceeding the transition temperature of the superconductor. Analytical criteria for the instability threshold are developed using the linear stability analysis. The criteria are found to match quantitatively the instability onsets obtained in simulations.

  8. 38. METAL WORKING TOOLS AND MACHINES ADJACENT TO THE CIRCA ...

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

    38. METAL WORKING TOOLS AND MACHINES ADJACENT TO THE CIRCA 1900 MICHIGAN MACHINERY MFG. CO. PUNCH PRESS NEAR THE CENTER OF THE FACTORY BUILDING. AT THE LEFT FOREGROUND IS A MOVABLE TIRE BENDER FOR SHAPING ELI WINDMILL WHEEL RIMS. AT THE CENTER IS A FLOOR-MOUNTED CIRCA 1900 SNAG GRINDER OF THE TYPE USED FOR SMOOTHING ROUGH CASTINGS. ON THE WHEELED WORK STATION IS A SUNNEN BUSHING GRINDER, BEHIND WHICH IS A TRIPOD CHAIN VICE. IN THE CENTER BACKGROUND IS A WOODEN CHEST OF DRAWERS WHICH CONTAINS A 'RAG DRAWER' STILL FILLED WITH CLOTH RAGS PLACED IN THE FACTORY BUILDING AT THE INSISTENCE OF LOUISE (MRS. ARTHUR) KREGEL FOR THE CONVENIENCE AND CLEANLINESS OF WORKERS. IN THE LEFT BACKGROUND IS A CIRCA 1900 CROSS-CUTOFF CIRCULAR SAW. - Kregel Windmill Company Factory, 1416 Central Avenue, Nebraska City, Otoe County, NE

  9. Atomic oxygen effects on metals

    NASA Technical Reports Server (NTRS)

    Fromhold, Albert T.

    1987-01-01

    The effect of specimen geometry on the attack of metals by atomic oxygen is addressed. This is done by extending the coupled-currents approach in metal oxidation to spherical and cylindrical geometries. Kinetic laws are derived for the rates of oxidation of samples having these geometries. It is found that the burn-up time for spherical particles of a given diameter can be as much as a factor of 3 shorter than the time required to completely oxidize a planar sample of the same thickness.

  10. Assessment of heavy metal levels in surface sediments of estuaries and adjacent coastal areas in China

    NASA Astrophysics Data System (ADS)

    Liu, Xianbin; Li, Deliang; Song, Guisheng

    2017-03-01

    This article investigates the variations of contamination levels of heavy metals such as copper, lead, chromium, cadmium, zinc, arsenic, and mercury over time in surface sediments of the Changjiang River Estuary (CRE), Yellow River Estuary (YRE), Pearl River Estuary (PRE), and their adjacent coastal areas in China. The contamination factor (CF), pollution load index (PLI), and geoaccumulation index ( I geo) are used to evaluate the quality of the surface sediments in the study areas. The results showed that the CRE, YRE, and their adjacent coastal areas were at a low risk of contamination in terms of heavy metals, while the PRE and its adjacent coastal area were at a moderate level. By comparison, the concentrations of heavy metals in the surface sediments of the YRE and its adjacent coastal area were relatively lower than those in the CRE, PRE, and their adjacent coastal areas.

  11. Assessment of heavy metal levels in surface sediments of estuaries and adjacent coastal areas in China

    NASA Astrophysics Data System (ADS)

    Liu, Xianbin; Li, Deliang; Song, Guisheng

    2016-05-01

    This article investigates the variations of contamination levels of heavy metals such as copper, lead, chromium, cadmium, zinc, arsenic, and mercury over time in surface sediments of the Changjiang River Estuary (CRE), Yellow River Estuary (YRE), Pearl River Estuary (PRE), and their adjacent coastal areas in China. The contamination factor (CF), pollution load index (PLI), and geoaccumulation index (I geo) are used to evaluate the quality of the surface sediments in the study areas. The results showed that the CRE, YRE, and their adjacent coastal areas were at a low risk of contamination in terms of heavy metals, while the PRE and its adjacent coastal area were at a moderate level. By comparison, the concentrations of heavy metals in the surface sediments of the YRE and its adjacent coastal area were relatively lower than those in the CRE, PRE, and their adjacent coastal areas.

  12. Permeability tensor for a metamaterial adjacent to a metal

    NASA Astrophysics Data System (ADS)

    Porvatkina, Olga V.; Tishchenko, Alexey A.; Strikhanov, Mikhail N.

    2017-01-01

    In our work, we investigate magnetic properties of metamaterial-metal interface with the help of the local field theory combined with the method of images. Proceeding from microscopic description of the substance and calculating its macroscopic properties, for the first time the modified Clausius-Mossotti relation has been obtained for permeability of the metamaterial bordering a metal.

  13. Comprehensive assessment of heavy metal contamination in sediment of the Pearl River Estuary and adjacent shelf.

    PubMed

    Yang, Yongqiang; Chen, Fanrong; Zhang, Ling; Liu, Jinsong; Wu, Shijun; Kang, Mingliang

    2012-09-01

    Total metal concentrations (Cr, Ni, Cu, Zn, and Pb), acid volatile sulfide and simultaneously extracted metals (AVS-SEM), and heavy metal fractionation were used to assess the heavy metals contamination status and ecological risk in the sediments of the Pearl River Estuary (PRE) and adjacent shelf. Elevated concentrations at estuarine sites and lower concentrations at adjacent shelf sites are observed, especially for Cu and Zn. Within the PRE, the concentration of heavy metals in the western shore was mostly higher than that in the middle shore. The metals from anthropogenic sources mainly occur in the labile fraction and may be taken up by organisms as the environmental parameters change. A combination of total metal concentrations, metal contamination index and sequential extraction analysis is necessary to get the comprehensive information on the baseline, anthropogenic discharge and bioavailability of heavy metals.

  14. Atomic Bond Deficiency Defects in Amorphous Metals

    NASA Astrophysics Data System (ADS)

    Zhu, Aiwu; Shiflet, Gary J.; Poon, S. Joseph

    2012-10-01

    Atomic bond deficiency (BD) is considered to be characteristic structural defects in amorphous metals. They are the necessary feature of local atomic configurations that facilitate various atomic transports under different driving forces. Compared with vacancies in crystalline solids, they are "small" in terms of their formation energies, volume costs, and elementary steps involved in atomic transport. This article reviews the authors' recent efforts made to analyze how various local configurations containing BD are related to amorphous metal's unique characteristics, such as glass transition, diffusion, shear flow, and structural relaxation.

  15. Atomization of metal (Materials Preparation Center)

    SciTech Connect

    2010-01-01

    Atomization of metal requires high pressure gas and specialized chambers for cooling and collecting the powders without contamination. The critical step for morphological control is the impingement of the gas on the melt stream. The video is a color video of a liquid metal stream being atomized by high pressure gas. This material was cast at the Ames Laboratorys Materials Preparation Center http://www.mpc.ameslab.gov WARNING - AUDIO IS LOUD.

  16. Advanced atom chips with two metal layers.

    SciTech Connect

    Stevens, James E.; Blain, Matthew Glenn; Benito, Francisco M.; Biedermann, Grant

    2010-12-01

    A design concept, device layout, and monolithic microfabrication processing sequence have been developed for a dual-metal layer atom chip for next-generation positional control of ultracold ensembles of trapped atoms. Atom chips are intriguing systems for precision metrology and quantum information that use ultracold atoms on microfabricated chips. Using magnetic fields generated by current carrying wires, atoms are confined via the Zeeman effect and controllably positioned near optical resonators. Current state-of-the-art atom chips are single-layer or hybrid-integrated multilayer devices with limited flexibility and repeatability. An attractive feature of multi-level metallization is the ability to construct more complicated conductor patterns and thereby realize the complex magnetic potentials necessary for the more precise spatial and temporal control of atoms that is required. Here, we have designed a true, monolithically integrated, planarized, multi-metal-layer atom chip for demonstrating crossed-wire conductor patterns that trap and controllably transport atoms across the chip surface to targets of interest.

  17. Atomic Manipulation on Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Ternes, Markus; Lutz, Christopher P.; Heinrich, Andreas J.

    Half a century ago, Nobel Laureate Richard Feynman asked in a now-famous lecture what would happen if we could precisely position individual atoms at will [R.P. Feynman, Eng. Sci. 23, 22 (1960)]. This dream became a reality some 30 years later when Eigler and Schweizer were the first to position individual Xe atoms at will with the probe tip of a low-temperature scanning tunneling microscope (STM) on a Ni surface [D.M. Eigler, E.K. Schweizer, Nature 344, 524 (1990)].

  18. Atomic Transport in Metallic Glasses.

    DTIC Science & Technology

    1983-11-01

    creep, amorphous metals, canpositionally modulated films, structural relaxation, iso-configurational flow, bimolecular kinetics, Stokes-Einstein relation ...34 731471 60 rcoe F I iov s isasso Einstain relation from the viscosity. - S/N8CUN@4* 40 CLASSIPICATIOOW OF T04lS PAGEL(010 fON41 EW PREFACE This report...12- tion, B is related to the macroscopic interdiffusion coefficient, B, by r 2 K 13 I+ -.1 (2) where f; is the second derivative, with respect to

  19. Long-Term Retention of an Intraorbital Metallic Foreign Body Adjacent to the Optic Nerve

    PubMed Central

    Siedlecki, Andrew N.; Deng, Jie; Miller, Donald M.

    2016-01-01

    We report the case of an asymptomatic 47 year-old male patient who suffered a penetrating wound from a metallic foreign body that became embedded adjacent to the optic nerve for over thirty years, as well as the associated examination, imaging, and fundus photography. Intraorbital metallic foreign bodies can be well tolerated and may not require surgical intervention despite proximity to important structures. PMID:27818817

  20. Atomically Precise Metal Nanoclusters for Catalytic Application

    SciTech Connect

    Jin, Rongchao

    2016-11-18

    The central goal of this project is to explore the catalytic application of atomically precise gold nanoclusters. By solving the total structures of ligand-protected nanoclusters, we aim to correlate the catalytic properties of metal nanoclusters with their atomic/electronic structures. Such correlation unravel some fundamental aspects of nanocatalysis, such as the nature of particle size effect, origin of catalytic selectivity, particle-support interactions, the identification of catalytically active centers, etc. The well-defined nanocluster catalysts mediate the knowledge gap between single crystal model catalysts and real-world conventional nanocatalysts. These nanoclusters also hold great promise in catalyzing certain types of reactions with extraordinarily high selectivity. These aims are in line with the overall goals of the catalytic science and technology of DOE and advance the BES mission “to support fundamental research to understand, predict, and ultimately control matter and energy at the level of electrons, atoms, and molecules”. Our group has successfully prepared different sized, robust gold nanoclusters protected by thiolates, such as Au25(SR)18, Au28(SR)20, Au38(SR)24, Au99(SR)42, Au144(SR)60, etc. Some of these nanoclusters have been crystallographically characterized through X-ray crystallography. These ultrasmall nanoclusters (< 2 nm diameter) exhibit discrete electronic structures due to quantum size effect, as opposed to quasicontinuous band structure of conventional metal nanoparticles or bulk metals. The available atomic structures (metal core plus surface ligands) of nanoclusters serve as the basis for structure-property correlations. We have investigated the unique catalytic properties of nanoclusters (i.e. not observed in conventional nanogold catalysts) and revealed the structure-selectivity relationships. Highlights of our

  1. Carbon nanotube-clamped metal atomic chain

    PubMed Central

    Tang, Dai-Ming; Yin, Li-Chang; Li, Feng; Liu, Chang; Yu, Wan-Jing; Hou, Peng-Xiang; Wu, Bo; Lee, Young-Hee; Ma, Xiu-Liang; Cheng, Hui-Ming

    2010-01-01

    Metal atomic chain (MAC) is an ultimate one-dimensional structure with unique physical properties, such as quantized conductance, colossal magnetic anisotropy, and quantized magnetoresistance. Therefore, MACs show great potential as possible components of nanoscale electronic and spintronic devices. However, MACs are usually suspended between two macroscale metallic electrodes; hence obvious technical barriers exist in the interconnection and integration of MACs. Here we report a carbon nanotube (CNT)-clamped MAC, where CNTs play the roles of both nanoconnector and electrodes. This nanostructure is prepared by in situ machining a metal-filled CNT, including peeling off carbon shells by spatially and elementally selective electron beam irradiation and further elongating the exposed metal nanorod. The microstructure and formation process of this CNT-clamped MAC are explored by both transmission electron microscopy observations and theoretical simulations. First-principles calculations indicate that strong covalent bonds are formed between the CNT and MAC. The electrical transport property of the CNT-clamped MAC was experimentally measured, and quantized conductance was observed. PMID:20427743

  2. Separation of metal ions in nitrate solution by ultrasonic atomization

    NASA Astrophysics Data System (ADS)

    Sato, Masanori; Ikeno, Masayuki; Fujii, Toshitaka

    2004-11-01

    In the ultrasonic atomization of metal nitrate solutions, the molar ratio of metal ions is changed between solution and mist. Small molar metal ions tend to be transferred to mist by ultrasonic wave acceleration, while large molar ions tend to remain in solution. As a result, metal ions can be separated by ultrasonic atomization. We show experimental data and propose a conceptual mechanism for the ultrasonic separation of metal ions.

  3. Separation of metal ions in nitrate solution by ultrasonic atomization.

    PubMed

    Sato, Masanori; Ikeno, Masayuki; Fujii, Toshitaka

    2004-11-15

    In the ultrasonic atomization of metal nitrate solutions, the molar ratio of metal ions is changed between solution and mist. Small molar metal ions tend to be transferred to mist by ultrasonic wave acceleration, while large molar ions tend to remain in solution. As a result, metal ions can be separated by ultrasonic atomization. We show experimental data and propose a conceptual mechanism for the ultrasonic separation of metal ions.

  4. Trends in trace organic and metal concentrations in the Pechora and Kara Seas and adjacent rivers

    SciTech Connect

    Brooks, J.M.; Champ, M.A.; Wade, T.L.; Kennicutt, M.C. II; Chambers, L.; Davis, T.

    1995-12-31

    Trace organic (pesticides, PCBs, PAHs and dioxin/furan) and trace metal concentrations have been measured in surficial sediment and tissue (i.e., clam, fish liver and flesh) samples from the Pechora and Kara Seas and their adjacent rivers -- Pechora, Ob and Yenisey Rivers. Total PAH, PCB and total DDT and chlordane concentrations ranged in surficial sediments from n.d. to 810 ppb, n.d.--8.7 ppb, n.d.--1.2 ppb, and n.d.--1.2 ppb, respectively, in a suite of 40 samples from the Kara Sea and its adjacent rivers. The highest concentrations of many of the trace organic and metal contaminants were found in the lower part of the Yenisey River below the salt wedge. Some trace metals (As for example) were elevated in the Pechora River dispositional plume region. Dioxin ranged from 1.36 to 413 ppt in a subset of 20 sediment samples. Higher trace organic contaminant concentrations compared to sediments were found in tissue samples from the region, especially fish liver samples. Concentrations as high as 1,114 ppb total PAHs, 89 ppb chlordane, 1,011 ppb for total DDT and 663 ppb PCBs were found in some fish liver samples. Dioxin concentrations in tissue samples ranged from 11.7 to 61 ppt. Concentrations of many trace organic and metal contaminants in these Russian marginal seas are influenced by inputs from these large Arctic rivers. Many organic contaminant concentrations in sediments are low, however detecting these compounds in tissue show they are bioavailable.

  5. Toxicity and bioavailability of metals in the Missouri River adjacent to a lead refinery

    USGS Publications Warehouse

    Chapman, Duane C.; Allert, Ann L.; Fairchild, James F.; May, Thomas W.; Schmitt, Christopher J.; Callahan, Edward V.

    2001-01-01

    This study is an evaluation of the potential environmental impacts of contaminated groundwater from the ASARCO metals refining facility adjacent to the Missouri River in Omaha, Nebraska. Surface waters, sediments, and sediment pore waters were collected from the Burt-Izard drain, which transects the facility, and from the Missouri River adjacent to the facility. Groundwater was also collected from the facility. Waters and sediments were analyzed for inorganic contaminants, and the toxicity of the waters was evaluated with the Ceriodaphnia dubia 7-day test. Concentrations of several elemental contaminants were highly elevated in the groundwater, but not in river sediment pore waters. Lead concentrations were moderately elevated in whole sediment at one site, but lead concentrations in pore waters were low due to apparent sequestration by acid-volatile sulfides. The groundwater sample was highly toxic to C. dubia, causing 100% mortality. Even at the lowest groundwater concentration tested (6.25%) C. dubia survival was reduced; however, at that concentration, reproduction was not significantly different from upstream porewater reference samples. Sediment pore waters were not toxic, except reproduction in pore water collected from one downstream site was somewhat reduced. The decrease in reproduction could not be attributed to measured elemental contaminants.

  6. Bonds Between Metal Atoms: A New Mode of Transition Metal Chemistry.

    ERIC Educational Resources Information Center

    Cotton, F. Albert; Chisholm, Malcolm H.

    1982-01-01

    Discusses polynuclear metal clusters (containing two or more metal atoms bonded to one another as well as to nonmetallic elements), including their formation and applications. Studies of bonds between metal atoms reveal superconductors, organic-reaction catalysts, and photosensitive complexes that may play a role in solar energy. (JN)

  7. Fractal atomic-level percolation in metallic glasses.

    PubMed

    Chen, David Z; Shi, Crystal Y; An, Qi; Zeng, Qiaoshi; Mao, Wendy L; Goddard, William A; Greer, Julia R

    2015-09-18

    Metallic glasses are metallic alloys that exhibit exotic material properties. They may have fractal structures at the atomic level, but a physical mechanism for their organization without ordering has not been identified. We demonstrated a crossover between fractal short-range (<2 atomic diameters) and homogeneous long-range structures using in situ x-ray diffraction, tomography, and molecular dynamics simulations. A specific class of fractal, the percolation cluster, explains the structural details for several metallic-glass compositions. We postulate that atoms percolate in the liquid phase and that the percolating cluster becomes rigid at the glass transition temperature.

  8. Atomizing apparatus for making polymer and metal powders and whiskers

    DOEpatents

    Otaigbe, Joshua U.; McAvoy, Jon M.; Anderson, Iver E.; Ting, Jason; Mi, Jia; Terpstra, Robert

    2003-03-18

    Method for making polymer particulates, such as spherical powder and whiskers, by melting a polymer material under conditions to avoid thermal degradation of the polymer material, atomizing the melt using gas jet means in a manner to form atomized droplets, and cooling the droplets to form polymer particulates, which are collected for further processing. Atomization parameters can be controlled to produce polymer particulates with controlled particle shape, particle size, and particle size distribution. For example, atomization parameters can be controlled to produce spherical polymer powders, polymer whiskers, and combinations of spherical powders and whiskers. Atomizing apparatus also is provided for atoomizing polymer and metallic materials.

  9. Hall Determination of Atomic Radii of Alkali Metals

    ERIC Educational Resources Information Center

    Houari, Ahmed

    2008-01-01

    I will propose here an alternative method for determining atomic radii of alkali metals based on the Hall measurements of their free electron densities and the knowledge of their crystal structure. (Contains 2 figures.)

  10. Atomic Natural Orbital Basis Sets for Transition Metals

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Taylor, Peter R.

    1993-01-01

    We show that atomic natural orbitals are an excellent way to contract transition-metal basis sets, even though the different low-lying electronic states may have very different basis set requirements.

  11. Endohedral metal atoms in pristine and functionalized fullerene cages.

    PubMed

    Yamada, Michio; Akasaka, Takeshi; Nagase, Shigeru

    2010-01-19

    Fullerene, an allotropic form of carbon made up of spherical molecules formed from pentagonal and hexagonal rings, was first discovered in 1985. Because fullerenes have spacious inner cavities, atoms and clusters can be encapsulated inside the fullerene cages to form endohedral fullerenes. In particular, the unique structural and electronic properties of endohedral metallofullerenes (EMFs), where metal atoms are encapsulated within the fullerene, have attracted wide interest from physicists and chemists as well as materials scientists and biologists. The remarkable characteristics of these molecules originate in the electron transfer from the encapsulated metal atoms to the carbon cage. The positions and movements of the encapsulated metal atoms are important determinants of the chemical and physical properties of EMFs. In this Account, we specifically describe the positions and dynamic behavior of the metal atoms encapsulated in pristine and functionalized fullerene cages. First, we examined whether the metal atoms are attached rigidly to cage carbons or move around. Our systematic investigations of EMFs, including M@C(2v)-C(82), M(2)@D(2)(10611)-C(72), M(2)@D(3h)(5)-C(78), M(2)@I(h)-C(80), and M(2)@D(5h)-C(80), revealed that the metal positions and movements vary widely with different cage structures and numbers of metal atoms. Second, we wanted to understand whether we could control the positions and movements of the untouchable metal atoms in EMFs. One possible way to modulate this behavior was through attachment of a molecule to the outer surface of the cage. We developed synthetic methods to modify EMFs and have examined the metal positions and movements in the functionalized carbon cages. Remarkably, we could alter the dynamic behavior of the encaged metal atoms in M(2)@I(h)-C(80) drastically through chemical modification of the outer cage. We anticipate that the control of metal atom structures and dynamics within a cage could be valuable for designing

  12. The shells of atomic structure in metallic glasses

    NASA Astrophysics Data System (ADS)

    Pan, S. P.; Feng, S. D.; Qiao, J. W.; Dong, B. S.; Qin, J. Y.

    2016-02-01

    We proposed a scheme to describe the spatial correlation between two atoms in metallic glasses. Pair distribution function in a model iron was fully decomposed into several shells and can be presented as the spread of nearest neighbor correlation via distance. Moreover, angle distribution function can also be decomposed into groups. We demonstrate that there is close correlation between pair distribution function and angle distribution function for metallic glasses. We think that our results are very helpful understanding the atomic structure of metallic glasses.

  13. Statistical thermodynamics and atomic structure of metallic glasses

    NASA Astrophysics Data System (ADS)

    Lass, Eric Andrew

    The purpose of this research is to develop an improved atomic scale understanding of the thermodynamic and kinetic behavior of a metallic glass. A realistic link between the macroscopic and atomic behavior of a metallic glass has not yet been achieved. The most widespread model describing the amorphous state, borrowed from the description of liquids, is the free volume model. It is primarily phenomenological, and does not explain the observed properties of a metallic glass in many aspects. This is because the idea of free volume in a metallic glass is fundamentally flawed in several respects. For example, unlike in the liquid phase, atomic mobility is limited in a glass, and requires thermal activation. Recently, structural models have been developed based on the idea of efficient atomic packing. While geometric these models successfully describe atomic structure, the underlying governing principles, thermodynamics, are mitigated or often neglected. The model described in this work takes advantage of the short-range atomic order inherent in metallic glasses. Developed around the central atoms model (CAM), it uses a statistical thermodynamic approach, and can more accurately describe the amorphous state on the atomic level. Each atom is considered to be surrounded by a "cage" of nearest-neighbors (NNs). In an ideal metallic glass, these cages are described by geometrically preferred configurations. The enthalpy of each possible NN cage is calculated from the energy of a cluster of two, three, or four atoms. The structure and thermodynamics of the metallic glass are dependent on the probability distributions of NN cages. Defects, termed bond deficiencies (BDs), are introduced into the model, and are analogous to vacancies in a crystalline material, except they occupy less volume, and cost less energy to create. These defects are considered to be thermodynamically stable, and provide the primary vehicle of atomic transport. CAM is applied to ideal and defect

  14. Distribution and source identification of trace metals in the sediment of Yellow River Estuary and the adjacent Laizhou Bay

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Ling, Min; Liu, Ru-hai; Yu, Ping; Tang, Ai-kun; Luo, Xian-xiang; Ma, Qimin

    2017-02-01

    Rapid economic development in the Yellow River basin has inevitably resulted in increase of pollution in the estuary, and concern for both the environment and protection against pollutants is increasing. Contents of trace metals (Cu, Pb Zn, Cr, Cd, As, Hg), Fe, Al, total organic carbon (TOC), and their granulometry were determined in surface sediment samples from the Yellow River estuary and its adjacent areas. Metal contents were significantly correlated each other. Clay, TOC and heavy metal contents showed similar distribution characteristics, with concentrations increased from the land to the sea. The distribution of grain size plays an important role in influencing the distribution of trace metals. Heavy metal concentrations showed a significant relationship with Fe and Al content, while most heavy metals were not enriched. These results were also confirmed by the analysis of enrichment factors and principal component analysis of the metals. The metal content of the Yellow River Estuary sediments was similar to the content observed 20 years ago, but the concentrations of most metals in Laizhou Bay decreased. The decrease in the carrying sediment of the Yellow River might be responsible for this pattern.

  15. Atomic and electronic structure of Ni-Nb metallic glasses

    SciTech Connect

    Yuan, C. C.; Yang, Y.-F. Xi, X. K.

    2013-12-07

    Solid state {sup 93}Nb nuclear magnetic resonance spectroscopy has been employed to investigate the atomic and electronic structures in Ni-Nb based metallic glass (MG) model system. {sup 93}Nb nuclear magnetic resonance (NMR) isotropic metallic shift of Ni{sub 60}Nb{sub 35}Sn{sub 5} has been found to be ∼100 ppm lower than that of Ni{sub 60}Nb{sub 35}Zr{sub 5} MG, which is correlated with their intrinsic fracture toughness. The evolution of {sup 93}Nb NMR isotropic metallic shifts upon alloying is clearly an electronic origin, as revealed by both local hyperfine fields analysis and first-principle computations. This preliminary result indicates that, in addition to geometrical considerations, atomic form factors should be taken into a description of atomic structures for better understanding the mechanical behaviors of MGs.

  16. Simulation of powder metal fabrication with high pressure gas atomization

    SciTech Connect

    Kuntz, D.W.; Payne, J.L.

    1994-12-31

    A computational/analytical technique has been developed which models the physics of high pressure gas atomization. The technique uses an uncoupled approach, such that the gas flowfield is initially calculated with a commercially-available Navier-Stokes code. The liquid metal droplet breakup, dynamics, and thermodynamics, are then calculated using the pre-computed flowfield by a separate computer program written by the authors. The atomization code models the primary breakup of the liquid metal stream, tracks the droplets resulting from primary breakup through the flowfield until they undergo secondary breakup, and then tracks the subdroplets until they breakup, solidify, or leave the flowfield region of interest. The statistical properties of the metal powder produced are then computed from the characteristics of these droplets. Comparisons between experimental measurements and computations indicate that the Navier-Stokes code is predicting the gas flowfield well, and that the atomization code is properly modeling the physics of the droplet dynamics and breakup.

  17. Application of the model of delocalized atoms to metallic glasses

    NASA Astrophysics Data System (ADS)

    Sanditov, D. S.; Darmaev, M. V.; Sanditov, B. D.

    2017-01-01

    The parameters of the model of delocalized atoms applied to metallic glasses have been calculated using the data on empirical constants of the Vogel-Fulcher-Tammann equation (for the temperature dependence of viscosity). It has been shown that these materials obey the same glass-formation criterion as amorphous organic polymers and inorganic glasses. This fact qualitatively confirms the universality of the main regularities of the liquid-glass transition process for all amorphous materials regardless of their origin. The energy of the delocalization of an atom in metallic glasses, Δɛ e ≈ 20-25 kJ/mol, coincides with the results obtained for oxide inorganic glasses. It is substantially lower than the activation energies for a viscous flow and for ion diffusion. The delocalization of an atom (its displacement from the equilibrium position) for amorphous metallic alloys is a low-energy small-scale process similar to that for other glass-like systems.

  18. Atomic resolution electron microscopy of small metal clusters

    NASA Astrophysics Data System (ADS)

    Bovin, J.-O.; Malm, J.-O.

    1991-03-01

    Atomic resolution imaging of cluster structures has been performed with high resolution transmission electron microscopy (HRTEM). Metal particles of the sizes 1 nanometer to tens of nanometers have been surface profile imaged on different supports; like zeolites, cordierite and amorphous carbon. It is shown that organic ligands in Schmid-clusters coordinated to the metal surface are desorbed or destroyed by the electron beam. Dynamic events on the surfaces and in the bulk of small metal particles have been recorded for small crystals of Au, Pt, Rh and Pb and can be classified under three headings; The smaller the crystals are the faster rearrangements of the crystal structure; “clouds” of atoms existing outside some surfaces are involved in extensive structural rearrangements of the surface or crystal surface growth; localized atom hopping on surfaces during crystal growth and desorption also occurs.

  19. Relating Dynamic Properties to Atomic Structure in Metallic Glasses

    SciTech Connect

    Sheng, H.W.; Ma, E.; Kramer, Matthew J.

    2012-07-18

    Atomic packing in metallic glasses is not completely random but displays various degrees of structural ordering. While it is believed that local structures profoundly affect the properties of glasses, a fundamental understanding of the structure–property relationship has been lacking. In this article, we provide a microscopic picture to uncover the intricate interplay between structural defects and dynamic properties of metallic glasses, from the perspective of computational modeling. Computational methodologies for such realistic modeling are introduced. Exploiting the concept of quasi-equivalent cluster packing, we quantify the structural ordering of a prototype metallic glass during its formation process, with a new focus on geometric measures of subatomic “voids.” Atomic sites connected with the voids are found to be crucial in terms of understanding the dynamic, including vibrational and atomic transport, properties. Normal mode analysis is performed to reveal the structural origin of the anomalous boson peak (BP) in the vibration spectrum of the glass, and its correlation with atomic packing cavities. Through transition-state search on the energy landscape of the system, such structural disorder is found to be a facilitating factor for atomic diffusion, with diffusion energy barriers and diffusion pathways significantly varying with the degree of structural relaxation/ordering. The implications of structural defects for the mechanical properties of metallic glasses are also discussed.

  20. Optical response of alkali metal atoms confined in nanoporous glass

    SciTech Connect

    Burchianti, A; Marinelli, C; Mariotti, E; Bogi, A; Marmugi, L; Giomi, S; Maccari, M; Veronesi, S; Moi, L

    2014-03-28

    We study the influence of optical radiation on adsorption and desorption processes of alkali metal atoms confined in nanoporous glass matrices. Exposure of the sample to near-IR or visible light changes the atomic distribution inside the glass nanopores, forcing the entire system to evolve towards a different state. This effect, due to both atomic photodesorption and confinement, causes the growth and evaporation of metastable nanoparticles. It is shown that, by a proper choice of light characteristics and pore size, these processes can be controlled and tailored, thus opening new perspectives for fabrication of nanostructured surfaces. (nanoobjects)

  1. Alloyed 2D Metal-Semiconductor Atomic Layer Junctions.

    PubMed

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

    2016-03-09

    Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1-xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices.

  2. Evolution of atomic rearrangements in deformation in metallic glasses.

    PubMed

    Shang, B S; Li, M Z; Yao, Y G; Lu, Y J; Wang, W H

    2014-10-01

    Atomic rearrangements induced by shear stress are fundamental for understanding deformation mechanisms in metallic glasses (MGs). Using molecular dynamic simulation, the atomic rearrangements characterized by nonaffine displacements (NADs) and their spatial distribution and evolution with tensile stress in Cu50Zr50 MG were investigated. It was found that in the elastic regime the atomic rearrangements with the largest NADs are relatively homogeneous in space, but exhibit strong spatial correlation, become localized and inhomogeneous, and form large clusters as strain increases, which may facilitate the so-called shear transformation zones. Furthermore, initially they prefer to take place around Cu atoms which have more nonicosahedral configurations. As strain increases, the preference decays and disappears in the plastic regime. The atomic rearrangements with the smallest NADs are preferentially located around Cu atoms, too, but with more icosahedral or icosahedral-like atomic configurations. The preference is maintained in the whole deformation process. In contrast, the atomic rearrangements with moderate NADs distribute homogeneously, and do not show explicit preference or spatial correlation, acting as matrix during deformation. Among the atomic rearrangements with different NADs, those with largest and smallest NADs are nearest neighbors initially, but separating with increasing strain, while those with largest and moderate NADs always avoid to each other. The correlations in the fluctuations of the NADs confirm the long-range strain correlation and the scale-free characteristic of NADs in both elastic and plastic deformation, which suggests a universality of the scaling in the plastic flow in MGs.

  3. Clustered field evaporation of metallic glasses in atom probe tomography.

    PubMed

    Zemp, J; Gerstl, S S A; Löffler, J F; Schönfeld, B

    2016-03-01

    Field evaporation of metallic glasses is a stochastic process combined with spatially and temporally correlated events, which are referred to as clustered evaporation (CE). This phenomenon is investigated by studying the distance between consecutive detector hits. CE is found to be a strongly localized phenomenon (up to 3nm in range) which also depends on the type of evaporating ions. While a similar effect in crystals is attributed to the evaporation of crystalline layers, CE of metallic glasses presumably has a different - as yet unknown - physical origin. The present work provides new perspectives on quantification methods for atom probe tomography of metallic glasses.

  4. Transition-Metal Substitution Doping in Synthetic Atomically Thin Semiconductors

    SciTech Connect

    Gao, Jian; Kim, Young Duck; Liang, Liangbo; Idrobo, Juan Carlos; Chow, Phil; Tan, Jiawei; Li, Baichang; Li, Lu; Sumpter, Bobby G.; Lu, Toh-Ming; Meunier, Vincent; Hone, James; Koratkar, Nikhil

    2016-09-20

    Semiconductor impurity doping has enabled an entire generation of technology. The emergence of alternative semiconductor material systems, such as transition metal dichalcogenides (TMDCs), requires the development of scalable doping strategies. We report an unprecedented one-pot synthesis for transition-metal substitution in large-area, synthetic monolayer TMDCs. Electron microscopy, optical and electronic transport characterization and ab initio calculations indicate that our doping strategy preserves the attractive qualities of TMDC monolayers, including semiconducting transport and strong direct-gap luminescence. These results are expected to encourage exploration of transition-metal substitution in two-dimensional systems, potentially enabling next-generation optoelectronic technology in the atomically-thin regime.

  5. Metal nanoparticles via the atom-economy green approach.

    PubMed

    Kalidindi, Suresh Babu; Sanyal, Udishnu; Jagirdar, Balaji R

    2010-05-03

    Metal nanoparticles (NPs) of Cu (air-stable), Ag, and Au have been prepared using an atom-economy green approach. Simple mechanical stirring of solid mixtures (no solvent) of a metal salt and ammonia borane at 60 degrees C resulted in the formation of metal NPs. In this reaction, ammonia borane is transformed into a BNH(x) polymer, which protects the NPs formed and halts their growth. This results in the formation of the BNH(x) polymer protected monodisperse NPs. Thus, ammonia borane used in these reactions plays a dual role (reducing agent and precursor for the stabilizing agent).

  6. Metal elements in the bottom sediments of the Changjiang Estuary and its adjacent continental shelf of the East China Sea.

    PubMed

    Cao, Lu; Hong, Gi Hoon; Liu, Sumei

    2015-06-15

    The metal elements (Al, Fe, Mn, Cr, Co, Ni, Cu, Zn, As, Pb and Ca) in the bottom sediment of the Changjiang Estuary and its adjacent continental shelf of the East China Sea were studied to map their spatial distribution and to assess their potential risk to the marine biota. These metal concentrations except Ca were generally higher in the inner shelf and northeastern part, and were found to decrease from the coast to the offshore of the Changjiang Estuary. Sedimentary Ca was most abundant in the outer shelf sediments and decreased in inner shelf. Arsenic (As) appeared to be contaminated due to economic development from 1980s in the inner shelf overall, but the potential ecological risk from the selected metals was low in the coastal sea off the Changjiang.

  7. Induce magnetism into silicene by embedding transition-metal atoms

    SciTech Connect

    Sun, Xiaotian; Wang, Lu E-mail: yyli@suda.edu.cn; Lin, Haiping; Hou, Tingjun; Li, Youyong E-mail: yyli@suda.edu.cn

    2015-06-01

    Embedding transition-metal (TM) atoms into nonmagnetic nanomaterials is an efficient way to induce magnetism. Using first-principles calculations, we systematically investigated the structural stability and magnetic properties of TM atoms from Sc to Zn embedded into silicene with single vacancy (SV) and double vacancies (DV). The binding energies for different TM atoms correlate with the TM d-shell electrons. Sc, Ti, and Co show the largest binding energies of as high as 6 eV, while Zn has the lowest binding energy of about 2 eV. The magnetic moment of silicene can be modulated by embedding TM atoms from V to Co, which mainly comes from the 3d orbitals of TM along with partly contributions from the neighboring Si atoms. Fe atom on SV and Mn atom on DV have the largest magnetic moment of more than 3 μB. In addition, we find that doping of N or C atoms on the vacancy site could greatly enhance the magnetism of the systems. Our results provide a promising approach to design silicene-based nanoelectronics and spintronics device.

  8. Heavy metals accumulation in parts of paddy Oryza sativa L. grown in paddy field adjacent to ultrabasic soil

    NASA Astrophysics Data System (ADS)

    Hadif, Waqeed Mahdi; Rahim, Sahibin Abd; Sahid, Ismail; Bhuiyan, Atiqur Rahman; Ibrahim, Izyanti

    2015-09-01

    The present study was carried out to evaluate the accumulation and translocation of heavy metals from soil around the root zone to various parts of the paddy plant, namely the roots, stems, leaves and rice grains. This study was conducted in 2014 in paddy field adjacent to ultrabasic soil (field 1 and 2) located in Ranau, Sabah and one field (Field 3) taken as control located at the UKM experimental plot in peninsular of Malaysia. The plant species used in the present investigation is Paddy Batu. The heavy metals studied were Chromium (Cr), Iron (Fe) and Nickel (Ni). Heavy metals in soil and plant were extracted by wet digestion method. Heavy metals present in paddy plants and soils extract were measured using the ICP-MS. Heavy metals concentrations in the plant parts in descending order is the root > leaves > stem > rice grain. Lower concentration of all heavy metals in soils and plant parts was shown by the control site (Field 3) in UKM Bangi. Higher concentration of heavy metals occurred in the roots compared to other above ground parts (stem, leaves, and grains) of the paddy plant in all of the paddy field. The bioaccumulation factor (BAF) of heavy metals in all locations were recorded in descending order as Ni > Cr > Fe, the BAF values for all metals in the rice grains were low, whereas the BAF values were recorded high for Ni in all locations. The results also showed that Fe was the most predominant metal ion in the roots, followed by Ni then Cr.

  9. Electronic metal-support interactions in single-atom catalysts.

    PubMed

    Hu, Pingping; Huang, Zhiwei; Amghouz, Zakariae; Makkee, Michiel; Xu, Fei; Kapteijn, Freek; Dikhtiarenko, Alla; Chen, Yaxin; Gu, Xiao; Tang, Xingfu

    2014-03-24

    The synthesis of single-atom catalysts and the control of the electronic properties of catalytic sites to arrive at superior catalysts is a major challenge in heterogeneous catalysis. A stable supported single-atom silver catalyst with a controllable electronic state was obtained by anti-Ostwald ripening. An electronic perturbation of the catalytic sites that is induced by a subtle change in the structure of the support has a strong influence on the intrinsic reactivity. The higher depletion of the 4d electronic state of the silver atoms causes stronger electronic metal-support interactions, which leads to easier reducibility and higher catalytic activity. These results may improve our understanding of the nature of electronic metal-support interactions and lead to structure-activity correlations.

  10. Elastic properties and atomic bonding character in metallic glasses

    SciTech Connect

    Rouxel, T.; Yokoyama, Y.

    2015-07-28

    The elastic properties of glasses from different metallic systems were studied in the light of the atomic packing density and bonding character. We found that the electronegativity mismatch (Δe{sup −}) between the host- and the major solute-elements provides a plausible explanation to the large variation observed for Poisson's ratio (ν) among metallic glasses (MGs) (from 0.28 for Fe-based to 0.43 for Pd-based MGs), notwithstanding a similar atomic packing efficiency (C{sub g}). Besides, it is found that ductile MGs correspond to Δe{sup −} smaller than 0.5 and to a relatively steep atomic potential well. Ductility is, thus, favored in MGs exhibiting a weak bond directionality on average and opposing a strong resistance to volume change.

  11. Atomic Diffusion and Molecular Self-Assembly on Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Jewell, April D.

    The research described herein focuses on understanding and exploiting nanometer-scale surface phenomena with respect to surface reactivity and self-assembled systems. Using scanning tunneling miscroscopy, atoms and small molecules ( i.e., fewer than 30 atoms) adsorbed on metal surfaces were studied with the objective being to capture, understand, and manipulate the events occurring at the interface between gases and solid surfaces. The specific approach was to examine a variety of different but related chemical species in order to understand how chemical functionality affects the assembly behavior of technologically important species on metal surfaces. Using this systematic approach, in which, for example, only a single atom (or group of atoms) in the adsorbed species was varied, it was possible to uncover subtle differences in assembly behavior and overlayer stability. These differences are explained in terms of the chemical properties of the differing atom(s), which are based on well-established periodic trends and governed by electrostatics. Similar studies focusing on varying ligand functionality are also presented. Findings from this research add to our understanding of fundamental chemical interactions that govern assembly at the gas/solid interface. Importantly, the work here contributes to the establishment of heuristic rules that, in the future, could help predict assembly behavior. The impact of this research has the potential to transform our approach to sensor technology, heterogeneous catalysis, and other related fields.

  12. Metal Contents in Lichens from Nature Reserves Adjacent to Urban Ecosystems

    NASA Astrophysics Data System (ADS)

    Meysurova, A. F.; Notov, A. A.

    2016-11-01

    The gross and average contents of 18 metals (Al, As, Cd, Ge, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Pb, Sb, Sn, Ti, V, Zn) were determined by ICP-AES analysis in samples of Hypogymnia physodes collected from regional nature reserves (NR) in the cities of Tver and Konakovo. The average contents of six metals (Zn, Mo, Cr, Ti, Al, Fe) and the gross contents of eight metals (Zn, Mo, Co, Cu, Cr, Ti, Al, Fe) in these cities were higher than the background levels for Tver Region. The contents of other metals did not exceed background levels. The concentrations of most metals were higher in samples from Tver than in those from Konakovo due to the specifics of their economic infrastructures. The Bobachevskaya Grove NR (Tver) had the most pronounced technological metal pollution. Areas with significant fragments of forest communities were less polluted.

  13. Origin of metallicity in atomic Ag wires on Si(557)

    NASA Astrophysics Data System (ADS)

    Krieg, U.; Lichtenstein, T.; Brand, C.; Tegenkamp, C.; Pfnür, H.

    2015-04-01

    We investigated the metallicity of Ag-\\sqrt{3} ordered atomic wires close to one monolayer (ML) coverage, which are formed on Si(557) via self assembly. For this purpose we combined high resolution electron energy loss spectroscopy with tunneling microscopy. By extending the excess Ag coverage up to 0.6 ML on samples annealed at high temperatures where partial desorption occurs, we demonstrate that one-dimensional metallicity in the Ag-\\sqrt{3}× \\sqrt{3} R30° ordered atomic wires on the (111) mini-terraces originates only from Ag atoms in excess of (local) monolayer coverage, which are adsorbed and localized at the highly stepped parts of the Si(557) surface. Thus these Ag atoms act as extrinsic dopants on the atomic scale, causing coverage dependent subband filling and increasing localization as a function of doping concentration. The second layer lattice gas as well as Ag islands on the (111) terraces turn out not to be relevant as dopants. We simulated the peculiar saturation behavior within a modified lattice gas model and give evidence that the preparation dependent saturation of doping is due to changes of average terrace size and step morphology induced by high temperature treatment.

  14. From single atoms to self-assembled quantum single-atomic nanowires: noble metal atoms on black phosphorene monolayers.

    PubMed

    Zhao, X J; Shan, Wen-Wen; He, Hao; Xue, Xinlian; Guo, Z X; Li, S F

    2017-03-15

    Transition metal (TM) nanostructures, such as one dimensional (1D) nanowires with/without substrates, usually possess drastically different properties from their bulk counterparts, due to their distinct stacking and electronic confinement. Correspondingly, it is of great importance to establish the dominant driving force in forming 1D single-metal-atom-wires (SMAWs). Here, with first-principles calculations, taking the black phosphorene (BP) monolayer as a prototype 2D substrate, we investigate the energetic and kinetic properties of all the 5d-TM atoms on the 2D substrate to reveal the mechanism of formation of SMAWs. In contrast to other 5d- and 4d-TMs, noble metal elements Pd and Pt are found to prefer to grow along the trough in an atom-by-atom manner, self-assembling into SMAWs with a significant magic growth behavior. This is due to distinct binding energies and diffusion barriers along the trough, i.e., zig-zag direction, as compared to other directions of the BP. The present findings are valuable in the fabrication and modulation of 1D nanostructures which can be anticipated to possess desirable functionalities for potential applications such as in nanocatalysis, nanosensors, and related areas.

  15. Issues involved in the atomic layer deposition of metals

    NASA Astrophysics Data System (ADS)

    Grubbs, Robert Kimes

    Auger Electron Spectroscopy (AES) was used to study the nucleation and growth of tungsten on aluminum oxide surfaces. Tungsten metal was deposited using Atomic Layer Deposition (ALD) techniques. ALD uses sequential surface reactions to deposit material with atomic layer control. W ALD is performed using sequential exposures of WF6 and Si2H6. The step-wise nature of W ALD allows nucleation studies to be performed by analyzing the W surface concentration after each ALD reaction. Nucleation and growth regions can be identified by quantifying the AES signal intensities from both the W surface and the Al2O3 substrate. W nucleation occurred in 3 ALD reaction cycles. The AES results yielded a nucleation rate of 1.0 A/ALD cycle and a growth rate of ≈3 A/ALD cycle. AES studies also explored the nucleation and growth of Al2O3 on W. Al2O3 nucleated in 1 ALD cycle giving a nucleation rate of 3.5 A/ALD cycle and a subsequent growth rate of 1.0 A/ALD cycle. Mass spectrometry was then used to study the ALD reaction chemistry of tungsten deposition. Because of the step-wise nature of the W ALD chemistry, each W ALD reaction could be studied independently. The gaseous mass products were identified from both the WF6 and Si2H6 reactions. H2, HF and SiF4 mass products were observed for the WF6 reaction. The Si2H6 reaction displayed a room temperature reaction and a 200°C reaction. Products from the room temperature Si2H6 reaction were H2 and SiF3H. The reaction at 200°C yielded only H2 as a reaction product. H2 desorption from the surface contributes to the 200°C Si2H6 reaction. AES was used to confirm that the gas phase reaction products are correlated with a change in the surface species. Atomic hydrogen reduction of metal halides and oganometallic compounds provides another method for depositing metals with atomic layer control. The quantity of atomic hydrogen necessary to perform this chemistry is critical to the metal ALD process. A thermocouple probe was constructed to

  16. Schottky barrier amorphous silicon solar cell with thin doped region adjacent metal Schottky barrier

    DOEpatents

    Carlson, David E.; Wronski, Christopher R.

    1979-01-01

    A Schottky barrier amorphous silicon solar cell incorporating a thin highly doped p-type region of hydrogenated amorphous silicon disposed between a Schottky barrier high work function metal and the intrinsic region of hydrogenated amorphous silicon wherein said high work function metal and said thin highly doped p-type region forms a surface barrier junction with the intrinsic amorphous silicon layer. The thickness and concentration of p-type dopants in said p-type region are selected so that said p-type region is fully ionized by the Schottky barrier high work function metal. The thin highly doped p-type region has been found to increase the open circuit voltage and current of the photovoltaic device.

  17. Probing Magnetism in 2D Molecular Networks after in Situ Metalation by Transition Metal Atoms.

    PubMed

    Schouteden, K; Ivanova, Ts; Li, Z; Iancu, V; Janssens, E; Van Haesendonck, C

    2015-03-19

    Metalated molecules are the ideal building blocks for the bottom-up fabrication of, e.g., two-dimensional arrays of magnetic particles for spintronics applications. Compared to chemical synthesis, metalation after network formation by an atom beam can yield a higher degree of control and flexibility and allows for mixing of different types of magnetic atoms. We report on successful metalation of tetrapyridyl-porphyrins (TPyP) by Co and Cr atoms, as demonstrated by scanning tunneling microscopy experiments. For the metalation, large periodic networks formed by the TPyP molecules on a Ag(111) substrate are exposed in situ to an atom beam. Voltage-induced dehydrogenation experiments support the conclusion that the porphyrin macrocycle of the TPyP molecule incorporates one transition metal atom. The newly synthesized Co-TPyP and Cr-TPyP complexes exhibit striking differences in their electronic behavior, leading to a magnetic character for Cr-TPyP only as evidenced by Kondo resonance measurements.

  18. Steady-state superradiance with alkaline-earth-metal atoms

    SciTech Connect

    Meiser, D.; Holland, M. J.

    2010-03-15

    Alkaline-earth-metal-like atoms with ultranarrow transitions open the door to a new regime of cavity quantum electrodynamics. That regime is characterized by a critical photon number that is many orders of magnitude smaller than what can be achieved in conventional systems. We show that it is possible to achieve superradiance in steady state with such systems. We discuss the basic underlying mechanisms as well as the key experimental requirements.

  19. Atom-by-Atom and Concerted Hopping of Adatom Pairs on an Open Metal Surface

    SciTech Connect

    Bogicevic, A.; Ovesson, S.; Lundqvist, B.I.; Jennison, D.R.

    1999-08-25

    Atom-by-atom and concerted hopping of ad-dimers on the open (100) surface of fcc metals are studied by means of density-functional calculations. The adatom interaction is relatively short-ranged, and beyond next-nearest neighbors ad-dimers are effectively dissociated. Diffusion takes place by a simple shearing process, favored because it maximizes adatom coordination at the transition state This holds for Al, Au, and Rh, and is likely a general result because geometrical arguments dominate over details of the electronic structure.

  20. Nonlinear pressure shifts of alkali-metal atoms in xenon

    NASA Astrophysics Data System (ADS)

    McGuyer, Bart; Xia, Tian; Jau, Yuan-Yu; Happer, William

    2011-05-01

    Compact, portable atomic frequency standards are based on the microwave resonance frequencies of alkali-metal atoms in inert buffer gases. The frequency shift of these resonances due to collisions with the buffer gas is known as the pressure shift. We demonstrate that the microwave resonance frequencies of ground-state 87Rb and 133Cs atoms have a nonlinear dependence on the pressure of the buffer gas Xe. Previous work has demonstrated a nonlinear dependence in Ar and Kr, but not He and N2, which is thought to be due to the loosely-bound van der Waals molecules that are known to form between alkali-metal and buffer-gas atoms in Ar, Kr, and Xe, but not He and N2. Surprisingly, we find that the nonlinearities in Xe are of the opposite sign to those in Ar and Kr, even though the overall shifts for each of these gases are negative. This discrepancy suggests that though the shifts due to the molecules in Ar and Kr are positive, the shifts due to the molecules in Xe are negative. No nonlinearities were observed in the buffer gas Ne to within our experimental accuracy, which suggests that molecules do not form in Ne. Additionally, we present improved measurements of the shifts of Rb and Cs in He and N2 and of Rb in Ar and Kr. This work was supported by the Air Force Office of Scientific Research and the Department of Defense through the NDSEG program.

  1. Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities.

    PubMed

    Jin, Rongchao; Zeng, Chenjie; Zhou, Meng; Chen, Yuxiang

    2016-09-28

    Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1-3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the stability, metal-ligand interfacial bonding, ligand assembly on particle surfaces, aesthetic structural patterns, periodicities, and emergence of the metallic state) and to develop a range of potential applications such as in catalysis, biomedicine, sensing, imaging, optics, and energy conversion. Although most of the research activity currently focuses on thiolate-protected gold nanoclusters, important progress has also been achieved in other ligand-protected gold, silver, and bimetal (or alloy) nanoclusters. All of these types of unique nanoparticles will bring unprecedented opportunities, not only in understanding the fundamental questions of nanoparticles but also in opening up new horizons for scientific studies of nanoparticles.

  2. EXAFS studies of the local atomic environment in metal-metal glasses

    SciTech Connect

    Wong, J.; Lytle, F. W.; Liebermann, H. H.; Tanner, L. E.

    1980-01-01

    The interatomic distances and nearest neighbor coordinations of constituent atoms in a series of metal-metal glasses: M'/sub 100-x/M''/sub x/ where M' = Zr, Nb, M'' = Fe, Ni, Cu and x varies from 30 to 60 at %, have been determined using the EXAFS technique in conjunction with the x-ray synchrotron source at Stanford. Fourier transforms of the EXAFS signals clearly indicate there are like as well as unlike atom pairs in the first coordination shell about both the M' and M'' atoms. The ratio of like and unlike pairs scales linearly with composition and is indicative of random mixing in these binary glasses. The M'-M'' separation are shorter than sum of the Goldschmidt radii and implies chemical interaction between the M' and M'' atoms.

  3. Heavy metal distribution in surface sediments from the continental shelf adjacent to Nazaré canyon

    NASA Astrophysics Data System (ADS)

    Oliveira, A.; Palma, C.; Valença, M.

    2011-12-01

    The continental shelf surface sediments around the Nazaré canyon have been analyzed for heavy metal contamination. Organic carbon content and grain size were also determined. The shelf area around the Nazaré canyon shows mean concentrations of Cr, Cu, Hg, Ni, Pb and Zn within the limits recommended by OSPAR (2008). Some enrichment and human impact was found for Cr and especially Pb. Local rivers, mainly the Mondego and southern creeks seem to be the major sources of heavy metals for the Nazaré area, showing similar contamination levels. A set of reference values for non-contaminated fine surface sediments (<63 μm) in the North-Eastern Atlantic are proposed for As, Al, Cd, Cr, Cu, Fe, Hg, Li, Mn, Ni, Pb and Zn.

  4. Electronic Relaxation Processes of Transition Metal Atoms in Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    Kautsch, Andreas; Lindebner, Friedrich; Koch, Markus; Ernst, Wolfgang E.

    2014-06-01

    Spectroscopy of doped superfluid helium nanodroplets (He_N) gives information about the influence of this cold, chemically inert, and least interacting matrix environment on the excitation and relaxation dynamics of dopant atoms and molecules. We present the results from laser induced fluorescence (LIF), photoionization (PI), and mass spectroscopy of Cr and Cu doped He_N. From these results, we can draw a comprehensive picture of the complex behavior of such transition metal atoms in He_N upon photo-excitation. The strong Cr and Cu ground state transitions show an excitation blueshift and broadening with respect to the bare atom transitions which can be taken as indication for the solvation inside the droplet. From the originally excited states the atoms relax to energetically lower states and are ejected from the He_N. The relaxation processes include bare atom spin-forbidden transitions, which clearly bears the signature of the He_N influence. Two-color resonant two-photon ionization (2CR2PI) also shows the formation of bare atoms and small Cr-He_n and Cu-He_n clusters in their ground and metastable states ^c. Currently, Cr dimer excitation studies are in progress and a brief outlook on the available results will be given. C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, 2011. A. Kautsch, M. Koch, and W. E. Ernst, J. Phys. Chem. A, 117 (2013) 9621-9625, DOI: 10.1021/jp312336m F. Lindebner, A. Kautsch, M. Koch, and W. E. Ernst, Int. J. Mass Spectrom. (2014) in press, DOI: 10.1016/j.ijms.2013.12.022 M. Koch, A. Kautsch, F. Lackner, and W. E. Ernst, submitted to J. Phys. Chem. A

  5. Advanced Electrochemistry of Individual Metal Clusters Electrodeposited Atom by Atom to Nanometer by Nanometer.

    PubMed

    Kim, Jiyeon; Dick, Jeffrey E; Bard, Allen J

    2016-11-15

    Metal clusters are very important as building blocks for nanoparticles (NPs) for electrocatalysis and electroanalysis in both fundamental and applied electrochemistry. Attention has been given to understanding of traditional nucleation and growth of metal clusters and to their catalytic activities for various electrochemical applications in energy harvesting as well as analytical sensing. Importantly, understanding the properties of these clusters, primarily the relationship between catalysis and morphology, is required to optimize catalytic function. This has been difficult due to the heterogeneities in the size, shape, and surface properties. Thus, methods that address these issues are necessary to begin understanding the reactivity of individual catalytic centers as opposed to ensemble measurements, where the effect of size and morphology on the catalysis is averaged out in the measurement. This Account introduces our advanced electrochemical approaches to focus on each isolated metal cluster, where we electrochemically fabricated clusters or NPs atom by atom to nanometer by nanometer and explored their electrochemistry for their kinetic and catalytic behavior. Such approaches expand the dimensions of analysis, to include the electrochemistry of (1) a discrete atomic cluster, (2) solely a single NP, or (3) individual NPs in the ensemble sample. Specifically, we studied the electrocatalysis of atomic metal clusters as a nascent electrocatalyst via direct electrodeposition on carbon ultramicroelectrode (C UME) in a femtomolar metal ion precursor. In addition, we developed tunneling ultramicroelectrodes (TUMEs) to study electron transfer (ET) kinetics of a redox probe at a single metal NP electrodeposited on this TUME. Owing to the small dimension of a NP as an active area of a TUME, extremely high mass transfer conditions yielded a remarkably high standard ET rate constant, k(0), of 36 cm/s for outer-sphere ET reaction. Most recently, we advanced nanoscale

  6. The concentration of radionuclides and metals in vegetation adjacent to and in the SRL Seepage Basins

    SciTech Connect

    Murphy, C. E. Jr.

    1992-12-14

    In 1991 the trees on the dikes surrounding the SRL Seepage Basins were sampled and analyzed to inventory the contaminants transported from the basins into the vegetation. Tree leaves and wood were collected and analyzed for {sup 90}Sr, {sup 60}Co, {sup 137}Cs, {sup 238}Pu, {sup 239,240}Pu, {sup 242,244}Cm, {sup 241}Am, Ba, Cr, Hg, Mg, Mn, Ni, and Pb. The concentrations of contaminants were influenced by sample type (leaves versus wood), species type (pines versus hardwoods), and location relative to distance from the basin. The total inventory of each contaminant in the trees was estimated. The relationships between leaf and wood, pines and hardwood, location, and mass of the material in each of these classes were used to weight the total inventory estimate. The radionuclide with the largest inventory was 0.7 mCi for {sup 90}Sr. The metallic contaminant with the largest inventory was Mn at 200 gm.

  7. The concentration of radionuclides and metals in vegetation adjacent to and in the SRL Seepage Basins

    SciTech Connect

    Murphy, C. E. Jr.

    1992-12-14

    In 1991 the trees on the dikes surrounding the SRL Seepage Basins were sampled and analyzed to inventory the contaminants transported from the basins into the vegetation. Tree leaves and wood were collected and analyzed for [sup 90]Sr, [sup 60]Co, [sup 137]Cs, [sup 238]Pu, [sup 239,240]Pu, [sup 242,244]Cm, [sup 241]Am, Ba, Cr, Hg, Mg, Mn, Ni, and Pb. The concentrations of contaminants were influenced by sample type (leaves versus wood), species type (pines versus hardwoods), and location relative to distance from the basin. The total inventory of each contaminant in the trees was estimated. The relationships between leaf and wood, pines and hardwood, location, and mass of the material in each of these classes were used to weight the total inventory estimate. The radionuclide with the largest inventory was 0.7 mCi for [sup 90]Sr. The metallic contaminant with the largest inventory was Mn at 200 gm.

  8. Plasmon confinement in atomically thin and flat metallic films

    NASA Astrophysics Data System (ADS)

    Nagao, T.; Yaginuma, S.; Liu, C.; Inaoka, T.; Nazarov, V. U.; Nakayama, T.; Aono, M.

    2007-09-01

    We report on the direct measurement of dispersion relations of plasmons confined in atomically thin metal films and wires by electron energy loss spectroscopy in wide energy-momentum range. Ultrathin Ag films are prepared on single crystal Si surfaces by molecular beam epitaxy, and its crystallinity is checked by electron diffraction. For the case of multi-atomic-layer Ag films, two plasmon modes are observed at around 3.9 eV and 1.8 eV which are localized at the top and the bottom surfaces of the films, respectively. For the case of Ag monoatomic layer, a single mode is observed that steeply disperses in the mid-infrared range. Nonlocal and quantum effects are found to be essential in understanding its full plasmon dispersion curve up to the critical wave number of Landau damping. For the case of Au atom chains, an anisotropic sound-wave-like plasmon dispersion is found that clearly shows 1D plasmon confinement in each atom chain.

  9. Adjacency graphs and long-range interactions of atoms in quasi-degenerate states: applied graph theory

    NASA Astrophysics Data System (ADS)

    Adhikari, C. M.; Debierre, V.; Jentschura, U. D.

    2017-01-01

    We analyze, in general terms, the evolution of energy levels in quantum mechanics, as a function of a coupling parameter, and demonstrate the possibility of level crossings in systems described by irreducible matrices. In long-range interactions, the coupling parameter is the interatomic distance. We demonstrate the utility of adjacency matrices and adjacency graphs in the analysis of "hidden" symmetries of a problem; these allow us to break reducible matrices into irreducible subcomponents. A possible breakdown of the no-crossing theorem for higher-dimensional irreducible matrices is indicated, and an application to the 2 S-2 S interaction in hydrogen is briefly described. The analysis of interatomic interactions in this system is important for further progress on optical measurements of the 2 S hyperfine splitting.

  10. Atomic picture of elastic deformation in a metallic glass

    DOE PAGES

    Wang, X. D.; Aryal, S.; Zhong, C.; ...

    2015-03-17

    The tensile behavior of a Ni₆₀Nb₄₀ metallic glass (MG) has been studied by using ab initio density functional theory (DFT) calculation with a large cell containing 1024 atoms (614 Ni and 410 Nb). We provide insight into how a super elastic limit can be achieved in a MG. Spatially inhomogeneous responses of single atoms and also major polyhedra are found to change greatly with increasing external stress when the strain is over 2%, causing the intrinsically viscoelastic behavior. We uncover the origin of the observed super elastic strain limit under tension (including linear and viscoelastic strains) in small-sized MG samples,more » mainly caused by inhomogeneous distribution of excess volumes in the form of newly formed subatomic cavities.« less

  11. Atomic-level level dislocation dynamics in irradiated metals

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2015-01-01

    Primary damage and microstructure evolution in structural nuclear materials operating under conditions of a high flux of energetic atomic particles and high temperature and stress lead to formation of a high concentration, non-homogeneous distribution of defect clusters in the form of dislocation loops, voids, gas-filled bubbles and radiation-induced precipitates of nanometer scale. They cause changes in many material properties. Being obstacles to dislocation glide, they strongly affect mechanical properties in particular. This gives rise to an increase in yield and flow stress and a reduction in ductility. Atomic-scale computer simulation can provide details of how these effects are influenced by obstacle structure, applied stress, strain rate and temperature. Processes such as obstacle cutting, transformation, absorption and drag are observed. Some recent results for body-centered and face-centered cubic metals are described in this review and, where appropriate, comparisons drawn with predictions based on elasticity theory of crystal defects.

  12. Atomic picture of elastic deformation in a metallic glass.

    PubMed

    Wang, X D; Aryal, S; Zhong, C; Ching, W Y; Sheng, H W; Zhang, H; Zhang, D X; Cao, Q P; Jiang, J Z

    2015-03-17

    The tensile behavior of a Ni60Nb40 metallic glass (MG) has been studied by using ab initio density functional theory (DFT) calculation with a large cell containing 1024 atoms (614 Ni and 410 Nb). We provide insight into how a super elastic limit can be achieved in a MG. Spatially inhomogeneous responses of single atoms and also major polyhedra are found to change greatly with increasing external stress when the strain is over 2%, causing the intrinsically viscoelastic behavior. We uncover the origin of the observed super elastic strain limit under tension (including linear and viscoelastic strains) in small-sized MG samples, mainly caused by inhomogeneous distribution of excess volumes in the form of newly formed subatomic cavities.

  13. Application of Density Functional Theory to Systems Containing Metal Atoms

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.

    2006-01-01

    The accuracy of density functional theory (DFT) for problems involving metal atoms is considered. The DFT results are compared with experiment as well as results obtained using the coupled cluster approach. The comparisons include geometries, frequencies, and bond energies. The systems considered include MO2, M(OH)+n, MNO+, and MCO+2. The DFT works well for frequencies and geometries, even in case with symmetry breaking; however, some examples have been found where the symmetry breaking is quite severe and the DFT methods do not work well. The calculation of bond energies is more difficult and examples of successes as well as failures of DFT will be given.

  14. Atomic scale modelling of hexagonal structured metallic fission product alloys.

    PubMed

    Middleburgh, S C; King, D M; Lumpkin, G R

    2015-04-01

    Noble metal particles in the Mo-Pd-Rh-Ru-Tc system have been simulated on the atomic scale using density functional theory techniques for the first time. The composition and behaviour of the epsilon phases are consistent with high-entropy alloys (or multi-principal component alloys)-making the epsilon phase the only hexagonally close packed high-entropy alloy currently described. Configurational entropy effects were considered to predict the stability of the alloys with increasing temperatures. The variation of Mo content was modelled to understand the change in alloy structure and behaviour with fuel burnup (Mo molar content decreases in these alloys as burnup increases). The predicted structures compare extremely well with experimentally ascertained values. Vacancy formation energies and the behaviour of extrinsic defects (including iodine and xenon) in the epsilon phase were also investigated to further understand the impact that the metallic precipitates have on fuel performance.

  15. Atomic scale modelling of hexagonal structured metallic fission product alloys

    PubMed Central

    Middleburgh, S. C.; King, D. M.; Lumpkin, G. R.

    2015-01-01

    Noble metal particles in the Mo-Pd-Rh-Ru-Tc system have been simulated on the atomic scale using density functional theory techniques for the first time. The composition and behaviour of the epsilon phases are consistent with high-entropy alloys (or multi-principal component alloys)—making the epsilon phase the only hexagonally close packed high-entropy alloy currently described. Configurational entropy effects were considered to predict the stability of the alloys with increasing temperatures. The variation of Mo content was modelled to understand the change in alloy structure and behaviour with fuel burnup (Mo molar content decreases in these alloys as burnup increases). The predicted structures compare extremely well with experimentally ascertained values. Vacancy formation energies and the behaviour of extrinsic defects (including iodine and xenon) in the epsilon phase were also investigated to further understand the impact that the metallic precipitates have on fuel performance. PMID:26064629

  16. Zero-Temperature Structures of Atomic Metallic Hydrogen

    NASA Astrophysics Data System (ADS)

    McMahon, Jeffrey; Ceperley, David

    2011-03-01

    Since the first prediction of an atomic metallic phase of hydrogen by Wigner and Huntington over 75 years ago, there have been many theoretical efforts aimed at determining the crystal structures of the zero-temperature phases. We present results from ab initio random structure searching with density functional theory performed to determine the ground state structures from 500 GPa to 5 TPa. We estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500 GPa (rs = 1.225), which then remains stable to 2.5 TPa (rs = 0.969). At higher pressures, hydrogen stabilizes in an . . . ABCABC . . . planar structure that is remarkably similar to the ground state of lithium, which compresses to the face-centered cubic lattice beyond 5 TPa (rs < 0.86). Our results provide a complete ab initio description of the atomic metallic crystal structures of hydrogen, resolving one of the most fundamental and long outstanding issues concerning the structures of the elements.

  17. Inhibiting Metal Oxide Atomic Layer Deposition: Beyond Zinc Oxide.

    PubMed

    Sampson, Matthew D; Emery, Jonathan D; Pellin, Michael J; Martinson, Alex B F

    2017-04-05

    Atomic layer deposition (ALD) of several metal oxides is selectivity inhibited on alkanethiol self-assembled monolayers (SAMs) on Au, and the eventual nucleation mechanism is investigated. The inhibition ability of the SAM is significantly improved by the in situ H2-plasma pretreatment of the Au substrate prior to the gas-phase deposition of a long-chain alkanethiol, 1-dodecanethiol (DDT). This more rigorous surface preparation inhibits even aggressive oxide ALD precursors, including trimethylaluminum and water, for at least 20 cycles. We study the effect that the ALD precursor purge times, growth temperature, alkanethiol chain length, alkanethiol deposition time, and plasma treatment time have on Al2O3 ALD inhibition. This is the first example of Al2O3 ALD inhibition from a vapor-deposited SAM. The inhibitions of Al2O3, ZnO, and MnO ALD processes are compared, revealing the versatility of this selective surface treatment. Atomic force microscopy and grazing-incidence X-ray fluorescence further reveal insight into the mechanism by which the well-defined surface chemistry of ALD may eventually be circumvented to allow metal oxide nucleation and growth on SAM-modified surfaces.

  18. Sources of heavy metals in surface sediments and an ecological risk assessment from two adjacent Plateau reservoirs.

    PubMed

    Wu, Binbin; Wang, Guoqiang; Wu, Jin; Fu, Qing; Liu, Changming

    2014-01-01

    The concentrations of heavy metals (mercury (Hg), cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu) and arsenic (As)) in surface water and sediments were investigated in two adjacent drinking water reservoirs (Hongfeng and Baihua Reservoirs) on the Yunnan-Guizhou Plateau in Southwest China. Possible pollution sources were identified by spatial and statistical analyses. For both reservoirs, Cd was most likely from industrial activities, and As was from lithogenic sources. For the Hongfeng Reservoir, Pb, Cr and Cu might have originated from mixed sources (traffic pollution and residual effect of former industrial practices), and the sources of Hg included the inflows, which were different for the North (industrial activities) and South (lithogenic origin) Lakes, and atmospheric deposition resulting from coal combustion. For the Baihua Reservoir, the Hg, Cr and Cu were primarily derived from industrial activities, and the Pb originated from traffic pollution. The Hg in the Baihua Reservoir might also have been associated with coal combustion pollution. An analysis of ecological risk using sediment quality guidelines showed that there were moderate toxicological risks for sediment-dwelling organisms in both reservoirs, mainly from Hg and Cr. Ecological risk analysis using the Hakanson index suggested that there was a potential moderate to very high ecological risk to humans from fish in both reservoirs, mainly because of elevated levels of Hg and Cd. The upstream Hongfeng Reservoir acts as a buffer, but remains an important source of Cd, Cu and Pb and a moderately important source of Cr, for the downstream Baihua Reservoir. This study provides a replicable method for assessing aquatic ecosystem health in adjacent plateau reservoirs.

  19. Sources of Heavy Metals in Surface Sediments and an Ecological Risk Assessment from Two Adjacent Plateau Reservoirs

    PubMed Central

    Wu, Binbin; Wang, Guoqiang; Wu, Jin; Fu, Qing; Liu, Changming

    2014-01-01

    The concentrations of heavy metals (mercury (Hg), cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu) and arsenic (As)) in surface water and sediments were investigated in two adjacent drinking water reservoirs (Hongfeng and Baihua Reservoirs) on the Yunnan-Guizhou Plateau in Southwest China. Possible pollution sources were identified by spatial and statistical analyses. For both reservoirs, Cd was most likely from industrial activities, and As was from lithogenic sources. For the Hongfeng Reservoir, Pb, Cr and Cu might have originated from mixed sources (traffic pollution and residual effect of former industrial practices), and the sources of Hg included the inflows, which were different for the North (industrial activities) and South (lithogenic origin) Lakes, and atmospheric deposition resulting from coal combustion. For the Baihua Reservoir, the Hg, Cr and Cu were primarily derived from industrial activities, and the Pb originated from traffic pollution. The Hg in the Baihua Reservoir might also have been associated with coal combustion pollution. An analysis of ecological risk using sediment quality guidelines showed that there were moderate toxicological risks for sediment-dwelling organisms in both reservoirs, mainly from Hg and Cr. Ecological risk analysis using the Hakanson index suggested that there was a potential moderate to very high ecological risk to humans from fish in both reservoirs, mainly because of elevated levels of Hg and Cd. The upstream Hongfeng Reservoir acts as a buffer, but remains an important source of Cd, Cu and Pb and a moderately important source of Cr, for the downstream Baihua Reservoir. This study provides a replicable method for assessing aquatic ecosystem health in adjacent plateau reservoirs. PMID:25010771

  20. Rhenium-catalysed dehydrogenative borylation of primary and secondary C(sp3)-H bonds adjacent to a nitrogen atom.

    PubMed

    Murai, Masahito; Omura, Tetsuya; Kuninobu, Yoichiro; Takai, Kazuhiko

    2015-03-18

    Rhenium-catalysed C(sp(3))-H bond borylation in the absence of any oxidant, hydrogen acceptor, or external ligand, with the generation of H2 as the sole byproduct is described. The transformation, which represents a rare example of rhenium-catalysed C(sp(3))-H bond functionalisation, features high atom efficiency and simple reaction conditions.

  1. Contribution of the upper river, the estuarine region, and the adjacent sea to the heavy metal pollution in the Yangtze Estuary.

    PubMed

    Yin, Su; Wu, Yuehan; Xu, Wei; Li, Yangyang; Shen, Zhenyao; Feng, Chenghong

    2016-07-01

    To determine whether the discharge control of heavy metals in the Yangtze River basin can significantly change the pollution level in the estuary, this study analyzed the sources (upper river, the estuarine region, and the adjacent sea) of ten heavy metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, and Zn) in dissolved and particulate phases in the surface water of the estuary during wet, normal, and dry seasons. Metal sources inferred from section fluxes agree with those in statistical analysis methods. Heavy metal pollution in the surface water of Yangtze Estuary primarily depends on the sediment suspension and the wastewater discharge from estuary cities. Upper river only constitutes the main source of dissolved heavy metals during the wet season, while the estuarine region and the adjacent sea (especially the former) dominate the dissolved metal pollution in the normal and dry seasons. Particulate metals are mainly derived from sediment suspension in the estuary and the adjacent sea, and the contribution of the upper river can be neglected. Compared with the hydrologic seasons, flood-ebb tides exert a more obvious effect on the water flow directions in the estuary. Sediment suspension, not the upper river, significantly affects the suspended particulate matter concentration in the estuary.

  2. Ground-state structures of atomic metallic hydrogen.

    PubMed

    McMahon, Jeffrey M; Ceperley, David M

    2011-04-22

    Ab initio random structure searching using density functional theory is used to determine the ground-state structures of atomic metallic hydrogen from 500 GPa to 5 TPa. Including proton zero-point motion within the harmonic approximation, we estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500 GPa (r(s)=1.23) that remains stable to 1 TPa (r(s)=1.11). At higher pressures, hydrogen stabilizes in an …ABCABC… planar structure that is similar to the ground state of lithium, but with a different stacking sequence. With increasing pressure, this structure compresses to the face-centered cubic lattice near 3.5 TPa (r(s)=0.92).

  3. Metallic atoms and ions in comets: Comet Halley 1986 3

    NASA Technical Reports Server (NTRS)

    Ibadov, S.

    1992-01-01

    The origin of metallic atoms and ions in the cometary comae is investigated theoretically. Two effects are revealed in the comas of bright comets: (1) the Na anomalous type effect is possible within the gas-dust jets of comet P/Halley 1986 3 due to cooling cometary dust by cryogenic gas flow from the nucleus; and (2) the production of ions of refractory elements (Fe(+), Si(+), etc.) at large heliocentric distances is possible in the comas of the Halley type dusty comets due to high-velocity impacts between cometary and zodiacal dust particles. Spectral observations of comets with high sensitivity and spatial resolution are important for studying both comets and interplanetary dust.

  4. Superradiance of several atoms near a metal nanosphere

    SciTech Connect

    Protsenko, I E; Uskov, A V

    2015-06-30

    Assuming that the number of emitters (atoms) near a spherical metal nanoparticle is large (more than a few hundred), so that their interaction with each other is strong and sufficient for the emergence of their collective states (Dicke states), it is shown that the nanoparticle accelerates the superradiance of the emitters in a similar way as it accelerates the spontaneous emission of a single emitter. In this case, part of the energy stored by the emitters is absorbed by a nanoparticle, and the rest of the energy is radiated as a superradiance pulse. For the parameters selected in this paper, the energy absorbed by the nanoparticle is approximately equal to the emitted energy. We have found the collective states of the emitters and nanoparticle and have derived expressions for the time dependence of the superradiance pulse power, pulse duration and time delay with respect to the moment of excitation of the emitters. (superradiance)

  5. Tune-out wavelengths for the alkaline-metal atoms

    NASA Astrophysics Data System (ADS)

    Wei-Wei, Yu; Rong-Mei, Yu; Yong-Jun, Cheng; Ya-Jun, Zhou

    2016-02-01

    An approximation formula is developed to determine the tune-out wavelengths for the ground states of the alkaline-metal atoms lithium, sodium and cesium from the existing relativistic reduced matrix elements and experimental energies. The first longest tune-out wavelengths for Li, Na, and Cs are 670.971 nm, 589.557 nm, and 880.237 nm, respectively. This is in good agreement with the previous high precise results of 670.971626 nm, 589.5565 nm, and 880.25 nm from the relativistic all-order many-body perturbation theory (RMBPT) calculation [Phys. Rev. A 84 043401 (2011)]. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304063 and 11174066) and the Youth Foundation of Liaoning Normal University, China (Grant No. LS2014L002).

  6. Magnetism and surface structure of atomically controlled ultrathin metal films.

    SciTech Connect

    Shiratsuchi, Yu.; Yamamoto, M.; Bader, S. D.; Materials Science Division; Osaka Univ.

    2007-01-01

    We review the correlation of magnetism and surface structure in ultrathin metal films, including the tailoring of novel magnetic properties using atomic scale control of the nanostructure. We provide an overview of modern fabrication and characterization techniques used to create and explore these fascinating materials, and highlight important phenomena of interest. We also discuss techniques that control and characterize both the magnetic and structural properties on an atomic scale. Recent advances in the development and applications of these techniques allow nanomagnetism to be investigated in an unprecedented manner. A system cannot necessarily retain a two-dimensional structure as it enters the ultrathin region, but it can transform into a three-dimensional, discontinuous structure due to the Volmer-Weber growth mechanism. This structural transformation can give rise to superparamagnetism. During this evolution, competing factors such as interparticle interactions and the effective magnetic anisotropy govern the magnetic state. These magnetic parameters are influenced by the nanostructure of the film. In particular, controlling the magnetic anisotropy is critical for determining the magnetic properties. Surface effects play especially important roles in influencing both the magnitude and direction of the magnetic anisotropy in ultrathin films. By properly altering the surface structure, the strength and direction of the magnetic anisotropy are controlled via spin-orbit and/or dipole interactions.

  7. The Atomic scale structure of liquid metal-electrolyte interfaces

    NASA Astrophysics Data System (ADS)

    Murphy, B. M.; Festersen, S.; Magnussen, O. M.

    2016-07-01

    Electrochemical interfaces between immiscible liquids have lately received renewed interest, both for gaining fundamental insight as well as for applications in nanomaterial synthesis. In this feature article we demonstrate that the atomic scale structure of these previously inaccessible interfaces nowadays can be explored by in situ synchrotron based X-ray scattering techniques. Exemplary studies of a prototypical electrochemical system - a liquid mercury electrode in pure NaCl solution - reveal that the liquid metal is terminated by a well-defined atomic layer. This layering decays on length scales of 0.5 nm into the Hg bulk and displays a potential and temperature dependent behaviour that can be explained by electrocapillary effects and contributions of the electronic charge distribution on the electrode. In similar studies of nanomaterial growth, performed for the electrochemical deposition of PbFBr, a complex nucleation and growth behaviour is found, involving a crystalline precursor layer prior to the 3D crystal growth. Operando X-ray scattering measurements provide detailed data on the processes of nanoscale film formation.

  8. Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms

    SciTech Connect

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd

    2014-11-15

    Comproportionation reactions of rare-earth metal trihalides (RX{sub 3}) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ((T{sub 3}R{sub 11})X{sub 15}-type, P6{sub 3}/m), tetramers ((T{sub 4}R{sub 16})X{sub 28}(R{sub 4}) (P-43m), (T{sub 4}R{sub 16})X{sub 20} (P4{sub 2}/nnm), (T{sub 4}R{sub 16})X{sub 24}(RX{sub 3}){sub 4} (I4{sub 1}/a) and (T{sub 4}R{sub 16})X{sub 23} (C2/m) types of structure) and pentamers ((Ru{sub 5}La{sub 14}){sub 2}Br{sub 39}, Cc) of (TR{sub r}){sub n} (n=2–5) clusters. These oligomers are further enveloped by inner (X{sup i}) as well as outer (X{sup a}) halido ligands, which possess diverse functionalities and interconnect like oligomers through i–i, i–a and/or a–i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of (TR{sub 6}) octahedra via common edges are more frequent than trimers and pentamers, in which the (TR{sub r}) clusters share common faces. - Graphical abstract: Rare earth-metal cluster complexes with endohedral transition metal atoms (TR{sub 6}) may connect via common edges or faces to form dimers, trimers, tetramers and pentamers of which the tetramers are the most prolific. Packing effects and electron counts play an important role. - Highlights: • Rare-earth metal cluster complexes encapsulate transition metal atoms. • Oligomers are built via connection of octahedral clusters via common edges or faces. • Dimers through pentamers with closed structures are known. • Tetramers including a tetrahedron of endohedral atoms are the most prolific.

  9. Trace metal mobility and microbial community structure in tropical soils: examples from adjacent forest and grassland ecosystems

    NASA Astrophysics Data System (ADS)

    Wilson, A. D.; Roberts, J. A.; MacPherson, G. L.; Mauck, B. S.; Stallard, R. F.

    2004-12-01

    Many factors determine the quality and sustainability of a soil environment and changes in land use can impact significantly soil geochemistry and the associated soil microbial communities. Native tropical forests and human-constructed grasslands on Barro Colorado Island provide an excellent setting for comparing changes in soil ecosystems in undisturbed and altered landscapes. The goals of this study were to examine biological, chemical, and mineralogical changes in soil properties as a function of land use changes during the wet and dry seasons. Soil pits were excavated at two study sites, a tropical forest and an adjacent plot that has been converted to grassland, during March 2002 and August 2003. The 1 meter deep pits were sampled at 5 cm intervals and characterized for soil organic matter content, soil moisture, community structure and total lipid biomass of the soil microbial community, mineralogy, and trace metal distribution using a sequential extraction method. Results demonstrate that forested soils exhibit higher organic matter content than grassland soils regardless of soil moisture content. Total lipid biomass of the active soil microbial population decreases with depth in both soils, but is elevated in the forested soil, likely correlating with the organic matter content in this system. Diversity of the soil microbial community, determined by PLFA analysis, decreases sharply at the base of the root zone and general trends in community structure are similar in both soils. XRD analysis of the soils reveal that the weathering profile in the forest has extended to a greater depth, but these differences in the mineralogy profile do not exert significant control on trace element mobility. Vanadium, copper, zinc, and aluminum show strong affinities for the organically bound fraction in both soils.

  10. Trapping and moving metal atoms with a six-leg molecule

    NASA Astrophysics Data System (ADS)

    Gross, Leo; Rieder, Karl-Heinz; Moresco, Francesca; Stojkovic, Sladjana M.; Gourdon, André; Joachim, Christian

    2005-12-01

    Putting to work a molecule able to collect and carry adatoms in a controlled way on a surface is a solution for fabricating atomic structures atom by atom. Investigations have shown that the interaction of an organic molecule with the surface of a metal can induce surface reconstruction down to the atomic scale. In this way, well-defined nanostructures such as chains of adatoms, atomic trenches and metal-ligand compounds have been formed. Moreover, the progress in manipulation techniques induced by a scanning tunnelling microscope (STM) has opened up the possibility of studying artificially built molecular-metal atomic scale structures, and allowed the atom-by-atom doping of a single C60 molecule by picking up K atoms. The present work goes a step further and combines STM manipulation techniques with the ability of a molecule to assemble an atomic nanostructure. We present a well-designed six-leg single hexa-t-butyl-hexaphenylbenzene (HB-HPB) molecule, which collects and carries up to six copper adatoms on a Cu(111) surface when manipulated with a STM tip. The `HB-HPB-Cu atoms' complex can be further manipulated, bringing its Cu freight to a predetermined position on the surface where the metal atoms can finally be released.

  11. Tuning Fermi-surface properties through quantum confinement in metallic metalattices: New metals from old atoms

    NASA Astrophysics Data System (ADS)

    Crespi, Vincent H.; Han, J. E.

    2001-03-01

    We describe a new class of nanoscale structured metals wherein the effects of quantum confinement are combined with dispersive metallic electronic states to induce modifications to the fundamental low-energy microscopic properties of a three-dimensional metal: the density of states, the distribution of Fermi velocities, and the collective electronic response (J. E. Han and Vincent H. Crespi, to appear in Phys. Rev. Lett.). The metalattice, metal-infiltrated colloidal lattice, possesses two very different length scales, lattice constants of metal atoms and of colloidal spheres. We compute the electronic properties of the metalattice using an empirical tight-binding method. As a result of the hierarchy in the two length scales, electronic states bifurcate into two classes with weak and strong dispersion. The dispersive states reflect the symmetry of the colloidal lattice and have major contribution to the transport properties such as inversion of Fermi velocity and optical response. We also discuss the magnetic structure of the metalattice with magnetic infiltrants such as Pd and Rh.

  12. The atomic level journey from aqueous polyoxometalate to metal oxide

    SciTech Connect

    Hou, Yu; Fast, Dylan B.; Ruther, Rose E.; Amador, Jenn M.; Fullmer, Lauren B.; Decker, Shawn R.; Zakharov, Lev N.; Dolgos, Michelle R. Nyman, May

    2015-01-15

    Aqueous precursors tailored for the deposition of thin film materials are desirable for sustainable, simple, low energy production of advanced materials. Yet the simple practice of using aqueous precursors is complicated by the multitude of interactions that occur between ions and water during dehydration. Here we use lithium polyoxoniobate salts to investigate the fundamental interactions in the transition from precursor cluster to oxide film. Small-angle X-ray scattering of solutions, total X-ray scattering of intermediate gels, and morphological and structural characterization of the lithium niobate thin films reveal the atomic level transitions between these states. The studies show that (1) lithium–[H{sub 2}Nb{sub 6}O{sub 19}]{sup 6−} has drastically different solution behaviour than lithium–[Nb{sub 6}O{sub 19}]{sup 8−}, linked to the precursor salt structure (2) in both compositions, the intermediate gel preserves the polyoxoniobate clusters and show similar local order and (3) the morphology and phases of deposited films reflect the ions behaviour throughout the journey from cluster solution to metal oxide. - Graphical abstract: Aqueous lithium polyoxoniobate salts were used to prepare lithium niobate (LiNbO{sub 3}) thin films. Fundamental studies were performed to investigate the interactions in the transition from precursor cluster to the oxide film. It was found that acid–base and ion-association chemistries of the aqueous and gel systems significantly affect the key processes in this atom-level journey. - Highlights: • Lithium polyoxoniobate clusters were synthesized with control over Li:Nb ratio as precursors for LiNbO{sub 3} films. • X-ray scattering studies in solution and the solid-state revealed differences controlled by Li:Nb ratio. • Film deposition studies revealed phase, composition and morphology is controlled by Li:Nb ratio. • Cluster to film transformation was revealed using total X-ray scattering and TGA.

  13. Atomic mobility and strain localization in amorphous metals.

    PubMed

    Delogu, Francesco

    2008-02-22

    Molecular dynamics simulations are employed to investigate the atomic mobility in Ni(50)Zr(50) amorphous alloys under both static conditions and shearing. Diffusion occurs under static conditions via cooperative stringlike motion involving atoms with large volumes. Atomic mobility is instead governed by rearrangements localized in shear transformation zones (STZs) under shearing. Local atomic volume plays in both cases a key role, the atomic ensembles involved in diffusion and STZ activity being strongly correlated.

  14. Fullerene film on metal surface: Diffusion of metal atoms and interface model

    SciTech Connect

    Li, Wen-jie; Li, Hai-Yang; Li, Hong-Nian; Wang, Peng; Wang, Xiao-Xiong; Wang, Jia-Ou; Wu, Rui; Qian, Hai-Jie; Ibrahim, Kurash

    2014-05-12

    We try to understand the fact that fullerene film behaves as n-type semiconductor in electronic devices and establish a model describing the energy level alignment at fullerene/metal interfaces. The C{sub 60}/Ag(100) system was taken as a prototype and studied with photoemission measurements. The photoemission spectra revealed that the Ag atoms of the substrate diffused far into C{sub 60} film and donated electrons to the molecules. So the C{sub 60} film became n-type semiconductor with the Ag atoms acting as dopants. The C{sub 60}/Ag(100) interface should be understood as two sub-interfaces on both sides of the molecular layer directly contacting with the substrate. One sub-interface is Fermi level alignment, and the other is vacuum level alignment.

  15. Ionization of Rydberg atoms colliding with a metal surface

    SciTech Connect

    Sjakste, J.; Borisov, A. G.; Gauyacq, J. P.

    2006-04-15

    We report on a theoretical study of the ionization process of Xe* Rydberg atoms colliding with a metal surface, in the presence of an external electric field. The evolution of the Xe* outer electron is studied by a wave packet propagation approach, allowing to include all dynamical aspects of the collision, in particular nonadiabatic inter-Rydberg transitions. We investigate how the different Xe* Stark states formed in the external field couple together and ionize on the surface and how the different polarizations of the electronic cloud in the Xe* states are reflected in their ionization properties. We show that the presence of the external electric field can significantly perturb the dynamics of the ionization process. Our results account for recent results from Dunning et al. [Nucl. Inst. Meth. B 203, 69 (2003)]. In particular, it is explained how the external electric field present in the experimental procedure of Dunning et al. leads to the apparent absence of a polarization effect in the ionization process.

  16. Metal-Free Radical [2+2+1] Carbocyclization of Benzene-Linked 1,n-Enynes: Dual C(sp(3))-H Functionalization Adjacent to a Heteroatom.

    PubMed

    Hu, Ming; Fan, Jian-Hong; Liu, Yu; Ouyang, Xuan-Hui; Song, Ren-Jie; Li, Jin-Heng

    2015-08-10

    A new metal-free oxidative radical [2+2+1] carbocyclization of benzene-linked 1,n-enynes with two C(sp(3))-H bonds adjacent to the same heteroatom is described. This method achieves two C(sp(3))-H oxidative functionalizations and an annulation, thus providing efficient and general access to a variety of fused five-membered carbocyclic hydrocarbons.

  17. PREPARATION OF OXALATES OF METALS OF ATOMIC NUMBER GREATER THAN 88

    DOEpatents

    Duffield, R.B.

    1959-02-01

    A method is presented for the preparation of oxalates of metals of atomic number greater than 88. A solid peroxide of the heavy metal is contacted with an aqueous oxalic acid solution ai a temperature of about 50 C for a period of time sufficient to form the insoluble metal oxalate which is subsequentiy recovered as a pures crystalline compound.

  18. Selective silver atom interaction at β-SiC(100) surfaces: From anisotropic diffusion to metal atomic wires and stripes

    NASA Astrophysics Data System (ADS)

    D'Angelo, M.; Aristov, V. Yu.; Soukiassian, P.

    2007-07-01

    Silver (Ag) atom interaction on β-SiC(100) surface reconstructions is investigated by atom-resolved scanning tunneling microscopy. On the 3×2 (Si-rich) reconstruction, the adsorbate-adsorbate interaction is dominant with no surface wetting, leading to Ag cluster formation. In contrast, on the c(4×2) Si-terminated reconstruction, almost equivalent Ag-Ag and Ag-surface interactions allow selective one dimensional nano-object formation including Ag atomic wires and stripes following the substrate registry. Their orientation is mediated by anisotropic Ag atom diffusion occurring along Si-dimer rows at 25°C and perpendicularly to them at elevated temperatures, suggesting dimer flipping as diffusion barrier. These metal nanowires potentially open up cross-wiring capability in massively parallel Si atomic lines network.

  19. Evolution of Conducting Channels in Metallic Atomic Contacts under Elastic Deformation

    NASA Astrophysics Data System (ADS)

    Cuevas, J. C.; Levy Yeyati, A.; Martín-Rodero, A.; Rubio Bollinger, G.; Untiedt, C.; Agraït, N.

    1998-10-01

    We investigate both experimentally and theoretically the evolution of conductance in metallic one-atom contacts under elastic deformation. While simple metals like Au exhibit almost constant conductance plateaus, Al and Pb show inclined plateaus with positive and negative slopes. It is shown how these behaviors can be understood in terms of the orbital structure of the atoms forming the contact. This analysis provides further insight into the issue of conductance quantization in metallic contacts revealing important aspects of their atomic and electronic structures.

  20. Method and apparatus for atomization and spraying of molten metals

    DOEpatents

    Hobson, D.O.; Alexeff, I.; Sikka, V.K.

    1988-07-19

    A method and device for dispersing molten metal into fine particulate spray, the method comprises applying an electric current through the molten metal and simultaneously applying a magnetic field to the molten metal in a plane perpendicular to the electric current, whereby the molten metal is caused to form into droplets at an angle perpendicular to both the electric current and the magnetic field. The device comprises a structure for providing a molten metal, appropriately arranged electrodes for applying an electric current through the molten metal, and a magnet for providing a magnetic field in a plane perpendicular to the electric current. 11 figs.

  1. The Application of DFT to Systems Containing Metal Atoms

    NASA Technical Reports Server (NTRS)

    Ricca, Alessandra; Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    1996-01-01

    The application of density functional theory (DFT) to a series of metal containing systems will be described. The focus will be on the calculation of accurate bond energies, especially metal-ligand successive bond energies. The DFT results will be compared with experiment and other levels of theory. If time permits, metal clusters will also be discussed.

  2. Transition-Metal Substitution Doping in Synthetic Atomically Thin Semiconductors.

    PubMed

    Gao, Jian; Kim, Young Duck; Liang, Liangbo; Idrobo, Juan Carlos; Chow, Phil; Tan, Jiawei; Li, Baichang; Li, Lu; Sumpter, Bobby G; Lu, Toh-Ming; Meunier, Vincent; Hone, James; Koratkar, Nikhil

    2016-11-01

    Large-area "in situ" transition-metal substitution doping for chemical-vapor-deposited semiconducting transition-metal-dichalcogenide monolayers deposited on dielectric substrates is demonstrated. In this approach, the transition-metal substitution is stable and preserves the monolayer's semiconducting nature, along with other attractive characteristics, including direct-bandgap photoluminescence.

  3. Ionic Hamiltonians for transition metal atoms: effective exchange coupling and Kondo temperature

    NASA Astrophysics Data System (ADS)

    Flores, F.; Goldberg, E. C.

    2017-02-01

    An ionic Hamiltonian for describing the interaction between a metal and a d-shell transition metal atom having an orbital singlet state is introduced and its properties analyzed using the Schrieffer-Wolf transformation (exchange coupling) and the poor man’s scaling method (Kondo temperature). We find that the effective exchange coupling between the metal and the atom has an antiferromagnetic or a ferromagnetic interaction depending on the kind of atomic fluctuations, either S\\to S-1/2 or S\\to S+1/2 , associated with the metal-atom coupling. We present a general scheme for all those processes and calculate, for the antiferromagnetic interaction, the corresponding Kondo-temperature.

  4. Local Stoichiometry and Atomic Interdiffusion during Reactive Metal/Mercury-Cadmium-Telluride Junction Formation.

    DTIC Science & Technology

    1987-10-23

    CHART NATIONAL BUREAU OF STANDARDS- 1963-A IfP LOCAL STOICHIOMETRY AND ATOMIC INTERDIFFUSION DURING REACTIVE METAL/ MERCURY- CADMIUM -TELLURIDE...TITLE rand Subtitle) S. TYPE OF REPORT PERIOED LOCAL STOICHIOMETRY AND ATOMIC INTERDIFFUSION Interim, 1/8 DURING REACTIVE METAL/MERCURY- CADMIUM ...identliy by block nuembw) Ag, Ge and Sm overlayers on Mercury- Cadmium -Telluride surfaces exhibit widely different interface reactivity and yield a

  5. Thermochemical analyses of the oxidative vaporization of metals and oxides by oxygen molecules and atoms

    NASA Technical Reports Server (NTRS)

    Kohl, F. J.; Leisz, D. M.; Fryburg, G. C.; Stearns, C. A.

    1977-01-01

    Equilibrium thermochemical analyses are employed to describe the vaporization processes of metals and metal oxides upon exposure to molecular and atomic oxygen. Specific analytic results for the chromium-, platinum-, aluminum-, and silicon-oxygen systems are presented. Maximum rates of oxidative vaporization predicted from the thermochemical considerations are compared with experimental results for chromium and platinum. The oxidative vaporization rates of chromium and platinum are considerably enhanced by oxygen atoms.

  6. 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.

  7. Interaction mechanisms between ceramic particles and atomized metallic droplets

    NASA Astrophysics Data System (ADS)

    Wu, Yue; Lavernia, Enrique J.

    1992-10-01

    The present study was undertaken to provide insight into the dynamic interactions that occur when ceramic particles are placed in intimate contact with a metallic matrix undergoing a phase change. To that effect, Al-4 wt pct Si/SiCp composite droplets were synthesized using a spray atomization and coinjection approach, and their solidification microstructures were studied both qualitatively and quantitatively. The present results show that SiC particles (SiCp) were incor- porated into the matrix and that the extent of incorporation depends on the solidification con- dition of the droplets at the moment of SiC particle injection. Two factors were found to affect the distribution and volume fraction of SiC particles in droplets: the penetration of particles into droplets and the entrapment and/or rejection of particles by the solidification front. First, during coinjection, particles collide with the atomized droplets with three possible results: they may penetrate the droplets, adhere to the droplet surface, or bounce back after impact. The extent of penetration of SiC particles into droplets was noted to depend on the kinetic energy of the particles and the magnitude of the surface energy change in the droplets that occurs upon impact. In liquid droplets, the extent of penetration of SiC particles was shown to depend on the changes in surface energy, ΔEs, experienced by the droplets. Accordingly, large SiC particles encoun- tered more resistance to penetration relative to small ones. In solid droplets, the penetration of SiC particles was correlated with the dynamic pressure exerted by the SiC particles on the droplets during impact and the depth of the ensuing crater. The results showed that no pene- tration was possible in such droplets. Second, once SiC particles have penetrated droplets, their final location in the microstructure is governed by their interactions with the solidification front. As a result of these interactions, both entrapment and rejection of

  8. Graphene as a flexible template for controlling magnetic interactions between metal atoms.

    PubMed

    Lee, Sungwoo; Kim, Dongwook; Robertson, Alex W; Yoon, Euijoon; Hong, Suklyun; Ihm, Jisoon; Yu, Jaejun; Warner, Jamie H; Lee, Gun-Do

    2017-03-01

    Metal-doped graphene produces magnetic moments that have potential application in spintronics. Here we use density function theory computational methods to show how the magnetic interaction between metal atoms doped in graphene can be controlled by the degree of flexure in a graphene membrane. Bending graphene by flexing causes the distance between two substitutional Fe atoms covalently bonded in graphene to gradually increase and these results in the magnetic moment disappearing at a critical strain value. At the critical strain, a carbon atom can enter between the two Fe atoms and blocks the interaction between relevant orbitals of Fe atoms to quench the magnetic moment. The control of interactions between doped atoms by exploiting the mechanical flexibility of graphene is a unique approach to manipulating the magnetic properties and opens up new opportunities for mechanical-magnetic 2D device systems.

  9. Graphene as a flexible template for controlling magnetic interactions between metal atoms

    NASA Astrophysics Data System (ADS)

    Lee, Sungwoo; Kim, Dongwook; Robertson, Alex W.; Yoon, Euijoon; Hong, Suklyun; Ihm, Jisoon; Yu, Jaejun; Warner, Jamie H.; Lee, Gun-Do

    2017-03-01

    Metal-doped graphene produces magnetic moments that have potential application in spintronics. Here we use density function theory computational methods to show how the magnetic interaction between metal atoms doped in graphene can be controlled by the degree of flexure in a graphene membrane. Bending graphene by flexing causes the distance between two substitutional Fe atoms covalently bonded in graphene to gradually increase and these results in the magnetic moment disappearing at a critical strain value. At the critical strain, a carbon atom can enter between the two Fe atoms and blocks the interaction between relevant orbitals of Fe atoms to quench the magnetic moment. The control of interactions between doped atoms by exploiting the mechanical flexibility of graphene is a unique approach to manipulating the magnetic properties and opens up new opportunities for mechanical-magnetic 2D device systems.

  10. Characteristics of Spontaneous Emission of Polarized Atoms in Metal Dielectric Multiple Layer Structures

    NASA Astrophysics Data System (ADS)

    Zhao, Li-Ming; Gu, Ben-Yuan; Zhou, Yun-Song

    2007-11-01

    The spontaneous emission (SE) progress of polarized atoms in a stratified structure of air-dielectric(D0)-metal(M)-dielectric(D1)-air can be controlled effectively by changing the thickness of the D1 layer and rotating the polarized direction of atoms. It is found that the normalized SE rate of atoms located inside the D0 layer crucially depends on the atomic position and the thickness of the D1 layer. When the atom is located near the D0-M interface, the normalized atomic SE rate as a function of the atomic position is abruptly onset for the thin D1 layer. However, with the increasing thickness of the D1 layer, the corresponding curve profile exhibits plateau and stays nearly unchanged. The substantial change of the SE rate stems from the excitation of the surface plasmon polaritons in metal-dielectric interface, and the feature crucially depends on the thickness of D1 layer. If atoms are positioned near the D0-air interface, the substantial variation of the normalized SE rate appears when rotating the polarized direction of atoms. These findings manifest that the atomic SE processes can be flexibly controlled by altering the thickness of the dielectric layer D1 or rotating the orientation of the polarization of atoms.

  11. Quantitative Evaluation of Heavy Metals and Trace Elements in the Urinary Bladder: Comparison Between Cancerous, Adjacent Non-cancerous and Normal Cadaveric Tissue.

    PubMed

    Abdel-Gawad, Mahmoud; Elsobky, Emad; Shalaby, Mahmoud M; Abd-Elhameed, Mohamed; Abdel-Rahim, Mona; Ali-El-Dein, Bedeir

    2016-12-01

    The role of heavy metals and trace elements (HMTE) in the development of some cancers has been previously reported. Bladder carcinoma is a frequent malignancy of the urinary tract. The most common risk factors for bladder cancer are exposure to industrial carcinogens, cigarette smoking, gender, and possibly diet. The aim of this study was to evaluate HTME concentrations in the cancerous and adjacent non-cancerous tissues and compare them with those of normal cadaveric bladder. This prospective study included 102 paired samples of full-thickness cancer and adjacent non-cancerous bladder tissues of radical cystectomy (RC) specimens that were histologically proven as invasive bladder cancer (MIBC). We used 17 matched controls of non-malignant bladder tissue samples from cadavers. All samples were processed and evaluated for the concentration of 22 HMTE by using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Outcome analysis was made by the Mann-Whitney U, chi-square, Kruskal-Wallis, and Wilcoxon signed ranks tests. When compared with cadaveric control or cancerous, the adjacent non-cancerous tissue had higher levels of six elements (arsenic, lead, selenium, strontium, zinc, and aluminum), and when compared with the control alone, it had a higher concentration of calcium, cadmium, chromium, potassium, magnesium, and nickel. The cancerous tissue had a higher concentration of cadmium, lead, chromium, calcium, potassium, phosphorous, magnesium, nickel, selenium, strontium, and zinc than cadaveric control. Boron level was higher in cadaveric control than cancerous and adjacent non-cancerous tissue. Cadmium level was higher in cancerous tissue with node-positive than node-negative cases. The high concentrations of cadmium, lead, chromium, nickel, and zinc, in the cancerous together with arsenic in the adjacent non-cancerous tissues of RC specimens suggest a pathogenic role of these elements in BC. However, further work-up is needed to support this

  12. He atom surface spectroscopy: Surface lattice dynamics of insulators, metals and metal overlayers

    SciTech Connect

    Not Available

    1990-01-01

    During the first three years of this grant (1985--1988) the effort was devoted to the construction of a state-of-the-art He atom scattering (HAS) instrument which would be capable of determining the structure and dynamics of metallic, semiconductor or insulator crystal surfaces. The second three year grant period (1988--1991) has been dedicated to measurements. The construction of the instrument went better than proposed; it was within budget, finished in the proposed time and of better sensitivity and resolution than originally planned. The same success has been carried over to the measurement phase where the concentration has been on studies of insulator surfaces, as discussed in this paper. The experiments of the past three years have focused primarily on the alkali halides with a more recent shift to metal oxide crystal surfaces. Both elastic and inelastic scattering experiments were carried out on LiF, NaI, NaCl, RbCl, KBr, RbBr, RbI, CsF, CsI and with some preliminary work on NiO and MgO.

  13. [Spatial distribution and pollution assessment of heavy metals in the tidal reach and its adjacent sea estuary of Daliaohe area, China ].

    PubMed

    Zhang, Lei; Qin, Yan-wen; Ma, Ying-qun; Zhao, Yan-min; Shi, Yao

    2014-09-01

    The aim of this article was to explore the pollution level of heavy metals in the tidal reach and its adjacent sea estuary of Daliaohe area. The contents and spatial distribution of As, Cd, Cr, Cu, Ph and Zn in surface water, suspended solids and surface sediments were analyzed respectively. The integrated pollution index and geoaccumulation index were used to evaluate the contamination degree of heavy metals in surface water and surface sediments respectively. The results indicated that the contents of heavy metals in surface water was in the order of Pb < Cu < Cd < Cr < As < Zn. The heavy metal contents in surface water increased from river to sea. Compared with the contents of heavy metals in surface water of the typical domestic estuary in China, the overall contents of heavy metals in surface water were at a higher level. The contents of heavy metals in suspended solids was in the order of Cd < Cu < As < Cr metals in surface sediments was in the order of Cd metals in water, suspended solids and sediment. In particular, the effects of salinity and suspended solids matter were most significant. The integrated pollution index assessment showed that the water quality was good except individual stations. The geoaccumulation index assessment showed that As was the major pollution element in surface sediments.

  14. Atomic transport at liquid metal/Al{sub 2}O{sub 3} interfaces

    SciTech Connect

    Saiz, Eduardo; Cannon, Rowland M.; Tomsia, Antoni P.

    2000-10-12

    In this work, atomic force microscopy (AFM) has been used to identify the controlling transport mechanisms at metal/oxide interfaces and measure the corresponding diffusivities. Interfacial transport rates in our experiments are two to four orders of magnitude faster than any previously reported rates for the oxide surface. The interfacial diffusivities and the degree of interfacial anisotropy depend on the oxygen activity of the system. Atomic transport at metal/oxide interfaces plays a defining role in many technological processes, and these experiments provide fundamental data for the formulation of the atomic theory needed to explain many of the observed phenomena.

  15. Atomic-Scale Tuning of Layered Binary Metal Oxides for High Temperature Moving Assemblies

    DTIC Science & Technology

    2015-06-01

    AFRL-OSR-VA-TR-2015-0166 Atomic -Scale Tuning of Layered Binary Metal OxideS ASHLIE MARTINI UNIVERSITY OF CALIFORNIA MERCED Final Report 06/01/2015...COVERED (From - To)      01-05-2012 to 30-04-2015 4.  TITLE AND SUBTITLE Atomic -Scale Tuning of Layered Binary Metal Oxides for High Temperature Moving...understand, at an atomic level, the material properties that influence the thermal, mechanical and tribological behavior of intrinsically layered binary

  16. Atomic-scale heterogeneity of a multicomponent bulk metallic glass with excellent glass forming ability.

    PubMed

    Fujita, T; Konno, K; Zhang, W; Kumar, V; Matsuura, M; Inoue, A; Sakurai, T; Chen, M W

    2009-08-14

    We report the atomic structure of a multicomponent Cu45Zr45Ag10 bulk metallic glass investigated by state-of-the-art experimental and computational techniques. In comparison with a binary Cu50Zr50 metallic glass, Zr-rich interpenetrating clusters centered by paired and stringed Ag atoms and Cu-rich icosahedra are widely observed in the ternary Cu45Zr45Ag10 alloy. The atomic-scale heterogeneity caused by chemical short- and medium-range order is found to play a key role in stabilizing the liquid phase and in improving the glass forming ability of the multicomponent alloy.

  17. Non-Adiabatic Atomic Transitions: Computational Cross Section Calculations of Alkali Metal-Noble Gas Collisions

    DTIC Science & Technology

    2011-09-01

    collisions were computationally simulated. The alkali metals were potassium, rubidium, and cesium and the noble gas partners were helium, neon, and argon...195 20. Spin-Orbit split energies of Potassium, Rubidium, and Cesium ...composed of an alkali metal typically Rubidium[26, 37] or Cesium [5, 18]. The unique character of the alkali atoms, having a single valence electron in

  18. Decay time of hollow argon atoms formed below metal and dielectric surfaces

    NASA Astrophysics Data System (ADS)

    Briand, J. P.; Phaneuf, R.; Aryal, N. B.; Baral, K. K.; Thomas, C. M.; Esteves, D. A.

    2013-09-01

    Slow highly charged ions penetrating surfaces quickly capture many electrons in highly excited states, leaving empty the innermost shells, forming hollow atoms. These hollow atoms then fill their innermost shells in a stepwise manner through a long cascade of Auger and x-ray transitions. We have measured the mean emission depths of the series of x rays emitted during the decay cascade of Ar hollow atoms formed below the surface of metal and dielectric materials. It has been found that the decay times of these hollow atoms are much longer in dielectrics than in metals, and at keV/q kinetic energies, at depths of the order of 10-20 nm, considerably deeper than any expected value. These findings have been tentatively explained by the different responses of metals and dielectrics to the slow penetration of a highly charged ion.

  19. Assessment of heavy metal accumulation in macrophyte, agricultural soil, and crop plants adjacent to discharge zone of sponge iron factory

    NASA Astrophysics Data System (ADS)

    Gupta, S.; Nayek, S.; Saha, R. N.; Satpati, S.

    2008-08-01

    The present study deals with the characterization of effluent released from sponge iron industries and distribution of heavy metals in soil and macrophytes near to effluent discharge channel. Apart from this, accumulation of heavy metals in nearby soil and vegetation system irrigated with effluent-contaminated water is also the subject of this study. Physico-chemical analysis of effluent reveals that the concentration of total suspended solids (TSS), total hardness (TH), iron (Fe2+), and oil and grease are greater than the IS (1981) norms for discharge of water into inland water body. The soil along the sides of the effluent channel also shows higher concentration of heavy metals than the background soil. The enrichment of the heavy metals are in the order of Chromium (Cr) > Iron (Fe) > Manganese (Mn) > Zinc (Zn) > Copper (Cu) > Cadmium (Cd). Macrophytes growing along the sides of the effluent channel also show significant accumulation of heavy metals almost in the same order as accumulated in soil. Higher uptake of heavy metals by these varieties reveals that these species can be used for future phytoremediation. The effluent as well as contaminated water is extensively used for irrigation for growing vegetables like tomato ( Lycopersicon esculatum) in the surrounding areas. Heavy metal accumulation in this agricultural soil are in the sequence of Cr > Fe > Mn > Zn > Cu > Cd. More or less similar type of accumulation pattern are also found in tomato plants except Fe and Zn exceeding Cr and Mn. Transfer Factor of heavy metals from soil to tomato plants (TFS) shows average value of <1, suggesting less uptake of heavy metals from soil. Among the plant parts studied, fruit shows least accumulation. Although tomato plants show some phenotypic changes, the survival of tomato plants as well as least accumulation of metals in fruit reveals their tolerance to heavy metals. Therefore it may be suggested that this plant can be grown successfully in the heavy metal

  20. Recent advances in transition metal-catalyzed N -atom transfer reactions of azides

    PubMed Central

    Driver, Tom G.

    2011-01-01

    Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids. PMID:20617243

  1. Atomic oxygen-metal surface studies as applied to mass spectrometer measurements of upper planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Sjolander, G. W.

    1976-01-01

    The problem of atomic oxygen loss in mass spectrometer ion sources can be reduced to an understanding of the possible surface interactions between oxygen atoms and the metal surface of the ion source. Results are presented for an experimental study in which an atomic oxygen beam apparatus and a mass spectrometer were used to measure the oxygen atom reflection, recombination, general surface reaction, and occlusion probabilities on six different engineering surfaces as a function of atomic oxygen exposure. The materials studied are gold, Nichrome V, aluminum, titanium, silver, and platinum. The variation in measured reflection probability seems to occur with metals that form oxides, Nichrome V being stable in terms of reflection stability. Recombination is observed an all surfaces except aluminum and platinum. Variation in the complete set of measurements in a single experiment is the result of varying surface conditions.

  2. Spatio-temporal distribution and environmental risk of sedimentary heavy metals in the Yangtze River Estuary and its adjacent areas.

    PubMed

    Chen, Bin; Liu, Jian; Qiu, Jiandong; Zhang, Xilin; Wang, Shuang; Liu, Jinqing

    2016-12-01

    Twenty-five surface sediments and one sediment core sample were collected from the study area. Grain size, major elements, and heavy metals were determined. The content of fine-grained sediments (silt and clay), as well as the concentrations of major elements and heavy metals, showed seaward decreasing trends, with high content in the coastal areas of the East China Sea (ECS) and south west of Jeju Island. Low enrichment factor (EF) and geoaccumulation index (Igeo) values were found, indicating that the ecological risk of heavy metals was low. The EF values obtained from the high-resolution sedimentary records of heavy metals in the Yangtze River Estuary could be divided into Stage 1 (1950s to the late 1970s) and Stage 2 (late 1970s to the current sampling day), which coincided with economic development of the Yangtze River Basin, implementation of environmental protection, and impoundment of the Three Gorges Dam.

  3. Defining nanoscale metal features on an atomically clean silicon surface with a stencil.

    PubMed

    Linklater, A; Nogami, J

    2008-07-16

    Metal features with nanometer scale edge definition have been created on an atomically clean Si(001) surface with a stencil. These features were subsequently characterized by scanning tunneling microscopy and scanning electron microscopy. The stencil was brought into contact with the substrate while allowing the stencil to pivot so that it self-aligned parallel to the substrate surface. With this simple method, feature edge spreading was reduced to less than 10 nm in the best case. At the same time, atomic resolution images of the metal feature/silicon boundary showed significant spreading of a sub-monolayer of metal beyond the deposited area. This spreading may pose a limit on the ultimate resolution that can be achieved for metals deposited on atomically clean silicon surfaces.

  4. Note: Design principles of a linear array multi-channel effusive metal-vapor atom source

    SciTech Connect

    Jana, B.; Majumder, A.; Thakur, K. B.; Das, A. K.

    2013-10-15

    Atomic beams can easily be produced by allowing atoms to effuse through a channel. In an earlier investigation [A. Majumder et al., Vacuum 83, 989 (2009)], we had designed, fabricated, and characterized an effusive metal-vapor source using collinear-array of multi-channel. In this note, we describe the theoretical basis of designing the source. Atom density in atomic beam has been estimated using a set of analytical expressions for long-channel operated in transparent mode. Parametric studies on aspect ratio of channel, inter-channel separation, beam width, and vertical distance from the source are carried out. They are useful in providing physical picture and optimizing design parameters.

  5. Change in atomic coordination in a heavily deformed metallic glass

    SciTech Connect

    Liu, Y.; Schumacher, G.; Riesemeier, H.; Banhart, J.

    2014-05-28

    The local structure around Ni and La atoms in Al{sub 85}Ni{sub 10}La{sub 5} amorphous powder after ball milling was investigated by X-ray absorption spectroscopy. A continuous decrease in coordination number of Ni and La as a function of milling time was observed, while the nearest neighbour distance and the mean square atomic displacement did not change, pointing at the creation of free volume around the Ni and La atoms. These structural changes resemble those of a liquid upon temperature increase. The results are described by a shear band model in which the coordination numbers of Ni and La are different within and outside a shear band.

  6. Analytical study of ultrasound influence on the molten metals atomization

    NASA Astrophysics Data System (ADS)

    Antonnikova, A.; Arkhipov, V.; Boiko, V.; Basalaev, S.; Konovalenko, A.; Zolotorev, N.

    2016-04-01

    This paper focuses on the study of influence of ultrasound on liquid atomization using ejection nozzles. Two principles of influence of ultrasound on the atomization process such as a change of conditions on gas-liquid boundary during the generation of ultrasound oscillation in the gas and liquid jet (film) disintegration under the action of capillary forces in cases of generation of ultrasound oscillation in the liquid are considered. The optimal values of the ultrasound oscillation frequencies are calculated. Two constructions of the nozzles patented are proposed.

  7. Deformation analysis of amorphous metals based on atomic elastic stiffness coefficients

    NASA Astrophysics Data System (ADS)

    Yashiro, K.; Nishimura, M.; Tomita, Y.

    2006-06-01

    The elastic limit of a crystal can be evaluated by the positiveness of elastic stiffness coefficients, Bijkl. We had demonstrated that the nucleation of lattice defects such as dislocation and cleavage cracking can be predicted by the atomic Bijkl at each atom point. Amorphous metals and bulk metallic glasses draw intense interest whether the criteria are applicable or not since they are regarded as the ultimate of lattice defects. In the present study, an amorphous Ni-Al binary alloy is made by a usual melt-quench simulation and subjected to tension by means of molecular dynamics simulation. During simulations, the positiveness of atomic Bijkl is discussed for all atoms. Contrary to an Ni-Al crystal, many atoms show negative value even in the initial equilibrium of the amorphous before loading. These unstable atoms turn out to be the non-clustered atom or the outer-shell of the local cluster such as 12(0, 0, 12, 0) icosahedron. On the other hand, the centre atoms of the local clusters show high stability resulting in the positive Bijkl of the whole system. It is also demonstrated that the change in the atomic Bijkl can reveal the collapse and re-configuration of local clusters during the deformation.

  8. Metal debris concentrations in soft tissues adjacent to loosened femoral stems is higher in uncemented than cemented implants

    PubMed Central

    2014-01-01

    Background There are still many questions related to aseptic femoral stem loosening. Systemic and local immune responses to the implanted “foreign body” is one of the reasons for loosening. The purpose of the study was to measure metal ion concentration (Ti, Co, Cr, Mo, Ni, Al) around loosened femoral stems and compare their levels around uncemented and cemented implants. Methods This paper reports 50 hips operated for isolated stem loosening, in 50 patients at the mean age of 57 years (from 21 to 87). There were 25 cemented (Co,Cr29,Mo,Ni) and 25 uncemented (Ti, Al) stems. The mean follow-up from primary hip replacement to revision was 10.1 years (from 0.5 to 17). During the procedure, scar tissue around the stem was taken for analysis of metal ions. Results The concentrations of titanium and aluminium in soft tissues around uncemented loosened stems were higher than cemented ones (p < 0.001, p < 0.001 respectively). However, no statistically significant differences were observed between both types of stems in terms of ions of the metal of which cemented implants had been made of (Co, Cr, Mo, Ni). Conclusions In soft tissue around a loosened stem, the concentrations of metal ions from implants are much higher in case of uncemented stems than of cemented ones. Metal ions from vitalium femoral heads were found around uncemented stems in similar values to cemented streams. PMID:25098913

  9. Stable isolated metal atoms as active sites for photocatalytic hydrogen evolution.

    PubMed

    Xing, Jun; Chen, Jian Fu; Li, Yu Hang; Yuan, Wen Tao; Zhou, Ying; Zheng, Li Rong; Wang, Hai Feng; Hu, P; Wang, Yun; Zhao, Hui Jun; Wang, Yong; Yang, Hua Gui

    2014-02-17

    The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co-catalysts. Generally, the noble metals have been widely applied as co-catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co-catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO2 , a model photocatalystic system, by a facile one-step method. The isolated metal atom based photocatalysts show excellent stability for H2 evolution and can lead to a 6-13-fold increase in photocatalytic activity over the metal clusters loaded on TiO2 by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.

  10. Recent Advances in Atomic Metal Doping of Carbon-based Nanomaterials for Energy Conversion.

    PubMed

    Bayatsarmadi, Bita; Zheng, Yao; Vasileff, Anthony; Qiao, Shi-Zhang

    2017-04-12

    Nanostructured metal-contained catalysts are one of the most widely used types of catalysts applied to facilitate some of sluggish electrochemical reactions. However, the high activity of these catalysts cannot be sustained over a variety of pH ranges. In an effort to develop highly active and stable metal-contained catalysts, various approaches have been pursued with an emphasis on metal particle size reduction and doping on carbon-based supports. These techniques enhances the metal-support interactions, originating from the chemical bonding effect between the metal dopants and carbon support and the associated interface, as well as the charge transfer between the atomic metal species and carbon framework. This provides an opportunity to tune the well-defined metal active centers and optimize their activity, selectivity and stability of this type of (electro)catalyst. Herein, recent advances in synthesis strategies, characterization and catalytic performance of single atom metal dopants on carbon-based nanomaterials are highlighted with attempts to understand the electronic structure and spatial arrangement of individual atoms as well as their interaction with the supports. Applications of these new materials in a wide range of potential electrocatalytic processes in renewable energy conversion systems are also discussed with emphasis on future directions in this active field of research.

  11. Adsorption and migration of single metal atoms on the calcite (10.4) surface.

    PubMed

    Pinto, H; Haapasilta, V; Lokhandwala, M; Öberg, S; Foster, Adam S

    2017-04-05

    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca-Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface.

  12. Adsorption and migration of single metal atoms on the calcite (10.4) surface

    NASA Astrophysics Data System (ADS)

    Pinto, H.; Haapasilta, V.; Lokhandwala, M.; Öberg, S.; Foster, Adam S.

    2017-04-01

    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface.

  13. Charge transfer and formation of reduced Ce3+ upon adsorption of metal atoms at the ceria (110) surface.

    PubMed

    Nolan, Michael

    2012-04-07

    The modification of cerium dioxide with nanoscale metal clusters is intensely researched for catalysis applications, with gold, silver, and copper having been particularly well studied. The interaction of the metal cluster with ceria is driven principally by a localised interaction between a small number of metal atoms (as small as one) and the surface and understanding the fundamentals of the interaction of metal atoms with ceria surfaces is therefore of great interest. Much attention has been focused on the interaction of metals with the (111) surface of ceria, since this is the most stable surface and can be grown as films, which are probed experimentally. However, nanostructures exposing other surfaces such as (110) show high activity for reactions including CO oxidation and require further study; these nanostructures could be modified by deposition of metal atoms or small clusters, but there is no information to date on the atomic level details of metal-ceria interactions involving the (110) surface. This paper presents the results of density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) calculations of the adsorption of a number of different metal atoms at an extended ceria (110) surface; the metals are Au, Ag, Cu, Al, Ga, In, La, Ce, V, Cr, and Fe. Upon adsorption all metals are oxidised, transferring electron(s) to the surface, resulting in localised surface distortions. The precise details depend on the identity of the metal atom. Au, Ag, Cu each transfer one electron to the surface, reducing one Ce ion to Ce(3+), while of the trivalent metals, Al and La are fully oxidised, but Ga and In are only partially oxidised. Ce and the transition metals are also partially oxidised, with the number of reduced Ce ions possible in this surface no more than three per adsorbed metal atom. The predicted oxidation states of the adsorbed metal atoms should be testable in experiments on ceria nanostructures modified with metal atoms.

  14. Charge transfer and formation of reduced Ce{sup 3+} upon adsorption of metal atoms at the ceria (110) surface

    SciTech Connect

    Nolan, Michael

    2012-04-07

    The modification of cerium dioxide with nanoscale metal clusters is intensely researched for catalysis applications, with gold, silver, and copper having been particularly well studied. The interaction of the metal cluster with ceria is driven principally by a localised interaction between a small number of metal atoms (as small as one) and the surface and understanding the fundamentals of the interaction of metal atoms with ceria surfaces is therefore of great interest. Much attention has been focused on the interaction of metals with the (111) surface of ceria, since this is the most stable surface and can be grown as films, which are probed experimentally. However, nanostructures exposing other surfaces such as (110) show high activity for reactions including CO oxidation and require further study; these nanostructures could be modified by deposition of metal atoms or small clusters, but there is no information to date on the atomic level details of metal-ceria interactions involving the (110) surface. This paper presents the results of density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) calculations of the adsorption of a number of different metal atoms at an extended ceria (110) surface; the metals are Au, Ag, Cu, Al, Ga, In, La, Ce, V, Cr, and Fe. Upon adsorption all metals are oxidised, transferring electron(s) to the surface, resulting in localised surface distortions. The precise details depend on the identity of the metal atom. Au, Ag, Cu each transfer one electron to the surface, reducing one Ce ion to Ce{sup 3+}, while of the trivalent metals, Al and La are fully oxidised, but Ga and In are only partially oxidised. Ce and the transition metals are also partially oxidised, with the number of reduced Ce ions possible in this surface no more than three per adsorbed metal atom. The predicted oxidation states of the adsorbed metal atoms should be testable in experiments on ceria nanostructures modified with metal atoms.

  15. Overlap Integrals for Atom-Metal Surface Interactions.

    DTIC Science & Technology

    1985-05-01

    of using the numerical wavefunctions from this model, we shall consider the metal electrons as particle - in - a - box . Such ’ wavefunctions are good...electronic wavevector parallel to the surface. f(z) is the one-dimensional particle - in - a - box wavefunction: 21/2.𔃼 f(z) = () sin(kz* e ) (9a)z k for -L < z

  16. The importance of atomic and molecular correlation on the bonding in transition metal compounds

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Walch, Stephen P.

    1986-01-01

    The determination of accurate spectroscopic parameters for molecular systems containing transition metal atoms is shown to require extensive data sets and a high level correlation treatment, and techniques and their limitations are considered. Extensive results reported on the transition metal atoms, hydrides, oxides, and dimers makes possible the design of a calculation to correctly describe the mixing of different atomic asymptotes, and to give a correct balance between molecular bonding and exchange interactions. Examples considered include the dipole moment of the 2Delta state of NiH, which can help determine the mixture of 3d(8)4s(2) and 3d(9)4s(1) in the NiH wavefunction, and the bonding in CrO, where an equivalent description of the relative energies associated with the Cr 3d-3d atomic exchange and the Cr-O bond is important.

  17. Metal content monitoring in Hypericum perforatum pharmaceutical derivatives by atomic absorption and emission spectrometry.

    PubMed

    Gomez, María R; Soledad, Cerutti; Olsina, Roberto A; Silva, María F; Martínez, Luis D

    2004-02-18

    Metals have been investigated in different plant materials in order to establish their normal concentration range and consider their role in plants as part of human medicinal treatment. Metal monitoring as a pattern recognition method is a promising tool in the characterization and/or standardization of phytomedicines. In the present work measurable amounts of Ca, Cu, K, Li, Mg, Mn, Na, Ni, and Zn were detected in phytopharmaceutical derivatives of Hypericum perforatum by atomic techniques. Atomic methodologies like flame atomic absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAAS) allow reliable determination of mineral content in pharmaceutical quality control of medicinal plants. Additionally, capillary electrophoresis (CE) patterns of characteristic components (fingerprints) have been performed for the search of adulterants in phytopharmaceutical products.

  18. Theoretical research program to predict the properties of molecules and clusters containing transition metal atoms

    NASA Technical Reports Server (NTRS)

    Walch, S.

    1984-01-01

    The primary focus of this research has been the theoretical study of transition metal (TM) chemistry. A major goal of this work is to provide reliable information about the interaction of H atoms with iron metal. This information is needed to understand the effect of H atoms on the processes of embrittlement and crack propagation in iron. The method in the iron hydrogen studies is the cluster method in which the bulk metal is modelled by a finite number of iron atoms. There are several difficulties in the application of this approach to the hydrogen iron system. First the nature of TM-TM and TM-H bonding for even diatomic molecules was not well understood when these studies were started. Secondly relatively large iron clusters are needed to provide reasonable results.

  19. A model of optical trapping cold atoms using a metallic nano wire with surface plasmon effect

    NASA Astrophysics Data System (ADS)

    Thi Phuong Lan, Nguyen; Thi Nga, Do; Viet, Nguyen Ai

    2016-06-01

    In this work, we construct a new model of optical trapping cold atoms with a metallic nano wire by using surface plasmon effect generated by strong field of laser beams. Using the skin effect, we send a strong oscillated electromagnetic filed through the surface of a metallic nano wire. The local field generated by evanescent effect creates an effective attractive potential near the surface of metallic nano wires. The consideration of some possible boundary and frequency conditions might lead to non-trivial bound state solution for a cold atom. We discus also the case of the laser reflection optical trap with shell-core design, and compare our model with another recent schemes of cold atom optical traps using optical fibers and carbon nanotubes.

  20. Self-Assembly of Silver Metal Clusters of Small Atomicity on Cyclic Peptide Nanotubes.

    PubMed

    Cuerva, Miguel; García-Fandiño, Rebeca; Vázquez-Vázquez, Carlos; López-Quintela, M Arturo; Montenegro, Javier; Granja, Juan R

    2015-11-24

    Subnanometric noble metal clusters, composed by only a few atoms, behave like molecular entities and display magnetic, luminescent and catalytic activities. However, noncovalent interactions of molecular metal clusters, lacking of any ligand or surfactant, have not been seen at work. Theoretically attractive and experimentally discernible, van der Waals forces and noncovalent interactions at the metal/organic interfaces will be crucial to understand and develop the next generation of hybrid nanomaterials. Here, we present experimental and theoretical evidence of noncovalent interactions between subnanometric metal (0) silver clusters and aromatic rings and their application in the preparation of 1D self-assembled hybrid architectures with ditopic peptide nanotubes. Atomic force microscopy, fluorescence experiments, circular dichroism and computational simulations verified the occurrence of these interactions in the clean and mild formation of a novel peptide nanotube and metal cluster hybrid material. The findings reported here confirmed the sensitivity of silver metal clusters of small atomicity toward noncovalent interactions, a concept that could find multiple applications in nanotechnology. We conclude that induced supramolecular forces are optimal candidates for the precise spatial positioning and properties modulation of molecular metal clusters. The reported results herein outline and generalize the possibilities that noncovalent interactions will have in this emerging field.

  1. Dynamic decoupling and local atomic order of a model multicomponent metallic glass-former.

    PubMed

    Kim, Jeongmin; Sung, Bong June

    2015-06-17

    The dynamics of multicomponent metallic alloys is spatially heterogeneous near glass transition. The diffusion coefficient of one component of the metallic alloys may also decouple from those of other components, i.e., the diffusion coefficient of each component depends differently on the viscosity of metallic alloys. In this work we investigate the dynamic heterogeneity and decoupling of a model system for multicomponent Pd43Cu27Ni10P20 melts by using a hard sphere model that considers the size disparity of alloys but does not take chemical effects into account. We also study how such dynamic behaviors would relate to the local atomic structure of metallic alloys. We find, from molecular dynamics simulations, that the smallest component P of multicomponent Pd43Cu27Ni10P20 melts becomes dynamically heterogeneous at a translational relaxation time scale and that the largest major component Pd forms a slow subsystem, which has been considered mainly responsible for the stabilization of amorphous state of alloys. The heterogeneous dynamics of P atoms accounts for the breakdown of Stokes-Einstein relation and also leads to the dynamic decoupling of P and Pd atoms. The dynamically heterogeneous P atoms decrease the lifetime of the local short-range atomic orders of both icosahedral and close-packed structures by orders of magnitude.

  2. Comparison of void strengthening in fcc and bcc metals : large-scale atomic-level modelling.

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2005-01-01

    Strengthening due to voids can be a significant radiation effect in metals. Treatment of this by elasticity theory of dislocations is difficult when atomic structure of the obstacle and dislocation is influential. In this paper, we report results of large-scale atomic-level modelling of edge dislocation-void interaction in fcc (copper) and bcc (iron) metals. Voids of up to 5 nm diameter were studied over the temperature range from 0 to 600 K. We demonstrate that atomistic modelling is able to reveal important effects, which are beyond the continuum approach. Some arise from features of the dislocation core and crystal structure, others involve dislocation climb and temperature effects.

  3. Photoabsorption by ground-state alkali-metal atoms.

    NASA Technical Reports Server (NTRS)

    Weisheit, J. C.

    1972-01-01

    Principal-series oscillator strengths and ground-state photoionization cross sections are computed for sodium, potassium, rubidium, and cesium. The degree of polarization of the photoelectrons is also predicted for each atom. The core-polarization correction to the dipole transition moment is included in all of the calculations, and the spin-orbit perturbation of valence-p-electron orbitals is included in the calculations of the Rb and Cs oscillator strengths and of all the photoionization cross sections. The results are compared with recent measurements.

  4. Atomic structure of biodegradable Mg-based bulk metallic glass.

    PubMed

    Christie, J K

    2015-05-21

    We have used highly accurate first-principles molecular dynamics simulations to elucidate the structure of Mg60Zn35Ca5 and Mg72Zn23Ca5 bulk metallic glasses, which are candidate materials for biomedical implants; these two compositions exhibit different behaviours when implanted. The environments of each species are different, and average coordination numbers are ∼13 for Mg, ∼11 for Zn and ∼18-19 for Ca. A wide range of local environments were found and icosahedral motifs, often seen in bulk metallic glasses, were among the most common for both Mg and Zn. Through the computation of a chemical short-range order parameter, a moderate avoidance of Zn-Zn bonding over Zn-Mg or Zn-Ca was observed. No statistically significant difference in structure was observed between the two compositions.

  5. Metal furnace heated by flame as a hydride atomizer for atomic absorption spectrometry: Sb determination in environmental and pharmaceutical samples.

    PubMed

    Figueiredo, Eduardo Costa; Dĕdina, Jirí; Arruda, Marco Aurélio Zezzi

    2007-10-15

    The present work describes a metallic hydride atomizer for atomic absorption spectrometry, by evaluating the performance of the Inconel 600((R)) tube. For this purpose, stibine was used as the model volatile compound and antimony determination in river and lake sediments and in pharmaceutical samples was carried out to assess the metal furnace performance. Some parameters are evaluated such as those referring to the generation and transport of the hydride (such as KBH(4) and acid concentrations, carrier gas flow rate, injected volume, etc.), as well as those referring to the metal furnace (such as tube hole area, flame composition, long-term stability, etc.). The method presents linear Sb concentration from 2 to 80mugL(-1) range (r>0.998; n=3) and the analytical frequency of ca. 140h(-1). The limit of detection (LOD) is 0.23mugL(-1) and the precision, expressed as R.S.D., is less than 5% (40mugL(-1); n=10). The accuracy is evaluated through the reference materials, and the results are similar at 95% confidence level according to the t-test.

  6. The atomic nature of polymer-metal interactions in adhesion, friction and wear

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.; Brainard, W. A.

    1973-01-01

    Adhesion experiments with polytetra-fluoroethylene (PTFE) and polyimide contacting tungsten indicate that the polymers bond chemically to the clean metal surface. Polymer chain fragments which transfer to the surface of tungsten in field ion microscopy adhesion studies are highly oriented. Auger emission spectroscopy of PTFE transfer films to various metal surfaces indicates that the PTFE is bonded to the metal surface via the carbon atom. With PTFE in sliding contact with different orientations of aluminum, metal orientation is found to influence surfaces in sliding. The lowest friction and least amount of surface damage is detected on the highest atomic density (111) plane. The friction process itself can initiate polymer film formation from simple organic molecules.

  7. Unsaturated binuclear cyclopentadienylrhenium carbonyl derivatives: metal-metal multiple bonds and agostic hydrogen atoms.

    PubMed

    Xu, Bing; Li, Qian-shu; Xie, Yaoming; King, R Bruce; Schaefer, Henry F

    2008-08-04

    The cyclopentadienylrhenium carbonyls Cp 2Re 2(CO) n (Cp = eta (5)-C 5H 5; n = 5, 4, 3, 2) have been studied by density functional theory. The global minima for the Cp 2Re 2(CO) n ( n = 5, 4, 3, 2) derivatives are predicted to be the singly bridged structure Cp 2Re 2(CO) 4(mu-CO) with a formal Re-Re single bond; the doubly semibridged structure Cp 2Re 2(CO) 4 with a formal ReRe double bond; the triply bridged structure Cp 2Re 2(mu-CO) 3 with a formal ReRe triple bond; and the doubly bridged structure Cp 2Re 2(mu-CO) 2, respectively. The first three of these predicted structures have been realized experimentally in the stable compounds (eta (5)-C 5H 5) 2Re 2(CO) 4(mu-CO), (eta (5)-Me 5C 5) 2Re 2(CO) 4 and (eta (5)-Me 5C 5) 2Re 2(mu-CO) 3. In addition, structures of the type Cp 2Re-Re(CO) n with both rings bonded only to one metal and unknown in manganese chemistry are also found for rhenium but at energies significantly above the global minima. The unsaturated Cp 2Re-Re(CO) n structures ( n = 4, 3, 2) have agostic Cp hydrogen atoms forming C-H-Re bridges to the unsaturated Re(CO) n group with a Re-H distance as short as 2.04 A.

  8. Activation energies of metal atomization and nitrate and sulfate decomposition in concentrated matrices (10 -1 M).

    NASA Astrophysics Data System (ADS)

    Le Bihan, A.; Le Garrec, H.; Cabon, J. Y.; Guern, Y.

    1998-08-01

    This paper reports on activation energies measured during copper and manganese atomization in a graphite furnace in the presence of large amounts of nitrate and sulfate matrices. It also deals with activation energies corresponding to the decomposition of these matrices and to the atomization of their metal, i.e. Na, Ca or Mg. These results were obtained from Arrhenius-type calculations carried out on specific and non-specific absorbance values. Atomization was achieved under a very high gas flow which allowed us to get to the source function. Some of the calculated energies were compared to reaction energies deduced from tables of thermodynamic data.

  9. Characteristics of flows of energetic atoms reflected from metal targets during ion bombardment

    NASA Astrophysics Data System (ADS)

    Kuzmichev, A.; Perevertaylo, V.; Tsybulsky, L.; Volpian, O.

    2016-07-01

    Particle number and energy reflection coefficients for energetic neutralized gas ions (Ar and O atoms) backscattered from metal targets during ion bombardment have been calculated using TRIM code. The energy distributions of reflected atoms are computed, too, and their dependence on the primary ion energy and the angle of ion incidence is determined. The obtained data confirm the possibility of employing energetic atoms reflection for generation of high energy neutral beams and point out to take this phenomenon into account under analysis of the ion technology for coating deposition.

  10. Tuning the electronic and magnetic properties of borophene by 3d transition-metal atom adsorption

    NASA Astrophysics Data System (ADS)

    Li, J. Y.; Lv, H. Y.; Lu, W. J.; Shao, D. F.; Xiao, R. C.; Sun, Y. P.

    2016-12-01

    The electronic and magnetic properties of borophene functionalized by 3d transition metal (TM) atom adsorption are investigated by using first-principles calculations. The results show that the 3d TM atoms can be adsorbed on borophene with high binding energies ranging between 5.9 and 8.3 eV. Interestingly, the originally nonmagnetic borophene tends to be ferromagnetic when Ti, V, Cr, Mn, and Fe atoms are adsorbed, and the magnetic moments are dominated by the TM atoms. The origin of the ferromagnetism is discussed based on the Stoner criterion. Our results indicate that the magnetic properties of borophene can be effectively tuned through the adsorption of 3d TM atoms, which could have promising applications in spintronics and nanoelectronics.

  11. Correlation between atomic structure evolution and strength in a bulk metallic glass at cryogenic temperature.

    PubMed

    Tan, J; Wang, G; Liu, Z Y; Bednarčík, J; Gao, Y L; Zhai, Q J; Mattern, N; Eckert, J

    2014-01-28

    A model Zr41.25Ti13.75Ni10Cu12.5Be22.5 (at.%) bulk metallic glass (BMG) is selected to explore the structural evolution on the atomic scale with decreasing temperature down to cryogenic level using high energy X-ray synchrotron radiation. We discover a close correlation between the atomic structure evolution and the strength of the BMG and find out that the activation energy increment of the concordantly atomic shifting at lower temperature is the main factor influencing the strength. Our results might provide a fundamental understanding of the atomic-scale structure evolution and may bridge the gap between the atomic-scale physics and the macro-scale fracture strength for BMGs.

  12. Characterization of Graphene and Transition Metal Dichalcogenide at the Atomic Scale

    NASA Astrophysics Data System (ADS)

    Liu, Zheng; Lin, Yung-Chang; Warner, Jamie H.; Teng, Po-Yuan; Yeh, Chao-Hui; Chiu, Po-Wen; Iijima, Sumio; Suenga, Kazu

    2015-12-01

    Edge structures and atomic defects are of fundamental importance since they can significantly affect the physical and chemical properties of low-dimensional materials, such as nanoribbons, and therefore merit thorough investigations at the atomic level. Recent developments of direct imaging and analytical techniques using an aberration-corrected scanning transmission electron microscope (STEM) have provided direct access to information on the local atomic structure and the chemical composition at the atomic scale. In this review, we report on the discrimination of single atoms including dopant atoms on a monolayered transition-metal dichalcogenide (TMD) nanoribbon and a single nitrogen adatom on graphene by time-resolved annular dark-field (ADF) imaging and spatially resolved electron energy loss spectroscopy (EELS). We also show that in situ scanning transmission electron microscopy can be used to monitor the structural transformation between semiconducting (2H) and metallic (1T) phases in monolayer MoS2, and can enable direct observation of in-plane graphene growth at a step edge of a bi-layer graphene and domain boundary formation during growth with atomic-resolution.

  13. Magnetic properties of Pd atomic chains formed during submonolayer deposition of 3d metals on Pd(110)

    NASA Astrophysics Data System (ADS)

    Stepanyuk, O. V.; Ignatiev, P. A.; Negulyaev, N. N.; Saletsky, A. M.; Hergert, W.

    2012-06-01

    Recently, an unusual intermixing-driven scenario for the growth of atomic Pd chains on a Pd(110) surface during deposition of 3d metal atoms has been predicted (Stepanyuk 2009 Phys. Rev. B 79 155410) and confirmed by STM and STS experiments (Wie et al 2009 Phys. Rev. Lett. 103 225504). Performing ab initio calculations we demonstrate that Pd atomic chains grown above embedded Fe atoms exhibit magnetic properties which depend on the substrate mediated exchange interaction between the Fe atoms.

  14. Magnetic properties of Pd atomic chains formed during submonolayer deposition of 3d metals on Pd(110).

    PubMed

    Stepanyuk, O V; Ignatiev, P A; Negulyaev, N N; Saletsky, A M; Hergert, W

    2012-06-13

    Recently, an unusual intermixing-driven scenario for the growth of atomic Pd chains on a Pd(110) surface during deposition of 3d metal atoms has been predicted (Stepanyuk 2009 Phys. Rev. B 79 155410) and confirmed by STM and STS experiments (Wie et al 2009 Phys. Rev. Lett. 103 225504). Performing ab initio calculations we demonstrate that Pd atomic chains grown above embedded Fe atoms exhibit magnetic properties which depend on the substrate mediated exchange interaction between the Fe atoms.

  15. Investigation of the Interactions and Bonding between Carbon and Group VIII Metals at the Atomic Scale.

    PubMed

    Zoberbier, Thilo; Chamberlain, Thomas W; Biskupek, Johannes; Suyetin, Mikhail; Majouga, Alexander G; Besley, Elena; Kaiser, Ute; Khlobystov, Andrei N

    2016-03-23

    The nature and dynamics of bonding between Fe, Ru, Os, and single-walled carbon nanotubes (SWNTs) is studied by aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM). The metals catalyze a wide variety of different transformations ranging from ejection of carbon atoms from the nanotube sidewall to the formation of hollow carbon shells or metal carbide within the SWNT, depending on the nature of the metal. The electron beam of AC-HRTEM serves the dual purpose of providing energy to the specimen and simultaneously enabling imaging of chemical transformations. Careful control of the electron beam parameters, energy, flux, and dose allowed direct comparison between the metals, demonstrating that their chemical reactions with SWNTs are determined by a balance between the cohesive energy of the metal particles and the strength of the metal-carbon σ- or π-bonds. The pathways of transformations of a given metal can be drastically changed by applying different electron energies (80, 40, or 20 keV), thus demonstrating AC-HRTEM as a new tool to direct and study chemical reactions. The understanding of interactions and bonding between SWNT and metals revealed by AC-HRTEM at the atomic level has important implications for nanotube-based electronic devices and catalysis.

  16. Electronic and magnetic properties of NbSe2 monolayer doped vacancy and transition metal atoms

    NASA Astrophysics Data System (ADS)

    Manchanda, Priyanka; Sellmyer, David; Skomski, Ralph

    2015-03-01

    Two-dimensional transition-metal dichalcogenides (2D TMDs) have attracted much attention recently due to potential applications including optoelectronic devices. Atomically thin layers of materials such as MoS2, WS2, NbS2, NbSe2, TaTe2 can easily be synthesized by exfoliation techniques and exhibit variety electronic phases such as metal, semiconductor, superconductor depending on the choice of metal. Most of the TMDs are nonmagnetic and various techniques have been proposed to induce or modulate magnetic properties that are essential for nanoelectronic device applications. We use DFT calculations to analyze the effect of strain, hydrogen adsorption, and doping. Emphasis is on the magnetic properties of NbSe2 monolayers containing vacancies and 3 d transition metal atoms. We find that magnetism can be induced by vacancy creation and transition metal-substitution in NbSe2, with effects similar to strain and hydrogen adsorption. The moment mainly arises from the localized nonbonding 3d electrons of the transition-metal atoms. Our findings contribute to the ongoing search ``for-better-than-graphene'' thin-film materials for novel electronic devices. This research is partially supported by DOE BES (DE-FG02-04ER46152).

  17. Tuning inter-dot tunnel coupling of an etched graphene double quantum dot by adjacent metal gates

    PubMed Central

    Wei, Da; Li, Hai-Ou; Cao, Gang; Luo, Gang; Zheng, Zhi-Xiong; Tu, Tao; Xiao, Ming; Guo, Guang-Can; Jiang, Hong-Wen; Guo, Guo-Ping

    2013-01-01

    Graphene double quantum dots (DQDs) open to use charge or spin degrees of freedom for storing and manipulating quantum information in this new electronic material. However, impurities and edge disorders in etched graphene nano-structures hinder the ability to control the inter-dot tunnel coupling, tC, the most important property of the artificial molecule. Here we report measurements of tC in an all-metal-side-gated graphene DQD. We find that tC can be controlled continuously about a factor of four by employing a single gate. Furthermore, tC, can be changed monotonically about another factor of four as electrons are gate-pumped into the dot one by one. The results suggest that the strength of tunnel coupling in etched graphene DQDs can be varied in a rather broad range and in a controllable manner, which improves the outlook to use graphene as a base material for qubit applications. PMID:24213723

  18. New look at the atomic volumes of the. beta. -form of the transplutonium metals

    SciTech Connect

    Haire, R.G.; Benedict, U.; Peterson, J.R.; Dufour, C.; Dabos, S.

    1986-01-01

    The atomic volumes of the beta-form of the first four transplutonium metals were evaluated using data for samples prepared by thermal and by pressure treatment. The volumes derived for curium, berkelium, and californium metals quenched from elevated temperatures were found to be consistently larger than those for ''pressure-quenched'' samples, whose volumes were in good agreement with values for the alpha-forms. The cubic lattice parameters from ''pressure-quenched'' samples also provided a more consistent trend than those obtained from thermally quenched samples when compared to the parameters for the mononitrides of the metals.

  19. [Novel Hyphenated Techniques of Atomic Spectrometry for Metal Species Interaction with Biomolecules].

    PubMed

    Li, Yan; Yan, Xiu-ping

    2015-09-01

    Trace metals may be adopted by biological systems to assist in the syntheses and metabolic functions of genes (DNA and RNA) and proteins in the environment. These metals may be beneficial or may pose a risk to humans and other life forms. Novel hybrid techniques are required for studies on the interaction between different metal species and biomolecules, which is significant for biology, biochemistry, nutrition, agriculture, medicine, pharmacy, and environmental science. In recent years, our group dwells on new hyphenated techniques based on capillary electrophoresis (CE), electrothermal atomic absorption spectrometry (ETAAS), and inductively coupled plasma mass spectroscopy (ICP-MS), and their application for different metal species interaction with biomolecules such as DNA, HSA, and GSH. The CE-ETAAS assay and CE-ICP-MS assay allow sensitively probing the level of biomolecules such as DNA damage by different metal species and extracting the kinetic and thermodynamic information on the interactions of different metal species with biomolecules, provides direct evidences for the formation of different metal species--biomolecule adducts. In addition, the consequent structural information were extracted from circular dichroism (CD) and X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The present works represent the most complete and extensive study to date on the interactions between different metal species with biomolecules, and also provide new evidences for and insights into the interactions of different metal species with biomolecules for further understanding of the toxicological effects of metal species.

  20. Excited state distribution of reflected hydrogen atoms at metal surfaces - Development of theoretical models

    NASA Astrophysics Data System (ADS)

    Kato, D.; Kenmotsu, T.; Ohya, K.; Tanabe, T.

    2009-06-01

    Numerical methods were developed to study single electron capture by translating hydrogen atoms above metal surfaces. The present method gives predictions for hitherto unknown population distribution of excited species in hydrogen atoms reflected at the metal surfaces. The excited state abundance was calculated for Mo surface. Kinetic energy distribution of the reflected atoms was taken into account with the aid of the Monte-Carlo simulation code (ACAT). Energy distribution associated with the 3d 2 excited state in reflected neutrals consistently explains peak energy variation with incident energies of Doppler-shifted D α lines measured by Tanabe et al. Occupation probability of the magnetic sub-levels is obtained to be highly polarized. It suggests strong anisotropy in angular distribution of photon emission from the excited states created via the surface electron capture.

  1. EAM potentials for BCC, FCC and HCP metals with farther neighbor atoms

    NASA Astrophysics Data System (ADS)

    Jin, Hak-Son; An, Jong-Do; Jong, Yon-Song

    2015-07-01

    The modified analytic embedded atom method (EAM) theory considering farther neighbor atoms is improved. We not only adopt an end processing function and an enhanced smooth continuous condition of the pair potential, but also adjust model parameters of multi-body potential by fitting cohesion energies, mono-vacancy formation energies, Rose equation curves, energy differences between several structures, elastic parameters and the equilibrium conditions of crystals. The calculation results of structure energy differences misfit the experiment data for several metallic materials in the unimproved EAM, because its model parameters have not considered these differences. After the modification, the coincidence degree of the structure energy—the reduced distance r/r 1 from the present model with that from the Rose equation is greatly improved for Cr. The calculated results of structure stabilities are in good agreement with experiment data and other calculated results for all considered metals, significantly better than the unimproved model with farther neighbor atoms.

  2. Hydration process of alkaline-earth metal atoms in water clusters

    NASA Astrophysics Data System (ADS)

    Okai, Nobuhiro; Ishikawa, Haruki; Fuke, Kiyokazu

    2005-10-01

    Ionization potentials (IPs) of water clusters containing alkaline-earth metal atoms are measured by a photoionization threshold method to examine the hydration process of the metal atoms in clusters. IPs of Mg(H 2O) n and Ca(H 2O) n are found to decrease with increasing n and become constant at 3.18 eV for n ⩾ 9 and n ⩾ 8, respectively. The observed constant IP agrees with an estimated photoelectric threshold (3.2 eV) of bulk ice. From the comparison with the results on the theoretical calculations as well as the IPs for alkali atom-water clusters, the anomalous size dependence of IPs is ascribed to the formation of an ion-pair state.

  3. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

    PubMed Central

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P.; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-01-01

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry. PMID:26286479

  4. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

    NASA Astrophysics Data System (ADS)

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P.; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-08-01

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

  5. Maximum noble-metal efficiency in catalytic materials: atomically dispersed surface platinum.

    PubMed

    Bruix, Albert; Lykhach, Yaroslava; Matolínová, Iva; Neitzel, Armin; Skála, Tomáš; Tsud, Nataliya; Vorokhta, Mykhailo; Stetsovych, Vitalii; Ševčíková, Klára; Mysliveček, Josef; Fiala, Roman; Václavů, Michal; Prince, Kevin C; Bruyère, Stéphanie; Potin, Valérie; Illas, Francesc; Matolín, Vladimír; Libuda, Jörg; Neyman, Konstantin M

    2014-09-22

    Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst's surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria "nanopocket", which binds Pt(2+) so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt-CeO2 nanocomposites showing high Pt efficiency in fuel-cell catalysis we also identify these anchoring sites.

  6. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water.

    PubMed

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-08-19

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

  7. Metallic nanoparticle-based strain sensors elaborated by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Puyoo, E.; Malhaire, C.; Thomas, D.; Rafaël, R.; R'Mili, M.; Malchère, A.; Roiban, L.; Koneti, S.; Bugnet, M.; Sabac, A.; Le Berre, M.

    2017-03-01

    Platinum nanoparticle-based strain gauges are elaborated by means of atomic layer deposition on flexible polyimide substrates. Their electro-mechanical response is tested under mechanical bending in both buckling and conformational contact configurations. A maximum gauge factor of 70 is reached at a strain level of 0.5%. Although the exponential dependence of the gauge resistance on strain is attributed to the tunneling effect, it is shown that the majority of the junctions between adjacent Pt nanoparticles are in a short circuit state. Finally, we demonstrate the feasibility of an all-plastic pressure sensor integrating Pt nanoparticle-based strain gauges in a Wheatstone bridge configuration.

  8. Superior Stable and Long Life Sodium Metal Anodes Achieved by Atomic Layer Deposition.

    PubMed

    Zhao, Yang; Goncharova, Lyudmila V; Lushington, Andrew; Sun, Qian; Yadegari, Hossein; Wang, Biqiong; Xiao, Wei; Li, Ruying; Sun, Xueliang

    2017-03-03

    Na-metal batteries are considered as the promising alternative candidate for Li-ion battery beneficial from the wide availability and low cost of sodium, high theoretical specific capacity, and high energy density based on the plating/stripping processes and lowest electrochemical potential. For Na-metal batteries, the crucial problem on metallic Na is one of the biggest challenges. Mossy or dendritic growth of Na occurs in the repetitive Na stripping/plating process with an unstable solid electrolyte interphase layer of nonuniform ionic flux, which can not only lead to the low Coulombic efficiency, but also can create short circuit risks, resulting in possible burning or explosion. In this communication, the atomic layer deposition of Al2 O3 coating is first demonstrated for the protection of metallic Na anode for Na-metal batteries. By protecting Na foil with ultrathin Al2 O3 layer, the dendrites and mossy Na formation have been effectively suppressed and lifetime has been significantly improved. Furthermore, the thickness of protective layer has been further optimized with 25 cycles of Al2 O3 layer presenting the best performance over 500 cycles. The novel design of atomic layer deposition protected metal Na anode may bring in new opportunities to the realization of the next-generation high energy-density Na metal batteries.

  9. Extended metal-atom chains with an inert second row transition metal: [Ru5(mu5-tpda)4X2] (tpda2- = tripyridyldiamido dianion, X = Cl and NCS).

    PubMed

    Yin, Caixia; Huang, Gin-Chen; Kuo, Ching-Kuo; Fu, Ming-Dung; Lu, Hao-Cheng; Ke, Jhih-Hong; Shih, Kai-Neng; Huang, Yi-Lin; Lee, Gene-Hsiang; Yeh, Chen-Yu; Chen, Chun-hsien; Peng, Shie-Ming

    2008-08-06

    EMACs (extended metal-atom chains) offer a unique platform for the exploration of metal-metal interactions. There has been significant advances on the synthesis of EMACs, such as lengthening the chains up to 11 metal atoms thus far, integrating naphthyridine moieties for tuning the charge carried at metal centers, and manipulation of metal-metal interactions. However, the metal centers in EMACs hitherto are limited to first row transition metals which are more labile than those relatively inert ones with electrons filled in the 4d and 5d shells. In this Communication, the synthesis, crystallographic, magnetic, and electrical conducting studies of [Ru5(mu5-tpda)4Cl2] and [Ru5(mu5-tpda)4(NCS)2], the first pentanuclear EMACs of second-row transition metal, are reported.

  10. Atomic collisions in suprafluid helium-nanodroplets: timescales for metal-cluster formation derived from He-density functional theory.

    PubMed

    Hauser, Andreas W; Volk, Alexander; Thaler, Philipp; Ernst, Wolfgang E

    2015-04-28

    Collision times for the coinage metal atoms Cu, Ag and Au in He-droplets are derived from helium density functional theory and molecular dynamics simulations. The strength of the attractive interaction between the metal atoms turns out to be less important than the mass of the propagating metal atoms. Even for small droplets consisting of a few thousand helium atoms, the collision times are shortest for Cu, followed by Ag and Au, despite the higher binding energy of Au2 compared to Cu2.

  11. Atomic collisions in suprafluid helium-nanodroplets: timescales for metal-cluster formation derived from He-density functional theory

    PubMed Central

    Volk, Alexander; Thaler, Philipp

    2015-01-01

    Collision times for the coinage metal atoms Cu, Ag and Au in He-droplets are derived from helium density functional theory and molecular dynamics simulations. The strength of the attractive interaction between the metal atoms turns out to be less important than the mass of the propagating metal atoms. Even for small droplets consisting of a few thousand helium atoms, the collision times are shortest for Cu, followed by Ag and Au, despite the higher binding energy of Au2 compared to Cu2. PMID:25812719

  12. Atomic layer deposition to prevent metal transfer from implants: An X-ray fluorescence study

    NASA Astrophysics Data System (ADS)

    Bilo, Fabjola; Borgese, Laura; Prost, Josef; Rauwolf, Mirjam; Turyanskaya, Anna; Wobrauschek, Peter; Kregsamer, Peter; Streli, Christina; Pazzaglia, Ugo; Depero, Laura E.

    2015-12-01

    We show that Atomic Layer Deposition is a suitable coating technique to prevent metal diffusion from medical implants. The metal distribution in animal bone tissue with inserted bare and coated Co-Cr alloys was evaluated by means of micro X-ray fluorescence mapping. In the uncoated implant, the migration of Co and Cr particles from the bare alloy in the biological tissues is observed just after one month and the number of particles significantly increases after two months. In contrast, no metal diffusion was detected in the implant coated with TiO2. Instead, a gradient distribution of the metals was found, from the alloy surface going into the tissue. No significant change was detected after two months of aging. As expected, the thicker is the TiO2 layer, the lower is the metal migration.

  13. Valley splitting in the transition-metal dichalcogenide monolayer via atom adsorption.

    PubMed

    Chen, Xiaofang; Zhong, Liangshuai; Li, Xiao; Qi, Jingshan

    2017-02-09

    In this letter we study the valley degeneracy splitting of the transition-metal dichalcogenide monolayer by first-principles calculations. The local magnetic moments are introduced into the system when the transition-metal atoms are adsorbed on the monolayer surface. The Zeeman effect arising from the local magnetic moment at transition-metal atom sites lifts the valley degeneracy. Anomalous charge, spin and valley Hall effects can be accessed due to valley splitting when we can only excite carriers of one valley. The valley splitting depends on the direction of magnetization and thus can be tuned continuously by an external magnetic field. This tunable valley splitting offers a practical avenue for exploring device paradigms based on the spin and valley degrees of freedom.

  14. s-wave elastic scattering of antihydrogen off atomic alkali-metal targets

    SciTech Connect

    Sinha, Prabal K.; Ghosh, A. S.

    2006-03-15

    We have investigated the s-wave elastic scattering of antihydrogen atoms off atomic alkali-metal targets (Li, Na, K, and Rb) at thermal energies (10{sup -16}-10{sup -4} a.u.) using an atomic orbital expansion technique. The elastic cross sections of these systems at thermal energies are found to be very high compared to H-H and H-He systems. The theoretical models employed in this study are so chosen to consider long-range forces dynamically in the calculation. The mechanism of cooling suggests that Li may be considered to be a good candidate as a buffer gas for enhanced cooling of antihydrogen atoms to ultracold temperature.

  15. Tunable meta-atom using liquid metal embedded in stretchable polymer

    SciTech Connect

    Liu, Peng; Yang, Siming; Wang, Qiugu; Jiang, Huawei; Song, Jiming; Dong, Liang; Jain, Aditya; Koschny, Thomas; Soukoulis, Costas M.

    2015-07-07

    Reconfigurable metamaterials have great potential to alleviate complications involved in using passive metamaterials to realize emerging electromagnetic functions, such as dynamical filtering, sensing, and cloaking. This paper presents a new type of tunable meta-atoms in the X-band frequency range (8–12 GHz) toward reconfigurable metamaterials. The meta-atom is made of all flexible materials compliant to the surface of an interaction object. It uses a liquid metal-based split-ring resonator as its core constituent embedded in a highly flexible elastomer. We demonstrate that simple mechanical stretching of the meta-atom can lead to the great flexibility in reconfiguring its resonance frequency continuously over more than 70% of the X-band frequency range. The presented meta-atom technique provides a simple approach to dynamically tune response characteristics of metamaterials over a broad frequency range.

  16. Bonding between strongly repulsive metal atoms: an oxymoron made real in a confined space of endohedral metallofullerenes.

    PubMed

    Popov, Alexey A; Avdoshenko, Stas M; Pendás, Angel Martín; Dunsch, Lothar

    2012-08-21

    Endohedral metallofullerenes (EMFs) are able to encapsulate up to four metal atoms. In EMFs, metal atoms are positively charged because of the electron transfer from the endohedral metal atoms to the carbon cage. It results in the strong Coulomb repulsion between the positively charged ions trapped in the confined inner space of the fullerene. At the same time, in many EMFs, such as Lu(2)@C(76), Y(2)@C(79)N, M(2)@C(82) (M = Sc, Y, Lu, etc.), Y(3)@C(80), or Sc(4)O(2)@C(80), metals do not adopt their highest oxidation states, thus yielding a possibility of the covalent metal-metal bonding. In some other EMFs (e.g., La(2)@C(80)), metal-metal bonding evolves as the result of the electrochemical or chemical reduction, which leads to the population of the metal-based LUMO with pronounced metal-metal bonding character. This article highlights different aspects of the metal-metal bonding in EMFs. It is concluded that the valence state of the metal atoms in dimetallofullerenes is not dependent on their third ionization potential, but is determined by their ns(2)(n- 1)d(1)→ns(1)(n- 1)d(2) excitation energies. Peculiarities of the metal-metal bonding in EMFs are described in terms of molecular orbital analysis as well as topological approaches such as Quantum Theory of Atoms in Molecules and Electron Localization Function. Interplay of Coulomb repulsion and covalent bonding is analyzed in the framework of the Interacting Quantum Atom approach.

  17. Atomic-scale roughness of Li metal surface evident in soft X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Prendergast, David; Wan, Liwen; Liang, Yufeng; Chuang, Yi-De; Qiao, Ruimin; Yan, Shishen; Yang, Wanli

    2015-03-01

    Realizing Li metal electrodes depends on fundamental understanding and efficient control of surface properties, which requires reliable characterization of the Li metal surface. Controlled experiments of Li K-edge soft X-ray absorption spectroscopy (XAS) reveal evidence of steady oxidation of the Li metal surface even under ultrahigh vacuum (UHV) conditions. The XAS of the short-lived Li metal surface, prepared by in-situ scratching, exhibits a prominent peak at 55.6 eV, more intense and at a slightly higher energy than the first peak expected for bulk Li metal at 55 eV. First-principles XAS calculations explain the origin of both the increased intensity and energy shift. This required the use of surface structural models with under-coordinated Li atoms and an estimated 4 Åinelastic mean-free-path for Auger electrons, implying extreme surface sensitivity of the measurements to the first 2-3 atomic layers. This work provides a benchmark on both experiment and theory for further studies of Li and other reactive metal surfaces, which are currently under scrutiny for next-generation energy storage devices. DP, LW, and YL acknowledge support from the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the US Dept. of Energy, Office of Science, Basic Energy Sciences.

  18. Metal-atom fluorescence from the quenching of metastable rare gases by metal carbonyls

    SciTech Connect

    Hollingsworth, W.E.

    1982-11-01

    A flowing afterglow apparatus was used to study the metal fluorescence resulting from the quenching of metastable rare-gas states by metal carbonyls. The data from the quenching or argon, neon, and helium by iron and nickel carbonyl agreed well with a restricted degree of freedom model indicating a concerted bond-breaking dissociation.

  19. Spatial Distributions of Metal Atoms During Carbon SWNTs Formation: Measurements and Modelling

    NASA Technical Reports Server (NTRS)

    Cau, M.; Dorval, N.; Attal-Tretout, B.; Cochon, J. L.; Loiseau, A.; Farhat, S.; Hinkov, I.; Scott, C. D.

    2004-01-01

    Experiments and modelling have been undertaken to clarify the role of metal catalysts during single-wall carbon nanotube formation. For instance, we wonder whether the metal catalyst is active as an atom, a cluster, a liquid or solid nanoparticle [1]. A reactor has been developed for synthesis by continuous CO2-laser vaporisation of a carbon-nickel-cobalt target in laminar helium flow. The laser induced fluorescence technique [2] is applied for local probing of gaseous Ni, Co and CZ species throughout the hot carbon flow of the target heated up to 3500 K. A rapid depletion of C2 in contrast to the spatial extent of metal atoms is observed in the plume (Fig. 1). This asserts that C2 condenses earlier than Ni and Co atoms.[3, 4]. The depletion is even faster when catalysts are present. It may indicate that an interaction between metal atoms and carbon dimers takes place in the gas as soon as they are expelled from the target surface. Two methods of modelling are used: a spatially I-D calculation developed originally for the arc process [5], and a zero-D time dependent calculation, solving the chemical kinetics along the streamlines [6]. The latter includes Ni cluster formation. The peak of C2 density is calculated close to the target surface where the temperature is the highest. In the hot region, C; is dominant. As the carbon products move away from the target and mix with the ambient helium, they recombine into larger clusters, as demonstrated by the peak of C5 density around 1 mm. The profile of Ni-atom density compares fairly well with the measured one (Fig. 2). The early increase is due to the drop of temperature, and the final decrease beyond 6 mm results from Ni cluster formation at the eutectic temperature (approx.1600 K).

  20. Strain tuning of magnetism in transition-metal atom doped phosphorene

    NASA Astrophysics Data System (ADS)

    Zhai, Caiyun; Dai, Xianqi; Li, Wei; Ma, Yaqiang; Wang, Tianxing; Tang, Yanan

    2017-01-01

    Using first-principles calculations, we studied the magnetic properties of 3d transition-metal (TM) atoms doped phosphorene. The magnetic moments are 1.02, 2.00, 3.00, 4.04, 1.01 and 0.93 μB for Ti, V, Cr, Mn, Fe and Ni doped phosphorene, respectively. However, there is no spin polarized state in the Sc and Co doped systems. TM atoms doped phosphorene system becomes a magnetic half-metal or a magnetic semiconductor, which depends on the species of impurity atoms. The strain is a promising way to tune the magnetic moment of TM atoms doped phosphorene systems. A small biaxial strain could induce a magnetic transition from a state with magnetic moment to another state in phosphorene doped by Fe or Mn atom. For Mn doped system, the magnetic moment changes from 2 μB to 4 μB. For Fe doped system, the magnetic moment changes from 1 μB to 3 μB. The results establish the potential for black phosphorus utilization in innovative spintronic devices.

  1. Second-Nearest-Neighbor Correlations from Connection of Atomic Packing Motifs in Metallic Glasses and Liquids

    PubMed Central

    Ding, Jun; Ma, Evan; Asta, Mark; Ritchie, Robert O.

    2015-01-01

    Using molecular dynamics simulations, we have studied the atomic correlations characterizing the second peak in the radial distribution function (RDF) of metallic glasses and liquids. The analysis was conducted from the perspective of different connection schemes of atomic packing motifs, based on the number of shared atoms between two linked coordination polyhedra. The results demonstrate that the cluster connections by face-sharing, specifically with three common atoms, are most favored when transitioning from the liquid to glassy state, and exhibit the stiffest elastic response during shear deformation. These properties of the connections and the resultant atomic correlations are generally the same for different types of packing motifs in different alloys. Splitting of the second RDF peak was observed for the inherent structure of the equilibrium liquid, originating solely from cluster connections; this trait can then be inherited in the metallic glass formed via subsequent quenching of the parent liquid through the glass transition, in the absence of any additional type of local structural order. Increasing ordering and cluster connection during cooling, however, may tune the position and intensity of the split peaks. PMID:26616762

  2. Second-Nearest-Neighbor Correlations from Connection of Atomic Packing Motifs in Metallic Glasses and Liquids

    SciTech Connect

    Ding, Jun; Ma, Evan; Asta, Mark; Ritchie, Robert O.

    2015-11-30

    Using molecular dynamics simulations, we have studied the atomic correlations characterizing the second peak in the radial distribution function (RDF) of metallic glasses and liquids. The analysis was conducted from the perspective of different connection schemes of atomic packing motifs, based on the number of shared atoms between two linked coordination polyhedra. The results demonstrate that the cluster connections by face-sharing, specifically with three common atoms, are most favored when transitioning from the liquid to glassy state, and exhibit the stiffest elastic response during shear deformation. These properties of the connections and the resultant atomic correlations are generally the same for different types of packing motifs in different alloys. Splitting of the second RDF peak was observed for the inherent structure of the equilibrium liquid, originating solely from cluster connections; this trait can then be inherited in the metallic glass formed via subsequent quenching of the parent liquid through the glass transition, in the absence of any additional type of local structural order. In conclusion, increasing ordering and cluster connection during cooling, however, may tune the position and intensity of the split peaks.

  3. Second-Nearest-Neighbor Correlations from Connection of Atomic Packing Motifs in Metallic Glasses and Liquids

    DOE PAGES

    Ding, Jun; Ma, Evan; Asta, Mark; ...

    2015-11-30

    Using molecular dynamics simulations, we have studied the atomic correlations characterizing the second peak in the radial distribution function (RDF) of metallic glasses and liquids. The analysis was conducted from the perspective of different connection schemes of atomic packing motifs, based on the number of shared atoms between two linked coordination polyhedra. The results demonstrate that the cluster connections by face-sharing, specifically with three common atoms, are most favored when transitioning from the liquid to glassy state, and exhibit the stiffest elastic response during shear deformation. These properties of the connections and the resultant atomic correlations are generally the samemore » for different types of packing motifs in different alloys. Splitting of the second RDF peak was observed for the inherent structure of the equilibrium liquid, originating solely from cluster connections; this trait can then be inherited in the metallic glass formed via subsequent quenching of the parent liquid through the glass transition, in the absence of any additional type of local structural order. In conclusion, increasing ordering and cluster connection during cooling, however, may tune the position and intensity of the split peaks.« less

  4. Capturing local atomic environment dependence of activation barriers in metals using cluster expansion models

    NASA Astrophysics Data System (ADS)

    Kulkarni, Nimish; Chatterjee, Abhijit

    2016-10-01

    It is well known that surface diffusion in metals can proceed via multiple mechanisms, such as hop, exchange and other types of concerted moves. However, the manner in which kinetic rates associated with a mechanism can depend sensitively on local atomic environment is relatively less understood. We describe recent attempts in our research group to capture the atomic environment dependence using the cluster expansion model (CEM). In particular, we focus on hop and exchange moves at the (001) surface in homoepitaxy, and show that while CEM can work remarkably well in most cases, it can sometimes provide inaccurate predictions for concerted moves.

  5. Molecular-dynamics simulations of collisions between energetic clusters of atoms and metal substrates

    SciTech Connect

    Hsieh, H.; Averback, R.S. ); Sellers, H. ); Flynn, C.P. )

    1992-02-15

    The collisional dynamics between clusters of Cu, Ni, or Al atoms, with energies of 92 eV to 1.0 keV and sizes of 4 to 92 atoms, and substrates of these same metals were studied using molecular-dynamics computer simulations. A diverse behavior was observed, depending sensitively on the size and energy of the cluster, the elastic and chemical properties of the cluster-substrate combination, and the relative mass of the cluster and substrate atoms. For the 92-atom Cu clusters impacting a Cu substrate, the cluster can form a glob'' on the surface at low energy, while penetrating the substrate and heavily deforming it at high energies. When the cluster energy exceeds {approx}25 eV/atom, the substrate suffers radiation damage. The 92-atom Al clusters do not much deform Ni substrates, but rather tend to spread epitaxially over the surface, despite the 15% lattice mismatch. For 1-keV collisions, several Al atoms dissociate from the cluster, either reflecting into the vacuum or scattering over the surface. 326-eV Ni clusters embed themselves almost completely within Al substrates and form localized amorphous zones. The potentials for these simulations were derived from the embedded-atom method, although modified to treat the higher-energy events. IAb initioP linear-combination-of-atomic-orbitals--molecular-orbitals calculations were employed to test these potentials over a wide range of energies. A simple model for the expected macroscopic behavior of cluster-solid interactions is included as an appendix for a comparison with the atomistic description offered by the simulations.

  6. Evaluation of a carbon-rod atomizer for routine determination of trace metals by atomic-absorption spectroscopy applications to analysis of lubricating oil and crude oil.

    PubMed

    Hall, G; Bratzel, M P; Chakrabarti, C L

    1973-08-01

    A carbon-rod atomizer (CRA) fitted with a 'mini-Massmann' carbon rod was evaluated for routine analysis of petroleum and petroleum products for trace metal content by atomic-absorption spectroscopy. Aspects investigated included sensitivity, detection limit, effect of solvent type, and interferences. The results of analysis of oil samples with this technique were compared with those obtained by other techniques. Metals studied were silver, copper, iron, nickel, and lead. Sensitivity and detection limit values obtained with the CRA were similar to those obtained with the carbon-filament atomizer. Strong 'solvent effects' were observed as well as interference by cations. On the basis of this study, design changes for the CRA are suggested, with the object of minimizing 'solvent effects' and interferences, increasing the atomization efficiency, and increasing the residence time of the atomic vapour in the optical path of the instrumental system.

  7. In situ nucleation of carbon nanotubes by the injection of carbon atoms into metal particles

    NASA Astrophysics Data System (ADS)

    Rodríguez-Manzo, Julio A.; Terrones, Mauricio; Terrones, Humberto; Kroto, Harold W.; Sun, Litao; Banhart, Florian

    2007-05-01

    The synthesis of carbon nanotubes (CNTs) of desired chiralities and diameters is one of the most important challenges in nanotube science and achieving such selectivity may require a detailed understanding of their growth mechanism. We report the formation of CNTs in an entirely condensed phase process that allows us, for the first time, to monitor the nucleation of a nanotube on the spherical surface of a metal particle. When multiwalled CNTs containing metal particle cores are irradiated with an electron beam, carbon from graphitic shells surrounding the metal particles is ingested into the body of the particle and subsequently emerges as single-walled nanotubes (SWNTs) or multiwalled nanotubes (MWNTs) inside the host nanotubes. These observations, at atomic resolution in an electron microscope, show that there is direct bonding between the tubes and the metal surface from which the tubes sprout and can be readily explained by bulk diffusion of carbon through the body of catalytic particles, with no evidence of surface diffusion.

  8. Optimization of a hydride generation metallic furnace atomic absorption spectrometry (HG-MF-AAS) method for tin determination: analytical and morphological parameters of a metallic atomizer.

    PubMed

    Moretto Galazzi, Rodrigo; Arruda, Marco Aurélio Zezzi

    2013-12-15

    The present work describes a metallic tube as hydride atomizer for atomic absorption spectrometry. Its performance is evaluated through tin determination, and the accuracy of the method assessed through the analysis of sediment and water samples. Some chemical parameters (referring to the generation of the hydride) such as acid, NaOH and THB concentrations, as well as physical parameters (referring to the transport of the hydride) such as carrier, acetylene, air flow-rates, flame composition, coil length, tube hole area, among others, are evaluated for optimization of the method. Scanning electron microscopy is used for evaluating morphological parameters in both new and used (after 150 h) tube atomizers. The method presents linear Sn concentration from 50 to 1000 µg L(-1) (r>0.9995; n=3) and the analytical frequency of ca. 40 h(-1). The limit of detection (LOD) is 7.1 µg L(-1) and the precision, expressed as RSD is less than 4% (200 µg L(-1); n=10). The accuracy is evaluated through reference materials, and the results are similar at 95% confidence level according to the t-test.

  9. Synthesis and stabilization of supported metal catalysts by atomic layer deposition.

    PubMed

    Lu, Junling; Elam, Jeffrey W; Stair, Peter C

    2013-08-20

    Supported metal nanoparticles are among the most important catalysts for many practical reactions, including petroleum refining, automobile exhaust treatment, and Fischer-Tropsch synthesis. The catalytic performance strongly depends on the size, composition, and structure of the metal nanoparticles, as well as the underlying support. Scientists have used conventional synthesis methods including impregnation, ion exchange, and deposition-precipitation to control and tune these factors, to establish structure-performance relationships, and to develop better catalysts. Meanwhile, chemists have improved the stability of metal nanoparticles against sintering by the application of protective layers, such as polymers and oxides that encapsulate the metal particle. This often leads to decreased catalytic activity due to a lack of precise control over the thickness of the protective layer. A promising method of catalyst synthesis is atomic layer deposition (ALD). ALD is a variation on chemical vapor deposition in which metals, oxides, and other materials are deposited on surfaces by a sequence of self-limiting reactions. The self-limiting character of these reactions makes it possible to achieve uniform deposits on high-surface-area porous solids. Therefore, design and synthesis of advanced catalysts on the nanoscale becomes possible through precise control over the structure and composition of the underlying support, the catalytic active sites, and the protective layer. In this Account, we describe our advances in the synthesis and stabilization of supported metal catalysts by ALD. After a short introduction to the technique of ALD, we show several strategies for metal catalyst synthesis by ALD that take advantage of its self-limiting feature. Monometallic and bimetallic catalysts with precise control over the metal particle size, composition, and structure were achieved by combining ALD sequences, surface treatments, and deposition temperature control. Next, we describe

  10. Direct observation of atomic-level nucleation and growth processes from an ultrathin metallic glass films

    NASA Astrophysics Data System (ADS)

    Huang, K. Q.; Cao, C. R.; Sun, Y. T.; Li, J.; Bai, H. Y.; Gu, L.; Zheng, D. N.; Wang, W. H.

    2016-01-01

    Till date, there have been no direct atomic-level experimental observations of the earliest stages of the nucleation and growth processes of nanocrystals formed by thermally induced crystallization in ultrathin metallic glasses (MGs). Here, we present a study of the crystallization process in atomically thin and highly stable MG films using double spherical aberration-corrected scanning transmission electron microscopy (Cs-TEM). Taking advantage of the stability of MG films with a slow crystallization process and the atomic-level high resolution of Cs-TEM, we observe the formation of the nucleus precursor of nanocrystals formed by atom aggregation followed by concomitant coalescence and stepwise evolution of the shape of the nanocrystals with a monodispersed and separated bimodal size distribution. Molecular dynamics simulation of the atomic motion in the glass film on a rigid amorphous substrate confirms the stepwise evolution processes of atom aggregation, cluster formation, cluster movement on the substrate, and cluster coalescence into larger crystalline particles. Our results might provide a better fundamental understanding of the nucleation and growth processes of nanocrystals in thin MG films.

  11. Direct observation of atomic-level nucleation and growth processes from an ultrathin metallic glass films

    SciTech Connect

    Huang, K. Q.; Cao, C. R.; Sun, Y. T.; Li, J.; Bai, H. Y.; Zheng, D. N. E-mail: dzheng@iphy.ac.cn Wang, W. H. E-mail: dzheng@iphy.ac.cn; Gu, L. E-mail: dzheng@iphy.ac.cn

    2016-01-07

    Till date, there have been no direct atomic-level experimental observations of the earliest stages of the nucleation and growth processes of nanocrystals formed by thermally induced crystallization in ultrathin metallic glasses (MGs). Here, we present a study of the crystallization process in atomically thin and highly stable MG films using double spherical aberration-corrected scanning transmission electron microscopy (Cs-TEM). Taking advantage of the stability of MG films with a slow crystallization process and the atomic-level high resolution of Cs-TEM, we observe the formation of the nucleus precursor of nanocrystals formed by atom aggregation followed by concomitant coalescence and stepwise evolution of the shape of the nanocrystals with a monodispersed and separated bimodal size distribution. Molecular dynamics simulation of the atomic motion in the glass film on a rigid amorphous substrate confirms the stepwise evolution processes of atom aggregation, cluster formation, cluster movement on the substrate, and cluster coalescence into larger crystalline particles. Our results might provide a better fundamental understanding of the nucleation and growth processes of nanocrystals in thin MG films.

  12. Does soil water saturation mobilize metals from riparian soils to adjacent surface water? A field monitoring study in a metal contaminated region.

    PubMed

    Van Laer, Liesbeth; Smolders, Erik

    2013-06-01

    In the Noorderkempen (NW Belgium), a large area (about 280 km(2)) is contaminated with cadmium (Cd) and zinc (Zn) due to historical pollution by the Zn smelters. Direct aquatic emissions of metals have diminished over time, however the surface water metal concentration largely exceeds quality standards, mainly during winter periods. Monitoring data were analyzed to reveal whether these fluctuations are related to seasonal redox reactions in associated contaminated riparian soils that drain into the rivers. A field survey was set up with soil pore-water and groundwater monitored for three years in transects of soil monitoring points perpendicular to rivers at contaminated and non-contaminated sites. Site averaged surface water concentrations of a 15 year dataset exceeded local quality standards 4 to 200-fold. Winter averaged metal concentrations significantly exceeded the corresponding summer values 1.3-1.8 (Zn) and 1.5-2.4 fold (Cd). Zinc and Cd concentrations in water were positively related to Fe and Mn but not to Ca, K or Na suggesting that redox reactions and not dilution processes are involved. In ground- and pore-water of the associated riparian soils, the concentrations of Zn fluctuate by the same order of magnitude as in surface water but were generally smaller than in the corresponding contaminated rivers. In addition, correlations of dissolved Zn with Fe and Mn were lacking. This analysis suggests that redox reactions in streams, and not in riparian soils, explain the seasonal trends of Zn and Cd in surface water. Hence, river sediments and not riparian soils may be the cause of the winter peaks of Zn and Cd in these rivers.

  13. Fabrication and design of metal nano-accordion structures using atomic layer deposition and interference lithography.

    PubMed

    Min, J-H; Bagal, A; Mundy, J Z; Oldham, C J; Wu, B-I; Parsons, G N; Chang, C-H

    2016-03-07

    Metal nanostructures have attractive electrical and thermal properties as well as structural stability, and are important for applications in flexible conductors. In this study, we have developed a method to fabricate and control novel complex platinum nanostructures with accordion-like profile using atomic layer deposition on lithographically patterned polymer templates. The template removal process results in unique structural transformation of the nanostructure profile, which has been studied and modeled. Using different template duty cycles and aspect ratios, we have demonstrated a wide variety of cross-sectional profiles from wavy geometry to pipe array patterns. These complex thin metal nanostructures can find applications in flexible/stretchable electronics, photonics and nanofluidics.

  14. Tune-out wavelengths of alkali-metal atoms and their applications

    SciTech Connect

    Arora, Bindiya; Safronova, M. S.; Clark, Charles W.

    2011-10-15

    Using first-principles calculations, we identify ''tune-out'' optical wavelengths, {lambda}{sub zero}, for which the ground-state frequency-dependent polarizabilities of alkali-metal atoms vanish. Our approach uses high-precision, relativistic all-order method in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. We discuss the use of tune-out wavelengths for sympathetic cooling in two-species mixtures of alkali metals with group II and other elements of interest. Special cases in which these wavelengths coincide with strong resonance transitions in a target system are identified.

  15. Copper Benzenetricarboxylate Metal-Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition.

    PubMed

    Lemaire, Paul C; Zhao, Junjie; Williams, Philip S; Walls, Howard J; Shepherd, Sarah D; Losego, Mark D; Peterson, Gregory W; Parsons, Gregory N

    2016-04-13

    Chemically functional microporous metal-organic framework (MOF) crystals are attractive for filtration and gas storage applications, and recent results show that they can be immobilized on high surface area substrates, such as fiber mats. However, fundamental knowledge is still lacking regarding initial key reaction steps in thin film MOF nucleation and growth. We find that thin inorganic nucleation layers formed by atomic layer deposition (ALD) can promote solvothermal growth of copper benzenetricarboxylate MOF (Cu-BTC) on various substrate surfaces. The nature of the ALD material affects the MOF nucleation time, crystal size and morphology, and the resulting MOF surface area per unit mass. To understand MOF nucleation mechanisms, we investigate detailed Cu-BTC MOF nucleation behavior on metal oxide powders and Al2O3, ZnO, and TiO2 layers formed by ALD on polypropylene substrates. Studying both combined and sequential MOF reactant exposure conditions, we find that during solvothermal synthesis ALD metal oxides can react with the MOF metal precursor to form double hydroxy salts that can further convert to Cu-BTC MOF. The acidic organic linker can also etch or react with the surface to form MOF from an oxide metal source, which can also function as a nucleation agent for Cu-BTC in the mixed solvothermal solution. We discuss the implications of these results for better controlled thin film MOF nucleation and growth.

  16. Formation and atomic configuration of binary metallic glasses studied by ion beam mixing and molecular dynamics simulation

    SciTech Connect

    Tai, K. P.; Gao, N.; Dai, X. D.; Li, J. H.; Liu, B. X.

    2007-06-15

    Metallic glasses are obtained in an immiscible Ag-Nb system with overall composition ranging from 25 to 90 at. % of Nb by ion beam mixing. Interestingly, the diffraction analysis shows that the formed Nb-rich metallic glass features are two distinct atomic configurations. In atomistic modeling, an n-body Ag-Nb potential is derived, under the assistance of ab initio calculation, and then applied in molecular dynamics simulations. An atomic configuration is discovered, i.e., an icositetrahedral ordering, and as well as an icosahedral ordering observed in the Ag-Nb metallic glasses and in some previously reported systems. Simulations confirm that the two dominate local atomic packing units are formed through a structural phase transition from the Nb-based bcc and fcc solid solutions, respectively, suggesting a concept of structural heredity that the crystalline structure of the constituent metals play a decisive role in determining the atomic structure of the resultant metallic glasses.

  17. Submolecular Imaging by Noncontact Atomic Force Microscopy with an Oxygen Atom Rigidly Connected to a Metallic Probe.

    PubMed

    Mönig, Harry; Hermoso, Diego R; Díaz Arado, Oscar; Todorović, Milica; Timmer, Alexander; Schüer, Simon; Langewisch, Gernot; Pérez, Rubén; Fuchs, Harald

    2016-01-26

    In scanning probe microscopy, the imaging characteristics in the various interaction channels crucially depend on the chemical termination of the probe tip. Here we analyze the contrast signatures of an oxygen-terminated copper tip with a tetrahedral configuration of the covalently bound terminal O atom. Supported by first-principles calculations we show how this tip termination can be identified by contrast analysis in noncontact atomic force and scanning tunneling microscopy (NC-AFM, STM) on a partially oxidized Cu(110) surface. After controlled tip functionalization by soft indentations of only a few angstroms in an oxide nanodomain, we demonstrate that this tip allows imaging an organic molecule adsorbed on Cu(110) by constant-height NC-AFM in the repulsive force regime, revealing its internal bond structure. In established tip functionalization approaches where, for example, CO or Xe is deliberately picked up from a surface, these probe particles are only weakly bound to the metallic tip, leading to lateral deflections during scanning. Therefore, the contrast mechanism is subject to image distortions, artifacts, and related controversies. In contrast, our simulations for the O-terminated Cu tip show that lateral deflections of the terminating O atom are negligible. This allows a detailed discussion of the fundamental imaging mechanisms in high-resolution NC-AFM experiments. With its structural rigidity, its chemically passivated state, and a high electron density at the apex, we identify the main characteristics of the O-terminated Cu tip, making it a highly attractive complementary probe for the characterization of organic nanostructures on surfaces.

  18. Surface field analysis of splitting of orbitals of atoms and ions approaching a metal surface.

    NASA Technical Reports Server (NTRS)

    Rao, P. V. S.; Waber, J. T.

    1971-01-01

    The splitting of p- and d-orbitals of an atom or an ion which is caused by the locally varying potential near the surface of a realistic metal has been studied for bcc and fcc substrates. A quasi-ionic model is reasonable at close distance, inasmuch as the electron gas does not completely screen the ionic cores. The arrangement of ion cores near the surface causes the potential to vary in three dimensions. Expressions for energy levels were derived for an unsymmetric group using the quasi-ionic model and techniques used in the treatment of crystal field of nearest neighbors. A number of cases involving ions, as well as atoms in the vicinity of a metal substrate were numerically evaluated.

  19. General trend for adsorbate-induced segregation of subsurface metal atoms in bimetallic surfaces

    NASA Astrophysics Data System (ADS)

    Menning, Carl A.; Chen, Jingguang G.

    2009-05-01

    It is well known that the unique chemical properties of transition metal alloys depend on the configuration of metal atoms of the bimetallic surfaces. Using density functional theory calculations, the thermodynamic potential for segregation of an admetal from the subsurface to surface configuration is shown to correlate linearly with the difference in occupied d-band center, Δɛd, between these two configurations for a wide range of bimetallic systems. The thermodynamic potential for segregation is also shown to increase with the Pauling electronegativity for several adsorbates, including atomic H, O, C, N, S, and Se. A generalized equation is provided to predict the stable surface configuration for the bimetallic systems with different adsorbates.

  20. 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.

  1. Superconducting state in the atomic metallic hydrogen just above the pressure of the molecular dissociation

    NASA Astrophysics Data System (ADS)

    Szcze&şacute; niak, R.; Szcze&şacute; niak, D.; Drzazga, E. A.

    2012-11-01

    Above the pressure of ˜500 GPa, the molecular metallic hydrogen gets converted into the atomic phase. The properties of the superconducting state in the metallic hydrogen just above the molecular-atomic phase transition have been examined in the paper (p=539 GPa). The numerical calculations have been conducted in the framework of the Eliashberg formalism. It has been stated that the critical temperature (TC) is equal to 360 K when the Coulomb pseudopotential takes the value of 0.1. In the considered case, TC considerably exceeds the value calculated with the help of the McMillan or Allen-Dynes formula. The remaining thermodynamic parameters significantly diverge from the canonical values predicted by the BCS theory. In particular: RΔ≡2Δ(0)/kBTC=4.95, RC≡ΔC(TC)/CN(TC)=2.78, and RH≡TCCN(TC)/HC2(0)=0.126.

  2. Giant perpendicular magnetic anisotropy of an individual atom on two-dimensional transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Odkhuu, Dorj

    2016-08-01

    Exploring magnetism and magnetic anisotropy in otherwise nonmagnetic two-dimensional materials, such as graphene and transition metal dichalcogenides, is at the heart of spintronics research. Herein, using first-principles calculations we explore the possibility of reaching an atomic-scale perpendicular magnetic anisotropy by carefully exploring the large spin-orbit coupling, orbital magnetism, and ligand field in a suitable choice of a two-dimensional structure with transition metal adatoms. More specifically, we demonstrate perpendicular magnetic anisotropy energies up to an order of 100 meV per atom in individual ruthenium and osmium adatoms at a monosulfur vacancy in molybdenum disulfide. We further propose a phenomenological model where a spin state transition that involves hybridization between molybdenum a1 and adatomic e' orbitals is a possible mechanism for magnetization reversal from an in-plane to perpendicular orientation.

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

    SciTech Connect

    Lutz, Jesse J.; Hutson, Jeremy M.

    2014-01-07

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

  4. Strain-induced metal-semiconductor transition observed in atomic carbon chains

    NASA Astrophysics Data System (ADS)

    La Torre, A.; Botello-Mendez, A.; Baaziz, W.; Charlier, J.-C.; Banhart, F.

    2015-03-01

    Carbyne, the sp1-hybridized phase of carbon, is still a missing link in the family of carbon allotropes. While the bulk phases of carbyne remain elusive, the elementary constituents, that is, linear chains of carbon atoms, have already been observed using the electron microscope. Isolated atomic chains are highly interesting one-dimensional conductors that have stimulated considerable theoretical work. Experimental information, however, is still very limited. Here we show electrical measurements and first-principles transport calculations on monoatomic carbon chains. When the 1D system is under strain, the chains are semiconducting corresponding to the polyyne structure with alternating bond lengths. Conversely, when the chain is unstrained, the ohmic behaviour of metallic cumulene with uniform bond lengths is observed. This confirms the recent prediction of a metal-insulator transition that is induced by strain. The key role of the contacting leads explains the rectifying behaviour measured in monoatomic carbon chains in a nonsymmetric contact configuration.

  5. Protein-protected luminescent noble metal quantum clusters: an emerging trend in atomic cluster nanoscience.

    PubMed

    Xavier, Paulrajpillai Lourdu; Chaudhari, Kamalesh; Baksi, Ananya; Pradeep, Thalappil

    2012-01-01

    Noble metal quantum clusters (NMQCs) are the missing link between isolated noble metal atoms and nanoparticles. NMQCs are sub-nanometer core sized clusters composed of a group of atoms, most often luminescent in the visible region, and possess intriguing photo-physical and chemical properties. A trend is observed in the use of ligands, ranging from phosphines to functional proteins, for the synthesis of NMQCs in the liquid phase. In this review, we briefly overview recent advancements in the synthesis of protein protected NMQCs with special emphasis on their structural and photo-physical properties. In view of the protein protection, coupled with direct synthesis and easy functionalization, this hybrid QC-protein system is expected to have numerous optical and bioimaging applications in the future, pointers in this direction are visible in the literature.

  6. Barrier-free subsurface incorporation of 3d metal atoms into Bi(111) films

    DOE PAGES

    Klein, C.; Vollmers, N. J.; Gerstmann, U.; ...

    2015-05-27

    By combining scanning tunneling microscopy with density functional theory it is shown that the Bi(111) surface provides a well-defined incorporation site in the first bilayer that traps highly coordinating atoms such as transition metals (TMs) or noble metals. All deposited atoms assume exactly the same specific sevenfold coordinated subsurface interstitial site while the surface topography remains nearly unchanged. Notably, 3d TMs show a barrier-free incorporation. The observed surface modification by barrier-free subsorption helps to suppress aggregation in clusters. Thus, it allows a tuning of the electronic properties not only for the pure Bi(111) surface, but may also be observed formore » topological insulators formed by substrate-stabilized Bi bilayers.« less

  7. Assessment of heavy metals contamination in sediments from three adjacent regions of the Yellow River using metal chemical fractions and multivariate analysis techniques.

    PubMed

    Ma, Xiaoling; Zuo, Hang; Tian, Mengjing; Zhang, Liyang; Meng, Jia; Zhou, Xuening; Min, Na; Chang, Xinyuan; Liu, Ying

    2016-02-01

    Metal chemical fractions obtained by optimized BCR three-stage extraction procedure and multivariate analysis techniques were exploited for assessing 7 heavy metals (Cr, Pb, Cd, Co, Cu, Zn and Ni) in sediments from Gansu province, Ningxia and Inner Mongolia Autonomous Regions of the Yellow River in Northern China. The results indicated that higher susceptibility and bioavailability of Cr and Cd with a strong anthropogenic source were due to their higher availability in the exchangeable fraction. A portion of Pb, Cd, Co, Zn, and Ni in reducible fraction may be due to the fact that they can form stable complexes with Fe and Mn oxides. Substantial amount of Pb, Co, Ni and Cu was observed as oxidizable fraction because of their strong affinity to the organic matters so that they can complex with humic substances in sediments. The high geo-accumulation indexes (I(geo)) for Cr and Cd showed their higher environmental risk to the aquatic biota. Principal component analysis (PCA) revealed that high toxic Cr and Cd in polluted sites (Cd in S10, S11 and Cr in S13) may be contributed to anthropogenic sources, it was consistent with the results of dual hierarchical clustering analysis (DHCA), which could give more details about contributing sources.

  8. Optical emission spectroscopy of metal-halide lamps: Radially resolved atomic state distribution functions of Dy and Hg

    NASA Astrophysics Data System (ADS)

    Nimalasuriya, T.; Flikweert, A. J.; Stoffels, W. W.; Haverlag, M.; van der Mullen, J. J. A. M.; Pupat, N. B. M.

    2006-03-01

    Absolute line intensity measurements are performed on a metal-halide lamp. Several transitions of atomic and ionic Dy and atomic Hg are measured at different radial positions from which we obtain absolute atomic and ionic Dy intensity profiles. From these profiles we construct the radially resolved atomic state distribution function (ASDF) of the atomic and ionic Dy and the atomic Hg. From these ASDFs several quantities are determined as functions of radial position, such as the (excitation) temperature, the ion ratio Hg+/Dy+, the electron density, the ground state, and the total density of Dy atoms and ions. Moreover, these ASDFs give us insight about the departure from equilibrium. The measurements show a hollow density profile for the atoms and the ionization of atoms in the center. In the outer parts of the lamp molecules dominate.

  9. Superconductivity, cohesive energy density, and electron-atom ratio in metals

    NASA Technical Reports Server (NTRS)

    England, C.; Lawson, D. D.; Hrubes, J. D.

    1981-01-01

    It is shown that superconductivity above 8 K occurs in alloys and metallic compounds within relatively narrow regions of cohesive energy density with a sharp peak which includes Nb3Ge, SiV3, Nb3Ga, and NbN. When cross-correlated with the electron-atom ratio, high-temperature superconductivity can be observed in only a few regions. This suggests a search for superconductors with high-transition temperatures and critical fields within these regions.

  10. Properties of the triplet metastable states of the alkaline-earth-metal atoms

    SciTech Connect

    Mitroy, J.; Bromley, M.W.J.

    2004-11-01

    The static and dynamic properties of the alkaline-earth-metal atoms in their metastable state are computed in a configuration interaction approach with a semiempirical model potential for the core. Among the properties determined are the scalar and tensor polarizabilities, the quadrupole moment, some of the oscillator strengths, and the dispersion coefficients of the van der Waals interaction. A simple method for including the effect of the core on the dispersion parameters is described.

  11. An embedded-atom-method model for alkali-metal vibrations.

    PubMed

    Wilson, R B; Riffe, D M

    2012-08-22

    We present an embedded-atom-method (EAM) model that accurately describes the vibrational dynamics in the alkali metals Li, Na, K, Rb and Cs. The bulk dispersion curves, frequency-moment Debye temperatures and temperature-dependent entropy Debye temperatures are all in excellent agreement with experimental results. The model is also well suited for studying surface vibrational dynamics in these materials, as illustrated by calculations for the Na(110) surface.

  12. Energy transfer from PO excited states to alkali metal atoms in the phosphorus chemiluminescence flame

    PubMed Central

    Khan, Ahsan U.

    1980-01-01

    Phosphorus chemiluminescence under ambient conditions of a phosphorus oxidation flame is found to offer an efficient electronic energy transferring system to alkali metal atoms. The lowest resonance lines, 2P3 / 2,½→2S½, of potassium and sodium are excited by energy transfer when an argon stream at 80°C carrying potassium or sodium atoms intersects a phosphorus vapor stream, either at the flame or in the postflame region. The lowest electronically excited metastable 4IIi state of PO or the (PO[unk]PO)* excimer is considered to be the probable energy donor. The (PO[unk]PO)* excimer results from the interaction of the 4IIi state of one PO molecule with the ground 2IIr state of another. Metastability of the donor state is strongly indicated by the observation of intense sensitized alkali atom fluorescence in the postflame region. PMID:16592925

  13. Atomic-Level Mechanisms of Nucleation of Pure Liquid Metals during Rapid Cooling.

    PubMed

    Han, Jiajia; Wang, Cuiping; Liu, Xingjun; Wang, Yi; Liu, Zi-Kui; Jiang, Jianzhong

    2015-12-21

    To obtain a material with the desired performance, the atomic-level mechanisms of nucleation from the liquid to solid phase must be understood. Although this transition has been investigated experimentally and theoretically, its atomic-level mechanisms remain debatable. In this work, the nucleation mechanisms of pure Fe under rapid cooling conditions are investigated. The local atomic packing stability and liquid-to-solid transition-energy pathways of Fe are studied using molecular dynamics simulations and first-principle calculations. The results are expressed as functions of cluster size in units of amorphous clusters (ACs) and body-centered cubic crystalline clusters (BCC-CCs). We found the prototypes of ACs in supercooled liquids and successfully divided these ACs to three categories according to their transition-energy pathways. The information obtained in this study could contribute to our current understanding of the crystallization of metallic melts during rapid cooling.

  14. The Influence of Stray Fields on the Ionization of Rydberg atoms at Metallic Surfaces

    NASA Astrophysics Data System (ADS)

    Neufeld, Dennis; Pu, Yu; Dunning, F. Barry

    2010-03-01

    The effect of local surface electric (``patch'') fields on the ionization of xenon Rydberg atoms at metallic surfaces is examined. The patch fields are determined from measurements of the potential variations across the target surfaces using Kelvin probe force microscopy. These measurements are used in conjunction with a simple over-the-barrier model of ionization to predict the surface ionization characteristics for Rydberg atoms with a range of different n and angles of incidence. These predictions are in good agreement with experimental measurements demonstrating the important role that patch fields play during Rydberg atom-surface interactions and suggesting that such interactions can provide a sensitive probe of stray fields at surfaces. These techniques are extended to lithographically patterned structures comprising two sets of interleaved ``comb-like'' electrodes to which different potentials can be applied. This allows control of the surface patch fields and direct study of their effects.

  15. Unveiling the structural arrangements responsible for the atomic dynamics in metallic glasses during physical aging

    PubMed Central

    Giordano, V. M.; Ruta, B

    2016-01-01

    Understanding and controlling physical aging, that is, the spontaneous temporal evolution of out-of-equilibrium systems, represents one of the greatest tasks in material science. Recent studies have revealed the existence of a complex atomic motion in metallic glasses, with different aging regimes in contrast with the typical continuous aging observed in macroscopic quantities. By combining dynamical and structural synchrotron techniques, here for the first time we directly connect previously identified microscopic structural mechanisms with the peculiar atomic motion, providing a broader unique view of their complexity. We show that the atomic scale is dominated by the interplay between two processes: rearrangements releasing residual stresses related to a cascade mechanism of relaxation, and medium range ordering processes, which do not affect the local density, likely due to localized relaxations of liquid-like regions. As temperature increases, a surprising additional secondary relaxation process sets in, together with a faster medium range ordering, likely precursors of crystallization. PMID:26787443

  16. Atomic interaction mechanism for designing the interface of W/Zr-based bulk metallic glass composites

    NASA Astrophysics Data System (ADS)

    Li, Z. K.; Fu, H. M.; Sha, P. F.; Zhu, Z. W.; Wang, A. M.; Li, H.; Zhang, H. W.; Zhang, H. F.; Hu, Z. Q.

    2015-03-01

    The interaction between active element Zr and W damages the W fibers and the interface and decreases the mechanical properties, especially the tensile strength of the W fibers reinforced Zr-based bulk metallic glass composites (BMGCs). From the viewpoint of atomic interaction, the W-Zr interaction can be restrained by adding minor elements that have stronger interaction with W into the alloy. The calculation about atomic interaction energy indicates that Ta and Nb preferred to segregate on the W substrate surface. Sessile drop experiment proves the prediction and corresponding in-situ coating appears at the interface. Besides, the atomic interaction mechanism was proven to be effective in many other systems by the sessile drop technique. Considering the interfacial morphology, Nb was added into the alloy to fabricate W/Zr-based BMGCs. As expected, the Nb addition effectively suppressed the W-Zr reaction and damage to W fibers. Both the compressive and tensile properties are improved obviously.

  17. Atomic interaction mechanism for designing the interface of W/Zr-based bulk metallic glass composites.

    PubMed

    Li, Z K; Fu, H M; Sha, P F; Zhu, Z W; Wang, A M; Li, H; Zhang, H W; Zhang, H F; Hu, Z Q

    2015-03-11

    The interaction between active element Zr and W damages the W fibers and the interface and decreases the mechanical properties, especially the tensile strength of the W fibers reinforced Zr-based bulk metallic glass composites (BMGCs). From the viewpoint of atomic interaction, the W-Zr interaction can be restrained by adding minor elements that have stronger interaction with W into the alloy. The calculation about atomic interaction energy indicates that Ta and Nb preferred to segregate on the W substrate surface. Sessile drop experiment proves the prediction and corresponding in-situ coating appears at the interface. Besides, the atomic interaction mechanism was proven to be effective in many other systems by the sessile drop technique. Considering the interfacial morphology, Nb was added into the alloy to fabricate W/Zr-based BMGCs. As expected, the Nb addition effectively suppressed the W-Zr reaction and damage to W fibers. Both the compressive and tensile properties are improved obviously.

  18. Composition-dependent metallic glass alloys correlate atomic mobility with collective glass surface dynamics.

    PubMed

    Nguyen, Duc; Zhu, Zhi-Guang; Pringle, Brian; Lyding, Joseph; Wang, Wei-Hua; Gruebele, Martin

    2016-06-22

    Glassy metallic alloys are richly tunable model systems for surface glassy dynamics. Here we study the correlation between atomic mobility, and the hopping rate of surface regions (clusters) that rearrange collectively on a minute to hour time scale. Increasing the proportion of low-mobility copper atoms in La-Ni-Al-Cu alloys reduces the cluster hopping rate, thus establishing a microscopic connection between atomic mobility and dynamics of collective rearrangements at a glass surface made from freshly exposed bulk glass. One composition, La60Ni15Al15Cu10, has a surface resistant to re-crystallization after three heating cycles. When thermally cycled, surface clusters grow in size from about 5 glass-forming units to about 8 glass-forming units, evidence of surface aging without crystal formation, although its bulk clearly forms larger crystalline domains. Such kinetically stable glass surfaces may be of use in applications where glassy coatings stable against heating are needed.

  19. Pd atomic chain formation as a result of submonolayer deposition of 3d metals on Pd(110).

    PubMed

    Wei, D H; Gao, C L; Zakeri, Kh; Przybylski, M

    2009-11-27

    Submonolayer deposition of 3d transition metals such as Cr, Mn, Fe, Co, and Ni on Pd(110) at room temperature causes the formation of monoatomic chains of Pd as identified with scanning tunneling microscopy and spectroscopy. In agreement with recent theoretical predictions [Phys. Rev. B 79, 155410 (2009)], the substitution of Pd substrate atoms with the deposited atoms of 3d metals is found to be responsible for the formation of Pd atomic chains. This finding clarifies the long-debated issue about the chemical composition of the atomic chains grown on Pd(110) and points out the intriguing processes in the formation of self-assembled and self-organized nanostructures.

  20. A classical description of subnanometer resolution by atomic features in metallic structures.

    PubMed

    Trautmann, S; Aizpurua, J; Götz, I; Undisz, A; Dellith, J; Schneidewind, H; Rettenmayr, M; Deckert, V

    2017-01-07

    Recent experiments have evidenced sub-nanometer resolution in plasmonic-enhanced probe spectroscopy. Such a high resolution cannot be simply explained using the commonly considered radii of metallic nanoparticles on plasmonic probes. In this contribution the effects of defects as small as a single atom found on spherical plasmonic particles acting as probing tips are investigated in connection with the spatial resolution provided. The presence of abundant edge and corner sites with atomic scale dimensions in crystalline metallic nanoparticles is evident from transmission electron microscopy (TEM) images. Electrodynamic calculations based on the Finite Element Method (FEM) are implemented to reveal the impact of the presence of such atomic features in probing tips on the lateral spatial resolution and field localization. Our analysis is developed for three different configurations, and under resonant and non-resonant illumination conditions, respectively. Based on this analysis, the limits of field enhancement, lateral resolution and field confinement in plasmon-enhanced spectroscopy and microscopy are inferred, reaching values below 1 nanometer for reasonable atomic sizes.

  1. A variational method for density functional theory calculations on metallic systems with thousands of atoms.

    PubMed

    Ruiz-Serrano, Álvaro; Skylaris, Chris-Kriton

    2013-08-07

    A new method for finite-temperature density functional theory calculations which significantly increases the number of atoms that can be simulated in metallic systems is presented. A self-consistent, direct minimization technique is used to obtain the Helmholtz free energy of the electronic system, described in terms of a set of non-orthogonal, localized functions which are optimized in situ using a periodic-sinc basis set, equivalent to plane waves. Most parts of the calculation, including the demanding operation of building the Hamiltonian matrix, have a computational cost that scales linearly with the number of atoms in the system. Also, this approach ensures that the Hamiltonian matrix has a minimal size, which reduces the computational overhead due to diagonalization, a cubic-scaling operation that is still required. Large basis set accuracy is retained via the optimization of the localized functions. This method allows accurate simulations of entire metallic nanostructures, demonstrated with calculations on a supercell of bulk copper with 500 atoms and on gold nanoparticles with up to 2057 atoms.

  2. Determination of the neutral oxygen atom density in a plasma reactor loaded with metal samples

    NASA Astrophysics Data System (ADS)

    Mozetic, Miran; Cvelbar, Uros

    2009-08-01

    The density of neutral oxygen atoms was determined during processing of metal samples in a plasma reactor. The reactor was a Pyrex tube with an inner diameter of 11 cm and a length of 30 cm. Plasma was created by an inductively coupled radiofrequency generator operating at a frequency of 27.12 MHz and output power up to 500 W. The O density was measured at the edge of the glass tube with a copper fiber optics catalytic probe. The O atom density in the empty tube depended on pressure and was between 4 and 7 × 1021 m-3. The maximum O density was at a pressure of about 150 Pa, while the dissociation fraction of O2 molecules was maximal at the lowest pressure and decreased with increasing pressure. At about 300 Pa it dropped below 10%. The measurements were repeated in the chamber loaded with different metallic samples. In these cases, the density of oxygen atoms was lower than that in the empty chamber. The results were explained by a drain of O atoms caused by heterogeneous recombination on the samples.

  3. Tunable electronic and magnetic properties in stanene by 3d transition metal atoms absorption

    NASA Astrophysics Data System (ADS)

    Xing, Dan-Xu; Ren, Ceng-Ceng; Zhang, Shu-Feng; Feng, Yong; Chen, Xin-Lian; Zhang, Chang-Wen; Wang, Pei-Ji

    2017-03-01

    The electronic and magnetic properties of transition metal (TM) atoms (V, Cr, Mn, Fe, Co, Ni) adsorption on stanene are investigated by first-principles calculations. The results indicate that the TM atoms prefer to be relaxed on a H site on stanene except V atom which lies on the valley site. Fe-absorbed stanene is a spin gapless semiconductor with up-spin electron and down-spin hole carriers allowing the coexistence of charge current and the pure spin current. Co-absorbed stanene lies in the half metal phase. The V-, Cr-, Mn-, and Cu-absorbed stanene turn the stanene into metal, while Ni- and Zn-absorbed stanene open a narrow band gap. For V-, Cr-, Mn-, Fe-, and Co-absorbed stanene, the magnetic moment of the TM will survive while the Ni-, Cu-, and Zn-absorbed stanene will be non-magnetic material. These findings may have great potential in the design of new electrically controllable spintronic devices.

  4. Dispersion coefficients for H and He interactions with alkali-metal and alkaline-earth-metal atoms

    SciTech Connect

    Mitroy, J.; Bromley, M.W.J.

    2003-12-01

    The van der Waals coefficients C{sub 6}, C{sub 8}, and C{sub 10} for H and He interactions with the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are determined from oscillator strength sum rules. The oscillator strengths were computed using a combination of ab initio and semiempirical methods. The dispersion parameters generally agree with close to exact variational calculations for Li-H and Li-He at the 0.1% level of accuracy. For larger systems, there is agreement with relativistic many-body perturbation theory estimates of C{sub 6} at the 1% level. These validations for selected systems attest to the reliability of the present dispersion parameters. About half the present parameters lie within the recommended bounds of the Standard and Certain compilation [J. Chem. Phys. 83, 3002 (1985)].

  5. Monolacunary Keggin polyoxometalates connected to ten 4d or 4f metal atoms.

    PubMed

    Pang, Haijun; Gómez-García, Carlos J; Peng, Jun; Ma, Huiyuan; Zhang, Chunjing; Wu, Qingyin

    2013-12-21

    The rational self-assembly of mono-lacunary Keggin clusters with 4d and 4f metal salts via a conventional method has yielded two novel polyoxometalate-based 4d-4f heterometallic compounds containing lacunary Keggin anions connected to ten metal atoms: {[Ag{Ag2(H2O)4}{Ln(H2O)6}2H ⊂ {SiW11Ln(H2O)4O39}2]·nH2O (Ln = Ce and n = 7 for 1, Ln = Pr and n = 3 for 2). Their structures were determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. A structural feature in 1 and 2 is that each [SiW11O39](8-) cluster (SiW11) is connected to ten metals (five Ag(+) and five Ln(3+) cations), representing the highest number of connected metal atoms to any mono-lacunary Keggin anion to date. This large connectivity leads to a structure with a purely inorganic 3D framework with two kinds of channels along the [100] and [010] directions. The magnetic properties of both compounds show the expected magnetic moments (0.8 and 1.6 amu K mol(-1) per Ce(3+) and Pr(3+) ion, respectively) and confirm the presence of isolated Ce(3+) and Pr(3+) ions.

  6. Icositetrahedral and icosahedral atomic configurations observed in the Nb-Ag metallic glasses synthesized by ion beam mixing

    SciTech Connect

    Tai, K. P.; Gao, N.; Dai, X. D.; Li, J. H.; Lai, W. S.; Liu, B. X.

    2006-08-28

    Metallic glasses are obtained in an immiscible Nb-Ag system by ion beam mixing and an atomic configuration in the amorphous structure is discovered, i.e., an icositetrahedral ordering, which, together with an icosahedral ordering also observed in the Nb-Ag metallic glasses and in some previously reported systems, helps in formulating a structural spectrum of the amorphous solids. The experimental characterization and atomistic modeling with an ab initio derived Nb-Ag potential demonstrate the significance of structural heredity, i.e., the crystalline structures of the constituent metals play a decisive role in determining the atomic structure of the metallic glasses in the system.

  7. Atomic layer deposition by reaction of molecular oxygen with tetrakisdimethylamido-metal precursors

    SciTech Connect

    Provine, J Schindler, Peter; Torgersen, Jan; Kim, Hyo Jin; Karnthaler, Hans-Peter; Prinz, Fritz B.

    2016-01-15

    Tetrakisdimethylamido (TDMA) based precursors are commonly used to deposit metal oxides such as TiO{sub 2}, ZrO{sub 2}, and HfO{sub 2} by means of chemical vapor deposition and atomic layer deposition (ALD). Both thermal and plasma enhanced ALD (PEALD) have been demonstrated with TDMA-metal precursors. While the reactions of TDMA-type precursors with water and oxygen plasma have been studied in the past, their reactivity with pure O{sub 2} has been overlooked. This paper reports on experimental evaluation of the reaction of molecular oxygen (O{sub 2}) and several metal organic precursors based on TDMA ligands. The effect of O{sub 2} exposure duration and substrate temperature on deposition and film morphology is evaluated and compared to thermal reactions with H{sub 2}O and PEALD with O{sub 2} plasma.

  8. Determination of toxic metals in some herbal drugs through atomic absorption spectroscopy.

    PubMed

    Hina, Bushra; Rizwani, Ghazala Hafeez; Naseem, Shahid

    2011-07-01

    This study presents a picture of occurrence of heavy metals (Pb, Cd, Cu, Cr, Co, Fe, Ni, Zn) in some selected valuable herbal drugs (G. glabra, O. bracteatum, V. odorata , F. vulgare, C. cyminum, C. sativum, and Z. officinalis) purchased from three different zones (southern, eastern, and western) of Karachi city using atomic absorption spectrophotometer. Heavy metal concentrations in these drugs were found in the range of: 3.26-30.46 for Pb, 1.6-4.91 for Cd, 0.65-120.21 for Cu, 83.74-433.76 for Zn, 1.61-186.75 for Cr, 0.48-76.97 for Ni, 5.54-77.97 for Co and 65.68-1652.89 µg/g for Fe. Percentage of heavy metals that were found beyond the permissible limits were: 71.4% for Pb, 28.51% for Cd, 14.2% for Cu, and 9.5 % for Cr. Significant difference was noticed for each heavy metal among herbal drugs as well as their zones of collection using two way ANOVA followed by least significant (LSD) test at p<0.05.Purpose of this research is to detect each type of heavy metal contaminant of herbal drugs by environmental pollution, as well as to highlight the health risks associated with the use of such herbal drugs that contain high levels of toxic heavy metals.

  9. Inner hydrogen atom transfer in benzo-fused low symmetrical metal-free tetraazaporphyrin and phthalocyanine analogues: density functional theory studies.

    PubMed

    Qi, Dongdong; Zhang, Yuexing; Cai, Xue; Jiang, Jianzhuang; Bai, Ming

    2009-02-01

    Density functional theory (DFT) calculations were carried out to study the inner hydrogen atom transfer in low symmetrical metal-free tetrapyrrole analogues ranging from tetraazaporphyrin H(2)TAP (A(0)B(0)C(0)D(0)) to naphthalocyanine H(2)Nc (A(2)B(2)C(2)D(2)) via phthalocyanine H(2)Pc (A(1)B(1)C(1)D(1)). All the transition paths of sixteen different compounds (A(0)B(0)C(0)D(0)-A(2)B(2)C(2)D(2) and A(0)B(0)C(m)D(n), m atom transfer. Introducing fused benzene rings onto the hydrogen-releasing pyrrole rings can increase the transitivity of inner hydrogen atom and thus lower the transfer barrier of this inner hydrogen atom while fusing benzene rings onto the hydrogen-accepting pyrrole rings will increase the hydrogen transfer barrier to this pyrrole ring. The transient cis-isomer intermediate with hydrogen atoms joined to the two adjacent pyrrole rings with less fused benzene rings is much stable than the others. It is also found that the benzene rings fused directly onto pyrrole rings have more effect on the inner hydrogen atom transfer than the outer benzene rings fused onto the periphery of isoindole rings. The present work, representing the first effort towards systematically understanding the effect of ring enlargement through asymmetrical peripheral fusion of benzene ring(s) onto the TAP skeleton on the inner hydrogen transfer of tetrapyrrole derivatives, will be helpful in clarifying the N-H tautomerization phenomenon and detecting the cis-porphyrin isomer in bio-systems.

  10. Oligomeric rare-earth metal cluster complexes with endohedral transition metal atoms

    NASA Astrophysics Data System (ADS)

    Steinberg, Simon; Zimmermann, Sina; Brühmann, Matthias; Meyer, Eva; Rustige, Christian; Wolberg, Marike; Daub, Kathrin; Bell, Thomas; Meyer, Gerd

    2014-11-01

    Comproportionation reactions of rare-earth metal trihalides (RX3) with the respective rare-earth metals (R) and transition metals (T) led to the formation of 22 oligomeric R cluster halides encapsulating T, in 19 cases for the first time. The structures of these compounds were determined by single-crystal X-ray diffraction and are composed of trimers ({T3R11}X15-type, P63/m), tetramers ({T4R16}X28{R4} (P-43m), {T4R16}X20 (P42/nnm), {T4R16}X24(RX3)4 (I41/a) and {T4R16}X23 (C2/m) types of structure) and pentamers ({Ru5La14}2Br39, Cc) of {TRr}n (n=2-5) clusters. These oligomers are further enveloped by inner (Xi) as well as outer (Xa) halido ligands, which possess diverse functionalities and interconnect like oligomers through i-i, i-a and/or a-i bridges. The general features of the crystal structures for these new compounds are discussed and compared to literature entries as well as different structure types with oligomeric T centered R clusters. Dimers and tetramers originating from the aggregation of {TR6} octahedra via common edges are more frequent than trimers and pentamers, in which the {TRr} clusters share common faces.

  11. Ab Initio Density Funcitonal Calculations of Adsorption of Transiton Metal Atoms on theta-Al2O3 (010) Surface

    SciTech Connect

    Narula, Chaitanya Kumar; Stocks, George Malcolm

    2012-01-01

    The catalytic properties of metal clusters and particles depend on their environment, however, little is known so far about the subnanometer metal particles, smallest being single atoms, supported on metal oxide substrates, especially, the systems that can be experimentally synthesized. Employing first principles density functional theory approach, we have studied single metal atoms, Ni, Pt, Pd, Cu, Au, and Ag, adsorbed on a -Al2O3 (010) surface. We find that metal adsorption on a dry alumina surface follows the binding strength order of Pd>Pt>Ni>Cu>Au>Ag. Interestingly, Ni, Pt, and Pd atoms, supported on alumina, exhibit no magnetization whereas Cu, Ag, and Au exhibit unpaired electrons. The bonding picture that emerges from this study shows that Ni, Pt, and Pd, are d10 species with d-s hybrid character that are able to interact with the 2p orbital of surface oxygen. The interaction of Group 11 (Cu, Ag, Au) atoms with 010 surface of -Al2O3 is superficially similar to that of Group 10 metals. Group 11 metals with filled d orbitals have low tendency for d-s hybridization due to larger energy gaps than Group 10 metals. As a result of the overlap with O 2p, the d orbital shifts to lower energy. The magnetization of Group 11 metals is primarily due to single electrons in s orbitals.

  12. Atomic Resolution of the Structure of a Metal Support Interface: Triosmium Clusters on MgO (110)

    SciTech Connect

    Browning, Nigel D.; Chi, Miaofang; Gates, Bruce C.; kulkarni, Apoorva; Ortalan, Volkan

    2010-01-01

    Aberration-corrected STEM images of MgO-supported triosmium clusters show that the osmium atoms reside atop magnesium atoms. On the basis of the results, structural models of the clusters that include the metal-support interaction are derived.

  13. Ultrafast valley dynamics in atomically thin transition metal dichalcogenides (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Bratschitsch, Rudolf

    2016-10-01

    Monolayer transition metal dichalcogenides such as MoS2, WS2, MoSe2, WSe2, and MoTe2 received a lot of attention recently due to their atomic thickness in combination with an optical band gap in the visible or infrared. These properties render them a promising material class for new opto-electronic devices. Strong spin-orbit coupling together with the absence of inversion symmetry leads to an emission of polarized photoluminescence after excitation with circularly polarized light. Therefore, the K and K' valley of the semiconductor can be selectively addressed by left and right handed circularly polarized light, which is interesting for valleytronic applications. To understand the mechanisms governing the creation and destruction of valley polarization, time-resolved experiments are necessary. While stationary photoluminescence experiments show nearly perfect valley polarization, indicating very slow intervalley scattering processes, first valley-selective pump-probe experiments yielded a strong signal immediately after optical excitation in both the pumped and unpumped valley, suggesting a small valley polarization. To understand this behavior, we performed a joint experiment-theory study on the time-resolved valley dynamics in atomically thin WS2. We find strong intervalley Coulomb coupling governing the dynamics in the atomically thin semiconductor. Our results are also applicable to the other transition metal dichalcogenides MoS2, MoSe2, and WSe2, where strong intervalley Coulomb coupling is expected.

  14. Ultrathin two-dimensional atomic crystals as stable interfacial layer for improvement of lithium metal anode.

    PubMed

    Yan, Kai; Lee, Hyun-Wook; Gao, Teng; Zheng, Guangyuan; Yao, Hongbin; Wang, Haotian; Lu, Zhenda; Zhou, Yu; Liang, Zheng; Liu, Zhongfan; Chu, Steven; Cui, Yi

    2014-10-08

    Stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. Here, we demonstrate a promising novel electrode design by growing two-dimensional (2D) atomic crystal layers including hexagonal boron nitride (h-BN) and graphene directly on Cu metal current collectors. Lithium ions were able to penetrate through the point and line defects of the 2D layers during the electrochemical deposition, leading to sandwiched lithium metal between ultrathin 2D layers and Cu. The 2D layers afford an excellent interfacial protection of Li metal due to their remarkable chemical stability as well as mechanical strength and flexibility, resulting from the strong intralayer bonds and ultrathin thickness. Smooth Li metal deposition without dendritic and mossy Li formation was realized. We showed stable cycling over 50 cycles with Coulombic efficiency ∼97% in organic carbonate electrolyte with current density and areal capacity up to the practical value of 2.0 mA/cm(2)and 5.0 mAh/cm(2), respectively, which is a significant improvement over the unprotected electrodes in the same electrolyte.

  15. Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization.

    PubMed

    Derycke, Vincent; Soukiassian, Patrick G; Amy, Fabrice; Chabal, Yves J; D'angelo, Marie D; Enriquez, Hanna B; Silly, Mathieu G

    2003-04-01

    Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.

  16. Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization

    NASA Astrophysics Data System (ADS)

    Derycke, Vincent; Soukiassian, Patrick G.; Amy, Fabrice; Chabal, Yves J.; D'Angelo, Marie D.; Enriquez, Hanna B.; Silly, Mathieu G.

    2003-04-01

    Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.

  17. Determination of metal concentration in fat supplements for swine nutrition by atomic absorption spectroscopy.

    PubMed

    Cocchi, Marina; Faeti, Valerio; Manfredini, Matteo; Manzini, Daniela; Marchetti, Andrea; Sighinolfi, Simona

    2005-01-01

    The presence of some essential and toxic metals in fat supplements for swine diet was investigated. Collected samples represented a relevant production of the Italian industry. In particular, some samples were enriched with antioxidants or waste cooking oils. The method for the determination of Ca, Cu, Cd, Fe, Mg, Mn, Ni, Pb, and Zn in fat samples was developed by means of a certified reference material (CRM 186) and a representative fatty sample (RFS). All samples were digested in closed vessels in a microwave oven and then analyzed by flame atomic absorption or graphite furnace atomic absorption spectrometry. The entire analytical method provided a satisfactory repeatability and reproducibility confirmed by agreement between the experimental recovery data obtained for the CRM 186 sample and, with the method of standard additions, for the RFS material. The samples generally showed a small amount of metals compared with the recommended daily intake for the essential elements. On the other hand, some samples contained a significant concentration, from an analytical point of view, of Cd, Ni, and Pb. Principal component analysis (PCA) was applied to inspect the experimental data obtained from samples analysis. Basically no differences were detected in terms of metal concentration among the fat supplements analyzed.

  18. Considerable knock-on displacement of metal atoms under a low energy electron beam.

    PubMed

    Gu, Hengfei; Li, Geping; Liu, Chengze; Yuan, Fusen; Han, Fuzhou; Zhang, Lifeng; Wu, Songquan

    2017-03-15

    Under electron beam irradiation, knock-on atomic displacement is commonly thought to occur only when the incident electron energy is above the incident-energy threshold of the material in question. However, we report that when exposed to intense electrons at room temperature at a low incident energy of 30 keV, which is far below the theoretically predicted incident-energy threshold of zirconium, Zircaloy-4 (Zr-1.50Sn-0.25Fe-0.15Cr (wt.%)) surfaces can undergo considerable displacement damage. We demonstrate that electron beam irradiation of the bulk Zircaloy-4 surface resulted in a striking radiation effect that nanoscale precipitates within the surface layer gradually emerged and became clearly visible with increasing the irradiation time. Our transmission electron microscope (TEM) observations further reveal that electron beam irradiation of the thin-film Zircaly-4 surface caused the sputtering of surface α-Zr atoms, the nanoscale atomic restructuring in the α-Zr matrix, and the amorphization of precipitates. These results are the first direct evidences suggesting that displacement of metal atoms can be induced by a low incident electron energy below threshold. The presented way to irradiate may be extended to other materials aiming at producing appealing properties for applications in fields of nanotechnology, surface technology, and others.

  19. Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition

    NASA Astrophysics Data System (ADS)

    Chen, Borui; Ji, Dengxin; Cheney, Alec; Zhang, Nan; Song, Haomin; Zeng, Xie; Thomay, Tim; Gan, Qiaoqiang; Cartwright, Alexander

    2016-09-01

    Atomic layer lithography is a recently reported new technology to fabricate deep-subwavelength features down to 1-2 nm, based on combinations of electron beam lithography (EBL) and atomic layer deposition (ALD). However, the patterning area is relatively small as limited by EBL, and the fabrication yield is not very high due to technical challenges. Here we report an improved procedure to fabricate flat metallic surfaces with sub-10 nm features based on ALD processes. To demonstrate the scalability of the new manufacturing method, we combine the ALD process with large area optical interference patterning, which is particularly promising for the development of practical applications for nanoelectronics and nanophotonics with extremely strong confinement of electromagnetic fields.

  20. Metallic atomically-thin layered silicon epitaxially grown on silicene/ZrB2

    DOE PAGES

    Gill, Tobias; Fleurence, Antoine; Warner, Ben; ...

    2017-01-19

    We observe a new two-dimensional (2D) silicon crystal, using low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) and it's formed by depositing additional Si atoms onto spontaneously-formed epitaxial silicene on a ZrB2 thin film. From scanning tunnelling spectroscopy (STS) studies, we find that this atomically-thin layered silicon has distinctly different electronic properties. Angle resolved photoelectron spectroscopy (ARPES) reveals that, in sharp contrast to epitaxial silicene, the layered silicon exhibits significantly enhanced density of states at the Fermi level resulting from newly formed metallic bands. Furthermore, the 2D growth of this material could allow for direct contacting to themore » silicene surface and demonstrates the dramatic changes in electronic structure that can occur by the addition of even a single monolayer amount of material in 2D systems.« less

  1. Gas-phase catalysis by atomic and cluster metal ions: the ultimate single-site catalysts.

    PubMed

    Böhme, Diethard K; Schwarz, Helmut

    2005-04-15

    Gas-phase experiments with state-of-the-art techniques of mass spectrometry provide detailed insights into numerous elementary processes. The focus of this Review is on elementary reactions of ions that achieve complete catalytic cycles under thermal conditions. The examples chosen cover aspects of catalysis pertinent to areas as diverse as atmospheric chemistry and surface chemistry. We describe how transfer of oxygen atoms, bond activation, and coupling of fragments can be mediated by atomic or cluster metal ions. In some cases truly unexpected analogies of the idealized gas-phase ion catalysis can be drawn with related chemical transformations in solution or the solid state, and so improve our understanding of the intrinsic operation of a practical catalyst at a strictly molecular level.

  2. Metallic atomically-thin layered silicon epitaxially grown on silicene/ZrB 2

    DOE PAGES

    Gill, Tobias G.; Fleurence, Antoine; Warner, Ben; ...

    2017-02-17

    We observe a new two-dimensional (2D) silicon crystal, using low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) and it's formed by depositing additional Si atoms onto spontaneously-formed epitaxial silicene on a ZrB2 thin film. From scanning tunnelling spectroscopy (STS) studies, we find that this atomically-thin layered silicon has distinctly different electronic properties. Angle resolved photoelectron spectroscopy (ARPES) reveals that, in sharp contrast to epitaxial silicene, the layered silicon exhibits significantly enhanced density of states at the Fermi level resulting from newly formed metallic bands. Furthermore, the 2D growth of this material could allow for direct contacting to themore » silicene surface and demonstrates the dramatic changes in electronic structure that can occur by the addition of even a single monolayer amount of material in 2D systems.« less

  3. Preconcentration of heavy metals in urine and quantification by inductively coupled plasma atomic emission spectrometry.

    PubMed

    López-Artíguez, M; Cameán, A; Repetto, M

    1993-01-01

    This paper describes a method for the determination of heavy metals (Co, Ni, Cu, Cd, Pb) in urine by inductively coupled plasma atomic emission spectrometry (ICP-AES). The method proposed requires purification of the samples with activated charcoal under acidic conditions before preconcentration by complexation with ammonium pyrrolidinedithiocarbamate (APDC). The formed complexes are extracted with methyl isobutyl ketone (MIBK) and the resulting residue is finally digested under acid oxidant conditions. Because of its low detection limit (below 10 micrograms/L), this procedure can be applied conveniently for toxicological diagnostic purposes.

  4. Atomic layer deposition of metal oxides on pristine and functionalized graphene.

    PubMed

    Wang, Xinran; Tabakman, Scott M; Dai, Hongjie

    2008-07-02

    We investigate atomic layer deposition (ALD) of metal oxide on pristine and functionalized graphene. On pristine graphene, ALD coating can only actively grow on edges and defect sites, where dangling bonds or surface groups react with ALD precursors. This affords a simple method to decorate and probe single defect sites in graphene planes. We used perylene tetracarboxylic acid (PTCA) to functionalize the graphene surface and selectively introduced densely packed surface groups on graphene. Uniform ultrathin ALD coating on PTCA graphene was achieved over a large area. The functionalization method could be used to integrate ultrathin high-kappa dielectrics in future graphene electronics.

  5. Finite-field evaluation of the Lennard-Jones atom-wall interaction constant C{sub 3} for alkali-metal atoms

    SciTech Connect

    Johnson, W.R.; Dzuba, V.A.; Safronova, U.I.; Safronova, M.S.

    2004-02-01

    A finite-field scaling method is applied to evaluate the Lennard-Jones interaction constant C{sub 3} for alkali-metal atoms. The calculations are based on the relativistic single-double approximation in which single and double excitations of Dirac-Hartree-Fock wave functions are included to all orders in perturbation theory.

  6. Study of the embedded atom method of atomistic calculations for metals and alloys

    SciTech Connect

    Johnson, R.A.

    1990-10-01

    Two projects were completed in the past year. The stability of a series of binary alloys was calculated using the embedded-atom method (EAM) with an analytic form for two-body potentials derived previously. Both disordered alloys and intermetallic compounds with the L1{sub 0} and L1{sub 2} structures were studied. The calculated heats of solution of alloys of Cu, Ag, Au, Ni, and Pt were satisfactory, while results for alloys containing Pd were too high. Atomistic calculations using the EAM were also carried out for point defects in hcp metals. By comparison with results in the literature, it was found that many body effects from the EAM significantly alter predicted physical properties of hcp metals. For example, the EAM calculations yield anisotropic vacancy diffusion with greater vacancy mobility in the basal plane, and imply that diffusion will start at a lower fraction of the melting temperature.

  7. Indium-defect interactions in FCC and BCC metals studied using the modified embedded atom method

    NASA Astrophysics Data System (ADS)

    Zacate, M. O.

    2016-12-01

    With the aim of developing a transferable potential set capable of predicting defect formation, defect association, and diffusion properties in a wide range of intermetallic compounds, the present study was undertaken to test parameterization strategies for determining empirical pair-wise interaction parameters in the modified embedded atom method (MEAM) developed by Baskes and coworkers. This report focuses on indium-solute and indium-vacancy interactions in FCC and BCC metals, for which a large set of experimental data obtained from perturbed angular correlation measurements is available for comparison. Simulation results were found to be in good agreement with experimental values after model parameters had been adjusted to reproduce as best as possible the following two sets of quantities: (1) lattice parameters, formation enthalpies, and bulk moduli of hypothetical equiatomic compounds with the NaCl crystal structure determined using density functional theory and (2) dilute solution enthalpies in metals as predicted by Miedema's semi-empirical model.

  8. Laser-material interaction during atom probe tomography of oxides with embedded metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Shinde, D.; Arnoldi, L.; Devaraj, A.; Vella, A.

    2016-10-01

    Oxide-supported metal nano-particles are of great interest in catalysis but also in the development of new large-spectrum-absorption materials. The design of such nano materials requires three-dimensional characterization with a high spatial resolution and elemental selectivity. The laser assisted Atom Probe Tomography (La-APT) presents both these capacities if an accurate understanding of laser-material interaction is developed. In this paper, we focus on the fundamental physics of field evaporation as a function of sample geometry, laser power, and DC electric field for Au nanoparticles embedded in MgO. By understanding the laser-material interaction through experiments and a theoretical model of heat diffusion inside the sample after the interaction with laser pulse, we point out the physical origin of the noise and determine the conditions to reduce it by more than one order of magnitude, improving the sensitivity of the La-APT for metal-dielectric composites.

  9. Estimated valence-level Lamb shifts for group 1 and group 11 metal atoms

    NASA Astrophysics Data System (ADS)

    Pyykkö, Pekka; Tokman, Maria; Labzowsky, L. N.

    1998-02-01

    The leading Lamb-shift terms are evaluated for the valence electrons of neutral alkali-metal and coinage metal atoms (groups 1 and 11, respectively). The vacuum polarization (VP) contribution is treated using the Uehling potential and the self-energy (SE) contribution using either a density-based α3 expression or the ESE/EVP ratios by Johnson and Soff [At. Data Nucl. Data Tables 33, 405 (1985)]. Both Dirac-Fock and model-potential wave functions are tested. The result for the valence ns electron is a destabilization, rising at moderate Z values (30-80) as Z2 and more steeply at high Z. The (n-1)d electrons suffer an indirect stabilization. The effects are opposite those of kinetic Dirac relativity and about 1-2% of them. They are roughly half of the valence Breit interaction and rise to about 0.5% of the ionization potential for Z=111-119.

  10. Chemically assisted release of transition metals in graphite vaporizers for atomic spectrometry

    NASA Astrophysics Data System (ADS)

    Katskov, Dmitri; Darangwa, Nicholas; Grotti, Marco

    2006-05-01

    The processes associated with the vaporization of microgram samples and modifiers in a graphite tube ET AAS were investigated by the example of transition metals. The vapor absorption spectra and vaporization behavior of μg-amounts Cd, Zn, Cu, Ag, Au, Ni, Co, Fe, Mn and Cr were studied using the UV spectrometer with CCD detector, coupled with a continuum radiation source. The pyrocoated, Ta or W lined tubes, with Ar or He as internal gases, and filter furnace were employed in the comparative experiments. It was found that the kinetics of atomic vapor release changed depending on the specific metal-substrate-gas combination; fast vaporization at the beginning was followed by slower 'tailing.' The absorption continuum, overlapped by black body radiation at longer wavelengths, accompanied the fast vaporization mode for all metals, except Cd and Zn. The highest intensity of the continuum was observed in the pyrocoated tube with Ar. For Cu and Ag the molecular bands overlapped the absorption continuum; the continuum and bands were suppressed in the filter furnace. It is concluded that the exothermal interaction of sample vapor with the material of the tube causes the energy evolution in the gas phase. The emitted heat is dispersed near the tube wall in the protective gas and partially transferred back to the surface of the sample, thus facilitating the vaporization. The increased vapor flow causes over-saturation and gas-phase condensation in the absorption volume at some distance from the wall, where the gas temperature is not affected by the reaction. The condensation is accompanied by the release of phase transition energy via black body radiation and atomic emission. The particles of condensate and molecular clusters cause the scattering of light and molecular absorption; slow decomposition of the products of the sample vapor-substrate reaction produces the 'tailing' of atomic absorption signal. The interaction of graphite with metal vapor or oxygen, formed in the

  11. Collimated, single-pass atom source from a pulsed alkali metal dispenser for laser-cooling experiments

    SciTech Connect

    Moore, Kevin L.; Purdy, Thomas P.; Murch, Kater W.; Leslie, Sabrina; Gupta, Subhadeep; Stamper-Kurn, Dan M.

    2005-02-01

    We have developed an improved scheme for loading atoms into a magneto-optical trap (MOT) from a directed rubidium alkali metal dispenser in <10{sup -10} Torr ultrahigh vacuum conditions. A current-driven dispenser was surrounded with a cold absorbing 'shroud' held at {<=}0 deg. C, pumping rubidium atoms not directed into the MOT. This nearly eliminates background atoms and reduces the detrimental rise in pressure normally associated with these devices. The system can be well-described as a current-controlled, rapidly switched, two-temperature thermal beam, and was used to load a MOT with 3x10{sup 8} atoms.

  12. Surface modification of nanodiamond through metal free atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Zeng, Guangjian; Liu, Meiying; Shi, Kexin; Heng, Chunning; Mao, Liucheng; Wan, Qing; Huang, Hongye; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

    2016-12-01

    Surface modification of nanodiamond (ND) with poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)] has been achieved by using metal free surface initiated atom transfer radical polymerization (SI-ATRP). The ATRP initiator was first immobilized on the surface of ND through direct esterification reaction between hydroxyl group of ND and 2-bromoisobutyryl bromide. The initiator could be employed to obtain ND-poly(MPC) nanocomposites through SI-ATRP using an organic catalyst. The final functional materials were characterized by 1H nuclear magnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermo gravimetric analysis in detailed. All of these characterization results demonstrated that ND-poly(MPC) have been successfully obtained via metal free photo-initiated SI-ATRP. The ND-poly(MPC) nanocomposites shown enhanced dispersibility in various solvents as well as excellent biocompatibility. As compared with traditional ATRP, the metal free ATRP is rather simple and effective. More importantly, this preparation method avoided the negative influence of metal catalysts. Therefore, the method described in this work should be a promising strategy for fabrication of polymeric nanocomposites with great potential for different applications especially in biomedical fields.

  13. Compact metal probes: a solution for atomic force microscopy based tip-enhanced Raman spectroscopy.

    PubMed

    Rodriguez, R D; Sheremet, E; Müller, S; Gordan, O D; Villabona, A; Schulze, S; Hietschold, M; Zahn, D R T

    2012-12-01

    There are many challenges in accomplishing tip-enhanced Raman spectroscopy (TERS) and obtaining a proper tip is probably the greatest one. Since tip size, composition, and geometry are the ultimate parameters that determine enhancement of intensity and lateral resolution, the tip becomes the most critical component in a TERS experiment. However, since the discovery of TERS the cantilevers used in atomic force microscopy (AFM) have remained basically the same: commercial silicon (or silicon nitride) tips covered by a metallic coating. The main issues of using metal-coated silicon cantilevers, such as wearing off of the metal layer or increased tip radius, can be completely overcome by using all-metal cantilevers. Until now in TERS experiments such probes have only been used in a scanning tunneling microscope or in a tuning fork-based shear force microscope but not in AFM. In this work for the first time, we show the use of compact silver cantilevers that are fully compatible with contact and tapping modes in AFM demonstrating their superb performance in TERS experiments.

  14. Metal-Free Atom Transfer Radical Polymerization of Methyl Methacrylate with ppm Level of Organic Photocatalyst.

    PubMed

    Huang, Zhicheng; Gu, Yu; Liu, Xiaodong; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2016-10-28

    It is well known that the recently developed photoinduced metal-free atom transfer radical polymerization (ATRP) has been considered as a promising methodology to completely eliminate transition metal residue in polymers. However, a serious problem needs to be improved, namely, large amount of organic photocatalysts should be used to keep the controllability over molecular weights and molecular weight distributions. In this work, a novel photocatalyst 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) with strong excited state reduction potential is successfully used to mediate a metal-free ATRP of methyl methacrylate just with parts per million (ppm) level usage under irradiation of blue light emitting diode at room temperature, using ethyl α-bromophenyl-acetate as a typical initiator with high initiator efficiency. The polymerization kinetic study, multiple controlled "on-off" light switching cycle regulation, and chain extension experiment confirm the "living"/controlled features of this promising photoinduced metal-free ATRP system with good molecular weight control in the presence of ppm level photocatalyst 4CzIPN.

  15. Numerical modelling of emission of a two-level atom near a metal nanoparticle with account for tunnelling of an electron from an atom into a particle

    SciTech Connect

    Fedorovich, S V; Protsenko, I E

    2016-01-31

    We report the results of numerical modelling of emission of a two-level atom near a metal nanoparticle under resonant interaction of light with plasmon modes of the particle. Calculations have been performed for different polarisations of light by a dipole approximation method and a complex multipole method. Depending on the distance between a particle and an atom, the contribution of the nonradiative process of electron tunnelling from a two-level atom into a particle, which is calculated using the quasi-classical approximation, has been taken into account and assessed. We have studied spherical gold and silver particles of different diameters (10 – 100 nm). The rates of electron tunnelling and of spontaneous decay of the excited atomic state are found. The results can be used to develop nanoscale plasmonic emitters, lasers and photodetectors. (nanooptics)

  16. Atomic Layer Deposition Route To Tailor Nanoalloys of Noble and Non-noble Metals.

    PubMed

    Ramachandran, Ranjith K; Dendooven, Jolien; Filez, Matthias; Galvita, Vladimir V; Poelman, Hilde; Solano, Eduardo; Minjauw, Matthias M; Devloo-Casier, Kilian; Fonda, Emiliano; Hermida-Merino, Daniel; Bras, Wim; Marin, Guy B; Detavernier, Christophe

    2016-09-27

    Since their early discovery, bimetallic nanoparticles have revolutionized various fields, including nanomagnetism and optics as well as heterogeneous catalysis. Knowledge buildup in the past decades has witnessed that the nanoparticle size and composition strongly impact the nanoparticle's properties and performance. Yet, conventional synthesis strategies lack proper control over the nanoparticle morphology and composition. Recently, atomically precise synthesis of bimetallic nanoparticles has been achieved by atomic layer deposition (ALD), alleviating particle size and compositional nonuniformities. However, this bimetal ALD strategy applies to noble metals only, a small niche within the extensive class of bimetallic alloys. We report an ALD-based approach for the tailored synthesis of bimetallic nanoparticles containing both noble and non-noble metals, here exemplified for Pt-In. First, a Pt/In2O3 bilayer is deposited by ALD, yielding precisely defined Pt-In nanoparticles after high-temperature H2 reduction. The nanoparticles' In content can be accurately controlled over the whole compositional range, and the particle size can be tuned from micrometers down to the nanometer scale. The size and compositional flexibility provided by this ALD-approach will trigger the fabrication of fully tailored bimetallic nanomaterials, including superior nanocatalysts.

  17. Higher-order C{sub n} dispersion coefficients for the alkali-metal atoms

    SciTech Connect

    Mitroy, J.; Bromley, M.W.J.

    2005-04-01

    The van der Waals coefficients, from C{sub 11} through to C{sub 16} resulting from second-, third-, and fourth-order perturbation theory are estimated for the alkali-metal (Li, Na, K, and Rb) atoms. The dispersion coefficients are also computed for all possible combinations of the alkali-metal atoms and hydrogen. The parameters are determined from sum rules after diagonalizing a semiempirical fixed core Hamiltonian in a large basis. Comparisons of the radial dependence of the C{sub n}/r{sup n} potentials give guidance as to the radial regions in which the various higher-order terms can be neglected. It is seen that including terms up to C{sub 10}/r{sup 10} results in a dispersion interaction that is accurate to better than 1% whenever the inter-nuclear spacing is larger than 20a{sub 0}. This level of accuracy is mainly achieved due to the fortuitous cancellation between the repulsive (C{sub 11},C{sub 13},C{sub 15}) and attractive (C{sub 12},C{sub 14},C{sub 16}) dispersion forces.

  18. Three-photon process for producing a degenerate gas of metastable alkaline-earth-metal atoms

    NASA Astrophysics Data System (ADS)

    Barker, D. S.; Pisenti, N. C.; Reschovsky, B. J.; Campbell, G. K.

    2016-05-01

    We present a method for creating a quantum degenerate gas of metastable alkaline-earth-metal atoms. This has yet to be achieved due to inelastic collisions that limit evaporative cooling in the metastable states. Quantum degenerate samples prepared in the 1S0 ground state can be rapidly transferred to either the 3P2 or 3P0 state via a coherent three-photon process. Numerical integration of the density-matrix evolution for the fine structure of bosonic alkaline-earth-metal atoms shows that transfer efficiencies of ≃90 % can be achieved with experimentally feasible laser parameters in both Sr and Yb. Importantly, the three-photon process can be set up such that it imparts no net momentum to the degenerate gas during the excitation, which will allow for studies of metastable samples outside the Lamb-Dicke regime. We discuss several experimental challenges to successfully realizing our scheme, including the minimization of differential ac Stark shifts between the four states connected by the three-photon transition.

  19. Atomic clusters triggering nucleation and solidification of the metallic glass melt

    NASA Astrophysics Data System (ADS)

    Li, Gong; Zhang, Lijun; Zhan, Zaiji; Yu, Pengfei; Liaw, Peter K.; Liu, Riping

    2017-03-01

    The Zr41Ti14Cu12.5Ni10Be22.5 (atomic percent, at. %) melts embedded in a flux of the dehydrated B2O3 were under cooled by the repeated treatment of melting. The maximum melt undercooling of ΔT = 145 K achieved for this melt corresponds to a comparatively large relative undercooling of 0.15 times the melting-point temperature of Tm˜ about 953 K(ΔT/Tm = 0.15). The solidification and nucleation behaviors of the Zr41Ti14Cu12.5Ni10Be22.5 undercooled melts triggered by Ni, Ti, Cu, and Zr clusters introduced by sputtering these pure metal targets are studied. An anomalous solidification triggered by Zr-atomic clusters above the Zr41Ti14Cu12.5Ni10Be22.5 melting temperature of 140 K is observed. The instability of a metallic-glass (MG) liquid near the thermodynamic critical temperature is present. The nucleation in the undercooled Zr41Ti14Cu12.5Ni10Be22.5 is investigated by Monte Carlo simulations and analyzed by the classical nucleation theory. This letter reveals an effective research method on investigating the instability of a MG liquid near the thermodynamic critical temperature.

  20. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Zhong, C.; Zhang, H.; Cao, Q. P.; Wang, X. D.; Zhang, D. X.; Ramamurty, U.; Jiang, J. Z.

    2016-08-01

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and “liquid-like” regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested.

  1. Handshake electron transfer from hydrogen Rydberg atoms incident at a series of metallic thin films.

    PubMed

    Gibbard, J A; Softley, T P

    2016-06-21

    Thin metallic films have a 1D quantum well along the surface normal direction, which yields particle-in-a-box style electronic quantum states. However the quantum well is not infinitely deep and the wavefunctions of these states penetrate outside the surface where the electron is bound by its own image-charge attraction. Therefore a series of discrete, vacant states reach out from the thin film into the vacuum increasing the probability of electron transfer from an external atom or molecule to the thin film, especially for the resonant case where the quantum well energy matches that of the atom. We show that "handshake" electron transfer from a highly excited Rydberg atom to these thin-film states is experimentally measurable. Thicker films have a wider 1D box, changing the energetic distribution and image-state contribution to the thin film wavefunctions, resulting in more resonances. Calculations successfully predict the number of resonances and the nature of the thin-film wavefunctions for a given film thickness.

  2. Handshake electron transfer from hydrogen Rydberg atoms incident at a series of metallic thin films

    NASA Astrophysics Data System (ADS)

    Gibbard, J. A.; Softley, T. P.

    2016-06-01

    Thin metallic films have a 1D quantum well along the surface normal direction, which yields particle-in-a-box style electronic quantum states. However the quantum well is not infinitely deep and the wavefunctions of these states penetrate outside the surface where the electron is bound by its own image-charge attraction. Therefore a series of discrete, vacant states reach out from the thin film into the vacuum increasing the probability of electron transfer from an external atom or molecule to the thin film, especially for the resonant case where the quantum well energy matches that of the atom. We show that "handshake" electron transfer from a highly excited Rydberg atom to these thin-film states is experimentally measurable. Thicker films have a wider 1D box, changing the energetic distribution and image-state contribution to the thin film wavefunctions, resulting in more resonances. Calculations successfully predict the number of resonances and the nature of the thin-film wavefunctions for a given film thickness.

  3. Atomic structures of a liquid-phase bonded metal/nitride heterointerface

    PubMed Central

    Kumamoto, Akihito; Shibata, Naoya; Nayuki, Kei-ichiro; Tohei, Tetsuya; Terasaki, Nobuyuki; Nagatomo, Yoshiyuki; Nagase, Toshiyuki; Akiyama, Kazuhiro; Kuromitsu, Yoshirou; Ikuhara, Yuichi

    2016-01-01

    Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood. Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices. PMID:26961157

  4. Resonant charging and stopping power of slow channelling atoms in a crystalline metal

    NASA Astrophysics Data System (ADS)

    Mason, D. R.; Race, C. P.; Foo, M. H. F.; Horsfield, A. P.; Foulkes, W. M. C.; Sutton, A. P.

    2012-07-01

    Fast moving ions travel great distances along channels between low-index crystallographic planes, slowing through collisions with electrons, until finally they hit a host atom initiating a cascade of atomic displacements. Statistical penetration ranges of incident particles are reliably used in ion-implantation technologies, but a full, necessarily quantum-mechanical, description of the stopping of slow, heavy ions is challenging and the results of experimental investigations are not fully understood. Using a self-consistent model of the electronic structure of a metal, and explicit treatment of atomic structure, we find by direct simulation a resonant accumulation of charge on a channelling ion analogous to the Okorokov effect but originating in electronic excitation between delocalized and localized valence states on the channelling ion and its transient host neighbours, stimulated by the time-periodic potential experienced by the channelling ion. The charge resonance reduces the electronic stopping power on the channelling ion. These are surprising and interesting new chemical aspects of channelling, which cannot be predicted within the standard framework of ions travelling through homogeneous electron gases or by considering either ion or target in isolation.

  5. Atomic structures of a liquid-phase bonded metal/nitride heterointerface.

    PubMed

    Kumamoto, Akihito; Shibata, Naoya; Nayuki, Kei-Ichiro; Tohei, Tetsuya; Terasaki, Nobuyuki; Nagatomo, Yoshiyuki; Nagase, Toshiyuki; Akiyama, Kazuhiro; Kuromitsu, Yoshirou; Ikuhara, Yuichi

    2016-03-10

    Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood. Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices.

  6. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study

    PubMed Central

    Zhong, C.; Zhang, H.; Cao, Q. P.; Wang, X. D.; Zhang, D. X.; Ramamurty, U.; Jiang, J. Z.

    2016-01-01

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and “liquid-like” regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested. PMID:27480496

  7. Deformation behavior of metallic glasses with shear band like atomic structure: a molecular dynamics study.

    PubMed

    Zhong, C; Zhang, H; Cao, Q P; Wang, X D; Zhang, D X; Ramamurty, U; Jiang, J Z

    2016-08-02

    Molecular dynamics simulations were employed to investigate the plastic deformation within the shear bands in three different metallic glasses (MGs). To mimic shear bands, MG specimens were first deformed until flow localization occurs, and then the volume of the material within the localized regions was extracted and replicated. Homogeneous deformation that is independent of the size of the specimen was observed in specimens with shear band like structure, even at a temperature that is far below the glass transition temperature. Structural relaxation and rapid cooling were employed to examine the effect of free volume content on the deformation behavior. This was followed by detailed atomic structure analyses, employing the concepts of Voronoi polyhedra and "liquid-like" regions that contain high fraction of sub-atomic size open volumes. Results suggest that the total fraction of atoms in liquid-like regions is a key parameter that controls the plastic deformation in MGs. These are discussed in the context of reported experimental results and possible strategies for synthesizing monolithic amorphous materials that can accommodate large tensile plasticity are suggested.

  8. Atomic structures of a liquid-phase bonded metal/nitride heterointerface

    NASA Astrophysics Data System (ADS)

    Kumamoto, Akihito; Shibata, Naoya; Nayuki, Kei-Ichiro; Tohei, Tetsuya; Terasaki, Nobuyuki; Nagatomo, Yoshiyuki; Nagase, Toshiyuki; Akiyama, Kazuhiro; Kuromitsu, Yoshirou; Ikuhara, Yuichi

    2016-03-01

    Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood. Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices.

  9. Atomic many-body effects and Lamb shifts in alkali metals

    NASA Astrophysics Data System (ADS)

    Ginges, J. S. M.; Berengut, J. C.

    2016-05-01

    We present a detailed study of the radiative potential method [V. V. Flambaum and J. S. M. Ginges, Phys. Rev. A 72, 052115 (2005), 10.1103/PhysRevA.72.052115], which enables the accurate inclusion of quantum electrodynamics (QED) radiative corrections in a simple manner in atoms and ions over the range 10 ≤Z ≤120 , where Z is the nuclear charge. Calculations are performed for binding energy shifts to the lowest valence s , p , and d waves over the series of alkali-metal atoms Na to E119. The high accuracy of the radiative potential method is demonstrated by comparison with rigorous QED calculations in frozen atomic potentials, with deviations on the level of 1%. The many-body effects of core relaxation and second- and higher-order perturbation theory on the interaction of the valence electron with the core are calculated. The inclusion of many-body effects tends to increase the size of the shifts, with the enhancement particularly significant for d waves; for K to E119, the self-energy shifts for d waves are only an order of magnitude smaller than the s -wave shifts. It is shown that taking into account many-body effects is essential for an accurate description of the Lamb shift.

  10. Metal-Assisted Oxo Atom Addition to an Fe(III) Thiolate.

    PubMed

    Villar-Acevedo, Gloria; Lugo-Mas, Priscilla; Blakely, Maike N; Rees, Julian A; Ganas, Abbie S; Hanada, Erin M; Kaminsky, Werner; Kovacs, Julie A

    2017-01-11

    Cysteinate oxygenation is intimately tied to the function of both cysteine dioxygenases (CDOs) and nitrile hydratases (NHases), and yet the mechanisms by which sulfurs are oxidized by these enzymes are unknown, in part because intermediates have yet to be observed. Herein, we report a five-coordinate bis-thiolate ligated Fe(III) complex, [Fe(III)(S2(Me2)N3(Pr,Pr))](+) (2), that reacts with oxo atom donors (PhIO, IBX-ester, and H2O2) to afford a rare example of a singly oxygenated sulfenate, [Fe(III)(η(2)-S(Me2)O)(S(Me2))N3(Pr,Pr)](+) (5), resembling both a proposed intermediate in the CDO catalytic cycle and the essential NHase Fe-S(O)(Cys114) proposed to be intimately involved in nitrile hydrolysis. Comparison of the reactivity of 2 with that of a more electron-rich, crystallographically characterized derivative, [Fe(III)S2(Me2)N(Me)N2(amide)(Pr,Pr)](-) (8), shows that oxo atom donor reactivity correlates with the metal ion's ability to bind exogenous ligands. Density functional theory calculations suggest that the mechanism of S-oxygenation does not proceed via direct attack at the thiolate sulfurs; the average spin-density on the thiolate sulfurs is approximately the same for 2 and 8, and Mulliken charges on the sulfurs of 8 are roughly twice those of 2, implying that 8 should be more susceptible to sulfur oxidation. Carboxamide-ligated 8 is shown to be unreactive towards oxo atom donors, in contrast to imine-ligated 2. Azide (N3(-)) is shown to inhibit sulfur oxidation with 2, and a green intermediate is observed, which then slowly converts to sulfenate-ligated 5. This suggests that the mechanism of sulfur oxidation involves initial coordination of the oxo atom donor to the metal ion. Whether the green intermediate is an oxo atom donor adduct, Fe-O═I-Ph, or an Fe(V)═O remains to be determined.

  11. Light non-metallic atom (B, N, O and F)-doped graphene: a first-principles study.

    PubMed

    Wu, M; Cao, C; Jiang, J Z

    2010-12-17

    First-principles calculations are performed to study the geometry, electronic structure and magnetic properties of light non-metallic atom-doped graphene (B, N, O and F). The planar structure and the quasi-linear energy dispersion near the Dirac point remain through doping with B and N atoms, by which p-type doping and n-type doping graphene are respectively induced. A bandgap of about 0.5 eV is generated through O doping, and geometrically the O atom is also in the graphene plane. No magnetic moment is detected in B- , N- and O-doped graphene. For F doping, the F atom bonds with one of the carbon atoms close to the vacancy, with the other two carbon atoms undergoing a Jahn-Teller distortion. A weak polarized magnetic moment of 0.71 µ(B) is detected through F doping.

  12. Determination of subnanogram per cubic meter concentrations of metals in the air of a trace metal clean room by impaction graphite furnace atomic absorption and laser excited atomic fluorescence spectrometry.

    PubMed

    Liang, Z W; Wei, G T; Irwin, R L; Walton, A P; Michel, R G; Sneddon, J

    1990-07-15

    Air, drawn by vacuum through a jet, was impacted against the inside surface of an atomic absorption graphite electrothermal atomizer (ETA). The amounts of the particles thus collected were determined at the ng m-3 level by graphite furnace atomic absorption or at the pg m-3 level by laser excited atomic fluorescence. The overall reproducibility of two sets of measurements, made 7 months apart, was 23%, with no significant difference between the two sets of data, based on Student's "t" test at the 95% confidence level. Short-term reproducibility varied from 13% to 34% depending upon the air concentration of the metal. The method shows promise for monitoring long-term effectiveness of the filtering systems in trace metal clean rooms. It was not possible to test for accuracy, due to the low concentrations involved, but accuracy was expected to be within a factor of 2 or 3 of the actual value, based on theoretical aspects of impaction.

  13. New chemistry for the growth of first-row transition metal films by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Klesko, Joseph Peter

    redox non-innocent nature of a series of recently-reported 1,4-di-tert-butyl-1,3-diazabutadienyl complexes. Other metal complexes using the same ligand system are subsequently evaluated for use as ALD precursors. Finally, a novel approach is described for the stoichiometric control of first-row transition metal manganese and cobalt borate films, whereby the film composition is governed by the elements present in a single precursor. Computational techniques such as density functional theory (DFT) using nucleus-independent chemical shift (NICS) are used to determine the electronic structure and predict the relative reducing power of organic coreagents. Potential ALD precursors are analyzed by 1H and 13C NMR, IR, thermogravimetric and differential thermal analyses (TGA/DTA), melting point and solid state decomposition measurements, magnetic susceptibility measurements, preparative sublimation studies, and solution-screening reactions. Deposition parameters are optimized for successful ALD processes. The composition and surface morphology of the resultant films are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), X-ray diffractometry (XRD), time-of-flight elastic recoil detection analysis (TOF-ERDA), ultraviolet-visible spectroscopy (UV-Vis), and four-point probe resistivity measurements.

  14. Electronic and magnetic properties of 1T-HfS2 by doping transition-metal atoms

    NASA Astrophysics Data System (ADS)

    Zhao, Xu; Wang, Tianxing; Wang, Guangtao; Dai, Xianqi; Xia, Congxin; Yang, Lin

    2016-10-01

    We explored the electronic and magnetic properties of 1T-HfS2 doped by transition metal (TM) atom using the first-principles calculation. We doped the transition metal atoms from the IIIB to VIB groups in nonmagnetic 1T-HfS2. Numerical results show that the pristine 1T-HfS2 is a semiconductor with indirect gaps of 1.250 eV. Magnetism can be observed for V, Cr, Mn, Fe, Co, and Cu doping. The polarized charges mainly arise from the localized 3d electrons of the TM atom. The strong p-d hybridization was found between the 3d orbitals of TM and 3p orbitals of S. The substituted 1T-HfS2 can be a metal, semiconductor or half-metal. Analysis of the band structure and magnetic properties indicates that TM-doped HfS2 (TM = V, Fe, Cu) are promising systems to explore two-dimensional diluted magnetic semiconductors. The formation energy calculations also indicate that it is energetically favorable and relatively easier to incorporate transition metal atom into the HfS2 under S-rich experimental conditions. In contrast, V-doped HfS2 has relatively wide half-metallic gap and low formation energy. So V-doped 1T-HfS2 is ideal for spin injection, which is important for application in semiconductor spintronics.

  15. Adsorption of metal atoms at a buckled graphene grain boundary using model potentials

    SciTech Connect

    Helgee, Edit E.; Isacsson, Andreas

    2016-01-15

    Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable.

  16. Nonlocal response of metallic nanospheres probed by light, electrons, and atoms.

    PubMed

    Christensen, Thomas; Yan, Wei; Raza, Søren; Jauho, Antti-Pekka; Mortensen, N Asger; Wubs, Martijn

    2014-02-25

    Inspired by recent measurements on individual metallic nanospheres that cannot be explained with traditional classical electrodynamics, we theoretically investigate the effects of nonlocal response by metallic nanospheres in three distinct settings: atomic spontaneous emission, electron energy loss spectroscopy, and light scattering. These constitute two near-field and one far-field measurements, with zero-, one-, and two-dimensional excitation sources, respectively. We search for the clearest signatures of hydrodynamic pressure waves in nanospheres. We employ a linearized hydrodynamic model, and Mie-Lorenz theory is applied for each case. Nonlocal response shows its mark in all three configurations, but for the two near-field measurements, we predict especially pronounced nonlocal effects that are not exhibited in far-field measurements. Associated with every multipole order is not only a single blueshifted surface plasmon but also an infinite series of bulk plasmons that have no counterpart in a local-response approximation. We show that these increasingly blueshifted multipole plasmons become spectrally more prominent at shorter probe-to-surface separations and for decreasing nanosphere radii. For selected metals, we predict hydrodynamic multipolar plasmons to be measurable on single nanospheres.

  17. Atomic-layer-deposition-assisted formation of carbon nanoflakes on metal oxides and energy storage application.

    PubMed

    Guan, Cao; Zeng, Zhiyuan; Li, Xianglin; Cao, Xiehong; Fan, Yu; Xia, Xinhui; Pan, Guoxiang; Zhang, Hua; Fan, Hong Jin

    2014-01-29

    Nanostructured carbon is widely used in energy storage devices (e.g., Li-ion and Li-air batteries and supercapacitors). A new method is developed for the generation of carbon nanoflakes on various metal oxide nanostructures by combining atomic layer deposition (ALD) and glucose carbonization. Various metal oxide@nanoflake carbon (MO@f-C) core-branch nanostructures are obtained. For the mechanism, it is proposed that the ALD Al2 O3 and glucose form a composite layer. Upon thermal annealing, the composite layer becomes fragmented and moves outward, accompanied by carbon deposition on the alumina skeleton. When tested as electrochemical supercapacitor electrode, the hierarchical MO@f-C nanostructures exhibit better properties compared with the pristine metal oxides or the carbon coating without ALD. The enhancement can be ascribed to increased specific surface areas and electric conductivity due to the carbon flake coating. This peculiar carbon coating method with the unique hierarchical nanostructure may provide a new insight into the preparation of 'oxides + carbon' hybrid electrode materials for energy storage applications.

  18. Limits to metallic conduction in atomic-scale quasi-one-dimensional silicon wires.

    PubMed

    Weber, Bent; Ryu, Hoon; Tan, Y-H Matthias; Klimeck, Gerhard; Simmons, Michelle Y

    2014-12-12

    The recent observation of ultralow resistivity in highly doped, atomic-scale silicon wires has sparked interest in what limits conduction in these quasi-1D systems. Here we present electron transport measurements of gated Si:P wires of widths 4.6 and 1.5 nm. At 4.6 nm we find an electron mobility, μ(el)≃60  cm²/V s, in excellent agreement with that of macroscopic Hall bars. Metallic conduction persists to millikelvin temperatures where we observe Gaussian conductance fluctuations of order δG∼e²/h. In thinner wires (1.5 nm), metallic conduction breaks down at G≲e²/h, where localization of carriers leads to Coulomb blockade. Metallic behavior is explained by the large carrier densities in Si:P δ-doped systems, allowing the occupation of all six valleys of the silicon conduction band, enhancing the number of 1D channels and hence the localization length.

  19. Research Investigation Directed Toward Extending the Useful Range of the Electromagnetic Spectrum. [atomic spectra and electronic structure of alkali metals

    NASA Technical Reports Server (NTRS)

    Hartmann, S. R.; Happer, W.

    1974-01-01

    The report discusses completed and proposed research in atomic and molecular physics conducted at the Columbia Radiation Laboratory from July 1972 to June 1973. Central topics described include the atomic spectra and electronic structure of alkali metals and helium, molecular microwave spectroscopy, the resonance physics of photon echoes in some solid state systems (including Raman echoes, superradiance, and two photon absorption), and liquid helium superfluidity.

  20. Aspherical-atom modeling of coordination compounds by single-crystal X-ray diffraction allows the correct metal atom to be identified.

    PubMed

    Dittrich, Birger; Wandtke, Claudia M; Meents, Alke; Pröpper, Kevin; Mondal, Kartik Chandra; Samuel, Prinson P; Amin Sk, Nurul; Singh, Amit Pratap; Roesky, Herbert W; Sidhu, Navdeep

    2015-02-02

    Single-crystal X-ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid-state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical-atom least-squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld-atom refinement (Acta Crystallogr. Sect. A- 2008, 64, 383-393; IUCrJ. 2014, 1,61-79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B- 2013, 69, 91-104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear-coordinate 3d metal complexes, for which the wrong element is found if standard independent-atom model scattering factors are relied upon, are studied, and it is shown that only aspherical-atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed.

  1. [Determination of metals in Ginkgo biloba leaves by atomic absorption spectrometry with microwave digestion].

    PubMed

    Jiang, Bo; Jiang, Guo-Bin; Liu, Chang-Jian; Ma, Kun; Jin, Li-Ming; Gao, Jiang-Mei

    2010-03-01

    Microwave digestion technique was used in the decomposition of Ginkgo biloba leaves from six different trees at the same age in the same area. HNO3-H2O2 (5 : 1 v/v) was used as microwave digestion agent at a suitable temperature and time. The contents of Ca, Mg, K, Na, Cu, Zn and Zn/Cu were determined by flame atomic absorption spectrometry to study the distribution rule of metallic elements in the trees at the same age and in the same area. The recovery ratio ranged from 95.2% to 104.6%. The results showed that there were certain differences between different trees in the distribution of metallic elements. The contents of calcium were from 39 586 to 48 320 microg x g(-1), and those of magnesium from 10 076 to 12 918 microg x g(-1), of potassium from 2 004 to 5 240 microg x g(-1), of sodium from 9.05 to 35.30 microg x g(-1), and of copper from 1.50 to 3.05 microg x g(-1), while Zn/Cu values were from 2.68 to 5.93 in the leaves of 6 different trees in the same growing area. Therefore there were abounding calcium, magnesium and potassium, while the content of sodium and Zn/Cu values were lower, and the metal contents were different in the leaves. The experimental results provided useful bases for studying the distribution rule of metallic elements in Ginkgo biloba leaves, the relationship between the contents of calcium, magnesium, potassium and sodium and the Zn/Cu value in ginkgo biloba leaves and the treatment for cardio-cerebral vascular disease.

  2. Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: a review.

    PubMed

    Herrero Latorre, C; Álvarez Méndez, J; Barciela García, J; García Martín, S; Peña Crecente, R M

    2012-10-24

    New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes--due to their high adsorption and desorption capacities--have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.

  3. Substrate co-doping modulates electronic metal-support interactions and significantly enhances single-atom catalysis.

    PubMed

    Shi, J L; Wu, J H; Zhao, X J; Xue, X L; Gao, Y F; Guo, Z X; Li, S F

    2016-11-24

    Transitional metal nanoparticles or atoms deposited on appropriate substrates can lead to highly economical, efficient, and selective catalysis. One of the greatest challenges is to control the electronic metal-support interactions (EMSI) between the supported metal atoms and the substrate so as to optimize their catalytic performance. Here, from first-principles calculations, we show that an otherwise inactive Pd single adatom on TiO2(110) can be tuned into a highly effective catalyst, e.g. for O2 adsorption and CO oxidation, by purposefully selected metal-nonmetal co-dopant pairs in the substrate. Such an effect is proved here to result unambiguously from a significantly enhanced EMSI. A nearly linear correlation is noted between the strength of the EMSI and the activation of the adsorbed O2 molecule, as well as the energy barrier for CO oxidation. Particularly, the enhanced EMSI shifts the frontier orbital of the deposited Pd atom upward and largely enhances the hybridization and charge transfer between the O2 molecule and the Pd atom. Upon co-doping, the activation barrier for CO oxidation on the Pd monomer is also reduced to a level comparable to that on the Pd dimer which was experimentally reported to be highly efficient for CO oxidation. The present findings provide new insights into the understanding of the EMSI in heterogeneous catalysis and can open new avenues to design and fabricate cost-effective single-atom-sized and/or nanometer-sized catalysts.

  4. Method 200.7: Determination of Metals and Trace Elements in Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry

    EPA Pesticide Factsheets

    SAM lists this method for preparation and analysis of aqueous liquid and drinking water samples. This method will determine metal-containing compounds as the total metal (e.g., total arsenic), using inductively coupled plasma-atomic emission spectrometry.

  5. Electric Field Dependent Photoluminescence in Atomically Thin Transition Metal Dichalcogenides van der Waals Heterostructures

    NASA Astrophysics Data System (ADS)

    Jauregui, Luis A.; High, Alex A.; Dibos, Alan; Joe, Andrew; Gulpinar, Elgin; Park, Hongkun; Kim, Philip

    uregui, Alex A. High, Alan Dibos, Andrew Joe, Elgin Gulpinar, Hongkun Park, Philip Kim Harvard University, Physics Department -abstract- Single layer transition metal dichalcogenides (TMDC) are 2-dimensional (2D) semiconductors characterized by a direct optical bandgap and large exciton binding energies (>100 meV). We fabricate CQW heterostructures made of 2D TMDCs with hexagonal Boron nitride (BN) as atomically thin barrier and gate dielectric, with top and bottom gate electrodes. We study the evolution of photoluminescence (PL) spectrum with varying BN barrier thickness, electric field, temperature and polarization. Our measured low-temperature (T = 3K) PL peaks show full width at half maxima on the order of ~3meV. We identify the photoluminescence peaks, corresponding to the charged exciton emission, which red shifts and its brightness increases while the neutral exciton emission becomes darker for increasing electric field.

  6. Selective Aerobic Oxidation of Alcohols over Atomically-Dispersed Non-Precious Metal Catalysts

    SciTech Connect

    Xie, Jiahan; Yin, Kehua; Serov, Alexey; Artyushkova, Kateryna; Pham, Hien N.; Sang, Xiahan; Unocic, Raymond R.; Atanassov, Plamen; Datye, Abhaya K.; Davis, Robert J.

    2016-12-15

    Catalytic oxidation of alcohols often requires the presence of expensive transition metals. We show that earth-abundant Fe atoms dispersed throughout a nitrogen-containing carbon matrix catalyze the oxidation of benzyl alcohol and 5-hydroxymethylfurfural by O2 in the aqueous phase. Furthermore, the activity of the catalyst can be regenerated by a mild treatment in H2. An observed kinetic isotope effect indicates that β-H elimination from the alcohol is the kinetically relevant step in the mechanism, which can be accelerated by substituting Fe with Cu. Dispersed Cr, Co, and Ni also convert alcohols, demonstrating the general utility of metal–nitrogen–carbon materials for alcohol oxidation catalysis. Oxidation of aliphatic alcohols is substantially slower than that of aromatic alcohols, but adding 2,2,6,6-tetramethyl-1-piperidinyloxy as a co-catalyst with Fe can significantly improve the reaction rate.

  7. Selective Aerobic Oxidation of Alcohols over Atomically-Dispersed Non-Precious Metal Catalysts

    DOE PAGES

    Xie, Jiahan; Yin, Kehua; Serov, Alexey; ...

    2016-12-15

    Catalytic oxidation of alcohols often requires the presence of expensive transition metals. We show that earth-abundant Fe atoms dispersed throughout a nitrogen-containing carbon matrix catalyze the oxidation of benzyl alcohol and 5-hydroxymethylfurfural by O2 in the aqueous phase. Furthermore, the activity of the catalyst can be regenerated by a mild treatment in H2. An observed kinetic isotope effect indicates that β-H elimination from the alcohol is the kinetically relevant step in the mechanism, which can be accelerated by substituting Fe with Cu. Dispersed Cr, Co, and Ni also convert alcohols, demonstrating the general utility of metal–nitrogen–carbon materials for alcohol oxidationmore » catalysis. Oxidation of aliphatic alcohols is substantially slower than that of aromatic alcohols, but adding 2,2,6,6-tetramethyl-1-piperidinyloxy as a co-catalyst with Fe can significantly improve the reaction rate.« less

  8. A half-metallic half-Heusler alloy having the largest atomic-like magnetic moment at optimized lattice constant

    NASA Astrophysics Data System (ADS)

    Zhang, R. L.; Damewood, L.; Fong, C. Y.; Yang, L. H.; Peng, R. W.; Felser, C.

    2016-11-01

    For half-Heusler alloys, the general formula is XYZ, where X can be a transition or alkali metal element, Y is another transition metal element, typically Mn or Cr, and Z is a group IV element or a pnicitide. The atomic arrangements within a unit-cell show three configurations. Before this study, most of the predictions of half-metallic properties of half-Heusler alloys at the lattice constants differing from their optimized lattice constant. Based on the electropositivity of X and electronegativity of Z for half-Heusler alloys, we found that one of the configurations of LiCrS exhibits half-metallic properties at its optimized lattice constant of 5.803Å, and has the maximum atomic-like magnetic moment of 5μB. The challenges of its growth and the effects of the spin-orbit effect in this alloy will be discussed.

  9. Changes in the shape of atomic lines of alkali metals in sonoluminescence spectra of solutions of surfactants and halogenides

    NASA Astrophysics Data System (ADS)

    Kazachek, M. V.; Gordeychuk, T. V.

    2013-11-01

    The multibubble sonoluminescence spectra of aqueous solutions of sodium dodecyl sulfate, of the mixture of sodium dodecyl sulfate with lithium and potassium chlorides, and of sodium and potassium halogenides were measured near the lines of metals at an ultrasonic frequency of 20 kHz. The Na, Li, and K lines in spectra of surfactant solutions are noticeably narrower than those obtained in solutions of metal chlorides. The width of Na lines in spectra of metal fluorides, chlorides, and iodides remains constant, while that of the K line increases with increasing atomic weight of a halogen. The results are discussed in the context of the effect that the bonding strength of an atom possibly has on the formation of metal lines in sonoluminescence spectra.

  10. Structure of the alkali-metal-atom + strontium molecular ions: Towards photoassociation and formation of cold molecular ions

    SciTech Connect

    Aymar, M.; Dulieu, O.; Guerout, R.

    2011-08-14

    The potential energy curves, permanent and transition dipole moments, and the static dipolar polarizability, of molecular ions composed of one alkali-metal atom and a strontium ion are determined with a quantum chemistry approach. The molecular ions are treated as effective two-electron systems and are treated using effective core potentials including core polarization, large gaussian basis sets, and full configuration interaction. In the perspective of upcoming experiments aiming at merging cold atom and cold ion traps, possible paths for radiative charge exchange, photoassociation of a cold lithium or rubidium atom and a strontium ion are discussed, as well as the formation of stable molecular ions.

  11. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    NASA Astrophysics Data System (ADS)

    Antonowicz, J.; Pietnoczka, A.; Pekała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-01

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  12. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    SciTech Connect

    Antonowicz, J. Pietnoczka, A.; Pękała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-28

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  13. Bonding with parallel spins: high-spin clusters of monovalent metal atoms.

    PubMed

    Danovich, David; Shaik, Sason

    2014-02-18

    Bonding is a glue of chemical matter and is also a useful concept for designing new molecules. Despite the fact that electron pairing remains the bonding mechanism in the great majority of molecules, in the past few decades scientists have had a growing interest in discovering novel bonding motifs. As this Account shows, monovalent metallic atoms having exclusively parallel spins, such as (11)Li10, (11)Au10, and (11)Cu10, can nevertheless form strongly bound clusters, without having even one traditional bond due to electron pairing. These clusters, which also can be made chiral, have high magnetic moments. We refer to this type as no-pair ferromagnetic (NPFM) bonding, which characterizes the (n+1)Mn clusters, which were all predicted by theoretical computations. The small NPFM alkali clusters that have been "synthesized" to date, using cold-atom techniques, support the computational predictions. In this Account, we describe the origins of NPFM bonding using a valence bond (VB) analysis, which shows that this bonding motif arises from bound triplet electron pairs that spread over all the close neighbors of a given atom in the cluster. The bound triplet pair owes its stabilization to the resonance energy provided by the mixing of the local ionic configurations, [(3)M(↑↑)(-)]M(+) and M(+)[(3)M(↑↑)(-)], and the various excited covalent configurations (involving pz and dz(2) atomic orbitals) into the repulsive covalent structure (3)(M↑↑M) with the s(1)s(1) electronic configuration. The NPFM bond of the bound triplet is described by a resonating wave function with "in-out" and "out-in" pointing hybrids. The VB model accounts for the tendency of NPFM clusters to assume polyhedral shapes with rather high symmetry. In addition, this model explains the very steep rise of the bonding energy per atom (De/n), which starts out small in the (3)M2 dimer (<1 kcal/mol) and reaches 12-19 kcal/mol for clusters with 10 atoms. The model further predicts that usage of

  14. Wear-metal analysis in engine oil by microwave digestion and atomic absorption spectroscopy. Final report, August 1987-January 1988

    SciTech Connect

    Muse, W.T.

    1990-05-01

    Digestion procedures are described for the analysis of wear metals in National Bureau of Standards (NBS) oil samples by a closed vessel microwave digestion system. Samples were analyzed by flame atomic absorption spectroscopy. Recoveries of Al, Fe, Ni, Cu, and Pb in the 300-ppm NBS oil ranged from 98 to 103% with standard deviations from 3 to 14%. This method serves as a relatively quick matrix destruction technique for the quantitation of metals in oil.

  15. Trends in Ground-State Entropies for Transition Metal Based Hydrogen Atom Transfer Reactions

    SciTech Connect

    Mader, Elizabeth A.; Manner, Virginia W.; Markle, Todd F.; Wu, Adam; Franz, James A.; Mayer, James M.

    2009-03-10

    Reported herein are thermochemical studies of hydrogen atom transfer (HAT) reactions involving transition metal H-atom donors MIILH and oxyl radicals. [FeII(H2bip)3]2+, [FeII(H2bim)3]2+, [CoII(H2bim)3]2+ and RuII(acac)2(py-imH) [H2bip = 2,2’-bi-1,4,5,6-tetrahydro¬pyrimidine, H2bim = 2,2’-bi-imidazoline, acac = 2,4-pentandionato, py-imH = 2-(2’-pyridyl)¬imidazole)] each react with TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) or tBu3PhO• (2,4,6-tri-tert-butylphenoxyl) to give the deprotonated, oxidized metal complex MIIIL, and TEMPOH or tBu3PhOH. Solution equilibrium measurements for the reactions of Co and Fe complexes with TEMPO show a large, negative ground-state entropy for hydrogen atom transfer: ΔSºHAT = -30 ± 2 cal mol-1 K-1 for the two iron complexes and -41 ± 2 cal mol-1 K-1 for [CoII(H2bim)3]2+. The ΔSºHAT for TEMPO + RuII(acac)2(py-imH) is much closer to zero, 4.9 ± 1.1 cal mol-1 K-1. Calorimetric measurements quantitatively confirm the enthalpy of reaction for [FeII(H2bip)3]2+ + TEMPO, thus also confirming ΔSºHAT. Calorimetry on TEMPOH + tBu3PhO• gives ΔHºHAT = 11.2 ± 0.5 kcal mol-1 which matches the enthalpy predicted from the difference in literature solution BDEs. An evaluation of the literature BDEs of both TEMPOH and tBu3PhOH is briefly presented and new estimates are included on the relative enthalpy of solvation for tBu3PhO• vs. tBu3PhOH. The primary contributor to the large magnitude of the ground-state entropy |ΔSºHAT| for the metal complexes is vibrational entropy, ΔSºvib. The common assumption that ΔSºHAT ≈ 0 for HAT reactions, developed for organic and small gas phase molecules, does not hold for transition metal based HAT reactions. The trend in magnitude of |ΔSºHAT| for reactions with TEMPO, RuII(acac)2(py-imH) << [FeII(H2bip)3]2+ = [FeII(H2bim)3]2+ < [CoII(H2bim)3]2+, is surprisingly well predicted by the trends for electron transfer half-reaction entropies, ΔSºET, in aprotic solvents. ΔSºET and

  16. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage.

    PubMed

    Cho, Eun Seon; Ruminski, Anne M; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  17. Highly scalable, atomically thin WSe2 grown via metal-organic chemical vapor deposition.

    PubMed

    Eichfeld, Sarah M; Hossain, Lorraine; Lin, Yu-Chuan; Piasecki, Aleksander F; Kupp, Benjamin; Birdwell, A Glen; Burke, Robert A; Lu, Ning; Peng, Xin; Li, Jie; Azcatl, Angelica; McDonnell, Stephen; Wallace, Robert M; Kim, Moon J; Mayer, Theresa S; Redwing, Joan M; Robinson, Joshua A

    2015-02-24

    Tungsten diselenide (WSe2) is a two-dimensional material that is of interest for next-generation electronic and optoelectronic devices due to its direct bandgap of 1.65 eV in the monolayer form and excellent transport properties. However, technologies based on this 2D material cannot be realized without a scalable synthesis process. Here, we demonstrate the first scalable synthesis of large-area, mono and few-layer WSe2 via metal-organic chemical vapor deposition using tungsten hexacarbonyl (W(CO)6) and dimethylselenium ((CH3)2Se). In addition to being intrinsically scalable, this technique allows for the precise control of the vapor-phase chemistry, which is unobtainable using more traditional oxide vaporization routes. We show that temperature, pressure, Se:W ratio, and substrate choice have a strong impact on the ensuing atomic layer structure, with optimized conditions yielding >8 μm size domains. Raman spectroscopy, atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (TEM) confirm crystalline monoto-multilayer WSe2 is achievable. Finally, TEM and vertical current/voltage transport provide evidence that a pristine van der Waals gap exists in WSe2/graphene heterostructures.

  18. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    DOE PAGES

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; ...

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in themore » total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. In conclusion, these multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.« less

  19. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    SciTech Connect

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. In conclusion, these multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  20. Accurate nonrelativistic ground-state energies of 3d transition metal atoms

    SciTech Connect

    Scemama, A.; Applencourt, T.; Giner, E.; Caffarel, M.

    2014-12-28

    We present accurate nonrelativistic ground-state energies of the transition metal atoms of the 3d series calculated with Fixed-Node Diffusion Monte Carlo (FN-DMC). Selected multi-determinantal expansions obtained with the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) method and including the most prominent determinants of the full configuration interaction expansion are used as trial wavefunctions. Using a maximum of a few tens of thousands determinants, fixed-node errors on total DMC energies are found to be greatly reduced for some atoms with respect to those obtained with Hartree-Fock nodes. To the best of our knowledge, the FN-DMC/(CIPSI nodes) ground-state energies presented here are the lowest variational total energies reported so far. They differ from the recently recommended non-variational values of McCarthy and Thakkar [J. Chem. Phys. 136, 054107 (2012)] only by a few percents of the correlation energy. Thanks to the variational property of FN-DMC total energies, our results provide exact lower bounds for the absolute value of all-electron correlation energies, |E{sub c}|.

  1. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    NASA Astrophysics Data System (ADS)

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  2. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    PubMed Central

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-01-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments. PMID:26902901

  3. Atomic-Scale Mechanisms of Void Hardening in BCC and FCC Metals

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2010-01-01

    Strengthening due to voids can be a significant effect of radiation damage in metals, but treatment of this by elasticity theory of dislocations is difficult when the mechanisms controlling the obstacle strength are atomic in nature. Results are reported of atomic-scale modelling to compare edge dislocation-void interaction in fcc copper and bcc iron. Voids of up to 6 nm diameter in iron and 8 nm diameter in copper were studied over the temperature range 0 to 600 K at different applied strain rates. Voids in iron are strong obstacles, for the dislocation has to adopt a dipole-like configuration at the void before breaking away. The dipole unzips at the critical stress when the dislocation is able to climb by absorbing vacancies and leave the void surface. Dislocation dissociation into Shockley partials in copper prevents dislocation climb and affects the strength of small and large voids differently. Small voids are much weaker obstacles than those in iron because the partials break from a void individually. Large voids are at least as strong as those in iron, but the controlling mechanism depends on temperature.

  4. Selective metal deposition at graphene line defects by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Kim, Kwanpyo; Lee, Han-Bo-Ram; Johnson, Richard W.; Tanskanen, Jukka T.; Liu, Nan; Kim, Myung-Gil; Pang, Changhyun; Ahn, Chiyui; Bent, Stacey F.; Bao, Zhenan

    2014-09-01

    One-dimensional defects in graphene have a strong influence on its physical properties, such as electrical charge transport and mechanical strength. With enhanced chemical reactivity, such defects may also allow us to selectively functionalize the material and systematically tune the properties of graphene. Here we demonstrate the selective deposition of metal at chemical vapour deposited graphene’s line defects, notably grain boundaries, by atomic layer deposition. Atomic layer deposition allows us to deposit Pt predominantly on graphene’s grain boundaries, folds and cracks due to the enhanced chemical reactivity of these line defects, which is directly confirmed by transmission electron microscopy imaging. The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited Pt, yields a superior platform for sensing applications. Using Pt-graphene hybrid structures, we demonstrate high-performance hydrogen gas sensors at room temperature and show its advantages over other evaporative Pt deposition methods, in which Pt decorates the graphene surface non-selectively.

  5. Monitoring the dissolution process of metals in the gas phase: reactions of nanoscale Al and Ga metal atom clusters and their relationship to similar metalloid clusters.

    PubMed

    Burgert, Ralf; Schnöckel, Hansgeorg

    2008-05-14

    Formation and dissolution of metals are two of the oldest technical chemical processes. On the atomic scale, these processes are based on the formation and cleavage of metal-metal bonds. During the past 15 years we have studied intensively the intermediates during the formation process of metals, i.e. the formation of compounds containing many metal-metal bonds between naked metal atoms in the center and ligand-bearing metal atoms at the surface. We have called the clusters metalloid or, more generally, elementoid clusters. Via a retrosynthetic route, the many different Al and Ga metalloid clusters which have been structurally characterized allow us to understand also the dissolution process; i.e. the cleavage of metal-metal (M-M) bonds. However, this process can be detected much more directly by the reaction of single metal atom clusters in the gas phase under high vacuum conditions. A suitable tool to monitor the dissolution process of a metal cluster in the gas phase is FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry. Snapshots during these cleavage processes are possible because only every 1-10 s is there a contact between a cluster molecule and an oxidizing molecule (e.g. Cl2). This period is long, i.e. the formation of the primary product (a smaller metal atom cluster) is finished before the next collision happens. We have studied three different types of reaction:(1) Step-by-step fragmentation of a structurally known metalloid cluster allows us to understand the bonding principle of these clusters because in every step only the weakest bond is broken.(2) There are three oxidation reactions of an Al13(-) cluster molecule with Cl2, HCl and O2 central to this review. These three reactions represent three different reaction types, (a) an exothermic reaction (Cl2), (b) an endothermic reaction (HCl), and (c) a kinetically limited reaction based on spin conservation rules (O2).(3) Finally, we present the reaction of a metalloid cluster with Cl2

  6. Atomic oxygen stimulated outgassing

    NASA Technical Reports Server (NTRS)

    Linton, Roger C.; Reynolds, John M.

    1991-01-01

    The passive Long Duration Exposure Facility (LDEF) Experiment A0034, Atomic Oxygen Simulated Outgassing, consisted of two identical one-sixth tray modules, exposing selected thermal control coatings to atomic oxygen and the combined space environment on the leading edge and, for reference, to the relative wake environment on the trailing edge. Optical mirrors were included adjacent to the thermal coatings for deposition of outgassing products. Ultraviolet grade windows and metal covers were provided for additional assessment of the effects of the various environmental factors. Preliminary results indicate that orbital atomic oxygen is both a degrading and a optically restorative factor in the thermo-optical properties of selected thermal coatings. There is evidence of more severe optical degradation on collector mirrors adjacent to coatings that were exposed to the RAM-impinging atomic oxygen. This evidence of atomic oxygen stimulated outgassing is discussed in relation to alternative factors that could affect degradation. The general effects of the space environment on the experiment hardware as well as the specimens are discussed.

  7. Dispersion coefficients for the interactions of the alkali-metal and alkaline-earth-metal ions and inert-gas atoms with a graphene layer

    NASA Astrophysics Data System (ADS)

    Kaur, Kiranpreet; Arora, Bindiya; Sahoo, B. K.

    2015-09-01

    Largely motivated by a number of applications, the van der Waals dispersion coefficients C3 of the alkali-metal ions Li+,Na+,K+, and Rb+, the alkaline-earth-metal ions Ca+,Sr+,Ba+, and Ra+, and the inert-gas atoms He, Ne, Ar, and Kr with a graphene layer are determined precisely within the framework of the Dirac model. For these calculations, we evaluate the dynamic polarizabilities of the above atomic systems very accurately by evaluating the transition matrix elements employing relativistic many-body methods and using the experimental values of the excitation energies. The dispersion coefficients are given as functions of the separation distance of an atomic system from the graphene layer and the ambiance temperature during the interactions. For easy extraction of these coefficients, we give a logistic fit to the functional forms of the dispersion coefficients in terms of the separation distances at room temperature.

  8. Reversible mechano-electrochemical writing of metallic nanostructures with the tip of an atomic force microscope

    PubMed Central

    Kress, Marina; Wagner, Andreas; Schimmel, Thomas

    2012-01-01

    Summary We recently introduced a method that allows the controlled deposition of nanoscale metallic patterns at defined locations using the tip of an atomic force microscope (AFM) as a “mechano-electrochemical pen”, locally activating a passivated substrate surface for site-selective electrochemical deposition. Here, we demonstrate the reversibility of this process and study the long-term stability of the resulting metallic structures. The remarkable stability for more than 1.5 years under ambient air without any observable changes can be attributed to self-passivation. After AFM-activated electrochemical deposition of copper nanostructures on a polycrystalline gold film and subsequent AFM imaging, the copper nanostructures could be dissolved by reversing the electrochemical potential. Subsequent AFM-tip-activated deposition of different copper nanostructures at the same location where the previous structures were deleted, shows that there is no observable memory effect, i.e., no effect of the previous writing process on the subsequent writing process. Thus, the four processes required for reversible information storage, “write”, “read”, “delete” and “re-write”, were successfully demonstrated on the nanometer scale. PMID:23365795

  9. A Tandem Catalyst with Multiple Metal Oxide Interfaces Produced by Atomic Layer Deposition.

    PubMed

    Ge, Huibin; Zhang, Bin; Gu, Xiaomin; Liang, Haojie; Yang, Huimin; Gao, Zhe; Wang, Jianguo; Qin, Yong

    2016-06-13

    Ideal heterogeneous tandem catalysts necessitate the rational design and integration of collaborative active sites. Herein, we report on the synthesis of a new tandem catalyst with multiple metal-oxide interfaces based on a tube-in-tube nanostructure using template-assisted atomic layer deposition, in which Ni nanoparticles are supported on the outer surface of the inner Al2 O3 nanotube (Ni/Al2 O3 interface) and Pt nanoparticles are attached to the inner surface of the outer TiO2 nanotube (Pt/TiO2 interface). The tandem catalyst shows remarkably high catalytic efficiency in nitrobenzene hydrogenation over Pt/TiO2 interface with hydrogen formed in situ by the decomposition of hydrazine hydrate over Ni/Al2 O3 interface. This can be ascribed to the synergy effect of the two interfaces and the confined nanospace favoring the instant transfer of intermediates. The tube-in-tube tandem catalyst with multiple metal-oxide interfaces represents a new concept for the design of highly efficient and multifunctional nanocatalysts.

  10. Efficient methods for screening of metal organic framework membranes for gas separations using atomically detailed models.

    PubMed

    Keskin, Seda; Sholl, David S

    2009-10-06

    Metal organic frameworks (MOFs) define a diverse class of nanoporous materials having potential applications in adsorption-based and membrane-based gas separations. We have previously used atomically detailed models to predict the performance of MOFs for membrane-based separations of gases, but these calculations require considerable computational resources and time. Here, we introduce an efficient approximate method for screening MOFs based on atomistic models that will accelerate the modeling of membrane applications. The validity of this approximate method is examined by comparison with detailed calculations for CH4/H2, CO2/CH4, and CO2/H2 mixtures at room temperature permeating through IRMOF-1 and CuBTC membranes. These results allow us to hypothesize a connection between two computationally efficient correlations predicting mixture adsorption and mixture self-diffusion properties and the validity of our approximate screening method. We then apply our model to six additional MOFs, IRMOF-8, -9, -10, and -14, Zn(bdc)(ted)0.5, and COF-102, to examine the effect of chemical diversity and interpenetration on the performance of metal organic framework membranes for light gas separations.

  11. Atomic structure of Mg-based metallic glasses from molecular dynamics and neutron diffraction.

    PubMed

    Gulenko, Anastasia; Forto Chungong, Louis; Gao, Junheng; Todd, Iain; Hannon, Alex C; Martin, Richard A; Christie, Jamieson K

    2017-03-13

    We use a combination of classical molecular dynamics simulation and neutron diffraction to identify the atomic structure of five different Mg-Zn-Ca bulk metallic glasses, covering a range of compositions with substantially different behaviour when implanted in vitro. There is very good agreement between the structures obtained from computer simulation and those found experimentally. Bond lengths and the total correlation function do not change significantly with composition. The zinc and calcium bonding shows differences between composition: the distribution of Zn-Ca bond lengths becomes narrower with increasing Zn content, and the preference for Zn and Ca to avoid bonding to themselves or each other becomes less strong, and, for Zn-Ca, transforms into a positive preference to bond to each other. This transition occurs at about the same Zn content at which the behaviour on implantation changes, hinting at a possible structural connection. A very broad distribution of Voronoi polyhedra are also found, and this distribution broadens with increasing Zn content. The efficient cluster packing model, which is often used to describe the structure of bulk metallic glasses, was found not to describe these systems well.

  12. Assessment of toxic metals in raw and processed milk samples using electrothermal atomic absorption spectrophotometer.

    PubMed

    Kazi, Tasneem Gul; Jalbani, Nusrat; Baig, Jameel Ahmed; Kandhro, Ghulam Abbas; Afridi, Hassan Imran; Arain, Mohammad Balal; Jamali, Mohammad Khan; Shah, Abdul Qadir

    2009-09-01

    Milk and dairy products have been recognized all over the world for their beneficial influence on human health. The levels of toxic metals (TMs) are an important component of safety and quality of milk. A simple and efficient microwave assisted extraction (MAE) method has been developed for the determination of TMs (Al, Cd, Ni and Pb), in raw and processed milk samples. A Plackett-Burman experimental design and 2(3)+star central composite design, were applied in order to determine the optimum conditions for MAE. Concentrations of TMs were measured by electrothermal atomic absorption spectrometry. The accuracy of the optimized procedure was evaluated by standard addition method and conventional wet acid digestion method (CDM), for comparative purpose. No significant differences were observed (P>0.05), when comparing the values obtained by the proposed MAE method and CDM (paired t-test). The average relative standard deviation of the MAE method varied between 4.3% and 7.6% based on analyte (n=6). The proposed method was successfully applied for the determination of understudy TMs in milk samples. The results of raw and processed milk indicated that environmental conditions and manufacturing processes play a key role in the distribution of toxic metals in raw and processed milk.

  13. Laser-material interaction during atom probe tomography of oxides with embedded metal nanoparticles

    SciTech Connect

    Shinde, D.; Arnoldi, L.; Devaraj, A.; Vella, A.

    2016-10-28

    Oxide-supported metal nano-particles are of great interest in catalysis but also in the development of new large-spectrum-absorption materials. The design of such nano materials requires three-dimensional characterization with a high spatial resolution and elemental selectivity. The laser assisted Atom Probe Tomography (La-APT) presents both these capacities if an accurate understanding of laser-material interaction is developed. In this paper, we focus on the fundamental physics of field evaporation as a function of sample geometry, laser power, and DC electric field for Au nanoparticles embedded in MgO. By understanding the laser-material interaction through experiments and a theoretical model of heat diffusion inside the sample after the interaction with laser pulse, we point out the physical origin of the noise and determine the conditions to reduce it by more than one order of magnitude, improving the sensitivity of the La-APT for metal-dielectric composites. Published by AIP Publishing.

  14. In situ gas phase measurements during metal alkylamide atomic layer deposition.

    PubMed

    Maslar, J E; Kimes, W A; Sperling, B A

    2011-09-01

    Metal alkylamide compounds, such as tetrakis(ethylmethylamido) hafnium (TEMAH), represent a technologically important class of metalorganic precursors for the deposition of metal oxides and metal nitrides via atomic layer deposition (ALD) or chemical vapor deposition. The development of in situ diagnostics for processes involving these compounds could be beneficial in, e.g., developing deposition recipes and validating equipment-scale simulations. This report describes the performance of the combination of two techniques for the simultaneous, rapid measurement of the three major gas phase species during hafnium oxide thermal ALD using TEMAH and water: TEMAH, water, and methylethyl amine (MEA), the only major reaction by-product. For measurement of TEMAH and MEA, direct absorption methods based on a broadband infrared source with different mid-IR bandpass filters and utilizing amplitude modulation and synchronous detection were developed. For the measurement of water, wavelength modulation spectroscopy utilizing a near-IR distributed feedback diode laser was used. Despite the relatively simple reactor geometry employed here (a flow tube), differences were easily observed in the time-dependent species distributions in 300 mL/min of a helium carrier gas and in 1000 mL/min of a nitrogen carrier gas. The degree of TEMAH entrainment was lower in 300 mL/min of helium compared to that in 1000 mL/min of nitrogen. The capability to obtain detailed time-dependent species concentrations during ALD could potentially allow for the selection of carrier gas composition and flow rates that would minimize parasitic wall reactions. However, when nitrogen was employed at the higher flow rates, various flow effects were observed that, if detrimental to a deposition process, would effectively limit the upper range of useful flow rates.

  15. Physical bounds of metallic nanofingers obtained by mechano-chemical atomic force microscope nanolithography

    NASA Astrophysics Data System (ADS)

    Akhavan, O.; Abdolahad, M.

    2009-01-01

    To obtain metallic nanofingers applicable in surface acoustic wave (SAW) sensors, a mechano-chemical atomic force microscope (AFM) nanolithography on a metallic thin film (50 nm in thickness)/piezoelectric substrate covered by a spin-coated polymeric mask layer (50-60 nm in thickness) was implemented. The effective shape of cross-section of the before and after etching grooves have been determined by using the AFM tip deconvolution surface analysis, structure factor, and power spectral density analyses. The wet-etching process improved the shape and aspect ratio (height/width) of the grooves and also smoothed the surface within them. We have shown that the relaxed surface tension of the polymeric mask layer resulted in a down limitation in width and length of the lithographed nanofingers. The surface tension of the mask layer can be changed by altering the initial concentration of the polymer in the deposition process. As the surface tension reduced, the down limitation decreased. In fact, an extrapolation of the analyzed statistical data has indicated that by decreasing the surface tension from 39 to 10 nN/nm, the minimum obtainable width and length of the metallic nanofingers was changed from about 55 nm and 2 μm to 15 nm and 0.44 μm, respectively. Using the extrapolation's results, we have shown that the future SAW sensors buildable by this nanolithography method possess a practical bound in their synchronous frequency (˜58 GHz), mass sensitivity (˜6125 MHz-mm 2/ng), and the limit of mass resolution (˜4.88 × 10 -10 ng/mm 2).

  16. In situ dissolution or deposition of Ytterbium (Yb) metal in microhotplate wells for a miniaturized atomic clock.

    PubMed

    Manginell, Ronald P; Moorman, Matthew W; Anderson, John M; Burns, George R; Achyuthan, Komandoor E; Wheeler, David R; Schwindt, Peter D D

    2012-10-22

    Current atomic clocks are burdened by size, weight, power and portability limitations to satisfy a broad range of potential applications. One critical need in the fabrication of a miniaturized atomic clock is small, low-power metallic sources. Exploiting the relatively high vapor pressure of ytterbium (Yb) and its dissolution in anhydrous ammonia, we report two independent techniques for depositing Yb inside a well micromachined into a microhotplate. Subsequent in situ evaporation of Yb from the microhotplate well serves as a low-power metallic source suitable for atomic clocks. The deposition and evaporation of Yb were confirmed using a variety of physicochemical techniques including quartz crystal microbalance, scanning electron microscopy, energy dispersive X-ray spectroscopy, and laser fluorescence. We also describe the fabrication of the microhotplate device, an integral component of our Yb-based miniature atomic clock. The Yb deposition/evaporation on a microhotplate well is thus useful as a low power Yb source during the fabrication of a miniaturized atomic clock, and this technique could be used for other applications requiring a vapor of a metal that has a moderate vapor pressure.

  17. Increased D-D Fusion Reaction Boosted by Electron Screening at the Inner Shell of Metal Atoms

    NASA Astrophysics Data System (ADS)

    Luo, Nie; Miley, George

    2004-10-01

    Recent experiments indicate an abnormally high electron screening effect on the D-D fusion cross-section during low energy (< 10 keV) bombardment of select deuterated metals [1]. The authors attribute this effect to a contribution from core electrons ignored in normal screening calculations [2]. This research studies the contribution of the atomic potential distribution on the classical dynamics of keV deuterons in a host metal, taken here as Pd. A standard atomic code is used to obtain the atomic electron charge density and the potential profile in the metal atom. Using these results, the deuterons are found to spend most of their penetration time near the Pd M shell. This effect drastically increases the probability of a rendezvous between two deuterons in a rather confined area roughly 0.1 angstrom from the Pd nucleus. This mechanism, combined with the increased tunneling rate due to screening from the high electron density at M-shell, enhances the low energy D-D fusion cross-section for metal hydrides. Results from these calculations and comparisons with experimental data will be presented. [1] F. Strieder, C. Rolfs, C. Spitaleri, and P.Corvisiero, Naturwissenschaften, 88 (2001) 461. [2] G. H. Miley, H. Hora, N. Luo, ¡°Screening in Low Energy Nuclear Reactions of Importance to Nuclear Astrophysics¡±, APS April Mtg. (2004), Denver, CO.

  18. Sample preparation of solid samples for metal determination by atomic spectroscopy - An overview and selected recent applications

    SciTech Connect

    Sneddon, J.; Hardaway, C.; Bobbadi, K.; Reddy, A.

    2006-07-01

    Classical methods involving dry dissolution, wet decomposition, and microwave methods for digestion/dissolution of solid samples for metal determination by various atomic spectroscopic techniques are discussed. Recent applications of solid sample preparation are presented including soils, sediments, food, cosmetics, oils, and coal.

  19. Correlations between dynamics and atomic structures in Cu64.5Zr35.5 metallic glass

    NASA Astrophysics Data System (ADS)

    Wang, C. Z.; Zhang, Y.; Zhang, F.; Mendelev, M. I.; Kramer, M. J.; Ho, K. M.

    2015-03-01

    The atomic structure of Cu-Zr metallic glasses (MGs) has been widely accepted to be heterogeneous and dominated by icosahedral short range order (ISRO). However, the correlations between dynamics and atomic structures in Cu-Zr MGs remain an enigma. Using molecular dynamics (MD) simulations, we investigated the correlations between dynamics and atomic structures in Cu64.5Zr35.5 MG. The atomic structures are characterized using ISRO and the Bergman-type medium range order (BMRO). The simulation and analysis results show that the majority of the mobile atoms are not involved in ISRO or BMRO, indicating that the dynamical heterogeneity has a strong correlation to structural heterogeneity. Moreover, we found that the localized soft vibration modes below 1.0 THz are mostly concentrated on the mobile atoms. The diffusion was studied using the atomic trajectory collected in an extended time interval of 1.2 μs at 700 K in MD simulations. It was found that the long range diffusion in MGs is highly heterogeneous, which is confined to the liquid-like regions and strongly avoids the ISRO and the Bergman-type MRO. All These results clearly demonstrate strong correlations between dynamics (in terms of dynamical heterogeneity and diffusion) and atomic structures in Cu64.5Zr35.5 MGs. This work was supported by the U.S. Department of Energy, Basic Energy Sciences, Division of Materials Science and Engineering under the Contract No. DE-AC02-07CH11358.

  20. Size-confined growth of atom-precise nanoclusters in metal-organic frameworks and their catalytic applications

    NASA Astrophysics Data System (ADS)

    Liu, Lingli; Song, Yongbo; Chong, Hanbao; Yang, Sha; Xiang, Ji; Jin, Shan; Kang, Xi; Zhang, Jun; Yu, Haizhu; Zhu, Manzhou

    2016-01-01

    Using MOFs as size-selection templates, we have for the first time synthesized atom-precise Au11:PPh3 nanoclusters (NCs) and Au13Ag12:PPh3 NCs with high purity by a one-step, in situ reduction method. Specifically, we found that the product released from the frameworks of ZIF-8 is exclusively the Au11:PPh3 NCs rather than polydispersed NCs, and inside MIL-101(Cr) the Au13Ag12:PPh3 NCs constitute the exclusive product. The metal NC@MOF composites are also demonstrated for catalytic application. The high catalytic efficiency for the oxidation of benzyl alcohol indicates that atom-precise noble metal NCs@MOFs may act as a promising class of heterogeneous catalysts. The atom-precise NCs obtained in the MOF templated synthesis imply the future possibility of using MOFs of various pore sizes for the size-selective synthesis of atomically precise NCs. Meanwhile, metal NCs@MOFs will contribute to the understanding of the mechanism of nanocatalyst surface reactions and hence opens up enormous opportunities in heterogeneous catalysis.Using MOFs as size-selection templates, we have for the first time synthesized atom-precise Au11:PPh3 nanoclusters (NCs) and Au13Ag12:PPh3 NCs with high purity by a one-step, in situ reduction method. Specifically, we found that the product released from the frameworks of ZIF-8 is exclusively the Au11:PPh3 NCs rather than polydispersed NCs, and inside MIL-101(Cr) the Au13Ag12:PPh3 NCs constitute the exclusive product. The metal NC@MOF composites are also demonstrated for catalytic application. The high catalytic efficiency for the oxidation of benzyl alcohol indicates that atom-precise noble metal NCs@MOFs may act as a promising class of heterogeneous catalysts. The atom-precise NCs obtained in the MOF templated synthesis imply the future possibility of using MOFs of various pore sizes for the size-selective synthesis of atomically precise NCs. Meanwhile, metal NCs@MOFs will contribute to the understanding of the mechanism of nanocatalyst

  1. Shifts in the ESR Spectra of Alkali-Metal Atoms (Li, Na, K, Rb) on Helium Nanodroplets

    PubMed Central

    Hauser, Andreas W; Gruber, Thomas; Filatov, Michael; Ernst, Wolfgang E

    2013-01-01

    He-droplet-induced changes of the hyperfine structure constants of alkali-metal atoms are investigated by a combination of relativistically corrected ab initio methods with a simulation of the helium density distribution based on He density functional theory. Starting from an accurate description of the variation of the hyperfine structure constant in the M–He diatomic systems (M=Li, Na, K, Rb) as a function of the interatomic distance we simulate the shifts induced by droplets of up to 10 000 4He atoms. All theoretical predictions for the relative shifts in the isotropic hyperfine coupling constants of the alkali-metal atoms attached to helium droplets of different size are then tied to a single, experimentally derived parameter of Rb. PMID:23125112

  2. Tunable electronic structures of germanium monochalcogenide nanosheets via light non-metallic atom functionalization: a first-principles study.

    PubMed

    Ding, Yi; Wang, Yanli

    2016-08-17

    Germanium monochalcogenides, i.e. GeS and GeSe sheets, are isoelectronic analogues of phosphorene, which have been synthesized in recent experiments (P. Ramasamy et al., J. Mater. Chem. C, 2016, 4, 479). Utilizing first-principles calculations, we have investigated their tunable electronic and magnetic properties via light non-metallic atom (B, C, N, O, Si, P, S) functionalization. We find that on these GeS and GeSe sheets O and S adatoms prefer to locate at the top site above the Ge atom, while the other ones like to occupy the anion site, which push the original S/Se atom to the hollow site instead. O and S adatoms slightly affect the semiconducting behaviour of the doped systems, while B, C, N, Si, P ones will drastically modify their band structures and induce versatile spintronic properties. Through the supercell calculations, B and C adatoms are found to induce a bipolar semiconducting behaviour in the decorated systems, while the N/P adatom will cause a spin-gapless-semiconducting/nearly-half-metallic feature in them. The B/C/N/Si/P-substituted GeS/GeSe sheet can be formed by removing the hollow-site S/Se atom from the adatom-decorated structures, which exhibit an opposite semiconducting/metallic behaviour to their phosphorene counterparts. A general odd-even rule is proposed for this phenomenon, which shows that an odd (even) number of valence electron difference between the substitution and host atoms would cause a metallic (semiconducting) feature in the substituted systems. Our study demonstrates that atom functionalization is an efficient way to tailor the properties of GeS and GeSe nanosheets, which have adaptable electronic properties for potential applications in nanoelectronics and spintronics.

  3. The effect of long-term wastewater irrigation on accumulation and transfer of heavy metals in Cupressus sempervirens leaves and adjacent soils.

    PubMed

    Farahat, Emad; Linderholm, Hans W

    2015-04-15

    Wastewater reuse for agriculture is an important management strategy in areas with limited freshwater resources, yielding potential economic and environmental benefits. Here the effects of long-term irrigation with wastewater on the nutrient contents of green and senesced leaves of Cupressus sempervirens L. were assessed for three planted forests in Egypt. Stoichiometric ratios, transfer factors for nutrients from soil to plant and enrichment factors in contaminated soils were estimated and compared to a ground water irrigated control site. Under wastewater irrigation, C. sempervirens transferred most of the estimated nutrients, particularly heavy metals, from green to senesced leaves. This could be a self-protecting mechanism under continuous wastewater irrigation. The accumulation of four metals (Zn, Mn, Cu and Cd) with transfer factors>1 for wastewater-irrigated trees, indicated the ability for metal accumulation of C. sempervirens. Stoichiometric ratios decreased under wastewater irrigation compared to the control site and global trends, which suggests nutrient disorders in these plants. The values of enrichment factors in the wastewater-irrigated soils showed remarkable availability and distribution of metals. Decreased resorption of metals by senesced leaves of C. sempervirens will add considerable amount of these metals to the soils, which will likely have adverse affects on the desert ecosystem components.

  4. A difference in using atomic layer deposition or physical vapour deposition TiN as electrode material in metal-insulator-metal and metal-insulator-silicon capacitors.

    PubMed

    Groenland, A W; Wolters, R A M; Kovalgin, A Y; Schmitz, J

    2011-09-01

    In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the MIM capacitors the bottom electrode is a patterned 100 nm TiN layer (called BE type 1), deposited via sputtering, while MIS capacitors have a flat bottom electrode (called BE type 2-silicon substrate). A high quality 50-100 nm thick SiO2 layer, made by inductively-coupled plasma CVD at 150 degrees C, is deposited as a dielectric on top of both types of bottom electrodes. BE type 1 (MIM) capacitors have a varying from low to high concentration of structural defects in the SiO2 layer. BE type 2 (MIS) capacitors have a low concentration of structural defects and are used as a reference. Two sets of each capacitor design are fabricated with the TiN top electrode deposited either via physical vapour deposition (PVD, i.e., sputtering) or atomic layer deposition (ALD). The MIM and MIS capacitors are electrically characterized in terms of the leakage current at an electric field of 0.1 MV/cm (I leak) and for different structural defect concentrations. It is shown that the structural defects only show up in the electrical characteristics of BE type 1 capacitors with an ALD TiN-based top electrode. This is due to the excellent step coverage of the ALD process. This work clearly demonstrates the sensitivity to process-induced structural defects, when ALD is used as a step in process integration of conductors on insulation materials.

  5. Fundamental studies of diffusion barriers for copper metallization and atomic layer deposited high-kappa films

    NASA Astrophysics Data System (ADS)

    Majumder, Prodyut

    Copper is used as interconnect material due to its lower resistivity, higher melting point and higher electromigration resistance than those of Al. However, Cu diffuses rapidly into Si and SiO2, to form Cu-silicides at temperatures as low as 200°C. Being highly resistive, Cu-silicides are detrimental in the performance of the integrated circuits. The continued downscaling of device dimensions has placed a high priority on the development of thin diffusion barrier layers in copper metallization. The effectiveness and performance of Mo-based bi-layers, such as Mo/WN, Mo/Ti, and Mo/TiN, and a ternary single layer, Mo-V nitride, deposited using magnetron sputtering are investigated in this work. The Cu/barrier film(s)/Si structures are annealed at high temperatures in N2 and the interactions between the layers along with the possible formation of any anneal-induced reaction products are evaluated using different techniques. The formation of Cu3Si due to the intermixing of Cu and Si is indicative of barrier breakdown. The decreasing device dimensions in microelectronic circuits set high demands for film conformality as the barrier layer thickness is anticipated to decrease to 1.9 nm for the 25 nm node (by 2015). In order to meet future requirement of ultrathin barriers, the apparently counter-intuitive approach of using insulating films, such as HfO2 and Al2O 3, deposited using atomic layer deposition (ALD) technique has been studied and revealed interesting and promising results. In microelectronics fabrication, there is also a need for thin films with high dielectric constant (kappa) in order to continue device dimension reduction of logic and memory devices. With conventional SiO2 based materials, continued scale minimization mandates single digit atomic layer thicknesses of the dielectric layers that lead to the ultimate limitation of quantum mechanical tunneling. To overcome this limitation, high-kappa metal oxides have been recognized as future gate dielectrics

  6. Catalytic oxidation of H2 by N2O in the gas phase: O-atom transport with atomic metal cations.

    PubMed

    Blagojevic, Voislav; Bozović, Andrea; Orlova, Galina; Bohme, Diethard K

    2008-10-16

    Twenty-five atomic cations, M (+), that lie within the thermodynamic window for O-atom transport catalysis of the oxidation of hydrogen by nitrous oxide, have been checked for catalytic activity at room temperature with kinetic measurements using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Only 4 of these 25 atomic cations were seen to be catalytic: Fe (+), Os (+), Ir (+), and Pt (+). Two of these, Ir (+) and Pt (+), are efficient catalysts, while Fe (+) and Os (+) are not. Eighteen atomic cations (Cr (+), Mn (+), Co (+), Ni (+), Cu (+), Ge (+), Se (+), Mo (+), Ru (+), Rh (+), Sn (+), Te (+), Re (+), Pb (+), Bi (+), Eu (+), Tm (+), and Yb (+)) react too slowly at room temperature either in their oxidation with N 2O to form MO (+) or in the reduction of MO (+) by H 2. Many of these reactions are known to be spin forbidden and a few actually may lie outside the thermodynamic window. Three alkaline-earth metal monoxide cations, CaO (+), SrO (+), and BaO (+), were observed to favor MOH (+) formation in their reactions with H 2. A potential-energy landscape is computed for the oxidation of H 2 with N 2O catalyzed by Fe (+)( (6)D) that vividly illustrates the operation of an ionic catalyst and qualitatively accounts for the relative inefficiency of this catalyst.

  7. Estimation of stability constants for metal-ligand complexes containing neutral nitrogen donor atoms with applications to natural organic matter

    NASA Astrophysics Data System (ADS)

    Atalay, Yasemin B.; Di Toro, Dominic M.; Carbonaro, Richard F.

    2013-12-01

    Linear free energy relationships (LFERs) were developed for estimating 1:1 metal-ligand stability constants (log KML) for small organic molecules containing neutral nitrogen donor atoms. A data set of 44 monodentate and 112 bidentate ligands for six metal ions: Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ was employed to parameterize the LFER equations. Monodentate and bidentate log KML values were adequately described using Irving-Rossotti LFERs previously developed for ligands containing negatively-charged oxygen functional groups. Modifications to the LFER equations were necessary to account for steric hindrances to metal complexation by primary, secondary, and tertiary amines. The resulting LFER equations can be used to estimate log KML values for monodentate and bidentate ligands with neutral nitrogen donor groups where such values do not currently exist in the literature. Comparison of these results to our previous work with negatively-charged oxygen donor atoms reveals that neutral nitrogen functional groups are weaker than their oxygen counterparts for metal ions classified as “hard” on the basis of Hard-Soft Acid-Base (HSAB) theory. For “soft” metals, the opposite is true. These LFERs can be used to incorporate nitrogen functional groups in models for metal ion binding to natural organic matter (NOM).

  8. Antibiotic resistance gene abundances associated with antibiotics and heavy metals in animal manures and agricultural soils adjacent to feedlots in Shanghai; China.

    PubMed

    Ji, Xiuling; Shen, Qunhui; Liu, Fang; Ma, Jing; Xu, Gang; Wang, Yuanlong; Wu, Minghong

    2012-10-15

    Eight antibiotic resistance genes (ARGs), 7 heavy metals, and 6 antibiotics were quantified in manures and soils collected from multiple feedlots in Shanghai. The samples were analyzed to determine if ARG abundances were associated with heavy metal concentration and independent of antibiotics. The results revealed the presence of chloramphenicol, sulfonamides and tetracyclines at concentration ranges of 3.27-17.85, 5.85-33.37 and 4.54-24.66 mg kg(-1), respectively. Typical heavy metals, such as Cu, Zn, and As, were detected at concentration ranges of 32.3-730.1, 75.9-4333.8, and 2.6-617.2 mg kg(-1). All ARGs tested were detected in the collected samples except tetB(P), which was absent in animal manures. Overall, sulfonamide ARGs were more abundant than tetracycline ARGs. Except for sulII, only a weak positive correlation was found between ARGs and their corresponding antibiotics. On the contrary, significant positive correlations (p<0.05) were found between some ARGs and typical heavy metals. For example, sulA and sulIII were strongly correlated with levels of Cu, Zn and Hg. The data demonstrated that the presence of ARGs was relatively independent of their respective antibiotic inducer. In addition to antibiotics, toxic heavy metals, such as Hg, Cu, and Zn, exerted a strong selection pressure and acted as complementary factors for ARG abundance.

  9. Selected metal levels of commercially valuable seaweeds adjacent to and distant from point sources of contamination in Nova Scotia and New Brunswick

    SciTech Connect

    Sharp, G.J. ); Samant, H.S.; Vaidya, O.C. )

    1988-06-01

    The harvesting of marine plants on a commercial scale was a significant industry in the Maritime Provinces of Canada by the end of World War II. These seaweeds have been traditionally utilized as foodstuffs either as a processed extract or a semi-processed plant. The Maritime coastline is becoming industrialized; there is also potential for expansion of the marine plant industry beyond traditional harvest areas. Therefore, the quality of material from new areas must be examined prior to exploitation as well as monitoring of traditional areas. The bioaccumulated of metals by marine plants was recognized in early measurements of trace element concentrations which were above ambient water values. Before growth and reproductive inhibition are caused by severe effects of heavy metal pollution, food quality changes may occur. The Food Chemical Code (U.S.A.) limits heavy metals in the extracts of seaweeds. Sediment and water samples taken in connection with the Ocean Dumping Control Act of Canada have identified several sites with elevated heavy metal content in the Maritimes. The purpose of this study was to examine heavy metal levels in commercially important seaweeds from traditional harvest areas and areas near point sources of pollution. The authors wished to provide a baseline for the future and identify existing problem areas.

  10. Structural, electronic, and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

    NASA Astrophysics Data System (ADS)

    Luo, Jia; Xiang, Gang; Yu, Tian; Lan, Mu; Zhang, Xi

    2016-09-01

    By using first-principles calculations within the framework of density functional theory, the electronic and magnetic properties of 3d transitional metal (TM) atoms (from Sc to Zn) adsorbed monolayer GaAs nanosheets (GaAsNSs) are systematically investigated. Upon TM atom adsorption, GaAsNS, which is a nonmagnetic semiconductor, can be tuned into a magnetic semiconductor (Sc, V, and Fe adsorption), a half-metal (Mn adsorption), or a metal (Co and Cu adsorption). Our calculations show that the strong p-d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the GaAsNSs with Sc, V, and Fe adsorption. However, the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit, resulting in a stronger exchange interaction. Our results may be useful for electronic and magnetic applications of GaAsNS-based materials. Project supported by the National Natural Science Foundation of China (Grant No. 11174212).

  11. High Throughput Atomic Layer Deposition Processes: High Pressure Operations, New Reactor Designs, and Novel Metal Processing

    NASA Astrophysics Data System (ADS)

    Mousa, MoatazBellah Mahmoud

    Atomic Layer Deposition (ALD) is a vapor phase nano-coating process that deposits very uniform and conformal thin film materials with sub-angstrom level thickness control on various substrates. These unique properties made ALD a platform technology for numerous products and applications. However, most of these applications are limited to the lab scale due to the low process throughput relative to the other deposition techniques, which hinders its industrial adoption. In addition to the low throughput, the process development for certain applications usually faces other obstacles, such as: a required new processing mode (e.g., batch vs continuous) or process conditions (e.g., low temperature), absence of an appropriate reactor design for a specific substrate and sometimes the lack of a suitable chemistry. This dissertation studies different aspects of ALD process development for prospect applications in the semiconductor, textiles, and battery industries, as well as novel organic-inorganic hybrid materials. The investigation of a high pressure, low temperature ALD process for metal oxides deposition using multiple process chemistry revealed the vital importance of the gas velocity over the substrate to achieve fast depositions at these challenging processing conditions. Also in this work, two unique high throughput ALD reactor designs are reported. The first is a continuous roll-to-roll ALD reactor for ultra-fast coatings on porous, flexible substrates with very high surface area. While the second reactor is an ALD delivery head that allows for in loco ALD coatings that can be executed under ambient conditions (even outdoors) on large surfaces while still maintaining very high deposition rates. As a proof of concept, part of a parked automobile window was coated using the ALD delivery head. Another process development shown herein is the improvement achieved in the selective synthesis of organic-inorganic materials using an ALD based process called sequential vapor

  12. High aspect ratio iridescent three-dimensional metal–insulator–metal capacitors using atomic layer deposition

    SciTech Connect

    Burke, Micheal Blake, Alan; Djara, Vladimir; O'Connell, Dan; Povey, Ian M.; Cherkaoui, Karim; Monaghan, Scott; Scully, Jim; Murphy, Richard; Hurley, Paul K.; Pemble, Martyn E.; Quinn, Aidan J.

    2015-01-01

    The authors report on the structural and electrical properties of TiN/Al{sub 2}O{sub 3}/TiN metal–insulator–metal (MIM) capacitor structures in submicron three-dimensional (3D) trench geometries with an aspect ratio of ∼30. A simplified process route was employed where the three layers for the MIM stack were deposited using atomic layer deposition (ALD) in a single run at a process temperature of 250 °C. The TiN top and bottom electrodes were deposited via plasma-enhanced ALD using a tetrakis(dimethylamino)titanium precursor. 3D trench devices yielded capacitance densities of 36 fF/μm{sup 2} and quality factors >65 at low frequency (200 Hz), with low leakage current densities (<3 nA/cm{sup 2} at 1 V). These devices also show strong optical iridescence which, when combined with the covert embedded capacitance, show potential for system in package (SiP) anticounterfeiting applications.

  13. Determination of effective atomic number and electron density of heavy metal oxide glasses

    NASA Astrophysics Data System (ADS)

    Ali, A. M.; El-Khayatt, A. M.; Akkurt, I.

    2016-03-01

    The effective atomic number (Zeff) and effective electron density (Neff) of eight heavy metal oxide (HMO) glasses have been determined using the Monte Carlo simulation code MCNP for the energy range of 10 keV-10 MeV. The interpolation method was employed to extract Zeff and Neff values from the simulation and that calculated with the help of XCOM program. Comparisons are also made with predictions from the Auto-Zeff software in the same energy region. Wherever possible, the simulated values of Zeff and Neff are compared with experimental data. In general, a very good agreement was noticed. It was found that the Zeff and Neff vary with photon energy and do not have extended intermediate regions where Compton scattering is truly dominating; only dips slightly above ∼1.5 MeV were recorded. Zeff and Neff are found to increase with PbO and Bi2O3 contents. It was found that the Zeff value rather than the Neff value is a better indicator for PbO and/or Bi2O3 contents.

  14. Synthesis, characterization and biological approach of metal chelates of some first row transition metal ions with halogenated bidentate coumarin Schiff bases containing N and O donor atoms.

    PubMed

    Prabhakara, Chetan T; Patil, Sangamesh A; Toragalmath, Shivakumar S; Kinnal, Shivashankar M; Badami, Prema S

    2016-04-01

    The impregnation of halogen atoms in a molecule is an emerging trend in pharmaceutical chemistry. The presence of halogens (Cl, Br, I and F) increases the lipophilic nature of molecule and improves the penetration of lipid membrane. The presence of electronegative halogen atoms increases the bio- activity of core moiety. In the present study, Co(II), Ni(II) and Cu(II) complexes are synthesised using Schiff bases (HL(I) and HL(II)), derived from 8-formyl-7-hydroxy-4-methylcoumarin/3-chloro-8-formyl-7-hydroxy-4-methylcoumarin with 2,4-difluoroaniline/o-toluidine respectively. The synthesized compounds were characterized by spectral (IR, NMR, UV-visible, Mass, ESI-MS, ESR), thermal, fluorescence and molar conductivity studies. All the synthesized metal complexes are completely soluble in DMF and DMSO. The non-electrolytic nature of the metal complexes was confirmed by molar conductance studies. Elemental analysis study suggest [ML2(H2O)2] stoichiometry, here M=Co(II), Ni(II) and Cu(II), L=deprotonated ligand. The obtained IR data supports the binding of metal ion to Schiff base. Thermal study suggests the presence of coordinated water molecules. Electronic spectral results reveal six coordinated geometry for the synthesized metal complexes. The Schiff bases and their metal complexes were evaluated for antibacterial (Pseudomonas aureginosa and Proteus mirabilis), antifungal (Aspergillus niger and Rhizopus oryzae), anthelmintic (Pheretima posthuma) and DNA cleavage (Calf Thymus DNA) activities.

  15. Fabrication of metallic single electron transistors featuring plasma enhanced atomic layer deposition of tunnel barriers

    NASA Astrophysics Data System (ADS)

    Karbasian, Golnaz

    The continuing increase of the device density in integrated circuits (ICs) gives rise to the high level of power that is dissipated per unit area and consequently a high temperature in the circuits. Since temperature affects the performance and reliability of the circuits, minimization of the energy consumption in logic devices is now the center of attention. According to the International Technology Roadmaps for Semiconductors (ITRS), single electron transistors (SETs) hold the promise of achieving the lowest power of any known logic device, as low as 1x10-18 J per switching event. Moreover, SETs are the most sensitive electrometers to date, and are capable of detecting a fraction of an electron charge. Despite their low power consumption and high sensitivity for charge detection, room temperature operation of these devices is quite challenging mainly due to lithographical constraints in fabricating structures with the required dimensions of less than 10 nm. Silicon based SETs have been reported to operate at room temperature. However, they all suffer from significant variation in batch-to-batch performance, low fabrication yield, and temperature-dependent tunnel barrier height. In this project, we explored the fabrication of SETs featuring metal-insulator-metal (MIM) tunnel junctions. While Si-based SETs suffer from undesirable effect of dopants that result in irregularities in the device behavior, in metal-based SETs the device components (tunnel barrier, island, and the leads) are well-defined. Therefore, metal SETs are potentially more predictable in behavior, making them easier to incorporate into circuits, and easier to check against theoretical models. Here, the proposed fabrication method takes advantage of unique properties of chemical mechanical polishing (CMP) and plasma enhanced atomic layer deposition (PEALD). Chemical mechanical polishing provides a path for tuning the dimensions of the tunnel junctions, surpassing the limits imposed by electron beam

  16. V-shaped metallic-wire cantilevers for combined atomic force microscopy and Fowler-Nordheim imaging

    NASA Astrophysics Data System (ADS)

    Peterson, Charles A.; Workman, Richard K.; Yao, Xiaowei; Hunt, Jeffery P.; Sarid, Dror

    1998-12-01

    A method for fabricating V-shaped cantilevers from a flattened Pt/Ir metal wire for combined atomic force microscopy and Fowler-Nordheim imaging is described. These novel cantilevers have been found to be more robust then conventional ones used for scanning capacitance and magnetic force microscopy as their conductivity is maintained even after a large number of surface scans. The use of a V-shaped geometry improves on earlier single-beam geometries by reducing rms imaging noise. Characterization of these cantilevers and combined atomic force microscopy and Fowler-Nordheim images are reported.

  17. Effect of interface atomic structure on the electronic properties of nano-sized metal-oxide interfaces.

    PubMed

    Qin, Wei; Hou, Jiechang; Bonnell, Dawn A

    2015-01-14

    We report that the size dependence of electronic properties at nanosized metal-semiconducting oxide interfaces is significantly affected by the interface atomic structure. The properties of interfaces with two orientations are compared over size range of 20-200 nm. The difference in interface atomic structure leads to electronic structure differences that alter electron transfer paths. Specifically, interfaces with a higher concentration of undercoordinated Ti result in enhanced tunneling due to the presence of defect states or locally reduced tunnel barrier widths. This effect is superimposed on the mechanisms of size dependent properties at such small scales.

  18. Hydrogen abstraction from metal surfaces: when electron-hole pair excitations strongly affect hot-atom recombination.

    PubMed

    Galparsoro, Oihana; Pétuya, Rémi; Busnengo, Fabio; Juaristi, Joseba Iñaki; Crespos, Cédric; Alducin, Maite; Larregaray, Pascal

    2016-11-23

    Using molecular dynamics simulations, we predict that the inclusion of nonadiabatic electronic excitations influences the dynamics of preadsorbed hydrogen abstraction from the W(110) surface by hydrogen scattering. The hot-atom recombination, which involves hyperthermal diffusion of the impinging atom on the surface, is significantly affected by the dissipation of energy mediated by electron-hole pair excitations at low coverage and low incidence energy. This issue is of importance as this abstraction mechanism is thought to largely contribute to molecular hydrogen formation from metal surfaces.

  19. Surface chemistry of the atomic layer deposition of metals and group III oxides

    NASA Astrophysics Data System (ADS)

    Goldstein, David Nathan

    Atomic Layer Deposition (ALD) is a thin-film growth technique offering precise control of film thickness and the ability to coat high-aspect-ratio features such as trenches and nanopowders. Unlike other film growth techniques, ALD does not require harsh processing conditions and is not limited by line-of-sight deposition. Emerging applications for ALD materials include semiconductor devices, gas sensors, and water-diffusion barriers. The chemistry behind ALD involves understanding how the precursors interact with surfaces to deposit the desired material. All ALD precursors need to be stable on the substrate to ensure self-limiting behavior yet reactive enough to be easily removed with the second reagent. Recent precursor development has provided many volatile organometallic compounds for most of the periodic table. As the number of precursors increases, proper precursor choice becomes crucial. This is because the film properties, growth rates, and growth temperature vary widely between the precursors. Many of the above traits can be predicted with knowledge of the precursor reaction mechanisms. This thesis aims to link surface reaction mechanisms to observed growth and nucleation trends in metal and oxide ALD systems. The first portion of this thesis explores the mechanisms of two ALD oxide systems. First, I examine the mechanism of ALD alumina with ozone. Ozone is used as an oxidant in the semiconductor industry because the deposited Al 2O3 films possess better insulating properties and ozone is easier to purge from a vacuum system. FT-IR analysis reveals a complicated array of surface intermediates such as formate, carbonate, and methoxy groups that form during Al2O3 growth with ozone. Next, a new method to deposit thin films of Ga2O3 is introduced. Gallium oxide is a transparent conducting oxide that needs expensive solid precursors to be deposited by ALD. I show that trimethylgallium is a good high-temperature ALD precursor that deposits films of Ga2O 3 with

  20. Polycyclic aromatic hydrocarbons and metals in transplanted lichen (Pseudovernia furfuracea) at sites adjacent to a solid-waste landfill in central Italy.

    PubMed

    Protano, C; Guidotti, M; Owczarek, M; Fantozzi, L; Blasi, G; Vitali, M

    2014-05-01

    The aim of the study was to evaluate the airborne contamination by polycyclic aromatic hydrocarbons (PAHs) and some heavy metals (arsenic [As], cadmium [Cd], chromium [Cr], copper [Cu], nickel [Ni], lead [Pb], and zinc [Zn]) of different pollution scenarios around a solid-waste landfill in central Italy using the lichen Pseudovernia furfuracea as a monitoring tool. For this purpose, eight stations around a landfill characterized by different air pollution sources (industrial, agricultural, residential areas, and roads with different traffic intensities), together with three stations far from the landfill (control areas), were monitored using a set of 22 lichen samples (11 samples analysed for PAHs and metals after 4 months, and 11 samples analysed for metals after 8 months). After 4 months of exposure, the lichen content of all of the analysed elements was greater than that in the pre-exposed lichens. In addition, the Cu and Pb concentration after 8 months was greater than the level after 4 months. The order of metal concentration was Zn > Pb > Cu (or Cu > Pb) > Cr > Ni > As > Cd in all cases. The range of ∑11PAHs concentration was 634-1,371 ng/g dw (three to seven times greater than the amount in the pre-exposed lichens). The ∑11PAHs were dominated (>70 %) by compounds with three aromatic rings. The comparison of the levels of air pollutants among the monitored stations shows nonrelevant spatial patterns between the landfill stations and the control areas; the levels of PAHs and metals found in the lichen samples around the landfill seemed to be more related to the general diffusion of these pollutants in that area.

  1. Influence of 3 d metal atoms on the geometry, electronic structure, and stability of a Mg13H26 cluster

    NASA Astrophysics Data System (ADS)

    Shelyapina, M. G.; Siretskiy, M. Yu.

    2010-09-01

    This paper reports on the results of the theoretical investigation of magnesium hydride nanoclusters doped with 3 d metals (from Sc to Zn). The influence of transition metal atoms on the geometry, electronic structure, and energy characteristics of the clusters has been analyzed. The results of the performed calculations have been compared with the available experimental data. This comparison has made it possible to predict which 3 d transition elements can serve as the most effective catalysts for the improvement of the thermodynamic characteristics of MgH2.

  2. Preparation of Supported Metal Catalysts by Atomic and Molecular Layer Deposition for Improved Catalytic Performance

    NASA Astrophysics Data System (ADS)

    Gould, Troy D.

    Creating catalysts with enhanced selectivity and activity requires precise control over particle shape, composition, and size. Here we report the use of atomic layer deposition (ALD) to synthesize supported Ni, Pt, and Ni-Pt catalysts in the size regime (< 3 nm) where nanoscale properties can have a dramatic effect on reaction activity and selectivity. This thesis presents the first ALD synthesis of non-noble metal nanoparticles by depositing Ni on Al2O3 with two half-reactions of Ni(Cp)2 and H2. By changing the number of ALD cycles, Ni weight loadings were varied from 4.7 wt% to 16.7 wt% and the average particle sizes ranged from 2.5 to 3.3 nm, which increased the selectivity for C 3H6 hydrogenolysis by an order of magnitude over a much larger Ni/Al2O3 catalyst. Pt particles were deposited by varying the number of ALD cycles and the reaction chemistry (H2 or O 2) to control the particle size from approximately 1 to 2 nm, which allowed lower-coordinated surface atoms to populate the particle surface. These Pt ALD catalysts demonstrated some of the highest oxidative dehydrogenation of propane selectivities (37%) of a Pt catalyst synthesized by a scalable technique. Dry reforming of methane (DRM) is a reaction of interest due to the recent increased recovery of natural gas, but this reaction is hindered from industrial implementation because the Ni catalysts are plagued by deactivation from sintering and coking. This work utilized Ni ALD and NiPt ALD catalysts for the DRM reaction. These catalysts did not form destructive carbon whiskers and had enhanced reaction rates due to increased bimetallic interaction. To further limit sintering, the Ni and NiPt ALD catalysts were coated with a porous alumina matrix by molecular layer deposition (MLD). The catalysts were evaluated for DRM at 973 K, and the MLD-coated Ni catalysts outperformed the uncoated Ni catalysts in either activity (with 5 MLD cycles) or stability (with 10 MLD cycles). In summary, this thesis developed a

  3. Barrier-free subsurface incorporation of 3d metal atoms into Bi(111) films

    SciTech Connect

    Klein, C.; Vollmers, N. J.; Gerstmann, U.; Zahl, P.; Lukermann, D.; Jnawali, G.; Pfnur, H.; Sutter, P.; Tegenkamp, C.; Schmidt, W. G.; Horn-von Hoegen, M.

    2015-05-27

    By combining scanning tunneling microscopy with density functional theory it is shown that the Bi(111) surface provides a well-defined incorporation site in the first bilayer that traps highly coordinating atoms such as transition metals (TMs) or noble metals. All deposited atoms assume exactly the same specific sevenfold coordinated subsurface interstitial site while the surface topography remains nearly unchanged. Notably, 3d TMs show a barrier-free incorporation. The observed surface modification by barrier-free subsorption helps to suppress aggregation in clusters. Thus, it allows a tuning of the electronic properties not only for the pure Bi(111) surface, but may also be observed for topological insulators formed by substrate-stabilized Bi bilayers.

  4. Extended x-ray absorption fine structure studies of the atomic structure of nanoparticles in different metallic matrices.

    PubMed

    Baker, S H; Roy, M; Gurman, S J; Binns, C

    2009-05-06

    It has been appreciated for some time that the novel properties of particles in the size range 1-10 nm are potentially exploitable in a range of applications. In order to ultimately produce commercial devices containing nanosized particles, it is necessary to develop controllable means of incorporating them into macroscopic samples. One way of doing this is to embed the nanoparticles in a matrix of a different material, by co-deposition for example, to form a nanocomposite film. The atomic structure of the embedded particles can be strongly influenced by the matrix. Since some of the key properties of materials, including magnetism, strongly depend on atomic structure, the ability to determine atomic structure in embedded nanoparticles is very important. This review focuses on nanoparticles, in particular magnetic nanoparticles, embedded in different metal matrices. Extended x-ray absorption fine structure (EXAFS) provides an excellent means of probing atomic structure in nanocomposite materials, and an overview of this technique is given. Its application in probing catalytic metal clusters is described briefly, before giving an account of the use of EXAFS in determining atomic structure in magnetic nanocomposite films. In particular, we focus on cluster-assembled films comprised of Fe and Co nanosized particles embedded in various metal matrices, and show how the crystal structure of the particles can be changed by appropriate choice of the matrix material. The work discussed here demonstrates that combining the results of structural and magnetic measurements, as well as theoretical calculations, can play a significant part in tailoring the properties of new magnetic cluster-assembled materials.

  5. Atomic and electronic structure of CdTe/metal (Cu, Al, Pt) interfaces and their influence to the Schottky barrier

    NASA Astrophysics Data System (ADS)

    Odkhuu, Dorj; Miao, Mao-sheng; Aqariden, F.; Grein, Christoph; Kioussis, Nicholas

    2016-11-01

    Schottky barrier heights (SBHs) and other features of the interfaces are determining factors for the performance of the CdTe based high-energy photon detectors. Although known for long time that SBH is sensitive to surface treatment and metal contact growth method, there is a lack of understanding of the effect of the atomic and electronic structures of CdTe/metal interface on the SBH. Employing first-principles electronic structure calculations, we have systematically studied the structural stability and electronic properties of a number of representing structures of Cd Terminated CdTe/metal (Cu, Pt, and Al) interfaces. Comparison of the total energies of the various optimized structural configurations allows to identify the existence of Te-metal alloy formation at the interface. The SBHs of Cu, Pt, and Al metal contacts with a number of stable interface structures are determined by aligning the band edges of bulk CdTe with the Fermi level of the metal/CdTe system. We find that the metal-induced states in the gap play an essential role in determining the SBH.

  6. In-situ atomic force microscopy observation revealing gel-like plasticity on a metallic glass surface

    NASA Astrophysics Data System (ADS)

    Lu, Y. M.; Zeng, J. F.; Huang, J. C.; Kuan, S. Y.; Nieh, T. G.; Wang, W. H.; Pan, M. X.; Liu, C. T.; Yang, Y.

    2017-03-01

    It has been decade-long and enduring efforts to decipher the structural mechanism of plasticity in metallic glasses; however, it still remains a challenge to directly reveal the structural change, if any, that precedes; and dominant plastics flow in them. Here, by using the dynamic atomic force microscope as an "imaging" as well as a "forcing" tool, we unfold a real-time sequence of structural evolution occurring on the surface of an Au-Si thin film metallic glass. In sharp contrast to the common notion that plasticity comes along with mechanical softening in bulk metallic glasses, our experimental results directly reveal three types of nano-sized surface regions, which undergo plasticity but exhibit different characters of structural evolution following the local plasticity events, including stochastic structural rearrangement, unusual local relaxation and rejuvenation. As such, yielding on the metallic-glass surface manifests as a dynamic equilibrium between local relaxation and rejuvenation as opposed to shear instability in bulk metallic-glasses. Our finding demonstrates that plasticity on the metallic glass surface of Au-Si metallic glass bears much resemblance to that of the colloidal gels, of which nonlinear rheology rather than shear instability governs the constitutive behavior of plasticity.

  7. Spin-Orbit-Coupled Correlated Metal Phase in Kondo Lattices: An Implementation with Alkaline-Earth Atoms

    NASA Astrophysics Data System (ADS)

    Isaev, L.; Schachenmayer, J.; Rey, A. M.

    2016-09-01

    We show that an interplay between quantum effects, strong on-site ferromagnetic exchange interaction, and antiferromagnetic correlations in Kondo lattices can give rise to an exotic spin-orbit coupled metallic state in regimes where classical treatments predict a trivial insulating behavior. This phenomenon can be simulated with ultracold alkaline-earth fermionic atoms subject to a laser-induced magnetic field by observing dynamics of spin-charge excitations in quench experiments.

  8. Collisions of alkali-metal atoms Cs and Rb in the ground state. Spin exchange cross sections

    NASA Astrophysics Data System (ADS)

    Kartoshkin, V. A.

    2016-09-01

    Collisions of alkali-metal atoms 133Cs and 85Rb in the ground state are considered in the energy interval of 10-4-10-2 au. Complex cross sections of the spin exchange, which allow one to calculate the processes of polarization transfer and the relaxation times, as well as the magnetic resonance frequency shifts caused by spin exchange Cs-Rb collisions, are obtained.

  9. Cyclotron dynamics of a Kondo singlet in a spin-orbit-coupled alkaline-earth-metal atomic gas

    NASA Astrophysics Data System (ADS)

    Jiang, Bo-Nan; Lv, Hao; Wang, Wen-Li; Du, Juan; Qian, Jun; Wang, Yu-Zhu

    2014-11-01

    We propose a scheme to investigate the interplay between the Kondo-exchange interaction and the quantum spin Hall effect with ultracold fermionic alkaline-earth-metal atoms trapped in two-dimensional optical lattices using ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling regime, although the loop trajectory of the mobile atom disappears, collective dynamics of an atom pair in two clock states can exhibit an unexpected spin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall effect of the Kondo singlet. We demonstrate that the collective cyclotron dynamics of the spin-zero Kondo singlet is governed by an effective Harper-Hofstadter model in addition to second-order diagonal tunneling.

  10. One- and two-photon spectroscopy of highly excited states of alkali-metal atoms on helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Pifrader, Alexandra; Allard, Olivier; Auböck, Gerald; Callegari, Carlo; Ernst, Wolfgang E.; Huber, Robert; Ancilotto, Francesco

    2010-10-01

    Alkali-metal atoms captured on the surface of superfluid helium droplets are excited to high energies (≈3 eV) by means of pulsed lasers, and their laser-induced-fluorescence spectra are recorded. We report on the one-photon excitation of the (n +1)p←ns transition of K, Rb, and Cs (n =4, 5, and 6, respectively) and on the two-photon one-color excitation of the 5d←5s transition of Rb. Gated-photon-counting measurements are consistent with the relaxation rates of the bare atoms, hence consistent with the reasonable expectation that atoms quickly desorb from the droplet and droplet-induced relaxation need not be invoked.

  11. Antiferromagnetic half metallicity in codoped chalcopyrite semiconductors Cu(Al 1 - 2 xAxBx)Se2 (A and B are 3d transition-metal atoms)

    NASA Astrophysics Data System (ADS)

    Shahjahan, M.; Oguchi, T.

    2016-06-01

    Electronic structures and magnetic properties of group I-III-VI2 chalcopyrite-type compounds Cu(Al 1 - 2 xAxBx)Se2 are calculated using the Korringa-Kohn-Rostoker Green's function method, where A (Ti, V, Cr, Mn) and B (Fe, Co, Ni) are 3d transition metal atoms, and x is atomic concentration. We found that codoping of Cr-Co and V-Ni pairs at Al site of host CuAlSe2 exhibit antiferromagnetic (AF) half metallicity with low Curie temperature (TC). The AF half metallic property is supported by nullified net magnetic moment and compensated density of states in the minority spin direction. On the other hand, codoping of Cr-Ni, Mn-Co, V-Co, and Ti-Co pairs at Al site of host CuAlSe2 manifest ferrimagnetic half metallicity with a small net magnetization and keeping antiparallel local spin moments. In Mn-Co case TC is close to room temperature. Besides, Cr-Fe, V-Fe, and Ti-Ni codoping cases lead to an instable magnetic ordering and therefore obtain a disordered local moment (spin-glass like) state.

  12. Nature of the interaction between rare gas atoms and transition metal doped silicon clusters: the role of shielding effects.

    PubMed

    Ngan, Vu Thi; Janssens, Ewald; Claes, Pieterjan; Fielicke, André; Nguyen, Minh Tho; Lievens, Peter

    2015-07-21

    Mass spectrometry experiments show an exceptionally weak bonding between Si7Mn(+) and rare gas atoms as compared to other exohedrally transition metal (TM) doped silicon clusters and other SinMn(+) (n = 5-10) sizes. The Si7Mn(+) cluster does not form Ar complexes and the observed fraction of Xe complexes is low. The interaction of two cluster series, SinMn(+) (n = 6-10) and Si7TM(+) (TM = Cr, Mn, Cu, and Zn), with Ar and Xe is investigated by density functional theory calculations. The cluster-rare gas binding is for all clusters, except Si7Mn(+) and Si7Zn(+), predominantly driven by short-range interaction between the TM dopant and the rare gas atoms. A high s-character electron density on the metal atoms in Si7Mn(+) and Si7Zn(+) shields the polarization toward the rare gas atoms and thereby hinders formation of short-range complexes. Overall, both Ar and Xe complexes are similar except that the larger polarizability of Xe leads to larger binding energies.

  13. Ab initio effective core potentials for molecular calculations. Potentials for the transition metal atoms Sc to Hg

    SciTech Connect

    Hay, P.J.; Wadt, W.R.

    1985-01-01

    Ab initio effective core potentials (ECP's) have been generated to replace the Coulomb, exchange, and core-orthogonality effects of the chemically inert core electron in the transition metal atoms Sc to Hg. For the second and third transition series relative ECP's have been generated which also incorporate the mass--velocity and Darwin relativistic effects into the potential. The ab initio ECP's should facilitate valence electron calculations on molecules containing transition-metal atoms with accuracies approaching all-electron calculations at a fraction of the computational cost. Analytic fits to the potentials are presented for use in multicenter integral evaluation. Gaussian orbital valence basis sets are developed for the (3d,4s,4p), (4d,5s,5p), and (5d,6s,6p) orbitals of the first, second, and third transition series atoms, respectively. All-electron and valence-electron atomic excitation energies are also compared for the low-lying states of Sc--Hg, and the valence-electron calculations are found to reproduce the all-electron excitation energies (typically within a few tenths of an eV).

  14. Atomic-layer electroless deposition: a scalable approach to surface-modified metal powders.

    PubMed

    Cappillino, Patrick J; Sugar, Joshua D; El Gabaly, Farid; Cai, Trevor Y; Liu, Zhi; Stickney, John L; Robinson, David B

    2014-04-29

    Palladium has a number of important applications in energy and catalysis in which there is evidence that surface modification leads to enhanced properties. A strategy for preparing such materials is needed that combines the properties of (i) scalability (especially on high-surface-area substrates, e.g. powders); (ii) uniform deposition, even on substrates with complex, three-dimensional features; and (iii) low-temperature processing conditions that preserve nanopores and other nanostructures. Presented herein is a method that exhibits these properties and makes use of benign reagents without the use of specialized equipment. By exposing Pd powder to dilute hydrogen in nitrogen gas, sacrificial surface PdH is formed along with a controlled amount of dilute interstitial hydride. The lattice expansion that occurs in Pd under higher H2 partial pressures is avoided. Once the flow of reagent gas is terminated, addition of metal salts facilitates controlled, electroless deposition of an overlayer of subnanometer thickness. This process can be cycled to create thicker layers. The approach is carried out under ambient processing conditions, which is an advantage over some forms of atomic layer deposition. The hydride-mediated reaction is electroless in that it has no need for connection to an external source of electrical current and is thus amenable to deposition on high-surface-area substrates having rich, nanoscale topography as well as on insulator-supported catalyst particles. STEM-EDS measurements show that conformal Rh and Pt surface layers can be formed on Pd powder with this method. A growth model based on energy-resolved XPS depth profiling of Rh-modified Pd powder is in general agreement. After two cycles, deposits are consistent with 70-80% coverage and a surface layer with a thickness from 4 to 8 Å.

  15. Adsorption of alkali, alkaline-earth, simple and 3d transition metal, and nonmetal atoms on monolayer MoS{sub 2}

    SciTech Connect

    Li, X. D.; Fang, Y. M.; Wu, S. Q. E-mail: wsq@xmu.edu.cn; Zhu, Z. Z. E-mail: wsq@xmu.edu.cn

    2015-05-15

    Single adsorption of different atoms on pristine two-dimensional monolayer MoS{sub 2} have been systematically investigated by using density functional calculations with van der Waals correction. The adatoms cover alkali metals, alkaline earth metals, main group metal, 3d-transition metals, coinage metal and nonmetal atoms. Depending on the adatom type, metallic, semimetallic or semiconducting behavior can be found in direct bandgap monolayer MoS{sub 2}. Additionally, local or long-range magnetic moments of two-dimensional MoS{sub 2} sheet can also attained through the adsorption. The detailed atomic-scale knowledge of single adsorption on MoS{sub 2} monolayer is important not only for the sake of a theoretical understanding, but also device level deposition technological application.

  16. Understanding Atom Probe Tomography of Oxide-Supported Metal Nanoparticles by Correlation with Atomic-Resolution Electron Microscopy and Field Evaporation Simulation.

    PubMed

    Devaraj, Arun; Colby, Robert; Vurpillot, François; Thevuthasan, Suntharampillai

    2014-04-17

    Oxide-supported metal nanoparticles are widely used in heterogeneous catalysis. The increasingly detailed design of such catalysts necessitates three-dimensional characterization with high spatial resolution and elemental selectivity. Laser-assisted atom probe tomography (APT) is uniquely suited to the task but faces challenges with the evaporation of metal/insulator systems. Correlation of APT with aberration-corrected scanning transmission electron microscopy (STEM), for Au nanoparticles embedded in MgO, reveals preferential evaporation of the MgO and an inaccurate assessment of nanoparticle composition. Finite element field evaporation modeling is used to illustrate the evolution of the evaporation front. Nanoparticle composition is most accurately predicted when the MgO is treated as having a locally variable evaporation field, indicating the importance of considering laser-oxide interactions and the evaporation of various molecular oxide ions. These results demonstrate the viability of APT for analysis of oxide-supported metal nanoparticles, highlighting the need for developing a theoretical framework for the evaporation of heterogeneous materials.

  17. Polymerization of a divalent/tetravalent metal-storing atom-mimicking dendrimer

    PubMed Central

    Albrecht, Ken; Hirabayashi, Yuki; Otake, Masaya; Mendori, Shin; Tobari, Yuta; Azuma, Yasuo; Majima, Yutaka; Yamamoto, Kimihisa

    2016-01-01

    The phenylazomethine dendrimer (DPA) has a layer-by-layer electron density gradient that is an analog of the Bohr atom (atom mimicry). In combination with electron pair mimicry, the polymerization of this atom-mimicking dendrimer was achieved. The valency of the mimicked atom was controlled by changing the chemical structure of the dendrimer. By mimicking a divalent atom, a one-dimensional (1D) polymer was obtained, and by using a planar tetravalent atom mimic, a 2D polymer was obtained. These poly(dendrimer) polymers could store Lewis acids (SnCl2) in their unoccupied orbitals, thus indicating that these poly(dendrimer) polymers consist of a series of nanocontainers. PMID:27957538

  18. Polymerization of a divalent/tetravalent metal-storing atom-mimicking dendrimer.

    PubMed

    Albrecht, Ken; Hirabayashi, Yuki; Otake, Masaya; Mendori, Shin; Tobari, Yuta; Azuma, Yasuo; Majima, Yutaka; Yamamoto, Kimihisa

    2016-12-01

    The phenylazomethine dendrimer (DPA) has a layer-by-layer electron density gradient that is an analog of the Bohr atom (atom mimicry). In combination with electron pair mimicry, the polymerization of this atom-mimicking dendrimer was achieved. The valency of the mimicked atom was controlled by changing the chemical structure of the dendrimer. By mimicking a divalent atom, a one-dimensional (1D) polymer was obtained, and by using a planar tetravalent atom mimic, a 2D polymer was obtained. These poly(dendrimer) polymers could store Lewis acids (SnCl2) in their unoccupied orbitals, thus indicating that these poly(dendrimer) polymers consist of a series of nanocontainers.

  19. Magnetic properties of Mg12O12 nanocage doped with transition metal atoms (Mn, Fe, Co and Ni): DFT study

    NASA Astrophysics Data System (ADS)

    Javan, Masoud Bezi

    2015-07-01

    Binding energy of the Mg12O12 nanocage doped with transition metals (TM=Mn, Fe, Co and Ni) in endohedrally, exohedrally and substitutionally forms were studied using density functional theory with the generalized gradient approximation exchange-correlation functional along 6 different paths inside and outside of the Mg12O12 nanocage. The most stable structures were determined with full geometry optimization near the minimum of the binding energy curves of all the examined paths inside and outside of the Mg12O12 nanocage. The results reveal that for all stable structures, the Ni atom has a larger binding energy than the other TM atoms. It is also found that for all complexes additional peaks contributed by TM-3d, 4s and 4p states appear in the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gap of the host MgO cluster. The mid-gap states are mainly due to the hybridization between TM-3d, 4s and 4p orbitals and the cage π orbitals. The magnetic moment of the endohedrally doped TM atoms in the Mg12O12 are preserved to some extent due to the interaction between the TM and Mg12O12 nanocage, in contrast to the completely quenched magnetic moment of the Fe and Ni atoms in the Mg11(TM)O12 complexes. Furthermore, charge population analysis shows that charge transfer occurs from TM atom to the cage for endohedrally and substitutionally doping.

  20. Determination of metal atoms incorporated in molecular intermediates: an STM study of acetylide on Ag(1 1 0)

    NASA Astrophysics Data System (ADS)

    Guo, X.-C.; Madix, R. J.

    2004-08-01

    Many inorganic molecular intermediates, such as imide, nitrate, and sulfite, incorporate a stoichiometric number of added metal atoms into their structures on Ag(1 1 0) or Cu(1 1 0). In this paper an example of such general behavior is illustrated with an organic molecular intermediate--acetylide (C 2) on Ag(1 1 0). Acetylide is produced by reacting acetylene with oxygen atoms on the Ag(1 1 0)- p(2 × 1)-O surface. Acetylides form row structures along the <1 1¯ 0> axis, which, as coverage increases, are compressed along the <0 0 1> axis to form nominal " p(2 × 2)", " p(2 × 3)", " p(2 × 1)", and " p(14 × 1)" structures. The final acetylide structure incorporates 0.55 ML silver atoms, which may be released upon titration with acetic acid. A buckled structure is proposed where acetylide bonds to two added silver atoms in a linear configuration in the trough along the <1 1¯ 0> axis with seven equally spaced silver atoms in a p(13 × 1) unit cell.

  1. Selective electrodesorption based atomic layer deposition (SEBALD): a novel electrochemical route to deposit metal clusters on Ag(111).

    PubMed

    Innocenti, M; Bellandi, S; Lastraioli, E; Loglio, F; Foresti, M L

    2011-09-20

    The possibility of synergic effects of some metals on the catalytic activity of silver led us to study the way to perform controlled deposition on silver. In fact, many metals of technological interest such as Co, Ni, and Fe cannot be deposited at underpotential on silver, and any attempt to control the deposition at overpotential, even at potentials slightly negative of the Nernst value, did not allow an effective control. However, due to the favorable energy gain involved in the formation of the corresponding sulfides, these metals can be deposited at underpotential on sulfur covered silver. The deposition is surface limited and the successive electrodesorption of sulfur leaves confined clusters of metals. The method can also be used to obtain metal clusters of different size. In fact, the alternate underpotential deposition of elements that form a compound is the basis of the electrochemical atomic layer epitaxy (ECALE), and the reiteration of the basic cycle allows us to obtain sulfide deposits whose thickness increases with the number of cycles. Therefore, the successive selective desorption of sulfur leaves increasing amounts of metals.

  2. Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Elliott, S. D.; Dey, G.; Maimaiti, Y.

    2017-02-01

    Reaction cycles for the atomic layer deposition (ALD) of metals are presented, based on the incomplete data that exist about their chemical mechanisms, particularly from density functional theory (DFT) calculations. ALD requires self-limiting adsorption of each precursor, which results from exhaustion of adsorbates from previous ALD pulses and possibly from inactivation of the substrate through adsorption itself. Where the latter reaction does not take place, an "abbreviated cycle" still gives self-limiting ALD, but at a much reduced rate of deposition. Here, for example, ALD growth rates are estimated for abbreviated cycles in H2-based ALD of metals. A wide variety of other processes for the ALD of metals are also outlined and then classified according to which a reagent supplies electrons for reduction of the metal. Detailed results on computing the mechanism of copper ALD by transmetallation are summarized and shown to be consistent with experimental growth rates. Potential routes to the ALD of other transition metals by using complexes of non-innocent diazadienyl ligands as metal sources are also evaluated using DFT.

  3. Study of local atomic and electronic structure in glassy metallic alloys. Progress report, December 1, 1979-November 1, 1980

    SciTech Connect

    Messmer, R.P.; Wong, J.

    1980-01-01

    During the first reporting period, March 1, 1979-December 1, 1979, small clusters such as Fe/sub 4/, Ni/sub 4/, Ni/sub 2/Fe/sub 2/ alone and containing the metalloid atoms P and B were investigated. The effect of P and B on the magnetic moment of the clusters was investigated and found to parallel the known experimental trend. Significant metal-metalloid bonding was found in all the clusters studied. During the present reporting period a detailed analysis of the bonding in these small clusters was carried out. As a result of this detailed analysis a very significant conclusion has been reached: there are preferential metal-metalloid interactions which are predicted on the basis of the calculations. Room temperature extended x-ray absorption fine structure (EXAFS) spectra above the K absorption edge of metal constituents in the following metal-metalloid and metal-metal glasses have been measured in the February and June 1980 runs at Stanford Synchrotron Radiation Laboratory: Fe/sub 1-x/B/sub x/, (FeNi)/sub 1-x/B/sub x/, Ni/sub 1-x/B/sub x/; Zr/sub 1-x/M/sub x/ (M- Fe, Co, Ni and Cu) and Nb/sub 1-x/Ni/sub x/.

  4. Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations.

    PubMed

    Elliott, S D; Dey, G; Maimaiti, Y

    2017-02-07

    Reaction cycles for the atomic layer deposition (ALD) of metals are presented, based on the incomplete data that exist about their chemical mechanisms, particularly from density functional theory (DFT) calculations. ALD requires self-limiting adsorption of each precursor, which results from exhaustion of adsorbates from previous ALD pulses and possibly from inactivation of the substrate through adsorption itself. Where the latter reaction does not take place, an "abbreviated cycle" still gives self-limiting ALD, but at a much reduced rate of deposition. Here, for example, ALD growth rates are estimated for abbreviated cycles in H2-based ALD of metals. A wide variety of other processes for the ALD of metals are also outlined and then classified according to which a reagent supplies electrons for reduction of the metal. Detailed results on computing the mechanism of copper ALD by transmetallation are summarized and shown to be consistent with experimental growth rates. Potential routes to the ALD of other transition metals by using complexes of non-innocent diazadienyl ligands as metal sources are also evaluated using DFT.

  5. Investigating the atomic level influencing factors of glass forming ability in NiAl and CuZr metallic glasses.

    PubMed

    Sedighi, Sina; Kirk, Donald Walter; Singh, Chandra Veer; Thorpe, Steven John

    2015-09-21

    Bulk metallic glasses are a relatively new class of amorphous metal alloy which possess unique mechanical and magnetic properties. The specific concentrations and combinations of alloy elements needed to prevent crystallization during melt quenching remains poorly understood. A correlation between atomic properties that can explain some of the previously identified glass forming ability (GFA) anomalies of the NiAl and CuZr systems has been identified, with these findings likely extensible to other transition metal-transition metal and transition metal-metalloid (TM-M) alloy classes as a whole. In this work, molecular dynamics simulation methods are utilized to study thermodynamic, kinetic, and structural properties of equiatomic CuZr and NiAl metallic glasses in an attempt to further understand the underlying connections between glass forming ability, nature of atomic level bonding, short and medium range ordering, and the evolution of structure and relaxation properties in the disordered phase. The anomalous breakdown of the fragility parameter as a useful GFA indicator in TM-M alloy systems is addressed through an in-depth investigation of bulk stiffness properties and the evolution of (pseudo)Gruneisen parameters over the quench domain, with the efficacy of other common glass forming ability indicators similarly being analyzed through direct computation in respective CuZr and NiAl systems. Comparison of fractional liquid-crystal density differences in the two systems revealed 2-3 times higher values for the NiAl system, providing further support for its efficacy as a general purpose GFA indicator.

  6. Controlling magnetism of MoS2 sheets by embedding transition-metal atoms and applying strain.

    PubMed

    Zhou, Yungang; Su, Qiulei; Wang, Zhiguo; Deng, Huiqiu; Zu, Xiaotao

    2013-11-14

    Prompted by recent experimental achievement of transition metal (TM) atoms substituted in MoS2 nanostructures during growth or saturating existing vacancies (Sun et al., ACS Nano, 2013, 7, 3506; Deepak et al., J. Am. Chem. Soc., 2007, 129, 12549), we explored, via density functional theory, the magnetic properties of a series of 3d TM atoms substituted in a MoS2 sheet, and found that Mn, Fe, Co, Ni, Cu and Zn substitutions can induce magnetism in the MoS2 sheet. The localizing unpaired 3d electrons of TM atoms respond to the introduction of a magnetic moment. Depending on the species of TM atoms, the substituted MoS2 sheet can be a metal, semiconductor or half-metal. Remarkably, the applied elastic strain can be used to control the strength of the spin-splitting of TM-3d orbitals, leading to an effective manipulation of the magnetism of the TM-substituted MoS2 sheet. We found that the magnetic moment of the Mn- and Fe-substituted MoS2 sheets can monotonously increase with the increase of tensile strain, while the magnetic moment of Co-, Ni-, Cu- and Zn-substituted MoS2 sheets initially increases and then decreases with the increase of tensile strain. An instructive mechanism was proposed to qualitatively explain the variation of magnetism with elastic strain. The finding of the magnetoelastic effect here is technologically important for the fabrication of strain-driven spin devices on MoS2 nanostructures, which allows us to go beyond the current scope limited to the spin devices within graphene and BN-based nanostructures.

  7. Ionic liquid-based extraction followed by graphite-furnace atomic absorption spectrometry for the determination of trace heavy metals in high-purity iron metal.

    PubMed

    Matsumiya, Hiroaki; Kato, Tatsuya; Hiraide, Masataka

    2014-02-01

    The analysis of high-purity materials for trace impurities is an important and challenging task. The present paper describes a facile and sensitive method for the determination of trace heavy metals in high-purity iron metal. Trace heavy metals in an iron sample solution were rapidly and selectively preconcentrated by the extraction into a tiny volume of an ionic liquid [1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide] for the determination by graphite-furnace atomic absorption spectrometry (GFAAS). A nitrogen-donating neutral ligand, 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ), was found to be effective in the ionic liquid-based selective extraction, allowing the nearly complete (~99.8%) elimination of the iron matrix. The combination with the optimized GFAAS was successful. The detectability reached sub-μg g(-1) levels in iron metal. The novel use of TPTZ in ionic liquid-based extraction followed by GFAAS was successfully applied to the determination of traces of Co, Ni, Cu, Cd, and Pb in certified reference materials for high-purity iron metal.

  8. Nutrients, heavy metals and microbial communities co-driven distribution of antibiotic resistance genes in adjacent environment of mariculture.

    PubMed

    Zhao, Zelong; Wang, Jing; Han, Ying; Chen, Jingwen; Liu, Guangfei; Lu, Hong; Yan, Bin; Chen, Shiaoshing

    2017-01-01

    With the rapid development of aquaculture, the large amounts of pollutants were discharged into the aquatic environment, where the detected antibiotic resistance genes (ARGs) have drawn increasing attention due to their potential threats to ecological environment and human health. Thus, the impact of mariculture on ARGs was assessed and the underlying mechanism of their propagation was explained. Sediments from eight sampling sites were collected along a mariculture drainage ditch, and the sediment in Yellow River Delta National Park was used as a non-mariculture control. Microbial ARGs qPCR array and illumina sequencing of 16S rRNA gene were applied to examine the changing patterns of ARGs and bacterial communities. Results showed that 18 ARGs (3 fluoroquinolone, 1 aminoglycoside, 3 macrolide-lincosamide-streptogramin B, 2 tetracycline, and 9 beta-lactam resistance genes) were influenced by mariculture, and ARGs abundance and diversity were significantly increased in mariculture sediments (p < 0.05). A remarkable shift in bacterial community structure and composition was also observed. The abundance of most of ARGs were significantly decreased in the estuary samples, implying that seawater had a significant dilution effect on the ARGs emission from the mariculture sites. Partial redundancy analysis showed that nutrients, heavy metals, and bacteria communities might directly and indirectly contribute to ARGs propagation, suggesting that the profile and dissemination of ARGs were driven by the combined effects of multiple factors in mariculture-impacted sites.

  9. Modeling STM tips by single absorbed atoms on W(100) films: 3d, 4d and 5d transition metal atoms

    NASA Astrophysics Data System (ADS)

    Hofer, Werner; Redinger, Josef; Kresse, Georg; Podloucky, Raimund

    2000-03-01

    In order to provide comprehensive data on the electronic structure of realistic STM-tips we have calculated W(100) films with single 3d, 4d and 5d transition metal apex atoms by first principles molecular dynamics and full potential methods. Molecular dynamics using ultrasoft pseudopotentials (VASP) has been used to determine the relaxation of the surface layers. The electronic structure of the relaxed film has been calculated by a first principles full potential method with two-dimensional boundary conditions (FLEUR), which seems most suitable to reproduce subtle surface effects. The results suggest that the chemical nature of the tip apex determines to a high degree achievable corrugations and that correct results for the current and corrugation values in a perturbation approach can only be obtained by including the full electronic structure of the tip.

  10. Correlating the Energetics and Atomic Motions of the Metal-Insulator Transition of M1 Vanadium Dioxide

    PubMed Central

    Booth, Jamie M.; Drumm, Daniel W.; Casey, Phil S.; Smith, Jackson S.; Seeber, Aaron J.; Bhargava, Suresh K.; Russo, Salvy P.

    2016-01-01

    Materials that undergo reversible metal-insulator transitions are obvious candidates for new generations of devices. For such potential to be realised, the underlying microscopic mechanisms of such transitions must be fully determined. In this work we probe the correlation between the energy landscape and electronic structure of the metal-insulator transition of vanadium dioxide and the atomic motions occurring using first principles calculations and high resolution X-ray diffraction. Calculations find an energy barrier between the high and low temperature phases corresponding to contraction followed by expansion of the distances between vanadium atoms on neighbouring sub-lattices. X-ray diffraction reveals anisotropic strain broadening in the low temperature structure’s crystal planes, however only for those with spacings affected by this compression/expansion. GW calculations reveal that traversing this barrier destabilises the bonding/anti-bonding splitting of the low temperature phase. This precise atomic description of the origin of the energy barrier separating the two structures will facilitate more precise control over the transition characteristics for new applications and devices. PMID:27211303

  11. Atomic-scale dynamics of a model glass-forming metallic liquid: Dynamical crossover, dynamical decoupling, and dynamical clustering

    NASA Astrophysics Data System (ADS)

    Jaiswal, Abhishek; Egami, Takeshi; Zhang, Yang

    2015-04-01

    The phase behavior of multicomponent metallic liquids is exceedingly complex because of the convoluted many-body and many-elemental interactions. Herein, we present systematic studies of the dynamical aspects of a model ternary metallic liquid Cu40Zr51Al9 using molecular dynamics simulations with embedded atom method. We observed a dynamical crossover from Arrhenius to super-Arrhenius behavior in the transport properties (self diffusion coefficient, self relaxation time, and shear viscosity) bordered at Tx˜1300 K. Unlike in many molecular and macromolecular liquids, this crossover phenomenon occurs well above the melting point of the system (Tm˜900 K) in the equilibrium liquid state; and the crossover temperature Tx is roughly twice of the glass-transition temperature of the system (Tg). Below Tx, we found the elemental dynamics decoupled and the Stokes-Einstein relation broke down, indicating the onset of heterogeneous spatially correlated dynamics in the system mediated by dynamic communications among local configurational excitations. To directly characterize and visualize the correlated dynamics, we employed a nonparametric, unsupervised machine learning technique and identified dynamical clusters of atoms with similar atomic mobility. The revealed average dynamical cluster size shows an accelerated increase below Tx and mimics the trend observed in other ensemble averaged quantities that are commonly used to quantify the spatially heterogeneous dynamics such as the non-Gaussian parameter α2 and the four-point correlation function χ4.

  12. Subnanometer three-dimensional atom-probe investigation of segregation at MgO/Cu ceramic/metal heterophase interfaces.

    PubMed

    Sebastian, J T; Rüsing, J; Hellman, O C; Seidman, D N; Vriesendorp, W; Kooi, B J; De Hosson JTh

    2001-10-01

    Three-dimensional atom-probe (3DAP) microscopy has been applied to the study of segregation at ceramic/metal (C/M) interfaces. In this article, results on the MgO/Cu(X) (where X = Ag or Sb) systems are summarized. Nanometer-size MgO precipitates with atomically clean and atomically sharp interfaces were prepared in these systems by internal oxidation. Segregation of the ternary component (Ag or Sb) at the MgO/Cu heterophase interface was enhanced by extended low-temperature anneals. Magnesia precipitates in the 3DAP reconstructions were delineated as isoconcentration surfaces, and segregation of each ternary component at the C/M interfaces was analyzed with the proximity histogram method developed at Northwestern University. This method allows the direct extraction of the Gibbsian interfacial excess of solute at the C/M interfaces from the experimental data. A value of (3.2+/-2.0) x 10(17)m(-2) at 500 degrees C is obtained for the segregation of Ag at a MgO/Cu(Ag) interface, while a value of (2.9+/-0.9) x 10(18) m(-2) at 500 degrees C is obtained for the segregation of Sb at a MgO/Cu(Sb) interface. The larger Gibbsian excess for Sb segregation at this ceramic/metal heterophase interface is most likely due to the so-called pdeltaV effect.

  13. Atomic-scale dynamics of a model glass-forming metallic liquid: Dynamical crossover, dynamical decoupling, and dynamical clustering

    DOE PAGES

    Jaiswal, Abhishek; Egami, Takeshi; Zhang, Yang

    2015-04-01

    The phase behavior of multi-component metallic liquids is exceedingly complex because of the convoluted many-body and many-elemental interactions. Herein, we present systematic studies of the dynamic aspects of such a model ternary metallic liquid Cu40Zr51Al9 using molecular dynamics simulation with embedded atom method. We observed a dynamical crossover from Arrhenius to super-Arrhenius behavior in the transport properties (diffusion coefficient, relaxation times, and shear viscosity) bordered at Tx ~1300K. Unlike in many molecular and macromolecular liquids, this crossover phenomenon occurs in the equilibrium liquid state well above the melting temperature of the system (Tm ~ 900K), and the crossover temperature ismore » roughly twice of the glass-transition temperature (Tg). Below Tx, we found the elemental dynamics decoupled and the Stokes-Einstein relation broke down, indicating the onset of heterogeneous spatially correlated dynamics in the system mediated by dynamic communications among local configurational excitations. To directly characterize and visualize the correlated dynamics, we employed a non-parametric, unsupervised machine learning technique and identified dynamical clusters of atoms with similar atomic mobility. The revealed average dynamical cluster size shows an accelerated increase below Tx and mimics the trend observed in other ensemble averaged quantities that are commonly used to quantify the spatially heterogeneous dynamics such as the non-Gaussian parameter and the four-point correlation function.« less

  14. Non-destructive functionalisation for atomic layer deposition of metal oxides on carbon nanotubes: effect of linking agents and defects

    NASA Astrophysics Data System (ADS)

    Kemnade, N.; Shearer, C. J.; Dieterle, D. J.; Cherevan, A. S.; Gebhardt, P.; Wilde, G.; Eder, D.

    2015-02-01

    The hybridisation of metal oxides and nanocarbons has created a promising new class of functional materials for environmental and sustainable energy applications. The performance of such hybrids can be further improved by rationally designing interfaces and morphologies. Atomic layer deposition (ALD) is among the most powerful techniques for the controlled deposition of inorganic compounds, due to its ability to form conformal coatings on porous substrates at low temperatures with high surface sensitivity and atomic control of film thickness. The hydrophobic nature of the nanocarbon surface has so far limited the applicability of ALD on CNTs. Herein we investigate the role of structural defects in CNTs, both intrinsic and induced by acid treatment, on coverage, uniformity and crystallinity of ZnO coatings. Furthermore, we demonstrate the potential of small aromatic molecules, including benzyl alcohol (BA), naphthalene carboxylic acid (NA) and pyrene carboxylic acid (PCA), as active nucleation sites and linking agents. Importantly, only PCA exhibits sufficiently strong interactions with the pristine CNT surface to withstand desorption under reaction conditions. Thus, PCA enables a versatile and non-destructive alternative route for the deposition of highly uniform metal oxide coatings onto pristine CNTs via ALD over a wide temperature range and without the typical surface corrosion induced by covalent functionalisation. Importantly, preliminary tests demonstrated that the improved morphology obtained with PCA has indeed considerably increased the hybrid's photocatalytic activity towards hydrogen evolution via sacrificial water splitting. The concept demonstrated in this work is transferable to a wide range of other inorganic compounds including metal oxides, metal (oxy)nitrides and metal chalcogenides on a variety of nanocarbons.The hybridisation of metal oxides and nanocarbons has created a promising new class of functional materials for environmental and

  15. Alkali metal atoms in strong magnetic fields: "Guiding" atomic transitions foretell the characteristics of all transitions of the D1 line

    NASA Astrophysics Data System (ADS)

    Sargsyan, A.; Hakhumyan, G.; Papoyan, A.; Sarkisyan, D.

    2015-03-01

    It has been shown that the D1 line of atomic vapors of alkali metals excited by π-polarized radiation in a strong transverse magnetic field includes specific "guiding" (indicating) atomic transitions between the magnetic sublevels of the hyperfine structure. The dependence of the frequency shift of the guiding transitions on the magnetic field, as well as on their dipole moments, is asymptotic for all other transitions. An experiment with a nanocell with Rb vapor with a thickness of half the wavelength (λ/2 method) for ensuring a sub-Doppler spectral resolution has completely confirmed the presence of guiding transitions. Two groups of six transitions for 85Rb and two groups of four transitions for 87Rb have been detected in the absorption spectra in magnetic fields above 4 kG. A guiding transition has been identified in each of four groups. Four transitions forbidden at B = 0 have been also detected; with an increase in the magnetic field, their probabilities also approach the probabilities of the guiding transitions.

  16. Atomized spraying of liquid metal droplets on desired substrate surfaces as a generalized way for ubiquitous printed electronics

    NASA Astrophysics Data System (ADS)

    Zhang, Qin; Gao, Yunxia; Liu, Jing

    2014-09-01

    A direct electronics printing technique through atomized spraying for patterning room-temperature liquid metal droplets on desired substrate surfaces is proposed and experimentally demonstrated for the first time. This method is highly flexible and capable of fabricating electronic components on various target objects, with either flat or rough surfaces, made of different materials, or having different orientations from 2D to 3D geometrical configurations. With a pre-designed mask, the liquid metal ink can be directly deposited on the substrate to form various specific patterns which lead to the rapid prototyping of electronic devices. Further, extended printing strategies were also suggested to illustrate the adaptability of the method. For example, it can be used for making transparent conductive film with an optical transmittance of 47 % and a sheet resistance of 5.167Ω/□ due to natural porous structure. Different from the former direct writing technology where large surface tension and poor adhesion between the liquid metal and the substrate often impede the flexible printing process, the liquid metal here no longer needs to be pre-oxidized to guarantee its applicability on target substrates. One critical mechanism was that the atomized liquid metal microdroplets can be quickly oxidized in the air due to its large specific surface area, resulting in a significant increase of the adhesion capacity and thus firm deposition of the ink to the substrate. This study paved a generalized way for pervasively and directly printing electronics on various substrates which are expected to be significant in a wide spectrum of electrical engineering areas.

  17. Colloidal europium nanoparticles via a solvated metal atom dispersion approach and their surface enhanced Raman scattering studies.

    PubMed

    Urumese, Ancila; Jenjeti, Ramesh Naidu; Sampath, S; Jagirdar, Balaji R

    2016-08-15

    Chemistry of lanthanide metals in their zerovalent state at the nanoscale remains unexplored due to the high chemical reactivity and difficulty in synthesizing nanoparticles by conventional reduction methods. In the present study, europium(0) nanoparticles, the most reactive of all the rare earth metals have been synthesized by solvated metal atom dispersion (SMAD) method using hexadecyl amine as the capping agent. The as-prepared europium nanoparticles show surface Plasmon resonance (SPR) band in the visible region of the electromagnetic spectrum. This lead to the investigation of its surface enhanced Raman scattering (SERS) using visible light excitation source. The SERS activity of europium nanoparticles has been followed using 4-aminothiophenol and biologically important molecules such as hemoglobin and Cyt-c as the analytes. This is the first example of lanthanide metal nanoparticles as SERS substrate which can possibly be extended to other rare-earth metals. Since hemoglobin absorbs in the visible region, the use of visible light excitation source leads to surface enhanced resonance Raman spectroscopy (SERRS). The interaction of biomolecules with Eu(0) has been followed using FT-IR and UV-visible spectroscopy techniques. The results indicate that there is no major irreversible change in the structure of biomolecules upon interaction with europium nanoparticles.

  18. Determination of heavy metal contents by atomic absorption spectroscopy (AAS) in some medicinal plants from Pakistani and Malaysian origin.

    PubMed

    Akram, Sobia; Najam, Rahila; Rizwani, Ghazala H; Abbas, Syed Atif

    2015-09-01

    This study depicts a profile of existence of heavy metals (Cu, Ni, Zn, Cd, Hg, Mn, Fe, Na, Ca, and Mg) in some important herbal plants like (H. Integrifolia, D. regia, R. communis, C. equisetifolia, N. oleander, T. populnea, M. elengi, H. schizopetalus, P. pterocarpum) from Pakistan and an antidiabetic Malaysian herbal drug product containing (Punica granatum L. (Mast) Hook, Momordica charantia L., Tamarindus indica L., Lawsonia inermis L.) using atomic absorption spectrophotometer. Heavy metals in these herbal plants and Malaysian product were in the range of 0.02-0.10 ppm of Cu, 0.00-0.02 ppm of Ni, 0.02-0.29 ppm of Zn, 0.00-0.04 ppm of Cd, 0.00-1.33 ppm of Hg, 0.00-0.54 ppm of Mn, 0.22-3.16 ppm of Fe, 0.00-9.17 ppm of Na, 3.27-15.63 ppm of Ca and 1.85-2.03 ppm of Mg. All the metals under study were within the prescribed limits except mercury. Out of 10 medicinal plants/product under study 07 were beyond the limit of mercury permissible limits. Purpose of this study is to determine heavy metals contents in selected herbal plants and Malaysian product, also to highlight the health concerns related to the presence of toxic levels of heavy metals.

  19. The Determination of Trace Metals in Saline Waters and Biological Tissues Using the Heated Graphite Atomizer

    NASA Technical Reports Server (NTRS)

    Segar, D. A.

    1971-01-01

    A selective, volatalization technique utilizing the heated graphite atomizer atomic absorption technique has been developed for the analysis of iron in sea water. A similar technique may be used to determine vanadium, copper, nickel and cobalt in saline waters when their concentrations are higher than those normally encountered'in unpolluted sea waters. A preliminary solvent extraction using ammonium pyrolidine dithiocarbamate and methyl iso-butyl ketone permits the determination of a number of elements including iron, copper, zinc, nickel, cobalt and lead in sea water. The heated graphite atomized technique has also been applied to the determination of a range of trace transition elements in marine plant and animal tissues.

  20. Atomically Thin B doped g-C3N4 Nanosheets: High-Temperature Ferromagnetism and calculated Half-Metallicity

    PubMed Central

    Gao, Daqiang; Liu, Yonggang; Liu, Peitao; Si, Mingsu; Xue, Desheng

    2016-01-01

    Since the graphitic carbon nitride (g-C4N3), which can be seen as C-doped graphitic-C3N4 (g-C3N4), was reported to display ferromagnetic ground state and intrinsic half-metallicity (Du et al., PRL,108,197207,2012), it has attracted numerous research interest to tune the electronic structure and magnetic properties of g-C3N4 due to their potential applications in spintronic devices. In this paper, we reported the experimentally achieving of high temperature ferromagnetism in metal-free ultrathin g-C3N4 nanosheets by introducing of B atoms. Further, first-principles calculation results revealed that the current flow in such a system was fully spin-polarized and the magnetic moment was mainly attributed to the p orbital of N atoms in B doped g-C3N4 monolayer, giving the theoretic evidence of the ferromagnetism and half-metallicity. Our finding provided a new perspective for B doped g-C3N4 spintronic devices in future. PMID:27762348

  1. The Direct Calculation of Solid and Liquid Free Energies of Metals and Alloys Using the Embedded Atom Method

    NASA Astrophysics Data System (ADS)

    Song, Xueyu; Morris, James

    2003-03-01

    We present a method of directly and accurately calculating the free energy of metals and alloys, directly from models such as the Embedded Atom Method (EAM). An effective pair potential is defined, and used in an extended Weeks-Chandler-Andersen (WCA) approach. An effective hard-sphere density is defined, and perturbations from the hard-sphere limit are calculated using the pair correlation functions calculated from density functional theory. Calculations using the Mei and Davenport EAM potential for Al, with the modifications of Sturgeon and Laird, demonstrate the accuracy of the approach for both the liquid and solid phases by comparison with simulations. These results are the first step toward the direct calculation of the solid-liquid interfacial free energy for metallic systems, an important parameter for classical nucleation theory and for solidification dynamics. Our recent simulation results for the interfacial free energy provides an important test of the inhomogeneous theory. We also present preliminary results for binary systems, where the direct calculation of phase diagrams based upon the inter-atomic potentials will be compared with simulations. The approach will also allow for the direct calculation of the properties of under-cooled liquid metals and alloys.

  2. Atomically Thin B doped g-C3N4 Nanosheets: High-Temperature Ferromagnetism and calculated Half-Metallicity

    NASA Astrophysics Data System (ADS)

    Gao, Daqiang; Liu, Yonggang; Liu, Peitao; Si, Mingsu; Xue, Desheng

    2016-10-01

    Since the graphitic carbon nitride (g-C4N3), which can be seen as C-doped graphitic-C3N4 (g-C3N4), was reported to display ferromagnetic ground state and intrinsic half-metallicity (Du et al., PRL,108,197207,2012), it has attracted numerous research interest to tune the electronic structure and magnetic properties of g-C3N4 due to their potential applications in spintronic devices. In this paper, we reported the experimentally achieving of high temperature ferromagnetism in metal-free ultrathin g-C3N4 nanosheets by introducing of B atoms. Further, first-principles calculation results revealed that the current flow in such a system was fully spin-polarized and the magnetic moment was mainly attributed to the p orbital of N atoms in B doped g-C3N4 monolayer, giving the theoretic evidence of the ferromagnetism and half-metallicity. Our finding provided a new perspective for B doped g-C3N4 spintronic devices in future.

  3. Atomically Thin B doped g-C3N4 Nanosheets: High-Temperature Ferromagnetism and calculated Half-Metallicity.

    PubMed

    Gao, Daqiang; Liu, Yonggang; Liu, Peitao; Si, Mingsu; Xue, Desheng

    2016-10-20

    Since the graphitic carbon nitride (g-C4N3), which can be seen as C-doped graphitic-C3N4 (g-C3N4), was reported to display ferromagnetic ground state and intrinsic half-metallicity (Du et al., PRL,108,197207,2012), it has attracted numerous research interest to tune the electronic structure and magnetic properties of g-C3N4 due to their potential applications in spintronic devices. In this paper, we reported the experimentally achieving of high temperature ferromagnetism in metal-free ultrathin g-C3N4 nanosheets by introducing of B atoms. Further, first-principles calculation results revealed that the current flow in such a system was fully spin-polarized and the magnetic moment was mainly attributed to the p orbital of N atoms in B doped g-C3N4 monolayer, giving the theoretic evidence of the ferromagnetism and half-metallicity. Our finding provided a new perspective for B doped g-C3N4 spintronic devices in future.

  4. Atomically precise arrays of fluorescent silver clusters: a modular approach for metal cluster photonics on DNA nanostructures.

    PubMed

    Copp, Stacy M; Schultz, Danielle E; Swasey, Steven; Gwinn, Elisabeth G

    2015-03-24

    The remarkable precision that DNA scaffolds provide for arraying nanoscale optical elements enables optical phenomena that arise from interactions of metal nanoparticles, dye molecules, and quantum dots placed at nanoscale separations. However, control of ensemble optical properties has been limited by the difficulty of achieving uniform particle sizes and shapes. Ligand-stabilized metal clusters offer a route to atomically precise arrays that combine desirable attributes of both metals and molecules. Exploiting the unique advantages of the cluster regime requires techniques to realize controlled nanoscale placement of select cluster structures. Here we show that atomically monodisperse arrays of fluorescent, DNA-stabilized silver clusters can be realized on a prototypical scaffold, a DNA nanotube, with attachment sites separated by <10 nm. Cluster attachment is mediated by designed DNA linkers that enable isolation of specific clusters prior to assembly on nanotubes and preserve cluster structure and spectral purity after assembly. The modularity of this approach generalizes to silver clusters of diverse sizes and DNA scaffolds of many types. Thus, these silver cluster nano-optical elements, which themselves have colors selected by their particular DNA templating oligomer, bring unique dimensions of control and flexibility to the rapidly expanding field of nano-optics.

  5. Investigation of atomic anti-site disorder and ferrimagnetic order in the half-metallic Heusler alloy Mn2VGa.

    PubMed

    Ramesh Kumar, K; Harish Kumar, N; Babu, P D; Venkatesh, S; Ramakrishnan, S

    2012-08-22

    The band structure calculation for the compound Mn(2)VGa carried out using the plane wave self-consistent field package with generalized gradient approximation shows that the compound is nearly half-metallic at the equilibrium lattice parameter. However, theoretical investigations have shown that a certain percentage of atomic anti-site disorder can destroy the half-metallic nature of the sample. Hence it is important to quantify the site disorder in these systems. We have deduced the percentage of atomic anti-site disorder from the refinement of the higher angle room temperature (300 K) neutron diffraction (ND) pattern and it was observed to be roughly 8% in our sample. The field variation of resistance recorded at different temperatures shows a positive slope at low temperatures and a negative slope at higher temperatures, indicating the half-metallic character at low temperatures. The ab initio calculations predict a ferrimagnetic ground state for this system. The analysis of the magnetic structure from ND data measured at 6 K yields magnetic moment values of 1.28 μ(B) and -0.7 μ(B) for Mn and V, respectively, confirming the ferrimagnetic ordering.

  6. Estimation of Enthalpy of Formation of Liquid Transition Metal Alloys: A Modified Prescription Based on Macroscopic Atom Model of Cohesion

    NASA Astrophysics Data System (ADS)

    Raju, Subramanian; Saibaba, Saroja

    2016-09-01

    The enthalpy of formation Δo H f is an important thermodynamic quantity, which sheds significant light on fundamental cohesive and structural characteristics of an alloy. However, being a difficult one to determine accurately through experiments, simple estimation procedures are often desirable. In the present study, a modified prescription for estimating Δo H f L of liquid transition metal alloys is outlined, based on the Macroscopic Atom Model of cohesion. This prescription relies on self-consistent estimation of liquid-specific model parameters, namely electronegativity ( ϕ L) and bonding electron density ( n b L ). Such unique identification is made through the use of well-established relationships connecting surface tension, compressibility, and molar volume of a metallic liquid with bonding charge density. The electronegativity is obtained through a consistent linear scaling procedure. The preliminary set of values for ϕ L and n b L , together with other auxiliary model parameters, is subsequently optimized to obtain a good numerical agreement between calculated and experimental values of Δo H f L for sixty liquid transition metal alloys. It is found that, with few exceptions, the use of liquid-specific model parameters in Macroscopic Atom Model yields a physically consistent methodology for reliable estimation of mixing enthalpies of liquid alloys.

  7. Protein linear indices of the 'macromolecular pseudograph alpha-carbon atom adjacency matrix' in bioinformatics. Part 1: prediction of protein stability effects of a complete set of alanine substitutions in Arc repressor.

    PubMed

    Marrero-Ponce, Yovani; Medina-Marrero, Ricardo; Castillo-Garit, Juan A; Romero-Zaldivar, Vicente; Torrens, Francisco; Castro, Eduardo A

    2005-04-15

    A novel approach to bio-macromolecular design from a linear algebra point of view is introduced. A protein's total (whole protein) and local (one or more amino acid) linear indices are a new set of bio-macromolecular descriptors of relevance to protein QSAR/QSPR studies. These amino-acid level biochemical descriptors are based on the calculation of linear maps on Rn[f k(xmi):Rn-->Rn] in canonical basis. These bio-macromolecular indices are calculated from the kth power of the macromolecular pseudograph alpha-carbon atom adjacency matrix. Total linear indices are linear functional on Rn. That is, the kth total linear indices are linear maps from Rn to the scalar R[f k(xm):Rn-->R]. Thus, the kth total linear indices are calculated by summing the amino-acid linear indices of all amino acids in the protein molecule. A study of the protein stability effects for a complete set of alanine substitutions in the Arc repressor illustrates this approach. A quantitative model that discriminates near wild-type stability alanine mutants from the reduced-stability ones in a training series was obtained. This model permitted the correct classification of 97.56% (40/41) and 91.67% (11/12) of proteins in the training and test set, respectively. It shows a high Matthews correlation coefficient (MCC=0.952) for the training set and an MCC=0.837 for the external prediction set. Additionally, canonical regression analysis corroborated the statistical quality of the classification model (Rcanc=0.824). This analysis was also used to compute biological stability canonical scores for each Arc alanine mutant. On the other hand, the linear piecewise regression model compared favorably with respect to the linear regression one on predicting the melting temperature (tm) of the Arc alanine mutants. The linear model explains almost 81% of the variance of the experimental tm (R=0.90 and s=4.29) and the LOO press statistics evidenced its predictive ability (q2=0.72 and scv=4.79). Moreover, the

  8. Atomic layer deposition of metal sulfide thin films using non-halogenated precursors

    SciTech Connect

    Martinson, Alex B. F.; Elam, Jeffrey W.; Pellin, Michael J.

    2015-05-26

    A method for preparing a metal sulfide thin film using ALD and structures incorporating the metal sulfide thin film. The method includes providing an ALD reactor, a substrate, a first precursor comprising a metal and a second precursor comprising a sulfur compound. The first and the second precursors are reacted in the ALD precursor to form a metal sulfide thin film on the substrate. In a particular embodiment, the metal compound comprises Bis(N,N'-di-sec-butylacetamidinato)dicopper(I) and the sulfur compound comprises hydrogen sulfide (H.sub.2S) to prepare a Cu.sub.2S film. The resulting metal sulfide thin film may be used in among other devices, photovoltaic devices, including interdigitated photovoltaic devices that may use relatively abundant materials for electrical energy production.

  9. Controlled synthesis of racemic indenyl rare-earth metal complexes via the cooperation between the intramolecular coordination of donor atoms and a bridge.

    PubMed

    Zhou, Shuangliu; Wu, Zhangshuan; Zhou, Lingmin; Wang, Shaowu; Zhang, Lijun; Zhu, Xiancui; Wei, Yun; Zhai, Jinhua; Wu, Jie

    2013-06-03

    The reactions of Me2Si(C9H6CH2CH2-DG)2 (DG = NMe2 (1), CH2NMe2 (2), OMe (3), and N(CH2CH2)2O (4)) with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 in toluene afforded a series of racemic divalent rare-earth metal complexes: {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2-DG)2}RE (DG = NMe2, RE = Yb (6) and Eu (7); DG = CH2NMe2, RE = Yb (8), Eu (9), and Sm (10); DG = OMe, RE = Yb (11) and Eu (12); DG = N(CH2CH2)2O, RE = Yb (13) and Eu (14)). Similarly, the racemic divalent rare-earth metal complexes {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2CH2NMe2)(C9H5CH2CH2OMe)}RE (RE = Yb (15) and Eu (16)) were also obtained. The reaction of Me2Si(C9H5CH2CH2OMe)2Li2 with NdCl3 gave a racemic dimeric neodymium chloride {η(5):η(1):η(5)-Me2Si(C9H5CH2CH2OMe)2NdCl}2 (17), whereas the reaction of Me2Si(C9H5CH2CH2NMe2)2Li2 with SmCl3 afforded a racemic dinuclear samarium chloride bridged by lithium chloride {η(5):η(1):η(5):η(1)-Me2Si(C9H5CH2CH2NMe2)2SmCl}2(μ-LiCl) (18). Further reaction of complex 18 with LiCH2SiMe3 provided an unexpected rare-earth metal alkyl complex {η(5):η(1):η(5):η(1):σ-Me2Si(C9H5CH2CH2NMe2)[(C9H5CH2CH2N(CH2)Me]}Sm (19) through the activation of an sp(3) C-H bond α-adjacent to the nitrogen atom. Complexes 19 and {η(5):η(1):η(5):η(1):σ-Me2Si(C9H5CH2CH2NMe2)[(C9H5CH2CH2N(CH2)Me]}Y (20) were also obtained by one-pot reactions of Me2Si(C9H5CH2CH2NMe2)2Li2 with RECl3 followed by treatment with LiCH2SiMe3. All compounds were fully characterized by spectroscopic methods and elemental analysis. Complexes 6-10 and 14-20 were further characterized by single-crystal X-ray diffraction analysis. All of the prepared rare-earth metal complexes were racemic, suggesting that racemic organo rare-earth metal complexes could be controllably synthesized by the cooperation between a bridge and the intramolecular coordination of donor atoms.

  10. Conduction electrons as dissipation channel in friction experiments at the metal-metal transition of LSMO measured by contact-resonance atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Pfahl, V.; Phani, M. K.; Büchsenschütz-Göbeler, M.; Kumar, A.; Moshnyaga, V.; Arnold, W.; Samwer, K.

    2017-01-01

    We report on friction measurements on a La0.6Sr0.4MnO3 (LSMO) thin film using atomic force microscopy cantilever contact-resonances. There is a contribution to the damping of the cantilever oscillations, which is caused by micro-sliding of the cantilever tip on the surface of the thin film. This frictional part decreases with temperature parallel to the increase in the resistivity of the thin film. The LSMO is well-known for a ferromagnetic to paramagnetic phase transition that occurs without changes in the rhombohedral (R-3c) crystalline structure. The magnetic transition at the Curie temperature TC ˜ 360 K is accompanied by a metal-to-metal transition with a large increase in electrical resistivity. The behavior of the cantilever damping constant demonstrates that there is a direct coupling between mechanical friction and the mobility of the electrons in the LSMO film.

  11. Impact of deformation on the atomic structures and dynamics of a Cu-Zr metallic glass: A molecular dynamics study

    SciTech Connect

    Zhang, Y.; Mendelev, M. I.; Wang, C. Z.; Ott, R.; Zhang, F.; Besser, M. F.; Ho, K. M.; Kramer, M. J.

    2014-11-03

    Despite numerous studies on the atomic structures of Cu-Zr metallic glasses (MGs), their inherent structural ordering, e.g., medium-range order (MRO), remains difficult to describe. Specifically lacking is an understanding of how the MRO responds to deformation and the associated changes in atomic mobility. In this paper, we focus on the impact of deformation on MRO and associated effect on diffusion in a well-relaxed Cu64.5Zr35.5 MG by molecular dynamics simulations. The Cu-Zr MG exhibits a larger elastic limit of 0.035 and a yield stress of 3.5 GPa. The cluster alignment method was employed to characterize the icosahedral short-range order (ISRO) and Bergman-type medium-range order (BMRO) in the models upon loading and unloading. From this analysis, we find the disruption of both ISRO and BMRO occurs as the strain reaches about 0.02, well below the elastic limit. Within the elastic limit, the total fractions of ISRO or BMRO can be fully recovered upon unloading. The diffusivity increases six to eight times in regions undergoing plastic deformation, which is due to the dramatic disruption of the ISRO and BMRO. As a result, by mapping the spatial distributions of the mobile atoms, we demonstrate the increase in atomic mobility is due to the extended regions of disrupted ISRO and more importantly BMRO.

  12. Impact of deformation on the atomic structures and dynamics of a Cu-Zr metallic glass: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Mendelev, M. I.; Wang, C. Z.; Ott, R.; Zhang, F.; Besser, M. F.; Ho, K. M.; Kramer, M. J.

    2014-11-01

    Despite numerous studies on the atomic structures of Cu-Zr metallic glasses (MGs), their inherent structural ordering, e.g., medium-range order (MRO), remains difficult to describe. Specifically lacking is an understanding of how the MRO responds to deformation and the associated changes in atomic mobility. In this paper, we focus on the impact of deformation on MRO and associated effect on diffusion in a well-relaxed C u64.5Z r35.5 MG by molecular dynamics simulations. The Cu-Zr MG exhibits a larger elastic limit of 0.035 and a yield stress of 3.5 GPa. The cluster alignment method was employed to characterize the icosahedral short-range order (ISRO) and Bergman-type medium-range order (BMRO) in the models upon loading and unloading. From this analysis, we find the disruption of both ISRO and BMRO occurs as the strain reaches about 0.02, well below the elastic limit. Within the elastic limit, the total fractions of ISRO or BMRO can be fully recovered upon unloading. The diffusivity increases six to eight times in regions undergoing plastic deformation, which is due to the dramatic disruption of the ISRO and BMRO. By mapping the spatial distributions of the mobile atoms, we demonstrate the increase in atomic mobility is due to the extended regions of disrupted ISRO and more importantly BMRO.

  13. Impact of deformation on the atomic structures and dynamics of a Cu-Zr metallic glass: A molecular dynamics study

    DOE PAGES

    Zhang, Y.; Mendelev, M. I.; Wang, C. Z.; ...

    2014-11-03

    Despite numerous studies on the atomic structures of Cu-Zr metallic glasses (MGs), their inherent structural ordering, e.g., medium-range order (MRO), remains difficult to describe. Specifically lacking is an understanding of how the MRO responds to deformation and the associated changes in atomic mobility. In this paper, we focus on the impact of deformation on MRO and associated effect on diffusion in a well-relaxed Cu64.5Zr35.5 MG by molecular dynamics simulations. The Cu-Zr MG exhibits a larger elastic limit of 0.035 and a yield stress of 3.5 GPa. The cluster alignment method was employed to characterize the icosahedral short-range order (ISRO) andmore » Bergman-type medium-range order (BMRO) in the models upon loading and unloading. From this analysis, we find the disruption of both ISRO and BMRO occurs as the strain reaches about 0.02, well below the elastic limit. Within the elastic limit, the total fractions of ISRO or BMRO can be fully recovered upon unloading. The diffusivity increases six to eight times in regions undergoing plastic deformation, which is due to the dramatic disruption of the ISRO and BMRO. As a result, by mapping the spatial distributions of the mobile atoms, we demonstrate the increase in atomic mobility is due to the extended regions of disrupted ISRO and more importantly BMRO.« less

  14. Adsorption of Pd atoms on γ-Al 2O 3: a density functional study of metal-support interactions

    NASA Astrophysics Data System (ADS)

    Márquez, Antonio M.; Sanz, Javier Fernández

    2004-11-01

    The Pd/γ-Al2O3 interface at low coverage has been theoretically studied by means of periodic-supercell density functional calculations. The most stable (1 1 0) γ-Al2O3 clean surface plane has been modelled by using a six layers slab stoichiometric model of 40 atoms. A single Pd atom has been deposited on top of the surface in different positions, first freezing the surface structure and later allowing the surface to relax. The results indicate that the metal-support interaction is dominated by the strong Lewis acid properties of the tetrahedral cationic sites. It is also shown that in the octahedral cationic sites, adsorption of single Pd atoms induces a significant relaxation of the substrate. While the interaction energy with the preferred site is strong (∼3.8 eV), small differences are found for nearby sites, indicating a high mobility of Pd atoms on the surface, at least on the channels.

  15. TRANSITION METAL CATALYSIS IN CONTROLLED RADICAL POLYMERIZATION: ATOM TRANSFER RADICAL POLYMERIZATION. (R826735)

    EPA Science Inventory

    Novel and diversified macromolecular structures, which include polymers with designed topologies (top), compostions (middle), and functionalities (bottom), can be prepared by atom transfer radical polymerization processes. These polymers can be synthesized from a large variety of...

  16. Experimental and Theoretical Studies of Pressure Broadened Alkali-Metal Atom Resonance Lines

    NASA Technical Reports Server (NTRS)

    Shindo, F.; Zhu, C.; Kirby, K.; Babb, J. F.

    2006-01-01

    We are carrying out a joint theoretical and experimental research program to study the broadening of alkali atom resonance lines due to collisions with helium and molecular hydrogen for applications to spectroscopic studies of brown dwarfs and extrasolar giant planets.

  17. Metal vapor target for precise studies of ion-atom collisions

    SciTech Connect

    Chen, W. Vorobyev, G.; Herfurth, F.; Hillenbrand, P.-M.; Spillmann, U.; Guo, D.; Trotsenko, S.; Gumberidze, A.; Stöhlker, Th.

    2014-05-15

    Although different ion-atom collisions have been studied in various contexts, precise values of cross-sections for many atomic processes were seldom obtained. One of the main uncertainties originates from the value of target densities. In this paper, we describe a unique method to measure a target density precisely with a combination of physical vapor deposition and inductively coupled plasma optical emission spectrometry. This method is preliminarily applied to a charge transfer cross-section measurement in collisions between highly charged ions and magnesium vapor. The final relative uncertainty of the target density is less than 2.5%. This enables the precise studies of atomic processes in ion-atom collisions, even though in the trial test the deduction of precise capture cross-sections was limited by other systematic errors.

  18. Determining the quantum-coherent to semiclassical transition in atomic-scale quasi-one-dimensional metals

    NASA Astrophysics Data System (ADS)

    Weber, Bent; Simmons, Michelle Y.

    2016-08-01

    Atomic-scale silicon wires, patterned by scanning tunneling microscopy (STM) and degenerately doped with phosphorus (P), have attracted significant interest owing to their exceptionally low resistivity and semiclassical Ohmic conduction at temperatures as low as T =4.2 K . Here, we investigate the transition from semiclassical diffusive to quantum-coherent conduction in a 4.6 nm wide wire as we decrease the measurement temperature. By analyzing the temperature dependence of universal conductance fluctuations (UCFs) and one-dimensional (1D) weak localization (WL)—fundamental manifestations of quantum-coherent transport in quasi-1D metals—we show that transport evolves from quantum coherent to semiclassical at T ˜4 K . Remarkably, our study confirms that universal concepts of mesoscopic physics such as UCF and 1D WL retain their validity in quasi-1D metallic conductors down to the atomic scale.

  19. Measuring the spin polarization of alkali-metal atoms using nuclear magnetic resonance frequency shifts of noble gases

    SciTech Connect

    Liu, X. H.; Luo, H.; Qu, T. L. Yang, K. Y.; Ding, Z. C.

    2015-10-15

    We report a novel method of measuring the spin polarization of alkali-metal atoms by detecting the NMR frequency shifts of noble gases. We calculated the profile of {sup 87}Rb D1 line absorption cross sections. We then measured the absorption profile of the sample cell, from which we calculated the {sup 87}Rb number densities at different temperatures. Then we measured the frequency shifts resulted from the spin polarization of the {sup 87}Rb atoms and calculated its polarization degrees at different temperatures. The behavior of frequency shifts versus temperature in experiment was consistent with theoretical calculation, which may be used as compensative signal for the NMRG closed-loop control system.

  20. Structural properties of Al and TiAl3 metallic glasses — An embedded atom method study

    NASA Astrophysics Data System (ADS)

    Tahiri, M.; Trady, S.; Hasnaoui, A.; Mazroui, M.; Saadouni, K.; Sbiaai, K.

    2016-06-01

    In this paper, we investigated the structural properties of metallic glasses (MGs). We emphasized our study on monatomic Al and binary TiAl3 systems. The calculations are performed by using the molecular dynamics (MD) simulation based on semi-empirical many-body potentials derived from the embedded atom method. The structure is analyzed using the radial distribution function (RDF), the common neighbor analysis (CNA) and the coordination numbers (CNs). Our results demonstrated that it is possible to form MGs in both systems upon fast cooling from the liquid state. This is confirmed by the fact that the system energy and/or volume during the cooling stage decrease continuously with a slight change and by atomic scale analysis using the RDF, CNA and CN analyzing techniques. Furthermore, this specific study shows that under the same conditions, the icosahedral structures appeared in TiAl3 are more abundant than in pure Al. Implications of these findings are discussed.

  1. Visualization and quantification of transition metal atomic mixing in Mo1−xWxS2 single layers

    PubMed Central

    Dumcenco, Dumitru O; Kobayashi, Haruka; Liu, Zheng; Huang, Ying-Sheng; Suenaga, Kazu

    2013-01-01

    The alloying behaviour of materials is a well-known problem in all kinds of compounds. Revealing the heteroatomic distributions in two-dimensional crystals is particularly critical for their practical use as nano-devices. Here we obtain statistics of the homo- and heteroatomic coordinates in single-layered Mo1−xWxS2 from the atomically resolved scanning transmission electron microscope images and successfully quantify the degree of alloying for the transition metal elements (Mo or W). The results reveal the random alloying of this mixed dichalcogenide system throughout the chemical compositions (x=0 to 1). Such a direct route to gain an insight into the alloying degree on individual atom basis will find broad applications in characterizing low-dimensional heterocompounds and become an important complement to the existing theoretical methods. PMID:23322039

  2. Transition rates for lithium-like ions, sodium-like ions, and neutral alkali-metal atoms

    SciTech Connect

    Johnson, W.R.; Liu, Z.W.; Sapirstein, J.

    1996-11-01

    Third-order many-body perturbation theory is used to obtain E1 transition amplitudes for ions of the lithium and sodium isoelectronic sequences and for the neutral alkali-metal atoms potassium, rubidium, cesium, and francium. Complete angular reductions of the first, second, and third-order amplitudes are given. Tables of transition energies and rates are given for the 2p{sub {1/2}} {yields} 2s{sub {1/2}}, 2p{sub 3/2} {yields} 2s{sub {1/2}}, 3s{sub {1/2}} {yields} 2p{sub {1/2}}, and 3s{sub {1/2}} {yields} 2p{sub 3/2} transitions in the lithium isoelectronic sequence and for the corresponding 3p{sub 1/2} {yields} 3s{sub 1/2}, 3p{sub 3/2} {yields} 3s{sub {1/2}}, 4s{sub {1/2}} {yields} 3p{sub 1/2}, and 4s{sub {1/2}} {yields} 3p{sub 3/2} transitions in the sodium sequence. For neutral alkali atoms, amplitudes of np{sub {1/2}} {yields} ns{sub {1/2}}, np{sub 3/2} {yields} ns{sub {1/2}}, (n + 1)s{sub {1/2}} {yields} np{sub {1/2}}, and (n + 1)s{sub {1/2}} {yields} np{sub 3/2} transitions are evaluated, where n is the principal quantum number of the valence electron in the atomic ground state, Semi-empirical corrections for the omitted fourth- and higher-order terms in perturbation theory are given for the neutral alkali-metal atoms. Comparisons with previous high-precision calculations and with experiment are made. 42 refs., 1 fig., 12 tabs.

  3. Sensitive determination of the spin polarization of optically pumped alkali-metal atoms using near-resonant light

    PubMed Central

    Ding, Zhichao; Long, Xingwu; Yuan, Jie; Fan, Zhenfang; Luo, Hui

    2016-01-01

    A new method to measure the spin polarization of optically pumped alkali-metal atoms is demonstrated. Unlike the conventional method using far-detuned probe light, the near-resonant light with two specific frequencies was chosen. Because the Faraday rotation angle of this approach can be two orders of magnitude greater than that with the conventional method, this approach is more sensitive to the spin polarization. Based on the results of the experimental scheme, the spin polarization measurements are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this approach. PMID:27595707

  4. Sensitive determination of the spin polarization of optically pumped alkali-metal atoms using near-resonant light.

    PubMed

    Ding, Zhichao; Long, Xingwu; Yuan, Jie; Fan, Zhenfang; Luo, Hui

    2016-09-06

    A new method to measure the spin polarization of optically pumped alkali-metal atoms is demonstrated. Unlike the conventional method using far-detuned probe light, the near-resonant light with two specific frequencies was chosen. Because the Faraday rotation angle of this approach can be two orders of magnitude greater than that with the conventional method, this approach is more sensitive to the spin polarization. Based on the results of the experimental scheme, the spin polarization measurements are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this approach.

  5. Sensitive determination of the spin polarization of optically pumped alkali-metal atoms using near-resonant light

    NASA Astrophysics Data System (ADS)

    Ding, Zhichao; Long, Xingwu; Yuan, Jie; Fan, Zhenfang; Luo, Hui

    2016-09-01

    A new method to measure the spin polarization of optically pumped alkali-metal atoms is demonstrated. Unlike the conventional method using far-detuned probe light, the near-resonant light with two specific frequencies was chosen. Because the Faraday rotation angle of this approach can be two orders of magnitude greater than that with the conventional method, this approach is more sensitive to the spin polarization. Based on the results of the experimental scheme, the spin polarization measurements are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this approach.

  6. Infrared spectra of the ethynyl metal hydrides produced in reactions of laser-ablated Mn and Re atoms with acetylene.

    PubMed

    Cho, Han-Gook; Andrews, Lester

    2011-05-19

    The ethynyl metal hydride molecules (HM-C≡CH) are identified in the matrix infrared spectra from reactions of laser-ablated Mn and Re atoms with acetylene using D and (13)C isotopic substitution and density functional computed frequencies. The assignment of strong M-H as well as C≡C bond stretching product absorptions suggests oxidative C-H insertion during reagent codeposition and subsequent photolysis. The unique linear structure calculated for HMn-C≡CH is parallel to C(3v) structures found recently for Mn complexes including CH(3)-MnF.

  7. Strong correlation of atomic thermal motion in the first coordination shell of a Cu-Zr metallic glass

    SciTech Connect

    Zhang, Y.; Mattern, N.; Eckert, J.

    2013-02-25

    We demonstrate a strong correlation of atomic thermal motions in the first coordination shell of Cu{sub 50}Zr{sub 50} metallic glass using molecular dynamics simulations, which explains directly the small thermal expansion coefficient calculated by the first maxima of pair correlation functions. The vibrational anisotropy in the glass is found to be even higher than in crystalline copper. The parallel-perpendicular anisotropy gradually decreases upon heating. The anisotropy in Zr-Zr is the strongest bonds among all the interatomic bonds, which is also very stable near the glass transition at 700 K. Structurally, the anisotropy can be correlated to Cu-centered (0 2 8 1) clusters.

  8. Atomic-layer alignment tuning for giant perpendicular magnetocrystalline anisotropy of 3d transition-metal thin films.

    PubMed

    Hotta, K; Nakamura, K; Akiyama, T; Ito, T; Oguchi, T; Freeman, A J

    2013-06-28

    The magnetocrystalline anisotropy (MA) of Fe-based transition-metal thin films, consisting of only magnetic 3d elements, was systematically investigated from full-potential linearized augmented plane-wave calculations. The results predict that giant MA with a perpendicular magnetic easy axis (PMA) can be achieved by tuning the atomic-layer alignments in an Fe-Ni thin film. This giant PMA arises from the spin-orbit coupling interaction between occupied and unoccupied Ni dx2-y2,xy bands crossing the Fermi level. A promising 3d transition-metal thin film for the MgO-based magnetic tunnel junctions with the giant PMA was, thus, demonstrated.

  9. Metal atom dynamics in superbulky metallocenes: a comparison of (Cp(BIG))2Sn and (Cp(BIG))2Eu.

    PubMed

    Harder, Sjoerd; Naglav, Dominik; Schwerdtfeger, Peter; Nowik, Israel; Herber, Rolfe H

    2014-02-17

    Cp(BIG)2Sn (Cp(BIG) = (4-n-Bu-C6H4)5cyclopentadienyl), prepared by reaction of 2 equiv of Cp(BIG)Na with SnCl2, crystallized isomorphous to other known metallocenes with this ligand (Ca, Sr, Ba, Sm, Eu, Yb). Similarly, it shows perfect linearity, C-H···C(π) bonding between the Cp(BIG) rings and out-of-plane bending of the aryl substituents toward the metal. Whereas all other Cp(BIG)2M complexes show large disorder in the metal position, the Sn atom in Cp(BIG)2Sn is perfectly ordered. In contrast, (119)Sn and (151)Eu Mößbauer investigations on the corresponding Cp(BIG)2M metallocenes show that Sn(II) is more dynamic and loosely bound than Eu(II). The large displacement factors in the group 2 and especially in the lanthanide(II) metallocenes Cp(BIG)2M can be explained by static metal disorder in a plane parallel to the Cp(BIG) rings. Despite parallel Cp(BIG) rings, these metallocenes have a nonlinear Cpcenter-M-Cpcenter geometry. This is explained by an ionic model in which metal atoms are polarized by the negatively charged Cp rings. The extent of nonlinearity is in line with trends found in M(2+) ion polarizabilities. The range of known calculated dipole polarizabilities at the Douglas-Kroll CCSD(T) level was extended with values (atomic units) for Sn(2+) 15.35, Sm(2+)(4f(6) (7)F) 9.82, Eu(2+)(4f(7) (8)S) 8.99, and Yb(2+)(4f(14) (1)S) 6.55. This polarizability model cannot be applied to predominantly covalently bound Cp(BIG)2Sn, which shows a perfectly ordered structure. The bent geometry of Cp*2Sn should therefore not be explained by metal polarizability but is due to van der Waals Cp*···Cp* attraction and (to some extent) to a small p-character component in the Sn lone pair.

  10. Surface structures from low energy electron diffraction: Atoms, small molecules and an ordered ice film on metal surfaces

    SciTech Connect

    Materer, Nicholas F.

    1995-09-01

    We investigated the surface bonding of various adsorbates (0, S, C2H3 and NO) along with the resulting relaxation of the Pt(111) surface using low energy electron diffiraction (LEED). LEED experiments have been performed on these ordered overlayers along with theoretical structural analysis using automated tensor LEED (ATLEED). The resulting surface structures of these ordered overlayers exhibit similar adsorbate-induced relaxations. In all cases the adsorbate occupies the fcc hollow site and induces an approximately 0.1 A buckling of the metal surface. The three metal atoms directly bonded to the adsorbate are ``pulled`` out of the surface and the metal atom that is not bound to the adsorbate is `pushed`` inward. In order to understand the reliability of such details, we have carried out a comprehensive study of various non-structural parameters used in a LEED computation. We also studied the adsorption of water on the Pt(lll) surface. We ordered an ultra thin ice film on this surface. The film`s surface is found to be the (0001) face of hexagonal ice. This surface is apparently terminated by a full-bilayer, in which the uppermost water molecules have large vibrational amplitudes even at temperatures as low as 90 K. We examined two other metal surfaces besides Pt(111): Ni(111) and Fe(lll). On Ni(111), we have studied the surface under a high coverage of NO. On both Ni(111) and Pt(111) NO molecules occupy the hollow sites and the N-0 bond distances are practically identical. The challenging sample preparation of an Fe(111) surface has been investigated and a successful procedure has been obtained. The small interlayer spacing found on Fe(111) required special treatment in the LEED calculations. A new ATLEED program has been developed to handle this surface.

  11. Investigating the atomic level influencing factors of glass forming ability in NiAl and CuZr metallic glasses

    SciTech Connect

    Sedighi, Sina; Kirk, Donald Walter; Singh, Chandra Veer Thorpe, Steven John

    2015-09-21

    Bulk metallic glasses are a relatively new class of amorphous metal alloy which possess unique mechanical and magnetic properties. The specific concentrations and combinations of alloy elements needed to prevent crystallization during melt quenching remains poorly understood. A correlation between atomic properties that can explain some of the previously identified glass forming ability (GFA) anomalies of the NiAl and CuZr systems has been identified, with these findings likely extensible to other transition metal–transition metal and transition metal–metalloid (TM–M) alloy classes as a whole. In this work, molecular dynamics simulation methods are utilized to study thermodynamic, kinetic, and structural properties of equiatomic CuZr and NiAl metallic glasses in an attempt to further understand the underlying connections between glass forming ability, nature of atomic level bonding, short and medium range ordering, and the evolution of structure and relaxation properties in the disordered phase. The anomalous breakdown of the fragility parameter as a useful GFA indicator in TM–M alloy systems is addressed through an in-depth investigation of bulk stiffness properties and the evolution of (pseudo)Gruneisen parameters over the quench domain, with the efficacy of other common glass forming ability indicators similarly being analyzed through direct computation in respective CuZr and NiAl systems. Comparison of fractional liquid-crystal density differences in the two systems revealed 2-3 times higher values for the NiAl system, providing further support for its efficacy as a general purpose GFA indicator.

  12. Nitrogen dioxide reactions with 46 atomic main-group and transition metal cations in the gas phase: room temperature kinetics and periodicities in reactivity.

    PubMed

    Jarvis, Michael J Y; Blagojevic, Voislav; Koyanagi, Gregory K; Bohme, Diethard K

    2013-02-14

    Experimental results are reported for the gas-phase room-temperature kinetics of chemical reactions between nitrogen dioxide (NO(2)) and 46 atomic main-group and transition metal cations (M(+)). Measurements were taken with an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer in helium buffer gas at a pressure of 0.35 ± 0.01 Torr and at 295 ± 2 K. The atomic cations were produced at ca. 5500 K in an ICP source and allowed to decay radiatively and to thermalize to room temperature by collisions with Ar and He atoms prior to reaction with NO(2). Measured apparent bimolecular rate coefficients and primary reaction product distributions are reported for all 46 atomic metal cations and these provide an overview of trends across and down the periodic table. Three main types of reactions were observed: O-atom transfer to form either MO(+) or NO(+), electron transfer to form NO(2)(+), and addition to form MNO(2)(+). Bimolecular O-atom transfer was observed to predominate. Correlations are presented between reaction efficiency and the O-atom affinity of the metal cation and between the prevalence of NO(+) product formation and the electron recombination energy of the product metal oxide cation. Some second-order reactions are evident with metal cations that react inefficiently. Most interesting of these is the formation of the MNO(+) cation with Rh(+) and Pd(+). The higher-order chemistry with NO(2) is very diverse and includes the formation of numerous NO(2) ion clusters and a number of tri- and tetraoxide metal cations. Group 2 metal dioxide cations (CaO(2)(+), SrO(2)(+), BaO(2)(+)) exhibit a unique reaction with NO(2) to form MO(NO)(+) ions perhaps by NO transfer from NO(2) concurrent with O(2) formation by recombination of a NO(2) and an oxide oxygen.

  13. Analysis of metals in marine sediments by microwave extraction and flame, hydride generation and cold vapor atomic-absorption spectrometry

    SciTech Connect

    Martinez-Garcia, M.L.; Zubieta, A.C.; Lorenzo, S.M.; Lopez-Mahia, P.; Rodriguez, D.P.

    1999-01-01

    A simple and fast metal extraction method that combines closed vessels and microwave heating for the simultaneous extraction of ten selected heavy metals (As, Cd, Co, Cr, Hg, Mn, Ni, Pb, Zn) from marine sediments is proposed. Digestion conditions, i.e., power and times microwave irradiation, reagent extractant, sample amount, were optimized to recover the potentially available metallic fraction not bound in silicates. A nitric acid and two step microwave program was established. The resulting solutions were analyzed by flame (FAAS), hydride generation (HG-AAS) and cold vapor (CV-AAS) atomic absorption spectrometry. Quantifications were made using direct calibration with aqueous standards. The recoveries of the spiked samples investigated ranged from 89 to 113%. The results obtained from analyzing the BCR certified reference sediment CRM 277 Estuarine Sediment were in good agreement with the certified values (93--105%), except for low values for chromium (79%). The relative standard deviations for the determination of metals were less than 4%. Finally, the technique designed herein was applied to sediment samples from La Coruna estuary, NW Spain.

  14. Real-time studies of the atomic layer deposition of metal oxides using Ambient pressure x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Schnadt, Joachim; Head, Ashley R.; Chaudhary, Shilpi; Yngman, Sofie; Johansson, Niclas; Snezhkova, Olesia; Knudsen, Jan; Andersen, Jesper N.; Bluhm, Hendrik; Mikkelsen, Anders; Timm, Rainer

    2014-03-01

    Performing atomic layer deposition (ALD) of metal oxides at pressures around 0.01 mbar slows the half reactions of the process to allow in situ real-time probing of changes in the surface electronic structure using Ambient pressure x-ray photoelectron spectroscopy (APXPS). By monitoring the ALD process as it occurs, new details on the mechanisms of interface formation and thin film growth can be obtained. The deposition of HfO2 on InAs and the deposition of TiO2 on rutile titania from transition metal complexes and water were studied with APXPS. Predictable, cyclic chemical shifts of ligand and substrate ionizations are seen in the growth of the films, but the kinetics of the film growth differs for the two systems. Upon exposure to the titania surface, the titanium precursor reacts straightaway and gradually proceeds to completion. In contrast, the hafnium precursor does not interact with the surface immediately. Once an activation barrier is surpassed, the reaction occurs instantaneously. By understanding the reactivity of different precursors, the ALD process can be more easily optimized in applications that require thin films of metal oxides such as metal-oxide-semiconductor devices and catalytic surfaces. Support by the Swedish Research Council (grant no. 2010-5080) is gratefully acknowledged.

  15. Using metallic noncontact atomic force microscope tips for imaging insulators and polar molecules: tip characterization and imaging mechanisms.

    PubMed

    Gao, David Zhe; Grenz, Josef; Watkins, Matthew Benjamin; Federici Canova, Filippo; Schwarz, Alexander; Wiesendanger, Roland; Shluger, Alexander L

    2014-05-27

    We demonstrate that using metallic tips for noncontact atomic force microscopy (NC-AFM) imaging at relatively large (>0.5 nm) tip-surface separations provides a reliable method for studying molecules on insulating surfaces with chemical resolution and greatly reduces the complexity of interpreting experimental data. The experimental NC-AFM imaging and theoretical simulations were carried out for the NiO(001) surface as well as adsorbed CO and Co-Salen molecules using Cr-coated Si tips. The experimental results and density functional theory calculations confirm that metallic tips possess a permanent electric dipole moment with its positive end oriented toward the sample. By analyzing the experimental data, we could directly determine the dipole moment of the Cr-coated tip. A model representing the metallic tip as a point dipole is described and shown to produce NC-AFM images of individual CO molecules adsorbed onto NiO(001) in good quantitative agreement with experimental results. Finally, we discuss methods for characterizing the structure of metal-coated tips and the application of these tips to imaging dipoles of large adsorbed molecules.

  16. Redox-inactive metal ions promoted the catalytic reactivity of non-heme manganese complexes towards oxygen atom transfer.

    PubMed

    Choe, Cholho; Yang, Ling; Lv, Zhanao; Mo, Wanling; Chen, Zhuqi; Li, Guangxin; Yin, Guochuan

    2015-05-21

    Redox-inactive metal ions can modulate the reactivity of redox-active metal ions in a variety of biological and chemical oxidations. Many synthetic models have been developed to help address the elusive roles of these redox-inactive metal ions. Using a non-heme manganese(II) complex as the model, the influence of redox-inactive metal ions as a Lewis acid on its catalytic efficiency in oxygen atom transfer was investigated. In the absence of redox-inactive metal ions, the manganese(II) catalyst is very sluggish, for example, in cyclooctene epoxidation, providing only 9.9% conversion with 4.1% yield of epoxide. However, addition of 2 equiv. of Al(3+) to the manganese(II) catalyst sharply improves the epoxidation, providing up to 97.8% conversion with 91.4% yield of epoxide. EPR studies of the manganese(II) catalyst in the presence of an oxidant reveal a 16-line hyperfine structure centered at g = 2.0, clearly indicating the formation of a mixed valent di-μ-oxo-bridged diamond core, Mn(III)-(μ-O)2-Mn(IV). The presence of a Lewis acid like Al(3+) causes the dissociation of this diamond Mn(III)-(μ-O)2-Mn(IV) core to form monomeric manganese(iv) species which is responsible for improved epoxidation efficiency. This promotional effect has also been observed in other manganese complexes bearing various non-heme ligands. The findings presented here have provided a promising strategy to explore the catalytic reactivity of some di-μ-oxo-bridged complexes by adding non-redox metal ions to in situ dissociate those dimeric cores and may also provide clues to understand the mechanism of methane monooxygenase which has a similar diiron diamond core as the intermediate.

  17. Linear Free Energy Relationships for Metal-Ligand Complexation: Bidentate Binding to Negatively-Charged Oxygen Donor Atoms

    PubMed Central

    Carbonaro, Richard F.; Atalay, Yasemin B.; Di Toro, Dominic M.

    2011-01-01

    Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log KML = χOO(αO log KHL,1 + αO log KHL,2) where KML is the metal-ligand stability constant for a 1:1 complex, KHL,1 and KHL,2 are the proton-ligand stability constants (the ligand pKa values), and αO is the Irving-Rossotti slope. The parameter χOO is metal specific and has slightly different values for 5 and 6 membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, α-hydroxycarboxylic acids, and α-ketocarboxylic acids, a modification of the LFER where log KHL,2 is set equal to zero is required. The chemical interpretation of χOO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log KML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log KML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems. PMID:21833149

  18. Linear free energy relationships for metal-ligand complexation: Bidentate binding to negatively-charged oxygen donor atoms

    NASA Astrophysics Data System (ADS)

    Carbonaro, Richard F.; Atalay, Yasemin B.; Di Toro, Dominic M.

    2011-05-01

    Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log KML = χOO( αO log KHL,1 + αO log KHL,2) where KML is the metal-ligand stability constant for a 1:1 complex, KHL,1 and KHL,2 are the proton-ligand stability constants (the ligand p Ka values), and αO is the Irving-Rossotti slope. The parameter χOO is metal specific and has slightly different values for five and six membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log KML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, α-hydroxycarboxylic acids, and α-ketocarboxylic acids, a modification of the LFER where log KHL,2 is set equal to zero is required. The chemical interpretation of χOO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu-NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log KML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log KML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems.

  19. 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.

  20. Measurement method for the nuclear anapole moment of laser-trapped alkali-metal atoms

    SciTech Connect

    Gomez, E.; Aubin, S.; Sprouse, G. D.; Orozco, L. A.; DeMille, D. P.

    2007-03-15

    Weak interactions within a nucleus generate a nuclear spin dependent, parity-violating electromagnetic moment, the anapole moment. We analyze a method to measure the nuclear anapole moment through the electric dipole transition it induces between hyperfine states of the ground level. The method requires tight confinement of the atoms to position them at the antinode of a standing wave Fabry-Perot cavity driving the anapole-induced microwave E1 transition. We explore the necessary limits in the number of atoms, excitation fields, trap type, interrogation method, and systematic tests necessary for such measurements in francium, the heaviest alkali.

  1. Methods for analysis of selected metals in water by atomic absorption

    USGS Publications Warehouse

    Fishman, Marvin J.; Downs, Sanford C.

    1966-01-01

    This manual describes atomic-absorption-spectroscopy methods for determining calcium, copper, lithium, magnesium, manganese, potassium, sodium, strontium and zinc in atmospheric precipitation, fresh waters, and brines. The procedures are intended to be used by water quality laboratories of the Water Resources Division of the U.S. Geological Survey. Detailed procedures, calculations, and methods for the preparation of reagents are given for each element along with data on accuracy, precision, and sensitivity. Other topics discussed briefly are the principle of atomic absorption, instrumentation used, and special analytical techniques.

  2. [Atomic beam studies of the interaction of hydrogen with transition metal surfaces

    SciTech Connect

    Not Available

    1992-01-01

    We have constructed two experimental facilities during the term of this grant. In the first three years we constructed a helium atom scattering (HAS) facility with both elastic (EHAS) and inelastic (IHAS) scattering measurement capabilities to investigate the structural and dynamical aspects of solid surfaces and thin films. A pioneering surface metastable atom magnetic diffraction (SMAMD) facility was constructed and developed over the past four years, which makes possible the investigation of long-range electron spin-ordering on the surfaces of insulating magnetic crystals. The following were studied: H overlayers and Ag, Cu on Pd(111), reconstructed Au(111), and NiO(100).

  3. Electronic, Mechanical, and Dielectric Properties of Two-Dimensional Atomic Layers of Noble Metals

    NASA Astrophysics Data System (ADS)

    Kapoor, Pooja; Kumar, Jagdish; Kumar, Arun; Kumar, Ashok; Ahluwalia, P. K.

    2017-01-01

    We present density functional theory-based electronic, mechanical, and dielectric properties of monolayers and bilayers of noble metals (Au, Ag, Cu, and Pt) taken with graphene-like hexagonal structure. The Au, Ag, and Pt bilayers stabilize in AA-stacked configuration, while the Cu bilayer favors the AB stacking pattern. The quantum ballistic conductance of the noble-metal mono- and bilayers is remarkably increased compared with their bulk counterparts. Among the studied systems, the tensile strength is found to be highest for the Pt monolayer and bilayer. The noble metals in mono- and bilayer form show distinctly different electron energy loss spectra and reflectance spectra due to the quantum confinement effect on going from bulk to the monolayer limit. Such tunability of the electronic and dielectric properties of noble metals by reducing the degrees of freedom of electrons offers promise for their use in nanoelectronics and optoelectronics applications.

  4. All-electron KKR Calculations for Metallic Systems with Thousands of Atoms Per Cell via Sparse Matrix Iterative Solvers

    NASA Astrophysics Data System (ADS)

    Khan, Suffian; Alam, Aftab; Johnson, Duane

    2009-03-01

    To perform electronic-structure calculations for inherently large systems, such as a quantum dots or interfaces like domain walls, we must perform the calculations over very large unit cells (10^4 to 10^8 atoms). For the inverse Green's function G-1, KKR methods typically solve for G by direct inversion. Using a screened, k-space hybrid KKR, we solve Dyson's equation for the Green's function using a reference state via G = Gref [ I - (t - tref) Gref]-1, scattering matrices t and tref are known and the non-Hermitian tensor Gref is chosen for convenience and sparsity [1]. The approach is O(N) for bandgap materials, whereas it is O(N^2) for metals but with a potentially large prefactor. Based upon Sparse Approximate Inverse (or SPAI) technique [2], we generalize the algorithm for complex, non-Hermitian matrices, then use the method as a preconditioner for the inversion to reduce the iteration counts (hence, reduce the prefactor) of the iterative Krylov-space inverses, such as TFQMR, to address large-scale metallic systems. Parallel iterative and energy contour solves are made also. We explore the numerical efficiency and scaling versus atoms per unit cells. [1] Smirnov and Johnson, Comp. Phys. Comm. 148, 74-80 (2002). [2] Grote and Huckle, SIAM J. Sci. Comput. 18, 8

  5. Kinetic and Mechanistic Studies of Carbon-to-Metal Hydrogen Atom Transfer Involving Os-Centered Radicals: Evidence for Tunneling

    SciTech Connect

    Lewandowska-Androlojc, Anna; Grills, David C.; Zhang, Jie; Bullock, R. Morris; Miyazawa, Akira; Kawanishi, Yuji; Fujita, Etsuko

    2014-03-05

    We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C-H bond is accomplished by a single metal-centered radical. Studies by means of time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene and 1,4-cyclohexadiene to Cp(CO)2Os• and (n5-iPr4C5H)(CO)2Os• radicals, formed by photoinduced homolysis of the corresponding osmium dimers. The rate constants for hydrogen abstraction from these hydrocarbons were found to be in the range 1.54 × 105 M 1 s 1 -1.73 × 107 M 1 s-1 at 25 °C. For the first time, kinetic isotope effects for carbon-to-metal hydrogen atom transfer were determined. Large primary kinetic isotope effects of 13.4 ± 1.0 and 16.6 ± 1.4 were observed for the hydrogen abstraction from xanthene to form Cp(CO)2OsH and (n5-iPr4C5H)(CO)2OsH, respectively, at 25 °C. Temperature-dependent measurements of the kinetic isotope effects over a 60 -C temperature range were carried out to obtain the difference in activation energies and the pre-exponential factor ratio. For hydrogen atom transfer from xanthene to (n5-iPr4C5H)(CO)2Os•, the (ED - EH) = 3.25 ± 0.20 kcal/mol and AH/AD = 0.056 ± 0.018 values are greater than the semi-classical limits and thus suggest a quantum mechanical tunneling mechanism. The work at BNL was carried out under contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Geosciences & Biosciences, Office of Basic Energy Sciences. RMB also thanks the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences for support. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

  6. Determination of the Relative Atomic Masses of Metals by Liberation of Molecular Hydrogen

    ERIC Educational Resources Information Center

    Waghorne, W. Earle; Rous, Andrew J.

    2009-01-01

    Students determine the relative atomic masses of calcium, magnesium, and aluminum by reaction with hydrochloric acid and measurement of the volume of hydrogen gas liberated. The experiment demonstrates stoichiometry and illustrates clearly that mass of the reagent is not the determinant of the amounts in chemical reactions. The experiment is…

  7. Spectral Emission of fast non-Maxwellian Atoms at metallic Surfaces in low density Plasmas

    NASA Astrophysics Data System (ADS)

    Dickheuer, Sven; Marchuk, Oleksandr; Brandt, Christian; Pospieszczyk, Albrecht

    2016-09-01

    We have observed Doppler shifted components of the Balmer-lines emitted by fast non-Maxwellian atoms using different targets in a linear magnetized plasma in the PSI-2 device. In a pure hydrogen plasma the Doppler shifted components of the Balmer emission lines cannot be detected above the signal-to-noise-ratio. However, in a mixed H/Ar plasma with composition of 1:1 the Doppler red- and blue-shifted components can be clearly observed. The Balmer-lines are analyzed by optical emission spectroscopy at observations angles of 35° and 90°. For target materials we use Ag, Pd, Fe and C. An acceleration potential can be applied to the target to change the kinetic energy of the incoming ions between 40 and 200 eV enabling the observation of the Doppler shifted components. The emission mechanism is discussed in details and is probably due to excitation transfer from metastable argon atoms to the fast hydrogen atoms. The Doppler shifted signal can be used to determine the properties of the surfaces, e.g., the energy and angular distribution of reflected atoms. Also the spectral reflectance of the target surface can be obtained and tested against the reference data and measurements with light calibration sources.

  8. Density Functional Theory of Open-Shell Systems. The 3d-Series Transition-Metal Atoms and Their Cations.

    PubMed

    Luo, Sijie; Averkiev, Boris; Yang, Ke R; Xu, Xuefei; Truhlar, Donald G

    2014-01-14

    The 3d-series transition metals (also called the fourth-period transition metals), Sc to Zn, are very important in industry and biology, but they provide unique challenges to computing the electronic structure of their compounds. In order to successfully describe the compounds by theory, one must be able to describe their components, in particular the constituent atoms and cations. In order to understand the ingredients required for successful computations with density functional theory, it is useful to examine the performance of various exchange-correlation functionals; we do this here for 4s(N)3d(N') transition-metal atoms and their cations. We analyze the results using three ways to compute the energy of the open-shell states: the direct variational method, the weighted-averaged broken symmetry (WABS) method, and a new broken-symmetry method called the reinterpreted broken symmetry (RBS) method. We find the RBS method to be comparable in accuracy with the WABS method. By examining the overall accuracy in treating 18 multiplicity-changing excitations and 10 ionization potentials with the RBS method, 10 functionals are found to have a mean-unsigned error of <5 kcal/mol, with ωB97X-D topping the list. For local density functionals, which are more practical for extended systems, the M06-L functional is the most accurate. And by combining the results with our previous studies of p-block and 4d-series elements as well as databases for alkyl bond dissociation, main-group atomization energies, and π-π noncovalent interactions, we find five functionals, namely, PW6B95, MPW1B95, M08-SO, SOGGA11-X, and MPWB1K, to be highly recommended. We also studied the performance of PW86 and C09 exchange functionals, which have drawn wide interest in recent studies due to their claimed ability to reproduce Hartree-Fock exchange at long distance. By combining them with four correlation functionals, we find the performance of the resulting functionals disappointing both for 3d

  9. Atomic-scale dynamics of a model glass-forming metallic liquid: Dynamical crossover, dynamical decoupling, and dynamical clustering

    SciTech Connect

    Jaiswal, Abhishek; Egami, Takeshi; Zhang, Yang

    2015-04-01

    The phase behavior of multi-component metallic liquids is exceedingly complex because of the convoluted many-body and many-elemental interactions. Herein, we present systematic studies of the dynamic aspects of such a model ternary metallic liquid Cu40Zr51Al9 using molecular dynamics simulation with embedded atom method. We observed a dynamical crossover from Arrhenius to super-Arrhenius behavior in the transport properties (diffusion coefficient, relaxation times, and shear viscosity) bordered at Tx ~1300K. Unlike in many molecular and macromolecular liquids, this crossover phenomenon occurs in the equilibrium liquid state well above the melting temperature of the system (Tm ~ 900K), and the crossover temperature is roughly twice of the glass-transition temperature (Tg). Below Tx, we found the elemental dynamics decoupled and the Stokes-Einstein relation broke down, indicating the onset of heterogeneous spatially correlated dynamics in the system mediated by dynamic communications among local configurational excitations. To directly characterize and visualize the correlated dynamics, we employed a non-parametric, unsupervised machine learning technique and identified dynamical clusters of atoms with similar atomic mobility. The revealed average dynamical cluster size shows an accelerated increase below Tx and mimics the trend observed in other ensemble averaged quantities that are commonly used to quantify the spatially heterogeneous dynamics such as the non-Gaussian parameter and the four-point correlation function.

  10. Accelerating solidification process simulation for large-sized system of liquid metal atoms using GPU with CUDA

    SciTech Connect

    Jie, Liang; Li, KenLi; Shi, Lin; Liu, RangSu; Mei, Jing

    2014-01-15

    Molecular dynamics simulation is a powerful tool to simulate and analyze complex physical processes and phenomena at atomic characteristic for predicting the natural time-evolution of a system of atoms. Precise simulation of physical processes has strong requirements both in the simulation size and computing timescale. Therefore, finding available computing resources is crucial to accelerate computation. However, a tremendous computational resource (GPGPU) are recently being utilized for general purpose computing due to its high performance of floating-point arithmetic operation, wide memory bandwidth and enhanced programmability. As for the most time-consuming component in MD simulation calculation during the case of studying liquid metal solidification processes, this paper presents a fine-grained spatial decomposition method to accelerate the computation of update of neighbor lists and interaction force calculation by take advantage of modern graphics processors units (GPU), enlarging the scale of the simulation system to a simulation system involving 10 000 000 atoms. In addition, a number of evaluations and tests, ranging from executions on different precision enabled-CUDA versions, over various types of GPU (NVIDIA 480GTX, 580GTX and M2050) to CPU clusters with different number of CPU cores are discussed. The experimental results demonstrate that GPU-based calculations are typically 9∼11 times faster than the corresponding sequential execution and approximately 1.5∼2 times faster than 16 CPU cores clusters implementations. On the basis of the simulated results, the comparisons between the theoretical results and the experimental ones are executed, and the good agreement between the two and more complete and larger cluster structures in the actual macroscopic materials are observed. Moreover, different nucleation and evolution mechanism of nano-clusters and nano-crystals formed in the processes of metal solidification is observed with large

  11. Accelerating solidification process simulation for large-sized system of liquid metal atoms using GPU with CUDA

    NASA Astrophysics Data System (ADS)

    Jie, Liang; Li, KenLi; Shi, Lin; Liu, RangSu; Mei, Jing

    2014-01-01

    Molecular dynamics simulation is a powerful tool to simulate and analyze complex physical processes and phenomena at atomic characteristic for predicting the natural time-evolution of a system of atoms. Precise simulation of physical processes has strong requirements both in the simulation size and computing timescale. Therefore, finding available computing resources is crucial to accelerate computation. However, a tremendous computational resource (GPGPU) are recently being utilized for general purpose computing due to its high performance of floating-point arithmetic operation, wide memory bandwidth and enhanced programmability. As for the most time-consuming component in MD simulation calculation during the case of studying liquid metal solidification processes, this paper presents a fine-grained spatial decomposition method to accelerate the computation of update of neighbor lists and interaction force calculation by take advantage of modern graphics processors units (GPU), enlarging the scale of the simulation system to a simulation system involving 10 000 000 atoms. In addition, a number of evaluations and tests, ranging from executions on different precision enabled-CUDA versions, over various types of GPU (NVIDIA 480GTX, 580GTX and M2050) to CPU clusters with different number of CPU cores are discussed. The experimental results demonstrate that GPU-based calculations are typically 9∼11 times faster than the corresponding sequential execution and approximately 1.5∼2 times faster than 16 CPU cores clusters implementations. On the basis of the simulated results, the comparisons between the theoretical results and the experimental ones are executed, and the good agreement between the two and more complete and larger cluster structures in the actual macroscopic materials are observed. Moreover, different nucleation and evolution mechanism of nano-clusters and nano-crystals formed in the processes of metal solidification is observed with large-sized system.

  12. Simultaneous determination of trace heavy metals in ambient aerosols by inductively coupled plasma atomic emission spectrometry after pre-concentration with sodium diethyldithiocarbamate.

    PubMed

    Talebi, S M; Malekiha, M

    2008-07-01

    The simultaneous determination of heavy metals associated with airborne particulate matter in the atmosphere of the city Isfahan (Iran) was performed by inductively coupled plasma atomic emission spectrometry (ICP-AES) after pre-concentration with sodium diethyldithiocarbamate. The preconcentration procedure developed found instrumental to determine the trace heavy metals associated with ambient aerosols collected at a short sampling period or collected from rural areas where the concentrations of these metals are much less than those in urban areas. Several samples were analyzed by both flame atomic absorption spectrometry (FAAS) as a conventional method and the proposed method. The results obtained by the two methods were found in good agreement. The method was applied to the determination of atmospheric level of heavy metals in rural area and also for study of variation in levels of heavy metals in urban atmosphere during the days and nights.

  13. Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO2 Laser Bombardment

    NASA Astrophysics Data System (ADS)

    Lie, Zener Sukra; Khumaeni, Ali; Kurihara, Kazuyoshi; Kurniawan, Koo Hendrik; Lee, Yong Inn; Fukumoto, Ken-ichi; Kagawa, Kiichiro; Niki, Hideaki

    2011-12-01

    To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H--He and F--He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

  14. Excitation Mechanism of H, He, C, and F Atoms in Metal-Assisted Atmospheric Helium Gas Plasma Induced by Transversely Excited Atmospheric-Pressure CO2 Laser Bombardment

    NASA Astrophysics Data System (ADS)

    Sukra Lie, Zener; Khumaeni, Ali; Kurihara, Kazuyoshi; Hendrik Kurniawan, Koo; Inn Lee, Yong; Fukumoto, Ken-ichi; Kagawa, Kiichiro; Niki, Hideaki

    2011-12-01

    To clarify the excitation mechanism of hydrogen in transversely excited atmospheric-pressure (TEA) CO2 laser-induced helium gas plasma, atomic emission characteristics of H, C, F, and He were studied using a Teflon sheet (thickness of 2 mm) attached to a metal subtarget. The TEA CO2 laser (750 mJ, 200 ns) was focused on the Teflon sheet in the surrounding He gas at 1 atm. Atomic emissions of H, C, F, and He occurred with a long lifetime, a narrow spectrum width, and a low-background spectrum. The correlation emission intensity curves of H-He and F-He indicated a parabolic functions. To explain the emission characteristics, we offered a model in which helium metastable atoms (He*) play an important role in the excitation processes; namely, atoms collide with helium metastable atoms (He*) to be ionized by the Penning effect, and then recombine with electrons to produce excited states, from which atomic emissions occur.

  15. Laser-Excited Atomic Fluorescence and Ionization in a Graphite Furnace for the Determination of Metals and Nonmetals

    NASA Astrophysics Data System (ADS)

    Butcher, David James

    1990-01-01

    Here is reported novel instrumentation for atomic spectrometry that combined the use of a pulsed laser system as the light source and an electrothermal atomizer as the atom cell. The main goal of the research was to develop instrumentation that was more sensitive for elemental analysis than commercially available instruments and could be used to determine elements in real sample matrices. Laser excited atomic fluorescence spectrometry (LEAFS) in an electrothermal atomizer (ETA) was compared to ETA atomic absorption spectrometry (AAS) for the determination of thallium, manganese, and lead in food and agricultural standard reference materials (SRMs). Compared to ETA AAS, ETA LEAFS has a longer linear dynamic range (LDR) (5-7 orders of magnitude compared to 2-3 orders of magnitude) and higher sensitivity (10 ^{-16} to 10^{ -14} g as compared to 10^{ -13} to 10^{-11} g). Consequently, ETA LEAFS allows elemental analysis to be done over a wider range of concentrations with less dilution steps. Thallium was accurately determined in biological samples by ETA LEAFS at amounts five to one hundred times below the ETA AAS detection limit. ETA AAS and ETA LEAFS were compared for the determination of lead and manganese, and in general, the accuracies and precisions of ETA AAS were the same, with typical precisions between 3% and 6%. Fluorine was determined using laser excited molecular fluorescence spectrometry (LEMOFS) in an ETA. Molecular fluorescence from magnesium fluoride was collected, and the detection limit of 0.3 pg fluorine was two to six orders of magnitude more sensitive than other methods commonly used for the determination of fluorine. Significant interferences from ions were observed, but the sensitivity was high enough that fluorine could be determined in freeze dried urine SRMs by diluting the samples by a factor of one hundred to remove the interferences. Laser enhanced ionization (LEI) in an ETA was used for the determination of metals. For thallium, indium

  16. Method for removal of metal atoms from aqueous solution using suspended plant cells

    DOEpatents

    Jackson, Paul J.; Torres, deceased, Agapito P.; Delhaize, Emmanuel

    1992-01-01

    The use of plant suspension cultures to remove ionic metallic species and TNT-based explosives and their oxidation products from aqueous solution is described. Several plant strains were investigated including D. innoxia, Citrus citrus, and Black Mexican Sweet Corn. All showed significant ability to remove metal ions. Ions removed to sub-ppm levels include barium, iron, and plutonium. D. innoxia cells growing in media containing weapons effluent contaminated with Ba.sup.2+ also remove TNT, other explosives and oxidation products thereof from solution. The use of dead, dehydrated cells were also found to be of use in treating waste directly.

  17. Surface energy calculation - metals with 1 and 2 delocalized electrons per atom

    NASA Astrophysics Data System (ADS)

    Halas, S.; Durakiewicz, T.; Joyce, J. J.

    2002-05-01

    In this paper we calculate surface energy (SE) of monovalent, divalent and some trivalent metals. For these metals for which SE can be solely expressed by dimensionless Wigner-Seitz density parameter, rs, of delocalized electrons: SE=C 1r s-5+C 2r s-3.5-C 3r s-4, where constants C1, C2 and C3 have been calculated on the basis of Sommerfeld's free electron and surface plasma models. Excellent agreement with experimental data was obtained. On the basis of our model SE values for Fr and Ra have been predicted as well.

  18. The atomic nature of polymer-metal interactions in adhesion, friction and wear

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.; Brainard, W. A.

    1974-01-01

    The adhesion, friction, and wear behavior of the solid polymers PTFE and polyimide in contact with various metals were studied using field ion microscopy, Auger emission spectroscopy, and scanning electron microscopy. Results indicate that the polymers will transfer to a clean tungsten surface on simple tough contact, forming a chemical bond. With PTFE, it is hypothesized that the bonding is of the carbon to the metal surface, while with the polyimide, both oxygen and carbon bonding to the tungsten surface are possible. In sliding contact, the friction process itself can initiate polymer film formation. The formation of such films has been suggested as a form of extreme pressure lubrication.

  19. Ph(i-PrO)SiH2: An Exceptional Reductant for Metal-Catalyzed Hydrogen Atom Transfers.

    PubMed

    Obradors, Carla; Martinez, Ruben M; Shenvi, Ryan A

    2016-04-13

    We report the discovery of an outstanding reductant for metal-catalyzed radical hydrofunctionalization reactions. Observations of unexpected silane solvolysis distributions in the HAT-initiated hydrogenation of alkenes reveal that phenylsilane is not the kinetically preferred reductant in many of these transformations. Instead, isopropoxy(phenyl)silane forms under the reaction conditions, suggesting that alcohols function as important silane ligands to promote the formation of metal hydrides. Study of its reactivity showed that isopropoxy(phenyl)silane is an exceptionally efficient stoichiometric reductant, and it is now possible to significantly decrease catalyst loadings, lower reaction temperatures, broaden functional group tolerance, and use diverse, aprotic solvents in iron- and manganese-catalyzed hydrofunctionalizations. As representative examples, we have improved the yields and rates of alkene reduction, hydration, hydroamination, and conjugate addition. Discovery of this broadly applicable, chemoselective, and solvent-versatile reagent should allow an easier interface with existing radical reactions. Finally, isotope-labeling experiments rule out the alternative hypothesis of hydrogen atom transfer from a redox-active β-diketonate ligand in the HAT step. Instead, initial HAT from a metal hydride to directly generate a carbon-centered radical appears to be the most reasonable hypothesis.

  20. Reconciling simulated melting and ground-state properties of metals with a modified embedded-atom method potential.

    PubMed

    Sushko, G B; Verkhovtsev, A V; Kexel, Ch; Korol, A V; Schramm, S; Solov'yov, A V

    2016-04-13

    We propose a modification of the embedded-atom method-type potential aiming at reconciling simulated melting and ground-state properties of metals by means of classical molecular dynamics. Considering titanium, magnesium, gold, and platinum as case studies, we demonstrate that simulations performed with the modified force field yield quantitatively correctly both the melting temperature of the metals and their ground-state properties. It is shown that the accounting for the long-range interatomic interactions noticeably affects the melting point assessment. The introduced modification weakens the interaction at interatomic distances exceeding the equilibrium one by a characteristic vibration amplitude defined by the Lindemann criterion, thus allowing for the correct simulation of melting, while keeping its behavior in the vicinity of the ground state minimum. The modification of the many-body potential has a general nature and can be applicable to metals with different characteristics of the electron structure as well as for many different molecular and solid state systems experiencing phase transitions.

  1. Measurement of Trace Metals in Tobacco and Cigarette Ash by Inductively Coupled Plasma-Atomic Emission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, W.; Finlayson-Pitts, B. J.

    2003-01-01

    The ICP AES experiment reported here is suitable for use in a junior- or senior-level undergraduate instrumental analysis laboratory. The objective of this experiment is to analyze trace metals present in cigarette tobacco, the cigarette filter, and the ash obtained when the cigarette is burned. Two different brands of cigarettes, one with and one without a filter, were used. The filter was analyzed before and after smoke was drawn through it. The trace metals were extracted using concentrated nitric acid at room temperature and at 100 °C respectively, to test the extraction efficiency. Some tobacco samples were spiked with ZnCl2 and FeCl3 to assess the efficiency of the recovery. Zinc and iron are shown to be present in tobacco, filter, and ash, while chromium was above the detection limit only in the ash. These metals are concentrated in the ash compared to the tobacco by factors of ˜4 (Zn), 12 17 (Fe), and ≥ 2 (Cr). If sufficient laboratory time is available, this experiment could be paired with one using atomic absorption (AA) to demonstrate the advantages and disadvantages of ICP when compared to AA.

  2. The determination of wear metals in used lubricating oils by flame atomic absorption spectrometry using sulphanilic acid as ashing agent.

    PubMed

    Ekanem, E J; Lori, J A; Thomas, S A

    1997-11-01

    A simple and reliable ashing procedure is proposed for the preparation of used lubricating oil samples for the determination of calcium, magnesium, zinc, iron, chromium and nickel by flame atomic absorption spectrometry. Sulphanilic acid was added to oil samples and the mixture coked and the coke ashed at 550 degrees C. The solutions of the ash were analysed by flame AAS for the metals. The release of calcium, zinc, iron and chromium was improved by the addition of sulphanilic acid to samples. The relative standard deviations of metal concentration results in the initial oil samples were 1.5% for Ca (1500 mg l(-1) level), 0.3% for Mg (100 mg l(-1) level), 3.1% for Zn (1500 mg l(-1) level), 0.7% for Fe (500 mg l(-1) level), 0.02% for Cr (50 mg l(-1) level) and 0.002% for Ni (10 mg l(-1) level). The optimum sample size for efficient metal release was 20 g while the optimum sulphanilic acid to oil ratio was 0.05 g per gram of oil for Zn and Cr and 0.10 g for Ca and Fe. Results obtained by this procedure were highly reproducible and comparable with those obtained for the same samples using standard procedures.

  3. Nonlinear pressure shifts of alkali-metal atoms in inert gases.

    PubMed

    Gong, F; Jau, Y-Y; Happer, W

    2008-06-13

    Precise measurements show that the microwave resonance frequencies of ground-state Rb or Cs atoms have a nonlinear dependence on the pressure of the buffer gases Ar and Kr. No nonlinearities were observed in the gases He or N(2). These observations strongly suggest that the nonlinearities are due to the van der Waals molecules that form in Ar and Kr, but not in He or N(2). The nonlinear part of the shifts is largest in the pressure range of a few tens of torr, similar to the operating pressures of gas-cell atomic clocks. The observed shifts are very well described by a simple function, parametrized by the effective three-body formation rate of molecules and by the effective product of the collisionally limited lifetime times the shift of the hyperfine coupling coefficient in the molecule.

  4. Atomic origin of high-temperature electron trapping in metal-oxide-semiconductor devices

    SciTech Connect

    Shen, Xiao; Dhar, Sarit; Pantelides, Sokrates T.

    2015-04-06

    MOSFETs based on wide-band-gap semiconductors are suitable for operation at high temperature, at which additional atomic-scale processes that are benign at lower temperatures can get activated, resulting in device degradation. Recently, significant enhancement of electron trapping was observed under positive bias in SiC MOSFETs at temperatures higher than 150 °C. Here, we report first-principles calculations showing that the enhanced electron trapping is associated with thermally activated capturing of a second electron by an oxygen vacancy in SiO{sub 2} by which the vacancy transforms into a structure that comprises one Si dangling bond and a bond between a five-fold and a four-fold Si atoms. The results suggest a key role of oxygen vacancies and their structural reconfigurations in the reliability of high-temperature MOS devices.

  5. Atomic-level interaction of an edge dislocation and localized obstacles in fcc and bcc metals.

    SciTech Connect

    Osetskiy, Yury N; Bacon, David J

    2004-01-01

    Interaction between a moving dislocation and localized obstacles determines microstructure-induced hardening. The mechanisms and parameters of such interactions are necessary inputs to large scale dislocation dynamics modelling. We have developed a model to investigate these characteristics at the atomic level for dislocation-obstacle interactions under both static (T=0K) and dynamic (T>0K) conditions. We present results on hardening due to pinning of edge dislocations at obstacles such as voids, coherent precipitates and stacking fault tetrahedra in bcc-iron and fcc-copper at temperatures from 0 to 600K. It is demonstrated that atomic-scale simulation is required to determine the effects of stress, strain rate and temperature and that such effects cannot always be rationalized within continuum theory.

  6. Spontaneous Decay and Atomic Fluorescence Near a Metal Surface of an Absorbing Dielectric.

    DTIC Science & Technology

    1987-10-01

    classical and quantum mechanics the radiation field must obey Maxwell’s equations , and therefore the spatial dependence of the field is identical in both...theories. In the classical paper by Chance et alI the atomic lifetimes near a dielectric were found from semiclassical considerations. Other... semiclassical theories of fluorescence the dipole moment is merely a vector in configuration space, which can be given an arbitrary direction. One then

  7. NMR Investigation of Atomic Structure and Dynamics of Bulk Metallic Glasses

    DTIC Science & Technology

    2013-09-17

    only by the second-order quadrupole effect , and wide satellite transitions 1m m  ( 1/ 2m   ) broadened by the first-order quadrupole...dependence on temperature is significantly stronger than paramagnetic effects caused by RKKY coupling between individual Gd spins and host Al nuclei...asymmetry of the local free energy by an amount  and causes mechanical polarization of STZs. This effectively increases the probability for atoms to

  8. Slurry sampling graphite furnace atomic absorption spectrometry: determination of trace metals in mineral coal.

    PubMed

    Silva, M M; Goreti, M; Vale, R; Caramão, E B

    1999-12-06

    A procedure for lead, cadmium and copper determination in coal samples based on slurry sampling using an atomic absorption spectrometer equipped with a transversely heated graphite tube atomizer is proposed. The slurries were prepared by weighing the samples directly into autosampler cups (5-30 mg) and adding a 1.5 ml aliquot of a diluent mixture of 5% v/v HNO(3), 0.05% Triton X-100 and 10% ethanol. The slurry was homogenized by manual stirring before measurement. Slurry homogenization using ultrasonic agitation was also investigated for comparison. The effect of particle size and the use of different diluent compositions on the slurry preparation were investigated. The temperature programmes were optimized on the basis of pyrolysis and atomization curves. Absorbance characteristics with and without the addition of a palladium-magnesium modifier were compared. The use of 0.05% m/v Pd and 0.03% m/v Mg was found satisfactory for stabilizing Cd and Pb. The calibration was performed with aqueous standards. In addition, a conventional acid digestion procedure was applied to verify the efficiency of the slurry sampling. Better recoveries of the analytes were obtained when the particle size was reduced to <37 mum. Several certified coal reference materials (BCR Nos. 40, 180, and 181) were analyzed, and good agreement was obtained between the results from the proposed slurry sampling method and the certificate values.

  9. Tunable band gap photoluminescence from atomically thin transition-metal dichalcogenide alloys.

    PubMed

    Chen, Yanfeng; Xi, Jinyang; Dumcenco, Dumitru O; Liu, Zheng; Suenaga, Kazu; Wang, Dong; Shuai, Zhigang; Huang, Ying-Sheng; Xie, Liming

    2013-05-28

    Band gap engineering of atomically thin two-dimensional (2D) materials is the key to their applications in nanoelectronics, optoelectronics, and photonics. Here, for the first time, we demonstrate that in the 2D system, by alloying two materials with different band gaps (MoS2 and WS2), tunable band gap can be obtained in the 2D alloys (Mo(1-x)W(x)S(2) monolayers, x = 0-1). Atomic-resolution scanning transmission electron microscopy has revealed random arrangement of Mo and W atoms in the Mo(1-x)W(x)S(2) monolayer alloys. Photoluminescence characterization has shown tunable band gap emission continuously tuned from 1.82 eV (reached at x = 0.20) to 1.99 eV (reached at x = 1). Further, density functional theory calculations have been carried out to understand the composition-dependent electronic structures of Mo(1-x)W(x)S(2) monolayer alloys.

  10. Metallated metal-organic frameworks

    DOEpatents

    Bury, Wojciech; Farha, Omar K.; Hupp, Joseph T.; Mondloch, Joseph E.

    2017-02-07

    Porous metal-organic frameworks (MOFs) and metallated porous MOFs are provided. Also provided are methods of metallating porous MOFs using atomic layer deposition and methods of using the metallated MOFs as catalysts and in remediation applications.

  11. On the road to metallic nanoparticles by rational design: bridging the gap between atomic-level theoretical modeling and reality by total scattering experiments

    NASA Astrophysics Data System (ADS)

    Prasai, Binay; Wilson, A. R.; Wiley, B. J.; Ren, Y.; Petkov, Valeri

    2015-10-01

    The extent to which current theoretical modeling alone can reveal real-world metallic nanoparticles (NPs) at the atomic level was scrutinized and demonstrated to be insufficient and how it can be improved by using a pragmatic approach involving straightforward experiments is shown. In particular, 4 to 6 nm in size silica supported Au100-xPdx (x = 30, 46 and 58) explored for catalytic applications is characterized structurally by total scattering experiments including high-energy synchrotron X-ray diffraction (XRD) coupled to atomic pair distribution function (PDF) analysis. Atomic-level models for the NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modeling Sutton-Chen (SC) method. Models are matched against independent experimental data and are demonstrated to be inaccurate unless their theoretical foundation, i.e. the SC method, is supplemented with basic yet crucial information on the length and strength of metal-to-metal bonds and, when necessary, structural disorder in the actual NPs studied. An atomic PDF-based approach for accessing such information and implementing it in theoretical modeling is put forward. For completeness, the approach is concisely demonstrated on 15 nm in size water-dispersed Au particles explored for bio-medical applications and 16 nm in size hexane-dispersed Fe48Pd52 particles explored for magnetic applications as well. It is argued that when ``tuned up'' against experiments relevant to metals and alloys confined to nanoscale dimensions, such as total scattering coupled to atomic PDF analysis, rather than by mere intuition and/or against data for the respective solids, atomic-level theoretical modeling can provide a sound understanding of the synthesis-structure-property relationships in real-world metallic NPs. Ultimately this can help advance nanoscience and technology a step closer to producing metallic NPs by rational design.The extent to which current theoretical modeling alone can

  12. Towards a low-spin configuration in extended metal atom chains. Theoretical study of trimetallic systems with 22 metal electrons.

    PubMed

    Tabookht, Zahra; de Graaf, Coen; López, Xavier

    2012-01-14

    Different electronic configurations of a series of trinuclear heterometallic chains with 22 metallic electrons, MM'M(dpa)(4)X(2) (M = Co, Rh; M' = Ni, Pd; X = Cl, NCS), have been modelled in search of new systems with novel electrical properties. For this purpose, we explore the possibility of obtaining low-spin (extensively closed-shell) states by introducing chemical changes to the reference compound CoPdCo(dpa)(4)Cl(2) (1), isoelectronic to the herein studied systems, but possessing magnetically coupled localized electrons. The discussion is based on the orbital energies obtained by the DFT methodology. Among the systems herein analysed, CoNiCo(dpa)(4)(NCS)(2) has only two unpaired electrons vs. six in the case of 1, its closed-shell configuration appearing at high energies. For Rh(2)M-based chains, changes go a step further and the RhPdRh(dpa)(4)Cl(2) and RhPdRh(dpa)(4)(NCS)(2) molecules present a closed-shell ground state in close competition with the broken symmetry solution with S = ½ on each Rh(II). One-electron reduction of the latter compounds has been computed with marked structural changes. Our calculations show that the two lowest 23-electron states are separated by 7-8 kcal mol(-1) in favour of the state with an unpaired localized electron on the δ(Pd-N)* orbital instead of the delocalized one (σ(nb))(2)(σ*)(1).

  13. On the road to metallic nanoparticles by rational design: bridging the gap between atomic-level theoretical modeling and reality by total scattering experiments.

    PubMed

    Prasai, Binay; Wilson, A R; Wiley, B J; Ren, Y; Petkov, Valeri

    2015-11-14

    The extent to which current theoretical modeling alone can reveal real-world metallic nanoparticles (NPs) at the atomic level was scrutinized and demonstrated to be insufficient and how it can be improved by using a pragmatic approach involving straightforward experiments is shown. In particular, 4 to 6 nm in size silica supported Au(100-x)Pd(x) (x = 30, 46 and 58) explored for catalytic applications is characterized structurally by total scattering experiments including high-energy synchrotron X-ray diffraction (XRD) coupled to atomic pair distribution function (PDF) analysis. Atomic-level models for the NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modeling Sutton-Chen (SC) method. Models are matched against independent experimental data and are demonstrated to be inaccurate unless their theoretical foundation, i.e. the SC method, is supplemented with basic yet crucial information on the length and strength of metal-to-metal bonds and, when necessary, structural disorder in the actual NPs studied. An atomic PDF-based approach for accessing such information and implementing it in theoretical modeling is put forward. For completeness, the approach is concisely demonstrated on 15 nm in size water-dispersed Au particles explored for bio-medical applications and 16 nm in size hexane-dispersed Fe48Pd52 particles explored for magnetic applications as well. It is argued that when "tuned up" against experiments relevant to metals and alloys confined to nanoscale dimensions, such as total scattering coupled to atomic PDF analysis, rather than by mere intuition and/or against data for the respective solids, atomic-level theoretical modeling can provide a sound understanding of the synthesis-structure-property relationships in real-world metallic NPs. Ultimately this can help advance nanoscience and technology a step closer to producing metallic NPs by rational design.

  14. The use of ion chromatography-dc plasma atomic emission spectrometry for the speciation of trace metals

    SciTech Connect

    Urasa, I.T.

    1991-09-20

    The original objects of this research program were: to interface d.c. plasma atomic emission spectrometer with an ion chromatograph; to characterize and optimize the combined systems for application in the speciation of metals in aqueous solutions; to use this system in the study of the solution chemistry of various metals; and to find ways in which the measurement sensitivity of the method can be enhanced, thereby allowing the detection of metal species at low ppb concentration levels. This approach has been used to study the chemistry of and speciate several elements in solution including: arsenic, chromium, iron, manganese, nickel phosphorus, platinum, selenium, and vanadium. During the course of this research, we have found that the solution chemistry of the elements studied and the speciation data obtained can vary considerably depending on the solution, and the chromatographic conditions employed. The speciation of chromium, iron, and vanadium was found to be highly influenced by the acidity of the sample. The element selective nature of the d.c. plasma detector allows these changes to be monitored, thereby providing quantitative information on the new moieties formed. New approaches are being developed including the use of chelating ligands as preconcentration agents for purposes of reducing further the detection limits of the elements of interest and to improve the overall element speciation scheme. New thrusts are being directed towards the employment of post-column derivatization method coupled with colorimetric measurements to detect and quantify metal species eluting from the chromatographic column. The influence of sample acidity on these investigations will be carefully evaluated. These new thrusts are described in the accompanying Project Renewal Proposal.

  15. Atomic and electronic structure of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass from ab initio simulations

    SciTech Connect

    Kumar, Vijay; Fujita, T.; Chen, M. W.; Inoue, A.; Konno, K.; Matsuura, M.; Kawazoe, Y.

    2011-10-01

    The atomic structure of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass has been simulated using an ab initio molecular dynamics method with projector-augmented wave pseudopotentials for electron-ion interaction and generalized gradient approximation for exchange-correlation energy. The calculated extended x-ray absorption fine structure (EXAFS) spectra of Pd-K and Ni-K edges, the mass density, and the electronic structure agree remarkably well with the available experimental data and the EXAFS spectra measured at the SPring-8 synchrotron radiation facility. Our results show that the atomic structure can be described in terms of P-centered polyhedra. There are no two P atoms that are nearest neighbors at this composition, and this could be a reason for the observed optimal P concentration of about 20 at.%. The neighboring polyhedra share metal (M) atoms and form a polar covalently bonded random network of P-M-P favoring certain angles. The remaining M atoms act as metallic glue with a tendency of nanoscale clustering of Pd-Pd and Ni-Ni atoms.

  16. Atomically modified thin interface in metal-dielectric hetero-integrated systems: control of electronic properties.

    PubMed

    Iida, Kenji; Nobusada, Katsuyuki

    2017-04-12

    We have performed first-principles studies of the electronic properties of Cu-diamond hetero-integrated systems, particularly placing emphasis on elucidating the effects of surface modification of diamond with H or O. It is found that the electronic properties crucially depend on the chemical compositions of the modified atomically thin interface region. The local density of states (LDOS) of the H-terminated diamond moiety near the Cu surface exhibits a clearly different distribution from that near the vacuum region, whereas the LDOS of the O-terminated diamond is almost independent of the Cu deposition. In other words, the effects of the electronic interactions between Cu and diamond on the electronic properties in the interface region are readily controlled by surface modification with only one atomic (i.e. H or O) layer. Electric field (EF) effects on the Cu-diamond systems also strongly depend on the electronic details, i.e. atomistic modification in the interface regions. In particular, at the interface between the H-terminated diamond moiety and the vacuum region, its conduction band energy is strongly affected by an applied EF much more than the valence band energy; that is, the band gap can be varied with an applied EF. The band gap variation is found to be attributed to an atomistic level difference in the spatial extension of the valence and conduction bands and thus is not explained with a macroscopic band diagram model. It has been demonstrated that the electronic properties of hetero-integrated systems are described and controlled well by carefully designing atomically thin interface regions.

  17. Atomically modified thin interface in metal-dielectric hetero-integrated systems: control of electronic properties

    NASA Astrophysics Data System (ADS)

    Iida, Kenji; Nobusada, Katsuyuki

    2017-04-01

    We have performed first-principles studies of the electronic properties of Cu-diamond hetero-integrated systems, particularly placing emphasis on elucidating the effects of surface modification of diamond with H or O. It is found that the electronic properties crucially depend on the chemical compositions of the modified atomically thin interface region. The local density of states (LDOS) of the H-terminated diamond moiety near the Cu surface exhibits a clearly different distribution from that near the vacuum region, whereas the LDOS of the O-terminated diamond is almost independent of the Cu deposition. In other words, the effects of the electronic interactions between Cu and diamond on the electronic properties in the interface region are readily controlled by surface modification with only one atomic (i.e. H or O) layer. Electric field (EF) effects on the Cu-diamond systems also strongly depend on the electronic details, i.e. atomistic modification in the interface regions. In particular, at the interface between the H-terminated diamond moiety and the vacuum region, its conduction band energy is strongly affected by an applied EF much more than the valence band energy; that is, the band gap can be varied with an applied EF. The band gap variation is found to be attributed to an atomistic level difference in the spatial extension of the valence and conduction bands and thus is not explained with a macroscopic band diagram model. It has been demonstrated that the electronic properties of hetero-integrated systems are described and controlled well by carefully designing atomically thin interface regions.

  18. Determination of heavy metals in solid emission and immission samples using atomic absorption spectroscopy

    SciTech Connect

    Fara, M.; Novak, F.

    1995-12-01

    Both flame and electrothermal methods of atomic absorption spectroscopy (AAS) have been applied to the determination of Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, TI, Se, V and Zn in emission and emission (deposition) samples decomposed in open PTFE test-tubes by individual fuming-off hydrofluoric, perchloroic and nitric acid. An alternative hydride technique was also used for As and Se determination and Hg was determined using a self-contained AAS analyzer. A graphite platform proved good to overcome non-spectral interferences in AAS-ETA. Methods developed were verified by reference materials (inc. NBS 1633a).

  19. Anomalous Insulator-Metal Transition in Boron Nitride-Graphene Hybrid Atomic Layers

    DTIC Science & Technology

    2012-08-13

    locally centered atomic or- bital (LCAO) basis set, and the Perdew-Burke-Ernzerhof (PBE) exchange- correlation functional.36 The occupation of the Kohn-Sham...Stausholm-Møller, M. Strange, G. A. Tritsaris, M. Vanin, M. Walter, B. Hammer , H. Häkkinen, G. K. H. Madsen, R. M. Nieminen, J. K. Nørskov, M. Puska, T. T... Schmidt , and M. Martin, Nat. Mater. 7, 391 (2008). 43V. M. Pudalov, JETP Lett. 66, 175 (1997). 44S. Das Sarma and E. H. Hwang, Phys. Rev. Lett. 83, 164

  20. Ring State for Single Transition Metal Atoms on Boron Nitride on Rh(111)

    NASA Astrophysics Data System (ADS)

    Natterer, Fabian Donat; Patthey, François; Brune, Harald

    2012-08-01

    The low-temperature adsorption of isolated transition metal adatoms (Mn, Co, and Fe) onto hexagonal boron nitride monolayers on Rh(111) creates a bistable adsorption complex. The first state considerably weakens the hexagonal boron nitride- (h-BN-) substrate bond for 60 BN unit cells, leading to a highly symmetric ring in STM images, while the second state is imaged as a conventional adatom and leaves the BN-substrate interaction intact. We demonstrate reversible switching between the two states and, thus, controlled pinning and unpinning of the h-BN layer from the metal substrate. I(z) and dln⁡I/dz curves are used to reveal the BN deformation in the ring state.

  1. Electronic Spectra of Some Linear Triatomic Molecules Containing Transition Metal Atoms

    NASA Astrophysics Data System (ADS)

    Merer, Anthony J.

    2000-06-01

    Gerhard Herzberg was always interested in obtaining spectra of new free radicals, and he was particularly skilled at identifying the carriers from internal evidence such as missing lines, rotational constants and the numbers of different spectra that appeared on isotope substitution. Our recent sub-Doppler experiments with transition metals show that nuclear hyperfine structure provides another piece of evidence, of the type which Herzberg would have appreciated. Laser ablation of group 4-6 metals in the presence of methane has led to the discovery of the family of the simplest possible organometallic compounds, linear triatomic molecules with the formula MCH. These are unstable free radicals which have extensive electronic spectra in the visible and near infra-red; the spectra are very complicated because of strong vibronic coupling between the close-lying electronic states, but the molecular structures and vibrational frequencies can be obtained from them.

  2. Three-body recombination in cold helium-helium-alkali-metal-atom collisions

    SciTech Connect

    Suno, Hiroya; Esry, B. D.

    2009-12-15

    Three-body recombination in helium-helium-alkali-metal collisions at cold temperatures is studied using the adiabatic hyperspherical representation. The rates for the three-body recombination processes {sup 4}He+{sup 4}He+X->{sup 4}He+{sup 4}HeX and {sup 4}He+{sup 4}He+X->{sup 4}He{sub 2}+X, with X={sup 7}Li, {sup 23}Na, {sup 39}K, {sup 85}Rb, and {sup 133}Cs, are calculated at nonzero collision energies by including not only zero total angular momentum, J=0, states but also J>0 states. The three-body recombination rates show a relatively weak dependence on the alkali-metal species, differing from each other only by about one order of magnitude, except for the {sup 4}He-{sup 4}He-{sup 23}Na system.

  3. Atomic scale characterization and surface chemistry of metal modified titanate nanotubes and nanowires

    NASA Astrophysics Data System (ADS)

    Kukovecz, Ákos; Kordás, Krisztián; Kiss, János; Kónya, Zoltán

    2016-10-01

    Titanates are salts of polytitanic acid that can be synthesized as nanostructures in a great variety concerning crystallinity, morphology, size, metal content and surface chemistry. Titanate nanotubes (open-ended hollow cylinders measuring up to 200 nm in length and 15 nm in outer diameter) and nanowires (solid, elongated rectangular blocks with length up to 1500 nm and 30-60 nm diameter) are the most widespread representatives of the titanate nanomaterial family. This review covers the properties and applications of these two materials from the surface science point of view. Dielectric, vibrational, electron and X-ray spectroscopic results are comprehensively discussed first, then surface modification methods including covalent functionalization, ion exchange and metal loading are covered. The versatile surface chemistry of one-dimensional titanates renders them excellent candidates for heterogeneous catalytic, photocatalytic, photovoltaic and energy storage applications, therefore, these fields are also reviewed.

  4. Atomic Structure of Ca40+xMg25Cu35-x Metallic Glasses (Postprint)

    DTIC Science & Technology

    2012-06-21

    believed to depend on the type of short range order (SRO) and medium range order ( MRO ) of alloying elements in the amorphous structure. It is... MRO . III. RESULTS A. Neutron diffraction analysis The experimental SSFs, S(Q), for the four samples are shown in Figure 1(a) and the RDFs, G(r), are...presence of MRO , in metallic glasses can produce structures that have only a small energetic disadvantage relative to the equilibrium crystalline

  5. Atomic Layer Deposition of Metal Oxides on sp2-Graphitic Carbon Substrates

    DTIC Science & Technology

    2014-03-31

    Na2SO4 Aqueous Electrolyte ………………………………...11 iv Approved for public release; distribution unlimited. 1.0 SUMMARY This research concentrated on the...sodium sulfate (Alfa Aesar, 99.99% metals basis) aqueous electrolyte under a continuous argon (Airgas, Prepurified) purge. Platinum counter electrodes...of the semi-circle is indicative of the charge-transfer resistance for the electrode/ electrolyte interface. A smaller radius indicates a lower

  6. Scanning Tunneling Microscopy of Atoms and Charge - Waves in Transition Metal Chalcogenides at 4.2K

    NASA Astrophysics Data System (ADS)

    Giambattista, Brian William

    A scanning tunneling microscope (STM) operating at 4.2K has been used to study transition metal chalcogenides. Experiments have been performed on members of the group IV and V dichalcogenides (TaSe_2, TaS_2, VSe_2, NbSe_2, TiSe_2, and TiS_2 ) and on the trichalcogenide NbSe_3 . The compounds and phases studied exhibit a wide range of charge-density wave (CDW) behavior. The STM response correlates well with the electronic structure of the given material. Large amplitude CDWs form in the octahedrally coordinated 1T phase Ta compounds. The STM images on these compounds are dominated by a strong modulation at the CDW wavelength of sqrt{13} a_{rm o}. The trigonal prismatic 2H phase compounds (TaSe_2, TaS_2, NbSe_2) have a weak ~3 x 3 CDW. The scans on these materials show a dominant atomic modulation accompanied by a weak CDW superlattice. The alternating coordination 4Hb phase Ta compounds show images characteristic of the coordination of the surface sandwich. 1T-VSe_2 shows a STM response dominated by the atomic modulation with a weak superimposed CDW modulation. The scans on the group IV Ti compounds show a large atomic modulation, along with a 2 x 2 CDW superlattice in the case of TiSe_2. The images of NbSe_3 resolve the chain structure of this material along with the CDW superlattice. The STM response, including the relative roles of the CDW and atomic modulations, will be analyzed for all materials in terms of the electronic structure of the material and the possible contributions of corrugation enhancement mechanisms. The ability of the STM to detect localized defects in both the CDW and atomic lattices will be demonstrated. Current vs. voltage and differential conductance vs. voltage measurements have been performed. The materials with large amplitude CDWs show a strong increase in conductivity at a voltage corresponding to the CDW gap voltage. A value is obtained for the indirect semiconducting bandgap of 1T-TiS_2. Measurement of the effective barrier height as

  7. Phenyl Benzo[b]phenothiazine as a Visible Light Photoredox Catalyst for Metal-Free Atom Transfer Radical Polymerization.

    PubMed

    Dadashi-Silab, Sajjad; Pan, Xiangcheng; Matyjaszewski, Krzysztof

    2016-12-23

    This paper reports use of phenyl benzo[b]phenothiazine (Ph-benzoPTZ) as a visible light-induced metal-free atom transfer radical polymerization (ATRP) photoredox catalyst. Well-controlled polymerizations of various methacrylate monomers were conducted under a 392 nm visible light LED using Ph-benzoPTZ to activate different alkyl halides. The use of the photocatalyst enabled temporal control over the growth of polymer chains during intermittent on/off periods. The polymerization was initiated and progressed only under stimulation by light and completely stopped in the absence of light. Block copolymers were synthesized to demonstrate high retention of chain end fidelity in the polymers and livingness of the process.

  8. Effect of composition of electrolyte cathode on emission intensity of metal atoms in the discharge plasma at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Sirotkin, N. A.; Titov, V. A.

    2017-01-01

    The emission spectra and the plasma parameters of discharges were investigated. Water solutions of copper and nickel chlorides with additions of sodium chloride were used as electrolyte cathodes. The change of the relative intensities of the emission lines of the elements (Cu and Ni) with increasing NaCl concentrations in the solution is shown. The gas temperature and the reduced electric field strength in the plasma were founded. The electron energy distribution function and the excitation rate coefficients for emitting states of copper and nickel atoms by the numerical solution of the Boltzmann equation were obtained. It was shown that in plasma emission spectroscopy measuring it is necessaryto considerthe correlation between rates of excitation and composition of the sample solution in order to determine the concentration of metal ions in the water solutions.

  9. [Investigation of enhancing effect for hydride generation-atomic fluorescence of transition metal elements].

    PubMed

    Sun, Han-Wen; Suo, Ran

    2008-11-01

    A mechanism of hydride generation based on disassembly reaction of hydrogen-transferred interim state [M(BH4)m]* was developed by investigating the effect of reaction medium acidity on hydride generation. The effects of Co2+ and Ni2+, phenanthroline and 8-hydroxyquinoline on hydride generation-atomic fluorescence signals of Zn, Cd, Cu and Ni were studied, respectively, and their enhancing mechnism was discussed. The enhancing effect Co2+ and Ni2+ on the fluorescence signals of Zn and Cd was due to the increase in transmission efficiency of hydride of Zn and Cd. There was a synergic enhancing effect between phenanthroline or 8-hydroxyquinoline and Co2+ on the fluorescence signals of Zn and Cd, however no synergic enhancing effect between phenanthroline and 8-hydroxyquinoline on the fluorescence signals of Zn and Cd. The simulative action of cationic surfactant, anion surfactant and non-ionic surfactant surfactant to hydride generation was investigated. It is shown that both cationic surfactant and non-ionic surfactant have obvious enhancing effect on the fluorescence signals of analytes because of the decrease in surface tension of reaction solution. The release characteristics of hydride from the absorption solution containing surfactant was ulteriorly examined by using graphite furnace atomic absorption spectrometry, and the mechanism of enhancing effect of surfactant on hydride generation and transmission was proposed.

  10. First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties.

    PubMed

    Ma, Dongwei; Lu, Zhansheng; Ju, Weiwei; Tang, Yanan

    2012-04-11

    BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.

  11. Identifying the Atomic-Level Effects of Metal Composition on the Structure and Catalytic Activity of Peptide-Templated Materials.

    PubMed

    Merrill, Nicholas A; McKee, Erik M; Merino, Kyle C; Drummy, Lawrence F; Lee, Sungsik; Reinhart, Benjamin; Ren, Yang; Frenkel, Anatoly I; Naik, Rajesh R; Bedford, Nicholas M; Knecht, Marc R

    2015-12-22

    Bioinspired approaches for the formation of metallic nanomaterials have been extensively employed for a diverse range of applications including diagnostics and catalysis. These materials can often be used under sustainable conditions; however, it is challenging to control the material size, morphology, and composition simultaneously. Here we have employed the R5 peptide, which forms a 3D scaffold to direct the size and linear shape of bimetallic PdAu nanomaterials for catalysis. The materials were prepared at varying Pd:Au ratios to probe optimal compositions to achieve maximal catalytic efficiency. These materials were extensively characterized at the atomic level using transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, and atomic pair distribution function analysis derived from high-energy X-ray diffraction patterns to provide highly resolved structural information. The results confirmed PdAu alloy formation, but also demonstrated that significant surface structural disorder was present. The catalytic activity of the materials was studied for olefin hydrogenation, which demonstrated enhanced reactivity from the bimetallic structures. These results present a pathway to the bioinspired production of multimetallic materials with enhanced properties, which can be assessed via a suite of characterization methods to fully ascertain structure/function relationships.

  12. All-electron KKR Calculations for Metallic Systems with Thousands of Atoms Per Cell via Sparse Matrix Iterative Solvers

    NASA Astrophysics Data System (ADS)

    Khan, Suffian; Johnson, Duane

    2010-03-01

    To perform electronic-structure calculations for inherently large systems, such as a quantum dots with heterogeneous interfaces, we must perform the calculations over very large unit cells (10^4 to 10^8 atoms). KKR methods typically solve for G by direct inversion G-1, with known analytic form. Using a screened, k-space hybrid KKR, we solve Dyson's equation for the Green's function using a reference state via G = Gref [ I - (t - tref) Gref]-1, scattering matrices t and tref are known and the non-Hermitian tensor Gref is chosen for convenience and sparsity [1]. The approach is O(N) for bandgap materials, whereas it is O(N^2) for metals but with a potentially large prefactor. We use Krylov-space solvers to reduce storage and exploit known symmetries. Parallel iterative and energy contour solves are made also. We explore the numerical efficiency and scaling versus atoms per unit cells. [1] Smirnov and Johnson, Comp! ^1Phys. Comm. 148, 74-80 (2002).

  13. Effect of hydrogen atoms on the structures of trinuclear metal carbonyl clusters: trinuclear manganese carbonyl hydrides.

    PubMed

    Liu, Xian-mei; Wang, Chao-yang; Li, Qian-shu; Xie, Yaoming; King, R Bruce; Schaefer, Henry F

    2009-05-18

    The structures of the trinuclear manganese carbonyl hydrides H(3)Mn(3)(CO)(n) (n = 12, 11, 10, 9) have been investigated by density functional theory (DFT). Optimization of H(3)Mn(3)(CO)(12) gives the experimentally known structure in which all carbonyl groups are terminal and each edge of a central Mn(3) equilateral triangle is bridged by a single hydrogen atom. This structure establishes the canonical distance 3.11 A for the Mn-Mn single bond satisfying the 18-electron rule. The central triangular (mu-H)(3)Mn(3) unit is retained in the lowest energy structure of H(3)Mn(3)(CO)(11), which may thus be derived from the H(3)Mn(3)(CO)(12) structure by removal of a carbonyl group with concurrent conversion of one of the remaining carbonyl groups into a semibridging carbonyl group to fill the resulting hole. The potential energy surface of H(3)Mn(3)(CO)(10) is relatively complicated with six singlet and five triplet structures. One of the lower energy H(3)Mn(3)(CO)(10) structures has one of the hydrogen atoms bridging the entire Mn(3) triangle and the other two hydrogen atoms bridging Mn-Mn edges. This H(3)Mn(3)(CO)(10) structure achieves the favored 18-electron configuration with a very short MnMn triple bond of 2.36 A. The other low energy H(3)Mn(3)(CO)(10) structure retains the (mu-H)(3)Mn(3) core of H(3)Mn(3)(CO)(12) but has a unique six-electron donor eta(2)-mu(3) carbonyl group bridging the entire Mn(3) triangle similar to the unique carbonyl group in the known compound Cp(3)Nb(3)(CO)(6)(eta(2)-mu(3)-CO). For H(3)Mn(3)(CO)(9) a structure with a central (mu(3)-H)(2)Mn(3) trigonal bipyramid lies >20 kcal/mol below any of the other structures. Triplet structures were found for the unsaturated H(3)Mn(3)(CO)(n) (n = 11, 10, 9) systems but at significantly higher energies than the lowest lying singlet structures.

  14. Nonlinear absorption in ionic liquids with transition metallic atoms in the anion

    NASA Astrophysics Data System (ADS)

    Nóvoa-López, José A.; López Lago, Elena; Seijas, Julio A.; Pilar Vázquez-Tato, M.; Troncoso, Jacobo; de la Fuente, Raúl; Salgueiro, José R.; Michinel, Humberto

    2016-02-01

    Nonlinear absorption has been investigated by open aperture Z-scan in ionic liquids obtained by combination of 1-butyl-3-methyl-imidazolium cations with anions containing a transition metal (Co, Zn, Cu or Ni) and thiocyanate groups. The laser source was a Ti:Sapphire oscillator (80-fs pulses, λ = 810 nm, repetition rate of 80.75 MHz). All liquids present quite low heat capacities that favor the development of strong thermal effects. Thermal effects and nonlinear absorption make them potential materials for optical limiting purposes.

  15. Local Atomic Structure of Ca-Mg-Zn Metallic Glasses (Postprint)

    DTIC Science & Technology

    2010-09-16

    cluster packing ECP model of amor - phous structure,20 the Ca-Mg-Zn ternary glasses are repre- sented as 10,9 efficient cluster packing structures...diffraction data as the basis on which to model the amor - phous structure of a series of ternary Ca60MgXZn40−X X =10,15,20,25 at. % metallic glasses using...Reverse Monte Carlo RMC methods. The effect of alloy composition on the structure and GFA is examined and the average amor - phous structure identified

  16. Surfaces of Al-based complex metallic alloys: atomic structure, thin film growth and reactivity

    PubMed Central

    Ledieu, Julian; Gaudry, Émilie; Fournée, Vincent

    2014-01-01

    We present a review on recent work performed on periodic complex metallic alloy (CMA) surfaces. The electronic and crystallographic structures of clean pseudo-tenfold, pseudo-twofold, sixfold surfaces will be presented along with the recent findings on CMA of lower structural complexity, i.e. with a smaller unit cell. The use of CMA surfaces as templates for thin film growth and the formation of surface alloy will also be introduced. The reactivity of these complex surfaces and their impact in the field of heterogeneous catalysis will be discussed. Finally, common trends among these systems will be highlighted when possible and future challenges will be examined. PMID:27877673

  17. Diffusion anisotropy of poor metal solute atoms in hcp-Ti

    SciTech Connect

    Scotti, Lucia Mottura, Alessandro

    2015-05-28

    Atom migration mechanisms influence a wide range of phenomena: solidification kinetics, phase equilibria, oxidation kinetics, precipitation of phases, and high-temperature deformation. In particular, solute diffusion mechanisms in α-Ti alloys can help explain their excellent high-temperature behaviour. The purpose of this work is to study self- and solute diffusion in hexagonal close-packed (hcp)-Ti, and its anisotropy, from first-principles using the 8-frequency model. The calculated diffusion coefficients show that diffusion energy barriers depend more on bonding characteristics of the solute rather than the size misfit with the host, while the extreme diffusion anisotropy of some solute elements in hcp-Ti is a result of the bond angle distortion.

  18. Diffusion anisotropy of poor metal solute atoms in hcp-Ti.

    PubMed

    Scotti, Lucia; Mottura, Alessandro

    2015-05-28

    Atom migration mechanisms influence a wide range of phenomena: solidification kinetics, phase equilibria, oxidation kinetics, precipitation of phases, and high-temperature deformation. In particular, solute diffusion mechanisms in α-Ti alloys can help explain their excellent high-temperature behaviour. The purpose of this work is to study self- and solute diffusion in hexagonal close-packed (hcp)-Ti, and its anisotropy, from first-principles using the 8-frequency model. The calculated diffusion coefficients show that diffusion energy barriers depend more on bonding characteristics of the solute rather than the size misfit with the host, while the extreme diffusion anisotropy of some solute elements in hcp-Ti is a result of the bond angle distortion.

  19. Atomic and molecular oxygen adsorbed on (111) transition metal surfaces: Cu and Ni

    SciTech Connect

    López-Moreno, S.; Romero, A. H.

    2015-04-21

    Density functional theory is used to investigate the reaction of oxygen with clean copper and nickel [111]-surfaces. We study several alternative adsorption sites for atomic and molecular oxygen on both surfaces. The minimal energy geometries and adsorption energies are in good agreement with previous theoretical studies and experimental data. From all considered adsorption sites, we found a new O{sub 2} molecular precursor with two possible dissociation paths on the Cu(111) surface. Cross barrier energies for the molecular oxygen dissociation have been calculated by using the climbing image nudge elastic band method, and direct comparison with experimental results is performed. Finally, the structural changes and adsorption energies of oxygen adsorbed on surface when there is a vacancy nearby the adsorption site are also considered.

  20. Determination of some heavy metals by flame atomic absorption spectrometry before coprecipitation with neodymium hydroxide.

    PubMed

    Soylak, Mustafa; Kizil, Nebiye

    2011-01-01

    A procedure is described for the determination of trace amounts of Cd(II), Ni(II), Cu(II), Pb(II), Fe(III), Co(II), and Mn(II) that combines flame atomic absorption spectrometry with neodymium hydroxide coprecipitation. The influences of analytical parameters (amount of neodymium, pH of the model solutions, etc.) that affect quantitative recoveries of the analyte ions were investigated. The effects of concomitant ions were also examined. The detection limits for analytes were found in the range of 0.2-3.3 microg/L. The validation of the presented procedure was controlled by analysis of certified reference materials (National Institute of Standards and Technology 1570a spinach leaves and TMDA 54.4 fortified lake water). The applications of the procedure were performed by the analysis of water, food, and herbal plants from Turkey.

  1. Tunable plasmonic response of metallic nanoantennna heterodimer arrays modified by atomic-layer deposition

    NASA Astrophysics Data System (ADS)

    Wambold, Raymond A.; Borst, Benjamin D.; Qi, Jie; Weisel, Gary J.; Willis, Brian G.; Zimmerman, Darin T.

    2016-04-01

    We present a systematic study of tunable, plasmon extinction characteristics of arrays of nanoscale antennas that have potential use as sensors, energy-harvesting devices, catalytic converters, in near-field optical microscopy, and in surface-enhanced spectroscopy. Each device is composed of a palladium triangular-prism antenna and a flat counter-electrode. Arrays of devices are fabricated on silica using electron-beam lithography, followed by atomic-layer deposition of copper. Optical extinction is measured by employing a broadband light source in a confocal, transmission arrangement. We characterize the plasmon resonance behavior by examining the dependence on device length, the gap spacing between the electrodes, material properties, and the device array density, all of which contribute in varying degrees to the measured response. We employ finite-difference time-domain simulations to demonstrate good qualitative agreement between experimental trends and theory and use scanning electron microscopy to correlate plasmonic extinction characteristics with changes in morphology.

  2. Atomic layer deposition of metal oxide patterns on nonwoven fiber mats using localized physical compression.

    PubMed

    Sweet, William J; Oldham, Christopher J; Parsons, Gregory N

    2014-06-25

    Patterning is an essential part of many industrial processes from printing to semiconductor manufacturing. In this work, we demonstrate a new method to pattern and selectively coat nonwoven textiles by atomic layer deposition (ALD) using compressive mask patterning. A physical mask combined with mechanical compression allows lateral definition and fidelity of the ALD coating to be controlled. We produce features of several sizes on different nonwoven fiber materials and demonstrate the ability to limit diffusion effects to within <200 μm of the pattern edge. Lateral and vertical penetration of reactive growth species into nonwoven mats is investigated by plan-view and cross-sectional imaging. Vertical growth is also analyzed by imaging coating depth into fiber mat stacks. We develop a fully quantitative transport model that describes well the effect of fiber structure and mechanical compression on the extent of coating under the physical mask. This method could be implemented for high-volume patterning for applications including flexible electronics.

  3. Ground state of Ho atoms on Pt(111) metal surfaces: Implications for magnetism

    NASA Astrophysics Data System (ADS)

    Karbowiak, M.; Rudowicz, C.

    2016-05-01

    We investigated the ground state of Ho atoms adsorbed on the Pt(111) surface, for which conflicting results exist. The density functional theory (DFT) calculations yielded the Ho ground state as | Jz=±8 > . Interpretation of x-ray absorption spectroscopy and x-ray magnetic circular dichroism spectra and the magnetization curves indicated the ground state as | Jz=±6 > . Superposition model is employed to predict the crystal-field (CF) parameters based on the structural data for the system Ho/Pt(111) obtained from the DFT modeling. Simultaneous diagonalization of the free-ion (HFI) and the trigonal CF Hamiltonian (HCF) within the whole configuration 4 f10 of H o3 + ion was performed. The role of the trigonal CF terms, neglected in the pure uniaxial CF model used previously for interpretation of experimental spectra, is found significant, whereas the sixth-rank CF terms may be neglected in agreement with the DFT predictions. The results provide substantial support for the experimental designation of the | Jz=±6 > ground state, albeit with subtle difference due to admixture of other | Jz> states, but run against the DFT-based designation of the | Jz=±8 > ground state. A subtle splitting of the ground energy level with the state (predominantly), | Jz=±6 > is predicted. This paper provides better insight into the single-ion magnetic behavior of the Ho/Pt(111) system by helping to resolve the controversy concerning the Ho ground state. Experimental techniques with greater resolution powers are suggested for direct confirmation of this splitting and C3 v symmetry experienced by the Ho atom.

  4. Significant impact on cathode performance of lithium-ion batteries by precisely controlled metal oxide nanocoatings via atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Li, Xifei; Liu, Jian; Meng, Xiangbo; Tang, Yongji; Banis, Mohammad Norouzi; Yang, Jinli; Hu, Yuhai; Li, Ruying; Cai, Mei; Sun, Xueliang

    2014-02-01

    LiCoO2 in the commercial lithium ion batteries has been suffering from its poor cycling performance at high cutoff voltages. In this study, we employ an atomic layer deposition (ALD) technique to surface-modify a LiCoO2 material with various thickness-controlled metal oxide (TiO2, ZrO2 and Al2O3) coatings to improve its battery performance. The effects of the metal oxide coatings on the electrochemical performance of LiCoO2 electrode are studied in detail. It is demonstrated that a uniform and dense coating via the ALD route on LiCoO2 powder can lower the battery performance due to an obvious decrease in lithium diffusion and electron transport with the coating layers. In contrast, it is revealed that a direct coating on prefabricated LiCoO2 electrodes performs much better than a coating on LiCoO2 powders. It is further disclosed that the improved electrochemical performance of coated LiCoO2 electrode is highly dependent on the coating materials. Of the three coating materials, the Al2O3 coating results in the best cycling stability while the ZrO2 coating contributes to the best rate capability. It is thus suggested that the coating materials are functionally specific, and for the best improvement of a cathode, a particular coating material should be sought.

  5. Metal ions and flexibility in a viral RNA pseudoknot at atomic resolution

    SciTech Connect

    Egli, Martin; Minasov, George; Su, Li; Rich, Alexander

    2010-03-05

    Many pathogenic viruses use programmed -1 ribosomal frameshifting to regulate translation of their structural and enzymatic proteins from polycistronic mRNAs. Frameshifting is commonly stimulated by a pseudoknot located downstream from a slippery sequence, the latter positioned at the ribosomal A and P sites. We report here the structures of two crystal forms of the frameshifting RNA pseudoknot from beet western yellow virus at resolutions of 1.25 and 2.85 {angstrom}. Because of the very high resolution of 1.25 {angstrom}, ten mono- and divalent metal ions per asymmetric unit could be identified, giving insight into potential roles of metal ions in stabilizing the pseudoknot. A magnesium ion located at the junction of the two pseudoknot stems appears to play a crucial role in stabilizing the structure. Because the two crystal forms exhibit mostly unrelated packing interactions and local crystallographic disorder in the high-resolution form was resolvable, the two structures offer the most detailed view yet of the conformational preference and flexibility of an RNA pseudoknot.

  6. Cage-Core Interactions in Fullerenes Enclosing Metal Clusters with Multiple Scandium and Yttrium Atoms.

    NASA Astrophysics Data System (ADS)

    Dan, Liu; Hagelberg, Frank

    2007-03-01

    Pronounced stability has been reported for metallofullerenes of the form NSc3@CN (N = 68, 78) /1/. In response of these and related findings, Density Functional Theory studies have been performed on the relation between cage-core interactions and the geometry as well as stability of endofullerenes with metal impurities containing Sc and Y. Substantial electron transfer from the metal core to the fullerene cage combines with electron backdonation, involving the interaction between the occupied orbitals of the negatively charged cage and the unoccupied d orbitals of the positively charged core. The Hueckel 4n+2 rule, well established in organic chemistry, is shown to provide a valuable heuristic tool for understanding the intramolecular electron transfer and the related stability gain /1/. The usefulness of the aromaticity concept for explaining and predicting the architecture of metallofullerenes is further exemplified by the units Sc2@C84 and Y2@C84 which were analyzed in spin triplet and singlet conditions. The Sc2 core turns out to be realized by two separated ions, while Y2 forms a bound subunit. These findings are in agreement with conclusions based on the 4n + 2 rule, assisted by Nucleus Independent Chemical Shift (NICS) calculations. /1/ Stevenson, S.; Fowler, P.W.; Heine, T.; Duchamp, J.C.; Rice, G.; Glass, T.; Harich, K.; Hadju, F.; Bible, R.; Dorn, H.C. Nature, 2000, 408, 427, /2/ S. S. Park, D. Liu, F. Hagelberg, J. Phys. Chem. A 109, 8865 (2005).

  7. Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H2.

    PubMed

    Joo, Ji Bong; Dillon, Robert; Lee, Ilkeun; Yin, Yadong; Bardeen, Christopher J; Zaera, Francisco

    2014-06-03

    The production of hydrogen from water with semiconductor photocatalysts can be promoted by adding small amounts of metals to their surfaces. The resulting enhancement in photocatalytic activity is commonly attributed to a fast transfer of the excited electrons generated by photon absorption from the semiconductor to the metal, a step that prevents deexcitation back to the ground electronic state. Here we provide experimental evidence that suggests an alternative pathway that does not involve electron transfer to the metal but requires it to act as a catalyst for the recombination of the hydrogen atoms made via the reduction of protons on the surface of the semiconductor instead.

  8. Analysis of an Air Conditioning Coolant Solution for Metal Contamination Using Atomic Absorption Spectroscopy: An Undergraduate Instrumental Analysis Exercise Simulating an Industrial Assignment

    ERIC Educational Resources Information Center

    Baird, Michael J.

    2004-01-01

    A real-life analytical assignment is presented to students, who had to examine an air conditioning coolant solution for metal contamination using an atomic absorption spectroscopy (AAS). This hands-on access to a real problem exposed the undergraduate students to the mechanism of AAS, and promoted participation in a simulated industrial activity.

  9. Comparative studies of metal air pollution by atomic spectrometry techniques and biomonitoring with moss and lichens.

    PubMed

    State, Gabriel; Popescu, Ion V; Radulescu, Cristiana; Macris, Cristina; Stihi, Claudia; Gheboianu, Anca; Dulama, Ioana; Niţescu, Ovidiu

    2012-09-01

    Our study was dedicated to the analysis of air pollution level with metals in Dambovita County, Romania; maps of the concentration distributions for air pollutants were drawn; statistical analysis includes calculation of the background concentrations and the contamination factors. The highest values of the contamination factor CF is 63.1 ± 6.63 for mosses samples and 33.12 ± 3.96 for lichens and it indicates extreme contaminations in the surroundings of steel works and an electric plant. The comparison of the distribution maps for Cr, Cu, Fe, Ni, Pb and Zn concentrations enables the identification of the pollution sources, the limits of areas with very high levels of pollution, the comparison of the concentration gradients in some areas and the influence of woodlands on the spread of pollutants through the air.

  10. Green's-function approach to nonresonance multiphoton absorption in the alkali-metal atoms

    NASA Astrophysics Data System (ADS)

    McGuire, E. J.

    1981-01-01

    An exact Green's function is constructed for the one-electron Schrödinger equation using a central potential obtained from a piecewise linear approximation to -rV(r) of Herman and Skillman. With the Green's function two- and three-photon ionization cross sections are calculated for He(1s)(2s) 1S, 3S, and the alkali metals, and compared to other calculations and experiments. Resonances in the cross sections occur at model eigenvalues rather than experimental energy levels. It is demonstrated that the resonances can be made to occur at experimental values either by simple shifts in the wavelength scale, by adjusting the ionization energy in the calculation, or by including the eigenvalue differences in a finite sum. However, as these are perturbation-theory calculations and not applicable at very high intensities or on resonance, only the wings of the resonance structure are included in the calculation.

  11. Mechanics of nanoscale metallic multilayers: from atomic-scale to micro-scale

    SciTech Connect

    Wang, Jian; Hoagland, Richard G; Misra, Amit

    2008-01-01

    Layered composites of Cu/Nb with incoherent interfaces achieve very high strength levels. Interfaces play a crucial role in materials strength by acting as barriers to slip. Atomistic models of Cu/Nb bilayers are used to explore the origins of this resistance. The models clearly show that dislocations near an interface experience an attraction toward the interface. This attraction is caused by shear of the interface induced by the stress field of the dislocation. More importantly, atomistic simulations also reveal that interfacial dislocations easily move in interfaces by both glide and climb. Integrating these findings into a micro-scale model, we develop a three-dimensional crystal elastic-plastic model to describe the mechanical behavior of nanoscale metallic multi layers.

  12. Reactions of methyl fluoride with atomic transition-metal and main-group cations: gas-phase room-temperature kinetics and periodicities in reactivity.

    PubMed

    Zhao, Xiang; Koyanagi, Gregory K; Bohme, Diethard K

    2006-09-14

    Reactions of CH(3)F have been surveyed systematically at room temperature with 46 different atomic cations using an inductively coupled plasma/selected-ion flow tube tandem mass spectrometer. Rate coefficients and product distributions were measured for the reactions of fourth-period atomic ions from K(+) to Se(+), of fifth-period atomic ions from Rb(+) to Te(+) (excluding Tc(+)), and of sixth-period atomic ions from Cs(+) to Bi(+). Primary reaction channels were observed corresponding to F atom transfer, CH(3)F addition, HF elimination, and H(2) elimination. The early-transition-metal cations exhibit a much more active chemistry than the late-transition-metal cations, and there are periodic features in the chemical activity and reaction efficiency that maximize with Ti(+), As(+), Y(+), Hf(+), and Pt(+). F atom transfer appears to be thermodynamically controlled, although a periodic variation in efficiency is observed within the early-transition-metal cations which maximizes with Ti(+), Y(+), and Hf(+). Addition of CH(3)F was observed exclusively (>99%) with the late-fourth-period cations from Mn(+) to Ga(+), the fifth-period cations from Ru(+) to Te(+), and the sixth-period cations from Hg(+) to Bi(+) as well as Re(+). Periodic trends are observed in the effective bimolecular rate coefficient for CH(3)F addition, and these are consistent with expected trends in the electrostatic binding energies of the adduct ions and measured trends in the standard free energy of addition. HF elimination is the major reaction channel with As(+), while dehydrogenation dominates the reactions of W(+), Os(+), Ir(+), and Pt(+). Sequential F atom transfer is observed with the early-transition-metal cations, with the number of F atoms transferred increasing across the periodic table from two to four, maximizing at four for the group 5 cations Nb(+)(d(4)) and Ta(+)(d(3)s(1)), and stopping at two with V(+)(d(4)). Sequential CH(3)F addition was observed with many atomic cations and all of

  13. Atom-efficient route for converting incineration ashes into heavy metal sorbents.

    PubMed

    Chiang, Yi Wai; Santos, Rafael M; Vanduyfhuys, Kenneth; Meesschaert, Boudewijn; Martens, Johan A

    2014-01-01

    Bottom ashes produced from municipal solid-waste incineration are suitable for sorbent synthesis because of their inherent composition, high alkalinity, metastable mineralogy, and residual heat. This work shows that bottom ashes can be atom-efficiently converted into valuable sorbents without the need for costly and hazardous chemicals. The ashes were hydrothermally treated in rotary autoclaves at autogenic pH conditions to promote the conversion of precursor mineral phases into zeolites and layered silicate hydrates. Two main mineral phases were formed: katoite and sodium aluminum phosphate silicate hydrate. These mineral alterations are accompanied by a tenfold increase in specific surface area and a twofold reduction in average particle size. Performance evaluation of the new sorbents for Cd(2+), Zn(2+), and Pb(2+) adsorption at pH5 indicates sorption capacities of 0.06, 0.08, and 0.22 mmol g(-1), respectively, which are similar to those of natural adsorbents and synthetic materials obtained from more demanding synthesis conditions.

  14. Atomic-scale simulations of material behaviors and tribology properties for BCC metal film

    NASA Astrophysics Data System (ADS)

    H, D. Aristizabal; P, A. Parra; P, López; E, Restrepo-Parra

    2016-01-01

    This work has two main purposes: (i) introducing the basic concepts of molecular dynamics analysis to material scientists and engineers, and (ii) providing a better understanding of instrumented indentation measurements, presenting an example of nanoindentation and scratch test simulations. To reach these purposes, three-dimensional molecular dynamics (MD) simulations of nanoindentation and scratch test technique were carried out for generic thin films that present BCC crystalline structures. Structures were oriented in the plane (100) and placed on FCC diamond substrates. A pair wise potential was employed to simulate the interaction between atoms of each layer and a repulsive radial potential was used to represent a spherical tip indenting the sample. Mechanical properties of this generic material were obtained by varying the indentation depth and dissociation energy. The load-unload curves and coefficient of friction were found for each test; on the other hand, dissociation energy was varied showing a better mechanical response for films that present grater dissociation energy. Structural change evolution was observed presenting vacancies and slips as the depth was varied. Project supported by la DirecciónNacional de Investigación of the Universidad Nacional de Colombia, “the Theoretical Study of Physical Properties of Hard Materials for Technological Applications” (Grant No. 20101007903).

  15. Single d-metal atoms on F(s) and F(s+) defects of MgO(001): a theoretical study across the periodic table.

    PubMed

    Neyman, Konstantin M; Inntam, Chan; Matveev, Alexei V; Nasluzov, Vladimir A; Rösch, Notker

    2005-08-24

    Single d-metal atoms on oxygen defects F(s) and F(s+) of the MgO(001) surface were studied theoretically. We employed an accurate density functional method combined with cluster models, embedded in an elastic polarizable environment, and we applied two gradient-corrected exchange-correlation functionals. In this way, we quantified how 17 metal atoms from groups 6-11 of the periodic table (Cu, Ag, Au; Ni, Pd, Pt; Co, Rh, Ir; Fe, Ru, Os; Mn, Re; and Cr, Mo, W) interact with terrace sites of MgO. We found bonding with F(s) and F(s+) defects to be in general stronger than that with O2- sites, except for Mn-, Re-, and Fe/F(s) complexes. In M/F(s) systems, electron density is accumulated on the metal center in a notable fashion. The binding energy on both kinds of O defects increases from 3d- to 4d- to 5d-atoms of a given group, at variance with the binding energy trend established earlier for the M/O2- complexes, 4d < 3d < 5d. Regarding the evolution of the binding energy along a period, group 7 atoms are slightly destabilized compared to their group 6 congeners in both the F(s) and F(s+) complexes; for later transition elements, the binding energy increases gradually up to group 10 and finally decreases again in group 11, most strongly on the F(s) site. This trend is governed by the negative charge on the adsorbed atoms. We discuss implications for an experimental detection of metal atoms on oxide supports based on computed core-level energies.

  16. Dynamic effects of surface plasmons on the lifetimes of neutral excited rare-gas atoms physisorbed on metal surfaces Radiative and nonradiative processes

    NASA Astrophysics Data System (ADS)

    Mavroyannis, Constantine

    We have considered the excitation spectra of neutral rare-gas atoms physisorbed on metal surfaces. The adsorbed atom and its image interact through the dipole-dipole interaction and radiate to each other as well. The charge of the image atom is screened by the dielectric function of the surface plasmons. Due to the common radiation field between the atom and its image, the excitation spectra consist of the symmetric and antisymmetric modes, respectively. Each of them splits into two excitations: the atomic-like and the surface plasmon-like excitations, which arise because of the presence of the surface plasmons. The surface plasmon-like excitations appear near the surface plasmon frequencies and consist of broad spectral lines, which have large radiative widths and small relative intensities in comparison with those of the atomic like excitations, that emerge near the atomic frequencies. The spectral functions describing the symmetric and antisymmetric modes have been calculated in the presence of the plasmon damping and consist of asymmetric Lorentzian lines, where the extent of the asymmetry depends on the strength of the surface plasmons. Competition between the cooperative radiative and non-radiative processes takes place. In the absence of plasmon damping or when the effective radiative damping is greater than the damping of the surface plasmons, the largest enhancement of the relative intensities per atom occurs for the spectra of the symmetric modes of the excited Xe, Kr and Ar when they are physisorbed on Mg with K and Li holding the second and third place, respectively. The relative intensities per atom for the spectra of Xe, Kr and Ar on the surfaces of A1, Cu, Ag and Au are much less than the corresponding ones for the single free atoms in question, respectively. The enhancement or the decrease of the maximum relative intensity per atom is due to the dynamic effect arising from the presence of the surface plasmons. In the opposite limit, when the

  17. 137Cs, 239+240Pu and 240Pu/239Pu atom ratios in the surface waters of the western North Pacific Ocean, eastern Indian Ocean and their adjacent seas.

    PubMed

    Yamada, Masatoshi; Zheng, Jian; Wang, Zhong-Liang

    2006-07-31

    Surface seawater samples were collected along the track of the R/V Hakuho-Maru cruise (KH-96-5) from Tokyo to the Southern Ocean. The (137)Cs activities were determined for the surface waters in the western North Pacific Ocean, the Sulu and Indonesian Seas, the eastern Indian Ocean, the Bay of Bengal, the Andaman Sea, and the South China Sea. The (137)Cs activities showed a wide variation with values ranging from 1.1 Bq m(-3) in the Antarctic Circumpolar Region of the Southern Ocean to 3 Bq m(-3) in the western North Pacific Ocean and the South China Sea. The latitudinal distributions of (137)Cs activity were not reflective of that of the integrated deposition density of atmospheric global fallout. The removal rates of (137)Cs from the surface waters were roughly estimated from the two data sets of Miyake et al. [Miyake Y, Saruhashi K, Sugimura Y, Kanazawa T, Hirose K. Contents of (137)Cs, plutonium and americium isotopes in the Southern Ocean waters. Pap Meteorol Geophys 1988;39:95-113] and this study to be 0.016 yr(-1) in the Sulu and Indonesian Seas, 0.033 yr(-1) in the Bay of Bengal and Andaman Sea, and 0.029 yr(-1) in the South China Sea. These values were much lower than that in the coastal surface water of the western Northwest Pacific Ocean. This was likely due to less horizontal and vertical mixing of water masses and less scavenging. (239+240)Pu activities and (240)Pu/(239)Pu atom ratios were also determined for the surface waters in the western North Pacific Ocean, the Sulu and Indonesian Seas and the South China Sea. The (240)Pu/(239)Pu atom ratios ranged from 0.199+/-0.026 to 0.248+/-0.027 on average, and were significantly higher than the global stratospheric fallout ratio of 0.18. The contributions of the North Pacific Proving Grounds close-in fallout Pu were estimated to be 20% for the western North Pacific Ocean, 39% for the Sulu and Indonesian Seas and 42% for the South China Sea by using the two end-member mixing model. The higher (240)Pu/(239)Pu

  18. Heat capacity measurements of atoms and molecules adsorbed on evaporated metal films

    SciTech Connect

    Kenny, T.W.

    1989-05-01

    Investigations of the properties of absorbed monolayers have received great experimental and theoretical attention recently, both because of the importance of surface processes in practical applications such as catalysis, and the importance of such systems to the understanding of the fundamentals of thermodynamics in two dimensions. We have adapted the composite bolometer technology to the construction of microcalorimeters. For these calorimeters, the adsorption substrate is an evaporated film deposited on one surface of an optically polished sapphire wafer. This approach has allowed us to make the first measurements of the heat capacity of submonolayer films of /sup 4/He adsorbed on metallic films. In contrast to measurements of /sup 4/He adsorbed on all other insulating substrates, we have shown that /sup 4/He on silver films occupies a two-dimensional gas phase over a broad range of coverages and temperatures. Our apparatus has been used to study the heat capacity of Indium flakes. CO multilayers, /sup 4/He adsorbed on sapphire and on Ag films and H/sub 2/ adsorbed on Ag films. The results are compared with appropriate theories. 68 refs., 19 figs.

  19. Metal Free Azide-Alkyne Click Reaction: Role of Substituents and Heavy Atom Tunneling.

    PubMed

    Karmakar, Sharmistha; Datta, Ayan

    2015-09-03

    Metal free click reactions provide an excellent noninvasive tool to modify and understand the processes in biological systems. Release of ring strain in cyclooctynes on reaction with azides on the formation of triazoles results in small activation energies for various intermolecular Huisgen reactions (1-9). Substitution of difluoro groups at the α, α' position of the cyclooctyne ring enhances the rates of cycloadditions by 10 and 20 times for methyl azide and benzyl azide respectively at room temperature. The computed rate enhancement on difluoro substitution using direct dynamical calculations using the canonical variational transition state theory (CVT/CAG) with small curvature tunneling (SCT) corrections are in excellent agreement with the experimental results. For the intramolecular click reaction (10) notwithstanding its much higher activation energy, quantum mechanical tunneling (QMT) enhances the rate of cycloaddition significantly and increases the N(14)/N(15) primary kinetic isotope effect at 298 K. QMT is shown to be rather efficient in 10 due to a thin barrier of ∼2.4 Å. The present study shows that tunneling effects can be significant for intramolecular click reactions.

  20. Atomic scale modeling of defect production and microstructure evolution in irradiated metals

    SciTech Connect

    Diaz de la Rubia, T.; Soneda, N.; Shimomura, Y.

    1997-04-01

    Irradiation effects in materials depend in a complex way on the form of the as-produced primary damage state and its spatial and temporal evolution. Thus, while collision cascades produce defects on a time scale of tens of picosecond, diffusion occurs over much longer time scales, of the order of seconds, and microstructure evolution over even longer time scales. In this report the authors present work aimed at describing damage production and evolution in metals across all the relevant time and length scales. They discuss results of molecular dynamics simulations of displacement cascades in Fe and V. They show that interstitial clusters are produced in cascades above 5 keV, but not vacancy clusters. Next, they discuss the development of a kinetic Monte Carlo model that enables calculations of damage evolution over much longer time scales (1000`s of s) than the picosecond lifetime of the cascade. They demonstrate the applicability of the method by presenting predictions on the fraction of freely migrating defects in {alpha}Fe during irradiation at 600 K.